WorldWideScience

Sample records for surface structural transition

  1. Effect of surface attractive strength on structural transitions of a confined HP lattice protein

    Energy Technology Data Exchange (ETDEWEB)

    Pattanasiri, Busara [University of Georgia, Athens, GA; Li, Ying Wai [ORNL; Wuest, Thomas [ETH Zurich, Switzerland; Landau, David P [University of Georgia, Athens, GA

    2015-01-01

    We investigate the influence of surface attractive strength on structural transitions of a hydrophobic-polar (HP) lattice protein confined in a slit formed by two parallel, attractive walls. We apply Wang-Landau sampling together with efficient Monte Carlo updates to estimate the density of states of the system. The conformational transitions, namely, the debridging process and hydrophobic core formation, can be identified by analyzing the specific heat together with several structural observables, such as the numbers of surface contacts, the number of hydrophobic pairs, and radii of gyration in different directions. As temperature decreases, we find that the occurrence of the debridging process is conditional depending on the surface attractive strength. This, in turn, affects the nature of the hydrophobic core formation that takes place at a lower temperature. We illustrate these observations with the aid of a HP protein chain with 48 monomers.

  2. Surface electronic structure and isomerization reactions of alkanes on some transition metal oxides

    Science.gov (United States)

    Katrib, A.; Logie, V.; Saurel, N.; Wehrer, P.; Hilaire, L.; Maire, G.

    1997-04-01

    XP spectra of some reduced transition metal oxides are presented. Different number of free nd,( n + 1)s valence electrons in each case could be observed by the presence of a certain density of states (DOS) at the Fermi-level in the valence band (VB) energy region of the XP spectrum. Catalytic isomerization reactions of 2-methylpentane yielding 3-methylpentane and n-hexane at 350°C have been observed on these reduced valence surface states. The bifunctionel mechanism in terms of metallic and acidic sites required for such reactions is proposed by considering the metallic properties of the rutile deformed structure through the C-axis in the case of MoO 2 and WO 2, while the oxygen atom(s) in the lattice structure exhibit Brönsted acidic properties. On the other hand, highly reduced or clean surfaces of these transition metals yield hydrogenolysis catalytic reactions for the same reactant with methane as the major product. In all cases, the exposure of the lower valence oxidation states of bulk transition metal oxides to air results in the surface partial oxidation to the stable oxides such as MoO 3, WO 3, V 2O 5 and Nb 2O 5.

  3. Optically excited structural transition in atomic wires on surfaces at the quantum limit

    Science.gov (United States)

    Frigge, T.; Hafke, B.; Witte, T.; Krenzer, B.; Streubühr, C.; Samad Syed, A.; Mikšić Trontl, V.; Avigo, I.; Zhou, P.; Ligges, M.; von der Linde, D.; Bovensiepen, U.; Horn-von Hoegen, M.; Wippermann, S.; Lücke, A.; Sanna, S.; Gerstmann, U.; Schmidt, W. G.

    2017-03-01

    Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

  4. Optically excited structural transition in atomic wires on surfaces at the quantum limit.

    Science.gov (United States)

    Frigge, T; Hafke, B; Witte, T; Krenzer, B; Streubühr, C; Samad Syed, A; Mikšić Trontl, V; Avigo, I; Zhou, P; Ligges, M; von der Linde, D; Bovensiepen, U; Horn-von Hoegen, M; Wippermann, S; Lücke, A; Sanna, S; Gerstmann, U; Schmidt, W G

    2017-03-29

    Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

  5. Surface Properties of Titanium dioxide and its Structural Modifications by Reactions with Transition Metals

    Science.gov (United States)

    Halpegamage, Sandamali

    polymorph. So far, a reasonable explanation as to why these differences exist was not reported. In our studies, we used high quality epitaxial rutile and anatase thin films which enabled isolating the surface effects from the bulk effects and show that it is the difference between the charge carrier diffusion lengths that causes this difference in activities. In addition to that, using different surface orientations of rutile-TiO 2, we show that the anisotropic bulk charge carrier mobility may contribute to the orientation dependent photoactivity. Moreover, we show that different surface preparation methods also affect the activity of the sample and vacuum reduction results in an enhanced activity. In an effort to modify the TiO2 surfaces with monolayer/mixed monolayer oxides, we carried out experiments on (011) orientation of single crystal rutile TiO2 with few of the selected transition metal oxides namely Fe, V, Cr and Ni. We found that for specific oxidation conditions a monolayer mixed oxide is formed for all M (M= Fe, V, Cr, Ni), with one common structure with the composition MTi2O5. For small amounts of M the surface segregates into pure TiO2(011)-2x1 and into domains of MTi2O5 indicating that this mixed monolayer oxide is a low energy line phase in a compositional surface phase diagram. The oxygen pressure required for the formation of this unique monolayer structure increases in the order of Venthalpy of formation of oxide for these transition metals. The structure proposed for the stable MTi2O5 mixed monolayer oxide by DFT-based simulations was verified by X-ray photoemission diffraction measurements performed at a synchrotron facility.

  6. Atomic structure of the adsorption of transition metals on silicon surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Cocoletzi, G.H. [IF-BUAP, 72000 Puebla (Mexico); Takeuchi, N. [CCMC-UNAM, Ensenada, BCN (Mexico)

    2007-07-01

    Full text: Solid state devices are useful for their high sensitivity in a small volume. Applications of such devices as dose materials include semi-conducting dose-rate, and dose-reading measuring devices. Transition metals (TM) have electronic and atomic properties similar to those of rare earth elements when they are adsorbed on silicon surfaces. The interfaces of transition metals silicides with Si (111) have very small lattice mismatches, sharp interfaces, and low Schottky barrier, making them ideal in electronic devices, such as infrared detectors and rectifying contacts. In this work we shall describe our first principles total energy calculations to investigate structural properties of bulk ScSi and YSi, the two dimensional arrangement of ScSi{sub 2} and YSi{sub 2} on the Si(111) surface, and the growth of a few layers of ScSi{sub 1.7} and YSi{sub 1.7} on the Si(111) surface. Our calculated bulk structural parameters are in excellent agreement with experimental values. It will be shown that one monolayer of a TM on Si( l l 1) yields a two dimensional phase with (lxl) periodicity consisting of a layer of TM atoms on T4 sites and a Si bilayer on top. This double layer of Si atoms is very close to ideal Si(111)-(1x1) surface, but rotated 180 with respect to the rest of the crystal. More layers of TM silicide epitaxially grown on Si(l 11) result in a hexagonal structure similar to bulk ScSi2 and YSi2: graphite-like Si planes (with vacancies) intercalated with TM planes, and forming a ({radical}3x{radical}3) arrangement with a ScSi{sub 1.7} and YSi{sub 1.7} stoichiometry. The top Si layer does not contain vacancies and it does not present a graphite-like structure, but forms a bilayer arrangement as in bulk Si. (Author)

  7. Turbulence Structure of the Unstable Atmospheric Surface Layer and Transition to the Outer Layer

    Science.gov (United States)

    McNaughton, K. G.

    We present a new model of the structure of turbulence in the unstable atmospheric surface layer, and of the structural transition between this and the outer layer. The archetypal element of wall-bounded shear turbulence is the Theodorsen ejection amplifier (TEA) structure, in which an initial ejection of air from near the ground into an ideal laminar and logarithmic flow induces vortical motion about a hairpin-shaped core, which then creates a second ejection that is similar to, but larger than, the first. A series of TEA structures form a TEA cascade. In real turbulent flows TEA structures occur in distorted forms as TEA-like (TEAL) structures. Distortion terminates many TEAL cascades and only the best-formed TEAL structures initiate new cycles. In an extended log layer the resulting shear turbulence is a complex, self-organizing, dissipative system exhibiting self-similar behaviour under inner scaling. Spectral results show that this structure is insensitive to instability. This is contrary to the fundamental hypothesis of Monin--Obukhov similarity theory. All TEAL cascades terminate at the top of the surface layer where they encounter, and are severely distorted by, powerful eddies of similar size from the outer layer. These eddies are products of the breakdown of the large eddies produced by buoyancy in the outer layer. When the outer layer is much deeper than the surface layer the interacting eddies are from the inertial subrange of the outer Richardson cascade. The scale height of the surface layer, zs, is then found by matching the powers delivered to the creation of emerging TEAL structures to the power passing down the Richardson cascade in the outer layer. It is zs = u* 3ks, where u*s friction velocity, k is the von Káán constant and s is the rate of dissipation of turbulence kinetic energy in the outer layer immediately above the surface layer. This height is comparable to the Obukhov length in the fully convective boundary layer. Aircraft and tower

  8. The impact of surface geometry, cavitation, and condensation on wetting transitions: posts and reentrant structures

    Science.gov (United States)

    Panter, J. R.; Kusumaatmaja, H.

    2017-03-01

    The fundamental impacts of surface geometry on the stability of wetting states, and the transitions between them are elucidated for square posts and reentrant structures in three dimensions. We identify three principal outcomes of particular importance for future surface design of liquid-repellent surfaces. Firstly, we demonstrate and quantify how capillary condensation and vapour cavitation affect wetting state stabilities. At high contact angles, cavitation is enhanced about wide, closely-spaced square posts, leading to the existence of suspended states without an associated collapsed state. At low contact angles, narrow reentrant pillars suppress condensation and enable the suspension of even highly wetting liquids. Secondly, two distinct collapse mechanisms are observed for 3D reentrant geometries, base contact and pillar contact, which are operative at different pillar heights. As well as morphological differences in the interface of the penetrating liquid, each mechanism is affected differently by changes in the contact angle with the solid. Finally, for highly-wetting liquids, condensates are shown to critically modify the transition pathways in both the base contact and pillar contact modes.

  9. Formation and structural phase transition in Co atomic chains on a Cu(775) surface

    Energy Technology Data Exchange (ETDEWEB)

    Syromyatnikov, A. G.; Kabanov, N. S.; Saletsky, A. M.; Klavsyuk, A. L., E-mail: klavsyuk@physics.msu.ru [Moscow State University (Russian Federation)

    2017-01-15

    The formation of Co atomic chains on a Cu(775) surface is investigated by the kinetic Monte Carlo method. It is found that the length of Co atomic chains formed as a result of self-organization during epitaxial growth is a random quantity and its mean value depends on the parameters of the experiment. The existence of two structural phases in atomic chains is detected using the density functional theory. In the first phase, the separations between an atom and its two nearest neighbors in a chain are 0.230 and 0.280 nm. In the second phase, an atomic chain has identical atomic spacings of 0.255 nm. It is shown that the temperature of the structural phase transition depends on the length of the atomic chain.

  10. Fermi Surface and Order Parameter Driven Vortex Lattice Structure Transitions in Twin-Free YBa2Cu3O7

    DEFF Research Database (Denmark)

    White, J.S.; Hinkov, V.; Heslop, R.W.;

    2009-01-01

    fields. It is separated from a low-field hexagonal phase of different orientation and distortion by a first-order transition at 2.0(2) T that is probably driven by Fermi surface effects. We argue that another first-order transition at 6.7(2) T, into a rhombic structure with a distortion of opposite sign......, marks a crossover from a regime where Fermi surface anisotropy is dominant, to one where the VL structure and distortion is controlled by the order-parameter anisotropy....

  11. Asymmetries in transition metal XPS spectra: metal nanoparticle structure, and interaction with the graphene-structured substrate surface.

    Science.gov (United States)

    Sacher, E

    2010-03-16

    Transition-metal XPS spectra have traditionally been considered to possess a natural asymmetry, extending to the high-binding-energy side. This is based on the fact that these spectra have generally been found experimentally to have such an asymmetry, as well as on the confirmation of asymmetry offered by the Doniach-Sunjić equation, an equation based on the proposal that the conduction electron scattering amplitude for interband absorption or emission in metals, at the Fermi level, is a singularity. Our discovery that metal nanoparticles, prepared under vacuum and characterized without exposure to air, have symmetric peaks, which become asymmetric with time, informed us that these peak asymmetries have other sources. On the basis of our belief that all metal spectra are composed of symmetric peaks, where the asymmetries are attributed to overlapping minor peaks that are consistent with known physical and chemical phenomena associated with that metal, we have shown that, for the metals that we have studied, these asymmetries contain much information, otherwise unavailable, on the structures, contaminants, oxidation, and interfacial interactions of nanoparticle surfaces. The existence of this information has been demonstrated for several metals, and its value is shown by its use in explaining the strong interfacial bonding of the nanoparticles with substrates having graphene structures. A possible future research direction is offered in the field of metal-metal interactions in nanoparticle alloys.

  12. Surface structure determinations of crystalline ionic thin films grown on transition metal single crystal surfaces by low energy electron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Roberts, Joel Glenn [Univ. of California, Berkeley, CA (United States)

    2000-05-01

    The surface structures of NaCl(100), LiF(100) and alpha-MgCl2(0001) adsorbed on various metal single crystals have been determined by low energy electron diffraction (LEED). Thin films of these salts were grown on metal substrates by exposing the heated metal surface to a molecular flux of salt emitted from a Knudsen cell. This method of investigating thin films of insulators (ionic salts) on a conducting substrate (metal) circumvents surface charging problems that plagued bulk studies, thereby allowing the use of electron-based techniques to characterize the surface.

  13. Nanocrystals in compression: unexpected structural phase transition and amorphization due to surface impurities

    Science.gov (United States)

    Liu, Gang; Kong, Lingping; Yan, Jinyuan; Liu, Zhenxian; Zhang, Hengzhong; Lei, Pei; Xu, Tao; Mao, Ho-Kwang; Chen, Bin

    2016-06-01

    We report an unprecedented surface doping-driven anomaly in the compression behaviors of nanocrystals demonstrating that the change of surface chemistry can lead to an interior bulk structure change in nanoparticles. In the synchrotron-based X-ray diffraction experiments, titania nanocrystals with low concentration yttrium dopants at the surface are found to be less compressible than undoped titania nanocrystals. More surprisingly, an unexpected TiO2(ii) phase (α-PbO2 type) is induced and obvious anisotropy is observed in the compression of yttrium-doped TiO2, in sharp contrast to the compression behavior of undoped TiO2. In addition, the undoped brookite nanocrystals remain with the same structure up to 30 GPa, whereas the yttrium-doped brookite amorphizes above 20 GPa. The abnormal structural evolution observed in yttrium-doped TiO2 does not agree with the reported phase stability of nano titania polymorphs, thus suggesting that the physical properties of the interior of nanocrystals can be controlled by the surface, providing an unconventional and new degree of freedom in search for nanocrystals with novel tunable properties that can trigger applications in multiple areas of industry and provoke more related basic science research.We report an unprecedented surface doping-driven anomaly in the compression behaviors of nanocrystals demonstrating that the change of surface chemistry can lead to an interior bulk structure change in nanoparticles. In the synchrotron-based X-ray diffraction experiments, titania nanocrystals with low concentration yttrium dopants at the surface are found to be less compressible than undoped titania nanocrystals. More surprisingly, an unexpected TiO2(ii) phase (α-PbO2 type) is induced and obvious anisotropy is observed in the compression of yttrium-doped TiO2, in sharp contrast to the compression behavior of undoped TiO2. In addition, the undoped brookite nanocrystals remain with the same structure up to 30 GPa, whereas the yttrium

  14. Electronic Structure and Band Gap of Fullerenes on Tungsten Surfaces: Transition from a Semiconductor to a Metal Triggered by Annealing.

    Science.gov (United States)

    Monazami, Ehsan; McClimon, John B; Rondinelli, James; Reinke, Petra

    2016-12-21

    The understanding and control of molecule-metal interfaces is critical to the performance of molecular electronics and photovoltaics devices. We present a study of the interface between C60 and W, which is a carbide-forming transition metal. The complex solid-state reaction at the interface can be exploited to adjust the electronic properties of the molecule layer. Scanning tunneling microscopy/spectroscopy measurements demonstrate the progression of this reaction from wide band gap (>2.5 eV) to metallic molecular surface during annealing from 300 to 800 K. Differential conduction maps with 10(4) scanning tunneling spectra are used to quantify the transition in the density of states and the reduction of the band gap during annealing with nanometer spatial resolution. The electronic transition is spatially homogeneous, and the surface band gap can therefore be adjusted by a targeted annealing step. The modified molecules, which we call nanospheres, are quite resistant to ripening and coalescence, unlike any other metallic nanoparticle of the same size. Densely packed C60 and isolated C60 molecules show the same transition in electronic structure, which confirms that the transformation is controlled by the reaction at the C60-W interface. Density functional theory calculations are used to develop possible reaction pathways in agreement with experimentally observed electronic structure modulation. Control of the band gap by the choice of annealing temperature is a unique route to tailoring molecular-layer electronic properties.

  15. Spatially resolved surface valence gradient and structural transformation of lithium transition metal oxides in lithium-ion batteries.

    Science.gov (United States)

    Liu, Hanshuo; Bugnet, Matthieu; Tessaro, Matteo Z; Harris, Kristopher J; Dunham, Mark J R; Jiang, Meng; Goward, Gillian R; Botton, Gianluigi A

    2016-10-26

    Layered lithium transition metal oxides are one of the most important types of cathode materials in lithium-ion batteries (LIBs) that possess high capacity and relatively low cost. Nevertheless, these layered cathode materials suffer structural changes during electrochemical cycling that could adversely affect the battery performance. Clear explanations of the cathode degradation process and its initiation, however, are still under debate and not yet fully understood. We herein systematically investigate the chemical evolution and structural transformation of the LiNixMnyCo1-x-yO2 (NMC) cathode material in order to understand the battery performance deterioration driven by the cathode degradation upon cycling. Using high-resolution electron energy loss spectroscopy (HR-EELS) we clarify the role of transition metals in the charge compensation mechanism, particularly the controversial Ni(2+) (active) and Co(3+) (stable) ions, at different states-of-charge (SOC) under 4.6 V operation voltage. The cathode evolution is studied in detail from the first-charge to long-term cycling using complementary diagnostic tools. With the bulk sensitive (7)Li nuclear magnetic resonance (NMR) measurements, we show that the local ordering of transition metal and Li layers (R3[combining macron]m structure) is well retained in the bulk material upon cycling. In complement to the bulk measurements, we locally probe the valence state distribution of cations and the surface structure of NMC particles using EELS and scanning transmission electron microscopy (STEM). The results reveal that the surface evolution of NMC is initiated in the first-charging step with a surface reduction layer formed at the particle surface. The NMC surface undergoes phase transformation from the layered structure to a poor electronic and ionic conducting transition-metal oxide rock-salt phase (R3[combining macron]m → Fm3[combining macron]m), accompanied by irreversible lithium and oxygen loss. In addition to the

  16. Surface adsorption of lattice HP proteins: Thermodynamics and structural transitions using Wang-Landau sampling

    Science.gov (United States)

    Li, Ying Wai; Wüst, Thomas; Landau, David P.

    2012-12-01

    Wang-Landau sampling has been applied to investigate the thermodynamics and structural properties of a lattice hydrophobic-polar heteropolymer (the HP protein model) interacting with an attractive substrate. For simplicity, we consider a short HP sequence consisting of only 36 monomers interacting with a substrate which attracts all monomers in the sequence. The conformational “phase transitions” have been identified by a canonical analysis of the specific heat and suitable structural observables. Three major “transitions”, namely, adsorption, hydrophobic core formation and “flattening” of adsorbed structures, are observed. Depending on the surface attractive strength relative to the intra-protein attraction among the H monomers, these processes take place in different sequences upon cooling.

  17. METABALL-BASED TRANSITION SURFACES

    Institute of Scientific and Technical Information of China (English)

    Li Lingfeng; Tan Jianrong; Chen Yuanpeng

    2005-01-01

    Metaball-based constraint deformation technique is used to change the definition of r, the straight-line distance from a space point to a constraint center in the original calculation of the potential function. By replacing the parameter of the parametrized surface w with the straight-line distance r, a method of building transition surfaces according to connected boundary curves and skeleton curves is proposed. The method has no restrictions on boundary curves that control the space shapes of transition surfaces or on types of skeleton curves, thus transition surfaces, which reach C1 continuity and are more abundant in shapes and natural, can be obtained.

  18. Potential-induced structural transitions of DL-homocysteine monolayers on Au(111) electrode surfaces

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Demetriou, Anna; Welinder, Anne Christina

    2005-01-01

    -S reductive desorption at -0.8 V (SCE) in 0.1 M NaOH, while the charge is only about 8 x 10(-6) C cm(-2) (pH 7.7) for the 0 to -0.1 V peak. This suggests a capacitive origin. The peak potential and shape depend on pH. At pH 7.7 both cathodic and anodic peak currents reach a maximum, but drop at both higher....... This process is reversible. We propose that the voltammetric peaks are capacitive. The ordered domains are formed only around the potential of zero charge (pzc) and dissipate at potentials on either side of the peak, inducing mirror charge flow in the metallic electrode as the charged -COO- and -NH3+ groups...... approach the surface. No bands for carboxylate coordinated to the surface were observed in SNIFTIRS implying more subtle orientation changes of the charged groups on transcending the voltammetric peak. This scenario is incorporated in a simple phenomenological model....

  19. Atomic Structure of a Spinel-like Transition Al2O3 (100) Surface

    DEFF Research Database (Denmark)

    Jensen, Thomas Nørregaard; Meinander, Kristoffer; Helveg, Stig

    2014-01-01

    We study a crystalline epitaxial alumina thin film with the characteristics of a spinel-type transition Al2O3(100) surface by using atom-resolved noncontact atomic force microscopy and density functional theory. It is shown that the films are terminated by an Al-O layer rich in Al vacancies...

  20. Structural transition metal chemistry

    CERN Document Server

    Anderson, K M

    2002-01-01

    This thesis is divided up into five chapters as outlined below. Chapter 1 gives the background to the techniques used in this thesis including X-ray structure determination and ab initio methods. An overview of some recent studies using ab initio methods to study transition metal complexes is also given. Chapter 2 investigates structural trans influence in a number of transition metal and p-block complexes. The database and ab initio studies showed that the classical trans influence model based on Pt(II) chemistry does not always hold. For some systems (eg. d sup 1 sup 0 s sup 0 for Sb sup V and Sn sup I sup V) the cis influence is of similar magnitude to the trans influence. For other systems (d sup 0), the trans influence is not as powerful as usually assumed. Chapter 3 is an investigation into the bridging chloride unit. A database study was performed on three systems (M-CI-M', M-CI...H and M-CI...Li/Na/K). Reaction pathway analysis was carried out for the M-CI-M' case and showed that bond order is not con...

  1. Toward quantitative STM: Scanning tunneling microscopy study of structure and dynamics of adsorbates on transition metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Dunphy, J.C.

    1995-05-01

    STM was applied to chemisorbed S layers on Re(000l) and Mo(100) surfaces. As function of coverage on both these surfaces, S orders into several different overlayer structures, which have been studied by dynamic LEED. STM images of all these structures were obtained. Approximate location of S atoms in the structures was determined by inspecting the images, especially the regions containing defects. Results are in agreement with LEED except for the p(2{times}l) overlayer of sulfur on Mo(100). The STM images were compared to calculations made with Electron Scattering Quantum Chemistry (ESQC) theory. Variation of contrast in experimental images is explained as a result of changes in STM tip termination structure. STM image contrast is a result of changes in the interference between different paths for the tunneling electrons. The simplest structure on the Mo(100) surface was used as a model for developing and testing a method of quantitative structure determination with the STM. Experimental STM images acquired under a range of tunneling conditions were compared to theoretical calculations of the images as a function of surface structure to determine the structure which best fit. Results matched within approximately 0.1 Angstroms a LEED structural determination. At lower S coverage, diffusion of S atoms over the Re(0001) surface and the lateral interaction between these atoms were investigated by application of a new image analysis technique. The interaction between the S and a coadsorbed CO layer was also studied, and CO was found to induce compression of the S overlayer. A similar result was found for Au deposited on the sulfur covered Mo(100) surface. The interaction between steps on the Mo surface was found to be influenced by S adsorption and this observation was interpreted with the theory of equilibrium crystal shape. Design of an STM instrument which operates at cryogenic and variable sample temperatures, and its future applications, are described.

  2. Toward quantitative STM: Scanning tunneling microscopy study of structure and dynamics of adsorbates on transition metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Dunphy, James Christopher [Univ. of California, Berkeley, CA (United States)

    1995-05-01

    STM was applied to chemisorbed S layers on Re(000l) and Mo(100) surfaces. As function of coverage on both these surfaces, S orders into several different overlayer structures, which have been studied by dynamic LEED. STM images of all these structures were obtained. Approximate location of S atoms in the structures was determined by inspecting the images, especially the regions containing defects. Results are in agreement with LEED except for the p(2xl) overlayer of sulfur on Mo(100). The STM images were compared to calculations made with Electron Scattering Quantum Chemistry (ESQC) theory. Variation of contrast in experimental images is explained as a result of changes in STM tip termination structure. STM image contrast is a result of changes in the interference between different paths for the tunneling electrons. The simplest structure on the Mo(100) surface was used as a model for developing and testing a method of quantitative structure determination with the STM. Experimental STM images acquired under a range of tunneling conditions were compared to theoretical calculations of the images as a function of surface structure to determine the structure which best fit. Results matched within approximately 0.1 Angstroms a LEED structural determination. At lower S coverage, diffusion of S atoms over the Re(0001) surface and the lateral interaction between these atoms were investigated by application of a new image analysis technique. The interaction between the S and a coadsorbed CO layer was also studied, and CO was found to induce compression of the S overlayer. A similar result was found for Au deposited on the sulfur covered Mo(100) surface. The interaction between steps on the Mo surface was found to be influenced by S adsorption and this observation was interpreted with the theory of equilibrium crystal shape. Design of an STM instrument which operates at cryogenic and variable sample temperatures, and its future applications, are described.

  3. Transition between the 1 x 1 and ({radical}3 x 2{radical}3)R30{degree} surface structures of GaN in the vapor-phase environment

    Energy Technology Data Exchange (ETDEWEB)

    Munkholm, A.; Thompson, C.; Stephenson, G. B.; Eastman, J. A.; Auciello, O.; Fini, P.; Speck, J. S.; DenBaars, S. P.

    2000-01-12

    Out-of-plane structures of the GaN(0001) surface in the metal-organic chemical vapor deposition (MOCVD) environment have been determined using in situ grazing-incidence X-ray scattering. The authors measured 11{bar 2}{ell} crystal truncation rod intensities at a variety of temperatures and ammonia partial pressures on both sides of the 1 x 1 to ({radical}3 x 2{radical}3)R30{degree} surface phase transition. The out-of-plane structure of the ({radical}3 x 2{radical}3)R30{degree} phase appears to be nearly independent of temperature below the transition, while the structure of the 1 x 1 phase changes increase rapidly as the phase transition is approached from above. A model for the structure of the 1 x 1 phase with a partially-occupied top Ga layer agrees well with the data. The observed temperature dependence is consistent with a simple model of the equilibrium between the vapor phase and the surface coverage of Ga and N. In addition, the authors present results on the kinetics of reconstruction domain coarsening following a quench into the ({radical}3 x 2{radical}3)R30{degree} phase field.

  4. Structural Transition in Supercritical Fluids

    Directory of Open Access Journals (Sweden)

    Boris I. Sedunov

    2011-01-01

    Full Text Available The extension of the saturation curve ( on the PT diagram in the supercritical region for a number of monocomponent supercritical fluids by peak values for different thermophysical properties, such as heat capacities and and compressibility has been studied. These peaks signal about some sort of fluid structural transition in the supercritical region. Different methods give similar but progressively diverging curves st( for this transition. The zone of temperatures and pressures near these curves can be named as the zone of the fluid structural transition. The outstanding properties of supercritical fluids in this zone help to understand the physical sense of the fluid structural transition.

  5. Understanding of catalysis on early transition metal oxide-based catalysts through exploration of surface structure and chemistry during catalysis using in-situ approaches

    Energy Technology Data Exchange (ETDEWEB)

    Tao, Franklin [Univ. of Kansas, Lawrence, KS (United States). Dept. of Chemical and Petroleum Engineering. Dept. of Chemistry

    2015-09-14

    Two main categories of heterogeneous catalysts are metal and metal oxide which catalyze 80% chemical reactions at solid-gas and solid-liquid interfaces. Metal oxide catalysts are much more complicated than metal catalysts. The reason is that the cations of the metal atoms could exhibit a few different oxidation states on surface of the same catalyst particle such as Co3O4 or change of their oxidation states under different reactive environments. For a metal catalyst, there is only one oxidation state typically. In addition, surface of a metal oxide can be terminated with multiple surface functionalities including O atoms with different binding configurations and OH group. For metal, only metal atoms are exposed typically. Obviously, the complication of surface chemistry and structure of a metal oxide makes studies of surface of an oxide catalyst very challenging. Due to the complication of surface of a meal oxide, the electronic and geometric structures of surface of a metal oxide and the exposed species have received enormous attention since oxide catalysts catalyze at least 1/3 chemical reactions in chemical and energy industries. Understanding of catalytic reactions on early transition metal oxide-based catalysts is fundamentally intriguing and of great practical interest in energy- and environment-related catalysis. Exploration of surface chemistry of oxide-based catalysts at molecular level during catalysis has remained challenging though it is critical in deeply understanding catalysis on oxide-based catalysts and developing oxide-based catalysts with high activity and selectivity. Thus, the overall objective of this project is to explore surface chemistry and structure of early transition metal oxide-based catalysts through in-situ characterization of surface of catalysts, measurements of catalytic performances, and then build an intrinsic correlation of surface chemistry and structure with their catalytic performances in a few

  6. Structural transitions in clusters

    Science.gov (United States)

    Ghazali, A.; Lévy, J.-C. S.

    1997-02-01

    Monatomic clusters are studied by Monte Carlo relaxation using generalized Lennard-Jones potentials. A transition from an icosahedral symmetry to a crystalline symmetry with stacking faults is always observed. Bcc-based soft atom clusters are found to have a lower energy than the corresponding hcp and fcc ones below the melting point.

  7. Structure, Mobility, and Composition of Transition Metal Catalyst Surfaces. High-Pressure Scanning Tunneling Microscopy and Ambient-Pressure X-ray Photoelectron Spectroscopy Studies

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Zhongwei [Univ. of California, Berkeley, CA (United States)

    2013-12-06

    Surface structure, mobility, and composition of transition metal catalysts were studied by high-pressure scanning tunneling microscopy (HP-STM) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) at high gas pressures. HP-STM makes it possible to determine the atomic or molecular rearrangement at catalyst surfaces, particularly at the low-coordinated active surface sites. AP-XPS monitors changes in elemental composition and chemical states of catalysts in response to variations in gas environments. Stepped Pt and Cu single crystals, the hexagonally reconstructed Pt(100) single crystal, and Pt-based bimetallic nanoparticles with controlled size, shape and composition, were employed as the model catalysts for experiments in this thesis.

  8. Data supporting beta-amyloid dimer structural transitions and protein–lipid interactions on asymmetric lipid bilayer surfaces using MD simulations on experimentally derived NMR protein structures

    Directory of Open Access Journals (Sweden)

    Sara Y. Cheng

    2016-06-01

    Full Text Available This data article supports the research article entitled “Maximally Asymmetric Transbilayer Distribution of Anionic Lipids Alters the Structure and interaction with Lipids of an Amyloidogenic Protein Dimer Bound to the Membrane Surface” [1]. We describe supporting data on the binding kinetics, time evolution of secondary structure, and residue-contact maps of a surface-absorbed beta-amyloid dimer protein on different membrane surfaces. We further demonstrate the sorting of annular and non-annular regions of the protein/lipid bilayer simulation systems, and the correlation of lipid-number mismatch and surface area per lipid mismatch of asymmetric lipid membranes.

  9. Structural Transitions in Cholesteric Liquid Crystal Droplets

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Ye; Bukusoglu, Emre; Martinez-Gonzalez, Jose A.; Rahimi, Mohammad; Roberts, Tyler F.; Zhang, Rui; Wang, Xiaoguang; Abbott, Nicholas L.; de Pablo, Juan J.

    2016-07-01

    Confinement of cholesteric liquid crystals (ChLC) into droplets leads to a delicate interplay between elasticity, chirality, and surface energy. In this work, we rely on a combination of theory and experiments to understand the rich morphological behavior that arises from that balance. More specifically, a systematic study of micrometer-sized ChLC droplets is presented as a function of chirality and surface energy (or anchoring). With increasing chirality, a continuous transition is observed from a twisted bipolar structure to a radial spherical structure, all within a narrow range of chirality. During such a transition, a bent structure is predicted by simulations and confirmed by experimental observations. Simulations are also able to capture the dynamics of the quenching process observed in experiments. Consistent with published work, it is found that nanoparticles are attracted to defect regions on the surface of the droplets. For weak anchoring conditions at the nanoparticle surface, ChLC droplets adopt a morphology similar to that of the equilibrium helical phase observed for ChLCs in the bulk. As the anchoring strength increases, a planar bipolar structure arises, followed by a morphological transition to a bent structure. The influence of chirality and surface interactions are discussed in the context of the potential use of ChLC droplets as stimuli-responsive materials for reporting molecular adsorbates.

  10. Symmetry structure and phase transitions

    Indian Academy of Sciences (India)

    Ashok Goyal; Meenu Dahiya; Deepak Chandra

    2003-05-01

    We study chiral symmetry structure at finite density and temperature in the presence of external magnetic field and gravity, a situation relevant in the early Universe and in the core of compact stars. We then investigate the dynamical evolution of phase transition in the expanding early Universe and possible formation of quark nuggets and their survival.

  11. Surface mobility and structural transitions of poly(n-alkyl methacrylates) probed by dynamic contact angle measurements

    NARCIS (Netherlands)

    Damme, van H.S.; Hogt, A.H.; Feijen, J.

    1986-01-01

    Dynamic contact angles and contact-angle hysteresis of a series of poly(n-alkyl methacrylates) (PAMA) were investigated using the Wilhelmy plate technique. The mobility of polymer surface chains, segments, and side groups affected the measured contact angles and their hysteresis. A model is presente

  12. Surface mobility and structural transitions of poly(n-alkyl methacrylates) probed by dynamic contact angle measurements

    OpenAIRE

    Van Damme; Hogt, A.H.; Feijen, J.

    1986-01-01

    Dynamic contact angles and contact-angle hysteresis of a series of poly(n-alkyl methacrylates) (PAMA) were investigated using the Wilhelmy plate technique. The mobility of polymer surface chains, segments, and side groups affected the measured contact angles and their hysteresis. A model is presented in which contact-angle hysteresis of PAMA's is explained in terms of the reorientation of polymer chains and segments at the interface of the polymers with water and air. The contact angles obser...

  13. Transition-Systems, Event Structures, and Unfoldings

    DEFF Research Database (Denmark)

    Nielsen, Mogens; Rozenberg, Grzegorz; Thiagarajan, P.S.

    1995-01-01

    A subclass of transition systems called elementary transition systems can be identified with the help of axioms based on a structural notion called regions. Elementary transition systems have been shown to be the transition system model of a basic system model of net theory called elementary net ...... event structures. We then propose an operation of unfolding elementary transition systems into occurrence transition systems, We prove that it is "correct" in a strong categorical sense....

  14. Wetting transition on patterned surfaces: transition states and energy barriers.

    Science.gov (United States)

    Ren, Weiqing

    2014-03-18

    We study the wetting transition on microstructured hydrophobic surfaces. We use the string method [J. Chem. Phys. 2007, 126, 164103; J. Chem. Phys. 2013, 138, 134105] to accurately compute the transition states, the energy barriers, and the minimum energy paths for the wetting transition from the Cassie-Baxter state to the Wenzel state. Numerical results are obtained for the wetting of a hydrophobic surface textured with a square lattice of pillars. It is found that the wetting of the solid substrate occurs via infiltration of the liquid in a single groove, followed by lateral propagation of the liquid front. The propagation of the liquid front proceeds in a stepwise manner, and a zipping mechanism is observed during the infiltration of each layer. The minimum energy path for the wetting transition goes through a sequence of intermediate metastable states, whose wetted areas reflect the microstructure of the patterned surface. We also study the dependence of the energy barrier on the drop size and the gap between the pillars.

  15. Roughening transitions of driven surface growth

    Energy Technology Data Exchange (ETDEWEB)

    Sanchez, A. [Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)]|[Departamento de Mathematicas, Escuela Politecnica Superior, Universidad Carlos III, E-28911 Leganes, Madrid (Spain); Cai, D.; Gronbech-Jensen, N.; Bishop, A.R. [Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Wang, Z.J. [Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)]|[The James Franck Institute, 5640 Ellis Avenue, Chicago, Illinois 60637 (United States)

    1995-05-15

    A model of surface growth given by a two-dimensional discrete, driven, damped sine-Gordon equation is studied using Langevin dynamics. Our large-scale simulations show that the equilibrium Kosterlitz-Thouless roughening transition splits into two crossovers (or transitions) under the external force of, e.g., vapor-surface chemical potential difference. Three different regimes are characterized in terms of roughness, growth rate, and height-height correlations---the onset of a rough phase is accompanied by the suppression of oscillatory growth. Our results are interpreted consistently within a renormalization-group framework. We discuss the generality of our conclusions and propose specific comparisons with experiments.

  16. Electronic structure of hcp transition metals

    DEFF Research Database (Denmark)

    Jepsen, O.; Andersen, O. Krogh; Mackintosh, A. R.

    1975-01-01

    Using the linear muffin-tin-orbital method described in the previous paper, we have calculated the electronic structures of the hcp transition metals, Zr, Hf, Ru, and Os. We show how the band structures of these metals may be synthesized from the sp and d bands, and illustrate the effects...... mRy. Very small pieces of Fermi surface, which have not yet been observed experimentally, are predicted for Os. The limited amount of experimental information available for Zr can be fairly satisfactorily interpreted if the calculated d bands are raised by about 10-20 mRy relative to the sp bands...

  17. The glass-liquid transition of water on hydrophobic surfaces.

    Science.gov (United States)

    Souda, Ryutaro

    2008-09-28

    Interactions of thin water films with surfaces of graphite and vitrified room-temperature ionic liquid [1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF(6)])] were investigated using time-of-flight secondary ion mass spectrometry as a function of temperature and annealing time to elucidate the glass-liquid transition of water at the molecular level. Surface diffusion of water occurs at temperatures higher than 120 K, thereby forming three-dimensional clusters (a two-dimensional layer) on the [bmim][PF(6)] (graphite) surface. The hydrophobic effect of the surface decreases with increasing coverage of water; the bulklike properties evolve up to 40 ML, as evidenced by the occurrence of film dewetting at around the conventional glass transition temperature (140 K). Results also showed that aging is necessary for the water monolayer (a 40 ML water film) to dewet the graphite ([bmim][PF(6)]) surface. The occurrence of aging is explainable by the successive evolution of two distinct liquids during the glass-liquid transition: low density liquid is followed by supercooled liquid water. The water monolayer on graphite is characterized by the preferred orientation of unpaired OH groups toward the surface; this structure is arrested during the aging time despite the occurrence of surface diffusion. However, the water monolayer formed on the [bmim][PF(6)] surface agglomerates immediately after the commencement of surface diffusion. The structure of low density liquid tends to be arrested by the attractive interaction with the neighbors.

  18. The Structural Phase Transition in Solid DCN

    DEFF Research Database (Denmark)

    Dietrich, O. W.; Mackenzie, Gordon A.; Pawley, G. S.

    1976-01-01

    Neutron scattering measurements on deuterated hydrogen cyanide have shown that the structural phase transition from a tetragonal to an orthorhombic form at 160 K is a first order transition. A transverse acoustic phonon mode, which has the symmetry of the transition was observed at very low energ...... energies and showed “softening” as the transition was approached from above.......Neutron scattering measurements on deuterated hydrogen cyanide have shown that the structural phase transition from a tetragonal to an orthorhombic form at 160 K is a first order transition. A transverse acoustic phonon mode, which has the symmetry of the transition was observed at very low...

  19. Silicon surface structure-controlled oleophobicity.

    Science.gov (United States)

    Liu, Yan; Xiu, Yonghao; Hess, Dennis W; Wong, C P

    2010-06-01

    Superoleophobic surfaces display contact angles >150 degrees with liquids that have lower surface energies than does water. The design of superoleophobic surfaces requires an understanding of the effect of the geometrical shape of etched silicon surfaces on the contact angle and hysteresis observed when different liquids are brought into contact with these surfaces. This study used liquid-based metal-assisted etching and various silane treatments to create superoleophobic surfaces on a Si(111) surface. Etch conditions such as the etch time and etch solution concentration played critical roles in establishing the oleophobicity of Si(111). When compared to Young's contact angle, the apparent contact angle showed a transition from a Cassie to a Wenzel state for low-surface-energy liquids as different silane treatments were applied to the silicon surface. These results demonstrated the relationship between the re-entrant angle of etched surface structures and the contact angle transition between Cassie and Wenzel behavior on etched Si(111) surfaces.

  20. Helical surface structures

    CERN Document Server

    Brandenburg, A; Brandenburg, Axel; Blackman, Eric G.

    2002-01-01

    Over the past few years there has been growing interest in helical magnetic field structures seen at the solar surface, in coronal mass ejections, as well as in the solar wind. Although there is a great deal of randomness in the data, on average the extended structures are mostly left-handed on the northern hemisphere and right-handed on the southern. Surface field structures are also classified as dextral (= right bearing) and sinistral (= left bearing) occurring preferentially in the northern and southern hemispheres respectively. Of particular interest here is a quantitative measurement of the associated emergence rates of helical structures, which translate to magnetic helicity fluxes. In this review, we give a brief survey of what has been found so far and what is expected based on models. Particular emphasis is put on the scale dependence of the associated fields and an attempt is made to estimate the helicity flux of the mean field vs. fluctuating field.

  1. Structural Transitions in Dense Networks

    CERN Document Server

    Lambiotte, R; Bhat, U; Redner, S

    2016-01-01

    We introduce an evolving network model in which a new node attaches to a randomly selected target node and also to each of its neighbors with probability $p$. The resulting network is sparse for $p<\\frac{1}{2}$ and dense (average degree increasing with number of nodes $N$) for $p\\geq \\frac{1}{2}$. In the dense regime, individual networks realizations built by this copying mechanism are disparate and not self-averaging. Further, there is an infinite sequence of structural anomalies at $p=\\frac{2}{3}$, $\\frac{3}{4}$, $\\frac{4}{5}$, etc., where the dependences on $N$ of the number of triangles (3-cliques), 4-cliques, undergo phase transitions. When linking to second neighbors of the target can occur, the probability that the resulting graph is complete---where all nodes are connected---is non-zero as $N\\to\\infty$.

  2. Music: Creativity and Structure Transitions

    Science.gov (United States)

    Pietrocini, Emanuela

    Music, compared to other complex forms of representation, is fundamentally characterized by constant evolution and a dynamic succession of structure reference models. This is without taking into account historical perspective, the analysis of forms and styles, or questions of a semantic nature; the observation rather refers to the phenomenology of the music system. The more abstract a compositional model, the greater the number and frequency of variables that are not assimilated to the reference structure; this "interference" which happens more often than not in an apparently casual manner, modifies the creative process to varying but always substantial degrees: locally, it produces a disturbance in perceptive, formal and structural parameters, resulting more often than not in a synaesthetic experience; globally, on the other hand, it defines the terms of a transition to a new state, in which the relations between elements and components modify the behavior of the entire system from which they originated. It is possible to find examples of this phenomenon in the whole range of musical production, in particular in improvisations, in the use of the Basso Continuo, and in some contrapuntal works of the baroque period, music whose temporal dimension can depart from the limits of mensurability and symmetry to define an open compositional environment in continuous evolution.

  3. Extending Modal Transition Systems with Structured Labels

    DEFF Research Database (Denmark)

    Bauer, Sebastian S.; Juhl, Line; Larsen, Kim Guldstrand

    2012-01-01

    We introduce a novel formalism of label-structured modal transition systems that combines the classical may/must modalities on transitions with structured labels that represent quantitative aspects of the model. On the one hand, the specification formalism is general enough to include models like...... study modal and thorough refinement, determinization, parallel composition, conjunction, quotient, and logical characterization of label-structured modal transition systems....

  4. Brain surface parameterization using Riemann surface structure.

    Science.gov (United States)

    Wang, Yalin; Gu, Xianfeng; Hayashi, Kiralee M; Chan, Tony F; Thompson, Paul M; Yau, Shing-Tung

    2005-01-01

    We develop a general approach that uses holomorphic 1-forms to parameterize anatomical surfaces with complex (possibly branching) topology. Rather than evolve the surface geometry to a plane or sphere, we instead use the fact that all orientable surfaces are Riemann surfaces and admit conformal structures, which induce special curvilinear coordinate systems on the surfaces. Based on Riemann surface structure, we can then canonically partition the surface into patches. Each of these patches can be conformally mapped to a parallelogram. The resulting surface subdivision and the parameterizations of the components are intrinsic and stable. To illustrate the technique, we computed conformal structures for several types of anatomical surfaces in MRI scans of the brain, including the cortex, hippocampus, and lateral ventricles. We found that the resulting parameterizations were consistent across subjects, even for branching structures such as the ventricles, which are otherwise difficult to parameterize. Compared with other variational approaches based on surface inflation, our technique works on surfaces with arbitrary complexity while guaranteeing minimal distortion in the parameterization. It also offers a way to explicitly match landmark curves in anatomical surfaces such as the cortex, providing a surface-based framework to compare anatomy statistically and to generate grids on surfaces for PDE-based signal processing.

  5. Simplified Approach to Predicting Rough Surface Transition

    Science.gov (United States)

    Boyle, Robert J.; Stripf, Matthias

    2009-01-01

    Turbine vane heat transfer predictions are given for smooth and rough vanes where the experimental data show transition moving forward on the vane as the surface roughness physical height increases. Consiste nt with smooth vane heat transfer, the transition moves forward for a fixed roughness height as the Reynolds number increases. Comparison s are presented with published experimental data. Some of the data ar e for a regular roughness geometry with a range of roughness heights, Reynolds numbers, and inlet turbulence intensities. The approach ta ken in this analysis is to treat the roughness in a statistical sense , consistent with what would be obtained from blades measured after e xposure to actual engine environments. An approach is given to determ ine the equivalent sand grain roughness from the statistics of the re gular geometry. This approach is guided by the experimental data. A roughness transition criterion is developed, and comparisons are made with experimental data over the entire range of experimental test co nditions. Additional comparisons are made with experimental heat tran sfer data, where the roughness geometries are both regular as well a s statistical. Using the developed analysis, heat transfer calculatio ns are presented for the second stage vane of a high pressure turbine at hypothetical engine conditions.

  6. Evolution of vortex-surface fields in transitional boundary layers

    Science.gov (United States)

    Yang, Yue; Zhao, Yaomin; Xiong, Shiying

    2016-11-01

    We apply the vortex-surface field (VSF), a Lagrangian-based structure-identification method, to the DNS database of transitional boundary layers. The VSFs are constructed from the vorticity fields within a sliding window at different times and locations using a recently developed boundary-constraint method. The isosurfaces of VSF, representing vortex surfaces consisting of vortex lines with different wall distances in the laminar stage, show different evolutionary geometries in transition. We observe that the vortex surfaces with significant deformation evolve from wall-parallel planar sheets through hairpin-like structures and packets into a turbulent spot with regeneration of small-scale hairpins. From quantitative analysis, we show that a small number of representative or influential vortex surfaces can contribute significantly to the increase of the drag coefficient in transition, which implies a reduced-order model based on VSF. This work has been supported in part by the National Natural Science Foundation of China (Grant Nos. 11472015, 11522215 and 11521091), and the Thousand Young Talents Program of China.

  7. Structural changes concurrent with ferromagnetic transition

    Institute of Scientific and Technical Information of China (English)

    Yang Sen; Bao Hui-Xin; Zhou Chao; Wang Yu; Ren Xiao-Bing; Song Xiao-Ping; Yoshitaka Matsushita

    2013-01-01

    Ferromagnetic transition has generally been considered to involve only an ordering of magnetic moment with no change in the host crystal structure or symmetry,as evidenced by a wealth of crystal structure data from conventional X-ray diffractometry (XRD).However,the existence of magnetostriction in all known ferromagnetic systems indicates that the magnetic moment is coupled to the crystal lattice; hence there is a possibility that magnetic ordering may cause a change in crystal structure.With the development of high-resolution synchrotron XRD,more and more magnetic transitions have been found to be accompanied by simultaneous structural changes.In this article,we review our recent progress in understanding the structural change at a ferromagnetic transition,including synchrotron XRD evidence of structural changes at the ferromagnetic transition,a phenomenological theory of crystal structure changes accompanying ferromagnetic transitions,new insight into magnetic morphotropic phase boundaries (MPB) and so on.Two intriguing implications of non-centric symmetry in the ferromagnetic phase and the first-order nature of ferromagnetic transition are also discussed here.In short,this review is intended to give a self-consistent and logical account of structural change occurring simultaneously with a ferromagnetic transition,which may provide new insight for developing highly magneto-responsive materials.

  8. Cohesion and coordination effects on transition metal surface energies

    Science.gov (United States)

    Ruvireta, Judit; Vega, Lorena; Viñes, Francesc

    2017-10-01

    Here we explore the accuracy of Stefan equation and broken-bond model semiempirical approaches to obtain surface energies on transition metals. Cohesive factors are accounted for either via the vaporization enthalpies, as proposed in Stefan equation, or via cohesive energies, as employed in the broken-bond model. Coordination effects are considered including the saturation degree, as suggested in Stefan equation, employing Coordination Numbers (CN), or as the ratio of broken bonds, according to the bond-cutting model, considering as well the square root dependency of the bond strength on CN. Further, generalized coordination numbers CN bar are contemplated as well, exploring a total number of 12 semiempirical formulations on the three most densely packed surfaces of 3d, 4d, and 5d Transition Metals (TMs) displaying face-centered cubic (fcc), body-centered cubic (bcc), or hexagonal close-packed (hcp) crystallographic structures. Estimates are compared to available experimental surface energies obtained extrapolated to zero temperature. Results reveal that Stefan formula cohesive and coordination dependencies are only qualitative suited, but unadvised for quantitative discussion, as surface energies are highly overestimated, favoring in addition the stability of under-coordinated surfaces. Broken-bond cohesion and coordination dependencies are a suited basis for quantitative comparison, where square-root dependencies on CN to account for bond weakening are sensibly worse. An analysis using Wulff shaped averaged surface energies suggests the employment of broken-bond model using CN to gain surface energies for TMs, likely applicable to other metals.

  9. Structural Changes in Serbian Industry during Transition

    Directory of Open Access Journals (Sweden)

    Ivan Nikolić

    2013-07-01

    Full Text Available Transition is a complex process whereby a country in transition is stimulating structural changes wishing to achieve economic growth and improved social wellbeing. In this paper the authors aim to show that during transition in Serbia there such changes in the structure of manufacturing industry occurred, which resulted with only modest ​​growth that in fact was slower than in other transitional countries. By the means of theoretical and empirical approach – deductive methods, statistical and mathematical evaluation the authors have come to conclusion that structural changes did not improve industry branches like the hi-tech industry that contribute the most to PPP generation. At the same time, some low productive industries have gained on importance, therefore keeping the standard on the low levels without possibility to rapidly converge towards EU average, which was set as an ultimate goal of transition in Serbia.

  10. The Structural Phase Transition in Solid DCN

    DEFF Research Database (Denmark)

    Dietrich, O. W.; Mackenzie, Gordon A.; Pawley, G. S.

    1975-01-01

    Neutron scattering measurements on deuterated hydrogen cyanide have shown that the structural phase change from a tetragonal to an orthorhombic form at 160K is a first-order transition. A transverse acoustic phonon mode, which has the symmetry of the phase change, was observed at very low energies...... and showed 'softening' as the transition temperature was approached from above....

  11. An Application Study of Transition Surface Reconstruction in Reverse Engineering

    Institute of Scientific and Technical Information of China (English)

    LUJing-ping; HEYu-lin; LIAOXiao-ping

    2004-01-01

    the reconstruction of transition surface is one of time consuming activities during surface modeling in reverse engineering. Yet currently available software applications suffer from shortcoming in processing the connection among free form surfaces. In this paper, a new method is put forward combining Surfacer with Unigraphics to resolve this problem: Curves and surfaces are first constructed in Surfacer, then, the finished data is imported into Unigraphics based on IGES format. At last, the transition surface can be reconstructed in Unigraphics. The application of this method in transition surface reconstruction is illustrated by means of two case studies,showing the connection between free form surfaces; filleting and rounding among multiple surfaces; transition surface between two sets of surfaces.

  12. Transition State Theory for dissipative systems without a dividing surface

    CERN Document Server

    Revuelta, F; Benito, R M; Borondo, F

    2015-01-01

    Transition State Theory is a central cornerstone in reaction dynamics. Its key step is the identification of a dividing surface that is crossed only once by all reactive trajectories. This assumption is often badly violated, especially when the reactive system is coupled to an environment. The calculations made in this way then overestimate the reaction rate and the results depend critically on the choice of the dividing surface. In this Letter, we study the phase space of a stochastically driven system close to an energetic barrier in order to identify the geometric structure unambiguously determining the reactive trajectories, which is then incorporated in a simple rate formula for reactions in condensed phase that is both independent of the dividing surface and exact.

  13. Surface entropy of liquid transition and noble metals

    Science.gov (United States)

    Gosh, R. C.; Das, Ramprosad; Sen, Sumon C.; Bhuiyan, G. M.

    2015-07-01

    Surface entropy of liquid transition and noble metals has been investigated using an expression obtained from the hard-sphere (HS) theory of liquid. The expression is developed from the Mayer's extended surface tension formula [Journal of Non-Crystalline Solids 380 (2013) 42-47]. For interionic interaction in metals, Brettonet-Silbert (BS) pseudopotentials and embedded atom method (EAM) potentials have been used. The liquid structure is described by the variational modified hypernetted chain (VMHNC) theory. The essential ingredient of the expression is the temperature dependent effective HS diameter (or packing fraction), which is calculated from the aforementioned potentials together with the VMHNC theory. The obtained results for the surface entropy using the effective HS diameter are found to be good in agreement with the available experimental as well as other theoretical values.

  14. Coherent structures in transitional pipe flow

    Science.gov (United States)

    Hellström, Leo H. O.; Ganapathisubramani, Bharathram; Smits, Alexander J.

    2016-06-01

    Transition to turbulence in pipe flow is investigated experimentally using a temporally resolved dual-plane particle image velocimetry approach, at a Reynolds number of 3440. The flow is analyzed using proper orthogonal decomposition and it is shown that the flow can be divided into two regions: a pseudolaminar region governed by the presence of azimuthally steady traveling waves, and turbulent slugs. The evolution of the structures within the slugs is identified by using the temporally resolved data along with the dual-plane velocity field. These structures are shown to be remarkably similar to the large-scale motions found in fully turbulent flows, with a streamwise and spatiotemporal extent about four pipe radii. The transition between structures is characterized by the detachment and decay of an old structure and the initiation of a new structure at the wall.

  15. Transition of cellulose crystalline structure and surface morphology of biomass as a function of ionic liquid pretreatment and its relation to enzymatic hydrolysis.

    Science.gov (United States)

    Cheng, Gang; Varanasi, Patanjali; Li, Chenlin; Liu, Hanbin; Melnichenko, Yuri B; Simmons, Blake A; Kent, Michael S; Singh, Seema

    2011-04-11

    Cellulose is inherently resistant to breakdown, and the native crystalline structure (cellulose I) of cellulose is considered to be one of the major factors limiting its potential in terms of cost-competitive lignocellulosic biofuel production. Here we report the impact of ionic liquid pretreatment on the cellulose crystalline structure in different feedstocks, including microcrystalline cellulose (Avicel), switchgrass (Panicum virgatum), pine ( Pinus radiata ), and eucalyptus ( Eucalyptus globulus ), and its influence on cellulose hydrolysis kinetics of the resultant biomass. These feedstocks were pretreated using 1-ethyl-3-methyl imidazolium acetate ([C2mim][OAc]) at 120 and 160 °C for 1, 3, 6, and 12 h. The influence of the pretreatment conditions on the cellulose crystalline structure was analyzed by X-ray diffraction (XRD). On a larger length scale, the impact of ionic liquid pretreatment on the surface roughness of the biomass was determined by small-angle neutron scattering (SANS). Pretreatment resulted in a loss of native cellulose crystalline structure. However, the transformation processes were distinctly different for Avicel and for the biomass samples. For Avicel, a transformation to cellulose II occurred for all processing conditions. For the biomass samples, the data suggest that pretreatment for most conditions resulted in an expanded cellulose I lattice. For switchgrass, first evidence of cellulose II only occurred after 12 h of pretreatment at 120 °C. For eucalyptus, first evidence of cellulose II required more intense pretreatment (3 h at 160 °C). For pine, no clear evidence of cellulose II content was detected for the most intense pretreatment conditions of this study (12 h at 160 °C). Interestingly, the rate of enzymatic hydrolysis of Avicel was slightly lower for pretreatment at 160 °C compared with pretreatment at 120 °C. For the biomass samples, the hydrolysis rate was much greater for pretreatment at 160 °C compared with pretreatment

  16. Electron Scattering at Surfaces and Interfaces of Transition Metals

    Science.gov (United States)

    Zheng, Pengyuan

    The effect of surfaces on the electron transport at reduced scales is attracting continuous interest due to its broad impact on both the understanding of materials properties and their application for nanoelectronics. The size dependence of for conductor's electrical resistivity rho due to electron surface scattering is most commonly described within the framework of Fuchs and Sondheimer (FS) and their various extensions, which uses a phenomenological scattering parameter p to define the probability of electrons being elastically (i.e. specularly) scattered by the surface without causing an increase of rho at reduced size. However, a basic understanding of what surface chemistry and structure parameters determine the specularity p is still lacking. In addition, the assumption of a spherical Fermi surface in the FS model is too simple for transition metals to give accurate account of the actual surface scattering effect. The goal of this study is to develop an understanding of the physics governing electron surface/interface scattering in transition metals and to study the significance of their Fermi surface shape on surface scattering. The advancement of the scientific knowledge in electron surface and interface scattering of transition metals can provide insights into how to design high-conductivity nanowires that will facilitate the viable development of advanced integrated circuits, thermoelectric power generation and spintronics. Sequential in situ and ex situ transport measurements as a function of surface chemistry demonstrate that electron surface/interface scattering can be engineered by surface doping, causing a decrease in the rho. For instance, the rho of 9.3-nm-thick epitaxial and polycrystalline Cu is reduced by 11--13% when coated with 0.75 nm Ni. This is due to electron surface scattering which exhibits a specularity p = 0.7 for the Cu-vacuum interface that transitions to completely diffuse (p = 0) when exposed to air. In contrast, Ni-coated surfaces

  17. Dynamic effects induced transition of droplets on biomimetic superhydrophobic surfaces.

    Science.gov (United States)

    Jung, Yong Chae; Bhushan, Bharat

    2009-08-18

    Superhydrophobic surfaces have considerable technological potential for various applications because of their extreme water-repellent properties. Dynamic effects, such as the bouncing and vibration of a droplet, can destroy the composite solid-air-liquid interface. The impact pressure of a bouncing droplet and the inertia force of a vibrating droplet affect the transition from a solid-air-liquid interface to a solid-liquid interface. Therefore, it is necessary to study the dynamic effect of droplets under various system parameters (impact velocity and frequency and amplitude of vibration). A new model for the prediction of the wetting and dewetting process during droplet vibration based on the relationship between the adhesion force and the inertia force of a droplet is proposed. To investigate whether micro-, nano-, and hierarchical structures can resist the destabilizing factors responsible for the transition, a study of bouncing and vibration of a water droplet is systematically conducted on various surfaces. The physics of wetting phenomena for water droplet studies is of fundamental importance in the geometrical design of superhydrophobic surfaces.

  18. Flat surfaces and stability structures

    OpenAIRE

    2014-01-01

    We identify spaces of half-translation surfaces, equivalently complex curves with quadratic differential, with spaces of stability structures on Fukaya-type categories of punctured surfaces. This is achieved by new methods involving the complete classification of objects in these categories, which are defined in an elementary way. We also introduce a number of tools to deal with surfaces of infinite area, where structures similar to those in cluster algebra appear.

  19. High-temperature phase transitions and domain structures of KLiSO{sub 4}. Studied by polarisation-optics, X-ray topography and liquid-crystal surface decoration

    Energy Technology Data Exchange (ETDEWEB)

    Scherf, Christian; Chung, Su Jin; Hahn, Theo; Klapper, Helmut [RWTH Aachen Univ. (Germany). Inst. fuer Kristallographie; Ivanov, Nicolay R. [Russian Academy of Sciences, Moscow (Russian Federation). Shubnikov Inst. of Crystallography

    2017-07-01

    The transitions between the room temperature phase III (space group P6{sub 3}) and the two high-temperature phases II (Pcmn) and I (P6{sub 3}/mmc) of KLiSO{sub 4} and the domain structures generated by them were investigated by high-temperature polarisation optics (birefringence) and room-temperature X-ray topography, optical activity and nematic-liquid-crystal (NLC) surface decoration. The transition from the polar hexagonal phase III into the centrosymmetric orthorhombic phase II at 708 K leads, due to the loss of the trigonal axis and the radial temperature gradient of the optical heating chamber used, to a roughly hexagonal arrangement of three sets of thin orthorhombic {110} lamelleae with angles of 60 (120 ) between them. The associated twin law ''reflection m{110}{sub orth}'' corresponds to the frequent growth twin m{10 anti 10}{sub hex} of phase III. The domains are easily ferroelastically switched. Upon further heating above 949 K into phase I (P6{sub 3}/mmc) all domains vanish. Upon cooling back into phase II the three domain states related by 60 (120 ) reflections m{110}{sub orth} re-appear, however (due to the higher thermal agitation at 949 K) with a completely different domain structure consisting of many small, irregularly arranged {110}{sub orth} domains. Particular attention is paid to the domain structure of the hexagonal room temperature phase III generated during the re-transition from the orthorhombic phase II. Curiously, from the expected three twin laws inversion anti 1, rotation 2 perpendicular to [001]{sub hex} and reflection m{10 anti 10}{sub hex} only the latter, which corresponds to the frequent growth twinning, has been found. Finally a short treatise of the structural relations of the KLiSO{sub 4} high-temperature polymorphs is given.

  20. Bioinspired structured surfaces.

    Science.gov (United States)

    Bhushan, Bharat

    2012-01-24

    Nature has evolved objects with desired functionality using commonly found materials. Nature capitalizes on hierarchical structures to achieve functionality. The understanding of the functions provided by objects and processes found in nature can guide us to produce nanomaterials, nanodevices, and processes with desirable functionality. Various natural objects which provide functionality of commercial interest have been characterized to understand how a natural object provides functionality. We have modeled and fabricated structures in the lab using nature's route and developed optimum structures. Once it is understood how nature does it, optimum structures have been fabricated using smart materials and fabrication techniques. This feature article provides an overview of four topics: Lotus effect, rose petal effect, gecko feet, and shark skin.

  1. The effect of surfaces on the domain structure

    Science.gov (United States)

    Korneta, W.; Pytel, Z.

    1987-12-01

    The second-order phase transition from the paramagnetic phase to the ferromagnetic phase with domain structure in a ferromagnetic film with strong uniaxial anisotropy is studied. The easy axis is perpendicular to the surface of the film. It is assumed that the short range interactions depend on the distance to the surface. The phase diagram of the film and the form of the domain structure which occurs at the phase transition temperature are obtained.

  2. A new approach to define surface/sub-surface transition in gravel beds

    Science.gov (United States)

    Haynes, Heather; Ockelford, Anne-Marie; Vignaga, Elisa; Holmes, William

    2012-12-01

    The vertical structure of river beds varies temporally and spatially in response to hydraulic regime, sediment mobility, grain size distribution and faunal interaction. Implicit are changes to the active layer depth and bed porosity, both critical in describing processes such as armour layer development, surface-subsurface exchange processes and siltation/ sealing. Whilst measurements of the bed surface are increasingly informed by quantitative and spatial measurement techniques (e.g., laser displacement scanning), material opacity has precluded the full 3D bed structure analysis required to accurately define the surface-subsurface transition. To overcome this problem, this paper provides magnetic resonance imaging (MRI) data of vertical bed porosity profiles. Uniform and bimodal (σ g = 2.1) sand-gravel beds are considered following restructuring under sub-threshold flow durations of 60 and 960 minutes. MRI data are compared to traditional 2.5D laser displacement scans and six robust definitions of the surface-subsurface transition are provided; these form the focus of discussion.

  3. Structural Transitions in Topologically Constrained DNA

    Science.gov (United States)

    Leger, J.; Romano, G.; Sarkar, A.; Robert, J.; Bourdieu, L.; Chatenay, D.; Marko, J. F.

    2000-03-01

    We propose a theoretical explanation for results of recent single molecule micromanipulation experiments (Leger et al, PRL 83, 1066, 1999) on double-stranded DNA with fixed linking number. The topological constraint leads to novel structural transitions, including a shift of the usual 60 pN B-form to S-form transition force plateau up to a force of 100 pN when linking is fixed at zero. Our model needs five distinct states to explain the four different observed transitions. The various constant-force plateaus observed for different fixed values of linking correspond to a mixture of different pairs of states, weighted to satisfy the topological constraint. Our model allows us to conclude that sufficiently overtwisted DNA (positive linkage number) undergoes a transition from B-form DNA to a mixture of S-form and P-form DNA at a force plateau near 45 pN, and then to homogeneous P-form DNA at a force plateau near 110 pN. A similar two-step transition occurs for undertwisted DNA, and by analysing the twisting necessary to produce pure S-form DNA we conclude that the S-state has helix repeat of 38 bp. Support from the Whitaker Foundation, the NSF, the ACS-PRF and Research Corporation is gratefully acknowledged.

  4. Surface segregation energies in transition-metal alloys

    DEFF Research Database (Denmark)

    Ruban, Andrei; Skriver, Hans Lomholt; Nørskov, Jens Kehlet

    1999-01-01

    We present a database of 24 x 24 surface segregation energies of single transition metal impurities in transition-metal hosts obtained by a Green's-function linear-muffin-tin-orbitals method in conjunction with the coherent potential and atomic sphere approximations including a multipole correction...

  5. Surface Micromachined Arrays of Transition-Edge Detectors Project

    Data.gov (United States)

    National Aeronautics and Space Administration — An innovative surface micromachining technique is described for the fabrication of closely-packed arrays of transition edge sensor (TES) x-ray microcalorimeters....

  6. FAMILY STRUCTURE TRANSITIONS AND MATERNAL PARENTING STRESS

    OpenAIRE

    Cooper, Carey E.; McLanahan, Sara S.; Meadows, Sarah O.; Brooks-Gunn, Jeanne

    2009-01-01

    Data from the Fragile Families and Child Wellbeing Study (N = 4,176) are used to examine family structure transitions and maternal parenting stress. Using multilevel modeling, we find that mothers who exit coresidential relationships with biological fathers or enter coresidential relationships with nonbiological fathers report higher levels of parenting stress than mothers in stable coresidential relationships. Mothers who enter coresidential relationships with biological fathers report lower...

  7. Growth and structure of titanium dioxide on the transition metal surfaces Re(10-10) and Ru(0001); Wachstum und Struktur von Titandioxid auf den Uebergangsmetalloberflaechen Re(10-10) und Ru(0001)

    Energy Technology Data Exchange (ETDEWEB)

    Rosenthal, D.

    2007-03-15

    In this work, we studied the growth and structure of titanium dioxide films on two morphologically different transition metal surfaces, namely the trench-like rhenium(10-10) and the hexagonal ruthenium(0001). The following methods were used: X-ray photoelectron and Auger-electron spectroscopy (XPS and AES), low energy electron diffraction (LEED), low energy Helium-ion scattering (LEIS), scanning tunneling microscopy (STM) and X-ray diffraction (XRD). Titanium dioxide films on rhenium(10-10) were synthesized by co-adsorption of titanium vapor in an oxygen atmosphere up to a thickness of 500 Aa and investigated by means of LEED, LEIS, XPS and XRD. In order to calibrate the titanium flux, the growth mode of titanium on the Re(10-10) surface was determined by means of LEIS, XPS and LEED. The growth of titanium dioxide on the hexagonal ruthenium(0001) surface was investigated by means of STM, XPS and AES. Due to the alloying affinity of Ti and Ru, a titanium oxide film pre-grown at low temperature was finally/fully oxidized at elevated temperature and pressure. First experiments concerning the growth of gold on these titanium dioxide films are presented. One important result of the ongoing work is the imaging of gold clusters with 2-5 atoms in the troughs of rutile(110) beside the typically observed clusters with 3 nm diameter by STM. (orig.)

  8. Methanol Oxidation on Model Elemental and Bimetallic Transition Metal Surfaces

    DEFF Research Database (Denmark)

    Tritsaris, G. A.; Rossmeisl, J.

    2012-01-01

    Direct methanol fuel cells are a key enabling technology for clean energy conversion. Using density functional theory calculations, we study the methanol oxidation reaction on model electrodes. We discuss trends in reactivity for a set of monometallic and bimetallic transition metal surfaces, flat...... sites on the surface and to screen for novel bimetallic surfaces of enhanced activity. We suggest platinum copper surfaces as promising anode catalysts for direct methanol fuel cells....

  9. Structural phase transitions in monolayer molybdenum dichalcogenides

    Science.gov (United States)

    Choe, Duk-Hyun; Sung, Ha June; Chang, Kee Joo

    2015-03-01

    The recent discovery of two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) has provided opportunities to develop ultimate thin channel devices. In contrast to graphene, the existence of moderate band gap and strong spin-orbit coupling gives rise to exotic electronic properties which vary with layer thickness, lattice structure, and symmetry. TMDs commonly appear in two structures with distinct symmetries, trigonal prismatic 2H and octahedral 1T phases which are semiconducting and metallic, respectively. In this work, we investigate the structural and electronic properties of monolayer molybdenum dichalcogenides (MoX2, where X = S, Se, Te) through first-principles density functional calculations. We find a tendency that the semiconducting 2H phase is more stable than the metallic 1T phase. We show that a spontaneous symmetry breaking of 1T phase leads to various distorted octahedral (1T') phases, thus inducing a metal-to-semiconductor transition. We discuss the effects of carrier doping on the structural stability and the modification of the electronic structure. This work was supported by the National Research Foundation of Korea (NRF) under Grant No. NRF-2005-0093845 and Samsung Science and Technology Foundation under Grant No. SSTFBA1401-08.

  10. Characterization of monomeric intermediates during VSV glycoprotein structural transition.

    Directory of Open Access Journals (Sweden)

    Aurélie A Albertini

    2012-02-01

    Full Text Available Entry of enveloped viruses requires fusion of viral and cellular membranes, driven by conformational changes of viral glycoproteins. Crystal structures provide static pictures of pre- and post-fusion conformations of these proteins but the transition pathway remains elusive. Here, using several biophysical techniques, including analytical ultracentrifugation, circular dichroïsm, electron microscopy and small angle X-ray scattering, we have characterized the low-pH-induced fusogenic structural transition of a soluble form of vesicular stomatitis virus (VSV glycoprotein G ectodomain (G(th, aa residues 1-422, the fragment that was previously crystallized. While the post-fusion trimer is the major species detected at low pH, the pre-fusion trimer is not detected in solution. Rather, at high pH, G(th is a flexible monomer that explores a large conformational space. The monomeric population exhibits a marked pH-dependence and adopts more elongated conformations when pH decreases. Furthermore, large relative movements of domains are detected in absence of significant secondary structure modification. Solution studies are complemented by electron micrographs of negatively stained viral particles in which monomeric ectodomains of G are observed at the viral surface at both pH 7.5 and pH 6.7. We propose that the monomers are intermediates during the conformational change and thus that VSV G trimers dissociate at the viral surface during the structural transition.

  11. Exoplanet transits enable high-resolution spectroscopy across spatially resolved stellar surfaces

    CERN Document Server

    Dravins, Dainis; Dahlén, Erik; Pazira, Hiva

    2016-01-01

    Observations of stellar surfaces - except for the Sun - are hampered by their tiny angular extent, while observed spectral lines are smeared by averaging over the stellar surface, and by stellar rotation. Exoplanet transits can be used to analyze stellar atmospheric structure, yielding high-resolution spectra across spatially highly resolved stellar surfaces, free from effects of spatial smearing and the rotational wavelength broadening present in full-disk spectra. During a transit, stellar surface portions successively become hidden, and differential spectroscopy between various transit phases provides spectra of those surface segments then hidden behind the planet. The small area subtended by even a large planet (about 1% of a main-sequence star) offers high spatial resolution but demands very precise observations. We demonstrate the reconstruction of photospheric FeI line profiles at a spectral resolution R=80,000 across the surface of the solar-type star HD209458. Any detailed understanding of stellar at...

  12. Dilution in Transition Zone between Rising Plumes and Surface Plumes

    DEFF Research Database (Denmark)

    Larsen, Torben

    2004-01-01

    The papers presents some physical experiments with the dilution of sea outfall plumes with emphasize on the transition zone where the relative fast flowing vertical plume turns to a horizontal surface plume following the slow sea surface currents. The experiments show that a considerable dilution...

  13. Direct NO decomposition over stepped transition-metal surfaces

    DEFF Research Database (Denmark)

    Falsig, Hanne; Bligaard, Thomas; Christensen, Claus H.

    2007-01-01

    We establish the full potential energy diagram for the direct NO decomposition reaction over stepped transition-metal surfaces by combining a database of adsorption energies on stepped metal surfaces with known Bronsted-Evans-Polanyi (BEP) relations for the activation barriers of dissociation...

  14. Bottom Fixed Platform Dynamics Models Assessing Surface Ice Interactions for Transitional Depth Structures in the Great Lakes: FAST8 – IceDyn

    Energy Technology Data Exchange (ETDEWEB)

    Karr, Dale G. [Univ. of Michigan, Ann Arbor, MI (United States); Yu, Bingbin [Principle Power, Inc., Emeryville, CA (United States); Sirnivas, Senu [National Renewable Energy Lab. (NREL), Golden, CO (United States)

    2015-04-01

    To create long-term solutions for offshore wind turbines in a variety of environmental conditions, CAE tools are needed to model the design-driving loads that interact with an offshore wind turbine system during operation. This report describes our efforts in augmenting existing CAE tools used for offshore wind turbine analysis with a new module that can provide simulation capabilities for ice loading on the system. This augmentation was accomplished by creating an ice-loading module coupled to FAST8, the CAE tool maintained by the NREL for simulating land-based and offshore wind turbine dynamics. The new module includes both static and dynamic ice loading that can be applied during a dynamic simulation of the response of an offshore wind turbine. The ice forces can be prescribed, or influenced by the structure’s compliant response, or by the dynamics of both the structure and the ice floe. The new module covers ice failure modes of spalling, buckling, crushing, splitting, and bending. The supporting structure of wind turbines can be modeled as a vertical or sloping form at the waterline. The Inward Battered Guide Structure (IBGS) foundation designed by Keystone Engineering for the Great Lakes was used to study the ice models coupled to FAST8. The IBGS foundation ice loading simulations in FAST8 were compared to the baseline simulation case without ice loading. The ice conditions reflecting those from Lake Huron at Port Huron and Lake Michigan at North Manitou were studied under near rated wind speed of 12 m/s for the NREL 5-MW reference turbine. Simulations were performed on ice loading models 1 through 4 and ice model 6 with their respective sub-models. The purpose of ice model 5 is to investigate ice loading on sloping structures such as ice-cones on a monopile and is not suitable for multi-membered jacketed structures like the IBGS foundation. The key response parameters from the simulations, shear forces and moments from the tower base and IBGS foundation

  15. Trends in catalytic NO decomposition over transition metal surfaces

    DEFF Research Database (Denmark)

    Falsig, Hanne; Bligaard, Thomas; Rass-Hansen, Jeppe

    2007-01-01

    The formation of NOx from combustion of fossil and renewable fuels continues to be a dominant environmental issue. We take one step towards rationalizing trends in catalytic activity of transition metal catalysts for NO decomposition by combining microkinetic modelling with density functional...... theory calculations. We show specifically why the key problem in using transition metal surfaces to catalyze direct NO decomposition is their significant relative overbinding of atomic oxygen compared to atomic nitrogen....

  16. Surface structure of oriented PET films

    CERN Document Server

    Kirov, K

    2001-01-01

    crystallinity and the level of molecular orientation of the polymer are highest at the film surface and gradually decrease away from it. The same trend for an increase in structural order nearer the film surface was observed in a series of PET films drawn uniaxially in laboratory conditions. The observed strong dependence of stratification in the oriented films on drawing ratio, lead to the conclusion, that the structural gradients arise as a result of viscous flow. The molecular mechanism of stratification is discussed and leads to the idea of enhanced chain mobility at the PET film surface. The idea is in line with recent studies showing a depression of the glass transition temperature of free polymer surfaces. In addition, the results on structure formation in PET films during drawing, give support to the existing view that polymer crystallisation is assisted by a spinodal-decomposition nucleation process. Polymer films are widely used as substrates in nano-composite materials and therefore have to possess...

  17. Filling transitions on rough surfaces: inadequacy of Gaussian surface models

    CERN Document Server

    Dufour, Renaud; Herminghaus, Stephan

    2015-01-01

    We present numerical studies of wetting on various topographic substrates, including random topographies. We find good agreement with recent predictions based on an analytical interface-displacement-type theory \\cite{Herminghaus2012, Herminghaus2012a}. The phase diagrams are qualitatively as predicted, but differently in this study the critical points are found to lie within the physical parameter range (i.e., at positive contact angle) in all cases studied. Notably, it is corroborated that Gaussian random surfaces behave qualitatively different from all non-Gaussian topographies investigated, exhibiting a qualitatively different phase diagram. This shows that Gaussian random surfaces must be used with great care in the context of wetting phenomena.

  18. Wetting transitions on textured hydrophilic surfaces

    Science.gov (United States)

    Ishino, C.; Okumura, K.

    2008-04-01

    We consider the quasi-static energy of a drop on a textured hydrophilic surface, with taking the contact angle hysteresis (CAH) into account. We demonstrate how energy varies as the contact state changes from the Cassie state (in which air is trapped at the drop bottom) to the Wenzel state (in which liquid fills the texture at the drop bottom) assuming that the latter state nucleates from the center of the drop bottom. When the textured substrate is hydrophilic enough to allow spontaneous penetration of liquid film of the texture thickness, the present theory asserts that the drop develops into an experimentally observed state in which a drop looks like an egg fried without flipped over (sunny-side up) with a well-defined radius of “the egg yolk.” Otherwise, the final contact state of the drop becomes like a Wenzel state, but with the contact circle smaller than the original Wenzel state due to the CAH. We provide simple analytical estimations for the yolk radius of the “sunny-side-up” state and for the final radius of the contact circle of the pseudo-Wenzel state.

  19. Structure of the moon's surface

    CERN Document Server

    Fielder, Gilbert

    1961-01-01

    Structure of the Moon's Surface aims to assemble and marshal relevant matter, and to produce a largely unprejudiced text which brings lunar studies up to date and stresses the importance of certain features of the Moon which have frequently been disregarded in the past, largely because of lack of knowledge about them. The book contains 14 chapters organized into two parts. Part I reviews and summarizes important physical problems. These include the liberations of the moon; height determinations of points of the moon's surface; the figure of the moon; and the moon's temperature and atmosphere.

  20. Glass transition near the free surface studied by synchrotron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Sikorski, M.

    2008-06-15

    A comprehensive picture of the glass transition near the liquid/vapor interface of the model organic glass former dibutyl phthalate is presented in this work. Several surface-sensitive techniques using x-ray synchrotron radiation were applied to investigate the static and dynamic aspects of the formation of the glassy state from the supercooled liquid. The amorphous nature of dibutyl phthalate close to the free surface was confirmed by grazing incidence X-ray diffraction studies. Results from X-ray reflectivity measurements indicate a uniform electron density distribution close to the interface excluding the possibility of surface freezing down to 175 K. Dynamics on sub-{mu}m length-scales at the surface was studied with coherent synchrotron radiation via x-ray photon correlation spectroscopy. From the analysis of the dispersion relation of the surface modes, viscoelastic properties of the dibutyl phthalate are deduced. The Kelvin-Voigt model of viscoelastic media was found to describe well the properties of the liquid/vapor interface below room temperature. The data show that the viscosity at the interface matches the values reported for bulk dibutyl phthalate. The scaled relaxation rate at the surface agrees with the bulk data above 210 K. Upon approaching the glass transition temperature the free surface was observed to relax considerably faster close to the liquid/vapor interface than in bulk. The concept of higher relaxation rate at the free surface is also supported by the results of the quasielastic nuclear forward scattering experiment, during which dynamics on molecular length scales around the calorimetric glass transition temperature is studied. The data were analyzed using mode-coupling theory of the glass transition and the model of the liquid(glass)/vapor interface, predicting inhomogeneous dynamics near the surface. The quasielastic nuclear forward scattering data can be explained when the molecular mobility is assumed to decrease with the increasing

  1. Electronic Structure and Catalysis on Metal Surfaces

    Science.gov (United States)

    Greeley, Jeff; Norskov, Jens K.; Mavrikakis, Manos

    2002-10-01

    The powerful computational resources available to scientists today, together with recent improvements in electronic structure calculation algorithms, are providing important new tools for researchers in the fields of surface science and catalysis. In this review, we discuss first principles calculations that are now capable of providing qualitative and, in many cases, quantitative insights into surface chemistry. The calculations can aid in the establishment of chemisorption trends across the transition metals, in the characterization of reaction pathways on individual metals, and in the design of novel catalysts. First principles studies provide an excellent fundamental complement to experimental investigations of the above phenomena and can often allow the elucidation of important mechanistic details that would be difficult, if not impossible, to determine from experiments alone.

  2. Spectroscopic ellipsometry of SrTiO{sub 3} crystals applied to antiferrodistortive surface phase transition

    Energy Technology Data Exchange (ETDEWEB)

    Dejneka, Alexandr; Jastrabik, Lubomir [Institute of Physics ASCR, Na Slovance 2, 18221 Prague (Czech Republic); Trepakov, Vladimir [Institute of Physics ASCR, Na Slovance 2, 18221 Prague (Czech Republic); Ioffe Physiclal-Technical Institute RAS, 194 021 St-Petersburg (Russian Federation)

    2010-08-15

    This work is devoted to the ellipsometric study of antiferrodistortive (AFD) O{sub h}{sup 1}{yields} D{sub 4h}{sup 18} cubic-to-tetragonal phase transition (PT) of SrTiO{sub 3} surface. Strong influence of surface defect structure on magnitude and temperature evolutions of surface refractive index related to PT was found and investigated. It is shown that even small surface imperfections result in enhancement and strong changes of the surface refractive index when approaching the temperature of PT. This effect is caused by emergence and evolutions in the surface of the structural changes corresponding to order parameter at the temperatures sufficiently higher than transition temperature in the bulk. In the case of structurally perfect crystal surface, the features of the temperature dependence of surface refractive index appeared to be very small and visible at the temperatures a little smaller than transition temperature for bulk that agrees well with predictions of Kaganov-Omel'yanchuk theory. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  3. Patterned nonadhesive surfaces: superhydrophobicity and wetting regime transitions.

    Science.gov (United States)

    Nosonovsky, Michael; Bhushan, Bharat

    2008-02-19

    Nonadhesive and water-repellent surfaces are required for many tribological applications. We study mechanisms of wetting of patterned superhydrophobic Si surfaces, including the transition between various wetting regimes during microdroplet evaporation in environmental scanning electron microscopy (ESEM) and for contact angle and contact angle hysteresis measurements. Wetting involves interactions at different scale levels: macroscale (water droplet size), microscale (surface texture size), and nanoscale (molecular size). We propose a generalized formulation of the Wenzel and Cassie equations that is consistent with the broad range of experimental data. We show that the contact angle hysteresis involves two different mechanisms and how the transition from the metastable partially wetted (Cassie) state to the homogeneously wetted (Wenzel) state depends upon droplet size and surface pattern parameters.

  4. Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface

    Directory of Open Access Journals (Sweden)

    Vasily F. Shabanov

    2013-08-01

    Full Text Available Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface.

  5. Phase transition and surface sublimation of a mobile Potts model.

    Science.gov (United States)

    Bailly-Reyre, A; Diep, H T; Kaufman, M

    2015-10-01

    We study in this paper the phase transition in a mobile Potts model by the use of Monte Carlo simulation. The mobile Potts model is related to a diluted Potts model, which is also studied here by a mean-field approximation. We consider a lattice where each site is either vacant or occupied by a q-state Potts spin. The Potts spin can move from one site to a nearby vacant site. In order to study the surface sublimation, we consider a system of Potts spins contained in a recipient with a concentration c defined as the ratio of the number of Potts spins N(s) to the total number of lattice sites N(L)=N(x)×N(y)×N(z). Taking into account the attractive interaction between the nearest-neighboring Potts spins, we study the phase transitions as functions of various physical parameters such as the temperature, the shape of the recipient, and the spin concentration. We show that as the temperature increases, surface spins are detached from the solid phase to form a gas in the empty space. Surface order parameters indicate different behaviors depending on the distance to the surface. At high temperatures, if the concentration is high enough, the interior spins undergo a first-order phase transition to an orientationally disordered phase. The mean-field results are shown as functions of temperature, pressure, and chemical potential, which confirm in particular the first-order character of the transition.

  6. Wetting, prewetting and surface transitions in type-I superconductors

    Science.gov (United States)

    Indekeu, J. O.; van Leeuwen, J. M. J.

    1995-02-01

    Within the Ginzburg-Landau theory, which is quantitatively correct for classical superconductors, it is shown that a type-I superconductor can display an interface delocalization or “wetting” transition, in which a macroscopically thick superconducting layer intrudes from the surface into the bulk normal phase. The condition for this transition to occur is that the superconducting order parameter | ψ| 2 is enhanced at the surface. This corresponds to a negative surface extrapolation length b. The wetting transition takes place at bulk two-phase coexistence of normal and superconducting phases, at a temperature TD below the critical temperature Tc, and at magnetic field HD = Hc( TD). The field is applied parallel to the surface. Surprisingly, the order of the wetting transition is controlled by a bulk material constant, the Ginzburg-Landau parameter κ. This is very unusual, since in other systems (fluids, Ising magnets,…) the order of the wetting transition depends on surface parameters that are difficult to determine or control. For superconductors, first-order wetting is predicted for 0 ≤ κ wetting for 0.374 wetting, the prewetting extension is also found. Unlike in standard wetting problems, the prewetting line does not terminate at a critical point but changes from first to second order at a tricritical point. Twinning-plane superconductivity (TPS) is reinterpreted as a prewetting phenomenon. The possibility of critical wetting in superconductors is especially interesting because this phenomenon has largely eluded experimental verification in any system until now. Furthermore, superconductors provide a realization of wetting in systems with short-range (exponentially decaying) interactions. This is very different from the usual long-range (algebraically decaying) interactions, such as van der Waals forces, and has important consequences for the wetting characteristics.

  7. (Electronic structure and reactivities of transition metal clusters)

    Energy Technology Data Exchange (ETDEWEB)

    1992-01-01

    The following are reported: theoretical calculations (configuration interaction, relativistic effective core potentials, polyatomics, CASSCF); proposed theoretical studies (clusters of Cu, Ag, Au, Ni, Pt, Pd, Rh, Ir, Os, Ru; transition metal cluster ions; transition metal carbide clusters; bimetallic mixed transition metal clusters); reactivity studies on transition metal clusters (reactivity with H{sub 2}, C{sub 2}H{sub 4}, hydrocarbons; NO and CO chemisorption on surfaces). Computer facilities and codes to be used, are described. 192 refs, 13 figs.

  8. Noncollinear magnetism in surfaces and interfaces of transition metals

    Energy Technology Data Exchange (ETDEWEB)

    Tan, Huahai

    2009-09-15

    Noncollinear (NC) magnetism is common in nature, especially when there exist geometrical frustration and chemical imparity in the system. In this work we studied the NC magnetism and the response to external magnetic fields in surfaces and interfaces of transition metals by using an semi-empirical tight-binding (TB) method that parameterized to the ab initio TB-LMTO calculations. We implemented this method to study two systems. The first one is the system of 6 Mn monolayers on Fe(001) substrate. Due to the complex structure and magnetic properties of Mn, we found 23 collinear magnetic configurations but only one NC configuration. The collinear ground state has a layered antiferromagnetic (AFM) coupling which agrees with previous experiments and calculations. In the NC configuration the local AFM coupling in the Mn layers is preserved, but the surface is 90 degree coupled to the substrate. Similar to the experiment in CdCr{sub 2}O{sub 4}, we obtained a collinear plateau in the NC evolution of the average magnetic moment in Mn slab under external magnetic fields. Another is the system of a Cr monolayer on a stepped Fe(001) substrate. As expected, the local AFM coupling in the interface of Cr and Fe are preserved. However, the edge Cr atoms is about 90 coupled to their nearest Fe neighbors. We also simulated the procedure of adding more Cr coverages gradually to a Cr bilayer coverage. As coverages increase, the magnetic moments in the Cr interface reduce, and the collinear plateau becomes wider as coverages increase. However, the saturation fields in both the two systems are extremely high, around 10 kT.We expect that when the effect of temperature is taken into account, and in some proper systems, the saturation fields could be largely reduced to the scale that can be implemented in experiment, and our study may shed light on information storage devices with ultrahigh storage density. (orig.)

  9. 微纳复合结构表面稳定润湿状态及转型过程的热力学分析∗%Thermo dynamic analysis of stable wetting states and wetting transition of micro/nanoscale structured surface

    Institute of Scientific and Technical Information of China (English)

    2015-01-01

    Superhydrophobicity of biological surfaces with micro/nanoscale hierarchical roughness has recently been given great attention and widely reported in many experimental studies due to the unique wettability. For example, the dual-scale structure of the lotus leaf not only shows high contact angle and low contact angle hysteresis but also presents good stability and mechanical properties. Though lots of experimental studies on the wettability of artificial hierarchical rough surface have been carried out, a thorough analysis on the contribution of micro- and nano-scaled roughness to the metastable wetting states and their transition is still lack. In this paper, a thermodynamic approach is applied to analyze all the wetting states (including four stable wetting states and five transition states) of a water droplet on a surface with micro/nanoscale hierarchical roughness, and the corresponding free energy expressions and apparent contact angle equations are deduced. The stable wetting states are confirmed by the principle of minimum free energy. And the calculated results by these state equations can fit well with the experimental results reported in the literature when compared with the previous models. Meanwhile, the influence of micro/nanoscale roughness on the stable wetting states and metastable-stable transition has been analyzed thermodynamically. It is found that there is a synergistic effect of micro and nanoscale roughness on wettability, which nlay result in many different wetting states. There are four wetting states during increasing relative pitch of a microscaled structure at a given nanoscaled structure, but two wetting states can be obtained as increasing relative pitch of nanoscaled structure at a given microscaled structure. The change of nondimensional energy and nondimensional energy barrier in the metastable-stable transition process of water droplet wetting micro and nanoscaled structure is quantitatively analyzed. Results indicate that the

  10. Pressure-driven magnetic and structural transitions in the 122-pnictides

    Science.gov (United States)

    Widom, Michael; Quader, Khandker

    2014-03-01

    Pnictides of the family AFe2As2, where A is an alkali earth element, exhibit several phase transitions in their structure and magnetic order as functions of applied pressure. We employ density functional theory total energy calculations at T=0K to model these transitions for the entire set of alkali earths (A=Ca, Sr, Ba, Ra) which form the 122 family. Three distinct types of transition occur: an enthalpic transition in which the striped antiferromagnetic orthorhombic (OR-AFM) phase swaps thermodynamic stability with a competing tetragonal phase; a magnetic transition in which the OR-AFM phase loses its magnetism and orthorhombicity; a lattice parameter anomaly in which the tetragonal c-axis collapses. We identify this last transition as a ``Lifshitz transition'' caused by a change in Fermi surface topology. Depending on the element A, the tetragonal state exhibiting the Lifthitz transition might be metastable (A=Ca) or stable (A=Sr, Ba and Ra).

  11. Pressure-induced structural transition of nonionic micelles

    Indian Academy of Sciences (India)

    V K Aswal; R Vavrin; J Kohlbrecher; A G Wagh

    2008-11-01

    We report dynamic light scattering and small angle neutron scattering studies of the pressure-induced structural transition of nonionic micelles of surfactant polyoxyethylene 10 lauryl ether (C12E10) in the pressure range 0 to 2000 bar. Measurements have been performed on 1 wt% C12E10 in aqueous solution with and without the addition of KF. Micelles undergo sphere to lamellar structural transitions as the pressure is increased. On addition of KF, rod-like micelles exist at ambient pressure, which results in rod-like to lamellar structural transition at a much lower pressure in the presence of KF. Micellar structural transitions have been observed to be reversible.

  12. Evolution of material surfaces in the temporal transition in channel flow

    CERN Document Server

    Zhao, Yaomin; Chen, Shiyi

    2016-01-01

    We report a Lagrangian study on the evolution of material surfaces in the K-type temporal transitional channel flow. Based on the Eulerian velocity field from the DNS, a backward-particle-tracking method is applied to solve the transport equation of the Lagrangian scalar field, and then the iso-surfaces of the Lagrangian field can be extracted as material surfaces in the evolution. Three critical issues for Lagrangian investigations on the evolution of coherent structures using material surfaces are addressed. First, the initial scalar field is uniquely determined based on proposed criteria, so that the initial material surfaces can be approximated as vortex surfaces, and keep invariant in the initial laminar state. Second, the evolution of typical material surfaces initially from different wall distances is presented, and then the influential material surface with the maximum deformation is identified. Large vorticity variations with the maximum curvature growth of vortex lines are also observed on this surf...

  13. Surface analysis of transition metal oxalates: Damage aspects

    Energy Technology Data Exchange (ETDEWEB)

    Chenakin, S.P., E-mail: chenakin@imp.kiev.ua [Université Libre de Bruxelles (ULB), Chimie-Physique des Matériaux, B-1050 Bruxelles (Belgium); Institute of Metal Physics, Nat. Acad. Sci. of Ukraine, Akad. Vernadsky Blvd. 36, 03680 Kiev (Ukraine); Szukiewicz, R. [Université Libre de Bruxelles (ULB), Chimie-Physique des Matériaux, B-1050 Bruxelles (Belgium); Barbosa, R.; Kruse, N. [Université Libre de Bruxelles (ULB), Chimie-Physique des Matériaux, B-1050 Bruxelles (Belgium); Voiland School of Chemical Engineering and Bioengineering, Washington State University, 155 Wegner Hall, Pullman, WA 99164-6515 (United States)

    2016-05-15

    Highlights: • Gas evolution from the Mn, Co, Ni and Cu oxalate hydrates in vacuum, during exposure to X-rays and after termination of X-ray irradiation is studied. • A comparative study of the damage caused by X-rays in NiC{sub 2}O{sub 4} and CuC{sub 2}O{sub 4} is carried out. • Effect of Ar{sup +} bombardment on the structure and composition of CoC{sub 2}O{sub 4} is studied. - Abstract: The behavior of transition metal oxalates in vacuum, under X-ray irradiation and low-energy Ar{sup +} ion bombardment was studied. A comparative mass-spectrometric analysis was carried out of gas evolution from the surface of Mn, Co, Ni and Cu oxalate hydrates in vacuum, during exposure to X-rays and after termination of X-ray irradiation. The rates of H{sub 2}O and CO{sub 2} liberation from the oxalates were found to be in an inverse correlation with the temperatures of dehydration and decomposition, respectively. X-ray photoelectron spectroscopy (XPS) was employed to study the X-ray induced damage in NiC{sub 2}O{sub 4} and CuC{sub 2}O{sub 4} by measuring the various XP spectral characteristics and surface composition of the oxalates as a function of time of exposure to X-rays. It was shown that Cu oxalate underwent a significantly faster degradation than Ni oxalate and demonstrated a high degree of X-ray induced reduction from the Cu{sup 2+} to the Cu{sup 1+} chemical state. 500 eV Ar{sup +} sputter cleaning of CoC{sub 2}O{sub 4} for 10 min was found to cause a strong transformation of the oxalate structure which manifested itself in an appreciable alteration of the XP core-level and valence band spectra. The analysis of changes in stoichiometry and comparison of XP spectra of bombarded oxalate with respective spectra of a reference carbonate CoCO{sub 3} implied that the bombardment-induced decomposition of CoC{sub 2}O{sub 4} gave rise to the formation of CoO-like and disordered CoCO{sub 3}-like phases.

  14. Minimum action transition paths connecting minima on an energy surface

    Science.gov (United States)

    Koehl, Patrice

    2016-11-01

    Dynamics is essential to the biological functions of many bio-molecules, yet our knowledge of dynamics remains fragmented. Experimental techniques for studying bio-molecules either provide high resolution information on static conformations of the molecule or provide low-resolution, ensemble information that does not shed light on single molecule dynamics. In parallel, bio-molecular dynamics occur at time scale that are not yet attainable through detailed simulation methods. These limitations are especially noticeable when studying transition paths. To address this issue, we report in this paper two methods that derive meaningful trajectories for proteins between two of their conformations. The first method, MinActionPath, uses approximations of the potential energy surface for the molecule to derive an analytical solution of the equations of motion related to the concept of minimum action path. The second method, RelaxPath, follows the same principle of minimum action path but implements a more sophisticated potential, including a mixed elastic potential and a collision term to alleviate steric clashes. Using this new potential, the equations of motion cannot be solved analytically. We have introduced a relaxation method for solving those equations. We describe both the theories behind the two methods and their implementations, focusing on the specific techniques we have used that make those implementations amenable to study large molecular systems. We have illustrated the performance of RelaxPath on simple 2D systems. We have also compared MinActionPath and RelaxPath to other methods for generating transition paths on a well suited test set of large proteins, for which the end points of the trajectories as well as an intermediate conformation between those end points are known. We have shown that RelaxPath outperforms those other methods, including MinActionPath, in its ability to generate trajectories that get close to the known intermediates. We have also shown

  15. Minimum action transition paths connecting minima on an energy surface.

    Science.gov (United States)

    Koehl, Patrice

    2016-11-14

    Dynamics is essential to the biological functions of many bio-molecules, yet our knowledge of dynamics remains fragmented. Experimental techniques for studying bio-molecules either provide high resolution information on static conformations of the molecule or provide low-resolution, ensemble information that does not shed light on single molecule dynamics. In parallel, bio-molecular dynamics occur at time scale that are not yet attainable through detailed simulation methods. These limitations are especially noticeable when studying transition paths. To address this issue, we report in this paper two methods that derive meaningful trajectories for proteins between two of their conformations. The first method, MinActionPath, uses approximations of the potential energy surface for the molecule to derive an analytical solution of the equations of motion related to the concept of minimum action path. The second method, RelaxPath, follows the same principle of minimum action path but implements a more sophisticated potential, including a mixed elastic potential and a collision term to alleviate steric clashes. Using this new potential, the equations of motion cannot be solved analytically. We have introduced a relaxation method for solving those equations. We describe both the theories behind the two methods and their implementations, focusing on the specific techniques we have used that make those implementations amenable to study large molecular systems. We have illustrated the performance of RelaxPath on simple 2D systems. We have also compared MinActionPath and RelaxPath to other methods for generating transition paths on a well suited test set of large proteins, for which the end points of the trajectories as well as an intermediate conformation between those end points are known. We have shown that RelaxPath outperforms those other methods, including MinActionPath, in its ability to generate trajectories that get close to the known intermediates. We have also shown

  16. Instantons and surface tension at a first-order transition

    Science.gov (United States)

    Gupta, Sourendu

    1994-04-01

    We study the dynamics of the first-order phase transition in the two-dimensional 15-state Potts model, both at and off equilibrium. We find that phase changes take place through nucleation in both cases, and finite volume effects are described well through an instanton computation. Thus a dynamical measurement of the surface tension is possible. We find that the order-disorder surface tension is compatible with perfect wetting. An accurate treatment of fluctuations about the instanton solution is seen to be of great importance. Current Address: Theory Group, TIFR, Homi Bhabha Road, Bombay 400005, India.

  17. Surface structure of AU3Cu(001)

    DEFF Research Database (Denmark)

    Eckstein, G.A.; Maupai, S.; Dakkouri, A.S.

    1999-01-01

    The surface morphology, composition, and structure of Au3Cu(001) as determined by scanning tunneling microscopy and surface x-ray diffraction are presented. Atomic resolution STM images reveal distinctive geometric features. The analysis of the surface x-ray diffraction data provides clear evidence...... for the surface structure. [S0163-1829(99)04535-X]....

  18. LEED STUDY OF NAXWO3 TUNGSTEN BRONZE - STRUCTURAL RELAXATION OF A PEROVSKITE SURFACE

    NARCIS (Netherlands)

    PEACOR, SD; HIBMA, T

    1993-01-01

    We have performed a low energy electron diffraction study of the sodium tungsten bronze, NaxWO3, x = 0.8, surface. Temperature dependent changes of both polished and cleaved surfaces indicate structural phase transitions of the surface structure, and reflect the general trend in structural phase tra

  19. Phase transition of a symmetric diblock copolymer induced by nanorods with different surface chemistry

    Science.gov (United States)

    Guo, Yu-qi; Pan, Jun-xing; Sun, Min-na; Zhang, Jin-jun

    2017-01-01

    We investigate the phase transition of a symmetric diblock copolymer induced by nanorods with different surface chemistry. The results demonstrate that the system occurs the phase transition from a disordered structure to ordered parallel lamellae and then to the tilted layered structure as the number of rods increases. The dynamic evolution of the domain size and the order parameter of the microstructure are also examined. Furthermore, the influence of rod property, rod-phase interaction, rod-rod interaction, rod length, and polymerization degree on the behavior of the polymer system is also investigated systematically. Moreover, longer amphiphilic nanorods tend to make the polymer system form the hexagonal structure. It transforms into a perpendicular lamellar structure as the polymerization degree increases. Our simulations provide an efficient method for determining how to obtain the ordered structure on the nanometer scales and design the functional materials with optical, electronic, and magnetic properties.

  20. Universal wetting transition of an evaporating water droplet on superhydrophobic surfaces

    Science.gov (United States)

    Tsai, Peichun Amy; Bussonnière, Adrien; Bigdeli, Masoud; Chueh, Di-Yen; Liu, Qingxia; Chen, Peilin

    2016-11-01

    An evaporating water droplet on a superhydrophobic surface undergoes a wetting transition from a heterogeneous wetting (Cassie-Baxter) to homogeneous wetting (Wenzel) state. The critical transition is manifested by a sudden decrease of contact angle, when "Fakir" water drop permeates the minute hydrophobic cavities. This breakdown of superhydrophobicity would hinder various applications of self-cleaning, low-frictional, and potentially ice-phobic properties of superhydrophobic materials. In this work, we experimentally investigate such wetting transition using hydrophobic nanostructures. With a theoretical model, we find a universal criterion of the critical contact angle at the transition point. The prediction of critical contact angle, which solely depends on the geometrical parameters of the hydrophobic pillars, agree well with various data for both micro- and nano-structures.

  1. Utilizing dynamic tensiometry to quantify contact angle hysteresis and wetting state transitions on nonwetting surfaces.

    Science.gov (United States)

    Kleingartner, Justin A; Srinivasan, Siddarth; Mabry, Joseph M; Cohen, Robert E; McKinley, Gareth H

    2013-11-05

    Goniometric techniques traditionally quantify two parameters, the advancing and receding contact angles, that are useful for characterizing the wetting properties of a solid surface; however, dynamic tensiometry, which measures changes in the net force on a surface during the repeated immersion and emersion of a solid into a probe liquid, can provide further insight into the wetting properties of a surface. We detail a framework for analyzing tensiometric results that allows for the determination of wetting hysteresis, wetting state transitions, and characteristic topographical length scales on textured, nonwetting surfaces, in addition to the more traditional measurement of apparent advancing and receding contact angles. Fluorodecyl POSS, a low-surface-energy material, was blended with commercially available poly(methyl methacrylate) (PMMA) and then dip- or spray-coated onto glass substrates. These surfaces were probed with a variety of liquids to illustrate the effects of probe liquid surface tension, solid surface chemistry, and surface texture on the apparent contact angles and wetting hysteresis of nonwetting surfaces. Woven meshes were then used as model structured substrates to add a second, larger length scale for the surface texture. When immersed into a probe liquid, these spray-coated mesh surfaces can form a metastable, solid-liquid-air interface on the largest length scale of surface texture. The increasing hydrostatic pressure associated with progressively greater immersion depths disrupts this metastable, composite interface and forces penetration of the probe liquid into the mesh structure. This transition is marked by a sudden change in the wetting hysteresis, which can be systematically probed using spray-coated, woven meshes of varying wire radius and spacing. We also show that dynamic tensiometry can accurately and quantitatively characterize topographical length scales that are present on microtextured surfaces.

  2. Generic folding and transition hierarchies for surface adsorption of hydrophobic-polar lattice model proteins

    Science.gov (United States)

    Li, Ying Wai; Wüst, Thomas; Landau, David P.

    2013-01-01

    The thermodynamic behavior and structural properties of hydrophobic-polar (HP) lattice proteins interacting with attractive surfaces are studied by means of Wang-Landau sampling. Three benchmark HP sequences (48mer, 67mer, and 103mer) are considered with different types of surfaces, each of which attract either all monomers, only hydrophobic (H) monomers, or only polar (P) monomers, respectively. The diversity of folding behavior in dependence of surface strength is discussed. Analyzing the combined patterns of various structural observables, such as, e.g., the derivatives of the numbers of surface contacts, together with the specific heat, we are able to identify generic categories of folding and transition hierarchies. We also infer a connection between these transition categories and the relative surface strengths, i.e., the ratio of the surface attractive strength to the interchain attraction among H monomers. The validity of our proposed classification scheme is reinforced by the analysis of additional benchmark sequences. We thus believe that the folding hierarchies and identification scheme are generic for HP proteins interacting with attractive surfaces, regardless of chain length, sequence, or surface attraction.

  3. X-Ray Studies of Phase Transitions on Surfaces

    DEFF Research Database (Denmark)

    Als-Nielsen, Jens Aage

    1984-01-01

    The density variation across the surface from vapor to liquid in liquid crystal materials has been measured in the isotropic, nematic and smectic A phases by specular reflection of X rays with grazing angles from θc to θB (total reflection angle and Bragg angle for smectic A layering, respectively......) using synchroton X-rays in HASYLAB, Hamburg. Crystalline surface structures may be deduced from X-ray diffraction, utilizing the evanescent beam occuring for grazing angles less than θc to obtain surface sensitivity. Results from the reconstruction of Au(110) surface are reviewed....

  4. Structural Transitions of Solvent-Free Oligomer-Grafted Nanoparticles

    KAUST Repository

    Chremos, Alexandros

    2011-09-01

    Novel structural transitions of solvent-free oligomer-grafted nanoparticles are investigated by using molecular dynamics simulations of a coarse-grained bead-spring model. Variations in core size and grafting density lead to self-assembly of the nanoparticles into a variety of distinct structures. At the boundaries between different structures, the nanoparticle systems undergo thermoreversible transitions. This structural behavior, which has not been previously reported, deviates significantly from that of simple liquids. The reversible nature of these transitions in solvent-free conditions offers new ways to control self-assembly of nanoparticles at experimentally accessible conditions. © 2011 American Physical Society.

  5. On real structures on rigid surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Kulikov, Vik S [Steklov Mathematical Institute, Russian Academy of Sciences (Russian Federation); Kharlamov, V M [Institut de Recherche Matematique Avanee Universite Louis Pasteur et CNRS 7 rue Rene Descartes (France)

    2002-02-28

    We construct examples of rigid surfaces (that is, surfaces whose deformation class consists of a unique surface) with a particular behaviour with respect to real structures. In one example the surface has no real structure. In another it has a unique real structure, which is not maximal with respect to the Smith-Thom inequality. These examples give negative answers to the following problems: the existence of real surfaces in each deformation class of complex surfaces, and the existence of maximal real surfaces in every complex deformation class that contains real surfaces. Moreover, we prove that there are no real surfaces among surfaces of general type with p{sub g}=q=0 and K{sup 2}=9. These surfaces also provide new counterexamples to the 'Dif = Def' problem.

  6. Super water repellent surface 'strictly' mimicking the surface structure of lotus leaf

    Energy Technology Data Exchange (ETDEWEB)

    Cha, Tae Gon; Kim, Ho Young [Seoul National University, Seoul (Korea, Republic of); Yi, Jin Woo; Lee, Kwang Ryeol; Moon, Myoung Woon [Korea Advanced Institute of Science and Technology, Daejeon (Korea, Republic of)

    2009-07-01

    To achieve the hierarchy of roughness as observed in lotus leaves, most artificial water-repellent surfaces have nano-asperities on top of micropillars. However, observation of real lotus leaves through SEM reveals that nonoscale roughness covers the entire surface including the base as well as bumps. Thus we fabricate surfaces having the same hierarchical roughness structure as the lotus leaf by forming nanopillars on both micropillars and base. We compare the measures of water-repellency (static contact angle, contact angle hysteresis, and transition pressure between the Cassie and Wenzel states) of the lotus-like surface with those of surfaces having single micro- and nano- roughness. The results show that nanoscale roughness covering entire surface area leads to superior water-repellency to other surface roughness structures. We also give a theoretical consideration of this observation.

  7. Surface structure of polymer Gels and emerging functions

    CERN Document Server

    Kobiki, Y

    1999-01-01

    We report the surface structure of polymer gels on a submicrometer scale during the volume phase transition. Sponge-like domains with a mesoscopic scale were directly observed in water by using at atomic force microscope (AFM). The surface structure characterized by the domains is discussed in terms of the root-mean-square roughness and the auto-correlation function, which were calculated from the AFM images. In order to demonstrate the role of surface structure in determining the macroscopic properties of film-like poly (N-isopropylacrylamide: NIPA) gels. It was found that the temperature dependence, as well as the absolute values of the static contact angle, were strongly dependent on the bulk network inhomogeneities. The relation between the mesoscopic structure and the macroscopic properties is qualitatively discussed in terms of not only the changes in the chemical, but also in the physical, surface properties of the NIPA gels in response to a temperature change.

  8. Atomic and molecular adsorption on transition-metal carbide (111) surfaces from density-functional theory: a trend study of surface electronic factors

    DEFF Research Database (Denmark)

    Vojvodic, Aleksandra; Ruberto, C.; Lundqvist, Bengt

    2010-01-01

    This study explores atomic and molecular adsorption on a number of early transition-metal carbides (TMCs) in NaCl structure by means of density-functional theory calculations. The investigated substrates are the TM-terminated TMC(111) surfaces, of interest because of the presence of different types......, surface relaxations, Bader charges, and surface-localized densities of states (DOSs). Detailed comparisons between surface and bulk DOSs reveal the existence of transition-metal localized SRs (TMSRs) in the pseudogap and of several C-localized SRs (CSRs) in the upper valence band on all considered TMC(111......C, delta-MoC, TaC, and WC (in NaCl structure) and the adsorbates H, B, C, N, O, F, NH, NH2, and NH3. Trends in adsorption strength are explained in terms of surface electronic factors, by correlating the calculated adsorption-energy values with the calculated surface electronic structures. The results...

  9. The Role of Structure in the Protein Dynamical Transition

    CERN Document Server

    He, Yunfen

    2008-01-01

    The protein dynamical transition is investigated as a function of protein structure using terahertz time domain spectroscopy (THz-TDS). Measurements performed for native state and denatured hen egg white lysozyme (HEWL) show that protein structure is not necessary for the dynamical transition. We find the temperature dependence follows activated behavior and there is no evidence of a fragile to strong transition. Measurements of short chain poly alanine show a dynamical transition down to penta-alanine, however no transition is observed for di-alanine or tri-alanine. These measurements demonstrate that the temperature dependence arises strictly from the interaction of the side chains with the solvent. The lack of a transition for shorter chain polypeptides may indicate the temperature dependence arises from a net ordering of the adjacent water which scales with the length of the polypeptide chain.

  10. Surface immobilization of antibody on silk fibroin through conformational transition.

    Science.gov (United States)

    Lu, Qiang; Wang, Xiaoqin; Zhu, Hesun; Kaplan, David L

    2011-07-01

    In recent studies silk fibroin has been explored as a new material platform for biosensors. Based on these developments, a procedure for the immobilization of antibodies on silk fibroin substrates was developed as a route to functionalizing these biosensor systems. By controlling the conformational transition of the silk fibroin, a primary antibody was immobilized and enriched at the surface of silk fibroin substrates under mild reaction conditions to maintain antibody function. Compared to chemical crosslinking, the immobilization efficiency in the present approach was increased significantly. This method, achieving high loading of antibody while retaining function, improves the feasibility of silk fibroin as a platform material for biosensor applications.

  11. Surface tension in the cold and dense chiral transition and astrophysical applications

    CERN Document Server

    Palhares, L F

    2011-01-01

    The surface tension of cold and dense QCD phase transitions has appeared recently as a key ingredient in different astrophysical scenarios, ranging from core-colapse supernovae explosions to compact star structure. If the surface tension is low enough, observable consequences are possible. Its value is however not known from first-principle methods in QCD, calling for effective approaches. Working within the framework of homogeneous nucleation by Langer, we discuss the steps that are needed to obtain the nucleation parameters from a given effective potential. As a model for deriving the effective potential for the chiral transition, we adopt the linear sigma model with constituent quarks at very low temperatures, which provides an effective description for the thermodynamics of the strong interaction in cold and dense matter, and predict a surface tension of Sigma ~ 5--15 MeV/fm^2, well below previous estimates. Including temperature effects and vacuum logarithmic corrections, we find a clear competition betw...

  12. Existence of topological nontrivial surface states in strained transition metals: W, Ta, Mo, and Nb

    Science.gov (United States)

    Thonig, Danny; Rauch, Tomáš; Mirhosseini, Hossein; Henk, Jürgen; Mertig, Ingrid; Wortelen, Henry; Engelkamp, Bernd; Schmidt, Anke B.; Donath, Markus

    2016-10-01

    We show that a series of transition metals with strained body-centered cubic lattice—W, Ta, Nb, and Mo—hosts surface states that are topologically protected by mirror symmetry and, thus, exhibits nonzero topological invariants. These findings extend the class of topologically nontrivial systems by topological crystalline transition metals. The investigation is based on calculations of the electronic structures and of topological invariants. The signatures of a Dirac-type surface state in W(110), e.g., the linear dispersion and the spin texture, are verified. To further support our prediction, we investigate Ta(110) both theoretically and experimentally by spin-resolved inverse photoemission: unoccupied topologically nontrivial surface states are observed.

  13. Problem of phase transitions in nuclear structure

    Energy Technology Data Exchange (ETDEWEB)

    Scharff-Goldhaber, G

    1980-01-01

    Phase transitions between rotational and vibrational nuclei are discussed from the point of view of the variable moment of inertia model. A three-dimensional plot of the ground-state moments of inertia of even-even nuclei vs N and Z is shown. 3 figures. (RWR)

  14. The Structural Phase Transition in Octaflournaphtalene

    DEFF Research Database (Denmark)

    Mackenzie, Gordon A.; Arthur, J. W.; Pawley, G. S.

    1977-01-01

    The phase transition in octafluoronaphthalene has been investigated by Raman scattering and neutron powder diffraction. The weight of the experimental evidence points to a unit cell doubling in the a direction, but with no change in space group symmetry. Lattice dynamics calculations support...

  15. The Meaning of Surface Structure and Deep Structure to Translation

    Institute of Scientific and Technical Information of China (English)

    罗源

    2014-01-01

    Surface structure and deep structure first come up with by Chomsky is an innovative action in linguistics. Despite the arguments involved around surface structure and deep structure, it is instructional to English-Chinese translation to some degree and its scientific connotation is meaningful to deepen language study and construct related disciplinary both in theory and practice.

  16. Influence of magnetic fields on structural martensitic transitions

    Energy Technology Data Exchange (ETDEWEB)

    Lashley, J C [Los Alamos National Laboratory; Cooley, J C [Los Alamos National Laboratory; Smith, J L [Los Alamos National Laboratory; Fisher, R A [NON LANL; Modic, K A [Los Alamos National Laboratory; Yang, X- D [TEMPLE UNIV; Riseborough, P S [TEMPLE UNIV.; Opeil, C P [BOSTON COLLEGE; Finlayson, T R [UNIV OF MELBOURNE; Goddard, P A [UNIV OF OXFORD; Silhanek, A V [INPAC

    2009-01-01

    We show evidence that a structural martensitic transition is related to significant changes in the electronic structure, as revealed in thermodynamic measurements made in high-magnetic fields. The magnetic field dependence is considered unusual as many influential investigations of martensitic transitions have emphasized that the structural transitions are primarily lattice dynamical and are driven by the entropy due to the phonons. We provide a theoretical framework which can be used to describe the effect of magnetic field on the lattice dynamics in which the field dependence originates from the dielectric constant.

  17. Locally homogeneous structures on Hopf surfaces

    CERN Document Server

    McKay, Benjamin

    2009-01-01

    We study holomorphic locally homogeneous geometric structures modelled on line bundles over the projective line. We classify these structures on primary Hopf surfaces. We write out the developing map and holonomy morphism of each of these structures explicitly on each primary Hopf surface.

  18. Tuning Wettability and Adhesion of Structured Surfaces

    Science.gov (United States)

    Badge, Ila

    Structured surfaces with feature size ranging from a few micrometers down to nanometers are of great interest in the applications such as design of anti-wetting surfaces, tissue engineering, microfluidics, filtration, microelectronic devices, anti-reflective coatings and reversible adhesives. A specific surface property demands particular roughness geometry along with suitable surface chemistry. Plasma Enhanced Chemical Vapor Deposition (PECVD) is a technique that offers control over surface chemistry without significantly affecting the roughness and thus, provides a flexibility to alter surface chemistry selectively for a given structured surface. In this study, we have used PECVD to fine tune wetting and adhesion properties. The research presented focuses on material design aspects as well as the fundamental understanding of wetting and adhesion phenomena of structured surfaces. In order to study the effect of surface roughness and surface chemistry on the surface wettability independently, we developed a model surface by combination of colloidal lithography and PECVD. A systematically controlled hierarchical roughness using spherical colloidal particles and surface chemistry allowed for quantitative prediction of contact angles corresponding to metastable and stable wetting states. A well-defined roughness and chemical composition of the surface enabled establishing a correlation between theory predictions and experimental measurements. We developed an extremely robust superhydrophobic surface based on Carbon-Nanotubes (CNT) mats. The surface of CNTs forming a nano-porous mesh was modified using PECVD to deposit a layer of hydrophobic coating (PCNT). The PCNT surface thus formed is superhydrophobic with almost zero contact angle hysteresis. We demonstrated that the PCNT surface is not wetted under steam condensation even after prolonged exposure and also continues to retain its superhydrophobicity after multiple frosting-defrosting cycles. The anti

  19. Rheological characteristics of soft rock structural surface

    Institute of Scientific and Technical Information of China (English)

    陈沅江; 吴超; 傅衣铭

    2008-01-01

    There are two mechanisms of the coarse surface asperity resistance effect and rubbing resistance effect in the course of the soft rock structural surface creep,of which the former plays a dominant role in hindering the deformation in the starting creep phase,so that the structural surface creep usually displays the strong surface roughness effect,and so does the latter when the asperities in the coarse surface were fractured by shearing.Under the low stress condition,there are only two phases of the decelerating creep and the constant creep for the soft rock structural surface,and as the stress increases and overcomes the rubbing resistance,the accelerating creep failure of the structural surface will happen suddenly.Therefore,a multiple rheological model,which combines the nonlinear NEWTON body(NN) of a certain mass and the empirical plastic body(EM) with the classical SAINT VENANT body,NEWTON body,KELVIN body and HOOKE body,could be used to comprehensively describe the creep characteristics of the soft rock structural surface.Its mechanical parameter values will vary owing to the different surface roughness of the structural surface.The parameters of GH,GK and ηL are positively linearly correlative to the surface roughness.The surface roughness and m are negative exponential function correlation.The long-term strength τS is positively correlative to the surface roughness.

  20. Exotic geometric structures on Kodaira surfaces

    CERN Document Server

    McKay, Benjamin

    2012-01-01

    On all compact complex surfaces (modulo finite unramified coverings), we classify all of the locally homogeneous geometric structures which are locally isomorphic to the exotic homogeneous surfaces of Lie.

  1. Surface energy exchanges along a tundra-forest transition and feedbacks to climate

    Science.gov (United States)

    Beringer, J.; Chapin, F. S.; Thompson, Catharine Copass; McGuire, A.D.

    2005-01-01

    Surface energy exchanges were measured in a sequence of five sites representing the major vegetation types in the transition from arctic tundra to forest. This is the major transition in vegetation structure in northern high latitudes. We examined the influence of vegetation structure on the rates of sensible heating and evapotranspiration to assess the potential feedbacks to climate if high-latitude warming were to change the distribution of these vegetation types. Measurements were made at Council on the Seward Peninsula, Alaska, at representative tundra, low shrub, tall shrub, woodland (treeline), and boreal forest sites. Structural differences across the transition from tundra to forest included an increase in the leaf area index (LAI) from 0.52 to 2.76, an increase in canopy height from 0.1 to 6.1 m, and a general increase in canopy complexity. These changes in vegetation structure resulted in a decrease in albedo from 0.19 to 0.10 as well as changes to the partitioning of energy at the surface. Bulk surface resistance to water vapor flux remained virtually constant across sites, apparently because the combined soil and moss evaporation decreased while transpiration increased along the transect from tundra to forest. In general, sites became relatively warmer and drier along the transect with the convective fluxes being increasingly dominated by sensible heating, as evident by an increasing Bowen ratio from 0.94 to 1.22. The difference in growing season average daily sensible heating between tundra and forest was 21 W m-2. Fluxes changed non-linearly along the transition, with both shrubs and trees substantially enhancing heat transfer to the atmosphere. These changes in vegetation structure that increase sensible heating could feed back to enhance warming at local to regional scales. The magnitude of these vegetation effects on potential high-latitude warming is two to three times greater than suggested by previous modeling studies. ?? 2005 Elsevier B.V. All

  2. Quantum Theory of Hyperfine Structure Transitions in Diatomic Molecules.

    Science.gov (United States)

    Klempt, E.; And Others

    1979-01-01

    Described is an advanced undergraduate laboratory experiment in which radio-frequency transitions between molecular hyperfine structure states may be observed. Aspects of the quantum theory applied to the analysis of this physical system, are discussed. (Authors/BT)

  3. Metallic layered composite materials produced by explosion welding: Structure, properties, and structure of the transition zone

    Science.gov (United States)

    Mal'tseva, L. A.; Tyushlyaeva, D. S.; Mal'tseva, T. V.; Pastukhov, M. V.; Lozhkin, N. N.; Inyakin, D. V.; Marshuk, L. A.

    2014-10-01

    The structure, morphology, and microhardness of the transition zone in multilayer metallic composite joints are studied, and the cohesion strength of the plates to be joined, the mechanical properties of the formed composite materials, and fracture surfaces are analyzed. The materials to be joined are plates (0.1-1 mm thick) made of D16 aluminum alloy, high-strength maraging ZI90-VI (03Kh12N9K4M2YuT) steel, BrB2 beryllium bronze, and OT4-1 titanium alloy. Composite materials made of different materials are shown to be produced by explosion welding. The dependence of the interface shape (smooth or wavelike) on the physicomechanical properties of the materials to be joined is found. The formation of a wavelike interface is shown to result in the formation of intense-mixing regions in transition zones. Possible mechanisms of layer adhesion are discussed.

  4. Rydberg and π-π* transitions in film surfaces of various kinds of nylons studied by attenuated total reflection far-ultraviolet spectroscopy and quantum chemical calculations: peak shifts in the spectra and their relation to nylon structure and hydrogen bondings.

    Science.gov (United States)

    Morisawa, Yusuke; Yasunaga, Manaka; Sato, Harumi; Fukuda, Ryoichi; Ehara, Masahiro; Ozaki, Yukihiro

    2014-10-09

    Attenuated total reflection far-ultraviolet (ATR-FUV) spectra in the 145-260 nm region were measured for surfaces (thickness 50-200 nm) of various kinds of nylons in cast films to explore their electronic transitions in the FUV region. ATR-FUV spectra show two major bands near 150 and 200 nm in the surface condensed phase of nylons. Transmittance (Tr) spectra were also observed in particular for the analysis of valence excitations. Time-dependent density functional theory (TD-DFT/CAM-B3LYP) calculations were carried out using the model systems to provide the definitive assignments of their absorption spectra and to elucidate their peak shifts in several nylons, in particular, focusing on their crystal alignment structures and intermolecular hydrogen bondings. Two major bands of nylon films near 150 and 200 nm are characterized as σ-Rydberg 3p and π-π* transitions of nylons, respectively. These assignments are also coherent with those of liquid n-alkanes (n = 5-14) and liquid amides observed previously. The Rydberg transitions are delocalized over the hydrocarbon chains, while the π-π* transitions are relatively localized at the amide group. Differences in the peak positions and intensity were found in both ATR- and Tr-FUV spectra for different nylons. A red-shift of the π-π* amide band in the FUV spectra of nylon-6 and nylon-6/6 models in α-form is attributed to the crystal structure pattern and the intermolecular hydrogen bondings, which result in the different delocalization character of the π-π* transitions and transition dipole coupling.

  5. Structural transition of FeSe under high pressure

    Institute of Scientific and Technical Information of China (English)

    Li Wei; Chen Jun-Fang; He Qin-Yu; Wang Teng; Pan Zhong-Liang

    2011-01-01

    The density functional calculations of the energy band structure and density of state for the tetragonal PbO-type phase α-FeSe and hexagonal NiAs-type phase β-FeSe are reported in this paper. The structural phase transition from tetragonal to hexagonal FeSe under high pressure is investigated, it is found that the calculated transition pressure for the α→β phase transformation is 8.5 GPa. Some fluctuations in the transition pressure maybe occurred by different external factors such as temperature and stress condition. There is about 17% volume collapse accompanying the α→β phase transformation.

  6. Structural Transitions of a Twisted and Stretched DNA Molecule

    Science.gov (United States)

    Léger, J. F.; Romano, G.; Sarkar, A.; Robert, J.; Bourdieu, L.; Chatenay, D.; Marko, J. F.

    1999-08-01

    We report results of a micromanipulation study of single double-helical DNA molecules at forces up to 150 pN. Depending on whether the DNA winding is allowed to relax, or held fixed, qualitatively different structural transitions are observed. By studying the transitions as a function of winding the different DNA structures underlying them are characterized; this allows us to report the first estimate of S-DNA helicity. A model is introduced to describe these transitions; in addition to B-DNA, we find that four DNA states are needed to describe the experiments.

  7. Cooperative structural transitions in amyloid-like aggregation

    Science.gov (United States)

    Steckmann, Timothy; Bhandari, Yuba R.; Chapagain, Prem P.; Gerstman, Bernard S.

    2017-04-01

    Amyloid fibril aggregation is associated with several horrific diseases such as Alzheimer's, Creutzfeld-Jacob, diabetes, Parkinson's, and others. Although proteins that undergo aggregation vary widely in their primary structure, they all produce a cross-β motif with the proteins in β-strand conformations perpendicular to the fibril axis. The process of amyloid aggregation involves forming myriad different metastable intermediate aggregates. To better understand the molecular basis of the protein structural transitions and aggregation, we report on molecular dynamics (MD) computational studies on the formation of amyloid protofibrillar structures in the small model protein ccβ, which undergoes many of the structural transitions of the larger, naturally occurring amyloid forming proteins. Two different structural transition processes involving hydrogen bonds are observed for aggregation into fibrils: the breaking of intrachain hydrogen bonds to allow β-hairpin proteins to straighten, and the subsequent formation of interchain H-bonds during aggregation into amyloid fibrils. For our MD simulations, we found that the temperature dependence of these two different structural transition processes results in the existence of a temperature window that the ccβ protein experiences during the process of forming protofibrillar structures. This temperature dependence allows us to investigate the dynamics on a molecular level. We report on the thermodynamics and cooperativity of the transformations. The structural transitions that occurred in a specific temperature window for ccβ in our investigations may also occur in other amyloid forming proteins but with biochemical parameters controlling the dynamics rather than temperature.

  8. Phase transitions in antiferromagnets with a NaCl structure

    Energy Technology Data Exchange (ETDEWEB)

    Kassan-Ogly, F.A. [Institute of Metal Physics, Ural Division, Russian Academy of Sciences, ul. S.Kovalevskoi 18, Ekaterinburg 620219 (Russian Federation)]. E-mail: felix.kassan-ogly@imp.uran.ru; Filippov, B.N. [Institute of Metal Physics, Ural Division, Russian Academy of Sciences, ul. S.Kovalevskoi 18, Ekaterinburg 620219 (Russian Federation)

    2006-05-15

    A revised derivation scheme of possible magnetic structures in an FCC lattice with the nearest- and next-nearest-neighbor interactions taken into account is proposed. A model of simultaneous magnetic and structural phase transitions of the first order is developed for antiferromagnets with a NaCl structure and with a strong cubic magnetic anisotropy on the base of synthesis of magnetic modified 6-state Potts model and theoretical models of structural phase transitions in cubic crystals. It is shown that the high-temperature diffuse magnetic scattering of neutrons transforms into magnetic Bragg reflections below Neel point.

  9. Phase transitions in antiferromagnets with a NaCl structure

    Science.gov (United States)

    Kassan-Ogly, F. A.; Filippov, B. N.

    2006-05-01

    A revised derivation scheme of possible magnetic structures in an FCC lattice with the nearest- and next-nearest-neighbor interactions taken into account is proposed. A model of simultaneous magnetic and structural phase transitions of the first order is developed for antiferromagnets with a NaCl structure and with a strong cubic magnetic anisotropy on the base of synthesis of magnetic modified 6-state Potts model and theoretical models of structural phase transitions in cubic crystals. It is shown that the high-temperature diffuse magnetic scattering of neutrons transforms into magnetic Bragg reflections below Néel point.

  10. The local structure of transition metal doped semiconducting boron carbides

    Energy Technology Data Exchange (ETDEWEB)

    Liu Jing; Dowben, P A [Department of Physics and Astronomy and the Nebraska Center for Materials and Nanoscience, Behlen Laboratory of Physics, University of Nebraska-Lincoln, PO Box 880111, Lincoln, NE 68588-0111 (United States); Luo Guangfu; Mei Waining [Department of Physics, University of Nebraska at Omaha, Omaha, NE 68182-0266 (United States); Kizilkaya, Orhan [J. Bennett Johnston Sr. Center for Advanced Microstructures and Devices, Louisiana State University, 6980 Jefferson Hwy., Baton Rouge LA 70806 (United States); Shepherd, Eric D; Brand, J I [College of Engineering, and the Nebraska Center for Materials and Nanoscience, N209 Walter Scott Engineering Center, 17th and Vine Streets, University of Nebraska-Lincoln, Lincoln, NE 68588-0511 (United States)

    2010-03-03

    Transition metal doped boron carbides produced by plasma enhanced chemical vapour deposition of orthocarborane (closo-1,2-C{sub 2}B{sub 10}H{sub 12}) and 3d metal metallocenes were investigated by performing K-edge extended x-ray absorption fine structure and x-ray absorption near edge structure measurements. The 3d transition metal atom occupies one of the icosahedral boron or carbon atomic sites within the icosahedral cage. Good agreement was obtained between experiment and models for Mn, Fe and Co doping, based on the model structures of two adjoined vertex sharing carborane cages, each containing a transition metal. The local spin configurations of all the 3d transition metal doped boron carbides, Ti through Cu, are compared using cluster and/or icosahedral chain calculations, where the latter have periodic boundary conditions.

  11. Post-perovskite Transition in Anti-structure.

    Science.gov (United States)

    Wang, Bosen; Ohgushi, Kenya

    2016-11-30

    The discovery of the post-perovskite transition, which is the structural transition from the perovskite to post-perovskite structure in MgSiO3 under pressure, has aroused great interests in geosciences. Despite of previous extensive studies, key factors of the post-perovsktie transition are still under hot debate primarily due to the big difficulty in performing systematic experiments under extreme conditions. Hence, search for new materials showing the post-perovskite transition under ambient pressure has been highly expected. We here report a new-type of materials Cr3AX (A = Ga, Ge; X = C, N), which exhibits the post-perovskite transition as a function of "chemical pressure" at ambient physical pressure. The detailed structural analysis indicates that the tolerance factor, which is the measure of the ionic radius mismatch, plays the key role in the post-perovskite transition. Moreover, we found a tetragonal perovskite structure with loss of inversion symmetry between the cubic perovskite and orthorhombic post-perovskite structures. This finding stimulates a search for a ferroelectric state in MgSiO3.

  12. Post-perovskite Transition in Anti-structure

    Science.gov (United States)

    Wang, Bosen; Ohgushi, Kenya

    2016-11-01

    The discovery of the post-perovskite transition, which is the structural transition from the perovskite to post-perovskite structure in MgSiO3 under pressure, has aroused great interests in geosciences. Despite of previous extensive studies, key factors of the post-perovsktie transition are still under hot debate primarily due to the big difficulty in performing systematic experiments under extreme conditions. Hence, search for new materials showing the post-perovskite transition under ambient pressure has been highly expected. We here report a new-type of materials Cr3AX (A = Ga, Ge; X = C, N), which exhibits the post-perovskite transition as a function of “chemical pressure” at ambient physical pressure. The detailed structural analysis indicates that the tolerance factor, which is the measure of the ionic radius mismatch, plays the key role in the post-perovskite transition. Moreover, we found a tetragonal perovskite structure with loss of inversion symmetry between the cubic perovskite and orthorhombic post-perovskite structures. This finding stimulates a search for a ferroelectric state in MgSiO3.

  13. A comparative DFT study of the catalytic activity of the 3d transition metal sulphides surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Gomez-Balderas, R. (Depto de F& amp; #237; s. y Qu& amp; #237; m. Te& amp; #243; rica. Edif. B, Fac. de Qu& amp; #237; mica, UNAM ); Oviedo-Roa, R (Instituto Mexicano del Petroleo); Martinez-Magadan, J M.(Instituto Mexicano del Petroleo); Amador, C. (Depto de F& amp; #237; s. y Qu& amp; #237; m. Te& amp; #243; rica. Edif. B, Fac. de Qu& amp; #237; mica, UNAM ); Dixon, David A.(BATTELLE (PACIFIC NW LAB))

    2002-10-10

    The catalytic activity of the first transition metal series sulphides for hydrodesulfurization (HDS) reactions exhibits a particular behaviour when analysed as a function of the metal position in the Periodic Table. This work reports a comparative study of the electronic structure of the bulk and of the (0 0 1) metal surface (assumed to be the reactive surface) for the Sc-Zn monosulphides. The systems were modeled using the NiAs prototype crystal structure for the bulk and by applying the supercell model with seven atomic layers for (0 0 1) surfaces. The electronic structure of closed-packed solids code based on the density-functional theory and adopting the muffin-tin approximation to the potential was employed in the calculations of the electronic properties. For the Co and Ni sulphides, the density of states (DOS) variations between the metal atom present in the bulk and the ones exposed at the surface show that at the surface, there exists a higher DOS in the occupied states region just below the Fermi level. This feature might indicate a good performance of these two metal sulphides substrates in the HDS reactions favouring a donation, back-donation mechanism. In contrast, the DOS at the surface of Mn is increased in the unoccupied states region, just above the Fermi level. This suggests the possibility of a strong interaction with charge dontating sulphur adsorbate atoms poisoning the active substrate surface.

  14. Moulding of Sub-micrometer Surface Structures

    DEFF Research Database (Denmark)

    Pranov, Henrik; Rasmussen, Henrik K.; Larsen, Niels Bent

    2006-01-01

    The experiments strongly suggest that the possibility to injection mould sub-micrometer surface structures in polymers mainly relates to the forces originating from the adhesive energy between polymer and shim.......The experiments strongly suggest that the possibility to injection mould sub-micrometer surface structures in polymers mainly relates to the forces originating from the adhesive energy between polymer and shim....

  15. Evidence for water structuring forces between surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Stanley, Christopher B [ORNL; Rau, Dr. Donald [National Institutes of Health

    2011-01-01

    Structured water on apposing surfaces can generate significant energies due to reorganization and displacement as the surfaces encounter each other. Force measurements on a multitude of biological structures using the osmotic stress technique have elucidated commonalities that point toward an underlying hydration force. In this review, the forces of two contrasting systems are considered in detail: highly charged DNA and nonpolar, uncharged hydroxypropyl cellulose. Conditions for both net repulsion and attraction, along with the measured exclusion of chemically different solutes from these macromolecular surfaces, are explored and demonstrate features consistent with a hydration force origin. Specifically, the observed interaction forces can be reduced to the effects of perturbing structured surface water.

  16. Modeling of laser induced periodic surface structures

    NARCIS (Netherlands)

    Skolski, J.Z.P.; Römer, G.R.B.E.; Huis in 't Veld, A.J.; Mitko, V.S.; Obona, J.V.; Ocelik, V.; Hosson, J.T.M. de

    2010-01-01

    In surfaces irradiated by short laser pulses, Laser Induced Periodic Surface Structures (LIPSS) have been observed on all kind of materials for over forty years. These LIPSS, also referred to as ripples, consist of wavy surfaces with periodicity equal or smaller than the wavelength of the laser radi

  17. Insight into Structural Phase Transitions from Density Functional Theory

    Science.gov (United States)

    Ruzsinszky, Adrienn

    2014-03-01

    Structural phase transitions caused by high pressure or temperature are very relevant in materials science. The high pressure transitions are essential to understand the interior of planets. Pressure or temperature induced phase transitions can be relevant to understand other phase transitions in strongly correlated systems or molecular crystals.Phase transitions are important also from the aspect of method development. Lower level density functionals, LSDA and GGAs all fail to predict the lattice parameters of different polymorphs and the phase transition parameters at the same time. At this time only nonlocal density functionals like HSE and RPA have been proved to resolve the geometry-energy dilemma to some extent in structural phase transitions. In this talk I will report new results from the MGGA_MS family of meta-GGAs and give an insight why this type of meta-GGAs can give a systematic improvement of the geometry and phase transition parameters together. I will also present results from the RPA and show a possible way to improve beyond RPA.

  18. Topological transitions of the Fermi surface of osmium under pressure: an LDA+DMFT study

    Science.gov (United States)

    Feng, Qingguo; Ekholm, Marcus; Tasnádi, Ferenc; Jönsson, H. Johan M.; Abrikosov, Igor A.

    2017-03-01

    The influence of pressure on the electronic structure of Os has attracted substantial attention recently due to reports on isostructural electronic transitions in this metal. Here, we theoretically investigate the Fermi surface of Os from ambient to high pressure, using density functional theory combined with dynamical mean field theory. We provide a detailed discussion of the calculated Fermi surface and its dependence on the level of theory used for the treatment of the electron–electron interactions. Although we confirm that Os can be classified as weakly correlated metal, the inclusion of local quantum fluctuations between 5{{d}} electrons beyond the local density approximation explains the most recent experimental reports regarding the occurrence of electronic topological transitions in Os.

  19. Surface order-disorder phase transitions and percolation

    CERN Document Server

    Gimenez, M Cecilia; Ramirez-Pastor, Antonio J

    2008-01-01

    In the present paper, the connection between surface order-disorder phase transitions and the percolating properties of the adsorbed phase has been studied. For this purpose, four lattice-gas models in presence of repulsive interactions have been considered. Namely, monomers on honeycomb, square and triangular lattices, and dimers (particles occupying two adjacent adsorption sites) on square substrates. By using Monte Carlo simulation and finite-size scaling analysis, we obtain the percolation threshold $\\theta_c$ of the adlayer, which presents an interesting dependence with $w/k_BT$ (being $w$, $k_B$ and $T$, the lateral interaction energy, the Boltzmann's constant and temperature, respectively). For each geometry and adsorbate size, a phase diagram separating a percolating and a non-percolating region is determined.

  20. Effect of point defects and disorder on structural phase transitions

    Energy Technology Data Exchange (ETDEWEB)

    Toulouse, J.

    1997-06-01

    Since the beginning in 1986, the object of this project has been Structural Phase Transitions (SPT) in real as opposed to ideal materials. The first stage of the study has been centered around the role of Point Defects in SPT`s. Our intent was to use the previous knowledge we had acquired in the study of point defects in non-transforming insulators and apply it to the study of point defects in insulators undergoing phase transitions. In non-transforming insulators, point defects, in low concentrations, marginally affect the bulk properties of the host. It is nevertheless possible by resonance or relaxation methods to study the point defects themselves via their local motion. In transforming solids, however, close to a phase transition, atomic motions become correlated over very large distances; there, even point defects far removed from one another can undergo correlated motions which may strongly affect the transition behavior of the host. Near a structural transition, the elastic properties win be most strongly affected so as to either raise or decrease the transition temperature, prevent the transition from taking place altogether, or simply modify its nature and the microstructure or domain structure of the resulting phase. One of the well known practical examples is calcium-stabilized zirconia in which the high temperature cubic phase is stabilized at room temperature with greatly improved mechanical properties.

  1. BEP-relations for N2 dissociation over stepped transition metal and alloy surfaces

    DEFF Research Database (Denmark)

    Fronczek-Munter, Ture Rønved; Bligaard, Thomas; Christensen, Claus H.

    2008-01-01

    We present density functional theory (DFT) calculations for N(2) dissociation on stepped face-centred cubic (211) surface slabs. By using the same crystal structure, the same adsorption site for atomic nitrogen, and the same transition-state bond length of N(2) over a range of pure metal surfaces...... is a general electronic structure effect, and that geometric effects are responsible for the scatter which is normally observed around the BEP line. The BEP relation is also shown to be valid for both surface and bulk alloys. The scatter is, however, larger than for the pure elements. This can be understood...... as a larger geometrical variance. To analyze the accuracy of the DFT calculations a detailed convergence study is performed for several adsorbates on stepped hexagonal close-packed and face-centred cubic Ru slabs....

  2. Transition State Structure of RNA Depurination by Saporin L3.

    Science.gov (United States)

    Yuan, Hongling; Stratton, Christopher F; Schramm, Vern L

    2016-05-20

    Saporin L3 from the leaves of the common soapwort is a catalyst for hydrolytic depurination of adenine from RNA. Saporin L3 is a type 1 ribosome inactivating protein (RIP) composed only of a catalytic domain. Other RIPs have been used in immunotoxin cancer therapy, but off-target effects have limited their development. In the current study, we use transition state theory to understand the chemical mechanism and transition state structure of saporin L3. In favorable cases, transition state structures guide the design of transition state analogues as inhibitors. Kinetic isotope effects (KIEs) were determined for an A14C mutant of saporin L3. To permit KIE measurements, small stem-loop RNAs that contain an AGGG tetraloop structure were enzymatically synthesized with the single adenylate bearing specific isotopic substitutions. KIEs were measured and corrected for forward commitment to obtain intrinsic values. A model of the transition state structure for depurination of stem-loop RNA (5'-GGGAGGGCCC-3') by saporin L3 was determined by matching KIE values predicted via quantum chemical calculations to a family of intrinsic KIEs. This model indicates saporin L3 displays a late transition state with the N-ribosidic bond to the adenine nearly cleaved, and the attacking water nucleophile weakly bonded to the ribosyl anomeric carbon. The transition state retains partial ribocation character, a feature common to most N-ribosyl transferases. However, the transition state geometry for saporin L3 is distinct from ricin A-chain, the only other RIP whose transition state is known.

  3. Crystal-Size-Dependent Structural Transitions in Nanoporous Crystals: Adsorption-Induced Transitions in ZIF-8

    KAUST Repository

    Zhang, Chen

    2014-09-04

    © 2014 American Chemical Society. Understanding the crystal-size dependence of both guest adsorption and structural transitions of nanoporous solids is crucial to the development of these materials. We find that nano-sized metal-organic framework (MOF) crystals have significantly different guest adsorption properties compared to the bulk material. A new methodology is developed to simulate the adsorption and transition behavior of entire MOF nanoparticles. Our simulations predict that the transition pressure significantly increases with decreasing particle size, in agreement with crystal-size-dependent experimental measurements of the N2-ZIF-8 system. We also propose a simple core-shell model to examine this effect on length scales that are inaccessible to simulations and again find good agreement with experiments. This study is the first to examine particle size effects on structural transitions in ZIFs and provides a thermodynamic framework for understanding the underlying mechanism.

  4. Structural Transitions and Aggregation in Amyloidogenic Proteins

    Science.gov (United States)

    Steckmann, Timothy; Chapagain, Prem; Gerstman, Bernard; Computational and Theoretical Biophysics Group at Florida International University Team

    2014-03-01

    Amyloid fibrils are a common component in many debilitating human neurological diseases such as Alzheimer's and Parkinson's. A detailed molecular-level understanding of the formation process of amyloid fibrils is crucial for developing methods to slow down or prevent these horrific diseases. Alpha-helix to beta-sheet structural transformation is commonly observed in the process of fibril formation. We performed replica-exchange molecular dynamics simulations of structural transformations in an engineered model peptide cc-beta. Several sets of simulations with different number of cc-beta monomers were considered. Conversion of alpha-helix monomers to beta strands and the aggregation of beta strand monomers into sheets were analyzed as a function of the system size. Hydrogen bond analysis was performed and the beta-aggregate structures were characterized by a nematic order parameter.

  5. Numerical simulation of condensation on structured surfaces.

    Science.gov (United States)

    Fu, Xiaowu; Yao, Zhaohui; Hao, Pengfei

    2014-11-25

    Condensation of liquid droplets on solid surfaces happens widely in nature and industrial processes. This phase-change phenomenon has great effect on the performance of some microfluidic devices. On the basis of micro- and nanotechnology, superhydrophobic structured surfaces can be well-fabricated. In this work, the nucleating and growth of droplets on different structured surfaces are investigated numerically. The dynamic behavior of droplets during the condensation is simulated by the multiphase lattice Boltzmann method (LBM), which has the ability to incorporate the microscopic interactions, including fluid-fluid interaction and fluid-surface interaction. The results by the LBM show that, besides the chemical properties of surfaces, the topography of structures on solid surfaces influences the condensation process. For superhydrophobic surfaces, the spacing and height of microridges have significant influence on the nucleation sites. This mechanism provides an effective way for prevention of wetting on surfaces in engineering applications. Moreover, it suggests a way to prevent ice formation on surfaces caused by the condensation of subcooled water. For hydrophilic surfaces, however, microstructures may be submerged by the liquid films adhering to the surfaces. In this case, microstructures will fail to control the condensation process. Our research provides an optimized way for designing surfaces for condensation in engineering systems.

  6. Optically induced structural phase transitions in ion Coulomb crystals

    DEFF Research Database (Denmark)

    Horak, Peter; Dantan, Aurelien Romain; Drewsen, Michael

    2012-01-01

    , such as body-centered cubic and face-centered cubic, can be suppressed by a proper choice of the potential depth and periodicity. Furthermore, by varying the harmonic trap parameters and/or the optical potential in time, controlled transitions between crystal structures can be obtained with close to unit......We investigate numerically the structural dynamics of ion Coulomb crystals confined in a three-dimensional harmonic trap when influenced by an additional one-dimensional optically induced periodical potential. We demonstrate that transitions between thermally excited crystal structures...

  7. Structures and transitions in tungsten grain boundaries

    Energy Technology Data Exchange (ETDEWEB)

    Frolov, T. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Zhu, Q. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Marian, J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Rudd, R. E. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2017-02-07

    The objective of this study is to develop a computational methodology to predict structure, energies of tungsten grain boundaries as a function of misorientation and inclination. The energies and the mobilities are the necessary input for thermomechanical model of recrystallization of tungsten for magnetic fusion applications being developed by the Marian Group at UCLA.

  8. [Oligoglycine surface structures: molecular dynamics simulation].

    Science.gov (United States)

    Gus'kova, O A; Khalatur, P G; Khokhlov, A R; Chinarev, A A; Tsygankova, S V; Bovin, N V

    2010-01-01

    The full-atomic molecular dynamics (MD) simulation of adsorption mode for diantennary oligoglycines [H-Gly4-NH(CH2)5]2 onto graphite and mica surface is described. The resulting structure of adsorption layers is analyzed. The peptide second structure motives have been studied by both STRIDE (structural identification) and DSSP (dictionary of secondary structure of proteins) methods. The obtained results confirm the possibility of polyglycine II (PGII) structure formation in diantennary oligoglycine (DAOG) monolayers deposited onto graphite surface, which was earlier estimated based on atomic-force microscopy measurements.

  9. An absorbing phase transition from a structured active particle phase

    Energy Technology Data Exchange (ETDEWEB)

    Lopez, Cristobal [Instituto Mediterraneo de Estudios Avanzados IMEDEA (CSIC-UIB), Campus de la Universidad de las Islas Baleares, E-07122 Palma de Mallorca (Spain); Ramos, Francisco [Departamento de Electromagnetismo y Fisica de la Materia and Instituto de Fisica Teorica y Computacional Carlos I, Facultad de Ciencias, Universidad de Granada, 18071 Granada (Spain); Hernandez-GarcIa, Emilio [Instituto Mediterraneo de Estudios Avanzados IMEDEA (CSIC-UIB), Campus de la Universidad de las Islas Baleares, E-07122 Palma de Mallorca (Spain)

    2007-02-14

    In this work we study the absorbing state phase transition of a recently introduced model for interacting particles with neighbourhood-dependent reproduction rates. The novelty of the transition is that as soon as the active phase is reached by increasing a control parameter a periodically arranged structure of particle clusters appears. A numerical study in one and two dimensions shows that the system falls into the directed percolation universality class.

  10. Structure and functions of fungal cell surfaces

    Science.gov (United States)

    Nozawa, Y.

    1984-01-01

    A review with 24 references on the biochemistry, molecular structure, and function of cell surfaces of fungi, especially dermatophytes: the chemistry and structure of the cell wall, the effect of polyene antibiotics on the morphology and function of cytoplasmic membranes, and the chemical structure and function of pigments produced by various fungi are discussed.

  11. Structural transitions in condensed colloidal virus phases

    Science.gov (United States)

    Schmidt, Nathan; Barr, Steve; Udit, Andrew; Gutierrez, Leonardo; Nguyen, Thanh; Finn, M. G.; Luijten, Erik; Wong, Gerard

    2010-03-01

    Analogous to monatomic systems colloidal phase behavior is entirely determined by the interaction potential between particles. This potential can be tuned using solutes such as multivalent salts and polymers with varying affinity for the colloids to create a hierarchy of attractions. Bacteriophage viruses are a naturally occurring type of colloidal particle with characteristics difficult to achieve by laboratory synthesis. They are monodisperse, nanometers in size, and have heterogeneous surface charge distributions. We use the MS2 and Qbeta bacteriophages (diameters 27-28nm) to understand the interplay between different attraction mechanisms on nanometer-sized colloids. Small Angle X-ray Scattering (SAXS) is used to characterize the inter-particle interaction between colloidal viruses using several polymer species and different salt types.

  12. Surface-plasmons lasing in double-graphene-layer structures

    Energy Technology Data Exchange (ETDEWEB)

    Dubinov, A. A. [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Institute for Physics of Microstructures of Russian Academy of Sciences, and Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation); Aleshkin, V. Ya. [Institute for Physics of Microstructures of Russian Academy of Sciences, and Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation); Ryzhii, V. [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Center for Photonics and Infrared Engineering, Bauman Moscow State Technical University, Moscow 105005 (Russian Federation); Shur, M. S. [Department of Electrical, Electronics, and System Engineering, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Otsuji, T. [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan)

    2014-01-28

    We consider the concept of injection terahertz lasers based on double-graphene-layer (double-GL) structures with metal surface-plasmon waveguide and study the conditions of their operation. The laser under consideration exploits the resonant radiative transitions between GLs. This enables the double-GL laser room temperature operation and the possibility of voltage tuning of the emission spectrum. We compare the characteristics of the double-GL lasers with the metal surface-plasmon waveguides with those of such laser with the metal-metal waveguides.

  13. Structural phase transitions in boron carbide under stress

    Science.gov (United States)

    Korotaev, P.; Pokatashkin, P.; Yanilkin, A.

    2016-01-01

    Structural transitions in boron carbide B4C under stress were studied by means of first-principles molecular dynamics in the framework of density functional theory. The behavior depends strongly on degree of non-hydrostatic stress. Under hydrostatic stress continuous bending of the three-atom C-B-C chain was observed up to 70 GPa. The presence of non-hydrostatic stress activates abrupt reversible chain bending, which is displacement of the central boron atom in the chain with the formation of weak bonds between this atom and atoms in the nearby icosahedra. Such structural change can describe a possible reversible phase transition in dynamical loading experiments. High non-hydrostatic stress achieved in uniaxial loading leads to disordering of the initial structure. The formation of carbon chains is observed as one possible transition route.

  14. Theory of magnetic transition metal nanoclusters on surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Lounis, S.

    2007-04-17

    This thesis is motivated by the quest for the understanding and the exploration of complex magnetism provided by atomic scale magnetic clusters deposited on surfaces or embedded in the bulk. Use is made of the density functional theory (DFT). Acting within this framework, we have developed and implemented the treatment of non-collinear magnetism into the Juelich version of the full-potential Korringa-Kohn-Rostoker Green Function (KKR-GF) method. Firstly, the method was applied to 3d transition-metal clusters on different ferromagnetic surfaces. Different types of magnetic clusters where selected. In order to investigate magnetic frustration due to competing interactions within the ad-cluster we considered a (001) oriented surface of fcc metals, a topology which usually does not lead to non-collinear magnetism. We tuned the strength of the magnetic coupling between the ad-clusters and the ferromagnetic surface by varying the substrate from the case of Ni(001) with a rather weak hybridization of the Ni d-states with the adatom d-states to the case of Fe{sub 3ML}/Cu(001) with a much stronger hybridization due to the larger extend of the Fe wavefunctions. On Ni(001), the interaction between the Cr- as well as the Mn-dimer adatoms is of antiferromagnetic nature, which is in competition with the interaction with the substrate atoms. After performing total energy calculations we find that for Cr-dimer the ground state is collinear whereas the Mn-dimer prefers the non-collinear configuration as ground state. Bigger clusters are found to be magnetically collinear. These calculations were extended to 3d multimers on Fe{sub 3ML}/Cu(001). All neighboring Cr(Mn) moments in the compact tetramer are antiferromagnetically aligned in-plane, with the directions slightly tilted towards (outwards from) the substrate to gain some exchange interaction energy. The second type of frustration was investigated employing a Ni(111) surface, a surface with a triangular lattice of atoms, were

  15. a Monte Carlo Study of Carbon Monoxide Layers Adsorbed on Ionic Substrates:. Structures and Phase Transitions

    Science.gov (United States)

    Vu, Ngoc-Thanh; Jack, David B.

    We have studied the order-disorder phase transitions of carbon monoxide layers adsorbed on sodium chloride and lithium flouride substrates using the Metropolis Monte Carlo method. The simulations have been performed in the temperature range from 5 K to 60 K. At low temperature and monolayer coverage, both of these systems form ordered phases which disorder as the temperature is increased. The transition temperature (Tc) is between 30 K and 35 K for CO/NaCl, and from 40 K to 45 K for CO/LiF. Below Tc, both systems have an ordered p(2 × 1) type structure due to correlated azimuthal orientations. Above Tc, both systems undergo a phase transition to an azimuthally disordered p(1 × 1) structure, i.e. one with no preferred orientation in the surface plane. The heat capacity shows a characteristic divergence at the transition temperature. Coverages of less than a monolayer of the CO/NaCl system have also been studied. The CO molecules are found to aggregate and form islands with an ordered structure in the middle of the islands. These islands also undergo an order-disorder transition but at lower temperatures. Multilayer systems were found to destabilize the p(2 × 1) structure of the bottommost layer in favor of a p(1 × 1) structure with the upper layers adopting the bulk structure.

  16. Electric controlling of surface metal-insulator transition in the doped BaTiO3 film

    Science.gov (United States)

    Xun, Wei; Hao, Xiang; Pan, Tao; Zhong, Jia-Lin; Ma, Chun-Lan; Hou, Fang; Wu, Yin-Zhong

    2017-07-01

    Based on first-principles calculations, the BaTiO3(BTO) film with local La-doping is studied. For a selected concentration and position of doping, the surface metal-insulator transition occurs under the applied electric field, and the domain appears near the surface for both bipolar states. Furthermore, for the insulated surface state, i.e., the downward polarization state in the doped film, the gradient bandgap structure is achieved, which favors the absorption of solar energy. Our investigation can provide an alternative avenue in modification of surface property and surface screening effect in polar materials.

  17. Electric controlling of surface metal-insulator transition in the doped BaTiO3 film

    Directory of Open Access Journals (Sweden)

    Wei Xun

    2017-07-01

    Full Text Available Based on first-principles calculations, the BaTiO3(BTO film with local La-doping is studied. For a selected concentration and position of doping, the surface metal-insulator transition occurs under the applied electric field, and the domain appears near the surface for both bipolar states. Furthermore, for the insulated surface state, i.e., the downward polarization state in the doped film, the gradient bandgap structure is achieved, which favors the absorption of solar energy. Our investigation can provide an alternative avenue in modification of surface property and surface screening effect in polar materials.

  18. Structural Transitions in Supercoiled Stretched DNA

    Science.gov (United States)

    v, Croquette

    1998-03-01

    Using magnetic micromanipulation techniques [Strick 96]( uc(T.R.) Strick, J.-F. Allemand, D. Bensimon, A. Bensimon) and uc(V.) Croquette, "The elasticity of a single supercoiled DNA molecule", Science, 271, 1835 (1996)., we have studied the mechanical properties (force versus extension) of single DNA molecules under a wide range of torsional stresses (supercoiling). We show that unwinding the DNA double helix leads to a phase separation between regular B-DNA and denaturation bubbles. The fraction of denatured molecule increases linearly with the degree of unwinding, beginning at a value of 1% unwinding. We have confirmed this denatured state by hybridization of homologous single-stranded DNA probes and by a chemical attack of the exposed bases. Surprisingly, when we overwind the molecule, the elasticity curves we obtain may also be interpreted by the coexistence of two phases, B-DNA and a new phase which we note P-DNA. The fraction of this new phase increases smoothly with overwinding, beginning at 3 % and continuing up to 300 %. Our results indicate that this new phase is four times more twisted that the standard B-DNA and is 1.75 times longer. Although the structure of this phase is not yet known, such a high twisting can only be attained if the sugar-phosphate backbones of the two strands are twisted closely while the bases are expelled outside of the molecule's core, in a structure reminiscent of the one proposed by Pauling. Indeed we have shown that this new phase is sensitive to chemical attack whereas the B-DNA is not. This new phase begins to appear on a molecule overwound by 3 % and stretched by a force of 5 pN, conditions typically encountered in vivo during gene transcription. This new phase may thus play a biological role biophysique-ADN>(for more details).

  19. Structure, Hydrodynamics, and Phase Transition of Freely Suspended Liquid Crystals

    Science.gov (United States)

    Clark, Noel A.

    2000-01-01

    Smectic liquid crystals are phases of rod shaped molecules organized into one dimensionally (1D) periodic arrays of layers, each layer being between one and two molecular lengths thick. In the least ordered smectic phases, the smectics A and C, each layer is a two dimensional (2D) liquid. Additionally there are a variety of more ordered smectic phases having hexatic short range translational order or 2D crystalline quasi long range translational order within the layers. The inherent fluid-layer structure and low vapor pressure of smectic liquid crystals enable the long term stabilization of freely suspended, single component, layered fluid films as thin as 30A, a single molecular layer. The layering forces the films to be an integral number of smectic layers thick, quantizing their thickness in layer units and forcing a film of a particular number of layers to be physically homogeneous with respect to its layer structure over its entire area. Optical reflectivity enables the precise determination of the number of layers. These ultrathin freely suspended liquid crystal films are structures of fundamental interest in condensed matter and fluid physics. They are the thinnest known stable condensed phase fluid structures and have the largest surface-to-volume ratio of any stable fluid preparation, making them ideal for the study of the effects of reduced dimensionality on phase behavior and on fluctuation and interface phenomena. Their low vapor pressure and quantized thickness enable the effective use of microgravity to extend the study of basic capillary phenomena to ultrathin fluid films. Freely suspended films have been a wellspring of new liquid crystal physics. They have been used to provide unique experimental conditions for the study of condensed phase transitions in two dimensions. They are the only system in which the hexatic has been unambiguously identified as a phase of matter, and the only physical system in which fluctuations of a 2D XY system and

  20. Coherent flow structures at earth's surface

    National Research Council Canada - National Science Library

    Venditti, J.G; Best, J.L; Church, M; Hardy, R.J

    2013-01-01

    This book reviews the recent progress in the study of the turbulent flows that sculpt the Earth's surface, focusing in particular on the organized structures that have been identified in recent years...

  1. Susceptibilities to DNA Structural Transitions within Eukaryotic Genomes

    Science.gov (United States)

    Zhabinskaya, Dina; Benham, Craig; Madden, Sally

    2012-02-01

    We analyze the competitive transitions to alternate secondary DNA structures in a negatively supercoiled DNA molecule of kilobase length and specified base sequence. We use statistical mechanics to calculate the competition among all regions within the sequence that are susceptible to transitions to alternate structures. We use an approximate numerical method since the calculation of an exact partition function is numerically cumbersome for DNA molecules of lengths longer than hundreds of base pairs. This method yields accurate results in reasonable computational times. We implement algorithms that calculate the competition between transitions to denatured states and to Z-form DNA. We analyze these transitions near the transcription start sites (TSS) of a set of eukaryotic genes. We find an enhancement of Z-forming regions upstream of the TSS and a depletion of denatured regions around the start sites. We confirm that these finding are statistically significant by comparing our results to a set of randomized genes with preserved base composition at each position relative to the gene start sites. When we study the correlation of these transitions in orthologous mouse and human genes we find a clear evolutionary conservation of both types of transitions around the TSS.

  2. Correlating simulated surface marks with near-surface tornado structure

    Science.gov (United States)

    Zimmerman, Michael I.

    Tornadoes often leave behind patterns of debris deposition, or "surface marks", which provide a direct signature of their near surface winds. The intent of this thesis is to investigate what can be learned about near-surface tornado structure and intensity through the properties of surface marks generated by simulated, debris-laden tornadoes. Earlier work showed through numerical simulations that the tornado's structure and intensity is highly sensitive to properties of the near-surface flow and can change rapidly in time for some conditions. The strongest winds often occur within tens of meters of the surface where the threat to human life and property is highest, and factors such as massive debris loadings and asymmetry of the main vortex have proven to be critical complications in some regimes. However, studying this portion of the flow in the field is problematic; while Doppler radar provides the best tornado wind field measurements, it cannot probe below about 20 m, and interpretation of Doppler data requires assumptions about tornado symmetry, steadiness in time, and correlation between scatterer and air velocities that are more uncertain near the surface. As early as 1967, Fujita proposed estimating tornado wind speeds from analysis of aerial photography and ground documentation of surface marks. A handful of studies followed but were limited by difficulties in interpreting physical origins of the marks, and little scientific attention has been paid to them since. Here, Fujita's original idea is revisited in the context of three-dimensional, large-eddy simulations of tornadoes with fully-coupled debris. In this thesis, the origins of the most prominent simulated marks are determined and compared with historical interpretations of real marks. The earlier hypothesis that cycloidal surface marks were directly correlated with the paths of individual vortices (either the main vortex or its secondary vortices, when present) is unsupported by the simulation results

  3. Long Range Surface Plasmons in Multilayer Structures

    CERN Document Server

    Delfan, Aida

    2013-01-01

    We present a new strategy, based on a Fresnel coefficient pole analysis, for designing an asymmetric multilayer structure that supports long range surface plasmons (LRSP). We find that the electric field intensity in the metal layer of a multilayer LRSP structure can be even slightly smaller than in the metal layer of the corresponding symmetric LRSP structure, minimizing absorption losses and resulting in LRSP propagation lengths up to 2mm. With a view towards biosensing applications, we also present semi-analytic expressions for a standard surface sensing parameter in arbitrary planar resonant structures, and in particular show that for an asymmetric structure consisting of a gold film deposited on a multilayer of SiO2 and TiO2 a surface sensing parameter G = 1.28(1/nm) can be achieved.

  4. Transition from Reconstruction toward Thin Film on the (110) Surface of Strontium Titanate.

    Science.gov (United States)

    Wang, Z; Loon, A; Subramanian, A; Gerhold, S; McDermott, E; Enterkin, J A; Hieckel, M; Russell, B C; Green, R J; Moewes, A; Guo, J; Blaha, P; Castell, M R; Diebold, U; Marks, L D

    2016-04-13

    The surfaces of metal oxides often are reconstructed with a geometry and composition that is considerably different from a simple termination of the bulk. Such structures can also be viewed as ultrathin films, epitaxed on a substrate. Here, the reconstructions of the SrTiO3 (110) surface are studied combining scanning tunneling microscopy (STM), transmission electron diffraction, and X-ray absorption spectroscopy (XAS), and analyzed with density functional theory calculations. Whereas SrTiO3 (110) invariably terminates with an overlayer of titania, with increasing density its structure switches from n × 1 to 2 × n. At the same time the coordination of the Ti atoms changes from a network of corner-sharing tetrahedra to a double layer of edge-shared octahedra with bridging units of octahedrally coordinated strontium. This transition from the n × 1 to 2 × n reconstructions is a transition from a pseudomorphically stabilized tetrahedral network toward an octahedral titania thin film with stress-relief from octahedral strontia units at the surface.

  5. Laser surface alloying of aluminium-transition metal alloys

    Directory of Open Access Journals (Sweden)

    Almeida, A.

    1998-04-01

    Full Text Available Laser surface alloying has been used as a tool to produce hard and corrosion resistant Al-transition metal (TM alloys. Cr and Mo are particularly interesting alloying elements to produce stable highstrength alloys because they present low diffusion coefficients and solid solubility in Al. To produce Al-TM surface alloys a two-step laser process was developed: firstly, the material is alloyed using low scanning speed and secondly, the microstructure is modified by a refinement step. This process was used in the production of Al-Cr, Al-Mo and Al-Nb surface alloys by alloying Cr, Mo or Nb powder into an Al and 7175 Al alloy substrate using a CO2 laser. This paper presents a review of the work that has been developed at Instituto Superior Tecnico on laser alloying of Al-TM alloys, over the last years.

    En el presente trabajo se estudia la aleación superficial mediante láser de aluminio con metales de transición. El cromo y el molibdeno son particularmente interesantes porque producen aleaciones de alta resistencia y por el bajo coeficiente de difusión y solución sólida en aluminio. Para producir estas aleaciones se ha seguido un procedimiento desarrollado en dos partes. En primer lugar, el material se alea usando una baja velocidad de procesado y en segundo lugar la estructura se modifica mediante un refinamiento posterior. Este procedimiento se ha empleado en la producción de aleaciones Al-Cr, Al-Mo y Al-Nb mediante aleación con láser de CO2 de polvos de Cr, Mo o Nb en aluminio y la aleación 7175. Este trabajo es una revisión del desarrollado en el Instituto Superior Técnico de Lisboa en los últimos años.

  6. Transition from diffusive to localized regimes in surface corrugated waveguides

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Martin, A.; Saenz, J. J. [Universidad Autonoma de Madrid, Madrid (Spain); Nieto-Vesperinas, M. [Instituto de Ciencias de Materiales de Madrid, Madrid (Spain)

    2001-03-01

    Exact calculations of transmission and reflection coefficients in surface randomly corrugated waveguides are presented. The elastic scattering of diffuse light classical waves from a rough surface induces a diffusive transport along the waveguide axis. As the length of the corrugated part of the waveguide increases, a transition from the diffusive to the localized regime is observed. This involves an analogy with electron conduction in nano wires, and hence, a concept analogous to that of resistance can be introduced. An oscillatory behavior of different transport properties (elastic mean free path, localization length, enhanced backscattering), versus the wavelength is predicted. An analysis of the transmission coefficients (transmitted speckle) shows that as the length of the corrugated part of the waveguide increases there is a strong preference to forward coupling through the lowest mode. This marks a clear anisotropy in the forward propagation which is absent in the case of volume disorder. The statistics of reflection coefficients is analyzed, first using random matrix theory (Rm) to analytically deduce the probability densities in the localization regime, afterwards exact numerical calculations of the coupling to backward modes in surface corrugated waveguides will be put forward for comparison. We show that the reflected speckle distribution are independent of the transport regime, at variance with the regime transition found in the transmission case. Despite the strong anisotropy, the analysis of the probability distributions of both transmitted and reflected waves confirms the distributions predicted by Random Matrix Theory for volume disorder. [Spanish] Presentamos calculos exactos de los coeficientes de transmision y reflexion en guias de onda con desorden de superficie. La dispersion elastica de luz difusa o de otras ondas clasicas por una superficie rugosa induce un transporte difusivo a lo largo del eje de la guia. A medida que la longitud de la zona

  7. Pressure induced structural phase transition in IB transition metal nitrides compounds

    Energy Technology Data Exchange (ETDEWEB)

    Soni, Shubhangi; Kaurav, Netram, E-mail: netramkaurav@yahoo.co.uk; Jain, A. [Department of Physics, Govt. Holkar Science college, A. B. Road, Indore-452001 India (India); Shah, S. [Department of Physics, P. M. B. Gujarati Science College, Indore-452001 (India); Choudhary, K. K. [Department of Physics, National Defence Academy, Khadakwasla, Pune-411 0231 India (India)

    2015-06-24

    Transition metal mononitrides are known as refractory compounds, and they have, relatively, high hardness, brittleness, melting point, and superconducting transition temperature, and they also have interesting optical, electronic, catalytic, and magnetic properties. Evolution of structural properties would be an important step towards realizing the potential technological scenario of this material of class. In the present study, an effective interionic interaction potential (EIOP) is developed to investigate the pressure induced phase transitions in IB transition metal nitrides TMN [TM = Cu, Ag, and Au] compounds. The long range Coulomb, van der Waals (vdW) interaction and the short-range repulsive interaction upto second-neighbor ions within the Hafemeister and Flygare approach with modified ionic charge are properly incorporated in the EIOP. The vdW coefficients are computed following the Slater-Kirkwood variational method, as both the ions are polarizable. The estimated value of the phase transition pressure (Pt) and the magnitude of the discontinuity in volume at the transition pressure are consistent as compared to the reported data.

  8. Structure-based prediction of protein-folding transition paths

    CERN Document Server

    Jacobs, William M

    2016-01-01

    We propose a general theory to describe the distribution of protein-folding transition paths. We show that transition paths follow a predictable sequence of high-free-energy transient states that are separated by free-energy barriers. Each transient state corresponds to the assembly of one or more discrete, cooperative units, which are determined directly from the native structure. We show that the transition state on a folding pathway is reached when a small number of critical contacts are formed between a specific set of substructures, after which folding proceeds downhill in free energy. This approach suggests a natural resolution for distinguishing parallel folding pathways and provides a simple means to predict the rate-limiting step in a folding reaction. Our theory identifies a common folding mechanism for proteins with diverse native structures and establishes general principles for the self-assembly of polymers with specific interactions.

  9. Pressure dependence of structural phase transition and superconducting transition in CsI

    CERN Document Server

    Nirmala-Louis, C

    2003-01-01

    The self-consistent band structure calculation for CsI performed both in CsCl and HCP structures using the TB-LMTO method is reported. The equilibrium lattice constant, bulk modulus and the phase-transition pressure at which the compound undergoes structural phase transition from CsCl to HCP are predicted from the total-energy calculations. The band structure, density of states (DOS), electronic charge distributions, metallization and superconducting transition temperature (T sub c) of CsI are obtained as a function of pressure for both the CsCl and HCP structures. It is found that the charge transfer from s and p states to d state causes metallization and superconductivity in CsI. The highest T sub c estimated is 2.11 K and the corresponding pressure is 1.8 Mbar. This value is in agreement with the recent experimental observation. The experimental trend - ''metallization and superconductivity is rather insensitive to the crystal structure of CsI'' - is also confirmed in our work. (Abstract Copyright [2003], ...

  10. Dissociation of N2, NO, and CO on transition metal surfaces

    DEFF Research Database (Denmark)

    Mavrikakis, Manos; Hansen, Lars Bruno; Mortensen, Jens Jørgen;

    1999-01-01

    Using density functional theory we study the dissociation of N2, NO, and CO on transition metal surfaces. We discuss an efficient method to locate the minimum energy path and the transition state, and review recent calculations using this method to determine the transition state for dissociation...

  11. The Surface Structure of Relative Clauses

    Science.gov (United States)

    Lucas, Michael A.

    1974-01-01

    This article attempts to show that a more rigorous approach to surface structure analysis can reveal distinctions just as subtle as those discovered through analyzing deep structures or transformations. Relative clauses are examined in relation to nominal constructions, and alternatives to restrictive and non-restrictive classifications are…

  12. Sub-µm structured lotus surfaces manufacturing

    DEFF Research Database (Denmark)

    Worgull, Matthias; Heckele, Mathias; Mappes, Timo

    2009-01-01

    . Unlike to stochastic methods, patterning with a LIGA-mold insert it is possible to structure surfaces very uniformly or even with controlled variations (e.g., with gradients). In this paper we present the process chain to realize polymer sub-lm structures with minimum lateral feature size of 400 nm...

  13. Sub-µ structured Lotus Surfaces Manufacturing

    DEFF Research Database (Denmark)

    Worgull, Matthias; Heckele, Mathias; Mappes, Timo

    2008-01-01

    . Unlike to stochastic methods, patternin¬g with a LIGA-mold insert it is possible to structure surfaces very uniformly or even with controlled variations (e.g. with gradients). In this paper we present the process chain to realize polymer sub-micro structures with minimum lateral feature size of 400 nm...

  14. Pressurizable structures comprising different surface sections

    NARCIS (Netherlands)

    Koussios, S.; Bergsma, O.K.; Beukers, A.

    2004-01-01

    The invention relates to composite pressurizable structures which are overwound with fibres or are braided. The pressurizable structures comprise axial sections which in turn comprise both concave and convex surfaces. The shape characteristics are related to geodesic as well as non-geodesic trajecto

  15. Local structural ordering in surface-confined liquid crystals

    Science.gov (United States)

    Śliwa, I.; Jeżewski, W.; Zakharov, A. V.

    2017-06-01

    The effect of the interplay between attractive nonlocal surface interactions and attractive pair long-range intermolecular couplings on molecular structures of liquid crystals confined in thin cells with flat solid surfaces has been studied. Extending the McMillan mean field theory to include finite systems, it has been shown that confining surfaces can induce complex orientational and translational ordering of molecules. Typically, local smectic A, nematic, and isotropic phases have been shown to coexist in certain temperature ranges, provided that confining cells are sufficiently thick, albeit finite. Due to the nonlocality of surface interactions, the spatial arrangement of these local phases can display, in general, an unexpected complexity along the surface normal direction. In particular, molecules located in the vicinity of surfaces can still be organized in smectic layers, even though nematic and/or isotropic order can simultaneously appear in the interior of cells. The resulting surface freezing of smectic layers has been confirmed to occur even for rather weak surface interactions. The surface interactions cannot, however, prevent smectic layers from melting relatively close to system boundaries, even when molecules are still arranged in layers within the central region of the system. The internal interfaces, separating individual liquid-crystal phases, are demonstrated here to form fronts of local finite-size transitions that move across cells under temperature changes. Although the complex molecular ordering in surface confined liquid-crystal systems can essentially be controlled by temperature variations, specific thermal properties of these systems, especially the nature of the local transitions, are argued to be strongly conditioned to the degree of molecular packing.

  16. Longitudinal surface structures (flowstripes on Antarctic glaciers

    Directory of Open Access Journals (Sweden)

    N. F. Glasser

    2011-11-01

    Full Text Available Longitudinal surface structures (''flowstripes'' are common on many glaciers but their origin and significance are poorly understood. In this paper we present observations of the development of these longitudinal structures from four different Antarctic glacier systems (the Lambert Glacier/Amery Ice Shelf area, outlet glaciers in the Ross Sea sector, ice-shelf tributary glaciers on the Antarctic Peninsula, and the onset zone of a tributary to the Recovery Glacier Ice Stream in the Filchner Ice Shelf area. Mapping from optical satellite images demonstrates that longitudinal surface structures develop in two main situations: (1 as relatively wide flow stripes within glacier flow units and (2 as relatively narrow flow stripes where there is convergent flow around nunataks or at glacier confluence zones. Our observations indicate that the confluence features are narrower, sharper, and more clearly defined features. They are characterised by linear troughs or depressions on the ice surface and are much more common than the former type. Longitudinal surface structures within glacier flow units have previously been explained as the surface expression of localised bed perturbations but a universal explanation for those forming at glacier confluences is lacking. Here we propose that these features are formed at zones of ice acceleration and extensional flow at glacier confluences. We provide a schematic model for the development of longitudinal surface structures based on extensional flow that can explain their ridge and trough morphology as well as their down-ice persistence.

  17. Colloids with high-definition surface structures

    Science.gov (United States)

    Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg

    2007-01-01

    Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of ≈107 to 108 particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors. PMID:17592149

  18. Colloids with high-definition surface structures.

    Science.gov (United States)

    Chen, Hsien-Yeh; Rouillard, Jean-Marie; Gulari, Erdogan; Lahann, Joerg

    2007-07-03

    Compared with the well equipped arsenal of surface modification methods for flat surfaces, techniques that are applicable to curved, colloidal surfaces are still in their infancy. This technological gap exists because spin-coating techniques used in traditional photolithographic processes are not applicable to the curved surfaces of spherical objects. By replacing spin-coated photoresist with a vapor-deposited, photodefinable polymer coating, we have now fabricated microstructured colloids with a wide range of surface patterns, including asymmetric and chiral surface structures, that so far were typically reserved for flat substrates. This high-throughput method can yield surface-structured colloidal particles at a rate of approximately 10(7) to 10(8) particles per operator per day. Equipped with spatially defined binding pockets, microstructured colloids can engage in programmable interactions, which can lead to directed self-assembly. The ability to create a wide range of colloids with both simple and complex surface patterns may contribute to the genesis of previously unknown colloidal structures and may have important technological implications in a range of different applications, including photonic and phononic materials or chemical sensors.

  19. Financial structure and monetary policy transmission in transition countries

    NARCIS (Netherlands)

    Elbourne, A.; de Haan, J.

    2006-01-01

    Using the structural vector autoregressive methodology, we present estimates of monetary transmission for the new and future EU member countries in Central and Eastern Europe. Unlike most previous research we include ten transition countries. We examine to what extent monetary transmission in these

  20. Discovery of Water Structural Transitions near Interfaces of Polarizable Solutes

    Science.gov (United States)

    Dinpajooh, Mohammadhasan; Matyushov, Dmitry

    2015-03-01

    The standard harmonic approximation describing polarization around the solute is expected to break down with increasing solute polarizability. The focus of this study is to investigate the structure of water around dipolar-polarizable solutes by Monte Carlo (MC) simulations in the non-harmonic regime. We observe a structural transition in the water hydration shell and its condensation, which are driven by increasing the solute polarizability. There is also a crossover in the orientational structure near the point of breakdown of the harmonic approximation. At lower polarizabilities, waters in the hydration shell point their hydrogens toward the solute. The dipoles flip their orientations at the transition to the non-harmonic regime. Both the hydration shell compressibility and the electric field susceptibility display maxima in the transition region. Using the water electric field at the center of the polarizable solute as the order parameter, a Landau-type model is formulated. Its predictions are in reasonable agreement with MC simulations performed for hard sphere and Lennard Jones polarizable solutes in a TIP3P water model. The observed structural transition suggests a general crossover phenomenon driven by the stabilization energy required to polarize the solute. This research was supported by the National Science Foundation (CHE-1213288). CPU time was provided by the National Science Foundation through XSEDE resources (TG-MCB080116N).

  1. Optically induced structural phase transitions in ion Coulomb crystals

    DEFF Research Database (Denmark)

    Horak, Peter; Dantan, Aurelien Romain; Drewsen, Michael

    2012-01-01

    , such as body-centered cubic and face-centered cubic, can be suppressed by a proper choice of the potential depth and periodicity. Furthermore, by varying the harmonic trap parameters and/or the optical potential in time, controlled transitions between crystal structures can be obtained with close to unit...

  2. Financial structure and monetary policy transmission in transition countries

    NARCIS (Netherlands)

    Elbourne, A.; de Haan, J.

    Using the structural vector autoregressive methodology, we present estimates of monetary transmission for the new and future EU member countries in Central and Eastern Europe. Unlike most previous research we include ten transition countries. We examine to what extent monetary transmission in these

  3. Fermi surface reconstruction and multiple quantum phase transitions in the antiferromagnet CeRhIn5.

    Science.gov (United States)

    Jiao, Lin; Chen, Ye; Kohama, Yoshimitsu; Graf, David; Bauer, E D; Singleton, John; Zhu, Jian-Xin; Weng, Zongfa; Pang, Guiming; Shang, Tian; Zhang, Jinglei; Lee, Han-Oh; Park, Tuson; Jaime, Marcelo; Thompson, J D; Steglich, Frank; Si, Qimiao; Yuan, H Q

    2015-01-20

    Conventional, thermally driven continuous phase transitions are described by universal critical behavior that is independent of the specific microscopic details of a material. However, many current studies focus on materials that exhibit quantum-driven continuous phase transitions (quantum critical points, or QCPs) at absolute zero temperature. The classification of such QCPs and the question of whether they show universal behavior remain open issues. Here we report measurements of heat capacity and de Haas-van Alphen (dHvA) oscillations at low temperatures across a field-induced antiferromagnetic QCP (Bc0 ≈ 50 T) in the heavy-fermion metal CeRhIn5. A sharp, magnetic-field-induced change in Fermi surface is detected both in the dHvA effect and Hall resistivity at B0* ≈ 30 T, well inside the antiferromagnetic phase. Comparisons with band-structure calculations and properties of isostructural CeCoIn5 suggest that the Fermi-surface change at B0* is associated with a localized-to-itinerant transition of the Ce-4f electrons in CeRhIn5. Taken in conjunction with pressure experiments, our results demonstrate that at least two distinct classes of QCP are observable in CeRhIn5, a significant step toward the derivation of a universal phase diagram for QCPs.

  4. Nature inspired structured surfaces for biomedical applications.

    Science.gov (United States)

    Webb, H K; Hasan, J; Truong, V K; Crawford, R J; Ivanova, E P

    2011-01-01

    Nature has created an array of superhydrophobic surfaces that possess water-repellent, self-cleaning and anti-icing properties. These surfaces have a number of potential applications in the biomedical industry, as they have the potential to control protein adsorption and cell adhesion. Natural superhydrophobic surfaces are typically composed of materials with a low intrinsic surface free-energy (e.g the cuticular waxes of lotus leaves and insect wings) with a hierarchical structural configuration. This hierarchical surface topography acts to decrease the contact area of water droplets in contact with the surface, thereby increasing the extent of the air/water interface, resulting in water contact angles greater than 150º. In order to employ these surfaces in biotechnological applications, fabrication techniques must be developed so that these multi-scale surface roughness characteristics can be reproduced. Additionally, these fabrication techniques must also be able to be applied to the material required for the intended application. An overview of some of the superhydrophobic surfaces that exist in nature is presented, together with an explanation of the theories of their wettability. Also included is a description of some of the biomedical applications of superhydrophobic surfaces and fabrication techniques that can be used to mimic superhydrophobic surfaces found in nature.

  5. Structural phase diagrams for the surface of a solid - A total-energy, renormalization-group approach

    Science.gov (United States)

    Ihm, J.; Lee, D. H.; Joannopoulos, J. D.; Xiong, J. J.

    1983-11-01

    Total-energy calculations based on microscopic electronic structure are combined with position-space renormalization-group calculations to predict the structural phase transitions of the Si(100) surface as a function of temperature. It is found that two distinct families of reconstructed geometries can exist on the surface, with independent phase transitions occurring within each. Two critical temperatures representing order-disorder transitions are calculated.

  6. Water and Ethanol Droplet Wetting Transition during Evaporation on Omniphobic Surfaces

    Science.gov (United States)

    Chen, Xuemei; Weibel, Justin A.; Garimella, Suresh V.

    2015-11-01

    Omniphobic surfaces with reentrant microstructures have been investigated for a range of applications, but the evaporation of high- and low-surface-tension liquid droplets placed on such surfaces has not been rigorously studied. In this work, we develop a technique to fabricate omniphobic surfaces on copper substrates to allow for a systematic examination of the effects of surface topography on the evaporation dynamics of water and ethanol droplets. Compared to a water droplet, the ethanol droplet not only evaporates faster, but also inhibits Cassie-to-Wenzel wetting transitions on surfaces with certain geometries. We use an interfacial energy-based description of the system, including the transition energy barrier and triple line energy, to explain the underlying transition mechanism and behaviour observed. Suppression of the wetting transition during evaporation of droplets provides an important metric for evaluating the robustness of omniphobic surfaces requiring such functionality.

  7. Two Network Structure Indicators for Conventional Public Transit

    Institute of Scientific and Technical Information of China (English)

    Min Fu; Hao Wang; Wei Wang; Sida Luo; De Zhao

    2016-01-01

    The significance of network structure indicators for the planning and management of conventional public transit is widely acknowledged. In order to improve and enrich the conventional public transit assessment system, two network structure indicators are proposed. Firstly, according to the obvious defects lying in the traditional no⁃linear coefficient, the realistic no⁃linear coefficient γRNL , a modified no⁃linear coefficient indicator, is put forward, which takes into account the effects of barriers in a city. Secondly, to cover the gap of an indicator which can reflect the coverage homogeneity of a transit network, the length dimension LD is proposed on the basis of Fractal Theory. Finally, a case study is applied to verify the validity and practicability of the two indicators in problem diagnosis using regression analysis. The results validate thatγRNL can evaluate the detour of bus lines more reasonably than the previous no⁃linear coefficient because it reflects the layout of bus lines, and LD can represent the rate of change of the network density, adding a new member to the scheme of network structure indicators for public transit.

  8. Protein conformational transitions at the liquid-gas interface as studied by dilational surface rheology.

    Science.gov (United States)

    Noskov, Boris A

    2014-04-01

    Experimental results on the dynamic dilational surface elasticity of protein solutions are analyzed and compared. Short reviews of the protein behavior at the liquid-gas interface and the dilational surface rheology precede the main sections of this work. The kinetic dependencies of the surface elasticity differ strongly for the solutions of globular and non-globular proteins. In the latter case these dependencies are similar to those for solutions of non-ionic amphiphilic polymers and have local maxima corresponding to the formation of the distal region of the surface layer (type I). In the former case the dynamic surface elasticity is much higher (>60 mN/m) and the kinetic dependencies are monotonical and similar to the data for aqueous dispersions of solid nanoparticles (type II). The addition of strong denaturants to solutions of bovine serum albumin and β-lactoglobulin results in an abrupt transition from the type II to type I dependencies if the denaturant concentration exceeds a certain critical value. These results give a strong argument in favor of the preservation of the protein globular structure in the course of adsorption without any denaturants. The addition of cationic surfactants also can lead to the non-monotonical kinetic dependencies of the dynamic surface elasticity indicating destruction of the protein tertiary and secondary structures. The addition of anionic surfactants gives similar results only for the protein solutions of high ionic strength. The influence of cationic surfactants on the local maxima of the kinetic dependencies of the dynamic surface elasticity for solutions of a non-globular protein (β-casein) differs from the influence of anionic surfactants due to the heterogeneity of the charge distribution along the protein chain. In this case one can use small admixtures of ionic surfactants as probes of the adsorption mechanism. The effect of polyelectrolytes on the kinetic dependencies of the dynamic surface elasticity of protein

  9. Classical theory of resonant transition radiation in multilayer structures.

    Science.gov (United States)

    Pardo, B; André, J M

    2001-01-01

    A rigorous classical electromagnetic theory of the transition radiation in finite and infinite multilayer structures is presented. It makes the standard results of thin-film optics, such as the matrix formalism, accountable; it allows thus an exact treatment of the propagation of the waves induced by the electron. This method is applied to the particular case of the periodic structures to treat the resonant transition radiation (RTR). It is noted that the present theory gives, in the hard x-ray domain, results previously published. The reason for this approach is to make the numerical calculations rigorous and easy. The numerical results of our theory are compared to experimental RTR data obtained recently by Yamada et al. [Phys. Rev. A 59, 3673 (1999)] with a nickel-carbon multilayer structure.

  10. Interlocking order parameter fluctuations in structural transitions between adsorbed polymer phases.

    Science.gov (United States)

    Martins, Paulo H L; Bachmann, Michael

    2016-01-21

    By means of contact-density chain-growth simulations of a simple coarse-grained lattice model for a polymer grafted at a solid homogeneous substrate, we investigate the complementary behavior of the numbers of surface-monomer and monomer-monomer contacts under various solvent and thermal conditions. This pair of contact numbers represents an appropriate set of order parameters that enables the distinct discrimination of significantly different compact phases of polymer adsorption. Depending on the transition scenario, these order parameters can interlock in perfect cooperation. The analysis helps understand the transitions from compact filmlike adsorbed polymer conformations into layered morphologies and dissolved adsorbed structures, respectively, in more detail.

  11. High pressure structural phase transitions of PbPo

    Energy Technology Data Exchange (ETDEWEB)

    Bencherif, Y.; Boukra, A. [Departement de Physique, Faculte des Sciences, Universite de Mostaganem (Algeria); Departement de Physique, Universite des Sciences et de la Technologie d' Oran, USTO, Oran (Algeria); Zaoui, A., E-mail: azaoui@polytech-lille.fr [Universite Lille Nord de France, LGCgE (EA 4515) Lille1, Polytech' Lille, Cite Scientifique, Avenue Paul Langevin, 59655 Villeneuve D' Ascq Cedex (France); Ferhat, M. [Departement de Physique, Universite des Sciences et de la Technologie d' Oran, USTO, Oran (Algeria)

    2012-09-01

    First-principles calculations have been performed to investigate the high pressure phase transitions and dynamical properties of the less known lead polonium compound. The calculated ground state parameters for the NaCl phase show good agreement with the experimental data. The obtained results show that the intermediate phase transition for this compound is the orthorhombic Pnma phase. The PbPo undergoes from the rocksalt to Pnma phase at 4.20 GPa. Further structural phase transition from intermediate to CsCl phase has been found at 8.5 GPa. In addition, phonon dispersion spectra were derived from linear-response to density functional theory. In particular, we show that the dynamical properties of PbPo exhibit some peculiar features compared to other III-V compounds. Finally, thermodynamics properties have been also addressed from quasiharmonic approximation.

  12. The additional phase transition of DPPC monolayers at high surface pressure confirmed by GIXD study

    DEFF Research Database (Denmark)

    Shen, Chen; Serna, Jorge B. de la; Struth, Bernd

    Pulmonary surfactant forms the alveolar monolayer at the air/aqueous interface within the lung. During the breathing process, the surface pressure periodically varies from ~40mN/m up to ~70mN/m. The film is mechanically stable during this rapid and reversible expansion. The monolayer consists...... of ~90% of lipid with 10% integrated proteins. Among its lipid compounds, di- palmitoyl-phosphatidylcholine (DPPC) dominates (~45wt%). No other lipid but DPPC was so far reported to be compressible to very high surface pressure (~70mN/m) before its monolayer collapsed. Its liquid......-expanded/liquid-condensed (LE/LC) phase transition at ~10mN/m is well known. Here we present results from Langmuir isotherm measurements that evidence a so far not documented second phase transition at elevated surface pressure Π (~50mN/m). The varying lateral structures of the monolayer at 8mN/m, 20mN/m, 30mN/m, 40mN/m, 50m...

  13. Disorder-induced structural transitions in topological insulating Ge-Sb-Te compounds

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jeongwoo; Jhi, Seung-Hoon, E-mail: jhish@postech.ac.kr [Department of Physics, Pohang University of Science and Technology, Pohang 790-784 (Korea, Republic of)

    2015-05-21

    The mechanism for the fast switching between amorphous, metastable, and crystalline structures in chalcogenide phase-change materials has been a long-standing puzzle. Based on first-principles calculations, we study the atomic and electronic properties of metastable Ge{sub 2}Sb{sub 2}Te{sub 5} and investigate the atomic disorder to understand the transition between crystalline hexagonal and cubic structures. In addition, we study the topological insulating property embedded in these compounds and its evolution upon structural changes and atomic disorder. We also discuss the role of the surface-like states arising from the topological insulating property in the metal-insulator transition observed in the hexagonal structure.

  14. A phase transition in energy-filtered RNA secondary structures

    CERN Document Server

    Han, Hillary S W

    2012-01-01

    In this paper we study the effect of energy parameters on minimum free energy (mfe) RNA secondary structures. Employing a simplified combinatorial energy model, that is only dependent on the diagram representation and that is not sequence specific, we prove the following dichotomy result. Mfe structures derived via the Turner energy parameters contain only finitely many complex irreducible substructures and just minor parameter changes produce a class of mfe-structures that contain a large number of small irreducibles. We localize the exact point where the distribution of irreducibles experiences this phase transition from a discrete limit to a central limit distribution and subsequently put our result into the context of quantifying the effect of sparsification of the folding of these respective mfe-structures. We show that the sparsification of realistic mfe-structures leads to a constant time and space reduction and that the sparsifcation of the folding of structures with modified parameters leads to a lin...

  15. Surface structure and electronic properties of materials

    Science.gov (United States)

    Siekhaus, W. J.; Somorjai, G. A.

    1975-01-01

    A surface potential model is developed to explain dopant effects on chemical vapor deposition. Auger analysis of the interaction between allotropic forms of carbon and silicon films has shown Si-C formation for all forms by glassy carbon. LEED intensity measurements have been used to determine the mean square displacement of surface atoms of silicon single crystals, and electron loss spectroscopy has shown the effect of structure and impurities on surface states located within the band gap. A thin film of Al has been used to enhance film crystallinity at low temperature.

  16. Atomic and electronic structure of surfaces theoretical foundations

    CERN Document Server

    Lannoo, Michel

    1991-01-01

    Surfaces and interfaces play an increasingly important role in today's solid state devices. In this book the reader is introduced, in a didactic manner, to the essential theoretical aspects of the atomic and electronic structure of surfaces and interfaces. The book does not pretend to give a complete overview of contemporary problems and methods. Instead, the authors strive to provide simple but qualitatively useful arguments that apply to a wide variety of cases. The emphasis of the book is on semiconductor surfaces and interfaces but it also includes a thorough treatment of transition metals, a general discussion of phonon dispersion curves, and examples of large computational calculations. The exercises accompanying every chapter will be of great benefit to the student.

  17. Direct investigations of deformation and yield induced structure transitions in polyamide 6 below glass transition temperature with WAXS and SAXS

    DEFF Research Database (Denmark)

    Guo, Huilong; Wang, Jiayi; Zhou, Chengbo;

    2015-01-01

    Deformation and yield induced structure transitions of polyamide 6 (PA6) were detected with the combination of the wide- and small-angle X-ray scattering (WAXS and SAXS) at 30 degrees C below glass transition temperature (T-g) of PA6. During deformation, gamma-alpha phase transition was found at ...

  18. Universal wetting transition of an evaporating water droplet on hydrophobic micro- and nano-structures.

    Science.gov (United States)

    Bussonnière, Adrien; Bigdeli, Masoud B; Chueh, Di-Yen; Liu, Qingxia; Chen, Peilin; Tsai, Peichun Amy

    2017-02-07

    Water-repellent, rough surfaces have a remarkable and beneficial wetting property: when a water droplet comes in contact with a small fraction of the solid, both liquid-solid adhesion and hydrodynamic drag are reduced. As a prominent example from nature, the lotus leaf-comprised of a wax-like material with micro- and nano-scaled roughness-has recently inspired numerous syntheses of superhydrophobic substrates. Due to the diverse applications of superhydrophobicity, much research has been devoted to the fabrication and investigations of hydrophobic micro-structures using established micro-fabrication techniques. However, wetting transitions remain relatively little explored. During evaporation, a water droplet undergoes a wetting transition from a (low-frictional) partial to (adhesive) complete contact with the solid, destroying the superhydrophobicity and the self-cleaning properties of the slippery surface. Here, we experimentally examine the wetting transition of a drying droplet on hydrophobic nano-structures, a previously unexplored regime. In addition, using a theoretical analysis we found a universal criterion of this wetting transition that is characterized by a critical contact angle. Different from previous results showing different critical droplet sizes, our results show a universal, geometrically-dependent, critical contact angle, which agrees well with various data for both hydrophobic micro- and nano-structures.

  19. Family structure and the transition to early parenthood.

    Science.gov (United States)

    Hofferth, Sandra L; Goldscheider, Frances

    2010-05-01

    With the rise in out-of-wedlock childbearing and divorce in the last quarter of the twentieth century, an increasing proportion of children have been exposed to a variety of new family forms. Little research has focused on the consequences of childhood family structure for men's transition to fatherhood or on the family processes that account for the effects of family structure on the likelihood that young women and men become first-time unmarried parents, what we now call "fragile families." The data come from the linked Children and Young Adult samples of the 1979 National Longitudinal Survey of Youth (NLSY79), which provide information on the children of the women of the NLSY79 from birth until they enter young adulthood. Females growing up with a single parent and males experiencing an unstable family transition to parenthood early, particularly to nonresidential fatherhood for males. For males, the effects are strongly mediated by parenting processes and adolescent behaviors and are shaped by economic circumstances. Having experienced multiple transitions as a child is associated with a reduced likelihood that males father their first child within marriage and an increased likelihood that they become fathers within cohabitation, demonstrating how changes in family structure alter family structure patterns over time and generations.

  20. Electronic structure tuning via surface modification in semimetallic nanowires

    Science.gov (United States)

    Sanchez-Soares, Alfonso; O'Donnell, Conor; Greer, James C.

    2016-12-01

    Electronic structure properties of nanowires (NWs) with diameters of 1.5 and 3 nm based on semimetallic α -Sn are investigated by employing density functional theory and perturbative GW methods. We explore the dependence of electron affinity, band structure, and band-gap values with crystallographic orientation, NW cross-sectional size, and surface passivants of varying electronegativity. We consider four chemical terminations in our study: methyl (CH3), hydrogen (H ), hydroxyl (OH ), and fluorine (F ). Results suggest a high degree of elasticity of Sn-Sn bonds within the Sn NWs' cores with no significant structural variations for nanowires with different surface passivants. Direct band gaps at Brillouin-zone centers are found for most studied structures with quasiparticle corrected band-gap magnitudes ranging from 0.25 to 3.54 eV in 1.5-nm-diameter structures, indicating an exceptional range of properties for semimetal NWs below the semimetal-to-semiconductor transition. Band-gap variations induced by changes in surface passivants indicate the possibility of realizing semimetal-semiconductor interfaces in NWs with constant cross-section and crystallographic orientation, allowing the design of novel dopant-free NW-based electronic devices.

  1. Light and phospholipid driven structural transitions in nematic microdroplets

    Energy Technology Data Exchange (ETDEWEB)

    Dubtsov, A. V., E-mail: alexanderdubtsov@gmail.com; Pasechnik, S. V.; Shmeliova, D. V. [Moscow State University of Instrument Engineering and Computer Science, Stromynka 20, Moscow 107996 (Russian Federation); Kralj, Samo [Condensed Matter Physics Department, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana (Slovenia); FNM, University of Maribor, Koroska 160, 2000 Maribor (Slovenia)

    2014-10-13

    We studied the UV-irradiation and phospholipid driven bipolar-radial structural transitions within azoxybenzene nematic liquid crystal (LC) droplets dispersed in water. It was found that the UV-irradiation induced trans-cis isomerisation of LC molecules could enable structural transitions into radial-type configurations at a critical UV-irradiation time t{sub c}. In particular, we show that under appropriate conditions, a value of t{sub c} could sensitively fingerprint the concentration of phospholipid molecules present in LC-water dispersions. This demonstrated proof-of-principle mechanism could be exploited for development of sensitive detectors for specific nanoparticles (NPs), where value of t{sub c} reveals concentration of NPs.

  2. A phase transition in energy-filtered RNA secondary structures

    DEFF Research Database (Denmark)

    Han, Hillary Siwei; reidys, Christian

    2012-01-01

    In this paper we study the effect of energy parameters on minimum free energy (mfe) RNA secondary structures. Employing a simplified combinatorial energy model, that is only dependent on the diagram representation and that is not sequence specific, we prove the following dichotomy result. Mfe...... structures derived via the Turner energy parameters contain only finitely many complex irreducible substructures and just minor parameter changes produce a class of mfe-structures that contain a large number of small irreducibles. We localize the exact point where the distribution of irreducibles experiences...... this phase transition from a discrete limit to a central limit distribution and subsequently put our result into the context of quantifying the effect of sparsification of the folding of these respective mfe-structures. We show that the sparsification of realistic mfe-structures leads to a constant time...

  3. A phase transition in energy-filtered RNA secondary structures.

    Science.gov (United States)

    Han, Hillary S W; Reidys, Christian M

    2012-10-01

    In this article we study the effect of energy parameters on minimum free energy (mfe) RNA secondary structures. Employing a simplified combinatorial energy model that is only dependent on the diagram representation and is not sequence-specific, we prove the following dichotomy result. Mfe structures derived via the Turner energy parameters contain only finitely many complex irreducible substructures, and just minor parameter changes produce a class of mfe structures that contain a large number of small irreducibles. We localize the exact point at which the distribution of irreducibles experiences this phase transition from a discrete limit to a central limit distribution and, subsequently, put our result into the context of quantifying the effect of sparsification of the folding of these respective mfe structures. We show that the sparsification of realistic mfe structures leads to a constant time and space reduction, and that the sparsification of the folding of structures with modified parameters leads to a linear time and space reduction. We, furthermore, identify the limit distribution at the phase transition as a Rayleigh distribution.

  4. Melamine structures on the Au(111) surface

    NARCIS (Netherlands)

    Silly, Fabien; Shaw, Adam Q.; Castell, Martin R.; Briggs, G. A. D.; Mura, Manuela; Martsinovich, Natalia; Kantorovich, Lev

    2008-01-01

    We report on a joint experimental and theoretical study of the ordered structures of melamine molecules formed on the Au(111)-(22 x root 3) surface. Scanning tunneling microscopy (STM) images taken under UHV conditions reveal two distinct monolayers one of which has never been reported before on gol

  5. Designing visual appearance using a structured surface

    DEFF Research Database (Denmark)

    Johansen, Villads Egede; Thamdrup, Lasse Højlund; Smitrup, Christian;

    2015-01-01

    We present an approach for designing nanostructured surfaces with prescribed visual appearances, starting at design analysis and ending with a fabricated sample. The method is applied to a silicon wafer structured using deep ultraviolet lithography and dry etching and includes preliminary design ...

  6. Noise control for rapid transit cars on elevated structures

    Science.gov (United States)

    Hanson, C. E.

    1983-03-01

    Noise control treatments for the propulsion motor noise of rapid transit cars on concrete elevated structures and the noise reduction from barrier walls were investigated by using acoustical scale models and supplemented by field measurements of noise from trains operated by the Port Authority Transportation Corporation (PATCO) in New Jersey. The results show that vehicle skirts and undercar sound absorption can provide substantial cost-effective reductions in propulsion noise at the wayside of transit systems with concrete elevated guideways. The acoustical scale model noise reductions applied to PATCO vehicles on concrete elevated structures show reductions in the A-weighted noise levels of 5 dB for undercar sound absorption, 5 dB for vehicle skirts, and 10 dB for combined undercar absorption and vehicle skirts. Acoustical scale model results for sound barrier walls lined with absorptive treatment showed reductions from 7 dB to 12 dB of noise from vehicles in the far track, depending on the height of the wall, and reductions from 12 dB to 20 dB of noise from vehicles on the near track. Transit vehicles at high speeds where propulsion system noise dominates are 7 dB(A) noisier at 50 ft on concrete elevated structures than on at-grade on tie and ballast. Of this amount, 3 dB is due to loss of ground effect, and 4 dB is due to the absence of undercar absorption provided by ballast.

  7. Geometric structure and information change in phase transitions

    Science.gov (United States)

    Kim, Eun-jin; Hollerbach, Rainer

    2017-06-01

    We propose a toy model for a cyclic order-disorder transition and introduce a geometric methodology to understand stochastic processes involved in transitions. Specifically, our model consists of a pair of forward and backward processes (FPs and BPs) for the emergence and disappearance of a structure in a stochastic environment. We calculate time-dependent probability density functions (PDFs) and the information length L , which is the total number of different states that a system undergoes during the transition. Time-dependent PDFs during transient relaxation exhibit strikingly different behavior in FPs and BPs. In particular, FPs driven by instability undergo the broadening of the PDF with a large increase in fluctuations before the transition to the ordered state accompanied by narrowing the PDF width. During this stage, we identify an interesting geodesic solution accompanied by the self-regulation between the growth and nonlinear damping where the time scale τ of information change is constant in time, independent of the strength of the stochastic noise. In comparison, BPs are mainly driven by the macroscopic motion due to the movement of the PDF peak. The total information length L between initial and final states is much larger in BPs than in FPs, increasing linearly with the deviation γ of a control parameter from the critical state in BPs while increasing logarithmically with γ in FPs. L scales as |lnD | and D-1 /2 in FPs and BPs, respectively, where D measures the strength of the stochastic forcing. These differing scalings with γ and D suggest a great utility of L in capturing different underlying processes, specifically, diffusion vs advection in phase transition by geometry. We discuss physical origins of these scalings and comment on implications of our results for bistable systems undergoing repeated order-disorder transitions (e.g., fitness).

  8. Pool Boiling Heat Transfer on structured Surfaces

    Science.gov (United States)

    Addy, J.; Olbricht, M.; Müller, B.; Luke, A.

    2016-09-01

    The development in the process and energy sector shows the importance of efficient utilization of available resources to improve thermal devices. To achieve this goal, all thermal components have to be optimized continuously. Various applications of multi-phase heat and mass transfer have to be improved. Therefore, the heat transfer and the influence of surface roughness in nucleate boiling with the working fluid propane is experimentally investigated on structured mild steel tubes, because only few data are available in the literature. The mild steel tube is sandblasted to obtain different surface roughness. The measurements are carried out over wide ranges of heat flux and pressure. The experimental results are compared with correlations from literature and the effect of surface roughness on the heat transfer is discussed. It is shown that the heat transfer coefficient increases with increasing surface roughness, heat flux and reduced pressure at nucleate pool boiling.

  9. Investigation of Surface Roughness Effect on Transition Edge Sensor Microcalorimeters Using Multilayer Readout Wiring

    Science.gov (United States)

    Kuromaru, G.; Kuwabara, K.; Miyazaki, N.; Suzuki, S.; Hosoya, S.; Koizumi, Y.; Ohashi, T.; Ishisaki, Y.; Ezoe, Y.; Yamada, S.; Mitsuda, K.; Hidaka, M.; Satoh, T.

    2016-07-01

    We are developing a transition edge sensor (TES) using multilayer readout wiring for future X-ray astronomy satellites. Although we fabricated a first full 20 × 20 pixels TES array, we could not confirm transition of the TES. Considering possible causes, we focused on surface roughness of the TES film. We checked the fabrication process steps that can influence the surface roughness step by step, and changed wiring material (Al to Nb) and also a process condition of an ion milling. As a result, we succeeded to reduce the surface roughness from 4.5 to 2.5 nm rms at 1 \\upmu m scale. However, the transition was not observed probably because the TES films in our samples with surface roughness more than {˜ }1 nm rms tend not to show the transition. Therefore, to suppress the surface roughness even more, we discuss possible process effects and mitigations.

  10. Microstructure and structural phase transitions in iron-based superconductors

    Institute of Scientific and Technical Information of China (English)

    Wang Zhen; Cai Yao; Yang Huai-Xin; Tian Huan-Fang; Wang Zhi-Wei; Ma Chao; Chen Zhen

    2013-01-01

    Crystal structures and microstructural features,such as structural phase transitions,defect structures,and chemical and structural inhomogeneities,are known to have profound effects on the physical properties of superconducting materials.Recently,many studies on the structural properties of Fe-based high-Tc superconductors have been published.This review article will mainly focus on the typical microstructural features in samples that have been well characterized by physical measurements.(i) Certain common structural features are discussed,in particular,the crystal structural features for different superconducting families,the local structural distortions in the Fe2Pn2 (Pn =P,As,Sb) or Fe2Ch2 (Ch =S,Se,Te) blocks,and the structural transformations in the 122 system.(ii) In FeTe(Se) (11 family),the superconductivity,chemical and structural inhomogeneities are investigated and discussed in correlation with superconductivity.(iii) In the K0.8Fe1.6+xSe2 system,we focus on the typical compounds with emphasis on the Fe-vacancy order and phase separations.The microstructural features in other superconducting materials are also briefly discussed.

  11. Family Structure and the Transition to Early Parenthood

    OpenAIRE

    Hofferth, Sandra L.; Goldscheider, Frances

    2010-01-01

    With the rise in out-of-wedlock childbearing and divorce in the last quarter of the twentieth century, an increasing proportion of children have been exposed to a variety of new family forms. Little research has focused on the consequences of childhood family structure for men’s transition to fatherhood or on the family processes that account for the effects of family structure on the likelihood that young women and men become first-time unmarried parents, what we now call “fragile families.”...

  12. Size Driven Ferroelectric-Paraelectric Phase Transition from the Surface Energy Viewpoint

    Institute of Scientific and Technical Information of China (English)

    钟维烈; 王渊旭; 张沛霖

    2003-01-01

    The size driven ferroelectric-paraelectric phase transition in a ferroelectric of small size is studied within the framework of Landau phase transition theory. The transition is a consequence of the competition between decreasing the volume free energy by polarization and increasing the surface energy of the ferroelectric phase,which has a surface energy density higher than that in the paraelectric phase. A simple expression for the ferroelectric critical size as a function of the Landau free energy coefficients and the surface energy density is derived.

  13. Spontaneous structural transition in phospholipid-inspired aromatic phosphopeptide nanostructures.

    Science.gov (United States)

    Pellach, Michal; Atsmon-Raz, Yoav; Simonovsky, Eyal; Gottlieb, Hugo; Jacoby, Guy; Beck, Roy; Adler-Abramovich, Lihi; Miller, Yifat; Gazit, Ehud

    2015-01-01

    Phospholipid membranes could be considered a prime example of the ability of nature to produce complex yet ordered structures, by spontaneous and efficient self-assembly. Inspired by the unique properties and architecture of phospholipids, we designed simple amphiphilic decapeptides, intended to fold in the center of the peptide sequence, with a phosphorylated serine "head" located within a central turn segment, and two hydrophobic "tails". The molecular design also included the integration of the diphenylalanine motif, previously shown to facilitate self-assembly and increase nanostructure stability. Secondary structure analysis of the peptides indeed indicated the presence of stabilized conformations in solution, with a central turn connecting two hydrophobic "tails", and interactions between the hydrophobic strands. The mechanisms of assembly into supramolecular structures involved structural transitions between different morphologies, which occurred over several hours, leading to the formation of distinctive nanostructures, including half-elliptical nanosheets and curved tapes. The phosphopeptide building blocks appear to self-assemble via a particular combination of aromatic, hydrophobic and ionic interactions, as well as hydrogen bonding, as demonstrated by proposed constructed simulated models of the peptides and self-assembled nanostructures. Molecular dynamics simulations also gave insight into mechanisms of structural transitions of the nanostructures at a molecular level. Because of the biocompatibility of peptides, the phosphopeptide assemblies allow for expansion of the library of biomolecular nanostructures available for future design and application of biomedical devices.

  14. Phase transitions for scaling of structural correlations in directed networks

    CERN Document Server

    van der Hoorn, Pim

    2015-01-01

    Analysis of degree-degree dependencies in complex networks, and their impact on processes on networks requires null models, i.e. models that generate uncorrelated scale-free networks. Most models to date however show structural negative dependencies, caused by finite size effects. We analyze the behavior of these structural negative degree-degree dependencies, using rank based correlation measures, in the directed Erased Configuration Model. We obtain expressions for the scaling as a function of the exponents of the distributions. Moreover, we show that this scaling undergoes a phase transition, where one region exhibits scaling related to the natural cut-off of the network while another region has scaling similar to the structural cut-off for uncorrelated networks. By establishing the speed of convergence of these structural dependencies we are able to asses statistical significance of degree-degree dependencies on finite complex networks when compared to networks generated by the directed Erased Configurati...

  15. Temperature- and electric-field-induced inverse Freedericksz transition in a nematogen with weak surface anchoring

    Science.gov (United States)

    Kumar, T. Arun; Sathyanarayana, P.; Sastry, V. S. S.; Takezoe, Hideo; Madhusudana, N. V.; Dhara, Surajit

    2010-07-01

    We report electric field dependence of the anchoring transition in a mesogen on cooling in a cell with perfluoropolymer treated surfaces. Below a crossover voltage Vco the transition is discontinuous between planar and homeotropic alignments, and as the temperature is lowered, the transition temperature decreases quadratically with the field. Above Vco the transition is continuous between planar and tilted alignments, the transition temperature decreasing essentially linearly with the rms field. We develop a simple model to account for these results and argue that the higher field regime corresponds to a temperature driven inverse Freedericksz transition in which the director orientation starts tilting at the weakly anchored surfaces while the tilt angle remains zero at the midplane of the cell.

  16. Structurally tuned iridescent surfaces inspired by nature

    Energy Technology Data Exchange (ETDEWEB)

    Deparis, Olivier; Rassart, Marie; Vandenbem, Cedric; Welch, Victoria; Vigneron, Jean Pol [Laboratoire de Physique du Solide, University of Namur, 61 rue de Bruxelles, 5000 Namur (Belgium); Lucas, Stephane [Laboratoire d' Analyses par Reactions Nucleaires, University of Namur, 61 rue de Bruxelles, 5000 Namur (Belgium)], E-mail: olivier.deparis@fundp.ac.be

    2008-01-15

    Iridescent surfaces exhibit vivid colours which change with the angle of incidence or viewing due to optical wave interference in the multilayer structure present at the wavelength scale underneath the surface. In nature, one can find examples of iridescent Coleoptera for which the hue changes either greatly or slightly with the angle. Because these species typically make these structures from a single biological material (usually chitin) and air or water as the low refractive index component, they have evolved by adjusting the layer thicknesses in order to display quite different iridescent aspects. Taking inspiration from this proven strategy, we have designed and fabricated periodic TiO{sub 2}/SiO{sub 2} multilayer films in order to demonstrate the concept of structurally tuned iridescent surfaces. Titanium or silicon oxide layers were deposited on a glass substrate using dc reactive or RF magnetron sputtering techniques, respectively. Two structures were designed for which the period and the TiO{sub 2}/SiO{sub 2} layer thickness ratio were varied in such a way that the films displayed radically different iridescent aspects: a reddish-to-greenish changing hue and a stable bluish hue. The fabricated samples were characterized through specular reflectance/transmittance measurements. Modelling of transmittance spectra using standard multilayer film theory confirmed the high quality of the twelve-period Bragg reflectors. The chromaticity coordinates, which were calculated from measured reflectance spectra taken at different angles, were in accordance with theoretical predictions.

  17. Microscopically derived potential energy surfaces from mostly structural considerations

    Energy Technology Data Exchange (ETDEWEB)

    Ermamatov, M.J. [Instituto de Física, Universidade Federal Fluminense, 24210-340, Niterói, Rio de Janeiro (Brazil); Institute of Nuclear Physics, Ulughbek, Tashkent 100214 (Uzbekistan); Hess, Peter O., E-mail: hess@nucleares.unam.mx [Instituto de Ciencias Nucleares, UNAM, Circuito Exterior, C.U., A.P. 70-543, 04510, Mexico D.F. (Mexico)

    2016-08-15

    A simple procedure to estimate the quadrupole Potential-Energy-Surface (PES) is presented, using mainly structural information, namely the content of the shell model space and the Pauli exclusion principle. Further microscopic properties are implicitly contained through the use of results from the Möller and Nix tables or experimental information. A mapping to the geometric potential is performed yielding the PES. The General Collective Model is used in order to obtain an estimate on the spectrum and quadrupole transitions, adjusting only the mass parameter. First, we test the conjecture on known nuclei, deriving the PES and compare them to known data. We will see that the PES approximates very well the structure expected. Having acquired a certain confidence, we predict the PES of several chain of isotopes of heavy and super-heavy nuclei and at the end we investigate the structure of nuclei in the supposed island of stability. One of the main points to show is that simple assumptions can provide already important information on the structure of nuclei outside known regions and that spectra and electromagnetic transitions can be estimated without using involved calculations and assumptions. The procedure does not allow to calculate binding energies. The method presented can be viewed as a starting point for further improvements.

  18. Doubly Reentrant Cavities Prevent Catastrophic Wetting Transitions on Intrinsically Wetting Surfaces

    KAUST Repository

    Domingues, Eddy

    2017-06-05

    Omniphobic surfaces, i.e. which repel all known liquids, have proven of value in applications ranging from membrane distillation to underwater drag reduction. A limitation of currently employed omniphobic surfaces is that they rely on perfluorinated coatings, increasing cost and environmental impact, and preventing applications in harsh environments. There is, thus, a keen interest in rendering conventional materials, such as plastics, omniphobic by micro/nano-texturing rather than via chemical make-up, with notable success having been achieved for silica surfaces with doubly reentrant micropillars. However, we found a critical limitation of microtextures comprising of pillars that they undergo catastrophic wetting transitions (apparent contact angles, θr → 0° from θr > 90°) in the presence of localized physical damages/defects or on immersion in wetting liquids. In response, a doubly reentrant cavity microtexture is introduced, which can prevent catastrophic wetting transitions in the presence of localized structural damage/defects or on immersion in wetting liquids. Remarkably, our silica surfaces with doubly reentrant cavities could exhibited apparent contact angles, θr ≈ 135° for mineral oil, where the intrinsic contact angle, θo ≈ 20°. Further, when immersed in mineral oil or water, doubly reentrant microtextures in silica (θo ≈ 40° for water) were not penetrated even after several days of investigation. Thus, microtextures comprising of doubly reentrant cavities might enable applications of conventional materials without chemical modifications, especially in scenarios that are prone to localized damages or immersion in wetting liquids, e.g. hydrodynamic drag reduction and membrane distillation.

  19. Doubly Reentrant Cavities Prevent Catastrophic Wetting Transitions on Intrinsically Wetting Surfaces.

    Science.gov (United States)

    Domingues, Eddy M; Arunachalam, Sankara; Mishra, Himanshu

    2017-06-28

    Omniphobic surfaces, that is, which repel all known liquids, have proven of value in applications ranging from membrane distillation to underwater drag reduction. A limitation of currently employed omniphobic surfaces is that they rely on perfluorinated coatings, increasing cost and environmental impact and preventing applications in harsh environments. Thus, there is a keen interest in rendering conventional materials, such as plastics, omniphobic by micro/nanotexturing rather than via chemical makeup, with notable success having been achieved for silica surfaces with doubly reentrant micropillars. However, we found a critical limitation of microtextures comprising pillars that they undergo catastrophic wetting transitions (apparent contact angles, θr → 0° from θr > 90°) in the presence of localized physical damages/defects or on immersion in wetting liquids. In response, a doubly reentrant cavity microtexture is introduced, which can prevent catastrophic wetting transitions in the presence of localized structural damage/defects or on immersion in wetting liquids. Remarkably, our silica surfaces with doubly reentrant cavities could exhibit apparent contact angles, θr ≈ 135° for mineral oil, where the intrinsic contact angle, θo ≈ 20°. Further, when immersed in mineral oil or water, doubly reentrant microtextures in silica (θo ≈ 40° for water) were not penetrated even after several days of investigation. Thus, microtextures comprising doubly reentrant cavities might enable applications of conventional materials without chemical modifications, especially in scenarios that are prone to localized damages or immersion in wetting liquids, for example, hydrodynamic drag reduction and membrane distillation.

  20. Reduction of aqueous transition metal species on the surfaces of Fe(II)-containing oxides

    Science.gov (United States)

    White, A.F.; Peterson, M.L.

    1996-01-01

    Experimental studies demonstrate that structural Fe(II) in magnetite and ilmenite heterogeneously reduce aqueous ferric, cupric, vanadate, and chromate ions at the oxide surfaces over a pH range of 1-7 at 25??C. For an aqueous transition metal m, such reactions are 3[Fe2+Fe3+2]O4(magnetite) + 2/nmz ??? 4[Fe3+2]O3(maghemite) + Fe2+ + 2/nmz-n and 3[Fe2+Ti]O3(ilmenite) + 2/nmz ??? Fe3+2Ti3O9(pseudorutile) + Fe2+ + 2/nmz-n, where z is the valance state and n is the charge transfer number. The half cell potential range for solid state oxidation [Fe(II)] ??? [Fe(III)] is -0.34 to -0.65 V, making structural Fe(II) a stronger reducing agent than aqueous Fe2+ (-0.77 V). Reduction rates for aqueous metal species are linear with time (up to 36 h), decrease with pH, and have rate constants between 0.1 and 3.3 ?? 10-10 mol m-2 s-1. Iron is released to solution both from the above reactions and from dissolution of the oxide surface. In the presence of chromate, Fe2+ is oxidized homogeneously in solution to Fe3+. X-ray photoelectron spectroscopy (XPS) denotes a Fe(III) oxide surface containing reduced Cr(III) and V(IV) species. Magnetite and ilmenite electrode potentials are insensitive to increases in divalent transition metals including Zn(II), Co(II), Mn(II), and Ni(II) and reduced V(IV) and Cr(III) but exhibit a log-linear concentration-potential response to Fe(III) and Cu(II). Complex positive electrode responses occur with increasing Cr(VI) and V(V) concentrations. Potential dynamic scans indicate that the high oxidation potential of dichromate is capable of suppressing the cathodic reductive dissolution of magnetite. Oxide electrode potentials are determined by the Fe(II)/Fe(III) composition of the oxide surface and respond to aqueous ion potentials which accelerate this oxidation process. Natural magnetite sands weathered under anoxic conditions are electrochemically reactive as demonstrated by rapid chromate reduction and the release of aqueous Fe(III) to experimental

  1. Electron-phonon coupling and structural phase transitions in early transition metal oxides and chalcogenides

    Science.gov (United States)

    Farley, Katie Elizabeth

    Pronounced nonlinear variation of electrical transport characteristics as a function of applied voltage, temperature, magnetic field, strain, or photo-excitation is usually underpinned by electronic instabilities that originate from the complex interplay of spin, orbital, and lattice degrees of freedom. This dissertation focuses on two canonical materials that show pronounced discontinuities in their temperature-dependent resistivity as a result of electron---phonon and electron---electron correlations: orthorhombic TaS3 and monoclinic VO2. Strong electron-phonon interactions in transition metal oxides and chalcogenides results in interesting structural and electronic phase transitions. The properties of the material can be changed drastically in response to external stimuli such as temperature, voltage, or light. Understanding the influence these interactions have on the electronic structure and ultimately transport characteristics is of utmost importance in order to take these materials from a fundamental aspect to prospective applications such as low-energy interconnects, steep-slope transistors, and synaptic neural networks. This dissertation describes synthetic routes to nanoscale TaS3 and VO2, develops mechanistic understanding of their electronic instabilities, and in the case of the latter system explores modulation of the electronic and structural phase transition via the incorporation of substitutional dopant atoms. We start in chapter 2 with a detailed study of the synthesis and electronic transport properties of TaS3, which undergoes a Peierls' distortion to form a charge density wave. Scaling this material down to the nanometer-sized regime allows for interrogation of single or discrete phase coherent domains. Using electrical transport and broad band noise measurements, the dynamics of pinning/depinning of the charge density wave is investigated. Chapter 3 provides a novel synthetic approach to produce high-edge-density MoS2 nanorods. MoS2 is a

  2. Superhydrophobic Behavior on Nano-structured Surfaces

    Science.gov (United States)

    Schaeffer, Daniel

    2008-05-01

    Superhydrophobic behavior is observed in natural occurrences and has been thoroughly studied over the past few years. Water repellant properties on uniform arrays of vertically aligned nano-cones were investigated to determine the highest achievable contact angle (a measure of water drop repellency), which is measured from the reference plane on which the water drop sits to the tangent line of the point at which the drop makes contact with the reference plane. At low aspect ratios (height vs. width of the nano-cones), surface tension pulls the water into the nano-cone array, resulting in a wetted surface. Higher aspect ratios reverse the effect of the surface tension, resulting in a larger contact angle that causes water drops to roll off the surface. Fiber drawing, bundling, and redrawing are used to produce the structured array glass composite surface. Triple-drawn fibers are fused together, annealed, and sliced into thin wafers. The surface of the composite glass is etched to form nano-cones through a differential etching process and then coated with a fluorinated self-assembled monolayer (SAM). Cone aspect ratios can be varied through changes in the chemistry and concentration of the etching acid solution. Superhydrophobic behavior occurs at contact angles >150 and it is predicted and measured that optimal behavior is achieved when the aspect ratio is 4:1, which displays contact angles >=175 .

  3. Childhood obesity in transition zones: an analysis using structuration theory.

    Science.gov (United States)

    Chan, Christine; Deave, Toity; Greenhalgh, Trisha

    2010-07-01

    Childhood obesity is particularly prevalent in areas that have seen rapid economic growth, urbanisation, cultural transition, and commodification of food systems. Structuration theory may illuminate the interaction between population and individual-level causes of obesity. We conducted in-depth ethnographies of six overweight/obese and four non-overweight preschool children in Hong Kong, each followed for 12-18 months. Analysis was informed by Stones' strong structuration theory. Risk factors played out differently for different children as social structures were enacted at the level of family and preschool. The network of caregiving roles and relationships around the overweight/obese child was typically weak and disjointed, and the primary caregiver appeared confused by mixed messages about what is normal, expected and legitimate behaviour. In particular, external social structures created pressure to shift childcare routines from the logic of nurturing to the logic of consumption. Our findings suggest that threats to what Giddens called ontological security in the primary caregiver may underpin the poor parenting, family stress and weak mealtime routines that mediate the relationship between an obesogenic environment and the development of obesity in a particular child. This preliminary study offers a potentially transferable approach for studying emerging epidemics of diseases of modernity in transition societies.

  4. Phase transition of 2×2 adsorbates on FCC(1 1 1) and HCP(0 0 0 1) surfaces

    Science.gov (United States)

    Sakamoto, Yoshifumi

    2003-04-01

    Order-disorder transition of adsorbates at metal surfaces is discussed based on Monte Carlo calculations for a lattice gas model on a triangular net. Repulsive interactions up to second neighbour sites and fixed concentration 1/4 of particles of lattice gas, are assumed for the 2×2 ordered structure. Calculated phase diagram and the critical exponent for susceptibility are presented. Stress is put on cases other than the second-order transition belonging to the four-state Potts universality class.

  5. Interest rates and structural shocks in European transition economies

    Directory of Open Access Journals (Sweden)

    Rajmund Mirdala

    2014-12-01

    Full Text Available European transition economies are still suffering from negative implications of economic crisis. Significant decrease in the key interest rates was followed by reduced maneuverability of central banks in providing incentives into real economies. Responsiveness of short-term interest rates to the structural shocks provides unique platform to investigate sources of their unexpected volatility and associated effects on monetary policy decision making. Moreover, sources of interest rates volatility may help to reveal side effects of the exchange rate regime choice. In the paper we analyze sources of the short-term nominal interest rates volatility in ten European transition economies by employing SVAR methodology. We observed unique patterns of the short-term interest rates responsiveness in countries with different exchange rate arrangements that contributes to the fixed versus flexible exchange rate dilemma.

  6. Discovery of elusive structures of multifunctional transition-metal borides.

    Science.gov (United States)

    Liang, Yongcheng; Wu, Zhaobing; Yuan, Xun; Zhang, Wenqing; Zhang, Peihong

    2016-01-14

    A definitive determination of crystal structures is an important prerequisite for designing and exploiting new functional materials. Even though tungsten and molybdenum borides (TMBx) are the prototype for transition-metal light-element compounds with multiple functionalities, their elusive crystal structures have puzzled scientists for decades. Here, we discover that the long-assumed TMB2 phases with the simple hP3 structure (hP3-TMB2) are in fact a family of complex TMB3 polytypes with a nanoscale ordering along the axial direction. Compared with the energetically unfavorable and dynamically unstable hP3-TMB2 phase, the energetically more favorable and dynamically stable TMB3 polytypes explain the experimental structural parameters, mechanical properties, and X-ray diffraction (XRD) patterns better. We demonstrate that such a structural and compositional modification from the hP3-TMB2 phases to the TMB3 polytypes originates from the relief of the strong antibonding interaction between d electrons by removing one third of metal atoms systematically. These results resolve the longstanding structural mystery of this class of metal borides and uncover a hidden family of polytypic structures. Moreover, these polytypic structures provide an additional hardening mechanism by forming nanoscale interlocks that may strongly hinder the interlayer sliding movements, which promises to open a new avenue towards designing novel superhard nanocomposite materials by exploiting the coexistence of various polytypes.

  7. Resistance given by tiling grain surface with micro surface structures in polycrystalline metal oxide

    Science.gov (United States)

    Moriyama, T.; Yamasaki, T.; Ohno, T.; Kishida, S.; Kinoshita, K.

    2016-12-01

    Practical use of Resistive Random Access Memory (ReRAM) depends on thorough understanding of the resistive switching (RS) mechanism in transition metal oxides. Although most of ReRAM samples have polycrystalline structures, both experimental studies and theoretical calculations do not often consider the effects that grain boundaries have on the RS mechanism. This paper discusses what determines resistance values in a Pt/polycrystalline NiO/Pt ReRAM structures by using both experiments and first-principles calculations. Electrical measurements suggest that the RS is caused in the grain boundaries of NiO films. First-principles calculations indicate that slight displacements of atoms with a small energy change of 0.04 eV per atom on the surfaces exposed in the grain boundaries can drastically change conductivities. We propose the tiling model, in which grain surfaces are composed by insulating and conductive micro surface structures, and the surface resistances are determined by the tiling patterns.

  8. Preparation of transition metal nanoparticles and surfaces modified with (co)polymers synthesized by RAFT

    Science.gov (United States)

    McCormick, III, Charles L.; Lowe, Andrew B.; Sumerlin, Brent S.

    2011-12-27

    A new, facile, general one-phase method of generating thiol-functionalized transition metal nanoparticles and surfaces modified by (co)polymers synthesized by the RAFT method is described. The method includes the steps of forming a (co)polymer in aqueous solution using the RAFT methodology, forming a colloidal transition metal precursor solution from an appropriate transition metal; adding the metal precursor solution or surface to the (co)polymer solution, adding a reducing agent into the solution to reduce the metal colloid in situ to produce the stabilized nanoparticles or surface, and isolating the stabilized nanoparticles or surface in a manner such that aggregation is minimized. The functionalized surfaces generated using these methods can further undergo planar surface modifications, such as functionalization with a variety of different chemical groups, expanding their utility and application.

  9. Advances on surface structural determination by LEED

    Energy Technology Data Exchange (ETDEWEB)

    Soares, Edmar A; De Carvalho, Vagner E [Departamento de Fisica, ICEX, Universidade Federal de Minas Gerais, 31270-090, Belo Horizonte, MG (Brazil); De Castilho, Caio M C, E-mail: edmar@fisica.ufmg.br [Grupo de Fisica de SuperfIcies e Materiais, Instituto de Fisica and Instituto Nacional de Ciencia e Tecnologia em Energia e Ambiente (CIENAM)INCT-E and A, Universidade Federal da Bahia, Campus Universitario da Federacao, 40170-115, Salvador, BA (Brazil)

    2011-08-03

    In the last 40 years, low energy electron diffraction (LEED) has proved to be the most reliable quantitative technique for surface structural determination. In this review, recent developments related to the theory that gives support to LEED structural determination are discussed under a critical analysis of the main theoretical approximation-the muffin-tin calculation. The search methodologies aimed at identifying the best matches between theoretical and experimental intensity versus voltage curves are also considered, with the most recent procedures being reviewed in detail. (topical review)

  10. Advances on surface structural determination by LEED.

    Science.gov (United States)

    Soares, Edmar A; de Castilho, Caio M C; de Carvalho, Vagner E

    2011-08-03

    In the last 40 years, low energy electron diffraction (LEED) has proved to be the most reliable quantitative technique for surface structural determination. In this review, recent developments related to the theory that gives support to LEED structural determination are discussed under a critical analysis of the main theoretical approximation-the muffin-tin calculation. The search methodologies aimed at identifying the best matches between theoretical and experimental intensity versus voltage curves are also considered, with the most recent procedures being reviewed in detail.

  11. Structured light for focusing surface plasmon polaritons.

    Science.gov (United States)

    Hu, Z J; Tan, P S; Zhu, S W; Yuan, X-C

    2010-05-10

    We propose a structureless method for focusing surface plasmon polaritons (SPPs) on a flat metal film under illumination of radially polarized cogwheel-like structured light beams. Without metal structures, the locally induced SPPs can further be propagated following the predefined patterns to form symmetric focal spots with dimensions beyond diffraction limit. Benefiting from the radial polarization, this method can be employed to pattern various center-symmetric evanescent distributions for generating SPPs reconfigurably. The SPPs will be propagating and focusing in radial directions.

  12. Bacterial cell surface structures in Yersinia enterocolitica.

    Science.gov (United States)

    Białas, Nataniel; Kasperkiewicz, Katarzyna; Radziejewska-Lebrecht, Joanna; Skurnik, Mikael

    2012-06-01

    Yersinia enterocolitica is a widespread member of the family of Enterobacteriaceae that contains both non-virulent and virulent isolates. Pathogenic Y. enterocolitica strains, especially belonging to serotypes O:3, O:5,27, O:8 and O:9 are etiologic agents of yersiniosis in animals and humans. Y. enterocolitica cell surface structures that play a significant role in virulence have been subject to many investigations. These include outer membrane (OM) glycolipids such as lipopolysaccharide (LPS) and enterobacterial common antigen (ECA) and several cell surface adhesion proteins present only in virulent Y. enterocolitica, i.e., Inv, YadA and Ail. While the yadA gene is located on the Yersinia virulence plasmid the Ail, Inv, LPS and ECA are chromosomally encoded. These structures ensure the correct architecture of the OM, provide adhesive properties as well as resistance to antimicrobial peptides and to host innate immune response mechanisms.

  13. Single crystal surface structure by bragg scattering

    DEFF Research Database (Denmark)

    Nielsen, Mogens

    1985-01-01

    X-ray diffraction is becoming an important tool in the measurements of surface structures. Single crystalline samples are used as in Low Energy Electron Diffraction (LEED)-studies. The X-ray technique is somewhat more involved due to the need of bright, collimated photon sources, in general...... synchrotron X-rays, and of very accurate angular settings in the ultrahigh-vacuum environment of the sample. We present the technique and discuss examples of experimental results....

  14. A general scheme for the estimation of oxygen binding energies on binary transition metal surface alloys

    DEFF Research Database (Denmark)

    Greeley, Jeffrey Philip; Nørskov, Jens Kehlet

    2005-01-01

    A simple scheme for the estimation of oxygen binding energies on transition metal surface alloys is presented. It is shown that a d-band center model of the alloy surfaces is a convenient and appropriate basis for this scheme; variations in chemical composition, strain effects, and ligand effects...... for the estimation of oxygen binding energies on a wide variety of transition metal alloys. (c) 2005 Elsevier B.V. All rights reserved....

  15. Temperature dependence of the structure of protein hydration water and the liquid-liquid transition.

    Science.gov (United States)

    Accordino, S R; Malaspina, D C; Rodriguez Fris, J A; Alarcón, L M; Appignanesi, G A

    2012-03-01

    We study the temperature dependence of the structure and orientation of the first hydration layers of the protein lysozyme and compare it with the situation for a model homogeneous hydrophobic surface, a graphene sheet. We show that in both cases these layers are significantly better structured than bulk water. The geometrical constraint of the interface makes the water molecules adjacent to the surface lose one water-water hydrogen bond and expel the fourth neighbors away from the surface, lowering local density. We show that a decrease in temperature improves the ordering of the hydration water molecules, preserving such a geometrical effect. For the case of graphene, this favors an ice Ih-like local structuring, similar to the water-air interface but in the opposite way along the c axis of the basal plane (while the vicinal water molecules of the air interface orient a hydrogen atom toward the surface, the oxygens of the water molecules close to the graphene plane orient a lone pair in such a direction). In turn, the case of the first hydration layers of the lysozyme molecule is shown to be more complicated, but still displaying signs of both kinds of behavior, together with a tendency of the proximal water molecules to hydrogen bond to the protein both as donors and as acceptors. Additionally, we make evident the existence of signatures of a liquid-liquid transition (Widom line crossing) in different structural parameters at the temperature corresponding to the dynamic transition incorrectly referred to as "the protein glass transition."

  16. Structural phase transitions in high-temperature superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Tatarenko, H.M. [Toulon Univ., 83 - Le Garde (France). Lab. des Materiaux Multiphases et Interfaces; Nihoul, G.E. [Toulon Univ., 83 - Le Garde (France). Lab. des Materiaux Multiphases et Interfaces

    1995-11-01

    This chapter is devoted to the study of the order-disorder like phase transitions which occur in the high-temperature superconductors (HTS). We mainly consider Lanthanium based compounds like La{sub 2}CuO{sub 4+{delta}} or La{sub 2-x}M{sub x}CuO{sub 4+{delta}} (where M is an alkali atom Ba, Sr, Ca, Na, K, ..) and Yttrium based superconductors like YBa{sub 2}Cu{sub 3}O{sub 6+{delta}}. Different kinds of ordered structures were found in these compounds by X-ray and neutron diffraction, as well as by High Resolution Electron Microscopy imaging and are described. The theoretical models, which describe the structural evolution as temperature and/or concentration of the different components vary, are considered in detail. The relation between structural instabilities and high-temperature superconductivity is discussed. (orig.)

  17. Turbulent transport and structural transition in confined plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, Kimitaka; Itoh, Sanae; Fukuyama, Atsushi; Yagi, Masatoshi

    1996-10-01

    Theory of the far-nonequilibrium transport of plasmas is described. Analytic as well as simulation studies are developed. The subcritical nature of turbulence and the mechanism for self-sustaining are discussed. The transport coefficient is obtained. The pressure gradient is introduced as an order parameter, and the bifurcation from the collisional transport to the turbulent one is shown. The generation of the electric field and its influence on the turbulent transport are analyzed. The bifurcation of the radial electric field structure is addressed. The hysteresis appears in the flux-gradient relation. This bifurcation causes the multifold states in the plasma structure, driving the transition in transport coefficient or the self-generating oscillations in the flux. Structural formation and dynamics of plasma profiles are explained. (author)

  18. Turbulent transport and structural transition in confined plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, Kimitaka [National Inst. for Fusion Science, Nagoya (Japan); Itoh, Sanae-I; Yagi, Masatoshi [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Fukuyama, Atsushi [Okayama Univ. (Japan). School of Engineering

    1997-05-01

    The theory of far-nonequilibrium transport of plasmas is described. Analytic as well as simulation studies are developed. The subcritical nature coefficient is obtained. The pressure gradient is introduced as an order parameter, and the bifurcation from collisional to turbulent transport is shown. The generation of the electric field and its influence on the turbulent transport are analysed. The bifurcation of the radial electric field structure is addressed. Hysteresis appears in the flux-gradient relation. This bifurcation causes the multifold states in the plasma structure, driving the transition in the transport coefficient or the self-generating oscillations in the flux. The structural formation and dynamics of plasma profiles are explained. (Author).

  19. On the structure of the transition disk around TW Hya

    CERN Document Server

    Menu, J; Henning, T; Chandler, C J; Linz, H; Benisty, M; Lacour, S; Min, M; Waelkens, C; Andrews, S M; Calvet, N; Carpenter, J M; Corder, S A; Deller, A T; Greaves, J S; Harris, R J; Isella, A; Kwon, W; Lazio, J; Bouquin, J -B Le; Ménard, F; Mundy, L G; Pérez, L M; Ricci, L; Sargent, A I; Storm, S; Testi, L; Wilner, D J

    2014-01-01

    For over a decade, the structure of the inner cavity in the transition disk of TW Hydrae has been a subject of debate. Modeling the disk with data obtained at different wavelengths has led to a variety of proposed disk structures. Rather than being inconsistent, the individual models might point to the different faces of physical processes going on in disks, such as dust growth and planet formation. Our aim is to investigate the structure of the transition disk again and to find to what extent we can reconcile apparent model differences. A large set of high-angular-resolution data was collected from near-infrared to centimeter wavelengths. We investigated the existing disk models and established a new self-consistent radiative-transfer model. A genetic fitting algorithm was used to automatize the parameter fitting. Simple disk models with a vertical inner rim and a radially homogeneous dust composition from small to large grains cannot reproduce the combined data set. Two modifications are applied to this sim...

  20. Mid-infrared surface plasmon coupled emitters utilizing intersublevel transitions in InAs quantum dots.

    Energy Technology Data Exchange (ETDEWEB)

    Lyon, Stephen A. (Princeton University, Princeton, NJ); Chow, Weng Wah; Passmore, Brandon Scott; Ribaudo, Troy (University of Massachusetts Lowell, Lowell, MA); Adams, David (University of Massachusetts Lowell, Lowell, MA); Wasserman, Daniel (University of Massachusetts Lowell, Lowell, MA); Shaner, Eric Arthur

    2010-08-01

    We demonstrate mid-infrared electroluminescence from intersublevel transitions in self-assembled InAs quantum dots coupled to surface plasmon modes on metal hole arrays. Subwavelength metal hole arrays with different periodicity are patterned into the top contact of the broadband (9-15 {micro}m) quantum dot material and the measured electroluminescence is compared to devices without a metal hole array. The resulting normally directed emission is narrowed and a splitting in the spectral structure is observed. By applying a coupled quantum electrodynamic model and using reasonable values for quantum dot distributions and plasmon linewidths we are able to reproduce the experimentally measured spectral characteristics of device emission when using strong coupling parameters.

  1. Using force fields methods for locating transition structures

    Science.gov (United States)

    Jensen, Frank

    2003-11-01

    A previously proposed strategy of using force field methods for generating approximations to the geometry of transition structures is extended to also estimating an approximate Hessian matrix. These two components allow an automated method for locating first order saddle points, which is an essential requisite for studying chemical reactions of systems with many degrees of freedom. The efficiency of using an approximate force field Hessian matrix for initiating the geometry optimization is compared with the use of an exact Hessian. The force field Hessian in general requires more geometry steps to converge, but the additional computational cost is offset by the savings from not calculating the exact Hessian at the initial geometry.

  2. Spatial structure of compound dither in L/H transition

    Energy Technology Data Exchange (ETDEWEB)

    Toda, Shinichiro; Itoh, Kimitaka [National Inst. for Fusion Science, Toki, Gifu (Japan); Itoh, Sanae I.; Yagi, Masatoshi [Kyushu Univ., Fukuoka (Japan). Research Inst. for Applied Mechanics; Fukuyama, Atsushi [Kyoto Univ. (Japan). Dept. of Nuclear Engineering

    2000-03-01

    To study the plasma evolution and spatial structure at the L/H transition, the double hysteresis is examined by use of the 1-dimensional transport model equations. Three mechanisms for the bipolar losses, i.e., the loss cone loss, collisional bulk viscosity loss of ions and the anomalous loss are simultaneously retained. Five-fold multiple bifurcations are found to exist at the plasma edge, similar to the previous 0-dimensional study. Double hysteresis causes a self-generated oscillation, which is attributed to the compound dither, a kind of ELMs. Spatio-temporal evolution of the compound dither is analyzed. (author)

  3. Temperature Triggered Structural Transitions in Surfactant organized Self Assemblies

    Science.gov (United States)

    Rose, J. Linet; Balamurugan, S.; Sajeevan, Ajin C.; Sreejith, Lisa

    2011-10-01

    Preparation & characterization of tunable fluids is an emerging area with potential application in many fields. Surfactants self assemble in aqueous solution to give a rich variety of phase structures, the size and shape of which can be tuned by additives like salts, alcohols, amines, aromatics etc or external stimuli such as light, temperature etc. The addition of long chain aliphatic alcohol has significant influence on the surfactant aggregation, as it promotes morphological growth of micelles. The cationic surfactant, Cetyl Trimethyl Ammonium Bromide (CTAB) with nonanol in presence of potassium bromide (KBr) shows thermo tunable viscosity behaviour and optical switching behaviour. The solution is visually observed to transform from a turbid and less viscous phase at low temperature to clear and considerably viscous phase at high temperature. Temperature induced changes in turbidity and viscosity are consistent with the transition from vesicle to worm like micelle. It is also worth emphasizing that the transition is thermo reversible, so that vesicles that are disrupted into micelles upon heating can be reformed upon cooling. The thermo tunable transition from turbid to transparent state and the concomitant changes in viscosity are promising for the use in smart windows, monitoring of tumor growth or in other stimuli based application.

  4. Scaling Relationships for Adsorption Energies of C2 Hydrocarbons on Transition Metal Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Jones, G

    2011-08-18

    Using density functional theory calculations we show that the adsorption energies for C{sub 2}H{sub x}-type adsorbates on transition metal surfaces scale with each other according to a simple bond order conservation model. This observation generalizes some recently recognized adsorption energy scaling laws for AH{sub x}-type adsorbates to unsaturated hydrocarbons and establishes a coherent simplified description of saturated as well as unsaturated hydrocarbons adsorbed on transition metal surfaces. A number of potential applications are discussed. We apply the model to the dehydrogenation of ethane over pure transition metal catalysts. Comparison with the corresponding full density functional theory calculations shows excellent agreement.

  5. Bullet-to-streamer transition on the liquid surface of a plasma jet in atmospheric pressure

    Science.gov (United States)

    Yoon, S.-Y.; Kim, G.-H.; Kim, S.-J.; Bae, B.; Kim, N.-K.; Lee, H.; Bae, N.; Ryu, S.; Yoo, S. J.; Kim, S. B.

    2017-01-01

    This study investigated the transition of the plasma shape from a ring-shaped bullet to a pin-like streamer adjacent to the electrolyte surface in a kHz-driven helium atmospheric pressure plasma jet. The transition was observed by synchronized fast images, plasma propagation speed, time-resolved emission profile of Hβ, and spatially and temporally resolved helium metastable density. The transition height increased when electrolyte evaporation was enhanced. The plasma continued to discharge on the electrolyte surface even in the absence of metastable species, i.e., the discharge mechanism changed from Penning ionization between helium metastable and ambient nitrogen to electron collision on evaporated water.

  6. Structural and spectroscopic studies of surfaces

    CERN Document Server

    Laitenberger, P

    1996-01-01

    and on a 10ML thick Ar spacer layer, a remarkable substrate dependence is revealed. A new STM-based technique for fabricating simple metal-structures with dimensions in the 10-100nm regime which are partially electrically isolated from their environment was developed in collaboration with Dr. L. A. Silva. This technique employs the STM tip as a mechanical nanofabrication tool to machine gaps into a thin metallic film deposited on an insulating substrate, which laterally confine and electrically isolate the desired metal regions. Several metal structures, such as nanoscale wires and pads, were successfully created. Finally, the conceptual basis and present stage of construction of a new surface analytical tool, the Scanning Probe Energy Loss Spectrometer (SPELS), is discussed. The SPELS offers the exciting prospect of collecting structural as well as spectroscopic information with a spatial resolution of a few nanometres. Once successfully developed, it will be ideally suited for spectroscopic studies of nanos...

  7. Tunable Fermi surface topology and Lifshitz transition in bilayer graphene

    OpenAIRE

    Varlet, Anastasia; Mucha-Kruczyński, Marcin; Bischoff, Dominik; Simonet, Pauline; Taniguchi, Takashi; Watanabe, Kenji; Fal'ko, Vladimir; Ihn, Thomas; Ensslin, Klaus

    2015-01-01

    Bilayer graphene is a highly tunable material: not only can one tune the Fermi energy using standard gates, as in single-layer graphene, but the band structure can also be modified by external perturbations such as transverse electric fields or strain. We review the theoretical basics of the band structure of bilayer graphene and study the evolution of the band structure under the influence of these two external parameters. We highlight their key role concerning the ease to experimentally pro...

  8. Architectural Surfaces and Structures from Circular Arcs

    KAUST Repository

    Shi, Ling

    2013-12-01

    In recent decades, the popularity of freeform shapes in contemporary architecture poses new challenges to digital design. One of them is the process of rationalization, i.e. to make freeform skins or structures affordable to manufacture, which draws the most attention from geometry researchers. In this thesis, we aim to realize this process with simple geometric primitives, circular arcs. We investigate architectural surfaces and structures consisting of circular arcs. Our focus is lying on how to employ them nicely and repetitively in architectural design, in order to decrease the cost in manufacturing. Firstly, we study Darboux cyclides, which are algebraic surfaces of order ≤ 4. We provide a computational tool to identify all families of circles on a given cyclide based on the spherical model of M ̈obius geometry. Practical ways to design cyclide patches that pass through certain inputs are presented. In particular, certain triples of circle families on Darboux cyclides may be suitably arranged as 3-webs. We provide a complete classification of all possible 3-webs of circles on Darboux cyclides. We then investigate the circular arc snakes, which are smooth sequences of circu- lar arcs. We evolve the snakes such that their curvature, as a function of arc length, remains unchanged. The evolution of snakes is utilized to approximate given surfaces by circular arcs or to generated freeform shapes, and it is realized by a 2-step pro- cess. More interestingly, certain 6-arc snake with boundary constraints can produce a smooth self motion, which can be employed to build flexible structures. Another challenging topic is approximating smooth freeform skins with simple panels. We contribute to this problem area by approximating a negatively-curved 5 surface with a smooth union of rational bilinear patches. We provide a proof for vertex consistency of hyperbolic nets using the CAGD approach of the rational B ́ezier form. Moreover, we use Darboux transformations for the

  9. Temperature-mediated transition from Dyakonov-Tamm surface waves to surface-plasmon-polariton waves

    Science.gov (United States)

    Chiadini, Francesco; Fiumara, Vincenzo; Mackay, Tom G.; Scaglione, Antonio; Lakhtakia, Akhlesh

    2017-08-01

    The effect of changing the temperature on the propagation of electromagnetic surface waves (ESWs), guided by the planar interface of a homogeneous isotropic temperature-sensitive material (namely, InSb) and a temperature-insensitive structurally chiral material (SCM) was numerically investigated in the terahertz frequency regime. As the temperature rises, InSb transforms from a dissipative dielectric material to a dissipative plasmonic material. Correspondingly, the ESWs transmute from Dyakonov-Tamm surface waves into surface-plasmon-polariton waves. The effects of the temperature change are clearly observed in the phase speeds, propagation distances, angular existence domains, multiplicity, and spatial profiles of energy flow of the ESWs. Remarkably large propagation distances can be achieved; in such instances the energy of an ESW is confined almost entirely within the SCM. For certain propagation directions, simultaneous excitation of two ESWs with (i) the same phase speeds but different propagation distances or (ii) the same propagation distances but different phase speeds are also indicated by our results.

  10. Magnetic and structural transitions in crystals with a structure of the NaCl type

    Science.gov (United States)

    Kassan-Ogly, F. A.; Filippov, B. N.

    2009-04-01

    A model of simultaneous magnetic and structural first-order transitions in antiferromagnets with a strong cubic magnetic anisotropy has been constructed on the basis of a synthesis of magnetic modified 6-state and 8-state Potts models and the theoretical model of structural phase transitions in cubic crystals. A revised scheme has been suggested for the derivation of possible magnetic structures in the fcc lattice with allowance for competing interactions between the nearest and next-nearest neighbors. A calculation of the temperature evolution of high-temperature diffuse magnetic scattering of neutrons has been carried out to show that the mechanism of a magnetic transition at the Néel point is caused by the transformation of diffuse magnetic scattering into magnetic Bragg peaks.

  11. High fidelity simulation of nucleate boiling and transition to critical heat flux on enhanced structures

    Science.gov (United States)

    Yazdani, Miad; Alahyari, Abbas; Radcliff, Thomas; Soteriou, Marios

    2015-11-01

    Surface enhancement is often is the primary approach for improved heat transfer performance of two-phase thermal systems particularly when they operate in nucleate boiling regime. This paper exploits the modeling capability developed by Yazdani et al. for simulation of nucleate boiling and transition to critical heat flux to study the nucleation phenomenon on various enhanced structures. The multi-scale of two-phase flow associated with boiling phenomena is addressed through combination of deterministic CFD for the macro-scale transport, asymptotic based representation of micro-layer, and stochastic representation of surface roughness so as to allow a high-fidelity simulation of boiling on an arbitrary surface. In addition, given the excessive complexity of surface structures often used for enhancement of boiling heat transfer, a phase-field-based method is developed to generate the structures where the numerical parameters in the phase-field model determine the topology of a given structure. The ``generated'' structure is then embedded into the two-phase flow model through virtual boundary method for the boiling simulation. The model is validated against experimental data for the boiling curve and the critical heat flux as well as nucleation and bubble dynamics characteristics.

  12. Neisserial surface lipoproteins: structure, function and biogenesis.

    Science.gov (United States)

    Hooda, Yogesh; Shin, Hyejin E; Bateman, Thomas J; Moraes, Trevor F

    2017-03-01

    The surface of many Gram-negative bacteria contains lipidated protein molecules referred to as surface lipoproteins or SLPs. SLPs play critical roles in host immune evasion, nutrient acquisition and regulation of the bacterial stress response. The focus of this review is on the SLPs present in Neisseria, a genus of bacteria that colonise the mucosal surfaces of animals. Neisseria contains two pathogens of medical interest, namely Neisseria meningitidis and N. gonorrhoeae. Several SLPs have been identified in Neisseria and their study has elucidated key strategies used by these pathogens to survive inside the human body. Herein, we focus on the identification, structure and function of SLPs that have been identified in Neisseria. We also survey the translocation pathways used by these SLPs to reach the cell surface. Specifically, we elaborate on the strategies used by neisserial SLPs to translocate across the outer membrane with an emphasis on Slam, a novel outer membrane protein that has been implicated in SLP biogenesis. Taken together, the study of SLPs in Neisseria illustrates the widespread roles played by this family of proteins in Gram-negative bacteria. © FEMS 2017. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  13. Deciphering fine molecular details of proteins' structure and function with a Protein Surface Topography (PST) method.

    Science.gov (United States)

    Koromyslova, Anna D; Chugunov, Anton O; Efremov, Roman G

    2014-04-28

    Molecular surfaces are the key players in biomolecular recognition and interactions. Nowadays, it is trivial to visualize a molecular surface and surface-distributed properties in three-dimensional space. However, such a representation trends to be biased and ambiguous in case of thorough analysis. We present a new method to create 2D spherical projection maps of entire protein surfaces and manipulate with them--protein surface topography (PST). It permits visualization and thoughtful analysis of surface properties. PST helps to easily portray conformational transitions, analyze proteins' properties and their dynamic behavior, improve docking performance, and reveal common patterns and dissimilarities in molecular surfaces of related bioactive peptides. This paper describes basic usage of PST with an example of small G-proteins conformational transitions, mapping of caspase-1 intersubunit interface, and intrinsic "complementarity" in the conotoxin-acetylcholine binding protein complex. We suggest that PST is a beneficial approach for structure-function studies of bioactive peptides and small proteins.

  14. Structural Transition in Myelin Membrane as Initiator of Multiple Sclerosis.

    Science.gov (United States)

    Shaharabani, Rona; Ram-On, Maor; Avinery, Ram; Aharoni, Rina; Arnon, Ruth; Talmon, Yeshayahu; Beck, Roy

    2016-09-21

    In demyelinating diseases such as multiple sclerosis, disrupted myelin structures impair the functional role of the sheath as an insulating layer for proper nerve conduction. Though the etiology and recovery pathways remain unclear, in vivo studies show alterations in the lipid and the adhesive protein (myelin basic protein, MBP) composition. We find that in vitro cytoplasmic myelin membranes with modified lipid composition and low MBP concentration, as in demyelinating disease, show structural instabilities and pathological phase transition from a lamellar to inverted hexagonal, which involve enhanced local curvature. Similar curvatures are also found in vivo in diseased myelin sheaths. In addition, MBP dimers form a correlated mesh-like network within the inner membrane space, only in the vicinity of native lipid composition. These findings delineate the distinct functional roles of dominant constituents in cytoplasmic myelin sheaths, and shed new light on mechanisms disrupting lipid-protein complexes in the diseased state.

  15. Domain structure and phase transition in Sc-doped zirconia

    Science.gov (United States)

    Brunauer, G.; Boysen, H.; Frey, F.; Ehrenberg, H.

    2002-01-01

    The temperature dependence of the domain structure associated with the ferroelastic phase transition (Fm↔R bar 3 m) in ZrO2 doped with 11% Sc2O3 has been determined from a peak shape analysis of high-resolution synchrotron x-ray powder diffraction data. In the temperature region of coexisting phases the observed characteristic anisotropic broadening and asymmetry of the lines is modelled by three different phases: a main rhombohedral phase, a distorted rhombohedral phase with a smaller c/a ratio, and a cubic phase. The latter two are assigned to the internal structure of the domain walls between two adjacent twin domains. The size and amount of the cubic phase show an initially slow increase with temperature followed by a very steep increase and a slow one after that. The size of the (main) rhombohedral domains remains nearly constant, while (micro-) strain in the distorted regions gradually decreases.

  16. Structural transitions between epitaxially ordered phases in adsorbed submonolayers

    Science.gov (United States)

    Ostlund, S.; Berker, A. N.

    1980-06-01

    The global phase diagram of a triangular lattice-gas model for submonolayers adsorbed epitaxially on basal graphite is studied using a position-space renormalization method. This model has nearest-neighbor exclusion, and accomodates dominant third-neighbor interaction. Each cell of 12 sites is mapped onto a single local degree of freedom with a single-triplet-quadruplet structure. The lattice gas, with up to 20th-neighbor interactions, is thereby transformed into a nearest-neighbor model, which is then analyzed by a Migdal-Kadanoff renormalization transformation. At low temperatures, as coverage is increased from zero, gas, 2 × 2 solid, and 3×3 solid phases can be encountered, separated by first-order transitions. These solids undergo first-or higher-order transitions into fluid phases as temperature is increased at given density. Triple points, multicritical points, and/or critical end-points occur for various relative strengths of interactions. For certain plausible potentials, the 2 × 2 solid occurs at finite temperature, but not at zero temperature. Distinct liquid and gas phases, with a solid-liquid-gas triple point, are found in some cases. Contact is made with the phase diagram of methane physisorbed on basal graphite, suggesting that the effective hard-core radius of methane is increased by adsorption. A phase diagram very similar to that exhibited by oxygen chemisorbed on nickel (111), with both 2 × 2 and 3×3 structures, is also obtained.

  17. Structure and thermodynamics of surface recognition

    Energy Technology Data Exchange (ETDEWEB)

    Gupta, G.

    1998-11-01

    This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Interactions of the surface glycoprotein, gp120, with the receptors of host cells define the pathogenesis of HIV-1, the virus that causes AIDS. gp120 is made of several disulfide-bridged loops--the amino acid sequences of some of these loops are fairly conserved whereas the rest are variable. The third variable (V3) loop has been the target of vaccine design for quite some time since this loop is involved in various steps of viral pathogenesis. However, this loop also happens to be the most variable one. The authors have carried out structural and immunological studies to determine the sequence-structure-antigenicity correlations of the HIV-1 V3 loops. This resulted in the identification of a secondary structure at the tip of the V3 loop that remains invariant in spite of the sequence variation. The authors designed a multi-valent V3-based antigen that presents multiple copies of the same tip element several times in the same structure. During the course of this project, they realized that the protective epitopes of gp120 should be judged in the context of the native structure. Therefore, the authors developed a method to obtain a model of gp120 that is consistent with all the immunology and virology data. This model is useful in choosing or designing gp120 subdomains for vaccine development.

  18. Non-linear modelling of the effects of strain on transition metal surfaces

    Science.gov (United States)

    Shuttleworth, I. G.

    2016-12-01

    A sequence of polynomial expressions have been shown to describe the strained surface energy of low-index hexagonal and square transition metal surfaces. Distinguishable functions describe the hexagonal FCC (1 1 1) and HCP (0 0 0 1) surfaces, but a single function describes the FCC (1 0 0) and BCC (1 0 0) surfaces. A far weaker dependence exists between the strained surface energy and the electronic state of the surface, and the competition between geometric and electronic states across is discussed.

  19. Engineering electrocatalytic activity in nanosized perovskite cobaltite through surface spin-state transition

    Science.gov (United States)

    Zhou, Shiming; Miao, Xianbing; Zhao, Xu; Ma, Chao; Qiu, Yuhao; Hu, Zhenpeng; Zhao, Jiyin; Shi, Lei; Zeng, Jie

    2016-05-01

    The activity of electrocatalysts exhibits a strongly dependence on their electronic structures. Specifically, for perovskite oxides, Shao-Horn and co-workers have reported a correlation between the oxygen evolution reaction activity and the eg orbital occupation of transition-metal ions, which provides guidelines for the design of highly active catalysts. Here we demonstrate a facile method to engineer the eg filling of perovskite cobaltite LaCoO3 for improving the oxygen evolution reaction activity. By reducing the particle size to ~80 nm, the eg filling of cobalt ions is successfully increased from unity to near the optimal configuration of 1.2 expected by Shao-Horn's principle. Consequently, the activity is significantly enhanced, comparable to those of recently reported cobalt oxides with eg~1.2 configurations. This enhancement is ascribed to the emergence of spin-state transition from low-spin to high-spin states for cobalt ions at the surface of the nanoparticles, leading to more active sites with increased reactivity.

  20. Surface-induced liquid-gas transition in salt-free solutions of model charged colloids.

    Science.gov (United States)

    Budkov, Yu A; Frolov, A I; Kiselev, M G; Brilliantov, N V

    2013-11-21

    We report a novel phenomenon of a surface-induced phase transition in salt-free solutions of charged colloids. We develop a theory of this effect and confirm it by Molecular Dynamics simulations. To describe the colloidal solution we apply a primitive model of electrolyte with a strong asymmetry of charge and size of the constituent particles - macroions and counterions. To quantify interactions of the colloidal particles with the neutral substrate we use a short-range potential which models dispersion van der Waals forces. These forces cause the attraction of colloids to the surface. We show that for high temperatures and weak attraction, only gradual increase of the macroion concentration in the near-surface layer is observed with increase of interaction strength. If however temperature drops below some threshold value, a new dense (liquid) phase is formed in the near-surface layer. It can be interpreted as a surface-induced first-order phase transition with a critical point. Using an appropriately adopted Maxwell construction, we find the binodal. Interestingly, the observed near-surface phase transition can occur at the absence of the bulk phase transition and may be seemingly classified as prewetting transition. The reported effect could be important for various technological applications where formation of colloidal particle layers with the desired properties is needed.

  1. Can dead zones create transition disk like structures?

    CERN Document Server

    Pinilla, Paola; Ovelar, Maria de Juan; Birnstiel, Til

    2016-01-01

    [Abridged] Regions of low ionisation where the activity of the magneto-rotational instability is suppressed, the so called dead zones, have been suggested to explain gaps and asymmetries of transition disks. We investigate the gas and dust evolution simultaneously assuming simplified prescriptions for a dead zone and a magnetohydrodynamic (MHD) wind acting on the disk. We explore whether or not the resulting gas and dust distribution can create signatures similar to the ones observed in transition disks. For the dust evolution, we include the transport, growth, and fragmentation of dust particles. To compare with observations, we produce synthetic images in scattered optical light and in thermal emission at mm wavelengths. In all models with a dead zone, a bump in the gas surface density is produced, which is able to efficiently trap large particles ($\\gtrsim1$ mm) at the outer edge of the dead zone. The gas bump reaches an amplitude of a factor of $\\sim5$, which can be enhanced by the presence of a MHD wind ...

  2. Wetting, prewetting and surface freezing transitions in fluid Ga-based alloys a surface light scattering study

    CERN Document Server

    Freyland, W; Mechdiev, I

    2003-01-01

    The surface energy and entropy of liquid Ga-Bi and Ga-Pb alloys have been studied by means of surface light scattering measurements at various compositions and temperatures between the respective eutectic and monotectic points. Analysis of these results using the Gibbs adsorption equation gives evidence for wetting and prewetting transitions in these alloys completely consistent with a tetra-point wetting scenario (Dietrich S and Schick M 1997 Surf. Sci. 382 178). Surface freezing transitions are observed for conditions near the liquidus curves. In view of their viscoelastic properties and their relation with the wetting film characteristics, we suggest a simple explanation for the observed surface freezing phenomena in terms of nucleation of strongly undercooled wetting films.

  3. APPLICATIONS OF SURFACE SPLINEFUNCTIONS TO STRUCTURAL ANALYSIS IN COAL GEOLOGY

    Institute of Scientific and Technical Information of China (English)

    HanJinyan; YuZhiwei

    1996-01-01

    A surface spline function is used to fit a coal seam surface in structural analysis in coal geology. From the surface spline function, the first and second partial derivatives can also be derived and used to structural analysis, especially for recognition of the concealed structures. The detection of structures related to faulting is emphasized.

  4. Nanoscale surface topographies for structural colors

    DEFF Research Database (Denmark)

    Clausen, Jeppe Sandvik

    The thesis describes and demonstrates the possibilities for utilization of structural colors in mass fabricated plastic products as replacement for or in combination with pigments and inks. The motivation is the possible advantages related to re-cycling and re-use of plastic by limiting the number...... of materials in a given plastic part. Also, the reduction of process steps and materials leads to a reduction of the fabrication costs. In the thesis only surfaces, which may be fabricated using replication based methods, such as injection molding, are considered. Nanostructures with sizes comparable......-polymer interface is suppressed. This improves the ability to see through a clear plastic in the presence of specular reflection. The tapered nanostructures are also utilized to enhance the chroma of pigmented polymers. Larger tapered structures fabricated in a similar manor are shown to work as color filters...

  5. Suppression of Structural Phase Transition in VO2 by Epitaxial Strain in Vicinity of Metal-insulator Transition

    Science.gov (United States)

    Yang, Mengmeng; Yang, Yuanjun; Bin Hong; Wang, Liangxin; Hu, Kai; Dong, Yongqi; Xu, Han; Huang, Haoliang; Zhao, Jiangtao; Chen, Haiping; Song, Li; Ju, Huanxin; Zhu, Junfa; Bao, Jun; Li, Xiaoguang; Gu, Yueliang; Yang, Tieying; Gao, Xingyu; Luo, Zhenlin; Gao, Chen

    2016-03-01

    Mechanism of metal-insulator transition (MIT) in strained VO2 thin films is very complicated and incompletely understood despite three scenarios with potential explanations including electronic correlation (Mott mechanism), structural transformation (Peierls theory) and collaborative Mott-Peierls transition. Herein, we have decoupled coactions of structural and electronic phase transitions across the MIT by implementing epitaxial strain on 13-nm-thick (001)-VO2 films in comparison to thicker films. The structural evolution during MIT characterized by temperature-dependent synchrotron radiation high-resolution X-ray diffraction reciprocal space mapping and Raman spectroscopy suggested that the structural phase transition in the temperature range of vicinity of the MIT is suppressed by epitaxial strain. Furthermore, temperature-dependent Ultraviolet Photoelectron Spectroscopy (UPS) revealed the changes in electron occupancy near the Fermi energy EF of V 3d orbital, implying that the electronic transition triggers the MIT in the strained films. Thus the MIT in the bi-axially strained VO2 thin films should be only driven by electronic transition without assistance of structural phase transition. Density functional theoretical calculations further confirmed that the tetragonal phase across the MIT can be both in insulating and metallic states in the strained (001)-VO2/TiO2 thin films. This work offers a better understanding of the mechanism of MIT in the strained VO2 films.

  6. Structure-Reactivity Relationships in Multi-Component Transition Metal Oxide Catalysts FINAL Report

    Energy Technology Data Exchange (ETDEWEB)

    Altman, Eric I. [Yale Univ., New Haven, CT (United States)

    2015-10-06

    The focus of the project was on developing an atomic-level understanding of how transition metal oxide catalysts function. Over the course of several renewals the specific emphases shifted from understanding how local structure and oxidation state affect how molecules adsorb and react on the surfaces of binary oxide crystals to more complex systems where interactions between different transition metal oxide cations in an oxide catalyst can affect reactivity, and finally to the impact of cluster size on oxide stability and reactivity. Hallmarks of the work were the use of epitaxial growth methods to create surfaces relevant to catalysis yet tractable for fundamental surface science approaches, and the use of scanning tunneling microscopy to follow structural changes induced by reactions and to pinpoint adsorption sites. Key early findings included the identification of oxidation and reduction mechanisms on a tungsten oxide catalyst surface that determine the sites available for reaction, identification of C-O bond cleavage as the rate limiting step in alcohol dehydration reactions on the tungsten oxide surface, and demonstration that reduction does not change the favored reaction pathway but rather eases C-O bond cleavage and thus reduces the reaction barrier. Subsequently, a new reconstruction on the anatase phase of TiO2 relevant to catalysis was discovered and shown to create sites with distinct reactivity compared to other TiO2 surfaces. Building on this work on anatase, the mechanism by which TiO2 enhances the reactivity of vanadium oxide layers was characterized and it was found that the TiO2 substrate can force thin vanadia layers to adopt structures they would not ordinarily form in the bulk which in turn creates differences in reactivity between supported layers and bulk samples. From there, the work progressed to studying well-defined ternary oxides where synergistic effects between the two cations can induce

  7. Atomic and molecular adsorption on transition-metal carbide (111) surfaces from density-functional theory: a trend study of surface electronic factors.

    Science.gov (United States)

    Vojvodic, A; Ruberto, C; Lundqvist, B I

    2010-09-22

    This study explores atomic and molecular adsorption on a number of early transition-metal carbides (TMCs) in NaCl structure by means of density-functional theory calculations. The investigated substrates are the TM-terminated TMC(111) surfaces, of interest because of the presence of different types of surface resonances (SRs) on them and because of their technological importance in growth processes. Also, TM compounds have shown potential in catalysis applications. Trend studies are conducted with respect to both period and group in the periodic table, choosing the substrates ScC, TiC, VC, ZrC, NbC, δ-MoC, TaC, and WC (in NaCl structure) and the adsorbates H, B, C, N, O, F, NH, NH(2), and NH(3). Trends in adsorption strength are explained in terms of surface electronic factors, by correlating the calculated adsorption-energy values with the calculated surface electronic structures. The results are rationalized by use of a concerted-coupling model (CCM), which has previously been applied successfully to the description of adsorption on TiC(111) and TiN(111) surfaces (Ruberto et al 2007 Solid State Commun. 141 48). First, the clean TMC(111) surfaces are characterized by calculating surface energies, surface relaxations, Bader charges, and surface-localized densities of states (DOSs). Detailed comparisons between surface and bulk DOSs reveal the existence of transition-metal localized SRs (TMSRs) in the pseudogap and of several C-localized SRs (CSRs) in the upper valence band on all considered TMC(111) surfaces. The spatial extent and the dangling bond nature of these SRs are supported by real-space analyses of the calculated Kohn-Sham wavefunctions. Then, atomic and molecular adsorption energies, geometries, and charge transfers are presented. An analysis of the adsorbate-induced changes in surface DOSs reveals a presence of both adsorbate-TMSR and adsorbate-CSRs interactions, of varying strengths depending on the surface and the adsorbate. These variations are

  8. Surface phase transitions upon reduction of epitaxial WO{sub 3}(1 0 0) thin films

    Energy Technology Data Exchange (ETDEWEB)

    Li, M.; Altman, E.I.; Posadas, A.; Ahn, C.H

    2004-01-15

    The surface structure and morphology of WO{sub 3}(1 0 0) thin films were studied using scanning tunneling microscopy (STM) and low-energy electron diffraction. The films experienced a net-reducing environment when annealed in oxygen at 800 K leading to surface phase transitions from p(2x2) to p(4x2), and from p(4x2) to a mix p(4x2) and p(3x2). Increasing the annealing temperature to 830 K in ultra-high-vacuum (UHV) led to a fully p(3x2) reconstructed surface. Continued UHV annealing above 800 K caused (1x1) islands to appear on the p(3x2) surface and the film color to darken. Eventually, prolonged UHV annealing led to a (1x1)-terminated surface with straight steps oriented in [0 0 1] or [0 1 0] directions due to crystallographic shear planes. The randomly spaced steps on the (1x1) surface indicated variations in the local stoichiometry in the film. An added row model proposed for the p(4x2) structure is also shown to be consistent with the p(3x2) structure. The formation of the p(4x2) structure from the p(2x2) structure was attributed to W{sup 5+} migration into the bulk to form the troughs between the added rows. Reduction of the p(4x2) structure caused the troughs to narrow rather than deepen, suggesting that W{sup 5+} or added row surface diffusion competes with migration of reduced W ions into the bulk when the p(3x2) structure forms. The STM images also show evidence that the (1x1) structure forms through coalescence of the added rows.

  9. Structural phase transition and elastic properties of mercury chalcogenides

    Energy Technology Data Exchange (ETDEWEB)

    Varshney, Dinesh, E-mail: vdinesh33@rediffmail.com [School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore 452001 (India); Shriya, S. [School of Physics, Vigyan Bhavan, Devi Ahilya University, Khandwa Road Campus, Indore 452001 (India); Khenata, R. [Laboratoire de Physique Quantique et de Modelisation Mathematique (LPQ3M), Departement de Technologie, Universite de Mascara, 29000 Mascara (Algeria)

    2012-08-15

    Pressure induced structural transition and elastic properties of ZnS-type (B3) to NaCl-type (B1) structure in mercury chalcogenides (HgX; X = S, Se and Te) are presented. An effective interionic interaction potential (EIOP) with long-range Coulomb, as well charge transfer interactions, Hafemeister and Flygare type short-range overlap repulsion extended up to the second neighbor ions and van der Waals interactions are considered. Emphasis is on the evaluation of the pressure dependent Poisson's ratio {nu}, the ratio R{sub BT/G} of B (bulk modulus) over G (shear modulus), anisotropy parameter, Shear and Young's modulus, Lame constant, Kleinman parameter, elastic wave velocity and thermodynamical property as Debye temperature. The Poisson's ratio behavior infers that Mercury chalcogenides are brittle in nature. To our knowledge this is the first quantitative theoretical prediction of the pressure dependence of elastic and thermodynamical properties explicitly the ductile (brittle) nature of HgX and still awaits experimental confirmations. Highlights: Black-Right-Pointing-Pointer Vast volume discontinuity in phase diagram infers transition from ZnS to NaCl structure. Black-Right-Pointing-Pointer The shear elastic constant C{sub 44} is nonzero confirms the mechanical stability. Black-Right-Pointing-Pointer Pressure dependence of {theta}{sub D} infers the softening of lattice with increasing pressure. Black-Right-Pointing-Pointer Estimated bulk, shear and tetragonal moduli satisfied elastic stability criteria. Black-Right-Pointing-Pointer In both B3 and B1 phases, C{sub 11} and C{sub 12} increase linearly with pressure.

  10. Surface Effects on the Mott-Hubbard Transition in Archetypal V{2}O{3}.

    Science.gov (United States)

    Lantz, G; Hajlaoui, M; Papalazarou, E; Jacques, V L R; Mazzotti, A; Marsi, M; Lupi, S; Amati, M; Gregoratti, L; Si, L; Zhong, Z; Held, K

    2015-12-04

    We present an experimental and theoretical study exploring surface effects on the evolution of the metal-insulator transition in the model Mott-Hubbard compound Cr-doped V{2}O{3}. We find a microscopic domain formation that is clearly affected by the surface crystallographic orientation. Using scanning photoelectron microscopy and x-ray diffraction, we find that surface defects act as nucleation centers for the formation of domains at the temperature-induced isostructural transition and favor the formation of microscopic metallic regions. A density-functional theory plus dynamical mean-field theory study of different surface terminations shows that the surface reconstruction with excess vanadyl cations leads to doped, and hence more metallic, surface states, which explains our experimental observations.

  11. Electronic origin of structural transition in 122 Fe based superconductors

    Science.gov (United States)

    Ghosh, Haranath; Sen, Smritijit; Ghosh, Abyay

    2017-03-01

    Direct quantitative correlations between the orbital order and orthorhombicity is achieved in a number of Fe-based superconductors of 122 family. The former (orbital order) is calculated from first principles simulations using experimentally determined doping and temperature dependent structural parameters while the latter (the orthorhombicity) is taken from already established experimental studies; when normalized, both the above quantities quantitatively corresponds to each other in terms of their doping as well as temperature variations. This proves that the structural transition in Fe-based materials is electronic in nature due to orbital ordering. An universal correlations among various structural parameters and electronic structure are also obtained. Most remarkable among them is the mapping of two Fe-Fe distances in the low temperature orthorhombic phase, with the band energies Edxz, Edyz of Fe at the high symmetry points of the Brillouin zone. The fractional co-ordinate zAs of As which essentially determines anion height is inversely (directly) proportional to Fe-As bond distances (with exceptions of K doped BaFe2As2) for hole (electron) doped materials as a function of doping. On the other hand, Fe-As bond-distance is found to be inversely (directly) proportional to the density of states at the Fermi level for hole (electron) doped systems. Implications of these results to current issues of Fe based superconductivity are discussed.

  12. Structural transitions in Cowpea chlorotic mottle virus (CCMV)

    Science.gov (United States)

    Liepold, Lars O.; Revis, Jennifer; Allen, Mark; Oltrogge, Luke; Young, Mark; Douglas, Trevor

    2005-12-01

    Viral capsids act as molecular containers for the encapsulation of genomic nucleic acid. These protein cages can also be used as constrained reaction vessels for packaging and entrapment of synthetic cargos. The icosahedral Cowpea chlorotic mottle virus (CCMV) is an excellent model for understanding the encapsulation and packaging of both genomic and synthetic materials. High-resolution structural information of the CCMV capsid has been invaluable for evaluating structure-function relationships in the assembled capsid but does not allow insight into the capsid dynamics. The dynamic nature of the CCMV capsid might play an important role in the biological function of the virus. The CCMV capsid undergoes a pH and metal ion dependent reversible structural transition where 60 separate pores in the capsid open or close, exposing the interior of the protein cage to the bulk medium. In addition, the highly basic N-terminal domain of the capsid, which is disordered in the crystal structure, plays a significant role in packaging the viral cargo. Interestingly, in limited proteolysis and mass spectrometry experiments the N-terminal domain is the first part of the subunit to be cleaved, confirming its dynamic nature. Based on our fundamental understanding of the capsid dynamics in CCMV, we have utilized these aspects to direct packaging of a range of synthetic materials including drugs and inorganic nanoparticles.

  13. Self-Organized Growth, Structure, and Magnetism of Monatomic Transition-Metal Oxide Chains

    Science.gov (United States)

    Ferstl, Pascal; Hammer, Lutz; Sobel, Christopher; Gubo, Matthias; Heinz, Klaus; Schneider, M. Alexander; Mittendorfer, Florian; Redinger, Josef

    2016-07-01

    We report on the self-organized growth of monatomic transition-metal oxide chains of (3 ×1 ) periodicity and unusual M O2 stoichiometry (M =Ni , Co, Fe, Mn) on Ir(100). We analyze their structural and magnetic properties by means of quantitative LEED, STM, and density functional theory (DFT) calculations. LEED analyses reveal a fascinating common atomic structure in which the transition-metal atoms sit above a missing-row structure of the surface and are coupled to the substrate only via oxygen atoms. This structure is confirmed by DFT calculations with structural parameters deviating by less than 1.7 pm. The DFT calculations predict that the NiO2 chains are nonmagnetic, CoO2 chains are ferromagnetic, while FeO2 and MnO2 are antiferromagnetic. All structures show only weak magnetic interchain coupling. Further, we demonstrate the growth of oxide chains of binary alloys of Co and Ni or Fe on Ir(100), which allows us to produce well-controlled ensembles of ferromagnetic chains of different lengths separated by nonmagnetic or antiferromagnetic segments.

  14. A stable lithium-rich surface structure for lithium-rich layered cathode materials

    Science.gov (United States)

    Kim, Sangryun; Cho, Woosuk; Zhang, Xiaobin; Oshima, Yoshifumi; Choi, Jang Wook

    2016-11-01

    Lithium ion batteries are encountering ever-growing demand for further increases in energy density. Li-rich layered oxides are considered a feasible solution to meet this demand because their specific capacities often surpass 200 mAh g-1 due to the additional lithium occupation in the transition metal layers. However, this lithium arrangement, in turn, triggers cation mixing with the transition metals, causing phase transitions during cycling and loss of reversible capacity. Here we report a Li-rich layered surface bearing a consistent framework with the host, in which nickel is regularly arranged between the transition metal layers. This surface structure mitigates unwanted phase transitions, improving the cycling stability. This surface modification enables a reversible capacity of 218.3 mAh g-1 at 1C (250 mA g-1) with improved cycle retention (94.1% after 100 cycles). The present surface design can be applied to various battery electrodes that suffer from structural degradations propagating from the surface.

  15. Structural Studies of Adeno-Associated Virus Serotype 8 Capsid Transitions Associated with Endosomal Trafficking

    Energy Technology Data Exchange (ETDEWEB)

    Nam, Hyun-Joo; Gurda, Brittney L.; McKenna, Robert; Potter, Mark; Byrne, Barry; Salganik, Maxim; Muzyczka, Nicholas; Agbandje-McKenna, Mavis (Florida)

    2012-09-17

    The single-stranded DNA (ssDNA) parvoviruses enter host cells through receptor-mediated endocytosis, and infection depends on processing in the early to late endosome as well as in the lysosome prior to nuclear entry for replication. However, the mechanisms of capsid endosomal processing, including the effects of low pH, are poorly understood. To gain insight into the structural transitions required for this essential step in infection, the crystal structures of empty and green fluorescent protein (GFP) gene-packaged adeno-associated virus serotype 8 (AAV8) have been determined at pH values of 6.0, 5.5, and 4.0 and then at pH 7.5 after incubation at pH 4.0, mimicking the conditions encountered during endocytic trafficking. While the capsid viral protein (VP) topologies of all the structures were similar, significant amino acid side chain conformational rearrangements were observed on (i) the interior surface of the capsid under the icosahedral 3-fold axis near ordered nucleic acid density that was lost concomitant with the conformational change as pH was reduced and (ii) the exterior capsid surface close to the icosahedral 2-fold depression. The 3-fold change is consistent with DNA release from an ordering interaction on the inside surface of the capsid at low pH values and suggests transitions that likely trigger the capsid for genome uncoating. The surface change results in disruption of VP-VP interface interactions and a decrease in buried surface area between VP monomers. This disruption points to capsid destabilization which may (i) release VP1 amino acids for its phospholipase A2 function for endosomal escape and nuclear localization signals for nuclear targeting and (ii) trigger genome uncoating.

  16. Structural studies of adeno-associated virus serotype 8 capsid transitions associated with endosomal trafficking.

    Science.gov (United States)

    Nam, Hyun-Joo; Gurda, Brittney L; McKenna, Robert; Potter, Mark; Byrne, Barry; Salganik, Maxim; Muzyczka, Nicholas; Agbandje-McKenna, Mavis

    2011-11-01

    The single-stranded DNA (ssDNA) parvoviruses enter host cells through receptor-mediated endocytosis, and infection depends on processing in the early to late endosome as well as in the lysosome prior to nuclear entry for replication. However, the mechanisms of capsid endosomal processing, including the effects of low pH, are poorly understood. To gain insight into the structural transitions required for this essential step in infection, the crystal structures of empty and green fluorescent protein (GFP) gene-packaged adeno-associated virus serotype 8 (AAV8) have been determined at pH values of 6.0, 5.5, and 4.0 and then at pH 7.5 after incubation at pH 4.0, mimicking the conditions encountered during endocytic trafficking. While the capsid viral protein (VP) topologies of all the structures were similar, significant amino acid side chain conformational rearrangements were observed on (i) the interior surface of the capsid under the icosahedral 3-fold axis near ordered nucleic acid density that was lost concomitant with the conformational change as pH was reduced and (ii) the exterior capsid surface close to the icosahedral 2-fold depression. The 3-fold change is consistent with DNA release from an ordering interaction on the inside surface of the capsid at low pH values and suggests transitions that likely trigger the capsid for genome uncoating. The surface change results in disruption of VP-VP interface interactions and a decrease in buried surface area between VP monomers. This disruption points to capsid destabilization which may (i) release VP1 amino acids for its phospholipase A2 function for endosomal escape and nuclear localization signals for nuclear targeting and (ii) trigger genome uncoating.

  17. Reconstructing Earth's Surface Oxidation Across The Archean- Proterozoic Transition

    Science.gov (United States)

    Kaufman, A. J.; Guo, Q.; Strauss, H.; Schröder, S.; Gutzmer, J.; Wing, B. A.; Baker, M.; Bekker, A.; Jin, Q.; Kim, S.; Farquhar, J.

    2010-12-01

    The Archean-Proterozoic transition is characterized by the widespread deposition of organic-rich shale, sedimentary iron formation, glacial diamictite, and marine carbonates recording profound carbon isotope anomalies, but notably lacks bedded evaporites. All deposits reflect environmental changes in oceanic and atmospheric redox states, in part associated with Earth’s earliest ice ages. Time-series data for multiple sulfur isotopes from carbonate associated sulfate as well as sulfides in the glaciogenic Duitschland Formation of the Transvaal Supergroup, South Africa, capture the concomitant buildup of sulfate in the ocean and the loss of mass independent sulfur isotope fractionation. This is arguably associated with the atmospheric rise of oxygen (as well as the protective ozone layer) coincident with profound changes in ocean chemistry and biology. The loss of the MIF signal within the Duitschland succession is in phase with the earliest recorded positive carbon isotope anomaly, convincingly linking these environmental perturbations to the Great Oxidation Event (ca. 2.3 Ga). The emergence of cyanobacteria and oxygenic photosynthesis may be associated with a geochemical “whiff of oxygen” recorded in 2.5 Ga sediments. If true, the delay in the GOE can then be understood in terms of a finite sink for molecular oxygen - ferrous iron, which was abundant in deep Neoarchean seawater and sequestered in a worldwide episode of iron formation deposition ending shortly before accumulation of the Duitschland Formation. Insofar as early Paleoproterozoic glaciation is associated with oxygenation of a methane-rich atmosphere, we conclude that Earth’s earliest ice age(s) and the onset of a modern and far more energetic carbon cycle are directly related to the global expansion of cyanobacteria that released oxygen to the environment, and of eukaryotes that respired it.

  18. Investigation of spin-reorientation phase transitions at surface and in volume of alpha-Fe sub 2 O sub 3 monocrystals

    CERN Document Server

    Kamzin, A S

    2002-01-01

    The magnetic structure of the surface layer and volume and the processes, observed by the spin-reorientation phase transition (SRPT), are studied in the direct comparison of the properties of the thin surface layer and the volume of the hematite (alpha-Fe sub 2 O sub 3) macroscopic crystals. The method of simultaneous gamma, X-ray and electron Moessbauer spectroscopy was used in the studies. The direct data on the existence of the transition layer on the hematite crystals surface are obtained. It is established, that the Morin-type SRPT in the sample volume occurs by a jump (the first-order phase transition). The SRPT in the surface layer as well as in the crystal volume is accompanied by formation of the intermediate state, wherein the low- and high-temperature phases coexist. The obtained experimental data on the SRPT mechanism in the surface layer agree well with the conclusions of the phenomenological theory

  19. Learning surface molecular structures via machine vision

    Science.gov (United States)

    Ziatdinov, Maxim; Maksov, Artem; Kalinin, Sergei V.

    2017-08-01

    Recent advances in high resolution scanning transmission electron and scanning probe microscopies have allowed researchers to perform measurements of materials structural parameters and functional properties in real space with a picometre precision. In many technologically relevant atomic and/or molecular systems, however, the information of interest is distributed spatially in a non-uniform manner and may have a complex multi-dimensional nature. One of the critical issues, therefore, lies in being able to accurately identify (`read out') all the individual building blocks in different atomic/molecular architectures, as well as more complex patterns that these blocks may form, on a scale of hundreds and thousands of individual atomic/molecular units. Here we employ machine vision to read and recognize complex molecular assemblies on surfaces. Specifically, we combine Markov random field model and convolutional neural networks to classify structural and rotational states of all individual building blocks in molecular assembly on the metallic surface visualized in high-resolution scanning tunneling microscopy measurements. We show how the obtained full decoding of the system allows us to directly construct a pair density function—a centerpiece in analysis of disorder-property relationship paradigm—as well as to analyze spatial correlations between multiple order parameters at the nanoscale, and elucidate reaction pathway involving molecular conformation changes. The method represents a significant shift in our way of analyzing atomic and/or molecular resolved microscopic images and can be applied to variety of other microscopic measurements of structural, electronic, and magnetic orders in different condensed matter systems.

  20. The structural and compositional transition of the meniscal roots into the fibrocartilage of the menisci.

    Science.gov (United States)

    Andrews, Stephen H J; Rattner, Jerome B; Jamniczky, Heather A; Shrive, Nigel G; Adesida, Adetola B

    2015-02-01

    resemble the meniscus wedge shape. These observations support the concept of root continuity with the outer portion of the meniscus, thereby connecting with the hoop-like structure of the peripheral meniscus. OPT identified continuous collagen organization from the root into the meniscal body in longitudinal sections. In the radial direction, the morphology of the root continues into the meniscal body consistent with the serially sectioned bovine menisci. Blood vessels were prevalent on the periphery of the root. These blood vessels then arborized to cover the anterior femoral surface of the meniscus. This is the first study of the structural transition between the insertional ligaments (roots) and the fibrocartilagenous body of the menisci. These new structural details are important to understanding the meniscal load-bearing mechanism in the knee.

  1. Design of a lunar surface structure

    Science.gov (United States)

    Mottaghi, Sohrob

    The next step for manned exploration and settlement is a return to the Moon. In such a return, the most challenging task is the construction of structures for habitation, considering the Moon's hostile environment. Therefore the question is: What is the best way to erect habitable structures on the lunar surface? Given the cost associated with bringing material to the Moon, In-Situ Resource Utilization (ISRU) is viewed by most as the basis for a successful manned exploration and settlement of the Solar system. Along these lines, we propose an advanced concept where the use of freeform fabrication technologies by autonomous mini-robots can form the basis for habitable lunar structures. Also, locally-available magnesium is proposed as the structural material. While it is one of the most pervasive metals in the regolith, magnesium has been only suggested only briefly as a viable option in the past. Therefore, a study has been conducted on magnesium and its alloys, taking into account the availability of the alloying elements on the Moon. An igloo-shaped magnesium structure, covered by sandbags of regolith shielding and supported on a sintered regolith foundation, is considered as a potential design of a lunar base, as well as the test bed for the proposed vision. Three studies are carried out: First a static analysis is conducted which proves the feasibility of the proposed material and method. Second, a thermal analysis is carried out to study the effect of the regolith shielding as well as the sensitivity of such designs to measurement uncertainties of regolith and sintered thermal properties. The lunar thermal environment is modeled for a potential site at 88º latitude in the lunar South Pole Region. Our analysis shows that the uncertainties are in an acceptable range where a three-meter thick shield is considered. Also, the required capacity of a thermal rejection system is estimated, choosing the thermal loads to be those of the Space Station modules. In the

  2. Electronic structure of benzene adsorbed on Ni and Cu surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Weinelt, M.; Nilsson, A.; Wassdahl, N. [Uppsala Univ. (Sweden)] [and others

    1997-04-01

    Benzene has for a long time served as a prototype adsorption system of large molecules. It adsorbs with the molecular plane parallel to the surface. The bonding of benzene to a transition metal is typically viewed to involve the {pi} system. Benzene adsorbs weakly on Cu and strongly on Ni. It is interesting to study how the adsorption strength is reflected in the electronic structure of the adsorbate-substrate complex. The authors have used X-ray Emission (XE) and X-ray Absorption (XA) spectroscopies to selectively study the electronic states localized on the adsorbed benzene molecule. Using XES the occupied states can be studies and with XAS the unoccupied states. The authors have used beamline 8.0 and the Swedish endstation equipped with a grazing incidence x-ray spectrometer and a partial yield absorption detector. The resolution in the XES and XAS were 0.5 eV and 0.05 eV, respectively.

  3. Effects of transition metal oxide doping on the structure of sodium metaphosphate glasses

    Energy Technology Data Exchange (ETDEWEB)

    Zotov, N.; Kirfel, A.; Beuneu, B.; Delaplane, R.; Hohlwein, D.; Reinauer, F.; Glaum, R

    2004-07-15

    Neutron diffraction measurements of transition metal-oxide-doped sodium metaphosphate glasses and melts show an anomalous increase of the first sharp diffraction peak both with increasing transition metal content and temperature due to progressive increase of the structural disorder.

  4. Electronic Structure of the fcc Transition Metals Ir, Rh, Pt, and Pd

    DEFF Research Database (Denmark)

    Andersen, O. Krogh

    1970-01-01

    /atom)/Ry, respectively. Spin-orbit coupling is important for all four metals and the coupling parameter varies by 30% over the d bandwidth. Detailed comparisons with de Haas—van Alphen Fermi-surface dimensions have previously been presented and the agreement was very good. Comparison with measured electronic specific......We give a complete description of a relativistic augmented-plane-wave calculation of the band structures of the paramagnetic fcc transition metals Ir, Rh, Pt, and Pd. The width and position of the d band decrease in the sequence Ir, Pt, Rh, Pd; and N(EF)=13.8,23.2,18.7, and 32.7 (states...

  5. Transition absorption as a mechanism of surface photoelectron emission from metals

    DEFF Research Database (Denmark)

    Zhukovsky, Sergei; Protsenko, Igor E.; Ikhsanov, Renat Sh;

    2015-01-01

    Transition absorption of a photon by an electron passingthrough a boundary between two media with different permit-tivities is described both classically and quantum mechani-cally. Transition absorption is shown to make a substantialcontribution to photoelectron emission at a metal/semicon-ductor....../semicon-ductor interface in nanoplasmonic systems, and is put forth asa possible microscopic mechanism of the surface photoelec-tric effect in photodetectors and solar cells containing plas-monic nanoparticles....

  6. Transition absorption as a mechanism of surface photoelectron emission from metals

    DEFF Research Database (Denmark)

    Zhukovsky, Sergei; Protsenko, Igor E.; Ikhsanov, Renat Sh

    2015-01-01

    Transition absorption of a photon by an electron passingthrough a boundary between two media with different permit-tivities is described both classically and quantum mechani-cally. Transition absorption is shown to make a substantialcontribution to photoelectron emission at a metal....../semicon-ductor interface in nanoplasmonic systems, and is put forth asa possible microscopic mechanism of the surface photoelec-tric effect in photodetectors and solar cells containing plas-monic nanoparticles....

  7. Structure of nuclear transition matrix elements for neutrinoless double- decay

    Indian Academy of Sciences (India)

    P K Rath

    2010-08-01

    The structure of nuclear transition matrix elements (NTMEs) required for the study of neutrinoless double- decay within light Majorana neutrino mass mechanism is disassembled in the PHFB model. The NTMEs are calculated using a set of HFB intrinsic wave functions, the reliability of which has been previously established by obtaining an overall agreement between the theoretically calculated spectroscopic properties and the available experimental data. Presently, we study the role of short-range correlations, radial evolution of NTMEs and deformation effects due to quadrupolar correlations. In addition, limits on effective light neutrino mass $\\langle m_{} \\rangle$ are extracted from the observed limits on half-lives $T_{1/2}^{0}$ of neutrinoless double- decay.

  8. Liquid-Liquid Structure Transition in Metallic Melts: Experimental Evidence by Viscosity Measurement

    Institute of Scientific and Technical Information of China (English)

    WANG Yu-Qing; WU Yu-Qin; BIAN Xiu-Fang

    2007-01-01

    Temperature dependence of viscosity for more than ten kinds of metallic melts is analysed based on viscosity measurements. An obvious turning point is observed on the Arrhenius curves. Since viscosity is one of the physical properties sensitive to structure, its discontinuous change with temperature reveals the possible liquidliquid structure transition in the metallic melts. Furthermore, an integrated liquid structure transition diagram of the Sn-Bi system is presented. The universality of liquid-liquid structure transition is also discussed simply.

  9. Femtosecond laser surface structuring technique for making human enamel and dentin surfaces superwetting

    Science.gov (United States)

    Vorobyev, A. Y.; Guo, Chunlei

    2013-12-01

    It is known that good wettability of enamel and dentin surfaces is a key factor in enhancing adhesion of restorative materials in dentistry. Here, we report on a femtosecond laser surface texturing approach that makes both the enamel and dentine surfaces superwetting. In contrast to the traditional chemical etching that yields random surface structures, this new approach produces engineered surface structures. The surface structure engineered and tested here is an array of femtosecond laser-produced parallel microgrooves that generates a strong capillary force. Due to the powerful capillary action, water is rapidly sucked into this engineered surface structure and spreads even on a vertical surface.

  10. Sticky water surfaces: Helix-coil transitions suppressed in a cell-penetrating peptide at the air-water interface

    Science.gov (United States)

    Schach, Denise; Globisch, Christoph; Roeters, Steven J.; Woutersen, Sander; Fuchs, Adrian; Weiss, Clemens K.; Backus, Ellen H. G.; Landfester, Katharina; Bonn, Mischa; Peter, Christine; Weidner, Tobias

    2014-12-01

    GALA is a 30 amino acid synthetic peptide consisting of a Glu-Ala-Leu-Ala repeat and is known to undergo a reversible structural transition from a disordered to an α-helical structure when changing the pH from basic to acidic values. In its helical state GALA can insert into and disintegrate lipid membranes. This effect has generated much interest in GALA as a candidate for pH triggered, targeted drug delivery. GALA also serves as a well-defined model system to understand cell penetration mechanisms and protein folding triggered by external stimuli. Structural transitions of GALA in solution have been studied extensively. However, cell penetration is an interfacial effect and potential biomedical applications of GALA would involve a variety of surfaces, e.g., nanoparticles, lipid membranes, tubing, and liquid-gas interfaces. Despite the apparent importance of interfaces in the functioning of GALA, the effect of surfaces on the reversible folding of GALA has not yet been studied. Here, we use sum frequency generation vibrational spectroscopy (SFG) to probe the structural response of GALA at the air-water interface and IR spectroscopy to follow GALA folding in bulk solution. We combine the SFG data with molecular dynamics simulations to obtain a molecular-level picture of the interaction of GALA with the air-water interface. Surprisingly, while the fully reversible structural transition was observed in solution, at the water-air interface, a large fraction of the GALA population remained helical at high pH. This "stickiness" of the air-water interface can be explained by the stabilizing interactions of hydrophobic leucine and alanine side chains with the water surface.

  11. On the onset of surface condensation: formation and transition mechanisms of condensation mode

    Science.gov (United States)

    Sheng, Qiang; Sun, Jie; Wang, Qian; Wang, Wen; Wang, Hua Sheng

    2016-08-01

    Molecular dynamics simulations have been carried out to investigate the onset of surface condensation. On surfaces with different wettability, we snapshot different condensation modes (no-condensation, dropwise condensation and filmwise condensation) and quantitatively analyze their characteristics by temporal profiles of surface clusters. Two different types of formation of nanoscale droplets are identified, i.e. the formations with and without film-like condensate. We exhibit the effect of surface tensions on the formations of nanoscale droplets and film. We reveal the formation mechanisms of different condensation modes at nanoscale based on our simulation results and classical nucleation theory, which supplements the ‘classical hypotheses’ of the onset of dropwise condensation. We also reveal the transition mechanism between different condensation modes based on the competition between surface tensions and reveal that dropwise condensation represents the transition states from no-condensation to filmwise condensation.

  12. Insight into structural phase transitions from the decoupled anharmonic mode approximation

    Science.gov (United States)

    Adams, Donat J.; Passerone, Daniele

    2016-08-01

    We develop a formalism (decoupled anharmonic mode approximation, DAMA) that allows calculation of the vibrational free energy using density functional theory even for materials which exhibit negative curvature of the potential energy surface with respect to atomic displacements. We investigate vibrational modes beyond the harmonic approximation and approximate the potential energy surface with the superposition of the accurate potential along each normal mode. We show that the free energy can stabilize crystal structures at finite temperatures which appear dynamically unstable at T  =  0. The DAMA formalism is computationally fast because it avoids statistical sampling through molecular dynamics calculations, and is in principle completely ab initio. It is free of statistical uncertainties and independent of model parameters, but can give insight into the mechanism of a structural phase transition. We apply the formalism to the perovskite cryolite, and investigate the temperature-driven phase transition from the P21/n to the Immm space group. We calculate a phase transition temperature between 710 and 950 K, in fair agreement with the experimental value of 885 K. This can be related to the underestimation of the interaction of the vibrational states. We also calculate the main axes of the thermal ellipsoid and can explain the experimentally observed increase of its volume for the fluorine by 200-300% throughout the phase transition. Our calculations suggest the appearance of tunneling states in the high temperature phase. The convergence of the vibrational DOS and of the critical temperature with respect of reciprocal space sampling is investigated using the polarizable-ion model.

  13. Turbulence vertical structure of the boundary layer during the afternoon transition

    Directory of Open Access Journals (Sweden)

    C. Darbieu

    2014-12-01

    Full Text Available We investigate the decay of planetary boundary layer (PBL turbulence in the afternoon, from the time the surface buoyancy flux starts to decrease until sunset. Dense observations of mean and turbulent parameters were acquired during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST field experiment by several meteorological surface stations, sounding balloons, radars, lidars, and two aircraft flying extensively during the afternoon transition. We analyzed a case study based on some of those observations and Large-Eddy Simulation (LES data focusing on the turbulent vertical structure throughout the afternoon transition. The decay of turbulence is quantified through the temporal and vertical evolution of (1 the turbulence kinetic energy (TKE, (2 the characteristic length scales of turbulence, (3 the shape of the turbulence spectra. A spectral analysis of LES data, airborne and surface measurements is performed in order to (1 characterize the variation of the turbulent decay with height and (2 study the distribution of turbulence over eddy size. This study points out the LES ability to reproduce the turbulence evolution throughout the afternoon. LES and observations agree that the afternoon transition can be divided in two phases: (1 a first phase during which the TKE decays with a low rate, with no significant change in turbulence characteristics, (2 a second phase characterized by a larger TKE decay rate and a change spectral shape, implying an evolution of eddy size distribution and energy cascade from low to high wavenumber. The changes observed either on TKE decay (during the first phase or on the vertical wind spectra shape (during the second phase of the afternoon transition occur first in the upper region of the PBL. The higher within the PBL, the stronger the spectra shape changes.

  14. Surface phase, morphology, and charge distribution transitions on vacuum and ambient annealed SrTi O3 (100)

    Science.gov (United States)

    Dagdeviren, Omur E.; Simon, Georg H.; Zou, Ke; Walker, Fred J.; Ahn, Charles; Altman, Eric I.; Schwarz, Udo D.

    2016-05-01

    The surface structures of SrTi O3 (100) single crystals were examined as a function of annealing time and temperature in either oxygen atmosphere or ultrahigh vacuum (UHV) using noncontact atomic force microscopy (NC-AFM), Auger electron spectroscopy (AES), and low-energy electron diffraction (LEED). Samples were subsequently analyzed for the effect the modulation of their charge distribution had on their surface potential. It was found that the evolution of the SrTi O3 surface roughness, stoichiometry, and reconstruction depends on the preparation scheme. LEED revealed phase transitions from a (1 ×1 ) termination to an intermediate c (4 ×2 ) reconstruction to ultimately a (√ 13 ×√ 13 ) -R 33 .7∘ surface phase when the surface was annealed in an oxygen flux, while the reverse transition from (√ 13 ×√ 13 ) -R 33 .7∘ to c (4 ×2 ) was observed when samples were annealed in UHV. When the surface reverted to c (4 ×2 ) , AES data indicated decreases in both the surface Ti and O concentrations. These findings were corroborated by NC-AFM imaging, where initially Ti O2 -terminated crystals developed half-unit cell high steps following UHV annealing, which is typically attributed to a mix of SrO and Ti O2 terminations. Surface roughness evolved nonmonotonically with UHV annealing temperature, which is explained by electrostatic modulations of the surface potential caused by increasing oxygen depletion. This was further corroborated by experiments in which the apparent roughness tracked in NC-AFM could be correlated with changes in the surface charge distribution that were controlled by applying a bias voltage to the sample. Based on these findings, it is suggested that careful selection of preparation procedures combined with application of an electric field may be used to tune the properties of thin films grown on SrTi O3 .

  15. Cell surface glycan alterations in epithelial mesenchymal transition process of Huh7 hepatocellular carcinoma cell.

    Directory of Open Access Journals (Sweden)

    Shan Li

    Full Text Available BACKGROUND AND OBJECTIVE: Due to recurrence and metastasis, the mortality of Hepatocellular carcinoma (HCC is high. It is well known that the epithelial mesenchymal transition (EMT and glycan of cell surface glycoproteins play pivotal roles in tumor metastasis. The goal of this study was to identify HCC metastasis related differential glycan pattern and their enzymatic basis using a HGF induced EMT model. METHODOLOGY: HGF was used to induce HCC EMT model. Lectin microarray was used to detect the expression of cell surface glycan and the difference was validated by lectin blot and fluorescence cell lectin-immunochemistry. The mRNA expression levels of glycotransferases were determined by qRT-PCR. RESULTS: After HGF treatment, the Huh7 cell lost epithelial characteristics and obtained mesenchymal markers. These changes demonstrated that HGF could induce a typical cell model of EMT. Lectin microarray analysis identified a decreased affinity in seven lectins ACL, BPL, JAC, MPL, PHA-E, SNA, and SBA to the glycan of cell surface glycoproteins. This implied that glycan containing T/Tn-antigen, NA2 and bisecting GlcNAc, Siaα2-6Gal/GalNAc, terminal α or βGalNAc structures were reduced. The binding ability of thirteen lectins, AAL, LCA, LTL, ConA, NML, NPL, DBA, HAL, PTL II, WFL, ECL, GSL II and PHA-L to glycan were elevated, and a definite indication that glycan containing terminal αFuc and ± Sia-Le, core fucose, α-man, gal-β(α GalNAc, β1,6 GlcNAc branching and tetraantennary complex oligosaccharides structures were increased. These results were further validated by lectin blot and fluorescence cell lectin-immunochemistry. Furthermore, the mRNA expression level of Mgat3 decreased while that of Mgat5, FucT8 and β3GalT5 increased. Therefore, cell surface glycan alterations in the EMT process may coincide with the expression of glycosyltransferase. CONCLUSIONS: The findings of this study systematically clarify the alterations of cell surface

  16. Surface plasmon exciton transition in ultra-thin silver and silver iodide films

    Science.gov (United States)

    Bharathi Mohan, D.; Sreejith, K.; Sunandana, C. S.

    2007-10-01

    Silver thin films in the thickness range 2 10 nm produced by thermal evaporation onto glass substrates were systematically iodized and carefully characterized by X-ray diffraction, atomic force microscopy (AFM) and optical absorption spectroscopy. While the uniodized films are X-ray amorphous in keeping with their quasi-continuous nature and 2D islanded structure, briefly iodized films showed characteristic beta AgI structure. Most interestingly, AFM of Ag films revealed uniform triangle-shaped embryos whose shape does not change appreciably upon iodization. Optical absorption spectra of uniodized Ag films show intense surface plasmon resonance (SPR) features with maxima at 440, 484 and 498 nm for the films of thicknesses 2, 5 and 10 nm, respectively, with 5 nm films showing properties characteristic of optimally matched dielectric and electronic properties of the substrate and sample, respectively. Finally, an interesting and unique SPR exciton phase transition is observed as the ultra-thin films are progressively iodized. These Ag and AgI films could be promising candidates for plasmonic and nanophotonic applications.

  17. Structure of the airflow above surface waves

    Science.gov (United States)

    Buckley, Marc; Veron, Fabrice

    2016-04-01

    Weather, climate and upper ocean patterns are controlled by the exchanges of momentum, heat, mass, and energy across the ocean surface. These fluxes are, in turn, influenced by the small-scale physics at the wavy air-sea interface. We present laboratory measurements of the fine-scale airflow structure above waves, achieved in over 15 different wind-wave conditions, with wave ages Cp/u* ranging from 1.4 to 66.7 (where Cp is the peak phase speed of the waves, and u* the air friction velocity). The experiments were performed in the large (42-m long) wind-wave-current tank at University of Delaware's Air-Sea Interaction laboratory (USA). A combined Particle Image Velocimetry and Laser Induced Fluorescence system was specifically developed for this study, and provided two-dimensional airflow velocity measurement as low as 100 um above the air-water interface. Starting at very low wind speeds (U10~2m/s), we directly observe coherent turbulent structures within the buffer and logarithmic layers of the airflow above the air-water interface, whereby low horizontal velocity air is ejected away from the surface, and higher velocity fluid is swept downward. Wave phase coherent quadrant analysis shows that such turbulent momentum flux events are wave-phase dependent. Airflow separation events are directly observed over young wind waves (Cp/u*wind waves (Cp/u*=3.7). Over slightly older wind waves (Cp/u* = 6.5), the measured wave-induced airflow perturbations are qualitatively consistent with linear critical layer theory.

  18. Thermal Tomography of Asteroid Surface Structure

    CERN Document Server

    Harris, Alan

    2016-01-01

    Knowledge of the surface thermal inertia of an asteroid can provide insight into surface structure: porous material has a lower thermal inertia than rock. We develop a means to estimate thermal inertia values of asteroids and use it to show that thermal inertia appears to increase with spin period in the case of main-belt asteroids (MBAs). Similar behavior is found on the basis of thermophysical modeling for near-Earth objects (NEOs). We interpret our results in terms of rapidly increasing material density and thermal conductivity with depth, and provide evidence that thermal inertia increases by factors of 10 (MBAs) to 20 (NEOs) within a depth of just 10 cm. Our results are consistent with a very general picture of rapidly changing material properties in the topmost regolith layers of asteroids and have important implications for calculations of the Yarkovsky effect, including its perturbation of the orbits of potentially hazardous objects and those of asteroid family members after the break-up event. Eviden...

  19. Protein-mediated surface structuring in biomembranes

    Directory of Open Access Journals (Sweden)

    Maggio B.

    2005-01-01

    Full Text Available The lipids and proteins of biomembranes exhibit highly dissimilar conformations, geometrical shapes, amphipathicity, and thermodynamic properties which constrain their two-dimensional molecular packing, electrostatics, and interaction preferences. This causes inevitable development of large local tensions that frequently relax into phase or compositional immiscibility along lateral and transverse planes of the membrane. On the other hand, these effects constitute the very codes that mediate molecular and structural changes determining and controlling the possibilities for enzymatic activity, apposition and recombination in biomembranes. The presence of proteins constitutes a major perturbing factor for the membrane sculpturing both in terms of its surface topography and dynamics. We will focus on some results from our group within this context and summarize some recent evidence for the active involvement of extrinsic (myelin basic protein, integral (Folch-Lees proteolipid protein and amphitropic (c-Fos and c-Jun proteins, as well as a membrane-active amphitropic phosphohydrolytic enzyme (neutral sphingomyelinase, in the process of lateral segregation and dynamics of phase domains, sculpturing of the surface topography, and the bi-directional modulation of the membrane biochemical reactivity.

  20. Thermal Tomography of Asteroid Surface Structure

    Science.gov (United States)

    Harris, Alan W.; Drube, Line

    2016-12-01

    Knowledge of the surface thermal inertia of an asteroid can provide insight into its surface structure: porous material has a lower thermal inertia than rock. We develop a means to estimate thermal inertia values of asteroids and use it to show that thermal inertia appears to increase with spin period in the case of main-belt asteroids (MBAs). Similar behavior is found on the basis of thermophysical modeling for near-Earth objects (NEOs). We interpret our results in terms of rapidly increasing material density and thermal conductivity with depth, and provide evidence that thermal inertia increases by factors of 10 (MBAs) to 20 (NEOs) within a depth of just 10 cm. Our results are consistent with a very general picture of rapidly changing material properties in the topmost regolith layers of asteroids and have important implications for calculations of the Yarkovsky effect, including its perturbation of the orbits of potentially hazardous objects and those of asteroid family members after the break-up event. Evidence of a rapid increase of thermal inertia with depth is also an important result for studies of the ejecta-enhanced momentum transfer of impacting vehicles (“kinetic impactors”) in planetary defense.

  1. The role or structural criteria in transition theory

    NARCIS (Netherlands)

    Jagers op Akkerhuis, Gerard A.J.M.

    2016-01-01

    In a recent publication Szathmáry has updated Major Evolutionary Transitions theory to a version 2.0. The major transition theory recognises transitions based on the select use of functional criteria, notably: cooperation, competition reduction and reproduction as part of a larger unit. These

  2. Photoelectron spectroscopy bulk and surface electronic structures

    CERN Document Server

    Suga, Shigemasa

    2014-01-01

    Photoelectron spectroscopy is now becoming more and more required to investigate electronic structures of various solid materials in the bulk, on surfaces as well as at buried interfaces. The energy resolution was much improved in the last decade down to 1 meV in the low photon energy region. Now this technique is available from a few eV up to 10 keV by use of lasers, electron cyclotron resonance lamps in addition to synchrotron radiation and X-ray tubes. High resolution angle resolved photoelectron spectroscopy (ARPES) is now widely applied to band mapping of materials. It attracts a wide attention from both fundamental science and material engineering. Studies of the dynamics of excited states are feasible by time of flight spectroscopy with fully utilizing the pulse structures of synchrotron radiation as well as lasers including the free electron lasers (FEL). Spin resolved studies also made dramatic progress by using higher efficiency spin detectors and two dimensional spin detectors. Polarization depend...

  3. Phase transitions and interface fluctuations in double wedges and bi-pyramids with competing surface fields

    Science.gov (United States)

    Müller, M.; Milchev, A.; Binder, K.; Landau, D. P.

    2008-08-01

    The interplay between surface and interface effects on binary AB mixtures that are confined in unconventional geometries is investigated by Monte Carlo simulations and phenomenological considerations. Both double-wedge and bi-pyramid confinements are considered and competing surface fields are applied at the two opposing halves of the system. Below the bulk critical temperature, domains of opposite order parameter are stabilized at the corresponding corners and an interface runs across the middle of the bi-partite geometry. Upon decreasing the temperature further one encounters a phase transition at which the AB symmetry is broken. The interface is localized in one of the two wedges or pyramids, respectively, and the order parameter is finite. In both cases, the transition becomes discontinuous in the thermodynamic limit but it is not a first-order phase transition. In an antisymmetric double wedge geometry the transition is closely related to the wedge-filling transition. Choosing the ratio of the cross-section L × L of the wedge and its length L y according to L y / L 3 = const., simulations and phenomenological consideration show that the new type of phase transition is characterized by critical exponents α = 3/4, β = 0, and γ = 5/4 for the specific heat, order parameter, and susceptibility, respectively. In an antisymmetric bi-pyramid the transition occurs at the cone-filling transition of a single pyramid. The important critical fluctuations are associated with the uniform translation of the interface and they can be described by a Landau-type free energy. Monte Carlo results provide evidence that the coefficients of this Landau-type free energy exhibit a system-size dependence, which gives rise to critical amplitudes that diverge with system size and result in a transition that becomes discontinuous in the thermodynamic limit.

  4. Structure transition of nano-titania during calcination

    Institute of Scientific and Technical Information of China (English)

    李国华; 王大伟; 徐铸德; 陈卫祥

    2003-01-01

    In order to study the structure transition during calcination, nano-titania powders prepared by hydrolyzing precipitation approach and calcined at 300, 400, 500, 600 and 700 ℃ were characterized by XRD, TEM and electron diffraction(ED), respectively. The results show that titania powders calcined below 500 ℃ are almost composed of anatase, rutile appears below 500 ℃ and its ratio increases gradually with increase of calcin temperature;nano-titania particles are smaller than 40 nm mostly and the dispersion is related to calcining temperature; the interplanar distances of nano-anatase single crystalline change gradually when calcing temperature increases to 500 ℃; so do that of nano-rutile single crystalline when calcining temperature charges from 600 to 700 ℃. The conclusions can be drawn that the temperature of transformation from anatase to rutile is below 500 ℃ and the process carries on gradually. Both inter-planar distances and the structure of nano-titania transform gradually with increasing calcing temperature.

  5. Domain structure and phase transition in Sc-doped zirconia

    Energy Technology Data Exchange (ETDEWEB)

    Brunauer, G.; Boysen, H.; Frey, F. [Institute for Crystallography und Applied Mineralogy, LMU Muenchen, Munich (Germany); Ehrenberg, H. [Institute for Materials Science, TU Darmstadt, Darmstadt (Germany)

    2002-01-21

    The temperature dependence of the domain structure associated with the ferroelastic phase transition (Fm{sup 3-bar}m{r_reversible}R{sup 3-bar}m) in ZrO{sub 2} doped with 11% Sc{sub 2}O{sub 3} has been determined from a peak shape analysis of high-resolution synchrotron x-ray powder diffraction data. In the temperature region of coexisting phases the observed characteristic anisotropic broadening and asymmetry of the lines is modelled by three different phases: a main rhombohedral phase, a distorted rhombohedral phase with a smaller c/a ratio, and a cubic phase. The latter two are assigned to the internal structure of the domain walls between two adjacent twin domains. The size and amount of the cubic phase show an initially slow increase with temperature followed by a very steep increase and a slow one after that. The size of the (main) rhombohedral domains remains nearly constant, while (micro-) strain in the distorted regions gradually decreases. (author)

  6. Energy level structure and quantum phase transitions of spin systems with nonaxially symmetric Hamiltonians

    Energy Technology Data Exchange (ETDEWEB)

    Lopez-Moreno, Enrique; Grether, M; Velazquez, Victor, E-mail: elm@hp.fciencias.unam.mx [Facultad de Ciencias, Departamento de Fisica, Universidad Nacional Autonoma de Mexico, Cd. Universitaria, Circuito Exterior, 04510 Mexico DF (Mexico)

    2011-11-25

    A general spin system with a nonaxially symmetric Hamiltonian containing J{sub x}, J{sub z}-linear and J{sub z}-quadratic terms, widely used in many-body fermionic and bosonic systems and in molecular magnetism, is considered for the variations of general parameters describing intensity interaction changes of each of its terms. For this model Hamiltonian, a semiclassical energy surface (ES) is obtained by means of the coherent-state formalism. An analysis of this ES function, based on catastrophe theory, determines the separatrix in the control parameter space of the system Hamiltonian: the loci of singularities representing semiclassical phase transitions. Here we show that distinct regions of qualitatively different spectrum structures, as well as a singular behavior of quantum states, are ruled by this separatrix: here we show that the separatrix not only describes ground-state singularities, which have been associated with quantum phase transitions, but also reveals the structure of the excited spectrum, distinguishing different quantum phases within the parameter space. Finally, we consider magnetic susceptibility and heat capacity of the system at finite temperature, in order to study thermal properties and thermodynamical phase transitions in the perspective of the separatrix of this Hamiltonian system. (paper)

  7. The Turbulent-Laminar Transition on the Rocket Surface During the Injection

    Directory of Open Access Journals (Sweden)

    I. I. Yurchenko

    2014-01-01

    Full Text Available The variety of turbulent-laminar transition criteria in such environments as the launch vehicle injection points to the essential influence of spherical nose roughness, which is included in one form or another in the critical Reynolds numbers for a lot of explorers of blunt bodies. Some of researchers of the reentry bodies have founded the correlation functions between the momentum thickness Reynolds number and Max number as the transition criteria.In this article we have considered results of flight tests carried out using launch vehicles to define boundary layer regime on the payload fairing surface. The measurements were carried out using specially designed complex of gages consisted of calorimeters, surface temperature gages, and pressure gages. The turbulent-laminar transition was defined in accordance with the sharp change of calorimeter readings and flow separation pressure gages indication.The universal criterion of turbulent-laminar transition has been identified for blunted payload fairings i.e. Reynolds number Reek based on the boundary layer edge parameters in the sonic point of the payload fairing spherical nose and surface roughness height k, which gives the best correlation of all data of flight experiment conducted to define turbulent-laminar transition in boundary layer. The criterion allows defining time margins when boundary layer regime is turbulent at Reek=20±14 existing on space head surfaces and at Reek=6±5 the boundary layer regime is totally laminar.It was defined that under conditions when there are jointly high background disturbances of free stream flux at operation of main launch vehicle engines and influence of the surface roughness the critical value of Reynolds number is an order-diminished value as compared to the values obtained in wind tunnels and in free flight.It was found that with decreasing of roughness influence in growing boundary layer the flow disturbances evolution wide apart the payload fairing

  8. Droplet impact on superheated micro-structured surfaces

    NARCIS (Netherlands)

    Tran, A.T.; Staat, H.J.J.; Susarrey-Arce, A.; Foertsch, T.C.; Houselt, van A.; Gardeniers, J.G.E.; Prosperetti, A.; Lohse, D.; Sun, C.

    2013-01-01

    When a droplet impacts upon a surface heated above the liquid's boiling point, the droplet either comes into contact with the surface and boils immediately (contact boiling), or is supported by a developing vapor layer and bounces back (film boiling, or Leidenfrost state). We study the transition be

  9. Effect of chain end group on surface glass transition temperature of thin polymer film

    Science.gov (United States)

    Jiang, Xiqun; Yang, Chang Zheng; Tanaka, Keiji; Takahara, Atsushi; Kajiyama, Tisato

    2001-04-01

    Surface glass transition behaviors of proton end capped poly(2-vinylpyridine) (P2VP-H) and perfluoroalkyl end capped poly(2-vinylpyridine) (P2VP-C 2C 8F) thin films were investigated based on temperature-dependent lateral force microscopic (TDLFM) measurement. It is found that the species of chain end groups have significant influence on the surface glass transition temperature of the thin polymer film. For both samples, it is revealed that the surface glass transition temperatures decrease significantly in comparison to the bulk ones, and the magnitude order of reduction in surface Tg for P2VP-C 2C 8F is larger than that for P2VP-H. The apparent activation energy of surface α-relaxation calculated from the Arrhenius plot is ca. 292±40 and 212±40 kJ/mol for P2VP-H and P2VP-C 2C 8F, respectively, and is much smaller than the bulk one. The depression of the surface Tg for thin polymer films is explained by the excess free volume induced by the enrichment of chain end groups at the surface.

  10. Crystalline structures of poly(L-lactide) formed under pressure and structure transitions with heating

    DEFF Research Database (Denmark)

    Huang, Shaoyong; Li, Hongfei; Yu, Donghong;

    2013-01-01

    The isothermally crystallized poly(L-lactide) (PLLA) samples were obtained at 135 °C under pressures (Pc) ranging from 1 bar to 2.5 kbar. The crystalline structures, the structure transition, and thermal properties of the prepared samples were investigated by wide-angle X-ray diffraction (WAXD...... on the peculiarities of crystalline structure and crystallization behaviors, low and high pressure regions were revealed: disordered α crystal was formed in the high pressure region (>1 kbar). A layer located intermediate between crystalline and melt-like regions was observed, which finally took on crystalline order....... Reformation, disorder to order transformation, and recrystallization during heating completely changed the previous crystalline and stacking structure, a more stable crystalline structure was newly formed. The melting behaviors of samples indicate the crystalline and stacking structure formed under high...

  11. Crystalline structures of poly(L-lactide) formed under pressure and structure transitions with heating

    DEFF Research Database (Denmark)

    Huang, Shaoyong; Li, Hongfei; Yu, Donghong

    2013-01-01

    . Reformation, disorder to order transformation, and recrystallization during heating completely changed the previous crystalline and stacking structure, a more stable crystalline structure was newly formed. The melting behaviors of samples indicate the crystalline and stacking structure formed under high......The isothermally crystallized poly(L-lactide) (PLLA) samples were obtained at 135 °C under pressures (Pc) ranging from 1 bar to 2.5 kbar. The crystalline structures, the structure transition, and thermal properties of the prepared samples were investigated by wide-angle X-ray diffraction (WAXD......), real time synchrotron small-angle X-ray scattering (SR-SAXS) and differential scanning calorimetry (DSC) during this process. The structural parameters, such as the size of crystallites, the inverse spacing, the long periods and lamellae thicknesses decrease with pressure increasing. Based...

  12. Magnetic surface domain imaging of uncapped epitaxial FeRh(001) thin films across the temperature-induced metamagnetic transition

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Xianzhong; Matthes, Frank; Bürgler, Daniel E., E-mail: d.buergler@fz-juelich.de; Schneider, Claus M. [Peter Grünberg Institut, Electronic Properties (PGI-6) and Jülich-Aachen Research Alliance, Fundamentals of Future Information Technology (JARA-FIT), Forschungszentrum Jülich, D-52425 Jülich (Germany)

    2016-01-15

    The surface magnetic domain structure of uncapped epitaxial FeRh/MgO(001) thin films was imaged by in-situ scanning electron microscopy with polarization analysis (SEMPA) at various temperatures between 122 and 450 K. This temperature range covers the temperature-driven antiferromagnetic-to-ferromagnetic phase transition in the body of the films that was observed in-situ by means of the more depth-sensitive magneto-optical Kerr effect. The SEMPA images confirm that the interfacial ferromagnetism coexisting with the antiferromagnetic phase inside the film is an intrinsic property of the FeRh(001) surface. Furthermore, the SEMPA data display a reduction of the in-plane magnetization occuring well above the phase transition temperature which, thus, is not related to the volume expansion at the phase transition. This observation is interpreted as a spin reorientation of the surface magnetization for which we propose a possible mechanism based on temperature-dependent tetragonal distortion due to different thermal expansion coefficients of MgO and FeRh.

  13. Magnetic surface domain imaging of uncapped epitaxial FeRh(001 thin films across the temperature-induced metamagnetic transition

    Directory of Open Access Journals (Sweden)

    Xianzhong Zhou

    2016-01-01

    Full Text Available The surface magnetic domain structure of uncapped epitaxial FeRh/MgO(001 thin films was imaged by in-situ scanning electron microscopy with polarization analysis (SEMPA at various temperatures between 122 and 450 K. This temperature range covers the temperature-driven antiferromagnetic-to-ferromagnetic phase transition in the body of the films that was observed in-situ by means of the more depth-sensitive magneto-optical Kerr effect. The SEMPA images confirm that the interfacial ferromagnetism coexisting with the antiferromagnetic phase inside the film is an intrinsic property of the FeRh(001 surface. Furthermore, the SEMPA data display a reduction of the in-plane magnetization occuring well above the phase transition temperature which, thus, is not related to the volume expansion at the phase transition. This observation is interpreted as a spin reorientation of the surface magnetization for which we propose a possible mechanism based on temperature-dependent tetragonal distortion due to different thermal expansion coefficients of MgO and FeRh.

  14. Surface topology and electronic structure of layered strontium ruthenates

    Energy Technology Data Exchange (ETDEWEB)

    Bienert, Robert; Klinke, Melanie; Waelsch, Michael; Mietke, Sebastian; Matzdorf, Rene [Experimentalphysik II, Universitaet Kassel (Germany); Peng, Jin; Mao, Zhiqiang [Department of Physics, Tulane University, New Orleans (United States)

    2012-07-01

    In complex materials the interplay of properties like crystal structure, electronic structure and magnetism results in very interesting physical phenomena. The Ruddlesden-Popper series of layered Strontium Ruthenates Sr{sub n+1}Ru{sub n}O{sub 3n+1} describes one class of these materials. The double and triple layer systems behave like a Fermi liquid up to the transition temperature of 15 K and 24 K, respectively. In both compounds the local density of states (LDOS) shows a peak within the dip-like feature around the Fermi energy E{sub F}. Using low-temperature (LT) STM and STS we studied the temperature dependence of the LDOS in the range from 4.7 to 35 K. By increasing the temperature the peak within the dip in the LDOS at E{sub F} is only affected by thermal broadening. The surface unit cell of the Strontium Ruthenates exhibits a c(2 x 2) super structure, which is stable from 4.7 K up to room temperature as shown by our atomically resolved LT STM images and room temperature LEED experiments.

  15. Dewetting Transitions of Dropwise Condensation on Nanotexture-Enhanced Superhydrophobic Surfaces.

    Science.gov (United States)

    Lv, Cunjing; Hao, Pengfei; Zhang, Xiwen; He, Feng

    2015-12-22

    Although realizing dewetting transitions of droplets spontaneously on solid textured surfaces is quite challenging, it has become a key research topic in many practical applications that require highly efficient removal of liquid. Despite intensive efforts over the past few decades, due to impalement of vapor pockets inducing strong pinning of the contact lines, how to realize the self-removal of small droplets trapped in the textures remains an urgent problem. We report an in situ spontaneous dewetting transition of condensed droplets occurring on pillared surfaces with two-tier roughness, from the valleys to the tops of the pillars, owing to the nanotexture-enhanced superhydrophobicity, as well as the topology of the micropillars. Three wetting transition modes are observed. It is found that a further decreased Laplace pressure on the top side of the individual droplets accounts for such a surprising transition and self-removal of condensed water. An explicit model is constructed, which quite effectively predicts the Laplace pressure of droplets trapped by the textures. Our model also reveals that the critical size of the droplet for transition scales as the spacing of the micropillars. These findings are expected to be crucial to a fundamental understanding, as well as a remarkable strategy to guide the fabrication, of optimum super-water-repellant surfaces.

  16. Surface antiferromagnetism and incipient metal-insulator transition in strained manganite films

    KAUST Repository

    Cossu, Fabrizio

    2013-06-21

    Using first-principles calculations, we show that the (001) surface of the ferromagnet La0.7Sr0.3MnO3 under an epitaxial compressive strain favors antiferromagnetic (AF) order in the surface layers, coexisting with ferromagnetic (FM) bulk order. Surface antiferromagnetism is accompanied by a very marked surface-related spectral pseudogap, signaling an incomplete metal-insulator transition at the surface. The different relaxation and rumpling of the MnO2 and LaO surface planes in the two competing magnetic phases cause distinct work-function changes, which are of potential diagnostic use. The AF phase is recognized as an extreme surface-assisted case of the combination of in-plane AF super-exchange and vertical FM double-exchange couplings that rules magnetism in manganites under in-plane compression.

  17. Equilibrium Geometries, Reaction Pathways, and Electronic Structures of Ethanol Adsorbed on the Si (111) Surface

    CERN Document Server

    Gavrilenko, A V; Gavrilenko, V I

    2008-01-01

    Equilibrium atomic configurations and electron energy structure of ethanol adsorbed on the Si (111) surface are studied by the first-principles density functional theory. Geometry optimization is performed by the total energy minimization method. Several equilibrium atomic configurations of ethanol, both undissociated and dissociated, on the Si (111) surface are found. Reaction pathways and predicted transition states are discussed in comparison with available experimental data in terms of the feasibility of the reactions occurring. Analysis of atom and orbital resolved projected density of states indicate substantial modifications of the Si surface valence and conduction bands due to the adsorption of ethanol affecting the electrical properties of the surface.

  18. [Function of surface membrane structures in Thiobacillus thiooxidans].

    Science.gov (United States)

    Pivovarova, T A; Karavaĭko, G I

    1975-01-01

    The function of the surface membrane structures was studied with cytochemical techniques on ultrathin sections of Thiobacillus thiooxidans. The transport of elementary sulphur inside the cell involves the surface membrane structures, while oxidation of the sulphur to sulphuric acid takes place on the outer surface of the cytoplasmic membrane. The surface membrane structures are supposed also to participate in the primary dissolution of elementary sulphur at the site of contact of the cells with the mineral.

  19. Heat transfer and fluid mechanics measurements in transitional boundary layers on convex-curved surfaces

    Science.gov (United States)

    Wang, T.; Simon, T. W.

    1987-01-01

    The test section of the present experiment to ascertain the effects of convex curvature and freestream turbulence on boundary layer momentum and heat transfer during natural transition provided a two-dimensional boundary layer flow on a uniformly heated curved surface, with bending to various curvature radii, R. Attention is given to results for the cases of R = infinity, 180 cm, and 90 cm, each with two freestream turbulence intensity levels. While the mild convex curvature of R = 180 cm delays transition, further bending to R = 90 cm leads to no signifucant further delay of transition. Cases with both curvature and higher freestream disturbance effects exhibit the latter's pronounced dominance. These data are pertinent to the development of transition prediction models for gas turbine blade design.

  20. Transitions between smooth and complex stick-slip sliding of surfaces

    Science.gov (United States)

    Gourdon, Delphine; Israelachvili, Jacob N.

    2003-08-01

    Shear measurements were performed on mica surfaces with molecularly thin films of squalane (C30H62) confined between them. Squalane is a branched hydrocarbon liquid that can be in the liquid, glassy, or liquid-crystalline state under confinement. The friction forces, especially the transitions between smooth and intermittent (e.g., stick-slip) sliding, were measured over a wider range of applied loads (pressures), sliding velocities (shear rates), and temperatures than in previous studies. The results reveal that, depending on the conditions, qualitatively different behavior can arise in the same system. These include both abrupt and continuous transitions, both upper and lower critical transition temperatures, short and very long transient effects, and chaotic, sawtooth, or sinusoidal stick-slip that can slowly decay with time or distance sheared. The differences between these branched and simpler, e.g., spherical, unbranched molecules are compared, as well as with unlubricated (dry) surfaces and macroscopic (geological) systems.

  1. Modification of transition's factor in the compact surface-potential-based MOSFET model

    Directory of Open Access Journals (Sweden)

    Kevkić Tijana

    2016-01-01

    Full Text Available The modification of an important transition's factor which enables continual behavior of the surface potential in entire useful range of MOSFET operation is presented. The various modifications have been made in order to obtain an accurate and computationally efficient compact MOSFET model. The best results have been achieved by introducing the generalized logistic function (GL in fitting of considered factor. The smoothness and speed of the transition of the surface potential from the depletion to the strong inversion region can be controlled in this way. The results of the explicit model with this GL functional form for transition's factor have been verified extensively with the numerical data. A great agreement was found for a wide range of substrate doping and oxide thickness. Moreover, the proposed approach can be also applied on the case where quantum mechanical effects play important role in inversion mode.

  2. Effective modification of MgO with surface transition metal oxides for NF3 decomposition

    Institute of Scientific and Technical Information of China (English)

    Yanan Wang; Xiufeng Xu; Pei Sheng; Hongguang Li; Tingting Wang; Youfen Huang; Fangshu Liu

    2011-01-01

    NF3 decomposition over transition metal oxides coated MgO reagents in the absence of water is investigated.The results show that NF3 can be decomposed completely over pure MgO but the time of NF3 steady full conversion kept as short as 80 min,while the reactivities of coated MgO reagents were remarkably enhanced by transition metal oxides,for example the time of NF3 complete conversion over 12%Fe/MgO extended to 380 min.It is suggested that not only an increase in surface area but also a significant enhancement in the fluorination of MgO substrate caused by the surface transition metal oxides result in an improved reactivity of coated MgO reagents for NF3 decomposition.

  3. Bulk and surface phase transitions in the three-dimensional O(4) spin model

    Science.gov (United States)

    Deng, Youjin

    2006-05-01

    We investigate the O(4) spin model on the simple-cubic lattice by means of the Wolff cluster algorithm. Using the toroidal boundary condition, we locate the bulk critical point at coupling Kc=0.935856(2) , and determine the bulk thermal magnetic renormalization exponents as yt=1.3375(15) and yh=2.4820(2) , respectively. The universal ratio Q=⟨m2⟩2/⟨m4⟩ is also determined as 0.9142(1). The precision of these estimates significantly improves over that of the existing results. Then, we simulate the critical O(4) model with two open surfaces on which the coupling strength K1 can be varied. At the ordinary transitions, the surface magnetic exponent is determined as yh1(o)=1.0202(12) . Further, we find a so-called special surface transition at κ=K1/K-1=1.258(20) . At this point, the surface thermal exponent yt1(s) is rather close to zero, and we cannot exclude that the corresponding surface transition is Kosterlitz-Thouless-like. The surface magnetic exponent is yh1(s)=1.816(2) .

  4. Bulk and surface phase transitions in the three-dimensional O4 spin model.

    Science.gov (United States)

    Deng, Youjin

    2006-05-01

    We investigate the O(4) spin model on the simple-cubic lattice by means of the Wolff cluster algorithm. Using the toroidal boundary condition, we locate the bulk critical point at coupling K(c) = 0.935 856(2), and determine the bulk thermal magnetic renormalization exponents as y(t) = 1.337 5(15) and y(h) = 2.482 0(2), respectively. The universal ratio Q=m(2)(2)/m(4) is also determined as 0.9142(1). The precision of these estimates significantly improves over that of the existing results. Then, we simulate the critical O(4) model with two open surfaces on which the coupling strength K(1) can be varied. At the ordinary transitions, the surface magnetic exponent is determined as y((o))(h1) = 1.020 2(12). Further, we find a so-called special surface transition at (k) = K(1)/K-1 = 1.258(20). At this point, the surface thermal exponent y(s)(t1) is rather close to zero, and we cannot exclude that the corresponding surface transition is Kosterlitz-Thouless-like. The surface magnetic exponent is y((s))/h1 = 1.816(2).

  5. Trends in the Hydrodeoxygenation Activity and Selectivity of Transition Metal Surfaces

    DEFF Research Database (Denmark)

    Lausche, Adam C.; Falsig, Hanne; Jensen, Anker Degn

    2014-01-01

    This paper reports the use of a combination of density functional theory and microkinetic modelling to establish trends in the hydrodeoxygenation rates and selectivites of transition metal surfaces. Biomass and biomass-derived chemicals often contain large fractions of oxygenates. Removal of the ...

  6. Hot Electron Photoemission from Plasmonic Nanostructures: The Role of Surface Photoemission and Transition Absorption

    DEFF Research Database (Denmark)

    Babicheva, Viktoriia; Zhukovsky, Sergei; Ikhsanov, Renat Sh;

    2015-01-01

    We study mechanisms of photoemission of hot electrons from plasmonic nanoparticles. We analyze the contribution of "transition absorption", i.e., loss of energy of electrons passing through the boundary between different materials, to the surface mechanism of photoemission. We calculate photoemis...

  7. Surface energy from order parameter profile: At the QCD phase transition

    Science.gov (United States)

    Frei, Z.; Patkos, A.

    1989-01-01

    The order parameter profile between coexisting confined and plasma regions at the quantum chromodynamic (QCD) phase transition is constructed. The dimensionless combination of the surface energy (Sigma) and the correlation length (Zeta) is estimated to be Sigma Zeta 3 approximately equals 0.8.

  8. Scaling relationships for adsorption energies of C2 hydrocarbons on transition metal surfaces

    DEFF Research Database (Denmark)

    Jones, Glenn; Studt, Felix; Abild-Pedersen, Frank;

    2011-01-01

    Using density functional theory calculations we show that the adsorption energies for C2Hx-type adsorbates on transition metal surfaces scale with each other according to a simple bond order conservation model. This observation generalizes some recently recognized adsorption energy scaling laws f...

  9. Divacancy binding energy, formation energy and surface energy of BCC transition metals using MEAM potentials

    Science.gov (United States)

    Uniyal, Shweta; Chand, Manesh; Joshi, Subodh; Semalty, P. D.

    2016-05-01

    The modified embedded atom method (MEAM) potential parameters have been employed to calculate the unrelaxed divacancy formation energy, binding energy and surface energies for low index planes in bcc transition metals. The calculated results of divacancy binding energy and vacancy formation energy compare well with experimental and other available calculated results.

  10. Crystal structure and phase transition of thermoelectric SnSe.

    Science.gov (United States)

    Sist, Mattia; Zhang, Jiawei; Brummerstedt Iversen, Bo

    2016-06-01

    Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (∼ 810 K). Anharmonic Gram-Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed.

  11. Phase Transition and Structure of Silver Azide at High Pressure

    Energy Technology Data Exchange (ETDEWEB)

    D Hou; F Zhang; C Ji; T Hannon; H Zhu; J Wu; V Levitas; Y Ma

    2011-12-31

    Silver azide (AgN{sub 3}) was compressed up to 51.3 GPa. The results reveal a reversible second-order orthorhombic-to-tetragonal phase transformation starting from ambient pressure and completing at 2.7 GPa. The phase transition is accompanied by a proximity of cell parameters a and b, a 3{sup o} rotation of azide anions, and a change of coordination number from 4-4 (four short, four long) to eight fold. The crystal structure of the high pressure phase is determined to be in I4/mcm space group, with Ag at 4a, N{sub 1} at 4d, and N{sub 2} at 8h Wyckoff positions. Both of the two phases have anisotropic compressibility: the orthorhombic phase exhibits an anomalous expansion under compression along a-axis and is more compressive along b-axis than c-axis; the tetragonal phase is more compressive along the interlayer direction than the intralayer directions. The bulk moduli of the orthorhombic and tetragonal phases are determined to be K{sub OT} = 39{+-}5 GPa with K{sub OT'} = 10{+-}7 and K{sub OT} = 57 {+-}2 GPa with K{sub OT'} = 6.6{+-}0.2, respectively.

  12. Surface structures and dielectric response of ultrafine BaTiO{sub 3} particles

    Energy Technology Data Exchange (ETDEWEB)

    Jiang, B.; Peng, J.L.; Bursill, L.A

    1998-09-01

    Characteristic differences are observed for the dielectric response and microstructures of BaTiO{sub 3} nanoscale fine powders prepared using sol gel (SG) and steric acid gel (SAG) methods. The former exhibit a critical size below which there is no paraelectric/ferroelectric phase transition whereas BaTiO{sub 3} prepared via the SAG route remained cubic for all conditions. Atomic resolution images of both varieties showed a high density of interesting surface steps and facets. Computer simulated images of surface structure models showed that the outer (100) surface was typically a BaO layer and that at corners and ledges the steps are typically finished with Ba+2 ions; i.e. the surfaces and steps are Ba-rich. Otherwise the surfaces were typically clean and free of amorphous layers. The relationship between the observed surfaces structures and theoretical models for size effects on the dielectric properties is discussed. (authors) 22 refs., 2 tabs., 8 figs.

  13. Mechanically robust superhydrophobicity on hierarchically structured Si surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Xiu Yonghao; Hess, Dennis W [School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, GA 30332-0100 (United States); Liu Yan; Wong, C P, E-mail: dennis.hess@chbe.gatech.edu, E-mail: cp.wong@mse.gatech.edu [School of Materials Science and Engineering, Georgia Institute of Technology, 771 Ferst Drive, Atlanta, GA 30332-0245 (United States)

    2010-04-16

    Improvement of the robustness of superhydrophobic surfaces is critical in order to achieve commercial applications of these surfaces in such diverse areas as self-cleaning, water repellency and corrosion resistance. In this study, the mechanical robustness of superhydrophobic surfaces was evaluated on hierarchically structured silicon surfaces. The effect of two-scale hierarchical structures on robustness was investigated using an abrasion test and the results compared to those of superhydrophobic surfaces fabricated from polymeric materials and from silicon that contains only nanostructures. Unlike the polymeric and nanostructure-only surfaces, the hierarchical structures retained superhydrophobic behavior after mechanical abrasion.

  14. On the structure of Si(100) surface

    DEFF Research Database (Denmark)

    Back, Seoin; Schmidt, Johan Albrecht; Ji, Hyunjun;

    2013-01-01

    We revisit a dangling theoretical question of whether the surface reconstruction of the Si(100) surface would energetically favor the symmetric or buckled dimers on the intrinsic potential energy surfaces at 0 K. This seemingly simple question is still unanswered definitively since all existing...

  15. Surface transition on ice induced by the formation of a grain boundary.

    Directory of Open Access Journals (Sweden)

    Christian Pedersen

    Full Text Available Interfaces between individual ice crystals, usually referred to as grain boundaries, play an important part in many processes in nature. Grain boundary properties are, for example, governing the sintering processes in snow and ice which transform a snowpack into a glacier. In the case of snow sintering, it has been assumed that there are no variations in surface roughness and surface melting, when considering the ice-air interface of an individual crystal. In contrast to that assumption, the present work suggests that there is an increased probability of molecular surface disorder in the vicinity of a grain boundary. The conclusion is based on the first detailed visualization of the formation of an ice grain boundary. The visualization is enabled by studying ice crystals growing into contact, at temperatures between -20°C and -15°C and pressures of 1-2 Torr, using Environmental Scanning Electron Microscopy. It is observed that the formation of a grain boundary induces a surface transition on the facets in contact. The transition does not propagate across facet edges. The surface transition is interpreted as the spreading of crystal dislocations away from the grain boundary. The observation constitutes a qualitatively new finding, and can potentially increase the understanding of specific processes in nature where ice grain boundaries are involved.

  16. The formation energy for steps and kinks on cubic transition metal surfaces

    DEFF Research Database (Denmark)

    Vitos, Levente; Skriver, Hans Lomholt; Kollàr, Janos

    1999-01-01

    We have used our first-principles database of surface energies for metals in conjunction with the concept of vicinal surfaces to derive the energies of formation of monoatomic steps and corresponding kinks on close-packed surface facets of bcc and fee transition metals. The entries in the database...... allow for a direct calculation of the energies of a number of important steps. For the remaining steps and for all the kinks the energies of formation have been estimated from pair potential expansions of the entries in the database. (C) 1999 Elsevier Science B.V. All rights reserved....

  17. Structural transitions of CTAB micelles in a protic ionic liquid.

    Science.gov (United States)

    López-Barrón, Carlos R; Wagner, Norman J

    2012-09-04

    Micellar solutions of hexadecyltrimethylammonium bromide (CTAB) in a protic ionic liquid, ethylammonium nitrate (EAN), are studied by shear rheology, polarizing optical microscopy (POM), conductivity measurements, and small angle neutron scattering (SANS). Three concentration regimes are examined: A dilute regime (with concentrations [CTAB] concentrated regime (45 wt % conductivity is not sensitive to the L(1)-Hex transition, which corroborates the absence of topological transitions.

  18. The role of structural criteria in transitions theory

    NARCIS (Netherlands)

    Jagers op Akkerhuis, Gerard A.J.M.

    2016-01-01

    The Major Evolutionary Transitions theory of Szathmáry and Maynard Smith is famous for its contribution to the understanding of complex wholes in biology. Typical for Major Evolutionary Transitions theory is the select use of functional criteria, notably, cooperation, competition reduction and re

  19. Counterintuitive dispersion effect near surface plasmon resonances in Otto structures

    Science.gov (United States)

    Wang, Lin; Wang, Li-Gang; Ye, Lin-Hua; Al-Amri, M.; Zhu, Shi-Yao; Zubairy, M. Suhail

    2016-07-01

    In this paper, we investigate the counterintuitive dispersion effect associated with the poles and zeros of reflection and transmission functions in an Otto configuration when a surface plasmon resonance is excited. We show that the zeros and/or poles in the reflection and transmission functions may move into the upper-half complex-frequency plane (CFP), and these locations of the zeros and poles determine the dispersion properties of the whole structures (i.e., the frequency-dependent change of both reflected and transmitted phases). Meanwhile, we demonstrate various dispersion effects (both normal and abnormal) related to the changes of the poles and zeros in both reflection and transmission functions when considering the properties of metal substrates. For a realistic metal substrate in an Otto structure, there are the optimal thickness and incident angle, which correspond to the transitions of the zeros in the reflection function from the upper-half to lower-half CFP. These properties may be helpful to manipulate light propagation in optical devices.

  20. Low-temperature structural phase transition in deuterated and protonated lithium acetate dihydrate

    Energy Technology Data Exchange (ETDEWEB)

    Schroeder, F., E-mail: schroeder@kristall.uni-frankfurt.d [Goethe-Universitaet Frankfurt am Main, Institut fuer Geowissenschaften, Abt. Kristallographie, Altenhoeferallee 1, 60438 Frankfurt am Main (Germany); Winkler, B.; Haussuehl, E. [Goethe-Universitaet Frankfurt am Main, Institut fuer Geowissenschaften, Abt. Kristallographie, Altenhoeferallee 1, 60438 Frankfurt am Main (Germany); Cong, P.T.; Wolf, B. [Goethe-Universitaet Frankfurt am Main, Physikalisches Institut, Max-von-Laue-Strasse 1, 60438 Frankfurt am Main (Germany); Avalos-Borja, M. [Instituto Potosino de Investigacion Cientifica y Tecnologica, A.C. Camino a la Presa San Jose 2055, Col. Lomas 4 seccion CP 78216, San Luis Potosi (Mexico); Quilichini, M.; Hennion, B. [Laboratoire Leon Brillouin, CEN Saclay, 91191 Gif-sur-Yvette (France)

    2010-08-15

    Heat capacity measurements of protonated lithium acetate dihydrate show a structural phase transition at T = 12 K. This finding is in contrast to earlier work, where it was thought that only the deuterated compound undergoes a low temperature structural phase transition. This finding is confirmed by low temperature ultrasound spectroscopy, where the structural phase transition is associated with a velocity decrease of the ultrasonic waves, i.e. with an elastic softening. We compare the thermodynamic properties of the protonated and deuterated compounds and discuss two alternatives for the mechanism of the phase transition based on the thermal expansion measurements.

  1. Surface hot-film method for the measurement of transition, separation and reattachment points

    Science.gov (United States)

    Nakayama, Akihiko; Stack, John P.; Lin, John C.; Valarezo, Walter O.

    1993-01-01

    A real-time method of determining positions of laminar-to-turbulent transition region, separation and reattachment points and stagnation points using an array of simultaneously operated surface-mounted hot-film sensors has been developed and applied to a wind-tunnel test of a multielement airfoil model. Determination of various types of transitions and flow directions in various regimes of flows seen on multielement airfoils are possible without precise sensor calibration or laborious post-test data analysis. The results agree with established method and theoretical methods, but determination of turbulent reattachment points are not yet satisfactory.

  2. Spatially resolved spectroscopy across stellar surfaces. I. Using exoplanet transits to analyze 3D stellar atmospheres

    Science.gov (United States)

    Dravins, Dainis; Ludwig, Hans-Günter; Dahlén, Erik; Pazira, Hiva

    2017-09-01

    Context. High-precision stellar analyses require hydrodynamic modeling to interpret chemical abundances or oscillation modes. Exoplanet atmosphere studies require stellar background spectra to be known along the transit path while detection of Earth analogs require stellar microvariability to be understood. Hydrodynamic 3D models can be computed for widely different stars but have been tested in detail only for the Sun with its resolved surface features. Model predictions include spectral line shapes, asymmetries, and wavelength shifts, and their center-to-limb changes across stellar disks. Aims: We observe high-resolution spectral line profiles across spatially highly resolved stellar surfaces, which are free from the effects of spatial smearing and rotational broadening present in full-disk spectra, enabling comparisons to synthetic profiles from 3D models. Methods: During exoplanet transits, successive stellar surface portions become hidden and differential spectroscopy between various transit phases provides spectra of small surface segments temporarily hidden behind the planet. Planets cover no more than 1% of any main-sequence star, enabling high spatial resolution but demanding very precise observations. Realistically measurable quantities are identified through simulated observations of synthetic spectral lines. Results: In normal stars, line profile ratios between various transit phases may vary by 0.5%, requiring S/N ≳ 5000 for meaningful spectral reconstruction. While not yet realistic for individual spectral lines, this is achievable for cool stars by averaging over numerous lines with similar parameters. Conclusions: For bright host stars of large transiting planets, spatially resolved spectroscopy is currently practical. More observable targets are likely to be found in the near future by ongoing photometric searches.

  3. The single path rotational structure of n-photon transitions in diatomic molecules

    Science.gov (United States)

    Maïnos, C.; Castex, M. C.

    The present work considers the n-photon rovibronic transitions in the case where some predominant molecular path is present. Each molecular path produces a distinct rotational structure. The intensity of any rotational line as well the polarization intensity ratio are derived. A single path, relative weighting tensor is introduced which describes the influence of the molecular transitional path on the rotational structure.

  4. Structural and Electrochemical Characterization of Lithium Transition Metal Phosphates

    Science.gov (United States)

    Hashambhoy, Ayesha Maria

    The lithium ion battery has emerged as one of the most promising hybrid vehicle energy storage systems of the future. Of the potential cathode chemistries explored, lithium transition metal phosphates have generated a significant amount of interest due to their low-cost precursors, potential ease of synthesis, stability, and their environmentally friendly nature. This is in contrast to layered oxide systems such as LiCoO2, which have long been considered state of the art, but are now being reevaluated due to their structural instability at elevated temperatures, and higher cost. In particular, LiFePO4 has an operating potential comparable to those batteries available on the market (˜3.5V vs. Li/Li+), and higher theoretical specific capacity (170mAh/g vs. that of LiCoO2 which is 140mAh/g). The manganese analog to LiFePO4, LiMnPO4, exhibits a higher operating potential (˜4.1V v Li/Li+), and the same theoretical capacity, however Li-ion diffusion through this structure is much more rate limited and its theoretical capacity cannot be realized at rates suitable for commercial applications. The purpose of this work was threefold: 1) To explore the impact of Fe substitution on Mn sites in LiMnPO 4. 2) To examine the effects of alterations to the particle/electrolyte interface on rate capability. 3) To explore a novel fabrication route for LiMnPO4 using microwaves, and determine an optimal power and time combination for best performance. The coexistence of Fe and Mn on the transition metal site M, of LiMPO 4 resulted in an improved apparent Li-ion diffusivity in both Fe and Mn regimes as compared to that observed for LiFePO4 and LiMnPO 4 respectively. Calculations made from two different analysis methods, cyclic voltammetry (CV) and galvanostatic intermittent titration (GITT) drew this same conclusion. The signature characteristics observed from the CVs pertaining to single and dual phase reactions led to a delithiation model of LiFe0.5Mn0.5PO4 proposing the localization

  5. CO adsorption on metal-oxide surfaces doped with transition-metal adatoms

    Energy Technology Data Exchange (ETDEWEB)

    Blomqvist, Janne; Lehman, Lauri; Salo, Petri [Department of Applied Physics, Aalto University, FI-00076 Aalto (Finland)

    2012-05-15

    Using first principles density functional theory calculations, we have studied the adsorption of carbon monoxide (CO) on clean, Ag and Pd doped MgO(001), TiO{sub 2}(110), and {alpha}-Al{sub 2}O{sub 3}(0001) surfaces. Our results show that adsorption of CO on the clean surfaces is generally weak. Ag doping improves the adsorption only weakly, except on the TiO{sub 2} surface. The presence of Pd, however, significantly improves adsorption on all the surfaces studied. On the doped surfaces, the best adsorption sites are always the sites on top of the transition metal adatom, and the interaction range is 3-4 Aa around an isolated adatom. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  6. Metal-insulator transition and nanoscale phase separation in a hole-doped surface reconstruction

    Science.gov (United States)

    Mulugeta, Daniel; Snijders, Paul; Weitering, Hanno

    2014-03-01

    Doping, the deliberate introduction of impurities to alter electronic or magnetic properties, has been a tremendously successful method to study and understand systems with multiple competing interactions, as reflected in both the widespread use of doped semiconductors and in the large number of emergent electronic phases in doping-dependent phase diagrams of e.g. complex oxides. In low dimensional systems, however, the perturbation to the crystal lattice by the dopant atoms can overwhelm a delicate balance of interactions in e.g. a ground state with coexisting phases. Here we introduce a modulation doping technique used to dope holes in a surface reconstruction of Sn on Si(111). Using variable and low temperature scanning tunneling microscopy and spectroscopy, we observe a doping-induced metal-insulator phase transition that is of a displacive nature, contrasting with the order-disorder nature of other surface phase transitions. Moreover, the transition leads to an intrinsic nanoscale phase coexistence at 5 K never before observed on semiconductor surfaces. Clearly, modulation doping allows us to study the delicate balance of interactions in the phase diagram of low-dimensional electronic surface systems that is otherwise experimentally inaccessible. Funded by NSF DMR.

  7. Transition from Cassie to impaled state during drop impact on groove-textured solid surfaces.

    Science.gov (United States)

    Vaikuntanathan, V; Sivakumar, D

    2014-05-07

    Liquid drops impacted on textured surfaces undergo a transition from the Cassie state characterized by the presence of air pockets inside the roughness valleys below the drop to an impaled state with at least one of the roughness valleys filled with drop liquid. This occurs when the drop impact velocity exceeds a particular value referred to as the critical impact velocity. The present study investigates such a transition process during water drop impact on surfaces textured with unidirectional parallel grooves referred to as groove-textured surfaces. The process of liquid impalement into a groove in the vicinity of drop impact through de-pinning of the three-phase contact line (TPCL) beneath the drop as well as the critical impact velocity were identified experimentally from high speed video recordings of water drop impact on six different groove-textured surfaces made from intrinsically hydrophilic (stainless steel) as well as intrinsically hydrophobic (PDMS and rough aluminum) materials. The surface energy of various 2-D configurations of liquid-vapor interface beneath the drop near the drop impact point was theoretically investigated to identify the locally stable configurations and establish a pathway for the liquid impalement process. A force balance analysis performed on the liquid-vapor interface configuration just prior to TPCL de-pinning provided an expression for the critical drop impact velocity, Uo,cr, beyond which the drop state transitions from the Cassie to an impaled state. The theoretical model predicts that Uo,cr increases with the increase in pillar side angle, α, and intrinsic hydrophobicity whereas it decreases with the increase in groove top width, w, of the groove-textured surface. The quantitative predictions of the theoretical model were found to show good agreement with the experimental measurements of Uo,cr plotted against the surface texture geometry factor in our model, {tan(α/2)/w}(0.5).

  8. Surface conduction at phase transitions in (Au,Ag)/Si(1 1 1) submonolayer films

    Energy Technology Data Exchange (ETDEWEB)

    Tsukanov, D.A., E-mail: tsukanov@iacp.dvo.ru [Institute of Automation and Control Processes, FEB RAS, Vladivostok 690041 (Russian Federation); Far Eastern Federal University, Vladivostok 690950 (Russian Federation); Ryzhkova, M.V.; Borisenko, E.A. [Institute of Automation and Control Processes, FEB RAS, Vladivostok 690041 (Russian Federation); Bondarenko, L.V.; Matetskiy, A.V.; Gruznev, D.V. [Institute of Automation and Control Processes, FEB RAS, Vladivostok 690041 (Russian Federation); Far Eastern Federal University, Vladivostok 690950 (Russian Federation); Zotov, A.V. [Institute of Automation and Control Processes, FEB RAS, Vladivostok 690041 (Russian Federation); Far Eastern Federal University, Vladivostok 690950 (Russian Federation); Vladivostok State University of Economics and Service, Vladivostok 690600 (Russian Federation); Saranin, A.A. [Institute of Automation and Control Processes, FEB RAS, Vladivostok 690041 (Russian Federation); Far Eastern Federal University, Vladivostok 690950 (Russian Federation)

    2012-10-01

    Highlights: Black-Right-Pointing-Pointer Structural reordering occurs upon Ag adsorption onto Si(1 1 1){alpha}-{radical}3 Multiplication-Sign {radical}3-Au surface phase at 350 Degree-Sign C. Black-Right-Pointing-Pointer The new surface structure identified as Si(1 1 1){radical}93 Multiplication-Sign {radical}93-(Au,Ag) has been found by LEED and STM. Black-Right-Pointing-Pointer Electrical conductivity of various (Au,Ag)/Si(1 1 1) nanostructures has been characterized. - Abstract: Surface structure and electrical conductance of the (Au,Ag)/Si(1 1 1) two-dimensional system have been studied in situ with low-energy electron diffraction, scanning tunneling microscopy and four-point probe technique. The new surface structure identified as Si(1 1 1){radical}93 Multiplication-Sign {radical}93-(Au,Ag) has been found to form upon deposition of {approx}0.1 ML of Ag onto Si(1 1 1){alpha}-{radical}3 Multiplication-Sign {radical}3-Au surface held at 350 Degree-Sign C. With further Ag deposition at this growth temperature, the surface structure evolves to Si(1 1 1)2{radical}3 Multiplication-Sign 2{radical}3 and eventually to Si(1 1 1){radical}21 Multiplication-Sign {radical}21. Structural transformations have been found to be accompanied by non-monotonous changeover of the surface conductance. Possible factors affecting the surface conductivity are discussed.

  9. Structural phase transitions and topological defects in ion Coulomb crystals

    Energy Technology Data Exchange (ETDEWEB)

    Partner, Heather L. [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany); Nigmatullin, Ramil [Institute of Quantum Physics, Albert-Einstein Allee-11, Ulm University, 89069 Ulm (Germany); Burgermeister, Tobias; Keller, Jonas; Pyka, Karsten [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany); Plenio, Martin B. [Center for Integrated Quantum Science and Technology, Albert-Einstein-Allee 11, Ulm University, 89069 Ulm (Germany); Institute for Theoretical Physics, Albert-Einstein-Allee 11, Ulm University, 89069 Ulm (Germany); Retzker, Alex [Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Givat Ram (Israel); Zurek, Wojciech H. [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87544 (United States); Campo, Adolfo del [Department of Physics, University of Massachusetts Boston, Boston, MA 02125 (United States); Mehlstäubler, Tanja E., E-mail: tanja.mehlstaeubler@ptb.de [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)

    2015-03-01

    We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed nonadiabatically. For a second order phase transition, the Kibble–Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.

  10. Structural phase transitions and topological defects in ion Coulomb crystals

    Energy Technology Data Exchange (ETDEWEB)

    Partner, Heather L. [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Nigmatullin, Ramil [Institute of Quantum Physics, Ulm Univ., Ulm (Germany); Burgermeister, Tobias [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Keller, Jonas [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Pyka, Karsten [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany); Plenio, Martin B. [Center for Integrated Quantum Science and Technology, Ulm Univ., Ulm, (Germany):Institute for Theoretical Physics, Ulm Univ.,Ulm, (Germany); Retzker, Alex [Racah Institute of Physics, The Hebrew University of Jerusalem, Givat Ram (Israel); Zurek, Wojciech Hubert [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); del Campo, Adolfo [Univ. of Massachusetts, Amherst, MA (United States). Dept. of Physics; Mehlstaubler, Tanja E. [Physikalisch-Technische Bundesanstalt, Braunschweig (Germany)

    2014-11-19

    We use laser-cooled ion Coulomb crystals in the well-controlled environment of a harmonic radiofrequency ion trap to investigate phase transitions and defect formation. Topological defects in ion Coulomb crystals (kinks) have been recently proposed for studies of nonlinear physics with solitons and as carriers of quantum information. Defects form when a symmetry breaking phase transition is crossed non-adiabatically. For a second order phase transition, the Kibble-Zurek mechanism predicts that the formation of these defects follows a power law scaling in the rate of the transition. We demonstrate a scaling of defect density and describe kink dynamics and stability. We further discuss the implementation of mass defects and electric fields as first steps toward controlled kink preparation and manipulation.

  11. Phase transitions of adsorbed atoms on the surface of a carbon nanotube.

    Science.gov (United States)

    Wang, Zenghui; Wei, Jiang; Morse, Peter; Dash, J Gregory; Vilches, Oscar E; Cobden, David H

    2010-01-29

    Phase transitions of adsorbed atoms and molecules on two-dimensional substrates are well explored, but similar transitions in the one-dimensional limit have been more difficult to study experimentally. Suspended carbon nanotubes can act as nanoscale resonators with remarkable electromechanical properties and the ability to detect adsorption at the level of single atoms. We used single-walled carbon nanotube resonators to study the phase behavior of adsorbed argon and krypton atoms as well as their coupling to the substrate electrons. By monitoring the resonance frequency in the presence of gases, we observed the formation of monolayers on the cylindrical surface, phase transitions within them, and simultaneous modification of the electrical conductance.

  12. Shear moduli in bcc-fcc structure transition of colloidal crystals.

    Science.gov (United States)

    Zhou, Hongwei; Xu, Shenghua; Sun, Zhiwei; Zhu, Ruzeng

    2015-10-14

    Shear moduli variation in the metastable-stable structure transition of charged colloidal crystals was investigated by the combination techniques of torsional resonance spectroscopy and reflection spectrometer. Modulus of the system increases with the proceeding of the transition process and it finally reaches the maximum value at the end of the transition. For colloidal crystals in stable state, the experimental moduli show good consistence with theoretical expectations. However, in the transition process, the moduli are much smaller than theoretical ones and this can be chalked up to crystalline imperfection in the transition state.

  13. Shear moduli in bcc-fcc structure transition of colloidal crystals

    Science.gov (United States)

    Zhou, Hongwei; Xu, Shenghua; Sun, Zhiwei; Zhu, Ruzeng

    2015-10-01

    Shear moduli variation in the metastable-stable structure transition of charged colloidal crystals was investigated by the combination techniques of torsional resonance spectroscopy and reflection spectrometer. Modulus of the system increases with the proceeding of the transition process and it finally reaches the maximum value at the end of the transition. For colloidal crystals in stable state, the experimental moduli show good consistence with theoretical expectations. However, in the transition process, the moduli are much smaller than theoretical ones and this can be chalked up to crystalline imperfection in the transition state.

  14. Phonons on the clean metal surfaces and in adsorption structures

    Science.gov (United States)

    Rusina, Galina G.; Chulkov, Evgenii V.

    2013-06-01

    The state-of-the-art studies of the vibrational dynamics of clean metal surfaces and metal surface structures formed upon the sub-monolayer adsorption of the atoms of various elements are considered. A brief historical survey of the milestones of investigations of surface phonons is presented. The results of studies of the atomic structure and vibration characteristics of surfaces with low and high Miller indices and adsorption structures are analyzed. It is demonstrated that vicinal surfaces of FCC metals tend to exhibit specific vibrational modes located on the step and polarized along the step. Irrespective of the type and position of adsorption or the substrate structure, the phonon spectra of sub-monolayer adsorption structures always tend to display two modes for combined translational displacements of adatoms and for coupled vibrations of substrate atoms and adatoms polarized in the direction normal to the surface. The bibliography includes 202 references.

  15. Effects of surface anchoring on the electric Frederiks transition in ferronematic systems

    Science.gov (United States)

    Farrokhbin, Mojtaba; Kadivar, Erfan

    2016-11-01

    The effects of anchoring phenomenon on the electric Frederiks transition threshold field in a nematic liquid crystal doped with ferroelectric nanoparticles are discussed. The polarizability of these nanoparticles in combination with confinement effects cause the drastic effects on the ferronematic systems. This study is based on Frank free energy and Rapini-Papoular surface energy for ferronematic liquid crystal having finite anchoring condition. In the case of different anchoring boundary conditions, the Euler-Lagrange equation of the total free energy is numerically solved by using the finite difference method together with the relaxation method and Maxwell construction to select the physical solutions and therefore investigate the effects of different anchoring strengths on the Frederiks transition threshold field. Maxwell construction method is employed to select three periodic solutions for nematic liquid crystal director at the interfaces of a slab. In the interval from zero to half- π, there is only one solution for the director orientation. In this way, NLC director rotates toward the normal to the surface as the applied electric field increases at the walls. Our numerical results illustrate that above Frederiks transition and in the intermediate anchoring strength, nematic molecules illustrate the different orientation at slab boundaries. We also study the effects of different anchoring strengths, nanoparticle volume fractions and polarizations on the Frederiks transition threshold field. We report that decreasing in the nanoparticle polarization results in the saturation Frederiks threshold. However, this situation does not happen for the nanoparticles volume fraction.

  16. The effect of shadow fronts on dynamics of the surface layer during evening transitions

    Science.gov (United States)

    Pardyjak, E.; Hoch, S. W.; Jensen, D. D.; Gunawardena, N.; Di Sabatino, S.; Whiteman, C. D.; Leo, L.; Hocut, C. M.; Higgins, C. W.; Fernando, H. J.

    2013-12-01

    Two MATERHORN-X (Mountain Terrain Atmospheric Modeling and Observation Program) field campaigns were conducted at Dugway, UT, USA during the last year. An Autumn Campaign from 25 September - 21 October 2012 and a Spring Campaign from 1- 31 May 2013. A subset of the campaigns included dense observations along the East Slope of Granit Peak (40.096° N, -113.253° W). Observations included five multi-sonic anemometer eddy covariance towers (two with full energy budget stations), eleven small energy budget stations, fifteen automated weather stations, a distributed temperature sensing (DTS) system, hot-film anemometry, infrared camera surface temperature observations and up to three Doppler lidars. For this presentation, our analysis will focus on characterizing the response of mean wind and thermodynamics variables, as well as turbulence quantities during the evening transitions on East Slope. Previous observations have indicated that the dynamics of turbulence during evening transitions in steep mountainous terrain rapidly follows surface temperature changes associated with shadows produced by the local topography. The observations of flow transitions over the more moderate East Slope of Granite (~3-8%) indicate that wind shift direction and turbulence decay is not as tightly coupled to the shadow. Details of the transition response will be presented in the context of a new process model.

  17. Structure and phase transition of a two-dimensional dusty plasma

    Institute of Scientific and Technical Information of China (English)

    刘斌; 刘艳红; 陈雁萍; 杨思泽; 王龙

    2003-01-01

    The structure and phase transition of a two-dimensional (2D) dusty plasma have been investigated in detail by molecular dynamics simulation. Pair correlation function, static structure factor, mean square displacement, and bond angle correlation function have been calculated to characterize the structural properties. The variation of internal energy, shear modulus, particle trajectories and structural properties with temperature has been monitored to study the phase transition of the 2D dusty plasma system. The simulation results are in favour of a two-step continuous transition for this kind of plasma.

  18. Dissipative surface solitons in periodic structures

    CERN Document Server

    Kartashov, Yaroslav V; Vysloukh, Victor A

    2010-01-01

    We report dissipative surface solitons forming at the interface between a semi-infinite lattice and a homogeneous Kerr medium. The solitons exist due to balance between amplification in the near-surface lattice channel and two-photon absorption. The stable dissipative surface solitons exist in both focusing and defocusing media, when propagation constants of corresponding states fall into a total semi-infinite and or into one of total finite gaps of the spectrum (i.e. in a domain where propagation of linear waves is inhibited for the both media). In a general situation, the surface solitons form when amplification coefficient exceeds threshold value. When a soliton is formed in a total finite gap there exists also the upper limit for the linear gain.

  19. Surface tension and disjoining pressure of free-standing smectic films above the bulk smectic-A-isotropic transition temperature

    Energy Technology Data Exchange (ETDEWEB)

    Zakharov, A. V., E-mail: avz0911@yahoo.com [Saint Petersburg Institute for Machine Sciences, The Russian Academy of Sciences, Saint Petersburg 199178 (Russian Federation); Śliwa, Izabela, E-mail: izasliwa@ifmpan.poznan.pl [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan (Poland)

    2014-03-28

    We have carried out a numerical study of both the structural and thermodynamic properties of free-standing smectic films for the case of enhanced pair interaction in the bounding layers. Calculations, based upon the extended McMillan's mean-field theory with anisotropic forces, show that the layer-thinning transitions are characterized by abrupt drops to lower values, both for a disjoining pressure and a fluctuation-induced long-range interaction between the smectic film surfaces, and then continues to increase with a larger positive slope. Reasonable agreement between the theoretically predicted and the experimentally obtained data on the surface tension of the partially fluorinated 5-n-alkyl-2-(4-n-(perfluoroalkyl-metheleneoxy)phenyl) film has been obtained.

  20. Coal surface structure and thermodynamics. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Larsen, J.W.; Wernett, P.C.; Glass, A.S.; Quay, D.; Roberts, J.

    1994-05-01

    Coals surfaces were studied using static surface adsorption measurements, low angle x-ray scattering (LAXS), inverse gas chromatography (IGC) and a new {sup 13}C NMR relaxation technique. A comparison of surface areas determined by hydrocarbon gas adsorption and LAXS led to the twin conclusions that the hydrocarbons had to diffuse through the solid to reach isolated pores and that the coal pores do not form interconnected networks, but are largely isolated. This conclusion was confirmed when IGC data for small hydrocarbons showed no discontinuities in their size dependence as usually observed with porous solids. IGC is capable of providing adsorption thermodynamics of gases on coal surfaces. The interactions of non-polar molecules and coal surfaces are directly proportioned to the gas molecular polarizability. For bases, the adsorption enthalpy is equal to the polarizability interaction plus the heat of hydrogen bond formation with phenol. Amphoteric molecules have more complex interactions. Mineral matter can have highly specific effects on surface interactions, but with most of the molecules studied is not an important factor.

  1. Surface term for the capillary condensation transitions in a slit geometry

    OpenAIRE

    Urrutia, Ignacio; Szybisz, Leszek

    2006-01-01

    It is shown that a bare simple fluid model (SFM) proposed some years ago for studying adsorption between two semi-infinite solid walls can be improved by modifying the surface term in the grand potential for the film phase. Such a correction substantially improves the agreement between the predictions for phase transitions provided by that SFM and results obtained from calculations carried out for $^4$He with the density-functional method at zero temperature. The corrective term depends on th...

  2. Electronic Structures of Square Planar Coordinated Transition Metal Ions in Compounds with Gillespite Structure

    Institute of Scientific and Technical Information of China (English)

    林传易

    1990-01-01

    Electronic structures of square planar coordinated transition metal ions in BaCuSi4O10 and CaCrSi4O10 are investigated using the ligand-field theory(LFT),angular overlap model(AOM) and iterative extended Hueckel molecular orbital theory(IET).The electronic energy levels of the natural mineral dioptase are also investigated,in which the Cu2+ ions occupy the sites of pseudo D4h symmetry,Both LFT and AOM predict that the crystal-field levels of transition metal ions in these compounds follow such an order that E(2B1g)transitions obtained from point charge calcuations are in good agreement with those observed.However,the energy-level order cannot be determined unambiguously from the IET calculation because it depends on the values of parameters chosen for the calculation.

  3. The atomic structure of low-index surfaces of the intermetallic compound InPd

    Energy Technology Data Exchange (ETDEWEB)

    McGuirk, G. M.; Ledieu, J.; Gaudry, É.; Weerd, M.-C.; Fournée, V. de, E-mail: vincent.fournee@univ-lorraine.fr [Institut Jean Lamour (UMR 7198 CNRS-Université de Lorraine), Parc de Saurupt, F-54011 Nancy Cedex (France); Hahne, M.; Gille, P. [Department of Earth and Environmental Sciences, Crystallography Section, Ludwig-Maximilians-Universität München, Theresienstrasse 41, D-80333 München (Germany); Ivarsson, D. C. A.; Armbrüster, M. [Faculty of Natural Sciences, Institute of Chemistry, Materials for Innovative Energy Concepts, Technische Universität Chemnitz, D-09107 Chemnitz (Germany); Ardini, J.; Held, G. [Department of Chemistry, University of Reading, Reading RG6 6AD (United Kingdom); Diamond Light Source Ltd, Didcot OX11 0DE (United Kingdom); Maccherozzi, F. [Diamond Light Source Ltd, Didcot OX11 0DE (United Kingdom); Bayer, A. [Lehrstuhl für Physikalische Chemie II, Universität Erlangen-Nürnberg, Egerlandstraße 3, D-91058 Erlangen (Germany); Lowe, M. [Surface Science Research Centre and Department of Physics, The University of Liverpool, Liverpool L69 3BX (United Kingdom); Pussi, K. [Department of Mathematics and Physics, Lappeenranta University of Technology, P.O. Box 20, FIN-53851 Lappeenranta (Finland); Diehl, R. D. [Department of Physics, Penn State University, University Park, Pennsylvania 16802 (United States)

    2015-08-21

    The intermetallic compound InPd (CsCl type of crystal structure with a broad compositional range) is considered as a candidate catalyst for the steam reforming of methanol. Single crystals of this phase have been grown to study the structure of its three low-index surfaces under ultra-high vacuum conditions, using low energy electron diffraction (LEED), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). During surface preparation, preferential sputtering leads to a depletion of In within the top few layers for all three surfaces. The near-surface regions remain slightly Pd-rich until annealing to ∼580 K. A transition occurs between 580 and 660 K where In segregates towards the surface and the near-surface regions become slightly In-rich above ∼660 K. This transition is accompanied by a sharpening of LEED patterns and formation of flat step-terrace morphology, as observed by STM. Several superstructures have been identified for the different surfaces associated with this process. Annealing to higher temperatures (≥750 K) leads to faceting via thermal etching as shown for the (110) surface, with a bulk In composition close to the In-rich limit of the existence domain of the cubic phase. The Pd-rich InPd(111) is found to be consistent with a Pd-terminated bulk truncation model as shown by dynamical LEED analysis while, after annealing at higher temperature, the In-rich InPd(111) is consistent with an In-terminated bulk truncation, in agreement with density functional theory (DFT) calculations of the relative surface energies. More complex surface structures are observed for the (100) surface. Additionally, individual grains of a polycrystalline sample are characterized by micro-spot XPS and LEED as well as low-energy electron microscopy. Results from both individual grains and “global” measurements are interpreted based on comparison to our single crystals findings, DFT calculations and previous literature.

  4. A transitioning Arctic surface energy budget: the impacts of solar zenith angle, surface albedo and cloud radiative forcing

    Energy Technology Data Exchange (ETDEWEB)

    Sedlar, Joseph; Tjernstroem, Michael; Leck, Caroline [Stockholm University, Department of Meteorology, Stockholm (Sweden); Mauritsen, Thorsten [Max-Planck-Institute for Meteorology, Hamburg (Germany); Shupe, Matthew D.; Persson, P.O.G. [University of Colorado, NOAA-ESRL-PSD, Boulder, CO (United States); Brooks, Ian M.; Birch, Cathryn E. [University of Leeds, School of Earth and Environment, Leeds (United Kingdom); Sirevaag, Anders [University of Bergen, Bjerknes Center for Climate Research, Bergen (Norway); Nicolaus, Marcel [Norwegian Polar Institute, Tromsoe (Norway); Alfred Wegener Institute for Polar and Marine Research, Bremerhaven (Germany)

    2011-10-15

    Snow surface and sea-ice energy budgets were measured near 87.5 N during the Arctic Summer Cloud Ocean Study (ASCOS), from August to early September 2008. Surface temperature indicated four distinct temperature regimes, characterized by varying cloud, thermodynamic and solar properties. An initial warm, melt-season regime was interrupted by a 3-day cold regime where temperatures dropped from near zero to -7 C. Subsequently mean energy budget residuals remained small and near zero for 1 week until once again temperatures dropped rapidly and the energy budget residuals became negative. Energy budget transitions were dominated by the net radiative fluxes, largely controlled by the cloudiness. Variable heat, moisture and cloud distributions were associated with changing air-masses. Surface cloud radiative forcing, the net radiative effect of clouds on the surface relative to clear skies, is estimated. Shortwave cloud forcing ranged between -50 W m{sup -2} and zero and varied significantly with surface albedo, solar zenith angle and cloud liquid water. Longwave cloud forcing was larger and generally ranged between 65 and 85 W m{sup -2}, except when the cloud fraction was tenuous or contained little liquid water; thus the net effect of the clouds was to warm the surface. Both cold periods occurred under tenuous, or altogether absent, low-level clouds containing little liquid water, effectively reducing the cloud greenhouse effect. Freeze-up progression was enhanced by a combination of increasing solar zenith angles and surface albedo, while inhibited by a large, positive surface cloud forcing until a new air-mass with considerably less cloudiness advected over the experiment area. (orig.)

  5. An improved d-band model of the catalytic activity of magnetic transition metal surfaces

    CERN Document Server

    Bhattacharjee, Satadeep; Lee, S C

    2016-01-01

    The d-band center model of Hammer and N{\\o}rskov is widely used in understanding and predicting catalytic activity on transition metal (TM) surfaces. Here, we demonstrate that this model is inadequate for capturing the complete catalytic activity of the magnetically polarized TM surfaces and propose its generalization. We validate the generalized model through comparison of adsorption energies of the NH$_3$ molecule on the surfaces of 3d TMs (V, Cr, Mn, Fe, Co, Ni, Cu and Zn) determined with spin-polarized density functional theory (DFT)-based methods with the predictions of our model. Compared to the conventional d-band model, where the nature of the metal-adsorbate interaction is entirely determined through the energy and the occupation of the d-band center, we emphasize that for the surfaces with high spin polarization, the metal-adsorbate system can be stabilized through a competition of the spin-dependent metal-adsorbate interactions.

  6. Detection of molecular interactions at membrane surfaces through colloid phase transitions

    Science.gov (United States)

    Baksh, Michael M.; Jaros, Michal; Groves, Jay T.

    2004-01-01

    The molecular architecture of-and biochemical processes within-cell membranes play important roles in all living organisms, with many drugs and infectious disease agents targeting membranes. Experimental studies of biochemical reactions on membrane surfaces are challenging, as they require a membrane environment that is fluid (like cell membranes) but nevertheless allows for the efficient detection and characterization of molecular interactions. One approach uses lipid membranes supported on solid substrates such as silica or polymers: although the membrane is trapped near the solid interface, it retains natural fluidity and biological functionality and can be implanted with membrane proteins for functional studies. But the detection of molecular interactions involving membrane-bound species generally requires elaborate techniques, such as surface plasmon resonance or total internal reflection fluorescence microscopy. Here we demonstrate that colloidal phase transitions of membrane-coated silica beads provide a simple and label-free method for monitoring molecular interactions on lipid membrane surfaces. By adjusting the lipid membrane composition and hence the pair interaction potential between the membrane-supporting silica beads, we poise our system near a phase transition so that small perturbations on the membrane surface induce dramatic changes in the macroscopic organization of the colloid. We expect that this approach, used here to probe with high sensitivity protein binding events at membrane surfaces, can be applied to study a broad range of cell membrane processes.

  7. Phase transitions in thin films with competing surface fields and gradients.

    Science.gov (United States)

    Pang, Lijun; Landau, D P; Binder, K

    2011-10-01

    As a generic model for phase equilibria under confinement in a thin-film geometry in the presence of a gradient in the field conjugate to the order parameter, an Ising-lattice gas system is studied by both Monte Carlo simulations and a phenomenological theory. Choosing an L×L×D geometry with L≫D and periodic boundary conditions in the x,y directions, we place competing surface fields on the two L×L surfaces. In addition, a field gradient g is present in the z direction across the film, in competition with the surface fields. At temperatures T exceeding the critical temperature of the interface localization-delocalization transition, one finds a phase coexistence between oppositely oriented domains, aligned parallel to the surface fields and separated by an interface in the center of the film, for small enough g. For a weak gradient, a second-order transition to a monodomain state occurs, but it becomes first order if g exceeds a tricritical threshold. For sufficiently large gradients, another domain state becomes stabilized with domains oriented antiparallel to the surface fields.

  8. Hydroxyl migration disorders the surface structure of hydroxyapatite nanoparticles

    Science.gov (United States)

    Cheng, Xiajie; Wu, Hong; Zhang, Li; Ma, Xingtao; Zhang, Xingdong; Yang, Mingli

    2017-09-01

    The surface structure of nano-hydroxyapatite (HAP) was investigated using a combined simulated annealing and molecular dynamics method. The stationary structures of nano-HAP with 4-7 nm in diameter and annealed under different temperatures were analyzed in terms of pair distribution function, structural factor, mean square displacement and atomic coordination number. The particles possess different structures from bulk crystal. A clear radial change in their atomic arrangements was noted. From core to surface the structures change from ordered to disordered. A three-shell model was proposed to describe the structure evolution of nano-HAP. Atoms in the core zone keep their arrangements as in crystal, while atoms in the surface shell are in short-range order and long-range disorder, adopting a typically amorphous structure. Atoms in the middle shell have small displacements and/or deflections but basically retain their original locations as in crystal. The disordered shell is about 1 nm in thickness, in agreement with experimental observations. The disordering mainly stems from hydroxyl migration during which hydroxyls move to the surface and bond with the exposed Ca ions, and their left vacancies bring about a rearrangement of nearby atoms. The disordering is to some extent different for particles unannealed under different temperatures, resulting from fewer number of migrated hydroxyls at lower temperatures. Particles with different sizes have similar surface structures, and their surface energy decreases with increasing size. Moreover, the surface energy is reduced by hydroxyl migration because the exposed Ca ions on the surface are ionically bonded with the migrated hydroxyls. Our calculations proposed a new structure model for nano-HAP, which indicates a surface structure with activities different from those without surface reorganization. This is particularly interesting because most bioactivities of biomaterials are dominated by their surface activity.

  9. Three-dimensional electronic structures and the metal-insulator transition in Ruddlesden-Popper iridates

    Science.gov (United States)

    Yamasaki, A.; Fujiwara, H.; Tachibana, S.; Iwasaki, D.; Higashino, Y.; Yoshimi, C.; Nakagawa, K.; Nakatani, Y.; Yamagami, K.; Aratani, H.; Kirilmaz, O.; Sing, M.; Claessen, R.; Watanabe, H.; Shirakawa, T.; Yunoki, S.; Naitoh, A.; Takase, K.; Matsuno, J.; Takagi, H.; Sekiyama, A.; Saitoh, Y.

    2016-09-01

    In this study, we systematically investigate three-dimensional (3D) momentum (ℏ k )-resolved electronic structures of Ruddlesden-Popper-type iridium oxides Srn +1IrnO3 n +1 using soft-x-ray (SX) angle-resolved photoemission spectroscopy (ARPES). Our results provide direct evidence of an insulator-to-metal transition that occurs upon increasing the dimensionality of the IrO2-plane structure. This transition occurs when the spin-orbit-coupled jeff=1 /2 band changes its behavior in the dispersion relation and moves across the Fermi energy. In addition, an emerging band along the Γ (0,0,0)-R (π ,π ,π ) direction is found to play a crucial role in the metallic characteristics of SrIrO3. By scanning the photon energy over 350 eV, we reveal the 3D Fermi surface in SrIrO3 and kz-dependent oscillations of photoelectron intensity in Sr3Ir2O7 . In contrast to previously reported results obtained using low-energy photons, folded bands derived from lattice distortions and/or magnetic ordering make significantly weak (but finite) contributions to the k -resolved photoemission spectrum. At the first glance, this leads to the ambiguous result that the observed k -space topology is consistent with the unfolded Brillouin zone (BZ) picture derived from a nonrealistic simple square or cubic Ir lattice. Through careful analysis, we determine that a superposition of the folded and unfolded band structures has been observed in the ARPES spectra obtained using photons in both ultraviolet and SX regions. To corroborate the physics deduced using low-energy ARPES studies, we propose to utilize SX-ARPES as a powerful complementary technique, as this method surveys more than one whole BZ and provides a panoramic view of electronic structures.

  10. Electronic correlations at the alpha-gamma structural phase transition in paramagnetic iron

    OpenAIRE

    Leonov, I.; Poteryaev, A. I.; Anisimov, V. I.; Vollhardt, D.

    2010-01-01

    We compute the equilibrium crystal structure and phase stability of iron at the alpha(bcc)-gamma(fcc) phase transition as a function of temperature, by employing a combination of ab initio methods for calculating electronic band structures and dynamical mean-field theory. The magnetic correlation energy is found to be an essential driving force behind the alpha-gamma structural phase transition in paramagnetic iron.

  11. Evolution of karst conduit networks in transition from pressurised flow to free surface flow

    Science.gov (United States)

    Perne, M.; Covington, M. D.; Gabrovšek, F.

    2014-06-01

    We present a novel modelling approach to study the evolution of conduit networks in soluble rocks. Unlike the models presented so far, the model allows a transition from pressurised (pipe) flow to a free surface (open channel) flow in evolving discrete conduit networks. It calculates flow, solute transport and dissolutional enlargement within each time step and steps through time until a stable flow pattern establishes. The flow in each time step is calculated by calling the EPA Storm Water Management Model (EPA SWMM), which efficiently solves the 1-D Saint Venant equations in a network of conduits. We present several cases with low dip and sub-vertical networks to demonstrate mechanisms of flow pathway selection. In low dip models the inputs were randomly distributed to several junctions. The evolution of pathways progresses upstream: initially pathways linking outlets to the closest inputs evolve fastest because the gradient along these pathways is largest. When a pathway efficiently drains the available recharge, the head drop along the pathway attracts flow from the neighbouring upstream junctions and new connecting pathways evolve. The mechanism progresses from the output boundary inwards until all inputs are connected to the stable flow system. In the pressurised phase, each junction is drained by at least one conduit, but only one conduit remains active in the vadose phase. The selection depends on the initial geometry of a junction, initial distribution of diameters, the evolution in a pressurised regime, and on the dip of the conduits, which plays an important role in vadose entrenchment. In high dip networks, the vadose zone propagates downwards and inwards from the rim of the massif. When a network with randomly distributed initial diameters is supplied with concentrated recharge from the adjacent area, the sink point regresses up upstream along junctions connected to the prominent pathways. Large conductive structures provide deep penetration of high

  12. Evolution of karst conduit networks in transition from pressurised flow to free surface flow

    Directory of Open Access Journals (Sweden)

    M. Perne

    2014-06-01

    Full Text Available We present a novel modelling approach to study the evolution of conduit networks in soluble rocks. Unlike the models presented so far, the model allows a transition from pressurised (pipe flow to a free surface (open channel flow in evolving discrete conduit networks. It calculates flow, solute transport and dissolutional enlargement within each time step and steps through time until a stable flow pattern establishes. The flow in each time step is calculated by calling the EPA Storm Water Management Model (EPA SWMM, which efficiently solves the 1-D Saint Venant equations in a network of conduits. We present several cases with low dip and sub-vertical networks to demonstrate mechanisms of flow pathway selection. In low dip models the inputs were randomly distributed to several junctions. The evolution of pathways progresses upstream: initially pathways linking outlets to the closest inputs evolve fastest because the gradient along these pathways is largest. When a pathway efficiently drains the available recharge, the head drop along the pathway attracts flow from the neighbouring upstream junctions and new connecting pathways evolve. The mechanism progresses from the output boundary inwards until all inputs are connected to the stable flow system. In the pressurised phase, each junction is drained by at least one conduit, but only one conduit remains active in the vadose phase. The selection depends on the initial geometry of a junction, initial distribution of diameters, the evolution in a pressurised regime, and on the dip of the conduits, which plays an important role in vadose entrenchment. In high dip networks, the vadose zone propagates downwards and inwards from the rim of the massif. When a network with randomly distributed initial diameters is supplied with concentrated recharge from the adjacent area, the sink point regresses up upstream along junctions connected to the prominent pathways. Large conductive structures provide deep

  13. Structural Analysis of Labor Market Transitions Using Indirect Inference

    DEFF Research Database (Denmark)

    An, Mark Yuing; Liu, Ming

    1996-01-01

    In the econometric analysis of labor market transitions, the data generating process is often specified as a continuous-time semi-Markovian process with a finite state space. With typically short panel data, analysts have long been concerne d with the initial conditions problem.......In the econometric analysis of labor market transitions, the data generating process is often specified as a continuous-time semi-Markovian process with a finite state space. With typically short panel data, analysts have long been concerne d with the initial conditions problem....

  14. Molecular weight dependence of surface flow near the bulk glass transition temperature

    Science.gov (United States)

    Chai, Yu; Salez, Thomas; Benzaquen, Michael; Raphael, Elie; Forrest, James A.

    2014-03-01

    We present the study on molecular weight dependent sub-Tg surface dynamics of polymer thin films by using the Nano-step experiment [McGraw et al. Soft Matter 7, 7832 (2011)]. By varying the molecular weight, we are able to probe the surface dynamics of the free surface below Tg with the polymer size comparable to the surface depth. In particular, we define and use a correlation function to compare measured and calculated profiles to analyze the transition from the bulk flow to flow restricted to the surface region. Surprisingly, even for the polymers with Mw = 22,000 surface flow is still observed below the bulk Tg value. A numerical simulation of random walk is used to find the fraction of polymer of which all of the polymer segments are located in the free surface region. The simulation results indicate that there are still a significant fraction of polymer molecules where all segments are in the near free surface region. These molecules can undergo flow consistent with the experimental results.

  15. UV spectral filtering by surface structured multilayer mirrors

    NARCIS (Netherlands)

    Huang, Q.; Paardekooper, Daniel Mathijs; Zoethout, E.; Medvedev, V. V.; van de Kruijs, Robbert; Bosgra, Jeroen; Louis, Eric; F. Bijkerk,

    2014-01-01

    A surface structured extreme ultraviolet multilayer mirror was developed showing full band suppression of UV (lambda = 100-400 nm) and simultaneously a high reflectance of EUV light (lambda = 13.5 nm). The surface structure consists of Si pyramids, which are substantially transparent for EUV but

  16. UV spectral filtering by surface structured multilayer mirrors

    NARCIS (Netherlands)

    Huang, Q.; Paardekooper, Daniel Mathijs; Zoethout, E.; Medvedev, V. V.; van de Kruijs, Robbert; Bosgra, Jeroen; Louis, Eric; F. Bijkerk,

    2014-01-01

    A surface structured extreme ultraviolet multilayer mirror was developed showing full band suppression of UV (lambda = 100-400 nm) and simultaneously a high reflectance of EUV light (lambda = 13.5 nm). The surface structure consists of Si pyramids, which are substantially transparent for EUV but ref

  17. Structures of surface and interface of amorphous ice

    Science.gov (United States)

    Kumagai, Yu; Ikeda-Fukazawa, Tomoko

    2017-06-01

    To investigate the surface structure, we performed molecular dynamics calculations of amorphous ice. The result shows that a low density layer, which forms a few hydrogen bonds with weaker strength, exists in the surface. Furthermore, the sintering processes were simulated to investigate the structure of grain boundary formed from the adsorption of two surfaces. The result indicates that a low density region exists in a boundary between amorphous ice grains. The structures of surface and interface of amorphous ice have important implications for adsorption, diffusion, and chemical reaction in ice grains of interstellar molecular clouds.

  18. Hierarchically structured superoleophobic surfaces with ultralow contact angle hysteresis.

    Science.gov (United States)

    Kota, Arun K; Li, Yongxin; Mabry, Joseph M; Tuteja, Anish

    2012-11-14

    Hierarchically structured, superoleophobic surfaces are demonstrated that display one of the lowest contact angle hysteresis values ever reported - even with extremely low-surface-tension liquids such as n-heptane. Consequently, these surfaces allow, for the first time, even ≈2 μL n-heptane droplets to bounce and roll-off at tilt angles. ≤ 2°.

  19. Metrology of sub-micron structured polymer surfaces

    DEFF Research Database (Denmark)

    Quagliotti, Danilo; Tosello, Guido; Salaga, J.

    surface replication of the tool insert component when moulding the polymer melt [1]. This aspect is particularly critical when dealing with increasingly small dimensional scales in micro- and nano-structured surfaces [2, 3].In this context, a metrological investigation of polymer replicated surfaces using...

  20. Structure dependence of Pt surface activated ammonia oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Santen, R A van; Offermans, W K [Schuit Institute of Catalysis, Laboratory of Inorganic Chemistry and Catalysis, Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven (Netherlands); Ricart, J M; Novell-Leruth, G [Department of Chemical Physics and Inorganic Chemistry, University Rovira I Virgili, C/ Marcel.lI Domingo s/n, 43007 Tarragona (Spain); Perez-RamIrez, J [Institute of Chemical Research of Catalonia (ICIQ) and Catalan, Institution for Research and Advanced Studies (ICREA), Avinguda Paisos Catalans 16, 43007, Tarragona (Spain)], E-mail: r.a.v.santen@tue.nl

    2008-06-01

    Computational advances that enable the prediction of the structures and the energies of surface reaction intermediates are providing essential information to the formulation of theories of surface chemical reactivity. In this contribution this is illustrated for the activation of ammonia by coadsorbed oxygen and hydroxyl on the Pt(111), Pt(100), and Pt(211) surfaces.

  1. Strike-Slip Faulting Processes on Ganymede: Global Morphological Mapping and Structural Interpretation of Grooved and Transitional Terrains

    Science.gov (United States)

    Burkhard, L. M.; Cameron, M. E.; Smith-Konter, B. R.; Seifert, F.; Pappalardo, R. T.; Collins, G. C.

    2015-12-01

    Ganymede's fractured surface reveals many large-scale, morphologically distinct regions of inferred distributed shear and strike-slip faulting that may be important to the structural development of its surface and in the transition from dark to light (grooved) materials. To better understand the role of strike-slip tectonism in shaping Ganymede's complex icy surface, we perform a detailed mapping of key examples of strike-slip morphologies (i.e., en echelon structures, strike-slip duplexes, laterally offset pre-existing features, and possible strained craters) from Galileo and Voyager images. We focus on complex structures associated with grooved terrain (e.g. Nun Sulcus, Dardanus Sulcus, Tiamat Sulcus, and Arbela Sulcus) and terrains transitional from dark to light terrain (e.g. the boundary between Nippur Sulcus and Marius Regio, including Byblus Sulcus and Philus Sulcus). Detailed structural interpretations suggest strong evidence of strike-slip faulting in some regions (i.e., Nun and Dardanus Sulcus); however, further investigation of additional strike-slip structures is required of less convincing regions (i.e., Byblus Sulcus). Where applicable, these results are synthesized into a global database representing an inferred sense of shear for many of Ganymede's fractures. Moreover, when combined with existing observations of extensional features, these results help to narrow down the range of possible principal stress directions that could have acted at the regional or global scale to produce grooved terrain on Ganymede.

  2. Surface induces different crystal structures in a room temperature switchable spin crossover compound.

    Science.gov (United States)

    Gentili, Denis; Liscio, Fabiola; Demitri, Nicola; Schäfer, Bernhard; Borgatti, Francesco; Torelli, Piero; Gobaut, Benoit; Panaccione, Giancarlo; Rossi, Giorgio; Degli Esposti, Alessandra; Gazzano, Massimo; Milita, Silvia; Bergenti, Ilaria; Ruani, Giampiero; Šalitroš, Ivan; Ruben, Mario; Cavallini, Massimiliano

    2016-01-01

    We investigated the influence of surfaces in the formation of different crystal structures of a spin crossover compound, namely [Fe(L)2] (LH: (2-(pyrazol-1-yl)-6-(1H-tetrazol-5-yl)pyridine), which is a neutral compound thermally switchable around room temperature. We observed that the surface induces the formation of two different crystal structures, which exhibit opposite spin transitions, i.e. on heating them up to the transition temperature, one polymorph switches from high spin to low spin and the second polymorph switches irreversibly from low spin to high spin. We attributed this inversion to the presence of water molecules H-bonded to the complex tetrazolyl moieties in the crystals. Thin deposits were investigated by means of polarized optical microscopy, atomic force microscopy, X-ray diffraction, X-ray absorption spectroscopy and micro Raman spectroscopy; moreover the analysis of the Raman spectra and the interpretation of spin inversion were supported by DFT calculations.

  3. Surface Nano-Structuring by Adsorption and Chemical Reactions

    OpenAIRE

    Ken-ichi Tanaka

    2010-01-01

    Nano-structuring of the surface caused by adsorption of molecules or atoms and by the reaction of surface atoms with adsorbed species are reviewed from a chemistry viewpoint. Self-assembly of adsorbed species is markedly influenced by weak mutual interactions and the local strain of the surface induced by the adsorption. Nano-structuring taking place on the surface is well explained by the notion of a quasi-molecule provided by the reaction of surface atoms with adsorbed species. Self-assembl...

  4. Fragmentation pathways of nanofractal structures on surfaces

    DEFF Research Database (Denmark)

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

    2011-01-01

    We present a theoretical analysis of the post-growth processes occurring in nanofractals grown on a surface. For this study we have developed a method that accounts for the internal dynamics of particles in a fractal. We demonstrate that the detachment of particles from the fractal and their diff......We present a theoretical analysis of the post-growth processes occurring in nanofractals grown on a surface. For this study we have developed a method that accounts for the internal dynamics of particles in a fractal. We demonstrate that the detachment of particles from the fractal...... and their diffusion within the fractal and over the surface determines the shape of the islands remaining on a surface after the fractal fragmentation. We consider different scenarios of fractal post-growth relaxation and analyze the time evolution of the island's morphology. The results of our calculations...... are compared with available experimental observations, and experiments in which the post-growth relaxation of deposited nanostructures can be tested are suggested....

  5. Structural optimization of super-repellent surfaces

    DEFF Research Database (Denmark)

    Cavalli, Andrea; Bøggild, Peter; Okkels, Fridolin

    2013-01-01

    Micro-patterning is an effective way to achieve surfaces with extreme liquid repellency. This technique does not rely on chemical coatings and is therefore a promising concept for application in food processing and bio-compatibile coatings. This super-repellent behaviour is obtained by suspending...

  6. Fragmentation pathways of nanofractal structures on surfaces

    DEFF Research Database (Denmark)

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

    2011-01-01

    We present a theoretical analysis of the post-growth processes occurring in nanofractals grown on a surface. For this study we have developed a method that accounts for the internal dynamics of particles in a fractal. We demonstrate that the detachment of particles from the fractal and their diff...

  7. The Influence of Surface Anisotropy Crystalline Structure on Wetting of Sapphire by Molten Aluminum

    Science.gov (United States)

    Aguilar-Santillan, Joaquin

    2013-05-01

    The wetting of sapphire by molten aluminum was investigated by the sessile drop technique from 1073 K to 1473 K (800 °C to 1200 °C) at PO2 <10-15 Pa under Ar atmosphere. This study focuses on sapphire crystalline structure and its principle to the interface. The planes " a" and " b" are oxygen terminated structures and wet more by Al, whereas the " c" plane is an aluminum terminated structure. A wetting transition at 1273 K (1000 °C) was obtained and a solid surface tension proves the capillarity trends of the couple.

  8. Inhibition of a structural phase transition in one-dimensional organometal halide perovskite nanorods grown inside porous silicon nanotube templates

    Science.gov (United States)

    Arad-Vosk, N.; Rozenfeld, N.; Gonzalez-Rodriguez, R.; Coffer, J. L.; Sa'ar, A.

    2017-02-01

    One-dimensional organo-metal halide perovskite (C H3N H3Pb I3 ) nanorods whose diameter and length are dictated by the inner size of porous silicon nanotube templates have been grown, characterized, and compared to bulk perovskites in the form of microwires. We have observed a structural phase transition for bulk perovskites, where the crystal structure changes from tetragonal to orthorhombic at about 160 K, as opposed to small diameter one-dimensional perovskite nanorods, of the order of 30-70 nm in diameter, where the phase transition is inhibited and the dominant phase remains tetragonal. Two major experimental techniques, infrared absorption spectroscopy and photoluminescence, were utilized to probe the temperature dependence of the perovskite phases over the 4-300 K temperature range. Yet, different characteristics of the phase transition were measured by the two spectroscopic methods and explained by the presence of small, tetragonal inclusions embedded in the orthorhombic phase. The inhibition of the phase transition is attributed to the large surface area of these one-dimensional perovskite nanorods, which gives rise to a large stress that, in turn, prevents the formation of the orthorhombic phase. The absence of phase transition enables the measurement of the tetragonal bandgap energy down to low temperatures.

  9. Laser Surface Preparation and Bonding of Aerospace Structural Composites

    Science.gov (United States)

    Belcher, M. A.; Wohl, C. J.; Hopkins, J. W.; Connell, J. W.

    2010-01-01

    Adhesive bonds are critical to the integrity of built-up structures. Disbonds can often be detected but the strength of adhesion between surfaces in contact is not obtainable without destructive testing. Typically the number one problem in a bonded structure is surface contamination, and by extension, surface preparation. Standard surface preparation techniques, including grit blasting, manual abrasion, and peel ply, are not ideal because of variations in their application. Etching of carbon fiber reinforced plastic (CFRP) panels using a neodymium-doped yttrium aluminum garnet (Nd:YAG) laser appears to be a highly precise and promising way to both clean a composite surface prior to bonding and provide a bond-promoting patterned surface akin to peel ply without the inherent drawbacks from the same (i.e., debris and curvature). CFRP surfaces prepared using laser patterns conducive to adhesive bonding were compared to typical prebonding surface treatments through optical microscopy, contact angle goniometry, and post-bonding mechanical testing.

  10. The transition to turbulence in parallel flows: transition to turbulence or to regular structures

    CERN Document Server

    Pomeau, Yves

    2015-01-01

    We propose a scenario for the formation of localized turbulent spots in transition flows, which is known as resulting from the subcritical character of the transition. We show that it is not necessary to add 'by hand" a term of random noise in the equations, in order to describe the existence of long wavelength fluctuations as soon as the bifurcated state is beyond the Benjamin-Feir instability threshold. We derive the instability threshold for generalized complex Ginzburg-Landau equation which displays subcriticality. Beyond and close to the Benjamin-Feir threshold we show that the dynamics is mainly driven by the phase of the complex amplitude which obeys Kuramoto-Sivashinsky equation while the fluctuations of the modulus are smaller and slaved to the phase (as already proved for the supercritical case). On the opposite, below the Benjamin-Feir instability threshold, the bifurcated state does loose the randomness associated to turbulence so that the transition becomes of the mean-field type as in noiseless ...

  11. Structural and electronic properties of hydrosilylated silicon surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Baumer, A.

    2005-11-15

    The structural and electronic properties of alkyl-terminated Si surfaces prepared by thermallyinduced hydrosilylation have been studied in detail in the preceding chapters. Various surfaces have been used for the functionalization ranging from crystalline Si over amorphous hydrogenated Si to nanoscaled materials such as Si nanowires and nanoparticles. In each case, the alkyl-terminated surfaces have been compared to the native oxidized and H-terminated surfaces. (orig.)

  12. Transition of surface energy budget in the Gobi Desert between spring and summer seasons

    Science.gov (United States)

    Smith, Eric A.; Reiter, Elmar R.; Gao, Youxi

    1986-01-01

    The surface energetics of the southwest Gobi Desert, including the temporal variations and diurnally averaged properties of the surface energy budget components, was investigated. The field program was conducted during the spring and summer of 1984, with the measurement system designed to monitor radiative exchange, heat/moisture storage in the soil, and sensible and latent heat exhange between the ground and the atmosphere. Results of the analysis reveal a seasonal transition feature not expected of a midlatitude desert. Namely, the differences in both surface radiation exchange and the distibution of sensible and latent heat transfer arise within a radiatively forced environment that barely deviates from spring to summer in terms of available solar energy at the surface. Both similarities and differences in the spring and summer surface energy budgets arise from differences imparted to the system by an increase in the summertime atmospheric moisture content. Changes in the near-surface mixing ratio are shown to alter the effectiveness of the desert surface in absorbing radiative energy and redistibuting it to the lower atmosphere through sensible and latent heat exchange.

  13. Carbon Nanomaterials: Surface Structure and Morphology

    Science.gov (United States)

    Mansurov, Z. A.; Shabanova, T. A.; Mofa, N. N.; Glagolev, V. A.

    2014-09-01

    We propose a classification of individual nanoparticles on the basis of the form of the surface and the internal architectural packing for investigations carried out with the help of transmission electron microscopy. The investigated samples contain individual nanoparticles of seven kinds in different ratios: rounded, tubular, fibrous, fi lm, "veil," "active" particles and "particles with regular geometric contours." The classification was made on the basis of an analysis of the results of investigations of the surfaces and internal architectural packing of carbon particles obtained in different physiochemical processes (carbonization, carburizing, arc discharge, mechanochemical treatment, plasma chemistry, and in carbon-containing fl ames). For the source materials, we used waste of farming products and widely distributed mineral raw materials.

  14. Dyeing of Snow Surfaces to Observe Structure

    Science.gov (United States)

    1993-06-01

    of freezeup problems important to obtain a clear visual perspective and with water. We found that both coloring agents to obtain good photographic...a dye of methanol coloring in with floodlights, whereas Figure 7b is a view of the water. Freezeup at the sprayer nozzle was one same area lighted...from behind, problem and the snow surface had a blemished appearance because of the addition of the water, which then froze. Freezeup may not be a

  15. Surface Structure Enhanced Microchannel Flow Boiling

    OpenAIRE

    Zhu, Yangying; Antao, Dion Savio; Chu, Kuang-Han; Chen, Siyu; Hendricks, Terry J.; Zhang, Tiejun; Wang, Evelyn N.

    2016-01-01

    We investigated the role of surface microstructures in two-phase microchannels on suppressing flow instabilities and enhancing heat transfer. We designed and fabricated microchannels with well-defined silicon micropillar arrays on the bottom heated microchannel wall to promote capillary flow for thin film evaporation while facilitating nucleation only from the sidewalls. Our experimental results show significantly reduced temperature and pressure drop fluctuation especially at high heat fluxe...

  16. Adsorption and dissociation of dinitrogen on transition metal (Ta, W and Re) doped MgO surface

    KAUST Repository

    Yadav, Manoj Kumar

    2016-06-16

    The adsorption and dissociation of dinitrogen on transition metal (Ta, W and Re) doped MgO(100) surface has been studied employing density functional theory. It is found that all these transition metals (TM) on MgO(100) surface are capable of adsorbing dinitrogen (N2), however there is no dissociative adsorption of N2 on single transition metal dopant. When two TM atoms are doped on MgO(100) surface, dissociative adsorption of dinitrogen occurs in all the three cases. Whether the dissociation is spontaneous or is it associated with activation barrier depends on the orientation of N2 molecule approaching the dopant site.

  17. Modification of the surface electronic and chemical properties of Pt(111) by subsurface 3d transition metals

    DEFF Research Database (Denmark)

    Kitchin, J. R.; Nørskov, Jens Kehlet; Barteau, M. A.;

    2004-01-01

    The modification of the electronic and chemical properties of Pt(111) surfaces by subsurface 3d transition metals was studied using density-functional theory. In each case investigated, the Pt surface d-band was broadened and lowered in energy by interactions with the subsurface 3d metals......, resulting in weaker dissociative adsorption energies of hydrogen and oxygen on these surfaces. The magnitude of the decrease in adsorption energy was largest for the early 3d transition metals and smallest for the late 3d transition metals. In some cases, dissociative adsorption was calculated...

  18. Structural phase transition and elastic properties of thorium pnictides at high pressure

    Indian Academy of Sciences (India)

    Kuldeep Kholiya; B R K Gupta

    2007-04-01

    In the present paper we have pointed out the weaknesses of the approach by Aynyas et al [1] to study the structural phase transition and elastic properties of thorium pnictides. The calculated values of phase transition pressure and other elastic properties using the realistic and actual approach are also given and compared with the experimental and previous theoretical work.

  19. Evolution of kinetically controlled In-induced surface structure on Si(5 5 7) surface

    Science.gov (United States)

    Chauhan, Amit Kumar Singh; Eldose, Nirosh M.; Mishra, Monu; Niazi, Asad; Nair, Lekha; Gupta, Govind

    2014-09-01

    This paper introduces issue of kinetically controlled and temperature driven superstructural phase transition of Indium (In) on atomically clean high index Si(5 5 7)-7 × 1 surface. Auger electron spectroscopy analysis reveals that at room-temperature (RT) with a controlled incident flux of 0.002 ML/s; In overlayers evolve through the Frank-van der Merwe growth mode and yield a (1 × 1) diffraction pattern for coverage ≥1 ML. For substrate temperature 500 °C island growth is observed. On annealing the In/Si(5 5 7) interface in the temperature range 250-340 °C, clusters to two dimensional (2D) layer transformation on top of a stable monolayer is predominated. In-situ RT and HT adsorption and thermal desorption phenomena revealed the formation of coverage and temperature dependent thermally stable In induced superstructural phases such as (4 × 1) at 0.5 ML (520 °C), (√3 × √3-R30°) at 0.3 ML (560 °C) and (7 × 7) at 0.1 ML (580 °C). These indium induced superstructures could be utilized as potential substrate for the growth of various exotic 1D/2D structures.

  20. Tile Surface Thermocouple Measurement Challenges from the Orbiter Boundary Layer Transition Flight Experiment

    Science.gov (United States)

    Campbell, Charles H.; Berger, Karen; Anderson, Brian

    2012-01-01

    Hypersonic entry flight testing motivated by efforts seeking to characterize boundary layer transition on the Space Shuttle Orbiters have identified challenges in our ability to acquire high quality quantitative surface temperature measurements versus time. Five missions near the end of the Space Shuttle Program implemented a tile surface protuberance as a boundary layer trip together with tile surface thermocouples to capture temperature measurements during entry. Similar engineering implementations of these measurements on Discovery and Endeavor demonstrated unexpected measurement voltage response during the high heating portion of the entry trajectory. An assessment has been performed to characterize possible causes of the issues experienced during STS-119, STS-128, STS-131, STS-133 and STS-134 as well as similar issues encountered during other orbiter entries.

  1. Pressure controlled transition into a self-induced topological superconducting surface state

    KAUST Repository

    Zhu, Zhiyong

    2014-02-07

    Ab-initio calculations show a pressure induced trivial-nontrivial-trivial topological phase transition in the normal state of 1T-TiSe2. The pressure range in which the nontrivial phase emerges overlaps with that of the superconducting ground state. Thus, topological superconductivity can be induced in protected surface states by the proximity effect of superconducting bulk states. This kind of self-induced topological surface superconductivity is promising for a realization of Majorana fermions due to the absence of lattice and chemical potential mismatches. For appropriate electron doping, the formation of the topological superconducting surface state in 1T-TiSe 2 becomes accessible to experiments as it can be controlled by pressure.

  2. Glass-to-Rubber Transition of Polymer Thin Films and Their Surface Dynamical Properties

    Institute of Scientific and Technical Information of China (English)

    X.P.Wang; H.F.Zhang; Xudong Xiao; Ophelia K.C.Tsui

    2000-01-01

    @@ Glass-to-rubber transition temperature, Tg' of polystyrene(PS) (Mw=500K, Mw/Mn=1.03)thin films (thickness, d= 100 to 2000 A) deposited on Si with native oxide was determined by variable angle spectroscopic ellipsometry(VASE. We observed that the Tg of the polymer films decreased monotonically as the film thickness was decreased. It had previously been proposed that this was due to a highly mobile surface rubbery layer that existed even well below Tg' We used atomic force microscopic(AFM)adhesion measurement as a direct probe to investigate the surface dynamical properties of the PS samples and a thin film ofpoly(tert-butyl acrylate) (PtBA) (Mw= 148K, Mw/Mn=17, and Tg bullk=50℃). By comparing the AFM results and those obtained from shear modulus measurements of a bulk sample, we found no enhancement in the molecular relaxation at the free surface of these samples.

  3. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Wen; Zhou, Zhaofeng, E-mail: zfzhou@xtu.edu.cn; Zhong, Yuan; Zhang, Ting; Huang, Yongli [Key Laboratory of Low-Dimensional Materials and Application Technologies(Ministry of Education)Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Changqing [NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore)

    2015-11-15

    Incorporating the bond order-length-strength (BOLS) notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (T{sub N}) of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the T{sub N} by adjusting the atomic cohesive energy. The T{sub N} is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN) imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numerical match between predictions and measurements reveals that the T{sub N} of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.

  4. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    Directory of Open Access Journals (Sweden)

    Wen Zhang

    2015-11-01

    Full Text Available Incorporating the bond order-length-strength (BOLS notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (TN of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the TN by adjusting the atomic cohesive energy. The TN is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numerical match between predictions and measurements reveals that the TN of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.

  5. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    Science.gov (United States)

    Zhang, Wen; Zhou, Zhaofeng; Zhong, Yuan; Zhang, Ting; Huang, Yongli; Sun, Changqing

    2015-11-01

    Incorporating the bond order-length-strength (BOLS) notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (TN) of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the TN by adjusting the atomic cohesive energy. The TN is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN) imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numerical match between predictions and measurements reveals that the TN of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.

  6. Polarization effects and work function differences for transition metal surfaces: A perturbation LCAO MO approach

    Science.gov (United States)

    Shustorovich, Evgeny

    1981-05-01

    An analytical LCAO MO perturbation model has been developed for treating the polarization p-d contributions to the internal surface dipole moments of transition metal surfaces. The results are applied for treating changes in work functions (Ø) under chemisorption. The main conclusions are as follows. (1) Chemisorption of electropositive A (such as alkali metals) will always decrease Ø on all surfaces. (2) Chemisorption of electronegative A (such as H or halogens) can result in either increase or decrease in Ø depending on the nature of A and M. The smallest differences in A vs. M electronegativity are most likely to produce the paradoxical change ΔØ<0. The results obtained agree with experiment.

  7. Interplay of radiative and nonradiative transitions in surface hopping with radiation-molecule interactions

    Energy Technology Data Exchange (ETDEWEB)

    Bajo, Juan José [Departamento de Química-Física I, Universidad Complutense de Madrid, 28040 Madrid (Spain); Granucci, Giovanni, E-mail: giovanni.granucci@unipi.it; Persico, Maurizio [Università di Pisa, Dipartimento di Chimica e Chimica Industriale, via Risorgimento 35, 56126 Pisa (Italy)

    2014-01-28

    We implemented a method for the treatment of field induced transitions in trajectory surface hopping simulations, in the framework of the local diabatization scheme, especially suited for on-the-fly dynamics. The method is applied to a simple one-dimensional model with an avoided crossing and compared with quantum wavepacket dynamics. The results show the importance of introducing a proper decoherence correction to surface hopping, in order to obtain meaningful results. Also the energy conservation policy of standard surface hopping must be revised: in fact, the quantum wavepacket energetics is well reproduced if energy absorption/emission is allowed for in the hops determined by radiation-molecule coupling. To our knowledge, this is the first time the issues of decoherence and energy conservation have been analyzed in depth to devise a mixed quantum-classical method for dynamics with molecule-field interactions.

  8. Surfactant-modified diffusion on transition-metal surfaces (reprinted with the addition of the appendices)

    Energy Technology Data Exchange (ETDEWEB)

    FEIBELMAN,PETER J.; KELLOGG,GARY LEE

    2000-03-01

    Wanting to convert surface impurities from a nuisance to a systematically applicable nano-fabrication tool, the authors have sought to understand how such impurities affect self-diffusion on transition-metal surfaces. Their field-ion microscope experiments reveal that in the presence of surface hydrogen, self-diffusion on Rh(100) is promoted, while on Pt(100), not only is it inhibited, but its mechanism changes. First-principles calculations aimed at learning how oxygen fosters perfect layerwise growth on a growing Pt(111) crystal contradict the idea in the literature that it does so by directly promoting transport over Pt island boundaries. The discovery that its real effect is to burn off adventitious adsorbed carbon monoxide demonstrates the predictive value of state-of-the-art calculation methods.

  9. DFT-GGA errors in NO chemisorption energies on (111) transition metal surfaces: Possible origins and correction schemes

    CERN Document Server

    Huang, Xu

    2013-01-01

    Here we investigate whether well-known DFT-GGA errors in predicting the chemisorption energy ($E_{\\rm chem}$) of CO on transition metal surfaces manifest in analogous NO chemisorption systems. To verify the occurrence of DFT-GGA overestimation of the back-donation mechanism in NO Chemisorption, we use electronic structure analysis to show that the partially filled molecular NO 2$\\pi^{*}$ orbital rehybridizes with the transition metal $d$-band to form new bonding and anti-bonding states. We relate the back-donation charge transfer associated with chemisorption to the promotion of an electron from the 5$\\sigma$ orbital to the 2$\\pi^{*}$ orbital in the gas-phase NO G$^{2}\\Sigma^{-}\\leftarrow \\rm{X}^{2}\\Pi$ excitation. We establish linear relationships between $E_{\\rm chem}$ and $\\Delta E_{\\rm G\\leftarrow X}$ and go on to formulate an $E_{\\rm chem}$ correction scheme in the style of Mason {\\it et al.}, {[Physical Review B {\\bf 69}, 161401(R)]}. We apply the NO $E_{\\rm chem}$ correction method to the (111) surface...

  10. Imprinted and injection-molded nano-structured optical surfaces

    DEFF Research Database (Denmark)

    Christiansen, Alexander Bruun; Højlund-Nielsen, Emil; Clausen, Jeppe Sandvik

    2013-01-01

    Inspired by nature, nano-textured surfaces have attracted much attention as a method to realize optical surface functionality. The moth-eye antireflective structure and the structural colors of Morpho butterflies are wellknown examples used for inspiration for such biomimetic research...... of light from polymer surfaces and their implication for creating structural colors is discussed. In the case of injection-moulding compatible designs, the maximum reflection of nano-scale textured surfaces cannot exceed the Fresnel reflection of a corresponding flat polymer surface, which is approx. 4...... % for normal incidence. Diffraction gratings provide strong color reflection defined by the diffraction orders. However, the apperance varies strongly with viewing angles. Three different methods to address the strong angular-dependence of diffraction grating based structural color are discussed....

  11. High-resolution structural studies of ultra-thin magnetic, transition metal overlayers and two-dimensional transition metal oxides using synchrotron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Kellar, S.A. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry]|[Lawrence Berkeley National Lab., CA (United States). Advanced Light Source Div.

    1997-05-01

    This thesis report the surface-structure determination of three, ultra-thin magnetic transition-metal films, Fe/Au(100), Mn/Ni(100), and Mn/Cu(100) using Angle-Resolved Photoemission Extended Fine Structure (ARPEFS) and photoelectron holography. These structural studies are the first to use non-s initial states in the ARPEFS procedure. This thesis also reports an ARPEFS surface-structure determination of a two-dimensional transition-metal oxide, [(1 x 1)O/W(110)] x 12. The authors have analyzed the ARPFES signal from the Au 4f{sub 7/5} core level of the Au(1 ML)/Fe(15 ML)/Au(100) system. The analysis shows that the Fe grows layer by layer with one monolayer of gold, acting as a surfactant, remaining on top of the growing Fe layers. These surface gold atoms sit in the four-fold hollow site, 1.67 {+-} 0.02 A above the iron surface. The grown Fe layer is very much like the bulk, bcc iron, with an interlayer spacing of 1.43 {+-} 0.03 A. Analysis of the Mn 3p ARPEFS signals from c(2 x 2)Mn/Ni(100) and c(2 x 2)Mn/Cu(100) shows that the Mn forms highly corrugated surface alloys. The corrugation of the Mn/Ni(100) and Mn/Cu(100) systems are 0.24 {+-} 0.02 A and 0.30 {+-} 0.04 A respectively. In both cases the Mn is sticking above the plane of the surface substrate atoms. For the Mn/Ni(100) system the first layer Ni is contracted 4% from the bulk value. The Mn/Cu(100) system shows bulk spacing for the substrate Cu. Photoelectron holography shows that the Mn/Ni interface is very abrupt with very little Mn leaking into the second layer, while the Mn/Cu(100) case has a significant amount of Mn leaking into the second layer. A new, five-element electrostatic electron lens was developed for hemispherical electron-energy analyzers. This lens system can be operated at constant transverse or constants angular magnification, and has been optimized for use with the very small photon-spot sizes. Improvements to the hemispherical electron-energy analyzer are also discussed.

  12. Highly charged ions interacting with carbon surfaces : An influence of surface structure?

    NARCIS (Netherlands)

    Morgenstern, R; Winters, D; Schlatholter, T; Hoekstra, R

    Auger electron spectroscopy has been used to investigate the reaction of various carbon surfaces - including fullerene covered metal surfaces - on the impact of highly charged ions. An influence of the electronic surface structure on the interaction is clearly observed. However, the goal of

  13. Thermodynamic analysis on an anisotropically superhydrophobic surface with a hierarchical structure

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Jieliang [Division of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology, Tsinghua University, Room 3407, Building 9003, 100084 Beijing (China); Su, Zhengliang [Division of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology, Tsinghua University, Room 3407, Building 9003, 100084 Beijing (China); Department of Automotive Engineering, Tsinghua University, Beijing 100084 (China); Yan, Shaoze, E-mail: yansz@mail.tsinghua.edu.cn [Division of Intelligent and Biomechanical Systems, State Key Laboratory of Tribology, Tsinghua University, Room 3407, Building 9003, 100084 Beijing (China)

    2015-12-01

    Graphical abstract: - Highlights: • We model the superhydrophobic surface with anisotropic and hierarchical structure. • Anisotropic wetting only shows in noncomposite state (not in composite state). • Transition from noncomposite to composite state on dual-scale structure is hard. • Droplets tend to roll in the particular direction. • Droplets tend to stably remain in one preferred thermodynamic state. - Abstract: Superhydrophobic surfaces, which refer to the surfaces with contact angle higher than 150° and hysteresis less than 10°, have been reported in various studies. However, studies on the superhydrophobicity of anisotropic, hierarchical surfaces are limited and the corresponding thermodynamic mechanisms could not be explained thoroughly. Here we propose a simplified surface model of anisotropic patterned surface with dual scale roughness. Based on the thermodynamic method, we calculate the equilibrium contact angle (ECA) and the contact angle hysteresis (CAH) on the given surface. We show here that the hierarchical structure has much better anisotropic wetting properties than the single-scale one, and the results shed light on the potential application in controllable micro-/nano-fluidic systems. Our studies can be potentially applied for the fabrication of anisotropically superhydrophobic surfaces.

  14. The Dynamics and Structures of Adsorbed Surfaces

    DEFF Research Database (Denmark)

    Nielsen, M; Ellenson, W. D.; McTague, J. P.

    1978-01-01

    Reviews neutron scattering work performed on films of simple gas atoms and molecules adsorbed primarily on graphite surfaces. Exfoliated graphite substrates such as Grafoil were first used in this kind of measurements about five years ago and new results have been reported at an increasing pace...... of molecules such as NH3 or the internal modes of adsorbed molecules such as C4H10. Neutron scattering measurements where substrates other than graphite products are used as the adsorbents will not be reviewed here. However, the power of the technique will be demonstrated in an example of H2 physisorbed...

  15. Adjusting to change: linking family structure transitions with parenting and boys' adjustment.

    Science.gov (United States)

    Martinez, Charles R; Forgatch, Marion S

    2002-06-01

    This study examined links between family structure transitions and children's academic, behavioral, and emotional outcomes in a sample of 238 divorcing mothers and their sons in Grades 1-3. Multiple methods and agents were used in assessing family process variables and child outcomes. Findings suggest that greater accumulations of family transitions were associated with poorer academic functioning, greater acting-out behavior, and worse emotional adjustment for boys. However, in all three cases, these relationships were mediated by parenting practices: Parental academic skill encouragement mediated the relationship between transitions and academic functioning, and a factor of more general effective parenting practices mediated the relationships between transitions and acting out and emotional adjustment.

  16. Phase Transition of MoS2 Bilayer Structures

    DEFF Research Database (Denmark)

    Pandey, Mohnish; Bothra, Pallavi; Pati, Swapan K.

    2016-01-01

    In the present study, using density functional calculations we have investigated a possible mechanism for the structural phase transition of the semiconducting bilayer 2H-MoS2 via lithiation. The results indicate that the addition of lithium to the bilayer 2H-MoS2 transforms the bilayer to a hete...... microscopic mechanism of the phase transition in MoS2 and enriches the atomic scale understanding of the interaction of MoS2 with the alkali ions and other transition metal dichalcogenides manifesting a similar phase transition....

  17. Evolution of kinetically controlled In-induced surface structure on Si(5 5 7) surface

    Energy Technology Data Exchange (ETDEWEB)

    Chauhan, Amit Kumar Singh [Physics of Energy Harvesting, (CSIR-NPL), Dr. K.S. Krishnan Road, New Delhi 110012 (India); Department of Physics, JMI, New Delhi 110025 (India); Eldose, Nirosh M.; Mishra, Monu [Physics of Energy Harvesting, (CSIR-NPL), Dr. K.S. Krishnan Road, New Delhi 110012 (India); Niazi, Asad; Nair, Lekha [Department of Physics, JMI, New Delhi 110025 (India); Gupta, Govind, E-mail: govind@nplindia.org [Physics of Energy Harvesting, (CSIR-NPL), Dr. K.S. Krishnan Road, New Delhi 110012 (India)

    2014-09-30

    Highlights: • Evolution of In induced superstructures on Si(5 5 7) surface during RT and HT adsorption/desorption process. • Kinetics is governed by substrate temperature which exhibits various growth modes (FM, SK, VB) under different conditions. • Strain relaxation play significant role in the commencement of desorption/rearrangement of atoms. • A consolidated phase diagram of In/Si(5 5 7) interface has been reported with new √3 × √3-R30° and 4 × 1 phases. - Abstract: This paper introduces issue of kinetically controlled and temperature driven superstructural phase transition of Indium (In) on atomically clean high index Si(5 5 7)-7 × 1 surface. Auger electron spectroscopy analysis reveals that at room-temperature (RT) with a controlled incident flux of 0.002 ML/s; In overlayers evolve through the Frank-van der Merwe growth mode and yield a (1 × 1) diffraction pattern for coverage ≥1 ML. For substrate temperature <500°C, growth of In follows Stranski–Krastanov growth mode while for temperature >500°C island growth is observed. On annealing the In/Si(5 5 7) interface in the temperature range 250–340°C, clusters to two dimensional (2D) layer transformation on top of a stable monolayer is predominated. In-situ RT and HT adsorption and thermal desorption phenomena revealed the formation of coverage and temperature dependent thermally stable In induced superstructural phases such as (4 × 1) at 0.5 ML (520°C), (√3 × √3-R30°) at 0.3 ML (560°C) and (7 × 7) at 0.1 ML (580°C). These indium induced superstructures could be utilized as potential substrate for the growth of various exotic 1D/2D structures.

  18. Ultrathin metasurface with topological transition for manipulating spoof surface plasmon polaritons

    CERN Document Server

    Yang, Yihao; Jing, Liqiao; Shao, Zheping; Koschny, Thomas; Soukoulis, Costas M; Chen, Hongsheng

    2016-01-01

    Metasurfaces, with intrinsically planar nature and subwavelength thickness, provide us unconventional methodologies to not only mold the flow of propagating waves but also manipulate near-field waves. Plasmonic metasurfaces with topological transition for controlling surface plasmon polaritons (SPPs) recently have been experimentally demonstrated, which, however, are limited to optical frequencies. In this work, we proposed and experimentally characterized an ultrathin metasurface with the topological transition for manipulating spoof SPPs at low frequency. We demonstrated rich interesting phenomena based on this metasurface, including frequency-dependent spatial localization, non-diffraction propagation, negative refraction, and dispersion-dependent spin-momentum locking of spoof SPPs. Comparing with traditional three-dimensional metamaterials, our metasurface exhibits low propagation loss and compatibility with the photonic integrated circuit, which may find plenty of applications in spatial multiplexers, f...

  19. Dehydrogenative silane coupling on silicon surfaces via early transition metal catalysis.

    Science.gov (United States)

    Li, Yun-Hui; Buriak, Jillian M

    2006-02-01

    Derivatization of silicon surfaces is an area of intense interest due to the centrality of silicon in the microelectronics industry and because of potential promise for a myriad of other applications. In this paper, we investigate the feasibility of Si-Si bond formation directly on the surface to contrast with the more widely studied Si-C and Si-O bond forming reactions. Functionalization of hydride-terminated silicon surfaces with silanes is carried out via early transition metal mediated dehydrogenative silane coupling reactions. Zirconocene and titanocene catalyst systems were evaluated for heterocoupling of a molecular silane, RSiH3, with a surface Si-H group on Si(s). The zirconocene catalysts proved to be much more reactive than the titanium system, and so the former was examined exclusively. The silanes, aromatic or aliphatic, are bonded to the silicon surface through direct Si-Si bonds, although the level of incorporation of the trihydroarylsilanes was substantially higher than that of the aliphatic silanes. The reaction proceeds on nanocrystalline hydride-terminated porous silicon surfaces, as well as flat Si(100)-H(x) and Si(111)-H interfaces. The reactions were studied by a variety of techniques, including FTIR, SIMS, and XPS.

  20. Structure and surface properties of supported oxides

    Energy Technology Data Exchange (ETDEWEB)

    Leyrer, J.; Vielhaber, B.; Zaki, M.I.; Zhuang Shuxian; Weitkamp, J.; Knoezinger, H.

    1985-09-15

    Supported molybdate catalysts have been prepared on Al/sub 2/O/sub 3/,TiO/sub 2/, CeO/sub 2/, ZrO/sub 2/ and SiO/sub 2/ by impregnation from aqueous solution. The isoelectric point (IEPS) of the support surfaces determines the primary adsorption interaction of the molybdate species with the surface at a given pH. Raman spectroscopy shows monolayer formation on Al/sub 2/O/sub 3/, TiO/sub 2/ and CeO/sub 2/, while high proportions of MoO/sub 3/ are detected on SiO/sub 2/ and ZrO/sub 2/. Strong support effects influence the reducibility of the supported molybdate, which decreases in the sequence Mo/TiO/sub 2/ > Mo/ > CeO/sub 2/ > Mo/Al/sub 2/O/sub 3/ > Mo/ZrO/sub 2/. The dispersion of the monolayer on TiO/sub 2/, CeO/sub 2/ and Al/sub 2/O/sub 3/ seems to be fairly stable under reduction conditions, indicating strong chemical interaction with the supports.

  1. Beyond the surface atlas: A roadmap and gazetteer for surface symmetry and structure

    Science.gov (United States)

    Jenkins, Stephen J.; Pratt, Stephanie J.

    2007-10-01

    Throughout the development of single-crystal surface science, interest has predominantly focussed on the high-symmetry planes of crystalline materials, which typically present simple stable structures with small primitive unit cells. This concentration of effort has rapidly and substantially advanced our understanding of fundamental surface phenomena, and provides a sound basis for detailed study of more complex planes. The intense current interest in these is partly motivated by their regular arrays of steps, kinks or other low-coordination structural features, whose properties are little understood and may mimic specific highly-reactive sites on dispersed nanoparticles. Furthermore, the lower symmetry of these planes may give rise to other equally interesting properties such as intrinsic chirality, with exciting potential applications in enantioselective heterogeneous catalysis, biosensors and surface magnetism. To aid exploration of this new territory for surface science requires a depth of understanding that goes beyond the character of individual surfaces to encompass the global relationships between all possible surfaces of a given material, both in their structure and in their symmetry. In this report we present a rigorous conceptual framework for ideal crystalline surfaces within which the symmetry and structure of all possible surface orientations are described. We illustrate the versatility of our generally-applicable approach by comparing fcc, bcc and hcp materials. The entire scheme naturally derives from the very simple basis that the fundamental distinction between symmetry and structure is paramount. Where symmetry is concerned, our approach recognises that the surface is not a two-dimensional (2D) object but actually a truncated three-dimensional (3D) one. We therefore derive a symmetry scheme specifically formulated for surfaces and naturally encompassing their chirality where necessary. Our treatment of surface structure, on the other hand

  2. Structural Transition in SrZnO Laser Pulse Deposited Alloy

    Directory of Open Access Journals (Sweden)

    Albrithen H. A.

    2017-03-01

    Full Text Available We have discovered a structural transition for the SrZnO alloy films from a wurtzite to a rock-salt structure, leading to a reduction in the (112̲0/(0001 surface energy ratio. The films were grown by pulsed laser deposition using different SrO ratios, x. We have revealed that growth at a higher temperature, 750°C, resulted in a sharp 0002 peak at a low SrO content (5%, whereas growth at a higher SrO content (10% resulted in a non-crystalline film with minute crystallites with a (112̲0 orientation. Generally the crystallinity decreased as the SrO content increased. No results obtained for the crystalline films showed any orientation of significant peaks besides the peak attributed to the (0001 plane, suggesting epitaxial growth. Optical measurements showed difference in transmission widows of alloys with different SrO percentage, and this was correlated to SrO influence on growth mode as indicated by scanning electron imaging. The studied SrZnO films, with SrO/(SrO + ZnO ≤ 0.25, were grown by pulsed laser deposition using different SrO ratios, x. The effects of temperature and oxygen pressure during growth on the films’ structural properties were investigated. XRD results indicate that the film crystallinity was improved as the temperature and O2 pressure increased up to 650°C and 0.5 Torr, respectively.

  3. Ab initio determination of dark structures in radiationless transitions for aromatic carbonyl compounds.

    Science.gov (United States)

    Fang, Wei-Hai

    2008-03-01

    Mechanistic photodissociation of a polyatomic molecule has long been regarded as an intellectually challenging area of chemical physics, the results of which are relevant to atmospheric chemistry, biological systems, and many application fields. Carbonyl compounds play a unique role in the development of our understanding of the spectroscopy, photochemistry, and photophysics of polyatomic molecules and their photodissociation has been the subject of numerous studies over many decades. Upon irradiation, a molecule can undergo internal conversion (IC) and intersystem crossing (ISC) processes, besides photochemical and other photophysical processes. Transient intermediates formed in the IC and ISC radiationless processes, which are termed "dark", are not amenable to detection by conventional light absorption or emission. However, these dark intermediates play critical roles in IC and ISC processes and thus are essential to understanding mechanistic photochemistry of a polyatomic molecule. We have applied the multiconfiguration complete active space self-consistent field (CASSCF) method to determine the dark transient structures involved in radiationless processes for acetophenone and the related aromatic carbonyl compounds. The electronic and geometric structures predicted for the dark states are in a good agreement with those determined by ultrafast electron diffraction experiments. Intersection structure of different electronic states provides a very efficient "funnel" for the IC or ISC process. However, experimental determination of the intersection structure involved in radiationless transitions of a polyatomic molecule is impossible at present. We have discovered a minimum energy crossing point among the three potential energy surfaces (S1, T1, and T2) that appears to be common to a wide variety of aromatic carbonyl compounds with a constant structure. This new type of crossing point holds the key to understanding much about radiationless processes after

  4. Notes on Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities

    OpenAIRE

    Hyun-Kyung Chung; Per Jönsson; Alexander Kramida

    2013-01-01

    Atomic structure and transition probabilities are fundamental physical data required in many fields of science and technology. Atomic physics codes are freely available to other community users to generate atomic data for their interest, but the quality of these data is rarely verified. This special issue addresses estimation of uncertainties in atomic structure and transition probability calculations, and discusses methods and strategies to assess and ensure the quality of theoretical atomic...

  5. Phase transitions in nanosystems caused by interface motion: the Ising bipyramid with competing surface fields.

    Science.gov (United States)

    Milchev, A; Müller, M; Binder, K

    2005-09-01

    The phase behavior of a large but finite Ising ferromagnet in the presence of competing surface magnetic fields +/-H(s) is studied by Monte Carlo simulations and by phenomenological theory. Specifically, the geometry of a double pyramid of height 2L is considered, such that the surface field is positive on the four upper triangular surfaces of the bipyramid and negative on the lower ones. It is shown that the total spontaneous magnetization vanishes (for L --> infinity) at the temperature Tf(H), related to the "filling transition" of a semi-infinite pyramid, which can be well below the critical temperature of the bulk. The discontinuous vanishing of the magnetization is accompanied by a susceptibility that diverges with a Curie-Weiss power law, when the transition is approached from either side. A Landau theory with size-dependent critical amplitudes is proposed to explain these observations, and confirmed by finite size scaling analysis of the simulation results. The extension of these results to other nanosystems (gas-liquid systems, binary mixtures, etc.) is briefly discussed.

  6. Crossing the dividing surface of transition state theory. III. Once and only once. Selecting reactive trajectories

    Energy Technology Data Exchange (ETDEWEB)

    Lorquet, J. C., E-mail: jc.lorquet@ulg.ac.be [Department of Chemistry, University of Liège, Sart-Tilman (Bâtiment B6), B-4000 Liège 1 (Belgium)

    2015-09-14

    The purpose of the present work is to determine initial conditions that generate reacting, recrossing-free trajectories that cross the conventional dividing surface of transition state theory (i.e., the plane in configuration space passing through a saddle point of the potential energy surface and perpendicular to the reaction coordinate) without ever returning to it. Local analytical equations of motion valid in the neighborhood of this planar surface have been derived as an expansion in Poisson brackets. We show that the mere presence of a saddle point implies that reactivity criteria can be quite simply formulated in terms of elements of this series, irrespective of the shape of the potential energy function. Some of these elements are demonstrated to be equal to a sum of squares and thus to be necessarily positive, which has a profound impact on the dynamics. The method is then applied to a three-dimensional model describing an atom-diatom interaction. A particular relation between initial conditions is shown to generate a bundle of reactive trajectories that form reactive cylinders (or conduits) in phase space. This relation considerably reduces the phase space volume of initial conditions that generate recrossing-free trajectories. Loci in phase space of reactive initial conditions are presented. Reactivity is influenced by symmetry, as shown by a comparative study of collinear and bent transition states. Finally, it is argued that the rules that have been derived to generate reactive trajectories in classical mechanics are also useful to build up a reactive wave packet.

  7. Structures Formation on the Y-TZP-AI2O3 Ceramic Composites Surface

    Science.gov (United States)

    Kulkov, Sergei; Sevostyanova, Irina; Sablina, Tatiana; Buyakova, Svetlana; Pshenichnyy, Artem; Savchenko, Nickolai

    2016-07-01

    The paper discusses the structure of Y-TZP-Al2O3 ceramics produced from nanopowders and friction surface, wear resistance, friction coefficient of Y-TZP-AEO3 composites rubbed against a steel disk counterface at a pressure of 5 MPa in a range of sliding speeds from 0.2 to 47 m/s. Analysis by X-ray diffraction, scanning electron microscopy showed that the high wear resistance of Y-TZP-Al2O3 composites at high sliding speeds is due to high-temperature phase transitions and protective film formation on the friction surface.

  8. Nematic films at chemically structured surfaces

    Science.gov (United States)

    Silvestre, N. M.; Telo da Gama, M. M.; Tasinkevych, M.

    2017-02-01

    We investigate theoretically the morphology of a thin nematic film adsorbed at flat substrate patterned by stripes with alternating aligning properties, normal and tangential respectively. We construct a simple ‘exactly-solvable’ effective interfacial model where the liquid crystal distortions are accounted for via an effective interface potential. We find that chemically patterned substrates can strongly deform the nematic-air interface. The amplitude of this substrate-induced undulations increases with decreasing average film thickness and with increasing surface pattern pitch. We find a regime where the interfacial deformation may be described in terms of a material-independent universal scaling function. Surprisingly, the predictions of the effective interfacial model agree semi-quantitatively with the results of the numerical solution of a full model based on the Landau-de Gennes theory coupled to a square-gradient phase field free energy functional for a two phase system.

  9. Imprinted and injection-molded nano-structured optical surfaces

    Science.gov (United States)

    Christiansen, Alexander B.; Højlund-Nielsen, Emil; Clausen, Jeppe; Caringal, Gideon P.; Mortensen, N. Asger; Kristensen, Anders

    2013-09-01

    Inspired by nature, nano-textured surfaces have attracted much attention as a method to realize optical surface functionality. The moth-eye antireflective structure and the structural colors of Morpho butterflies are well- known examples used for inspiration for such biomimetic research. In this paper, nanostructured polymer surfaces suitable for up-scalable polymer replication methods, such as imprinting/embossing and injection-molding, are discussed. The limiting case of injection-moulding compatible designs is investigated. Anti-reflective polymer surfaces are realized by replication of Black Silicon (BSi) random nanostructure surfaces. The optical transmission at normal incidence is measured for wavelengths from 400 nm to 900 nm. For samples with optimized nanostructures, the reflectance is reduced by 50 % compared to samples with planar surfaces. The specular and diffusive reflection of light from polymer surfaces and their implication for creating structural colors is discussed. In the case of injection-moulding compatible designs, the maximum reflection of nano-scale textured surfaces cannot exceed the Fresnel reflection of a corresponding flat polymer surface, which is approx. 4 % for normal incidence. Diffraction gratings provide strong color reflection defined by the diffraction orders. However, the apperance varies strongly with viewing angles. Three different methods to address the strong angular-dependence of diffraction grating based structural color are discussed.

  10. First order magneto-structural transition in functional magnetic materials: phase-coexistence and metastability

    Indian Academy of Sciences (India)

    S B Roy; M K Chattopadhyay; M A Manekar; K J S Sokhey; P Chaddah

    2006-11-01

    First order magneto-structural transition plays an important role in the functionality of various magnetic materials of current interest like manganese oxide systems showing colossal magnetoresistance, Gd5(Ge, Si)4 alloys showing giant magnetocaloric effects and magnetic shape memory alloys. The key features of this magneto-structural transition are phase-coexistence and metastability. This generality is highlighted with experimental results obtained in a particular class of materials. A generalized framework of disorder influenced first order phase transition is introduced to understand the interesting experimental results which have some bearing on the functionality of the concerned materials.

  11. Structure sensitivity of CO dissociation on Rh surfaces

    DEFF Research Database (Denmark)

    Mavrikakis, Manos; Baumer, M.; Freund, H.J.;

    2002-01-01

    Using periodic self-consistent density functional calculations it is shown that the barrier for CO dissociation is similar to120 kJ/mol lower on the stepped Rh(211) surface than on the close-packed Rh(111) surface. The stepped surface binds molecular CO and the dissociation products more strongly...... than the flat surface, but the effect is considerably weaker than the effect of surface structure on the dissociation barrier. Our findings are compared with available experimental data, and the consequences for CO activation in methanation and Fischer-Tropsch reactions are discussed....

  12. Temperature-Dependent Surface States and Transitions of Si(111)-7x7.

    Science.gov (United States)

    1984-09-01

    TRANSTONS OF Si(Il1)-7x7 by J. E. Demuth, B. N. J. Persson and A. J. Scheil-Sorokin Prepared for Publication in Physical Review Letters IBM T. J. Watson...NUMBER 24 PHYSICAL REVIEW LETTERS 12 DEiEMiER 1983 Temperature-Dependent Surface States and Transitions of Si(11l)-7x7 J. E. Demuth, B. N. J. Persson...8217 ’ " " " .. . .; " ’ " ’ " " " " "h " - -’ ; - ’ . . ": - - VOLUME 51, NUMBER 24 PHYSICAL REVIEW LETTERS 12

  13. Surface term for the capillary condensation transitions in a slit geometry

    Science.gov (United States)

    Urrutia, Ignacio; Szybisz, Leszek

    2006-11-01

    It is shown that a bare simple fluid model (SFM) proposed some years ago for studying adsorption between two semi-infinite solid walls can be improved by modifying the surface term in the grand potential for the film phase. Such a correction substantially improves the agreement between the predictions for phase transitions provided by that SFM and results obtained from calculations carried out for He4 with the density-functional method at zero temperature. The corrective term depends on the strength of the adsorption potential and observables of bulk helium.

  14. Scaling properties of adsorption energies for hydrogen-containing molecules on transition-metal surfaces

    DEFF Research Database (Denmark)

    Abild-Pedersen, Frank; Greeley, Jeffrey Philip; Studt, Felix

    2007-01-01

    with the adsorption energy of the central, C, N, O, or S atom, the scaling constant depending only on x. A model is proposed to understand this behavior. The scaling model is developed into a general framework for estimating the reaction energies for hydrogenation and dehydrogenation reactions.......Density functional theory calculations are presented for CHx, x=0,1,2,3, NHx, x=0,1,2, OHx, x=0,1, and SHx, x=0,1 adsorption on a range of close-packed and stepped transition-metal surfaces. We find that the adsorption energy of any of the molecules considered scales approximately...

  15. Electronic structure of disordered alloys, surfaces and interfaces

    CERN Document Server

    Turek, Ilja; Kudrnovský, Josef; Šob, Mojmír; Weinberger, Peter

    1997-01-01

    At present, there is an increasing interest in the prediction of properties of classical and new materials such as substitutional alloys, their surfaces, and metallic or semiconductor multilayers. A detailed understanding based on a thus of the utmost importance for fu­ microscopic, parameter-free approach is ture developments in solid state physics and materials science. The interrela­ tion between electronic and structural properties at surfaces plays a key role for a microscopic understanding of phenomena as diverse as catalysis, corrosion, chemisorption and crystal growth. Remarkable progress has been made in the past 10-15 years in the understand­ ing of behavior of ideal crystals and their surfaces by relating their properties to the underlying electronic structure as determined from the first principles. Similar studies of complex systems like imperfect surfaces, interfaces, and mul­ tilayered structures seem to be accessible by now. Conventional band-structure methods, however, are of limited use ...

  16. Functional oxide structures on a surface of metals and alloys

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    @@ The investigations of the plasma electrolytic processes in our laboratory are aimed to the development of conditions of formation of oxide layers with determined composition, structure and functional properties on the surface of valve metals (Al, Ti) and their alloys.

  17. Protein Adsorption to Surface Chemistry and Crystal Structure Modification of Titanium Surfaces

    Directory of Open Access Journals (Sweden)

    Ryo Jimbo

    2010-07-01

    Full Text Available Objectives: To observe the early adsorption of extracellular matrix and blood plasma proteins to magnesium-incorporated titanium oxide surfaces, which has shown superior bone response in animal models.Material and Methods: Commercially pure titanium discs were blasted with titanium dioxide (TiO2 particles (control, and for the test group, TiO2 blasted discs were further processed with a micro-arc oxidation method (test. Surface morphology was investigated by scanning electron microscopy, surface topography by optic interferometry, characterization by X-ray photoelectron spectroscopy (XPS, and by X-ray diffraction (XRD analysis. The adsorption of 3 different proteins (fibronectin, albumin, and collagen type I was investigated by an immunoblotting technique.Results: The test surface showed a porous structure, whereas the control surface showed a typical TiO2 blasted structure. XPS data revealed magnesium-incorporation to the anodic oxide film of the surface. There was no difference in surface roughness between the control and test surfaces. For the protein adsorption test, the amount of albumin was significantly higher on the control surface whereas the amount of fibronectin was significantly higher on the test surface. Although there was no significant difference, the test surface had a tendency to adsorb more collagen type I.Conclusions: The magnesium-incorporated anodized surface showed significantly higher fibronectin adsorption and lower albumin adsorption than the blasted surface. These results may be one of the reasons for the excellent bone response previously observed in animal studies.

  18. The first order phase-transition of polycrystal solid surfaces with nanothickness

    Institute of Scientific and Technical Information of China (English)

    Y.A. Minaev

    2006-01-01

    The fundamental equations of thermodynamics of a film have been used for describing a fundamental property of solid crystalline materials i.e. the first-order phase transition on the grain boundaries by the formation of two-dimensional liquid. The generalized equation that is obtained is used for calculating the premelting temperature of any metal, which has a value in the range of 0.55-0.86 of the melting point. The experimental diffusion coefficient of nitrogen in steel at premelting temperature is the same as in the liquid phase. The described phenomenon of phase transition on the grain boundaries decreases in case of radical modification of the existing process engineering of handling metals. It also provides a precise physical explanation to the super plasticity of fine-structure metal alloys.

  19. Underwater 3D Surface Scanning using Structured Light

    OpenAIRE

    Törnblom, Nils

    2010-01-01

    In this thesis project, an underwater 3D scanner based on structured light has been constructed and developed. Two other scanners, based on stereoscopy and a line-swept laser, were also tested. The target application is to examine objects inside the water filled reactor vessel of nuclear power plants. Structured light systems (SLS) use a projector to illuminate the surface of the scanned object, and a camera to capture the surfaces' reflection. By projecting a series of specific line-patterns...

  20. Dimers on Surface Graphs and Spin Structures. I

    DEFF Research Database (Denmark)

    Cimasoni, David; Reshetikhin, Nicolai

    2007-01-01

    Partition functions for dimers on closed oriented surfaces are known to be alternating sums of Pfaffians of Kasteleyn matrices. In this paper, we obtain the formula for the coefficients in terms of discrete spin structures.......Partition functions for dimers on closed oriented surfaces are known to be alternating sums of Pfaffians of Kasteleyn matrices. In this paper, we obtain the formula for the coefficients in terms of discrete spin structures....

  1. Molecular dynamics simulation of phase and structural transitions in model lung surfactant mixtures

    Science.gov (United States)

    Duncan, Susan L.

    Lung surfactant (LS) is a complex mixture of lipids and proteins that reduces and regulates the surface tension in the lungs, thereby decreasing the work of breathing. A thorough understanding of LS function is critical to the development and optimization of synthetic surfactants for the treatment of neonatal and adult respiratory distress syndrome. We have utilized coarse-grained (CG) molecular dynamics simulation to study the dynamic, hysteretic changes occurring in the structure and phase of model surfactant mixtures with varying temperature, pressure and composition. In particular, we have studied the effects of the LS components palmitoyloleoylphosphatidylglycerol (POPG), palmitoyloleoylphosphatidylcholine (POPC), palmitic acid (PA), cholesterol, and two surface-active proteins SP-B 1--25 (the 25-residue N-terminal fragment of SP-B), and SP-C on model surfactant monolayers containing the primary lipid component dipalmitoylphosphatidylcholine (DPPC). The results indicate that POPG, POPC, SP-B1--25 and SP-C act as fluidizers and PA and cholesterol act as condensing agents, which change the phase-transition temperature, LC-LE phase distribution, and the extent of hysteresis. To explore the role of LS proteins SP-B and SP-C in storing and redelivering lipid from lipid monolayers during the compression and re-expansion occurring in lungs during breathing, we have simulated 2D-to-3D transitions at the interface. These simulations show that at near-zero surface tension the presence of a fluidizing agent, such as POPG, SP-C, or SP-B 1--25 decreases the monolayers resistance to bending allowing the monolayers to form large undulations and ultimately folds. Another folding mechanism is also observed in monolayers containing peptides, involving the lipid-mediated aggregation of the peptides into a defect, from which the fold can nucleate. The occurrence of folding depends on the hydrophobic character of the peptides; if the number of hydrophobic residues is decreased

  2. Synthesis, Structure and Reactivity of Molecules Attached to Electrode Surfaces.

    Science.gov (United States)

    2014-09-26

    Structure and Reactivity of Molecules Attached to Electrode Surfaces", AFOSR #81-0149 III. REPORTING PERIOD: April 15, 1981 through April 14, 1985 IV...Adsorption .... ............... 17 9. Effect of Surface Roughness on Adsorbate Orientation and Reactivity . 20 10. Ordered/ Disordered Packing in Chemisorbed... reactivity only when present in the edge-pendant orientation. Clearly, molecular orientation (i.e., mode of +. .4 o,, -12- attachment to the surface) is a

  3. Electron-Hole Counting Approach to Surface Atomic Structure

    Science.gov (United States)

    Chadi, D. J.

    The observed reconstructions of III-V semiconductor surfaces are shown to be consistent with constraints imposed by a simple "electron-hole" counting rule proposed by Pashley. The rule ensures that the predicted surfaces are nonmetallic, nonpolar, and at least, metastable since the compensation of the "donor" electrons leaves no occupied states in the upper part of the band gap which can easily induce other reconstructions. Applications of the method to the problem of surface structure and passivation are examined.

  4. Effective Quantification of the Paper Surface 3D Structure

    OpenAIRE

    Fidjestøl, Svein

    2005-01-01

    This thesis covers the topic of image processing in relation to the segmentation and analysis of pores protruding the surface in the three dimensional surface structure of paper. The successful analysis of pores is related to a greater goal of relating such an analysis to the perceived quality of the surface of a paper sample. The first part of the thesis gives an introduction to the context of image processing in relation to paper research. Also, an overview of the image processing framewor...

  5. Morphology control of laser-induced periodic surface structure on the surface of nickel by femtosecond laser

    Institute of Scientific and Technical Information of China (English)

    Fantong Meng; Jie Hu; Weina Han; Penjun Liu; Qingsong Wang

    2015-01-01

    An interesting transition between low spatial frequency laser-induced periodic surface structure (LIPSS) and high spatial frequency LIPSS (HSFL) on the surface of nickel is revealed by changing the scanning speed and the laser fluence.The experimental results show the proportion of HSFL area in the overall LIPSS (i.e.,K) presents a quasi-parabola function trend with the polarization orientation under a femtosecond (fs) laser single-pulse train.Moreover,an obvious fluctuation dependence of K on the pulse delay is observed under a fs laser dual-pulse train.The peak value of the fluctuation is found to be determined by the polarization orientation of the dual-pulse train.

  6. Surface structure of coherently strained ceria ultrathin films

    Science.gov (United States)

    Shi, Yezhou; Stone, Kevin H.; Guan, Zixuan; Monti, Matteo; Cao, Chuntian; El Gabaly, Farid; Chueh, William C.; Toney, Michael F.

    2016-11-01

    Cerium oxide, or ceria, is an important material for solid oxide fuel cells and water splitting devices. Although the ceria surface is active in catalytic and electrochemical reactions, how its catalytic properties are affected by the surface structure under operating conditions is far from understood. We investigate the structure of the coherently strained Ce O2 ultrathin films on yttria-stabilized zirconia (001) single crystals by specular synchrotron x-ray diffraction (XRD) under oxidizing conditions as a first step to study the surface structure in situ. An excellent agreement between the experiment data and the model is achieved by using a "stacks and islands" model that has a two-component roughness. One component is due to the tiny clusters of nanometer scale in lateral dimensions on each terrace, while the other component is due to slightly different Ce O2 thickness that span over hundreds of nanometers on neighboring terraces. We attribute the nonuniform thickness to step depairing during the thin film deposition that is supported by the surface morphology results on the microscopic level. Importantly, our model also shows that the polarity of the ceria surface is removed by a half monolayer surface coverage of oxygen. The successful resolution of the ceria surface structure using in situ specular synchrotron XRD paves the way to study the structural evolution of ceria as a fuel cell electrode under catalytically relevant temperatures and gas pressures.

  7. Geometry of the valence transition induced surface reconstruction of Sm(0001)

    CERN Document Server

    Lundgren, E; Nyholm, R; Torrelles, X; Rius, J; Delin, A; Grechnev, A; Eriksson, O; Konvicka, C; Schmid, M; Varga, P

    2002-01-01

    We present a structural determination of the surface reconstruction of the Sm(0001) surface using surface x-ray diffraction, scanning tunneling microscopy, and {\\it ab initio} calculations. The reconstruction is associated with a large (22%) expansion of the atomic radius for the top monolayer surface Sm atoms. The mechanism driving the surface reconstruction in Sm is unique among all elements and is connected to the strong correlations of the $4f$ electrons in Sm and the intermediate valence observed in certain Sm compounds. The atoms constituting the top monolayer of Sm(0001) have vastly different chemical properties compared to the layer underneath and behave as if they were an adsorbate of a different chemical species.

  8. Anatase (101)-like Structural Model Revealed for Metastable Rutile TiO2(011) Surface.

    Science.gov (United States)

    Xu, Meiling; Shao, Sen; Gao, Bo; Lv, Jian; Li, Quan; Wang, Yanchao; Wang, Hui; Zhang, Lijun; Ma, Yanming

    2017-03-08

    Titanium dioxide has been widely used as an efficient transition metal oxide photocatalyst. However, its photocatalytic activity is limited to the ultraviolet spectrum range due to the large bandgap beyond 3 eV. Efforts to reduce the bandgap to achieve a broader spectrum range of light absorption have been successfully attempted via the experimental synthesis of dopant-free metastable surface structures of rutile-type TiO2 (011) 2 × 1. This new surface phase possesses a reduced bandgap of ∼2.1 eV, showing great potential for an excellent photocatalyst covering a wide range of visible light. There is a need to establish the atomistic structure of this metastable surface to understand the physical cause for the bandgap reduction and to improve the future design of photocatalysts. Here, we report computational investigations in an effort to unravel this surface structure via swarm structure-searching simulations. The established structure adopts the anatase (101)-like structure model, where the topmost 2-fold O atoms form a quasi-hexagonal surface pattern and bond with the unsaturated 5-fold and 4-fold Ti atoms in the next layer. The predicted anatase (101)-like surface model can naturally explain the experimental observation of the STM images, the electronic bandgap, and the oxidation state of Ti(4+). Dangling bonds on the anatase (101)-like surface are abundant making it a superior photocatalyst. First-principles molecular dynamics simulations have supported the high photocatalytic activity by showing that water and formic acid molecules dissociate spontaneously on the anatase (101)-like surface.

  9. Laser Induced Periodic Surface Structures induced by surface plasmons coupled via roughness

    Science.gov (United States)

    Gurevich, E. L.; Gurevich, S. V.

    2014-05-01

    In this paper the formation mechanisms of the femtosecond laser-induced periodic surface structures (LIPSS) are discussed. One of the most frequently used theories explains the structures by interference between the incident laser beam and surface plasmon-polariton waves. The latter is most commonly attributed to the coupling of the incident laser light to the surface roughness. We demonstrate that this excitation of surface plasmons contradicts the results of laser-ablation experiments. As an alternative approach to the excitation of LIPSS we analyse development of hydrodynamic instabilities in the melt layer.

  10. Laser Induced Periodic Surface Structures induced by surface plasmons coupled via roughness

    Energy Technology Data Exchange (ETDEWEB)

    Gurevich, E.L., E-mail: gurevich@lat.rub.de [Chair of Applied Laser Technology, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum (Germany); Gurevich, S.V., E-mail: gurevics@uni-muenster.de [Institute for Theoretical Physics, University of Münster, Wilhelm-Klemm-Straße 9, 48149 Münster (Germany)

    2014-05-01

    In this paper the formation mechanisms of the femtosecond laser-induced periodic surface structures (LIPSS) are discussed. One of the most frequently used theories explains the structures by interference between the incident laser beam and surface plasmon-polariton waves. The latter is most commonly attributed to the coupling of the incident laser light to the surface roughness. We demonstrate that this excitation of surface plasmons contradicts the results of laser-ablation experiments. As an alternative approach to the excitation of LIPSS we analyse development of hydrodynamic instabilities in the melt layer.

  11. Osteoblast Behavior on Hierarchical Micro-/Nano-Structured Titanium Surface

    Institute of Scientific and Technical Information of China (English)

    Weiyan Meng; Yanmin Zhou; Yanjing Zhang; Qing Cai; Liming Yang; Jinghui Zhao; Chnnyan Li

    2011-01-01

    In the present work, osteoblast behavior on a hierarchical micro-/nano-structured titanium surface was investigated. A hierarchical hybrid micro-/nano-structured titanium surface topography was produced via Electrolytic Etching (EE). MG-63 cells were cultured on disks for 2 h to 7 days. The osteoblast response to the hierarchical hybrid micro-/nano-structured titanium surface was evaluated through the osteoblast cell morphology, attachment and proliferation. For comparison, MG-63 cells were also cultured on Sandblasted and Acid-etched (SLA) as well as Machined (M) surfaces respectively. The results show significant differences in the adhesion rates and proliferation levels of MG-63 cells on EE, SLA, and M surfaces. Both adhesion rate and proliferation level on EE surface are higher than those on SLA and M surfaces. Therefore, we may expect that, comparing with SLA and M surfaces, bone growth on EE surface could be accelerated and bone formation could be promoted at an early stage, which could be applied in the clinical practices for immediate and early-stage loadings.

  12. Structures of multidomain proteins adsorbed on hydrophobic interaction chromatography surfaces.

    Science.gov (United States)

    Gospodarek, Adrian M; Sun, Weitong; O'Connell, John P; Fernandez, Erik J

    2014-12-05

    In hydrophobic interaction chromatography (HIC), interactions between buried hydrophobic residues and HIC surfaces can cause conformational changes that interfere with separations and cause yield losses. This paper extends our previous investigations of protein unfolding in HIC chromatography by identifying protein structures on HIC surfaces under denaturing conditions and relating them to solution behavior. The thermal unfolding of three model multidomain proteins on three HIC surfaces of differing hydrophobicities was investigated with hydrogen exchange mass spectrometry (HXMS). The data were analyzed to obtain unfolding rates and Gibbs free energies for unfolding of adsorbed proteins. The melting temperatures of the proteins were lowered, but by different amounts, on the different surfaces. In addition, the structures of the proteins on the chromatographic surfaces were similar to the partially unfolded structures produced in the absence of a surface by temperature as well as by chemical denaturants. Finally, it was found that patterns of residue exposure to solvent on different surfaces at different temperatures can be largely superimposed. These findings suggest that protein unfolding on various HIC surfaces might be quantitatively related to protein unfolding in solution and that details of surface unfolding behavior might be generalized.

  13. Phase Transitions in Sampling Algorithms and the Underlying Random Structures

    Science.gov (United States)

    Randall, Dana

    Sampling algorithms based on Markov chains arise in many areas of computing, engineering and science. The idea is to perform a random walk among the elements of a large state space so that samples chosen from the stationary distribution are useful for the application. In order to get reliable results, we require the chain to be rapidly mixing, or quickly converging to equilibrium. For example, to sample independent sets in a given graph G, the so-called hard-core lattice gas model, we can start at any independent set and repeatedly add or remove a single vertex (if allowed). By defining the transition probabilities of these moves appropriately, we can ensure that the chain will converge to a use- ful distribution over the state space Ω. For instance, the Gibbs (or Boltzmann) distribution, parameterized by Λ> 0, is defined so that p(Λ) = π(I) = Λ|I| /Z, where Z = sum_{J in Ω} Λ^{|J|} is the normalizing constant known as the partition function. An interesting phenomenon occurs as Λ is varied. For small values of Λ, local Markov chains converge quickly to stationarity, while for large values, they are prohibitively slow. To see why, imagine the underlying graph G is a region of the Cartesian lattice. Large independent sets will dominate the stationary distribution π when Λ is sufficiently large, and yet it will take a very long time to move from an independent set lying mostly on the odd sublattice to one that is mostly even. This phenomenon is well known in the statistical physics community, and characterizes by a phase transition in the underlying model.

  14. Influence of Surface Transition Layers on Phase Transformation and Pyroelectric Properties of Ferroelectric Thin Film

    Institute of Scientific and Technical Information of China (English)

    SUN Pu-Nan; L(U) Tian-Quan; CHEN Hui; CAO Wen-Wu

    2008-01-01

    Taking into account surface transition layers (STLs), we study the phase transformation and pyroelectric properties of ferroelectric thin films by employing the transverse Ising model (TIM) in the framework of the mean field approximation. The distribution functions representing the intra-layer and inter-layer couplings between the two nearest neighbour pseudo-spins are introduced to characterize STLs. Compared with the results obtained by the traditional treatments for the thin films using only the single surface transition layer (SSL), it is shown that the STL model reflects a more realistic and comprehensive situation of films. The effects of various parameters on the phase transformation properties have shown that STL can make the Curie temperature of the film higher or lower than that of the corresponding bulk material, and the thickness of STL is a key factor influencing the film properties. For a film with definite thickness, there exists a critical STL thickness at which ferroelectricity will disappear when the intra-layer and inter-layer interactions are weak.

  15. A sharp interface method for compressible liquid–vapor flow with phase transition and surface tension

    Energy Technology Data Exchange (ETDEWEB)

    Fechter, Stefan, E-mail: stefan.fechter@iag.uni-stuttgart.de [Institut für Aerodynamik und Gasdynamik, Universität Stuttgart, Pfaffenwaldring 21, 70569 Stuttgart (Germany); Munz, Claus-Dieter, E-mail: munz@iag.uni-stuttgart.de [Institut für Aerodynamik und Gasdynamik, Universität Stuttgart, Pfaffenwaldring 21, 70569 Stuttgart (Germany); Rohde, Christian, E-mail: Christian.Rohde@mathematik.uni-stuttgart.de [Institut für Angewandte Analysis und Numerische Simulation, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart (Germany); Zeiler, Christoph, E-mail: Christoph.Zeiler@mathematik.uni-stuttgart.de [Institut für Angewandte Analysis und Numerische Simulation, Universität Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart (Germany)

    2017-05-01

    The numerical approximation of non-isothermal liquid–vapor flow within the compressible regime is a difficult task because complex physical effects at the phase interfaces can govern the global flow behavior. We present a sharp interface approach which treats the interface as a shock-wave like discontinuity. Any mixing of fluid phases is avoided by using the flow solver in the bulk regions only, and a ghost-fluid approach close to the interface. The coupling states for the numerical solution in the bulk regions are determined by the solution of local two-phase Riemann problems across the interface. The Riemann solution accounts for the relevant physics by enforcing appropriate jump conditions at the phase boundary. A wide variety of interface effects can be handled in a thermodynamically consistent way. This includes surface tension or mass/energy transfer by phase transition. Moreover, the local normal speed of the interface, which is needed to calculate the time evolution of the interface, is given by the Riemann solution. The interface tracking itself is based on a level-set method. The focus in this paper is the description of the two-phase Riemann solver and its usage within the sharp interface approach. One-dimensional problems are selected to validate the approach. Finally, the three-dimensional simulation of a wobbling droplet and a shock droplet interaction in two dimensions are shown. In both problems phase transition and surface tension determine the global bulk behavior.

  16. A sharp interface method for compressible liquid-vapor flow with phase transition and surface tension

    Science.gov (United States)

    Fechter, Stefan; Munz, Claus-Dieter; Rohde, Christian; Zeiler, Christoph

    2017-05-01

    The numerical approximation of non-isothermal liquid-vapor flow within the compressible regime is a difficult task because complex physical effects at the phase interfaces can govern the global flow behavior. We present a sharp interface approach which treats the interface as a shock-wave like discontinuity. Any mixing of fluid phases is avoided by using the flow solver in the bulk regions only, and a ghost-fluid approach close to the interface. The coupling states for the numerical solution in the bulk regions are determined by the solution of local two-phase Riemann problems across the interface. The Riemann solution accounts for the relevant physics by enforcing appropriate jump conditions at the phase boundary. A wide variety of interface effects can be handled in a thermodynamically consistent way. This includes surface tension or mass/energy transfer by phase transition. Moreover, the local normal speed of the interface, which is needed to calculate the time evolution of the interface, is given by the Riemann solution. The interface tracking itself is based on a level-set method. The focus in this paper is the description of the two-phase Riemann solver and its usage within the sharp interface approach. One-dimensional problems are selected to validate the approach. Finally, the three-dimensional simulation of a wobbling droplet and a shock droplet interaction in two dimensions are shown. In both problems phase transition and surface tension determine the global bulk behavior.

  17. Transition process leading to microbubble emission boiling on horizontal circular heated surface in subcooled pool

    Science.gov (United States)

    Ueno, Ichiro; Ando, Jun; Horiuchi, Kazuna; Saiki, Takahito; Kaneko, Toshihiro

    2016-11-01

    Microbubble emission boiling (MEB) produces a higher heat flux than critical heat flux (CHF) and therefore has been investigated in terms of its heat transfer characteristics as well as the conditions under which MEB occurs. Its physical mechanism, however, is not yet clearly understood. We carried out a series of experiments to examine boiling on horizontal circular heated surfaces of 5 mm and of 10 mm in diameter, in a subcooled pool, paying close attention to the transition process to MEB. High-speed observation results show that, in the MEB regime, the growth, condensation, and collapse of the vapor bubbles occur within a very short time. In addition, a number of fine bubbles are emitted from the collapse of the vapor bubbles. By tracking these tiny bubbles, we clearly visualize that the collapse of the vapor bubbles drives the liquid near the bubbles towards the heated surface, such that the convection field around the vapor bubbles under MEB significantly differs from that under nucleate boiling. Moreover, the axial temperature gradient in a heated block (quasi-heat flux) indicates a clear difference between nucleate boiling and MEB. A combination of quasi-heat flux and the measurement of the behavior of the vapor bubbles allows us to discuss the transition to MEB. This work was financially supported by the 45th Research Grant in Natural Sciences from The Mitsubishi Foundation (2014 - 2015), and by Research Grant for Boiler and Pressurized Vessels from The Japan Boiler Association (2016).

  18. Surface modification induced phase transformation and structure variation on the rapidly solidified recast layer of titanium

    Energy Technology Data Exchange (ETDEWEB)

    Tsai, Ming-Hung [Department of Mechanical Engineering and Graduate Institute of Mechanical and Precision Engineering, National Kaoshiung University of Applied Sciences, Kaoshiung 807, Taiwan (China); School of Dentistry, College of Oral Medicine, Taipei Medical University, Taipei 110, Taiwan (China); Haung, Chiung-Fang [School of Dental Technology, College of Oral Medicine, Taipei Medical University, Taipei 110, Taiwan (China); Division of Family and Operative Dentistry, Department of Dentistry, Taipei Medical University Hospital, Taipei 110, Taiwan (China); Research Center for Biomedical Devices and Prototyping Production, Taipei Medical University, Taipei 110, Taiwan (China); Shyu, Shih-Shiun [Department of Dentistry, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, New Taipei City 231, Taiwan (China); Chou, Yen-Ru [Research Center for Biomedical Devices and Prototyping Production, Taipei Medical University, Taipei 110, Taiwan (China); Graduate Institute of Biomedical Materials and Tissue Engineering, College of Oral Medicine, Taipei Medical University, Taipei 110, Taiwan (China); Research Center for Biomedical Implants and Microsurgery Devices, Taipei Medical University, Taipei 110, Taiwan (China); Lin, Ming-Hong [Department of Mechanical Engineering and Graduate Institute of Mechanical and Precision Engineering, National Kaoshiung University of Applied Sciences, Kaoshiung 807, Taiwan (China); Peng, Pei-Wen, E-mail: apon@tmu.edu.tw [School of Dental Technology, College of Oral Medicine, Taipei Medical University, Taipei 110, Taiwan (China); and others

    2015-08-15

    In this study, neodymium-doped yttrium orthovanadate (Nd:YVO{sub 4}) as a laser source with different scanning speeds was used on biomedical Ti surface. The microstructural and biological properties of laser-modified samples were investigated by means of optical microscope, electron microscope, X-ray diffraction, surface roughness instrument, contact angle and cell cytotoxicity assay. After laser modification, the rough volcano-like recast layer with micro-/nanoporous structure and wave-like recast layer with nanoporous structure were generated on the surfaces of laser-modified samples, respectively. It was also found out that, an α → (α + rutile-TiO{sub 2}) phase transition occurred on the recast layers of laser-modified samples. The Ti surface becomes hydrophilic at a high speed laser scanning. Moreover, the cell cytotoxicity assay demonstrated that laser-modified samples did not influence the cell adhesion and proliferation behaviors of osteoblast (MG-63) cell. The laser with 50 mm/s scanning speed induced formation of rough volcano-like recast layer accompanied with micro-/nanoporous structure, which can promote cell adhesion and proliferation of MG-63 cell on Ti surface. The results indicated that the laser treatment was a potential technology to enhance the biocompatibility for titanium. - Highlights: • Laser induced the formation of recast layer with micro-/nanoporous structure on Ti. • An α → (α + rutile-TiO{sub 2}) phase transition was observed within the recast layer. • The Ti surface becomes hydrophilic at a high speed laser scanning. • Laser-modified samples exhibit good biocompatibility to osteoblast (MG-63) cell.

  19. Color effects from scattering on random surface structures in dielectrics

    DEFF Research Database (Denmark)

    Clausen, Jeppe; Christiansen, Alexander B; Garnæs, Jørgen;

    2012-01-01

    We show that cheap large area color filters, based on surface scattering, can be fabricated in dielectric materials by replication of random structures in silicon. The specular transmittance of three different types of structures, corresponding to three different colors, have been characterized....... The angle resolved scattering has been measured and compared to predictions based on the measured surface topography and by the use of non-paraxial scalar diffraction theory. From this it is shown that the color of the transmitted light can be predicted from the topography of the randomly textured surfaces....

  20. Bionic Duplication of Fresh Navodon septentrionalis Fish Surface Structures

    Directory of Open Access Journals (Sweden)

    Bing Qu

    2011-01-01

    Full Text Available Biomimetic superhydrophobic surface was fabricated by replicating topography of the fresh fish skin surface of Navodon septentrionalis with polydimethylsiloxane (PDMS elastomer. A two-step replicating method was developed to make the surface structure of the fresh fish skin be replicated with high fidelity. After duplication, it was found that the static contact angle of the replica was as large as 173°. Theoretic analysis based on Young's and Cassie-Baxter (C-B model was performed to explain the relationship between structure and hydrophobicity.

  1. Transitions between imperfectly ordered crystalline structures: A phase switch Monte Carlo study

    OpenAIRE

    Wilms, Dorothea; Wilding, Nigel B.; Binder, Kurt

    2012-01-01

    A model for two-dimensional colloids confined laterally by "structured boundaries" (i.e., ones that impose a periodicity along the slit) is studied by Monte Carlo simulations. When the distance D between the confining walls is reduced at constant particle number from an initial value D_0, for which a crystalline structure commensurate with the imposed periodicity fits, to smaller values, a succession of phase transitions to imperfectly ordered structures occur. These structures have a reduced...

  2. Fuel Pellets from Wheat Straw: The Effect of Lignin Glass Transition and Surface Waxes on Pelletizing Properties

    DEFF Research Database (Denmark)

    Stelte, Wolfgang; Clemons, Craig; Holm, Jens K.;

    2012-01-01

    and a high concentration of hydrophobic waxes on its outer surface that may limit the pellet strength. The present work studies the impact of the lignin glass transition on the pelletizing properties of wheat straw. Furthermore, the effect of surface waxes on the pelletizing process and pellet strength...... are investigated by comparing wheat straw before and after organic solvent extraction. The lignin glass transition temperature for wheat straw and extracted wheat straw is determined by dynamic mechanical thermal analysis. At a moisture content of 8%, transitions are identified at 53°C and 63°C, respectively....... Pellets are pressed from wheat straw and straw where the waxes have been extracted from. Two pelletizing temperatures were chosen—one below and one above the glass transition temperature of lignin. The pellets compression strength, density, and fracture surface were compared to each other. Pellets pressed...

  3. Structural semiconductor-to-semimetal phase transition in two-dimensional materials induced by electrostatic gating.

    Science.gov (United States)

    Li, Yao; Duerloo, Karel-Alexander N; Wauson, Kerry; Reed, Evan J

    2016-01-01

    Dynamic control of conductivity and optical properties via atomic structure changes is of technological importance in information storage. Energy consumption considerations provide a driving force towards employing thin materials in devices. Monolayer transition metal dichalcogenides are nearly atomically thin materials that can exist in multiple crystal structures, each with distinct electrical properties. By developing new density functional-based methods, we discover that electrostatic gating device configurations have the potential to drive structural semiconductor-to-semimetal phase transitions in some monolayer transition metal dichalcogenides. Here we show that the semiconductor-to-semimetal phase transition in monolayer MoTe2 can be driven by a gate voltage of several volts with appropriate choice of dielectric. We find that the transition gate voltage can be reduced arbitrarily by alloying, for example, for Mo(x)W(1-x)Te2 monolayers. Our findings identify a new physical mechanism, not existing in bulk materials, to dynamically control structural phase transitions in two-dimensional materials, enabling potential applications in phase-change electronic devices.

  4. Riblet Sensor -- Light Scattering on Micro Structured Surface Coatings

    CERN Document Server

    Imlau, Mirco; Voit, Kay-Michael; Tschentscher, Juliane; Dieckmann, Volker

    2016-01-01

    With the application of appropriate surface structuring on aircrafts, up to 8\\% fuel may be saved in regular air traffic. Before these techniques can be introduced into productive environments, a controlling method for the quality of surface structuring is needed to be used during fabrication and service, ensuring persistent quality of the structured coatings and a justified decision for surface renewal. In this project, these important requirements for achieving the improvements defined above are fulfilled. We have shown that fast sampling is possible using noncontacting laser probing, and we have presented a working preliminary configuration for the sensor. In the theoretical part, a model for the interaction between a probing laser beam and the surface is developed and the resulting wavefront is derived. This is done using a combination of Huygens-Fresnel diffraction theory and geometrical optics. The model is then used to counsel the design of the experimental setup, to interpret the emerging data and to ...

  5. Coherent Structures in Transition of a Flat-Plate Boundary Layer at Ma=0.7

    Institute of Scientific and Technical Information of China (English)

    ZHOU Ying; LI Xin-Liang; FU De-Xun; MA Yan-Wen

    2007-01-01

    @@ Direct numerical simulation (DNS) of a spatially evolving flat-plate boundary layer transition process at free stream Mach number 0.7 is performed. Tollmien-Schlichting (T-S) waves are added on the inlet boundary as the disturbances before transition. Typical coherent structures in the transition process are investigated based on the second invariant of velocity gradient tensor. The instantaneous shear stress and the mean velocity profile in the transition region are studied. In our view, the fact that the peak value of shear stress in the stress concentration area increases and exceeds a threshold value during the later stage of the transition process plays an important role in the laminar breakdown process.

  6. Phase transitions, interfacial fluctuations and hidden symmetries for fluids near structured walls

    Indian Academy of Sciences (India)

    A O Parry; J M Romero-Enrique

    2005-05-01

    Fluids adsorbed at micro-patterned and geometrically structured substrates can exhibit novel phase transitions and interfacial fluctuation effects distinct from those characteristic of wetting at planar, homogeneous walls. We review recent theoretical progress in this area paying particular attention to filling transitions pertinent to fluid adsorption near wedges, which have highlighted a deep connection between geometrical and contact angles. We show that filling transitions are not only characterized by large scale interfacial fluctuations leading to universal critical singularities but also reveal hidden symmetries with short-ranged critical wetting transitions and properties of dimensional reduction. We propose a non-local interfacial model which fulfills all these properties and throws light on long-standing problems regarding the order of the 3D short-range critical wetting transition.

  7. Structure of adsorbed monolayers. The surface chemical bond

    Energy Technology Data Exchange (ETDEWEB)

    Somorjai, G.A.; Bent, B.E.

    1984-06-01

    This paper attempts to provide a summary of what has been learned about the structure of adsorbed monolayers and about the surface chemical bond from molecular surface science. While the surface chemical bond is less well understood than bonding of molecules in the gas phase or in the solid state, our knowledge of its properties is rapidly accumulating. The information obtained also has great impact on many surface science based technologies, including heterogeneous catalysis and electronic devices. It is hoped that much of the information obtained from studies at solid-gas interfaces can be correlated with molecular behavior at solid-liquid interfaces. 31 references, 42 figures, 1 table.

  8. A genetic algorithm approach in interface and surface structure optimization

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Jian [Iowa State Univ., Ames, IA (United States)

    2010-01-01

    The thesis is divided into two parts. In the first part a global optimization method is developed for the interface and surface structures optimization. Two prototype systems are chosen to be studied. One is Si[001] symmetric tilted grain boundaries and the other is Ag/Au induced Si(111) surface. It is found that Genetic Algorithm is very efficient in finding lowest energy structures in both cases. Not only existing structures in the experiments can be reproduced, but also many new structures can be predicted using Genetic Algorithm. Thus it is shown that Genetic Algorithm is a extremely powerful tool for the material structures predictions. The second part of the thesis is devoted to the explanation of an experimental observation of thermal radiation from three-dimensional tungsten photonic crystal structures. The experimental results seems astounding and confusing, yet the theoretical models in the paper revealed the physics insight behind the phenomena and can well reproduced the experimental results.

  9. Seasonal transition of precipitation characteristics associated with land surface conditions in and around Bangladesh

    Science.gov (United States)

    Ono, M.; Takahashi, H. G.

    2016-10-01

    This study examined the seasonal transition of precipitation characteristics and its association with land surface conditions in and around Bangladesh, where land surface conditions are predominantly wet. Hourly rain rate data from the Global Satellite Mapping of Precipitation Microwave-Infrared Combined Product and 10 day soil moisture data from the Advanced Microwave Scanning Radiometer Earth Observing System were used over the 7 years from 2003 to 2009. Area mean values of soil moisture, and precipitation amount, frequency, and intensity were calculated for each 10 day period. Results showed that higher precipitation amount and frequency were observed over the wet soil conditions, which indicates that soil moisture was influenced by previous precipitation events. However, the soil moisture could also control the precipitation characteristics. The seasonal and interannual variations in all regions suggested that precipitation amount and frequency increased in moist soil conditions, which is associated with an increase of water vapor supplied from the moist land surface. Over a flat plain (87°E-91°E, 23°N-25°N), a higher afternoon precipitation intensity was observed over drier land surfaces. This relationship was observed on seasonal and interannual variations. This suggests that the land surface conditions in this region can affect the afternoon precipitation intensity to some extent, although changes of atmospheric conditions can be a major factor particularly for the seasonal changes. However, this relationship was not observed in mountainous regions. This can be explained by other factors, such as thermally induced local circulations by the surrounding topography, being stronger than the impact of land surface conditions.

  10. Formation of Surface Corrosion-Resistant Nanocrystalline Structures on Steel.

    Science.gov (United States)

    Nykyforchyn, Hryhoriy; Kyryliv, Volodymyr; Maksymiv, Olha; Slobodyan, Zvenomyra; Tsyrulnyk, Oleksandr

    2016-12-01

    Engineering materials with nanocrystalline structure could be exploited under simultaneous action of mechanical loading and corrosion environments; therefore, their corrosion resistance is important. Surface nanocrystalline structure was generated on middle carbon steels by severe plastic deformation using the method of mechanical pulse friction treatment. This treatment additionally includes high temperature phase transformation and alloying. Using a complex of the corrosive, electrochemical and physical investigations, it was established that nanocrystalline structures can be characterized by lower or increased corrosion resistance in comparison with the reference material. It is caused by the action of two confronting factors: arising energy level and anticorrosive alloying of the surface layer.

  11. Surface Appendages of Archaea: Structure, Function, Genetics and Assembly

    Directory of Open Access Journals (Sweden)

    Sarah Siu

    2013-01-01

    Full Text Available Organisms representing diverse subgroupings of the Domain Archaea are known to possess unusual surface structures. These can include ones unique to Archaea such as cannulae and hami as well as archaella (archaeal flagella and various types of pili that superficially resemble their namesakes in Bacteria, although with significant differences. Major advances have occurred particularly in the study of archaella and pili using model organisms with recently developed advanced genetic tools. There is common use of a type IV pili-model of assembly for several archaeal surface structures including archaella, certain pili and sugar binding structures termed bindosomes. In addition, there are widespread posttranslational modifications of archaellins and pilins with N-linked glycans, with some containing novel sugars. Archaeal surface structures are involved in such diverse functions as swimming, attachment to surfaces, cell to cell contact resulting in genetic transfer, biofilm formation, and possible intercellular communication. Sometimes functions are co-dependent on other surface structures. These structures and the regulation of their assembly are important features that allow various Archaea, including thermoacidophilic, hyperthermophilic, halophilic, and anaerobic ones, to survive and thrive in the extreme environments that are commonly inhabited by members of this domain.

  12. The twistorial structure of loop-gravity transition amplitudes

    CERN Document Server

    Speziale, Simone

    2012-01-01

    The spin foam formalism provides transition amplitudes for loop quantum gravity. Important aspects of the dynamics are understood, but many open questions are pressing on. In this paper we address some of them using a twistorial description, which brings new light on both classical and quantum aspects of the theory. At the classical level, we clarify the covariant properties of the discrete geometries involved, and the role of the simplicity constraints in leading to SU(2) Ashtekar-Barbero variables. We identify areas and Lorentzian dihedral angles in twistor space, and show that they form a canonical pair. The primary simplicity constraints are solved by simple twistors, parametrized by SU(2) spinors and the dihedral angles. We construct an SU(2) holonomy and prove it to correspond to the Ashtekar-Barbero connection. We argue that the role of secondary constraints is to provide a non trivial embedding of the cotangent bundle of SU(2) in the space of simple twistors. At the quantum level, a Schroedinger repre...

  13. Phase transition, phase transition mechanism and crystal structure of a new compound-Ca2FeWO6

    Institute of Scientific and Technical Information of China (English)

    傅正民; 李文秀

    1995-01-01

    A new compound Ca2FeWO6 has been synthesized by solid state sintering. The phase transition of this compound was investigated by means of differential thermal analysis (DTA), X-ray powder diffraction and other methods. It is discovered that the compound has a displacive phase transition of the first order at (706±5)℃. The low temperature phase. α-Ca2FeWO6. belongs to orthorhombic system, with space group Pmm2. Its lattice parameters at room temperature are; a = 0.77051 nm, 6=0.54242nm and r = 0.551 08 nm, the measured density is Dm = 6.04g/cm3, and each unit cell contains two formula weight. The high temperature phase, β-Ca2FeWO6, belongs to the cubic system, with space group Fm3m and the lattice parameter is a = 0.780 8 nm at 750℃, z = 4. The calculated density is Dx = 5.802g/cm3, The crystal structures of α-Ca2FeWO6 and β-Ca2FeWO6 were also determined by means of the X-ray polycrystal diffraction method. The phase transition mechanism is expounded in detail.

  14. Phase transition, phase transition temperature and crystal structure of a new compound----Ca2PdWO6

    Institute of Scientific and Technical Information of China (English)

    傅正民; 李文秀

    1996-01-01

    A new compound Ca2PdWO6 has been synthesized by solid state sintering. The phase transition of this compound was investigated by means of differential thermal analysis (DTA), X-ray phase analysis, precise measurement of lattice parameters and other methods. It is discovered that the compound has a displacive phase transition of the first order at (806+5)C. The low temperature phase, a-Ca2PdWO6, belongs to orthorhombic system, with space group Pmm2. Its lattice parameters at room temperature are: a=0.79946nm, b=0.55404nm and c=0.58008nm. The measured density is Dm=6.26g/cm3, and each unit cell contains two formula weights. The high temperature phase, Ca2PdWO6, belongs to the cubic system, with space group fm3m and the lattice parameter is a = 0.810 3 nm at 860C; Z = 4. The calculated density is Dx=5.821g/cm3. The crystal structure of Ca2PdWO6 and Ca,PdWO6 was also determined by means of the X-ray polycrystal diffraction method. The factors influencing phase transition temperature are discussed in detail.

  15. Structural phase transition of CdTe: an ab initio study.

    Science.gov (United States)

    Alptekin, Sebahaddin

    2013-01-01

    A constant pressure ab initio MD technique and density functional theory with a generalized gradient approximation (GGA) was used to study the pressure-induced phase transition in zinc-blende CdTe. We found that CdTe undergoes a structural first-order phase transition to [Formula: see text] (binary β-tin) tetragonal structure in the constant pressure molecular dynamics simulation at 20 GPa. When the pressure was increased to 50 GPa, the phase of tetragonal structure converted to a new Imm2 orthorhombic structure. These phase transformations were also calculated by using the enthalpy calculations. Transition phases, lattice parameters and bulk properties we attained are comparable with experimental and theoretical data.

  16. Sliding surface searching method for slopes containing a potential weak structural surface

    Directory of Open Access Journals (Sweden)

    Aijun Yao

    2014-06-01

    Full Text Available Weak structural surface is one of the key factors controlling the stability of slopes. The stability of rock slopes is in general concerned with set of discontinuities. However, in soft rocks, failure can occur along surfaces approaching to a circular failure surface. To better understand the position of potential sliding surface, a new method called simplex-finite stochastic tracking method is proposed. This method basically divides sliding surface into two parts: one is described by smooth curve obtained by random searching, the other one is polyline formed by the weak structural surface. Single or multiple sliding surfaces can be considered, and consequently several types of combined sliding surfaces can be simulated. The paper will adopt the arc-polyline to simulate potential sliding surface and analyze the searching process of sliding surface. Accordingly, software for slope stability analysis using this method was developed and applied in real cases. The results show that, using simplex-finite stochastic tracking method, it is possible to locate the position of a potential sliding surface in the slope.

  17. Sliding surface searching method for slopes containing a potential weak structural surface

    Institute of Scientific and Technical Information of China (English)

    Aijun Yao; Zhizhou Tian; Yongjun Jin

    2014-01-01

    Weak structural surface is one of the key factors controlling the stability of slopes. The stability of rock slopes is in general concerned with set of discontinuities. However, in soft rocks, failure can occur along surfaces approaching to a circular failure surface. To better understand the position of potential sliding surface, a new method called simplex-finite stochastic tracking method is proposed. This method basically divides sliding surface into two parts: one is described by smooth curve obtained by random searching, the other one is polyline formed by the weak structural surface. Single or multiple sliding surfaces can be considered, and consequently several types of combined sliding surfaces can be simu-lated. The paper will adopt the arc-polyline to simulate potential sliding surface and analyze the searching process of sliding surface. Accordingly, software for slope stability analysis using this method was developed and applied in real cases. The results show that, using simplex-finite stochastic tracking method, it is possible to locate the position of a potential sliding surface in the slope.

  18. First-principles calculations of structure and high pressure phase transition in gallium nitride

    Institute of Scientific and Technical Information of China (English)

    Tan Li-Na; Hu Cui-E; Yu Bai-Ru; Chen Xiang-Rong

    2007-01-01

    The phase transitions of semiconductor GaN from the Wurtzite (WZ) structure and the zinc-blende (ZB) structure to the rocksalt (RS) structure are investigated by using the first-principles plane-wave pseudopotential density functional method combined with the ultrasoft pseudopotential scheme in the generalized gradient approximation (GGA)correction. It is found that the phase transitions from the WZ structure and the ZB structure to the RS structure occur at pressures of 46.1 GPa and 45.2 GPa, respectively. The lattice parameters, bulk moduli and their pressure derivatives of these structures of GaN are also calculated. Our results are consistent with available experimental and other theoretical results. The dependence of the normalized formula-unit volume V/Vo on pressure P is also successfully obtained.

  19. River stage influences on uranium transport in a hydrologically dynamic groundwater-surface water transition zone: U TRANSPORT IN A GROUNDWATER-SURFACE WATER TRANSITION ZONE

    Energy Technology Data Exchange (ETDEWEB)

    Zachara, John M. [Pacific Northwest National Laboratory, Richland Washington USA; Chen, Xingyuan [Pacific Northwest National Laboratory, Richland Washington USA; Murray, Chris [Pacific Northwest National Laboratory, Richland Washington USA; Hammond, Glenn [Sandia National Laboratories, Albuquerque New Mexico USA

    2016-03-01

    A tightly spaced well-field within a groundwater uranium (U) plume in the groundwater-surface water transition zone was monitored for a three year period for groundwater elevation and dissolved solutes. The plume discharges to the Columbia River, which displays a dramatic spring stage surge resulting from mountain snowmelt. Groundwater exhibits a low hydrologic gradient and chemical differences with river water. River water intrudes the site in spring. Specific aims were to assess the impacts of river intrusion on dissolved uranium (Uaq), specific conductance (SpC), and other solutes, and to discriminate between transport, geochemical, and source term heterogeneity effects. Time series trends for Uaq and SpC were complex and displayed large temporal well-to well variability as a result of water table elevation fluctuations, river water intrusion, and changes in groundwater flow directions. The wells were clustered into subsets exhibiting common temporal behaviors resulting from the intrusion dynamics of river water and the location of source terms. Concentration hot spots were observed in groundwater that varied in location with increasing water table elevation. Heuristic reactive transport modeling with PFLOTRAN demonstrated that mobilized U was transported between wells and source terms in complex trajectories, and was diluted as river water entered and exited the groundwater system. While uranium time-series concentration trends varied significantly from year to year as a result of climate-caused differences in the spring hydrograph, common and partly predictable response patterns were observed that were driven by water table elevation, and the extent and duration of the river water intrusion event.

  20. Nanoscale Structuring of Surfaces by Using Atomic Layer Deposition.

    Science.gov (United States)

    Sobel, Nicolas; Hess, Christian

    2015-12-01

    Controlled structuring of surfaces is interesting for a wide variety of areas, including microelectronic device fabrication, optical devices, bio(sensing), (electro-, photo)catalysis, batteries, solar cells, fuel cells, and sorption. A unique feature of atomic layer deposition (ALD) is the possibility to form conformal uniform coatings on arbitrarily shaped materials with controlled atomic-scale thickness. In this Minireview, we discuss the potential of ALD for the nanoscale structuring of surfaces, highlighting its versatile application to structuring both planar substrates and powder materials. Recent progress in the application of ALD to porous substrates has even made the nanoscale structuring of high-surface-area materials now feasible, thereby enabling novel applications, such as those in the fields of catalysis and alternative energy.

  1. Sorting of droplets by migration on structured surfaces

    Directory of Open Access Journals (Sweden)

    Wilfried Konrad

    2011-04-01

    Full Text Available Background: Controlled transport of microdroplets is a topic of interest for various applications. It is well known that liquid droplets move towards areas of minimum contact angle if placed on a flat solid surface exhibiting a gradient of contact angle. This effect can be utilised for droplet manipulation. In this contribution we describe how controlled droplet movement can be achieved by a surface pattern consisting of cones and funnels whose length scales are comparable to the droplet diameter.Results: The surface energy of a droplet attached to a cone in a symmetry-preserving way can be smaller than the surface energy of a freely floating droplet. If the value of the contact angle is fixed and lies within a certain interval, then droplets sitting initially on a cone can gain energy by moving to adjacent cones.Conclusion: Surfaces covered with cone-shaped protrusions or cavities may be devised for constructing “band-conveyors” for droplets. In our approach, it is essentially the surface structure which is varied, not the contact angle. It may be speculated that suitably patterned surfaces are also utilised in biological surfaces where a large variety of ornamentations and surface structuring are often observed.

  2. Characterizing structural transitions using localized free energy landscape analysis.

    Directory of Open Access Journals (Sweden)

    Nilesh K Banavali

    Full Text Available BACKGROUND: Structural changes in molecules are frequently observed during biological processes like replication, transcription and translation. These structural changes can usually be traced to specific distortions in the backbones of the macromolecules involved. Quantitative energetic characterization of such distortions can greatly advance the atomic-level understanding of the dynamic character of these biological processes. METHODOLOGY/PRINCIPAL FINDINGS: Molecular dynamics simulations combined with a variation of the Weighted Histogram Analysis Method for potential of mean force determination are applied to characterize localized structural changes for the test case of cytosine (underlined base flipping in a GTCAGCGCATGG DNA duplex. Free energy landscapes for backbone torsion and sugar pucker degrees of freedom in the DNA are used to understand their behavior in response to the base flipping perturbation. By simplifying the base flipping structural change into a two-state model, a free energy difference of upto 14 kcal/mol can be attributed to the flipped state relative to the stacked Watson-Crick base paired state. This two-state classification allows precise evaluation of the effect of base flipping on local backbone degrees of freedom. CONCLUSIONS/SIGNIFICANCE: The calculated free energy landscapes of individual backbone and sugar degrees of freedom expectedly show the greatest change in the vicinity of the flipping base itself, but specific delocalized effects can be discerned upto four nucleotide positions away in both 5' and 3' directions. Free energy landscape analysis thus provides a quantitative method to pinpoint the determinants of structural change on the atomic scale and also delineate the extent of propagation of the perturbation along the molecule. In addition to nucleic acids, this methodology is anticipated to be useful for studying conformational changes in all macromolecules, including carbohydrates, lipids, and proteins.

  3. Structure and reactivity of water at biomaterial surfaces.

    Science.gov (United States)

    Vogler, E A

    1998-02-01

    Molecular self association in liquids is a physical process that can dominate cohesion (interfacial tension) and miscibility. In water, self association is a powerful organizational force leading to a three-dimensional hydrogen-bonded network (water structure). Localized perturbations in the chemical potential of water as by, for example, contact with a solid surface, induces compensating changes in water structure that can be sensed tens of nanometers from the point of origin using the surface force apparatus (SFA) and ancillary techniques. These instruments reveal attractive or repulsive forces between opposing surfaces immersed in water, over and above that anticipated by continuum theory (DLVO), that are attributed to a variable density (partial molar volume) of a more-or-less ordered water structure, depending on the water wettability (surface energy) of the water-contacting surfaces. Water structure at surfaces is thus found to be a manifestation of hydrophobicity and, while mechanistic/theoretical interpretation of experimental results remain the subject of some debate in the literature, convergence of experimental observations permit, for the first time, quantitative definition of the relative terms 'hydrophobic' and 'hydrophilic'. In particular, long-range attractive forces are detected only between surfaces exhibiting a water contact angle theta > 65 degrees (herein defined as hydrophobic surfaces with pure water adhesion tension tau O = gamma O cos theta 30 dyn/cm). These findings suggest at least two distinct kinds of water structure and reactivity: a relatively less-dense water region against hydrophobic surfaces with an open hydrogen-bonded network and a relatively more-dense water region against hydrophilic surfaces with a collapsed hydrogen-bonded network. Importantly, membrane and SFA studies reveal a discrimination between biologically-important ions that preferentially solubilizes divalent ions in more-dense water regions relative to less

  4. Atomic and molecular oxygen adsorbed on (111) transition metal surfaces: Cu and Ni

    Energy Technology Data Exchange (ETDEWEB)

    López-Moreno, S., E-mail: sinlopez@uacam.mx [Centro de Investigación en Corrosión, Universidad Autónoma de Campeche, Av. Héroe de Nacozari 480, Campeche, Campeche 24029 (Mexico); Romero, A. H. [Physics Department, West Virginia University, Morgantown, West Virginia 26506-6315 (United States)

    2015-04-21

    Density functional theory is used to investigate the reaction of oxygen with clean copper and nickel [111]-surfaces. We study several alternative adsorption sites for atomic and molecular oxygen on both surfaces. The minimal energy geometries and adsorption energies are in good agreement with previous theoretical studies and experimental data. From all considered adsorption sites, we found a new O{sub 2} molecular precursor with two possible dissociation paths on the Cu(111) surface. Cross barrier energies for the molecular oxygen dissociation have been calculated by using the climbing image nudge elastic band method, and direct comparison with experimental results is performed. Finally, the structural changes and adsorption energies of oxygen adsorbed on surface when there is a vacancy nearby the adsorption site are also considered.

  5. Stability-to-instability transition in the structure of large-scale networks

    Science.gov (United States)

    Hu, Dandan; Ronhovde, Peter; Nussinov, Zohar

    2012-12-01

    We examine phase transitions between the “easy,” “hard,” and “unsolvable” phases when attempting to identify structure in large complex networks (“community detection”) in the presence of disorder induced by network “noise” (spurious links that obscure structure), heat bath temperature T, and system size N. The partition of a graph into q optimally disjoint subgraphs or “communities” inherently requires Potts-type variables. In earlier work [Philos. Mag.1478-643510.1080/14786435.2011.616547 92, 406 (2012)], when examining power law and other networks (and general associated Potts models), we illustrated that transitions in the computational complexity of the community detection problem typically correspond to spin-glass-type transitions (and transitions to chaotic dynamics in mechanical analogs) at both high and low temperatures and/or noise. The computationally “hard” phase exhibits spin-glass type behavior including memory effects. The region over which the hard phase extends in the noise and temperature phase diagram decreases as N increases while holding the average number of nodes per community fixed. This suggests that in the thermodynamic limit a direct sharp transition may occur between the easy and unsolvable phases. When present, transitions at low temperature or low noise correspond to entropy driven (or “order by disorder”) annealing effects, wherein stability may initially increase as temperature or noise is increased before becoming unsolvable at sufficiently high temperature or noise. Additional transitions between contending viable solutions (such as those at different natural scales) are also possible. Identifying community structure via a dynamical approach where “chaotic-type” transitions were found earlier. The correspondence between the spin-glass-type complexity transitions and transitions into chaos in dynamical analogs might extend to other hard computational problems. In this work, we examine large

  6. PHASE ANALYSIS AND CRYSTAL STRUCTURE STUDIES ON BINARY ALLOYS OF ALUMINUM WITH TRANSITION METALS.

    Science.gov (United States)

    In order to provide the necessary background for detailed crystal-chemistry studies in the field of binary aluminum - transition metal systems, extensive investigations have been carried out on the phase relations of a large number of such systems. The results of these studies are briefly summarized, as are also the results of crystal structure determinations of a few alumi num - transition metal phases. (Author)

  7. Orientation dependence of structural transition in fcc Al driven under uniaxial compression by atomistic simulations

    Institute of Scientific and Technical Information of China (English)

    Li Li; Shao Jian-Li; Duan Su-Qing; Liang Jiu-Qing

    2011-01-01

    By molecular dynamics simulations employing an embedded atom method potential, we have investigated structural transformations in single crystal Al caused by uniaxial strain loading along the[001],[011]and[111]directions.We find that the structural transition is strongly dependent on the crystal orientations. The entire structure phase transition only occurs when loading along the[001]direction, and the increased amplitude of temperature for[001]loading is evidently lower than that for other orientations. The morphology evolutions of the structural transition for [011]and[111]loadings are analysed in detail. The results indicate that only 20% of atoms transit to the hcp phase for[011]and[111]loadings, and the appearance of the hcp phase is due to the partial dislocation moving forward on {111}fcc family. For[011]loading, the hcp phase grows to form laminar morphology in four planes, which belong to the{111}fcc family;while for[111]loading, the hcp phase grows into a laminar structure in three planes, which belong to the {111}fcc family except for the(111)plane. In addition, the phase transition is evaluated by using the radial distribution functions.

  8. Competing structures in two dimensions: Square-to-hexagonal transition

    Science.gov (United States)

    Gränz, Barbara; Korshunov, Sergey E.; Geshkenbein, Vadim B.; Blatter, Gianni

    2016-08-01

    We study a system of particles in two dimensions interacting via a dipolar long-range potential D /r3 and subject to a square-lattice substrate potential V (r ) with amplitude V and lattice constant b . The isotropic interaction favors a hexagonal arrangement of the particles with lattice constant a , which competes against the square symmetry of the underlying substrate lattice. We determine the minimal-energy states at fixed external pressure p generating the commensurate density n =1 /b2=(4/3 ) 1 /2/a2 in the absence of thermal and quantum fluctuations, using both analytical techniques based on the harmonic and continuum elastic approximations as well as numerical relaxation of particle configurations. At large substrate amplitude V >0.2 eD, with eD=D /b3 the dipolar energy scale, the particles reside in the substrate minima and hence arrange in a square lattice. Upon decreasing V , the square lattice turns unstable with respect to a zone-boundary shear mode and deforms into a period-doubled zigzag lattice. Analytic and numerical results show that this period-doubled phase in turn becomes unstable at V ≈0.074 eD towards a nonuniform phase developing an array of domain walls or solitons; as the density of solitons increases, the particle arrangement approaches that of a rhombic (or isosceles triangular) lattice. At a yet smaller substrate value estimated as V ≈0.046 eD, a further solitonic transition establishes a second nonuniform phase which smoothly approaches the hexagonal (or equilateral triangular) lattice phase with vanishing amplitude V . At small but finite amplitude V , the hexagonal phase is distorted and hexatically locked at an angle of φ ≈3 .8∘ with respect to the substrate lattice. The square-to-hexagonal transformation in this two-dimensional commensurate-incommensurate system thus involves a complex pathway with various nontrivial lattice- and modulated phases.

  9. Phase Behavior and Structural Transitions in Sodium Dodecyl Sulfonate Microemulsions

    Institute of Scientific and Technical Information of China (English)

    杨根生; 施介华; 等

    2002-01-01

    The forming mechanism of microemulsion of sodium dodecyl sulfonate.alcohols,water and isooctane was studied,with particular emphasis on the effect of molecular weight and concentration of alocohols.Phase diagram of the four components,alcohol, sodium dodecyl sulfonate,water and isooctane,was used as a means of study,through which the microemulsion regions were determined.Phase diagram of sodium dodecyl sulfonate/n-pentanol/isooctane/water system at km=2(km=Wn-pentanol/WSDS)is presented. The variation of conductivities of different microemulsion samples with water was measured.From the conductivities we investigated a change in structure from water droplets in oil(W/O)at low water content to liquid crystal at intermediate water content and a structure of oil droplets in water(O/W)at high water content.

  10. Pressure-induced structural transitions in MgH2.

    Science.gov (United States)

    Vajeeston, P; Ravindran, P; Kjekshus, A; Fjellvåg, H

    2002-10-21

    The stability of MgH2 has been studied up to 20 GPa using density-functional total-energy calculations. At ambient pressure alpha-MgH2 takes a TiO2-rutile-type structure. alpha-MgH2 is predicted to transform into gamma-MgH2 at 0.39 GPa. The calculated structural data for alpha- and gamma-MgH2 are in very good agreement with experimental values. At equilibrium the energy difference between these modifications is very small, and as a result both phases coexist in a certain volume and pressure field. Above 3.84 GPa gamma-MgH2 transforms into beta-MgH2, consistent with experimental findings. Two further transformations have been identified at still higher pressure: (i) beta- to delta-MgH2 at 6.73 GPa and (ii) delta- to epsilon-MgH2 at 10.26 GPa.

  11. Complex transition to cooperative behavior in a structured population model.

    Directory of Open Access Journals (Sweden)

    Luciano Miranda

    Full Text Available Cooperation plays an important role in the evolution of species and human societies. The understanding of the emergence and persistence of cooperation in those systems is a fascinating and fundamental question. Many mechanisms were extensively studied and proposed as supporting cooperation. The current work addresses the role of migration for the maintenance of cooperation in structured populations. This problem is investigated in an evolutionary perspective through the prisoner's dilemma game paradigm. It is found that migration and structure play an essential role in the evolution of the cooperative behavior. The possible outcomes of the model are extinction of the entire population, dominance of the cooperative strategy and coexistence between cooperators and defectors. The coexistence phase is obtained in the range of large migration rates. It is also verified the existence of a critical level of structuring beyond that cooperation is always likely. In resume, we conclude that the increase in the number of demes as well as in the migration rate favor the fixation of the cooperative behavior.

  12. Understanding surface structure and chemistry of single crystal lanthanum aluminate

    KAUST Repository

    Pramana, Stevin S.

    2017-03-02

    The surface crystallography and chemistry of a LaAlO3 single crystal, a material mainly used as a substrate to deposit technologically important thin films (e.g. for superconducting and magnetic devices), was analysed using surface X-ray diffraction and low energy ion scattering spectroscopy. The surface was determined to be terminated by Al-O species, and was significantly different from the idealised bulk structure. Termination reversal was not observed at higher temperature (600 °C) and chamber pressure of 10−10 Torr, but rather an increased Al-O occupancy occurred, which was accompanied by a larger outwards relaxation of Al from the bulk positions. Changing the oxygen pressure to 10−6 Torr enriched the Al site occupancy fraction at the outermost surface from 0.245(10) to 0.325(9). In contrast the LaO, which is located at the next sub-surface atomic layer, showed no chemical enrichment and the structural relaxation was lower than for the top AlO2 layer. Knowledge of the surface structure will aid the understanding of how and which type of interface will be formed when LaAlO3 is used as a substrate as a function of temperature and pressure, and so lead to improved design of device structures.

  13. Transitioning Enhanced Land Surface Initialization and Model Verification Capabilities to the Kenya Meteorological Department (KMD)

    Science.gov (United States)

    Case, Jonathan L.; Mungai, John; Sakwa, Vincent; Zavodsky, Bradley T.; Srikishen, Jayanthi; Limaye, Ashutosh; Blankenship, Clay B.

    2016-01-01

    Flooding, severe weather, and drought are key forecasting challenges for the Kenya Meteorological Department (KMD), based in Nairobi, Kenya. Atmospheric processes leading to convection, excessive precipitation and/or prolonged drought can be strongly influenced by land cover, vegetation, and soil moisture content, especially during anomalous conditions and dry/wet seasonal transitions. It is thus important to represent accurately land surface state variables (green vegetation fraction, soil moisture, and soil temperature) in Numerical Weather Prediction (NWP) models. The NASA SERVIR and the Short-term Prediction Research and Transition (SPoRT) programs in Huntsville, AL have established a working partnership with KMD to enhance its regional modeling capabilities. SPoRT and SERVIR are providing experimental land surface initialization datasets and model verification capabilities for capacity building at KMD. To support its forecasting operations, KMD is running experimental configurations of the Weather Research and Forecasting (WRF; Skamarock et al. 2008) model on a 12-km/4-km nested regional domain over eastern Africa, incorporating the land surface datasets provided by NASA SPoRT and SERVIR. SPoRT, SERVIR, and KMD participated in two training sessions in March 2014 and June 2015 to foster the collaboration and use of unique land surface datasets and model verification capabilities. Enhanced regional modeling capabilities have the potential to improve guidance in support of daily operations and high-impact weather and climate outlooks over Eastern Africa. For enhanced land-surface initialization, the NASA Land Information System (LIS) is run over Eastern Africa at 3-km resolution, providing real-time land surface initialization data in place of interpolated global model soil moisture and temperature data available at coarser resolutions. Additionally, real-time green vegetation fraction (GVF) composites from the Suomi-NPP VIIRS instrument is being incorporated

  14. Structures, Phase Transitions and Tricritical Behavior of the Hybrid Perovskite Methyl Ammonium Lead Iodide

    Science.gov (United States)

    Whitfield, P. S.; Herron, N.; Guise, W. E.; Page, K.; Cheng, Y. Q.; Milas, I.; Crawford, M. K.

    2016-01-01

    We have examined the crystal structures and structural phase transitions of the deuterated, partially deuterated and hydrogenous organic-inorganic hybrid perovskite methyl ammonium lead iodide (MAPbI3) using time-of-flight neutron and synchrotron X-ray powder diffraction. Near 330 K the high temperature cubic phases transformed to a body-centered tetragonal phase. The variation of the order parameter Q for this transition scaled with temperature T as Q ∼ (Tc−T)β, where Tc is the critical temperature and the exponent β was close to ¼, as predicted for a tricritical phase transition. However, we also observed coexistence of the cubic and tetragonal phases over a range of temperature in all cases, demonstrating that the phase transition was in fact first-order, although still very close to tricritical. Upon cooling further, all the tetragonal phases transformed into a low temperature orthorhombic phase around 160 K, again via a first-order phase transition. Based upon these results, we discuss the impact of the structural phase transitions upon photovoltaic performance of MAPbI3 based solar cells. PMID:27767049

  15. Correlation between oxygen adsorption energy and electronic structure of transition metal macrocyclic complexes.

    Science.gov (United States)

    Liu, Kexi; Lei, Yinkai; Wang, Guofeng

    2013-11-28

    Oxygen adsorption energy is directly relevant to the catalytic activity of electrocatalysts for oxygen reduction reaction (ORR). In this study, we established the correlation between the O2 adsorption energy and the electronic structure of transition metal macrocyclic complexes which exhibit activity for ORR. To this end, we have predicted the molecular and electronic structures of a series of transition metal macrocyclic complexes with planar N4 chelation, as well as the molecular and electronic structures for the O2 adsorption on these macrocyclic molecules, using the density functional theory calculation method. We found that the calculated adsorption energy of O2 on the transition metal macrocyclic complexes was linearly related to the average position (relative to the lowest unoccupied molecular orbital of the macrocyclic complexes) of the non-bonding d orbitals (d(z(2)), d(xy), d(xz), and d(yz)) which belong to the central transition metal atom. Importantly, our results suggest that varying the energy level of the non-bonding d orbitals through changing the central transition metal atom and/or peripheral ligand groups could be an effective way to tuning their O2 adsorption energy for enhancing the ORR activity of transition metal macrocyclic complex catalysts.

  16. Structures, Phase Transitions and Tricritical Behavior of the Hybrid Perovskite Methyl Ammonium Lead Iodide

    Science.gov (United States)

    Whitfield, P. S.; Herron, N.; Guise, W. E.; Page, K.; Cheng, Y. Q.; Milas, I.; Crawford, M. K.

    2016-10-01

    We have examined the crystal structures and structural phase transitions of the deuterated, partially deuterated and hydrogenous organic-inorganic hybrid perovskite methyl ammonium lead iodide (MAPbI3) using time-of-flight neutron and synchrotron X-ray powder diffraction. Near 330 K the high temperature cubic phases transformed to a body-centered tetragonal phase. The variation of the order parameter Q for this transition scaled with temperature T as Q ˜ (Tc-T)β, where Tc is the critical temperature and the exponent β was close to ¼, as predicted for a tricritical phase transition. However, we also observed coexistence of the cubic and tetragonal phases over a range of temperature in all cases, demonstrating that the phase transition was in fact first-order, although still very close to tricritical. Upon cooling further, all the tetragonal phases transformed into a low temperature orthorhombic phase around 160 K, again via a first-order phase transition. Based upon these results, we discuss the impact of the structural phase transitions upon photovoltaic performance of MAPbI3 based solar cells.

  17. Kinetics of nucleotide-dependent structural transitions in the kinesin-1 hydrolysis cycle.

    Science.gov (United States)

    Mickolajczyk, Keith J; Deffenbaugh, Nathan C; Arroyo, Jaime Ortega; Andrecka, Joanna; Kukura, Philipp; Hancock, William O

    2015-12-29

    To dissect the kinetics of structural transitions underlying the stepping cycle of kinesin-1 at physiological ATP, we used interferometric scattering microscopy to track the position of gold nanoparticles attached to individual motor domains in processively stepping dimers. Labeled heads resided stably at positions 16.4 nm apart, corresponding to a microtubule-bound state, and at a previously unseen intermediate position, corresponding to a tethered state. The chemical transitions underlying these structural transitions were identified by varying nucleotide conditions and carrying out parallel stopped-flow kinetics assays. At saturating ATP, kinesin-1 spends half of each stepping cycle with one head bound, specifying a structural state for each of two rate-limiting transitions. Analysis of stepping kinetics in varying nucleotides shows that ATP binding is required to properly enter the one-head-bound state, and hydrolysis is necessary to exit it at a physiological rate. These transitions differ from the standard model in which ATP binding drives full docking of the flexible neck linker domain of the motor. Thus, this work defines a consensus sequence of mechanochemical transitions that can be used to understand functional diversity across the kinesin superfamily.

  18. Isostructural solid-solid phase transition in monolayers of soft core-shell particles at fluid interfaces: structure and mechanics.

    Science.gov (United States)

    Rey, Marcel; Fernández-Rodríguez, Miguel Ángel; Steinacher, Mathias; Scheidegger, Laura; Geisel, Karen; Richtering, Walter; Squires, Todd M; Isa, Lucio

    2016-04-21

    We have studied the complete two-dimensional phase diagram of a core-shell microgel-laden fluid interface by synchronizing its compression with the deposition of the interfacial monolayer. Applying a new protocol, different positions on the substrate correspond to different values of the monolayer surface pressure and specific area. Analyzing the microstructure of the deposited monolayers, we discovered an isostructural solid-solid phase transition between two crystalline phases with the same hexagonal symmetry, but with two different lattice constants. The two phases corresponded to shell-shell and core-core inter-particle contacts, respectively; with increasing surface pressure the former mechanically failed enabling the particle cores to come into contact. In the phase-transition region, clusters of particles in core-core contacts nucleate, melting the surrounding shell-shell crystal, until the whole monolayer moves into the second phase. We furthermore measured the interfacial rheology of the monolayers as a function of the surface pressure using an interfacial microdisk rheometer. The interfaces always showed a strong elastic response, with a dip in the shear elastic modulus in correspondence with the melting of the shell-shell phase, followed by a steep increase upon the formation of a percolating network of the core-core contacts. These results demonstrate that the core-shell nature of the particles leads to a rich mechanical and structural behavior that can be externally tuned by compressing the interface, indicating new routes for applications, e.g. in surface patterning or emulsion stabilization.

  19. Electron backscatter diffraction characterization of laser-induced periodic surface structures on nickel surface

    Science.gov (United States)

    Sedao, Xxx; Maurice, Claire; Garrelie, Florence; Colombier, Jean-Philippe; Reynaud, Stéphanie; Quey, Romain; Blanc, Gilles; Pigeon, Florent

    2014-05-01

    We report on the structural investigation of laser-induced periodic surface structures (LIPSS) generated in polycrystalline nickel target after multi-shot irradiation by femtosecond laser pulses. Electron backscatter diffraction (EBSD) is used to reveal lattice rotation caused by dislocation storage during LIPSS formation. Localized crystallographic damages in the LIPSS are detected from both surface and cross-sectional EBSD studies. A surface region (up to 200 nm) with 1-3° grain disorientation is observed in localized areas from the cross-section of the LIPSS. The distribution of the local disorientation is inhomogeneous across the LIPSS and the subsurface region.

  20. Crystallography and surface structure an introduction for surface scientists and nanoscientists

    CERN Document Server

    Hermann, Klaus

    2017-01-01

    A valuable learning tool as well as a reference, this book provides students and researchers in surface science and nanoscience with the theoretical crystallographic foundations, which are necessary to understand local structure and symmetry of bulk crystals, including ideal and real single crystal surfaces. The author deals with the subject at an introductory level, providing numerous graphic examples to illustrate the mathematical formalism. The book brings together and logically connects many seemingly disparate structural issues and notations used frequently by surface scientists and nanoscientists. Numerous exercises of varying difficulty, ranging from simple questions to small research projects, are included to stimulate discussions about the different subjects.