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1

Anisotropic magnetic and transport properties of UNiGe

Magnetism in UNiGe which adopts the orthorhombic TiNiSi type of structure with lattice constants a = 700.7 pm, b = 423.7 pm, c = 720.7 pm is strongly anisotropy. The Curie-Weiss behavior of the susceptibility above 90 K yields values of {Theta}{sub p} equal to {minus}98, 3 and 41 K for the a, b and c axis, respectively. Also the electrical resistivity is anisotropic and reflects magnetic phase transitions at 41.5 and 50 K, in very good agreement with specific-beat data. An antiferromagnetic structure of U moments of about 1.4 {mu}B with a propagation vector q = (0, 0.5, 0.5) can be concluded from neutron-diffraction studies at low temperatures. Two metamagnetic transitions are observed in high-field magnetization data at 4.2 K in fields applied along the b (at 17 and 25 T) and c (at 3 and 10 T) axes yielding parallel alignment of the magnetic moments in fields above the second transition. The magnetization measured at 35 T amounts to 1.45 {mu}{sub B}/fu. The huge magnetic anisotropy is reflected in the weak linear magnetic response to fields along the a axis yielding only 0.23 {mu}{sub B}/f.u. at 35 T. The destruction of antiferromagnetic ordering in high fields is accompanied by a reduction of about 80% of the electrical resistivity. The huge magnetic anisotropy and giant magnetoresistance which is also observed in other UTX compounds (T = transition metal, X = P-metal) can be understood in terms of anisotropic 5f-ligand hybridization.

Prokes, K.; Nakotte, H.; Brueck, E.; Boer, F.R. de [Univ. of Amsterdam (Netherlands). Van der Waals-Zeeman Lab.] [Univ. of Amsterdam (Netherlands). Van der Waals-Zeeman Lab.; Havela, L.; Sechovsky, V.; Svoboda, P. [Charles Univ., Prague (Czech Republic). Dept. of Metal Physics] [Charles Univ., Prague (Czech Republic). Dept. of Metal Physics; Maletta, H. [Hahn-Meitner-Inst., Berlin (Germany)] [Hahn-Meitner-Inst., Berlin (Germany)

1994-03-01

2

Anisotropic transport properties in tilted c-axis MgB2 thin films

NASA Astrophysics Data System (ADS)

We report on superconducting magnesium diboride MgB2 thin films grown on both YSZ and MgO substrates, with two different orientations, namely [110] and [211]. MgB2 off-axis growth mode (namely, with the c-axis tilted with respect to the film surface's normal) is achievable on these substrates. Depending on the type and orientation of the substrate, tilting angle can be varied. As a consequence of tilted growth, anisotropic transport properties are observed. In very thin films, resistance measurements provide an estimate of the resistivity anisotropic ratio ?c/?ab, where ?c is the resistivity along the c axis and ?ab is the in-plane resistivity. All these findings clearly demonstrate that tilted MgB2 films offer new exciting possibilities to both investigate intrinsic fundamental properties of MgB2 and to explore possible applications in planar superconducting devices.

Orgiani, P.; Chen, Ke; Cui, Yi; Li, Qi; Ferrando, V.; Putti, M.; Iavarone, M.; Di Capua, R.; Ciancio, R.; Vaglio, R.; Maritato, L.; Xi, X. X.

2010-02-01

3

Strain-induced anisotropic transport properties of LaBaCo?O?.?+? thin films on NdGaO? substrates.

Thin films of double-perovskite structural LaBaCo2O5.5+? were epitaxially grown on (110) NdGaO3 substrates by pulsed laser deposition. Microstructural studies by high-resolution X-ray diffraction and transmission electron microscopy revealed that the films have an excellent quality epitaxial structure. In addition, strong in-plane anisotropic strains were measured. Electrical transport properties of the films were characterized by an ultra-high-vacuum four-probe scanning tunneling microscopy system at different temperatures. It was found that the anisotropic in-plane strain can significantly tune the values of film resistance up to 590%. PMID:24824560

Liu, Ming; Zou, Qiang; Ma, Chunrui; Collins, Greg; Mi, Shao-Bo; Jia, Chun-Lin; Guo, Haiming; Gao, Hongjun; Chen, Chonglin

2014-06-11

4

Neutron transport problems in anisotropic media

In nuclear reactor physics, neutron transport in media having anisotropic properties is of interest in modelling largely voided configurations, such as boiling-water and gas-cooled reactors. In order to treat such problems, neutronic methods need to be extended and adapted. The present work is devoted to the solution of transport problems for materials in which cross-sections are dependent on the direction

G Lapenta; P Ravetto; M. M Rostagno; R Jacqmin; F Malvagi; G Rimpault

2001-01-01

5

Anisotropic magnetothermal transport and spin Seebeck effect

NASA Astrophysics Data System (ADS)

The anisotropic properties of thermal transport in insulating or conducting ferromagnets are derived on the basis of the Onsager reciprocity relations applied to a magnetic system. It is shown that the angular dependence of the temperature gradient takes the same form as that of the anisotropic magnetoresistance, including anomalous and planar Hall contributions. The measured thermocouple generated between the extremities of the nonmagnetic electrode in thermal contact to the ferromagnet follows this same angular dependence. The sign and amplitude of the magnetovoltaic signal is controlled by the difference of the Seebeck coefficients of the thermocouple.

Wegrowe, J.-E.; Drouhin, H.-J.; Lacour, D.

2014-03-01

6

NASA Astrophysics Data System (ADS)

A new method based on the adaptation of the Pulse Transient Hot Strip technique to slab sample geometry has been developed for studying thermal conductivity and thermal diffusivity of anisotropic thin film materials (<50 ?m) with thermal conductivity in the 0.01-100 W/mK range, deposited on thin substrates (i.e., wafers). Strength of this technique is that it provides a well-controlled thermal probing depth, making it possible to probe a predetermined depth of the sample layer and thereby avoiding the influence from material(s) deeper down in the sample. To verify the technique a series of measurements were conducted on a y-cut single crystal quartz wafer. A Hot Strip sensor (32-?m wide, 3.2-mm long) was deposited along two orthogonal crystallographic (x- and z-) directions and two independent pulse transients were recorded. Thereafter, the data was fitted to our theoretical model, and the anisotropic thermal transport properties were determined. Using a thermal probing depth of only 30 ?m, we obtained a thermal conductivity along the perpendicular (parallel) direction to the z-, i.e., optic axis of 6.48 (11.4) W/mK, and a thermal diffusivity of 3.62 (6.52) mm2/s. This yields a volumetric specific heat of 1.79 MJ/mK. These values agree well with tabulated data on bulk crystalline quartz supporting the accuracy of the technique, and the obtained standard deviation of less than 2.7% demonstrates the precision of this new measurement technique.

Ma, Y.; Gustavsson, J. S.; Haglund, Å.; Gustavsson, M.; Gustafsson, S. E.

2014-04-01

7

Elastic properties of spherically anisotropic piezoelectric composites

NASA Astrophysics Data System (ADS)

Effective elastic properties of spherically anisotropic piezoelectric composites, whose spherically anisotropic piezoelectric inclusions are embedded in an infinite non-piezoelectric matrix, are theoretically investigated. Analytical solutions for the elastic displacements and the electric potentials under a uniform external strain are derived exactly. Taking into account of the coupling effects of elasticity, permittivity and piezoelectricity, the formula is derived for estimating the effective elastic properties based on the average field theory in the dilute limit. An elastic response mechanism is revealed, in which the effective elastic properties increase as inclusion piezoelectric properties increase and inclusion dielectric properties decrease. Moreover, a piezoelectric response mechanism, of which the effective piezoelectric response vanishes due to the symmetry of spherically anisotropic composite, is also disclosed.

Wei, En-Bo; Gu, Guo-Qing; Poon, Ying-Ming

2010-09-01

8

Anisotropic photocatalytic properties of hematite

. Hematite is a semiconducting mineral with a role in natural photoelectrochemical processes, and has been studied from the\\u000a viewpoint of solar energy utilization. Hematite is an anisotropic conductor, with faster conduction parallel to (001) planes.\\u000a Flatband potentials and photocurrent onset potentials for natural hematite single crystals and synthetic nanocrystalline hematite\\u000a films are similar, and show Nernstian behavior within error. At

Carrick M. Eggleston; Angela J. A. Shankle; Amanda J. Moyer; Ilkay Cesar; Michael Grätzel

2009-01-01

9

NASA Astrophysics Data System (ADS)

In this chapter, we first review the fundamental theoretical concepts of mesoscopic transport for low-dimensional systems and disordered materials. Emphasis is put on the Landauer formulation of electronic transmission, weak localization and Aharonov-Bohm phenomena, as well as Coulomb interactions through screening effects and Luttinger liquid model. A pedagogical effort is made to present the currently established physics of quantum conduction in some analytical detail, enabling the reader to further deepen the understanding of more specialized literature. In a subsequent part, the main theoretical features of quantum transport in carbon nanotubes are elaborated, mostly within the non-interacting electron regime, that is to date less controversial. The experimental part starts with a discussion of the commonly employed measurement techniques. Several transport experiments are then analyzed, with a particular focus on device-oriented aspects (field effect, Schottky barriers, etc). Finally, the main physical properties of nanotube-based composites are outlined, followed by a presentation of our current understanding of thermal properties of carbon tubules.

Roche, S.; Akkermans, E.; Chauvet, O.; Hekking, F.; Martel, R.; Issi, J.-P.; Montambaux, G.; Poncharal, Ph.

10

THE ANISOTROPIC TRANSPORT EFFECTS ON DILUTE PLASMAS

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.

Devlen, Ebru, E-mail: ebru.devlen@ege.edu.tr [Department of Astronomy and Space Sciences, Faculty of Science, University of Ege, Bornova 35100, Izmir (Turkey)

2011-04-20

11

Transport and Anisotropic Diffusion in Time-Dependent Flow Visualization

Transport and Anisotropic Diffusion in Time-Dependent Flow Visualization D. BÂ¨urkle T. PreuÃ?er by deformation to the velocity field in 2D or on surfaces in 3D. The Line Integral Convolution (LIC) approach to the visualization of flow fields. This method was based on the solution of an anisotropic diffusion prob- lem

Preusser, Tobias

12

Transport equations for multicomponent anisotropic space plasmas - A review

NASA Technical Reports Server (NTRS)

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.

Barakat, A. R.; Schunk, R. W.

1982-01-01

13

Ground state properties of an anisotropic bilinear-biquadratic model

NASA Astrophysics Data System (ADS)

In this paper, we consider anisotropic properties of a one-dimensional bilinear-biquadratic spin model with S = 1. The Hamiltonian with anisotropic parameter is studied numerically by using Lanczos exact diagonalization method at a critical point. It is found that the momentum corresponding to the ground state is affected by anisotropic parameter regularly, especially when total spin z-component is not zero.

Wang, Jinlong

2014-08-01

14

Experimental evidence of strong in-plane anisotropy in electrical properties of the confined electron gas at the SrTiO{sub 3}-LaAlO{sub 3} interface on top of (LaAlO{sub 3}){sub 0.3}(Sr{sub 2}AlTaO{sub 3}){sub 0.7} substrates is provided by detailed transport measurements. Structured measurement geometries in multiple directions are used to show dependence of the sheet resistance with the in-plane angle {theta}, which is fitted with a sine function with a period of 180{sup o}. The carrier density remains constant and a directional dependence of the carrier mobility of more than one order of magnitude is determined with respect to the orientation of the unit cell height steps present at the SrTiO{sub 3}-LaAlO{sub 3} interface.

Brinks, Peter [University of Twente, Enschede, Netherlands; Siemons, Wolter [ORNL; Kleibeuker, Josee [University of Twente, Enschede, Netherlands; Koster, Gertjan [University of Twente, Enschede, Netherlands; Rijnders, Guus [MESA+ University of Twente, Enschede, Netherlands; Huijben, Mark [University of Twente, Enschede, Netherlands

2011-01-01

15

Anisotropic transport equations on a Poincare grid

NASA Astrophysics Data System (ADS)

The strong anisotropy of plasma transport presents a challenge for numerical modelling. For the case of 3-D transport equations, when standard finite difference, finite volume or finite element methods are used it is essential that one mesh coordinate be aligned with magnetic field lines, as otherwise false numerical diffusion will swamp true diffusion in directions across the magnetic field. But this alignment cannot be obtained for complicated magnetic geometries such as tokamak fields with error component or stellerator fields including islands and ergodic regions. We are implementing a calculation procedure for such situations in which the equations are discretized on an unstructured mesh obtained by field line tracing. The points of the mesh belong to an associated Poincare plot, but there is no underlying global coordinate system on which the mesh would be regular. A suitable finite difference discretization on such a mesh avoids the problem of false numerical diffusion. Our work focuses at first on the case of a single scalar equation, esp. the electron heat transport equation, with interest in the boundary region of Wendelstein 7-X.

Braams, Bastiaan J.; McTaggart, Neil; Bonnin, Xavier; Runov, Alexander; Schneider, Ralf

2002-11-01

16

Anisotropic magnetization and transport properties of RAgSb{sub 2} (R=Y, La-Nd, Sm, Gd-Tm)

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.

Myers, Kenneth D.

1999-11-08

17

COMPLEX IDENTIFICATION OF THERMOPHYSICAL PROPERTIES OF ANISOTROPIC COMPOSITE MATERIAL

The statement and solution algorithm of a two-dimensional thermal conductivity inverse problem on complex identification of thermophysical properties of anisotropic complex material is presented. An experimental facility for carrying out thermophysical research has been worked out. The problem of optimal designing of temperature measurements has been solved in the course of the experiment. Data on the complex of thermophysical properties

O. M. ALIFANOV; Y. JARNY

18

Measurement of Anisotropic Mechanical Properties of the Tectorial Membrane

NASA Astrophysics Data System (ADS)

The tectorial membrane (TM) in the cochlea is an anisotropic tissue with a key role in hearing. The TM's structural andmechanical anisotropy is provided by oriented collagen bundles about 1 micron thick. Here we report the three elastic moduli that characterize the TM, as well as the novel technique used to measure the mechanical properties of an anisotropic material. We have measured mechanical anisotropy by combining Atomic Force Microscopy (AFM) and optical tracking of microspheres. The surface Green's tensor for an incompressible anisotropic material was then used to compute the elastic moduli from imposed forces and the resulting surface deformations. Our results suggest a critical role of TM's strong anisotropy by enhancing the cochlear amplifier.

Gavara, N.; Chadwick, R. S.

2009-02-01

19

NASA Astrophysics Data System (ADS)

We report on the possibility to generate highly anisotropic quantum conductivity in disordered graphene-based superlattices. Our quantum simulations, based on an efficient real-space implementation of the Kubo-Greenwood formula, show that in disordered graphene superlattices the strength of multiple scattering phenomena can strongly depend on the transport measurement geometry. This eventually yields the coexistence of a ballistic waveguide and a highly resistive channel (Anderson insulator) in the same two-dimensional platform, evidenced by a ?yy/?xx ratio varying over several orders of magnitude, and suggesting the possibility of building graphene electronic circuits based on the unique properties of chiral massless Dirac fermions in graphene.

Pedersen, Jesper Goor; Cummings, Aron W.; Roche, Stephan

2014-04-01

20

Direct Imaging of Anisotropic Material Properties using Photorefractive Laser Ultrasound

Anisotropic properties of materials can be determined by measuring the propagation of elastic waves in different directions. A laser imaging approach is presented that utilizes the adaptive property of photorefractive materials to produce a real-time measurement of the antisymmetric Lamb or flexural traveling wave mode displacement and phase. Continuous excitation is employed and the data is recorded and displayed in all directions simultaneously at video camera frame rates. Fourier transform of the data produces an image of the wave slowness in all planar directions. The results demonstrate imaging of microstructural isotropy and anisotropy and stress induced ansiotropy in plates.

K.L. Telschow; R.S. Schley; S.M. Watson; V.A. Deason

1999-06-01

21

Direct Imaging of Anisotropic Material Properties using Photorefractive Laser Ultrasound

Anisotropic properties of materials can be determined by measuring the propagation of elastic waves in different directions. A laser imaging approach is presented that utilizes the adaptive property of photorefractive materials to produce a real-time measurement of the antisymmetric Lamb or flexural traveling wave mode displacement and phase. Continuous excitation is employed and the data is recorded and displayed in all directions simultaneously at video camera frame rates. Fourier transform of the data produces an image of the wave slowness in all planar directions. The results demonstrate imaging of microstructural isotropy and anisotropy and stress induced ansiotropy in plates.

Telschow, Kenneth Louis; Deason, Vance Albert; Schley, Robert Scott; Watson, Scott Marshall

1999-07-01

22

NASA Astrophysics Data System (ADS)

hydraulic properties such as hydraulic conductivity (K) are ubiquitously heterogeneous and typically only a statistical characterization can be sought. Additionally, statistical anisotropy at typical characterization scales is the rule. Thus, regardless of the processes governing solute transport at the local (pore) scale, transport becomes non-Fickian. Mass-transfer models provide an efficient tool that reproduces observed anomalous transport; in some cases though, these models lack predictability as model parameters cannot readily be connected to the physical properties of aquifers. In this study, we focus on a multirate mass-transfer model (MRMT), and in particular the apparent capacity coefficient (?), which is a strong indicator of the potential of immobile zones to capture moving solute. We aim to find if the choice of an apparent ? can be phenomenologically related to measures of statistical anisotropy. We analyzed an ensemble of random simulations of three-dimensional log-transformed multi-Gaussian permeability fields with stationary anisotropic correlation under convergent flow conditions. It was found that apparent ? also displays an anisotropic behavior, physically controlled by the aquifer directional connectivity, which in turn is controlled by the anisotropic correlation model. A high hydraulic connectivity results in large ? values. These results provide new insights into the practical use of mass-transfer models for predictive purposes.

Pedretti, D.; Fernández-Garcia, D.; Sanchez-Vila, X.; Bolster, D.; Benson, D. A.

2014-02-01

23

NASA Astrophysics Data System (ADS)

Heat transport in magnetized plasmas is a problem of fundamental interest in controlled fusion. In Ref.footnotetext D. del-Castillo-Negrete, and L. Chac'on, Phys. Rev. Lett., 106, 195004 (2011); Phys. Plasmas 19, 056112 (2012). we proposed a Lagrangian-Green's function (LG) method to study this problem in the strongly anisotropic (?=0) regime. The LG method bypasses the need to discretize the transport operators on a grid and it is applicable to general parallel flux closures and 3-D magnetic fields. Here we apply the LG method to parallel transport (with local and nonlocal parallel flux closures) in reversed shear magnetic field configurations known to exhibit robust transport barriers in the vicinity of the extrema of the q-profile. By shearless Cantori (SC) we mean the invariant Cantor sets remaining after the destruction of toroidal flux surfaces with zero magnetic shear, q^'=0. We provide numerical evidence of the role of SC in the anomalously slow relaxation of radial temperature gradients in chaotic magnetic fields with no transport barriers. The spatio-temporal evolution of temperature pulses localized in the reversed shear region exhibits non-diffusive self-similar evolution and nonlocal effective radial transport.

Blasevski, D.; Del-Castillo-Negrete, D.

2012-10-01

24

Anisotropic MRI contrast reveals enhanced ionic transport in plastic crystals.

Organic ionic plastic crystals (OIPCs) are attractive as solid-state electrolytes for electrochemical devices such as lithium-ion batteries and solar and fuel cells. OIPCs offer high ionic conductivity, nonflammability, and versatility of molecular design. Nevertheless, intrinsic ion transport behavior of OIPCs is not fully understood, and their measured properties depend heavily on thermal history. Solid-state magnetic resonance imaging experiments reveal a striking image contrast anisotropy sensitive to the orientation of grain boundaries in polycrystalline OIPCs. Probing triethyl(methyl)phosphonium bis(fluorosulfonyl)imide (P1222FSI) samples with different thermal history demonstrates vast variations in microcrystallite alignment. Upon slow cooling from the melt, microcrystallites exhibit a preferred orientation throughout the entire sample, leading to an order of magnitude increase in conductivity as probed using impedance spectroscopy. This investigation describes both a new conceptual window and a new characterization method for understanding polycrystalline domain structure and transport in plastic crystals and other solid-state conductors. PMID:25312993

Romanenko, Konstantin; Jin, Liyu; Madsen, Louis A; Pringle, Jennifer M; O'Dell, Luke A; Forsyth, Maria

2014-11-01

25

High field dielectric properties of anisotropic polymer-ceramic composites

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.

Tomer, V.; Randall, C. A. [Center of Dielectric Studies, Materials Research Institute, Materials Research Laboratory Bldg., Pennsylvania State University, Pennsylvania 16802I (United States)

2008-10-01

26

NASA Astrophysics Data System (ADS)

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 s

Crowgey, Benjamin Reid

27

Plasmonic cloaking for irregular objects with anisotropic scattering properties

NASA Astrophysics Data System (ADS)

Here we extend the plasmonic cloaking technique to irregularly shaped objects with anisotropic scattering response. The scattering-cancellation approach to cloaking [A. Alù and N. Engheta, Phys. Rev. E 72, 016623 (2005)] has been extensively applied in the past to symmetrical geometries and canonical shapes. However, recent papers have raised some doubts concerning the fact that its use may not be as effective when dealing with strongly anisotropic and noncanonical geometries. Our goal here is to extend the plasmonic cloaking technique to irregular obstacles and to show that proper cloak design may provide a significant and uniform scattering reduction, independent of angle of incidence, position, and polarization of the illumination. We investigate how the volumetric effect of scattering cancellation provided by plasmonic media may drastically suppress the scattering for these irregular geometries independent of the illumination angle, and we shed some light on the physical mechanisms and the design rules at the basis of this cloaking technique when applied to objects whose scattering properties are dependent upon polarization and angle of incidence.

Tricarico, S.; Bilotti, F.; Alù, A.; Vegni, L.

2010-02-01

28

NASA Astrophysics Data System (ADS)

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 regions 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.

Blazevski, Daniel; del-Castillo-Negrete, Diego

2013-06-01

29

Anomalous Transport Processes in Anisotropically Expanding Quark-Gluon Plasmas

NASA Astrophysics Data System (ADS)

We derive an expression for the anomalous viscosity in an anisotropically expanding quark-gluon-plasma, which arises from interactions of thermal partons with dynamically generated color fields. The anomalous viscosity dominates over the collisional viscosity for large velocity gradients or weak coupling. This effect may provide an explanation for the apparent ``nearly perfect'' liquidity of the matter produced in nuclear collisions at RHIC without the assumption that it is a strongly coupled state.

Asakawa, M.; Bass, S. A.; Müller, B.

2006-10-01

30

Strain modulated anisotropic geometric, electronic and thermoelectric properties of Black Phosphorus

The anisotropic geometric, electronic, and thermoelectric (TE) properties of bulk black phosphorus (BP) with strain applied have been systematically investigated using first-principles calculations combined with semi-classical Boltzmann transport theory. The layer thickness of one single layer inside bulk BP, exhibiting maximum with a tensile strain of $4\\%$ applied, is slightly larger than that of freestanding phosphorene. The lattice constant $b$ always increase whatever compressive or tensile strain is applied along the $z$ direction, showing an unusual mechanical response with a negative Possion ratio, which may due to the hinge-like structure. The electronic properties are sensitive to strain, as an increasing compressive strain would lead to the band gap transiting from direct to indirect ($0.578 \\mathrm{GPa}$), and then to zero ($1.699 \\mathrm{GPa}$), while the tensile strain would enlarge the band gap almost linearly. When there is no strain applied, the $ZT$ value is found to be maximal along $x$ dir...

Qin, Guangzhao; Yue, Sheng-Ying; Cui, Hui-Juan; Zheng, Qing-Rong; Yan, Qing-Bo; Su, Gang

2014-01-01

31

Effective Transport Properties

NASA Astrophysics Data System (ADS)

In this chapter we study a particular case of multiphase systems, namely two-phase materials in which one of the phases is randomly dispersed in the other, so that the composite can be viewed on a macroscale as an effective continuum, with well defined properties. In general, the theoretical determination of the parameter for an effective medium requires, as a rule, the solution of a corresponding transport problem at the microscale, which takes into account the morphology of the system and its evolution. As the mathematical problem is well-posed on a microscale, this can be accomplished using, for example, the multiple scale approach shown in Chap.

Mauri, Roberto

32

Measurement of anisotropic thermophysical properties of cylindrical Li-ion cells

NASA Astrophysics Data System (ADS)

Cylindrical Li-ion cells have demonstrated among the highest power density of all Li-ion cell types and typically employ a spiral electrode assembly. This spiral assembly is expected to cause large anisotropy in thermal conductance between the radial and axial directions due to the large number of interfaces between electrode and electrolyte layers in the radial conduction path, which are absent in the axial direction. This paper describes a novel experimental technique to measure the anisotropic thermal conductivity and heat capacity of Li-ion cells using adiabatic unsteady heating. Analytical modeling of the method is presented and is shown to agree well with finite-element simulation models. Experimental measurements indicate that radial thermal conductivity is two orders of magnitude lower than axial thermal conductivity for cylindrical 26650 and 18650 LiFePO4 cells. Due to the strong influence of temperature on cell performance and behavior, accounting for this strong anisotropy is critical when modeling battery behavior and designing battery cooling systems. This work improves the understanding of thermal transport in Li-ion cells, and presents a simple method for measuring anisotropic thermal transport properties in cylindrical cells.

Drake, S. J.; Wetz, D. A.; Ostanek, J. K.; Miller, S. P.; Heinzel, J. M.; Jain, A.

2014-04-01

33

Spin amplification, reading, and writing in transport through anisotropic magnetic molecules, and reading spin information in molecular memory devices. Magnetic anisotropy is found to be crucial for slow of a magnetic field. We propose schemes for reading and writing spin information based on our findings. DOI: 10

von Oppen, Felix

34

Macrodispersivity tensor for nonreactive solute transport in isotropic and anisotropic fractal porous media: Analytical solutions Hongbin Zhan1 and Stephen W. Wheatcraft Hydrology/Hydrogeology Program the tortuosity of solute particles is larger, leading to more mixing in the transverse direction, which in turn

Zhan, Hongbin

35

Critical currents in weakly textured MgB2 : Nonlinear transport in anisotropic heterogeneous media

NASA Astrophysics Data System (ADS)

A model for highly nonlinear transport in heterogeneous media consisting of anisotropic particles with a preferred orientation is proposed and applied to the current transport in weakly textured magnesium diboride, MgB2 . It essentially explains why, unlike in conventional superconductors, a significant macroscopic anisotropy of the critical currents can be induced by the preparation of MgB2 tapes. The field and angular dependence of the critical current is calculated for various degrees of texture and compared to experimental data.

Eisterer, M.; Häßler, W.; Ková?, P.

2009-11-01

36

Stochastic analyses and Monte Carlo simulations were conducted for nonergodic transport of a nonreactive solute plume in three-dimensional heterogeneous and statistically anisotropic aquifers under uniform mean flow along the x axis. The hydraulic conductivity, K(x), is modeled as a random field which is assumed to be lognormally distributed with an anisotropic exponential covariance. The simulation model is validated with good

You-Kuan Zhang; Byong-min Seo

2004-01-01

37

Anisotropic quantum transport in a network of vertically aligned graphene sheets.

Novel anisotropic quantum transport was observed in a network of vertically aligned graphene sheets (VAGSs), which can be regarded as composed of plenty of quasi-parallel, nearly intrinsic, freestanding monolayers of graphene. When a magnetic field was perpendicular to most graphene sheets, magnetoresistance (MR) curves showed a weak localization (WL) effect at low field and a maximum value at a critical field ascribed to diffusive boundary scattering. While the magnetic field was parallel to the graphene sheets, the MR maximum disappeared and exhibited a transition from WL to weak antilocalization (WAL) with increasing temperature and magnetic field. Edges as atomically sharp defects are the main elastic and inelastic intervalley scattering sources, and inelastic scattering is ascribed to electron-electron intervalley scattering in the ballistic regime. This is the first time simultaneously observing WL, WAL and diffusive boundary scattering in such a macroscopic three-dimensional graphene system. These indicate the VAGS network is a robust platform for the study of the intrinsic physical properties of graphene. PMID:25090659

Huang, J; Guo, L-W; Li, Z-L; Chen, L-L; Lin, J-J; Jia, Y-P; Lu, W; Guo, Y; Chen, X-L

2014-08-27

38

Spatial frequency analysis of anisotropic drug transport in tumor samples

NASA Astrophysics Data System (ADS)

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.

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

39

Tailoring anisotropic wetting properties on submicrometer-scale periodic grooved surfaces.

The use of simple plasma treatments and polymer deposition to tailor the anisotropic wetting properties of one-dimensional (1D) submicrometer-scale grooved surfaces, fabricated using interferometric lithography in photoresist polymer films, is reported. Strongly anisotropic wetting phenomena are observed for as-prepared 1D grooved surfaces for both positive and negative photoresists. Low-pressure plasma treatments with different gas compositions (e.g., CHF(3), CF(4), O(2)) are employed to tailor the anisotropic wetting properties from strongly anisotropic and hydrophobic to hydrophobic with very high contact angle and superhydrophilic with a smaller degree of wetting anisotropy and without changing the structural anisotropy. The change of the surface wetting properties for these 1D patterned surfaces is attributed to a change in surface chemical composition, monitored using XPS. In addition, the initial anisotropic wetting properties on 1D patterned samples could be modified by coating plasma treated samples with a thin layer of polymer. We also demonstrated that the wetting properties of 1D grooved surfaces in a Si substrate could be tuned with similar plasma treatments. The ability to tailor anisotropic wetting on 1D patterned surfaces will find many applications in microfluidic devices, lab-on-a-chip systems, microreactors, and self-cleaning surfaces. PMID:20085338

Xia, Deying; He, Xiang; Jiang, Ying-Bing; Lopez, Gabriel P; Brueck, S R J

2010-02-16

40

Dipole Spontaneous Emission Near Planar Anisotropic Layers with Hyperbolic Metamaterial Properties

NASA Astrophysics Data System (ADS)

Analytical expressions were obtained for the rates of spontaneous emission of an atom (molecule) located near planar anisotropic layers with hyperbolic metamaterial properties. The distribution of the electric field excited by a dipole source in an anisotropic layer followed a complicated pattern. It was shown that the emission rate into the half-space behind the layers could exceed substantially the emission rate into the half-space in front of the layers.

Guzatov, D. V.

2014-07-01

41

Transport Properties of Nanocomposites

, and vital information regarding the electrical properties of the fibers and fiberfiber junctions was obtained for the case of two stabilizers used during composite preparation ? Gum Arabic (GA) and Poly(3,4-ethylenedioxythiophene) poly...

Narayanunni, Vinay

2010-07-14

42

Transport properties in the atmosphere of Jupiter

NASA Technical Reports Server (NTRS)

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.

Biolsi, L., Jr.

1979-01-01

43

Anisotropic Pressure, Transport, and Shielding of Magnetic Perturbations

We compute the effect on a tokamak of applying a nonaxisymmetric magnetic perturbation ??. 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 ??. Here, we analytically compute the pressure anisoptropy, anisoptropy, pll, p? ? 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.

H.E. Mynick and A.H. Boozer

2008-05-23

44

Anisotropic mechanical properties of recrystallized commercial grade Fe–20%Cr ferritic oxide dispersion strengthened alloys were investigated. Recrystallized microstructures were modified through preannealing and partial-recrystallization heat treatments, resulting in more isotropic mechanical properties in both longitudinal and transverse directions.

Hee Y. Kim; Oh Y. Kwon; Jinsung Jang; Soon H. Hong

2006-01-01

45

We propose a Lagrangian numerical algorithm for a time-dependent, anisotropic tem- perature 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 lo- cal and nonlocal 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. Al- gorithmically, 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 par- allel transport term when the perpendicular to parallel transport coefficient ratio / becomes arbitrarily small, and is shown to capture the correct limiting solution when / 0. Therefore, the approach is asymptotic-preserving. We demonstrate the ca- pabilities of the scheme with several numerical experiments with varying magnetic field complexity in two dimensions, including the case of transport across a magnetic island.

Chacon, Luis [ORNL; Del-Castillo-Negrete, Diego B [ORNL; Hauck, C. [Oak Ridge National Laboratory (ORNL)

2014-01-01

46

Theory of graphene transport properties

NASA Astrophysics Data System (ADS)

Graphene is of great fundamental interest and has potential applications in disruptive novel technologies. In order to study the novel phenomena in graphene, it is essential to understand its electron transport properties and in particular the main factors limiting its transport mobility. In this dissertation, we study the transport properties of graphene in the presence of electron-hole puddles induced by charged impurities which are invariably present in the graphene environment. We calculate the graphene conductivity by taking into account the non-mean-field two-component nature of transport in the highly inhomogeneous density and potential landscape, where activated transport across the potential fluctuations in the puddle regimes coexists with regular metallic diffusive transport. Our theoretical calculation explains the non-monotonic feature of the temperature dependent transport, which is experimentally generically observed in low mobility graphene samples. Our theory also predicts the existence of an intriguing "disorder by order" phenomenon in graphene transport where higher-quality (and thus more ordered) samples, while having higher mobility at high carrier density, will manifest more strongly insulating (and thus effectively more disordered) behavior as the carrier density is lowered compared with lower quality samples (with higher disorder), which exhibit an approximate resistivity saturation phenomenon at low carrier density near the Dirac point. This predicted behavior, simulating a metal-insulator transition, arises from the suppression of Coulomb disorder induced inhomogeneous puddles near the charge neutrality point in high quality graphene samples. We then study carrier transport through graphene on SrTiO3 substrates by considering the relative contributions of Coulomb and resonant impurity scattering to graphene resistivity. We establish that the nonuniversal high-density behavior of sigma(n) in different graphene samples on various substrates arises from the competition among different scattering mechanisms, and it is entirely possible for graphene transport to be dominated by qualitatively different scattering mechanisms at high and low carrier densities. Finally, we calculate the graphene conductivity as a function of carrier density, taking into account possible correlations in the spatial distribution of the Coulomb impurity disorder in the environment. We find that the conductivity could increase with increasing impurity density if there is sufficient inter-impurity correlation present in the system.

Li, Qiuzi

47

NASA Astrophysics Data System (ADS)

Transmittance and reflectance from spruce wood and bovine ligamentum nuchae as two different fibrous media are examined by time-of-flight spectroscopy for varying source detector separations and several orientations of the fibers in the sample. The anisotropic diffusion theory is used to obtain the absorption coefficient and the diffusion coefficients parallel and perpendicular to the fibers. The results are compared to those obtained with the isotropic diffusion theory. It is shown that for increasing source detector separations, the retrieved optical properties change as expected from Monte Carlo simulations performed in a previous study. This confirms that the anisotropic diffusion theory yields useful results for certain experimental conditions.

Simon, Emanuel; Krauter, Philipp; Kienle, Alwin

2014-07-01

48

Transmittance and reflectance from spruce wood and bovine ligamentum nuchae as two different fibrous media are examined by time-of-flight spectroscopy for varying source detector separations and several orientations of the fibers in the sample. The anisotropic diffusion theory is used to obtain the absorption coefficient and the diffusion coefficients parallel and perpendicular to the fibers. The results are compared to those obtained with the isotropic diffusion theory. It is shown that for increasing source detector separations, the retrieved optical properties change as expected from Monte Carlo simulations performed in a previous study. This confirms that the anisotropic diffusion theory yields useful results for certain experimental conditions. PMID:25055055

Simon, Emanuel; Krauter, Philipp; Kienle, Alwin

2014-07-01

49

Mesoscopic simulations of two-dimensional grain growth with anisotropic grain-boundary properties.

Grain-boundary (GB) properties in a polycrystalline system are generally anisotropic; in particular, both the GB energy and the mobility depend on the GB misorientation. Here the effect of anisotropic GB properties on two- dimensional grain growth is investigated by computer simulation. A stochastic velocity Monte Carlo algorithm based on a variational formulation for the dissipated power is implemented. The simulations show that grain growth leads to an increase in the fraction of small-angle GBs during the growth process. The average grain area is found to grow with a smaller exponent than in a system with isotropic GB properties. An extended von Neumann-Mullins relation based on averaged GB properties is proposed.

Moldovan, D.; Wolf, D.; Phillpot, S. R.; Haslam, A. J.; Materials Science Division

2002-05-10

50

Anisotropic electronic properties of a-axis-oriented Sr2IrO4 epitaxial thin-films

NASA Astrophysics Data System (ADS)

We have investigated the transport and optical properties along the c-axis of a-axis-oriented Sr2IrO4 epitaxial thin-films grown on LaSrGaO4 (100) substrates. The c-axis resistivity is approximately one order of magnitude larger than that of the ab-plane. Optical absorption spectra with E?c polarization show both Ir 5d intersite transitions and charge-transfer transitions (O 2p to Ir 5d), while E//c spectra show only the latter. The structural anisotropy created by biaxial strain in a-axis-oriented thin-films also changes the electronic structure and gap energy. These a-axis-oriented, epitaxial thin-films provide a powerful tool to investigate the highly anisotropic electronic properties of Sr2IrO4.

Nichols, J.; Korneta, O. B.; Terzic, J.; De Long, L. E.; Cao, G.; Brill, J. W.; Seo, S. S. A.

2013-09-01

51

Magnetic properties of electrons confined in an anisotropic cylindrical potential

NASA Astrophysics Data System (ADS)

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.

Nedelkoski, Zlatko; Petreska, Irina

2014-11-01

52

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.

Qian Chen

2008-08-18

53

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° 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°. 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. PMID:22128987

Liao, H-S; Juang, B-J; Chang, W-C; Lai, W-C; Huang, K-Y; Chang, C-S

2011-11-01

54

Electronic transport properties of topological insulator films and low dimensional superconductors

NASA Astrophysics Data System (ADS)

In this review, we present a summary of some recent experiments on topological insulators (TIs) and superconducting nanowires and films. Electron-electron interaction (EEI), weak anti-localization (WAL) and anisotropic magneto-resistance (AMR) effect found in topological insulator films by transport measurements are reported. Then, transport properties of superconducting films, bridges and nanowires and proximity effect in non-superconducting nanowires are described. Finally, the interplay between topological insulators and superconductors (SCs) is also discussed.

Xing, Ying; Sun, Yi; Singh, Meenakshi; Zhao, Yan-Fei; Chan, Moses H. W.; Wang, Jian

2013-10-01

55

A Harris sheet magnetic field with maximum magnitude B 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

Michael L. Goodman; Michael L

2011-01-01

56

The effect of anisotropic heat transport on magnetic islands in 3-D configurations

NASA Astrophysics Data System (ADS)

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-Schlüter current effects. Implications for finite pressure-induced island healing are discussed.

Schlutt, M. G.; Hegna, C. C.

2012-08-01

57

Measurement of anisotropic energy transport in flowing polymers by using a holographic technique

Almost no experimental data exist to test theories for the nonisothermal flow of complex fluids. To provide quantitative tests for newly proposed theories, we have developed a holographic grating technique to study energy transport in an amorphous polymer melt subject to flow. Polyisobutylene with weight-averaged molecular mass of 85 kDa is sheared at a rate of 10 s–1, and all nonzero components of the thermal conductivity tensor are measured as a function of time, after cessation. Our results are consistent with proposed generalizations to the energy balance for microstructural fluids, including a generalized Fourier's law for anisotropic media. The data are also consistent with a proposed stress-thermal rule for amorphous polymer melts. Confirmation of the universality of these results would allow numerical modelers to make quantitative predictions for the nonisothermal flow of polymer melts. PMID:15340152

Schieber, Jay D.; Venerus, David C.; Bush, Kendall; Balasubramanian, Venkat; Smoukov, Stoyan

2004-01-01

58

Measurement of anisotropic energy transport in flowing polymers by using a holographic technique.

Almost no experimental data exist to test theories for the nonisothermal flow of complex fluids. To provide quantitative tests for newly proposed theories, we have developed a holographic grating technique to study energy transport in an amorphous polymer melt subject to flow. Polyisobutylene with weight-averaged molecular mass of 85 kDa is sheared at a rate of 10 s(-1), and all nonzero components of the thermal conductivity tensor are measured as a function of time, after cessation. Our results are consistent with proposed generalizations to the energy balance for microstructural fluids, including a generalized Fourier's law for anisotropic media. The data are also consistent with a proposed stress-thermal rule for amorphous polymer melts. Confirmation of the universality of these results would allow numerical modelers to make quantitative predictions for the nonisothermal flow of polymer melts. PMID:15340152

Schieber, Jay D; Venerus, David C; Bush, Kendall; Balasubramanian, Venkat; Smoukov, Stoyan

2004-09-01

59

We have investigated the electrical properties of anisotropic conductive adhesive (ACA) joint using submicrometer-sized (~500 nm in diameter) silver (Ag) particle as conductive filler with the effect of ?-conjugated self-assembled molecular wires. The ACAs with submicrometer-sized Ag particles have higher current carrying capability (~3400 mA) than those with micro-sized Au-coated polymer particles (~2000 mA) and Ag nanoparticles (~2500 mA). More

Rongwei Zhang; Yi Li; Myung Jin Yim; Kyoung Sik Moon; D. D. Lu; C. P. Wong

2009-01-01

60

Anisotropic material properties of fused deposition modeling ABS

Rapid Prototyping (RP) technologies provide the ability to fabricate initial prototypes from various model materials. Stratasys Fused Deposition Modeling (FDM) is a typical RP process that can fabricate prototypes out of ABS plastic. To predict the mechanical behavior of FDM parts, it is critical to understand the material properties of the raw FDM process material, and the effect that FDM

Sung-Hoon Ahn; Michael Montero; Dan Odell; Shad Roundy; Paul K. Wright

2002-01-01

61

Anisotropic transport properties of ferromagnetic-superconducting bilayers

in this review by two features. First, in the pre- ceding works the magnetic field was assumed to be constant in space, whereas in our problem the average magnetic field is zero, it is strongly inhomogeneous in space. Therefore, in our system equal numbers... vortices increases when approaching the domain walls and can be expressed as nv(x)5(pm? /Lf0)@1/sin(px/L)#, where m?5m2(ev0 /f0) is the renormalized magnetization of the FM stripe. The vorti- ces spontaneously appear in the superconductor. We assume...

Kayali, MA; Pokrovsky, Valery L.

2004-01-01

62

A Numerical Model of Anisotropic Mass Transport Through Grain Boundary Networks

NASA Astrophysics Data System (ADS)

Tin (Sn) thin films are commonly used in electronic circuit applications as coatings on contacts and solders for joining components. It is widely observed, for some such system, that whiskers---long, thin crystalline structures---emerge and grow from the film. The Sn whisker phenomenon has become a highly active research area since Sn whiskers have caused a large amount of damage and loss in manufacturing, military, medical and power industries. Though lead (Pb) addition to Sn has been used to solve this problem for over five decades, the adverse environmental and health effects of Pb have motivated legislation to severely constrain Pb use in society. People are researching and seeking the reasons which cause whiskers and corresponding methods to solve the problem. The contributing factors to cause a Sn whisker are potentially many and much still remains unknown. Better understanding of fundamental driving forces should point toward strategies to improve (a) the accuracy with which we can predict whisker formation, and (b) our ability to mitigate the phenomenon. This thesis summarizes recent important research achievements in understanding Sn whisker formation and growth, both experimentally and theoretically. Focus is then placed on examining the role that anisotropy in grain boundary diffusivity plays in determining whisker characteristics (specifically, whether they form and, if so, where on a surface). To study this aspect of the problem and to enable future studies on stress driven grain boundary diffusion, this thesis presents a numerical anisotropic mass transport model. In addition to presenting details of the model and implementation, model predictions for a set of increasingly complex grain boundary networks are discussed. Preliminary results from the model provide evidence that anisotropic grain boundary diffusion may be a primary driving mechanism in whisker formation.

Wang, Yibo

63

NASA Astrophysics Data System (ADS)

A generic stochastic method is presented that rapidly evaluates numerical bulk flux solutions to the one-dimensional integrodifferential radiative transport equation, for coherent irradiance of optically anisotropic suspensions of nonspheroidal bioparticles, such as blood. As Fermat rays or geodesics enter the suspension, they evolve into a bundle of random paths or trajectories due to scattering by the suspended bioparticles. Overall, this can be interpreted as a bundle of Markov trajectories traced out by a "gas" of Brownian-like point photons being scattered and absorbed by the homogeneous distribution of uncorrelated cells in suspension. By considering the cumulative vectorial intersections of a statistical bundle of random trajectories through sets of interior data planes in the space containing the medium, the effective equivalent information content and behavior of the (generally unknown) analytical flux solutions of the radiative transfer equation rapidly emerges. The fluxes match the analytical diffuse flux solutions in the diffusion limit, which verifies the accuracy of the algorithm. The method is not constrained by the diffusion limit and gives correct solutions for conditions where diffuse solutions are not viable. Unlike conventional Monte Carlo and numerical techniques adapted from neutron transport or nuclear reactor problems that compute scalar quantities, this vectorial technique is fast, easily implemented, adaptable, and viable for a wide class of biophotonic scenarios. By comparison, other analytical or numerical techniques generally become unwieldy, lack viability, or are more difficult to utilize and adapt. Illustrative calculations are presented for blood medias at monochromatic wavelengths in the visible spectrum.

Miller, Steven

1998-03-01

64

Turbulent anomalous transport and anisotropic electron heating in a return current system

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.

Lee, Kuang Wu; Buechner, Joerg [Max-Planck-Institut fuer Sonnensystemforschung, 37191 Katlenburg-Lindau (Germany)

2011-02-15

65

We show how Lagrangian coordinates provide an effective representation of how difficult non-linear, hyperbolic transport problems in porous media can be dealt with. Recalling Lagrangian description first, we then derive some basic but remarkable properties useful for the numerical computation of projected transport operators. We furthermore introduce new generalized Lagrangian coordinates with their application to the Darcy–Muskat two-phase flow models.

F. Plouraboué; A. Bergeon; M. Azaïez

2001-01-01

66

Upscaling of elastic properties of anisotropic sedimentary rocks

NASA Astrophysics Data System (ADS)

In this paper, the term `upscaling' means the theoretical prediction of rock's elastic properties at lower frequency (seismic or cross-well data) using higher frequency logging data on sonic velocities (VP, VS1 and VS2), porosity and density. The mineral composition and water saturation derived from other logs are used. Due to the special treatment of sonic logging data provided by the dipole sonic probe, all the sonic velocities are obtained in the principal coordinate system of the rock's stiffness tensor. The upscaling procedure includes two steps. The first step involves the solution of an inverse problem on reconstruction of the parameters of the rock's microstructure from the logging data. The inversion is based on the effective medium theory. As a result of the inverse problem solution, the effective stiffness tensor is found for depths at which the sonic wave velocities are measured. At the second step, the velocities of waves at given lower frequencies are calculated as propagating in a layered medium. The number of layers in the medium depends on the given frequency and logging step. Each layer of the medium has the stiffness tensor found at the first step. This upscaling procedure has been applied to a wellbore for which the dipole sonic data are available. The rocks penetrated by the well are shales. In general, the resulting medium exhibits orthorhombic symmetry at sonic frequency. This symmetry results from the preferential orientation of clay platelets and grain-related cracks and vertical cracks. The existence of the latter is indicated by the dipole sonic tool. Depending on the microstructure parameters (orientation of clay platelets and cracks, pore/crack connectivity and shale mineralogical composition), the shales, at lower frequency, have either transversely isotropic symmetry (with the vertical axis of symmetry, a.k.a. VTI) or orthorhombic symmetry.

Bayuk, Irina O.; Ammerman, Mike; Chesnokov, Evgeni M.

2008-02-01

67

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.

Filippov, V. V., E-mail: wwfilippow@mail.ru [Lipetsk State Pedagogical University (Russian Federation); Bormontov, E. N. [Voronezh State University (Russian Federation)

2013-07-15

68

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...

69

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...

70

NASA Astrophysics Data System (ADS)

The goal of elucidating the physical mechanisms underlying the propagation of ultrasonic waves in anisotropic soft tissue such as myocardium has posed an interesting and largely unsolved problem in the field of physics for the past 30 years. In part because of the vast complexity of the system being studied, progress towards understanding and modeling the mechanisms that underlie observed acoustic parameters may first require the guidance of careful experiment. Knowledge of the causes of observed ultrasonic properties in soft tissue including attenuation, speed of sound, and backscatter, and how those properties are altered with specific pathophysiologies, may lead to new noninvasive approaches to the diagnosis of disease. The primary aim of this Dissertation is to contribute to an understanding of the physics that underlies the mechanisms responsible for the observed interaction of ultrasound with myocardium. To this end, through-transmission and backscatter measurements were performed by varying acoustic properties as a function of angle of insonification relative to the predominant myofiber direction and by altering the material properties of myocardium by increased protein cross-linking induced by chemical fixation as an extreme form of changes that may occur in certain pathologies such as diabetes. Techniques to estimate acoustic parameters from backscatter were broadened and challenges to implementing these techniques in vivo were addressed. Provided that specific challenges identified in this Dissertation can be overcome, techniques to estimate attenuation from ultrasonic backscatter show promise as a means to investigate the physical interaction of ultrasound with anisotropic biological media in vivo. This Dissertation represents a step towards understanding the physics of the interaction of ultrasonic waves with anisotropic biological media.

Baldwin, Steven L.

71

NASA Astrophysics Data System (ADS)

In-plane anisotropic carrier transport in single-crystalline grains of the dip-coated 6,13-bis(triisopropylsilylethynyl) (TIPS) pentacene film is studied by using the time-resolved microscopic optical second-harmonic generation (TRM-SHG). The TRM-SHG imaging directly visualizes the directional dependence of the carrier velocity, indicating the anisotropic carrier mobility of the TIPS pentacene single crystal. Results showed that the mobility anisotropy is smaller than that obtained from the current-voltage (I-V) characteristics. Overestimation of the mobility anisotropy using the I-V characteristics, compared with that obtained from the TRM-SHG measurement, is ascribed to the effect of the grain boundary on the carrier transport.

Manaka, Takaaki; Matsubara, Kohei; Abe, Kentaro; Iwamoto, Mitsumasa

2013-10-01

72

Anisotropic magnetic properties and giant magnetocaloric effect of single-crystal PrSi

NASA Astrophysics Data System (ADS)

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.

Das, Pranab Kumar; Bhattacharyya, Amitava; Kulkarni, Ruta; Dhar, S. K.; Thamizhavel, A.

2014-04-01

73

High pressure growth and anisotropic properties of MgB2 single crystals

NASA Astrophysics Data System (ADS)

Single crystals of MgB2 have been grown with a high pressure cubic anvil technique. They grow via the peritectic decomposition of a nitride MgNB_9. The crystals are of a size up to 1.5x0.9x0.2mm^3 with a weight up to 230?g. Typically they have transition temperatures between 38 and 38.6 K with a width of 0.3-0.5 K. Investigations of the P-T phase diagram prove that the MgB2 phase is stable at least up to 2190^oC at high hydrostatic pressure in the presence of Mg vapor under high pressure. Small variations of Tc are caused by doping with metal impurities from the precursor or by annealing of defects introduced during the crystal growth process. The high quality of the crystals allowed the accurate determination of magnetic, transport (electric and heat) and optical properties as well as scanning tunnelling spectroscopy (STS), point contact spectroscopy and decoration studies. Investigations of crystals with torque magnetometry show that H_c2^||c is very low (24 kOe at 15 K) and saturates with decreasing temperature, while H_c2^||ab increases up to 140 kOe at 15K. The upper critical field anisotropy ?H = H_c2^||ab/H_c2^||c was found to be temperature dependent (decreasing from ?H 6 at 15 K to 2.8 at 35 K). The effective anisotropy ?_eff, as calculated from reversible torque data near T_c, is field dependent (increasing roughly linearly from ?_eff 2 in zero field to 3.7 in 10 kOe). This is in disagreement with the anisotropic Ginzburg-Landau theory, which predicts that the anisotropy is temperature and field independent. The temperature and field dependence of the anisotropy is related to the double gap structure of MgB2 with a large two-dimensional gap and small three-dimensional gap, the latter of which is rapidly suppressed in a magnetic field. Decoration experiments and STS visualize a hexagonal vortex lattice. STS and point contact spectroscopy spectra evidence two gaps with a weight depending on the tunnelling direction. Magneto-optic investigations in the far infrared region with H||c show a clear signature of the smaller of the two superconducting gaps, completely disappearing only in fields higher than H_c2^||c.

Karpinski, Janusz

2003-03-01

74

Imaging the anisotropic elastic properties of paper with the INEEL laser ultrasonic camera

NASA Astrophysics Data System (ADS)

An important material property in the paper industry is the anisotropic stiffness distribution due to the fibrous microstructure of paper. Ultrasonic methods offer a means of determining the stiffness of sheets of paper from the anisotropic propagation characteristics of elastic Lamb waves along the machine direction (MD) and the cross direction (CD). Currently, piezoelectric ultrasonic methods are employed in the industry to measure the elastic polar diagram of paper through multiple contacting measurements made in all directions. This paper describes a new approach utilizing the INEEL Laser Ultrasonic Camera to provide a complete image of the elastic waves traveling in all directions in the plane of the paper sheet. This approach is based on optical dynamic holographic methods that record the out of plane ultrasonic motion over the entire paper surface simultaneously without scanning. The full-field imaging technique offers great potential for increasing the speed of the measurement and it ultimately provides a great deal of information concerning local property variations and flaws in the paper. This report shows the success of the method and the manner in which it yields the elastic polar diagram for the paper from the dispersive flexural or antisymmetric Lamb wave.

Deason, V. A.; Telschow, K. L.; Schley, R. S.; Watson, S. M.

2000-05-01

75

Anisotropic optical properties of YBa sub 2 Cu sub 3 O sub 7

Based upon the published results of YBa{sub 2}Cu{sub 3}O{sub 7} single-crystal reflectance spectra measured at room temperature, the empirical anisotropic spectral density functions and quasidielectric functions {epsilon}{sub 1{ital j}}+{ital i}{epsilon}{sub 2{ital j}} ({ital j}={ital a},{ital b},{ital c}) are determined in the 0.05 to 6 eV spectral range. These functions are an excellent fit to the reflectance spectra of samples in single-crystal, twin-crystal, and polycrystalline forms; they agree well with the published anisotropic transport and ellipsometry data. For polarizations along the {ital a} and {ital b} axes, the numerically determined empirical spectral density functions have shown two interband absorption peaks at 2.5 and 5 eV. For energy above 3 eV, the spectral density functions do not agree with the published theoretical interband conductivities that are derived from the band structure calculations.

Nee, T. (Research Department, Naval Air Warfare Center Weapons Division, China Lake, California 93555-6001 (United States))

1992-06-15

76

Dual Transport Properties of Anion Exchanger 1

Previous results suggested that specific point mutations in human anion exchanger 1 (AE1) convert the electroneutral anion exchanger into a monovalent cation conductance. In the present study, the transport site for anion exchange and for the cation leak has been studied by cysteine scanning mutagenesis and sulfhydryl reagent chemistry. Moreover, the role of some highly conserved amino acids within members of the SLC4 family to which AE1 belongs has been assessed in AE1 transport properties. The results suggest that the same transport site within the AE1 spanning domain is involved in anion exchange or in cation transport. A functioning mechanism for this transport site is proposed according to transport properties of the different studied point mutations of AE1. PMID:21257764

Barneaud-Rocca, Damien; Borgese, Franck; Guizouarn, Helene

2011-01-01

77

NASA Astrophysics Data System (ADS)

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.

Turba, K.; Hurst, R. C.; Hähner, P.

2012-09-01

78

Study of the Anisotropic Properties of Argillite Under Moisture and Mechanical Loads

NASA Astrophysics Data System (ADS)

Due to various factors, such as sedimentation, layered morphology of clay minerals, in situ stress, etc., argillite rocks often exhibit anisotropic behavior. In order to study the anisotropic properties of the Callovo-Oxfordian (COx) argillite of the Meuse-Haute-Marne site in France considered as a possible host rock for high-level radioactive nuclear waste repository, a series of tests including uniaxial compression and dehydration and hydration at different constant applied stress levels are carried out. In this study, a specific setup combining moisture and mechanical loading with optical observation is used and it allows to continuously capture surface images from which the full-field strains are determined by using Digital Image Correlation techniques. The results show evidence of the mechanical and hydric anisotropy of the material. The anisotropy parameters are identified, assuming the studied argillite as transversely isotropic. The shrinkage and swelling depend on the applied stress and the angle with respect to the vertical direction of the mechanical load and the stratification plane, and this dependence is quantified. The non-linearity and the hysteresis observed during dehydration and hydration cycles are discussed.

Yang, Diansen; Chanchole, Serge; Valli, Pierre; Chen, Liufeng

2013-03-01

79

Three-Dimensional Antiferromagnetic Order and Anisotropic Magnetic Properties in Bi2CuO4

NASA Astrophysics Data System (ADS)

The structure and magnetic properties of Bi2CuO4 have been studied by neutron and X-ray diffraction, magnetic susceptibility and magnetization measurements. Three-dimensional (3D) and anisotropic antiferromagnetism is revealed for this compound rather than the previously anticipated one-dimensional one. Long-range antiferromagnetic order associated with a ferromagnetic stacking of Cu2+ spins along the [001] axis starts to develop below TN{=}42 K. A magnetic moment of 0.85± 0.05 ?B/Cu which is larger than those of Cu2+ spins in the two-dimensional Heisenberg antiferromagnets such as La2CuO4 and Sr2CuCl2O2 reflects the 3D character in Bi2CuO4. A non-linear magnetization curve under an inplane magnetic field is analyzed quantitatively by a continuous spin rotation in the (001) plane.

Yamada, Kazuyoshi; Takada, Ken-ichi; Hosoya, Syoichi; Watanabe, Yousuke; Endoh, Yasuo; Tomonaga, Norihisa; Suzuki, Takashi; Ishigaki, Toru; Kamiyama, Takashi; Asano, Hajime; Izumi, Fujio

1991-07-01

80

NASA Astrophysics Data System (ADS)

We have investigated the magnetic susceptibility, the electrical resistivity, the specific heat, the thermoelectric power, the Hall coefficient, and the thermal conductivity of the Al13Fe4 and Al13(Fe,Ni)4 monoclinic approximants to the decagonal quasicrystal. While the Al13Fe4 crystals are structurally well ordered, the ternary derivative Al13(Fe,Ni)4 contains substitutional disorder and is considered as a disordered version of the Al13Fe4 . The crystallographic-direction-dependent measurements were performed along the a? , b , and c directions of the monoclinic unit cell, where the (a?,c) atomic planes are stacked along the b direction. The electronic transport and the magnetic properties exhibit significant anisotropy. The stacking b direction is the most conducting direction for the electricity and heat. The effect of substitutional disorder in Al13(Fe,Ni)4 is manifested in the large residual resistivity ?(T?0) and significantly reduced thermal conductivity of this compound, as compared to the ordered Al13Fe4 . Specific-heat measurements reveal that the electronic density of states at the Fermi level of both compounds is high. The anisotropic Hall coefficient RH reflects complex structure of the anisotropic Fermi surface that contains electronlike and holelike contributions. Depending on the combination of directions of the current and the magnetic field, electronlike (RH<0) or holelike (RH>0) contributions may dominate, or the two contributions compensate each other (RH?0) . Similar complicated anisotropic behavior was observed also in the thermopower. The anisotropic Fermi surface was calculated ab initio using the atomic parameters of the refined Al13Fe4 structural model that is also presented in this work.

Pop?evi?, P.; Smontara, A.; Ivkov, J.; Wencka, M.; Komelj, M.; Jegli?, P.; Vrtnik, S.; Bobnar, M.; Jagli?i?, Z.; Bauer, B.; Gille, P.; Borrmann, H.; Burkhardt, U.; Grin, Yu.; Dolinšek, J.

2010-05-01

81

Computing Thermodynamic And Transport Properties Of Air

NASA Technical Reports Server (NTRS)

EQAIRS computer program is set of FORTRAN 77 routines for computing thermodynamic and transport properties of equilibrium air for temperatures from 100 to 30,000 K. Computes properties from 11-species, curve-fit mathematical model. Successfully implemented on DEC VAX-series computer running VMS, Sun4-series computer running SunOS, and IBM PC-compatible computer running MS-DOS.

Thompson, Richard A.; Gupta, Roop N.; Lee, Kam-Pui

1994-01-01

82

Measuring the elastic properties of anisotropic materials by means of indentation experiments

The unloading process in an indentation experiment is usually modeled by considering the contact of a rigid punch with an elastically isotropic half space. Here we extend the analysis to elastically anisotropic solids, We review some of the basic formulae for describing the indentation of elastically anisotropic solids with axisymmetric indenters, We show how the indentation modulus can be calculated

JOOST J. VLASSAK; W. D. NIX

1994-01-01

83

NASA Astrophysics Data System (ADS)

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.

Olariu, C. S.; Padurariu, L.; Stanculescu, R.; Baldisserri, C.; Galassi, C.; Mitoseriu, L.

2013-12-01

84

We show that Monte Carlo simulations of neutral particle transport in planar-geometry anisotropically scattering media, using the exponential transform with angular biasing as a variance reduction device, are governed by a new “Boltzmann Monte Carlo” (BMC) equation, which includes particle weight as an extra independent variable. The weight moments of the solution of the BMC equation determine the moments of

Taro Ueki; Edward W Larsen

1998-01-01

85

The Anisotropic Elastic Properties of the Sarcolemma of the Frog Semitendinosus Muscle Fiber

Tension and curvature of the sarcolemmal tube of the frog muscle fiber were measured at different extensions and were used to calculate the anisotropic elastic properties of the sarcolemma. A model was derived to obtain the four parameters of the elasticity matrix of the sarcolemma. Sarcolemmal thickness was taken as 0.1 ?m. Over the range of reversible sarcolemmal tube extension, the longitudinal elastic modulus EL = 6.3 × 107 dyn/cm2, the circumferential modulus Ec = 0.88 × 107 dyn/cm2, the longitudinal Poisson's ratio ?L = 1.2, and the circumferential Poisson's ratio ?c = 0.18. At tubular rest length EL = 1.2 × 107 dyn/cm2. The sarcolemma is less extensible in the longitudinal direction along the fiber axis than in the circumferential direction. It can be extended reversibly to 48% of its rest length, equivalent to extending the intact fiber from a sarcomere length of 3 ?m to about 4.5 ?m. The sarcolemma does not contribute to intact fiber tension at fiber sarcomere lengths <3 ?m, and between 3 and 4 ?m its contribution is about 20%. It also exerts a pressure on the myoplasm, which can be calculated by means of the model. The longitudinal elastic modulus of the whole fiber is 1 × 105 dyn/cm2 at a sarcomere length of 2.33 ?m. ImagesFIGURE 6FIGURE 7 PMID:4541138

Rapoport, Stanley I.

1973-01-01

86

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.

Cho, B.

1995-11-01

87

NASA Astrophysics Data System (ADS)

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.

Wang, Lei; Wang, Xiaodong

2014-06-01

88

An explicite expression for ground state energy of the anisotropic XY chain in transverse magnetic field has been derived. The ground state energy has been expressed in terms of elliptic integrals of the first, second and third kind. The smoothness properties of resulting expression have been examined. We have confirmed known 2d-Ising type behaviour on certain lines of phase diagram and calculated few first subleading exponents; they can be computed up to arbitrary order from our expressions. We have also explicitely demonstrated that the ground-state energy is infinitely differentiable on the boundary between ferromagnetic and oscillatory phases.

Tomasz Maci??ek; Jacek Wojtkiewicz

2014-09-20

89

Transport approach to anisotropic flows from viscous hydro regime to high pT

NASA Astrophysics Data System (ADS)

We discuss the build up of the elliptic flow v2 in a transport approach at fixed viscosity. We point out that in the indermediate transverse momentum region flows are also sensitive to microscopic details of the cross section, while hydrodynamics suffers from large uncertainties due to the non-equilibrium correction to the distribution function. We show, exploring the temperature dependence of ?/s, that a study of v2 in a wide pT range allows to understand the difference behind the collective flows at LHC respect to RHIC. In particular the transport approach provides a tool able to naturally describe the rise and fall and saturation of the v2(pT).

Plumari, Salvatore; Puglisi, Armando; Scardina, Francesco; Greco, Vincenzo

2013-09-01

90

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

Cuenca, Jacques; Göransson, Peter

2012-08-01

91

Modeling graphene: Magnetic, transport and optical properties

NASA Astrophysics Data System (ADS)

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

Chang, Yi Chen

92

NASA Astrophysics Data System (ADS)

We report the analytic formula of an electromagnetic Gaussian-Schell-model (EGSM) beam propagating through the turbulent biological tissues. With the help of this formula, the changes in characteristics of the beam such as the spectral density, the spectral degree of coherence, the spectral degree of polarization, and the spectral degree of cross-polarization of the EGSM beam passing through the biological tissues are illustrated and compared by numerical examples. The changes in anisotropic and isotropic EGSM beams are indicated. Necessary comparisons and analyses of the beams generated by the anisotropic source and the isotropic source through the turbulent biological tissues are given. Moreover, the influence of the light source and turbulence of tissues on the changes of the spectral degree of cross-polarization of the EGSM beam passing through the biological tissues are compared in the near-field and the far-field.

Liu, Xiaoying; Zhao, Daomu

2012-10-01

93

Transport properties of dense matter. II

Exact solutions for the transport coefficients of a multicomponent system of several interacting Fermi liquids are given in the low temperature limit. The transport coefficients are found by solving a set of coupled Boltzmann transport equations. These solutions for the transport coefficients are used to evaluate the thermal conductivity and viscosity of neutron star matter in the density regime where

E. Flowers; N. Itoh

1979-01-01

94

Purpose To evaluate the utility of mechanical anisotropy (shear storage modulus parallel to fiber/shear storage modulus perpendicular to fiber) measured by combined magnetic resonance (MR) elastography and diffusion-tensor imaging ( DTI diffusion-tensor imaging ) technique (anisotropic MR elastography) to distinguish between healthy and necrotic muscle with different degrees of muscle necrosis in the mdx mouse model of muscular dystrophy. Materials and Methods The experimental protocol was approved by the regional animal ethics committee. Twenty-one mdx and 21 wild-type ( WT wild type ) mice were used in our study. Animals were divided into exercised and sedentary groups. Anisotropic MR elastography was used to obtain mechanical anisotropic shear moduli for the lateral gastrocnemius and plantaris muscles in a 7-T MR imager, from which the mechanical anisotropic ratio was calculated. The animals were imaged before and after 10 weeks of a horizontal treadmill running protocol. Spearman rank correlations were used to compare MR elastographic data with muscle necrotic area percentage from histologic analysis. Mechanical anisotropy in WT wild type and mdx mice muscle were compared by using t test and one-way analysis of variance, and receiver operating characteristic curves were constructed by using statistical software. Results Anisotropic MR elastography was able to be used to distinguish between the muscles of mdx and WT wild type mice, with an area under the receiver operating characteristic curve of 0.8. Strong negative correlation (rs = -0.701; P < .001) between the mechanical anisotropic ratio and the percentage of muscle necrotic area was found. By comparing mice with no or mild (0%-5% mean necrotic area) and severe (>5% mean necrotic area) muscle necrosis, an area under the receiver operating characteristic curve of 0.964 was achieved. Diffusion parameters alone were unable to distinguish between the WT wild type and mdx mice at any time point. Conclusion The mechanical anisotropic ratio of the shear storage moduli measured by an anisotropic MR elastographic technique can distinguish between healthy muscle and dystrophic muscle. © RSNA, 2014. PMID:25105354

Qin, Eric C; Jugé, Lauriane; Lambert, Simon A; Paradis, Valérie; Sinkus, Ralph; Bilston, Lynne E

2014-12-01

95

Correlations among magnetic, electrical and magneto-transport properties of NiFe nanohole arrays.

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

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

96

Anisotropic thermal transport in Bi2223/Ag superconducting tape with sandwiched structure

NASA Astrophysics Data System (ADS)

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.

Naito, Tomoyuki; Fujishiro, Hiroyuki; Osabe, Goro; Fujikami, Jun

2013-01-01

97

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.

Souza, W.R.; Voss, C.I.

1987-01-01

98

Real versus synthesized fractal surfaces: contact mechanics and transport properties

and safety of nuclear power plants or cryotechnic rocket engines, where the sealing of some units as for transport properties for this class of surfaces. This validates the overall procedure described in this work by surface flattening. To estimate these transport properties, we propose a three step-procedure which

Paris-Sud XI, UniversitÃ© de

99

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.

Goodman, Michael L., E-mail: mgoodman@wvhtf.org [Advanced Technologies Group, West Virginia High Technology Consortium Foundation, 1000 Galliher Drive, Fairmont, WV 26554 (United States)

2011-04-10

100

NASA Astrophysics Data System (ADS)

A Harris sheet magnetic field with maximum magnitude B 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.

Goodman, Michael L.

2011-04-01

101

Anisotropic properties and conduction mechanism of TlInSe2 chain semiconductor

NASA Astrophysics Data System (ADS)

TlInSe2 chain crystals were prepared using the modification of the Bridgman technique. The grown crystals were identified by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), and X-ray diffraction (XRD). We investigate the anisotropy of transport properties for the first time for TlInSe2 crystals. Temperature dependence of the dc electrical conductivity, Hall coefficient, Hall mobility, and charge carrier concentration were investigated in the temperature range 184-455 K. The conduction mechanism of TlInSe2 crystals was studied, and measurements revealed that the dc behavior of the grown crystals can be described by Mott's variable range hopping (VRH) model in the low temperature range, while it is due to thermoionic emission of charge carriers over the chain boundaries above 369 K. The Mott temperature, the density of states at the Fermi level, and the average hopping distance are estimated in the two crystallographic directions. The temperature dependence of the ac conductivity and the frequency exponent, s, is reasonably well interpreted in terms of the correlated barrier-hopping CBH model.

Ebnalwaled, A. A.; Al-Orainy, R. H.

2013-09-01

102

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

103

NASA Astrophysics Data System (ADS)

The compound Fe2Ti O5 (FTO) is a well-known uniaxial anisotropic spin-glass insulator with two successive glassy freezing temperatures, i.e., transverse (TT F= 9 K ) and longitudinal (TL F= 55 K ) . In this article, we present the results of measurements of complex dielectric behavior, electric polarization as a function of temperature (T ), in addition to characterization by magnetic susceptibility and heat capacity, primarily to explore magnetoelectric (ME) coupling and multiglass properties in uniaxial anisotropic spin-cluster-glass FTO. The existence of two magnetic transitions is reflected in the isothermal magnetodielectric (MD) behavior in the sense that the sign of MD is different in the T regime T `TT F . The data in addition provide evidence for the glassy dynamics of electric dipoles; interestingly, this occurs at much higher temperature (˜100-150 K) than TL F, with high remnant polarization at 10 K (˜4000 ? C /m2) attributable to short-range magnetic correlations, thereby offering a route to attain ME coupling above 77 K.`

Sharma, Shivani; Basu, Tathamay; Shahee, Aga; Singh, K.; Lalla, N. P.; Sampathkumaran, E. V.

2014-10-01

104

Transport properties of the quark gluon plasma

NASA Astrophysics Data System (ADS)

We use kinetic theory to investigate two transport properties of high temperature Quark Gluon Plasma (QGP) in the weak coupling limit. Bulk viscosity of QGP is calculated along with the splitting/joining functions in the deep Landau-Pomeranchuk-Migdal (LPM) regime. Within the framework of kinetic theory and in particular using the linearized Boltzmann equation we calculate the bulk viscosity of QGP to leading-order in the strong coupling constant gs. We also provide the first two coefficients of the series in inverse powers of log[1/gs] of the leading-order answer. We find that for realistic values of the strong coupling constant bulk viscosity can be neglected in comparison to shear viscosity. Calculation of jet quenching or the energy loss of high energy jets is dominated by radiative energy loss. In order to calculate the radiative energy loss of high energy jets at finite temperature we need to take the LPM effect into account. This requires the calculation of the splitting/joining functions. We manage to calculate these functions analytically in the deep LPM regime to next-to-leading logarithmic order in the ratio of the momentum of the jet to the temperature. Our result is general enough to be valid for systems that have an isotropic momentum distribution.

Dogan, Caglar

105

Applications of asymmetric nanotextured parylene surface using its wetting and transport properties

NASA Astrophysics Data System (ADS)

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.

Sekeroglu, Koray

106

NASA Astrophysics Data System (ADS)

We report on the anisotropic optical properties of single-crystal tin monosulfide (SnS). The components ?a, ?b, and ?c of the pseudodielectric-function tensor ??? = ??1? + i??2? 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.

Banai, R. E.; Burton, L. A.; Choi, S. G.; Hofherr, F.; Sorgenfrei, T.; Walsh, A.; To, B.; Cröll, A.; Brownson, J. R. S.

2014-07-01

107

NASA Astrophysics Data System (ADS)

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.

Ortiz, Aurélie U.; Boutin, Anne; Fuchs, Alain H.; Coudert, François-Xavier

2012-11-01

108

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.

Gorelikov, G. A.; Fridman, Yu. A., E-mail: frid@crimea.edu [Vernadskii Tavria National University (Ukraine)

2013-07-15

109

Magneto-transport properties of gapped graphene.

Based on the Kubo formula, we have studied the electron transport properties of a gapped graphene in the presence of a strong magnetic field. By solving the Dirac equation, we find that the Landau level spectra in two valleys differ from each other in that the n = 0 level in the K valley is located at top of the valence band, whereas it is at the bottom of the conduction band in the K' valley. Thus, in an individual valley, the symmetry between conduction and valence bands is broken by the presence of a magnetic field. By using the self-consistent Born approximation to treat the long range potential scattering, we formulate the diagonal and the Hall conductivities in terms of the Green function. To perform the numerical calculation, we find that a large bandgap can suppress the quantum Hall effect, owing to the enhancement of the bandgap squeezing the spacing between the low-lying Landau levels. On the other hand, if the bandgap is not very large, the odd integer quantum Hall effect experimentally, observed in the gapless graphene, remains in the gapped one. However, such a result does not indicate the half integer quantum Hall effect in an individual valley of the gapped graphene. This is because the heights of the Hall plateaux in either valley can be continuously tuned by the variation of the bandgap. More interestingly, we find that the height of the diagonal conductivity peak corresponding to the n = 0 Landau level is independent of the bandgap if the scattering is not very strong. In the weak scattering limit, we demonstrate analytically that such a peak takes a universal value e(2)/(hpi), regardless of the bandgap. PMID:20220217

Jiang, Liwei; Zheng, Yisong; Li, Haidong; Shen, Honghai

2010-04-01

110

Transport, thermal, and magnetic properties in heavy-fermion superconductor Ce 2CoIn 8

NASA Astrophysics Data System (ADS)

We have grown high purity single crystals of Ce 2CoIn 8 using the self-flux technique, and have investigated its transport, thermal, and magnetic properties, including the anisotropic features. Single crystals of Ce 2CoIn 8 were grown in the lower temperature region to avoid the formation of un-wanted phases such as CeCoIn 5 and CeIn 3 impurities. The results of the structural and physical measurements imply that the present single crystals have high purity. The electrical resistivity and specific heat measurements demonstrate that Ce 2CoIn 8 has a superconducting ground state with a distinct non-Fermi liquid character. This indicates that the superconductivity in Ce 2CoIn 8 arises out of the verge of the underlying quantum critical instability mediated by the antiferromagnetic correlations. Additionally, we investigate the crystalline electric field (CEF) energy scheme based on the temperature dependence of the specific heat and the anisotropic features in the susceptibility. We propose one of the CEF level schemes calculated on the basis of the CEF model that the first and second CEF states are located at ?1 = 82 K and ?2 = 102 K above the ground state doublet, respectively.

Yamashita, Tetsuro; Ohara, Shigeo; Sakamoto, Isao

2011-12-01

111

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.

Friedel, Michael J.

2001-01-01

112

Theoretical investigation of thermoelectric transport properties of cylindrical Bi nanowires

We report here a theoretical model for the transport properties of cylindrical Bi nanowires. Based on the band structure of Bi nanowires and the semiclassical transport model, the thermoelectric figure of merit Z1DT is calculated for Bi nanowires with various wire diameters and wire orientations. The results show the trigonal axis is the most favorable wire orientation for thermoelectric applications,

Yu-Ming Lin; Xiangzhong Sun; M. S. Dresselhaus

2000-01-01

113

NASA Astrophysics Data System (ADS)

Bio-molecular films of the DNA base guanine were characterized by ellipsometry from the Infrared (IR) to Vacuum Ultraviolet (VUV) spectral range, X-ray diffraction (XRD) and atomic force microscopy (AFM). In this study we in particular focus on the contact-less and reference-free characterization of thin anisotropic bio-molecular films by ellipsometry. Ellipsometric spectra in the IR as well as in the UV-VUV spectral range are molecule specific and the absorption bands could be used to identify molecules deposited on a substrate, since both the vibrational and electronic excitations are molecule specific. Especially we demonstrate that the measured pseudo-dielectric function in the mid infrared (MIR) spectral range can be used as a characteristic fingerprint for DNA base molecules and their orientation in a thin film. Moreover an interpretation of the ellipsometric spectra in an optical model delivers the dielectric function and could give information about the molecular structure, orientation and conductivity. The determination of average molecular orientations from IR and UV/VUV ellipsometry spectra is discussed.

Hinrichs, K.; Silaghi, S. D.; Cobet, C.; Esser, N.; Zahn, D. R. T.

2005-11-01

114

The purpose of this project is not so much to compare different methods in analyzing the solute transport problems as to evaluate whether the dispersivity involved in the Advection-Dispersion Equation (ADE) can be relatively intrinsic to aquifers when more detailed groundwater flow fields are taken into account in the mathematical model. Here, the 'more detailed groundwater flow field' means that (1) it is anisotropic and three-dimensional, and (2) it is estimated from three-dimensional depth-specific drawdown data. Of course, the solute transport phenomenon is accordingly considered to be three-dimensional and under the influence of aquifer anisotropy, and is analyzed using three-dimensional depth-specific tracer test data.

Chen, C.S.; Holmes, C.; Li, W.; Chace, D.; Fort, M.

1993-05-01

115

Transport properties of pancreatic cancer describe gemcitabine delivery and response

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

Koay, Eugene J.; Truty, Mark J.; Cristini, Vittorio; Thomas, Ryan M.; Chen, Rong; Chatterjee, Deyali; Kang, Ya'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

116

Transport properties of quantum-classical systems.

Correlation function expressions for calculating transport coefficients for quantum-classical systems are derived. The results are obtained by starting with quantum transport coefficient expressions and replacing the quantum time evolution with quantum-classical Liouville evolution, while retaining the full quantum equilibrium structure through the spectral density function. The method provides a variety of routes for simulating transport coefficients of mixed quantum-classical systems, composed of a quantum subsystem and a classical bath, by selecting different but equivalent time evolution schemes of any operator or the spectral density. The structure of the spectral density is examined for a single harmonic oscillator where exact analytical results can be obtained. The utility of the formulation is illustrated by considering the rate constant of an activated quantum transfer process that can be described by a many-body bath reaction coordinate. PMID:15974726

Kim, Hyojoon; Kapral, Raymond

2005-06-01

117

Molecular transport properties through carbon nanotube membrane

NASA Astrophysics Data System (ADS)

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

Majumder, Mainak

118

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...

119

Determination of the anisotropic elastic properties of Ge1Sb2Te4

NASA Astrophysics Data System (ADS)

The elastic properties of Ge-Sb-Te (GST) alloys are important for phase-change devices (such as CD-RW, DVD-RW, Blu-ray, or phase-change random access memory) because the transition between the crystalline and amorphous phases involves a volume change accommodated by a strain estimated to be between 150 MPa and 10 GPa. However, the elastic properties of GST alloys are poorly characterized and the experimental and theoretical values show large discrepancies. We carry out a careful analysis of the elastic properties of a model system, crystalline Ge1Sb2Te4, using density functional theory and elastic anisotropy considerations. We show that Ge1Sb2Te4 exhibits significant anisotropy in its elastic properties.

Marmier, Arnaud; Kohary, Krisztian; Wright, C. David

2011-06-01

120

Abstract Objective. A major aspect in evaluating the quality of dental materials is their physical properties. Their properties should be a best fit of the ones of dental hard tissues. Manufacturers give data sheets for each material. The properties listed are characterized by a specific value. This assumes (but does not prove) that there is no direction dependence of the properties. However, dental enamel has direction-dependent properties which additionally vary with location in the tooth. The aim of this paper is to show the local direction dependence of physical properties like the elastic modulus or the thermal expansion in dental hard tissues. With this knowledge the 'perfect filling/dental material' could be characterized. Materials and method. Enamel sections of ?400-500 ?m thickness have been cut with a diamond saw from labial/buccal to palatal/lingual (canine, premolar and molar) and parallel to labial (incisor). Crystallite arrangements have been measured in over 400 data points on all types of teeth with x-ray scattering techniques, known from materials science. Results. X-ray scattering measurements show impressively that dental enamel has a strong direction dependence of its physical properties which also varies with location within the tooth. Dental materials possess only little or no property direction dependence. Therefore, a mismatch was found between enamel and dental materials properties. Conclusion. Since dental materials should possess equal (direction depending) properties, worthwhile properties could be characterized by transferring the directional properties of enamel into a property 'wish list' which future dental materials should fulfil. Hereby the 'perfect dental material' can be characterized. PMID:24460030

Raue, Lars; Hartmann, Christiane D; Rödiger, Matthias; Bürgers, Ralf; Gersdorff, Nikolaus

2014-11-01

121

Transport properties of a modified Lorentz gas

We present a detailed study of the first simple mechanical system that shows fully realistic transport behavior while still being exactly solvable at the level of equilibrium statistical mechanics. The system under consideration is a Lorentz gas with fixed freely-rotating circular scatterers interacting with point particles via perfectly rough collisions. Upon imposing a temperature and/or a chemical potential gradient, a stationary state is attained for which local thermal equilibrium holds for low values of the imposed gradients. Transport in this system is normal, in the sense that the transport coefficients which characterize the flow of heat and matter are finite in the thermodynamic limit. Moreover, the two flows are non-trivially coupled, satisfying Onsager's reciprocity relations to within numerical accuracy as well as the Green-Kubo relations . We further show numerically that an applied electric field causes the same currents as the corresponding chemical potential gradient in first order of the applied field. Puzzling discrepancies in higher order effects (Joule heating) are also observed. Finally, the role of entropy production in this purely Hamiltonian system is shortly discussed.

H. Larralde; F. Leyvraz; C. Mejia-Monasterio

2002-10-05

122

Unsaturated Zone and Saturated Zone Transport Properties (U0100)

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.

J. Conca

2000-12-20

123

Calix[4]pyrrole-based anion transporters with tuneable transport properties.

Three new bis-1,2,3-triazole strapped calix[4]pyrroles have been prepared via'click' chemistry and their anion complexation and lipid bilayer transport properties studied by a combination of single crystal X-ray diffraction studies, (1)H NMR titration techniques, isothermal titration calorimetry and lipid bilayer anion transport studies in POPC vesicles. Bilayer transport efficiency for transmembrane chloride transport was found to directly depend on the length of the alkyl chain present in the bis-triazole strap. PMID:20676429

Yano, Masafumi; Tong, Christine C; Light, Mark E; Schmidtchen, Franz P; Gale, Philip A

2010-10-01

124

Modelling the anisotropic seismic properties of partially molten rocks found at mid-ocean ridges

The problem of modelling the seismic properties of mid-ocean ridge rocks of the axial magma chamber (AMC) and the low-velocity triangle (LVT) immediately below it has been addressed using two samples from Oman ophiolite as examples. The specimens are a layered gabbro from the lower oceanic crustal sequence and a harzburgite from the upper most mantle section at the palaeo

David Mainprice

1997-01-01

125

d Original Contribution VISCOELASTIC AND ANISOTROPIC MECHANICAL PROPERTIES OF IN VIVO

properties, such as electromyography (EMG), which records the muscle electrical activity (Aminoff 1987), surface mechanomyography (sMMG) (Orizio 1993) or acceleromyography (Viby-Mogensen et al. 2003), which respectively records pressure or acceleration on the skin surface during a contraction. These techniques

Paris 7 - Denis Diderot, UniversitÃ©

126

NASA Astrophysics Data System (ADS)

The solutions of idealized fully nonlinear cloud resolving numerical simulations of orographic convective precipitation display statistical multiscaling, similar to what is commonly found in observations in the atmosphere. This result is verified even in the absence of scaling in the initial conditions or terrain forcing, suggesting that this scaling behavior should be a general property of the nonlinear solutions of the Navier-Stokes like equations governing the atmospheric dynamics. By taking advantage of this scale invariance property, statistical downscaling methods can be constructed which can be used as sub-grid scale parameterizations and provide a way to bridge between coarser resolution numerical simulations and the high resolution needs of hydrological applications. However, the horizontal scaling exponent function (and respective multifractal parameters) varies with atmospheric and terrain properties, particularly small scale terrain spectra, atmospheric stability and mean wind speed. This result qualitatively agrees with the predictions of linear stability analysis that suggests the governing role of these parameters in embedded convective structures. Hence multiscaling statistical parameters should be computed for each particular geographical location and atmospheric conditions, bringing the necessity of development of relationships to predict them from coarse grid atmospheric data and terrain spectra. The spatial anisotropy (both vertical and horizontal) of the scaling exponent function for rain, cloud and velocity fields is also investigated. Based on the computed statistical multifractal exponents, multifractal simulations are performed to test the ability of these cascade models in reproducing the statistical properties of the atmospheric fields and the sensitivity of the statistical properties of the fields to variations in the multifractal parameters. Finally, simulations with scaling terrain forcing are created and the relationship between scaling of rain, cloud and wind fields and topography is explored.

Nogueira, M.; Barros, A. P.; Miranda, P. M.

2011-12-01

127

Enhancement of wall jet transport properties

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.

Claunch, S.D.; Farrington, R.B.

1997-02-04

128

Enhancement of wall jet transport properties

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.

Claunch, Scott D. (Broomfield, CO); Farrington, Robert B. (Golden, CO)

1997-01-01

129

Anisotropic flow coefficients and their fluctuations are investigated for Au+Au collisions at center of mass energy $\\sqrt{s_{NN}}$ = 200 GeV by using a multi-phase 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 $v_n$ (for n = 2, 3 and 4) are performed, in which event distributions of $v_n$ for different orders are consistent with Gaussian shapes over all centrality bins. Systematic studies on centrality, transverse momentum ($p_{T}$) and pseudo-rapidity ($\\eta$) dependencies of anisotropic flows and quantitative estimations of the flow fluctuations are presented. The $p_{T}$ and $\\eta$ dependencies of absolute fluctuations for both $v_2$ and $v_3$ follow similar trends as their flow coefficients. Relative fluctuation of triangular flow $v_3$ is slightly centrality-dependent, which is quite different from that of elliptic flow $v_2$. 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.

L. Ma; G. L. Ma; Y. G. Ma

2014-04-23

130

Thermodynamic and transport properties of sodium liquid and vapor

Data have been reviewed to obtain thermodynamically consistent equations for thermodynamic and transport properties of saturated sodium liquid and vapor. Recently published Russian recommendations and results of equation of state calculations on thermophysical properties of sodium have been included in this critical assessment. Thermodynamic properties of sodium liquid and vapor that have been assessed include: enthalpy, heat capacity at constant pressure, heat capacity at constant volume, vapor pressure, boiling point, enthalpy of vaporization, density, thermal expansion, adiabatic and isothermal compressibility, speed of sound, critical parameters, and surface tension. Transport properties of liquid sodium that have been assessed include: viscosity and thermal conductivity. For each property, recommended values and their uncertainties are graphed and tabulated as functions of temperature. Detailed discussions of the analyses and determinations of the recommended equations include comparisons with recommendations given in other assessments and explanations of consistency requirements. The rationale and methods used in determining the uncertainties in the recommended values are also discussed.

Fink, J.K.; Leibowitz, L.

1995-01-01

131

High temperature transport properties of air

NASA Technical Reports Server (NTRS)

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).

Levin, E.; Partridge, Harry; Stallcop, J. R.

1987-01-01

132

Transport properties of high-temperature Jupiter atmosphere components

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.

Bruno, D.; Colonna, G.; De Pascale, O.; Laricchiuta, A. [Department of Chemistry, University of Bari, via Orabona 4 Bari 70125 (Italy); Catalfamo, C.; Diomede, P. [CNR-IMIP Bari, via Orabona 4 Bari 70125 (Italy); Capitelli, M.; Gorse, C.; Longo, S. [Department of Chemistry, University of Bari, via Orabona 4 Bari 70125 (Italy); CNR-IMIP Bari, via Orabona 4 Bari 70125 (Italy); Giordano, D. [Aerothermodynamics Section, ESA-ESTEC, Keplerlaan 1 2200 AG Noordwijk (Netherlands); Pirani, F. [Department of Chemistry, University of Perugia, via Elce di Sotto 8 Perugia 06123 (Italy)

2010-11-15

133

The mechanical properties of SC-15 epoxy can be significantly enhanced when reinforced with nanofillers. In this study, SC-15\\u000a epoxy is loaded with iron oxide nanoparticles and chemically functionalized single-wall carbon nanotubes and cured in a modest\\u000a magnetic field. Magnetic analysis shows that the iron oxide nanoparticles flocculate to form chains and create a structural\\u000a anisotropy in the system. Measurements of

O. Malkina; H. Mahfuz; K. D. Sorge; V. K. Rangari

2011-01-01

134

NASA Astrophysics Data System (ADS)

We use THz time-domain spectroscopy to investigate the far-infrared properties of vanadium dioxide thin films, strain-engineered through epitaxial growth on (100)R TiO2 substrates. The films exhibit a large uniaxial tensile strain along the rutile c-axis. X-ray diffraction measurements reveal a structural transition temperature of 340 K, whereas independent THz conductivity measurements yield a metal-insulator transition temperature of 365 K along cR. Analysis of these results suggests a Mott-Hubbard behavior along the cR-axis. Along cR the conductivity is approximately 5500 (? cm)-1, comparable to bulk single crystals. The tensile strain leads to remarkably uniform cracking oriented along the rutile c-axis, resulting in a large conductivity anisotropy in our single-crystal epitaxial thin films. We discuss our results in the context of previous measurements and calculations of the properties of VO2, under different strain conditions. This work demonstrates the potential of strain engineering to tune the properties of complex materials while also serving as a powerful discriminatory tool for probing microscopic responses.

Abreu, Elsa; Liu, Mengkun; Lu, Jiwei; West, Kevin G.; Kittiwatanakul, Salinporn; Yin, Wenjing; Wolf, Stuart A.; Averitt, Richard D.

2012-08-01

135

136

Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5?K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems. PMID:25399635

Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Zhang, Hong-Rui; Liu, Yao; Zhang, Ying; Wang, Shuan-Hu; Wu, Rong-Rong; Zhang, Ming; Bao, Li-Fu; Sun, Ji-Rong; Shen, Bao-Gen

2014-01-01

137

Transport properties in nontwist area-preserving maps

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.

Szezech Jr., J. D. [Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo (Brazil); Caldas, I. L. [Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo (Brazil); Lopes, S. R. [Departamento de Fisica, Universidade Federal do Parana, Curitiba (Brazil); Viana, R. L. [Departamento de Fisica, Universidade Federal do Parana, Curitiba (Brazil); Morrison, P. J. [Univ. of Texas at Austin (United States)

2009-10-23

138

Measurement of the radiative transport properties of reticulated alumina foams

This paper presents a method for determining radiative transport properties of reticulated materials. The method has both experimental and analytical components. A polar nephelometer is used to measure the scattering profile of a sample of the reticulated material. The results of a Monte Carlo simulation of the experiment are then combined with the experimental results to give the scatter albedo and extinction coefficient. This paper presents the results of using this method to determine the radiative transport properties of four different porosities (10, 20, 30, 65 pores per inch) of cylindrical reticulated alumina samples ranging in thickness form 0.5 inches to 2. 5 inches.

Hale, M.J.; Bohn, M.S.

1992-12-01

139

NASA Astrophysics Data System (ADS)

The m-plane GaN films grown on LiAlO2(100) by metal-organic chemical vapor deposition exhibit anisotropic crystallographic properties. The Williamson-Hall plots point out they are due to the different tilts and lateral correlation lengths of mosaic blocks parallel and perpendicular to GaN[0001] in the growth plane. The symmetric and asymmetric reciprocal space maps reveal the strain of m-plane GaN to be biaxial in-plane compress ?xx=-0.79% and ?zz=-0.14% with an out-of-plane dilatation ?yy=0.38%. This anisotropic strain further separates the energy levels of top valence band at ? point. The energy splitting as 37meV as well as in-plane polarization anisotropy for transitions are found by the polarized photoluminescence spectra at room temperature.

Liu, B.; Zhang, R.; Xie, Z. L.; Kong, J. Y.; Yao, J.; Liu, Q. J.; Zhang, Z.; Fu, D. Y.; Xiu, X. Q.; Chen, P.; Han, P.; Shi, Y.; Zheng, Y. D.; Zhou, S. M.; Edwards, G.

2008-06-01

140

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) 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

141

Void bounds for fluid transport properties of sea ice

Arctic and Antarctic sea ice plays a critical role in the global oceanclimate system, as well as in polar biology. Sea ice is a porous composite of pure ice with brine and air inclusions whose microstructure varies significantly with temperature. The fluid transport properties of sea ice control a broad range of geophysical and biological processes. Yet little is known,

K. M. Golden; A. L. Heaton; H. Eicken; V. I. Lytle

2005-01-01

142

Transport Properties of Random Media: A New Effective Medium Theory

We present a new method for efficient, accurate calculations of transport properties of random media. It is based on the principle that the wave energy density should be uniform when averaged over length scales larger than the size of the scatterers. This scheme captures the effects of resonant scattering of the individual scatterer exactly, as well as the multiple scattering

K. Busch; C. M. Soukoulis

1995-01-01

143

Transport properties at nano scales via first principles studies

There are two main difficulties for the first principles study of transport properties at the nano scale. The first is that many-body interactions need to be taken into account for the infinite system without periodic boundary conditions. The other is that the system is usually in a non-equilibrium state. Both of these two difficulties are beyond the ability of conventional

Chun Zhang

2004-01-01

144

Rotationally anisotropic surface second-harmonic generation (SHG) has been measured from a clean, well-ordered Cu(110) single-crystal surface as a function of both surface temperature and Ag coverage. For the clean Cu(110) surface, the temperature dependence of the SH response at a fixed azimuthal angle can be correlated with a surface phase transformation. A large decrease in the rotationally anisotropic SH response as a function of surface temperature can be related to changes in the surface disorder. The results are compared with other studies of Cu(110) surface structure using both x-ray and He-atom scattering. The rotationally anisotropic SH response has also been measured as a function of Ag coverage with the Cu(110) surface temperature fixed at 300 K. The results closely follow the formation of an ordered Ag(111)-like overlayer, the nucleation of three-dimensional Ag nanoclusters (<20 {angstrom} thick) that enhance the anisotropic SH response, and the subsequent growth of a {approximately}10 monolayer thick Ag film. Variations in the rotationally anisotropic SH response as a function of Ag coverage are used to separate the resonant surface electronic contributions to the nonlinear susceptibility of the interface. 22 refs., 4 figs.

Hoffbauer, M.A.; McVeigh, V.J.

1990-01-01

145

Transport properties in semiconducting NbS2 nanoflakes

NASA Astrophysics Data System (ADS)

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.

Huang, Y. H.; Peng, C. C.; Chen, R. S.; Huang, Y. S.; Ho, C. H.

2014-09-01

146

Measurement of gas transport properties for chemical vapor infiltration

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.

Starr, T.L.; Hablutzel, N. [Georgia Inst. of Tech., Atlanta, GA (United States). School of Materials Science and Engineering

1996-12-01

147

Rapid Salt Exchange by Coupled Ultrafiltration and Dialysis in Anisotropic Hollow Fibers

Anisotropic hollow fibers allow construction of a dialyzing system that provides extremely large membrane surface in a small laboratory-sized system. Possessing the added property of high ultrafiltration flux, these fibers reduce salt exchange times from days to hours. In this system the exchange of salt by dialytic transport is largely unaffected by recirculation rate, solute type, or content, but is

William F. Blatt; Lita Nelsen; Eliseo M. Zipilivan; Mark C. Porter

1972-01-01

148

Review on measurement techniques of transport properties of nanowires

NASA Astrophysics Data System (ADS)

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.

Rojo, Miguel Muñoz; Calero, Olga Caballero; Lopeandia, A. F.; Rodriguez-Viejo, J.; Martín-Gonzalez, Marisol

2013-11-01

149

Review on measurement techniques of transport properties of nanowires.

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

Rojo, Miguel Muñoz; Calero, Olga Caballero; Lopeandia, A F; Rodriguez-Viejo, J; Martín-Gonzalez, Marisol

2013-12-01

150

Transport, noise, and conservation properties in gyrokinetic plasmas

NASA Astrophysics Data System (ADS)

The relationship between various transport properties (such as particle and heat flux, entropy production, heating, and collisional dissipation) [1] is examined in electrostatic gyrokinetic simulations of ITG modes in simple geometry. The effect of the parallel velocity nonlinearity on the achievement of steady-state solutions and the transport properties of these solutions is examined; the effects of nonadiabatic electrons are also considered. We also examine the effectiveness of the electromagnetic split-weight scheme [2] in reducing the noise and improving the conservation properties (energy, momentum, particle number, etc.) of gyrokinetic plasmas. [1] W. W. Lee and W. M. Tang, Phys. Fluids 31, 612 (1988). [2] W. W. Lee, J. L. V. Lewandowski, T. S. Hahm, and Z.Lin, Phys. Plasmas 8, 4435 (2001).

Jenkins, Thomas

2005-10-01

151

Transport properties of Fe/GaAs/Ag(001) system.

We present results of ab initio transport calculations for epitaxial magnetic tunnel junctions Fe/GaAs/Ag(001). The electronic structure is calculated by means of the tight-binding linear muffin-tin orbital method and the ballistic conductances are evaluated within the Kubo-Landauer formalism which includes the effect of the spin-orbit interaction. Particular attention is paid to the dependence of the conductances on the orientation of magnetization direction of the Fe electrode with respect to the crystal lattice and on the thickness of the tunneling barrier. We have found that the in-plane tunneling anisotropic magnetoresistance (TAMR) exhibits a non-monotonic thickness dependence with a maximum around 7.5 nm of GaAs. This behavior is ascribed to a hybridization of interface resonances formed on both sides of the junction and manifested as hot spots in k[]-resolved conductances. For thicker GaAs barriers, the relative intensity of the hot spots is reduced on account of the contribution from a narrow central region of the two-dimensional Brillouin zone which leads to the final decrease of the TAMR effect. PMID:23035515

Sýkora, Rudolf; Turek, Ilja

2012-09-01

152

NASA Astrophysics Data System (ADS)

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.

Pedretti, D.; Fernandez-Garcia, D.; Bolster, D.; Sanchez-Vila, X.; Benson, D.

2012-04-01

153

Charge carrier transport properties in layer structured hexagonal boron nitride

NASA Astrophysics Data System (ADS)

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/T0)-? 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-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.

Doan, T. C.; Li, J.; Lin, J. Y.; Jiang, H. X.

2014-10-01

154

Diluted magnetic semiconductors: Actual structure and magnetic and transport properties

An experimental investigation is conducted into electrical-transport, magnetic, optical, and structural properties of GaAs-based\\u000a diluted-magnetic-semiconductor heterostructures containing a Ga1?x\\u000a In\\u000a x\\u000a As quantum well and a Mn delta layer 0.5–1.8 ML thick, separated by a GaAs spacer of thickness 3 nm. Ferromagnetic features\\u000a are observed in the electrical transport and the Hall effect, which involve the flow of holes across

M. A. Chuev; B. A. Aronzon; E. M. Pashaev; M. V. Koval’chuk; I. A. Subbotin; V. V. Rylkov; V. V. Kvardakov; P. G. Medvedev; B. N. Zvonkov; O. V. Vikhrova

2008-01-01

155

Intrinsic electronic and transport properties of graphyne sheets and nanoribbons

NASA Astrophysics Data System (ADS)

Graphyne, a two-dimensional carbon allotrope like graphene but containing doubly and triply bonded carbon atoms, has been proven to possess amazing electronic properties as graphene. Although the electronic, optical, and mechanical properties of graphyne and graphyne nanoribbons (NRs) have been previously studied, their electron transport behaviors have not been understood. Here we report a comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (?, ?, ?, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method. Among the four graphyne sheets, 6,6,12-graphyne displays notable directional anisotropy in the transport properties. Among the GyNRs, those with armchair edges are nonmagnetic semiconductors whereas those with zigzag edges can be either antiferromagnetic or nonmagnetic semiconductors. Among the armchair GyNRs, the ?-GyNRs and 6,6,12-GyNRs exhibit distinctive negative differential resistance (NDR) behavior. On the other hand, the zigzag ?-GyNRs and zigzag 6,6,12-GyNRs exhibit symmetry-dependent transport properties, that is, asymmetric zigzag GyNRs behave as conductors with nearly linear current-voltage dependence, whereas symmetric GyNRs produce very weak currents due to the presence of a conductance gap around the Fermi level under finite bias voltages. Such symmetry-dependent behavior stems from different coupling between ?* and ? subbands. Unlike ?- and 6,6,12-GyNRs, both zigzag ?-GyNRs and zigzag ?-GyNRs exhibit NDR behavior regardless of the symmetry.Graphyne, a two-dimensional carbon allotrope like graphene but containing doubly and triply bonded carbon atoms, has been proven to possess amazing electronic properties as graphene. Although the electronic, optical, and mechanical properties of graphyne and graphyne nanoribbons (NRs) have been previously studied, their electron transport behaviors have not been understood. Here we report a comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (?, ?, ?, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method. Among the four graphyne sheets, 6,6,12-graphyne displays notable directional anisotropy in the transport properties. Among the GyNRs, those with armchair edges are nonmagnetic semiconductors whereas those with zigzag edges can be either antiferromagnetic or nonmagnetic semiconductors. Among the armchair GyNRs, the ?-GyNRs and 6,6,12-GyNRs exhibit distinctive negative differential resistance (NDR) behavior. On the other hand, the zigzag ?-GyNRs and zigzag 6,6,12-GyNRs exhibit symmetry-dependent transport properties, that is, asymmetric zigzag GyNRs behave as conductors with nearly linear current-voltage dependence, whereas symmetric GyNRs produce very weak currents due to the presence of a conductance gap around the Fermi level under finite bias voltages. Such symmetry-dependent behavior stems from different coupling between ?* and ? subbands. Unlike ?- and 6,6,12-GyNRs, both zigzag ?-GyNRs and zigzag ?-GyNRs exhibit NDR behavior regardless of the symmetry. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03167e

Wu, Wenzhi; Guo, Wanlin; Zeng, Xiao Cheng

2013-09-01

156

In this article, we extend the one-speed multi-layer models to neutron reflection and transmission developed in our earlier work (de Abreu, M.P., 2005. Multi-layer models to neutron reflection and transmission for whole-core transport calculations, Annals of Nuclear Energy 32, 215) to multigroup transport theory. We begin by considering a two-layer boundary region, and we develop for such a region discrete

Marcos Pimenta de Abreu

2006-01-01

157

Intrinsic electronic and transport properties of graphyne sheets and nanoribbons.

Graphyne, a two-dimensional carbon allotrope like graphene but containing doubly and triply bonded carbon atoms, has been proven to possess amazing electronic properties as graphene. Although the electronic, optical, and mechanical properties of graphyne and graphyne nanoribbons (NRs) have been previously studied, their electron transport behaviors have not been understood. Here we report a comprehensive study of the intrinsic electronic and transport properties of four distinct polymorphs of graphyne (?, ?, ?, and 6,6,12-graphynes) and their nanoribbons (GyNRs) using density functional theory coupled with the non-equilibrium Green's function (NEGF) method. Among the four graphyne sheets, 6,6,12-graphyne displays notable directional anisotropy in the transport properties. Among the GyNRs, those with armchair edges are nonmagnetic semiconductors whereas those with zigzag edges can be either antiferromagnetic or nonmagnetic semiconductors. Among the armchair GyNRs, the ?-GyNRs and 6,6,12-GyNRs exhibit distinctive negative differential resistance (NDR) behavior. On the other hand, the zigzag ?-GyNRs and zigzag 6,6,12-GyNRs exhibit symmetry-dependent transport properties, that is, asymmetric zigzag GyNRs behave as conductors with nearly linear current-voltage dependence, whereas symmetric GyNRs produce very weak currents due to the presence of a conductance gap around the Fermi level under finite bias voltages. Such symmetry-dependent behavior stems from different coupling between ?* and ? subbands. Unlike ?- and 6,6,12-GyNRs, both zigzag ?-GyNRs and zigzag ?-GyNRs exhibit NDR behavior regardless of the symmetry. PMID:23949158

Wu, Wenzhi; Guo, Wanlin; Zeng, Xiao Cheng

2013-10-01

158

Large collective motions regulate the functional properties of glutamate transporter trimers

Large collective motions regulate the functional properties of glutamate transporter trimers Jie, 2011 (sent for review April 1, 2011) Glutamate transporters clear synaptically released glutamate large collective motions contribute to the functional dynamics of glutamate transporters. Neuronal

Benos, Takis

159

The objective of this thesis is to better understand the transport and seismoelectric (SE) properties of porous permeable rock. Accurate information of rock transport properties, together with pore geometry, can aid us to ...

Zhan, Xin, Ph. D. Massachusetts Institute of Technology

2010-01-01

160

Using moisture transport properties of rice seed components for identifying fissure resistance

Fissure resistance was related to the moisture transport properties of Cypress, Lemont, LaGrue, and Teqing rice varieties. The moisture transport properties, moisture diffusivity and resistance, were calculated using a three-dimensional moisture...

Thomas, Audrey Elizabeth

2012-06-07

161

Experimental methods for determination of transport properties of magma

NASA Astrophysics Data System (ADS)

The experimental techniques for measuring at high temperatures and pressures the transport properties of magma, a concentrated solution of silicates, are at a primitive stage. The fluxes of energy, mass, and momentum are usually interrelated in nature and are difficult to isolate in the laboratory. The measurement of thermal conductivity, a property of magma related to heat transport, is usually obtained by observing the temperature at two points in a cylindrical sample at different distances from a coaxial line heat source. There are no reported measurements of thermal conductivity in molten rocks under pressure. Electrical conductivity is obtained by measuring the flow of electricity between two conductors imbedded in the sample at various stages of melting under pressure. Elastic energy is transmitted and collected by means of transducers attached through suitable refractory extension rods to the ends of a cylindrical specimen held at specified pressures and temperatures to measure seismic wave velocities. The diffusion coefficient, the property of a chemical constituent of magma related to mass transport, has been measured for the self-diffusion of elements in multicomponent liquids, diffusion of elements between dissimilar liquids, diffusion of volatiles into or out of liquids, and isotopic exchange. At least five methods have been used at atmospheric pressure to obtain diffusion coefficients: (1) diffusion couple; (2) thin source; (3) thick source; (4) capillary-reservoir; and (5) bulk gain or loss. The results of only one method, involving a thin source, have been reported for an investigation carried out at a series of high pressures in the melt region. The variation of composition has been determined with measurements of index of refraction, autoradiography, ion and electron microprobe traverses, radioactivity of sections or their successive remainders, mass spectrometric analysis of sections, and weight gain or loss. Viscosity, the property of magma related to momentum transport, has been measured in magmas at high pressure with a sinking- or floating-sphere technique, rotating concentric cylinder, and capillary extrusion. Both viscosity and density, hence the kinematic viscosity, can be determined for the applied conditions from the Stokes relation by varying the density and size of the spheres in the sink-float technique. The Stokes-Einstein relationship between diffusivity and viscosity does not appear to hold for silicate magmas. Only one attempt has been made to study the flow of fluid through porous media, infiltration, at high pressures and temperatures. Convection, which appears to be the major transport process in magma, is amenable to laboratory investigation. Opportunities for research still lie in the investigation of the primary transport properties of magma at high pressures. The coupling of the fluxes will subsequently require evaluation.

Yoder, H. S.

162

Transport properties of anyons in random topological environments

NASA Astrophysics Data System (ADS)

The quasi-one-dimensional transport of Abelian and non-Abelian anyons is studied in the presence of a random topological background. In particular, we consider the quantum walk of an anyon that braids around islands of randomly filled static anyons of the same type. Two distinct behaviors are identified. We analytically demonstrate that all types of Abelian anyons localize purely due to the statistical phases induced by their random anyonic environment. In contrast, we numerically show that non-Abelian Ising anyons do not localize. This is due to their entanglement with the anyonic environment, which effectively induces dephasing. Our study demonstrates that localization properties strongly depend on nonlocal topological interactions, and it provides a clear distinction in the transport properties of Abelian and non-Abelian anyons.

Zatloukal, V.; Lehman, L.; Singh, S.; Pachos, J. K.; Brennen, G. K.

2014-10-01

163

Transport properties of two finite armchair graphene nanoribbons

In this work, we present a theoretical study of the transport properties of two finite and parallel armchair graphene nanoribbons connected to two semi-infinite leads of the same material. Using a single ?-band tight binding Hamiltonian and based on Green’s function formalisms within a real space renormalization techniques, we have calculated the density of states and the conductance of these systems considering the effects of the geometric confinement and the presence of a uniform magnetic field applied perpendicularly to the heterostructure. Our results exhibit a resonant tunneling behaviour and periodic modulations of the transport properties as a function of the geometry of the considered conductors and as a function of the magnetic flux that crosses the heterostructure. We have observed Aharonov-Bohm type of interference representing by periodic metal-semiconductor transitions in the DOS and conductance curves of the nanostructures. PMID:23279756

2013-01-01

164

In the present study we expand our analysis of using two contrasting organic solvent additives (toluene and THF) in an ionic liquid (IL)/Li NTf(2) electrolyte. Multinuclear Pulsed-Field Gradient (PFG) NMR, spin-lattice (T(1)) relaxation times and conductivity measurements over a wide temperature range are discussed in terms of transport properties and structuring of the liquid. The conductivity of both additive samples is enhanced the most at low temperatures, with THF slightly more effective than toluene. Both the anion and lithium self-diffusivity are enhanced in the same order by the additives (THF > toluene) while that of the pyrrolidinium cation is marginally enhanced. (1)H spin-lattice relaxation times indicate a reasonable degree of structuring and anisotropic motion within all of the samples and both (19)F and (7)Li highlight the effectiveness of THF at influencing the lithium coordination within these systems. PMID:21279209

Bayley, Paul M; Best, A S; MacFarlane, D R; Forsyth, M

2011-03-14

165

Thermal transport properties of strontium intercalated titanium diselenide

NASA Astrophysics Data System (ADS)

Polycrystalline SrxTiSe2 (x = 0.04, 0.14, 0.2) alloy was prepared using solid state reaction method and hot press sintering. The effects Sr content were studied on the thermal transport properties of the material. As grown material shows pure TiSe2 phase. Increasing the strontium content reduces thermal conductivity of the material. This is attributed to large number of interfaces and weakly bound Sr atom which acts like a phonon scatterer.

Patel, M.; Bhatt, R.; Bhattacharya, S.; Basu, R.; Haque, F. Z.; Singh, A.; Aswal, D. K.; Gupta, S. K.

2013-06-01

166

Transport and thermodynamic properties of mesoscopic quantum systems

The transport properties of three-dimensional quantum microconstrictions in field-free conditions and under the influence of magnetic fields of arbitrary strengths and directions are studied via a generalized Buttiker model. It is shown that conductance quantization is influenced by the geometry of the microconstriction (that is, its length and the shape of its transverse cross-section). In a weak longitudinal magnetic field,

Andrew Germanovich Scherbakov

1997-01-01

167

Transport and ordering properties of geometrically frustrated metallic pyrochlore magnets

Motivated by recent experiments on the Pr2Ir2O7 metallic pyrochlore material, we study the ordering of the localized 4f Pr moments coupled to the itinerant 5d electrons from Ir. A Monte Carlo method is used to study the condition for spin-ice ordering, and the accompanying change of transport property due to spin ordering. We find that the effects from hybridization between

Ka-Ming Tam; Michel Gingras

2009-01-01

168

Transport properties of mid-infrared colloidal quantum dot films

The transport and thermal properties of HgTe colloidal quantum dot films with cut-off wavelengths in the mid-IR are investigated. The cut-off wavelength of this material can be tuned over the 3-5 \\mu m range, which makes it a promising alternative to existing high cost detectors. Post deposition processes such as ligand exchange and atomic layer deposition are investigated as a way to increase the carrier mobility.

Lhuillier, Emmanuel; Guyot-Sionnest, Philippe; 10.1117/12.906423

2012-01-01

169

NASA Astrophysics Data System (ADS)

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)

Kovalevskiy, Mikhail

2013-04-01

170

An Eulerian perturbation scheme is applied to study transport of a reactive chemical experiencing linear nonequilibrium sorption with deterministic rate constants in a heterogeneous porous medium. Exact solutions for the mean concentrations are used to obtain mean values of spatial moments through the third moments. Comparisons are made with results obtained for the identical problem in a Lagrangian frame [Dagan

Bill X. Hu; John H. Cushman

1997-01-01

171

National Technical Information Service (NTIS)

The purpose of this project is not so much to compare different methods in analyzing the solute transport problems as to evaluate whether the dispersivity involved in the Advection-Dispersion Equation (ADE) can be relatively intrinsic to aquifers when mor...

C. S. Chen, C. Holmes, W. Li D. Chace, M. Fort

1993-01-01

172

By calculating the magnetic field distribution in a stacked pancake coil with use of finite element method and by taking into account the transport properties obtained in a short tape sample, we predict the electric field vs. current density, E–J, characteristics depending on the position inside the coil. The thermal quench behavior of the coil has been calculated by the

T. Kiss; S. Noda; S. Nishimura; K. Ohya; D. Utsunomiya; Yu. A. Ilyn; H. Okamoto

2001-01-01

173

Recent advances in modeling thermodynamic and transport properties of electrolyte solutions are reviewed. In particular, attention is focused on mixed-solvent electrolyte models, equations of state for high-temperature and supercritical electrolyte systems and transport property models for multicomponent, concentrated solutions. The models are analyzed with respect to their capability of computing thermodynamic and transport properties in wide ranges of conditions and

Andrzej Anderko; Peiming Wang; Marshall Rafal

2002-01-01

174

Radiation Transport Properties of Polyethylene-Fiber Composites

NASA Technical Reports Server (NTRS)

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.

Kaul, Raj K.; Barghouty, A. F.; Dahche, H. M.

2003-01-01

175

Space radiation transport properties of polyethylene-based composites

NASA Technical Reports Server (NTRS)

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.

Kaul, R. K.; Barghouty, A. F.; Dahche, H. M.

2004-01-01

176

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.

Allen G Hunt

2008-06-09

177

Strain induced peculiarities in transport properties of Bi nanowires

NASA Astrophysics Data System (ADS)

We report results on the effect of strain on the thermopower and electrical resistance of glass-coated individual Bi nanowires. Here, we show that there is a critical diameter of wires below which the contribution of holes to the charge transport in pure Bi nanowires is more significant than that of electrons. The properties of Bi nanowires are examined in the light of a strain induced electronic topological transition. At low temperatures, the thermopower dependences on strain exhibit a non-monotonic behavior inherent in thinner wires, where the thermopower is dominated by the diffusion transport mechanism of holes. The hole-dominated transport can be transformed into electron-dominated transport through a smooth manipulation with the phonon spectrum and Fermi surface by applying a uniaxial strain. A fairly high value of the thermoelectric power factor (S2/? = 89 ?W cm-1 K-2) was found in the temperature range of 80-300 K, where the dominant mechanism contributing to the thermopower is diffusive thermoelectric generation with electrons as the majority carrier.

Condrea, E.; Gilewski, A.; Nicorici, A.

2013-05-01

178

Strain induced peculiarities in transport properties of Bi nanowires.

We report results on the effect of strain on the thermopower and electrical resistance of glass-coated individual Bi nanowires. Here, we show that there is a critical diameter of wires below which the contribution of holes to the charge transport in pure Bi nanowires is more significant than that of electrons. The properties of Bi nanowires are examined in the light of a strain induced electronic topological transition. At low temperatures, the thermopower dependences on strain exhibit a non-monotonic behavior inherent in thinner wires, where the thermopower is dominated by the diffusion transport mechanism of holes. The hole-dominated transport can be transformed into electron-dominated transport through a smooth manipulation with the phonon spectrum and Fermi surface by applying a uniaxial strain. A fairly high value of the thermoelectric power factor (S(2)/? = 89 ?W cm(-1) K(-2)) was found in the temperature range of 80-300 K, where the dominant mechanism contributing to the thermopower is diffusive thermoelectric generation with electrons as the majority carrier. PMID:23615862

Condrea, E; Gilewski, A; Nicorici, A

2013-05-22

179

Thermoelectric transport properties of molybdenum from abinitio simulations

NASA Astrophysics Data System (ADS)

We employ abinitio simulations based on density functional theory (DFT) to calculate the electronic transport coefficients (electrical conductivity, thermal conductivity, and thermopower) of molybdenum over a broad range of thermodynamic states. By comparing to available experimental data, we show that DFT is able to describe the desired transport properties of this refractory metal with high accuracy. Most noteworthy, both the positive sign and the quantitative values of the thermopower of solid molybdenum are reproduced very well. We calculate the electrical and thermal conductivity in the solid and the fluid phase between 1000 and 20 000 K and a wide span in density and develop empirical fit formulas for direct use in practical applications, such as magneto-hydrodynamics simulations. The influence of thermal expansion in conductivity measurements at constant pressure is also discussed in some detail.

French, Martin; Mattsson, Thomas R.

2014-10-01

180

Low temperature carrier transport properties in isotopically controlled germanium

NASA Astrophysics Data System (ADS)

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 Ge-75 and Ge-70 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 (Ge-74)/(Ge-70) 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.

Itoh, K.

1994-12-01

181

Transport and magnetic properties of BaVSe3

NASA Astrophysics Data System (ADS)

We report a comprehensive study of transport, magnetotransport, and magnetic properties of single crystals of BaVSe3 . The paramagnetic metal-ferromagnetic metal transition at 43 K was followed as a function of pressure by measuring the electrical resistivity and the thermoelectric power. The exponent of the low-temperature power-law dependence of the resistivity increases with pressure. The effective magnetic moment obtained from magnetic susceptibility in the paramagnetic regime is ?eff=1.40?B . The study was completed by band-structure calculations based on density-functional theory both at ambient and high pressures. Transport coefficients of BaVSe3 resemble the high-pressure phase of BaVS3 , which suggest that the replacement of sulfur with selenium can be viewed as chemical pressure.

Akrap, Ana; Stevanovi?, Vladan; Herak, Mirta; Miljak, Marko; Bariši?, Neven; Berger, Helmuth; Forró, László

2008-12-01

182

Low temperature carrier transport properties in isotopically controlled germanium

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.

Itoh, K.

1994-12-01

183

Multi-scale mechanical and transport properties of a hydrogel.

In this paper, molecular dynamic simulation was used to study the effect of water on the equilibrated structure and mechanical properties of cross-linked hydrogel at multiple scales. The hydrogel consisted of Polyethylene glycol diglycidyl ether (PEGDGE) as epoxy and the Jeffamine, poly-oxy-alkylene-amines, as curing agent. The results for systems with various water contents indicated that the cross-links were more hydrophilic within the hydrogel structure. Effects of cross-linking on the transport properties were also investigated by computing diffusion coefficients of water molecules. A new Coarse-Grained (CG) scheme for hydrogels is proposed, and validated by comparing the transport properties with the all-atom method, demonstrating the capability of the model to capture the correct dynamic evolution of the system. The all-atom model of the hydrogel was mapped to the CG model using the MARTINI force field. This method resulted in a more realistic representation of the stiffness of the system, compared to the previous experimental studies in the literature. The variation of the stiffness of the hydrogel as a function of the water content showed that 40% water content is the optimal value for mechanical performance of the hydrogel. PMID:24967978

Salahshoor, Hossein; Rahbar, Nima

2014-09-01

184

Thermal transport and thermoelectric properties of beta-graphyne nanostructures.

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

Ouyang, Tao; Hu, Ming

2014-06-20

185

Thermal transport and thermoelectric properties of beta-graphyne nanostructures

NASA Astrophysics Data System (ADS)

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.

Ouyang, Tao; Hu, Ming

2014-06-01

186

Robust electronic and transport properties of graphene break nanojunctions

NASA Astrophysics Data System (ADS)

We report a systematic research on structural, electronic, and transport properties of a variety of graphene nanoribbon (GNR) break junctions, with different widths and edge chiralities. Our extensive molecular dynamics simulations provide insight into a variety of possible geometries of the break junctions that are obtained by stretching of the graphene ribbons beyond their breaking points. One or more carbon chains can emerge as structural bridges in the junctions. All investigated ruptured systems obey conduction gaps even when their geometries significantly differ by the number of the bridging chains and the variety of their contacts with GNR electrodes.

Erdogan, E.; Popov, I.; Seifert, G.

2011-06-01

187

Stacking-order dependent transport properties of trilayer graphene

NASA Astrophysics Data System (ADS)

We report markedly different transport properties of ABA- and ABC-stacked trilayer graphenes. Our experiments in double-gated trilayer devices provide evidence that a perpendicular electric field opens an energy gap in the ABC trilayer, while it causes the increase of a band overlap in the ABA trilayer. In a perpendicular magnetic field, the ABA trilayer develops quantum Hall plateaus at filling factors of ?=2,4,6,... with a step of ??=2, whereas the inversion-symmetric ABC trilayer exhibits plateaus at ?=6 and 10 with fourfold spin and valley degeneracy.

Jhang, S. H.; Craciun, M. F.; Schmidmeier, S.; Tokumitsu, S.; Russo, S.; Yamamoto, M.; Skourski, Y.; Wosnitza, J.; Tarucha, S.; Eroms, J.; Strunk, C.

2011-10-01

188

NASA Astrophysics Data System (ADS)

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.

Cuenca, Jacques; Van der Kelen, Christophe; Göransson, Peter

2014-02-01

189

NASA Astrophysics Data System (ADS)

Groundwater-level data from an aquifer test utilizing four pumped wells conducted in the South Pasco wellfield in Pasco County, Florida, USA, were analyzed to determine the anisotropic transmissivity tensor, storativity, and leakance in the vicinity of the wellfield. A weighted least-squares procedure was used to analyze drawdowns measured at eight observation wells, and it was determined that the major axis of transmissivity extends approximately from north to south and the minor axis extends approximately from west to east with an angle of anisotropy equal to N4.54°W. The transmissivity along the major axis {( {T_{{? ? }} } )} is 14,019 m2 day-1, and the transmissivity along the minor axis {( {T_{{? ? }} } )} is 4,303 m2 day-1. The equivalent transmissivity Te = {( {T_{{? ? }} T_{{? ? }} } )}^{1/2} = 7,767{{m}2 } day^{-1}, and the ratio of anisotropy is 3.26. The storativity of the aquifer is 7.52 × 10-4, and the leakance of the overlying confining unit is 1.37 × 10-4 day-1. The anisotropic properties determined for the South Pasco wellfield in this investigation confirm the results of previous aquifer tests conducted in the wellfield and help to quantify the NW-SE to NE-SW trends for regional fracture patterns and inferred solution-enhanced flow zones in west-central Florida.

Motz, Louis H.

2009-06-01

190

Electron transport properties of carbon nanotube-graphene contacts

NASA Astrophysics Data System (ADS)

The properties of carbon nanotube-graphene junctions are investigated with first-principles electronic structure and electron transport calculations. Contact properties are found to be key factors in determining the performance of nanotube based electronic devices. In a typical single-walled carbon nanotube-metal junction, there is a p-type Schottky barrier of up to ˜0.4 eV which depends on the nanotube diameter. Calculations of the Schottky barrier height in carbon nanotube-graphene contacts indicate that low barriers of 0.09 eV and 0.04 eV are present in nanotube-graphene contacts ((8,0) and (10,0) nanotubes, respectively). Junctions with a finite contact region are investigated with simulations of the current-voltage characteristics. The results suggest the suitability of the junctions for applications and provide insight to explain recent experimental findings.

Cook, Brandon G.; French, William R.; Varga, Kálmán

2012-10-01

191

Electronic and transport properties of LiCoO2.

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

Andriyevsky, Bohdan; Doll, Klaus; Jacob, Timo

2014-10-01

192

Simplified curve fits for the transport properties of equilibrium air

NASA Technical Reports Server (NTRS)

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).

Srinivasan, S.; Tannehill, J. C.

1987-01-01

193

FLUID- THERMODYNAMIC AND TRANSPORT PROPERTIES OF FLUIDS (IBM PC VERSION)

NASA Technical Reports Server (NTRS)

The accurate computation of the thermodynamic and transport properties of fluids is a necessity for many engineering calculations. The FLUID program was developed to calculate the thermodynamic and transport properties of pure fluids in both the liquid and gas phases. Fluid properties are calculated using a simple gas model, empirical corrections, and an efficient numerical interpolation scheme. FLUID produces results that are in very good agreement with measured values, while being much faster than older more complex programs developed for the same purpose. A Van der Waals equation of state model is used to obtain approximate state values. These values are corrected for real-gas effects by model correction factors obtained from tables based on experimental data. These tables also accurately compensate for the special circumstances which arise whenever phase conditions occur. Viscosity and thermal conductivity values are computed directly from tables. Interpolation within tables is based on Lagrange's three point formula. A set of tables must be generated for each fluid implemented. FLUID currently contains tables for nine fluids including dry air and steam. The user can add tables for any fluid for which adequate thermal property data is available. The FLUID routine is structured so that it may easily be incorporated into engineering programs. The IBM 360 version of FLUID was developed in 1977. It is written in FORTRAN IV and has been implemented on an IBM 360 with a central memory requirement of approximately 222K of 8 bit bytes. The IBM PC version of FLUID is written in Microsoft FORTRAN 77 and has been implemented on an IBM PC with a memory requirement of 128K of 8 bit bytes. The IBM PC version of FLUID was developed in 1986.

Fessler, T. E.

1994-01-01

194

FLUID- THERMODYNAMIC AND TRANSPORT PROPERTIES OF FLUIDS (IBM VERSION)

NASA Technical Reports Server (NTRS)

The accurate computation of the thermodynamic and transport properties of fluids is a necessity for many engineering calculations. The FLUID program was developed to calculate the thermodynamic and transport properties of pure fluids in both the liquid and gas phases. Fluid properties are calculated using a simple gas model, empirical corrections, and an efficient numerical interpolation scheme. FLUID produces results that are in very good agreement with measured values, while being much faster than older more complex programs developed for the same purpose. A Van der Waals equation of state model is used to obtain approximate state values. These values are corrected for real-gas effects by model correction factors obtained from tables based on experimental data. These tables also accurately compensate for the special circumstances which arise whenever phase conditions occur. Viscosity and thermal conductivity values are computed directly from tables. Interpolation within tables is based on Lagrange's three point formula. A set of tables must be generated for each fluid implemented. FLUID currently contains tables for nine fluids including dry air and steam. The user can add tables for any fluid for which adequate thermal property data is available. The FLUID routine is structured so that it may easily be incorporated into engineering programs. The IBM 360 version of FLUID was developed in 1977. It is written in FORTRAN IV and has been implemented on an IBM 360 with a central memory requirement of approximately 222K of 8 bit bytes. The IBM PC version of FLUID is written in Microsoft FORTRAN 77 and has been implemented on an IBM PC with a memory requirement of 128K of 8 bit bytes. The IBM PC version of FLUID was developed in 1986.

Fessler, T. E.

1994-01-01

195

Collective excitations and low-temperature transport properties of bismuth

NASA Astrophysics Data System (ADS)

We examine the influence of collective excitations on the transport properties (resistivity and magneto-optical conductivity) for semimetals, focusing on the case of bismuth. We show, using a random-phase approximation (RPA), that the properties of the system are drastically affected by the presence of an acoustic-plasmon mode, which is a consequence of the presence of two types of carriers (electrons and holes) in this system. We find a crossover temperature T* separating two different regimes of transport. At high temperatures where T>T*, we show that Baber scattering explains quantitatively the dc resistivity experiments, while at low temperatures where T

Chudzinski, P.; Giamarchi, T.

2011-09-01

196

Collective excitations and low temperature transport properties of bismuth

NASA Astrophysics Data System (ADS)

We examine the influence of collective excitations on the transport properties (resistivity and magneto-optical conductivity) for semimetals, focusing on the case of bismuth. We show, using a random-phase approximation (RPA), that the properties of the system are drastically affected by the presence of an acoustic-plasmon mode, which is a consequence of the presence of two types of carriers (electrons and holes) in this system. We find a crossover temperature T^* separating two different regimes of transport. At high temperatures where T > T^*, the Baber scattering explains quantitatively the dc resistivity experiments, while at low temperatures where T < T^*, the interactions of the carriers with this collective mode lead to a T^5 behavior of the resistivity. We examine other consequences of the presence of this mode. In particular a two-plasmon edge feature in the magneto-optical conductivity is predicted. We compare our results with the experimental findings on bismuth. We discuss the limitations and extensions of our results beyond the RPA, and examine the case of other semimetals such as 1T-TiSe2.

Chudzinski, Piotr; Giamarchi, Thierry

2012-02-01

197

Electronic structures and transport properties of silicene on Ag surface

NASA Astrophysics Data System (ADS)

It has been predicted from first-principle that ``silicene'', a two-dimensional buckled honeycomb structure of silicon, is thermally stable and has a graphene-like band structure. In experiments, epitaxial silicene were observed to form at hexagonal Ag(111) and ZrB2(0001) surfaces. However, electronic structure and transport properties related to silicene have not been thoroughly studied. In this work, we have studied band structures of silicene on top of Ag surface using density-functional theory. The effective band structure mapped onto 1x1 unit cell of monolayer silicene on Ag(111) surface could be compared directly with Angle-Resolved Photoemission Spectra (ARPES). We have also studied electronic transport property across monolayer and bilayer silicene sheets using the Non-Equilibrium Green's Function (NEGF) method. The transmission curve shows a maximum at Fermi energy for the monolayer silicene case, but shows a minimum for the bilayer silicene case, which can be explained by their band structures.

Wang, Yun-Peng; Cheng, Hai-Ping

2013-03-01

198

TASK 7 DEMONSTRATION OF THAMES FOR MICROSTRUCTURE AND TRANSPORT PROPERTIES

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.

Langton, C.; Bullard, J.; Stutzman, P.; Snyder, K.; Garboczi, E.

2010-03-29

199

Transport and dynamic properties of high temperature superconducting thin films

Transport and dynamic properties of laser deposited predominantly c-axis oriented crystalline Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7{minus}x} (Y-Ba-Cu-O) superconducting thin films are investigated in this dissertation which may lead to new devices and applications and also help to understand the fundamental properties of high-Tc, materials. The transport current induced resistive transitions in Y-Ba-Cu-O superconducting thin films have been studied. It was found that the I-V curves for these films had two non-linear regimes, a gradual and an abrupt transition to the normal state. Comparative studies of I-V characteristics of thin film bridges of different geometries at the temperatures below {Tc} and SEM voltage imaging of current induced dissipative regions in the same samples were performed. From these measurements it is found that a non-linear gradual transition region in the I-V curves is caused by macroscopic effects (current crowding, substrate defects, film thickness variation, etc.), and by microscopic dissipation effects. Also it was found that an abrupt transition to the normal state in the I-V curve is due to Joule heating. The dynamic electrical properties of Y-Ba-Cu-O superconducting thin films on strontium titanate and MgO substrates have been studied. A fast non-linear switching of a high {Tc} film between the dissipative and superconducting states was demonstrated. These measurements have shown that the rise and the fall times of these transitions are at least 250 psec (which is limited by the speed capabilities of available electronics). Application of such a non-linear switching in a novel noise discrimination scheme was proposed and demonstrated for speeds of several hundred MHz. The proposed method is simple and effective in the enhancement of signal-to-noise ratio in digital electronic circuits.

Frenkel, A.

1989-01-01

200

NASA Astrophysics Data System (ADS)

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, kBTconf=<|?rU(rN)|2>/, where ?r is the nabla operator of position vector r. As far as we know, Tconf was never calculated with the anisotropic Gay-Berne potential, whereas the calculation of Tconf 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.

Ghoufi, Aziz; Morineau, Denis; Lefort, Ronan; Malfreyt, Patrice

2011-01-01

201

NASA Astrophysics Data System (ADS)

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.

Vetrov, S. Ya; Pankin, P. S.; Timofeev, I. V.

2014-09-01

202

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...

203

Effects of disorder on the transport properties of chemically derived graphene

Transport properties of chemically derived graphene (CDG) are strongly influenced by the concentration of defects that are introduced during synthesis. We present a comprehensive transport study on a range of CDG films with varying degrees of disorder. The electric properties of CDG were found to be tunable over several orders of magnitude via controlled oxidation and reduction. The structural properties

Goki Eda; James Ball; Ye Xiao; Robert Maher; Lesley Cohen; Thomas Anthopoulos; Manish Chhowalla

2011-01-01

204

Transport and thermodynamic properties of mesoscopic quantum systems

NASA Astrophysics Data System (ADS)

The transport properties of three-dimensional quantum microconstrictions in field-free conditions and under the influence of magnetic fields of arbitrary strengths and directions are studied via a generalized Buttiker model. It is shown that conductance quantization is influenced by the geometry of the microconstriction (that is, its length and the shape of its transverse cross-section). In a weak longitudinal magnetic field, when rsb{c}? d, where rsb{c} is the cyclotron radius and d the effective transverse size of the narrowing of the microconstriction, the conductance exhibits Aharonov-Bohm type behavior. This behavior transforms in the strong field limit, rsb{c}? d, into Shubnikov-de Haas oscillations with a superimposed Aharonov-Bohm fine-structure. The dependence of the Aharonov-Bohm type features on the length of the microconstriction and on temperature are demonstrated. Effects of the shapes of the cross sections of three-dimensional nanowires on electronic conductance quantization are studied for both hard- and soft-wall potentials. In both models the quantum conductance is determined by both the area and shape of the narrowmost part of the nanowire. For the hard-wall potential the semiclassical (Weyl) correction to the Sharvin formula provides an adequate approximation to the average quantized conductance. For nanowires modeled by soft-wall potentials the average quantum conductance may be well estimated using a classical approximation. Magnetic field switching and blockade of quantum transport through three-dimensional metallic and semimetallic nanowires with a small number of conducting channels are proposed. Temperature enhancement of magnetotransport in such wires is predicted. Thermoelectric properties of nanowires in a magnetic field are studied. Magnetic splitting of thermopower peaks associated with electronic energy levels which are degenerate at zero field, leading to the development of separate thermopower peaks at larger fields, are predicted. A method for numerical calculation of the conductance through microconstrictions based on the time-dependent Schrodinger equation is developed, allowing investigations of electronic transport in complex situations. An algorithm for conductance calculations via propagation of wave packets is presented, and results for electronic transport through various constrictions are given, including model calculations of the conductance of a one-atom contact in the scanning tunneling microscope.

Scherbakov, Andrew Germanovich

205

Critical transport properties of random metals in large magnetic fields

The threshold behavior of the transport properties of a random metal in the critical region near a metal–insulator transition is strongly affected by the measuring electromagnetic fields. In spite of the randomness, the electrical conductivity exhibits striking phase-coherent effects due to broken symmetry, which greatly sharpen the transition compared with the predictions of effective medium theories, as previously explained for electrical conductivities. Here broken symmetry explains the sign reversal of the T ? 0 magnetoconductance of the metal–insulator transition in Si(B,P), also previously not understood by effective medium theories. Finally, the symmetry-breaking features of quantum percolation theory explain the unexpectedly very small electrical conductivity temperature exponent ? = 0.22(2) recently observed in Ni(S,Se)2 alloys at the antiferromagnetic metal–insulator transition below T = 0.8 K. PMID:11038580

Phillips, J. C.

1997-01-01

206

Electron-neutron scattering and transport properties of neutron stars

We show that electrons can couple to the neutron excitations in neutron stars and find that this can limit their contribution to the transport properties of dense matter, especially the shear viscosity. The coupling between electrons and neutrons is induced by protons in the core, and by ions in the crust. We calculate the effective electron-neutron interaction for the kinematics of relevance to the scattering of degenerate electrons at high density. We use this interaction to calculate the electron thermal conductivity, electrical conductivity, and shear viscosity in the neutron star inner crust, and in the core where we consider both normal and superfluid phases of neutron-rich matter. In some cases, particularly when protons are superconducting and neutrons are in their normal phase, we find that electron-neutron scattering can be more important than the other scattering mechanisms considered previously.

Bertoni, Bridget; Rrapaj, Ermal

2014-01-01

207

Electron-neutron scattering and transport properties of neutron stars

We show that electrons can couple to the neutron excitations in neutron stars and find that this can limit their contribution to the transport properties of dense matter, especially the shear viscosity. The coupling between electrons and neutrons is induced by protons in the core, and by ions in the crust. We calculate the effective electron-neutron interaction for the kinematics of relevance to the scattering of degenerate electrons at high density. We use this interaction to calculate the electron thermal conductivity, electrical conductivity, and shear viscosity in the neutron star inner crust, and in the core where we consider both normal and superfluid phases of neutron-rich matter. In some cases, particularly when protons are superconducting and neutrons are in their normal phase, we find that electron-neutron scattering can be more important than the other scattering mechanisms considered previously.

Bridget Bertoni; Sanjay Reddy; Ermal Rrapaj

2014-09-27

208

Dark matter transport properties and rapidly rotating neutron stars

Neutron stars are attractive places to look for dark matter because their high densities allow repeated interactions. Weakly interacting massive particles (WIMPs) may scatter efficiently in the core or in the crust of a neutron star. In this paper we focus on WIMP contributions to transport properties, such as shear viscosity or thermal conductivity, because these can be greatly enhanced by long mean free paths. We speculate that WIMPs increase the shear viscosity of neutron star matter and help stabilize r-mode oscillations. These are collective oscillations where the restoring force is the Coriolis force. At present r-modes are thought to be unstable in many observed rapidly rotating stars. If WIMPs stabilize the r-modes, this would allow neutron stars to spin rapidly. This likely requires WIMP-nucleon cross sections near present experimental limits and an appropriate density of WIMPs in neutron stars.

C. J. Horowitz

2012-05-16

209

Dynamical properties and transport coefficients of Kihara linear fluids

NASA Astrophysics Data System (ADS)

Transport properties of spherical and linear molecules modeled by the Kihara potential are studied by molecular dynamics simulations. Diffusion coefficients, shear viscosities, and thermal conductivities are calculated for a wide range of the fluid region and for several elongations. The corresponding individual and collective correlation functions are discussed along with angular velocity and reorientational correlation functions. Relaxation times and simple models relevant to orientational motion are also studied. The results obtained are discussed in a corresponding states framework, using previous Gibbs ensemble Monte Carlo data for the liquid-vapor equilibria of the models. In this way, the role of elongation can be studied. It is found that in most of the liquid region, the diffusion coefficient is weakly dependent on elongation. On the other hand, both viscosity and thermal conductivity are found to decrease with elongation. The dependence of transport coefficients on density and temperature is also discussed. On testing the Stokes-Einstein relation, it was observed that, unlike previous findings for hard spheres, stick boundary conditions perform just as good as slip boundary conditions for the Lennard-Jones fluid and the low-elongated Kihara fluid.

MacDowell, L. G.; Garzón, B.; Calero, S.; Lago, S.

1997-03-01

210

Thermal transport properties of defective graphene: A molecular dynamics investigation

NASA Astrophysics Data System (ADS)

In this work the thermal transport properties of graphene nanoribbons with randomly distributed vacancy defects are investigated by the reverse non-equilibrium molecular dynamics method. We find that the thermal conductivity of the graphene nanoribbons decreases as the defect coverage increases and is saturated in a high defect ratio range. Further analysis reveals a strong mismatch in the phonon spectrum between the unsaturated carbon atoms in 2-fold coordination around the defects and the saturated carbon atoms in 3-fold coordination, which induces high interfacial thermal resistance in defective graphene and suppresses the thermal conductivity. The defects induce a complicated bonding transform from sp2 to hybrid sp—sp2 network and trigger vibration mode density redistribution, by which the phonon spectrum conversion and strong phonon scattering at defect sites are explained. These results shed new light on the understanding of the thermal transport behavior of graphene-based nanomaterials with new structural configurations and pave the way for future designs of thermal management phononic devices.

Yang, Yu-Lin; Lu, Yu

2014-10-01

211

Transport properties of polyaniline-cellulose-acetate blends

NASA Astrophysics Data System (ADS)

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.

Planès, Jérôme; Wolter, Andreas; Cheguettine, Yasmina; Pro?, Adam; Genoud, Françoise; Nechtschein, Maxime

1998-09-01

212

Transport properties of tomato fruit tonoplast membrane vesicles

To study the role of the tonoplast in tomato fruit development, methods were developed to isolate sealed tonoplast membrane vesicles. Low density (approx. 1.23 g/cc) membrane vesicles they found to possess a NO/sub 3//sup -/-sensitive H/sup +/-translocating ATPase. The properties of this H/sup +/-ATPase are similar to those described for other tonoplast H/sup +/-ATPases. ATP-dependent Ca/sup + +/ transport into the vesicles proceeded by two mechanisms, one operative at low Ca/sup + +/ concentrations (1 ..mu..M) and inhibited by vanadate, and the other operative at high Ca/sup + +/ concentrations (10 ..mu..M) and inhibited by NO/sub 3//sup -/. Their present results indicate that the high affinity (vanadate-sensitive) Ca/sup + +/ transporter resides in E.R. membrane that contaminates the tonoplast preparation. Citrate uptake in tonoplast vesicles is stimulated by ATP and inhibited by NO/sub 3//sup -/ suggesting that citrate uptake is driven indirectly by the H/sup +/-ATPase. The substrate for sugar uptake is UDP-glucose resulting in the appearance of sucrose inside the tonoplast vesicle. No evidence for ATP stimulation of glucose, fructose, or sucrose uptake was observed.

Oleski, N.; Joyce, D.; Osteryoung, K.; Bennett, A.B.

1986-04-01

213

NASA Astrophysics Data System (ADS)

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.

Soh, Wee Tee; Zhong, Xiaoxi; Ong, C. K.

2014-09-01

214

Tunneling anisotropic magnetoresistance in epitaxial CoFe/n-GaAs junctions

NASA Astrophysics Data System (ADS)

Magnetic and transport properties of a fully epitaxial CoFe/n-GaAs junction were investigated. The CoFe film grown on the GaAs showed strong magnetic anisotropy in which uniaxial anisotropy with an easy axis of [11¯0] dominated with a slight cubic anisotropy having easy axes of [110] and [11¯0] superimposed. Tunneling anisotropic magnetoresistance (TAMR) was observed at 4.2 K in the CoFe/n-GaAs junction. Angular dependence of the tunnel resistance showed uniaxial-type anisotropic tunnel resistance between the [110] and [11¯0] directions in the (001) plane that varied strongly with a bias voltage. The observed TAMR effect can be explained by the anisotropic electronic structure due to Rashba and Dresselhaus spin-orbit interactions.

Uemura, Tetsuya; Imai, Yosuke; Harada, Masanobu; Matsuda, Ken-ichi; Yamamoto, Masafumi

2009-05-01

215

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.

Berryman, J.G.

2007-10-02

216

Anisotropically structured magnetic aerogel monoliths.

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

Heiligtag, Florian J; Airaghi Leccardi, Marta J I; Erdem, Derya; Süess, Martin J; Niederberger, Markus

2014-10-01

217

NASA Astrophysics Data System (ADS)

In cast Sm2Fe17 ingots minor fractions of SmFe2 and SmFe3 may occur. Nitrogenation of such alloy-powders inidicates that only Sm2Fe17 forms an interstitial solid solution whereas SmFe2 and SmFe3 decompose directly into SmN and ?-Fe. From Sm2Fe17Nx alloy powders with an average particle size of about 3 ?m anisotropic magnets were prepared by adding 15 wt% Zn-powder. Annealing at 390 ºC results in intrinsic coercivities > 15 kOe promoted by the formation of an unknown binary Fe8Zn92-compound. Whereas annealing at temperatures > 420 ºC leads to the formation of binary Fe3Zn7 and ternary Sm2FeZn2. By the formation of Sm2FeZn2 from Sm2Fe17Nx+Zn some ?-Fe occurs inducing a step in the demagnetization curve J(H).

Wall, B.; Katter, M.; Rodewald, W.; Velicescu, M.

218

Anisotropically structured magnetic aerogel monoliths

NASA Astrophysics Data System (ADS)

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

Heiligtag, Florian J.; Airaghi Leccardi, Marta J. I.; Erdem, Derya; Süess, Martin J.; Niederberger, Markus

2014-10-01

219

Magnetic and transport properties of diluted granular multilayers

NASA Astrophysics Data System (ADS)

The magnetic and transport properties of Co80Fe20(t)/Al2O3(4 nm) multilayers with low nominal thicknesses t =0.7 and 0.9 nm of Co80Fe20 granular layers are studied. Magnetic studies find a superparamagnetic state above the blocking temperature Tb (of field-cooled/zero-field-cooled splitting) that grows with t and decreases with H. The low-voltage Ohmic tunnel transport passes to non-Ohmic I ?V3/2 law for applied fields above ˜500 V/cm. At fixed V, the temperature dependence of conductance reveals an anomalous dip around ˜220 K, which can be attributed to the effect of surface contamination by supercooled water. Current-in-plane tunnel magnetoresistance (MR) ratio tends, at lower t, to higher maximum values (˜8% at room temperature) but to lower field sensitivity. This may indicate growing discorrelation effect (e.g., between shrinking areas of correlated moments) in this regime and corroborates the deficit of granule magnetization estimated from the Inoue-Maekawa MR fit, compared to that from direct magnetization measurements. MR displays a mean-field-like critical behavior when t approaches the point of superparamagnetic/superferromagnetic transition (tc˜1.3 nm at room temperature) from below, different from the formerly reported percolationlike behavior at approaching it from above. With growing temperature, MR reveals, beyond the common decrease, an anomalous plateau from Tb˜30-50 K up to some higher value T?˜150-200 K, not seen at higher t.

Silva, H. G.; Gomes, H. L.; Pogorelov, Y. G.; Pereira, L. M. C.; Kakazei, G. N.; Sousa, J. B.; Araújo, J. P.; Mariano, J. F. L.; Cardoso, S.; Freitas, P. P.

2009-12-01

220

Structure and Anisotropic Properties of BaFe2-xNixAs2 (x = 0, 1, and 2) Single Crystals

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(?T)/dT, and d?/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 (P?) 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.

Safa-Sefat, Athena [ORNL; Jin, Rongying [ORNL; McGuire, Michael A [ORNL; Sales, Brian C [ORNL; Mandrus, David [ORNL; Ronning, F. [Los Alamos National Laboratory (LANL); Bauer, E D [Los Alamos National Laboratory (LANL); Mozharivskyj, Yurij [McMaster University

2009-01-01

221

Low Temperature Carrier Transport Properties in Isotopically Controlled Germanium

NASA Astrophysics Data System (ADS)

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 ^{74}Ge and ^{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 (^{74 }Ge) / (^{70}Ge) ratios of the starting Ge materials, respectively. This method also guarantees unprecedented doping uniformity. Using such samples we 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. We have also performed infrared absorption spectroscopy studies of compensated Ge samples, investigating the line broadening mechanism due to random electric fields arising from ionized impurity centers. In the study of neutral impurity scattering, we find excellent agreement between the low temperature experimental mobility and phase shift calculations for the hydrogen atom scaled to shallow impurities in semiconductors. In the ionized impurity scattering study, none of the theories we have tested so far explains our low temperature experimental mobilities in highly compensated Ge (K>0.3). We discuss possible problems associated with the theories, in particular, the treatment of the screening mechanism. In the study of low temperature hopping conduction, we show results of temperature dependent resistivity measurements as a function of both the net-carrier concentration and the compensation ratio. These results are compared with the theoretical prediction of variable range hopping conduction. A transport study of samples close to the metal -insulator transition allows us to probe the nature of this important phenomenon. Our NTD isotopically engineered samples with extreme dopant uniformity are ideal systems to re-examine some of the previously published results. Our results suggest that one of the most controversial findings reported recently is most likely an artifact arising from inhomogeneous dopant distribution. Lastly, we discuss low-temperature infrared absorption spectroscopy studies of p-type Ge:Ga,As samples as a function of the compensation ratio. The observed Ga impurity absorption peaks broaden linearly with the ionized impurity concentration due to the quadrupole interactions between Ga bound holes and the electric field gradients. Experimental linewidths are quantitatively compared to existing theories of electric field broadening. We find excellent agreement with the theory which is based on the correlated distribution of ionized impurity centers.

Itoh, Kohei

222

Abstract: At the United States Department of Energy Hanford Site a spill of radioactive Technetium has been migrating horizontally in the vadose zone rather than flowing vertically to the water table. This result has been interpreted as being due to horizontal anisotropy in the hydraulic conductivity, K, (a tendency for fluids to migrate more easily in the horizontal direction) due to high horizontal connectivity of sedimentary deposits with a tendency for larger values of K. Such layers have larger components of silt and clay than the predominantly sandy soils at the Hanford site. It is generally accepted that effects of such anisotropy tend to be greater at smaller length scales, probably because of the lack of perfect correlations at large length scales. It has also been suggested that this anisotropy in K is maximized under relatively dry conditions when finer soils (with smaller pores) trap moisture more effectively than sands and gravels. The random component of the distribution of the Hanford flood deposits requires a probabilistic framework for the calculation of K. The work on this project had two main components: 1) to use continuum percolation theory applied to random fractal models to produce a general framework for calculating distributions of K under anisotropic conditions and as a function of system scale, 2) to apply the scheme for calculation to the Hanford site. The results of the general calculation (submitted for publication in Philosophical Magazine) are that the mean horizontal and vertical K values become equal in the limit of large system size (in agreement with general perception above) while the distributions of K values cause significant overlap of expected experimental values of K in the vertical and horizontal directions already at intermediate length scales. In order to make these calculation specific to the Hanford site, however, values of the appropriate length scales to describe the Hanford subsurface as well as to describe the maximum anisotropy in K (largest ratio of horizontal to vertical values) must be provided. The data analyzed so far (received from Pacific Northwest National Laboratory Researchers, Dr. Glendon Gee and Dr. Mark Rockhold) has suggested that the majority of the finer soils in the Hanford subsurface have particularly low values of K at low moisture contents rather than particularly large values as expected by most researchers. Preliminary results suggest that about 50% of the Hanford Site subsurface may contain soils which preferentially retain water under dry conditions, however, only about 20% of these appear to be highly conductive as well. Thus only about 10% of the Hanford subsurface may actually contain soil which not only retains water preferentially under generally dry conditions, but which also has unusually high hydraulic conductivity. If this is the case, then the argument that such highly conductive regions may tend to be connected, even for short distances in the horizontal direction, may fall apart. So several alternate hypotheses have to be considered: 1) that the very small proportion (ca. 10%) of soils which retain water and are highly conductive is sufficient to percolate, even though typical percolation probabilities tend to be 15% or higher, 2) the subset of soils analyzed (from the DOE sponsored Vadose Zone Transport Study Site) is not a representative sample, 3) the horizontal transport is occurring at higher moisture contents. Further research on this particular aspect is thus required, and will be performed in the summer of 2006.

Hunt, A. G.

2006-01-06

223

NASA Technical Reports Server (NTRS)

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.

Gordon, S.; Mcbride, B.; Zeleznik, F. J.

1984-01-01

224

Geometrical and transport properties of single fractures: influence of the roughness of the fracture

Geometrical and transport properties of single fractures: influence of the roughness of the fracture walls H. Auradou Univ Pierre et Marie Curie-Paris6, Univ Paris-Sud, CNRS, F-91405. Lab FAST, Bat reviews the main features of the transport properties of single fractures. A particular attention paid

Paris-Sud XI, UniversitÃ© de

225

Interfacial and transport properties of nanoconstrained inorganic and organic materials

NASA Astrophysics Data System (ADS)

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 °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.

Kocherlakota, Lakshmi Suhasini

226

NASA Technical Reports Server (NTRS)

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.

Gordon, S.

1982-01-01

227

Valuation of utility and transportation property: a classified annotated bibliography

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).

Clatanoff, R.M.

1983-01-01

228

Transport Properties of Ce, Sm, and Ho Doped Bismuth Antimony

NASA Astrophysics Data System (ADS)

Bi88Sb12 alloy has been doped with Ce, Sm, and Ho prepared under two different fabrication conditions. The first being ball milled for 12 hours and a hot pressed at 240 ^oC and the second ball milled for 6 hours and hot pressed at 200 ^oC. It is found that Ce, Sm, and Ho dopants all have a similar impact on the transport properties. A ZT enhancement is seen due to doping which is an effect of an enhanced Seebeck coefficient as a result of a decrease in the carrier concentration most likely caused by a widening band gap. The alteration of the band gap does not appear to be caused by the magnetic moments of Ce, Sm, and Ho based on the similar change to the gap size with the widely varying magnetic moments of the dopants. Also, similar results were not obtained with Fe doped samples, where Fe has a magnetic moment similar to Ce and greater than Sm.

Lukas, K. C.; Zhao, H.; Ren, Z. F.; Opeil, C. P.

2013-03-01

229

Transport properties of ionic liquid electrolytes with organic diluents.

Ionic liquids (ILs) form a novel class of electrolytes with unique properties that make them attractive candidates for electrochemical devices. In the present study a range of electrolytes were prepared based on the IL N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl) amide ([C(3)mpyr][NTf(2)]) and LiNTf(2) salt. The traditional organic solvent diluents vinylene carbonate (VC), ethylene carbonate (EC), tetrahydrofuran (THF) and toluene were used as additives at two concentrations, 10 and 20 mol%, leading to a ratio of about 0.6 and 1.3 diluent molecules to lithium ions, respectively. Most promisingly, the lithium ions see the greatest effect in the presence of all the diluents, except toluene, producing a lithium self-diffusion coefficient of almost a factor of 2.5 times greater for THF at 20 mol%. Raman spectroscopy subtly indicates that THF may be effectively breaking up a small portion of the lithium ion-anion interaction. While comparing the measured molar conductivity to that calculated from the self-diffusion coefficients of the constituents indicates that the diluents cause an increase in the overall ion clustering. This study importantly highlights that selective ion transport enhancement is achievable in these materials. PMID:19672530

Bayley, Paul M; Lane, George H; Rocher, Nathalie M; Clare, Bronya R; Best, Adam S; MacFarlane, Douglas R; Forsyth, Maria

2009-09-01

230

The electronic transport properties of porous zigzag graphene clusters

NASA Astrophysics Data System (ADS)

By omitting some carbon atoms from middle of a zigzag graphene cluster, and Hydrogen termination of sp2 orbital, we make the different porous zigzag graphene clusters, and investigate the electron transport properties of the structures by the non-equilibrium Green function method at zero bias regime. It is shown that, the conductance of porous clusters depends on the final symmetry of porous cluster and the local imbalance number (nA-nB), in which nA and nB are the number of omitted atoms from A-sublattice and B-sublattice respectively. Also it is shown that, if three carbon atoms (one type-A and two type-B sites) are omitted the conductance for |E-Ef|?5 eV is significantly higher than the conductance of original zigzag graphene cluster due to the increment in less affected conducting channels. We show that, spin flipping occurs under Rashba spin orbit interaction at E=Ef, when three atoms are omitted from the original cluster. Therefore the local imbalance number and final symmetry of porous graphene cluster can be used as a rule for designing porous graphene devices and the device can be used in spintronic applications.

Simchi, Hamidreza; Esmaeilzadeh, Mahdi; Mazidabadi, Hossein

2013-12-01

231

Thermodynamic and transport properties of unconventional superconductors and multiferroics

NASA Astrophysics Data System (ADS)

Often, the phase diagram for a given material can be quite complex, presenting evidence for multiple orders and it is the task of the condensed matter community to describe and quantify knowledge of these properties. Significant insight can often be gained by comparing model calculations of basic thermodynamic and transport properties of a material with experiment. Here we consider two classes of novel materials whose rich phase diagrams are actively under investigation: unconventional superconductors and multiferroics. In 2006, H. Hosono discovered a new class of iron-based superconducting materials which are not conventional superconductors. After the initial discovery, there is a range of questions of immediate interest; foremost among them is what is the structure and symmetry of the superconducting state, a question which took roughly a decade to answer for the cuprate superconductors. We present calculations that help reveal the structure of the superconducting gap using angle dependent specific heat measurements. We then calculate the electronic Raman scattering intensity for several polarizations of light and different models of disorder, providing information about the anisotropy and location of nodes in the superconducting gap. Understanding the influence of disorder is considered crucial because currently conflicting experimental results may be due to differences in sample quality. Recently, there has also been interest in multiferroics: materials with simultaneous non-zero polarization and magnetic order. We present calculations of fundamental thermodynamic properties, mean field behavior for the simplest ferromagnetic-ferroelectric, characterize topological defects, and use the perturbative renormalization group to help understand the critical point, as a beginning towards understanding the multitude multiferroic materials with increasingly complex magnetic and polar order. The first two chapters review conventional superconductivity and its unconventional counterpart found in the cuprates and pnictides. The original work constituting the body of this dissertation appears in chapters three through five. Chapter five contains a brief introduction to the topics which are relevant for multiferroics before presenting the original work. Portions of this thesis are based on the author's publications and are cited when relevant.

Boyd, G. R.

232

Transport and Dynamic Properties of High Temperature Superconducting Thin Films.

NASA Astrophysics Data System (ADS)

Transport and dynamic properties of laser deposited predominantly c-axis oriented crystalline Y_1 Ba_2Cu_3O _{rm 7-x} (Y-Ba-Cu -O) superconducting thin films are investigated in this dissertation which may lead to new devices and applications and also help to understand the fundamental properties of high T_ {rm c} materials. The transport current induced resistive transitions in Y-Ba-Cu-O superconducting thin films have been studied. It was found that the I-V curves for these films had two non -linear regimes, a gradual and an abrupt transition to the normal state. Comparative studies of I-V characteristics of thin film bridges of different geometries at the temperatures below T_{rm c} and SEM voltage imaging of current induced dissipative regions in the same samples were performed. From these measurements it is found that a non-linear gradual transition region in the I-V curves is caused by macroscopic effects (current "crowding", substrate defects, film thickness variation, etc.), and by microscopic dissipation effects. Also it was found that an abrupt transition to the normal state in the I-V curve is due to Joule heating. The dynamic electrical properties of Y-Ba-Cu-O superconducting thin films on strontium titanate and MgO substrates have been studied. A fast non-linear switching of a high T_{rm c} film between the dissipative and superconducting states was demonstrated. These measurements have shown that the rise and the fall times of these transitions are at least 250 psec (which is limited by the speed capabilities of available electronics). Application of such a non-linear switching in a novel noise discrimination scheme was proposed and demonstrated for speeds of several hundred MHz. The proposed method is simple and effective in the enhancement of signal-to-noise ratio in digital electronic circuits. The optical response of Y-Ba-Cu-O bridge and meander type thin film devices has been investigated. CW optical response to a He-Ne laser radiation (wavelength of 0.63 ?m) was predominantly bolometric. The pulsed optical response was studied with Q-switched and mode-locked Q-swithced short pulses from a Nd:YAG laser at the wavelength of 1.06 mum. Two distinct components contributing to the optical response were identified: a non-bolometric (as fast as 1ns) and a bolometric component (several ns). The bolometric component is stronger at temperatures in the vicinity of the transition region to the normal state. The non-bolometric component is dominant at temperatures below the transition region showing weak temperature dependence and a linear dependence on the bias current. The results are discussed using flux model and electron-phonon scattering relaxation dynamics based on BCS theory.

Frenkel, Anatoly

233

NASA Technical Reports Server (NTRS)

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.

Hansen, C Frederick; Heims, Steve P

1958-01-01

234

41 CFR 302-7.10 - Is property acquired en route eligible for transportation at Government expense?

Code of Federal Regulations, 2010 CFR

...STORAGE OF PROPERTY 7-TRANSPORTATION AND TEMPORARY STORAGE OF HOUSEHOLD GOODS AND PROFESSIONAL BOOKS, PAPERS, AND EQUIPMENT (PBP&E) General Rules § 302-7.10 Is property acquired en route eligible for transportation at Government expense?...

2010-07-01

235

Analysis Of Transport Properties of Mechanically Alloyed Lead Tin Telluride

NASA Astrophysics Data System (ADS)

The work described in this thesis had two objectives. The first objective was to develop a physically based computational model that could be used to predict the electronic conductivity, Seebeck coefficient, and thermal conductivity of Pb1-xSnxTe alloys over the 400 K to 700 K temperature as a function of Sn content and doping level. The second objective was to determine how the secondary phase inclusions observed in Pb1-xSn xTe alloys made by consolidating mechanically alloyed elemental powders impact the ability of the material to harvest waste heat and generate electricity in the 400 K to 700 K temperature range. The motivation for this work was that though the promise of this alloy as an unusually efficient thermoelectric power generator material in the 400 K to 700 K range had been demonstrated in the literature, methods to reproducibly control and subsequently optimize the materials thermoelectric figure of merit remain elusive. Mechanical alloying, though not typically used to fabricate these alloys, is a potential method for cost-effectively engineering these properties. Given that there are deviations from crystalline perfection in mechanically alloyed material such as secondary phase inclusions, the question arises as to whether these defects are detrimental to thermoelectric function or alternatively, whether they enhance thermoelectric function of the alloy. The hypothesis formed at the onset of this work was that the small secondary phase SnO2inclusions observed to be present in the mechanically alloyed Pb1-xSnxTe would increase the thermoelectric figure of merit of the material over the temperature range of interest. It was proposed that the increase in the figure of merit would arise because the inclusions in the material would not reduce the electrical conductivity to as great an extent as the thermal conductivity. If this were to be true, then the experimentally measured electronic conductivity in mechanically alloyed Pb1-xSnxTe alloys that have these inclusions would not be less than that expected in alloys without these inclusions while the portion of the thermal conductivity that is not due to charge carriers (the lattice thermal conductivity) would be less than what would be expected from alloys that do not have these inclusions. Furthermore, it would be possible to approximate the observed changes in the electrical and thermal transport properties using existing physical models for the scattering of electrons and phonons by small inclusions. The approach taken to investigate this hypothesis was to first experimentally characterize the mobile carrier concentration at room temperature along with the extent and type of secondary phase inclusions present in a series of three mechanically alloyed Pb1-xSnxTe alloys with different Sn content. Second, the physically based computational model was developed. This model was used to determine what the electronic conductivity, Seebeck coefficient, total thermal conductivity, and the portion of the thermal conductivity not due to mobile charge carriers would be in these particular Pb1-x SnxTe alloys if there were to be no secondary phase inclusions. Third, the electronic conductivity, Seebeck coecient and total thermal conductivity was experimentally measured for these three alloys with inclusions present at elevated temperatures. The model predictions for electrical conductivity and Seebeck coefficient were directly compared to the experimental elevated temperature electrical transport measurements. The computational model was then used to extract the lattice thermal conductivity from the experimentally measured total thermal conductivity. This lattice thermal conductivity was then compared to what would be expected from the alloys in the absence of secondary phase inclusions. Secondary phase inclusions were determined by X-ray diraction analysis to be present in all three alloys to a varying extent. The inclusions were found not to significantly degrade electrical conductivity at temperatures above 400 K in these alloys, though they do dramatically impact elect

Krishna, Rajalakshmi

236

The effect of interlayer coupling on the transport properties and dissipation in a magnetic field is reviewed for superconducting multilayers including highly-anisotropic high-temperature superconductors (HTS). For the applied field parallel to the superconducting layers the absence of any Lorentz-force dependence of the dissipation leads to an explanation other than flux motion. This is consistent with a Josephson junction dissipation which dominates flux motion of the insulating regions between layers. However, in is seen to cross over from phase slips at Josephson junctions to depinning of vortices from the external field at high fields and temperatures. For fields perpendicular to the superconducting layers the much greater resistive broadening in HTS is due to dissipation by thermally-activated flux motion, consistent with a lack of intrinsic pinning. We show experimental evidence that the associated flux motion occurs as a result of a crossover from three dimensional (3D) vortex lines to 2D independent pancake-like vortices, residing in the Cu-O layers. This 3D to 2D crossover occurs after k{sub B}T exceeds the Josephson coupling energy.

Gray, K.E.; Hettinger, J.D.; Kim, D.H.

1994-06-01

237

High field transport properties of a bilayer graphene

NASA Astrophysics Data System (ADS)

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.

Bhargavi, K. S.; Kubakaddi, S. S.

2014-02-01

238

EquilTheTA: Thermodynamic and transport properties of complex equilibrium plasmas

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.

Colonna, G.; D'Angola, A. [CNR-IMIP Bari, via Amendola 122/D - 70126 Bari (Italy); DIFA, Universita della Basilicata, via dell'Ateneo Lucano, 1085100 Potenza (Italy)

2012-11-27

239

Highly Anisotropic Elements for Acoustic Pentamode Applications

NASA Astrophysics Data System (ADS)

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.

Layman, Christopher N.; Naify, Christina J.; Martin, Theodore P.; Calvo, David C.; Orris, Gregory J.

2013-07-01

240

The effect of the transport properties of epoxy based coatings on metallic substrate corrosion

An attempt is made to correlate the protective properties of different epoxy based coatings with their water transport propertieS. Rust formation on the support and blister growth on the varnish are strongly affected by the equilibrium uptake and diffusion coefficient of water. An evaluation of these parameters can give useful information on the capability of different paints.

P. Mastronardi; C. Carfagna; L. Nicolais

1983-01-01

241

Effect of edge states on the transport properties of pentacene-graphene nanojunctions

NASA Astrophysics Data System (ADS)

We investigate the effect of edge states on the transport properties of pentacene-graphene nanojunctions on the basis of DFT and NEGF formalism. The calculations reveal that strong interaction between pentacene and zigzag GNR leads to edge-induced transmission channels at the Fermi region which controls the low-bias current. Effects of substitution by electron withdrawing and donating groups on the transport properties of molecular pentacene have also been discussed, some of which show spin resolved transport properties with negative differential resistance behavior which may have potential application in spintronics devices.

Pramanik, Anup; Mandal, Bikash; Sarkar, Sunandan; Sarkar, Pranab

2014-03-01

242

Transport properties in the integer quantum Hall effect

In this thesis, I study the transport physics near the integer Quantum Hall plateau transitions. The central part of this work is the development and the implementation of a large scale numerical transfer matrix algorithm for calculation of the conductance. Combined with the technique of finite size scaling, it enables the first study of mesoscopic transport behavior in systems large

Bozidar Jovanovic

1999-01-01

243

Anisotropic flow: Achievements, Difficulties, Expectations

Anisotropic flow measurements play a crucial role in understanding the physics and bulk properties of the system created in heavy ion collisions. In this talk I briefly review the most important results obtained so far, recent developments in the analysis techniques and the interpretation of the results, and what should we expect next, both at RHIC and LHC. I also discuss event anisotropies sensitive to the strong parity violation effects.

Sergei A. Voloshin

2008-05-09

244

Abstract A numerical method based on contrast-enhanced MRI to predict the transport properties of spinal structures is presented and used for a population of 32 low back pain patients. Sixty-eight one-dimensional finite element models aimed to replicate the transport of Gd-HP-DO3A were developed, one for each intervertebral disc was investigated. Each model had the same disc height as that measured on the MRI images of specific patients. Transport properties of the vertebral structures were inversely calculated in order to minimize the error between the predicted Gd-HP-DO3A concentration and those determined by MRI acquisitions for specific patients 6 h after a contrast agent injection. Within some limits numerical predictions were generally representative of the Gd-HP-DO3A concentration behavior estimated by contrast-enhanced MRIs. The predicted properties showed high variability within the population. Transport properties were markedly higher than the bulk diffusion coefficients of the nutrients. No significant differences (p=0.31) were observed between the caudal and the cranial endplate zones. Discs had higher transport properties than endplate zones (p<0.001). Comparisons among different age groups revealed no significant differences of the transport properties with aging. The discrepancies between the predictions and the bulk diffusion coefficients of nutrients and Gd-HP-DO3A in water highlighted the complexities of quantifying transport across the EPZs and intervertebral disc. PMID:24633746

Galbusera, Fabio; Tibiletti, Marta; Brayda-Bruno, Marco; Neidlinger-Wilke, Cornelia; Wilke, Hans-Joachim

2014-10-01

245

NASA Astrophysics Data System (ADS)

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.

van Kats, C. M.

2008-10-01

246

Structural, electrical and anisotropic properties of Tl{sub 4}Se{sub 3}S chain crystals

The structure, the anisotropy effect on the current transport mechanism and the space charge limited current in Tl{sub 4}Se{sub 3}S chain crystals have been studied by means of X-ray diffraction, electrical conductivity measurements along and perpendicular to the crystal's c-axis and the current voltage characteristics. The temperature-dependent electrical conductivity analysis in the region of 150-400 K, revealed the domination of the thermionic emission of charge carriers over the chain boundaries above 210 and 270 K along and perpendicular to the c-axis, respectively. Below these temperatures, the variable range hopping is dominant. At a consistent temperature range, the thermionic emission analysis results in conductivity activation energies of 280 and 182 meV, along and perpendicular to the c-axis, respectively. Likewise, the hopping parameters are altered significantly by the conductivity anisotropy. The current-voltage characteristics revealed the existence of hole trapping state being located at 350 meV above the valence band of the crystal.

Qasrawi, A.F., E-mail: atef_qasrawi@atilim.edu.tr [Group of Physics, Faculty of Engineering, Atilim University, 06836 Ankara (Turkey); Department of Physics, Arab-American University, Jenin, West Bank, Palestine (Country Unknown); Gasanly, N.M. [Department of Physics, Middle East Technical University, 06531 Ankara (Turkey)

2009-10-15

247

Transport properties at nano scales via first principles studies

NASA Astrophysics Data System (ADS)

There are two main difficulties for the first principles study of transport properties at the nano scale. The first is that many-body interactions need to be taken into account for the infinite system without periodic boundary conditions. The other is that the system is usually in a non-equilibrium state. Both of these two difficulties are beyond the ability of conventional first principles methods to reconcile. Recently, a new first principles approach which combines the Non-equilibrium Green's Functions Technique (NGFT) and the Density Functional Theory (DFT) was proposed. DFT has been proved to be successful in molecular and solid state physics. Currently used DFT approximations can take into account 'most' many-body effects and NGFT naturally includes the non-equilibrium effects. The new approach uses NGFT to treat the non-periodic boundary conditions and DFT to treat many body interactions. This approach has been successfully used in molecular electronics. The thesis is organized in the following way. First: we introduce the main ideas of combining NGFT and DFT, and then apply this method to a light-driven molecular switch. The switch, made of a single molecule, is one of the most important elements of nano-electronics. However, most proposed molecular switches are driven either by an external bias voltage or by STM manipulation, neither of which is ideal for nano-scale circuits. The switch we designed has a high on-off conductance ratio and more importantly, can be driven by photons. In following chapters, we generalize the method to the spin-dependent case and apply it to a magnetic layered structure. We implemented the method within the framework of the Layer Korringa-Kohn-Rostoker (LKKR) approach, which is particularly well-adapted to the layered structure and found a bias-enhanced tunneling magneto-resistance (TMR) for the Fe/FeO/MgO/Fe junction. Our results are important not only for application, but also for understanding of the voltage-dependence of TMR for layered structures. The experimental studies show that the bias voltage usually kills the TMR of amorphous magnetic tunneling junctions. Our study shows that for an impurity-free layered structure, a different behavior of TMR may occur.

Zhang, Chun

248

Anisotropic thermal properties of the polar crystal Cs{sub 2}TeMo{sub 3}O{sub 12}

A Cs{sub 2}TeMo{sub 3}O{sub 12} single crystal with dimensions of 17 mm Multiplication-Sign 17 mm Multiplication-Sign 18 mm was grown using the top-seeded solution growth method. Thermal properties, including thermal expansion, specific heat, thermal diffusivity and thermal conductivity, were investigated as a function of temperature. The average linear thermal expansion coefficients along different crystallographic directions were measured to be {alpha}{sub a}=7.34 Multiplication-Sign 10{sup -6} K{sup -1} and {alpha}{sub c}=32.02 Multiplication-Sign 10{sup -6} K{sup -1} over the temperature range of 30-430 Degree-Sign C. The specific heat was measured to be 0.400-0.506 J g{sup -1} K{sup -1} from 22 Degree-Sign C to 440 Degree-Sign C. The thermal conductivity was calculated to be 1.86 and 0.76 W m{sup -1} K{sup -1} at 22 Degree-Sign C along the a and c axes, respectively. With increasing temperature from 22 to 430 Degree-Sign C, the thermal conductivity decreases by 33.0% along the a axis, while it decreases by 18.5% below 200 Degree-Sign C and then remains unchanged along the c axis. The relationship between structure and the thermal properties is also discussed. - Graphical Abstract: Centimeter-sized crystals of polar Cs{sub 2}TeMo{sub 3}O{sub 12} were grown using the top-seeded solution growth method. The relative large anisotropy in thermal expansion and thermal conductivity of Cs{sub 2}TeMo{sub 3}O{sub 12} is attributable to its layered structure. Highlights: Black-Right-Pointing-Pointer Cs{sub 2}TeMo{sub 3}O{sub 12} single crystals with dimensions of 17 Multiplication-Sign 17 Multiplication-Sign 18 mm{sup 3} were grown. Black-Right-Pointing-Pointer Thermal properties of Cs{sub 2}TeMo{sub 3}O{sub 12} were studied as a function of temperature. Black-Right-Pointing-Pointer The thermal expansion anisotropy of Cs{sub 2}TeMo{sub 3}O{sub 12} is explained using its structure. Black-Right-Pointing-Pointer To protect Cs{sub 2}TeMo{sub 3}O{sub 12} crystal, a small cooling rate should be used during growth. Black-Right-Pointing-Pointer A large temperature gradient should be avoided during processing and application.

Zhang, Junjie; Zhang, Zhonghan; Sun, Youxuan; Zhang, Chengqian [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, Shandong (China)] [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, Shandong (China); Tao, Xutang, E-mail: txt@icm.sdu.edu.cn [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, Shandong (China)] [State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, Shandong (China)

2012-11-15

249

in the experimentally detected dielectric response of organic semi- conductor copper phthalocyanine. While a giantIntrinsic dielectric properties and charge transport in oligomers of organic semiconductor copper. Huang and Q. M. Zhang Electrical Engineering Department and Materials Research Institute

Bobnar, Vid

250

Transport properties of high-temperature air in a magnetic field

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.

Bruno, D. [Institute of Inorganic Methodologies and Plasmas, CNR, 70126 Bari (Italy); Capitelli, M.; Catalfamo, C. [Department of Chemistry, University of Bari, 70126 Bari (Italy); Giordano, D. [Aerothermodynamics Section, ESA-ESTEC, 2200 AG Noordwijk (Netherlands)

2011-01-15

251

Optical characterization of complex mechanical and thermal transport properties

Time-resolved impulsive stimulated light scattering (ISS), also known as transient grating spectroscopy, was used to investigate phonon mediated thermal transport in semiconductors and mechanical degrees of freedom linked ...

Johnson, Jeremy A. (Jeremy Andrew)

2011-01-01

252

Using a Flume to Demonstrate Fluid Properties and Sediment Transport

NSDL National Science Digital Library

A 20-foot long recirculating flume is used for a series of demonstrations designed to help students explore the principles of fluid dynamics and sediment transport. The design and construction of the flume and four demonstrations are described in the attached activity. The demonstrations build upon each other so that students have a chance to develop an understanding of sedimentary transport processes and the deposits they produce.

Singer, Jill

253

Facilitation of bacterial transport for the purpose of bioaugmentation of contaminant degradation may be achieved by a number of methods typically involving changes in the properties of the groundwater or changes in the characteristics of the bacterial surface. Facilitated bacterial transport was investigated in laboratory experiments monitoring bacterial retention in quartz sand and glass bead mini-columns. Bacterial attachment efficiencies were

William P Johnson; Michael J Martin; Mark J Gross; Bruce E Logan

1996-01-01

254

Transport properties of two-dimensional electron systems on silicon (111) surfaces

We theoretically study transport properties of a two-dimensional electron system on a hydrogen-passivated Si(111) surface in the field-effect-transistor (FET) configuration. We calculate the density- and temperature-dependent mobility and resistivity for the recently fabricated Si(111)-vacuum FET by using a semiclassical Boltzmann theory including screened charged impurity scattering. We find reasonable agreement with the corresponding experimental transport properties, indicating that the screened

E. H. Hwang; S. Das Sarma

2007-01-01

255

Incidence, reflection and transmission angles in anisotropic media

The mathematical description of phenomena related to wave propagation in anisotropic media is considerably more complicated\\u000a than that for isotropic media. This complexity stems from many physical properties distinguishing the anisotropic from isotropic\\u000a medium. Therefore, calculating the angles of reflection and transmission for a ray impining on a boundary between two anisotropic\\u000a media become more complicated in mathematical implication. Snell

Bing-Ming Zhang; Min-Yu Dong; Zhong-Ping Qian

1999-01-01

256

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.

Murray, Chris; Allen-King, Richelle; Weissmann, Gary

2006-06-01

257

Controlling anisotropic nanoparticle growth through plasmon excitation

Inorganic nanoparticles exhibit size-dependent properties that are of interest for applications ranging from biosensing and catalysis to optics and data storage. They are readily available in a wide variety of discrete compositions and sizes. Shape-selective synthesis strategies now also yield shapes other than nanospheres, such as anisotropic metal nanostructures with interesting optical properties. Here we demonstrate that the previously described

Rongchao Jin; Y. Charles Cao; Encai Hao; Gabriella S. Métraux; George C. Schatz; Chad A. Mirkin

2003-01-01

258

The influence of Ni-rich nanoclusters on the anisotropic magnetic properties of CdSb doped with Ni

NASA Astrophysics Data System (ADS)

The magnetic properties of oriented CdSb single crystals doped with 2 at% of Ni are investigated. From measurements of magnetic irreversibility defined by deviation of the zero-field-cooled (ZFC) susceptibility from the field-cooled (FC) susceptibility, the value of the mean anisotropy field BK ~ 4 kG is obtained. The ZFC susceptibility displays a broad maximum at a blocking temperature, Tb, depending on B according to the law [Tb(B)/Tb(0)]1/2 = 1 - B/BK with Tb(0) ~ 100 K. The field dependence of the magnetization exhibits saturation above ~20-30 kG with values of Ms different for B along the [1 0 0], [0 1 0] and [0 0 1] axes. The temperature dependence of Ms is weak, increasing slightly upon cooling the sample below ~100 K. The temperature dependence of the coercive field, Bc(T), is weak above Tb but is enhanced strongly with decreasing temperature below Tb. The anisotropy of Bc is inverted with respect to the anisotropy of Ms. Such behaviour can be attributed to spheroidal Ni-rich Ni1-xSbx nanoparticles with a high aspect ratio, broad size distribution and distribution of the orientation of the major axis around a preferred direction. The relation Bc Lt BK and the anisotropies of Ms and Bc are consistent with reversal of the magnetization by the curling mode, whereas the Tb(B) dependence is typical of the coherent rotation mode. This difference is connected to the proximity of the average transversal cluster radius to a critical value for transition between the two magnetization reversal modes within a wide crossover interval, due to broad distribution of the cluster sizes.

Laiho, R.; Lashkul, A. V.; Lisunov, K. G.; Lähderanta, E.; Ojala, I.; Zakhvalinskii, V. S.

2006-03-01

259

Transport, magnetic, thermodynamic, and optical properties in Ti-doped Sr2RuO4

NASA Astrophysics Data System (ADS)

We report on electrical resistivity, magnetic susceptibility, and magnetization on heat-capacity and optical experiments in single crystals of Sr2Ru1-xTixO4. Samples with x=0.1 and 0.2 reveal purely semiconducting resistivity behavior along c and the charge transport is close to localization within the ab plane. A strong anisotropy in the magnetic susceptibility appears at temperatures below 100 K. Moreover magnetic ordering in the c direction with a moment of order 0.01 ?B/f.u. occurs at low temperatures. On doping the low-temperature linear term of the heat capacity becomes significantly reduced and probably is dominated by spin fluctuations. Finally, the optical conductivity reveals the anisotropic character of the dc resistance, with the in-plane conductance roughly following a Drude-type behavior and an insulating response along c.

Pucher, K.; Hemberger, J.; Mayr, F.; Fritsch, V.; Loidl, A.; Scheidt, E.-W.; Klimm, S.; Horny, R.; Horn, S.; Ebbinghaus, S. G.; Reller, A.; Cava, R. J.

2002-03-01

260

Disorder-induced variability of transport properties of sub-5 nm-wide graphene nanoribbons

NASA Astrophysics Data System (ADS)

Transport properties of sub-5 nm-wide graphene nanoribbons (GNRs) are investigated by using atomistic non-equilibrium Green's function (NEGF) simulations and semiclassical mobility simulations of large ensembles of randomly generated nanoribbons. Realistic GNRs with dimensions targeting the 12 nm CMOS node are investigated by accounting for edge defects, vacancies and potential fluctuations. Effects of disorder on transmission, transport gap, mean free path, density of states and acoustic phonon limited carrier mobility are explored for various disorder strengths and GNR widths in the 1-5 nm range. We report the high variability of GNR transport properties that could be a strong limiter for potential nanoelectronics applications of GNRs.

Poljak, M.; Wang, M.; Song, E. B.; Suligoj, T.; Wang, K. L.

2013-06-01

261

NASA Astrophysics Data System (ADS)

The effects of the electric and magnetic field variation on multiferroic heterostructure were studied in this work. Thin films of polycrystalline Fe50Pt50 (FePt) were grown by dc-sputtering on top of the commercial slabs of lead magnesium niobate-lead titanate (PMN-PT). The sample was a (011)-cut single crystal and had one side polished. In this condition, the PMN-PT/FePt operates in the L-T (longitudinal magnetized-transverse polarized) mode. A FePt thin film of 20 nm was used in this study to avoid the characteristic broad microwave absorption line associated with these films above thicknesses of 40 nm. For the in-plane easy magnetization axis (01-1), a microwave magnetoelectric (ME) coupling of 28 Oe cm kV -1 was estimated, whereas a value of 42 Oe cm kV -1 was obtained through the hard magnetization axis (100). Insight into the effects of the in-plane strain anisotropy on the ME coupling is obtained from the dc-magnetization loops. It was observed that the trend was opposite along the easy and hard magnetic directions. In particular, along the easy-magnetic axis (01-1), a square and narrow loop with a factor of Mr/MS of 0.96 was measured at 10 kV/cm. Along the hard-magnetic axis, a factor of 0.16 at 10 kV/cm was obtained. Using electric tuning via microwave absorption at X-band (9.78 GHz), we observe completely different trends along the easy and hard magnetic directions; Multiple absorption lines along the latter axis compared to a single and narrower absorption line along the former. In spite of its intrinsic complexity, we propose a model which gives good agreement both for static and microwave properties. These observations are of fundamental interest for future ME microwave components, such as filters, phase-shifters, and resonators.

Vargas, Jose M.; Gómez, Javier

2014-10-01

262

Temperature dependence of electronic transport property in ferroelectric polymer films

NASA Astrophysics Data System (ADS)

The leakage current mechanism of ferroelectric copolymer of polyvinylidene fluoride with trifluoroethylene prepared by Langmuir-Blodgett was investigated in the temperature range from 100 K to 350 K. The electron as the dominant injected carrier was observed in the ferroelectric copolymer films. The transport mechanisms in copolymer strongly depend on the temperature and applied voltage. From 100 K to 200 K, Schottky emission dominates the conduction. With temperature increasing, the Frenkel-Poole emission instead of the Schottky emission to conduct the carrier transport. When the temperature gets to 260 K, the leakage current becomes independent of temperature, and the space charge limited current conduction was observed.

Zhao, X. L.; Wang, J. L.; Tian, B. B.; Liu, B. L.; Zou, Y. H.; Wang, X. D.; Sun, S.; Sun, J. L.; Meng, X. J.; Chu, J. H.

2014-10-01

263

Anisotropic transport properties of high-temperature superconductors were extensively investigated for YBa{sub 2}Cu{sub 3}O{sub {ital y}} crystals prepared by a crystal-pulling technique. Since the crystals are as large as 4{times}4{times}2 mm{sup 3}, we have successfully measured their resistivity, Hall coefficient, and thermopower along both the in-plane and out-of-plane directions, by using samples cut from the same crystal. The measured in-plane data have revealed that our samples are slightly overdoped when highly oxygenated. This means that our samples have the least anisotropic resistivities between the in-plane and out-of-plane directions among high-{ital T}{sub {ital c}} cuprates. The Hall coefficient and the thermopower along the out-of-plane direction qualitatively agree with the band calculation, but the scattering time along the out-of-plane direction is anomalously short. Thus, it is concluded that the two-dimensional nature in the electronic states of high-{ital T}{sub {ital c}} cuprates is mainly characterized by the anomalously short scattering time along the out-of-plane direction, not by the anisotropic effective masses.

Terasaki, I.; Sato, Y.; Miyamoto, S.; Tajima, S.; Tanaka, S. [Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135 (Japan)] [Superconductivity Research Laboratory, International Superconductivity Technology Center, 1-10-13 Shinonome, Koto-ku, Tokyo 135 (Japan)

1995-12-01

264

Transport properties of carbon dioxide through amine functionalized carrier membranes

COâ facilitated transport was studied using a membrane with amine sites covalently bound to the polymer backbone and ion exchange membranes which have amine complexing agents (carrier) as counterions. The two types of membranes were compared, and several amine functionalities for the ion-exchange membrane were studied. Although the covalently bonded membranes had a larger absorption capacity than amine functionalized Nafion

Takeo Yamaguchi; Lars M. Boetje; Carl A. Koval; Richard D. Noble; Christopher N. Bowman

1995-01-01

265

Estimation of Effective Transport Properties in Packed Bed Reactors

Packed bed reactors are commonly used for carrying out heterogeneous chemical reactions, and the attendant complexities arising out of the interactions of the momentum, heat, and mass transport processes make the design of such units a very involved and cumbersome task. The strategy for rational design depends strongly on the nature of the reaction scheme and its sensitivity to perturbations

B. D. Kulkarni; L. K. Doraiswamy

1980-01-01

266

Transport Properties of the Dust Components in Weakly Ionized Plasma

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.

Vaulina, O. S.; Adamovich, X. G.; Petrov, O. F.; Fortov, V. E. [Institute for High Temperatures, RAS, Moscow (Russian Federation)

2008-09-07

267

Calorimetric and transport properties of Zircalloy 2, Zircalloy 4, and Inconel 625

This paper presents the measurements and the results on thermal and electrical transport properties of three nuclear reactor cladding materials: Zircalloy 2, Zircalloy 4, and Inconel 625. Study of these materials constituted a part of the IAEA coordinated research program aimed at the generation and establishment of a reliable and complete database of the thermal properties of reactor materials. Measured

K. D. Magli?; N. Lj. Perovi?; A. M. Stanimirovi?

1994-01-01

268

conductivity is significant to electrical engineering disciplines.2,3 Recent work has also focused on utilizingStudy of Fluid and Transport Properties of Porous Anodic Aluminum Membranes by Dynamic Atomic Force their potential applications, little research has been conducted on PAAMs' hydrodynamic properties

Chan, Derek Y C

269

Calculation of Mechanical, Thermodynamic and Transport Properties of Metalic Glass formers

Calculation of Mechanical, Thermodynamic and Transport Properties of Metalic Glass formers Tahir C properties of pure metals and binary alloys in solid, liquid and glass phases. Here, we will describe the kinetics and thermodynamics of supercooled bulk metallic glass forming liquids is of critical importance

Ã?agin, Tahir

270

NASA Astrophysics Data System (ADS)

An experimental investigation was made of the spatial spectrum of waves emitted by an anisotropic optical LiNbO3:Ti waveguide when a guided mode was converted into a leaky wave by interaction with a surface acoustic wave (SAW). The spectrum of the emitted field was modified greatly by the propagation of the diffracted radiation along a part of the anisotropic waveguide which was free of the SAW. The efficiency of the interaction with the SAW increased by two orders of magnitude for the radiation modes characterized by the maximum coupling coefficient.

Petrov, D. V.; Tsarev, A. V.; Yakovkin, I. B.

1988-01-01

271

NASA Technical Reports Server (NTRS)

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.

Svehla, R. A.; Mcbride, B. J.

1973-01-01

272

Relations between anisotropic diffusion and robust statis tics are described in this pa- per. Specifically, we show that anisotropic diffusion can be seen as a robust estimation procedure that estimates a piecewise smooth image from a noi sy input image. The \\

Michael J. Black; Guillermo Sapiro; David H. Marimont; David Heeger

1998-01-01

273

Thermodynamic and transport property modeling in super critical water

Supercritical water oxidation (SCWO) is a thermally-based, remediation and waste-treatment process that relies on unique property changes of water when water is heated and pressurized above its critical point. Above its ...

Kutney, Michael C. (Michael Charles)

2005-01-01

274

A Monge Property for the D-dimensional Transportation Problem

In 1963, Hoffman gave necessary and sufficient conditions under which a family of O(mn)-time greedy algorithms solves the classical two-dimensional transportation problem with m sources and n sinks. One member of this family, an algorithm based on the “northwest corner rule”, is of particular interest, as its running time is easily reduced to O(m + n). When restricted to this

Wolfgang W. Bein; Peter Brucker; James K. Park; Pramod K. Pathak

1995-01-01

275

Theoretical studies of the transport properties in compound semiconductors

NASA Technical Reports Server (NTRS)

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.

Segall, Benjamin

1994-01-01

276

Analysis of Data from Pumping Tests in Anisotropic Aquifers

In conventional methods of aquifer tests homogeneous and isotropic aquifers are assumed. In many instances, however, the aquifers tested are anisotropic. Procedures are outlined for determining the principal directions of anisotropy and the hydraulic properties of homogeneous anisotropic aquifers. Data from pumping tests in leaky or nonleaky aquifers are used. The aquifers are uniform in thickness, and the flow therein

MAHDI S. HANTUSH

1966-01-01

277

RAY-CENTRED COORDINATE SYSTEMS IN ANISOTROPIC MEDIA

RAY-CENTRED COORDINATE SYSTEMS IN ANISOTROPIC MEDIA L. Klime#20; s Department of Geophysics: March 23, 2006 ABSTRACT Whereas the ray{centred coordinates for isotropic media by Popov and P#20;sen#20, there is considerable freedom in selecting the ray{centred coordinates for anisotropic media. We describe the properties

Cerveny, Vlastislav

278

THE TOPOLOGICAL DERIVATIVE IN ANISOTROPIC by Marc Bonneta

THE TOPOLOGICAL DERIVATIVE IN ANISOTROPIC ELASTICITY by Marc Bonneta , Gabriel Delgadob,c (a POems A comprehensive treatment of the topological derivative for anisotropic elasticity is presented, with both properties. A formula for the topological derivative of any cost functional defined in terms of regular

Paris-Sud XI, UniversitÃ© de

279

Characterizing N-dimensional anisotropic Brownian motion by the distribution of diffusivities.

Anisotropic diffusion processes emerge in various fields such as transport in biological tissue and diffusion in liquid crystals. In such systems, the motion is described by a diffusion tensor. For a proper characterization of processes with more than one diffusion coefficient, an average description by the mean squared displacement is often not sufficient. Hence, in this paper, we use the distribution of diffusivities to study diffusion in a homogeneous anisotropic environment. We derive analytical expressions of the distribution and relate its properties to an anisotropy measure based on the mean diffusivity and the asymptotic decay of the distribution. Both quantities are easy to determine from experimental data and reveal the existence of more than one diffusion coefficient, which allows the distinction between isotropic and anisotropic processes. We further discuss the influence on the analysis of projected trajectories, which are typically accessible in experiments. For the experimentally most relevant cases of two- and three-dimensional anisotropic diffusion, we derive specific expressions, determine the diffusion tensor, characterize the anisotropy, and demonstrate the applicability for simulated trajectories. PMID:24320252

Heidernätsch, Mario; Bauer, Michael; Radons, Günter

2013-11-14

280

Characterizing N-dimensional anisotropic Brownian motion by the distribution of diffusivities

NASA Astrophysics Data System (ADS)

Anisotropic diffusion processes emerge in various fields such as transport in biological tissue and diffusion in liquid crystals. In such systems, the motion is described by a diffusion tensor. For a proper characterization of processes with more than one diffusion coefficient, an average description by the mean squared displacement is often not sufficient. Hence, in this paper, we use the distribution of diffusivities to study diffusion in a homogeneous anisotropic environment. We derive analytical expressions of the distribution and relate its properties to an anisotropy measure based on the mean diffusivity and the asymptotic decay of the distribution. Both quantities are easy to determine from experimental data and reveal the existence of more than one diffusion coefficient, which allows the distinction between isotropic and anisotropic processes. We further discuss the influence on the analysis of projected trajectories, which are typically accessible in experiments. For the experimentally most relevant cases of two- and three-dimensional anisotropic diffusion, we derive specific expressions, determine the diffusion tensor, characterize the anisotropy, and demonstrate the applicability for simulated trajectories.

Heidernätsch, Mario; Bauer, Michael; Radons, Günter

2013-11-01

281

solubility increases with pressure [10]. Water substantially influences physical properties of liquids [11First-Principles Study of Enhancement of Transport Properties of Silica Melt by Water Bijaya B-principles molecular dynamics simulations show that water (8.25 wt%) dramatically affects the transport properties

Stixrude, Lars

282

Microsphere-chain waveguides: Focusing and transport properties

NASA Astrophysics Data System (ADS)

It is shown that the focusing properties of polystyrene microsphere-chain waveguides (MCWs) formed by sufficiently large spheres (D ? 20?, where D is the sphere diameter and ? 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 D ? 10? 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.

Allen, Kenneth W.; Darafsheh, Arash; Abolmaali, Farzaneh; Mojaverian, Neda; Limberopoulos, Nicholaos I.; Lupu, Anatole; Astratov, Vasily N.

2014-07-01

283

Anisotropic magnetoresistance in an antiferromagnetic semiconductor

NASA Astrophysics Data System (ADS)

Recent studies in devices comprising metal antiferromagnets have demonstrated the feasibility of a novel spintronic concept in which spin-dependent phenomena are governed by an antiferromagnet instead of a ferromagnet. Here we report experimental observation of the anisotropic magnetoresistance in an antiferromagnetic semiconductor Sr2IrO4. Based on ab initio calculations, we associate the origin of the phenomenon with large anisotropies in the relativistic electronic structure. The antiferromagnet film is exchange coupled to a ferromagnet, which allows us to reorient the antiferromagnet spin-axis in applied magnetic fields via the exchange spring effect. We demonstrate that the semiconducting nature of our AFM electrode allows us to perform anisotropic magnetoresistance measurements in the current-perpendicular-to-plane geometry without introducing a tunnel barrier into the stack. Temperature-dependent measurements of the resistance and anisotropic magnetoresistance highlight the large, entangled tunabilities of the ordinary charge and spin-dependent transport in a spintronic device utilizing the antiferromagnet semiconductor.

Fina, I.; Marti, X.; Yi, D.; Liu, J.; Chu, J. H.; Rayan-Serrao, C.; Suresha, S.; Shick, A. B.; Železný, J.; Jungwirth, T.; Fontcuberta, J.; Ramesh, R.

2014-09-01

284

Tuning the electronic transport properties of grapheme through functionalisation with fluorine

We demonstrate the possibility to tune the electronic transport properties of graphene mono-layers and multi-layers by functionalisation with fluorine. For mono-layer samples, with increasing the fluorine content, we observe a transition from electronic transport through Mott variable range hopping (VRH) in two dimensions to Efros-Shklovskii VRH. Multi-layer fluorinated graphene with high concentration of fluorine show two-dimensional Mott VRH transport, whereas CF0.28 multi-layer flakes exhibit thermally activated transport through near neighbour hopping. Our experimental findings demonstrate that the ability to control the degree of functionalisation of graphene is instrumental to engineer different electronic properties in graphene materials. PMID:21910905

2011-01-01

285

Scale-and shape-dependent transport property of nanoporous materials

NASA Astrophysics Data System (ADS)

A cellular material was proposed as an ideal candidate for multifunctional material achieving various optimal properties in many length scales. The superior performances on mechanical, thermal, electrical, and fluidic properties have been explored in analytic, numerical, and experimental studies. Since the cellular materials have wide range of potential applications in microscopic devices, characterization in small length scale gains more attentions recently. For this assessment, the atomistic approach as well as continuum approach becomes crucial to characterize its performance in multiscales. One of the key multifunctional features of the nanoporous microstructures would be high fluidic performance. Some studies investigated macroscopic transport properties, but less has been done to address the scale- and shape-dependent transport properties for their microscopic fluidics applications. In this study, we investigated complex flow patterns and transport properties of porous structures in microscopic scales. To address the geometry-dependent transport properties, a non-equilibrium molecular dynamics was employed in the atomistic scale. Various flow channels in the porous materials were introduced to address the size and shape effect of the flow patterns in small length scales.

Hyun, Sangil; Koo, Eunhae

2013-02-01

286

THERMODYNAMIC AND TRANSPORT PROPERTIES OF SILICATE MELTS AND MAGMA

of parental source material.28 29 Magma Rheology30 The rheological properties of magma depend on temperature, bulk composition, pressure, phase31 assemblage (melt ï¿½ crystals ï¿½ vapor), particle size and shape capacity. The EOS relates the39 density of a substance to its composition, pressure and temperature

Spera, Frank J.

287

Low-field carrier transport properties in biased bilayer graphene

NASA Astrophysics Data System (ADS)

Based on a semiclassical Boltzmann transport equation in random phase approximation, we develop a theoretical model to understand low-field carrier transport in biased bilayer graphene, which takes into account the charged impurity scattering, acoustic phonon scattering, and surface polar phonon scattering as three main scattering mechanisms. The surface polar optical phonon scattering of carriers in supported bilayer graphene is thoroughly studied using the Rode iteration method. By considering the metal-BLG contact resistance as the only one free fitting parameter, we find that the carrier density dependence of the calculated total conductivity agrees well with that observed in experiment under different temperatures. The conductivity results also suggest that in high carrier density range, the metal-BLG contact resistance can be a significant factor in determining the BLG conductivity at low temperature, and both acoustic phonon scattering and surface polar phonon scattering play important roles at higher temperature, especially for BLG samples with a low doping concentration, which can compete with charged impurity scattering.

Hu, Bo

2014-07-01

288

Thermal transport and fire retardance properties of cellular aluminum alloys

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.

Lu, T.J.; Chen, C. [Univ. of Cambridge (United Kingdom). Dept. of Engineering] [Univ. of Cambridge (United Kingdom). Dept. of Engineering

1999-03-31

289

Studies of Transport Properties of Fractures: Final Report

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.

Stephen R. Brown

2006-06-30

290

Magnetic property effect on transport processes in resistance spot welding

NASA Astrophysics Data System (ADS)

This study investigates the effects of the Curie temperature and magnetic permeability on transport variables, solute distribution and nugget shapes during resistance spot welding. The Curie temperature is the temperature below which a metal or alloy is ferromagnetic with a high magnetic permeability, and above which it is paramagnetic with a small magnetic permeability. The model proposed here accounts for electromagnetic force, heat generation and contact resistance at the faying surface and electrode-workpiece interfaces and bulk resistance in workpieces. Contact resistance includes constriction and film resistances, which are functions of hardness, temperature, electrode force and surface condition. The computed results show that transport variables and nugget shapes can be consistently interpreted from the delay of response time and jump of electric current density as a result of finite magnetic diffusion, rather than through the examination of the variations of dynamic electrical resistance with time. The molten nugget on the faying surface is initiated earlier with increasing magnetic permeability and Curie temperature. A high Curie temperature enhances convection and solute mixing, and readily melts through the workpiece surface near the electrode edge. Any means to reduce the Curie temperature or magnetic permeability, such as adjusting the solute content, can be a good way to control weld quality. This study can also be applied to interpret the contact problems encountered in various electronics and packaging technologies, and so on.

Wei, P. S.; Wu, T. H.

2011-08-01

291

Direct measurements of transport and water properties through the Bering Strait

Four years of temperature, salinity, and velocity data enable a direct computation of volume transport and a temporal description of water properties exchanged through the Bering Strait. The mean volume transport over the 4-year period (September 1990 through September 1994) is 0.83 Sv northward with a weekly standard deviation of 0.66 Sv. The maximum error in this mean estimate is

A. T. Roach; K. Aagaard; C. H. Pease; S. A. Salo; T. Weingartner; V. Pavlov; M. Kulakov

1995-01-01

292

The single-file water transport through a biomimic water channel consisting of a (6,6) carbon nanotube (CNT) with different types of external point charges is studied using molecular dynamics simulations. It is demonstrated that, as in the aquaporins, asymmetrically positioned charges cannot generate robust unidirectional water flow in the CNT. Thermal fluctuation in bulk water competes with charge affinity to steer the water transport, resulting in nonmonotonic flow with intermittent reversal of transport direction. The energetic analysis suggests that the water-water interaction, determined by dipole orientation configuration, influences the transport rate significantly. These findings can provide correct biomimic understanding of water transport properties and will benefit the design of efficient functional nanofluidic devices. PMID:20000381

Zuo, Guangchao; Shen, Rong; Ma, Shaojie; Guo, Wanlin

2010-01-26

293

On the Anisotropic Nature of MRI-Driven Turbulence in Astrophysical Disks

The magnetorotational instability is thought to play an important role in enabling accretion in sufficiently ionized astrophysical disks. The rate at which MRI-driven turbulence transports angular momentum is related to both the strength of the amplitudes of the fluctuations on various scales and the degree of anisotropy of the underlying turbulence. This has motivated several studies of the distribution of turbulent power in spectral space. In this paper, we investigate the anisotropic nature of MRI-driven turbulence using a pseudo-spectral code and introduce novel ways to robustly characterize the underlying turbulence. We show that the general flow properties vary in a quasi-periodic way on timescales comparable to 10 inverse angular frequencies motivating the temporal analysis of its anisotropy. We introduce a 3D tensor invariant analysis to quantify and classify the evolution of the anisotropic turbulent flow. This analysis shows a continuous high level of anisotropy, with brief sporadic transitions towa...

Murphy, Gareth C

2014-01-01

294

Transport properties of graphene under periodic and quasiperiodic magnetic superlattices

NASA Astrophysics Data System (ADS)

We study the transmission of Dirac electrons through the one-dimensional periodic, Fibonacci, and Thue-Morse magnetic superlattices (MS), which can be realized by two different magnetic blocks arranged in certain sequences in graphene. The numerical results show that the transmission as a function of incident energy presents regular resonance splitting effect in periodic MS due to the split energy spectrum. For the quasiperiodic MS with more layers, they exhibit rich transmission patterns. In particular, the transmission in Fibonacci MS presents scaling property and fragmented behavior with self-similarity, while the transmission in Thue-Morse MS presents more perfect resonant peaks which are related to the completely transparent states. Furthermore, these interesting properties are robust against the profile of MS, but dependent on the magnetic structure parameters and the transverse wave vector.

Lu, Wei-Tao; Wang, Shun-Jin; Wang, Yong-Long; Jiang, Hua; Li, Wen

2013-08-01

295

Electrical transport properties of CaB6

NASA Astrophysics Data System (ADS)

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 negative—for weakly metallic samples—to positive values—for samples in a localized regime.

Stankiewicz, Jolanta; Sesé, Javier; Balakrishnan, Geetha; Fisk, Zachary

2014-10-01

296

Electric transport and magnetic properties in multilayer graphene

NASA Astrophysics Data System (ADS)

We discuss electric transport and orbital magnetism of multilayer graphenes in a weak-magnetic field using the matrix decomposition technique. At zero temperature, the minimum conductivity is given by that of the monolayer system multiplied by the layer number N , independent of the interlayer hopping t . When the interlayer hopping satisfies the condition t??/? with ? being collision time of impurity scattering, [N/2] kinks and [N/2]+1 plateaux appear in the Fermi-energy (gate voltage) dependence of the conductivity and the Hall conductivity, respectively. These behaviors are interpreted as multiband effects. We also found that the Hall conductivity and the magnetic susceptibility take minimum value as a function of temperature, for certain value of the gate voltage. This behavior is explained by Fermi-energy dependence of these functions at zero temperature.

Nakamura, Masaaki; Hirasawa, Lila

2008-01-01

297

Electronic transport properties through thiophenes on switchable domains

The electronic transport of electrons and holes through stacks of $\\alpha$,$\\ome ga$-dicyano-$\\beta$,$\\beta$'-dibutyl- quaterthiophene (DCNDBQT) as part of a nov el organic ferroic field-effect transistor (OFFET) is investigated. The novel ap plication of a ferroelectric instead of a dielectric substrate provides the poss ibility to switch bit-wise the ferroelectric domains and to employ the polarizat ion of these domains as a gate field in an organic semiconductor. A device conta ining very thin DCNDBQT films of around 20 nm thickness is intended to be suitab le for logical as well as optical applications. We investigate the device proper ties with the help of a phenomenological model called multilayer organic light-e mitting diodes (MOLED), which was extended to transverse fields. The results sho wed, that space charge and image charge effects play a crucial role in these org anic devices.

T. Kunze; S. Gemming; V. Pankoke; K. Morawetz; R. Luschtinetz; G. Seifert

2009-09-11

298

Direct measurements of transport properties are essential for site characterization

Direct measurements of transport parameters on subsurface sediments using, the UFA method provided detailed hydrostratigraphic mapping, and subsurface flux distributions at a mixed-waste disposal site at Hanford. Seven hundred unsaturated conductivity measurements on fifty samples were obtained in only six months total of UFA run time. These data are used to provide realistic information to conceptual models, predictive models and restoration strategies. The UFA instrument consists of an ultracentrifuge with a constant, ultralow flow pump that provides fluid to the sample surface through a rotating seal assembly and microdispersal system. Effluent from the sample is collected in a transparent, volumetrically-calibrated chamber at the bottom of the sample assembly. Using a strobe light, an observer can check the chamber while the sample is being centrifuged. Materials can be run in the UFA as recomposited samples or in situ samples can be subcored directly into the sample UFA chamber.

Wright, J. [Pacific Northwest Lab., Richland, WA (United States); Conca, J.L. [Washington State Univ. Tri-Cities, Richland, WA (United States). Environmental Sciences

1994-08-01

299

Magnetic and transport properties of magnetite thin films

Magnetite (Fe3O4) films were prepared by DC reactive magnetron sputtering at various oxygen partial pressures with the ratio ? of oxygen to argon changing from 0.50:50 to 0.70:50 at room temperature, and then the Fe3O4 films were annealed at 480°C for 80min. The properties of the films were studied by X-ray diffraction, scanning electron microscopy, magnetic hysteresis loops, magnetoresistance (MR),

Guomin Zhang; Chongfei Fan; Liqing Pan; Fengping Wang; Ping Wu; Hong Qiu; Yousong Gu; Yue Zhang

2005-01-01

300

Aging effects on the transport properties in conducting polymer polypyrrole

NASA Astrophysics Data System (ADS)

We present electronic transport studies of the aging process in naphtalene-sulfonate-doped polypyrrole. They include in situ conductivity measurements as a function of the aging time up to 1 month, and conductivity and thermoelectric power measurements in the temperature range 300-15 K for different aging times at 120 °C in room atmosphere. We show that while the short-aging-time decay of the conductivity may be accounted for by a law of the type ?0-?(ta)~?ta, the long-aging-time evolution is well described by a stretched exponential, ?=?0exp[-(ta/?)1/2]. Moreover, two distinct temperature dependences have been identified: (i) ?=?0exp[-(T0/T)1/2] for aged samples and (ii) ?=?0exp[-T1/T+T0] for as-synthesized or lightly aged samples. The thermal variation of the thermoelectric power can be described by the following law: S(T)=AT+B+C/T, where the relative weight of the linear term, A, appears to be a decreasing function of the aging time. All the results are comprehensively explained in terms of conducting grains separated by insulating barriers in which the conduction is controlled by a hopping process of the charge carriers between the grains. The aging phenomenon is found to consist of a decrease of the grain size, in parallel with a broadening of the barriers, as in a corrosion process. As the aging time increases, the size of the conducting grains decreases and then goes below a critical value that is responsible for a crossover in the transport mechanism and therefore in the time dependence of the conductivity as experimentally observed. In the aged samples, this model leads to the existence of a single expression that accounts for both the temperature and the aging-time dependences of the conductivity, i.e., ln?(ta,T)~-(ta/T)1/2.

Sixou, B.; Mermilliod, N.; Travers, J. P.

1996-02-01

301

The transport properties and new device design: the case of 6,6,12-graphyne nanoribbons.

By performing first-principle quantum transport calculations, we studied the transport properties of three kinds of 6,6,12-graphyne nanoribbons with different edges and different cutting directions. The nanoribbon with zigzag edges shows metallic properties and the spin-polarized currents show an obvious negative differential resistance effect, the other two nanoribbons terminated by a phenyl ring are semiconductors and spin-unpolarized. We also designed several nanowire devices based on these 6,6,12-graphyne nanoribbons, such as rectifier, spin filter diode, spin FET and spin caloritronics devices. These results indicate that 6,6,12-graphyne is a potential candidate for spintronics and spin caloritronics. PMID:23584607

Ni, Yun; Yao, Kai-Lun; Fu, Hua-Hua; Gao, Guo-Ying; Zhu, Si-Cong; Luo, Bo; Wang, Shu-Ling; Li, Rui-Xue

2013-05-21

302

Structural and transport properties of Yb substituted YBaCo4O7

NASA Astrophysics Data System (ADS)

We investigate a series of compounds of the type, Y1-xYbxBaCo4O7, to study the effect of chemical pressure on the structural and electrical transport properties of a geometrically frustrated cobaltite, YBaCo4O7. Rietveld analysis of XRD data were carried out for all the samples studied. The four probe resistivity measurements were carried out to understand the transport mechanism in these compounds at temperatures below room temperatures. These results are presented and discussed in the context of ongoing efforts in studying geometrically frustrated magnetic compounds with novel physical properties.

Singh, Bharat; Kumar, Naresh; Gaur, N. K.; Rayaprol, S.

2012-06-01

303

Electronic and Transport Properties of Quasi-1D Wires of Biological Molecules

NASA Astrophysics Data System (ADS)

In the search for organic materials with good charge-transport properties, artificial stacks of biological molecules are considered attractive candidates [1,2]. In this spirit, we present ab-initio DFT calculations of the structural, electronic, and quantum-transport properties of quasi-1D wires based on guanine and eumelanin molecules [3]. Hereby, a special focus is put on the results for the electronic bandwidths and the consequences for potential applications. [4pt] [1] R. di Felice et al., Phys. Rev. B 65, 045104 (2001) [0pt] [2] P. Meredith et al., Pigment Cell Res. 19, 572 (2006) [0pt] [3] B. Oetzel et al. (unpublished)

Oetzel, Björn; Matthes, Lars; Tandetzky, Falk; Ortmann, Frank; Bechstedt, Friedhelm; Hannewald, Karsten

2010-03-01

304

Walker diffusion method for calculation of transport properties of composite materials

The morphology of a multiphase microstructure greatly influences the macroscopic transport properties of the composite material. These properties are shown to be related to the diffusion coefficient of a random (nonbiased) walker. The proper diffusion rules are found by considering an isomorphic image of the microstructure in which distinct populations of walkers correspond to the phase domains, with the walker density of a population proportional to the transport coefficient of the corresponding domain. To demonstrate the method, it is applied to disordered two-phase percolating composites. {copyright} {ital 1999} {ital The American Physical Society}

DeW. Van Siclen, C. [Idaho National Engineering and Environmental Laboratory, Idaho Falls, Idaho 83415 (United States)] [Idaho National Engineering and Environmental Laboratory, Idaho Falls, Idaho 83415 (United States)

1999-03-01

305

NASA Astrophysics Data System (ADS)

Anisotropic in-plane strain can be induced in (Pb,Sr)TiO3 (PST) thin film by using orthorhombic NdGaO3 (110) as a substrate. High-resolution x-ray diffraction was used to measure the strain of the PST thin film. A rocking curve with full width at half maximum of ˜0.04° illustrated that the film had nearly perfect single-crystalline quality. Reciprocal space maps around the (001), (103), and (013) reflections of the PST film revealed anisotropic in-plane strain of 485 ppm along [100] and 26 ppm along [010], respectively. Coplanar capacitance measurements also showed systematic changes in the dielectric constant and tunability due to strain; about a 15% difference in tunability at surface field of 50 kV/cm and a 20% difference in the zero-field dielectric constant were observed along [100] and [010], respectively.

Lin, Y.; Chen, X.; Liu, S. W.; Chen, C. L.; Lee, Jang-Sik; Li, Y.; Jia, Q. X.; Bhalla, A.

2004-01-01

306

Anisotropic in-plane strain can be induced in (Pb,Sr)TiO3 (PST) thin film by using orthorhombic NdGaO3 (110) as a substrate. High-resolution x-ray diffraction was used to measure the strain of the PST thin film. A rocking curve with full width at half maximum of ~0.04° illustrated that the film had nearly perfect single-crystalline quality. Reciprocal space maps around the (001), (103),

Y. Lin; X. Chen; S. W. Liu; C. L. Chen; Jang-Sik Lee; Y. Li; Q. X. Jia; A. Bhalla

2004-01-01

307

Conformally flat polytropes for anisotropic matter

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.

Herrera, L; Barreto, W; Ospino, J

2014-01-01

308

Conformally flat polytropes for anisotropic matter

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.

L. Herrera; A. Di Prisco; W. Barreto; J. Ospino

2014-10-24

309

Diversity in Expression Patterns and Functional Properties in the Rice HKT Transporter Family1[W

Plant growth under low K+ availability or salt stress requires tight control of K+ and Na+ uptake, long-distance transport, and accumulation. The family of membrane transporters named HKT (for High-Affinity K+ Transporters), permeable either to K+ and Na+ or to Na+ only, is thought to play major roles in these functions. Whereas Arabidopsis (Arabidopsis thaliana) possesses a single HKT transporter, involved in Na+ transport in vascular tissues, a larger number of HKT transporters are present in rice (Oryza sativa) as well as in other monocots. Here, we report on the expression patterns and functional properties of three rice HKT transporters, OsHKT1;1, OsHKT1;3, and OsHKT2;1. In situ hybridization experiments revealed overlapping but distinctive and complex expression patterns, wider than expected for such a transporter type, including vascular tissues and root periphery but also new locations, such as osmocontractile leaf bulliform cells (involved in leaf folding). Functional analyses in Xenopus laevis oocytes revealed striking diversity. OsHKT1;1 and OsHKT1;3, shown to be permeable to Na+ only, are strongly different in terms of affinity for this cation and direction of transport (inward only or reversible). OsHKT2;1 displays diverse permeation modes, Na+-K+ symport, Na+ uniport, or inhibited states, depending on external Na+ and K+ concentrations within the physiological concentration range. The whole set of data indicates that HKT transporters fulfill distinctive roles at the whole plant level in rice, each system playing diverse roles in different cell types. Such a large diversity within the HKT transporter family might be central to the regulation of K+ and Na+ accumulation in monocots. PMID:19482918

Jabnoune, Mehdi; Espeout, Sandra; Mieulet, Delphine; Fizames, Cecile; Verdeil, Jean-Luc; Conejero, Genevieve; Rodriguez-Navarro, Alonso; Sentenac, Herve; Guiderdoni, Emmanuel; Abdelly, Chedly; Very, Anne-Alienor

2009-01-01

310

Transport properties of stripe-ordered high Tc cuprates

Transport measurements provide important characterizations of the nature of stripe order in the cuprates. Initial studies of systems such as La{sub 1.6?x}Nd{sub 0.4}Sr{sub x}CuO{sub 4} demonstrated the strong anisotropy between in-plane and c-axis resistivities, but also suggested that stripe order results in a tendency towards insulating behavior within the planes at low temperature. More recent work on La{sub 2?x}Ba{sub x}CuO{sub 4} with x = 1/8 has revealed the occurrence of quasi-two-dimensional superconductivity that onsets with spin-stripe order. The suppression of three-dimensional superconductivity indicates a frustration of the interlayer Josephson coupling, motivating a proposal that superconductivity and stripe order are intertwined in a pair-density-wave state. Complementary characterizations of the low-energy states near the Fermi level are provided by measurements of the Hall and Nernst effects, each revealing intriguing signatures of stripe correlations and ordering. We review and discuss this work.

Jie, Q.; Han, S.J.; Dimitrov, I.; Tranquada, J.M.; Li, Q.

2012-01-01

311

The purpose of this project is not so much to compare different methods in analyzing the solute transport problems as to evaluate whether the dispersivity involved in the Advection-Dispersion Equation (ADE) can be relatively intrinsic to aquifers when more detailed groundwater flow fields are taken into account in the mathematical model. Here, the 'more detailed groundwater flow field' means that

C. S. Chen; C. Holmes; W. Li; D. Chace; M. Fort

1993-01-01

312

Optical, electronic, and transport properties of nanocrystalline titanium nitride thin films

Spectroscopic ellipsometry (SE) was employed to get insights on the optical, electronic, and transport properties of nanocrystalline titanium nitride (TiNx) films with respect to their microstructure and stoichiometry. The films' properties can be tailored by varying the energy of bombarding ions during sputter deposition and the substrate temperature (Td). The best metallic behavior of TiNx (resistivity 40 muOmega cm and

P. Patsalas; S. Logothetidis

2001-01-01

313

We describe at the quantum-chemical level the main parameters that control charge transport at the molecular scale in discotic liquid crystals. The focus is on stacks made of triphenylene, hexaazatriphenylene, hexaazatrinaphthylene, and hexabenzocoronene molecules and derivatives thereof. It is found that a subtle interplay between the chemical structure of the molecules and their relative positions within the stacks determines the charge transport properties; the molecular features required to promote high charge mobilities in discotic materials are established on the basis of the calculated structure-property relationships. We predict a significant increase in the charge mobility when going from triphenylene to hexaazatrinaphthylene; this finding has been confirmed by measurements carried out with the pulse-radiolysis time-resolved microwave conductivity technique. PMID:15012158

Lemaur, Vincent; da Silva Filho, Demetrio A; Coropceanu, Veaceslav; Lehmann, Matthias; Geerts, Yves; Piris, Jorge; Debije, Michael G; van de Craats, Anick M; Senthilkumar, Kittusamy; Siebbeles, Laurens D A; Warman, John M; Brédas, Jean-Luc; Cornil, Jérôme

2004-03-17

314

Electronic and transport properties of Cobalt-based valence tautomeric molecules and polymers

NASA Astrophysics Data System (ADS)

The advancement of molecular spintronics requires further understandings of the fundamental electronic structures and transport properties of prototypical spintronics molecules and polymers. Here we present a density functional based theoretical study of the electronic structures of Cobalt-based valence tautomeric molecules Co^III(SQ)(Cat)L Co^II(SQ)2L and their polymers, where SQ refers to the semiquinone ligand, and Cat the catecholate ligand, while L is a redox innocent backbone ligand. The conversion from low-spin Co^III ground state to high-spin Co^II excited state is realized by imposing an on-site potential U on the Co atom and elongating the Co-N bond. Transport properties are subsequently calculated by extracting electronic Wannier functions from these systems and computing the charge transport in the ballistic regime using a Non-Equilibrium Green's Function (NEGF) approach. Our transport results show distinct charge transport properties between low-spin ground state and high-spin excited state, hence suggesting potential spintronics devices from these molecules and polymers such as spin valves.

Chen, Yifeng; Calzolari, Arrigo; Buongiorno Nardelli, Marco

2011-03-01

315

Transport and magnetic properties of rare-earth nitrides

NASA Astrophysics Data System (ADS)

There is controversy about the conducting character of the rare-earth nitrides, with reports existing from metallic to moderately wide band-gap semiconductors. In a programme intended to clarify that issue we have grown thin films of the rare-earth mononitrides GdN, SmN, DyN and ErN by ion assisted deposition (IAD). Their stoichiometry and nanocrystalline structure have been characterised by RBS, SIMS, XRD, TEM, and EXAFS. The as-prepared materials are very reactive in the atmosphere, but they are effectively passivated by capping layers of either MgF2 or IAD GaN. Their magnetic properties have been studied from ambient temperature to 5 K and found to be in agreement with reported behaviour in the literature. The conductivity is typical of semiconductors, as regards both its magnitude and its temperature dependence.

Trodahl, Joe; Granville, Simon; Ruck, Ben; Budde, Felix; Bittar, Tony; Williams, Grant

2006-03-01

316

NASA Astrophysics Data System (ADS)

Numerous laboratory and theoretical studies on the physical properties of rocks and their relationships - lead mainly in the framework of petroleum exploration - show that rock physics is necessary for an accurate quantitative interpretation of geophysical observations. Moreover joint inversion of different geophysical datasets is emerging as an important tool to enhance resolution and decrease inversion artifacts in imaging of structurally complex areas such as volcanoes. In many cases, the coupling between the inverted parameters is based on empirical or theoretical relationships derived from laboratory data. Consequently rock physics can be used to: interpret simultaneously several geophysical datasets on volcanoes when they are available, improve the imaging of volcano structures, and better understand the coupled processes that can occur during volcanic unrest. It's in this context that we lead a laboratory study on the transport properties (permeability, thermal and electrical conductivities) and seismic properties (velocity and attenuation of P and S waves) of volcanic rocks representative of Montagne Pelée (Martinique) deposits. In this presentation we will focus on (1) the seismic properties and (2) the relations between seismic and transport properties. The 43 samples collected are representative of the main lithological units of this volcano: vesicular lava blocks and indurated ashed from indurated block-and-ash flows also called breccias, vesicular lava blocks from "Pelean nuee ardente" flows, scoriae from scoria flows, pumices from ash-and-pumices flows, and dense lava blocks from lava flows and lava domes. Their total porosity varies over a wide range from 4 to 73%. Since the samples present similar chemical and mineralogical compositions (andesites), the main difference between the samples comes from their pore structure and reflects differences in the mechanisms of magma degassing and vesiculation during their formation (Bernard et al., 2007). This allows us to investigate the effect of the pore space characteristics on the studied properties and on their relationships. Results show that ultrasonic velocities in water saturated samples vary with increasing porosity from 5,4 to 2 km/s for P-waves and from 3 to 0,9 km/s for S-waves. Seismic quality factors are relatively low and range between 27 and 3 for P-waves and between 40 and 5 for S-waves. Seismic velocities and attenuation coefficients correlate with porosity. But the links between seismic and transport properties are generally stronger, and particularly between P-wave attenuation and electrical formation factor. This indicates large similarities in the characteristics of the pore space that control the seismic and transport properties in volcanic rocks. Thereafter seismic measurements can help to monitor fluid flows in volcanic and geothermal areas.

Bernard, M.-L.; Zamora, M.

2012-04-01

317

Transport properties of high-temperature superconductors: Surface vs bulk effect

We investigate surface-related transport properties of high-temperature superconductors. We find the mean vortex velocity under applied transport current determined by the activation energies for vortex penetration and exit through the Bean-Livingston barrier. We determine the current distribution between the surfaces of superconductor and the field and current dependencies of the transport activation energies. For a three-dimensional superconductor the transport activation energy, {ital U}{sub {ital s}}{sup 3D}, is found to decrease with the external field, {ital H}, and transport current, {ital J}, as {ital U}{sub {ital s}}{sup 3D}{proportional_to}{ital H}{sup {minus}1/2} and {ital U}{sub {ital s}}{sup 3D}{proportional_to}{ital J}{sup {minus}1/2}, respectively. In the quasi-two-dimensional compounds, {ital U}{sub {ital s}}{sup 2D} decays logarithmically with field and current. The interplay between the surface and the bulk contributions to the transport properties, such as current-voltage characteristics, is discussed. {copyright} {ital 1996 The American Physical Society.}

Burlachkov, L. [Jack and Pearl Resnick Institute for Advanced Technology and Institute of Superconductivity, Department of Physics, Bar-Ilan University, Ramat-Gan 52900 (Israel)] [Jack and Pearl Resnick Institute for Advanced Technology and Institute of Superconductivity, Department of Physics, Bar-Ilan University, Ramat-Gan 52900 (Israel); Koshelev, A.E.; Vinokur, V.M. [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)] [Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)

1996-09-01

318

Transport properties of Dirac fermions in two dimensions

NASA Astrophysics Data System (ADS)

The Dirac equation in particle physics is used to describe spin 1/2 fermions (such as electrons) moving at relativistic speeds. In condensed matter physics, this is usually not relevant, since particles in matter move slowly compared to the speed of light. However, recent progress has revealed two-dimensional realizations of Dirac fermions in condensed matter systems with zero mass and a redefined "speed of light." One of these systems, graphene, has been studied theoretically for decades as a building block of graphite. The other, the topological insulator, is quite new; this state of matter was predicted less than 10 years ago. Graphene was first isolated in 2004, and since then there has been an explosion of graphene research in the physics community. Much of the recent excitement has to do with the potential applications of graphene in devices. In this dissertation, I will discuss two problems related to graphene devices, and in particular how to use the strong interaction of graphene with its surroundings as an asset. I will show that a Boltzmann transport theory with all scattering mechanisms describes the current vs voltage of a graphene sheet extremely well using no adjustable parameters. One crucial element of this model is the transfer of energy from electrons directly to the substrate via scattering with optical phonons at the interface. The interaction is due to an electric field that is set up by these optical phonons, which is so strongly interacting in part due to the two dimensionality of the graphene. I will also discuss the adsorption of He atoms on a graphene sheet. This causes a change in the graphene conductivity which is large enough to be measurable. Work in this direction could provide a route to graphene sensors. The topological insulator is a recently predicted state of matter which is nominally an insulator but has metallic surface states which are topologically protected. This topological protection arises from the symmetry of the system, which requires a two-fold degeneracy at any time reversal symmetric momentum, and a band inversion, which provides a swapping of the conduction and valance band at a surface. These two conditions imply that an odd number of states will cross the gap even in the presence of disorder (as long as that disorder is time reversal symmetric). This manifests as a Dirac cone at the surface of insulators such as Bi2Se3 and Bi2Te 3. To be a true topological insulator, one must have a bulk insulator; experimentally however, most samples are bulk conductors. While rapid improvement is being made through techniques such as doping, one of the goals of the research presented in this thesis is to work towards a transport signal which is unique to the surface state even in the presence of a conducting bulk. In this direction, quantum corrections to the magnetoresistance have been shown to fail, as both bulk and surface have similar experimental signals. However work in this dissertation shows that we can still gain some insight by modeling the experimental data with the theory of quantum corrections. I will show evidence that electron-electron interactions are necessary to understand the low temperature conductivity of Bi2Se3 thin films. One unambiguous transport signal is the quantum Hall response; the energy of Dirac fermions in a strong magnetic field is quite different than their parabolic counterparts. Given this, a question that arises is the nature of the fractional quantum Hall effect in topological insulator surface states. I will predict the conditions under which the fractional quantum Hall effect is stable. Finally, one of the reasons topological insulators have gained so much enthusiasm is the potential application to topological quantum computation. This may be made possible if the theoretical predictions of particles called Majorana fermions could be realized experimentally. I discuss evidence that two necessary (although not sufficient) conditions are met: topological insulators can be made superconducting and there is evidence for the formation of vo

DaSilva, Ashley M.

319

Enhancement of non-resonant dielectric cloaks using anisotropic composites

NASA Astrophysics Data System (ADS)

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.

Takezawa, Akihiro; Kitamura, Mitsuru

2014-01-01

320

A law of mixtures for transport properties in binary particulate composites

A connected-grain model was developed earlier to explain mechanical and thermal properties of porous ceramics and sedimentary rocks. We have now generalized this model for binary particulate composites, based on simulation of a connected-grain structure of individual components of the composites by randomly selecting individual grains and shrinking them. Repetition of this procedure results in a structure of a binary particulate composite that contains channels of individual components, through which transport occurs. We developed a generalized law of mixtures in which transport properties are expressed as scaling relationships that depend on the shrinking parameter expressed as an exponent. This parameter provides the skewness of the distribution of the grains. The model is compared with various transport properties of binary composites reported in the literature. In addition, the model is tested on YBa{sub 2}Cu{sub 3}O{sub x} superconductors and Ag composites that were fabricated in our laboratory and tested for electrical conductivity and elastic modulus. This test demonstrates how the model predicts two entirely different transport properties through their common microstructure and grain-size distribution. {copyright} {ital 1998 American Institute of Physics.}

Duncan, K.L.; Lodenquai, J.F. [Physics Department, University of the West Indies, Mona, Kingston 7 (Jamaica)] [Physics Department, University of the West Indies, Mona, Kingston 7 (Jamaica); Wagh, A.S.; Goretta, K.C. [Energy Technology Division, Argonne National Laboratory, Argonne, Illinois 60439-4838 (United States)] [Energy Technology Division, Argonne National Laboratory, Argonne, Illinois 60439-4838 (United States)

1998-09-01

321

A new method for evaluation of transport properties in CdTe and CZT detectors

The precise evaluation of transport properties of both electrons and holes in compound semiconductor detectors, like CdTe or CZT, is of great interest for the development of these devices. Although the electron behaviour can be measured in most cases, that of holes is much more difficult. Both alpha or gamma radiations, as well as conventional computer simulations, have shown their

M. Jung; J. Morel; P. Fougères; M. Hage-Ali; P. Siffert

1999-01-01

322

Microstructure and transport properties of ZnO:Mn diluted magnetic semiconductor thin films

Microstructure and transport properties of ZnO:Mn diluted magnetic semiconductor thin films Z. Yang semiconductor thin film. The high-resolution imaging and electron diffraction reveal that the ZnO:Mn thin film of the anomalous Hall effect in the ZnO:Mn thin film. Â© 2009 American Institute of Physics. DOI: 10

Yang, Zheng

323

In a recent paper [C. DeW. Van Siclen, Phys. Rev. E 59, 2804 (1999)], a random-walk algorithm was proposed as the best method to calculate transport properties of composite materials. It was claimed that the method is applicable both to discrete and continuum systems. The limitations of the proposed algorithm are analyzed. We show that the algorithm does not capture

Dinko Cule; Salvatore Torquato

2000-01-01

324

Transport Properties and Performance of Polymer Electrolyte Membranes for the Hybrid Sulfur and SO2 crossover in the hybrid sulfur cycle electrolyzer were quantified for a poly phenylene -based SO2 to the hydrogen stream, and result in a loss of sulfur from the system. Recent research has

Weidner, John W.

325

Modulation of Drug Transport Properties by Multicomponent Diffusion in Surfactant Aqueous Solutions

Modulation of Drug Transport Properties by Multicomponent Diffusion in Surfactant Aqueous Solutions ReceiVed July 1, 2008 Diffusion coefficients of drug compounds are crucial parameters used for modeling diffusion. A multicomponent diffusion study on drug-surfactant-water ternary mixtures is reported here

Annunziata, Onofrio

326

High pressure apparatus for transport properties study in high magnetic field

We have designed a high pressure apparatus for measuring electrical-transport properties at low temperatures, high magnetic field and hydrostatic pressure up to 10 kbar. Details of the high-pressure cell and an exemplary study on UNiAI are described and discussed briefly.

Alsmadi, A. M. (Abdel M.); Nakotte, H. (Heinrich); Honda, F.; Sechovsky, V. (Vladimir); Mikulina, O. (Olga); Kamarad, J.; Lacerda, A. H. (Alex H.)

2002-01-01

327

Transport and Phase Equilibria Properties for Steam Flooding of Heavy Oils

The objectives of this research included experimental determination and rigorous modeling and computation of phase equilibrium diagrams, volumetric, and transport properties of hydrocarbon/CO2/water mixtures at pressures and temperatures typical of steam injection processes for thermal recovery of heavy oils.

Gabitto, Jorge; Barufet, Maria

2002-11-20

328

Transport and Phase Equilibria Properties for Steam Flooding of Heavy Oils

The objectives of this research included experimental determination and rigorous modeling and computation of phase equilibria, volumetric, and transport properties of hydrocarbon/CO2/water mixtures at pressures and temperatures typical of steam injection processes for thermal recovery of heavy oils.

Gabitto, Jorge; Barrufet, Maria

2001-12-18

329

Frequency distribution of water and solute transport properties derived from pan sampler data

Frequency distribution of water and solute transport properties derived from pan sampler data Jan Boll,1 John S. Selker,2 Gil Shalit,3 and Tammo S. Steenhuis4 Abstract. Modeling of water and solute at each site. In each experiment a solute pulse was added followed by artificial or natural rainfall

Walter, M.Todd

330

MEASUREMENT OF TRANSPORT PROPERTIES FOR THE DRIED LAYER OF COFFEE SOLUTION UNDERGOING FREEZE DRYING

A mathematical model has developed to determine the thermal conductivity and permeability for the dried layer of liquid sample undergoing sublimation dehydration. A microcomputer-based automatic measurement system has developed for the data acquisition as well as determination of these transport properties applying the drying data to the model. Aqueous solutions of 29-45 % soluble coffee solid were freeze dried under

Yasuyuki Sagara; Jum-ichi Ichiba

1994-01-01

331

Measurements of water uptake and transport properties in anion-exchange membranes

Keywords: Direct ethanol fuel cells Anion-exchange membrane Water uptake Water diffusivity Mass cells are hindered by the poisoning problem of carbon dioxide [1,2]. However, with the emergence. In developing acid proton electrolyte membrane fuel cells (PEMFCs), the water uptake and transport properties

Zhao, Tianshou

332

Transport properties of low-sanidine single-crystals, glasses and melts at high temperature

1 Transport properties of low-sanidine single-crystals, glasses and melts at high temperature Maik = 8221 + 9 figures + 5 tables Keywords: laser-flash analysis, high-temperature, thermal diffusivity, viscosity, density, IR spectroscopy, low-sanidine, single-crystal, glass, melt #12;2 Abstract. Thermal

Spera, Frank J.

333

Transport properties of glass-forming liquids suggest that dynamic crossover temperature is as important as the glass transition temperature Francesco Mallamacea,b,c,1 , Caterina Brancaa , Carmelo, for all 84 liquids. The crossover temperature, TÃ?, located well above the calorimetric glass transition

Stanley, H. Eugene

334

Thermoelectric Transport Properties of Single Bismuth Nanowires S. B. Cronin1

Thermoelectric Transport Properties of Single Bismuth Nanowires S. B. Cronin1 , Y.-M. Lin3 , M thermoelectric material. Bi nanowires, however, have been predicted to have a high thermoelectric efficiency [1,2]. The thermoelectric enhancement is based on the sharp features in the one-dimensional density of states

Cronin, Steve

335

Transport Properties of DNA Bases Placed in Graphene Nano-gap

NASA Astrophysics Data System (ADS)

There has been significant demand and research activity for the development of new DNA sequencing technologies employing transverse transport techniques. We present systematic first principles studies based on Density Functional Theory of the transport properties and current-voltage characteristics of nucleotide molecules of the DNA bases, placed in 1.2 nm gap formed between the zigzag edges of graphene nano-electrodes. The linear dispersion of the graphene electrons and the local spin-polarization associated with the zigzag edges allow the exploration of both the charge- and spin-current signatures of the DNA bases to sequence DNA. We will present results in the tunneling regime of the charge- and spin-transport properties as the geometrical conformation of the bases is varied. Such signatures may be used experimentally for developing an efficient means of sequencing larger strands of DNA.

Wolowiec, Christian; Kioussis, Nick; Novikov, Dmitri

2009-03-01

336

The transport properties of the molecular-scale B2C and BC3 electronic devices

NASA Astrophysics Data System (ADS)

The transport properties of the molecular-scale B2C and BC3 electronic devices are investigated with an ab initio method combined with a nonequilibrium Green function technique. The effects of different BC graphenes and ribbon lengths on the transport properties of the devices are significant. The results show that the devices with different BC graphenes and sizes have unusual transmission coefficients, which leads to special current transport mechanisms for the devices. Notably, the current strength of the device with the shortest ribbon length is the largest in three B2C devices, but the current strength of the device with the shortest ribbon length is the smallest for BC3 device.

Li, Guiqin; Li, Runqin

2012-09-01

337

Effect of stabilizer on dynamic thermal transport property of ZnO nanofluid

In this paper, we investigate the effect of adding a stabilizer on the dynamic thermal properties of ZnO nanofluid (containing 5 to 10 nm diameter of ZnO nanocrystals) measured using a 3? method. Addition of the stabilizer leads to the stabilization of the nanofluid and also substantial reduction of the enhancement of thermal transport compared to that seen in the bare ZnO nanofluid. This also alters the frequency dependence of the thermal transport and the characteristic time scale associated with it. It is suggested that the addition of the stabilizer inhibits the thermodiffusion-assisted local aggregation thus leading to substantial reduction of the enhancement of thermal transport properties of the bare nanofluid as proposed in some recent models, and this also alters the characteristic time scales by altering the scale of aggregation. PMID:23497347

2013-01-01

338

Orientation effect on the electronic transport properties of C24 fullerene molecule

NASA Astrophysics Data System (ADS)

The transport properties of the cage-like molecule depend on its orientation between the electrodes, but the investigation on the mechanism has not been found. Using first-principle density-functional theory (DFT) and non-equilibrium Green’s function (NEGF) formalism for quantum transport calculation, we study the electronic transport properties of C24 fullerene molecule with different orientations in Au-C24-Au two-probe system. The effects of k-point sampling on the Brillouin zone are explored. Our results show that the negative differential resistance of C24 molecule is found in such a system and can be tuned by the molecule's orientation in the two-probe system. We also proposed a mechanism for it. The I-V characteristic under bias voltage is determined. The present findings could be helpful for the application of the C24 molecule in the field of single molecular devices or nanometer electronics.

Zhao, Wen-Kai; Yang, Chuan-Lu; Zhao, Jing-Fen; Wang, Mei-Shan; Ma, Xiao-Guang

2012-06-01

339

Transport and infrared photoresponse properties of InN nanorods/Si heterojunction

The present work explores the electrical transport and infrared (IR) photoresponse properties of InN nanorods (NRs)/n-Si heterojunction grown by plasma-assisted molecular beam epitaxy. Single-crystalline wurtzite structure of InN NRs is verified by the X-ray diffraction and transmission electron microscopy. Raman measurements show that these wurtzite InN NRs have sharp peaks E2(high) at 490.2 cm-1 and A1(LO) at 591 cm-1. The current transport mechanism of the NRs is limited by three types of mechanisms depending on applied bias voltages. The electrical transport properties of the device were studied in the range of 80 to 450 K. The faster rise and decay time indicate that the InN NRs/n-Si heterojunction is highly sensitive to IR light. PMID:22122843

2011-01-01

340

Characterization of an Anisotropic Hydrogel Tissue Substrate for Infusion Testing

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

Lee, Sung Jin; Pishko, Gregory L.; Astary, Garret W.; Mareci, Thomas H.; Sarntinoranont, Malisa

2010-01-01

341

Gravitational stresses in anisotropic rock masses

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.

Amadei, B.; Savage, W.Z.; Swolfs, H.S.

1987-01-01

342

NASA Astrophysics Data System (ADS)

The transport of mineral dust aerosols is a global phenomenon with strong climate implications. Depending on the travel distance over source regions, the atmospheric conditions and the residence time in the atmosphere, various transformation processes (size-selective sedimentation, mixing, condensation of gaseous species, and weathering) can modify the physical and chemical properties of mineral dust, which, in turn, can change the dust's optical properties. The model predictions of the radiative effect by mineral dust still suffer of the lack of certainty of these properties, and their temporal evolution with transport time. Within the frame of the ChArMex project (Chemistry-Aerosol Mediterranean experiment, http://charmex.lsce.ipsl.fr/), two intensive airborne campaigns (TRAQA, TRansport and Air QuAlity, 18 June - 11 July 2012, and ADRIMED, Aerosol Direct Radiative Impact in the regional climate in the MEDiterranean region, 06 June - 08 July 2013) have been performed over the Central and Western Mediterranean, one of the two major transport pathways of African mineral dust. In this study we have set up a systematic strategy to determine the optical, physical and optical properties of mineral dust to be compared to an equivalent dataset for dust close to source regions in Africa. This study is based on airborne observations onboard the SAFIRE ATR-42 aircraft, equipped with state of the art in situ instrumentation to measure the particle scattering and backscattering coefficients (nephelometer at 450, 550, and 700 nm), the absorption coefficient (PSAP at 467, 530, and 660 nm), the extinction coefficient (CAPS at 530 nm), the aerosol optical depth (PLASMA at 340 to 1640 nm), the size distribution in the extended range 40 nm - 30 µm by the combination of different particle counters (SMPS, USHAS, FSSP, GRIMM) and the chemical composition obtained by filter sampling. The chemistry and transport model CHIMERE-Dust have been used to classify the air masses according to the dust origin and transport. Case studies of dust transport from known but differing origins (source regions in Tunisia, Algeria, and Mauritania) and at different times after transport, will be presented. Results will be compared to equivalent measurements over source regions interpreted in terms of the evolution of the particle size distribution, chemical composition and optical properties.

Denjean, Cyrielle; Di Biagio, Claudia; Chevaillier, Servanne; Gaimoz, Cécile; Grand, Noel; Loisil, Rodrigue; Triquet, Sylvain; Zapf, Pascal; Roberts, Greg; Bourrianne, Thierry; Torres, Benjamin; Blarel, Luc; Sellegri, Karine; Freney, Evelyn; Schwarzenbock, Alfons; Ravetta, François; Laurent, Benoit; Mallet, Marc; Formenti, Paola

2014-05-01

343

We have investigated the effects of buffer strain relaxation on the transport properties of two-dimensional electron gases (2DEGs). The 2DEGs consist of modulation-doped In{sub 0.53}Ga{sub 0.47}As/In{sub 0.52}Al{sub 0.48}As heterostructures grown lattice-mismatched to GaAs via compositionally step-graded In{sub {ital x}}Ga{sub 1{minus}{ital x}}As buffers, with different composition gradients, or lattice-matched to InP. We find a variation in 2DEG electronic properties which occurs simultaneously with large differences in epilayer tilt and mosaic spread in the step-graded buffers. This indicates a correlation between the {ital mechanism} of buffer strain relaxation and the 2DEG transport properties. {copyright} {ital 1996 American Institute of Physics.}

Goldman, R.S.; Kavanagh, K.L.; Wieder, H.H. [Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California 92093-0407 (United States)] [Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California 92093-0407 (United States); Robbins, V.M. [Hewlett-Packard Laboratories, Palo Alto, California 94304 (United States)] [Hewlett-Packard Laboratories, Palo Alto, California 94304 (United States); Ehrlich, S.N. [School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)] [School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907 (United States); Feenstra, R.M. [IBM Research Division, P.O. Box 218, Yorktown Heights, New York 10598 (United States)] [IBM Research Division, P.O. Box 218, Yorktown Heights, New York 10598 (United States)

1996-12-01

344

Inversion of Shear Wave Anisotropic Parameters in Strongly Anisotropic Formations

Deepwater reservoirs use highly deviated wells to reduce cost and enhance hydrocarbon recovery. Due to the strong anisotropic nature of many of the marine sediments, anisotropic seismic imaging and interpretation can improve ...

Tang, Xiaoming

2006-01-01

345

Tunneling anisotropic magnetoresistance of helimagnet tunnel junctions

NASA Astrophysics Data System (ADS)

We theoretically investigate the angular- and spin-dependent transport in normal-metal/helical-multiferroic/ferromagnetic heterojunctions. We find a tunneling anisotropic magnetoresistance (TAMR) effect due to the spiral magnetic order in the tunnel junction and to an effective spin-orbit coupling induced by the topology of the localized magnetic moments in the multiferroic spacer. The predicted TAMR effect is efficiently controllable by an external electric field due to the magnetoelectric coupling.

Jia, Chenglong; Berakdar, Jamal

2010-02-01

346

The kinetic coefficients of high-quality single crystals of ternary layered n-PbBi{sub 4}Te{sub 7} compounds have been measured in the temperature range of 77-400 K. These crystals, doped with electroactive Cd and Ag impurities, were grown by Czochralski pulling with melt supply through a floating crucible. A significant anisotropy of the thermoelectric properties is found. The means of incorporation of electroactive impurities into the ternary compound lattice is established. The experimental values of the Nernst-Ettingshausen coefficient have been analyzed together with the Seebeck, Hall, and conductivity data. The features of transport phenomena in PbBi{sub 4}Te{sub 7} can be explained within the single-band model of nonparabolic energy spectrum and mixed mechanism of electron scattering from acoustic phonons and the Coulomb potential of impurities. It is suggested that acoustic phonon scattering is dominant along the cleavage plane, whereas the impurity scattering dominates along the trigonal axis.

Zhitinskaya, M. K., E-mail: m_zhitinskaya@mail.ru; Nemov, S. A.; Muhtarova, A. A. [St. Petersburg State Politechnical University (Russian Federation); Shelimova, L. E.; Svechnikova, T. E. [Russian Academy of Sciences, Baikov Institute of Metallurgy and Materials Science (Russian Federation); Konstantinov, P. P. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2010-06-15

347

1. The electrical properties and the active transport processes of the isolated urinary bladder of the urodele, Amphiuma means, were studied by mounting this tissue as a flat sheet between two halves of a lucite chamber. The mean transepithelial potential difference was 70-2 +/- 2-3 mV (serosa positive), the mean short-circuit current was 10-9 +/- 0-5 micrionA/mg of dry weight and the mean transepithelial d.c. resistance was 6540 +/- 374 omega mg of dry weight. 2. The short-circuit current (Isc) accounted for 92% of the net 22Na+ flux from the mucosa to the serosa. The difference resulted from a transport of 36Cl- in the same direction as sodium. 3. The active sodium transport exhibited typical saturation kinetics, having a Km of 15-4 m-equiv/l. and approaching zero order at 60-70 m-equiv/l. The transepithelial potential difference increased linearly with the log of the mucosal sodium concentration at a rate of 50-3 mV per tenfold concentration change. 4. In the absence of the major anions (HCO3- and Cl-) from the bathing solutions, the electrical properties and the sodium influx decreased to less than 40% of their control values. The presence of only one of these two anions in the serosal bathing solution was sufficient to maintain these parameters. 5. Amiloride (10(-5)M) and ouabain (10(-6)M) inhibited the sodium transport 97% and 85% respectively. Amphotericin B (10(-6)M) stimulated the sodium transport 47%. Furosemide (10(-3)M) inhibited the chloride transport 43%. The sodium transport was insensitive to the action of two enurohypophyseal peptides tested, lysine-vasotocin and pitocin. Images Plate 1 PMID:850164

Degnan, K J; Zadunaisky, J A

1977-01-01

348

Synthesis and Quantum Transport Properties of Bi2Se3 Topological Insulator Nanostructures

Bi2Se3 nanocrystals with various morphologies, including nanotower, nanoplate, nanoflake, nanobeam and nanowire, have been synthesized. Well-distinguished Shubnikov-de Haas (SdH) oscillations were observed in Bi2Se3 nanoplates and nanobeams. Careful analysis of the SdH oscillations suggests the existence of Berry's phase ?, which confirms the quantum transport of the surface Dirac fermions in both Bi2Se3 nanoplates and nanobeams without intended doping. The observation of the singular quantum transport of the topological surface states implies that the high-quality Bi2Se3 nanostructures have superiorities for investigating the novel physical properties and developing the potential applications. PMID:23405278

Yan, Yuan; Liao, Zhi-Min; Zhou, Yang-Bo; Wu, Han-Chun; Bie, Ya-Qing; Chen, Jing-Jing; Meng, Jie; Wu, Xiao-Song; Yu, Da-Peng

2013-01-01

349

In this paper we investigate the influence of material and device properties on the ballistic transport in epitaxial monolayer graphene and epitaxial quasi-free-standing monolayer graphene. Our studies comprise (a) magneto-transport in two-dimensional (2D) Hall bars, (b) temperature- and magnetic-field-dependent bend resistance of unaligned and step-edge-aligned orthogonal cross junctions, and (c) the influence of the lead width of the cross junctions on ballistic transport. We found that ballistic transport is highly sensitive to scattering at the step edges of the silicon carbide substrate. A suppression of the ballistic transport is observed if the lead width of the cross junction is reduced from 50 nm to 30 nm. In a 50 nm wide device prepared on quasi-free-standing graphene we observe a gradual transition from the ballistic into the diffusive transport regime if the temperature is increased from 4.2 to about 50 K, although 2D Hall bars show a temperature-independent mobility. Thus, in 1D devices additional temperature-dependent scattering mechanisms play a pivotal role. PMID:22971877

Bock, Claudia; Weingart, Sonja; Karaissaridis, Epaminondas; Kunze, Ulrich; Speck, Florian; Seyller, Thomas

2012-10-01

350

NASA Astrophysics Data System (ADS)

We investigate with state of the art density functional theory the structural, electronic, and transport properties of a class of recently synthesized nanostructures based on triarylamine derivatives. First, we consider the single molecule precursors in the gas phase and calculate their static properties, namely (i) the geometrical structure of the neutral and cationic ions, (ii) the electronic structure of the frontier molecular orbitals, and (iii) the ionization potential, hole extraction potential, and internal reorganization energy. This initial study does not evidence any direct correlation between the properties of the individual molecules and their tendency to self-assembly. Subsequently, we investigate the charge transport characteristics of the triarylamine derivatives nanowires, by using Marcus theory. For one derivative we further construct an effective Hamiltonian including intermolecular vibrations and evaluate the mobility from the Kubo formula implemented with Monte Carlo sampling. These two methods, valid respectively in the sequential hopping and polaronic band limit, give us values for the room-temperature mobility in the range 0.1-12 cm2/Vs. Such estimate confirms the superior transport properties of triarylamine-based nanowires, and make them an attracting materials platform for organic electronics.

Akande, Akinlolu; Bhattacharya, Sandip; Cathcart, Thomas; Sanvito, Stefano

2014-02-01

351

The recently introduced approach describing coupled quark and gluon anisotropic fluids is generalized to include explicitly the transitions between quarks and gluons. We study the effects of such processes on the thermalization rate of anisotropic systems. We find that the quark-gluon transitions may enhance the overall thermalization rate in the cases where the initial momentum anisotropies correspond to mixed oblate-prolate or prolate configurations. On the other hand, no effect on the thermalization rate is found in the case of oblate configurations. The observed regularities are connected with the late-time behavior of the analyzed systems which is described either by the exponential decay or the power law.

Wojciech Florkowski; Radoslaw Maj

2013-09-11

352

NASA Astrophysics Data System (ADS)

A key part of the FutureGen concept is to support the production of hydrogen to fuel a "hydrogen economy," with the use of clean burning hydrogen in power-producing fuel cells, as well as for use as a transportation fuel. One of the key technical barriers to FutureGen deployment is reliable and efficient hydrogen separation technology. Most Hydrogen Transport Membrane (HTM) research currently focuses on separation technology and hydrogen flux characterization. No significant work has been performed on thermo-mechanical properties of HTMs. The objective of the thesis is to understand the structure-property correlation of HTM and to characterize (1) thermo mechanical properties under different reducing environments and thermal cycles (thermal shock), and (2) evaluate the stability of the novel HTM material. A novel HTM cermet bulk sample was characterized for its physical and mechanical properties at both room temperature and at elevated temperature up to 1000°C. Micro-structural properties and residual stresses were evaluated in order to understand the changing mechanism of the microstructure and its effects on the mechanical properties of materials. A correlation of the microstructural and thermo mechanical properties of the HTM system was established for both HTM and the substrate material. Mechanical properties of both selected structural ceramics and the novel HTM cermet bulk sample are affected mainly by porosity and microstructural features, such as grain size and pore size-distribution. The Young's Modulus (E-value) is positively correlated to the flexural strength for materials with similar crystallographic structure. However, for different crystallographic materials, physical properties are independent of mechanical properties. Microstructural properties, particularly, grain size and crystallographic structure, and thermodynamic properties are the main factors affecting the mechanical properties at both room and high temperatures. The HTM cermet behaves more like an elastic material at room temperature and as a ductile material at temperature above 850°C. The oxidation and the plasticity of Pd phase mainly affected the mechanical properties of HTM cermet at high temperature, also as a result of thermal cycling. Residual stress induced in the HTM by thermo cycles also plays a very critical role in defining the thermo-mechanical properties.

Zhang, Yongjun

353

NASA Astrophysics Data System (ADS)

By adopting a new tensor method, we derived an analytical propagation formula for the cross-spectral density of partially coherent twisted anisotropic Gaussian Schell-model (GSM) beams through dispersive and absorbing media. Using the derived formula, we studied the evolution properties and spectrum properties of twisted anisotropic GSM beams in dispersive and absorbing media. The results show that the dispersive and absorbing media have strong influences on the propagation properties of twisted anisotropic GSM beams and their spectrum evolution. Our method provides a simple and convenient way to study the propagation of twisted anisotropic GSM beams in media with complex refractive index. 2002 Optical Society of America

Cai, Yangjian; Lin, Qiang; Ge, Di

2002-10-01

354

Effects of confinement on the transport properties of CSA doped polyaniline

NASA Astrophysics Data System (ADS)

Polyaniline doped with camphor sulfonic acid (CSA) and cast from m-cresol can exhibit metallic behavior depending on the conditions of preparation. Under standard methods of preparation the transport properties of cast films generally lie on the insulating side of the metal-insulator transition. We have confined CSA doped PANi into the cylindrical pores of a dielectrically inert porous matrix and measured the temperature dependence of the resistance. The resistance of the confined polymer is seen to have a weaker dependence at low temperatures than that of the cast film. Further analysis of the results show that the charge transport of the confined polymer has moved into the metallic regime while that of the cast film lies in the insulating regime. Reduced barriers to charge transport that result from the suppression of microphase separation of the non-dopable forms of polyaniline due to extreme confinement in the porous matrix are believed to be responsible for this crossover.

Perez, Raul; Leon, Neliza; Ramos, Idalia; Pinto, Nicholas; Kahol, Pawan

2006-03-01

355

Code of Federal Regulations, 2013 CFR

...Who pays for the transportation costs when foreign excess personal...PROPERTY Personal Property Whose Disposal Requires Special Handling ...pays for the transportation costs when foreign excess personal...is responsible for all direct costs involved in the...

2013-07-01

356

Code of Federal Regulations, 2010 CFR

...Who pays for the transportation costs when foreign excess personal...PROPERTY Personal Property Whose Disposal Requires Special Handling ...pays for the transportation costs when foreign excess personal...is responsible for all direct costs involved in the...

2010-07-01

357

Code of Federal Regulations, 2012 CFR

...Who pays for the transportation costs when foreign excess personal...PROPERTY Personal Property Whose Disposal Requires Special Handling ...pays for the transportation costs when foreign excess personal...is responsible for all direct costs involved in the...

2012-01-01

358

Code of Federal Regulations, 2011 CFR

2011-01-01

359

Calorimetric and transport properties of Zircalloy 2, Zircalloy 4, and Inconel 625

This paper presents the measurements and the results on thermal and electrical transport properties of three nuclear reactor cladding materials: Zircalloy 2, Zircalloy 4, and Inconel 625. Study of these materials constituted a part of the IAEA coordinated research program aimed at the generation and establishment of a reliable and complete database of the thermal properties of reactor materials. Measured properties include thermal diffusivity, specific heat, and electrical resistivity. Thermal diffusivity was measured by the laser pulse technique. Specific heat and electrical resistivity were measured using a millisecond-resolution direct electrical pulse heating technique. Thermal conductivity was computed from the experimentally determined thermal diffusivity and specific heat functions and the room temperature density values. Measurements were performed in the 20 to 1500{degrees}C temperature range, depending on the material and property concerned.

Maglic, K.D.; Perovic, N.Lj.; Stanimirovic, A.M. [Institute of Nuclear Sciences, Belgrade (Yugoslavia)

1994-07-01

360

Calorimetric and transport properties of Zircalloy 2, Zircalloy 4, and Inconel 625

NASA Astrophysics Data System (ADS)

This paper presents the measurements and the results on thermal and electrical transport properties of three nuclear reactor cladding materials: Zircalloy 2, Zircalloy 4, and Inconel 625. Study of these materials constituted a part of the IAEA coordinated research program aimed at the generation and establishment of a reliable and complete database of the thermal properties of reactor materials. Measured properties include thermal diffusivity, specific heat, and electrical resistivity. Thermal diffusivity was measured by the laser pulse technique. Specific heat and electrical resistivity were measured using a millisecond-resolution direct electrical pulse heating technique. Thermal conductivity was computed from the experimentally determined thermal difusivity and specific heat functions and the room temperature density values. Measurements were performed in the 20 to 1500°C temperature range, depending on the material and property concerned.

Magli?, K. D.; Perovi?, N. Lj.; Stanimirovi?, A. M.

1994-07-01

361

NASA Technical Reports Server (NTRS)

The thermodynamic and transport properties of selected cryogens had programmed into a series of computer routines. Input variables are any two of P, rho or T in the single phase regions and either P or T for the saturated liquid or vapor state. The output is pressure, density, temperature, entropy, enthalpy for all of the fluids and in most cases specific heat capacity and speed of sound. Viscosity and thermal conductivity are also given for most of the fluids. The programs are designed for access by remote terminal; however, they have been written in a modular form to allow the user to select either specific fluids or specific properties for particular needs. The program includes properties for hydrogen, helium, neon, nitrogen, oxygen, argon, and methane. The programs include properties for gaseous and liquid states usually from the triple point to some upper limit of pressure and temperature which varies from fluid to fluid.

Mccarty, R. D.

1980-01-01

362

Magnetization and electric transport properties of single-crystal MgB2 nanowires.

High quality single-crystal magnesium diboride (MgB(2)) nanowires with lengths exceeding 10 ?m were successfully synthesized by hybrid physical chemical vapor deposition. The magnetization and electrical transport properties of single-crystal MgB(2) nanowires (NWs) were measured. The superconducting transition temperature of the NWs was 37 K, as confirmed by magnetization measurements. The disordered behavior of the nanowires was observed by four-terminal current-voltage characteristic measurements of an individual NW from T = 10 to 300 K. The temperature-dependent resistivity curves for seven NWs collapsed into a universal curve described by the variable range hopping model, showing intrinsic nonmetallic transport properties. This implies that the granular superconducting defect states are critical to the superconductivity of the individual MgB(2) NWs. PMID:23092962

Wu, Cen-Shawn; Chang, Yu-Cheng; Chen, Weimeng; Chen, Chinping; Feng, Qingrong

2012-11-23

363

Magnetization and electric transport properties of single-crystal MgB2 nanowires

NASA Astrophysics Data System (ADS)

High quality single-crystal magnesium diboride (MgB2) nanowires with lengths exceeding 10 ?m were successfully synthesized by hybrid physical chemical vapor deposition. The magnetization and electrical transport properties of single-crystal MgB2 nanowires (NWs) were measured. The superconducting transition temperature of the NWs was 37 K, as confirmed by magnetization measurements. The disordered behavior of the nanowires was observed by four-terminal current-voltage characteristic measurements of an individual NW from T = 10 to 300 K. The temperature-dependent resistivity curves for seven NWs collapsed into a universal curve described by the variable range hopping model, showing intrinsic nonmetallic transport properties. This implies that the granular superconducting defect states are critical to the superconductivity of the individual MgB2 NWs.

Wu, Cen-Shawn; Chang, Yu-Cheng; Chen, Weimeng; Chen, Chinping; Feng, Qingrong

2012-11-01

364

The combined effect of bulk and interface electron-phonon couplings on the transport properties is investigated in a model for organic semiconductors gated with polarizable dielectrics. While the bulk electron-phonon interaction affects the behavior of mobility in the coherent regime below room temperature, the interface coupling is dominant for the activated high $T$ contribution of localized polarons. In order to improve the description of the transport properties, the presence of disorder is needed in addition to electron-phonon couplings. The effects of a weak disorder largely enhance the activation energies of mobility and induce the small polaron formation at lower values of electron-phonon couplings in the experimentally relevant window $150 Korganic field-effect transistors.

C. A. Perroni; V. Cataudella

2011-09-28

365

Transport properties of gases and binary liquids near the critical point

NASA Technical Reports Server (NTRS)

A status report is presented on the anomalies observed in the behavior of transport properties near the critical point of gases and binary liquids. The shear viscosity exhibits a weak singularity near the critical point. An analysis is made of the experimental data for those transport properties, thermal conductivity and thermal diffusivity near the gas-liquid critical point and binary diffusion coefficient near the critical mixing point, that determine the critical slowing down of the thermodynamic fluctuations in the order parameter. The asymptotic behavior of the thermal conductivity appears to be closely related to the asymptotic behavior of the correlation length. The experimental data for the thermal conductivity and diffusivity are shown to be in substantial agreement with current theoretical predictions.

Sengers, J. V.

1972-01-01

366

Universal Thermodynamic and Spin Transport Properties of Strongly Interacting Fermi Gases

NASA Astrophysics Data System (ADS)

We perform a high-precision measurement of the equation of state of a Fermi gas with unitarity limited interactions by in- situ imaging of ultracold ^6Li at a Feshbach resonance. We observe the superfluid phase transition in the chemical potential, entropy, compressibility and heat capacity, and provide a new value of the Bertsch parameter ?S. In a separate set of measurements, we determine the spin transport properties of strongly interacting Fermi gases by spatially separating the two spin components and allowing the system to relax to equilibrium (arXiv:1101.0780v1). We find that the spin diffusivity approaches a universal minimum value set by the ratio of Planck's constant to the atomic mass, and determine the spin susceptibility from spin transport properties.

Sommer, Ariel; Ku, Mark; Cheuk, Lawrence; Zwierlein, Martin W.

2011-06-01

367

Effects of Substitutional Doping in Electronic Transport Properties of Carbon Nanotubes

NASA Astrophysics Data System (ADS)

We have numerically investigated electronic transport properties in single-walled carbon nanotubes (SWCNTs) doped with boron (B) and nitrogen (N) substitutional impurities. Our calculations are performed by the ab initio density functional theory (DFT) and the nonequilibrium Green's function (NEGF) approach. We show that the electronic transmissions are moderated after the doping on both metallic and semiconducting CNTs. In B and N codoping nanotubes, depending on the arrangements of B and N substitutions, electronic and transport properties have been also modified. Calculating from electronic transmissions under bias, I-V characteristics of doped CNTs are demonstrated. In our simulations, we find that the substituting impurities in the semiconducting CNT raise the conductivity regardless of p- or n-type doping, whereas the conductivity of metallic CNTs is reduced by doping.

Tsuyuki, Hiroyoshi; Shiibashi, Tomohiro; Sakamoto, Shoichi; Tomiya, Mitsuyoshi

2013-09-01

368

Crystallization and Transport Properties of Amorphous Cr-Si Thin Film Thermoelectrics

NASA Astrophysics Data System (ADS)

We studied the thermoelectric properties, crystallization, and stability of amorphous and nanocrystalline states in Cr-Si composite films. Amorphous films, prepared by magnetron sputtering, were transformed into the nanocrystalline state by annealing with in situ thermopower and electrical resistivity measurements. We have found that the amorphous state is stable in these film composites to about 550 K. Prior to crystallization, the amorphous films undergo a structural relaxation, detected by peculiarities in the temperature dependences of the transport properties, but not visible in x-ray or electron diffraction. The magnitude and temperature dependences of electrical conductivity and thermopower indicate that electron transport in the amorphous films is through extended states. The amorphous films are crystallized at annealing temperatures above 550 K into a nanocrystalline composite with an average grain size of 10-20 nm.

Novikov, S. V.; Burkov, A. T.; Schumann, J.

2014-06-01

369

Electronic structure and transport properties of the Heusler compound Co2TiAl

NASA Astrophysics Data System (ADS)

The properties of the Heusler compound Co2TiAl were investigated in detail by experimental techniques and theoretical methods. X-ray diffraction measurements indicate that as-cast samples of the compound exhibit the L21 structure with a small amount of B2-type disorder. This leads to a reduced saturation magnetization per formula unit of 0.747 ?B. The Curie temperature is approximately 120 K. The transport properties are influenced by the change in the electronic structure at the Curie temperature, as revealed experimentally by conductivity, thermal transport and specific heat measurements. Different theoretical models based on ab initio calculations of the electronic structure are used to explain the experimental observations.

Graf, Tanja; Fecher, Gerhard H.; Barth, Joachim; Winterlik, Jürgen; Felser, Claudia

2009-04-01

370

Anomalous Transport Properties in Fe Intercalation Compound Fe x TiSe2 Single Crystals

NASA Astrophysics Data System (ADS)

The transport and magnetic properties of single-crystalline Fe-intercalation-compound Fe x TiSe2 have been compared with the transport properties of single-crystalline Ti-self-intercalation-compound Ti x TiSe2. At low concentration of intercalated guest atoms, Fe x TiSe2 exhibits carrier localization behavior without magnetic ordering, while Ti x TiSe2 shows an itinerant behavior. The superstructure and the carrier localization observed in Fe x TiSe2 single crystals simultaneously disappear at the critical concentration x c˜0.07, which agrees well with theoretical value based on a percolation theory. Fe intercalation compounds show paramagnetism and nonexistence of magnetism is attributed to the large distance between guest Fe atoms. We discuss the effect of guest intercalation on the stability of superstructure formed in the host.

Sasaki, M.; Ohnishi, A.; Kikuchi, T.; Kitaura, M.; Shimada, K.; Kim, H.-J.

2010-11-01

371

Electronic and transport properties of V-shaped defect zigzag MoS2 nanoribbons

NASA Astrophysics Data System (ADS)

Based on the nonequilibrium Green's function (NEGF) in combination with density functional theory (DFT) calculations, we study the electronic structures and transport properties of zigzag MoS2 nanoribbons (ZMNRs) with V-shaped vacancy defects on the edge. The vacancy formation energy results show that the zigzag vacancy is easier to create on the edge of ZMNR than the armchair vacancy. Both of the defects can make the electronic band structures of ZMNRs change from metal to semiconductor. The calculations of electronic transport properties depict that the currents drop off clearly and rectification ratios increase in the defected systems. These effects would open up possibilities for their applications in novel nanoelectronic devices.

Li, Xin-Mei; Long, Meng-Qiu; Cui, Li-Ling; Xiao, Jin; Xu, Hui

2014-04-01

372

Growth atmosphere dependence of transport properties of NiO epitaxial thin films

NASA Astrophysics Data System (ADS)

Recent possible applications in nonvolatile resistive switching memory devices renewed the interests in the transport properties of NiO. The variation on the conductivities of NiO films was reported to strongly affect the resistive switching phenomena. The conduction mechanism of NiO has been interpreted in terms of the bulk p-type conduction mechanism via Ni deficiencies (Ni1-?O). Here we investigate the growth atmosphere dependence on the transport properties of NiO thin films epitaxially grown on MgO (001) substrate. The conductivities of NiO thin films showed completely an opposite tendency compared to the bulk p-type conduction mechanism. Microstructural analysis demonstrates that the conductivity of low temperature grown NiO thin films strongly correlates with tailing the band edge via the deterioration of entire film crystallinity rather than the grain boundaries including second phases.

Oka, Keisuke; Yanagida, Takeshi; Nagashima, Kazuki; Tanaka, Hidekazu; Kawai, Tomoji

2008-07-01

373

Electrical transport properties of (La(1-x)X(x))MnO(3) (X = Ca, Sr), which exhibits the so-called colossal magnetoresistance (CMR) effect, are investigated in the framework of linear response theory combined with first-principles calculation. The calculation is performed by applying the coherent potential approximation and Kubo-Greenwood formula to the KKR Green's function method. In order to reveal the mechanism that underlies the CMR effects, the dc conductivities of the system in A (layered)-, C (stripe)-, and G (111)-type antiferromagnetic states as well as the local moment disordered state are calculated as a function of x. It is found that the conductivity of the system strongly depends on the magnetic structure and is highly anisotropic in the cases of A- and C-type antiferromagnetic structures. Also, it is concluded that a drastic change in the conductivity is expected when the system undergoes a magnetic transition, and that this might be closely related to the observed CMR effect. It is pointed out that, for such a drastic change in the conductivity to occur associated with the magnetic transition, the half-metallic nature of the Mn local electronic structure must be essential. PMID:23060537

Ogura, M; Akai, H

2012-11-14

374

Transport properties of Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} meander lines

The authors have measured the electrical transport properties of 10 cm long Tl{sub 2}Ba{sub 2}CaCu{sub 2}O{sub 8} thin film meander lines in magnetic fields up to 18T. The large resistance of the meander line effectively increased the electric field, or equivalently, resistivity sensitivity by two orders of magnitude. In moderate magnetic fields the critical current density is found to depend only on the component of the magnetic field normal to the ab planes owing to the highly anisotropic nature of the system. The resistivity versus temperature was measured as a function of magnetic field up to 18T. The linear resistivity is found to vanish in a manner consistent with the occurrence of a second order phase transition. The critical exponent v(z-1) is virtually field independent with a value 5.3 {+-}1 consistent with previous measurements of a three dimensional vortex glass transition in YBa{sub 2}Cu{sub 3}O{sub 7} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. The critical regime is 10-15K wide in agreement with values for Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} at high magnetic field.

Fleshler, S.; Maley, M.P.; Jia, Quanxi; Wu, Xin Di; Lacerda, A.

1995-12-31

375

Magnetic and transport properties of Mn2CoAl oriented films

NASA Astrophysics Data System (ADS)

The structure, magnetic, and transport properties of thin films of the Heusler ferrimagnet Mn2CoAl have been investigated for properties related to spin gapless semiconductors. Oriented films were grown by molecular beam epitaxy on GaAs substrates and the structure was found to transform from tetragonal to cubic for increasing annealing temperature. The anomalous Hall resistivity is found to be proportional to the square of the longitudinal resistivity and magnetization expected for a topological Berry curvature origin. A delicate balance of the spin-polarized carrier type when coupled with voltage gate-tuning could significantly impact advanced electronic devices.

Jamer, Michelle E.; Assaf, Badih A.; Devakul, Trithep; Heiman, Don

2013-09-01

376

Electronic Transport Properties of Pentacene Single Crystals upon Exposure to Air

We report the effect of air exposure on the electronic properties of pentacene single crystals. Air can diffuse reversibly in and out of the crystals and controls the physical properties. We discern two competing mechanisms that modulate the electronic transport. The presence of oxygen increases the hole conduction, as in dark four O2 molecules introduce one charge carrier. This effect is enhanced by the presence of visible light. Contrarily, water, present in ambient air, is incorporated in the crystal lattice and forms trapping sites for injected charges.

Oana D. Jurchescu; Jacob Baas; Thomas T. M. Palstra

2005-01-24

377

Atomistic molecular dynamics simulations were performed on a low-molecular-weight nitroplasticized Estane® mixture representative of the binder used in PBX-9501. Pressure-volume-temperature (PVT) behavior over a wide range of pressures and temperatures above the order-disorder temperature (ODT) of Estane was determined and represented with the empirical Tait and Sun equations of state. The effect of temperature, pressure, and plasticization on transport properties

H. Davande; D. Bedrov; G. D. Smith

2008-01-01

378

Transport properties via surface localized states of Ru, Rh and Pd thin films on Ag(111)

NASA Astrophysics Data System (ADS)

We investigate the transport properties of some 4d transition metal (i.e. Ru, Rh and Pd) thin films fabricated on Ag(111) based on first principles calculation. We calculate the conductance observed by double tipped scanning tunnelling microscope and find that the conductances through Ru and Rh thin films are majority spin polarized. We discuss these results and compare them with our previous study for Fe thin films.

Kishi, Tomoya; Kasai, Hideaki; Nakanishi, Hiroshi; David, Melanie; Diño, Wilson Agerico; Komori, Fumio

2005-09-01

379

Growth temperature dependence of transport properties of InAs epilayers grown on GaP

with a lattice mismatch of 7%. In the present study, InAs was grown on the wide-band-gap semiconductor GaPGrowth temperature dependence of transport properties of InAs epilayers grown on GaP Victor Souwa 23 June 2000 Undoped InAs was grown by molecular-beam epitaxy directly on GaP at a set of different

Woodall, Jerry M.

380

Magnetic Properties of Mn-Doped ZnO Nanostructures Synthesized by Chemical Vapor Transport

NASA Astrophysics Data System (ADS)

Mn-doped ZnO nanostructures have been fabricated by chemical vapor transport (CVT). Nanobelts, nanorods and nanowires have different growth directions because of their different growth environments. X-ray diffraction, electron paramagnetic resonance and Raman spectrum methods have been used to identify the substitution of a Zn site with Mn ions. Despite their different morphologies, these nanostructures possess the same magnetic properties. Magnetization was paramagnetic and antiferromagnetic. No ferromagnetism was observed even at T=5 K.

Zhang, Hua-Wei; Shi, Er-Wei; Chen, Zhi-Zhan; Liu, Xue-Chao; Xiao, Bing

2006-10-01

381

1.A study has been made of the oxygen and carbon dioxide transporting properties of the blood of three species of crab,Goneplax rhomboides, a species which constructs semi-permanent burrows in sublittoral muds, andAtelecyclus rotundatus andLiocarcinus depurator which simply bury themselves in the substratum. Investigations were also made of thein vivo blood\\/gas parameters in these three species. The oxygen carrying capacity of

A. C. Taylor; S. Morris; C. R. Bridges

1985-01-01

382

Growth atmosphere dependence of transport properties of NiO epitaxial thin films

Recent possible applications in nonvolatile resistive switching memory devices renewed the interests in the transport properties of NiO. The variation on the conductivities of NiO films was reported to strongly affect the resistive switching phenomena. The conduction mechanism of NiO has been interpreted in terms of the bulk p-type conduction mechanism via Ni deficiencies (Ni1-deltaO). Here we investigate the growth

Keisuke Oka; Takeshi Yanagida; Kazuki Nagashima; Hidekazu Tanaka; Tomoji Kawai

2008-01-01

383

Collapse and Expansion of Anisotropic Plane Symmetric Source

This paper deals with the collapse and expansion of relativistic anisotropic self-gravitating source. The field equations for non-radiating and non-static plane symmetric anisotropic source have been evaluated. The non-radiating property of the fluid leads to evaluation of the metric functions. We have classified the dynamical behavior of gravitational source as expansion and collapse. The collapse in this case leads to the final stage without the formation of apparent horizons while such horizons exists in case of spherical anisotropic source. The matching of interior and exterior regions provides the continuity of masses over the boundary surface.

G. Abbas

2013-12-23

384

NASA Technical Reports Server (NTRS)

A survey is presented of representative equations for various thermophysical properties of fluids in the critical region. Representative equations for the transport properties are included. Semi-empirical modifications of the theoretically predicted asymtotic critical behavior that yield simple and practical representations of the fluid properties in the critical region are emphasized.

Sengers, J. V.; Basu, R. S.; Sengers, J. M. H. L.

1981-01-01

385

Subsurface transport of plutonium (Pu) may be facilitated by the formation of intrinsic Pu colloids. While this colloid-facilitated transport is largely governed by the electrokinetic properties and dispersion stability (resistance to aggregation) of the colloids, reported experimental data is scarce. Here, we quantify the dependence of ?-potential of intrinsic Pu(IV) colloids on pH and their aggregation rate on ionic strength. Results indicate an isoelectric point of pH 8.6 and a critical coagulation concentration of 0.1 M of 1:1 electrolyte at pH 11.4. The ?-potential/pH dependence of the Pu(IV) colloids is similar to that of goethite and hematite colloids. Colloid interaction energy calculations using these values reveal an effective Hamaker constant of the intrinsic Pu(IV) colloids in water of 1.85 × 10(-19) J, corresponding to a relative permittivity of 6.21 and refractive index of 2.33, in agreement with first principles calculations. This relatively high Hamaker constant combined with the positive charge of Pu(IV) colloids under typical groundwater aquifer conditions led to two contradicting hypotheses: (a) the Pu(IV) colloids will exhibit significant aggregation and deposition, leading to a negligible subsurface transport or (b) the Pu(IV) colloids will associate with the relatively stable native groundwater colloids, leading to a considerable subsurface transport. Packed column transport experiments supported the second hypothesis. PMID:23675849

Abdel-Fattah, Amr I; Zhou, Dongxu; Boukhalfa, Hakim; Tarimala, Sowmitri; Ware, S Doug; Keller, Arturo A

2013-06-01

386

Functional Properties of the Arabidopsis Peptide Transporters AtPTR1 and AtPTR5*

The Arabidopsis di- and tripeptide transporters AtPTR1 and AtPTR5 were expressed in Xenopus laevis oocytes, and their selectivity and kinetic properties were determined by voltage clamping and by radioactive uptake. Dipeptide transport by AtPTR1 and AtPTR5 was found to be electrogenic and dependent on protons but not sodium. In the absence of dipeptides, both transporters showed proton-dependent leak currents that were inhibited by Phe-Ala (AtPTR5) and Phe-Ala, Trp-Ala, and Phe-Phe (AtPTR1). Phe-Ala was shown to reduce leak currents by binding to the substrate-binding site with a high apparent affinity. Inhibition of leak currents was only observed when the aromatic amino acids were present at the N-terminal position. AtPTR1 and AtPTR5 transport activity was voltage-dependent, and currents increased supralinearly with more negative membrane potentials and did not saturate. The voltage dependence of the apparent affinities differed between Ala-Ala, Ala-Lys, and Ala-Asp and was not conserved between the two transporters. The apparent affinity of AtPTR1 for these dipeptides was pH-dependent and decreased with decreasing proton concentration. In contrast to most proton-coupled transporters characterized so far, ?Imax increased at high pH, indicating that regulation of the transporter by pH overrides the importance of protons as co-substrate. PMID:20937801

Hammes, Ulrich Z.; Meier, Stefan; Dietrich, Daniela; Ward, John M.; Rentsch, Doris

2010-01-01

387

A two-dimensional mathematical model for simulating the transport and fate of organic chemicals in a laboratory scale, single layer aquifer is presented. The aquifer can be nonhomogeneous and anisotropic with respect to its fluid flow properties. he physical model has open inlet ...

388

REPRESENTING AEROSOL DYNAMICS AND PROPERTIES IN CHEMICAL TRANSPORT MODELS BY THE METHOD OF MOMENTS.

Atmospheric aerosols, suspensions of solid or liquid particles, are an important multi-phase system. Aerosols scatter and absorb shortwave (solar) radiation, affecting climate (Charlson et al., 1992; Schwartz, 1996) and visibility; nucleate cloud droplet formation, modifying the reflectivity of clouds (Twomey et al., 1984; Schwartz and Slingo, 1996) as well as contributing to composition of cloudwater and to wet deposition (Seinfeld and Pandis, 1998); and affect human health through inhalation (NRC, 1998). Existing and prospective air quality regulations impose standards on concentrations of atmospheric aerosols to protect human health and welfare (EPA, 1998). Chemical transport and transformation models representing the loading and geographical distribution of aerosols and precursor gases are needed to permit development of effective and efficient strategies for meeting air quality standards, and for examining aerosol effects on climate retrospectively and prospectively for different emissions scenarios. Important aerosol properties and processes depend on their size distribution: light scattering, cloud nucleating properties, dry deposition, and penetration into airways of lungs. The evolution of the mass loading itself depends on particle size because of the size dependence of growth and removal processes. For these reasons it is increasingly recognized that chemical transport and transformation models must represent not just the mass loading of atmospheric particulate matter but also the aerosol microphysical properties and the evolution of these properties if aerosols are to be accurately represented in these models. If the size distribution of the aerosol is known, a given property can be evaluated as the integral of the appropriate kernel function over the size distribution. This has motivated the approach of determining aerosol size distribution, and of explicitly representing this distribution and its evolution in chemical transport models.

SCHWARTZ,S.E.; MCGRAW,R.; BENKOVITZ,C.M.; WRIGHT,D.L.

2001-04-01

389

Thermal transport in hexagonal boron nitride nanoribbons

NASA Astrophysics Data System (ADS)

The thermal transport properties of hexagonal boron nitride nanoribbons (BNNRs) are investigated. By calculating the phonon spectrum and thermal conductance, it is found that the BNNRs possess excellent thermal transport properties. The thermal conductance of BNNRs can be comparable to that of graphene nanoribbons (GNRs) and even exceed the latter below room temperature. A fitting formula is obtained to describe the features of thermal conductance in BNNRs, which reveals a critical role of the T1.5 dependence in determining the thermal transport. In addition, an obviously anisotropic thermal transport phenomenon is observed in the nanoribbons. The thermal conductivity of zigzag-edged BNNRs is shown to be about 20% larger than that of armchair-edged nanoribbons at room temperature. The findings indicate that the BNNRs can be applied as important components of excellent thermal devices.

Ouyang, Tao; Chen, Yuanping; Xie, Yuee; Yang, Kaike; Bao, Zhigang; Zhong, Jianxin

2010-06-01

390

Thermal transport in hexagonal boron nitride nanoribbons.

The thermal transport properties of hexagonal boron nitride nanoribbons (BNNRs) are investigated. By calculating the phonon spectrum and thermal conductance, it is found that the BNNRs possess excellent thermal transport properties. The thermal conductance of BNNRs can be comparable to that of graphene nanoribbons (GNRs) and even exceed the latter below room temperature. A fitting formula is obtained to describe the features of thermal conductance in BNNRs, which reveals a critical role of the T(1.5) dependence in determining the thermal transport. In addition, an obviously anisotropic thermal transport phenomenon is observed in the nanoribbons. The thermal conductivity of zigzag-edged BNNRs is shown to be about 20% larger than that of armchair-edged nanoribbons at room temperature. The findings indicate that the BNNRs can be applied as important components of excellent thermal devices. PMID:20484794

Ouyang, Tao; Chen, Yuanping; Xie, Yuee; Yang, Kaike; Bao, Zhigang; Zhong, Jianxin

2010-06-18

391

By adopting a new tensor method, we derived an analytical propagation formula for the cross-spectral density of partially coherent twisted anisotropic Gaussian Schell-model (GSM) beams through dispersive and absorbing media. Using the derived formula, we studied the evolution properties and spectrum properties of twisted anisotropic GSM beams in dispersive and absorbing media. The results show that the dispersive and absorbing

Yangjian Cai; Qiang Lin; Di Ge

2002-01-01

392

The effect of the proximity of Au nanoparticles on the transport and magnetic properties of ultrathin La2/3Sr1/3MnO3 (LSMO) films has been investigated. We find a huge increase of the resistivity of the manganite (by four orders of magnitude for a Au nominal thickness of 2 nm), which is accompanied by a strong decrease of the Curie temperature. A combined scanning transmission electron microscopy and electron energy loss spectroscopy (STEM-EELS) analysis shows that interfaces are coherent and atomically sharp, and that the structural quality is very high. On the other end, a strong reduction of the Mn oxidation state is seen upon Au capping. NMR data show a strong attenuation of the double exchange signal upon formation of Au nanoparticles. Ab-initio calculations indicate a negligible influence of Au on LSMO at an ideal interface, with the LSMO surface magnetic and electronic properties essentially unchanged upon creation of the Au/LSMO interface. In view of these calculations, the experimental results cannot be explained in terms of purely electrostatic effects induced by the proximity of a noble metal. Here we propose that the main driving force underlying the observed change in physical properties is the high reactivity of Au nanoparticles which can locally pump oxygen from the manganite, thus favouring a phase separation ensuing from O inhomogeneity which deteriorates the transport and electrical properties.

Brivio, S. [Politecnico di Milano; Magen Dominguez, Cesar [ORNL; Sidorenko, A [Universita degli Studi di Parma; Petti, D. [Politecnico di Milano; Cantoni, M. [Politecnico di Milano; Finazzi, M [Politecnico di Milano; Ciccacci, F [Politecnico di Milano; Renzi, R [Universita degli Studi di Parma; Varela del Arco, Maria [ORNL; Picozzi, S. [CNR-INFM, L-Aquila, Italy; Bertacco, R. [Politecnico di Milano

2010-01-01

393

NASA Astrophysics Data System (ADS)

With the capability of producing nearly 600 TW annually, solar power is one renewable energy source with the potential to meet a large fraction of the world's burgeoning energy demand. To make solar technology cost-competitive with carbon-based fuels, cheaper devices need to be realized. Solution-processed solar cells from nanocrystal inks of earth abundant materials satisfy this requirement. Nonetheless, a major hurdle in commercializing such devices is poor charge transport through nanocrystal thin films. The efficiency of charge transport through nanocrystal thin films is strongly dependent on the quality of the nanocrystals, as well as their optoelectronic properties. Therefore, the first part of this dissertation is focused on synthesizing high quality nanocrystals of Cu2ZnSnS4, a promising earth abundant photovoltaic absorber material. The optoelectronic properties of the nanocrystals were tuned by altering the copper to zinc ratio, as well as by introducing selenium to create Cu2ZnSn(S1-xSe x)4 solid solutions. Photoelectrochemical characterization was used to test the Cu2ZnSnS4 and Cu2ZnSn(S 1-xSex)4 nanocrystal thin films. The results identify minority carrier diffusion and recombination via the redox shuttle as the major loss mechanisms hindering efficient charge transport through the nanocrystal thin films. One way to solve this issue is to sinter the nanocrystals together, creating large grains for efficient charge transport. Although this may be quick and effective, it can lead to the formation of structural defects, among other issues. To this end, using a different copper-based material, namely Cu2Se, and simple surface chemistry treatments, an alternative route to enhance charge transport through nanocrystals thin films is proposed.

Riha, Shannon C.

394

Computer programs for thermodynamic and transport properties of hydrogen (tabcode-II)

NASA Technical Reports Server (NTRS)

The thermodynamic and transport properties of para and equilibrium hydrogen have been programmed into a series of computer routines. Input variables are the pair's pressure-temperature and pressure-enthalpy. The programs cover the range from 1 to 5000 psia with temperatures from the triple point to 6000 R or enthalpies from minus 130 BTU/lb to 25,000 BTU/lb. Output variables are enthalpy or temperature, density, entropy, thermal conductivity, viscosity, at constant volume, the heat capacity ratio, and a heat transfer parameter. Property values on the liquid and vapor boundaries are conveniently obtained through two small routines. The programs achieve high speed by using linear interpolation in a grid of precomputed points which define the surface of the property returned.

Roder, H. M.; Mccarty, R. D.; Hall, W. J.

1972-01-01

395

Modeling electronic structure and transport properties of graphene with resonant scattering centers

We present a detailed numerical study of the electronic properties of single-layer graphene with resonant ("hydrogen") impurities and vacancies within a framework of noninteracting tight-binding model on a honeycomb lattice. The algorithms are based on the numerical solution of the time-dependent Schr\\"{o}dinger equation and applied to calculate the density of states, \\textit{quasieigenstates}, AC and DC conductivities of large samples containing millions of atoms. Our results give a consistent picture of evolution of electronic structure and transport properties of functionalized graphene in a broad range of concentration of impurities (from graphene to graphane), and show that the formation of impurity band is the main factor determining electrical and optical properties at intermediate impurity concentrations, together with a gap opening when approaching the graphane limit.

Shengjun Yuan; Hans De Raedt; Mikhail I. Katsnelson

2010-07-22

396

Mechanical and transport properties of IBAD/EDDC-SmBCO coated conductor tapes during fatigue loading

NASA Astrophysics Data System (ADS)

In electrical devices like superconducting motor, generator and SMES, HTS coated conductor (CC) tapes will be subjected to alternating stress or strain during manufacturing and operation. The repeated loading will affect the mechanical integrity and eventually the electrical transport property of CC tapes. Therefore in such applications, electro-mechanical property of CC tapes should be evaluated. In this study, the endurance of an IBAD/EDDC-SmBCO CC tape under high-cycle fatigue loading has been evaluated. Applied maximum stress and fatigue life ( S-N) relation was obtained at 77 K. The mechanical properties and the critical current, I c, of the sample under fatigue loading were investigated at 77 K. Considering the practical operating environment, the effect of the stress ratio R, on the degradation behavior of I c under fatigue loading was also examined.

Shin, Hyung-Seop; Dedicatoria, Marlon J.

2011-06-01

397

Reliable control in the crystal quality of synthesized III-V nanowires (NWs) is particularly important to manipulate their corresponding electronic transport properties for technological applications. In this report, a "two-step" growth process is adopted to achieve single-crystalline GaAs NWs, where an initial high-temperature nucleation process is employed to ensure the formation of high Ga supersaturated Au7Ga3 and Au2Ga alloy seeds, instead of the low Ga supersaturated Au7Ga2 seeds observed in the conventional "single-step" growth. These two-step NWs are long (>60 ?m) and thick (>80 nm) with the minimal defect concentrations and uniform growth orientations. Importantly, these NWs exhibit p-type conductivity as compared to the single-step grown n-type NWs for the same diameter range. This NW conductivity difference (p- versus n-channel) is shown to originate from the donor-like crystal defects, such as As precipitates, induced by the low Ga supersaturated multicrystalline Au7Ga2 alloy seeds. Then the well-controlled crystal quality for desired electronic properties is further explored in the application of large-scale p-type GaAs NW parallel array FETs as well as the integration of both p- and n-type GaAs NWs into CMOS inverters. All these illustrate the successful control of NW crystal defects and corresponding electronic transport properties via the manipulation of Ga supersaturation in the catalytic alloy tips with different preparation methods. The understanding of this relationship between NW crystal quality and electronic transport properties is critical and preferential to the future development of nanoelectronic materials, circuit design, and fabrication. PMID:24016352

Han, Ning; Hou, Jared J; Wang, Fengyun; Yip, SenPo; Yen, Yu-Ting; Yang, Zai-Xing; Dong, Guofa; Hung, TakFu; Chueh, Yu-Lun; Ho, Johnny C

2013-10-22

398

Parallel Anisotropic Tetrahedral Adaptation

NASA Technical Reports Server (NTRS)

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.

Park, Michael A.; Darmofal, David L.

2008-01-01

399

Hopping Conduction and Bacteria: Transport Properties of Disordered Reaction-Diffusion Systems

NASA Astrophysics Data System (ADS)

Reaction-diffusion (RD) systems are used to model everything from the formation of animal coat patterns to the spread of genes in a population to the seasonal variation of plankton density in the ocean. In all of these problems, disorder plays a large role, but determining its effects on transport properties in RD systems has been a challenge. We present here both analytical and numerical studies of a particular disordered RD system consisting of particles which are allowed to diffuse and compete for resources (2A->A) with spatially homogeneous rates, reproduce (A->2A) in certain areas (``oases''), and die (A->0) everywhere else (the ``desert''). In the low oasis density regime, transport is mediated through rare ``hopping events'' in which a small number of particles diffuse through the desert from one oasis to another; the situation is mathematically analogous to hopping conduction in doped semiconductors, and this analogy, along with some ideas from first passage percolation theory, allows us to make some quantitative predictions about the transport properties of the system on a large scale.

Missel, Andrew; Dahmen, Karin

2008-03-01

400

Transport properties for an electroneutral Yukawa-type fluid in the MSA

NASA Astrophysics Data System (ADS)

In the framework of a linear response theory, in which Onsager’s continuity equations are combined with the Mean Spherical Approximation (MSA) from the theory of correlation functions in equilibrium, and using a Green’s function formalism, we consider the transport properties of electrolytes. The interaction between the ions in the electrolyte is represented by an intermolecular Yukawa potential which satisfies the electroneutrality condition. The model contains an adjustable parameter z which takes into account the effects of the solvent. Transport processes in an ionic solution are determined by two dominant forces: the relaxation and the electrophoretic forces; their contributions to the transport properties are calculated using the Fuoss-Onsager theory. We find the conductivity and the self-diffusion coefficient for a family of electrolytes using the linear response theory. The predictions of our model can be adjusted by means of the parameter z. The electrophoretic effect, due to the hydrodynamic interaction between the ions, is calculated using the Rotne-Prager tensor. Our theoretical results are in good agreement with experimental data for electrolytes 1-1, even for high concentrations. We applied this theory also to two unsymmetrical electrolytes, namely the aqueous solutions of MgCl2 and CaCl2, with results in good accord with experimental data.

Montes-Perez, J.; Herrera, J. N.

2014-01-01

401

NASA Astrophysics Data System (ADS)

The transport and gain properties of quantum cascade (QC) structures are investigated using a nonequilibrium Green’s function (NGF) theory which includes quantum effects beyond a Boltzmann transport description. In the NGF theory, we include interface roughness, impurity, and electron-phonon scattering processes within a self-consistent Born approximation, and electron-electron scattering in a mean-field approximation. With this theory we obtain a description of the nonequilibrium stationary state of QC structures under an applied bias, and hence we determine transport properties, such as the current-voltage characteristic of these structures. We define two contributions to the current, one contribution driven by the scattering-free part of the Hamiltonian, and the other driven by the scattering Hamiltonian. We find that the dominant part of the current in these structures, in contrast to simple superlattice structures, is governed mainly by the scattering Hamiltonian. In addition, by considering the linear response of the stationary state of the structure to an applied optical field, we determine the linear susceptibility, and hence the gain or absorption spectra of the structure. A comparison of the spectra obtained from the more rigorous NGF theory with simpler models shows that the spectra tend to be offset to higher values in the simpler theories.

Lee, S.-C.; Wacker, A.

2002-12-01

402

Quasidislocations in anisotropic bicrystals

NASA Astrophysics Data System (ADS)

Weertman has recently pointed out that an elastic line singularity of dislocation/force line character but of zero Burgers vector and zero line force can move at the Stoneley velocity along the interface in a bicrystal of two different isotropic materials [J. Weertman, Phys. Rev. Lett. 93, 2655 (2004)]. The theory of this quasidislocation is generalized to the case of anisotropic bicrystals. The quasidislocation-Stoneley wave connection remains generally true and is further elucidated.

Lothe, Jens

2005-08-01

403

Oriented assembled TiO2 hierarchical nanowire arrays with fast electron transport properties.

Developing high surface area nanostructured electrodes with rapid charge transport is essential for artificial photosynthesis, solar cells, photocatalysis, and energy storage devices. Substantial research efforts have been recently focused on building one-dimensional (1D) nanoblocks with fast charge transport into three-dimensional (3D) hierarchical architectures. However, except for the enlargement in surface area, there is little experimental evidence of fast electron transport in these 3D nanostructure-based solar cells. In this communication, we report single-crystal-like 3D TiO2 branched nanowire arrays consisting of 1D branch epitaxially grown from the primary trunk. These 3D branched nanoarrays not only demonstrate 71% enlargement in large surface area (compared with 1D nanowire arrays) but also exhibit fast charge transport property (comparable to that in 1D single crystal nanoarrays), leading to 52% improvement in solar conversion efficiency. The orientated 3D assembly strategy reported here can be extended to assemble other metal oxides with one or multiple components and thus represents a critical avenue toward high-performance optoelectronics. PMID:24628675

Sheng, Xia; He, Dongqing; Yang, Jie; Zhu, Kai; Feng, Xinjian

2014-04-01

404

Anisotropic Total Variation Filtering

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.

Grasmair, Markus, E-mail: Markus.Grasmair@univie.ac.a [University of Vienna, Computational Science Center (Austria); Lenzen, Frank, E-mail: Frank.Lenzen@iwr.uni-heidelberg.d [University of Heidelberg, Heidelberg Collaboratory for Image Processing (Germany)

2010-12-15

405

NSDL National Science Digital Library

The Ejs Anisotropic Oscillator model displays the dynamics of a mass connected to two opposing springs. The simulation displays the motion of the mass as well as the trajectory plot. The initial position of the mass can be changed by dragging. The unstretched lengths of the springs can changed as well via textboxes. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. Ejs Anisotropic Oscillator model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_ehu_oscillations_anisotropic.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models for classical mechanics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Aguirregabiria, Juan

2008-10-09

406

India, a country over one billion population has been facing serious difficulty of urban congestion and traffic jams since 1970's in her major cities. Public transport system in Mumbai has been overworking three times its capacity. Public transport system in Delhi, Colcutta and Chennai is also under strain. Elevated railway and underground railway could be options to support overworked surface

Makarand Gulawani

407

DFT-NEGF study of transport properties and NDR behavior in fused furan and thiophene dimmers

NASA Astrophysics Data System (ADS)

The nonequilibrium Green's function approach in combination with density-functional theory is used to perform quantum mechanical calculations of the electron transport properties of furan and thiophene dimmers. Both the molecular systems have two S-linker and translated into the Gold junction with (1 1 1) surfaces. The studied molecular junctions at zero bias voltage are HOMO-based junctions and currents through these systems are driven by hole transport. The current-voltage characteristics of the both studied molecular junctions illustrate that negative differential resistance (NDR) feature is observed over the bias voltage of 2.0 V. Higher conductivity of fused furan dimmer and NDR character have been explained by the monitoring of the transmission resonance peak across the bias window against varying bias voltages.

Zahedi, Ehsan

2012-12-01

408

Transport properties of a single-quantum dot Aharonov-Bohm interferometer

NASA Astrophysics Data System (ADS)

We consider a two-terminal Aharonov-Bohm (AB) interferometer with a quantum dot inserted in one path of the AB ring. We investigate the transport properties of this system in and out of the Kondo regime. We utilize perturbation theory to calculate the electron self-energy of the quantum dot with respect to the intradot Coulomb interaction. We show the expression of the Kondo temperature as a function of the AB phase together with its dependence on other characteristics such as the linewidth of the ring and the finite Coulomb interaction and the energy levels of the quantum dot. The current oscillates periodically as a function of the AB phase. The amplitude of the current oscillation decreases with increasing Coulomb interaction. For a given temperature, the electron transport through the AB interferometer can be selected to be in or out of the Kondo regime by changing the magnetic flux threading perpendicular to the AB ring of the system.

Son, D. N.; Arboleda, N., Jr.; Dino, W. A.; Kasai, H.

2007-05-01

409

Loading-Dependent Transport Properties of Zeolitic Imidazolate Frameworks Probed by In-Situ PFG NMR

NASA Astrophysics Data System (ADS)

Zeolitic imidazolate frameworks (ZIFs), a unique subclass of metal-organic frameworks (MOFs) recently reported by Yaghi group and others, are attracting worldwide attention. Our systematic work on the adsorption and molecular transport in ZIFs has revealed some unique properties of these new materials that could not have been anticipated from standard structural characterization results. More specifically, the rearrangement of the imidazolate linkers (and in some cases, the framework structure) driven by adsorbate-adsorbent interaction causes the window sizes and accessible pore space of ZIFs to deviate (in some cases, drastically) from the values determined by low-temperature single-crystal X-ray crystallography and typical physisorption experiments carried out at liquid nitrogen temperature (77 K) with H2, N2 and Ar. Here we show the high degree of structural flexibility of ZIFs at near ambient temperatures and report the first time their unique adsorption and transport characteristics.

Kortunov, Pavel; Ni, Zheng; Paur, Charanjit; Reyes, Sebastian; Zengel, John

2011-03-01

410

NASA Astrophysics Data System (ADS)

The Kubo formula for the electrical conductivity is expressed in terms of a weighted sum of Drude-like contributions associated to the exact eigenstates of the interacting system, each characterized by its own frequency-dependent relaxation time. This alternative formulation considerably simplifies the access to the static properties (dc conductivity) and resolves the long-standing difficulty to connect the Boltzmann transport theory and the Kubo formula. In particular, at the lowest order of the perturbation theory, the correct transport scattering lifetime depending on the momentum k, which appears in the Boltzmann theory, instead of the single-electron lifetime appearing in the Green function, can be recovered. This alternative formulation is applied to (i) the elastic scattering in metals, and (ii) the inelastic scattering in the Fröhlich polaron model to obtain the exact result of the mobility in the low-temperature weak-coupling limit.

De Filippis, G.; Cataudella, V.; de Candia, A.; Mishchenko, A. S.; Nagaosa, N.

2014-07-01

411

Injection and transport properties of fast electrons in ultraintense laser-solid interactions

Fast electron injection and transport in solid foils irradiated by sub-picosecond-duration laser pulses with peak intensity equal to 4 Multiplication-Sign 10{sup 20} W/cm{sup 2} is investigated experimentally and via 3D simulations. The simulations are performed using a hybrid-particle-in-cell (PIC) code for a range of fast electron beam injection conditions, with and without inclusion of self-generated resistive magnetic fields. The resulting fast electron beam transport properties are used in rear-surface plasma expansion calculations to compare with measurements of proton acceleration, as a function of target thickness. An injection half-angle of {approx}50 Degree-Sign -70 Degree-Sign is inferred, which is significantly larger than that derived from previous experiments under similar conditions.

Coury, M.; Carroll, D. C.; Yuan, X. H.; Gray, R. J.; MacLellan, D. A.; Powell, H.; Quinn, M. N.; Tresca, O.; McKenna, P. [Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Robinson, A. P. L.; Lancaster, K. L.; Neely, D. [Central Laser Facility, STFC Rutherford Appleton Laboratory, Oxfordshire OX11 0QX (United Kingdom); Brenner, C. M. [Department of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Central Laser Facility, STFC Rutherford Appleton Laboratory, Oxfordshire OX11 0QX (United Kingdom); Burza, M.; Wahlstroem, C.-G. [Department of Physics, Lund University, P.O. Box 118, S-22100 Lund (Sweden); Li, Y. T.; Lin, X. X. [Beijing National Laboratory of Condensed Matter Physics Institute of Physics, CAS, Beijing 100190 (China)

2013-04-15

412

Transport properties of gallium nitride nanowire metal-oxide-semiconductor transistor

NASA Astrophysics Data System (ADS)

We investigated the transport properties of [112¯0]-gallium nitride (GaN)/gallium oxide (Ga2O3) single nanowire metal-oxide-semiconductor field-effect-transistor grown on (0001) sapphire substrates. With 0.1 ?m gate-length and 60 nm wire-size, the device exhibits maximum transconductance of 85 ?S, saturation current of 105 ?A, and unity current gain bandwidth ft at 95 GHz. From a three-dimensional (3D) diffusion-and-drift model analysis, polarization-induced negative space charge of -3 × 1012 cm-2 at the back interface of GaN/sapphire, positive space charge of 7 × 1012 cm-2 at the inclined semi-polar {11¯01¯} GaN/Ga2O3 interfaces with screening by two-dimensional electron gas to keep charge neutrality were found responsible for the high-speed transport characteristics.

Yu, J.-W.; Li, C.-K.; Chen, C.-Y.; Wu, Y.-R.; Chou, L.-J.; Peng, L.-H.

2011-10-01

413

NASA Astrophysics Data System (ADS)

Superlattice thin films of the perovskite-type oxide proton conductor SrZr0.95Y0.05O3/SrTiO3 was fabricated by pulsed laser deposition. Their structural and proton transport properties were reported. X-ray diffraction analysis and selected area electron diffraction revealed that the thin films were epitaxially grown on MgO(001) substrate. High-density edge dislocations and a columnar structure were observed in the films by high-resolution electron microscopy. The in-plane electrical conductivity of the thin films was determined by impedance spectroscopy. The contribution of proton transport to the total conductivity of the films was confirmed by H2O/D2O exchange measurement. The conductivity of superlattice films was increased by introducing heterointerfaces. The high activation energy (Ea=1.0 eV) was explained by the grain-boundary effect of the columnar structure in the films.

Kuwata, Naoaki; Sata, Noriko; Tsurui, Takao; Yugami, Hiroo

2005-12-01

414

Thermodynamic and transport properties of two-temperature SF{sub 6} plasmas

This paper deals with thermodynamic and transport properties of SF{sub 6} plasmas in a two-temperature model for both thermal equilibrium and non-equilibrium conditions. The species composition and thermodynamic properties are numerically determined using the two-temperature Saha equation and Guldberg-Waage equation according to deviation of van de Sanden et al. Transport properties including diffusion coefficient, viscosity, thermal conductivity, and electrical conductivity are calculated with most recent collision interaction potentials by adopting Devoto's electron and heavy particle decoupling approach but expanded to the third-order approximation (second-order for viscosity) in the frame of Chapman-Enskog method. The results are computed for various values of pressures from 0.1 atm to 10 atm and ratios of the electron temperature to the heavy particle temperature from 1 to 20 with electron temperature range from 300 to 40 000 K. In the local thermodynamic equilibrium regime, results are compared with available results of previously published studies.

Wang Weizong [State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an Shaanxi 710049 (China); Department of Electrical Engineering and Electronics, University of Liverpool, Brownlow Hill, Liverpool L69 3GJ (United Kingdom); Rong Mingzhe; Wu Yi [State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an Shaanxi 710049 (China); Spencer, Joseph W.; Yan, Joseph D.; Mei, DanHua [Department of Electrical Engineering and Electronics, University of Liverpool, Brownlow Hill, Liverpool L69 3GJ (United Kingdom)

2012-08-15

415

Water is a major component of fluids in the Earth’s mantle, where its properties are substantially different from those at ambient conditions. At the pressures and temperatures of the mantle, experiments on aqueous fluids are challenging, and several fundamental properties of water are poorly known; e.g., its dielectric constant has not been measured. This lack of knowledge of water dielectric properties greatly limits our ability to model water–rock interactions and, in general, our understanding of aqueous fluids below the Earth’s crust. Using ab initio molecular dynamics, we computed the dielectric constant of water under the conditions of the Earth’s upper mantle, and we predicted the solubility products of carbonate minerals. We found that MgCO3 (magnesite)—insoluble in water under ambient conditions—becomes at least slightly soluble at the bottom of the upper mantle, suggesting that water may transport significant quantities of oxidized carbon. Our results suggest that aqueous carbonates could leave the subducting lithosphere during dehydration reactions and could be injected into the overlying lithosphere. The Earth’s deep carbon could possibly be recycled through aqueous transport on a large scale through subduction zones. PMID:23513225

Pan, Ding; Spanu, Leonardo; Harrison, Brandon; Sverjensky, Dimitri A.; Galli, Giulia

2013-01-01

416

Electrical transport and magnetic properties of a possible electron-doped layered manganese oxide

NASA Astrophysics Data System (ADS)

We report on the structural, transport, and magnetic properties of La0.67Sr0.33MnOx thin films grown in vacuum by pulsed-laser deposition. The as-grown thin films have both the matrix La1.34Sr0.66MnO4 phase with K2NiF4 structure and an embedded MnO phase. The electrical transport and magnetic properties of the films are determined mainly by those of the matrix phase. By annealing, the as-grown thin films can be transformed into the normal La0.67Sr0.33MnO3 single phase, which shows the expected colossal magnetoresistance effect. Based on the composition of the matrix phase, and the structural, electrical, and magnetic properties of the films, we propose that the matrix phase is possibly electron doped with a mixed valence of Mn2+/Mn3+ instead of the Mn3+/Mn4+ as in the hole-doped case.

Zhao, Y. G.; Li, Y. H.; Ogale, S. B.; Rajeswari, M.; Smolyaninova, V.; Wu, T.; Biswas, A.; Salamanca-Riba, L.; Greene, R. L.; Ramesh, R.; Venkatesan, T.; Scott, J. H.

2000-02-01

417

Transport mechanism and regulatory properties of the human amino acid transporter ASCT2 (SLC1A5).

The kinetic mechanism of the transport catalyzed by the human glutamine/neutral amino acid transporter hASCT2 over-expressed in P. pastoris was determined in proteoliposomes by pseudo-bi-substrate kinetic analysis of the Na(+)-glutamineex/glutaminein transport reaction. A random simultaneous mechanism resulted from the experimental analysis. Purified functional hASCT2 was chemically cross-linked to a stable dimeric form. The oligomeric structure correlated well with the kinetic mechanism of transport. Half-saturation constants (Km) of the transporter for the other substrates Ala, Ser, Asn and Thr were measured both on the external and internal side. External Km were much lower than the internal ones confirming the asymmetry of the transporter. The electric nature of the transport reaction was determined imposing a negative inside membrane potential generated by K(+) gradients in the presence of valinomycin. The transport reaction resulted to be electrogenic and the electrogenicity originated from external Na(+). Internal Na(+) exerted a stimulatory effect on the transport activity which could be explained by a regulatory, not a counter-transport, effect. Native and deglycosylated hASCT2 extracted from HeLa showed the same transport features demonstrating that the glycosyl moiety has no role in transport function. Both in vitro and in vivo interactions of hASCT2 with the scaffold protein PDZK1 were revealed. PMID:25052780

Scalise, Mariafrancesca; Pochini, Lorena; Panni, Simona; Pingitore, Piero; Hedfalk, Kristina; Indiveri, Cesare

2014-11-01

418

NASA Astrophysics Data System (ADS)

Time-nonlocal transport models can describe non-Fickian diffusion observed in geological media, but the physical meaning of parameters can be ambiguous, and most applications are limited to curve-fitting. This study explores methods for predicting the parameters of a temporally tempered Lévy motion (TTLM) model for transient sub-diffusion in mobile-immobile like alluvial settings represented by high-resolution hydrofacies models. The TTLM model is a concise multi-rate mass transfer (MRMT) model that describes a linear mass transfer process where the transfer kinetics and late-time transport behavior are controlled by properties of the host medium, especially the immobile domain. The intrinsic connection between the MRMT and TTLM models helps to estimate the main time-nonlocal parameters in the TTLM model (which are the time scale index, the capacity coefficient, and the truncation parameter) either semi-analytically or empirically from the measurable aquifer properties. Further applications show that the TTLM model captures the observed solute snapshots, the breakthrough curves, and the spatial moments of plumes up to the fourth order. Most importantly, the a priori estimation of the time-nonlocal parameters outside of any breakthrough fitting procedure provides a reliable “blind” prediction of the late-time dynamics of subdiffusion observed in a spectrum of alluvial settings. Predictability of the time-nonlocal parameters may be due to the fact that the late-time subdiffusion is not affected by the exact location of each immobile zone, but rather is controlled by the time spent in immobile blocks surrounding the pathway of solute particles. Results also show that the effective dispersion coefficient has to be fitted due to the scale effect of transport, and the mean velocity can differ from local measurements or volume averages. The link between medium heterogeneity and time-nonlocal parameters will help to improve model predictability for non-Fickian transport in alluvial settings.

Zhang, Yong; Green, Christopher T.; Baeumer, Boris

2014-05-01

419

Time-nonlocal transport models can describe non-Fickian diffusion observed in geological media, but the physical meaning of parameters can be ambiguous, and most applications are limited to curve-fitting. This study explores methods for predicting the parameters of a temporally tempered Lévy motion (TTLM) model for transient sub-diffusion in mobile–immobile like alluvial settings represented by high-resolution hydrofacies models. The TTLM model is a concise multi-rate mass transfer (MRMT) model that describes a linear mass transfer process where the transfer kinetics and late-time transport behavior are controlled by properties of the host medium, especially the immobile domain. The intrinsic connection between the MRMT and TTLM models helps to estimate the main time-nonlocal parameters in the TTLM model (which are the time scale index, the capacity coefficient, and the truncation parameter) either semi-analytically or empirically from the measurable aquifer properties. Further applications show that the TTLM model captures the observed solute snapshots, the breakthrough curves, and the spatial moments of plumes up to the fourth order. Most importantly, the a priori estimation of the time-nonlocal parameters outside of any breakthrough fitting procedure provides a reliable “blind” prediction of the late-time dynamics of subdiffusion observed in a spectrum of alluvial settings. Predictability of the time-nonlocal parameters may be due to the fact that the late-time subdiffusion is not affected by the exact location of each immobile zone, but rather is controlled by the time spent in immobile blocks surrounding the pathway of solute particles. Results also show that the effective dispersion coefficient has to be fitted due to the scale effect of transport, and the mean velocity can differ from local measurements or volume averages. The link between medium heterogeneity and time-nonlocal parameters will help to improve model predictability for non-Fickian transport in alluvial settings.

Zhang, Yong; Green, Christopher T.; Baeumer, Boris

2014-01-01

420

Effects of malnutrition on microvillus membrane glucose transport and physical properties.

We examined sodium-dependent glucose transport, membrane lipid composition, and membrane fluidity in microvillus membrane vesicles isolated from the distal intestine of infant rabbits subjected to protein-energy malnutrition and age-matched controls. In vesicles from malnourished animals, sodium-dependent glucose transport was significantly enhanced, as evidenced by a twofold increase in maximal transport capacity, Jmax. Carrier affinity for glucose, as assessed by the Km of the transport process, was unaffected. These alternations were associated with marked changes in microvillus membrane composition. Malnourished animals had an increase in the lipid-to-protein ratio of the microvillus membrane, which suggests that malnutrition might be associated with either a reduction in membrane protein or an increase in membrane lipid. This would be expected to increase the fluidity of the microvillus membrane. However, we observed no differences in either the static or dynamic component of membrane fluidity, using multiple fluorescent probes, between dietary groups. Further analysis of membrane lipids was undertaken to establish whether quantitative differences in lipid subclasses could explain this discrepancy. We found that nutrient deprivation produced numerous alterations in membrane lipids. The major findings were an increase in both the cholesterol-to-phospholipid and phosphatidylethanolamine-to-phosphatidylcholine ratios. Both alterations would be expected to decrease membrane fluidity and presumably represent a compensatory response to the loss of membrane protein. Thus chronic postnatal protein-energy malnutrition initiates several adaptive responses that include major alterations in the chemical composition of the microvillus membrane. The resulting effect preserves efficient glucose transport and maintains the physical properties of the microvillus membrane. PMID:2124419

Butzner, J D; Brockway, P D; Meddings, J B

1990-12-01

421

Anisotropic Reinforcement of Acute Anteroapical Infarcts Improves Pump Function

Background We hypothesize that a therapy that improves LV pump function early after infarction should decrease the need for compensation through sympathetic activation and dilation, thereby reducing the risk of developing heart failure. The mechanical properties of healing myocardial infarcts are an important determinant of left ventricular (LV) function, yet improving function by altering infarct properties has proven unexpectedly difficult. Using a computational model, we recently predicted that stiffening a large anterior infarct anisotropically (in only one direction) would improve LV function, while isotropic stiffening, the focus of previous studies and therapies, would not. The goal of this study was to test the novel strategy of anisotropic infarct reinforcement. Methods and Results We tested the effects of anisotropic infarct reinforcement in 10 open-chest dogs with large anteroapical infarcts that depressed LV pump function. We measured regional mechanics, LV volumes, and cardiac output at a range of preloads at Baseline, 45 minutes after coronary ligation (Ischemia), and 30 minutes later, following surgical reinforcement in the longitudinal direction (Anisotropic). Ischemia shifted the end-systolic pressure-volume relationship (ESPVR) and cardiac output curves rightward, decreasing cardiac output at matched end-diastolic pressure (EDP) by 44%. Anisotropic reinforcement significantly improved systolic function without impairing diastolic function, recovering half the deficit in overall LV function. Conclusions We conclude that anisotropic reinforcement is a promising new approach to improving LV function following a large myocardial infarction. PMID:22665716

Fomovsky, Gregory M.; Clark, Samantha A.; Parker, Katherine M.; Ailawadi, Gorav; Holmes, Jeffrey W.

2012-01-01

422

Anisotropic stress and stability in modified gravity models

The existence of anisotropic stress of a purely geometrical origin seems to be a characteristic of higher order gravity models, and has been suggested as a probe to test these models observationally, for example, in weak lensing experiments. In this paper, we seek to find a class of higher order gravity models of f(R,G) type that would give us a zero anisotropic stress and study the consequences for the viability of the actual model. For the special case of a de Sitter background, we identify a subclass of models with the desired property. We also find a direct link between anisotropic stress and the stability of the model as well as the presence of extra degrees of freedom, which seems to be a general feature of higher order gravity models. Particularly, setting the anisotropic stress equal to zero for a de Sitter background leads to a singularity that makes it impossible to reach the de Sitter evolution.

Saltas, Ippocratis D. [Astronomy Centre, University of Sussex, Falmer, Brighton BN1 9QH (United Kingdom); Kunz, Martin [Departement de Physique Theorique, Universite de Geneve, 1211 Geneva 4 (Switzerland)

2011-03-15

423

Electronic transport property of single-crystalline hexagonal tungsten trioxide nanowires

NASA Astrophysics Data System (ADS)

Hexagonal WO3 nanowires were prepared on Si substrate by thermal evaporation of WO3 powder. A single WO3 nanowire was assembled on a pair of Pt electrodes by electric field assembly. The electrical transport behavior indicates that the back-to-back SBs structure is formed, which show nonlinear and asymmetric I-V properties. Through measurement of the I-V curve and the calculation of barrier height difference under illumination, it is found that the electrical asymmetry results from the asymmetric barrier height of the two Schottky barriers, which are dominated by the surface states of nanowire caused by O2 adsorption in the electric assembling process.

Wang, S. J.; Lu, W. J.; Cheng, G.; Cheng, K.; Jiang, X. H.; Du, Z. L.

2009-06-01

424

NASA Astrophysics Data System (ADS)

In a recent paper [C. DeW. Van Siclen, Phys. Rev. E 59, 2804 (1999)], a random-walk algorithm was proposed as the best method to calculate transport properties of composite materials. It was claimed that the method is applicable both to discrete and continuum systems. The limitations of the proposed algorithm are analyzed. We show that the algorithm does not capture the peculiarities of continuum systems (e.g., ``necks'' or ``choke points'') and we argue that it is the stochastic analog of the finite-difference method.

Kim, In Chan; Cule, Dinko; Torquato, Salvatore

2000-04-01

425

Electrochromic Property of MoO3 Thin Films Deposited by Chemical Vapor Transport Synthesis

NASA Astrophysics Data System (ADS)

The transmittance of electrochromic MoO3 thin films by chemical vapor transport (CVT) deposition and post-annealing on indium tin oxide (ITO) glass reached 80% with low reflectivity. Optical analysis demonstrated a 3.60 eV band gap energy in MoO3 thin film. Transmittance changes of 50% between coloration and decoloration (?30 and ?80%) at 533 nm under the bias change frequency revealed reversible electrochromic properties and stability. A coloration efficiency of the annealed MoO3 thin film was 23.7 cm2/C. Coloration responsibility was predominant with reliable performances by bias change.

Kim, Dae-Gun; Kim, Se Hoon; Do Kim, Young

2011-10-01

426

Effect of hot-press sintering temperature on thermal transport properties of TiSe2

NASA Astrophysics Data System (ADS)

Titanium diselenide (TiSe2) alloy was prepared using solid state reaction method and hot press sintering. The effects of hot press sintering temperatures on TiSe2 were studied on the thermal transport properties of the material. As grown material shows pure TiSe2 phase and layer structure. Increasing sintering temperature results in reduced electrical resistivity ? whereas the Seebeck coefficient, ? show no significant relative change. Reduced electrical resistivity may be attributed to the increased crystalline nature. This results in improved power factor showing the optimum condition for producing better TiSe2 thermoelectric material.

Bhatt, R.; Bhattacharya, S.; Basu, R.; Patel, M.; Singh, A.; Bhatt, P.; Aswal, D. K.; Gupta, S. K.

2013-06-01

427

NASA Technical Reports Server (NTRS)

Conjugated phenylene(ethynylene) molecular wires are of interest as potential candidates for molecular electronic devices. Scanning tunneling microscopic study of the topography and current-voltage (I-V) characteristics of self-assembled monolayers of two types of molecular wires are presented here. The study shows that the topography and I-Vs, for small scan voltages, of the two wires are quite similar and that the electronic and structural changes introduced by the substitution of an electronegative N atom in the central phenyl ring of these wires does not significantly alter the self-assembly or the transport properties.

Dholakia, Geetha R.; Fan, Wendy; Koehne, Jessica; Han, Jie; Meyyappan, M.

2003-01-01

428

Photothermal deflection investigation of bulk Si and GaSb transport properties

NASA Astrophysics Data System (ADS)

The photo-thermal deflection technique (PTD) is used to study the transport properties such as non-radiative lifetime of minority carriers ( ? nr), electronic diffusivity ( D) and surface recombination velocity ( S) in bulk silicon (Si) and gallium antimonide (GaSb) semiconductors. A generalized one-dimensional theoretical model has been also developed, and the coincidence between experimental curves giving the normalized amplitude and phase variations versus square root modulation frequency and the corresponding theoretical curves makes possible to deduce the electronic parameters cited above.

Ilahi, S.; Saadalah, F.; Yacoubi, N.

2013-02-01

429

NASA Astrophysics Data System (ADS)

We present exemplary results of extensive studies of mechanical, electronic and transport properties of covalent functionalization of graphene monolayers (GML). We report new results of ab initio studies for covalent functionalization of GML with -NH2 groups up to 12.5 % concentration. Our studies are performed in the framework of the density functional theory (DFT) and non-equilibrium Green's function (NEGF). We discuss the stability (adsorption energy), elastic moduli, electronic structure, band gaps, and effective electron masses as a function of the density of the adsorbed molecules. We also show the conductance and current - voltage I(V) characteristics for these systems.

Milowska, Karolina Z.; Birowska, Magdalena; Majewski, Jacek A.

2013-12-01

430

Transport Properties of Over-doped Epitaxial NdCeCuO Films

The transport properties of slightly overdoped Nd2?x\\u000a Ce\\u000a x\\u000a CuO4??\\u000a (NCCO) c-axis oriented thin films with x=0.17 have been investigated in the temperature range from 2.5 K to 300 K and in magnetic fields up to 6 T applied perpendicular\\u000a to the CuO2 planes. The films have been grown by a dc sputtering technique in on-axis configuration. They have been optimized on

A. Guarino; C. Cirillo; A. Leo; S. Santandrea; G. Grimaldi; A. Polcari; R. Fittipaldi; C. Attanasio; P. Romano; A. Romano; A. Vecchione; A. Nigro

2011-01-01