Anisotropic bias dependent transport property of defective phosphorene layer
Umar Farooq, M.; Hashmi, Arqum; Hong, Jisang
2015-01-01
Phosphorene is receiving great research interests because of its peculiar physical properties. Nonetheless, no systematic studies on the transport properties modified due to defects have been performed. Here, we present the electronic band structure, defect formation energy and bias dependent transport property of various defective systems. We found that the defect formation energy is much less than that in graphene. The defect configuration strongly affects the electronic structure. The band gap vanishes in single vacancy layers, but the band gap reappears in divacancy layers. Interestingly, a single vacancy defect behaves like a p-type impurity for transport property. Unlike the common belief, we observe that the vacancy defect can contribute to greatly increasing the current. Along the zigzag direction, the current in the most stable single vacancy structure was significantly increased as compared with that found in the pristine layer. In addition, the current along the armchair direction was always greater than along the zigzag direction and we observed a strong anisotropic current ratio of armchair to zigzag direction. PMID:26198318
Anisotropic bias dependent transport property of defective phosphorene layer.
Umar Farooq, M; Hashmi, Arqum; Hong, Jisang
2015-01-01
Phosphorene is receiving great research interests because of its peculiar physical properties. Nonetheless, no systematic studies on the transport properties modified due to defects have been performed. Here, we present the electronic band structure, defect formation energy and bias dependent transport property of various defective systems. We found that the defect formation energy is much less than that in graphene. The defect configuration strongly affects the electronic structure. The band gap vanishes in single vacancy layers, but the band gap reappears in divacancy layers. Interestingly, a single vacancy defect behaves like a p-type impurity for transport property. Unlike the common belief, we observe that the vacancy defect can contribute to greatly increasing the current. Along the zigzag direction, the current in the most stable single vacancy structure was significantly increased as compared with that found in the pristine layer. In addition, the current along the armchair direction was always greater than along the zigzag direction and we observed a strong anisotropic current ratio of armchair to zigzag direction. PMID:26198318
Anisotropic bias dependent transport property of defective phosphorene layer
NASA Astrophysics Data System (ADS)
Umar Farooq, M.; Hashmi, Arqum; Hong, Jisang
2015-07-01
Phosphorene is receiving great research interests because of its peculiar physical properties. Nonetheless, no systematic studies on the transport properties modified due to defects have been performed. Here, we present the electronic band structure, defect formation energy and bias dependent transport property of various defective systems. We found that the defect formation energy is much less than that in graphene. The defect configuration strongly affects the electronic structure. The band gap vanishes in single vacancy layers, but the band gap reappears in divacancy layers. Interestingly, a single vacancy defect behaves like a p-type impurity for transport property. Unlike the common belief, we observe that the vacancy defect can contribute to greatly increasing the current. Along the zigzag direction, the current in the most stable single vacancy structure was significantly increased as compared with that found in the pristine layer. In addition, the current along the armchair direction was always greater than along the zigzag direction and we observed a strong anisotropic current ratio of armchair to zigzag direction.
Anisotropic transport properties of zinc-blend ZnTe/CrTe heterogeneous junction nanodevices
NASA Astrophysics Data System (ADS)
Yao, Wei; Yao, K. L.; Gao, G. Y.; Zhu, S. C.; Fu, H. H.
2012-11-01
Motivated by the molecular-beam epitaxial growth of zinc-blend-type CrTe thin films on ZnTe, we present a theoretical study on the spin-polarized transport properties of ZnTe/CrTe p-n junction as spin diode and CrTe/ZnTe/CrTe magnetic tunnel junction for (001) and (011) surfaces. Both ZnTe(001)/CrTe(001) and ZnTe(011)/CrTe(011) p-n junctions show excellent spin diode effect, the majority spin current of positive voltage is much larger than that of negative voltage and the minority spin current is absolutely inhibited. The ZnTe(001)/CrTe(001) p-n junction has lower "turn off" current and higher rectification ratio (about 105) than the ZnTe(011)/CrTe(011) which shows obvious anisotropy. We also find that the tunneling magneto resistance ratio of the CrTe/ZnTe/CrTe magnetic tunnel junction is up to about 4 × 109%.
Zou, Q; Liu, M; Wang, G Q; Lu, H L; Yang, T Z; Guo, H M; Ma, C R; Xu, X; Zhang, M H; Jiang, J C; Meletis, E I; Lin, Y; Gao, H J; Chen, C L
2014-05-14
Highly epitaxial LaBaCo2O5.5+? (LBCO) thin films were grown on different miscut (001) SrTiO3 substrates (miscut angle of 0.5°, 3.0°, and 5.0°) to study the substrate surface step terrace effect on the in-plane electrical transport properties. The microstructure studies by X-ray diffraction and transmission electron microscopy indicate that the as-grown films are A-site disordered cubic perovskite structures with the c-axis highly oriented along the film growth direction. The four-probe scanning tunneling microscopy (STM) studies show that the LBCO thin films grown on the vicinal SrTiO3 substrates have a typical semiconductor behavior with the substrate surface terrace step inducing anisotropic electronic transport properties. These results indicate that in highly epitaxial thin films the surface terrace step induced local strains can play an important role in controlling the electronic transport properties and the anisotropic nature. PMID:24716582
Anisotropic flow in transport + hydrodynamics hybrid approaches
NASA Astrophysics Data System (ADS)
Petersen, Hannah
2014-12-01
This contribution to the focus issue covers anisotropic flow in hybrid approaches. The historical development of hybrid approaches and their impact on the interpretation of flow measurements is reviewed. The major ingredients of a hybrid approach and the transition criteria between transport and hydrodynamics are discussed. The results for anisotropic flow in (event-by-event) hybrid approaches are presented. Some hybrid approaches rely on hadronic transport for the late stages for the reaction (so called afterburner) and others employ transport approaches for the early non-equilibrium evolution. In addition, there are â€˜fullâ€™ hybrid calculations where a fluid evolution is dynamically embedded in a transport simulation. After demonstrating the success of hybrid approaches at high Relativistic Heavy Ion Collider and Large Hadron Collider energies, existing hybrid caluclations for collective flow observables at lower beam energies are discussed and remaining challenges outlined.
Intricate short-range ordering and strongly anisotropic transport properties of Li(1-x)Sn(2+x)As?.
Lee, Kathleen; Kaseman, Derrick; Sen, Sabyasachi; Hung, Ivan; Gan, Zhehong; Gerke, Birgit; Pöttgen, Rainer; Feygenson, Mikhail; Neuefeind, Jörg; Lebedev, Oleg I; Kovnir, Kirill
2015-03-18
A new ternary compound, Li(1-x)Sn(2+x)As2, 0.2 < x < 0.4, was synthesized via solid-state reaction of elements. The compound crystallizes in a layered structure in the R3?m space group (No. 166) with Sn-As layers separated by layers of jointly occupied Li/Sn atoms. The Sn-As layers are comprised of Sn3As3 puckered hexagons in a chair conformation that share all edges. Li/Sn atoms in the interlayer space are surrounded by a regular As6 octahedron. Thorough investigation by synchrotron X-ray and neutron powder diffraction indicate no long-range Li/Sn ordering. In contrast, the local Li/Sn ordering was revealed by synergistic investigations via solid-state (6,7)Li NMR spectroscopy, HRTEM, STEM, and neutron and X-ray pair distribution function analyses. Due to their different chemical natures, Li and Sn atoms tend to segregate into Li-rich and Sn-rich regions, creating substantial inhomogeneity on the nanoscale. The inhomogeneous local structure has a high impact on the physical properties of the synthesized compounds: the local Li/Sn ordering and multiple nanoscale interfaces result in unexpectedly low thermal conductivity and highly anisotropic resistivity in Li(1-x)Sn(2+x)As2. PMID:25702752
On the anisotropic elastic properties of hydroxyapatite.
NASA Technical Reports Server (NTRS)
Katz, J. L.; Ukraincik, K.
1971-01-01
Experimental measurements of the isotropic elastic moduli on polycrystalline specimens of hydroxyapatite and fluorapatite are compared with elastic constants measured directly from single crystals of fluorapatite in order to derive a set of pseudo single crystal elastic constants for hydroxyapatite. The stiffness coefficients thus derived are given. The anisotropic and isotropic elastic properties are then computed and compared with similar properties derived from experimental observations of the anisotropic behavior of bone.
Synthesis of cubic SrCoO3 single crystal and its anisotropic magnetic and transport properties.
Long, Youwen; Kaneko, Yoshio; Ishiwata, Shintaro; Taguchi, Yasujiro; Tokura, Yoshinori
2011-06-22
A large-size single crystal of nearly stoichiometric SrCoO(3) was prepared with a two-step method combining the floating-zone technique and subsequent high oxygen pressure treatment. SrCoO(3) crystallizes in a cubic perovskite structure with space group Pm3m, and displays an itinerant ferromagnetic behavior with the Curie temperature of 305 K. The easy magnetization axis is found to be along the [111] direction, and the saturation moment is 2.5 µ(B)/f.u., in accord with the picture of the intermediate spin state. The resistivity at low temperatures (T) is proportional to T(2), indicative of the possible effect of orbital fluctuation in the intermediate spin ferromagnetic metallic state. Unusual anisotropic magnetoresistance is also observed and its possible origin is discussed. PMID:21628787
Theoretical studies of anisotropic energy transport in TATB crystals
NASA Astrophysics Data System (ADS)
Kroonblawd, Matthew; Sewell, Thomas
2015-06-01
Anisotropic thermal transport properties were determined theoretically for single crystals of the insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) using molecular dynamics. TATB exhibits a graphitic-like layered packing structure with a two-dimensional hydrogen-bonding network within, but not between, the molecule-thick layers that comprise the crystal. Anisotropic thermal conductivity coefficients were determined for initially defect-free and defective TATB crystals at various temperatures and pressures, and direction-dependent relaxation of idealized hot spots was studied. The room temperature, atmospheric pressure thermal conductivity for TATB is predicted to be generally greater and more anisotropic than the thermal conductivities of other molecular explosives; conduction within the layers is at least 68% greater than conduction between them. The phonon mean free path length is predicted to be less than 1 nm. Decreases in thermal conductivity induced by molecular vacancy defects are also anisotropic and exhibit a linear dependence on defect density. Results from the hot-spot relaxation simulations were compared with and fit to an analytical solution for the one-dimensional continuum heat equation by treating the thermal diffusivity as a parameter. Validity of the continuum heat equation predictions for TATB is assessed for length scales below 20 nm.
THE ANISOTROPIC TRANSPORT EFFECTS ON DILUTE PLASMAS
Devlen, Ebru
2011-04-20
We examine the linear stability analysis of a hot, dilute, and differentially rotating plasma by considering anisotropic transport effects. In dilute plasmas, the ion Larmor radius is small compared with its collisional mean free path. In this case, the transport of heat and momentum along the magnetic field lines becomes important. This paper presents a novel linear instability that may be more powerful and greater than ideal magnetothermal instability and ideal magnetorotational instability in the dilute astrophysical plasmas. This type of plasma is believed to be found in the intracluster medium (ICM) of galaxy clusters and radiatively ineffective accretion flows around black holes. We derive the dispersion relation of this instability and obtain the instability condition. There is at least one unstable mode that is independent of the temperature gradient direction for a helical magnetic field geometry. This novel instability is driven by the gyroviscosity coupled with differential rotation. Therefore, we call it gyroviscous-modified magnetorotational instability (GvMRI). We examine how the instability depends on signs of the temperature gradient and the gyroviscosity and also on the magnitude of the thermal frequency and on the values of the pitch angle. We provide a detailed physical interpretation of the obtained results. The GvMRI is applicable not only to the accretion flows and ICM but also to the transition region between cool dense gas and the hot low-density plasma in stellar coronae, accretion disks, and the multiphase interstellar medium because it is independent of the temperature gradient direction.
NASA Astrophysics Data System (ADS)
Guo, Ruiqiang; Wang, Xinjiang; Kuang, Youdi; Huang, Baoling
2015-09-01
Tin selenide (SnSe) and tin sulfide (SnS) have recently attracted particular interest due to their great potential for large-scale thermoelectric applications. A complete prediction of the thermoelectric performance and the understanding of underlying heat and charge transport details are the key to further improvement of their thermoelectric efficiency. We conduct comprehensive investigations of both thermal and electrical transport properties of SnSe and SnS using first-principles calculations combined with the Boltzmann transport theory. Due to the distinct layered lattice structure, SnSe and SnS exhibit similarly anisotropic thermal and electrical behaviors. The cross-plane lattice thermal conductivity ?L is 40 -60 % lower than the in-plane values. Extremely low ?L is found for both materials because of high anharmonicity, while the average ?L of SnS is ˜8 % higher than that of SnSe from 300 to 750 K. It is suggested that nanostructuring would be difficult to further decrease ?L because of the short mean free paths of dominant phonon modes (1-30 nm at 300 K), while alloying would be efficient in reducing ?L considering that the relative ?L contribution (˜65 %) of optical phonons is remarkably large. On the electrical side, the anisotropic electrical conductivities are mainly due to the different effective masses of holes and electrons along the a , b , and c axes. This leads to the highest optimal ZT values along the b axis and lowest ones along the a axis in both p -type materials. However, the n -type ones exhibit the highest ZT s along the a axis due to the enhancement of power factor when the chemical potential gradually approaches the secondary conduction band valley that causes significant increase in electron mobility and density of states. Owing to the larger mobility and smaller ?L along the given direction, SnSe exhibits larger optimal ZTs compared with SnS in both p - and n -type materials. For both materials, the peak ZT s of n -type materials are much higher than those of p -type ones along the same direction. The predicted highest ZT values at 750 K are 1.0 in SnSe and 0.6 in SnS along the b axis for the p -type doping, while those for the n -type doping reach 2.7 in SnSe and 1.5 in SnS along the a axis, rendering them among the best bulk thermoelectric materials for large-scale applications. Our calculations show reasonable agreements with the experimental results and quantitatively predict the great potential in further enhancing the thermoelectric performance of SnSe and SnS, especially for the n -type materials.
Numerical investigation of nanoparticles transport in anisotropic porous media.
Salama, Amgad; Negara, Ardiansyah; El Amin, Mohamed; Sun, Shuyu
2015-10-01
In this work the problem related to the transport of nanoparticles in anisotropic porous media is investigated numerically using the multipoint flux approximation. Anisotropy of porous media properties is an essential feature that exists almost everywhere in subsurface formations. In anisotropic media, the flux and the pressure gradient vectors are no longer collinear and therefore interesting patterns emerge. The transport of nanoparticles in subsurface formations is affected by several complex processes including surface charges, heterogeneity of nanoparticles and soil grain collectors, interfacial dynamics of double-layer and many others. We use the framework of the theory of filtration in this investigation. Processes like particles deposition, entrapment, as well as detachment are accounted for. From the numerical methods point of view, traditional two-point flux finite difference approximation cannot handle anisotropy of media properties. Therefore, in this work we use the multipoint flux approximation (MPFA). In this technique, the flux components are affected by more neighboring points as opposed to the mere two points that are usually used in traditional finite volume methods. We also use the experimenting pressure field approach which automatically constructs the global system of equations by solving multitude of local problems. This approach facilitates to a large extent the construction of the global system. A set of numerical examples is considered involving two-dimensional rectangular domain. A source of nanoparticles is inserted in the middle of the anisotropic layer. We investigate the effects of both anisotropy angle and anisotropy ratio on the transport of nanoparticles in saturated porous media. It is found that the concentration plume and porosity contours follow closely the principal direction of anisotropy of permeability of the central domain. PMID:26212784
Disentangling scaling properties in anisotropic fracture.
Bouchbinder, Eran; Procaccia, Itamar; Sela, Shani
2005-12-16
Structure functions of rough fracture surfaces in isotropic materials exhibit complicated scaling properties due to the broken isotropy in the fracture plane generated by a preferred propagation direction. Decomposing the structure functions into the even order irreducible representations of the SO(2) symmetry group indexed by (m = 0, 2, 4, . . .) results in a lucid and quickly convergent description. The scaling exponent of the isotropic sector (m = 0) dominates at small length scales. One can reconstruct the anisotropic structure functions using only the isotropic and the first nonvanishing anisotropic sector (m = 2) [or at most the next one (m = 4)]. The scaling exponent of the isotropic sector should be observed in a proposed, yet unperformed, experiment. PMID:16384468
Field dependent spin transport of anisotropic Heisenberg chain
NASA Astrophysics Data System (ADS)
Rezania, H.
2016-04-01
We have addressed the static spin conductivity and spin Drude weight of one-dimensional spin-1/2 anisotropic antiferromagnetic Heisenberg chain in the finite magnetic field. We have investigated the behavior of transport properties by means of excitation spectrum in terms of a hard core bosonic representation. The effect of in-plane anisotropy on the spin transport properties has also been studied via the bosonic model by Green's function approach. This anisotropy is considered for exchange constants that couple spin components perpendicular to magnetic field direction. We have found the temperature dependence of the spin conductivity and spin Drude weight in the gapped field induced spin-polarized phase for various magnetic field and anisotropy parameters. Furthermore we have studied the magnetic field dependence of static spin conductivity and Drude weight for various anisotropy parameters. Our results show the regular part of spin conductivity vanishes in isotropic case however Drude weight has a finite non-zero value and the system exhibits ballistic transport properties. We also find the peak in the static spin conductivity factor moves to higher temperature upon increasing the magnetic field at fixed anisotropy. The static spin conductivity is found to be monotonically decreasing with magnetic field due to increase of energy gap in the excitation spectrum. Furthermore we have studied the temperature dependence of spin Drude weight for different magnetic field and various anisotropy parameters.
Transport equations for multicomponent anisotropic space plasmas - A review
NASA Technical Reports Server (NTRS)
Barakat, A. R.; Schunk, R. W.
1982-01-01
An attempt is made to present a unified approach to the study of transport phenomena in multicomponent anisotropic space plasmas. In particular, a system of generalized transport equations is presented that can be applied to widely different plasma flow conditions. The generalized transport equations can describe subsonic and supersonic flows, collision-dominated and collisionless flows, plasma flows in rapidly changing magnetic field configurations, multicomponent plasma flows with large temperature differences between the interacting species, and plasma flows that contain anisotropic temperature distributions. In addition, if Maxwell's equations of electricity and magnetism are added to the system of transport equations, they can be used to model electrostatic shocks, double layers, and magnetic merging processes. These transport equations also contain terms which act to regulate both the heat flow and temperature anisotropy, processes which appear to be operating in the solar wind.
Anisotropic thermal transport in phosphorene: effects of crystal orientation
NASA Astrophysics Data System (ADS)
Liu, Te-Huan; Chang, Chien-Cheng
2015-06-01
As an intrinsic thermally anisotropic material, the thermal properties of phosphorene must vary with respect to the crystal chirality. Nevertheless, previous studies of heat transfer in phosphorene have been limited to the 0.0° (zigzag, ZZ) and 90.0° (armchair, AC) chiralities. In this study, we investigate the orientation-dependent thermal transport in phosphorene sheets with a complete set of crystal chirality ranging from 0.0° to 90.0° using the Boltzmann transport equation (BTE) associated with the first-principles calculations. It was found that in the phosphorene sheets, the intrinsic thermal conductivity is a smooth monotonic decreasing function of the crystal chirality, which exhibits sinusoidal behavior bounded by the two terminated values 48.9 (0.0°) and 27.8 (90.0°) W m-1 K-1. The optical modes have unusually large contributions to heat transfer, which account for almost 30% of the total thermal conductivity of phosphorene sheets. This is because the optical phonons have comparable group velocities and relaxation times to the acoustic phonons.
Anisotropic thermal transport in phosphorene: effects of crystal orientation.
Liu, Te-Huan; Chang, Chien-Cheng
2015-06-28
As an intrinsic thermally anisotropic material, the thermal properties of phosphorene must vary with respect to the crystal chirality. Nevertheless, previous studies of heat transfer in phosphorene have been limited to the 0.0° (zigzag, ZZ) and 90.0° (armchair, AC) chiralities. In this study, we investigate the orientation-dependent thermal transport in phosphorene sheets with a complete set of crystal chirality ranging from 0.0° to 90.0° using the Boltzmann transport equation (BTE) associated with the first-principles calculations. It was found that in the phosphorene sheets, the intrinsic thermal conductivity is a smooth monotonic decreasing function of the crystal chirality, which exhibits sinusoidal behavior bounded by the two terminated values 48.9 (0.0°) and 27.8 (90.0°) W m(-1) K(-1). The optical modes have unusually large contributions to heat transfer, which account for almost 30% of the total thermal conductivity of phosphorene sheets. This is because the optical phonons have comparable group velocities and relaxation times to the acoustic phonons. PMID:26024364
Investigation of anisotropic thermal transport in cross-linked polymers
NASA Astrophysics Data System (ADS)
Simavilla, David Nieto
Thermal transport in lightly cross-linked polyisoprene and polybutadine subjected to uniaxial elongation is investigated experimentally. We employ two experimental techniques to assess the effect that deformation has on this class of materials. The first technique, which is based on Forced Rayleigh Scattering (FRS), allows us to measure the two independent components of the thermal diffusivity tensor as a function of deformation. These measurements along with independent measurements of the tensile stress and birefringence are used to evaluate the stress-thermal and stress-optic rules. The stress-thermal rule is found to be valid for the entire range of elongations applied. In contrast, the stress-optic rule fails for moderate to large stretch ratios. This suggests that the degree of anisotropy in thermal conductivity depends on both orientation and tension in polymer chain segments. The second technique, which is based on infrared thermography (IRT), allows us to measure anisotropy in thermal conductivity and strain induced changes in heat capacity. We validate this method measurements of anisotropic thermal conductivity by comparing them with those obtained using FRS. We find excellent agreement between the two techniques. Uncertainty in the infrared thermography method measurements is estimated to be about 2-5 %. The accuracy of the method and its potential application to non-transparent materials makes it a good alternative to extend current research on anisotropic thermal transport in polymeric materials. A second IRT application allows us to investigate the dependence of heat capacity on deformation. We find that heat capacity increases with stretch ratio in polyisoprene specimens under uniaxial extension. The deviation from the equilibrium value of heat capacity is consistent with an independent set of experiments comparing anisotropy in thermal diffusivity and conductivity employing FRS and IRT techniques. We identify finite extensibility and strain-induced crystallization as the possible causes explaining our observations and evaluate their contribution making use of classical rubber elasticity results. Finally, we study of the role of evaporation-induced thermal effects in the well-know phenomena of the tears of wine. We develop a transport model and support its predictions by experimentally measuring the temperature gradient present in wine and cognac films using IRT. Our results demonstrate that the Marangoni flow responsible for wine tears results from both composition and temperature gradients, whose relative contribution strongly depends on the thermodynamic properties of ethanol-water mixtures. The methods developed here can be used to obtain a deeper understanding of Marangoni flows, which are ubiquitous in nature and modern technology.
Optical properties of anisotropic exciton: Hyperspherical theory
NASA Astrophysics Data System (ADS)
Muljarov, E. A.; Yablonskii, A. L.; Tikhodeev, S. G.; Bulatov, A. E.; Birman, Joseph L.
1999-02-01
A perturbation Brillouin-Wigner approach to anisotropic exciton problem, based on a hyperspherical formalism, is developed. The binding energies and oscillator strengths of elongated as well as flattened excitons are calculated numerically. It is shown that with an increase of the anisotropy degree the oscillator strengths are markedly redistributing between optically active and formerly inactive states, making the latter optically active.
Anisotropic magnetization and transport properties of RAgSb{sub 2} (R=Y, La-Nd, Sm, Gd-Tm)
Myers, Kenneth D.
1999-11-08
This study of the RAgSb{sub 2} series of compounds arose as part of an investigation of rare earth intermetallic compounds containing antimony with the rare earth in a position with tetragonal point symmetry. Materials with the rare earth in a position with tetragonal point symmetry frequently manifest strong anisotropies and rich complexity in the magnetic properties, and yet are simple enough to analyze. Antimony containing intermetallic compounds commonly possess low carrier densities and have only recently been the subject of study. Large single grain crystals were grown of the RAgSb{sub 2} (R=Y, La-Nd, Sm, Gd-Tm) series of compounds out of a high temperature solution. This method of crystal growth, commonly known as flux growth is a versatile method which takes advantage of the decreasing solubility of the target compound with decreasing temperature. Overall, the results of the crystal growth were impressive with the synthesis of single crystals of LaAgSb{sub 2} approaching one gram. However, the sample yield diminishes as the rare earth elements become smaller and heavier. Consequently, no crystals could be grown with R=Yb or Lu. Furthermore, EuAgSb{sub 2} could not be synthesized, likely due to the divalency of the Eu ion. For most of the RAgSb{sub 2} compounds, strong magnetic anisotropies are created by the crystal electric field splitting of the Hund's rule ground state. This splitting confines the local moments to lie in the basal plane (easy plane) for the majority of the members of the series. Exceptions to this include ErAgSb{sub 2} and TmAgSb{sub 2}, which have moments along the c-axis (easy axis) and CeAgSb{sub 2}, which at intermediate temperatures has an easy plane, but exchange coupling at low temperatures is anisotropic with an easy axis. Additional anisotropy is also observed within the basal plane of DyAgSb{sub 2}, where the moments are restricted to align along one of the {l_angle}110{r_angle} axes. Most of the RAgSb{sub 2} compounds containing magnetic rare earths, antiferromagnetically ordered at low temperatures. The ordering temperatures of these compounds are approximately proportional to the de Gennes factor, which suggests that the RKKY interaction is the dominant exchange interaction between local moments. Although metamagnetic transitions were observed in many members of the series, the series of sharp step-like transitions in DyAgSb{sub 2} are impressive. In this compound, up to 11 different magnetic states are stable depending on the magnitude and direction of the applied field. The saturated magnetization of these states and the critical fields needed to induce a phase transition vary with the direction of the applied field. Through detailed study of the angular dependence of the magnetization and critical fields, the net distribution of magnetic moments was determined for most, of the metamagnetic states. In DyAgSb{sub 2}, the crystal electric field (CEF) splitting of the Hund's rule ground state creates a strong anisotropy where the local Dy{sup 3+} magnetic moments are constrained to one of the equivalent {l_angle}110{r_angle} directions within the basal plane. The four position clock model was introduced to account for this rich metamagnetic system. Within this model, the magnetic moments are constrained to one of four equivalent orientations within the basal plane and interactions are calculated for up third nearest neighbors. The theoretical phase diagram, generated from the coupling constants is in excellent agreement with the experimental phase diagram. Further investigation of this compound using magnetic X-ray or neutron diffraction would be extremely useful to verify the net distributions of moments and determine the wave vectors of each of the ordered states.
Effective Dirac Hamiltonian for anisotropic honeycomb lattices: Optical properties
NASA Astrophysics Data System (ADS)
Oliva-Leyva, M.; Naumis, Gerardo G.
2016-01-01
We derive the low-energy Hamiltonian for a honeycomb lattice with anisotropy in the hopping parameters. Taking the reported Dirac Hamiltonian for the anisotropic honeycomb lattice, we obtain its optical conductivity tensor and its transmittance for normal incidence of linearly polarized light. Also, we characterize its dichroic character due to the anisotropic optical absorption. As an application of our general findings, which reproduce the previous case of uniformly strained graphene, we study the optical properties of graphene under a nonmechanical distortion.
Theory for propulsion and transport in an anisotropic fluid
NASA Astrophysics Data System (ADS)
Powers, Thomas; Krieger, Madison; Spagnolie, Saverio
2013-11-01
Swimming microorganisms are typically found in complex fluids, which are full of polymers. When these polymers align, the fluid becomes anisotropic. We seek to understand how anisotropy affects swimming when the stroke is prescribed. We model the anisotropic fluid with a nematic liquid crystal. The swimmer is a two-dimensional sheet deforming via propagating transverse or longitudinal waves. We find that the nature of anchoring conditions for the nematic degrees of freedom plays a critical role in determining the swimming speed. Furthermore, we study the fluid transport induced by the swimmers motion by calculating the flux of fluid in the laboratory frame. Finally, we elucidate the various limits of the nematic theory, such as the six-fold symmetric hexatic case and Ericksen's transversely isotropic fluid.
The anisotropic properties of high temperature superconductors - an ARPES study
NASA Astrophysics Data System (ADS)
Kaminski, Adam; Fretwell, Helen; Mesot, Joel; Rozenkrantz, Stephan; Djendjinovic, Marin; Campuzano, Juan; Randeria, Mohit; Norman, Michael; Sato, Takafumi; Takahashi, Takashi; Kadowaki, Kazuo; Hinks, David; Raffy, Helen
2001-03-01
It is now well established that cuprates are d-wave superconductors. Natural question arises concerning the symmetry of other electronic properties in these materials and their relation to anisotropic order parameter. We present our recent ARPES measurements of these properties performed on a the same sample of single cristal BISCO 2212.
Anisotropic Tribological Properties of Silicon Carbide
NASA Technical Reports Server (NTRS)
Miyoshi, K.; Buckley, D. H.
1980-01-01
The anisotropic friction, deformation and fracture behavior of single crystal silicon carbide surfaces were investigated in two categories. The categories were called adhesive and abrasive wear processes, respectively. In the adhesive wear process, the adhesion, friction and wear of silicon carbide were markedly dependent on crystallographic orientation. The force to reestablish the shearing fracture of adhesive bond at the interface between silicon carbide and metal was the lowest in the preferred orientation of silicon carbide slip system. The fracturing of silicon carbide occurred near the adhesive bond to metal and it was due to primary cleavages of both prismatic (10(-1)0) and basal (0001) planes.
Anisotropic properties of spin avalanches in crystals of nanomagnets
NASA Astrophysics Data System (ADS)
Dion, C. M.; Jukimenko, O.; Modestov, M.; Marklund, M.; Bychkov, V.
2013-01-01
Anisotropy effects for spin avalanches in crystals of nanomagnets are studied theoretically with the external magnetic field applied at an arbitrary angle to the easy axis. Starting with the Hamiltonian for a single nanomagnet in the crystal, two essential quantities characterizing spin avalanches are calculated: the activation and Zeeman energies. The calculation is performed numerically for a wide range of angles and analytical formulas are derived within the limit of small angles. The anisotropic properties of a single nanomagnet lead to anisotropic behavior of the magnetic deflagration speed. Modifications of the magnetic deflagration speed are investigated for different angles between the external magnetic field and the easy axis of the crystals. Anisotropic properties of magnetic detonation are also studied, which concern, first of all, the temperature behind the leading shock and the characteristic time of spin switching in the detonation.
NASA Astrophysics Data System (ADS)
Wei, En-Bo; Gu, Guo-Qing; Poon, Ying-Ming; Franklin, G. Shin
2010-02-01
Transformation field method (TFM) is developed to estimate the anisotropic dielectric properties of crystal composites having arbitrary shapes and dielectric properties of crystal inclusions, whose principal dielectric axis are different from those of anisotropic crystal matrix. The complicated boundary-value problem caused by inclusion shapes is circumvented by introducing a transformation electric field into the crystal composites regions, and the effective anisotropic dielectric responses are formulated in terms of the transformation field. Furthermore, the numerical results show that the effective anisotropic dielectric responses of crystal composites periodically vary as a function of the rotating angle between the principal dielectric axes of inclusion and matrix crystal materials. It is found that at larger inclusion volume fraction the inclusion shapes induce profound effect on the effective anisotropic dielectric responses.
Oxygen-driven anisotropic transport in ultra-thin manganite films
Wang, Baomin; You, Lu; Ren, Peng; Yin, Xinmao; Peng, Yuan; Xia, Bin; Wang, Lan; Yu, Xiaojiang; Mui Poh, Sock; Yang, Ping; Yuan, Guoliang; Chen, Lang; Rusydi, Andrivo; Wang, Junling
2013-01-01
Transition metal oxides have a range of unique properties due to coupling of charge, spin, orbital and lattice degrees of freedom and nearly degenerate multiple ground states. These properties make them interesting for applications and for fundamental investigations. Here we report a new phase with abnormal transport anisotropy in La0.7Sr0.3MnO3 ultra-thin films under large tensile strain. This anisotropy is absent in films under smaller tensile strain or compressive strain. Furthermore, thickness and magnetic-field-dependent experiments suggest that the tensile-strain-induced two-dimensional character is crucial for the observed phenomena. X-ray absorption spectroscopy results indicate that this anisotropy is likely driven by O 2p orbital, which hybridizes with Mn 3d. Ab initio calculations confirm this result. Our results may help to understand the anisotropic transport behaviour observed in other systems. PMID:24219875
Anisotropic spin transport in (110) GaAs quantum wells.
Couto, O D D; Iikawa, F; Rudolph, J; Hey, R; Santos, P V
2007-01-19
Mobile piezoelectric potentials are used to coherently transport electron spins in GaAs (110) quantum wells (QW) over distances exceeding 60 microm. We demonstrate that the dynamics of mobile spins under external magnetic fields depends on the direction of motion in the QW plane. This transport anisotropy is an intrinsic property of moving spins associated with the bulk inversion asymmetry of the underlying GaAs lattice. PMID:17358707
Elastic properties of anisotropic domain wall lattices
Battye, Richard A.; Moss, Adam; Chachoua, Elie
2006-06-15
Interest in the elastic properties of regular lattices constructed from domain walls has recently been motivated by cosmological applications as solid dark energy. This work investigates the particularly simple examples of triangular, hexagonal, and square lattices in two dimensions and a variety of more complicated lattices in three dimensions which have cubic symmetry. The relevant rigidity coefficients are computed taking into account nonaffine perturbations where necessary, and these are used to evaluate the propagation velocity for any macroscopic scale perturbation mode. Using this information we assess the stability of the various configurations. It is found that triangular lattices are isotropic and stable, whereas hexagonal lattices are unstable. It is argued that the simple orthonormal cases of a square in two dimensions and the cube in three are stable, except to perturbations of infinite extent. We also find that the more complicated case of a rhombic dodecahedral lattice is stable, except to the existence of transverse modes in certain directions, whereas a lattice formed from truncated octahedra is unstable.
Anisotropic wetting properties on various shape of parallel grooved microstructure.
Tie, Lu; Guo, Zhiguang; Liu, Weimin
2015-09-01
It has been revealed experimentally that some superhydrophobic surfaces in nature, such as rice leaf, show strong anisotropic wetting behavior. In this work, based on a thermodynamic approach, the effects of profile shape of parallel grooved microstructure on free energy (FE) with its barrier (FEB) and equilibrium contact angle (ECA) with its hysteresis (CAH) for various orientations of different parallel micro texture surface have been systematically investigated in detail. The results indicated that the anisotropy of wetting properties strongly depended on the specific topographical features and wetting state. In particular, a paraboloidal profile of parallel micro-texture surface is used as an important example to theoretically establish the relationship between surface geometry and anisotropic wetting behavior for optimal design, showing that the wetting behavior of the composite state is similar to that of the non-composite state and the anisotropy will possibly be appeared with the decrease of height or intrinsic contact angle of paraboloidal profile of micro texture. PMID:25982937
Anisotropic linear elastic properties of fractal-like composites.
Carpinteri, Alberto; Cornetti, Pietro; Pugno, Nicola; Sapora, Alberto
2010-11-01
In this work, the anisotropic linear elastic properties of two-phase composite materials, made up of square inclusions embedded in a matrix, are investigated. The inclusions present a fractal hierarchical distribution and are supposed to have the same Poisson's ratio as the matrix but a different Young's modulus. The effective elastic moduli of the medium are computed at each fractal iteration by coupling a position-space renormalization-group technique with a finite element analysis. The study allows to obtain and generalize some fundamental properties of fractal composite materials. PMID:21230552
Anisotropic Radiation Transport Experiments on the OMEGA Laser
NASA Astrophysics Data System (ADS)
Hager, Jonathan; Lanier, Nick; Kline, John; Flippo, Kirk; Workman, Jonathan; Bruns, H. C.; Schneider, M.; Saculla, M.; McCarville, T.
2014-10-01
A new experimental platform is being developed at the OMEGA laser to generate an anisotropic radiation source to provide data that will challenge our implementation of Implicit Monte Carlo (IMC) radiation transport models. A low density silica aerogel foam physics package is mounted to a laser driven half-hohlraum. The x-ray drive from the hohlraum is modified by a filter and aperture to decrease the optical thickness of the foam and increase the source anisotropy, respectively. Point projection backlighting is used to measure the hydrodynamic response to the Marshak wave once it goes subsonic. The temperature of the driven foam can also be inferred using absorption spectroscopy when a titanium dopant is introduced. Experimental results using a Ti doped foam will be presented with analytic calculations and 2-D radiation hydrodynamic simulations demonstrating the impact of the source anisotropy on the measurable parameters in the foam. This work performed under the auspices of the U.S. Department of Energy by LANL under Contract DE-AC52-06NA25396.
Structural, anisotropic and electronic properties of C96 under pressure
NASA Astrophysics Data System (ADS)
Xing, Mengjiang; Li, Binhua; Yu, Zhengtao; Chen, Qi
2016-01-01
An investigation of the structural, elastic, electronic and anisotropic properties of C96 under high pressure has been calculated using first-principles calculations based on density functional theory, as implemented in the Cambridge Serial Total Energy Package code. At elevated pressures, the elastic constants and shear modulus, Young's modulus and Poisson's ratio for C96 increase with pressure increasing. The anisotropy studies of Young's modulus, shear modulus, Poisson's ratio, Zener anisotropy index, the universal elastic anisotropy index AU and hardness show that C96 exhibits a small anisotropy. The sound velocities, Debye temperature and band gap of C96 under high pressure are also calculated.
NASA Technical Reports Server (NTRS)
Biolsi, Louis; Biolsi, David
1987-01-01
The strong long-range interactions between (among) charged species require the inclusion of higher order contributions to the transport properties (viscosity, thermal conductivity, diffusion) of ionized gases than are required for neutral gases. These higher order contributions have been rewritten so that they are given in terms of universal functions which can be tabulated. Tables which provide for the rapid calculation of some higher order contributions to the transport properties of both ions and electrons are given. Some results which are useful for calculating the higher order contributions to the transport properties of mixtures of ions are also given. These results are applied to the ionic species in air at high temperatures.
The anisotropic compressive mechanical properties of the rabbit patellar tendon.
Williams, Lakiesha N; Elder, Steven H; Bouvard, J L; Horstemeyer, M F
2008-01-01
In this study, we examine the transverse and longitudinal compressive mechanical behavior of the rabbit patellar tendon. The anisotropic compressive properties are of interest, because compression occurs where the tendon attaches to bone and where the tendon wraps around bone leading to the development of fibro-cartilaginous matrices. We quantified the time dependent viscoelastic and anisotropic behavior of the tendon under compression. For both orientations, sections of patellar tendon were drawn from mature male white New Zealand rabbits in preparation for testing. The tendons were sequentially compressed to 40% strain at strain rates of 0.1, 1 and 10% strain(s) using a computer-controlled stepper motor driven device under physiological conditions. Following monotonic loading, the tendons were subjected to stress relaxation. The tendon equilibrium compressive modulus was quantified to be 19.49+/-11.46 kPa for the transverse direction and 1.11+/-0.57 kPa for the longitudinal direction. The compressive modulus at applied strain rates of 0.1, 1 and 10% strain(s) in the transverse orientation were 13.48+/-2.31, 18.24+/-4.58 and 20.90+/-8.60 kPa, respectively. The compressive modulus at applied strain rates of 0.1, 1 and 10% strain/s in the longitudinal orientation were 0.19+/-0.11, 1.27+/-1.38 and 3.26+/-3.49 kPa, respectively. The modulus values were almost significantly different for the examination of the effect of orientation on the equilibrium modulus (p=0.054). Monotonic loading of the tendon showed visual differences of the strain rate dependency; however, no significant difference was shown in the statistical analysis of the effect of strain rate on compressive modulus. The statistical analysis of the effect of orientation on compressive modulus showed a significant difference. The difference shown in the orientation analysis validated the anisotropic nature of the tendon. PMID:19065006
High field dielectric properties of anisotropic polymer-ceramic composites
Tomer, V.; Randall, C. A.
2008-10-01
Using dielectrophoretic assembly, we create anisotropic composites of BaTiO{sub 3} particles in a silicone elastomer thermoset polymer. We study a variety of electrical properties in these composites, i.e., permittivity, dielectric breakdown, and energy density as function of ceramic volume fraction and connectivity. The recoverable energy density of these electric-field-structured composites is found to be highly dependent on the anisotropy present in the system. Our results indicate that x-y-aligned composites exhibit higher breakdown strengths along with large recoverable energy densities when compared to 0-3 composites. This demonstrates that engineered anisotropy can be employed to control dielectric breakdown strengths and nonlinear conduction at high fields in heterogeneous systems. Consequently, manipulation of anisotropy in high-field dielectric properties can be exploited for the development of high energy density polymer-ceramic systems.
NASA Astrophysics Data System (ADS)
Crowgey, Benjamin Reid
Rectangular waveguide methods are appealing for measuring isotropic and anisotropic materials because of high signal strength due to field confinement, and the ability to control the polarization of the applied electric field. As a stepping stone to developing methods for characterizing materials with fully-populated anisotropic tensor characteristics, techniques are presented in this dissertation to characterize isotropic, biaxially anisotropic, and gyromagnetic materials. Two characterization techniques are investigated for each material, and thus six different techniques are described. Additionally, a waveguide standard is introduced which may be used to validate the measurement of the permittivity and permeability of materials at microwave frequencies. The first characterization method examined is the Nicolson-Ross-Weir (NRW) technique for the extraction of isotropic parameters of a sample completely filling the cross-section of a rectangular waveguide. A second technique is proposed for the characterization of an isotropic conductor-backed sample filling the cross-section of a waveguide. If the sample is conductor-backed, and occupies the entire cross-section, a transmission measurement is not available, and thus a method must be found for providing two sufficiently different reflection measurements.The technique proposed here is to place a waveguide iris in front of the sample, exposing the sample to a spectrum of evanescent modes. By measuring the reflection coefficient with and without an iris, the necessary two data may be obtained to determine the material parameters. A mode-matching approach is used to determine the theoretical response of a sample placed behind the waveguide iris. This response is used in a root-searching algorithm to determine permittivity and permeability by comparing to measurements of the reflection coefficient. For the characterization of biaxially anisotropic materials, the first method considers an extension of the NRW technique for characterization of a sample filling the cross-section of a waveguide. Due to the rectangular nature of the waveguide, typically three different samples are manufactured from the same material in order to characterize the six complex material parameters. The second technique for measuring the electromagnetic properties of a biaxially anisotropic material sample uses a reduced-aperture waveguide sample holder designed to accommodate a cubical sample. All the tensor material parameters can then be determined by measuring the reflection and transmission coefficients of a single sample placed into several orientations. The parameters are obtained using a root-searching algorithm by comparing theoretically computed and measured reflection and transmission coefficients. The theoretical coefficients are determined using a mode matching technique. The first technique for characterizing the electromagnetic properties of gyromagnetic materials considers requires filling the cross-section of a waveguide. The material parameters are extracted from the measured reflection and transmission coefficients. Since the cross-sectional dimensions of waveguides become prohibitively large at low frequencies, and it is at these frequencies that the gyromagnetic properties are most pronounced, sufficiently large samples may not be available. Therefore, the second technique uses a reduced-aperture sample holder that does not require the sample to fill the entire cross section of the guide. The theoretical reflection and transmission coefficients for both methods are determined using a mode matching technique. A nonlinear least squares method is employed to extract the gyromagnetic material parameters. Finally, this dissertation introduces a waveguide standard that acts as a surrogate material with both electric and magnetic properties and is useful for verifying systems designed to characterize engineered materials using the NRW technique. A genetic algorithm is used to optimize the all-metallic structure to produce a surrogate with both relative permittivity and permeability near six across S-band, and with low sensitivity to changes in geometry to reduce the effects of fabrication errors.
Anisotropic magnetism and spin-dependent transport in Co nanoparticle embedded ZnO thin films
NASA Astrophysics Data System (ADS)
Li, D. Y.; Zeng, Y. J.; Pereira, L. M. C.; Batuk, D.; Hadermann, J.; Zhang, Y. Z.; Ye, Z. Z.; Temst, K.; Vantomme, A.; Van Bael, M. J.; Van Haesendonck, C.
2013-07-01
Oriented Co nanoparticles were obtained by Co ion implantation in crystalline ZnO thin films grown by pulsed laser deposition. Transmission electron microscopy revealed the presence of elliptically shaped Co precipitates with nanometer size, which are embedded in the ZnO thin films, resulting in anisotropic magnetic behavior. The low-temperature resistance of the Co-implanted ZnO thin films follows the Efros-Shklovskii type variable-range-hopping. Large negative magnetoresistance (MR) exceeding 10% is observed in a magnetic field of 1 T at 2.5 K and the negative MR survives up to 250 K (0.3%). The negative MR reveals hysteresis as well as anisotropy that correlate well with the magnetic properties, clearly demonstrating the presence of spin-dependent transport.
Spin-orbit interaction induced anisotropic property in interacting quantum wires
2011-01-01
We investigate theoretically the ground state and transport property of electrons in interacting quantum wires (QWs) oriented along different crystallographic directions in (001) and (110) planes in the presence of the Rashba spin-orbit interaction (RSOI) and Dresselhaus SOI (DSOI). The electron ground state can cross over different phases, e.g., spin density wave, charge density wave, singlet superconductivity, and metamagnetism, by changing the strengths of the SOIs and the crystallographic orientation of the QW. The interplay between the SOIs and Coulomb interaction leads to the anisotropic dc transport property of QW which provides us a possible way to detect the strengths of the RSOI and DSOI. PACS numbers: 73.63.Nm, 71.10.Pm, 73.23.-b, 71.70.Ej PMID:21711717
Shape-Dependent Nonlinear Optical Properties of Anisotropic Gold Nanoparticles.
Hua, Yi; Chandra, Kavita; Dam, Duncan Hieu M; Wiederrecht, Gary P; Odom, Teri W
2015-12-17
This Letter reports the shape-dependent third-order nonlinear optical properties of anisotropic gold nanoparticles. We characterized the nonlinear absorption coefficients of nanorods, nanostars, and nanoshells using femtosecond Z-scan measurements. By comparing nanoparticle solutions with a similar linear extinction at the laser excitation wavelength, we separated shape effects from that of the localized surface plasmon wavelength. We found that the nonlinear response depended on particle shape. Using pump-probe spectroscopy, we measured the ultrafast transient response of nanoparticles, which supported the strong saturable absorption observed in nanorods and weak nonlinear response in nanoshells. We found that the magnitude of saturable absorption as well as the ultrafast spectral responses of nanoparticles were affected by the linear absorption of the nanoparticles. PMID:26595327
Anisotropic Elastic Resonance Scattering model for the Neutron Transport equation
Mohamed Ouisloumen; Abderrafi M. Ougouag; Shadi Z. Ghrayeb
2014-11-24
The resonance scattering transfer cross-section has been reformulated to account for anisotropic scattering in the center-of-mass of the neutron-nucleus system. The main innovation over previous implementations is the relaxation of the ubiquitous assumption of isotropic scattering in the center-of-mass and the actual effective use of scattering angle distributions from evaluated nuclear data files in the computation of the angular moments of the resonant scattering kernels. The formulas for the high order anisotropic moments in the laboratory system are also derived. A multi-group numerical formulation is derived and implemented into a module incorporated within the NJOY nuclear data processing code. An ultra-fine energy mesh cross section library was generated using these new theoretical models and then was used for fuel assembly calculations with the PARAGON lattice physics code. The results obtained indicate a strong effect of this new model on reactivity, multi-group fluxes and isotopic inventory during depletion.
The Control of Anisotropic Transport in Manganites by Stripy Domains
NASA Astrophysics Data System (ADS)
Ju, Changcheng; Lu, Xiaomei; Chu, Yinghao
2014-03-01
Epitaxial thin film acts as a significant tool to investigate novel phenomena of complex oxide systems. Extrinsic constraint1 of uniform or certain designed buffer layer strain could be easily implanted to these materials. However, the strain distribution might be quite complicated by involving micro- or nano-lattice distortions which could partially relax the strain and determine the complex phase diagrams of thin film, meanwhile introducing structural and physical inhomogeneities. In this work , we report 71° striped ferroelectric domains created in BFO can also epitaxially lock the perovskite manganites leading to the emerge of ordered structural domain. LSMO/BFO hetero-epitaxial samples are deposited by PLD. The 71° periodic striped domains and coherent growth are demonstrated by PFM and X-ray analysis. Plan-view TEM and X-ray RSM have been used to confirm the epitaxial relationships of the functional layers and IP lattice constant. Both the simulation and structural analysis demonstrate we can create a periodic ordered stripe structural domain in LSMO. And this will leave an anisotropic distribution of structural domain walls which makes it possible to capture the anisotropic tunneling for strong electron-lattice coupling in manganites. Temperature-dependent resistivity measurements reveal a substantial anisotropic resistivities and a remarkable shift of the MI transition between the perpendicular and parallel to the stripe domain directions.
Tan, Jinwang; Tartakovsky, Alexandre M.; Ferris, Kim F.; Ryan, Emily M.
2016-01-01
Dendrite formation on the electrode surface of high energy density lithium (Li) batteries causes safety problems and limits their applications. Suppressing dendrite growth could significantly improve Li battery performance. Dendrite growth and morphology is a function of the mixing in the electrolyte near the anode interface. Most research into dendrites in batteries focuses on dendrite formation in isotropic electrolytes (i.e., electrolytes with isotropic diffusion coefficient). In this work, an anisotropic diffusion reaction model is developed to study the anisotropic mixing effect on dendrite growth in Li batteries. The model uses a Lagrangian particle-based method to model dendrite growth in an anisotropic electrolyte solution. The model is verified by comparing the numerical simulation results with analytical solutions, and its accuracy is shown to be better than previous particle-based anisotropic diffusion models. Several parametric studies of dendrite growth in an anisotropic electrolyte are performed and the results demonstrate the effects of anisotropic transport on dendrite growth and morphology, and show the possible advantages of anisotropic electrolytes for dendrite suppression.
Blazevski, Daniel; del-Castillo-Negrete, Diego
2013-06-01
A study of anisotropic heat transport in reversed shear (nonmonotonic q-profile) magnetic fields is presented. The approach is based on a recently proposed Lagrangian-Green's function method that allows an efficient and accurate integration of the parallel (i.e., along the magnetic field) heat transport equation. The magnetic field lines are described by a nontwist Hamiltonian system, known to exhibit separatrix reconnection and robust shearless (dq/dr=0) transport barriers. The changes in the magnetic field topology due to separatrix reconnection lead to bifurcations in the equilibrium temperature distribution. For perturbations of moderate amplitudes, magnetic chaos is restricted to bands flanking the shearless region. As a result, the temperature flattens in the chaotic bands and develops a very sharp radial gradient at the shearless region. For perturbations with larger amplitude, shearless Cantori (i.e., critical magnetic surfaces located at the minimum of the q profile) give rise to anomalous temperature relaxation involving widely different time scales. The first stage consists of the relatively fast flattening of the radial temperature profile in the chaotic bands with negligible flux across the shearless region that, for practical purposes, on a short time scale acts as an effective transport barrier despite the lack of magnetic flux surfaces. In the long-time scale, heat starts to flow across the shearless region, albeit at a comparatively low rate. The transport of a narrow temperature pulse centered at the reversed shear region exhibits weak self-similar scaling with non-Gaussian scaling functions indicating that transport at this scale cannot be modeled as a diffusive process with a constant diffusivity. Evidence of nonlocal effective radial transport is provided by the existence of regionsÂ with nonzero heat flux and zero temperature gradient. Parametric flux-gradient plots exhibit multivalued loops that question the applicability of the Fourier-Fick's prescription even in the presence of a finite pinch velocity. PMID:23848788
Nanostructured SnS with inherent anisotropic optical properties for high photoactivity
NASA Astrophysics Data System (ADS)
Patel, Malkeshkumar; Chavda, Arvind; Mukhopadhyay, Indrajit; Kim, Joondong; Ray, Abhijit
2016-01-01
In view of the worldwide energy challenge in the 21st century, the technology of semiconductor-based photoelectrochemical (PEC) water splitting has received considerable attention as an alternative approach for solar energy harvesting and storage. Two-dimensional (2D) structures such as nanosheets have the potential to tap the solar energy by unlocking the functional properties at the nanoscale. Tin(ii) sulfide is a fascinating solar energy material due to its anisotropic material properties. In this manuscript, we report on exploiting the 2D structure modulated optical properties of nanocrystalline SnS thin film synthesized by chemical spray pyrolysis using ambient transport in the harvesting of solar energy. We obtained the nanostructured SnS with well-preserved dimensions and morphologies with one step processing. The work demonstrates that the intrinsically ordered SnS nanostructure on FTO coated glass can tap the incident radiation in an efficient manner. The structure-property relationship to explain the photo-response in nanocrystalline-SnS is verified experimentally and theoretically. The novel design scheme for antireflection coating along with the anisotropic properties of SnS is conceived for realizing a PEC cell. The developed PEC cell consists of a SnS photoanode which shows considerably high photocurrent density of 7 mA cm-2 with aqueous media under AM 1.5G, 100 mW cm-2 exposure with notably stable operation. Electrochemical impedance spectroscopy revealed that a non-ideal capacitive behavior as well as drift assisted transport across the solid-state interface is responsible for such a high photo-current density in the nanocrystalline-SnS photoanode.In view of the worldwide energy challenge in the 21st century, the technology of semiconductor-based photoelectrochemical (PEC) water splitting has received considerable attention as an alternative approach for solar energy harvesting and storage. Two-dimensional (2D) structures such as nanosheets have the potential to tap the solar energy by unlocking the functional properties at the nanoscale. Tin(ii) sulfide is a fascinating solar energy material due to its anisotropic material properties. In this manuscript, we report on exploiting the 2D structure modulated optical properties of nanocrystalline SnS thin film synthesized by chemical spray pyrolysis using ambient transport in the harvesting of solar energy. We obtained the nanostructured SnS with well-preserved dimensions and morphologies with one step processing. The work demonstrates that the intrinsically ordered SnS nanostructure on FTO coated glass can tap the incident radiation in an efficient manner. The structure-property relationship to explain the photo-response in nanocrystalline-SnS is verified experimentally and theoretically. The novel design scheme for antireflection coating along with the anisotropic properties of SnS is conceived for realizing a PEC cell. The developed PEC cell consists of a SnS photoanode which shows considerably high photocurrent density of 7 mA cm-2 with aqueous media under AM 1.5G, 100 mW cm-2 exposure with notably stable operation. Electrochemical impedance spectroscopy revealed that a non-ideal capacitive behavior as well as drift assisted transport across the solid-state interface is responsible for such a high photo-current density in the nanocrystalline-SnS photoanode. Electronic supplementary information (ESI) available. See DOI: 10.1039/C5NR06731F
Nanostructured SnS with inherent anisotropic optical properties for high photoactivity.
Patel, Malkeshkumar; Chavda, Arvind; Mukhopadhyay, Indrajit; Kim, Joondong; Ray, Abhijit
2016-01-21
In view of the worldwide energy challenge in the 21(st) century, the technology of semiconductor-based photoelectrochemical (PEC) water splitting has received considerable attention as an alternative approach for solar energy harvesting and storage. Two-dimensional (2D) structures such as nanosheets have the potential to tap the solar energy by unlocking the functional properties at the nanoscale. Tin(ii) sulfide is a fascinating solar energy material due to its anisotropic material properties. In this manuscript, we report on exploiting the 2D structure modulated optical properties of nanocrystalline SnS thin film synthesized by chemical spray pyrolysis using ambient transport in the harvesting of solar energy. We obtained the nanostructured SnS with well-preserved dimensions and morphologies with one step processing. The work demonstrates that the intrinsically ordered SnS nanostructure on FTO coated glass can tap the incident radiation in an efficient manner. The structure-property relationship to explain the photo-response in nanocrystalline-SnS is verified experimentally and theoretically. The novel design scheme for antireflection coating along with the anisotropic properties of SnS is conceived for realizing a PEC cell. The developed PEC cell consists of a SnS photoanode which shows considerably high photocurrent density of 7 mA cm(-2) with aqueous media under AM 1.5G, 100 mW cm(-2) exposure with notably stable operation. Electrochemical impedance spectroscopy revealed that a non-ideal capacitive behavior as well as drift assisted transport across the solid-state interface is responsible for such a high photo-current density in the nanocrystalline-SnS photoanode. PMID:26745636
Anisotropic vanadium dioxide sculptured thin films with superior thermochromic properties
Sun, Yaoming; Xiao, Xiudi; Xu, Gang; Dong, Guoping; Chai, Guanqi; Zhang, Hua; Liu, Pengyi; Zhu, Hanmin; Zhan, Yongjun
2013-01-01
VO2 (M) STF through reduction of V2O5 STF was prepared. The results illustrate that V2O5 STF can be successfully obtained by oblique angle thermal evaporation technique. After annealing at 550Â°C/3â€…min, the V2O5 STF deposited at 85Â° can be easily transformed into VO2 STF with slanted columnar structure and superior thermochromic properties. After deposition SiO2 antireflective layer, Tlum of VO2 STF is enhanced 26% and Î”Tsol increases 60% compared with that of normal VO2 thin films. Due to the anisotropic microstructure of VO2 STF, angular selectivity transmission of VO2 STF is observed and the solar modulation ability is further improved from 7.2% to 8.7% when light is along columnar direction. Moreover, the phase transition temperature of VO2 STF can be depressed into 54.5Â°C without doping. Considering the oblique incidence of sunlight on windows, VO2 STF is more beneficial for practical application as smart windows compared with normal homogenous VO2 thin films. PMID:24067743
Anisotropic properties of the enamel organic extracellular matrix.
do Espírito Santo, Alexandre R; Novaes, Pedro D; Line, Sérgio R P
2006-05-01
Enamel biosynthesis is initiated by the secretion, processing, and self-assembly of a complex mixture of proteins. This supramolecular ensemble controls the nucleation of the crystalline mineral phase. The detection of anisotropic properties by polarizing microscopy has been extensively used to detect macromolecular organizations in ordinary histological sections. The aim of this work was to study the birefringence of enamel organic matrix during the development of rat molar and incisor teeth. Incisor and molar teeth of rats were fixed in 2% paraformaldehyde/0.5% glutaraldehyde in 0.2 M phosphate-buffered saline (PBS), pH 7.2, and decalcified in 5% nitric acid/4% formaldehyde. After paraffin embedding, 5-microm-thick sections were obtained, treated with xylene, and hydrated. Form birefringence curves were obtained after measuring optical retardations in imbibing media, with different refractive indices. Our observations showed that enamel organic matrix of rat incisor and molar teeth is strongly birefringent, presenting an ordered supramolecular structure. The birefringence starts during the early secretion phase and disappears at the maturation phase. The analysis of enamel organic matrix birefringence may be used to detect the effects of genetic and environmental factors on the supramolecular orientation of enamel matrix and their effects on the structure of mature enamel. PMID:16674708
Probing Anisotropic Surface Properties of Molybdenite by Direct Force Measurements.
Lu, Zhenzhen; Liu, Qingxia; Xu, Zhenghe; Zeng, Hongbo
2015-10-27
Probing anisotropic surface properties of layer-type mineral is fundamentally important in understanding its surface charge and wettability for a variety of applications. In this study, the surface properties of the face and the edge surfaces of natural molybdenite (MoS2) were investigated by direct surface force measurements using atomic force microscope (AFM). The interaction forces between the AFM tip (Si3N4) and face or edge surface of molybdenite were measured in 10 mM NaCl solutions at various pHs. The force profiles were well-fitted with classical DLVO (Derjaguin-Landau-Verwey-Overbeek) theory to determine the surface potentials of the face and the edge surfaces of molybdenite. The surface potentials of both the face and edge surfaces become more negative with increasing pH. At neutral and alkaline conditions, the edge surface exhibits more negative surface potential than the face surface, which is possibly due to molybdate and hydromolybdate ions on the edge surface. The point of zero charge (PZC) of the edge surface was determined around pH 3 while PZC of the face surface was not observed in the range of pH 3-11. The interaction forces between octadecyltrichlorosilane-treated AFM tip (OTS-tip) and face or edge surface of molybdenite were also measured at various pHs to study the wettability of molybdenite surfaces. An attractive force between the OTS-tip and the face surface was detected. The force profiles were well-fitted by considering DLVO forces and additional hydrophobic force. Our results suggest the hydrophobic feature of the face surface of molybdenite. In contrast, no attractive force between the OTS-tip and the edge surface was detected. This is the first study in directly measuring surface charge and wettability of the pristine face and edge surfaces of molybdenite through surface force measurements. PMID:26434695
Spatial frequency analysis of anisotropic drug transport in tumor samples
NASA Astrophysics Data System (ADS)
Russell, Stewart; Samkoe, Kimberley S.; Gunn, Jason R.; Hoopes, P. Jack; Nguyen, Thienan A.; Russell, Milo J.; Alfano, Robert R.; Pogue, Brian W.
2014-01-01
Directional Fourier spatial frequency analysis was used on standard histological sections to identify salient directional bias in the spatial frequencies of stromal and epithelial patterns within tumor tissue. This directional bias is shown to be correlated to the pathway of reduced fluorescent tracer transport. Optical images of tumor specimens contain a complex distribution of randomly oriented aperiodic features used for neoplastic grading that varies with tumor type, size, and morphology. The internal organization of these patterns in frequency space is shown to provide a precise fingerprint of the extracellular matrix complexity, which is well known to be related to the movement of drugs and nanoparticles into the parenchyma, thereby identifying the characteristic spatial frequencies of regions that inhibit drug transport. The innovative computational methodology and tissue validation techniques presented here provide a tool for future investigation of drug and particle transport in tumor tissues, and could potentially be used a priori to identify barriers to transport, and to analyze real-time monitoring of transport with respect to therapeutic intervention.
Enhanced charge transport kinetics in anisotropic, stratified photoanodes.
Yazdani, Nuri; Bozyigit, Deniz; Utke, Ivo; Buchheim, Jakob; Youn, Seul Ki; Patscheider, Jörg; Wood, Vanessa; Park, Hyung Gyu
2014-02-12
The kinetics of charge transport in mesoporous photoanodes strongly constrains the design and power conversion efficiencies of dye sensitized solar cells (DSSCs). Here, we report a stratified photoanode design with enhanced kinetics achieved through the incorporation of a fast charge transport intermediary between the titania and charge collector. Proof of concept photoanodes demonstrate that the inclusion of the intermediary not only enhances effective diffusion coefficients but also significantly suppresses charge recombination, leading to diffusion lengths two orders of magnitude greater than in standard mesoporous titania photoanodes. The intermediary concept holds promise for higher-efficiency DSSCs. PMID:24467298
Probing anisotropic heat transport using time-domain thermoreflectance with offset laser spots
NASA Astrophysics Data System (ADS)
Feser, Joseph P.; Cahill, David G.
2012-10-01
An analytic solution is derived for the time-domain thermoreflectance signal that occurs using non-concentric pump and probe beams on multilayer anisotropic materials. When in-plane heat transport is negligible, the experimental signal is the same as for the concentric case. However, for samples where in-plane heat diffusion distances are comparable to the spot size, the signal is sensitive to in-plane heat transport. This sensitivity to in-plane transport can be exploited to measure the in-plane thermal conductivity. Examples with experimental data are given for thin-film Al and the in-plane thermal conductivity of pyrolytic graphite.
Anisotropic heat transport in integrable and chaotic 3-D magnetic fields
Del-Castillo-Negrete, Diego B; Blazevski, D.; Chacon, Luis
2012-01-01
A study of anisotropic heat transport in 3-D chaotic magnetic fields is presented. The approach is based on the recently proposed Lagrangian-Green s function (LG) method in Ref. [1] that allows an efficient and accurate integration of the parallel transport equation applicable to general magnetic fields with local or non-local parallel flux closures. We focus on reversed shear magnetic field configurations known to exhibit separatrix reconnection and shearless transport barriers. The role of reconnection and magnetic field line chaos on temperature transport is studied. Numerical results are presented on the anomalous relaxation of radial temperature gradients in the presence of shearless Cantori partial barri- ers. Also, numerical evidence of non-local effective radial temperature transport in chaotic fields is presented. Going beyond purely parallel transport, the LG method is generalized to include finite perpendicular diffusivity, and the problem of temperature flattening inside a magnetic island is studied.
Anisotropic Pressure, Transport, and Shielding of Magnetic Perturbations
H.E. Mynick and A.H. Boozer
2008-05-23
We compute the effect on a tokamak of applying a nonaxisymmetric magnetic perturbation Î´Î’. An equilibrium with scalar pressure p yields zero net radial current, and therefore zero torque. Thus, the usual approach, which assumes scalar pressure, is not self-consistent, and masks the close connection which exists between that radial current and the in-surface currents, which provide shielding or amplification of Î´Î’. Here, we analytically compute the pressure anisoptropy, anisoptropy, pll, pâŠ¥ â‰ p, and from this, both the radial and in-surface currents. The surface-average of the radial current recovers earlier expressions for ripple transport, while the in-surface currents provide an expression for the amount of self-consistent shielding the plasma provides.
An Algorithm for the Transport of Anisotropic Neutrons
NASA Technical Reports Server (NTRS)
Tweed, J.
2005-01-01
One major obstacle to human space exploration is the possible limitations imposed by the adverse effect of long-term exposure to the space environment. Even before human spaceflight began, the potentially brief exposure of astronauts to the very intense random solar particle events (SPE) were of great concern. A new challenge appears in deep space exploration from exposure to the low-intensity heavy-ion flux of the galactic cosmic rays (GCR) since the missions are of long duration and the accumulated GCR exposures can be high. Because cancer induction rates increase behind low to rather large thicknesses of aluminum shielding, according to available biological data on mammalian exposures to GCR like ions, the shield requirements for a Mars mission are prohibitively expensive in terms of mission launch costs. Therefore, a critical issue in the Human Exploration and Development of Space enterprise is cost effective mitigation of risk associated with ionizing radiation exposure. In order to estimate astronaut risk to GCR exposure and associated cancer risks and health hazards, it is necessary to do shield material studies. To determine an optimum radiation shield material it is necessary to understand nuclear interaction processes such as fragmentation and secondary particle production which is a function of energy dependent cross sections. This requires knowledge of material transmission characteristics either through laboratory testing or improved theoretical modeling. Here ion beam transport theory is of importance in that testing of materials in the laboratory environment generated by particle accelerators is a necessary step in materials development and evaluation for space use. The approximations used in solving the Boltzmann transport equation for the space setting are often not sufficient for laboratory work and those issues are a major emphasis of the present work.
Sofer, Zden?k; Sedmidubský, David; Huber, Št?pán; Luxa, Jan; Bouša, Daniel; Boothroyd, Chris; Pumera, Martin
2016-03-01
Layered elemental materials, such as black phosphorus, exhibit unique properties originating from their highly anisotropic layered structure. The results presented herein demonstrate an anomalous anisotropy for the electrical, magnetic, and electrochemical properties of black phosphorus. It is shown that heterogeneous electron transfer from black phosphorus to outer- and inner-sphere molecular probes is highly anisotropic. The electron-transfer rates differ at the basal and edge planes. These unusual properties were interpreted by means of calculations, manifesting the metallic character of the edge planes as compared to the semiconducting properties of the basal plane. This indicates that black phosphorus belongs to a group of materials known as topological insulators. Consequently, these effects render the magnetic properties highly anisotropic, as both diamagnetic and paramagnetic behavior can be observed depending on the orientation in the magnetic field. PMID:26822395
Zhang, Rujing; Chen, Qiao; Zhen, Zhen; Jiang, Xin; Zhong, Minlin; Zhu, Hongwei
2015-09-01
Assembling particular building blocks into composites with diverse targeted structures has attracted considerable interest for understanding its new properties and expanding the potential applications. Anisotropic organization is considered as a frequently used targeted architecture and possesses many peculiar properties because of its unusual shapes. Here, we show that anisotropic graphene monoliths (AGMs), three-dimensional architectures of well-aligned graphene sheets obtained by a dip-coating method using cellulose acetate fibers as templates show thermal-insulating, fire-retardant, and anisotropic properties. They exhibit a feature of higher mechanical strength and thermal/electrical conductivities in the axial direction than in the radial direction. Elastic polymer resins are then introduced into the pores of the AGMs to form conductive and flexible composites. The composites, as AGMs, retain the unique anisotropic properties, revealing opposite resistance change under compressions in different directions. The outstanding anisotropic properties of AGMs make them possible to be applied in the fields of thermal insulation, integrated circuits, and electromechanical devices. PMID:26284380
NASA Astrophysics Data System (ADS)
Zheng, J.; Zhu, J.; Wang, Z.; Fang, F.; Pain, C. C.; Xiang, J.
2015-06-01
A new anisotropic hr-adaptive mesh technique has been applied to modelling of multiscale transport phenomena, which is based on a discontinuous Galerkin/control volume discretization on unstructured meshes. Over existing air quality models typically based on static-structured grids using a locally nesting technique, the advantage of the anisotropic hr-adaptive model has the ability to adapt the mesh according to the evolving pollutant distribution and flow features. That is, the mesh resolution can be adjusted dynamically to simulate the pollutant transport process accurately and effectively. To illustrate the capability of the anisotropic adaptive unstructured mesh model, three benchmark numerical experiments have been setup for two-dimensional (2-D) transport phenomena. Comparisons have been made between the results obtained using uniform resolution meshes and anisotropic adaptive resolution meshes.
Anisotropic gold nanoparticles: synthesis, properties, applications, and toxicity.
Li, Na; Zhao, Pengxiang; Astruc, Didier
2014-02-10
Anisotropic gold nanoparticles (AuNPs) have attracted the interest of scientists for over a century, but research in this field has considerably accelerated since 2000 with the synthesis of numerous 1D, 2D, and 3D shapes as well as hollow AuNP structures. The anisotropy of these nonspherical, hollow, and nanoshell AuNP structures is the source of the plasmon absorption in the visible region as well as in the near-infrared (NIR) region. This NIR absorption is especially sensitive to the AuNP shape and medium and can be shifted towards the part of the NIR region in which living tissue shows minimum absorption. This has led to crucial applications in medical diagnostics and therapy ("theranostics"), especially with Au nanoshells, nanorods, hollow nanospheres, and nanocubes. In addition, Au nanowires (AuNWs) can be synthesized with longitudinal dimensions of several tens of micrometers and can serve as plasmon waveguides for sophisticated optical devices. The application of anisotropic AuNPs has rapidly spread to optical, biomedical, and catalytic areas. In this Review, a brief historical survey is given, followed by a summary of the synthetic modes, variety of shapes, applications, and toxicity issues of this fast-growing class of nanomaterials. PMID:24421264
Molecular anisotropic magnetoresistance
NASA Astrophysics Data System (ADS)
Otte, Fabian; Heinze, Stefan; Mokrousov, Yuriy
2015-12-01
Using density functional theory calculations, we demonstrate that the effect of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude with respect to conventional bulk ferromagnets in junctions containing molecules sandwiched between ferromagnetic leads. We study ballistic transport in metal-benzene complexes contacted by 3 d transition-metal wires. We show that a gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symmetry filtering properties of the molecules. We further discuss how this molecular anisotropic magnetoresistance (MAMR) can be tuned by the proper choice of materials and their electronic properties.
Viscous corrections to anisotropic flow and transverse momentum spectra from transport theory
NASA Astrophysics Data System (ADS)
Plumari, Salvatore; Guardo, Giovanni Luca; Greco, Vincenzo; Ollitrault, Jean-Yves
2015-09-01
Viscous hydrodynamics is commonly used to model the evolution of the matter created in an ultra-relativistic heavy-ion collision. It provides a good description of transverse momentum spectra and anisotropic flow. These observables, however, cannot be consistently derived using viscous hydrodynamics alone, because they depend on the microscopic interactions at freeze-out. We derive the ideal hydrodynamic limit and the first-order viscous correction to anisotropic flow (v2, v3 and v4) and momentum spectrum using a transport calculation. The linear response coefficient to the initial anisotropy, vn (pT) /Îµn, depends little on n in the ideal hydrodynamic limit. The viscous correction to the spectrum depends not only on the differential cross section, but also on the initial momentum distribution. This dependence is not captured by standard second-order viscous hydrodynamics. The viscous correction to anisotropic flow increases with pT, but this increase is slower than usually assumed in viscous hydrodynamic calculations. In particular, it is too slow to explain the observed maximum of vn at pT âˆ¼ 3 GeV / c.
Charged-particle Transport in Magnetic Turbulence. I. A Globally Anisotropic Field
NASA Astrophysics Data System (ADS)
Sun, P.; Jokipii, J. R.
2015-12-01
Collisionless magnetohydrodynamic Turbulence is common in large scale astrophysical environments. The determination of the transport of charged particles both parallel and perpendicular in such a system is of considerable interest. Quasi-linear analysis or direct numerical simulation can be used to find the effects of the turbulent magnetic field on the transport of charged particles. A number of different magnetic turbulence models have been proposed in the last several decades. We present here the results of studying particle transport in synthesized, anisotropic turbulence and compare the results with those obtained using the standard isotropic turbulence model in a series of papers. In this paper we consider the magnetic field turbulence model with global anisotropy.
The Isotropy Problem of Ultra-High Energy Cosmic Rays: The Effects of Anisotropic Transport
NASA Astrophysics Data System (ADS)
Kumar, Rahul; Eichler, David
2013-04-01
Time dependent anisotropic transport of ultra-high energy cosmic rays (UHECRs) from point-like sources in the Galaxy is calculated in various ways. To fully account for the discreteness of UHECR sources in space and time, the Monte Carlo method is used to randomly place sources in the Galaxy and calculate the anisotropy of UHECR flux, given specific realisations of source distribution. We show that reduction in the rate of cross-field transport reduces the anisotropy. However, if the crossfield transport is very small, drift of UHECRs in the Galactic magnetic field (GMF) becomes the dominant contributor to the anisotropy. Test particle simulations further illustrate the effect of drift and verify our analytical calculation. The surprisingly low anisotropy measured by Auger can be interpreted as intermittency of UHECR sources, without invoking a flat source distribution and/or a high source rate. Frequent events that follow star formation, such as hypernovae, imply an anisotropy that exceeds the Auger limit.
Anisotropic thermal property measurement of carbon-fiber/epoxy composite materials
NASA Astrophysics Data System (ADS)
Tian, Tian
This work originated from a need for understanding heat transfer in carbon-fiber/epoxy natural-gas tanks undergoing rapid heating during refilling. The dissertation is focused on the determination of the anisotropic thermal properties of carbon-fiber/epoxy composite materials for in-plane and through-thickness directions. An effective anisotropic parameter estimation system consisting of the 3Ï‰ experimental technique and an anisotropic two-dimensional heat transfer model is developed. In the present work, the 3Ï‰ method, an experimental technique that has been well established to evaluate the thermal properties of isotropic materials, especially thin film materials, is extended to treat the thermal properties of bulk anisotropic materials. A platinum film deposited on the sample surface is periodically heated by a sinusoidally oscillating current at frequency Ï‰, and thereby causes a time-harmonic electrical resistance variation at frequency 2Ï‰. The heat-induced resistance variation at frequency 2Ï‰ coupled with the current at frequency Ï‰ produces a voltage variation component at frequency 3Ï‰. The phase and amplitude data of the voltage signal at frequency 3Ï‰ are collected from the experiment. An impedance analysis model is employed to convert the voltage data to temperature data. The anisotropic thermal properties are deduced from an inverse parameter estimation model, which is a least-square systematic comparison between experimental data and the theoretical model. The anisotropic theoretical model is based on the Green's function approach. A careful sensitivity analysis is used to demonstrate the feasibility of simultaneous estimation of the in-plane and through-thickness thermal conductivities. Poly methyl methacrylate (PMMA) samples were applied as reference samples to verify the measurement system. The parameter estimation result for experimental data from PMMA samples agree very well with handbook values. Experimental results from carbon-fiber/epoxy samples are presented.
Chacon, Luis; del-Castillo-Negrete, Diego; Hauck, Cory D.
2014-09-01
We propose a Lagrangian numerical algorithm for a time-dependent, anisotropic temperature transport equation in magnetized plasmas in the large guide field regime. The approach is based on an analytical integral formal solution of the parallel (i.e., along the magnetic field) transport equation with sources, and it is able to accommodate both local and non-local parallel heat flux closures. The numerical implementation is based on an operator-split formulation, with two straightforward steps: a perpendicular transport step (including sources), and a Lagrangian (field-line integral) parallel transport step. Algorithmically, the first step is amenable to the use of modern iterative methods, while the second step has a fixed cost per degree of freedom (and is therefore scalable). Accuracy-wise, the approach is free from the numerical pollution introduced by the discrete parallel transport term when the perpendicular to parallel transport coefficient ratio X_{?} /X_{?} becomes arbitrarily small, and is shown to capture the correct limiting solution when ? = X?L^{2}_{?}/X1L^{2}_{?} ? 0 (with L?? L? , the parallel and perpendicular diffusion length scales, respectively). Therefore, the approach is asymptotic-preserving. We demonstrate the capabilities of the scheme with several numerical experiments with varying magnetic field complexity in two dimensions, including the case of transport across a magnetic island.
Magnetic properties of electrons confined in an anisotropic cylindrical potential
NASA Astrophysics Data System (ADS)
Nedelkoski, Zlatko; Petreska, Irina
2014-11-01
In the present paper a theoretical model, describing the effects of external electric and magnetic fields on an electron confined in an anisotropic parabolic potential, is considered. The exact wave functions are used to calculate electron current and orbital magnetic dipole momentum for the single electron. Exact expressions, giving the force and energy of the dipole-dipole interaction, are also determined. Further, the system is coupled to a heat bath, and mean values and fluctuations of the magnetic dipole momentum, utilizing the canonical ensemble are calculated. Influences of the temperature, as well as the external magnetic field, expressed via the Larmor frequency are analyzed. We also include the dependencies of the magnetic dipole momentum and its fluctuations on the effective mass of the electron, considering some experimental values for low-dimensional systems, that are extensively studied for various applications in electronics. Our results suggest that the average momentum or its fluctuations are strongly related to the effective mass of the electron. Having on mind that parabolically shaped potentials have very wide area of application in the low-dimensional systems, such as quantum dots and rings, carbon nanotubes, we believe that the proposed model and the consequent analysis is of general importance, since it offers exact analytical approach.
Zhang, Hang; Hu, Zhongliang; Ma, Zhijun; Gecevi?ius, Mindaugas; Dong, Guoping; Zhou, Shifeng; Qiu, Jianrong
2016-01-27
Polymeric nanofibers containing gold nanorods (GNRs) are aligned in a uniform orientation through electrospinning. The dispersive and absorptive parts of the third-order optical nonlinear optical refractive index of the composite film measured by polarization dependent z-scan method are demonstrated to be anisotropically enhanced. Anisotropic optical response of the aligned GNRs and its connection with the ultrafast electron dynamics are discussed in light of the results of resonant femtosecond pump-probe experiments. The significant appearance of anisotropic nonlinear optical properties of ensembles of GNRs is attributed to the sensitive excitation of longitudinal surface plasmon resonance (LSPR) of highly aligned GNRs. For the macroscopic applications of ensembles of GNRs, such as passive mode-locking and all-optical switching, the experimental results demonstrate that the alignment of GNRs through electrospinning should be very high efficient, and economic. PMID:26731010
Anisotropic effective-medium modeling of the elastic properties of shales
Hornby, B.E. Bullard Labs., Cambridge . Dept. of Earth Sciences); Schwartz, L.M. ); Hudson, J.A. )
1994-10-01
Shales are complex porous materials, normally consisting of percolating and interpenetrating fluid and solid phases. The solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure. The shape, orientation, and connection of the two phases control the anisotropic elastic properties of the composite solid. The authors develop a theoretical framework that allows one to predict the effective elastic properties of shales. Its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments. The theory is based on a combination of anisotropic formulations of the self-consistent (SCA) and differential effective-medium (DEM) approximations. This combination guarantees that both the fluid and solid phases percolate at all porosities. The modeling of the elastic properties of shales proceeds in four steps. First, the authors consider the case of an aligned biconnected clay-fluid composite composed of ellipsoidal inclusions. Anisotropic elastic constants are estimated for a clay-fluid composite as a function of the fluid-filled porosity and the aspect ratio of the inclusions. Second, a new processing technique is developed to estimate the distribution of clay platelet orientations from digitized scanning electron microphotographs (SEM). Third, the derived clay platelet distribution is employed to estimate the effective elastic parameters of a solid comprising clay-fluid composites oriented at different angles. Finally, silt minerals are included in the calculations as isolated spherical inclusions.
Identifying the complete space of feasible anisotropic properties in polycrystalline microstructures
NASA Astrophysics Data System (ADS)
Proust, Gwenaelle
Current engineering design focuses mainly on the geometrical optimization of a component, while the material selection is often limited to picking a material based on a set of properties reported in handbooks. The inherent anisotropic behavior of materials is often ignored in the design process, and is usually assumed to be addressed by the safety factor employed. This simple treatment of material selection in the design and optimization process often leads to inefficient design. In this study, we present a rigorous and a comprehensive procedure that facilitates the treatment of material microstructure as a continuous design variable in the elastic-plastic design of structural components made from anisotropic polycrystalline metals. The mechanical behavior of a metal is influenced by several details of its microstructure, including chemical composition, grain size distribution, crystallographic texture, among others. Here, we focus on the crystallographic texture (also called Orientation Distribution Function or ODF) as the main microstructural parameter controlling the anisotropic elastic-plastic properties of interest. The property closures that we have delineated describe the complete set of feasible property combinations for a given polycrystalline material system, while accounting for all possible textures. The property closures are obtained here using a spectral representation of ODF and its relationship with rigorous first order bounds on the effective properties of interest in design. Using the proposed methodology, we successfully developed a few examples of property closures for face centered cubic (fcc) and hexagonal close-packed (hcp) metals. The mechanical anisotropic behavior at the single crystal level for face centered cubic metals has been characterized using the nanoindentation technique along with orientation imaging mapping. This methodology shows promising possibilities to extract fundamental elastic and plastic parameters. However, the methods proposed in the literature to extract data from the load-displacement curves cause discrepancy between the experimental and expected values. The discrepancy could be attributed to the induced plastic deformation among other factors.
Qian Chen
2008-08-18
The generation, motion, and interaction of dislocations play key roles during the plastic deformation process of crystalline solids. 3D Dislocation Dynamics has been employed as a mesoscale simulation algorithm to investigate the collective and cooperative behavior of dislocations. Most current research on 3D Dislocation Dynamics is based on the solutions available in the framework of classical isotropic elasticity. However, due to some degree of elastic anisotropy in almost all crystalline solids, it is very necessary to extend 3D Dislocation Dynamics into anisotropic elasticity. In this study, first, the details of efficient and accurate incorporation of the fully anisotropic elasticity into 3D discrete Dislocation Dynamics by numerically evaluating the derivatives of Green's functions are described. Then the intrinsic properties of perfect dislocations, including their stability, their core properties and disassociation characteristics, in newly discovered rare earth-based intermetallics and in conventional intermetallics are investigated, within the framework of fully anisotropic elasticity supplemented with the atomistic information obtained from the ab initio calculations. Moreover, the evolution and interaction of dislocations in these intermetallics as well as the role of solute segregation are presented by utilizing fully anisotropic 3D dislocation dynamics. The results from this work clearly indicate the role and the importance of elastic anisotropy on the evolution of dislocation microstructures, the overall ductility and the hardening behavior in these systems.
Liao, H.-S.; Juang, B.-J.; Chang, W.-C.; Lai, W.-C.; Chang, C.-S.; Huang, K.-Y.
2011-11-15
The diverse atomic configurations induce the anisotropic surface properties. For investigating anisotropic phenomena, we developed a rotational positioning system adapted to atomic force microscope (AFM). This rotational positioning system is applied to revolve the measured sample to defined angular direction, and it composed of an inertial rotational stepper and a visual angular measurement. The inertial rotational stepper with diameter 30 mm and height 7.6 mm can be easily attached to the AFM-system built in any general optical microscope. Based on a clearance less bearing and the inertial driving method, its bidirectional angular resolution reaches 0.005 deg. per step. For realizing a close-loop controlled angular positioning function, the visual measurement method is utilized. Through the feedback control, the angular positioning error is less than 0.01 deg. For verifying the system performance, we used it to investigate the anisotropic surface properties of graphite. Through a modified cantilever tip, the atomic-scale stick-slip, and the anisotropic friction phenomena can be distinctly detected.
Charmonium properties in deconfinement phase in anisotropic lattice QCD
Iida, H.; Doi, T.; Ishii, N.; Suganuma, H.; Tsumura, K.
2006-10-01
J/{psi} and {eta}{sub c} above the QCD critical temperature T{sub c} are studied in anisotropic quenched lattice QCD, considering whether the cc systems above T{sub c} are spatially compact (quasi-)bound states or scattering states. We adopt the standard Wilson gauge action and O(a)-improved Wilson quark action with renormalized anisotropy a{sub s}/a{sub t}=4.0 at {beta}=6.10 on 16{sup 3}x(14-26) lattices, which correspond to the spatial lattice volume V{identical_to}L{sup 3}{approx_equal}(1.55 fm){sup 3} and temperatures T{approx_equal}(1.11-2.07)T{sub c}. We investigate the cc system above T{sub c} from the temporal correlators with spatially extended operators, where the overlap with the ground state is enhanced. To clarify whether compact charmonia survive in the deconfinement phase, we investigate spatial boundary-condition dependence of the energy of cc systems above T{sub c}. In fact, for low-lying S-wave cc scattering states, it is expected that there appears a significant energy difference {delta}E{identical_to}E(APBC)-E(PBC){approx_equal}2{radical}(m{sub c}{sup 2}+3{pi}{sup 2}/L{sup 2})-2m{sub c} (m{sub c}: charm quark mass) between periodic and antiperiodic boundary conditions on the finite-volume lattice. In contrast, for compact charmonia, there is no significant energy difference between periodic and antiperiodic boundary conditions. As a lattice QCD result, almost no spatial boundary-condition dependence is observed for the energy of the cc system in J/{psi} and {eta}{sub c} channels for T{approx_equal}(1.11-2.07)T{sub c}. This fact indicates that J/{psi} and {eta}{sub c} would survive as spatially compact cc (quasi-)bound states below 2T{sub c}. We also investigate a P-wave channel at high temperature with maximal entropy method and find no low-lying peak structure corresponding to {chi}{sub c1} at 1.62T{sub c}.
Picosecond Acoustic Measurement of Anisotropic Properties of Thin Films
Perton, M.; Rossignol, C.; Chigarev, N.; Audoin, B.
2007-03-21
Properties of thin metallic films have been studied extensively by means of laser-picosecond ultrasonics. Generation of longitudinal and shear waves via thermoelastic mechanism and large source has been only demonstrated for waves vectors along the normal to the interface. However, such measurements cannot provide complete information about elastic properties of films. As it has been already shown for nanosecond ultrasonics, the knowledge of group or phase velocities in several directions for sources with small lateral size allows determining the stiffness tensor coefficients of a sample. The experimental set-up was prepared to obtain the thinnest size for the source to achieve acoustic diffraction. The identification of the stiffness tensor components, based on the inversion of the bulk waves phase velocities, is applied to signals simulated and experimentally recorded for a material with hexagonal properties. First estimation of stiffness tensor coefficients for thin metallic film 2.1 {mu}m has been performed.
Magnetic properties of anisotropic Sr-La-system ferrite magnets
Yamamoto, H.; Nagakura, M. ); Terada, H. )
1990-05-01
This paper presents an experiment carried out to investigate the effect of La{sub 2}O{sub 3} addition to the magnetic and physical properties of strontium ferrite magnets. It was found that the La{sub 2}O{sub 3} addition to SrO {center dot} 6Fe{sub 2}O{sub 3} (stoichiometric composition) was very useful in stabilizing the magnetoplumbite structure and that these Sr-La-system ferrites had excellent properties as a permanenent magnet. Compositions were chosen according to the formula ((SrO){sub 1/n+1}(Fe{sub 2}O{sub 3}){sub n/n+1}){sub 100{minus}x}(La{sub 2}O{sub 3}){sub x}, where n was varied between 5.0 and 6.5, and x between 0 and 5.0. The optimum conditions for making magnets and some properties of typical specimens are discussed.
Anisotropic properties of human cortical bone with osteogenesis imperfecta.
Katti, Kalpana S; Gu, Chunju; Katti, Dinesh R
2016-02-01
The heterogeneity of bone shape and size variation is modulated by genetic, mechanical, nutritional, and hormonal patterning throughout its lifetime. Microstructural changes across cross sections are a result of mechanistic optimization that results over the years of evolution while being based on universal, time-invariant ingredients and patterns. Here we report changes across anatomical sections of bone with osteogenesis imperfecta (OI) that undermines the work of evolution through genetic mutation. This work examines the microstructure and molecular composition of different anatomical positions (anterior, medial, posterior, and lateral regions) in the diaphysis of an OI human tibia. The study shows that although there is no significant microstructural difference, molecular changes are observed using FTIR revealing differences in molecular composition of the four anatomical positions. In addition, the nanomechanical properties of anterior section of OI bone seem more heterogeneous. The nanomechanical properties of interstitial lamellae in all these bone samples are consistently greater than those of osteonal lamellae. The nanomechanical properties of bone depend on its anatomical section and on the measurement direction as well. Variations in molecular structure with anatomical positions and also corresponding differences in nanomechanical properties are reported. These are compared to those observed typically in healthy bone illustrating the unique influence of OI on bone multiscale behavior which results from an evolutionary process lasting for many years. PMID:26399513
The effect of anisotropic heat transport on magnetic islands in 3-D configurations
Schlutt, M. G.; Hegna, C. C.
2012-08-15
An analytic theory of nonlinear pressure-induced magnetic island formation using a boundary layer analysis is presented. This theory extends previous work by including the effects of finite parallel heat transport and is applicable to general three dimensional magnetic configurations. In this work, particular attention is paid to the role of finite parallel heat conduction in the context of pressure-induced island physics. It is found that localized currents that require self-consistent deformation of the pressure profile, such as resistive interchange and bootstrap currents, are attenuated by finite parallel heat conduction when the magnetic islands are sufficiently small. However, these anisotropic effects do not change saturated island widths caused by Pfirsch-Schlueter current effects. Implications for finite pressure-induced island healing are discussed.
Anisotropic parton escape is the dominant source of azimuthal anisotropy in transport models
NASA Astrophysics Data System (ADS)
He, Liang; Edmonds, Terrence; Lin, Zi-Wei; Liu, Feng; Molnar, Denes; Wang, Fuqiang
2016-02-01
We trace the development of azimuthal anisotropy (vn, n = 2 , 3) via parton-parton collision history in two transport models. The parton vn is studied as a function of the number of collisions of each parton in Au + Au and d + Au collisions at âˆš{sNN} = 200Â GeV. It is found that the majority of vn comes from the anisotropic escape probability of partons, with no fundamental difference at low and high transverse momenta. The contribution to vn from hydrodynamic-type collective flow is found to be small. Only when the parton-parton cross-section is set unrealistically large does this contribution start to take over. Our findings challenge the current paradigm emerged from hydrodynamic comparisons to anisotropy data.
Nonlinear and Anisotropic Tensile Properties of Graft Materials used in Soft Tissue Applications
Yoder, Jonathon H; Elliott, Dawn M
2010-01-01
Background The mechanical properties of extracellular matrix grafts that are intended to augment or replace soft tissues should be comparable to the native tissue. Such grafts are often used in fiber-reinforced tissue applications that undergo multi-axial loading and therefore knowledge of the anisotropic and nonlinear properties are needed, including the moduli and Poisson's ratio in two orthogonal directions within the plane of the graft. The objective of this study was to measure the tensile mechanical properties of several marketed grafts: Alloderm, Restore, CuffPatch, and OrthADAPT. Methods The degree of anisotropy and nonlinearity within each graft was evaluated from uniaxial tensile tests and compared to their native tissue. Results The Alloderm graft was anisotropic in both the toe and linear-region of the stress-strain response, was highly nonlinear, and generally had low properties. The Restore and CuffPatch grafts had similar stress-strain responses, were largely isotropic, had a linear-region modulus of 18 MPa, and were nonlinear. OrthADAPT was anisotropic in the linear region (131 vs 47 MPa) and was highly nonlinear. The Poisson ratio for all grafts was between 0.4 and 0.7, except for the parallel orientation of Restore which was greater than 1.0. Interpretation Having an informed understanding of how the available grafts perform mechanically will allow for better assessment by the physician for which graft to apply depending upon its application. PMID:20129728
Transport properties in the atmosphere of Jupiter
NASA Technical Reports Server (NTRS)
Biolsi, L., Jr.
1979-01-01
The computer program used to obtain transport properties for the Hulburt-Hirschfelder potential was tested. Transport properties for the C-C interaction were calculated. Rough estimates for transport properties for the important ablation species were obtained as well as estimates of transport properties for some of the species associated with photochemical smog. The results are discussed.
Phonon heat conduction in layered anisotropic crystals
NASA Astrophysics Data System (ADS)
Minnich, A. J.
2015-02-01
The thermal properties of anisotropic crystals are of both fundamental and practical interest, but transport phenomena in anisotropic materials such as graphite remain poorly understood because solutions of the Boltzmann equation often assume isotropy. Here, we extend an analytic solution of the transient, frequency-dependent Boltzmann equation to highly anisotropic solids and examine its predictions for graphite. We show that this simple model predicts key results, such as long c -axis phonon mean free paths and a negative correlation of cross-plane thermal conductivity with in-plane group velocity, that were previously observed with computationally expensive molecular-dynamics simulations. Further, using our analytic solution, we demonstrate a method to reconstruct the anisotropic mean free path spectrum of crystals with arbitrary dispersion relations without any prior knowledge of their harmonic or anharmonic properties using observations of quasiballistic heat conduction. These results provide a useful analytic framework to understand thermal transport in anisotropic crystals.
Interventional nerve visualization via the intrinsic anisotropic optical properties of the nerves
NASA Astrophysics Data System (ADS)
Chin, Kenneth W.; Meijerink, Andries; Chin, Patrick T. K.
2015-07-01
We present an optical concept to visualize nerves during surgical interventions. The concept relies on the anisotropic optical properties of the nerves which allows for specific switching of the optical reflection by the nervous tissue. Using a low magnification polarized imaging system we are able to visualize the on and off switching of the optical reflection of the nervous tissue, enabling a non-invasive nerve specific real-time nerve visualization during surgery.
Optical Properties of Anisotropic Polycrystalline Ce+3 activated LSO
Roy, Sudesna; Lingertat, Helmut; Brecher, Charles; Sarin, Vinod
2012-01-01
Polycrystalline cerium activated lutetium oxyorthosilicate (LSO:Ce) is highly desirable technique to make cost effective and highly reproducible radiation detectors for medical imaging. In this article methods to improve transparency in polycrystalline LSO:Ce were explored. Two commercially available powders of different particulate sizes (average particle size 30 and 1500 nm) were evaluated for producing dense LSO:Ce by pressure assisted densification routes, such as hot pressing and hot isostatic pressing. Consolidation of the powders at optimum conditions produced three polycrystalline ceramics with average grain sizes of 500 nm, 700 and 2000 nm. Microstructural evolution studies showed that for grain sizes larger than 1 µm, anisotropy in thermal expansion coefficient and elastic constants of LSO, resulted in residual stress at grain boundaries and triple points that led to intragranular microcracking. However, reducing the grain size below 1 µm effectively avoids microcracking, leading to more favorable optical properties. The optical scattering profiles generated by a Stover scatterometer, measured by a He-Ne laser of wavelength 633 nm, showed that by reducing the grain size from 2 µm to 500 nm, the in-line transmission increased by a factor of 103. Although these values were encouraging and showed that small changes in grain size could increase transmission by almost 3 orders of magnitude, even smaller grain sizes need to be achieved in order to get truly transparent material with high in-line transmission. PMID:23505329
Anisotropic magnetic properties of dysprosium iron garnet (DyIG)
NASA Astrophysics Data System (ADS)
Lahoubi, M.; Younsi, W.; Soltani, M.-L.; Ouladdiaf, B.
2010-01-01
The magnetic properties of dysprosium iron garnet (DyIG) have been studied by performing high resolution powder neutron diffraction experiments and high dc fields magnetizations on single crystals. Among all the reflections (hkl) indexed in the nuclear cubic space group (CSG) Ia bar 3 d with h+k+l=2n and k=[000], the superstructure lines (hkl)* forbidden by the symmetry (222)* and (622)* are not observed in the patterns at all temperatures. The pattern at 130 K is well interpreted within the magnetic modes F belonging to the irreducible representation (IR) T1g of the CSG and identified to the room temperature ferrimagnetic Néel model. The high magnetic field behavior of the spontaneous collinear magnetic structure (MS) along the easy axis (EA) <111> is isotropic. Below 130 K, the patterns exhibit additional magnetic superstructure lines. They are associated to the appearance of the spontaneous non collinear MS which is described in the subgroup of the CSG, R bar 3 c within the IR A2g. A strong magnetization anisotropy (MA) is observed at 1.5 K in the low symmetry phases
NASA Astrophysics Data System (ADS)
Chen, D. P.; Wang, Xiaolin; Lin, C. T.; Dou, S. X.
2007-10-01
Large single crystals of ?-NaxCoO2 ( x=0.91 , 0.92, and 0.93) have been successfully fabricated by using the traveling solvent floating zone method. Details on the crystal growth are discussed. The crystal structures were characterized using powder x-ray diffraction and Rietveld refinement. The magnetic susceptibility measurements show that the magnetic properties depend strongly on x . The compound was found to be antiferromagnetic at TN?20K for x=0.91 and x=0.92 , and paramagnetic for x=0.93 . The in-plane and out-of-plane anisotropies were observed for the x=0.91 crystals. In addition, the derived anisotropic g -factor ratios (gab/gc) from the anisotropic susceptibility along H?ab and H?c decreased significantly as the sodium composition increased from x=0.91 to x=0.93 .
Transport Properties for Combustion Modeling
Brown, N.J.; Bastein, L.; Price, P.N.
2010-02-19
This review examines current approximations and approaches that underlie the evaluation of transport properties for combustion modeling applications. Discussed in the review are: the intermolecular potential and its descriptive molecular parameters; various approaches to evaluating collision integrals; supporting data required for the evaluation of transport properties; commonly used computer programs for predicting transport properties; the quality of experimental measurements and their importance for validating or rejecting approximations to property estimation; the interpretation of corresponding states; combination rules that yield pair molecular potential parameters for unlike species from like species parameters; and mixture approximations. The insensitivity of transport properties to intermolecular forces is noted, especially the non-uniqueness of the supporting potential parameters. Viscosity experiments of pure substances and binary mixtures measured post 1970 are used to evaluate a number of approximations; the intermediate temperature range 1 < T* < 10, where T* is kT/{var_epsilon}, is emphasized since this is where rich data sets are available. When suitable potential parameters are used, errors in transport property predictions for pure substances and binary mixtures are less than 5 %, when they are calculated using the approaches of Kee et al.; Mason, Kestin, and Uribe; Paul and Warnatz; or Ern and Giovangigli. Recommendations stemming from the review include (1) revisiting the supporting data required by the various computational approaches, and updating the data sets with accurate potential parameters, dipole moments, and polarizabilities; (2) characterizing the range of parameter space over which the fit to experimental data is good, rather than the current practice of reporting only the parameter set that best fits the data; (3) looking for improved combining rules, since existing rules were found to under-predict the viscosity in most cases; (4) performing more transport property measurements for mixtures that include radical species, an important but neglected area; (5) using the TRANLIB approach for treating polar molecules and (6) performing more accurate measurements of the molecular parameters used to evaluate the molecular heat capacity, since it affects thermal conductivity, which is important in predicting flame development.
Turbulent anomalous transport and anisotropic electron heating in a return current system
NASA Astrophysics Data System (ADS)
Lee, Kuang Wu; Büchner, Jörg
2011-02-01
Anisotropic electron heating due to self-generated electromagnetic turbulences is observed in collisionless return current plasmas. The corresponding energy conversion, electron heating, and associated anomalous momentum transport are investigated by means of a two-dimensional electromagnetic particle-in-cell simulation code. The return current model consists of two counterstreaming electron beams with different temperatures and a stationary ion background. First, a general multifluid dispersion analyzer is presented in a clear matrix form that allows to study electron streaming instabilities. The numerical simulation confirms the predicted electrostatic electron-electron acoustic instability. Generating electromagnetic waves, the system evolves into a nonlinear stage. As a result, the electron drifts are slowed down due to turbulence-induced anomalous momentum exchange. Localized electric and magnetic field fluctuations play major roles in the energy conversion. Perpendicular electron heating follows the growth of magnetic field perturbations and the slowing of the electron drifts. Parallel and perpendicular electron heating occurs at different time scales. It is shown that the longer lasting perpendicular electron heating is caused by preheated parallel electron flows. The deflection of the preheated parallel electron flows in the localized turbulences, which is essentially a two-dimensional effect, leads to perpendicular electron heating even after the saturation of parallel electron heating. We conclude that the self-generated magnetic turbulence dominates the anomalous transport process in the late stage of return current system evolution.
Monte Carlo inversion of ultrasonic array data to map anisotropic weld properties.
Zhang, Jie; Hunter, Alan; Drinkwater, Bruce W; Wilcox, Paul D
2012-11-01
The quality of an ultrasonic array image depends on accurate information about its acoustic properties. Inaccurate acoustic properties can cause image degradation such as blurring, mislocation of reflectors, and the introduction of artifacts. In this paper, for the specific case of an inhomogeneous and anisotropic austenitic steel weld, Monte Carlo Markov Chain (MCMC) inversion is used to estimate unknown acoustic properties from array data. The approach uses active beacons that transmit ultrasound through the anisotropic weld; the ultrasound is then captured by a receiving array. A forward model of the ultrasonic array data is then optimized with respect to the experimental data using an MCMC inversion. The result of this process is the extraction of a material property map that describes the anisotropy distribution within the weld region. These extracted material properties are then used within an imaging algorithm-the total focusing method in this paper-to produce autofocused images. This MCMC inversion approach is first applied to simulated data to test the convergence, robustness, and accuracy of the method and its implementation. The extracted weld map is used to show improved imaging of defects within the weld, relative to an image formed assuming a constant velocity. Finally, the MCMC inversion approach is used on experimental data from a 110-mm-thick steel plate containing an austenitic weld. Here the extracted weld map is used to show that defect location errors of greater than 5 mm are reduced to around 2 mm when the extracted weld map is used. PMID:23192812
NASA Astrophysics Data System (ADS)
Gillman, A.; Matouš, K.; Atkinson, S.
2013-02-01
In this paper, a systematic method is presented for developing microstructure-statistics-property relations of anisotropic polydisperse particulate composites using microcomputer tomography (micro-CT). Micro-CT is used to obtain a detailed three-dimensional representation of polydisperse microstructures, and an image processing pipeline is developed for identifying particles. In this work, particles are modeled as idealized shapes in order to guide the image processing steps and to provide a description of the discrete micro-CT data set in continuous Euclidean space. n-point probability functions used to describe the morphology of mixtures are calculated directly from real microstructures. The statistical descriptors are employed in the Hashin-Shtrikman variational principle to compute overall anisotropic bounds and self-consistent estimates of the thermal-conductivity tensor. We make no assumptions of statistical isotropy nor ellipsoidal symmetry, and the statistical description is obtained directly from micro-CT data. Various mixtures consisting of polydisperse ellipsoidal and spherical particles are prepared and studied to show how the morphology impacts the overall anisotropic thermal-conductivity tensor.
Anisotropic Spin Transport and Strong Visible-Light Absorbance in Few-Layer SnSe and GeSe.
Shi, Guangsha; Kioupakis, Emmanouil
2015-10-14
SnSe and GeSe are layered compound semiconductors that can be exfoliated to form two-dimensional materials. In this work, we use predictive calculations based on density functional and many-body perturbation theory to study the electronic and optical properties of single-layer, double-layer, and bulk SnSe and GeSe. The fundamental band gap is direct in single-layer and double-layer GeSe, but indirect in single-layer and double-layer SnSe. Moreover, the interplay of spin-orbit coupling and lack of inversion symmetry in the monolayer structures results in anisotropic spin splitting of the energy bands, with potential applications in directionally dependent spin transport. We also show that single-layer and double-layer SnSe and GeSe exhibit unusually strong optical absorbance in the visible range. Our results suggest that single-layer and double-layer SnSe and GeSe are promising materials for ultrathin-film photovoltaic applications with theoretical upper bounds to the conversion efficiency that approach the efficiency records realized in organic and dye-sensitized solar cells. PMID:26393677
Hu, Tao; Hong, Jisang
2015-10-28
Phosphorene is receiving great research interests because of its peculiar physical properties. Nonetheless, the phosphorus has a trouble of degradation due to oxidation. Hereby, we propose that the electrical and optical anisotropic properties can be preserved by encapsulating into hexagonal boron nitride (h-BN). We found that the h-BN contributed to enhancing the band gap of the phosphorene layer. Comparing the band gap of the pristine phosphorene layer, the band gap of the phosphorene/BN(1ML) system was enhanced by 0.15 eV. It was further enhanced by 0.31 eV in the BN(1ML)/phosphorene/BN(1ML) trilayer structure. However, the band gap was not further enhanced when we increased the thickness of the h-BN layers even up to 4 MLs. Interestingly, the anisotropic effective mass and optical property were still preserved in BN/phosphorene/BN heterostructures. Overall, we predict that the capping of phosphorene by the h-BN layers can be an excellent solution to protect the intrinsic properties of the phosphorene. PMID:26439467
Simulation of charge transport in ion channels and nanopores with anisotropic permittivity
Mashl, R. Jay; Lee, Kyu Il; Jakobsson, Eric; Ravaioli, Umberto
2010-01-01
Ion channels are part of nature's solution for regulating biological environments. Every ion channel consists of a chain of amino acids carrying a strong and sharply varying permanent charge, folded in such a way that it creates a nanoscopic aqueous pore spanning the otherwise mostly impermeable membranes of biological cells. These naturally occurring proteins are particularly interesting to device engineers seeking to understand how such nanoscale systems realize device-like functions. Availability of high-resolution structural information from X-ray crystallography, as well as large-scale computational resources, makes it possible to conduct realistic ion channel simulations. In general, a hierarchy of simulation methodologies is needed to study different aspects of a biological system like ion channels. Biology Monte Carlo (BioMOCA), a three-dimensional coarse-grained particle ion channel simulator, offers a powerful and general approach to study ion channel permeation. BioMOCA is based on the Boltzmann Transport Monte Carlo (BTMC) and Particle-Particle-Particle-Mesh (P3M) methodologies developed at the University of Illinois at Urbana-Champaign. In this paper we briefly discuss the various approaches to simulating ion flow in channel systems that are currently being pursued by the biophysics and engineering communities, and present the effect of having anisotropic dielectric constants on ion flow through a number of nanopores with different effective diameters. PMID:20445807
Malet, F.; Reimann, S. M.; Kristensen, T.; Kavoulakis, G. M.
2011-03-15
We study the rotational properties of a dipolar Bose-Einstein condensate confined in a quasi-two-dimensional anisotropic trap for an arbitrary orientation of the dipoles with respect to their plane of motion. Within the mean-field approximation, we find that the lowest-energy state of the system depends strongly on the relative strength between the dipolar and the contact interactions, as well as on the size and the orientation of the dipoles and the size and the orientation of the deformation of the trapping potential.
Landau levels and magneto-transport property of monolayer phosphorene.
Zhou, X Y; Zhang, R; Sun, J P; Zou, Y L; Zhang, D; Lou, W K; Cheng, F; Zhou, G H; Zhai, F; Chang, Kai
2015-01-01
We investigate theoretically the Landau levels (LLs) and magneto-transport properties of phosphorene under a perpendicular magnetic field within the framework of the effective kÂ·p Hamiltonian and tight-binding (TB) model. At low field regime, we find that the LLs linearly depend both on the LL index n and magnetic field B, which is similar with that of conventional semiconductor two-dimensional electron gas. The Landau splittings of conduction and valence band are different and the wavefunctions corresponding to the LLs are strongly anisotropic due to the different anisotropic effective masses. An analytical expression for the LLs in low energy regime is obtained via solving the decoupled Hamiltonian, which agrees well with the numerical calculations. At high magnetic regime, a self-similar Hofstadter butterfly (HB) spectrum is obtained by using the TB model. The HB spectrum is consistent with the LL fan calculated from the effective kÂ·p theory in a wide regime of magnetic fields. We find the LLs of phosphorene nanoribbon depend strongly on the ribbon orientation due to the anisotropic hopping parameters. The Hall and the longitudinal conductances (resistances) clearly reveal the structure of LLs. PMID:26159856
Landau levels and magneto-transport property of monolayer phosphorene
Zhou, X. Y.; Zhang, R.; Sun, J. P.; Zou, Y. L.; Zhang, D.; Lou, W. K.; Cheng, F.; Zhou, G. H.; Zhai, F.; Chang, Kai
2015-01-01
We investigate theoretically the Landau levels (LLs) and magneto-transport properties of phosphorene under a perpendicular magnetic field within the framework of the effective k·p Hamiltonian and tight-binding (TB) model. At low field regime, we find that the LLs linearly depend both on the LL index n and magnetic field B, which is similar with that of conventional semiconductor two-dimensional electron gas. The Landau splittings of conduction and valence band are different and the wavefunctions corresponding to the LLs are strongly anisotropic due to the different anisotropic effective masses. An analytical expression for the LLs in low energy regime is obtained via solving the decoupled Hamiltonian, which agrees well with the numerical calculations. At high magnetic regime, a self-similar Hofstadter butterfly (HB) spectrum is obtained by using the TB model. The HB spectrum is consistent with the LL fan calculated from the effective k·p theory in a wide regime of magnetic fields. We find the LLs of phosphorene nanoribbon depend strongly on the ribbon orientation due to the anisotropic hopping parameters. The Hall and the longitudinal conductances (resistances) clearly reveal the structure of LLs. PMID:26159856
Landau levels and magneto-transport property of monolayer phosphorene
NASA Astrophysics Data System (ADS)
Zhou, X. Y.; Zhang, R.; Sun, J. P.; Zou, Y. L.; Zhang, D.; Lou, W. K.; Cheng, F.; Zhou, G. H.; Zhai, F.; Chang, Kai
2015-07-01
We investigate theoretically the Landau levels (LLs) and magneto-transport properties of phosphorene under a perpendicular magnetic field within the framework of the effective kÂ·p Hamiltonian and tight-binding (TB) model. At low field regime, we find that the LLs linearly depend both on the LL index n and magnetic field B, which is similar with that of conventional semiconductor two-dimensional electron gas. The Landau splittings of conduction and valence band are different and the wavefunctions corresponding to the LLs are strongly anisotropic due to the different anisotropic effective masses. An analytical expression for the LLs in low energy regime is obtained via solving the decoupled Hamiltonian, which agrees well with the numerical calculations. At high magnetic regime, a self-similar Hofstadter butterfly (HB) spectrum is obtained by using the TB model. The HB spectrum is consistent with the LL fan calculated from the effective kÂ·p theory in a wide regime of magnetic fields. We find the LLs of phosphorene nanoribbon depend strongly on the ribbon orientation due to the anisotropic hopping parameters. The Hall and the longitudinal conductances (resistances) clearly reveal the structure of LLs.
Transport properties in the atmosphere of Jupiter
NASA Technical Reports Server (NTRS)
Biolsi, L., Jr.
1978-01-01
The calculation of transport properties near the surface of a probe entering the atmosphere of Jupiter is discussed for (1) transport properties in the pure Jovian atmosphere, (2) transport properties for collisions between monatomic carbon atoms, including the effect of excited electronic states, (3) transport properties at the boundaries for mixing of the pure Jovian atmosphere and the atmosphere due to the injection of gaseous ablation products, and (4) transport properties for interactions involving some of the molecular ablation products. The transport properties were calculated using the kinetic theory of gases. Transport collision integrals were calculated for only a limited set of empirical and semiempirical interaction potentials. Since the accuracy of the fit of these empirical potentials to the true potential usually determines the accuracy of the calculation of the transport properties, the various interaction potentials used in these calculations are discussed.
Anisotropic magnetic properties and giant magnetocaloric effect of single-crystal PrSi
NASA Astrophysics Data System (ADS)
Das, Pranab Kumar; Bhattacharyya, Amitava; Kulkarni, Ruta; Dhar, S. K.; Thamizhavel, A.
2014-04-01
A single crystal of PrSi was grown by the Czochralski method in a tetra-arc furnace. Powder x-ray diffraction of the as-grown crystal revealed that PrSi crystallizes in an FeB-type structure with space group Pnma (No. 62). The anisotropic magnetic properties were investigated by means of magnetic susceptibility, isothermal magnetization, electrical transport, and heat capacity measurements. Magnetic susceptibility data clearly indicate the ferromagnetic transition in PrSi with a TC of 52 K. The relative easy axis of magnetization was found to be the [010] direction. Heat capacity data confirm the bulk nature of the transition at 52 K and exhibit a huge anomaly at the transition. A sharp rise in the low-temperature heat capacity has been observed (below 5 K) which is attributed to the 141Pr nuclear Schottky heat capacity arising from the hyperfine field of the Pr moment. The estimated Pr magnetic moment 2.88 ?B/Pr from the hyperfine splitting is in agreement with the saturation magnetization value obtained from the magnetization data measured at 2 K. From the crystal electric field analysis of the magnetic susceptibility, magnetization, and heat capacity data it is found that the degenerate J =4 Hund's rule derived state of the Pr3+ ion splits into nine singlets with an overall splitting of 284 K, the first excited singlet state separated by just 9 K from the ground state. The magnetic ordering in PrGe appears to be due to the exchange-generated admixture of low-lying crystal field levels. The magnetocaloric effect (MCE) has been investigated from magnetization data along all three principal crystallographic directions. The large magnetic entropy change, -?SM=22.2 J/kg K, and the relative cooling power, RCP = 460 J/kg, characteristic of the giant magnetocaloric effect are achieved near the transition temperature (TC = 52 K) for H = 70 kOe along [010]. Furthermore, the PrSi single crystal exhibits a giant MCE anisotropy.
NASA Astrophysics Data System (ADS)
Hallberg, Håkan; Zhu, Yaochan
2015-10-01
In the present study, mesoscale simulations of grain growth in UO2 are performed using a 2D level set representation of the polycrystal grain boundary network, employed in a finite element setting. Anisotropic grain boundary properties are considered by evaluating how grain boundary energy and mobility varies with local grain boundary character. This is achieved by considering different formulations of the anisotropy of grain boundary properties, for example in terms of coincidence site lattice (CSL) correspondence. Such modeling approaches allow tracing of the stability of a number of characteristic low-? boundaries in the material during grain growth. The present simulations indicate that anisotropic grain boundary properties have negligible influence on the grain growth rate. However, considering the evolution of grain boundary character distribution and the grain size distribution, it is found that neglecting anisotropic boundary properties will strongly bias predictions obtained from numerical simulations.
Filippov, V. V.; Bormontov, E. N.
2013-07-15
A macroscopic model of the Hall effects and magnetoresistance in anisotropic semiconductor wafers is developed. The results obtained by solving the electrodynamic boundary problem allow the potential and eddy currents in anisotropic semiconductors to be calculated at different current-contact locations, depending on the parameters of the sample material's anisotropy. The results of this study are of great practical importance for investigating the physical properties of anisotropic semiconductors and simulating the electron-transport phenomena in devices based on anisotropic semiconductors.
NASA Astrophysics Data System (ADS)
Lu, Wanglin; Ma, Xiaomeng; Fei, Zhen; Zhou, Jianguang; Zhang, Zhiyong; Jin, Chuanhong; Zhang, Ze
2015-07-01
In this study, we correlated the angular dependence of the Raman response of black phosphorus to its crystallographic orientation by using transmission electron microscopy and Raman spectroscopy. It was found that the intensity of the Ag 2 mode reached a maximum when the polarization direction of the incident light was parallel to the zigzag crystallographic orientation. Notably, it was further confirmed that the zigzag crystallographic direction exhibited superior conductance and carrier mobility. Because of the lattice extension along the armchair direction, an intensification of the anisotropic Raman response was observed. This work provides direct evidence of the correlation between anisotropic properties and crystallographic direction and represents a turning point in the discussion of the angular-dependent electronic properties of black phosphorus.
Tan, Yang; Shyam, Amit; Choi, Wanhuk Brian; Lara-Curzio, Edgar; Sampath, Sanjay
2010-01-01
The determination of elastic properties of plasma-sprayed ceramic and metallic coatings is difficult due to their complex microstructure, which involves a myriad array of pores, interfaces and other defects. Furthermore, the splat-based build-up of the coating results in transverse anisotropy in the elastic properties. In this paper, we report on the anisotropic elastic properties of these coatings determined by resonant ultrasound spectroscopy (RUS). This approach along with the analysis presented enables, for the first time, the determination of elastic properties as a function of direction and temperature for these complex systems with concomitant implications for design. The coating systems investigated included plasma-sprayed yttria-stabilized zirconia (YSZ) and nickel. An additional nickel coating deposited by high-velocity oxygen-fuel process was investigated and its elastic properties were compared to those of plasma-sprayed nickel. Average Young s moduli of the coatings were independently measured by using the instrumented indentation method. The elastic properties determined from the RUS and indentation methodologies allowed description of the microstructure elastic property relationships in the coatings.
Dispersion properties of transverse anisotropic liquid crystal core photonic crystal fibers
NASA Astrophysics Data System (ADS)
Karasawa, Naoki
2016-04-01
The dispersion properties of liquid crystal core photonic crystal fibers for different core diameters have been calculated by a full vectorial finite difference method. In calculations, air holes are assumed to be arranged in a regular hexagonal array in fused silica and a central hole is filled with liquid crystal to create a core. In this study, three types of transverse anisotropic configurations, where liquid crystal molecules are oriented in a transverse plane, and a planar configuration, where liquid crystal molecules are oriented in a propagation direction, are considered. The large changes of the dispersion properties are found when the orientation of the liquid crystal molecules is changed from a planar configuration to a uniform configuration, where all molecules are oriented in the same direction in a transverse plane. Since the orientation of liquid crystal molecules may be controlled by applying an electric field, it could be utilized for various applications including the spectral control of supercontinuum generation.
NASA Astrophysics Data System (ADS)
Turba, K.; Hurst, R. C.; Hähner, P.
2012-09-01
The small punch testing technique was used to assess both creep and fracture properties of the MA956 oxide dispersion strengthened ferritic steel. The anisotropy in mechanical properties was addressed, as well as the alloy's susceptibility to thermal embrittlement. Strong anisotropy was found in the material's creep resistance at 725 °C for longer rupture times. Anisotropic behavior was also observed for the ductile-brittle transition temperature (DBTT). The origin of the anisotropy can be related to the strongly directional microstructure which enables a large amount of intergranular cracking during straining at both high and low temperatures. The DBTT of the alloy is very high, and can be further increased by at least 200 °C after 1000 h of ageing at 475 °C, due to the formation of the Cr-rich ?' phase. The particularly high susceptibility of the MA956 to thermal embrittlement is mainly a consequence of its high chromium content.
NASA Astrophysics Data System (ADS)
Hudson, Stephen; Hutter, Jeffrey; Millon, Leonardo; Wan, Wankei; Nieh, Mu-Ping
2009-03-01
Poly(vinyl alcohol) (PVA) hydrogels are formed from PVA solution by creation of physical cross-links during freeze/thaw cycling. By choosing a suitable freeze/thaw protocol and applying a strain during thermal processing, gels with permanent, anisotropic bulk mechanical properties matching those of cardiovascular tissues can be made, making them useful for applications ranging from artificial heart valves to vascular grafts. We have performed small- and ultra small-angle neutron scattering (SANS and USANS) measurements covering length scales from 2 nm to 10 Î¼m, and modeled the structure as interconnected PVA blobs of size 20 to 50 nm arranged in fractal aggregates extending to at least 10 Î¼m. Here, we discuss the relationship between the microstructure and bulk mechanical properties. Strength increases with the number of thermal cycles due to reinforcement of the small-scale gel phase, while anisotropy is due to elongation of the much larger fractal aggregates.
Anisotropic Mechanical and Giant Magneto-Impedance Properties of Cobalt-Rich Amorphous Ribbons
NASA Astrophysics Data System (ADS)
Tran, H. T.; Devkota, J.; Eggers, T.; Wingo, J.; Cai, W.; Skorvanek, I.; Srikanth, H.; Phan, M. H.
2016-01-01
A comparative study was performed on the mechanical and giant magneto-impedance (GMI) properties in the longitudinal and transverse directions of Co69Fe4Ni1Mo2B12Si12 amorphous ribbons. Both mechanical and GMI properties were found to be anisotropic. Kerr microscopy shows the presence of a stripe-type domain structure with the magnetic easy axis parallel to the longitudinal direction. The fracture strength, elastic modulus, and fracture toughness in the transverse direction was higher than those in the longitudinal direction. A larger GMI response was achieved in the transverse direction at a frequency range where both the domain wall motion and spin rotation dominantly contributed to the effective permeability and hence the magneto-impedance. The current study paves the way for designing Co-rich amorphous ribbons as desirable components in electronics such as magnetic sensors.
Impact of magnetic properties on the Casimir torque between anisotropic metamaterial plates
Deng Gang; Liu Zhongzhu; Luo Jun
2009-12-15
The quantized surface mode technique is used to calculate the Casimir torque between two parallel anisotropic metamaterial plates with in-plane optical axes, and our main concern is focused on the impact of the magnetic properties of the plates on the Casimir torque. Our result shows that at small separation, the Casimir torque between the two plates with frequency dependent permeabilities is larger than that between two nonmagnetic plates, while at large separation it is smaller. This can be explained as a result of the impact of both magnetic properties and material dispersion of the plates. The impact of the Drude background in connected metallic metamaterial is also discussed. These phenomena provide us with new understanding about the Casimir effect and show great potential in application.
NASA Astrophysics Data System (ADS)
Sun, Hong-xiang; Zhang, Shu-yi; Xia, Jian-ping
2015-06-01
The propagation characteristics of laser-generated Rayleigh waves in coating-substrate structures with anisotropic and viscoelastic properties have been investigated quantitatively. Based on the plane strain theory, finite element models for simulating laser-generated Rayleigh waves in coating-substrate structures are established, in which the carbon fiber-reinforced epoxy matrix composite and aluminum are used as the coating and/or the substrate alternately. The numerical results exhibit that the characteristics of the laser-generated Rayleigh waves, including attenuation, velocity, and dispersion, are mainly and closely related to the anisotropic and viscoelastic properties of the composite in the coating-substrate structures.
Chen, D. P.; Wang, Xiaolin; Dou, S. X.; Lin, C. T.
2007-10-01
Large single crystals of {alpha}-Na{sub x}CoO{sub 2} (x=0.91, 0.92, and 0.93) have been successfully fabricated by using the traveling solvent floating zone method. Details on the crystal growth are discussed. The crystal structures were characterized using powder x-ray diffraction and Rietveld refinement. The magnetic susceptibility measurements show that the magnetic properties depend strongly on x. The compound was found to be antiferromagnetic at T{sub N}{approx_equal}20 K for x=0.91 and x=0.92, and paramagnetic for x=0.93. The in-plane and out-of-plane anisotropies were observed for the x=0.91 crystals. In addition, the derived anisotropic g-factor ratios (g{sub ab}/g{sub c}) from the anisotropic susceptibility along H parallel ab and H parallel c decreased significantly as the sodium composition increased from x=0.91 to x=0.93.
Yang, Dingzheng; Xie, Lei; Bobicki, Erin; Xu, Zhenghe; Liu, Qingxia; Zeng, Hongbo
2014-09-16
Understanding the surface properties and interactions of nonspherical particles is of both fundamental and practical importance in the rheology of complex fluids in various engineering applications. In this work, natural chrysotile, a phyllosilicate composed of 1:1 stacked silica and brucite layers which coil into cylindrical structure, was chosen as a model rod-shaped particle. The interactions of chrysotile brucite-like basal or bilayered edge planes and a silicon nitride tip were measured using an atomic force microscope (AFM). The force-distance profiles were fitted using the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which demonstrates anisotropic and pH-dependent surface charge properties of brucite-like basal plane and bilayered edge surface. The points of zero charge (PZC) of the basal and edge planes were estimated to be around pH 10-11 and 6-7, respectively. Rheology measurements of 7 vol % chrysotile (with an aspect ratio of 14.5) in 10 mM NaCl solution showed pH-dependent yield stress with a local maximum around pH 7-9, which falls between the two PZC values of the edge and basal planes of the rod particles. On the basis of the surface potentials of the edge and basal planes obtained from AFM measurements, theoretical analysis of the surface interactions of edge-edge, basal-edge, and basal-basal planes of the chrysotile rods suggests the yield stress maximum observed could be mainly attributed to the basal-edge attractions. Our results indicate that the anisotropic surface properties (e.g., charges) of chrysotile rods play an important role in the particle-particle interaction and rheological behavior, which also provides insight into the basic understanding of the colloidal interactions and rheology of nonspherical particles. PMID:25115179
J Park; J Li; G Divoux; L Madsen; R Moore
2011-12-31
Relations between morphology and transport sensitively govern proton conductivity in perfluorsulfonate ionomers (PFSIs) and thus determine useful properties of these technologically important materials. In order to understand such relations, we have conducted a broad systematic study of H{sup +}-form PFSI membranes over a range of uniaxial extensions and water uptakes. On the basis of small-angle X-ray scattering (SAXS) and {sup 2}H NMR spectroscopy, uniaxial deformation induces a strong alignment of ionic domains along the stretching direction. We correlate ionic domain orientation to transport using pulsed-field-gradient {sup 1}H NMR measurements of water diffusion coefficients along the three orthogonal membrane directions. Intriguingly, we observe that uniaxial deformation enhances water transport in one direction (parallel-to-draw direction) while reducing it in the other two directions (two orthogonal directions relative to the stretching direction). We evaluate another important transport parameter, proton conductivity, along two orthogonal in-plane directions. In agreement with water diffusion experiments, orientation of ionic channels increases proton conduction along the stretching direction while decreasing it in the perpendicular direction. These findings provide valuable fodder for optimal application of PFSI membranes as well as for the design of next generation polymer electrolyte membranes.
Strong in-plane anisotropic optical properties of monolayer, few-layer and bulk ReSe2
NASA Astrophysics Data System (ADS)
Zhao, Huan; Guo, Qiushi; Wang, Luhao; Xia, Fengnian; Wang, Han
2015-03-01
Recently, there has been growing interest in the anisotropic properties of certain two-dimensional (2D) materials with reduced lattice symmetry, such as black phosphorus, for developing novel applications in nanoelectronics and infrared optoelectronics. In this work, we report the strong anisotropic optical and electronic properties of monolayer, few-layer and bulk ReSe2, an emerging member of the 2D transition metal dichalcogenides (TMDCs) family. With its bulk bandgap around 1.1 eV and potentially tunable with layer number and strain, ReSe2 may complement black phosphorus for optoelectronic applications utilizing its anisotropic properties in the near-infrared and visible range. Through careful investigations of the polarization-resolved Raman spectroscopy, photoluminescence (PL), polarization-resolved optical extinction spectrum, angle-resolved DC conductance and first principles calculations, we observed and explained the consistent dependence of phonon, optical and electrical properties of ReSe2 on its in-plane crystal orientation. Our results reveal the interesting anisotropic properties of 2D ReSe2 and shed light on its potential applications in electronics and optoelectronics. This work was supported by the Army Research Laboratory.
Graphene aerogel/epoxy composites with exceptional anisotropic structure and properties.
Wang, Zhenyu; Shen, Xi; Akbari Garakani, Mohammad; Lin, Xiuyi; Wu, Ying; Liu, Xu; Sun, Xinying; Kim, Jang-Kyo
2015-03-11
3D interconnected graphene aerogels (GAs) are prepared through one-step chemical reduction and rational assembly of graphene oxide (GO) sheets, so that the difficulties to uniformly disperse the individual graphene sheets in the polymer matrixes are avoided. Apart from ultralow density, high porosity, high electrical conductivity, and excellent compressibility, the resulting GAs possess a cellular architecture with a high degree of alignment when the graphene content is above a threshold, âˆ¼0.5 wt %. The composites prepared by infiltrating GA with epoxy resin present excellent electrical conductivities, together with high mechanical properties and fracture toughness. The unusual anisotropic structure gives rise to âˆ¼67% and âˆ¼113% higher electrical conductivity and fracture toughness of the composites, respectively, in the alignment direction than that transverse to it. PMID:25691257
Naff, R.L.
1998-01-01
The late-time macrodispersion coefficients are obtained for the case of flow in the presence of a small-scale deterministic transient in a three-dimensional anisotropic, heterogeneous medium. The transient is assumed to affect only the velocity component transverse to the mean flow direction and to take the form of a periodic function. For the case of a highly stratified medium, these late-time macrodispersion coefficients behave largely as the standard coefficients used in the transport equation. Only in the event that the medium is isotropic is it probable that significant deviations from the standard coefficients would occur.
Kong, Tai; Bud'ko, Sergey L.; Canfield, Paul C.
2015-01-30
We present a detailed study of single crystalline K2Cr3As3 and analyze its thermodynamic and transport properties, anisotropic Hc2(T), and initial pressure dependence of Tc. In zero field, the temperature-dependent resistivity is metallic. Deviation from a linear temperature dependence is evident below 100 K and a T3 dependence is roughly followed from just above Tc (~10K) to ~40K. Anisotropic Hc2(T) data were measured up to 140 kOe with field applied along and perpendicular to the rodlike crystals. For the applied field perpendicular to the rod, Hc2(T) is linear with a slope ~â€“70 kOe/K. For field applied along the rod, the slopemoreÂ Â» is about â€“120 kOe/K below 70 kOe. Above 70 kOe, the magnitude of the slope decreases to ~â€“70 kOe/K. The electronic specific heat coefficient Î³, just above Tc, is 73 mJ/mol K2; the Debye temperature Î˜D is 220 K. As a result, the specific heat jump at the superconducting transition Î”C~2.2Î³Tc. Finally, for hydrostatic pressures up to ~7 kbar, Tc decreases under pressure linearly at a rate of â€“0.034K/kbar.Â«Â less
Anisotropic transport in single-crystal molybdenum bronze, Li0.33MoO3
NASA Astrophysics Data System (ADS)
Moshfeghyeganeh, Saeed; Cohn, Joshua L.; Neumeier, John J.
2015-03-01
We present transport measurements (resistivity, thermopower, thermal conductivity) on single crystals of the quasi-one-dimensional semiconductor Li0.33MoO3 in the temperature range 200-500 K. First synthesized and studied long ago, the thermal and thermoelectric properties for this compound have not been previously reported. We find extreme anisotropy in the Seebeck coefficient within the a - c planes, with Sc -Sa ~= 300 ? V/K near room temperature. The thermal conductivity at room temperature in the a - c planes was ~ 1 . 5 - 2 W/mK and 7-8 times smaller along b*. We also report x-ray studies of the out-of-plane (b*) lattice constants indicating a small structural transition at T ~ 350 K that coincides with anomalies in the transport properties. This material is based upon work supported by the U.S. Department of Energy Office of Basic Energy Sciences Grant DE-FG02-12ER46888 (Univ. Miami) and the National Science Foundation under Grant DMR-0907036 (Mont. St. Univ.).
NASA Astrophysics Data System (ADS)
Zhubayev, Alimzhan; Houben, Maartje; Smeulders, David; Barnhoorn, Auke
2014-05-01
The Posidonia Shale Formation (PSF) is one of the possible resource shales for unconventional gas in Northern Europe and currently is of great interest to hydrocarbon exploration and production. Due to low permeability of shales, economically viable production requires hydraulic fracturing of the reservoir. The design of hydrofractures requires an estimate of stress state within the reservoir and geomechanical properties such as Young's modulus and Poisson's ratio. Shales are often highly anisotropic and the models which neglect shale anisotropy may fail to predict the behaviour of hydrofractures. Seismic attenuation anisotropy, on the other hand, can play a key role in quantitative rock characterization. Where the attenuation anisotropy can potentially be linked to anisotropic permeability of shales, its fluid/gas saturation and preferred development of anisotropic fracture orientations. In this research, by utilizing the so-called Thomsen's notations, the elastic anisotropy of our (fractured and unfractured) shales has been investigated using a pulse transmission technique in the ultrasonic frequency range (0.3-1 MHz). Assuming transverse isotropy of the shales, and taking the axis x3 as the axis of rotational symmetry, directional Young's moduli and Poisson's ratios were obtained. The Young's modulus measured parallel to bedding (E1) is found to be larger than the Young's modulus measured orthogonal to bedding (E3). In case of the Poisson's ratios, we found that Î½31 is larger than Î½12, where Î½ijrelates elastic strain in xj direction to stress applied in xi direction. Finally, attenuation anisotropy in dry and layer-parallel fractured Posidonia shale samples has been studied in the same frequency range. The attenuation of compressional (QP-1) and shear (QS-1) waves increases substantially with a macro (or wavelength) fracture introduction, especially for P and S waves propagating orthogonal to the bedding. In non-fractured and fractured dry shales, QP-1 is always larger than QS-1. This inequality was also found for the fractured shale using different fluids (water, oil) on the fracture surface. A high-viscosity fluid decreases QP-1 and QS-1 in both (orthogonal and parallel to the bedding) directions, and the QP-1 to QS-1 ratio decreases with the increase of fluid viscosity.
Anisotropic superconducting properties of nanowires at the LaAlO3/SrTiO3 (110) interface
NASA Astrophysics Data System (ADS)
Irvin, Patrick; Huang, Mengcheng; Annadi, Anil; Cheng, Guanglei; Levy, Jeremy; Gopinadhan, Kalon; Venkatesan, Thirumalai; Ariando, Ariando
2015-03-01
The superconducting properties of nanowires created on anisotropic SrTiO3 (110) surfaces were investigated. Nanowires are created using conductive AFM (c-AFM) lithography at the LaAlO3/SrTiO3(110) interface along the (001) and (1 1 0) crystallographic directions. In these devices we observe anisotropic superconductivity. The upper critical magnetic field along the (001) and (1 1 0) directions are found to be markedly different with a superconducting dome that is shifted for the two orientations. These observations can be explained by anisotropic orbital binding of Ti and O atoms or the differences in the spin-orbit coupling along the two different directions. We gratefully acknowledge support for this work from NSF (DMR-1124131, DMR-1104191), AFOSR (FA9550-12-1-0057, FA9550-12-1-0268), and CRP-NRF (Tailoring Oxide Electronics).
Anisotropic photonic properties of III-V nanowires in the zinc-blende and wurtzite phase.
Wilhelm, Christophe; Larrue, Alexandre; Dai, Xing; Migas, Dmitri; Soci, Cesare
2012-03-01
Some critical aspects of the anisotropic absorption and emission properties of quasi one-dimensional structures are reviewed in the context of III-V compound semiconductor nanowires. The unique optical and electronic properties of III-V nanowires stem from the combination of dielectric effects due to their large aspect ratio, and their specific crystallographic structure which can differ significantly from the bulk case. The growth conditions leading to single-crystal nanowires with either zinc blende or wurtzite phase are first presented. Dipole selection rules for interband transitions in common III-V compounds are then summarized for the two different phases, and corroborated by ab initio Density Functional Theory calculations of the oscillator strength. The optical anisotropy is discussed considering both the effect of refractive index mismatch between the nanowire and its surroundings and the polarization of the emitting dipoles set by the nanowire crystallographic structure and orientation. Finite Difference Time Domain simulations are finally employed to illustrate the influence of the emitting dipole orientation and the nanowire diameter on the distribution of radiation in the far-field. The importance of the correlation between structural and optoelectronic properties is highlighted in view of potential applications in future nanowire photonics. PMID:22327202
Effects of nanofiber on the electrical properties of anisotropic conductive adhesives (ACAs).
Suk, Kyoung-Lim; Chung, Chang-Kyu; Paik, Kyung-Wook
2013-01-01
The effects of nanofiber on the electrical properties of anisotropic conductive films (ACFs) were investigated from the perspectives of the joint and insulation resistances. To obtain stable electrical properties for fine-pitch chip-on-film (COF) packages, two kinds of nanofiber ACFs were demonstrated: (1) polystyrene (PS) and polyacrylonitrile (PAN) nanofiber ACFs, which were formed by laminating ACFs on the top and bottom sides of PS and PAN nanofibers, and (2) PAN nanofiber coupled with conductive particle (PAN/Cp nanofiber) ACF, which was made by laminating non conductive films (NCFs) on both sides of a PAN/Cp nanofiber. The effects of the nanofiber thickness, melting, and structure on the electrical properties of the nanofiber ACFs were analyzed. Among the two different nanofiber ACFs, the PAN/Cp nanofiber ACF showed the most stable joint resistance (below 4 mOmega) and insulation resistance (above 10(8) Omega (between 7 microm bump space) due to the thin insulation layer. PMID:23646737
The Transport Properties of Activated Carbon Fibers
DOE R&D Accomplishments Database
di Vittorio, S. L.; Dresselhaus, M. S.; Endo, M.; Issi, J-P.; Piraux, L.
1990-07-01
The transport properties of activated isotropic pitch-based carbon fibers with surface area 1000 m{sup 2}/g have been investigated. We report preliminary results on the electrical conductivity, the magnetoresistance, the thermal conductivity and the thermopower of these fibers as a function of temperature. Comparisons are made to transport properties of other disordered carbons.
TRANSPORT PROPERTY MEASUREMENTS OF HFC-236EA
The report gives results of an evaluation of transport properties of 1, 1, 1, 2, 3, 3-hexafluoropropane (HFC-236ea), with liquid viscosity and thermal conductivity being the two main transport properties of interest. In addition, the specific heat and density of refrigerant/lubri...
TRANSPORT PROPERTY MEASUREMENTS OF HFC-236EA
The report gives results of an evaluation of transport properties of 1,1,1,2,3,3,-hexafluoropropane (HFC-236ea), with liquid viscosity and thermal conductivity being the two main transport properties of interest. In addition, the specific heat and density of refrigerant/lubrican...
Transport properties of fission product vapors
Im, K.H.; Ahluwalia, R.K.
1983-07-01
Kinetic theory of gases is used to calculate the transport properties of fission product vapors in a steam and hydrogen environment. Provided in tabular form is diffusivity of steam and hydrogen, viscosity and thermal conductivity of the gaseous mixture, and diffusivity of cesium iodide, cesium hydroxide, diatomic tellurium and tellurium dioxide. These transport properties are required in determining the thermal-hydraulics of and fission product transport in light water reactors.
Direct method for calculating temperature-dependent transport properties
NASA Astrophysics Data System (ADS)
Liu, Yi; Yuan, Zhe; Wesselink, R. J. H.; Starikov, Anton A.; van Schilfgaarde, Mark; Kelly, Paul J.
2015-06-01
We show how temperature-induced disorder can be combined in a direct way with first-principles scattering theory to study diffusive transport in real materials. Excellent (good) agreement with experiment is found for the resistivity of Cu, Pd, Pt (and Fe) when lattice (and spin) disorder are calculated from first principles. For Fe, the agreement with experiment is limited by how well the magnetization (of itinerant ferromagnets) can be calculated as a function of temperature. By introducing a simple Debye-like model of spin disorder parameterized to reproduce the experimental magnetization, the temperature dependence of the average resistivity, the anisotropic magnetoresistance, and the spin polarization of a Ni80Fe20 alloy are calculated and found to be in good agreement with existing data. Extension of the method to complex, inhomogeneous materials as well as to the calculation of other finite-temperature physical properties within the adiabatic approximation is straightforward.
Chai, Chen-Ket; Speelman, Lambert; Oomens, Cees W J; Baaijens, Frank P T
2014-03-01
Accurate material models and associated parameters of atherosclerotic plaques are crucial for reliable biomechanical plaque prediction models. These biomechanical models have the potential to increase our understanding of plaque progression and failure, possibly improving risk assessment of plaque rupture, which is the main cause of ischaemic strokes and myocardial infarction. However, experimental biomechanical data on atherosclerotic plaque tissue is scarce and shows a high variability. In addition, most of the biomechanical models assume isotropic behaviour of plaque tissue, which is a general over-simplification. This review discusses the past and the current literature that focus on mechanical properties of plaque derived from compression experiments, using unconfined compression, micro-indentation or nano-indentation. Results will be discussed and the techniques will be mutually compared. Thereafter, an in-house developed indentation method combined with an inverse finite element method is introduced, allowing analysis of the local anisotropic mechanical properties of atherosclerotic plaques. The advantages and limitations of this method will be evaluated and compared to other methods reported in literature. PMID:24480703
Xie, Xiao Lu; Li, Chun Hua; Yang, Yong Xiao; Jin, Lu; Tan, Jian Jun; Zhang, Xiao Yi; Su, Ji Guo; Wang, Cun Xin
2015-09-01
The transporter MsbA is a kind of multidrug resistance ATP-binding cassette transporter that can transport lipid A, lipopolysaccharides, and some amphipathic drugs from the cytoplasmic to the periplasmic side of the inner membrane. In this work, we explored the allosteric pathway of MsbA from the inward- to outward-facing states during the substrate transport process with the adaptive anisotropic network model. The results suggest that the allosteric transitions proceed in a coupled way. The large-scale closing motions of the nucleotide-binding domains occur first, accompanied with a twisting motion at the same time, which becomes more obvious in middle and later stages, especially for the later. This twisting motion plays an important role for the rearrangement of transmembrane helices and the opening of transmembrane domains on the periplasmic side that mainly take place in middle and later stages respectively. The topological structure plays an important role in the motion correlations above. The conformational changes of nucleotide-binding domains are propagated to the transmembrane domains via the intracellular helices IH1 and IH2. Additionally, the movement of the transmembrane domains proceeds in a nonrigid body, and the two monomers move in a symmetrical way, which is consistent with the symmetrical structure of MsbA. These results are helpful for understanding the transport mechanism of the ATP-binding cassette exporters. PMID:26148303
NASA Astrophysics Data System (ADS)
Bhattacharjee, A.; Smith, C.; Vasquez, B.
2010-11-01
There has been a steady accumulation of observational evidence that the solar wind may be thought of as spaghetti: a network of individual magnetic flux tubes each with its own magnetic and plasma characteristics. As early as 1963, Parker referred to these tubes as magnetic and plasma ``filaments,'' and the picture has undergone several refinements since then [Bartley et al. 1966, Marliani et al. 1973, Tu and Marsch 1990, Bruno et al. 2001], culminating in the recent work of Borovsky [2008] who has suggested that these are fossil structures that originate at the solar surface. We use the weakly compressible MHD turbulence model [Bhattacharjee et al., 1998], which incorporates the effect of background spatial inhomogeneities, to describe such structures. We revisit the model equations, showing their relation to recent work by Hunana and Zank [2010]. For a model of interchange-instability driven turbulence, we then use the 1998 model equations to make predictions for the beta scaling of the anisotropic magnetic fluctuation spectra (the so-called variance anisotropy) observed by ACE, and show that the predictions bracket the observations well. We also predict the scaling of the anisotropic transport coefficients for particles and thermal energy.
NASA Astrophysics Data System (ADS)
Olariu, C. S.; Padurariu, L.; Stanculescu, R.; Baldisserri, C.; Galassi, C.; Mitoseriu, L.
2013-12-01
Anisotropic porous Pb(Zr,Ti)O3 ceramics with various porosity degrees have been studied in order to determine the role of the pore shape and orientation on the low-field dielectric properties. Ceramic samples with formula Pb(Zr0.52Ti0.48)0.976Nb0.024O3 with different porosity degrees (dense, 10%, 20%, 40% vol.) have been prepared by solid state reaction. Taking into consideration the shape and orientation of the pore inclusions, the dielectric properties of porous ceramics have been described by using adapted mixing rules models. Rigorous bounds, derived on the basis on Variational Principle, were used to frame dielectric properties of porous composites. The finite element method (FEM) was additionally used to simulate the dielectric response of the porous composites under various applied fields. Among the few effective medium approximation models adapted for anisotropic oriented inclusions, the best results were obtained in case of needle-like shape inclusions (which do not correspond to the real shape of microstructure inclusions). The general case of Wiener bounds limited well the dielectric properties of anisotropic porous composites in case of parallel orientation. Among the theoretical approaches, FEM technique allowed to simulate the distribution of potential and electric field inside composites and provided a very good agreement between the computed permittivity values and experimental ones.
Influence of anisotropic elasticity on the mechanical properties of fivefold twinned nanowires
NASA Astrophysics Data System (ADS)
Niekiel, Florian; Spiecker, Erdmann; Bitzek, Erik
2015-11-01
Previous atomistic simulations and experiments have shown an increased Young's modulus and yield strength of fivefold twinned (FT) face-centered cubic metal nanowires (NWs) when compared to single crystalline (SC) NWs of the same orientation. Here we report the results of atomistic simulations of SC and FT Ag, Al, Au, Cu and Ni NWs with diameters between 2 and 50 nm under tension and compression. The simulations show that the differences in Young's modulus between SC and FT NWs are correlated with the elastic anisotropy of the metal, with Al showing a decreased Young's modulus. We develop a simple analytical model based on disclination theory and constraint anisotropic elasticity to explain the trend in the difference of Young's modulus between SC and FT NWs. Taking into account the role of surface stresses and the elastic properties of twin boundaries allows to account for the observed size effect in Young's modulus. The model furthermore explains the different relative yield strengths in tension and compression as well as the material and loading dependent failure mechanisms in FTNWs.
Structure and anisotropic properties of single crystals nickel doped barium iron arsenide
Ronning, Filip; Bauer, Eric D; Sefat, A S; Jin, R; Mcguire, M A; Sales, B C; Mandrus, D
2009-01-01
The crystal structure, anisotropic electrical resistivity and magnetic susceptibility, as well as specific heat results of the pure single crystals of BaFe{sub 2}As{sub 2}, BaFeNiAs{sub 2}, and BaNi{sub 2}As{sub 2} are surveyed. BaFe{sub 2}As{sub 2} properties demonstrate the equivalence of C(T), Fisher's d({chi}T)/dT and d{rho}/dT results in determining the antiferromagnetic transition at T{sub N} = 132(1) K. BaNi{sub 2}As{sub 2} shows a structural phase transition from a high-temperature tetragonal phase to a low-temperature triclinic pol symmetry at T{sub 0} 131 K, with superconducting critical temperature well below at {Tc} 0.69 K. BaFeNiAs{sub 2} does not show any sign of superconductivity and gives behavioral similarity to BaCo{sub 2}As{sub 2}, a renomalized paramagnetic metal.
NASA Astrophysics Data System (ADS)
Wang, Lei; Wang, Xiaodong
2014-06-01
Resulting from the nature of anisotropy of coal media, it is a meaningful work to evaluate pressure transient behavior and flow characteristics within coals. In this article, a complete analytical model called the elliptical flow model is established by combining the theory of elliptical flow in anisotropic media and Fick's laws about the diffusion of coalbed methane. To investigate pressure transient behavior, analytical solutions were first obtained through introducing a series of special functions (Mathieu functions), which are extremely complex and are hard to calculate. Thus, a computer program was developed to establish type curves, on which the effects of the parameters, including anisotropy coefficient, storage coefficient, transfer coefficient and rate constant, were analyzed in detail. Calculative results show that the existence of anisotropy would cause great pressure depletion. To validate new analytical solutions, previous results were used to compare with the new results. It is found that a better agreement between the solutions obtained in this work and the literature was achieved. Finally, a case study is used to explain the effects of the parameters, including rock total compressibility coefficient, coal medium porosity and anisotropic permeability, sorption time constant, Langmuir volume and fluid viscosity, on bottom-hole pressure behavior. It is necessary to coordinate these parameters so as to reduce the pressure depletion.
Transport properties of alumina nanofluids
NASA Astrophysics Data System (ADS)
Wong, Kau-Fui Vincent; Kurma, Tarun
2008-08-01
Recent studies have showed that nanofluids have significantly greater thermal conductivity compared to their base fluids. Large surface area to volume ratio and certain effects of Brownian motion of nanoparticles are believed to be the main factors for the significant increase in the thermal conductivity of nanofluids. In this paper all three transport properties, namely thermal conductivity, electrical conductivity and viscosity, were studied for alumina nanofluid (aluminum oxide nanoparticles in water). Experiments were performed both as a function of volumetric concentration (3-8%) and temperature (2-50 °C). Alumina nanoparticles with a mean diameter of 36 nm were dispersed in water. The effect of particle size was not studied. The transient hot wire method as described by Nagaska and Nagashima for electrically conducting fluids was used to test the thermal conductivity. In this work, an insulated platinum wire of 0.003 inch diameter was used. Initial calibration was performed using de-ionized water and the resulting data was within 2.5% of standard thermal conductivity values for water. The thermal conductivity of alumina nanofluid increased with both increase in temperature and concentration. A maximum thermal conductivity of 0.7351 W m-1 K-1 was recorded for an 8.47% volume concentration of alumina nanoparticles at 46.6 °C. The effective thermal conductivity at this concentration and temperature was observed to be 1.1501, which translates to an increase in thermal conductivity by 22% when compared to water at room temperature. Alumina being a good conductor of electricity, alumina nanofluid displays an increasing trend in electrical conductivity as volumetric concentration increases. A microprocessor-based conductivity/TDS meter was used to perform the electrical conductivity experiments. After carefully calibrating the conductivity meter's glass probe with platinum tip, using a standard potassium chloride solution, readings were taken at various volumetric concentrations. A 3457.1% increase in the electrical conductivity was measured for a small 1.44% volumetric concentration of alumina nanoparticles in water. The highest value of electrical conductivity, 314 µS cm-1, was recorded for a volumetric concentration of 8.47%. In the determination of the kinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constant temperature bath was used. Calibrated capillary viscometers were used to measure flow under gravity at precisely controlled temperatures. The capillary viscometers were calibrated with de-ionized water at different temperatures, and the resulting kinematic viscosity values were found to be within 3% of the standard published values. An increase of 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration of alumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid, 2.901 42 mm2 s-1, was obtained at 0 °C for an 8.47% volumetric concentration of alumina nanoparticles. The experimental results of the present work will help researchers arrive at better theoretical models.
Transport properties of alumina nanofluids.
Wong, Kau-Fui Vincent; Kurma, Tarun
2008-08-27
Recent studies have showed that nanofluids have significantly greater thermal conductivity compared to their base fluids. Large surface area to volume ratio and certain effects of Brownian motion of nanoparticles are believed to be the main factors for the significant increase in the thermal conductivity of nanofluids. In this paper all three transport properties, namely thermal conductivity, electrical conductivity and viscosity, were studied for alumina nanofluid (aluminum oxide nanoparticles in water). Experiments were performed both as a function of volumetric concentration (3-8%) and temperature (2-50?°C). Alumina nanoparticles with a mean diameter of 36 nm were dispersed in water. The effect of particle size was not studied. The transient hot wire method as described by Nagaska and Nagashima for electrically conducting fluids was used to test the thermal conductivity. In this work, an insulated platinum wire of 0.003 inch diameter was used. Initial calibration was performed using de-ionized water and the resulting data was within 2.5% of standard thermal conductivity values for water. The thermal conductivity of alumina nanofluid increased with both increase in temperature and concentration. A maximum thermal conductivity of 0.7351 W m(-1) K(-1) was recorded for an 8.47% volume concentration of alumina nanoparticles at 46.6?°C. The effective thermal conductivity at this concentration and temperature was observed to be 1.1501, which translates to an increase in thermal conductivity by 22% when compared to water at room temperature. Alumina being a good conductor of electricity, alumina nanofluid displays an increasing trend in electrical conductivity as volumetric concentration increases. A microprocessor-based conductivity/TDS meter was used to perform the electrical conductivity experiments. After carefully calibrating the conductivity meter's glass probe with platinum tip, using a standard potassium chloride solution, readings were taken at various volumetric concentrations. A 3457.1% increase in the electrical conductivity was measured for a small 1.44% volumetric concentration of alumina nanoparticles in water. The highest value of electrical conductivity, 314 µS cm(-1), was recorded for a volumetric concentration of 8.47%. In the determination of the kinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constant temperature bath was used. Calibrated capillary viscometers were used to measure flow under gravity at precisely controlled temperatures. The capillary viscometers were calibrated with de-ionized water at different temperatures, and the resulting kinematic viscosity values were found to be within 3% of the standard published values. An increase of 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration of alumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid, 2.901?42 mm(2) s(-1), was obtained at 0?°C for an 8.47% volumetric concentration of alumina nanoparticles. The experimental results of the present work will help researchers arrive at better theoretical models. PMID:21730657
NASA Astrophysics Data System (ADS)
Karasawa, Naoki
2015-03-01
Temperature dependence of the dispersion properties of liquid crystal core photonic crystal fibers with large air fraction in clads between 300 and 2000 nm for different core diameters have been calculated by a multipole method, which is modified to treat anisotropic inclusions rigorously. In calculations, air holes are assumed to be arranged in a regular hexagonal array in fused silica and a central hole is filled with liquid crystal to create a core. Below the clearing point temperature, the liquid crystal molecules are assumed to be oriented parallel to the cylindrical axis of the holes, where the liquid crystal is highly anisotropic. The large changes of the dispersion properties are found at the clearing point temperature, where the liquid crystal becomes isotropic.
Anisotropic strain in SmSe and SmTe: Implications for electronic transport
NASA Astrophysics Data System (ADS)
Kuroda, Marcelo A.; Jiang, Zhengping; Povolotskyi, Michael; Klimeck, Gerhard; Newns, Dennis M.; Martyna, Glenn J.
2014-12-01
Mixed valence rare-earth samarium compounds Sm X (X =Se,Te ) have been recently proposed as candidate materials for use in high-speed, low-power digital switches driven by stress induced changes of resistivity. At room temperature these materials exhibit a pressure driven insulator-to-metal transition with resistivity decreasing by up to seven orders of magnitude over a small pressure range. Thus, the application of only a few GPa's to the piezoresistor (Sm X ) allows the switching device to perform complex logic. Here we study from first principles the electronic properties of these compounds under uniaxial strain and discuss the implications for carrier transport. Based on changes in the band structure and a model we show that the piezoresistive response is mostly governed by the reduction of band gap with strain. Furthermore, the piezoresistive reponse becomes optimal when the Fermi level is pinned near the localized valence band. The piezoresistive effect under uniaxial strain, which must be taken into account in thin films and other systems with reduced dimensionality, is also studied. Under uniaxial strain we find that the piezoresistive response can be substantially larger than in the isotropic case. Analysis of the complex band structure of SmSe yields a tunneling length of the order of 1 nm. This suggest that the conduction mechanism governing the piezoresistive effect in bulk, i.e., thermal promotion of electrons, should still be dominant in few-nanometer-thick films.
Sansalone, V; Naili, S; Bousson, V; Bergot, C; Peyrin, F; Zarka, J; Laredo, J D; Haïat, G
2010-07-20
Cortical bone is a multiscale composite material. Its elastic properties are anisotropic and heterogeneous across its cross-section, due to endosteal bone resorption which might affect bone strength. The aim of this paper was to describe a homogenization method leading to the estimation of the variation of the elastic coefficients across the bone cross-section and along the bone longitudinal axis. The method uses the spatial variations of bone porosity and of the degree of mineralization of the bone matrix (DMB) obtained from the analysis of 3-D synchrotron micro-computed tomography images. For all three scales considered (the foam (100 nm), the ultrastructure (5 microm) and the mesoscale (500 microm)), the elastic coefficients were determined using the Eshelby's inclusion problem. DMB values were used at the scale of the foam. Collagen was introduced at the scale of the ultrastructure and bone porosity was introduced at the mesoscale. The pores were considered as parallel cylinders oriented along the bone axis. Each elastic coefficient was computed for different regions of interest, allowing an estimation of its variations across the bone cross-section and along the bone longitudinal axis. The method was applied to a human femoral neck bone specimen, which is a site of osteoporotic fracture. The computed elastic coefficients for cortical bone were in good agreement with experimental results, but some discrepancies were obtained in the endosteal part (trabecular bone). These results highlight the importance of accounting for the heterogeneity of cortical bone properties across bone cross-section and along bone longitudinal axis. PMID:20392446
Transport properties of ground state oxygen atoms
NASA Technical Reports Server (NTRS)
Holland, Paul M.; Biolsi, Louis
1988-01-01
The transport properties of dilute monatomic gases depend on the two-body interactions between like atoms. When two ground-state oxygen atoms interact, they can follow any of 18 potential energy curves corresponding to O2, all of which contribute to the transport properties of the ground-state atoms. Transport collision integrals have been calculated for those interactions with an attractive minimum in the potential, and repulsive ab initio potential-energy curves have been accurately represented. Results are given for viscosity, thermal conductivity, and diffusion and they are compared with previous theoretical calculations.
NASA Astrophysics Data System (ADS)
Malkina, Olga
SC-15 epoxy is used in many industrial applications and it is well known that the mechanical and viscoelastic properties of epoxy can be significantly enhanced when reinforced with nanofillers. In this work, SC-15 epoxy is reinforced by loading with magnetically-active nanofillers and cured in a modest magnetic field. Because of the significant magnetic response of the nanofillers, this is a low cost and relatively easy technique for imposing a strong magnetic anisotropy to the system without the need of a superconducting magnet. It is also found that this method is an effective way of enhancing the mechanical properties of epoxy. Three systems were prepared and studied. The first is a dilute system of various concentrations of Fe2O3 nanoparticles in SC-15 epoxy. The second systems is a combination of Fe2O3 nanoparticles and chemically-functionalized single-walled carbon nanotubes (SWCNT(COOH)s) in SC-15 epoxy. The third is a dilute system of SWCNT(COOH)s decorated with Fe3O4 particles through a sonochemical oxidation process in SC-15 epoxy. Samples have an initial cure of 6 hrs in a magnetic filed of 10 kOe followed by an additional 24 hrs of post curing at room temperature. These are compared to the control samples that do not have initial field curing. Tensile and compressive stress-strain analysis of the prepared systems shows that mechanical properties such as tensile strength, tensile modulus and compressive strength are enhanced with the inclusion of these nanofillers. It is also found that there is an anisotropic enhancement of these properties with respect to the imposed curing field. An interesting phenomenon is observed with the increase in modulus of toughness and fracture strain with nanotube inclusion. These parameters are drastically enhanced after curing the systems in a magnetic field. While there is a modest shift in glass transition temperature during viscoelastic analysis, the thermal stability of the created systems is not compromised. Results of these mechanical enhancements will be compared with other nanoloading techniques from literature.
Chai, Chen-Ket; Akyildiz, Ali C; Speelman, Lambert; Gijsen, Frank J H; Oomens, Cees W J; van Sambeek, Marc R H M; van der Lugt, Aad; Baaijens, Frank P T
2015-03-01
Biomechanical models have the potential to predict failure of atherosclerotic plaques and to improve the risk assessment of plaque rupture. The applicability of these models depends strongly on the used material models. Current biomechanical models employ isotropic material models, although it is generally accepted that plaque tissue behaves highly anisotropic. The aim of the present study is to determine the local anisotropic mechanical properties of human atherosclerotic plaque tissue by means of micro-indentation tests. The indentation was performed on top of an inverted confocal microscope allowing the visualisation and quantification of the collagen fibre deformations perpendicular to the indentation direction of the plaque. Based on this, the anisotropic properties of plaque tissue perpendicular to the indentation direction (middle of the fibrous cap, shoulder of the cap, remaining intima tissue) were derived. There were no significant differences between the different indentation locations for the fibre stiffness (total median 80.6kPa, 25th-75th percentile 17.7-157.0kPa), and fibre dispersion. PMID:25553556
Cho, B.
1995-11-01
The interaction of superconductivity with magnetism has been one of the most interesting and important phenomena in solid state physics since the 1950`s when small amounts of magnetic impurities were incorporated in superconductors. The discovery of the magnetic superconductors RNi{sub 2}B{sub 2}C (R = rare earth, Y) offers a new system to study this interaction. The wide ranges of superconducting transition (T{sub c}) and antiferromagnetic (AF) ordering temperatures (T{sub N}) (0 K {le} T{sub c} {le} 16 K, 0 K {le} T{sub N} {le} 20 K) give a good opportunity to observe a variety of interesting phenomena. Single crystals of high quality with appropriate size and mass are crucial in examining the anisotropic intrinsic properties. Single crystals have been grown successfully by an unusual high temperature flux method and characterized thoroughly by X-ray, electrical transport, magnetization, neutron scattering, scanning electron microscopy, and other measurements.
Transport Properties and Transport Phenomena in Casting Nickel Superalloys
NASA Astrophysics Data System (ADS)
Felicelli, S. D.; Sung, P. K.; Poirier, D. R.; Heinrich, J. C.
1998-11-01
Nickel superalloys that are used in the high-temperature regions of gas-turbine engines are cast by directional solidification (DS). In the DS processes, the castings are cooled from below, and three zones exist during solidification: (1) an all-solid zone at the bottom, (2) a "mushy zone" that is comprised of solid and liquid material, and (3) an overlying all-liquid zone. Computer simulations can be useful in predicting the complex transport phenomena that occur during solidification, but realistic simulations require accurate values of the transport properties. In addition to transport properties, the thermodynamic equilibria between the solid and liquid during solidification must also be known with reasonable accuracy. The importance of using reasonably accurate estimations of the transport properties is illustrated by two-dimensional simulations of the convection during solidification and the coincidental macrosegregation in the DS castings of multicomponent Ni-base alloys. In these simulations, we examine the sensitivity of the calculated results to measured partition ratios, thermal expansion coefficients, and viscosities that are estimated by regression analyses and correlations of existing property data.
Eslami, Hossein; Mohammadzadeh, Laila; Mehdipour, Nargess
2012-03-14
While polymers are known as thermal insulators, recent studies show that stretched single chains of polymers have a very high thermal conductivity. In this work, our new simulation scheme for simulation of heat flow in nanoconfined fluids [H. Eslami, L. Mohammadzadeh, and N. Mehdipour, J. Chem. Phys. 135, 064703 (2011)] is employed to study the effect of chain ordering (stretching) on the rate of heat transfer in polyamide-6,6 nanoconfined between graphene surfaces. Our results for the heat flow in the parallel direction (the plane of surfaces) show that the coefficient of thermal conductivity depends on the intersurface distance and is much higher than that of the bulk polymer. A comparison of results in this work with our former findings on the heat flow in the perpendicular direction, with the coefficient of heat conductivity less than the bulk sample, reveal that well-organized polymer layers between the confining surfaces show an anisotropic heat conduction; the heat conduction in the direction parallel to the surfaces is much higher than that in the perpendicular direction. The origin of such anisotropy in nanometric heat flow is shown to be the dramatic anisotropy in chain conformations (chain stretching) beside the confining surfaces. The results indicate that the coefficients of heat conductivity in both directions, normal and parallel to the surfaces, depend on the degree of polymer layering between the surfaces and the pore width. PMID:22423855
NASA Astrophysics Data System (ADS)
Eslami, Hossein; Mohammadzadeh, Laila; Mehdipour, Nargess
2012-03-01
While polymers are known as thermal insulators, recent studies show that stretched single chains of polymers have a very high thermal conductivity. In this work, our new simulation scheme for simulation of heat flow in nanoconfined fluids [H. Eslami, L. Mohammadzadeh, and N. Mehdipour, J. Chem. Phys. 135, 064703 (2011)], 10.1063/1.3623471 is employed to study the effect of chain ordering (stretching) on the rate of heat transfer in polyamide-6,6 nanoconfined between graphene surfaces. Our results for the heat flow in the parallel direction (the plane of surfaces) show that the coefficient of thermal conductivity depends on the intersurface distance and is much higher than that of the bulk polymer. A comparison of results in this work with our former findings on the heat flow in the perpendicular direction, with the coefficient of heat conductivity less than the bulk sample, reveal that well-organized polymer layers between the confining surfaces show an anisotropic heat conduction; the heat conduction in the direction parallel to the surfaces is much higher than that in the perpendicular direction. The origin of such anisotropy in nanometric heat flow is shown to be the dramatic anisotropy in chain conformations (chain stretching) beside the confining surfaces. The results indicate that the coefficients of heat conductivity in both directions, normal and parallel to the surfaces, depend on the degree of polymer layering between the surfaces and the pore width.
Xu, He; Li, Haiyan; Ke, Qinfei; Chang, Jiang
2015-04-29
The development of vascular scaffolds with controlled mechanical properties and stimulatory effects on biological activities of endothelial cells still remains a significant challenge to vascular tissue engineering. In this work, we reported an innovative approach to prepare a new type of vascular scaffolds with anisotropically and heterogeneously aligned patterns using electrospinning technique with unique wire spring templates, and further investigated the structural effects of the patterned electrospun scaffolds on mechanical properties and angiogenic differentiation of human umbilical vein endothelial cells (HUVECs). Results showed that anisotropically aligned patterned nanofibrous structure was obtained by depositing nanofibers on template in a structurally different manner, one part of nanofibers densely deposited on the embossments of wire spring and formed cylindrical-like structures in the transverse direction, while others loosely suspended and aligned along the longitudinal direction, forming a three-dimensional porous microstructure. We further found that such structures could efficiently control the mechanical properties of electrospun vascular scaffolds in both longitudinal and transverse directions by altering the interval distances between the embossments of patterned scaffolds. When HUVECs were cultured on scaffolds with different microstructures, the patterned scaffolds distinctively promoted adhesion of HUVECs at early stage and proliferation during the culture period. Most importantly, cells experienced a large shape change associated with cell cytoskeleton and nuclei remodeling, leading to a stimulatory effect on angiogenesis differentiation of HUVECs by the patterned microstructures of electrospun scaffolds, and the scaffolds with larger distances of intervals showed a higher stimulatory effect. These results suggest that electrospun scaffolds with the anisotropically and heterogeneously aligned patterns, which could efficiently control the mechanical properties and bioactivities of the scaffolds, might have great potential in vascular tissue engineering application. PMID:25826222
Coupled light transport-heat diffusion model for laser dosimetry with dynamic optical properties
London, R.A.; Glinsky, M.E.; Zimmerman, G.B.; Eder, D.C.; Jacques, S.L.
1995-03-01
The effect of dynamic optical properties on the spatial distribution of light in laser therapy is studied via numerical simulations. A two-dimensional, time dependent computer program called LATIS is used. Laser light transport is simulated with a Monte Carlo technique including anisotropic scattering and absorption. Thermal heat transport is calculated with a finite difference algorithm. Material properties are specified on a 2-D mesh and can be arbitrary functions of space and time. Arrhenius rate equations are solved for tissue damage caused by elevated temperatures. Optical properties are functions of tissue damage, as determined by previous measurements. Results are presented for the time variation of the light distribution and damage within the tissue as the optical properties of the tissue are altered.
NASA Astrophysics Data System (ADS)
Wei, Qin; Zhu, Jianguo; Chen, Wei
2016-01-01
The mechanical properties of plasma-sprayed thermal barrier coatings (TBC) are of great scientific and technological significance for the design and fabrication of TBC systems. The ultrasonic method combined with a sing-around method for mechanical properties measurement of TBC is deduced and the elastic modulus can be determined in the spray, or longitudinal, direction, and the transverse direction. Tested specimens of plasma-sprayed TBC are detached from the substrate and treated with thermal exposure at 1400 Â°C. The elastic moduli along the longitudinal and transverse directions of the TBCs are measured by different types of ultrasonic waves combined with a sing-around method, while the Poisson's ratio is also obtained simultaneously. The experimental results indicate that the magnitude of longitudinal elastic modulus is larger than that of the transverse one, and thus the plasma-sprayed TBC has an anisotropic mechanical property. Moreover, the elastic moduli along both longitudinal and transverse directions change with high-temperature exposure time, which consists of a rapid increasing stage followed by a slow decreasing stage. In addition, the magnitude of Poisson's ratio increases slightly from 0.05 to 0.2 with the high-temperature exposure time. Generally, the microstructures in the plasma-sprayed coatings and their evolution in a high-temperature environment are the main causes of the varying anisotropic mechanical properties.
NASA Astrophysics Data System (ADS)
Wei, Qin; Zhu, Jianguo; Chen, Wei
2016-02-01
The mechanical properties of plasma-sprayed thermal barrier coatings (TBC) are of great scientific and technological significance for the design and fabrication of TBC systems. The ultrasonic method combined with a sing-around method for mechanical properties measurement of TBC is deduced and the elastic modulus can be determined in the spray, or longitudinal, direction, and the transverse direction. Tested specimens of plasma-sprayed TBC are detached from the substrate and treated with thermal exposure at 1400 Â°C. The elastic moduli along the longitudinal and transverse directions of the TBCs are measured by different types of ultrasonic waves combined with a sing-around method, while the Poisson's ratio is also obtained simultaneously. The experimental results indicate that the magnitude of longitudinal elastic modulus is larger than that of the transverse one, and thus the plasma-sprayed TBC has an anisotropic mechanical property. Moreover, the elastic moduli along both longitudinal and transverse directions change with high-temperature exposure time, which consists of a rapid increasing stage followed by a slow decreasing stage. In addition, the magnitude of Poisson's ratio increases slightly from 0.05 to 0.2 with the high-temperature exposure time. Generally, the microstructures in the plasma-sprayed coatings and their evolution in a high-temperature environment are the main causes of the varying anisotropic mechanical properties.
Electronic and transport properties of phosphorene nanoribbons
NASA Astrophysics Data System (ADS)
Wu, Qingyun; Shen, Lei; Yang, Ming; Cai, Yongqing; Huang, Zhigao; Feng, Yuan Ping
2015-07-01
By combining density functional theory and nonequilibrium Green's function, we study the electronic and transport properties of monolayer black phosphorus nanoribbons (PNRs). First, we investigate the band gap of PNRs and its modulation by the ribbon width and an external transverse electric field. Our calculations indicate a giant Stark effect in PNRs, which can switch on transport channels of semiconducting PNRs under low bias, inducing an insulator-metal transition. Next, we study the transport channels in PNRs via the calculations of the current density and local electron transmission pathway. In contrast to graphene and MoS2 nanoribbons, the carrier transport channels under low bias are mainly located in the interior of both armchair and zigzag PNRs, and immune to a small amount of edge defects. Last, a device of the PNR-based dual-gate field-effect transistor, with high on/off ratio of 103, is proposed based on the giant electric-field tuning effect.
NASA Astrophysics Data System (ADS)
Yang, Zihao; Kent, Thomas F.; Yang, Jing; Jin, Hyungyu; Heremans, Joseph P.; Myers, Roberto C.
2015-12-01
Here we report on the effect of rare-earth Gd doping on the magnetic properties and magnetotransport of GaN two-dimensional electron gasses (2DEGs). Samples are grown by plasma-assisted molecular-beam epitaxy and consist of AlN/GaN heterostructures where Gd is ? doped within a polarization-induced 2DEG. Ferromagnetism is observed in these Gd-doped 2DEGs with a Curie temperature above room temperature and an anisotropic spontaneous magnetization preferring an out-of-plane (c -axis) orientation. At magnetic fields up to 50 kOe, the magnetization remains smaller for the in-plane configuration than for the out-of-plane configuration, which is indicative of exchange-coupled spins locked along the polar c axis. The sample with the lowest Gd concentration (2.3 ×1014c m-2 ) exhibits a saturation magnetization of 41.1 ?B/ G d3 + at 5 K revealing that the Gd ion spins (7 ?B ) alone do not account for the magnetization. Surprisingly, control samples grown without any Gd display inconsistent magnetic properties; in some control samples weak ferromagnetism is observed, and in others paramagnetism is observed. The ferromagnetic 2DEGs do not exhibit the anomalous Hall effect; the Hall resistance varies nonlinearly with the magnetic field but does not track the magnetization, indicating the lack of coupling between the ferromagnetic phase and the conduction-band electrons within the 2DEG.
Magnetotransport Properties of the Highly Anisotropic Helimagnet Cr1/3NbS2
NASA Astrophysics Data System (ADS)
Bornstein, Alexander; Ghimire, Nirmal; Mandrus, David; Parker, David; Lee, Minhyea
2014-03-01
Unusual electrical transports properties such as the topological Hall Effect in non-trivial spin textures have demonstrated great potential for controlling electrical properties via underlying spin degree of freedom. In particular, magnetic systems with no-inversion symmetry in their crystal structure are promising candidates to search for these effects due to their tendency to support non-collinear spin configurations, a requirement for non-trivial spin texture. Here, we study the in-plane magnetotransport properties in the chiral helimagnet Cr1/3NbS2, which falls in such a category and has larger crystalline anisotropy relative to other known systems (e.g. MnSi). At low temperature (T <
Sun, Bao-Zhen; Ma, Zuju; He, Chao; Wu, Kechen
2015-11-28
Thermoelectrics interconvert heat to electricity and are of great interest in waste heat recovery, solid-state cooling and so on. Here we assessed the potential of SnS2 and SnSe2 as thermoelectric materials at the temperature gradient from 300 to 800 K. Reflecting the crystal structure, the transport coefficients are highly anisotropic between a and c directions, in particular for the electrical conductivity. The preferred direction for both materials is the a direction in TE application. Most strikingly, when 800 K is reached, SnS2 can show a peak power factor (PF) of 15.50 ?W cm(-1) K(-2) along the a direction, while a relatively low value (11.72 ?W cm(-1) K(-2)) is obtained in the same direction of SnSe2. These values are comparable to those observed in thermoelectrics such as SnSe and SnS. At 300 K, the minimum lattice thermal conductivity (?min) along the a direction is estimated to be about 0.67 and 0.55 W m(-1) K(-1) for SnS2 and SnSe2, respectively, even lower than the measured lattice thermal conductivity of Bi2Te3 (1.28 W m(-1) K(-1) at 300 K). The reasonable PF and ?min suggest that both SnS2 and SnSe2 are potential thermoelectric materials. Indeed, the estimated peak ZT can approach 0.88 for SnSe2 and a higher value of 0.96 for SnS2 along the a direction at a carrier concentration of 1.94 × 10(19) (SnSe2) vs. 2.87 × 10(19) cm(-3) (SnS2). The best ZT values in SnX2 (X = S, Se) are comparable to that in Bi2Te3 (0.8), a typical thermoelectric material. We hope that this theoretical investigation will provide useful information for further experimental and theoretical studies on optimizing the thermoelectric properties of SnX2 materials. PMID:26486877
Cuenca, Jacques; GÃ¶ransson, Peter
2012-08-01
This paper presents a method for simultaneously identifying both the elastic and anelastic properties of the porous frame of anisotropic open-cell foams. The approach is based on an inverse estimation procedure of the complex stiffness matrix of the frame by performing a model fit of a set of transfer functions of a sample of material subjected to compression excitation in vacuo. The material elastic properties are assumed to have orthotropic symmetry and the anelastic properties are described using a fractional-derivative model within the framework of an augmented Hooke's law. The inverse estimation problem is formulated as a numerical optimization procedure and solved using the globally convergent method of moving asymptotes. To show the feasibility of the approach a numerically generated target material is used here as a benchmark. It is shown that the method provides the full frequency-dependent orthotropic complex stiffness matrix within a reasonable degree of accuracy. PMID:22894184
NASA Astrophysics Data System (ADS)
Lee, Ji-Hwan; Park, Jong-Hun; Jung, Young-Kwang; Soon, Aloysius
2015-03-01
Current materials-related calculations employ the density-functional theory (DFT), commonly using the (semi-)local-density approximations for the exchange-correlation (xc) functional. The accuracy to studying the electronic structure depends not only on the employed approximation to the xc potential but also upon the system which is being investigated. The difficulties in arriving at a reasonable description of van der Waals (vdW) interactions by DFT-based models, is to date a big challenge. This stems from the well-known fact that vdW interaction is a non-local correlation effect which is not captured in the deployed (semi-)local xc functionals. In this work, using various flavours of vdW-corrected DFT xc functionals, we study the lattice and mechanical properties (including the elastic constants and anisotropic stress-strain curves) of the coinage metals (copper, silver, and gold), and critically assess the reliability of the different vdW-corrected DFT methods in describing their anisotropic mechanical properties which are less reported on in the literature.
NASA Astrophysics Data System (ADS)
Zheng, J.; Zhu, J.; Wang, Z.; Fang, F.; Pain, C. C.; Xiang, J.
2015-10-01
An integrated method of advanced anisotropic hr-adaptive mesh and discretization numerical techniques has been, for first time, applied to modelling of multiscale advection-diffusion problems, which is based on a discontinuous Galerkin/control volume discretization on unstructured meshes. Over existing air quality models typically based on static-structured grids using a locally nesting technique, the advantage of the anisotropic hr-adaptive model has the ability to adapt the mesh according to the evolving pollutant distribution and flow features. That is, the mesh resolution can be adjusted dynamically to simulate the pollutant transport process accurately and effectively. To illustrate the capability of the anisotropic adaptive unstructured mesh model, three benchmark numerical experiments have been set up for two-dimensional (2-D) advection phenomena. Comparisons have been made between the results obtained using uniform resolution meshes and anisotropic adaptive resolution meshes. Performance achieved in 3-D simulation of power plant plumes indicates that this new adaptive multiscale model has the potential to provide accurate air quality modelling solutions effectively.
Souza, W.R.; Voss, C.I.
1987-01-01
The groundwater system in southern Oahu, Hawaii consists of a thick, areally extensive freshwater lens overlying a zone of transition to a thick saltwater body. This system is analyzed in cross section with a variable-density groundwater flow and solute transport model on a regional scale. The simulation is difficult, because the coastal aquifer system has a saltwater transition zone that is broadly dispersed near the discharge area, but is very sharply defined inland. Steady-state simulation analysis of the transition zone in the layered basalt aquifer of southern Oahu indicates that a small transverse dispersivity is characteristic of horizontal regional flow. Further, in this system flow is generally parallel to isochlors and steady-state behavior is insensitive to the longitudinal dispersivity. Parameter analysis identifies that only six parameters control the complex hydraulics of the system: horizontal and vertical hydraulic conductivity of the basalt aquifer; hydraulic conductivity of the confining "caprock" layer; leakance below the caprock; specific yield; and aquifer matrix compressibility. The best-fitting models indicate the horizontal hydraulic conductivity is significantly greater than the vertical hydraulic conductivity. These models give values for specific yield and aquifer compressibility which imply a considerable degree of compressive storage in the water table aquifer. ?? 1987.
Anisotropic colloidal transport and periodic stick-slip motion in cholesteric finger textures.
Chen, Kui; Metcalf, Linnea P; Rivas, David P; Reich, Daniel H; Leheny, Robert L
2015-06-01
We have investigated the mobility of discoidal colloidal particles sedimenting within cholesteric finger textures formed by mixtures of the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) and the chiral dopant 4-(2-methylbutyl)-4'-cyanobiphenyl (CB15) with cholesteric pitch p between 24 and 114 Î¼m. The nickel disks, with radius 17 Î¼m and thickness 300 nm, displayed varied transport behavior that depended on the size of the pitch and the orientation of the gravitational force with respect to the cholesteric axis. In textures with small pitch (p < 40 Î¼m), the disks moved perpendicular to the axis irrespective of the orientation of gravity as a result of an elastic retarding force that prevented motion along the axis. In textures with larger pitch, the disks similarly moved perpendicular to the axis when the angle between the force and axis was large. When the angle was small, the disks displayed stick-slip motion caused by periodic yielding of the finger texture. A model considering viscous drag on the particles and the elastic energy cost of deforming the finger texture describes the stick-slip motion accurately. The effective drag viscosities obtained from the disk motion are anomalously large compared with those of pure nematic 5CB indicating a large contribution to the dissipation from the motion of disclinations in the texture in the vicinity of the translating disks. PMID:25875803
Anisotropic thermal transport in Bi2223/Ag superconducting tape with sandwiched structure
NASA Astrophysics Data System (ADS)
Naito, Tomoyuki; Fujishiro, Hiroyuki; Osabe, Goro; Fujikami, Jun
2013-01-01
The thermal conductivity, ?(T), of the Bi2223/Ag tape reinforced by metal tapes (stainless steel (SS) or copper-based alloy (CA)) from both side was evaluated along the length (l) and width (w) directions. ?(T) along the l-direction was measured directly using a single tape and that along the w-direction was estimated from the ?(T) measured for a stacked bundle which consists of several sandwiched Bi2223/Ag tapes. We analyzed the obtained ?(T) curves using an equivalent heat current circuit, and found that the heat transports along both directions were nearly the same and that the route of heat-flow depended on the species of the reinforcing metal. The absolute values of ?(T) at 77 K along the l- and w- directions for the Bi2223/Ag-SS tape were 174 and 140 W m-1 K-1 and those for the Bi2223/Ag-CA tape were 206 and 206 W m-1 K-1, respectively, the values of which were approximately 30-40% and 10-15% smaller than those of the standard Bi2223/Ag tape.
Magnetic properties of anisotropic Nd(Fe,Mo)12N(x)
NASA Astrophysics Data System (ADS)
Yang, Ying-Chang; Liu, Zun0xiao; Zhang, Xiao-Dong; Cheng, Ben-Pei; Ge, Sen-Lin
1994-08-01
Anisotropic magnets based on Nd(Fe,Mo)12N(x) nitrides were prepared by a milling process. Particle size dependence of the coerciviy has been investigated. The optimizing size which accompanies the highest coercive force was examined by transmission electron microscopy (TEM). A coercive force iH(sub c) of up to 6.2 kOe, and a maximum energy product (BH)max of up to 12.0 MG Oe were obtained., The mechanism of the coercivities is discussed with a comparison of the powders prepared by mechanical alloying. The variation of coercive force as a function of temperature is reported.
NASA Astrophysics Data System (ADS)
Carbone, G.; Lorenz, B.; Persson, B. N. J.; Wohlers, A.
2009-07-01
In this paper we extend the theory of contact mechanics and rubber friction developed by one of us (B.N.J. Persson, J. Chem. Phys. 115, 3840 (2001)) to the case of surfaces with anisotropic surface roughness. As an application we calculate the viscoelastic contribution to the rubber friction. We show that the friction coefficient may depend significantly on the sliding direction, while the area of contact depends weakly on the sliding direction. We have carried out experiments for rubber blocks sliding on unidirectionally polished steel surfaces. The experimental data are in a good qualitative agreement with the theory.
Crystal growth and anisotropic thermal properties of the nonlinear and polar oxide Cs2TeW3O12
NASA Astrophysics Data System (ADS)
Feng, Jiang-He; Xiang, Xu; Mao, Jiang-Gao
2015-12-01
Large crystal of the nonlinear optical and polar oxide Cs2TeW3O12 with a size of 20×15×4 mm3 has been grown by the top-seeded solution growth (TSSG) method. This crystal can be thermally stable up to 808 °C and melts incongruently. It possesses a large transparent range of 0.415-5.250 ?m. Thermal properties, including thermal expansion, specific heat, thermal diffusivity and thermal conductivity were investigated. The average linear thermal expansion coefficients were calculated based on the measurement in the temperature range of 30-390 °C. It exhibits strong anisotropic thermal expansion which was discussed according to the relationships between the structure and thermal properties. Furthermore, laser-induced damage threshold has been estimated to be 591.28 MW/cm2 with a laser wavelength of 1064 nm and pulse duration of 8 ns.
Anisotropic charge transport in large single crystals of ?-conjugated organic molecules
NASA Astrophysics Data System (ADS)
Hourani, Wael; Rahimi, Khosrow; Botiz, Ioan; Vinzenz Koch, Felix Peter; Reiter, Günter; Lienerth, Peter; Heiser, Thomas; Bubendorff, Jean-Luc; Simon, Laurent
2014-04-01
The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of ?-? stacking (along the long axis of the single crystal) with a mobility value in the order of 10-3 cm2 V-1 s-1, and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm2 V-1 s-1. The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the ?-? stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility.
Vishnuvardhan, J; Krishnamurthy, C V; Balasubramaniam, Krishnan
2009-02-01
A novel blind inversion method using Lamb wave S(0) and A(0) mode velocities is proposed for the complete determination of elastic moduli, material symmetries, as well as principal plane orientations of anisotropic plates. The approach takes advantage of genetic algorithm, introduces the notion of "statistically significant" elastic moduli, and utilizes their sensitivities to velocity data to reconstruct the elastic moduli. The unknown material symmetry and the principal planes are then evaluated using the method proposed by Cowin and Mehrabadi [Q. J. Mech. Appl. Math. 40, 451-476 (1987)]. The blind inversion procedure was verified using simulated ultrasonic velocity data sets on materials with transversely isotropic, orthotropic, and monoclinic symmetries. A modified double ring configuration of the single transmitter and multiple receiver compact array was developed to experimentally validate the blind inversion approach on a quasi-isotropic graphite-epoxy composite plate. This technique finds application in the area of material characterization and structural health monitoring of anisotropic platelike structures. PMID:19206853
Goodman, Michael L.
2011-04-10
A Harris sheet magnetic field with maximum magnitude B{sub 0} and length scale L is combined with the anisotropic electrical conductivity, viscosity, and thermoelectric tensors for an electron-proton plasma to define a magnetohydrodynamic model that determines the steady state of the plasma. The transport tensors are functions of temperature, density, and magnetic field strength, and are computed self-consistently as functions of position x normal to the current sheet. The flow velocity, magnetic field, and gravitational force lie along the z-axis. The plasma is supported against gravity by the viscous force. Analytic solutions are obtained for temperature, density, and velocity. They are valid over a broad range of temperature, density, and magnetic field strength, and so may be generally useful in astrophysical applications. Numerical examples of solutions in the parameter range of the solar atmosphere are presented. The objective is to compare Joule and viscous heating rates, determine the velocity shear that generates viscous forces that support the plasma and are self-consistent with a mean outward mass flux comparable to the solar wind mass flux, and compare the thermoelectric and conduction current contributions to the Joule heating rate. The ratio of the viscous to Joule heating rates per unit mass can exceed unity by orders of magnitude, and increases rapidly with L. The viscous heating rate can be concentrated outside the region where the current density is localized, corresponding to a resistively heated layer of plasma bounded by viscously heated plasma. The temperature gradient drives a thermoelectric current density that can have a magnitude greater than that of the electric-field-driven conduction current density, so thermoelectric effects are important in determining the Joule heating rate.
NASA Astrophysics Data System (ADS)
Tian, Xiaojuan; Itkis, Mikhail E.; Bekyarova, Elena B.; Haddon, Robert C.
2013-04-01
Thermal interface materials (TIMs) are crucial components of high density electronics and the high thermal conductivity of graphite makes this material an attractive candidate for such applications. We report an investigation of the in-plane and through-plane electrical and thermal conductivities of thin thermal interface layers of graphite nanoplatelet (GNP) based composites. The in-plane electrical conductivity exceeds its through-plane counterpart by three orders of magnitude, whereas the ratio of the thermal conductivities is about 5. Scanning electron microscopy reveals that the anisotropy in the transport properties is due to the in-plane alignment of the GNPs which occurs during the formation of the thermal interface layer. Because the alignment in the thermal interface layer suppresses the through-plane component of the thermal conductivity, the anisotropy strongly degrades the performance of GNP-based composites in the geometry required for typical thermal management applications and must be taken into account in the development of GNP-based TIMs.
Tian, Xiaojuan; Itkis, Mikhail E.; Bekyarova, Elena B.; Haddon, Robert C.
2013-01-01
Thermal interface materials (TIMs) are crucial components of high density electronics and the high thermal conductivity of graphite makes this material an attractive candidate for such applications. We report an investigation of the in-plane and through-plane electrical and thermal conductivities of thin thermal interface layers of graphite nanoplatelet (GNP) based composites. The in-plane electrical conductivity exceeds its through-plane counterpart by three orders of magnitude, whereas the ratio of the thermal conductivities is about 5. Scanning electron microscopy reveals that the anisotropy in the transport properties is due to the in-plane alignment of the GNPs which occurs during the formation of the thermal interface layer. Because the alignment in the thermal interface layer suppresses the through-plane component of the thermal conductivity, the anisotropy strongly degrades the performance of GNP-based composites in the geometry required for typical thermal management applications and must be taken into account in the development of GNP-based TIMs.
Electronic and transport properties of nanotubes
NASA Astrophysics Data System (ADS)
Charlier, Jean-Christophe; Blase, Xavier; Roche, Stephan
2007-04-01
This article reviews the electronic and transport properties of carbon nanotubes. The focus is mainly theoretical, but when appropriate the relation with experimental results is mentioned. While simple band-folding arguments will be invoked to rationalize how the metallic or semiconducting character of nanotubes is inferred from their topological structure, more sophisticated tight-binding and ab initio treatments will be introduced to discuss more subtle physical effects, such as those induced by curvature, tube-tube interactions, or topological defects. The same approach will be followed for transport properties. The fundamental aspects of conduction regimes and transport length scales will be presented using simple models of disorder, with the derivation of a few analytic results concerning specific situations of short- and long-range static perturbations. Further, the latest developments in semiempirical or ab initio simulations aimed at exploring the effect of realistic static scatterers (chemical impurities, adsorbed molecules, etc.) or inelastic electron-phonon interactions will be emphasized. Finally, specific issues, going beyond the noninteracting electron model, will be addressed, including excitonic effects in optical experiments, the Coulomb-blockade regime, and the Luttinger liquid, charge density waves, or superconducting transition.
Ortiz, AurÃ©lie U; Boutin, Anne; Fuchs, Alain H; Coudert, FranÃ§ois-Xavier
2012-11-01
We performed ab initio calculations of the elastic constants of five flexible metal-organic frameworks (MOFs): MIL-53(Al), MIL-53(Ga), MIL-47, and the square and lozenge structures of DMOF-1. Tensorial analysis of the elastic constants reveals a highly anisotropic elastic behavior, some deformation directions exhibiting very low Young's modulus and shear modulus. This anisotropy can reach a 400:1 ratio between the most rigid and weakest directions, in stark contrast to the case of nonflexible MOFs such as MOF-5 and ZIF-8. In addition, we show that flexible MOFs can display extremely large negative linear compressibility. These results uncover the microscopic roots of stimuli-induced structural transitions in flexible MOFs, by linking the local elastic behavior of the material and its multistability. PMID:23215398
NASA Astrophysics Data System (ADS)
Ortiz, AurÃ©lie U.; Boutin, Anne; Fuchs, Alain H.; Coudert, FranÃ§ois-Xavier
2012-11-01
We performed ab initio calculations of the elastic constants of five flexible metal-organic frameworks (MOFs): MIL-53(Al), MIL-53(Ga), MIL-47, and the square and lozenge structures of DMOF-1. Tensorial analysis of the elastic constants reveals a highly anisotropic elastic behavior, some deformation directions exhibiting very low Youngâ€™s modulus and shear modulus. This anisotropy can reach a 400âˆ¶1 ratio between the most rigid and weakest directions, in stark contrast to the case of nonflexible MOFs such as MOF-5 and ZIF-8. In addition, we show that flexible MOFs can display extremely large negative linear compressibility. These results uncover the microscopic roots of stimuli-induced structural transitions in flexible MOFs, by linking the local elastic behavior of the material and its multistability.
Anisotropic thermal properties of monoclinic Yb:KLu(WO4)2 crystals
NASA Astrophysics Data System (ADS)
Zhang, Jianxiu; Wang, Kunpeng; Wang, Jiyang; Zhang, Huaijin; Yu, Wentao; Wang, Xuping; Wang, Zhengping; Lu, Qingming; Ba, Mingfang; Ran, D. G.; Ling, Z. C.; Xia, H. R.
2005-08-01
Yb :KLu(WO4)2 (KLuW) crystals with large size and good optical quality have been grown by the top-seeded solution growth (TSSG) method. The melting point and specific heat, anisotropic thermal expansion and thermal conductivity have been measured. The Jackson factor Î± of a series of observed faces (hkl) on Yb:KLuW crystals have been calculated. In addition, the microhardness has also been measured. We find that the thermal expansion anisotropy of Yb:KLuW is weaker than KGd(WO4)2 (KGW) and KYb(WO4)2 (KYbW) and the thermal conductivity is up to 4.4Wm-1k-1 along [205] directions at 25Â°C, which is the greatest in their family.
Gorelikov, G. A.; Fridman, Yu. A.
2013-07-15
The spectra of coupled magnetoelastic waves in a semi-infinite strongly anisotropic easy-plane ferromagnet with a rigidly fixed face are analyzed for two variants of fixation (in the basal plane and perpendicularly to it). The phase states of the system are determined. Differences in the phase diagrams and elementary excitation spectra depending on the choice of the sample fixation plane are considered. When rotational invariance is taken into account, the nonreciprocity effect for the velocities of sound in a crystal appears. It is shown that the velocity of sound in the sample considerably depends on the symmetry of the imposed mechanical boundary conditions. The phase diagrams of the system under investigation are presented.
Thermodynamic and transport properties of gaseous tetrafluoromethane in chemical equilibrium
NASA Technical Reports Server (NTRS)
Hunt, J. L.; Boney, L. R.
1973-01-01
Equations and in computer code are presented for the thermodynamic and transport properties of gaseous, undissociated tetrafluoromethane (CF4) in chemical equilibrium. The computer code calculates the thermodynamic and transport properties of CF4 when given any two of five thermodynamic variables (entropy, temperature, volume, pressure, and enthalpy). Equilibrium thermodynamic and transport property data are tabulated and pressure-enthalpy diagrams are presented.
Banai, R. E.; Brownson, J. R. S.; Burton, L. A.; Walsh, A.; Choi, S. G. To, B.; Hofherr, F.; Sorgenfrei, T.; Cröll, A.
2014-07-07
We report on the anisotropic optical properties of single-crystal tin monosulfide (SnS). The components ?{sub a}, ?{sub b}, and ?{sub c} of the pseudodielectric-function tensor (?)=(??)+i(??) spectra are taken from 0.73 to 6.45 eV by spectroscopic ellipsometry. The measured (?) spectra are in a good agreement with the results of the calculated dielectric response from hybrid density functional theory. The (?) spectra show the direct band-gap onset and a total of eight above-band-gap optical structures that are associated with the interband-transition critical points (CPs). We obtain accurate CP energies by fitting analytic CP expressions to second-energy-derivatives of the (?) data. Their probable electronic origins and implications for photovoltaic applications are discussed.
Upscaling of Thermal Transport Properties in Enhanced Geothermal Systems
NASA Astrophysics Data System (ADS)
Johnson, S.; Hao, Y.; Chiaramonte, L.
2010-12-01
: Engineered Geothermal Systems (EGS) have garnered significant attention as a possible source of geographically disperse, carbon-free energy without the environmental impact of many other renewable energy sources. However, a significant barrier to the adoption of EGS is the uncertainty in whether a specific site is amenable to engineering and how fluid injection rates can affect, either through stimulation of the fracture network or through deleterious channeling of the thermal fluid, the heat extraction rate possible in a specific reservoir. Because of the uncertainties involved in determining the exact fracture network topology extant in any particular reservoir, it is desirable to have a stochastic description (distribution) of the possible heat extraction rates that could be achieved. This work provides both an approach and application of the approach for simulating several synthetic fracture networks. The approach uses a coupled geomechanics and discrete fracture network (DFN) solver coupled uni-directionally with a reservoir scale, hydro-thermal transport code, the Non-isothermal Unsaturated-Saturated Flow and Transport simulation code (NUFT), to capture the coupled hydro-thermo-mechanical behavior of these synthetic networks. Particular attention is paid to the upscaling approach used to determine effective permeability and thermal transfer coefficients that are used in the dual porosity/permeability (DKM) model employed in NUFT. This upscaling is based on a multi-scale treatment of the domain, starting with the upscaling of permeability from explicitly represented fractures in the DFN model, which considers the fracture-scale effects of fluid injection, to a finely resolved, unstructured mesh representation of the subdomain. Effective properties of this subdomain are then determined for a variety of sub-sampled discrete fracture network topologies. The result catalog of spatially correlated thermal and fluid properties are then used to populate the properties of an anisotropic regular grid representation of the reservoir. The resultant reservoir-scale system considering the fully-coupled hydro-thermo-mechanical problem is then simulated to determine the resultant heat transfer rate for each synthetic fracture network realization. To complete the parametric study, several fractally spatially distributed systems are realized for each fractal dimension value. The resultant distributions of heat transfer rate and the trends emergent from this study will be presented. Auspices: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Magnetic and transport properties of oxide thin films
NASA Astrophysics Data System (ADS)
Hong, Yuanjia
My dissertation research focuses on the investigation of the transport and magnetic properties of transition metal and rare earth doped oxides, particularly SnO2 and HfO2 thin films. Cr- and Fe-doped SnO 2 films were deposited on Al2O3 substrates by pulsed-laser deposition. X-ray-diffraction patterns (XRD) show that the films have rutile structure and grow epitaxially along the (101) plane. The diffraction peaks of Cr-doped samples exhibit a systematic shift toward higher angles with increasing Cr concentration. This indicates that Cr dissolves in SnO 2. On the other hand, there is no obvious shift of the diffraction peaks of the Fe-doped samples. The magnetization curves indicate that the Cr-doped SnO2 films are paramagnetic at 300 and 5 K. The Fe-doped SnO 2 samples exhibit ferromagnetic behaviour at 300 and 5 K. Zero-field-cooled and field-cooled curves indicate super paramagnetic behavior above the blocking temperature of 100 K, suggesting that it is possible that there are ferromagnetic particles in the Fe-doped films. The anisotropic magnetoresistance (AMR) was not observed in any of the samples. It was found that a Sn0.98Cr0.02O2 film became ferromagnetic at room temperature after annealing in H2. We have calculated the activation energy and found it decreasing with the annealing, which is explained by the increased oxygen vacancies/defects due to the H2 treatment of the films. The ferromagnetism may be associated with the presence of oxygen vacancies although AMR was not observed in the samples. Pure HfO2 and Gd-doped HfO2 thin films have been grown on different single crystal substrates by pulsed laser deposition. XRD patterns show that the pure HfO2 thin films are of single monoclinic phase. Gd-doped HfO2 films have the same XRD patterns except that their diffraction peaks have a shift toward lower angles, which indicates that Gd dissolves in HfO2. Transmission electron microscopy images show a columnar growth of the films. Very weak ferromagnetism is observed in pure and Gd-doped HfO2 films on different substrates at 300 and 5 K, which is attributed to either impure target materials or signals from the substrates. The magnetic properties do not change significantly with post deposition annealing of the HfO2 films. Keywords. SnO2, HfO2, pulsed laser deposition, thin film, epitaxial growth, magnetic thin films, ferromagnetic materials, transport properties.
Nonlinear electrical transport properties in silicene
NASA Astrophysics Data System (ADS)
Yang, Tao; Lin, Q.; Wang, C. M.
2015-10-01
By considering screened electron-impurity scattering with Coulombic potential and all intravalley and intervalley electron-phonon interactions due to deformation potential couplings, we explore the nonlinear electrical transport properties of massive Dirac electrons in a monolayer silicene with a balance-equation scheme. The strong effects of the energy gap on both linear and nonlinear drift velocity and resistivity are demonstrated. The tunable values over 50% for mobility and 1800% for resistivity by vertical electric field are predicted, indicating valuable application prospects in silicene-based devices.
Electronic transport properties of silicon clusters
NASA Astrophysics Data System (ADS)
Matsuura, Yukihito
2016-02-01
The electronic transport properties of silicon clusters were examined via theoretical calculations using the first-principles method. Additionally, p-type doping and n-type doping were analyzed by calculating conductance and current of boron- and phosphorus-doped silicon clusters. The p-type doping and n-type doping provided a new transmission peak at an energy level around the Fermi level to increase conductance. Furthermore, simultaneous boron and phosphorus doping resulted in noticeable rectifying characteristics, with the current drive in forward bias being three times higher than that in the reverse bias. A p-n junction was achieved even on a molecular scale.
NASA Astrophysics Data System (ADS)
Lam, Wai Sze Tiffany
Optical components made of anisotropic materials, such as crystal polarizers and crystal waveplates, are widely used in many complex optical system, such as display systems, microlithography, biomedical imaging and many other optical systems, and induce more complex aberrations than optical components made of isotropic materials. The goal of this dissertation is to accurately simulate the performance of optical systems with anisotropic materials using polarization ray trace. This work extends the polarization ray tracing calculus to incorporate ray tracing through anisotropic materials, including uniaxial, biaxial and optically active materials. The 3D polarization ray tracing calculus is an invaluable tool for analyzing polarization properties of an optical system. The 3x3 polarization ray tracing P matrix developed for anisotropic ray trace assists tracking the 3D polarization transformations along a ray path with series of surfaces in an optical system. To better represent the anisotropic light-matter interactions, the definition of the P matrix is generalized to incorporate not only the polarization change at a refraction/reflection interface, but also the induced optical phase accumulation as light propagates through the anisotropic medium. This enables realistic modeling of crystalline polarization elements, such as crystal waveplates and crystal polarizers. The wavefront and polarization aberrations of these anisotropic components are more complex than those of isotropic optical components and can be evaluated from the resultant P matrix for each eigen-wavefront as well as for the overall image. One incident ray refracting or reflecting into an anisotropic medium produces two eigenpolarizations or eigenmodes propagating in different directions. The associated ray parameters of these modes necessary for the anisotropic ray trace are described in Chapter 2. The algorithms to calculate the P matrix from these ray parameters are described in Chapter 3 for anisotropic ray tracing. x. Chapter 4 presents the data reduction of the P matrix of a crystal waveplate. The diattenuation is embedded in the singular values of P. The retardance is divided into two parts: (A) The physical retardance induced by OPLs and surface interactions, and (B) the geometrical transformation induced by geometry of a ray path, which is calculated by the geometrical transform Q matrix. The Q matrix of an anisotropic intercept is derived from the generalization of s- and p-bases at the anisotropic intercept; the p basis is not confined to the plane of incidence due to the anisotropic refraction or reflection. Chapter 5 shows how the multiple P matrices associated with the eigenmodes resulting from propagation through multiple anisotropic surfaces can be combined into one P matrix when the multiple modes interfere in their overlapping regions. The resultant P matrix contains diattenuation induced at each surface interaction as well as the retardance due to ray propagation and total internal reflections. The polarization aberrations of crystal waveplates and crystal polarizers are studied in Chapter 6 and Chapter 7. A wavefront simulated by a grid of rays is traced through the anisotropic system and the resultant grid of rays is analyzed. The analysis is complicated by the ray doubling effects and the partially overlapping eigen-wavefronts propagating in various directions. The wavefront and polarization aberrations of each eigenmode can be evaluated from the electric field distributions. The overall polarization at the plane of interest or the image quality at the image plane are affected by each of these eigen-wavefronts. Isotropic materials become anisotropic due to stress, strain, or applied electric or magnetic fields. In Chapter 8, the P matrix for anisotropic materials is extended to ray tracing in stress birefringent materials which are treated as spatially varying anisotropic materials. Such simulations can predict the spatial retardance variation throughout the stressed optical component and its effects on the point spread function and mod
Anisotropic transport in the quasi-one-dimensional semiconductor Li0.33MoO3
NASA Astrophysics Data System (ADS)
Moshfeghyeganeh, S.; Cote, A. N.; Neumeier, J. J.; Cohn, J. L.
2016-03-01
Transport measurements (electrical resistivity, Seebeck coefficient, and thermal conductivity) in the temperature range 80-500 K are presented for single crystals of the quasi-one-dimensional (Q1D) semiconductor Li0.33MoO3. Opposite signs are observed for the Seebeck coefficient along the trinclinic a and c axes, with Sc - Sa â‰ƒ 250 Î¼V/K near room temperature and â‰ƒ100 Î¼V/K at 380 K. The thermal conductivity at room temperature in the a-c planes was Ëœ2 W/m K and Ëœ10 times smaller along b*. A weak structural anomaly at Ts â‰ˆ 355 K, identified in the temperature-dependent lattice constants, coincides with anomalies in the electrical properties. Analysis of the electronic transport at T > Ts favors an intrinsic semiconductor picture for transport along the most conducting Q1D axis and small-polaronic transport along the other directions, providing insight into the origin of the Seebeck anisotropy.
Electronic transport properties of assembled carbon nanoribbons.
GirÃ£o, Eduardo Costa; Cruz-Silva, Eduardo; Meunier, Vincent
2012-07-24
Graphitic nanowiggles (GNWs) are 1D systems with segmented graphitic nanoribbon GNR edges of varying chiralities. They are characterized by the presence of a number of possible different spin distributions along their edges and by electronic band-gaps that are highly sensitive to the details of their geometry. These two properties promote these experimentally observed carbon nanostructures as some of the most promising candidates for developing high-performance nanodevices. Here, we highlight this potential with a detailed understanding of the electronic processes leading to their unique spin-state dependent electronic quantum transport properties. The three classes of GNWs containing at least one zigzag edge (necessary to the observation of multiple-magnetic states) are considered in two distinct geometries: a perfectly periodic system and in a one-GNW-cell system sandwiched between two semi-infinite terminals made up of straight GNRs. The present calculations establish a number of elementary rules to relate fundamental electronic transport functionality, electronic energy, the system geometry, and spin state. PMID:22735039
Properties of (311) planes anisotropically etched in (100) silicon by TMAH
NASA Astrophysics Data System (ADS)
Resnik, Drago; Vrtacnik, Danilo; Aljancic, Uros; Mozek, Matej; Amon, Slavko
2001-09-01
This paper presents an investigation focused on the formation of (311) planes by wet anisotropic etching of (100) silicon in 5% TMAH etchant. Atomistic model of (311) plane formation is proposed, suggesting that (311) planes are composed of (111) and (100) steps. Surface roughness that is in most cases consequence of hillock formation at low concentrations of TMAH and etch rates of (311) and (100) planes were studied as a function of etch temperature, time and addition of small amounts of ammonium peroxodisulfate (APODS). It was found that the smooth (311) planes without hillocks can be obtained only by etching in 5% TMAH with addition of 0,5% APODS. Due to obvious decomposition of APODS in the etching process determined by increased surface roughness, replenishing of additive is mandatory. Stirring experiments with 5%TMAH solution showed increased surface roughness and reduced etch rates of (100) and (311) plane. Dissolution rates of thermal oxide, LPCVD nitride and PECVD oxide and nitride were determined in temperature range from 60 degree(s)C-90 degree(s)C in 5% TMAH. APODS additive was found to have minor influence.
Anisotropic Fermi surface from holography
NASA Astrophysics Data System (ADS)
Fang, Li Qing; Ge, Xian-hui; Wu, Jian-Pin; Leng, Hong-Qiang
2015-06-01
We investigate the probe holographic fermions by using an anisotropic charged black brane solution. We derive the equation of motion of probe bulk fermions with one Fermi momentum along the anisotropic and one along the isotropic directions. We then numerically solve the equation and analyze the properties of Green function with these two momentums. We find in this case the shape of Fermi surface is anisotropic. However, for both Fermi momentums perpendicular to the anisotropic direction, the Fermi surface is isotropic. We verify that our system obeys the recently conjectured bound for thermoelectric diffusion constants for the stable branch of the black brane solutions.
Phonon transport properties in pillared silicon film
NASA Astrophysics Data System (ADS)
Wei, Zhiyong; Yang, Juekuan; Bi, Kedong; Chen, Yunfei
2015-10-01
The phonon transport property of pillared silicon film is systematically investigated by molecular dynamics simulation and lattice dynamics calculation. It is found that the thermal conductivity can be reduced to as low as 28.6% of the conductivity of plain ones. Although the reduced thermal conductivity can be explained qualitatively by increased surface roughness, our calculations show that the pillars modify the phonon dispersion relation and reduce the phonon group velocity due to the local resonance effects. Furthermore, by analyzing the participation ratio spectra, it is shown that the pillars reduce the mode participation ratio over the whole range of frequency. We found that the mode localization around the pillars is another important factor to reduce the thermal conductivity of pillared film. The present investigations indicate that the pillared film may have potential application in thermoelectric energy conversion.
Transport properties of epitaxial lift off films
NASA Astrophysics Data System (ADS)
Mena, R. A.; Schacham, S. E.; Young, P. G.; Haugland, E. J.; Alterovitz, S. A.
1993-05-01
Transport properties of epitaxially lifted-off (ELO) films were characterized using conductivity, Hall, and Shubnikov-de Haas measurements. A 10-15 percent increase in the 2D electron gas concentration was observed in these films as compared with adjacent conventional samples. We believe this result to be caused by a backgating effect produced by a charge build up at the interface of the ELO film and the quartz substrate. This increase results in a substantial decrease in the quantum lifetime in the ELO samples, by 17-30 percent, but without a degradation in carrier mobility. Under persistent photoconductivity, only one subband was populated in the conventional structure, while in the ELO films the population of the second subband was clearly visible. However, the increase of the second subband concentration with increasing excitation is substantially smaller than anticipated due to screening of the backgating effect.
Electronic transport properties of (fluorinated) metal phthalocyanine
NASA Astrophysics Data System (ADS)
Fadlallah, M. M.; Eckern, U.; Romero, A. H.; SchwingenschlÃ¶gl, U.
2016-01-01
The magnetic and transport properties of the metal phthalocyanine (MPc) and F16MPc (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn and Ag) families of molecules in contact with Sâ€“Au wires are investigated by density functional theory within the local density approximation, including local electronic correlations on the central metal atom. The magnetic moments are found to be considerably modified under fluorination. In addition, they do not depend exclusively on the configuration of the outer electronic shell of the central metal atom (as in isolated MPc and F16MPc) but also on the interaction with the leads. Good agreement between the calculated conductance and experimental results is obtained. For M = Ag, a high spin filter efficiency and conductance is observed, giving rise to a potentially high sensitivity for chemical sensor applications.
Transport properties of quark and gluon plasmas
Heiselberg, H.
1993-12-01
The kinetic properties of relativistic quark-gluon and electron-photon plasmas are described in the weak coupling limit. The troublesome Rutherford divergence at small scattering angles is screened by Debye screening for the longitudinal or electric part of the interactions. The transverse or magnetic part of the interactions is effectively screened by Landau damping of the virtual photons and gluons transferred in the QED and QCD interactions respectively. Including screening a number of transport coefficients for QCD and QED plasmas can be calculated to leading order in the interaction strength, including rates of momentum and thermal relaxation, electrical conductivity, viscosities, flavor and spin diffusion of both high temperature and degenerate plasmas. Damping of quarks and gluons as well as color diffusion in quark-gluon plasmas is, however, shown not to be sufficiently screened and the rates depends on an infrared cut-off of order the ``magnetic mass,`` m{sub mag} {approximately} g{sup 2}T.
Correlations among magnetic, electrical and magneto-transport properties of NiFe nanohole arrays.
Leitao, D C; Ventura, J; Teixeira, J M; Sousa, C T; Pinto, S; Sousa, J B; Michalik, J M; De Teresa, J M; Vazquez, M; Araujo, J P
2013-02-13
In this work, we use anodic aluminum oxide (AAO) templates to build NiFe magnetic nanohole arrays. We perform a thorough study of their magnetic, electrical and magneto-transport properties (including the resistance R(T), and magnetoresistance MR(T)), enabling us to infer the nanohole film morphology, and the evolution from granular to continuous film with increasing thickness. In fact, different physical behaviors were observed to occur in the thickness range of the study (2 nm < t < 100 nm). For t < 10 nm, an insulator-to-metallic crossover was visible in R(T), pointing to a granular film morphology, and thus being consistent with the presence of electron tunneling mechanisms in the magnetoresistance. Then, for 10 nm < t < 50 nm a metallic R(T) allied with a larger anisotropic magnetoresistance suggests the onset of morphological percolation of the granular film. Finally, for t > 50 nm, a metallic R(T) and only anisotropic magnetoresistance behavior were obtained, characteristic of a continuous thin film. Therefore, by combining simple low-cost bottom-up (templates) and top-down (sputtering deposition) techniques, we are able to obtain customized magnetic nanostructures with well-controlled physical properties, showing nanohole diameters smaller than 35 nm. PMID:23315433
Structural and magnetic properties of an anisotropic M-type LaCo-substituted strontium hexaferrite
NASA Astrophysics Data System (ADS)
Tyrman, Muriel; Pasko, Alexandre; De La BarriÃ¨re, Olivier; Mazaleyrat, FrÃ©dÃ©ric
2015-11-01
Rare-earth-free permanent magnets returned to the forefront of scientific and technological concerns about the environmental and economical issues. The emergence of new markets, control of costs and availability of raw materials encourage to look for alternative materials containing much less, or no, rare earth elements selected from the most common and most available. The hexaferrite doped with lanthanum and cobalt present interesting properties to succeed the rare-earth magnets. The structural and magnetic properties of a strontium hexaferrite are presented in this paper, and two models are developed in order to correlate structural and magnetic properties. Contribution to the topical issue "Electrical Engineering Symposium (SGE 2014)", edited by Adel Razek
Friedel, Michael J.
2001-01-01
This report describes a model for simulating transient, Variably Saturated, coupled water-heatsolute Transport in heterogeneous, anisotropic, 2-Dimensional, ground-water systems with variable fluid density (VST2D). VST2D was developed to help understand the effects of natural and anthropogenic factors on quantity and quality of variably saturated ground-water systems. The model solves simultaneously for one or more dependent variables (pressure, temperature, and concentration) at nodes in a horizontal or vertical mesh using a quasi-linearized general minimum residual method. This approach enhances computational speed beyond the speed of a sequential approach. Heterogeneous and anisotropic conditions are implemented locally using individual element property descriptions. This implementation allows local principal directions to differ among elements and from the global solution domain coordinates. Boundary conditions can include time-varying pressure head (or moisture content), heat, and/or concentration; fluxes distributed along domain boundaries and/or at internal node points; and/or convective moisture, heat, and solute fluxes along the domain boundaries; and/or unit hydraulic gradient along domain boundaries. Other model features include temperature and concentration dependent density (liquid and vapor) and viscosity, sorption and/or decay of a solute, and capability to determine moisture content beyond residual to zero. These features are described in the documentation together with development of the governing equations, application of the finite-element formulation (using the Galerkin approach), solution procedure, mass and energy balance considerations, input requirements, and output options. The VST2D model was verified, and results included solutions for problems of water transport under isohaline and isothermal conditions, heat transport under isobaric and isohaline conditions, solute transport under isobaric and isothermal conditions, and coupled water-heat-solute transport. The first three problems considered in model verification were compared to either analytical or numerical solutions, whereas the coupled problem was compared to measured laboratory results for which no known analytic solutions or numerical models are available. The test results indicate the model is accurate and applicable for a wide range of conditions, including when water (liquid and vapor), heat (sensible and latent), and solute are coupled in ground-water systems. The cumulative residual errors for the coupled problem tested was less than 10-8 cubic centimeter per cubic centimeter, 10-5 moles per kilogram, and 102 calories per cubic meter for liquid water content, solute concentration and heat content, respectively. This model should be useful to hydrologists, engineers, and researchers interested in studying coupled processes associated with variably saturated transport in ground-water systems.
Transport properties of supercooled confined water
NASA Astrophysics Data System (ADS)
Mallamace, F.; Branca, C.; Broccio, M.; Corsaro, C.; Gonzalez-Segredo, N.; Spooren, J.; Stanley, H. E.; Chen, S.-H.
2008-07-01
This article presents an overview of recent experiments performed on transport properties of water in the deeply supercooled region, a temperature region of fundamental importance in the science of water. We report data of nuclear magnetic resonance, quasi-elastic neutron scattering, Fourier-transform infrared spectroscopy, and Raman spectroscopy, studying water confined in nanometer-scale environments. When contained within small pores, water does not crystallise, and can be supercooled well below its homogeneous nucleation temperature Th. On this basis it is possible to carry out a careful analysis of the well known thermodynamical anomalies of water. Studying the temperature and pressure dependencies of water dynamics, we show that the liquid-liquid phase transition (LLPT) hypothesis represents a reliable model for describing liquid water. In this model, water in the liquid state is a mixture of two different local structures, characterised by different densities, namely the low density liquid (LDL) and the high-density liquid (HDL). The LLPT line should terminate at a special transition point: a low-T liquid-liquid critical point. We discuss the following experimental findings on liquid water: (i) a crossover from non-Arrhenius behaviour at high T to Arrhenius behaviour at low T in transport parameters; (ii) a breakdown of the Stokes-Einstein relation; (iii) the existence of a Widom line, which is the locus of points corresponding to maximum correlation length in the p-T phase diagram and which ends in the liquid-liquid critical point; (iv) the direct observation of the LDL phase; (v) a minimum in the density at approximately 70 K below the temperature of the density maximum. In our opinion these results represent the experimental proofs of the validity of the LLPT hypothesis.
Strain-mediated magnetic and transport properties of epitaxial LuxFe3-xO4 films
NASA Astrophysics Data System (ADS)
Wang, P.; Jin, C.; Zheng, D. X.; Bai, H. L.
2015-10-01
Strain mediated structure, magnetic, and transport properties of spinel ferrites were investigated by growing epitaxial LuxFe3-xO4 (LFO, 0 ? x ? 0.26 ) films on SrTiO3 and MgO substrates with in-plane compressive and tensile strains, respectively. The lattice parameter of LFO films decreases on SrTiO3 substrates, while increases on MgO substrates with the increasing Lu content. The LFO films on SrTiO3 substrates exhibit larger saturation magnetization and smaller exchange bias and coercive field. Phase shift of anisotropic magnetoresistance is also observed in the LFO films on SrTiO3 substrates. In addition, the nonmagnetic Lu3+ ions in spinel ferrites enhance the spin canting, which further increases the exchange bias and coercive field and strengthens the four-fold symmetry of anisotropic magnetoresistance and the two-fold symmetry of planar Hall effect.
Geometrical and transport properties of Bentheimer sandstone under deformation
NASA Astrophysics Data System (ADS)
Jasinski, Lukasz; Thovert, Jean Francois; Mourzenko, Valeri; Gland, Nicolas; Youssef, Souhail; Vizika, Olga; Adler, Pierre
2010-05-01
During industrial, geoscientific or environmental drilling campaigns, rock samples are often extracted few km below surface under large pressures p and their in situ properties may significantly differ from the ones measured in the lab close to atmospheric pressure p_a. Our first objective is to derive from measurements made at pa the geometric and transport properties at p. In petroleum industry, during production, the vertical effective stress in the reservoir increases as the pore pressure decreases from few hundreds to few tens bar; in average the horizontal effective stress increases as well, but at a lower rate along an oedometric path, favoring shear stress and reservoir depletion; a complex geology induces locally a variety of stress paths between the two extreme hydrostatic and uniaxial paths. For storage, CO2 might be injected into deep geological formations; such a re-injection will decrease the effective stress. Therefore, our second objective is to test numerically the sensitivity of transport properties to stress path. The methodology can be summarized as follows. First, the rock geometry on the pore scale is obtained by microtomography. The major geometric characteristics are derived by extracting the pore skeleton. Second, the sample is submitted to hydrostatic, oedometric or uniaxial deformations. Then, the permeability K is derived by routines based on finite volume discretization operating on cubic or on unstructured tetrahedral elements. This methodology is applied to a real Bentheimer sandstone of porosity E close to 0.23-0.24. It is binarized with 5003 and 10003 voxels equal to 6 and 3 microns. E, the correlation function, the specific area, the hydraulic radius, the skeleton and the percolation properties of the pore space are calculated. The influence of various boundary conditions on K in the uncompressed sample is studied; K is slightly anisotropic. Then, the sample is submitted to the overall deformations and the influence of the loading path analyzed; two deformations of 1% were successively applied and their results compared to a single step of 2%; results were practically identical. During deformation, the relative volume changes in the solid and pore space are of the same order of magnitude. The relative variation of E is -1.20e for hydrostatic and oedometric compressions, and -1.28e for uniaxial compression where e is the trace of the mean strain tensor. During deformation K [Darcy] can be approximated by power laws, 1164 epsilon4.13 for hydrostatic, 709 epsilon3.79 for oedometric and 2005 epsilon4.49 for uniaxial compressions, respectively. The numerical results were compared to lab data. Bentheimer samples were compressed according to different stress paths while K is measured. Due to frictional end-effects, standard permeability measurements on full sample length can be seriously affected leading to an underestimation of K and erroneous evolutions. Numerical results for K and evolutions are more compatible with improved measurements on an intermediate length using local pore fluid samplers.
Geometrical and transport properties of Bentheimer sandstone under deformation
NASA Astrophysics Data System (ADS)
Jasinski, L.; Mourzenko, V.; Thovert, J.; Gland, N.; Youssef, S.; Vizika, O.; Adler, P. M.
2009-12-01
During industrial, geoscientific or environmental drilling campaigns, rock samples are often extracted few km below surface under large pressures p and their in situ properties may significantly differ from the ones measured in the lab close to atmospheric pressure p_a. Our first objective is to derive from measurements made at p_a the geometric and transport properties at p. In petroleum industry, during production, the vertical effective stress in the reservoir increases as the pore pressure decreases from few hundreds to few tens bar; in average the horizontal effective stress increases as well, but at a lower rate along an oedometric path, favoring shear stress and reservoir depletion; a complex geology induces locally a variety of stress paths between the two extreme hydrostatic and uniaxial paths. For storage, CO2 might be injected into deep geological formations; such a re-injection will decrease the effective stress. Therefore, our second objective is to test numerically the sensitivity of transport properties to stress path. The methodology can be summarized as follows. First, the rock geometry on the pore scale is obtained by microtomography. The major geometric characteristics are derived by extracting the pore skeleton. Second, the sample is submitted to hydrostatic, oedometric or uniaxial deformations. Then, the permeability K is derived by routines based on finite volume discretization operating on cubic or on unstructured tetrahedral elements. This methodology is applied to a real Bentheimer sandstone of porosity E close to 0.23-0.24. It is binarized with 500^3 and 1000^3 voxels equal to 6 and 3 microns. E, the correlation function, the specific area, the hydraulic radius, the skeleton and the percolation properties of the pore space are calculated. The influence of various boundary conditions on K in the uncompressed sample is studied; K is slightly anisotropic. Then, the sample is submitted to the overall deformations and the influence of the loading path analyzed; two deformations of 1% were successively applied and their results compared to a single step of 2%; results were practically identical. During deformation, the relative volume changes in the solid and pore space are of the same order of magnitude. The relative variation of E is -1.20e for hydrostatic and oedometric compressions, and -1.28e for uniaxial compression where e is the trace of the mean strain tensor. During deformation K [Darcy] can be approximated by power laws, 1164 epsilon^{4.13} for hydrostatic, 709 \\epsilon^{3.79} for oedometric and 2005 \\epsilon^{4.49} for uniaxial compressions, respectively. The numerical results were compared to lab data. Bentheimer samples were compressed according to different stress paths while K is measured. Due to frictional end-effects, standard permeability measurements on full sample length can be seriously affected leading to an underestimation of K and erroneous evolutions. Numerical results for K and evolutions are more compatible with improved measurements on an intermediate length using local pore fluid samplers.
Anisotropic metamaterial optical fibers.
Pratap, Dheeraj; Anantha Ramakrishna, S; Pollock, Justin G; Iyer, Ashwin K
2015-04-01
Internal physical structure can drastically modify the properties of waveguides: photonic crystal fibers are able to confine light inside a hollow air core by Bragg scattering from a periodic array of holes, while metamaterial loaded waveguides for microwaves can support propagation at frequencies well below cutoff. Anisotropic metamaterials assembled into cylindrically symmetric geometries constitute light-guiding structures that support new kinds of exotic modes. A microtube of anodized nanoporous alumina, with nanopores radially emanating from the inner wall to the outer surface, is a manifestation of such an anisotropic metamaterial optical fiber. The nanopores, when filled with a plasmonic metal such as silver or gold, greatly increase the electromagnetic anisotropy. The modal solutions in such anisotropic circular waveguides can be uncommon Bessel functions with imaginary orders. PMID:25968741
Modeling graphene: Magnetic, transport and optical properties
NASA Astrophysics Data System (ADS)
Chang, Yi Chen
Graphene, with its unique linear dispersion near the Fermi energy, has attracted great attention since its successful isolation from highly oriented pyrolytic graphite in 2004. Many important properties have been identified in graphene, including a remarkably high mobility at room temperature, an unusual quantum hall effect, and an ambipolar electric field effect. It has been proposed as a candidate for many applications, such as optical modulators, spintronic devices, and solar cells. Understanding the fundamental properties of graphene is therefore important. In this dissertation, I present a study of transport, magnetism and optical properties of graphene. In the first chapter, I introduce the electronic properties of mono layer and few layer graphene. In the second chapter, I present low temperature transport measurements in few layer graphene. An electric-field induced semimetal-to-metal transition is observed based on the temperature dependence of the resistance for different applied gate voltages. At small gate voltages the resistance decreases with increasing temperature due to the increase in carrier concentration resulting from thermal excitation of electron-hole pairs, as it is characteristic of a semimetal. At large gate, voltages excitations of electron-hole pairs are suppressed, and the resistance increases with increasing temperature because of the decrease in mean free path due to electron-phonon scattering, as is characteristic of a metal. The electron and hole mobilities are almost equal, so there is approximate electron-hole symmetry. The data are analyzed according to two different theoretical models for few-layer graphene. A simple two band (STB) model, two overlapping bands with quadratic energy-versus-momentum dispersion relations, is used to explain the experimental observations. The best fitting parameter for the overlap energy is found to be 16 meV. However, at low temperatures, the STB suggests that the conductivity is gate independent in the small gate voltage regime, which is not observed in the data. By considering frustration of the electronic potential due to impurities from the substrate, a Gaussian-distribution puddle model can successfully describe the observed transport behavior in the low temperature, small gate voltage regime. In the third chapter, I investigate the effects of point and line defects in monolayer graphene within the framework of the Hubbard model, using a self-consistent mean field theory. These defects are found to induce characteristic patterns into the electronic density of states and cause non-uniform distributions of magnetic moments in the vicinity of the impurity sites. Specifically, defect induced resonances in the local density of states are observed at energies close to the Dirac points. The magnitudes of the frequencies of these resonance states are shown to decrease with the strength of the scattering potential, whereas their amplitudes decay algebraically with increasing distance from the defect. For the case of defect clusters, we observe that with increasing defect cluster size the local magnetic moments in the vicinity of the cluster center are strongly enhanced. Furthermore, non-trivial impurity induced magnetic patterns are observed in the presence of line defects: zigzag line defects are found to introduce stronger-amplitude magnetic patterns than armchair line defects. When the scattering strength of these topological defects is increased, the induced patterns of magnetic moments become more strongly localized. In the fourth chapter, I theoretically study the electronic properties properties in graphene dots under mechanical deformation, using both tight binding lattice model and effective Dirac model. We observed an edge state, which is tunned by an effective quantum well originating from a strain-induced gauge field. Applying a uniaxial strain along the zigzag or armchair directions enhances or dampens the edge state due to the development of edge quantum wells. When an arc bending deformation is applied, the inner and outer edges of graphene dot display edge states caused by the induced nonuniform gauge field. These states suggest that an effective single well potential is introduced by a strong nonuniform pseudo-magnetic field, leading to a pseudo quantum Hall effect. Furthermore, we find that introducing a Hubbard term on the mean-field level induces a strong polarization between the A and B sublattices, which provides an experimental test of the theory presented here. Finally, I study charge impurity induced plasmon resonance in graphene by using the self-consistent method within random phase approximation (RPA). I attribute the observed increase in excitation energy to the increasing carrier density due to stronger impurity potentials. On the other hand, the carrier density within low energy region is decreased when impurity size is increased, as result of lower excitation frequency. The plasmon patterns show that the dipole resonances are supported for the lower excitation frequency due to a simple transition process. For higher excitation frequencies, quadrapole resonance is observed because the transitions between higher energy levels become possible. With increasing impurity size, a larger spatial range of plasmons is observed.
Engineering of micro- and nanostructured surfaces with anisotropic geometries and properties.
Tawfick, Sameh; De Volder, Michael; Copic, Davor; Park, Sei Jin; Oliver, C Ryan; Polsen, Erik S; Roberts, Megan J; Hart, A John
2012-04-01
Widespread approaches to fabricate surfaces with robust micro- and nanostructured topographies have been stimulated by opportunities to enhance interface performance by combining physical and chemical effects. In particular, arrays of asymmetric surface features, such as arrays of grooves, inclined pillars, and helical protrusions, have been shown to impart unique anisotropy in properties including wetting, adhesion, thermal and/or electrical conductivity, optical activity, and capability to direct cell growth. These properties are of wide interest for applications including energy conversion, microelectronics, chemical and biological sensing, and bioengineering. However, fabrication of asymmetric surface features often pushes the limits of traditional etching and deposition techniques, making it challenging to produce the desired surfaces in a scalable and cost-effective manner. We review and classify approaches to fabricate arrays of asymmetric 2D and 3D surface features, in polymers, metals, and ceramics. Analytical and empirical relationships among geometries, materials, and surface properties are discussed, especially in the context of the applications mentioned above. Further, opportunities for new fabrication methods that combine lithography with principles of self-assembly are identified, aiming to establish design principles for fabrication of arbitrary 3D surface textures over large areas. PMID:22396318
NASA Astrophysics Data System (ADS)
Ueoka, Yoshihiro; Shingu, Kenta; Yano, Hiroshi; Hatayama, Tomoaki; Fuyuki, Takashi
2012-11-01
The origin of anisotropic electrical properties on 4H-SiC trench metal-oxide-semiconductor field-effect transistors (MOSFETs) with large off-axis angles has been discussed from the viewpoints of charge pumping current and surface roughness. The channel mobility (µch) on (11bar 20) tilted toward [000bar 1] was high and that on (bar 1bar 120) tilted toward [0001] was low. The roughness at the SiC/SiO2 interfaces was measured after the removal of the oxide. A rough surface was observed on (bar 1bar 120). A locally thick gate oxide results in a nonuniform inversion layer, which is the main origin of the anisotropic electrical properties of the trench MOSFETs on off-axis substrates.
ElAM: A computer program for the analysis and representation of anisotropic elastic properties
NASA Astrophysics Data System (ADS)
Marmier, Arnaud; Lethbridge, Zoe A. D.; Walton, Richard I.; Smith, Christopher W.; Parker, Stephen C.; Evans, Kenneth E.
2010-12-01
The continuum theory of elasticity has been used for more than a century and has applications in many fields of science and engineering. It is very robust, well understood and mathematically elegant. In the isotropic case elastic properties are easily represented, but for non-isotropic materials, even in the simple cubic symmetry, it can be difficult to visualise how properties such as Young's modulus or Poisson's ratio vary with stress/strain orientation. The ElAM ( Elastic Anisotropy Measures) code carries out the required tensorial operations (inversion, rotation, diagonalisation) and creates 3D models of an elastic property's anisotropy. It can also produce 2D cuts in any given plane, compute averages following diverse schemes and query a database of elastic constants to support meta-analyses. Program summaryProgram title: ElAM1.0 Catalogue identifier: AEHB_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHB_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 43 848 No. of bytes in distributed program, including test data, etc.: 2 498 882 Distribution format: tar.gz Programming language: Fortran90 Computer: Any Operating system: Linux, Windows (XP, Vista) RAM: Depends chiefly on the size of the arrays representing elastic properties in 3D Classification: 7.7 Nature of problem: Representation of elastic moduli and ratios, and of wave velocities, in 3D; automatic discovery of unusual elastic properties. Solution method: Stiffness matrix (6×6) inversion and conversion to compliance tensor (3×3×3×3), tensor rotation, dynamic matrix diagonalisation, simple optimisation, postscript and VRML output preparation. Running time: Dependent on angular accuracy and size of elastic constant database (from a few seconds to a few hours). The tests provided take from a few seconds for test0 to approximately 1 hour for test4.
Transport properties of alkali metal doped fullerides
NASA Astrophysics Data System (ADS)
Yadav, Daluram; Yadav, Nishchhal
2015-07-01
We have studied the intercage interactions between the adjacent C60 cages and expansion of lattice due to the intercalation of alkali atoms based on the spring model to estimate phonon frequencies from the dynamical matrix for the intermolecular alkali-C60 phonons. We considered a two-peak model for the phonon density of states to investigate the nature of electron pairing mechanism for superconducting state in fullerides. Coulomb repulsive parameter and the electron phonon coupling strength are obtained within the random phase approximation. Transition temperature, Tc, is obtained in a situation when the free electrons in lowest molecular orbital are coupled with alkali-C60 phonons as 5 K, which is much lower as compared to reported Tc (20 K). The superconducting pairing is mainly driven by the high frequency intramolecular phonons and their effects enhance it to 22 K. The importance of the present study, the pressure effect and normal state transport properties are calculated within the same model leading superconductivity.
Equilibrium and transport properties of constrained systems
NASA Astrophysics Data System (ADS)
Chaudhuri, Debasish
2006-10-01
Systems under external confinement and constraints often show interesting properties. In this thesis, we study some systems under external confinement. We begin by finding out the probability distribution of end-to-end separation of a Worm Like Chain (WLC) polymer whose ends are positionally (and orientationally) constrained. We use Monte-Carlo simulations (MC) and a theoretical mapping of the WLC to a quantum particle moving on the surface of an unit sphere to find multimodality in Helmholtz ensemble as a generic signature of semi-flexibility. Secondly, we study Laser Induced Freezing using a Kosterlitz-Thouless type renormalization group calculation and a restricted MC simulation to obtain phase diagrams for Hard Disk, Soft Disk and DLVO potentials. They show very good agreement with phase diagrams simulated by other groups. Lastly, we study the strain response and failure mechanism of a two-dimensional solid confined within a hard wall channel using MC and molecular dynamics simulations. We find a reversible plastic failure through solid-smectic coexistence and observe layering transitions. Mean field calculations can capture some of these features. We study the heat transport in this system thorugh nonequilibrium molecular dynamics simulations and find strong signatures of the transitions. We propose a simple free volume calculation that reproduces some qualitative features of the strain response of heat current for small strains.
Boire, Adeline; Menut, Paul; Morel, Marie-HÃ©lÃ¨ne; Sanchez, Christian
2015-04-30
In this Article, we investigated the interaction properties of wheat gliadins, properties that are at the basis of their functionality in wheat grain and in food matrixes. We established the equation of state of our isolate by osmotic compression and characterized the concentration-induced structural transitions, from the secondary structure of proteins to the rheological properties. We evidenced three thermodynamical regimes corresponding to several structuring regimes. First, for Î¦ < 0.03, gliadins behave as repulsive colloids, with a positive second virial coefficient, arising presumably from their surface charge density and/or their steric repulsion. No intermolecular interaction was detected by FT-IR, suggesting that proteins form a stable dispersion. In the second regime, the system becomes more easily compressible, i.e., less repulsive and/or more attractive. It is associated with the disappearance of Î²-sheet intramolecular structures of the proteins in favor of random coils/Î±-helix and intermolecular Î²-sheet interactions. This coincides with the appearance of elasticity and the increase of the apparent viscosity. Finally, in the last regime, for Î¦ > 0.16, FT-IR spectra show that proteins are strongly interacting via intermolecular interactions. A correlation peak develops in SAXS, revealing a global order in the dispersion. Interestingly, the osmotic pressure applied to extract the solvent is higher than expected from a hard-sphere-like protein and we highlighted a liquid-like state at very high concentration (>450 g L(-1)) which is in contrast with most proteins that form gel or glass at such concentration. In the discussion, we questioned the existence of supramolecular assemblies and the role of the solvation that would lead to this specific behavior. PMID:25839358
Diameter dependence of the transport properties of antimony telluride nanowires.
Zuev, Yuri M; Lee, Jin Seok; Galloy, ClÃ©ment; Park, Hongkun; Kim, Philip
2010-08-11
We report measurements of electronic, thermoelectric, and galvanomagnetic properties of individual single crystal antimony telluride (Sb(2)Te(3)) nanowires with diameters in the range of 20-100 nm. Temperature-dependent resistivity and thermoelectric power (TEP) measurements indicate hole dominant diffusive thermoelectric generation with an enhancement of the TEP for smaller diameter wires up to 110 microV/K at T = 300 K. We measure the magnetoresistance in magnetic fields both parallel and perpendicular to the nanowire [110] axis, where strong anisotropic positive magnetoresistance behavior was observed. PMID:20698617
Anisotropic flow and flow fluctuations for Au + Au at ?sNN =200 GeV in a multiphase transport model
NASA Astrophysics Data System (ADS)
Ma, L.; Ma, G. L.; Ma, Y. G.
2014-04-01
Anisotropic flow coefficients and their fluctuations are investigated for Au + Au collisions at center-of-mass energy ?sNN = 200 GeV by using a multiphase transport model with string melting scenario. Experimental results of azimuthal anisotropies by means of the two- and four-particle cumulants are generally well reproduced by the model including both parton cascade and hadronic rescatterings. Event-by-event treatments of the harmonic flow coefficients vn (for n =2, 3, and 4) are performed, in which event distributions of vn for different orders are consistent with Gaussian shapes over all centrality bins. Systematic studies on centrality, transverse momentum (pT), and pseudorapidity (?) dependencies of anisotropic flows and quantitative estimations of the flow fluctuations are presented. The pT and ? dependencies of absolute fluctuations for both v2 and v3 follow trends similar to their flow coefficients. Relative fluctuation of triangular flow v3 is slightly centrality dependent, which is quite different from that of elliptic flow v2. It is observed that parton cascade has a large effect on the flow fluctuations, but hadronic scatterings make little contribution to the flow fluctuations, which indicates flow fluctuations are mainly modified during partonic evolution stage.
Transport properties of silver selenomolybdate glassy ionic conductors
NASA Astrophysics Data System (ADS)
Deb, B.; Ghosh, A.
2012-11-01
Transport properties of silver selenomolybdate glassy ionic conductors have been reported for wide composition and temperature ranges. It has been observed that the transport properties of these glasses depend strongly on the modifier content as well as on the glass formers ratio. A direct correlation between the ion transport and the modification of the glass structure has been predicted. Transport properties of these glasses are also strongly influenced by the existence of dual character of SeO2 as a glass former and a glass modifier. Structural models for different compositions have also been proposed.
NASA Astrophysics Data System (ADS)
Delette, G.
2015-09-01
Models of polycrystalline microstructures, representative for sintered permanent magnets with various grain size distributions and alignment degrees, were generated by the Voronoï tessellation technique. The polycrystalline models were meshed and then a stress/strain analysis was performed with the Finite Element Method (FEM) in order to derive the relation between the homogenized properties (thermal expansion coefficient, elastic constants) and the degree of grain alignment. Residual stresses after sintering were also analyzed and a possible mechanism involved in the decrease in mechanical strength is discussed. It is argued that small sized and poorly aligned grains dispersed in the polycrystalline material are highly stressed after elaboration and could be responsible for the initiation of failure.
Neoclassical Transport Properties of Tokamak Plasmas
Weyssow, B.
2004-03-15
The classical transport theory is strictly valid for a plasma in a homogeneous and stationary magnetic field. In the '60, experiments have shown that this theory does not apply as a local theory of transport in Tokamaks. It was shown that global geometric characteristics of the confining elements have a strong influence on the transport. Three regimes of collisionality are characteristic of the neoclassical transport theory: the banana regime (the electronic diffusion coefficient increases starting from zero), the plateau regime (the diffusion coefficient is almost independent of the collisionality) and the Pfirsch-Schlueter regime (the electronic diffusion coefficient again increases with the collisionality)
Wang, Christopher C-B.; Chahine, Nadeen O.; Hung, Clark T.; Ateshian, Gerard A.
2010-01-01
The precise nature of the material symmetry of articular cartilage in compression remains to be elucidated. The primary objective of this study was to determine the equilibrium compressive Young’s moduli and Poisson’s ratios of bovine cartilage along multiple directions (parallel and perpendicular to the split line direction, and normal to the articular surface) by loading small cubic specimens (0.9×0.9×0.8 mm, n=15) in unconfined compression, with the expectation that the material symmetry of cartilage could be determined more accurately with the help of a more complete set of material properties. The second objective was to investigate how the tension-compression nonlinearity of cartilage might alter the interpretation of material symmetry. Optimized digital image correlation was used to accurately determine the resultant strain fields within the specimens under loading. Experimental results demonstrated that neither the Young’s moduli nor the Poisson’s ratios exhibit the same values when measured along the three loading directions. The main findings of this study are that the framework of linear orthotropic elasticity (as well as higher symmetries of linear elasticity) is not suitable to describe the equilibrium response of articular cartilage nor characterize its material symmetry; a framework which accounts for the distinctly different responses of cartilage in tension and compression is more suitable for describing the equilibrium response of cartilage; within this framework, cartilage exhibits no lower than orthotropic symmetry. PMID:12594982
Anisotropic adhesion of micropillars with spatula pads.
Seo, Seungwan; Lee, Jehong; Kim, Kwang-Seop; Ko, Kwang Hee; Lee, Jong Hyun; Lee, Jongho
2014-02-12
Natural gecko adhesive structures consisting of angled setae, branched into thin spatulas, have remarkable properties including easily attachable and releasable anisotropic adhesion. The geometrically asymmetric structures lead to anisotropic adhesive properties. Inspired by the gecko, we fabricated an array of micropillars with asymmetric spatula pads from elastomeric materials. This paper describes the anisotropic properties of the micropillars with spatula pads as established by experimental measurements and observation together with finite element analysis. The results indicate that the structural difference of the spatula pad at one edge of the micropillar provides the anisotropic adhesive properties. PMID:24446878
Pristine Basal- and Edge-Plane-Oriented Molybdenite MoS2 Exhibiting Highly Anisotropic Properties.
Tan, Shu Min; Ambrosi, Adriano; Sofer, Zden?k; Huber, Št?pán; Sedmidubský, David; Pumera, Martin
2015-05-01
The layered structure of molybdenum disulfide (MoS2 ) is structurally similar to that of graphite, with individual sheets strongly covalently bonded within but held together through weak van der Waals interactions. This results in two distinct surfaces of MoS2 : basal and edge planes. The edge plane was theoretically predicted to be more electroactive than the basal plane, but evidence from direct experimental comparison is elusive. Herein, the first study comparing the two surfaces of MoS2 by using macroscopic crystals is presented. A careful investigation of the electrochemical properties of macroscopic MoS2 pristine crystals with precise control over the exposure of one plane surface, that is, basal plane or edge plane, was performed. These crystals were characterized thoroughly by AFM, Raman spectroscopy, X-ray photoelectron spectroscopy, voltammetry, digital simulation, and DFT calculations. In the Raman spectra, the basal and edge planes show anisotropy in the preferred excitation of E2g and A1g phonon modes, respectively. The edge plane exhibits a much larger heterogeneous electron transfer rate constant k(0) of 4.96×10(-5) and 1.1×10(-3) ?cm?s(-1) for [Fe(CN)6 ](3-/4-) and [Ru(NH3 )6 ](3+/2+) redox probes, respectively, compared to the basal plane, which yielded k(0) tending towards zero for [Fe(CN)6 ](3-/4-) and about 9.3×10(-4) ?cm?s(-1) for [Ru(NH3 )6 ](3+/2+) . The industrially important hydrogen evolution reaction follows the trend observed for [Fe(CN)6 ](3-/4-) in that the basal plane is basically inactive. The experimental comparison of the edge and basal planes of MoS2 crystals is supported by DFT calculations. PMID:25821017
Research Update: Structural and transport properties of (Ca,La)FeAs2 single crystal
NASA Astrophysics Data System (ADS)
Caglieris, F.; Sala, A.; Fujioka, M.; Hummel, F.; Pallecchi, I.; Lamura, G.; Johrendt, D.; Takano, Y.; Ishida, S.; Iyo, A.; Eisaki, H.; Ogino, H.; Yakita, H.; Shimoyama, J.; Putti, M.
2016-02-01
Structural and transport properties in the normal and superconducting states are investigated in a Ca0.8La0.2FeAs2 single crystal with Tc = 27 K, belonging to the newly discovered 112 family of iron based superconductors. The transport critical current density Jc for both field directions measured in a focused ion beam patterned microbridge reveals a weakly field dependent and low anisotropic behaviour with a low temperature value as high as Jc(B = 0) Ëœ 105 A/cm2. This demonstrates not only bulk superconductivity but also the potential of 112 superconductors towards applications. Interestingly, this superconducting compound undergoes a structural transition below 100 K which is evidenced by temperature-dependent X-ray diffraction measurements. Data analysis of Hall resistance and magnetoresistivity indicate that magnetotransport properties are largely dominated by an electron band, with a change of regime observed in correspondence of the onset of a structural transition. In the low temperature regime, the contribution of a hole band to transport is suggested, possibly playing a role in determining the superconducting state.
Applications of asymmetric nanotextured parylene surface using its wetting and transport properties
NASA Astrophysics Data System (ADS)
Sekeroglu, Koray
In this thesis, basic digital fluidics devices were introduced using polymeric nanorods (nano-PPX) inspired from nature. Natural inspiration ignited this research by observing butterfly wings, water strider legs, rye grass leaves, and their asymmetric functions. Nano-PPX rods, manufactured by an oblique angle polymerization (OAP) method, are asymmetrically aligned structures that have unidirectional wetting properties. Nano-PPX demonstrates similar functions to the directional textured surfaces of animals and plants in terms of wetting, adhesion, and transport. The water pin-release mechanism on the asymmetric nano-PPX surface with adhesion function provides a great transport property. How the asymmetry causes transport is discussed in terms of hysteresis and interface contact of water droplets. In this study, the transport property of nano-PPX rods is used to guide droplets as well as transporting cargo such as microgels. With the addition of tracks on the nano-PPX rods, the surfaces were transformed into basic digital fluidics devices. The track-assisted nano-PPX has been employed to applications (i.e. sorting, mixing, and carrying cargo particles). Thus, digital fluidics devices fabricated on nano-PPX surface is a promising pathway to assemble microgels in the field of bioengineering. The characterization of the nano textured surface was completed using methods such as Scanning Electron Microscopy, Atomic Force Microscopy, Contact Angle Goniometry, and Fourier Transform Infra-Red Spectroscopy. These methods helped to understand the physical and chemical properties of nano-PPX. Parameters such as advancing and receding contact angles, nanorod tilt angle, and critical drop volumes were utilized to investigate the anisotropic wetting properties of nano-PPX surface. This investigation explained the directional wetting behavior of the surface as well as approaching new design parameters for adjusting surface properties. The nanorod tilt angle was a key parameter, thus changing the angle provided the surface with essential wetting properties. This adjustment on the nano-PPX surface exhibited excellent control on water droplet transport as well as guided the droplets from desired points to targets. The results demonstrated that it is possible to create railroad-like paths to manipulate the droplet movements by deforming the nano-PPX surface. Controlling physical properties of the surface granted the inspiration for fabricating basic fluidic devices to sort and mix droplets. These devices are promising for assembly purposes in terms of using microgels in engineering applications (i.e. building blocks for bioengineering). The surface has potential for further development to achieve the directed assembly of microgels into close proximity.
NASA Astrophysics Data System (ADS)
Song, Dongxing; Jing, Dengwei; Luo, Bing; Geng, Jiafeng; Ren, Yuxun
2015-07-01
Magnetic field can enhance both thermal conductivity and Lorentz force resistance of the magnetic nanofluids (MNFs), in which the former is favored while the latter often leads to pressure drop of the flow. It is assumed that there would exist a balance between the magnetic field induced thermal conductivity and Lorentz force if one can appropriately adjust the angle of the imposing magnetic field with respect to the direction of the flow. In the present study, the effects of direction of magnetic field ( Î±) on anisotropic thermodynamic properties of magnetic nanofluids in channel were studied. The effects of direction of magnetic field on thermal conductivity, Nusselt number, global total entropy generation, and other parameters, such as velocity, temperature, and concentration, have been discussed in detail. A greater Î± can lead to a larger thermal conductivity normal to the walls of channel and a more uniform temperature field. However, the velocity of magnetic nanofluid tends to decrease. There is a threshold for magnetic intensity (B). When magnetic intensity becomes large than the threshold, its effect on thermal conductivity will tends to be constant. The effect of increase of Î± is found to be similar to that of increasing Hartmann number ( H a ) and both can lead to augment of Lorentz resistance force along flow direction. With the increases of Î± and H a , both heat transfer efficiency (Nu) and global total entropy generation ( ST ) increase. Here, ST indicates the extent of loss of useful work due to the irreversibility of the process. A comprehensive utility index, Iu , is defined for evaluation of the performance of a practical heat transfer system employing MNFs. For the case where the purpose of heat transfer is to cool an equipment such as electrical device, guaranteeing heat transfer efficiency (Nu) is more important than decreasing useful energy loss ( ST ); thus, we propose a large Î± relative to the flow direction. For industrial processes, where energy loss ( ST ) have to be particularly considered, a small Î± is recommended.
Molecular Properties of Bacterial Multidrug Transporters
Putman, Monique; van Veen, Hendrik W.; Konings, Wil N.
2000-01-01
One of the mechanisms that bacteria utilize to evade the toxic effects of antibiotics is the active extrusion of structurally unrelated drugs from the cell. Both intrinsic and acquired multidrug transporters play an important role in antibiotic resistance of several pathogens, including Neisseria gonorrhoeae, Mycobacterium tuberculosis, Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Vibrio cholerae. Detailed knowledge of the molecular basis of drug recognition and transport by multidrug transport systems is required for the development of new antibiotics that are not extruded or of inhibitors which block the multidrug transporter and allow traditional antibiotics to be effective. This review gives an extensive overview of the currently known multidrug transporters in bacteria. Based on energetics and structural characteristics, the bacterial multidrug transporters can be classified into five distinct families. Functional reconstitution in liposomes of purified multidrug transport proteins from four families revealed that these proteins are capable of mediating the export of structurally unrelated drugs independent of accessory proteins or cytoplasmic components. On the basis of (i) mutations that affect the activity or the substrate specificity of multidrug transporters and (ii) the three-dimensional structure of the drug-binding domain of the regulatory protein BmrR, the substrate-binding site for cationic drugs is predicted to consist of a hydrophobic pocket with a buried negatively charged residue that interacts electrostatically with the positively charged substrate. The aromatic and hydrophobic amino acid residues which form the drug-binding pocket impose restrictions on the shape and size of the substrates. Kinetic analysis of drug transport by multidrug transporters provided evidence that these proteins may contain multiple substrate-binding sites. PMID:11104814
Xu, Wenxiang; Wang, Han; Niu, Yanze; Bai, Jingtao
2016-01-01
With advances in interfacial properties characterization technologies, the interfacial volume fraction is a feasible parameter for evaluating effective physical properties of materials. However, there is a need to determine the interfacial volume fraction around anisotropic fibers and a need to assess the influence of such the interfacial property on effective properties of fibrous materials. Either ways, the accurate prediction of interfacial volume fraction is required. Towards this end, we put forward both theoretical and numerical schemes to determine the interfacial volume fraction in fibrous materials, which are considered as a three-phase composite structure consisting of matrix, anisotropic hard spherocylinder fibers, and soft interfacial layers with a constant dimension coated on the surface of each fiber. The interfacial volume fraction actually represents the fraction of space not occupied by all hard fibers and matrix. The theoretical scheme that adopts statistical geometry and stereological theories is essentially an analytic continuation from spherical inclusions. By simulating such three-phase chopped fibrous materials, we numerically derive the interfacial volume fraction. The theoretical and numerical schemes provide a quantitative insight that the interfacial volume fraction depends strongly on the fiber geometries like fiber shape, geometric size factor, and fiber size distribution. As a critical interfacial property, the present contribution can be further drawn into assessing effective physical properties of fibrous materials, which will be demonstrated in another paper (Part II) of this series. PMID:26747814
NASA Astrophysics Data System (ADS)
Xu, Wenxiang; Wang, Han; Niu, Yanze; Bai, Jingtao
2016-01-01
With advances in interfacial properties characterization technologies, the interfacial volume fraction is a feasible parameter for evaluating effective physical properties of materials. However, there is a need to determine the interfacial volume fraction around anisotropic fibers and a need to assess the influence of such the interfacial property on effective properties of fibrous materials. Either ways, the accurate prediction of interfacial volume fraction is required. Towards this end, we put forward both theoretical and numerical schemes to determine the interfacial volume fraction in fibrous materials, which are considered as a three-phase composite structure consisting of matrix, anisotropic hard spherocylinder fibers, and soft interfacial layers with a constant dimension coated on the surface of each fiber. The interfacial volume fraction actually represents the fraction of space not occupied by all hard fibers and matrix. The theoretical scheme that adopts statistical geometry and stereological theories is essentially an analytic continuation from spherical inclusions. By simulating such three-phase chopped fibrous materials, we numerically derive the interfacial volume fraction. The theoretical and numerical schemes provide a quantitative insight that the interfacial volume fraction depends strongly on the fiber geometries like fiber shape, geometric size factor, and fiber size distribution. As a critical interfacial property, the present contribution can be further drawn into assessing effective physical properties of fibrous materials, which will be demonstrated in another paper (Part II) of this series.
Transport properties of Dirac semimetal Cd3As2
NASA Astrophysics Data System (ADS)
Liang, Tian; Gibson, Quinn; Xiong, Jun; Liu, Minhao; Hirschberger, Maximilian; Cava, Robert; Ong, Nai Phuan
2014-03-01
The semimetal Cd3As2 has emerged as an attractive candidate for a Dirac semimetal. A recent LDA calculation reveals that, at the Fermi energy, it has two bulk Dirac nodes which straddle the ? point along the kz axis. The Dirac nodes were recently observed by ARPES. We have made extensive transport measurements of Cd3As2. Because of possible Cd vacancy disorder in the very large unit cell (160 atoms), the SdH oscillations reveal a quantum lifetime that is moderately damped. Despite the disorder, the observed resistivity ? in some crystals displays a RRR of 1000. At 4 K, the residual resistivity is anomalously low (30 n ? cm). We estimate that the mobility exceeds 106 cm2V-1s-1. A magnetic field H strongly increases ? by factors of 100 to 1000 at 10 Tesla. This giant magnetoresistance (MR) is highly anisotropic. The MR is largest when H is perpendicular to the axis (110) and minimal when H is ?(110). We will discuss possible origins of this unusual anisotropic giant MR. We also discuss the possibility of detecting an enhanced longitudinal MR associated with charge pumping between Weyl nodes (the chiral anomaly). Supported by Army Research Office (ARO W911NF-11-1-0379) and NSF-MRSEC Grant DMR 0819860.
Neoclassical transport properties and their limits in NSTX
NASA Astrophysics Data System (ADS)
Houlberg, W. A.; Strand, P. I.; Shaing, K. C.
2001-10-01
The low aspect ratio and low toroidal field of NSTX enhance its neoclassical transport properties, but also push the limits of standard neoclassical models. Particle and energy transport, plasma rotation, the radial electric field, and bootstrap current are examined for typical NSTX discharges. Regimes of inward and outward impurity transport driven by a combination of the inductive electric field (Ware pinch), inward transport on the deuterium density gradient, and outward transport on the ion temperature gradient are identified. Orbit losses and atomic physics effects near the plasma boundary lead to modifications in the bootstrap current and impurity transport properties in the H-mode pedestal. Potato orbit effects near the axis, included as a viscosity modification, can enhance the ion energy transport, but are reduced by orbit squeezing. The low aspect ratio and high beta of NSTX plasmas provide a critical test of the limits of neoclassical theory.
NASA Astrophysics Data System (ADS)
Sofin, R. G. S.; Wu, Han-Chun; Ramos, R.; Arora, S. K.; Shvets, I. V.
2015-11-01
We studied Fe3O4 (110) films grown epitaxially on MgO (110) substrates using oxygen plasma assisted molecular beam epitaxy. The films with thickness of 30-200 nm showed anisotropic in-plane partial strain relaxation. Magneto resistance (MR) measurements with current and magnetic field along ?001? direction showed higher MR compared to ?1 ¯ 10 ? direction. Maximum value of MR was measured at Verwey transition temperature for both directions. We explain the observed anisotropy in the MR on the basis of the effects of anisotropic misfit strain, and the difference between the density of antiferromagnetically coupled antiphase boundaries formed along ?001? and ?1 ¯ 10 ? crystallographic directions, suggesting the dependence of spin polarisation on the anisotropic strain relaxation along the said crystallographic directions.
NASA Astrophysics Data System (ADS)
Swartz, C. H.; Petersen, J. E.; Welch, E. W.; Myers, T. H.
2016-01-01
The success of PbTe as a thermoelectric material has generated growing interest in its charge carrier transport properties. The Boltzmann transport equation (BTE) is solved in a way which takes anisotropy, non-parabolicity, and inelastic scattering fully into account, and an inaccuracy arising from the standard treatment of phonon emission scattering is corrected. The method is used to calculate the conductivity and Hall coefficient of n-PbTe over a wide range of temperatures and doping levels, and it is found that room temperature measurements of PbTe may underestimate the true carrier concentration in some cases by a factor of 2. Experimental results on both bulk and epitaxial samples are in reasonable agreement with the predictions. A conducting p-type layer is also observed in the epitaxial films, exhibiting both persistent photoconductivity and sensitivity to air exposure.
Li, Yijing; Barbic, Jernej
2015-10-01
The Finite Element Method (FEM) is commonly used to simulate isotropic deformable objects in computer graphics. Several applications (wood, plants, muscles) require modeling the directional dependence of the material elastic properties in three orthogonal directions. We investigate linear orthotropic materials, a special class of linear anisotropic materials where the shear stresses are decoupled from normal stresses, as well as general linear (non-orthotropic) anisotropic materials. Orthotropic materials generalize transversely isotropic materials, by exhibiting different stiffness in three orthogonal directions. Orthotropic materials are, however, parameterized by nine values that are difficult to tune in practice, as poorly adjusted settings easily lead to simulation instabilities. We present a user-friendly approach to setting these parameters that is guaranteed to be stable. Our approach is intuitive as it extends the familiar intuition known from isotropic materials. Similarly to linear orthotropic materials, we also derive a stability condition for a subset of general linear anisotropic materials, and give intuitive approaches to tuning them. In order to simulate large deformations, we augment linear corotational FEM simulations with our orthotropic and general anisotropic materials. PMID:26340037
Anisotropic enhanced backscattering induced by anisotropic diffusion
NASA Astrophysics Data System (ADS)
Bret, B. P. J.; Lagendijk, A.
2004-09-01
The enhanced backscattering cone displaying a strong anisotropy from a material with anisotropic diffusion is reported. The constructive interference of the wave is preserved in the helicity preserving polarization channel and completely lost in the nonpreserving one. The internal reflectivity at the interface modifies the width of the backscatter cone. The reflectivity coefficient is measured by angular-resolved transmission. This interface property is found to be isotropic, simplifying the backscatter cone analysis. The material used is a macroporous semiconductor, gallium phosphide, in which pores are etched in a disordered position but with a preferential direction.
NASA Astrophysics Data System (ADS)
Pedretti, D.; Fernandez-Garcia, D.; Bolster, D.; Sanchez-Vila, X.; Benson, D.
2012-04-01
For risk assessment and adequate decision making regarding remediation strategies in contaminated aquifers, solute fate in the subsurface must be modeled correctly. In practical situations, hydrodynamic transport parameters are obtained by fitting procedures, that aim to mathematically reproduce solute breakthrough (BTC) observed in the field during tracer tests. In recent years, several methods have been proposed (curve-types, moments, nonlocal formulations) but none of them combine the two main characteristic effects of convergent flow tracer tests (which are the most used tests in the practice): the intrinsic non-stationarity of the convergent flow to a well and the ubiquitous multiscale hydraulic heterogeneity of geological formations. These two effects separately have been accounted for by a lot of methods that appear to work well. Here, we investigate both effects at the same time via numerical analysis. We focus on the influence that measurable statistical properties of the aquifers (such as the variance and the statistical geometry of correlation scales) have on the shape of BTCs measured at the pumping well during convergent flow tracer tests. We built synthetic multigaussian 3D fields of heterogeneous hydraulic conductivity fields with variable statistics. A well is located in the center of the domain to reproduce a forced gradient towards it. Constant-head values are imposed on the boundaries of the domains, which have 251x251x100 cells. Injections of solutes take place by releasing particles at different distances from the well and using a random walk particle tracking scheme with constant local coefficient of dispersivity. The results show that BTCs partially display the typical anomalous behavior that has been commonly referred to as the effect of heterogeneity and connectivity (early and late arrival times of solute differ from the one predicted by local formulations). Among the most salient features, the behaviors of BTCs after the peak (the slope of the BTCs in log-log scales, which is the diagnostic plot to infer power-law type nonlocal distribution parameters due to hydraulic heterogeneity) indicate that anisotropy generates apparent higher capacity coefficients in certain directions. At very late times, however, the slopes display similar values, indicating that at these spatial scales (injection distances comparable with the integral scales), particles are stacked in low K areas for much longer than the advection times in higher K zones.
Highly anisotropic thermal conductivity of arsenene: An ab initio study
NASA Astrophysics Data System (ADS)
Zeraati, Majid; Vaez Allaei, S. Mehdi; Abdolhosseini Sarsari, I.; Pourfath, Mahdi; Donadio, Davide
2016-02-01
Elemental two-dimensional (2D) materials exhibit intriguing heat transport and phononic properties. Here we have investigated the lattice thermal conductivity of newly proposed arsenene, the 2D honeycomb structure of arsenic, using ab initio calculations. Solving the Boltzmann transport equation for phonons, we predict a highly anisotropic thermal conductivity of 30.4 and 7.8 W/mK along the zigzag and armchair directions, respectively, at room temperature. Our calculations reveal that phonons with mean free paths between 20 nm and 1 Î¼ m provide the main contribution to the large thermal conductivity in the zigzag direction; mean free paths of phonons contributing to heat transport in the armchair directions range between 20 and 100 nm. The obtained anisotropic thermal conductivity and feasibility of synthesis, in addition to high electron mobility reported elsewhere, make arsenene a promising material for nanoelectronic applications and thermal management.
Wills, E.E.
1981-03-01
A finite element space-angle synthesis (FESAS) solution of the steady state anisotropic Boltzmann equation in a two-dimensional cylindrical geometry was developed. Starting from a variational principle the Bubnov-Galerkin solution method was applied to the second order even parity form of the Boltzmann equation. A trial function flux expansion in bicubic splines and spherical (surface) harmonics was used. A first scatter (collision) source and an exponentially varying atmosphere were also incorporated. FESAS was developed as an alternate solution approach and an improvement in comparison to the methods of Monte Carlo and discrete ordinates. FESAS does not have the inherent characteristics which have produced the ray effect problem in discrete ordinates; also, FESAS may result in lower computational costs. The second order even parity form of the Boltzmann equation was derived and shown to be symmetric, positive definite and self-adjoint. The equivalence of a variational minimization principle and the Bubnov-Galerkin method of weighted residuals was established. The FESAS system of equations was expanded and a numerical computer solution approach was implemented.
Anisotropic universe with anisotropic sources
Aluri, Pavan K.; Panda, Sukanta; Sharma, Manabendra; Thakur, Snigdha E-mail: sukanta@iiserb.ac.in E-mail: snigdha@iiserb.ac.in
2013-12-01
We analyze the state space of a Bianchi-I universe with anisotropic sources. Here we consider an extended state space which includes null geodesics in this background. The evolution equations for all the state observables are derived. Dynamical systems approach is used to study the evolution of these equations. The asymptotic stable fixed points for all the evolution equations are found. We also check our analytic results with numerical analysis of these dynamical equations. The evolution of the state observables are studied both in cosmic time and using a dimensionless time variable. Then we repeat the same analysis with a more realistic scenario, adding the isotropic (dust like dark) matter and a cosmological constant (dark energy) to our anisotropic sources, to study their co-evolution. The universe now approaches a de Sitter space asymptotically dominated by the cosmological constant. The cosmic microwave background anisotropy maps due to shear are also generated in this scenario, assuming that the universe contains anisotropic matter along with the usual (dark) matter and vacuum (dark) energy since decoupling. We find that they contribute dominantly to the CMB quadrupole. We also constrain the current level of anisotropy and also search for any cosmic preferred axis present in the data. We use the Union 2 Supernovae data to this extent. An anisotropy axis close to the mirror symmetry axis seen in the cosmic microwave background data from Planck probe is found.
Molecular transport properties through carbon nanotube membrane
NASA Astrophysics Data System (ADS)
Majumder, Mainak
Molecular transport through hollow cores of crystalline carbon nanotubes (CNTs) are of considerable interest from the fundamental and application point of view. This dissertation focuses on understanding molecular transport through a membrane platform consisting of open ended CNTs with ˜ 7 nm core diameter and ˜ 1010 CNTs/cm2 encapsulated in an inert polymer matrix. While ionic diffusion through the membrane is close to bulk diffusion expectations, gases and liquids were respectively observed to be transported ˜ 10 times faster than Knudsen diffusion and ˜ 10000--100000 times faster than hydrodynamic flow predictions. This phenomenon has been attributed to the non-interactive and frictionless graphitic interface. Functionalization of the CNT tips was observed to change selectivity and flux through the CNT membranes with analogy to 'gate-keeper' functionality in biological membranes. An electro-chemical diazonium grafting chemistry was utilized for enhancing the functional density on the CNT membranes. A strategy to confine the reactions at the CNT tips by a fast flowing liquid column was also designed. Characterization using electrochemical impedance spectroscopy and dye assay indicated ˜ 5--6 times increase in functional density. Electrochemical impedance spectroscopy experiments on CNT membrane/electrode functionalized with charged macro-molecules showed voltage-controlled conformational change. Similar chemistry has been applied for realizing 'voltage-gated' transport channels with potential application in trans-dermal drug delivery. Electrically-facilitated transport (a geometry in which an electric field gradient acts across the membrane) through the CNT and functionalized CNT membranes was observed to be electrosmotically controlled. Finally, a simulation framework based on continuum electrostatics and finite elements has been developed to further the understanding of transport through the CNT membranes. KEYWORDS: carbon nanotube membrane, nano-scale hydrodynamics, diazonium grafting, voltage-gated membrane, finite element analysis
Kataoka, Keisuke; Yasumoto, Tetsuaki; Manabe, Yousuke; Sato, Hiroyasu; Yamano, Akihito; Katagiri, Toshimasa
2013-02-21
An anisotropic tunnel microporous crystal was prepared. Active transportation of anthracene as a guest molecule in the anisotropic tunnels was observed. The direction of anthracene movement implies that the anisotropic tunnel did not work as a flap-check valve. The direction of the movement was consistent with that caused by a Brownian ratchet. PMID:22692420
Lee, Barry
2010-05-01
This paper presents a new multigrid method applied to the most common Sn discretizations (Petrov-Galerkin, diamond-differenced, corner-balanced, and discontinuous Galerkin) of the mono-energetic Boltzmann transport equation in the optically thick and thin regimes, and with strong anisotropic scattering. Unlike methods that use scalar DSA diffusion preconditioners for the source iteration, this multigrid method is applied directly to an integral equation for the scalar flux. Thus, unlike the former methods that apply a multigrid strategy to the scalar DSA diffusion operator, this method applies a multigrid strategy to the integral source iteration operator, which is an operator for 5 independent variables in spatial 3-d (3 in space and 2 in angle) and 4 independent variables in spatial 2-d (2 in space and 2 in angle). The core smoother of this multigrid method involves applications of the integral operator. Since the kernel of this integral operator involves the transport sweeps, applying this integral operator requires a transport sweep (an inversion of an upper triagular matrix) for each of the angles used. As the equation is in 5-space or 4-space, the multigrid approach in this paper coarsens in both angle and space, effecting efficient applications of the coarse integral operators. Although each V-cycle of this method is more expensive than a V-cycle for the DSA preconditioner, since the DSA equation does not have angular dependence, the overall computational efficiency is about the same for problems where DSA preconditioning {\\it is} effective. This new method also appears to be more robust over all parameter regimes than DSA approaches. Moreover, this new method is applicable to a variety of Sn spatial discretizations, to problems involving a combination of optically thick and thin regimes, and more importantly, to problems with anisotropic scattering cross-sections, all of which DSA approaches perform poorly or not applicable at all. This multigrid approach is most effective in neutron scattering applications, where the total cross-section coefficient $\\sigma_t$ and spatial meshsize $h$ satisfies $\\sigma_t h\\approx 1.$ For this case, coarsening can be done aggressively. For problems with $\\sigma_t h\\approx 10,$ this multigrid scheme requires a moderately coarsened multiple-coarsening scheme. An even slow coarsening, an angle semi-coarsening, is required for problems with $\\sigma_t h$ ranges between 100 and 1000, which occur in high-energy photon applications.
PROPERTIES OF INTERFACES AND TRANSPORT ACROSS THEM
Much of the biological activity in cell cytoplasm occurs in compartments which are thought to form by phase separation, and many of the functions of these compartments occur by the transport or exchange of molecules across interfaces. Thus, a fundamentally based discussion of th...
Shi, Wen; Zhao, Tianqi; Xi, Jinyang; Wang, Dong; Shuai, Zhigang
2015-10-14
Tuning carrier concentration via chemical doping is the most successful strategy to optimize the thermoelectric figure of merit. Nevertheless, how the dopants affect charge transport is not completely understood. Here we unravel the doping effects by explicitly including the scattering of charge carriers with dopants on thermoelectric properties of poly(3,4-ethylenedioxythiophene), PEDOT, which is a p-type thermoelectric material with the highest figure of merit reported. We corroborate that the PEDOT exhibits a distinct transition from the aromatic to quinoid-like structure of backbone, and a semiconductor-to-metal transition with an increase in the level of doping. We identify a close-to-unity charge transfer from PEDOT to the dopant, and find that the ionized impurity scattering dominates over the acoustic phonon scattering in the doped PEDOT. By incorporating both scattering mechanisms, the doped PEDOT exhibits mobility, Seebeck coefficient and power factors in very good agreement with the experimental data, and the lightly doped PEDOT exhibits thermoelectric properties superior to the heavily doped one. We reveal that the thermoelectric transport is highly anisotropic in ordered crystals, and suggest to utilize large power factors in the direction of polymer backbone and low lattice thermal conductivity in the stacking and lamellar directions, which is viable in chain-oriented amorphous nanofibers. PMID:26406937
Transport properties of pancreatic cancer describe gemcitabine delivery and response
Koay, Eugene J.; Truty, Mark J.; Cristini, Vittorio; Thomas, Ryan M.; Chen, Rong; Chatterjee, Deyali; Kang, Yaâ€™an; Bhosale, Priya R.; Tamm, Eric P.; Crane, Christopher H.; Javle, Milind; Katz, Matthew H.; Gottumukkala, Vijaya N.; Rozner, Marc A.; Shen, Haifa; Lee, Jeffery E.; Wang, Huamin; Chen, Yuling; Plunkett, William; Abbruzzese, James L.; Wolff, Robert A.; Varadhachary, Gauri R.; Ferrari, Mauro; Fleming, Jason B.
2014-01-01
Background. The therapeutic resistance of pancreatic ductal adenocarcinoma (PDAC) is partly ascribed to ineffective delivery of chemotherapy to cancer cells. We hypothesized that physical properties at vascular, extracellular, and cellular scales influence delivery of and response to gemcitabine-based therapy. Methods. We developed a method to measure mass transport properties during routine contrast-enhanced CT scans of individual human PDAC tumors. Additionally, we evaluated gemcitabine infusion during PDAC resection in 12 patients, measuring gemcitabine incorporation into tumor DNA and correlating its uptake with human equilibrative nucleoside transporter (hENT1) levels, stromal reaction, and CT-derived mass transport properties. We also studied associations between CT-derived transport properties and clinical outcomes in patients who received preoperative gemcitabine-based chemoradiotherapy for resectable PDAC. Results. Transport modeling of 176 CT scans illustrated striking differences in transport properties between normal pancreas and tumor, with a wide array of enhancement profiles. Reflecting the interpatient differences in contrast enhancement, resected tumors exhibited dramatic differences in gemcitabine DNA incorporation, despite similar intravascular pharmacokinetics. Gemcitabine incorporation into tumor DNA was inversely related to CT-derived transport parameters and PDAC stromal score, after accounting for hENT1 levels. Moreover, stromal score directly correlated with CT-derived parameters. Among 110 patients who received preoperative gemcitabine-based chemoradiotherapy, CT-derived parameters correlated with pathological response and survival. Conclusion. Gemcitabine incorporation into tumor DNA is highly variable and correlates with multiscale transport properties that can be derived from routine CT scans. Furthermore, pretherapy CT-derived properties correlate with clinically relevant endpoints. Trial registration. Clinicaltrials.gov NCT01276613. Funding. Lustgarten Foundation (989161), Department of Defense (W81XWH-09-1-0212), NIH (U54CA151668, KCA088084). PMID:24614108
Lagrangian transport properties of pulmonary interfacial flows
Smith, Bradford J.; Lukens, Sarah; Yamaguchi, Eiichiro; Gaver, Donald P.
2012-01-01
Disease states characterized by airway fluid occlusion and pulmonary surfactant insufficiency, such as respiratory distress syndrome, have a high mortality rate. Understanding the mechanics of airway reopening, particularly involving surfactant transport, may provide an avenue to increase patient survival via optimized mechanical ventilation waveforms. We model the occluded airway as a liquid-filled rigid tube with the fluid phase displaced by a finger of air that propagates with both mean and sinusoidal velocity components. Finite-time Lyapunov exponent (FTLE) fields are employed to analyse the convective transport characteristics, taking note of Lagrangian coherent structures (LCSs) and their effects on transport. The Lagrangian perspective of these techniques reveals flow characteristics that are not readily apparent by observing Eulerian measures. These analysis techniques are applied to surfactant-free velocity fields determined computationally, with the boundary element method, and measured experimentally with micro particle image velocimetry (?-PIV). We find that the LCS divides the fluid into two regimes, one advected upstream (into the thin residual film) and the other downstream ahead of the advancing bubble. At higher oscillatory frequencies particles originating immediately inside the LCS experience long residence times at the air–liquid interface, which may be conducive to surfactant transport. At high frequencies a well-mixed attractor region is identified; this volume of fluid cyclically travels along the interface and into the bulk fluid. The Lagrangian analysis is applied to velocity data measured with 0.01 mg ml?1 of the clinical pulmonary surfactant Infasurf in the bulk fluid, demonstrating flow field modifications with respect to the surfactant-free system that were not visible in the Eulerian frame. PMID:23049141
FIELD DETERMINATION OF SOIL HYDRAULIC AND CHEMICAL TRANSPORT PROPERTIES
Technology Transfer Automated Retrieval System (TEKTRAN)
Hydraulic and chemical transport properties are the major inputs in predictive models that simulate the movement of water and chemicals through the vadose zone. However, there is a lack of field measurements of such properties to verify models describing water and chemical movement through the soil...
Magnetic and Transport Properties of Mn-ion implanted Si
NASA Astrophysics Data System (ADS)
Preisler, V.; Ogawa, M.; Han, X.; Wang, K. L.
2010-01-01
We investigate the magnetic and transport properties of Mn-ion implanted Si. Both temperature dependent and field dependent measurements of the samples using a SQUID magnometer reveal ferromagnetic properties at room temperature. Magnetotransport measurements show a large positive magnetoresistance up to 4.5 T with no signs of saturation.
Physical transport properties of marine microplastic pollution
NASA Astrophysics Data System (ADS)
Ballent, A.; Purser, A.; Mendes, P. de Jesus; Pando, S.; Thomsen, L.
2012-12-01
Given the complexity of quantitative collection, knowledge of the distribution of microplastic pollution in many regions of the world ocean is patchy, both spatially and temporally, especially for the subsurface environment. However, with knowledge of typical hydrodynamic behavior of waste plastic material, models predicting the dispersal of pelagic and benthic plastics from land sources into the ocean are possible. Here we investigate three aspects of plastic distribution and transport in European waters. Firstly, we assess patterns in the distribution of plastics found in fluvial strandlines of the North Sea and how distribution may be related to flow velocities and distance from source. Second, we model transport of non-buoyant preproduction pellets in the Nazaré Canyon of Portugal using the MOHID system after assessing the density, settling velocity, critical and depositional shear stress characteristics of such waste plastics. Thirdly, we investigate the effect of surface turbulences and high pressures on a range of marine plastic debris categories (various densities, degradation states and shapes tested) in an experimental water column simulator tank and pressure laboratory. Plastics deposited on North Sea strandlines varied greatly spatially, as a function of material composition and distance from source. Model outputs indicated that such dense production pellets are likely transported up and down canyon as a function of tidal forces, with only very minor net down canyon movement. Behaviour of plastic fragments under turbulence varied greatly, with the dimensions of the material, as well as density, playing major determining roles. Pressure was shown to affect hydrodynamic behaviours of only low density foam plastics at pressures ? 60 bar.
Fractures in anisotropic media
NASA Astrophysics Data System (ADS)
Shao, Siyi
Rocks may be composed of layers and contain fracture sets that cause the hydraulic, mechanical and seismic properties of a rock to be anisotropic. Coexisting fractures and layers in rock give rise to competing mechanisms of anisotropy. For example: (1) at low fracture stiffness, apparent shear-wave anisotropy induced by matrix layering can be masked or enhanced by the presence of a fracture, depending on the fracture orientation with respect to layering, and (2) compressional-wave guided modes generated by parallel fractures can also mask the presence of matrix layerings for particular fracture orientations and fracture specific stiffness. This report focuses on two anisotropic sources that are widely encountered in rock engineering: fractures (mechanical discontinuity) and matrix layering (impedance discontinuity), by investigating: (1) matrix property characterization, i.e., to determine elastic constants in anisotropic solids, (2) interface wave behavior in single-fractured anisotropic media, (3) compressional wave guided modes in parallel-fractured anisotropic media (single fracture orientation) and (4) the elastic response of orthogonal fracture networks. Elastic constants of a medium are required to understand and quantify wave propagation in anisotropic media but are affected by fractures and matrix properties. Experimental observations and analytical analysis demonstrate that behaviors of both fracture interface waves and compressional-wave guided modes for fractures in anisotropic media, are affected by fracture specific stiffness (controlled by external stresses), signal frequency and relative orientation between layerings in the matrix and fractures. A fractured layered medium exhibits: (1) fracture-dominated anisotropy when the fractures are weakly coupled; (2) isotropic behavior when fractures delay waves that are usually fast in a layered medium; and (3) matrix-dominated anisotropy when the fractures are closed and no longer delay the signal. The theory and experimental results in this report demonstrate that the presence of fractures in anisotropic material can be unambiguously interpreted if experimental measurements are made as a function of stress, which eliminates many fracture-generated discrete modes (e.g., interface waves, and leaky guided-modes). Orthogonal fracture networks that are often encountered in field exploration bring in additional challenges for seismic/acoustic data interpretation. An innovative wavefront imaging system with a bi-axial load frame was designed and implemented on orthogonally-fractured samples to determine the effect of fracture networks on elastic wave propagation. The effects of central wave guiding and extra time delays along a fracture intersection were observed in experiments and was analyzed. Interpreting data from media with intersecting fracture sets must account for fracture intersections and the non-uniformity of fracture properties caused by local tectonic conditions or other physical process such as non-uniform fluid distributions within a network and/or chemical alterations.
Enhancement of wall jet transport properties
Claunch, S.D.; Farrington, R.B.
1997-02-04
By enhancing the natural instabilities in the boundary layer and in the free shear layer of a wall jet, the boundary is minimized thereby increasing the transport of heat and mass. Enhancing the natural instabilities is accomplished by pulsing the flow of air that creates the wall jet. Such pulsing of the flow of air can be accomplished by sequentially occluding and opening a duct that confines and directs the flow of air, such as by rotating a disk on an axis transverse to the flow of air in the duct. 17 figs.
Enhancement of wall jet transport properties
Claunch, Scott D. (Broomfield, CO); Farrington, Robert B. (Golden, CO)
1997-01-01
By enhancing the natural instabilities in the boundary layer and in the free shear layer of a wall jet, the boundary is minimized thereby increasing the transport of heat and mass. Enhancing the natural instabilities is accomplished by pulsing the flow of air that creates the wall jet. Such pulsing of the flow of air can be accomplished by sequentially occluding and opening a duct that confines and directs the flow of air, such as by rotating a disk on an axis transverse to the flow of air in the duct.
Electronic and transport properties of artificial gold chains.
Calzolari, Arrigo; Cavazzoni, Carlo; Buongiorno Nardelli, Marco
2004-08-27
We study the electronic and transport properties of artificial Au atomic chains on a NiAl(110) surface template using state-of-the-art first principles calculations. Au chains display remarkable one-dimensional electronic properties that can be tuned by the selective adsorption of small molecules: a single CO group is shown to modulate the electronic wave functions, acting as a "chemical scissor" along the chain, to strongly modify the coherent transport properties of the system, and to help design one-dimensional nanodevices through artificial profiling of energy barriers. PMID:15447121
NASA Astrophysics Data System (ADS)
Kovalevskiy, Mikhail
2013-04-01
The KTB German Superdeep Well (Germany, Windischeschenbach) has limiting depth of 9101 m. It is one of the world deepest well among the continental boreholes. A study of physical parameters including elastic ones of the massif intersected by the well allowed to represent a real pattern of changing properties and the state of crystalline rocks in upper and middle part of the Earth crust. Such a deep section enables performing analyses of large spectrum of geological and geophysical objects, such as minerals, crystalline rocks, geological strata, formation complexes et al. Recently obtained results permit to get a general idea of elastic-anisotropic properties of crystalline rocks extracted from great depths. A study of properties and state of rocks along the KTB section will make it possible to most precisely determine regular changes of the Earth's rock properties within a large range of depths. Below are the results of investigation of elastic-anisotropic properties for 13 core samples of the KTB rocks in the range of 4.1 to 7.1 km. In this interval the well has penetrated metamorphosed rocks [1]. The measurements have been done by an acoustopolarization method with recent improvements and with devices for determination of sample elastic properties [2 3]. The data obtained are the result of extended study into the KTB rock samples by the method [4]. Study of rock samples from the KTB Superdeep Well in the 4100-7100 m depth range showed that they all are elastic anisotropic and pertain to a orthorhombic symmetry type. Virtually the degree of linear acoustic anisotropic absorption (LAAA) effect has been detected in all samples. Its appearance is likely related to directional orientation of mineral grains as well as to the generation of microcracks during drilling and lithostatic stress release. The several samples showed an angular unconformity between the LAAA orientation and elastic symmetry elements. The shear waves depolarization (DSW) effect was detected in garnet amphibolites samples. There was observed a tendency to persistence in propagation rate of compression and shear wave velocities. The pattern of change in anisotropy factors for compression and shear waves in depth shows itself in a similar way. There is an inverse correlation between density and anisotropy. R E F E R E N C E S 1. Emmermann R., Althaus E., Giese P., Stockhert B.. KTB Hauptbohrung. Results of Geoscientific Investigation in the KTB Field Laboratory. Final Report: 0-9101m. KTB Report 95-2. Hannover. 1995. 2. Gorbatsevich F.F. Acoustopolariscopy of rock forming minerals and crystalline rocks. Apatity, Kola Science Centre RAS, 2002, p. 140. (In Russian) 3. Kovalevskiy M.V. Automated hardware-software complex Acoustpol: Tutorial: Apatity, «K & M» Publ., 2009. 54p. (In Russian). 4. Kovalevsky M.V., Gorbatsevich F.F., Harms U., Dahlheim H.-A. Ultrasonic polarization measurements of elastic-anisotropic properties of metamorphized rocks on the slit of German KTB Superdeep Well // Geophysical magazine.- Geophysics Institute of NAS of Ukraine. -2012.- Issue 34.-#2.-P. 36-48. (In Russian)
High temperature transport properties of air
NASA Technical Reports Server (NTRS)
Levin, E.; Partridge, Harry; Stallcop, J. R.
1987-01-01
A general computer code was developed to allow calculation of atom-atom and ion-atom transport collision integrals from accurate potential energy curves described by a set of discrete data points for a broad range of scattering conditions. This code is based upon semiclassical approximations that properly account for quantum mechanical behavior such as tunneling effects near a barrier maximum, resonance charge exchange, and nuclear symmetry effects. Transport collision integrals were determined for N-N, O-O, N(+)-N, and O(+)-O interactions from complete sets of accurate potential functions derived from combined experimental and ab initio structure calculations. For the O-O case, this includes results for excited states. The calculated values of the N(+)-N and O(+)-O resonance charge exchange cross section Q(ex) agree well with measurements from beam experiment that are available at high energies where the diffusion cross section Q(d) satisfies Q(d) approximately equal to 2Q(ex).
CET89 - CHEMICAL EQUILIBRIUM WITH TRANSPORT PROPERTIES, 1989
NASA Technical Reports Server (NTRS)
Mcbride, B.
1994-01-01
Scientists and engineers need chemical equilibrium composition data to calculate the theoretical thermodynamic properties of a chemical system. This information is essential in the design and analysis of equipment such as compressors, turbines, nozzles, engines, shock tubes, heat exchangers, and chemical processing equipment. The substantial amount of numerical computation required to obtain equilibrium compositions and transport properties for complex chemical systems led scientists at NASA's Lewis Research Center to develop CET89, a program designed to calculate the thermodynamic and transport properties of these systems. CET89 is a general program which will calculate chemical equilibrium compositions and mixture properties for any chemical system with available thermodynamic data. Generally, mixtures may include condensed and gaseous products. CET89 performs the following operations: it 1) obtains chemical equilibrium compositions for assigned thermodynamic states, 2) calculates dilute-gas transport properties of complex chemical mixtures, 3) obtains Chapman-Jouguet detonation properties for gaseous species, 4) calculates incident and reflected shock properties in terms of assigned velocities, and 5) calculates theoretical rocket performance for both equilibrium and frozen compositions during expansion. The rocket performance function allows the option of assuming either a finite area or an infinite area combustor. CET89 accommodates problems involving up to 24 reactants, 20 elements, and 600 products (400 of which may be condensed). The program includes a library of thermodynamic and transport properties in the form of least squares coefficients for possible reaction products. It includes thermodynamic data for over 1300 gaseous and condensed species and transport data for 151 gases. The subroutines UTHERM and UTRAN convert thermodynamic and transport data to unformatted form for faster processing. The program conforms to the FORTRAN 77 standard, except for some input in NAMELIST format. It requires about 423 KB memory, and is designed to be used on mainframe, workstation, and mini computers. Due to its memory requirements, this program does not readily lend itself to implementation on MS-DOS based machines.
Anisotropic properties of a single superconducting CaCuO2/SrTiO3 interface
NASA Astrophysics Data System (ADS)
Salvato, M.; Tieri, G.; Balestrino, G.; Di Castro, D.
2015-09-01
The transport properties of CaCuO2/SrTiO3 single interfaces are studied by resistance versus temperature measurements in external magnetic fields. The superconducting anisotropy ? ={? }a-b/{? }c, where {? }a-b and {? }c are the superconducting coherence lengths parallel and perpendicular to the interface, respectively, shows values higher than that previously obtained for CaCuO2/SrTiO3 superlattices deposited in the same conditions. The larger anisotropy, observed for the single interfaces, indicates that the charge carriers are confined inside a thin superconducting layer next to the interface rather than spread throughout the whole CaCuO2 block. The activation energy and the irreversibility line confirm this hypothesis, suggesting that quasi two-dimensional transport is dominant in this system. The interpretation of the experimental data in the framework of the Berezinskii-Kosterlitz-Thouless theory confirms that the thickness of the superconducting sheet layer is about 1 nm, corresponding roughly to two CaCuO2 unit cells.
Unsaturated Zone and Saturated Zone Transport Properties (U0100)
J. Conca
2000-12-20
This Analysis/Model Report (AMR) summarizes transport properties for the lower unsaturated zone hydrogeologic units and the saturated zone at Yucca Mountain and provides a summary of data from the Busted Butte Unsaturated Zone Transport Test (UZTT). The purpose of this report is to summarize the sorption and transport knowledge relevant to flow and transport in the units below Yucca Mountain and to provide backup documentation for the sorption parameters decided upon for each rock type. Because of the complexity of processes such as sorption, and because of the lack of direct data for many conditions that may be relevant for Yucca Mountain, data from systems outside of Yucca Mountain are also included. The data reported in this AMR will be used in Total System Performance Assessment (TSPA) calculations and as general scientific support for various Process Model Reports (PMRs) requiring knowledge of the transport properties of different materials. This report provides, but is not limited to, sorption coefficients and other relevant thermodynamic and transport properties for the radioisotopes of concern, especially neptunium (Np), plutonium (Pu), Uranium (U), technetium (Tc), iodine (I), and selenium (Se). The unsaturated-zone (UZ) transport properties in the vitric Calico Hills (CHv) are discussed, as are colloidal transport data based on the Busted Butte UZTT, the saturated tuff, and alluvium. These values were determined through expert elicitation, direct measurements, and data analysis. The transport parameters include information on interactions of the fractures and matrix. In addition, core matrix permeability data from the Busted Butte UZTT are summarized by both percent alteration and dispersion.
Anisotropic resistivity tomography
NASA Astrophysics Data System (ADS)
Herwanger, J. V.; Pain, C. C.; Binley, A.; de Oliveira, C. R. E.; Worthington, M. H.
2004-08-01
Geophysical tomographic techniques have the potential to remotely detect and characterize geological features, such as fractures and spatially varying lithologies, by their response to signals passed through these features. Anisotropic behaviour in many geological materials necessitates the generalization of tomographic methods to include anisotropic material properties in order to attain high-quality images of the subsurface. In this paper, we present a finite element (FE) based direct-current electrical inversion method to reconstruct the conductivity tensor at each node point of a FE mesh from electrical resistance measurements. The inverse problem is formulated as a functional optimization and the non-uniqueness of the electrical inverse problem is overcome by adding penalty terms for structure and anisotropy. We use a modified Levenberg-Marquardt method for the functional optimization and the resulting set of linear equation is solved using pre-conditioned conjugate gradients. The method is tested using both synthetic and field experiments in cross-well geometry. The acquisition geometry for both experiments uses a cross-well experiment at a hard-rock test site in Cornwall, southwest England. Two wells, spaced at 25.7 m, were equipped with electrodes at a 1 m spacing at depths from 21-108 m and data were gathered in pole-pole geometry. The test synthetic model consists of a strongly anisotropic and conductive body underlain by an isotropic resistive formation. Beneath the resistive formation, the model comprises a moderately anisotropic and moderately conductive half-space, intersected by an isotropic conductive layer. This model geometry was derived from the interpretation of a seismic tomogram and available geological logs and the conductivity values are based on observed conductivities. We use the test model to confirm the ability of the inversion scheme to recover the (known) true model. We find that all key features of the model are recovered. However, the inversion model is smoother than the true model and the difference in absolute value of anisotropy and conductivity between features is slightly underestimated. Using an anisotropic conductivity distribution aggravates the problem of non-uniqueness of the solution of the inverse electrical problem. This problem can be overcome by applying appropriate structural and anisotropy constraints. We find that running a suite of inversions with varying constraint levels and subsequent examination of the results (including the inspection of residual maps) offers a viable method for choosing appropriate numerical values for the imposed constraints. Inversion of field data reveals a strongly anisotropic subsurface with marked spatial variations of both magnitude of anisotropy and conductivity. Average conductivities range from 0.001 S m-1 (= 1000 ? m) to 0.003 S m-1 (= 333 ? m) and anisotropy values range from 0 per cent to more than 300 per cent. As an independent test of the reliability of the structures revealed by anisotropic electric tomography, anisotropic seismic traveltime tomograms were calculated. We find a convincing structural agreement between the two independently derived images. Areas of high electric anisotropy coincide with seismically anisotropic areas and we observe an anticorrelation between electric conductivity and seismic velocity. Both observations are consistent with anisotropy anomalies caused by fracturing or layering.
NASA Astrophysics Data System (ADS)
Kotov, Valeri N.; Sushkov, Oleg P.
2005-11-01
We study the in-plane resistivity anisotropy in the spin-glass phase of the high- Tc cuprates, on the basis of holes moving in a spiral spin background. This picture follows from analysis of the extended t-J model with Coulomb impurities. In the variable-range hopping regime the resistivity anisotropy is found to have a maximum value of around 90%, and it decreases with temperature, in excellent agreement with experiments in La2-x Srx Cu O4 . In our approach the transport anisotropy is due to the noncollinearity of the spiral spin state, rather than an intrinsic tendency of the charges to self-organize.
Electron-Transport Properties of Few-Layer Black Phosphorus.
Xu, Yuehua; Dai, Jun; Zeng, Xiao Cheng
2015-06-01
We perform the first-principles computational study of the effect of number of stacking layers and stacking style of the few-layer black phosphorus (BPs) on the electronic properties, including transport gap, current-voltage (i-v) relation, and differential conductance. Our computation is based on the nonequilibrium Green's function approach combined with density functional theory calculations. Specifically, we compute electron-transport properties of monolayer BP, bilayer BP, and trilayer BP as well as bilayer BPs with AB-, AA-, or AC-stacking. We find that the stacking number has greater influence on the transport gap than the stacking type. Conversely, the stacking type has greater influence on i-v curve and differential conductance than on the transport gap. This study offers useful guidance for determining the number of stacking layers and the stacking style of few-layer BP sheets in future experimental measurements and for potential applications in nanoelectronic devices. PMID:26266491
Allen G Hunt
2008-06-09
43Tc99 is spreading mostly laterally through the U.S. Department of Energy Hanford site sediments. At higher tensions in the unsaturated zone, the hydraulic conductivity may be strongly anisotropic as a consequence of finer soils to retain more water than coarser ones, and for these soils to have been deposited primarily in horizontal structures. We have tried to develop a consistent modeling procedure that could predict the behavior of Tc plumes. Our procedure consists of: (1) Adapting existing numerical recipes based on critical path analysis to calculate the hydraulic conductivity, K, as a function of tension, h, (2) Statistically correlating the predicted K at various values of the tension with fine content, (3) Seeking a tension value, for which the anisotropy and the horizontal K values are both sufficiently large to accommodate multi-kilometer spreading, (4) Predicting the distribution of K values for vertical flow as a function of system support volume, (5) Comparing the largest likely K value in the vertical direction with the expected K in the horizontal direction, (6) Finding the length scale at which the two K values are roughly equal, (7) Comparing that length scale with the horizontal spreading of the plume. We find that our predictions of the value of the tension at which the principle spreading is likely occurring compares very well with experiment. However, we seem to underestimate the physical length scale at which the predominantly horizontal spreading begins to take on significant vertical characteristics. Our data and predictions would seem to indicate that this should happen after horizontal transport of somewhat over a km, but the chiefly horizontal transport appears to continue out to scales of 10km or so.
Transport properties of high-temperature Jupiter atmosphere components
Bruno, D.; Colonna, G.; De Pascale, O.; Laricchiuta, A.; Catalfamo, C.; Diomede, P.; Capitelli, M.; Gorse, C.; Longo, S.; Giordano, D.; Pirani, F.
2010-11-15
Transport properties of high-temperature helium and hydrogen plasmas as well as Jupiter atmosphere have been calculated for equilibrium and nonequilibrium conditions using higher approximations of the Chapman-Enskog method. A complete database of transport cross sections for relevant interactions has been derived, including minority species, by using both ab initio and phenomenological potentials. Inelastic collision integrals terms, due to resonant charge-exchange channels, have been also considered.
Anisotropic magnetic properties of Dy{sub 6}Cr{sub 4}Al{sub 43} single crystal
Maurya, Arvind Thamizhavel, A. Dhar, S. K.
2014-04-24
We have studied the anisotropic magnetic behavior of the rare earth intermetallic compound Dy{sub 6}Cr{sub 4}Al{sub 43}. This compound crystallizes in the hexagonal symmetry and orders ferromagnetically at 8.3 K as confirmed by the magnetic susceptibility and heat capacity measurements. A significant anisotropy in the magnetization is observed between the c axis and the ab-plane. The easy axis liesin theab-plane at low temperatures; however it orients itselfalong the c-axis above 170 K as inferred from the susceptibility data.
Transport properties of interacting magnetic islands in tokamak plasmas
Gianakon, T.A.; Callen, J.D.; Hegna, C.C.
1993-10-01
This paper explores the equilibrium and transient transport properties of a mixed magnetic topology model for tokamak equilibria. The magnetic topology is composed of a discrete set of mostly non-overlapping magnetic islands centered on the low-order rational surfaces. Transport across the island regions is fast due to parallel transport along the stochastic magnetic field lines about the separatrix of each island. Transport between island regions is assumed to be slow due to a low residual cross-field transport. In equilibrium, such a model leads to: a nonlinear dependence of the heat flux on the pressure gradient; a power balance diffusion coefficient which increases from core to edge; and profile resiliency. Transiently, such a model also exhibits a heat pulse diffusion coefficient larger than the power balance diffusion coefficient.
Transport properties of a discrete helical electrostatic quadrupole
Meitzler, C.R.; Antes, K.; Datte, P.; Huson, F.R. ); Xiu, L. . Inst. for Beam Particle Dynamics)
1991-01-01
The helical electrostatic quadrupole (HESQ) lens has been proposed as a low energy beam transport system which permits intense H{sup {minus}} beams to be focused into an RFQ without seriously increasing the beam's emittance. A stepwise continuous HESQ lens has been constructed, and preliminary tests have shown that the structure does provide focusing. In order to understand the transport properties of this device, further detailed studies have been performed. Emittances were measured 3.5 cm from the end of the HESQ at two different voltages on the HESQ electrodes. A comparison of these experimental results with a linear model of the HESQ beam transport is made. 4 refs., 5 figs.
Transport properties in nontwist area-preserving maps
Szezech Jr., J. D.; Caldas, I. L.; Lopes, S. R.; Viana, R. L.; Morrison, P. J.
2009-10-23
Nontwist systems, common in the dynamical descriptions of fluids and plasmas, possess a shearless curve with a concomitant transport barrier that eliminates or reduces chaotic transport, even after its breakdown. In order to investigate the transport properties of nontwist systems, we analyze the barrier escape time and barrier transmissivity for the standard nontwist map, a paradigm of such systems. We interpret the sensitive dependence of these quantities upon map parameters by investigating chaotic orbit stickiness and the associated role played by the dominant crossing of stable and unstable manifolds.
Transport properties associated with carbon-phenolic ablators
NASA Technical Reports Server (NTRS)
Biolsi, L.
1982-01-01
Entry vehicle heat shields designed for entry into the atmosphere of the outer planets are usually made of carbonaceous material such as carbon-phenolic ablator. Ablative injection of this material is an important mechanism for reducing the heat at the surface of the entry vehicle. Conductive transport properties in the shock layer are important for some entry conditions. The kinetic theory of gases has been used to calculate the transport properties for 17 gaseous species obtained from the ablation of carbon-phenolic heat shields. Results are presented for the pure species and for the gas mixture.
Transport properties of self-consolidating concrete
Sonebi, M.; Nanukuttan, S.
2009-03-15
This study reports the findings from an investigation carried out to study the effect of the mixture variations on the durability of medium- and high-strength self-consolidating concrete (SCC). The mixture variations studied include the type of mineral admixtures, such as limestone powder (LSP) and pulverized fuel ash (PFA), and viscosity-modifying admixtures (VMA) for both medium- and high-strength SCC. Air permeability, water permeability, capillary absorption, and chloride diffusivity were used to assess the durability of SCC mixtures in comparison with normal, vibrated concretes. The results showed that SCC mixtures, for medium- and high-strength grades using PFA followed by LSP give lower permeability, properties compared with normal concretes. SCC made with VMA had a higher sorptivity, air permeability, and water permeability compared with other SCC mixtures, which can be attributed to higher water-cement ratio (w/c) and lack of pore filling effect. An in-place migration coefficient was obtained using the in-place ion migration test. This was used to compare the potential diffusivity of different concretes. The results indicated that SCC, for both grades of strength, made with PFA showed much lower diffusivity values in comparison with other mixtures, whereas the SCC mixtures with VMA showed higher diffusivity.
Kundu, T; Yang, X; Nakatani, H; Takeda, N
2015-02-01
Acoustic source localization techniques generally assume straight line propagation of waves from the acoustic source to the sensor. However, it is well-known that in anisotropic plates the acoustic energy does not always propagate in straight lines. Even for isotropic plates containing a cavity or an inclusion between the acoustic source and the sensor the straight line propagation assumption is violated. In such cases only options available in localizing acoustic source is to use relatively expensive distributed sensor systems, or to follow time reversal techniques based on the impulse response functions which is labor intensive and computationally demanding. A two-step hybrid technique is proposed in this paper for predicting acoustic source in anisotropic plates. During the first step it was assumed that the waves propagated along straight lines from the acoustic source to the sensor. The source was localized with this simplifying assumption. Then this first prediction was improved in the second step by solving an optimization problem. Experimental results showed that the second step always moved the estimates towards the actual source location. Thus it always reduced the prediction error irrespective of whether the final prediction coincided with the actual source location or not. PMID:25245206
Tadiello, L; D'Arienzo, M; Di Credico, B; Hanel, T; Matejka, L; Mauri, M; Morazzoni, F; Simonutti, R; Spirkova, M; Scotti, R
2015-05-28
Silica-styrene butadiene rubber (SBR) nanocomposites were prepared by using shape-controlled spherical and rod-like silica nanoparticles (NPs) with different aspect ratios (AR = 1-5), obtained by a sol-gel route assisted by a structure directing agent. The nanocomposites were used as models to study the influence of the particle shape on the formation of nanoscale immobilized rubber at the silica-rubber interface and its effect on the dynamic-mechanical behavior. TEM and AFM tapping mode analyses of nanocomposites demonstrated that the silica particles are surrounded by a rubber layer immobilized at the particle surface. The spherical filler showed small contact zones between neighboring particles in contact with thin rubber layers, while anisotropic particles (AR > 2) formed domains of rods preferentially aligned along the main axis. A detailed analysis of the polymer chain mobility by different time domain nuclear magnetic resonance (TD-NMR) techniques evidenced a population of rigid rubber chains surrounding particles, whose amount increases with the particle anisotropy, even in the absence of significant differences in terms of chemical crosslinking. Dynamic measurements demonstrate that rod-like particles induce stronger reinforcement of rubber, increasing with the AR. This was related to the self-alignment of the anisotropic silica particles in domains able to immobilize rubber. PMID:25899456
Anisotropic in-plane strain and transport in epitaxial Nd0.2Sr0.8MnO3 thin films
NASA Astrophysics Data System (ADS)
Neupane, K. P.; Neumeier, J. J.; Cohn, J. L.
2009-12-01
The structure, morphology, and electrical properties of epitaxial a-axis-oriented thin films of Nd0.2Sr0.8MnO3 are reported for thicknesses of 10 nm?t?150 nm. Films were grown with both tensile and compressive strain on various substrates. It is found that the elongated crystallographic c-axes of the films remain fully strained to the substrates for all thicknesses in both strain states. Relaxation of the a and b axes is observed for t ?65 nm, with films grown under tensile strain developing uniaxial crack arrays (running along the c axis) due to a highly anisotropic thermal expansion. For the latter films, the room-temperature in-plane electrical resistivity anisotropy, ?b/?c, increases approximately exponentially with increasing film thickness to values of ˜1000 in the thickest films studied. Films under tension have their Néel temperatures enhanced by ?25 K independent of thickness, consistent with an enhancement in ferromagnetic exchange along their expanded c axes.
Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo
2016-01-01
We report the anisotropic structural and optical properties of semi-polar (11â€“22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11â€“22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4Â° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1â€“100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting. PMID:26861595
Cuenca, Jacques Van der Kelen, Christophe; GÃ¶ransson, Peter
2014-02-28
This paper proposes an inverse estimation method for the characterisation of the elastic and anelastic properties of the frame of anisotropic open-cell foams used for sound absorption. A model of viscoelasticity based on a fractional differential constitutive equation is used, leading to an augmented Hooke's law in the frequency domain, where the elastic and anelastic phenomena appear as distinctive terms in the stiffness matrix. The parameters of the model are nine orthotropic elastic moduli, three angles of orientation of the material principal directions and three parameters governing the anelastic frequency dependence. The inverse estimation consists in numerically fitting the model on a set of transfer functions extracted from a sample of material. The setup uses a seismic-mass measurement repeated in the three directions of space and is placed in a vacuum chamber in order to remove the air from the pores of the sample. The method allows to reconstruct the full frequency-dependent complex stiffness matrix of the frame of an anisotropic open-cell foam and in particular it provides the frequency of maximum energy dissipation by viscoelastic effects. The characterisation of a melamine foam sample is performed and the relation between the fractional-derivative model and other types of parameterisations of the augmented Hooke's law is discussed.
Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo
2016-01-01
We report the anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11-22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1-100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting. PMID:26861595
NASA Astrophysics Data System (ADS)
Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo
2016-02-01
We report the anisotropic structural and optical properties of semi-polar (11â€“22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11â€“22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4Â° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1â€“100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting.
Characterization of anisotropic acoustic metamaterial slabs
NASA Astrophysics Data System (ADS)
Park, Jun Hyeong; Lee, Hyung Jin; Kim, Yoon Young
2016-01-01
In an anisotropic acoustic metamaterial, the off-diagonal components of its effective mass density tensor should be considered in order to describe the anisotropic behavior produced by arbitrarily shaped inclusions. However, few studies have been carried out to characterize anisotropic acoustic metamaterials. In this paper, we propose a method that uses the non-diagonal effective mass density tensor to determine the behavior of anisotropic acoustic metamaterials. Our method accurately evaluates the effective properties of anisotropic acoustic metamaterials by separately dealing with slabs made of single and multiple unit cells along the thickness direction. To determine the effective properties, the reflection and transmission coefficients of an acoustic metamaterial slab are calculated, and then the wave vectors inside of the slab are determined using these coefficients. The effective material properties are finally determined by utilizing the spatial dispersion relation of the anisotropic acoustic metamaterial. Since the dispersion relation of an anisotropic acoustic metamaterial is explicitly used, its effective properties can be easily determined by only using a limited number of normal and oblique plane wave incidences into a metamaterial slab, unlike existing approaches requiring a large number of wave incidences. The validity of the proposed method is verified by conducting wave simulations for anisotropic acoustic metamaterial slabs with Z-shaped elastic inclusions of tilted principal material axes.
Presentation outline: transport principles, effective solubility; gasoline composition; and field examples (plume diving).
Presentation conclusions: MTBE transport follows from - phyiscal and chemical properties and hydrology. Field examples show: MTBE plumes > benzene plu...
Properties and Transport Behavior among 12 Different Environmental Escherichia coli
Technology Transfer Automated Retrieval System (TEKTRAN)
Escherichia coli is a commonly used indicator organism for detecting the presence of fecal-borne pathogenic microorganisms in water supplies. The importance of E. coli as an indicator organism has led to numerous studies looking at cell properties and transport behavior of this microorganism. In man...
Thermal transport properties of complex oxides from first principles
NASA Astrophysics Data System (ADS)
Bhatti, Aqyan; Jain, Ankit; McGaughey, Alan; Benedek, Nicole
2015-03-01
Thermal transport properties of materials are key parameters in the design of many engineering devices. For this reason, it is highly desirable to be able to control or tailor the thermal properties of materials for specific applications. Complex oxides are attractive in this regard, due to their low and potentially highly tunable thermal conductivity. However, the theoretical description of the thermal transport properties of oxides presents a number of challenges compared to conventional semiconductors. For example, oxides tend to have complex crystal structures and the atoms interact through long-range electrostatic forces. In this talk, we use the example of PbTiO3 to discuss some of the challenges and opportunities associated with thermal transport predictions in complex oxides. For example, many oxides contain very low-lying optical branches, which may provide important acoustic-optical scattering channels. In addition, it is often possible to tune the frequencies of such optical modes with epitaxial strain. We also link the observed negative thermal expansion behavior of PbTiO3 to two zone-boundary modes with large, negative Grüneisen parameters and comment on the consequences of this finding for the thermal transport properties of this material.
Oxygen transport properties estimation by DSMC-CT simulations
Bruno, Domenico; Frezzotti, Aldo; Ghiroldi, Gian Pietro
2014-12-09
Coupling DSMC simulations with classical trajectories calculations is emerging as a powerful tool to improve predictive capabilities of computational rarefied gas dynamics. The considerable increase of computational effort outlined in the early application of the method (Koura,1997) can be compensated by running simulations on massively parallel computers. In particular, GPU acceleration has been found quite effective in reducing computing time (Ferrigni,2012; Norman et al.,2013) of DSMC-CT simulations. The aim of the present work is to study rarefied Oxygen flows by modeling binary collisions through an accurate potential energy surface, obtained by molecular beams scattering (Aquilanti, et al.,1999). The accuracy of the method is assessed by calculating molecular Oxygen shear viscosity and heat conductivity following three different DSMC-CT simulation methods. In the first one, transport properties are obtained from DSMC-CT simulations of spontaneous fluctuation of an equilibrium state (Bruno et al, Phys. Fluids, 23, 093104, 2011). In the second method, the collision trajectory calculation is incorporated in a Monte Carlo integration procedure to evaluate the Taxman’s expressions for the transport properties of polyatomic gases (Taxman,1959). In the third, non-equilibrium zero and one-dimensional rarefied gas dynamic simulations are adopted and the transport properties are computed from the non-equilibrium fluxes of momentum and energy. The three methods provide close values of the transport properties, their estimated statistical error not exceeding 3%. The experimental values are slightly underestimated, the percentage deviation being, again, few percent.
Transport properties of a Bentheim sandstone under deformation.
Jasinski, L; Sangaré, D; Adler, P M; Mourzenko, V V; Thovert, J-F; Gland, N; Békri, S
2015-01-01
The mechanical and transport properties of a Bentheim sandstone are studied both experimentally and numerically. Three classical classes of loads are applied to a sample whose permeability is measured. The elasticity and the Stokes equations are discretized on unstructured tetrahedral meshes which precisely follow the deformations of the sample. Numerical results are presented, discussed, and compared to the available experimental data. PMID:25679736
Computer programs for thermodynamic and transport properties of hydrogen
NASA Technical Reports Server (NTRS)
Hall, W. J.; Mc Carty, R. D.; Roder, H. M.
1968-01-01
Computer program subroutines provide the thermodynamic and transport properties of hydrogen in tabular form. The programs provide 18 combinations of input and output variables. This program is written in FORTRAN 4 for use on the IBM 7044 or CDC 3600 computers.
Reference Fluid Thermodynamic and Transport Properties Database (REFPROP)
National Institute of Standards and Technology Data Gateway
SRD 23 NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP) (PC database for purchase)Â Â NIST 23 contains revised data in a Windows version of the database, including 105 pure fluids and allowing mixtures of up to 20 components. The fluids include the environmentally acceptable HFCs, traditional HFCs and CFCs and 'natural' refrigerants like ammonia
Transport properties in semiconducting NbS2 nanoflakes
NASA Astrophysics Data System (ADS)
Huang, Y. H.; Peng, C. C.; Chen, R. S.; Huang, Y. S.; Ho, C. H.
2014-09-01
The electronic transport properties in individual niobium disulphide (NbS2) nanoflakes mechanically exfoliated from the bulk crystal with three rhombohedral (3R) structure grown by chemical vapor transport were investigated. It is found that the conductivity values of the single-crystalline nanoflakes are approximately two orders of magnitude lower than that of their bulk counterparts. Temperature-dependent conductivity measurements show that the 3R-NbS2 nanoflakes exhibit semiconducting transport behavior, which is also different from the metallic character in the bulk crystals. In addition, the noncontinuous conductivity variations were observed at the temperature below 180 K for both the nanoflakes and the bulks, which is attributed to the probable charge density wave transition. The photoconductivities in the semiconducting nanoflakes were also observed under the excitation at 532 nm wavelength. The probable mechanisms resulting in the different transport behaviors between the NbS2 nanostructure and bulk were discussed.
Transport properties in semiconducting NbS{sub 2} nanoflakes
Huang, Y. H.; Chen, R. S. Ho, C. H.; Peng, C. C.; Huang, Y. S.
2014-09-01
The electronic transport properties in individual niobium disulphide (NbS{sub 2}) nanoflakes mechanically exfoliated from the bulk crystal with three rhombohedral (3R) structure grown by chemical vapor transport were investigated. It is found that the conductivity values of the single-crystalline nanoflakes are approximately two orders of magnitude lower than that of their bulk counterparts. Temperature-dependent conductivity measurements show that the 3R-NbS{sub 2} nanoflakes exhibit semiconducting transport behavior, which is also different from the metallic character in the bulk crystals. In addition, the noncontinuous conductivity variations were observed at the temperature below 180â€‰K for both the nanoflakes and the bulks, which is attributed to the probable charge density wave transition. The photoconductivities in the semiconducting nanoflakes were also observed under the excitation at 532â€‰nm wavelength. The probable mechanisms resulting in the different transport behaviors between the NbS{sub 2} nanostructure and bulk were discussed.
Measurement of gas transport properties for chemical vapor infiltration
Starr, T.L.; Hablutzel, N.
1996-12-01
In the chemical vapor infiltration (CVI) process for fabricating ceramic matrix composites (CMCs), transport of gas phase reactant into the fiber preform is a critical step. The transport can be driven by pressure or by concentration. This report describes methods for measuring this for CVI preforms and partially infiltrated composites. Results are presented for Nicalon fiber cloth layup preforms and composites, Nextel fiber braid preforms and composites, and a Nicalon fiber 3-D weave composite. The results are consistent with a percolating network model for gas transport in CVI preforms and composites. This model predicts inherent variability in local pore characteristics and transport properties, and therefore, in local densification during processing; this may lead to production of gastight composites.
Mass-Transport Properties In Growth Of Crystals From Vapors
NASA Technical Reports Server (NTRS)
Wiedemeier, H.
1992-01-01
Brief report summarizes results of experimental and theoretical studies of mass-transport properties of GeSe/Gel4 and Hg0.8Cd0.2Te systems in connection with growth of crystals in closed ampoules. Primary emphasis in studies was on thermochemical analyses, on development of mathematical models to predict diffusion-limited mass transport, and on comparison of theoretically predicted with experimental fluxes. Results applied to design, preparation, performance, and analysis of crystal-growth experiments of semiconducting materials on Earth and in outer space. Model extended to predict mass flux and overall composition of transport products of Hg0.8Cd0.2Te transport system.
Variational nodal perturbation theory with anisotropic scattering
Laurin-Kovitz, K.F.; Palmiotti, G.; Lewis, E.E.
1997-09-01
The variational nodal perturbation method previously developed in two- and three-dimensional Cartesian and hexagonal geometries using the diffusion and full or simplified spherical harmonics transport approximations, is extended to treat problems with anisotropic scattering. The requisite solution to the adjoint transport equation with anisotropic scattering in formulated and incorporated into the VARIANT (VARIational Anisotropic Nodal Transport) option of the Argonne National Laboratory DIF3D production code. The method, which calculates changes in the critical eigenvalue due to perturbations arising from changes in the material cross sections, is demonstrated by applying perturbations to an anisotropic hexagonal benchmark. Exact and first order perturbation theory are used to calculate changes in the critical eigenvalue and compared to the change obtained by direct calculation in VARIANT. The time savings obtained by using perturbation theory is substantial; times for base forward and adjoint calculations are much greater than the times for perturbation calculations.
Menaka; Sharma, Soma; Ramanujachary, Kandalam V; Lofland, Samuel E; Ganguli, Ashok K
2011-08-15
Anisotropic nanostructures of nickel borate with controlled size and morphology have been synthesized by a precursor-mediated route. The nickel boron precursor has been synthesized using microemulsions using Tergitol as a surfactant. Microemulsions with various co-surfactants (1-butanol, 1-hexanol and 1-octanol) have been used to obtain uniform nanorods (dia 3-5 nm, length 25 nm) and nanospindles (dia 30 nm, length 400 nm). A higher chain length of the co-surfactant (octanol) leads to more uniform rods rather than spindles (butanol). These nanorods show antiferromagnetic behavior with the Néel temperature ranging from 44 to 47 K. Though there is no marked variation in N?el temperature, the magnetic moment increases drastically with the anisotropy of nanorods (thinner rods). PMID:21605870
Review on measurement techniques of transport properties of nanowires.
Rojo, Miguel MuÃ±oz; Calero, Olga Caballero; Lopeandia, A F; Rodriguez-Viejo, J; MartÃn-Gonzalez, Marisol
2013-12-01
Physical properties at the nanoscale are novel and different from those in bulk materials. Over the last few decades, there has been an ever growing interest in the fabrication of nanowire structures for a wide variety of applications including energy generation purposes. Nevertheless, the study of their transport properties, such as thermal conductivity, electrical conductivity or Seebeck coefficient, remains an experimental challenge. For instance, in the particular case of nanostructured thermoelectrics, theoretical calculations have shown that nanowires offer a promising way of enhancing the hitherto low efficiency of these materials in the conversion of temperature differences into electricity. Therefore, within the thermoelectrical community there has been a great experimental effort in the measurement of these quantities in actual nanowires. The measurements of these properties at the nanoscale are also of interest in fields other than energy, such as electrical components for microchips, field effect transistors, sensors, and other low scale devices. For all these applications, knowing the transport properties is mandatory. This review deals with the latest techniques developed to perform the measurement of these transport properties in nanowires. A thorough overview of the most important and modern techniques used for the characterization of different kinds of nanowires will be shown. PMID:24113712
Wentzel-Bardeen singularity in coupled Luttinger liquids: Transport properties
Martin, T.
1994-08-26
The recent progress on 1 D interacting electrons systems and their applications to study the transport properties of quasi one dimensional wires is reviewed. We focus on strongly correlated elections coupled to low energy acoustic phonons in one dimension. The exponents of various response functions are calculated, and their striking sensitivity to the Wentzel-Bardeen singularity is discussed. For the Hubbard model coupled to phonons the equivalent of a phase diagram is established. By increasing the filling factor towards half filling the WB singularity is approached. This in turn suppresses antiferromagnetic fluctuations and drives the system towards the superconducting regime, via a new intermediate (metallic) phase. The implications of this phenomenon on the transport properties of an ideal wire as well as the properties of a wire with weak or strong scattering are analyzed in a perturbative renormalization group calculation. This allows to recover the three regimes predicted from the divergence criteria of the response functions.
Vetrov, S Ya; Timofeev, I V; Pankin, P S
2014-09-30
We have studied the spectral properties of a one-dimensional photonic crystal with a structure defect that represents an anisotropic nanocomposite layer sandwiched between two multilayer dielectric mirrors. The nanocomposite consists of metallic nanoscale inclusions of orientationally ordered spheroidal shape, dispersed in a transparent matrix, and is characterised by an effective resonant permittivity. Each of the two orthogonal polarisations of probe radiation corresponds to a particular plasmon resonant frequency of the nanocomposite. The problem of calculating the transmittance spectrum of the waves with s- and p-polarisations for such structures is solved. Spectral manifestation of splitting of the defect mode depending on the structure parameters and volumetric fraction of the nanospheroids is studied. The essential dependence of the position of maxima of the defect modes in the bandgap of the photonic crystal and their splitting on the incidence angle, polarisation, and the ratio of lengths of the polar and equatorial semi-axes of the spheroidal nanoparticles is shown. (photonic crystals)
NASA Astrophysics Data System (ADS)
Ghoufi, Aziz; Morineau, Denis; Lefort, Ronan; Malfreyt, Patrice
2011-01-01
Molecular simulations in the isothermal statistical ensembles require that the macroscopic thermal and mechanical equilibriums are respected and that the local values of these properties are constant at every point in the system. The thermal equilibrium in Monte Carlo simulations can be checked through the calculation of the configurational temperature, {k_BT_{conf}={< |nabla _r U({r}^N)|2>}/{< nabla _r{^2} U({r}^N) >}}, where nabla _r is the nabla operator of position vector r. As far as we know, T_{conf} was never calculated with the anisotropic Gay-Berne potential, whereas the calculation of T_{conf} is much more widespread with more common potentials (Lennard Jones, electrostatic, …). We establish here an operational expression of the macroscopic and local configurational temperatures, and we investigate locally the isotropic liquid phase, the liquid / vapor interface, and the isotropic-nematic transition by Monte Carlo simulations.
Sakakibara, H. Ando, H.; Kuroki, Y.; Kawai, S.; Ueda, K.; Asano, H.
2015-05-07
Epitaxial bilayers of antiferromagnetic Mn{sub 3}GaN/ferromagnetic Co{sub 3}FeN with an antiperovskite structure were grown by reactive magnetron sputtering, and their structural, magnetic, and electrical properties were investigated. Exchange coupling with an exchange field H{sub ex} of 0.4 kOe at 4â€‰K was observed for Mn{sub 3}GaN (20â€‰nm)/Co{sub 3}FeN (5â€‰nm) bilayers. Negative anisotropic magnetoresistance (AMR) effect in Co{sub 3}FeN was observed and utilized to detect magnetization reversal in exchange-coupled Mn{sub 3}GaN/Co{sub 3}FeN bilayers. The AMR results showed evidence for current-induced spin transfer torque in antiferromagnetic Mn{sub 3}GaN.
Magneto-optical transport properties of monolayer phosphorene
NASA Astrophysics Data System (ADS)
Tahir, M.; Vasilopoulos, P.; Peeters, F. M.
2015-07-01
The electronic properties of monolayer phosphorene are exotic due to its puckered structure and large intrinsic direct band gap. We derive and discuss its band structure in the presence of a perpendicular magnetic field. Further, we evaluate the magneto-optical Hall and longitudinal optical conductivities as functions of temperature, magnetic field, and Fermi energy, and show that they are strongly influenced by the magnetic field. The imaginary part of the former and the real part of the latter exhibit regular interband oscillations as functions of the frequency ? in the range ? ? ˜1.5 -2 eV . Strong intraband responses in the latter and weak ones in the former occur at much lower frequencies. The magneto-optical response can be tuned in the microwave-to-terahertz and visible frequency ranges in contrast with a conventional two-dimensional electron gas or graphene in which the response is limited to the terahertz regime. This ability to isolate carriers in an anisotropic structure may make phosphorene a promising candidate for new optical devices.
Transport processes in partially saturate concrete: Testing and liquid properties
NASA Astrophysics Data System (ADS)
Villani, Chiara
The measurement of transport properties of concrete is considered by many to have the potential to serve as a performance criterion that can be related to concrete durability. However, the sensitivity of transport tests to several parameters combined with the low permeability of concrete complicates the testing. Gas permeability and diffusivity test methods are attractive due to the ease of testing, their non-destructive nature and their potential to correlate to in-field carbonation of reinforced concrete structures. This work was aimed at investigating the potential of existing gas transport tests as a way to reliably quantify transport properties in concrete. In this study gas permeability and diffusivity test methods were analyzed comparing their performance in terms of repeatability and variability. The influence of several parameters was investigated such as moisture content, mixture proportions and gas flow. A closer look to the influence of pressure revealed an anomalous trend of permeability with respect to pressure. An alternative calculation is proposed in an effort to move towards the determination of intrinsic material properties that can serve as an input for service life prediction models. The impact of deicing salts exposure was also analyzed with respect to their alteration of the degree of saturation as this may affect gas transport in cementitious materials. Limited information were previously available on liquid properties over a wide range of concentrations. To overcome this limitation, this study quantified surface tension, viscosity in presence of deicing salts in a broad concentration range and at different temperatures. Existing models were applied to predict the change of fluid properties during drying. Vapor desorption isotherms were obtained to investigate the influence of deicing salts presence on the non-linear moisture diffusion coefficient. Semi-empirical models were used to quantify the initiation and the rate of drying using liquid properties and pore structure information as inputs. Concrete exposed to deicing salts resulted to have a reduced gas transport due to the higher degree of saturation (DOS). The higher DOS is believed to contribute to the premature deterioration observed in concrete pavements exposed to deicing salts. Moisture diffusion and moisture profiles in concrete are known to directly relate with the stresses generated during shrinkage and creep mechanisms. The alteration due to the presence of shrinkage reducing admixtures on drying was also investigated in this work. Liquid properties were used to predict the diffusion coefficient in presence of SRA. Moisture profiles obtained using Fick's second law for diffusion were compared to relative humidity profiles measured on concrete slabs. Results confirm that a qualitative prediction of drying in concrete elements is realistic when using this type of approach.
Modelling of the transport properties of topologically protected edge states
NASA Astrophysics Data System (ADS)
Dang, Xiaoqian; Burton, J. D.; Tsymbal, Evgeny
2014-03-01
One of the great successes of modern condensed matter physics is the discovery of topological insulators (TI). A thorough investigation of their transport properties, along with proposed device geometries, could bring such materials from fundamental research to potential applications. Here we report on theoretical investigations of transport properties of simple systems which incorporate TIs and their protected edge states. We utilize the tight-binding form of the Bernevig-Hughes-Zhang model as a prototype for generic topological insulators. Transport properties are investigated theoretically by constructing the Green's functions and employing the Landauer-Büttiker formalism. We study the limitations to scattering-free transport around defects/impurities through topologically protected edge states, as well as the prospect of metal-TI-metal tunnel junctions where the protected edge states reside between the metal electrode and the insulating bulk of the TI. Elucidating the fundamental physical effects that occur in these (and other) systems will be an integral step in establishing TIs as a building block for potential electronic device applications.
Charge carrier transport properties in layer structured hexagonal boron nitride
Doan, T. C.; Li, J.; Lin, J. Y.; Jiang, H. X.
2014-10-15
Due to its large in-plane thermal conductivity, high temperature and chemical stability, large energy band gap (~ 6.4 eV), hexagonal boron nitride (hBN) has emerged as an important material for applications in deep ultraviolet photonic devices. Among the members of the III-nitride material system, hBN is the least studied and understood. The study of the electrical transport properties of hBN is of utmost importance with a view to realizing practical device applications. Wafer-scale hBN epilayers have been successfully synthesized by metal organic chemical deposition and their electrical transport properties have been probed by variable temperature Hall effect measurements. The results demonstrate that undoped hBN is a semiconductor exhibiting weak p-type at high temperatures (> 700?°K). The measured acceptor energy level is about 0.68 eV above the valence band. In contrast to the electrical transport properties of traditional III-nitride wide bandgap semiconductors, the temperature dependence of the hole mobility in hBN can be described by the form of ? ? (T/T{sub 0}){sup ??} with ? = 3.02, satisfying the two-dimensional (2D) carrier transport limit dominated by the polar optical phonon scattering. This behavior is a direct consequence of the fact that hBN is a layer structured material. The optical phonon energy deduced from the temperature dependence of the hole mobility is ?? = 192 meV (or 1546 cm{sup -1}), which is consistent with values previously obtained using other techniques. The present results extend our understanding of the charge carrier transport properties beyond the traditional III-nitride semiconductors.
Transport properties of single TiO2 nanotubes
NASA Astrophysics Data System (ADS)
Stiller, Markus; Barzola-Quiquia, José; Lorite, Israel; Esquinazi, Pablo; Kirchgeorg, Robin; Albu, Sergiu P.; Schmuki, Patrik
2013-10-01
We investigated the electric transport properties of single TiO2 nanotubes separated from an anodic titania nanotube array. The temperature dependence of the resistance measured with the conventional four point method of all investigated samples show a Mott variable range hopping behavior. The results obtained with two contacts indicate the existence of a potential barrier between the Cr/Au contacts and samples surfaces, which influence is clearly observable at temperatures <150 K. Impedance spectroscopy in the frequency range of 40 Hz to 1 MHz carried out at room temperature indicates that the electronic transport of these polycrystalline tubes is dominated by the grain cores.
Transport properties of the Fermi hard-sphere system
NASA Astrophysics Data System (ADS)
Mecca, Angela; Lovato, Alessandro; Benhar, Omar; Polls, Artur
2016-03-01
The transport properties of neutron star matter play an important role in many astrophysical processes. We report the results of a calculation of the shear viscosity and thermal conductivity coefficients of the hard-sphere fermion system of degeneracy Î½ =2 , that can be regarded as a model of pure neutron matter. Our approach is based on the effective interaction obtained from the formalism of correlated basis functions and the cluster expansion technique. The resulting transport coefficients show a strong sensitivity to the quasiparticle effective mass, reflecting the effect of second-order contributions to the self-energy that are not taken into account in nuclear matter studies available in the literature.
Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Liu, Yao; Wu, Rong-Rong; Zhang, Xi-Xiang; Sun, Ji-Rong; Shen, Bao-Gen
2015-01-01
Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories. PMID:25909177
Anisotropic materials in OLEDs for high outcoupling efficiency.
Callens, Michiel Koen; Yokoyama, Daisuke; Neyts, Kristiaan
2015-08-10
We present the results of an optical study in which we evaluate the effect of anisotropic electron transport layers (ETL) and anisotropic hole transport layers (HTL) on the outcoupling efficiency of bottom emitting organic light emitting diodes (OLEDs). We demonstrate that optical anisotropy can have a profound influence on the outcoupling efficiency and introduce a number of design rules which ensure that light extraction is enhanced by anisotropic layers. PMID:26367963
Electronic properties and quantum transport in Graphene-based nanostructures
NASA Astrophysics Data System (ADS)
Dubois, S. M.-M.; Zanolli, Z.; Declerck, X.; Charlier, J.-C.
2009-11-01
Carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) represent a novel class of low-dimensional materials. All these graphene-based nanostructures are expected to display the extraordinary electronic, thermal and mechanical properties of graphene and are thus promising candidates for a wide range of nanoscience and nanotechnology applications. In this paper, the electronic and quantum transport properties of these carbon nanomaterials are reviewed. Although these systems share the similar graphene electronic structure, confinement effects are playing a crucial role. Indeed, the lateral confinement of charge carriers could create an energy gap near the charge neutrality point, depending on the width of the ribbon, the nanotube diameter, the stacking of the carbon layers regarding the different crystallographic orientations involved. After reviewing the transport properties of defect-free systems, doping and topological defects (including edge disorder) are also proposed as tools to taylor the quantum conductance in these materials. Their unusual electronic and transport properties promote these carbon nanomaterials as promising candidates for new building blocks in a future carbon-based nanoelectronics, thus opening alternatives to present silicon-based electronics devices.
Anisotropically structured magnetic aerogel monoliths.
Heiligtag, Florian J; Airaghi Leccardi, Marta J I; Erdem, Derya; SÃ¼ess, Martin J; Niederberger, Markus
2014-11-01
Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture. PMID:25255203
Anisotropically structured magnetic aerogel monoliths
NASA Astrophysics Data System (ADS)
Heiligtag, Florian J.; Airaghi Leccardi, Marta J. I.; Erdem, Derya; Süess, Martin J.; Niederberger, Markus
2014-10-01
Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture.Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture. Electronic supplementary information (ESI) available: Digital photographs of dispersions and gels with different water-to-ethanol ratios; magnetic measurements of an anatase aerogel containing 0.25 mol% Fe3O4 nanoparticles; XRD patterns of the iron oxide and titania nanoparticles. See DOI: 10.1039/c4nr04694c
Thermodynamic and anisotropic properties of single crystalline RCo2Ge2 (R = Y, La-Nd, Sm-Tm)
NASA Astrophysics Data System (ADS)
Kong, Tai; Buffon, Malinda; Lin, Xiao; Thaler, Alex; Cunningham, Charles; Bud'Ko, Sergey; Canfield, Paul
2013-03-01
Single crystals of RCo2Ge2 (R = Y, La-Nd, Sm-Tm) were grown using a self-flux method and were characterized from 1.8-300 K by heat capacity, magnetization and in-plane resistivity measurements. Anisotropic metamagnetism was studied at 1.8 K up to 9 T. Due to a strong crystal electric field (CEF) effect, the magnetic ordering temperatures of the heavy rare earth members do not follow the de Gennes scaling, but rather a CEF modified trend. The RCo2Ge2 series offers an opportunity to study different types of magnetic anisotropy ranging from Heisenberg-like GdCo2Ge2 to Ising-like TbCo2Ge2. Correlation between the local moments and conduction electrons as well as the influence of interplay between CEF effect and long-range indirect exchange interaction (RKKY type) will also be discussed. This work is supported by the US DOE, Basic Energy Sciences under Contract No. DE-AC02-07CH11358.
Modeling transport properties of inhomogeneous superconductor-metal composites
Borroto, A.; Altshuler, E.; Del RÃo, L.; Arronte, M.; Johansen, T. H.
2014-11-17
We propose a model for a superconductor-metal composite that allows to derive intrinsic transport properties of the superconducting phase based on 2D images of its cross section, and a minimal set of parameters. The method is tested experimentally by using, as model composite, a â€œtransversal bridgeâ€ made on a Bi{sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub 10+x} (BSCCO)-Ag multi-filamentary tape. It is shown that the approach allows to predict the measured Iâˆ’âŒ©EâŒª curves of the filaments. In addition, one can determine the critical current anisotropy between the longitudinal and transverse directions of the Ag-BSCCO tape, and also of its superconducting filaments separately, which emphasizes the role of the morphology of the composite in the transport properties.
Transport properties of Î²-FeSi2
NASA Astrophysics Data System (ADS)
Arushanov, Ernest; Lisunov, Konstantin G.
2015-07-01
The aim of this paper is to summarize considerable experimental efforts undertaken within the last decades in the investigations of transport properties of Î²-FeSi2. The Î²-FeSi2 compound is the most investigated among a family of semiconducting silicides. This material has received considerable attention as an attractive material for optoelectronic, photonics, photovoltaics and thermoelectric applications. Previous reviews of the transport properties of Î²-FeSi2 have been given by Lange and Ivanenko et al. about 15 years ago. The Hall effect, the conductivity, the mobility and the magnetoresistance data are presented. Main attention is paid to the discussion of the impurity (defect) band conductivity, the anomalous Hall effect, the scattering mechanisms of charge carriers, as well as to the hopping conduction and the magnetoresistance.
Electrical Transport Properties of Liquid Al-Cu Alloys
NASA Astrophysics Data System (ADS)
Thakore, B. Y.; Khambholja, S. G.; Suthar, P. H.; Jani, A. R.
2010-06-01
Electrical transport properties viz. electrical resistivity, thermoelectric power and thermal conductivity of liquid Al-Cu alloys as a function of Cu concentration have been studied in the present paper. Ashcroft empty core model potential has been used to incorporate the ion-electron interaction. To incorporate the exchange and correlation effects, five different forms of local field correction functions viz. Hartree, Taylor, Ichimaru et al., Farid et al. and Sarkar et al. have been used. The transport properties of binary system have been studied using Faber-Ziman formulation combined with Ashcroft-Langreth (AL) partial structure factor. The computed values of electrical resistivity are compared with experimental data and for low Cu concentration, good agreement has been observed. Further, thermoelectric power and thermal conductivity have also been predicted.
Relaxation and transport properties of liquid n-triacontane
NASA Astrophysics Data System (ADS)
Kondratyuk, N. D.; Lankin, A. V.; Norman, G. E.; Stegailov, V. V.
2015-11-01
Molecular modelling is used to calculate transport properties and to study relaxation of liquid n-triacontane (C30H62). The problem is important in connection with the behavior of liquid isolators in a pre-breakdown state. Two all-atom models and a united-atom model are used. Shear viscosity is calculated using the Green-Kubo formula. The force fields are compared with each other using the following criteria: the required time for one molecular dynamics step, the compliance of the main physical and transport properties with experimental values. The problem of the system equilibration is considered. The united-atom potential is used to model the n-triacontane liquid with an initial directional orientation. The time of relaxation to the disordered state, when all molecules orientations are randomized, are obtained. The influence of the molecules orientations on the shear viscosity value and the shear viscosity relaxation are treated.
Low temperature transport properties of Ce-Al metallic glasses
Zeng, Q. S.; Rotundu, C. R.; Mao, W. L.; Dai, J. H.; Xiao, Y. M.; Chow, P.; Chen, X. J.; Qin, C. L.; Mao, H.-k.; Jiang, J. Z.
2011-01-01
The low temperature transport properties of Ce_{75- x} Al_{25+ x} (x = 0, 10, and 15 at. %) metallic glasses were investigated. Magnetic field and composition tuned magnetoresistances changing from negative to positive values were observed at low temperature. It was suggested that these peculiar phenomena were caused by the tunable competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yoshida interaction in Ce-Al metallic glass with the variation in Ce content and magnetic field. Further magnetization and Ce-2p3d resonant inelastic x-ray scattering spectroscopy measurements supported this scenario. These Ce-Al metallic glasses could provide an interesting model system for the investigation of 4f electron behaviors in complex condensed matter with tunable transport properties.
Electrical transport properties of polycrystalline monolayer molybdenum disulfide.
Najmaei, Sina; Amani, Matin; Chin, Matthew L; Liu, Zheng; Birdwell, A Glen; O'Regan, Terrance P; Ajayan, Pulickel M; Dubey, Madan; Lou, Jun
2014-08-26
Semiconducting MoS2 monolayers have shown many promising electrical properties, and the inevitable polycrystallinity in synthetic, large-area films renders understanding the effect of structural defects, such as grain boundaries (GBs, or line-defects in two-dimensional materials), essential. In this work, we first examine the role of GBs in the electrical-transport properties of MoS2 monolayers with varying line-defect densities. We reveal a systematic degradation of electrical characteristics as the line-defect density increases. The two common MoS2 GB types and their specific roles are further examined, and we find that only tilt GBs have a considerable effect on the MoS2 electrical properties. By examining the electronic states and sources of disorder using temperature-dependent transport studies, we adopt the Anderson model for disordered systems to explain the observed transport behaviors in different temperature regimes. Our results elucidate the roles played by GBs in different scenarios and give insights into their underlying scattering mechanisms. PMID:25019978
Viscoelastic properties of actin networks influence material transport
NASA Astrophysics Data System (ADS)
Stam, Samantha; Weirich, Kimberly; Gardel, Margaret
2015-03-01
Directed flows of cytoplasmic material are important in a variety of biological processes including assembly of a mitotic spindle, retraction of the cell rear during migration, and asymmetric cell division. Networks of cytoskeletal polymers and molecular motors are known to be involved in these events, but how the network mechanical properties are tuned to perform such functions is not understood. Here, we construct networks of either semiflexible actin filaments or rigid bundles with varying connectivity. We find that solutions of rigid rods, where unimpeded sliding of filaments may enhance transport in comparison to unmoving tracks, are the fastest at transporting network components. Entangled solutions of semiflexible actin filaments also transport material, but the entanglements provide resistance. Increasing the elasticity of the actin networks with crosslinking proteins slows network deformation further. However, the length scale of correlated transport in these networks is increased. Our results reveal how the rigidity and connectivity of biopolymers allows material transport to occur over time and length scales required for physiological processes. This work was supported by the U. Chicago MRSEC
NASA Astrophysics Data System (ADS)
Qiu, Q. Y.; Alpay, S. P.; Nagarajan, V.
2010-06-01
We develop a nonlinear thermodynamic model to predict the phase stability of ultrathin epitaxial (001)-oriented ferroelectric PbZr1-xTixO3 (PZT) films with x =1.0, 0.9, 0.8, and 0.7 on substrates which induce anisotropic in-plane strains. The theoretical formalism incorporates the relaxation by misfit dislocations at the film deposition temperature, the possibility of formation of ferroelectric polydomain structures, and the effect of the internal electric field that is generated due to incomplete charge screening at the film-electrode interfaces and the termination of the ferroelectric layer. This analysis allows the development of misfit strain phase diagrams that provide the regions of stability of monodomain and polydomain structures at a given temperature, film thickness, and composition. It is shown that the range of stability for rotational monodomain phase is markedly increased in comparison to the same ferroelectric films on isotropic substrates. Furthermore, the model finds a strong similarity between ultrathin PbTiO3 and relatively thicker PZT films in terms of phase stability. The combinations of the in-plane misfit strains that yield a phase transition sequence that results in a polarization rotation from the c-phase (polarization parallel to the [001] direction in the film) to the r-phase, and eventually to an in-plane polarization parallel to the [110] direction (the aa-phase) is determined to be the path with the most attractive dielectric and piezoelectric coefficients resulting in enhancements of 10 to 100 times in the dielectric permittivity and piezoresponse compared to bulk tetragonal ferroelectrics of the same PZT composition.
The magnetic and transport properties of template-synthesized carbon-based and related nanomaterials
NASA Astrophysics Data System (ADS)
Friedman, Adam Louis
The porous alumina template-assisted method of nanoscale materials preparation provides a simple, relatively inexpensive, yet highly controllable and repeatable process for nanomaterial synthesis. Various nanostructures can then be made utilizing the porous structure as a scaffold. In this dissertation we study the porous alumina anodization process, the synthesis of porous alumina-assisted materials, and the basic physical properties of these materials, primarily concentrating on the magnetic and transport properties. First, we study the porous alumina formation process as a function of anodization voltage, acid type, and acid concentration. We find that while acid type strongly affects the growth characteristics of porous alumina, pH does not. We also study the stability of pore formation. We characterize the two- and three-dimensional stability of the growth process. We find that in three dimensions, an unstable formation region as a function of pH and voltage will cause the formation of dendrite structures. Next, we study the synthesis of materials in the porous alumina templates. Through chemical self-assembly, electrodeposition is able to make a wide variety of nanowires and nanotubes and we seek to optimize this process. Third, we study the optical properties Au and Ag nanowire arrays embedded in porous alumina. We find that such materials have use as negative index metamaterials owing to the existence of both transverse and longitudinal surface plasmon resonances. Next, we study the basic magnetic properties of new PAni-ferromagnet composite nanostructures and compare these properties to the magnetic properties of the nanotubes and the nanowires alone. We find the high dielectric properties of the PAni to strongly shield the ferromagnetic nanowires from magnetostatic interactions. Fifth, we make devices out of carbon nanotubes synthesized by CVD in the alumina templates. We investigate the transport properties of these carbon nanotubes. Further, we find that the contact resistances, which are normally on the order of mega-ohms for these tubes, can be lowered to the order of kilo-ohms by annealing in H 2/Ar atmosphere. We find that the disorder in these carbon nanotubes allows for the uptake of H during the annealing process. These H-complex hydrogen impurities, along with C and H adatoms, induce ferromagnetism in the carbon nanotubes. We carry out a magnetic study on the annealed carbon nanotubes. Moreover, the ferromagnetism of the carbon nanotubes results in hysteric magnetoresistance. We study this effect, attributing it to strong magneto-viscosity effects and anisotropic magnetoresistance. We also study the transport and magnetotransport properties of the annealed carbon nanotubes as a function of temperature and inner diameter. We find that there is an order-disorder transition that occurs at lower temperatures that resembles behavior predicted in disordered carbon fibers by the Bright model. We also find that the nanotubes behave as one-dimensional Luttinger liquids. Finally, as a means of comparison, we fabricate and study the properties of monolayer graphene devices.
Theoretical study of anisotropic MHD turbulence with low magnetic Reynolds number
NASA Astrophysics Data System (ADS)
Sukoriansky, Semion; Zemach, Efi
2016-03-01
Flows of electrically conducting fluids under the action of external magnetic field present an example of strongly anisotropic turbulence. Such flows are not only important for different engineering applications, but also provide an interesting framework for studies of quasi-two-dimensional turbulence with strongly modified transport properties in easily controllable laboratory experiments. We present theoretical results that advance our understanding of magnetohydrodynamic (MHD) flows with low magnetic Reynolds number by treating this phenomenon within the quasi-normal scale elimination (QNSE) theory. Previous applications of the theory to turbulent flows with stable stratification and solid body rotation have demonstrated that QNSE is a powerful tool for studies of anisotropic turbulent flows. We derive expressions for scale-dependent eddy viscosities and eddy diffusivities in the directions parallel and normal to the external magnetic field and investigate progressive anisotropization of turbulent transport of momentum and passive scalar. The theory yields analytical expressions for anisotropic one-dimensional spectra of MHD turbulence. In particular, the theory sheds light upon the modification of the Kolmogorov kâ€‘5/3 spectrum by anisotropic Ohmic (Joule) dissipation.
Spin Dependent Transport Properties of Metallic and Semiconducting Nanostructures
NASA Astrophysics Data System (ADS)
Sapkota, Keshab R.
Present computing and communication devices rely on two different classes of technologies; information processing devices are based on electrical charge transport in semiconducting materials while information storage devices are based on orientation of electron spins in magnetic materials. A realization of a hybrid-type device that is based on charge as well as spin properties of electrons would perform both of these actions thereby enhancing computation power to many folds and reducing power consumptions. This dissertation focuses on the fabrication of such spin-devices based on metallic and semiconducting nanostructures which can utilize spin as well as charge properties of electrons. A simplified design of the spin-device consists of a spin injector, a semiconducting or metallic channel, and a spin detector. The channel is the carrier of the spin signal from the injector to the detector and therefore plays a crucial role in the manipulation of spin properties in the device. In this work, nanostructures like nanowires and nanostripes are used to function the channel in the spin-device. Methods like electrospinning, hydrothermal, and wet chemical were used to synthesize nanowires while physical vapor deposition followed by heat treatment in controlled environment was used to synthesis nanostripes. Spin-devices fabrication of the synthesized nanostructures were carried out by electron beam lithography process. The details of synthesis of nanostructures, device fabrication procedures and measurement techniques will be discussed in the thesis. We have successfully fabricated the spin-devices of tellurium nanowire, indium nanostripe, and indium oxide nanostripe and studied their spin transport properties for the first time. These spin-devices show large spin relaxation length compared to normal metals like copper and offer potentials for the future technologies. Further, Heusler alloys nanowires like nanowires of Co 2FeAl were synthesized and studied for electrical transport properties since such systems are halfmetallic in nature and promise the possibilities of spin injection and detection. The study was extended to dilute magnetic semiconducting nanowire system of Cd1-xMnxTe which possess both magnetic and semiconducting properties. In summary, the studies made in this thesis will offer a new understanding of spin transport behavior for future technology.
Semiconducting black phosphorus: synthesis, transport properties and electronic applications.
Liu, Han; Du, Yuchen; Deng, Yexin; Ye, Peide D
2015-05-01
Phosphorus is one of the most abundant elements preserved in earth, and it comprises a fraction of ?0.1% of the earth crust. In general, phosphorus has several allotropes, and the two most commonly seen allotropes, i.e. white and red phosphorus, are widely used in explosives and safety matches. In addition, black phosphorus, though rarely mentioned, is a layered semiconductor and has great potential in optical and electronic applications. Remarkably, this layered material can be reduced to one single atomic layer in the vertical direction owing to the van der Waals structure, and is known as phosphorene, in which the physical properties can be tremendously different from its bulk counterpart. In this review article, we trace back to the research history on black phosphorus of over 100 years from the synthesis to material properties, and extend the topic from black phosphorus to phosphorene. The physical and transport properties are highlighted for further applications in electronic and optoelectronics devices. PMID:25307017
Space radiation transport properties of polyethylene-based composites
NASA Technical Reports Server (NTRS)
Kaul, R. K.; Barghouty, A. F.; Dahche, H. M.
2004-01-01
Composite materials that can serve as both effective shielding materials against cosmic-ray and energetic solar particles in deep space, as well as structural materials for habitat and spacecraft, remain a critical and mission enabling component in mission planning and exploration. Polyethylene is known to have excellent shielding properties due to its low density, coupled with high hydrogen content. Polyethylene-fiber reinforced composites promise to combine this shielding effectiveness with the required mechanical properties of structural materials. Samples of polyethylene-fiber reinforced epoxy matrix composite 1-5 cm thick were prepared at the NASA Marshall Space Flight Center and tested against a 500 MeV/nucleon Fe beam at the HIMAC facility of NIRS in Chiba, Japan. This paper presents measured and calculated results for the radiation transport properties of these samples.
Radiation Transport Properties of Polyethylene-Fiber Composites
NASA Technical Reports Server (NTRS)
Kaul, Raj K.; Barghouty, A. F.; Dahche, H. M.
2003-01-01
Composite materials that can both serve as effective shielding materials against cosmic-ray and energetic solar particles in deep space as well as structural materials for habitat and spacecraft remain a critical and mission enabling piece in mission planning and exploration. Polyethylene is known to have excellent shielding properties due to its low density coupled with high hydrogen content. Polyethylene fiber reinforced composites promise to combine this shielding effectiveness with the required mechanical properties of structural materials. Samples of Polyethylene-fiber reinforced epoxy matrix composite 1-5 cm thick were prepared at NASA's Marshall Space Flight Center and tested against 500 MeV/nucleon Fe beam at the HIMAC facility of NIRS in Chiba, Japan. This paper presents measured and calculated results for the radiation transport properties of these samples.
Linear elastic properties derivation from microstructures representative of transport parameters.
Hoang, Minh Tan; Bonnet, Guy; Tuan Luu, Hoang; Perrot, Camille
2014-06-01
It is shown that three-dimensional periodic unit cells (3D PUC) representative of transport parameters involved in the description of long wavelength acoustic wave propagation and dissipation through real foam samples may also be used as a standpoint to estimate their macroscopic linear elastic properties. Application of the model yields quantitative agreement between numerical homogenization results, available literature data, and experiments. Key contributions of this work include recognizing the importance of membranes and properties of the base material for the physics of elasticity. The results of this paper demonstrate that a 3D PUC may be used to understand and predict not only the sound absorbing properties of porous materials but also their transmission loss, which is critical for sound insulation problems. PMID:24907783
NASA Astrophysics Data System (ADS)
Kosaka, Masataka; Monde, Masanori
2015-09-01
For safe and fast fueling of hydrogen in a fuel cell electric vehicle at hydrogen fueling stations, an understanding of the heat transferred from the gas into the tank wall (carbon fiber reinforced plastic (CFRP) material) during hydrogen fueling is necessary. Its thermal properties are needed in estimating heat loss accurately during hydrogen fueling. The CFRP has anisotropic thermal properties, because it consists of an adhesive agent and layers of the CFRP which is wound with a carbon fiber. In this paper, the thermal diffusivity and thermal conductivity of the tank wall material were measured by an inverse solution for one-dimensional unsteady heat conduction. As a result, the thermal diffusivity and thermal conductivity were 2.09 × 10^{-6}{ m}2{\\cdot }{s}^{-1} and 3.06{ W}{\\cdot }{m}{\\cdot }^{-1}{K}^{-1} for the axial direction, while they were 6.03 × 10^{-7} {m}2{\\cdot }{s}^{-1} and 0.93 {W}{\\cdot }{m}^{-1}{\\cdot }{K}^{-1} for the radial direction. The thermal conductivity for the axial direction was about three times higher than that for the radial direction. The thermal diffusivity shows the same trend in both directions because the thermal capacity, ? c , is independent of direction, where ? is the density and c is the heat capacity.
NASA Astrophysics Data System (ADS)
Kosaka, Masataka; Monde, Masanori
2015-11-01
For safe and fast fueling of hydrogen in a fuel cell electric vehicle at hydrogen fueling stations, an understanding of the heat transferred from the gas into the tank wall (carbon fiber reinforced plastic (CFRP) material) during hydrogen fueling is necessary. Its thermal properties are needed in estimating heat loss accurately during hydrogen fueling. The CFRP has anisotropic thermal properties, because it consists of an adhesive agent and layers of the CFRP which is wound with a carbon fiber. In this paper, the thermal diffusivity and thermal conductivity of the tank wall material were measured by an inverse solution for one-dimensional unsteady heat conduction. As a result, the thermal diffusivity and thermal conductivity were 2.09 × 10^{-6}{ m}2{\\cdot }{s}^{-1} and 3.06{ W}{\\cdot }{m}{\\cdot }^{-1}{K}^{-1} for the axial direction, while they were 6.03 × 10^{-7} {m}2{\\cdot }{s}^{-1} and 0.93 {W}{\\cdot }{m}^{-1}{\\cdot }{K}^{-1} for the radial direction. The thermal conductivity for the axial direction was about three times higher than that for the radial direction. The thermal diffusivity shows the same trend in both directions because the thermal capacity, ? c, is independent of direction, where ? is the density and c is the heat capacity.
Structure and Anisotropic Properties of BaFe2-xNixAs2 (x = 0, 1, and 2) Single Crystals
Safa-Sefat, Athena; Jin, Rongying; McGuire, Michael A; Sales, Brian C; Mandrus, David; Ronning, F.; Bauer, E D; Mozharivskyj, Yurij
2009-01-01
The crystal structure, anisotropic electrical resistivity and magnetic susceptibility, as well as specific heat results from single crystals of BaFe2As2, BaNi2As2, and BaFeNiAs2 are surveyed. BaFe2As2 properties demonstrate the equivalence of C(T), Fisher s d(ï£T)/dT, and dï²/dT results in determining the antiferromagnetic transition at TN = 132(1) K. BaNi2As2 shows a structural phase transition from a high-temperature tetragonal phase to a low-temperature triclinic (PÄ«) phase at T0 = 131 K. The superconducting critical temperature for BaNi2As2 is well below T0 and at Tc = 0.69 K. BaFeNiAs2 does not show any sign of superconductivity to 0.4 K and exhibits properties similar to BaCo2As2, a renormalized paramagnetic metal.
Upscaling flow and transport properties in synthetic porous media
NASA Astrophysics Data System (ADS)
Jasinski, Lukasz; Dabrowski, Marcin
2015-04-01
Flow and transport through the porous media has instances in nature and industry: contaminant migration in geological formations, gas/oil extraction from proppant filled hydraulic fractures and surrounding porous matrix, underground carbon dioxide sequestration and many others. We would like to understand the behavior of propagating solute front in such medium, mainly flow preferential pathways and the solute dispersion due to the porous medium geometry. The motivation of our investigation is to find connection between the effective flow and transport properties and porous media geometry in 2D and 3D for large system sizes. The challenge is to discover a good way of upscaling flow and transport processes to obtain results comparable to these calculated on pore-scale in much faster way. We study synthetic porous media made of densely packed poly-disperse disk-or spherical-shaped grains in 2D and 3D, respectively. We use various protocols such as the random sequential addition (RSA) algorithm to generate densely packed grains. Imposed macroscopic pressure gradient invokes fluid flow through the pore space of generated porous medium samples. As the flow is considered in the low Reynolds number regime, a stationary velocity field is obtained by solving the Stokes equations by means of finite element method. Void space between the grains is accurately discretized by using body-fitting triangular or tetrahedral mesh. Finally, pure advection of a front carried by the velocity field is studied. Periodicity in all directions is applied to microstructure, flow and transport processes. Effective permeability of the media can be calculated by integrating the velocity field on cross sections, whereas effective dispersion coefficient is deduced by application of centered moment methods on the concentration field of transported solute in time. The effective parameters are investigated as a function of geometrical parameters of the media, such as porosity, specific surface area and fractal dimension of the pore space geometry. Discretization effects are taken into account. Furthermore, as we aim to simulate transport processes in complex and large systems in 3D, following upscaling technique is checked against the original calculations. The pore space of the media is approximated in the form of a capillary network by converting the pore space throats between the grains into lines in 2D and polygons in 3D. Effective flow and transport properties are calculated on such network models and compared with the results obtained for original geometry.
Reservoir transport and poroelastic properties from oscillating pore pressure experiments
NASA Astrophysics Data System (ADS)
Hasanov, Azar K.
Hydraulic transport properties of reservoir rocks, permeability and storage capacity are traditionally defined as rock properties, responsible for the passage of fluids through the porous rock sample, as well as their storage. The evaluation of both is an important part of any reservoir characterization workflow. Moreover, permeability and storage capacity are main inputs into any reservoir simulation study, routinely performed by reservoir engineers on almost any major oil and gas field in the world. An accurate reservoir simulation is essential for production forecast and economic analysis, hence the transport properties directly control the profitability of the petroleum reservoir and their estimation is vital for oil and gas industry. This thesis is devoted to an integrated study of reservoir rocks' hydraulic, streaming potential and poroelastic properties as measured with the oscillating pore pressure experiment. The oscillating pore pressure method is traditionally used to measure hydraulic transport properties. We modified the method and built an experimental setup, capable of measuring all aforementioned rock properties simultaneously. The measurements were carried out for four conventional reservoir-rock quality samples at a range of oscillation frequencies and effective stresses. An apparent frequency dependence of permeability and streaming potential coupling coefficient was observed. Measured frequency dispersion of drained poroelastic properties indicates an intrinsically inelastic nature of the porous mineral rock frame. Standard Linear Model demonstrated the best fit to the experimental dispersion data. Pore collapse and grain crushing effects took place during hydrostatic loading of the dolomitic sample and were observed in permeability, coupling coefficient and poroelastic measurements simultaneously. I established that hydraulically-measured storage capacities are overestimated by almost one order of magnitude when compared to elastically-derived ones. The fact that the values of storage capacities as estimated from the hydraulic component of the oscillating pore pressure experiment are unreliable was also demonstrated by comparing poroelastic Biot and Skempton coefficients. These coefficients were estimated both from hydraulic and strain measurements and the comparison of two datasets points out ambiguity of hydraulic measurements. I also introduce a novel method, which allowed us to estimate the permeability from the full range of acquired frequency data by utilizing a nonlinear least-squares regression. I additionally performed numerical simulation of oscillatory fluid flow. The simulated frequency-dependent results displayed an excellent agreement with both analytical solution and experimental data. This agreement proves that numerical simulation is a powerful tool in predicting frequency response of a porous rock sample to harmonic pore pressure excitations.
Thermal transport and thermoelectric properties of beta-graphyne nanostructures.
Ouyang, Tao; Hu, Ming
2014-06-20
Graphyne, an allotrope of graphene, is currently a hot topic in the carbon-based nanomaterials research community. Taking beta-graphyne as an example, we performed a comprehensive study of thermal transport and related thermoelectric properties by means of nonequilibrium Green's function (NEGF). Our simulation demonstrated that thermal conductance of beta-graphyne is only approximately 26% of that of the graphene counterpart and also shows evident anisotropy. Meanwhile, thermal conductance of armchair beta-graphyne nanoribbons (A-BGYNRs) presents abnormal stepwise width dependence. As for the thermoelectric property, we found that zigzag beta-graphyne nanoribbons (Z-BGYNRs) possess superior thermoelectric performance with figure of merit value achieving 0.5 at room temperature, as compared with graphene nanoribbons (~0.05). Aiming at obtaining a better thermoelectric coefficient, we also investigated Z-BGYNRs with geometric modulations. The results show that the thermoelectric performance can be enhanced dramatically (figure of merit exceeding 1.5 at room temperature), and such enhancement strongly depends on the width of the nanoribbons and location and quantity of geometric modulation. Our findings shed light on transport properties of beta-graphyne as high efficiency thermoelectrics. We anticipate that our simulation results could offer useful guidance for the design and fabrication of future thermoelectric devices. PMID:24859889
Coefficients for calculating thermodynamic and transport properties of individual species
NASA Technical Reports Server (NTRS)
Mcbride, Bonnie J.; Gordon, Sanford; Reno, Martin A.
1993-01-01
Libraries of thermodynamic data and transport properties are given for individual species in the form of least-squares coefficients. Values of C(sup 0)(sub p)(T), H(sup 0)(T), and S(sup 0)(T) are available for 1130 solid, liquid, and gaseous species. Viscosity and thermal conductivity data are given for 155 gases. The original C(sup 0)(sub p)(T) values were fit to a fourth-order polynomial with integration constants for H(sup 0)(T) and S(sup 0)(T). For each species the integration constant for H(sup 0)(T) includes the heat of formation. Transport properties have a different functional form. The temperature range for most of the data is 300 to 5000 K, although some of the newer thermodynamic data have a range of 200 to 6000 K. Because the species are mainly possible products of reaction, the data are useful for chemical equilibrium and kinetics computer codes. Much of the data has been distributed for several years with the NASA Lewis equilibrium program CET89. The thermodynamic properties of the reference elements were updated along with about 175 species that involve the elements carbon, hydrogen, oxygen, and nitrogen. These sets of data will be distributed with the NASA Lewis personal computer program for calculating chemical equilibria, CETPC.
Low temperature carrier transport properties in isotopically controlled germanium
Itoh, K.
1994-12-01
Investigations of electronic and optical properties of semiconductors often require specimens with extremely homogeneous dopant distributions and precisely controlled net-carrier concentrations and compensation ratios. The previous difficulties in fabricating such samples are overcome as reported in this thesis by growing high-purity Ge single crystals of controlled {sup 75}Ge and {sup 70}Ge isotopic compositions, and doping these crystals by the neutron transmutation doping (NTD) technique. The resulting net-impurity concentrations and the compensation ratios are precisely determined by the thermal neutron fluence and the [{sup 74}Ge]/[{sup 70}Ge] ratios of the starting Ge materials, respectively. This method also guarantees unprecedented doping uniformity. Using such samples the authors have conducted four types of electron (hole) transport studies probing the nature of (1) free carrier scattering by neutral impurities, (2) free carrier scattering by ionized impurities, (3) low temperature hopping conduction, and (4) free carrier transport in samples close to the metal-insulator transition.
Structural and robustness properties of smart-city transportation networks
NASA Astrophysics Data System (ADS)
Zhang, Zhen-Gang; Ding, Zhuo; Fan, Jing-Fang; Meng, Jun; Ding, Yi-Min; Ye, Fang-Fu; Chen, Xiao-Song
2015-09-01
The concept of smart city gives an excellent resolution to construct and develop modern cities, and also demands infrastructure construction. How to build a safe, stable, and highly efficient public transportation system becomes an important topic in the process of city construction. In this work, we study the structural and robustness properties of transportation networks and their sub-networks. We introduce a complementary network model to study the relevance and complementarity between bus network and subway network. Our numerical results show that the mutual supplement of networks can improve the network robustness. This conclusion provides a theoretical basis for the construction of public traffic networks, and it also supports reasonable operation of managing smart cities. Project supported by the Major Projects of the China National Social Science Fund (Grant No. 11 & ZD154).
Transport properties of the hot and dense sQGP
NASA Astrophysics Data System (ADS)
Berrehrah, H.; Bratkovskaya, E.; Cassing, W.; Marty, R.
2015-05-01
The transport properties of the quark gluon plasma (QGP) are studied in a QCD medium at finite temperature and chemical potential. We calculate the shear viscosity ?(T,?q) and the electric conductivity ?e(T, ?q) for a system of interacting massive and broad quasi-particles as described by the dynamical quasi-particle model “DQPM” at finite temperature T and quark chemical potential ?q within the relaxation time approximation. Our results are in a good agreement with lattice QCD at finite temperature and show clearly the increase of the transport coefficients with increasing T and ?q. Our results provide the basic ingredients for the study of the hot and dense matter in the Beam Energy Scan (BES) at RHIC and CBM at FAIR.
Transport properties of zigzag graphene nanoribbon decorated with copper clusters
Berahman, M.; Sheikhi, M. H.
2014-09-07
Using non-equilibrium green function with density functional theory, the present study investigates the transport properties of decorated zigzag graphene nanoribbon with a copper cluster. We have represented the decoration of zigzag graphene nanoribbon with single copper atom and cluster containing two and three copper atoms. In all the cases, copper atoms tend to occupy the edge state. In addition, we have shown that copper can alter the current-voltage characteristic of zigzag graphene nanoribbon and create new fluctuations and negative differential resistance. These alternations are made due to discontinuity in the combination of orbitals along the graphene nanoribbon. Decoration alters these discontinuities and creates more visible fluctuations. However, in low bias voltages, the changes are similar in all the cases. The study demonstrates that in the decorated zigzag graphene nanoribbon, the edge states are the main states for transporting electron from one electrode to another.
Transport properties of ultrathin black phosphorus on hexagonal boron nitride
NASA Astrophysics Data System (ADS)
Doganov, Rostislav A.; Koenig, Steven P.; Yeo, Yuting; Watanabe, Kenji; Taniguchi, Takashi; Özyilmaz, Barbaros
2015-02-01
Ultrathin black phosphorus, or phosphorene, is a two-dimensional material that allows both high carrier mobility and large on/off ratios. Similar to other atomic crystals, like graphene or layered transition metal dichalcogenides, the transport behavior of few-layer black phosphorus is expected to be affected by the underlying substrate. The properties of black phosphorus have so far been studied on the widely utilized SiO2 substrate. Here, we characterize few-layer black phosphorus field effect transistors on hexagonal boron nitride—an atomically smooth and charge trap-free substrate. We measure the temperature dependence of the field effect mobility for both holes and electrons and explain the observed behavior in terms of charged impurity limited transport. We find that in-situ vacuum annealing at 400 K removes the p-doping of few-layer black phosphorus on both boron nitride and SiO2 substrates and reduces the hysteresis at room temperature.
Transport properties of individual C{sub 60}-molecules
Géranton, G.; Seiler, C.; Evers, F.; Center for Functional Nanostructures, Karlsruhe Institute of Technology, Campus South, D-76131 Karlsruhe; Institut für Theorie der Kondensierten Materie, Karlsruhe Institute of Technology, Campus South, D-76128 Karlsruhe ; Bagrets, A.; Steinbuch Center for Supercomputing, Karlsruhe Institute of Technology, D-76128 Karlsruhe ; Venkataraman, L.
2013-12-21
Electrical and thermal transport properties of C{sub 60} molecules are investigated with density-functional-theory based calculations. These calculations suggest that the optimum contact geometry for an electrode terminated with a single-Au atom is through binding to one or two C-atoms of C{sub 60} with a tendency to promote the ?sp{sup 2}-hybridization into an ?sp{sup 3}-type one. Transport in these junctions is primarily through an unoccupied molecular orbital that is partly hybridized with the Au, which results in splitting the degeneracy of the lowest unoccupied molecular orbital triplet. The transmission through these junctions, however, cannot be modeled by a single Lorentzian resonance, as our results show evidence of quantum interference between an occupied and an unoccupied orbital. The interference results in a suppression of conductance around the Fermi energy. Our numerical findings are readily analyzed analytically within a simple two-level model.
Transport Properties in Superconducting Wires Coupled to Ferromagnetic Leads
NASA Astrophysics Data System (ADS)
Chen, Qiao; Zhang, Ya-Min; Xu, H. Q.; Xu, Ning
2016-02-01
We investigate the transport properties of a pair of Majorana bound states in both serial configuration and T-shape configuration with ferromagnetic leads. By using a non-equilibrium Green's function method, the formula of current and shot noise are obtained. The numerical results show that the coupling between the Majorana bounds states at the ends of a wire can be tuned by the polarization P and polarization angle Î¸ intimately in serial configuration. However, this coupling in T-shape configuration is only affected by ferromagnetic leads faintly. In addition, the Fano factor in both configurations is influenced by the polarization P and polarization angle Î¸ intimately at low bias region. Because of the different transport mechanisms, the serial configuration and T-shape configuration show sub-Poissonian and super-Poissonian shot noise at low bias, respectively.
Transport properties of plastic separator for renewable energy applications
NASA Astrophysics Data System (ADS)
Sharma, A. L.; Thakur, A. K.
2013-06-01
We report innovative results on optimization of intercalated polymer-clay nanocomposite endowed with desirable properties; (i) very high ionic conductivity (Ëœ10-3 S cm-1) at room temperature, (ii) tionËœ99% and cation transport number (tLi+)Ëœ67%: Intercalation of (PAN)8LiCF3SO3 complex into dodecylamine modified montmorillonite clay (DMMT) nanometric channels has been confirmed by Transmission electron microscopy (TEM) analysis. The optimized polymer film serves dual purpose of electrolyte and separator in energy storage devices.
The Effect of Microstructure On Transport Properties of Porous Electrodes
NASA Astrophysics Data System (ADS)
Peterson, Serena W.
The goal of this work is to further understand the relationships between porous electrode microstructure and mass transport properties. This understanding allows us to predict and improve cell performance from fundamental principles. The investigated battery systems are the widely used rechargeable Li-ion battery and the non-rechargeable alkaline battery. This work includes three main contributions in the battery field listed below. Direct Measurement of Effective Electronic Transport in Porous Li-ion Electrodes. An accurate assessment of the electronic conductivity of electrodes is necessary for understanding and optimizing battery performance. The bulk electronic conductivity of porous LiCoO2-based cathodes was measured as a function of porosity, pressure, carbon fraction, and the presence of an electrolyte. The measurements were performed by delamination of thin-film electrodes from their aluminum current collectors and by use of a four-line probe. Imaging and Correlating Microstructure To Conductivity. Transport properties of porous electrodes are strongly related to microstructure. An experimental 3D microstructure is needed not only for computation of direct transport properties, but also for a detailed electrode microstructure characterization. This work utilized X-ray tomography and focused ion beam (FIB)/scanning electron microscopy (SEM) to obtain the 3D structures of alkaline battery cathodes. FIB/SEM has the advantage of detecting carbon additives; thus, it was the main tomography tool employed. Additionally, protocols and techniques for acquiring, processing and segmenting series of FIB/SEM images were developed as part of this work. FIB/SEM images were also used to correlate electrodes' microstructure to their respective conductivities for both Li-ion and alkaline batteries. Electrode Microstructure Metrics and the 3D Stochastic Grid Model. A detailed characterization of microstructure was conducted in this work, including characterization of the volume fraction, nearest neighbor probability, domain size distribution, shape factor, and Fourier transform coefficient. These metrics are compared between 2D FIB/SEM, 3D FIB/SEM and X-ray structures. Among those metrics, the first three metrics are used as a basis for SG model parameterization. The 3D stochastic grid (SG) model is based on Monte Carlo techniques, in which a small set of fundamental inter-domain parameters are used to generate structures. This allows us to predict electrode microstructure and its effects on both electronic and ionic properties.
Anisotropic optical film embedded with cellulose nanowhisker.
Kim, Dah Hee; Song, Young Seok
2015-10-01
We investigated anisotropic optical behaviors of composite films embedded with CNWs. To control the orientation of CNWs, elongation was applied to the composite film. Morphological and mechanical analyses of the specimens were carried out to examine the influence of the applied extension. The CNWs were found to be aligned in the elongated direction, yielding remarkable anisotropic microstructure and optical properties. As the applied elongation and CNW loading increased, the resulting degree of polarization and birefringence increased due to increased interactions between the embedded particles. This study suggests a way to prepare an anisotropic optical component with nanoparticles of which the microstructures, such as orientation and filler content, can be controlled. PMID:26076646
Novel Properties of a Mouse ?-Aminobutyric Acid Transporter (GAT4)
Karakossian, M.H.; Spencer, S.R.; Gomez, A.Q.; Padilla, O.R.; Sacher, A.; Loo, D.D.F.; Nelson, N.; Eskandari, S.
2010-01-01
We expressed the mouse ?-aminobutyric acid (GABA) transporter GAT4 (homologous to rat/human GAT-3) in Xenopus laevis oocytes and examined its functional and pharmacological properties by using electrophysiological and tracer uptake methods. In the coupled mode of transport (Na+/Cl?/GABA cotransport), there was tight coupling between charge flux and GABA flux across the plasma membrane (2 charges/GABA). Transport was highly temperature-dependent with a temperature coeffcient (Q10) of 4.3. The GAT4 turnover rate (1.5 s?1; ?50 mV, 21°C) and temperature dependence suggest physiological turnover rates of 15–20 s?1. No uncoupled current was observed in the presence of Na+. In the absence of external Na+, GAT4 exhibited two distinct uncoupled currents. (i) A Cl? leak current (IleakCl) was observed when Na+ was replaced with choline or tetraethylammonium. The reversal potential of (IleakCl) followed the Cl? Nernst potential. (ii) A Li+ leak current (IleakLi) was observed when Na+ was replaced with Li+. Both leak currents were inhibited by Na+, and both were temperature-independent (Q10 ? 1). The two leak modes appeared not to coexist, as Li+ inhibited (IleakCl). The results suggest the existence of cation- and anion-selective channel-like pathways in GAT4. Flufenamic acid inhibited GAT4 Na+/C1?/GABA cotransport, IleakLi, and IleakCl, (Ki ? 30 ?M), and the voltage-induced presteady-state charge movements (Ki ? 440 ?M). Flufenamic acid exhibited little or no selectivity for GAT1, GAT2, or GAT3. Sodium and GABA concentration jumps revealed that slow Na+ binding to the transporter is followed by rapid GABA-induced translocation of the ligands across the plasma membrane. Thus, Na+ binding and associated conformational changes constitute the rate-limiting steps in the transport cycle. PMID:15981712
NASA Astrophysics Data System (ADS)
van Kats, C. M.
2008-10-01
The driving forces for fundamental research in colloid science are the ability to manage the material properties of colloids and to unravel the forces that play a role between colloids to be able to control and understand the processes where colloids play an important role. Therefore we are searching for colloidal materials with specific physical properties to better understand our surrounding world.Until recently research in colloid science was mainly focused on spherical (isotropic) particles. Monodisperse spherical colloids serve as a model system as they exhibit similar phase behaviour as molecular and atomic systems. Nevertheless, in many cases the spherical shape is not sufficient to reach the desired research goals. Recently the more complex synthesis methods of anisotropic model colloids has strongly developed. This thesis should be regarded as a contribution to this research area. Anisotropic colloids can be used as a building block for complex structures and are expected not only to lead to the construction of full photonic band gap materials. They will also serve as new, more realistic, models systems for their molecular analogues. Therefore the term ‘molecular colloids” is sometimes used to qualify these anisotropic colloidal particles. In the introduction of this thesis, we give an overview of the main synthesis techniques for anisotropic colloids. Chapter 2 describes the method of etching silicon wafers to construct monodisperse silicon rods. They subsequently were oxidized and labeled (coated) with a fluorescent silica layer. The first explorative phase behaviour of these silica rods was studied. The particles showed a nematic ordering in charge stabilized suspensions. Chapter 3 describes the synthesis of colloidal gold rods and the (mesoporous) silica coating of gold rods. Chapter 4 describes the physical and optical properties of these particles when thermal energy is added. This is compared to the case where the particles are irradiated with femtosecond laserpulses of variable wavelengths. We show that we can grow a silica layer on the gold rods with controllable thickness. In future this can be used to control the alignment of the gold rods a 3D crystal in an electric field. The silica coated gold rods can be used in optical switches. In chapter 4 we show to have a very local control of changing the aspect ratio of gold rods by irradiation with femtosecond laserpulses of 82 MHz with a threshold of ~ 2 picojoules to deform the particles. In chapter 5 and 6 we show how, starting from spherical particles, dimers (dumbbells), trimers and multimers can be formed by controlled aggregation. Chapter 7 finally shows an overview of syntheses where the pores of (mainly) silica particles is decreased. We show that the pores of the given particles could be decreased from macroporous to (ultra)microporous. Through a full control of pore size particles can selectively be filled with materials (for instance a drug) and be controllably closed. This opens a route for synthesis of particles that can be used as molecular filters or in biomedical applications such as smart drug delivery.
Simplified curve fits for the transport properties of equilibrium air
NASA Technical Reports Server (NTRS)
Srinivasan, S.; Tannehill, J. C.
1987-01-01
New, improved curve fits for the transport properties of equilibruim air have been developed. The curve fits are for viscosity and Prandtl number as functions of temperature and density, and viscosity and thermal conductivity as functions of internal energy and density. The curve fits were constructed using grabau-type transition functions to model the tranport properties of Peng and Pindroh. The resulting curve fits are sufficiently accurate and self-contained so that they can be readily incorporated into new or existing computational fluid dynamics codes. The range of validity of the new curve fits are temperatures up to 15,000 K densities from 10 to the -5 to 10 amagats (rho/rho sub o).
Graphene on graphene antidot lattices: Electronic and transport properties
NASA Astrophysics Data System (ADS)
Gregersen, Søren Schou; Pedersen, Jesper Goor; Power, Stephen R.; Jauho, Antti-Pekka
2015-03-01
Graphene bilayer systems are known to exhibit a band gap when the layer symmetry is broken by applying a perpendicular electric field. The resulting band structure resembles that of a conventional semiconductor with a parabolic dispersion. Here, we introduce a bilayer graphene heterostructure, where single-layer graphene is placed on top of another layer of graphene with a regular lattice of antidots. We dub this class of graphene systems GOAL: graphene on graphene antidot lattice. By varying the structure geometry, band-structure engineering can be performed to obtain linearly dispersing bands (with a high concomitant mobility), which nevertheless can be made gapped with a perpendicular field. We analyze the electronic structure and transport properties of various types of GOALs, and draw general conclusions about their properties to aid their design in experiments.
Stacking dependence of carrier transport properties in multilayered black phosphorous.
Sengupta, A; Audiffred, M; Heine, T; Niehaus, T A
2016-02-24
We present the effect of different stacking orders on carrier transport properties of multi-layer black phosphorous. We consider three different stacking orders AAA, ABA and ACA, with increasing number of layers (from 2 to 6 layers). We employ a hierarchical approach in density functional theory (DFT), with structural simulations performed with generalized gradient approximation (GGA) and the bandstructure, carrier effective masses and optical properties evaluated with the meta-generalized gradient approximation (MGGA). The carrier transmission in the various black phosphorous sheets was carried out with the non-equilibrium green's function (NEGF) approach. The results show that ACA stacking has the highest electron and hole transmission probabilities. The results show tunability for a wide range of band-gaps, carrier effective masses and transmission with a great promise for lattice engineering (stacking order and layers) in black phosphorous. PMID:26809017
Electronic and transport properties of LiCoO2.
Andriyevsky, Bohdan; Doll, Klaus; Jacob, Timo
2014-11-14
Using first principles density functional theory (DFT), the electronic and magnetic properties as well as the Li-ion migration in LiCoO2 have been studied with a gradient corrected functional. The magnetic properties were also investigated in addition using a gradient corrected functional in combination with an on-site repulsion U and a hybrid functional. We find LiCoO2 to be non-magnetic under ambient conditions. A magnetic ground state can be obtained by a volume expansion corresponding to a negative pressure of -8 GPa due to a competition between Hund's rules favoring magnetism on the Co(3+) ions and the crystal field splitting, which suppresses magnetism at zero pressure. The barrier for lithium transport is determined to be 0.44 eV from nudged elastic band (NEB) calculations on the Li0.917CoO2 system. PMID:25264622
Simplified curve fits for the transport properties of equilibrium air
NASA Astrophysics Data System (ADS)
Srinivasan, S.; Tannehill, J. C.
1987-12-01
New, improved curve fits for the transport properties of equilibruim air have been developed. The curve fits are for viscosity and Prandtl number as functions of temperature and density, and viscosity and thermal conductivity as functions of internal energy and density. The curve fits were constructed using grabau-type transition functions to model the tranport properties of Peng and Pindroh. The resulting curve fits are sufficiently accurate and self-contained so that they can be readily incorporated into new or existing computational fluid dynamics codes. The range of validity of the new curve fits are temperatures up to 15,000 K densities from 10 to the -5 to 10 amagats (rho/rho sub o).
Predicting the transport properties of sedimentary rocks from microgeometry
Schlueter, E.M.
1995-02-01
The author investigates through analysis and experiment how pore geometry, topology, and the physics and chemistry of mineral-fluid and fluid-fluid interactions affect the flow of fluids through consolidated/partially consolidated porous media. The approach is to measure fluid permeability and electrical conductivity of rock samples using single and multiple fluid phases that can be frozen in place (wetting and nonwetting) over a range of pore pressures. These experiments are analyzed in terms of the microphysics and microchemistry of the processes involved to provide a theoretical basis for the macroscopic constitutive relationships between fluid-flow and geophysical properties that the authors develop. The purpose of these experiments and their analyses is to advance the understanding of the mechanisms and factors that control fluid transport in porous media. This understanding is important in characterizing porous media properties and heterogeneities before simulating and monitoring the progress of complex flow processes at the field scale in permeable media.
Predicting the transport properties of sedimentary rocks from microgeometry
Schlueter, E.M.
1993-01-01
We investigate through analysis and experiment how pore geometry, topology, and the physics and chemistry of mineral-fluid and fluid-fluid interactions affect the flow of fluids through consolidated/partially consolidated porous media. Our approach is to measure fluid permeability and electrical conductivity of rock samples using single and multiple fluid phases that can be frozen in place (wetting and nonwetting) over a range of pore pressures. These experiments are analyzed in terms of the microphysics and microchemistry of the processes involved to provide a theoretical basis for the macroscopic constitutive relationships between fluid-flow and geophysical properties that we develop. The purpose of these experiments and their analyses is to advance the understanding of the mechanisms and factors that control fluid transport in porous media. This understanding is important in characterizing porous media properties and heterogeneities before simulating and monitoring the progress of complex flow processes at the field scale in permeable media.
Stacking dependence of carrier transport properties in multilayered black phosphorous
NASA Astrophysics Data System (ADS)
Sengupta, A.; Audiffred, M.; Heine, T.; Niehaus, T. A.
2016-02-01
We present the effect of different stacking orders on carrier transport properties of multi-layer black phosphorous. We consider three different stacking orders AAA, ABA and ACA, with increasing number of layers (from 2 to 6 layers). We employ a hierarchical approach in density functional theory (DFT), with structural simulations performed with generalized gradient approximation (GGA) and the bandstructure, carrier effective masses and optical properties evaluated with the meta-generalized gradient approximation (MGGA). The carrier transmission in the various black phosphorous sheets was carried out with the non-equilibrium greenâ€™s function (NEGF) approach. The results show that ACA stacking has the highest electron and hole transmission probabilities. The results show tunability for a wide range of band-gaps, carrier effective masses and transmission with a great promise for lattice engineering (stacking order and layers) in black phosphorous.
Anisotropic Ripple Deformation in Phosphorene.
Kou, Liangzhi; Ma, Yandong; Smith, Sean C; Chen, Changfeng
2015-05-01
Two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS2. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticity theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications. PMID:26263304
NASA Astrophysics Data System (ADS)
Freire, V.-M.; Corbella, C.; Bertran, E.; Portal-Marco, S.; Rubio-Roy, M.; Andújar, J.-L.
2012-06-01
The singular properties of hydrogenated amorphous carbon (a-C:H) thin films deposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD), such as hardness and wear resistance, make it suitable as protective coating with low surface energy for self-assembly applications. In this paper, we designed fluorine-containing a-C:H (a-C:H:F) nanostructured surfaces and we characterized them for self-assembly applications. Sub-micron patterns were generated on silicon through laser lithography while contact angle measurements, nanotribometer, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the surface. a-C:H:F properties on lithographied surfaces such as hydrophobicity and friction were improved with the proper relative quantity of CH4 and CHF3 during deposition, resulting in ultrahydrophobic samples and low friction coefficients. Furthermore, these properties were enhanced along the direction of the lithography patterns (in-plane anisotropy). Finally, self-assembly properties were tested with silica nanoparticles, which were successfully assembled in linear arrays following the generated patterns. Among the main applications, these surfaces could be suitable as particle filter selector and cell colony substrate.
NASA Astrophysics Data System (ADS)
Akiyama, Y.; Kawazu, T.; Noda, T.; Sakaki, H.
2010-01-01
We have studied electron transport in n-AlGaAs/GaAs heterojunction FET channels, in which chains of InGaAs nano-islands are embedded along quasi-periodic steps. By using two samples, conductance Gpara(Vg) parallel to the steps and Gperp(Vg) perpendicular to them were measured at 80 K as functions of gate voltage Vg. At sufficiently high Vg, Gpara at 80 K is several times as high as Gperp, which manifests the anisotropic two-dimensional transport of electrons. When Vg is reduced to -0.7 V, Gperp almost vanishes, while Gpara stays sizable unless Vg is set below -0.8 V. These results indicate that "inter-chain" barriers play stronger roles than "intra-chain" barriers.
NASA Astrophysics Data System (ADS)
Proust, Gwénaëlle; Kalidindi, Surya R.
2006-08-01
Microstructure-sensitive design (MSD) is a novel mathematical framework that facilitates a rigorous consideration of the material microstructure as a continuous design variable in the engineering design enterprise [Adams, B.L., Henrie, A., Henrie, B., Lyon, M., Kalidindi, S.R., Garmestani, H., 2001. Microstructure-sensitive design of a compliant beam. J. Mech. Phys. Solids 49(8), 1639-1663; Adams, B.L., Lyon, M., Henrie, B., 2004. Microstructures by design: linear problems in elastic-plastic design. Int. J. Plasticity 20(8-9), 1577-1602; Kalidindi, S.R., Houskamp, J.R., Lyons, M., Adams, B.L., 2004. Microstructure sensitive design of an orthotropic plate subjected to tensile load. Int. J. Plasticity 20(8-9), 1561-1575]. MSD employs spectral representations of the local state distribution functions in describing the microstructure quantitatively, and these in turn enable development of invertible linkages between microstructure and effective properties using established homogenization (composite) theories. As a natural extension of the recent publications in MSD, we provide in this paper a detailed account of the methods that can be readily used by mechanical designers to construct first-order elastic-plastic property closures. The main focus in this paper is on the crystallographic texture (also called Orientation Distribution Function or ODF) as the main microstructural parameter controlling the elastic and yield properties of cubic (fcc and bcc) polycrystalline metals. The following specific advances are described in this paper: (i) derivation of rigorous first-order bounds for the off-diagonal terms of the effective elastic stiffness tensor and their incorporation in the MSD framework, (ii) delineation of the union of the property closures corresponding to both the upper and lower bound theories resulting in comprehensive first-order closures, (iii) development of generalized and readily usable expressions for effective anisotropic elastic-plastic properties that could be applied to all cubic polycrystals, and (iv) identification of the locations of readily available or easily processable ODFs (e.g. textures that are produced by rolling, drawing, etc.) on the property closures. It is anticipated that the advances communicated in this paper will make the mathematical framework of MSD highly accessible to the mechanical designers.
Highly Anisotropic Elements for Acoustic Pentamode Applications
NASA Astrophysics Data System (ADS)
Layman, Christopher N.; Naify, Christina J.; Martin, Theodore P.; Calvo, David C.; Orris, Gregory J.
2013-07-01
Pentamode metamaterials are a class of acoustic metafluids that are characterized by a divergence free modified stress tensor. Such materials have an unconventional anisotropic stiffness and isotropic mass density, which allow themselves to mimic other fluid domains. Here we present a pentamode design formed by an oblique honeycomb lattice and producing customizable anisotropic properties. It is shown that anisotropy in the stiffness can exceed 3 orders of magnitude, and that it can be realistically tailored for transformation acoustic applications.
Controlling the Electrical Transport Properties of Nanocontacts to Nanowires.
Lord, Alex M; Maffeis, Thierry G; Kryvchenkova, Olga; Cobley, Richard J; Kalna, Karol; Kepaptsoglou, Despoina M; Ramasse, Quentin M; Walton, Alex S; Ward, Michael B; Köble, Jürgen; Wilks, Steve P
2015-07-01
The ability to control the properties of electrical contacts to nanostructures is essential to realize operational nanodevices. Here, we show that the electrical behavior of the nanocontacts between free-standing ZnO nanowires and the catalytic Au particle used for their growth can switch from Schottky to Ohmic depending on the size of the Au particles in relation to the cross-sectional width of the ZnO nanowires. We observe a distinct Schottky to Ohmic transition in transport behavior at an Au to nanowire diameter ratio of 0.6. The current-voltage electrical measurements performed with a multiprobe instrument are explained using 3-D self-consistent electrostatic and transport simulations revealing that tunneling at the contact edge is the dominant carrier transport mechanism for these nanoscale contacts. The results are applicable to other nanowire materials such as Si, GaAs, and InAs when the effects of surface charge and contact size are considered. PMID:26042356
TASK 7 DEMONSTRATION OF THAMES FOR MICROSTRUCTURE AND TRANSPORT PROPERTIES
Langton, C.; Bullard, J.; Stutzman, P.; Snyder, K.; Garboczi, E.
2010-03-29
The goal of the Cementitious Barriers Partnership (CBP) is to develop a reasonable and realible set of tools to reduce the uncertainty in predicting the structural, hydraulic and chemical performance of cement barriers used in nuclear applications that are exposed to dynamic environmental conditions over extended time frames. One of these tools, the responsibility of NIST, is THAMES (Thermodynamic Hydration and Microstructure Evolution Simulator), which is being developed to describe cementitious binder microstructures and calculate important engineering properties during hydration and degradation. THAMES is designed to be a 'micro-probe', used to evaluate changes in microstructure and properties occurring over time because of hydration or degradation reactions in a volume of about 0.001 mm{sup 3}. It will be used to map out microstructural and property changes across reaction fronts, for example, with spatial resolution adequate to be input into other models (e.g., STADIUM{reg_sign}, LeachSX{trademark}) in the integrated CBP package. THAMES leverages thermodynamic predictions of equilibrium phase assemblages in aqueous geochemical systems to estimate 3-D virtual microstructures of a cementitious binder at different times during the hydration process or potentially during degradation phenomena. These virtual microstructures can then be used to calculate important engineering properties of a concrete made from that binder at prescribed times. In this way, the THAMES model provides a way to calculate the time evolution of important material properties such as elastic stiffness, compressive strength, diffusivity, and permeability. Without this model, there would be no way to update microstructure and properties for the barrier materials considered as they are exposed to the environment, thus greatly increasing the uncertainty of long-term transport predictions. This Task 7 report demonstrates the current capabilities of THAMES. At the start of the CBP project, THAMES did not exist, so that it is in the early stages of development. However, extensive experience with 3-D microstructure models at NIST is making possible a timely development process.
NASA Astrophysics Data System (ADS)
Wu, Linmin; Zhang, Jing
2015-12-01
The mechanical properties of LixCoO2 under various Li concentrations and associated anisotropy have been systematically studied using the first principles method. During the lithium intercalation process, the Young's modulus, bulk modulus, shear modulus, and ultimate strength increase with increasing lithium concentration. Strong anisotropy of mechanical properties between a-axis and c-axis in LixCoO2 is identified at low lithium concentrations, and the anisotropy decreases with increasing lithium concentration. The observed lithium concentration dependence and anisotropy are explained by analyzing the charge transfer using Bader charge analysis, bond order analysis, and bond strength by investigating partial density of states and charge density difference. With the decrease of Li concentration, the charge depletion in the bonding regions increases, indicating a weaker Co-O bond strength. Additionally, the Young's modulus, bulk modulus, shear modulus, and toughness are obtained by simulating ab initio tensile tests. From the simulated stress-strain curves, LixCoO2 shows the highest toughness, which is in contraction with Pugh criterion prediction based on elastic properties only.
Huang, Jin-Dou; Li, Wen-Liang; Wen, Shu-Hao; Dong, Bin
2015-04-15
Recently, diketopyrrolopyrrole (DPP)-based materials have attracted much interest due to their promising performance as a subunit in organic field effect transistors. Using density functional theory and charge-transport models, we investigated the electronic structure and microscopic charge transport properties of the cyanated bithiophene-functionalized DPP molecule (compound 1). First, we analyzed in detail the partition of the total relaxation (polaron) energy into the contributions from each vibrational mode and the influence of bond-parameter variations on the local electron-vibration coupling of compound 1, which well explains the effects of different functional groups on internal reorganization energy (Î»). Then, we investigated the structural and electronic properties of compound 1 in its isolated molecular state and in the solid state form, and further simulated the angular resolution anisotropic mobility for both electron- and hole-transport using two different simulation methods: (i) the mobility orientation function proposed in our previous studies (method 1); and (ii) the master equation approach (method 2). The calculated electron-transfer mobility (0.00003-0.784 cm(2) V(-1) s(-1) from method 1 and 0.02-2.26 cm(2) V(-1) s(-1) from method 2) matched reasonably with the experimentally reported value (0.07-0.55 cm(2) V(-1) s(-1) ). To the best of our knowledge, this is the first time that the transport parameters of compound 1 were calculated in the context of band model and hopping models, and both calculation results suggest that the intrinsic hole mobility is higher than the corresponding intrinsic electron mobility. Our calculation results here will be instructive to further explore the potential of other higher DPP-containing quinoidal small molecules. PMID:25706355
Hydrophobic organic contaminant transport property heterogeneity in the Borden Aquifer
NASA Astrophysics Data System (ADS)
Allen-King, Richelle M.; Kalinovich, Indra; Dominic, David F.; Wang, Guohui; Polmanteer, Reid; Divine, Dana
2015-03-01
We determined that the spatial heterogeneity in aquifer properties governing the reactive transport of volatile organic contaminants is defined by the arrangement of lithofacies. We measured permeability (k) and perchloroethene sorption distribution coefficient (Kd) for lithofacies that we delineated for samples from the Canadian Forces Base Borden Aquifer. We compiled existing data and collected 57 new cores to characterize a 30 m section of the aquifer near the test location of Mackay et al. (1986). The k and Kd were measured for samples taken at six elevations from all cores to create a data set consisting of nearly 400 colocated measurements. Through analysis of variance (corrected for multiple comparisons), we determined that the 12 originally mapped lithofacies could be grouped into five relatively distinct chemohydrofacies that capture the variability of both transport properties. The mean of ln k by lithofacies was related to the grain size and the variance was relatively consistent. In contrast, both the mean and variance of ln Kd were greater for more poorly sorted lithofacies, which were also typically more coarse-grained. Half of the aquifer sorption capacity occurred in the three highest-sorbing lithofacies but comprised only 20% of its volume. The model of the aquifer that emerged is that of discontinuous scour-fill deposits of medium sand, generally characterized by greater Kd and k, within laterally extensive fine-grained to very fine-grained sands of lower Kd and k. Our findings demonstrate the importance of considering source rock composition, transport, and deposition processes when constructing conceptual models of chemohydrofacies.
Thermomagnetic Transport in Polycrystalline Samples
NASA Astrophysics Data System (ADS)
Zebarjadi, M.
2015-10-01
Polycrystalline/single-phase nanocomposite samples are used widely for thermoelectrics and many other applications. The presence of many interfaces improves the thermoelectric properties by suppressing phonon transport more than electron transport. When polycrystalline samples are made out of anisotropic crystals, it is not clear how the transport properties are related to those of single crystal. In this paper, we describe a simple process of averaging over different crystallographic directions to calculate the properties of isotropic polycrystalline samples made out of anisotropic crystals. We apply the developed averaging model to (Bi0.2Sb0.8)2Te3 samples for which experimental data are available. We further point out the importance of thermomagnetic measurements in providing additional information on electron relaxation times, compared with what regular thermoelectric measurements reveal.
Anisotropic colloidal crystal particles from microfluidics.
Cheng, Yao; Zhu, Cun; Xie, Zhuoying; Gu, Hongcheng; Tian, Tian; Zhao, Yuanjin; Gu, Zhongze
2014-05-01
Anisotropic colloidal crystal particles (CCPs) have showed their great potential in biotechnology and structural materials due to their anisotropic shapes and tunable optical property. However, their controllable generation is still a challenge. Here, a novel microfluidic approach is developed to generate anisotropic CCPs. The microfluidic device is composed of an injection capillary and a collection capillary with available size and shape. Based on the device, the anisotropic particles with non-close-packed colloidal crystal structures are achieved by photo-polymerizing droplet templates in a confined collection capillary with different shapes and sizes. Moreover, anisotropic close-packed CCPs can be made from non-close-packed CCPs through a thermal process. It is demonstrated that the anisotropic CCPs in different sizes, structural colors and shapes (rods, cuboids and disks) can be generated. These distinguishable features of resultant particles make them ideal barcodes for high-throughput bioassays. In order to prove it, DNA multiplex detection is carried out. The experimental results indicate that achieved particles have a great encoding capacity and are highly practical for multiplex coding bioassays. Therefore, we believe that the anisotropic CCPs would be highly promising barcodes in biomedical applications, including high-throughput bioassays and cell culture research where multiplexing is needed. PMID:24594033
NASA Astrophysics Data System (ADS)
Spinner, Neil S.; Hinnant, Katherine M.; Mazurick, Ryan; Brandon, Andrew; Rose-Pehrsson, Susan L.; Tuttle, Steven G.
2016-04-01
Cylindrical 18650-type surrogate cells were designed and fabricated to mimic the thermophysical properties and behavior of active lithium-ion batteries. An internal jelly roll geometry consisting of alternating stainless steel and mica layers was created, and numerous techniques were used to estimate thermophysical properties. Surrogate cell density was measured to be 1593 Â± 30 kg/m3, and heat capacity was found to be 727 Â± 18 J/kg-K. Axial thermal conductivity was determined to be 5.1 Â± 0.6 W/m-K, which was over an order of magnitude higher than radial thermal conductivity due to jelly roll anisotropy. Radial heating experiments were combined with numerical and analytical solutions to the time-dependent, radial heat conduction equation, and from the numerical method an additional estimate for heat capacity of 805 Â± 23 J/kg-K was found. Using both heat capacities and analysis techniques, values for radial thermal conductivity were between 0.120 and 0.197 W/m-K. Under normal operating conditions, relatively low radial temperature distributions were observed; however, during extreme battery failure with a hexagonal cell package, instantaneous radial temperature distributions as high as 43-71 Â°C were seen. For a vertical cell package, even during adjacent cell failure, similar homogeneity in internal temperatures were observed, demonstrating thermal anisotropy.
Quantifying Effective Flow and Transport Properties in Heterogeneous Porous Media
NASA Astrophysics Data System (ADS)
Heidari, P.; Li, L.
2012-12-01
Spatial heterogeneity, the spatial variation in physical and chemical properties, exists at almost all scales and is an intrinsic property of natural porous media. It is important to understand and quantify how small-scale spatial variations determine large-scale "effective" properties in order to predict fluid flow and transport behavior in the natural subsurface. In this work, we aim to systematically understand and quantify the role of the spatial distribution of sand grains of different sizes in determining effective dispersivity and effective permeability using quasi-2D flow-cell experiments and numerical simulations. Two dimensional flow cells (20 cm by 20 cm) were packed with the same total amount of fine and coarse sands however with different spatial patterns. The homogeneous case has the completely mixed fine and coarse sands. The four zone case distributes the fine sand in four identical square zones within the coarse sand matrix. The one square case has all the fine sands in one square block. With the one square case pattern, two more experiments were designed in order to examine the effect of grain size contrast on effective permeability and dispersivity. Effective permeability was calculated based on both experimental and modeling results. Tracer tests were run for all cases. Advection dispersion equations were solved to match breakthrough data and to obtain average dispersivity. We also used Continuous Time Random Walk (CTRW) to quantify the non-Fickian transport behavior for each case. For the three cases with the same grain size contrast, the results show that the effective permeability does not differ significantly. The effective dispersion coefficient is the smallest for the homogeneous case (0.05 cm) and largest for the four zone case (0.27 cm). With the same pattern, the dispersivity value is the largest with the highest size contrast (0.28 cm), which is higher than the one with the lowest case by a factor of 2. The non-Fickian behavior was quantified by the ? value within the CTRW framework. Fickian transport will result in ? values larger than 2 while its deviation from 2 indicates the extent of non-Fickian behavior. Among the three cases with the same grain size contrast, the ? value is closest to 2 in the homogeneous case (1.95), while smallest in the four zone case (1.89). In the one square case, with the highest size contrast, the ? value was 1.57, indicating increasing extent of non-Fickian behavior with higher size contrast. This study is one step toward understanding how small-scale spatial variation in physical properties affect large-scale flow and transport behavior. This step is important in predicting subsurface transport processes that are relevant to earth sciences, environmental engineering, and petroleum engineering.
Electrical transport properties of single-layer WS2.
Ovchinnikov, Dmitry; Allain, Adrien; Huang, Ying-Sheng; Dumcenco, Dumitru; Kis, Andras
2014-08-26
We report on the fabrication of field-effect transistors based on single layers and bilayers of the semiconductor WS2 and the investigation of their electronic transport properties. We find that the doping level strongly depends on the device environment and that long in situ annealing drastically improves the contact transparency, allowing four-terminal measurements to be performed and the pristine properties of the material to be recovered. Our devices show n-type behavior with a high room-temperature on/off current ratio of âˆ¼10(6). They show clear metallic behavior at high charge carrier densities and mobilities as high as âˆ¼140 cm(2)/(V s) at low temperatures (above 300 cm(2)/(V s) in the case of bilayers). In the insulating regime, the devices exhibit variable-range hopping, with a localization length of about 2 nm that starts to increase as the Fermi level enters the conduction band. The promising electronic properties of WS2, comparable to those of single-layer MoS2 and WSe2, together with its strong spin-orbit coupling, make it interesting for future applications in electronic, optical, and valleytronic devices. PMID:25069042
Transport properties of ribbon-shaped carbon fibers: Property-structure relationship
NASA Astrophysics Data System (ADS)
Gallego, Nidia Constanza
Mesophase pitch-based carbon fibers are an ideal material for applications in which high rates of heat dissipation and low mass are required. Unfortunately, the high cost of current commercial high thermal conductivity mesophase pitch-based carbon fibers has limited their use in high volume applications. Understanding how the structure develops during the fiber formation process and how this structure relates to the final fiber properties is the way to optimizing the fiber properties while reducing the processing costs. Ribbon-shaped fibers have been developed at Clemson University and are being evaluated as a low-cost high thermal conductivity alternative fiber to traditional round-shaped fibers. However, the characterization of the thermal transport properties of carbon fibers is a difficult and time-consuming process. The objectives of this study were to evaluate the transport (both thermal and electronic) properties of ribbon-shaped fibers produced from an AR mesophase at different processing conditions, to characterize the structure of these fibers, to study their structure-property relationships, and to develop a model capable of estimating the thermal conductivity of carbon fibers based upon their structural parameters. For this purpose, several sets of ribbon fibers were produced from an AR mesophase at different spinning temperatures and shear rates and heat treated at a final temperature of 2400°C. The electrical resistivities, magnetoresistances and thermal conductivities of these fibers were measured and the structural parameters were determined with x-ray techniques. Two approaches (a short-fiber composite, and a periodic composite) were utilized to model the relationship between the structure of the fiber and its thermal conductivity. The results of this study confirmed that ribbon-shaped fibers develop excellent transport properties at lower graphitization temperatures than those used commercially for round-shaped fibers. Additionally, for the first time, two models that directly relate the structure of the carbon fiber to its thermal conductivity were developed.
Transport Properties of n-POLYANILINE/p-POROUS Silicon Heterojunctions
NASA Astrophysics Data System (ADS)
Farag, A. A. M.; Ashery, A.; Yahia Abed, M.; Shenashen, M. A.; Hindia, T. A.
The donor/acceptor heterojunction devices having configuration n-PANI/p-PSi were fabricated by in-situ chemical oxidative polymerization method of aniline on p-type porous silicon. The structure of n-PANI/p-PSi junctions was examined by scanning electron microscopy and X-ray diffraction spectroscopy. The dark current-voltage measurements were performed in the temperature range of 303-393 K to determine the electrical transport mechanisms of these devices. Rectifying properties were obtained and capacitance-voltage at 1 MHz behavior indicates an abrupt interface. At low forward bias, the current was found to be limited by thermionic emission of holes from p-PSi over the PANI/PSi barrier in the PANI thin film. For relatively higher voltage, the conduction was dominated by a space charge limited current mechanism, with an exponential distribution of traps. Also, various electrical parameters were determined from the I-V and C-V analysis.
Shear strain induced modulation to the transport properties of graphene
NASA Astrophysics Data System (ADS)
He, Xin; Gao, Li; Tang, Ning; Duan, Junxi; Xu, Fujun; Wang, Xinqiang; Yang, Xuelin; Ge, Weikun; Shen, Bo
2014-08-01
Applying shear strain has been considered as a hopeful method to open a band gap of graphene. To study the transport properties of graphene under shear strain, a device was fabricated to apply shear strain, up to 16.7%, to graphene grown by chemical vapor deposition method. A top gate with ionic liquid as the dielectric material was used to tune the carrier density. The conductance of the Dirac point and carrier mobility is found to increase with a comparatively small increasing strain but then decrease with a larger one. Such a behavior might be related to several factors: the wrinkles, the transverse conducting channels, and the grain boundaries of graphene. Our study is helpful to further understand the strain engineering in graphene.
The electrical transport properties of liquid Rb using pseudopotential theory
Patel, A. B. Bhatt, N. K. Thakore, B. Y. Jani, A. R.; Vyas, P. R.
2014-04-24
Certain electric transport properties of liquid Rb are reported. The electrical resistivity is calculated by using the self-consistent approximation as suggested by Ferraz and March. The pseudopotential due to Hasegawa et al for full electron-ion interaction, which is valid for all electrons and contains the repulsive delta function due to achieve the necessary s-pseudisation was used for the calculation. Temperature dependence of structure factor is considered through temperature dependent potential parameter in the pair potential. Finally, thermo-electric power and thermal conductivity are obtained. The outcome of the present study is discussed in light of other such results, and confirms the applicability of pseudopotential at very high temperature via temperature dependent pair potential.
Optical and transport properties of dense liquid silica
Qi, Tingting; Millot, Marius; Kraus, Richard G.; Hamel, Sebastien; Root, Seth
2015-06-15
Using density-functional-theory based molecular dynamics and the Kubo-Greenwood linear response theory, we evaluated the high-pressure equation of state and the optical and transport properties of quartz and fused silica shock-compressed to 2000 GPa. The computed Hugoniots and corresponding optical reflectivity values are in very good agreement with published data for quartz, and new data that we obtained on fused silica using magnetically launched flyer plate experiments. The rise of optical reflectivity upon shock compression appears to be primarily a temperature-driven mechanism, which is relatively insensitive to small density variation. We observed that the electrical conductivity does not display Drude-like frequency dependence, especially at lower temperatures. In addition, the Wiedemann-Franz relation between electrical and thermal conductivities was found to be invalid. It suggests that even at three-fold compression, warm dense liquid silica on the Hugoniot curve is still far away from the degenerate limit.
Dynamical and transport properties of liquid gallium at high pressures.
Sheppard, D; Mazevet, S; Cherne, F J; Albers, R C; Kadau, K; Germann, T C; Kress, J D; Collins, L A
2015-06-01
Quantum molecular dynamics (QMD) simulations are used to calculate the equation of state, structure, and transport properties of liquid gallium along the principal shock Hugoniot. The calculated Hugoniot is in very good agreement with experimental data up to a pressure of 150 GPa as well as with our earlier classical molecular dynamics calculations using a modified embedded atom method (MEAM) potential. The self-diffusion and viscosity calculated using QMD agree with experimental measurements better than the MEAM results, which we attribute to capturing the complexity of the electronic structure at elevated temperatures. Calculations of the DC conductivity were performed around the Hugoniot. Above a density of 7.5 g/cm(3), the temperature increases rapidly along the Hugoniot, and the optical conductivity decreases, indicating simple liquid metal behavior. PMID:26172802
Dynamical and transport properties of liquid gallium at high pressures
NASA Astrophysics Data System (ADS)
Sheppard, D.; Mazevet, S.; Cherne, F. J.; Albers, R. C.; Kadau, K.; Germann, T. C.; Kress, J. D.; Collins, L. A.
2015-06-01
Quantum molecular dynamics (QMD) simulations are used to calculate the equation of state, structure, and transport properties of liquid gallium along the principal shock Hugoniot. The calculated Hugoniot is in very good agreement with experimental data up to a pressure of 150 GPa as well as with our earlier classical molecular dynamics calculations using a modified embedded atom method (MEAM) potential. The self-diffusion and viscosity calculated using QMD agree with experimental measurements better than the MEAM results, which we attribute to capturing the complexity of the electronic structure at elevated temperatures. Calculations of the DC conductivity were performed around the Hugoniot. Above a density of 7.5 g/cm3, the temperature increases rapidly along the Hugoniot, and the optical conductivity decreases, indicating simple liquid metal behavior.
Optical and transport properties of dense liquid silica
NASA Astrophysics Data System (ADS)
Qi, Tingting; Millot, Marius; Kraus, Richard G.; Root, Seth; Hamel, Sebastien
2015-06-01
Using density-functional-theory based molecular dynamics and the Kubo-Greenwood linear response theory, we evaluated the high-pressure equation of state and the optical and transport properties of quartz and fused silica shock-compressed to 2000 GPa. The computed Hugoniots and corresponding optical reflectivity values are in very good agreement with published data for quartz, and new data that we obtained on fused silica using magnetically launched flyer plate experiments. The rise of optical reflectivity upon shock compression appears to be primarily a temperature-driven mechanism, which is relatively insensitive to small density variation. We observed that the electrical conductivity does not display Drude-like frequency dependence, especially at lower temperatures. In addition, the Wiedemann-Franz relation between electrical and thermal conductivities was found to be invalid. It suggests that even at three-fold compression, warm dense liquid silica on the Hugoniot curve is still far away from the degenerate limit.
Electrical Transport Properties of Liquid Sn-Sb Binary Alloys
NASA Astrophysics Data System (ADS)
Thakore, B. Y.; Suthar, P. H.; Khambholja, S. G.; Jani, A. R.
2010-06-01
The study of electrical transport properties viz. electrical resistivity, thermo electrical power and thermal conductivity of liquid Sn-Sb binary alloys have been made by our well recognized single parametric model potential. In the present work, screening functions due to Hartree, Taylor, Ichimaru et al.. Farid et al.. and Sarkar et al.. have been employed to incorporate the exchange and correlation effects. The liquid alloy is studied as a function of its composition at temperature 823 K according to the Faber-Ziman model. Further, thermoelectric power and thermal conductivity have been predicted. The values of electrical resistivity of binary alloys computed with Ichimaru et al. and Farid et al.. screening function are in good agreement with the experimental data.
Theoretical study on transport properties of photo-reactive molecules
NASA Astrophysics Data System (ADS)
Oyama, Norihisa; Kondo, Hisashi; Nara, Jun; Ohno, Takahisa
2007-03-01
Azobenzene and stilbene molecules are powerful candidates for ultra-fast optical switches because of their ultra-fast photo-isomerization (trans-> cis and cis-> trans). These molecules have similar molecular structures. However, the isomerization mechanisms are completely different. In this work, we investigate the transport properties of both azobenzene and stilbene molecules based on the non-equilibrium green function (NEGF) method, and compare the results. This study was supported by RSS21 project and Grant-in-Aid for Scientific Research (No.17064017) of MEXT of the Japanese government. The calculations in this work were carried out partly using the Numerical Materials Simulator in National Institute for Materials Science (NIMS), and partly using the NEC-SX5 at Cybermedia Center, Osaka University.
Anisotropic models for compact stars
NASA Astrophysics Data System (ADS)
Maurya, S. K.; Gupta, Y. K.; Ray, Saibal; Dayanandan, Baiju
2015-05-01
In the present paper we obtain an anisotropic analog of the Durgapal and Fuloria (Gen Relativ Gravit 17:671, 1985) perfect fluid solution. The methodology consists of contraction of the anisotropic factor with the help of both metric potentials and . Here we consider the same as Durgapal and Fuloria (Gen Relativ Gravit 17:671, 1985) did, whereas is as given by Lake (Phys Rev D 67:104015, 2003). The field equations are solved by the change of dependent variable method. The solutions set mathematically thus obtained are compared with the physical properties of some of the compact stars, strange star as well as white dwarf. It is observed that all the expected physical features are available related to the stellar fluid distribution, which clearly indicates the validity of the model.
Yin, Jun; Chaitanya, Kadali; Ju, Xue-Hai
2016-03-01
The crystal structures of known anthra-tetrathiophene (ATT) and its three fluorinated derivatives (ATT1, ATT2 and ATT3) were predicted by the Monte Carlo-simulated annealing method with the embedded electrostatic potential (ESP) charges. The most stable crystal structures were further optimized by the density functional theory with the dispersion energy (DFT-D) method. In addition, the effect of the electron-withdrawing fluorine atoms on the molecular geometry, molecular stacking, electronic and transport properties of title compounds were investigated by the density functional theory and the incoherent charge-hopping model. The calculated results show that the introduction of fluorine atoms does not affect the molecular planarity but decreases the HOMO-LUMO gap, which is beneficial to electron injection and provides more charge carrier stabilization. The improved electron mobility from ATT to ATT3 is attributed to the favorable molecular packing with strong Ï€-Ï€ interaction and the short stacking distance. ATT2 and ATT3 exhibit remarkable angular dependence of mobilities and anisotropic behaviors. The band structures reveal that all the paths with larger transfer integrals are along the directions of large dispersions in the valence band (VB) and conduction band (CB). ATT3 has the largest electron mobility (0.48 cm(2)V(-1)s(-1)) among the four compounds, indicating that fluorination is an effective approach to improve electron transport. PMID:26774641
Electron Transport Materials: Synthesis, Properties and Device Performance
Cosimbescu, Lelia; Wang, Liang; Helm, Monte L.; Polikarpov, Evgueni; Swensen, James S.; Padmaperuma, Asanga B.
2012-06-01
We report the design, synthesis and characterization, thermal and photophysical properties of two silane based electron transport materials, dibenzo[b,d]thiophen-2-yltriphenylsilane (Si{phi}87) and (dibenzo[b,d]thiophen-2-yl)diphenylsilane (Si{phi}88) and their performance in blue organic light emitting devices (OLEDs). The utility of these materials in blue OLEDs with iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C']picolinate (Firpic) as the phosphorescent emitter was demonstrated. Using the silane Si{phi}87 as the electron transport material (ETm) an EQE of 18.2% was obtained, with a power efficiency of 24.3 lm/W (5.8V at 1mA/cm{sup 2}), in a heterostructure. When Si{phi}88 is used, the EQE is 18.5% with a power efficiency of 26.0 lm/W (5.5V at 1mA/cm{sup 2}).
Hole transporting properties of tris(8-hydroxyquinoline) aluminum (Alq3)
NASA Astrophysics Data System (ADS)
Fong, H. H.; So, S. K.
2006-11-01
The hole transporting properties of tris (8-hydroxyquinoline) aluminum (Alq3) were investigated by time-of-flight (TOF) technique between 278 and 373K, and under an applied field range of 0.6-1.3MV/cm. At room temperature, the hole mobility has a value between 10-9 and 10-8cm2V-1s-1. The hole mobility is at least two orders of magnitude less than electron under identical preparation and measurement conditions. Generally, all hole TOF transients of Alq3 exhibit a nondispersive behavior, with a clear plateau region and a dispersion tail. Two disorder transport models, namely, the Gaussian disorder model (GDM) and the correlated disorder model (CDM), were applied to analyze the temperature and field dependent hole mobility data. The GDM, however, is found to be invalid because it fails to produce a meaningful positional disorder parameter. The CDM gives a better fit to the data, yet the model is still not satisfactory.
Transport properties of elastically coupled fractional Brownian motors
NASA Astrophysics Data System (ADS)
Lv, Wangyong; Wang, Huiqi; Lin, Lifeng; Wang, Fei; Zhong, Suchuan
2015-11-01
Under the background of anomalous diffusion, which is characterized by the sub-linear or super-linear mean-square displacement in time, we proposed the coupled fractional Brownian motors, in which the asymmetrical periodic potential as ratchet is coupled mutually with elastic springs, and the driving source is the external harmonic force and internal thermal fluctuations. The transport mechanism of coupled particles in the overdamped limit is investigated as the function of the temperature of baths, coupling constant and natural length of the spring, the amplitude and frequency of driving force, and the asymmetry of ratchet potential by numerical stimulations. The results indicate that the damping force involving the information of historical velocity leads to the nonlocal memory property and blocks the traditional dissipative motion behaviors, and it even plays a cooperative role of driving force in drift motion of the coupled particles. Thus, we observe various non-monotonic resonance-like behaviors of collective directed transport in the mediums with different diffusion exponents.
Transport properties of liquid metal hydrogen under high pressures
NASA Technical Reports Server (NTRS)
Brown, R. C.; March, N. H.
1972-01-01
A theory is developed for the compressibility and transport properties of liquid metallic hydrogen, near to its melting point and under high pressure. The interionic force law is assumed to be of the screened Coulomb type, because hydrogen has no core electrons. The random phase approximation is used to obtain the structure factor S(k) of the system in terms of the Fourier transform of this force law. The long wavelenth limit of the structure factor S(o) is related to the compressibility, which is much lower than that of alkali metals at their melting points. The diffusion constant at the melting point is obtained in terms of the Debye frequency, using a frequency spectrum analogous with the phonon spectrum of a solid. A similar argument is used to obtain the combined shear and bulk viscosities, but these depend also on S(o). The transport coefficients are found to be about the same size as those of alkali metals at their melting points.
Transport properties of polyaniline-cellulose-acetate blends
NASA Astrophysics Data System (ADS)
Planès, Jérôme; Wolter, Andreas; Cheguettine, Yasmina; Pro?, Adam; Genoud, Françoise; Nechtschein, Maxime
1998-09-01
Transport properties of polyaniline (PANI)-cellulose acetate (CA) conducting blends have been investigated at various length scales and temperatures. We report on the results of dc and ac conductivity measurements, magnetoresistance and electron-spin resonance (ESR) performed on composite films with PANI weight fraction p ranging from the percolation threshold-pc~=0.1%-to a few percent. Three different PANI doping agents have been tested, namely, camphor sulfonic acid (CSA), di(i-octyl phosphate) (DiOP) and phenyl phosphonic acid (PPA). The percolative behavior of ?dc resembles that of published results on PANI/PMMA blends. The onset frequency ?? of the dispersion in ?ac appears to follow the scaling law: ??~?zdc with z~=1. The temperature dependence is of the form of ln?(T)~-(T0/T)? the exponent decreasing from 0.75 to 0.5 with increasing p. The microscopic metallic character of transport is found in ESR and microwave measurements. Spin-dependent conductivity is inferred from the (B/T)2 universal behavior of magnetoresistance. Those results are discussed in conjunction with the ongoing debate on the nature of disorder in conducting polymers-homogeneous versus heterogeneous.
Coherent structures and transport properties in magnetized plasmas
NASA Astrophysics Data System (ADS)
Serianni, G.; Agostini, M.; Antoni, V.; Cavazzana, R.; Martines, E.; Sattin, F.; Scarin, P.; Spada, E.; Spolaore, M.; Vianello, N.; Zuin, M.
2007-12-01
A common feature of magnetized plasmas is the presence of fluctuations, which can lead to fully developed turbulence. Often large events—called bursts—emerge from the remaining low-level turbulence, giving an intermittent character to fluctuations; namely the statistical properties of fluctuations are found to depend on the temporal scale over which the investigation is conducted. In magnetized plasmas, the bursts are generally believed to be due to the presence of magnetic-field-aligned structures. Moreover, it has been experimentally shown that the intermittent events detected in the signals are associated with a relevant contribution to the loss of particles from the plasma. All these observations are common to plasmas spanning a wide range of temperature and density and magnetically confined both in linear and toroidal devices. In particular, in high-temperature plasmas for thermonuclear fusion, research aims at devising suitable ways to control transport by acting on the plasma structures, for instance by biasing the plasma edge using electrodes. This paper gives a characterization of the structures found in magnetized plasmas and of their contribution to the particle transport; moreover, the effect of the velocity shear on structures is addressed. Emphasis will be laid on to the most advanced diagnostics allowing the reconstruction of turbulent structures by optical and electrostatic techniques.
Transport properties of nanoconstrictions in armchair graphene ribbons
NASA Astrophysics Data System (ADS)
Romanovsky, Igor; Yannouleas, Constantine; Landman, Uzi
2014-03-01
The transport properties of nanoconstrictions and quantum-point contacts formed in atomically precise segmented armchair graphene nanoribbons (SaGRs) are investigated using a tight-binding non-equilibrium Green's function (TB-NEGF) approach and relativistic quantum-field theory modeling.[2] The TB behavior is accounted for by a one-dimensional Dirac-transfer-matrix (DTM) model using variable-mass (scalar-field) barriers assigned to the junctions between the nanoribbon segments. It is shown that the topology of the junctions (sharp versus smooth) and the ratio of length over width of the constriction are the principal factors influencing the height of the mass barriers, and thus they control the extent of trapping and confinement by the constriction of graphene's relativistic carriers, even in the case of all-metallic SaGRs. A rich variety of transport patterns ensues, ranging from ballistic quantized conductance to resonant tunneling associated with Coulomb blockade. Supported by the U.S. D.O.E. (FG05-86ER-45234).
Transport properties of ultrathin black phosphorus on hexagonal boron nitride
Doganov, Rostislav A.; Ã–zyilmaz, Barbaros; Koenig, Steven P.; Yeo, Yuting; Watanabe, Kenji; Taniguchi, Takashi
2015-02-23
Ultrathin black phosphorus, or phosphorene, is a two-dimensional material that allows both high carrier mobility and large on/off ratios. Similar to other atomic crystals, like graphene or layered transition metal dichalcogenides, the transport behavior of few-layer black phosphorus is expected to be affected by the underlying substrate. The properties of black phosphorus have so far been studied on the widely utilized SiO{sub 2} substrate. Here, we characterize few-layer black phosphorus field effect transistors on hexagonal boron nitrideâ€”an atomically smooth and charge trap-free substrate. We measure the temperature dependence of the field effect mobility for both holes and electrons and explain the observed behavior in terms of charged impurity limited transport. We find that in-situ vacuum annealing at 400â€‰K removes the p-doping of few-layer black phosphorus on both boron nitride and SiO{sub 2} substrates and reduces the hysteresis at room temperature.
Predicting the transport properties of sedimentary rocks from microstructure
Schlueter, E.M.
1995-01-01
Understanding transport properties of sedimentary rocks, including permeability, relative permeability, and electrical conductivity, is of great importance for petroleum engineering, waste isolation, environmental restoration, and other applications. These transport properties axe controlled to a great extent by the pore structure. How pore geometry, topology, and the physics and chemistry of mineral-fluid and fluid-fluid interactions affect the flow of fluids through consolidated/partially consolidated porous media are investigated analytically and experimentally. Hydraulic and electrical conductivity of sedimentary rocks are predicted from the microscopic geometry of the pore space. Cross-sectional areas and perimeters of individual pores are estimated from two-dimensional scanning electron microscope (SEM) photomicrographs of rock sections. Results, using Berea, Boise, Massilon, and Saint-Gilles sandstones show close agreement between the predicted and measured permeabilities. Good to fair agreement is found in the case of electrical conductivity. In particular, good agreement is found for a poorly cemented rock such as Saint-Gilles sandstone, whereas the agreement is not very good for well-cemented rocks. The possible reasons for this are investigated. The surface conductance contribution of clay minerals to the overall electrical conductivity is assessed. The effect of partial hydrocarbon saturation on overall rock conductivity, and on the Archie saturation exponent, is discussed. The region of validity of the well-known Kozeny-Carman permeability formulae for consolidated porous media and their relationship to the microscopic spatial variations of channel dimensions are established. It is found that the permeabilities predicted by the Kozeny-Carman equations are valid within a factor of three of the observed values methods.
RELATIONSHIP BETWEEN CELL SURFACE PROPERTIES AND TRANSPORT OF BACTERIA THROUGH SOIL
A study was conducted to relate the properties of Enterobacter, Pseudomonas, Bacillus, Achromobacter, Flavobacterium, and Arthrobacter strains to their transport with water moving through soil. the bacteria differed markedly in their extent of transport; their hydrophobicity, as...
Soh, Wee Tee; Ong, C. K.; Zhong, Xiaoxi
2014-09-15
FeAlSi (Sendust) is known to possess excellent soft magnetic properties comparable to traditional soft magnetic alloys such as NiFe (Permalloy), while having a relatively higher resistance for lower eddy current losses. However, their dynamic magnetic and magneto-transport properties are not well-studied. Via the spin rectification effect, we electrically characterize a series of obliquely sputtered FeAlSi films at ferromagnetic resonance. The variations of the anisotropy fields and damping with oblique angle are extracted and discussed. In particular, two-magnon scattering is found to dominate the damping behavior at high oblique angles. An analysis of the results shows large anomalous Hall effect and anisotropic magneto-resistance across all samples, which decreases sharply with increasing oblique incidence.
Testing different formulations of leading-order anisotropic hydrodynamics
NASA Astrophysics Data System (ADS)
Tinti, Leonardo; Ryblewski, Radoslaw; Florkowski, Wojciech; Strickland, Michael
2016-02-01
A recently obtained set of the equations for leading-order (3+1)D anisotropic hydrodynamics is tested against exact solutions of the Boltzmann equation with the collisional kernel treated in the relaxation time approximation. In order to perform detailed comparisons, the new anisotropic hydrodynamics equations are reduced to the boost-invariant and transversally homogeneous case. The agreement with the exact solutions found using the new anisotropic hydrodynamics equations is similar to that found using previous, less general formulations of anisotropic hydrodynamics. In addition, we find that, when compared to a state-of-the-art second-order viscous hydrodynamics framework, leading-order anisotropic hydrodynamics better reproduces the exact solution for the pressure anisotropy and gives comparable results for the bulk pressure evolution. Finally, we compare the transport coefficients obtained using linearized anisotropic hydrodynamics with results obtained using second-order viscous hydrodynamics.
Anisotropic nanomaterials: structure, growth, assembly, and functions
Sajanlal, Panikkanvalappil R.; Sreeprasad, Theruvakkattil S.; Samal, Akshaya K.; Pradeep, Thalappil
2011-01-01
Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications. PMID:22110867
Generalized thermodynamic and transport properties. II. Molecular liquids
NASA Astrophysics Data System (ADS)
Bertolini, D.; Tani, A.
2011-03-01
In the present paper, we extend the method described in paper I [D. Bertolini and A. Tani, preceding paper, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.83.031201 83, 031201 (2011)] to molecular liquids, which allows us to solve the exact kinetic equation proposed by de Schepper [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.38.271 38, 271 (1988)] without approximations. In particular, generalized thermodynamic properties (enthalpy, specific heat, and thermal expansion coefficient) and transport properties (longitudinal viscosity, thermal conductivity) have been calculated for three liquids of increasing complexity, namely dimethyl sulfoxide, hydrogen fluoride, and SPC/E water. All results have been obtained by the molecular formalism as well as the atomic one, corrected for intramolecular correlations that are due to the models adopted. As done for simple liquids, the coupling between the viscous stress tensor and the energy flux vector has been calculated exactly. We also show that the Markov assumption for the dynamics related to thermal conductivity can only be adopted with caution.
Kleinpeter, Erich; Lämmermann, Anica; Kühn, Heiner
2011-02-21
The inversion of the flexible five-membered ring in tetrahydrodicyclopentadiene (TH-DCPD) derivatives remains fast on the NMR timescale even at 103 K. Since the intramolecular exchange process could not be sufficiently slowed for spectroscopic evaluation, the conformational equilibrium is thus inaccessible by dynamic NMR. Fortunately, the spatial magnetic properties of the aryl and carbonyl groups attached to the DCPD skeleton can be employed in order to evaluate the conformational state of the system. In this context, the anisotropic effects of the functional groups in the (1)H NMR spectra prove to be the molecular response property of spatial nucleus independent chemical shifts (NICS). PMID:21152640
Transport properties and nanosensors of oxide nanowires and nanobelts
NASA Astrophysics Data System (ADS)
Lao, Changshi
ZnO is one of the most important materials for electronics, optoelectronics, piezoelectricity and optics. With a wide band gap of 3.37eV and an exiton binding energy of 60meV, ZnO ID nanostructures exhibit promising properties in a lot of optical device applications. It is also an important piezoelectric material and has applications in a new category of nanodevices, nano-piezotronics. Demonstrated prototype of devices includes nanogenerators, piezoelectric-FET, and a series of evolutive devices based on the concept of nanogenerator. This is based on working principle of a semiconductor and piezoelectric coupled property. This thesis is about the growth, characterization and device fabrication of ZnO nanowires and nanobelts for sensors and UV detectors. First, the fundamental synthesis of ZnO nanostructurs is investigated, particularly polar surface dominated nanostructues, to illustrate the unique growth configurations of ZnO nanobelts, nanorings and nanosprings. Detail study in this part includes nanobelts, nanorings, nanocombs, nanonetworks, and nanodiskettes synthesis. Important factors in driving the nanostructure synthesis mechanism are analyzed, such as the chemical activities of different surface of ZnO, the abundant of available Zn ions in the vapor, and the polar surface dominated effects. These factors contribute to the large abundant available ZnO nanostructures. Then, the devices fabricated methods using individual nanowires/nanobelts and their electrical transport properties were carefully characterized. In this part, dominant factors which are critical for nanobelt device performance are investigated, such as the contact properties, interface effects, and durability testing. Also, a metal doping method is studied to explore the controlling and modification of nanowire electric and optical properties. Research results obtained here provide a basic and thoroughly understanding the control process and fabrication criteria in building a functional nanobelt based device. Further more, I will present the surface functionalization of nanobelt for largely improving its electrical, optoelectronic and chemical performance. Surface functionalization of nanobelts is proven to be an effective method in enhancing the semiconductor and metal contact. Piezoelectric field-effect transistors will be demonstrated as a powerful approach as chemical sensors. Finally, a technique is illustrated for functionalizing the surfaces of ZnO nanobelts for enhancing its UV sensitivity by over five orders of magnitude. This demonstrates an effective approach for fabricatiing ultrasensitive UV detectors. The research results presented in this thesis have made great contribution to the growth, device fabrication and novel applications of ZnO nanostructures for photonics, optoelectronics and sensors.
Berryman, J.G.
2007-10-02
Some arguments of Bristow (1960) concerning the effects of cracks on elastic and transport (i.e., electrical or thermal conduction) properties of cold-worked metals are reexamined. The discussion is posed in terms of a modern understanding of bounds and estimates for physical properties of polycrystals--in contrast to Bristow's approach using simple mixture theory. One type of specialized result emphasized here is the cross-property estimates and bounds that can be obtained using the methods presented. Our results ultimately agree with those of Bristow, i.e., confirming that microcracking is not likely to be the main cause of the observed elastic behavior of cold-worked metals. However, it also becomes clear that the mixture theory approach to the analysis is too simple and that crack-crack interactions are necessary for proper quantitative study of Bristow's problem.
Optical and Transport Properties of Organic Molecules: Methods and Applications
NASA Astrophysics Data System (ADS)
Strubbe, David Alan
Organic molecules are versatile and tunable building blocks for technology, in nanoscale and bulk devices. In this dissertation, I will consider some important applications for organic molecules involving optical and transport properties, and develop methods and software appropriate for theoretical calculations of these properties. Specifically, we will consider second-harmonic generation, a nonlinear optical process; photoisomerization, in which absorption of light leads to mechanical motion; charge transport in junctions formed of single molecules; and optical excitations in pentacene, an organic semiconductor with applications in photovoltaics, optoelectronics, and flexible electronics. In the Introduction (Chapter 1), I will give an overview of some phenomenology about organic molecules and these application areas, and discuss the basics of the theoretical methodology I will use: density-functional theory (DFT), time-dependent density-functional theory (TDDFT), and many-body perturbation theory based on the GW approximation. In the subsequent chapters, I will further discuss, develop, and apply this methodology. 2. I will give a pedagogical derivation of the methods for calculating response properties in TDDFT, with particular focus on the Sternheimer equation, as will be used in subsequent chapters. I will review the many different response properties that can be calculated (dynamic and static) and the appropriate perturbations used to calculate them. 3. Standard techniques for calculating response use either integer occupations (as appropriate for a system with an energy gap) or fractional occupations due to a smearing function, used to improve convergence for metallic systems. I will present a generalization which can be used to compute response for a system with arbitrary fractional occupations. 4. Chloroform (CHCl3) is a small molecule commonly used as a solvent in measurements of nonlinear optics. I computed its hyperpolarizability for second-harmonic generation with TDDFT with a real-space grid, finding good agreement with calculations using localized bases and with experimental measurements, and that the response is very long-ranged in space. 5. N C 60 is an endohedral fullerene, a sphere of carbon containing a single N atom inside, which is weakly coupled electronically. I show with TDDFT calculations that a laser pulse can excite the vibrational mode of this N atom, transiently turning on and off the system's ability to undergo second-harmonic generation. The calculated susceptibility is as large as some commercially used frequency-doubling materials. 6. A crucial question in understanding experimental measurements of nonlinear optics and their relation to device performance is the effect of the solution environment on the properties of the isolated molecules. I will consider possible explanations for the large enhancement of the hyperpolarizability of chloroform in solution, demonstrate an ab initio method of calculating electrostatic effects with local-field factors, and derive the equations necessary for a full calculation of liquid chloroform. 7. Many-body perturbation theory, in the GW approximation for quasiparticle band-structure and Bethe-Salpeter equation for optical properties, is a powerful method for calculations in solids, nanostructures, and molecules. The BerkeleyGW code is a freely available implementation of this methodology which has been extensively tested and efficiently parallelized for use on large systems. 8. Molecular junctions, in which a single molecule is contacted to two metallic leads, are interesting systems for studying nanoscale transport. I will present a method called DFT+Sigma which approximates many-body perturbation theory to enable accurate and efficient calculations of the conductance of these systems. 9. Azobenzene is a molecule with the unusual property that it can switch reversible between two different geometries, cis and trans, upon absorption of light. I have calculated the structures of these two forms when absorbed on the Au(111) surface, to understand scanning tunneling microscope studies and elucidate the switching mechanism on the surface. I have also calculated the conductance of the two forms in a molecular junction. 10. The Seebeck and Peltier thermoelectric effects can interconvert electricity and heat, and are parametrized by the Seebeck coefficient. Standard methods in quantum transport for computing this quantity are problematic numerically. I will show this fact in a simple model and derive a more robust and efficient approach. 11. Pentacene is an organic semiconductor which shows exciton self-trapping in its optical spectra. I will present a method for calculation of excited-state forces with the Bethe-Salpeter equation that can be applied to study the geometrical relaxation that occurs upon absorption of light by pentacene.
Interfacial and transport properties of nanoconstrained inorganic and organic materials
NASA Astrophysics Data System (ADS)
Kocherlakota, Lakshmi Suhasini
Nanoscale constraints impact the material properties of both organic and inorganic systems. The systems specifically studied here are (i) nanoconstrained polymeric systems, poly(l-trimethylsilyl-1-propyne) (PTMSP) and poly(ethylene oxide) (PEO) relevant to gas separation membranes (ii) Zwitterionic polymers poly(sulfobetaine methacrylate)(pSBMA), poly(carboxybetaine acrylamide) (pCBAA), and poly(oligo(ethylene glycol) methyl methacrylate) (PEGMA) brushes critical for reducing bio-fouling (iii) Surface properties of N-layer graphene sheets. Interfacial constraints in ultrathin poly(l-trimethylsilyl-1-propyne) (PTMSP) membranes yielded gas permeabilities and CO2/helium selectivities that exceed bulk PTMSP membrane transport properties by up to three-fold for membranes of submicrometer thickness. Indicative of a free volume increase, a molecular energetic mobility analysis (involving intrinsic friction analysis) revealed enhanced methyl side group mobilities in thin PTMSP membranes with maximum permeation, compared to bulk films. Aging studies conducted over the timescales relevant to the conducted experiments signify that the free volume states in the thin film membranes are highly unstable in the presence of sorbing gases such as CO2. To maintain this high free volume configuration of polymer while improving the temporal stability an "inverse" architecture to conventional polymer nanocomposites was investigated, in which the polymer phase of PTMSP and PEO were interfacially and dimensionally constrained in nanoporous anodic aluminum oxide (AAO) membranes. While with this architecture the benefits of nanocomposite and ultrathin film membranes of PTMSP could be reproduced and improved upon, also the temporal stability could be enhanced substantially. The PEO-AAO nanocomposite membranes also revealed improved gas selectivity properties of CO2 over helium. In the thermal transition studies of zwitterionic pSBMA brushes a reversible critical transition temperature of 60 Â°C in 27 nm films was evidenced, indicating changes in molecular conformations with respect to the temperature. pCBAA and pEGMA brushes displayed no thermal transitions, suggesting that the molecular conformations of these systems were insensitive to temperature in the investigated regime. The surface energy of a dimensionally constrained inorganic system, graphene is studied via local Hamaker constant determination from a single graphene layer to bulk graphite. Intrinsic friction scattering analysis of dipolar fluctuations of the Van der Waals interactions between an atomic force microscopy tip and graphene layers revealed a four-fold reduction in the surface energy from bulk HOPG to graphene. A numerical analysis based on electron energy loss spectroscopy confirms quantitatively the results.
Molecular Simulation of Phase Equilibria and Transport Properties
NASA Astrophysics Data System (ADS)
Bereolos, Peter James
1995-01-01
Molecular simulations are used to test models and theories through comparison with experimental results and theoretical predictions. Three areas are covered: transport properties, free energy measurement, and phase diagram calculation. Transport properties of isotropic fluids composed of hard ellipsoids of revolution are studied using molecular dynamics simulation. The self diffusion coefficient, the shear viscosity, and the thermal conductivity are evaluated for a range of densities and elongations and are compared to the predictions of an Enskog kinetic theory for nonspherical bodies. The simulation and the kinetic theory values for the shear viscosity and the thermal conductivity show the same qualitative behavior, that is, increasing with density and with particle nonsphericity. Quantitatively, there is good agreement at low densities (up to 30% of closest packing); at higher densities (60% of closest packing) deviations from Enskog theory are larger than, and in the opposite direction to those seen for hard spheres. The Stokes-Einstein and Debye relations are tested, and indicate a transition from a kinetic theory region towards the hydrodynamic limit as density increases. A new Monte Carlo method of free energy calculation, which does not rely on particle insertion is analyzed. The justification for the use of the method in the NVT ensemble is shown. The method is extended into the isothermal-isobaric ensemble where it is successfully applied to a variety of hard molecules. Analysis shows that the single particle sampling portion of the method should not be extended to the NPT ensemble. Isothermal phase diagrams for a variety of mixtures are determined by a combination of semi-grand ensemble simulation and orthogonal collocation integration. The semi-grand ensemble avoids problems of particle insertion that are encountered in some other widely used techniques. Orthogonal collocation allows the simulations to be run in parallel as opposed to stepwise integration techniques. The orthogonal collocation method is first studied numerically on an ideal system to demonstrate its superiority in suppressing error propagation. Next, Lennard-Jones mixtures, including some which form azeotropes, are examined and compared with prior works. Finally, three systems of real molecules, Krypton-Argon Methane-Ethane, and Ethane -Carbon Dioxide are simulated and compared with experimental results.
NASA Astrophysics Data System (ADS)
Tayarani-Yoosefabadi, Z.; Harvey, D.; Bellerive, J.; Kjeang, E.
2016-01-01
Gas diffusion layer (GDL) materials in polymer electrolyte membrane fuel cells (PEMFCs) are commonly made hydrophobic to enhance water management by avoiding liquid water blockage of the pores and facilitating reactant gas transport to the adjacent catalyst layer. In this work, a stochastic microstructural modeling approach is developed to simulate the transport properties of a commercial carbon paper based GDL under a range of PTFE loadings and liquid water saturation levels. The proposed novel stochastic method mimics the GDL manufacturing process steps and resolves all relevant phases including fiber, binder, PTFE, liquid water, and gas. After thorough validation of the general microstructure with literature and in-house data, a comprehensive set of anisotropic transport properties is simulated for the reconstructed GDL in different PTFE loadings and liquid water saturation levels and validated through a comparison with in-house ex situ experimental data and empirical formulations. In general, the results show good agreement between simulated and measured data. Decreasing trends in porosity, gas diffusivity, and permeability is obtained by increasing the PTFE loading and liquid water content, while the thermal conductivity is found to increase with liquid water saturation. Using the validated model, new correlations for saturation dependent GDL properties are proposed.
Directional wetting in anisotropic inverse opals.
Phillips, Katherine R; Vogel, Nicolas; Burgess, Ian B; Perry, Carole C; Aizenberg, Joanna
2014-07-01
Porous materials display interesting transport phenomena due to restricted motion of fluids within the nano- to microscale voids. Here, we investigate how liquid wetting in highly ordered inverse opals is affected by anisotropy in pore geometry. We compare samples with different degrees of pore asphericity and find different wetting patterns depending on the pore shape. Highly anisotropic structures are infiltrated more easily than their isotropic counterparts. Further, the wetting of anisotropic inverse opals is directional, with liquids filling from the side more easily. This effect is supported by percolation simulations as well as direct observations of wetting using time-resolved optical microscopy. PMID:24941308
NASA Technical Reports Server (NTRS)
Gordon, S.
1982-01-01
Thermodynamic and transport combustion properties were calculated for a wide range of conditions for the reaction of hydrocarbons with air. Three hydrogen-carbon atom ratios (H/C = 1.7, 2.0, 2.1) were selected to represent the range of aircraft fuels. For each of these H/C ratios, combustion properties were calculated for the following conditions: Equivalence ratio: 0, 0.25, 0.5, 0.75, 1.0, 1.25 Water - dry air mass ratio: 0, 0.03 Pressure, kPa: 1.01325, 10.1325, 101.325, 1013.25, 5066.25 (or in atm: 0.01, 0.1, 1, 10, 50) Temperature, K: every 10 degrees from 200 to 900 K; every 50 degrees from 900 to 3000 K Temperature, R: every 20 degrees from 360 to 1600 R; very 100 degrees from 1600 to 5400 R. The properties presented are composition, density, molecular weight, enthalphy, entropy, specific heat at constant pressure, volume derivatives, isentropic exponent, velocity of sound, viscosity, thermal conductivity, and Prandtl number. Property tables are based on composites that were calculated by assuming both: (1) chemical equilibrium (for both homogeneous and heterogeneous phases) and (2) constant compositions for all temperatures. Properties in SI units are presented in this report for the Kelvin temperature schedules.
Fabrication and transport properties of silicon nanoelectronic devices
NASA Astrophysics Data System (ADS)
Robinson, Stephen John
It is estimated that the scaling of conventional silicon MOSFETs will end around the year 2020. While this certainly does not preclude the use of silicon in future devices, it does require new thoughts on the types of practical devices that can be used in integrated circuits. Namely, those that reduce power and work at least partly on the principles of quantum mechanics (such as spintronic or tunneling devices) will tend to be favored. The research presented herein is based on the fabrication and transport properties of nanometer-scale devices in silicon. The most promising of these structures are nanowires fabricated with a scanning tunneling microscope (STM). These high-density nanowires display the low-temperature phenomena of weak localization and one-dimensional conduction. Long-term applications of such nanowires and derivative devices include alternatives to conventional CMOS transistors and very sensitive charge and/or spin-detection devices. In addition, focused ion beams (FIBs) have been used to directly and precisely implant ions in the hope that they may be used to contact nanodevices, but surface damage may preclude that possibility.
Cross-plane phonon transport properties of molybdenum disulphide
NASA Astrophysics Data System (ADS)
Wei, Zhiyong; Liu, Biao; Liu, Chenhan; Bi, Kedong; Yang, Juekuan; Chen, Yunfei
2015-11-01
The cross-plane thermal conductivity of a molybdenum disulphide (MoS2) film is calculated from the nonequilibrium molecular dynamics simulation. The results show that, unlike graphite which has a slow convergent speed, the thermal conductivity of MoS2 tends to a convergent value when the film thickness is beyond about 40?nm. We also construct the cross-plane thermal conductivity of bulk MoS2 as an accumulation function of the phonon mean free path (MFP). It is found that phonons with MFPs below 40?nm contribute ~90% of the MoS2 cross-plane thermal conductivity at room temperature. This critical size of the phonon MFP is about two orders of magnitude smaller than that of graphite. Further calculations show that the shorter cross-plane phonon MFPs in bulk MoS2 may result from the lower phonon cut-off frequency and the mismatch of phonon density of state between Mo and S due to the mass difference. The phonon transport properties obtained would be helpful in the design and optimization of MoS2-based devices.
Valuation of utility and transportation property: a classified annotated bibliography
Clatanoff, R.M.
1983-01-01
A selected, classified, annotated bibliography is presented with 270 references to published works on the appraisal and assessment of utilities and transportation companies. It does not include works on the taxation of these enterprises unless material on valuation is included, and it does not include works on valuation unless material on these enterprises is included. The bibliography does not include references to articles on current events; for these the reader should consult such publications as Engineering News-Record; Public Utilities Fortnightly; Commerce Clearing House's State Tax Review (for news of statutory law and regulations), and the Assessment and Valuation Legal Reporter (for news of case law). Works selected for inclusion were chosen primarily from those published since 1970. Charles F. Conlon's 1971 paper, The Unitary Approach to the Appraisal of Public Utility Property for Tax Purposes, concludes with a classified bibliography of publications up to 1970. Certain major pre-1970 works, which readers would expecte to find in a bibliography on this topic, are listed here, as are all the references from an earlier IAAO bibliography (which this one supersedes).
NASA Astrophysics Data System (ADS)
Sahoo, Pranati
Increasing energy demands and decreasing natural energy resources have sparked search for alternative clean and renewable energy sources. For instance, currently there is a tremendous interest in thermoelectric and photovoltaic solar energy production technologies. Half-Heusler (HH) alloys are among the most popular material systems presently under widespread investigations for high temperature thermoelectric energy conversion. Approaches to increase the thermoelectric figure of merit (ZT) of HH range from (1) chemical substitution of atoms with different masses within the same atomic position in the crystal structure to optimize carrier concentration and enhance phonon scattering via mass fluctuation and (2) embedding secondary phonon scattering centers in the matrix (nanostructuring) to further reduce thermal conductivity. This work focuses on three material systems. The first part describes the synthesis and properties (thermal conductivity, electrical conductivity, magnetic) of various oxide nanostructures (NiO, Co3O4) which were subsequently used as inclusion phases in a HH matrix to reduce the thermal conductivity. Detailed reviews of the past efforts along with the current effort to optimize synthetic routes are presented. The effects of the synthesis conditions on the thermoelectric properties of compacted pellets of NiO and Co3O4 are also discussed. The second part of the work discusses the development of synthetic strategies for the fabrication of p-type and n-type bulk nanostructured thermoelectric materials made of a half-Heusler matrix based on (Ti,Hf)CoSb, containing nanostructures with full-Heusler (FH) compositions and structures coherently embedded inside the half-Heusler matrix. The role of the nanostructures in the regulation of phonon and charge carrier transports within the half-heusler matrix is extensively discussed by combining transport data and electron microscopy images. It was found that the FH nanoinclusions form staggered heterojunctions with a valence band (VB) offset energy at the HH/FH phase boundaries. The resulting energy barrier discriminates existing holes with respect to their energy by trapping low energy holes, while promoting the transport of high energy holes through the VB of the FH-quantum dots. This "carrier culling" results in surprisingly large increase in the mobility and the effective mass of high energy holes contributing to electronic conduction. The simultaneous reduction in the density and the increase in the effective mass of holes resulted in large enhancements of the thermopower, whereas the increase in the mobility minimizes the drop in the electrical conductivity. In the third part, the application of this concept of nanostructuring on the Copper Selenide material system is described. Various synthetic approaches such as liquid assisted solid-state reaction and mechanical alloying are utilized for the fabrication of copper selenide compositions. We found that the mechanical alloying clearly decreases the thermal conductivity of the composition as well increases the Seebeck due to decrease in carrier concentrations.
Understanding electronic structure and transport properties in nanoscale junctions
NASA Astrophysics Data System (ADS)
Dhungana, Kamal B.
Understanding the electronic structure and the transport properties of nanoscale materials are pivotal for designing future nano-scale electronic devices. Nanoscale materials could be individual or groups of molecules, nanotubes, semiconducting quantum dots, and biomolecules. Among these several alternatives, organic molecules are very promising and the field of molecular electronics has progressed significantly over the past few decades. Despite these progresses, it has not yet been possible to achieve atomic level control at the metal-molecule interface during a conductance measurement, which hinders the progress in this field. The lack of atomic level information of the interface also makes it much harder for theorist to interpret the experimental results. To identify the junction configuration that possibly exists during the experimental measurement of conductance in molecular junction, we created an ensemble of Ruthanium-bis(terpyridine) molecular devices, and studied the transport behavior in these molecular junctions. This helps us identifying the junction geometry that yields the experimentally measured current-voltage characteristics. Today's electronic devices mostly ignore the spin effect of an electron. The inclusion of spin effect of an electron on solid-state transistor allows us to build more efficient electronic devices; this also alleviates the problem of huge heat dissipation in the nanoscale electronic devices. Different materials have been utilized to build three terminals spin transistor since its inception in 1950. In search of suitable candidates for the molecular spin transistor, we have recently designed a spin-valve transistor based on an organometallic molecule; a large amplification (320 %) in tunnel magneto-resistance (TMR) is found to occur at an experimentally accessible gate field. This suggests that the organic molecules can be utilized for making the next generation three terminal spintronic devices. Similarly, we have designed a spin transistor based on boron nitride nanotube (BNNT) quantum dot. The TMR and exchange energy in BNNT based spin transistor are found to switch sign with the increase of the gate field. The direct application of BNNT in electronic devices in several instances is hindered due to its large band gap. However, the functionalization of BNNT with different foreign species allows us to tune the band gap of BNNT. Fluorine functionalization in BNNT increases its conductance by more then 2 orders, as well as it induces strong magnetism in BNNT. The fluorine functionalization in BNNT thus has opened up the possibility of using the BNNT in future electronics and spintronics. Our study shows that a long range ferromagnetic spin ordering exists in the fluorinated BNNT even at a temperature much above the room temperature. Our spin polarized transport study further shows that the fluorine functionalization in BNNT not only enhances its conductance by more than two orders but also makes it a perfect spin filter with efficiency more than 99%. Our transport study is based upon an orbital dependent density functional theory and a single particle Green's function approach.
NASA Astrophysics Data System (ADS)
Schwen, Andreas; Backus, Jason; Walton, Riley J.; Wendroth, Ole
2014-05-01
Leaching of solutes below the root zone has been identified as a main source of potential groundwater pollution. In structured soils, preferential flow paths can have a significant influence on rapid leaching of solutes. Dye tracer experiments have been frequently used to map the spatial distribution of macropore structures. However, the relative influence of the macropore network on solute leaching under field conditions and its correlation with physical properties of the matric soil (texture, density, mechanical strength) and land use effects have not been analyzed yet and require innovative sampling techniques. The objectives of the present study were to map the macropore network and analyze the leaching behaviour of a conservative tracer under two contrasting land uses. Ponded infiltration experiments with Potassiumbromide (KBr) and Brilliant Blue (BB) were conducted on a silt loam soil in Lexington, KY. Two land use systems, grassland and cropland (wheat), were tested. At soil water content close to field capacity, a total of 30 mm multi-tracer solution was infiltrated on an area of 1.2 × 0.7 m with a ponding head of 20 mm. The concentrations of KBr and BB were 10 and 5 g/L, respectively. After 24 hours, 10 profile sections (width: 100 cm, depth: 70 cm) were excavated in steps of 5 cm and sampled. Dye stained areas were mapped based on digital image analysis. The relative dye coverage was calculated as a function of depth. Vane shear resistance was measured as a proxy for soil mechanical strength. At every other profile section, the soil was sampled for soil water content at regular intervals along a 10 × 10 cm raster. X-ray fluorescence analysis was used to derive concentrations of Br, SiO2 and Al2O3, the latter two being used as proxy for soil particle size distribution. Anisotropic variance and covariance analysis was applied to derive direction-dependent correlations between physical, mechanical, and hydrological observations and to identify the relative influence of the macropore network and land use regime on solute leaching.
NASA Technical Reports Server (NTRS)
Thompson, R. A.
1994-01-01
Accurate numerical prediction of high-temperature, chemically reacting flowfields requires a knowledge of the physical properties and reaction kinetics for the species involved in the reacting gas mixture. Assuming an 11-species air model at temperatures below 30,000 degrees Kelvin, SPECIES (Computer Codes for the Evaluation of Thermodynamic Properties, Transport Properties, and Equilibrium Constants of an 11-Species Air Model) computes values for the species thermodynamic and transport properties, diffusion coefficients and collision cross sections for any combination of the eleven species, and reaction rates for the twenty reactions normally occurring. The species represented in the model are diatomic nitrogen, diatomic oxygen, atomic nitrogen, atomic oxygen, nitric oxide, ionized nitric oxide, the free electron, ionized atomic nitrogen, ionized atomic oxygen, ionized diatomic nitrogen, and ionized diatomic oxygen. Sixteen subroutines compute the following properties for both a single species, interaction pair, or reaction, and an array of all species, pairs, or reactions: species specific heat and static enthalpy, species viscosity, species frozen thermal conductivity, diffusion coefficient, collision cross section (OMEGA 1,1), collision cross section (OMEGA 2,2), collision cross section ratio, and equilibrium constant. The program uses least squares polynomial curve-fits of the most accurate data believed available to provide the requested values more quickly than is possible with table look-up methods. The subroutines for computing transport coefficients and collision cross sections use additional code to correct for any electron pressure when working with ionic species. SPECIES was developed on a SUN 3/280 computer running the SunOS 3.5 operating system. It is written in standard FORTRAN 77 for use on any machine, and requires roughly 92K memory. The standard distribution medium for SPECIES is a 5.25 inch 360K MS-DOS format diskette. The contents of the diskettes are compressed using the PKWARE archiving tools. The utility to unarchive the files, PKUNZIP.EXE, is included. This program was last updated in 1991. SUN and SunOS are registered trademarks of Sun Microsystems, Inc.
Highly anisotropic physics in phosphorene
NASA Astrophysics Data System (ADS)
Ezawa, Motohiko
2015-04-01
Phosphorene, monolayer black phosphorus, is a highly anistropicmaterial, where the band structure is Dirac like in one direction and Schrödinger like in the other direction. We present several analytic formulas to demonstrate the electronic properties. The conductance is highly anisotropic reflecting the anisotropy of the band structure. We also deteminethe cyclotron motion in phosphoreneand Landau level quantization by using the Bohr-Sommerfeldquantization. We show that the Landau-level energy behaves as B2/3 as a function of external magnetic field, which is highly contrasted to the case of graphene where the Landau-level energy behaves as ?B.
Avalanche properties in a transport model based on critical-gradient fluctuation dynamics
Garcia, L.; Carreras, B.A.
2005-09-15
A simple one-dimensional transport model based on critical-gradient fluctuation dynamics is applied to describe some of the properties of plasma-turbulence-induced transport. This model combines avalanche-like transport with diffusion. The particle flux is self-regulated by the stability properties of the fluctuations. A high-gradient edge region emerges where transport dynamics is close to marginal stability. In steady state, the core remains at the subcritical gradient. The avalanches change from quasiperiodic events triggered mostly near the edge region to intermittent transport events depending on the noise level of the particle source.
Correlating Transport Behavior with Cell Properties for Eight Porcine Escherichia coli Isolates
Technology Transfer Automated Retrieval System (TEKTRAN)
In this study we investigate how growth stage and depositional environment affect variability of cell properties and transport behavior of eight porcine E. coli isolates. We compared the surface properties and transport behavior for cells harvested at two different growth stages (exponential and sta...
The synthesis and transport properties of the complex salt /TMPD/ /TCNQ/2
NASA Technical Reports Server (NTRS)
Somoano, R.; Hadek, V.; Yen, S. P. S.; Rembaum, A.; Deck, R.
1975-01-01
The syntheses and transport properties of the complex salt /TMPD/ /TCNQ/2 are described. At high temperatures, the complex is a magnetic semiconductor with transport properties intermediate between those found in the highly conducting and poorly conducting TCNQ salts. The complex undergoes a transition below 50-60 K to a state exhibiting singlet-triplet behavior with weakly alternating exchange coupling.
NASA Technical Reports Server (NTRS)
Gordon, S.; Mcbride, B.; Zeleznik, F. J.
1984-01-01
An addition to the computer program of NASA SP-273 is given that permits transport property calculations for the gaseous phase. Approximate mixture formulas are used to obtain viscosity and frozen thermal conductivity. Reaction thermal conductivity is obtained by the same method as in NASA TN D-7056. Transport properties for 154 gaseous species were selected for use with the program.
Transport properties of multicomponent thermal plasmas: Grad method versus Chapman-Enskog method
Porytsky, P.; Krivtsun, I.; Demchenko, V.; Reisgen, U.; Mokrov, O.; Zabirov, A.; Gorchakov, S.; Timofeev, A.; Uhrlandt, D.
2013-02-15
Transport properties (thermal conductivity, viscosity, and electrical conductivity) for multicomponent Ar-Fe thermal plasmas at atmospheric pressure have been determined by means of two different methods. The transport coefficients set based on Grad's method is compared with the data obtained when using the Chapman-Enskog's method. Results from both applied methods are in good agreement. It is shown that the Grad method is suitable for the determination of transport properties of the thermal plasmas.
Decoupling Mechanical and Ion Transport Properties in Polymer Electrolyte Membranes
NASA Astrophysics Data System (ADS)
McIntosh, Lucas D.
Polymer electrolytes are mixtures of a polar polymer and salt, in which the polymer replaces small molecule solvents and provides a dielectric medium so that ions can dissociate and migrate under the influence of an external electric field. Beginning in the 1970s, research in polymer electrolytes has been primarily motivated by their promise to advance electrochemical energy storage and conversion devices, such as lithium ion batteries, flexible organic solar cells, and anhydrous fuel cells. In particular, polymer electrolyte membranes (PEMs) can improve both safety and energy density by eliminating small molecule, volatile solvents and enabling an all-solid-state design of electrochemical cells. The outstanding challenge in the field of polymer electrolytes is to maximize ionic conductivity while simultaneously addressing orthogonal mechanical properties, such as modulus, fracture toughness, or high temperature creep resistance. The crux of the challenge is that flexible, polar polymers best-suited for polymer electrolytes (e.g., poly(ethylene oxide)) offer little in the way of mechanical robustness. Similarly, polymers typically associated with superior mechanical performance (e.g., poly(methyl methacrylate)) slow ion transport due to their glassy polymer matrix. The design strategy is therefore to employ structured electrolytes that exhibit distinct conducting and mechanically robust phases on length scales of tens of nanometers. This thesis reports a remarkably simple, yet versatile synthetic strategy---termed polymerization-induced phase separation, or PIPS---to prepare PEMs exhibiting an unprecedented combination of both high conductivity and high modulus. This performance is enabled by co-continuous, isotropic networks of poly(ethylene oxide)/ionic liquid and highly crosslinked polystyrene. A suite of in situ, time-resolved experiments were performed to investigate the mechanism by which this network morphology forms, and it appears to be tied to the disordered structure observed in diblock polymer melts near the order-disorder transition. In the resulting solid PEMs, the conductivity and modulus are both high, exceeding the 1 mS/cm and approaching the 1 GPa metrics, respectively, often cited for lithium-metal batteries. In the final chapter, an alternative synthetic route to generate nanostructured PEMs is presented. This strategy relies on the formation of a thermodynamically stable network morphology exhibited by a triblock terpolymer prepared with crosslinking moieties along the backbone. Although the mechanical properties of the resulting PEM are excellent, the conductivity is found to be somewhat limited by network defects that result from the solvent-casting procedure.
Large collective motions regulate the functional properties of glutamate transporter trimers.
Jiang, Jie; Shrivastava, Indira H; Watts, Spencer D; Bahar, Ivet; Amara, Susan G
2011-09-13
Glutamate transporters clear synaptically released glutamate to maintain precise communication between neurons and limit glutamate neurotoxicity. Although much progress has been made on the topology, structure, and function of these carriers, few studies have addressed large-scale structural motions collectively associated with substrate transport. Here we show that a series of single cysteine substitutions in the helical hairpin HP2 of excitatory amino acid transporter 1 form intersubunit disulfide cross-links within the trimer. After cross-linking, substrate uptake, but not substrate-activated anion conductance, is completely inhibited in these mutants. These disulfide bridges link residue pairs > 40 ? apart in the outward-facing crystal structure, and can be explained by concerted subunit movements predicted by the anisotropic network model (ANM). The existence of these global motions is further supported by the observation that single cysteine substitutions at the extracellular part of the transmembrane domain 8 can also be cross-linked by copper phenanthroline as predicted by the ANM. Interestingly, the transport domain in the un-cross-linked subunit of the trimer assumes an inward-facing orientation, suggesting that individual subunits potentially undergo separate transitions between outward- and inward-facing forms, rather than an all-or-none transition of the three subunits, a mechanism also supported by ANM-predicted intrinsic dynamics. These results shed light on how large collective motions contribute to the functional dynamics of glutamate transporters. PMID:21876140
NASA Astrophysics Data System (ADS)
Oganisian, K.; Gluchowski, P.; Kinzhybalo, V.; Macalik, B.; Vogt, A.; Strek, W.
2015-06-01
Novel magnetic iron boron nitride (Fe:BN) composite nanoceramics were fabricated by hot isostatic pressing. Their structure, morphology, magnetic and electronic transport properties were investigated by X-ray diffraction, scanning electron microscopy, magnetic and resistivity measurements. Experimental results show that structure and electric transport properties can be drastically changed for the samples synthesized at similar temperatures but different pressures, whereas their magnetic properties change just slightly. This study demonstrates the possibility of producing the Fe:BN nanoceramics exhibiting high magnetic induction with tunable structure and electronic transport properties.
Fluids in fractal porous media: scaling of transport properties
NASA Astrophysics Data System (ADS)
Toledo, Pedro G.; Ted Davis, H.; Scriven, L. E.
1992-06-01
This work describes recent progress in modeling transport properties of natural porous media at low saturations of a wetting phase, i.e. when total wetting phase saturation Sw is the sum of thin-films and pendular structures inventories. Capillary pressure Pc, hydraulic conductivity Kw, electrical conductivity ? w, and the capillary dispersion coefficient Dc have been observed to obey power laws in the wetting phase saturation. We relate power-law behavior at low wetting phase saturations, i.e. at high capillary pressures, to the thin-film physics of the wetting phase and the fractal character of the pore space of natural porous media. If wetting phase inventory is primarily pendular structures, and if thin films control the hydraulic resistance of wetting phase we deduce the power laws X = SbXw, with X = Pc, Kw, ?w and Dc, where for capillary pressure bPc = -1/(3 - D), for hydraulic conductivity bKw = 3/ m(3 - D), for electrical conductivity b?w = 1/ m(3 - D), and for capillary dispersion coefficient bDc = [3 - m(4 - D)]/ m(3 - D), where m is the exponent in the relation of disjoining pressure and film thickness and D is the fractal dimension of the surface between the pore space and solid matrix. Recent experimental work lends support to these scaling laws in the cases of natural sandstones and clayey soils. Recent displacement experiments show anomalously rapid spreading of wetting liquid during imbibition into a prewet porous medium. We explain this phenomenon, called hyperdispersion, as viscous flow along fractal pore walls in thin films of thickness h governed by disjoining forces and capillarity. Asymptotic analysis of the “capillary diffusion” equation indicates hyperdispersive behavior for -2< bDc <0.
Temperature dependence of transport properties in liquid metals
NASA Astrophysics Data System (ADS)
Sayem El-Daher, Moustafa
2001-12-01
Using the Ziman formula, which results from solving the linearized Boltzmann equation, the electrical and thermal resistivities of selected metals in the liquid state are calculated over a range of temperatures, at and above the melting point. In previous studies of liquid metals, the electrical resistivity was calculated for only a very few cases and only at the melting point. In most cases the calculated structure factor S(q), if used, was obtained from simple models like the hard sphere or empty-core pair potential model. By doing the calculations over a range of temperatures, beyond the melting point and using a better S(q), we gain considerable insight into the transport properties of liquid metals. By calculating the thermal resistivity over the same range of temperatures we explain the deviation of the ratio of electrical and thermal resistivities from the Wiedemann-Franz law, which holds well for lower temperatures. The form factor is calculated for each liquid metal based on the model potential suggested by Taylor et al., including screening effects, by using the screening function of Geldart and Taylor. The liquid structure factors are calculated, in some cases, from the radial distribution function obtained from Monte Carlo simulations based on the same model potential mentioned above and used in the form factor construction. Both the calculated structure factors and the experimental structure factors obtained from x-ray scattering are used in the Ziman formula to obtain the thermal and electrical resistivities. The results are compared to experimental values and to other theoretical calculations done at the melting point for each of the selected metals using different model potentials and form factors or other theoretical methods.
High field transport properties of a bilayer graphene
NASA Astrophysics Data System (ADS)
Bhargavi, K. S.; Kubakaddi, S. S.
2014-02-01
The high electric field transport properties namely, hot electron energy loss rate P, momentum loss rate Q, electron temperature Te and drift velocity Vd are studied theoretically in a bilayer graphene (BLG) by employing the momentum and energy balance technique. P and Q are investigated as a function of Te by considering the electron interaction with the acoustic phonons (APs) and the surface polar phonons (SPPs). In the Bloch-Grüneisen regime P (Q) due to APs is ~Te4 (Te2.5), with a new feature of a kink appearing due to the chiral nature of the electrons. The predicted Te4 is consistent with the recent experimental observation of heat resistance (Yan et al. Nature Nanotechnology 3 (2012) 472 [35]). Hot phonon effect is taken into account for SPPs. A dip has been observed in the hot phonon distribution of SPPs, a new feature, which is not found in conventional two-dimensional electron gas, and this can be attributed to the chiral nature of the electrons. P (Q) due to SPPs is found to be dominant at about Te>150 (180) K for a lattice temperature T=4.2 K. It is observed that the hot phonon effect is found to reduce P and Q due to SPPs significantly. Te and Vd are calculated as a function of the electric field E by taking into account the additional channels for momentum relaxation due to Coulomb impurity (CI) and short-range disorder (SD). Te is found to increase with the increasing electric field and is significantly enhanced by the hot phonon effect. Low field Vd is found to be limited by CI, SD and APs and in the high field region it reaches a near saturation value. The hot phonon effect tends to reduce the value of Vd. The presence of disorders CI and SD reduces Vd significantly and in clean samples larger saturation velocity can be achieved at a relatively smaller E.
Thickness dependence of magnetic and transport properties in organic-CoFe discontinuous multilayers
NASA Astrophysics Data System (ADS)
Wang, W. X.; Wang, Y. P.; Zhang, X.-G.; Wang, Y.; Zou, Jin; Han, X. F.
2010-05-01
Spin-dependent transport measurement in 3-hexadecyl pyrrole (3HDP) with a CoFe layer and the current-in-plane geometry is reported. Transport properties indicate the CoFe layers are discontinuous when their thicknesses are smaller than 6 nm. The temperature dependence of the conductance suggests that the transport mechanism is likely small polaron hopping. The observed positive magnetoresistance ratio at low temperature gives evidence of spin-conserving transport.
Conformally flat polytropes for anisotropic matter
NASA Astrophysics Data System (ADS)
Herrera, L.; Di Prisco, A.; Barreto, W.; Ospino, J.
2014-12-01
We analyze in detail conformally flat spherically symmetric fluid distributions, satisfying a polytropic equation of state. Among the two possible families of relativistic polytropes, only one contains models which satisfy all the required physical conditions. The ensuing configurations are necessarily anisotropic and show interesting physical properties. Prospective applications of the presented models to the study of super-Chandrasekhar white dwarfs, are discussed.
NASA Technical Reports Server (NTRS)
Hansen, C Frederick; Heims, Steve P
1958-01-01
Thermodynamic and transport properties of high temperature air, and the reaction rates for the important chemical processes which occur in air, are reviewed. Semiempirical, analytic expressions are presented for thermodynamic and transport properties of air. Examples are given illustrating the use of these properties to evaluate (1) equilibrium conditions following shock waves, (2) stagnation region heat flux to a blunt high-speed body, and (3) some chemical relaxation lengths in stagnation region flow.
Structural Properties of the Brazilian Air Transportation Network.
Couto, Guilherme S; da Silva, Ana Paula Couto; Ruiz, Linnyer B; Benevenuto, Fabrício
2015-09-01
The air transportation network in a country has a great impact on the local, national and global economy. In this paper, we analyze the air transportation network in Brazil with complex network features to better understand its characteristics. In our analysis, we built networks composed either by national or by international flights. We also consider the network when both types of flights are put together. Interesting conclusions emerge from our analysis. For instance, Viracopos Airport (Campinas City) is the most central and connected airport on the national flights network. Any operational problem in this airport separates the Brazilian national network into six distinct subnetworks. Moreover, the Brazilian air transportation network exhibits small world characteristics and national connections network follows a power law distribution. Therefore, our analysis sheds light on the current Brazilian air transportation infrastructure, bringing a novel understanding that may help face the recent fast growth in the usage of the Brazilian transport network. PMID:26312421
Monotonic solution of heterogeneous anisotropic diffusion problems
NASA Astrophysics Data System (ADS)
Aricò, Costanza; Tucciarelli, Tullio
2013-11-01
Anisotropic problems arise in various areas of science and engineering, for example groundwater transport and petroleum reservoir simulations. The pure diffusive anisotropic time-dependent transport problem is solved on a finite number of nodes, that are selected inside and on the boundary of the given domain, along with possible internal boundaries connecting some of the nodes. An unstructured triangular mesh, that attains the Generalized Anisotropic Delaunay condition for all the triangle sides, is automatically generated by properly connecting all the nodes, starting from an arbitrary initial one. The control volume of each node is the closed polygon given by the union of the midpoint of each side with the “anisotropic” circumcentre of each final triangle. A structure of the flux across the control volume sides similar to the standard Galerkin Finite Element scheme is derived. A special treatment of the flux computation, mainly based on edge swaps of the initial mesh triangles, is proposed in order to obtain a stiffness M-matrix system that guarantees the monotonicity of the solution. The proposed scheme is tested using several literature tests and the results are compared with analytical solutions, as well as with the results of other algorithms, in terms of convergence order. Computational costs are also investigated.
Gravitational stresses in anisotropic rock masses
Amadei, B.; Savage, W.Z.; Swolfs, H.S.
1987-01-01
This paper presents closed-form solutions for the stress field induced by gravity in anisotropic rock masses. These rocks are assumed to be laterally restrained and are modelled as a homogeneous, orthotropic or transversely isotropic, linearly elastic material. The analysis, constrained by the thermodynamic requirement that strain energy be positive definite, gives the following important result: inclusion of anisotropy broadens the range of permissible values of gravity-induced horizontal stresses. In fact, for some ranges of anisotropic rock properties, it is thermodynamically admissible for gravity-induced horizontal stresses to exceed the vertical stress component; this is not possible for the classical isotropic solution. Specific examples are presented to explore the nature of the gravity-induced stress field in anisotropic rocks and its dependence on the type, degree and orientation of anisotropy with respect to the horizontal ground surface. ?? 1987.
Anisotropic power-law k-inflation
NASA Astrophysics Data System (ADS)
Ohashi, Junko; Soda, Jiro; Tsujikawa, Shinji
2013-11-01
It is known that power-law k-inflation can be realized for the Lagrangian P=Xg(Y), where X=-(??)2/2 is the kinetic energy of a scalar field ? and g is an arbitrary function in terms of Y=Xe??/Mpl (? is a constant and Mpl is the reduced Planck mass). In the presence of a vector field coupled to the inflaton with an exponential coupling f(?)?e??/Mpl, we show that the models with the Lagrangian P=Xg(Y) generally give rise to anisotropic inflationary solutions with ?/H=constant, where ? is an anisotropic shear and H is an isotropic expansion rate. Provided these anisotropic solutions exist in the regime where the ratio ?/H is much smaller than 1, they are stable attractors irrespective of the forms of g(Y). We apply our results to concrete models of k-inflation such as the generalized dilatonic ghost condensate and the Dirac-Born-Infeld model and we numerically show that the solutions with different initial conditions converge to the anisotropic power-law inflationary attractors. Even in the de Sitter limit (??0) such solutions can exist, but in this case the null energy condition is generally violated. The latter property is consistent with the Wald’s cosmic conjecture stating that the anisotropic hair does not survive on the de Sitter background in the presence of matter respecting the dominant/strong energy conditions.
Matter sourced anisotropic stress for dark energy
NASA Astrophysics Data System (ADS)
Chang, Baorong; Lu, Jianbo; Xu, Lixin
2014-11-01
Usually a dark energy as a perfect fluid is characterized by the ratio of pressure to energy density (w =p /? ) and the ratio of their perturbations in its rest frame (cs2=? p /? ? ). However, a dark energy would have other characteristics beyond its equation of state and the effective speed of sound. Here the extra property is the anisotropic stress sourced by matter as a simple extension to the perfect fluid model. At the background level, this anisotropic stress is zero with respect to the cosmological principle, but not at the first-order perturbation. We tested the viability of the existence of this kind of anisotropic stress by using the currently available cosmic observations through the geometrical and dynamical measurements. Using the Markov-chain Monte Carlo method, we found that the upper bounds on the anisotropic stress which enters into the summation of the Newtonian potentials should be of the order O (1 0-3)?m . We did not find any strong evidence for the existence of this matter-sourced anisotropic stress, even in the 1 ? region.
Transport and optical properties of low-dimensional complex systems
NASA Astrophysics Data System (ADS)
Iurov, Andrii
Over the last five years of my research work, I, my research was mainly concerned with certain crucial tunneling, transport and optical properties of novel low-dimensional graphitic and carbon-based materials as well as topological insulators. Both single-electron and many-body problems were addressed. We investigated the Dirac electrons transmission through a potential barrier in the presence of circularly polarized light. An anomalous photon-assisted enhanced transmission is predicted and explained in a comparison with the well-known Klein paradox. It is demonstrated that the perfect transmission for nearly-head-on collision in an infinite graphene is suppressed in gapped dressed states of electrons, which is further accompanied by shift of peaks as a function of the incident angle away from the head-on collision. We calculate the energy bands for graphene monolayers when electrons move through a periodic electrostatic potential in the presence of a uniform perpendicular magnetic field. We clearly demonstrate the quantum fractal nature of the energy bands at reasonably low magnetic fields. We present results for the energy bands as functions of both wave number and magnetic flux through the unit cells of the resulting moiÅ•e superlattice. This feature is also observed at extremely high magnetic fields. We have discovered a novel feature in the plasmon excitations for a pair of Coulomb-coupled non-concentric spherical two-dimensional electron gases (S2DEGs). Our results show that the plasmon excitations for such pairs depend on the orientation with respect to the external electromagnetic probe field. The origin of this anisotropy of the inter-sphere Coulomb interaction is due to the directional asymmetry of the electrostatic coupling of electrons in excited states which depend on both the angular momentum quantum number L and its projection M on the axis of quantization taken as the probe E-field direction. Such an effect from the plasmon spatial correlation is expected to be experimentally observable by employing circularly-polarized light or a helical light beam for incidence. The S2DEG serves as a simple model for fullerenes as well as metallic dimers, when the energy bands are far apart. Magnetoplasmons in gapped graphene have been investigated and the exchange energy dependence on magnetic field is presented.
Quantum chaos and electron transport properties in a quantum waveguide
NASA Astrophysics Data System (ADS)
Lee, Hoshik
We numerically investigate electron transport properties in an electron waveguide which can be constructed in 2DEG of the heterostructure of GaAs and AlGaAs. We apply R-matrix theory to solve a Schrodinger equation and construct a S-matrix, and we then calculate conductance of an electron waveguide. We study single impurity scattering in a waveguide. A delta-function model as a single impurity is very attractive, but it has been known that delta-function potential does not give a convergent result in two or higher space dimensions. However, we find that it can be used as a single impurity in a waveguide with the truncation of the number of modes. We also compute conductance for a finite size impurity by using R-matrix theory. We propose an appropriate criteria for determining the cut-off mode for a delta-function impurity that reproduces the conductance of a waveguide when a finite impurity presents. We find quantum scattering echoes in a ripple waveguide. A ripple waveguide (or cavity) is widely used for quantum chaos studies because it is easy to control a particle's dynamics. Moreover we can obtain an exact expression of Hamiltonian matrix with for the waveguide using a simple coordinate transformation. Having an exact Hamiltonian matrix reduces computation time significantly. It saves a lot of computational needs. We identify three families of resonance which correspond to three different classical phase space structures. Quasi bound states of one of those resonances reside on a hetero-clinic tangle formed by unstable manifolds and stable manifolds in the phase space of a corresponding classical system. Resonances due to these states appear in the conductance in a nearly periodic manner as a function of energy. Period from energy frequency gives a good agreement with a prediction of the classical theory. We also demonstrate wavepacket dynamics in a ripple waveguide. We find quantum echoes in the transmitted probability of a wavepacket. The period of echoes also agrees with the classical predictions. We also compute the electron transmission probability through a multi-ripple electron waveguide. We find an effect analogous to the Dicke effect in the multi-ripple electron waveguide. We show that one of the S-matrix poles, that of the super-radiant resonance state, withdraws further from the real axis as each ripple is added. The lifetime of the super-radiant state, for N quantum dots, decreases as 1N . This behavior of the lifetime of the super-radiant state is a signature of the Dicke effect.
Quasiparticle band structures and thermoelectric transport properties of p-type SnSe
Shi, Guangsha; Kioupakis, Emmanouil
2015-02-14
We used density functional and many-body perturbation theory to calculate the quasiparticle band structures and electronic transport parameters of p-type SnSe both for the low-temperature Pnma and high-temperature Cmcm phases. The Pnma phase has an indirect band gap of 0.829?eV, while the Cmcm has a direct band gap of 0.464?eV. Both phases exhibit multiple local band extrema within an energy range comparable to the thermal energy of carriers from the global extrema. We calculated the electronic transport coefficients as a function of doping concentration and temperature for single-crystal and polycrystalline materials to understand the previous experimental measurements. The electronic transport coefficients are highly anisotropic and are strongly affected by bipolar transport effects at high temperature. Our results indicate that SnSe exhibits optimal thermoelectric performance at high temperature when doped in the 10{sup 19}–10{sup 20?}cm{sup ?3} range.
Thermodynamic and transport properties of air/water mixtures
NASA Technical Reports Server (NTRS)
Fessler, T. E.
1981-01-01
Subroutine WETAIR calculates properties at nearly 1,500 K and 4,500 atmospheres. Necessary inputs are assigned values of combinations of density, pressure, temperature, and entropy. Interpolation of property tables obtains dry air and water (steam) properties, and simple mixing laws calculate properties of air/water mixture. WETAIR is used to test gas turbine engines and components operating in relatively humid air. Program is written in SFTRAN and FORTRAN.
EquilTheTA: Thermodynamic and transport properties of complex equilibrium plasmas
Colonna, G.; D'Angola, A.
2012-11-27
EquilTheTA (EQUILibrium for plasma THErmodynamics and Transport Applications) is a web-based software which calculates chemical equilibrium product concentrations from any set of reactants and determines thermodynamic and transport properties for the product mixture in wide temperature and pressure ranges. The program calculates chemical equilibrium by using a hierarchical approach, thermodynamic properties and transport coefficients starting from recent and accurate databases of atomic and molecular energy levels and collision integrals. In the calculations, Debye length and cut-off are consistently updated and virial corrections (up to third order) can be considered. Transport coefficients are calculated by using high order approximations of the Chapman-Enskog method.
Equations of state and transport properties of mixtures in the warm dense regime
Hou, Yong; Dai, Jiayu; Kang, Dongdong; Ma, Wen; Yuan, Jianmin
2015-02-15
We have performed average-atom molecular dynamics to simulate the CH and LiH mixtures in the warm dense regime, and obtained equations of state and the ionic transport properties. The electronic structures are calculated by using the modified average-atom model, which have included the broadening of energy levels, and the ion-ion pair potentials of mixtures are constructed based on the temperature-dependent density functional theory. The ionic transport properties, such as ionic diffusion and shear viscosity, are obtained through the ionic velocity correlation functions. The equations of state and transport properties for carbon, hydrogen and lithium, hydrogen mixtures in a wide region of density and temperature are calculated. Through our computing the average ionization degree, average ion-sphere diameter and transition properties in the mixture, it is shown that transport properties depend not only on the ionic mass but also on the average ionization degree.
Enhancement of non-resonant dielectric cloaks using anisotropic composites
NASA Astrophysics Data System (ADS)
Takezawa, Akihiro; Kitamura, Mitsuru
2014-01-01
Cloaking techniques conceal objects by controlling the flow of electromagnetic waves to minimize scattering. Herein, the effectiveness of homogenized anisotropic materials in non-resonant dielectric multilayer cloaking is studied. Because existing multilayer cloaking by isotropic materials can be regarded as homogenous anisotropic cloaking from a macroscopic view, anisotropic materials can be efficiently designed through optimization of their physical properties. Anisotropic properties can be realized in two-phase composites if the physical properties of the material are within appropriate bounds. The optimized anisotropic physical properties are identified by a numerical optimization technique based on a full-wave simulation using the finite element method. The cloaking performance measured by the total scattering width is improved by about 2.8% and 25% in eight- and three-layer cylindrical cloaking materials, respectively, compared with multilayer cloaking by isotropic materials. In all cloaking examples, the optimized microstructures of the two-phase composites are identified as the simple lamination of two materials, which maximizes the anisotropy. The same performance as published for eight-layer cloaking by isotropic materials is achieved by three-layer cloaking using the anisotropic material. Cloaking with an approximately 50% reduction of total scattering width is achieved even in an octagonal object. Since the cloaking effect can be realized using just a few layers of the laminated anisotropic dielectric composite, this may have an advantage in the mass production of cloaking devices.
Enhancement of non-resonant dielectric cloaks using anisotropic composites
Takezawa, Akihiro Kitamura, Mitsuru
2014-01-15
Cloaking techniques conceal objects by controlling the flow of electromagnetic waves to minimize scattering. Herein, the effectiveness of homogenized anisotropic materials in non-resonant dielectric multilayer cloaking is studied. Because existing multilayer cloaking by isotropic materials can be regarded as homogenous anisotropic cloaking from a macroscopic view, anisotropic materials can be efficiently designed through optimization of their physical properties. Anisotropic properties can be realized in two-phase composites if the physical properties of the material are within appropriate bounds. The optimized anisotropic physical properties are identified by a numerical optimization technique based on a full-wave simulation using the finite element method. The cloaking performance measured by the total scattering width is improved by about 2.8% and 25% in eight- and three-layer cylindrical cloaking materials, respectively, compared with multilayer cloaking by isotropic materials. In all cloaking examples, the optimized microstructures of the two-phase composites are identified as the simple lamination of two materials, which maximizes the anisotropy. The same performance as published for eight-layer cloaking by isotropic materials is achieved by three-layer cloaking using the anisotropic material. Cloaking with an approximately 50% reduction of total scattering width is achieved even in an octagonal object. Since the cloaking effect can be realized using just a few layers of the laminated anisotropic dielectric composite, this may have an advantage in the mass production of cloaking devices.
41 CFR 302-7.10 - Is property acquired en route eligible for transportation at Government expense?
Code of Federal Regulations, 2010 CFR
2010-07-01
... PROPERTY 7-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL BOOKS, PAPERS, AND EQUIPMENT (PBP&E) General Rules Â§ 302-7.10 Is property acquired en route eligible for transportation...
41 CFR 302-7.11 - Is property acquired en route eligible for transportation at Government expense?
Code of Federal Regulations, 2013 CFR
2013-07-01
... PROPERTY 7-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL BOOKS, PAPERS, AND EQUIPMENT (PBP&E) General Rules Â§ 302-7.11 Is property acquired en route eligible for transportation...
41 CFR 302-7.10 - Is property acquired en route eligible for transportation at Government expense?
Code of Federal Regulations, 2011 CFR
2011-07-01
... PROPERTY 7-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL BOOKS, PAPERS, AND EQUIPMENT (PBP&E) General Rules Â§ 302-7.10 Is property acquired en route eligible for transportation...
41 CFR 302-7.11 - Is property acquired en route eligible for transportation at Government expense?
Code of Federal Regulations, 2012 CFR
2012-07-01
... PROPERTY 7-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL BOOKS, PAPERS, AND EQUIPMENT (PBP&E) General Rules Â§ 302-7.11 Is property acquired en route eligible for transportation...
NASA Astrophysics Data System (ADS)
Zhou, Jiawei; Liao, Bolin; Chen, Gang
2016-04-01
The transport properties of semiconductors are key to the performance of many solid-state devices (transistors, data storage, thermoelectric cooling and power generation devices, etc). An understanding of the transport details can lead to material designs with better performances. In recent years simulation tools based on first-principles calculations have been greatly improved, being able to obtain the fundamental ground-state properties of materials (such as band structure and phonon dispersion) accurately. Accordingly, methods have been developed to calculate the transport properties based on an ab initio approach. In this review we focus on the thermal, electrical, and thermoelectric transport properties of semiconductors, which represent the basic transport characteristics of the two degrees of freedom in solidsâ€”electronic and lattice degrees of freedom. Starting from the coupled electron-phonon Boltzmann transport equations, we illustrate different scattering mechanisms that change the transport features and review the first-principles approaches that solve the transport equations. We then present the first-principles results on the thermal and electrical transport properties of semiconductors. The discussions are grouped based on different scattering mechanisms including phonon-phonon scattering, phonon scattering by equilibrium electrons, carrier scattering by equilibrium phonons, carrier scattering by polar optical phonons, scatterings due to impurities, alloying and doping, and the phonon drag effect. We show how the first-principles methods allow one to investigate transport properties with unprecedented detail and also offer new insights into the electron and phonon transport. The current status of the simulation is mentioned when appropriate and some of the future directions are also discussed.
Magnetic and transport properties of Co1±? Cr2?? Se4
NASA Astrophysics Data System (ADS)
Svitlyk, Volodymyr; Kolodiazhnyi, Taras; Cranswick, Lachlan M. D.; Luke, Graeme; Mozharivskyj, Yurij
2015-10-01
Single crystals of {{{Co}}}1+/- ? {{{Cr}}}2\\mp ? {{{Se}}}4 were grown using chemical vapor method with CrCl3 as a transporting agent. Magnetic measurements on the {{{Co}}}1+/- ? {{{Cr}}}2\\mp ? {{{Se}}}4 crystals confirm an antiferromagnetic ordering below the Neel temperature of T N = 230 K. Neutron diffraction studies performed on the {{{Co}}}1+/- ? {{{Cr}}}2\\mp ? {{{Se}}}4 powder show that the long-range antiferromagnetic ordering is accompanied by a doubling of the c crystallographic axe. For the {{{Co}}}1+/- ? {{{Cr}}}2\\mp ? {{{Se}}}4 single crystals electrical resistivity displays an anisotropic behavior: resistivitiy within the (100) plane increases till T N and then decreases as temperature increases. Resistivity in the orthogonal direction increases with temperature with a change in the slope above T N. Muon spin relaxation experiments on the {{{Co}}}1+/- ? {{{Cr}}}2\\mp ? {{{Se}}}4 crystals confirm both the long-range magnetic order and ordering temperature established by other techniques.
NASA Astrophysics Data System (ADS)
Pérez, Claudio; Bianchi, María Martha; Gassmann, Marisa; Pisso, Ignacio
2014-05-01
Accumulated pollen in stratified fossil reservoirs is used to infer temporal changes in vegetation composition. Transport and dispersal by winds are known to introduce large biases in the interpretation of polynic records. In order to calibrate the models used to infer information about past species distributions, human activities and climate, contemporary time series of polynic records are assessed and modelled. In this study we analyse measurements collected hourly in Bariloche, Argentina (41° 10' S, 71° 15' W, 850 masl) of the species Weinmannia trichosperma, a characteristic forest tree which grows only the western (Chilean) slopes of the Andes, but not on the eastern (Argentinian) slopes where the measurements were collected. Instead of the simplistic Gaussian plume mixing model that is usually employed by the palynological community, we apply a full 3D Lagrangian dispersion model to interpret the observations and assess the impact of long-range transport over the Andean mountain range. The Lagrangian calculation of the origins of the air masses (the "backward footprint") is consistent not only with the Chilean Weinmania pollen measurements but also with a set of species only found on the dryer steppe located to the east of the measurement site in Argentina. The agreement of the modelling results indicates that significant interpretation mistakes may arise from inconsistent transport treatment. We also discuss the further application of inverse trajectory modelling to the estimation of source intensity.
NASA Astrophysics Data System (ADS)
Gutzov, S.; Danchova, N.; Tsekov, R.; Barreno, I.; Ruiz del Portal, X.; Ulbikas, J.
2015-10-01
A new hybrid woven micromesh containing metal and polyester wires with a 2D porosity of about 30% has been created. The anisotropic microcomposite is developed as a new material with wide applications in thermal and electrical engineering. The mesh material is carefully characterized using electron microscopy, fluorescence microscopy, chemical analysis, thermal conductivity measurements and differential scanning calorimetry.
Anisotropic eddy viscosity models
NASA Technical Reports Server (NTRS)
Carati, D.; Cabot, W.
1996-01-01
A general discussion on the structure of the eddy viscosity tensor in anisotropic flows is presented. The systematic use of tensor symmetries and flow symmetries is shown to reduce drastically the number of independent parameters needed to describe the rank 4 eddy viscosity tensor. The possibility of using Onsager symmetries for simplifying further the eddy viscosity is discussed explicitly for the axisymmetric geometry.
Anisotropic Ambient Volume Shading.
Ament, Marco; Dachsbacher, Carsten
2016-01-01
We present a novel method to compute anisotropic shading for direct volume rendering to improve the perception of the orientation and shape of surface-like structures. We determine the scale-aware anisotropy of a shading point by analyzing its ambient region. We sample adjacent points with similar scalar values to perform a principal component analysis by computing the eigenvectors and eigenvalues of the covariance matrix. In particular, we estimate the tangent directions, which serve as the tangent frame for anisotropic bidirectional reflectance distribution functions. Moreover, we exploit the ratio of the eigenvalues to measure the magnitude of the anisotropy at each shading point. Altogether, this allows us to model a data-driven, smooth transition from isotropic to strongly anisotropic volume shading. In this way, the shape of volumetric features can be enhanced significantly by aligning specular highlights along the principal direction of anisotropy. Our algorithm is independent of the transfer function, which allows us to compute all shading parameters once and store them with the data set. We integrated our method in a GPU-based volume renderer, which offers interactive control of the transfer function, light source positions, and viewpoint. Our results demonstrate the benefit of anisotropic shading for visualization to achieve data-driven local illumination for improved perception compared to isotropic shading. PMID:26529745
Guedj, C.; Hung, L.; Sottile, F.; Zobelli, A.; Blaise, P.; Olevano, V.
2014-12-01
The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO{sub 2}) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO{sub 2}, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO{sub 2} may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectric permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.
NASA Astrophysics Data System (ADS)
Guedj, C.; Hung, L.; Zobelli, A.; Blaise, P.; Sottile, F.; Olevano, V.
2014-12-01
The effect of nanocrystal orientation on the energy loss spectra of monoclinic hafnia (m-HfO2) is measured by high resolution transmission electron microscopy (HRTEM) and valence energy loss spectroscopy (VEELS) on high quality samples. For the same momentum-transfer directions, the dielectric properties are also calculated ab initio by time-dependent density-functional theory (TDDFT). Experiments and simulations evidence anisotropy in the dielectric properties of m-HfO2, most notably with the direction-dependent oscillator strength of the main bulk plasmon. The anisotropic nature of m-HfO2 may contribute to the differences among VEELS spectra reported in literature. The good agreement between the complex dielectric permittivity extracted from VEELS with nanometer spatial resolution, TDDFT modeling, and past literature demonstrates that the present HRTEM-VEELS device-oriented methodology is a possible solution to the difficult nanocharacterization challenges given in the International Technology Roadmap for Semiconductors.
Functional properties of ion channels and transporters in tumour vascularization
Fiorio Pla, Alessandra; Munaron, Luca
2014-01-01
Vascularization is crucial for solid tumour growth and invasion, providing metabolic support and sustaining metastatic dissemination. It is now accepted that ion channels and transporters play a significant role in driving the cancer growth at all stages. They may represent novel therapeutic, diagnostic and prognostic targets for anti-cancer therapies. On the other hand, although the expression and role of ion channels and transporters in the vascular endothelium is well recognized and subject of recent reviews, only recently has their involvement in tumour vascularization been recognized. Here, we review the current literature on ion channels and transporters directly involved in the angiogenic process. Particular interest will be focused on tumour angiogenesis in vivo as well as in the different steps that drive this process in vitro, such as endothelial cell proliferation, migration, adhesion and tubulogenesis. Moreover, we compare the ‘transportome’ system of tumour vascular network with the physiological one. PMID:24493751
Transport properties of novel molybdenum bronze oxide materials
NASA Astrophysics Data System (ADS)
Hagmann, Joseph; Le, Son; Schneemeyer, Lynn; Olsen, Patti; Siegrist, Theo; Richter, Curt; Seiler, David
2015-03-01
Reduced ternary molybdenum oxides, or bronzes, offer an attractive materials platform to study a wide variety of remarkable physical phenomena, including charge density waves and superconductivity, in a system with highly varied structural chemistry. Interesting electronic behaviors in these materials arise from the strong hybridization of the 4d states of high-valent Mo with O p orbitals (conditions amenable to itinerancy) and reduced dimensionality arising from ordered O vacancies. This study aims to demonstrate the transport phenomena in a series of novel molybdenum bronze materials, including the new electrochemically-grown molybdenum bronzes, K3Li3Mo15O47, and the rare earth molybdenum bronze, HoMo16O44, and relate these behaviors to their experimentally-characterized structures. Dependence of the transport behavior on numerous experimental parameters, including temperature, magnetic field, drive voltage and drive current, and gate voltage, is presented to fully reveal charge carrier transport in these materials.
NASA Technical Reports Server (NTRS)
Lanyi, Janos K.
1977-01-01
Cell envelope vesicles prepared from H. halobium contain bacteriorhodopsin and upon illumination protons are ejected. Coupled to the proton motive force is the efflux of Na(+). Measurements of Na-22 flux, exterior pH change, and membrane potential, Delta(psi) (with the dye 3,3'-dipentyloxadicarbocyanine) indicate that the means of Na(+) transport is sodium/proton exchange. The kinetics of the pH changes and other evidence suggests that the antiport is electrogenic (H(+)/Na(++ greater than 1). The resulting large chemical gradient for Na(+) (outside much greater than inside), as well as the membrane potential, will drive the transport of 18 amino acids. The I9th, glutamate, is unique in that its accumulation is indifferent to Delta(psi): this amino acid is transported only when a chemical gradient for Na(+) is present. Thus, when more and more NaCl is included in the vesicles glutamate transport proceeds with longer and longer lags. After illumination the gradient of H+() collapses within 1 min, while the large Na(+) gradient and glutamate transporting activity persists for 10- 15 min, indicating that proton motive force is not necessary for transport. A chemical gradient of Na(+), arranged by suspending vesicles loaded with KCl in NaCl, drives glutamate transport in the dark without other sources of energy, with V(sub max) and K(sub m) comparable to light-induced transport. These and other lines of evidence suggest that the transport of glutamate is facilitated by symport with Na(+), in an electrically neutral fashion, so that only the chemical component of the Na(+) gradient is a driving force.
Transport properties of high-temperature air in a magnetic field
Bruno, D.; Capitelli, M.; Catalfamo, C.; Giordano, D.
2011-01-15
Transport properties of equilibrium air plasmas in a magnetic field are calculated with the Chapman-Enskog method. The range considered for the temperature is [50-50 000] K and for the magnetic induction is [0-300] T.
NASA Astrophysics Data System (ADS)
He, Jing-Jing; Yan, Xiao-Hong; Guo, Yan-Dong; Liu, Chun-Sheng; Xiao, Yang; Meng, Lan
2016-02-01
The electron transport properties of zigzag graphene nanoribbons (ZGNRs) with upright standing carbon chains are investigated by using first-principles calculations. The calculated results show a significant odd-even dependence. The currents of even-numbered chain configurations are small because a suppression emerges around the Fermi energy in the transmission spectra under a finite bias. However the I - V curves of odd-numbered chain structures display metallic properties with a big transmission peak in the transmission spectra, indicating the high conductance. These properties offer an interesting method by modifying the odd-even parity of the carbon chains to tune the electron transport properties of ZGNRS.
Kondo effect goes anisotropic in vanadate oxide superlattices
NASA Astrophysics Data System (ADS)
Rotella, H.; Pautrat, A.; Copie, O.; Boullay, P.; David, A.; Mercey, B.; Morales, M.; Prellier, W.
2015-11-01
We study the transport properties in SrVO3/LaVO3 (SVO/LVO) superlattices deposited on SrTiO3 (STO) substrates. We show that the electronic conduction occurs in the metallic LVO layers with a galvanomagnetism typical of a 2D Fermi surface. In addition, a Kondo-like component appears in both the thermal variation of resistivity and the magnetoresistance. Surprisingly, in this system where the STO interface does not contribute to the measured conduction, the Kondo correction is strongly anisotropic. We show that the growth temperature allows a direct control of this contribution. Finally, the key role of vanadium mixed valency stabilized by oxygen vacancies is enlightened.
Kondo effect goes anisotropic in vanadate oxide superlattices.
Rotella, H; Pautrat, A; Copie, O; Boullay, P; David, A; Mercey, B; Morales, M; Prellier, W
2015-11-01
We study the transport properties in SrVO3/LaVO3 (SVO/LVO) superlattices deposited on SrTiO3 (STO) substrates. We show that the electronic conduction occurs in the metallic LVO layers with a galvanomagnetism typical of a 2D Fermi surface. In addition, a Kondo-like component appears in both the thermal variation of resistivity and the magnetoresistance. Surprisingly, in this system where the STO interface does not contribute to the measured conduction, the Kondo correction is strongly anisotropic. We show that the growth temperature allows a direct control of this contribution. Finally, the key role of vanadium mixed valency stabilized by oxygen vacancies is enlightened. PMID:26444931
Anisotropic magnetoresistance effect in sub-micron nickel disks
NASA Astrophysics Data System (ADS)
Wren, T.; Kazakova, O.
2015-05-01
The hysteretic transport properties of vortex states in sub-micron nickel disks are measured using the anisotropic magnetoresistance (AMR) effect and correlated with the magnetization state of the disks using in-situ magnetic force microscopy and micromagnetic modelling. The magnetoresistance behavior is described by a simple AMR model; however, the nucleation and annihilation fields of the vortex state differ when the magnetic field is applied parallel (0°) or perpendicular (90°) to the applied current within the sample plane. In the 0° orientation, the vortex magnetoresistance behaves similar to that reported in the literature. However, in the 90° orientation, the vortex nucleates and annihilates at lower applied fields than in the 0° orientation. Moreover, in the latter orientation, the annihilation process occurs in a two-step transition. This difference is attributed to the effect of the inhomogeneous current distribution within the magnetic disk.
Surface and Subsurface Solute Transport Properties at Row and Inter-Row Positions
Technology Transfer Automated Retrieval System (TEKTRAN)
Although numerous studies have investigated the effects of crop production practices on soil water dynamics, not much information is available on the impact of row position on solute transport. A field experiment was carried out to evaluate surface and subsurface solute transport properties in plant...
Walker Diffusion Method for Calculation of Transport Properties of Finite Composite Systems
Van Siclen, Clinton D
2002-01-01
A heterogeneous medium may be represented by a scalar field of local transport coefficients (e.g., conductivity) or by a “resistor network” derived from that scalar field. In either case the effective (macroscopic) and local (microscopic) transport properties may be calculated by the walker diffusion method. Some sample calculations for disordered systems are presented to demonstrate the method.
Bolster, C H; Haznedaroglu, B Z; Walker, S L
2009-01-01
Escherichia coli is a commonly used indicator organism for detecting the presence of fecal-borne pathogenic microorganisms in water supplies. The importance of E. coli as an indicator organism has led to numerous studies looking at cell properties and transport behavior of this microorganism. In many of these studies, however, only a single strain of E. coli was used even though research has shown that significant genetic variability exists among different strains of E. coli. If this genetic diversity results in differences in cell properties that affect transport, different strains of E. coli may exhibit different rates of transport in the environment. Therefore, the objectives of our study were to investigate the variability in surface characteristics and transport behavior of E. coli isolates obtained from six different sources: beef cattle, dairy cattle, horse, human, poultry, and wildlife. Cell properties such as electrophoretic mobility, cell size and shape, hydrophobicity, charge density, and extracellular polymeric substance composition were measured for each isolate. In addition, the transport behavior of each isolate was assessed by measuring transport through 10-cm packed beds of clean quartz sand. Our results show a large diversity in cell properties and transport behavior for the different E. coli isolates. This diversity in transport behavior must be taken into account when making assessments of the suitability of using E. coli as an indicator organism for specific pathogenic microorganisms in groundwater environments as well as modeling the movement of E. coli in the subsurface. PMID:19202016
The phase diagram and transport properties for hydrogen-helium fluid planets
NASA Technical Reports Server (NTRS)
Stevenson, D. J.; Salpeter, E. E.
1977-01-01
The properties of pure hydrogen and helium are examined, taking into account metallic hydrogen, molecular hydrogen, and the molecular-metallic transition. Metallic hydrogen-helium mixtures are considered along with molecular hydrogen-helium mixtures, the total phase diagram, and minor constituents, including deuterium. The transport properties of the metallic and the molecular phase are also discussed, giving attention to electrical conductivity, thermal conductivity, viscosity, self-diffusion, interdiffusion, radiative opacity, and second-order transport coefficients.
A generalized anisotropic deformation formulation for geomaterials
NASA Astrophysics Data System (ADS)
Lei, Z.; Rougier, Esteban; Knight, E. E.; Munjiza, A.; Viswanathan, H.
2015-10-01
In this paper, the combined finite-discrete element method (FDEM) has been applied to analyze the deformation of anisotropic geomaterials. In the most general case geomaterials are both non-homogeneous and non-isotropic. With the aim of addressing anisotropic material problems, improved 2D FDEM formulations have been developed. These formulations feature the unified hypo-hyper elastic approach combined with a multiplicative decomposition-based selective integration for volumetric and shear deformation modes. This approach is significantly different from the co-rotational formulations typically encountered in finite element codes. Unlike the co-rotational formulation, the multiplicative decomposition-based formulation naturally decomposes deformation into translation, rotation, plastic stretches, elastic stretches, volumetric stretches, shear stretches, etc. This approach can be implemented for a whole family of finite elements from solids to shells and membranes. This novel 2D FDEM based material formulation was designed in such a way that the anisotropic properties of the solid can be specified in a cell by cell basis, therefore enabling the user to seed these anisotropic properties following any type of spatial variation, for example, following a curvilinear path. In addition, due to the selective integration, there are no problems with volumetric or shear locking with any type of finite element employed.
Transport Properties of the Dust Components in Weakly Ionized Plasma
Vaulina, O. S.; Adamovich, X. G.; Petrov, O. F.; Fortov, V. E.
2008-09-07
The experimental study of transport processes are presented for the dusty plasma in radio-frequency (RF-) capacitive discharge. Validity of the Langevin and Green-Kubo equations for the description of dynamics of dusty grains is verified. Experimental examination of the Einstein-Stokes relation between the viscosity and diffusion constants is carried out.
Characterization of an Anisotropic Hydrogel Tissue Substrate for Infusion Testing
Lee, Sung Jin; Pishko, Gregory L.; Astary, Garret W.; Mareci, Thomas H.; Sarntinoranont, Malisa
2010-01-01
Artificial tissue models that capture specific transport properties are useful for investigating physical phenomena important to drug delivery. In this study, an in vitro tissue model was developed and characterized with the goal of mimicking aligned tissue. An anisotropic porous medium was developed by the construction of a 1% agarose hydrogel implanted with different volume fractions (~ 5, 10, and 20%) of 10-?m-diameter glass fibers. The developed substrate was able to capture anisotropic transport after the direct infusion of a macromolecular tracer, Evans blue albumin (EBA). To further characterize the test substrate, the diffusion tensor of water was measured by diffusion tensor imaging, and the ratios of the diffusivities in the directions parallel and perpendicular to the glass fibers were 1.16, 1.20, and 1.26 for 5, 10, and 20% fiber volume fractions, respectively. The hydraulic conductivity was estimated by the measurement of pressure gradients across samples under controlled microflow conditions in the direction parallel to implanted fibers. The hydraulic conductivities at various hydrogel concentrations without fibers and in a 1% hydrogel with various fiber volume fractions were measured; for example, K|| = 1.20 × 10?12 m4 N?1 s?1 (where K|| is the conductivity component in the direction parallel to the glass fibers) for 20% fiber volume fractions. Also, EBA distributions were fit to porous medium transport models to estimate hydraulic conductivity in the direction perpendicular to glass fibers. The estimated ratio of directional hydraulic conductivity, K||/K? (where K? is the conductivity component in the direction perpendicular to the glass fibers), ranged from approximately 3 to 5, from 6 to 10, and from 40 to 90 for 5, 10, and 20% fiber volume fractions, respectively. These agarose hydrogel models provided convenient media for quantifying infusion protocols at low flow rates. PMID:20852678
Anisotropic conductivity tensor imaging using magnetic induction tomography.
Gürsoy, D; Scharfetter, H
2010-08-01
Magnetic induction tomography aims to reconstruct the electrical conductivity distribution of the human body using non-contact measurements. The potential of the method has been demonstrated by various simulation studies and a number of phantom experiments. These studies have all relied on models having isotropic distributions of conductivity, although the human body has a highly heterogeneous structure with partially anisotropic properties. Therefore, whether the conventional modeling approaches used so far are appropriate for clinical applications or not is still an open question. To investigate the problem, we performed a simulation study to investigate the feasibility of (1) imaging anisotropic perturbations within an isotropic medium and (2) imaging isotropic perturbations inside a partially anisotropic background. The first is the case for the imaging of anomalies that have anisotropic characteristics and the latter is the case e.g. in lung imaging where an anisotropic skeletal muscle tissue surrounds the lungs and the rib cage. An anisotropic solver based on the singular value decomposition was used to attain conductivity tensor images to be compared with the ones obtained from isotropic solvers. The results indicate the importance of anisotropic modeling in order to obtain satisfactory reconstructions, especially for the imaging of the anisotropic anomalies, and address the resolvability of the conductivity tensor components. PMID:20647614
Murray, Chris; Allen-King, Richelle; Weissmann, Gary
2006-06-01
This project is testing the hypothesis that sedimentary lithofacies determine the geochemical and physical hydrologic properties that control reactive solute transport (Figure 1). We are testing that hypothesis for one site, a portion of the saturated zone at the Hanford Site (Ringold Formation), and for a model solute, carbon tetrachloride (CT). The representative geochemical and physical aquifer properties selected for quantification in the proposed project are the properties that control CT transport: hydraulic conductivity (K) and reactivity (sorption distribution coefficient, Kd, and anaerobic transformation rate constant, kn). We are combining observations at outcrop analog sites (to measure lithofacies dimensions and statistical relations) with measurements from archived and fresh core samples (for geochemical experiments and to provide additional constraint to the stratigraphic model) from the Ringold Formation to place local-scale lithofacies successions, and their distinct hydrologic property distributions, into the basinal context, thus allowing us to estimate the spatial distributions of properties that control reactive solute transport in the subsurface.
Symersky, Jindrich; Guo, Yi; Wang, Jimin; Lu, Min
2015-11-01
NorM from Neisseria gonorrhoeae (NorM-NG) belongs to the multidrug and toxic compound extrusion (MATE) family of membrane-transport proteins, which can extrude cytotoxic chemicals across cell membranes and confer multidrug resistance. Here, the structure determination of NorM-NG is described, which had been hampered by low resolution (? 4 Å), data anisotropy and pseudo-merohedral twinning. The crystal structure was solved using molecular replacement and was corroborated by conducting a difference Fourier analysis. The NorM-NG structure displays an extracellular-facing conformation, similar to that of NorM-NG bound to a crystallization chaperone. The approaches taken to determine the NorM-NG structure and the lessons learned from this study are discussed, which may be useful for analyzing X-ray diffraction data with similar shortcomings. PMID:26527145
Comparison on thermal transport properties of graphene and phosphorene nanoribbons
NASA Astrophysics Data System (ADS)
Peng, Xiao-Fang; Chen, Ke-Qiu
2015-11-01
We investigate ballistic thermal transport at low temperatures in graphene and phosphorene nanoribbons (PNRS) modulated with a double-cavity quantum structure. A comparative analysis for thermal transport in these two kinds of nanomaterials is made. The results show that the thermal conductance in PNRS is greater than that in graphene nanoribbons (GNRS). The ratio kG/kP (kG is the thermal conductivity in GNRS and kP is the thermal conductivity in PNRS) decreases with lower temperature or for narrower nanoribbons, and increases with higher temperature or for wider nanoribbons. The greater thermal conductance and thermal conductivity in PNRS originate from the lower cutoff frequencies of the acoustic modes.
Comparison on thermal transport properties of graphene and phosphorene nanoribbons
Peng, Xiao-Fang; Chen, Ke-Qiu
2015-01-01
We investigate ballistic thermal transport at low temperatures in graphene and phosphorene nanoribbons (PNRS) modulated with a double-cavity quantum structure. A comparative analysis for thermal transport in these two kinds of nanomaterials is made. The results show that the thermal conductance in PNRS is greater than that in graphene nanoribbons (GNRS). The ratio kG/kP (kG is the thermal conductivity in GNRS and kP is the thermal conductivity in PNRS) decreases with lower temperature or for narrower nanoribbons, and increases with higher temperature or for wider nanoribbons. The greater thermal conductance and thermal conductivity in PNRS originate from the lower cutoff frequencies of the acoustic modes. PMID:26577958
Comparison on thermal transport properties of graphene and phosphorene nanoribbons.
Peng, Xiao-Fang; Chen, Ke-Qiu
2015-01-01
We investigate ballistic thermal transport at low temperatures in graphene and phosphorene nanoribbons (PNRS) modulated with a double-cavity quantum structure. A comparative analysis for thermal transport in these two kinds of nanomaterials is made. The results show that the thermal conductance in PNRS is greater than that in graphene nanoribbons (GNRS). The ratio kG/kP (kG is the thermal conductivity in GNRS and kP is the thermal conductivity in PNRS) decreases with lower temperature or for narrower nanoribbons, and increases with higher temperature or for wider nanoribbons. The greater thermal conductance and thermal conductivity in PNRS originate from the lower cutoff frequencies of the acoustic modes. PMID:26577958
The effect of electron induced hydrogenation of graphene on its electrical transport properties
Woo, Sung Oh; Teizer, Winfried; WPI-Advanced Institute for Materials Research, Tohoku University, Sendai
2013-07-22
We report a deterioration of the electrical transport properties of a graphene field effect transistor due to energetic electron irradiation on a stack of Poly Methyl Methacrylate (PMMA) on graphene (PMMA/graphene bilayer). Prior to electron irradiation, we observed that the PMMA layer on graphene does not deteriorate the carrier transport of graphene but improves its electrical properties instead. As a result of the electron irradiation on the PMMA/graphene bilayer, the Raman “D” band appears after removal of PMMA. We argue that the degradation of the transport behavior originates from the binding of hydrogen generated during the PMMA backbone secession process.
Understanding hopping transport and thermoelectric properties of conducting polymers
NASA Astrophysics Data System (ADS)
Ihnatsenka, S.; Crispin, X.; Zozoulenko, I. V.
2015-07-01
We calculate the conductivity ? and the Seebeck coefficient S for the phonon-assisted hopping transport in conducting polymers poly(3,4-ethylenedioxythiophene) or PEDOT, experimentally studied by Bubnova et al. [J. Am. Chem. Soc. 134, 16456 (2012)], 10.1021/ja305188r. We use the Monte Carlo technique as well as the semianalytical approach based on the transport energy concept. We demonstrate that both approaches show a good qualitative agreement for the concentration dependence of ? and S . At the same time, we find that the semianalytical approach is not in a position to describe the temperature dependence of the conductivity. We find that both Gaussian and exponential density of states (DOS) reproduce rather well the experimental data for the concentration dependence of ? and S giving similar fitting parameters of the theory. The obtained parameters correspond to a hopping model of localized quasiparticles extending over 2-3 monomer units with typical jumps over a distance of 3-4 units. The energetic disorder (broadening of the DOS) is estimated to be 0.1 eV. Using the Monte Carlo calculation we reproduce the activation behavior of the conductivity with the calculated activation energy close to the experimentally observed one. We find that for a low carrier concentration a number of free carriers contributing to the transport deviates strongly from the measured oxidation level. Possible reasons for this behavior are discussed. We also study the effect of the dimensionality on the charge transport by calculating the Seebeck coefficient and the conductivity for the cases of three-, two-, and one-dimensional motion.
Theoretical studies of the transport properties in compound semiconductors
NASA Technical Reports Server (NTRS)
Segall, Benjamin
1994-01-01
This final report is an overview of the work done on Cooperative Agreement NCC 3-55 with the Solid State Technology Branch of the NASA-Lewis Research Center (LeRC). Over the period of time that the agreement was in effect, the principal investigator and, in the last three years, the co-principal investigator worked on a significant number of projects and interacted with members of the Solid State Technology (SST) branch in a number of different ways. For the purpose of this report, these efforts will be divided into five categories: 1) work directly with experimental electrical transport studies conducted by members of the SST branch; 2) theoretical work on electrical transport in compound semiconductors; 3) electronic structure calculations which are relevant to the electrical transport in polytypes of SiC and SiC-AlN alloys; 4) the electronic structure calculations of polar interfaces; and 5) consultative and supportive activities related to experiments and other studies carried out by SST branch members. Work in these categories is briefly discussed.
Nonconformal viscous anisotropic hydrodynamics
NASA Astrophysics Data System (ADS)
Bazow, Dennis; Heinz, Ulrich; Martinez, Mauricio
2015-06-01
We generalize the derivation of viscous anisotropic hydrodynamics from kinetic theory to allow for nonzero particle masses. The macroscopic theory is obtained by taking moments of the Boltzmann equation after expanding the distribution function around a spheroidally deformed local momentum distribution whose form has been generalized by the addition of a scalar field that accounts nonperturbatively (i.e., already at leading order) for bulk viscous effects. Hydrodynamic equations for the parameters of the leading-order distribution function and for the residual (next-to-leading order) dissipative flows are obtained from the three lowest moments of the Boltzmann equation. The approach is tested for a system undergoing (0 +1 )-dimensional boost-invariant expansion for which the exact solution of the Boltzmann equation in the relaxation time approximation is known. Nonconformal viscous anisotropic hydrodynamics is shown to approximate this exact solution more accurately than any other known hydrodynamic approximation.
Parallel Anisotropic Tetrahedral Adaptation
NASA Technical Reports Server (NTRS)
Park, Michael A.; Darmofal, David L.
2008-01-01
An adaptive method that robustly produces high aspect ratio tetrahedra to a general 3D metric specification without introducing hybrid semi-structured regions is presented. The elemental operators and higher-level logic is described with their respective domain-decomposed parallelizations. An anisotropic tetrahedral grid adaptation scheme is demonstrated for 1000-1 stretching for a simple cube geometry. This form of adaptation is applicable to more complex domain boundaries via a cut-cell approach as demonstrated by a parallel 3D supersonic simulation of a complex fighter aircraft. To avoid the assumptions and approximations required to form a metric to specify adaptation, an approach is introduced that directly evaluates interpolation error. The grid is adapted to reduce and equidistribute this interpolation error calculation without the use of an intervening anisotropic metric. Direct interpolation error adaptation is illustrated for 1D and 3D domains.
Electronic and transport properties of PSi@MoS2 nanocables.
Sun, Cuicui; Zhang, Guiling; Shang, Yan; Yang, Zhao-Di; Sun, Xiaojun
2016-02-01
Electronic structures and transport properties of prototype MoS2 nanotube (15, 0) nanocables, including undoped PSi@MoS2 and B- and P-doped PSi@MoS2 (where PSi refers to polysilane), are investigated using the density functional theory (DFT) and the non-equilibrium Green's function (NEGF) methods. It is found that transport properties of two-probe systems by sandwiching finite long nanocables between two Au electrodes are basically in agreement with the electronic structures of their corresponding infinitely long systems. Encapsulating undoped and doped PSi nanowires inside the MoS2 nanotubes could not significantly affect the electronic and transport properties. B-doping and P-doping upon PSi play different roles in the electronic and transport properties. B-doping may exert constructive and destructive effects on electron transport depending on its position and applied bias direction, while P-doping displays a negligible effect. In addition, we found that bi-doping by two adjacent B atoms could slightly enhance the conductivity. These results could offer some clues for conducting experiments to achieve nanoelectronic devices with intrinsic transport properties of MoS2 nanotubes. PMID:26648018
Scaling properties and anomalous transport of particles inside the stochastic layer
NASA Astrophysics Data System (ADS)
Zaslavsky, G. M.; Abdullaev, S. S.
1995-05-01
Particle motion in a two-wave field is considered as a model for studying the kinetic (transport) properties inside the stochastic layer. The existence of an exact renormalization invariance of the separatrix with respect to the perturbation parameter and the approximate renormalization invariance for the exact equation of motion near a saddle point is shown. High accuracy symplectic integration is used to obtain the distribution function, its moments, and transport exponents. Scaling properties and anomalous transport have been found. It is shown that, depending on the parameters of the system, there is a possibility of modifying the fine (islands) structure of the stochastic layer, which leads to variations of the transport properties from the anomalous to the normal (Gaussian) ones.
NASA Astrophysics Data System (ADS)
Tsai, C. Y.; Chen, H. R.; Chang, F. C.; Kuo, H. H.; Cheng, H. M.; Tsai, W. C.; Chu, Y. H.; Lai, C. H.; Hsieh, W. F.
2014-04-01
We investigate the anisotropic stress dependent magnetic and phonon behaviors in self-assembled CoFe2O4-PbTiO3 (CFO-PTO) nanostructures deposited on SrRuO3 buffered SrTiO3 substrates of various thickness. The increased vertical compressed stress with increasing thickness enhances the vertical magnetic anisotropy of CFO while gradually reducing the vertical polarization of PTO. By applying the magnetic-field dependent Raman scattering, the CFO-A1g and T2g(1) phonon frequencies shift oppositely because of the magnetostriction. Moreover, the PTO-A1 mode intensities anomalously enhance and the A1 and E mode frequencies, respectively, increase and decrease, which prove the existence of the stress-mediated magnetoelectric (ME) effect. This study shows that the ME transmission process is dominated by interfacial stress, which is critical for enhancing the ME efficiency.
Anisotropic Total Variation Filtering
Grasmair, Markus; Lenzen, Frank
2010-12-15
Total variation regularization and anisotropic filtering have been established as standard methods for image denoising because of their ability to detect and keep prominent edges in the data. Both methods, however, introduce artifacts: In the case of anisotropic filtering, the preservation of edges comes at the cost of the creation of additional structures out of noise; total variation regularization, on the other hand, suffers from the stair-casing effect, which leads to gradual contrast changes in homogeneous objects, especially near curved edges and corners. In order to circumvent these drawbacks, we propose to combine the two regularization techniques. To that end we replace the isotropic TV semi-norm by an anisotropic term that mirrors the directional structure of either the noisy original data or the smoothed image. We provide a detailed existence theory for our regularization method by using the concept of relaxation. The numerical examples concluding the paper show that the proposed introduction of an anisotropy to TV regularization indeed leads to improved denoising: the stair-casing effect is reduced while at the same time the creation of artifacts is suppressed.
Microsphere-chain waveguides: Focusing and transport properties
Allen, Kenneth W. Astratov, Vasily N.; Darafsheh, Arash; Abolmaali, Farzaneh; Mojaverian, Neda; Limberopoulos, Nicholaos I.; Lupu, Anatole
2014-07-14
It is shown that the focusing properties of polystyrene microsphere-chain waveguides (MCWs) formed by sufficiently large spheres (Dâ€‰â‰¥â€‰20Î», where D is the sphere diameter and Î» is the wavelength of light) scale with the sphere diameter as predicted by geometrical optics. However, this scaling behavior does not hold for mesoscale MCWs with Dâ€‰â‰¤â€‰10Î» resulting in a periodical focusing with gradually reducing beam waists and in extremely small propagation losses. The observed effects are related to properties of nanojet-induced and periodically focused modes in such structures. The results can be used for developing focusing microprobes, laser scalpels, and polarization filters.
Transport properties in a superconducting proximity sandwich, Kondo effect
Mori, N.
1981-04-01
Temperature-dependent properties are evaluated in a superconducting Kondo alloy induced by the proximity effect. These include (i) the order parameter, (ii) the dc Josephson current, and (iii) the thermal conductivity and ultrasonic attenuation, in the case when there is reentance of superconductivity. The calculations are based on the theory given by Kaiser, in which the McMillan tunneling model and the Mueller-Hartmann-Zittartz theory are combined. The temperature dependence of pair-breaking is reflected directly in the above properties in much the same way as in an intrinsic Kondo superconductor, indicating that proximity-effect studies may provide detailed information on the Kondo effect in superconductivity.
NASA Astrophysics Data System (ADS)
Swanson, Ryan D.; Binley, Andrew; Keating, Kristina; France, Samantha; Osterman, Gordon; Day-Lewis, Frederick D.; Singha, Kamini
2015-02-01
The advection-dispersion equation (ADE) fails to describe commonly observed non-Fickian solute transport in saturated porous media, necessitating the use of other models such as the dual-domain mass-transfer (DDMT) model. DDMT model parameters are commonly calibrated via curve fitting, providing little insight into the relation between effective parameters and physical properties of the medium. There is a clear need for material characterization techniques that can provide insight into the geometry and connectedness of pore spaces related to transport model parameters. Here, we consider proton nuclear magnetic resonance (NMR), direct-current (DC) resistivity, and complex conductivity (CC) measurements for this purpose, and assess these methods using glass beads as a control and two different samples of the zeolite clinoptilolite, a material that demonstrates non-Fickian transport due to intragranular porosity. We estimate DDMT parameters via calibration of a transport model to column-scale solute tracer tests, and compare NMR, DC resistivity, CC results, which reveal that grain size alone does not control transport properties and measured geophysical parameters; rather, volume and arrangement of the pore space play important roles. NMR cannot provide estimates of more-mobile and less-mobile pore volumes in the absence of tracer tests because these estimates depend critically on the selection of a material-dependent and flow-dependent cutoff time. Increased electrical connectedness from DC resistivity measurements are associated with greater mobile pore space determined from transport model calibration. CC was hypothesized to be related to length scales of mass transfer, but the CC response is unrelated to DDMT.
Localized Spectroscopy of Anisotropic Superconductors
NASA Astrophysics Data System (ADS)
Byers, Jeff M.
Both the experimental and theoretical aspects of high-temperature superconductivity have challenged condensed matter physics. In order to find the mechanism behind the pairing interaction responsible for superconductivity in the cuprates, one of the most useful pieces of information is the symmetry of the superconducting order parameter. To date the determination of this vital piece of information has not reached any clear consensus despite much effort. One means of probing the order parameter symmetry of a superconductor is through the energy gap that quasiparticles experience near the Fermi surface. By obtaining information on how the the gap varies as a function of momentum, one acquires the ability to compare the different proposed mechanisms. This dissertation offers a new perspective on probing the anisotropy of the superconducting gap via localized tunneling spectroscopy. The advent of scanning tunneling microscopy/scanning tunneling spectroscopy (STM/STS) and nanofabrication has opened up new possibilities for directly exploring the physics of systems at short length scales and doing so with sub-meV energy resolution typical of tunneling experiments. STM imaging of a superconducting surface does not probe the superconducting gap anisotropy but rather the angle-averaged gap, however, if translational symmetry is broken by an impurity or nanofabricated object then the spatial correlations around the site are shown to reveal the anisotropy of the superconducting gap. The basic theory for localized tunneling spectroscopy of a superconductor both in and out of equilibrium is presented via the Keldysh nonequilibrium Green's function technique. Numerical calculations are done for the case of spatial correlations around an impurity on the surface of a superconductor with an anisotropic gap. A detailed calculation is presented for the transport and interference effects between two nanofabricated point contacts on the surface of a grounded anisotropic superconductor.
NASA Technical Reports Server (NTRS)
Svehla, R. A.; Mcbride, B. J.
1973-01-01
A FORTRAN IV computer program for the calculation of the thermodynamic and transport properties of complex mixtures is described. The program has the capability of performing calculations such as:(1) chemical equilibrium for assigned thermodynamic states, (2) theoretical rocket performance for both equilibrium and frozen compositions during expansion, (3) incident and reflected shock properties, and (4) Chapman-Jouguet detonation properties. Condensed species, as well as gaseous species, are considered in the thermodynamic calculation; but only the gaseous species are considered in the transport calculations.
Rice, Pamela J; Horgan, Brian P; Rittenhouse, Jennifer L
2010-06-01
The off-site transport of pesticides with runoff is both an agronomic and environmental concern, resulting from reduced control of target pests in the area of application and contamination of surrounding ecosystems. Experiments were designed to measure the quantity of pesticides in runoff from creeping bentgrass (Agrostis palustris) turf managed as golf course fairway to gain a better understanding of factors that influence chemical availability and mass transport. Less than 1 to 23% of applied chloropyrifos, flutolanil, mecoprop-p (MCPP), dimethylamine salt of 2,4-dichlorophenoxyacetic acid (2,4-D), or dicamba was measured in edge-of-plot runoff when commercially available pesticide formulations were applied at label rates 23 +/- 9 h prior to simulated precipitation (62 +/- 13 mm). Time differential between hollow tine core cultivation and runoff did not significantly influence runoff volumes or the percentage of applied chemicals transported in the runoff. With the exception of chlorpyrifos, all chemicals of interest were detected in the initial runoff samples and throughout the runoff events. Chemographs of the five pesticides followed trends in agreement with mobility classifications associated with their soil organic carbon partition coefficient (K(OC).) Data collected from the present study provides information on the transport of chemicals with runoff from turf, which can be used in model simulations to predict nonpoint source pollution potentials and estimate ecological risks. PMID:20821562
Technology Transfer Automated Retrieval System (TEKTRAN)
The off-site transport of pesticides with runoff is both an agronomic and environmental concern resulting from reduced control of target pests in the area of application and contamination of surrounding ecosystems. Experiments were designed to measure the quantity of pesticides in runoff from creepi...
Direct pore-scale computation of material and transport properties for North Sea reservoir rocks
NASA Astrophysics Data System (ADS)
Øren, P.-E.; Bakke, S.; Held, R.
2007-12-01
This work investigates two complex, heterogeneous sandstone lithofacies in a North Sea petroleum reservoir field. We compare samples acquired by X-ray microtomography with numerically reconstructed lithofacies, obtained from a geological process based reconstruction technique. Effective material and transport properties of these digitized rocks, such as electrical resistivity, elastic moduli, fluid permeability, and magnetic resonance (NMR), are computed. The comparison largely reveals an excellent agreement of calculated effective properties between the actual and reconstructed pore structures. A dependence of the effective properties on the specific mineralogy could be investigated in case of the reconstructed rocks. Our results allow for an interpretation of trends in effective medium properties and facilitate the construction of cross-property relations for the investigated lithofacies. The present study demonstrates the potential and feasibility of combining computer generated rocks with numerical calculations to derive material and transport properties for reservoir rocks.
Transport properties of droplet clusters in gravity-free fields
NASA Technical Reports Server (NTRS)
Brenner, Howard
1986-01-01
Clusters of liquid droplets are suspended in an atmosphere of saturated vapor and are subjected to an external force field. This system can be modeled as a continuum whose macroscopic properties may be determined by applying the generalized theory of Taylor dispersion.
Renormalized anisotropic exchange for representing heat assisted magnetic recording media
Jiao, Yipeng; Liu, Zengyuan; Victora, R. H.
2015-05-07
Anisotropic exchange has been incorporated in a description of magnetic recording media near the Curie temperature, as would be found during heat assisted magnetic recording. The new parameters were found using a cost function that minimized the difference between atomistic properties and those of renormalized spin blocks. Interestingly, the anisotropic exchange description at 1.5?nm discretization yields very similar switching and magnetization behavior to that found at 1.2?nm (and below) discretization for the previous isotropic exchange. This suggests that the increased accuracy of anisotropic exchange may also reduce the computational cost during simulation.
Renormalized anisotropic exchange for representing heat assisted magnetic recording media
NASA Astrophysics Data System (ADS)
Jiao, Yipeng; Liu, Zengyuan; Victora, R. H.
2015-05-01
Anisotropic exchange has been incorporated in a description of magnetic recording media near the Curie temperature, as would be found during heat assisted magnetic recording. The new parameters were found using a cost function that minimized the difference between atomistic properties and those of renormalized spin blocks. Interestingly, the anisotropic exchange description at 1.5 nm discretization yields very similar switching and magnetization behavior to that found at 1.2 nm (and below) discretization for the previous isotropic exchange. This suggests that the increased accuracy of anisotropic exchange may also reduce the computational cost during simulation.
Thermal transport and fire retardance properties of cellular aluminum alloys
Lu, T.J.; Chen, C.
1999-03-31
Closed-cell aluminum alloy foams exhibit exceptional resistance to fire. It is unclear why this happens, although the protection imparted by oxide Al{sub 2}O{sub 3} layers has been suggested. This work attempts to uncover the thermal transport processes in metallic foams. The apparent thermal conductivities of two-dimensional foams having a variety of cellular microstructures are first calculated. These include regular honeycombs, Voronoi structures and Johnson-Mehl models. The effects of several types of geometric imperfection--Plateau borders, cell-edge misalignments, fractured cell edges, missing cells, inclusions and cell size variations--are studied by using analytical as well as finite element methods. The focus is on metallic foams where the transport of heat is dominated by solid conduction and thermal radiation; contributions from gaseous conduction and convection are neglected. The coupling of solid conduction with thermal radiation is dealt with by using the method of finite elements. These results are then applied to solve the transient temperature field of a cellular metal plate subjected to a sudden introduction of a high-temperature source of heat such as fire. The factors which dictate the thermal and structural fire retardance of cellular metallic foams are identified.
Electron transport properties of sub-3-nm diameter copper nanowires
NASA Astrophysics Data System (ADS)
Jones, Sarah L. T.; Sanchez-Soares, Alfonso; Plombon, John J.; Kaushik, Ananth P.; Nagle, Roger E.; Clarke, James S.; Greer, James C.
2015-09-01
Density functional theory and density functional tight binding are applied to model electron transport in copper nanowires of approximately 1- and 3-nm diameters with varying crystal orientation and surface termination. The copper nanowires studied are found to be metallic irrespective of diameter, crystal orientation, and/or surface termination. Electron transmission is highly dependent on crystal orientation and surface termination. Nanowires oriented along the [110] crystallographic axis consistently exhibit the highest electron transmission while surface oxidized nanowires show significantly reduced electron transmission compared to unterminated nanowires. Transmission per unit area is calculated in each case; for a given crystal orientation we find that this value decreases with diameter for unterminated nanowires but is largely unaffected by diameter in surface oxidized nanowires for the size regime considered. Transmission pathway plots show that transmission is larger at the surface of unterminated nanowires than inside the nanowire and that transmission at the nanowire surface is significantly reduced by surface oxidation. Finally, we present a simple model which explains the transport per unit area dependence on diameter based on transmission pathways results.
Properties of Ca2+ Transport in Mitochondria of Drosophila melanogaster*
von Stockum, Sophia; Basso, Emy; Petronilli, Valeria; Sabatelli, Patrizia; Forte, Michael A.; Bernardi, Paolo
2011-01-01
We have studied the pathways for Ca2+ transport in mitochondria of the fruit fly Drosophila melanogaster. We demonstrate the presence of ruthenium red (RR)-sensitive Ca2+ uptake, of RR-insensitive Ca2+ release, and of Na+-stimulated Ca2+ release in energized mitochondria, which match well characterized Ca2+ transport pathways of mammalian mitochondria. Following larger matrix Ca2+ loading Drosophila mitochondria underwent spontaneous RR-insensitive Ca2+ release, an event that in mammals is due to opening of the permeability transition pore (PTP). Like the PTP of mammals, Drosophila Ca2+-induced Ca2+ release could be triggered by uncoupler, diamide, and N-ethylmaleimide, indicating the existence of regulatory voltage- and redox-sensitive sites and was inhibited by tetracaine. Unlike PTP-mediated Ca2+ release in mammals, however, it was (i) insensitive to cyclosporin A, ubiquinone 0, and ADP; (ii) inhibited by Pi, as is the PTP of yeast mitochondria; and (iii) not accompanied by matrix swelling and cytochrome c release even in KCl-based medium. We conclude that Drosophila mitochondria possess a selective Ca2+ release channel with features intermediate between the PTP of yeast and mammals. PMID:21984833
Studies of Transport Properties of Fractures: Final Report
Stephen R. Brown
2006-06-30
We proposed to study several key factors controlling the character and evolution of fracture system permeability and transport processes. We suggest that due to surface roughness and the consequent channeling in single fractures and in fracture intersections, the tendency of a fracture system to plug up, remain permeable, or for permeability to increase due to chemical dissolution/precipitation conditions will depend strongly on the instantaneous flow channel geometry. This geometry will change as chemical interaction occurs, thus changing the permeability through time. To test this hypothesis and advance further understanding toward a predictive capability, we endeavored to physically model and analyze several configurations of flow and transport of inert and chemically active fluids through channels in single fractures and through fracture intersections. This was an integrated program utilizing quantitative observations of fractures and veins in drill core, quantitative and visual observations of flow and chemical dissolution and precipitation within replicas of real rough-walled fractures and fracture intersections, and numerical modeling via lattice Boltzmann methods.
Data-driven imaging in anisotropic media
Volker, Arno; Hunter, Alan
2012-05-17
Anisotropic materials are being used increasingly in high performance industrial applications, particularly in the aeronautical and nuclear industries. Some important examples of these materials are composites, single-crystal and heavy-grained metals. Ultrasonic array imaging in these materials requires exact knowledge of the anisotropic material properties. Without this information, the images can be adversely affected, causing a reduction in defect detection and characterization performance. The imaging operation can be formulated in two consecutive and reciprocal focusing steps, i.e., focusing the sources and then focusing the receivers. Applying just one of these focusing steps yields an interesting intermediate domain. The resulting common focus point gather (CFP-gather) can be interpreted to determine the propagation operator. After focusing the sources, the observed travel-time in the CFP-gather describes the propagation from the focus point to the receivers. If the correct propagation operator is used, the measured travel-times should be the same as the time-reversed focusing operator due to reciprocity. This makes it possible to iteratively update the focusing operator using the data only and allows the material to be imaged without explicit knowledge of the anisotropic material parameters. Furthermore, the determined propagation operator can also be used to invert for the anisotropic medium parameters. This paper details the proposed technique and demonstrates its use on simulated array data from a specimen of Inconel single-crystal alloy commonly used in the aeronautical and nuclear industries.
NASA Astrophysics Data System (ADS)
Auroy, M.; Poyet, S.; Le Bescop, P.; Torrenti, J.-M.
2013-07-01
Within the context of long-lived intermediate level radioactive waste geological disposal, reinforced concrete would be used. In service life conditions, the concrete structures would be subjected to drying and carbonation. Carbonation relates to the reaction between carbon dioxide (CO2) and the main hydrates of the cement paste (portlandite and C-S-H). Beyond the fall of the pore solution pH, indicative of steel depassivation, carbonation induces mineralogical and microstructural changes (due to portlandite and C-S-H dissolution and calcium carbonate precipitation). This results in the modification of the transport properties, which can impact the structure durability. Because concrete durability depends on water transport, this study focuses on the influence of carbonation on water transport properties. In fact, the transport properties of sound materials are known but they still remain to be assessed for carbonated ones. An experimental program has been designed to investigate the transport properties in carbonated materials. Four hardened cement pastes, differing in mineralogy, are carbonated in an accelerated carbonation device (in controlled environmental conditions) at CO2 partial pressure of about 3%. Once fully carbonated, all the data needed to describe water transport, using a simplified approach, will be evaluated.
Electronic transport properties of one dimensional lithium nanowire using density functional theory
Thakur, Anil; Kumar, Arun; Chandel, Surjeet; Ahluwalia, P. K.
2015-05-15
Single nanowire electrode devices are a unique platform for studying as energy storage devices. Lithium nanowire is of much importance in lithium ion batteries and therefore has received a great deal of attention in past few years. In this paper we investigated structural and electronic transport properties of Li nanowire using density functional theory (DFT) with SIESTA code. Electronic transport properties of Li nanowire are investigated theoretically. The calculations are performed in two steps: first an optimized geometry for Li nanowire is obtained using DFT calculations, and then the transport relations are obtained using NEGF approach. SIESTA and TranSIESTA simulation codes are used in the calculations correspondingly. The electrodes are chosen to be the same as the central region where transport is studied, eliminating current quantization effects due to contacts and focusing the electronic transport study to the intrinsic structure of the material. By varying chemical potential in the electrode regions, an I-V curve is traced which is in agreement with the predicted behavior. Agreement of bulk properties of Li with experimental values make the study of electronic and transport properties in lithium nanowires interesting because they are promising candidates as bridging pieces in nanoelectronics. Transmission coefficient and V-I characteristic of Li nano wire indicates that Li nanowire can be used as an electrode device.
Electronic transport properties of one dimensional lithium nanowire using density functional theory
NASA Astrophysics Data System (ADS)
Thakur, Anil; Kumar, Arun; Chandel, Surjeet; Ahluwalia, P. K.
2015-05-01
Single nanowire electrode devices are a unique platform for studying as energy storage devices. Lithium nanowire is of much importance in lithium ion batteries and therefore has received a great deal of attention in past few years. In this paper we investigated structural and electronic transport properties of Li nanowire using density functional theory (DFT) with SIESTA code. Electronic transport properties of Li nanowire are investigated theoretically. The calculations are performed in two steps: first an optimized geometry for Li nanowire is obtained using DFT calculations, and then the transport relations are obtained using NEGF approach. SIESTA and TranSIESTA simulation codes are used in the calculations correspondingly. The electrodes are chosen to be the same as the central region where transport is studied, eliminating current quantization effects due to contacts and focusing the electronic transport study to the intrinsic structure of the material. By varying chemical potential in the electrode regions, an I-V curve is traced which is in agreement with the predicted behavior. Agreement of bulk properties of Li with experimental values make the study of electronic and transport properties in lithium nanowires interesting because they are promising candidates as bridging pieces in nanoelectronics. Transmission coefficient and V-I characteristic of Li nano wire indicates that Li nanowire can be used as an electrode device.
Collective Transport Properties of Driven Skyrmions with Random Disorder
NASA Astrophysics Data System (ADS)
Reichhardt, C.; Ray, D.; Reichhardt, C. J. Olson
2015-05-01
We use particle-based simulations to examine the static and driven collective phases of Skyrmions interacting with random quenched disorder. We show that nondissipative effects due to the Magnus term reduce the depinning threshold and strongly affect the Skyrmion motion and the nature of the dynamic phases. The quenched disorder causes the Hall angle to become drive dependent in the moving Skyrmion phase, while different flow regimes produce distinct signatures in the transport curves. For weak disorder, the Skyrmions form a pinned crystal and depin elastically, while for strong disorder the system forms a pinned amorphous state that depins plastically. At high drives the Skyrmions can dynamically reorder into a moving crystal, with the onset of reordering determined by the strength of the Magnus term.
Collective transport properties of driven Skyrmions with random disorder.
Reichhardt, C; Ray, D; Reichhardt, C J Olson
2015-05-29
We use particle-based simulations to examine the static and driven collective phases of Skyrmions interacting with random quenched disorder. We show that nondissipative effects due to the Magnus term reduce the depinning threshold and strongly affect the Skyrmion motion and the nature of the dynamic phases. The quenched disorder causes the Hall angle to become drive dependent in the moving Skyrmion phase, while different flow regimes produce distinct signatures in the transport curves. For weak disorder, the Skyrmions form a pinned crystal and depin elastically, while for strong disorder the system forms a pinned amorphous state that depins plastically. At high drives the Skyrmions can dynamically reorder into a moving crystal, with the onset of reordering determined by the strength of the Magnus term. PMID:26066455
Electrical transport properties of CaB6
NASA Astrophysics Data System (ADS)
Stankiewicz, Jolanta; SesÃ©, Javier; Balakrishnan, Geetha; Fisk, Zachary
2014-10-01
We report results from a systematic electron-transport study in a broad temperature range on 12 CaB6 single crystals. None of the crystals were intentionally doped. The different carrier densities observed presumably arise from slight variations in the Ca:B stoichiometry. In these crystals, the variation of the electrical resistivity and of the Hall effect with temperature can be consistently accounted for by the model we propose, in which B-antisite defects (B atom replacing Ca atom) are "amphoteric." The magnetotransport measurements reveal that most of the samples we have studied are close to a metal-insulator transition at low temperatures. The magnetoresistance changes smoothly from negativeâ€”for weakly metallic samplesâ€”to positive valuesâ€”for samples in a localized regime.
Quantum Hall ferromagnets and transport properties of buckled Dirac materials
NASA Astrophysics Data System (ADS)
Luo, Wenchen; Chakraborty, Tapash
2015-10-01
We study the ground states and low-energy excitations of a generic Dirac material with spin-orbit coupling and a buckling structure in the presence of a magnetic field. The ground states can be classified into three types under different conditions: SU(2), easy-plane, and Ising quantum Hall ferromagnets. For the SU(2) and the easy-plane quantum Hall ferromagnets there are goldstone modes in the collective excitations, while all the modes are gapped in an Ising-type ground state. We compare the Ising quantum Hall ferromagnet with that of bilayer graphene and present the domain-wall solution at finite temperatures. We then specify the phase transitions and transport gaps in silicene in Landau levels 0 and 1. The phase diagram depends strongly on the magnetic field and the dielectric constant. We note that there exist triple points in the phase diagrams in Landau level N =1 that could be observed in experiments.
Spin-polarized transport properties of GdN nanocontacts
NASA Astrophysics Data System (ADS)
Sivkov, Ilia N.; Brovko, Oleg O.; Stepanyuk, Valeri S.
2014-05-01
Gadolinium nitride (GdN) nanocontacts were recently experimentally shown to be efficient spin filters. Our study is aimed at identifying and analyzing the physical processes responsible for the high spin polarization of the tunneling current in GdN nanostructures. By the example of planar contacts and atomic chains attached to Cu electrodes we assert, using first principle techniques, that a 100% spin-filtering effect can be indeed achieved in GdN nanocontacts. Our analysis shows that the spin filtering is due to the predominant role of nitrogen majority p states in the electron transport, while minority conductance decays exponentially with contact size due to the presence of a minority band gap at the Fermi level. Additionally, GdN zigzag infinite chains are found to be as efficient spin filters as their planar contact counterparts, also exhibiting a 100% spin-filtering effect, which is robust against chain geometry changes.
Charge transport properties of CdMnTe radiation detectors
Kim K.; Rafiel, R.; Boardman, M.; Reinhard, I.; Sarbutt, A.; Watt, G.; Watt, C.; Uxa, S.; Prokopovich, D.A.; Belas, E.; Bolotnikov, A.E.; James, R.B.
2012-04-11
Growth, fabrication and characterization of indium-doped cadmium manganese telluride (CdMnTe)radiation detectors have been described. Alpha-particle spectroscopy measurements and time resolved current transient measurements have yielded an average charge collection efficiency approaching 100 %. Spatially resolved charge collection efficiency maps have been produced for a range of detector bias voltages. Inhomogeneities in the charge transport of the CdMnTe crystals have been associated with chains of tellurium inclusions within the detector bulk. Further, it has been shown that the role of tellurium inclusions in degrading chargecollection is reduced with increasing values of bias voltage. The electron transit time was determined from time of flight measurements. From the dependence of drift velocity on applied electric field the electron mobility was found to be n = (718 55) cm2/Vs at room temperature.
Synthesis and properties of hole-transporting fluorene linked bistriphenylamine
NASA Astrophysics Data System (ADS)
Promarak, Vinich; Ichikawa, Musubu; Sudyoadsuk, Taweesak; Saengsuwan, Sayant; Keawin, Tinnagon
2007-11-01
An amorphous hole-transporting material, 2,7-bis(4-diphenylaminophenyl)-9,9-bis-n-hexylfluorene (DAF), was synthesized by Suzuki cross-coupling reaction. DAF showed UV-vis absorption bands at 301 and 370 nm in dichloromethane solution and the photoluminescence spectrum showed a maximum peak at 426 nm in a purplish blue region. Cyclic voltammetry (CV) and differential scanning calorimetry (DSC) analysis revealed that DAF was an electrochemically stable amorphous material. It was fabricated as HTL with the device configuration of ITO/DAF/Alq3/LiF:Al. A bright green emission from Alq3 layer with a maximum brightness of 6500 cd/m2 was observed at 15 V and a low turn-on voltage of 3.8 V.
Transport properties of ferromagnet/insulator/semiconductor tunnel junctions
NASA Astrophysics Data System (ADS)
Manago, T.; Suzuki, Y.; Tamura, E.
2002-06-01
Spin-dependent transport of the photoexcited electrons in the semiconductor (p-GaAs)/insulator (Al2O3)/ferromagnetic metal (permalloy) junctions was investigated. As samples, homogeneous tunneling junctions were prepared on the flat and As-defect-free GaAs(111)B homoepitaxial surface by in situ oxidation of the Al layer and successive metallization by permalloy deposition. Spin-polarized electrons were excited in the GaAs by circularly polarized light and injected into the permalloy layer. Since the permalloy has almost zero magnetic circular dichroism at the vicinity of the band gap energy of GaAs, we can detect spin-dependent current exclusively. As a result, the energy dependence of the observed helicity asymmetry (1.44-3.05 eV) of the photoinduced current shows the absence of the spin-dependent tunneling in the sample. The importance of controlling the electron lifetime to obtain the spin-dependent tunneling was discussed.
Anisotropic quantum boxes in corrugated superlattices
NASA Astrophysics Data System (ADS)
Langbein, W.; Lüerßen, D.; Kalt, H.; Braun, W.; Ploog, K.
1996-06-01
We report on the observation of isolated, anisotropically confined electronic states of the type-I transition in (113)-grown, type-II GaAs/AlAs superlattices. They are formed by fluctuations of the periodic interface corrugation. Electronic states related to the X conduction-band minimum act, at elevated temperatures, as a transport channel to these ? quantum boxes. The extremely narrow emission lines of the quantum boxes show an enhanced optical anisotropy compared to the luminescence of the extended states, revealing the anisotropic nature of the localization sites. This is confirmed by a comparison of the experimental luminescence energy and anisotropy with the results of a multiband k.p calculation for a quantum wire model system.
Seismic signatures of reservoir transport properties and pore fluid distribution
Akbar, N. ); Mavko, G.; Nur, A.; Dvorkin, J. . Dept. of Geophysics)
1994-08-01
The authors investigate the effects of permeability, frequency, and fluid distribution on the viscoelastic behavior of rock. The viscoelastic response of rock to seismic waves depends on the relative motion of pore fluid with respect to the solid phase. They consider wave-induced squirt fluid flow at two scales: (1) local microscopic flow at the smallest scale of saturation heterogeneity (e.g., within a single pore) and (2) macroscopic flow at a larger scale of fluid-saturated and dry patches. They explore the circumstances under which each of these mechanisms prevails. They examine such flows under the conditions of uniform confining (bulk) compression and obtain the effective dynamic bulk modulus of rock. The solutions are formulated in terms of generalized frequencies that depend on frequency, saturation, fluid and gas properties, and on the macroscopic properties of rock such as permeability, porosity, and dry bulk modulus. The study includes the whole range of saturation and frequency; therefore, the authors provide the missing link between the low-frequency limit and the high-frequency limit given by Mavko and Jizba. Further, they compare their model with Biot's theory and introduce a geometrical factor whose numeric value gives an indication as to whether local fluid squirt or global mechanisms dominate the viscoelastic properties of porous materials. The important results of their theoretical modeling are: (1) a hysteresis of acoustic velocity versus saturation resulting from variations in fluid distributions, and (2) two peaks of acoustic wave attenuation--one at low frequency and another at higher frequency (caused by local flow). Both theoretical results are compared with experimental data.
Anisotropic Weyl symmetry and cosmology
Moon, Taeyoon; Oh, Phillial; Sohn, Jongsu E-mail: ploh@skku.edu
2010-11-01
We construct an anisotropic Weyl invariant theory in the ADM formalism and discuss its cosmological consequences. It extends the original anisotropic Weyl invariance of Ho?ava-Lifshitz gravity using an extra scalar field. The action is invariant under the anisotropic transformations of the space and time metric components with an arbitrary value of the critical exponent z. One of the interesting features is that the cosmological constant term maintains the anisotropic symmetry for z = ?3. We also include the cosmological fluid and show that it can preserve the anisotropic Weyl invariance if the equation of state satisfies P = z?/3. Then, we study cosmology of the Einstein-Hilbert-anisotropic Weyl (EHaW) action including the cosmological fluid, both with or without anisotropic Weyl invariance. The correlation of the critical exponent z and the equation of state parameter ?-bar provides a new perspective of the cosmology. It is also shown that the EHaW action admits a late time accelerating universe for an arbitrary value of z when the anisotropic conformal invariance is broken, and the anisotropic conformal scalar field is interpreted as a possible source of dark energy.
Electrical transport and magnetic properties of CeGe
NASA Astrophysics Data System (ADS)
Marcano, N.; Espeso, J. I.; Noakes, D. R.; Kalvius, G. M.; GÃ³mez Sal, J. C.
2005-04-01
Although CeGe is a simple binary alloy, little information on its magnetic properties is available. Earlier studies suggested antiferromagnetic order below T=10.5 K. We present the results of a detailed resistivity and magnetoresistance study down to 2 K together with Î¼SR spectroscopic data. The measurements verify the transition into long-range magnetic order at the temperature reported. Anomalous behaviour of the resistivity around TN is interpreted in terms of the formation of superzone magnetic gaps in the ordered phase. The Î¼SR spectra for T< TN indicate a complex antiferromagnetic spin structure.
Structure evolution and electrical transport property of Si nanowire
NASA Astrophysics Data System (ADS)
Wang, Y.; Li, Q. Q.; Dong, J. C.; He, Y. Z.; Li, H.
2015-02-01
Various optimized Si and its alloy nanowires, from a monoatomic chain to helical and multishell coaxial cylinder, have been obtained. Results reveal that the structure of the Si nanowires transforms as the radii of the carbon nanotubes increase, despite of the chirality of the CNTs. We also calculate the physical properties, such as density of states, transmission functions, current-voltage (I-V) characteristics, and conductance spectra (G-V) of optimized nanowires and alloy nanowires sandwiched between two gold contacts. Interestingly, compared with the pure Si nanowires, the conductance of the alloy nanowires is even lower.
Transport Properties of Equilibrium Argon Plasma in a Magnetic Field
Bruno, D.; Laricchiuta, A.; Chikhaoui, A.; Kustova, E. V.; Giordano, D.
2005-05-16
Electron electrical conductivity coefficients of equilibrium Argon plasma in a magnetic field are calculated up to the 12th Chapman-Enskog approximation at pressure of 1 atm and 0.1 atm for temperatures 500K-20000K; the magnetic Hall parameter spans from 0.01 to 100. The collision integrals used in the calculations are discussed. The convergence properties of the different approximations are assessed. The degree of anisotropy introduced by the presence of the magnetic field is evaluated. Differences with the isotropic case can be very substantial. The biggest effects are visible at high ionization degrees, i.e. high temperatures, and at strong magnetic fields.
Modeling of anisotropic wound healing
NASA Astrophysics Data System (ADS)
Valero, C.; Javierre, E.; García-Aznar, J. M.; Gómez-Benito, M. J.; Menzel, A.
2015-06-01
Biological soft tissues exhibit non-linear complex properties, the quantification of which presents a challenge. Nevertheless, these properties, such as skin anisotropy, highly influence different processes that occur in soft tissues, for instance wound healing, and thus its correct identification and quantification is crucial to understand them. Experimental and computational works are required in order to find the most precise model to replicate the tissues' properties. In this work, we present a wound healing model focused on the proliferative stage that includes angiogenesis and wound contraction in three dimensions and which relies on the accurate representation of the mechanical behavior of the skin. Thus, an anisotropic hyperelastic model has been considered to analyze the effect of collagen fibers on the healing evolution of an ellipsoidal wound. The implemented model accounts for the contribution of the ground matrix and two mechanically equivalent families of fibers. Simulation results show the evolution of the cellular and chemical species in the wound and the wound volume evolution. Moreover, the local strain directions depend on the relative wound orientation with respect to the fibers.
Extensive characterization of anisotropic conductors in the Montgomery geometry
NASA Astrophysics Data System (ADS)
Corraze, B.; Ribault, M.
1994-04-01
In very anisotropic materials the transport properties of a single crystal may be equivalent to those of a long thin bar. In this geometry we show that an extension of the Montgomery method [1] allows a detailed discussion of the experimental results. It is then possible to establish the correct value of the anisotropy of the resistivity tensor. The method is used to show that in La2CuO{4+0.018}, the conductivity is activated in the Cu-O planes while it results from variable range hopping process perpendicular to the planes as previously established. Dans le cas de matÃ©riaux trÃ¨s anisotropes, les propriÃ©tÃ©s de transport d'un monocristal peuvent Ãªtre Ã©quivalentes Ã celle d'une longue barre de section quasi carrÃ©e. Dans cette gÃ©omÃ©trie, nous avons analysÃ© en dÃ©tail les erreurs introduites par l'emploi de la technique de Montgomery [1]. Nous proposons une extension de cette mÃ©thode. Dans ces conditions, nous montrons qu'une analyse complÃ¨te peut aisÃ©ment permettre de choisir une gÃ©omÃ©trie de test conduisant Ã la dÃ©termination de l'anisotropie rÃ©elle du matÃ©riau et de sa variation thermique. La mÃ©thode est utilisÃ©e pour montrer que, dans le composÃ© La2CuO{4+0.018}, la conductivitÃ© est activÃ©e dans les plans Cu-O alors que, perpendiculairement aux plans, nous avons montrÃ© prÃ©cÃ©demment qu'elle rÃ©sulte d'un processus de sauts.
Magnetic colloid by PLA: Optical, magnetic and thermal transport properties
NASA Astrophysics Data System (ADS)
Pandey, B. K.; Shahi, A. K.; Gopal, Ram
2015-08-01
Ferrofluids of cobalt and cobalt oxide nanoparticles (NPs) have been successfully synthesized using liquid phase-pulse laser ablation (LP-PLA) in ethanol and double distilled water, respectively. The mechanism of laser ablation in liquid media and formation process for Co target in double distilled water (DDW) and ethanol are speculated based on the reactions between laser generated highly nascent cobalt species and vaporized solvent media in a confined high temperature and pressure at the plume-surrounding liquid interface region. Optical absorption, emission, vibrational and rotational properties have been investigated using UV-vis absorption, photoluminescence (PL) and Fourier transform-infra red (FT-IR) spectroscopy, respectively. In this study optical band gap of cobalt oxide ferrofluids has been engineered using different pulse energy of Nd:YAG laser in the range of (2.80-3.60 eV). Vibrating sample magnetometer (VSM) is employed to determine the magnetic properties of ferrofluids of cobalt and cobalt oxide NPs while their thermal conductivities are examined using rotating disc method. Ferrofluids have gained enormous curiosity due to many technological applications, i.e. drug delivery, coolant and heating purposes.
Enhanced Raman Scattering on In-plane Anisotropic Layered Materials
Liang, Liangbo; Meunier, Vincent; Sumpter, Bobby G.; Ling, Xi; Lin, Jingjing; Zhang, Shuqing; Mao, Nannan; Zhang, Na; Tong, Lianming; Zhang, Jin
2015-11-19
Surface-enhanced Raman scattering (SERS) on two-dimensional (2D) layered materials has provided a unique platform to study the chemical mechanism (CM) of the enhancement due to its natural separation from electromagnetic enhancement. The CM stems from the basic charge interactions between the substrate and molecules. Despite the extensive studies of the energy alignment between 2D materials and molecules, an understanding of how the electronic properties of the substrate are explicitly involved in the charge interaction is still unclear. Lately, a new group of 2D layered materials with anisotropic structure, including orthorhombic black phosphorus (BP) and triclinic rhenium disulphide (ReS2), has attractedmoreÂ Â» great interest due to their unique anisotropic electrical and optical properties. Herein, we report a unique anisotropic Raman enhancement on few-layered BP and ReS2 using copper phthalocyanine (CuPc) molecules as a Raman probe, which is absent on isotropic graphene and h-BN. According to detailed Raman tensor analysis and density functional theory calculations, anisotropic charge interactions due to the anisotropic carrier mobilities of the 2D materials are responsible for the angular dependence of the Raman enhancement. Our findings not only provide new insights into the CM process in SERS, but also open up new avenues for the exploration and application of the electronic properties of anisotropic 2D layered materials.Â«Â less
Enhanced Raman Scattering on In-plane Anisotropic Layered Materials
Liang, Liangbo; Meunier, Vincent; Sumpter, Bobby G.; Ling, Xi; Lin, Jingjing; Zhang, Shuqing; Mao, Nannan; Zhang, Na; Tong, Lianming; Zhang, Jin
2015-11-19
Surface-enhanced Raman scattering (SERS) on two-dimensional (2D) layered materials has provided a unique platform to study the chemical mechanism (CM) of the enhancement due to its natural separation from electromagnetic enhancement. The CM stems from the basic charge interactions between the substrate and molecules. Despite the extensive studies of the energy alignment between 2D materials and molecules, an understanding of how the electronic properties of the substrate are explicitly involved in the charge interaction is still unclear. Lately, a new group of 2D layered materials with anisotropic structure, including orthorhombic black phosphorus (BP) and triclinic rhenium disulphide (ReS2), has attracted great interest due to their unique anisotropic electrical and optical properties. Herein, we report a unique anisotropic Raman enhancement on few-layered BP and ReS2 using copper phthalocyanine (CuPc) molecules as a Raman probe, which is absent on isotropic graphene and h-BN. According to detailed Raman tensor analysis and density functional theory calculations, anisotropic charge interactions due to the anisotropic carrier mobilities of the 2D materials are responsible for the angular dependence of the Raman enhancement. Our findings not only provide new insights into the CM process in SERS, but also open up new avenues for the exploration and application of the electronic properties of anisotropic 2D layered materials.