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Sample records for volmer-weber growth mechanism

  1. Volmer-Weber growth stages of polycrystalline metal films probed by in situ and real-time optical diagnostics

    Science.gov (United States)

    Abadias, G.; Simonot, L.; Colin, J. J.; Michel, A.; Camelio, S.; Babonneau, D.

    2015-11-01

    The Volmer-Weber growth of high-mobility metal films is associated with the development of a complex compressive-tensile-compressive stress behavior as the film deposition proceeds through nucleation of islands, coalescence, and formation of a continuous layer. The tensile force maximum has been attributed to the end of the islands coalescence stage, based on ex situ morphological observations. However, microstructural rearrangements are likely to occur in such films during post-deposition, somewhat biasing interpretations solely based on ex situ analysis. Here, by combining two simultaneous in situ and real-time optical sensing techniques, based on surface differential reflectance spectroscopy (SDRS) and change in wafer curvature probed by multibeam optical stress sensor (MOSS), we provide direct evidence that film continuity does coincide with tensile stress maximum during sputter deposition of a series of metal (Ag, Au, and Pd) films on amorphous SiOx. Stress relaxation after growth interruption was testified from MOSS, whose magnitude scaled with adatom mobility, while no change in SDRS signal could be revealed, ruling out possible changes of the surface roughness at the micron scale.

  2. Effect of growth mechanisms on the deformation of a unit cell and polarization reversal in barium-strontium titanate heterostructures on magnesium oxide

    Science.gov (United States)

    Mukhortov, V. M.; Golovko, Yu. I.; Biryukov, S. V.; Anokhin, A.; Yuzyuk, Yu. I.

    2016-01-01

    The effect of a growth mechanism on the unit cell strain and the related change in the properties of single-crystal Ba0.8Sr0.2TiO3 films grown on MgO substrates according to the Frank-van der Merwe and Volmer-Weber growth mechanisms is studied. The unit cell strain is shown to depend substantially on the film thickness and the growth mechanism. It is found that the same film-substrate pair can be used to vary stresses in the film from two-dimensional tensile to compressive stresses due to a change in the growth mechanism and the film thickness.

  3. LEED INVESTIGATION OF THE 1ST STAGES OF GROWTH OF AG ON TIS2(001)

    NARCIS (Netherlands)

    RAO, GH; WEITERING, HH; HIBMA, T

    1991-01-01

    The growth of Ag onto TiS2(001) follows the Volmer-Weber growth mode, i.e., it forms 3D islands right from the start. LEED patterns show that these islands have the bulk silver lattice constant and are oriented in such a way that rows of Ag are parallel to rows of sulphur atoms. The LEED pattern

  4. Ab initio calculation of the growth of Te nanorods and Bi2Te3 nanoplatelets

    Institute of Scientific and Technical Information of China (English)

    Tian Xiao-Qing; Du Shi-Xuan; Gao Hong-Jun

    2008-01-01

    In this paper the growth mechanism of a Te/Bi2Te3 novel structure is studied by ab-initio calculations.The results show that the growth of Te nanorods is determined by the adsorption energy of Te atoms on different crystalline Te surfaces.The adsorption energy of Te on the Te (001) surface is 3.29 eV,which is about 0.25 eV higher than that of Te on the Te (110).This energy difference makes the preferential growth direction along the < 001> direction.In addition,the higher surface energy of Bi2Te3 (110) and the lattice misfit between crystalline Bi2Te3 and Te along < 001> direction are considered to explain the growth of the Bi2Te3 nanoplatelets,in which Volmer-Weber model is used.The theoretical results axe in agreement with experimental observation.

  5. Stranski-Krastanov mechanism of growth and the effect of misfit sign on quantum dots nucleation

    Science.gov (United States)

    Prieto, J. E.; Markov, I.

    2017-10-01

    The thermodynamics of the Stranski-Krastanov mode of epitaxial growth and the effect of the sign of the lattice misfit are discussed. The Stranski-Krastanov mode of growth represents a sequence of layer-by-layer or Frank-van der Merwe growth followed by the formation of three-dimensional (3D) islands or Volmer-Weber growth. The occurrence of both growth modes mentioned above is in compliance with the wettability criterion of Bauer. The positive wetting function required for the occurrence of the Volmer-Weber growth is originated by the vertical displacements of the atoms close to the edges of the two-dimensional (2D) islands as a result of the relaxation of the lattice misfit. The monolayer high islands become unstable against bilayer islands, bilayer islands in turn become unstable against trilayer islands, etc. beyond some critical islands sizes. Monolayer islands appear as necessary precursors of three-dimensional (3D) islands. The critical island size for mono-bilayer transformation increases steeply with decreasing lattice misfit and diverges at a critical value of the misfit. This value divides the regions of Frank-van der Merwe and Stranski-Krastanov modes in a phase diagram of coordinates wetting-misfit. The transformation of monolayer to multilayer islands takes place either by consecutive nucleation and growth of 2D islands (layer-by-layer transformation), or by nucleation and lateral (2D) growth of multilayer islands (multilayer 2D transformation). The former occurs in the case of ;stiff; overlayer materials and mostly in compressed overlayers. The latter takes place in the case of ;soft; materials like Pb and In, mostly in tensile overlayers. Tensile films show non-nucleation transformation compared with the nucleation-like behavior of compressed films.

  6. Liquid phase epitaxial growth of bismuth based superconductors

    Science.gov (United States)

    Takemoto, J.; Miyashita, S.; Inoue, T.; Komatsu, H.

    1996-05-01

    The liquid phase epitaxial growth of superconducting films of Bi 2Sr 2CaCu 2O y (2212 phase) and Bi 2Sr 2CuO z (2201 phase) were carried out on three types of substrates; SrTiO 3, LaAlO 3 and NdGaO 3. Twinning structures of the 2212 phase were observed in the films grown on the SrTiO 3 (100) and LaAlO 3 (100) substrates which belong to the cubic crystal system, while nearly twin-free structures were obtained when the film was grown on the NdGaO 3 (001) substrate (orthorhombic system). Atomic force microscopy revealed a 2201 phase film with a reasonably flat area (several μm 2) grown on the LaAlO 3 (100) substrate. It was observed that the 2212 phase nucleated on the substrate following the Volmer-Weber type mechanism (three-dimensional island growth mode). The enlarging processes of the island layers were discussed.

  7. Epitaxial growth of single-crystalline Ni46Co4Mn37In13 thin film and investigation of its magnetoresistance

    Directory of Open Access Journals (Sweden)

    Chao Jing

    2014-02-01

    Full Text Available Single-crystalline thin film of Ni46Co4Mn37In13 alloy grown on MgO(0 0 1 was prepared by Pulsed Laser Deposition (PLD method. The epitaxial growth process was monitored by in situ Reflection High Energy Electron Diffraction (RHEED. Structure measurements reveal that the single-crystalline Ni46Co4Mn37In13 film could be stabilized on MgO(0 0 1 as a face-centered-cubic (fcc structure. From the evolution of RHEED, it can be deduced from the patterns that Volmer-Weber growth mechanism (3-D dominates at the initial stage. Then, it becomes layer-by-layer growth mechanism (2-D with the increase of the film thickness. Lastly, growth mechanism converts back to 3-D when the film is thick enough. Both electrical resistance and magnetoresistance (MR were measured at various temperatures using Physical Property Measurement System (PPMS. The electrical resistance measurement indicates that the film sample does not have martensitic transformation in the measurement temperature range. However, with the temperature increasing, the film sample exhibits a transition from metallic to semiconductor-like properties. Moreover, a small negative magnetoresistance was observed at different temperature, which can be explained by the spin-dependent scattering of the conduction electrons.

  8. Nucleation, growth and properties of Co nanostructures electrodeposited on n-Si(1 1 1)

    Energy Technology Data Exchange (ETDEWEB)

    Khelladi, Mohamed Redha; Mentar, Loubna [Laboratoire de Chimie, Ingenierie Moleculaire et Nanostructures, Universite F. Abbas-Setif, 19000 (Algeria); Azizi, Amor, E-mail: aziziamor@yahoo.fr [Laboratoire de Chimie, Ingenierie Moleculaire et Nanostructures, Universite F. Abbas-Setif, 19000 (Algeria); Kadirgan, Figen [Departments of Chemistry, Istanbul Technical University, Maslak 34469, Istanbul (Turkey); Schmerber, Guy; Dinia, Aziz [Institut de Physique et Chimie des Materiaux de Strasbourg (IPCMS), UMR 7504 CNRS - Universite de Strasbourg, 23 rue du Loess, BP 43, F-67034 Strasbourg Cedex 2 (France)

    2012-02-01

    In the present work, cobalt thin films deposited directly on n-Si(1 1 1) surfaces by electrodeposition in Watts bath have been investigated. The electrochemical deposition and properties of deposits were studied using cyclic voltammetry (CV), chronoamperometry (CA), ex situ atomic force microscopy (AFM), X-ray diffraction (XRD) and alternating gradient field magnetometer (AGFM) techniques. The nucleation and growth kinetics at the initial stages of Co studied by current transients indicate a 3D island growth (Volmer-Weber); it is characterized by an instantaneous nucleation mechanism followed by diffusion limited growth. According to this model, the estimated nucleus density and diffusion coefficient are on the order of magnitude of 10{sup 6} cm{sup -2} and 10{sup -5} cm{sup 2} s{sup -1}, respectively. AFM characterization of the deposits shows a granular structure of the electrodeposited layers. XRD measurements indicate a small grain size with the presence of a mixture of hcp and fcc Co structures. The hysteresis loops with a magnetic field in the parallel and perpendicular direction and showed that the easy magnetization axis of Co thin film is in the film plane.

  9. Electrochemical island growth

    Science.gov (United States)

    Guo, Lian

    metals onto foreign substrates usually occurs through Volmer-Weber island growth, and hence the structure and properties of thin films are critically dependent on the mechanism of nucleation and growth. For example, high nucleus densities are essential for achieving island coalescence at small thickness. A new approach to control thin film microstructure through control of island geometry is demonstrated. It is shown that by promoting anisotropic island growth, film coalescence can be achieved at smaller thickness and with lower island densities.

  10. Analysis of cucl thin-film deposition and growth by close-space sublimation

    Science.gov (United States)

    Nicholson, Anthony

    There is a growing need to implement high fidelity, scalable computational models to various thin-film photovoltaic industries. Developing accurate simulations that govern the thermal and species-transport diffusion characteristics within thin-film manufacturing processes will lead to better predictions of thin-film uniformity at varied deposition conditions that ultimately save time, money, and resources. Thin-film deposition and growth of Copper I Chloride (CuCl) by the Close-Space Sublimation (CSS) process was investigated in an extensive range of operating and thermal conditions. A simulation model based on the ANSYS FLUENT RTM solver platform was developed to encompass the kinetic behavior of the CuCl species within the CSS domain while predicting the growth rate at varied system parameters. Surface physics associated with the process, notably sublimation and adsorption, were studied, quantified, and applied to the continuum-based thin-film deposition model. Experimentation of CuCl thin-film growth was performed across a range of substrate and source temperatures for verification of the model's computational accuracy. Furthermore, characterization of the inherent growth mode exhibited by CuCl was studied in conjunction with simulation and experimental tasks. It was concluded that the simulation model provided predictions for the CuCl thickness as a function of temperature within the range of typical CSS conditions. Equally important was the elucidation of the CuCl growth mechanism, which displays a Volmer-Weber growth mode on the Fluorine-doped Tin Oxide coated layer of the substrate. Such knowledge along with the current modeling capabilities will be useful in extending the computational method to predicting the non-uniformities present in CuCl and other thin-film depositions.

  11. Growth of thin films of TiN on MgO(100) monitored by high-pressure RHEED

    DEFF Research Database (Denmark)

    Pryds, Nini; Cockburn, D.; Rodrigo, Katarzyna Agnieszka

    2008-01-01

    is produced by PLD directly from a TiN target. At the initial stage of the growth (average thickness similar to 2.4 nm) the formation of islands is observed. During the continuous growth the islands merge into a smooth surface as indicated by the RHEED, atomic force microscopy and field emission scanning...... electron microscopy. These observations are in good agreement with the three-dimensional Volmer-Weber growth type, by which three-dimensional crystallites are formed and later cause a continuous surface roughening. This leads to an exponential decrease in the intensity of the specular spot in the RHEED......Reflection high-energy electron diffraction (RHEED) operated at high pressure has been used to monitor the initial growth of titanium nitride (TiN) thin films on single-crystal (100) MgO substrates by pulsed laser deposition (PLD). This is the first RHEED study where the growth of TiN films...

  12. Growth of Al on a W(110) surface

    Energy Technology Data Exchange (ETDEWEB)

    Choi, D.S., E-mail: dschoi@kangwon.ac.kr; Kim, D.H.

    2012-07-01

    Using low energy electron diffraction and low energy ion scattering spectroscopy, we investigated the growth mode of Al on a W(110) surface at room temperature and at 1000 K. We found that Al grew on the W(110) surface in the Frank-van der Merwe mode when the W substrate was kept at room temperature during Al deposition. It was found that at a coverage higher than 2 monolayer (ML) in Al grown at room temperature, Al atoms had a well-ordered face centered cubic (fcc) (111) surface. The [11{sup Macron }0] direction of the Al grown at room temperature on the (111) surface was parallel to the [001] direction of the W(110) substrate surface. When the temperature of the W substrate was kept at 1000 K, the adsorbed Al atoms grew in the Volmer-Weber mode. The 1.5 ML Al/W(110) surface prepared at 1000 K shows two domains of the fcc Al(111) surfaces along with a W(110) surface. We also found that the early stage of Al film growth shows W(110) structure. However as the film becomes thicker (above 3.5-4 layers) the Al face is turned into fcc (111) face. - Highlights: Black-Right-Pointing-Pointer We investigated the growth behavior of Al on the W(110) surface. Black-Right-Pointing-Pointer Al grew in the Frank-van der Merwe mode when the W was kept at room temperature. Black-Right-Pointing-Pointer Al grew in the Volmer-Weber mode when the W was kept at 1000 K. Black-Right-Pointing-Pointer The Al film grown at room temperature has the (111) surface. Black-Right-Pointing-Pointer [11{sup Macron }0] direction on the Al(111) was the same as [001] on the W(110) substrate.

  13. Controlling nucleation of monolayer WSe2 during metal-organic chemical vapor deposition growth

    Science.gov (United States)

    Eichfeld, Sarah M.; Oliveros Colon, Víctor; Nie, Yifan; Cho, Kyeongjae; Robinson, Joshua A.

    2016-06-01

    Tungsten diselenide (WSe2) is a semiconducting, two-dimensional (2D) material that has gained interest in the device community recently due to its electronic properties. The synthesis of atomically thin WSe2, however, is still in its infancy. In this work we elucidate the requirements for large selenium/tungsten precursor ratios and explain the effect of nucleation temperature on the synthesis of WSe2 via metal-organic chemical vapor deposition (MOCVD). The introduction of a nucleation-step prior to growth demonstrates that increasing nucleation temperature leads to a transition from a Volmer-Weber to Frank-van der Merwe growth mode. Additionally, the nucleation step prior to growth leads to an improvement of WSe2 layer coverage on the substrate. Finally, we note that the development of this two-step technique may allow for improved control and quality of 2D layers grown via CVD and MOCVD processes.

  14. Dependence of mesoscopic growth on molecular configuration in Langmuir-Blodgett multilayers

    Science.gov (United States)

    Mukherjee, S.; Datta, A.

    2009-10-01

    Systematic studies by atomic force microscopy and X-ray reflectivity of three monolayer Langmuir-Blodgett films of M-Stearate (M = Cd, Zn, Mn) show change in surface morphology and growth mode with change in metal ions in the headgroup. Growth proceeds via Volmer Weber mode in CdSt, Stranski-Krastanov mode in ZnSt and Frank Van der Merwe mode in MnSt, as ascertained from fractal dimensions and out-of-plane density profiles. This is closely related with increase in number of metal ions incorporated per headgroup with change in metal ions in the order Cd, Zn and Mn. A preliminary correlation with metal atomic number is noted.

  15. Potentiostatic controlled nucleation and growth modes of electrodeposited cobalt thin films on n-Si(1 1 1)

    Science.gov (United States)

    Mechehoud, Fayçal; Khelil, Abdelbacet; Eddine Hakiki, Nour; Bubendorff, Jean-Luc

    2016-08-01

    The nucleation and growth of Co electrodeposits on n-Si(1 1 1) substrate have been investigated as a function of the applied potential in a large potential range using electrochemical techniques (voltammetry and chrono-amperometry) and surface imaging by atomic force microscopy (AFM). The surface preparation of the sample is crucial and we achieve a controlled n-Si(1 1 1) surface with mono-atomic steps and flat terraces. Using Scharifker-Hills models for fitting the current-time transients, we show that a transition from an instantaneous nucleation process to a progressive one occurs when the overpotential increases. A good agreement between the nucleation and growth parameters extracted from the models and the AFM data's is observed. The growth is of the Volmer-Weber type with a roughness and a spatial extension in the substrate plane of the deposited islands that increase with thickness.

  16. Electron molecular beam epitaxy: Layer-by-layer growth of complex oxides via pulsed electron-beam deposition

    Energy Technology Data Exchange (ETDEWEB)

    Comes, Ryan; Liu Hongxue; Lu Jiwei [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Gu, Man [Department of Physics, University of Virginia, Charlottesville, Virginia 22904 (United States); Khokhlov, Mikhail; Wolf, Stuart A. [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Guilford College, Greensboro, North Carolina 27410 (United States)

    2013-01-14

    Complex oxide epitaxial film growth is a rich and exciting field, owing to the wide variety of physical properties present in oxides. These properties include ferroelectricity, ferromagnetism, spin-polarization, and a variety of other correlated phenomena. Traditionally, high quality epitaxial oxide films have been grown via oxide molecular beam epitaxy or pulsed laser deposition. Here, we present the growth of high quality epitaxial films using an alternative approach, the pulsed electron-beam deposition technique. We demonstrate all three epitaxial growth modes in different oxide systems: Frank-van der Merwe (layer-by-layer); Stranski-Krastanov (layer-then-island); and Volmer-Weber (island). Analysis of film quality and morphology is presented and techniques to optimize the morphology of films are discussed.

  17. Electron molecular beam epitaxy: Layer-by-layer growth of complex oxides via pulsed electron-beam deposition

    Science.gov (United States)

    Comes, Ryan; Gu, Man; Khokhlov, Mikhail; Liu, Hongxue; Lu, Jiwei; Wolf, Stuart A.

    2013-01-01

    Complex oxide epitaxial film growth is a rich and exciting field, owing to the wide variety of physical properties present in oxides. These properties include ferroelectricity, ferromagnetism, spin-polarization, and a variety of other correlated phenomena. Traditionally, high quality epitaxial oxide films have been grown via oxide molecular beam epitaxy or pulsed laser deposition. Here, we present the growth of high quality epitaxial films using an alternative approach, the pulsed electron-beam deposition technique. We demonstrate all three epitaxial growth modes in different oxide systems: Frank-van der Merwe (layer-by-layer); Stranski-Krastanov (layer-then-island); and Volmer-Weber (island). Analysis of film quality and morphology is presented and techniques to optimize the morphology of films are discussed.

  18. Linear optical studies of metal surfaces: Diffusion, growth, and surface dynamics

    Science.gov (United States)

    Nabighian, Edward Ara

    Through the use of laser-induced thermal desorption, a monolayer density grating is produced on a Ni(111) substrate. Using linear optical diffraction from this grating we monitor surface diffusion. By varying the angular direction of the grating we also monitor the azimuthal dependence of diffusion over 360° rotation. For hydrogen on Ni(111) we measured the diffusion rates from 65 K to 240 K, yielding diffusion rates which vary from 2 × 10 -15 cm2/sec to 2 × 10-7 cm2/sec. The results reveal energies of diffusion in both the classical overbarrier hopping and phonon-assisted quantum regimes. For xenon on Ni(111) we measured the diffusion rates from 30 K to 60 K, yielding diffusion rates which vary from 1.3 × 10-10 cm2/sec to 1 × 10-9 cm2/sec. In the case of xenon diffusion, the results also reveal an unusually low diffusivity. In addition, growth measurements of xenon on Ni(111) were studied from 35 K to 60 K using an optical reflectance difference technique. The growth of xenon was found to change mechanisms as temperature varied. At 35 K xenon grows in 3-dimensional islands (Volmer-Weber growth), at 40 K xenon grows as 2-dimensional islands (Frank van der Merwe growth), and above 60 K xenon grows to a thickness of only one monolayer. We can not only monitor the growth mechanism, but the growth rate as well. Finally we use optical reflectance difference to monitor sputtering and annealing on the Ni(111) substrate. The competing surface roughening of sputtering and surface reordering of annealing was found to follow an Arrhenius form with an activation energy of Ea = 1.1 eV/atom given by direct atom evaporation from step edges. By monitoring the formation of islands and pits on the surface during sputtering at various temperatures we are able to determine that above 823 K the annealing process reorders the surface faster than sputtering can create surface roughness. As temperature decreases we see an increase in island and pit formation due to the lessened

  19. Comparison study of catalyst nanoparticle formation and carbon nanotube growth: Support effect

    Science.gov (United States)

    Wang, Yunyu; Luo, Zhiquan; Li, Bin; Ho, Paul S.; Yao, Zhen; Shi, Li; Bryan, Eugene N.; Nemanich, Robert J.

    2007-06-01

    A comparison study has been conducted on the formation of catalyst nanoparticles on a high surface tension metal and low surface tension oxide for carbon nanotube (CNT) growth via catalytic chemical vapor deposition (CCVD). Silicon dioxide (SiO2) and tantalum have been deposited as supporting layers before deposition of a thin layer of iron catalyst. Iron nanoparticles were formed after thermal annealing. It was found that densities, size distributions, and morphologies of iron nanoparticles were distinctly different on the two supporting layers. In particular, iron nanoparticles revealed a Volmer-Weber growth mode on SiO2 and a Stranski-Krastanov mode on tantalum. CCVD growth of CNTs was conducted on iron/tantalum and iron/SiO2. CNT growth on SiO2 exhibited a tip growth mode with a slow growth rate of less than 100nm /min. In contrast, the growth on tantalum followed a base growth mode with a fast growth rate exceeding 1μm/min. For comparison, plasma enhanced CVD was also employed for CNT growth on SiO2 and showed a base growth mode with a growth rate greater than 2μm /min. The enhanced CNT growth rate on tantalum was attributed to the morphologies of iron nanoparticles in combination with the presence of an iron wetting layer. The CNT growth mode was affected by the adhesion between the catalyst and support as well as CVD process.

  20. Ultra thin films of nanocrystalline Ge studied by AFM and interference enhanced Raman scattering

    Indian Academy of Sciences (India)

    S Balaji; S Mohan; D V S Muthu; A K Sood

    2003-10-01

    Initial growth stages of the ultra thin films of germanium (Ge) prepared by ion beam sputter deposition have been studied using atomic force microscope (AFM) and interference enhanced Raman scattering. The growth of the films follows Volmer-Weber growth mechanism. Analysis of the AFM images shows that Ostwald ripening of the grains occurs as the thickness of the film increases. Raman spectra of the Ge films reveal phonon confinement along the growth direction and show that the misfit strain is relieved for film thickness greater than 4 nm.

  1. Role of limited hydrogen and flow interval on the growth of single crystal to continuous graphene by low-pressure chemical vapor deposition

    Science.gov (United States)

    Borah, Munu; Pathak, Abhishek K.; Singh, Dilip K.; Pal, Prabir; Dhakate, Sanjay R.

    2017-02-01

    A method for defect-free large crystallite graphene growth remains unknown despite much research effort. In this work, we discuss the role of flow duration of H2 gas for the production of graphene as per requirement and production at a minimum flow rate considering the safety issue of hydrogen utilization. The copper substrate used for growth was treated for different time intervals (0 to 35 min) in H2 flow prior to growth. Structural and chemical changes occurring in the copper substrate surface were probed by grazing incidence x-ray diffraction and x-ray photoelectron spectroscopy. The results were correlated with the Raman spectroscopy data, which can quantify the quality of graphene. With increasing H2 flow interval, secondary nucleation sites were observed and growth favored few-layer graphene structures. The surface-adsorbed oxygen molecules and its conversion to an OH terminated surface with increasing hydrogen flow interval was found to be a key factor in enhancing nucleation density. The Stranski-Krastanov type of nucleation was observed for samples grown with different time intervals of H2 treatment, except 5 min of H2 flow prior to growth for which the Volmer-Weber type of growth favored monolayer graphene crystallite growth.

  2. The crack growth mechanism in asphaltic mixes

    NARCIS (Netherlands)

    Jacobs, .M.M.J.; Hopman, P.C.; Molenaar, A.A.A.

    1995-01-01

    The crack growth mechanism in asphalt concrete (Ac) mixes is studied. In cyclic tests on several asphaltic mixes crack growth is measured, both with crack foils and with cOD-gauges. It is found that crack growth in asphaltic mixes is described by three processes which are parallel in time: cohesive

  3. Nucleation-Mediated Lateral Growth of Crystalline Islands on Foreign Substrate: an Origin of Long-Range Ordering in Pattern Formation

    Science.gov (United States)

    Wang, Mu; Shu, Dajun; Peng, Ruwen; Ming, Naiben

    2007-06-01

    Heteroepitaxial thin film growth may start by nucleating three-dimensional (3D) or two-dimensional (2D) islands on foreign substrate. Depending on the interfacial energies, heteroepitaxial growth can be categorized into three modes: Frank-van der Merwe (FM), Stranski-Krastanow (SK), and Volmer-Weber (VW). In this lecture, we concentrate on the detail process of horizontal extension of a crystalline island on foreign substrate via successive nucleation at the concave corner of the crystal facet and the foreign substrate. It is demonstrated that due to the difference of surface tensions at the concave corner, once a nucleus appears at the corner, the crystallographic orientation of the nucleus is spontaneously twisted. By successive nucleation at the concave corner, the crystalline layer develops laterally, with its crystallographic orientation continuously rotated. Such a previously untouched effect could be the physical origin to form a few regular spatial patterns in the interfacial growth. A theory is developed, which provides a criterion to observe such an effect in the nucleation-mediated lateral growth.

  4. Direct growth of Ge quantum dots on a graphene/SiO2/Si structure using ion beam sputtering deposition.

    Science.gov (United States)

    Zhang, Z; Wang, R F; Zhang, J; Li, H S; Zhang, J; Qiu, F; Yang, J; Wang, C; Yang, Y

    2016-07-29

    The growth of Ge quantum dots (QDs) using the ion beam sputtering deposition technique has been successfully conducted directly on single-layer graphene supported by SiO2/Si substrate. The results show that the morphology and size of Ge QDs on graphene can be modulated by tuning the Ge coverage. Charge transfer behavior, i.e. doping effect in graphene has been demonstrated at the interface of Ge/graphene. Compared with that of traditional Ge dots grown on Si substrate, the positions of both corresponding photoluminescence (PL) peaks of Ge QDs/graphene hybrid structure undergo a large red-shift, which can probably be attributed to the lack of atomic intermixing and the existence of surface states in this hybrid material. According to first-principles calculations, the Ge growth on the graphene should follow the so-called Volmer-Weber mode instead of the Stranski-Krastanow one which is observed generally in the traditional Ge QDs/Si system. The calculations also suggest that the interaction between Ge and graphene layer can be enhanced with the decrease of the Ge coverage. Our results may supply a prototype for fabricating novel optoelectronic devices based on a QDs/graphene hybrid nanostructure.

  5. Coordination polyhedron growth mechanism model and growth habit of crystals

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A new growth mechanism model, coordination polyhedron growth mechanism model, is introduced from the angle of the coordination of anion and cation to each other at the interface. It is pointed out that the force driving the growth unit to enter the crystal lattice is the electrostatic attraction force between ions, whose relative size can be approximately measured by the electrostatic bond strength (EBS) that reaches a nearest neighbor anion (or cation) in the parent phase from a cation (or anion) at the interface. The growth habits of NaCl, ZnS, CaF2 and CsI crystals are discussed, and a new growth habit rule is proposed as follows. When the growth rate of a crystal is determined by the step generation rate, the growth habit of this crystal is related to the coordination number of the ion with the smallest coordination rate at the interface of various crystal faces. The smaller the coordination number of the ion at the interface, the faster the growth rate of corresponding crystal face. When the growth of a crystal depends on the step movement rate, the growth habit of this crystal is related to the density of the ion with the smallest coordination rate at the interface of various crystal faces. The smaller the densities of the ion at the interface is, the faster the growth rate of corresponding crystal face will be.

  6. Statistical mechanics of stochastic growth phenomena

    CERN Document Server

    Alekseev, Oleg

    2016-01-01

    We develop statistical mechanics for stochastic growth processes as applied to Laplacian growth by using its remarkable connection with a random matrix theory. The Laplacian growth equation is obtained from the variation principle and describes adiabatic (quasi-static) thermodynamic processes in the two-dimensional Dyson gas. By using Einstein's theory of thermodynamic fluctuations we consider transitional probabilities between thermodynamic states, which are in a one-to-one correspondence with planar domains. Transitions between these domains are described by the stochastic Laplacian growth equation, while the transitional probabilities coincide with the free-particle propagator on the infinite dimensional complex manifold with the K\\"ahler metric.

  7. The mathematics and mechanics of biological growth

    CERN Document Server

    Goriely, Alain

    2017-01-01

    This monograph presents a general mechanical theory for biological growth. It provides both a conceptual and a technical foundation for the understanding and analysis of problems arising in biology and physiology. The theory and methods is illustrated on a wide range of examples and applications. A process of extreme complexity, growth plays a fundamental role in many biological processes and is considered to be the hallmark of life itself. Its description has been one of the fundamental problems of life sciences, but until recently, it has not attracted much attention from mathematicians, physicists, and engineers. The author herein presents the first major technical monograph on the problem of growth since D’Arcy Wentworth Thompson’s 1917 book On Growth and Form. The emphasis of the book is on the proper mathematical formulation of growth kinematics and mechanics. Accordingly, the discussion proceeds in order of complexity and the book is divided into five parts. First, a general introduction on the pro...

  8. Concepts on Low Temperature Mechanical Grain Growth

    Energy Technology Data Exchange (ETDEWEB)

    Sharon, John Anthony [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Metallurgy and Materials Joining Dept.; Boyce, Brad Lee [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States). Metallurgy and Materials Joining Dept.

    2013-11-01

    In metals, as grain size is reduced below 100nm, conventional dislocation plasticity is suppressed resulting in improvements in strength, hardness, and wears resistance. Existing and emerging components use fine grained metals for these beneficial attributes. However, these benefits can be lost in service if the grains undergo growth during the component’s lifespan. While grain growth is traditionally viewed as a purely thermal process that requires elevated temperature exposure, recent evidence shows that some metals, especially those with nanocrystalline grain structure, can undergo grain growth even at room temperature or below due to mechanical loading. This report has been assembled to survey the key concepts regarding how mechanical loads can drive grain coarsening at room temperature and below. Topics outlined include the atomic level mechanisms that facilitate grain growth, grain boundary mobility, and the impact of boundary structure, loading scheme, and temperature.

  9. Growth and development: hereditary and mechanical modulations.

    Science.gov (United States)

    Mao, Jeremy J; Nah, Hyun-Duck

    2004-06-01

    Growth and development is the net result of environmental modulation of genetic inheritance. Mesenchymal cells differentiate into chondrogenic, osteogenic, and fibrogenic cells: the first 2 are chiefly responsible for endochondral ossification, and the last 2 for sutural growth. Cells are influenced by genes and environmental cues to migrate, proliferate, differentiate, and synthesize extracellular matrix in specific directions and magnitudes, ultimately resulting in macroscopic shapes such as the nose and the chin. Mechanical forces, the most studied environmental cues, readily modulate bone and cartilage growth. Recent experimental evidence demonstrates that cyclic forces evoke greater anabolic responses of not only craniofacial sutures, but also cranial base cartilage. Mechanical forces are transmitted as tissue-borne and cell-borne mechanical strain that in turn regulates gene expression, cell proliferation, differentiation, maturation, and matrix synthesis, the totality of which is growth and development. Thus, hereditary and mechanical modulations of growth and development share a common pathway via genes. Combined approaches using genetics, bioengineering, and quantitative biology are expected to bring new insight into growth and development, and might lead to innovative therapies for craniofacial skeletal dysplasia including malocclusion, dentofacial deformities, and craniofacial anomalies such as cleft palate and craniosynostosis, as well as disorders associated with the temporomandibular joint.

  10. Introducing Viewpoints of Mechanics into Basic Growth Analysis-(XIII) : Comparing Growth Mechanics between Logistic Functions and Basic Growth Functions-

    OpenAIRE

    Shimojo, Masataka; Shao, Tao; Ishimatsu, Satoshi; Tanoue, Jun; Kakihara, Hidetoshi; Sata, Chiemi; Fukudome, Hayato; Ishiwaka, Reiko; Asano, Yoki; Nakano, Yutaka; Tobisa, Manabu; Masuda, Yasuhisa

    2009-01-01

    This study was conducted to compare growth mechanics between logistic functions and basic growth functions. The results obtained were as follows. Differential equation for basic growth function showed that the square of growth rate was described using the product of weight and growth acceleration. This form was similar to Newton's law of motion where differential of momentum is described using the product of mass of an object and acceleration. However, differential equation for logistic funct...

  11. Mechanism for diamond growth from methyl radicals

    Science.gov (United States)

    Harris, Stephen J.

    1990-06-01

    We use a 9-carbon model compound to describe a proposed mechanism for homoepitaxial growth of diamond from methyl radicals on a hydrogenated, electrically neutral (100) surface. We estimate enthalpy and entropy changes for each step in the mechanism using group additivity methods, taking into account the types of bonding and steric repulsions found on the (100) surface. Rate constants are estimated based on analogous reactions for hydrocarbon molecules, while gas phase species concentrations are taken from our previous measurements. The rate equations are then integrated. The method, which contains no adjustable parameters or phenomenological constants, predicts a growth rate of between 0.06 and 0.6 μm/h, depending on the local details of the surface. Uncertainties related to the use of a model compound rather than diamond are discussed. The analysis demonstrates that the proposed mechanism is feasible.

  12. Structure and Growth Mechanism of Lanthanum Chromate

    Institute of Scientific and Technical Information of China (English)

    Li Shengli; Liu Weiming; Ling Ziyu; Sun Liangcheng; Ao Qing; Fu Guifu

    2005-01-01

    The unit cell of lanthanum chromate was constructed by calculating equivalent points. By means of calculation of the hole octahedrally surrounded by O2- ions, it was considered that the sintered property of lanthanum chromate and the stability of Cr-O octahedron might be promoted by mixing a little Ca2+ ions. The growth mechanism was discussed in terms of structural ledge observed by SEM, the surfaces of the structural ledges parallel to (001), (010) and (110) planes, respectively. The misfit between (110) and (001) planes is only 0.0021 on common atomic plane, and the interconnection of the structured ledge may occur during crystal growth.

  13. Mechanical growth and morphogenesis of seashells

    KAUST Repository

    Moulton, D.E.

    2012-10-01

    Seashells grow through the local deposition of mass along the aperture. Many mathematical descriptions of the shapes of shells have been provided over the years, and the basic logarithmic coiling seen in mollusks can be simulated with few parameters. However, the developmental mechanisms underlying shell coiling are largely not understood and the ubiquitous presence of ornamentation such as ribs, tubercles, or spines presents yet another level of difficulty. Here we develop a general model for shell growth based entirely on the local geometry and mechanics of the aperture and mantle. This local description enables us to efficiently describe both arbitrary growth velocities and the evolution of the shell aperture itself. We demonstrate how most shells can be simulated within this framework. We then turn to the mechanics underlying the shell morphogenesis, and develop models for the evolution of the aperture. We demonstrate that the elastic response of the mantle during shell deposition provides a natural mechanism for the formation of three-dimensional ornamentation in shells. © 2012 Elsevier Ltd.

  14. Mechanisms of nuclear lamina growth in interphase.

    Science.gov (United States)

    Zhironkina, Oxana A; Kurchashova, Svetlana Yu; Pozharskaia, Vasilisa A; Cherepanynets, Varvara D; Strelkova, Olga S; Hozak, Pavel; Kireev, Igor I

    2016-04-01

    The nuclear lamina represents a multifunctional platform involved in such diverse yet interconnected processes as spatial organization of the genome, maintenance of mechanical stability of the nucleus, regulation of transcription and replication. Most of lamina activities are exerted through tethering of lamina-associated chromatin domains (LADs) to the nuclear periphery. Yet, the lamina is a dynamic structure demonstrating considerable expansion during the cell cycle to accommodate increased number of LADs formed during DNA replication. We analyzed dynamics of nuclear growth during interphase and changes in lamina structure as a function of cell cycle progression. The nuclear lamina demonstrates steady growth from G1 till G2, while quantitative analysis of lamina meshwork by super-resolution microscopy revealed that microdomain organization of the lamina is maintained, with lamin A and lamin B microdomain periodicity and interdomain gap sizes unchanged. FRAP analysis, in contrast, demonstrated differences in lamin A and B1 exchange rates; the latter showing higher recovery rate in S-phase cells. In order to further analyze the mechanism of lamina growth in interphase, we generated a lamina-free nuclear envelope in living interphase cells by reversible hypotonic shock. The nuclear envelope in nuclear buds formed after such a treatment initially lacked lamins, and analysis of lamina formation revealed striking difference in lamin A and B1 assembly: lamin A reassembled within 30 min post-treatment, whereas lamin B1 did not incorporate into the newly formed lamina at all. We suggest that in somatic cells lamin B1 meshwork growth is coordinated with replication of LADs, and lamin A meshwork assembly seems to be chromatin-independent process.

  15. Crossover from layering to island formation in Langmuir-Blodgett growth: Role of long-range intermolecular forces

    Science.gov (United States)

    Mukherjee, Smita; Datta, Alokmay

    2011-04-01

    Combined studies by atomic force microscopy, x-ray reflectivity, and Fourier transform infrared spectroscopy on transition-metal stearate (M-St, M = Mn, Co, Zn, and Cd) Langmuir-Blodgett films clearly indicate association of bidentate coordination of the metal-carboxylate head group to layer-by-layer growth as observed in MnSt and CoSt and partially in ZnSt. Crossover to islandlike growth, as observed in CdSt and ZnSt, is associated with the presence of unidentate coordination in the head group. Morphological evolutions as obtained from one, three, and nine monolayers (MLs) of M-St films are consistent with Frank van der Merwe, Stranski-Krastanov, and Volmer Weber growth modes for M=Mn/Co, Zn, and Cd, respectively, as previously assigned, and are found to vary with number (n) of metal atoms per head group, viz. n=1 (Mn/Co), n=0.75 (Zn), and n=0.5 (Cd). The parameter n is found to decide head-group coordination such that n=1.0 corresponds to bidentate and n=0.5 corresponds to unidentate coordination; the intermediate value in Zn corresponds to a mixture of both. The dependence of the growth mode on head-group structure is explained by the fact that in bidentate head groups, with the in-plane dipole moment being zero, intermolecular forces between adjacent molecules are absent and hence growth proceeds via layering. On the other hand, in unidentate head groups, the existence of a nonzero in-plane dipole moment results in the development of weak in-plane intermolecular forces between adjacent molecules causing in-plane clustering leading to islandlike growth.

  16. Crossover from layering to island formation in Langmuir-Blodgett growth: role of long-range intermolecular forces.

    Science.gov (United States)

    Mukherjee, Smita; Datta, Alokmay

    2011-04-01

    Combined studies by atomic force microscopy, x-ray reflectivity, and Fourier transform infrared spectroscopy on transition-metal stearate (M-St, M = Mn, Co, Zn, and Cd) Langmuir-Blodgett films clearly indicate association of bidentate coordination of the metal-carboxylate head group to layer-by-layer growth as observed in MnSt and CoSt and partially in ZnSt. Crossover to islandlike growth, as observed in CdSt and ZnSt, is associated with the presence of unidentate coordination in the head group. Morphological evolutions as obtained from one, three, and nine monolayers (MLs) of M-St films are consistent with Frank van der Merwe, Stranski-Krastanov, and Volmer Weber growth modes for M=Mn/Co, Zn, and Cd, respectively, as previously assigned, and are found to vary with number (n) of metal atoms per head group, viz. n=1 (Mn/Co), n=0.75 (Zn), and n=0.5 (Cd). The parameter n is found to decide head-group coordination such that n=1.0 corresponds to bidentate and n=0.5 corresponds to unidentate coordination; the intermediate value in Zn corresponds to a mixture of both. The dependence of the growth mode on head-group structure is explained by the fact that in bidentate head groups, with the in-plane dipole moment being zero, intermolecular forces between adjacent molecules are absent and hence growth proceeds via layering. On the other hand, in unidentate head groups, the existence of a nonzero in-plane dipole moment results in the development of weak in-plane intermolecular forces between adjacent molecules causing in-plane clustering leading to islandlike growth.

  17. Molecular-beam epitaxy growth and structural characterization of semiconductor-ferromagnet heterostructures by grazing incidence X-ray diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Satapathy, D.K.

    2005-12-19

    The present work is devoted to the growth of the ferromagnetic metal MnAs on the semiconductor GaAs by molecular-beam epitaxy (MBE). The MnAs thin films are deposited on GaAs by molecular-beam epitaxy (MBE). Grazing incidence diffraction (GID) and reflection high-energy electron diffraction (RHEED) are used in situ to investigate the nucleation, evolution of strain, morphology and interfacial structure during the MBE growth. Four stages of the nucleation process during growth of MnAs on GaAs(001) are revealed by RHEED azimuthal scans. GID shows that further growth of MnAs films proceed via the formation of relaxed islands at a nominal thickness of 2.5 ML which increase in size and finally coalesce to form a continuous film. Early on, an ordered array of misfit dislocations forms at the interface releasing the misfit strain even before complete coalescence occurs. The fascinating complex nucleation process of MnAs on GaAs(0 0 1) contains elements of both Volmer-Weber and Stranski-Krastanov growth. A nonuniform strain amounting to 0.66%, along the [1 -1 0] direction and 0.54%, along the [1 1 0] direction is demonstrated from x-ray line profile analysis. A high correlation between the defects is found along the GaAs[1 1 0] direction. An extremely periodic array of misfit dislocations with a period of 4.95{+-}0.05 nm is formed at the interface along the [1 1 0] direction which releases the 7.5% of misfit. The inhomogeneous strain due to the periodic dislocations is confined at the interface within a layer of 1.6 nm thickness. The misfit along the [1 -1 0] direction is released by the formation of a coincidence site lattice. (orig.)

  18. Influence of temperature on the controlled growth kinetics and superstructural phase formation of indium on a reconstructed Si (113) 3 × 2 surface

    Science.gov (United States)

    Krishna TC, Shibin; Deshmukh, Rahul; Singh Chauhan, Amit Kumar; Goswami, Lalit; Govind

    2014-03-01

    The kinetics of growth, thermal stability and superstructural phase formation of the indium atom on a reconstructed Si (113) 3 × 2 surface at room temperature (RT), as well as at high substrate temperature (HT), is discussed. It was observed that at a very low flux rate of 0.08 ML min-1, In-adsorption at RT follows the Frank-van der Merwe (FM) growth mode, while for HT (>200 °C), In-islands (the Volmer-Weber-growth mode) were formed. The residual thermal desorption (RTD) analysis revealed the anomalous behaviour of temperature-driven layering to the clustering rearrangement of In atoms on the Si (113) surface for RT- and 200 °C-grown systems. The RTD study also demonstrates the effect of temperature on growth kinetics as well as on the multilayer/monolayer desorption pathway. The calculated bilayer desorption energy was found to be different for RT- (T B, 0.48 eV) and HT- (T B, 1.57 eV) grown In/Si(113) systems, while the monolayer desorption energy (T M, 2.56 eV) was the same in both the cases. Various coverage-dependent superstructural phases, such as Si(113) 3 × 2 + 3 × 1, 3 × 1, 3 × 2 + 1 × 3 and 1 × 1, have been observed during the RT- and HT-growth of In on the Si (113) surface. A complete phase diagram of In/Si(113) is deduced which depicts the evolution of novel phases as a function of substrate temperature and coverage.

  19. Grafted silane monolayers: reconsideration of growth mechanisms

    Science.gov (United States)

    Ivanov, D. A.; Nysten, B.; Jonas, A. M.; Legras, R.

    1998-03-01

    Chemical force microscopy is a new technique devised to image chemical heterogeneities on surfaces. It requires the chemical modification of Atomic Force Microscopy (AFM) tips in order to create chemical probes. In this respect, self-assembled monolayers (SAM) of alkylchlorosilanes are particularly interesting as modifying agents for AFM tips. We report here our results on the kinetics of silanization and on the structure of such SAM's grafted on model surfaces (hydroxylated Si(100) wafers). AFM, contact angle measurements, X-ray reflectivity and X-ray photoelectron spectroscopy were used to characterize SAM's of octadecyltrichlorosilane (OTS) and octadecyldimethylchlorosilane (ODMS) grown from hexadecane and toluene solutions. The mechanism of grafting of OTS follows two stages. The first rapid stage corresponds to the nucleation and growth of island-like monolayer domains. The second slower stage is related to the densification of the monolayer. SAM's of ODMS were found to form thinner layers as compared to OTS, due to their lower grafting density probably resulting in a more disordered state of grafted alkyl chains. We also address the problems concerning the relationships between the quality of final SAM structures and the water content as well as the nature of the solvent used for silanization.

  20. Mechanics, growth, and class II corrections.

    Science.gov (United States)

    Hultgren, B W; Isaacson, R J; Erdman, A G; Worms, F W

    1978-10-01

    Growth of the orofacial region is quantitatively described by locating the center of mandibular rotation relative to the cranial base. The center of mandibular rotation is positioned by the ratio of vertical facial growth (AFH/PFH) and the direction of condylar growth. Appliance therapy is associated with changes in the means of both of these parameters. These changes reduce or stop favorable anterior mandibular rotation and redirect the mean condylar growth vector more posteriorly. When appliance therapy is stopped, these parameters return toward their resting values. The mean direction of the condylar growth vector became even more anteriorly directed after treatment than the pretreatment mean value. These data support the hypothesis that orthodontic appliances significantly alter the facial growth pattern and when they are stopped, the growth pattern tends to rebound to or beyond the pretreatment values.

  1. Temperature Dependence of Growth Mechanism for Nanoscale High Tc Superconductors

    Institute of Scientific and Technical Information of China (English)

    Wu-Ming Chen; Mustafa Yavuz; Jian-Xun Jin

    2008-01-01

    The growth mechanisms of high temper- ature Yttrium- and Bismuth-based-superconductors were investigated at nanoscale. We started with studying the growth relationships among the three phases of Bi-2201, Bi-2212, and Bi-2233, and then extended to another growth mechanism of Bi-2223 and the growth of yttrium-based high-temperature nanosupercon- ductors (nano-YBCO). A time dependence of growth experiment was performed. In this experiment, the Bi-based superconductors grew within different sintering periods, and its three phases were determined by X-ray diffraction. And then, a time dependence of growth model was suggested to explain the experimental facts. With this model, governing equations were derived to quantitatively describe the growth and decomposition mechanisms during sintering period. The results calculated from the derived equations were well in agreement with the experimental data. We also suggested an alternative growth mechanism for the Bi-2223 phase, which was supported by an observation of transmission electron microscopy (TEM). The nano-YBCO also grew, and their orthorhombic crystal structures were determined by the TEM. The superconducting properties of Bi-2223 were investigated by the measurements of ac magnetic susceptibility. It is expected that the derived equations will fit the alter- native experimental growth mechanism of the Bi-2223 phase and the nano-YBCO growth mechanism, too.

  2. Advances in the understanding of crystal growth mechanisms

    CERN Document Server

    Nishinaga, T; Harada, J; Sasaki, A; Takei, H

    1997-01-01

    This book contains the results of a research project entitled Crystal Growth Mechanisms on an Atomic Scale, which was carried out for 3 years by some 72 reseachers. Until recently in Japan, only the technological aspects of crystal growth have been emphasized and attention was paid only to its importance in industry. However the scientific aspects also need to be considered so that the technology of crystal growth can be developed even further. This project therefore aimed at understanding crystal growth and the emphasis was on finding growth mechanisms on an atomic scale.

  3. A Simple Mechanical Experiment on Exponential Growth

    Science.gov (United States)

    McGrew, Ralph

    2015-01-01

    With a rod, cord, pulleys, and slotted masses, students can observe and graph exponential growth in the cord tension over a factor of increase as large as several hundred. This experiment is adaptable for use either in algebra-based or calculus-based physics courses, fitting naturally with the study of sliding friction. Significant parts of the…

  4. Introducing Viewpoints of Mechanics into Basic Growth Analysis : (VII) Mathematical Properties of Basic Growth Mechanics in Ruminant

    OpenAIRE

    Shimojo, Masataka; Shao, Tao; Masuda, Yasuhisa

    2008-01-01

    This study was conducted to investigate mathematical properties of basic growth mechanics in ruminant by introducing newly developed viewpoints into mathematical operations of basic growth function. The negative sign, which appeared naturally by taking the square root of the differential equation based on basic growth mechanics, gave mathematical contradictions to the differential principle. In the process of correcting those contradictions, viewpoints of interest were newly introduced to giv...

  5. Mechanically induced alterations in cultured skeletal muscle growth

    Science.gov (United States)

    Vandenburgh, H. H.; Hatfaludy, S.; Karlisch, P.; Shansky, J.

    1991-01-01

    Model systems are available for mechanically stimulating cultured skeletal muscle cells by passive tensile forces which simulate those found in vivo. When applied to embryonic muscle cells in vitro these forces induce tissue organogenesis, metabolic adaptations, and muscle cell growth. The mechanical stimulation of muscle cell growth correlates with stretch-induced increases in the efflux of prostaglandins PGE2 and PGF2(alpha) in a time and frequency dependent manner. These prostaglandins act as mechanical 'second messengers' regulating skeletal muscle protein turnover rates. Since they also effect bone remodelling in response to tissue loading and unloading, secreted prostaglandins may serve as paracrine growth factors, coordinating the growth rates of muscle and bone in response to external mechanical forces. Cell culture model systems will supplement other models in understanding mechanical transduction processes at the molecular level.

  6. Mechanically induced alterations in cultured skeletal muscle growth

    Science.gov (United States)

    Vandenburgh, H. H.; Hatfaludy, S.; Karlisch, P.; Shansky, J.

    1991-01-01

    Model systems are available for mechanically stimulating cultured skeletal muscle cells by passive tensile forces which simulate those found in vivo. When applied to embryonic muscle cells in vitro these forces induce tissue organogenesis, metabolic adaptations, and muscle cell growth. The mechanical stimulation of muscle cell growth correlates with stretch-induced increases in the efflux of prostaglandins PGE2 and PGF2(alpha) in a time and frequency dependent manner. These prostaglandins act as mechanical 'second messengers' regulating skeletal muscle protein turnover rates. Since they also effect bone remodelling in response to tissue loading and unloading, secreted prostaglandins may serve as paracrine growth factors, coordinating the growth rates of muscle and bone in response to external mechanical forces. Cell culture model systems will supplement other models in understanding mechanical transduction processes at the molecular level.

  7. Mechanisms of pancreatic beta-cell growth and regeneration

    DEFF Research Database (Denmark)

    Nielsen, Jens Høiriis

    1989-01-01

    Information about the mechanism of beta-cell growth and regeneration may be obtained by studies of insulinoma cells. In the present study the growth and function of the rat insulinoma cell lines RINm5F and 5AH were evaluated by addition of serum, hormones, and growth factors. It was found...... of insulin mRNA content showed that the insulinoma cells only contained about 2% of that of normal rat beta-cells. These results are discussed in relation to the role of growth factors, oncogenes, and differentiation in the growth and regeneration of beta-cells....

  8. Differential growth triggers mechanical feedback that elevates Hippo signaling.

    Science.gov (United States)

    Pan, Yuanwang; Heemskerk, Idse; Ibar, Consuelo; Shraiman, Boris I; Irvine, Kenneth D

    2016-10-26

    Mechanical stress can influence cell proliferation in vitro, but whether it makes a significant contribution to growth control in vivo, and how it is modulated and experienced by cells within developing tissues, has remained unclear. Here we report that differential growth reduces cytoskeletal tension along cell junctions within faster-growing cells. We propose a theoretical model to explain the observed reduction of tension within faster-growing clones, supporting it by computer simulations based on a generalized vertex model. This reduced tension modulates a biomechanical Hippo pathway, decreasing recruitment of Ajuba LIM protein and the Hippo pathway kinase Warts, and decreasing the activity of the growth-promoting transcription factor Yorkie. These observations provide a specific mechanism for a mechanical feedback that contributes to evenly distributed growth, and we show that genetically suppressing mechanical feedback alters patterns of cell proliferation in the developing Drosophila wing. By providing experimental support for the induction of mechanical stress by differential growth, and a molecular mechanism linking this stress to the regulation of growth in developing organs, our results confirm and extend the mechanical feedback hypothesis.

  9. Mechanisms of muscle growth and atrophy in mammals and Drosophila

    National Research Council Canada - National Science Library

    Piccirillo, Rosanna; Demontis, Fabio; Perrimon, Norbert; Goldberg, Alfred L

    2014-01-01

    .... Although the pathogenesis of this condition has been primarily studied in mammals, Drosophila is emerging as an attractive system to investigate some of the mechanisms involved in muscle growth and atrophy. Results...

  10. Growth mechanism and quantum confinement effect of silicon nanowires

    Institute of Scientific and Technical Information of China (English)

    冯孙齐; 俞大鹏; 张洪洲; 白志刚; 丁彧; 杭青岭; 邹英华; 王晶晶

    1999-01-01

    The methods for synthesizing one-dimensional Si nanowires with controlled diameter are introduced. The mechanism for the growth of Si nanowires and the growth model for different morphologies of Si nanowires are described, and the quantum confinement effect of the Si nanowires is presented.

  11. Introducing Viewpoints of Mechanics into Basic Growth Analysis (1) : Three Aspects of Growth Mechanics compared with Three Law of Motion

    OpenAIRE

    Shimojo, Masataka; Ikeda, Kentaro; Asano, Yoki; Ishiwaka, Reiko; Sato, Hiroyuki; Nakano, Yutaka; Tobisa, Manabu; Oba, Noriko; Eguchi, Minako; Masuda, Yasuhisa

    2006-01-01

    This study was conducted to analyze growth phenomena by introducing mechanical viewpoints into basic growth analysis. Relating weight (W), absolute growth rate (AGR) and growth acceleration (GA) suggested that (AGR)^2, which was described as the product of W and GA, looked like force involved in the growth of an animal or a plant. This might be due to the resemblance to the second law of Newton’s three laws of motion, where the product of mass and acceleration is related with force to an obje...

  12. Molecular Dynamic Simulation of Thin Film Growth Stress Evolution

    Science.gov (United States)

    Zheng, Haifeng

    2011-12-01

    With the increasing demand for thin films across a wide range of technology, especially in electronic and magnetic applications, controlling the stresses in deposited thin films has become one of the more important challenges in modern engineering. It is well known that large intrinsic stress---in the magnitude of several gigapascals---can result during the thin film preparation. The magnitude of stress depends on the deposition technique, film thickness, types and structures of materials used as films and substrates, as well as other factors. Such large intrinsic stress may lead to film cracking and peeling in case of tensile stress, and delamination and blistering in case of compression. However it may also have beneficial effects on optoelectronics and its applications. For example, intrinsic stresses can be used to change the electronic band gap of semiconducting materials. The far-reaching fields of microelectronics and optoelectronics depend critically on the properties, behavior, and reliable performance of deposited thin films. Thus, understanding and controlling the origins and behavior of such intrinsic stresses in deposited thin films is a highly active field of research. In this study, on-going tensile stress evolution during Volmer-Weber growth mode was analyzed through numerical methods. A realistic model with semi-cylinder shape free surfaces was used and molecular dynamics simulations were conducted. Simulations were at room temperature (300 K), and 10 nanometer diameter of islands were used. A deposition rate that every 3 picoseconds deposit one atom was chosen for simulations. The deposition energy was and lattice orientation is [0 0 1]. Five different random seeds were used to ensure average behaviors. In the first part of this study, initial coalescence stress was first calculated by comparing two similar models, which only differed in the distance between two neighboring islands. Three different substrate thickness systems were analyzed to

  13. Inhibition mechanism of aspartic acid on crystal growth of hydroxyapatite

    Institute of Scientific and Technical Information of China (English)

    HUANG Su-ping; ZHOU Ke-chao; LI Zhi-you

    2007-01-01

    The effects of aspartic acid on the crystal growth, morphology of hydroxyapatite(HAP) crystal were investigated, and the inhibition mechanism of aspartic acid on the crystal growth of hydroxyapatite was studied. The results show that the crystal growth rate of HAP decreases with the increase of the aspartic acid concentration, and the HAP crystal is thinner significantly compared with that without amino acid, which is mainly due to the (10(-)10) surface of HAP crystal being inhibited by the aspartic acids. The calculation analysis indicates that the crystal growth mechanism of HAP, following surface diffusion controlled mechanism, is not changed due to the presence of aspartic acid. AFM result shows that the front of terrace on vicinal growth hillocks is pinned, which suggests that the aspartic acid is adsorbed onto the (10(-)10) surface of HAP and interacts with the Ca2+ ions of HAP surface, so as to block the growth active sites and result in retarding of the growth of HAP crystal.

  14. Thermo-Mechanical Fatigue Crack Growth of RR1000

    Directory of Open Access Journals (Sweden)

    Christopher John Pretty

    2017-01-01

    Full Text Available Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP testing produces accelerated crack growth rates compared with out-of-phase (OOP due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180° OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles.

  15. Thermo-Mechanical Fatigue Crack Growth of RR1000

    Science.gov (United States)

    Pretty, Christopher John; Whitaker, Mark Thomas; Williams, Steve John

    2017-01-01

    Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF) evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180° OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles. PMID:28772394

  16. Thermo-Mechanical Fatigue Crack Growth of RR1000.

    Science.gov (United States)

    Pretty, Christopher John; Whitaker, Mark Thomas; Williams, Steve John

    2017-01-04

    Non-isothermal conditions during flight cycles have long led to the requirement for thermo-mechanical fatigue (TMF) evaluation of aerospace materials. However, the increased temperatures within the gas turbine engine have meant that the requirements for TMF testing now extend to disc alloys along with blade materials. As such, fatigue crack growth rates are required to be evaluated under non-isothermal conditions along with the development of a detailed understanding of related failure mechanisms. In the current work, a TMF crack growth testing method has been developed utilising induction heating and direct current potential drop techniques for polycrystalline nickel-based superalloys, such as RR1000. Results have shown that in-phase (IP) testing produces accelerated crack growth rates compared with out-of-phase (OOP) due to increased temperature at peak stress and therefore increased time dependent crack growth. The ordering of the crack growth rates is supported by detailed fractographic analysis which shows intergranular crack growth in IP test specimens, and transgranular crack growth in 90° OOP and 180° OOP tests. Isothermal tests have also been carried out for comparison of crack growth rates at the point of peak stress in the TMF cycles.

  17. Selective LPCVD growth of graphene on patterned copper and its growth mechanism

    Science.gov (United States)

    Zhang, M.; Huang, B.-C.; Wang, Y.; Woo, J. C. S.

    2016-12-01

    Copper-catalyzed graphene low-pressure chemical-vapor deposition (LPCVD) growth has been regarded as a viable solution towards its integration to CMOS technology, and the wafer-bonding method provides a reliable alternative for transferring the selective graphene grown on a patterned metal film for IC manufacturing. In this paper, selective LPCVD graphene growth using patterned copper dots has been studied. The Raman spectra of grown films have demonstrated large dependence on the growth conditions. To explain the results, the growth mechanisms based on surface adsorption and copper-vapor-assisted growth are investigated by the comparison between the blanket copper films with/without the additional copper source. The copper vapor density is found to be critical for high-quality graphene growth. In addition, the copper-vapor-assisted growth is also evidenced by the carbon deposition on the SiO2 substrate of the patterned-copper-dot sample and chamber wall during graphene growth. This growth mechanism explains the correlation between the growth condition and Raman spectrum for films on copper dots. The study on the copper-catalyzed selective graphene growth on the hard substrate paves the way for the synthesis and integration of the 2D material in VLSI.

  18. Growth of ZnO nanostructures on Au-coated Si: Influence of growth temperature on growth mechanism and morphology

    DEFF Research Database (Denmark)

    Kumar, Rajendra; McGlynn, E.; Biswas, M.;

    2008-01-01

    ZnO nanostructures were grown on Au-catalyzed Si silicon substrates using vapor phase transport at growth temperatures from 800 to 1150 degrees C. The sample location ensured a low Zn vapor supersaturation during growth. Nanostructures grown at 800 and 850 degrees C showed a faceted rodlike...... growth tended to dominate resulting in the formation of a porous, nanostructured morphology. In all cases growth was seen only on the Au-coated region. Our results show that the majority of the nanostructures grow via a vapor-solid mechanism at low growth temperatures with no evidence of Au nanoparticles...... morphology with mainly one-dimensional (1D) growth along the nanorod axis. Samples grown at intermediate temperatures (900, 950, and 1050 degrees C) in all cases showed significant three dimensional (3D) growth at the base of 1D nanostructures. At higher growth temperatures (1100 and 1150 degrees C) 3D...

  19. Novel mechanisms of growth hormone regulation: growth hormone-releasing peptides and ghrelin

    Directory of Open Access Journals (Sweden)

    A.-M.J. Lengyel

    2006-08-01

    Full Text Available Growth hormone secretion is classically modulated by two hypothalamic hormones, growth hormone-releasing hormone and somatostatin. A third pathway was proposed in the last decade, which involves the growth hormone secretagogues. Ghrelin is a novel acylated peptide which is produced mainly by the stomach. It is also synthesized in the hypothalamus and is present in several other tissues. This endogenous growth hormone secretagogue was discovered by reverse pharmacology when a group of synthetic growth hormone-releasing compounds was initially produced, leading to the isolation of an orphan receptor and, finally, to its endogenous ligand. Ghrelin binds to an active receptor to increase growth hormone release and food intake. It is still not known how hypothalamic and circulating ghrelin is involved in the control of growth hormone release. Endogenous ghrelin might act to amplify the basic pattern of growth hormone secretion, optimizing somatotroph responsiveness to growth hormone-releasing hormone. It may activate multiple interdependent intracellular pathways at the somatotroph, involving protein kinase C, protein kinase A and extracellular calcium systems. However, since ghrelin has a greater ability to release growth hormone in vivo, its main site of action is the hypothalamus. In the current review we summarize the available data on the: a discovery of this peptide, b mechanisms of action of growth hormone secretagogues and ghrelin and possible physiological role on growth hormone modulation, and c regulation of growth hormone release in man after intravenous administration of these peptides.

  20. Thermochromic VO2 on Zinnwaldite Mica by pulsed laser deposition

    Science.gov (United States)

    Mathevula, L.; Ngom, B. D.; Kotsedi, L.; Sechogela, P.; Doyle, T. B.; Ghouti, M.; Maaza, M.

    2014-09-01

    VO2 thin films have been deposited by pulsed laser deposition on Zinnwaldite Mica substrates. The crystal structure, chemical composition, morphology were determined and the semiconductor/metal transition (SMT) properties of the deposited films were investigated. Without any post annealing, the films exhibit a textured nature with a VO2 (0 1 1) preferred crystallographic orientation and an elevated thermal variation of the electric resistance ratio RS/RM through the SMT at T ≈ 68 °C of the order of 104 and a narrow ∼7 °C hysteresis. In addition, the growth of the VO2 crystallites seem to be governed likely by a Volmer-Weber or Stranski-Krastanov mechanisms and certainly not a Frank-van Der Merwe process.

  1. Signaling mechanisms in cortical axon growth, guidance and branching

    Directory of Open Access Journals (Sweden)

    Katherine eKalil

    2011-09-01

    Full Text Available Precise wiring of cortical circuits during development depends upon axon extension, guidance and branching to appropriate targets. Motile growth cones at axon tips navigate through the nervous system by responding to molecular cues, which modulate signaling pathways within axonal growth cones. Intracellular calcium signaling has emerged as a major transducer of guidance cues but exactly how calcium signaling pathways modify the actin and microtubule cytoskeleton to evoke growth cone behaviors and axon branching is still mysterious. Axons must often pause in their outgrowth while their branches extend into targets. Some evidence suggests a competition between growth of axons and branches but the mechanisms are poorly understood. Since it is difficult to study growing axons deep within the mammalian brain, much of what we know about signaling pathways and cytoskeletal dynamics has come from studies of axonal growth cones, in many cases from non-mammalian species, growing in tissue culture. Consequently it is not well understood how guidance cues relevant to mammalian neural development in vivo signal to the growth cone cytoskeleton during axon outgrowth and guidance. In this review we describe our recent work in dissociated cultures of developing rodent sensorimotor cortex in the context of the current literature on molecular guidance cues, calcium signaling pathways and cytoskeletal dynamics that regulate growth cone behaviors. A major challenge is to relate findings in tissue culture to mechanisms of cortical development in vivo. Toward this goal, we describe our recent work in cortical slices, which preserve the complex cellular and molecular environment of the mammalian brain but allow direct visualization of growth cone behaviors and calcium signaling. Findings from this work suggest that mechanisms regulating axon growth and guidance in dissociated culture neurons also underlie development of cortical connectivity in vivo.

  2. Fluid mechanics in crystal growth - The 1982 Freeman scholar lecture

    Science.gov (United States)

    Ostrach, S.

    1983-01-01

    An attempt is made to unify the current state of knowledge in crystal growth techniques and fluid mechanics. After identifying important fluid dynamic problems for such representative crystal growth processes as closed tube vapor transport, open reactor vapor deposition, and the Czochralski and floating zone melt growth techniques, research results obtained to date are presented. It is noted that the major effort to date has been directed to the description of the nature and extent of bulk transport under realistic conditions, where bulk flow determines the heat and solute transport which strongly influence the temperature and concentration fields in the vicinity of the growth interface. Proper treatment of near field, or interface, problems cannot be given until the far field, or global flow, involved in a given crystal growth technique has been adequately described.

  3. Mechanisms and applications of plant growth promoting rhizobacteria: Current perspective

    Directory of Open Access Journals (Sweden)

    Munees Ahemad

    2014-01-01

    Full Text Available Plant growth promoting rhizobacteria are the soil bacteria inhabiting around/on the root surface and are directly or indirectly involved in promoting plant growth and development via production and secretion of various regulatory chemicals in the vicinity of rhizosphere. Generally, plant growth promoting rhizobacteria facilitate the plant growth directly by either assisting in resource acquisition (nitrogen, phosphorus and essential minerals or modulating plant hormone levels, or indirectly by decreasing the inhibitory effects of various pathogens on plant growth and development in the forms of biocontrol agents. Various studies have documented the increased health and productivity of different plant species by the application of plant growth promoting rhizobacteria under both normal and stressed conditions. The plant-beneficial rhizobacteria may decrease the global dependence on hazardous agricultural chemicals which destabilize the agro-ecosystems. This review accentuates the perception of the rhizosphere and plant growth promoting rhizobacteria under the current perspectives. Further, explicit outlooks on the different mechanisms of rhizobacteria mediated plant growth promotion have been described in detail with the recent development and research. Finally, the latest paradigms of applicability of these beneficial rhizobacteria in different agro-ecosystems have been presented comprehensively under both normal and stress conditions to highlight the recent trends with the aim to develop future insights.

  4. Testing Transmission Mechanisms on Economic Growth in Malaysia

    OpenAIRE

    Wai Ching Poon

    2010-01-01

    This paper examines various transmission mechanism channels on economic growth in Malaysia over the quarterly period 1980:1-2004:4 using bounds testing approach. The bounds test reveals evidence of cointegration between the real GDP and the real exchange rate and share prices that address the exchange rate and asset price channels as the key transmission mechanisms in the conduct of the monetary policy stance. Nevertheless, the saving interest rate and credit channels are of insignificant.

  5. Growth Mechanism of Pumpkin-Shaped Vaterite Hierarchical Structures

    Science.gov (United States)

    Ma, Guobin; Xu, Yifei; Wang, Mu

    2015-03-01

    CaCO3-based biominerals possess sophisticated hierarchical structures and promising mechanical properties. Recent researches imply that vaterite may play an important role in formation of CaCO3-based biominerals. However, as a less common polymorph of CaCO3, the growth mechanism of vaterite remains not very clear. Here we report the growth of a pumpkin-shaped vaterite hierarchical structure with a six-fold symmetrical axis and lamellar microstructure. We demonstrate that the growth is controlled by supersaturation and the intrinsic crystallographic anisotropy of vaterite. For the scenario of high supersaturation, the nucleation rate is higher than the lateral extension rate, favoring the ``double-leaf'' spherulitic growth. Meanwhile, nucleation occurs preferentially in as determined by the crystalline structure of vaterite, modulating the grown products with a hexagonal symmetry. The results are beneficial for an in-depth understanding of the biomineralization of CaCO3. The growth mechanism may also be applicable to interpret the formation of similar hierarchical structures of other materials. The authors gratefully acknowledge the financial support from National Science Foundation of China (Grant Nos. 51172104 and 50972057) and National Key Basic Research Program of China (Grant No. 2010CB630705).

  6. Quantifying mechanical force in axonal growth and guidance

    Directory of Open Access Journals (Sweden)

    Ahmad Ibrahim Mahmoud Athamneh

    2015-09-01

    Full Text Available Mechanical force plays a fundamental role in neuronal development, physiology, and regeneration. In particular, research has shown that force is involved in growth cone-mediated axonal growth and guidance as well as stretch-induced elongation when an organism increases in size after forming initial synaptic connections. However, much of the details about the exact role of force in these fundamental processes remain unknown. In this review, we highlight (1 standing questions concerning the role of mechanical force in axonal growth and guidance and (2 different experimental techniques used to quantify forces in axons and growth cones. We believe that satisfying answers to these questions will require quantitative information about the relationship between elongation, forces, cytoskeletal dynamics, axonal transport, signaling, substrate adhesion, and stiffness contributing to directional growth advance. Furthermore, we address why a wide range of force values have been reported in the literature, and what these values mean in the context of neuronal mechanics. We hope that this review will provide a guide for those interested in studying the role of force in development and regeneration of neuronal networks.

  7. Emergent patterns of growth controlled by multicellular form and mechanics

    Science.gov (United States)

    Nelson, Celeste M.; Jean, Ronald P.; Tan, John L.; Liu, Wendy F.; Sniadecki, Nathan J.; Spector, Alexander A.; Chen, Christopher S.

    2005-01-01

    Spatial patterns of cellular growth generate mechanical stresses that help to push, fold, expand, and deform tissues into their specific forms. Genetic factors are thought to specify patterns of growth and other behaviors to drive morphogenesis. Here, we show that tissue form itself can feed back to regulate patterns of proliferation. Using microfabrication to control the organization of sheets of cells, we demonstrated the emergence of stable patterns of proliferative foci. Regions of concentrated growth corresponded to regions of high tractional stress generated within the sheet, as predicted by a finite-element model of multicellular mechanics and measured directly by using a micromechanical force sensor array. Inhibiting actomyosin-based tension or cadherin-mediated connections between cells disrupted the spatial pattern of proliferation. These findings demonstrate the existence of patterns of mechanical forces that originate from the contraction of cells, emerge from their multicellular organization, and result in patterns of growth. Thus, tissue form is not only a consequence but also an active regulator of tissue growth. PMID:16049098

  8. Mechanisms and pathways of growth failure in primordial dwarfism

    Science.gov (United States)

    Klingseisen, Anna; Jackson, Andrew P.

    2011-01-01

    The greatest difference between species is size; however, the developmental mechanisms determining organism growth remain poorly understood. Primordial dwarfism is a group of human single-gene disorders with extreme global growth failure (which includes Seckel syndrome, microcephalic osteodysplastic primordial dwarfism I [MOPD] types I and II, and Meier-Gorlin syndrome). Ten genes have now been identified for microcephalic primordial dwarfism, encoding proteins involved in fundamental cellular processes including genome replication (ORC1 [origin recognition complex 1], ORC4, ORC6, CDT1, and CDC6), DNA damage response (ATR [ataxia-telangiectasia and Rad3-related]), mRNA splicing (U4atac), and centrosome function (CEP152, PCNT, and CPAP). Here, we review the cellular and developmental mechanisms underlying the pathogenesis of these conditions and address whether further study of these genes could provide novel insight into the physiological regulation of organism growth. PMID:21979914

  9. Mechanisms and pathways of growth failure in primordial dwarfism.

    Science.gov (United States)

    Klingseisen, Anna; Jackson, Andrew P

    2011-10-01

    The greatest difference between species is size; however, the developmental mechanisms determining organism growth remain poorly understood. Primordial dwarfism is a group of human single-gene disorders with extreme global growth failure (which includes Seckel syndrome, microcephalic osteodysplastic primordial dwarfism I [MOPD] types I and II, and Meier-Gorlin syndrome). Ten genes have now been identified for microcephalic primordial dwarfism, encoding proteins involved in fundamental cellular processes including genome replication (ORC1 [origin recognition complex 1], ORC4, ORC6, CDT1, and CDC6), DNA damage response (ATR [ataxia-telangiectasia and Rad3-related]), mRNA splicing (U4atac), and centrosome function (CEP152, PCNT, and CPAP). Here, we review the cellular and developmental mechanisms underlying the pathogenesis of these conditions and address whether further study of these genes could provide novel insight into the physiological regulation of organism growth.

  10. Anomalous mechanical behavior and crack growth of oxide glasses

    Science.gov (United States)

    Seaman, Jared Hilliard

    This thesis is concerned with analytically describing anomalous mechanical behaviors of glass. A new slow crack growth model is presented that considers a semi-elliptical crack in a cylindrical glass rod subjected to 4-point bending that is both loaded statically and under a time-dependent load. This model is used to explain a suppression of the loading-rate dependency of ion-exchanged strengthened glass. The stress relaxation behavior of an ion-exchanged strengthened glass is then analyzed in view of a newly observed water-assisted surface stress relaxation mechanism. By making refinements to a time-dependent Maxwell material model for stress buildup and relaxation, the anomalous subsurface compressive stress peak in ion-exchanged strengthened glass is explained. The notion of water-assisted stress relaxation is extended to the crack tip, where high tensile stresses exist. A toughening effect has historically been observed for cracks aged at subcritical stress intensity factors, where crack tip stress relaxation is hypothesized. A simple fracture mechanics model is developed that estimates a shielding stress intensity factor that is then superimposed with the far-field stress intensity factor. The model is used to estimate anomalous "restart" times for aged cracks. The same model predicts a non-linear crack growth rate for cracks loaded near the static fatigue limit. Double cantilever beam slow crack growth experiments were performed and new slow crack growth data for soda-lime silicate glass was collected. Interpretation of this new experimental slow crack growth data suggests that the origin of the static fatigue limit in glass is due to water-assisted stress relaxation. This thesis combines a number of studies that offer a new unified understanding of historical anomalous mechanical behaviors of glass. These anomalies are interpreted as simply the consequence of slow crack growth and water-assisted surface stress relaxation.

  11. Growth Mechanism of Gold Nanorods in Binary Surfactant System

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Bo-Mi; Seo, Sun-Hwa; Joe, Ara; Shim, Kyu-Dong; Jang, Eue-Soon [Kumoh National Institute of Technology, Gumi (Korea, Republic of)

    2016-06-15

    In order to reveal the growth mechanism of gold nanorods (GNRs) in a binary surfactant system, we synthesized various GNRs by changing the concentration of the surfactants, AgNO{sub 3}, and HBr in the growth solution. We found that the benzyldime thylhexadecylammoniumchloride surfactant had weak interaction with the gold ions, but it could reduce the membrane fluidity. In addition, we could dramatically decrease the cetyltrimethylammonium bromide concentration required for GNR growth by adding an HBr solution. Notably, Ag{sup +} ions were necessary to break the symmetry of the seed crystals for GNR growth, but increasing the concentration of Ag{sup +} and Br{sup -} ions caused a decrease in the template size.

  12. Growth mechanism and magnon excitation in NiO nanowalls

    Directory of Open Access Journals (Sweden)

    Yang Chun

    2011-01-01

    Full Text Available Abstract The nanosized effects of short-range multimagnon excitation behavior and short-circuit diffusion in NiO nanowalls synthesized using the Ni grid thermal treatment method were observed. The energy dispersive spectroscopy mapping technique was used to characterize the growth mechanism, and confocal Raman scattering was used to probe the antiferromagnetic exchange energy J 2 between next-nearest-neighboring Ni ions in NiO nanowalls at various growth temperatures below the Neel temperature. This study shows that short spin correlation leads to an exponential dependence of the growth temperatures and the existence of nickel vacancies during the magnon excitation. Four-magnon configurations were determined from the scattering factor, revealing a lowest state and monotonic change with the growth temperature. PACS: 75.47.Lx; 61.82.Rx; 75.50.Tt; 74.25.nd; 72.10.Di

  13. Mechanisms ofvascularization inmurine models ofprimary andmetastatic tumor growth

    Institute of Scientific and Technical Information of China (English)

    Edina Bugyik; Ferenc RenyiVamos; Vanessza Szabo; KatalinDezso; Nora Ecker; Andras Rokusz; Peter Nagy; Balazs Dome; Sandor Paku

    2016-01-01

    Directed capillary ingrowth has long been considered synonymous with tumor vascularization. However, the vascu‑lature of primary tumors and metastases is not necessarily formed by endothelial cell sprouting; instead, malignant tumors can acquire blood vessels via alternative vascularization mechanisms, such as intussusceptive microvascular growth, vessel co‑option, and glomeruloid angiogenesis. Importantly, in response to anti‑angiogenic therapies, malig‑nant tumors can switch from one vascularization mechanism to another. In this article, we brielfy review the biological features of these mechanisms and discuss on their signiifcance in medical oncology.

  14. A generic mechanism for adaptive growth rate regulation.

    Directory of Open Access Journals (Sweden)

    Chikara Furusawa

    2008-01-01

    Full Text Available How can a microorganism adapt to a variety of environmental conditions despite the existence of a limited number of signal transduction mechanisms? We show that for any growing cells whose gene expression fluctuate stochastically, the adaptive cellular state is inevitably selected by noise, even without a specific signal transduction network for it. In general, changes in protein concentration in a cell are given by its synthesis minus dilution and degradation, both of which are proportional to the rate of cell growth. In an adaptive state with a higher growth speed, both terms are large and balanced. Under the presence of noise in gene expression, the adaptive state is less affected by stochasticity since both the synthesis and dilution terms are large, while for a nonadaptive state both the terms are smaller so that cells are easily kicked out of the original state by noise. Hence, escape time from a cellular state and the cellular growth rate are negatively correlated. This leads to a selection of adaptive states with higher growth rates, and model simulations confirm this selection to take place in general. The results suggest a general form of adaptation that has never been brought to light--a process that requires no specific mechanisms for sensory adaptation. The present scheme may help explain a wide range of cellular adaptive responses including the metabolic flux optimization for maximal cell growth.

  15. A generic mechanism for adaptive growth rate regulation.

    Science.gov (United States)

    Furusawa, Chikara; Kaneko, Kunihiko

    2008-01-01

    How can a microorganism adapt to a variety of environmental conditions despite the existence of a limited number of signal transduction mechanisms? We show that for any growing cells whose gene expression fluctuate stochastically, the adaptive cellular state is inevitably selected by noise, even without a specific signal transduction network for it. In general, changes in protein concentration in a cell are given by its synthesis minus dilution and degradation, both of which are proportional to the rate of cell growth. In an adaptive state with a higher growth speed, both terms are large and balanced. Under the presence of noise in gene expression, the adaptive state is less affected by stochasticity since both the synthesis and dilution terms are large, while for a nonadaptive state both the terms are smaller so that cells are easily kicked out of the original state by noise. Hence, escape time from a cellular state and the cellular growth rate are negatively correlated. This leads to a selection of adaptive states with higher growth rates, and model simulations confirm this selection to take place in general. The results suggest a general form of adaptation that has never been brought to light--a process that requires no specific mechanisms for sensory adaptation. The present scheme may help explain a wide range of cellular adaptive responses including the metabolic flux optimization for maximal cell growth.

  16. Synthesis, Growth Mechanism, and Applications of Zinc Oxide Nanomaterials

    Institute of Scientific and Technical Information of China (English)

    Shulin JI; Changhui YE

    2008-01-01

    This article reviews recent progresses in growth mechanism, synthesis, and applications of zinc oxide nanomaterials (mainly focusing on one-dimensional (1D) nanomaterials). In the first part of this article, we briefly introduce the importance, the synthesis methods and growth mechanisms, the properties and applications of ZnO 1D nanomaterials. In the second part of this article, the growth mechanisms of ZnO 1D nanomaterials will be discussed in detail in the framework of vapor-liquid-solid (VLS), vapor-solid (VS), and aqueous solution growth (ASG) approaches. Both qualitative and quantitative information will be provided to show how a controlled synthesis of ZnO 1D nanomaterials can be achieved. In the third part of this article, we present recent progresses in our group for the synthesis of ZnO 1D nanomaterials, and the results from other groups will only be mentioned briefly. Especially, experiment designing according to theories will be elaborated to demonstrate the concept of controlled synthesis. In the fourth part of this article, the properties and potential applications of ZnO 1D nanomaterials will be treated. Finally, a summary part will be presented in the fifth section. The future trend of research for ZnO 1D nanomaterials will be pointed out and key issues to be solved will be proposed.

  17. Microstructure and stopped growth mechanism of Y123 bulk fabricated by directional infiltration and growth

    Institute of Scientific and Technical Information of China (English)

    DONG Hao; HU Rui; LI Jin-shan; KOU Hong-chao; XUE Xiang-yi; CHANG Hui; CAO Hai-tao; ZHOU Lian

    2008-01-01

    The infiltration-growth process was used as an alternative to conventional melt processing techniques for the preparation of bulk YBa2Cu3O7-x(Y123) with freely dispersed small size Y2BaCuO5(Y211) particles. Bulk YBCO superconductors with uniformly distributed particles of micron-sized Y211 were prepared by the directional infiltration and growth(DIG). The microstructure changes of the Y211 particles at various stages of processing were studied. About 70% of Y211 particles are under 1μn in the final sample. The different stopped growth mechanism of this material along the c axis and ab plane was discussed.Undercooling and viscosity lead to tanglesome thick boundary layer. So the Y123 growth along c axis is stopped. Yttrium lack in front of the ab plane is the main reason why the growth stops at this direction.

  18. Grain growth by Ordered Coalescence of crystallites in Ceramics : Grain Growth Mechanisms, Microstructure Evolution and Sintering

    OpenAIRE

    Hu, Jianfeng

    2013-01-01

    Grain growth and densification process play the two most crucial roles on the microstructure evolution and the achieved performances during sintering of ceramics. In this thesis, the grain growth of SrTiO3, BaTiO3-SrTiO3 solid solutions and Si3N4 ceramics during spark plasma sintering (SPS) were investigated by electron microscopy. SrTiO3 ceramics starting from nanopowders were fabricated by SPS. A novel grain growth mechanism was discovered and named as ordered coalescence (OC) of nanocrysta...

  19. Fibrous tissues growth and remodeling: Evolutionary micro-mechanical theory

    Science.gov (United States)

    Lanir, Yoram

    2017-10-01

    Living fibrous tissues are composite materials having the unique ability to adapt their size, shape, structure and mechanical properties in response to external loading. This adaptation, termed growth and remodeling (G&R), occurs throughout life and is achieved via cell-induced turnover of tissue constituents where some are degraded and new ones are produced. Realistic mathematical modeling of G&R provides insight into the basic processes, allows for hypotheses testing, and constitutes an essential tool for establishing clinical thresholds of pathological remodeling and for the production of tissue substitutes aimed to achieve target structure and properties. In this study, a general 3D micro-mechanical multi-scale theory of G&R in fibrous tissue was developed which connects between the evolution of the tissue structure and properties, and the underlying mechano-biological turnover events of its constituents. This structural approach circumvents a fundamental obstacle in modeling growth mechanics since the growth motion is not bijective. The model was realized for a flat tissue under two biaxial external loadings using data-based parameter values. The predictions show close similarity to characteristics of remodeled adult tissue including its structure, anisotropic and non-linear mechanical properties, and the onset of in situ pre-strain and pre-stress. The results suggest that these important features of living fibrous tissues evolve as they grow.

  20. Adrenergic receptor control mechanism for growth hormone secretion.

    Science.gov (United States)

    Blackard, W G; Heidingsfelder, S A

    1968-06-01

    The influence of catecholamines on growth hormone secretion has been difficult to establish previously, possibly because of the suppressive effect of the induced hyperglycemia on growth hormone concentrations. In this study, an adrenergic receptor control mechanism for human growth hormone (HGH) secretion was uncovered by studying the effects of alpha and beta receptor blockade on insulin-induced growth hormone elevations in volunteer subjects. Alpha adrenergic blockade with phentolamine during insulin hypoglycemia, 0.1 U/kg, inhibited growth hormon elevations to 30-50% of values in the same subjects during insulin hypoglycemia without adrenergic blockade. More complete inhibition by phentolamine could not be demonstrated at a lower dose of insulin (0.05 U/kg). Beta adrenergic blockade with propranolol during insulin hypoglycemia significantly enhanced HGH concentrations in paired experiments. The inhibiting effect of alpha adrenergic receptor blockade on HGH concentrations could not be attributed to differences in blood glucose or free fatty acid values; however, more prolonged hypoglycemia and lower plasma free fatty acid values may have been a factor in the greater HGH concentrations observed during beta blockade. In the absence of insulin induced hypoglycemia, neither alpha nor beta adrenergic receptor blockade had a detectable effect on HGH concentrations. Theophylline, an inhibitor of cyclic 3'5'-AMP phosphodiesterase activity, also failed to alter plasma HGH concentrations. These studies demonstrate a stimulatory effect of alpha receptors and a possible inhibitory effect of beta receptors on growth hormone secretion.

  1. Research and Development of Growth Design System for Mechanical Products

    Institute of Scientific and Technical Information of China (English)

    YANG Bo; ZE Xiangbo; YANG Tao; CUI Weihua; LIU Luning

    2006-01-01

    By applying genetic engineering methodology into the incremental product growth design, a generic structural design approach is put forward, as well as an intelligent evolution strategy of the product units growth, which is based on the multilevel Decomposition and Reconstruction of product gene. To guarantee a successful transformation from functional requirement to geometry constraints between parts in the incremental growth design of mechanical product, the integrated design method incorporates the design requirements and assembly perspective into product genetic information. The mathematical model of state transition during incremental design process are given at first, based on which product can grow step by step from functional requirement to the final geometrical product structure automatically. And then, to quantify the measurement of assembly efficiency, a mathematical model as well as a technology to quantify assembly constraints was developed by application of some fuzzy logic algorithms. Finally, examples have been proved that the approach is promising.

  2. Activation energies of grain growth mechanisms in aluminum coatings

    Energy Technology Data Exchange (ETDEWEB)

    Jankowski, Alan [Lawrence Livermore National Laboratory, Chemistry and Materials Science, CA (United States)]. E-mail: jankowski1@11nl.gov; Ferreira, James [Lawrence Livermore National Laboratory, Chemistry and Materials Science, CA (United States); Hayes, Jeffrey [Lawrence Livermore National Laboratory, Mechanical Engineering, Livermore, CA 94551-9900 (United States)

    2005-11-22

    To produce a specific grain size in metallic coatings requires precise control of the time at temperature during the deposition process. Aluminum coatings are deposited using electron-beam evaporation onto heated substrate surfaces of both mica and lithium flouride. The grain size of the coating is determined upon examination of the microstructure in plan view and cross-section. Ideal grain growth is observed over the entire experimental range of temperature examined from 413 to 843 K. A transition in the activation energy for grain growth from 0.87 to 2.04 eV atom{sup -1} is observed as the temperature increases from < 526 K to > 588 K. The transition is indicative of the dominant mechanism for grain growth shifting with increasing temperature from grain boundary to lattice diffusion.

  3. Growth limit of carbon onions – A continuum mechanical study

    DEFF Research Database (Denmark)

    Todt, Melanie; Bitsche, Robert; Hartmann, Markus A.

    2014-01-01

    The growth of carbon onions is simulated using continuum mechanical shell models. With this models it is shown that, if a carbon onion has grown to a critical size, the formation of an additional layer leads to the occurrence of a structural instability. This instability inhibits further growth...... of carbon onions and, thus, can be a reason for the limited size of such particles. The loss of stability is mainly evoked by van der Waals interactions between misfitting neighboring layers leading to self-equilibrating stress states in the layers due to mutual accommodation. The influence of the curvature...... model gives insight into mechanisms which are assumed to limit the size of carbon onions and can serve as basis for further investigations, e.g., of the formation of nanodiamonds in the center of carbon onions. © 2013 Elsevier Ltd. All rights reserved....

  4. Boehmite (AlOOH) nanostrips and their growth mechanism

    KAUST Repository

    Dar, Farooq Ahmad

    2015-02-04

    Crystalline nanostrips of AlOOH have been prepared at 240∘C through a fast route. Powder X-ray diffraction studies reveal that the as-prepared nanostrips are highly crystalline in nature and by morphological investigations using FESEM, it was revealed that the strips have average length of 210 nm and width of 60 ± 20 nm. A plausible theory is proposed which reveals the growth mechanism of nanostrips.

  5. Alteration of placental haemostatic mechanisms in idiopathic intrauterine growth restriction

    Directory of Open Access Journals (Sweden)

    Jaime Eduardo Bernal Villegas

    2012-08-01

    Full Text Available Intrauterine growth restriction is a complication of pregnancy with a high probability of perinatal morbidity and mortality. It appears tobe caused by abnormal development of placental vasculature. Haemostatic processes are important for the development of the placenta,and an imbalance between procoagulant and anticoagulant factors has been associated with risk of intrauterine growth restriction.Objective. To evaluate coagulation abnormalities in placenta of pregnancies complicated with idiopathic intrauterine growth restriction.Materials and methods. Five placentas from pregnancies with idiopathic intrauterine growth restriction were compared to 19 controls.We performed gross and histological examination of the placenta. Analysis was made of both mRNA expression by real-time PCRand protein by ELISA of tissue factor and thrombomodulin in placental tissue. Results. Results based on histological evaluation wereconsistent with an increased prothrombotic state in placentas from pregnancies with idiopathic intrauterine growth restriction, andthrombosis of chorionic vessels was the most important finding. The study showed an increased expression of tissue factor protein(p=0.0411 and an increase in the ratio of tissue factor/thrombomodulin mRNA (p=0.0411 and protein (p=0.0215 in placentas frompregnancies with idiopathic intrauterine growth restriction. There were no statistically significant differences neither between cases andcontrols in the mRNA levels of tissue factor or thrombomodulin nor at the protein level of thrombomodulin. Conclusion. Evidence ofalteration of local haemostatic mechanisms at the level of the placenta, including abnormal expression of tissue factor and tissue factor/thrombomodulin ratio, in pregnancies that occur with idiopathic intrauterine growth restriction is presented.

  6. Ludwig Prandtl and the growth of fluid mechanics in Germany

    Science.gov (United States)

    Eckert, Michael

    2017-07-01

    Ludwig Prandtl (1875-1953) has been called the father of modern aerodynamics. His name is associated most famously with the boundary layer concept, but also with several other topics in 20th-century fluid mechanics, particularly turbulence (Prandtl's mixing length). Among his disciples are pioneers of modern fluid mechanics like Heinrich Blasius, Theodore von Kármán, and Walter Tollmien. Furthermore, Prandtl founded the Aerodynamische Versuchsanstalt (AVA) and the Kaiser-Wilhelm-Institut für Strömungsforschung in Göttingen, nuclei for the growth of fluid mechanics in Germany. In this article I trace this development on the basis of my recent biography of Prandtl.

  7. Plant Growth-Promoting Bacteria: Mechanisms and Applications

    Directory of Open Access Journals (Sweden)

    Bernard R. Glick

    2012-01-01

    Full Text Available The worldwide increases in both environmental damage and human population pressure have the unfortunate consequence that global food production may soon become insufficient to feed all of the world's people. It is therefore essential that agricultural productivity be significantly increased within the next few decades. To this end, agricultural practice is moving toward a more sustainable and environmentally friendly approach. This includes both the increasing use of transgenic plants and plant growth-promoting bacteria as a part of mainstream agricultural practice. Here, a number of the mechanisms utilized by plant growth-promoting bacteria are discussed and considered. It is envisioned that in the not too distant future, plant growth-promoting bacteria (PGPB will begin to replace the use of chemicals in agriculture, horticulture, silviculture, and environmental cleanup strategies. While there may not be one simple strategy that can effectively promote the growth of all plants under all conditions, some of the strategies that are discussed already show great promise.

  8. Nucleation and growth mechanisms during electropolymerization of substituted 3-alkylthiophenes

    Energy Technology Data Exchange (ETDEWEB)

    Soto, J.P. [Facultad de Ciencias Basicas y Matematicas, Instituto de Quimica, Pontificia Universidad Catolica de Valparaiso, Brasil 2950, Valparaiso (Chile)], E-mail: juan.soto@ucv.cl; Diaz, F.R.; Valle, M.A. del; Velez, J.H. [Laboratorio de Polimeros, Facultad de Quimica, Pontificia Universidad Catolica de Chile, Vicuna Mackenna 4860, Macul, Santiago (Chile); East, G.A. [Instituto de Quimica, Universidade de Brasilia, Campus Universitario Darcy Ribeiro, CEP 70904-970, Brasilia, DF (Brazil)

    2008-03-30

    In the present work the electrochemical study of compounds based on 3-(({omega}-bromoalkyloxy) methyl) thiophene, varying the length of the alkyl chain between 6 and 12 carbon atoms, is reported. Electropolymerization of the monomers was achieved by potentiodynamic (cyclic voltammetry, CV) and potentiostatic (constant potential) techniques. Voltammograms obtained by CV show that all monomers can be electrochemically oxidized at potentials about 1800 mV to synthesize the respective polymer. Besides, the potential shifts to more anodic potentials on successive scans, increasing thus the resistivity of the material. Nucleation and growth mechanism (NGM) of electropolymerization was investigated by a potentiostatic technique (j-t). Deconvolution of the current-time transient data fitted with a theoretical model suggests that at short times the instantaneous nucleation with two-dimensional growth (IN2D) contribution prevails, followed by an instantaneous nucleation with three-dimensional growth controlled by the charge transfer (IN3Dct) contribution and, finally at longer times, the instantaneous nucleation with three-dimensional growth controlled by diffusion (IN3Ddif) contribution becomes important. The predominance of each contribution to the NGM depends on the monomer being electropolymerized, and the electrolysis time. The morphology predicted from these NGMs fully correlates with that determined by SEM.

  9. Thermochemistry and growth mechanism of SiC nanowires

    Science.gov (United States)

    Chen, Jianjun; Ding, Lijuan; Xin, Lipeng; Zeng, Fan; Chen, Jun

    2017-09-01

    The chemical reaction thermodynamics and a novel two-stage growth mechanism of SiC nanowires synthesized by carbothermal reduction reactions were investigated based on the Si-C-O systems over a wide temperature range (1050 ≤ T ≤ 2000 K). The carbothermal reduction reaction process involves the fast formation of gaseous SiO and CO crucial intermediates, and the further carbon reduction of SiO to SiC. The relationship between the free energy changes and temperature at different pressures was also discussed. Some fundamental data in the work can help to analyze the thermochemistry of the carbothermal reduction reaction in the Si-C-O system, which is beneficial to optimize the temperature, pressure and the input precursors for controlling the SiC nanowire growth.

  10. Ubiquitination-dependent mechanisms regulate synaptic growth and function.

    Science.gov (United States)

    DiAntonio, A; Haghighi, A P; Portman, S L; Lee, J D; Amaranto, A M; Goodman, C S

    2001-07-26

    The covalent attachment of ubiquitin to cellular proteins is a powerful mechanism for controlling protein activity and localization. Ubiquitination is a reversible modification promoted by ubiquitin ligases and antagonized by deubiquitinating proteases. Ubiquitin-dependent mechanisms regulate many important processes including cell-cycle progression, apoptosis and transcriptional regulation. Here we show that ubiquitin-dependent mechanisms regulate synaptic development at the Drosophila neuromuscular junction (NMJ). Neuronal overexpression of the deubiquitinating protease fat facets leads to a profound disruption of synaptic growth control; there is a large increase in the number of synaptic boutons, an elaboration of the synaptic branching pattern, and a disruption of synaptic function. Antagonizing the ubiquitination pathway in neurons by expression of the yeast deubiquitinating protease UBP2 (ref. 5) also produces synaptic overgrowth and dysfunction. Genetic interactions between fat facets and highwire, a negative regulator of synaptic growth that has structural homology to a family of ubiquitin ligases, suggest that synaptic development may be controlled by the balance between positive and negative regulators of ubiquitination.

  11. Action Mechanism of Chamaecyparis obtusa Oil on Hair Growth.

    Science.gov (United States)

    Park, Young-Ok; Kim, Su-Eun; Kim, Young-Chul

    2013-12-31

    This study was carried out to examine the action mechanism of Chamaecyparis obtusa oil (CO) on hair growth in C57BL/6 mice. For alkaline phosphatase (ALP) and γ-glutamyl transpeptidase (γ-GT) activities in the skin tissue, at week 4, the 3% minoxidil (MXD) and 3% CO treatment groups showed an ALP activity that was significantly higher by 85% (p < 0.001) and 48% (p < 0.05) and an γ-GT activity that was significantly higher by 294% (p < 0.01) and 254% (p < 0.05) respectively, as compared to the saline (SA) treatment group. For insulin-like growth factor-1 (IGF-1) mRNA expression in the skin tissue, at week 4, the MXD and CO groups showed a significantly higher expression by 204% (p < 0.05) and 426% (p < 0.01) respectively, as compared to the SA group. At week 4, vascular endothelial growth factor (VEGF) expression in the MXD and CO groups showed a significantly higher expression by 74% and 96% (p < 0.05) respectively, however, epidermal growth factor (EGF) expression in the MXD and CO groups showed a significantly lower expression by 66% and 61% (p < 0.05) respectively, as compared to the SA group. Stem cell factor (SCF) expression in the MXD and CO groups was observed by immunohistochemistry as significant in a part of the bulge around the hair follicle and in a part of the basal layer of the epidermis. Taking all the results together, on the basis of effects on ALP and γ-GT activity, and the expression of IGF-1, VEGF and SCF, which are related to the promotion of hair growth, it can be concluded that CO induced a proliferation and division of hair follicle cells and maintained the anagen phase. Because EGF expression was decreased significantly, CO could delay the transition to the catagen phase.

  12. Solid catalytic growth mechanism of micro-coiled carbon fibers

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Micro-coiled carbon fibers were prepared by catalytic pyrolysisof acetylene with nano-sized nickel powder catalyst using the substrate method. The morphology of micro-coiled carbon fibers was observed through field emission scanning electron microscopy. It was found that the fiber and coil diameter of the obtained micro-coiled carbon fibers is about 500—600 nm and 4—5 μm, respectively. Most of the micro-coiled carbon fibers obtained were regular double carbon coils, but a few irregular ones were also observed. On the basis of the experimental observation, a solid catalytic growth mechanism of micro-coiled carbon fibers was proposed.

  13. Mechanisms of Muscle Growth and Atrophy in Mammals and Drosophila

    Science.gov (United States)

    Piccirillo, Rosanna; Demontis, Fabio; Perrimon, Norbert; Goldberg, Alfred L.

    2014-01-01

    The loss of skeletal muscle mass (atrophy) that accompanies disuse and systemic diseases is highly debilitating. Although the pathogenesis of this condition has been primarily studied in mammals, Drosophila is emerging as an attractive system to investigate some of the mechanisms involved in muscle growth and atrophy. In this review, we highlight the outstanding unsolved questions that may benefit from a combination of studies in both flies and mammals. In particular, we discuss how different environmental stimuli and signaling pathways influence muscle mass and strength and how a variety of disease states can cause muscle wasting. PMID:24038488

  14. Growth mechanism of nanowires: binary and ternary chalcogenides

    Science.gov (United States)

    Singh, N. B.; Coriell, S. R.; Su, Ching Hua; Hopkins, R. H.; Arnold, B.; Choa, Fow-Sen; Cullum, Brian

    2016-05-01

    Semiconductor nanowires exhibit very exciting optical and electrical properties including high transparency and a several order of magnitude better photocurrent than thin film and bulk materials. We present here the mechanism of nanowire growth from the melt-liquid-vapor medium. We describe preliminary results of binary and ternary selenide materials in light of recent theories. Experiments were performed with lead selenide and thallium arsenic selenide systems which are multifunctional material and have been used for detectors, acoustooptical, nonlinear and radiation detection applications. We observed that small units of nanocubes and elongated nanoparticles arrange and rearrange at moderate melt undercooling to form the building block of a nanowire. Since we avoided the catalyst, we observed self-nucleation and uncontrolled growth of wires from different places. Growth of lead selenide nanowires was performed by physical vapor transport method and thallium arsenic selenide nanowire by vapor-liquid-solid (VLS) method. In some cases very long wires (>mm) are formed. To achieve this goal experiments were performed to create situation where nanowires grew on the surface of solid thallium arsenic selenide itself.

  15. Growth Mechanisms of CdS Nanocrystals in Aqueous Media

    Directory of Open Access Journals (Sweden)

    Loredana Latterini

    2012-06-01

    Full Text Available CdS nanocrystals were prepared in water-in-oil microemulsions. The nanocrystal properties, absorption and luminescence spectra and size distributions, were monitored at different times after mixing the microemulsions of the two precursors to obtain information on their growth mechanism. In particular, CdS nanocrystals were prepared using water-in-heptane or water-in-nonane microemulsions. The results obtained from the investigation of nanocrystals prepared using heptane as the organic phase, confirmed that nanocrystal nucleation is fast while their growth is determined by droplet exchange content rate. Size distribution histograms obtained from the sample at early time points after mixing presented a bimodal population having average sizes of 3.0 ± 0.1 and 5.8 ± 0.1 nm, thus indicating that surface process controls the nanocrystal growth. With longer reaction times the occurrence of water droplet coalescence is likely responsible for the formation of nanocrystal agglomerates. Using a water-in-nonane microemulsion, the droplet exchange rate can be modified, thus leading to smaller CdS nanocrystals. However, the development of structural defects cannot be excluded, as evidenced by the luminescence spectra of the suspension. In general, aging of the nanocrystal in the pristine microemulsion resulted in the development of cubic semiconductor nanostructures.

  16. Spine growth mechanisms: friction and seismicity at Mt. Unzen, Japan

    Science.gov (United States)

    Hornby, Adrian; Kendrick, Jackie; Hirose, Takehiro; Henton De Angelis, Sarah; De Angelis, Silvio; Umakoshi, Kodo; Miwa, Takahiro; Wadsworth, Fabian; Dingwell, Don; Lavallee, Yan

    2014-05-01

    The final episode of dome growth during the 1991-1995 eruption of Mt. Unzen was characterised by spine extrusion accompanied by repetitive seismicity. This type of cyclic activity has been observed at several dome-building volcanoes and recent work suggests a source mechanism of brittle failure of magma in the conduit. Spine growth may proceed by densification and closure of permeable pathways within the uppermost conduit magma, leading to sealing of the dome and inflation of the edifice. Amplified stresses on the wall rock and plug cause brittle failure near the conduit wall once static friction forces are overcome, and during spine growth these fractures may propagate to the dome surface. The preservation of these features is rare, and the conduit is typically inaccessible; therefore spines, the extruded manifestation of upper conduit material, provide the opportunity to study direct evidence of brittle processes in the conduit. At Mt. Unzen the spine retains evidence for brittle deformation and slip, however mechanical constraints on the formation of these features and their potential impact on eruption dynamics have not been well constrained. Here, we conduct an investigation into the process of episodic spine growth using high velocity friction apparatus at variable shear slip rate (0.4-1.5 m.s-1) and normal stress (0.4-3.5 MPa) on dome rock from Mt. Unzen, generating frictional melt at velocity >0.4 m.s-1 and normal stress >0.7 MPa. Our results show that the presence of frictional melt causes a deviation from Byerlee's frictional rule for rock friction. Melt generation is a disequilibrium process: initial amphibole breakdown leads to melt formation, followed by chemical homogenization of the melt layer. Ultimately, the experimentally generated frictional melts have a similar final chemistry, thickness and comminuted clast size distribution, thereby facilitating the extrapolation of a single viscoelastic model to describe melt-lubricated slip events at Mt

  17. The effect of mechanical discontinuities on the growth of faults

    Science.gov (United States)

    Bonini, Lorenzo; Basili, Roberto; Bonanno, Emanuele; Toscani, Giovanni; Burrato, Pierfrancesco; Seno, Silvio; Valensise, Gianluca

    2016-04-01

    The growth of natural faults is controlled by several factors, including the nature of host rocks, the strain rate, the temperature, and the presence of fluids. In this work we focus on the mechanical characteristics of host rocks, and in particular on the role played by thin mechanical discontinuities on the upward propagation of faults and on associated secondary effects such as folding and fracturing. Our approach uses scaled, analogue models where natural rocks are simulated by wet clay (kaolin). A clay cake is placed above two rigid blocks in a hanging wall/footwall configuration on either side of a planar fault. Fault activity is simulated by motor-controlled movements of the hanging wall. We reproduce three types of faults: a 45°-dipping normal fault, a 45°-dipping reverse fault and a 30°-dipping reverse fault. These angles are selected as representative of most natural dip-slip faults. The analogues of the mechanical discontinuities are obtained by precutting the wet clay cake before starting the hanging wall movement. We monitor the experiments with high-resolution cameras and then obtain most of the data through the Digital Image Correlation method (D.I.C.). This technique accurately tracks the trajectories of the particles of the analogue material during the deformation process: this allows us to extract displacement field vectors plus the strain and shear rate distributions on the lateral side of the clay block, where the growth of new faults is best seen. Initially we run a series of isotropic experiments, i.e. experiments without discontinuities, to generate a reference model: then we introduce the discontinuities. For the extensional models they are cut at different dip angles, from horizontal to 45°-dipping, both synthetic and antithetic with respect to the master fault, whereas only horizontal discontinuities are introduced in the contractional models. Our experiments show that such discontinuities control: 1) the propagation rate of faults

  18. Microdroplet growth mechanism during water condensation on superhydrophobic surfaces.

    Science.gov (United States)

    Rykaczewski, Konrad

    2012-05-22

    By promoting dropwise condensation of water, nanostructured superhydrophobic coatings have the potential to dramatically increase the heat transfer rate during this phase change process. As a consequence, these coatings may be a facile method of enhancing the efficiency of power generation and water desalination systems. However, the microdroplet growth mechanism on surfaces which evince superhydrophobic characteristics during condensation is not well understood. In this work, the sub-10 μm dynamics of droplet formation on nanostructured superhydrophobic surfaces are studied experimentally and theoretically. A quantitative model for droplet growth in the constant base (CB) area mode is developed. The model is validated using optimized environmental scanning electron microscopy (ESEM) imaging of microdroplet growth on a superhydrophobic surface consisting of immobilized alumina nanoparticles modified with a hydrophobic promoter. The optimized ESEM imaging procedure increases the image acquisition rate by a factor of 10-50 as compared to previous research. With the improved imaging temporal resolution, it is demonstrated that nucleating nanodroplets coalesce to create a wetted flat spot with a diameter of a few micrometers from which the microdroplet emerges in purely CB mode. After the droplet reaches a contact angle of 130-150°, its base diameter increases in a discrete steplike fashion. The droplet height does not change appreciably during this steplike base diameter increase, leading to a small decrease of the contact angle. Subsequently, the drop grows in CB mode until it again reaches the maximum contact angle and increases its base diameter in a steplike fashion. This microscopic stick-and-slip motion can occur up to four times prior to the droplet coalescence with neighboring drops. Lastly, the constant contact angle (CCA) and the CB growth models are used to show that modeling formation of a droplet with a 150° contact angle in the CCA mode rather than in

  19. Gravitropism of cucumber hypocotyls: biophysical mechanism of altered growth

    Science.gov (United States)

    Cosgrove, D. J.

    1990-01-01

    The biophysical basis for the changes in cell elongation rate during gravitropism was examined in aetiolated cucumber (Cucumis sativus L.) hypocotyls. Bulk osmotic pressures on the two sides of the stem and in the epidermal cells were not altered during the early time course of gravitropism. By the pressure-probe technique, a small increase in turgor (0.3 bar, 30 kPa) was detected on the upper (inhibited) side, whereas there was a negligible decrease in turgor on the lower (stimulated) side. These small changes in turgor and water potential appeared to be indirect, passive consequences of the altered growth and the small resistance for water movement from the xylem, and indicated that the change in growth was principally due to changes in wall properties. The results indicate that the hydraulic conductance of the water-transport pathway was large (.25 h-1 bar-1) and the water potential difference supporting cell expansion was no greater than 0.3 bar (30 kPa). From pressure-block experiments, it appeared that upon gravitropic stimulation (1) the yield threshold of the lower half of the stem did not decrease and (2) the wall on the upper side of the stem was not made more rigid by a cross-linking process. Mechanical measurements of the stress/strain properties of the walls showed that the initial development of gravitropism did not involve an alteration of the mechanical behaviour of the isolated walls. Thus, gravitropism in cucumber hypocotyls occurs principally by an alteration of the wall relaxation process, without a necessary change in wall mechanical properties.

  20. Solution-solid-solid mechanism: superionic conductors catalyze nanowire growth.

    Science.gov (United States)

    Wang, Junli; Chen, Kangmin; Gong, Ming; Xu, Bin; Yang, Qing

    2013-09-11

    The catalytic mechanism offers an efficient tool to produce crystalline semiconductor nanowires, in which the choice, state, and structure of catalysts are active research issues of much interest. Here we report a novel solution-solid-solid (SSS) mechanism for nanowire growth catalyzed by solid-phase superionic conductor nanocrystals in low-temperature solution. The preparation of Ag2Se-catalyzed ZnSe nanowires at 100-210 °C is exampled to elucidate the SSS model, which can be extendable to grow other II-VI semiconductor (e.g., CdSe, ZnS, and CdS) nanowires by the catalysis of nanoscale superionic-phase silver or copper(I) chalcogenides (Ag2Se, Ag2S, and Cu2S). The exceptional catalytic ability of these superionic conductors originates from their structure characteristics, known for high-density vacancies and fast mobility of silver or copper(I) cations in the rigid sublattice of Se(2-) or S(2-) ions. Insights into the SSS mechanism are provided based on the formation of solid solution and the solid-state ion diffusion/transport at solid-solid interface between catalyst and nanowire.

  1. Growth Mechanism of a Unique Hierarchical Vaterite Structure

    Science.gov (United States)

    Ma, Guobin; Xu, Yifei; Wang, Mu

    2013-03-01

    Calcium carbonate is one of the most significant minerals in nature as well as in biogenic sources. Calcium carbonate occurs naturally in three crystalline polymorphs, i.e., calcite, aragonite, and vaterite. Although it has been attracted much research attention to understanding of the formation mechanisms of the material, the properties of the vaterite polymorph is not well known. Here we report synthesis and formation mechanism of a unique hierarchical structure of vaterite. The material is grown by a controlled diffusion method. The structure possesses a core and an outer part. The core is convex lens-like and is formed by vaterite nanocrystals that have small misorientations. The outer part is separated into six garlic clove-like segments. Each segment possesses piles of plate-like vaterite crystals, and the orientations of the plates continuously change from pile to pile. Based on real-time experimental results and the structural analysis, a growth mechanism is presented. Work supported by NSFC (Grant No. 51172104) and MOST of China (Grant No. 2101CB630705)

  2. Molecular modifiers reveal a mechanism of pathological crystal growth inhibition

    Science.gov (United States)

    Chung, Jihae; Granja, Ignacio; Taylor, Michael G.; Mpourmpakis, Giannis; Asplin, John R.; Rimer, Jeffrey D.

    2016-08-01

    Crystalline materials are crucial to the function of living organisms, in the shells of molluscs, the matrix of bone, the teeth of sea urchins, and the exoskeletons of coccoliths. However, pathological biomineralization can be an undesirable crystallization process associated with human diseases. The crystal growth of biogenic, natural and synthetic materials may be regulated by the action of modifiers, most commonly inhibitors, which range from small ions and molecules to large macromolecules. Inhibitors adsorb on crystal surfaces and impede the addition of solute, thereby reducing the rate of growth. Complex inhibitor-crystal interactions in biomineralization are often not well elucidated. Here we show that two molecular inhibitors of calcium oxalate monohydrate crystallization—citrate and hydroxycitrate—exhibit a mechanism that differs from classical theory in that inhibitor adsorption on crystal surfaces induces dissolution of the crystal under specific conditions rather than a reduced rate of crystal growth. This phenomenon occurs even in supersaturated solutions where inhibitor concentration is three orders of magnitude less than that of the solute. The results of bulk crystallization, in situ atomic force microscopy, and density functional theory studies are qualitatively consistent with a hypothesis that inhibitor-crystal interactions impart localized strain to the crystal lattice and that oxalate and calcium ions are released into solution to alleviate this strain. Calcium oxalate monohydrate is the principal component of human kidney stones and citrate is an often-used therapy, but hydroxycitrate is not. For hydroxycitrate to function as a kidney stone treatment, it must be excreted in urine. We report that hydroxycitrate ingested by non-stone-forming humans at an often-recommended dose leads to substantial urinary excretion. In vitro assays using human urine reveal that the molecular modifier hydroxycitrate is as effective an inhibitor of nucleation

  3. An Unbiased Analysis of Candidate Mechanisms for the Regulation of Drosophila Wing Disc Growth

    Science.gov (United States)

    Vollmer, Jannik; Iber, Dagmar

    2016-01-01

    The control of organ size presents a fundamental open problem in biology. A declining growth rate is observed in all studied higher animals, and the growth limiting mechanism may therefore be evolutionary conserved. Most studies of organ growth control have been carried out in Drosophila imaginal discs. We have previously shown that the area growth rate in the Drosophila eye primordium declines inversely proportional to the increase in its area, which is consistent with a dilution mechanism for growth control. Here, we show that a dilution mechanism cannot explain growth control in the Drosophila wing disc. We computationally evaluate a range of alternative candidate mechanisms and show that the experimental data can be best explained by a biphasic growth law. However, also logistic growth and an exponentially declining growth rate fit the data very well. The three growth laws correspond to fundamentally different growth mechanisms that we discuss. Since, as we show, a fit to the available experimental growth kinetics is insufficient to define the underlying mechanism of growth control, future experimental studies must focus on the molecular mechanisms to define the mechanism of growth control. PMID:27995964

  4. Inflammation and intracranial aneurysms: mechanisms of initiation, growth, and rupture

    Directory of Open Access Journals (Sweden)

    Peter S Amenta

    2015-06-01

    Full Text Available Outcomes following aneurysmal subarachnoid hemorrhage remain poor in many patients, despite advances in microsurgical and endovascular management. Consequently, considerable effort has been placed in determining the mechanisms of aneurysm formation, growth, and rupture. Various environmental and genetic factors are implicated as key components in the aneurysm pathogenesis. Currently, sufficient evidence exists to incriminate the inflammatory response as the common pathway leading to aneurysm generation and rupture. Central to this model is the interaction between the vessel wall and inflammatory cells. Dysfunction of the endothelium and vascular smooth muscle cells (VSMCs promotes a chronic pathological inflammatory response that progressively weakens the vessel wall. We review the literature pertaining to the cellular and chemical mechanisms of inflammation that contribute to aneurysm development. Hemodynamic stress and alterations in blood flow are discussed regarding their role in promoting chronic inflammation. Endothelial cell and VSMC dysfunction are examined concerning vascular remodeling. The contribution of inflammatory cytokines, especially tumor necrosis factor-α is illustrated. Inflammatory cell infiltration, particularly macrophage-mediated deterioration of vascular integrity, is reviewed. We discuss the inflammation as a means to determine aneurysms at greatest risk of rupture. Finally, future therapeutic implications of pharmacologic modulation of the inflammation are discussed.

  5. SPA-LEED study of the morphology and nucleation of a novel growth mode and the "devil's staircase" on lead/silicon(111)

    Science.gov (United States)

    Yeh, Wang-Chi Vincent

    In this thesis we describe two intriguing and unexpected discoveries we made in the Pb/Si(111). A novel growth mode was discovered on Pb thin film grown on Si(111)-7 x 7 reconstructed surface: nano-scale islands of uniform 7-layer height with steep edges and flat tops can form below room temperature. This growth mode is different from the three common modes: Frank-van der Merwe, Volmer-Weber, and Stranski-Krastanov modes. The three common modes could be explained by thermodynamic considerations on the surface free energy and do not lead to the type of self-organization we have discovered. This novel mode is explained by quantum size effects (QSE), which states that the confinement of electrons inside a well requires that the dimensions of the well meet the requirements of energy quantization: the electron wavefunctions have to form standing waves within the confining well. Further study showed that different stable heights that differ by two-layer difference could be selected by changing deposition temperature, total coverage, annealing temperature, or initial interface. Oxygen covered structures are found to retain their selected height up to almost room temperature. In addition, a novel "devil's staircase" was discovered in Pb/Si(111) between coverage 6/5 ML and 4/3 ML. Experimentally it has been an outstanding challenge to show a "devil's staircase" since physical phenomena are not expected to be described by non-differentiable functions, i.e., the stability curve Deltamu vs. theta of a "devil's staircase". This novel staircase differs from conventional ones in the difference between their two generating phases: their [11¯0] dimensions differ by two lattice constants instead of one. It was found unexpectedly that such a staircase can form with macroscopic spatial extent (˜0.5 mm) even at low temperature (T ˜ 120K) where atoms are not expected to mobile! This unusual result suggests that a high degree of self-organization is possible in the system of Pb/Si(111).

  6. Microfluidic Technology: Uncovering the Mechanisms of Nanocrystal Nucleation and Growth.

    Science.gov (United States)

    Lignos, Ioannis; Maceiczyk, Richard; deMello, Andrew J

    2017-05-16

    The controlled and reproducible formation of colloidal semiconductor nanocrystals (or quantum dots) is of central importance in nanoscale science and technology. The tunable size- and shape-dependent properties of such materials make them ideal candidates for the development of efficient and low-cost displays, solar cells, light-emitting devices, and catalysts. The formidable difficulties associated with the macroscale preparation of semiconductor nanocrystals (possessing bespoke optical and chemical properties) result from the fact that underlying reaction mechanisms are complex and that the reactive environment is difficult to control. Automated microfluidic reactors coupled with monitoring systems and optimization algorithms aim to elucidate complex reaction mechanisms that govern both nucleation and growth of nanocrystals. Such platforms are ideally suited for the efficient optimization of reaction parameters, assuring the reproducible synthesis of nanocrystals with user-defined properties. This Account aims to inform the nanomaterials community about how microfluidic technologies can supplement flask experimentation for the ensemble investigation of formation mechanisms and design of semiconductor nanocrystals. We present selected studies outlining the preparation of quantum dots using microfluidic systems with integrated analytics. Such microfluidic reaction systems leverage the ability to extract real-time information regarding optical, structural, and compositional characteristics of quantum dots during nucleation and growth stages. The Account further highlights our recent research activities focused on the development and application of droplet-based microfluidics with integrated optical detection systems for the efficient and rapid screening of reaction conditions and a better understanding of the mechanisms of quantum dot synthesis. We describe the features and operation of fully automated microfluidic reactors and their subsequent application to high

  7. Crystal growth mechanisms of the (0 1 0) face of α-lactose monohydrate crystals

    Science.gov (United States)

    Dincer, T. D.; Ogden, M. I.; Parkinson, G. M.

    2009-04-01

    The growth rates of the (0 1 0) face of α-lactose monohydrate crystals were measured at 30, 40 and 50 °C in the relative supersaturation range 0.55-2.33 in aqueous solutions. The mechanisms of growth were investigated. Spiral growth was found to be the mechanism of growth up to a critical relative supersaturation ( s-1) crit=1.9 at 30 °C. Above the critical relative supersaturation, the crystal growth mechanisms were predicted to change. All growth models fit equally well to the growth rates. No two-dimensional nucleation was observed above critical supersaturation by AFM. On the other hand increased step height and roughness on the edges of steps were observed. It was concluded that the growth mechanism of the (0 1 0) face of α-lactose monohydrate crystal is spiral growth. A parabolic relationship was obtained below critical supersaturation followed by a linear relationship with relative supersaturation.

  8. Mechanisms of Enhanced Rice Growth and Nitrogen Uptake by Nitrate

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Rice is being increasingly cultivated in intermittently irrigated regions and also in aerobic soil in which Nitrate (NO3-)plays important role in nutrition of plant. However, there is no information regarding the influence of nitrate on the overall growth and uptake of nitrogen (N) in rice plant. Solution culture experiments were carried out to study the effects of NO3-on the plant growth, uptake of N, and uptake kinetics of NH4+ in four typical rice (Oryza sativa L.) cultivars (conventional indica, conventional japonica, hybrid indica, and hybrid japonica), and on plasma membrane potential in roots of two conventional rice cultivars (indica and japonica) at the seedling stage. The results obtained indicated that a ratio of 50/50 NH4+-N/NO3--N increased the average biomass of rice shoots and roots by 20% when compared with that of 100/0NH4+-N/NO3--N. In case of the 50/50 ratio, as compared with the 100/0 ratio, total N accumulated in shoots and roots of rice increased on an average by 42% and 57%, respectively. Conventional indica responds to NO3- more than any other cultivars that were tested. The NO3- supply increased the maximum uptake rate (Vmax) of NH4+ by rice but did not show any effect on the apparent Michaelis-Menten constant (Km) value, with the average value of Vmax for NH4+ among the four cultivars being increased by 31.5% in comparison with those in the absence of NO3-. This suggested that NO3-significantly increased the numbers of the ammonium transporters. However, the lack of effect on the Km value also suggested that the presence of NO3- had no effect on the affinity of the transporters for NH4+. The plasma membrane potential in the roots of conventional indica and japonica were greatly increased by the addition of NO3-, suggesting that NO3- could improve the uptake of N by roots of the rice plant. In conclusion, the mechanisms by which NO3- enhances the growth and N uptake of rice plant was found by the increased value of Vmax of NH4+ and

  9. Controlled growth mechanism of poly (3-hexylthiophene) nanowires

    Science.gov (United States)

    Kiymaz, D.; Yagmurcukardes, M.; Tomak, A.; Sahin, H.; Senger, R. T.; Peeters, F. M.; Zareie, H. M.; Zafer, C.

    2016-11-01

    Synthesis of 1D-polymer nanowires by a self-assembly method using marginal solvents is an attractive technique. While the formation mechanism is poorly understood, this method is essential in order to control the growth of nanowires. Here we visualized the time-dependent assembly of poly (3-hexyl-thiophene-2,5-diyl) (P3HT) nanowires by atomic force microscopy and scanning tunneling microscopy. The assembly of P3HT nanowires was carried out at room temperature by mixing cyclohexanone (CHN), as a poor solvent, with polymer solution in 1,2-dichlorobenzene (DCB). Both π-π stacking and planarization, obtained at the mix volume ratio of P3HT (in DCB):CHN (10:7), were considered during the investigation. We find that the length of nanowires was determined by the ordering of polymers in the polymer repetition direction. Additionally, our density functional theory calculations revealed that the presence of DCB and CHN molecules that stabilize the structural distortions due to tail group of polymers was essential for the core-wire formation.

  10. Dynamical mechanism of antifreeze proteins to prevent ice growth

    CERN Document Server

    Kutschan, B; Thoms, S

    2014-01-01

    The fascinating ability of algae, insects and fishes to survive at temperatures below normal freezing is realized by antifreeze proteins (AFPs). Antifreeze proteins (AFPs) are surface-active molecules and interact with the diffusive water/ice interface preventing a complete solidification. A new dynamical mechanism is proposed how these proteins inhibit the freezing of water. We apply a Ginzburg-Landau type approach to describe the phase separation in the two-component system (ice, AFP). The free energy density involves two fields: one for the ice phase with low AFP concentration, and one for the liquid water with high AFP concentration. The time evolution of the ice reveals microstructures as a result of phase separation in the presence of AFPs. We observe a faster clustering of pre-ice structure connected with a locking of grain size by the action of AFP which is an essentially dynamical process. The adsorption of additional water molecules are inhibited and the further growth of ice grains are stopped. The...

  11. Low dimensional silver nanostructures: synthesis, growth mechanism, properties and applications.

    Science.gov (United States)

    Jiang, Xuchuan; Yu, Aibing

    2010-12-01

    This work presents a review of the recent advances on the low-dimensional (LD) silver nanostructures (e.g., one-dimensional nanorods and nanowires, and two-dimensional nanoplates and nanodisks). First, the methods, either physical or chemical, for the synthesis of silver LD nanostructures are introduced. Then, the use is discussed of advanced experimental techniques (e.g., transmission electron microscope, high-resolution transmission electron microscope, scanning electron microscope, atomic force microscope, ultraviolet-visible and Raman spectra) and theoretical techniques at different time and length scales from quantum mechanics (e.g., ab initio simulation and density function theory) to molecular dynamics method for understanding the principles of governing particle growth, as well as discrete dipolar approximate method for understanding the optical properties of different shapes and sizes of silver LD nanostructures. Subsequently, the functional applications of the LD silver nanostructures in different areas such optical, electronic, and sensing, particularly for those related to surface plasma resonance are summarized based on the recent findings. Finally, some perspectives and comments for future investigation of silver nanostructures are also briefly discussed.

  12. Mechanism of Microbubble Growth at Mitral Mechanical Heart Valve (MHV) Closure

    Science.gov (United States)

    Rambod, Edmond; Beizaie, Masoud; Shusser, Michael; Gharib, Morteza

    1999-11-01

    The growth mechanism of microbubbles at mitral MHV closure has been experimentally studied. In the heart, some of the tiny bubbles grow explosively and form larger and persistent bubbles. An experimental set-up was designed to allow the passage of micron-size bubbles through an 80 micron-wide slot, simulating a typical gap between the housing ring and the occluders in MHV. The bubbles were generated using an air-liquid dispenser and were delivered to the system via a 250 micron-diameter hypedermic needle positioned vertically near the slot. A solenoid valve was used to deliver a 10cc volume of liquid in 25ms time through the slot. High-speed imaging was used to study the impact of flow through the slot on bubble growth. The velocity of liquid through the slot was assessed to be in the range of 12-15 m/s. Our observations confirmed the rapid and drastic growth of microbubbles following their passage through the narrow slot, due to pressure drop. Vortices, which were induced by flow separation on the downstream of the slot, caused the grown bubbles to shatter and form more stable bubbles.

  13. MECHANISMS OF FLUID SHEAR-INDUCED INHIBITION OF POPULATION GROWTH IN A RED-TIDE DINOFLAGELLATE

    Science.gov (United States)

    Net population growth of some dinoflagellates is inhibited by fluid shear at shear stresses comparable with those generated during oceanic turbulence. Decreased net growth may occur through lowered cell division, increased mortality, or both. The dominant mechanism under various ...

  14. Correction: β-Sialon nanowires, nanobelts and hierarchical nanostructures: morphology control, growth mechanism and cathodoluminescence properties

    Science.gov (United States)

    Huang, Juntong; Huang, Zhaohui; Liu, Yangai; Fang, Minghao; Chen, Kai; Huang, Yaoting; Huang, Saifang; Ji, Haipeng; Yang, Jingzhou; Wu, Xiaowen; Zhang, Shaowei

    2016-07-01

    Correction for `β-Sialon nanowires, nanobelts and hierarchical nanostructures: morphology control, growth mechanism and cathodoluminescence properties' by Juntong Huang, et al., Nanoscale, 2014, 6, 424-432.

  15. VEGF and colon cancer growth beyond angiogenesis: does VEGF directly mediate colon cancer growth via a non-angiogenic mechanism?

    Science.gov (United States)

    Ahluwalia, Amrita; Jones, Michael K; Matysiak-Budnik, Tamara; Tarnawski, Andrzej S

    2014-01-01

    In this article we review the role of vascular endothelial growth factor (VEGF) in colon cancer growth and the underlying mechanisms. Angiogenesis, the growth of new capillary blood vessels in the body, is critical for tissue injury healing and cancer growth. In 1971, Judah Folkman proposed the concept that tumor growth beyond 2 mm is critically dependent on angiogenesis. Tumors including colon cancers release angiogenic growth factors that stimulate blood vessels to grow into the tumors thus providing oxygen and nutrients that enable exponential growth. VEGF is the most potent angiogenic growth factor. Several studies have highlighted the role of VEGF in colon cancer, specifically in the stimulation of angiogenesis. This role of VEGF is strongly supported by studies showing that inhibition of VEGF using the blocking antibody, bevacizumab, results in decreased angiogenesis and abrogation of cancer growth. In the United States, bevacizumab in combination with chemotherapy is FDA approved for the treatment of metastatic colon cancer. However, the source of VEGF in colon cancer tissue, the mechanisms of VEGF generation in colon cancer cells and the molecular pathways involved in VEGF mediated angiogenesis in colon cancer are not fully known. The possibility that VEGF directly stimulates cancer cell growth in an autocrine manner has not been explored in depth.

  16. Mechanical forces and their second messengers in stimulating cell growth in vitro

    Science.gov (United States)

    Vandenburgh, Herman H.

    1992-01-01

    Mechanical forces play an important role in modulating the growth of a number of different tissues including skeletal muscle, smooth muscle, cardiac muscle, bone, endothelium, epithelium, and lung. As interest increases in the molecular mechanisms by which mechanical forces are transduced into growth alterations, model systems are being developed to study these processes in tissue culture. This paper reviews the current methods available for mechanically stimulating tissue cultured cells. It then outlines some of the putative 'mechanogenic' second messengers involved in altering cell growth. Not surprisingly, many mechanogenic second messengers are the same as those involved in growth factor-induced cell growth. It is hypothesized that from an evolutionary standpoint, some second messenger systems may have initially evolved for unicellular organisms to respond to physical forces such as gravity and mechanical perturbation in their environment. As multicellular organisms came into existence, they appropriated these mechanogenic second messenger cascades for cellular regulation by growth factors.

  17. H2-Assistance One-Step Growth of Si Nanowires and Their Growth Mechanism

    Institute of Scientific and Technical Information of China (English)

    QIU Ming-Xia; RUAN Shuang-Chen; GAO Biao; HUO Kai-Fu; ZHAI Jian-Pang; LI Ling; LIAO Hui; XU Xin-Tong

    2011-01-01

    Large-scale nanowires are grown on Si wafers by the catalyst-free one-step thermal reaction method in Ar/H2 mixture atmosphere at 1000℃. The x-ray diffraction and energy dispersive x-ray spectroscopy results reveal that the final nanowires are of silicon nanostructures. The Held emission scanning electron microscopy shows that these self-organized Si nanowires (SiNWs) possess curly crowns with diameters varying from 10 to 300 nm and lengths of up to several hundreds of micrometers. The transmission electron microscopy indicates that the nanowires are pure Si with amorphous structures. All the measurement results show that no silicon oxide is generated in our products. The growth mechanism is proposed tentatively. Silicon oxide is reduced into Si nanoparticles under the Ar/H2 mixture, which is the main reason for the formation of such SiNWs. Our experiments offer a method of preparing Si nanostructures by simply reducing silicon oxide at high temperature.%Large-scale nanowires are grown on Si wafers by the catalyst-free one-step thermal reaction method in Ar/H2 mixture atmosphere at 1000℃.The x-ray diffraction and energy dispersive x-ray spectroscopy results reveal that the final nanowires are of silicon nanostructures.The field emission scanning electron microscopy shows that these self-organized Si nanowires (SiNWs) possess curly crowns with diameters varying from 10 to 300nm and lengths of up to several hundreds of micrometers.The transmission electron microscopy indicates that the nanowires are pure Si with amorphous structures.All the measurement results show that no silicon oxide is generated in our products.The growth mechanism is proposed tentatively.Silicon oxide is reduced into Si nanoparticles under the Ar/H2 mixture,which is the main reason for the formation of such SiNWs.Our experiments offer a method of preparing Si nanostructures by simply reducing silicon oxide at high temperature.Silicon nanowires (SiNWs) have higher carrier mobility,a larger

  18. Nucleation of CdTe thin films deposited by close-space sublimation under a nitrogen ambient

    Energy Technology Data Exchange (ETDEWEB)

    Major, J.D. [Department of Physics, Durham University, South Road, Durham, DH1 3LE (United Kingdom); Proskuryakov, Y.Y. [Department of Physics, Durham University, South Road, Durham, DH1 3LE (United Kingdom); Durose, K. [Department of Physics, Durham University, South Road, Durham, DH1 3LE (United Kingdom)]. E-mail: ken.durose@durham.ac.uk; Green, S. [School of Engineering, Durham University, South Road, Durham, DH1 3LE (United Kingdom)

    2007-05-31

    The early stages of the close-space sublimation growth of CdTe/ITO (indium tin oxide) at 500deg. C under 26.7 kPa (200 Torr) of N{sub 2} were investigated, the relatively high pressure being used to slow the growth. Film development was monitored over 60 mins by ex-situ AFM (atomic force microscopy), the growth being controlled by a shutter. The films formed by the 'island' or Volmer-Weber growth mechanism. Developments in the areal island growth rate, the island density and spatial distribution type were explained using growth mechanisms. Significant changes in these phenomena at t {>=} 10 mins were attributed to a change in growth mechanism from surface migration limited, to a regime in which island coalescence and direct impingement of vapour species on the islands became important. Since the islands are characterised by distinct crystalline facets, this indicates the growth mechanism to be uninterrupted step-flow like addition of material to each island. Arguments are given to relate the final grain size in the films to the density of nuclei that are stable to re-evaporation after t = 10 mins.

  19. Epitaxial Growth of Two-Dimensional Layered Transition-Metal Dichalcogenides: Growth Mechanism, Controllability, and Scalability

    KAUST Repository

    Li, Henan

    2017-07-06

    Recently there have been many research breakthroughs in two-dimensional (2D) materials including graphene, boron nitride (h-BN), black phosphors (BPs), and transition-metal dichalcogenides (TMDCs). The unique electrical, optical, and thermal properties in 2D materials are associated with their strictly defined low dimensionalities. These materials provide a wide range of basic building blocks for next-generation electronics. The chemical vapor deposition (CVD) technique has shown great promise to generate high-quality TMDC layers with scalable size, controllable thickness, and excellent electronic properties suitable for both technological applications and fundamental sciences. The capability to precisely engineer 2D materials by chemical approaches has also given rise to fascinating new physics, which could lead to exciting new applications. In this Review, we introduce the latest development of TMDC synthesis by CVD approaches and provide further insight for the controllable and reliable synthesis of atomically thin TMDCs. Understanding of the vapor-phase growth mechanism of 2D TMDCs could benefit the formation of complicated heterostructures and novel artificial 2D lattices.

  20. Rapid, bilateral changes in growth rate and curvature during gravitropism of cucumber hypocotyls: implications for mechanism of growth control

    Science.gov (United States)

    Cosgrove, D. J.

    1990-01-01

    The growth response of etiolated cucumber (Cucumis sativus L.) hypocotyls to gravitropic stimulation was examined by means of time-lapse photography and high-resolution analysis of surface expansion and curvature. In comparison with video analysis, the technique described here has five- to 20-fold better resolution; moreover, the mathematical fitting method (cubic splines) allows direct estimation of local and integrated curvature. After switching seedlings from a vertical to horizontal position, both upper and lower surfaces of the stem reacted after a lag of about 11 min with a two- to three-fold increase in surface expansion rate on the lower side and a cessation of expansion, or slight compression, on the upper surface. This growth asymmetry was initiated simultaneously along the length of the hypocotyl, on both upper and lower surfaces, and did not migrate basipetally from the apex. Later stages in the gravitropic response involved a complex reversal of the growth asymmetry, with the net result being a basipetal migration of the curved region. This secondary growth reversal may reflect oscillatory and/or self-regulatory behaviour of growing cells. With some qualifications, the kinetics and pattern of growth response are consistent with a mechanism involving hormone redistribution, although they do not prove such a mechanism. The growth kinetics require a growth mechanism which can be stimulated by two- to three-fold or completely inhibited within a few minutes.

  1. Pattern and mechanism of urban spatial growth in Nanjing City,1979-2007

    Institute of Scientific and Technical Information of China (English)

    ZHANG Zhen-long; MA Guo-qiang

    2010-01-01

    Urban spatial growth has become a hot topic of geographic science and urban research.Exploring the patterns and mechanisms of urban growth is the prerequisite to understand the urbanization process of China.The paper provides a spatial analysis method of using Remote Sensing(RS)and Geographic Information System(GIS),and presents major patterns and mechanisms of urhan spatial growth during the period from 1979 to 2007 in Nanjing City.Firstly,the paper introduces the data,study area and methodology of the research.Then,the patterns of urban spatial growth are identified.Subsequently,the main mechanisms of urban spatial growth are analyzed.Finally,some conclusions are drawn definitely.The features of urban spatial growth in Nanjing are as follows: during 1979-1988,urban spatial growth of each district was slow,and the inner growth was in excess of suburban growth;during the period of 1988-2000.urban growth of suburban was in excess of inner city the most insensitive growth appeared in the southeast,and the growth of each aspect was relatively insensitive expect east and west; during the period of 2000-2007,urban growth of suburban was violent,the most insensitive growth appeared in the southeast,and the urban growth of each direction was insensitive except the west.The mechanisms of urban.spatial growth are complex,the main ones of which are social and economic development.Besides,the guiding of urban planning and influence of urban spatial structure are quite obvious.

  2. Entrepreneurship, institutions and growth in European regions : a uniform mechanism

    NARCIS (Netherlands)

    Bruns, K.; Bosma, N.S.; Sanders, M.W.J.L.; Schramm, M.C.

    2015-01-01

    In this paper we present an alternative empirical strategy that sheds light on the importance of institutional quality for regional economic growth. The fundamental problem in this type of research is that institutional quality cannot be measured directly. Existing proxies are typically highly corre

  3. Mechanism of Growth Enhancement of Plants Induced by Active Species in Plasmas

    Science.gov (United States)

    Watanabe, Satoshi; Ono, Reoto; Hayashi, Nobuya

    2015-09-01

    Plant growth enhances when seeds are irradiated by plasma. However the mechanism of the growth enhancement by plasma has not been clarified. In this study, growth enhancement of plants using various active species and variation of plant cells are investigated. RF plasma is generated under conditions where pressure is 60 Pa and input electrical power is 60 W. Irradiation period varies from 0 (control) to 75 min. Air plasma shows maximum growth of plants with irradiation period of 60 min on the other hand, oxygen plasma shows the maximum growth with irradiation period of 15 min. From change of gaseous species and pressure dependence, growth enhancing factor is expected to be active oxygen species produced in plasma. According to gene expression analysis of Arabidopsis, there are two speculated mechanism of plant growth enhancement. The first is acceleration of cell cycle by gene expressions of photosynthesis and glycolytic pathway, and the second is increase of cell size via plant hormone production.

  4. Mechanisms of environmental chemicals that enable the cancer hallmark of evasion of growth suppression

    Science.gov (United States)

    Nahta, Rita; Al-Mulla, Fahd; Al-Temaimi, Rabeah; Amedei, Amedeo; Andrade-Vieira, Rafaela; Bay, Sarah; G. Brown, Dustin; Calaf, Gloria M.; Castellino, Robert C.; Cohen-Solal, Karine A.; Colacci, Annamaria; Cruickshanks, Nichola; Dent, Paul; Di Fiore, Riccardo; Forte, Stefano; Goldberg, Gary S.; Hamid, Roslida A.; Krishnan, Harini; Laird, Dale W.; Lasfar, Ahmed; Marignani, Paola A.; Memeo, Lorenzo; Mondello, Chiara; Naus, Christian C.; Ponce-Cusi, Richard; Raju, Jayadev; Roy, Debasish; Roy, Rabindra; P. Ryan, Elizabeth; Salem, Hosni K.; Scovassi, A. Ivana; Singh, Neetu; Vaccari, Monica; Vento, Renza; Vondráček, Jan; Wade, Mark; Woodrick, Jordan; Bisson, William H.

    2015-01-01

    As part of the Halifax Project, this review brings attention to the potential effects of environmental chemicals on important molecular and cellular regulators of the cancer hallmark of evading growth suppression. Specifically, we review the mechanisms by which cancer cells escape the growth-inhibitory signals of p53, retinoblastoma protein, transforming growth factor-beta, gap junctions and contact inhibition. We discuss the effects of selected environmental chemicals on these mechanisms of growth inhibition and cross-reference the effects of these chemicals in other classical cancer hallmarks. PMID:26106139

  5. An assessment of calcite crystal growth mechanisms based on crystal size distributions

    Science.gov (United States)

    Kile, D.E.; Eberl, D.D.; Hoch, A.R.; Reddy, M.M.

    2000-01-01

    Calcite crystal growth experiments were undertaken to test a recently proposed model that relates crystal growth mechanisms to the shapes of crystal size distributions (CSDs). According to this approach, CSDs for minerals have three basic shapes: (1) asymptotic, which is related to a crystal growth mechanism having constant-rate nucleation accompanied by surface-controlled growth; (2) lognormal, which results from decaying-rate nucleation accompanied by surface-controlled growth; and (3) a theoretical, universal, steady-state curve attributed to Ostwald ripening. In addition, there is a fourth crystal growth mechanism that does not have a specific CSD shape, but which preserves the relative shapes of previously formed CSDs. This mechanism is attributed to supply-controlled growth. All three shapes were produced experimentally in the calcite growth experiments by modifying nucleation conditions and solution concentrations. The asymptotic CSD formed when additional reactants were added stepwise to the surface of solutions that were supersaturated with respect to calcite (initial Ω = 20, where Ω = 1 represents saturation), thereby leading to the continuous nucleation and growth of calcite crystals. Lognormal CSDs resulted when reactants were added continuously below the solution surface, via a submerged tube, to similarly supersaturated solutions (initial Ω = 22 to 41), thereby leading to a single nucleation event followed by surface-controlled growth. The Ostwald CSD resulted when concentrated reactants were rapidly mixed, leading initially to high levels of supersaturation (Ω >100), and to the formation and subsequent dissolution of very small nuclei, thereby yielding CSDs having small crystal size variances. The three CSD shapes likely were produced early in the crystallization process, in the nanometer crystal size range, and preserved during subsequent growth. Preservation of the relative shapes of the CSDs indicates that a supply-controlled growth mechanism

  6. Mechanically driven growth of quasi-two dimensional microbial colonies

    CERN Document Server

    Farrell, F D C; Marenduzzo, D; Waclaw, B

    2013-01-01

    We study colonies of non-motile, rod-shaped bacteria growing on solid substrates. In our model, bacteria interact purely mechanically, by pushing each other away as they grow, and consume a diffusing nutrient. We show that mechanical interactions control the velocity and shape of the advancing front, which leads to features that cannot be captured by established Fisher-Kolmogorov models. In particular, we find that the velocity depends on the elastic modulus of bacteria or their stickiness to the surface. Interestingly, we predict that the radius of an incompressible, strictly two-dimensional colony cannot grow linearly in time. Importantly, mechanical interactions can also account for the nonequilibrium transition between circular and branching colonies, often observed in the lab.

  7. A structure-based extracellular matrix expansion mechanism of fibrous tissue growth.

    Science.gov (United States)

    Kalson, Nicholas S; Lu, Yinhui; Taylor, Susan H; Starborg, Tobias; Holmes, David F; Kadler, Karl E

    2015-05-20

    Embryonic growth occurs predominately by an increase in cell number; little is known about growth mechanisms later in development when fibrous tissues account for the bulk of adult vertebrate mass. We present a model for fibrous tissue growth based on 3D-electron microscopy of mouse tendon. We show that the number of collagen fibrils increases during embryonic development and then remains constant during postnatal growth. Embryonic growth was explained predominately by increases in fibril number and length. Postnatal growth arose predominately from increases in fibril length and diameter. A helical crimp structure was established in embryogenesis, and persisted postnatally. The data support a model where the shape and size of tendon is determined by the number and position of embryonic fibroblasts. The collagen fibrils that these cells synthesise provide a template for postnatal growth by structure-based matrix expansion. The model has important implications for growth of other fibrous tissues and fibrosis.

  8. Hybrid accretionary/collisional mechanism of Paleozoic Asian continental growth

    Science.gov (United States)

    Schulmann, Karel; Lexa, Ondrej; Janousek, Vojtech; Pavla, Stipska; Yingde, Jiang; Alexandra, Guy; Min, Sun

    2016-04-01

    Continental crust is formed above subduction zones by well-known process of "juvenile crust growth". This new crust is in modern Earth assembled into continents by two ways: (i) short-lived collisions of continental blocks with the Eurasian continent along the "Alpine-Himalayan collisional/interior orogens" in the heart of the Pangean continental plates realm; and (ii) long lived lateral accretion of ocean-floor fragments along "circum-Pacific accretionary/peripheral orogens" at the border of the Pacific oceanic plate. This configuration has existed since the late Proterozoic, when the giant accretionary Terra Australis Orogen developed at periphery of an old Palaeo-Pacific ocean together with collisional Caledonian and Variscan orogens. At the same time, the large (ca. 9 millions km2) Central Asian Orogenic Belt (CAOB) developed in the NE part of the Pangea. This orogen reveals features of both peripheral and interior orogens, which implies that the generally accepted "peripheral-accretionary" and "interior- collisional" paradigm is not applicable here. To solve this conundrum a new model of unprecedented Phanerozoic continental growth is proposed. In this model, the CAOB precursor evolved at the interface of old exterior and young interior oceans. Subsequently, the new lithospheric domain was transferred by advancing subduction into the interior of the Pangean mostly continental realm. During this process the oceanic crust was transformed into continental crust and it was only later when this specific lithosphere was incorporated into the Asian continent. If true, this concept represents revolutionary insight into processes of crustal growth explaining the enigma of anchoring hybrid lithosphere inside a continent without its subduction or Tibetan-type thickening.

  9. Perception mechanism of gravity stimuli in hypergravity-induced growth inhibition of azuki bean roots.

    Science.gov (United States)

    Soga, Kouichi; Wakabayashi, Kazuyuki; Kamisaka, Seiichiro; Hoson, Takayuki

    2003-10-01

    We reported that elongation growth of plant shoots and roots is suppressed by hypergravity, with the rate decreasing in proportion to logarithm of the magnitude of gravity. In hypergravity-induced growth inhibition of shoots, graviperception is supposed to be independent of that in gravitropism and to involve mechanoreceptors. However, the graviperception mechanism in the hypergravity-induced growth inhibition of roots is not known. In the present study, we compared the mechanism in the hypergravity-induced growth inhibition of roots with that in gravitropism. The removal of root cap did not influence hypergravity-induced growth inhibition of roots, although the gravitropic curvature was completely inhibited. Hypergravity had no effects on growth of azuki bean roots in the presence of lanthanum or gadolinium, which are blockers of mechanoreceptors. On the contrary, lanthanum or gadolinium at the same concentration did not influence gravitropism of roots. These results suggest that the graviperception mechanism in the hypergravity-induced growth inhibition of roots is independent of that in gravitropism. Hypergravity-induced growth inhibition of azuki bean roots was observed irrespective of the direction of stimuli, which disappeared in the presence of lanthanum or gadolinium. Thus, in the hypergravity-induced growth inhibition, roots may perceive the gravity signal by mechanoreceptors on the plasma membrane independently of the direction of stimuli, and may utilize it to regulate their growth rate.

  10. Micromechanical analysis of volumetric growth in the context of open systems thermodynamics and configurational mechanics. Application to tumor growth

    Science.gov (United States)

    Ganghoffer, J. F.; Boubaker, M. B.

    2016-11-01

    We adopt in this paper the physically and micromechanically motivated point of view that growth (resp. resorption) occurs as the expansion (resp. contraction) of initially small tissue elements distributed within a host surrounding matrix, due to the interfacial motion of their boundary. The interface motion is controlled by the availability of nutrients and mechanical driving forces resulting from the internal stresses that built in during the growth. A general extremum principle of the zero potential for open systems witnessing a change of their mass due to the diffusion of nutrients is constructed, considering the framework of open systems thermodynamics. We postulate that the shape of the tissue element evolves in such a way as to minimize the zero potential among all possible admissible shapes of the growing tissue elements. The resulting driving force for the motion of the interface sets a surface growth models at the scale of the growing tissue elements, and is conjugated to a driving force identified as the interfacial jump of the normal component of an energy momentum tensor, in line with Hadamard's structure theorem. The balance laws associated with volumetric growth at the mesoscopic level result as the averaging of surface growth mechanisms occurring at the microscopic scale of the growing tissue elements. The average kinematics has been formulated in terms of the effective growth velocity gradient and elastic rate of deformation tensor, both functions of time. This formalism is exemplified by the simulation of the avascular growth of multicell spheroids in the presence of diffusion of nutrients, showing the respective influence of mechanical and chemical driving forces in relation to generation of internal stresses.

  11. Micromechanical analysis of volumetric growth in the context of open systems thermodynamics and configurational mechanics. Application to tumor growth

    Science.gov (United States)

    Ganghoffer, J. F.; Boubaker, M. B.

    2017-03-01

    We adopt in this paper the physically and micromechanically motivated point of view that growth (resp. resorption) occurs as the expansion (resp. contraction) of initially small tissue elements distributed within a host surrounding matrix, due to the interfacial motion of their boundary. The interface motion is controlled by the availability of nutrients and mechanical driving forces resulting from the internal stresses that built in during the growth. A general extremum principle of the zero potential for open systems witnessing a change of their mass due to the diffusion of nutrients is constructed, considering the framework of open systems thermodynamics. We postulate that the shape of the tissue element evolves in such a way as to minimize the zero potential among all possible admissible shapes of the growing tissue elements. The resulting driving force for the motion of the interface sets a surface growth models at the scale of the growing tissue elements, and is conjugated to a driving force identified as the interfacial jump of the normal component of an energy momentum tensor, in line with Hadamard's structure theorem. The balance laws associated with volumetric growth at the mesoscopic level result as the averaging of surface growth mechanisms occurring at the microscopic scale of the growing tissue elements. The average kinematics has been formulated in terms of the effective growth velocity gradient and elastic rate of deformation tensor, both functions of time. This formalism is exemplified by the simulation of the avascular growth of multicell spheroids in the presence of diffusion of nutrients, showing the respective influence of mechanical and chemical driving forces in relation to generation of internal stresses.

  12. Atomistic mechanisms of orientation and temperature dependence in gold-catalyzed silicon growth

    Science.gov (United States)

    Wang, Yanming; Santana, Adriano; Cai, Wei

    2017-08-01

    Gold-catalyzed vapor-liquid-solid (VLS) growth is widely used in the synthesis of silicon-based low-dimensional nano-structures. However, its growth mechanisms are not fully understood yet. In this paper, we systematically study the orientation and temperature dependences in the VLS process, by means of long molecular dynamics (MD) simulations up to 100 ns using an MEAM potential that well reproduces the binary phase diagram. The crystal growth velocities are extracted from the simulations under various conditions for 〈110 〉 and 〈111 〉 orientations, respectively. Our data suggest a linear dependence of the growth velocity on the Si supersaturation for 〈110 〉 growth, in contrast to a non-linear dependence for 〈111 〉 growth. By analyzing the surface morphologies, this difference is linked to the continuous growth mechanism on the {110} substrate and the island nucleation controlled growth on the {111} substrate. Furthermore, we find that the 〈111 〉 growth in our MD simulations operates in the regime where the nucleation rate is higher than the island expansion rate. This is traced to the formation of a gold saturated monolayer above the nucleated Si island, impeding its further growth. Also, it is found that the atom activity near the {111} interface is lower, explaining the smaller growth velocity of the {111} surface than that of the {110} surface.

  13. Mediated attachment as a mechanism for growth of complex networks

    CERN Document Server

    Shekatkar, Snehal M

    2014-01-01

    Connection topologies of many networked systems like human brain, biological cell, world wide web, power grids, human society and ecological food webs markedly deviate from that of completely random networks indicating the presence of organizing principles behind their evolution. The five important features that characterize such networks are scale-free topology, small average path length, high clustering, hierarchical community structure and assortative mixing. Till now the generic mechanisms underlying the existence of these properties are not well understood. Here we show that potentially a single mechanism, which we call "mediated attachment", where two nodes get connected through a mediator or common neighbor, could be responsible for the emergence of all important properties of real networks. The mediated attachment naturally unifies scale-free topology, high clustering, small world nature, hierarchical community structure and dissortative nature of networks. Further, with additional mixing by age, this...

  14. Biological mechanisms discriminating growth rate and adult body weight phenotypes in two Chinese indigenous chicken breeds

    NARCIS (Netherlands)

    Dou, Tengfei; Zhao, Sumei; Rong, Hua; Gu, Dahai; Li, Qihua; Huang, Ying; Xu, Zhiqiang; Chu, Xiaohui; Tao, Linli; Liu, Lixian; Ge, Changrong; Pas, te Marinus F.W.; Jia, Junjing

    2017-01-01

    Background: Intensive selection has resulted in increased growth rates and muscularity in broiler chickens, in addition to adverse effects, including delayed organ development, sudden death syndrome, and altered metabolic rates. The biological mechanisms underlying selection responses remain

  15. Role of boric acid in nickel nanotube electrodeposition: a surface-directed growth mechanism.

    Science.gov (United States)

    Graham, Lauren M; Cho, Seungil; Kim, Sung Kyoung; Noked, Malachi; Lee, Sang Bok

    2014-01-18

    Nickel nanotubes have been synthesized by the popular and versatile method of template-assisted electrodeposition, and a surface-directed growth mechanism based on the adsorption of the nickel-borate complex has been proposed.

  16. Growth mechanism of InGaN nano-umbrellas

    Science.gov (United States)

    Zhang, Xin; Haas, Benedikt; Rouvière, Jean-Luc; Robin, Eric; Daudin, Bruno

    2016-11-01

    It is demonstrated that growing InGaN nanowires in metal-rich conditions on top of GaN nanowires results in a widening of the InGaN section. It is shown that the widening is eased by stacking faults (SFs) formation, revealing facets favorable to In incorporation. It is furthermore put in evidence that partial dislocations terminating SFs efficiently contribute to elastic strain relaxation. Indium accumulation on top of the InGaN section is found to result in an axial growth rate decrease, which has been assigned to increased N–N recombination and subsequent effective nitrogen flux decrease, eventually leading to the formation of InGaN nano-umbrellas/nanoplatelets.

  17. Mechanisms for catalytic carbon nanofiber growth studied by ab initio density functional theory calculations

    DEFF Research Database (Denmark)

    Abild-Pedersen, Frank; Nørskov, Jens Kehlet; Rostrup-Nielsen, Jens;

    2006-01-01

    Mechanisms and energetics of graphene growth catalyzed by nickel nanoclusters were studied using ab initio density functional theory calculations. It is demonstrated that nickel step-edge sites act as the preferential growth centers for graphene layers on the nickel surface. Carbon is transported...

  18. Growth plate cartilage shows different strain patterns in response to static versus dynamic mechanical modulation.

    Science.gov (United States)

    Kaviani, Rosa; Londono, Irene; Parent, Stefan; Moldovan, Florina; Villemure, Isabelle

    2016-08-01

    Longitudinal growth of long bones and vertebrae occurs in growth plate cartilage. This process is partly regulated by mechanical forces, which are one of the underlying reasons for progression of growth deformities such as idiopathic adolescent scoliosis and early-onset scoliosis. This concept of mechanical modulation of bone growth is also exploited in the development of fusionless treatments of these deformities. However, the optimal loading condition for the mechanical modulation of growth plate remains to be identified. The objective of this study was to evaluate the effects of in vitro static versus dynamic modulation and of dynamic loading parameters, such as frequency and amplitude, on the mechanical responses and histomorphology of growth plate explants. Growth plate explants from distal ulnae of 4-week-old swines were extracted and randomly distributed among six experimental groups: baseline ([Formula: see text]), control ([Formula: see text]), static ([Formula: see text]) and dynamic ([Formula: see text]). For static and dynamic groups, mechanical modulation was performed in vitro using an Indexed CartiGen bioreactor. A stress relaxation test combined with confocal microscopy and digital image correlation was used to characterize the mechanical responses of each explant in terms of peak stress, equilibrium stress, equilibrium modulus of elasticity and strain pattern. Histomorphometrical measurements were performed on toluidine blue tissue sections using a semi-automatic custom-developed MATLAB toolbox. Results suggest that compared to dynamic modulation, static modulation changes the strain pattern of the tissue and thus is more detrimental for tissue biomechanics, while the histomorphological parameters are not affected by mechanical modulation. Also, under dynamic modulation, changing the frequency or amplitude does not affect the biomechanical response of the tissue. Results of this study will be useful in finding optimal and non-damaging parameters

  19. Nanoscale grain growth behaviour of CoAl intermetallic synthesized by mechanical alloying

    Indian Academy of Sciences (India)

    S N Hosseini; M H Enayati; F Karimzadeh

    2014-05-01

    Grain growth behaviour of the nanocrystalline CoAl intermetallic compound synthesized by mechanical alloying has been studied by isothermal annealing at different temperatures and durations. X-ray diffraction method was employed to investigate structural evolutions during mechanical alloying and annealing processes. The disordered CoAl phase with the grain size of about 6 nm was formed via a gradual reaction during mechanical alloying. The results of isothermal annealing showed that the grain growth behaviour can be explained by the parabolic grain growth law. The grains were at nanometric scale after isothermal annealing up to 0.7 m. The grain growth exponent remained constant above 873 K indicating that grain growth mechanism does not change at high temperatures. The calculated activation energy indicated that the grain growth mechanism in the disordered CoAl phase at high temperatures was diffusing Co and Al atoms in two separate sublattices. Furthermore, an equation has been suggested to describe the grain growth kinetics of nanocrystalline CoAl under isothermal annealing at temperatures above 873 K (/m ≥ 0.5).

  20. Nucleation and growth mechanisms of nano magnesium hydride from the hydrogen sorption kinetics.

    Science.gov (United States)

    Mooij, Lennard; Dam, Bernard

    2013-07-21

    We use a combination of hydrogenography and Johnson-Mehl-Avrami-Kolmogorov (JMAK) analyses to identify (1) the driving force dependence of the nucleation and growth mechanism of MgH2 in thin film multilayers of Mg (10 nm) and (2) the nucleation and growth mechanism of Mg in the earlier formed MgH2, i.e. the hydrogen desorption process. We conclude that JMAK may be successfully applied to obtain the nucleation and growth mechanism of hydrogen absorption. The desorption mechanism, however, is not simply the reverse of the absorption mechanism. We find evidence that the barrier for nucleation of Mg is small. The dehydrogenation probably involves the formation of voids, which is energetically more favorable than elastic and plastic deformation of the multilayer.

  1. Transport, Growth Mechanisms, and Material Quality in GaN Epitaxial Lateral Overgrowth

    Energy Technology Data Exchange (ETDEWEB)

    Baca, Albert G.; Bartram, M.E.; Coltrin, M.E.; Crawford, M.H.; Han, J.; Missert, N.; Willan, C.C.

    1999-01-11

    Growth kinetics, mechanisms, and material quality in GaN epitaxial lateral over-growth (ELO) were examined using a single mask of systematically varied patterns. A 2-D gas phase reaction/diffusion model describes how transport of the Ga precursor to the growth surface enhances the lateral rate in the early stages of growth. In agreement with SEM studies of truncated growth runs, the model also predicts the dramatic decrease in the lateral rate that occurs as GaN over-growth reduces the exposed area of the mask. At the point of convergence, a step-flow coalescence mechanism is observed to fill in the area between lateral growth-fronts. This alternative growth mode in which a secondary growth of GaN is nucleated along a single convergence line, may be responsible for producing smooth films observed to have uniform cathodoluminescence (CL) when using 1{micro}m nucleation zones. Although emission is comprised of both UV ({approximately}365nm) and yellow ({approximately}550nm) components, the spectra suggest these films have reduced concentrations of threading dislocations normally associated with non-radiative recombination centers and defects known to accompany growth-front convergence lines.

  2. General frost growth mechanism on solid substrates with different stiffness.

    Science.gov (United States)

    Petit, Julien; Bonaccurso, Elmar

    2014-02-01

    Preventing or delaying frost formation on surfaces is of significant importance in many aspects of our daily life. Despite many efforts and improvements recently achieved in the design of new icephobic materials and substrates, not all proposed solutions are universally applicable and frost formation still remains a problem in need of further flexible solutions. In this respect, we propose to take benefit from the tunable viscoelastic properties of soft polymer gel substrates, since they are known to strongly influence the dropwise condensation process of water, and to investigate condensation frosting on them. Using polymer gels with different stiffness and a hard substrate as a reference, we demonstrate their ability to delay frost formation compared to recent results reported in the literature on other solid substrates and in particular on superhydrophobic surfaces. By investigating the frost front propagation we singled out a general behavior of its dynamic evolution consisting of two processes presenting two different time scales. This general growth appears to be independent of experimental conditions as well as substrate stiffness.

  3. Wedding Cake Growth Mechanism in One-Dimensional and Two-Dimensional Nanostructure Evolution.

    Science.gov (United States)

    Yin, Xin; Shi, Jian; Niu, Xiaobin; Huang, Hanchen; Wang, Xudong

    2015-11-11

    The kinetic processes and atomistic mechanisms in nanostructure growth are of fundamental interest to nanomaterial syntheses with precisely controlled morphology and functionality. By programming deposition conditions at time domain, we observed the wedding cake growth mechanism in the formation of 1D and 2D ZnO nanostructures. Within a narrow growth window, the surfaces of the 1D and 2D structures were covered with a unique concentric terrace feature. This mechanism was further validated by comparing the characteristic growth rates to the screw dislocation-driven model. An interesting 1D to 2D morphology transition was also found during the wedding cake growth, when the adatoms overcome the Ehrlich-Schwoebel (ES) barrier along the edge of the top crystal facet triggered by lowering the supersaturation. The wedding cake model might be a general growth mechanism for flat-tipped nanowires that do not possess any dislocations. This study enriches our understanding on the fundamental kinetics of nanostructured crystal growth and provides a transformative strategy to achieve rational design and control of nanoscale geometry.

  4. When biochemistry meets mechanics: a systems view of growth control in plants.

    Science.gov (United States)

    Sassi, Massimiliano; Traas, Jan

    2015-12-01

    The emergence of complex shapes during the development of plants is under the control of genetically determined molecular networks. Such regulatory networks, comprising hormones and transcription factors, regulate the collective behavior of cell growth within a tissue. Because all the cells within a tissue are linked together by the cell wall, their collective growth generates a good amount of mechanical stress. In the last few years a compelling amount of evidence has shown that growth-generated mechanical stress can feed back on plant developmental programs by modifying cell growth. This involves primarily responses from the microtubules and interaction with auxin transport and signaling. Here we discuss the most recent advances in the understanding of mechanical feedbacks in plant development. Copyright © 2015 Elsevier Ltd. All rights reserved.

  5. Mechanical modeling of the growth of salt structures

    Energy Technology Data Exchange (ETDEWEB)

    Alfaro, R.A.M.

    1993-05-01

    A 2D numerical model for studying the morphology and history of salt structures by way of computer simulations is presented. The model is based on conservation laws for physical systems, a fluid marker equation to keep track of the salt/sediments interface, and two constitutive laws for rocksalt. When buoyancy alone is considered, the fluid-assisted diffusion model predicts evolution of salt structures 2.5 times faster than the power-law creep model. Both rheological laws predict strain rates of the order of 4.0 {times} 10{sup {minus}15}s{sup {minus}1} for similar structural maturity level of salt structures. Equivalent stresses and viscosities predicted by the fluid-assisted diffusion law are 10{sup 2} times smaller than those predicted by the power-law creep rheology. Use of East Texas Basin sedimentation rates and power-law creep rheology indicate that differential loading is an effective mechanism to induce perturbations that amplify and evolve to mature salt structures, similar to those observed under natural geological conditions.

  6. General aspects of solid on liquid growth mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Laux, E; Charmet, J; Haquette, H; Banakh, O; Jeandupeux, L; Graf, B; Keppner, H, E-mail: Herbert.Keppner@he-arc.c [University of Applied Science Arc, Eplatures-Grise 17, CH-2300 La Chaux-de-Fonds (Switzerland)

    2009-08-01

    Liquids, in general, tend to have a lower density as solids and therefore it is not straightforward to deposit solid over liquids in a way that the liquid becomes hermetically sealed under the solid layer. The authors review that several phenomena that can easily be observed in nature are only due to particular anomalies and solid on liquid is rather an exception as the rule. Natural solid on liquid systems are lacking of thermal, mechanical or chemical stability. It is not surprising, that one is not at all used thinking about to e.g. replace the gate oxide in a thin film transistor by a thin film of oil, or, to find in other microsystems functional liquids between a stack of thin solid films. However, once this becomes a serious option, a large variety of new Microsystems with new functionalities can be easily designed. In another paper (this conference and [1]) the authors pioneered that the polymer Parylene (poly(p-xylylene)) can be deposited on liquids coming already quite close to the above mentioned vision. In this paper the authors ask if one can synthesize other solid on liquid systems and surprisingly conclude, based on experimental evidence, that solid on liquid deposition seems to rather be the rule and not the exception.

  7. Review: Wind impacts on plant growth, mechanics and damage.

    Science.gov (United States)

    Gardiner, Barry; Berry, Peter; Moulia, Bruno

    2016-04-01

    Land plants have adapted to survive under a range of wind climates and this involve changes in chemical composition, physical structure and morphology at all scales from the cell to the whole plant. Under strong winds plants can re-orientate themselves, reconfigure their canopies, or shed needles, leaves and branches in order to reduce the drag. If the wind is too strong the plants oscillate until the roots or stem fail. The mechanisms of root and stem failure are very similar in different plants although the exact details of the failure may be different. Cereals and other herbaceous crops can often recover after wind damage and even woody plants can partially recovery if there is sufficient access to water and nutrients. Wind damage can have major economic impacts on crops, forests and urban trees. This can be reduced by management that is sensitive to the local site and climatic conditions and accounts for the ability of plants to acclimate to their local wind climate. Wind is also a major disturbance in many plant ecosystems and can play a crucial role in plant regeneration and the change of successional stage.

  8. Strain-induced morphology manipulations of Si and Ge-based heterostructures on Si(0 0 1) surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Dentel, D.; Aiet-Mansour, K.; Bischoff, J.L.; Kubler, L.; Bolmont, D

    2004-07-31

    By using reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), high-resolution transmission electron microscopy (HRTEM) analyses, we show that the well-known Stranski-Krastanov growth mode of Ge/Si(0 0 1) can be modified in a Volmer-Weber one by C pre-deposition on the Si(0 0 1) surface or in a Frank-Van der Merve one by supplying atomic hydrogen during the Ge growth. By tuning the growth conditions and acting on the interplay of surface diffusion, strain and surface energy, morphology manipulations by the growth process control are therefore possible. The Si capping of these Ge self-assembled nanostructures also allows us to point out a correlation between the nucleation mechanism of the Ge or SiGe islands and their associated embedding process. On bare Si surfaces, the final morphology of the embedded Ge film is strongly dependent on the kinetic parameters of the capping layer. Indeed oriented migrations of both Si and Ge atoms are able to smooth or to maintain the islands on the surface. Si diffusions also contribute in a rapid restoration of a planar morphology. On Si(0 0 1)-c(4 x 4) the adatom migrations and consequently the covering mechanism of the Ge islands seems to be governed by the strain mapping related to the C pre-deposited surface. The first stages of the Si capping process have revealed the preservation of the Ge islands associated to an increase of the surface roughness.

  9. Mechanical tension promotes skin nerve regeneration by upregulating nerve growth factor expression

    Institute of Scientific and Technical Information of China (English)

    Hu Xiao; Dechang Wang; Ran Huo; Yibing Wang; Yongqiang Feng; Qiang Li

    2013-01-01

    This study aimed to explore the role of mechanical tension in hypertrophic scars and the change in nerve density using hematoxylin-eosin staining and S100 immunohistochemistry, and to observe the expression of nerve growth factor by western blot analysis. The results demonstrated that mechanical tension contributed to the formation of a hyperplastic scar in the back skin of rats, in conjunction with increases in both nerve density and nerve growth factor expression in the scar tissue. These experimental findings indicate that the cutaneous nervous system plays a role in hypertrophic scar formation caused by mechanical tension.

  10. ALKALINE PEROXIDE MECHANICAL PULPING OF FAST GROWTH PAULOWNIA WOOD

    Directory of Open Access Journals (Sweden)

    Ahmad Jahan Latibari,

    2011-11-01

    Full Text Available Alkaline peroxide mechanical pulping of paulownia wood harvested from exotic tree plantations in northern Iran was investigated. The fiber length, width, and cell wall thickness of this wood were measured as 0.82 mm, 40.3 μm, and 7.1 μm, respectively. The chemical composition including cellulose, lignin, and extractives soluble in ethanol-acetone, 1% NaOH, hot and cold water was determined as 49.5%, 25%, 12.1%, 26.9%, 11.4%, and 8.1% respectively. The ash content of this wood was 0.45%. Pre-washed chips were chemically treated at 70°C for 120 minutes with different combinations of three dosages (1.5, 3, and 4.5% of hydrogen peroxide and three dosages (1.5, 3, and 4.5% of sodium hydroxide prior to defibration. Other chemicals including DTPA, sodium silicate, and MgSO4 were constant at 0.5%, 3%, and 0.5%, respectively. The results showed that using a 1.5% hydrogen peroxide and 4.5% sodium hydroxide charge, the brightness of APMP pulp reached 68.7% ISO and higher chemical dosages did not improve the brightness; however, to produce APMP pulp with higher strength, a sodium hydroxide charge of 4.5% was needed. The tensile strength, tear strength, burst strength indices, and bulk density of the APMP pulp produced from 1.5% hydrogen peroxide and 4.5% sodium hydroxide were measured as 15.5Nm/g, 6.54mN.m2/g, 0.56kPa.m2/g, and 3.47cm3/g, respectively. The resulting pulp was bulky and is suitable for use in the middle layer of boxboard to provide the desired stiffness with a lower basis weight.

  11. Crack growth threshold under hold time conditions in DA Inconel 718 – A transition in the crack growth mechanism

    Directory of Open Access Journals (Sweden)

    E. Fessler

    2016-01-01

    Full Text Available Aeroengine manufacturers have to demonstrate that critical components such as turbine disks, made of DA Inconel 718, meet the certification requirements in term of fatigue crack growth. In order to be more representative of the in service loading conditions, crack growth under hold time conditions is studied. Modelling crack growth under these conditions is challenging due to the combined effect of fatigue, creep and environment. Under these conditions, established models are often conservative but the degree of conservatism can be reduced by introducing the crack growth threshold in models. Here, the emphasis is laid on the characterization of crack growth rates in the low ΔK regime under hold time conditions and in particular, on the involved crack growth mechanism. Crack growth tests were carried out at high temperature (550 °C to 650 °C under hold time conditions (up to 1200 s in the low ΔK regime using a K-decreasing procedure. Scanning electron microscopy was used to identify the fracture mode involved in the low ΔK regime. EBSD analyses and BSE imaging were also carried out along the crack path for a more accurate identification of the fracture mode. A transition from intergranular to transgranular fracture was evidenced in the low ΔK regime and slip bands have also been observed at the tip of an arrested crack at low ΔK. Transgranular fracture and slip bands are usually observed under pure fatigue loading conditions. At low ΔK, hold time cycles are believed to act as equivalent pure fatigue cycles. This change in the crack growth mechanism under hold time conditions at low ΔK is discussed regarding results related to intergranular crack tip oxidation and its effect on the crack growth behaviour of Inconel 718 alloy. A concept based on an “effective oxygen partial pressure” at the crack tip is proposed to explain the transition from transgranular to intergranular fracture in the low ΔK regime.

  12. Mechanical tension as a driver of connective tissue growth in vitro.

    Science.gov (United States)

    Wilson, Cameron J; Pearcy, Mark J; Epari, Devakara R

    2014-07-01

    We propose the progressive mechanical expansion of cell-derived tissue analogues as a novel, growth-based approach to in vitro tissue engineering. The prevailing approach to producing tissue in vitro is to culture cells in an exogenous "scaffold" that provides a basic structure and mechanical support. This necessarily pre-defines the final size of the implantable material, and specific signals must be provided to stimulate appropriate cell growth, differentiation and matrix formation. In contrast, surgical skin expansion, driven by increments of stretch, produces increasing quantities of tissue without trauma or inflammation. This suggests that connective tissue cells have the innate ability to produce growth in response to elevated tension. We posit that this capacity is maintained in vitro, and that order-of-magnitude growth may be similarly attained in self-assembling cultures of cells and their own extracellular matrix. The hypothesis that growth of connective tissue analogues can be induced by mechanical expansion in vitro may be divided into three components: (1) tension stimulates cell proliferation and extracellular matrix synthesis; (2) the corresponding volume increase will relax the tension imparted by a fixed displacement; (3) the repeated application of static stretch will produce sustained growth and a tissue structure adapted to the tensile loading. Connective tissues exist in a state of residual tension, which is actively maintained by resident cells such as fibroblasts. Studies in vitro and in vivo have demonstrated that cellular survival, reproduction, and matrix synthesis and degradation are regulated by the mechanical environment. Order-of-magnitude increases in both bone and skin volume have been achieved clinically through staged expansion protocols, demonstrating that tension-driven growth can be sustained over prolonged periods. Furthermore, cell-derived tissue analogues have demonstrated mechanically advantageous structural adaptation in

  13. Deducing growth mechanisms for minerals from the shapes of crystal size distributions

    Science.gov (United States)

    Eberl, D.D.; Drits, V.A.; Srodon, J.

    1998-01-01

    Crystal size distributions (CSDs) of natural and synthetic samples are observed to have several distinct and different shapes. We have simulated these CSDs using three simple equations: the Law of Proportionate Effect (LPE), a mass balance equation, and equations for Ostwald ripening. The following crystal growth mechanisms are simulated using these equations and their modifications: (1) continuous nucleation and growth in an open system, during which crystals nucleate at either a constant, decaying, or accelerating nucleation rate, and then grow according to the LPE; (2) surface-controlled growth in an open system, during which crystals grow with an essentially unlimited supply of nutrients according to the LPE; (3) supply-controlled growth in an open system, during which crystals grow with a specified, limited supply of nutrients according to the LPE; (4) supply- or surface-controlled Ostwald ripening in a closed system, during which the relative rate of crystal dissolution and growth is controlled by differences in specific surface area and by diffusion rate; and (5) supply-controlled random ripening in a closed system, during which the rate of crystal dissolution and growth is random with respect to specific surface area. Each of these mechanisms affects the shapes of CSDs. For example, mechanism (1) above with a constant nucleation rate yields asymptotically-shaped CSDs for which the variance of the natural logarithms of the crystal sizes (??2) increases exponentially with the mean of the natural logarithms of the sizes (??). Mechanism (2) yields lognormally-shaped CSDs, for which ??2 increases linearly with ??, whereas mechanisms (3) and (5) do not change the shapes of CSDs, with ??2 remaining constant with increasing ??. During supply-controlled Ostwald ripening (4), initial lognormally-shaped CSDs become more symmetric, with ??2 decreasing with increasing ??. Thus, crystal growth mechanisms often can be deduced by noting trends in ?? versus ??2 of CSDs for

  14. Chemical vapor deposition of carbon nanotubes: a review on growth mechanism and mass production.

    Science.gov (United States)

    Kumar, Mukul; Ando, Yoshinori

    2010-06-01

    This review article deals with the growth mechanism and mass production of carbon nanotubes (CNTs) by chemical vapor deposition (CVD). Different aspects of CNT synthesis and growth mechanism are reviewed in the light of latest progresses and understandings in the field. Materials aspects such as the roles of hydrocarbon, catalyst and catalyst support are discussed. Many new catalysts and new carbon sources are described. Growth-control aspects such as the effects of temperature, vapor pressure and catalyst concentration on CNT diameter distribution and single- or multi-wall formation are explained. Latest reports of metal-catalyst-free CNT growth are considered. The mass-production aspect is discussed from the perspective of a sustainable CNT technology. Existing problems and challenges of the process are addressed with future directions.

  15. Shape controlled synthesis and growth mechanism of one-dimensional zinc oxide nanomaterials

    Institute of Scientific and Technical Information of China (English)

    Yue Zhang; Ying Dai; Yunhua Huang; Cheng Zhou

    2004-01-01

    Some types of ZnO nanostructures with various shape and size, including tetrapod-like ZnO (T-ZnO) nanorods, nanowiresand nanoribbons, have been obtained by controlled growth process. The nanostructures of ZnO have been investigated by means offield-emission scanning electron microscope, transmission electron microscopy and high-resolution transmission electron micros-copy. The growth mechanisms of various ZnO nanosttrctures were proposed and discussed.

  16. Abnormal grain growth effects on the mechanical behavior of Ni electrodeposits

    Energy Technology Data Exchange (ETDEWEB)

    Arnould, O. [LMT-Cachan, ENS Cachan/CNRS-UMR 8535/Univ. Paris VI, Cachan (France); Lab. de Mecanique et Genie Civil, Univ. Montpellier II, Montpellier (France); Hubert, O.; Hild, F. [LMT-Cachan, ENS Cachan/CNRS-UMR 8535/Univ. Paris VI, Cachan (France)

    2004-07-01

    The study deals with the long-term reliability of a high precision pressure sensor using bellows. They are mainly made of electroplated Ni whose thermal stability is investigated by DSC. EBSD measurements and SEM observations give some evidence for an abnormal grain growth mechanism whose effects on the elasto-plastic properties of the Ni deposit are experimentally investigated. Abnormal grain growth leads to an increase in the elastic modulus and a strong decrease in the yield strength. (orig.)

  17. Structures and growth mechanisms of poly-(3-hydroxybutyrate) (PHB) crystallized from solution and thin melt film

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The spherulitic structures and morphologies of poly-(3-hydroxybutyrate) (PHB) crystallized from a so- lution and a thin melt film were investigated in this study. The formation mechanisms of banded spherulites under different crystallization conditions are proposed. It was found that the formation of banded spherulites was caused by the rhythmic crystal growth of the spherulites and lamellar twisting growth for the polymer crystallization from a thin melt film and a solution, respectively.

  18. Investigation of various growth mechanisms of solid tumour growth within the linear-quadratic model for radiotherapy

    Energy Technology Data Exchange (ETDEWEB)

    McAneney, H [School of Mathematics and Physics, Queen' s University Belfast, Belfast (United Kingdom); O' Rourke, S F C [School of Mathematics and Physics, Queen' s University Belfast, Belfast (United Kingdom)

    2007-02-21

    The standard linear-quadratic survival model for radiotherapy is used to investigate different schedules of radiation treatment planning to study how these may be affected by different tumour repopulation kinetics between treatments. The laws for tumour cell repopulation include the logistic and Gompertz models and this extends the work of Wheldon et al (1977 Br. J. Radiol. 50 681), which was concerned with the case of exponential re-growth between treatments. Here we also consider the restricted exponential model. This has been successfully used by Panetta and Adam (1995 Math. Comput. Modelling 22 67) in the case of chemotherapy treatment planning.Treatment schedules investigated include standard fractionation of daily treatments, weekday treatments, accelerated fractionation, optimized uniform schedules and variation of the dosage and {alpha}/{beta} ratio, where {alpha} and {beta} are radiobiological parameters for the tumour tissue concerned. Parameters for these treatment strategies are extracted from the literature on advanced head and neck cancer, prostate cancer, as well as radiosensitive parameters. Standardized treatment protocols are also considered. Calculations based on the present analysis indicate that even with growth laws scaled to mimic initial growth, such that growth mechanisms are comparable, variation in survival fraction to orders of magnitude emerged. Calculations show that the logistic and exponential models yield similar results in tumour eradication. By comparison the Gompertz model calculations indicate that tumours described by this law result in a significantly poorer prognosis for tumour eradication than either the exponential or logistic models. The present study also shows that the faster the tumour growth rate and the higher the repair capacity of the cell line, the greater the variation in outcome of the survival fraction. Gaps in treatment, planned or unplanned, also accentuate the differences of the survival fraction given

  19. Investigation of various growth mechanisms of solid tumour growth within the linear-quadratic model for radiotherapy

    Science.gov (United States)

    McAneney, H.; O'Rourke, S. F. C.

    2007-02-01

    The standard linear-quadratic survival model for radiotherapy is used to investigate different schedules of radiation treatment planning to study how these may be affected by different tumour repopulation kinetics between treatments. The laws for tumour cell repopulation include the logistic and Gompertz models and this extends the work of Wheldon et al (1977 Br. J. Radiol. 50 681), which was concerned with the case of exponential re-growth between treatments. Here we also consider the restricted exponential model. This has been successfully used by Panetta and Adam (1995 Math. Comput. Modelling 22 67) in the case of chemotherapy treatment planning.Treatment schedules investigated include standard fractionation of daily treatments, weekday treatments, accelerated fractionation, optimized uniform schedules and variation of the dosage and α/β ratio, where α and β are radiobiological parameters for the tumour tissue concerned. Parameters for these treatment strategies are extracted from the literature on advanced head and neck cancer, prostate cancer, as well as radiosensitive parameters. Standardized treatment protocols are also considered. Calculations based on the present analysis indicate that even with growth laws scaled to mimic initial growth, such that growth mechanisms are comparable, variation in survival fraction to orders of magnitude emerged. Calculations show that the logistic and exponential models yield similar results in tumour eradication. By comparison the Gompertz model calculations indicate that tumours described by this law result in a significantly poorer prognosis for tumour eradication than either the exponential or logistic models. The present study also shows that the faster the tumour growth rate and the higher the repair capacity of the cell line, the greater the variation in outcome of the survival fraction. Gaps in treatment, planned or unplanned, also accentuate the differences of the survival fraction given alternative growth

  20. Kinetics and Mechanisms of Cadmium Carbonate Heteroepitaxial Growth at the Calcite (101¯4) Surface

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.

    2014-06-01

    Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at calcite-water interfaces was investigated by exposing calcite (10-14) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the calcite substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and calcite shows perfect, dislocation-free epitaxy.

  1. Kinetics and mechanisms of cadmium carbonate heteroepitaxial growth at the calcite (10 1bar 4) surface

    Science.gov (United States)

    Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien

    2014-06-01

    Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at calcite-water interfaces was investigated by exposing calcite (10 1bar 4) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the calcite substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and calcite shows perfect, dislocation-free epitaxy.

  2. Calcium ion involvement in growth inhibition of mechanically stressed soybean (Glycine max) seedlings

    Science.gov (United States)

    Jones, R. S.; Mitchell, C. A.

    1989-01-01

    A 40-50% reduction in soybean [Glycine max (L.) Merr. cv. Century 84] hypocotyl elongation occurred 24 h after application of mechanical stress. Exogenous Ca2+ at 10 mM inhibited growth by 28% if applied with the Ca2+ ionophore A23187 to the zone of maximum hypocotyl elongation. La3+ was even more inhibitory than Ca2+, especially above 5 mM. Treatment with ethyleneglycol-bis-(beta-aminoethylether)-N, N, N', N'-tetraacetic acid (EGTA) alone had no effect on growth of non-stressed seedlings at the concentrations used but negated stress-induced growth reduction by 36% at 4 mM when compared to non-treated, stressed controls. Treatment with EDTA was ineffective in negating stress-induced growth inhibition. Calmodulin antagonists calmidazolium, chlorpromazine, and 48/80 also negated stress-induced growth reduction by 23, 50, and 35%, respectively.

  3. Growth promotion of Spirulina by steelmaking slag: application of solubility diagram to understand its mechanism.

    Science.gov (United States)

    Nogami, Reijiro; Nishida, Haruo; Hong, Dang Diem; Wakisaka, Minato

    2016-12-01

    A solubility diagram was employed to understand growth promotion of Arthrospira (Spirulina) platensis by steelmaking slag (SMS). The growth promotion effect of 112 % of freshwater microalga A. platensis was obtained using 5 g/L SMS. However, metabolites, such as pigments, and protein content of A. platensis were not significantly affected. Several metals dissolved in Spirulina-Ogawa-Terui medium were detected by inductively coupled plasma atomic emission spectrometry just after the addition of SMS. The solubility diagram provides information on the chemical speciation of metal elements based on pH and concentration. It is a useful tool to understand the effect of metals on microalgal growth. The metal elements used to control microalgal growth are essential minerals but also act as a source of oxidative stress. Regarding the affecting mechanism of SMS, iron may be the primary element regulating microalgal growth via pathway involving reactive oxygen species, as revealed by superoxide dismutase assay.

  4. Tribology. Mechanisms of antiwear tribofilm growth revealed in situ by single-asperity sliding contacts.

    Science.gov (United States)

    Gosvami, N N; Bares, J A; Mangolini, F; Konicek, A R; Yablon, D G; Carpick, R W

    2015-04-03

    Zinc dialkyldithiophosphates (ZDDPs) form antiwear tribofilms at sliding interfaces and are widely used as additives in automotive lubricants. The mechanisms governing the tribofilm growth are not well understood, which limits the development of replacements that offer better performance and are less likely to degrade automobile catalytic converters over time. Using atomic force microscopy in ZDDP-containing lubricant base stock at elevated temperatures, we monitored the growth and properties of the tribofilms in situ in well-defined single-asperity sliding nanocontacts. Surface-based nucleation, growth, and thickness saturation of patchy tribofilms were observed. The growth rate increased exponentially with either applied compressive stress or temperature, consistent with a thermally activated, stress-assisted reaction rate model. Although some models rely on the presence of iron to catalyze tribofilm growth, the films grew regardless of the presence of iron on either the tip or substrate, highlighting the critical role of stress and thermal activation.

  5. Growth mechanisms of zinc oxide and zinc sulfide films by mist chemical vapor deposition

    Science.gov (United States)

    Uno, Kazuyuki; Yamasaki, Yuichiro; Tanaka, Ichiro

    2017-01-01

    The growth mechanisms of zinc oxide and zinc sulfide films by mist chemical vapor deposition (mist-CVD) were experimentally investigated from the viewpoint of mist behaviors and chemical reactions. The proper growth model, either vaporization or the Leidenfrost model, was studied by supplying two kinds of mists with different kinds of sources, such as H2 16O and H2 18O for ZnO growth and ZnCl2 and thiourea for ZnS growth. Moreover, the origin of the oxygen atoms of ZnO was investigated using a quantitative analysis. The role of chloro complex of zinc in the growth of ZnS from aqueous solutions was also examined by systematic studies.

  6. Potassium channel conductance: a mechanism affecting hair growth both in vitro and in vivo.

    Science.gov (United States)

    Buhl, A E; Waldon, D J; Conrad, S J; Mulholland, M J; Shull, K L; Kubicek, M F; Johnson, G A; Brunden, M N; Stefanski, K J; Stehle, R G

    1992-03-01

    The opening of intracellular potassium channels has been suggested as a mechanism regulating hair growth. Enhancing the flux of potassium ions is a mechanism shared by several structurally diverse antihypertensive agents including minoxidil sulfate (the active metabolite of minoxidil), pinacidil, P-1075 (a potent pinacidil analog), RP-49,356, diazoxide, cromakalim, and nicorandil. Of these drugs, minoxidil, pinacidil, and diazoxide have been reported to elicit hypertrichosis in humans. This potassium channel hypothesis was examined by testing these drugs for effects on hair growth both in vitro and in vivo. For the in vitro studies, mouse vibrissae follicles were cultured for 3 d with drug and the effects on hair growth were measured by metabolic labeling. All drugs, except diazoxide, enhanced cysteine incorporation into the hair shafts of the cultured vibrissae. Diazoxide was poorly soluble and thus was tested only at low doses. Minoxidil, P-1075, cromakalim, and RP-49,356 were also evaluated in vivo by measuring hair growth effects in balding stumptail macaque monkeys. The drugs were administered topically to defined sites on balding scalps once per day for 4-5 months and the amount of hair grown was determined by monthly measurements of shaved hair weight. Three of the drugs produced significant increases in hair weight whereas, the RP-49,356 had no effect. These studies provide correlative evidence that the opening of potassium channels is an important regulatory mechanism for hair growth. This provides the impetus for further studies on this potentially important mechanism affecting hair biology.

  7. [Advances in studies on growth metabolism and response mechanisms of medicinal plants under drought stress].

    Science.gov (United States)

    Si, Can; Zhang, Jun-Yi; Xu, Hu-Chao

    2014-07-01

    Drought stress exerts a considerable effect on growth, physiology and secondary metabolisms of the medicinal plants. It could inhabit the growth of the medicinal plants but promote secretion of secondary metabolites. Other researches indicated that the medicinal plants could depend on the ABA signaling pathway and secreting osmotic substances to resist the drought stress and reduce the damage by it. The article concludes the changes in growth, physiology, secondary metabolisms and response mechanisms of medicinal plants to drought stress that provides a theoretical basis for exploring the relationship between medicinal plants and drought stress.

  8. Investigation of the growth process of Si nanowires using the vapour-liquid-solid mechanism

    Institute of Scientific and Technical Information of China (English)

    邢英杰; 俞大鹏; 奚中和; 薛增泉

    2002-01-01

    Silicon nanowires have been grown by the thermal decomposition of silane via the vapour-liquid-solid (VLS)mechanism. Three different stages of VLS growth (eutectic alloy formation, crystal nucleation and unidirectional growth)were studied separately using a scanning electron microscope and a high-resolution transmission electron microscope.Very short silicon nanowires prepared under particular conditions provide direct evidence of the VLS mechanism on a nanometre scale. Our results will be very helpful for the controllable synthesis of Si nanowires.

  9. Putting theory to the test: which regulatory mechanisms can drive realistic growth of a root?

    Directory of Open Access Journals (Sweden)

    Dirk De Vos

    2014-10-01

    Full Text Available In recent years there has been a strong development of computational approaches to mechanistically understand organ growth regulation in plants. In this study, simulation methods were used to explore which regulatory mechanisms can lead to realistic output at the cell and whole organ scale and which other possibilities must be discarded as they result in cellular patterns and kinematic characteristics that are not consistent with experimental observations for the Arabidopsis thaliana primary root. To aid in this analysis, a 'Uniform Longitudinal Strain Rule' (ULSR was formulated as a necessary condition for stable, unidirectional, symplastic growth. Our simulations indicate that symplastic structures are robust to differences in longitudinal strain rates along the growth axis only if these differences are small and short-lived. Whereas simple cell-autonomous regulatory rules based on counters and timers can produce stable growth, it was found that steady developmental zones and smooth transitions in cell lengths are not feasible. By introducing spatial cues into growth regulation, those inadequacies could be avoided and experimental data could be faithfully reproduced. Nevertheless, a root growth model based on previous polar auxin-transport mechanisms violates the proposed ULSR due to the presence of lateral gradients. Models with layer-specific regulation or layer-driven growth offer potential solutions. Alternatively, a model representing the known cross-talk between auxin, as the cell proliferation promoting factor, and cytokinin, as the cell differentiation promoting factor, predicts the effect of hormone-perturbations on meristem size. By down-regulating PIN-mediated transport through the transcription factor SHY2, cytokinin effectively flattens the lateral auxin gradient, at the basal boundary of the division zone, (thereby imposing the ULSR to signal the exit of proliferation and start of elongation. This model exploration underlines the

  10. Putting theory to the test: which regulatory mechanisms can drive realistic growth of a root?

    Science.gov (United States)

    De Vos, Dirk; Vissenberg, Kris; Broeckhove, Jan; Beemster, Gerrit T S

    2014-10-01

    In recent years there has been a strong development of computational approaches to mechanistically understand organ growth regulation in plants. In this study, simulation methods were used to explore which regulatory mechanisms can lead to realistic output at the cell and whole organ scale and which other possibilities must be discarded as they result in cellular patterns and kinematic characteristics that are not consistent with experimental observations for the Arabidopsis thaliana primary root. To aid in this analysis, a 'Uniform Longitudinal Strain Rule' (ULSR) was formulated as a necessary condition for stable, unidirectional, symplastic growth. Our simulations indicate that symplastic structures are robust to differences in longitudinal strain rates along the growth axis only if these differences are small and short-lived. Whereas simple cell-autonomous regulatory rules based on counters and timers can produce stable growth, it was found that steady developmental zones and smooth transitions in cell lengths are not feasible. By introducing spatial cues into growth regulation, those inadequacies could be avoided and experimental data could be faithfully reproduced. Nevertheless, a root growth model based on previous polar auxin-transport mechanisms violates the proposed ULSR due to the presence of lateral gradients. Models with layer-specific regulation or layer-driven growth offer potential solutions. Alternatively, a model representing the known cross-talk between auxin, as the cell proliferation promoting factor, and cytokinin, as the cell differentiation promoting factor, predicts the effect of hormone-perturbations on meristem size. By down-regulating PIN-mediated transport through the transcription factor SHY2, cytokinin effectively flattens the lateral auxin gradient, at the basal boundary of the division zone, (thereby imposing the ULSR) to signal the exit of proliferation and start of elongation. This model exploration underlines the value of

  11. Putting Theory to the Test: Which Regulatory Mechanisms Can Drive Realistic Growth of a Root?

    Science.gov (United States)

    De Vos, Dirk; Vissenberg, Kris; Broeckhove, Jan; Beemster, Gerrit T. S.

    2014-01-01

    In recent years there has been a strong development of computational approaches to mechanistically understand organ growth regulation in plants. In this study, simulation methods were used to explore which regulatory mechanisms can lead to realistic output at the cell and whole organ scale and which other possibilities must be discarded as they result in cellular patterns and kinematic characteristics that are not consistent with experimental observations for the Arabidopsis thaliana primary root. To aid in this analysis, a ‘Uniform Longitudinal Strain Rule’ (ULSR) was formulated as a necessary condition for stable, unidirectional, symplastic growth. Our simulations indicate that symplastic structures are robust to differences in longitudinal strain rates along the growth axis only if these differences are small and short-lived. Whereas simple cell-autonomous regulatory rules based on counters and timers can produce stable growth, it was found that steady developmental zones and smooth transitions in cell lengths are not feasible. By introducing spatial cues into growth regulation, those inadequacies could be avoided and experimental data could be faithfully reproduced. Nevertheless, a root growth model based on previous polar auxin-transport mechanisms violates the proposed ULSR due to the presence of lateral gradients. Models with layer-specific regulation or layer-driven growth offer potential solutions. Alternatively, a model representing the known cross-talk between auxin, as the cell proliferation promoting factor, and cytokinin, as the cell differentiation promoting factor, predicts the effect of hormone-perturbations on meristem size. By down-regulating PIN-mediated transport through the transcription factor SHY2, cytokinin effectively flattens the lateral auxin gradient, at the basal boundary of the division zone, (thereby imposing the ULSR) to signal the exit of proliferation and start of elongation. This model exploration underlines the value of

  12. Superconducting MgB2 flowers: growth mechanism and their superconducting properties

    Science.gov (United States)

    Seong, Won Kyung; Ranot, Mahipal; Lee, Ji Yeong; Yang, Cheol-Woong; Lee, Jae Hak; Oh, Young Hoon; Ahn, Jae-Pyoung; Kang, Won Nam

    2016-04-01

    We report for the first time the growth and the systematic study of the growth mechanism for flower-like MgB2 structures fabricated on the substrates for solid-state electronics by the hybrid physical-chemical vapor deposition (HPCVD) technique. The MgB2 flower has a width of 30 μm and a height of 10 μm. The superconductivity of MgB2 flowers was confirmed by a magnetization measurement, and the transition temperature is 39 K, which is comparable with high-quality bulk samples. The excellent current-carrying capability was demonstrated by MgB2 flowers. To understand the nucleation and growth mechanism of MgB2 flowers a very systematic study was performed by a high-resolution transmission electron microscope (HRTEM) and atom probe (AP) microscopy. The HRTEM revealed that the seed grain of a MgB2 flower has a [101¯0] direction, and the flower is composed of micro-columnar MgB2 grains having pyramidal tips and which are grown along the (0001) plane. A clear understanding of the growth mechanism for MgB2 flowers could lead to the growth of other low-dimensional MgB2 structures for superconducting electronic devices.

  13. Mechanical behavior of cells within a cell-based model of wheat leaf growth

    Directory of Open Access Journals (Sweden)

    Ulyana Zubairova

    2016-12-01

    Full Text Available Understanding the principles and mechanisms of cell growth coordination in plant tissue remains an outstanding challenge for modern developmental biology. Cell-based modeling is a widely used technique for studying the geometric and topological features of plant tissue morphology during growth. We developed a quasi-one-dimensional model of unidirectional growth of a tissue layer in a linear leaf blade that takes cell autonomous growth mode into account. The model allows for fitting of the visible cell length using the experimental cell length distribution along the longitudinal axis of a wheat leaf epidermis. Additionally, it describes changes in turgor and osmotic pressures for each cell in the growing tissue. Our numerical experiments show that the pressures in the cell change over the cell cycle, and in symplastically growing tissue, they vary from cell to cell and strongly depend on the leaf growing zone to which the cells belong. Therefore, we believe that the mechanical signals generated by pressures are important to consider in simulations of tissue growth as possible targets for molecular genetic regulators of individual cell growth.

  14. How to get (a)round : mechanisms controlling growth and division of coccoid bacteria

    NARCIS (Netherlands)

    Pinho, Mariana G.; Kjos, Morten; Veening, Jan-Willem

    2013-01-01

    Bacteria come in a range of shapes, including round, rod-shaped, curved and spiral cells. This morphological diversity implies that different mechanisms exist to guide proper cell growth, division and chromosome segregation. Although the majority of studies on cell division have focused on rod-shape

  15. Synthesis, crystal growth and mechanical properties of Bismuth Silicon Oxide (BSO) single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Riscob, B. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Institute for Plasma Research, Bhat, Gandhinagar 382428, Gujarat (India); Shkir, Mohd. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Ganesh, V. [Department of Physics, Kakatiya University, Warangal 506 009 (India); Vijayan, N.; Maurya, K.K. [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India); Kishan Rao, K. [Department of Physics, Kakatiya University, Warangal 506 009 (India); Bhagavannarayana, G., E-mail: bhagavan@mail.nplindia.ernet.in [CSIR – National Physical Laboratory, Crystal Growth and X-ray Analysis, New Delhi 110 012 (India)

    2014-03-05

    Highlights: • Synthesis of Bismuth Silicon Oxide (BSO). • Single crystal growth of BSO by Czochralski (Cz) method. • Complete mechanical analysis by device fabrication point of view. • Theoretical and experimental calculations of mechanical properties. -- Abstract: Bismuth Silicon Oxide (BSO) is an efficient material for piezo-electric and electro-optic applications. In this article, growth of BSO single crystal by high temperature Czochralski melt growth technique and its detailed mechanical characterization by Vickers microhardness, fracture toughness, crack propagation, brittleness index and yield strength have been reported. The raw material was synthesized by solid state reaction using the stoichiometric ratio of high purity bismuth tri-oxide and silicon di-oxide. The synthesized material was charged in the platinum crucible and then melted. The required rotation and pulling rate was optimized for BSO single crystal growth and good quality single crystal has been harvested after a time span of 5 days. Powder X-ray diffraction analysis confirms the parent crystallization phase of BSO. The experimentally studied mechanical behavior of the crystal is explained using various theoretical models. The anisotropic nature of the crystals is studied using Knoop indentation technique.

  16. COMPARE: a web accessible tool for investigating mechanisms of cell growth inhibition.

    Science.gov (United States)

    Zaharevitz, Daniel W; Holbeck, Susan L; Bowerman, Christopher; Svetlik, Penny A

    2002-01-01

    For more than 10 years the National Cancer Institute (NCI) has tested compounds for their ability to inhibit the growth of human tumor cell lines in culture (NCI screen). Work of Ken Paull [J. Natl. Cancer Inst. 81 (1989) 1088] demonstrated that compounds with similar mechanism of cell growth inhibition show similar patterns of activity in the NCI screen. This observation was developed into an algorithm called COMPARE and has been successfully used to predict mechanisms for a wide variety of compounds. More recently, this method has been extended to associate patterns of cell growth inhibition by compounds with measurements of molecular entities (such as gene expression) in the cell lines in the NCI screen. The COMPARE method and associated data are freely available on the Developmental Therapeutics Program (DTP) web site (http://dtp.nci.nih.gov/). Examples of the use of COMPARE on these web pages will be explained and demonstrated. Published by Elsevier Science Inc.

  17. Growth mechanisms and defects in boronated CVD diamond as identified by scanning tunneling microscopy

    Science.gov (United States)

    Kreutz, T. J.; Clausing, R. E.; Heatherly, L., Jr.; Warmack, R. J.; Thundat, T.; Feigerle, C. S.; Wandelt, K.

    1995-05-01

    Boron-doped CVD-diamond films were grown in a simple hot filament reactor. A set of samples grown using various methane-in-hydrogen concentrations has been examined by scanning tunneling microscopy in air. On the diamond (111) crystal faces monoatomic steps could be observed giving evidence for layer growth. At low CH4 concentrations the layers form triangular growth spirals. Screw dislocations in the middle of the spirals serve as continuous sources of steps for the layer growth producing (111) faces of high crystal perfection. At higher methane concentrations the crystal perfection declines and the (111) crystal faces exhibit a mosaic structure. The size of the subgrains in the mosaic pattern decreases with increasing CH4 concentration. Nucleation of new layers takes place at the subgrain boundaries. The topography of (001) crystal faces did not significantly change with the methane-in-hydrogen concentration and did not allow the determination of the underlying growth mechanism.

  18. Analysis of seismic sources for different mechanisms of fracture growth for microseismic monitoring applications

    Energy Technology Data Exchange (ETDEWEB)

    Duchkov, A. A., E-mail: DuchkovAA@ipgg.sbras.ru [Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, 630090 (Russian Federation); Novosibirsk State University, Novosibirsk, 630090 (Russian Federation); Stefanov, Yu. P., E-mail: stefanov@ispms.tsc.ru [Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, 630090 (Russian Federation)

    2015-10-27

    We have developed and illustrated an approach for geomechanic modeling of elastic wave generation (microsiesmic event occurrence) during incremental fracture growth. We then derived properties of effective point seismic sources (radiation patterns) approximating obtained wavefields. These results establish connection between geomechanic models of hydraulic fracturing and microseismic monitoring. Thus, the results of the moment tensor inversion of microseismic data can be related to different geomechanic scenarios of hydraulic fracture growth. In future, the results can be used for calibrating hydrofrac models. We carried out a series of numerical simulations and made some observations about wave generation during fracture growth. In particular when the growing fracture hits pre-existing crack then it generates much stronger microseismic event compared to fracture growth in homogeneous medium (radiation pattern is very close to the theoretical dipole-type source mechanism)

  19. Identification of Two New Mechanisms That Regulate Fruit Growth by Cell Expansion in Tomato

    Directory of Open Access Journals (Sweden)

    Constance Musseau

    2017-06-01

    Full Text Available Key mechanisms controlling fruit weight and shape at the levels of meristem, ovary or very young fruit have already been identified using natural tomato diversity. We reasoned that new developmental modules prominent at later stages of fruit growth could be discovered by using new genetic and phenotypic diversity generated by saturated mutagenesis. Twelve fruit weight and tissue morphology mutants likely affected in late fruit growth were selected among thousands of fruit size and shape EMS mutants available in our tomato EMS mutant collection. Their thorough characterization at organ, tissue and cellular levels revealed two major clusters controlling fruit growth and tissue morphogenesis either through (i the growth of all fruit tissues through isotropic cell expansion or (ii only the growth of the pericarp through anisotropic cell expansion. These likely correspond to new cell expansion modules controlling fruit growth and tissue morphogenesis in tomato. Our study therefore opens the way for the identification of new gene regulatory networks controlling tomato fruit growth and morphology.

  20. Formation and growth mechanism of TiC crystal in TiCp/Ti composites

    Institute of Scientific and Technical Information of China (English)

    金云学; 王宏伟; 曾松岩; 张二林

    2002-01-01

    Ti-C and Ti-Al-C alloys were prepared using gravity and directional solidification processes. Morphologies of TiC crystal were investigated by using SEM, XRD and EDX. Also, the formation and growth mechanism of TiC crystal have been analyzed on the basis of coordination polyhedron growth unit theory. During solidification of titanium alloys, the coordination polyhedron growth unit is TiC6. TiC6 growth units stack in a linking mode of edge to edge and form octahedral TiC crystal with {111} planes as present faces. Although the growing geometry of TiC crystal is decided by its lattice structure, the final morphology of TiC crystal depends on the effects of its growth environment. In solute concentration distribution, the super-saturation of C or TiC6 at the corners of octahedral TiC crystal is much higher than that of edges and faces of octahedral TiC crystal. At these corners the driving force for crystal growth is greater and the interface is instable which contribute to quick stacking rate of growth units at these corners and result in secondary dendrite arms along TiC crystallographic 〈100〉 directions. TiC crystal finally grows to be dendrites.

  1. Silicon oxide nanowire growth mechanisms revealed by real-time electron microscopy

    Science.gov (United States)

    Kolíbal, Miroslav; Novák, Libor; Shanley, Toby; Toth, Milos; Šikola, Tomáš

    2015-12-01

    Growth of one-dimensional materials is possible through numerous mechanisms that affect the nanowire structure and morphology. Here, we explain why a wide range of morphologies is observed when silicon oxide nanowires are grown on silicon substrates using liquid gallium catalyst droplets. We show that a gallium oxide overlayer is needed for nanowire nucleation at typical growth temperatures, and that it can decompose during growth and, hence, dramatically alter the nanowire morphology. Gallium oxide decomposition is attributed to etching caused by hydrogen that can be supplied by thermal dissociation of H2O (a common impurity). We show that H2O dissociation is catalyzed by silicon substrates at temperatures as low as 320 °C, identify the material supply pathways and processes that rate-limit nanowire growth under dry and wet atmospheres, and present a detailed growth model that explains contradictory results reported in prior studies. We also show that under wet atmospheres the Ga droplets can be mobile and promote nanowire growth as they traverse the silicon substrate.Growth of one-dimensional materials is possible through numerous mechanisms that affect the nanowire structure and morphology. Here, we explain why a wide range of morphologies is observed when silicon oxide nanowires are grown on silicon substrates using liquid gallium catalyst droplets. We show that a gallium oxide overlayer is needed for nanowire nucleation at typical growth temperatures, and that it can decompose during growth and, hence, dramatically alter the nanowire morphology. Gallium oxide decomposition is attributed to etching caused by hydrogen that can be supplied by thermal dissociation of H2O (a common impurity). We show that H2O dissociation is catalyzed by silicon substrates at temperatures as low as 320 °C, identify the material supply pathways and processes that rate-limit nanowire growth under dry and wet atmospheres, and present a detailed growth model that explains

  2. Thickness-dependent stress in plasma-deposited silicon dioxide films

    Science.gov (United States)

    Au, V.; Charles, C.; Bulla, D. A. P.; Love, J. D.; Boswell, R. W.

    2005-04-01

    Thick silicon dioxide (SiO2) films up to 5 μm have been deposited by helicon activated reactive evaporation (plasma assisted deposition with electron beam evaporation source) as both bilayer and trilayer structures, and the film stress was investigated in the context of optical waveguide fabrication. A model for stress in the SiO2-Si bilayer as a function of film thickness is formulated and interpreted in terms of Volmer-Weber film growth mechanisms. We find that island coalescence begins at a film thickness of less than 165 nm and continues until about 700 nm. Above approximately 1 μm thickness, the film continues growth as a continuous film. The stress in a deposited SiO2 film in an SiO2-Si-SiO2 trilayer structure was investigated by adapting the established Stoney's equation for a trilayer system, and comparing it with a thermally grown SiO2 trilayer. A constant value of stress is obtained for the deposited SiO2 film for film thickness >1μm which was consistently less than both measured and previously reported values of stress in thermally grown SiO2.

  3. Self-organization and nanostructure formation in chemical vapor deposition

    Science.gov (United States)

    Walgraef, Daniel

    2013-10-01

    When thin films are grown on a substrate by chemical vapor deposition, the evolution of the first deposited layers may be described, on mesoscopic scales, by dynamical models of the reaction-diffusion type. For monatomic layers, such models describe the evolution of atomic coverage due to the combined effect of reaction terms representing adsorption-desorption and chemical processes and nonlinear diffusion terms that are of the Cahn-Hilliard type. This combination may lead, below a critical temperature, to the instability of uniform deposited layers. This instability triggers the formation of nanostructures corresponding to regular spatial variations of substrate coverage. Patterns wavelengths and symmetries are selected by dynamical variables and not by variational arguments. According to the balance between reaction- and diffusion-induced nonlinearities, a succession of nanostructures including hexagonal arrays of dots, stripes, and localized structures of various types may be obtained. These structures may initiate different growth mechanisms, including Volmer-Weber and Frank-Van der Merwe types of growth. The relevance of this approach to the study of deposited layers of different species is discussed.

  4. Cyclic mechanical deformation stimulates human lung fibroblast proliferation and autocrine growth factor activity.

    Science.gov (United States)

    Bishop, J E; Mitchell, J J; Absher, P M; Baldor, L; Geller, H A; Woodcock-Mitchell, J; Hamblin, M J; Vacek, P; Low, R B

    1993-08-01

    Cellular hypertrophy and hyperplasia and increased extracellular matrix deposition are features of tissue hypertrophy resulting from increased work load. It is known, for example, that mechanical forces play a critical role in lung development, cardiovascular remodeling following pressure overload, and skeletal muscle growth. The mechanisms involved in these processes, however, remain unclear. Here we examined the effect of mechanical deformation on fibroblast function in vitro. IMR-90 human fetal lung fibroblasts grown on collagen-coated silastic membranes were subjected to cyclical mechanical deformation (10% increase in culture surface area; 1 Hz) for up to 5 days. Cell number was increased by 39% after 2 days of deformation (1.43 +/- .01 x 10(5) cells/membrane compared with control, 1.03 +/- 0.02 x 10(5) cells; mean +/- SEM; P < 0.02) increasing to 163% above control by 4 days (2.16 +/- 0.16 x 10(5) cells compared with 0.82 +/- 0.03 x 10(5) cells; P < 0.001). The medium from mechanically deformed cells was mitogenic for IMR-90 cells, with maximal activity in the medium from cells mechanically deformed for 2 days (stimulating cell replication by 35% compared with media control; P < 0.002). These data suggest that mechanical deformation stimulates human lung fibroblast replication and that this effect is mediated by the release of autocrine growth factors.

  5. Growth mechanism of NaClO3 and NaBrO3 crystals from aqueous solutions

    Indian Academy of Sciences (India)

    V Surender; N Arundhathi; K Kishan Rao

    2006-10-01

    A study of growth rates of NaClO3 and NaBrO3 has been carried out using a small growth cell by in situ observation. Normal growth rates of {100} faces of NaClO3 and {111} faces of NaBrO3 along $\\langle 110 \\rangle$ direction are measured under relatively high supersaturation ranging from 3–8%. In the initial stages of growth, {100}, {110} and {111} faces develop in NaClO3 and gradually all the faces are replaced by the {100} faces only. In the case of NaBrO3, mostly {111} faces develop with occasional occurrence of small {100} faces at the intersection of {111} faces. The growth mechanisms are investigated from growth rate vs supersaturation plots and from the observations of surface features. In the present supersaturation range, the growth mechanism appears to be due to two-dimensional growth mechanism.

  6. Modeling the coupled mechanics, transport, and growth processes in collagen tissues.

    Energy Technology Data Exchange (ETDEWEB)

    Holdych, David J.; Nguyen, Thao D.; Klein, Patrick A.; in' t Veld, Pieter J.; Stevens, Mark Jackson

    2006-11-01

    The purpose of this project is to develop tools to model and simulate the processes of self-assembly and growth in biological systems from the molecular to the continuum length scales. The model biological system chosen for the study is the tendon fiber which is composed mainly of Type I collagen fibrils. The macroscopic processes of self-assembly and growth at the fiber scale arise from microscopic processes at the fibrillar and molecular length scales. At these nano-scopic length scales, we employed molecular modeling and simulation method to characterize the mechanical behavior and stability of the collagen triple helix and the collagen fibril. To obtain the physical parameters governing mass transport in the tendon fiber we performed direct numerical simulations of fluid flow and solute transport through an idealized fibrillar microstructure. At the continuum scale, we developed a mixture theory approach for modeling the coupled processes of mechanical deformation, transport, and species inter-conversion involved in growth. In the mixture theory approach, the microstructure of the tissue is represented by the species concentration and transport and material parameters, obtained from fibril and molecular scale calculations, while the mechanical deformation, transport, and growth processes are governed by balance laws and constitutive relations developed within a thermodynamically consistent framework.

  7. Synthesis and in situ mechanism of nuclei growth of layered double hydroxides

    Indian Academy of Sciences (India)

    H S Panda; R Srivastava; D Bahadur

    2011-12-01

    A host–guest material such as layered double hydroxide (LDH) has generated immense interest in current research due to its technological importance, whereby its dimension significantly affect its mechanical and other physical properties. The purpose of this study was to prepare Mg/Al-LDHs by systematically varying the molar concentration of cations, aging time and pH. The prepared LDHs were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermal analysis and transmission electron microscopy to confirm their formation and morphology. We qualitatively observed a new growth route for LDH system which is dissimilar to the existing growth mechanism. The rate of growth is shown to be slower than the well known Ostwald ripening process. This unusual behaviour is due to the formation of effective passivation layer by Na+ ions around the generated LDHs nuclei. This suggested growth mechanism will be helpful in further controlling the particle size of other LDH, which may be useful for various future applications.

  8. Microarchitecture, but Not Bone Mechanical Properties, Is Rescued with Growth Hormone Treatment in a Mouse Model of Growth Hormone Deficiency

    Directory of Open Access Journals (Sweden)

    Erika Kristensen

    2012-01-01

    Full Text Available Growth hormone (GH deficiency is related to an increased fracture risk although it is not clear if this is due to compromised bone quality or a small bone size. We investigated the relationship between bone macrostructure, microarchitecture and mechanical properties in a GH-deficient (GHD mouse model undergoing GH treatment commencing at an early (prepubertal or late (postpubertal time point. Microcomputed tomography images of the femur and L4 vertebra were obtained to quantify macrostructure and vertebral trabecular microarchitecture, and mechanical properties were determined using finite element analyses. In the GHD animals, bone macrostructure was 25 to 43% smaller as compared to the GH-sufficient (GHS controls (P<0.001. GHD animals had 20% and 19% reductions in bone volume ratio (BV/TV and trabecular thickness (Tb.Th, respectively. Whole bone mechanical properties of the GHD mice were lower at the femur and vertebra (67% and 45% resp. than the GHS controls (P<0.001. Both early and late GH treatment partially recovered the bone macrostructure (15 to 32 % smaller than GHS controls and the whole bone mechanical properties (24 to 43% larger than GHD animals although there remained a sustained 27–52% net deficit compared to normal mice (P<0.05. Importantly, early treatment with GH led to a recovery of BV/TV and Tb.Th with a concomitant improvement of trabecular mechanical properties. Therefore, the results suggest that GH treatment should start early, and that measurements of microarchitecture should be considered in the management of GHD.

  9. Galactose inhibits auxin-induced growth of Avena coleoptiles by two mechanisms

    Science.gov (United States)

    Cheung, S. P.; Cleland, R. E.

    1991-01-01

    Galactose inhibits auxin-induced growth of Avena coleoptiles by at least two mechanisms. First, it inhibits auxin-induced H(+)-excretion needed for the initiation of rapid elongation. Galactose cannot be doing so by directly interfering with the ATPase since fusicoccin-induced H(+)-excretion is not affected. Secondly, galactose inhibits long-term auxin-induced growth, even in an acidic (pH 4.5) solution. This may be due to an inhibition of cell wall synthesis. However, galactose does not reduce the capacity of walls to be loosened by H+, given exogenously or excreted in response to fusicoccin.

  10. Nonlinear mechanics of surface growth for cylindrical and spherical elastic bodies

    Science.gov (United States)

    Sozio, Fabio; Yavari, Arash

    2017-01-01

    In this paper we formulate the initial-boundary value problems of accreting cylindrical and spherical nonlinear elastic solids in a geometric framework. It is assumed that the body grows as a result of addition of new (stress-free or pre-stressed) material on part of its boundary. We construct Riemannian material manifolds for a growing body with metrics explicitly depending on the history of applied external loads and deformation during accretion and the growth velocity. We numerically solve the governing equilibrium equations in the case of neo-Hookean solids and compare the accretion and residual stresses with those calculated using the linear mechanics of surface growth.

  11. A Novel Discovery of Growth Process for Ag Nanowires and Plausible Mechanism

    Directory of Open Access Journals (Sweden)

    Jiejun Zhu

    2016-01-01

    Full Text Available A novel growth process of silver nanowires was revealed by tracing the morphology evolution of Ag nanostructures fabricated by an improved polyol process. A mixture of Ag nanowires and nanoparticles was obtained with the usage of PVP-K25 (MW = 38,000. The products sampled at different reaction time were studied in detail using UV-visible absorption spectra and transmission electron microscopy (TEM. An interesting phenomenon unknown in the past was observed where Ag nanoparticles undergo an important dissolution-recrystallization process and Ag nanowires are formed at the expense of the preformed Ag nanoparticles. A plausible novel growth mechanism for the silver nanowires was proposed.

  12. Crack Growth Rate Modeling of a Titanium-Aluminide Alloy Under Thermal-Mechanical Cycling

    Science.gov (United States)

    1991-12-01

    is integrated using Simpson’s rule. The integration of f(t) from t = ta to t = tb is: fIb f(t) dt ,,---- [f(t4 ) + 4f(tj) + f(tb)1 (5.68) ie 6 where... Knott , J.F. International Journal of Fracture Mechanics 1971, pp 462-467 101. Halliday M.D. and Beevers, C.J., ’The d.c. Electrical Potential Method for...Test Methods for Fracture and Fatigue Crack Growth ASTM STP 877, 1985, pp 67-85. 108. Ritchie, R.O., Garrett, G.G., and Knott , J.F., " Crack-Growth

  13. Growth Mechanism of Strain-Dependent Morphological Change in PEDOT:PSS Films

    Science.gov (United States)

    Lee, Yoo-Yong; Choi, Gwang Mook; Lim, Seung-Min; Cho, Ju-Young; Choi, In-Suk; Nam, Ki Tae; Joo, Young-Chang

    2016-04-01

    Understanding the mechanism of the strain-dependent conductivity change in polymers in stretched conditions is important. We observed a strain-induced growth of the conductive regions of PEDOT:PSS films, induced by a coalescence of conductive PEDOT-rich cores. This growth due to coalescence leads to a gradual decrease in the electrical resistivity up to 95%, independent of the thickness of the PEDOT:PSS films. The primary mechanism for the evolution of the PEDOT-rich cores proceeds by the cores growing larger as they consuming relatively smaller cores. This process is caused by a strain-induced local rearrangement of PEDOT segments in the vicinity of PSS shells around the cores and also changes the chemical environment in PEDOT, induced by the electron-withdrawing effects around the PEDOT chains. The strain-induced growth mechanism is beneficial to understanding the phenomenon of polymeric chain rearrangement in mechanical deformation and to modulating the electrical conductivity for practical applications.

  14. Auxin-induced growth of Avena coleoptiles involves two mechanisms with different pH optima

    Science.gov (United States)

    Cleland, R. E.

    1992-01-01

    Although rapid auxin-induced growth of coleoptile sections can persist for at least 18 hours, acid-induced growth lasts for a much shorter period of time. Three theories have been proposed to explain this difference in persistence. To distinguish between these theories, the pH dependence for auxin-induced growth of oat (Avena sativa L.) coleoptiles has been determined early and late in the elongation process. Coleoptile sections from which the outer epidermis was removed to facilitate buffer entry were incubated, with or without 10 micromolar indoleacetic acid, in 20 millimolar buffers at pH 4.5 to 7.0 to maintain a fixed wall pH. During the first 1 to 2 hours after addition of auxin, elongation occurs by acid-induced extension (i.e. the pH optimum is <5 and the elongation varies inversely with the solution pH). Auxin causes no additional elongation because the buffers prevent further changes in wall pH. After 60 to 90 minutes, a second mechanism of auxin-induced growth, whose pH optimum is 5.5 to 6.0, predominates. It is proposed that rapid growth responses to changes in auxin concentration are mediated by auxin-induced changes in wall pH, whereas the prolonged, steady-state growth rate is controlled by a second, auxin-mediated process whose pH optimum is less acidic.

  15. Auxin-induced growth of Avena coleoptiles involves two mechanisms with different pH optima

    Science.gov (United States)

    Cleland, R. E.

    1992-01-01

    Although rapid auxin-induced growth of coleoptile sections can persist for at least 18 hours, acid-induced growth lasts for a much shorter period of time. Three theories have been proposed to explain this difference in persistence. To distinguish between these theories, the pH dependence for auxin-induced growth of oat (Avena sativa L.) coleoptiles has been determined early and late in the elongation process. Coleoptile sections from which the outer epidermis was removed to facilitate buffer entry were incubated, with or without 10 micromolar indoleacetic acid, in 20 millimolar buffers at pH 4.5 to 7.0 to maintain a fixed wall pH. During the first 1 to 2 hours after addition of auxin, elongation occurs by acid-induced extension (i.e. the pH optimum is Auxin causes no additional elongation because the buffers prevent further changes in wall pH. After 60 to 90 minutes, a second mechanism of auxin-induced growth, whose pH optimum is 5.5 to 6.0, predominates. It is proposed that rapid growth responses to changes in auxin concentration are mediated by auxin-induced changes in wall pH, whereas the prolonged, steady-state growth rate is controlled by a second, auxin-mediated process whose pH optimum is less acidic.

  16. Determination of the crystal growth mechanism of KCl in ethanol?water system

    Science.gov (United States)

    Liszi, I.; Hasznosné-Nezdei, M.; Lakatos, B. G.; Sapundzhiev, Ts. J.; Popov, R. G.

    1999-03-01

    The mechanism of crystal growth of KCl in ethanol-water system is studied by Nielsen's map-model, and the growth rate is estimated by the induction time (nucleation rate, growth rate) function in a salting-out crystallization system. In the experiments, the induction time and the particle size distribution of the final product were measured, and the solid-liquid interfacial tension was calculated from the induction period data. The map of rate control of crystal-growth for the KCl-ethanol-water salting out system was constructed by taking into consideration that the liquid-vapour interfacial tension varied with the variation of the ethanol concentration, and, as a consequence, the solid-liquid interfacial tension varied as well. As a result, diffusion controlled crystal growth was obtained as a rate-determining step for supersaturation ratios 0.01<0.45. For determining the crystal growth rate, the nucleation rate was estimated from the experimental average particle number and induction period, applying the assumption that all nuclei were born during the induction period. The results, obtained by using linear and non-linear regressions, have appeared to be in good agreement with the data published in the literature.

  17. Kinetic growth mechanisms of sputter-deposited Au films on mica: from nanoclusters to nanostructured microclusters

    Energy Technology Data Exchange (ETDEWEB)

    Ruffino, F.; Grimaldi, M.G. [Universita di Catania, Dipartimento di Fisica e Astronomia, Catania (Italy); CNR-IMM MATIS, Catania (Italy); Torrisi, V.; Marletta, G. [University of Catania and CSGI, Laboratory for Molecular Surface and Nanotechnology (LAMSUN), Department of Chemical Sciences, Catania (Italy)

    2010-07-15

    Au nanostructured film was deposited on mica by room temperature RF sputtering. The growth mechanism of the film was studied analyzing the evolution of the film morphology as a function of its thickness by the atomic force microscopy. In the early stages of a growth the film evolution proceeds by the nucleation and growth of nanoclusters. After a critical thickness the growth of microclusters formed by the joining of nanoclusters in preferential nucleation sites, onto a quasicontinuous film, is observed. We quantified the evolution of the mean nanoclusters height and surface density and of the film roughness. This data were analyzed by the dynamic scaling theory of growing interfaces obtaining the scaling and roughness exponents z and {beta} whose values suggest a conservative growth process. We also quantified the growth of the microclusters showing that it is consistent with a coalescence/impingement dynamic. About the formation of the microclusters, furthermore, we speculate that their origin is strongly correlated to the features of the sputtering technique in connection with the deposition on a high-diffusivity substrate. (orig.)

  18. Crystal growth mechanisms in miarolitic cavities in the Lake George ring complex and vicinity, Colorado

    Science.gov (United States)

    Kile, D.E.; Eberl, D.D.

    1999-01-01

    The Crystal Peak area of the Pikes Peak batholith, near Lake George in central Colorado, is world-renowned for its crystals of amazonite (the blue-green variety of microcline) and smoky quartz. Such crystals, collected from individual miarolitic pegmatites, have a remakably small variation in crystal size within each pegmatite, and the shapes of plots of their crystal size distributions (CSDs) are invariably lognormal or close to lognormal in all cases. These observations are explained by a crystal growth mechanism that was governed initially by surface-controlled kinetics, during which crystals tended to grow larger in proportion to their size, thereby establishing lognormal CSDs. Surface-controlled growth was followed by longer periods of supply controlled growth, during which growth rate was predominantly size-independent, consequently preserving the lognormal shapes of the CSDs and the small size variation. The change from surface- to supply controlled growth kinetics may have resulted from an increasing demand for nutrients that exceeded diffusion limitations of the system. The proposed model for crystal growth in this locality appears to be common in the geologic record, and can be used with other information, such as isotopic data, to deduce physico-chemical conditions during crystal formation.

  19. The role of mass balance equations in growth mechanics illustrated in surface and volume dissolutions.

    Science.gov (United States)

    Ateshian, Gerard A

    2011-01-01

    Growth mechanics problems require the solution of mass balance equations that include supply terms and account for mass exchanges among constituents of a mixture. Though growth may often be accompanied by a variety of concomitant phenomena that increase modeling complexity, such as solid matrix deformation, evolving traction-free configurations, cell division, and active cell contraction, it is important to distinguish these accompanying phenomena from the fundamental growth process that consists of deposition or removal of mass from the solid matrix. Therefore, the objective of this study is to present a canonical problem of growth, namely, dissolution of a rigid solid matrix in a solvent. This problem illustrates a case of negative growth (loss of mass) of the solid in a mixture framework that includes three species, a solid, a solvent, and a solute, where the solute is the product of the solid dissolution. By analyzing both volumetric and surface dissolutions, the two fundamental modes of growth are investigated within the unified framework of mixture theory.

  20. PAH growth initiated by propargyl addition: Mechanism development and computational kinetics

    KAUST Repository

    Raj, Abhijeet Dhayal

    2014-04-24

    Polycyclic aromatic hydrocarbon (PAH) growth is known to be the principal pathway to soot formation during fuel combustion, as such, a physical understanding of the PAH growth mechanism is needed to effectively assess, predict, and control soot formation in flames. Although the hydrogen abstraction C2H2 addition (HACA) mechanism is believed to be the main contributor to PAH growth, it has been shown to under-predict some of the experimental data on PAHs and soot concentrations in flames. This article presents a submechanism of PAH growth that is initiated by propargyl (C 3H3) addition onto naphthalene (A2) and the naphthyl radical. C3H3 has been chosen since it is known to be a precursor of benzene in combustion and has appreciable concentrations in flames. This mechanism has been developed up to the formation of pyrene (A4), and the temperature-dependent kinetics of each elementary reaction has been determined using density functional theory (DFT) computations at the B3LYP/6-311++G(d,p) level of theory and transition state theory (TST). H-abstraction, H-addition, H-migration, β-scission, and intramolecular addition reactions have been taken into account. The energy barriers of the two main pathways (H-abstraction and H-addition) were found to be relatively small if not negative, whereas the energy barriers of the other pathways were in the range of (6-89 kcal·mol-1). The rates reported in this study may be extrapolated to larger PAH molecules that have a zigzag site similar to that in naphthalene, and the mechanism presented herein may be used as a complement to the HACA mechanism to improve prediction of PAH and soot formation. © 2014 American Chemical Society.

  1. Mechanical induction of the tumorigenic β-catenin pathway by tumour growth pressure.

    Science.gov (United States)

    Fernández-Sánchez, María Elena; Barbier, Sandrine; Whitehead, Joanne; Béalle, Gaëlle; Michel, Aude; Latorre-Ossa, Heldmuth; Rey, Colette; Fouassier, Laura; Claperon, Audrey; Brullé, Laura; Girard, Elodie; Servant, Nicolas; Rio-Frio, Thomas; Marie, Hélène; Lesieur, Sylviane; Housset, Chantal; Gennisson, Jean-Luc; Tanter, Mickaël; Ménager, Christine; Fre, Silvia; Robine, Sylvie; Farge, Emmanuel

    2015-07-02

    The tumour microenvironment may contribute to tumorigenesis owing to mechanical forces such as fibrotic stiffness or mechanical pressure caused by the expansion of hyper-proliferative cells. Here we explore the contribution of the mechanical pressure exerted by tumour growth onto non-tumorous adjacent epithelium. In the early stage of mouse colon tumour development in the Notch(+)Apc(+/1638N) mouse model, we observed mechanistic pressure stress in the non-tumorous epithelial cells caused by hyper-proliferative adjacent crypts overexpressing active Notch, which is associated with increased Ret and β-catenin signalling. We thus developed a method that allows the delivery of a defined mechanical pressure in vivo, by subcutaneously inserting a magnet close to the mouse colon. The implanted magnet generated a magnetic force on ultra-magnetic liposomes, stabilized in the mesenchymal cells of the connective tissue surrounding colonic crypts after intravenous injection. The magnetically induced pressure quantitatively mimicked the endogenous early tumour growth stress in the order of 1,200 Pa, without affecting tissue stiffness, as monitored by ultrasound strain imaging and shear wave elastography. The exertion of pressure mimicking that of tumour growth led to rapid Ret activation and downstream phosphorylation of β-catenin on Tyr654, imparing its interaction with the E-cadherin in adherens junctions, and which was followed by β-catenin nuclear translocation after 15 days. As a consequence, increased expression of β-catenin-target genes was observed at 1 month, together with crypt enlargement accompanying the formation of early tumorous aberrant crypt foci. Mechanical activation of the tumorigenic β-catenin pathway suggests unexplored modes of tumour propagation based on mechanical signalling pathways in healthy epithelial cells surrounding the tumour, which may contribute to tumour heterogeneity.

  2. Dilation and Hypertrophy: A Cell-Based Continuum Mechanics Approach Towards Ventricular Growth and Remodeling

    Science.gov (United States)

    Ulerich, J.; Göktepe, S.; Kuhl, E.

    This manuscript presents a continuum approach towards cardiac growth and remodeling that is capable to predict chronic maladaptation of the heart in response to changes in mechanical loading. It is based on the multiplicative decomposition of the deformation gradient into and elastic and a growth part. Motivated by morphological changes in cardiomyocyte geometry, we introduce an anisotropic growth tensor that can capture both hypertrophic wall thickening and ventricular dilation within one generic concept. In agreement with clinical observations, we propose wall thickening to be a stress-driven phenomenon whereas dilation is introduced as a strain-driven process. The features of the proposed approach are illustrated in terms of the adaptation of thin heart slices and in terms overload-induced dilation in a generic bi-ventricular heart model.

  3. Longitudinal growth of skeletal myotubes in vitro in a new horizontal mechanical cell stimulator

    Science.gov (United States)

    Vandenburgh, Herman H.; Karlisch, Patricia

    1989-01-01

    A tissue-culture model system for growing skeletal-muscle cells under more dynamic conditions than found in normal tissue-culture environments is described. A computerized device presented allows mechanical stimulation of the cell's substratum by 300 to 400 pct in length in the horizontal plane. Cell growth rates and skeletal-muscle organogenesis are stimulated in this in vitro system. It is noted that longitudinal myotube growth observed is accompanied by increased rates of cell proliferation and myoblast fusion. Prestretching the collagen-coated substratum before cell plating is shown to lead to increased cell proliferation, myotube orientation, and longitudinal myotube growth. The effects of substratum stretching on myogenesis in the model system are also assessed and attributed to alterations in the cell's extracellular matrix.

  4. Sintering boron carbide ceramics without grain growth by plastic deformation as the dominant densification mechanism

    Science.gov (United States)

    Ji, Wei; Rehman, Sahibzada Shakir; Wang, Weimin; Wang, Hao; Wang, Yucheng; Zhang, Jinyong; Zhang, Fan; Fu, Zhengyi

    2015-10-01

    A new ceramic sintering approach employing plastic deformation as the dominant mechanism is proposed, at low temperature close to the onset point of grain growth and under high pressure. Based on this route, fully dense boron carbide without grain growth can be prepared at 1,675-1,700 °C and under pressure of (≥) 80 MPa in 5 minutes. The dense boron carbide shows excellent mechanical properties, including Vickers hardness of 37.8 GPa, flexural strength of 445.3 MPa and fracture toughness of 4.7 MPa•m0.5. Such a process should also facilitate the cost-effective preparation of other advanced ceramics for practical applications.

  5. Massive Si Phase and Its Growth Mechanism in Al-Si Casting Alloy

    Institute of Scientific and Technical Information of China (English)

    Hengcheng LIAO; Guoxiong SUN

    2004-01-01

    Optical microscope and scanning electron microscope were used to observe the microstructure of the Al-11.6%Si and Al-11.6%Si-0.4%Mg alloys and the morphology of the massive silicon particles. It is found that the massive silicon phase, observed in the unfully modified alloys with 0.010%Sr, disappears completely in the alloys fully modified with 0.020%Sr. The serrations and reentrant edges shown in the massive silicon particles with the conventional casting indicate that the TPRE mechanism plays an important role in the growth of the massive silicon phase. The ripples and steps suggest that the "lateral microscopic growth" may be another operating mechanism.

  6. Sintering boron carbide ceramics without grain growth by plastic deformation as the dominant densification mechanism.

    Science.gov (United States)

    Ji, Wei; Rehman, Sahibzada Shakir; Wang, Weimin; Wang, Hao; Wang, Yucheng; Zhang, Jinyong; Zhang, Fan; Fu, Zhengyi

    2015-10-27

    A new ceramic sintering approach employing plastic deformation as the dominant mechanism is proposed, at low temperature close to the onset point of grain growth and under high pressure. Based on this route, fully dense boron carbide without grain growth can be prepared at 1,675-1,700 °C and under pressure of (≥) 80 MPa in 5 minutes. The dense boron carbide shows excellent mechanical properties, including Vickers hardness of 37.8 GPa, flexural strength of 445.3 MPa and fracture toughness of 4.7 MPa•m(0.5). Such a process should also facilitate the cost-effective preparation of other advanced ceramics for practical applications.

  7. Selective synthesis and growth mechanism of CeVO4 nanoparticals via hydrothermal method

    Institute of Scientific and Technical Information of China (English)

    LIU Fengzhen; SHAO Xin; YIN Yibin; ZHAO Limin; SUN Qiaozhen; SHAO Zhuwei; LIU Xuehua; MENG Xianhua

    2011-01-01

    Selective-controlled structure and shape of CeVO4 nanocrystals were successfully synthesized via a hydrothermal method from electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). The influence of hydrothermal temperature, precursor solution concentration on the crystal and morphology of products were further studied. The results showed that the as-synthesized products exhibited pure single-crystal CeVO4 nanoparticles with tetragonal structure. The hydrothermal temperature and precursor solution concentration had important effects on the formation of CeVO4 nanoparticles. Furthermore, the growth mechanism of CeVO4 nanoparticles was explained with Ostwald ripening mechanism.

  8. Enhancement of the superconducting transition temperature of MgB2 by a strain-induced bond-stretching mode softening.

    Science.gov (United States)

    Pogrebnyakov, A V; Redwing, J M; Raghavan, S; Vaithyanathan, V; Schlom, D G; Xu, S Y; Li, Qi; Tenne, D A; Soukiassian, A; Xi, X X; Johannes, M D; Kasinathan, D; Pickett, W E; Wu, J S; Spence, J C H

    2004-10-01

    We report a systematic increase of the superconducting transition temperature T(c) with a biaxial tensile strain in MgB2 films to well beyond the bulk value. The tensile strain increases with the MgB2 film thickness, caused primarily by the coalescence of initially nucleated discrete islands (the Volmer-Weber growth mode.) The T(c) increase was observed in epitaxial films on SiC and sapphire substrates, although the T(c) values were different for the two substrates due to different lattice parameters and thermal expansion coefficients. We identified, by first-principles calculations, the underlying mechanism for the T(c) increase to be the softening of the bond-stretching E(2g) phonon mode, and we confirmed this conclusion by Raman scattering measurements. The result suggests that the E(2g) phonon softening is a possible avenue to achieve even higher T(c) in MgB2-related material systems.

  9. Thermochromic VO{sub 2} on Zinnwaldite Mica by pulsed laser deposition

    Energy Technology Data Exchange (ETDEWEB)

    Mathevula, L., E-mail: langu@tlabs.ac.za [UNESCO-UNISA Africa Chair in Nanosciences-Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West 7129, PO Box 722, Western Cape (South Africa); Ngom, B.D.; Kotsedi, L.; Sechogela, P. [UNESCO-UNISA Africa Chair in Nanosciences-Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West 7129, PO Box 722, Western Cape (South Africa); Doyle, T.B. [Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West 7129, PO Box 722, Western Cape (South Africa); School of Chemistry and Physics, University of KwaZulu-Natal, Durban 4001 (South Africa); Ghouti, M.; Maaza, M. [UNESCO-UNISA Africa Chair in Nanosciences-Nanotechnology, College of Graduate Studies, University of South Africa, Muckleneuk Ridge, PO Box 392, Pretoria (South Africa); Nanosciences African Network (NANOAFNET), iThemba LABS-National Research Foundation, 1 Old Faure Road, Somerset West 7129, PO Box 722, Western Cape (South Africa)

    2014-09-30

    Highlights: • Vanadium dioxide was successfully synthesized by pulsed laser deposition method on mica. • The morphology evolution within the samples is characterized by a change from isolated and less-percolating (0 1 1) VO{sub 2} crystallites to a percolating granular configuration. • Without any post annealing, the films exhibit a textured nature with a VO{sub 2} (0 1 1) preferred crystallographic orientation and an elevated thermal variation of the electric resistance ratio R{sub S}/R{sub M} through the SMT at T ≈ 68 °C of the order of 10{sup 4} and a narrow ∼7 °C hysteresis. - Abstract: VO{sub 2} thin films have been deposited by pulsed laser deposition on Zinnwaldite Mica substrates. The crystal structure, chemical composition, morphology were determined and the semiconductor/metal transition (SMT) properties of the deposited films were investigated. Without any post annealing, the films exhibit a textured nature with a VO{sub 2} (0 1 1) preferred crystallographic orientation and an elevated thermal variation of the electric resistance ratio R{sub S}/R{sub M} through the SMT at T ≈ 68 °C of the order of 10{sup 4} and a narrow ∼7 °C hysteresis. In addition, the growth of the VO{sub 2} crystallites seem to be governed likely by a Volmer-Weber or Stranski-Krastanov mechanisms and certainly not a Frank-van Der Merwe process.

  10. Atomistic insights into dislocation-based mechanisms of void growth and coalescence

    Science.gov (United States)

    Mi, Changwen; Buttry, Daniel A.; Sharma, Pradeep; Kouris, Demitris A.

    2011-09-01

    One of the low-temperature failure mechanisms in ductile metallic alloys is the growth of voids and their coalescence. In the present work we attempt to obtain atomistic insights into the mechanisms underpinning cavitation in a representative metal, namely Aluminum. Often the pre-existing voids in metallic alloys such as Al have complex shapes (e.g. corrosion pits) and the defromation/damage mechanisms exhibit a rich size-dependent behavior across various material length scales. We focus on these two issues in this paper through large-scale calculations on specimens of sizes ranging from 18 thousand to 1.08 million atoms. In addition to the elucidation of the dislocation propagation based void growth mechanism we highlight the observed length scale effect reflected in the effective stress-strain response, stress triaxiality and void fraction evolution. Furthermore, as expected, the conventionally used Gurson's model fails to capture the observed size-effects calling for a mechanistic modification that incorporates the mechanisms observed in our (and other researchers') simulation. Finally, in our multi-void simulations, we find that, the splitting of a big void into a distribution of small ones increases the load-carrying capacity of specimens. However, no obvious dependence of the void fraction evolution on void coalescence is observed.

  11. Vertically oriented few-layered HfS2 nanosheets: growth mechanism and optical properties

    Science.gov (United States)

    Zheng, Binjie; Chen, Yuanfu; Wang, Zegao; Qi, Fei; Huang, Zhishuo; Hao, Xin; Li, Pingjian; Zhang, Wanli; Li, Yanrong

    2016-09-01

    For the first time, large-area, vertically oriented few-layered hafnium disulfide (V-{{{HfS}}}2) nanosheets have been grown by chemical vapor deposition. The individual {{{HfS}}}2 nanosheets are well [001] oriented, with highly crystalline quality. Far different from conventional van der Waals epitaxial growth mechanism for two-dimensional transition metal dichalcogenides, a novel dangling-bond-assisted self-seeding growth mechanism is proposed to describe the growth of V-{{{HfS}}}2 nanosheets: difficult migration of {{{HfS}}}2 adatoms on substrate surface results in {{{HfS}}}2 seeds growing perpendicularly to the substrate; V-{{{HfS}}}2 nanosheets inherit the growth direction of {{{HfS}}}2 seeds; V-{{{HfS}}}2 nanosheets further expand in the in-plane direction with time evolution. Moreover, the V-{{{HfS}}}2 nanosheets show strong and broadened photons absorption from near infrared to ultraviolet; the V-{{{HfS}}}2-based photodetector exhibits an ultrafast photoresponse time of 24 ms, and a high photosensitivity ca. 103 for 405 nm laser.

  12. Growth-inhibitory Effects of Curcumin on Ovary Cancer Cells and Its Mechanisms

    Institute of Scientific and Technical Information of China (English)

    郑丽端; 童强松; 吴翠环

    2004-01-01

    Summary: To study the growth-inhibitory ettects ot curcumin on human ovary cancer A2780 cells in vitro and its molecular mechanisms, the growth inhibition rates of A2780 cancer cells, after being treated with 10 μmol/L-50 μmol/L curcumin for 6-24 h, were examined by MTT method. The morphological changes of cancer cells were observed under inversion microscopy. Cellular apoptotic rates were determined by using TUNEL. The protein expression levels of bcl-2, p53 and MDM2 in cancer cells were examined by SP immunohistochemistry. After being treated by various concentrations of curcumin, the growth of cancer cells was inhibited significantly. Some cancer cells presented characteristic morphological changes of apoptosis. The rates of apoptosis were 6.41% -28.48% (P<0.01). The expression of bcl-2 and p53 was decreased, which depended on the action time (P<0.01). There were no obvious changes in MDM2 expression. It was concluded that curcumin could significantly inhibit the growth of ovary cancer cells. The induction of apoptosis by down-regulating the expression of bcl-2 and p53 was probably one of its molecular mechanisms.

  13. GROWTH-INHIBITORY EFFECTS OF CURCUMIN ON Raji CELLS AND ITS MECHANISMS

    Institute of Scientific and Technical Information of China (English)

    CHEN Yan; WU Qing; LI Xin-gang

    2005-01-01

    Objective: To study the growth-inhibitory effects of curcumin on B-NHL cell line Raji cells in vitro and its molecular mechanisms. Methods: The growth inhibition rates of Raji cells, after being treated with 6.25 μmol/L~50 μmol/L curcumin for 12 h ~ 48 h, were examined by MTT assay. The apoptosis rate was detected by flow cytometry (FCM), the protein expression levels of bcl-2 and p53 in Raji cells were examined by SP immunohistochemistry. The expression of p53 in Raji cell were checked by RT-PCR. Results: After being treated by various concentrations of curcumin, the growth of Raji cells was inhibited significantly. The rates of apoptosis were 11.8% ~79.7% (P<0.01), the down regulation of p53 expression was observed within 24 h after the treatment of curcumin by RT-PCR. The expression of bcl-2 and p53 was decreased, which depended on the action time. Conclusion: Curcumin could significantly inhibit the growth of Raji cells. The induction of apoptosis by down-regulating the expression of bcl-2 and p53 was probably one of its molecular mechanisms.

  14. Transcriptome analysis of genetic mechanism of growth curve inflection point using a pig model

    Directory of Open Access Journals (Sweden)

    Linyuan Shen

    2015-12-01

    Full Text Available Animal growth curves play an important role for animal breeders to optimize feeding and management strategies (De Lange et al., 2001 [1]; Brossard et al., 2009 [2]; Strathe et al., 2010 [3]. However, the genetic mechanism of the phenotypic difference between the inflection point and noninflection points of the growth curve remains unclear. Here, we report the differentially expressed gene pattern in pig longissimus dorsi among three typical time points of the growth curve, inflection point (IP, before inflection point (BIP and after inflection point (AIP. The whole genome RNA-seq data was deposited at GenBank under the accession number PRJNA2284587. The RNA-seq libraries generated 117 million reads of 5.89 gigabases in length. Totals of 21,331, 20,996 and 20,139 expressed transcripts were identified in IP, UIP and AIP, respectively. Furthermore, we identified 757 differentially expressed genes (DEGs between IP and UIP, and 271 DEGs between AIP and IP. Function enrichment analysis of DEGs found that the highly expressed genes in IP were mainly enriched in energy metabolism, global transcriptional activity and bone development intensity. This study contributes to reveal the genetic mechanism of growth curve inflection point.

  15. Growth Inhibition and Apoptosis Inducing Mechanisms of Curcumin on Human Ovarian Cancer Cell Line A2780

    Institute of Scientific and Technical Information of China (English)

    ZHENG Li-duan; TONG Qiang-song; WU Cui-huan

    2006-01-01

    Objective: To explore the growth inhibition effects and apoptosis inducing mechanisms of curcumin on human ovarian cancer cell line A2780. Methods: After treatment with 10-50 μmol/L curcumin for 6-24 h, the growth activity of A2780 cancer cells were studied by [ 4, 5-dimethylthiazol-2-yl]-2, 5-diphenyItetrazolium bromide (MTT) colorimetry. Cellular apoptosis was inspected by flow cytometery and acridine orange-ethidium bromide fluorescent staining methods. The fragmentation of cellular chromosome DNA was detected by DNA ladder, the ultrastructural change was observed under a transmission electron microscope,and the protein levels of nuclear factor-kappa B (NF-κB, P65) and cysteinyl aspartate specific protease-3 (Caspase-3) in ovarian cancer cells were measured by immunohistochemistry. Results: After treatment with various concentrations of curcumin, the growth inhibition rates of cancer cells reached 62.05%- 89.24%,with sub-G1 peaks appearing on histogram. Part of the cancer cells showed characteristic morphological changes of apoptosis under fluorescence and electron microscopes, and the rate of apoptosis was 21.5 % -33.5%. The protein expression of NF-κB was decreased, while that of Caspase-3 was increased in a timedependent manner. Conclusion: Curcumin could significantly inhibit the growth of human ovarian cancer cells;inducing apoptosis through up-regulating Caspase-3 and down-regulating gene expression of NF-κB is probably one of its molecular mechanisms.

  16. Microspheres for the Growth of Silicon Nanowires via Vapor-Liquid-Solid Mechanism

    Directory of Open Access Journals (Sweden)

    Arancha Gómez-Martínez

    2014-01-01

    Full Text Available Silicon nanowires have been synthesized by a simple process using a suitable support containing silica and carbon microspheres. Nanowires were grown by thermal chemical vapor deposition via a vapor-liquid-solid mechanism with only the substrate as silicon source. The curved surface of the microsized spheres allows arranging the gold catalyst as nanoparticles with appropriate dimensions to catalyze the growth of nanowires. The resulting material is composed of the microspheres with the silicon nanowires attached on their surface.

  17. Atmospheric sulphuric acid and aerosol formation: implications from atmospheric measurements for nucleation and early growth mechanisms

    Directory of Open Access Journals (Sweden)

    S.-L. Sihto

    2006-01-01

    Full Text Available We have investigated the formation and early growth of atmospheric secondary aerosol particles building on atmospheric measurements. The measurements were part of the QUEST 2 campaign which took place in spring 2003 in Hyytiälä (Finland. During the campaign numerous aerosol particle formation events occurred of which 15 were accompanied by gaseous sulphuric acid measurements. Our detailed analysis of these 15 events is focussed on nucleation and early growth (to a diameter of 3 nm of fresh particles. It revealed that new particle formation seems to be a function of the gaseous sulphuric acid concentration to the power from one to two when the time delay between the sulphuric acid and particle number concentration is taken into account. From the time delay the growth rates of freshly nucleated particles from 1 nm to 3 nm were determined. The mean growth rate was 1.2 nm/h and it was clearly correlated with the gaseous sulphuric acid concentration. We tested two nucleation mechanisms – recently proposed cluster activation and kinetic type nucleation – as possible candidates to explain the observed dependences, and determined experimental nucleation coefficients. We found that some events are dominated by the activation mechanism and some by the kinetic mechanism. Inferred coefficients for the two nucleation mechanisms are the same order of magnitude as chemical reaction coefficients in the gas phase and they correlate with the product of gaseous sulphuric acid and ammonia concentrations. This indicates that besides gaseous sulphuric acid also ammonia has a role in nucleation.

  18. Novel Tissue‐Specific Mechanism of Regulation of Angiogenesis and Cancer Growth in Response to Hyperglycemia

    OpenAIRE

    Bhattacharyya, Sanghamitra; Sul, Kristina; Krukovets, Irene; Nestor, Carla; Li, Jianbo; Adognravi, Olga Stenina

    2012-01-01

    Background Hyperglycemia is an independent risk factor for the development of vascular diabetic complications, which are characterized by endothelial dysfunction and tissue‐specific aberrant angiogenesis. Tumor growth is also dependent on angiogenesis. Diabetes affects several cancers in a tissue‐specific way. For example, it positively correlates with the incidence of breast cancer but negatively correlates with the incidence of prostate cancer. The tissue‐specific molecular mechanisms activ...

  19. Biological mechanisms discriminating growth rate and adult body weight phenotypes in two Chinese indigenous chicken breeds.

    Science.gov (United States)

    Dou, Tengfei; Zhao, Sumei; Rong, Hua; Gu, Dahai; Li, Qihua; Huang, Ying; Xu, Zhiqiang; Chu, Xiaohui; Tao, Linli; Liu, Lixian; Ge, Changrong; Te Pas, Marinus F W; Jia, Junjing

    2017-06-20

    Intensive selection has resulted in increased growth rates and muscularity in broiler chickens, in addition to adverse effects, including delayed organ development, sudden death syndrome, and altered metabolic rates. The biological mechanisms underlying selection responses remain largely unknown. Non-artificially-selected indigenous Chinese chicken breeds display a wide variety of phenotypes, including differential growth rate, body weight, and muscularity. The Wuding chicken breed is a fast growing large chicken breed, and the Daweishan mini chicken breed is a slow growing small chicken breed. Together they form an ideal model system to study the biological mechanisms underlying broiler chicken selection responses in a natural system. The objective of this study was to study the biological mechanisms underlying differential phenotypes between the two breeds in muscle and liver tissues, and relate these to the growth rate and body development phenotypes of the two breeds. The muscle tissue in the Wuding breed showed higher expression of muscle development genes than muscle tissue in the Daweishan chicken breed. This expression was accompanied by higher expression of acute inflammatory response genes in Wuding chicken than in Daweishan chicken. The muscle tissue of the Daweishan mini chicken breed showed higher expression of genes involved in several metabolic mechanisms including endoplasmic reticulum, protein and lipid metabolism, energy metabolism, as well as specific immune traits than in the Wuding chicken. The liver tissue showed fewer differences between the two breeds. Genes displaying higher expression in the Wuding breed than in the Daweishan breed were not associated with a specific gene network or biological mechanism. Genes highly expressed in the Daweishan mini chicken breed compared to the Wuding breed were enriched for protein metabolism, ABC receptors, signal transduction, and IL6-related mechanisms. We conclude that faster growth rates and larger

  20. 晶体外延生长模式的完备理论描述与“后S-K异质兼容生长模式”的预言%Novel Comprehensive Theoretical Description of Epitaxial Crystal-Growth Modes and the Prediction of“Post S-K Compatible-Heterogeneous-Growth Mode”

    Institute of Scientific and Technical Information of China (English)

    任晓敏; 王琦

    2014-01-01

    指出了晶体外延生长模式现有理论描述的若干问题,包括:①弗兰克-范·德·默夫模式被描述为仅存在于衬底表面能优势度为正值的情形中,这和晶格失配度足够小的2种材料能够以该模式交替生长的实验事实不符;②对于不同的衬底表面能优势度,弗兰克-范·德·默夫模式与斯特兰斯基-克拉斯塔诺夫( S-K)模式之间的转换被描述为发生在某一固定的晶格失配度上,这显然是不合理的;③由弗兰克-范·德·默夫模式似可直接转换为沃尔默-韦伯模式,反之亦然,这一描述值得质疑。针对这些问题,提出了改进的、更加完备的理论描述,其中引入了“准弗兰克-范·德·默夫模式”的概念。在此基础上,提出了“后S-K异质兼容生长模式”的概念,并探讨了基于该模式实现高质量异质兼容体材料生长的可能性。%Some problems are found in currently-available theoretical description of epitaxial crystal-growth mods, including that①Frank-van der Merve mode is described as it only exists for positive domi-nance-level of the substrate surface energy and this is not in agreement with the experimental fact that a pair of materials with small enough lattice mismatch between them can grow alternately both in the Frank-van der Merve mode;②the transition between Frank-van der Merve mode and Stranski-Krastanow ( S-K) mode is regarded as it happens at a fixed lattice mismatch for different dominance-levels of the substrate surface energy and this description seems obviously unreasonable;③the direct transitions from Frank-van der Merve mode to Volmer-Weber mode and vice versa are supposed possible and the truthfulness of this understanding might be seriously suspected. Taking these problems into consideration, a modified and more comprehensive theoretical description is proposed and the concept of quasi-Frank-van der Merve mode is introduced in it. Based upon the

  1. Elaboration and characterization of boron doping during SiC growth by VLS mechanism

    Science.gov (United States)

    Soueidan, Maher; Ferro, Gabriel; Nsouli, Bilal; Roumié, Mohamad; Habka, Nada; Souliere, Véronique; Bluet, Jean-Marie; Kazan, Michel

    2011-07-01

    VLS mechanism was used for growing boron doped homoepitaxial SiC layers on 4H-SiC(0 0 0 1) 8° off substrate. Si-based melts were fed by propane in the temperature range 1450-1500 °C. Two main approaches were studied to incorporate boron during growth: (1) adding elemental B in the initial melt, with two different compositions: Si 90B 10 and Si 27Ge 68B 5; the growth was performed at 1500 °C; (2) adding B 2H 6 to the gas phase during growth with a melt composition of Si 25Ge 75; the growth was performed at 1450 °C. In most cases, the growth time was limited by liquid loss. The longest growth duration (1 h) was obtained when adding B 2H 6 to the gas phase. In the case of Si 90B 10 melt, the surface morphology exhibits large and parallel terraces whereas the step front is more undulated when adding Ge. Raman and photoluminescence characterizations performed on these layers confirmed the 4H polytype of the layers in addition to the presence of B, which results in a strong B-N donor-acceptor band. The thickness and the growth rate were determined by micro-Infrared spectroscopy. Particle Induced γ-ray Emission (PIGE) was tentatively used to detect B incorporation inside the grown layers. These results were compared to SIMS measurements from which B concentration was found to vary from 10 18 to 10 19 at cm -3.

  2. Mechanical picture of the linear transient growth of vortical perturbations in incompressible smooth shear flows

    Science.gov (United States)

    Chagelishvili, George; Hau, Jan-Niklas; Khujadze, George; Oberlack, Martin

    2016-08-01

    The linear dynamics of perturbations in smooth shear flows covers the transient exchange of energies between (1) the perturbations and the basic flow and (2) different perturbations modes. Canonically, the linear exchange of energies between the perturbations and the basic flow can be described in terms of the Orr and the lift-up mechanisms, correspondingly for two-dimensional (2D) and three-dimensional (3D) perturbations. In this paper the mechanical basis of the linear transient dynamics is introduced and analyzed for incompressible plane constant shear flows, where we consider the dynamics of virtual fluid particles in the framework of plane perturbations (i.e., perturbations with plane surfaces of constant phase) for the 2D and 3D case. It is shown that (1) the formation of a pressure perturbation field is the result of countermoving neighboring sets of incompressible fluid particles in the flow, (2) the keystone of the energy exchange mechanism between the basic flow and perturbations is the collision of fluid particles with the planes of constant pressure in accordance with the classical theory of elastic collision of particles with a rigid wall, making the pressure field the key player in this process, (3) the interplay of the collision process and the shear flow kinematics describes the transient growth of plane perturbations and captures the physics of the growth, and (4) the proposed mechanical picture allows us to reconstruct the linearized Euler equations in spectral space with a time-dependent shearwise wave number, the linearized Euler equations for Kelvin modes. This confirms the rigor of the presented analysis, which, moreover, yields a natural generalization of the proposed mechanical picture of the transient growth to the well-established linear phenomenon of vortex-wave-mode coupling.

  3. Potential mechanisms for hypoalgesia induced by anti-nerve growth factor immunoglobulin are identified using autoimmune nerve growth factor deprivation

    Science.gov (United States)

    Hoffman, E. Matthew; Zhang, Zijia; Anderson, Michael B.; Schechter, Ruben; Miller, Kenneth E.

    2011-01-01

    Nerve growth factor (NGF) antagonism has long been proposed as a chronic pain treatment. In 2010, the FDA suspended clinical trials using tanezumab, a humanized monoclonal anti-NGF antibody, to treat osteoarthritis due to worsening joint damage in 16 patients. Increased physical activity in the absence of acute pain which normally prevents self harm was purported as a potential cause. Such an adverse effect is consistent with an extension of tanezumab's primary mechanism of action by decreasing pain sensitivity below baseline levels. In animal inflammatory pain models, NGF antagonism decreases intraepidermal nerve fiber (IENF) density and attenuates increases in expression of nociception related proteins, such as calcitonin gene-related peptide (CGRP) and substance P (SP). Little is known of the effects of NGF antagonism in noninflamed animals and the hypoalgesia that ensues. In the current study, we immunized rats with NGF or cytochrome C (cytC) and examined 1) nocifensive behaviors with thermal latencies, mechanical thresholds, the hot plate test, and the tail flick test, 2) IENF density, and 3) expression of CGRP, SP, voltage-gated sodium channel 1.8 (Nav1.8), and glutaminase in subpopulations of dorsal root ganglion (DRG) neurons separated by size and isolectin B4 (IB4) labeling. Rats with high anti-NGF titers had delayed responses on the hot plate test but no other behavioral abnormalities. Delayed hot plate responses correlated with lower IENF density. CGRP and SP expression was decreased principally in medium (400-800 μm2) and small neurons (<400 μm2), respectively, regardless of IB4 labeling. Expression of Nav1.8 was only decreased in small and medium IB4 negative neurons. NGF immunization appears to result in a more profound antagonism of NGF than tanezumab therapy, but we hypothesize that decreases in IENF density and nociception related protein expression are potential mechanisms for tanezumab induced hypoalgesia. PMID:21802499

  4. Survey of Plant Growth-Promoting Mechanisms in Native Portuguese Chickpea Mesorhizobium Isolates.

    Science.gov (United States)

    Brígido, Clarisse; Glick, Bernard R; Oliveira, Solange

    2017-05-01

    Rhizobia may possess other plant growth-promoting mechanisms besides nitrogen fixation. These mechanisms and the tolerance to different environmental factors, such as metals, may contribute to the use of rhizobia inocula to establish a successful legume-rhizobia symbiosis. Our goal was to characterize a collection of native Portuguese chickpea Mesorhizobium isolates in terms of plant growth-promoting (PGP) traits and tolerance to different metals as well as to investigate whether these characteristics are related to the biogeography of the isolates. The occurrence of six PGP mechanisms and tolerance to five metals were evaluated in 61 chickpea Mesorhizobium isolates previously obtained from distinct provinces in Portugal and assigned to different species clusters. Chickpea microsymbionts show high diversity in terms of PGP traits as well as in their ability to tolerate different metals. All isolates synthesized indoleacetic acid, 50 isolates produced siderophores, 19 isolates solubilized phosphate, 12 isolates displayed acid phosphatase activity, and 22 exhibited cytokinin activity. Most isolates tolerated Zn or Pb but not Ni, Co, or Cu. Several associations between specific PGP mechanisms and the province of origin and species clusters of the isolates were found. Our data suggests that the isolate's tolerance to metals and ability to solubilize inorganic phosphate and to produce IAA may be responsible for the persistence and distribution of the native Portuguese chickpea Mesorhizobium species. Furthermore, this study revealed several chickpea microsymbionts with potential as PGP rhizobacteria as well as for utilization in phytoremediation strategies.

  5. Stiff mutant genes of phycomyces affect turgor pressure and wall mechanical properties to regulate elongation growth rate.

    Science.gov (United States)

    Ortega, Joseph K E; Munoz, Cindy M; Blakley, Scott E; Truong, Jason T; Ortega, Elena L

    2012-01-01

    Regulation of cell growth is paramount to all living organisms. In plants, algae and fungi, regulation of expansive growth of cells is required for development and morphogenesis. Also, many sensory responses of stage IVb sporangiophores of Phycomyces blakesleeanus are produced by regulating elongation growth rate (growth responses) and differential elongation growth rate (tropic responses). "Stiff" mutant sporangiophores exhibit diminished tropic responses and are found to be defective in at least five genes; madD, E, F, G, and J. Prior experimental research suggests that the defective genes affect growth regulation, but this was not verified. All the growth of the single-celled stalk of the stage IVb sporangiophore occurs in a short region termed the "growth zone." Prior experimental and theoretical research indicates that elongation growth rate of the stage IVb sporangiophore can be regulated by controlling the cell wall mechanical properties within the growth zone and the magnitude of the turgor pressure. A quantitative biophysical model for elongation growth rate is required to elucidate the relationship between wall mechanical properties and turgor pressure during growth regulation. In this study, it is hypothesized that the mechanical properties of the wall within the growth zone of stiff mutant sporangiophores are different compared to wild type (WT). A biophysical equation for elongation growth rate is derived for fungal and plant cells with a growth zone. Two strains of stiff mutants are studied, C149 madD120 (-) and C216 geo- (-). Experimental results demonstrate that turgor pressure is larger but irreversible wall deformation rates within the growth zone and growth zone length are smaller for stiff mutant sporangiophores compared to WT. These findings can explain the diminished tropic responses of the stiff mutant sporangiophores. It is speculated that the defective genes affect the amount of wall-building material delivered to the inner cell wall.

  6. Effects of an intervention on infant growth and development: evidence for different mechanisms at work.

    Science.gov (United States)

    Prado, Elizabeth L; Abbeddou, Souheila; Yakes Jimenez, Elizabeth; Somé, Jérôme W; Dewey, Kathryn G; Brown, Kenneth H; Hess, Sonja Y

    2017-04-01

    Millions of children in low-income and middle-income countries falter in linear growth and neurobehavioral development early in life. This faltering may be caused by risk factors that are associated with both growth and development, such as insufficient dietary intake and infection in infancy. Alternatively, these risk factors may be indicative of an environment that constrains both linear growth and development through different mechanisms. In a cluster-randomized trial in Burkina Faso, we previously found that provision of lipid-based nutrient supplements plus malaria and diarrhoea treatment from age 9 to 18 months resulted in positive effects of ~0.3 standard deviation on length-for-age z-score (LAZ) and of ~0.3 standard deviation on motor, language and personal-social development scores at age 18 months. In this paper, we examined whether the effect of the intervention on developmental scores was mediated by the effect on LAZ, or, alternatively, whether the intervention had independent effects on growth and development. For motor, language, and personal-social z-scores, the effect of the intervention decreased from 0.32 to 0.21, from 0.33 to 0.27 and from 0.35 to 0.29, respectively, when controlling for change in LAZ from 9 to 18 months. All effects remained significant. These results indicate that the intervention had independent positive effects on linear growth and development, suggesting that these effects occurred through different mechanisms. © 2016 John Wiley & Sons Ltd. © 2016 John Wiley & Sons Ltd.

  7. Growth, collapse, and stalling in a mechanical model for neurite motility

    CERN Document Server

    Recho, Pierre; Goriely, Alain

    2015-01-01

    Neurites, the long cellular protrusions that form the routes of the neuronal network are capable to actively extend during early morphogenesis or to regenerate after trauma. To perform this task, they rely on their cytoskeleton for mechanical support. In this paper, we present a three-component active gel model that describes neurites in the three robust mechanical states observed experimentally: collapsed, static, and motile. These states arise from an interplay between the physical forces driven by growth of the microtubule-rich inner core of the neurite and the acto-myosin contractility of its surrounding cortical membrane. In particular, static states appear as a mechanical traction/compression balance of these two parallel structures. The model predicts how the response of a neurite to a towing force depends on the force magnitude and recovers the response of neurites to several drug treatments that modulate the cytoskeleton active and passive properties.

  8. Crack growth of 10M Ni-Mn-Ga material in cyclic mechanical loading

    Science.gov (United States)

    Aaltio, I.; Ge, Y.; Pulkkinen, H.; Sjöberg, A.; Söderberg, O.; Liu, X. W.; Hannula, S.-P.

    The 10M martensitic Ni-Mn-Ga single crystal materials are usually applied in the magneto-mechanical actuators. Therefore, it is important to know the possible effect of the long-term cyclic shape changes on their structure and behavior. This can be evaluated with the mechanical fatigue testing. In the present study, the single crystal 10M Ni-Mn-Ga samples of different compositions were applied to strain-controlled uniaxial mechanical cycling in the multivariant state at ambient temperature. The experiments revealed distinctive changes of the twin variant structure, especially in the mobile twin area, density of twin boundaries, and in the tendency for fatigue crack growth. Characterization of the crack surface showed that the cracks in the microscale grow in a step-wise manner on specific crystallographic planes, i.e, twin boundary planes, but that the macroscopic crack does not occur only along crystallographic directions.

  9. A PAH growth mechanism and synergistic effect on PAH formation in counterflow diffusion flames

    KAUST Repository

    Wang, Yu

    2013-09-01

    A reaction mechanism having molecular growth up to benzene for hydrocarbon fuels with up to four carbon-atoms was extended to include the formation and growth of polycyclic aromatic hydrocarbons (PAHs) up to coronene (C24H12). The new mechanism was tested for ethylene premixed flames at low (20torr) and atmospheric pressures by comparing experimentally observed species concentrations with those of the computed ones for small chemical species and PAHs. As compared to several existing mechanisms in the literature, the newly developed mechanism showed an appreciable improvement in the predicted profiles of PAHs. The new mechanism was also used to simulate PAH formation in counterflow diffusion flames of ethylene to study the effects of mixing propane and benzene in the fuel stream. In the ethylene-propane flames, existing experimental results showed a synergistic effect in PAH concentrations, i.e. PAH concentrations first increased and then decreased with increasing propane mixing. This PAH behavior was successfully captured by the new mechanism. The synergistic effect was predicted to be more pronounced for larger PAH molecules as compared to the smaller ones, which is in agreement with experimental observations. In the experimental study in which the fuel stream of ethylene-propane flames was doped with benzene, a synergistic effect was mitigated for benzene, but was observed for large PAHs. This effect was also predicted in the computed PAH profiles for these flames. To explain these responses of PAHs in the flames of mixture fuels, a pathway analysis has been conducted, which show that several resonantly stabilized species as well as C4H4 and H atom contribute to the enhanced synergistic behaviors of larger PAHs as compared to the small ones in the flames of mixture fuels. © 2013 The Combustion Institute.

  10. Effects of Mechanical Harvesting on Sugarcane Stubble Quality and Growth of Ratoon

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    The experiment was conducted with the traditional manual harvesting and mechanical harvesting of sugarcane,to compare the effects of different harvesting method on the sugarcane stubble quality and the growth of ratoon.The experimental results are as follows.(i) The stubble height and breaking stubble rate of mechanical harvesting was significantly higher than manual harvesting,the stubble height of lodging species and difficult defoliation species increased in mechanical harvesting condition.Varieties with higher levels of fiber had lower rate of broken stubble.(ii) The effects of mechanical harvesting on germination of next year ratoon were quite different due to different varieties,indicating that the better perennial species have less impact than the poor perennial species.(iii) Compared with manual harvesting,mechanical harvesting had slightly higher plant height and single-stem weight and less effective stems number,the difference of cane yield was not significant,but sucrose content increased 0.53%.(iv) Mechanical harvesting combining with leaves crushing could reduce the impact on the germination of ratoon,improve the single-stem weight and increase the effective number of stems.

  11. Subcritical crack growth and mechanical weathering: a new consideration of how moisture influences rock erosion rates.

    Science.gov (United States)

    Eppes, Martha-Cary; Keanini, Russell; Hancock, Gregory S.

    2016-04-01

    The contributions of moisture to the mechanical aspects of rock weathering and regolith production are poorly quantified. In particular, geomorphologists have largely overlooked the role of subcritical crack growth processes in physical weathering and the fact that moisture strongly influences the rates of those processes. This influence is irrespective of the function that moisture plays in stress loading mechanisms like freezing or hydration. Here we present a simple numerical model that explores the efficacy of subcritical crack growth in granite rock subaerially exposed under a range of moisture conditions. Because most weathering-related stress loading for rocks found at, or near, Earth's surface (hereafter surface rocks) is cyclic, we modeled crack growth using a novel combination of Paris' Law and Charles' Law. This combination allowed us to apply existing empirically-derived data for the stress corrosion index of Charles' Law to fatigue cracking. For stress, we focused on the relatively straightforward case of intergranular stresses that arise during solar-induced thermal cycling by conductive heat transfer, making the assumption that such stresses represent a universal minimum weathering stress experienced by all surface rocks. Because all other tensile weathering-related stresses would be additive in the context of crack growth, however, our model can be adapted to include other stress loading mechanisms. We validated our calculations using recently published thermal-stress-induced cracking rates. Our results demonstrate that 1) weathering-induced stresses as modeled herein, and as published by others, are sufficient to propagate fractures subcritically over long timescales with or without the presence of water 2) fracture propagation rates increase exponentially with respect to moisture, specifically relative humidity 3) fracture propagation rates driven by thermal cycling are strongly dependent on the magnitude of diurnal temperature ranges and the

  12. Effects of curcumin on growth of human cervical cancer xenograft in nude mice and underlying mechanism

    Directory of Open Access Journals (Sweden)

    Aixue LIU

    Full Text Available Abstract The present study investigated the effects of curcumin (Cur on growth of human cervical cancer xenograft in nude mice and underlying mechanism. The nude mice modeled with human cervical cancer HeLa cell xenograft were treated with normal saline (control, 3 mg/kg Cisplatin, 50, 100 and 200 mg/kg Cur, respectively. The animal body weight and growth of tumor were measured. The expressions of Bax, Bcl-2, p53, p21, HIF-1α, VEGF and MIF protein in tumor tissue were determined. Results showed that, after treatment for 20 days, the tumor mass and tumor volume in 100 and 200 mg/kg Cur group were significantly lower than control group (P < 0.05. The expressions of Bax, p53 and p21 protein in tumor tissue in 200 mg/kg Cur group were significantly higher than control group (P < 0.05, and the expressions of Bcl-2, HIF-1α, VEGF and MIF protein in tumor tissue in 200 mg/kg Cur group were significantly lower than control group (P < 0.05. Cur can inhibit the growth of HeLa cell xenograft in nude mice. The possible mechanism may be related to its up-regulation of Bax, p53 and p21 protein expression in tumor tissue, and down-regulation of Bcl-2, HIF-1α, VEGF and MIF protein expression.

  13. Peri-Implantation Hormonal Milieu: Elucidating Mechanisms of Abnormal Placentation and Fetal Growth1

    Science.gov (United States)

    Mainigi, Monica A.; Olalere, Devvora; Burd, Irina; Sapienza, Carmen; Bartolomei, Marisa; Coutifaris, Christos

    2013-01-01

    ABSTRACT Assisted reproductive technologies (ART) have been associated with several adverse perinatal outcomes involving placentation and fetal growth. It is critical to examine each intervention individually in order to assess its relationship to the described adverse perinatal outcomes. One intervention ubiquitously used in ART is superovulation with gonadotropins. Superovulation results in significant changes in the hormonal milieu, which persist during the peri-implantation and early placentation periods. Epidemiologic evidence suggests that the treatment-induced peri-implantation maternal environment plays a critical role in perinatal outcomes. In this study, using the mouse model, we have isolated the exposure to the peri-implantation period, and we examine the effect of superovulation on placentation and fetal growth. We report that the nonphysiologic peri-implantation maternal hormonal environment resulting from gonadotropin stimulation appears to have a direct effect on fetal growth, trophoblast differentiation, and gene expression. This appears to be mediated, at least in part, through trophoblast expansion and invasion. Although the specific molecular and cellular mechanism(s) leading to these observations remain to be elucidated, identifying this modifiable risk factor will not only allow us to improve perinatal outcomes with ART, but help us understand the pathophysiology contributing to these outcomes. PMID:24352558

  14. Investigation of a Simplified Mechanism Model for Prediction of Gallium Nitride Thin Film Growth through Numerical Analysis

    Directory of Open Access Journals (Sweden)

    Chih-Kai Hu

    2017-03-01

    Full Text Available A numerical procedure was performed to simplify the complicated mechanism of an epitaxial thin-film growth process. In this study, three numerical mechanism models are presented for verifying the growth rate of the gallium nitride (GaN mechanism. The mechanism models were developed through rate of production analysis. All of the results can be compared in one schematic diagram, and the differences among these three mechanisms are pronounced at high temperatures. The simplified reaction mechanisms were then used as input for a two-dimensional computational fluid dynamics code FLUENT, enabling the accurate prediction of growth rates. Validation studies are presented for two types of laboratory-scale reactors (vertical and horizontal. A computational study including thermal and flow field was also performed to investigate the fluid dynamic in those reactors. For each study, the predictions agree acceptably well with the experimental data, indicating the reasonable accuracy of the reaction mechanisms.

  15. Mechanisms that increase the growth efficiency of diatoms in low light.

    Science.gov (United States)

    Fisher, Nerissa L; Halsey, Kimberly H

    2016-08-01

    Photoacclimation was studied in Thalassiosira pseudonana to help understand mechanisms underlying the success of diatoms in low-light environments, such as coastal and deep mixing ecosystems. Light harvesting and other cell characteristics were combined with oxygen and carbon production measurements to assess the water-splitting reaction at PSII ([Formula: see text]) and intermediate steps leading to net carbon production (NPPC). These measurements revealed that T. pseudonana is remarkably efficient at converting harvested light energy into biomass, with at least 57 % of [Formula: see text] retained as NPPC across all light-limited growth rates examined. Evidence for upregulation of ATP generation pathways that circumvent carbon fixation indicated that high growth efficiency at low light levels was at least partly due to increases in the efficiency of ATP production. Growth rate-dependent demands for ATP and NADPH were reflected in carbon composition and in unexpected shifts in the light-limited slope (α) of photosynthesis-irradiance relationships generated from chlorophyll-specific (14)C-uptake. Overall, these results suggest that pathway gating of carbon and energy flow depends on light availability and is a key factor promoting the efficiency of diatom growth at low light intensities.

  16. A homogenized constrained mixture (and mechanical analog) model for growth and remodeling of soft tissue.

    Science.gov (United States)

    Cyron, C J; Aydin, R C; Humphrey, J D

    2016-12-01

    Most mathematical models of the growth and remodeling of load-bearing soft tissues are based on one of two major approaches: a kinematic theory that specifies an evolution equation for the stress-free configuration of the tissue as a whole or a constrained mixture theory that specifies rates of mass production and removal of individual constituents within stressed configurations. The former is popular because of its conceptual simplicity, but relies largely on heuristic definitions of growth; the latter is based on biologically motivated micromechanical models, but suffers from higher computational costs due to the need to track all past configurations. In this paper, we present a temporally homogenized constrained mixture model that combines advantages of both classical approaches, namely a biologically motivated micromechanical foundation, a simple computational implementation, and low computational cost. As illustrative examples, we show that this approach describes well both cell-mediated remodeling of tissue equivalents in vitro and the growth and remodeling of aneurysms in vivo. We also show that this homogenized constrained mixture model suggests an intimate relationship between models of growth and remodeling and viscoelasticity. That is, important aspects of tissue adaptation can be understood in terms of a simple mechanical analog model, a Maxwell fluid (i.e., spring and dashpot in series) in parallel with a "motor element" that represents cell-mediated mechanoregulation of extracellular matrix. This analogy allows a simple implementation of homogenized constrained mixture models within commercially available simulation codes by exploiting available models of viscoelasticity.

  17. Brain IGF-1 receptors control mammalian growth and lifespan through a neuroendocrine mechanism.

    Directory of Open Access Journals (Sweden)

    Laurent Kappeler

    2008-10-01

    Full Text Available Mutations that decrease insulin-like growth factor (IGF and growth hormone signaling limit body size and prolong lifespan in mice. In vertebrates, these somatotropic hormones are controlled by the neuroendocrine brain. Hormone-like regulations discovered in nematodes and flies suggest that IGF signals in the nervous system can determine lifespan, but it is unknown whether this applies to higher organisms. Using conditional mutagenesis in the mouse, we show that brain IGF receptors (IGF-1R efficiently regulate somatotropic development. Partial inactivation of IGF-1R in the embryonic brain selectively inhibited GH and IGF-I pathways after birth. This caused growth retardation, smaller adult size, and metabolic alterations, and led to delayed mortality and longer mean lifespan. Thus, early changes in neuroendocrine development can durably modify the life trajectory in mammals. The underlying mechanism appears to be an adaptive plasticity of somatotropic functions allowing individuals to decelerate growth and preserve resources, and thereby improve fitness in challenging environments. Our results also suggest that tonic somatotropic signaling entails the risk of shortened lifespan.

  18. Molecular Mechanisms of Enhanced Bacterial Growth on Hexadecane with Red Clay.

    Science.gov (United States)

    Jung, Jaejoon; Jang, In-Ae; Ahn, Sungeun; Shin, Bora; Kim, Jisun; Park, Chulwoo; Jee, Seung Cheol; Sung, Jung-Suk; Park, Woojun

    2015-11-01

    Red clay was previously used to enhance bioremediation of diesel-contaminated soil. It was speculated that the enhanced degradation of diesel was due to increased bacterial growth. In this study, we selected Acinetobacter oleivorans DR1, a soil-borne degrader of diesel and alkanes, as a model bacterium and performed transcriptional analysis using RNA sequencing to investigate the cellular response during hexadecane utilization and the mechanism by which red clay promotes hexadecane degradation. We confirmed that red clay promotes the growth of A. oleivorans DR1 on hexadecane, a major component of diesel, as a sole carbon source. Addition of red clay to hexadecane-utilizing DR1 cells highly upregulated β-oxidation, while genes related to alkane oxidation were highly expressed with and without red clay. Red clay also upregulated genes related to oxidative stress defense, such as superoxide dismutase, catalase, and glutaredoxin genes, suggesting that red clay supports the response of DR1 cells to oxidative stress generated during hexadecane utilization. Increased membrane fluidity in the presence of red clay was confirmed by fatty acid methyl ester analysis at different growth phases, suggesting that enhanced growth on hexadecane could be due to increased uptake of hexadecane coupled with upregulation of downstream metabolism and oxidative stress defense. The monitoring of the bacterial community in soil with red clay for a year revealed that red clay stabilized the community structure.

  19. The statistical mechanics of complex signaling networks: nerve growth factor signaling.

    Science.gov (United States)

    Brown, K S; Hill, C C; Calero, G A; Myers, C R; Lee, K H; Sethna, J P; Cerione, R A

    2004-12-01

    The inherent complexity of cellular signaling networks and their importance to a wide range of cellular functions necessitates the development of modeling methods that can be applied toward making predictions and highlighting the appropriate experiments to test our understanding of how these systems are designed and function. We use methods of statistical mechanics to extract useful predictions for complex cellular signaling networks. A key difficulty with signaling models is that, while significant effort is being made to experimentally measure the rate constants for individual steps in these networks, many of the parameters required to describe their behavior remain unknown or at best represent estimates. To establish the usefulness of our approach, we have applied our methods toward modeling the nerve growth factor (NGF)-induced differentiation of neuronal cells. In particular, we study the actions of NGF and mitogenic epidermal growth factor (EGF) in rat pheochromocytoma (PC12) cells. Through a network of intermediate signaling proteins, each of these growth factors stimulates extracellular regulated kinase (Erk) phosphorylation with distinct dynamical profiles. Using our modeling approach, we are able to predict the influence of specific signaling modules in determining the integrated cellular response to the two growth factors. Our methods also raise some interesting insights into the design and possible evolution of cellular systems, highlighting an inherent property of these systems that we call 'sloppiness.'

  20. Theoretical study on the 4-angstrom carbon nanotube growth mechanisms inside microporous aluminum phosphate-5

    Science.gov (United States)

    Liu, Jianwen

    The growth mechanisms of mono-sized and parallel-aligned single wall carbon nanotube (CNT) in the microporous channels of AlPO4-5 are investigated by density functional theory calculations. Detailed mechanisms are proposed for the decomposition of TPA, the formation of aromatic ring, and the growth of carbon nanotubes. In the first part, the mechanisms for the dissociation of TPA are studied under three types of conditions. The unimolecular dissociation is initiated by the breaking of either the N-Calpha and Calpha -Cbeta bonds and leads to many complicated processes. Within the confined space inside neutral zeolite channels, the diffusion of H radicals enhances a cycle of reactions, which accounts for the experimental observation of dipropylamine and monopropylamine. In the presence of an acidic site, the dissociation of TPA goes through catalyzed successive steps to produce ammonia and propylene molecules. In the second part, A T5 cluster model is used to investigate mechanisms of propylene aromatization to benzene, which involves chemisorption, dimerization, cyclization and dehydrogenation. Propylene can be chemisorbed to form two distinct products, n-propoxide and i-propoxide, which can further be dimerizated to form longer chain olefins 1-hexene and 2-hexene (from n-propoxide), and 4-methyl-1-pentene and 4-methyl-2-penetene (from i-propoxide). Initiated by H2 elimination, these dimerization products can further go through cyclization process to generated either 6-member ring cyclohexene or 5-member ring methyl-cyclopentene. Catalyzed by zeolite, cyclohexene can directly dehydrogenate to form benzene whereas methyl-cyclopentene can dehydrogenate to form fulven, an isomer to benzene. Under acidic zeolite environment, a fulvene can readily be transformed to the thermodynamically more stable benzene. In the last part, two distinct paths are proposed to investigate the carbon nanotube growth mechanism using benzene as the growth seed and propylene as carbon

  1. New AFM Techniques for Investigating Molecular Growth Mechanisms of Protein Crystals

    Science.gov (United States)

    Li, Huayu; Nadarajah, Arunan; Konnert, John H.; Pusey, Marc L.

    1998-01-01

    Atomic Force Microscopy (AFM) has emerged as a powerful technique for investigating protein crystal growth. Earlier AFM studies were among the first to demonstrate that these crystals grew by dislocation and 2D nucleation growth mechanisms [1]. These investigations were restricted to the micron range where only surface features, such as dislocation hillocks and 2D islands are visible. Most AFM instruments can scan at higher resolutions and have the potential to resolve individual protein molecules at nanometer ranges. Such scans are essential for determining the molecular packing arrangements on crystal faces and for probing the growth process at the molecular level. However, at this resolution the AFM tip influences the image produced, with the resulting image being a convolution of the tip shape and the surface morphology [2]. In most studies this problem is resolved by deconvoluting the image to obtain the true surface morphology. Although deconvolution routines work reasonably well for simple one- dimensional shapes, for complex surfaces this approach does not produce accurate results. In this study we devised a new approach which takes advantage of the precise molecular order of crystal surfaces, combined with the knowledge of individual molecular shapes from the crystallographic data of the protein and the AFM tip shape. This information is used to construct expected theoretical AFM images by convoluting the tip shape with the constructed crystal surface shape for a given surface packing arrangement. By comparing the images from actual AFM scans with the constructed ones for different possible surface packing arrangements, the correct packing arrangement can be conclusively determined. This approach was used in this study to determine the correct one from two possible packing arrangements on (I 10) faces of tetragonal lysozyme crystals. Another novel AFM technique was also devised to measure the dimension of individual growth units of the crystal faces

  2. Characterization of single phase copper selenide nanoparticles and their growth mechanism

    Science.gov (United States)

    Patidar, D.; Saxena, N. S.

    2012-03-01

    The high quality Cu3Se2 phase of copper selenide nanoparticles was synthesized through the solution-phase chemical reaction between copper and selenium. In this synthesis process, hydrazine hydrate acts as reducing agent whereas ethylene glycol controls the nucleation and growth of particles. An effort has been made to explain the growth mechanism to form copper selenide nanoparticles through the coordination of selenium to the Cu2+ complexes with OH groups of ethylene glycol. Result indicates the formation of Cu3Se2 single phase nanoparticles. The particles with the average particle size 25 nm are spherical in shape having tetragonal structure. The particles are well crystallized having 94% degree of crystallinity. An effort has also been made to determine the energy band gap of copper selenide nanoparticles through the absorption spectra.

  3. Synthesis of ZnO nanosheets via electrodeposition method and their optical properties, growth mechanism

    Science.gov (United States)

    Yang, Jun; Wang, Yongqian; Kong, Junhan; Jia, Hanxiang; Wang, Zhengshu

    2015-08-01

    ZnO nanosheets were prepared by electrochemical deposition method at 80 °C on seeded Indium Tin Oxide conducting glass substrates. The seed layer was coated on ITO by spin coating and annealed at 350 °C for 30 min prior to electrochemical deposition growth. X-ray diffraction patterns (XRD) and field emission scanning electron microscope (FESEM) images confirmed that the ZnO nanosheets consist of polycrystalline structures. Room temperature photoluminescence spectra (PL) of the ZnO nanosheets exhibited band-edge ultraviolet (UV) and visible emission (blue) indicating the ZnO nanosheets had excellent optical properties. The UV-Vis absorption spectrum of ZnO nanosheets was shown a strong absorption at 300 nm. The ZnO nanosheets structure demonstrated higher photocatalytic activity during degradation of aqueous methylene blue under visible-light irradiation. Moreover, the growth mechanism of the ZnO nanosheets had been discussed.

  4. Study of Growth Mechanism of Lysozyme Crystal by Batch Crystallization Method

    Institute of Scientific and Technical Information of China (English)

    Hai Liang CUI; Yong YU; Wan Chun CHEN; Qi KANG

    2006-01-01

    The lysozyme crystals were made by batch crystallization method and the distribution of aggregate in solution were measured by dynamic light scattering. The results showed that the dimension of aggregate increased with the increase of the concentration of lysozyme and NaC1,lysozyme molecules aggregated gradually in solution and finally arrived at balance each other.The higher the concentrations of lysozyme and NaC1 were, the faster the growth rate of (110) face was. The growth rates of lysozyme crystal were obtained by a Zeiss microscope, and the effective surface energy (α) of growing steps were calculated about 4.01×l0-8 J.cm-2 according to the model of multiple two-dimensional nucleation mechanism.

  5. Preparation, Growth Mechanisms and Characterizations of ZnSe Films via the Solvothermal Method

    Institute of Scientific and Technical Information of China (English)

    LI Huan-yong; JIE Wan-qi; ZHAO Hai-tao

    2006-01-01

    With diethylamine as a solvent, ZnSe films were formed on the Si substrate directly from zinc and selenium through the modified solvothermal method. The effects of holding temperature, deposition time and substrate surface treatment on the quality and morphologies of the ZnSe films were investigated. The growth mechanism of ZnSe films was proved to be a layer-nucleation growth process, which was tied in with the Stranski-Krastanov (SK) model. ZnSe films were identified by the X-ray diffraction pattern (XRD), the scanning electron microscope (SEM), the X-ray photoelectron spectroscope (XPS) and the photoluminescence (PL) techniques. The results indicate that the modified solvothermal method with diethylamine as a solvent is suitable to prepare high quality ZnSe films.

  6. Characterization of debond growth mechanism in adhesively bonded composites under mode II static and fatigue loadings

    Science.gov (United States)

    Mall, S.; Kochhar, N. K.

    1988-01-01

    An experimental investigation of adhesively bonded composite joint was conducted to characterize the debond growth mechanism under mode II static and fatigue loadings. For this purpose, end-notched flexure specimens of graphite/epoxy (T300/5208) adherends bonded with EC 3445 adhesive were tested. In all specimen tested, the fatigue failure occurred in the form of cyclic debonding. The present study confirmed the result of previous studies that total strain-energy-release rate is the driving parameter for cyclic debonding. Further, the debond growth resistance under cyclic loading with full shear reversal (i.e., stress ratio, R = -1) is drastically reduced in comparison to the case when subjected to cyclic shear loading with no shear reversal (i.e., R = 0.1).

  7. Growth dynamics and gas transport mechanism of nanobubbles in graphene liquid cells

    Science.gov (United States)

    Shin, Dongha; Park, Jong Bo; Kim, Yong-Jin; Kim, Sang Jin; Kang, Jin Hyoun; Lee, Bora; Cho, Sung-Pyo; Hong, Byung Hee; Novoselov, Konstantin S.

    2015-02-01

    Formation, evolution and vanishing of bubbles are common phenomena in nature, which can be easily observed in boiling or falling water, carbonated drinks, gas-forming electrochemical reactions and so on. However, the morphology and the growth dynamics of the bubbles at nanoscale have not been fully investigated owing to the lack of proper imaging tools that can visualize nanoscale objects in the liquid phase. Here, we demonstrate for the first time that the nanobubbles in water encapsulated by graphene membrane can be visualized by in-situ ultra-high vacuum transmission electron microscopy. Our microscopic results indicate two distinct growth mechanisms of merging nanobubbles and the existence of a critical radius of nanobubbles that determines the unusually long stability of nanobubbles. Interestingly, the gas transport through ultrathin water membranes at nanobubble interface is free from dissolution, which is clearly different from conventional gas transport that includes condensation, transmission and evaporation.

  8. Growth dynamics and gas transport mechanism of nanobubbles in graphene liquid cells.

    Science.gov (United States)

    Shin, Dongha; Park, Jong Bo; Kim, Yong-Jin; Kim, Sang Jin; Kang, Jin Hyoun; Lee, Bora; Cho, Sung-Pyo; Hong, Byung Hee; Novoselov, Konstantin S

    2015-02-02

    Formation, evolution and vanishing of bubbles are common phenomena in nature, which can be easily observed in boiling or falling water, carbonated drinks, gas-forming electrochemical reactions and so on. However, the morphology and the growth dynamics of the bubbles at nanoscale have not been fully investigated owing to the lack of proper imaging tools that can visualize nanoscale objects in the liquid phase. Here, we demonstrate for the first time that the nanobubbles in water encapsulated by graphene membrane can be visualized by in-situ ultra-high vacuum transmission electron microscopy. Our microscopic results indicate two distinct growth mechanisms of merging nanobubbles and the existence of a critical radius of nanobubbles that determines the unusually long stability of nanobubbles. Interestingly, the gas transport through ultrathin water membranes at nanobubble interface is free from dissolution, which is clearly different from conventional gas transport that includes condensation, transmission and evaporation.

  9. Expression and subcellular localization of mechano-growth factor in osteoblasts under mechanical stretch

    Institute of Scientific and Technical Information of China (English)

    ZHANG BingBing; XIAN ChengYu; LUO YanFeng; WANG YuanLiang

    2009-01-01

    Mechano-growth factor (MGF) is a stretch sensitive factor in myocytes, and it might also be produced by other mechanocytes under mechanical stimulation. In this study, both the mRNA and protein expression of MGF were detected in stretched osteoblasts. Quantitative analysis showed that a cyclic stretching stimulation caused a quick and sharp increase of MGF mRNA and protein expression from a low basal level under no stretch; the mRNA and protein levels respectively peaked in 6 and 12 h to 5 and 5.2 fold over the basal level and returned to normal by 24 h. The subcellular distribution of MGF protein was revealed by immunofluorescence analysis to be restricted to the nucleus. We concluded that cyclic stretching stimulation could induce MGF expression in osteoblasts in a pulsing fashion; and the nuclear distribution of MGF suggested that MGF might act in mechanocytes as an autocrine growth factor.

  10. Mechanical Stimulus Inhibits the Growth of a Bone Tissue Model Cultured In Vitro

    Institute of Scientific and Technical Information of China (English)

    Zong-ming Wan; Lu Liu; Jian-yu Li; Rui-xin Li; Yong Guo; Hao Li; Jian-ming Zhang; Xi-zheng Zhang

    2013-01-01

    Objectives To construct the cancellous bone explant model and a method of culturing these bone tissues in vitro, and to investigate the effect of mechanical load on growth of cancellous bone tissue in vitro. Methods Cancellous bone were extracted from rabbit femoral head and cut into 1-mm-thick and 8-mm-diameter slices under sterile conditions. HE staining and scanning electron microscopy were employed to identify the histomorphology of the model after being cultured with a new dynamic load and circulating perfusion bioreactor system for 0, 3, 5, and 7 days, respectively. We built a three-dimensional model using microCT and analyzed the loading effects using finite element analysis. The model was subjected to mechanical load of 1000, 2000, 3000, and 4000μεrespectively for 30 minutes per day. After 5 days of continuous stimuli, the activities of alkaline phosphatase (AKP) and tartrate-resistant acid phosphatase (TRAP) were detected. Apoptosis was analyzed by DNA ladder detection and caspase-3/8/9 activity detection. Results After being cultured for 3, 5, and 7 days, the bone explant model grew well. HE staining showed the apparent nucleus in cells at the each indicated time, and electron microscope revealed the living cells in the bone tissue. The activities of AKP and TRAP in the bone explant model under mechanical load of 3000 and 4000μεwere significantly lower than those in the unstressed bone tissues (all P Conclusions The cancellous bone explant model extracted from the rabbit femoral head could be alive at least for 7 days in the dynamic load and circulating perfusion bioreactor system, however, pathological mechanical load could affect the bone tissue growth by apoptosis in vitro. The differentiation of osteoblasts and osteoclasts might be inhibited after the model is stimulated by mechanical load of 3000 and 4000με.

  11. Size-dependent crystalline fluctuation and growth mechanism of bismuth nanoparticles under electron beam irradiation

    Science.gov (United States)

    Wu, Sujuan; Jiang, Yi; Hu, Lijun; Sun, Jianguo; Wan, Piaopiao; Sun, Lidong

    2016-06-01

    Advanced nanofabrication requires accurate tailoring of various nanostructures with the assistance of electron or ion beam irradiation. However, evolution of the nanostructures under the beam irradiation significantly affects the fabrication process. It is thus of paramount importance to study the evolution behaviors and growth mechanism of the nanostructures. In this study, bismuth nanoparticles were selected to investigate crystalline fluctuation under electron beam irradiation via transmission electron microscopy. The results disclose size-dependent crystalline fluctuation of the nanoparticles. The particles exhibit crystalline and non-crystalline features for sizes of above 15 and below 4 nm, respectively, while a mixture of the two states is observed with sizes in between. The crystalline fluctuation facilitates the growth process of the particles when a crystalline particle is in contact with another non-crystalline one. This is promising for applications in nanofabrication where high quality interfaces are desired between two joining parts.Advanced nanofabrication requires accurate tailoring of various nanostructures with the assistance of electron or ion beam irradiation. However, evolution of the nanostructures under the beam irradiation significantly affects the fabrication process. It is thus of paramount importance to study the evolution behaviors and growth mechanism of the nanostructures. In this study, bismuth nanoparticles were selected to investigate crystalline fluctuation under electron beam irradiation via transmission electron microscopy. The results disclose size-dependent crystalline fluctuation of the nanoparticles. The particles exhibit crystalline and non-crystalline features for sizes of above 15 and below 4 nm, respectively, while a mixture of the two states is observed with sizes in between. The crystalline fluctuation facilitates the growth process of the particles when a crystalline particle is in contact with another non

  12. Crack Growth Mechanisms under Anti-Plane Shear in Composite Laminates

    Science.gov (United States)

    Horner, Allison Lynne

    The research conducted for this dissertation focuses on determining the mechanisms associated with crack growth in polymer matrix composite laminates subjected to anti-plane shear (mode III) loading. For mode III split-beam test methods were proposed, and initial evaluations were conducted. A single test method was selected for further evaluation. Using this test method, it was determined that the apparent mode III delamination toughness, GIIIc , depended on geometry, which indicated a true material property was not being measured. Transverse sectioning and optical microscopy revealed an array of transverse matrix cracks, or echelon cracks, oriented at approximately 45° and intersecting the plane of the delamination. Subsequent investigations found the echelon array formed prior to the onset of planar delamination advance and that growth of the planar delamination is always coupled to echelon array formation in these specimens. The evolution of the fracture surfaces formed by the echelon array and planar delamination were studied, and it was found that the development was similar to crack growth in homogenous materials subjected to mode III or mixed mode I-III loading, although the composite laminate architecture constrained the fracture surface development differently than homogenous materials. It was also found that, for split-beam specimens such as those used herein, applying an anti-plane shear load results in twisting of the specimen's uncracked region which gives rise to a mixed-mode I-III load condition. This twisting has been related to the apparent mode III toughness as well as the orientation of the transverse matrix cracks. A finite element model was then developed to study the mechanisms of initial echelon array formation. From this, it is shown that an echelon array will develop, but will become self-limiting prior to the onset of planar delamination growth.

  13. Growth and nitrogen uptake characteristics reveal outbreak mechanism of the opportunistic macroalga Gracilaria tenuistipitata.

    Directory of Open Access Journals (Sweden)

    Chao Wang

    Full Text Available Macroalgae has bloomed in the brackish lake of Shenzhen Bay, China continuously from 2010 to 2014. Gracilaria tenuistipitata was identified as the causative macroalgal species. The aim of this study was to explore the outbreak mechanism of G. tenuistipitata, by studying the effects of salinity and nitrogen sources on growth, and the different nitrogen sources uptake characteristic. Our experimental design was based on environmental conditions observed in the bloom areas, and these main factors were simulated in the laboratory. Results showed that salinity 12 to 20 ‰ was suitable for G. tenuistipitata growth. When the nitrogen sources' (NH4+, NO3- concentrations reached 40 µM or above, the growth rate of G. tenuistipitata was significantly higher. Algal biomass was higher (approximately 1.4 times when cultured with NH4+ than that with NO3- addition. Coincidentally, macroalgal bloom formed during times of moderate salinity (∼12 ‰ and high nitrogen conditions. The NH4+ and NO3- uptake characteristic was studied to understand the potential mechanism of G. tenuistipitata bloom. NH4+ uptake was best described by a linear, rate-unsaturated response, with the slope decreasing with time intervals. In contrast, NO3- uptake followed a rate-saturating mechanism best described by the Michaelis-Menten model, with kinetic parameters Vmax = 37.2 µM g-1 DM h-1 and Ks = 61.5 µM. Further, based on the isotope 15N tracer method, we found that 15N from NH4+ accumulated faster and reached an atom% twice than that of 15N from NO3-, suggesting when both NH4+ and NO3- were available, NH4+ was assimilated more rapidly. The results of the present study indicate that in the estuarine environment, the combination of moderate salinity with high ammonium may stimulate bloom formation.

  14. Growth and nitrogen uptake characteristics reveal outbreak mechanism of the opportunistic macroalga Gracilaria tenuistipitata.

    Science.gov (United States)

    Wang, Chao; Lei, Anping; Zhou, Kai; Hu, Zhengyu; Hao, Wenlong; Yang, Junda

    2014-01-01

    Macroalgae has bloomed in the brackish lake of Shenzhen Bay, China continuously from 2010 to 2014. Gracilaria tenuistipitata was identified as the causative macroalgal species. The aim of this study was to explore the outbreak mechanism of G. tenuistipitata, by studying the effects of salinity and nitrogen sources on growth, and the different nitrogen sources uptake characteristic. Our experimental design was based on environmental conditions observed in the bloom areas, and these main factors were simulated in the laboratory. Results showed that salinity 12 to 20 ‰ was suitable for G. tenuistipitata growth. When the nitrogen sources' (NH4+, NO3-) concentrations reached 40 µM or above, the growth rate of G. tenuistipitata was significantly higher. Algal biomass was higher (approximately 1.4 times) when cultured with NH4+ than that with NO3- addition. Coincidentally, macroalgal bloom formed during times of moderate salinity (∼12 ‰) and high nitrogen conditions. The NH4+ and NO3- uptake characteristic was studied to understand the potential mechanism of G. tenuistipitata bloom. NH4+ uptake was best described by a linear, rate-unsaturated response, with the slope decreasing with time intervals. In contrast, NO3- uptake followed a rate-saturating mechanism best described by the Michaelis-Menten model, with kinetic parameters Vmax = 37.2 µM g-1 DM h-1 and Ks = 61.5 µM. Further, based on the isotope 15N tracer method, we found that 15N from NH4+ accumulated faster and reached an atom% twice than that of 15N from NO3-, suggesting when both NH4+ and NO3- were available, NH4+ was assimilated more rapidly. The results of the present study indicate that in the estuarine environment, the combination of moderate salinity with high ammonium may stimulate bloom formation.

  15. Functional Development of the Human Gastrointestinal Tract: Hormone- and Growth Factor-Mediated Regulatory Mechanisms

    Directory of Open Access Journals (Sweden)

    Daniel Ménard

    2004-01-01

    Full Text Available The present review focuses on the control of gastrointestinal (GI tract development. The first section addresses the differences in general mechanisms of GI development in humans versus rodents, highlighting that morphogenesis of specific digestive organs and the differentiation of digestive epithelia occur not only at different stages of ontogeny but also at different rates. The second section provides an overview of studies from the author's laboratory at the Université de Sherbrooke pertaining to the development of the human fetal small intestine and colon. While both segments share similar morphological and functional characteristics, they are nevertheless modulated by distinct regulatory mechanisms. Using the organ culture approach, the author and colleagues were able to establish that hormones and growth factors, such as glucocorticoids, epidermal growth factor, insulin and keratinocyte growth factor, not only exert differential effects within these two segments, they can also trigger opposite responses in comparison with animal models. In the third section, emphasis is placed on the functional development of human fetal stomach and its various epithelial cell types; in particular, the glandular chief cells responsible for the synthesis and secretion of gastric enzymes such as pepsinogen-5 and gastric lipase. Bearing in mind that limitations of available cell models have, until now, greatly impeded the comprehension of molecular mechanisms regulating human gastric epithelial cell functions, the last section focuses on new human gastric epithelial cell models recently developed in the author's laboratory. These models comprise a novel primary culture system of human fetal gastric epithelium including, for the first time, functional chief cells, and human gastric epithelium cell lines cloned from the parental NCI-N87 strain. These new cells lines could serve important applications in the study of pathogenic action and epithelial

  16. Vapor condensation growth and evolution mechanism of ZnO nanorod flower structures

    Energy Technology Data Exchange (ETDEWEB)

    Haldar, S.R.; Chini, T.K.; Bhunia, S. [Surface Physics Division, Saha Institute of Nuclear Physics, Kolkata (India); Nayak, A. [Department of Physics, Presidency College, Kolkata (India); Ray, S.K. [Department of Physics and Meteorology, Indian Institute of Technology, Kharagpur (India); Yamamoto, N. [Department of Physics, Tokyo Institute of Technology (Japan); CREST, Japan Science and Technology Agency, Tokyo (Japan)

    2010-02-15

    ZnO flower-like nanostructures were grown on Ge (100) substrate, by a modified chemical vapor condensation technique of zinc acetate dihydrate at 300 C, without using any catalyst. These self-organized three-dimensional nanostructures were composed of hierarchical arrangement of ZnO nanorods of diameter {proportional_to}50 nm around a common nucleus and were distributed uniformly over the entire substrate surface. Evolution study of these structures indicates that the growth begins with a two-dimensional planar arrangement of left angle 0001 right angle -oriented ZnO nanorods. With increasing growth time, the expanding adjacent two-dimensional growth fronts approach each other, followed by which, the formation of three-dimensional flower-like structures evolve. Surface diffusion mechanism seems to play an important role in forming these nanostructures, which has been discussed in detail. Elaborate electron microscopic (SEM, TEM) techniques have been used to investigate the growth characteristics of the flower structures. The photoluminescence measurements showed pure free excitonic transition centered at about 3.249 eV with full width at half-maximum of about 141 meV at 300 K, which blue shifted to 3.361 eV at 10 K with corresponding half width of 7 meV with no defect-related bandgap peak due to relatively low growth temperature. The optical emission area was imaged through a cathodoluminescence technique. Scanning electron micrograph of a typical ZnO nanorod flower structure grown at 300 C on Ge(100). (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  17. Large scale flows in transitional plane Couette flow: a key ingredient of the spot growth mechanism

    CERN Document Server

    Couliou, M

    2015-01-01

    Using Particle Image Velocimetry (PIV) in a new experimental plane Couette flow, we investigate the dynamics of turbulent patches invading formerly laminar flows. We evidence experimentally for the first time in this geometry the existence of large scale flows. These flows appear as soon as laminar and turbulent domains coexist. Spectral analysis is used to study the dynamical evolution of these large scales as well as that of the small scales associated with turbulence. We show that large-scale flows grow before turbulent spots develop and we point out the crucial role they play in the growth mechanism and possibly also in the emergence of organised patterns.

  18. Understanding the growth mechanism of carbon nanotubes via the ``cluster volume to surface area" model

    Science.gov (United States)

    Mandati, Sreekanth; Kunstmann, Jens; Boerrnert, Felix; Schoenfelder, Ronny; Ruemmeli, Mark; Kar, Kamal K.; Cuniberti, Gianaurelio

    2010-03-01

    The influence of mixed catalysts for the high yield production of carbon nanotubes (CNTs) has been studied systematically. Based on extensive experimental data a ``Catalyst Volume to Surface Area'' (CVSA) model was developed to understand the influence of the process parameters on the yield and CNT diameter distribution [1]. In our study, we present a refined version of the CVSA model developed by combining experiments and simulations. We discuss our current understanding of the growth mechanism and how the model might be used to increase CNT yields by using mixed catalysts.[4pt] [1] S. Tetali et al., ACS Nano (2009), DOI: 10.1021/nn9012548.

  19. On the growth mechanism of nanoparticles in plasma during pulsed laser ablation in liquids

    Science.gov (United States)

    Taccogna, F.; Dell’Aglio, M.; Rutigliano, M.; Valenza, G.; De Giacomo, A.

    2017-04-01

    Particle-in-cell methodology is applied to study the simultaneous charging and coagulation of a nanoparticle, taking into account the self-consistent dynamics of surrounding plasma induced by laser ablation in liquid. The model uses, as an input, plasma temperature and electron number density which are experimentally obtained by high temporally resolved optical emission spectroscopy of the laser-induced plasma in water. Results show the important role of ions in the growth process and of the atom-induced evaporation process for the final nanoparticle size. The competition between different mechanisms of nanoparticle formation in the laser-induced plasma is finally discussed.

  20. Growth Mechanism of Different Morphologies of ZnO Crystals Prepared by Hydrothermal Method

    Institute of Scientific and Technical Information of China (English)

    Hu Wang; Juan Xie; Kangping Yan; Ming Duan

    2011-01-01

    Different morphologies of zinc oxide (ZnO), including microrods, hexagonal pyramid-like rods and flower-like rod aggregates, had been synthesized, respectively, on glass substrates by controlling the reaction conditions (such as precursor concentration, reaction time and pH value) of hydrothermal method. The morphologies of the as-obtained ZnO were observed with scanning electron microscopy and transmission electron microscopy. Also, the crystalline natures of different ZnO crystals were analyzed with X-ray diffraction. The possible growth mechanism of ZnO crystals with different morphologies was discussed.

  1. Facile synthesis of gold wavy nanowires and investigation of their growth mechanism.

    Science.gov (United States)

    Zhu, Cun; Peng, Hsin-Chieh; Zeng, Jie; Liu, Jingyue; Gu, Zhongze; Xia, Younan

    2012-12-19

    We describe a synthesis of Au wavy nanowires in an aqueous solution in the presence of cetyltrimethylammonium bromide (CTAB). The resultant Au nanowires automatically separated from the solution and floated at the air/water interface. We investigated the formation mechanism by characterizing the samples obtained at different stages of the synthesis. Both particle attachment and cold welding were found to be involved in the formation of such nanowires. Based on X-ray photoelectron spectroscopy and thermogravimetric analysis, the CTAB molecules adsorbed on the surface of a Au nanostructure went through a change in structure from a bilayer to a monolayer, converting the Au surface from hydrophilic to hydrophobic. As a result, the Au wavy nanowires were driven to the air/water interface during the synthesis. This growth mechanism is potentially extendable to many other systems involving small surfactant molecules.

  2. Concentration Effect of Reducing Agents on Green Synthesis of Gold Nanoparticles: Size, Morphology, and Growth Mechanism

    Science.gov (United States)

    Kim, Hyun-seok; Seo, Yu Seon; Kim, Kyeounghak; Han, Jeong Woo; Park, Youmie; Cho, Seonho

    2016-04-01

    Under various concentration conditions of reducing agents during the green synthesis of gold nanoparticles (AuNPs), we obtain the various geometry (morphology and size) of AuNPs that play a crucial role in their catalytic properties. Through both theoretical and experimental approaches, we studied the relationship between the concentration of reducing agent (caffeic acid) and the geometry of AuNPs. As the concentration of caffeic acid increases, the sizes of AuNPs were decreased due to the adsorption and stabilizing effect of oxidized caffeic acids (OXCAs). Thus, it turns out that optimal concentration exists for the desired geometry of AuNPs. Furthermore, we investigated the growth mechanism for the green synthesis of AuNPs. As the caffeic acid is added and adsorbed on the surface of AuNPs, the aggregation mechanism and surface free energy are changed and consequently resulted in the AuNPs of various geometry.

  3. Molecular mechanisms for the evolution of bacterial morphologies and growth modes.

    Science.gov (United States)

    Randich, Amelia M; Brun, Yves V

    2015-01-01

    Bacteria exhibit a rich diversity of morphologies. Within this diversity, there is a uniformity of shape for each species that is replicated faithfully each generation, suggesting that bacterial shape is as selectable as any other biochemical adaptation. We describe the spatiotemporal mechanisms that target peptidoglycan synthesis to different subcellular zones to generate the rod-shape of model organisms Escherichia coli and Bacillus subtilis. We then demonstrate, using the related genera Caulobacter and Asticcacaulis as examples, how the modularity of the core components of the peptidoglycan synthesis machinery permits repositioning of the machinery to achieve different growth modes and morphologies. Finally, we highlight cases in which the mechanisms that underlie morphological evolution are beginning to be understood, and how they depend upon the expansion and diversification of the core components of the peptidoglycan synthesis machinery.

  4. Molecular mechanisms for the evolution of bacterial morphologies and growth modes

    Directory of Open Access Journals (Sweden)

    Amelia M Randich

    2015-06-01

    Full Text Available Bacteria exhibit a rich diversity of morphologies. Within this diversity, there is a uniformity of shape for each species that is replicated faithfully each generation, suggesting that bacterial shape is as selectable as any other biochemical adaptation. We describe the spatiotemporal mechanisms that target peptidoglycan synthesis to different subcellular zones to generate the rod-shape of model organisms Escherichia coli and Bacillus subtilis. We then demonstrate, using the related genera Caulobacter and Asticcacaulis as examples, how the modularity of the core components of the peptidoglycan synthesis machinery permits repositioning of the machinery to achieve different growth modes and morphologies. Finally, we highlight cases in which the mechanisms that underlie morphological evolution are beginning to be understood, and how they depend upon the expansion and diversification of the core components of the peptidoglycan synthesis machinery.

  5. The Effect of No Agricultural Productivity Growth on Future Land Use and Climate through Biogeophysical Mechanisms

    Science.gov (United States)

    Davies-Barnard, T.; Valdes, P. J.; Singarayer, J. S.; Jones, C.

    2012-12-01

    Future land use and the consequent land cover change will have a significant impact on future climate through biogeophysical (albedo, surface roughness and latent heat transfer, etc.) as well as biogeochemical (greenhouse gas emissions etc.) mechanisms. One of the major determinants of the extent of land use induced land cover change is the agricultural productivity growth within the socio-economic models used for developing the RCP scenarios. There are considerable uncertainties in the size of agricultural productivity under climate change, as yields are projected to vary spatially in signal and strength. Previous climate modeling work has considered the impacts to the carbon cycle of different levels of agricultural productivity growth, but has failed to consider the biogeophysical effects of the land use induced land cover change on climate. Here we examine the climate impacts of the assumption of agricultural productivity growth and business as usual land use. The effects are considered through the biogeophysical land use induced land cover change, using the Hadley Centre climate model HadGEM2. The model simulations use the set biogeochemical climate forcing of the RCP 4.5 scenario, but the biogeophysical land use change specification is altered over a 100 year simulation. Simulations are run with combinations of no land use change; standard RCP 4.5 land use change; business as usual land use change; and zero agricultural productivity growth. The key effect of no agricultural productivity growth is that more cropland is required to feed the same population, necessitating cropland expansion. The expansion of cropland and consequent deforestation increases the albedo and gives an extensive cooling effect in the northern hemisphere (up to 2°C). Differences in global mean temperature between the zero agricultural productivity growth with business as usual land use change specified run and the standard RCP 4.5 run are -0.2°C by 2040 and -0.7°C by 2100. There is

  6. Understanding the growth mechanism of graphene on Ge/Si(001) surfaces

    Science.gov (United States)

    Dabrowski, J.; Lippert, G.; Avila, J.; Baringhaus, J.; Colambo, I.; Dedkov, Yu S.; Herziger, F.; Lupina, G.; Maultzsch, J.; Schaffus, T.; Schroeder, T.; Kot, M.; Tegenkamp, C.; Vignaud, D.; Asensio, M.-C.

    2016-08-01

    The practical difficulties to use graphene in microelectronics and optoelectronics is that the available methods to grow graphene are not easily integrated in the mainstream technologies. A growth method that could overcome at least some of these problems is chemical vapour deposition (CVD) of graphene directly on semiconducting (Si or Ge) substrates. Here we report on the comparison of the CVD and molecular beam epitaxy (MBE) growth of graphene on the technologically relevant Ge(001)/Si(001) substrate from ethene (C2H4) precursor and describe the physical properties of the films as well as we discuss the surface reaction and diffusion processes that may be responsible for the observed behavior. Using nano angle resolved photoemission (nanoARPES) complemented by transport studies and Raman spectroscopy as well as density functional theory (DFT) calculations, we report the direct observation of massless Dirac particles in monolayer graphene, providing a comprehensive mapping of their low-hole doped Dirac electron bands. The micrometric graphene flakes are oriented along two predominant directions rotated by 30° with respect to each other. The growth mode is attributed to the mechanism when small graphene “molecules” nucleate on the Ge(001) surface and it is found that hydrogen plays a significant role in this process.

  7. Growth, spectral, structural and mechanical properties of struvite crystal grown in presence of sodium fluoride

    Indian Academy of Sciences (India)

    K Suguna; M Thenmozhi; C Sekar

    2012-08-01

    Struvite or magnesium ammonium phosphate hexahydrate (MAP) is one of the components of urinary stone. Struvite stones are commonly found in women. It forms in human beings as a result of urinary tract infection with urea splitting organisms. These stones can grow rapidly forming “staghorn-calculi”, which is a painful urological disorder. Therefore, it is of prime importance to study the growth and inhibition of struvite crystals. The growth inhibition effect of struvite crystals in sodium metasilicate (SMS) gel in the presence of sodium fluoride has been carried out. Crystals obtained have been analysed by powder and single crystal XRD, SEM–EDX, FTIR and TG–DTA. The results show that the presence of fluoride significantly affects struvite crystal growth and the characteristics of the crystallites produced. The mechanical property of the grown crystals has been investigated by Vickers microhardness testing. Work hardening coefficient was found to be >1.6 for both pure and doped samples which suggests that the crystal belongs to the family of soft material. Presence of sodium fluoride further softened the crystal.

  8. NASCRAC - A computer code for fracture mechanics analysis of crack growth

    Science.gov (United States)

    Harris, D. O.; Eason, E. D.; Thomas, J. M.; Bianca, C. J.; Salter, L. D.

    1987-01-01

    NASCRAC - a computer code for fracture mechanics analysis of crack growth - is described in this paper. The need for such a code is increasing as requirements grow for high reliability and low weight in aerospace components. The code is comprehensive and versatile, as well as user friendly. The major purpose of the code is calculation of fatigue, corrosion fatigue, or stress corrosion crack growth, and a variety of crack growth relations can be selected by the user. Additionally, crack retardation models are included. A very wide variety of stress intensity factor solutions are contained in the code, and extensive use is made of influence functions. This allows complex stress gradients in three-dimensional crack problems to be treated easily and economically. In cases where previous stress intensity factor solutions are not adequate, new influence functions can be calculated by the code. Additional features include incorporation of J-integral solutions from the literature and a capability for estimating elastic-plastic stress redistribution from the results of a corresponding elastic analysis. An example problem is presented which shows typical outputs from the code.

  9. Growth hormone stimulation of serum insulin concentration in cattle: nutritional dependency and potential mechanisms.

    Science.gov (United States)

    Feng, J; Gu, Z; Wu, M; Gwazdauskas, F C; Jiang, H

    2009-08-01

    Previous studies on the effect of growth hormone (GH) on serum insulin concentration in cattle had generated seemingly conflicting results, and little was known about the mechanism by which GH affects serum insulin concentration in cattle, if it does. In this study, we determined whether the effect of GH on serum insulin concentration in cattle could be affected by the nutritional levels of the animal and whether GH increased serum insulin concentration in cattle by directly stimulating insulin release or insulin gene expression in the pancreatic islets. Administration of recombinant bovine GH increased serum insulin concentration in nonlactating, nonpregnant beef cows fed a daily concentrate meal in addition to ad libitum hay, but it had no effect in those cows fed hay only. Both GH treatments for 1 and 24h increased insulin concentrations in cultures of pancreatic islets isolated from growing cattle. Growth hormone treatment for 24h increased insulin mRNA expression in cultured bovine pancreatic islets. Growth hormone treatment for 16h increased reporter gene expression directed by a approximately 1,500-bp bovine insulin gene promoter in a rat insulin-producing beta cell line. Taken together, these results suggest that exogenous GH can increase serum insulin concentration in cattle, but this effect depends on the nutritional levels of fed cattle, and that GH increases serum insulin concentration in cattle by stimulating both insulin release and insulin gene expression in the pancreatic islets.

  10. Mechanisms of surface alloy segregation on faceted core-shell nanowire growth

    Science.gov (United States)

    Zhang, Qian; Voorhees, Peter W.; Davis, Stephen H.

    2017-03-01

    A general two-dimensional faceted model that accounts for capillarity and deposition of an AxB 1-x alloy is developed for the growth of the shell on a hexagonal core. With this model, the surface alloy segregation and morphological evolution in the processes of the faceted core-shell nanowire growth are studied both analytically and numerically. Mechanisms of formation of Al-rich stripes along { 112 } facets and Al-poor quantum dots/wires at the apices of { 112 } facets are identified. More specifically, it is found that diffusion tends to move the atoms from { 112 } facets to { 110 } facets. The formation of Al-rich stripes along the { 112 } facets is due to the large ratios of mobilities of Al atoms and Ga atoms on { 112 } facets, even though Al atoms diffuse slower than Ga on the { 110 } facets. In addition, the difference of interaction parameters in the enthalpy on different facets can also lead to lines of enhanced concentration of Al behind { 112 } facets. If the attachment rates of Al on the { 112 } facets are smaller than that on { 110 } facets, Al-poor dots will grow at the end of the Al-rich stripes because the growth process switches from diffusion dominant to deposition dominant when the size of the nanowire gets large. Moreover, influences of different parameters on the distribution of concentrations of the atoms in the shell are investigated in details.

  11. Influence of Ciglitazone on A549 Cells Growth in vitro and in vivo and Mechanism

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    The effect and mechanism of the ciglitazone on lung cancer cells A549 growth in vitro and in vivo were studied. Various concentrations of ciglitazone were added to the cultured A549 line, and the proliferation and differentiation of A549 cells were examined by MTT and cytometry analysis. A549 cells (1 × 106/mouse) were inoculated subcutaneously into 20 nude mice, which were randomly divided into two groups: the control group, the ciglitazone treated group. The weights of subcutaneous tumors were measured. The expression of cyclin D1 and P21 in the lung was detected by immohistochemistry and Western blot respectively. The results showed that the proliferation of A549 was inhibited significantly by ciglitazone in a dose- and time-dependent manner. There were more cells arrested in G1/G0 phase and the expression of PPARγ was markedly upregulated in ciglitazone-treated group. Direct injection of ciglitazone into A549-induced tumors could suppress tumor growth in nude mice and the growth inhibitory rate was 36 %. The expression of cyclin D1 was decreased and P21 increased significantly in ciglitazone-treated group as compared with control group. It was concluded that ciglitazone could inhibit A549 proliferation dose-dependently and time-dependently and induce differentiation, which might be related to the modulation of cell cycle interfered by PPARγ.

  12. Quantification of mechanical dyssynchrony in growth restricted fetuses and normal controls using speckle tracking echocardiography (STE).

    Science.gov (United States)

    Krause, Kristina; Möllers, Mareike; Hammer, Kerstin; Falkenberg, Maria Karina; Möllmann, Ute; Görlich, Dennis; Klockenbusch, Walter; Schmitz, Ralf

    2017-10-26

    To evaluate longitudinal mechanical dyssynchrony in normally grown fetuses by speckle tracking echocardiography (STE) and to compare longitudinal mechanical dyssynchrony in fetal growth restriction (FGR) with normal controls. A prospective study was performed on 30 FGR and 62 normally grown fetuses, including 30 controls matched by gestational age, using STE and a transversal four-chamber view. Data analysis was carried out with a high frame rate of about 175 frames/s. Dyssynchrony was analyzed offline with QLab 9 (Philips Medical Systems, Andover, MA, USA) as time differences between peaks in strain of both ventricles and the septum. Inter- and intraventricular and intraseptal dyssynchrony were obtained and inter- and intraobserver reliability was analyzed. Longitudinal mechanical dyssynchrony was feasible in all cases, with high inter- and intraobserver reliability. Levels of inter- and intraventricular dyssynchrony were higher in the FGR than in the control group. Speckle tracking echocardiography (STE) is a reliable technique for cardiac function assessment in the fetal heart. Interventricular dyssynchrony could be a potential parameter for early detection of subclinical myocardial dysfunction before other parameters demand intervention. The future clinical role of longitudinal mechanical dyssynchrony needs to be verified in larger studies and with a technique customized for prenatal echocardiography.

  13. Population ageing, policy reforms and economic growth in Japan: a computable OLG model with endogenous growth mechanism

    OpenAIRE

    Manabu Shimasawa

    2007-01-01

    We have developed a computable endogenous growth OLG model generated by the accumulation of human capital. To study whether policy reform against aging make any quantitative impacts through human capital formation on the Japanese economy and whether it has long-run effect, we simulate two policy change scenarios and compare the results of those with endogenous growth to those with exogenous growth. The results are very encouraging: (i) policy changes promote human capital accumulation and thu...

  14. Gallium-doped indium oxide nanoleaves: Structural characterization, growth mechanism and optical properties

    Science.gov (United States)

    Liu, Lizhu; Chen, Yiqing; Guo, Linliang; Guo, Taibo; Zhu, Yunqing; Su, Yong; Jia, Chong; Wei, Meiqin; Cheng, Yinfen

    2011-11-01

    The novel two-dimensional (2-D) Ga-doped In2O3 nanoleaves are synthesized by a simple one-step carbonthermal evaporation method using Cu-Sn alloy as the substrates. Two basic parts construct this leaf-like nanostructure: a long central trunk and two tapered nanoribbons in symmetric distribution in relation to the trunk. The Ga-In-O alloy particles are located at or close to the tips of the central trunks and serve as catalysts for the central trunk growth by the self-catalytic vapor-liquid-solid (VLS) mechanism. And the homoepitaxial growth of tapered nanoribbon on the surface of the central trunk can be explained by vapor-solid (VS) mechanism. The room-temperature photoluminescence (PL) measurement of this nanoscaled Ga-doped In2O3 transparent conducting oxide (TCO) detected two blue peaks located at 432 nm and 481 nm, respectively, which can be used by Ru-based dye and indicates potential application in dye-sensitized solar cells (DSSCs). The successful preparation of this novel 2-D Ga-doped In2O3 nanoleaves not only enriches the synthesis of TCO materials, but also provides new blocks in future architecture of functional nano-devices.

  15. Growth capacity and biochemical mechanisms involved in rhizobia tolerance to salinity and water deficit.

    Science.gov (United States)

    Mhamdi, Rakia; Nouairi, Issam; ben Hammouda, Thouraya; Mhamdi, Ridha; Mhadhbi, Haythem

    2015-04-01

    The aim of the present study was to evaluate abiotic stress tolerance of rhizobial strains belonging to Mesorhizobium, Sinorhizobium, and Rhizobium genera, as well as to investigate specie specific stress response mechanisms. Effect of NaCl and PEG on growth capacity, protein, lipid peroxydation (MDA), membrane fatty acid composition and antioxidant enzymes were investigated. Growth capacity and viability of overall rhizobia strains decreased proportionally to the increase of NaCl and PEG levels in the medium. Sinorhizobium strains appeared the most tolerant, where 4H41strain was able to grow at 800 mM NaCl and 40% PEG. On the other hand, growth of R. gallicum and M. mediterraneum was inhibited by 200 mM NaCl. The content of MDA was unchanged in Sinorhizobium strains under both stresses. For Mesorhizobium, only PEG treatment increased the content of MDA. Amount of the C19:0 cyclo fatty-acid was increased in both Sinorhizobium and Mesorhizobium tolerant strains. NaCl stress increased Superoxide dismutase (SOD) activity of overall species; especially the most tolerant strain 4H41. Both treatments increased catalase (CAT) activity in 4H41, TII7, and 835 strains. Obtained results suggest that major response of tolerant Sinorhizobium and Mesorhizobium strains to NaCl and PEG stresses is a preferential accumulation of the C19:0 cyclo fatty acid within bacterial membrane as mechanism to reduce fluidity and maintain integrity. Cell integrity and functioning is also assured by maintaining and/or increasing activity of SOD and CAT antioxidant enzymes for tolerant strains to omit structural and functional damages related to reactive oxygen species overproduced under stressful conditions.

  16. Three-dimensional analysis of the anatomical growth response of European conifers to mechanical disturbance.

    Science.gov (United States)

    Schneuwly, Dominique M; Stoffel, Markus; Dorren, Luuk K A; Berger, Frédéric

    2009-10-01

    Studies on tree reaction after wounding were so far based on artificial wounding or chemical treatment. For the first time, type, spread and intensity of anatomical responses were analyzed and quantified in naturally disturbed Larix decidua Mill., Picea abies (L.) Karst. and Abies alba Mill. trees. The consequences of rockfall impacts on increment growth were assessed at the height of the wounds, as well as above and below the injuries. A total of 16 trees were selected on rockfall slopes, and growth responses following 54 wounding events were analyzed on 820 cross-sections. Anatomical analysis focused on the occurrence of tangential rows of traumatic resin ducts (TRD) and on the formation of reaction wood. Following mechanical disturbance, TRD production was observed in 100% of L. decidua and P. abies wounds. The radial extension of TRD was largest at wound height, and they occurred more commonly above, rather than below, the wounds. For all species, an intra-annual radial shift of TRD was observed with increasing axial distance from wounds. Reaction wood was formed in 87.5% of A. alba following wounding, but such cases occurred only in 7.7% of L. decidua. The results demonstrate that anatomical growth responses following natural mechanical disturbance differ significantly from the reactions induced by artificial stimuli or by decapitation. While the types of reactions remain comparable between the species, their intensity, spread and persistence disagree considerably. We also illustrate that the external appearance of wounds does not reflect an internal response intensity. This study reveals that disturbance induced under natural conditions triggers more intense and more widespread anatomical responses than that induced under artificial stimuli, and that experimental laboratory tests considerably underestimate tree response.

  17. Growth process and mechanism of a multi-walled carbon nanotube nest deposited on a silicon nanoporous pillar array

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Weifen, E-mail: gingerwfj@yahoo.com.cn [Department of Mathematics and Information Science, North China Institute of Water Conservancy and Hydroelectric Power, No. 36 Beihuan Road, Zhengzhou 450011 (China); Jian Lv; Yang Xiaohui [Department of Mathematics and Information Science, North China Institute of Water Conservancy and Hydroelectric Power, No. 36 Beihuan Road, Zhengzhou 450011 (China); Li Xinjian [Department of Physics and Laboratory of Material Physics, Zhengzhou University, Zhengzhou 450052 (China)

    2010-03-01

    A large scale nest array of multi-walled carbon nanotubes (NACNTs) was grown on silicon nanoporous pillar array (Si-NPA) by thermal chemical vapor deposition. Through observing its macro/micromorphology and structure, ascertaining the catalyst component and its locations at different growth time by hiring field emission scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected area electron diffraction, the growth process was deduced. Its thermal properties were also investigated by using a thermogravimetric analyzer. Our experiments demonstrated that the CNTs growth by means of root-growth mechanism at the initial growth stage, then a continuous growth process with its tip open is suggested, finally, a schematic growth model of NACNT/Si-NPA was presented.

  18. Ultra thin films of gadolinium deposited by evaporation in ultra high vacuum conditions: Composition, growth and morphology

    Energy Technology Data Exchange (ETDEWEB)

    Herrera-Sancho, O.A.; Castro-Gonzalez, D.; Araya-Pochet, J.A. [Centro de Investigacion en Ciencia e Ingenieria de Materiales, Universidad de Costa Rica, 2060 San Pedro, San Jose (Costa Rica); Escuela de Fisica, Universidad de Costa Rica, 2060 San Pedro, San Jose (Costa Rica); Vargas-Castro, W.E., E-mail: william.vargascastro@ucr.ac.cr [Centro de Investigacion en Ciencia e Ingenieria de Materiales, Universidad de Costa Rica, 2060 San Pedro, San Jose (Costa Rica); Escuela de Fisica, Universidad de Costa Rica, 2060 San Pedro, San Jose (Costa Rica)

    2011-02-01

    Ultra-thin gadolinium films with thicknesses between 8 and 101 A were deposited on AT-cut crystalline quartz substrates under ultra high vacuum conditions, and subsequently subjected to composition and morphologic characterization through X-ray photo-spectroscopy analysis and atomic force microscopy. Oxygen contamination is found on the samples, and its amount is estimated in terms of the thickness of an oxygen layer over the gadolinium films after subtracting the contribution to the XPS spectra of the underlying background. Atomic force microscope pictures provide evidence of having metal island films, with two growing regimes: the Volmer-Weber mode for the thinner films considered and the Stranski-Krastanov growing mode for the thicker ones. From evaluation of the sticking coefficient, the shape of the islands is approximated in terms of oblate spheroid caps and variation of the contact angle with film mass thickness is reported.

  19. VO{sub 2} (A): Reinvestigation of crystal structure, phase transition and crystal growth mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Rao Popuri, Srinivasa [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara (Romania); Artemenko, Alla [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); Labrugere, Christine [CeCaMA, University of Bordeaux 1, ICMCB, 87 Avenue du Dr. A. Schweitzer, F-33608 Pessac (France); Miclau, Marinela [National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, 300224 Timisoara (Romania); Villesuzanne, Antoine [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France); Pollet, Michaël, E-mail: pollet@icmcb-bordeaux.cnrs.fr [ICMCB, CNRS, UPR 9048, F-33608 Pessac (France); University of Bordeaux, ICMCB, UPR 9048, F-33608 Pessac (France)

    2014-05-01

    Well crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal reaction in the presence of V{sub 2}O{sub 5} and oxalic acid. With the advantage of high crystalline samples, we propose P4/ncc as an appropriate space group at room temperature. From morphological studies, we found that the oriented attachment and layer by layer growth mechanisms are responsible for the formation of VO{sub 2} (A) micro rods. The structural and electronic transitions in VO{sub 2} (A) are strongly first order in nature, and a marked difference between the structural transition temperatures and electronic transitions temperature was evidenced. The reversible intra- (LTP-A to HTP-A) and irreversible inter- (HTP-A to VO{sub 2} (M1)) structural phase transformations were studied by in-situ powder X-ray diffraction. Attempts to increase the size of the VO{sub 2} (A) microrods are presented and the possible formation steps for the flower-like morphologies of VO{sub 2} (M1) are described. - Graphical abstract: Using a single step and template free hydrothermal synthesis, well crystallized VO{sub 2} (A) microrods were prepared and the P4/ncc space group was assigned to the room temperature crystal structure. Reversible and irreversible phase transitions among different VO{sub 2} polymorphs were identified and their progressive nature was highlighted. Attempts to increase the microrods size, involving layer by layer formation mechanisms, are presented. - Highlights: • Highly crystallized VO{sub 2} (A) microrods were grown via a single step hydrothermal process. • The P4/ncc space group was determined for VO{sub 2} (A) at room temperature. • The electronic structure and progressive nature of the structural phase transition were investigated. • A weak coupling between structural and electronic phase transitions was identified. • Different crystallite morphologies were discussed in relation with growth mechanisms.

  20. Shape, Thermodynamics, Kinetics and Growth Mechanisms of Metal and Bimetallic Nanoparticles

    Science.gov (United States)

    Peng, Lingxuan

    Metal and bimetallic nanoparticles are of interest and are widely used in various applications because of their unique optical, electronic, and catalytic properties, which differ from those of their bulk counterparts. Better understanding of the thermodynamic and kinetic properties of nanoparticles and their underlying growth mechanisms can serve as a basis for improving reproducibility and rational design of nanoparticle syntheses. The primary objective of this dissertation was to study the structural-related thermodynamic and kinetic properties of nanoparticles via the combination of experimental and theoretical techniques and to further unravel their underlying growth mechanisms. In this dissertation, the structure and elemental distribution of colloidally-synthesized bimetallic nanoparticles were characterized via scanning/transmission electron microscopy (S/TEM) and energy dispersive X-ray spectroscopy (EDX). In colloidally-synthesized bimetallic Pt/Pd nanoparticles, smooth composition gradients from the particle centers to their surfaces and corner enrichment of Pt were observed experimentally. A growth model was developed to demonstrate that the smooth composition gradients within the particles were the result of the difference in the deposition rate constants of Pd and Pt, causing Pd to deposit faster than Pt. The deposition rate constant ratio between Pd and Pt increased with total Pd and Pt precursor concentration. The corner Pt enrichment was a result of local thermodynamic control at the corners. At the nanoparticle corner, a Lyapunov stable solution could be achieved when the chemical potential at the corner equals the external chemical potential in the solution. This stable solution leads to size-independent corner rounding in colloidal synthesized nanoparticles. Strain-induced segregation in bimetallic multiply twinned particles, namely decahedral (Dh) and icosahedral (Ic) particles, was analyzed by an analytic first-order expansion within a

  1. [The skeletal regulating mechanisms and concepts in growth and development of cranial-facial bones and orthodontic treatment].

    Science.gov (United States)

    Chen, Song; Chen, Yang-xi

    2009-10-01

    There are three kinds of mechanisms regulating the growth and development of skeletal tissue: Bone growth, bone modeling and bone remodeling. However, in the current orthodontics literature, there continues to be substantial confusion regarding the usage of the term "bone remodeling". This article reviews the historical causes for this semantics problem and explains the difference between bone modeling and remodeling, as well as the detailed skeletal regulating mechanisms in the growth and development of cranial-facial bones and orthodontic treatment. At last, this article suggests Chinese orthodontists use the terms "bone modeling" and "bone remodeling" more precisely to avoid scientific confusion and barriers to scientific exchange with other biomedical disciplines.

  2. Auxin, ethylene and the regulation of root growth under mechanical impedance

    Science.gov (United States)

    Sharma, Rameshwar; Santisree, Parankusam; Nongmaithem, Sapana; Sreelakshmi, Yellamaraju

    2012-07-01

    Among the multitude functions performed by plant roots, little information is available about the mechanisms that allow roots to overcome the soil resistance, in order to grow in the soil to obtain water and nutrient. Tomato (Solanum lycopersicum) seedlings grown on horizontally placed agar plates showed a progressive decline in the root length with the increasing impedance of agar media. The incubation with 1-methylcyclopropane (1-MCP), an inhibitor of ethylene perception, led to aerial growth of roots. In contrast, in absence of 1-MCP control roots grew horizontally anchored to the agar surface. Though 1-MCP-treated and control seedlings showed differential ability to penetrate in the agar, the inhibition of root elongation was nearly similar for both treatments. While increased mechanical impedance also progressively impaired hypocotyl elongation in 1-MCP treated seedlings, it did not affect the hypocotyl length of control seedlings. The decline in root elongation was also associated with increased expression of DR5::GUS activity in the root tip signifying accumulation of auxin at the root tip. The increased expression of DR5::GUS activity in the root tip was also observed in 1-MCP treated seedlings, indicating independence of this response from ethylene signaling. Our results indicate operation of a sensing mechanism in root that likely operates independently of ethylene but involves auxin to determine the degree of impedance of the substratum.

  3. Cracks path growth in turbine blades with TBC under thermo – mechanical cyclic loadings

    Directory of Open Access Journals (Sweden)

    T. Sadowski

    2016-02-01

    Full Text Available Blades of combustion turbines are extremely loaded turbojet elements, which transmit operative energy onto a rotor. Experiences of many years indicate, that cracks initiation and propagation in the blades during the operation time can cause destruction not only of the engine, but sometimes an airplane. In high temperature one of the most often occuring interactions in the turbine engine are time variable force fields, caused by non-stationary flowing of an exhaust gas and aerodynamical interaction of the engine elements. The extremal thermo-mechanical loadings initiate gradual degradation process of the blades as a result of fatigue and material creep. More often Thermal Barrier Coatings (TBCs are applied on the turbine blade surface to provide protection not only against the high temperature but also against aggressive environment. The paper presents the advantages of applying of the TBC layers for increase of the cracks resistance to gradual degradation of the turbine blades. The level of save values of thermo-mechanical loading was estimated. Analysis of critical values of loading leading to crack initiation, further growth and the final blade fragmentation was performed. The most efforted places of the turbine blades were selected and crack paths due to thermo-mechanical cyclic loading were determined.

  4. Predictable 'meta-mechanisms' emerge from feedbacks between transpiration and plant growth and cannot be simply deduced from short-term mechanisms.

    Science.gov (United States)

    Tardieu, François; Parent, Boris

    2016-08-29

    Growth under water deficit is controlled by short-term mechanisms but, because of numerous feedbacks, the combination of these mechanisms over time often results in outputs that cannot be deduced from the simple inspection of individual mechanisms. It can be analysed with dynamic models in which causal relationships between variables are considered at each time-step, allowing calculation of outputs that are routed back to inputs for the next time-step and that can change the system itself. We first review physiological mechanisms involved in seven feedbacks of transpiration on plant growth, involving changes in tissue hydraulic conductance, stomatal conductance, plant architecture and underlying factors such as hormones or aquaporins. The combination of these mechanisms over time can result in non-straightforward conclusions as shown by examples of simulation outputs: 'over production of abscisic acid (ABA) can cause a lower concentration of ABA in the xylem sap ', 'decreasing root hydraulic conductance when evaporative demand is maximum can improve plant performance' and 'rapid root growth can decrease yield'. Systems of equations simulating feedbacks over numerous time-steps result in logical and reproducible emergent properties that can be viewed as 'meta-mechanisms' at plant level, which have similar roles as mechanisms at cell level.

  5. Expression of insulin-like growth factor I, insulin-like growth factor binding proteins, and collagen mRNA in mechanically loaded plantaris tendon

    DEFF Research Database (Denmark)

    Olesen, Jens L; Heinemeier, Katja M; Haddad, Fadia

    2006-01-01

    because they both are produced in fibroblast; however, the response of IGFBP-4 and -5 to mechanical loading and their role in IGF-I regulation in tendinous tissue are unknown. A splice variant of IGF-I, mechano-growth factor (MGF) is upregulated and known to be important for adaptation in loaded muscle...

  6. Reaction mechanisms in the organometallic vapor phase epitaxial growth of GaAs

    Science.gov (United States)

    Larsen, C. A.; Buchan, N. I.; Stringfellow, G. B.

    1988-01-01

    The decomposition mechanisms of AsH3, trimethylgallium (TMGa), and mixtures of the two have been studied in an atmospheric-pressure flow system with the use of D2 to label the reaction products which are analyzed in a time-of-flight mass spectrometer. AsH3 decomposes entirely heterogeneously to give H2. TMGa decomposes by a series of gas-phase steps, involving methyl radicals and D atoms to produce CH3D, CH4, C2H6, and HD. TMGa decomposition is accelerated by the presence of AsH3. When the two are mixed, as in the organometallic vapor phase epitaxial growth of GaAs, both compounds decompose in concert to produce only CH4. A likely model is that of a Lewis acid-base adduct that forms and subsequently eliminates CH4.

  7. Nucleation site and mechanism leading to growth of bulk-quantity Mn3O4 nanorods

    Science.gov (United States)

    Chen, Z. W.; Lai, J. K. L.; Shek, C. H.

    2005-05-01

    We report a simple and effective method for the generation of bulk-quantity nanorods of manganese oxide, Mn3O4, under surroundings of a suitable surfactant and alkaline solution. It is found that the Mn3O4 nanorod is smooth, straight, and that the geometrical shape is structurally perfect, which is produced with lengths from several hundreds nanometers to a few micrometers, and diameters range from 10nmto30nm. We amazedly found that the dripping speed of the NaOH solution plays an important role in formation of bulk-quantity Mn3O4 nanorods. The difference of dripping speed of the NaOH solution leads to a large difference of Mn3O4 morphologies, which is observed in the transmission electron microscopy images. The growth of the Mn3O4 nanorods is suggested first to follow a self-catalyzed solution-liquid-solid mechanism.

  8. Synthesis, growth, optical, mechanical and electrical properties of -lysine -lysinium dichloride nitrate (-LLDN) single crystal

    Indian Academy of Sciences (India)

    V Vasudevan; R Ramesh Babu; A Reicher Nelcy; G Bhagavannarayana; K Ramamurthi

    2011-06-01

    Semi-organic nonlinear optical material, -lysine -lysinium dichloride nitrate (2C6H15N2O$^{+}_{2}$.H+.NO$^{-}_{3}$.2Cl-) was synthesized at room temperature. Single crystals of -LLDN were grown by slow cooling solution growth technique. The grown crystal was confirmed by powder X-ray diffraction analysis. The crystalline perfection of the grown single crystal was characterized by high-resolution X-ray diffraction (HRXRD) studies. The cut-off wavelength was determined by UV-vis transmission spectral analysis. The frequency doubling of the grown crystal was confirmed by powder second harmonic generation (SHG) measurement. The refractive index and birefringence of the crystal were determined using He–Ne laser source. Mechanical property of the crystal was determined by Vickers hardness tester. The frequency and temperature dependence of dielectric constant (r), dielectric loss (tan ) and a.c. conductivity (ac) were also measured.

  9. Mechanism of the initial stages of nitrogen-doped single-walled carbon nanotube growth.

    Science.gov (United States)

    Susi, Toma; Lanzani, Giorgio; Nasibulin, Albert G; Ayala, Paola; Jiang, Tao; Bligaard, Thomas; Laasonen, Kari; Kauppinen, Esko I

    2011-06-21

    We have studied the mechanism of the initial stages of nitrogen-doped single-walled carbon nanotube growth illustrated for the case of a floating catalyst chemical vapor deposition system, which uses carbon monoxide (CO) and ammonia (NH(3)) as precursors and iron as a catalyst. We performed first-principles electronic-structure calculations, fully incorporating the effects of spin polarization and magnetic moments, to investigate the bonding and chemistry of CO, NH(3), and their fragments on a model Fe(55) icosahedral cluster. A possible dissociation path for NH(3) to atomic nitrogen and hydrogen was identified, with a reaction barrier consistent with an experimentally determined value we measured by tandem infrared and mass spectrometry. Both C-C and C-N bond formation reactions were found to be barrierless and exothermic, while a parasitic reaction of HCN formation had a barrier of over 1 eV.

  10. Growth, photoluminescence, thermal and mechanical behaviour of Ethyltriphenylphosphonium bromide dihydrate crystal

    Science.gov (United States)

    Parthasarathy, M.; Gopalakrishnan, R.

    2013-10-01

    Single crystal of Ethyltriphenylphosphonium bromide dihydrate (ETPB) was grown by slow evaporation solution growth technique. The grown crystal was confirmed by single crystal X-ray diffraction. The functional groups and vibrational frequencies were identified using FT-IR and FT-Raman spectral analyses. Optical properties were studied by UV-Visible and photoluminescence spectroscopic techniques to explore its efficacy towards device fabrication. Thermal characteristics of ETPB were studied using the TGA/DTA and DSC response curves. The mechanical behaviour of the grown crystal was studied using Vicker's microhardness tester and the work hardening coefficient was evaluated. The second harmonic generation of the title compound was tested by Kurtz-Perry powder technique.

  11. Syntrophic growth with direct interspecies electron transfer as the primary mechanism for energy exchange

    DEFF Research Database (Denmark)

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena; Aklujkar, Muktak

    2013-01-01

    Direct interspecies electron transfer (DIET) through biological electrical connections is an alternative to interspecies H2 transfer as a mechanism for electron exchange in syntrophic cultures. However, it has not previously been determined whether electrons received via DIET yield energy...... dehydrogenase, the pilus-associated c-type cytochrome OmcS and pili consistent with electron transfer via DIET. These results suggest that electrons transferred via DIET can serve as the sole energy source to support anaerobic respiration....... to support cell growth. In order to investigate this, co-cultures of Geobacter metallireducens, which can transfer electrons to wild-type G. sulfurreducens via DIET, were established with a citrate synthase-deficient G. sulfurreducens strain that can receive electrons for respiration through DIET only...

  12. Low-temperature catalyst activator: mechanism of dense carbon nanotube forest growth studied using synchrotron radiation

    Directory of Open Access Journals (Sweden)

    Akito Takashima

    2014-07-01

    Full Text Available The mechanism of the one-order-of-magnitude increase in the density of vertically aligned carbon nanotubes (CNTs achieved by a recently developed thermal chemical vapor deposition process was studied using synchrotron radiation spectroscopic techniques. In the developed process, a Ti film is used as the underlayer for an Fe catalyst film. A characteristic point of this process is that C2H2 feeding for the catalyst starts at a low temperature of 450°C, whereas conventional feeding temperatures are ∼800°C. Photoemission spectroscopy using soft and hard X-rays revealed that the Ti underlayer reduced the initially oxidized Fe layer at 450°C. A photoemission intensity analysis also suggested that the oxidized Ti layer at 450°C behaved as a support for nanoparticle formation of the reduced Fe, which is required for dense CNT growth. In fact, a CNT growth experiment, where the catalyst chemical state was monitored in situ by X-ray absorption spectroscopy, showed that the reduced Fe yielded a CNT forest at 450°C. Contrarily, an Fe layer without the Ti underlayer did not yield such a CNT forest at 450°C. Photoemission electron microscopy showed that catalyst annealing at the conventional feeding temperature of 800°C caused excess catalyst agglomeration, which should lead to sparse CNTs. In conclusion, in the developed growth process, the low-temperature catalyst activation by the Ti underlayer before the excess Fe agglomeration realised the CNT densification.

  13. Antiangiogenic mechanisms of PJ-8, a novel inhibitor of vascular endothelial growth factor receptor signaling.

    Science.gov (United States)

    Huang, Shiu-Wen; Lien, Jin-Cherng; Kuo, Sheng-Chu; Huang, Tur-Fu

    2012-05-01

    Angiogenesis occurs not only during tissue growth and development but also during wound healing and tumor progression. Angiogenesis is a balanced process controlled by proangiogenic and antiangiogenic molecules. As a critical factor in the induction of angiogenesis, vascular endothelial growth factor (VEGF) has become an attractive target for antiangiogenic and cancer therapeutic agents. In an effort to develop novel inhibitors to block VEGF signaling, we selected Pj-8, a benzimidazole derivative, and investigated its inhibitory mechanisms in human umbilical vascular endothelial cells (HUVECs). Pj-8 concentration-dependently inhibited VEGF-induced proliferation, migration and tube formation of HUVECs. Pj-8 also suppressed VEGF-induced microvessel sprouting from aortic rings ex vivo and suppressed neovascularization of implanted matrigel plugs in vivo. Pj-8 inhibited VEGF-induced phosphorylation of VEGF receptor (VEGFR) 2 and the downstream protein kinases, including Akt, focal adhesion kinase, extracellular signal-regulated kinases and Src. Results from in vitro kinase assay further demonstrated that Pj-8 suppressed the kinase activity of 3-phosphoinositide-dependent kinase 1 (PDK1). Using xenograft tumor angiogenesis model, Pj-8 markedly eliminated tumor-associated angiogenesis. Taken together, our findings suggest that Pj-8 inhibits VEGF and tumor cells MDA-MB-231-induced angiogenesis, and it may be a potential drug candidate in anticancer therapy. Downregulation of VEGFR2-mediated signaling may contribute to its antiangiogenic actions.

  14. Fundamental studies of growth mechanisms in physical vapour deposition of aluminium

    CERN Document Server

    Knorr, N J

    2000-01-01

    temperature could be independently controlled due to the low deposition rate of the aluminium. The depositions were performed in a UHV environment to ensure that film growth was not mediated by contamination. The ion energy range used was 10-75eV and the substrate temperature varied from -100 deg C to 200 deg C. The depositions were onto silicon (100) with a native oxide surface, except for a set of depositions which were performed on to silicon with the native oxide surface removed. The cleanliness of the depositions was verified using in-situ XPS analysis and after deposition the structure of the aluminium films was inferred from measurements using SEM, TEM, AFM XRD and Nano-indendation. This information allowed the mechanisms of growth of the aluminium films to be investigated. In addition to the extensive array of IBDR depositions a series of aluminium films were deposited using evaporation and sputtering. These films were grown at substrate temperatures between room temperate and 200 deg C. The use of ev...

  15. Green synthesis of Au nanoparticles using potato extract: stability and growth mechanism

    Science.gov (United States)

    Castillo-López, D. N.; Pal, U.

    2014-08-01

    We report on the synthesis of spherical, well-dispersed colloidal gold nanoparticles of 17.5-23.5 nm average sizes in water using potato extract (PE) both as reducing and stabilizing agent. The effects of PE content and the pH value of the reaction mixture have been studied. Formation and growth dynamics of the Au nanoparticles in the colloids were studied using transmission electron microscopy and UV-Vis optical absorption spectroscopy techniques. While the reductor content and, hence, the nucleation and growth rates of the nanoparticles could be controlled by controlling the PE content in the reaction solution, the stability of the nanoparticles depended strongly on the pH of the reaction mixture. The mechanisms of Au ion reduction and stabilization of Au nanoparticles by potato starch have been discussed. The use of common natural solvent like water and biological reductor like PE in our synthesis process opens up the possibility of synthesizing Au nanoparticles in fully green (environmental friendly) way, and the Au nanoparticles produced in such way should have good biocompatibility.

  16. Strong magnetic field-assisted growth of carbon nanofibers and its microstructural transformation mechanism

    Science.gov (United States)

    Luo, Chengzhi; Fu, Qiang; Pan, Chunxu

    2015-03-01

    It is well-known that electric and magnetic fields can control the growth direction, morphology and microstructure of one-dimensional carbon nanomaterials (1-DCNMs), which plays a key role for its potential applications in micro-nano-electrics and devices. In this paper, we introduce a novel process for controlling growth of carbon nanofibers (CNFs) with assistance of a strong magnetic field (up to 0.5 T in the center) in a chemical vapor deposition (CVD) system. The results reveal that: 1) The CNFs get bundled when grown in the presence of a strong magnetic field and slightly get aligned parallel to the direction of the magnetic field; 2) The CNFs diameter become narrowed and homogenized with increase of the magnetic field; 3) With the increase of the magnetic field, the microstructure of CNFs is gradually changed, i.e., the strong magnetic field makes the disordered ``solid-cored'' CNFs transform into a kind of bamboo-liked carbon nanotubes; 4) We propose a mechanism that the reason for these variations and transformation is due to diamagnetic property of carbon atoms, so that it has direction selectivity in the precipitation process.

  17. Subcellular localization and mechanism of secretion of vascular endothelial growth factor in human skeletal muscle.

    Science.gov (United States)

    Hoier, Birgitte; Prats, Clara; Qvortrup, Klaus; Pilegaard, Henriette; Bangsbo, Jens; Hellsten, Ylva

    2013-09-01

    The subcellular distribution and secretion of vascular endothelial growth factor (VEGF) was examined in skeletal muscle of healthy humans. Skeletal muscle biopsies were obtained from m.v. lateralis before and after a 2 h bout of cycling exercise. VEGF localization was conducted on preparations of teased muscle fibers by transmission electron microscopy (TEM) and confocal microscopy (CM). Muscle interstitial fluid was sampled from microdialysis probes placed in the thigh muscle. TEM and CM analysis revealed two primary sites of localization of VEGF: in vesicles located in the subsarcolemmal regions and between the contractile elements within the muscle fibers; and in pericytes situated on the skeletal muscle capillaries. Quantitation of the subsarcolemmal density of VEGF vesicles, calculated on top of myonuclei, in the muscle fibers revealed a ∼50% increase (P<0.05) after exercise. The observation of more VEGF vesicles close to sarcolemma after exercise, combined with a 5-fold increase (P<0.05) in VEGF in the interstitial fluid, suggest that VEGF-containing vesicles redistribute to sarcolemma and that VEGF is secreted to the extracellular fluid. This study provides the first evidence in humans for a mechanism by which skeletal muscle fibers can control capillary growth by releasing VEGF from intracellular vesicles during contraction.

  18. Microstructural mechanisms of cyclic deformation, fatigue crack initiation and early crack growth.

    Science.gov (United States)

    Mughrabi, Haël

    2015-03-28

    In this survey, the origin of fatigue crack initiation and damage evolution in different metallic materials is discussed with emphasis on the responsible microstructural mechanisms. After a historical introduction, the stages of cyclic deformation which precede the onset of fatigue damage are reviewed. Different types of cyclic slip irreversibilities in the bulk that eventually lead to the initiation of fatigue cracks are discussed. Examples of trans- and intercrystalline fatigue damage evolution in the low cycle, high cycle and ultrahigh cycle fatigue regimes in mono- and polycrystalline face-centred cubic and body-centred cubic metals and alloys and in different engineering materials are presented, and some microstructural models of fatigue crack initiation and early crack growth are discussed. The basic difficulties in defining the transition from the initiation to the growth of fatigue cracks are emphasized. In ultrahigh cycle fatigue at very low loading amplitudes, the initiation of fatigue cracks generally occupies a major fraction of fatigue life and is hence life controlling.

  19. An Exploration of Dynamics of the Moving Mechanism of the Growth Cone

    Directory of Open Access Journals (Sweden)

    Yun-Bo Duan

    2003-01-01

    Full Text Available A stochastic, nonlinear dynamic model is proposed to explain the growth cone at the tip of a cell process, such as a growing axon or dendrite of a neuron. The model explains the outward motion of the tip as an extension of the cytoskeleton, using the actin- myosin system as a molecular motor. The kinetic energy is supplied by heat from ATP hydrolysis in the form of random motion of water molecules embedding the actin- myosin. The mechanical structure is provided by the F-actin macromolecules forming a spiral filament. The myosin heads form a stochastic distribution of small spheres. They are attached by elastic springs to the spiral rods of the myosin filaments. Under thermal agitation the system sustains oscillation, which is directed by the interaction between the myosin heads and the actin filament. As the energy of oscillation is dissipated, the actin filament is moved toward the center of the growth cone. The joint probability density of movement of the actin filament is obtained by solving a non-stationary version of the FPK equation. By incorporating a probability distribution of actin filaments provided by the geometry of the tip, the directed motion of the tip is explained.

  20. Synthesis of nanostructured methotrexate/hydroxyapatite: Morphology control, growth mechanism, and bioassay explore.

    Science.gov (United States)

    Dai, Chao-Fan; Li, Shu-Ping; Li, Xiao-Dong

    2015-12-01

    In this study, a new structure of methotrexate/hydroxyapatite (MTX/HAp) nanorods via a facile hydrothermal route was reported. The as-synthesized samples were then characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis. In order to explore the formation mechanism, the effects of reaction time, MTX concentrations and addition of ethylene glycol (PEG) were emphatically examined. The results indicated that, with the increase in reaction time, the fibrous nanoparticles turned to needle-like and then to rod-like. Our study also proved that reaction time of 12h was enough for the full-growth of the nanostructure. Drug-loading capacities (AIn) rose dramatically in the first 12h and reached a plateau afterwards. Importantly, MTX played a critical role in the longitudinal growth of MTX/HAp nanostructure and polyethylene glyco (PEG) was a good dispersing agent to improve the monodispersity. As expected, the functional agent of MTX was served as both the target anticancer drug loaded in HAp and effective complex agents to modify and control the morphologies of MTX/HAp. Lastly, in vitro bioassay tests gave us evidence that obvious tumor inhibition can be achieved when MTX was hybridized with HAp.

  1. Segmentation of foreground apple targets by fusing visual attention mechanism and growth rules of seed points

    Energy Technology Data Exchange (ETDEWEB)

    Qu, W.; Shang, W.; Shao, Y.; Wang, D.; Yu, X.; Song, H.

    2015-07-01

    Accurate segmentation of apple targets is one of the most important problems to be solved in the vision system of apple picking robots. This work aimed to solve the difficulties that background targets often bring to foreground targets segmentation, by fusing the visual attention mechanism and the growth rule of seed points. Background targets could be eliminated by extracting the ROI (region of interest) of apple targets; the ROI was roughly segmented on the HSV color space, and then each of the pixels was used as a seed growing point. The growth rule of the seed points was adopted to obtain the whole area of apple targets from seed growing points. The proposed method was tested with 20 images captured in a natural scene, including 54 foreground apple targets and approximately 84 background apple targets. Experimental results showed that the proposed method can remove background targets and focus on foreground targets, while the k-means algorithm and the chromatic aberration algorithm cannot. Additionally, its average segmentation error rate was 13.23%, which is 2.71% higher than that of the k-means algorithm and 2.95% lower than that of the chromatic aberration algorithm. In conclusion, the proposed method contributes to the vision system of apple-picking robots to locate foreground apple targets quickly and accurately under a natural scene. (Author)

  2. Corn-derived carbohydrate inositol hexaphosphate inhibits Barrett's adenocarcinoma growth by pro-apoptotic mechanisms.

    Science.gov (United States)

    McFadden, David W; Riggs, Dale R; Jackson, Barbara J; Cunningham, Cynthia

    2008-02-01

    Inositol hexaphosphate (IP6) is a naturally occurring polyphosphorylated carbohydrate that is found in food sources high in fiber content. IP6 has been reported to have significant inhibitory effects against a variety of primary tumors. We hypothesized that IP6 would inhibit the cell growth rate of Barrett's adenocarcinoma in vitro. Two Barrett's-associated adenocarcinoma cell lines, SEG-1 and BIC-1, were treated with IP6 at 0.5, 1.0 and 5.0 mM concentrations. Cell viability was measured by MTT assay. Apoptosis and necrosis were evaluated by the Annexin V FITC assay. Reductions (PIP6 decreased late apoptosis and necrosis in BIC cells, whereas in SEG-1 cells, early apoptosis, late apoptosis and necrosis were all increased by IP6. IP6 decreases cellular growth by pro-apoptotic mechanisms. Our findings suggest that IP6 has the potential to become an effective adjunct for Barrett's adenocarcinoma. Further studies are needed to evaluate safety and clinical utility of this agent in patients with Barrett's adenocarcinoma.

  3. Using hierarchical linear growth models to evaluate protective mechanisms that mediate science achievement

    Science.gov (United States)

    von Secker, Clare Elaine

    The study of students at risk is a major topic of science education policy and discussion. Much research has focused on describing conditions and problems associated with the statistical risk of low science achievement among individuals who are members of groups characterized by problems such as poverty and social disadvantage. But outcomes attributed to these factors do not explain the nature and extent of mechanisms that account for differences in performance among individuals at risk. There is ample theoretical and empirical evidence that demographic differences should be conceptualized as social contexts, or collections of variables, that alter the psychological significance and social demands of life events, and affect subsequent relationships between risk and resilience. The hierarchical linear growth models used in this dissertation provide greater specification of the role of social context and the protective effects of attitude, expectations, parenting practices, peer influences, and learning opportunities on science achievement. While the individual influences of these protective factors on science achievement were small, their cumulative effect was substantial. Meta-analysis conducted on the effects associated with psychological and environmental processes that mediate risk mechanisms in sixteen social contexts revealed twenty-two significant differences between groups of students. Positive attitudes, high expectations, and more intense science course-taking had positive effects on achievement of all students, although these factors were not equally protective in all social contexts. In general, effects associated with authoritative parenting and peer influences were negative, regardless of social context. An evaluation comparing the performance and stability of hierarchical linear growth models with traditional repeated measures models is included as well.

  4. A Three-Dimensional Cellular Automata Model Coupling Energy and Curvature-Driven Mechanisms for Austenitic Grain Growth

    Science.gov (United States)

    Wang, Min; Zhou, Jianxin; Yin, Yajun; Nan, Hai; Zhang, Dongqiao; Tu, Zhixin

    2017-10-01

    A 3D cellular automata model is used to simulate normal austenitic grain growth in this study. The proposed model considers both the curvature- and thermodynamics-driven mechanisms of growth. The 3D grain growth kinetics shows good agreement with the Beck equation. Moreover, the growth exponent and grain size distribution calculated by the proposed model coincides well with experimental and simulation results from other researchers. A linear relationship is found between the average relative grain size and the grain face number. More specifically, for average relative grain sizes exceeding 0.5, the number of faces increases linearly with relative grain size. For average relative grain sizes meaning by adjusting the actual temperature, space, and time for austenitic grain growth. The calibrated results are found to be in agreement with the simulation results from other research as well as the experimental results. By means of calibration of the proposed model, we can reliably predict the grain size in actual grain growth.

  5. IL-18 inhibits growth of murine orthotopic prostate carcinomas via both adaptive and innate immune mechanisms.

    Directory of Open Access Journals (Sweden)

    Brian Wan-Chi Tse

    Full Text Available Interleukin(IL-18 is a pleiotrophic cytokine with functions in immune modulation, angiogenesis and bone metabolism. In this study, the potential of IL-18 as an immunotherapy for prostate cancer (PCa was examined using the murine model of prostate carcinoma, RM1 and a bone metastatic variant RM1(BM/B4H7-luc. RM1 and RM1(BM/B4H7-luc cells were stably transfected to express bioactive IL-18. These cells were implanted into syngeneic immunocompetent mice, with or without an IL-18-neutralising antibody (αIL-18, SK113AE4. IL-18 significantly inhibited the growth of both subcutaneous and orthotopic RM1 tumors and the IL-18 neutralizing antibody abrogated the tumor growth-inhibition. In vivo neutralization of interferon-gamma (IFN-γ completely eliminated the anti-tumor effects of IL-18 confirming an essential role of IFN-γ as a down-stream mediator of the anti-tumor activity of IL-18. Tumors from mice in which IL-18 and/or IFN-γ was neutralized contained significantly fewer CD4(+ and CD8(+ T cells than those with functional IL-18. The essential role of adaptive immunity was demonstrated as tumors grew more rapidly in RAG1(-/- mice or in mice depleted of CD4(+ and/or CD8(+ cells than in normal mice. The tumors in RAG1(-/- mice were also significantly smaller when IL-18 was present, indicating that innate immune mechanisms are involved. IL-18 also induced an increase in tumor infiltration of macrophages and neutrophils but not NK cells. In other experiments, direct injection of recombinant IL-18 into established tumors also inhibited tumor growth, which was associated with an increase in intratumoral macrophages, but not T cells. These results suggest that local IL-18 in the tumor environment can significantly potentiate anti-tumor immunity in the prostate and clearly demonstrate that this effect is mediated by innate and adaptive immune mechanisms.

  6. Insulin-like Growth Factors as Regulators of Cell Motility Signaling Mechanisms.

    Science.gov (United States)

    Leventhal, P S; Feldman, E L

    1997-01-01

    Accumulating evidence indicates that the insulin-like growth factors (IGFs) function not only as mitogenic factors, but also as promoters of cell motility. In this article we review the current knowledge concerning the biochemical mechanisms whereby the IGFs activate cell motility. A key aspect of IGF-stimulated cell motility is the ability of IGFs to promote actin polymerization at the leading edge of the cell. This effect of the IGFs is mediated by activation and autophosphorylation of the type I IGF receptor, followed by docking of insulin receptor substrate-1 (IRS-1), stimulation of phosphatidylinositol (PI) 3-kinase, and possibly activation of the small GTPase Rac. IGF-stimulated cell motility also requires the formation of new adhesions, a process associated with tyrosine phosphorylation of paxillin and focal adhesion kinase. Determining the biochemical mechanisms by which IGFs regulate cell motility should allow for a better understanding of bone remodeling, neurite outgrowth, tumor metastasis, placental formation, and skin and blood vessel repair. (c) 1997, Elsevier Science Inc. (Trends Endocrinol Metab 1997;8:1-6).

  7. MECHANISM OF INITIATING ENDOGENOUS GROWTH IN PERIPHERAL REGIONS: IN CASE OF AUTONOMOUS TERRITORIAL UNIT GAGAUZIA

    Directory of Open Access Journals (Sweden)

    Alla LEVITSKAIA

    2015-12-01

    Full Text Available This study shows the possible mechanism of initiation endogenous growth in peripheral regions with poorly developed industry and innovation infrastructure (in case of Autonomous Territorial Unit Gagauzia, Republic of Moldova. Understanding of scientific problem has required an attempt to create the concept of Innovation Development Systems in peripheral rural areas of countries with emerging market economies identifing the goal of this study. The empirical research base consists of two units: statistical data and the results of special studies conducted by the author. The analysis used the theoretical and empirical methods, including synthesis, scientific generalization, analogy forecasting, observation, interviews, document analysis, comparative analysis of scientific sources and documentation of legal framework forregion, a secondary analysis of data definition obtained from other research groups. Proposed mechanism will demonstrate the impact of Innovation and Education Cluster activity on increasing the innovative entrepreneurship activity, building relationships between cluster members and other elements of the Regional Innovation System. Subsequent investigations can be dedicated to search relationships in the development of innovative activity between regions of the RM and other countries in which universities play an important role in building the regional innovation development.

  8. New animal model to study epigenetic mechanisms mediating altered gravity effects upon cell growth and morphogenesis

    Science.gov (United States)

    Grigoryan, Eleonora N.; Dvorochkin, Natasha; Radugina, Elena A.; Poplinskaya, Valentina; Novikova, Julia; Almeida, Eduardo

    The gravitational field and its variations act as a major environmental factor that can impact morphogenesis developing through epigenetic molecular mechanisms. The mechanisms can be thoroughly investigated by using adequate animal models that reveal changes in the morpho-genesis of a growing organ as a function of gravitational effects. Two cooperative US/Russian experiments on Foton-M2 (2005) and Foton-M3 (2007) were the first to demonstrate differences in the shape of regenerating tails of space-flown and ground control newts. The space-flown and aquarium (simulated microgravity) animals developed lancet-shaped tails whereas 1 g con-trols (kept in space-type habitats) showed hook-like regenerates. These visual observations were supported by computer-aided processing of the images and statistical analysis of the results. Morphological examinations and cell proliferation measurements using BrdU demon-strated dorsal-ventral asymmetry as well as enhanced epithelial growth on the dorsal area of regenerating tails in 1 g newts. These findings were reproduced in laboratory tests on newts kept at 1 g and in large water tanks at cut g. The 1 g animals showed statistically significant deviations of the lancet-like tail shape typically seen in aquarium animals. Such modifications were found as early as regeneration stages III-IV and proved irreversible. The authors believe that the above phenomenon detected in newts used in many space experiments can serve as an adequate model for studying molecular mechanisms underlying gravitational effects upon animal morphogenesis.

  9. A phenomenological model for mechanically mediated growth, remodeling, damage, and plasticity of gel-derived tissue engineered blood vessels.

    Science.gov (United States)

    Raykin, Julia; Rachev, Alexander I; Gleason, Rudolph L

    2009-10-01

    Mechanical stimulation has been shown to dramatically improve mechanical and functional properties of gel-derived tissue engineered blood vessels (TEBVs). Adjusting factors such as cell source, type of extracellular matrix, cross-linking, magnitude, frequency, and time course of mechanical stimuli (among many other factors) make interpretation of experimental results challenging. Interpretation of data from such multifactor experiments requires modeling. We present a modeling framework and simulations for mechanically mediated growth, remodeling, plasticity, and damage of gel-derived TEBVs that merge ideas from classical plasticity, volumetric growth, and continuum damage mechanics. Our results are compared with published data and suggest that this model framework can predict the evolution of geometry and material behavior under common experimental loading scenarios.

  10. Predicting the growth of S i3N4 nanowires by phase-equilibrium-dominated vapor-liquid-solid mechanism

    Science.gov (United States)

    Zhang, Yongliang; Cai, Jing; Yang, Lijun; Wu, Qiang; Wang, Xizhang; Hu, Zheng

    2017-09-01

    Nanomaterial synthesis is experiencing a profound evolution from empirical science ("cook-and-look") to prediction and design, which depends on the deep insight into the growth mechanism. Herein, we report a generalized prediction of the growth of S i3N4 nanowires by nitriding F e28S i72 alloy particles across different phase regions based on our finding of the phase-equilibrium-dominated vapor-liquid-solid (PED-VLS) mechanism. All the predictions about the growth of S i3N4 nanowires, and the associated evolutions of lattice parameters and geometries of the coexisting Fe -Si alloy phases, are experimentally confirmed quantitatively. This progress corroborates the general validity of the PED-VLS mechanism, which could be applied to the design and controllable synthesis of various one-dimensional nanomaterials.

  11. Heteroepitaxial growth of cadmium carbonate at dolomite and calcite surfaces: Mechanisms and rates

    Science.gov (United States)

    Callagon, Erika Blanca R.; Lee, Sang Soo; Eng, Peter J.; Laanait, Nouamane; Sturchio, Neil C.; Nagy, Kathryn L.; Fenter, Paul

    2017-05-01

    The systematic variation of rates and the mechanism of cadmium uptake on the (1 0 4) surface of dolomite (CaMg(CO3)2) were investigated using in situ and ex situ atomic force microscopy (AFM), ex situ specular X-ray reflectivity (XR), and ex situ X-ray fluorescence (XRF). Selected experiments were performed on the calcite (CaCO3) (1 0 4) surface for comparison. Aqueous solutions of CdCl2, CaCl2, and NaHCO3, undersaturated with respect to calcite and supersaturated with respect to otavite (CdCO3) and the (CdxCa1-x)CO3 solid solution, were reacted with dolomite surfaces for minutes to days. Calcite substrates were reacted with solutions containing 1-50 μM CdCl2, and with no added Ca or CO3. Thin carbonate films following the Stranski-Krastanov growth mode were observed on both substrates. Specular XR and XRF revealed the formation of nm-thick Cd-rich carbonate films that were structurally ordered with respect to the dolomite (1 0 4) plane. Epitaxial films adopted the calcite crystal structure with a d104-spacing (3.00 Å) larger than those of pure dolomite (2.88 Å) and otavite (2.95 Å) indicating either a solid solution with x ≈ 0.5, or a strained Cd-rich carbonate with a composition near that of otavite. The growth rate r of this phase increases with the initial supersaturation of the solution with respect to the solid solution, βmax , and follows the empirical relationship, as determined from XRF measurements, given by:

  12. Real-Time Imaging of Self-Organization and Mechanical Competition in Carbon Nanotube Forest Growth.

    Science.gov (United States)

    Balakrishnan, Viswanath; Bedewy, Mostafa; Meshot, Eric R; Pattinson, Sebastian W; Polsen, Erik S; Laye, Fabrice; Zakharov, Dmitri N; Stach, Eric A; Hart, A John

    2016-12-27

    The properties of carbon nanotube (CNT) networks and analogous materials comprising filamentary nanostructures are governed by the intrinsic filament properties and their hierarchical organization and interconnection. As a result, direct knowledge of the collective dynamics of CNT synthesis and self-organization is essential to engineering improved CNT materials for applications such as membranes and thermal interfaces. Here, we use real-time environmental transmission electron microscopy (E-TEM) to observe nucleation and self-organization of CNTs into vertically aligned forests. Upon introduction of the carbon source, we observe a large scatter in the onset of nucleation of individual CNTs and the ensuing growth rates. Experiments performed at different temperatures and catalyst particle densities show the critical role of CNT density on the dynamics of self-organization; low-density CNT nucleation results in the CNTs becoming pinned to the substrate and forming random networks, whereas higher density CNT nucleation results in self-organization of the CNTs into bundles that are oriented perpendicular to the substrate. We also find that mechanical coupling between growing CNTs alters their growth trajectory and shape, causing significant deformations, buckling, and defects in the CNT walls. Therefore, it appears that CNT-CNT coupling not only is critical for self-organization but also directly influences CNT quality and likely the resulting properties of the forest. Our findings show that control of the time-distributed kinetics of CNT nucleation and bundle formation are critical to manufacturing well-organized CNT assemblies and that E-TEM can be a powerful tool to investigate the mesoscale dynamics of CNT networks.

  13. Innovation of a Regulatory Mechanism Modulating Semi-determinate Stem Growth through Artificial Selection in Soybean.

    Directory of Open Access Journals (Sweden)

    Yunfeng Liu

    2016-01-01

    Full Text Available It has been demonstrated that Terminal Flowering 1 (TFL1 in Arabidopsis and its functional orthologs in other plants specify indeterminate stem growth through their specific expression that represses floral identity genes in shoot apical meristems (SAMs, and that the loss-of-function mutations at these functional counterparts result in the transition of SAMs from the vegetative to reproductive state that is essential for initiation of terminal flowering and thus formation of determinate stems. However, little is known regarding how semi-determinate stems, which produce terminal racemes similar to those observed in determinate plants, are specified in any flowering plants. Here we show that semi-determinacy in soybean is modulated by transcriptional repression of Dt1, the functional ortholog of TFL1, in SAMs. Such repression is fulfilled by recently enabled spatiotemporal expression of Dt2, an ancestral form of the APETALA1/FRUITFULL orthologs, which encodes a MADS-box factor directly binding to the regulatory sequence of Dt1. In addition, Dt2 triggers co-expression of the putative SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (GmSOC1 in SAMs, where GmSOC1 interacts with Dt2, and also directly binds to the Dt1 regulatory sequence. Heterologous expression of Dt2 and Dt1 in determinate (tfl1 Arabidopsis mutants enables creation of semi-determinacy, but the same forms of the two genes in the tfl1 and soc1 background produce indeterminate stems, suggesting that Dt2 and SOC1 both are essential for transcriptional repression of Dt1. Nevertheless, the expression of Dt2 is unable to repress TFL1 in Arabidopsis, further demonstrating the evolutionary novelty of the regulatory mechanism underlying stem growth in soybean.

  14. Growth mechanism evolvement influence on out-of-plane texture of Y2O3 seed layer for coated conductors

    Science.gov (United States)

    Xia, Yudong; Tao, Bowan; Xiong, Jie; Zhang, Xin; Zhao, Yong

    2016-03-01

    The Y2O3 films were deposited on biaxially textured Ni-5%W (NiW) substrates at different substrate temperatures (Ts). The microstructures of the Y2O3 films were characterized by X-ray diffraction (XRD) θ-2θ scans and ω-scans. The Y2O3 lattice parameters and residual stress were measured and calculated by high-resolution reciprocal space mapping (HR-RSM). Results showed that the Y2O3 films deposited on the NiW substrate exhibited different growth mechanisms at different Ts. At a low temperature range, the Y2O3 films grew via the tilt growth mechanism. The Y2O3 film grown at Ts=620 °C exhibited the highest residual stress and sharpest out-of-plane texture. With the increase in Ts, the growth mechanism changed to the epitaxial growth mechanism. At Ts=720 °C, the Y2O3 underwent epitaxial growth on the NiW substrates, and the out-of-plane textures of Y2O3 and NiW were almost identical.

  15. MBE-VLS grown zinc selenide and zinc sulfide nanowires: Growth mechanisms and photoluminescence properties

    Science.gov (United States)

    Chan, Siu Keung

    A lot of effort was recently devoted in realizing semiconducting nanowires (NWs) that are considered as a channel for electrons and photons no wider than a few thousand atoms. Such a one-dimensional structure will find potential applications in nano-optoelectronics and nano-photonics. The control of the growth orientation of NWs is particularly important because it will eventually affect their optical and transport properties. The ordering of NWs has also been a recent focus due to the fact that some of the above mentioned applications require the NWs fabricated in regular and periodic arrays. In this study, the growth of ZnSe and ZnS nanowires using the molecular beam epitaxy technique via the vapor-liquid-solid reaction with Au alloy droplets as the catalyst is successfully demonstrated. The nanowires resulting from this approach were found to orient along some specific crystallographic directions. Through detailed structural characterization, we have revealed that the preferred growth orientation of NWs depends on the chosen size of the catalyst and growth temperature. A phenomenological model based on the minimization of the total system energy of a nanowire was proposed to explain these observations. Based on these findings, we have successfully grown vertical ZnSe nanowires with a diameter around 10 nm on a GaAs(110) substrate. The interactions between the catalyst and the direct-contact materials (either the GaAs substrate or the ZnSe buffer) were analyzed in details. Through this study, it was found that thermal annealing of Au alloy catalyst droplets on a ZnSe buffer surface could result in nano-trenches along the directions. Based on the results obtained from a number of surface profiling and chemical analysis techniques, a model is proposed to describe the possible formation mechanisms of the observed nanotrenches. An ordered ZnSe NW array fabricated on a GaAs (111) substrate with a novel pre-patterning method associated with plasma etching is also

  16. Mechanisms of Neuroblastoma Cell Growth Inhibition by CARP-1 Functional Mimetics

    Science.gov (United States)

    Muthu, Magesh; Cheriyan, Vino T.; Munie, Sara; Levi, Edi; Frank, John; Ashour, Abdelkader E.; Singh, Mandip; Rishi, Arun K.

    2014-01-01

    Neuroblastomas (NBs) are a clinically heterogeneous group of extra cranial pediatric tumors. Patients with high-risk, metastatic NBs have a long-term survival rate of below 40%, and are often resistant to current therapeutic modalities. Due to toxic side effects associated with radiation and chemotherapies, development of new agents is warranted to overcome resistance and effectively treat this disease in clinic. CARP-1 functional mimetics (CFMs) are an emerging class of small molecule compounds that inhibit growth of diverse cancer cell types. Here we investigated NB inhibitory potential of CFMs and the molecular mechanisms involved. CFM-1, -4, and -5 inhibited NB cell growth, in vitro, independent of their p53 and MYCN status. CFM-4 and -5 induced apoptosis in NB cells in part by activating pro-apoptotic stress-activated kinases (SAPKs) p38 and JNK, stimulating CARP-1 expression and cleavage of PARP1, while promoting loss of the oncogenes C and N-myc as well as mitotic cyclin B1. Treatments of NB cells with CFM-4 or -5 also resulted in loss of Inhibitory κB (IκB) α and β proteins. Micro-RNA profiling revealed upregulation of XIAP-targeting miR513a-3p in CFM-4-treated NB, mesothelioma, and breast cancer cells. Moreover, exposure of NB and breast cancer cells to CFM-4 or -5 resulted in diminished expression of anti-apoptotic XIAP1, cIAP1, and Survivin proteins. Expression of anti-miR513a-5p or miR513a-5p mimic, however, interfered with or enhanced, respectively, the breast cancer cell growth inhibition by CFM-4. CFMs also impacted biological properties of the NB cells by blocking their abilities to migrate, form colonies in suspension, and invade through the matrix-coated membranes. Our studies indicate anti-NB properties of CFM-4 and 5, and suggest that these CFMs and/or their future analogs have potential as anti-NB agents. PMID:25033461

  17. Mechanism and kinetics of spontaneous nanotube growth driven by screw dislocations.

    Science.gov (United States)

    Morin, Stephen A; Bierman, Matthew J; Tong, Jonathan; Jin, Song

    2010-04-23

    Single-crystal nanotubes are commonly observed, but their formation is often not understood. We show that nanotube growth can be driven by axial screw dislocations: Self-perpetuating growth spirals enable anisotropic growth, and the dislocation strain energy overcomes the surface energy required for creating a new inner surface forming hollow tubes spontaneously. This was demonstrated through solution-grown zinc oxide nanotubes and nanowires by controlling supersaturation using a flow reactor and confirmed using microstructural characterization. The agreement between experimental growth kinetics and those predicted from fundamental crystal growth theories confirms that the growth of these nanotubes is driven by dislocations.

  18. Growth of tapered silica nanowires with a shallow U-shaped vapor chamber: Growth mechanism and structural and optical properties

    Science.gov (United States)

    Zhang, Danqing; Zhang, Xi; Wei, Jianglin; Gu, Gangxu; Xiang, Gang

    2015-04-01

    Traditional chemical vapor deposition method modified with a shallow U-shaped vapor chamber has been used to synthesize tapered bamboo shoot-like (BS-like) amorphous SiO2 nanowires (NWs) on Si (100) substrates without catalyst. The key innovation of this approach lies in a creation of swirling flow of the reactant vapors during the growth, which leads to a harvest of tapered silica NWs with lengths up to several microns. The unique structures and corresponding luminescence properties of the BS-like NWs were studied and their relationship with the evaporated active reactants was explored. A thermodynamic model that considers the critical role of the vapor flow during the growth is proposed to understand the structural and optical features. The shallow U-shaped vapor chamber-aided approach may provide a viable way to tailor novel structure of NWs for potential applications in nano-devices.

  19. Growth of tapered silica nanowires with a shallow U-shaped vapor chamber: Growth mechanism and structural and optical properties

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Danqing; Zhang, Xi, E-mail: xizhang@scu.edu.cn; Wei, Jianglin; Gu, Gangxu; Xiang, Gang, E-mail: gxiang@scu.edu.cn [Department of Physics, Sichuan University, Chengdu 610064 (China); Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu 610064 (China)

    2015-04-28

    Traditional chemical vapor deposition method modified with a shallow U-shaped vapor chamber has been used to synthesize tapered bamboo shoot-like (BS-like) amorphous SiO{sub 2} nanowires (NWs) on Si (100) substrates without catalyst. The key innovation of this approach lies in a creation of swirling flow of the reactant vapors during the growth, which leads to a harvest of tapered silica NWs with lengths up to several microns. The unique structures and corresponding luminescence properties of the BS-like NWs were studied and their relationship with the evaporated active reactants was explored. A thermodynamic model that considers the critical role of the vapor flow during the growth is proposed to understand the structural and optical features. The shallow U-shaped vapor chamber-aided approach may provide a viable way to tailor novel structure of NWs for potential applications in nano-devices.

  20. Mechanism-based model of parasite growth and dihydroartemisinin pharmacodynamics in murine malaria.

    Science.gov (United States)

    Patel, Kashyap; Batty, Kevin T; Moore, Brioni R; Gibbons, Peter L; Bulitta, Jürgen B; Kirkpatrick, Carl M

    2013-01-01

    Murine models are used to study erythrocytic stages of malaria infection, because parasite morphology and development are comparable to those in human malaria infections. Mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) models for antimalarials are scarce, despite their potential to optimize antimalarial combination therapy. The aim of this study was to develop a mechanism-based growth model (MBGM) for Plasmodium berghei and then characterize the parasiticidal effect of dihydroartemisinin (DHA) in murine malaria (MBGM-PK-PD). Stage-specific (ring, early trophozoite, late trophozoite, and schizont) parasite density data from Swiss mice inoculated with Plasmodium berghei were used for model development in S-ADAPT. A single dose of intraperitoneal DHA (10 to 100 mg/kg) or vehicle was administered 56 h postinoculation. The MBGM explicitly reflected all four erythrocytic stages of the 24-hour P. berghei life cycle. Merozoite invasion of erythrocytes was described by a first-order process that declined with increasing parasitemia. An efflux pathway with subsequent return was additionally required to describe the schizont data, thus representing parasite sequestration or trapping in the microvasculature, with a return to circulation. A 1-compartment model with zero-order absorption described the PK of DHA, with an estimated clearance and distribution volume of 1.95 liters h(-1) and 0.851 liter, respectively. Parasite killing was described by a turnover model, with DHA inhibiting the production of physiological intermediates (IC(50), 1.46 ng/ml). Overall, the MBGM-PK-PD described the rise in parasitemia, the nadir following DHA dosing, and subsequent parasite resurgence. This novel model is a promising tool for studying malaria infections, identifying the stage specificity of antimalarials, and providing insight into antimalarial treatment strategies.

  1. How vein sealing boosts fracture widening rates - The buckling-enhanced aperture growth mechanism for syn-tectonic veins

    Science.gov (United States)

    Nüchter, Jens-Alexander

    2017-01-01

    The paper introduces the mechanism of buckling-enhanced aperture growth for syn-tectonic veins that formed in simple-shear dominated kinematic frameworks in the middle or lower crust. Apart from the well understood concepts of fracture widening driven by effective tensile stresses, buckling-enhanced fracture aperture growth relates widening to active outward buckling of more viscous incipient cement layers precipitated as hydrothermal minerals for the pore fluid on the walls of juvenile syn-tectonic veins, driven by fracture-parallel compressive creep strain in the host rocks. Thus, the mechanism proposed here follows similar principles as tectonic folding, although important differences exist. Inspired by the structural record of low-aspect ratio veins exposed in HP/LT metamorphic rocks cropping out on south Evia island, Greece, generic numerical models are calculated to study development of buckling instabilities in such incompletely cemented veins and their impact on aperture growth rates. The models indicate (1) that aperture growth rates increase with increasing viscosity contrast between the host rocks and the cement layers, (2) an increase in the thickness of the cement layers cause acceleration of aperture growth, (3) that support of restraining forces at the vein tips offered by the host rocks against buckling of the cement layers cause fully compressive states of stress ahead the fracture tips, and (4) that fracture aperture growth is possible against fully compressive fracture-normal stresses. The buckling-enhanced vein aperture growth mechanism yields important implications for the maintenance and decay of fracture-bound permeability and for the mechanical state of the middle and lower crust in seismically active regions.

  2. Mechanism of Cancer Growth Suppression of Alpha-Fetoprotein Derived Growth Inhibitory Peptides (GIP): Comparison of GIP-34 versus GIP-8 (AFPep). Updates and Prospects

    Energy Technology Data Exchange (ETDEWEB)

    Mizejewski, Gerald J. [Division of Translational Medicine, Wadsworth Center, New York State Department of Health, Empire State Plaza, Albany, NY 12201 (United States)

    2011-06-20

    The Alpha-fetoprotein (AFP) derived Growth Inhibitory Peptide (GIP) is a 34-amino acid segment of the full-length human AFP molecule that inhibits tumor growth and metastasis. The GIP-34 and its carboxy-terminal 8-mer segment, termed GIP-8, were found to be effective as anti-cancer therapeutic peptides against nine different human cancer types. Following the uptake of GIP-34 and GIP-8 into the cell cytoplasm, each follows slightly different signal transduction cascades en route to inhibitory pathways of tumor cell growth and proliferation. The parallel mechanisms of action of GIP-34 versus GIP-8 are demonstrated to involve interference of signaling transduction cascades that ultimately result in: (1) cell cycle S-phase/G2-phase arrest; (2) prevention of cyclin inhibitor degradation; (3) protection of p53 from inactivation by phosphorylation; and (4) blockage of K{sup +} ion channels opened by estradiol and epidermal growth factor (EGF). The overall mechanisms of action of both peptides are discussed in light of their differing modes of cell attachment and uptake fortified by RNA microarray analysis and electrophysiologic measurements of cell membrane conductance and resistance. As a chemotherapeutic adjunct, the GIPs could potentially aid in alleviating the negative side effects of: (1) tamoxifen resistance, uterine hyperplasia/cancer, and blood clotting; (2) Herceptin antibody resistance and cardiac (arrest) arrhythmias; and (3) doxorubicin's bystander cell toxicity.

  3. Mechanism of Cancer Growth Suppression of Alpha-Fetoprotein Derived Growth Inhibitory Peptides (GIP: Comparison of GIP-34 versus GIP-8 (AFPep. Updates and Prospects

    Directory of Open Access Journals (Sweden)

    Gerald J. Mizejewski

    2011-06-01

    Full Text Available The Alpha-fetoprotein (AFP derived Growth Inhibitory Peptide (GIP is a 34-amino acid segment of the full-length human AFP molecule that inhibits tumor growth and metastasis. The GIP-34 and its carboxy-terminal 8-mer segment, termed GIP-8, were found to be effective as anti-cancer therapeutic peptides against nine different human cancer types. Following the uptake of GIP-34 and GIP-8 into the cell cytoplasm, each follows slightly different signal transduction cascades en route to inhibitory pathways of tumor cell growth and proliferation. The parallel mechanisms of action of GIP-34 versus GIP-8 are demonstrated to involve interference of signaling transduction cascades that ultimately result in: (1 cell cycle S-phase/G2-phase arrest; (2 prevention of cyclin inhibitor degradation; (3 protection of p53 from inactivation by phosphorylation; and (4 blockage of K+ ion channels opened by estradiol and epidermal growth factor (EGF. The overall mechanisms of action of both peptides are discussed in light of their differing modes of cell attachment and uptake fortified by RNA microarray analysis and electrophysiologic measurements of cell membrane conductance and resistance. As a chemotherapeutic adjunct, the GIPs could potentially aid in alleviating the negative side effects of: (1 tamoxifen resistance, uterine hyperplasia/cancer, and blood clotting; (2 Herceptin antibody resistance and cardiac (arrest arrhythmias; and (3 doxorubicin’s bystander cell toxicity.

  4. Cortical bone development under the growth plate is regulated by mechanical load transfer.

    NARCIS (Netherlands)

    Tanck, E.J.M.; Hannink, G.J.; Ruimerman, R.; Buma, P.; Burger, E.H.; Huiskes, R.

    2006-01-01

    Longitudinal growth of long bones takes place at the growth plates. The growth plate produces new bone trabeculae, which are later resorbed or merged into the cortical shell. This process implies transition of trabecular metaphyseal sections into diaphyseal sections. We hypothesize that the developm

  5. Electric fields induce curved growth of Enterobacter cloacae, Escherichia coli, and Bacillus subtilis cells: implications for mechanisms of galvanotropism and bacterial growth.

    OpenAIRE

    Rajnicek, A M; McCaig, C. D.; Gow, N.A.

    1994-01-01

    Directional growth in response to electric fields (galvanotropism) is known for eukaryotic cells as diverse as fibroblasts, neurons, algae, and fungal hyphae. The mechanism is not understood, but all proposals invoke actin either directly or indirectly. We applied electric fields to bacteria (which are inherently free of actin) to determine whether actin was essential for galvanotropism. Field-treated (but not control) Enterobacter cloacae and Escherichia coli cells curved rapidly toward the ...

  6. The Mechanical Study of Vascular Endothelial Growth Factor on the Prevention of Restenosis after Angioplasty

    Institute of Scientific and Technical Information of China (English)

    LIU Qigong; LU Zaiying; ZHOU Honglian; YAN Jin; ZHANG Weidong

    2001-01-01

    The mechanism of vascular endothelial growth factor (VEGF) on the prevention of restenosis after angioplasty was investigated. The cultured vascular endothelial cells (VEC) were incubated with the conditioned medium (CM) from vascular smooth muscle cells (VSMC) infected with recombinant adenoviruses containing the hVEGF165 gene. To observe the effects of VEGF on proliferation and NO, ET, 6-keto-PGF1α secretion of VEC, WST-1 method, Griess method and radioimmunoassay were used respectively. The PDGF-B mRNA transcription in VECs was detected by RT-PCR. It was showed that NO, 6-keto-PGF1α and OD value were markedly increased in a dosedependent manner in the VEGF-treated groups as compared with those in the control group, while ET and PDGF-B mRNA were significantly decreased in the VEGF-treated groups (P<0. 05 or P<0. 01). Adenovirus vector mediated hVEGF165 gene could promote the proliferation of VECs and im prove NO, PGI2 secretion, inhibit ET secretionand PDGF-B mRNA transcription in the VECs. Theabove results offered further theoretical evidence for VEGF on the prevention of restenosis after angioplasty.

  7. Nuclear functions and subcellular trafficking mechanisms of the epidermal growth factor receptor family

    Science.gov (United States)

    2012-01-01

    Accumulating evidence suggests that various diseases, including many types of cancer, result from alteration of subcellular protein localization and compartmentalization. Therefore, it is worthwhile to expand our knowledge in subcellular trafficking of proteins, such as epidermal growth factor receptor (EGFR) and ErbB-2 of the receptor tyrosine kinases, which are highly expressed and activated in human malignancies and frequently correlated with poor prognosis. The well-characterized trafficking of cell surface EGFR is routed, via endocytosis and endosomal sorting, to either the lysosomes for degradation or back to the plasma membrane for recycling. A novel nuclear mode of EGFR signaling pathway has been gradually deciphered in which EGFR is shuttled from the cell surface to the nucleus after endocytosis, and there, it acts as a transcriptional regulator, transmits signals, and is involved in multiple biological functions, including cell proliferation, tumor progression, DNA repair and replication, and chemo- and radio-resistance. Internalized EGFR can also be transported from the cell surface to several intracellular compartments, such as the Golgi apparatus, the endoplasmic reticulum, and the mitochondria, in addition to the nucleus. In this review, we will summarize the functions of nuclear EGFR family and the potential pathways by which EGFR is trafficked from the cell surface to a variety of cellular organelles. A better understanding of the molecular mechanism of EGFR trafficking will shed light on both the receptor biology and potential therapeutic targets of anti-EGFR therapies for clinical application. PMID:22520625

  8. Human imprinting anomalies in fetal and childhood growth disorders: clinical implications and molecular mechanisms.

    Science.gov (United States)

    Azzi, Salah; Brioude, Fréderic; Le Bouc, Yves; Netchine, Irène

    2014-01-01

    Genomic imprinting is among the most important epigenetic mechanisms whereby expression of a subset of genes is restricted to a single parental allele. Loss of imprinting (LOI) through hypo or hyper methylation is involved in various human syndromes. These LOI occur early during development and usually impair growth. Some imprinting syndromes are the consequences of genetic anomalies, such as uniparental disomies (UPD) or copy number variations (deletion or duplications) involving the imprinted domains; others are due to LOI at the imprinting control regions (ICR) regulating each domain. Imprinting disorders are phenotypically heterogeneous, although some share various common clinical features such that diagnosis may be difficult. Multilocus imprinting defects associated with several syndromes have been increasingly reported in recent years, although there are no obvious clinical differences between monolocus and multilocus LOI patients. Subsequently, some rare mutations of transacting factors have been identified in patients with multilocus imprinting defects but they do not explain the majority of the cases; this therefore implies that other factors are involved. By contrast, no mutation of a transacting factor has yet been identified in monolocus LOI. The effect of the environment on the regulation of imprinting is clearly illustrated by studies of assisted reproductive technology (ART). The regulation of imprinting is complex and involves a huge range of genetic and environmental factors; the identification of these factors will undoubtedly help to elucidate the regulation of imprinting and contribute to the understanding of imprinting disorders. This would be beneficial for diagnostics, clinical follow up and the development of treatment guidelines.

  9. Syntrophic growth with direct interspecies electron transfer as the primary mechanism for energy exchange.

    Science.gov (United States)

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena; Aklujkar, Muktak; Liu, Fanghua; Shrestha, Minita; Summers, Zarath M; Malvankar, Nikhil; Flores, Dan Carlo; Lovley, Derek R

    2013-12-01

    Direct interspecies electron transfer (DIET) through biological electrical connections is an alternative to interspecies H2 transfer as a mechanism for electron exchange in syntrophic cultures. However, it has not previously been determined whether electrons received via DIET yield energy to support cell growth. In order to investigate this, co-cultures of Geobacter metallireducens, which can transfer electrons to wild-type G. sulfurreducens via DIET, were established with a citrate synthase-deficient G. sulfurreducens strain that can receive electrons for respiration through DIET only. In a medium with ethanol as the electron donor and fumarate as the electron acceptor, co-cultures with the citrate synthase-deficient G. sulfurreducens strain metabolized ethanol as fast as co-cultures with wild-type, but the acetate that G. metallireducens generated from ethanol oxidation accumulated. The lack of acetate metabolism resulted in less fumarate reduction and lower cell abundance of G. sulfurreducens. RNAseq analysis of transcript abundance was consistent with a lack of acetate metabolism in G. sulfurreducens and revealed gene expression levels for the uptake hydrogenase, formate dehydrogenase, the pilus-associated c-type cytochrome OmcS and pili consistent with electron transfer via DIET. These results suggest that electrons transferred via DIET can serve as the sole energy source to support anaerobic respiration. © 2013 John Wiley & Sons Ltd and Society for Applied Microbiology.

  10. Mechanism of Elevated Vascular Endothelial Growth Factor Levels in Peritoneal Fluids from Patients with Endometriosis

    Institute of Scientific and Technical Information of China (English)

    刘义; 吕立群

    2004-01-01

    In order to investigate the mechanism of elevated vascular endothelial growth factor (VEGF) in peritoneal fluids from patients with endometriosis, macrophages were recovered from peritoneal fluids obtained at the time of diagnostic laparoscopy from infertile women with endometriosis (EMT group, n = 20) and without endometriosis (control group, n = 20). Macrophages were cultured in vitro. The VEGF levels of peritoneal fluid and the supernatant of macrophages culture were determined by enzyme linked immunoassay (ELISA). Meanwhile, the eutopic (n = 20) and ectopic endometrium (n=20) from endometriosis patients, and normal edometrium (n=20) from non-endometriosis patients were obtained for the analysis of VEGF expression by labeled Streptavidin Biotin (LSAB). It was found that VEGF levels in peritoneal fluid and macrophages culture supernatant were significantly higher in EMT group than in control group (P<0.01). In normal endometrium, VEGF showed a cyclic changes and similar in eutopic and ectopic endometrium from patients with endometriosis. There was no difference in the intensity of VEGF in endometrium between two groups within each menstrual phase. It is suggested that altered VEGF production by peritoneal macrophages and ectopic endometrium secretion may contribute to the elevated VEGF levels in the peritoneal fluid of patients with endometriosis.

  11. Analysis of trophic responses in lesioned brain: focus on basic fibroblast growth factor mechanisms

    Directory of Open Access Journals (Sweden)

    Chadi G.

    1998-01-01

    Full Text Available The actions of fibroblast growth factors (FGFs, particularly the basic form (bFGF, have been described in a large number of cells and include mitogenicity, angiogenicity and wound repair. The present review discusses the presence of the bFGF protein and messenger RNA as well as the presence of the FGF receptor messenger RNA in the rodent brain by means of semiquantitative radioactive in situ hybridization in combination with immunohistochemistry. Chemical and mechanical injuries to the brain trigger a reduction in neurotransmitter synthesis and neuronal death which are accompanied by astroglial reaction. The altered synthesis of bFGF following brain lesions or stimulation was analyzed. Lesions of the central nervous system trigger bFGF gene expression by neurons and/or activated astrocytes, depending on the type of lesion and time post-manipulation. The changes in bFGF messenger RNA are frequently accompanied by a subsequent increase of bFGF immunoreactivity in astrocytes in the lesioned pathway. The reactive astrocytes and injured neurons synthesize increased amount of bFGF, which may act as a paracrine/autocrine factor, protecting neurons from death and also stimulating neuronal plasticity and tissue repair

  12. A complex mechanism for HDGF-mediated cell growth, migration, invasion, and TMZ chemosensitivity in glioma.

    Science.gov (United States)

    Song, Ye; Hu, Zheng; Long, Hao; Peng, Yuping; Zhang, Xi'an; Que, Tianshi; Zheng, Shihao; Li, Zhiyong; Wang, Gang; Yi, Liu; Liu, Zhen; Fang, Weiyi; Qi, Songtao

    2014-09-01

    HDGF is overexpressed in gliomas as compared to normal brain. We therefore analyzed the molecular mechanisms of HDGF action in gliomas. HDGF was downregulated in normal brain tissue as compared to glioma specimens at both the mRNA and the protein levels. In glioma samples, increased HDGF expression was associated with disease progression. Knocking down HDGF expression not only significantly decreased cellular proliferation, migration, invasion, and tumorigenesis, but also markedly enhanced TMZ-induced cytotoxicity and apoptosis in glioma cells. Mechanistic analyses revealed that CCND1, c-myc, and TGF-β were downregulated after stable HDGF knockdown in the U251 and U87 glioma cells. HDGF knockdown restored E-cadherin expression and suppressed mesenchymal cell markers such as vimentin, β-catenin, and N-cadherin. The expression of cleaved caspase-3 increased, while Bcl-2 decreased in each cell line following treatment with shHDGF and TMZ, as compared to TMZ alone. Furthermore, RNAi-based knockdown study revealed that HDGF is probably involved in the activation of both the PI3K/Akt and the TGF-β signaling pathways. Together, our data suggested that HDGF regulates glioma cell growth, apoptosis and epithelial-mesenchymal transition (EMT) probably through the Akt and the TGF-β signaling pathways. These results provide evidence that targeting HDGF or its downstream targets may lead to novel therapies for gliomas.

  13. Nuclear functions and subcellular trafficking mechanisms of the epidermal growth factor receptor family

    Directory of Open Access Journals (Sweden)

    Wang Ying-Nai

    2012-04-01

    Full Text Available Abstract Accumulating evidence suggests that various diseases, including many types of cancer, result from alteration of subcellular protein localization and compartmentalization. Therefore, it is worthwhile to expand our knowledge in subcellular trafficking of proteins, such as epidermal growth factor receptor (EGFR and ErbB-2 of the receptor tyrosine kinases, which are highly expressed and activated in human malignancies and frequently correlated with poor prognosis. The well-characterized trafficking of cell surface EGFR is routed, via endocytosis and endosomal sorting, to either the lysosomes for degradation or back to the plasma membrane for recycling. A novel nuclear mode of EGFR signaling pathway has been gradually deciphered in which EGFR is shuttled from the cell surface to the nucleus after endocytosis, and there, it acts as a transcriptional regulator, transmits signals, and is involved in multiple biological functions, including cell proliferation, tumor progression, DNA repair and replication, and chemo- and radio-resistance. Internalized EGFR can also be transported from the cell surface to several intracellular compartments, such as the Golgi apparatus, the endoplasmic reticulum, and the mitochondria, in addition to the nucleus. In this review, we will summarize the functions of nuclear EGFR family and the potential pathways by which EGFR is trafficked from the cell surface to a variety of cellular organelles. A better understanding of the molecular mechanism of EGFR trafficking will shed light on both the receptor biology and potential therapeutic targets of anti-EGFR therapies for clinical application.

  14. Growth mechanism and magnetism in carbothermal synthesized Fe3O4 nanoparticles from solution combustion precursors

    Science.gov (United States)

    Wang, Xuanli; Qin, Mingli; Cao, Zhiqin; Jia, Baorui; Gu, Yueru; Qu, Xuanhui; Volinsky, Alex A.

    2016-12-01

    Magnetic Fe3O4 nanoparticles were prepared by carbothermal reduction using solution combustion synthesis precursors derived from ferric nitrate (oxidizer), glycine (fuel) and glucose (carbon source) mixed solution. In this paper, the growth mechanism and magnetism in Fe3O4 nanoparticles were investigated by adjusting the glucose content in precursor and the heat temperature in carbothermal process. The products were analyzed by X-ray diffraction, Field emission scanning electron microscopy, Infrared adsorption method and Vibrating sample magnetometry. The results revealed that the more amount of glucose, the earlier Fe3O4 phase generated as temperature increasing. Depending on glucose content and thermal temperature, the average grain size of Fe3O4 nanoparticles varied from 19.9 nm to 48 nm and saturation magnetization changed from 21.2 emu/g to 71.77 emu/g, which indicated that the saturation magnetization of Fe3O4 nanoparticles fell off as the average grain size decreasing. These results were crucial not only from the application stand-point, but more importantly leaded to a new platform for further studies of high quality magnetic Fe3O4 particles at nanoscale.

  15. CdMoO{sub 4} micro-ellipsoids: controllable synthesis, growth mechanism, and photocatalytic activity

    Energy Technology Data Exchange (ETDEWEB)

    Dai, Ke; Gao, Tianyu [College of Resources and Environment, Huazhong Agricultural University, Hubei, Wuhan (China); Liu, Hui; Chen, Hao, E-mail: hchenhao@mail.hzau.edu.cn [College of Science, Huazhong Agricultural University, Hubei, Wuhan (China); Wang, Qi, E-mail: hchenhao@mail.hzau.edu.cn [School of Environment Sciences and Engineering, Zhejiang Gongshang University, Zhejiang, Hangzhou (China)

    2017-01-15

    CdMoO{sub 4} micro-ellipsoids were synthesized by a simple hydrothermal route with the assistance of nonionic surfactant Triton X-100 and characterized by X-ray diffraction, scanning electron microscopy and UV-Vis diffuse reflectance spectroscopy. The effects of hydrothermal pH, temperature, and time on the morphology and photocatalytic activity of CdMoO{sub 4} were investigated. With an initial hydrothermal pH of 5.00, CdMoO{sub 4} micro-ellipsoids were obtained at 180 °C for 24 h and found to possess the highest photocatalytic activity - 89% Rhodamine B can be degraded for 30 minutes presented in the 0.4 g/L CdMoO{sub 4} suspension. The formation mechanism of the CdMoO{sub 4} micro-ellipsoids was initiated by the formation of small nanoparticles and bulk structures afterwards, which was followed by the growth of micro-ellipsoids. Experiment results showed that the evolution of the micro-ellipsoids was an Ostwald ripening process. (author)

  16. Effect of growth hormone and melatonin on the brain: from molecular mechanisms to structural changes.

    Science.gov (United States)

    Kireev, Roman A; Cuesta, Sara; Vara, Elena; Tresguerres, Jesus A F

    2011-10-01

    Aging of the brain causes important reductions in quality of life and has wide socio-economic consequences. An increase in oxidative stress, and the associated inflammation and apoptosis, could be responsible for the pathogenesis of aging associated brain lesions. Melatonin has neuroprotective effects, by limiting the negative effects of oxygen and nitrogen free radicals. Growth hormone (GH) might exert additional neuro-protective and or neurogenic effects on the brain. The molecular mechanisms of the protective effects of GH and melatonin on the aging brain have been investigated in young and old Wistar rats. A reduction in the total number of neurons in the hilus of the dentate gyrus was evident at 24 months of age and was associated with a significant increase in inflammation markers as well as in pro-apoptotic parameters, confirming the role of apoptosis in its reduction. Melatonin treatment was able to enhance neurogenesis in old rats without modification of the total number of neurons, whereas GH treatment increased the total number of neurons without enhancing neurogenesis. Both GH and melatonin were able to reduce inflammation and apoptosis in the hippocampus. In conclusion, neuroprotective effects demonstrated by GH and melatonin in the hippocampus were exerted by decreasing inflammation and apoptosis.

  17. Multiple Mechanisms are Responsible for Transactivation of the Epidermal Growth Factor Receptor in Mammary Epithelial Cells

    Energy Technology Data Exchange (ETDEWEB)

    Rodland, Karin D.; Bollinger, Nikki; Ippolito, Danielle L.; Opresko, Lee; Coffey, Robert J.; Zangar, Richard C.; Wiley, H. S.

    2008-11-14

    REVIEW ENTIRE DOCUMENT AT: https://pnlweb.pnl.gov/projects/bsd/ERICA%20Manuscripts%20for%20Review/KD%20Rodland%20D7E80/HMEC_transactivation_ms01_15+Figs.pdf ABSTRACT: Using a single nontransformed strain of human mammary epithelial cells, we found that the ability of multiple growth factors and cytokines to induce ERK phosphorylation was dependent on EGFR activity. These included lysophosphatidic acid (LPA), uridine triphosphate, growth hormone, vascular endothelial growth factor, insulin-like growth factor-1 (IGF-1), and tumor necrosis factoralpha. In contrast, hepatocyte growth factor could stimulate ERK phosphorylation independent of EGFR activity...

  18. An atomistic study on configuration, mechanics and growth of nanoscale filaments

    Science.gov (United States)

    Shahabi, Alireza

    conformations in these electronically active filaments open up the possibility of non-linear stretchable interconnects, and we study their reliability by extracting the elastic stiffness of the various conformations. We extract force-displacement curves of scrolls and plectonemes in the various systems. Our analysis sheds light on the relation between the shape of the nanostructures and the elastic stiffness of the nanofilaments. In overall, our study provides us with a novel route to engineer the nanofilaments and tune their mechanical properties using a combination of physical constraints and mechanical loading. In the next part of the dissertation, we perform a comprehensive atomistic study of the nanoscale crystal growth mechanisms of Au-catalyzed silicon nanowires grown via the vapor liquid solid method (VLS) during early stages of the droplet to nanowire transition. The transition sets the size of the nanowire, and the principles of diameter selection remain poorly understood. Our analysis reveals the role of the initial configuration of the nanodroplet and the effect of surface tension on the success of the VLS growth process. We observe lateral extension of liquid feet from the sides of nanodroplet during the VLS process. In addition to the nanodroplet diameter, the liquid feet plays a crucial role on determining the final geometry of the nanowire. We also observe an important correlation between the rate of deposition of Si atoms and presence of the twining in the nanowire structure, which significantly affects its properties. Higher deposition rates result in incorporation of metallic impurities in the nanowire structure, which consequently results in the formation of twining deformation. Our MD studies uncover a previously ignored interplay between solute trapping of catalyst particles in the nanowire, and twin formation, and we discuss this effect in the context of past experimental reports on twin formation in semiconducting nanowires, and the ability to

  19. Solidification, growth mechanisms, and associated properties of Al-Si and magnesium lightweight casting alloys

    Energy Technology Data Exchange (ETDEWEB)

    Hosch, Timothy [Iowa State Univ., Ames, IA (United States)

    2010-01-01

    Continually rising energy prices have inspired increased interest in weight reduction in the automotive and aerospace industries, opening the door for the widespread use and development of lightweight structural materials. Chief among these materials are cast Al-Si and magnesium-based alloys. Utilization of Al-Si alloys depends on obtaining a modified fibrous microstructure in lieu of the intrinsic flake structure, a process which is incompletely understood. The local solidification conditions, mechanisms, and tensile properties associated with the flake to fiber growth mode transition in Al-Si eutectic alloys are investigated here using bridgman type gradient-zone directional solidification. Resulting microstructures are examined through quantitative image analysis of two-dimensional sections and observation of deep-etched sections showing three-dimensional microstructural features. The transition was found to occur in two stages: an initial stage dominated by in-plane plate breakup and rod formation within the plane of the plate, and a second stage where the onset of out-of-plane silicon rod growth leads to the formation of an irregular fibrous structure. Several microstructural parameters were investigated in an attempt to quantify this transition, and it was found that the particle aspect ratio is effective in objectively identifying the onset and completion velocity of the flake to fiber transition. The appearance of intricate out-of-plane silicon instability formations was investigated by adapting a perturbed-interface stability analysis to the Al-Si system. Measurements of silicon equilibrium shape particles provided an estimate of the anisotropy of the solid Si/liquid Al-Si system and incorporation of this silicon anisotropy into the model was found to improve prediction of the instability length scale. Magnesium alloys share many of the benefits of Al-Si alloys, with the added benefit of a 1/3 lower density and increased machinability. Magnesium castings

  20. Solidification, growth mechanisms, and associated properties of aluminum-silicon and magnesium lightweight casting alloys

    Science.gov (United States)

    Hosch, Timothy Al

    Continually rising energy prices have inspired increased interest in weight reduction in the automotive and aerospace industries, opening the door for the widespread use and development of lightweight structural materials. Chief among these materials are cast Al-Si and magnesium-based alloys. Utilization of Al-Si alloys depends on obtaining a modified fibrous microstructure in lieu of the intrinsic flake structure, a process which is incompletely understood. The local solidification conditions, mechanisms, and tensile properties associated with the flake to fiber growth mode transition in Al-Si eutectic alloys are investigated here using bridgman type gradient-zone directional solidification. Resulting microstructures are examined through quantitative image analysis of two-dimensional sections and observation of deep-etched sections showing three-dimensional microstructural features. The transition was found to occur in two stages: an initial stage dominated by in-plane plate breakup and rod formation within the plane of the plate, and a second stage where the onset of out-of-plane silicon rod growth leads to the formation of an irregular fibrous structure. Several microstructural parameters were investigated in an attempt to quantify this transition, and it was found that the particle aspect ratio is effective in objectively identifying the onset and completion velocity of the flake to fiber transition. The appearance of intricate out-of-plane silicon instability formations was investigated by adapting a perturbed-interface stability analysis to the Al-Si system. Measurements of silicon equilibrium shape particles provided an estimate of the anisotropy of the solid Si/liquid Al-Si system and incorporation of this silicon anisotropy into the model was found to improve prediction of the instability length scale. Magnesium alloys share many of the benefits of Al-Si alloys, with the added benefit of a 1/3 lower density and increased machinability. Magnesium castings

  1. Mechanism of void growth in irradiated NaCl based on exiton-induced formation of divacancies at dislocations

    NARCIS (Netherlands)

    Dubinko, [No Value; Vainshtein, DI; den Hartog, HW

    2005-01-01

    We propose a mechanism of void growth in di-atomic ionic crystals due to agglomeration of divacancies produced by interactions between dislocations and excitons. An exciton can cause movement of nearby dislocation jogs, resulting in the creation of equal numbers of anion and cation vacancies (Schott

  2. Vascular endothelial growth factor regulates osteoblast survival – evidence for an autocrine feedback mechanism

    Directory of Open Access Journals (Sweden)

    Street John

    2009-06-01

    Full Text Available Abstract Background Apoptosis of osteoblasts and osteoclasts regulates bone homeostasis. Skeletal injury in humans results in 'angiogenic' responses primarily mediated by vascular endothelial growth factor(VEGF, a protein essential for bone repair in animal models. Osteoblasts release VEGF in response to a number of stimuli and express receptors for VEGF in a differentiation dependent manner. This study investigates the putative role of VEGF in regulating the lifespan of primary human osteoblasts(PHOB in vitro. Methods PHOB were examined for VEGF receptors. Cultures were supplemented with VEGF(0–50 ng/mL, a neutralising antibody to VEGF, mAB VEGF(0.3 ug/mL and Placental Growth Factor (PlGF, an Flt-1 receptor-specific VEGF ligand(0–100 ng/mL to examine their effects on mineralised nodule assay, alkaline phosphatase assay and apoptosis.. The role of the VEGF specific antiapoptotic gene target BCl2 in apoptosis was determined. Results PHOB expressed functional VEGF receptors. VEGF 10 and 25 ng/mL increased nodule formation 2.3- and 3.16-fold and alkaline phosphatase release 2.6 and 4.1-fold respectively while 0.3 ug/mL of mAB VEGF resulted in approx 40% reductions in both. PlGF 50 ng/mL had greater effects on alkaline phosphatase release (103% increase than on nodule formation (57% increase. 10 ng/mL of VEGF inhibited spontaneous and pathological apoptosis by 83.6% and 71% respectively, while PlGF had no significant effect. Pretreatment with mAB VEGF, in the absence of exogenous VEGF resulted in a significant increase in apoptosis (14 vs 3%. VEGF 10 ng/mL increased BCl2 expression 4 fold while mAB VEGF decreased it by over 50%. Conclusion VEGF is a potent regulator of osteoblast life-span in vitro. This autocrine feedback regulates survival of these cells, mediated via a non flt-1 receptor mechanism and expression of BCl2 antiapoptotic gene.

  3. Growth, photosynthesis, and defense mechanism of antimony (Sb)-contaminated Boehmeria nivea L.

    Science.gov (United States)

    Chai, Li-Yuan; Mubarak, Hussani; Yang, Zhi-Hui; Yong, Wang; Tang, Chong-Jian; Mirza, Nosheen

    2016-04-01

    Ramie (Boehmeria nivea L.) is the oldest cash fiber crop in China and is widely grown in antimony (Sb) mining areas. To evaluate the extent of Sb resistance and tolerance, the growth, tolerance index (TI), Sb content in plant parts and in Hoagland solution, bioaccumulation factor (BF), photosynthesis, and physiological changes in Sb-contaminated B. nivea (20, 40, 80, and 200 mg L(-1) Sb) grown hydroponically were investigated. The Sb tolerance and resistance of ramie were clearly revealed by growth inhibition, a TI between 13 and 99 %, non-significant changes in the maximum quantum efficiency of photosystem (F v /F m ), energy-harvesting efficiency (photosystem II (PSII)) and single-photon avalanche diode (SPAD) value, a significant increase in Sb in plant parts, BF >1, and an increase in catalase (CAT) and malondialdehyde (MDA) at 200 mg L(-1) Sb. Under increasing Sb stress, nearly the same non-significant decline in the maximum quantum efficiency of photosystem (F v /F m ), energy-harvesting efficiency (PSII), relative quantum yield of photosystem II (φPSII), and photochemical quenching (qP), except for F v /F m at 20 mg L(-1) Sb, were recorded. SPAD values for chlorophyll under Sb stress showed an increasing trend, except for a slight decrease, i.e., Sb. With a continuous increase in MDA, superoxide dismutase (SOD), peroxidase (POD), and CAT activities were suppressed under Sb addition up to 40 mg L(-1) Sb and the addition of Sb enhanced enzyme production at 80 and 200 mg L(-1) Sb. A continuous decrease in SOD, POD, and CAT up to 40 mg L(-1) Sb and enhancements at ≥80 mg L(-1), along with the continuous enhancement of MDA activity and inhibited biomass production, clearly reveal the roles of these enzymes in detoxifying Sb stress and the defense mechanism of ramie at 80 mg L(-1) Sb. Thus, B. nivea constitutes a promising candidate for Sb phytoremediation at mining sites.

  4. Role of constitutive behavior and tumor-host mechanical interactions in the state of stress and growth of solid tumors.

    Directory of Open Access Journals (Sweden)

    Chrysovalantis Voutouri

    Full Text Available Mechanical forces play a crucial role in tumor patho-physiology. Compression of cancer cells inhibits their proliferation rate, induces apoptosis and enhances their invasive and metastatic potential. Additionally, compression of intratumor blood vessels reduces the supply of oxygen, nutrients and drugs, affecting tumor progression and treatment. Despite the great importance of the mechanical microenvironment to the pathology of cancer, there are limited studies for the constitutive modeling and the mechanical properties of tumors and on how these parameters affect tumor growth. Also, the contribution of the host tissue to the growth and state of stress of the tumor remains unclear. To this end, we performed unconfined compression experiments in two tumor types and found that the experimental stress-strain response is better fitted to an exponential constitutive equation compared to the widely used neo-Hookean and Blatz-Ko models. Subsequently, we incorporated the constitutive equations along with the corresponding values of the mechanical properties - calculated by the fit - to a biomechanical model of tumor growth. Interestingly, we found that the evolution of stress and the growth rate of the tumor are independent from the selection of the constitutive equation, but depend strongly on the mechanical interactions with the surrounding host tissue. Particularly, model predictions - in agreement with experimental studies - suggest that the stiffness of solid tumors should exceed a critical value compared with that of the surrounding tissue in order to be able to displace the tissue and grow in size. With the use of the model, we estimated this critical value to be on the order of 1.5. Our results suggest that the direct effect of solid stress on tumor growth involves not only the inhibitory effect of stress on cancer cell proliferation and the induction of apoptosis, but also the resistance of the surrounding tissue to tumor expansion.

  5. Growth mechanism of titanium dioxide nanowires for dye-sensitized solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Boercker, J E; Enache-Pommer, E; Aydil, E S [Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Avenue SE, Minneapolis, MN 55455 (United States)], E-mail: aydil@umn.edu

    2008-03-05

    Mesoporous films made of titanium dioxide nanowires are desirable for dye-sensitized solar cells because nanowires provide direct conduction pathways for photogenerated electrons. Anatase titanium dioxide nanowires with polycrystalline microstructure were synthesized on titanium foil using a three-step process. First, the top surface of the titanium foil was transformed to Na{sub 2}Ti{sub 2}O{sub 4}(OH){sub 2} nanotubes through hydrothermal oxidation in NaOH. Next, the Na{sub 2}Ti{sub 2}O{sub 4}(OH){sub 2} nanotubes were converted to H{sub 2}Ti{sub 2}O{sub 4}(OH){sub 2} nanotubes by ion exchange. Finally, the H{sub 2}Ti{sub 2}O{sub 4}(OH){sub 2} nanotubes were converted to polycrystalline anatase nanowires through a topotactic transformation. The film morphology evolution, crystal structure transformations and growth mechanism are described in detail. Titanium foil reacts with NaOH to form Na{sub 2}Ti{sub 2}O{sub 4}(OH){sub 2} sheets, which exfoliate and spiral into nanotubes. The Na{sub 2}Ti{sub 2}O{sub 4}(OH){sub 2} nanotubes are immersed in HCl solution to replace the Na{sup +} ions with H{sup +} ions. During the topotactic transformation of H{sub 2}Ti{sub 2}O{sub 4}(OH){sub 2} nanotubes to anatase TiO{sub 2} nanowires, the sheets made of edge bonded TiO{sub 6} octahedra in the H{sub 2}Ti{sub 2}O{sub 4}(OH){sub 2} nanotubes dehydrate and move towards each other to form anatase crystals oriented along the nanotube axis which creates a polycrystalline nanowire. These mesoporous TiO{sub 2} nanowire films were suitable for use as dye-sensitized solar cell photoanodes.

  6. Colloidal Magnetic Heterostructured Nanocrystals with Asymmetric Topologies: Seeded-Growth Synthetic Routes and Formation Mechanisms

    Directory of Open Access Journals (Sweden)

    Riccardo Scarfiello

    2016-12-01

    Full Text Available Colloidal inorganic nanocrystals, free-standing crystalline nanostructures generated and processed in solution phase, represent an important class of advanced nanoscale materials owing to the flexibility with which their physical–chemical properties can be controlled through synthetic tailoring of their compositional, structural and geometric features and the versatility with which they can be integrated in technological fields as diverse as optoelectronics, energy storage/ conversion/production, catalysis and biomedicine. In recent years, building upon mechanistic knowledge acquired on the thermodynamic and kinetic processes that underlie nanocrystal evolution in liquid media, synthetic nanochemistry research has made impressive advances, opening new possibilities for the design, creation and mastering of increasingly complex colloidal molecules, in which nanocrystal modules of different materials are clustered together via solid-state bonding interfaces into free-standing, easily processable multifunctional nanocomposite systems. This Review will provide a glimpse into this fast-growing research field by illustrating progress achieved in the wet-chemical development of last-generation breeds of all-inorganic heterostructured nanocrystals (HNCs in asymmetric non-onionlike geometries, inorganic analogues of polyfunctional organic molecules, in which distinct nanoscale crystalline modules are interconnected in hetero-dimer, hetero-oligomer and anisotropic multidomain architectures via epitaxial heterointerfaces of limited extension. The focus will be on modular HNCs entailing at least one magnetic material component combined with semiconductors and/or metals, which hold potential for generating enhanced or unconventional magnetic properties, while offering diversified or even new chemical-physical properties and functional capabilities. The available toolkit of synthetic strategies, all based on the manipulation of seeded-growth techniques

  7. Structural evolution, growth mechanism and photoluminescence properties of CuWO4 nanocrystals.

    Science.gov (United States)

    Souza, E L S; Sczancoski, J C; Nogueira, I C; Almeida, M A P; Orlandi, M O; Li, M S; Luz, R A S; Filho, M G R; Longo, E; Cavalcante, L S

    2017-09-01

    Copper tungstate (CuWO4) crystals were synthesized by the sonochemistry (SC) method, and then, heat treated in a conventional furnace at different temperatures for 1h. The structural evolution, growth mechanism and photoluminescence (PL) properties of these crystals were thoroughly investigated. X-ray diffraction patterns, micro-Raman spectra and Fourier transformed infrared spectra indicated that crystals heat treated and 100°C and 200°C have water molecules in their lattice (copper tungstate dihydrate (CuWO4·2H2O) with monoclinic structure), when the crystals are calcinated at 300°C have the presence of two phase (CuWO4·2H2O and CuWO4), while the others heat treated at 400°C and 500°C have a single CuWO4 triclinic structure. Field emission scanning electron microscopy revealed a change in the morphological features of these crystals with the increase of the heat treatment temperature. Transmission electron microscopy (TEM), high resolution-TEM images and selected area electron diffraction were employed to examine the shape, size and structure of these crystals. Ultraviolet-Visible spectra evidenced a decrease of band gap values with the increase of the temperature, which were correlated with the reduction of intermediary energy levels within the band gap. The intense photoluminescence (PL) emission was detected for the sample heat treat at 300°C for 1h, which have a mixture of CuWO4·2H2O and CuWO4 phases. Therefore, there is a synergic effect between the intermediary energy levels arising from these two phases during the electronic transitions responsible for PL emissions. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. Mechanisms of resistance to anti-epidermal growth factor receptor inhibitors in metastatic colorectal cancer

    Science.gov (United States)

    Sforza, Vincenzo; Martinelli, Erika; Ciardiello, Fortunato; Gambardella, Valentina; Napolitano, Stefania; Martini, Giulia; della Corte, Carminia; Cardone, Claudia; Ferrara, Marianna L; Reginelli, Alfonso; Liguori, Giuseppina; Belli, Giulio; Troiani, Teresa

    2016-01-01

    The prognosis of patients with metastatic colorectal cancer (mCRC) remain poor despite the impressive improvement of treatments observed over the last 20 years that led to an increase in median overall survival from 6 mo, with the only best supportive care, to approximately 30 mo with the introduction of active chemotherapy drugs and targeted agents. The monoclonal antibodies (moAbs) cetuximab and panitumumab, directed against the epidermal growth factor receptor (EGFR), undoubtedly represent a major step forward in the treatment of mCRC, given the relevant efficacy in terms of progression-free survival, overall survival, response rate, and quality of life observed in several phase III clinical trials among different lines of treatment. However, the anti-EGFR moAbs were shown only to be effective in a subset of patients. For instance, KRAS and NRAS mutations have been identified as biomarkers of resistance to these drugs, improving the selection of patients who might derive a benefit from these treatments. Nevertheless, several other alterations might affect the response to these drugs, and unfortunately, even the responders eventually become resistant by developing secondary (or acquired) resistance in approximately 13-18 mo. Several studies highlighted that the landscape of responsible alterations of both primary and acquired resistance to anti-EGFR drugs biochemically converge into MEK-ERK and PIK3CA-AKT pathways. In this review, we describe the currently known mechanisms of primary and acquired resistance to anti-EGFR moAbs together with the various strategies evaluated to prevent, overcame or revert them. PMID:27605871

  9. Red bayberry-like ZnTe microstructures: Controlled synthesis, growth mechanism and enhanced photocatalytic performance

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Xiao-Ping; Gu, Jie [Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018 (China); Zhou, Shao-Min [Key Lab for Special Functional Materials of Ministry of Education, Henan University, Kaifeng 475004 (China); Li, Xiao-Yun; Wang, Shun-Li; Jin, Li; Chen, Hui [Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018 (China); Shi, Jian-Jun, E-mail: jjshi61@126.com [Department of Physics, Zhejiang Sci-Tech University, Hangzhou 310018 (China)

    2015-04-05

    Graphical abstract: Different ZnTe microstructures with controllable morphologies were synthesized via a facile NaOH-mediated solvothermal menthod. The as-obtained Red bayberry-like ZnTe microstructures possessed remarkable photocatalytic capability reached up to about 90%. - Highlights: • For the first time, Red bayberry-like ZnTe is successful fabricated. • ZnTe microstructures with controllable morphology were synthesized. • NaOH played significant roles in the fabrication of Red bayberry-like ZnTe. • Red bayberry-like ZnTe exhibited remarkable photocatalytic activities. - Abstract: Uniform Red bayberry-like ZnTe microstructures have been synthesized by a facile solvothermal method. The effects of synthetic conditions, such as the amount of NaOH, the zinc source and reaction time were investigated. The results showed that the morphology of the ZnTe microstructures can be controlled by altering the concentration of NaOH. The growth mechanism of Red bayberry-like ZnTe microstructures was as follows: At the initial stage, the decomposition of Na{sub 2}TeO{sub 3} generates Te nucleus. Trigonal tellurium has a highly anisotropic crystal structure consisting of helical chains of covalently bound atoms, thus resulting in Te nanowires are firstly formed in the reaction. Subsequently, the Te nanowires were reduced by CH{sub 3}CHO generated from ethylene glycol, meanwhile the generated Te{sup 2−} ions combined with Zn{sup 2+} ions generates ZnTe nucleus, finally forming Red bayberry-like ZnTe. When used as a catalytic of organic pollutants, the as-obtained Red bayberry-like ZnTe showed strong photocatalytic capability reached up to about 90%. The high photocatalytic activities of the Red bayberry-like ZnTe would have a potential photocatalytic application in environmental purification.

  10. Growth mechanism of titanium dioxide nanowires for dye-sensitized solar cells.

    Science.gov (United States)

    Boercker, J E; Enache-Pommer, E; Aydil, E S

    2008-03-05

    Mesoporous films made of titanium dioxide nanowires are desirable for dye-sensitized solar cells because nanowires provide direct conduction pathways for photogenerated electrons. Anatase titanium dioxide nanowires with polycrystalline microstructure were synthesized on titanium foil using a three-step process. First, the top surface of the titanium foil was transformed to Na(2)Ti(2)O(4)(OH)(2) nanotubes through hydrothermal oxidation in NaOH. Next, the Na(2)Ti(2)O(4)(OH)(2) nanotubes were converted to H(2)Ti(2)O(4)(OH)(2) nanotubes by ion exchange. Finally, the H(2)Ti(2)O(4)(OH)(2) nanotubes were converted to polycrystalline anatase nanowires through a topotactic transformation. The film morphology evolution, crystal structure transformations and growth mechanism are described in detail. Titanium foil reacts with NaOH to form Na(2)Ti(2)O(4)(OH)(2) sheets, which exfoliate and spiral into nanotubes. The Na(2)Ti(2)O(4)(OH)(2) nanotubes are immersed in HCl solution to replace the Na(+) ions with H(+) ions. During the topotactic transformation of H(2)Ti(2)O(4)(OH)(2) nanotubes to anatase TiO(2) nanowires, the sheets made of edge bonded TiO(6) octahedra in the H(2)Ti(2)O(4)(OH)(2) nanotubes dehydrate and move towards each other to form anatase crystals oriented along the nanotube axis which creates a polycrystalline nanowire. These mesoporous TiO(2) nanowire films were suitable for use as dye-sensitized solar cell photoanodes.

  11. The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Part II. Fatigue crack growth rate

    Science.gov (United States)

    Margolin, B.; Minkin, A.; Smirnov, V.; Sorokin, A.; Shvetsova, V.; Potapova, V.

    2016-11-01

    The experimental data on the fatigue crack growth rate (FCGR) have been obtained for austenitic steel of 18Cr-10Ni-Ti grade (Russian analog of AISI 321 steel) irradiated up to neutron dose of 150 dpa with various radiation swelling. The performed study of the fracture mechanisms for cracked specimens under cyclic loading has explained why radiation swelling affects weakly FCGR unlike its effect on fracture toughness. Mechanical modeling of fatigue crack growth has been carried out and the dependencies for prediction of FCGR in irradiated austenitic steel with and with no swelling are proposed and verified with the obtained experimental results. As input data for these dependencies, FCGR for unirradiated steel and the tensile mechanical properties for unirradiated and irradiated steels are used.

  12. Growth mechanism and strain relaxation in zinc selenide and cadmium telluride/zinc telluride semiconductor thin films

    Science.gov (United States)

    Wei, Hsiang-Yi

    The application of II--VI semiconductor devices such as blue-green light emitters (ZnSe-based materials) and HgCdTe infrared detectors are limited by the high density of defects and lack of large size substrates that are lattice matched and chemically compatible with the films. By growing a single thick buffer layer or a composite buffer structure of dissimilar materials can lead to a final top layer that is structurally and chemically compatible with the active layer of the device. Low defect density and flat surface morphology are the basic requirements for an applicable buffer layer. In this work, transmission electron microscopy is used to investigate the crystalline structure and defect generation mechanism in buffer layers for the growth of ZnSe-based and HgCdTe films. We investigate the interface chemistry, defect density, and growth mechanism of ZnSe films grown on GaAs substrates with different surface processing techniques. Undesirable high density of funnel defects (˜1010 cm-2) are always observed when the growth is performed on the epi-ready GaAs. We also observe that Sb can act as a surfactant and promote a truly layer-by-layer growth mode when the ZnSe film is grown on Sb-stabilized GaAs substrates. The defect density can be reduced to values as low as in the low 103 cm-2 range, which is the lowest defect density ever reported for ZnSe films. Moreover, the ZnSe surface exhibits a characteristic brick-like pattern for all of the substrate preparation methods used (except for Sb-stabilized GaAs) and the thickness of the ZnSe epilayers for films grown at ˜280--330°C. At a much higher growth temperature (410°C), a corrugated surface forms with high periodicity along the [110] direction. We propose a kinetics-limited surface roughness mechanism for the ZnSe films based on a competition of nucleation of 2D islands followed by step evolution. In the CdTe/ZnTe/Si epitaxial system, we investigated the influence of different surface precursors on the growth

  13. A computational model that predicts reverse growth in response to mechanical unloading.

    Science.gov (United States)

    Lee, L C; Genet, M; Acevedo-Bolton, G; Ordovas, K; Guccione, J M; Kuhl, E

    2015-04-01

    Ventricular growth is widely considered to be an important feature in the adverse progression of heart diseases, whereas reverse ventricular growth (or reverse remodeling) is often considered to be a favorable response to clinical intervention. In recent years, a number of theoretical models have been proposed to model the process of ventricular growth while little has been done to model its reverse. Based on the framework of volumetric strain-driven finite growth with a homeostatic equilibrium range for the elastic myofiber stretch, we propose here a reversible growth model capable of describing both ventricular growth and its reversal. We used this model to construct a semi-analytical solution based on an idealized cylindrical tube model, as well as numerical solutions based on a truncated ellipsoidal model and a human left ventricular model that was reconstructed from magnetic resonance images. We show that our model is able to predict key features in the end-diastolic pressure-volume relationship that were observed experimentally and clinically during ventricular growth and reverse growth. We also show that the residual stress fields generated as a result of differential growth in the cylindrical tube model are similar to those in other nonidentical models utilizing the same geometry.

  14. Si and Ge nanostructures epitaxy on a crystalline insulating LaAlO{sub 3}(001) substrate

    Energy Technology Data Exchange (ETDEWEB)

    Bischoff, Jean-Luc; Mortada, Hussein; Dentel, Didier; Derivaz, Mickael [Institut de Science des Materiaux de Mulhouse (IS2M), LRC 7228 CNRS-UHA, Universite de Haute Alsace, Mulhouse (France); Ben Azzouz, Chiraz; Akremi, Abdelwahab; Chefi, Chaabanne [Equipe Surface et Interface (ESI) - Faculte des Sciences, Bizerte (Tunisia); Morales, Francisco Miguel; Herrera, Miriam; Manuel, Jose Manuel; Garcia, Rafael [Department of Materials Science, Metallurgical Engineering and Inorganic Chemistry, Cadiz University (Spain); Diani, Mustapha [Equipe de Recherche en Mecanique, Materiaux et Metallurgie, FST, Tanger (Morocco)

    2012-04-15

    We present a comparative structural study of the growth of Si and Ge deposited by molecular beam epitaxy (MBE) on a c(2 x 2) reconstructed LaAlO{sub 3}(001) substrate. Our findings are based on complementary experimental techniques such as in situ X-ray photoelectron spectroscopy (XPS), reflection high-energy electron diffraction (RHEED), low energy electron diffraction (LEED) and ex situ atomic force microscopy (AFM) and high resolution transmission electron microscopy (HRTEM). While the layers are amorphous and wet uniformly the substrate in a low deposition temperature range, above 500 C both Si and Ge growths proceed in a Volmer-Weber (VW) mode leading to the formation of nanocrystals (NCs). The islands are found to be composed of pure Si and Ge and to have abrupt interfaces with the substrate. Both semiconductors (SCs) crystallize in their own diamond structure leading to relaxed NCs. No facets could be observed on the crystalline islands. An epitaxial relationship is established for which the (001) planes of Si and Ge are parallel to the LaAlO{sub 3}(001) surface but are rotated by 45 around the [001] growth axis. The Ge lattice undergoes a second rotation of 6 with respect to the (001) growth axis. This 6 tilt is an original mechanism to partially compensate the strain in the Ge islands induced by the large misfit. Whereas a unique epitaxial relationship is pointed out for Si NCs, many Ge NCs are randomly orientated on the surface. This is interpreted by the fact that the Ge islands are less anchored to the substrate due to a large misfit and to the fact that the Ge-O bonds are weaker than the Si-O ones. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Effects of Mechanical Stress and Plant Density on Mechanical Characteristics, Growth, and Lifetime Reproduction of Tobacco Plants

    NARCIS (Netherlands)

    Anten, N.P.R.; Casado-Garcia, R.; Nagashima, H.

    2005-01-01

    Plastic increases in stem elongation in dense vegetation are generally believed to be induced by canopy shading, but because plants protect each other from wind, shielding (reduced mechanical stress) could also play a role. To address this issue, tobacco Nicotiana tabacum plants were subjected to

  16. Mechanisms of nerve growth factor signaling in bone nociceptors and in an animal model of inflammatory bone pain.

    Science.gov (United States)

    Nencini, Sara; Ringuet, Mitchell; Kim, Dong-Hyun; Chen, Yu-Jen; Greenhill, Claire; Ivanusic, Jason J

    2017-01-01

    Sequestration of nerve growth factor has been used successfully in the management of pain in animal models of bone disease and in human osteoarthritis. However, the mechanisms of nerve growth factor-induced bone pain and its role in modulating inflammatory bone pain remain to be determined. In this study, we show that nerve growth factor receptors (TrkA and p75) and some other nerve growth factor-signaling molecules (TRPV1 and Nav1.8, but not Nav1.9) are expressed in substantial proportions of rat bone nociceptors. We demonstrate that nerve growth factor injected directly into rat tibia rapidly activates and sensitizes bone nociceptors and produces acute behavioral responses with a similar time course. The nerve growth factor-induced changes in the activity and sensitivity of bone nociceptors we report are dependent on signaling through the TrkA receptor, but are not affected by mast cell stabilization. We failed to show evidence for longer term changes in expression of TrkA, TRPV1, Nav1.8 or Nav1.9 in the soma of bone nociceptors in a rat model of inflammatory bone pain. Thus, retrograde transport of NGF/TrkA and increased expression of some of the common nerve growth factor signaling molecules do not appear to be important for the maintenance of inflammatory bone pain. The findings are relevant to understand the basis of nerve growth factor sequestration and other therapies directed at nerve growth factor signaling, in managing pain in bone disease.

  17. Mechanisms promoting higher growth rate in arctic than in temperate shorebirds

    NARCIS (Netherlands)

    Schekkerman, H; Tulp, Ingrid; Piersma, T.; Visser, G.H.

    2003-01-01

    We compared prefledging growth, energy expenditure, and time budgets in the arctic-breeding red knot (Calidris canutus) to those in temperate shorebirds, to investigate how arctic chicks achieve a high growth rate despite energetic difficulties associated with precocial development in a cold climate

  18. High-Resolution Transmission Electron Microscopy Observation of Colloidal Nanocrystal Growth Mechanisms using Graphene Liquid Cells

    Energy Technology Data Exchange (ETDEWEB)

    Yuk, Jong Min; Park, Jungwon; Ercius, Peter; Kim, Kwanpyo; Hellebusch, Danny J.; Crommie, Michael F.; Lee, Jeong Yong; Zettl, A.; Alivisatos, A. Paul

    2011-12-12

    We introduce a new type of liquid cell for in-situ electron microscopy based upon entrapment of a liquid film between layers of graphene. We employ this cell to achieve high-resolution imaging of colloidal platinum nanocrystal growth. The ability to directly image and resolve critical steps at atomic resolution provides new insights into nanocrystal coalescence and reshaping during growth.

  19. Ten-Year Growth of Five Planted Hardwood Species Mechanical Weed Control on Sharkey Clay Soil

    Science.gov (United States)

    Roger M. Krinard; Harvey E. Kennedy

    1983-01-01

    Five hardwood species planted on Sharkey clay soil showed little practical difference in growth whether plots were mowed or diskedfor weed control in years 6 to 10, although disking had given better growth in the first 5 years. After 10 years, cottonwood (Populus deltoides Bartr. ex Marsh.) stem volume was at least three times greater than other species. Changes in...

  20. Epidermal growth factor receptor-targeted antibody therapy - Mechanisms of action and modulators of therapeutic efficacy

    NARCIS (Netherlands)

    Lammerts van Bueren, Jeroen Jilles

    2008-01-01

    Cancer is an increasing disease in the world population, and in recent years there has been substantial interest in the development of novel therapeutic agents specifically targeting growth factor receptors on tumor cells. The epidermal growth factor receptor (EGFR) represents a tyrosine kinase cell

  1. Functional Mechanism of Resveratrol in Inhabiting Growth of Cells ls174t and Its Mechanism in Subcutaneously Transplanted Tumor of Nude Mice

    Institute of Scientific and Technical Information of China (English)

    CHEN Jie; DONG Xin-shu; GUO Xing-gang

    2008-01-01

    To explore the functional mechanism of Resveratrol against colon cancer cells Is174t and the growth of colon cancer tissue of tumor-bearing mice,MTT method was used to observe the functions of resveratrol for inhibition against cells ls174t in vitro.Transmission electron microscope was used to observe the cell apoptosis.FCM assay was performed to measure the change of the cell apoptosis rate and of cell cycle,RT-PCR method was used to detect the expressions of bc1-2 and bax mRNA.Western blot method was used to detect the expressions of bc1-2 and bax protein.Cells isi74t were transplanted subcutaneously to nude mice to observe the effect of resveratrol on the growth of subcutaneously transplanted tumor.RT-PCR method was used to detect the expressions of bc1-2 and bax mRNA in the tumor tissue.Western blot method was used to detect the expressions of bc1-2 and bax protein in the tumor tissue.Resveratrol has an effect of inhibiting proliferation of cells ls174t in vitro(P<0.01).It is able to induce the apoptosis of cells Is174t,causing the decrease in the expression of bc1-2 and the increase in the expression of bax.Resveratrol could inhibit the growth of subcutaneously transplanted tumor of nude mice(P<0.05),causing the decrease in the expression of bc1-2 and the increase in the expression of bax.Resveratrol can inhibit the growth of cells 174t and the growth of subcutaneously transplanted tumor.The mechanism is possibly related to the induction of the cell apoptosis and the regulation of bc1-2/bax expression.

  2. Inferring Growth Control Mechanisms in Growing Multi-cellular Spheroids of NSCLC Cells from Spatial-Temporal Image Data.

    Directory of Open Access Journals (Sweden)

    Nick Jagiella

    2016-02-01

    Full Text Available We develop a quantitative single cell-based mathematical model for multi-cellular tumor spheroids (MCTS of SK-MES-1 cells, a non-small cell lung cancer (NSCLC cell line, growing under various nutrient conditions: we confront the simulations performed with this model with data on the growth kinetics and spatial labeling patterns for cell proliferation, extracellular matrix (ECM, cell distribution and cell death. We start with a simple model capturing part of the experimental observations. We then show, by performing a sensitivity analysis at each development stage of the model that its complexity needs to be stepwise increased to account for further experimental growth conditions. We thus ultimately arrive at a model that mimics the MCTS growth under multiple conditions to a great extent. Interestingly, the final model, is a minimal model capable of explaining all data simultaneously in the sense, that the number of mechanisms it contains is sufficient to explain the data and missing out any of its mechanisms did not permit fit between all data and the model within physiological parameter ranges. Nevertheless, compared to earlier models it is quite complex i.e., it includes a wide range of mechanisms discussed in biological literature. In this model, the cells lacking oxygen switch from aerobe to anaerobe glycolysis and produce lactate. Too high concentrations of lactate or too low concentrations of ATP promote cell death. Only if the extracellular matrix density overcomes a certain threshold, cells are able to enter the cell cycle. Dying cells produce a diffusive growth inhibitor. Missing out the spatial information would not permit to infer the mechanisms at work. Our findings suggest that this iterative data integration together with intermediate model sensitivity analysis at each model development stage, provide a promising strategy to infer predictive yet minimal (in the above sense quantitative models of tumor growth, as prospectively of

  3. Modeling cancer growth and its treatment by means of statistical mechanics entropy

    Science.gov (United States)

    Khordad, R.; Rastegar Sedehi, H. R.

    2016-08-01

    In this paper, we have modeled cancer growth and its treatment based on nonextensive entropies. To this end, five nonextensive entropies are employed to model the cancer growth. The used entropies are Tsallis, Rényi, Landsberg-Vedral, Abe and Escort. First, we have proposed the growth of cancer tumor as a function of time for all the entropies with different nonextensive parameter q. When the time passes, the entropies show a bounded growth for cancer tumor size. The speed of tumor size growth is different for all the entropies. The Tsallis and Escort ones have highest and lowest speed, respectively. For q>1, the Escort entropy cannot predict a bounded growth for cancer tumor size. Then, we have investigated the cancer tumor treatment by adding a cell-kill function to the evolution equation. For q1, a cell-kill term is a suitable case. According to the results, it is found that the nonextensive parameter q, type of entropy, and cell-kill function are important factors for modeling the cancer growth and its treatment.

  4. Mechanism of divergent growth factor effects in mesenchymal stem cell differentiation

    DEFF Research Database (Denmark)

    Kratchmarova, Irina; Blagoev, Blagoy; Haack-Sorensen, M.

    2005-01-01

    Closely related signals often lead to very different cellular outcomes. We found that the differentiation of human mesenchymal stem cells into bone-forming cells is stimulated by epidermal growth factor (EGF) but not platelet-derived growth factor (PDGF). We used mass spectrometry-based proteomics...... it as a possible control point. Indeed, chemical inhibition of PI3K in PDGF-stimulated cells removed the differential effect of the two growth factors, bestowing full differentiation effect onto PDGF. Thus, quantitative proteomics can directly compare entire signaling networks and discover critical differences...... capable of changing cell fate....

  5. Comparison between polymerized ionic liquids synthesized using chain-growth and step-growth mechanisms used as stationary phase in gas chromatography.

    Science.gov (United States)

    Roeleveld, Kevin; David, Frank; Lynen, Frédéric

    2016-06-17

    In this study the merits of polymerized imidazolium based ionic liquid (PIL) stationary phases obtained via condensation and free radical polymerizations are compared as stationary phases in gas chromatography (GC). Poly(1-vinyl-3-butyl-imidazolium - bis(trifluoromethane)sulfonamide) (poly(ViC4Im(+) NTf2(-))) was obtained via a chain-growth mechanism while poly(propylimidazolium-NTf2) (poly(C3Im(+) NTf2(-))) was synthesized via a step-growth polymerization. The thermal stability of both polymers was assessed using thermal gravimetric analysis and compared with bleeding profiles obtained from the statically coated GC columns (30m×0.25mm×0.25μm). The performance was compared to what could be obtained on commercially available 1,5-di(2,3-dimethylimidazolium)pentane(2+) 2NTf2(-) (SLB-IL111) ionic liquid based columns. It was observed that the step-growth polymer was more thermally stable, up to 325°C, while the chain-growth polymer showed initial degradation at 250°C. Both polymers allowed reaching minimal plate heights of 0.400-0.500mm for retained solutes such as benzaldehyde, acetophenone, 1-methylnaphthalene and aniline. Assessment of the McReynolds constants illustrated that the polarity of the step-growth polymer was similar to the SLB-IL111 column, while displaying improved column stability. The PIL phases and particularly the so far little studied condensation based polymer shows particular retention and satisfactory column performance for polar moieties such as esters, amine and carbonyl functionalities.

  6. A statistical mechanics model to predict electromigration induced damage and void growth in solder interconnects

    Science.gov (United States)

    Wang, Yuexing; Yao, Yao; Keer, Leon M.

    2017-02-01

    Electromigration is an irreversible mass diffusion process with damage accumulation in microelectronic materials and components under high current density. Based on experimental observations, cotton type voids dominate the electromigration damage accumulation prior to cracking in the solder interconnect. To clarify the damage evolution process corresponding to cotton type void growth, a statistical model is proposed to predict the stochastic characteristic of void growth under high current density. An analytical solution of the cotton type void volume growth over time is obtained. The synchronous electromigration induced damage accumulation is predicted by combining the statistical void growth and the entropy increment. The electromigration induced damage evolution in solder joints is developed and applied to verify the tensile strength deterioration of solder joints due to electromigration. The predictions agree well with the experimental results.

  7. Organizational mechanisms of inclusive growth: A critical realist perspective on scaling

    OpenAIRE

    Seelos, Christian; Mair, Johanna

    2010-01-01

    We investigate the challenge how the outcomes of innovation for inclusive growth, the novel organizational recipes, can be scaled to match the dimension of poverty. We conceptualize scaling as sustained event regularities between doing A and expected outcomes B. Building on a critical realist perspective, we develop an analytical framework of organizational closure and apply it to an extreme case, an organization with an inclusive growth model that has sustained event regularities for more th...

  8. Acetylsalicylic acid interferes with embryonic kidney growth and development by a prostaglandin-independent mechanism.

    Science.gov (United States)

    Welham, Simon J M; Sparrow, Alexander J; Gardner, David S; Elmes, Matthew J

    2017-01-06

    To evaluate the effects of the non-selective, non-steroidal anti-inflammatory drug (NSAID) acetylsalicylic acid (ASA), on ex vivo embryonic kidney growth and development. Pairs of fetal mouse kidneys at embryonic day 12.5 were cultured ex vivo in increasing concentrations of ASA (0.04-0.4 mg/mL) for up to 7 d. One organ from each pair was grown in control media and was used as the internal control for the experimental contralateral organ. In some experiments, organs were treated with ASA for 48 h and then transferred either to control media alone or control media containing 10 μmol/L prostaglandin E2 (PGE2) for a further 5 d. Fetal kidneys were additionally obtained from prostaglandin synthase 2 homozygous null or heterozygous (PTGS2(-/-) and PTGS2(-/+)) embryos and grown in culture. Kidney cross-sectional area was used to determine treatment effects on kidney growth. Whole-mount labelling to fluorescently detect laminin enabled crude determination of epithelial branching using confocal microscopy. Increasing ASA concentration (0.1, 0.2 and 0.4 mg/mL) significantly inhibited metanephric growth (P growth area to control levels. Application of control media alone after cessation of ASA exposure showed no benefit on kidney growth. Despite the apparent recovery of growth area with 10 μmol/L PGE2, no obvious renal tubular structures were formed. The number of epithelial tips generated after 48 h exposure to ASA was reduced by 40% (0.2 mg/mL; P growth of PTGS2(-/-) and PTGS2(+/-) kidneys in organ culture showed no differences, indicating that PTGS2 derived PGE2 may at best have a minor role. ASA reduces early renal growth and development but the role of prostaglandins in this may be minor.

  9. The Mechanism of Action of SOCS2 and its Role in Metabolism and Growth

    OpenAIRE

    Vesterlund, Mattias

    2013-01-01

    A well-known function of Growth Hormone (GH) is the regulation of postnatal longitudinal growth but it also affects other biological processes, for instance metabolism and inflammation. Actions of GH are tightly regulated at several levels and by several different factors and are initiated by GH binding to membrane bound GH receptors (GHR). The intracellular signaling of GH and other related hormones and cytokines is predominately mediated by the JAK-STAT pathway. This pathway is regulated in...

  10. Mechanism of growth hormone-induced postprandial carbohydrate intolerance in humans.

    Science.gov (United States)

    Butler, P; Kryshak, E; Rizza, R

    1991-04-01

    Growth hormone excess can cause postprandial carbohydrate intolerance. To determine the contribution of splanchnic and extrasplanchnic tissues to this process, subjects were fed an isotopically labeled mixed meal after either a 12-h infusion of saline or growth hormone (4 micrograms.kg-1.h-1 [corrected]). Growth hormone infusion resulted in higher glucose and insulin concentrations both before and after meal ingestion. Despite growth hormone-induced hyperglycemia and hyperinsulinemia, postprandial hepatic glucose release and carbon dioxide incorporation into glucose (a qualitative estimate of gluconeogenesis) were similar to those present during saline, suggesting altered hepatic regulation. This was confirmed when glucose was infused in the absence of growth hormone to achieve glucose (and insulin) concentrations comparable to those present during growth hormone infusion. Although growth hormone excess did not alter splanchnic uptake of ingested glucose, it resulted in a fivefold increase in postprandial hepatic glucose release (578 +/- 31 vs. 117 +/- 10 mg.kg-16 h-1, P less than 0.01), less suppression of carbon dioxide incorporation into glucose (-13 +/- 9 vs. -53 +/- 12 mg.kg-1. 6-h-1, P less than 0.01), and lower glucose uptake (1,130 +/- 59 vs. 1,850 +/- 150 mg.kg-1.6 h-1, P less than 0.01). The decrease in postprandial glucose uptake did not appear to be mediated by a change in substrate uptake since postprandial plasma concentrations and forearm balance of lactate, free fatty acids, and ketone bodies did not differ in the presence and absence of growth hormone excess.(ABSTRACT TRUNCATED AT 250 WORDS)

  11. The RARgamma selective agonist CD437 inhibits gastric cell growth through the mechanism of apoptosis.

    Science.gov (United States)

    Jiang, S Y; Lin, D Y; Shyu, R Y; Reichert, U; Yeh, M Y

    1999-04-01

    Retinoids are differentiation-inducing agents that exhibit multiple functions. Their activities are mediated through interaction with nuclear retinoic acid receptors (RAR) and retinoid X receptors (RXR). We have investigated the activities of synthetic retinoids on the growth of five gastric cancer cell lines. The effects of agonists selective for RARalpha, RARbeta and RARgamma (AM580, CD2019 and CD437, respectively) on cell growth were determined, in comparison to all-trans retinoic acid, by measuring total cellular DNA. AM580 and CD2019 had little or no effect on the growth of all five cell lines. In contrast, the RARgamma agonist CD437 inhibited cell growth up to 90-99% in both retinoic acid sensitive and resistant gastric cancer cells at a concentration of 1 microM. The growth suppression caused by CD437 was accompanied by the induction of apoptosis as judged by morphological criteria and DNA ladder formation. However, the extent of CD437-induced growth suppression was not correlated with RARgamma mRNA levels, which indicates that CD437 induces apoptosis in gastric cancer cells via an RARgamma independent pathway.

  12. Investigation of mechanical properties based on grain growth and microstructure evolution of alumina ceramics during two step sintering process

    Science.gov (United States)

    Khan, U. A.; Hussain, A.; Shah, M.; Shuaib, M.; Qayyum, F.

    2016-08-01

    Alumina ceramics having small grain size and high density yield good mechanical properties, which are required in most mechanical applications. Two Step Sintering (TSS) is used to develop dense alumina ceramics. In this research work the effect of sintering temperatures on microstructure and density of the alumina specimens developed by using TSS has been investigated. It has been observed that TSS is more efficient in controlling grain growth and increasing the density as compared to One Step Sintering (OSS) of alumina. Scanning electron micrographs of sintered alumina specimens have been compared. It has been observed that TSS proves to be a better technique for increasing density and controlling grain growth of alumina ceramics than OSS. More relative density, hardness, fracture toughness and small grain size was achieved by using TSS over OSS technique.

  13. Mind your errors: evidence for a neural mechanism linking growth mind-set to adaptive posterror adjustments.

    Science.gov (United States)

    Moser, Jason S; Schroder, Hans S; Heeter, Carrie; Moran, Tim P; Lee, Yu-Hao

    2011-12-01

    How well people bounce back from mistakes depends on their beliefs about learning and intelligence. For individuals with a growth mind-set, who believe intelligence develops through effort, mistakes are seen as opportunities to learn and improve. For individuals with a fixed mind-set, who believe intelligence is a stable characteristic, mistakes indicate lack of ability. We examined performance-monitoring event-related potentials (ERPs) to probe the neural mechanisms underlying these different reactions to mistakes. Findings revealed that a growth mind-set was associated with enhancement of the error positivity component (Pe), which reflects awareness of and allocation of attention to mistakes. More growth-minded individuals also showed superior accuracy after mistakes compared with individuals endorsing a more fixed mind-set. It is critical to note that Pe amplitude mediated the relationship between mind-set and posterror accuracy. These results suggest that neural mechanisms indexing on-line awareness of and attention to mistakes are intimately involved in growth-minded individuals' ability to rebound from mistakes.

  14. From Boron Cluster to Two-Dimensional Boron Sheet on Cu(111) Surface: Growth Mechanism and Hole Formation

    OpenAIRE

    Hongsheng Liu; Junfeng Gao; Jijun Zhao

    2013-01-01

    As attractive analogue of graphene, boron monolayers have been theoretically predicted. However, due to electron deficiency of boron atom, synthesizing boron monolayer is very challenging in experiments. Using first-principles calculations, we explore stability and growth mechanism of various boron sheets on Cu(111) substrate. The monotonic decrease of formation energy of boron cluster BN with increasing cluster size and low diffusion barrier for a single B atom on Cu(111) surface ensure cont...

  15. First-order Description of the Mechanical Fracture Behavior of Fine-Grained Surficial Marine Sediments During Gas Bubble Growth

    Science.gov (United States)

    2010-01-01

    10 F04O29 BARRY ET AL.: BUBBLE GROWTH BY FRACTURE P04029 Figure 3. Map of field site. Canard, Nova Scotia, Canada. appears to approximate the...Bottinger. and T. Dahm (2005), Buoyancy-driven fracture ascent: Experiments in layered gelatine. J. Volcano!. Geotherm . Res., 144. 273-285. doi...Journal Article 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE First-order description of the mechanical fracture behavior of fine-grained

  16. Mechanisms involved in the hydrothermal growth of ultra-thin and high aspect ratio ZnO nanowires

    Science.gov (United States)

    Demes, Thomas; Ternon, Céline; Morisot, Fanny; Riassetto, David; Legallais, Maxime; Roussel, Hervé; Langlet, Michel

    2017-07-01

    Hydrothermal synthesis of ZnO nanowires (NWs) with tailored dimensions, notably high aspect ratios (AR) and small diameters, is a major concern for a wide range of applications and still represents a challenging and recurring issue. In this work, an additive-free and reproducible hydrothermal procedure has been developed to grow ultra-thin and high AR ZnO NWs on sol-gel deposited ZnO seed layers. Controlling the substrate temperature and using a low reagent concentration (1 mM) has been found to be essential for obtaining such NWs. We show that the NW diameter remains constant at about 20-25 nm with growth time contrary to the NW length that can be selectively increased leading to NWs with ARs up to 400. On the basis of investigated experimental conditions along with thermodynamic and kinetic considerations, a ZnO NW growth mechanism has been developed which involves the formation and growth of nuclei followed by NW growth when the nuclei reach a critical size of about 20-25 nm. The low reagent concentration inhibits NW lateral growth leading to ultra-thin and high AR NWs. These NWs have been assembled into electrically conductive ZnO nanowire networks, which opens attractive perspectives toward the development of highly sensitive low-cost gas- or bio-sensors.

  17. Internalization mechanisms of the epidermal growth factor receptor after activation with different ligands.

    Directory of Open Access Journals (Sweden)

    Lasse Henriksen

    Full Text Available The epidermal growth factor receptor (EGFR regulates normal growth and differentiation, but dysregulation of the receptor or one of the EGFR ligands is involved in the pathogenesis of many cancers. There are eight ligands for EGFR, however most of the research into trafficking of the receptor after ligand activation focuses on the effect of epidermal growth factor (EGF and transforming growth factor-α (TGF-α. For a long time it was believed that clathrin-mediated endocytosis was the major pathway for internalization of the receptor, but recent work suggests that different pathways exist. Here we show that clathrin ablation completely inhibits internalization of EGF- and TGF-α-stimulated receptor, however the inhibition of receptor internalization in cells treated with heparin-binding EGF-like growth factor (HB-EGF or betacellulin (BTC was only partial. In contrast, clathrin knockdown fully inhibits EGFR degradation after all ligands tested. Furthermore, inhibition of dynamin function blocked EGFR internalization after stimulation with all ligands. Knocking out a number of clathrin-independent dynamin-dependent pathways of internalization had no effect on the ligand-induced endocytosis of the EGFR. We suggest that EGF and TGF-α lead to EGFR endocytosis mainly via the clathrin-mediated pathway. Furthermore, we suggest that HB-EGF and BTC also lead to EGFR endocytosis via a clathrin-mediated pathway, but can additionally use an unidentified internalization pathway or better recruit the small amount of clathrin remaining after clathrin knockdown.

  18. Mechanical stretch augments insulin-induced vascular smooth muscle cell proliferation by insulin-like growth factor-1 receptor

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Gang [Department of Pharmacology, Faculty of Medicine, Kagawa University, Kagawa (Japan); Department of Anesthesiology, First Affiliated Hospital of China Medical University, Shenyang (China); Hitomi, Hirofumi, E-mail: hitomi@kms.ac.jp [Department of Pharmacology, Faculty of Medicine, Kagawa University, Kagawa (Japan); Hosomi, Naohisa [Department of Cardiorenal and Cerebrovascular Medicine, Faculty of Medicine, Kagawa University, Kagawa (Japan); Lei, Bai; Nakano, Daisuke [Department of Pharmacology, Faculty of Medicine, Kagawa University, Kagawa (Japan); Deguchi, Kazushi; Mori, Hirohito; Masaki, Tsutomu [Department of Gastroenterology and Neurology, Faculty of Medicine, Kagawa University, Kagawa (Japan); Ma, Hong [Department of Anesthesiology, First Affiliated Hospital of China Medical University, Shenyang (China); Griendling, Kathy K. [Department of Medicine, Division of Cardiology, Emory University School of Medicine, Atlanta, GA (United States); Nishiyama, Akira [Department of Pharmacology, Faculty of Medicine, Kagawa University, Kagawa (Japan)

    2011-10-15

    Insulin resistance and hypertension have been implicated in the pathogenesis of cardiovascular disease; however, little is known about the roles of insulin and mechanical force in vascular smooth muscle cell (VSMC) remodeling. We investigated the contribution of mechanical stretch to insulin-induced VSMC proliferation. Thymidine incorporation was stimulated by insulin in stretched VSMCs, but not in un-stretched VSMCs. Insulin increased 2-deoxy-glucose incorporation in both stretched and un-stretched VSMCs. Mechanical stretch augmented insulin-induced extracellular signal-regulated kinase (ERK) and Akt phosphorylation. Inhibitors of epidermal growth factor (EGF) receptor tyrosine kinase and Src attenuated insulin-induced ERK and Akt phosphorylation, as well as thymidine incorporation, whereas 2-deoxy-glucose incorporation was not affected by these inhibitors. Moreover, stretch augmented insulin-like growth factor (IGF)-1 receptor expression, although it did not alter the expression of insulin receptor and insulin receptor substrate-1. Insulin-induced ERK and Akt activation, and thymidine incorporation were inhibited by siRNA for the IGF-1 receptor. Mechanical stretch augments insulin-induced VSMC proliferation via upregulation of IGF-1 receptor, and downstream Src/EGF receptor-mediated ERK and Akt activation. Similar to in vitro experiment, IGF-1 receptor expression was also augmented in hypertensive rats. These results provide a basis for clarifying the molecular mechanisms of vascular remodeling in hypertensive patients with hyperinsulinemia. -- Highlights: {yields} Mechanical stretch augments insulin-induced VSMC proliferation via IGF-1 receptor. {yields} Src/EGFR-mediated ERK and Akt phosphorylation are augmented in stretched VSMCs. {yields} Similar to in vitro experiment, IGF-1 receptor is increased in hypertensive rats. {yields} Results provide possible mechanisms of vascular remodeling in hypertension with DM.

  19. Visualization of the self-assembly of silica nanochannels reveals growth mechanism

    Science.gov (United States)

    Jung, Christophe; Schwaderer, Peter; Dethlefsen, Mark; Köhn, Ralf; Michaelis, Jens; Bräuchle, Christoph

    2011-02-01

    Self-assembled mesoporous structures with well-ordered nanoscale channels could be used in applications such as molecular separation, nano-optics, molecular electronics, nanomedicine and catalysis. However, the domain sizes that can be created in such systems are limited by our lack of a detailed understanding of the relevant growth processes. Here we report the real-time observation of domain growth in the self-assembly of silica nanochannels using fluorescence polarization imaging and atomic force microscopy. We show that transient lamellar structures precede the formation of hexagonal layers, and that the layer growth follows two distinct pathways. In addition, the domains are grown on a mesoporous film substrate, which acts as a sieve and allows control of the delivery of the reactive species. We use these insights and capabilities to grow layers of well-ordered silica nanochannels with domain sizes of up to ~0.3 mm.

  20. The stability of a rising droplet: an inertialess nonmodal growth mechanism

    CERN Document Server

    Gallino, Giacomo; Gallaire, Francois

    2015-01-01

    Past modal stability analysis (Kojima et al. 1984) predicted that a rising or sedimenting droplet in a viscous fluid is stable in the presence of surface tension no matter how small, in contrast with experimental and numerical results. By performing a non-modal stability analysis, we demonstrate the potential for transient growth of the interfacial energy of a rising droplet in the limit of inertialess Stokes equations. The predicted critical capillary numbers agree well with that from direct numerical simulations reported in the literature (Koh & Leal 1989). Boundary integral simulations are used to delineate the critical amplitude of the most destabilizing perturbations. The critical amplitude is negatively correlated with the linear optimal energy growth, implying that the transient growth is responsible for reducing the necessary perturbation amplitude required to escape the basin of attraction of the spherical solution.

  1. Experimental study on the mechanism of hydraulic fracture growth in a glutenite reservoir

    Science.gov (United States)

    Ma, Xinfang; Zou, Yushi; Li, Ning; Chen, Ming; Zhang, Yinuo; Liu, Zizhong

    2017-04-01

    Glutenite reservoirs are frequently significantly heterogeneous because of their unique depositional environment. The presence of gravel in this type of formation complicates the growth path of hydraulic fracture (HF). In this study, laboratory fracturing experiments were conducted on six large natural glutenite specimens (300 mm × 300 mm × 300 mm) using a true triaxial hydraulic fracturing system to investigate the growth law of HF in glutenite reservoirs. Before the experiments were performed, the rock properties of the gravel particles and matrix in the glutenite specimens were determined using various apparatuses. The effects of gravel size, horizontal differential stress, fracturing fluid type (or viscosity), and flow rate on the HF growth pattern, fracture width, and injection pressure were examined in detail. Similar to previous studies, four types of HF intersections with gravel particles, namely, termination, penetration, deflection, and attraction, were observed. The HF growth path in the glutenite specimens with large gravel (40 mm-100 mm) is likely branched and tortuous even under high horizontal differential stress. The HF growth path in the glutenite specimens with small gravel (less than 20 mm) is simple, but a process zone with multiple thin fractures may be created. Breakdown pressure may increase significantly when HF initiates from high-strength gravel particles, which are mainly composed of quartz. HF propagation is likely limited within high-strength gravel particles, thereby resulting in narrow fractures and even termination. The use of low-viscosity fluids, such as slickwater, and the low injection rate can further limit HF growth, particularly its width. As a response, high extension pressure builds up during fracturing.

  2. Acetylsalicylic acid interferes with embryonic kidney growth and development by a prostaglandin-independent mechanism

    Science.gov (United States)

    Welham, Simon J M; Sparrow, Alexander J; Gardner, David S; Elmes, Matthew J

    2017-01-01

    AIM To evaluate the effects of the non-selective, non-steroidal anti-inflammatory drug (NSAID) acetylsalicylic acid (ASA), on ex vivo embryonic kidney growth and development. METHODS Pairs of fetal mouse kidneys at embryonic day 12.5 were cultured ex vivo in increasing concentrations of ASA (0.04-0.4 mg/mL) for up to 7 d. One organ from each pair was grown in control media and was used as the internal control for the experimental contralateral organ. In some experiments, organs were treated with ASA for 48 h and then transferred either to control media alone or control media containing 10 μmol/L prostaglandin E2 (PGE2) for a further 5 d. Fetal kidneys were additionally obtained from prostaglandin synthase 2 homozygous null or heterozygous (PTGS2-/- and PTGS2-/+) embryos and grown in culture. Kidney cross-sectional area was used to determine treatment effects on kidney growth. Whole-mount labelling to fluorescently detect laminin enabled crude determination of epithelial branching using confocal microscopy. RESULTS Increasing ASA concentration (0.1, 0.2 and 0.4 mg/mL) significantly inhibited metanephric growth (P < 0.05). After 7 d of culture, exposure to 0.2 mg/mL and 0.4 mg/mL reduced organ size to 53% and 23% of control organ size respectively (P < 0.01). Addition of 10 μmol/L PGE2 to culture media after exposure to 0.2 mg/mL ASA for 48 h resulted in a return of growth area to control levels. Application of control media alone after cessation of ASA exposure showed no benefit on kidney growth. Despite the apparent recovery of growth area with 10 μmol/L PGE2, no obvious renal tubular structures were formed. The number of epithelial tips generated after 48 h exposure to ASA was reduced by 40% (0.2 mg/mL; P < 0.05) and 47% (0.4 mg/mL; P < 0.01). Finally, growth of PTGS2-/- and PTGS2+/- kidneys in organ culture showed no differences, indicating that PTGS2 derived PGE2 may at best have a minor role. CONCLUSION ASA reduces early renal growth and development but the

  3. Impact of bacterial priming on some stress tolerance mechanisms and growth of cold stressed wheat seedlings

    Directory of Open Access Journals (Sweden)

    Mohammed E.H. Osman

    2014-01-01

    Full Text Available The potential to enhance growth of cold stressed wheat by seed treatment (priming with the beneficial bacteria Bacillus amyloliquefaciens 5113 and Azospirillum brasilense NO40 were tested. Results showed an improved ability of bacteria-treated seedlings to survive at −5°C up to 12 h. Cold stress increased transcript levels of three stress marker genes and increased activity for the ascorbate-glutathione redox enzymes. However, primed and stressed seedlings generally showed smaller effects on the stress markers correlating with better growth and improved stress tolerance. Bacterial priming to improve crop plant performance at low temperature seems a useful strategy to explore further.

  4. Thyroid hormone increases fibroblast growth factor receptor expression and disrupts cell mechanics in the developing organ of corti.

    Science.gov (United States)

    Szarama, Katherine B; Gavara, Núria; Petralia, Ronald S; Chadwick, Richard S; Kelley, Matthew W

    2013-02-09

    Thyroid hormones regulate growth and development. However, the molecular mechanisms by which thyroid hormone regulates cell structural development are not fully understood. The mammalian cochlea is an intriguing system to examine these mechanisms, as cellular structure plays a key role in tissue development, and thyroid hormone is required for the maturation of the cochlea in the first postnatal week. In hypothyroid conditions, we found disruptions in sensory outer hair cell morphology and fewer microtubules in non-sensory supporting pillar cells. To test the functional consequences of these cytoskeletal defects on cell mechanics, we combined atomic force microscopy with live cell imaging. Hypothyroidism stiffened outer hair cells and supporting pillar cells, but pillar cells ultimately showed reduced cell stiffness, in part from a lack of microtubules. Analyses of changes in transcription and protein phosphorylation suggest that hypothyroidism prolonged expression of fibroblast growth factor receptors, and decreased phosphorylated Cofilin. These findings demonstrate that thyroid hormones may be involved in coordinating the processes that regulate cytoskeletal dynamics and suggest that manipulating thyroid hormone sensitivity might provide insight into the relationship between cytoskeletal formation and developing cell mechanical properties.

  5. Effects of mechanical stress or abscisic acid on growth, water status and leaf abscisic acid content of eggplant seedlings

    Science.gov (United States)

    Latimer, J. G.; Mitchell, C. A.

    1988-01-01

    Container-grown eggplant (Solanum melongena L. var esculentum Nees. 'Burpee's Black Beauty') seedlings were conditioned with brief, periodic mechanical stress or abscisic acid (ABA) in a greenhouse prior to outdoor exposure. Mechanical stress consisted of seismic (shaking) or thigmic (stem flexing) treatment. Exogenous ABA (10(-3) or 10(-4)M) was applied as a soil drench 3 days prior to outdoor transfer. During conditioning, only thigmic stress reduced stem elongation and only 10(-3) M ABA reduced relative growth rate (RGR). Both conditioning treatments increased leaf specific chlorophyll content, but mechanical stress did not affect leaf ABA content. Outdoor exposure of unconditioned eggplant seedlings decreased RGR and leaf-specific chlorophyll content, but tended to increase leaf ABA content relative to that of plants maintained in the greenhouse. Conditioning did not affect RGR of plants subsequently transferred outdoors, but did reduce stem growth. Seismic stress applied in the greenhouse reduced dry weight gain by plants subsequently transferred outdoors. Mechanical stress treatments increased leaf water potential by 18-25% relative to that of untreated plants.

  6. Numerical simulation of asymmetrically altered growth as initiation mechanism of scoliosis

    NARCIS (Netherlands)

    Van der Plaats, A.; Veldhuizen, A. G.; Verkerke, G. J.

    2007-01-01

    The causes of idiopathic scoliosis are still uncertain; buckling is mentioned often, but never proven. The authors hypothesize another option: unilateral postponement of growth of MM Rotatores or of ligamentum flavum and intertransverse ligament. In this paper, both buckling and the two new theories

  7. Kinetics of Vapor-Solid Phase Transitions: Structure, Growth, and Mechanism

    Science.gov (United States)

    Midya, Jiarul; Das, Subir K.

    2017-04-01

    The kinetics of the separation between low and high density phases in a single component Lennard-Jones model is studied via molecular dynamics simulations, at very low temperatures, in the space dimension d =2 . For densities close to the vapor branch of the coexistence curve, disconnected nanoscale clusters of the high density phase exhibit essentially ballistic motion. Starting from nearly circular shapes, at the time of nucleation, these clusters grow via sticky collisions, gaining filamentlike nonequilibrium structure at a later time, with a very low fractal dimensionality. The origin of the latter is shown to lie in the low mobility of the constituent particles, in the corresponding cluster reference frame, due to the (quasi-long-range) crystalline order. Standard self-similarity in the domain pattern, typically observed in the kinetics of phase transitions, is found to be absent. This invalidates the common method, that provides a growth law comparable to that in solid mixtures, of quantifying growth. An appropriate alternative approach, involving the fractality, quantifies the growth of the characteristic "length" to be a power law with time, the exponent being strongly temperature dependent. The observed growth law is in agreement with the outcome of a nonequilibrium kinetic theory.

  8. Mechanisms of dwell fatigue crack growth in an advanced nickel disc alloy RR1000

    Directory of Open Access Journals (Sweden)

    Yu S.Y.

    2014-01-01

    Full Text Available RR1000 is one of an advanced class of nickel-based superalloys developed for disc applications. Under one hour dwell fatigue loading, complex crack growth behaviour has been observed especially in a coarse grained version of this alloy. At a temperature of 700 ∘C in air an increase of nearly two orders of magnitude in crack growth rates compared to baseline fatigue crack growth rates may be seen. However for certain microstructural conditions, cracks can also demonstrate retardation following initial acceleration. When using a direct current potential difference (d.c.p.d technique for monitoring crack growth, a damage zone of a few hundred microns is often measured ahead of a fast growing crack. Advanced characterisation techniques including SEM, ECCI and X-ray tomography have been adopted in the current study to understand the observed damage zone and retardation phenomenon. It is found that damage zones measured by d.c.p.d reflect brittle and non-uniform advance of the crack resulting from continuous dynamic or quasi-dynamic fracture of an oxide intrusion ahead of the crack tip during the dwell period. In contrast, cracking of the oxide intrusion is less frequent or even prevented during dwell periods associated with a retarded and slow growing crack. Crack tip stress relaxation plays an important role in dictating whether or not dynamic cracking of the oxide intrusion can be avoided.

  9. On the mechanism of self-deceleration of the thin oxide film growth

    CERN Document Server

    Mukhambetov, D G

    2002-01-01

    The objective of this work was to investigate the kinetics of the two-phase oxide film growth on the alpha-Fe surface at temperatures of 650-750 K. We experimentally determined that the film thickness (h)-time oxidation (tau) relationship in the range denoted above is a logarithmic function, whereas Cabrera and Mott's theory gives a square law of film growth. In our work, analytical treatment of experimental data was made based on this theory, but we propose that self-deceleration of the film growth is caused not by attenuation of the electric intensity in the film because of an increase of h but by the shielding influence of the space charge of diffusing ions and electrons in that oxide film. With that purpose in view, the Debye shielding distance for plasma substance state in the oxide film was taken into consideration. The logarithmic law of oxide film growth was derived. Estimated calculations of this law's parameters were made that quantitatively correspond with literature data. The results obtained were...

  10. Nucleation and growth mechanisms for Pd-Pt bimetallic nanodendrites and their electrocatalytic properties

    National Research Council Canada - National Science Library

    Lim, Byungkwon; Jiang, Majiong; Yu, Taekyung; Camargo, Pedro H. C; Xia, Younan

    2010-01-01

    .... These nanostructures can be easily prepared by a one-step, seeded growth method that involves the reduction of K2PtCl4 by L-ascorbic acid in the presence of 9-nm truncated octahedral Pd seeds in an aqueous solution...

  11. Differing semaphorin 3A concentrations trigger distinct signaling mechanisms in growth cone collapse.

    Science.gov (United States)

    Manns, Richard P C; Cook, Geoffrey M W; Holt, Christine E; Keynes, Roger J

    2012-06-20

    Semaphorin-3A (Sema3A) is a major guidance cue in the developing nervous system. Previous studies have revealed a dependence of responses to Sema3A on local protein synthesis (PS) in axonal growth cones, but a recent study has called this dependence into question. To understand the basis of this discrepancy we used the growth cone collapse assay on chick dorsal root ganglion neurons. We show that the dependence of growth cone collapse on protein synthesis varies according to Sema3A concentration, from near-total at low concentration (625 ng/ml). Further, we show that neuropilin-1 (NP-1) mediates both PS-dependent and PS-independent collapse. Our findings are consistent with the operation of at least two distinct Sema3A signaling pathways: one that is PS-dependent, involving mammalian target of rapamycin, and one that is PS-independent, involving GSK-3β activation and operative at all concentrations of Sema3A examined. The results provide a plausible explanation for the discrepancy in PS-dependence reported in the literature, and indicate that different signaling pathways activated within growth cones can be modulated by changing the concentration of the same guidance cue.

  12. Hydrogen peroxide detoxification is a key mechanism for growth of ammonia-oxidizing archaea

    NARCIS (Netherlands)

    Kim, Jong-Geol; Park, Soo-Je; Sinninghe Damsté, Jaap S.|info:eu-repo/dai/nl/07401370X; Schouten, Stefan|info:eu-repo/dai/nl/137124929; Rijpstra, W. Irene C.; Jung, Man-Young; Kim, So-Jeong; Gwak, Joo-Han; Hong, Heeji; Si, Ok-Ja; Lee, Sanghoon; Madsen, Eugene L.; Rhee, Sung-Keun

    2016-01-01

    Ammonia-oxidizing archaea (AOA), that is, members of the Thaumarchaeota phylum, occur ubiquitously in the environment and are of major significance for global nitrogen cycling. However, controls on cell growth and organic carbon assimilation by AOA are poorly understood. We isolated an

  13. Control of bacterial biofilm growth on surfaces by nanostructural mechanics and geometry

    Science.gov (United States)

    Epstein, A. K.; Hochbaum, A. I.; Kim, Philseok; Aizenberg, J.

    2011-12-01

    Surface-associated communities of bacteria, called biofilms, pervade natural and anthropogenic environments. Mature biofilms are resistant to a wide range of antimicrobial treatments and therefore pose persistent pathogenic threats. The use of surface chemistry to inhibit biofilm growth has been found to only transiently affect initial attachment. In this work, we investigate the tunable effects of physical surface properties, including high-aspect-ratio (HAR) surface nanostructure arrays recently reported to induce long-range spontaneous spatial patterning of bacteria on the surface. The functional parameters and length scale regimes that control such artificial patterning for the rod-shaped pathogenic species Pseudomonas aeruginosa are elucidated through a combinatorial approach. We further report a crossover regime of biofilm growth on a HAR nanostructured surface versus the nanostructure effective stiffness. When the 'softness' of the hair-like nanoarray is increased beyond a threshold value, biofilm growth is inhibited as compared to a flat control surface. This result is consistent with the mechanoselective adhesion of bacteria to surfaces. Therefore by combining nanoarray-induced bacterial patterning and modulating the effective stiffness of the nanoarray—thus mimicking an extremely compliant flat surface—bacterial mechanoselective adhesion can be exploited to control and inhibit biofilm growth.

  14. Numerical simulation of asymmetrically altered growth as initiation mechanism of scoliosis

    NARCIS (Netherlands)

    Van der Plaats, A.; Veldhuizen, A. G.; Verkerke, G. J.

    The causes of idiopathic scoliosis are still uncertain; buckling is mentioned often, but never proven. The authors hypothesize another option: unilateral postponement of growth of MM Rotatores or of ligamentum flavum and intertransverse ligament. In this paper, both buckling and the two new theories

  15. The mechanism of growth of ZnO nanorods by reactive sputtering

    Science.gov (United States)

    Nandi, R.; Major, S. S.

    2017-03-01

    DC reactive magnetron sputtering of zinc target in argon-oxygen sputtering atmosphere has been used to grow ZnO thin films/nanorods on Si in a wide substrate temperature range of 300-750 °C and under different sputtering conditions, namely, DC power, sputtering pressure and oxygen percentage in the sputtering atmosphere. Powder X-ray diffraction, Raman spectroscopy and a combination of top-down and cross-sectional scanning electron microscopy studies of ZnO films and nanorods grown under different conditions, have shown that substrate temperature critically controls their growth behavior and morphology, eventually resulting in the growth of vertically c-axis oriented, highly aligned and separated ZnO nanorods at substrate temperatures of 700-750 °C. The strongly substrate temperature dependent growth of nanorods is explained by considering that the growth above 600 °C, takes place in the 'desorption regime', in which, the surface diffusion length decreases exponentially with temperature. The diameter of nanorods increases with increase of DC power or decrease of sputtering pressure, which is attributed to the increase of surface diffusion length at higher deposition flux. The morphology of ZnO nanorods is not significantly affected by oxygen percentage in the sputtering atmosphere, since it does not influence the deposition flux.

  16. Growth of NaBi(WO4)2 Dendrite and Mechanism

    Institute of Scientific and Technical Information of China (English)

    HONG Yong; AI Fei; PAN Xiu-Hong; JIN Wei-Qing; ZHONG Wei-Zhuo; SHINICHI Yoda

    2006-01-01

    @@ The solid-liquid interface motion of NaBi(WO4)2 (NBWO) melt crystal growth is observed in an in situ system,in which the whole processes of interface transition from flat interface and cellular to dendrite are visualized.

  17. Amelioration of iron toxicity: A mechanism for aluminum-induced growth stimulation in tea plants.

    Science.gov (United States)

    Hajiboland, Roghieh; Barceló, Juan; Poschenrieder, Charlotte; Tolrà, Roser

    2013-11-01

    Tea plants (Camellia sinensis) are well adapted to acid soils with high Al availability. These plants not only accumulate high leaf Al concentrations, but also respond to Al with growth stimulation. Decreased oxidative stress has been associated with this effect. Why tea plants not exposed to Al suffer from oxidative stress has not been clarified. In this study, hydroponically grown tea plants treated with 0 to 300 μM Al were analyzed for growth, Al and Fe accumulation, and Al distribution by means of morin and hematoxylin staining. Roots of control plants stained black with hematoxylin. This indicates the formation of a Fe-hematoxylin complex. Young leaves of controls accumulated more than 1000 mg Fe kg(-1) dry weight. This concentration is above the Fe-toxicity threshold in most species. Supply of Al stimulated growth and reduced Fe uptake and transport. These results indicate that Al-induced growth stimulation might be due to alleviation of a latent Fe toxicity occurring in tea plants without Al supply.

  18. Hydrogen peroxide detoxification is a key mechanism for growth of ammonia-oxidizing archaea

    NARCIS (Netherlands)

    Kim, Jong-Geol; Park, Soo-Je; Sinninghe Damsté, Jaap S.; Schouten, Stefan; Rijpstra, W. Irene C.; Jung, Man-Young; Kim, So-Jeong; Gwak, Joo-Han; Hong, Heeji; Si, Ok-Ja; Lee, Sanghoon; Madsen, Eugene L.; Rhee, Sung-Keun

    2016-01-01

    Ammonia-oxidizing archaea (AOA), that is, members of the Thaumarchaeota phylum, occur ubiquitously in the environment and are of major significance for global nitrogen cycling. However, controls on cell growth and organic carbon assimilation by AOA are poorly understood. We isolated an ammonia-oxidi

  19. Growth mechanisms for Si epitaxy on O atomic layers: Impact of O-content and surface structure

    Energy Technology Data Exchange (ETDEWEB)

    Jayachandran, Suseendran, E-mail: suseendran.jayachandran@imec.be [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Metallurgy and Materials, Castle Arenberg 44, B-3001 Leuven (Belgium); Billen, Arne [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Chemistry, Celestijnenlaan 200F, B-3001 Leuven (Belgium); Douhard, Bastien; Conard, Thierry; Meersschaut, Johan; Moussa, Alain; Caymax, Matty; Bender, Hugo [Imec, Kapeldreef 75, 3001 Leuven (Belgium); Vandervorst, Wilfried [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Physics and Astronomy, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Heyns, Marc [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Metallurgy and Materials, Castle Arenberg 44, B-3001 Leuven (Belgium); Delabie, Annelies [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Chemistry, Celestijnenlaan 200F, B-3001 Leuven (Belgium)

    2016-10-30

    Highlights: • O{sub 3} or O{sub 2} exposures on H-Si(100) result in O ALs with different surface structures. • Si-EPI on O AL using O{sub 3} process is by direct epitaxial growth mechanism. • Si-EPI on O AL using O{sub 2} process is by epitaxial lateral overgrowth mechanism. • Distortions by O AL, SiH{sub 4} flux rate and Si thickness has an impact on Si-EPI quality. - Abstract: The epitaxial growth of Si layers on Si substrates in the presence of O atoms is generally considered a challenge, as O atoms degrade the epitaxial quality by generating defects. Here, we investigate the growth mechanisms for Si epitaxy on O atomic layers (ALs) with different O-contents and structures. O ALs are deposited by ozone (O{sub 3}) or oxygen (O{sub 2}) exposure on H-terminated Si at 50 °C and 300 °C respectively. Epitaxial Si is deposited by chemical vapor deposition using silane (SiH{sub 4}) at 500 °C. After O{sub 3} exposure, the O atoms are uniformly distributed in Si-Si dimer/back bonds. This O layer still allows epitaxial seeding of Si. The epitaxial quality is enhanced by lowering the surface distortions due to O atoms and by decreasing the arrival rate of SiH{sub 4} reactants, allowing more time for surface diffusion. After O{sub 2} exposure, the O atoms are present in the form of SiO{sub x} clusters. Regions of hydrogen-terminated Si remain present between the SiO{sub x} clusters. The epitaxial seeding of Si in these structures is realized on H-Si regions, and an epitaxial layer grows by a lateral overgrowth mechanism. A breakdown in the epitaxial ordering occurs at a critical Si thickness, presumably by accumulation of surface roughness.

  20. Alternative splicing and expression of the insulin-like growth factor (IGF-1) gene in osteoblasts under mechanical stretch

    Institute of Scientific and Technical Information of China (English)

    XIAN Chengyu; WANG Yuanliang; ZHANG Bingbing; TANG Liling; PAN Jun; LUO Yanfeng; JIANG Peng; LI Dajun

    2006-01-01

    Insulin-like growth factor 1 (IGF-1) promotes osteoblasts differentiation and bone formation,and its expression is induced by mechanical stretch,thus IGF-1 has been considered an effector molecule that links mechanical stimulation and local tissue responses. In this study, a mechanical stretching device was designed to apply physiological level static or cyclic stretching stimulation to osteoblasts.Different isoforms of IGF-1 mRNA were amplified by RT-PCR from the cells using respective primers and these amplified products were sequenced. An isoform of IGF-1 splicing product was found to be selectively produced by osteoblasts under stretching stimulation. This IGF-1 isoform had identical sequence with the mechano growth factor (MGF) which was originally identified in muscle cells. Regulations of the expression of the liver-type IGF (L.IGF-1) and MGF in osteoblasts under stretch stimulation were further studied using semi-quantitative RT-PCR.Stretch stimulation was found to promot the expression of IGF-1 (L.IGF-1 and MGF), and for both isoforms expression was more effectively stimulated by cyclic stretch than static stretch. MGF was detected only in osteoblasts subjected to mechanical stretch,suggesting MGF was a stretch sensitive growth factor.Expression of MGF peaked earlier than that of L.IGF-1, which was similar to their regulation in muscie and suggested similar roles of MGF and L.IGF-1in bone as in muscle cells. The functions of MGF and L.IGF-1 in osteoblasts shall be established by further experimental studies.

  1. Interaction of Mechanical Load with Growth Hormone (GH) and Insulin-Like Growth Factor I (IGF-I) on Slow-Twitch Skeletal Muscle and Bone

    Science.gov (United States)

    Linderman, Jon K.; Gosselink, Kristin L.; Wang, Tommy J.; Mukku, Venkat R.; Grindeland, Richard E.

    1994-01-01

    Exogenous humoral growth factors, combined with increased mechanical loading, reportedly induce hypertrophy of fast-, but not slow-twitch skeletal muscles, and have little effect in attenuating atrophy of slow-twitch muscle associated with exposure to microgravity in animals with intact neuroendocrine systems. These observations suggest that anabolic adjuvants and muscle tension do not interact to stimulate growth or maintenance of slow-twitch skeletal muscle. The purpose of the present study was to determine whether a chronic increase in mechanical loading (synergistic ablation) or hindlimb unweighting (hindlimb suspension) interact with exogenous GH and IGF-I (Genentech, So San Francisco, CA) in the slow-twitch soleus muscles of female rats (approx. 250 g). Bilateral ablation of the plantaris and gastrocnemius muscles induced 38% and 40% increases in the absolute (mg/pair) and relative (mg/100 g body weight) weights of the soleus, respectively (p less than or = 0.05), in ambulatory rats. GH and IGF-I interacted with chronic loading to increase absolute soleus mass an additional 20% (p less than or = 0.05), and mixed and myofibrillar protein contents an additional 12% and 7%, respectively (NS). In contrast, hindlimb suspension (HLS) resulted in 20% and 18% decreases in the absolute and relative weights of the soleus, respectively (p less than or = 0.05); GH and IGF-I did not spare loss of soleus mass or protein content in HLS rats. HLS decreased tibial plate thickness approx. 11% (p less than or = 0.05), but not weights of the tibia or femus. GH and IGF-I increased tibial plate thickness approx. 30% (p less than or = 0.05), in ambulatory and HLS rats, and increased femur and tibial weights 12% (p less than or = 0.05) and 8% (NS), respectively, in ambulatory rats, but had no effect in HLS rats. Results of the present investigation suggest that GH and IGF-I can stimulate hypertrophy of slow-twitch skeletal muscle when chronically overloaded, but can also stimulate

  2. Interaction of Mechanical Load with Growth Hormone (GH) and Insulin-Like Growth Factor I (IGF-I) on Slow-Twitch Skeletal Muscle and Bone

    Science.gov (United States)

    Linderman, Jon K.; Gosselink, Kristin L.; Wang, Tommy J.; Mukku, Venkat R.; Grindeland, Richard E.

    1994-01-01

    Exogenous humoral growth factors, combined with increased mechanical loading, reportedly induce hypertrophy of fast-, but not slow-twitch skeletal muscles, and have little effect in attenuating atrophy of slow-twitch muscle associated with exposure to microgravity in animals with intact neuroendocrine systems. These observations suggest that anabolic adjuvants and muscle tension do not interact to stimulate growth or maintenance of slow-twitch skeletal muscle. The purpose of the present study was to determine whether a chronic increase in mechanical loading (synergistic ablation) or hindlimb unweighting (hindlimb suspension) interact with exogenous GH and IGF-I (Genentech, So San Francisco, CA) in the slow-twitch soleus muscles of female rats (approx. 250 g). Bilateral ablation of the plantaris and gastrocnemius muscles induced 38% and 40% increases in the absolute (mg/pair) and relative (mg/100 g body weight) weights of the soleus, respectively (p less than or = 0.05), in ambulatory rats. GH and IGF-I interacted with chronic loading to increase absolute soleus mass an additional 20% (p less than or = 0.05), and mixed and myofibrillar protein contents an additional 12% and 7%, respectively (NS). In contrast, hindlimb suspension (HLS) resulted in 20% and 18% decreases in the absolute and relative weights of the soleus, respectively (p less than or = 0.05); GH and IGF-I did not spare loss of soleus mass or protein content in HLS rats. HLS decreased tibial plate thickness approx. 11% (p less than or = 0.05), but not weights of the tibia or femus. GH and IGF-I increased tibial plate thickness approx. 30% (p less than or = 0.05), in ambulatory and HLS rats, and increased femur and tibial weights 12% (p less than or = 0.05) and 8% (NS), respectively, in ambulatory rats, but had no effect in HLS rats. Results of the present investigation suggest that GH and IGF-I can stimulate hypertrophy of slow-twitch skeletal muscle when chronically overloaded, but can also stimulate

  3. Mechanism of inhibitory action of the local anaesthetic trimecaine on the growth of algae (Chlorella vulgaris).

    Science.gov (United States)

    Sersen, F; Král'ová, K

    1994-08-01

    Using the model compound trimecaine, it was found that algicidal effects exhibited by the local anaesthetics of the acetanilide type were caused by two different mechanisms. The first inhibitory mechanism occurring at low concentrations of the anaesthetic is connected with the uncoupling of the photophosphorylations in algal chloroplasts and is accompanied by the enhancement of the oxygen evolving rate in algal photosynthesis. The second mechanism of inhibition of the photosynthesis in algae, taking place at higher concentrations of the anaesthetic, is connected with the damaging of the manganese containing protein on the donor side of photosystem 2 and is accompanied by a decrease of the oxygen evolving rate in algal photosynthesis.

  4. The Ang II-induced growth of vascular smooth muscle cells involves a phospholipase D-mediated signaling mechanism.

    Science.gov (United States)

    Freeman, E J

    2000-02-15

    Angiotensin (Ang) II acts as a mitogen in vascular smooth muscle cells (VSMC) via the activation of multiple signaling cascades, including phospholipase C, tyrosine kinase, and mitogen-activated protein kinase pathways. However, increasing evidence supports signal-activated phospholipases A(2) and D (PLD) as additional mechanisms. Stimulation of PLD results in phosphatidic acid (PA) formation, and PA has been linked to cell growth. However, the direct involvement of PA or its metabolite diacylglycerol (DAG) in Ang II-induced growth is unclear. PLD activity was measured in cultured rat VSMC prelabeled with [(3)H]oleic acid, while the incorporation of [(3)H]thymidine was used to monitor growth. We have previously reported the Ang II-dependent, AT(1)-coupled stimulation of PLD and growth in VSMC. Here, we show that Ang II (100 nM) and exogenous PLD (0.1-100 units/mL; Streptomyces chromofuscus) stimulated thymidine incorporation (43-208% above control). PA (100 nM-1 microM) also increased thymidine incorporation to 135% of control. Propranolol (100 nM-10 microM), which inhibits PA phosphohydrolase, blocked the growth stimulated by Ang II, PLD, or PA by as much as 95%, an effect not shared by other beta-adrenergic antagonists. Propranolol also increased the production of PA in the presence of Ang II by 320% and reduced DAG and arachidonic acid (AA) accumulation. The DAG lipase inhibitor RHC-80267 (1-10 microM) increased Ang II-induced DAG production, while attenuating thymidine incorporation and release of AA. Thus, it appears that activation of PLD, formation of PA, conversion of PA to DAG, and metabolism of DAG comprise an important signaling cascade in Ang II-induced growth of VSMC.

  5. Functions and Mechanisms of Fibroblast Growth Factor (FGF Signalling in Drosophila melanogaster

    Directory of Open Access Journals (Sweden)

    Hans-Arno J. Müller

    2013-03-01

    Full Text Available Intercellular signalling via growth factors plays an important role in controlling cell differentiation and cell movements during the development of multicellular animals. Fibroblast Growth Factor (FGF signalling induces changes in cellular behaviour allowing cells in the embryo to move, to survive, to divide or to differentiate. Several examples argue that FGF signalling is used in multi-step morphogenetic processes to achieve and maintain a transitional state of the cells required for the control of cell fate. In the genetic model Drosophila melanogaster, FGF signalling via the receptor tyrosine kinases Heartless (Htl and Breathless (Btl is particularly well studied. These FGF receptors affect gene expression, cell shape and cell–cell interactions during mesoderm layer formation, caudal visceral muscle (CVM formation, tracheal morphogenesis and glia differentiation. Here, we will address the current knowledge of the biological functions of FGF signalling in the fly on the tissue, at a cellular and molecular level.

  6. Self-catalytic crystal growth, formation mechanism, and optical properties of indium tin oxide nanostructures.

    Science.gov (United States)

    Liang, Yuan-Chang; Zhong, Hua

    2013-08-22

    In-Sn-O nanostructures with rectangular cross-sectional rod-like, sword-like, and bowling pin-like morphologies were successfully synthesized through self-catalytic growth. Mixed metallic In and Sn powders were used as source materials, and no catalyst layer was pre-coated on the substrates. The distance between the substrate and the source materials affected the size of the Sn-rich alloy particles during crystal growth in a quartz tube. This caused In-Sn-O nanostructures with various morphologies to form. An X-ray photoelectron spectroscope and a transmittance electron microscope with an energy-dispersive X-ray spectrometer were used to investigate the elemental binding states and compositions of the as-synthesized nanostructures. The Sn doping and oxygen vacancies in the In2O3 crystals corresponded to the blue-green and yellow-orange emission bands of the nanostructures, respectively.

  7. A Possible Mechanism for Overcoming the Electrostatic Barrier Against Dust Growth in Protoplanetary disks

    OpenAIRE

    2015-01-01

    The coagulation of dust particles under the conditions in protoplanetary disks is investigated. The study focuses on the repulsive electrostatic barrier against growth of charged dust grains. Taking into account the photoelectric effect leads to the appearance of a layer at intermediate heights where the dust has a close to zero charge, enabling the dust grains to grow efficiently. An increase in the coagulation rate comes about not only due to the lowering of the Coulomb barrier, but also be...

  8. Growth, optical, thermal and mechanical studies of methyl 4-hydroxybenzoate single crystals

    Science.gov (United States)

    Vijayan, N.; Ramesh Babu, R.; Gunasekaran, M.; Gopalakrishnan, R.; Ramasamy, P.

    2003-08-01

    Bulk single crystals of methyl 4-hydroxy benzoate have been successfully grown by slow evaporation solution growth technique at room temperature. The grown crystals have been subjected to spectroscopic studies like FT-IR and FT-Raman. The hardness of the crystal was measured by Vicker's microhardness tester. The lattice parameters have been calculated by X-ray diffraction technique and the values are in good agreement with the reported JCPDS file.

  9. Norgestrel and gestodene stimulate breast cancer cell growth through an oestrogen receptor mediated mechanism.

    OpenAIRE

    Catherino, W. H.; Jeng, M. H.; Jordan, V.C.

    1993-01-01

    There is great concern over the long-term influence of oral contraceptives on the development of breast cancer in women. Oestrogens are known to stimulate the growth of human breast cancer cells, and this laboratory has previously reported (Jeng & Jordan, 1991) that the 19-norprogestin norethindrone could stimulate the proliferation of MCF-7 human breast cancer cells. We studied the influence of the 19-norprogestins norgestrel and gestodene compared to a 'non' 19-norprogestin medroxyprogester...

  10. Growth mechanism of pulsed laser fabricated few-layer MoS₂ on metal substrates.

    Science.gov (United States)

    Loh, Tamie A J; Chua, Daniel H C

    2014-09-24

    Pulsed laser deposition (PLD) on metal substrates has recently been discovered to present an alternative method for producing highly crystalline few-layer MoS2. However, not every metal behaves in the same manner during film growth, and hence, it is crucial that the ability of various metals to produce crystalline MoS2 be thoroughly investigated. In this work, MoS2 was deposited on metal substrates, Al, Ag, Ni, and Cu, using a pulsed laser. Highly crystalline few-layer MoS2 was successfully grown on Ag, but is absent in Al, Ni, and Cu under specific growth conditions. This discrepancy was attributed to either excessively strong or insufficient adlayer-substrate interactions. In the case of Al, the effects of the strong interface interactions can be offset by increasing the amount of source atoms supplied, thereby producing semicrystalline few-layer MoS2. The results show that despite PLD being a physical vapor deposition technique, both physical and chemical processes play an important role in MoS2 growth on metal substrates.

  11. The mechanism by which an asymmetric distribution of plant growth hormone is attained

    Science.gov (United States)

    Bandurski, Robert S.; Schulze, Aga; Jensen, Philip; Desrosiers, Mark; Epel, Bernard; Kowalczyk, Stanley

    Zea mays (sweet corn) seedlings attain an asymmetric distribution of the growth hormone indole-3-acetic acid (IAA) within 3 minutes following a gravity stimulus. Both free and esterified IAA (that is total IAA) accumulate to a greater extent in the lower half of the mesocotyl cortex of a horizontally placed seedling than in the upper half. Thus, changes in the ratio of free IAA to ester IAA cannot account for the asymmetric distribution. Our studies demonstrate there is no de novo synthesis of IAA in young seedlings. We conclude that asymmetric IAA distribution is attained by a gravity-induced, potential-regulated gating of the movement of IAA from kernel to shoot and from stele to cortex. As a working theory, which we call the Potential Gating Theory, we propose that perturbation of the plant's bioelectric field, induced by gravity, causes opening and closing of transport channels in the plasmodesmata connecting the vascular stele to the surrounding cortical tissues. This results in asymmetric growth hormone distribution which results in the asymmetric growth characteristic of the gravitropic response.

  12. Florigen and anti-florigen - a systemic mechanism for coordinating growth and termination in flowering plants.

    Science.gov (United States)

    Lifschitz, Eliezer; Ayre, Brian G; Eshed, Yuval

    2014-01-01

    Genetic studies in Arabidopsis established FLOWERING LOCUS T (FT) as a key flower-promoting gene in photoperiodic systems. Grafting experiments established unequivocal one-to-one relations between SINGLE FLOWER TRUSS (SFT), a tomato homolog of FT, and the hypothetical florigen, in all flowering plants. Additional studies of SFT and SELF PRUNING (SP, homolog of TFL1), two antagonistic genes regulating the architecture of the sympodial shoot system, have suggested that transition to flowering in the day-neutral and perennial tomato is synonymous with "termination." Dosage manipulation of its endogenous and mobile, graft-transmissible levels demonstrated that florigen regulates termination and transition to flowering in an SP-dependent manner and, by the same token, that high florigen levels induce growth arrest and termination in meristems across the tomato shoot system. It was thus proposed that growth balances, and consequently the patterning of the shoot systems in all plants, are mediated by endogenous, meristem-specific dynamic SFT/SP ratios and that shifts to termination by changing SFT/SP ratios are triggered by the imported florigen, the mobile form of SFT. Florigen is a universal plant growth hormone inherently checked by a complementary antagonistic systemic system. Thus, an examination of the endogenous functions of FT-like genes, or of the systemic roles of the mobile florigen in any plant species, that fails to pay careful attention to the balancing antagonistic systems, or to consider its functions in day-neutral or perennial plants, would be incomplete.

  13. Florigen and anti-florigen - a systemic mechanism for coordinating growth and termination in flowering plants

    Directory of Open Access Journals (Sweden)

    Eliezer eLifschitz

    2014-09-01

    Full Text Available Genetic studies in Arabidopsis established FLOWERING LOCUS T (FT as a key flower-promoting gene in photoperiodic systems. Grafting experiments established unequivocal one-to-one relations between SFT (SINGLE FLOWER TRUSS, a tomato homolog of FT, and the hypothetical florigen, in all flowering plants. Additional studies of SFT and SP (SELF PRUNING, homolog of TFL1, two antagonistic genes regulating the architecture of the sympodial shoot system, have suggested that transition to flowering in the day-neutral and perennial tomato is synonymous with ‘termination’. Dosage manipulation of its endogenous and mobile, graft-transmissible levels demonstrated that florigen regulates termination and transition to flowering in an SP-dependent manner and, by the same token, that high florigen levels induce growth arrest and termination in meristems across the tomato shoot system. It was thus proposed that growth balances, and consequently the patterning of the shoot systems in all plants, are mediated by endogenous, meristem-specific SFT/SP ratios, and that shifts to termination by elevated SFT/SP ratios are triggered by mobile florigen. Florigen is a universal growth plant hormone inherently checked by a complementary antagonistic systemic system. Thus, an examination of the endogenous functions of FT-like genes, or of the systemic roles of the mobile florigen in any plant species, that fails to pay careful attention to the balancing antagonistic systems, or to consider its functions in day-neutral or perennial plants, would be incomplete.

  14. Growth of Pt thin films on Cu(111) and formation of Pt/Cu surface alloys: growth mechanism and diffusion barrier

    CERN Document Server

    Boo, J H; Lee, S B; Kwak, H T; Schröder, U; Linke, R; Wandelt, K

    1999-01-01

    Ultra-thin-platinum films evaporated on Cu(111) at 100 K and at room temperature were investigated by using in situ Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). A growth mechanism of the layer-by layer type was evidenced up to at least 5-ML of Pt. Over the first Pt monolayer, the Pt-Pt bond distances were strained about 7 % beyond the equilibrium bond distances found for bulk platinum. Surface alloys were formed by diffusing the Pt adatoms into the Cu(111) substrate at temperatures above 500 K with a diffusion barrier of 0.85 eV. For higher annealing temperatures, the Pt concentration got smaller. From an Auger depth profile, the diffusion barrier for surface alloy formation was estimated using Fick's second law.

  15. Mechano-growth factor induces migration of rat mesenchymal stem cells by altering its mechanical properties and activating ERK pathway

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Jiamin; Wu, Kewen; Lin, Feng; Luo, Qing; Yang, Li; Shi, Yisong [Key Laboratory of Biorheological Science and Technology, Ministry of Education, Bioengineering College, Chongqing University, Chongqing 400044 (China); Song, Guanbin, E-mail: song@cqu.edu.cn [Key Laboratory of Biorheological Science and Technology, Ministry of Education, Bioengineering College, Chongqing University, Chongqing 400044 (China); Sung, Kuo-Li Paul [Key Laboratory of Biorheological Science and Technology, Ministry of Education, Bioengineering College, Chongqing University, Chongqing 400044 (China); Department of Bioengineering, University of California, San Diego, La Jolla, CA 92093-0412 (United States)

    2013-11-08

    Highlights: •MGF induced the migration of rat MSC in a concentration-dependent manner. •MGF enhanced the mechanical properties of rMSC in inducing its migration. •MGF activated the ERK 1/2 signaling pathway of rMSC in inducing its migration. •rMSC mechanics may synergy with ERK 1/2 pathway in MGF-induced rMSC migration. -- Abstract: Mechano-growth factor (MGF) generated by cells in response to mechanical stimulation has been identified as a mechano effector molecule, playing a key role in regulating mesenchymal stem cell (MSC) function, including proliferation and migration. However, the mechanism(s) underlying how MGF-induced MSC migration occurs is still unclear. In the present study, MGF motivated migration of rat MSCs (rMSCs) in a concentration-dependent manner and optimal concentration of MGF at 50 ng/mL (defined as MGF treatment in this paper) was demonstrated. Notably, enhancement of mechanical properties that is pertinent to cell migration, such as cell traction force and cell stiffness were found to respond to MGF treatment. Furthermore, MGF increased phosphorylation of extracellular signal-regulated kinase (ERK), ERK inhibitor (i.e., PD98059) suppressed ERK phosphorylation, and abolished MGF-induced rMSC migration were found, demonstrating that ERK is involved molecule for MGF-induced rMSC migration. These in vitro evidences of MGF-induced rMSC migration and its direct link to altering rMSC mechanics and activating the ERK pathway, uncover the underlying biomechanical and biological mechanisms of MGF-induced rMSC migration, which may help find MGF-based application of MSC in clinical therapeutics.

  16. Effects of cerium on growth and physiological mechanism in plants under enhanced ultraviolet-B radiation

    Institute of Scientific and Technical Information of China (English)

    LIANG Chan-juan; HUANG Xiao-hua; TAO Wen-yi; ZHOU Qing

    2006-01-01

    Effect of cerium (Ce3+) on the growth, photosynthesis and antioxidant enzyme system in rape seedlings (Brassica juncea L.)exposed to two levels of UV-B radiation (T1: 0.15 W/m2 and T2:0.35 W/m2) was studied by hydroponics under laboratory conditions.After 5 d of UV-B treatment, the aboveground growth indices were obviously decreased by 13.2%-44.1%(T1) and 21.4%-49.3%(T2), compared to CK, and except active absorption area of roots, the belowground indices by 14.1%-35.6%(T1) and 20.3%-42.6%(T2). For Ce+UV-B treatments, the aboveground and belowground growth indices were decreased respectively by 4.1%-23.6%, 5.2%-23.3%(Ce+T1) and 10.8%-28.4%, 7.0%-27.8%(Ce+T2), lower than those of UV-B treatments. The decrease of growth indices appeared to be the result of changes of physiological processes. Two levels of UV-B radiation induced the decrease in chlorophyll content, net photosynthesis rate, transpiration rate, stomatal conductance and water use efficiency by 11.2%-25.9%(T1) and 20.9%-56.9%(T2), whereas increase in membrane permeability and activities of antioxidant enzymes including superoxide dismutase(SOD),catalase (CAT) and peroxidase (POD) by 6.9%, 22.8%, 21.5%, 9.5%(T1) and 36.6%, 122.3%, 103.5%, 208.9%(T2), respectively. The reduction of the photosynthetic parameters in Ce+UV-B treatments was lessened to 3.2%-13.8%(Ce+T1) and 4.9%-27.6%(Ce+T2),and the increase of membrane permeability and activities of antioxidant enzymes except POD in the same treatments were lessened to 2.4%, 8.4%, 6.6%(Ce+T1) and 30.1%, 116.7%, 75.4%(Ce+T2). These results indicate that the regulative effect of Ce on photosynthesis and antioxidant enzymatic function is the ecophysiological basis of alleviating the suppression of UV-B radiation on growth of seedlings. Furthermore, the protective effect of Ce on seedlings exposed to T1 level of UV-B radiation is superior to T2 level.

  17. PRIMA-1met (APR-246) inhibits growth of colorectal cancer cells with different p53 status through distinct mechanisms.

    Science.gov (United States)

    Li, Xiao-Lan; Zhou, Jianbiao; Chan, Zit-Liang; Chooi, Jing-Yuan; Chen, Zhi-Rong; Chng, Wee-Joo

    2015-11-03

    PRIMA-1met (APR-246) is a methylated derivative and structural analog of PRIMA-1 (p53 re-activation and induction of massive apoptosis). PRIMA-1met has been reported to restore both the wild type (wt) structure and function of mutant p53. Here, we show that PRIMA-1met is highly effective at limiting the growth of CRC cells regardless of p53 status. However, PRIMA-1met induces robust apoptosis only in CRC cells with mutant p53. Upregulation of Noxa, a proapoptotic molecule, is crucial for PRIMA-1met mediated activity. In human xenograft model of disease, PRIMA-1met effectively suppresses CRC tumor growth. Our results uncover distinct mechanisms of PRIMA-1met in CRC with different p53 status, thus providing a mechanistic rationale to evaluate the clinical efficacy of PRIMA-1met in CRC patients with different p53 status.

  18. Mechanisms of hadron inelastic scattering cross-section growth in multiperipheral model within the framework of perturbation theory. Part 3

    CERN Document Server

    Sharf, I V; Sokhrannyi, G O; Yatkin, K V; Rusov, V D

    2009-01-01

    The method for taking into account the interference contributions to hadron inelastic scattering cross-section is developed within the framework of the simplest multiperipheral model. This method is based on the self-acting scalar fi^3 field theory and the Laplace method using. It was shown that the considered in [1] mechanism of virtuality diminishing at the energy sqrt(s) growth with consideration of all considerable interference contributions into account can be responsible for the total hadron scattering cross-section growth which is experimentally observed. The offered model reproduces well at qualitative level the experimental dependence of total scattering cross-section on energy sqrt(s) with a characteristic minimum in the range sqrt(s) around 10 GeV.

  19. EBSD coupled to SEM in situ annealing for assessing recrystallization and grain growth mechanisms in pure tantalum.

    Science.gov (United States)

    Kerisit, C; Logé, R E; Jacomet, S; Llorca, V; Bozzolo, N

    2013-06-01

    An in situ annealing stage has been developed in-house and integrated in the chamber of a Scanning Electron Microscope equipped with an Electron BackScattered Diffraction system. Based on the Joule effect, this device can reach the temperature of 1200°C at heating rates up to 100°C/s, avoiding microstructural evolutions during heating. A high-purity tantalum deformed sample has been annealed at variable temperature in the range 750°C-1030°C, and classical mechanisms of microstructural evolutions such as recrystallization and grain coarsening phenomena have been observed. Quantitative measurements of grain growth rates provide an estimate of the mean grain boundary mobility, which is consistent with the value estimated from physical parameters reported for that material. In situ annealing therefore appears to be suited for complementing bulk measurements at relatively high temperatures, in the context of recrystallization and grain growth in such a single-phase material.

  20. Investigation of Nucleation Mechanism and Tapering Observed in ZnO Nanowire Growth by Carbothermal Reduction Technique.

    Science.gov (United States)

    Kar, Ayan; Low, Ke-Bin; Oye, Michael; Stroscio, Michael A; Dutta, Mitra; Nicholls, Alan; Meyyappan, M

    2011-12-01

    ZnO nanowire nucleation mechanism and initial stages of nanowire growth using the carbothermal reduction technique are studied confirming the involvement of the catalyst at the tip in the growth process. Role of the Au catalyst is further confirmed when the tapering observed in the nanowires can be explained by the change in the shape of the catalyst causing a variation of the contact area at the liquid-solid interface of the nanowires. The rate of decrease in nanowire diameter with length on the average is found to be 0.36 nm/s and this rate is larger near the base. Variation in the ZnO nanowire diameter with length is further explained on the basis of the rate at which Zn atoms are supplied as well as the droplet stability at the high flow rates and temperature. Further, saw-tooth faceting is noticed in tapered nanowires, and the formation is analyzed crystallographically.

  1. Investigation of Nucleation Mechanism and Tapering Observed in ZnO Nanowire Growth by Carbothermal Reduction Technique

    Directory of Open Access Journals (Sweden)

    Oye Michael

    2011-01-01

    Full Text Available Abstract ZnO nanowire nucleation mechanism and initial stages of nanowire growth using the carbothermal reduction technique are studied confirming the involvement of the catalyst at the tip in the growth process. Role of the Au catalyst is further confirmed when the tapering observed in the nanowires can be explained by the change in the shape of the catalyst causing a variation of the contact area at the liquid–solid interface of the nanowires. The rate of decrease in nanowire diameter with length on the average is found to be 0.36 nm/s and this rate is larger near the base. Variation in the ZnO nanowire diameter with length is further explained on the basis of the rate at which Zn atoms are supplied as well as the droplet stability at the high flow rates and temperature. Further, saw-tooth faceting is noticed in tapered nanowires, and the formation is analyzed crystallographically.

  2. Growth Mechanism of a Hybrid Structure Consisting of a Graphite Layer on Top of Vertical Carbon Nanotubes

    Directory of Open Access Journals (Sweden)

    Nicolo' Chiodarelli

    2012-01-01

    Full Text Available Graphene and carbon nanotubes (CNTs are both carbon-based materials with remarkable optical and electronic properties which, among others, may find applications as transparent electrodes or as interconnects in microchips, respectively. This work reports on the formation of a hybrid structure composed of a graphitic carbon layer on top of vertical CNT in a single deposition process. The mechanism of deposition is explained according to the thickness of catalyst used and the atypical growth conditions. Key factors dictating the hybrid growth are the film thickness and the time dynamic through which the catalyst film dewets and transforms into nanoparticles. The results support the similarities between chemical vapor deposition processes for graphene, graphite, and CNT.

  3. Original Ge-induced phenomena on various SiC(0 0 0 1) reconstructions

    Energy Technology Data Exchange (ETDEWEB)

    Ait-Mansour, K [Laboratoire de Physique et de Spectroscopie Electronique, UMR CNRS 7014, Universite de Haute Alsace, 68093 Mulhouse Cedex (France); Dentel, D [Laboratoire de Physique et de Spectroscopie Electronique, UMR CNRS 7014, Universite de Haute Alsace, 68093 Mulhouse Cedex (France); Kubler, L [Laboratoire de Physique et de Spectroscopie Electronique, UMR CNRS 7014, Universite de Haute Alsace, 68093 Mulhouse Cedex (France); Diani, M [LSGM, Departement de Physique, Faculte des Sciences et Techniques, Tanger BP 416 (Morocco); Derivaz, M [Laboratoire de Physique et de Spectroscopie Electronique, UMR CNRS 7014, Universite de Haute Alsace, 68093 Mulhouse Cedex (France); Bischoff, J L [Laboratoire de Physique et de Spectroscopie Electronique, UMR CNRS 7014, Universite de Haute Alsace, 68093 Mulhouse Cedex (France)

    2007-10-21

    Using complementary surface analysis techniques, we study the Ge growth on distinct SiC(0 0 0 1) reconstructions and elucidate complex mechanisms occurring by thermal activation. Two Si-rich reconstructions (3 x 3) and ({radical}3 x {radical}3)R30{sup 0}({radical}3), and one C-rich, (6{radical}3 x 6{radical}3)R30{sup 0}(6{radical}3), are concerned, on which Ge is found to grow in Stranski-Krastanov and Volmer-Weber modes, respectively. The best Ge-wetting layer is favoured on the {radical}3 (less Si-rich) because closest to a perfect truncated SiC(0 0 0 1) termination. At sufficiently high temperature, the Ge-wetting layer is organized in the form of a (4 x 4)Ge reconstruction for which we propose a first atomic model that is based on the 3 x 3 structure. Annealing Ge on the (3 x 3) and 6{radical}3 surfaces provokes spectacular successive 2D/3D and unusual 3D/2D transitions not only of Ge but also of Si and C, respectively, coming from the surface initial richness. In both cases, a phase separation is observed either in the 2D or 3D structures, which is unexpected for the Ge/Si binary system and somewhat usual for the Ge/C one. In the case of Ge on 6{radical}3, a special 2D heterostructure graphite/Ge/SiC is achieved at the atomic level. This acts as a Schottky barrier and then can be promising for future possible applications. (review article)

  4. Confocal microscopy for simultaneous imaging of Cu electrodeposit morphology and adsorbate fluorescence

    Energy Technology Data Exchange (ETDEWEB)

    Chung, D.S.; Alkire, R.C. [Univ. of Illinois, Urbana, IL (United States)

    1997-05-01

    Confocal laser scanning microscopy was used in situ during electrochemical experiments to track localized fluorescence patterns of adsorbed organic agents and to correlate such adsorption with changes in surface morphology accompanying electrolysis. In solutions of 5 {micro}M DiOC{sub 6}(3)/0.01 M H{sub 2}SO{sub 4}, with and without 0.05 M CuSo{sub 4}, confocal imaging revealed that DiOC{sub 6}(3) adsorbed to polycrystalline Au and inhibited cathodic processes occurring there. In the absence of dissolved Cu, DiOC{sub 6}(3) adsorption on Au remained unaltered by changes in cathodic potential up to {minus}750 mV (SSE). During Cu electrodeposition at {minus}550 and at {minus}650 mV (SSE), adsorbed DiOC{sub 6}(3) restricted nucleation of Cu to a small number of active sites where Cu grew hemispherically; and DiOC{sub 6}(3) adsorption was maintained across regions where nucleation had not occurred. Instantaneous nucleation was approached under such conditions. When DiOC{sub 6}(3) was present, copper growth proceeded according to the Volmer-Weber mechanism at {minus}650 mV (SSE). Results from secondary ion mass spectrometry indicated that DiOC{sub 6}(3), or a derivative of it, was incorporated into the deposit during Cu electrodeposition. During Electrodissolution of Cu on Au at 0 mV (SSE), adsorption of DiOC{sub 6}(3) occurred predominantly at surface sites of Cu rather than Au.

  5. Chemo-mechanical modeling of tumor growth in elastic epithelial tissue

    Energy Technology Data Exchange (ETDEWEB)

    Bratsun, Dmitry A., E-mail: bratsun@pspu.ru [Department of Applied Physics, Perm National Research Polytechnical University, Perm, 614990 (Russian Federation); Zakharov, Andrey P. [Department of Chemical Engineering, Technion-Israel Institute of Technology, Haifa, 32000 Israel (Israel); Theoretical Physics Department, Perm State Humanitarian Pedagogical University, Perm, 614990 (Russian Federation); Pismen, Len [Department of Chemical Engineering, Technion-Israel Institute of Technology, Haifa, 32000 Israel (Israel)

    2016-08-02

    We propose a multiscale chemo-mechanical model of the cancer tumor development in the epithelial tissue. The epithelium is represented by an elastic 2D array of polygonal cells with its own gene regulation dynamics. The model allows the simulation of the evolution of multiple cells interacting via the chemical signaling or mechanically induced strain. The algorithm includes the division and intercalation of cells as well as the transformation of normal cells into a cancerous state triggered by a local failure of the spatial synchronization of the cellular rhythms driven by transcription/translation processes. Both deterministic and stochastic descriptions of the system are given for chemical signaling. The transformation of cells means the modification of their respective parameters responsible for chemo-mechanical interactions. The simulations reproduce a distinct behavior of invasive and localized carcinoma. Generally, the model is designed in such a way that it can be readily modified to take account of any newly understood gene regulation processes and feedback mechanisms affecting chemo-mechanical properties of cells.

  6. Chemo-mechanical modeling of tumor growth in elastic epithelial tissue

    Science.gov (United States)

    Bratsun, Dmitry A.; Zakharov, Andrey P.; Pismen, Len

    2016-08-01

    We propose a multiscale chemo-mechanical model of the cancer tumor development in the epithelial tissue. The epithelium is represented by an elastic 2D array of polygonal cells with its own gene regulation dynamics. The model allows the simulation of the evolution of multiple cells interacting via the chemical signaling or mechanically induced strain. The algorithm includes the division and intercalation of cells as well as the transformation of normal cells into a cancerous state triggered by a local failure of the spatial synchronization of the cellular rhythms driven by transcription/translation processes. Both deterministic and stochastic descriptions of the system are given for chemical signaling. The transformation of cells means the modification of their respective parameters responsible for chemo-mechanical interactions. The simulations reproduce a distinct behavior of invasive and localized carcinoma. Generally, the model is designed in such a way that it can be readily modified to take account of any newly understood gene regulation processes and feedback mechanisms affecting chemo-mechanical properties of cells.

  7. Remote sensing of impervious surface growth: A framework for quantifying urban expansion and re-densification mechanisms

    Science.gov (United States)

    Shahtahmassebi, Amir Reza; Song, Jie; Zheng, Qing; Blackburn, George Alan; Wang, Ke; Huang, Ling Yan; Pan, Yi; Moore, Nathan; Shahtahmassebi, Golnaz; Sadrabadi Haghighi, Reza; Deng, Jing Song

    2016-04-01

    A substantial body of literature has accumulated on the topic of using remotely sensed data to map impervious surfaces which are widely recognized as an important indicator of urbanization. However, the remote sensing of impervious surface growth has not been successfully addressed. This study proposes a new framework for deriving and summarizing urban expansion and re-densification using time series of impervious surface fractions (ISFs) derived from remotely sensed imagery. This approach integrates multiple endmember spectral mixture analysis (MESMA), analysis of regression residuals, spatial statistics (Getis_Ord) and urban growth theories; hence, the framework is abbreviated as MRGU. The performance of MRGU was compared with commonly used change detection techniques in order to evaluate the effectiveness of the approach. The results suggested that the ISF regression residuals were optimal for detecting impervious surface changes while Getis_Ord was effective for mapping hotspot regions in the regression residuals image. Moreover, the MRGU outputs agreed with the mechanisms proposed in several existing urban growth theories, but importantly the outputs enable the refinement of such models by explicitly accounting for the spatial distribution of both expansion and re-densification mechanisms. Based on Landsat data, the MRGU is somewhat restricted in its ability to measure re-densification in the urban core but this may be improved through the use of higher spatial resolution satellite imagery. The paper ends with an assessment of the present gaps in remote sensing of impervious surface growth and suggests some solutions. The application of impervious surface fractions in urban change detection is a stimulating new research idea which is driving future research with new models and algorithms.

  8. Inhibition of prostate cancer growth by muscadine grape skin extract and resveratrol through distinct mechanisms.

    Science.gov (United States)

    Hudson, Tamaro S; Hartle, Diane K; Hursting, Stephen D; Nunez, Nomeli P; Wang, Thomas T Y; Young, Heather A; Arany, Praveen; Green, Jeffrey E

    2007-09-01

    The phytochemical resveratrol contained in red grapes has been shown to inhibit prostate cancer cell growth, in part, through its antioxidant activity. Muscadine grapes contain unique phytochemical constituents compared with other grapes and are potentially a source for novel compounds with antitumor activities. We compared the antitumor activities of muscadine grape skin extract (MSKE), which we show contains no resveratrol, with that of resveratrol using primary cultures of normal prostate epithelial cells (PrEC) and the prostate cancer cell lines RWPE-1, WPE1-NA22, WPE1-NB14, and WPE1-NB26, representing different stages of prostate cancer progression. MSKE significantly inhibited tumor cell growth in all transformed prostate cancer cell lines but not PrEC cells. Prostate tumor cell lines, but not PrEC cells, exhibited high rates of apoptosis in response to MSKE through targeting of the phosphatidylinositol 3-kinase-Akt and mitogen-activated protein kinase survival pathways. The reduction in Akt activity by MSKE is mediated through a reduction in Akt transcription, enhanced proteosome degradation of Akt, and altered levels of DJ-1, a known regulator of PTEN. In contrast to MSKE, resveratrol did not induce apoptosis in this model but arrested cells at the G(1)-S phase transition of the cell cycle associated with increased expression of p21 and decreased expression of cyclin D1 and cyclin-dependent kinase 4 proteins. These results show that MSKE and resveratrol target distinct pathways to inhibit prostate cancer cell growth in this system and that the unique properties of MSKE suggest that it may be an important source for further development of chemopreventive or therapeutic agents against prostate cancer.

  9. Molecular mechanisms of the synergy between cysteinyl-leukotrienes and receptor tyrosine kinase growth factors on human bronchial fibroblast proliferation

    Directory of Open Access Journals (Sweden)

    Hajime Yoshisue

    2006-12-01

    Full Text Available We have reported that cysteinyl-leukotrienes (cys-LTs synergise not only with epidermal growth factor (EGF but also with platelet-derived growth factor (PDGF and fibroblast growth factor (FGF to induce mitogenesis in human bronchial fibroblasts. We now describe the molecular mechanisms underlying this synergism. Mitogenesis was assessed by incorporation of [3H]thymidine into DNA and changes in protein phosphorylation by Western blotting. Surprisingly, no CysLT receptor antagonists (MK-571, montelukast, BAY u9773 prevented the synergistic mitogenesis. LTD4 did not cause phosphorylation of EGFR nor did it augment EGF-induced phosphorylation of EGFR, and the synergy between LTD4 and EGF was not blocked by the metalloproteinase inhibitor GM6001 or by an HB-EGF neutralising antibody. The EGFR-selective kinase inhibitor, AG1478, suppressed the synergy by LTD4 and EGF, but had no effect on the synergy with PDGF and FGF. While inhibitors of mitogen-activated protein kinase, phosphatidylinositol 3-kinase and protein kinase C (PKC prevented the synergy, these drugs also inhibited mitogenesis elicited by EGF alone. In contrast, pertussis toxin (PTX efficiently inhibited the potentiating effect of LTD4 on EGF-induced mitogenesis, as well as that provoked by PDGF or FGF, but had no effect on mitogenesis elicited by the growth factors alone. Whereas LTD4 alone did not augment phosphorylation of extracellular signal-regulated kinase (Erk-1/2 and Akt, it increased phosphorylation of PKC in a Gi-dependent manner. Addition of LTD4 prolonged the duration of EGF-induced phosphorylation of Erk-1/2 and Akt, both of which were sensitive to PTX. The effect of cys-LTs involves a PTX-sensitive and PKC-mediated intracellular pathway leading to sustained growth factor-dependent phosphorylation of Erk-1/2 and Akt.

  10. Fluid mechanics and mass transfer in melt crystal growth: Analysis of the floating zone and vertical Bridgman processes

    Science.gov (United States)

    Brown, R. A.

    1986-01-01

    This research program focuses on analysis of the transport mechanisms in solidification processes, especially one of interest to the Microgravity Sciences and Applications Program of NASA. Research during the last year has focused on analysis of the dynamics of the floating zone process for growth of small-scale crystals, on studies of the effect of applied magnetic fields on convection and solute segregation in directional solidification, and on the dynamics of microscopic cell formation in two-dimensional solidification of binary alloys. Significant findings are given.

  11. Influence of Activated Carbon Particles on Intermetallic Compound Growth Mechanism in Sn-Cu-Ni Composite Solder

    Directory of Open Access Journals (Sweden)

    Ramli M.I.I.

    2016-01-01

    Full Text Available The influence of Activated Carbon (AC particles on mechanical properties of Sn-Cu-Ni-xAC solder joint was investigated. Five different Activated Carbon (AC percentage addition (0 wt. %, 0.25 wt. %, 0.5 wt. %, 0.75 wt. %, and 1.0 wt. % were prepared via powder metallurgy (PM technique. Interfacial IMC thickness measurement and shear strength results showed that with thinner IMC layer (by increasing amount of wt.% of AC, the higher the shear strength of the joint. It is believed that the AC particles suppresses the interfacial IMC growth and thus improves the shear strength.

  12. Growth Mechanism and Optimized Parameters to Synthesize Nation-115 Nanowire Arrays with Anodic Aluminium Oxide Membranes as Templates

    Institute of Scientific and Technical Information of China (English)

    ZHANG Lu; PAN Cao-Feng; ZHU Jing

    2008-01-01

    @@ Nafion-115 nanowire arrays are synthesized with an extrusion method using AAO membranes as templates. It is indicated that the vacuum treating of AAO templates before surface decoration plays an important role in obtaining high filling rate of the Nafion-115 nanowires in the AAO templates, while the concentration of Nafion-115 DMSO solutions does not affect the filling rate greatly. The optimized parameters to synthesize the Nafion-115 nanowire arrays are studied. The filling rate of the Nafion-115 nanowires in the AAO templates synthesized with the optimized parameters is about 95%. The growth mechanism of Nafion-115 nanowires is discussed to qualitatively explain the experimental results.

  13. Synthesis process and growth mechanism of γ′-Fe4N nanoparticles by phase-transformation

    Institute of Scientific and Technical Information of China (English)

    CAO; Maosheng(曹茂盛); LIU; Haitao(刘海涛); CHEN; Yujin(陈玉金); WANG; Biao(王彪); ZHU; Jing(朱静)

    2003-01-01

    Multiphase Fe/N nanoparticles were synthesized by means of chemical vapor reaction, the influence of the preparing parameters on the properties of particles was studied carefully during the first nitriding process. The optimum process was determined. Single phaseγ'-Fe4N was prepared by twice-nitriding. Multiphase iron-nitride really transformsγ'-Fe4N nanoparticle of single-phase and uniform. Moreover, the mechanism of nanoparticle nucleation and growth, including phase-transformation, was revealed. In addition, the mircograph, particle size, physical phases, schemical constituents and magnetic properties before and after phase-transformation were characterized initially.

  14. Overall Planning of Development of Urban-Rural Areas:A Policy Mechanism for Urban-Rural Coordinated Growth

    Institute of Scientific and Technical Information of China (English)

    Sun Jin

    2004-01-01

    While analyzing overall planning and coordinated development of urban-rural areas, this paper shows that overall planning for the development of urban-rural areas is a requirement for the best use of productive forces. It means the setting up of a policy mechanism for coordinated growth.Recognizing this, the government should set up a way to lead and manage a unified program to increase service and decrease controlling administration power,while safeguarding and fulfilling the farmers' ownership to the means of production.

  15. Tunable growth of nanodendritic silver by galvanic-cell mechanism on formed activated carbon.

    Science.gov (United States)

    Wang, Fei; Lai, Yijian; Zhao, Binyuan; Hu, Xiaobin; Zhang, Di; Hu, Keao

    2010-06-07

    Well-defined silver dendritic nanostructures have been prepared in large quantities in an ambient environment using formed activated carbon (FAC) only. A reasonable mechanism (step 1: reduction by surface reductive groups; step 2: growing in the form of a galvanic cell) is suggested.

  16. Structural Reliability of Ceramics at High Temperature: Mechanisms of Fracture and Fatigue Crack Growth

    Energy Technology Data Exchange (ETDEWEB)

    Reinhold H. Dauskardt

    2005-08-01

    Final report of our DOE funded research program. Aim of the research program was to provide a fundamental basis from which the mechanical reliability of layered structures may be understood, and to provide guidelines for the development of technologically relevant layered material structures with optimum resistance to fracture and subcritical debonding. Progress in the program to achieve these goals is described.

  17. Cold atmospheric plasma in combination with mechanical treatment improves osteoblast growth on biofilm covered titanium discs.

    Science.gov (United States)

    Duske, Kathrin; Jablonowski, Lukasz; Koban, Ina; Matthes, Rutger; Holtfreter, Birte; Sckell, Axel; Nebe, J Barbara; von Woedtke, Thomas; Weltmann, Klaus Dieter; Kocher, Thomas

    2015-06-01

    Treatment of implants with peri-implantitis is often unsuccessful, because an instrumented implant surface and residual microbial biofilm impedes re-osseointegration. The application of cold atmospheric plasma (CAP) could be a simple and effective strategy to overcome the inherent problems of peri-implantitis treatment. CAP is able to destroy and eliminate bacterial biofilms. Additionally, it increases the wettability of titanium, which supports cellular attachment. In this study, the behaviour of osteoblasts on titanium discs was analysed after treatment of bacterial biofilms with CAP, brushing, or a combination of both. A human plaque biofilm was cultured on titanium discs. Treatment with a brush (BR), 1% oxygen/argon CAP (PL), or brushing combined with CAP (BR+PL) was used to eliminate the biofilm. Discs without biofilm (C), autoclaved biofilm (AUTO) and untreated biofilm (BIO) served as controls. Subsequently, human osteoblastic cell growth (MG-63) was observed after 1 and 24 h. Biofilm remnants on BR and PL impaired osteoblastic cell development, whereas the BR+PL provided an increased area of osteoblastic cells. A five-day cell growth was only detectable on BR+PL treated discs. The combination of established brushing and CAP application may be a promising strategy to treat peri-implantitis.

  18. Growth regulation mechanisms in higher plants under microgravity conditions - changes in cell wall metabolism.

    Science.gov (United States)

    Hoson, T; Kamisaka, S; Wakabayashi, K; Soga, K; Tabuchi, A; Tokumoto, H; Okamura, K; Nakamura, Y; Mori, R; Tanimoto, E; Takeba, G; Nishitani, K; Izumi, R; Ishioka, N; Kamigaichi, S; Aizawa, S; Yoshizaki, I; Shimazu, T; Fukui, K

    2000-06-01

    During Space Shuttle STS-95 mission, we cultivated seedlings of rice (Oryza sativa L. cv. Koshihikari and cv. Tan-ginbozu) and Arabidopsis (Arabidopsis thaliana L. cv. Columbia and cv. etr1-1) for 68.5, 91.5, and 136 hr on board, and then analyzed changes in the nature of their cell walls, growth, and morphogenesis under microgravity conditions. In space, elongation growth of both rice coleoptiles and Arabidopsis hypocotyls was stimulated. Also, the increase in the cell wall extensibility, especially that in the irreversible extensibility, was observed for such materials. The analyses of the amounts, the structure, and the physicochemical properties of the cell wall constituents indicated that the decreases in levels and molecular masses of cell wall polysaccharides were induced under microgravity conditions, which appeared to contribute to the increase in the wall extensibility. The activity of certain wall enzymes responsible for the metabolic turnover of the wall polysaccharides was increased in space. By the space flight, we also confirmed the occurrence of automorphogenesis of both seedlings under microgravity conditions; rice coleoptiles showed an adaxial bending, whereas Arabidopsis hypocotyls elongated in random directions. Furthermore, it was shown that spontaneous curvatures of rice coleoptiles in space were brought about uneven modifications of cell wall properties between the convex and the concave sides.

  19. Growth mechanism of palladium clusters on rutile TiO2(110) surface

    Institute of Scientific and Technical Information of China (English)

    Weina Zhao; Huaxiang Lin; Yi Li; Yongfan Zhang; Xin Huang; Wenkai Chen

    2012-01-01

    Oxide-supported transition metal systems have been the subject of enormous interest due to the improvement of catalytic properties relative to the separate metal.Thus in this paper,we embark on a systematic study for Pdn (n =1-5) clusters adsorbed on TiO2(110) surface based on DFT-GGA calculations utilizing periodic supercell models.A single Pd adatom on the defect-free surface prefers to adsorb at a hollow site bridging a protruded oxygen and a five-fold titanium atom along the [110] direction,while Pd dimer is located on the channels with the Pd-Pd bond parallel to the surface.According to the transition states (TSs) search,the adsorbed Pd trimer tends to triangular growth mode,rather than linear mode,while the Pd4 and Pd5 clusters prefer three-dimensional (3D) models.However,the oxygen vacancy has almost no influence on the promotion of Pdn cluster nucleation.Additionally,of particular significance is that the Pd-TiO2 interaction is the main driving force at the beginning of Pd nucleation,whereas the Pd-Pd interaction gets down to control the growth process of Pd cluster as the cluster gets larger.It is hoped that our theoretical study would shed light on further designing high-performance TiO2 supported Pd-based catalysts.

  20. Possible mechanisms by which pro- and prebiotics influence colon carcinogenesis and tumor growth.

    Science.gov (United States)

    Reddy, B S

    1999-07-01

    Oligofructose and inulin, selective fermentable chicory fructans, have been shown to stimulate the growth of bifidobacteria, which are regarded as beneficial strains in the colon. Studies were designed to evaluate inulin (Raftiline) and oligofructose (Raftilose) for their potential inhibitory properties against the development of colonic aberrant crypt foci (ACF) in rats. ACF are putative preneoplastic lesions from which adenomas and carcinomas may develop in the colon. The results of this study indicate that dietary administration of oligofructose and inulin inhibits the development of ACF in the colon, suggesting the potential colon tumor inhibitory properties of chicory fructans. The degree of ACF inhibition was more pronounced in animals given inulin than in those fed oligofructose. Because these prebiotics selectively stimulate the growth of bifidobacteria, ornithine decarboxylase (ODC) activities, ras-p21 ontoprotein expressions and tumor inhibitory activity of lyophilized cultures of Bifidobacterium longum against chemically induced colon and mammary carcinogenesis and against colonic tumor cell proliferation were examined. Dietary administration of lyophilized cultures of B. longum strongly suppressed colon and mammary tumor development and tumor burden. Inhibition of colon carcinogenesis was associated with a decrease in colonic mucosal cell proliferation and activities of colonic mucosal and tumor ornithine decarboxylase and ras-p21. Human clinical trials are likely to broaden our insight into the importance of the pre- and probiotics in health and disease.

  1. Identification of Accretion as Grain Growth Mechanism in Astrophysically Relevant Water&ice Dusty Plasma Experiment

    Science.gov (United States)

    Marshall, Ryan S.; Chai, Kil-Byoung; Bellan, Paul M.

    2017-03-01

    The grain growth process in the Caltech water–ice dusty plasma experiment has been studied using a high-speed camera and a long-distance microscope lens. It is observed that (i) the ice grain number density decreases fourfold as the average grain major axis increases from 20 to 80 μm, (ii) the major axis length has a log-normal distribution rather than a power-law dependence, and (iii) no collisions between ice grains are apparent. The grains have a large negative charge resulting in strong mutual repulsion and this, combined with the fractal character of the ice grains, prevents them from agglomerating. In order for the grain kinetic energy to be sufficiently small to prevent collisions between ice grains, the volumetric packing factor (i.e., ratio of the actual volume to the volume of a circumscribing ellipsoid) of the ice grains must be less than ∼0.1 depending on the exact relative velocity of the grains in question. Thus, it is concluded that direct accretion of water molecules is very likely to dominate the observed ice grain growth.

  2. Accelerated kinetics and mechanism of growth of boride layers on titanium under isothermal and cyclic diffusion

    Science.gov (United States)

    Sarma, Biplab

    2011-12-01

    The tendency of titanium (Ti) and its alloys to wear, gall and seize during high contact stresses between sliding surfaces severely limits their applications in bearings, gears etc. One way to mitigate these problems is to modify their surfaces by applying hard and wear resistant surface coatings. Boriding, which involves solid state diffusion of boron (B) into Ti, thereby forming hard surface layers consisting of TiB2 and TiB compounds has been shown to produce extremely high wear resistant surfaces in Ti and its alloys. The growth kinetics of these layers are, however, limited by the low diffusivities of B in the high melting TiB2 and TiB compounds. On the basis of the fact that HCP metals such as Ti show enhanced (anomalous) self-diffusion near the phase transition temperature, the first hypothesis of this work has been that the diffusivity enhancement should cause rapid ingress of B atoms, thereby accelerating the growth of the hard boride layers. Isothermal boriding experiments were performed close to phase transition temperature (890, 910, and 915°C) for time periods ranging from 3 to 24 hours. It was found that indeed a much deeper growth of TiB into the Ti substrate (˜75 mum) occurred at temperatures very close to the transition temperature (910°C), compared to that obtained at 1050°C. A diffusion model based on error-function solutions of Fick's second law was developed to quantitatively illustrate the combined effects of the normal B diffusion in the TiB phase and the anomalous B diffusion in Ti phase in accelerating TiB layer growth. Furthermore, isothermal boriding experiments close to transition temperature (900°C) for a period of 71 hours resulted in coating thickness well above 100 mum, while at 1050°C, the layer growth saturated after about 24 hours of treatment time. In the second part of this work, a novel approach named "cyclic-phase-changediffusion, (CPCD)," to create deeper TiB2 and TiB coating layers on CP-Ti by cyclic thermal processing

  3. Quantitative structure-activity relationships of insecticides and plant growth regulators: comparative studies toward understanding the molecular mechanism of action.

    Science.gov (United States)

    Iwamura, H; Nishimura, K; Fujita, T

    1985-01-01

    Emphasis was put on the comparative quantitative structure-activity approaches to the exploration of action mechanisms of structurally different classes of compounds showing the same type of activity as well as those of the same type of compounds having different actions. Examples were selected from studies performed on insecticides and plant growth regulators, i.e., neurotoxic carbamates, phosphates, pyrethroids and DDT analogs, insect juvenile hormone mimics, and cytokinin agonistic and antagonistic compounds. Similarities and dissimilarities in structures required to elicit activity between compounds classes were revealed in terms of physicochemical parameters, provoking further exploration and evoking insights into the molecular mechanisms of action which may lead to the development of new structures having better qualities. PMID:3905379

  4. Impacts of CO2 concentration on growth, lipid accumulation, and carbon-concentrating-mechanism-related gene expression in oleaginous Chlorella.

    Science.gov (United States)

    Fan, Jianhua; Xu, Hui; Luo, Yuanchan; Wan, Minxi; Huang, Jianke; Wang, Weiliang; Li, Yuanguang

    2015-03-01

    Biodiesel production by microalgae with photosynthetic CO2 biofixation is thought to be a feasible way in the field of bioenergy and carbon emission reduction. Knowledge of the carbon-concentrating mechanism plays an important role in improving microalgae carbon fixation efficiency. However, little information is available regarding the dramatic changes of cells suffered upon different environmental factors, such as CO2 concentration. The aim of this study was to investigate the growth, lipid accumulation, carbon fixation rate, and carbon metabolism gene expression under different CO2 concentrations in oleaginous Chlorella. It was found that Chlorella pyrenoidosa grew well under CO2 concentrations ranging from 1 to 20 %. The highest biomass and lipid productivity were 4.3 g/L and 107 mg/L/day under 5 % CO2 condition. Switch from high (5 %) to low (0.03 %, air) CO2 concentration showed significant inhibitory effect on growth and CO2 fixation rate. The amount of the saturated fatty acids was increased obviously along with the transition. Low CO2 concentration (0.03 %) was suitable for the accumulation of saturated fatty acids. Reducing the CO2 concentration could significantly decrease the polyunsaturated degree in fatty acids. Moreover, the carbon-concentrating mechanism-related gene expression revealed that most of them, especially CAH2, LCIB, and HLA3, had remarkable change after 1, 4, and 24 h of the transition, which suggests that Chlorella has similar carbon-concentrating mechanism with Chlamydomonas reinhardtii. The findings of the present study revealed that C. pyrenoidosa is an ideal candidate for mitigating CO2 and biodiesel production and is appropriate as a model for mechanism research of carbon sequestration.

  5. The Potential Mechanisms Underlying Aspirin-induced Inhibition of Ovarian Tumor Cell Growth

    Institute of Scientific and Technical Information of China (English)

    Yu LIU; Jin KE; Shi-Quan LIU; Fu-Xiang ZHOU; Cong-Hua XIE; Yun-Feng ZHOU

    2005-01-01

    @@ 1 Introduction Ovarian cancer remains the most lethal disease of the gynecological cancers. Owing to the lack of an effective screening approach combined with inadequate therapeutic approach for advanced disease, fewer than 25% of ovarian cancers are identified at an early curable stage. Thus these make ovarian cancer a strong candidate for chemoprevention. In 2001, Akhmedkhanov et al. demonstrated a 2-3 folds decrease in epithelial ovarian cancer associated with Aspirin use. These epidemiological observations suggest that an improved understanding of the mechanisms by which NSAID may decrease the development of ovarian cancer could lead to improved approaches for chemoprevention of this deadly disease. In this research, we explored the potential mechanism underlying epidemiological observations that ovarian cancer occurs at a lower frequency in women exposed to Aspirin(ASP).

  6. Growth of lenticular bubbles in relation to blistering and flaking mechanism

    Science.gov (United States)

    Kamada, Kohji; Higashida, Yutaka

    Consequences of a theory, which is based on a model of ductile extension of a crack in a material, is presented that explains blistering and flaking which appear after high energy ion bombardment. Distinction in mechanisms between blistering and flaking is clarified theoretically. Comparisons between the theory and experiments show very good correlations with respect to blister size. The relation between blister cover thickness and local bubble swelling is given theoretically, explaining the observations made by transmission electron microscopy.

  7. Growth of lenticular bubbles in relation to blistering and flaking mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Kamada, K.; Higashida, Y. (Nagoya Univ. (Japan). Inst. of Plasma Physics)

    1982-03-01

    Consequences of a theory, which is based on a model of ductile extension of a crack in a material, is presented that explains blistering and flaking which appear after high energy ion bombardment. Distinction in mechanisms between blistering and flaking is clarified theoretically. Comparisons between the theory and experiments show very good correlations with respect to blister size. The relation between blister cover thickness and local bubble swelling is given theoretically, explaining the observations made by transmission electron microscopy.

  8. The Arabidopsis Wave Complex: Mechanisms Of Localized Actin Polymerization And Growth

    Energy Technology Data Exchange (ETDEWEB)

    Daniel Szymanski

    2012-10-23

    The objective of this project was to discover the protein complexes and control mechanisms that determine the location of actin filament roadways in plant cells. Our work provided the first molecular description of protein complexes that are converted from inactive complexes to active actin filament nucleators in the cell. These discoveries provided a conceptual framework to control to roadways in plant cells that determine the location and delivery of plant metabolites and storage molecules that are relevant to the bioenergy economy.

  9. Effects of PVP on the preparation and growth mechanism of monodispersed Ni nanoparticles

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Monodispersed Ni nanoparticles were successfully prepared by chemical reduction with hydrazine hydrate in ethylene glycol.The effect of the amount of polyvinylpyrrolidone (PVP-K30) on the preparation of Ni nanoparticles was investigated.X-ray diffraction (XRD),transmission electron microscopy (TEM),and high resolution transmission electron microscopy (HRTEM) were employed to characterize the nickel particles are spherical in shape and are not agglomerated.A possible extensive mechanism of nickel nanoparticle formation has been suggested.

  10. Turing mechanism for homeostatic control of synaptic density during C. elegans growth

    Science.gov (United States)

    Brooks, Heather A.; Bressloff, Paul C.

    2017-07-01

    We propose a mechanism for the homeostatic control of synapses along the ventral cord of Caenorhabditis elegans during development, based on a form of Turing pattern formation on a growing domain. C. elegans is an important animal model for understanding cellular mechanisms underlying learning and memory. Our mathematical model consists of two interacting chemical species, where one is passively diffusing and the other is actively trafficked by molecular motors, which switch between forward and backward moving states (bidirectional transport). This differs significantly from the standard mechanism for Turing pattern formation based on the interaction between fast and slow diffusing species. We derive evolution equations for the chemical concentrations on a slowly growing one-dimensional domain, and use numerical simulations to demonstrate the insertion of new concentration peaks as the length increases. Taking the passive component to be the protein kinase CaMKII and the active component to be the glutamate receptor GLR-1, we interpret the concentration peaks as sites of new synapses along the length of C. elegans, and thus show how the density of synaptic sites can be maintained.

  11. Solution assisted growth mechanism and characterization of ZnS microspheres

    Science.gov (United States)

    Ghoderao, Karuna P.; Jamble, Shweta N.; Sawant, Jitendra P.; Kale, Rohidas B.

    2017-02-01

    The ZnS microspheres were synthesized via simple, efficient and cost-effective hydrothermal method. The x-ray diffraction study revealed nanocrystalline nature of the synthesized ZnS with the cubic crystal structure. Scanning and transmission electron microscopy observations revealed the formation of 3D microspheres that consist of numerous ZnS nanocrystals. The grown microspheres are also interconnected with each other by driving force of attachment. The obtained product has excellent elemental stoichiometric proportion as evidenced by the EDS technique. The electron diffraction pattern reveals the polycrystalline nature of obtained ZnS product. The band gap was measured from UV–Vis spectroscopic study and found to be blue shifted from the bulk band gap value. The PL study exhibits negligibly weak band edge emission and dominant, widespread defect-related green emission. The nucleation of a ZnS nanocrystals and subsequent growth into the microspheres is also discussed.

  12. Mechanism for Spontaneous Growth of Nanopillar Arrays in Ultrathin Films Subject to a Thermal Gradient

    CERN Document Server

    Dietzel, Mathias

    2010-01-01

    Several groups have reported spontaneous formation of periodic pillar-like arrays in molten polymer nanofilms confined within closely spaced substrates maintained at different temperatures. These formations have been attributed to a radiation pressure instability caused by acoustic phonons. In this work, we demonstrate how variations in the thermocapillary stress along the nanofilm interface can produce significant periodic protrusions in any viscous film no matter how small the initial transverse thermal gradient. The linear stability analysis of the interface evolution equation explores an extreme limit of B\\'{e}nard-Marangoni flow peculiar to films of nanoscale dimensions in which hydrostatic forces are altogether absent and deformation amplitudes are small in comparison to the pillar spacing. Finite element simulations of the full nonlinear equation are also used to examine the array pitch and growth rates beyond the linear regime. Inspection of the Lyapunov free energy as a function of time confirms that...

  13. Single-crystal star-like zinc oxide: synthesis, characterization and growth mechanism

    Institute of Scientific and Technical Information of China (English)

    WANG Qingxiao; YOU Liping; Zhang Xinzheng; WANG Rongming; LV Yuzhen; GUO Lin

    2006-01-01

    A novel star-like single-crystal ZnO structure was synthesized by a simple solvothermal method.The as-prepared products were characterized by XRD, SEM and TEM.The star-like ZnO, which shows sixfold symmetry, was constructed by six uniform arms distributing symmetrically around the [0001] zone axis.It is also found that the arms are not perpendicular to the [0001] zone axis and each arm is grown at a certain angle with the [0001] direction.CBED pattern and corresponding simulation demonstrate that the convex part of the star-like ZnO is O-terminated (000-1) plane and the concave part is Zn-terminated (0001) plane.H2S plays a crucial role in the synthesis process.The anisotropic growth habit along [0001] and [000-1] results in the formation of star-like structure.

  14. Growth Mechanism of Lipid-Based Nanodiscs -- a Model Membrane for Studying Kinetics of Particle Coalescence

    Science.gov (United States)

    Nieh, Mu-Ping; Dizon, Anthony; Li, Ming; Hu, Andrew; Fan, Tai-Hsi

    2012-02-01

    Lipid-based nanodiscs composed of long- and short- chain lipids [namely, dimyristoyl phosphatidylcholine (DMPC), dimyristoyl phosphatidylglycerol (DMPG) and dihexanoyl phosphatidylcholine (DHPC)] constantly form at high lipid concentrations and at low temperatures (i.e., below the melting transition temperature of DMPC, TM). The initial size of these nanodiscs (at high total lipid concentration, CL> 20 wt.%) is relatively uniform and of similar dimension (according to dynamic light scattering and small angle neutron scattering experiments), seemingly independent of thermal history. Upon dilution, the nanodiscs slowly coalesce and grow in size with time irreversibly. Our preliminary result shows that the growth rate strongly depends on several parameters such as charge density, CL and temperature. We have also found that the nanodisc coalescence is a reaction limit instead of diffusion limit process through a time-resolved study.

  15. A Possible Mechanism for Overcoming the Electrostatic Barrier Against Dust Growth in Protoplanetary disks

    CERN Document Server

    Akimkin, V

    2015-01-01

    The coagulation of dust particles under the conditions in protoplanetary disks is investigated. The study focuses on the repulsive electrostatic barrier against growth of charged dust grains. Taking into account the photoelectric effect leads to the appearance of a layer at intermediate heights where the dust has a close to zero charge, enabling the dust grains to grow efficiently. An increase in the coagulation rate comes about not only due to the lowering of the Coulomb barrier, but also because of the electrostatic attraction between grains of opposite charge due to the non-zero dispersion of the near-zero charge. Depending on the efficiency of mixing in the disk, the acceleration of the evolution of the dust in this layer could be important, both in the quasi-stationary stage of the disk evolution and during its dispersal.

  16. Subcellular localization and mechanism of secretion of vascular endothelial growth factor in human skeletal muscle

    DEFF Research Database (Denmark)

    Høier, Birgitte; Prats Gavalda, Clara; Qvortrup, Klaus

    2013-01-01

    The subcellular distribution and secretion of vascular endothelial growth factor (VEGF) was examined in skeletal muscle of healthy humans. Skeletal muscle biopsies were obtained from m.v. lateralis before and after a 2 h bout of cycling exercise. VEGF localization was conducted on preparations...... of teased muscle fibers by transmission electron microscopy (TEM) and confocal microscopy (CM). Muscle interstitial fluid was sampled from microdialysis probes placed in the thigh muscle. TEM and CM analysis revealed two primary sites of localization of VEGF: in vesicles located in the subsarcolemmal...... regions and between the contractile elements within the muscle fibers; and in pericytes situated on the skeletal muscle capillaries. Quantitation of the subsarcolemmal density of VEGF vesicles, calculated on top of myonuclei, in the muscle fibers revealed a ∼50% increase (P...

  17. Investigating the growth mechanism and optical properties of carbon-coated titanium dioxide nanoparticles

    KAUST Repository

    Anjum, Dalaver H.

    2013-10-01

    TiO2 nanoparticles (NPs) were prepared using flame synthesis and then characterized using transmission electron microscopy. We found that the flame method yields both crystalline TiO2 and amorphous TiO 2 NPs. TEM analysis revealed that only the crystalline TiO 2 NPs were coated with carbon. Based on this observation, we proposed a growth model for the diffusion and precipitation of carbon atoms in TiO 2 NPs. The optical properties of TiO2 NPs were investigated by performing valence electron energy loss spectrometry analysis. We observed that carbon-coated TiO2 NPs have higher absorption in the visible range due to their lower band-gap energy. © 2013 Elsevier B.V.

  18. Growth aspects, structural, optical, thermal and mechanical properties of benzotriazole pyridine-2-carboxylic acid single crystal

    Science.gov (United States)

    Thirunavukkarsu, A.; Sujatha, T.; Umarani, P. R.; Nizam Mohideen, M.; Silambarasan, A.; Kumar, R. Mohan

    2017-02-01

    Benzotriazole pyridine-2-carboxylic acid single crystal (BTPCA) was grown by slow evaporation solution growth technique. The cell parameters and crystallinity of BTPCA crystal were found by single crystal and powder X-ray diffraction studies. The presence of functional groups was studied by FT-IR analysis. UV-vis-NIR transmission studies reveal that the BTPCA crystal is transparent in the entire visible region with lower optical cut-off wavelength of 306 nm. The thermal stability, melting point and decomposition stages of BTPCA were analysed from the thermogravimetric and differential thermal analyses. The second harmonic output power of BTPCA was measured to be 2.5 times that of KDP reference crystal. Hardness studies reveal that grown crystal shows the reverse indentation size effect and breakeven point due to release of internal fatigue generated during indentation.

  19. Family Administration Mechanism and Family Business Growth in China%家族制与家族企业成长

    Institute of Scientific and Technical Information of China (English)

    郑月龙

    2012-01-01

    家族企业是我国民营企业的主流模式,受中国传统家文化、企业成长环境及企业家能力等因素的影响,家族制管理在推动家族企业成长进程中产生企业资源的挤出效应,从而揭示了中国家族企业偏好于采取网络化成长模式的必然性。%The mainstream patterns of private-owned firms are family business in China. Under the influence of traditional family culture, business growth conditions and entrepreneurs" capacities, family administration mechanism often produces a Crowding out Effect on business resource in the growth of enterprises. Furthermore, it reveals the Chi- nese family enterprises" inevitable choices about the network-based growth mode.

  20. Growth Mechanism and Surface Structure of Ge Nanocrystals Prepared by Thermal Annealing of Cosputtered GeSiO Ternary Precursor

    Directory of Open Access Journals (Sweden)

    Bo Zhang

    2014-01-01

    Full Text Available Ge nanocrystals (Ge-ncs embedded in a SiO2 superlattice structure were prepared by magnetron cosputtering and postdeposition annealing. The formation of spherical nanocrystals was confirmed by transmission electron microscopy and their growth process was studied by a combination of spectroscopic techniques. The crystallinity volume fraction of Ge component was found to increase with crystallite size, but its overall low values indicated a coexistence of crystalline and noncrystalline phases. A reduction of Ge-O species was observed in the superlattice during thermal annealing, accompanied by a transition from oxygen-deficient silicon oxide to silicon dioxide. A growth mechanism involving phase separation of Ge suboxides (GeOx was then proposed to explain these findings and supplement the existing growth models for Ge-ncs in SiO2 films. Further analysis of the bonding structure of Ge atoms suggested that Ge-ncs are likely to have a core-shell structure with an amorphous-like surface layer, which is composed of GeSiO ternary complex. The surface layer thickness was extracted to be a few angstroms and equivalent to several atomic layer thicknesses.

  1. Septin 9 induces lipid droplets growth by a phosphatidylinositol-5-phosphate and microtubule-dependent mechanism hijacked by HCV

    Science.gov (United States)

    Akil, Abdellah; Peng, Juan; Omrane, Mohyeddine; Gondeau, Claire; Desterke, Christophe; Marin, Mickaël; Tronchère, Hélène; Taveneau, Cyntia; Sar, Sokhavuth; Briolotti, Philippe; Benjelloun, Soumaya; Benjouad, Abdelaziz; Maurel, Patrick; Thiers, Valérie; Bressanelli, Stéphane; Samuel, Didier; Bréchot, Christian; Gassama-Diagne, Ama

    2016-01-01

    The accumulation of lipid droplets (LD) is frequently observed in hepatitis C virus (HCV) infection and represents an important risk factor for the development of liver steatosis and cirrhosis. The mechanisms of LD biogenesis and growth remain open questions. Here, transcriptome analysis reveals a significant upregulation of septin 9 in HCV-induced cirrhosis compared with the normal liver. HCV infection increases septin 9 expression and induces its assembly into filaments. Septin 9 regulates LD growth and perinuclear accumulation in a manner dependent on dynamic microtubules. The effects of septin 9 on LDs are also dependent on binding to PtdIns5P, which, in turn, controls the formation of septin 9 filaments and its interaction with microtubules. This previously undescribed cooperation between PtdIns5P and septin 9 regulates oleate-induced accumulation of LDs. Overall, our data offer a novel route for LD growth through the involvement of a septin 9/PtdIns5P signalling pathway. PMID:27417143

  2. White matter growth as a mechanism of cognitive development in children.

    Science.gov (United States)

    Mabbott, Donald J; Noseworthy, Michael; Bouffet, Eric; Laughlin, Suzanne; Rockel, Conrad

    2006-11-15

    We examined the functional role of white matter growth in cognitive development. Specifically, we used hierarchical regression analyses to test the unique contributions of age versus white matter integrity in accounting for the development of information processing speed. Diffusion tensor imaging was acquired for 17 children and adolescents (age range 6-17 years), with apparent diffusion coefficient (ADC) and fractional anisotropy (FA) calculated for 10 anatomically defined fiber pathways and 12 regions of hemispheric white matter. Measures of speeded visual-spatial searching, rapid picture naming, reaction time in a sustained attention task, and intelligence were administered. Age-related increases were evident across tasks, as well as for white matter integrity in hemispheric white matter. ADC was related to few measures. FA within multiple hemispheric compartments predicted rapid picture naming and standard error of reaction time in sustained attention, though it did not contribute significantly to the models after controlling for age. Independent of intelligence, visual-spatial searching was related to FA in a number of hemispheric regions. A novel finding was that only right frontal-parietal regions contributed uniquely beyond the effect of age in accounting for performance: age did not contribute to visual-spatial searching when FA within these regions was first included in the models. Considering we found that both FA in right frontal-parietal regions and speed of visual-spatial searching increased with age, our findings are consistent with the growth of regional white matter organization as playing an important role in increased speed of visual searching with age.

  3. Retinoic acid inhibits endometrial cancer cell growth via multiple genomic mechanisms.

    Science.gov (United States)

    Cheng, You-Hong; Utsunomiya, Hiroki; Pavone, Mary Ellen; Yin, Ping; Bulun, Serdar E

    2011-04-01

    Previous studies have indicated that retinoic acid (RA) may be therapeutic for endometrial cancer. However, the downstream target genes and pathways triggered by ligand-activated RA receptor α (RARα) in endometrial cancer cells are largely unknown. In this study, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, flow cytometry, and immunoblotting assays were used to assess the roles of RA and the RA agonist (AM580) in the growth of endometrial cancer cells. Illumina-based microarray expression profiling of endometrial Ishikawa cells incubated with and without AM580 for 1, 3, and 6 h was performed. We found that both RA and AM580 markedly inhibited endometrial cancer cell proliferation, while knockdown of RARα could block AM580 inhibition. Knockdown of RARα significantly increased proliferating cell nuclear antigen and BCL2 protein levels. Incubation of Ishikawa cells with or without AM580 followed by microarray expression profiling showed that 12 768 genes out of 47 296 gene probes were differentially expressed with significant P values. We found that 90 genes were the most regulated genes with the most significant P value (PAM580 highly regulated these genes, whereas chromatin immunoprecipitation-PCR assay demonstrated that ligand-activated RARα interacted with the promoter of these genes in intact endometrial cancer cells. AM580 also significantly altered 18 pathways including those related to cell growth, differentiation, and apoptosis. In conclusion, AM580 treatment of Ishikawa cells causes the differential expression of a number of RARα target genes and activation of signaling pathways. These pathways could, therefore, mediate the carcinogenesis of human endometrial cancer.

  4. Calcineurin /NFAT activation-dependence of leptin synthesis and vascular growth in response to mechanical stretch

    Directory of Open Access Journals (Sweden)

    Nadia Soudani

    2016-09-01

    Full Text Available Background and Aims- Hypertension and obesity are important risk factors of cardiovascular disease. They are both associated with high leptin levels and have been shown to promote vascular hypertrophy, through the RhoA/ROCK and ERK1/2 phosphorylation. Calcineurin/NFAT activation also induces vascular hypertrophy by upregulating various genes. This study aimed to decipher whether a crosstalk exists between the RhoA/ROCK pathway, Ca+2/calcineurin/NFAT pathway, and ERK1/2 phosphorylation in the process of mechanical stretch-induced vascular smooth muscle cell (VSMC hypertrophy and leptin synthesis. Methods and Results- Rat portal vein (RPV organ culture was used to investigate the effect of mechanical stretch and exogenous leptin (3.1 nM on VSMC hypertrophy and leptin synthesis. Results showed that stretching the RPV significantly upregulated leptin secretion, mRNA and protein expression, which were inhibited by the calcium channel blocker nifedipine (10 μM, the selective calcineurin inhibitor FK506 (1 nM and the ERK1/2 inhibitor PD98059 (1 μM. The transcription inhibitor actinomycin D (0.1M and the translation inhibitor cycloheximide (1 mM significantly decreased stretch-induced leptin protein expression. Mechanical stretch or leptin caused an increase in wet weight changes and protein synthesis, considered as hypertrophic markers, while they were inhibited by FK506 (0.1 nM; 1 nM. In addition, stretch or exogenous leptin significantly increased calcineurin activity and MCIP1 expression whereas leptin induced NFAT nuclear translocation in VSMCs. Moreover, in response to stretch or exogenous leptin, the Rho inhibitor C3 exoenzyme (30 ng/mL, the ROCK inhibitor Y-27632 (10 μM, and the actin depolymerization agents Latrunculin B (50 nM and cytochalasin D (1 μM reduced calcineurin activation and NFAT nuclear translocation. ERK1/2 phosphorylation was inhibited by FK506 and C3. Conclusions- Mechanical stretch-induced VSMC hypertrophy and leptin

  5. Growth mechanisms for Si epitaxy on O atomic layers: Impact of O-content and surface structure

    Science.gov (United States)

    Jayachandran, Suseendran; Billen, Arne; Douhard, Bastien; Conard, Thierry; Meersschaut, Johan; Moussa, Alain; Caymax, Matty; Bender, Hugo; Vandervorst, Wilfried; Heyns, Marc; Delabie, Annelies

    2016-10-01

    The epitaxial growth of Si layers on Si substrates in the presence of O atoms is generally considered a challenge, as O atoms degrade the epitaxial quality by generating defects. Here, we investigate the growth mechanisms for Si epitaxy on O atomic layers (ALs) with different O-contents and structures. O ALs are deposited by ozone (O3) or oxygen (O2) exposure on H-terminated Si at 50 °C and 300 °C respectively. Epitaxial Si is deposited by chemical vapor deposition using silane (SiH4) at 500 °C. After O3 exposure, the O atoms are uniformly distributed in Si-Si dimer/back bonds. This O layer still allows epitaxial seeding of Si. The epitaxial quality is enhanced by lowering the surface distortions due to O atoms and by decreasing the arrival rate of SiH4 reactants, allowing more time for surface diffusion. After O2 exposure, the O atoms are present in the form of SiOx clusters. Regions of hydrogen-terminated Si remain present between the SiOx clusters. The epitaxial seeding of Si in these structures is realized on H-Si regions, and an epitaxial layer grows by a lateral overgrowth mechanism. A breakdown in the epitaxial ordering occurs at a critical Si thickness, presumably by accumulation of surface roughness.

  6. Anthocyanin Incorporated Dental Copolymer: Bacterial Growth Inhibition, Mechanical Properties, and Compound Release Rates and Stability by 1H NMR

    Directory of Open Access Journals (Sweden)

    Halyna Hrynash

    2014-01-01

    Full Text Available Objective. To evaluate bacterial growth inhibition, mechanical properties, and compound release rate and stability of copolymers incorporated with anthocyanin (ACY; Vaccinium macrocarpon. Methods. Resin samples were prepared (Bis-GMA/TEGDMA at 70/30 mol% and incorporated with 2 w/w% of either ACY or chlorhexidine (CHX, except for the control group. Samples were individually immersed in a bacterial culture (Streptococcus mutans for 24 h. Cell viability (n=3 was assessed by counting the number of colony forming units on replica agar plates. Flexural strength (FS and elastic modulus (E were tested on a universal testing machine (n=8. Compound release and chemical stability were evaluated by UV spectrophotometry and 1H NMR (n=3. Data were analyzed by one-way ANOVA and Tukey’s test (α = 0.05. Results. Both compounds inhibited S. mutans growth, with CHX being most effective (P<0.05. Control resin had the lowest FS and E values, followed by ACY and CHX, with statistical difference between control and CHX groups for both mechanical properties (P<0.05. The 24 h compound release rates were ACY: 1.33 μg/mL and CHX: 1.92 μg/mL. 1H NMR spectra suggests that both compounds remained stable after being released in water. Conclusion. The present findings indicate that anthocyanins might be used as a natural antibacterial agent in resin based materials.

  7. 旅游系统非线性成长机制%Study on Tourism System Nonlinear Growth Mechanism

    Institute of Scientific and Technical Information of China (English)

    吴文智; 赵磊

    2012-01-01

    本文首先利用系统动力学分析了旅游系统非线性成长的基本形态,发现旅游系统非线性成长基本呈现出s形成长形态,并从旅游系统内外两方面对其进行了详实分析。然后,分别从旅游系统内部旅游者与旅游目的地二元结构之间进行动态演化博弈、对异质性旅游系统之间进行系统协同演化建模两方面,分析了旅游系统非线性成长的动态机制。接着运用面板数据对整体旅游系统、国内旅游者一旅游目的地旅游系统(DTS)和入境旅游者一旅游目的地系统(ITS)进行计量回归分析。实证结果显示,除整体旅游系统外,国内旅游系统和入境旅游系统具有显著的非线性成长经济效应。%Firstly, using system dynamics, this paper analyses nonlinear growth shapes of tourism system, find that tourism system nonlinear growth shows S shape, and carry out a detailed analysis from internal and external tourism system. Then this paper analyses dynamical mechanism of tourism system nonlinear growth from two aspects between dynamical evolutional game of tourist-tourism destination and system emergence models of heterogeneous tourism systems. Finally, using panel data, this paper measure econometric regression analysis for domestic tourist- tourism destination tourism system (DTS) and international tourist-tourism destination tourism system (ITS), and empirical results shows that aside from complete tourism system, destination tourism system (DTS) and international tourist-tourism destination tourism system (ITS) have significant nonlinear growth economic effects. With the unceasing enhancement of the tourism industry association fusion ability and tourism product production technology, the nonlinear growth of the tourism system in different stages shows different growing form. According to the tourist destination in the life cycle of cognitive prior theory, and the system dynamics analysis of

  8. Insulin-like growth factor binding protein-5 modulates muscle differentiation through an insulin-like growth factor-dependent mechanism.

    Science.gov (United States)

    James, P L; Stewart, C E; Rotwein, P

    1996-05-01

    The insulin-like growth factor binding proteins (IGFBPs) are a family of six secreted proteins which bind to and modulate the actions of insulin-like growth factors-I and -II (IGF-I and -II). IGFBP-5 is more conserved than other IGFBPs characterized to date, and is expressed in adult rodent muscle and in the developing myotome. We have shown previously that C2 myoblasts secrete IGFBP-5 as their sole IGFBP. Here we use these cells to study the function of IGFBP-5 during myogenesis, a process stimulated by IGFs. We stably transfected C2 cells with IGFBP-5 cDNAs under control of a constitutively active promoter. Compared with vector-transfected control cells, C2 myoblasts expressing the IGFBP-5 transgene in the sense orientation exhibit increased IGFBP-5 levels in the extracellular matrix during proliferation, and subsequently fail to differentiate normally, as assessed by both morphological and biochemical criteria. Compared to controls, IGFBP-5 sense myoblasts show enhanced survival in low serum medium, remaining viable for at least four weeks in culture. By contrast, myoblasts expressing the IGFBP-5 antisense transcript differentiate prematurely and more extensively than control cells. The inhibition of myogenic differentiation by high level expression of IGFBP-5 could be overcome by exogenous IGFs, with des (1-3) IGF-I, an analogue with decreased affinity for IGFBP-5 but normal affinity for the IGF-I receptor, showing the highest potency. These results are consistent with a model in which IGFBP-5 blocks IGF-stimulated myogenesis, and indicate that sequestration of IGFs in the extracellular matrix could be a possible mechanism of action. Our observations also suggest that IGFBP-5 normally inhibits muscle differentiation, and imply a role for IGFBP-5 in regulating IGF action during myogenic development in vivo.

  9. Controlled synthesis, growth mechanism and highly efficient solar photocatalysis of nitrogen-doped bismuth subcarbonate hierarchical nanosheets architectures.

    Science.gov (United States)

    Dong, Fan; Sun, Yanjuan; Ho, Wing-Kei; Wu, Zhongbiao

    2012-07-21

    The synthesis and self-assembly of hierarchical architectures from nanoscale building blocks with unique morphology, orientation and dimension have opened up new opportunities to enhance their functional performances and remain a great challenge. This work represents tunable synthesis of various types of 3D monodisperse in situ N-doped (BiO)(2)CO(3) hierarchical architectures composed of 2D single-crystal nanosheets with dominant (001) facets by a one-pot template-free hydrothermal method from bismuth citrate and ammonia solution. Depending on the concentration of ammonia solution, the morphology of N-doped (BiO)(2)CO(3), including dandelion-like, hydrangea-like and peony flower-like microspheres, can be selectively constructed due to different self-assembly patterns of nanosheets. It was revealed that the ammonia played dual roles in the formation of N-doped (BiO)(2)CO(3) architectures. One is to hydrolyze bismuth citrate, and the other is to behave as a nitrogen doping source. The in situ doped nitrogen substituted for oxygen in (BiO)(2)CO(3) and subsequently narrowed the band gap, making N-doped (BiO)(2)CO(3) visible light active. Due to the special nanosheets architectures, the prepared various N-doped (BiO)(2)CO(3) materials exhibited especially efficient photocatalytic activity and high durability for the removal of NO in air under both visible and UV light irradiation. Based on the direct observation of the growth process with respect to phase structure, chemical composition and morphological structure, a novel growth mechanism is revealed, which involves a unique multistep pathway, including reaction-nucleation, aggregation, crystallization, dissolution-recrystallization, and Ostwald ripening. The facile synthesis approach and the proposed growth mechanism could provide new insights into the design and controlled synthesis of inorganic hierarchical materials with new or enhanced properties.

  10. In-Plane Si Nanowire Growth Mechanism in Absence of External Si Flux.

    Science.gov (United States)

    Curiotto, Stefano; Leroy, Frédéric; Cheynis, Fabien; Müller, Pierre

    2015-07-01

    We report on a new mechanism of nanowire formation: during Au deposition on Si(110) substrates, Au-Si droplets grow, move spontaneously, and fabricate a Si nanowire behind them in the absence of Si external flux. Nanowires are formed by Si dissolved from the substrate at the advancing front of the droplets and transported backward to the crystallization front. The droplet shape is determined by the Si etching anisotropy. The nanowire formation can be tuned by changing experimental parameters like substrate temperature and Au deposition rate.

  11. Differential proliferation rates generate patterns of mechanical tension that orient tissue growth

    OpenAIRE

    2013-01-01

    Orientation of cell divisions is a key mechanism of tissue morphogenesis. In the growing Drosophila wing imaginal disc epithelium, most of the cell divisions in the central wing pouch are oriented along the proximal–distal (P–D) axis by the Dachsous-Fat-Dachs planar polarity pathway. However, cells at the periphery of the wing pouch instead tend to orient their divisions perpendicular to the P–D axis despite strong Dachs polarization. Here, we show that these circumferential divisions are ori...

  12. Nucleation and growth mechanisms of Al2O3 atomic layerdeposition on synthetic polycrystalline MoS2

    Science.gov (United States)

    Zhang, H.; Chiappe, D.; Meersschaut, J.; Conard, T.; Franquet, A.; Nuytten, T.; Mannarino, M.; Radu, I.; Vandervorst, W.; Delabie, A.

    2017-02-01

    Two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) are of great interest for applications in nano-electronic devices. Their incorporation requires the deposition of nm-thin and continuous high-k dielectric layers on the 2D TMDs. Atomic layer deposition (ALD) of high-k dielectric layers is well established on Si surfaces: the importance of a high nucleation density for rapid layer closure is well known and the nucleation mechanisms have been thoroughly investigated. In contrast, the nucleation of ALD on 2D TMD surfaces is less well understood and a quantitative analysis of the deposition process is lacking. Therefore, in this work, we investigate the growth of Al2O3 (using Al(CH3)3/H2O ALD) on MoS2 whereby we attempt to provide a complete insight into the use of several complementary characterization techniques, including X-ray photo-electron spectroscopy, elastic recoil detection analysis, scanning electron microscopy, and time-of-flight secondary ion mass spectrometry. To reveal the inherent reactivity of MoS2, we exclude the impact of surface contamination from a transfer process by direct Al2O3 deposition on synthetic MoS2 layers obtained by a high temperature sulfurization process. It is shown that Al2O3 ALD on the MoS2 surface is strongly inhibited at temperatures between 125°C and 300°C, with no growth occurring on MoS2 crystal basal planes and selective nucleation only at line defects or grain boundaries at MoS2 top surface. During further deposition, the as-formed Al2O3 nano-ribbons grow in both vertical and lateral directions. Eventually, a continuous Al2O3 film is obtained by lateral growth over the MoS2 crystal basal plane, with the point of layer closure determined by the grain size at the MoS2 top surface and the lateral growth rate. The created Al2O3/MoS2 interface consists mainly of van der Waals interactions. The nucleation is improved by contributions of reversible adsorption on the MoS2 basal planes by using low

  13. Texture control and growth mechanism of WSe2 film prepared by rapid selenization of W film

    Science.gov (United States)

    Li, Hongchao; Gao, Di; Li, Kun; Pang, Mengde; Xie, Senlin; Liu, Rutie; Zou, Jianpeng

    2017-02-01

    The tungsten diselenide (WSe2) films with different orientation present unique properties suitable for specific applications, such as WSe2 with a C-axis⊥substrate for optoelectronics and WSe2 with a C-axis // substrate for electrocatalysts. Orientation control of WSe2 is essential for realizing the practical applications. In this letter, a WSe2 film has been prepared via rapid selenization of a magnetron-sputtered tungsten (W) film. The influence of the magnetron-sputtered W film on WSe2 film growth was studied systematically. Scanning electron microscopy, X-ray diffractometry and high-resolution transmission electron microscopy were used to evaluate the morphology, microstructure and phase composition of the W and WSe2 films. The substrate temperature has a significant effect on the W film phase composition, but little effect on the WSe2 film orientation. The WSe2 orientation can be controlled by changing the W film microstructure. A dense W film that is deposited at low pressure is conducive to the formation of WSe2 with a C-axis⊥substrate, whereas a porous W film deposited at high pressure favors the formation of WSe2 with a C-axis // substrate. A growth model for the WSe2 film with different texture has been proposed based on the experimental results. The direction of selenium (Se) vapor diffusion differs at the top and side surfaces. This is a key factor for the preparation of anisotropic WSe2 films. Highly oriented WSe2 films with a C-axis⊥substrate grow from the dense W film deposited at low pressure because Se vapor can only diffuse into the W film from the top surface where it is converted into selenide. Highly oriented WSe2 with a C-axis // substrate can be achieved for the porous W film that is deposited at high pressure because the nanopores provide a fast transmission tunnel for Se vapor diffusion. These findings will contribute to the controlled fabrication of WSe2 film and provide a theoretical basis for its application.

  14. Synthesis, growth, optical and mechanical studies of ferroelectric urea-oxalic acid single crystals

    Science.gov (United States)

    Vizhi, R. Ezhil; Dhivya, R.; Babu, D. Rajan

    2016-10-01

    A single crystal of urea oxalic acid was grown by slow evaporation method. The lattice parameters are a=5.13 Å, b=12.48 Å, c=7.07 Å, β=98.13° with V=448.5 Å3 which belongs to monoclinic system with space group P21/c obtained from single crystal X-ray diffraction analysis. UV-visible spectrum was recorded from the wavelength region of 200-800 nm and its cutoff wavelength was found to be 270 nm. Optical energy band gap of 4.57 eV was determined using Tau's plot relation. Fourier transform infrared vibrational spectrum confirmed the presence of N-H asymmetric stretching which occurs at 3444 cm-1 and 1853 cm-1 arising due to the amide C=O symmetric stretching. The emission was observed at 364 nm from the photoluminescence spectrum. The mechanical stability of the grown crystal was estimated by Vickers microhardness studies and it is evident that the grown crystal belongs to soft material category. Hardness related parameters such as elastic stiffness constant, fracture mechanics, brittleness index and yield strength were also evaluated. The dielectric constant and dielectric loss of the grown crystal were carried out as a function of frequency for different temperatures.

  15. Controlled growth of DNA structures from repeating units using the vernier mechanism.

    Science.gov (United States)

    Greschner, Andrea A; Bujold, Katherine E; Sleiman, Hanadi F

    2014-08-11

    In this report, we demonstrate the assembly of length-programmed DNA nanostructures using a single 16 base sequence and its complement as building blocks. To achieve this, we applied the Vernier mechanism to DNA assembly, which uses a mismatch in length between two monomers to dictate the final length of the product. Specifically, this approach relies on the interaction of two DNA strands containing a different number (n, m) of complementary binding sites: these two strands will keep binding to each other until they come into register, thus generating a larger assembly whose length (n × m) is encoded by the number of binding sites in each strand. While the Vernier mechanism has been applied to other areas of supramolecular chemistry, here we present an application of its principles to DNA nanostructures. Using a single 16 base repeat and its complement, and varying the number of repeats on a given DNA strand, we show the consistent construction of duplexes up to 228 base pairs (bp) in length. Employing specific annealing protocols, strand capping, and intercalator chaperones allows us to further grow the duplex to 392 base pairs. We demonstrate that the Vernier method is not only strand-efficient, but also produces a cleaner, higher-yielding product than conventional designs.

  16. Neolignans from Saururus chinensis inhibit PC-3 prostate cancer cell growth via apoptosis and senescence-like mechanisms.

    Science.gov (United States)

    Song, Seo-Young; Lee, Inkyoung; Park, Chaehwa; Lee, Hyeon; Hahm, Jong-Cheon; Kang, Won Ki

    2005-10-01

    This study investigated the anticancer activity and related mechanisms of neolignans, especially threo, erythro-manassantin A (compound 2), which are isolated from Saururus chinensis, in PC-3 cells. Compound 2 strongly inhibited the proliferation of PC-3 cells in a dose-dependent manner. Different cell morphologies were observed depending on the concentration of compound 2, which suggested different growth inhibitory mechanisms. DNA flow cytometry indicated that both low and high concentrations of compound 2 induced the arrest of PC-3 cells in G1 phase. Western blot analyses showed that hyperphosphorylated Rb and E2F-1 were decreased, whereas hypophosphorylated Rb was increased. The cells treated with compound 2 at 200 ng/ml showed shrinkage morphologically, and the staining of annexin V-FITC revealed apoptotic cell death of these cells. The induction of apoptosis was accompanied by the cleavage of caspase-3, -8, and -9, as well as the downregulation of the Bcl-2 and the upregulation of Bax. By contrast, at low compound 2 concentration (1 ng/ml), the cells arrested in G1 showed characteristic changes in morphology, such as an enlarged, flattened cell shape; the majority strongly expressed SA-beta-galactosidase activity. The number of cells undergoing apoptosis was negligible, and no poly(ADP-ribose) polymerase (PARP) cleavage was observed. The increase of p21 was noticed. However, it appeared to be transient rather than sustained. The protein p27 may be important for maintaining the senescence machinery induced by compound 2 because p27 expression was increased at low concentration compared with that at high concentration. In conclusion, compound 2 showed a significant growth inhibitory effect in PC-3 cells via two different mechanisms, i.e., apoptosis at high concentration and senescence at low concentration.

  17. Fusarium graminearum growth inhibition mechanism using phenolic compounds from Spirulina sp

    Directory of Open Access Journals (Sweden)

    Fernanda Arnhold Pagnussatt

    2013-02-01

    Full Text Available The application of natural antifungal substances is motivated by the need for alternatives to existing methods that are not always applicable, efficient, or that do not pose risk to consumers or the environment. Furthermore, studies on the behaviour of toxigenic species in the presence of natural fungicides have enabled their safe application in the food chain In this study, Spirulina LEB-18 phenolic extract was assessed for its antifungal activity on 12 toxigenic strains of Fusarium graminearum isolated from barley and wheat. The susceptible metabolic pathways were assessed through the determination of structural compounds (glucosamine and ergosterol and enzyme activity of the microorganisms' primary metabolism. The results indicate that phenolic extracts reduced the growth rate of the toxigenic species investigated. The IC50 was obtained by applying 3 to 8% (p/p of phenolic compounds in relation to the culture medium. The use of this natural fungicide proved promising for the inhibition of fungal multiplication, especially in terms of the inactivation of enzymatic systems (amylase and protease of Fusarium graminearum.

  18. Mechanisms regulating invasiveness and growth of endometriosis lesions in rat experimental model and in humans.

    Science.gov (United States)

    Sotnikova, Natalia Yu; Antsiferova, Yulia S; Posiseeva, Lyubov V; Shishkov, Dmitrii N; Posiseev, Denis V; Filippova, Ekaterina S

    2010-05-15

    To compare the expression of MMP-2, TIMP-2, and TGFbeta2 mRNA in experimental and human endometriotic lesions and to assess the possibility of its cytokine regulation. Experimental laboratory study. Medical center. ANIMALS AND PATIENT(S): Thirty female Wistar rats, 17 women with endometriosis, 11 healthy women. Uterine transplants were attached to rat peritoneum via the surgical autotransplantation technique. The collection of endometriotic implants at 7, 14, and 21 days postsurgery and laparoscopic collection of peritoneal fluid, ectopic, and matched eutopic endometrium from women with endometriosis were performed. MMP-2, TIMP-2, TGFbeta2 mRNA expression in endometrium was assessed by real-time reverse-transcription polymerase chain reaction. In rats, the increase of MMP-2 and decrease of TIMP-2 mRNA expression was noted at the 7th day, and an increase of TGFbeta2 mRNA expression was seen at the 14th day postsurgery. In humans, elevation of TIMP-2 mRNA expression in eutopic endometrium and of MMP-2, TGFbeta2 mRNA expression in ectopic endometrium was observed. Autologous peritoneal fluid stimulated MMP-2 mRNA expression in eutopic endometrium of women with endometriosis. Cytokines derived from ectopic lesions mononuclear cells increased TGFbeta2 mRNA expression in endometrium of healthy women. Supposedly MMP-TIMP balance is important in promoting endometriotic tissue invasion and TGFbeta2 in regulating ectopic endometrium growth. Copyright 2010 American Society for Reproductive Medicine. Published by Elsevier Inc. All rights reserved.

  19. The evolution and mechanisms of unintentional doping in ZnO epitaxial growth

    Science.gov (United States)

    Wu, Kongping; Zhu, Shunming; Gu, Shulin

    2012-10-01

    In this study, the authors investigate the evolution of the electrical and optical properties of ZnO epilayers grown by the metal-organic chemical vapor deposition method on c-sapphire substrates. The electrical and optical properties of ZnO buffer were investigated by temperature-dependent Hall (TDH), CV and PL. According to fit TDH data, two shallow donors were found in ZnO buffer film, with their activation energy at about 50meV and 10meV, respectively. The shallow donor at the energy of about 50meV has also been assigned from fitted results of PL spectra. According to the reported results and our experiments, the shallow donor at 50meV has then been ascribed to the diffused Al from sapphire during high temperature annealing and epitaxial growth process. All these reveal that the high background-carrier concentration in the HT-grown ZnO epilayer originates from the thermally enhanced diffusion of Al atoms from the sapphire substrate. Therefore, the AlZn shallow donors should be the main origin of the high background-carrier concentration in the HT-grown ZnO epilayers.

  20. Growth mechanism of Ge-doped CZTSSe thin film by sputtering method and solar cells.

    Science.gov (United States)

    Li, Jinze; Shen, Honglie; Chen, Jieyi; Li, Yufang; Yang, Jiale

    2016-10-19

    Ge-doped CZTSSe thin films were obtained by covering a thin Ge layer on CZTS precursors, followed by a selenization process. The effect of the Ge layer thickness on the morphologies and structural properties of Ge-doped CZTSSe thin films were studied. It was found that Ge doping could promote grain growth to form a compact thin film. The lattice shrank in the top-half of the film due to the smaller atomic radius of Ge, leading to the formation of tensile stress. According to thermodynamic analysis, Sn was easier to be selenized than Ge. Thus, Ge preferred to remain on the surface and increased the surface roughness when the Ge layer was thin. CZTSe was easier to form than Ge-doped CZTSe, which caused difficulty in Ge doping. These results offered a theoretical and experimental guide for preparing Ge-doped CZTSSe thin films for the potential applications in low-cost solar cells. With a 10 nm Ge layer on the top of the precursor, the conversion efficiency of the solar cell improved to 5.38% with an open-circuit voltage of 403 mV, a short-circuit current density of 28.51 mA cm(-2) and a fill factor of 46.83% after Ge doping.

  1. Growth Mechanism and Morphology of ZnO/eosin-Y Hybrid Thin Films

    Institute of Scientific and Technical Information of China (English)

    MAR(I) Bernabé; SINGH Krishan-Chander; MOLLAR Miguel; MOYA Mónica; RANA Ravi

    2012-01-01

    Thin hybrid films of ZnO/eosin-Y were prepared by electrodeposition at-0.8 and -0.9 V in aqueous and non-aqueous baths at temperatures ranging from 40 to 90 ℃ with dye concentrations of 100 and 400 μmol· L-1.The films were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),energy-dispersive X-ray analysis (EDX),and absorption spectroscopy.The films prepared in a non-aqueous bath were non-porous and did not adsorb dye molecules on their surface.However,the films grown in aqueous media were porous in nature and adsorbed dye during the deposition of ZnO.Preferential growth of the film along the (002) face was observed,and the highest crystallinity was achieved when the film was deposited at 60 ℃.The maximum absorption was achieved for the films grown at 60 to 70 ℃,a deposition potential of-0.9 V,and a dye concentration of 100 μmol· L-1.

  2. Mechanisms of growth inhibition of Phytomonas serpens by the alkaloids tomatine and tomatidine

    Science.gov (United States)

    Medina, Jorge Mansur; Rodrigues, Juliany Cola Fernandes; Moreira, Otacilio C; Atella, Geórgia; de Souza, Wanderley; Barrabin, Hector

    2015-01-01

    Phytomonas serpens are flagellates in the family Trypanosomatidae that parasitise the tomato plant (Solanum lycopersicum L.), which results in fruits with low commercial value. The tomato glycoalkaloid tomatine and its aglycone tomatidine inhibit the growth of P. serpens in axenic cultures. Tomatine, like many other saponins, induces permeabilisation of the cell membrane and a loss of cell content, including the cytosolic enzyme pyruvate kinase. In contrast, tomatidine does not cause permeabilisation of membranes, but instead provokes morphological changes, including vacuolisation. Phytomonas treated with tomatidine show an increased accumulation of labelled neutral lipids (BODYPY-palmitic), a notable decrease in the amount of C24-alkylated sterols and an increase in zymosterol content. These results are consistent with the inhibition of 24-sterol methyltransferase (SMT), which is an important enzyme that is responsible for the methylation of sterols at the 24 position. We propose that the main target of tomatidine is the sterols biosynthetic pathway, specifically, inhibition of the 24-SMT. Altogether, the results obtained in the present paper suggest a more general effect of alkaloids in trypanosomatids, which opens potential therapeutic possibilities for the treatment of the diseases caused by these pathogens. PMID:25742263

  3. Application of EGFP-EGF fusions to explore mechanism of endocytosis of epidermal growth factor

    Institute of Scientific and Technical Information of China (English)

    Hua JIANG; Jie ZHANG; Bi-zhi SHI; Yu-hong XU; Zong-hai LI; Jian-ren GU

    2007-01-01

    Aim: To develop a simple method for monitoring protein localization of epidermal growth factor (EGF) in living cells. Methods: Enhanced green fluorescent protein (EGFP) was used as an autofluorescent tag to label EGF ligands. SDS-PAGE and Western blot analysis were used to detect the expression of the EGFP-tagged EGF (EGFP-EGF) protein. The cell-binding and internalization activity of EGFP-EGF were analyzed by fluorescence-activated cell sorting (FACS) and confocal micro-scopy. Results: EGFP-EGF protein was expressed in Escherichia coil and purified.A cell-binding assay demonstrated that the EGFP-EGF protein could bind effi-ciently to the cells expressing EGFR. The binding and intemalization of EGFP-EGF can be visualized even at a very low concentration under confocal microscopy.The FACS-based assay for internalization activity indicated the accumulation of internalized EGFP-EGF over time. Furthermore, the results of the competition assay indicated its EGFR binding specificity. Using such a method, it does not need to label EGF with chemicals and avoid light in the experimental process. Conclusion: The fusion protein EGFP-EGF has several characters including high sensitivity, stability and convenience for manipulation, and is a powerful tool for the study of EGF endocytosis.

  4. The pollen tube clear zone:Clues to the mechanism of polarized growth

    Institute of Scientific and Technical Information of China (English)

    Peter K Hepler; Lawrence J Winship

    2015-01-01

    Pollen tubes usually exhibit a prominent region at their apex called the “clear zone” because it lacks light refracting amyloplasts. A robust, long clear zone often associates with fast growing pollen tubes, and thus serves as an indicator of pollen tube health. Nevertheless we do not understand how it arises or how it is maintained. Here we review the structure of the clear zone, and attempt to explain the factors that contribute to its formation. While amyloplasts and vacuolar elements are excluded from the clear zone, virtually all other organelles are present including secretory vesicles, mitochondria, Golgi dictyosomes, and the endoplas-mic reticulum (ER). Secretory vesicles aggregate into an inverted cone appressed against the apical plasma membrane. ER elements move nearly to the extreme apex, whereas mitochondria and Golgi dictyosomes move less far forward. The cortical actin fringe assumes a central position in the control of cle