Crystallite growth kinetics of TiO2 surface modification with 9 mol% ZnO prepared by a coprecipitation process

International Nuclear Information System (INIS)

Ko, Horng-Huey; Hsi, Chi-Shiung; Wang, Moo-Chin; Zhao, Xiujian

2014-01-01

Highlights: • TiO 2 powder surface modification with 9 mol% ZnO was obtained. • Phase transformation from anatase to rutile was hindered by ZnO added. • Growth kinetic of anatase TiO 2 nanocrystallites in T-9Z powders was described as: D A,9 2 =2.42×10 5 ×exp(-39.9×10 3 /RT). • Growth kinetic of rutile TiO 2 nanocrystallites in T-9Z powders was described as: D R,9 2 =8.49×10 5 ×exp(-47.6×10 3 /RT) rutile TiO 2 . -- Abstract: The nanocrystallite growth of TiO 2 surface modification with 9 mol% ZnO prepared by a coprecipitation process has been studied. Thermogravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and UV–VIS–NIR spectrophotometry have been utilized to characterize the TiO 2 nanocrystallites surface modification with 9 mol% ZnO (denoted by T-9Z). The DTA result shows that the anatase TiO 2 first formed at 533 K and the completion of anatase TiO 2 crystallization occurred at 745 K for the T-9Z freeze-dried precursor powders. XRD results reveal that the anatase and rutile TiO 2 coexist when the T-9Z freeze-dried precursor powders were calcined at 523–973 K for 2 h. When the T-9Z freeze-dried precursor powders were calcined at 973 K for 2 h, rutile TiO 2 was the major phase, and the minor phases were anatase TiO 2 and Zn 2 Ti 3 O 8 . The phase was composed of the rutile TiO 2 and Zn 2 TiO 4 for the T-9Z freeze-dried precursor powders after calcination at 1273 K for 2 h. The growth kinetics of TiO 2 nanocrystallites in T-9Z powders were described as: D A,9 2 =2.42×10 5 ×exp(-39.9×10 3 /RT)and D R,9 2 =8.49×10 5 ×exp(-47.6×10 3 /RT) for anatase and rutile TiO 2 nanocrystallites respectively. The analysis results of UV/VIS/NIR spectra reveal that the T-9Z freeze-dried precursor powders after calcination have a red-shifted effect with increasing calcination temperature and can be used as a UVA-attenuating agent

Investigations of the kinetics of surfactant-assisted growth of cobalt/copper multilayers

Science.gov (United States)

Peterson, Brennan Lovelace

Surfactants---a term given to a broad family of surface additives used in thin film growth---provide a potentially useful tool for the deposition engineer. A long history of work on the field has produced a sometimes conflicting view of what surfactants do, and while their efficacy in improving magnetic films is well established, the attendant structural changes remain unclear. Early work on surfactant-assisted growth was generally confined to deposition at near equilibrium conditions: high temperature and very slow deposition rates on very smooth (single crystal) substrates. In the case of low temperature sputter deposition, the kinetic phenomena differ greatly from the near-equilibrium case: high rate, more interlayer diffusive pathways, high grain boundary density, and few well defined atomic steps. There are two major ideas which underlie and explain the use of surfactants. First, they are used to alter growth kinetics of a single material by changing the diffusion barriers on the growing surface. Second, surfactants alter the initial nucleation parameters in heteroepitaxial growth, which is often explained with reference to changes in the surface energy, gamma. Changes to these parameters result, in turn, to variations of the roughness and conformality of thin films grown with the assistance of surfactants. Finally, the roughness and conformality are critical for determining the performance of modern thin film magnetic sensors. As surfactants offer a way to alter the nucleation and growth kinetics, they offer tremendous potential benefits. However, before surfactants are trustworthy deposition tool, a better understanding of their structural effects and underlying surface energy and kinetic changes is necessary. In order to investigate these phenomena, DC magnetron sputtered [Co/Cu] multilayers were deposited on Si/SiO2 substrates using O2 , Ag, Pb, and In as surfactants. Oxygen was introduced during growth at partial pressures ranging from 10-9 to 10-6 Torr

Theoretical study of fractal growth and stability on surface

DEFF Research Database (Denmark)

Dick, Veronika V.; Solov'yov, Ilia; Solov'yov, Andrey V.

2009-01-01

We perform a theoretical study of the fractal growing process on surface by using the deposition, diffusion, aggregation method. We present a detailed analysis of the post-growth processes occurring in a nanofractal on surface. For this study we developed a method which describes the internal...... dynamics of particles in a fractal and accounts for their diffusion and detachment. We demonstrate that these kinetic processes are responsible for the formation of the final shape of the islands on surface after the post-growth relaxation....

Simulation of uranium oxides reduction kinetics by hydrogen. Reactivities of germination and growth

International Nuclear Information System (INIS)

Brun, C.

1997-01-01

The aim of this work is to simulate the reduction by hydrogen of the tri-uranium octo-oxide U 3 O 8 (obtained by uranium trioxide calcination) into uranium dioxide. The kinetics curves have been obtained by thermal gravimetric analysis, the hydrogen and steam pressures being defined. The geometrical modeling which has allowed to explain the trend of the kinetics curves and of the velocity curves is an anisotropic germination-growth modeling. The powder is supposed to be formed of spherical grains with the same radius. The germs of the new UO 2 phase appear at the surface of the U 3 O 8 grains with a specific germination frequency. The growth reactivity is anisotropic and is very large in the tangential direction to the grains surface. Then, the uranium dioxide growths inside the grain and the limiting step is the grain surface. The variations of the growth reactivity and of the germination specific frequency in terms of the gases partial pressures and of the temperature have been explained by two different mechanisms. The limiting step of the growth mechanism is the desorption of water in the uranium dioxide surface. Concerning the germination mechanism the limiting step is a water desorption too but in the tri-uranium octo-oxide surface. The same geometrical modeling and the same germination and growth mechanisms have been applied to the reduction of a tri-uranium octo-oxide obtained by calcination of hydrated uranium trioxide. The values of the germination specific frequency of this solid are nevertheless weaker than those of the solid obtained by direct calcination of the uranium trioxide. (O.M.)

Kinetics of growth of nanowhiskers (nanowires and nanotubes

Directory of Open Access Journals (Sweden)

Avramov Isak

2007-01-01

Full Text Available AbstractThe kinetics of nanowhiskers growth is studied theoretically taking into account the adatom diffusion from the surface to the top of needle. An exponential growth with time is expected for the initial stages of the process, when the lengthlof the whisker is smaller than the average diffusion length λ of adatoms. It transforms to linear growth rate forl > λ. The formation of nanotubes with a hollow core dislocation is explained by accounting for the role of the stress in the middle of screw dislocations. When the magnitude of the Burgers vector exceeds a critical value, it is energetically more favorable to remove the highly strained material around the dislocation line and to create a tube with an additional free surface. Additionally, there is an important size effect, due to the small radiusRof the nanowhisker. The interplay, between the contributions from the size effects and from the diffusion, explains why for the very thin nanowhiskers the lengthlis proportional to the radiusRwhile, otherwise the length is inversely proportional to it, i.e.,l∼1/R.

Investigation of Au/Au(100) film growth with energetic deposition by kinetic Monte Carlo simulation

International Nuclear Information System (INIS)

Zhang Qingyu; Ma Tengcai; Pan Zhengying; Tang Jiayong

2000-01-01

The Au/Au(100) epitaxial growth with energetic deposition was simulated by using kinetic Monte Carlo method. The influences of energetic atoms on morphology and atomistic processes in the early stage of film growth were investigated. The reentrant layer-by-layer growth was observed in the temperature range of 450 K to 100 K. The authors found the energetic atoms can promote the nucleation and island growth in the early stages of film growth and enhance the smoothness of film surface at temperatures of film growth in 3-dimensional mode and in quasi-two-dimensional mode. The atomistic mechanism that promotes the nucleation and island growth and enhances the smoothness of film surface is discussed

Growth kinetics and mass transport mechanisms of GaN columns by selective area metal organic vapor phase epitaxy

Science.gov (United States)

Wang, Xue; Hartmann, Jana; Mandl, Martin; Sadat Mohajerani, Matin; Wehmann, Hergo-H.; Strassburg, Martin; Waag, Andreas

2014-04-01

Three-dimensional GaN columns recently have attracted a lot of attention as the potential basis for core-shell light emitting diodes for future solid state lighting. In this study, the fundamental insights into growth kinetics and mass transport mechanisms of N-polar GaN columns during selective area metal organic vapor phase epitaxy on patterned SiOx/sapphire templates are systematically investigated using various pitch of apertures, growth time, and silane flow. Species impingement fluxes on the top surface of columns Jtop and on their sidewall Jsw, as well as, the diffusion flux from the substrate Jsub contribute to the growth of the GaN columns. The vertical and lateral growth rates devoted by Jtop, Jsw and Jsub are estimated quantitatively. The diffusion length of species on the SiOx mask surface λsub as well as on the sidewall surfaces of the 3D columns λsw are determined. The influences of silane on the growth kinetics are discussed. A growth model is developed for this selective area metal organic vapor phase epitaxy processing.

Kinetic Monte Carlo simulation of growth of Ge quantum dot multilayers with amorphous matrix

Energy Technology Data Exchange (ETDEWEB)

Endres, Jan, E-mail: endres.jan@gmail.com; Holý, Václav; Daniš, Stanislav [Charles University, Faculty of Mathematics and Physics (Czech Republic); Buljan, Maja [Ruđer Bošković Institute (Croatia)

2017-04-15

Kinetic Monte Carlo method is used to simulate the growth of germanium quantum dot multilayers with amorphous matrix. We modified a model for self-assembled growth of quantum dots in crystalline matrix for the case of the amorphous one. The surface morphology given as hills above the buried dots is the main driving force for the ordering of the quantum dots. In the simulations, we observed a short-range self-ordering in the lateral direction. The ordering in lateral and vertical direction depends strongly on the surface morphology, mostly on the strength how the deposited material replicates previous surfaces.

Nucleation and Growth Kinetics from LaMer Burst Data.

Science.gov (United States)

Chu, Daniel B K; Owen, Jonathan S; Peters, Baron

2017-10-12

In LaMer burst nucleation, the individual nucleation events happen en masse, quasi-simultaneously, and at nearly identical homogeneous conditions. These properties make LaMer burst nucleation important for applications that require monodispersed particles and also for theoretical analyses. Sugimoto and co-workers predicted that the number of nuclei generated during a LaMer burst depends only on the solute supply rate and the growth rate, independent of the nucleation kinetics. Some experiments confirm that solute supply kinetics control the number of nuclei, but flaws in the original theoretical analysis raise questions about the predicted roles of growth and nucleation kinetics. We provide a rigorous analysis of the coupled equations that govern concentrations of nuclei and solutes. Our analysis confirms that the number of nuclei is largely determined by the solute supply and growth rates, but our predicted relationship differs from that of Sugimoto et al. Moreover, we find that additional nucleus size dependent corrections should emerge in systems with slow growth kinetics. Finally, we show how the nucleation kinetics determine the particle size distribution. We suggest that measured particle size distributions might therefore provide ways to test theoretical models of homogeneous nucleation kinetics.

Crystallite growth kinetics of TiO{sub 2} surface modification with 9 mol% ZnO prepared by a coprecipitation process

Energy Technology Data Exchange (ETDEWEB)

Ko, Horng-Huey [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 80708, Taiwan (China); Hsi, Chi-Shiung [Department of Materials Science and Engineering, National United University, 1 Lein-Da, Kung-Ching Li, Miao-Li 36003, Taiwan (China); Wang, Moo-Chin, E-mail: mcwang@kmu.edu.tw [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 80708, Taiwan (China); Zhao, Xiujian, E-mail: opluse@whut.edu.cn [State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070 (China)

2014-03-05

Highlights: • TiO{sub 2} powder surface modification with 9 mol% ZnO was obtained. • Phase transformation from anatase to rutile was hindered by ZnO added. • Growth kinetic of anatase TiO{sub 2} nanocrystallites in T-9Z powders was described as: D{sub A,9}{sup 2}=2.42×10{sup 5}×exp(-39.9×10{sup 3}/RT). • Growth kinetic of rutile TiO{sub 2} nanocrystallites in T-9Z powders was described as: D{sub R,9}{sup 2}=8.49×10{sup 5}×exp(-47.6×10{sup 3}/RT) rutile TiO{sub 2}. -- Abstract: The nanocrystallite growth of TiO{sub 2} surface modification with 9 mol% ZnO prepared by a coprecipitation process has been studied. Thermogravimetric and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and UV–VIS–NIR spectrophotometry have been utilized to characterize the TiO{sub 2} nanocrystallites surface modification with 9 mol% ZnO (denoted by T-9Z). The DTA result shows that the anatase TiO{sub 2} first formed at 533 K and the completion of anatase TiO{sub 2} crystallization occurred at 745 K for the T-9Z freeze-dried precursor powders. XRD results reveal that the anatase and rutile TiO{sub 2} coexist when the T-9Z freeze-dried precursor powders were calcined at 523–973 K for 2 h. When the T-9Z freeze-dried precursor powders were calcined at 973 K for 2 h, rutile TiO{sub 2} was the major phase, and the minor phases were anatase TiO{sub 2} and Zn{sub 2}Ti{sub 3}O{sub 8}. The phase was composed of the rutile TiO{sub 2} and Zn{sub 2}TiO{sub 4} for the T-9Z freeze-dried precursor powders after calcination at 1273 K for 2 h. The growth kinetics of TiO{sub 2} nanocrystallites in T-9Z powders were described as: D{sub A,9}{sup 2}=2.42×10{sup 5}×exp(-39.9×10{sup 3}/RT)and D{sub R,9}{sup 2}=8.49×10{sup 5}×exp(-47.6×10{sup 3}/RT) for anatase and rutile TiO{sub 2} nanocrystallites respectively. The analysis results of UV/VIS/NIR spectra reveal that the T-9Z freeze

Ge(001):B gas-source molecular beam epitaxy: B surface segregation, hydrogen desorption, and film growth kinetics

Energy Technology Data Exchange (ETDEWEB)

Kim, H.; Greene, J.E. [Materials Science Department, the Coordinated Science Laboratory and the Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801 (United States)

1999-03-01

Ultrahigh B-doped Ge(001) layers, with concentrations C{sub B} up to 8{times}10{sup 21} cm{sup {minus}3}, were grown by gas-source molecular beam epitaxy from Ge{sub 2}H{sub 6} and B{sub 2}H{sub 6} at temperatures T{sub s}=325{degree}C (in the surface-reaction-limited regime) and 600{degree}C (in the flux-limited regime). The samples were quenched, D site exchanged for H, and D{sub 2} temperature-programed desorption (TPD) used to determine B coverages {theta}{sub B} as a function of C{sub B} and T{sub s} by comparison with B-adsorbed Ge(001) reference samples with known {theta}{sub B} values. During Ge(001):B film growth, strong surface B segregation to the second layer was observed with surface-to-bulk B concentration ratios ranging up to 6000. The TPD spectra exhibited {alpha}{sub 2} and {alpha}{sub 1} peaks associated with dideuteride and monodeuteride desorption as well as lower-temperature B-induced {alpha}{sub 2}{sup {asterisk}} and {alpha}{sub 1}{sup {asterisk}} peaks associated with deuterium desorption from Ge{sup {asterisk}} surface atoms with B backbonds. Increasing {theta}{sub B} expanded the area under {alpha}{sub 2}{sup {asterisk}} and {alpha}{sub 1}{sup {asterisk}} at the expense of {alpha}{sub 2} and {alpha}{sub 1} and decreased the total D coverage {theta}{sub D}. The TPD results were used to determine the B segregation enthalpy, {minus}0.64 eV, and to explain and model the effects of high B coverages on Ge(001) growth kinetics. At T{sub s}=325{degree}C, where B segregation is kinetically hindered, film deposition rates R{sub Ge} are not a strong function of C{sub B}, exhibiting only a small decrease at C{sub B}{approx_gt}5{times}10{sup 18} cm{sup {minus}3}. However, at T{sub s}=600{degree}C, R{sub Ge} decreases by up to 40{percent} with increasing C{sub B}{approx_gt}1{times}10{sup 18} cm{sup {minus}3}. This is due primarily to the combination of B-induced Ge dimer vacancies and the deactivation of surface dangling bonds caused by charge transfer

Correlation of thermodynamics and grain growth kinetics in nanocrystalline metals

International Nuclear Information System (INIS)

Song Xiaoyan; Zhang Jiuxing; Li Lingmei; Yang Keyong; Liu Guoquan

2006-01-01

We investigated the correlation of thermodynamics and grain growth kinetics of nanocrystalline metals both theoretically and experimentally. A model was developed to describe the thermodynamic properties of nanograin boundaries, which could give reliable predictions in the destabilization characteristics of nanograin structures and the slowing down of grain growth kinetics at a constant temperature. Both the temperature-varying and isothermal nanograin growth behaviors in pure nanocrystalline Co were studied to verify the thermodynamic predictions. The experimental results showing that discontinuous nanograin growth takes place at a certain temperature and grain growth rate decreases monotonically with time confirm our thermodynamics-based description of nanograin growth characteristics. Therefore, we propose a thermodynamic viewpoint to explain the deviation of grain growth kinetics in nanocrystalline metals from those of polycrystalline materials

Nucleation and growth kinetics for intercalated islands during deposition on layered materials with isolated pointlike surface defects

International Nuclear Information System (INIS)

Han, Yong; Lii-Rosales, A.; Zhou, Y.; Wang, C.-J.

2017-01-01

Theory and stochastic lattice-gas modeling is developed for the formation of intercalated metal islands in the gallery between the top layer and the underlying layer at the surface of layered materials. Our model for this process involves deposition of atoms, some fraction of which then enter the gallery through well-separated pointlike defects in the top layer. Subsequently, these atoms diffuse within the subsurface gallery leading to nucleation and growth of intercalated islands nearby the defect point source. For the case of a single point defect, continuum diffusion equation analysis provides insight into the nucleation kinetics. However, complementary tailored lattice-gas modeling produces a more comprehensive and quantitative characterization. We analyze the large spread in nucleation times and positions relative to the defect for the first nucleated island. We also consider the formation of subsequent islands and the evolution of island growth shapes. The shapes reflect in part our natural adoption of a hexagonal close-packed island structure. As a result, motivation and support for the model is provided by scanning tunneling microscopy observations of the formation of intercalated metal islands in highly-ordered pyrolytic graphite at higher temperatures.

Kinetic models of controllable pore growth of anodic aluminum oxide membrane

Science.gov (United States)

Huang, Yan; Zeng, Hong-yan; Zhao, Ce; Qu, Ye-qing; Zhang, Pin

2012-06-01

An anodized Al2O3 (AAO) membrane with apertures about 72 nm in diameter was prepared by two-step anodic oxidation. The appearance and pore arrangement of the AAO membrane were characterized by energy dispersive x-ray spectroscopy and scanning electron microscopy. It was confirmed that the pores with high pore aspect ratio were parallel, well-ordered, and uniform. The kinetics of pores growth in the AAO membrane was derived, and the kinetic models showed that pores stopped developing when the pressure ( σ) trended to equal the surface tension at the end of anodic oxidation. During pore expansion, the effects of the oxalic acid concentration and expansion time on the pore size were investigated, and the kinetic behaviors were explained with two kinetic models derived in this study. They showed that the pore size increased with extended time ( r= G· t+ G'), but decreased with increased concentration ( r = - K·ln c- K') through the derived mathematic formula. Also, the values of G, G', K, and K' were derived from our experimental data.

Reply to "Domain-growth kinetics of systems with soft walls''

DEFF Research Database (Denmark)

Mouritsen, Ole G.; Præstgaard, Eigil

1988-01-01

On the basis of computer-simulation results for three different models with soft domain walls it is argued that the zero-temperature domain-growth kinetics falls in a separate universality class characterized by a kinetic growth exponent n≃0.25. However, for finite temperatures there is a distinct...... crossover to Lifshitz-Allen-Cahn kinetics n=0.50, thus suggesting that the soft-wall and hard-wall universality classes become identical at finite temperatures....

Growth Kinetics and Size Distribution Dynamics of Viscous Secondary Organic Aerosol

Energy Technology Data Exchange (ETDEWEB)

Zaveri, Rahul A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Atmospheric Science and Global Change Div. (ASGC); Shilling, John E. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Atmospheric Science and Global Change Div. (ASGC); Zelenyuk, Alla [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Physical Sciences Div.; Liu, Jiumeng [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Atmospheric Science and Global Change Div. (ASGC); Bell, David M. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Physical Sciences Div.; Paul Scherrer Inst. (PSI), Villigen (Switzerland). Lab. of Atmospheric Chemistry; D’Ambro, Emma L. [Univ. of Washington, Seattle, WA (United States). Dept. of Atmospheric Sciences and Dept. of Chemistry; Gaston, Cassandra J. [Univ. of Washington, Seattle, WA (United States). Dept. of Atmospheric Sciences; Univ. of Miami, Miami, FL (United States). Rosenstiel School of Marine and Atmospheric Science; Thornton, Joel A. [Univ. of Washington, Seattle, WA (United States). Dept. of Atmospheric Sciences and Dept. of Chemistry; Laskin, Alexander [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL); Purdue Univ., West Lafayette, IN (United States). Dept. of Chemistry; Lin, Peng [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL); Purdue Univ., West Lafayette, IN (United States). Dept. of Chemistry; Wilson, Jacqueline [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Physical Sciences Div.; Easter, Richard C. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Atmospheric Science and Global Change Div. (ASGC); Wang, Jian [Brookhaven National Lab. (BNL), Upton, NY (United States). Environmental & Climate Sciences Dept.; Bertram, Allan K. [Univ. of British Columbia, Vancouver, BC (Canada). Dept. of Chemistry; Martin, Scot T. [Harvard Univ., Cambridge, MA (United States). School of Engineering and Applied Sciences (SEAS) and Dept. of Earth and Planetary Sciences; Seinfeld, John H. [California Inst. of Technology (CalTech), Pasadena, CA (United States). Div. of Chemistry and Chemical Engineering and Div. of Engineering and Applied Science; Worsnop, Douglas R. [Aerodyne Research, Billerica, MA (United States). Center for Aerosol and Cloud Chemistry

2017-12-15

Low bulk diffusivity inside viscous semisolid atmospheric secondary organic aerosol (SOA) can prolong equilibration time scale, but its broader impacts on aerosol growth and size distribution dynamics are poorly understood. In this article, we present quantitative insights into the effects of bulk diffusivity on the growth and evaporation kinetics of SOA formed under dry conditions from photooxidation of isoprene in the presence of a bimodal aerosol consisting of Aitken (ammonium sulfate) and accumulation (isoprene or α-pinene SOA) mode particles. Aerosol composition measurements and evaporation kinetics indicate that isoprene SOA is composed of several semivolatile organic compounds (SVOCs), with some reversibly reacting to form oligomers. Model analysis shows that liquid-like bulk diffusivities can be used to fit the observed evaporation kinetics of accumulation mode particles but fail to explain the growth kinetics of bimodal aerosol by significantly under-predicting the evolution of the Aitken mode. In contrast, the semisolid scenario successfully reproduces both evaporation and growth kinetics, with the interpretation that hindered partitioning of SVOCs into large viscous particles effectively promotes the growth of smaller particles that have shorter diffusion time scales. This effect has important implications for the growth of atmospheric ultrafine particles to climatically active sizes.

Hydrothermal Atomic Force Microscopy Investigation of Barite Growth: Role of Spectator Ions in Elementary Step Edge Growth Kinetics and Hillock Morphology [Supporting Information Only

Energy Technology Data Exchange (ETDEWEB)

Jindra, Sarah A. [Wright State Univ., Dayton, OH (United States); Bertagni, Angela L. [Wright State Univ., Dayton, OH (United States); Bracco, Jacquelyn N. [Wright State Univ., Dayton, OH (United States); Argonne National Lab. (ANL), Argonne, IL (United States); Higgins, Steven R. [Wright State Univ., Dayton, OH (United States)

2017-09-25

Here, to better understand the role of spectator ions in barite growth, the kinetics of step edge growth on barite (001) surfaces were studied under various salt solutions. Hydrothermal atomic force microscopy (HAFM) was used to investigate the effect of background electrolytes (NaCl, NaBr, and NaNO₃) as a function of saturation index and ionic strength (I) on barite growth sourced at dislocations at 108 °C. Results demonstrate that hillock morphology is affected by I, as well as type of anion, where the prevalence of steps aligned on the [010] direction is highest under Cl^–. There is a modest increase in kinetic coefficient of 55–130% with a 10-fold increase in I for each salt. In comparing the kinetic coefficients of the salts at low ionic strength (0.01 M), there is a moderate difference, suggesting that the anion may play a role in barium attachment.

Abnormal growth kinetics of h-BN epitaxial monolayer on Ru(0001) enhanced by subsurface Ar species

Science.gov (United States)

Wei, Wei; Meng, Jie; Meng, Caixia; Ning, Yanxiao; Li, Qunxiang; Fu, Qiang; Bao, Xinhe

2018-04-01

Growth kinetics of epitaxial films often follows the diffusion-limited aggregation mechanism, which shows a "fractal-to-compact" morphological transition with increasing growth temperature or decreasing deposition flux. Here, we observe an abnormal "compact-to-fractal" morphological transition with increasing growth temperature for hexagonal boron nitride growth on the Ru(0001) surface. The unusual growth process can be explained by a reaction-limited aggregation (RLA) mechanism. Moreover, introduction of the subsurface Ar atoms has enhanced this RLA growth behavior by decreasing both reaction and diffusion barriers. Our work may shed light on the epitaxial growth of two-dimensional atomic crystals and help to control their morphology.

Growth kinetics of boride coatings formed at the surface AISI M2 during dehydrated paste pack boriding

Energy Technology Data Exchange (ETDEWEB)

Doñu Ruiz, M.A., E-mail: mdonur0800@alumno.ipn.mx [Universidad Politécnica del Valle de México UPVM, Grupo Ciencia e Ingeniería de Materiales, Av. Mexiquense S/N Esquina Av. Universidad Politécnica, Col Villa Esmeralda, 54910 Tultitlan (Mexico); López Perrusquia, N.; Sánchez Huerta, D. [Universidad Politécnica del Valle de México UPVM, Grupo Ciencia e Ingeniería de Materiales, Av. Mexiquense S/N Esquina Av. Universidad Politécnica, Col Villa Esmeralda, 54910 Tultitlan (Mexico); Torres San Miguel, C.R.; Urriolagoitia Calderón, G.M. [Instituto Politécnico Nacional, SEPI-ESIME, Unidad Profesional Adolfo López Mateos Zacatenco, Edificio 5, 2do. Piso, Col. Lindavista, CP 07738 México, D.F. (Mexico); Cerillo Moreno, E.A. [Universidad Politécnica del Valle de México UPVM, Grupo Ciencia e Ingeniería de Materiales, Av. Mexiquense S/N Esquina Av. Universidad Politécnica, Col Villa Esmeralda, 54910 Tultitlan (Mexico); Cortes Suarez, J.V. [Univerisdad Autónoma Metropolitana Unidad Azcapotzalco, Av. San Pablo 180 Azcapotzalco 02200, Área de Ciencia de los Materiales, México, D.F. (Mexico)

2015-12-01

The growth kinetics of the boride coatings (FeB and Fe{sub 2}B) at the surface of AISI M2 high speed steels were studied in this work. Boriding thermochemical treatment was carried out by dehydrated paste pack at three different temperatures 1173, 1223, and 1273 K and four exposure times 1, 3, 5, and 7 h, respectively. The presence of FeB and Fe{sub 2}B phases was identified by scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction method. In order to obtain the boron diffusion coefficients at the FeB/Fe{sub 2}B boride coatings, a mathematical model based on the mass balance at the growing interfaces was proposed under certain assumptions. Likewise the parabolic growth constants and the boride incubation time were established as a function of the parameters η (T) and ε (T). The activation energy values estimated for the FeB and Fe{sub 2}B layers were 233.42 and 211.89 kJ mol{sup −1} respectively. A good agreement was obtained between the simulated values of boride layer thicknesses and the experimental results. Finally, empirical relationships of boride coating thickness as a function of boriding temperature and time are presented. - Highlights: • Formed boride coatings at the surface of AISI M2 high speed steels by new process dehydrated paste pack boriding. • The model was based on the mass balance equation at the FeB/Fe{sub 2}B and Fe{sub 2}B/Fe interfaces by considering the boride incubation time. • A good agreement was obtained between the simulated values of boride layers coatings and the experimental results.

From atoms to layers: in situ gold cluster growth kinetics during sputter deposition

Science.gov (United States)

Schwartzkopf, Matthias; Buffet, Adeline; Körstgens, Volker; Metwalli, Ezzeldin; Schlage, Kai; Benecke, Gunthard; Perlich, Jan; Rawolle, Monika; Rothkirch, André; Heidmann, Berit; Herzog, Gerd; Müller-Buschbaum, Peter; Röhlsberger, Ralf; Gehrke, Rainer; Stribeck, Norbert; Roth, Stephan V.

2013-05-01

The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction of morphological real space parameters, such as cluster size and shape, correlation distance, layer porosity and surface coverage, directly from reciprocal space scattering data. This approach enables a large variety of future investigations of the influence of different process parameters on the thin metal film morphology. Furthermore, our study allows for deducing the wetting behavior of gold cluster films on solid substrates and provides a better understanding of the growth kinetics in general, which is essential for optimization of manufacturing parameters, saving energy and resources.The adjustment of size-dependent catalytic, electrical and optical properties of gold cluster assemblies is a very significant issue in modern applied nanotechnology. We present a real-time investigation of the growth kinetics of gold nanostructures from small nuclei to a complete gold layer during magnetron sputter deposition with high time resolution by means of in situ microbeam grazing incidence small-angle X-ray scattering (μGISAXS). We specify the four-stage growth including their thresholds with sub-monolayer resolution and identify phase transitions monitored in Yoneda intensity as a material-specific characteristic. An innovative and flexible geometrical model enables the extraction

Adsorption/desorption kinetics of Na atoms on reconstructed Si (111)-7 x 7 surface

International Nuclear Information System (INIS)

Chauhan, Amit Kumar Singh; Govind; Shivaprasad, S.M.

2010-01-01

Self-assembled nanostructures on a periodic template are fundamentally and technologically important as they put forward the possibility to fabricate and pattern micro/nano-electronics for sensors, ultra high-density memories and nanocatalysts. Alkali-metal (AM) nanostructure grown on a semiconductor surface has received considerable attention because of their simple hydrogen like electronic structure. However, little efforts have been made to understand the fundamental aspects of the growth mechanism of self-assembled nanostructures of AM on semiconductor surfaces. In this paper, we report organized investigation of kinetically controlled room-temperature (RT) adsorption/desorption of sodium (Na) metal atoms on clean reconstructed Si (111)-7 x 7 surface, by X-ray photoelectron spectroscopy (XPS). The RT uptake curve shows a layer-by-layer growth (Frank-vander Merve growth) mode of Na on Si (111)-7 x 7 surfaces and a shift is observed in the binding energy position of Na (1s) spectra. The thermal stability of the Na/Si (111) system was inspected by annealing the system to higher substrate temperatures. Within a temperature range from RT to 350 o C, the temperature induced mobility to the excess Na atoms sitting on top of the bilayer, allowing to arrange themselves. Na atoms desorbed over a wide temperature range of 370 o C, before depleting the Si (111) surface at temperature 720 o C. The acquired valence-band (VB) spectra during Na growth revealed the development of new electronic-states near the Fermi level and desorption leads the termination of these. For Na adsorption up to 2 monolayers, decrease in work function (-1.35 eV) was observed, whereas work function of the system monotonically increases with Na desorption from the Si surface as observed by other studies also. This kinetic and thermodynamic study of Na adsorbed Si (111)-7 x 7 system can be utilized in fabrication of sensors used in night vision devices.

Mg doping and its effect on the semipolar GaN(1122) growth kinetics

International Nuclear Information System (INIS)

Lahourcade, L.; Wirthmueller, A.; Monroy, E.; Pernot, J.; Chauvat, M. P.; Ruterana, P.; Laufer, A.; Eickhoff, M.

2009-01-01

We report the effect of Mg doping on the growth kinetics of semipolar GaN(1122) synthesized by plasma-assisted molecular-beam epitaxy. Mg tends to segregate on the surface, inhibiting the formation of the self-regulated Ga film which is used as a surfactant for the growth of undoped and Si-doped GaN(1122). We observe an enhancement of Mg incorporation in GaN(1122) compared to GaN(0001). Typical structural defects or polarity inversion domains found in Mg-doped GaN(0001) were not observed for the semipolar films investigated in the present study.

Kinetic study of nucleation and crystal growth during oxalic precipitation in the nuclear industry

International Nuclear Information System (INIS)

Andrieu, Murielle

1999-01-01

In spite of an extensive use in chemical industry, most of precipitation processes are based on global and empirical knowledge. However, in the recent years, fundamental and phenomenological theories have been developed and they can be used to better understand the mechanisms of precipitation of plutonium IV oxalate, which is a significant stage of the irradiated fuel reprocessing. For this reason, appropriate methods were developed to study nucleation and crystal growth kinetics in a nuclear environment under a wide range of operating conditions. Each phenomena was studied individually in order to reduce the free parameters of the System. This study bears on the oxalates of plutonium and elements which simulate plutonium behaviour during the precipitation, neodymium III and uranium IV. A compact apparatus of a specific construction was used for nucleation measurements in accordance with the Nielsen's method. The state of the mixing was characterised at the reactor scale (macro-mixing) and at molecular scale (micro-mixing). The experimental results for the studied oxalates are in good agreement with the Volmer and Weber's theory. We propose primary nucleation kinetic laws over a wide range of operating conditions (temperature, non-stoichiometric conditions, acidity...). An original method, using a high seed charge, was developed for the determination of crystal growth kinetics, in a batch crystallizer. The crystal growth rate is first order with respect to the supersaturation and the kinetic constant follows an Arrhenius type relation with activation energies of 14, 29 and 36 kJ.mol -1 for respectively neodymium III, uranium IV and plutonium IV oxalates. The overall growth process is surface integration controlled, with a screw dislocation mechanism. [fr

Real-time imaging of vertically aligned carbon nanotube array growth kinetics

International Nuclear Information System (INIS)

Puretzky, A A; Eres, G; Rouleau, C M; Ivanov, I N; Geohegan, D B

2008-01-01

In situ time-lapse photography and laser irradiation are applied to understand unusual coordinated growth kinetics of vertically aligned carbon nanotube arrays including pauses in growth, retraction, and local equilibration in length. A model is presented which explains the measured kinetics and determines the conditions for diffusion-limited growth. Laser irradiation of the growing nanotube arrays is first used to prove that the nanotubes grow from catalyst particles at their bases, and then increase their growth rate and terminal lengths

The effect of cation:anion ratio in solution on the mechanism of barite growth at constant supersaturation: Role of the desolvation process on the growth kinetics

Science.gov (United States)

Kowacz, M.; Putnis, C. V.; Putnis, A.

2007-11-01

The mechanism of barite growth has been investigated in a fluid cell of an Atomic Force Microscope by passing solutions of constant supersaturation ( Ω) but variable ion activity ratio ( r=a/a) over a barite substrate.The observed dependence of step-spreading velocity on solution stoichiometry can be explained by considering non-equivalent attachment frequency factors for the cation and anion. We show that the potential for two-dimensional nucleation changes under a constant thermodynamic driving force due to the kinetics of barium integration into the surface, and that the growth mode changes from preexisting step advancement to island spreading as the cation/anion activity ratio increases. Scanning electron microscopy studies of crystals grown in bulk solutions support our findings that matching the ion ratio in the fluid to that of the crystal lattice does not result in maximum growth and nucleation rates. Significantly more rapid rates correspond to solution stoichiometries where [Ba 2+] is in excess with respect to [ SO42-]. Experiments performed in dilute aqueous solutions of methanol show that even 0.02 molar fraction of organic cosolvent in the growth solution significantly accelerates step growth velocity and nucleation rates (while keeping Ω the same as in the reference solution in water). Our observations suggest that the effect of methanol on barite growth results first of all from reduction of the barrier that prevents the Ba 2+ from reaching the surface and corroborate the hypothesis that desolvation of the cation and of the surface is the rate limiting kinetic process for two-dimensional nucleation and for crystal growth.

Kinetic-energy functionals studied by surface calculations

DEFF Research Database (Denmark)

Vitos, Levente; Skriver, Hans Lomholt; Kollár, J.

1998-01-01

The self-consistent jellium model of metal surfaces is used to study the accuracy of a number of semilocal kinetic-energy functionals for independent particles. It is shown that the poor accuracy exhibited by the gradient expansion approximation and most of the semiempirical functionals in the lo...... density, high gradient limit may be subtantially improved by including locally a von Weizsacker term. Based on this, we propose a simple one-parameter Pade's approximation, which reproduces the exact Kohn-Sham surface kinetic energy over the entire range of metallic densities....

Growth kinetics in multicomponent fluids

International Nuclear Information System (INIS)

Chen, S.; Lookman, T.

1995-01-01

The hydrodynamic effects on the late-stage kinetics in spinodal decomposition of multicomponent fluids are examined using a lattice Boltzmann scheme with stochastic fluctuations in the fluid and at the interface. In two dimensions, the three- and four-component immiscible fluid mixture (with a 1024 2 lattice) behaves like an off-critical binary fluid with an estimated domain growth of t 0.4 +/= 0.03 rather than t 1/3 as previously estimated, showing the significant influence of hydrodynamics. In three dimensions (with a 256 3 lattice), we estimate the growth as t 0.96 +/= 0.05 for both critical and off-critical quenches, in agreement with phenomenological theory

Treatment of polymer surfaces in plasma Part I. Kinetic model

International Nuclear Information System (INIS)

Tabaliov, N A; Svirachev, D M

2006-01-01

The surface tension of the polymer materials depends on functional groups over its surface. As a result from the plasma treatment the kind and concentration of the functional groups can be changed. In the present work, the possible kinetic reactions are defined. They describe the interaction between the plasma and the polymer surface of polyethylene terephthalate (PET). Basing on these reactions, the systems of differential kinetic equations are suggested. The solutions are obtained analytically for the system kinetic equations at defined circumstances

Grain growth kinetics for B2O3-doped ZnO ceramics

Directory of Open Access Journals (Sweden)

Yuksel Berat

2015-06-01

Full Text Available Grain growth kinetics in 0.1 to 2 mol % B2O3-added ZnO ceramics was studied by using a simplified phenomenological grain growth kinetics equation Gn = K0 · t · exp(-Q/RT together with the physical properties of sintered samples. The samples, prepared by conventional ceramics processing techniques, were sintered at temperatures between 1050 to 1250 °C for 1, 2, 3, 5 and 10 hours in air. The kinetic grain growth exponent value (n and the activation energy for the grain growth of the 0.1 mol % B2O3-doped ZnO ceramics were found to be 2.8 and 332 kJ/mol, respectively. By increasing B2O3 content to 1 mol %, the grain growth exponent value (n and the activation energy decreased to 2 and 238 kJ/mol, respectively. The XRD study revealed the presence of a second phase, Zn3B2O6 formed when the B2O3 content was > 1 mol %. The formation of Zn3B2O6 phase gave rise to an increase of the grain growth kinetic exponent and the grain growth activation energy. The kinetic grain growth exponent value (n and the activation energy for the grain growth of the 2 mol % B2O3-doped ZnO ceramics were found to be 3 and 307 kJ/mol, respectively. This can be attributed to the second particle drag (pinning mechanism in the liquid phase sintering.

Kinetic models of cell growth, substrate utilization and bio ...

African Journals Online (AJOL)

Bio-decolorization kinetic studies of distillery effluent in a batch culture were conducted using Aspergillus fumigatus. A simple model was proposed using the Logistic Equation for the growth, Leudeking-Piret kinetics for bio-decolorization, and also for substrate utilization. The proposed models appeared to provide a suitable ...

Linking genes to microbial growth kinetics: an integrated biochemical systems engineering approach

NARCIS (Netherlands)

Koutinas, M.; Kiparissides, A.; Silva-Rocha, R.; Lam, M.C.; Martins Dos Santos, V.A.P.; Lorenzo, de V.; Pistikopoulos, E.N.; Mantalaris, A.

2011-01-01

The majority of models describing the kinetic properties of a microorganism for a given substrate are unstructured and empirical. They are formulated in this manner so that the complex mechanism of cell growth is simplified. Herein, a novel approach for modelling microbial growth kinetics is

Morphology and Kinetics of Growth of CaCO3 Precipitates Formed in Saline Water at 30°C

Science.gov (United States)

Sui, Xin; Wang, Baohui; Wu, Haiming

2018-02-01

The crystallization kinetics and morphology of CaCO3 crystals precipitated from the high salinity oilfield water were studied. The crystallization kinetics measurements show that nucleation and nuclei growth obey the first order reaction kinetics. The induction period of precipitation is extended in the high salinity solutions. Morphological studies show that impurity ions remain mostly in the solution phase instead of filling the CaCO3 crystal lattice. The morphology of CaCO3 precipitates can be changed from a smooth surface (calcite) to rough spheres (vaterite), and spindle rod bundles, or spherical, ellipsoid, flowers, plates and other shapes (aragonite).

Calcite growth kinetics: Modeling the effect of solution stoichiometry

NARCIS (Netherlands)

Wolthers, M.; Nehrke, G.; Gustafsson, J.P.; Van Cappellen, P.

2012-01-01

Until recently the influence of solution stoichiometry on calcite crystal growth kinetics has attracted little attention, despite the fact that in most aqueous environments calcite precipitates from non-stoichiometric solution. In order to account for the dependence of the calcite crystal growth

A kinetic Monte Carlo simulation method of van der Waals epitaxy for atomistic nucleation-growth processes of transition metal dichalcogenides.

Science.gov (United States)

Nie, Yifan; Liang, Chaoping; Cha, Pil-Ryung; Colombo, Luigi; Wallace, Robert M; Cho, Kyeongjae

2017-06-07

Controlled growth of crystalline solids is critical for device applications, and atomistic modeling methods have been developed for bulk crystalline solids. Kinetic Monte Carlo (KMC) simulation method provides detailed atomic scale processes during a solid growth over realistic time scales, but its application to the growth modeling of van der Waals (vdW) heterostructures has not yet been developed. Specifically, the growth of single-layered transition metal dichalcogenides (TMDs) is currently facing tremendous challenges, and a detailed understanding based on KMC simulations would provide critical guidance to enable controlled growth of vdW heterostructures. In this work, a KMC simulation method is developed for the growth modeling on the vdW epitaxy of TMDs. The KMC method has introduced full material parameters for TMDs in bottom-up synthesis: metal and chalcogen adsorption/desorption/diffusion on substrate and grown TMD surface, TMD stacking sequence, chalcogen/metal ratio, flake edge diffusion and vacancy diffusion. The KMC processes result in multiple kinetic behaviors associated with various growth behaviors observed in experiments. Different phenomena observed during vdW epitaxy process are analysed in terms of complex competitions among multiple kinetic processes. The KMC method is used in the investigation and prediction of growth mechanisms, which provide qualitative suggestions to guide experimental study.

Modified energetics and growth kinetics on H-terminated GaAs (110)

International Nuclear Information System (INIS)

Galiana, B.; Benedicto, M.; Díez-Merino, L.; Tejedor, P.; Lorbek, S.; Hlawacek, G.; Teichert, C.

2013-01-01

Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As 4 , has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å 2 measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As 4 molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed

Modified energetics and growth kinetics on H-terminated GaAs (110)

Energy Technology Data Exchange (ETDEWEB)

Galiana, B. [Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain); Departamento de Física, Universidad Carlos III de Madrid, Avenida de la Universidad 30, 28911 Madrid (Spain); Benedicto, M.; Díez-Merino, L.; Tejedor, P. [Instituto de Ciencia de Materiales de Madrid, CSIC, Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain); Lorbek, S.; Hlawacek, G.; Teichert, C. [Institut für Physik, Montanuniversität Leoben, Franz Josef St., 18A-8700 Leoben (Austria)

2013-10-28

Atomic hydrogen modification of the surface energy of GaAs (110) epilayers, grown at high temperatures from molecular beams of Ga and As{sub 4}, has been investigated by friction force microscopy (FFM). The reduction of the friction force observed with longer exposures to the H beam has been correlated with the lowering of the surface energy originated by the progressive de-relaxation of the GaAs (110) surface occurring upon H chemisorption. Our results indicate that the H-terminated GaAs (110) epilayers are more stable than the As-stabilized ones, with the minimum surface energy value of 31 meV/Å{sup 2} measured for the fully hydrogenated surface. A significant reduction of the Ga diffusion length on the H-terminated surface irrespective of H coverage has been calculated from the FFM data, consistent with the layer-by-layer growth mode and the greater As incorporation coefficient determined from real-time reflection high-energy electron diffraction studies. Arsenic incorporation through direct dissociative chemisorption of single As{sub 4} molecules mediated by H on the GaAs (110) surface has been proposed as the most likely explanation for the changes in surface kinetics observed.

Growth kinetics and morphology of plasma electrolytic oxidation coating on aluminum

International Nuclear Information System (INIS)

Erfanifar, Eliyas; Aliofkhazraei, Mahmood; Fakhr Nabavi, Houman; Sharifi, Hossein; Rouhaghdam, Alireza Sabour

2017-01-01

Plasma electrolytic oxidation (PEO) was carried out on AA1190 aluminum alloy in mixed silicate-phosphate-based electrolyte in order to fabricate ceramic coating under constant current density. The variations of PEO coating duration with kinetics, surface roughness, amount and size of discharge channels were studied with respect to PEO processing time. The growth mechanism of the ceramic coating was described considering a variation of volume and diameters of discharge channels and pancakes during the PEO. Scanning electron microscope (SEM), atomic force microscope (AFM), and roughness tester were used to study the plasma discharge channels of the PEO coatings. In addition, the effect of alumina nanoparticles in the electrolyte as the suspension was studied on the geometric parameters of discharge channels. It seems that the nanoparticles are adsorbed to the locations of erupted molten oxide, where the dielectric breakdown occurs. Nanoparticles were embedded in the dense oxide layer and were adsorbed at the walls of voids and coatings surface. As a result, they caused significant changes in roughness parameters of the samples containing nanoparticles compared to those without nanoparticles. The obtained results showed that growth kinetics followed a linear trend with respect to PEO coating duration. It was also observed that in the absence of alumina nanoparticles, the average volume of the pancakes is 150% greater than the ones fabricated in the suspension of nanoparticles. Besides, increasing the PEO coating duration leads to adsorbing more nanoparticles on the coating surface, filling the voids, and flattening the surface, and alterations in R v , R sk , and R lo parameters. Correlation between the diameter of discharge channel (d c ) and thickness of the pancake (h) also showed a linear relation. - Highlights: • Precise calculation of thickness of pancake with AFM. • Study of different roughness parameters for PEO coating. • Calculation the amount of

Growth kinetics and morphology of plasma electrolytic oxidation coating on aluminum

Energy Technology Data Exchange (ETDEWEB)

Erfanifar, Eliyas; Aliofkhazraei, Mahmood, E-mail: maliofkh@gmail.com; Fakhr Nabavi, Houman; Sharifi, Hossein; Rouhaghdam, Alireza Sabour

2017-01-01

Plasma electrolytic oxidation (PEO) was carried out on AA1190 aluminum alloy in mixed silicate-phosphate-based electrolyte in order to fabricate ceramic coating under constant current density. The variations of PEO coating duration with kinetics, surface roughness, amount and size of discharge channels were studied with respect to PEO processing time. The growth mechanism of the ceramic coating was described considering a variation of volume and diameters of discharge channels and pancakes during the PEO. Scanning electron microscope (SEM), atomic force microscope (AFM), and roughness tester were used to study the plasma discharge channels of the PEO coatings. In addition, the effect of alumina nanoparticles in the electrolyte as the suspension was studied on the geometric parameters of discharge channels. It seems that the nanoparticles are adsorbed to the locations of erupted molten oxide, where the dielectric breakdown occurs. Nanoparticles were embedded in the dense oxide layer and were adsorbed at the walls of voids and coatings surface. As a result, they caused significant changes in roughness parameters of the samples containing nanoparticles compared to those without nanoparticles. The obtained results showed that growth kinetics followed a linear trend with respect to PEO coating duration. It was also observed that in the absence of alumina nanoparticles, the average volume of the pancakes is 150% greater than the ones fabricated in the suspension of nanoparticles. Besides, increasing the PEO coating duration leads to adsorbing more nanoparticles on the coating surface, filling the voids, and flattening the surface, and alterations in R{sub v}, R{sub sk}, and R{sub lo} parameters. Correlation between the diameter of discharge channel (d{sub c}) and thickness of the pancake (h) also showed a linear relation. - Highlights: • Precise calculation of thickness of pancake with AFM. • Study of different roughness parameters for PEO coating. • Calculation

Kinetics and mechanisms of the oxide film growth on the surface of α-Fe in transitional domains

International Nuclear Information System (INIS)

Mukhambetov, D.G.; Berber, N.N.; Kargin, D.B.; Chalaya, O.V.

2003-01-01

The object of this work was to study the kinetics of the α-Fe surface oxidation with prevailing cubic texture at temperatures of 450-500 deg. C. The basic conformity to natural laws and mechanisms of the two-phase thin oxide films grows are determined. (author)

Study of growth kinetic and modeling of ethanol production by ...

African Journals Online (AJOL)

... coefficient (0.96299). Based on Leudking-Piret model, it could be concluded that ethanol batch fermentation is a non-growth associated process. Key words: Kinetic parameters, simulation, cell growth, ethanol, Saccharomyces cerevisiae.

Effect of diffusion from a lateral surface on the rate of GaN nanowire growth

International Nuclear Information System (INIS)

Sibirev, N. V.; Tchernycheva, M.; Cirlin, G. E.; Patriarche, G.; Harmand, J. C.; Dubrovskii, V. G.

2012-01-01

The kinetics of the growth of GaN crystalline nanowires on a Si (111) surface with no catalyst is studied experimentally and theoretically. Noncatalytic GaN nanowires were grown by molecular-beam epitaxy with AlN inserts, which makes it possible to determine the rate of the vertical growth of nanowires. A model for the formation of GaN nanowires is developed, and an expression for their rate of growth is derived. It is shown that, in the general case, the dependence of the rate of growth on the nanowire diameter has a minimum. The diameter corresponding to the experimentally observed minimum of the rate of growth steadily increases with increasing diffusion flux from the lateral surface.

Growth Kinetics of Rhodococcus Erythropolis IGTS8 on Thiophene and Dimethylsulphoxide

International Nuclear Information System (INIS)

El-Temtamy, S.A.; Farahat, L.A.; Al-Shatnawi, D.F.; AI-Sayed, S.

2004-01-01

Sulfur oxides emissions through fossil fuel combustion posse environmental problems because these oxides are major cause of acid rain, which dissolve buildings, kills forests and poisons lakes. That is why world environmental regulations are becoming harder with respect to sulfur content in fossil fuels. The demand for new low-cost desulfurization technologies has led to renewed interest in bio desulfurization. In this work the growth kinetics of Rhodococcus Erythopolis IGTS8 have been studied on two model sulfur compounds that are found among other sulfur compounds in petroleum fractions. These are namely thiophene and dimethyl sulfoxide, DEMSO. Batch reactor and different substrate concentrations ranging between 1 and 8 gl -1 were used to study the growth kinetics. Growth on thiophene was shown to follow Monode kinetics with μ m ax =0.064 h -1 and K s = 2.8 gl -1 , on the other hand, growth on DEMSO was found to be substrate inhibited

Growth kinetics of four human breast carcinomas grown in nude mice

DEFF Research Database (Denmark)

Spang-Thomsen, M; Rygaard, K; Hansen, L

1989-01-01

with cell generation times of 42 to 60 hours. The three receptor-positive tumors had slower growth rate, larger tumor volume doubling time, and smaller growth fraction and labelling index than the receptor-negative tumor. However, no single proliferation parameter was sufficient to characterize the growth......The immune-deficient nude mouse with human tumor xenografts is an appropriate model system for performing detailed growth kinetic examinations. In the present study one estrogen and progesterone receptor-negative (T60) and three receptor-positive (Br-10, MCF-7, T61) human breast cancer xenografts...... in nude mice were investigated. The proliferative tumor characteristics were examined by growth curves, thymidine labelling technique, and flow cytometric DNA analysis performed on fine-needle aspirations. The results showed that the tumors had growth kinetics comparable to other human tumor types...

Growth kinetics and growth mechanism of ultrahigh mass density carbon nanotube forests on conductive Ti/Cu supports.

Science.gov (United States)

Sugime, Hisashi; Esconjauregui, Santiago; D'Arsié, Lorenzo; Yang, Junwei; Makaryan, Taron; Robertson, John

2014-09-10

We evaluate the growth kinetics and growth mechanism of ultrahigh mass density carbon nanotube forests. They are synthesized by chemical vapor deposition at 450 °C using a conductive Ti/Cu support and Co-Mo catalyst system. We find that Mo stabilizes Co particles preventing lift off during the initial growth stage, thus promoting the growth of ultrahigh mass density nanotube forests by the base growth mechanism. The morphology of the forest gradually changes with growth time, mostly because of a structural change of the catalyst particles. After 100 min growth, toward the bottom of the forest, the area density decreases from ∼ 3-6 × 10(11) cm(-2) to ∼ 5 × 10(10) cm(-2) and the mass density decreases from 1.6 to 0.38 g cm(-3). We also observe part of catalyst particles detached and embedded within nanotubes. The progressive detachment of catalyst particles results in the depletion of the catalyst metals on the substrate surfaces. This is one of the crucial reasons for growth termination and may apply to other catalyst systems where the same features are observed. Using the packed forest morphology, we demonstrate patterned forest growth with a pitch of ∼ 300 nm and a line width of ∼ 150 nm. This is one of the smallest patterning of the carbon nanotube forests to date.

Growth kinetics of borided layers: Artificial neural network and least square approaches

Science.gov (United States)

Campos, I.; Islas, M.; Ramírez, G.; VillaVelázquez, C.; Mota, C.

2007-05-01

The present study evaluates the growth kinetics of the boride layer Fe 2B in AISI 1045 steel, by means of neural networks and the least square techniques. The Fe 2B phase was formed at the material surface using the paste boriding process. The surface boron potential was modified considering different boron paste thicknesses, with exposure times of 2, 4 and 6 h, and treatment temperatures of 1193, 1223 and 1273 K. The neural network and the least square models were set by the layer thickness of Fe 2B phase, and assuming that the growth of the boride layer follows a parabolic law. The reliability of the techniques used is compared with a set of experiments at a temperature of 1223 K with 5 h of treatment time and boron potentials of 2, 3, 4 and 5 mm. The results of the Fe 2B layer thicknesses show a mean error of 5.31% for the neural network and 3.42% for the least square method.

Surface Area, and Oxidation Effects on Nitridation Kinetics of Silicon Powder Compacts

Science.gov (United States)

Bhatt, R. T.; Palczer, A. R.

1998-01-01

Commercially available silicon powders were wet-attrition-milled from 2 to 48 hr to achieve surface areas (SA's) ranging from 1.3 to 70 sq m/g. The surface area effects on the nitridation kinetics of silicon powder compacts were determined at 1250 or 1350 C for 4 hr. In addition, the influence of nitridation environment, and preoxidation on nitridation kinetics of a silicon powder of high surface area (approximately equals 63 sq m/g) was investigated. As the surface area increased, so did the percentage nitridation after 4 hr in N2 at 1250 or 1350 C. Silicon powders of high surface area (greater than 40 sq m/g) can be nitrided to greater than 70% at 1250 C in 4 hr. The nitridation kinetics of the high-surface-area powder compacts were significantly delayed by preoxidation treatment. Conversely, the nitridation environment had no significant influence on the nitridation kinetics of the same powder. Impurities present in the starting powder, and those accumulated during attrition milling, appeared to react with the silica layer on the surface of silicon particles to form a molten silicate layer, which provided a path for rapid diffusion of nitrogen and enhanced the nitridation kinetics of high surface area silicon powder.

Surface kinetic roughening caused by dental erosion: An atomic force microscopy study

Science.gov (United States)

Quartarone, Eliana; Mustarelli, Piercarlo; Poggio, Claudio; Lombardini, Marco

2008-05-01

Surface kinetic roughening takes place both in case of growth and erosion processes. Teeth surfaces are eroded by contact with acid drinks, such as those used to supplement mineral salts during sporting activities. Calcium-phosphate based (CPP-ACP) pastes are known to reduce the erosion process, and to favour the enamel remineralization. In this study we used atomic force microscopy (AFM) to investigate the surface roughening during dental erosion, and the mechanisms at the basis of the protection role exerted by a commercial CPP-ACP paste. We found a statistically significant difference (p<0.01) in the roughness of surfaces exposed and not exposed to the acid solutions. The treatment with the CPP-ACP paste determined a statistically significant reduction of the roughness values. By interpreting the AFM results in terms of fractal scaling concepts and continuum stochastic equations, we showed that the protection mechanism of the paste depends on the chemical properties of the acid solution.

Hydrocarbon fermentation: kinetics of microbial cell growth

Energy Technology Data Exchange (ETDEWEB)

Goma, G [Institut National des Sciences Appliquees, Toulouse; Ribot, D

1978-11-01

Modeling of microbial growth using nonmiscible substrate is studied when kinetics of substrate dissolution is rate limiting. When the substrate concentration is low, the growth rate is described by an analytical relation that can be identified as a Contois relationship. If the substrate concentration is greater than a critical value S/sub crit/, the potentially useful hydrocarbon S* concentration is described by S* = S/sub crit//(1 + S/sub crit//S). A relationship was found between S/sub crit/ and the biomass concentration X. When X increased, S/sub crit/ decreased. The cell growth rate is related to a relation ..mu.. = ..mu../sub m/(A(X/S/sub crit/)(1 + S/sub crit//S) + 1)/sup -1/. This model describes the evolution of the growth rate when exponential or linear growth occurs, which is related to physico-chemical properties and hydrodynamic fermentation conditions. Experimental data to support the model are presented.

Modified Gompertz equation for electrotherapy murine tumor growth kinetics: predictions and new hypotheses

International Nuclear Information System (INIS)

Cabrales, Luis E Bergues; Mateus, Miguel A O'Farril; Brooks, Soraida C Acosta; Palencia, Fabiola Suárez; Zamora, Lisset Ortiz; Quevedo, María C Céspedes; Seringe, Sarah Edward; Cuitié, Vladimir Crombet; Cabrales, Idelisa Bergues; González, Gustavo Sierra; Nava, Juan J Godina; Aguilera, Andrés Ramírez; Joa, Javier A González; Ciria, Héctor M Camué; González, Maraelys Morales; Salas, Miriam Fariñas; Jarque, Manuel Verdecia; González, Tamara Rubio

2010-01-01

Electrotherapy effectiveness at different doses has been demonstrated in preclinical and clinical studies; however, several aspects that occur in the tumor growth kinetics before and after treatment have not yet been revealed. Mathematical modeling is a useful instrument that can reveal some of these aspects. The aim of this paper is to describe the complete growth kinetics of unperturbed and perturbed tumors through use of the modified Gompertz equation in order to generate useful insight into the mechanisms that underpin this devastating disease. The complete tumor growth kinetics for control and treated groups are obtained by interpolation and extrapolation methods with different time steps, using experimental data of fibrosarcoma Sa-37. In the modified Gompertz equation, a delay time is introduced to describe the tumor's natural history before treatment. Different graphical strategies are used in order to reveal new information in the complete kinetics of this tumor type. The first stage of complete tumor growth kinetics is highly non linear. The model, at this stage, shows different aspects that agree with those reported theoretically and experimentally. Tumor reversibility and the proportionality between regions before and after electrotherapy are demonstrated. In tumors that reach partial remission, two antagonistic post-treatment processes are induced, whereas in complete remission, two unknown antitumor mechanisms are induced. The modified Gompertz equation is likely to lead to insights within cancer research. Such insights hold promise for increasing our understanding of tumors as self-organizing systems and, the possible existence of phase transitions in tumor growth kinetics, which, in turn, may have significant impacts both on cancer research and on clinical practice

Growth Kinetics and Modeling of Direct Oxynitride Growth with NO-O2 Gas Mixtures

Energy Technology Data Exchange (ETDEWEB)

Everist, Sarah; Nelson, Jerry; Sharangpani, Rahul; Smith, Paul Martin; Tay, Sing-Pin; Thakur, Randhir

1999-05-03

We have modeled growth kinetics of oxynitrides grown in NO-O₂ gas mixtures from first principles using modified Deal-Grove equations. Retardation of oxygen diffusion through the nitrided dielectric was assumed to be the dominant growth-limiting step. The model was validated against experimentally obtained curves with good agreement. Excellent uniformity, which exceeded expected walues, was observed.

The effect of substrate orientation on the kinetics and thermodynamics of initial oxide-film growth on metals

Energy Technology Data Exchange (ETDEWEB)

Reichel, Friederike

2007-11-19

This thesis addresses the effect of the parent metal-substrate orientation on the thermodynamics and kinetics of ultra-thin oxide-film growth on bare metals upon their exposure to oxygen gas at low temperatures (up to 650 K). A model description has been developed to predict the thermodynamically stable microstructure of a thin oxide film grown on its bare metal substrate as function of the oxidation conditions and the substrate orientation. For Mg and Ni, the critical oxide-film thickness is less than 1 oxide monolayer and therefore the initial development of an amorphous oxide phase on these metal substrates is unlikely. Finally, for Cu and densely packed Cr and Fe metal surfaces, oxide overgrowth is predicted to proceed by the direct formation and growth of a crystalline oxide phase. Further, polished Al single-crystals with {l_brace}111{r_brace}, {l_brace}100{r_brace} and {l_brace}110{r_brace} surface orientations were introduced in an ultra-high vacuum system for specimen processing and analysis. After surface cleaning and annealing, the bare Al substrates have been oxidized by exposure to pure oxygen gas. During the oxidation, the oxide-film growth kinetics has been established by real-time in-situ spectroscopic ellipsometry. After the oxidation, the oxide-film microstructures were investigated by angle-resolved X-ray photoelectron spectroscopy and low energy electron diffraction. Finally, high-resolution transmission electron microscopic analysis was applied to study the microstructure and morphology of the grown oxide films on an atomic scale. (orig.)

Tantalum high-temperature oxidation kinetics

International Nuclear Information System (INIS)

Grigor'ev, Yu.M.; Sarkisyan, A.A.; Merzhanov, A.G.

1981-01-01

Kinetics of heat release and scale growth during tantalum oxidation within 650-1300 deg C temperature range in oxygen-containing media is investigated. Kinetic equations and temperature and pressure dependences of constants are ound Applicability of the kinetic Lorie mechanism for the description of the tantalum oxidation kinetics applicably to rapid-passing processes is shown. It is stated that the process rate (reaction ability) is determined by adsorption desorption factors on the external surface of the ''protective'' oxide for the ''linear'' oxidation stage [ru

Effect of the Surface Layer of Iron Casting on the Growth of Protective Coating During Hot-Dip Galvanizing

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Kopyciński D.

2016-03-01

Full Text Available The paper presents the results of investigations of the growth of protective coating on the surface of ductile iron casting during the hot-dip galvanizing treatment. Ductile iron of the EN-GJS-600-3 grade was melted and two moulds made by different technologies were poured to obtain castings with different surface roughness parameters. After the determination of surface roughness, the hot-dip galvanizing treatment was carried out. Based on the results of investigations, the effect of casting surface roughness on the kinetics of the zinc coating growth was evaluated. It was found that surface roughness exerts an important effect on the thickness of produced zinc coating.

Effects of reaction-kinetic parameters on modeling reaction pathways in GaN MOVPE growth

Science.gov (United States)

Zhang, Hong; Zuo, Ran; Zhang, Guoyi

2017-11-01

In the modeling of the reaction-transport process in GaN MOVPE growth, the selections of kinetic parameters (activation energy Ea and pre-exponential factor A) for gas reactions are quite uncertain, which cause uncertainties in both gas reaction path and growth rate. In this study, numerical modeling of the reaction-transport process for GaN MOVPE growth in a vertical rotating disk reactor is conducted with varying kinetic parameters for main reaction paths. By comparisons of the molar concentrations of major Ga-containing species and the growth rates, the effects of kinetic parameters on gas reaction paths are determined. The results show that, depending on the values of the kinetic parameters, the gas reaction path may be dominated either by adduct/amide formation path, or by TMG pyrolysis path, or by both. Although the reaction path varies with different kinetic parameters, the predicted growth rates change only slightly because the total transport rate of Ga-containing species to the substrate changes slightly with reaction paths. This explains why previous authors using different chemical models predicted growth rates close to the experiment values. By varying the pre-exponential factor for the amide trimerization, it is found that the more trimers are formed, the lower the growth rates are than the experimental value, which indicates that trimers are poor growth precursors, because of thermal diffusion effect caused by high temperature gradient. The effective order for the contribution of major species to growth rate is found as: pyrolysis species > amides > trimers. The study also shows that radical reactions have little effect on gas reaction path because of the generation and depletion of H radicals in the chain reactions when NH2 is considered as the end species.

Growth mechanism of graphene on platinum: Surface catalysis and carbon segregation

International Nuclear Information System (INIS)

Sun, Jie; Lindvall, Niclas; Yurgens, August; Nam, Youngwoo; Cole, Matthew T.; Teo, Kenneth B. K.; Woo Park, Yung

2014-01-01

A model of the graphene growth mechanism of chemical vapor deposition on platinum is proposed and verified by experiments. Surface catalysis and carbon segregation occur, respectively, at high and low temperatures in the process, representing the so-called balance and segregation regimes. Catalysis leads to self-limiting formation of large area monolayer graphene, whereas segregation results in multilayers, which evidently “grow from below.” By controlling kinetic factors, dominantly monolayer graphene whose high quality has been confirmed by quantum Hall measurement can be deposited on platinum with hydrogen-rich environment, quench cooling, tiny but continuous methane flow and about 1000 °C growth temperature

Growth kinetics of dislocation loops in irradiated ceramic materials

International Nuclear Information System (INIS)

Ryazanov, A.I.; Kinoshita, C.

2002-01-01

Ceramic materials are expected to be applied in the future fusion reactor as radio frequency (RF) windows, toroidal insulating breaks and diagnostic probes. The radiation resistance of ceramic materials, degradation of the electrical properties and radiation induced conductivity of these materials under neutron irradiation are determined by the kinetics of the accumulation of point defects in the matrix and point defect cluster formation (dislocation loops, voids, etc.). Under irradiation, due to the ionization process, excitation of electronic subsystem and covalent type of interaction between atoms the point defects in ceramic materials are characterized by the charge state (e.g. an F + center, an oxygen vacancy with a single trapped electron) and the effective charge. For the investigation of radiation resistance of ceramic materials for future fusion applications it is very important to understand the physical mechanisms of formation and growth of dislocation loops and voids under irradiation taking into account in this system the effective charge of point defects. In the present paper the physical mechanisms of dislocation loop growth in ceramic material are investigated. For this aim a theoretical model is suggested for the description of the kinetics of point defect accumulation in the matrix taking into account the charge state of the point defects and the effect of an electric field on diffusion migration process of charged point defects. A self-consistent system of kinetic equations describing the generation of electrical fields near dislocation loops and diffusion migration of charged point defects in elastic and electrical fields is formulated. The solution of the kinetic equations allows to find the growth rate of dislocation loops in ceramic materials under irradiation taking into account the charge state of the point defects and the effect of electric and elastic stress fields near dislocation loop on the diffusion processes

The kinetics of chirality assignment in catalytic single-walled carbon nanotube growth and the routes towards selective growth.

Science.gov (United States)

Xu, Ziwei; Qiu, Lu; Ding, Feng

2018-03-21

Depending on its specific structure, or so-called chirality, a single-walled carbon nanotube (SWCNT) can be either a conductor or a semiconductor. This feature ensures great potential for building ∼1 nm sized electronics if chirality-selected SWCNTs could be achieved. However, due to the limited understanding of the growth mechanism of SWCNTs, reliable methods for chirality-selected SWCNTs are still pending. Here we present a theoretical model on the chirality assignment and control of SWCNTs during the catalytic growth. This study reveals that the chirality of a SWCNT is determined by the kinetic incorporation of pentagons, especially the last (6 th ) one, during the nucleation stage. Our analysis showed that the chirality of a SWCNT is randomly assigned on a liquid or liquid-like catalyst surface, and two routes of synthesizing chirality-selected SWCNTs, which are verified by recent experimental achievements, are demonstrated. They are (i) by using high melting point crystalline catalysts, such as Ta, W, Re, Os, or their alloys, and (ii) by frequently changing the chirality of SWCNTs during their growth. This study paves the way for achieving chirality-selective SWCNT growth for high performance SWCNT based electronics.

Kinetic study and growth behavior of template-based electrodeposited platinum nanotubes controlled by overpotential

Energy Technology Data Exchange (ETDEWEB)

Yousefi, E. [Department of Materials Science and Engineering, Sharif University of Technology, Azadi Ave., P.O.Box 11155-9466, Tehran (Iran, Islamic Republic of); Dolati, A., E-mail: dolati@sharif.edu [Department of Materials Science and Engineering, Sharif University of Technology, Azadi Ave., P.O.Box 11155-9466, Tehran (Iran, Islamic Republic of); Imanieh, I. [Department of Materials Science and Engineering, Sharif University of Technology, Azadi Ave., P.O.Box 11155-9466, Tehran (Iran, Islamic Republic of); Yashiro, H.; Kure-Chu, S.-Z. [Department of Chemistry and Bioengineering, Faculty of Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate, 020-8551 (Japan)

2017-02-01

Platinum nanotubes (PtNTs) are fabricated by potentiostatic electrodeposition at various overpotentials (−200 up to −400 mV versus SCE) in polycarbonate templates (PCTs) with pore diameter of 200 nm in a solution containing 5 mM H{sub 2}PtCl{sub 6} and 0.1 M H{sub 2}SO{sub 4}. The synthesized PtNTs are characterized by field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The electrochemical growth mechanism within nanoscopic pores and the relationship between morphological variations and kinetic parameters are investigated for the first time. It is shown that more porous structure of nanotubes forms at high overpotentials possibly due to preferably nucleation. The kinetics of electrodeposition process is studied by electrochemical techniques such as voltammetry and chronoamperometry. The linear diffusion coefficient at the early stage of the deposition and the radial diffusion coefficients at steady state regime are calculated as D = 8.39 × 10{sup −5} and 2.33–13.26 × 10{sup −8} cm{sup 2}/s, respectively. The synthesized PtNT electrode is tested as electrocatalyst for hydrogen peroxide oxidation in phosphate buffer solution (PBS) and shows a sensitivity as high as 2.89 mA per 1 μM that is an indication to its enlarged electrochemical surface area. - Highlights: • PtNT is electrodeposited in a 3-aminopropyltrimethoxysilane-modified PCT. • The electrochemical growth mechanism within nanoscopic pores is discussed. • The kinetics of PtNT electrodeposition is studied based on models for UME arrays. • Relationship between morphological variations vs. kinetic parameters is studied.

Second Harmonic Correlation Spectroscopy: Theory and Principles for Determining Surface Binding Kinetics.

Science.gov (United States)

Sly, Krystal L; Conboy, John C

2017-06-01

A novel application of second harmonic correlation spectroscopy (SHCS) for the direct determination of molecular adsorption and desorption kinetics to a surface is discussed in detail. The surface-specific nature of second harmonic generation (SHG) provides an efficient means to determine the kinetic rates of adsorption and desorption of molecular species to an interface without interference from bulk diffusion, which is a significant limitation of fluorescence correlation spectroscopy (FCS). The underlying principles of SHCS for the determination of surface binding kinetics are presented, including the role of optical coherence and optical heterodyne mixing. These properties of SHCS are extremely advantageous and lead to an increase in the signal-to-noise (S/N) of the correlation data, increasing the sensitivity of the technique. The influence of experimental parameters, including the uniformity of the TEM00 laser beam, the overall photon flux, and collection time are also discussed, and are shown to significantly affect the S/N of the correlation data. Second harmonic correlation spectroscopy is a powerful, surface-specific, and label-free alternative to other correlation spectroscopic methods for examining surface binding kinetics.

Is cancer a pure growth curve or does it follow a kinetics of dynamical structural transformation?

Science.gov (United States)

González, Maraelys Morales; Joa, Javier Antonio González; Cabrales, Luis Enrique Bergues; Pupo, Ana Elisa Bergues; Schneider, Baruch; Kondakci, Suleyman; Ciria, Héctor Manuel Camué; Reyes, Juan Bory; Jarque, Manuel Verdecia; Mateus, Miguel Angel O'Farril; González, Tamara Rubio; Brooks, Soraida Candida Acosta; Cáceres, José Luis Hernández; González, Gustavo Victoriano Sierra

2017-03-07

Unperturbed tumor growth kinetics is one of the more studied cancer topics; however, it is poorly understood. Mathematical modeling is a useful tool to elucidate new mechanisms involved in tumor growth kinetics, which can be relevant to understand cancer genesis and select the most suitable treatment. The classical Kolmogorov-Johnson-Mehl-Avrami as well as the modified Kolmogorov-Johnson-Mehl-Avrami models to describe unperturbed fibrosarcoma Sa-37 tumor growth are used and compared with the Gompertz modified and Logistic models. Viable tumor cells (1×10 5 ) are inoculated to 28 BALB/c male mice. Modified Gompertz, Logistic, Kolmogorov-Johnson-Mehl-Avrami classical and modified Kolmogorov-Johnson-Mehl-Avrami models fit well to the experimental data and agree with one another. A jump in the time behaviors of the instantaneous slopes of classical and modified Kolmogorov-Johnson-Mehl-Avrami models and high values of these instantaneous slopes at very early stages of tumor growth kinetics are observed. The modified Kolmogorov-Johnson-Mehl-Avrami equation can be used to describe unperturbed fibrosarcoma Sa-37 tumor growth. It reveals that diffusion-controlled nucleation/growth and impingement mechanisms are involved in tumor growth kinetics. On the other hand, tumor development kinetics reveals dynamical structural transformations rather than a pure growth curve. Tumor fractal property prevails during entire TGK.

The role of surface oxides on hydrogen sorption kinetics in titanium thin films

Science.gov (United States)

Hadjixenophontos, Efi; Michalek, Lukas; Roussel, Manuel; Hirscher, Michael; Schmitz, Guido

2018-05-01

Titanium is presently discussed as a catalyst to accelerate the hydrogenation kinetics of hydrogen storage materials. It is however known that H absorption in Ti decisively depends on the surface conditions (presence or absence of the natural surface oxide). In this work, we use Ti thin films of controlled thickness (50-800 nm) as a convenient tool for quantifying the atomic transport. XRD and TEM investigations allow us to follow the hydrogenation progress inside the film. Hydrogenation of TiO2/Ti bi-layers is studied at 300 °C, for different durations (10 s to 600 min) and at varying pressures of pure H2 atmosphere. Under these conditions, the hydrogenation is found to be linear in time. By comparing films with and without TiO2, as well as by studying the pressure dependence of hydrogenation, it is demonstrated that hydrogen transport across the oxide represents the decisive kinetic barrier rather than the splitting of H2 molecules at the surface. Hydrogenation appears by a layer-like reaction initiated by heterogeneous nucleation at the backside interface to the substrate. The linear growth constant and the H diffusion coefficient inside the oxide are quantified, as well as a reliable lower bound to the hydrogen diffusion coefficient in Ti is derived. The pressure dependence of hydrogen absorption is quantitatively modelled.

Layer-by-Layer Method for the Synthesis and Growth of Surface Mounted Metal-Organic Frameworks (SURMOFs

Directory of Open Access Journals (Sweden)

Osama Shekhah

2010-02-01

Full Text Available A layer-by-layer method has been developed for the synthesis of metal-organic frameworks (MOFs and their deposition on functionalized organic surfaces. The approach is based on the sequential immersion of functionalized organic surfaces into solutions of the building blocks of the MOF, i.e., the organic ligand and the inorganic unit. The synthesis and growth of different types of MOFs on substrates with different functionalization, like COOH, OH and pyridine terminated surfaces, were studied and characterized with different surface characterization techniques. A controlled and highly oriented growth of very homogenous films was obtained using this method. The layer-by-layer method offered also the possibility to study the kinetics of film formation in more detail using surface plasmon resonance and quartz crystal microbalance. In addition, this method demonstrates the potential to synthesize new classes of MOFs not accessible by conventional methods. Finally, the controlled growth of MOF thin films is important for many applications like chemical sensors, membranes and related electrodes.

Neutralization kinetics of charged polymer surface

Energy Technology Data Exchange (ETDEWEB)

Mukherjee, S. [Surface Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India); Mukherjee, M. [Surface Physics Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064 (India)], E-mail: manabendra.mukherjee@saha.ac.in

2008-04-15

In case of photoemission spectroscopy of an insulating material the data obtained from the charged surface are normally distorted due to differential charging. Recently, we have developed a controlled surface neutralization technique to study the kinetics of the surface charging. Using this technique and the associated data analysis scheme with an effective charging model, quantitative information from the apparently distorted photoemission data from PTFE surfaces were extracted. The surface charging was controlled by tuning the electron flood current as well as the X-ray intensity. The effective model was found to describe the charging consistently for both the cases. It was shown that the non-linear neutralization response of differential charging around a critical neutralizing electron flux or a critical X-ray emission current was due to percolation of equipotential surface domains. The obtained value of the critical percolation exponent {gamma} close to unity indicates a percolation similar to that of avalanche breakdown or chain reaction.

Thermally controlled growth of surface nanostructures on ion-modified AIII-BV semiconductor crystals

Science.gov (United States)

Trynkiewicz, Elzbieta; Jany, Benedykt R.; Wrana, Dominik; Krok, Franciszek

2018-01-01

The primary motivation for our systematic study is to provide a comprehensive overview of the role of sample temperature on the pattern evolution of several AIII-BV semiconductor crystal (001) surfaces (i.e., InSb, InP, InAs, GaSb) in terms of their response to low-energy Ar+ ion irradiation conditions. The surface morphology and the chemical diversity of such ion-modified binary materials has been characterized by means of scanning electron microscopy (SEM). In general, all surface textures following ion irradiation exhibit transitional behavior from small islands, via vertically oriented 3D nanostructures, to smoothened surface when the sample temperature is increased. This result reinforces our conviction that the mass redistribution of adatoms along the surface plays a vital role during the formation and growth process of surface nanostructures. We would like to emphasize that this paper addresses in detail for the first time the topic of the growth kinetics of the nanostructures with regard to thermal surface diffusion, while simultaneously offering some possible approaches to supplementing previous studies and therein gaining a new insight into this complex issue. The experimental results are discussed with reference to models of the pillars growth, abutting on preferential sputtering, the self-sustained etch masking effect and the redeposition process recently proposed to elucidate the observed nanostructuring mechanism.

Effect of Temperature and pH on Formulating the Kinetic Growth Parameters and Lactic Acid Production of Lactobacillus bulgaricus

Directory of Open Access Journals (Sweden)

Marzieh Aghababaie

2014-09-01

Results: Second order model for Xmax, μmax, P and K was significant but product formation parameters were almost constant. The optimum values of temperature and pH for attaining maximum biomass, maximum specific growth rate, and maximum acid production were obtained at 44 °C and 5.7, respectively. Conclusions: The attained empirical mathematical correlations of RSM alongside the kinetic equations could be used to determine growth conditions under predefined temperature and pH in the fermentation process. Keywords: Lactobacillus bulgaricus, Richards model, Response surface methodology, Lactic acid production, Luedeking-Piret model

Surface kinetic temperature mapping using satellite spectral data in ...

African Journals Online (AJOL)

The result revealed that despite the limited topographic differences of the rift lakes and their proximity, the surface kinetic temperature difference is high, mainly due to groundwater and surface water fluxes. From thermal signature analysis two hot springs below the lake bed of Ziway were discovered. The various hot springs ...

Growth and Desulfurization Kinetics of Rhodcoccus Erythropolis IGTS8 on Dibenzothiophen and Petroleum Fraction

International Nuclear Information System (INIS)

El-Temtamy, S.A.; Farahat, L.A.; Mostafa, Y.M.; Al-Shatnawi, D.F.; AI-Sayed, S.

2004-01-01

The growth Kinetics of Rhodococcus erythropolis IGTS8 on dibenzo-thiophene. DBT, of different initial concentrations as well as on two petroleum fractions namely untreated and hydrodesulfurized gasoline and gas oil have been investigated in batch cultures. Using dibenzothiophene as a substrate, the specific growth rates were found to decrease with increasing initial substrate concentration. The removal of dibenzothiophene from culture media was found to follow first order kinetics. The reaction rate constant., k, decreased with increasing substrate concentration. The decrease of both specific growth rate and reaction rate constant with increasing substrate concentration suggested substrate inhibition. The growth rate on untreated gasoline as well as on hydrodesulfurized gasoline gave nearly the same specific growth rates of 0.067 h-I while growth on gas oil gave a higher specific growth rate of 0.1h -1

Si(001):B gas-source molecular-beam epitaxy: Boron surface segregation and its effect on film growth kinetics

Energy Technology Data Exchange (ETDEWEB)

Kim, H.; Glass, G.; Spila, T.; Taylor, N.; Park, S.Y.; Abelson, J.R.; Greene, J.E. [Department of Materials Science, Coordinated Science Laboratory, and Materials Research Laboratory, University of Illinois, 1101 West Springfield, Urbana, Illinois 61801 (United States)

1997-09-01

B-doped Si(001) films, with concentrations C{sub B} up to 1.7{times}10{sup 22}cm{sup {minus}3}, were grown by gas-source molecular-beam epitaxy from Si{sub 2}H{sub 6} and B{sub 2}H{sub 6} at T{sub s}=500{endash}800{degree}C. D{sub 2} temperature-programed desorption (TPD) spectra were then used to determine B coverages {theta}{sub B} as a function of C{sub B} and T{sub s}. In these measurements, as-deposited films were flash heated to desorb surface hydrogen, cooled, and exposed to atomic deuterium until saturation coverage. Strong B surface segregation was observed with surface-to-bulk B concentration ratios ranging up to 1200. TPD spectra exhibited {beta}{sub 2} and {beta}{sub 1} peaks associated with dideuteride and monodeuteride desorption as well as lower-temperature B-induced peaks {beta}{sub 2}{sup {asterisk}} and {beta}{sub 1}{sup {asterisk}}. Increasing {theta}{sub B} increased the area under {beta}{sub 2}{sup {asterisk}} and {beta}{sub 1}{sup {asterisk}} at the expense of {beta}{sub 2} and {beta}{sub 1} and decreased the total D coverage {theta}{sub D}. The TPD results were used to determine the B segregation enthalpy, {minus}0.53eV, and to explain and model the effects of high B coverages on Si(001) growth kinetics. Film deposition rates R increase by {ge}50{percent} with increasing C{sub B}{tilde {gt}}1{times}10{sup 19}cm{sup {minus}3} at T{sub s}{le}550{degree}C, due primarily to increased H desorption rates from B-backbonded Si adatoms, and decrease by corresponding amounts at T{sub s}{ge}600{degree}C due to decreased adsorption site densities. At T{sub s}{ge}700{degree}C, high B coverages also induce {l_brace}113{r_brace} facetting. {copyright} {ital 1997 American Institute of Physics.}

Extracting surface diffusion coefficients from batch adsorption measurement data: application of the classic Langmuir kinetics model.

Science.gov (United States)

Chu, Khim Hoong

2017-11-09

Surface diffusion coefficients may be estimated by fitting solutions of a diffusion model to batch kinetic data. For non-linear systems, a numerical solution of the diffusion model's governing equations is generally required. We report here the application of the classic Langmuir kinetics model to extract surface diffusion coefficients from batch kinetic data. The use of the Langmuir kinetics model in lieu of the conventional surface diffusion model allows derivation of an analytical expression. The parameter estimation procedure requires determining the Langmuir rate coefficient from which the pertinent surface diffusion coefficient is calculated. Surface diffusion coefficients within the 10 -9 to 10 -6  cm 2 /s range obtained by fitting the Langmuir kinetics model to experimental kinetic data taken from the literature are found to be consistent with the corresponding values obtained from the traditional surface diffusion model. The virtue of this simplified parameter estimation method is that it reduces the computational complexity as the analytical expression involves only an algebraic equation in closed form which is easily evaluated by spreadsheet computation.

Parametric Investigation of the Isothermal Kinetics of Growth of Graphene on a Nickel Catalyst in the Process of Chemical Vapor Deposition of Hydrocarbons

Science.gov (United States)

Futko, S. I.; Shulitskii, B. G.; Labunov, V. A.; Ermolaeva, E. M.

2016-11-01

A kinetic model of isothermal synthesis of multilayer graphene on the surface of a nickel foil in the process of chemical vapor deposition, on it, of hydrocarbons supplied in the pulsed regime is considered. The dependences of the number of graphene layers formed and the time of their growth on the temperature of the process, the concentration of acetylene, and the thickness of the nickel foil were calculated. The regime parameters of the process of chemical vapor deposition, at which single-layer graphene and bi-layer graphene are formed, were determined. The dynamics of growth of graphene domains at chemical-vapor-deposition parameters changing in wide ranges was investigated. It is shown that the time dependences of the rates of growth of single-layer graphene and bi-layer graphene are nonlinear in character and that they are determined by the kinetics of nucleation and growth of graphene and the diffusion flow of carbon atoms in the nickel foil.

A global resource allocation strategy governs growth transition kinetics of Escherichia coli.

Science.gov (United States)

Erickson, David W; Schink, Severin J; Patsalo, Vadim; Williamson, James R; Gerland, Ulrich; Hwa, Terence

2017-11-02

A grand challenge of systems biology is to predict the kinetic responses of living systems to perturbations starting from the underlying molecular interactions. Changes in the nutrient environment have long been used to study regulation and adaptation phenomena in microorganisms and they remain a topic of active investigation. Although much is known about the molecular interactions that govern the regulation of key metabolic processes in response to applied perturbations, they are insufficiently quantified for predictive bottom-up modelling. Here we develop a top-down approach, expanding the recently established coarse-grained proteome allocation models from steady-state growth into the kinetic regime. Using only qualitative knowledge of the underlying regulatory processes and imposing the condition of flux balance, we derive a quantitative model of bacterial growth transitions that is independent of inaccessible kinetic parameters. The resulting flux-controlled regulation model accurately predicts the time course of gene expression and biomass accumulation in response to carbon upshifts and downshifts (for example, diauxic shifts) without adjustable parameters. As predicted by the model and validated by quantitative proteomics, cells exhibit suboptimal recovery kinetics in response to nutrient shifts owing to a rigid strategy of protein synthesis allocation, which is not directed towards alleviating specific metabolic bottlenecks. Our approach does not rely on kinetic parameters, and therefore points to a theoretical framework for describing a broad range of such kinetic processes without detailed knowledge of the underlying biochemical reactions.

Theoretical studies of growth processes and electronic properties of nanostructures on surfaces

Science.gov (United States)

Mo, Yina

Low dimensional nanostructures have been of particular interest because of their potential applications in both theoretical studies and industrial use. Although great efforts have been put into obtaining better understanding of the formation and properties of these materials, many questions still remain unanswered. This thesis work has focused on theoretical studies of (1) the growth processes of magnetic nanowires on transition-metal surfaces, (2) the dynamics of pentacene thin-film growth and island structures on inert surfaces, and (3) our proposal of a new type of semiconducting nanotube. In the first study, we elucidated a novel and intriguing kinetic pathway for the formation of Fe nanowires on the upper edge of a monatomic-layer-high step on Cu(111) using first-principles calculations. The identification of a hidden fundamental Fe basal line within the Cu steps prior to the formation of the apparent upper step edge Fe wire produces a totally different view of step-decorating wire structures and offers new possibilities for the study of the properties of these wires. Subsequent experiments with scanning tunneling microscopy unambiguously established the essential role of embedded Fe atoms as precursors to monatomic wire growth. A more general study of adatom behavior near transition-metal step edges illustrated a systematic trend in the adatom energetics and kinetics, resulted from the electronic interactions between the adatom and the surfaces. This work opens the possibility of controlled manufacturing of one-dimensional nanowires. In the second study, we investigated pentacene thin-films on H-diamond, H-silica and OH-silica surfaces via force field molecular dynamics simulations. Pentacene island structures on these surfaces were identified and found to have a 90-degree rotation relative to the structure proposed by some experimental groups. Our work may facilitate the design and control of experimental pentacene thin-film growth, and thus the development

Kinetic computer modeling of microwave surface-wave plasma production

International Nuclear Information System (INIS)

Ganachev, Ivan P.

2004-01-01

Kinetic computer plasma modeling occupies an intermediate position between the time consuming rigorous particle dynamic simulation and the fast but rather rough cold- or warm-plasma fluid models. The present paper reviews the kinetic modeling of microwave surface-wave discharges with accent on recent kinetic self-consistent models, where the external input parameters are reduced to the necessary minimum (frequency and intensity of the applied microwave field and pressure and geometry of the discharge vessel). The presentation is limited to low pressures, so that Boltzmann equation is solved in non-local approximation and collisional electron heating is neglected. The numerical results reproduce correctly the bi-Maxwellian electron energy distribution functions observed experimentally. (author)

Crystal growth kinetics in undercooled melts of pure Ge, Si and Ge-Si alloys

Science.gov (United States)

Herlach, Dieter M.; Simons, Daniel; Pichon, Pierre-Yves

2018-01-01

We report on measurements of crystal growth dynamics in semiconducting pure Ge and pure Si melts and in Ge100-xSix (x = 25, 50, 75) alloy melts as a function of undercooling. Electromagnetic levitation techniques are applied to undercool the samples in a containerless way. The growth velocity is measured by the utilization of a high-speed camera technique over an extended range of undercooling. Solidified samples are examined with respect to their microstructure by scanning electron microscopic investigations. We analyse the experimental results of crystal growth kinetics as a function of undercooling within the sharp interface theory developed by Peter Galenko. Transitions of the atomic attachment kinetics are found at large undercoolings, from faceted growth to dendrite growth. This article is part of the theme issue `From atomistic interfaces to dendritic patterns'.

Linking genes to microbial growth kinetics: an integrated biochemical systems engineering approach.

Science.gov (United States)

Koutinas, Michalis; Kiparissides, Alexandros; Silva-Rocha, Rafael; Lam, Ming-Chi; Martins Dos Santos, Vitor A P; de Lorenzo, Victor; Pistikopoulos, Efstratios N; Mantalaris, Athanasios

2011-07-01

The majority of models describing the kinetic properties of a microorganism for a given substrate are unstructured and empirical. They are formulated in this manner so that the complex mechanism of cell growth is simplified. Herein, a novel approach for modelling microbial growth kinetics is proposed, linking biomass growth and substrate consumption rates to the gene regulatory programmes that control these processes. A dynamic model of the TOL (pWW0) plasmid of Pseudomonas putida mt-2 has been developed, describing the molecular interactions that lead to the transcription of the upper and meta operons, known to produce the enzymes for the oxidative catabolism of m-xylene. The genetic circuit model was combined with a growth kinetic model decoupling biomass growth and substrate consumption rates, which are expressed as independent functions of the rate-limiting enzymes produced by the operons. Estimation of model parameters and validation of the model's predictive capability were successfully performed in batch cultures of mt-2 fed with different concentrations of m-xylene, as confirmed by relative mRNA concentration measurements of the promoters encoded in TOL. The growth formation and substrate utilisation patterns could not be accurately described by traditional Monod-type models for a wide range of conditions, demonstrating the critical importance of gene regulation for the development of advanced models closely predicting complex bioprocesses. In contrast, the proposed strategy, which utilises quantitative information pertaining to upstream molecular events that control the production of rate-limiting enzymes, predicts the catabolism of a substrate and biomass formation and could be of central importance for the design of optimal bioprocesses. Copyright © 2011 Elsevier Inc. All rights reserved.

The effect of the phase composition of compound layer on the growth kinetics of the nitrided layer

International Nuclear Information System (INIS)

Ratajski, J.; Olik, R.; Suszko, T.; Tacikowski, J.

2001-01-01

This paper presents a part of research work on the kinetics of formation and growth of nitrided layers on 40HM steel that was conducted within the research project devoted to the control of gaseous nitriding processes. The purpose of the research was to find answers to still opened questions connected with the optimization of the growth kinetics of nitrided layer. It has been demonstrated in particular how important in diffusion layer kinetics of growth on steel is the role-played by compound layer phase composition. Mainly, this refers to designing changes of parameters in processes where accurate formation of layer on precise parts with required tolerance of size changes is demanded. It comes out of the presented research that proper diffusion layer growth kinetics can be achieved when phase ε dominates in the compound layer. This domination of the phase ε influences speed of growth of the compound layer and first of all growth of diffusion layer. The obtained results are also a starting point of for working-out of good functional relations which could create good basis for design of algorithms of potential values changes in the function of the process time which provides the optimal kinetics of the growth of the layers. In this respect it has been achieved very good qualitative relation between the simulated distribution of nitrogen concentration in the layer and experimentally established distribution of hardness. (author)

Growth kinetics of tetragonal and monoclinic ZrO2 crystallites in 3 mol% yttria partially stabilized ZrO2 (3Y-PSZ) precursor powder

International Nuclear Information System (INIS)

Kuo, Chih-Wei; Lee, Kuen-Chan; Yen, Feng-Lin; Shen, Yun-Hwei; Lee, Huey-Er; Wen, Shaw-Bing; Wang, Moo-Chin; Stack, Margaret Mary

2014-01-01

Highlights: • The crystalline structures were composed of tetragonal and monoclinic ZrO 2 . • Growth kinetics of t-ZrO 2 in the 3Y-PSZ precursor powder is described as: D te 2 =(4.57±0.55)t 0.12±0.02 exp(-((24.79±0.38)×10 3 )/(RT) ). • Growth kinetics of m-ZrO 2 in the 3Y-PSZ precursor powder is described as: D m 2 =(4.40±1.63)t 0.17±0.08 exp(-((66.47±3.97)×10 3 )/(RT) ). - Abstract: The growth kinetics of tetragonal and monoclinic ZrO 2 crystallites in 3 mol% yttria partially stabilized ZrO 2 (3Y-PSZ) precursor powder has been investigated using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area analysis, transmission electron microscopy (TEM) and high resolution TEM (HRTEM). After calcination of the 3Y-PSZ precursor powder between 773 and 1073 K for 2 h, the crystalline structures were composed of tetragonal and monoclinic ZrO 2 as the primary and secondary phases, respectively. When the 3Y-PSZ precursor powder was calcined at 773 K for 2 h, the BET specific surface area was 97.13 m 2 /g, which is equivalent to a particle size of 10.30 nm. The crystallite sizes determined via XRD and BET agreed well, indicating that the powder was virtually non-agglomerated. The growth kinetics of tetragonal and monoclinic ZrO 2 crystallite isothermal growth in the 3Y-PSZ precursor powder are described by: D te 2 =(4.57±0.55)t 0.12±0.02 exp(-((24.79±0.38)×10 3 )/(RT) ) and D m 2 =(4.40±1.63)t 0.17±0.08 exp(-((66.47±3.97)×10 3 )/(RT) ), respectively, for 773K≤T≤1073K. D te and D m denote the crystallite size of tetragonal and monoclinic ZrO 2 at time t and temperature T, respectively

Kinetics of radiation-induced precipitation at the alloy surface

Science.gov (United States)

Lam, N. Q.; Nguyen, T.; Leaf, G. K.; Yip, S.

1988-05-01

Radiation-induced precipitation of a new phase at the surface of an alloy during irradiation at elevated temperatures was studied with the aid of a kinetic model of segregation. The preferential coupling of solute atoms with the defect fluxes gives rise to a strong solute enrichment at the surface, which, if surpassing the solute solubility limit, leads to the formation of a precipitate layer. The moving precipitate/matrix interface was accommodated by means of a mathematical scheme that transforms spatial coordinates into a reference frame in which the boundaries are immobile. Sample calculations were performed for precipitation of the γ'-Ni 3Si layer on Ni-Si alloys undergoing electron irradiation. The dependences of the precipitation kinetics on the defect-production rate, irradiation temperature, internal defect sink concentration and alloy composition were investigated systematically.

The impact of surface coverage on the kinetics of electron transfer through redox monolayers on a silicon electrode surface

International Nuclear Information System (INIS)

Ciampi, Simone; Choudhury, Moinul H.; Ahmad, Shahrul Ainliah Binti Alang; Darwish, Nadim; Brun, Anton Le; Gooding, J.Justin

2015-01-01

Graphical abstract: The impact of surface coverage on the kinetics of electron transfer through redox monolayers on a silicon electrode surface. ABSTRACT: The impact of the coverage of ferrocene moieties, attached to a silicon electrode modified via hydrosilylation of a dialkyne, on the kinetics of electron transfer between the redox species and the electrode is explored. The coverage of ferrocene is controlled by varying the coupling time between azidomethylferrocene and the distal alkyne of the monolayer via the copper assisted azide-alkyne cycloaddition reaction. All other variables in the surface preparation are maintained identical. What is observed is that the higher the surface coverage of the ferrocene moieties the faster the apparent rates of electron transfer. This surface coverage-dependent kinetic effect is attributed to electrons hopping between ferrocene moieties across the redox film toward hotspots for the electron transfer event. The origin of these hotspots is tentatively suggested to result from minor amounts of oxide on the underlying silicon surface that reduce the barrier for the electron transfer.

Effects of growth rate, cell size, motion, and elemental stoichiometry on nutrient transport kinetics.

Science.gov (United States)

Flynn, Kevin J; Skibinski, David O F; Lindemann, Christian

2018-04-01

Nutrient acquisition is a critical determinant for the competitive advantage for auto- and osmohetero- trophs alike. Nutrient limited growth is commonly described on a whole cell basis through reference to a maximum growth rate (Gmax) and a half-saturation constant (KG). This empirical application of a Michaelis-Menten like description ignores the multiple underlying feedbacks between physiology contributing to growth, cell size, elemental stoichiometry and cell motion. Here we explore these relationships with reference to the kinetics of the nutrient transporter protein, the transporter rate density at the cell surface (TRD; potential transport rate per unit plasma-membrane area), and diffusion gradients. While the half saturation value for the limiting nutrient increases rapidly with cell size, significant mitigation is afforded by cell motion (swimming or sedimentation), and by decreasing the cellular carbon density. There is thus potential for high vacuolation and high sedimentation rates in diatoms to significantly decrease KG and increase species competitive advantage. Our results also suggest that Gmax for larger non-diatom protists may be constrained by rates of nutrient transport. For a given carbon density, cell size and TRD, the value of Gmax/KG remains constant. This implies that species or strains with a lower Gmax might coincidentally have a competitive advantage under nutrient limited conditions as they also express lower values of KG. The ability of cells to modulate the TRD according to their nutritional status, and hence change the instantaneous maximum transport rate, has a very marked effect upon transport and growth kinetics. Analyses and dynamic models that do not consider such modulation will inevitably fail to properly reflect competitive advantage in nutrient acquisition. This has important implications for the accurate representation and predictive capabilities of model applications, in particular in a changing environment.

Analysis of Network Topologies Underlying Ethylene Growth Response Kinetics

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Aaron M. Prescott

2016-08-01

Full Text Available Most models for ethylene signaling involve a linear pathway. However, measurements of seedling growth kinetics when ethylene is applied and removed have resulted in more complex network models that include coherent feedforward, negative feedback, and positive feedback motifs. However, the dynamical responses of the proposed networks have not been explored in a quantitative manner. Here, we explore (i whether any of the proposed models are capable of producing growth-response behaviors consistent with experimental observations and (ii what mechanistic roles various parts of the network topologies play in ethylene signaling. To address this, we used computational methods to explore two general network topologies: The first contains a coherent feedforward loop that inhibits growth and a negative feedback from growth onto itself (CFF/NFB. In the second, ethylene promotes the cleavage of EIN2, with the product of the cleavage inhibiting growth and promoting the production of EIN2 through a positive feedback loop (PFB. Since few network parameters for ethylene signaling are known in detail, we used an evolutionary algorithm to explore sets of parameters that produce behaviors similar to experimental growth response kinetics of both wildtype and mutant seedlings. We generated a library of parameter sets by independently running the evolutionary algorithm many times. Both network topologies produce behavior consistent with experimental observations and analysis of the parameter sets allows us to identify important network interactions and parameter constraints. We additionally screened these parameter sets for growth recovery in the presence of sub-saturating ethylene doses, which is an experimentally-observed property that emerges in some of the evolved parameter sets. Finally, we probed simplified networks maintaining key features of the CFF/NFB and PFB topologies. From this, we verified observations drawn from the larger networks about mechanisms

Analysis of Network Topologies Underlying Ethylene Growth Response Kinetics.

Science.gov (United States)

Prescott, Aaron M; McCollough, Forest W; Eldreth, Bryan L; Binder, Brad M; Abel, Steven M

2016-01-01

Most models for ethylene signaling involve a linear pathway. However, measurements of seedling growth kinetics when ethylene is applied and removed have resulted in more complex network models that include coherent feedforward, negative feedback, and positive feedback motifs. The dynamical responses of the proposed networks have not been explored in a quantitative manner. Here, we explore (i) whether any of the proposed models are capable of producing growth-response behaviors consistent with experimental observations and (ii) what mechanistic roles various parts of the network topologies play in ethylene signaling. To address this, we used computational methods to explore two general network topologies: The first contains a coherent feedforward loop that inhibits growth and a negative feedback from growth onto itself (CFF/NFB). In the second, ethylene promotes the cleavage of EIN2, with the product of the cleavage inhibiting growth and promoting the production of EIN2 through a positive feedback loop (PFB). Since few network parameters for ethylene signaling are known in detail, we used an evolutionary algorithm to explore sets of parameters that produce behaviors similar to experimental growth response kinetics of both wildtype and mutant seedlings. We generated a library of parameter sets by independently running the evolutionary algorithm many times. Both network topologies produce behavior consistent with experimental observations, and analysis of the parameter sets allows us to identify important network interactions and parameter constraints. We additionally screened these parameter sets for growth recovery in the presence of sub-saturating ethylene doses, which is an experimentally-observed property that emerges in some of the evolved parameter sets. Finally, we probed simplified networks maintaining key features of the CFF/NFB and PFB topologies. From this, we verified observations drawn from the larger networks about mechanisms underlying ethylene

Growth kinetics of Staphylococcus aureus on Brie and Camembert cheeses.

Science.gov (United States)

Lee, Heeyoung; Kim, Kyungmi; Lee, Soomin; Han, Minkyung; Yoon, Yohan

2014-05-01

In this study, we developed mathematical models to describe the growth kinetics of Staphylococcus aureus on natural cheeses. A five-strain mixture of Staph. aureus was inoculated onto 15 g of Brie and Camembert cheeses at 4 log CFU/g. The samples were then stored at 4, 10, 15, 25, and 30 °C for 2-60 d, with a different storage time being used for each temperature. Total bacterial and Staph. aureus cells were enumerated on tryptic soy agar and mannitol salt agar, respectively. The Baranyi model was fitted to the growth data of Staph. aureus to calculate kinetic parameters such as the maximum growth rate in log CFU units (r max; log CFU/g/h) and the lag phase duration (λ; h). The effects of temperature on the square root of r max and on the natural logarithm of λ were modelled in the second stage (secondary model). Independent experimental data (observed data) were compared with prediction and the respective root mean square error compared with the RMSE of the fit on the original data, as a measure of model performance. The total growth of bacteria was observed at 10, 15, 25, and 30 °C on both cheeses. The r max values increased with storage temperature (PCamembert cheeses.

X-ray photoelectron spectroscopy study of the growth kinetics of biomimetically grown hydroxyapatite thin-film coatings

International Nuclear Information System (INIS)

McLeod, K.; Kumar, S.; Dutta, N.K.; Smart, R.St.C.; Voelcker, N.H.; Anderson, G.I.

2010-01-01

Hydroxyapatite (HA) thin-film coatings grown biomimetically using simulated body fluid (SBF) are desirable for a range of applications such as improved fixation of fine- and complex-shaped orthopedic and dental implants, tissue engineering scaffolds and localized and sustained drug delivery. There is a dearth of knowledge on two key aspects of SBF-grown HA coatings: (i) the growth kinetics over short deposition periods, hours rather than weeks; and (ii) possible difference between the coatings deposited with and without periodic SBF replenishment. A study centred on these aspects is reported. X-ray photoelectron spectroscopy (XPS) has been used to study the growth kinetics of SBF-grown HA coatings for deposition periods ranging from 0.5 h to 21 days. The coatings were deposited with and without periodic replenishment of SBF. The XPS studies revealed that: (i) a continuous, stable HA coating fully covered the titanium substrate after a growth period of 13 h without SBF replenishment; (ii) thicker HA coatings about 1 μm in thickness resulted after a growth period of 21 days, both with and without SBF replenishment; and (iii) the Ca/P ratio at the surface of the HA coating was significantly lower than that in its bulk. No significant difference between HA grown with and without periodic replenishment of SBF was found. The coatings were determined to be carbonated, a characteristic desirable for improved implant fixation. The atomic force and scanning electron microscopies results suggested that heterogeneous nucleation and growth are the primary deposition mode for these coatings. Primary osteoblast cell studies demonstrated the biocompatibility of these coatings, i.e., osteoblast colony coverage of approximately 80%, similar to the control substrate (tissue culture polystyrene).

X-ray photoelectron spectroscopy study of the growth kinetics of biomimetically grown hydroxyapatite thin-film coatings

Energy Technology Data Exchange (ETDEWEB)

McLeod, K. [Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095 (Australia); Kumar, S., E-mail: sunil.kumar@unisa.edu.au [Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095 (Australia); Dutta, N.K. [Ian Wark Research Institute, University of South Australia, Mawson Lakes, SA 5095 (Australia); Smart, R.St.C. [Applied Centre for Structural and Synchrotron Studies, University of South Australia, Mawson Lakes, SA 5095 (Australia); Voelcker, N.H. [School of Chemistry, Physics and Earth Sciences, Flinders University of South Australia, GPO Box 2100, Adelaide 5001 (Australia); Anderson, G.I. [School of Veterinary Science, University of Adelaide, Adelaide, SA 5005 (Australia)

2010-09-15

Hydroxyapatite (HA) thin-film coatings grown biomimetically using simulated body fluid (SBF) are desirable for a range of applications such as improved fixation of fine- and complex-shaped orthopedic and dental implants, tissue engineering scaffolds and localized and sustained drug delivery. There is a dearth of knowledge on two key aspects of SBF-grown HA coatings: (i) the growth kinetics over short deposition periods, hours rather than weeks; and (ii) possible difference between the coatings deposited with and without periodic SBF replenishment. A study centred on these aspects is reported. X-ray photoelectron spectroscopy (XPS) has been used to study the growth kinetics of SBF-grown HA coatings for deposition periods ranging from 0.5 h to 21 days. The coatings were deposited with and without periodic replenishment of SBF. The XPS studies revealed that: (i) a continuous, stable HA coating fully covered the titanium substrate after a growth period of 13 h without SBF replenishment; (ii) thicker HA coatings about 1 {mu}m in thickness resulted after a growth period of 21 days, both with and without SBF replenishment; and (iii) the Ca/P ratio at the surface of the HA coating was significantly lower than that in its bulk. No significant difference between HA grown with and without periodic replenishment of SBF was found. The coatings were determined to be carbonated, a characteristic desirable for improved implant fixation. The atomic force and scanning electron microscopies results suggested that heterogeneous nucleation and growth are the primary deposition mode for these coatings. Primary osteoblast cell studies demonstrated the biocompatibility of these coatings, i.e., osteoblast colony coverage of approximately 80%, similar to the control substrate (tissue culture polystyrene).

Synchrotron x-ray-diffraction study of the structure and growth of Xe films adsorbed on the Ag(111) surface

International Nuclear Information System (INIS)

Dai, P.; Wu, Z.; Angot, T.; Wang, S.; Taub, H.; Ehrlich, S.N.

1999-01-01

Synchrotron x-ray scattering has been used to investigate the structure and growth of perhaps the simplest of all films: xenon physisorbed on the Ag(111) surface. High-resolution x-ray scans of the in-plane structure and lower-resolution scans (specular and nonspecular) of the out-of-plane order were performed. The Xe films were prepared under both quasiequilibrium and kinetic growth conditions, and have fewer structural defects than those investigated previously by others on graphite substrates. Under quasiequilibrium conditions, the bulk Xe-Xe spacing is reached at monolayer completion, and the monolayer and bilayer lattice constants at coexistence are inferred equal to within 0.005 Angstrom, consistent with theoretical calculations. The Xe/vacuum interface profile for a complete monolayer and bilayer grown at quasiequilibrium is found to be sharper than for kinetically grown films. At coverages above two layers, diffraction scans along the Xe(01l) rod for quasiequilibrated films are consistent with the presence of two domains having predominantly an ABC stacking sequence and rotated 60 degree with respect to each other about the surface normal. Annealing of these films alters neither the population of the two domains nor the fraction of ABA stacking faults. The thickest film grown under quasiequilibrium conditions exceeds 220 Angstrom (resolution limited). Under kinetic growth conditions, x-ray intensity oscillations at the Xe anti-Bragg position of the specular rod are observed as a function of time, indicating nearly layer-by-layer growth. Up to four complete oscillations corresponding to a film of eight layers have been observed before the intensity is damped out; the number of oscillations is found to depend on the substrate temperature, the growth rate, and the quality of the Ag(111) substrate. The specular reflectivity from kinetically grown films at nominal coverages of three and four layers has been analyzed using a Gaussian model which gives a film

The kinetic boundary layer around an absorbing sphere and the growth of small droplets

International Nuclear Information System (INIS)

Widder, M.E.; Titulaer, U.M.

1989-01-01

Deviations from the classical Smoluchowski expression for the growth rate of a droplet in a supersaturated vapor can be expected when the droplet radius is not large compared to the mean free path of a vapor molecule. The growth rate then depends significantly on the structure of the kinetic boundary layer around a sphere. The authors consider this kinetic boundary layer for a dilute system of Brownian particles. For this system a large class of boundary layer problems for a planar wall have been solved. They show how the spherical boundary layer can be treated by a perturbation expansion in the reciprocal droplet radius. In each order one has to solve a finite number of planar boundary layer problems. The first two corrections to the planar problem are calculated explicitly. For radii down to about two velocity persistence lengths (the analog of the mean free path for a Brownian particle) the successive approximations for the growth rate agree to within a few percent. A reasonable estimate of the growth rate for all radii can be obtained by extrapolating toward the exactly known value at zero radius. Kinetic boundary layer effects increase the time needed for growth from 0 to 10 (or 2 1/2) velocity persistence lengths by roughly 35% (or 175%)

Development of a novel once-through flow visualization technique for kinetic study of bulk and surface scaling

Science.gov (United States)

Sanni, O.; Bukuaghangin, O.; Huggan, M.; Kapur, N.; Charpentier, T.; Neville, A.

2017-10-01

There is a considerable interest to investigate surface crystallization in order to have a full mechanistic understanding of how layers of sparingly soluble salts (scale) build on component surfaces. Despite much recent attention, a suitable methodology to improve on the understanding of the precipitation/deposition systems to enable the construction of an accurate surface deposition kinetic model is still needed. In this work, an experimental flow rig and associated methodology to study mineral scale deposition is developed. The once-through flow rig allows us to follow mineral scale precipitation and surface deposition in situ and in real time. The rig enables us to assess the effects of various parameters such as brine chemistry and scaling indices, temperature, flow rates, and scale inhibitor concentrations on scaling kinetics. Calcium carbonate (CaCO3) scaling at different values of the saturation ratio (SR) is evaluated using image analysis procedures that enable the assessment of surface coverage, nucleation, and growth of the particles with time. The result for turbidity values measured in the flow cell is zero for all the SR considered. The residence time from the mixing point to the sample is shorter than the induction time for bulk precipitation; therefore, there are no crystals in the bulk solution as the flow passes through the sample. The study shows that surface scaling is not always a result of pre-precipitated crystals in the bulk solution. The technique enables both precipitation and surface deposition of scale to be decoupled and for the surface deposition process to be studied in real time and assessed under constant condition.

Kinetics of Grain Growth in 718 Ni-Base Superalloy

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Huda Z.

2014-10-01

Full Text Available The Haynes® 718 Ni-base superalloy has been investigated by use of modern material characterization, metallographic and heat treatment equipment. Grain growth annealing experiments at temperatures in the range of 1050 – 1200 oC (1323–1473K for time durations in the range of 20 min-22h have been conducted. The kinetic equations and an Arrhenius-type equation have been applied to compute the grain-growth exponent n and the activation energy for grain growth, Qg, for the investigated alloy. The grain growth exponent, n, was computed to be in the range of 0.066-0.206; and the n values have been critically discussed in relation to the literature. The activation energy for grain growth, Qg, for the investigated alloy has been computed to be around 440 kJ/mol; and the Qg data for the investigated alloy has been compared with other metals and alloys and ceramics; and critically analyzed in relation to our results.

Kinetics of cesium lead halide perovskite nanoparticle growth; focusing and de-focusing of size distribution

Science.gov (United States)

Koolyk, Miriam; Amgar, Daniel; Aharon, Sigalit; Etgar, Lioz

2016-03-01

In this work we study the kinetics of cesium lead halide perovskite nanoparticle (NP) growth; the focusing and de-focusing of the NP size distribution. Cesium lead halide perovskite NPs are considered to be attractive materials for optoelectronic applications. Understanding the kinetics of the formation of these all-inorganic perovskite NPs is critical for reproducibly and reliably generating large amounts of uniformly sized NPs. Here we investigate different growth durations for CsPbI3 and CsPbBr3 NPs, tracking their growth by high-resolution transmission electron microscopy and size distribution analysis. As a result, we are able to provide a detailed model for the kinetics of their growth. It was observed that the CsPbI3 NPs exhibit focusing of the size distribution in the first 20 seconds of growth, followed by de-focusing over longer growth durations, while the CsPbBr3 NPs show de-focusing of the size distribution starting from the beginning of the growth. The monomer concentration is depleted faster in the case of CsPbBr3 than in the case of CsPbI3, due to faster diffusion of the monomers, which increases the critical radius and results in de-focusing of the population. Accordingly, focusing is not observed within 40 seconds of growth in the case of CsPbBr3. This study provides important knowledge on how to achieve a narrow size distribution of cesium lead halide perovskite NPs when generating large amounts of these promising, highly luminescent NPs.In this work we study the kinetics of cesium lead halide perovskite nanoparticle (NP) growth; the focusing and de-focusing of the NP size distribution. Cesium lead halide perovskite NPs are considered to be attractive materials for optoelectronic applications. Understanding the kinetics of the formation of these all-inorganic perovskite NPs is critical for reproducibly and reliably generating large amounts of uniformly sized NPs. Here we investigate different growth durations for CsPbI3 and CsPbBr3 NPs, tracking

Conductive atomic force microscopy study of InAs growth kinetics on vicinal GaAs (110)

International Nuclear Information System (INIS)

Tejedor, Paloma; Diez-Merino, Laura; Beinik, Igor; Teichert, Christian

2009-01-01

Conductive atomic force microscopy has been used to investigate the effect of atomic hydrogen and step orientation on the growth behavior of InAs on GaAs (110) misoriented substrates. Samples grown by conventional molecular beam epitaxy exhibit higher conductivity on [110]-multiatomic step edges, where preferential nucleation of InAs nanowires takes place by step decoration. On H-terminated substrates with triangular terraces bounded by [115]-type steps, three-dimensional InAs clusters grow selectively at the terrace apices as a result of a kinetically driven enhancement in upward mass transport via AsH x intermediate species and a reduction in the surface free energy.

CRYSTALLIZATION KINETICS OF AMMONIUM PERCHLORATE IN AN AGITATED VESSEL

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Nahidh Kaseer

2013-05-01

Full Text Available 31Overall crystal growth kinetics for ammonium perchlorate in laboratory scale batch  agitated vessel crystallizer have been determined from batch experiments performed in an integral mode. The effects of temperature between 30-60ºC, seed size 0.07, 0.120 and 0.275 mm and stirrer speed 160, 340, and 480 rpm, on the kinetics of crystal growth were investigated. Two different methods, viz. polynomial fitting and initial derivative were used to predict the kinetics expression. In general both methods gave comparable results for growth kinetics estimation. The order of growth process is not more than two. The activation energy for crystal growth of ammonium perchlorate was determined and found  to be equal to 5.8 kJ/ mole.            Finally, the influence of the affecting parameters on the crystal growth rate gives general expression that had an obvious dependence of the growth rate on each variables of concern (temperature, seed size, and stirrer speed .The general overall growth rate expression had shown that super saturation is the most significant variable. While the positive dependence of the stirrer speed demonstrates the importance of the diffusional step in the growth rate model. Moreover, the positive dependence of the seed size demonstrate the importance of the surface integration  step in the growth rate model. All the studied variables tend to suggest that the growth rate characteristics  of ammonium perchlorate from aqueous solution commenced in a batch crystallizer are diffusion kinetic controlled process.

Subdiffusion kinetics of nanoprecipitate growth and destruction in solid solutions

Science.gov (United States)

Sibatov, R. T.; Svetukhin, V. V.

2015-06-01

Based on fractional differential generalizations of the Ham and Aaron-Kotler precipitation models, we study the kinetics of subdiffusion-limited growth and dissolution of new-phase precipitates. We obtain the time dependence of the number of impurities and dimensions of new-phase precipitates. The solutions agree with the Monte Carlo simulation results.

Mathematical modeling and growth kinetics of Clostridium sporogenes in cooked beef

Science.gov (United States)

Clostridium sporogenes PA 3679 is a common surrogate for proteolytic Clostridium botulinum for thermal process development and validation. However, little information is available concerning the growth kinetics of C. sporogenes in food. Therefore, the objective of this study was to investigate the...

Hydroxyapatite growth induced by native extracellular matrix deposition on solid surfaces

Directory of Open Access Journals (Sweden)

Pramatarova L.

2005-02-01

Full Text Available Biological systems have a remarkable capability to produce perfect fine structures such as seashells, pearls, bones, teeth and corals. These structures are composites of interacting inorganic (calcium phosphate or carbonate minerals and organic counterparts. It is difficult to say with certainty which part has the primary role. For example, the growth of molluscan shell crystals is thought to be initiated from a solution by the extracellular organic matrix (ECM. According to this theory, the matrix induces nucleation of calcium containing crystals. Recently, an alternative theory has been put forward, stating that a class of granulocytic hemocytes would be directly involved in shell crystal production in oysters. In the work presented here the surface of AISI 316 stainless steel was modified by deposition of ECM proteins. The ability of the modified substrates to induce nucleation and growth of hydroxyapatite (HA from simulated body fluid (SBF was examined by a kinetic study using two methods: (1 a simple soaking process in SBF and (2 a laser-liquid-solid interaction (LLSI process which allows interaction between a scanning laser beam and a solid substrate immersed in SBF. The deposited HA layers were investigated by Fourier transform infrared spectroscopy (FTIR and scanning electron microscopy (SEM. It was found that a coating of stainless steel surface with native ECM proteins induced nucleation and growth of HA and facilitated its crystallization. By the process of simple soaking of the samples, irrespective of their horizontal or vertical position in the solution, HA layers were grown due to the reactive ECM-coated stainless steel surface. It was shown that the process occurring in the first stages of the growth was not only a result of the force of gravity. The application of the LLSI process strongly influenced HA formation on the ECM-modified substrates by promoting and enhancing the HA nucleation and growth through a synergistic effect

Kinetics of monolayer graphene growth by segregation on Pd(111)

International Nuclear Information System (INIS)

Mok, H. S.; Murata, Y.; Kodambaka, S.; Ebnonnasir, A.; Ciobanu, C. V.; Nie, S.; McCarty, K. F.

2014-01-01

Using in situ low-energy electron microscopy and density functional theory calculations, we follow the growth of monolayer graphene on Pd(111) via surface segregation of bulk-dissolved carbon. Upon lowering the substrate temperature, nucleation of graphene begins on graphene-free Pd surface and continues to occur during graphene growth. Measurements of graphene growth rates and Pd surface work functions establish that this continued nucleation is due to increasing C adatom concentration on the Pd surface with time. We attribute this anomalous phenomenon to a large barrier for attachment of C adatoms to graphene coupled with a strong binding of the non-graphitic C to the Pd surface

Kinetics of monolayer graphene growth by segregation on Pd(111)

Energy Technology Data Exchange (ETDEWEB)

Mok, H. S.; Murata, Y.; Kodambaka, S., E-mail: kodambaka@ucla.edu [Department of Materials Science and Engineering, University of California Los Angeles, Los Angeles, California 90095 (United States); Ebnonnasir, A.; Ciobanu, C. V. [Department of Mechanical Engineering and Materials Science Program, Colorado School of Mines, Golden, Colorado 80401 (United States); Nie, S.; McCarty, K. F. [Sandia National Laboratories, Livermore, California 94550 (United States)

2014-03-10

Using in situ low-energy electron microscopy and density functional theory calculations, we follow the growth of monolayer graphene on Pd(111) via surface segregation of bulk-dissolved carbon. Upon lowering the substrate temperature, nucleation of graphene begins on graphene-free Pd surface and continues to occur during graphene growth. Measurements of graphene growth rates and Pd surface work functions establish that this continued nucleation is due to increasing C adatom concentration on the Pd surface with time. We attribute this anomalous phenomenon to a large barrier for attachment of C adatoms to graphene coupled with a strong binding of the non-graphitic C to the Pd surface.

Influence of radioactivity on surface charging and aggregation kinetics of particles in the atmosphere.

Science.gov (United States)

Kim, Yong-Ha; Yiacoumi, Sotira; Lee, Ida; McFarlane, Joanna; Tsouris, Costas

2014-01-01

Radioactivity can influence surface interactions, but its effects on particle aggregation kinetics have not been included in transport modeling of radioactive particles. In this research, experimental and theoretical studies have been performed to investigate the influence of radioactivity on surface charging and aggregation kinetics of radioactive particles in the atmosphere. Radioactivity-induced charging mechanisms have been investigated at the microscopic level, and heterogeneous surface potential caused by radioactivity is reported. The radioactivity-induced surface charging is highly influenced by several parameters, such as rate and type of radioactive decay. A population balance model, including interparticle forces, has been employed to study the effects of radioactivity on particle aggregation kinetics in air. It has been found that radioactivity can hinder aggregation of particles because of similar surface charging caused by the decay process. Experimental and theoretical studies provide useful insights into the understanding of transport characteristics of radioactive particles emitted from severe nuclear events, such as the recent accident of Fukushima or deliberate explosions of radiological devices.

Study of growth kinetics in melt-textured YBa2Cu3O7-x

International Nuclear Information System (INIS)

Athur, S.P.; Selvamanickam, V.; Balachandran, U.; Salama, K.

1996-01-01

Directional solidification has been shown to be a successful way of achieving high current densities in bulk YBCO. The lack of understanding of the growth kinetics, however, makes it difficult to fabricate longer samples and reduce the processing times. To study the growth kinetics, quenching experiments of undoped YBa 2 Cu 3 O 7-x (Y-123) and Y-123 doped with Pt and Nd from above the peritectic temperature with different holding times, t, were conducted. The results of these experiments indicate that the average 211 particle size varies as t 1/3 . Growth rate experiments were also conducted on these samples to determine the maximum growth rate for plane front solidification, R max . This quantity was measured for undoped and doped Y-123 and its was found that the addition of Pt did not increase R max while the addition of Nd doubled the growth rate. Using the coarsening results together with the growth rate experiments, the diffusivity of Y in liquid and the 211-liquid interfacial energy for undoped and doped Y-123 were calculated. copyright 1996 Materials Research Society

Study on fermentation conditions of palm juice vinegar by response surface methodology and development of a kinetic model

Directory of Open Access Journals (Sweden)

S. Ghosh

2012-09-01

Full Text Available Natural vinegar is one of the fermented products which has some potentiality with respect to a nutraceutical standpoint. The present study is an optimization of the fermentation conditions for palm juice vinegar production from palm juice (Borassus flabellifer wine, this biochemical process being aided by Acetobacter aceti (NCIM 2251. The physical parameters of the fermentation conditions such as temperature, pH, and time were investigated by Response Surface Methodology (RSM with 2³ factorial central composite designs (CCD. The optimum pH, temperature and time were 5.5, 30 °C and 72 hrs for the highest yield of acetic acid (68.12 g / L. The quadratic model equation had a R² value of 0.992. RSM played an important role in elucidating the basic mechanisms in a complex situation, thus providing better process control by maximizing acetic acid production with the respective physical parameters. At the optimized conditions of temperature, pH and time and with the help of mathematical kinetic equations, the Monod specific growth rate ( µ max= 0.021 h-1, maximum Logistic specific growth rate ( µ 'max = 0.027 h-1 and various other kinetic parameters were calculated, which helped in validation of the experimental data. Therefore, the established kinetic models may be applied for the production of natural vinegar by fermentation of low cost palm juice.

Kinetic Monte Carlo simulation of surface segregation in Pd–Cu alloys

International Nuclear Information System (INIS)

Cheng, Feng; He, Xiang; Chen, Zhao-Xu; Huang, Yu-Gai

2015-01-01

The knowledge of surface composition and atomic arrangement is prerequisite for understanding of catalytic properties of an alloy catalyst. Gaining such knowledge is rather difficult, especially for those possessing surface segregation. Pd–Cu alloy is used in many fields and possesses surface segregation. In this paper kinetic Monte Carlo method is used to explore the surface composition and structure and to examine the effects of bulk composition and temperature on the surface segregation of Pd–Cu alloys. It is shown that the segregation basically completes within 900 s at 500 K. Below 900 K and within 20 min the enriched surface Cu atoms mainly come from the top five layers. For the first time we demonstrate that there exists a “bulk-inside flocking” or clustering phenomenon (the same component element congregates in bulk) in Pd–Cu alloys. Our results indicate that for alloys with higher Cu content there are small Pd ensembles like monomers, dimers and trimers with contiguous subsurface Pd atoms. - Highlights: • Kinetic Monte Carlo was first used to study surface segregation of Pd–Cu alloys. • Bulk-inside flocking (the same component element congregates in bulk) was observed. • Small Pd ensembles with contiguous subsurface Pd exist on surfaces of Cu-rich alloys

Kinetic Monte Carlo simulation of surface segregation in Pd–Cu alloys

Energy Technology Data Exchange (ETDEWEB)

Cheng, Feng [Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of MOE, Nanjing University (China); He, Xiang [Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008 (China); Chen, Zhao-Xu, E-mail: zxchen@nju.edu.cn [Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of MOE, Nanjing University (China); Huang, Yu-Gai [Institute of Theoretical and Computational Chemistry, School of Chemistry and Chemical Engineering, Key Laboratory of Mesoscopic Chemistry of MOE, Nanjing University (China); JiangSu Second Normal University, Nanjing (China)

2015-11-05

The knowledge of surface composition and atomic arrangement is prerequisite for understanding of catalytic properties of an alloy catalyst. Gaining such knowledge is rather difficult, especially for those possessing surface segregation. Pd–Cu alloy is used in many fields and possesses surface segregation. In this paper kinetic Monte Carlo method is used to explore the surface composition and structure and to examine the effects of bulk composition and temperature on the surface segregation of Pd–Cu alloys. It is shown that the segregation basically completes within 900 s at 500 K. Below 900 K and within 20 min the enriched surface Cu atoms mainly come from the top five layers. For the first time we demonstrate that there exists a “bulk-inside flocking” or clustering phenomenon (the same component element congregates in bulk) in Pd–Cu alloys. Our results indicate that for alloys with higher Cu content there are small Pd ensembles like monomers, dimers and trimers with contiguous subsurface Pd atoms. - Highlights: • Kinetic Monte Carlo was first used to study surface segregation of Pd–Cu alloys. • Bulk-inside flocking (the same component element congregates in bulk) was observed. • Small Pd ensembles with contiguous subsurface Pd exist on surfaces of Cu-rich alloys.

Kinetic theory of surface waves in plasma jets

International Nuclear Information System (INIS)

Shokri, B.

2002-01-01

The kinetic theory analysis of surface waves propagating along a semi-bounded plasma jet is presented. The frequency spectra and their damping rate are obtained in both the high and low frequency regions. Finally, the penetration of the static field in the plasma jet under the condition that the plasma jet velocity is smaller than the sound velocity is studied

Making waves: Kinetic processes controlling surface evolution during low energy ion sputtering

International Nuclear Information System (INIS)

Chan, W.L.; Chason, Eric

2007-01-01

When collimated beams of low energy ions are used to bombard materials, the surface often develops a periodic pattern or ''ripple'' structure. Different types of patterns are observed to develop under different conditions, with characteristic features that depend on the substrate material, the ion beam parameters, and the processing conditions. Because the patterns develop spontaneously, without applying any external mask or template, their formation is the expression of a dynamic balance among fundamental surface kinetic processes, e.g., erosion of material from the surface, ion-induced defect creation, and defect-mediated evolution of the surface morphology. In recent years, a comprehensive picture of the different kinetic mechanisms that control the different types of patterns that form has begun to emerge. In this article, we provide a review of different mechanisms that have been proposed and how they fit together in terms of the kinetic regimes in which they dominate. These are grouped into regions of behavior dominated by the directionality of the ion beam, the crystallinity of the surface, the barriers to surface roughening, and nonlinear effects. In sections devoted to each type of behavior, we relate experimental observations of patterning in these regimes to predictions of continuum models and to computer simulations. A comparison between theory and experiment is used to highlight strengths and weaknesses in our understanding. We also discuss the patterning behavior that falls outside the scope of the current understanding and opportunities for advancement

Growth and production kinetics of human x mouse and mouse hybridoma cells at reduced temperature and serum content.

Science.gov (United States)

Borth, N; Heider, R; Assadian, A; Katinger, H

1992-09-01

The growth and production kinetics of a mouse hybridoma cell line and a human-mouse heterohybridoma were analyzed under conditions of reduced temperature and serum content. The mouse hybridoma P24 had a constant cell specific production rate and RNA content, while the heterohybridoma 3D6-LC4 showed growth associated production kinetics and an increased RNA content at higher growth rates. This behaviour of 3D6-LC4 cells can be explained by the unusual cell cycle kinetics of this line, which can be arrested in any phase under growth limiting conditions, so that a low growth rate does not result in a greater portion of high producing G1-phase cells. Substrate limitation changes the cell cycle distribution of this cell line to a greater extent than low temperature or serum content, which indicates that this stress factor exerts a greater physiological control than assumed.

Particle growth kinetics over the Amazon rainforest

Science.gov (United States)

Pinterich, T.; Andreae, M. O.; Artaxo, P.; Kuang, C.; Longo, K.; Machado, L.; Manzi, A. O.; Martin, S. T.; Mei, F.; Pöhlker, C.; Pöhlker, M. L.; Poeschl, U.; Shilling, J. E.; Shiraiwa, M.; Tomlinson, J. M.; Zaveri, R. A.; Wang, J.

2016-12-01

Aerosol particles larger than 100 nm play a key role in global climate by acting as cloud condensation nuclei (CCN). Most of these particles, originated from new particle formation or directly emitted into the atmospheric, are initially too small to serve as CCN. These small particles grow to CCN size mainly through condensation of secondary species. In one extreme, the growth is dictated by kinetic condensation of very low-volatility compounds, favoring the growth of the smallest particles; in the other extreme, the process is driven by Raoult's law-based equilibrium partitioning of semi-volatile organic compound, favoring the growth of larger particles. These two mechanisms can lead to very different production rates of CCN. The growth of particles depends on a number of parameters, including the volatility of condensing species, particle phase, and diffusivity inside the particles, and this process is not well understood in part due to lack of ambient data. Here we examine atmospheric particle growth using high-resolution size distributions measured onboard the DOE G-1 aircraft during GoAmazon campaign, which took place from January 2014 to December 2015 near Manaus, Brazil, a city surrounded by natural forest for over 1000 km in every direction. City plumes are clearly identified by the strong enhancement of nucleation and Aitken mode particle concentrations over the clean background. As the plume traveled downwind, particle growth was observed, and is attributed to condensation of secondary species and coagulation (Fig.1). Observed aerosol growth is modeled using MOSAIC (Model for Simulating Aerosol Interactions and Chemistry), which dynamically partitions multiple compounds to all particle size bins by taking into account compound volatility, gas-phase diffusion, interfacial mass accommodation, particle-phase diffusion, and particle-phase reaction. The results from both wet and dry seasons will be discussed.

The surface oxidation kinetics of zirconium-niobium alloys and aα-Fe with prevailing cubical texture

International Nuclear Information System (INIS)

Mukhambetov, D.G.; Kargin, D.B.; Chalaya, O. V.; Berber, N.N.

2002-01-01

It is known, that the kinetics of oxidation of zirconium at formed heating is characterized by two consecutive stages. At the initial stage the thin protecting film will be derived. The relation of its depth from time h (t) is described predominantly by parabolic law. Some time later there can be a transition to the linear law of oxidation. The time moment divided these areas on the kinetic relation is called as a point of break. The film is formed at the second stage, has a developed grid of pores or cracks, can be flake away and be crumbled by losing its protective properties. At the oxidation of the surface shells of the heat generating elements and the technological channels of atomic boilers both stages are proceeded simultaneously. This phenomenon is called modular corrosion. Its consequences can be dangerous for the equipment. Its mechanism is not clear till now. Similar dependencies h(t), with the break point, beginning from which the thin film is transformed into the thick one were found by us at the oxidation α-Fe with prevailing cubical texture. The task of the work was to study the oxide film growth laws in order to clarify the mechanisms of transition of the thin film into the oxide layer on the α-Fe surface and Zr-Nb alloy modular corrosion emergence. Low-carbonate steel with contents 99.43 % of α-Fe was used as a model object of our research. In the texture of the steel surface planar direction [100] was prevalent. Its part accounted for about 40 %. The isothermal air oxidation was carried out in the interval of 450-500 deg. C . Phase composition of the film was determined with X-ray diffraction. The mathematical treatment of the dependencies h(t) obtained by experiment showed that the kinetics of the film growth can be conditionally divided into 4-stages. The initial stage is described by function logarithmic function, the other stages - by the power mode h n =A n ·t, namely, the second stage - is described by function close to cubical (n≅3

A comparative study of ethylene growth response kinetics in eudicots and monocots reveals a role for gibberellin in growth inhibition and recovery.

Science.gov (United States)

Kim, Joonyup; Wilson, Rebecca L; Case, J Brett; Binder, Brad M

2012-11-01

Time-lapse imaging of dark-grown Arabidopsis (Arabidopsis thaliana) hypocotyls has revealed new aspects about ethylene signaling. This study expands upon these results by examining ethylene growth response kinetics of seedlings of several plant species. Although the response kinetics varied between the eudicots studied, all had prolonged growth inhibition for as long as ethylene was present. In contrast, with continued application of ethylene, white millet (Panicum miliaceum) seedlings had a rapid and transient growth inhibition response, rice (Oryza sativa 'Nipponbare') seedlings had a slow onset of growth stimulation, and barley (Hordeum vulgare) had a transient growth inhibition response followed, after a delay, by a prolonged inhibition response. Growth stimulation in rice correlated with a decrease in the levels of rice ETHYLENE INSENSTIVE3-LIKE2 (OsEIL2) and an increase in rice F-BOX DOMAIN AND LRR CONTAINING PROTEIN7 transcripts. The gibberellin (GA) biosynthesis inhibitor paclobutrazol caused millet seedlings to have a prolonged growth inhibition response when ethylene was applied. A transient ethylene growth inhibition response has previously been reported for Arabidopsis ethylene insensitive3-1 (ein3-1) eil1-1 double mutants. Paclobutrazol caused these mutants to have a prolonged response to ethylene, whereas constitutive GA signaling in this background eliminated ethylene responses. Sensitivity to paclobutrazol inversely correlated with the levels of EIN3 in Arabidopsis. Wild-type Arabidopsis seedlings treated with paclobutrazol and mutants deficient in GA levels or signaling had a delayed growth recovery after ethylene removal. It is interesting to note that ethylene caused alterations in gene expression that are predicted to increase GA levels in the ein3-1 eil1-1 seedlings. These results indicate that ethylene affects GA levels leading to modulation of ethylene growth inhibition kinetics.

Barrierless growth of precursor-free, ultrafast laser-fragmented noble metal nanoparticles by colloidal atom clusters - A kinetic in situ study.

Science.gov (United States)

Jendrzej, Sandra; Gökce, Bilal; Amendola, Vincenzo; Barcikowski, Stephan

2016-02-01

Unintended post-synthesis growth of noble metal colloids caused by excess amounts of reactants or highly reactive atom clusters represents a fundamental problem in colloidal chemistry, affecting product stability or purity. Hence, quantified kinetics could allow defining nanoparticle size determination in dependence of the time. Here, we investigate in situ the growth kinetics of ps pulsed laser-fragmented platinum nanoparticles in presence of naked atom clusters in water without any influence of reducing agents or surfactants. The nanoparticle growth is investigated for platinum covering a time scale of minutes to 50days after nanoparticle generation, it is also supplemented by results obtained from gold and palladium. Since a minimum atom cluster concentration is exceeded, a significant growth is determined by time resolved UV/Vis spectroscopy, analytical disc centrifugation, zeta potential measurement and transmission electron microscopy. We suggest a decrease of atom cluster concentration over time, since nanoparticles grow at the expense of atom clusters. The growth mechanism during early phase (<1day) of laser-synthesized colloid is kinetically modeled by rapid barrierless coalescence. The prolonged slow nanoparticle growth is kinetically modeled by a combination of coalescence and Lifshitz-Slyozov-Wagner kinetic for Ostwald ripening, validated experimentally by the temperature dependence of Pt nanoparticle size and growth quenching by Iodide anions. Copyright © 2015. Published by Elsevier Inc.

Kinetic and biochemical studies on tumor growth. Comprehensive progress report, October 1, 1967--April 1, 1975

International Nuclear Information System (INIS)

Dethlefsen, L.A.

1975-01-01

The growth kinetics of four lines of the C3H mammary tumor have been studied by standard autoradiographic procedures in combination with volumetric growth curve analysis. Thus, such parameters as volumetric doubling time, mean cell generation time, growth fraction, and cell loss have been measured. Two of these lines (Slow and S102F) are currently being used for studying hormone responsiveness both in vivo and in vitro and the perturbed kinetics following insults with therapeutic agents. The respective values for the above parameters are: Slow; 21.0 days, 34 hours, 0.20, 9 percent per day, and S102F; 2.5 days, 17 hours, 0.60, 27 percent per day. A direct method ( 125 I-IUdR Method) for measuring cell loss has also been developed. This method consists of injecting mice with 125 I-IUdR and then measuring the loss of 125 I-activity from the tumor. The antigenic status of these tumors has been studied as one possible factor underlying the different growth kinetics. The mouse's immunological system was either suppressed (thymectomy and whole-body x-irradiation) or stimulated (previous exposure to tumor cells) and the percent takes, latent period, and growth rates measured. There was no evidence for a strong antigenic factor in any of these tumors. Hydroxyurea is being used as a tool for studying the perturbed cellular kinetics of the duodenum and the Slow and S102F tumors. The methods used are autoradiography, volumetric growth curve analysis, and measurements of the rates of DNA synthesis. Hormone effects on growth have been studied. Insulin had no effect but large doses of corticosterone (20 μg/ml and greater) were inhibitory and prolactin appeared to partially reverse these effects in the Slow line. (U.S.)

Microstructure development in Kolmogorov, Johnson-Mehl, and Avrami nucleation and growth kinetics

Science.gov (United States)

Pineda, Eloi; Crespo, Daniel

1999-08-01

A statistical model with the ability to evaluate the microstructure developed in nucleation and growth kinetics is built in the framework of the Kolmogorov, Johnson-Mehl, and Avrami theory. A populational approach is used to compute the observed grain-size distribution. The impingement process which delays grain growth is analyzed, and the effective growth rate of each population is estimated considering the previous grain history. The proposed model is integrated for a wide range of nucleation and growth protocols, including constant nucleation, pre-existing nuclei, and intermittent nucleation with interface or diffusion-controlled grain growth. The results are compared with Monte Carlo simulations, giving quantitative agreement even in cases where previous models fail.

Liquid phase electro epitaxy growth kinetics of GaAs-A three-dimensional numerical simulation study

International Nuclear Information System (INIS)

Mouleeswaran, D.; Dhanasekaran, R.

2006-01-01

A three-dimensional numerical simulation study for the liquid phase electro epitaxial growth kinetic of GaAs is presented. The kinetic model is constructed considering (i) the diffusive and convective mass transport, (ii) the heat transfer due to thermoelectric effects such as Peltier effect, Joule effect and Thomson effect, (iii) the electric current distribution with electromigration and (iv) the fluid flow coupled with concentration and temperature fields. The simulations are performed for two configurations namely (i) epitaxial growth from the arsenic saturated gallium rich growth solution, i.e., limited solution model and (ii) epitaxial growth from the arsenic saturated gallium rich growth solution with polycrystalline GaAs feed. The governing equations of liquid phase electro epitaxy are solved numerically with appropriate initial and boundary conditions using the central difference method. Simulations are performed to determine the following, a concentration profiles of solute atoms (As) in the Ga-rich growth solution, shape of the substrate evolution, the growth rate of the GaAs epitaxial film, the contributions of Peltier effect and electromigration of solute atoms to the growth with various experimental growth conditions. The growth rate is found to increase with increasing growth temperature and applied current density. The results are discussed in detail

Growth kinetics of racemic heptahelicene-2-carboxylic acid nanowires on calcite (104)

Czech Academy of Sciences Publication Activity Database

Einax, M.; Richter, T.; Nimmrich, M.; Rahe, P.; Stará, Irena G.; Starý, Ivo; Kühnle, A.; Maass, P.

2016-01-01

Roč. 145, č. 13 (2016), č. článku 134702. ISSN 0021-9606 Institutional support: RVO:61388963 Keywords : heptahelicene-2-carboxylic acid nanowires * nc-AFM * calcite * growth kinetics Subject RIV: CC - Organic Chemistry Impact factor: 2.965, year: 2016

Interplay of bistable kinetics of gene expression during cellular growth

International Nuclear Information System (INIS)

Zhdanov, Vladimir P

2009-01-01

In cells, the bistable kinetics of gene expression can be observed on the level of (i) one gene with positive feedback between protein and mRNA production, (ii) two genes with negative mutual feedback between protein and mRNA production, or (iii) in more complex cases. We analyse the interplay of two genes of type (ii) governed by a gene of type (i) during cellular growth. In particular, using kinetic Monte Carlo simulations, we show that in the case where gene 1, operating in the bistable regime, regulates mutually inhibiting genes 2 and 3, also operating in the bistable regime, the latter genes may eventually be trapped either to the state with high transcriptional activity of gene 2 and low activity of gene 3 or to the state with high transcriptional activity of gene 3 and low activity of gene 2. The probability to get to one of these states depends on the values of the model parameters. If genes 2 and 3 are kinetically equivalent, the probability is equal to 0.5. Thus, our model illustrates how different intracellular states can be chosen at random with predetermined probabilities. This type of kinetics of gene expression may be behind complex processes occurring in cells, e.g., behind the choice of the fate by stem cells

Plasma surface functionalization and dyeing kinetics of Pan-Pmma copolymers

OpenAIRE

Labay, C.; Canal, C.; Rodríguez, C.; Caballero, G.; Canal, J.M.

2013-01-01

Fiber surface modification with air corona plasma has been studied through dyeing kinetics under isothermal conditions at 30 °C on an acrylic-fiber fabric with a cationic dye (CI Basic Blue 3) analyzing the absorption, desorption and fixing on the surface of molecules having defined cationic character. The initial dyeing rate in the first 60 s indicates an increase of 58.3% in the dyeing rate due to the effect of corona plasma on the acrylic fiber surface. At the end of the dyeing process...

Kinetics of growth and sugar consumption in yeasts.

Science.gov (United States)

van Dijken, J P; Weusthuis, R A; Pronk, J T

1993-01-01

An overview is presented of the steady- and transient state kinetics of growth and formation of metabolic byproducts in yeasts. Saccharomyces cerevisiae is strongly inclined to perform alcoholic fermentation. Even under fully aerobic conditions, ethanol is produced by this yeast when sugars are present in excess. This so-called 'Crabtree effect' probably results from a multiplicity of factors, including the mode of sugar transport and the regulation of enzyme activities involved in respiration and alcoholic fermentation. The Crabtree effect in S. cerevisiae is not caused by an intrinsic inability to adjust its respiratory activity to high glycolytic fluxes. Under certain cultivation conditions, for example during growth in the presence of weak organic acids, very high respiration rates can be achieved by this yeast. S. cerevisiae is an exceptional yeast since, in contrast to most other species that are able to perform alcoholic fermentation, it can grow under strictly anaerobic conditions. 'Non-Saccharomyces' yeasts require a growth-limiting supply of oxygen (i.e. oxygen-limited growth conditions) to trigger alcoholic fermentation. However, complete absence of oxygen results in cessation of growth and therefore, ultimately, of alcoholic fermentation. Since it is very difficult to reproducibly achieve the right oxygen dosage in large-scale fermentations, non-Saccharomyces yeasts are therefore not suitable for large-scale alcoholic fermentation of sugar-containing waste streams. In these yeasts, alcoholic fermentation is also dependent on the type of sugar. For example, the facultatively fermentative yeast Candida utilis does not ferment maltose, not even under oxygen-limited growth conditions, although this disaccharide supports rapid oxidative growth.

Kinetic-energy induced smoothening and delay of epitaxial breakdown in pulsed-laser deposition

International Nuclear Information System (INIS)

Shin, Byungha; Aziz, Michael J.

2007-01-01

We have isolated the effect of kinetic energy of depositing species from the effect of flux pulsing during pulsed-laser deposition (PLD) on surface morphology evolution of Ge(001) homoepitaxy at low temperature (100 deg. C). Using a dual molecular beam epitaxy (MBE) PLD chamber, we compare morphology evolution from three different growth methods under identical experimental conditions except for the differing nature of the depositing flux: (a) PLD with average kinetic energy 300 eV (PLD-KE); (b) PLD with suppressed kinetic energy comparable to thermal evaporation energy (PLD-TH); and (c) MBE. The thicknesses at which epitaxial breakdown occurs are ranked in the order PLD-KE>MBE>PLD-TH; additionally, the surface is smoother in PLD-KE than in MBE. The surface roughness of the films grown by PLD-TH cannot be compared due to the early epitaxial breakdown. These results demonstrate convincingly that kinetic energy is more important than flux pulsing in the enhancement of epitaxial growth, i.e., the reduction in roughness and the delay of epitaxial breakdown

A comparative study of post-irradiation growth kinetics of spheroids and monolayers

International Nuclear Information System (INIS)

Dertinger, J.; Luecke-Huhle, C.

1975-01-01

Post-irradiation growth kinetics of γ-irradiated spheroid and monolayer cells in exponential growth phase was investigated by means of dose-response curves based on cell counts after specified time intervals following irradiation. A mathematical model of cell-growth after irradiation was fitted to these curves. The model parameters (related to division delay and growth of non-surviving cells) obtained from this analysis consistently indicated increasing resistance to sub-lethal damage of cells cultured as multicellular spheroids under conditions of increasing three-dimensional contact. In contrast, no indication of an increased radiation-resistance was found with cells cultured on a substratum under a variety of conditions. (author)

Real-time kinetic modeling of YSZ thin film roughness deposited by e-beam evaporation technique

International Nuclear Information System (INIS)

Galdikas, A.; Cerapaite-Trusinskiene, R.; Laukaitis, G.; Dudonis, J.

2008-01-01

In the present study, the process of yttrium-stabilized zirconia (YSZ) thin films deposition on optical quartz (SiO 2 ) substrates using e-beam deposition technique controlling electron gun power is analyzed. It was found that electron gun power influences the non-monotonous kinetics of YSZ film surface roughness. The evolution of YSZ thin film surface roughness was analyzed by a kinetic model. The model is based on the rate equations and includes processes of surface diffusion of the adatoms and the clusters, nucleation, growth and coalescence of islands in the case of thin film growth in Volmer-Weber mode. The analysis of the experimental results done by modeling explains non-monotonous kinetics and dependence of the surface roughness on the electron gun power. A good quantitative agreement with experimental results is obtained taking into account the initial roughness of the substrate surface and the amount of the clusters in the flux of evaporated material.

Evaporation kinetics of sessile water droplets on micropillared superhydrophobic surfaces.

Science.gov (United States)

Xu, Wei; Leeladhar, Rajesh; Kang, Yong Tae; Choi, Chang-Hwan

2013-05-21

Evaporation modes and kinetics of sessile droplets of water on micropillared superhydrophobic surfaces are experimentally investigated. The results show that a constant contact radius (CCR) mode and a constant contact angle (CCA) mode are two dominating evaporation modes during droplet evaporation on the superhydrophobic surfaces. With the decrease in the solid fraction of the superhydrophobic surfaces, the duration of a CCR mode is reduced and that of a CCA mode is increased. Compared to Rowan's kinetic model, which is based on the vapor diffusion across the droplet boundary, the change in a contact angle in a CCR (pinned) mode shows a remarkable deviation, decreasing at a slower rate on the superhydrophobic surfaces with less-solid fractions. In a CCA (receding) mode, the change in a contact radius agrees well with the theoretical expectation, and the receding speed is slower on the superhydrophobic surfaces with lower solid fractions. The discrepancy between experimental results and Rowan's model is attributed to the initial large contact angle of a droplet on superhydrophobic surfaces. The droplet geometry with a large contact angle results in a narrow wedge region of air along the contact boundary, where the liquid-vapor diffusion is significantly restricted. Such an effect becomes minor as the evaporation proceeds with the decrease in a contact angle. In both the CCR and CCA modes, the evaporative mass transfer shows the linear relationship between mass(2/3) and evaporation time. However, the evaporation rate is slower on the superhydrophobic surfaces, which is more significant on the surfaces with lower solid fractions. As a result, the superhydrophobic surfaces slow down the drying process of a sessile droplet on them.

A novel microculture kinetic assay (MiCK assay) for malignant cell growth and chemosensitivity.

Science.gov (United States)

Kravtsov, V D

1994-01-01

The THERMOmax microplate reader was adapted for monitoring the growth kinetics of human leukaemic OCI/AML-2 and mouse tumour J-774.1 cell lines in continuous culture. Fluid evaporation from wells, CO2 escape and contamination were prevented by hermetic sealing of the microcultures in wells of a 96-well microplate, thus enabling the cells to grow exponentially for 72 h under the conditions of the incubated microplate reader. For both OCI/AML-2 cells, which grow in suspension, and adherent J-774.1 cells, a linear correlation was demonstrated between the number of unstained cells seeded in a given microplate well and the optical density (OD) of that well. Therefore, the OD/time curve of the culture could be deemed to be its growth curve. By the use of the linear fit equation, the actual number of the cells in the wells was computable at any time point of the assay. In the chemosensitivity test, an inhibitory effect of ARA-C on the growth of the cells could be estimated by viewing of the growth curves plotted on the screen. The maximum kinetic rates (Vmax) of the curves in the control and the ARA-C-treated wells were compared, yielding a growth inhibition index (GII). Comparison of results of the kinetic chemosensitivity assay with those of a [3H]thymidine incorporation assay revealed that the novel assay is suitable for precise quantitation of the cell chemosensitivity, is more informative and has the added technical advantage of performance without recourse to radioactive or chemically hazardous substances.

Experimental investigation on oxidation kinetics of germanium by ozone

Energy Technology Data Exchange (ETDEWEB)

Wang, Xiaolei, E-mail: wangxiaolei@ime.ac.cn [Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China); Zhao, Zhiqian; Xiang, Jinjuan [Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China); Wang, Wenwu, E-mail: wangwenwu@ime.ac.cn [Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China); Zhang, Jing, E-mail: zhangj@ncut.edu.cn [Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China); Microelectronics Department, North China University of Technology, Beijing 100041 (China); Zhao, Chao; Ye, Tianchun [Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences, Beijing 100029 (China)

2016-12-30

Highlights: • Kinetics mechanism of Ge surface oxidation by ozone at low temperature is experimentally investigated. • The growth process contains initially linear growth region and following parabolic growth region. • The GeO{sub x} thickness vs. oxidation time plot obeys the well-known Deal-Grove or linear parabolic model. • The linear growth region includes the oxidation of two topmost Ge layers, and the oxidation of third layer and following layers of Ge is diffusion limited. • The activation energies for linear and parabolic regions are 0.04 and 0.55 eV, respectively. - Abstract: Oxidation kinetics of germanium surface by ozone at low temperature (≤400 °C) is experimentally investigated. The growth process contains two regions: initial linear growth region and following parabolic growth region. The GeO{sub x} thickness vs. oxidation time plot obeys the well-known Deal-Grove or linear parabolic model. The linear growth region contains reaction of oxygen atoms with surface bond and back bonds of outmost Ge layer. And the activation energy is experimentally estimated to be 0.06 eV. Such small activation energy indicates that the linear growth region is nearly barrier-less. The parabolic growth region starts when the oxygen atoms diffuse into back bonds of second outmost Ge layers. And the activation energy for this process is found to be 0.54 eV. Furthermore, in the ozone oxidation it is not O{sub 3} molecules but O radicals that go through the GeO{sub x} film.

Domain-growth kinetics and aspects of pinning: A Monte Carlo simulation study

DEFF Research Database (Denmark)

Castán, T.; Lindgård, Per-Anker

1991-01-01

By means of Monte Carlo computer simulations we study the domain-growth kinetics after a quench across a first-order line to very low and moderate temperatures in a multidegenerate system with nonconserved order parameter. The model is a continuous spin model relevant for martensitic transformati......By means of Monte Carlo computer simulations we study the domain-growth kinetics after a quench across a first-order line to very low and moderate temperatures in a multidegenerate system with nonconserved order parameter. The model is a continuous spin model relevant for martensitic...... to cross over from n = 1/4 at T approximately 0 to n = 1/2 with temperature for models with pinnings of types (a) and (b). For topological pinnings at T approximately 0, n is consistent with n = 1/8, a value conceivable for several levels of hierarchically interrelated domain-wall movement. When...

Growth kinetics of tin oxide nanocrystals in colloidal suspensions under hydrothermal conditions

International Nuclear Information System (INIS)

Lee, Eduardo J.H.; Ribeiro, Caue; Longo, Elson; Leite, Edson R.

2006-01-01

Colloidal suspensions of tin oxide nanocrystals were synthesized at room temperature by the hydrolysis reaction of tin chloride (II), in an ethanolic solution. The coarsening kinetics of such nanocrystals was studied by submitting the as-prepared suspensions to hydrothermal treatments at temperatures of 100, 150 and 200 deg. C for periods between 60 and 12,000 min. Transmission electron microscopy (TEM) was used to characterize the samples (i.e. distribution of nanocrystal size, average particle radius and morphology). The results show that the usual Ostwald ripening coarsening mechanism does not fit well the experimental data, which is an indicative that this process is not significant for SnO 2 nanocrystals, in the studied experimental conditions. The morphology evolution of the nanocrystals upon hydrothermal treatment indicates that growth by oriented attachment (OA) should be significant. A kinetic model that describes OA growth is successfully applied to fit the data

Film growth kinetics and electric field patterning during electrospray deposition of block copolymer thin films

Science.gov (United States)

Toth, Kristof; Hu, Hanqiong; Choo, Youngwoo; Loewenberg, Michael; Osuji, Chinedum

The delivery of sub-micron droplets of dilute polymer solutions to a heated substrate by electrospray deposition (ESD) enables precisely controlled and continuous growth of block copolymer (BCP) thin films. Here we explore patterned deposition of BCP films by spatially varying the electric field at the substrate using an underlying charged grid, as well as film growth kinetics. Numerical analysis was performed to examine pattern fidelity by considering the trajectories of charged droplets during flight through imposed periodic field variations in the vicinity of the substrate. Our work uncovered an unexpected modality for improving the resolution of the patterning process via stronger field focusing through the use of a second oppositely charged grid beneath a primary focusing array, with an increase in highly localized droplet deposition on the intersecting nodes of the grid. Substrate coverage kinetics are considered for homopolymer deposition in the context of simple kinetic models incorporating temperature and molecular weight dependence of diffusivity. By contrast, film coverage kinetics for block copolymer depositions are additionally convoluted with preferential wetting and thickness-periodicity commensurability effects. NSF GRFP.

Simulation of uranium oxides reduction kinetics by hydrogen. Reactivities of germination and growth; Modelisation de la cinetique de reduction d`oxydes d`uranium par l`hydrogene. Reactivites de germination et de croissance

Energy Technology Data Exchange (ETDEWEB)

Brun, C

1997-12-04

The aim of this work is to simulate the reduction by hydrogen of the tri-uranium octo-oxide U{sub 3}O{sub 8} (obtained by uranium trioxide calcination) into uranium dioxide. The kinetics curves have been obtained by thermal gravimetric analysis, the hydrogen and steam pressures being defined. The geometrical modeling which has allowed to explain the trend of the kinetics curves and of the velocity curves is an anisotropic germination-growth modeling. The powder is supposed to be formed of spherical grains with the same radius. The germs of the new UO{sub 2} phase appear at the surface of the U{sub 3}O{sub 8} grains with a specific germination frequency. The growth reactivity is anisotropic and is very large in the tangential direction to the grains surface. Then, the uranium dioxide growths inside the grain and the limiting step is the grain surface. The variations of the growth reactivity and of the germination specific frequency in terms of the gases partial pressures and of the temperature have been explained by two different mechanisms. The limiting step of the growth mechanism is the desorption of water in the uranium dioxide surface. Concerning the germination mechanism the limiting step is a water desorption too but in the tri-uranium octo-oxide surface. The same geometrical modeling and the same germination and growth mechanisms have been applied to the reduction of a tri-uranium octo-oxide obtained by calcination of hydrated uranium trioxide. The values of the germination specific frequency of this solid are nevertheless weaker than those of the solid obtained by direct calcination of the uranium trioxide. (O.M.) 45 refs.

Optimal design of multistage chemostats in series using different microbial growth kinetics

Energy Technology Data Exchange (ETDEWEB)

Qasim, Muhammad [Petroleum Engineering Technology, Abu Dhabi Polytechnic (United Arab Emirates)

2013-07-01

In this paper, the optimum design of multistage chemostats (CSTRs) was investigated. The optimal design was based on the minimum overall reactor volume using different volume for each chemostat. The paper investigates three different microbial growth kinetics; Monod kinetics, Contois kinetics and the Logistic equation. The total dimensionless residence time (theta Total) was set as the optimization objective function that was minimized by varying the intermediate dimensionless substrate concentration (alfa i). The effect of inlet substrate concentration (S0) to the first reactor on the optimized total dimensionless residence time was investigated at a constant conversion of 0.90. In addition, the effect of conversion on the optimized total dimensionless residence time was also investigated at constant inlet substrate concentration (S0). For each case, optimization was done using up to five chemostats in series.

A two-phase kinetic model for fungal growth in solid-state cultivation

NARCIS (Netherlands)

Hamidi-Esfahani, Z.; Hejazi, P.; Abbas Shojaosadati, S.; Hoogschagen, M.J.; Vasheghani-Farahani, E.; Rinzema, A.

2007-01-01

A new two-phase kinetic model including exponential and logistic models was applied to simulate the growth rate of fungi at various temperatures. The model parameters, expressed as a function of temperature, were determined from the oxygen consumption rate of Aspergillus niger during cultivation on

Kinetics of Si and Ge nanowires growth through electron beam evaporation

Directory of Open Access Journals (Sweden)

Artoni Pietro

2011-01-01

Full Text Available Abstract Si and Ge have the same crystalline structure, and although Si-Au and Ge-Au binary alloys are thermodynamically similar (same phase diagram, with the eutectic temperature of about 360°C, in this study, it is proved that Si and Ge nanowires (NWs growth by electron beam evaporation occurs in very different temperature ranges and fluence regimes. In particular, it is demonstrated that Ge growth occurs just above the eutectic temperature, while Si NWs growth occurs at temperature higher than the eutectic temperature, at about 450°C. Moreover, Si NWs growth requires a higher evaporated fluence before the NWs become to be visible. These differences arise in the different kinetics behaviors of these systems. The authors investigate the microscopic growth mechanisms elucidating the contribution of the adatoms diffusion as a function of the evaporated atoms direct impingement, demonstrating that adatoms play a key role in physical vapor deposition (PVD NWs growth. The concept of incubation fluence, which is necessary for an interpretation of NWs growth in PVD growth conditions, is highlighted.

Kinetics of Si and Ge nanowires growth through electron beam evaporation.

Science.gov (United States)

Artoni, Pietro; Pecora, Emanuele Francesco; Irrera, Alessia; Priolo, Francesco

2011-02-21

Si and Ge have the same crystalline structure, and although Si-Au and Ge-Au binary alloys are thermodynamically similar (same phase diagram, with the eutectic temperature of about 360°C), in this study, it is proved that Si and Ge nanowires (NWs) growth by electron beam evaporation occurs in very different temperature ranges and fluence regimes. In particular, it is demonstrated that Ge growth occurs just above the eutectic temperature, while Si NWs growth occurs at temperature higher than the eutectic temperature, at about 450°C. Moreover, Si NWs growth requires a higher evaporated fluence before the NWs become to be visible. These differences arise in the different kinetics behaviors of these systems. The authors investigate the microscopic growth mechanisms elucidating the contribution of the adatoms diffusion as a function of the evaporated atoms direct impingement, demonstrating that adatoms play a key role in physical vapor deposition (PVD) NWs growth. The concept of incubation fluence, which is necessary for an interpretation of NWs growth in PVD growth conditions, is highlighted.

Analytical solution of Luedeking-Piret equation for a batch fermentation obeying Monod growth kinetics.

Science.gov (United States)

Garnier, Alain; Gaillet, Bruno

2015-12-01

Not so many fermentation mathematical models allow analytical solutions of batch process dynamics. The most widely used is the combination of the logistic microbial growth kinetics with Luedeking-Piret bioproduct synthesis relation. However, the logistic equation is principally based on formalistic similarities and only fits a limited range of fermentation types. In this article, we have developed an analytical solution for the combination of Monod growth kinetics with Luedeking-Piret relation, which can be identified by linear regression and used to simulate batch fermentation evolution. Two classical examples are used to show the quality of fit and the simplicity of the method proposed. A solution for the combination of Haldane substrate-limited growth model combined with Luedeking-Piret relation is also provided. These models could prove useful for the analysis of fermentation data in industry as well as academia. © 2015 Wiley Periodicals, Inc.

On the kinetic barriers of graphene homo-epitaxy

International Nuclear Information System (INIS)

Zhang, Wei; Yu, Xinke; Xie, Ya-Hong; Cahyadi, Erica; Ratsch, Christian

2014-01-01

The diffusion processes and kinetic barriers of individual carbon adatoms and clusters on graphene surfaces are investigated to provide fundamental understanding of the physics governing epitaxial growth of multilayer graphene. It is found that individual carbon adatoms form bonds with the underlying graphene whereas the interaction between graphene and carbon clusters, consisting of 6 atoms or more, is very weak being van der Waals in nature. Therefore, small carbon clusters are quite mobile on the graphene surfaces and the diffusion barrier is negligibly small (∼6 meV). This suggests the feasibility of high-quality graphene epitaxial growth at very low growth temperatures with small carbon clusters (e.g., hexagons) as carbon source. We propose that the growth mode is totally different from 3-dimensional bulk materials with the surface mobility of carbon hexagons being the highest over graphene surfaces that gradually decreases with further increase in cluster size

The interaction of C60 on Si(111 7x7 studied by Supersonic Molecular Beams: interplay between precursor kinetic energy and substrate temperature in surface activated processes.

Directory of Open Access Journals (Sweden)

Lucrezia eAversa

2015-06-01

Full Text Available Buckminsterfullerene (C60 is a molecule fully formed of carbon that can be used, owing to its electronic and mechanical properties, as clean precursor for the growth of carbon-based materials, ranging from -conjugated systems (graphenes to synthesized species, e.g. carbides such as silicon carbide (SiC. To this goal, C60 cage rupture is the main physical process that triggers material growth. Cage breaking can be obtained either thermally by heating up the substrate to high temperatures (630°C, after C60 physisorption, or kinetically by using Supersonic Molecular Beam Epitaxy (SuMBE techniques. In this work, aiming at demonstrating the growth of SiC thin films by C60 supersonic beams, we present the experimental investigation of C60 impacts on Si(111 7x7 kept at 500°C for translational kinetic energies ranging from 18 to 30 eV. The attained kinetically activated synthesis of SiC submonolayer films is probed by in-situ surface electron spectroscopies (XPS and UPS. Furthermore, in these experimental conditions the C60-Si(111 7×7 collision has been studied by computer simulations based on a tight-binding approximation to Density Functional Theory, DFT. Our theoretical and experimental findings point towards a kinetically driven growth of SiC on Si, where C60 precursor kinetic energy plays a crucial role, while temperature is relevant only after cage rupture to enhance Si and carbon reactivity. In particular, we observe a counterintuitive effect in which for low kinetic energy (below 22 eV, C60 bounces back without breaking more effectively at high temperature due to energy transfer from excited phonons. At higher kinetic energy (22 < K < 30 eV, for which cage rupture occurs, temperature enhances reactivity without playing a major role in the cage break. These results are in good agreement with ab-initio molecular dynamics simulations. SuMBE is thus a technique able to drive materials growth at low temperature regime.

Growth kinetics of tetragonal and monoclinic ZrO{sub 2} crystallites in 3 mol% yttria partially stabilized ZrO{sub 2} (3Y-PSZ) precursor powder

Energy Technology Data Exchange (ETDEWEB)

Kuo, Chih-Wei [Department of Resources Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Lee, Kuen-Chan [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan (China); Yen, Feng-Lin, E-mail: flyen@kmu.edu.tw [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan (China); Shen, Yun-Hwei [Department of Resources Engineering, National Cheng Kung University, 1 Ta-Hsueh Road, Tainan 70101, Taiwan (China); Lee, Huey-Er [Department of Dentistry, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan (China); Department of Dentistry, Kaohsiung Medical University, Chung Ho Memorial Hospital, 100 Tzyou 1st Road, Kaohsiung 807, Taiwan (China); Wen, Shaw-Bing [General Education Center, Meiho Institute of Technology, 23 Pingguang Road, Neipu, Pingtung 91202, Taiwan (China); Wang, Moo-Chin, E-mail: mcwang@kmu.edu.tw [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 807, Taiwan (China); Stack, Margaret Mary [Department of Mechanical and Aerospace Engineering, University of Strathclyde, 75 Montrose Street, Glasgow (United Kingdom)

2014-04-01

Highlights: • The crystalline structures were composed of tetragonal and monoclinic ZrO{sub 2}. • Growth kinetics of t-ZrO{sub 2} in the 3Y-PSZ precursor powder is described as: D{sub te}{sup 2}=(4.57±0.55)t{sup 0.12±0.02}exp(-((24.79±0.38)×10{sup 3})/(RT) ). • Growth kinetics of m-ZrO{sub 2} in the 3Y-PSZ precursor powder is described as: D{sub m}{sup 2}=(4.40±1.63)t{sup 0.17±0.08}exp(-((66.47±3.97)×10{sup 3})/(RT) ). - Abstract: The growth kinetics of tetragonal and monoclinic ZrO{sub 2} crystallites in 3 mol% yttria partially stabilized ZrO{sub 2} (3Y-PSZ) precursor powder has been investigated using X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area analysis, transmission electron microscopy (TEM) and high resolution TEM (HRTEM). After calcination of the 3Y-PSZ precursor powder between 773 and 1073 K for 2 h, the crystalline structures were composed of tetragonal and monoclinic ZrO{sub 2} as the primary and secondary phases, respectively. When the 3Y-PSZ precursor powder was calcined at 773 K for 2 h, the BET specific surface area was 97.13 m{sup 2}/g, which is equivalent to a particle size of 10.30 nm. The crystallite sizes determined via XRD and BET agreed well, indicating that the powder was virtually non-agglomerated. The growth kinetics of tetragonal and monoclinic ZrO{sub 2} crystallite isothermal growth in the 3Y-PSZ precursor powder are described by: D{sub te}{sup 2}=(4.57±0.55)t{sup 0.12±0.02}exp(-((24.79±0.38)×10{sup 3})/(RT) ) and D{sub m}{sup 2}=(4.40±1.63)t{sup 0.17±0.08}exp(-((66.47±3.97)×10{sup 3})/(RT) ), respectively, for 773K≤T≤1073K. D{sub te} and D{sub m} denote the crystallite size of tetragonal and monoclinic ZrO{sub 2} at time t and temperature T, respectively.

Selection, isolation and growth kinetic study of a bacterial consortium obtained from the Potengi mangrove in the presence of crude oil

Energy Technology Data Exchange (ETDEWEB)

Costa, C.C.; Vaz, M.R.F.; Santos, E.S.; Macedo, G.R. [Universidade Federal do Rio Grande do Norte (UFRN), Natal, RN (Brazil). Dept. de Engenharia Quimica], E-mail: natcintia@gmail.com; Costa, J.G. da [Universidade Federal do Amazonas (UFAM), Coari, AM (Brazil). Inst. de Saude e Biotecnologia

2011-10-15

The selection, isolation and kinetic study of a bacterial consortium obtained from a sample of soil from the Potengi mangrove, located in the city of Natal, Rio Grande do Norte, Brazil, has been carried out using the enrichment culture technique to observe aspects such as the evaluation of main growth parameters. The kinetic study used a rotary incubator shaker at 150rpm, under 30 deg C. The bacterial consortium isolated from the estuary of the Potengi River showed a good acclimation in minimum mineral medium with 1% (v/v) of oil. The cell concentration reached 2.55 g/L at 16h of cultivation and surface tension dropped. The maximum productivity in cells obtained was of 0.3 g/L.h, the specific velocity of growth was of 0.075h{sup -1}, with a generation time (tg) of 9.24h. This study seeks to demonstrate that the consortium can be used as inoculants in biological treatments, capable of reducing the waste's degradation time. (author)

Enhanced Generic Phase-field Model of Irradiation Materials: Fission Gas Bubble Growth Kinetics in Polycrystalline UO2

Energy Technology Data Exchange (ETDEWEB)

Li, Yulan; Hu, Shenyang Y.; Montgomery, Robert O.; Gao, Fei; Sun, Xin

2012-05-30

Experiments show that inter-granular and intra-granular gas bubbles have different growth kinetics which results in heterogeneous gas bubble microstructures in irradiated nuclear fuels. A science-based model predicting the heterogeneous microstructure evolution kinetics is desired, which enables one to study the effect of thermodynamic and kinetic properties of the system on gas bubble microstructure evolution kinetics and morphology, improve the understanding of the formation mechanisms of heterogeneous gas bubble microstructure, and provide the microstructure to macroscale approaches to study their impact on thermo-mechanical properties such as thermo-conductivity, gas release, volume swelling, and cracking. In our previous report 'Mesoscale Benchmark Demonstration, Problem 1: Mesoscale Simulations of Intra-granular Fission Gas Bubbles in UO2 under Post-irradiation Thermal Annealing', we developed a phase-field model to simulate the intra-granular gas bubble evolution in a single crystal during post-irradiation thermal annealing. In this work, we enhanced the model by incorporating thermodynamic and kinetic properties at grain boundaries, which can be obtained from atomistic simulations, to simulate fission gas bubble growth kinetics in polycrystalline UO2 fuels. The model takes into account of gas atom and vacancy diffusion, vacancy trapping and emission at defects, gas atom absorption and resolution at gas bubbles, internal pressure in gas bubbles, elastic interaction between defects and gas bubbles, and the difference of thermodynamic and kinetic properties in matrix and grain boundaries. We applied the model to simulate gas atom segregation at grain boundaries and the effect of interfacial energy and gas mobility on gas bubble morphology and growth kinetics in a bi-crystal UO2 during post-irradiation thermal annealing. The preliminary results demonstrate that the model can produce the equilibrium thermodynamic properties and the morphology of gas

Estimation of the growth kinetics for the cooling crystallisation of paracetamol and ethanol solutions

Science.gov (United States)

Mitchell, Niall A.; Ó'Ciardhá, Clifford T.; Frawley, Patrick J.

2011-08-01

This work details the estimation of the growth kinetics of paracetamol in ethanol solutions for cooling crystallisation processes, by means of isothermal seeded batch experiments. The growth kinetics of paracetamol crystals were evaluated in isolation, with the growth rate assumed to be size independent. Prior knowledge of the Metastable Zone Width (MSZW) was required, so that supersaturation ratios of 1.7-1.1 could be induced in solution without the occurrence of nucleation. The technique involved the utilisation of two in-situ Process Analytical Techniques (PATs), with a Focused Beam Reflectance Measurement (FBRM ®) utilised to ensure that negligible nucleation occurred and an Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) probe employed for online monitoring of solute concentration. Initial Particle Size Distributions (PSDs) were used in conjunction with desupersaturation profiles to determine the growth rate as a function of temperature and supersaturation. Furthermore, the effects of seed loading and size on the crystal growth rate were investigated. A numerical model, incorporating the population balance equation and the method of moments, was utilised to describe the crystal growth process. Experimental parameters were compared to the model simulation, with the accuracy of the model validated by means of the final product PSDs and solute concentration.

Simulation of Nanowires on Metal Vicinal Surfaces: Effect of Growth Parameters and Energetic Barriers

Science.gov (United States)

Hamouda, Ajmi B. H.; Blel, Sonia; Einstein, T. L.

2012-02-01

Growing one-dimensional metal structures is an important task in the investigation of the electronic and magnetic properties of new devices. We used kinetic Monte-Carlo (kMC) method to simulate the formation of nanowires of several metallic and non-metallic adatoms on Cu and Pt vicinal surfaces. We found that mono-atomic chains form on step-edges due to energetic barriers (the so-called Ehrlich-shwoebel and exchange barriers) on step-edge. Creation of perfect wires is found to depend on growth parameters and binding energies. We measure the filling ratio of nanowires for different chemical species in a wide range of temperature and flux. Perfect wires were obtained at lower deposition rate for all tested adatoms, however we notice different temperature ranges. Our results were compared with experimental ones [Gambardella et al., Surf. Sci.449, 93-103 (2000), PRB 61, 2254-2262, (2000)]. We review the role of impurities in nanostructuring of surfaces [Hamouda et al., Phys. Rev. B 83, 035423, (2011)] and discuss the effect of their energetic barriers on the obtained quality of nanowires. Our work provides experimentalists with optimum growth parameters for the creation of a uniform distribution of wires on surfaces.

Morphology and grain structure evolution during epitaxial growth of Ag films on native-oxide-covered Si surface

International Nuclear Information System (INIS)

Hur, Tae-Bong; Kim, Hong Koo; Perello, David; Yun, Minhee; Kulovits, Andreas; Wiezorek, Joerg

2008-01-01

Epitaxial nanocrystalline Ag films were grown on initially native-oxide-covered Si(001) substrates using radio-frequency magnetron sputtering. Mechanisms of grain growth and morphology evolution were investigated. An epitaxially oriented Ag layer (∼5 nm thick) formed on the oxide-desorbed Si surface during the initial growth phase. After a period of growth instability, characterized as kinetic roughening, grain growth stagnation, and increase of step-edge density, a layer of nanocrystalline Ag grains with a uniform size distribution appeared on the quasi-two-dimensional layer. This hierarchical process of film formation is attributed to the dynamic interplay between incoming energetic Ag particles and native oxide. The cyclic interaction (desorption and migration) of the oxide with the growing Ag film is found to play a crucial role in the characteristic evolution of grain growth and morphology change involving an interval of grain growth stagnation

Surfaces of Microparticles in Colloids: Structure and Molecular Adsorption Kinetics

Science.gov (United States)

Dai, Hai-Lung

2002-03-01

Surfaces of micron and sub-micron size particles in liquid solution are probed by second harmonic generation (SHG) facilitated with femtosecond laser pulses. The particles probed include inorganic objects such as carbon black and color pigments, polymeric species like polystyrene beads, and biological systems such as blood cells and ecoli. In the experiments, dye molecules are first adsorbed onto the particle surface to allow generation of second harmonics upon light irradiation. Competition for adsorption between these surface dye molecules and the molecules of interest in the solution is then monitored by the SHG signal to reveal the molecular adsorption kinetics and surface structure. Specifically, surfactant adsorption on polymer surfaces, the structure of carbon black surface, and protein adsorption on biological surfaces, monitored by this technique, will be discussed.

Kinetic effects on the propagation of surface waves and their relevance to the heating of the solar corona

International Nuclear Information System (INIS)

Kuperus, M.; Heyvaerts, J.

1980-01-01

The MHD oscillations of the Alfven type running along surfaces of discontinuity generate motions in the discontinuity region which come rapidly out of phase. It is shown how the mathematical theory of this phase detuning predicts that surface wave should suffer dissipationless damping. Real damping is actually achieved by viscosity or kinetic effects. When detuning has grown to a large enough level, however, oscillations must be described by kinetic theory. Kinetic Alfven waves differ from perfect MHD Alfven waves in that they are able to propagate across the field. A theory of kinetic type oscillations in a finite thickness boundary is described, which predicts that surface waves generate intense kinetic Alfven waves in this boundary. The subsequent dissipation of these waves may be a powerful heating mechanism [fr

MODELING THE INHIBITORY EFFECT OF 1,2-EPOXYOCTANE ON THE GROWTH-KINETICS OF PSEUDOMONAS-OLEOVORANS

NARCIS (Netherlands)

VANDERMEER, AB; MIEDEMA, WA; LUYBEN, KCAM; BEENACKERS, AACM

During the production of 1,2-epoxyoctane from 1-octene by Pseudomonas oleovorans cells, both cell growth and epoxide production are inhibited by the product. To investigate this product inhibition the kinetics of cell growth were investigated as a function of epoxide concentration, in both a batch

Listeria monocytogenes Growth Kinetics in Milkshakes Made from Naturally and Artificially Contaminated Ice Cream

OpenAIRE

Salazar, Joelle K.; Bathija, Vriddi M.; Carstens, Christina K.; Narula, Sartaj S.; Shazer, Arlette; Stewart, Diana; Tortorello, Mary Lou

2018-01-01

This study assessed the growth of Listeria monocytogenes in milkshakes made using the process-contaminated ice cream associated with a listeriosis outbreak in comparison to milkshakes made with artificially contaminated ice cream. For all temperatures, growth kinetics including growth rates, lag phases, maximum populations, and population increases were determined for the naturally and artificially derived contaminants at 5, 10, 15, and 25°C storage for 144 h. The artificially inoculated L. m...

Priming Adipose-Derived Mesenchymal Stem Cells with Hyaluronan Alters Growth Kinetics and Increases Attachment to Articular Cartilage

Directory of Open Access Journals (Sweden)

Peter Succar

2016-01-01

Full Text Available Background. Biological therapeutics such as adipose-derived mesenchymal stem cell (MSC therapy are gaining acceptance for knee-osteoarthritis (OA treatment. Reports of OA-patients show reductions in cartilage defects and regeneration of hyaline-like-cartilage with MSC-therapy. Suspending MSCs in hyaluronan commonly occurs in animals and humans, usually without supporting data. Objective. To elucidate the effects of different concentrations of hyaluronan on MSC growth kinetics. Methods. Using a range of hyaluronan concentrations, we measured MSC adherence and proliferation on culture plastic surfaces and a novel cartilage-adhesion assay. We employed time-course and dispersion imaging to assess MSC binding to cartilage. Cytokine profiling was also conducted on the MSC-secretome. Results. Hyaluronan had dose-dependent effects on growth kinetics of MSCs at concentrations of entanglement point (1 mg/mL. At higher concentrations, viscosity effects outweighed benefits of additional hyaluronan. The cartilage-adhesion assay highlighted for the first time that hyaluronan-primed MSCs increased cell attachment to cartilage whilst the presence of hyaluronan did not. Our time-course suggested patients undergoing MSC-therapy for OA could benefit from joint-immobilisation for up to 8 hours. Hyaluronan also greatly affected dispersion of MSCs on cartilage. Conclusion. Our results should be considered in future trials with MSC-therapy using hyaluronan as a vehicle, for the treatment of OA.

GeSn growth kinetics in reduced pressure chemical vapor deposition from Ge2H6 and SnCl4

Science.gov (United States)

Aubin, J.; Hartmann, J. M.

2018-01-01

We have investigated the low temperature epitaxy of high Sn content GeSn alloys in a 200 mm industrial Reduced Pressure - Chemical Vapor Deposition tool from Applied Materials. Gaseous digermane (Ge2H6) and liquid tin tetrachloride (SnCl4) were used as the Ge and Sn precursors, respectively. The impact of temperature (in the 300-350 °C range), Ge2H6 and SnCl4 mass-flows on the GeSn growth kinetics at 100 Torr has been thoroughly explored. Be it at 300 °C or 325 °C, a linear GeSn growth rate increase together with a sub-linear Sn concentration increase occurred as the SnCl4 mass-flow increased, irrespective of the Ge2H6 mass flow (fixed or varying). The Sn atoms seemed to catalyze H desorption from the surface, resulting in higher GeSn growth rates for high SnCl4 mass-flows (in the 4-21 nm min-1 range). The evolution of the Sn content x with the F (SnCl4) 2 ·/F (Ge2H6) mass-flow ratio was fitted by x2/(1 - x) = n ·F (SnCl4) 2 ·/F (Ge2H6), with n = 0.25 (325 °C) and 0.60 (300 °C). We have otherwise studied the impact of temperature, in the 300-350 °C range, on the GeSn growth kinetics. The GeSn growth rate exponentially increased with the temperature, from 15 up to 32 nm min-1. The associated activation energy was low, i.e. Ea = 10 kcal mol-1. Meanwhile, the Sn content decreased linearly as the growth temperature increased, from 15% at 300 °C down to 6% at 350 °C.

Kinetic Behavior of Exchange-Driven Growth with Catalyzed-Birth Processes

Science.gov (United States)

Wang, Hai-Feng; Lin, Zhen-Quan; Kong, Xiang-Mu

2006-12-01

Two catalyzed-birth models of n-species (n>=2) aggregates with exchange-driven growth processes are proposed and compared. In the first one, the exchange reaction occurs between any two aggregates Amk and Amj of the same species with the rate kernels Km(k,j) = Kmkj (m = 1,2,...,n, n>=2), and aggregates of An species catalyze a monomer-birth of Al species (l = 1,2,...,n-1) with the catalysis rate kernel Jl(k,j) = Jlkjυ. The kinetic behaviors are investigated by means of the mean-field theory. We find that the evolution behavior of aggregate-size distribution alk(t) of Al species depends crucially on the value of the catalysis rate parameter υ: (i) alk(t) obeys the conventional scaling law in the case of υ0. In the second model, the mechanism of monomer-birth of An-species catalyzed by Al species is added on the basis of the first model, that is, the aggregates of Al and An species catalyze each other to cause monomer-birth. The kinetic behaviors of Al and An species are found to fall into two categories for the different υ: (i) growth obeying conventional scaling form with υ0.

Computer simulation of monolayer growth kinetics of Fe2B phase during the paste-boriding process: Influence of the paste thickness

International Nuclear Information System (INIS)

Keddam, M.

2006-01-01

This paper deals with the effect of boron paste thickness on the study of the monolayer growth kinetics of Fe 2 B phase forming on AISI 1045 steel by the paste-boriding process. A mathematical diffusion model based on the Fick's phenomenological equations was applied in order to estimate the growth rate constant at (Fe 2 B/γ-Fe) interface, the layer thickness of iron boride as well as the associated mass gain depending on the boriding parameters such as time, temperature and surface boron concentration related to the boron paste thickness. The simulation results are found to be in a fairly good agreement with the experimental data derived from the literature

Lifshitz-Allen-Cahn domain-growth kinetics of Ising models with conserved density

DEFF Research Database (Denmark)

Fogedby, Hans C.; Mouritsen, Ole G.

1988-01-01

The domain-growth kinetics of p=fourfold degenerate (2×1) ordering in two-dimensional Ising models with conserved density is studied as a function of temperature and range of Kawasaki spin exchange. It is found by computer simulations that the zero-temperature freezing-in behavior for nearest-nei...

Lateral interactions and non-equilibrium in surface kinetics

Science.gov (United States)

Menzel, Dietrich

2016-08-01

Work modelling reactions between surface species frequently use Langmuir kinetics, assuming that the layer is in internal equilibrium, and that the chemical potential of adsorbates corresponds to that of an ideal gas. Coverage dependences of reacting species and of site blocking are usually treated with simple power law coverage dependences (linear in the simplest case), neglecting that lateral interactions are strong in adsorbate and co-adsorbate layers which may influence kinetics considerably. My research group has in the past investigated many co-adsorbate systems and simple reactions in them. We have collected a number of examples where strong deviations from simple coverage dependences exist, in blocking, promoting, and selecting reactions. Interactions can range from those between next neighbors to larger distances, and can be quite complex. In addition, internal equilibrium in the layer as well as equilibrium distributions over product degrees of freedom can be violated. The latter effect leads to non-equipartition of energy over molecular degrees of freedom (for products) or non-equal response to those of reactants. While such behavior can usually be described by dynamic or kinetic models, the deeper reasons require detailed theoretical analysis. Here, a selection of such cases is reviewed to exemplify these points.

Batch growth kinetic studies of locally isolated cyanide-degrading Serratia marcescens strain AQ07.

Science.gov (United States)

Karamba, Kabiru Ibrahim; Ahmad, Siti Aqlima; Zulkharnain, Azham; Yasid, Nur Adeela; Ibrahim, Salihu; Shukor, Mohd Yunus

2018-01-01

The evaluation of degradation and growth kinetics of Serratia marcescens strain AQ07 was carried out using three half-order models at all the initial concentrations of cyanide with the values of regression exceeding 0.97. The presence of varying cyanide concentrations reveals that the growth and degradation of bacteria were affected by the increase in cyanide concentration with a total halt at 700 ppm KCN after 72 h incubation. In this study, specific growth and degradation rates were found to trail the substrate inhibition kinetics. These two rates fitted well to the kinetic models of Teissier, Luong, Aiba and Heldane, while the performance of Monod model was found to be unsatisfactory. These models were used to clarify the substrate inhibition on the bacteria growth. The analyses of these models have shown that Luong model has fitted the experimental data with the highest coefficient of determination ( R 2 ) value of 0.9794 and 0.9582 with the lowest root mean square error (RMSE) value of 0.000204 and 0.001, respectively, for the specific rate of degradation and growth. It is the only model that illustrates the maximum substrate concentration ( S m ) of 713.4 and empirical constant ( n ) of 1.516. Tessier and Aiba fitted the experimental data with a R 2 value of 0.8002 and 0.7661 with low RMSE of 0.0006, respectively, for specific biodegradation rate, while having a R 2 value of 0.9 and RMSE of 0.001, respectively, for specific growth rate. Haldane has the lowest R 2 value of 0.67 and 0.78 for specific biodegradation and growth rate with RMSE of 0.0006 and 0.002, respectively. This indicates the level of the bacteria stability in varying concentrations of cyanide and the maximum cyanide concentration it can tolerate within a specific time period. The biokinetic constant predicted from this model demonstrates a good ability of the locally isolated bacteria in cyanide remediation in industrial effluents.

Kinetics of boride layers formed on the surface of AISI 4140 steel

International Nuclear Information System (INIS)

Sen, S.; Sen, U.; Bindal, C.

2004-01-01

The present study reports on boride layer growth kinetics of borided AISI 4140 steel. Steels were boronized in molten borax, boric acid and ferro-silicon bath at 1123 K 1173 K and 1223 K for 2, 4, 6 and 8 hours. Boride layer thickness ranged from 38.4 to 225 μm. Layer growth kinetics were analysed by measuring the extent of penetration of FeB and Fe 2 B sublayers as a function of boronizing time and temperature in the range of 1123-1223 K. The depth of the tips of the most deeply penetrated FeB and Fe 2 B needles are taken as measures for diffusion in the fast directions. The kinetics of the reaction, K=K 0 exp(-Q/RT) have also been determined by varying the boriding temperature and time. The results showed that K increase with boronizing temperature. Activation energy (Q) for present study was determined as 215 kj.mol -1 . The diffusion coefficient (K) ranged from 3 x 10 -9 cm 2 s -1 to 2 x 10 -8 cm 2 s -1 . Also temperature-dependent constant (K 0 ) at temperatures 1123 K, 1173 K and 1223 K was 179.4 cm 2 s -1 . (orig.)

Kinetic electron emission from highly oriented pyrolytic graphite surfaces induced by singly charged ions

CERN Document Server

Cernusca, S; Winter, H; Aumayr, F; Loerincik, J; Sroubek, Z

2002-01-01

We present total electron yields determined by current measurements for normal impact of H sup + , H sub 2 sup + , H sub 3 sup + , C sup + , N sup + and O sup + ions (E<=10 keV) on a clean highly oriented pyrolytic graphite surface. The kinetic energy of the projectiles has been varied from near threshold up to 10 keV. By comparing the results to similar data obtained for a polycrystalline Au surface the role of different target properties for kinetic electron emission can be analysed.

Growth responses of Escherichia coli and Myxococcus xanthus on ...

African Journals Online (AJOL)

Bacteria colonize surfaces responding to the physicochemical properties of substrates. A systematic study was carried out with growing single bacterial colonies on the surface of agar media to decipher the interaction between bacterial growth and substrate stiffness. We investigated the growth kinetics of wild-type ...

Kinetics of final stages of spreading of melts on solid surfaces

International Nuclear Information System (INIS)

Khlynov, V.V.; Pastukhov, B.A.; Bokser, Eh.L.

1978-01-01

Kinetics of the spreading of Fe, Ni and Co melts over the surface of W-Re alloy (27% Re) was studied at 1580, 1500 and 1540 deg C, respectively. The time variant wetting spot radius and wetting angle were recorded using a modified Langmuir's method. Kinetic equations of the propagation of liquid interfacial layer and of the wetting, satisfactorily describing the obtained experimental data, have been derived. The melts have been found to spread by viscous flow and by migration atoms in small regions adjacent to the wetting perimeter

Comprehensive modeling of solid phase epitaxial growth using Lattice Kinetic Monte Carlo

International Nuclear Information System (INIS)

Martin-Bragado, Ignacio

2013-01-01

Damage evolution of irradiated silicon is, and has been, a topic of interest for the last decades for its applications to the semiconductor industry. In particular, sometimes, the damage is heavy enough to collapse the lattice and to locally amorphize the silicon, while in other cases amorphization is introduced explicitly to improve other implanted profiles. Subsequent annealing of the implanted samples heals the amorphized regions through Solid Phase Epitaxial Regrowth (SPER). SPER is a complicated process. It is anisotropic, it generates defects in the recrystallized silicon, it has a different amorphous/crystalline (A/C) roughness for each orientation, leaving pits in Si(1 1 0), and in Si(1 1 1) it produces two modes of recrystallization with different rates. The recently developed code MMonCa has been used to introduce a physically-based comprehensive model using Lattice Kinetic Monte Carlo that explains all the above singularities of silicon SPER. The model operates by having, as building blocks, the silicon lattice microconfigurations and their four twins. It detects the local configurations, assigns microscopical growth rates, and reconstructs the positions of the lattice locally with one of those building blocks. The overall results reproduce the (a) anisotropy as a result of the different growth rates, (b) localization of SPER induced defects, (c) roughness trends of the A/C interface, (d) pits on Si(1 1 0) regrown surfaces, and (e) bimodal Si(1 1 1) growth. It also provides physical insights of the nature and shape of deposited defects and how they assist in the occurrence of all the above effects

Implementing atomic force microscopy (AFM) for studying kinetics of gold nanoparticle's growth

DEFF Research Database (Denmark)

Georgiev, P.; Bojinova, A.; Kostova, B.

2013-01-01

In a novel experimental approach Atomic Force Microscopy (AFM) was applied as a tool for studying the kinetics of gold nanoparticle growth. The gold nanoparticles were obtained by classical Turkevich citrate synthesis at two different temperatures. From the analysis of AFM images during...... the synthesis process the nanoparticle s' sizes were obtained. To demonstrate the applicability and the reliability of the proposed experimental approach we studied the nanoparticles growth at two different temperatures by spectrophotometric measurements and compared them with the results from AFM experimental...

Understanding the reaction kinetics to optimize graphene growth on Cu by chemical vapor deposition

Energy Technology Data Exchange (ETDEWEB)

Kraus, Juergen; Boebel, Lena; Zwaschka, Gregor; Guenther, Sebastian [Technische Universitaet Muenchen, Zentralinstitut fuer Katalyseforschung, Chemie Department, Physikalische Chemie mit Schwerpunkt Katalyse, Garching (Germany)

2017-11-15

Understanding and controlling the growth kinetics of graphene is a prerequisite to synthesize this highly wanted material by chemical vapor deposition on Cu, e.g. for the construction of ultra-stable electron transparent membranes. It is reviewed that Cu foils contain a considerable amount of carbon in the bulk which significantly exceeds the expected amount of thermally equilibrated dissolved carbon in Cu and that this carbon must be removed before any high quality graphene may be grown. Starting with such conditioned Cu foils, systematic studies of the graphene growth kinetics in a reactive CH{sub 4}/H{sub 2} atmosphere allow to extract the following meaningful data: prediction of the equilibrium constant of the graphene formation reaction within a precision of a factor of two, the confirmation that the graphene growth proceeds from a C(ad)-phase on Cu which is in thermal equilibrium with the reactive gas phase, its apparent activation barrier and finally the prediction of the achievable growth velocity of the growing graphene flakes during chemical vapor deposition. As a result of the performed study, growth parameters are identified for the synthesis of high quality monolayer graphene with single crystalline domains of 100-1000 μm in diameter within a reasonable growth time. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Quantifying Variability in Growth and Thermal Inactivation Kinetics of Lactobacillus plantarum.

Science.gov (United States)

Aryani, D C; den Besten, H M W; Zwietering, M H

2016-08-15

The presence and growth of spoilage organisms in food might affect the shelf life. In this study, the effects of experimental, reproduction, and strain variabilities were quantified with respect to growth and thermal inactivation using 20 Lactobacillus plantarum strains. Also, the effect of growth history on thermal resistance was quantified. The strain variability in μmax was similar (P > 0.05) to reproduction variability as a function of pH, aw, and temperature, while being around half of the reproduction variability (P plantarum strains, and the pHmin was between 3.2 and 3.5, the aw,min was between 0.936 and 0.953, the [HLamax], at pH 4.5, was between 29 and 38 mM, and the Tmin was between 3.4 and 8.3°C. The average D values ranged from 0.80 min to 19 min at 55°C, 0.22 to 3.9 min at 58°C, 3.1 to 45 s at 60°C, and 1.8 to 19 s at 63°C. In contrast to growth, the strain variability in thermal resistance was on average six times higher than the reproduction variability and more than ten times higher than the experimental variability. The strain variability was also 1.8 times higher (P 10-log10 differences after thermal treatment. Accurate control and realistic prediction of shelf life is complicated by the natural diversity among microbial strains, and limited information on microbiological variability is available for spoilage microorganisms. Therefore, the objectives of the present study were to quantify strain variability, reproduction (biological) variability, and experimental variability with respect to the growth and thermal inactivation kinetics of Lactobacillus plantarum and to quantify the variability in thermal resistance attributed to growth history. The quantitative knowledge obtained on experimental, reproduction, and strain variabilities can be used to improve experimental designs and to adequately select strains for challenge growth and inactivation tests. Moreover, the integration of strain variability in prediction of microbial growth and

GROWTH KINETIC STUDY OF CHLORELLA VULGARIS USING LAB-SCALE AND PILOT-SCALE PHOTOBIOREACTOR: EFFECT OF CO2 CONCENTRATION

Directory of Open Access Journals (Sweden)

MAN KEE LAM

2016-07-01

Full Text Available In the present study, growth kinetic of Chlorella vulgaris was performed when the microalgae was cultivated with different concentrations of CO2 . The experiments were carried out using lab-scale and pilot-scale photobioreactors, and the growth results were analyzed using POLYMATH 6.0 with different growth kinetic models. The growth of the microalgae was found fitted well to the Richards growth model with attainable high R2 values as demonstrated in all studied cases, in concert with low values of root mean squares deviation (RMSD and variance. In addition, the output from the plots of experimental values versus predicted values and residual plots further confirmed the good fit of Richards model. The predicted specific growth rate from Richards model was similar to the experimental specific growth rate with deviation lesser than 5%. The attained results paved a preliminary prediction of microalgae growth characteristic when the cultivation is scaled-up to commercial scale.

Kinetic Monte Carlo simulation of formation of microstructures in liquid droplets

International Nuclear Information System (INIS)

Block, M; Kunert, R; Schoell, E; Boeck, T; Teubner, Th

2004-01-01

We study the deposition of indium droplets on a glass surface and the subsequent formation of silicon microcrystals inside these droplets. Kinetic Monte Carlo methods are used to analyse the influence of growth temperature, flux of incoming particles, surface coverage, and in particular an energy parameter simulating the surface tension, upon the morphology of growth. According to the experimental conditions of crystallization, a temperature gradient and diffusion in spherical droplets are included. The simulations explain the formation of silicon crystal structures in good agreement with the experiment. The dependence of their shape and the conditions of formation on the growth parameters are investigated in detail

He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth

International Nuclear Information System (INIS)

1992-01-01

Investigations in this laboratory have focused on the surface structure and dynamics of ionic insulators and on epitaxial growth onto alkali halide crystals. In the later the homoepitaxial growth of NaCl/NaCl(001) and the heteroepitaxial growth of KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been studied by monitoring the specular He scattering as a function of the coverage and by measuring the angular and energy distributions of the scattered He atoms. These data provide information on the surface structure, defect densities, island sizes and surface strain during the layer-by-layer growth. The temperature dependence of these measurements also provides information on the mobilities of the admolecules. He atom scattering is unique among surface probes because the low-energy, inert atoms are sensitive only to the electronic structure of the topmost surface layer and are equally applicable to all crystalline materials. It is proposed for the next year to exploit further the variety of combinations possible with the alkali halides in order to carry out a definitive study of epitaxial growth in the ionic insulators. The work completed so far, including measurements of the Bragg diffraction and surface dispersion at various stages of growth, appears to be exceptionally rich in detail, which is particularly promising for theoretical modeling. In addition, because epitaxial growth conditions over a wide range of lattice mismatches is possible with these materials, size effects in growth processes can be explored in great depth. Further, as some of the alkali halides have the CsCl structure instead of the NaCl structure, we can investigate the effects of the heteroepitaxy with materials having different lattice preferences. Finally, by using co-deposition of different alkali halides, one can investigate the formation and stability of alloys and even alkali halide superlattices

A Comparative Study of Ethylene Growth Response Kinetics in Eudicots and Monocots Reveals a Role for Gibberellin in Growth Inhibition and Recovery1[W][OA

Science.gov (United States)

Kim, Joonyup; Wilson, Rebecca L.; Case, J. Brett; Binder, Brad M.

2012-01-01

Time-lapse imaging of dark-grown Arabidopsis (Arabidopsis thaliana) hypocotyls has revealed new aspects about ethylene signaling. This study expands upon these results by examining ethylene growth response kinetics of seedlings of several plant species. Although the response kinetics varied between the eudicots studied, all had prolonged growth inhibition for as long as ethylene was present. In contrast, with continued application of ethylene, white millet (Panicum miliaceum) seedlings had a rapid and transient growth inhibition response, rice (Oryza sativa ‘Nipponbare’) seedlings had a slow onset of growth stimulation, and barley (Hordeum vulgare) had a transient growth inhibition response followed, after a delay, by a prolonged inhibition response. Growth stimulation in rice correlated with a decrease in the levels of rice ETHYLENE INSENSTIVE3-LIKE2 (OsEIL2) and an increase in rice F-BOX DOMAIN AND LRR CONTAINING PROTEIN7 transcripts. The gibberellin (GA) biosynthesis inhibitor paclobutrazol caused millet seedlings to have a prolonged growth inhibition response when ethylene was applied. A transient ethylene growth inhibition response has previously been reported for Arabidopsis ethylene insensitive3-1 (ein3-1) eil1-1 double mutants. Paclobutrazol caused these mutants to have a prolonged response to ethylene, whereas constitutive GA signaling in this background eliminated ethylene responses. Sensitivity to paclobutrazol inversely correlated with the levels of EIN3 in Arabidopsis. Wild-type Arabidopsis seedlings treated with paclobutrazol and mutants deficient in GA levels or signaling had a delayed growth recovery after ethylene removal. It is interesting to note that ethylene caused alterations in gene expression that are predicted to increase GA levels in the ein3-1 eil1-1 seedlings. These results indicate that ethylene affects GA levels leading to modulation of ethylene growth inhibition kinetics. PMID:22977279

Kinetics of interaction from low-energy-ion bombardment of surfaces

International Nuclear Information System (INIS)

Horton, C.C.

1988-01-01

The kinetics of interaction from low energy oxygen ion bombardment of carbon and Teflon surfaces have been investigated. The surfaces were bombarded with 4.5 to 93 eV oxygen ions and emitted species were observed with a mass spectrometer. To obtain the kinetic information, the ion beam was square pulse modulated and reaction products were observed as a function of time. The kinetic information is contained in the response of the emitted species to the pulsed ion beam. Oxygen bombardment of carbon produced CO in three parallel branches with each following an adsorption-desorption process. The fast branch, with a rate constants of 12,000/sec, appeared to be sputter induced an was absent below about 19 eV. The medium and slow branches, with rate constants of 850/sec and 45/sec respectively, has little energy dependence and appeared to be due to chemical sputtering from two sites. The ratio of the fraction of the medium branch to that of the slow was constant at 1:3. The bombardment of Teflon produced CF in two parallel branches, with one following a series process and the other an adsorb-desorb process. The rate constant of the other branch were 22,000/sec and 7,000/sec and the rate constant of the other branch was 90/sec. The total signal fell monotonically with decreasing ion energy with the fraction for each branch holding constant at 71% for the series and 29% for the adsorb-desorb

Impurity incorporation, deposition kinetics, and microstructural evolution in sputtered Ta films

Science.gov (United States)

Whitacre, Jay Fredric

There is an increasing need to control the microstructure in thin sputtered Ta films for application as high-temperature coatings or diffusion barriers in microelectronic interconnect structures. To this end, the relationship between impurity incorporation, deposition kinetics, and microstructural evolution was examined for room-temperature low growth rate DC magnetron sputtered Ta films. Impurity levels present during deposition were controlled by pumping the chamber to various base pressures before growth. Ar pressures ranging from 2 to 20 mTorr were used to create contrasting kinetic environments in the sputter gas. This affected both the distribution of adatom kinetic energies at the substrate as well as the rate of impurity desorption from the chamber walls: at higher Ar pressures adatoms has lower kinetic energies, and there was an increase in impurity concentration. X-ray diffraction, high-resolution transmission electron microscopy (HREM), transmission electron diffraction (TED), scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), and x-ray photoelectron. spectroscopy (XPS) were used to examine film crystallography, microstructure, and composition. A novel laboratory-based in-situ x-ray diffractometer was constructed. This new set-up allowed for the direct observation of microstructural evolution during growth. Films deposited at increasingly higher Ar pressures displayed a systematic decrease in grain size and degree of texturing, while surface morphology was found to vary from a nearly flat surface to a rough surface with several length scales of organization. In-situ x-ray results showed that the rate of texture evolution was found to be much higher in films grown using lower Ar pressures. These effects were studied in films less than 200 A thick using high resolution x-ray diffraction in conjunction with a synchrotron light source (SSRL B.L. 7-2). Films grown using higher Ar pressures (above 10 mTorr) with a pre-growth base

Comparison of molecular dynamics and kinetic modeling of gas-surface interactions

NARCIS (Netherlands)

Frezzotti, A.; Gaastra - Nedea, S.V.; Markvoort, A.J.; Spijker, P.; Gibelli, L.

2008-01-01

The interaction of a dilute monatomic gas with a solid surface is studied byMolecular Dynamics (MD) simulations and by numerical solutions of a recently proposed kinetic model. Following previous investigations, the heat transport between parallel walls and Couette flow have been adopted as test

Kinetics of boride layers formed on the surface of AISI 4140 steel

Energy Technology Data Exchange (ETDEWEB)

Sen, S.; Sen, U. [Sakarya Univ., Dept. of Metal Education, Sakarya (Turkey); Bindal, C. [Sakarya Univ., Dept. of Materials and Metallurgy, Sakarya (Turkey)

2004-07-01

The present study reports on boride layer growth kinetics of borided AISI 4140 steel. Steels were boronized in molten borax, boric acid and ferro-silicon bath at 1123 K 1173 K and 1223 K for 2, 4, 6 and 8 hours. Boride layer thickness ranged from 38.4 to 225 {mu}m. Layer growth kinetics were analysed by measuring the extent of penetration of FeB and Fe{sub 2}B sublayers as a function of boronizing time and temperature in the range of 1123-1223 K. The depth of the tips of the most deeply penetrated FeB and Fe{sub 2}B needles are taken as measures for diffusion in the fast directions. The kinetics of the reaction, K=K{sub 0} exp(-Q/RT) have also been determined by varying the boriding temperature and time. The results showed that K increase with boronizing temperature. Activation energy (Q) for present study was determined as 215 kj.mol{sup -1}. The diffusion coefficient (K) ranged from 3 x 10{sup -9} cm{sup 2}s{sup -1} to 2 x 10{sup -8} cm{sup 2}s{sup -1}. Also temperature-dependent constant (K{sub 0}) at temperatures 1123 K, 1173 K and 1223 K was 179.4 cm{sup 2}s{sup -1}. (orig.)

Domain growth kinetics in stratifying foam films

Science.gov (United States)

Zhang, Yiran; Sharma, Vivek

2015-11-01

Baking bread, brewing cappuccino, pouring beer, washing dishes, shaving, shampooing, whipping eggs and blowing bubbles all involve creation of aqueous foam films. Typical foam films consist of two surfactant-laden surfaces that are ~ 5 nm - 10 micron apart. Sandwiched between these interfacial layers is a fluid that drains primarily under the influence of viscous and interfacial forces, including disjoining pressure. Interestingly, a layered ordering of micelles inside the foam films (thickness characteristic scaling laws. Though several studies have focused on the expansion dynamics of isolated domains that exhibit a diffusion-like scaling, the change in expansion kinetics observed after domains contact with the Plateau border has not been reported and analyzed before.

Non-equilibrium Thermodynamic Dissolution Theory for Multi-Component Solid/Liquid Surfaces Involving Surface Adsorption and Radiolysis Kinetics

International Nuclear Information System (INIS)

Stout, R B

2001-01-01

A theoretical expression is developed for the dissolution rate response for multi-component radioactive materials that have surface adsorption kinetics and radiolysis kinetics when wetted by a multi-component aqueous solution. An application for this type of dissolution response is the performance evaluation of multi-component spent nuclear fuels (SNFs) for long term interim storage and for geological disposition. Typically, SNF compositions depend on initial composition, uranium oxide and metal alloys being most common, and on reactor burnup which results in a wide range of fission product and actinide concentrations that decay by alpha, beta, and gamma radiation. These compositional/burnup ranges of SNFs, whether placed in interim storage or emplaced in a geologic repository, will potentially be wetted by multi-component aqueous solutions, and these solutions may be further altered by radiolytic aqueous species due to three radiation fields. The solid states of the SNFs are not thermodynamically stable when wetted and will dissolve, with or without radiolysis. The following development of a dissolution theory is based on a non-equilibrium thermodynamic analysis of energy reactions and energy transport across a solid-liquid phase change discontinuity that propagates at a quasi-steady, dissolution velocity. The integral form of the energy balance equation is used for this spatial surface discontinuity analysis. The integral formulation contains internal energy functional of classical thermodynamics for both the SNFs' solid state and surface adsorption species, and the adjacent liquid state, which includes radiolytic chemical species. The steady-state concentrations of radiolytic chemical species are expressed by an approximate analysis of the decay radiation transport equation. For purposes of illustration a modified Temkin adsorption isotherm was assumed for the surface adsorption kinetics on an arbitrary, finite area of the solid-liquid dissolution interface. For

Alloyed surfaces: New substrates for graphene growth

Science.gov (United States)

Tresca, C.; Verbitskiy, N. I.; Fedorov, A.; Grüneis, A.; Profeta, G.

2017-11-01

We report a systematic ab-initio density functional theory investigation of Ni(111) surface alloyed with elements of group IV (Si, Ge and Sn), demonstrating the possibility to use it to grow high quality graphene. Ni(111) surface represents an ideal substrate for graphene, due to its catalytic properties and perfect matching with the graphene lattice constant. However, Dirac bands of graphene growth on Ni(111) are completely destroyed due to the strong hybridization between carbon pz and Ni d orbitals. Group IV atoms, namely Si, Ge and Sn, once deposited on Ni(111) surface, form an ordered alloyed surface with √{ 3} ×√{ 3} -R30° reconstruction. We demonstrate that, at variance with the pure Ni(111) surface, alloyed surfaces effectively decouple graphene from the substrate, resulting unstrained due to the nearly perfect lattice matching and preserves linear Dirac bands without the strong hybridization with Ni d states. The proposed surfaces can be prepared before graphene growth without resorting on post-growth processes which necessarily alter the electronic and structural properties of graphene.

Palladium mixed-metal surface-modified AB₅-type intermetallides enhance hydrogen sorption kinetics

Directory of Open Access Journals (Sweden)

Roman V. Denys

2010-09-01

Full Text Available Surface engineering approaches were adopted in the preparation of advanced hydrogen sorption materials, based on ‘low-temperature’, AB₅-type intermetallides. The approaches investigated included micro-encapsulation with palladium and mixed-metal mantles using electroless plating. The influence of micro-encapsulation on the surface morphology and kinetics of hydrogen charging were investigated. It was found that palladium-nickel (Pd-Ni co-deposition by electroless plating significantly improved the kinetics of hydrogen charging of the AB₅-type intermetallides at low hydrogen pressure and temperature, after long-term pre-exposure to air. The improvement in the kinetics of hydrogen charging was credited to a synergistic effect between the palladium and nickel atoms in the catalytic mantle and the formation of an ‘interfacial bridge’ for hydrogen diffusion by the nickel atoms in the deposited layer. The developed surface-modified materials may find application in highly selective hydrogen extraction, purification, and storage from impure hydrogen feeds.

Effects of hyperthermia on growth kinetics of Chinese hamster ovarian carcinoma cells

International Nuclear Information System (INIS)

Leeper, D.B.; Bobyock, S.B.

1987-01-01

The effects of hyperthermia on growth rate, cell volume, and density at plateau phase were studied in OvCa cells in monolayer culture in McCoy's 5a + 10% FCS. At 37 0 C, T/sub G/=9.3 hr, cell density at plateau was 32 x 10/sup 4//cm/sup 2/, and mean cell volume decreased from 1200 μ/sup 3/ at the onset of exponential growth to 850 μ/sup 3/ in plateau phase. Cells were acutely heated for 60' at 43 0 ,30' at 44 0 , or 15' at 45 0 (S.F.=20%) and incubated at 37 0 ; or were chronically heated for up to 80 hr at 39-42 0 . Acute heating at 43-45 0 delayed cell division for appx 13 hr after which growth resumed with a T/sub G/=18 hr. Incubation at 39-40 0 had no effect on T/sub G/, but temperatures of 40.5-42 0 increased T/sub G/ at ΔH=176 kcal/mole. Increasing incubation temperature decreased cell density at plateau phase and altered cell volume kinetics. Cell density in plateau phase was 20 x 10/sup 4//cm/sup 2/ at 39 0 , 13 x 10/sup 4//cm/sup 2/ at 40 0 , 5x10/sup 4//cm/sup 2/ at 41 0 . Growth was greatly reduced at 42 0 (T/sub G/=55 hr) and doubling did not occur before onset of cell lysis. The decrease in cell volume with growth of the culture was unaffected at 39 0 . However, at temperatures ≥40 0 cell volume transiently increase, and the rate of decrease in volume that normally occurred with growth at 37-39 0 was less such that at 41 0 there was no decrease in volume at all before cells entered plateau phase. The authors' hypothesis is that the effects of heat on growth kinetics are related to alterations in rates of protein synthesis. This is currently being tested

Shape transition of endotaxial islands growth from kinetically constrained to equilibrium regimes

Energy Technology Data Exchange (ETDEWEB)

Li, Zhi-Peng, E-mail: LI.Zhipeng@nims.go.jp [Department of Physics, National University of Singapore, 2 Science Drive 3, S117542 Singapore (Singapore); Global Research Center for Environment and Energy based on Nanomaterials Science, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan); Tok, Engsoon [Department of Physics, National University of Singapore, 2 Science Drive 3, S117542 Singapore (Singapore); Foo, Yonglim [Institute of Materials Research and Engineering, 3 Research Link, S117602 Singapore (Singapore)

2013-09-01

Graphical abstract: - Highlights: • All Fe{sub 13}Ge{sub 8} islands will grow into Ge(0 0 1) substrate at temperatures from 350 to 675 °C. • Shape transition occurred from kinetically constrained to equilibrium regime. • All endotaxial islands can be clarified into two types. • The mechanisms of endotaxial growth and shape transition have been rationalized. - Abstract: A comprehensive study of Fe grown on Ge(0 0 1) substrates has been conducted at elevated temperatures, ranging from 350 to 675 °C. All iron germinide islands, with the same Fe{sub 13}Ge{sub 8} phase, grow into the Ge substrate with the same epitaxial relationship. Shape transition occurs from small square islands (low temperatures), to elongated orthogonal islands or orthogonal nanowires (intermediate temperatures), and then finally to large square orthogonal islands (high temperatures). According to both transmission electron microscopy (TEM) and atomic force microscopy (AFM) investigations, all islands can be defined as either type-I or type-II. Type-I islands usually form at kinetically constrained growth regimes, like truncated pyramids. Type-II islands usually appear at equilibrium growth regimes forming a dome-like shape. Based on a simple semi-quantitative model, type-II islands have a lower total energy per volume than type-I, which is considered as the dominant mechanism for this type of shape transition. Moreover, this study not only elucidates details of endotaxial growth in the Fe–Ge system, but also suggests the possibility of controlled fabrication of temperature-dependent nanostructures, especially in materials with dissimilar crystal structures.

Plasma surface functionalization and dyeing kinetics of Pan-Pmma copolymers

Science.gov (United States)

Labay, C.; Canal, C.; Rodríguez, C.; Caballero, G.; Canal, J. M.

2013-10-01

Fiber surface modification with air corona plasma has been studied through dyeing kinetics under isothermal conditions at 30 °C on an acrylic-fiber fabric with a cationic dye (CI Basic Blue 3) analyzing the absorption, desorption and fixing on the surface of molecules having defined cationic character. The initial dyeing rate in the first 60 s indicates an increase of 58.3% in the dyeing rate due to the effect of corona plasma on the acrylic fiber surface. At the end of the dyeing process, the plasma-treated fabrics absorb 24.7% more dye, and the K/S value of the acrylic fabric increases by 8.8%. With selected dyestuff molecules, new techniques can be designed to amplify the knowledge about plasma-treated surface modifications of macromolecules.

Ge interactions on HfO2 surfaces and kinetically driven patterning of Ge nanocrystals on HfO2

International Nuclear Information System (INIS)

Stanley, Scott K.; Joshi, Sachin V.; Banerjee, Sanjay K.; Ekerdt, John G.

2006-01-01

Germanium interactions are studied on HfO 2 surfaces, which are prepared through physical vapor deposition (PVD) and by atomic layer deposition. X-ray photoelectron spectroscopy and temperature-programed desorption are used to follow the reactions of germanium on HfO 2 . Germanium chemical vapor deposition at 870 K on HfO 2 produces a GeO x adhesion layer, followed by growth of semiconducting Ge 0 . PVD of 0.7 ML Ge (accomplished by thermally cracking GeH 4 over a hot filament) also produces an initial GeO x layer, which is stable up to 800 K. PVD above 2.0 ML deposits semiconducting Ge 0 . Temperature programed desorption experiments of ∼1.0 ML Ge from HfO 2 at 400-1100 K show GeH 4 desorption below 600 K and GeO desorption above 850 K. These results are compared to Ge on SiO 2 where GeO desorption is seen at 550 K. Exploiting the different reactivity of Ge on HfO 2 and SiO 2 allows a kinetically driven patterning scheme for high-density Ge nanoparticle growth on HfO 2 surfaces that is demonstrated

H2-dependent attachment kinetics and shape evolution in chemical vapor deposition graphene growth

Science.gov (United States)

Meca, Esteban; Shenoy, Vivek B.; Lowengrub, John

2017-09-01

Experiments on graphene growth through chemical vapor deposition (CVD) involving methane (CH4) and hydrogen (H2) gases reveal a complex shape evolution and a non-monotonic dependence on the partial pressure of H2 ({{p}{{\\text{H}2}}} ). To explain these intriguing observations, we develop a microkinetic model for the stepwise decomposition of CH4 into mobile radicals and consider two possible mechanisms of attachment to graphene crystals: CH radicals to hydrogen-decorated edges of the crystals and C radicals to bare crystal edges. We derive an effective mass flux and an effective kinetic coefficient, both of which depend on {{p}{{\\text{H}2}}} , and incorporate these into a phase field model. The model reproduces both the non-monotonic dependence on {{p}{{\\text{H}2}}} and the characteristic shapes of graphene crystals observed in experiments. At small {{p}{{\\text{H}2}}} , growth is limited by the kinetics of attachment while at large {{p}{{\\text{H}2}}} growth is limited because the effective mass flux is small. We also derive a simple analytical model that captures the non-monotone behavior, enables the two mechanisms of attachment to be distinguished and provides guidelines for CVD growth of defect-free 2D crystals.

Kinetics of particle deposition at heterogeneous surfaces

Science.gov (United States)

Stojiljković, D. Lj.; Vrhovac, S. B.

2017-12-01

The random sequential adsorption (RSA) approach is used to analyze adsorption of spherical particles of fixed diameter d0 on nonuniform surfaces covered by square cells arranged in a square lattice pattern. To characterize such pattern two dimensionless parameters are used: the cell size α and the cell-cell separation β, measured in terms of the particle diameter d0. Adsorption is assumed to occur if the particle (projected) center lies within a cell area. We focus on the kinetics of deposition process in the case when no more than a single disk can be placed onto any square cell (α deposition process is not consistent with the power law behavior. However, if the geometry of the pattern approaches towards ;noninteracting conditions; (β > 1), when adsorption on each cell can be decoupled, approach of the coverage fraction θ(t) to θJ becomes closer to the exponential law. Consequently, changing the pattern parameters in the present model allows to interpolate the deposition kinetics between the continuum limit and the lattice-like behavior. Structural properties of the jammed-state coverings are studied in terms of the radial distribution function g(r) and spatial distribution of particles inside the cell. Various, non-trivial spatial distributions are observed depending on the geometry of the pattern.

Effects of temperature on domain-growth kinetics of fourfold-degenerate (2×1) ordering in Ising models

DEFF Research Database (Denmark)

Høst-Madsen, Anders; Shah, Peter Jivan; Hansen, Torben

1987-01-01

Computer-simulation techniques are used to study the domain-growth kinetics of (2×1) ordering in a two-dimensional Ising model with nonconserved order parameter and with variable ratio α of next-nearest- and nearest-neighbor interactions. At zero temperature, persistent growth characterized...

Features of the kinetics of heterogeneous reactions with phase transformations on catalyst surfaces

Energy Technology Data Exchange (ETDEWEB)

Berman, A D; Krylov, O V

1978-01-01

This paper presents a review of 41 bibliographic references to experiments on the adsorption of various gases (e.g., carbon monoxide, formic acid, ammonia, and oxygen) on metals (e.g., nickel, molybdenum, and platinum) and oxides covers observations of two-dimensional phases during adsorption; the kinetics of adsorption and catalysis associated with two-dimensional phase transitions; and several approximate models for describing the kinetics of heterogeneous catalysis which account for two-dimensional phase transformations on catalyst surfaces.

The kinetics of formation and transformation of silver atoms on solid surfaces subjected to ionizing irradiation

International Nuclear Information System (INIS)

Popovich, G.M.

1988-01-01

The paper discusses the results obtained in ESR-assisted studies of the kinetics of formation and transformation of silver atoms generated by γ-irradiation of silver-containing carriers. Three types of dependences have been established: (1) extreme; (2) saturation curves and (3) step-like. All the kinetic curves display, after a definite period of time, stable concentrations of adsorbed silver atoms per unit of the surface at a given temperature. Depending on the temperature of the experiment, the composition and nature of the carrier, the number of adsorbed silver ions, the irradiation dose and conditions of the experiment, a stable concentration of silver atoms at a given temperature may be equal to, higher or lower than the number of silver atoms measured immediately after γ-irradiation at a temperature of liquid nitrogen. A kinetic scheme is proposed to explain the obtained curves. The model suggests that the silver atoms adsorbed on the surface, as well as those formed after γ-irradiation, are bonded to the surface by various energies, which are related to heterogeneity of the carrier surface. (author)

SurfKin: an ab initio kinetic code for modeling surface reactions.

Science.gov (United States)

Le, Thong Nguyen-Minh; Liu, Bin; Huynh, Lam K

2014-10-05

In this article, we describe a C/C++ program called SurfKin (Surface Kinetics) to construct microkinetic mechanisms for modeling gas-surface reactions. Thermodynamic properties of reaction species are estimated based on density functional theory calculations and statistical mechanics. Rate constants for elementary steps (including adsorption, desorption, and chemical reactions on surfaces) are calculated using the classical collision theory and transition state theory. Methane decomposition and water-gas shift reaction on Ni(111) surface were chosen as test cases to validate the code implementations. The good agreement with literature data suggests this is a powerful tool to facilitate the analysis of complex reactions on surfaces, and thus it helps to effectively construct detailed microkinetic mechanisms for such surface reactions. SurfKin also opens a possibility for designing nanoscale model catalysts. Copyright © 2014 Wiley Periodicals, Inc.

Electric-Loading Enhanced Kinetics in Oxide Ceramics: Pore Migration, Sintering and Grain Growth: Final Report

Energy Technology Data Exchange (ETDEWEB)

Chen, I-Wei [Univ. of Pennsylvania, Philadelphia, PA (United States). Dept. of Materials Science & Engineering

2018-02-02

Solid oxide fuel cells and solid oxide electrolysis cells rely on solid electrolytes in which a large ionic current dominates. This project was initiated to investigate microstructural changes in such devices under electrochemical forces, because nominally insignificant processes may couple to the large ionic current to yield non-equilibrium phenomena that alter the microstructure. Our studies had focused on yttria-stabilized cubic zirconia (YSZ) widely used in these devices. The experiments have revealed enhanced grain growth at higher temperatures, pore and gas bubble migration at all temperatures, and the latter also lead to enhanced sintering of highly porous ceramics into fully dense ceramics at unprecedentedly low temperatures. These results have shed light on kinetic processes that fall completely outside the realm of classical ceramic processing. Other fast-oxygen oxide ceramics closely related to, and often used in conjunction with zirconia ceramics, have also be investigated, as are closely related scientific problems in zirconia ceramics. These include crystal structures, defects, diffusion kinetics, oxygen potentials, low temperature sintering, flash sintering, and coarsening theory, and all have resulted in greater clarity in scientific understanding. The knowledge is leveraged to provide new insight to electrode kinetics and near-electrode mixed conductivity and to new materials. In the following areas, our research has resulted in completely new knowledge that defines the state-of-the-art of the field. (a) Electrical current driven non-equilibrium phenomena, (b) Enhanced grain growth under electrochemically reducing conditions, (c) Development of oxygen potential polarization in electrically loaded electrolyte, (d) Low temperature sintering and grain growth, and (e) Structure, defects and cation kinetics of fluorite-structured oxides. Our research has also contributed to synthesis of new energy-relevant electrochemical materials and new understanding

Kinetic energy of ions produced with first-, second-, and multi-shot femtosecond laser ablation on a solid surface

International Nuclear Information System (INIS)

Kobayashi, Tohru; Kato, Toshiyuki; Kurata-Nishimura, Mizuki; Matsuo, Yukari; Kawai, Jun; Motobayashi, Tohru; Hayashizaki, Yoshihide

2007-01-01

We report that the kinetic energy of samarium (Sm) atom and Sm + ion produced by femtosecond laser ablation of solid samarium is strongly dependent on the number of ablation laser shots in the range from 1 to 10. By ablating the fresh surface (i.e. 1st shot), we find the kinetic energy of both Sm and Sm + ion to be the largest (24 and 250 eV, respectively). Almost 10 times larger kinetic energy of Sm + ion than that of Sm clearly indicates the contribution of Coulomb explosion in the acceleration process. From the second shot, kinetic energies of Sm and Sm + ion are lower than those of the first shot and almost constant (ca. 12 and 80 eV, respectively). This behaviour suggests the change in the nature of the solid surface after femtosecond laser ablation, which can be explained by the amorphization of ablated sample surface reported in recent studies

Bacterial growth kinetics

International Nuclear Information System (INIS)

Boonkitticharoen, V.; Ehrhardt, J.C.; Kirchner, P.T.

1989-01-01

Quantitative measurement of bacterial growth may be made using a radioassay technique. This method measures, by scintillation counting, the 14 CO 2 derived from the bacterial metabolism of a 14 C-labeled substrate. Mathematical growth models may serve as reliable tools for estimation of the generation rate constant (or slope of the growth curve) and provide a basis for evaluating assay performance. Two models, i.e., exponential and logistic, are proposed. Both models yielded an accurate fit to the data from radioactive measurement of bacterial growth. The exponential model yielded high precision values of the generation rate constant, with an average relative standard deviation of 1.2%. Under most conditions the assay demonstrated no changes in the slopes of growth curves when the number of bacteria per inoculation was changed. However, the radiometric assay by scintillation method had a growth-inhibiting effect on a few strains of bacteria. The source of this problem was thought to be hypersensitivity to trace amounts of toluene remaining on the detector

The development from kinetic coefficients of a predictive model for the growth of Eichhomia crassipes in the field. I. Generating kinetic coefficients for the model in greenhouse culture

Directory of Open Access Journals (Sweden)

C. F. Musil

1984-12-01

Full Text Available The kinetics of N- and P- limited growth of Eichhornia crassipes (Mart . Solms were investigated in greenhouse culture with the object of developing a model for predicting population sizes, yields, growth rates and frequencies and amounts of harvest, under varying conditions of nutrient loading and climate, to control both nutrient inputs and excessive growth in eutrophied aquatic systems. The kinetic coefficients, maximum specific growth rate (Umax, half saturation coefficient (Ks and yield coefficient (Yc were measured under N and P limitation in replicated batch culture experiments. Umax values and Ks concentrations derived under N limitation ranged from 5,37 to 8,86% d + and from 400 to 1 506 µg  N ℓ1respectively. Those derived under P limitation ranged from 4,51 to 10,89% d 1 and from 41 to 162 fig P ℓ1 respectively. Yc values (fresh mass basis determined ranged from 1 660 to 1 981 (87 to 98 dry mass basis for N and from 16 431 to 18 671 (867 to 980 dry mass basis for P. The reciprocals of Yc values (dry mass basis, expressed as percentages, adequately estimated the minimum limiting concentrations of N and P {% dry mass in the plant tissues. Kinetic coefficients determined are compared with those reported for algae. The experimental method used and results obtained are critically assessed.

On-line study of growth kinetics of single hyphae of Aspergillus oryzae in a flow-through cell

DEFF Research Database (Denmark)

Christiansen, Torben; Spohr, Anders Bendsen; Nielsen, Jens Bredal

1999-01-01

Using image analysis the growth kinetics of the single hyphae of the filamentous fungus Aspergillus oryzae has been determined on-line in a flow-through cell at different glucose concentrations in the range from 26 mg L-1 to 20 g L-1. The tip extension rate of the individual hyphae can be described...... with saturation type kinetics with respect to the length of the hyphae. The maximum tip extension rate is constant for all hyphae measured at the same glucose concentration, whereas the saturation constant for the hyphae varies significantly between the hyphae even within the same hyphal element. When apical...... branching occurs, it is observed that the tip extension rate decreases temporarily. The number of branches formed on a hypha is proportional to the length of the hypha that exceeds a certain minimum length required to support the growth of a new branch. The observed kinetics has been used to simulate...

Bubble extinction in Hele-Shaw flow with surface tension and kinetic undercooling regularization

International Nuclear Information System (INIS)

Dallaston, Michael C; McCue, Scott W

2013-01-01

We perform an analytic and numerical study of an inviscid contracting bubble in a two-dimensional Hele-Shaw cell, where the effects of both surface tension and kinetic undercooling on the moving bubble boundary are not neglected. In contrast to expanding bubbles, in which both boundary effects regularize the ill-posedness arising from the viscous (Saffman–Taylor) instability, we show that in contracting bubbles the two boundary effects are in competition, with surface tension stabilizing the boundary, and kinetic undercooling destabilizing it. This competition leads to interesting bifurcation behaviour in the asymptotic shape of the bubble in the limit it approaches extinction. In this limit, the boundary may tend to become either circular, or approach a line or ‘slit’ of zero thickness, depending on the initial condition and the value of a nondimensional surface tension parameter. We show that over a critical range of surface tension values, both these asymptotic shapes are stable. In this regime there exists a third, unstable branch of limiting self-similar bubble shapes, with an asymptotic aspect ratio (dependent on the surface tension) between zero and one. We support our asymptotic analysis with a numerical scheme that utilizes the applicability of complex variable theory to Hele-Shaw flow. (paper)

Comparison of skating kinetics and kinematics on ice and on a synthetic surface.

Science.gov (United States)

Stidwill, T J; Pearsall, David; Turcotte, Rene

2010-03-01

The recent popularization and technological improvements of synthetic or artificial ice surfaces provide an attractive alternative to real ice in venues where the latter is impractical to install. Potentially, synthetic ice (SI) may be installed in controlled laboratory settings to permit detailed biomechanical analysis of skating manoeuvres. Unknown, however, is the extent to which skating on SI replicates skating on traditional ice (ICE). Hence, the purpose of this study was to compare kinetic and kinematic forward skating parameters between SI and ICE surfaces. With 11 male hockey players, a portable strain gauge system adhered to the outside of the skate blade holder was used to measure skate propulsive force synchronized with electrogoniometers for tracking dynamic knee and ankle movements during forward skating acceleration. In general, the kinetic and kinematic variables investigated in this study showed minimal differences between the two surfaces (P > 0.06), and no individual variable differences were identified between the two surfaces (P > or = 0.1) with the exception of greater knee extension on SI than ICE (15.2 degrees to 11.0 degrees; P skating, and thus offer the potential for valid analogous conditions for in-lab testing and training.

UO2 Grain Growth: Developing Phase Field Models for Pore Dragging, Solute Dragging and Anisotropic Grain Boundary Energies

International Nuclear Information System (INIS)

Ahmed, K.; Tonks, M.; Zhang, Y.; Biner, B.

2016-01-01

A detailed phase field model for the effect of pore drag on grain growth kinetics was implemented in MARMOT. The model takes into consideration both the curvature-driven grain boundary motion and pore migration by surface diffusion. As such, the model accounts for the interaction between pore and grain boundary kinetics, which tends to retard the grain growth process. Our 2D and 3D simulations demonstrate that the model capture all possible pore-grain boundary interactions proposed in theoretical models. For high enough surface mobility, the pores move along with the migrating boundary as a quasi-rigid-body, albeit hindering its migration rate compared to the pore-free case. For less mobile pores, the migrating boundary can separate from the pores. For the pore-controlled grain growth kinetics, the model predicts a strong dependence of the growth rate on the number of pores, pore size, and surface diffusivity in agreement with theroretical models. An evolution equation for the grain size that includes these parameters was derived and showed to agree well with numerical solution. It shows a smooth transition from boundary-controlled kinetics to pore-controlled kinetics as the surface diffusivity decreases or the number of pores or their size increases. This equation can be utilized in BISON to give accurate estimate for the grain size evolution. This will be accomplished in the near future. The effect of solute drag and anisotropy of grain boundary on grain growth will be investigated in future studies.

Dynamics of barite growth in porous media quantified by in situ synchrotron X-ray tomography

Science.gov (United States)

Godinho, jose; Gerke, kirill

2016-04-01

Current models used to formulate mineral sequestration strategies of dissolved contaminants in the bedrock often neglect the effect of confinement and the variation of reactive surface area with time. In this work, in situ synchrotron X-ray micro-tomography is used to quantify barite growth rates in a micro-porous structure as a function of time during 13.5 hours with a resolution of 1 μm. Additionally, the 3D porous network at different time frames are used to simulate the flow velocities and calculate the permeability evolution during the experiment. The kinetics of barite growth under porous confinement is compared with the kinetics of barite growth on free surfaces in the same fluid composition. Results are discussed in terms of surface area normalization and the evolution of flow velocities as crystals fill the porous structure. During the initial hours the growth rate measured in porous media is similar to the growth rate on free surfaces. However, as the thinner flow paths clog the growth rate progressively decreases, which is correlated to a decrease of local flow velocity. The largest pores remain open, enabling growth to continue throughout the structure. Quantifying the dynamics of mineral precipitation kinetics in situ in 4D, has revealed the importance of using a time dependent reactive surface area and accounting for the local properties of the porous network, when formulating predictive models of mineral precipitation in porous media.

Bubble growth in a narrow horizontal space

International Nuclear Information System (INIS)

Stutz, Benoit; Goulet, Remi; Passos, Julio Cesar

2009-01-01

The purpose of this work is to develop an axis-symmetric two-phase flow model describing the growth of a single bubble squeezed between a horizontal heated upward-facing disc and an insulating surface placed parallel to the heated surface. Heat transfers at the liquid-vapour interfaces are predicted by the kinetic limit of vaporisation. The depths of the liquid films deposed on the surfaces (heated surface and confinement space) are determined using the Moriyama and Inoue correlation (1996). Transient heat transfers within the heated wall are taken into account. The model is applied to pentane bubble growth. The influence of the gap size, the initial temperature of the system, the thermal effusivity of the heated wall and the kinetic limit of vaporisation are studied. The results show that the expansion of the bubbles strongly depends on the gap size and can be affected by the effusivity of the material. Mechanical inertia effects are mainly dominant at the beginning of the bubble expansion. Pressure drop induced by viscous effects have to be taken into account for high capillary numbers. Heat transfers at the meniscus are negligible except at the early stages of the bubble growth. (author)

Bubble growth in a narrow horizontal space

Energy Technology Data Exchange (ETDEWEB)

Stutz, Benoit; Goulet, Remi [CETHIL, UMR5008, CNRS, INSA-Lyon, Universite Lyon1 (France); Passos, Julio Cesar [Universidade Federal de Santa Catarina (UFSC), Florianopolis, SC (Brazil). Dept. de Engenharia Mecanica. LABSOLAR

2009-07-01

The purpose of this work is to develop an axis-symmetric two-phase flow model describing the growth of a single bubble squeezed between a horizontal heated upward-facing disc and an insulating surface placed parallel to the heated surface. Heat transfers at the liquid-vapour interfaces are predicted by the kinetic limit of vaporisation. The depths of the liquid films deposed on the surfaces (heated surface and confinement space) are determined using the Moriyama and Inoue correlation (1996). Transient heat transfers within the heated wall are taken into account. The model is applied to pentane bubble growth. The influence of the gap size, the initial temperature of the system, the thermal effusivity of the heated wall and the kinetic limit of vaporisation are studied. The results show that the expansion of the bubbles strongly depends on the gap size and can be affected by the effusivity of the material. Mechanical inertia effects are mainly dominant at the beginning of the bubble expansion. Pressure drop induced by viscous effects have to be taken into account for high capillary numbers. Heat transfers at the meniscus are negligible except at the early stages of the bubble growth. (author)

Kinetic Behavior of Exchange-Driven Growth with Catalyzed-Birth Processes

International Nuclear Information System (INIS)

Wang Haifeng; Lin Zhenquan; Kong Xiangmu

2006-01-01

Two catalyzed-birth models of n-species (n≥2) aggregates with exchange-driven growth processes are proposed and compared. In the first one, the exchange reaction occurs between any two aggregates A m k and A m j of the same species with the rate kernels K m (k,j) = K m kj (m = 1,2,...,n, n≥2), and aggregates of A n species catalyze a monomer-birth of A l species (l = 1,2,...,n-1) with the catalysis rate kernel J l (k,j) = J l kj υ . The kinetic behaviors are investigated by means of the mean-field theory. We find that the evolution behavior of aggregate-size distribution a l k (t) of A l species depends crucially on the value of the catalysis rate parameter υ: (i) a l k (t) obeys the conventional scaling law in the case of υ≤0, (ii) a l k (t) satisfies a modified scaling form in the case of υ>0. In the second model, the mechanism of monomer-birth of A n -species catalyzed by A l species is added on the basis of the first model, that is, the aggregates of A l and A n species catalyze each other to cause monomer-birth. The kinetic behaviors of A l and A n species are found to fall into two categories for the different υ: (i) growth obeying conventional scaling form with υ≤0, (ii) gelling at finite time with υ>0.

Graphene growth and stability at nickel surfaces

International Nuclear Information System (INIS)

Lahiri, Jayeeta; S Miller, Travis; J Ross, Andrew; Adamska, Lyudmyla; Oleynik, Ivan I; Batzill, Matthias

2011-01-01

The formation of single-layer graphene by exposure of a Ni(111) surface to ethylene at low pressure has been investigated. Two different growth regimes were found. At temperatures between 480 and 650 deg. C, graphene grows on a pure Ni(111) surface in the absence of a carbide. Below 480 deg. C, graphene growth competes with the formation of a surface Ni 2 C carbide. This Ni 2 C phase suppresses the nucleation of graphene. Destabilization of the surface carbide by the addition of Cu to the surface layer facilitates the nucleation and growth of graphene at temperatures below 480 deg. C. In addition to the growth of graphene on Ni substrates, the interaction between graphene and Ni was also studied. This was done both experimentally by Ni deposition on Ni-supported graphene and by density functional theory calculation of the work of adhesion between graphene and Ni. For graphene sandwiched between two Ni-layers, the work of adhesion between graphene and the Ni substrate was found to be four times as large as that for the Ni-supported graphene without a top layer. This stronger interaction may cause the destruction of graphene that is shown experimentally to occur at ∼200 0 C when Ni is deposited on top of Ni-supported graphene. The destruction of graphene allows the Ni deposits to merge with the substrate Ni. After the completion of this process, the graphene sheet is re-formed on top of the Ni substrate, leaving no Ni at the surface.

Seedless Synthesis of Monodispersed Gold Nanorods with Remarkably High Yield: Synergistic Effect of Template Modification and Growth Kinetics Regulation.

Science.gov (United States)

Liu, Kang; Bu, Yanru; Zheng, Yuanhui; Jiang, Xuchuan; Yu, Aibing; Wang, Huanting

2017-03-08

Gold nanorods (AuNRs) are versatile materials due to their broadly tunable optical properties associated with their anisotropic feature. Conventional seed-mediated synthesis is, however, not only limited by the operational complexity and over-sensitivity towards subtle changes of experimental conditions but also suffers from low yield (≈15 %). A facile seedless method is reported to overcome these challenges. Monodispersed AuNRs with high yield (≈100 %) and highly adjustable longitudinal surface plasmon resonance (LSPR) are reproducibly synthesized. The parameters that influence the AuNRs growth were thoroughly investigated in terms of growth kinetics and soft-template regulation, offering a better understanding of the template-based mechanism. The facile synthesis, broad tunability of LSRP, high reproducibility, high yield, and ease of scale-up make this method promising for the future mass production of monodispersed AuNRs for applications in catalysis, sensing, and biomedicine. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

A kinetic model for growth and biosynthesis of medium-chain-length poly-(3-hydroxyalkanoates in Pseudomonas putida

Directory of Open Access Journals (Sweden)

M. S. M. Annuar

2008-06-01

Full Text Available A kinetic model is presented giving a mathematical description of batch culture of Pseudomonas putida PGA1 grown using saponified palm kernel oil as carbon source and ammonium as the limiting nutrient. The growth of the micro-organism is well-described using Tessier-type model which takes into account the inhibitory effect of ammonium at high concentrations. The ammonium consumption rate by the cells is related in proportion to the rate of growth. The intracellular production of medium-chain-length poly-(3-hydroxyalkanoates (PHA MCL by P. putida PGA1 cells is reasonably modeled by the modified Luedeking-Piret kinetics, which incorporate a function of product synthesis inhibition (or reduction by ammonium above a threshold level.

Size effect on order-disorder transition kinetics of FePt nanoparticles

International Nuclear Information System (INIS)

Zhang, Shuaidi; Qi, Weihong; Huang, Baiyun

2014-01-01

The kinetics of order-disorder transition of FePt nanoparticles during high temperature annealing is theoretically investigated. A model is developed to address the influence of large surface to volume ratio of nanoparticles on both the thermodynamic and kinetic aspect of the ordering process; specifically, the nucleation and growth of L1 0 ordered domain within disordered nanoparticles. The size- and shape-dependence of transition kinetics are quantitatively addressed by a revised Johnson-Mehl-Avrami equation that included corrections for deviations caused by the domination of surface nucleation in nanoscale systems and the non-negligible size of the ordered nuclei. Calculation results based on the model suggested that smaller nanoparticles are kinetically more active but thermodynamically less transformable. The major obstacle in obtaining completely ordered nanoparticles is the elimination of antiphase boundaries. The results also quantitatively confirmed the existence of a size-limit in ordering, beyond which, inducing order-disorder transitions through annealing is impossible. A good agreement is observed between theory, experiment, and computer simulation results

Transient disturbance growth in flows over convex surfaces

Science.gov (United States)

Karp, Michael; Hack, M. J. Philipp

2017-11-01

Flows over curved surfaces occur in a wide range of applications including airfoils, compressor and turbine vanes as well as aerial, naval and ground vehicles. In most of these applications the surface has convex curvature, while concave surfaces are less common. Since monotonic boundary-layer flows over convex surfaces are exponentially stable, they have received considerably less attention than flows over concave walls which are destabilized by centrifugal forces. Non-modal mechanisms may nonetheless enable significant disturbance growth which can make the flow susceptible to secondary instabilities. A parametric investigation of the transient growth and secondary instability of flows over convex surfaces is performed. The specific conditions yielding the maximal transient growth and strongest instability are identified. The effect of wall-normal and spanwise inflection points on the instability process is discussed. Finally, the role and significance of additional parameters, such as the geometry and pressure gradient, is analyzed.

Growth kinetics of vertically aligned carbon nanotube arrays in clean oxygen-free conditions.

Science.gov (United States)

In, Jung Bin; Grigoropoulos, Costas P; Chernov, Alexander A; Noy, Aleksandr

2011-12-27

Vertically aligned carbon nanotubes (CNTs) are an important technological system, as well as a fascinating system for studying basic principles of nanomaterials synthesis; yet despite continuing efforts for the past decade many important questions about this process remain largely unexplained. We present a series of parametric ethylene chemical vapor deposition growth studies in a "hot-wall" reactor using ultrapure process gases that reveal the fundamental kinetics of the CNT growth. Our data show that the growth rate is proportional to the concentration of the carbon feedstock and monotonically decreases with the concentration of hydrogen gas and that the most important parameter determining the rate of the CNT growth is the production rate of active carbon precursor in the gas phase reaction. The growth termination times obtained with the purified gas mixtures were strikingly insensitive to variations in both hydrogen and ethylene pressures ruling out the carbon encapsulation of the catalyst as the main process termination cause.

Short-time beta grain growth kinetics for a conventional titanium alloy

International Nuclear Information System (INIS)

Semiatin, S.L.; Sukonnik, I.M.

1996-01-01

The kinetics of beta grain growth during short-time, supertransus heat treatment of Ti-5Al-4V were determined using a salt-pot technique. The finite-time, subtransus temperature transient during salt-pot heating was quantified through measurements of the heat transfer coefficient characterizing conduction across the salt-titanium interface and a simple heat conduction analysis which incorporated this heat transfer coefficient. Grain size versus time data adjusted to account for the subtransus temperature transient were successfully fit to the parabolic grain growth law d n - d 0 n = kt exp(-Q/RT) using an exponent n equal to 2.0. Comparison of the present results to rapid, continuous heat treatment data in the literature for a similar titanium alloy revealed a number of semi-quantitative similarities

Insulin-like growth factors and leucine kinetics during exercise training in children with cystic fibrosis

NARCIS (Netherlands)

Gulmans, [No Value; van der Laag, J; Wattimena, D; van Doorn, J; Oostveen, D; Berger, R; van de Meer, K

Background: Little is known about the metabolic effects of exercise training in children with cystic fibrosis. The hypothesis for the current study was that in patients with declining clinical status, exercise increases circulating insulin-like growth factors (IGFs) and improves protein kinetics.

Kinetics of nickel silicide growth in silicon nanowires: From linear to square root growth

International Nuclear Information System (INIS)

Yaish, Y. E.; Beregovsky, M.; Katsman, A.; Cohen, G. M.

2011-01-01

The common practice for nickel silicide formation in silicon nanowires (SiNWs) relies on axial growth of silicide along the wire that is initiated from nickel reservoirs at the source and drain contacts. In the present work the silicide intrusions were studied for various parameters including wire diameter (25-50 nm), annealing time (15-120 s), annealing temperature (300-440 deg. C), and the quality of the initial Ni/Si interface. The silicide formation was investigated by high-resolution scanning electron microscopy, high-resolution transmission electron microscopy (TEM), and atomic force microscopy. The main part of the intrusion formed at 420 deg. C consists of monosilicide NiSi, as was confirmed by energy dispersive spectroscopy STEM, selected area diffraction TEM, and electrical resistance measurements of fully silicided SiNWs. The kinetics of nickel silicide axial growth in the SiNWs was analyzed in the framework of a diffusion model through constrictions. The model calculates the time dependence of the intrusion length, L, and predicts crossover from linear to square root time dependency for different wire parameters, as confirmed by the experimental data.

Morphological evolution of dissolving feldspar particles with anisotropic surface kinetics and implications for dissolution rate normalization and grain size dependence: A kinetic modeling study

Science.gov (United States)

Zhang, Li; Lüttge, Andreas

2009-11-01

With previous two-dimensional (2D) simulations based on surface-specific feldspar dissolution succeeding in relating the macroscopic feldspar kinetics to the molecular-scale surface reactions of Si and Al atoms ( Zhang and Lüttge, 2008, 2009), we extended our modeling effort to three-dimensional (3D) feldspar particle dissolution simulations. Bearing on the same theoretical basis, the 3D feldspar particle dissolution simulations have verified the anisotropic surface kinetics observed in the 2D surface-specific simulations. The combined effect of saturation state, pH, and temperature on the surface kinetics anisotropy has been subsequently evaluated, found offering diverse options for morphological evolution of dissolving feldspar nanoparticles with varying grain sizes and starting shapes. Among the three primary faces on the simulated feldspar surface, the (1 0 0) face has the biggest dissolution rate across an extensively wide saturation state range and thus acquires a higher percentage of the surface area upon dissolution. The slowest dissolution occurs to either (0 0 1) or (0 1 0) faces depending on the bond energies of Si-(O)-Si ( ΦSi-O-Si/ kT) and Al-(O)-Si ( ΦAl-O-Si/ kT). When the ratio of ΦSi-O-Si/ kT to ΦAl-O-Si/ kT changes from 6:3 to 7:5, the dissolution rates of three primary faces change from the trend of (1 0 0) > (0 1 0) > (0 0 1) to the trend of (1 0 0) > (0 0 1) > (0 1 0). The rate difference between faces becomes more distinct and accordingly edge rounding becomes more significant. Feldspar nanoparticles also experience an increasing degree of edge rounding from far-from-equilibrium to close-to-equilibrium. Furthermore, we assessed the connection between the continuous morphological modification and the variation in the bulk dissolution rate during the dissolution of a single feldspar particle. Different normalization treatments equivalent to the commonly used mass, cube assumption, sphere assumption, geometric surface area, and reactive

The Kinetics of Chirality Assignment in Catalytic Single Walled Carbon Nanotube Growth

OpenAIRE

Xu, Ziwei; Yan, Tianying; Ding, Feng

2014-01-01

Chirality-selected single-walled carbon nanotubes (SWCNTs) ensure a great potential of building ~1 nm sized electronics. However, the reliable method for chirality-selected SWCNT is still pending. Here we present a theoretical study on the SWCNT's chirality assignment and control during the catalytic growth. This study reveals that the chirality of a SWCNT is determined by the kinetic incorporation of the pentagon formation during SWCNT nucleation. Therefore, chirality is randomly assigned on...

Tumor cell proliferation kinetics and tumor growth rate

Energy Technology Data Exchange (ETDEWEB)

Tubiana, M

1989-01-01

The present knowledge on the growth rate and the proliferation kinetics of human tumor is based on the measurement of the tumor doubling times (DT) in several hundred patients and on the determination of the proportion of proliferating cells with radioactive thymidine or by flow cytometry in large numbers of patients. The results show that the DT of human tumor varies widely, from less than one week to over one year with a median value of approximately 2 months. The DTs are significantly correlated with the histological type. They depend upon (1) the duration of the cell cycle whose mean duration is 2 days with small variations from tumor to tumor, (2) the proportion of proliferating cells and consequently the cell birth rate which varies widely among tumors and which is significantly correlated to the DT, (3) the cell loss factors which also vary widely and which are the greatest when proliferation is most intensive. These studies have several clinical implications: (a) they have further increased our understanding of the natural history of human tumor, (b) they have therapeutic implications since tumor responsiveness and curability by radiation and drugs are strongly influenced by the cell kinetic parameters of the tumor, (c) the proportion of proliferating cells is of great prognostic value in several types of human cancers. The investigation of the molecular defects, which are correlated with the perturbation of control of cell proliferation, should lead to significant fundamental and therapeutic advances. (orig.).

In Situ AFM Study of Crystal Growth on a Barite (001 Surface in BaSO4 Solutions at 30 °C

Directory of Open Access Journals (Sweden)

Yoshihiro Kuwahara

2016-11-01

Full Text Available The growth behavior and kinetics of the barite (001 surface in supersaturated BaSO4 solutions (supersaturation index (SI = 1.1–4.1 at 30 °C were investigated using in situ atomic force microscopy (AFM. At the lowest supersaturation, the growth behavior was mainly the advancement of the initial step edges and filling in of the etch pits formed in the water before the BaSO4 solution was injected. For solutions with higher supersaturation, the growth behavior was characterized by the advance of the and [010] half-layer steps with two different advance rates and the formation of growth spirals with a rhombic to bow-shaped form and sector-shaped two-dimensional (2D nuclei. The advance rates of the initial steps and the two steps of 2D nuclei were proportional to the SI. In contrast, the advance rates of the parallel steps with extremely short step spacing on growth spirals were proportional to SI2, indicating that the lateral growth rates of growth spirals were directly proportional to the step separations. This dependence of the advance rate of every step on the growth spirals on the step separations predicts that the growth rates along the [001] direction of the growth spirals were proportional to SI2 for lower supersaturations and to SI for higher supersaturations. The nucleation and growth rates of the 2D nuclei increased sharply for higher supersaturations using exponential functions. Using these kinetic equations, we predicted a critical supersaturation (SI ≈ 4.3 at which the main growth mechanism of the (001 face would change from a spiral growth to a 2D nucleation growth mechanism: therefore, the morphology of bulk crystals would change.

Growth of non-toxigenic Clostridium botulinum mutant LNT01 in cooked beef: One-step kinetic analysis and comparison with C. sporogenes and C. perfringens.

Science.gov (United States)

Huang, Lihan

2018-05-01

The objective of this study was to investigate the growth kinetics of Clostridium botulinum LNT01, a non-toxigenic mutant of C. botulinum 62A, in cooked ground beef. The spores of C. botulinum LNT01 were inoculated to ground beef and incubated anaerobically under different temperature conditions to observe growth and develop growth curves. A one-step kinetic analysis method was used to analyze the growth curves simultaneously to minimize the global residual error. The data analysis was performed using the USDA IPMP-Global Fit, with the Huang model as the primary model and the cardinal parameters model as the secondary model. The results of data analysis showed that the minimum, optimum, and maximum growth temperatures of this mutant are 11.5, 36.4, and 44.3 °C, and the estimated optimum specific growth rate is 0.633 ln CFU/g per h, or 0.275 log CFU/g per h. The maximum cell density is 7.84 log CFU/g. The models and kinetic parameters were validated using additional isothermal and dynamic growth curves. The resulting residual errors of validation followed a Laplace distribution, with about 60% of the residual errors within ±0.5 log CFU/g of experimental observations, suggesting that the models could predict the growth of C. botulinum LNT01 in ground beef with reasonable accuracy. Comparing with C. perfringens, C. botulinum LNT01 grows at much slower rates and with much longer lag times. Its growth kinetics is also very similar to C. sporogenes in ground beef. The results of computer simulation using kinetic models showed that, while prolific growth of C. perfringens may occur in ground beef during cooling, no growth of C. botulinum LNT01 or C. sporogenes would occur under the same cooling conditions. The models developed in this study may be used for prediction of the growth and risk assessments of proteolytic C. botulinum in cooked meats. Published by Elsevier Ltd.

Crossing the mesoscale no-mans land via parallel kinetic Monte Carlo.

Energy Technology Data Exchange (ETDEWEB)

Garcia Cardona, Cristina (San Diego State University); Webb, Edmund Blackburn, III; Wagner, Gregory John; Tikare, Veena; Holm, Elizabeth Ann; Plimpton, Steven James; Thompson, Aidan Patrick; Slepoy, Alexander (U. S. Department of Energy, NNSA); Zhou, Xiao Wang; Battaile, Corbett Chandler; Chandross, Michael Evan

2009-10-01

The kinetic Monte Carlo method and its variants are powerful tools for modeling materials at the mesoscale, meaning at length and time scales in between the atomic and continuum. We have completed a 3 year LDRD project with the goal of developing a parallel kinetic Monte Carlo capability and applying it to materials modeling problems of interest to Sandia. In this report we give an overview of the methods and algorithms developed, and describe our new open-source code called SPPARKS, for Stochastic Parallel PARticle Kinetic Simulator. We also highlight the development of several Monte Carlo models in SPPARKS for specific materials modeling applications, including grain growth, bubble formation, diffusion in nanoporous materials, defect formation in erbium hydrides, and surface growth and evolution.

Delayed frost growth on jumping-drop superhydrophobic surfaces.

Science.gov (United States)

Boreyko, Jonathan B; Collier, C Patrick

2013-02-26

Self-propelled jumping drops are continuously removed from a condensing superhydrophobic surface to enable a micrometric steady-state drop size. Here, we report that subcooled condensate on a chilled superhydrophobic surface are able to repeatedly jump off the surface before heterogeneous ice nucleation occurs. Frost still forms on the superhydrophobic surface due to ice nucleation at neighboring edge defects, which eventually spreads over the entire surface via an interdrop frost wave. The growth of this interdrop frost front is shown to be up to 3 times slower on the superhydrophobic surface compared to a control hydrophobic surface, due to the jumping-drop effect dynamically minimizing the average drop size and surface coverage of the condensate. A simple scaling model is developed to relate the success and speed of interdrop ice bridging to the drop size distribution. While other reports of condensation frosting on superhydrophobic surfaces have focused exclusively on liquid-solid ice nucleation for isolated drops, these findings reveal that the growth of frost is an interdrop phenomenon that is strongly coupled to the wettability and drop size distribution of the surface. A jumping-drop superhydrophobic condenser minimized frost formation relative to a conventional dropwise condenser in two respects: preventing heterogeneous ice nucleation by continuously removing subcooled condensate, and delaying frost growth by limiting the success of interdrop ice bridge formation.

The shaping of zinc coating on surface steels and ductile iron casting

Directory of Open Access Journals (Sweden)

D. Kopyciński

2010-01-01

Full Text Available The studies aimed at an analysis of the formation and growth kinetics of zinc coating on reactive silicon-killed steels in a zinc bath. The growth kinetics of the produced zinc coatings was evaluated basing on the power-law growth equation. As regards galvanizing of the surface of products, investigation was done for various steel grades and ductile iron (DI taking into account the quality and thickness of coating. It has been proved that the chemical constitution of basis significantly influences the kinetics of growth of the individual phases in a zinc coating. This relationship was evaluated basing on the, so called, silicon and phosphorus equivalent ESi,P and coating thickness dependences were obtained.

Molecular dynamics studies of InGaN growth on nonpolar (11 2 \\xAF0 ) GaN surfaces

Science.gov (United States)

Chu, K.; Gruber, J.; Zhou, X. W.; Jones, R. E.; Lee, S. R.; Tucker, G. J.

2018-01-01

We have performed direct molecular dynamics (MD) simulations of heteroepitaxial vapor deposition of I nxG a1 -xN films on nonpolar (11 2 ¯0 ) wurtzite-GaN surfaces to investigate strain relaxation by misfit-dislocation formation. The simulated growth is conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN substrate. We apply time-and-position-dependent boundary constraints to affect the appropriate environments for the vapor phase, the near-surface solid phase, and the bulklike regions of the growing layer. The simulations employ a newly optimized Stillinger-Weber In-Ga-N system interatomic potential wherein multiple binary and ternary structures are included in the underlying density-functional theory and experimental training sets to improve the treatment of the In-Ga-N related interactions. To examine the effect of growth conditions, we study a matrix of 63 different MD-growth simulations spanning seven I nxG a1 -xN -alloy compositions ranging from x =0.0 to x =0.8 and nine growth temperatures above half the simulated melt temperature. We found a composition dependent temperature range where all kinetically trapped defects were eliminated, leaving only quasiequilibrium misfit and threading dislocations present in the simulated films. Based on the MD results obtained in this temperature range, we observe the formation of interfacial misfit and threading dislocation arrays with morphologies strikingly close to those seen in experiments. In addition, we compare the MD-observed thickness-dependent onset of misfit-dislocation formation to continuum-elasticity-theory models of the critical thickness and find reasonably good agreement. Finally, we use the three-dimensional atomistic details uniquely available in the MD-growth histories to directly observe the nucleation of dislocations at surface pits in the evolving free surface.

The effect of the Ca2+ to CO32- activity ratio on spiral growth at the calcite {1014} surface

DEFF Research Database (Denmark)

Larsen, Kirsten Kolbjørn; Bechgaard, Klaus; Stipp, Susan Louise Svane

2010-01-01

Variation in the Ca2+ to CO 2¿ activity ratio of natural waters is rarely considered in models intended to describe calcite 3 growth. Atomic force microscopy (AFM) and differential interference contrast (DIC) microscopy were used to examine spiral growth on calcite f10¿14g surfaces from solutions...... velocity is achieved at higher relative 3 CO 2¿ activity. The obtuse step velocity data fit the ‘kinetic ionic ratio’ model of Zhang and Nancollas (1998) well, but acute 3 step velocities cannot be described by this model. This is attributed to dissimilar dehydration frequencies for Ca2+ and CO 2¿ 3...

Selected mode of dendritic growth with n-fold symmetry in the presence of a forced flow

Science.gov (United States)

Alexandrov, D. V.; Galenko, P. K.

2017-07-01

The effect of n-fold crystal symmetry is investigated for a two-dimensional stable dendritic growth in the presence of a forced convective flow. We consider dendritic growth in a one-component undercooled liquid. The theory is developed for the parabolic solid-liquid surface of dendrite growing at arbitrary growth Péclet numbers keeping in mind small anisotropies of surface energy and growth kinetics. The selection criterion determining the stable growth velocity of the dendritic tip and its stable tip diameter is found on the basis of solvability analysis. The obtained criterion includes previously developed theories of thermally and kinetically controlled dendritic growth with convection for the case of four-fold crystal symmetry. The obtained nonlinear system of equations (representing the selection criterion and undercooling balance) for the determination of dendrite tip velocity and dendrite tip diameter is analytically solved in a parametric form. These exact solutions clearly demonstrate a transition between thermally and kinetically controlled growth regimes. In addition, we show that the dendrites with larger crystal symmetry grow faster than those with smaller symmetry.

Finite element modelling of the oxidation kinetics of Zircaloy-4 with a controlled metal-oxide interface and the influence of growth stress

International Nuclear Information System (INIS)

Zumpicchiat, Guillaume; Pascal, Serge; Tupin, Marc; Berdin-Méric, Clotilde

2015-01-01

Highlights: We developed two finite element models of zirconium-based alloy oxidation using the CEA Cast3M code to simulate the oxidation kinetics of Zircaloy-4: the diffuse interface model and the sharp interface model. We also studied the effect of stresses on the oxidation kinetics. The main results are: • Both models lead to parabolic oxidation kinetics in agreement with the Wagner’s theory. • The modellings enable to calculate the stress distribution in the oxide as well as in the metal. • A strong effect of the hydrostatic stress on the oxidation kinetics has been evidenced. • The stress gradient effect changes the parabolic kinetics into a sub-parabolic law closer to the experimental kinetics because of the stress gradient itself, but also because of the growth stress increase with the oxide thickness. - Abstract: Experimentally, zirconium-based alloys oxidation kinetics is sub-parabolic, by contrast with the Wagner theory which predicts a parabolic kinetics. Two finite element models have been developed to simulate this phenomenon: the diffuse interface model and the sharp interface model. Both simulate parabolic oxidation kinetics. The growth stress effects on oxygen diffusion are studied to try to explain the gap between theory and experience. Taking into account the influence of the hydrostatic stress and its gradient into the oxygen flux expression, sub-parabolic oxidation kinetics have been simulated. The sub-parabolic behaviour of the oxidation kinetics can be explained by a non-uniform compressive stress level into the oxide layer.

Grain growth kinetics of ringwoodite and majorite garnet mixtures and implications for the rheology of the transition zone

Science.gov (United States)

Ezad, I.; Dobson, D. P.; Brodholt, J. P.; Thomson, A.; Hunt, S.

2017-12-01

The grain size of the transition zone is a poorly known but important geophysical parameter. Among others, the grain size may control the rheology, seismic attenuation and radiative thermal conductivity of the mantle. However, the grain size of the transition zone minerals ringwoodite (Mg,Fe)2SiO4 and majorite garnet MgSiO3 under appropriate zone conditions is currently unknown and there are very few experiments with which to constrain it. In order to determine the grain size of the transition zone, the grain growth kinetics must be determined for a range of mantle compositions. We have, therefore, experimentally determined the grain growth kinetics of the lowermost transition zone minerals through multi anvil experiments at University College London (UCL). This is achieved through a comprehensive set of time series experiments at pressures of 21 GPa and temperatures relevant to the transition zone. We have also determined the effect of varying water content, oxygen fugacity, iron content and aluminium content also discussed by Dobson and Mariani., (2014). Our initial grain growth experiments conducted at 1200°C and 1400°C at 18 GPa show extremely slow grain growth kinetics; time series experiments extended to 105.8 seconds are unable to produce grains larger than 100 nm. This suggests that fine-grained material at the base of the transition zone will persist on geological timescales. Such small grains size suggests that diffusion creep might be the dominant deformation mechanism in this region. Reference: Dobson, D.P., Mariani, E., 2014. The kinetics of the reaction of majorite plus ferropericlase to ringwoodite: Implications for mantle upwellings crossing the 660 km discontinuity. Earth Planet. Sci. Lett. 408, 110-118. doi:10.1016/j.epsl.2014.10.009

KINETICS OF GROWTH AND ETHANOL PRODUCTION ON DIFFERENT CARBON SUBSTRATES USING GENETICALLY ENGINEERED XYLOSE-FERMENTING YEAST

Science.gov (United States)

Saccharomyces cerevisiae 424A (LNH-ST) strain was used for fermentation of glucose and xylose. Growth kinetics and ethanol productivity were calculated for batch fermentation on media containing different combinations of glucose and xylose to give a final sugar concentra...

Kinetic parameters of nitridation of molybdenum and niobium alloys with various structure states

International Nuclear Information System (INIS)

Solodkin, G.A.; Bulgach, A.A.; Likhacheva, T.E.

1985-01-01

Effect of preliminary plastic strain under rolling on kinetic parameters of nitridation of VN-2AEh, VN-3 niobium alloys and molybdenum alloy with hafnium is investigated. Extreme character of dependence of kinetic parameters of nitridation on the degree of reduction under rolling is determined. Preliminary plastic strain at negligible reduction is shown to accelerate growth of the zone of internal nitridation and decelerates growth of the nitride zone. Nitrogen atom removal from the surface to the centre is retarded at the increase of the degree of reduction up to 50% and higher. The degree of deformations is the higher the lower nitridation temperature is

Surface science an introduction

CERN Document Server

Hudson, John

1991-01-01

The whole field of surface science is covered in this work. Starting with a description of the structure and thermodynamics of clean surfaces, the book goes on to discuss kinetic theory of gases and molecular beam formation. This is followed by a largesection on gas-surface interactions, and another major section on energetic particle-surface interactions. The final chapter provides the background to crystal nucleation and growth. The approach adopted is interdisciplinary and slanted towards theexperimental side, with practical analytical techniques being used to illustrate general princi

To the problem on formation kinetics of absorption and polylayer films in anodic oxidation of cadmium in alkali hydroxides. Kinetics of irreversible absorption of oxide

International Nuclear Information System (INIS)

Grachev, D.K.

1978-01-01

An attempt is made to substantiate the formation of adsorption and polylayer films on cadmium electrode during its oxidation in KOH diluted solutions based on the interpretation of data from methods of the potential control. Using relaxation methods (voltammetry and chronoammetry) the conditions were determined at which irreversible abd sorption kinetics of the passivating oxide turns out to dominate the anodic dissolution process in the KOH 1-0.1 N solutions. Parts of monolayer and polylayer surface filling are shown. Kinetics of monolayer oxide growth is interpreted based on the Temkin-Zeldovich type equation for irreversible adsorption process. Ways of the kinetic equation precision are discussed for its full correspondence with the experiment obtained

Effect of microwave-assisted heating on chalcopyrite leaching of kinetics, interface temperature and surface energy

Directory of Open Access Journals (Sweden)

Tong Wen

Full Text Available The microwave-assisted leaching was a new approach to intensify the copper recovery from chalcopyrite by hydrometallurgy. In this work, the effect of microwave-assisted heating on chalcopyrite leaching of kinetics, interfacial reaction temperature and surface energy were investigated. The activation energy of chalcopyrite leaching was affected indistinctively by the microwave-assisted heating (39.1 kJ/mol compared with the conventional heating (43.9 kJ/mol. However, the boiling point of the leaching system increased through microwave-assisted heating. Because of the improved boiling point and the selective heating of microwave, the interfacial reaction temperature increased significantly, which gave rise to the increase of the leaching recovery of copper. Moreover, the surface energy of the chalcopyrite through microwave-assisted heating was also enhanced, which was beneficial to strengthen the leaching of chalcopyrite. Keywords: Microwave-assisted heating, Chalcopyrite, Leaching kinetics, Interface temperature, Surface energy

Release kinetics of platelet-derived and plasma-derived growth factors from autologous plasma rich in growth factors.

Science.gov (United States)

Anitua, Eduardo; Zalduendo, Mari Mar; Alkhraisat, Mohammad Hamdan; Orive, Gorka

2013-10-01

Many studies have evaluated the biological effects of platelet rich plasma reporting the final outcomes on cell and tissues. However, few studies have dealt with the kinetics of growth factor delivery by plasma rich in growth factors. Venous blood was obtained from three healthy volunteers and processed with PRGF-Endoret technology to prepare autologous plasma rich in growth factors. The gel-like fibrin scaffolds were then incubated in triplicate, in a cell culture medium to monitor the release of PDGF-AB, VEGF, HGF and IGF-I during 8 days of incubation. A leukocyte-platelet rich plasma was prepared employing the same technology and the concentrations of growth factors and interleukin-1β were determined after 24h of incubation. After each period, the medium was collected, fibrin clot was destroyed and the supernatants were stored at -80°C until analysis. The growth factor delivery is diffusion controlled with a rapid initial release by 30% of the bioactive content after 1h of incubation and a steady state release when almost 70% of the growth factor content has been delivered. Autologous fibrin matrix retained almost 30% of the amount of the growth factors after 8 days of incubation. The addition of leukocytes to the formula of platelet rich plasma did not increase the concentration of the growth factors, while it drastically increased the presence of pro-inflammatory IL-1β. Further studies employing an in vitro inflammatory model would be interesting to study the difference in growth factors and pro-inflammatory cytokines between leukocyte-free and leukocyte-rich platelet rich plasma. Copyright © 2013 Elsevier GmbH. All rights reserved.

Effect of evaporation on the growth kinetics in a model for two species

International Nuclear Information System (INIS)

El-Nashar, Hassan F.

2002-02-01

A surface growth model for two species is proposed, when deposition, surface diffusion and evaporation are considered, in (1+1)-dimensions. A Monte Carlo simulation is carried out, focusing on the effect of evaporation on the evolution of the amount of roughness. The results show that the interplay between deposition, surface diffusion and evaporation slows down the rate of growth of the surface width. In addition, when the rate of evaporation increases, the surface width grows faster to a higher value, in comparison to the case of low rate of evaporation. This introduces changes in the scaling exponents which show that evaporation should be given equal or as much consideration as deposition and surface relaxation. (author)

Surface plasmon resonance methodology for monitoring polymerization kinetics and morphology changes of brushes—evaluated with poly(N-isopropylacrylamide)

Energy Technology Data Exchange (ETDEWEB)

Emilsson, Gustav [Dept. of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Göteborg (Sweden); Schoch, Rafael L.; Oertle, Philipp [Biozentrum and the Swiss Nanoscience Institute, University of Basel, 4056 Basel (Switzerland); Xiong, Kunli [Dept. of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Göteborg (Sweden); Lim, Roderick Y.H. [Biozentrum and the Swiss Nanoscience Institute, University of Basel, 4056 Basel (Switzerland); Dahlin, Andreas B., E-mail: adahlin@chalmers.se [Dept. of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Göteborg (Sweden)

2017-02-28

Highlights: • Real-time monitoring of thickness and the kinetics of polymerization. • Probing brush height both above and below the lower critical solution temperature. • Quantitative analysis of thermal actuation of poly(N-isopropylacrylamide) brushes. - Abstract: Polymerization from surfaces and the resulting “brushes” have many uses in the development of novel materials and functional interfaces. However, it is difficult to accurately monitor the polymerization rate, which limits the use of polymer brushes in applications where control of thickness is desirable. We present a new methodology based on angular surface plasmon resonance (SPR) which provides real-time measurements of the thickness evolution during atom transfer radical polymerization, using poly(N-isopropylacrylamide) as an example. Our data analysis shows that the growth is linear with a rate of ∼20 nm/min in a water/methanol mixture up to ∼100 nm after which chain termination gradually reduces the growth rate. Further, we introduce an improved method in SPR which makes it possible to determine changes in brush height and refractive index during switching of responsive polymers. The ratio between heights in the coil to globule transition at 32 °C in water was found to be almost 5, independent of the initial absolute height up to ∼200 nm, in agreement with theory. Complementary quartz crystal microbalance and atomic force microscopy data confirm the accuracy of our results. With the methodology presented here the established SPR technique can be used for quantitative characterization of surface-initiated polymerization and responsive polymer brushes.

Diffusion of lactate and ammonium in relation to growth of Geotrichum candidum at the surface of solid media.

Science.gov (United States)

Aldarf, M; Fourcade, F; Amrane, A; Prigent, Y

2004-07-05

Geotrichum candidum was cultivated at the surface of solid model media containing peptone to simulate the composition of Camembert cheese. The surface growth of G. candidum induced the diffusion of substrates from the core to the rind and the diffusion of produced metabolites from the rind to the core. In the range of pH measured during G. candidum growth, constant diffusion coefficients were found for lactate and ammonium, 0.4 and 0.8 cm(2) day(-1), respectively, determined in sterile culture medium. Growth kinetics are described using the Verlhust model and both lactate consumption and ammonium production are considered as partially linked to growth. The experimental diffusion gradients of lactate and ammonium recorded during G. candidum growth have been fitted. The diffusion/reaction model was found to match with experimental data until the end of growth, except with regard to ammonium concentration gradients in the presence of lactate in the medium. Indeed, G. candidum preferentially assimilated peptone over lactate as a carbon source, resulting in an almost cessation of ammonium release before the end of growth. On peptone, it was found that the proton transfer did not account for the ammonium concentration gradients. Indeed, amino acids, being positively charged, are involved in the proton transfer at the beginning of growth. This effect can be neglected in the presence of lactate within the medium, and the sum of both lactate consumption and ammonium release gradients corresponded well to the proton transfer gradients, confirming that both components are responsible for the pH increase observed during the ripening of soft Camembert cheese. Copyright 2004 Wiley Periodicals, Inc.

Optimization of induction, subculture conditions, and growth kinetics of Angelica sinensis (Oliv.) Diels callus.

Science.gov (United States)

Huang, Bing; Han, Lijuan; Li, Shaomei; Yan, Chunyan

2015-01-01

Angelica sinensis (Oliv.) Diels is an important traditional Chinese medicine, and the medicinal position is its root. This perennial herb grows vigorously only in specific areas and the environment. Tissue culture induction of callus and plant regeneration is an important and effective way to obtain large scale cultures of A. sinensis. The objective was to optimize the inductive, subculture conditions, and growth kinetics of A. sinensis. Tissue culture conditions for A. sinensis were optimized using leaves and petioles (types I and II) as explants source. Murashige and Skoog (MS) and H media supplemented with 30 g/L sucrose, 7.5 g/L agar, and varying concentrations of plant growth regulators were used for callus induction. In addition, four different basal media supplemented with 1.0 mg/L 2,4-dichlorophenoxy acetic acid (2,4-D), 0.2 mg/L 6-benzyladenine (BA) and 30 g/L sucrose were optimized for callus subculture. Finally, growth kinetics of A. sinensis cultured on different subculture media was investigated based on callus properties, including fresh weight, dry weight, medium pH, callus relative fresh weight growth, callus relative growth rate (CRGR), and sucrose content. MS medium supplemented with 5 mg/L α-naphthaleneacetic acid, 0.5 mg/L BA, 0.7 mg/L 2,4-D, 30 g/L sucrose and 7.5 g/L agar resulted in optimal callus induction in A. sinensis while petiole I was found as the best plant organ for callus induction. The B5 medium supplemented with 1.0 mg/L 2,4-D, 0.2 mg/L BA and 30 g/L sucrose displayed the best results in A. sinensis callus subculture assays. The optimized conditions could be one of the most potent methods for large-scale tissue culture of A. sinensis.

Surface smoothening effects on growth of diamond films

Science.gov (United States)

Reshi, Bilal Ahmad; Kumar, Shyam; Kartha, Moses J.; Varma, Raghava

2018-04-01

We have carried out a detailed study of the growth dynamics of the diamond film during initial time on diamond substrates. The diamond films are deposited using Microwave Plasma Chemical Vapor Deposition (MPCVD) method for different times. Surface morphology and its correlation with the number of hours of growth of thin films was invested using atomic force microscopy (AFM). Diamond films have smooth interface with average roughness of 48.6873nm. The initial growth dynamics of the thin film is investigated. Interestingly, it is found that there is a decrease in the surface roughness of the film. Thus a smoothening effect is observed in the grown films. The film enters into the growth regime in the later times. Our results also find application in building diamond detector.

Cluster growth kinetics

International Nuclear Information System (INIS)

Dubovik, V.M.; Gal'perin, A.G.; Rikhvitskij, V.S.; Lushnikov, A.A.

2000-01-01

Processes of some traffic blocking coming into existence are considered as probabilistic ones. We study analytic solutions for models for the dynamics of both cluster growth and cluster growth with fragmentation in the systems of finite number of objects. Assuming rates constancy of both coalescence and fragmentation, the models under consideration are linear on the probability functions

Effects of substrate anisotropy and edge diffusion on submonolayer growth during molecular beam epitaxy: A Kinetic Monte Carlo study

International Nuclear Information System (INIS)

Devkota, J.; Shrestha, S.P.

2007-12-01

We have performed Kinetic Monte Carlo simulation work to study the effect of diffusion anisotropy, bonding anisotropy and edge diffusion on island formation at different temperatures during the sub-monolayer film growth in Molecular Beam Epitaxy. We use simple cubic solid on solid model and event based Bortz, Kalos and Labowitch (BKL) algorithm on the Kinetic Monte Carlo method to simulate the physical phenomena. We have found that the island morphology and growth exponent are found to be influenced by substrate anisotropy as well as edge diffusion, however they do not play a significant role in island elongation. The growth exponent and island size distribution are observed to be influenced by substrate anisotropy but are negligibly influenced by edge diffusion. We have found fractal islands when edge diffusion is excluded and compact islands when edge diffusion is included. (author)

The impact of nanoclay on the crystal growth kinetics and morphology of biodegradable poly(ethylene succinate) composite

CSIR Research Space (South Africa)

Bandyopadhyay, J

2012-07-01

Full Text Available The impact of nanoclay on the isothermal crystal growth kinetics and morphology of biodegradable poly(ethylene succinate) (PES) is reported. A PES composite (PESNC) containing 5 wt% organically modified montmorillonite, was prepared via solvent...

Surface preparation for the heteroepitactic growth of ceramic thin films

International Nuclear Information System (INIS)

Norton, M.G.; Summerfelt, S.R.; Carter, C.B.

1990-01-01

The morphology, composition, and crystallographic orientation of the substrate influence the nucleation and growth of deposited thin films. A method for the preparation of controlled, characteristic surfaces is reported. The surfaces are suitable for the heteroepitactic growth of thin films. When used in the formation of electron-transparent thin foils, the substrates can be used to investigate the very early stages of film growth using transmission electron microscopy. The substrate preparation involves the cleaning and subsequent annealing to generate a surface consisting of a series of steps. The step terraces are formed on the energetically stable surface, and controlled nucleation and growth of films at step edges is found. The substrate materials prepared using this technique include (001) MgO, (001) SrTiO 3 , and (001) LaAlO 3

Influence of deformation on dolomite rim growth kinetics

Science.gov (United States)

Helpa, Vanessa; Rybacki, Erik; Grafulha Morales, Luiz Fernando; Dresen, Georg

2015-04-01

Using a gas-deformation apparatus stacks of oriented calcite (CaCO3) and magnesite (MgCO3) single crystals were deformed at T = 750° C and P = 400 MPa to examine the influence of stress and strain on magnesio-calcite and dolomite (CaMg[CO3]2) growth kinetics. Triaxial compression and torsion tests performed at constant stresses between 7 and 38 MPa and test durations between 4 and 171 hours resulted in bulk strains of 0.03-0.2 and maximum shear strains of 0.8-5.6, respectively. The reaction rims consist of fine-grained (2-7 μm) dolomite with palisade-shaped grains growing into magnesite reactants and equiaxed granular dolomite grains next to calcite. In between dolomite and pure calcite, magnesio-calcite grains evolved with an average grain size of 20-40 μm. Grain boundaries tend to be straighter at high bulk strains and equilibrium angles at grain triple junctions are common within the magnesio-calcite layer. Transmission electron microscopy shows almost dislocation free palisades and increasing dislocation density within granular dolomite towards the magnesio-calcite boundary. Within magnesio-calcite grains, dislocations are concentrated at grain boundaries. Variation of time at fixed stress (˜17 MPa) yields a parabolic time dependence of dolomite rim width, indicating diffusion-controlled growth, similar to isostatic rim growth behavior. In contrast, the magnesio-calcite layer growth is enhanced compared to isostatic conditions. Triaxial compression at given time shows no significant change of dolomite rim thickness (11±2 μm) and width of magnesio-calcite layers (33±5 μm) with increasing stress. In torsion experiments, reaction layer thickness and grain size decrease from the center (low stress/strain) to the edge (high strain/stress) of samples. Chemical analysis shows nearly stoichiometric composition of dolomite palisades, but enhanced Ca content within granular grains, indicating local disequilibrium with magnesio-calcite, in particular for twisted

Factors influencing graphene growth on metal surfaces

Energy Technology Data Exchange (ETDEWEB)

Loginova, E; Bartelt, N C; McCarty, K F [Sandia National Laboratories, Livermore, CA (United States); Feibelman, P J [Sandia National Laboratories, Albuquerque, NM (United States)], E-mail: mccarty@sandia.gov

2009-06-15

Graphene forms from a relatively dense, tightly bound C-adatom gas when elemental C is deposited on or segregates to the Ru(0001) surface. Nonlinearity of the graphene growth rate with C-adatom density suggests that growth proceeds by addition of C atom clusters to the graphene edge. The generality of this picture has now been studied by use of low-energy electron microscopy (LEEM) to observe graphene formation when Ru(0001) and Ir(111) surfaces are exposed to ethylene. The finding that graphene growth velocities and nucleation rates on Ru have precisely the same dependence on adatom concentration as for elemental C deposition implies that hydrocarbon decomposition only affects graphene growth through the rate of adatom formation. For ethylene, that rate decreases with increasing adatom concentration and graphene coverage. Initially, graphene growth on Ir(111) is like that on Ru: the growth velocity is the same nonlinear function of adatom concentration (albeit with much smaller equilibrium adatom concentrations, as we explain with DFT calculations of adatom formation energies). In the later stages of growth, graphene crystals that are rotated relative to the initial nuclei nucleate and grow. The rotated nuclei grow much faster. This difference suggests firstly, that the edge-orientation of the graphene sheets relative to the substrate plays an important role in the growth mechanism, and secondly, that attachment of the clusters to the graphene is the slowest step in cluster addition, rather than formation of clusters on the terraces.

Growth kinetics of cellular precipitation in a Mg-8.5Al-0.5Zn-0.2Mn (wt.%) alloy

Energy Technology Data Exchange (ETDEWEB)

Contreras-Piedras, Edgar [Instituto Politecnico Nacional-ESIQIE-DIMM-ESFM, Apartado Postal 118-430, Admon. GAM, Mexico, D.F. 07051 (Mexico); Esquivel-Gonzalez, Ramon [Universidad del Valle de Mexico, Depto. Ingenierias, Paseo de las Aves 1, Col. San Mateo Nopala, Lomas Verdes, Naucalpan de Juarez, Edo. Mex. 53220 (Mexico); Lopez-Hirata, Victor M.; Saucedo-Munoz, M.L.; Paniagua-Mercado, Ana M. [Instituto Politecnico Nacional-ESIQIE-DIMM-ESFM, Apartado Postal 118-430, Admon. GAM, Mexico, D.F. 07051 (Mexico); Dorantes-Rosales, Hector J., E-mail: hectordorantes@yahoo.com [Instituto Politecnico Nacional-ESIQIE-DIMM-ESFM, Apartado Postal 118-430, Admon. GAM, Mexico, D.F. 07051 (Mexico)

2010-11-15

Research highlights: {yields} The growth kinetics of lamellar spacing follows the behavior predicted by Turnbull theory. {yields} The growth kinetics of cellular precipitation is a process controlled by grain boundary diffusion. {yields} The presence of two types of morphology for cellular precipitation depends on the aging temperature. {yields} The highest hardness peak is associated to a fine continuous precipitation at the lowest temperature. {yields} The lowest hardness is attributed to the fast coarsening process of both precipitations. - Abstract: Microstructural evolution and growth kinetics were studied in an isothermally aged Mg-8.5Al-0.5Zn-0.2Mn (wt.%) alloy by means of X-ray diffraction, scanning electron microscopy, Vickers hardness measurements and transmission electron microscopy. Specimens were solution-treated and then aged at 373, 473 and 573 K for different time period. The characterization results indicated the presence of both continuous and discontinuous precipitations of the Mg{sub 17}Al{sub 12}-{gamma} phase in a Mg-rich matrix. The discontinuous or cellular precipitation was present with a lamellar structure, and the growth kinetics was evaluated using the Johnson-Mehl-Avrami-Kolmogorov equation analysis, which gives a time exponent close to 1. This value confirms that cellular precipitation takes place on the saturation sites corresponding to grain boundaries. In addition, the activation energy for cellular precipitation was determined to be about 64.6 kJ mol{sup -1}. This also indicates a grain boundary diffusion process. The variation of cellular spacing with temperature follows the behavior expected by Turnbull theory. The highest hardness peak corresponded to the lowest aging temperature and it is associated with a fine continuous precipitation; while the lowest hardness peak was detected at the highest aging temperature and it is attributed to the rapid coarsening process of both precipitations.

Growth kinetics of cellular precipitation in a Mg-8.5Al-0.5Zn-0.2Mn (wt.%) alloy

International Nuclear Information System (INIS)

Contreras-Piedras, Edgar; Esquivel-Gonzalez, Ramon; Lopez-Hirata, Victor M.; Saucedo-Munoz, M.L.; Paniagua-Mercado, Ana M.; Dorantes-Rosales, Hector J.

2010-01-01

Research highlights: → The growth kinetics of lamellar spacing follows the behavior predicted by Turnbull theory. → The growth kinetics of cellular precipitation is a process controlled by grain boundary diffusion. → The presence of two types of morphology for cellular precipitation depends on the aging temperature. → The highest hardness peak is associated to a fine continuous precipitation at the lowest temperature. → The lowest hardness is attributed to the fast coarsening process of both precipitations. - Abstract: Microstructural evolution and growth kinetics were studied in an isothermally aged Mg-8.5Al-0.5Zn-0.2Mn (wt.%) alloy by means of X-ray diffraction, scanning electron microscopy, Vickers hardness measurements and transmission electron microscopy. Specimens were solution-treated and then aged at 373, 473 and 573 K for different time period. The characterization results indicated the presence of both continuous and discontinuous precipitations of the Mg 17 Al 12 -γ phase in a Mg-rich matrix. The discontinuous or cellular precipitation was present with a lamellar structure, and the growth kinetics was evaluated using the Johnson-Mehl-Avrami-Kolmogorov equation analysis, which gives a time exponent close to 1. This value confirms that cellular precipitation takes place on the saturation sites corresponding to grain boundaries. In addition, the activation energy for cellular precipitation was determined to be about 64.6 kJ mol -1 . This also indicates a grain boundary diffusion process. The variation of cellular spacing with temperature follows the behavior expected by Turnbull theory. The highest hardness peak corresponded to the lowest aging temperature and it is associated with a fine continuous precipitation; while the lowest hardness peak was detected at the highest aging temperature and it is attributed to the rapid coarsening process of both precipitations.

The effect of substrate modification on microbial growth on surfaces

International Nuclear Information System (INIS)

Brown, Angela Ann

1998-01-01

The principle aim of the program was to produce a novel, non-leaching antimicrobial surface for commercial development and future use in the liquid food packaging industry. Antimicrobial surfaces which exist presently have been produced to combat the growth of prokaryotic organisms and usually function as slow release systems. A system which could inhibit eukaryotic growth without contaminating the surrounding 'environment' with the inhibitor was considered of great commercial importance. The remit of this study was concerned with creating a surface which could control the growth of eukaryotic organisms found in fruit juice with particular interest in the yeast, Saccharomyces cerevisiae. Putative antimicrobial surfaces were created by the chemical modification of the test substrate polymers; nylon and ethylvinyl alcohol (EVOH). Surfaces were chemically modified by the covalent coupling of antimicrobial agents known to be active against the yeast Saccharomyces cerevisiae as ascertained by the screening process determining the minimum inhibitory concentration (MIC) values of agents in the desired test medium. During the study it was found that a number of surfaces did appear to inhibit yeast growth in fruit juice, however on further investigation the apparent inhibitory effect was discovered to be the result of un-bound material free in the test medium. On removing the possibility of any un-bound material present on the test surface, by a series of surface washings, the inhibitory effect on yeast growth was eliminated. Of the agents tested only one appeared to have an inhibitory effect which could be attributed to a true antimicrobial surface effect, Amical 48. As there is little known about this agent in the literature, its affect on yeast growth was examined and in particular a proposal for the mode of action on yeast is discussed, providing a plausible explanation for the inhibitory effect observed when this agent is covalently immobilised onto nylon. (author)

Salt effects on the air/solution interfacial properties of PEO-containing copolymers: equilibrium, adsorption kinetics and surface rheological behavior.

Science.gov (United States)

Llamas, Sara; Mendoza, Alma J; Guzmán, Eduardo; Ortega, Francisco; Rubio, Ramón G

2013-06-15

Lithium cations are known to form complexes with the oxygen atoms of poly(oxyethylene) chains. The effect of Li(+) on the surface properties of three block-copolymers containing poly(oxyethylene) (PEO) have been studied. Two types of copolymers have been studied, a water soluble one of the pluronic family, PEO-b-PPO-b-PEO, PPO being poly(propyleneoxyde), and two water insoluble ones: PEO-b-PS and PEO-b-PS-b-PEO, PS being polystyrene. In the case of the pluronic the adsorption kinetics, the equilibrium surface tension isotherm and the aqueous/air surface rheology have been measured, while for the two insoluble copolymers only the surface pressure and the surface rheology have been studied. In all the cases two different Li(+) concentrations have been used. As in the absence of lithium ions, the adsorption kinetics of pluronic solutions shows two processes, and becomes faster as [Li(+)] increases. The kinetics is not diffusion controlled. For a given pluronic concentration the equilibrium surface pressure increases with [Li(+)], and the isotherms show two surface phase transitions, though less marked than for [Li(+)]=0. A similar behavior was found for the equilibrium isotherms of PEO-b-PS and PEO-b-PS-b-PEO. The surface elasticity of these two copolymers was found to increase with [Li(+)] over the whole surface concentration and frequency ranges studied. A smaller effect was found in the case of the pluronic solutions. The results of the pluronic solutions were modeled using a recent theory that takes into account that the molecules can be adsorbed at the surface in two different states. The theory gives a good fit for the adsorption kinetics and a reasonably good prediction of the equilibrium isotherms for low and intermediate concentrations of pluronic. However, the theory is not able to reproduce the isotherm for [Li(+)]=0. Only a semi-quantitative prediction of the surface elasticity is obtained for [pluronic]≤1×10(-3) mM. Copyright © 2013 Elsevier Inc. All

Scratching the surface of ice: Interfacial phase transitions and their kinetic implications

Science.gov (United States)

Limmer, David

The surface structure of ice maintains a high degree of disorder down to surprisingly low temperatures. This is due to a number of underlying interfacial phase transitions that are associated with incremental changes in broken symmetry relative to the bulk crystal. In this talk I summarize recent work attempting to establish the nature and locations of these different phase transitions as well as how they depend on external conditions and nonequilibrium driving. The implications of this surface disorder is discussed in the context of simple kinetic processes that occur at these interfaces. Recent experimental work on the roughening transition is highlighted.

Kinetics of fatigue crack growth and crack paths in the old puddled steel after 100-years operating time

Directory of Open Access Journals (Sweden)

G. Lesiuk

2015-10-01

Full Text Available The goal of the authors’ investigations was determination of the fatigue crack growth in fragments of steel structures (of the puddled steel and its cyclic behavior. Tested steel elements coming from the turn of the 19th and 20th were gained from still operating ancient steel construction (a main hall of Railway Station, bridges etc.. This work is a part of investigations devoted to the phenomenon of microstructural degradation and its potential influence on their strength properties. The analysis of the obtained results indicated that those long operating steels subject to microstructure degradation processes consisting mainly in precipitation of carbides and nitrides inside ferrite grains, precipitation of carbides at ferrite grain boundaries and degeneration of pearlite areas [1, 2]. It is worth noticing that resistance of the puddled steel to fatigue crack propagation in the normalized state was higher. The authors proposed the new kinetic equation of fatigue crack growth rate in such a steel. Thus the relationship between the kinetics of degradation processes and the fatigue crack growth rate also have been shown. It is also confirmed by the materials research of the viaduct from 1885, which has not shown any significant changes in microstructure. The non-classical kinetic fatigue fracture diagrams (KFFD based on deformation ( or energy (W approach was also considered. In conjunction with the results of low- and high-cycle fatigue and gradual loss of ductility as a consequence (due to the microstructural degradation processes - it seems to be a promising construction of the new kinetics fatigue fracture diagrams with the energy approach.

Physiological-phased kinetic characteristics of microalgae Chlorella vulgaris growth and lipid synthesis considering synergistic effects of light, carbon and nutrients.

Science.gov (United States)

Liao, Qiang; Chang, Hai-Xing; Fu, Qian; Huang, Yun; Xia, Ao; Zhu, Xun; Zhong, Nianbing

2018-02-01

To comprehensively understand kinetic characteristics of microalgae growth and lipid synthesis in different phases, a phase-feeding strategy was proposed to simultaneously regulate light, carbon and nutrients in adaption, growth and stationary phases of microalgae cultivation. Physiological-phased kinetic characteristics of microalgae Chlorella vulgaris growth and lipid synthesis under synergistic effects of light, carbon and nutrients were investigated, and supply-demand relationships of electrons and energy between light and dark reactions of photosynthesis process were discussed. Finally, the optimized cultivation strategy for microalgae in various phases were obtained, under which the lipid productivity was significantly improved from 130.11 mg/L/d to 163.42 mg/L/d. The study provided some important guidance for the large-scale production of biofuels from microalgae. Copyright © 2017 Elsevier Ltd. All rights reserved.

Stochastic theory of interfacial enzyme kinetics: A kinetic Monte Carlo study

International Nuclear Information System (INIS)

Das, Biswajit; Gangopadhyay, Gautam

2012-01-01

Graphical abstract: Stochastic theory of interfacial enzyme kinetics is formulated. Numerical results of macroscopic phenomenon of lag-burst kinetics is obtained by using a kinetic Monte Carlo approach to single enzyme activity. Highlights: ► An enzyme is attached with the fluid state phospholipid molecules on the Langmuir monolayer. ► Through the diffusion, the enzyme molecule reaches the gel–fluid interface. ► After hydrolysing a phospholipid molecule it predominantly leaves the surface in the lag phase. ► The enzyme is strictly attached to the surface with scooting mode of motion and the burst phase appears. - Abstract: In the spirit of Gillespie’s stochastic approach we have formulated a theory to explore the advancement of the interfacial enzyme kinetics at the single enzyme level which is ultimately utilized to obtain the ensemble average macroscopic feature, lag-burst kinetics. We have provided a theory of the transition from the lag phase to the burst phase kinetics by considering the gradual development of electrostatic interaction among the positively charged enzyme and negatively charged product molecules deposited on the phospholipid surface. It is shown that the different diffusion time scales of the enzyme over the fluid and product regions are responsible for the memory effect in the correlation of successive turnover events of the hopping mode in the single trajectory analysis which again is reflected on the non-Gaussian distribution of turnover times on the macroscopic kinetics in the lag phase unlike the burst phase kinetics.

On the effect of pre-oxidation on the nitriding kinetics

DEFF Research Database (Denmark)

Friehling, Peter Bernhard; Somers, Marcel A. J.

2000-01-01

The oxidation of ferritic surfaces prior to gaseous nitriding has been reported to lead to improved uniformity of the compound layer thickness and enhanced nitriding kinetics. The present work considers the nucleation and growth of a model compound layer on pure iron and, using previous...... experimental and theoretical work reported in the literature, puts forward two hypotheses to explain the effects of pre-oxidation on compound layer formation. It is proposed that the nucleation of iron nitrides is enhanced by the presence of an iron-oxide layer and that the growth of an iron-nitride layer...... proceeds faster after pre-oxidation, due to a higher nitrogen content in the part of the compound layer closest to the surface....

Fibril growth kinetics link buffer conditions and topology of 3D collagen I networks.

Science.gov (United States)

Kalbitzer, Liv; Pompe, Tilo

2018-02-01

Three-dimensional fibrillar networks reconstituted from collagen I are widely used as biomimetic scaffolds for in vitro and in vivo cell studies. Various physicochemical parameters of buffer conditions for in vitro fibril formation are well known, including pH-value, ion concentrations and temperature. However, there is a lack of a detailed understanding of reconstituting well-defined 3D network topologies, which is required to mimic specific properties of the native extracellular matrix. We screened a wide range of relevant physicochemical buffer conditions and characterized the topology of the reconstituted 3D networks in terms of mean pore size and fibril diameter. A congruent analysis of fibril formation kinetics by turbidimetry revealed the adjustment of the lateral growth phase of fibrils by buffer conditions to be key in the determination of pore size and fibril diameter of the networks. Although the kinetics of nucleation and linear growth phase were affected by buffer conditions as well, network topology was independent of those two growth phases. Overall, the results of our study provide necessary insights into how to engineer 3D collagen matrices with an independent control over topology parameters, in order to mimic in vivo tissues in in vitro experiments and tissue engineering applications. The study reports a comprehensive analysis of physicochemical conditions of buffer solutions to reconstitute defined 3D collagen I matrices. By a combined analysis of network topology, i.e., pore size and fibril diameter, and the kinetics of fibril formation we can reveal the dependence of 3D network topology on buffer conditions, such as pH-value, phosphate concentration and sodium chloride content. With those results we are now able to provide engineering strategies to independently tune the topology parameters of widely used 3D collagen scaffolds based on the buffer conditions. By that, we enable the straightforward mimicking of extracellular matrices of in vivo

Reaction kinetics of metal deposition via surface limited red-ox replacement of underpotentially deposited metal monolayers

International Nuclear Information System (INIS)

Gokcen, Dincer; Bae, Sang-Eun; Brankovic, Stanko R.

2011-01-01

The study of the kinetics of metal deposition via surface limited red-ox replacement of underpotentially deposited metal monolayers is presented. The model system was Pt submonolayer deposition on Au(1 1 1) via red-ox replacement of Pb and Cu UPD monolayers on Au(1 1 1). The kinetics of a single replacement reaction was studied using the formalism of the comprehensive analytical model developed to fit the open circuit potential transients from deposition experiments. The practical reaction kinetics parameters like reaction half life, reaction order and reaction rate constant are determined and discussed with their relevance to design and control of deposition experiments. The effects of transport limitation and the role of the anions/electrolyte on deposition kinetics are investigated and their significance to design of effective deposition process is discussed.

Comparison of the growth kinetics of In{sub 2}O{sub 3} and Ga{sub 2}O{sub 3} and their suboxide desorption during plasma-assisted molecular beam epitaxy

Energy Technology Data Exchange (ETDEWEB)

Vogt, Patrick, E-mail: vogt@pdi-berlin.de; Bierwagen, Oliver, E-mail: bierwagen@pdi-berlin.de [Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5–7, D-10117 Berlin (Germany)

2016-08-08

We present a comprehensive study of the In{sub 2}O{sub 3} growth kinetics during plasma-assisted molecular beam epitaxy and compare it to that of the related oxide Ga{sub 2}O{sub 3} [P. Vogt and O. Bierwagen, Appl. Phys. Lett. 108, 072101 (2016)]. The growth rate and desorbing fluxes were measured during growth in-situ by a laser reflectometry set-up and line-of-sight quadrupole mass spectrometer, respectively. We extracted the In incorporation as a function of the provided In flux, different growth temperatures T{sub G}, and In-to-O flux ratios r. The data are discussed in terms of the competing formation of In{sub 2}O{sub 3} and desorption of the suboxide In{sub 2}O and O. The same three growth regimes as in the case of Ga{sub 2}O{sub 3} can be distinguished: (i) In-transport limited, O-rich (ii) In{sub 2}O-desorption limited, O-rich, and (iii) O-transport limited, In-rich. In regime (iii), In droplets are formed on the growth surface at low T{sub G}. The growth kinetics follows qualitatively that of Ga{sub 2}O{sub 3} in agreement with their common oxide and suboxide stoichiometry. The quantitative differences are mainly rationalized by the difference in In{sub 2}O and Ga{sub 2}O desorption rates and vapor pressures. For the In{sub 2}O, Ga{sub 2}O, and O desorption, we extracted the activation energies and frequency factors by means of Arrhenius-plots.

Simulating Growth Kinetics in a Data-Parallel 3D Lattice Photobioreactor

Directory of Open Access Journals (Sweden)

A. V. Husselmann

2013-01-01

Full Text Available Though there have been many attempts to address growth kinetics in algal photobioreactors, surprisingly little have attempted an agent-based modelling (ABM approach. ABM has been heralded as a method of practical scientific inquiry into systems of a complex nature and has been applied liberally in a range of disciplines including ecology, physics, social science, and microbiology with special emphasis on pathogenic bacterial growth. We bring together agent-based simulation with the Photosynthetic Factory (PSF model, as well as certain key bioreactor characteristics in a visual 3D, parallel computing fashion. Despite being at small scale, the simulation gives excellent visual cues on the dynamics of such a reactor, and we further investigate the model in a variety of ways. Our parallel implementation on graphical processing units of the simulation provides key advantages, which we also briefly discuss. We also provide some performance data, along with particular effort in visualisation, using volumetric and isosurface rendering.

Kinetics and thermodynamics studies on the BMP-2 adsorption onto hydroxyapatite surface with different multi-morphological features

Energy Technology Data Exchange (ETDEWEB)

Lu, Zhiwei; Huangfu, Changxin; Wang, Yanying; Ge, Hongwei; Yao, Yao; Zou, Ping; Wang, Guangtu [College of Science, Sichuan Agricultural University, Ya' an 625014 (China); He, Hua [Institute of Animal Genetics and Breeding, Sichuan Agricultural University, Wenjiang, Sichuan 611130 (China); Rao, Hanbing, E-mail: rhbscu@gmail.com [College of Science, Sichuan Agricultural University, Ya' an 625014 (China)

2015-07-01

The effect of the surface topography on protein adsorption process is of great significance for designing hydroxyapatite (HA) ceramic material surfaces. In this work, three different topographies of HA materials HA-sheet, HA-rod, and HA-whisker were synthesized and testified by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Brunauer–Emmett–Teller (BET) and a field emission scanning electron microscopy (FE-SEM). We have systematically investigated the adsorption kinetics and thermodynamics of bone morphogenetic proteins (BMP-2) on the three different topography surfaces of HA, respectively. The results showed that the maximum adsorption capacities of HA-sheet, HA-rod and HA-whisker were (219.96 ± 10.18), (247.13 ± 12.35), and (354.67 ± 17.73) μg · g{sup −1}, respectively. Kinetic parameters, rate constants, equilibrium adsorption capacities and related correlation coefficients, for each kinetic model were calculated as well as discussed. It demonstrated that the adsorption of BMP-2 onto HA could be described by the pseudo second-order equation. Adsorption of BMP-2 onto HA followed the Langmuir isotherm. It confirmed that compared with other samples HA-whisker had more adsorption sites for its high specific surface area which could provide more opportunities for protein molecules. The adsorption processes were endothermic (ΔH > 0), spontaneous (ΔG < 0) and entropy increasing (ΔS > 0). A possible adsorption mechanism has been proposed. In addition, the BMP-2 could be adsorbed to the surface which existed slight conformational changes by FT-IR. - Highlights: • A novel protein adsorption studies based on sheet, rod and whisker of HA were designed. • Kinetic and thermodynamics parameters of BMP-2 and HA bonded materials were evaluated. • Surface topographies of the HA effect BMP-2 adsorption • The HA-whisker material had excellent adsorption performance for protein enrichment. • The electrostatic interaction is responsible for the

Kinetics and thermodynamics studies on the BMP-2 adsorption onto hydroxyapatite surface with different multi-morphological features

International Nuclear Information System (INIS)

Lu, Zhiwei; Huangfu, Changxin; Wang, Yanying; Ge, Hongwei; Yao, Yao; Zou, Ping; Wang, Guangtu; He, Hua; Rao, Hanbing

2015-01-01

The effect of the surface topography on protein adsorption process is of great significance for designing hydroxyapatite (HA) ceramic material surfaces. In this work, three different topographies of HA materials HA-sheet, HA-rod, and HA-whisker were synthesized and testified by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Brunauer–Emmett–Teller (BET) and a field emission scanning electron microscopy (FE-SEM). We have systematically investigated the adsorption kinetics and thermodynamics of bone morphogenetic proteins (BMP-2) on the three different topography surfaces of HA, respectively. The results showed that the maximum adsorption capacities of HA-sheet, HA-rod and HA-whisker were (219.96 ± 10.18), (247.13 ± 12.35), and (354.67 ± 17.73) μg · g −1 , respectively. Kinetic parameters, rate constants, equilibrium adsorption capacities and related correlation coefficients, for each kinetic model were calculated as well as discussed. It demonstrated that the adsorption of BMP-2 onto HA could be described by the pseudo second-order equation. Adsorption of BMP-2 onto HA followed the Langmuir isotherm. It confirmed that compared with other samples HA-whisker had more adsorption sites for its high specific surface area which could provide more opportunities for protein molecules. The adsorption processes were endothermic (ΔH > 0), spontaneous (ΔG < 0) and entropy increasing (ΔS > 0). A possible adsorption mechanism has been proposed. In addition, the BMP-2 could be adsorbed to the surface which existed slight conformational changes by FT-IR. - Highlights: • A novel protein adsorption studies based on sheet, rod and whisker of HA were designed. • Kinetic and thermodynamics parameters of BMP-2 and HA bonded materials were evaluated. • Surface topographies of the HA effect BMP-2 adsorption • The HA-whisker material had excellent adsorption performance for protein enrichment. • The electrostatic interaction is responsible for the BMP-2

The kinetics of Scenedesmus obliquus microalgae growth utilizing carbon dioxide gas from biogas

International Nuclear Information System (INIS)

Thiansathit, Worrarat; Keener, Tim C.; Khang, Soon-Jai; Ratpukdi, Thunyalux; Hovichitr, Patcharee

2015-01-01

Microalgae Scenedesmus obliquus was cultured in a laboratory photobioreactor to determine the efficacy of using biogas as a carbon source for the microalgae's growth. The biogas contained ∼60% CH 4 and ∼40% CO 2 , and was derived from an anaerobic digester operating from animal wastes, and an anaerobic reactor utilizing high strength wastewater. The results showed that biogas is a viable carbon source for microalgae growth and that significant portions of the biogas' CO 2 can be utilized for algae growth, resulting in a biogas having a high concentration of methane. This paper develops the kinetic expressions for the algae's growth by assuming an autocatalytic reaction between carbon substrate and microalgae. The maximum specific growth rate and biomass productivity of S. obliquus were 0.56 d −1 and 0.145 g L −1 d −1 respectively. The biomass contained 51.8% carbon and higher heating value (HHV) was 22.9 MJ kg −1 . - Highlights: • Biogas is a viable carbon source for microalgae growth. • Biomass production rate and characteristics were assessed. • Scenedesmus obliquus can adjust to grow with high concentration of CO 2 in the carbon source

Kinetics of conformational changes of fibronectin adsorbed onto model surfaces.

Science.gov (United States)

Baujard-Lamotte, L; Noinville, S; Goubard, F; Marque, P; Pauthe, E

2008-05-01

Fibronectin (FN), a large glycoprotein found in body fluids and in the extracellular matrix, plays a key role in numerous cellular behaviours. We investigate FN adsorption onto hydrophilic bare silica and hydrophobic polystyrene (PS) surfaces using Fourier transform infrared spectroscopy-attenuated total reflection (FTIR-ATR) in aqueous medium. Adsorption kinetics using different bulk concentrations of FN were followed for 2h and the surface density of adsorbed FN and its time-dependent conformational changes were determined. When adsorption occurs onto the hydrophilic surface, FN molecules keep their native conformation independent of the adsorption conditions, but the amount of adsorbed FN increases with time and the bulk concentration. Although the protein surface density is the same on the hydrophobic PS surface, this has a strong impact on the average conformation of the adsorbed FN layer. Indeed, interfacial hydration changes induced by adsorption onto the hydrophobic surface lead to a decrease in unhydrated beta-sheet content and cause an increase in hydrated beta-strand and hydrated random domain content of adsorbed FN. This conformational change is mainly dependent on the bulk concentration. Indeed, at low bulk concentrations, the secondary structures of adsorbed FN molecules undergo strong unfolding, allowing an extended and hydrated conformation of the protein. At high bulk concentrations, the molecular packing reduces the unfolding of the stereoregular structures of the FN molecules, preventing stronger spreading of the protein.

He atom-surface scattering: Surface dynamics of insulators, overlayers and crystal growth

International Nuclear Information System (INIS)

Safron, S.A.; Skofronick, J.G.

1994-01-01

This progress report describes work carried out in the study of surface structure and dynamics of ionic insulators, the microscopic interactions controlling epitaxial growth and the formation of overlayers, and energy exchange in multiphonon surface scattering. The approach used is to employ high resolution helium atom scattering to study the geometry and structural features of the surfaces. Experiments have been carried out on the surface dynamics of RbCl and preliminary studies done on CoO and NiO. Epitaxial growth and overlayer dynamics experiments on the systems NaCl/NaCl(001), KBr/NaCl(001), NaCl/KBr(001) and KBr/RbCl(001) have been performed. They have collaborated with two theoretical groups to explore models of overlayer dynamics with which to compare and to interpret their experimental results. They have carried out extensive experiments on the multiphonon scattering of helium atoms from NaCl and, particularly, LiF. Work has begun on self-assembling organic films on gold and silver surfaces (alkyl thiols/Au(111) and Ag(111))

Growth kinetics of the intermetallic phase in diffusion-soldered (Cu-5 at.%Ni)/Sn/(Cu-5 at.%Ni) interconnections

NARCIS (Netherlands)

Wierzbicka-Miernik, A.; Miernik, K.; Wojewoda-Budka, J.; Szyszkiewicz, K.; Filipek, R.; Litynska-Dobrzynska, L.; Kodentsov, A.; Zieba, P.

2013-01-01

A stereological analysis was carried out in order to obtain the kinetics parameters of the (Cu1-xNix)6Sn5 growth in the diffusion soldered (Cu–5 at.%Ni)/Sn/(Cu–5 at.%Ni) interconnections where previously anomalous fast growth of this phase was described. The n-parameter in the equation x = ktn was

Modeling of metal nanocluster growth on patterned substrates and surface pattern formation under ion bombardment

Energy Technology Data Exchange (ETDEWEB)

Numazawa, Satoshi

2012-11-01

This work addresses the metal nanocluster growth process on prepatterned substrates, the development of atomistic simulation method with respect to an acceleration of the atomistic transition states, and the continuum model of the ion-beam inducing semiconductor surface pattern formation mechanism. Experimentally, highly ordered Ag nanocluster structures have been grown on pre-patterned amorphous SiO{sub 2} surfaces by oblique angle physical vapor deposition at room temperature. Despite the small undulation of the rippled surface, the stripe-like Ag nanoclusters are very pronounced, reproducible and well-separated. The first topic is the investigation of this growth process with a continuum theoretical approach to the surface gas condensation as well as an atomistic cluster growth model. The atomistic simulation model is a lattice-based kinetic Monte-Carlo (KMC) method using a combination of a simplified inter-atomic potential and experimental transition barriers taken from the literature. An effective transition event classification method is introduced which allows a boost factor of several thousand compared to a traditional KMC approach, thus allowing experimental time scales to be modeled. The simulation predicts a low sticking probability for the arriving atoms, millisecond order lifetimes for single Ag monomers and {approx}1 nm square surface migration ranges of Ag monomers. The simulations give excellent reproduction of the experimentally observed nanocluster growth patterns. The second topic specifies the acceleration scheme utilized in the metallic cluster growth model. Concerning the atomistic movements, a classical harmonic transition state theory is considered and applied in discrete lattice cells with hierarchical transition levels. The model results in an effective reduction of KMC simulation steps by utilizing a classification scheme of transition levels for thermally activated atomistic diffusion processes. Thermally activated atomistic movements

Modeling of metal nanocluster growth on patterned substrates and surface pattern formation under ion bombardment

Energy Technology Data Exchange (ETDEWEB)

Numazawa, Satoshi

2012-11-01

This work addresses the metal nanocluster growth process on prepatterned substrates, the development of atomistic simulation method with respect to an acceleration of the atomistic transition states, and the continuum model of the ion-beam inducing semiconductor surface pattern formation mechanism. Experimentally, highly ordered Ag nanocluster structures have been grown on pre-patterned amorphous SiO{sub 2} surfaces by oblique angle physical vapor deposition at room temperature. Despite the small undulation of the rippled surface, the stripe-like Ag nanoclusters are very pronounced, reproducible and well-separated. The first topic is the investigation of this growth process with a continuum theoretical approach to the surface gas condensation as well as an atomistic cluster growth model. The atomistic simulation model is a lattice-based kinetic Monte-Carlo (KMC) method using a combination of a simplified inter-atomic potential and experimental transition barriers taken from the literature. An effective transition event classification method is introduced which allows a boost factor of several thousand compared to a traditional KMC approach, thus allowing experimental time scales to be modeled. The simulation predicts a low sticking probability for the arriving atoms, millisecond order lifetimes for single Ag monomers and {approx}1 nm square surface migration ranges of Ag monomers. The simulations give excellent reproduction of the experimentally observed nanocluster growth patterns. The second topic specifies the acceleration scheme utilized in the metallic cluster growth model. Concerning the atomistic movements, a classical harmonic transition state theory is considered and applied in discrete lattice cells with hierarchical transition levels. The model results in an effective reduction of KMC simulation steps by utilizing a classification scheme of transition levels for thermally activated atomistic diffusion processes. Thermally activated atomistic movements

Modeling of the non isothermal and non isobaric transformations kinetics. Application to the kaolinite de-hydroxylation and to the tri-uranium octo-oxide reduction by hydrogen

International Nuclear Information System (INIS)

Perrin, St.

2002-12-01

The aim of this work is to be able to describe transformations, occurring when solids and gases are in non isothermal and non isobaric conditions, with kinetic models. A methodology has been used. Two essential processes have to be taken into account: the germination and the growth. The germs are supposed to be formed (at constant temperature and pressure) in the grains surface with a constant velocity by surface unit, (gamma), called germination surface frequency (number of germs.m -2 .s -1 . The growth velocity is characterized by a growth surface reactivity, (phi) (in mol.m -2 .s -1 ). With an appropriate transformation model, it is possible to obtain the variations of (gamma) and (phi) in terms of the temperature and pressure which are then used in the calculation of the velocity in non isothermal and non isobaric conditions. In order to validate the developed method, two reactions have been studied. For the first one, the kaolinite de-hydroxylation, an anisotropic germination-growth model, where the step limiting the growth is a diffusion step, has been developed in order to explain the experimental kinetic curves. Nevertheless the velocity curves calculated from this model do not allow to describe the reaction for some temperature variations. This result shows the difficulty to precisely determine the germination surface frequency what induces an important approximation on the kinetic curves. The second reaction is the tri-uranium octo-oxide reduction by hydrogen. It has been shown that this reaction occurs according to three successive transformations. A kinetic model has been developed for each of these reactions considering germination as instantaneous. At last, in comparing this model with the experimental velocity curves, a very good agreement has been verified as well as for a temperature variation than for a hydrogen partial pressure change during the reaction. (O.M.)

A Fibrocontractive Mechanochemical Model of Dermal Wound Closure Incorporating Realistic Growth Factor Kinetics

KAUST Repository

Murphy, Kelly E.

2012-01-13

Fibroblasts and their activated phenotype, myofibroblasts, are the primary cell types involved in the contraction associated with dermal wound healing. Recent experimental evidence indicates that the transformation from fibroblasts to myofibroblasts involves two distinct processes: The cells are stimulated to change phenotype by the combined actions of transforming growth factor β (TGFβ) and mechanical tension. This observation indicates a need for a detailed exploration of the effect of the strong interactions between the mechanical changes and growth factors in dermal wound healing. We review the experimental findings in detail and develop a model of dermal wound healing that incorporates these phenomena. Our model includes the interactions between TGFβ and collagenase, providing a more biologically realistic form for the growth factor kinetics than those included in previous mechanochemical descriptions. A comparison is made between the model predictions and experimental data on human dermal wound healing and all the essential features are well matched. © 2012 Society for Mathematical Biology.

A Fibrocontractive Mechanochemical Model of Dermal Wound Closure Incorporating Realistic Growth Factor Kinetics

KAUST Repository

Murphy, Kelly E.; Hall, Cameron L.; Maini, Philip K.; McCue, Scott W.; McElwain, D. L. Sean

2012-01-01

Fibroblasts and their activated phenotype, myofibroblasts, are the primary cell types involved in the contraction associated with dermal wound healing. Recent experimental evidence indicates that the transformation from fibroblasts to myofibroblasts involves two distinct processes: The cells are stimulated to change phenotype by the combined actions of transforming growth factor β (TGFβ) and mechanical tension. This observation indicates a need for a detailed exploration of the effect of the strong interactions between the mechanical changes and growth factors in dermal wound healing. We review the experimental findings in detail and develop a model of dermal wound healing that incorporates these phenomena. Our model includes the interactions between TGFβ and collagenase, providing a more biologically realistic form for the growth factor kinetics than those included in previous mechanochemical descriptions. A comparison is made between the model predictions and experimental data on human dermal wound healing and all the essential features are well matched. © 2012 Society for Mathematical Biology.

Comparison of Growth Kinetics of Various Pathogenic E. coli on Fresh Perilla Leaf

Directory of Open Access Journals (Sweden)

Juhui Kim

2013-08-01

Full Text Available Growth kinetics for Escherichia coli O157:H7 in perilla leaves were compared to those of pathogenic E. coli strains, including enteropathogenic (EPEC, enterotoxigenic (ETEC, enteroinvasive (EIEC and other enterohemorrhagic (EHEC at 13, 17, 24, 30 and 36 °C. Models for lag time (LT, specific growth rate (SGR and maximum population density (MPD as a function of temperature were developed. The performance of the models was quantified using the ratio method and an acceptable prediction zone method. Significant differences in SGR and LT among the strains were observed at all temperatures. Overall, the shortest LT was observed with E. coli O157:H7, followed by EPEC, other EHEC, EIEC and ETEC, while the fastest growth rates were noted in EPEC, followed by E. coli O157:H7, ETEC, other EHEC and EIEC. The models for E. coli O157:H7 in perilla leaves was suitable for use in making predictions for EPEC and other EHEC strains.

Anisotropic cell growth-regulated surface micropatterns in flower petals

Directory of Open Access Journals (Sweden)

Xiao Huang

2017-05-01

Full Text Available Flower petals have not only diverse macroscopic morphologies but are rich in microscopic surface patterns, which are crucial to their biological functions. Both experimental measurements and theoretical analysis are conducted to reveal the physical mechanisms underlying the formation of minute wrinkles on flower petals. Three representative flowers, daisy, kalanchoe blossfeldiana, and Eustoma grandiflorum, are investigated as examples. A surface wrinkling model, incorporating the measured mechanical properties and growth ratio, is used to elucidate the difference in their surface morphologies. The mismatch between the anisotropic epidermal cell growth and the isotropic secretion of surficial wax is found to dictate the surface patterns.

Modeling of Fusarium redolens Dzf2 mycelial growth kinetics and optimal fed-batch fermentation for beauvericin production.

Science.gov (United States)

Xu, Li-Jian; Liu, Yuan-Shuai; Zhou, Li-Gang; Wu, Jian-Yong

2011-09-01

Beauvericin (BEA) is a cyclic hexadepsipeptide mycotoxin with notable phytotoxic and insecticidal activities. Fusarium redolens Dzf2 is a highly BEA-producing fungus isolated from a medicinal plant. The aim of the current study was to develop a simple and valid kinetic model for F. redolens Dzf2 mycelial growth and the optimal fed-batch operation for efficient BEA production. A modified Monod model with substrate (glucose) and product (BEA) inhibition was constructed based on the culture characteristics of F. redolens Dzf2 mycelia in a liquid medium. Model parameters were derived by simulation of the experimental data from batch culture. The model fitted closely with the experimental data over 20-50 g l(-1) glucose concentration range in batch fermentation. The kinetic model together with the stoichiometric relationships for biomass, substrate and product was applied to predict the optimal feeding scheme for fed-batch fermentation, leading to 54% higher BEA yield (299 mg l(-1)) than in the batch culture (194 mg l(-1)). The modified Monod model incorporating substrate and product inhibition was proven adequate for describing the growth kinetics of F. redolens Dzf2 mycelial culture at suitable but not excessive initial glucose levels in batch and fed-batch cultures.

Investigations on the growth kinetics of Laves phase precipitates in 12% Cr creep-resistant steels: Experimental and DICTRA calculations

Energy Technology Data Exchange (ETDEWEB)

Prat, O. [Max Planck Institute fuer Eisenforschung GmbH, Max Planck Strasse 1, 40237 Duesseldorf (Germany)] [Universidad de Concepcion, Departamento de Ingenieria de Materiales, Edmundo Larenas 270, Concepcion (Chile); Garcia, J., E-mail: jose.garcia@helmholtz-berlin.de [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Rojas, D. [Max Planck Institute fuer Eisenforschung GmbH, Max Planck Strasse 1, 40237 Duesseldorf (Germany); Carrasco, C. [Universidad de Concepcion, Departamento de Ingenieria de Materiales, Edmundo Larenas 270, Concepcion (Chile); Inden, G. [Max Planck Institute fuer Eisenforschung GmbH, Max Planck Strasse 1, 40237 Duesseldorf (Germany)

2010-10-15

The growth kinetics of Laves phase precipitates (type Fe{sub 2}W) in the early stage of creep (650 deg. C for 10,000 h) in two 12% Cr ferrite-martensitic steels has been investigated. In one alloy the Laves phase formed on tempering, while in the second alloy the Laves phase precipitated during creep. Kinetic simulations were performed using the software DICTRA. The particle size of the Laves phase was measured on transmission electron microscopy samples. The equilibrium phase fraction of the Laves phase was reached in the first thousand hours. Simulations of particle growth showed good agreement with the experimental results. Competitive growth between M{sub 23}C{sub 6} and the Laves phase showed that M{sub 23}C{sub 6} carbides reached their equilibrium after 12 days, whereas the Laves phase reached equilibrium after 3 months. Simulations of the influence of the interfacial energy and addition of Co, Cu and Si on Laves phase precipitation are presented.

Investigations on the growth kinetics of Laves phase precipitates in 12% Cr creep-resistant steels: Experimental and DICTRA calculations

International Nuclear Information System (INIS)

Prat, O.; Garcia, J.; Rojas, D.; Carrasco, C.; Inden, G.

2010-01-01

The growth kinetics of Laves phase precipitates (type Fe 2 W) in the early stage of creep (650 deg. C for 10,000 h) in two 12% Cr ferrite-martensitic steels has been investigated. In one alloy the Laves phase formed on tempering, while in the second alloy the Laves phase precipitated during creep. Kinetic simulations were performed using the software DICTRA. The particle size of the Laves phase was measured on transmission electron microscopy samples. The equilibrium phase fraction of the Laves phase was reached in the first thousand hours. Simulations of particle growth showed good agreement with the experimental results. Competitive growth between M 23 C 6 and the Laves phase showed that M 23 C 6 carbides reached their equilibrium after 12 days, whereas the Laves phase reached equilibrium after 3 months. Simulations of the influence of the interfacial energy and addition of Co, Cu and Si on Laves phase precipitation are presented.

Conditions for mould growth on typical interior surfaces

DEFF Research Database (Denmark)

Møller, Eva B.; Andersen, Birgitte; Rode, Carsten

2017-01-01

Prediction of the risk for mould growth is an important parameter for the analysis and design of the hygrothermal performance of building constructions. However, in practice the mould growth does not always follow the predicted behavior described by the mould growth models. This is often explained...... by uncertainty in the real conditions of exposure. In this study, laboratory experiments were designed to determine mould growth at controlled transient climate compared to growth at constant climate. The experiment included three building materials with four different surface treatments. The samples were...

In situ photoemission spectroscopy using synchrotron radiation for O2 translational kinetic energy induced oxidation processes of partially-oxidized Si(001) surfaces

International Nuclear Information System (INIS)

Teraoka, Yuden; Yoshigoe, Akitaka

2001-01-01

The influence of translational kinetic energy of incident O 2 molecules for the passive oxidation process of partially-oxidized Si(001) surfaces has been studied by photoemission spectroscopy. The translational kinetic energy of O 2 molecules was controlled up to 3 eV by a supersonic seed beam technique using a high temperature nozzle. Two translational kinetic energy thresholds (1.0 eV and 2.6 eV) were found out in accordance with the first-principles calculation for the oxidation of clean surfaces. Si-2p photoemission spectra measured in representative translational kinetic energies revealed that the translational kinetic energy dependent oxidation of dimers and the second layer (subsurface) backbonds were caused by the direct dissociative chemisorption of O 2 molecules. Moreover, the difference in chemical bonds for oxygen atoms was found out to be as low and high binding energy components in O-1s photoemission spectra. Especially, the low binding energy component increased with increasing the translational kinetic energy that indicates the translational kinetic energy induced oxidation in backbonds. (author)

Applied electric field enhances DRG neurite growth: influence of stimulation media, surface coating and growth supplements

Science.gov (United States)

Wood, Matthew D.; Willits, Rebecca Kuntz

2009-08-01

Electrical therapies have been found to aid repair of nerve injuries and have been shown to increase and direct neurite outgrowth during stimulation. This enhanced neural growth existed even after the electric field (EF) or stimulation was removed, but the factors that may influence the enhanced growth, such as stimulation media or surface coating, have not been fully investigated. This study characterized neurite outgrowth and branching under various conditions: EF magnitude and application time, ECM surface coating, medium during EF application and growth supplements. A uniform, low-magnitude EF (24 or 44 V m-1) was applied to dissociated chick embryo dorsal root ganglia seeded on collagen or laminin-coated surfaces. During the growth period, cells were either exposed to NGF or N2, and during stimulation cells were exposed to either unsupplemented media (Ca2+) or PBS (no Ca2+). Parallel controls for each experiment included cells exposed to the chamber with no stimulation and cells remaining outside the chamber. After brief electrical stimulation (10 min), neurite length significantly increased 24 h after application for all conditions studied. Of particular interest, increased stimulation time (10-100 min) further enhanced neurite length on laminin but not on collagen surfaces. Neurite branching was not affected by stimulation on any surface, and no preferential growth of neurites was noted after stimulation. Overall, the results of this report suggest that short-duration electric stimulation is sufficient to enhance neurite length under a variety of conditions. While further data are needed to fully elucidate a mechanism for this increased growth, these data suggest that one focus of those investigations should be the interaction between the growth cone and the substrata.

Kinetics and thermodynamics studies on the BMP-2 adsorption onto hydroxyapatite surface with different multi-morphological features.

Science.gov (United States)

Lu, Zhiwei; Huangfu, Changxin; Wang, Yanying; Ge, Hongwei; Yao, Yao; Zou, Ping; Wang, Guangtu; He, Hua; Rao, Hanbing

2015-01-01

The effect of the surface topography on protein adsorption process is of great significance for designing hydroxyapatite (HA) ceramic material surfaces. In this work, three different topographies of HA materials HA-sheet, HA-rod, and HA-whisker were synthesized and testified by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Brunauer-Emmett-Teller (BET) and a field emission scanning electron microscopy (FE-SEM). We have systematically investigated the adsorption kinetics and thermodynamics of bone morphogenetic proteins (BMP-2) on the three different topography surfaces of HA, respectively. The results showed that the maximum adsorption capacities of HA-sheet, HA-rod and HA-whisker were (219.96 ± 10.18), (247.13 ± 12.35), and (354.67 ± 17.73) μg · g(-1), respectively. Kinetic parameters, rate constants, equilibrium adsorption capacities and related correlation coefficients, for each kinetic model were calculated as well as discussed. It demonstrated that the adsorption of BMP-2 onto HA could be described by the pseudo second-order equation. Adsorption of BMP-2 onto HA followed the Langmuir isotherm. It confirmed that compared with other samples HA-whisker had more adsorption sites for its high specific surface area which could provide more opportunities for protein molecules. The adsorption processes were endothermic (ΔH > 0), spontaneous (ΔG 0). A possible adsorption mechanism has been proposed. In addition, the BMP-2 could be adsorbed to the surface which existed slight conformational changes by FT-IR. Copyright © 2015 Elsevier B.V. All rights reserved.

Theoretical Analysis of the Relative Significance of Thermodynamic and Kinetic Dispersion in the dc and ac Voltammetry of Surface-Confined Molecules

KAUST Repository

Morris, Graham P.; Baker, Ruth E.; Gillow, Kathryn; Davis, Jason J.; Gavaghan, David J.; Bond, Alan M.

2015-01-01

© 2015 American Chemical Society. Commonly, significant discrepancies are reported in theoretical and experimental comparisons of dc voltammograms derived from a monolayer or close to monolayer coverage of redox-active surface-confined molecules. For example, broader-than-predicted voltammetric wave shapes are attributed to the thermodynamic or kinetic dispersion derived from distributions in reversible potentials (E⁰) and electrode kinetics (k⁰), respectively. The recent availability of experimentally estimated distributions of E⁰ and k⁰ values derived from the analysis of data for small numbers of surface-confined modified azurin metalloprotein molecules now allows more realistic modeling to be undertaken, assuming the same distributions apply under conditions of high surface coverage relevant to voltammetric experiments. In this work, modeling based on conventional and stochastic kinetic theory is considered, and the computationally far more efficient conventional model is shown to be equivalent to the stochastic one when large numbers of molecules are present. Perhaps unexpectedly, when experimentally determined distributions of E⁰ and k⁰ are input into the model, thermodynamic dispersion is found to be unimportant and only kinetic dispersion contributes significantly to the broadening of dc voltammograms. Simulations of ac voltammetric experiments lead to the conclusion that the ac method, particularly when the analysis of kinetically very sensitive higher-order harmonics is undertaken, are far more sensitive to kinetic dispersion than the dc method. ac methods are therefore concluded to provide a potentially superior strategy for addressing the inverse problem of determining the k⁰ distribution that could give rise to the apparent anomalies in surface-confined voltammetry.

Theoretical Analysis of the Relative Significance of Thermodynamic and Kinetic Dispersion in the dc and ac Voltammetry of Surface-Confined Molecules

KAUST Repository

Morris, Graham P.

2015-05-05

© 2015 American Chemical Society. Commonly, significant discrepancies are reported in theoretical and experimental comparisons of dc voltammograms derived from a monolayer or close to monolayer coverage of redox-active surface-confined molecules. For example, broader-than-predicted voltammetric wave shapes are attributed to the thermodynamic or kinetic dispersion derived from distributions in reversible potentials (E⁰) and electrode kinetics (k⁰), respectively. The recent availability of experimentally estimated distributions of E⁰ and k⁰ values derived from the analysis of data for small numbers of surface-confined modified azurin metalloprotein molecules now allows more realistic modeling to be undertaken, assuming the same distributions apply under conditions of high surface coverage relevant to voltammetric experiments. In this work, modeling based on conventional and stochastic kinetic theory is considered, and the computationally far more efficient conventional model is shown to be equivalent to the stochastic one when large numbers of molecules are present. Perhaps unexpectedly, when experimentally determined distributions of E⁰ and k⁰ are input into the model, thermodynamic dispersion is found to be unimportant and only kinetic dispersion contributes significantly to the broadening of dc voltammograms. Simulations of ac voltammetric experiments lead to the conclusion that the ac method, particularly when the analysis of kinetically very sensitive higher-order harmonics is undertaken, are far more sensitive to kinetic dispersion than the dc method. ac methods are therefore concluded to provide a potentially superior strategy for addressing the inverse problem of determining the k⁰ distribution that could give rise to the apparent anomalies in surface-confined voltammetry.

A nonlinear model for surface segregation and solute trapping during planar film growth

International Nuclear Information System (INIS)

Han, Xiaoying; Spencer, Brian J.

2007-01-01

Surface segregation and solute trapping during planar film growth is one of the important issues in molecular beam epitaxy, yet the study on surface composition has been largely restricted to experimental work. This paper introduces some mathematical models of surface composition during planar film growth. Analytical solutions are obtained for the surface composition during growth

Quantitative kinetics of proteolytic enzymes determined by a surface concentration-based assay using peptide arrays.

Science.gov (United States)

Jung, Se-Hui; Kong, Deok-Hoon; Park, Seoung-Woo; Kim, Young-Myeong; Ha, Kwon-Soo

2012-08-21

Peptide arrays have emerged as a key technology for drug discovery, diagnosis, and cell biology. Despite the promise of these arrays, applications of peptide arrays to quantitative analysis of enzyme kinetics have been limited due to the difficulty in obtaining quantitative information of enzymatic reaction products. In this study, we developed a new approach for the quantitative kinetics analysis of proteases using fluorescence-conjugated peptide arrays, a surface concentration-based assay with solid-phase peptide standards using dry-off measurements, and compared it with an applied concentration-based assay. For fabrication of the peptide arrays, substrate peptides of cMMP-3, caspase-3, caspase-9, and calpain-1 were functionalized with TAMRA and cysteine, and were immobilized onto amine-functionalized arrays using a heterobifunctional linker, N-[γ-maleimidobutyloxy]succinimide ester. The proteolytic activities of the four enzymes were quantitatively analyzed by calculating changes induced by enzymatic reactions in the concentrations of peptides bound to array surfaces. In addition, this assay was successfully applied for calculating the Michaelis constant (K(m,surf)) for the four enzymes. Thus, this new assay has a strong potential for use in the quantitative evaluation of proteases, and for drug discovery through kinetics studies including the determination of K(m) and V(max).

Hydrogen induced crack growth in Grade-12 titanium

International Nuclear Information System (INIS)

Ahn, T.M.; Lee, K.S.

1984-01-01

Internal hydrogen induced crack growth rates were measured in Grade-12 titanium which is a candidate material for high-level nuclear waste containers. As-received and hydrogen charged samples (5 ppM to 330 ppM hydrogen) were used for slow crack growth measurements at constant loads using a Krak Gauge. The testing temperature ranged from room temperature to 148 0 C. The crack growth kinetics under low to moderate loads are linear, but this linear rate is interrupted by discrete fast crack jump segments with parabolic or cubic type kinetics. These fast jump segments are thought to be associated with the passage of the crack front through the alpha-beta interface phase or with the initial loading sequence. By measuring striation spacings on the fracture surface, most crack growth rates observed are found to be in stage II. The striations are considered to be associated with hydride fracture. The crack path is either transgranular in the alpha phase or interfacial in the alpha phase adjacent to the beta phase. For transgranular growth, crack growth rates are constant and slower than those for interfacial growth which is associated with fast crack growth through a high hydrogen concentration region. Most stage II crack growth rates depend slightly on the stress intensity suggesting the contribution of plastic tearing process to stage II kinetics. The activation energies for crack growth are much lower than the activation energy of hydrogen diffusion through the alpha phase, implying that hydrogen is transported along dislocations, grain boundaries or interfaces. When the temperature is increased, the crack velocity first reaches a maximum and then decreases at higher temperatures. These temperature effects come from lower hydrogen concentration trapped at dislocations or from slower hydride nucleation kinetics, both at higher temperatures

In situ studies of the kinetics of surface topography development during ion irradiation

International Nuclear Information System (INIS)

Levinskas, R.; Pranevicius, L.

1996-01-01

Studies of the mechanical properties of the materials affected by 25-200 keV H + , He + , Ne + and Ar + ion irradiation in the range of fluences up to 2 · 10 17 cm -2 based on the analysis of acoustic emission signals, kinetics of the surface deformations measured by laser interferometric technique and the variations of the surface acoustic waves propagation velocity are conducted. The acoustic emissions source mechanisms under various ion irradiation conditions are discussed and relative contribution various possible mechanism are indicated. The correlation of experimental results obtained by different methods of analysis is done. (author). 11 refs, 5 figs

Surface growth mechanisms and structural faulting in the growth of large single and spherulitic titanosilicate ETS-4 crystals

Science.gov (United States)

Miraglia, Peter Q.; Yilmaz, Bilge; Warzywoda, Juliusz; Sacco, Albert

2004-10-01

Morphological, surface and crystallographic analyses of titanosilicate ETS-4 products, with diverse habits ranging from spherulitic particles composed of submicron crystallites to large single crystals, are presented. Pole figures revealed that crystal surfaces with a-, b- and c- axes corresponded to , and directions, respectively. Thus, technologically important 8-membered ring pores and titania chains in ETS-4 run along the b-axis of single crystals and terminate at the smallest crystal face. Height of the spiral growth steps observed on {1 0 0} and {0 0 1} surfaces corresponded to the interplanar spacings associated with their crystallographic orientation, and is equivalent to the thickness of building units that form the ETS-4 framework. Data suggest that the more viscous synthesis mixtures, with a large driving force for growth, increased the two- and three-dimensional nucleation, while limiting the transport of nutrients to the growth surface. These conditions increase the tendency for stacking fault formation on {1 0 0} surfaces and small angle branching, which eventually results in spherulitic growth. The growth of high quality ETS-4 single crystals (from less viscous synthesis mixtures) occurred at lower surface nucleation rates. Data suggest that these high quality, large crystals grew due to one-dimensional nucleation at spiral hillocks, and indicate that under these conditions un-faulted growth is preferred.

Heat and turbulent kinetic energy budgets for surface layer cooling induced by the passage of Hurricane Frances (2004)

Science.gov (United States)

Huang, Peisheng; Sanford, Thomas B.; Imberger, JöRg

2009-12-01

Heat and turbulent kinetic energy budgets of the ocean surface layer during the passage of Hurricane Frances were examined using a three-dimensional hydrodynamic model. In situ data obtained with the Electromagnetic-Autonomous Profiling Explorer (EM-APEX) floats were used to set up the initial conditions of the model simulation and to compare to the simulation results. The spatial heat budgets reveal that during the hurricane passage, not only the entrainment in the bottom of surface mixed layer but also the horizontal water advection were important factors determining the spatial pattern of sea surface temperature. At the free surface, the hurricane-brought precipitation contributed a negligible amount to the air-sea heat exchange, but the precipitation produced a negative buoyancy flux in the surface layer that overwhelmed the instability induced by the heat loss to the atmosphere. Integrated over the domain within 400 km of the hurricane eye on day 245.71 of 2004, the rate of heat anomaly in the surface water was estimated to be about 0.45 PW (1 PW = 1015 W), with about 20% (0.09 PW in total) of this was due to the heat exchange at the air-sea interface, and almost all the remainder (0.36 PW) was downward transported by oceanic vertical mixing. Shear production was the major source of turbulent kinetic energy amounting 88.5% of the source of turbulent kinetic energy, while the rest (11.5%) was attributed to the wind stirring at sea surface. The increase of ocean potential energy due to vertical mixing represented 7.3% of the energy deposited by wind stress.

Nucleation and growth kinetics of electrodeposited sulfate-doped polypyrrole: determination of the diffusion coefficient of SO(4)(2-) in the polymeric membrane.

Science.gov (United States)

Licona-Sánchez, T de J; Alvarez-Romero, G A; Mendoza-Huizar, L H; Galán-Vidal, C A; Palomar-Pardavé, M; Romero-Romo, M; Herrera-Hernández, H; Uruchurtu, J; Juárez-García, J M

2010-08-05

A kinetic study for the electrosynthesis of polypyrrole (Ppy) doped with SO(4)(2-) ions is presented. Ppy films were electrochemically polymerized onto a graphite-epoxy resin electrode. Experimental current density transients (j-t) were obtained for three different potentiometric behaviors: anionic, cationic, and a combination. Theoretical models were used to fit the experimental j-t data to determine the nucleation and growth processes controlling the polymer synthesis. It was encountered that, in all cases, pyrrole electropolimerization involves two concomitant processes, namely, a Ppy diffusion limited multiple 3D nucleation and growth and pyrrole electro-oxidation on the growing surface of the Ppy nuclei. SEM analysis of the electrodes surfaces reveals that Ppy deposition occurred over most of the electrode surface by multiple nucleation of hemispheres, as the theoretical model used for the analysis of the current transients required. Hemispherical particles formed the polymeric film displaying different sizes. The order for the particle size was as follows: anionic > anionic-cationic > cationic. These results are congruent with those obtained by theoretical analysis of the corresponding current transients. Analysis of the impedance measurements recorded on the anionic Ppy film, immersed in an aqueous solution with different sulfate ion concentrations evidenced that SO(4)(2-) ions diffuse through the Ppy film provoking a decrease of its electrical resistance and an increase of its dielectric constant. From the Warburg impedance coefficient, the sulfate coefficient of diffusion in the Ppy film was 1.38 x 10(-9) cm(2) s(-1).

Ozone disintegration kinetics in the reactor for tyres decomposition

International Nuclear Information System (INIS)

Golota, V.I.; Manujlenko, O.V.; Taran, G.V.; Pis'menetskij, A.S.; Zamuriev, A.A.

2010-01-01

The results of theoretical and experimental research of ozone disintegration kinetics in the chemical reactor which is developed for decomposition of tyres in the ozone-air environment are presented. Analytical expression for dependence of ozone concentration in the reactor from time and from parameters of the task, such as volume speed of ozone-air mixture feed on a reactor input, concentration of ozone on the input to the reactor, volume speed of output of the used mixture, reactor size, and square of its internal surface is obtained. It is shown that at the same speed of ozone-air mixture pro rolling through the reactor, with growth of ozone concentration on the input, value of stationary concentration in the reactor grows, remaining always less than concentration on the input. It is also shown that at the same ozone concentration on the input, with growth of speed of ozone-air mixture pro rolling through the reactor, value of stationary ozone concentration in the reactor also grows, remaining always less than ozone concentration on the input. The ozone disintegration kinetics in the reactor in a wide range of speed of ozone-air mixture pro rolling through the reactor (0.15, 0.30, 0.45, 0.60 m3/hour) and various ozone concentration on the input (5, 10, 15, 20 g/m3) is experimentally studied. It is shown that experimental results with good accuracy coincide with the theoretical. Direct experiment showed the essential influence of the internal surface of the reactor on the ozone disintegration kinetics.

Growth kinetics of hydrogen sulfide oxidizing bacteria in corroded concrete from sewers

International Nuclear Information System (INIS)

Jensen, Henriette Stokbro; Lens, Piet N.L.; Nielsen, Jeppe L.; Bester, Kai; Nielsen, Asbjorn Haaning; Hvitved-Jacobsen, Thorkild; Vollertsen, Jes

2011-01-01

Hydrogen sulfide oxidation by microbes present on concrete surfaces of sewer pipes is a key process in sewer corrosion. The growth of aerobic sulfur oxidizing bacteria from corroded concrete surfaces was studied in a batch reactor. Samples of corrosion products, containing sulfur oxidizing bacteria, were suspended in aqueous solution at pH similar to that of corroded concrete. Hydrogen sulfide was supplied to the reactor to provide the source of reduced sulfur. The removal of hydrogen sulfide and oxygen was monitored. The utilization rates of both hydrogen sulfide and oxygen suggested exponential bacterial growth with median growth rates of 1.25 d -1 and 1.33 d -1 as determined from the utilization rates of hydrogen sulfide and oxygen, respectively. Elemental sulfur was found to be the immediate product of the hydrogen sulfide oxidation. When exponential growth had been achieved, the addition of hydrogen sulfide was terminated leading to elemental sulfur oxidation. The ratio of consumed sulfur to consumed oxygen suggested that sulfuric acid was the ultimate oxidation product. To the knowledge of the authors, this is the first study to determine the growth rate of bacteria involved in concrete corrosion with hydrogen sulfide as source of reduced sulfur.

Saffman-Taylor fingers with kinetic undercooling

KAUST Repository

Gardiner, Bennett P. J.

2015-02-23

© 2015 American Physical Society. The mathematical model of a steadily propagating Saffman-Taylor finger in a Hele-Shaw channel has applications to two-dimensional interacting streamer discharges which are aligned in a periodic array. In the streamer context, the relevant regularization on the interface is not provided by surface tension but instead has been postulated to involve a mechanism equivalent to kinetic undercooling, which acts to penalize high velocities and prevent blow-up of the unregularized solution. Previous asymptotic results for the Hele-Shaw finger problem with kinetic undercooling suggest that for a given value of the kinetic undercooling parameter, there is a discrete set of possible finger shapes, each analytic at the nose and occupying a different fraction of the channel width. In the limit in which the kinetic undercooling parameter vanishes, the fraction for each family approaches 1/2, suggesting that this "selection" of 1/2 by kinetic undercooling is qualitatively similar to the well-known analog with surface tension. We treat the numerical problem of computing these Saffman-Taylor fingers with kinetic undercooling, which turns out to be more subtle than the analog with surface tension, since kinetic undercooling permits finger shapes which are corner-free but not analytic. We provide numerical evidence for the selection mechanism by setting up a problem with both kinetic undercooling and surface tension and numerically taking the limit that the surface tension vanishes.

Saffman-Taylor fingers with kinetic undercooling

KAUST Repository

Gardiner, Bennett P. J.; McCue, Scott W.; Dallaston, Michael C.; Moroney, Timothy J.

2015-01-01

© 2015 American Physical Society. The mathematical model of a steadily propagating Saffman-Taylor finger in a Hele-Shaw channel has applications to two-dimensional interacting streamer discharges which are aligned in a periodic array. In the streamer context, the relevant regularization on the interface is not provided by surface tension but instead has been postulated to involve a mechanism equivalent to kinetic undercooling, which acts to penalize high velocities and prevent blow-up of the unregularized solution. Previous asymptotic results for the Hele-Shaw finger problem with kinetic undercooling suggest that for a given value of the kinetic undercooling parameter, there is a discrete set of possible finger shapes, each analytic at the nose and occupying a different fraction of the channel width. In the limit in which the kinetic undercooling parameter vanishes, the fraction for each family approaches 1/2, suggesting that this "selection" of 1/2 by kinetic undercooling is qualitatively similar to the well-known analog with surface tension. We treat the numerical problem of computing these Saffman-Taylor fingers with kinetic undercooling, which turns out to be more subtle than the analog with surface tension, since kinetic undercooling permits finger shapes which are corner-free but not analytic. We provide numerical evidence for the selection mechanism by setting up a problem with both kinetic undercooling and surface tension and numerically taking the limit that the surface tension vanishes.

Analyzing the Molecular Kinetics of Water Spreading on Hydrophobic Surfaces via Molecular Dynamics Simulation.

Science.gov (United States)

Zhao, Lei; Cheng, Jiangtao

2017-09-07

In this paper, we report molecular kinetic analyses of water spreading on hydrophobic surfaces via molecular dynamics simulation. The hydrophobic surfaces are composed of amorphous polytetrafluoroethylene (PTFE) with a static contact angle of ~112.4° for water. On the basis of the molecular kinetic theory (MKT), the influences of both viscous damping and solid-liquid retarding were analyzed in evaluating contact line friction, which characterizes the frictional force on the contact line. The unit displacement length on PTFE was estimated to be ~0.621 nm and is ~4 times as long as the bond length of C-C backbone. The static friction coefficient was found to be ~[Formula: see text] Pa·s, which is on the same order of magnitude as the dynamic viscosity of water, and increases with the droplet size. A nondimensional number defined by the ratio of the standard deviation of wetting velocity to the characteristic wetting velocity was put forward to signify the strength of the inherent contact line fluctuation and unveil the mechanism of enhanced energy dissipation in nanoscale, whereas such effect would become insignificant in macroscale. Moreover, regarding a liquid droplet on hydrophobic or superhydrophobic surfaces, an approximate solution to the base radius development was derived by an asymptotic expansion approach.

Kinetic instability of AlGaN alloys during MBE growth under metal-rich conditions on m-plane GaN miscut towards the -c axis

Science.gov (United States)

Shirazi-HD, M.; Diaz, R. E.; Nguyen, T.; Jian, J.; Gardner, G. C.; Wang, H.; Manfra, M. J.; Malis, O.

2018-04-01

AlxGa1-xN layers with Al-composition above 0.6 (0.6 < x < 0.9) grown under metal-rich conditions by plasma-assisted molecular beam epitaxy on m-plane GaN miscut towards the -c axis are kinetically unstable. Even under excess Ga flux, the effective growth rate of AlGaN is drastically reduced, likely due to suppression of Ga-N dimer incorporation. The defect structure generated during these growth conditions is studied with energy dispersive x-ray spectroscopy scanning transmission electron microscopy as a function of Al flux. The AlGaN growth results in the formation of thin Al(Ga)N layers with Al-composition higher than expected and lower Al-composition AlGaN islands. The AlGaN islands have a flat top and are elongated along the c-axis (i.e., stripe-like shape). Possible mechanisms for the observed experimental results are discussed. Our data are consistent with a model in which Al-N dimers promote release of Ga-N dimers from the m-plane surface.

A unified approach to model uptake kinetics of trace elements in complex aqueous – solid solution systems

International Nuclear Information System (INIS)

Thien, Bruno M.J.; Kulik, Dmitrii A.; Curti, Enzo

2014-01-01

Highlights: • There are several models able to describe trace element partitioning in growing minerals. • To describe complex systems, those models must be embedded in a geochemical code. • We merged two models into a unified one suitable for implementation in a geochemical code. • This unified model was tested against coprecipitation experimental data. • We explored how our model reacts to solution depletion effects. - Abstract: Thermodynamics alone is usually not sufficient to predict growth-rate dependencies of trace element partitioning into host mineral solid solutions. In this contribution, two uptake kinetic models were analyzed that are promising in terms of mechanistic understanding and potential for implementation in geochemical modelling codes. The growth Surface Entrapment Model (Watson, 2004) and the Surface Reaction Kinetic Model (DePaolo, 2011) were shown to be complementary, and under certain assumptions merged into a single analytical expression. This Unified Uptake Kinetics Model was implemented in GEMS3K and GEM-Selektor codes ( (http://gems.web.psi.ch)), a Gibbs energy minimization package for geochemical modelling. This implementation extends the applicability of the unified uptake kinetics model to accounting for non-trivial factors influencing the trace element partitioning into solid solutions, such as the changes in aqueous solution composition and speciation, or the depletion effects in closed geochemical systems

Kinetic modeling of ethane pyrolysis at high conversion.

Science.gov (United States)

Xu, Chen; Al Shoaibi, Ahmed Sultan; Wang, Chenguang; Carstensen, Hans-Heinrich; Dean, Anthony M

2011-09-29

The primary objective of this study is to develop an improved first-principle-based mechanism that describes the molecular weight growth kinetics observed during ethane pyrolysis. A proper characterization of the kinetics of ethane pyrolysis is a prerequisite for any analysis of hydrocarbon pyrolysis and oxidation. Flow reactor experiments were performed with ~50/50 ethane/nitrogen mixtures with temperatures ranging from 550 to 850 °C at an absolute pressure of ~0.8 atm and a residence time of ~5 s. These conditions result in ethane conversions ranging from virtually no reaction to ~90%. Comparisons of predictions using our original mechanism to these data yielded very satisfactory results in terms of the temperature dependence of ethane conversion and prediction of the major products ethylene and hydrogen. However, there were discrepancies in some of the minor species concentrations that are involved in the molecular weight growth kinetics. We performed a series of CBS-QB3 analyses for the C(3)H(7), C(4)H(7), and C(4)H(9) potential energy surfaces to better characterize the radical addition reactions that lead to molecular weight growth. We also extended a published C(6)H(9) PES to include addition of vinyl to butadiene. The results were then used to calculate pressure-dependent rate constants for the multiple reaction pathways of these addition reactions. Inclusion of the unadjusted rate constants resulting from these analyses in the mechanism significantly improved the description of several of the species involved in molecular weight growth kinetics. We compare the predictions of this improved model to those obtained with a consensus model recently published as well as to ethane steam cracking data. We find that a particularly important reaction is that of vinyl addition to butadiene. Another important observation is that several radical addition reactions are partially equilibrated. Not only does this mean that reliable thermodynamic parameters are essential

Study the oxidation kinetics of uranium using XRD and Rietveld method

Science.gov (United States)

Zhang, Yanzhi; Guan, Weijun; Wang, Qinguo; Wang, Xiaolin; Lai, Xinchun; Shuai, Maobing

2010-03-01

The surface oxidation of uranium metal has been studied by X-ray diffraction (XRD) and Rietveld method in the range of 50~300°C in air. The oxidation processes are analyzed by XRD to determine the extent of surface oxidation and the oxide structure. The dynamics expression for the formation of UO2 was derived. At the beginning, the dynamic expression was nonlinear, but switched to linear subsequently for uranium in air and humid oxygen. That is, the growth kinetics of UO2 can be divided into two stages: nonlinear portion and linear portion. Using the kinetic data of linear portion, the activation energy of reaction between uranium and air was calculated about 46.0 kJ/mol. However the content of oxide as a function of time was linear in humid helium ambience. Contrast the dynamics results, it prove that the absence of oxygen would accelerate the corrosion rate of uranium in the humid gas. We can find that the XRD and Rietveld method are a useful convenient method to estimate the kinetics and thermodynamics of solid-gas reaction.

Small-Angle Neutron Scattering Investigation of Growth Modifiers on Hydrate Crystal Surfaces

Science.gov (United States)

Sun, Thomas; Hutter, Jeffrey L.; Lin, M.; King, H. E., Jr.

1998-03-01

Hydrates are crystals consisting of small molecules enclathrated within an ice-like water cage. Suppression of their growth is important in the oil industry. The presence of small quantities of specific polymers during hydrate crystallization can induce a transition from an octahedral to planar growth habit. This symmetry breaking is surprising because of the suppression of two 111 planes relative to the other six crystallographically equivalent faces. To better understand the surface effects leading to this behavior, we have studied the surface adsorption of these growth-modifing polymers onto the hydrate crytals using SANS. The total hydrate surface area, as measured by Porod scattering, increases in the presence of the growth modifier, but, no significant increase in polymer concentration on the crystal surfaces is found. Implications for possible growth mechanisms will be discussed.

Study on growth kinetics of hexadecylamine capped CdSe nanoparticles using its electronic properties

Energy Technology Data Exchange (ETDEWEB)

Oluwafemi, S.O., E-mail: tobi_55@yahoo.co [Department of Chemistry, University of Zululand, Private Bag X1001, Kwadlangezwa 3886 (South Africa); Revaprasadu, N. [Department of Chemistry, University of Zululand, Private Bag X1001, Kwadlangezwa 3886 (South Africa)

2009-05-01

The growth kinetics of hexadecylamine (HDA) capped CdSe synthesised via a novel, mild, effective, and facile non-organometallic route was studied using its electronic properties. The emission and optical maxima of all the nanoparticles synthesised are blue-shifted as the reaction time increases indicating decrease in particle size. The UV spectra show distinct excitonic features which can be attributed to the first electronic transition [1S{sub 3/2}(h)-1S(e)] occurring in CdSe nanoparticles with band-edge luminescence in their emission spectra. The extinction coefficient was determined for convenient and accurate measurements of the concentration of the nanocrystals. Nucleation is very fast and well separated from particle growth under this reaction condition. Two distinguishable stages of growth were observed: an early stage 0-10 min characterised by fast growth, with narrow size distribution and the late stage characterised by slow growth with slight defocusing of size distribution and large particle sizes. The diameter of the size ranges from 2.2 to 3.0 nm. About 94% of the available monomer concentration was consumed during the growth and the solubility of 3.0 nm CdSe in hexadecylamine is measured to be 9.216x10{sup -7} M{sup 2} at 433 deg. K.

Metal thin film growth on multimetallic surfaces: From quaternary metallic glass to binary crystal

Energy Technology Data Exchange (ETDEWEB)

Jing, Dapeng [Iowa State Univ., Ames, IA (United States)

2010-01-01

length while keeping the corresponding island width constant. Third, LEED indicates that, up to about 6 BL (12 ML), the Ag film adopts the (110) structure on lattice matched NiAl(110) surface, supporting the previous assignment based upon island heights measured in STM. Starting at 4.5 to 6 BL, (111) diffraction pattern is detected. This is also in agreement with previous STM study. Careful examinations of the LEED patterns reveal the slight difference in lattice constants between bulk Ag and bulk NiAl. At last, we performed STM studies of Ni deposition on NiAl(110) in the temperature range from 200 K to 400 K. Ni forms 'dense' Ni(100)-like islands on NiAl(110) with a zig-zag shaped stripe feature which is probably due to strain relief. DFT analysis provides insights into the island growth shapes, which are rationalized by the thermodynamics and kinetics of the film growth process. For thick Ni films (coverage exceeding 6 ML), a Ni(111)-like structure developed. Traditional MF theory is applied to analyze island density at 200 K. Deviation from homogeneous nucleation behavior for island size distribution and island density reveals the presence of heterogeneous nucleation mediated by the Ni antisite point defects on NiAl(110) surface.

Precipitation kinetics of Mg-carbonates, influence of organic ligands and consequences for CO2 mineral sequestration

International Nuclear Information System (INIS)

Gautier, Q.

2012-01-01

Forming magnesium carbonate minerals through carbonation of magnesium silicates has been proposed as a safe and durable way to store carbon dioxide, with a possibly high potential to offset anthropogenic CO 2 emissions. To date however, chemical reactions involved in this process are facing strong kinetic limitations, which originate in the low reactivity of both Mg-silicates and Mg-carbonates. Numerous studies have focused on the dissolution of Mg-silicates, under the questionable hypothesis that this step limits the whole process. This thesis work focuses instead on the mechanisms and rates of formation of magnesium carbonates, which are the final products of carbonation reactions. The first part of the work is dedicated to studying the influence on magnesite precipitation kinetics of three organic ligands known to accelerate Mg-silicates dissolution rates: oxalate, citrate and EDTA. With help of mixed-flow reactor experiments performed between 100 and 150 C, we show that these ligands significantly reduce magnesite growth rates, through two combined mechanisms: (1) complexation of Mg 2+ cations in aqueous solution, which was rigorously estimated from a thermodynamic database established through a critical review of the literature, and (2) adsorption of ligands to a limited number of surface sites, leading to a decrease of the precipitation rate constant. The observed growth inhibition is maximal with citrate. We then used hydrothermal atomic force microscopy to probe the origin of the documented growth inhibition. Our observations show that citrate and oxalate interact with the crystal growth process on magnesite surface, modifying the shape of growth hillocks as well as the step generation frequency through spiral growth. We also show that the ligands adsorb preferentially on different kink-sites, which is probably related to their different structures and chemical properties. We propose that the stronger magnesite growth inhibition caused by citrate is related

Analysis of the effect on growth kinetics of gamma prima phase in Inconel 713C alloys

International Nuclear Information System (INIS)

Thorp, S.I.; Versaci, R.A.; Ges, A.; Palacio, H.A.

1993-01-01

This work shows the analysis of the effect on growth kinetics of gamma prima phase in Inconel 713C alloy of two thermic treatments. In this study, SEM are used and the results are analyzed by means of the theory developed by Lifshitz, Slyozov and Wagner (LSW theory). The findings have revealed that with such theory it is not possible to determine if the process of growth is controlled either through diffusion or through diffusion in the interface as to the time employed in the experiment (2600 hours); the time required is approximately 10000 hours. (Author)

Effects of gas phase impurities on the topochemical-kinetic behaviour of uranium hydride development

International Nuclear Information System (INIS)

Bloch, J.; Brami, D.; Kremner, A.; Mintz, M.H.; Ben-Gurion Univ. of the Negev, Beersheba

1988-01-01

The hydriding kinetics of bulk uranium and U-0.1 wt.% Cr, in the presence of oxidizing gaseous impurities (oxygen and CO), were studied by combined rate measurements and metallographic examinations of partially reacted samples. The effect of the gaseous impurity (type and concentration) was examined metallographically, and the kinetic data were discussed in relation to these examinations. Below about 100 0 C the reaction of uranium with pure hydrogen consists of the following sequence of steps: (i) Surface nucleation; (ii) homogeneous growth (pitting); (iii) relatively fast lateral growth leading to the formation of a reaction front which penetrates into the sample at a constant rate. The effects of oxygen and CO on the hydriding kinetics were related to their abilities to block hydrogen penetration into the uranium. Thus, it was found that oxygen affects only the penetration through the oxide layer, whereas CO affects the penetration through both the oxide and hydride layers. (orig.)

Mesoscale Elucidation of Surface Passivation in the Li-Sulfur Battery Cathode.

Science.gov (United States)

Liu, Zhixiao; Mukherjee, Partha P

2017-02-15

The cathode surface passivation caused by Li 2 S precipitation adversely affects the performance of lithium-sulfur (Li-S) batteries. Li 2 S precipitation is a complicated mesoscale process involving adsorption, desorption and diffusion kinetics, which are affected profoundly by the reactant concentration and operating temperature. In this work, a mesoscale interfacial model is presented to study the growth of Li 2 S film on carbon cathode surface. Li 2 S film growth experiences nucleation, isolated Li 2 S island growth and island coalescence. The slow adsorption rate at small S 2- concentration inhibits the formation of nucleation seeds and the lateral growth of Li 2 S islands, which deters surface passivation. An appropriate operating temperature, especially in the medium-to-high temperature range, can also defer surface passivation. Fewer Li 2 S nucleation seeds form in such an operating temperature range, thereby facilitating heterogeneous growth and potentially inhibiting the lateral growth of the Li 2 S film, which may ultimately result in reduced surface passivation. The high specific surface area of the cathode microstructure is expected to mitigate the surface passivation.

Listeria monocytogenes Growth Kinetics in Milkshakes Made from Naturally and Artificially Contaminated Ice Cream

Directory of Open Access Journals (Sweden)

Joelle K. Salazar

2018-01-01

Full Text Available This study assessed the growth of Listeria monocytogenes in milkshakes made using the process-contaminated ice cream associated with a listeriosis outbreak in comparison to milkshakes made with artificially contaminated ice cream. For all temperatures, growth kinetics including growth rates, lag phases, maximum populations, and population increases were determined for the naturally and artificially derived contaminants at 5, 10, 15, and 25°C storage for 144 h. The artificially inoculated L. monocytogenes presented lower growth rates and shorter lag phases than the naturally contaminated populations at all temperatures except for 5°C, where the reverse was observed. At 25°C, lag phases of the naturally and artificially contaminated L. monocytogenes were 11.6 and 7.8 h, respectively. The highest increase in population was observed for the artificially inoculated pathogen at 15°C after 96 h (6.16 log CFU/mL of storage. Growth models for both contamination states in milkshakes were determined. In addition, this study evaluated the antimicrobial effectiveness of flavoring agents, including strawberry, chocolate and mint, on the growth of the pathogen in milkshakes during 10°C storage. All flavor additions resulted in decreased growth rates of L. monocytogenes for both contamination states. The addition of chocolate and mint flavoring also resulted in significantly longer lag phases for both contamination states. This study provides insight into the differences in growth between naturally and artificially contaminated L. monocytogenes in a food product.

Listeria monocytogenes Growth Kinetics in Milkshakes Made from Naturally and Artificially Contaminated Ice Cream.

Science.gov (United States)

Salazar, Joelle K; Bathija, Vriddi M; Carstens, Christina K; Narula, Sartaj S; Shazer, Arlette; Stewart, Diana; Tortorello, Mary Lou

2018-01-01

This study assessed the growth of Listeria monocytogenes in milkshakes made using the process-contaminated ice cream associated with a listeriosis outbreak in comparison to milkshakes made with artificially contaminated ice cream. For all temperatures, growth kinetics including growth rates, lag phases, maximum populations, and population increases were determined for the naturally and artificially derived contaminants at 5, 10, 15, and 25°C storage for 144 h. The artificially inoculated L. monocytogenes presented lower growth rates and shorter lag phases than the naturally contaminated populations at all temperatures except for 5°C, where the reverse was observed. At 25°C, lag phases of the naturally and artificially contaminated L. monocytogenes were 11.6 and 7.8 h, respectively. The highest increase in population was observed for the artificially inoculated pathogen at 15°C after 96 h (6.16 log CFU/mL) of storage. Growth models for both contamination states in milkshakes were determined. In addition, this study evaluated the antimicrobial effectiveness of flavoring agents, including strawberry, chocolate and mint, on the growth of the pathogen in milkshakes during 10°C storage. All flavor additions resulted in decreased growth rates of L. monocytogenes for both contamination states. The addition of chocolate and mint flavoring also resulted in significantly longer lag phases for both contamination states. This study provides insight into the differences in growth between naturally and artificially contaminated L. monocytogenes in a food product.

Reaction kinetics of dolomite rim growth

Science.gov (United States)

Helpa, V.; Rybacki, E.; Abart, R.; Morales, L. F. G.; Rhede, D.; Jeřábek, P.; Dresen, G.

2014-04-01

Reaction rims of dolomite (CaMg[CO3]2) were produced by solid-state reactions at the contacts of oriented calcite (CaCO3) and magnesite (MgCO3) single crystals at 400 MPa pressure, 750-850 °C temperature, and 3-146 h annealing time to determine the reaction kinetics. The dolomite reaction rims show two different microstructural domains. Elongated palisades of dolomite grew perpendicular into the MgCO3 interface with length ranging from about 6 to 41 µm. At the same time, a 5-71 µm wide rim of equiaxed granular dolomite grew at the contact with CaCO3. Platinum markers showed that the original interface is located at the boundary between the granular and palisade-forming dolomite. In addition to dolomite, a 12-80 µm thick magnesio-calcite layer formed between the dolomite reaction rims and the calcite single crystals. All reaction products show at least an axiotactic crystallographic relationship with respect to calcite reactant, while full topotaxy to calcite prevails within the granular dolomite and magnesio-calcite. Dolomite grains frequently exhibit growth twins characterized by a rotation of 180° around one of the equivalent axis. From mass balance considerations, it is inferred that the reaction rim of dolomite grew by counter diffusion of MgO and CaO. Assuming an Arrhenius-type temperature dependence, activation energies for diffusion of CaO and MgO are E a (CaO) = 192 ± 54 kJ/mol and E a (MgO) = 198 ± 44 kJ/mol, respectively.

Influence of growth parameters on the surface morphology and ...

Indian Academy of Sciences (India)

Unknown

surface features of the grown film like terracing, inclusions, meniscus lines, etc are ... Recently, studies carried out on the growth of InSb ..... is a critical factor in any epitaxial growth process and can ... However, this approach can lead to.

Reaction kinetic model of the surface-mediated formation of PCDD/F from pyrolysis of 2-chlorophenol on a CuP/Silica suface

Energy Technology Data Exchange (ETDEWEB)

Lomnicki, S.; Khachatryan, L.; Dellinger, B. [Louisiana State Univ., Baton Rouge (United States). Dept. of Chemistry

2004-09-15

One of the major challenges in developing predictive models of the surface mediated pollutant formation and fuel combustion is the construction of reliable reaction kinetic mechanisms and models. While the homogeneous, gas-phase chemistry of various light fuels such as hydrogen and methane is relatively well-known large uncertainties exist in the reaction paths of surface mediated reaction mechanisms for even these very simple species. To date, no detailed kinetic consideration of the surface mechanisms of formation of complex organics such as PCDD/F have been developed. In addition to the complexity of the mechanism, a major difficulty is the lack of reaction kinetic parameters (pre-exponential factor and activation energy) of surface reactions, Consequently, numerical studies of the surface-mediated formation of PCDD/F have often been incorporated only a few reactions. We report the development of a numerical multiple-step surface model based on experimental data of surface mediated (5% CuO/SiO2) conversion of 2-monochlorphenol (2-MCP) to PCDD/F under pyrolytic or oxidative conditions. A reaction kinetic model of the catalytic conversion of 2-MCP on the copper oxide catalyst under pyrolytic conditions was developed based on a detailed multistep surface reaction mechanism developed in our laboratory. The performance of the chemical model is assessed by comparing the numerical predictions with experimental measurements. SURFACE CHEMKIN (version 3.7.1) software was used for modeling. Our results confirm the validity of previously published mechanism of the reaction and provides new insight concerning the formation of PCDD/F formation in combustion processes. This model successfully explains the high yields of PCDD/F at low temperatures that cannot be explained using a purely gas-phase mode.

De-mercurization of wastewater by Bacillus cereus (JUBT1): Growth kinetics, biofilm reactor study and field emission scanning electron microscopic analysis

International Nuclear Information System (INIS)

Ghoshal, Sanjukta; Bhattacharya, Pinaki; Chowdhury, Ranjana

2011-01-01

Graphical abstract: The assembly of biofilm reactor, based on attached growth of Bacillus cereus (JUBT1) on rice husk packing, and an activated carbon filter has been able to ensure the removal of mercury up to near-zero level. Highlights: → A new mercury resistant bacterial strain, Bacillus cereus (JUBT1), has been isolated. → Growth kinetics has been determined. → Biofilm reactor using attached growth of bacteria ensures near-zero level of mercury. → Confinement of mercury is confirmed through energy dispersive spectrometric analysis. - Abstract: Removal of mercuric ions by a mercury resistant bacteria, called Bacillus cereus (JUBT1), isolated from the sludge of a local chlor-alkali industry, has been investigated. Growth kinetics of the bacteria have been determined. A multiplicative, non-competitive relationship between sucrose and mercury ions has been observed with respect to bacterial growth. A combination of biofilm reactor, using attached growth of Bacillus cereus (JUBT1) on rice husk packing, and an activated carbon filter has been able to ensure the removal of mercury up to near-zero level. Energy dispersive spectrometry analysis of biofilm and the activated carbon has proved the transformation of Hg 2+ to Hg 0 and its confinement in the system.

Nanoparticles dynamics on a surface: fractal pattern formation and fragmentation

DEFF Research Database (Denmark)

Dick, Veronika V.; Solov'yov, Ilia; Solov'yov, Andrey V.

2010-01-01

In this paper we review our recent results on the formation and the post-growth relaxation processes of nanofractals on surface. For this study we developed a method which describes the internal dynamics of particles in a fractal and accounts for their diffusion and detachment. We demonstrate...... that these kinetic processes determine the final shape of the islands on surface after post-growth relaxation. We consider different scenarios of fractal relaxation and analyze the time evolution of the island's morphology....

Development kinetics of silver clusters on silver halides

International Nuclear Information System (INIS)

Grzesiak, S.; Belloni, J.; Marignier, J.-L.

2008-01-01

Silver nuclei are produced by pulse radiolysis at the surface of AgCl nanocrystallites in the presence of an electron donor, the methyl viologen, which induces the growth of silver nuclei. The experimental results observed on the increase of the silver atom concentration and on the decay of the donor concentration during this process, which is similar to the photographic development by an electron donor, are compared with the kinetics obtained from numerical simulation. The model assumes that the formation of silver clusters with a supercritical nuclearity is required before the start of an electron transfer reaction from the two reduced forms of the donor methyl viologen to the silver clusters. The reaction is controlled by the access of the donor to the surface sites of the AgCl crystallite. The rate constant values of the successive steps of the mechanism are derived from the adjustment of calculated kinetics to experimental signals under various conditions, using a single set of parameters which are fairly suitable under all conditions studied

Control of bacterial biofilm growth on surfaces by nanostructural mechanics and geometry

International Nuclear Information System (INIS)

Epstein, A K; Hochbaum, A I; Kim, Philseok; Aizenberg, J

2011-01-01

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.

Surface growth kinematics via local curve evolution

KAUST Repository

Moulton, Derek E.

2012-11-18

A mathematical framework is developed to model the kinematics of surface growth for objects that can be generated by evolving a curve in space, such as seashells and horns. Growth is dictated by a growth velocity vector field defined at every point on a generating curve. A local orthonormal basis is attached to each point of the generating curve and the velocity field is given in terms of the local coordinate directions, leading to a fully local and elegant mathematical structure. Several examples of increasing complexity are provided, and we demonstrate how biologically relevant structures such as logarithmic shells and horns emerge as analytical solutions of the kinematics equations with a small number of parameters that can be linked to the underlying growth process. Direct access to cell tracks and local orientation enables for connections to be made to the underlying growth process. © 2012 Springer-Verlag Berlin Heidelberg.

Dissimilar kinetic behavior of electrically manipulated single- and double-stranded DNA tethered to a gold surface.

Science.gov (United States)

Rant, Ulrich; Arinaga, Kenji; Tornow, Marc; Kim, Yong Woon; Netz, Roland R; Fujita, Shozo; Yokoyama, Naoki; Abstreiter, Gerhard

2006-05-15

We report on the electrical manipulation of single- and double-stranded oligodeoxynucleotides that are end tethered to gold surfaces in electrolyte solution. The response to alternating repulsive and attractive electric surface fields is studied by time-resolved fluorescence measurements, revealing markedly distinct dynamics for the flexible single-stranded and stiff double-stranded DNA, respectively. Hydrodynamic simulations rationalize this finding and disclose two different kinetic mechanisms: stiff polymers undergo rotation around the anchoring pivot point; flexible polymers, on the other hand, are pulled onto the attracting surface segment by segment.

The kinetics of dolomite reaction rim growth under isostatic and non-isostatic pressure conditions

Science.gov (United States)

Helpa, V.; Rybacki, E.; Morales, L. G.; Abart, R.; Dresen, G. H.

2013-12-01

During burial and exhumation, rocks are simultaneously exposed to metamorphic reactions and tectonic stresses. Therefore, the reaction rate of newly formed minerals may depend on chemical and mechanical driving forces. Here, we investigate the reaction kinetics of dolomite (CaMg[CO3]2) rim growth by solid-state reactions experiments on oriented calcite (CaCO3) and magnesite (MgCO3) single crystals under isostatic and non-isostatic pressure conditions. Cylindrical samples of 3-5 mm length and 7 mm diameter were drilled and polished perpendicular to the rhombohedral cleavage planes of natural clear crystals. The tests were performed using a Paterson-type deformation apparatus at P = 400 MPa confining pressure, temperatures, T, between 750 and 850°C, and reaction durations, t, of 2 - 146 h to calculate the kinetic parameters of dolomite rim growth under isostatic stress conditions. For non-isostatic reaction experiments we applied in addition differential stresses, σ, up to 40 MPa perpendicular to the contact interface at T = 750°C for 4 - 171 h duration, initiating minor inelastic deformation of calcite. The thickness of the resulting dolomite reaction rims increases linearly with the square root of time, indicating a diffusion-controlled reaction. The rims consist of two different textural domains. Granular dolomite grains (≈ 2 -5 μm grain size) form next to calcite and elongated palisade-shaped grains (1-6 μm diameter) grow perpendicular to the magnesite interface. Texture measurements with the electron backscatter diffraction technique indicate that the orientations of dolomite grains are mainly influenced by the orientation of the calcite educt crystal, in particular in the granular rim. To some extent, the texture of dolomite palisades is also influenced by the orientation of magnesite. The thickness of the two individual layers increases with temperature. At 400 MPa isostatic pressure, T = 750°C and t = 29 hours, a 5 μm thick granular dolomite layer

Effect of strain on surface diffusion and nucleation

DEFF Research Database (Denmark)

Brune, Harald; Bromann, Karsten; Röder, Holger

1995-01-01

The influence of strain on diffusion and nucleation has been studied by means of scanning tunneling microscopy and effective-medium theory for Ag self-diffusion on strained and unstrained (111) surfaces. Experimentally, the diffusion barrier is observed to be substantially lower on a pseudomorphic...... effect on surface diffusion and nucleation in heteroepitaxy and are thus of significance for the film morphology in the kinetic growth regime....

Epitaxial growth of fcc Ti films on Al(001) surfaces

International Nuclear Information System (INIS)

Saleh, A.A.; Shutthanandan, V.; Shivaparan, N.R.; Smith, R.J.; Tran, T.T.; Chambers, S.A.

1997-01-01

High-energy ion scattering (HEIS), x-ray photoelectron spectroscopy, and x-ray photoelectron diffraction (XPD) were used to study the growth of thin Ti films on Al(001) surfaces. The Al surface peak area in the backscattered ion spectrum of MeV He + ions, incident along the [00 bar 1] direction, was used to monitor the atomic structure of the Ti films during growth. An initial decrease in the area was observed indicating epitaxial film growth. This decrease continued up to a critical film thickness of about 5.5 ML, after which point the structure of the film changed. Titanium films 3, 5, and 9 ML thick were characterized using XPD in the same chamber. Both the HEIS and XPD results show that the Ti films grow with an fcc structure on Al(001). A tetragonal distortion of 2.4% in the fcc Ti film was measured using ions incident along the [10 bar 1] direction. Although there is a general similarity of fcc Ti growth on both Al(001) and Al(110), the submonolayer growth regime does show differences for the two surfaces. copyright 1997 The American Physical Society

Investigation into fatigue crack growth and kinetic diagrams of fatigue failure

International Nuclear Information System (INIS)

Yarema, S.Ya.

1977-01-01

Studies on fatigue failure are discussed in terms of fatigue failure kinetic diagrams (FFKD), in which the fatigue crack growth rate is plotted against the stress intensity coefficient (SIC). The physical sense of the crack growth rate and SIC is discussed and their applicability for description of the material in the destruction zone, particularly in presence of various media. Variation of experimental parameters (loading and environment) is followed by a transition period during which the results of the experiment may depend on its history, so that FFKD would remain invariant. Advantages of tests under constant experimental conditions are shown. The ways to stabilize SIC are indicated and requirements to the samples are given. As an example, the tests of disc samples made of plate materials are given, where SIC does not depend on the crack length. The question of controlling the experimental conditions such as asymmetry and shape of the loading cycle, loading frequency, fluctuations of temperature and air composition is considered. The analytical functions describing FFKD are discussed. It is shown, that in appropriate dimensionless coordinates the FFKD of different materials merge into one curve

Continuum damage mechanics method for fatigue growth of surface cracks

International Nuclear Information System (INIS)

Feng Xiqiao; He Shuyan

1997-01-01

With the background of leak-before-break (LBB) analysis of pressurized vessels and pipes in nuclear plants, the fatigue growth problem of either circumferential or longitudinal semi-elliptical surface cracks subjected to cyclic loading is studied by using a continuum damage mechanics method. The fatigue damage is described by a scalar damage variable. From the damage evolution equation at the crack tip, a crack growth equation similar to famous Paris' formula is derived, which shows the physical meaning of Paris' formula. Thereby, a continuum damage mechanics approach is developed to analyze the configuration evolution of surface cracks during fatigue growth

THE SURFACE-MEDIATED UNFOLDING KINETICS OF GLOBULAR PROTEINS IS DEPENDENT ON MOLECULAR WEIGHT AND TEMPERATURE

Energy Technology Data Exchange (ETDEWEB)

Patananan, A.N.; Goheen, S.C.

2008-01-01

The adsorption and unfolding pathways of proteins on rigid surfaces are essential in numerous complex processes associated with biomedical engineering, nanotechnology, and chromatography. It is now well accepted that the kinetics of unfolding are characterized by chemical and physical interactions dependent on protein deformability and structure, as well as environmental pH, temperature, and surface chemistry. Although this fundamental process has broad implications in medicine and industry, little is known about the mechanism because of the atomic lengths and rapid time scales involved. Therefore, the unfolding kinetics of myoglobin, β-glucosidase, and ovalbumin were investigated by adsorbing the globular proteins to non-porous cationic polymer beads. The protein fractions were adsorbed at different residence times (0, 9, 10, 20, and 30 min) at near-physiological conditions using a gradient elution system similar to that in high-performance liquid chromatography. The elution profi les and retention times were obtained by ultraviolet/visible spectrophotometry. A decrease in recovery was observed with time for almost all proteins and was attributed to irreversible protein unfolding on the non-porous surfaces. These data, and those of previous studies, fi t a positively increasing linear trend between percent unfolding after a fi xed (9 min) residence time (71.8%, 31.1%, and 32.1% of myoglobin, β-glucosidase, and ovalbumin, respectively) and molecular weight. Of all the proteins examined so far, only myoglobin deviated from this trend with higher than predicted unfolding rates. Myoglobin also exhibited an increase in retention time over a wide temperature range (0°C and 55°C, 4.39 min and 5.74 min, respectively) whereas ovalbumin and β-glucosidase did not. Further studies using a larger set of proteins are required to better understand the physiological and physiochemical implications of protein unfolding kinetics. This study confi rms that surface

A Chemical-Adsorption Strategy to Enhance the Reaction Kinetics of Lithium-Rich Layered Cathodes via Double-Shell Surface Modification.

Science.gov (United States)

Guo, Lichao; Li, Jiajun; Cao, Tingting; Wang, Huayu; Zhao, Naiqin; He, Fang; Shi, Chunsheng; He, Chunnian; Liu, Enzuo

2016-09-21

Sluggish surface reaction kinetics hinders the power density of Li-ion battery. Thus, various surface modification techniques have been applied to enhance the electronic/ionic transfer kinetics. However, it is challenging to obtain a continuous and uniform surface modification layer on the prime particles with structure integration at the interface. Instead of classic physical-adsorption/deposition techniques, we propose a novel chemical-adsorption strategy to synthesize double-shell modified lithium-rich layered cathodes with enhanced mass transfer kinetics. On the basis of experimental measurement and first-principles calculation, MoO2S2 ions are proved to joint the layered phase via chemical bonding. Specifically, the Mo-O or Mo-S bonds can flexibly rotate to bond with the cations in the layered phase, leading to the good compatibility between the thiomolybdate adsorption layer and layered cathode. Followed by annealing treatment, the lithium-excess-spinel inner shell forms under the thiomolybdate adsorption layer and functions as favorable pathways for lithium and electron. Meanwhile, the nanothick MoO3-x(SO4)x outer shell protects the transition metal from dissolution and restrains electrolyte decomposition. The double-shell modified sample delivers an enhanced discharge capacity almost twice as much as that of the unmodified one at 1 A g(-1) after 100 cycles, demonstrating the superiority of the surface modification based on chemical adsorption.

Effect of Ingredient Loading on Surface Migration Kinetics of Additives in Vulcanized Natural Rubber Compounds

Directory of Open Access Journals (Sweden)

Bryan B. Pajarito

2014-12-01

Full Text Available Surface migration kinetics of chemical additives in vulcanized natural rubber compounds were studied as function of ingredient loading. Rubber sheets were compounded according to a 212-8 fractional factorial design of experiment, where ingredients were treated as factors varied at two levels of loading. Amount of migrated additives in surface of rubber sheets was monitored through time at ambient conditions. The maximum amount and estimated rate of additive migration were determined from weight loss kinetic curves. Attenuated total reflection–Fourier transform infrared (ATR-FTIR spectroscopy and optical microscopy were used to characterize the chemical structure and surface morphology of sheet specimens during additive migration. ANOVA results showed that increased loading of reclaimed rubber, CaCO3, and paraffin wax signif icantly decreased the maximum amount of additive migration; by contrast, increased loading of used oil, asphalt, and mercaptobenzothiazole disulphide (MBTS increased the maximum amount. Increased loading of sulfur, diphenylguanidine (DPG, and paraffin wax significantly decreased the additive migration rate; increased loading of used oil, asphalt, and stearic acid elicited an opposite effect. Comparison of ATRFTIR spectra of migrated and cleaned rubber surfaces showed signif icant variation in intensity of specif ic absorbance bands that are also present in infrared spectra of migrating chemicals. Paraffin wax, used oil, stearic acid, MBTS, asphalt, and zinc stearate were identified to bloom and bleed in the rubber sheets. Optical micrographs of migrated rubber surfaces revealed formation of white precipitates due to blooming and of semi-transparent wet patches due to bleeding.

Kinetic Monte Carlo study on the evolution of silicon surface roughness under hydrogen thermal treatment

Energy Technology Data Exchange (ETDEWEB)

Wang, Gang; Wang, Yu; Wang, Junzhuan; Pan, Lijia; Yu, Linwei; Zheng, Youdou; Shi, Yi, E-mail: yshi@nju.edu.cn

2017-08-31

Highlights: • The KMC method is adopted to investigate the relationships between surface evolution and hydrogen thermal treatment conditions. • The reduction in surface roughness is divided into two stages at relatively low temperatures, both exhibiting exponential dependence on the time. • The optimized surface structure can be obtained by precisely adjusting thermal treatment temperatures and hydrogen pressures. - Abstract: The evolution of a two-dimensional silicon surface under hydrogen thermal treatment is studied by kinetic Monte Carlo simulations, focusing on the dependence of the migration behaviors of surface atoms on both the temperature and hydrogen pressure. We adopt different activation energies to analyze the influence of hydrogen pressure on the evolution of surface morphology at high temperatures. The reduction in surface roughness is divided into two stages, both exhibiting exponential dependence on the equilibrium time. Our results indicate that a high hydrogen pressure is conducive to obtaining optimized surfaces, as a strategy in the applications of three-dimensional devices.

A description of stress driven bubble growth of helium implanted tungsten

International Nuclear Information System (INIS)

Sharafat, Shahram; Takahashi, Akiyuki; Nagasawa, Koji; Ghoniem, Nasr

2009-01-01

Low energy (<100 keV) helium implantation of tungsten has been shown to result in the formation of unusual surface morphologies over a large temperature range (700-2100 deg. C). Simulation of these macroscopic phenomena requires a multiscale approach to modeling helium transport in both space and time. We present here a multiscale helium transport model by coupling spatially-resolved kinetic rate theory (KRT) with kinetic Monte Carlo (KMC) simulation to model helium bubble nucleation and growth. The KRT-based HEROS Code establishes defect concentrations as well as stable helium bubble nuclei as a function of implantation parameters and position from the implanted surface and the KMC-based Mc-HEROS Code models the growth of helium bubbles due to migration and coalescence. Temperature- and stress-gradients can act as driving forces, resulting in biased bubble migration. The Mc-HEROS Code was modified to simulate the impact of stress gradients on bubble migration and coalescence. In this work, we report on bubble growth and gas release of helium implanted tungsten W/O stress gradients. First, surface pore densities and size distributions are compared with available experimental results for stress-free helium implantation conditions. Next, the impact of stress gradients on helium bubble evolution is simulated. The influence of stress fields on bubble and surface pore evolution are compared with stress-free simulations. It is shown that near surface stress gradients accelerate helium bubbles towards the free surface, but do not increasing average bubble diameters significantly.

Dependence of cancer cell adhesion kinetics on integrin ligand surface density measured by a high-throughput label-free resonant waveguide grating biosensor.

Science.gov (United States)

Orgovan, Norbert; Peter, Beatrix; Bősze, Szilvia; Ramsden, Jeremy J; Szabó, Bálint; Horvath, Robert

2014-02-07

A novel high-throughput label-free resonant waveguide grating (RWG) imager biosensor, the Epic® BenchTop (BT), was utilized to determine the dependence of cell spreading kinetics on the average surface density (v(RGD)) of integrin ligand RGD-motifs. v(RGD) was tuned over four orders of magnitude by co-adsorbing the biologically inactive PLL-g-PEG and the RGD-functionalized PLL-g-PEG-RGD synthetic copolymers from their mixed solutions onto the sensor surface. Using highly adherent human cervical tumor (HeLa) cells as a model system, cell adhesion kinetic data of unprecedented quality were obtained. Spreading kinetics were fitted with the logistic equation to obtain the spreading rate constant (r) and the maximum biosensor response (Δλmax), which is assumed to be directly proportional to the maximum spread contact area (Amax). r was found to be independent of the surface density of integrin ligands. In contrast, Δλmax increased with increasing RGD surface density until saturation at high densities. Interpreting the latter behavior with a simple kinetic mass action model, a 2D dissociation constant of 1753 ± 243 μm(-2) (corresponding to a 3D dissociation constant of ~30 μM) was obtained for the binding between RGD-specific integrins embedded in the cell membrane and PLL-g-PEG-RGD. All of these results were obtained completely noninvasively without using any labels.

Finite size effects in phase transformation kinetics in thin films and surface layers

International Nuclear Information System (INIS)

Trofimov, Vladimir I.; Trofimov, Ilya V.; Kim, Jong-Il

2004-01-01

In studies of phase transformation kinetics in thin films, e.g. crystallization of amorphous films, until recent time is widely used familiar Kolmogorov-Johnson-Mehl-Avrami (KJMA) statistical model of crystallization despite it is applicable only to an infinite medium. In this paper a model of transformation kinetics in thin films based on a concept of the survival probability for randomly chosen point during transformation process is presented. Two model versions: volume induced transformation (VIT) when the second-phase grains nucleate over a whole film volume and surface induced transformation (SIT) when they form on an interface with two nucleation mode: instantaneous nucleation at transformation onset and continuous one during all the process are studied. At VIT-process due to the finite film thickness effects the transformation profile has a maximum in a film middle, whereas that of the grains population reaches a minimum inhere, the grains density is always higher than in a volume material, and the thinner film the slower it transforms. The transformation kinetics in a thin film obeys a generalized KJMA equation with parameters depending on a film thickness and in limiting cases of extremely thin and thick film it reduces to classical KJMA equation for 2D- and 3D-system, respectively

Two step formation of metal aggregates by surface X-ray radiolysis under Langmuir monolayers: 2D followed by 3D growth

Directory of Open Access Journals (Sweden)

Smita Mukherjee

2015-12-01

Full Text Available In order to form a nanostructured metallic layer below a Langmuir monolayer, radiolysis synthesis was carried out in an adapted geometry that we call surface X-ray radiolysis. In this procedure, an X-ray beam produced by a synchrotron beamline intercepts the surface of an aqueous metal-ion solution covered by a Langmuir monolayer at an angle of incidence below the critical angle for total internal reflection. Underneath the organic layer, the X-ray beam induces the radiolytic synthesis of a nanostructured metal–organic layer whose ultrathin thickness is defined by the vertical X-ray penetration depth. We have shown that increasing the X-ray flux on the surface, which considerably enhances the kinetics of the silver layer formation, results in a second growth regime of silver nanocrystals. Here the formation of the oriented thin layer is followed by the appearance of a 3D powder of silver clusters.

Saturation mechanism of decaying ion temperature gradient driven turbulence with kinetic electrons

International Nuclear Information System (INIS)

Idomura, Yasuhiro

2016-01-01

We present full-f gyrokinetic simulations of the ion temperature gradient driven (ITG) turbulence including kinetic electrons. By comparing decaying ITG turbulence simulations with adiabatic and kinetic electron models, an impact of kinetic electrons on the ITG turbulence is investigated. It is found that significant electron transport occurs even in the ITG turbulence, and both ion and electron temperature profiles are relaxed. In steady states, both cases show upshifts of nonlinear critical ion temperature gradients from linear ones, while their saturation mechanisms are qualitatively different. In the adiabatic electron case, the ITG mode is stabilized by turbulence driven zonal flows. On the other hand, in the kinetic electron case, passing electrons transport shows fine resonant structures at mode rational surfaces, which generate corrugated density profiles. Such corrugated density profiles lead to fine radial electric fields following the neoclassical force balance relation. The resulting E × B shearing rate greatly exceeds the linear growth rate of the ITG mode. (author)

Study the oxidation kinetics of uranium using XRD and Rietveld method

Energy Technology Data Exchange (ETDEWEB)

Zhang Yanzhi; Guan Weijun; Wang Qinguo; Wang Xiaolin; Lai Xinchun; Shuai Maobing, E-mail: yanzhizh@163.com [China Academy of Engineering Physics, PO Box 919-71, Mianyang, Sichuan, 621900 (China)

2010-03-15

The surface oxidation of uranium metal has been studied by X-ray diffraction (XRD) and Rietveld method in the range of 50{approx}300deg. C in air. The oxidation processes are analyzed by XRD to determine the extent of surface oxidation and the oxide structure. The dynamics expression for the formation of UO{sub 2} was derived. At the beginning, the dynamic expression was nonlinear, but switched to linear subsequently for uranium in air and humid oxygen. That is, the growth kinetics of UO{sub 2} can be divided into two stages: nonlinear portion and linear portion. Using the kinetic data of linear portion, the activation energy of reaction between uranium and air was calculated about 46.0 kJ/mol. However the content of oxide as a function of time was linear in humid helium ambience. Contrast the dynamics results, it prove that the absence of oxygen would accelerate the corrosion rate of uranium in the humid gas. We can find that the XRD and Rietveld method are a useful convenient method to estimate the kinetics and thermodynamics of solid-gas reaction.

Growth of AlGaN under the conditions of significant gallium evaporation: phase separation and enhanced lateral growth

OpenAIRE

Mayboroda, I. O.; Knizhnik, A. A.; Grishchenko, Yu. V.; Ezubchenko, I. S.; Zanaveskin, Maxim L.; Presniakov, M. Yu.; Potapkin, B. V.; Ilyin, V. A.

2017-01-01

Growth kinetics of AlGaN in NH3 MBE under significant Ga desorption was studied. It was found that the addition of gallium stimulates 2D growth and provides better morphology of films compared to pure AlN. The effect was experimentally observed at up to 98% desorption of the impinging gallium. We found that, under the conditions of significant thermal desorption, larger amounts of gallium were retained at lateral boundaries of 3D surface features than at flat terraces because of the higher bi...

Step driven competitive epitaxial and self-limited growth of graphene on copper surface

Directory of Open Access Journals (Sweden)

Lili Fan

2011-09-01

Full Text Available The existence of surface steps was found to have significant function and influence on the growth of graphene on copper via chemical vapor deposition. The two typical growth modes involved were found to be influenced by the step morphologies on copper surface, which led to our proposed step driven competitive growth mechanism. We also discovered a protective role of graphene in preserving steps on copper surface. Our results showed that wide and high steps promoted epitaxial growth and yielded multilayer graphene domains with regular shape, while dense and low steps favored self-limited growth and led to large-area monolayer graphene films. We have demonstrated that controllable growth of graphene domains of specific shape and large-area continuous graphene films are feasible.

Transient surface states during the CBE growth of GaAs

Science.gov (United States)

Farrell, T.; Hill, D.; Joyce, T. B.; Bullough, T. J.; Weightman, P.

1997-05-01

We report the occurrence of a transient surface state during the initial stages of CBE GaAs(0 0 1) growth. The state was detected in real-time reflectance ( R) and reflectance anisotropy spectroscopy (RAS) growth monitoring. At low growth rates, less than 1 μm/h, beam equivalent pressure (BEP) of triethylgallium (TEG) BEPs there was a rapid increase in R at all monitoring wavelengths, followed by a monotonic decay to its pre-growth value. This transient increase in R was accompanied by a change in the RAS signal, the magnitude and sign of which varied with wavelength. The initial increase in R is shown to be associated with the development of a metallic-like surface whereas the changes in the RAS signal are consistent with the formation of Ga dimers.

Intrinsic anomalous surface roughening of TiN films deposited by reactive sputtering

International Nuclear Information System (INIS)

Auger, M. A.; Vazquez, L.; Sanchez, O.; Cuerno, R.; Castro, M.; Jergel, M.

2006-01-01

We study surface kinetic roughening of TiN films grown on Si(100) substrates by dc reactive sputtering. The surface morphology of films deposited for different growth times under the same experimental conditions were analyzed by atomic force microscopy. The TiN films exhibit intrinsic anomalous scaling and multiscaling. The film kinetic roughening is characterized by a set of local exponent values α loc =1.0 and β loc =0.39, and global exponent values α=1.7 and β=0.67, with a coarsening exponent of 1/z=0.39. These properties are correlated to the local height-difference distribution function obeying power-law statistics. We associate this intrinsic anomalous scaling with the instability due to nonlocal shadowing effects that take place during thin-film growth by sputtering

Kinetics and Mechanisms of Calcite Reactions with Saline Waters

Energy Technology Data Exchange (ETDEWEB)

Gorman, Brian P [Colorado School of Mines, Golden, CO (United States)

2015-09-02

Project Description: The general objective of the proposed research is to determine the kinetics and mechanisms of calcite reactions with saline waters over a wide range of saline water composition, pCO₂, and modest ranges in T and P. This will be accomplished by studying both reaction rates and solubility from changes in solution chemistry, and making nanoscale observations of calcite precipitate surface morphology and composition at the micro-to-nano-scale to provide an understanding of controlling reaction mechanisms and pathways. The specific objectives necessary to reach the general objective are: a) determination of how pCO₂, Ca²⁺, ionic strength and “foreign” ions influence reaction rates; and b) investigate the influence of these parameters on apparent kinetic solubility from dissolution and precipitation reactions. This information will clearly be central to the construction of reliable reaction-transport models to predict reservoir and formation response to increased CO₂ in saline waters. This program was initially collaborative with John Morse at Texas A&M, however his passing shortly after the beginning of this program resulted in abbreviated research time and effort. Summary of Results: Early studies using electron microscopy and spectroscopy indicated that carbonate precipitation from natural seawater (NSW) conditions onto aragonite substrates was mediated by a surface amorphous calcium carbonate layer. It was hypothesized that this ACC layer (observed after < 5days reaction time) was responsible for the abnormal reaction kinetics and also served as a metastable seed layer for growth of epitaxial aragonite. Further studies of the ACC formation mechanism indicated a strong dependence on the Mg concentration in solution. Subsequent studies at shorter times (10 hrs) on calcite substrates and in a wide range of supersaturation conditions did not indicate any ACC layer. Instead, an epitaxial layer by layer

Reaction kinetics of the formation of intermetallic Fe – Zn during hot - dip galvanizing of steel

Directory of Open Access Journals (Sweden)

P. Pokorny

2016-01-01

Full Text Available This review article mainly describes the composition of intermetallic Fe - Zn, i.e. zeta (ζ, delta (δ1k + δ1p, gamma1 (Γ1 and gamma (Γ on galvanized steel during low temperature galvanization (t ~ 450 °C. It gives detailed the formation, growth of individual phases during galvanization and their interaction. In terms of the kinetics, the formation of the coating is defined by a parabolic kinetic equation of the growth of different intermetallic phases under ideal conditions. From the available literature the rate constants of the formation of individual intermetallic phases and also for the total coating are cited. The composition of the intermetallic phases, iron content, crystal structure, and group symmetry in which the surface of galvanized steel forms.

A description of bubble growth and gas release of helium implanted tungsten

International Nuclear Information System (INIS)

Sharafat, S.; Hu, Q.; Ghoniem, N.; Tkahashi, A.

2007-01-01

Full text of publication follows: Bubble growth and gas release during annealing of helium implanted tungsten is described using a Kinetic Monte Carlo approach. The implanted spatial profiles of stable bubble nuclei are first determined using the Kinetic Rate Theory based helium evolution code, HEROS. The effects of implantation energy, temperature, and bias forces, such as temperature- and stress gradients on bubble migration and coalescence are investigated to explain experimental gas release measurements. This comprehensive helium bubble evolution and release model, demonstrates the impact of near surface (< 1 um) versus deep helium implantation on bubble evolution. Near surface implanted helium bubbles readily attain large equilibrium sizes, while matrix bubbles remain small with high helium pressures. Using the computer simulation, the various stages of helium bubble nucleation, growth, coalescence, and migration are demonstrated and compared with available experimental results. (authors)

The Effect of Growth Temperature and V/III Flux Ratio of MOCVD Antimony Based Semiconductors on Growth Rate and Surface Morphology

Directory of Open Access Journals (Sweden)

Ramelan Ari Handono

2017-01-01

Full Text Available Epitaxial Alx Ga1-x Sb layers on GaSb and GaAs substrates have been grown by atmospheric pressure metalorganic chemical vapor deposition using TMAl, TMGa and TMSb. Nomarski microscope and a profiler were employed to examine the surface morphology and growth rate of the samples. We report the effect of growth temperature and V/III flux ratio on growth rate and surface morphology. Growth temperatures in the range of 520°C and 680°C and V/III ratios from 1 to 5 have been investigated. A growth rate activation energy of 0.73 eV was found. At low growth temperatures between 520 and 540°C, the surface morphology is poor due to antimonide precipitates associated with incomplete decomposition of the TMSb. For layers grown on GaAs at 580°C and 600°C with a V/III ratio of 3 a high quality surface morphology is typical, with a mirror-like surface and good composition control. It was found that a suitable growth temperature and V/III flux ratio was beneficial for producing good AlGaSb layers. Undoped AlGaSb grown at 580°C with a V/III flux ratio of 3 at the rate of 3.5 μm/hour shows p-type conductivity with smooth surface morphology

Absorption kinetics of two highly concentrated preparations of growth hormone: 12 IU/ml compared to 56 IU/ml

DEFF Research Database (Denmark)

Laursen, Torben; Susgaard, Søren; Jensen, Flemming Steen

1994-01-01

was to compare the relative bioavailability of two highly concentrated (12 IU/ml versus 56 IU/ml) formulations of biosynthetic human growth hormone administered subcutaneously. After pretreatment with growth hormone for at least four weeks, nine growth hormone deficient patients with a mean age of 26.2 years......AbstractSend to: Pharmacol Toxicol. 1994 Jan;74(1):54-7. Absorption kinetics of two highly concentrated preparations of growth hormone: 12 IU/ml compared to 56 IU/ml. Laursen T1, Susgaard S, Jensen FS, Jørgensen JO, Christiansen JS. Author information Abstract The purpose of this study...... (range 17-43) were studied two times in a randomized design, the two studies being separated by at least one week. At the start of each study period (7 p.m.), growth hormone was injected subcutaneously in a dosage of 3 IU/m2. The 12 IU/ml preparation of growth hormone was administered on one occasion...

Effects of atomic hydrogen on the selective area growth of Si and Si1-xGex thin films on Si and SiO2 surfaces: Inhibition, nucleation, and growth

International Nuclear Information System (INIS)

Schroeder, T.W.; Lam, A.M.; Ma, P.F.; Engstrom, J.R.

2004-01-01

Supersonic molecular beam techniques have been used to study the nucleation of Si and Si 1-x Ge x thin films on Si and SiO 2 surfaces, where Si 2 H 6 and GeH 4 have been used as sources. A particular emphasis of this study has been an examination of the effects of a coincident flux of atomic hydrogen. The time associated with formation of stable islands of Si or Si 1-x Ge x on SiO 2 surfaces--the incubation time--has been found to depend strongly on the kinetic energy of the incident molecular precursors (Si 2 H 6 and GeH 4 ) and the substrate temperature. After coalescence, thin film morphology has been found to depend primarily on substrate temperature, with smoother films being grown at substrate temperatures below 600 deg. C. Introduction of a coincident flux of atomic hydrogen has a large effect on the nucleation and growth process. First, the incubation time in the presence of atomic hydrogen has been found to increase, especially at substrate temperatures below 630 deg. C, suggesting that hydrogen atoms adsorbed on Si-like sites on SiO 2 can effectively block nucleation of Si. Unfortunately, in terms of promoting selective area growth, coincident atomic hydrogen also decreases the rate of epitaxial growth rate, essentially offsetting any increase in the incubation time for growth on SiO 2 . Concerning Si 1-x Ge x growth, the introduction of GeH 4 produces substantial changes in both thin film morphology and the rate nucleation of poly-Si 1-x Ge x on SiO 2 . Briefly, the addition of Ge increases the incubation time, while it lessens the effect of coincident hydrogen on the incubation time. Finally, a comparison of the maximum island density, the time to reach this density, and the steady-state polycrystalline growth rate strongly suggests that all thin films [Si, Si 1-x Ge x , both with and without H(g)] nucleate at special sites on the SiO 2 surface, and grow primarily via direct deposition of adatoms on pre-existing islands

Effect on growth and cell cycle kinetics of estradiol and tamoxifen on MCF-7 human breast cancer cells grown in vitro and in nude mice

DEFF Research Database (Denmark)

Brünner, N; Bronzert, D; Vindeløv, L L

1989-01-01

The effects of estradiol and tamoxifen (TAM) on the estrogen-dependent human breast cancer cell line MCF-7 grown in vitro and in nude mice were compared. The effect on growth was determined by cell number in vitro and by tumor growth curves in nude mice. The effects on the cell cycle kinetics were...... determined by repeated flow cytometric DNA analyses in vitro and in vivo and by the technique of labeled mitosis in nude mouse-grown tumors. Under in vitro conditions, estradiol induced a pronounced increase in S-phase fraction and cell number. TAM inhibited growth of MCF-7 cells with a concomitant increase...... in the G1 phase from 60% to 75%. In nude mice, MCF-7 only formed tumors in estradiol-supplemented mice. No differences were observed in growth and cell kinetics between 0.1 and 1.0 mg of estradiol. Daily i.p. injections of TAM resulted in tumor growth inhibition with shrinkage of tumors. The flow...

Kinetics of Ni:C Thin Film Composition Formation at Different Temperatures and Fluxes

Directory of Open Access Journals (Sweden)

Gediminas KAIRAITIS

2013-09-01

Full Text Available In this work analysis considering Ni:C thin films growth on thermaly oxidized Si substrate by proposed kinetic model is presented. Model is built considering experimental results where microstructure evolution as a function of the substrate temperature and metal content of Ni:C nanocomposite films grown by hyperthermal ion deposition is investigated. The proposed kinetic model is based on the rate equations and includes processes of adsorption, surface segregation, diffusion, chemical reactions of constituents. The experimental depth profile curves were fitted by using proposed model. The obtained results show a good agreement with experiment taking into account concentration dependent diffusion. It is shown by modeling that with the increase of substrate temperature the process of nickel surface segregation becomes most important. DOI: http://dx.doi.org/10.5755/j01.ms.19.3.5234

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.

Growth Kinetics of Laves Phase and Its Effect on Creep Rupture Behavior in 9Cr Heat Resistant Steel

Institute of Scientific and Technical Information of China (English)

Zhi-xin XIA; Chuan-yang WANG; Chen LEI; Yun-ting LAI; Yan-fen ZHAO; Lu ZHANG

2016-01-01

The effects of Laves phase formation and growth on creep rupture behaviors of P92 steel at 883 K were studied.The microstructural evolution was characterized using scanning electron microscopy and transmission elec-tron microscopy.Kinetic modeling was carried out using the software DICTRA.The results indicated Fe2 (W,Mo) Laves phase has formed during creep with 200 MPa applied stress at 883 K for 243 h.The experimental results showed a good agreement with thermodynamic calculations.The plastic deformation of laths is the main reason of creep rupture under the applied stress beyond 160 MPa,whereas,creep voids initiated by coarser Laves phase play an effective role in creep rupture under the applied stress lower than 160 MPa.Laves phase particles with the mean size of 243 nm lead to the change of creep rupture feature.Microstructures at the vicinity of fracture surface,the gage portion and the threaded ends of creep rupture specimens were also observed,indicating that creep tensile stress enhances the coarsening of Laves phase.

Controlling the size and morphology of Au@Pd core-shell nanocrystals by manipulating the kinetics of seeded growth.

Science.gov (United States)

Li, Jing; Zheng, Yiqun; Zeng, Jie; Xia, Younan

2012-06-25

This article reports a systematic study of the seed-mediated growth of Au@Pd core-shell nanocrystals with a variety of controlled sizes and morphologies. The key to the success of this synthesis is to manipulate the reaction kinetics by tuning a set of reaction parameters, including the type and concentration of capping agent, the amount of ascorbic acid used as the reducing agent, and the injection rate used for the precursor solution. Starting from Au nanospheres of 11 nm in diameter as the seeds, Au@Pd core-shell nanocrystals with a number of morphologies, including octahedra, concave octahedra, rectangular bars, cubes, concave cubes, and dendrites, could all be obtained by simply altering the reaction rate. For the first time, it was possible to generate Au@Pd nanocrystals with concave structures on the surfaces while their sizes were kept below 20 nm. In addition, the as-prepared Au@Pd nanocubes can be used as seeds to generate Au@Pd@Au and Au@Pd@Au@Pd nanocrystals with multishelled structures. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The Effect of Landing Surface on the Plantar Kinetics of Chinese Paratroopers Using Half-Squat Landing

Science.gov (United States)

Li, Yi; Wu, Ji; Zheng, Chao; Huang, Rong Rong; Na, Yuhong; Yang, Fan; Wang, Zengshun; Wu, Di

2013-01-01

The objective of the study was to determine the effect of landing surface on plantar kinetics during a half-squat landing. Twenty male elite paratroopers with formal parachute landing training and over 2 years of parachute jumping experience were recruited. The subjects wore parachuting boots in which pressure sensing insoles were placed. Each subject was instructed to jump off a platform with a height of 60 cm, and land on either a hard or soft surface in a half-squat posture. Outcome measures were maximal plantar pressure, time to maximal plantar pressure (T-MPP), and pressure-time integral (PTI) upon landing on 10 plantar regions. Compared to a soft surface, hard surface produced higher maximal plantar pressure in the 1st to 4th metatarsal and mid-foot regions, but lower maximal plantar pressure in the 5th metatarsal region. Shorter T- MPP was found during hard surface landing in the 1st and 2nd metatarsal and medial rear foot. Landing on a hard surface landing resulted in a lower PTI than a soft surface in the 1stphalangeal region. For Chinese paratroopers, specific foot prosthesis should be designed to protect the1st to 4thmetatarsal region for hard surface landing, and the 1stphalangeal and 5thmetatarsal region for soft surface landing. Key Points Understanding plantar kinetics during the half-squat landing used by Chinese paratroopers can assist in the design of protective footwear. Compared to landing on a soft surface, a hard surface produced higher maximal plantar pressure in the 1st to 4th metatarsal and mid-foot regions, but lower maximal plantar pressure in the 5th metatarsal region. A shorter time to maximal plantar pressure was found during a hard surface landing in the 1st and 2nd metatarsals and medial rear foot. Landing on a hard surface resulted in a lower pressure-time integral than landing on a soft surface in the 1st phalangeal region. For Chinese paratroopers, specific foot prosthesis should be designed to protect the 1st to 4th metatarsal

Immobilization of epidermal growth factor on titanium and stainless steel surfaces via dopamine treatment

Energy Technology Data Exchange (ETDEWEB)

Kang, Jeonghwa [Nano Medical Engineering Laboratory, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama, 351-0198 (Japan); Department of Biological Sciences, Tokyo Metropolitan University, 1-1 Minami-Osawa, Tokyo, 192-0397 Japan (Japan); Sakuragi, Makoto; Shibata, Aya; Abe, Hiroshi; Kitajima, Takashi; Tada, Seiichi [Nano Medical Engineering Laboratory, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama, 351-0198 (Japan); Mizutani, Masayoshi; Ohmori, Hitoshi [Material Fabrication Laboratory, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama, 351-0198 (Japan); Ayame, Hirohito [Diagnostic Biochip Laboratory, RIKEN Center for Intellectual Property Strategies, 2-1 Hirosawa, Wako, Saitama, 351-0198 (Japan); Son, Tae Il [Bioscience and Biotechnology, Chung-Ang University, 40-1 San, Nae-Ri, Daeduck-myun, Ansung-si, Kyungki-do, 456-756 (Korea, Republic of); Aigaki, Toshiro [Department of Biological Sciences, Tokyo Metropolitan University, 1-1 Minami-Osawa, Tokyo, 192-0397 Japan (Japan); Ito, Yoshihiro, E-mail: y-ito@riken.jp [Nano Medical Engineering Laboratory, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako, Saitama, 351-0198 (Japan); Department of Biological Sciences, Tokyo Metropolitan University, 1-1 Minami-Osawa, Tokyo, 192-0397 Japan (Japan); Diagnostic Biochip Laboratory, RIKEN Center for Intellectual Property Strategies, 2-1 Hirosawa, Wako, Saitama, 351-0198 (Japan)

2012-12-01

Titanium and stainless steel were modified with dopamine for the immobilization of biomolecules, epidermal growth factor (EGF). First, the treatment of metal surfaces with a dopamine solution under different pH conditions was investigated. At higher pH, the dopamine solution turned brown and formed precipitates. Treatment of the metals with dopamine at pH 8.5 also resulted in the development of brown color at the surface of the metals. The hydrophobicity of the surfaces increased after treatment with dopamine, independently of pH. X-ray photoelectron spectroscopy revealed the formation of a significant amount of an organic layer on both surfaces at pH 8.5. According to ellipsometry measurements, the organic layer formed at pH 8.5 was about 1000 times as thick as that formed at pH 4.5. The amount of amino groups in the layer formed at pH 8.5 was also higher than that observed in the layer formed at pH 4.5. EGF molecules were immobilized onto the dopamine-treated surfaces via a coupling reaction using carbodiimide. A greater amount of EGF was immobilized on surfaces treated at pH 8.5 compared with pH 4.5. Significantly higher growth of rat fibroblast cells was observed on the two EGF-immobilized surfaces compared with non-immobilized surfaces in the presence of EGF. The present study demonstrated that metals can become bioactive via the surface immobilization of a growth factor and that the effect of the immobilized growth factor on metals was greater than that of soluble growth factor. - Highlights: Black-Right-Pointing-Pointer Epidermal growth factor was covalently immobilized on titan or stainless steel surfaces. Black-Right-Pointing-Pointer Amino groups were formed on the surfaces by the treatment and the growth factor was immobilized through amide bonds. Black-Right-Pointing-Pointer The immobilized epidermal growth factor accelerated cell proliferation more than soluble ones on the surfaces.

Surface science principles and current applications

CERN Document Server

Taglauer, E; Wandelt, K

1996-01-01

Modern technologies increasingly rely on low-dimensional physics at interfaces and in thin-films and nano-structures. Surface science holds a key position in providing the experimental methods and theoretical models for a basic understanding of these effects. This book includes case studies and status reports about research topics such as: surface structure determination by tensor-LEED and surface X-ray diffraction; the preparation and detection of low-dimensional electronic surface states; quantitative surface compositional analysis; the dynamics of adsorption and reaction of adsorbates, e.g. kinetic oscillations; the characterization and control of thin-film and multilayer growth including the influence of surfactants; a critical assessment of the surface physics approach to heterogeneous catalysis.

Kinetic study on coagulase formation and growth of 'Staphylococcus aureus': comparative and combined action of antibiotics and gamma radiation

International Nuclear Information System (INIS)

Kiortsis, M.

1980-01-01

Coagulase production is preserved in Staphylococcus aureus cultures although growth was strongly reduced after irradiation with 90,000 rads by a 60 Co source. Kinetic studies on the growth and coagulase formation by non-irradiated and irradiated bacteria are reported, using various antibiotics such as chloramphenicol, actinomycin D and mitomycin. Both chloramphenicol (1-50 μg/ml) and actinomycin D (0.05-0.8 μg/ml) added to S. aureus cultures reduce and finally inhibit growth rate and coagulase synthesis proportionally to their concentration in the medium; irradiated and non-irradiated cultures behave similarly to the inhibitory action of those antibiotics. Mitomycin between 0.2-9.6 μg/ml reduces growth, but enzyme production is slightly affected; high levels of coagulase are observed in non-growing cultures. Mitomycin and gamma radiation affecting DNA give similar results: inhibition of growth but not of enzyme formation. Kinetic studies show that coagulase is synthesized during the first five minutes either in irradiated or in non-irradiated cultures. Indication of a de novo synthesis, instead of a mere release of ready-formed enzyme, is given by using chloramphenicol or actinomycin which strongly inhibit coagulase production in irradiated S. aureus. Cultures treated by those antibiotics have their coagulase levels reduced to the same degree, were they irradiated or not; it is assumed that both types of cultures behave similarly, as far as enzyme production is concerned. A massive irradiation dose alone -or mitomycin in high concentrations alone- may suspend bacterial growth although enzyme synthesis continues. A similar result is obtained by combining lower irradiation doses with an appropriate antibiotic. The combined and/or synergistic actions of gamma radiation and antibiotics could successfully differentiate between the two cellular functions: growth and enzyme synthesis [fr

Understanding the effects of strain on morphological instabilities of a nanoscale island during heteroepitaxial growth

Energy Technology Data Exchange (ETDEWEB)

Feng, Lu; Wang, Jing; Wang, Shibin; Li, Linan; Shen, Min; Wang, Zhiyong; Chen, Zhenfei; Zhao, Yang [Tianjin Key Laboratory of Modern Engineering Mechanics, Tianjin 300072 (China); Department of Mechanics, Tianjin University, Tianjin 300072 (China)

2015-07-21

A comprehensive morphological stability analysis of a nanoscale circular island during heteroepitaxial growth is presented based on continuum elasticity theory. The interplay between kinetic and thermodynamic mechanisms is revealed by including strain-related kinetic processes. In the kinetic regime, the Burton-Cabrera-Frank model is adopted to describe the growth front of the island. Together with kinetic boundary conditions, various kinetic processes including deposition flow, adatom diffusion, attachment-detachment kinetics, and the Ehrlich-Schwoebel barrier can be taken into account at the same time. In the thermodynamic regime, line tension, surface energy, and elastic energy are considered. As the strain relief in the early stages of heteroepitaxy is more complicated than commonly suggested by simple consideration of lattice mismatch, we also investigate the effects of external applied strain and elastic response due to perturbations on the island shape evolution. The analytical expressions for elastic fields induced by mismatch strain, external applied strain, and relaxation strain are presented. A systematic approach is developed to solve the system via a perturbation analysis which yields the conditions of film morphological instabilities. Consistent with previous experimental and theoretical work, parametric studies show the kinetic evolution of elastic relaxation, island morphology, and film composition under various conditions. Our present work offers an effective theoretical approach to get a comprehensive understanding of the interplay between different growth mechanisms and how to tailor the growth mode by controlling the nature of the crucial factors.

A kinetic analysis of manual wheelchair propulsion during start-up on select indoor and outdoor surfaces

NARCIS (Netherlands)

Koontz, AM; Cooper, RA; Boninger, ML; Yang, YS; Impink, BG; van der Woude, LHV

2005-01-01

The objective of this study was to conduct a kinetic analysis of manual wheelchair propulsion during start-LIP on select indoor and Outdoor surfaces. Eleven manual wheelchairs were fitted with a SMART(Wheel) and their users were asked to Push on a Course consisting of high- and low-pile carpet,

Growth far from equilibrium: Examples from III-V semiconductors

Energy Technology Data Exchange (ETDEWEB)

Kuech, Thomas F. [Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Babcock, Susan E. [Department of Materials Science and Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States); Mawst, Luke [Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)

2016-12-15

The development of new applications has driven the field of materials design and synthesis to investigate materials that are not thermodynamically stable phases. Materials which are not thermodynamically stable can be synthesized and used in many applications. These materials are kinetically stabilized during use. The formation of such metastable materials requires both an understanding of the associated thermochemistry and the key surface transport processes present during growth. Phase separation is most easily accomplished at the growth surface during synthesis where mass transport is most rapid. These surface transport processes are sensitive to the surface stoichiometry, reconstruction, and chemistry as well as the growth temperature. The formation of new metastable semiconducting alloys with compositions deep within a compositional miscibility gap serves as model systems for the understanding of the surface chemical and physical processes controlling their formation. The GaAs{sub 1−y}Bi{sub y} system is used here to elucidate the role of surface chemistry in the formation of a homogeneous metastable composition during the chemical vapor deposition of the alloy system.

Oxidation and reduction kinetics of eutectic SnPb, InSn, and AuSn: a knowledge base for fluxless solder bonding applications

DEFF Research Database (Denmark)

Kuhmann, Jochen Friedrich; Preuss, A.; Adolphi, B.

1998-01-01

: (1) SnPb; (2) InSn; (3) AuSn. The studies of the oxidation kinetics show that the growth of the native oxide, which covers the solder surfaces from the start of all soldering operations is self-limiting. The rate of oxidation on the molten, metallic solder surfaces is significantly reduced...... and reduction kinetics, are applied to flip-chip (FC) bonding experiments in vacuum with and without the injection of H2. Wetting in vacuum is excellent but the self-alignment during flip-chip soldering is restricted. The desired, perfectly self-aligned FC-bonds have been only achieved, using evaporated...

Enhanced charging kinetics of porous electrodes: surface conduction as a short-circuit mechanism.

Science.gov (United States)

Mirzadeh, Mohammad; Gibou, Frederic; Squires, Todd M

2014-08-29

We use direct numerical simulations of the Poisson-Nernst-Planck equations to study the charging kinetics of porous electrodes and to evaluate the predictive capabilities of effective circuit models, both linear and nonlinear. The classic transmission line theory of de Levie holds for general electrode morphologies, but only at low applied potentials. Charging dynamics are slowed appreciably at high potentials, yet not as significantly as predicted by the nonlinear transmission line model of Biesheuvel and Bazant. We identify surface conduction as a mechanism which can effectively "short circuit" the high-resistance electrolyte in the bulk of the pores, thus accelerating the charging dynamics and boosting power densities. Notably, the boost in power density holds only for electrode morphologies with continuous conducting surfaces in the charging direction.

The effect of surface-bulk potential difference on the kinetics of intercalation in core-shell active cathode particles

Science.gov (United States)

Kazemiabnavi, Saeed; Malik, Rahul; Orvananos, Bernardo; Abdellahi, Aziz; Ceder, Gerbrand; Thornton, Katsuyo

2018-04-01

Surface modification of active cathode particles is commonly observed in battery research as either a surface phase evolving during the cycling process, or intentionally engineered to improve capacity retention, rate capability, and/or thermal stability of the cathode material. Here, a continuum-scale model is developed to simulate the galvanostatic charge/discharge of a cathode particle with core-shell heterostructure. The particle is assumed to be comprised of a core material encapsulated by a thin layer of a second phase that has a different open-circuit voltage. The effect of the potential difference between the surface and bulk phases (Ω) on the kinetics of lithium intercalation and the galvanostatic charge/discharge profiles is studied at different values of Ω, C-rates, and exchange current densities. The difference between the Li chemical potential in the surface and bulk phases of the cathode particle results in a concentration difference between these two phases. This leads to a charge/discharge asymmetry in the galvanostatic voltage profiles, causing a decrease in the accessible capacity of the particle. These effects are more significant at higher magnitudes of surface-bulk potential difference. The proposed model provides detailed insight into the kinetics and voltage behavior of the intercalation/de-intercalation processes in core-shell heterostructure cathode particles.

Intrinsic stress evolution during amorphous oxide film growth on Al surfaces

International Nuclear Information System (INIS)

Flötotto, D.; Wang, Z. M.; Jeurgens, L. P. H.; Mittemeijer, E. J.

2014-01-01

The intrinsic stress evolution during formation of ultrathin amorphous oxide films on Al(111) and Al(100) surfaces by thermal oxidation at room temperature was investigated in real-time by in-situ substrate curvature measurements and detailed atomic-scale microstructural analyses. During thickening of the oxide a considerable amount of growth stresses is generated in, remarkably even amorphous, ultrathin Al 2 O 3 films. The surface orientation-dependent stress evolutions during O adsorption on the bare Al surfaces and during subsequent oxide-film growth can be interpreted as a result of (i) adsorption-induced surface stress changes and (ii) competing processes of free volume generation and structural relaxation, respectively

Surface reconstruction: An effective method for the growth of mismatched materials

Energy Technology Data Exchange (ETDEWEB)

Sun, Yu; Zheng, Beining; Wu, Xiaofeng; Yuan, Long; Wu, Jie; Guo, Hongping; Huang, Keke; Feng, Shouhua, E-mail: shfeng@mail.jlu.edu.cn

2016-01-01

Graphical abstract: High quality thin film of GaSb was fabricated with molecular beam epitaxy technique on the reconstructed Si(1 1 1) surface. - Highlights: • Surface reconstruction formed by different surface treatments controls the heteroepitaxial growth. • Mismatched stress can be effectively released when the mismatched material epi-film tilts out of the epitaxial interface plane to create a coincidence-site lattice. • GaSb films grown on Si(1 1 1)-(5√3 × 5√3)-Sb surface show better crystal quality and morphology for its self-assembled 2D fishbone structure. - Abstract: The crystalline quality of epitaxial films depends on the degree of lattice match between substrates and films. Here, we report a growth strategy for large mismatched epi-films to grow GaSb films on Si(1 1 1) substrates. The epitaxial strategy can be influenced by controlling the surface reconstructions of Sb-treated Si(1 1 1). The film with the best quality was grown on Si(1 1 1)-(5√3 × 5√3)-Sb surface due to the stress release and the formation of a self-assembled 2D fishbone structure. Controlled surface engineering provides an effective pathway towards the growth of the large mismatched materials.

Tip-induced domain growth on the non-polar cuts of lithium niobate single-crystals

Science.gov (United States)

Alikin, D. O.; Ievlev, A. V.; Turygin, A. P.; Lobov, A. I.; Kalinin, S. V.; Shur, V. Ya.

2015-05-01

Currently, ferroelectric materials with designed domain structures are considered as a perspective material for new generation of photonic, data storage, and data processing devices. Application of external electric field is the most convenient way of the domain structure formation. Lots of papers are devoted to the investigation of domain kinetics on polar surface of crystals while the forward growth remains one of the most mysterious stages due to lack of experimental methods allowing to study it. Here, we performed tip-induced polarization reversal on X- and Y-non-polar cuts in single-crystal of congruent lithium niobate which allows us to study the forward growth with high spatial resolution. The revealed difference in the shape and length of domains induced on X- and Y-cuts is beyond previously developed theoretical approaches used for the theoretical consideration of the domains growth at non-polar ferroelectric surfaces. To explain experimental results, we used kinetic approach with anisotropy of screening efficiency along different crystallographic directions.

Growth of organic films on indoor surfaces

DEFF Research Database (Denmark)

Weschler, Charles J.; Nazaroff, W. W.

2017-01-01

predictions indicate that film growth would primarily be influenced by the gas-phase concentration of SVOCs with octanol-air partitioning (Koa) values in the approximate range 10≤log Koa≤13. Within the relevant range, SVOCs with lower values will equilibrate with the surface film more rapidly. Over time...

Evaluation of a kinetic model for computer simulation of growth and fermentation by Scheffersomyces (Pichia) stipitis fed D-xylose.

Science.gov (United States)

Slininger, P J; Dien, B S; Lomont, J M; Bothast, R J; Ladisch, M R; Okos, M R

2014-08-01

Scheffersomyces (formerly Pichia) stipitis is a potential biocatalyst for converting lignocelluloses to ethanol because the yeast natively ferments xylose. An unstructured kinetic model based upon a system of linear differential equations has been formulated that describes growth and ethanol production as functions of ethanol, oxygen, and xylose concentrations for both growth and fermentation stages. The model was validated for various growth conditions including batch, cell recycle, batch with in situ ethanol removal and fed-batch. The model provides a summary of basic physiological yeast properties and is an important tool for simulating and optimizing various culture conditions and evaluating various bioreactor designs for ethanol production. © 2014 Wiley Periodicals, Inc.

Kinetic model for hydroxyapatite precipitation on human enamel surface by electrolytic deposition

International Nuclear Information System (INIS)

Lei Caixia; Liao Yingmin; Feng Zude

2009-01-01

The electrolytic deposition (ELD) of hydroxyapatite (HAP) coating on human enamel surface for different loading times at varied temperatures (ranging from 37 deg. C to 85 deg. C) and varied current densities (ranging from 0.05 mA cm -2 to 10 mA cm -2 ) was investigated in this study. Thin film x-ray diffraction, Fourier transform infrared and micro-Raman spectra analysis, as well as an environmental scanning electron microscope, were used to characterize the coating. The results showed that only the HAP phase occurred on the enamel surface after ELD experiments. The contents of HAP deposits on the enamel surface linearly changed proportional to the square root of the loading time, which was in good agreement with the kinetic model of ELD of HAP coating based on one-dimensional diffusion. The induction periods were observed on all the regression lines, and the rate of the HAP coating formation on enamel showed a linear relationship with the current density. It was implied that the diffusion process was the rate-determining step in the ELD of the HAP coating on human enamel.

Investigation on CO catalytic oxidation reaction kinetics of faceted perovskite nanostructures loaded with Pt

KAUST Repository

Yin, S. M.

2017-01-18

Perovskite lead titanate nanostructures with specific {111}, {100} and {001} facets exposed, have been employed as supports to investigate the crystal facet effect on the growth and CO catalytic activity of Pt nanoparticles. The size, distribution and surface chemical states of Pt on the perovskite supports have been significantly modified, leading to a tailored conversion temperature and catalytic kinetics towards CO catalytic oxidation.

Investigation on CO catalytic oxidation reaction kinetics of faceted perovskite nanostructures loaded with Pt

KAUST Repository

Yin, S. M.; Duanmu, J. J.; Zhu, Yihan; Yuan, Y. F.; Guo, S. Y.; Yang, J. L.; Ren, Z. H.; Han, G. R.

2017-01-01

Perovskite lead titanate nanostructures with specific {111}, {100} and {001} facets exposed, have been employed as supports to investigate the crystal facet effect on the growth and CO catalytic activity of Pt nanoparticles. The size, distribution and surface chemical states of Pt on the perovskite supports have been significantly modified, leading to a tailored conversion temperature and catalytic kinetics towards CO catalytic oxidation.

Adsorption of surfactants on sand surface in enhanced oil recovery: Isotherms, kinetics and thermodynamic studies

Energy Technology Data Exchange (ETDEWEB)

Bera, Achinta; Kumar, T.; Ojha, Keka; Mandal, Ajay, E-mail: mandal_ajay@hotmail.com

2013-11-01

Adsorption of surfactants onto reservoir rock surface may result in the loss and reduction of their concentrations in surfactant flooding, which may render them less efficient or ineffective in practical applications of enhanced oil recovery (EOR) techniques. Surfactant flooding for EOR received attraction due to its ability to increase the displacement efficiency by lowering the interfacial tension between oil and water and mobilizing the residual oil. This article highlights the adsorption of surfactants onto sand surface with variation of different influencing factors. It has been experimentally found that adsorption of cationic surfactant on sand surface is more and less for anionic surfactant, while non-ionic surfactant shows intermediate behaviour. X-ray diffraction (XRD) study of clean sand particles has been made to determine the main component present in the sand particles. The interaction between sand particles and surfactant has been studied by Fourier Transform Infrared (FTIR) Spectroscopy of the sand particles before and after aging with surfactant. Salinity plays an important role in adsorption of anionic surfactant. Batch experiments were also performed to understand the effects of pH and adsorbent dose on the sorption efficiency. The sand particles exhibited high adsorption efficiency at low pH for anionic and nonionic surfactants. But opposite trend was found for cationic surfactant. Adsorption data were analyzed by fitting with Langmuir, Freundlich, Redlich-Peterson, and Sips isotherm models. Results show that the Langmuir isotherm and pseudo-second order kinetics models suit the equilibrium and kinetics of adsorption on sand surface. Thermodynamics feasibility of the adsorption process was also studied to verify the spontaneity of the process.

Structural transformation of nanocrystalline titania by sol-gel and the growth kinetics of crystallites

International Nuclear Information System (INIS)

Hu Linhua; Dai Songyuan; Wang Kongjia

2002-05-01

Structural transformation of nanocrystalline titania prepared by sol-gel with hydrolysis precursor titanium isopropoxide was investigated. At the same time, the growth kinetics of titania powders was also studied here. It was found that the grain size of the powders increased slowly with autoclave heating temperature up to 230 degree C, when hydrolysis pH was 0.9, but grew rapidly when heating temperature was higher that 230 degree C. The activation energies for growth of anatase crystallites in two temperature regions were calculated to be 18.5 kJ/mol and 59.7 kJ/mol respectively. The X-ray diffraction results show that the transformation from anatase phase to rutile phase starts at 230 degree C and structural transformation finished when temperature raises to 270 degree C, which is a temperature much more lower than that of the transformation by conventional literature reports

Kinetic and mechanism studies of the adsorption of lead onto waste cow bone powder (WCBP) surfaces.

Science.gov (United States)

Cha, Jihoon; Cui, Mingcan; Jang, Min; Cho, Sang-Hyun; Moon, Deok Hyun; Khim, Jeehyeong

2011-01-01

This study examines the adsorption isotherms, kinetics and mechanisms of Pb²(+) sorption onto waste cow bone powder (WCBP) surfaces. The concentrations of Pb²(+) in the study range from 10 to 90 mg/L. Although the sorption data follow the Langmuir and Freundlich isotherm, a detailed examination reveals that surface sorption or complexation and co-precipitation are the most important mechanisms, along with possibly ion exchange and solid diffusion also contributing to the overall sorption process. The co-precipitation of Pb²(+) with the calcium hydroxyapatite (Ca-HAP) is implied by significant changes in Ca²(+) and PO₄³⁻ concentrations during the metal sorption processes. The Pb²(+) sorption onto the WCBP surface by metal complexation with surface functional groups such as ≡ POH. The major metal surface species are likely to be ≡ POPb(+). The sorption isotherm results indicated that Pb²(+) sorption onto the Langmuir and Freundlich constant q(max) and K( F ) is 9.52 and 8.18 mg g⁻¹, respectively. Sorption kinetics results indicated that Pb²(+) sorption onto WCBP was pseudo-second-order rate constants K₂ was 1.12 g mg⁻¹ h⁻¹. The main mechanism is adsorption or surface complexation (≡POPb(+): 61.6%), co-precipitation or ion exchange [Ca₃(.)₉₃ Pb₁(.)₀₇ (PO₄)₃ (OH): 21.4%] and other precipitation [Pb 50 mg L⁻¹ and natural pH: 17%). Sorption isotherms showed that WCBP has a much higher Pb²(+) removal rate in an aqueous solution; the greater capability of WCBP to remove aqueous Pb²(+) indicates its potential as another promising way to remediate Pb²(+)-contaminated media.

In situ diffraction studies of electrode surface structure during gold electrodeposition

International Nuclear Information System (INIS)

Magnussen, O.M.; Krug, K.; Ayyad, A.H.; Stettner, J.

2008-01-01

Surface X-ray scattering (SXS) in transmission geometry provides a valuable tool for in situ structural studies of electrochemical interfaces under reaction conditions, as illustrated here for homoepitaxial electrodeposition on Au(1 0 0) and Au(1 1 1) electrodes. Employing diffusion-limited deposition conditions to separate the effects of potential and deposition rate, a mutual interaction between the interface structure and the growth behavior is found. Time-dependent SXS measurements during Au(1 0 0) homoepitaxy show with decreasing potential transitions from step flow to layer-by-layer growth, then to multilayer growth, and finally back to layer-by-layer growth. This complex growth behavior can be explained within the framework of kinetic growth theory by the effect of potential, Cl adsorbates and the Au surface structure, specifically the presence of the surface reconstruction, on the Au surface mobility. Conversely, the electrodeposition process influences the structure of the reconstructed Au surface, as illustrated for Au(1 1 1), where a significant deposition-induced compression of the Au surface layer as compared to Au(1 1 1) surfaces under ultrahigh vacuum conditions or in Au-free electrolyte is found. This compression increases towards more negative potentials, which may be explained by a release of potential-induced surface stress

Absence of surface stress change during pentacene thin film growth on the Si(111)-(7 x 7) surface: a buried reconstruction interface

International Nuclear Information System (INIS)

Kury, P; Horn von Hoegen, M; Heringdorf, F-J Meyer zu; Roos, K R

2008-01-01

We use high-resolution surface stress measurements to monitor the surface stress during the growth of pentacene (C 22 H 14 ) on the (7x7) reconstructed silicon (111) surface. No significant change in the surface stress is observed during the pentacene growth. Compared to the changes in the surface stress observed for Si and Ge deposition on the Si(111)-(7x7) surface, the insignificant change in the surface stress observed for the pentacene growth suggests that the pentacene molecules of the first adsorbate layer, although forming strong covalent bonds with the Si adatoms, do not alter the structure of the (7x7) reconstruction. The (7x7) reconstruction remains intact and, with subsequent deposition of pentacene, eventually becomes buried under the growing film. This failure of the pentacene to affect the structure of the reconstruction may represent a fundamental difference between the growth of organic thin films and that of inorganic thin films on semiconductor surfaces

Enhanced sensitivity in non-enzymatic glucose detection by improved growth kinetics of Ni-based nanostructures

Science.gov (United States)

Urso, M.; Pellegrino, G.; Strano, V.; Bruno, E.; Priolo, F.; Mirabella, S.

2018-04-01

Ni-based nanostructures are attractive catalytic materials for many electrochemical applications, among which are non-enzymatic sensing, charge storage, and water splitting. In this work, we clarify the synthesis kinetics of Ni(OH)2/NiOOH nanowalls grown by chemical bath deposition at room temperature and at 50 °C. We applied the results to non-enzymatic glucose sensing, reaching a highest sensitivity of 31 mA cm-2mM-1. Using scanning electron microscopy, x-ray diffraction analysis and Rutherford backscattering spectrometry we found that the growth occurs through two regimes: first, a quick random growth leading to disordered sheets of Ni oxy-hydroxide, followed by a slower growth of well-aligned sheets of Ni hydroxide. A high growth temperature (50 °C), leading mainly to well-aligned sheets, offers superior electrochemical properties in terms of charge storage, charge carrier transport and catalytic action, as confirmed by cyclic voltammetry and electrochemical impedance spectroscopy analyses. The reported results on the optimization and application of low-cost synthesis of these Ni-based nanostructures have a large potential for application in catalysis, (bio)sensing, and supercapacitors areas.

Non-linear self-reinforced growth of tearing modes with multiple rational surfaces

International Nuclear Information System (INIS)

Maschke, E.K.; Persson, M.; Dewar, R.L.; Australian National Univ., Canberra, ACT

1993-06-01

The non-linear evolution of tearing modes with multiple rational surfaces is discussed. It is demonstrated that, in the presence of small differential rotation, the non-linear growth might be faster than exponential. This growth occurs as the rotation frequencies of the plasma at the different rational surfaces go into equilibrium

Callus Growth Kinetics of Physic Nut (Jatropha curcas L.) and Content of Fatty Acids from Crude Oil Obtained In Vitro.

Science.gov (United States)

da Luz Costa, Jefferson; da Silva, André Luís Lopes; Bier, Mário César Jucoski; Brondani, Gilvano Ebling; Gollo, André Luiz; Letti, Luiz Alberto Junior; Erasmo, Eduardo Andrea Lemus; Soccol, Carlos Ricardo

2015-06-01

The callus growth kinetics allows identifying the appropriate moment for callus pealing and monitoring the accumulation of primary and secondary metabolites. The physic nut (Jatropha curcas L.) is a plant species used for biofuel production due to its high oil content; however, this plant presents a great amount of bioactive compounds which can be useful for industry. The aim of this research was to establish a calli growth curve and to evaluate the fatty acid profile of crude oil extracted from callus. The callus growth kinetics presented a sigmoid standard curve with six distinct phases: lag, exponential, linear, deceleration, stationary, and decline. Total soluble sugars were higher at the inoculation day. Reducing sugars were higher at the inoculation day and at the 80th day. The highest percentage of ethereal extract (oil content) was obtained at the 120th day of culture, reaching 18 % of crude oil from the callus. The calli produced medium-chain and long-chain fatty acids (from 10 to 18 carbon atoms). The palmitic acid was the fatty acid with the highest proportion in oil (55.4 %). The lipid profile obtained in callus oil was different from the seed oil profile.

A kinetic model of the formation of organic monolayers on hydrogen-terminated silicon by hydrosilation of alkenes.

Science.gov (United States)

Woods, M; Carlsson, S; Hong, Q; Patole, S N; Lie, L H; Houlton, A; Horrocks, B R

2005-12-22

We have analyzed a kinetic model for the formation of organic monolayers based on a previously suggested free radical chain mechanism for the reaction of unsaturated molecules with hydrogen-terminated silicon surfaces (Linford, M. R.; Fenter, P. M.; Chidsey, C. E. D. J. Am. Chem. Soc 1995, 117, 3145). A direct consequence of this mechanism is the nonexponential growth of the monolayer, and this has been observed spectroscopically. In the model, the initiation of silyl radicals on the surface is pseudo first order with rate constant, ki, and the rate of propagation is determined by the concentration of radicals and unreacted Si-H nearest neighbor sites with a rate constant, kp. This propagation step determines the rate at which the monolayer forms by addition of alkene molecules to form a track of molecules that constitute a self-avoiding random walk on the surface. The initiation step describes how frequently new random walks commence. A termination step by which the radicals are destroyed is also included. The solution of the kinetic equations yields the fraction of alkylated surface sites and the mean length of the random walks as a function of time. In mean-field approximation we show that (1) the average length of the random walk is proportional to (kp/ki)1/2, (2) the monolayer surface coverage grows exponentially only after an induction period, (3) the effective first-order rate constant describing the growth of the monolayer and the induction period (kt) is k = (2ki kp)1/2, (4) at long times the effective first-order rate constant drops to ki, and (5) the overall activation energy for the growth kinetics is the mean of the activation energies for the initiation and propagation steps. Monte Carlo simulations of the mechanism produce qualitatively similar kinetic plots, but the mean random walk length (and effective rate constant) is overestimated by the mean field approximation and when kp > ki, we find k approximately ki0.7kp0.3 and Ea = (0.7Ei+ 0.3Ep

Growth of pentacene on clean and modified gold surfaces

International Nuclear Information System (INIS)

Kaefer, Daniel; Ruppel, Lars; Witte, Gregor

2007-01-01

The growth and evolution of pentacene films on gold substrates have been studied. By combining complementary techniques including scanning tunneling microscopy, atomic force microscopy, scanning electron microscopy, near-edge x-ray-absorption fine structure, and x-ray diffraction, the molecular orientation, crystalline structure, and morphology of the organic films were characterized as a function of film thickness and growth parameters (temperature and rate) for different gold substrates ranging from Au(111) single crystals to polycrystalline gold. Moreover, the influence of precoating the various gold substrates with self-assembled monolayers (SAM's) of organothiols with different chemical terminations has been studied. On bare gold the growth of pentacene films is characterized by a pronounced dewetting while the molecular orientation within the resulting crystalline three-dimensional islands depends distinctly on the roughness and cleanliness of the substrate surface. After completion of the first wetting layer where molecules adopt a planar orientation parallel to the surface the molecules continue to grow in a tilted fashion: on Au(111) the long molecular axis is oriented parallel to the surface while on polycrystalline gold it is upstanding oriented and thus parallels the crystalline orientation of pentacene films grown on SiO 2 . On SAM pretreated gold substrates the formation of a wetting layer is effectively suppressed and pentacene grows in a quasi-layer-by-layer fashion with an upstanding orientation leading to rather smooth films. The latter growth mode is observed independently of the chemical termination of the SAM's and the roughness of the gold substrate. Possible reasons for the different growth mechanism as well as consequences for the assignment of spectroscopic data of thin pentacene film are discussed

Kinetics of passivation of a nickel-base alloy in high temperature water

Energy Technology Data Exchange (ETDEWEB)

Machet, A. [Laboratoire de Physico-Chimie des Surfaces, CNRS-ENSCP (UMR 7045), Ecole Nationale Superieure de Chimie de Paris, Universite Pierre et Marie Curie, F-75231 Paris cedex 05 (France)]|[Framatome ANP, Tour AREVA, F-92084 Paris-la-Defense (France); Galtayries, A.; Zanna, S.; Marcus, P. [Laboratoire de Physico-Chimie des Surfaces, CNRS-ENSCP (UMR 7045), Ecole Nationale Superieure de Chimie de Paris, Universite Pierre et Marie Curie, F-75231 Paris cedex 05 (France); Jolivet, P.; Scott, P. [Framatome ANP, Tour AREVA, F-92084 Paris-la-Defense (France); Foucault, M.; Combrade, P. [Framatome ANP, Centre Technique, F-71205 Le Creusot (France)

2004-07-01

The kinetics of passivation and the composition of the surface oxide layer, in high temperature and high pressure water, of a nickel-chromium-iron alloy (Alloy 600) have been investigated by X-ray Photoelectron Spectroscopy (XPS). The samples have been exposed for short (0.4 - 8.2 min) and longer (0 - 400 hours) time periods to high temperature (325 deg. C) and high pressure water (containing boron and lithium) under controlled hydrogen pressure. The experiments were performed in two types of autoclaves: a novel autoclave dedicated to short time periods and a classic static autoclave for the longer exposures. In the initial stage of passivation, a continuous ultra-thin layer of chromium oxide (Cr{sub 2}O{sub 3}) is rapidly formed on the surface with an external layer of chromium hydroxide. For longer times of passivation, the oxide layer is in a duplex form with an internal chromium oxide layer and an external layer of nickel hydroxide. The growth of the internal Cr{sub 2}O{sub 3} oxide layer has been fitted by three classical models (parabolic, logarithmic and inverse logarithmic laws) for the short passivation times, and the growth curves have been extrapolated to longer passivation periods. The comparison with the experimental results reveals that the kinetics of passivation of Alloy 600 in high temperature and high pressure water, for passivation times up to 400 hours, is well fitted by a logarithmic growth law. (authors)

Kinetics of passivation of a nickel-base alloy in high temperature water

International Nuclear Information System (INIS)

Machet, A.; Galtayries, A.; Zanna, S.; Marcus, P.; Jolivet, P.; Scott, P.; Foucault, M.; Combrade, P.

2004-01-01

The kinetics of passivation and the composition of the surface oxide layer, in high temperature and high pressure water, of a nickel-chromium-iron alloy (Alloy 600) have been investigated by X-ray Photoelectron Spectroscopy (XPS). The samples have been exposed for short (0.4 - 8.2 min) and longer (0 - 400 hours) time periods to high temperature (325 deg. C) and high pressure water (containing boron and lithium) under controlled hydrogen pressure. The experiments were performed in two types of autoclaves: a novel autoclave dedicated to short time periods and a classic static autoclave for the longer exposures. In the initial stage of passivation, a continuous ultra-thin layer of chromium oxide (Cr 2 O 3 ) is rapidly formed on the surface with an external layer of chromium hydroxide. For longer times of passivation, the oxide layer is in a duplex form with an internal chromium oxide layer and an external layer of nickel hydroxide. The growth of the internal Cr 2 O 3 oxide layer has been fitted by three classical models (parabolic, logarithmic and inverse logarithmic laws) for the short passivation times, and the growth curves have been extrapolated to longer passivation periods. The comparison with the experimental results reveals that the kinetics of passivation of Alloy 600 in high temperature and high pressure water, for passivation times up to 400 hours, is well fitted by a logarithmic growth law. (authors)

Grain Growth in Nanocrystalline Mg-Al Thin Films

Energy Technology Data Exchange (ETDEWEB)

Kruska, Karen; Rohatgi, Aashish; Vemuri, Venkata Rama Ses; Kovarik, Libor; Moser, Trevor H.; Evans, James E.; Browning, Nigel D.

2017-10-05

An improved understanding of grain growth kinetics in nanocrystalline materials, and in metals and alloys in general, is of continuing interest to the scientific community. In this study, Mg - Al thin films containing ~10 wt.% Al and with 14.5 nm average grain size were produced by magnetron-sputtering and subjected to heat-treatments. The grain growth evolution in the early stages of heat treatment at 423 K (150 °C), 473 K (200 °C) and 573K (300 °C) was observed with transmission electron microscopy and analyzed based upon the classical equation developed by Burke and Turnbull. The grain growth exponent was found to be 7±2 and the activation energy for grain growth was 31.1±13.4 kJ/mol, the latter being significantly lower than in bulk Mg-Al alloys. The observed grain growth kinetics are explained by the Al supersaturation in the matrix and the pinning effects of the rapidly forming beta precipitates and possibly shallow grain boundary grooves. The low activation energy is attributed to the rapid surface diffusion which is dominant in thin film systems.

Controlling drug delivery kinetics from mesoporous titania thin films by pore size and surface energy

Directory of Open Access Journals (Sweden)

Karlsson J

2015-07-01

Full Text Available Johan Karlsson, Saba Atefyekta, Martin Andersson Department of Chemical and Biological Engineering, Chalmers University of Technology, Gothenburg, Sweden Abstract: The osseointegration capacity of bone-anchoring implants can be improved by the use of drugs that are administrated by an inbuilt drug delivery system. However, to attain superior control of drug delivery and to have the ability to administer drugs of varying size, including proteins, further material development of drug carriers is needed. Mesoporous materials have shown great potential in drug delivery applications to provide and maintain a drug concentration within the therapeutic window for the desired period of time. Moreover, drug delivery from coatings consisting of mesoporous titania has shown to be promising to improve healing of bone-anchoring implants. Here we report on how the delivery of an osteoporosis drug, alendronate, can be controlled by altering pore size and surface energy of mesoporous titania thin films. The pore size was varied from 3.4 nm to 7.2 nm by the use of different structure-directing templates and addition of a swelling agent. The surface energy was also altered by grafting dimethylsilane to the pore walls. The drug uptake and release profiles were monitored in situ using quartz crystal microbalance with dissipation (QCM-D and it was shown that both pore size and surface energy had a profound effect on both the adsorption and release kinetics of alendronate. The QCM-D data provided evidence that the drug delivery from mesoporous titania films is controlled by a binding–diffusion mechanism. The yielded knowledge of release kinetics is crucial in order to improve the in vivo tissue response associated to therapeutic treatments. Keywords: mesoporous titania, controlled drug delivery, release kinetics, alendronate, QCM-D

Microstructural characterization and grain growth kinetics of atomized Fe-6%Si alloy

Energy Technology Data Exchange (ETDEWEB)

Florio Filho, A.; Bolfarini, C.; Kiminami, C.S. [Dept. de Engenharia de Materiais, Univ. Federal de Sao Carlos, Sao Carlos SP (Brazil)

2001-07-01

The microstructural characterization of the overspray powders is considered an important step to evaluate the as-cast microstructure of preforms fabricated by spray forming process. The particles generated during the high pressure gas atomization fly toward a substrate located at the middle height into the atomization chamber and consolidate to a dense deposit. The solidification process begins already during the flight of the droplets and high cooling rate can be achieved by the droplets of the molten metal during the atomization step. Consequently, the microstructure of the preform has some typical features presented by rapidly solidified metals as low level of porosity and segregation and it is strongly influenced by the thermal history of the droplets during flight. In the present work the microstructure of the particles of the Fe-6%Si alloy was analysed by light microscopy and scanning electron microscopy (SEM). The experimental determination of the kinetic exponent n for grain boundary migration in both powder and preform was determined by isothermal treatment under argon atmosphere. It has been stated that the larger the particle size the greater the grain size in Fe-6%Si alloy. It was observed also that the interface morphology is strongly related to the particle size. Furthermore, the grain growth kinetic in the preform seems to not obey the migration mechanism where the self diffusion of elemental Fe drive the boundary displacement. (orig.)

Mechanisms and energetics of surface atomic processes

International Nuclear Information System (INIS)

Tsong, T.T.

1991-01-01

The energies involved in various surface atomic processes such as surface diffusion, the binding of small atomic clusters on the surface, the interaction between two adsorbed atoms, the dissociation of an atom from a small cluster or from a surface layer, the binding of kink size atoms or atoms at different adsorption sites to the surface etc., can be derived from an analysis of atomically resolved field ion microscope images and a kinetic energy measurement of low temperature field desorbed ions using the time-of-flight atom-probe field ion microscope. These energies can be used to compare with theories and to understand the transport of atoms on the surface in atomic reconstructions, epitaxial growth of surface layers and crystal growth, adsorption layer superstructure formation, and also why an atomic ordering or atomic reconstruction at the surface is energetically favored. Mechanisms of some of the surface atomic processes are also clarified from these quantitative, atomic resolution studies. In this paper work in this area is bris briefly reviewed

Understanding the performance of sulfate reducing bacteria based packed bed reactor by growth kinetics study and microbial profiling.

Science.gov (United States)

Dev, Subhabrata; Roy, Shantonu; Bhattacharya, Jayanta

2016-07-15

A novel marine waste extract (MWE) as alternative nitrogen source was explored for the growth of sulfate reducing bacteria (SRB). Variation of sulfate and nitrogen (MWE) showed that SRB growth follows an uncompetitive inhibition model. The maximum specific growth rates (μmax) of 0.085 and 0.124 h(-1) and inhibition constants (Ki) of 56 and 4.6 g/L were observed under optimized sulfate and MWE concentrations, respectively. The kinetic data shows that MWE improves the microbial growth by 27%. The packed bed bioreactor (PBR) under optimized sulfate and MWE regime showed sulfate removal efficiency of 62-66% and metals removal efficiency of 66-75% on using mine wastewater. The microbial community analysis using DGGE showed dominance of SRB (87-89%). The study indicated the optimum dosing of sulfate and cheap organic nitrogen to promote the growth of SRB over other bacteria. Copyright © 2016 Elsevier Ltd. All rights reserved.

Coupling of kinetic Monte Carlo simulations of surface reactions to transport in a fluid for heterogeneous catalytic reactor modeling

International Nuclear Information System (INIS)

Schaefer, C.; Jansen, A. P. J.

2013-01-01

We have developed a method to couple kinetic Monte Carlo simulations of surface reactions at a molecular scale to transport equations at a macroscopic scale. This method is applicable to steady state reactors. We use a finite difference upwinding scheme and a gap-tooth scheme to efficiently use a limited amount of kinetic Monte Carlo simulations. In general the stochastic kinetic Monte Carlo results do not obey mass conservation so that unphysical accumulation of mass could occur in the reactor. We have developed a method to perform mass balance corrections that is based on a stoichiometry matrix and a least-squares problem that is reduced to a non-singular set of linear equations that is applicable to any surface catalyzed reaction. The implementation of these methods is validated by comparing numerical results of a reactor simulation with a unimolecular reaction to an analytical solution. Furthermore, the method is applied to two reaction mechanisms. The first is the ZGB model for CO oxidation in which inevitable poisoning of the catalyst limits the performance of the reactor. The second is a model for the oxidation of NO on a Pt(111) surface, which becomes active due to lateral interaction at high coverages of oxygen. This reaction model is based on ab initio density functional theory calculations from literature.

Growth of fibroblasts and endothelial cells on wettability gradient surfaces

NARCIS (Netherlands)

Ruardy, TG; Moorlag, HE; Schakenraad, JM; VanderMei, HC; Busscher, HJ

1997-01-01

The growth, spreading, and shape of human skin fibroblasts (PK 84) and human umbilical cord endothelial cells on dichlorodimethylsilane (DDS) and dimethyloctadecylchlorosilane (DOGS) gradient surfaces were investigated in the presence of serum proteins. Gradient surfaces were prepared on glass using

In-Situ Synchrotron Radiation Study of Formation and Growth of Crystalline CexZr1-xO2 Nanoparticles Synthesized in Supercritical Water

DEFF Research Database (Denmark)

Tyrsted, Christoffer; Becker-Christensen, Jacob; Hald, Peter

2010-01-01

-zirconia system, the growth of ceria and zirconia nanoparticles is fundamentally different under supercritical water conditions. For comparison, ex situ synthesis has also been performed using an in-house supercritical flow reactor. The resulting samples were analyzed using PXRD, small-angle X-ray scattering......In situ synchrotron powder X-ray diffraction (PXRD) measurements have been conducted to follow the nucleation and growth of crystalline CexZr1-xO2 nanoparticles synthesized in supercritical water with a full substitution variation (x = 0, 0.2, 0.5, 0.8, and 1.0). Direction-dependent growth curves...... are determined and described using reaction kinetic models. A distinct change in growth kinetics is observed with increasing cerium content. For x = 0.8 and 1.0 (high cerium content), the growth is initially limited by the surface reaction kinetics; however, at a size of ∼6 nm, the growth changes and becomes...

In situ AFM investigation of electrochemically induced surface-initiated atom-transfer radical polymerization.

Science.gov (United States)

Li, Bin; Yu, Bo; Zhou, Feng

2013-02-12

Electrochemically induced surface-initiated atom-transfer radical polymerization is traced by in situ AFM technology for the first time, which allows visualization of the polymer growth process. It affords a fundamental insight into the surface morphology and growth mechanism simultaneously. Using this technique, the polymerization kinetics of two model monomers were studied, namely the anionic 3-sulfopropyl methacrylate potassium salt (SPMA) and the cationic 2-(metharyloyloxy)ethyltrimethylammonium chloride (METAC). The growth of METAC is significantly improved by screening the ammonium cations by the addition of ionic liquid electrolyte in aqueous solution. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Adsorption Mechanism of Inhibitor and Guest Molecules on the Surface of Gas Hydrates.

Science.gov (United States)

Yagasaki, Takuma; Matsumoto, Masakazu; Tanaka, Hideki

2015-09-23

The adsorption of guest and kinetic inhibitor molecules on the surface of methane hydrate is investigated by using molecular dynamics simulations. We calculate the free energy profile for transferring a solute molecule from bulk water to the hydrate surface for various molecules. Spherical solutes with a diameter of ∼0.5 nm are significantly stabilized at the hydrate surface, whereas smaller and larger solutes exhibit lower adsorption affinity than the solutes of intermediate size. The range of the attractive force is subnanoscale, implying that this force has no effect on the macroscopic mass transfer of guest molecules in crystal growth processes of gas hydrates. We also examine the adsorption mechanism of a kinetic hydrate inhibitor. It is found that a monomer of the kinetic hydrate inhibitor is strongly adsorbed on the hydrate surface. However, the hydrogen bonding between the amide group of the inhibitor and water molecules on the hydrate surface, which was believed to be the driving force for the adsorption, makes no contribution to the adsorption affinity. The preferential adsorption of both the kinetic inhibitor and the spherical molecules to the surface is mainly due to the entropic stabilization arising from the presence of cavities at the hydrate surface. The dependence of surface affinity on the size of adsorbed molecules is also explained by this mechanism.

Influence of the step properties on submonolayer growth of Ge and Si at the Si(111) surface

Energy Technology Data Exchange (ETDEWEB)

Romanyuk, Konstantin

2009-10-21

The present work describes an experimental investigation of the influence of the step properties on the submonolayer growth at the Si(111) surface. In particular the influence of step properties on the morphology, shape and structural stability of 2D Si/Ge nanostructures was explored. Visualization, morphology and composition measurements of the 2D SiGe nanostructures were carried out by scanning tunneling microscopy (STM). The formation of Ge nanowire arrays on highly ordered kink-free Si stepped surfaces is demonstrated. The crystalline nanowires with minimal kink densities were grown using Bi surfactant mediated epitaxy. The nanowires extend over lengths larger than 1 {mu}m have a width of 4 nm. To achieve the desired growth conditions for the formation of such nanowire arrays, a modified variant of surfactant mediated epitaxy was explored. It was shown that controlling the surfactant coverage at the surface and/or at step edges modifies the growth properties of surface steps in a decisive way. The surfactant coverage at step edges can be associated with Bi passivation of the step edges. The analysis of island size distributions showed that the step edge passivation can be tuned independently by substrate temperature and by Bi rate deposition. The measurements of the island size distributions for Si and Ge in surfactant mediated growth reveal different scaling functions for different Bi deposition rates on Bi terminated Si(111) surface. The scaling function changes also with temperature. The main mechanism, which results in the difference of the scaling functions can be revealed with data of Kinetic Monte-Carlo simulations. According to the data of the Si island size distributions at different growth temperatures and different Bi deposition rates the change of SiGe island shape and preferred step directions were attributed to the change of the step edge passivation. It was shown that the change of the step edge passivation is followed by a change of the

Phase field simulation of grain growth in porous uranium dioxide

International Nuclear Information System (INIS)

Ahmed, Karim; Pakarinen, Janne; Allen, Todd; El-Azab, Anter

2014-01-01

Graphical abstract: Display Omitted -- Abstract: A novel phase field model has been developed to investigate grain growth in porous polycrystalline UO 2 . Based on a system of Cahn–Hilliard and Allen–Cahn equations, the model takes into consideration both the curvature driven grain boundary motion and pore migration by surface diffusion. As such, the model accounts for the interaction between pore and grain boundary kinetics, which tends to retard the growth process. The phase field model parameters are found in terms of measurable material properties. Hence, quantitative results that can be compared with experiments were obtained. The model has been used to investigate the effect of porosity on the kinetics of grain growth in UO 2 . It is found that, as the amount of porosity increases, grain growth in UO 2 gradually changes from boundary controlled growth to pore controlled growth. For high porosity levels, the grain growth completely stops after a short evolution time. It is also found that the inhomogeneous distribution of pores leads to abnormal grain growth even without taking into account the anisotropy in grain boundary energy and mobility. The effects of porosity, temperature and initial microstructure on grain growth were thoroughly investigated. The model predictions are in good agreement with published experimental results of grain growth in UO 2