While these samples are representative of the content of Science.gov,

they are not comprehensive nor are they the most current set.

We encourage you to perform a real-time search of Science.gov

to obtain the most current and comprehensive results.

Last update: August 15, 2014.

1

NASA Astrophysics Data System (ADS)

This work concerns the modeling of radiative transfer in anisotropic turbid media using diffusion theory. A theory for the relationship between microscopic scattering properties (i.e., an arbitrary differential scattering cross-section) and the macroscopic diffusion tensor, in the limit of independent scatterers, is presented. The theory is accompanied by a numerical method capable of performing the calculations. In addition, a boundary condition appropriate for modeling systems with anisotropic radiance is derived. It is shown that anisotropic diffusion theory, when based on these developments, indeed can describe radiative transfer in anisotropic turbid media. More specifically, it is reported that solutions to the anisotropic diffusion equation are in excellent agreement with Monte Carlo simulations, both in steady-state and time-domain. This stands in contrast to previous work on the topic, where inadequate boundary conditions and/or incorrect relations between microscopic scattering properties and the diffusion tensor have caused disagreement between simulations and diffusion theory. The present work thus falsify previous claims that anisotropic diffusion theory cannot describe anisotropic radiative transfer, and instead open for accurate quantitative diffusion-based modeling of anisotropic turbid materials.

Alerstam, Erik

2014-06-01

2

New transport properties of anisotropic holographic superfluids

NASA Astrophysics Data System (ADS)

We complete the analysis of transport phenomena in p-wave superfluids within gauge/gravity duality, using the SU(2) Einstein-Yang-Mills model with backreaction. In particular, we analyze the fluctuation modes of helicity zero in addition to the helicity one and two modes studied earlier. We compute a further transport coefficient, associated to the first normal stress difference, not previously considered in the holographic context. In the unbroken phase this is related to a minimally coupled scalar on the gravity side. Moreover we find transport phenomena related to the thermoelectric and piezoelectric effects, in particular in the direction of the condensate, as well as the flexoelectric effect. These are similar to phenomena observed in condensed matter systems.

Erdmenger, Johanna; Fernández, Daniel; Zeller, Hansjörg

2013-04-01

3

Linking elastic, mechanical and transport properties in anisotropically cracked rocks

Damage and crack porosity can result in a decrease of the mechanical strength of the rock, the development of elastic and mechanical anisotropy and the enhancement of transport properties. Using Non-Interactive Crack Effective Medium (NIC) theory as a fundamental tool, it is possible to calculate dry and wet elastic properties of cracked rocks in terms of a crack density tensor,

A. Schubnel; P. Benson; F. Nasseri; Y. Gueguen; P. Meredith; R. Young

2007-01-01

4

Numerical modelling of mass transport in an arterial wall with anisotropic transport properties.

Coronary artery disease results in blockages or narrowing of the artery lumen. Drug eluting stents (DES) were developed to replace bare metal stents in an effort to combat re-blocking of the diseased artery following treatment. The numerical models developed within this study focus on representing the changing trends of drug delivery from an idealised DES in an arterial wall with an anisotropic ultra-structure. To reduce the computational burden of solving coupled physics problems, a model reduction strategy was adopted. Particular focus has been placed upon adequately modelling the influence of strut compression as there is a paucity of numerical studies that account for changes in transport properties in compressed regions of the arterial wall due to stent deployment. This study developed an idealised numerical modelling framework to account for the changes in the directionally dependent porosity and tortuosities of the arterial wall as a result of radial strut compression. The results show that depending on the degree of strut compression, trends in therapeutic drug delivery within the arterial wall can be either increased or decreased. The study highlights the importance of incorporating compression into numerical models to better represent transport within the arterial wall and suggests an appropriate numerical modelling framework that could be utilised in more realistic patient specific arterial geometries. PMID:24210470

Denny, William J; Walsh, Michael T

2014-01-01

5

NASA Astrophysics Data System (ADS)

Self-assembly of block copolymers and surfactant mesophases can be can be utilized in creating composite materials with very fine periodic structures. Easy access to nm-scale features coupled with compositional variety and thus tunable physical properties makes these nanoscale heterogeneous materials excellent candidates for selective transport applications including ion-conduction, ultrafiltration and desalination. A critical limitation in their performance however arises from the tortuosity of randomly oriented self-assembled structures. We show that in appropriately engineered systems, magnetic fields provide a viable route for scalable control of morphology, producing well aligned materials over large length scales. Here we discuss this approach for the fabrication of ion conduction membranes, aligned carbon nanotube membranes and nanoporous films. We quantitatively assess the anisotropic transport properties of one such system and confront the data with models based on effective medium theory and composite conductivity calculations. The results demonstrate that directed self-assembly can provide non-trivial enhancement of the transport properties in these applications.

Osuji, Chinedum

2013-03-01

6

Anisotropic transport and magnetic properties of arrays of sub-micron wires

We report a comparative study of anisotropic magnetoresistance and magnetic properties in arrays of sub-micron Ni and Co wires electro-deposited in the cylindrical pores of track-etched polymer membranes. The variation of coercivity and squareness as a function of wire diameter for arrays of almost isolated sub-micron wires is reported in the range 30–500 nm. The Ni and Co-based systems demonstrate

L. Piraux; S. Dubois; E. Ferain; R. Legras; K. Ounadjela; J. M. George; J. L. Maurice; A. Fert

1997-01-01

7

Anisotropic magneto-transport properties of layered perovskite Sr3Fe2-xCoxC7-? crystals

NASA Astrophysics Data System (ADS)

We have grown a series of single crystals of layered perovskite oxide Sr3Fe2-xCoxO7-? (x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5) and systematically investigated anisotropic properties of magnetism and transport as a function of x. The magnetization and resistivity of Sr3Fe2-xCoxO7-? crystals exhibit a large anisotropy due to the highly anisotropic crystal structure: the magnetic easy axis is found to be the c axis (perpendicular to the layered structure), and the resistivity within the ab plane (within the layer) is much lower than that along the c axis. With increasing x up to 0.5, the emergence of ferromagnetic behavior with a nearly metallic conduction was observed.

Nakamura, R.; Tozawa, J.; Akaki, M.; Akahoshi, D.; Itatani, K.; Kuwahara, H.

2012-12-01

8

Anisotropic transport properties of Tl(1223) magnetically aligned ceramics and spray pyrolyzed films

Uniaxially textured TlBaSrCa2Cu3O9 bulk ceramics have been fabricated by slip casting in magnetic fields up to 9 Tesla followed by sintering and reduction annealing. The measured transport properties are compared with those of spray pyrolyzed thick films where the degree of texture is controlled through processing. Transport anisotropy is correlated to the degree of texture but not to the magnitude

J. E. Tkaczyk; K. W. Lay; B. A. Jones; B. J. Bednarczyk; J. A. DeLuca

1995-01-01

9

Strain-Induced Anisotropic Transport Properties of LaBaCo2O5.5+? Thin Films on NdGaO3 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

10

Mixed-state transport properties of anisotropic superconductors in an oblique field

The mixed-state in-plane magnetoresistance rxx and Hall resistance rxy have been investigated for highly anisotropic Tl2Ba2CaCu2O8 (Tl2212) and Nd1.85Ce0.15CuO4 (NCCO). To observe the effects of anisotropy we employ an experimental geometry where the magnetic field can be rotated by an angle theta off the c-axis while keeping the field perpendicular to the current direction. For both Tl2212 and NCCO we

T. W. Clinton; A. W. Smith; J. L. Peng; M. Eddy; R. L. Greene; C. J. Lobb

1994-01-01

11

Anisotropic transport properties of zinc-blend ZnTe/CrTe heterogeneous junction nanodevices

NASA Astrophysics Data System (ADS)

Motivated by the molecular-beam epitaxial growth of zinc-blend-type CrTe thin films on ZnTe, we present a theoretical study on the spin-polarized transport properties of ZnTe/CrTe p-n junction as spin diode and CrTe/ZnTe/CrTe magnetic tunnel junction for (001) and (011) surfaces. Both ZnTe(001)/CrTe(001) and ZnTe(011)/CrTe(011) p-n junctions show excellent spin diode effect, the majority spin current of positive voltage is much larger than that of negative voltage and the minority spin current is absolutely inhibited. The ZnTe(001)/CrTe(001) p-n junction has lower ``turn off'' current and higher rectification ratio (about 105) than the ZnTe(011)/CrTe(011) which shows obvious anisotropy. We also find that the tunneling magneto resistance ratio of the CrTe/ZnTe/CrTe magnetic tunnel junction is up to about 4 × 109%.

Yao, Wei; Yao, K. L.; Gao, G. Y.; Zhu, S. C.; Fu, H. H.

2012-11-01

12

Highly epitaxial LaBaCo2O5.5+? (LBCO) thin films were grown on different miscut (001) SrTiO3 substrates (miscut angle of 0.5°, 3.0°, and 5.0°) to study the substrate surface step terrace effect on the in-plane electrical transport properties. The microstructure studies by X-ray diffraction and transmission electron microscopy indicate that the as-grown films are A-site disordered cubic perovskite structures with the c-axis highly oriented along the film growth direction. The four-probe scanning tunneling microscopy (STM) studies show that the LBCO thin films grown on the vicinal SrTiO3 substrates have a typical semiconductor behavior with the substrate surface terrace step inducing anisotropic electronic transport properties. These results indicate that in highly epitaxial thin films the surface terrace step induced local strains can play an important role in controlling the electronic transport properties and the anisotropic nature. PMID:24716582

Zou, Q; Liu, M; Wang, G Q; Lu, H L; Yang, T Z; Guo, H M; Ma, C R; Xu, X; Zhang, M H; Jiang, J C; Meletis, E I; Lin, Y; Gao, H J; Chen, C L

2014-05-14

13

NASA Astrophysics Data System (ADS)

Adopting the model differential cross sections used by Reid (1979) and by Haddad et al. (1981), an investigation to asses the discrepancies observed in the transverse diffusion coefficients D T and other transport properties are performed by the Monte-Carlo simulation. The results show that the values of ND T drastically vary with the change of anisotropy in the scattering property against the common sense that ND T is determined solely by the reduced field E/N under a given momentum transfer cross section. Cross sections so far derived from the D T/µ data may be necessary to be reassesed if anisotropy in the scattering properties is considered.

Yamamoto, Kohji; Ikuta, Nobuaki

1994-03-01

14

Influence of macroscopic defects on transport in anisotropic conductors

The transport properties of highly anisotropic conductors, such as tetrathiafulvalene tetracyanoquinodimethane (TTF-TCNQ) or graphite, are strongly influenced by inclusions, which can be represented as regions of different conductivity. This paper presents a theoretical study of such effects in three dimensions. Both quasiplanar materials, such as graphite, and quasi-one-dimensional systems are considered, and two types of defects are studied: zero-conductivity defects

J. Garner; D. Stroud

1982-01-01

15

On the anisotropic elastic properties of hydroxyapatite.

NASA Technical Reports Server (NTRS)

Experimental measurements of the isotropic elastic moduli on polycrystalline specimens of hydroxyapatite and fluorapatite are compared with elastic constants measured directly from single crystals of fluorapatite in order to derive a set of pseudo single crystal elastic constants for hydroxyapatite. The stiffness coefficients thus derived are given. The anisotropic and isotropic elastic properties are then computed and compared with similar properties derived from experimental observations of the anisotropic behavior of bone.

Katz, J. L.; Ukraincik, K.

1971-01-01

16

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) mm(2)/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. PMID:24784644

Ma, Y; Gustavsson, J S; Haglund, A; Gustavsson, M; Gustafsson, S E

2014-04-01

17

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

18

Multislab multigroup transport theory with Lth order anisotropic scattering

The special case of a triangular transfer matrix relevant to multigroup transport theory in multislabs with Lth order anisotropic scattering is discussed, and the F\\/sub N\\/ method is used to establish accurate numerical results for a real problem.

R. D. M. Garcia; C. E. Siewert

1983-01-01

19

Multislab multigroup transport theory with Lth order anisotropic scattering

The special case of a triangular transfer matrix relevant to multigroup transport theory in multislabs with Lth order anisotropic scattering is discussed, and the F/sub N/ method is used to establish accurate numerical results for a real problem.

Garcia, R.D.M.; Siewert, C.E.

1983-05-01

20

Anisotropic transport in modulation doped quantum well structures

NASA Technical Reports Server (NTRS)

The degree of anisotropy in the anisotropic electron transport that has been observed in GaAs modulation-doped quantum wells grown by MBE on Al(0.3)Ga(0.7)As is related to the thickness and growth parameters of this substrate, which is grown just prior to the inverted interface. It is presently observed that the inverted interface has an anisotropic roughness which affects the 77 K low field electron transport parallel to the interface, and gives rise to anisotropic electron scattering in the GaAs modulation-doped quantum well.

Radulescu, D. C.; Wicks, G. W.; Schaff, W. J.; Calawa, A. R.; Eastman, L. F.

1987-01-01

21

Detonation theory for condensed phase explosives with anisotropic properties

NASA Astrophysics Data System (ADS)

Detonation theory for condensed phase explosives with anisotropic properties is relevant to energetic materials that are crystals in their unreacted state and have anisotropic material properties due to their underlying molecular structure. For example, crystalline, molecular explosives like PETN and azides, depending on which crystal face is shocked, initiate detonation at different shock pressures. We discuss our recent efforts to construct a theory of sustained detonation that has strong directionally dependent effects and properties. We propose a continuum, phase-field theory that is capable of describing the transition from anisotropic unreacted solid to reacted condensed products. The material behavior is allowed to include anisotropic elasticity, heat conduction and reaction.

Stewart, D. Scott; Fried, Laurence E.; Szuck, Matthew

2012-03-01

22

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

23

Anisotropic transport rates in heterogeneous porous media

We applied a recently developed method of aquifer characterization, which combines geophysics and geostatistics to create several heterogeneous realizations of a shallow fluvial aquifer that contain representations of sedimentary bounding surfaces. The influence of such small-scale (several centimeters) features on subsurface transport was investigated using high-resolution groundwater models of each of the subsurface realizations. Flow and transport through the models

Nicholas B. Engdahl; Gary S. Weissmann

2010-01-01

24

Dielectric Properties of Bulk Anisotropic Structures and Multiphase Mixtures

The method of electrodynamic averaging is described, by which one can obtain the effective dielectric permittivity of volume anisotropic structure determined by the shape of particles, their geometrical sizes, electromagnetic parameters and spatial dense media, to consider multiple interactions between scattering elements and dispersion properties of the media. Tensors of the dielectric permittivity of anisotropic structures are given as the

E. A. Skirta; N. A. Khizhnyak

1993-01-01

25

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

26

Detonation Theory for Condensed Phase Explosives with Anisotropic Properties

NASA Astrophysics Data System (ADS)

Energetic materials that are crystals in their unreacted state have anisotropic material properties due to their underlying molecular structure. For example crystalline explosives like PETN and azides have exhibit different threshold initiating shock pressure depending on which crystal face is shocked. We discuss our recent efforts to build theory of sustained detonation that has both strong directional dependence and effects. We use a continuum phase field theory that is capable of describing the transition from anisotropic unreacted solid to reacted condensed products. The material behavior is allowed to include anisotropic elasticity and heat conduction and directionally preferential diffusion and reaction.

Stewart, D. Scott; Szuck, Matthew; Fried, Laurence E.

2011-06-01

27

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

28

Anisotropic properties in Fe-Pt thick film magnets

As-deposited Fe-Pt thick films prepared by a pulsed laser deposition method with the laser power higher than 5 W had L1{sub 0} ordered phase without a substrate heating system. As the laser power increased, the properties of the obtained films changed from isotropic to anisotropic ones. It was also confirmed that x-ray diffraction analysis agrees with the anisotropic phenomenon in crystalline structure with increasing laser power.

Nakano, M.; Shibata, S.; Yanai, T.; Fukunaga, H. [Department of Electrical and Electronic Engineering, Nagasaki University, Nagasaki 852-8521 (Japan)

2009-04-01

29

The anisotropic properties of high temperature superconductors - an ARPES study

NASA Astrophysics Data System (ADS)

It is now well established that cuprates are d-wave superconductors. Natural question arises concerning the symmetry of other electronic properties in these materials and their relation to anisotropic order parameter. We present our recent ARPES measurements of these properties performed on a the same sample of single cristal BISCO 2212.

Kaminski, Adam; Fretwell, Helen; Mesot, Joel; Rozenkrantz, Stephan; Djendjinovic, Marin; Campuzano, Juan; Randeria, Mohit; Norman, Michael; Sato, Takafumi; Takahashi, Takashi; Kadowaki, Kazuo; Hinks, David; Raffy, Helen

2001-03-01

30

Anisotropic Tribological Properties of Silicon Carbide

NASA Technical Reports Server (NTRS)

The anisotropic friction, deformation and fracture behavior of single crystal silicon carbide surfaces were investigated in two categories. The categories were called adhesive and abrasive wear processes, respectively. In the adhesive wear process, the adhesion, friction and wear of silicon carbide were markedly dependent on crystallographic orientation. The force to reestablish the shearing fracture of adhesive bond at the interface between silicon carbide and metal was the lowest in the preferred orientation of silicon carbide slip system. The fracturing of silicon carbide occurred near the adhesive bond to metal and it was due to primary cleavages of both prismatic (10(-1)0) and basal (0001) planes.

Miyoshi, K.; Buckley, D. H.

1980-01-01

31

Optical Properties of Anisotropic Core-Shell Pyramidal Particles

This paper describes an approach to fabricate anisotropic core-shell particles by assembling dielectric beads within fabricated noble metal pyramidal structures. Particles with gold (Au) shells and different dielectric cores were generated, and their optical properties were characterized by single particle spectroscopy. Because of their unique geometry, these particles exhibit multiple plasmon resonances from visible to near-IR wavelengths.

Sweeney, Christina M.; Hasan, Warefta; Nehl, Colleen L.; Odom, Teri W.

2009-01-01

32

NASA Astrophysics Data System (ADS)

The macroscopic transport properties in a disordered potential, namely diffusion and weak/strong localization, closely depend on the microscopic and statistical properties of the disorder itself. This dependence is rich in counter-intuitive consequences. It can be particularly exploited in matter wave experiments, where the disordered potential can be tailored and controlled, and anisotropies are naturally present. In this work, we apply a perturbative microscopic transport theory and the self-consistent theory of Anderson localization to study the transport properties of ultracold atoms in anisotropic two-dimensional (2D) and three-dimensional (3D) speckle potentials. In particular, we discuss the anisotropy of single-scattering, diffusion and localization. We also calculate disorder-induced shift of the energy states and propose a method to include it, which amounts to renormalizing energies in the standard on-shell approximation. We show that the renormalization of energies strongly affects the prediction for the 3D localization threshold (mobility edge). We illustrate the theoretical findings with examples which are relevant for current matter wave experiments, where the disorder is created with laser speckle. This paper provides a guideline for future experiments aiming at the precise location of the 3D mobility edge and study of anisotropic diffusion and localization effects in 2D and 3D.

Piraud, M.; Pezzé, L.; Sanchez-Palencia, L.

2013-07-01

33

TOPICAL REVIEW: Textured silicon nitride: processing and anisotropic properties

NASA Astrophysics Data System (ADS)

Textured silicon nitride (Si3N4) has been intensively studied over the past 15 years because of its use for achieving its superthermal and mechanical properties. In this review we present the fundamental aspects of the processing and anisotropic properties of textured Si3N4, with emphasis on the anisotropic and abnormal grain growth of ?-Si3N4, texture structure and texture analysis, processing methods and anisotropic properties. On the basis of the texturing mechanisms, the processing methods described in this article have been classified into two types: hot-working (HW) and templated grain growth (TGG). The HW method includes the hot-pressing, hot-forging and sinter-forging techniques, and the TGG method includes the cold-pressing, extrusion, tape-casting and strong magnetic field alignment techniques for ?-Si3N4 seed crystals. Each processing technique is thoroughly discussed in terms of theoretical models and experimental data, including the texturing mechanisms and the factors affecting texture development. Also, methods of synthesizing the rodlike ?-Si3N4 single crystals are presented. Various anisotropic properties of textured Si3 N4 and their origins are thoroughly described and discussed, such as hardness, elastic modulus, bending strength, fracture toughness, fracture energy, creep behavior, tribological and wear behavior, erosion behavior, contact damage behavior and thermal conductivity. Models are analyzed to determine the thermal anisotropy by considering the intrinsic thermal anisotropy, degree of orientation and various microstructure factors. Textured porous Si3N4 with a unique microstructure composed of oriented elongated ?-Si3N4 and anisotropic pores is also described for the first time, with emphasis on its unique mechanical and thermal-mechanical properties. Moreover, as an important related material, textured ?-Sialon is also reviewed, because the presence of elongated ?-Sialon grains allows the production of textured ?-Sialon using the same methods as those used for textured ?-Si3N4 and ?-Sialon. Corrections were made to this article on 24 September 2008.

Zhu, Xinwen; Sakka, Yoshio

2008-07-01

34

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

35

Computational methods for predicting drug transport in anisotropic and heterogeneous brain tissue.

Effective drug delivery for many neurodegenerative diseases or tumors of the central nervous system is challenging. Targeted invasive delivery of large macromolecules such as trophic factors to desired locations inside the brain is difficult due to anisotropy and heterogeneity of the brain tissue. Despite much experimental research, prediction of bio-transport phenomena inside the brain remains unreliable. This article proposes a rigorous computational approach for accurately predicting the fate of infused therapeutic agents inside the brain. Geometric and physiological properties of anisotropic and heterogeneous brain tissue affecting drug transport are accounted for by in-vivo diffusion tensor magnetic resonance imaging data. The three-dimensional brain anatomy is reconstructed accurately from subject-specific medical images. Tissue anisotropy and heterogeneity are quantified with the help of diffusion tensor imaging (DTI). Rigorous first principles physical transport phenomena are applied to predict the fate of a high molecular weight trophic factor infused into the midbrain. Computer prediction of drug distribution in humans accounting for heterogeneous and anisotropic brain tissue properties have not been adequately researched in open literature before. PMID:18550067

Linninger, Andreas A; Somayaji, Mahadevabharath R; Erickson, Terrianne; Guo, Xiaodong; Penn, Richard D

2008-07-19

36

Oxygen-driven anisotropic transport in ultra-thin manganite films

Transition metal oxides have a range of unique properties due to coupling of charge, spin, orbital and lattice degrees of freedom and nearly degenerate multiple ground states. These properties make them interesting for applications and for fundamental investigations. Here we report a new phase with abnormal transport anisotropy in La0.7Sr0.3MnO3 ultra-thin films under large tensile strain. This anisotropy is absent in films under smaller tensile strain or compressive strain. Furthermore, thickness and magnetic-field-dependent experiments suggest that the tensile-strain-induced two-dimensional character is crucial for the observed phenomena. X-ray absorption spectroscopy results indicate that this anisotropy is likely driven by O 2p orbital, which hybridizes with Mn 3d. Ab initio calculations confirm this result. Our results may help to understand the anisotropic transport behaviour observed in other systems.

Wang, Baomin; You, Lu; Ren, Peng; Yin, Xinmao; Peng, Yuan; Xia, Bin; Wang, Lan; Yu, Xiaojiang; Mui Poh, Sock; Yang, Ping; Yuan, Guoliang; Chen, Lang; Rusydi, Andrivo; Wang, Junling

2013-01-01

37

Anisotropic Diffusion Coefficient in a Cylindrical Cell by Integral Transport Theory

The anisotropic diffusion coefficient has been calculated in a cylindrical cell with use made of the integral transport theory. The previous method of calculating the diffusion coefficient requires much computer time to evaluate the generalized first-flight collision probabilities between two mesh points for a square cell. To circumvent this drawback, we introduce new calculation methods for determining the anisotropic diffusion

Toshikazu TAKEDA; Tamotsu SEKIYA

1973-01-01

38

NASA Astrophysics Data System (ADS)

Transformation field method (TFM) is developed to estimate the anisotropic dielectric properties of crystal composites having arbitrary shapes and dielectric properties of crystal inclusions, whose principal dielectric axis are different from those of anisotropic crystal matrix. The complicated boundary-value problem caused by inclusion shapes is circumvented by introducing a transformation electric field into the crystal composites regions, and the effective anisotropic dielectric responses are formulated in terms of the transformation field. Furthermore, the numerical results show that the effective anisotropic dielectric responses of crystal composites periodically vary as a function of the rotating angle between the principal dielectric axes of inclusion and matrix crystal materials. It is found that at larger inclusion volume fraction the inclusion shapes induce profound effect on the effective anisotropic dielectric responses.

Wei, En-Bo; Gu, Guo-Qing; Poon, Ying-Ming; Franklin, G. Shin

2010-02-01

39

Anisotropic transport in modulation-doped quantum-well structures

NASA Technical Reports Server (NTRS)

Anisotropic electron transport has been observed in GaAs modulation-doped quantum wells grown by molecular-beam epitaxy on a thick (001) Al(0.3)Ga(0.7)As buffer grown at 620 C. Thicker quantum wells (150, 200, and 300 A) show progressively less anisotropy, which vanishes for a 300-A quantum well. The degree of anisotropy is also reduced or eliminated by suspending growth of the Al(0.3)Ga(0.7)As for a period of 300 s prior to growing the GaAs quantum well. Growing the Al(0.3)Ga(0.7)As buffer at higher temperatures (680 C) also reduces the degree of anisotropy. Higher two-dimensional electron gas sheet densities result in less anisotropy.The anisotropy is eliminated by replacing the thick Al(0.3)Ga(0.7)As buffer with a periodic multilayer structure comprising 15 A of GaAs and 200 A of Al(0.3)Ga(0.7)As. The degree of anisotropy is related to the thickness and growth parameters of the Al(0.3)Ga(0.7)As layer grown just prior to the growth of the GaAs.

Radulescu, D. C.; Wicks, G. W.; Schaff, W. J.; Calawa, A.R.; Eastman, L. F.

1987-01-01

40

National Technical Information Service (NTIS)

The theoretical basis, implementation information and numerical results are presented for VARIANT (VARIational Anisotropic Neutron Transport), a FORTRAN module of the DIF3D code system at Argonne National Laboratory. VARIANT employs the variational nodal ...

G. Palmiotti C. B. Carrico E. E. Lewis

1995-01-01

41

Anisometric Transport of Ions and Particles in Anisotropic Tissue Spaces

The results of time-lapse measurements and electron microscopic observations on the diffusion of histological dyes, colloidal particles, and heavy metal salts in excised chicken breast tendon are reported. In all cases, the transport was found to be anisometric, the extent of the spreading being much greater parallel than perpendicular to the collagen fibers. The diffusion of colloidal gold was shown to be governed by a random diffusion process, with coefficients of 3 to 5 × 10-7 and 1 to 2 × 10-7 cm2/sec for the parallel and perpendicular directions, respectively; the anisotropy was attributed to steric hindrance. In the diffusion of uranyl nitrate, a sharp boundary appeared at the leading edge of the diffusate and advanced at a rate proportional to the square root of time. Electron micrographs showed uranyl nitrate clusters localized in space on the surface of the collagen fibrils and tightly bound to the polar amino acid regions of the macromolecule. A model was proposed involving diffusion with attrition, and predicted a sharp boundary advancing proportionally to the square root of time and to the 0.65 power of the initial diffusate concentration. Application of the model to the experimental results for uranyl nitrate gave a diffusion coefficient of 10 × 10-7 and 4 × 10-7 cm2/sec for the parallel and perpendicular directions, respectively, and a possible explanation of this large difference was advanced. The importance of anisometric transport in anisotropic tissues was indicated. ImagesFigure 1Figure 4Figure 5Figure 6

Grover, N. B.

1966-01-01

42

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

43

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

44

Anisotropic linear elastic properties of fractal-like composites.

In this work, the anisotropic linear elastic properties of two-phase composite materials, made up of square inclusions embedded in a matrix, are investigated. The inclusions present a fractal hierarchical distribution and are supposed to have the same Poisson's ratio as the matrix but a different Young's modulus. The effective elastic moduli of the medium are computed at each fractal iteration by coupling a position-space renormalization-group technique with a finite element analysis. The study allows to obtain and generalize some fundamental properties of fractal composite materials. PMID:21230552

Carpinteri, Alberto; Cornetti, Pietro; Pugno, Nicola; Sapora, Alberto

2010-11-01

45

Calculation of anisotropic properties of dental enamel from synchrotron data.

Obtaining information about the intrinsic structure of polycrystalline materials is of prime importance owing to the anisotropic behaviour of individual crystallites. Grain orientation and its statistical distribution, i.e. the texture, have an important influence on the material properties. Crystallographic orientations play an important role in all kinds of polycrystalline materials such as metallic, geological and biological. Using synchrotron diffraction techniques the texture can be measured with high local and angular resolving power. Here methods are presented which allow the spatial orientation of the crystallites to be determined and information about the anisotropy of mechanical properties, such as elastic modulus or thermal expansion, to obtained. The methods are adapted to all crystal and several sample symmetries as well as to different phases, for example with overlapping diffraction peaks. To demonstrate the abilities of the methods, human dental enamel has been chosen, showing even overlapping diffraction peaks. Likewise it is of special interest to learn more about the orientation and anisotropic properties of dental enamel, since only basic information is available up to now. The texture of enamel has been found to be a tilted fibre texture of high strength (up to 12.5×). The calculated elastic modulus is up to 155 GPa and the thermal expansion up to 22.3 × 10(-6)°C(-1). PMID:21685670

Raue, Lars; Klein, Helmut

2011-07-01

46

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

47

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

48

The theoretical basis, implementation information and numerical results are presented for VARIANT (VARIational Anisotropic Neutron Transport), a FORTRAN module of the DIF3D code system at Argonne National Laboratory. VARIANT employs the variational nodal method to solve multigroup steady-state neutron diffusion and transport problems. The variational nodal method is a hybrid finite element method that guarantees nodal balance and permits spatial

G. Palmiotti; C. B. Carrico; E. E. Lewis

1995-01-01

49

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

50

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. PMID:23848788

Blazevski, Daniel; del-Castillo-Negrete, Diego

2013-06-01

51

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

52

Transport properties of ferrofluids.

Long-time self-diffusion coefficients of ferrofluid suspensions are derived from an effective Langevin equation approach. The dependences of these transport properties on the volume fraction of particles and the strength of interparticle interaction are investigated. Strong reduction of the rotational and the translational Brownian motion of the particles is manifested upon increase of particle-particle interaction or ferrofluid concentration. PMID:14524753

Hernández-Contreras, M; Ruíz-Estrada, H

2003-09-01

53

Properties of wave functions in homogeneous anisotropic media

NASA Astrophysics Data System (ADS)

The general solutions of the first, second, third, and fourth kinds to the wave equation in homogeneous anisotropic media are expressed by integrals over a finite range. The convergence of the series solution of wave functions in homogeneous anisotropic media [Phys. Rev. E 47, 664 (1993)] is discussed. The use of the wave functions in anisotropic media is demonstrated. The theory is expounded via an illustrative example of a two-dimensional scalar case. The analytical solution of plane-wave scattering by a conducting circular cylinder coated with anisotropic materials is formulated in terms of the series of wave functions for anisotropic media. Numerical results show that the solution in terms of wave functions of various kinds in anisotropic media gives essentially the same radar cross sections as obtained by Beker, Umashankar, and Taflove [Electromagnetics 10, 387 (1990)] using a different approach. Numerical results in the resonance region are presented for reference purposes. The analysis of this paper can be easily generalized to vector and tensor wave functions in homogeneous anisotropic media.

Ren, Wei; Wu, Xin Bao; Yi, Zhang; Lin, Wei Gan

1995-01-01

54

Electric field activated nonlinear anisotropic charge transport in doped polypyrrole

NASA Astrophysics Data System (ADS)

Electric field activated nonlinear transport is investigated in polypyrrole thin film in both in-plane and out-of-plane geometries down to 5 K and strong anisotropy is observed. A morphological model is suggested to explain the anisotropy through inter-chain and intra-chain transport. The deviation from the variable range hopping at low temperature is accounted by fluctuation assisted transport. From Zabrodaskii plots, it is found that electric field can tune the transport from insulating to metallic regime. Glazman-Matveev model is used to describe the nonlinear conduction. Field scaling analysis shows that conductance data at different temperature falls on to a single curve. Nonlinearity exponent, mT and characteristic length, LE are estimated to characterize the transport in both the geometries.

Varade, Vaibhav; Anjaneyulu, P.; Suchand Sangeeth, C. S.; Ramesh, K. P.; Menon, R.

2013-12-01

55

Anisotropic vanadium dioxide sculptured thin films with superior thermochromic properties.

VO2 (M) STF through reduction of V2O5 STF was prepared. The results illustrate that V2O5 STF can be successfully obtained by oblique angle thermal evaporation technique. After annealing at 550 °C/3 min, the V2O5 STF deposited at 85° can be easily transformed into VO2 STF with slanted columnar structure and superior thermochromic properties. After deposition SiO2 antireflective layer, Tlum of VO2 STF is enhanced 26% and ?Tsol increases 60% compared with that of normal VO2 thin films. Due to the anisotropic microstructure of VO2 STF, angular selectivity transmission of VO2 STF is observed and the solar modulation ability is further improved from 7.2% to 8.7% when light is along columnar direction. Moreover, the phase transition temperature of VO2 STF can be depressed into 54.5 °C without doping. Considering the oblique incidence of sunlight on windows, VO2 STF is more beneficial for practical application as smart windows compared with normal homogenous VO2 thin films. PMID:24067743

Sun, Yaoming; Xiao, Xiudi; Xu, Gang; Dong, Guoping; Chai, Guanqi; Zhang, Hua; Liu, Pengyi; Zhu, Hanmin; Zhan, Yongjun

2013-01-01

56

Properties of Anisotropic Disordered Superconductor System in Normal Metal. Abstract.

National Technical Information Service (NTIS)

An array of superconducting fibers in a matrix of normal metal is considered, a disordered but unidirectionally oriented and thus strongly anisotropic array having a high lossless current carrying capacity in a strong electric field. First is calculated t...

L. G. Aslamazov A. A. Dyachkov S. V. Lempitskiy

1987-01-01

57

Ultrasonic evaluation of interfacial properties in imperfect anisotropic layered substrates

Interface conditions in layered substrates are critical to the performance of these materials. Most studies of interface conditions in layered substrates are confined to the extreme cases and give no details about the intermediate cases. In this study the lowest order mode of the generalized Lamb wave was used to examine the interfacial properties of imperfect layered substrates. Anisotropic specimens of various configurations with controlled interface conditions were made with a meshed intervening layer technique. It was noted that at very low and very high frequencies the effect of anisotropy of the dispersion curve in a silicon layered substrate was significant. The results also showed that the position of the turning point in the dispersion curve was sensitive to bond quality variation. As the quality of bonding decreased, this turning point shifted toward low velocities and frequencies and finally resembled that of the completely misbonded case. Furthermore, empirical formula which relate the stiffness constant and the position of the turning point for a partially bonded material were also obtained. It is noteworthy that the position of the turning point does not vary significantly with orientation. By incorporating an effective interface layer into a multiple layer formulation and comparing the calculated results with the experimental data, the interfacial properties of the layered substrate were evaluated. Moreover, the shape of the dispersion curve of this lowest order mode was found to be dependent on the bond quality and anisotropy, but the dominating factor was the bond quality. Therefore, the turning point in the dispersion curve of the lowest order mode may be used to assess bond quality in an anistropic layered substrate.

Ko, R.T.

1993-01-01

58

Enhanced charge transport kinetics in anisotropic, stratified photoanodes.

The kinetics of charge transport in mesoporous photoanodes strongly constrains the design and power conversion efficiencies of dye sensitized solar cells (DSSCs). Here, we report a stratified photoanode design with enhanced kinetics achieved through the incorporation of a fast charge transport intermediary between the titania and charge collector. Proof of concept photoanodes demonstrate that the inclusion of the intermediary not only enhances effective diffusion coefficients but also significantly suppresses charge recombination, leading to diffusion lengths two orders of magnitude greater than in standard mesoporous titania photoanodes. The intermediary concept holds promise for higher-efficiency DSSCs. PMID:24467298

Yazdani, Nuri; Bozyigit, Deniz; Utke, Ivo; Buchheim, Jakob; Youn, Seul Ki; Patscheider, Jörg; Wood, Vanessa; Park, Hyung Gyu

2014-02-12

59

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

60

Anisotropic heat transport in integrable and chaotic 3-D magnetic fields

A study of anisotropic heat transport in 3-D chaotic magnetic fields is presented. The approach is based on the recently proposed Lagrangian-Green s function (LG) method in Ref. [1] that allows an efficient and accurate integration of the parallel transport equation applicable to general magnetic fields with local or non-local parallel flux closures. We focus on reversed shear magnetic field configurations known to exhibit separatrix reconnection and shearless transport barriers. The role of reconnection and magnetic field line chaos on temperature transport is studied. Numerical results are presented on the anomalous relaxation of radial temperature gradients in the presence of shearless Cantori partial barri- ers. Also, numerical evidence of non-local effective radial temperature transport in chaotic fields is presented. Going beyond purely parallel transport, the LG method is generalized to include finite perpendicular diffusivity, and the problem of temperature flattening inside a magnetic island is studied.

Del-Castillo-Negrete, Diego B [ORNL; Blazevski, D. [University of Texas, Austin; Chacon, Luis [ORNL

2012-01-01

61

The anisotropic mechanical properties of magnetically aligned fibrin gels were measured by magnetic resonance elastography (MRE) and by a standard mechanical test: unconfined compression. Soft anisotropic biomaterials are notoriously difficult to characterize, especially in vivo. MRE is well-suited for efficient, non-invasive, and non-destructive assessment of shear modulus. Direction-dependent differences in shear modulus were found to be statistically significant for gels

Ravi Namani; Matthew D. Wood; Shelly E. Sakiyama-Elbert; Philip V. Bayly

2009-01-01

62

An Algorithm for the Transport of Anisotropic Neutrons

NASA Technical Reports Server (NTRS)

One major obstacle to human space exploration is the possible limitations imposed by the adverse effect of long-term exposure to the space environment. Even before human spaceflight began, the potentially brief exposure of astronauts to the very intense random solar particle events (SPE) were of great concern. A new challenge appears in deep space exploration from exposure to the low-intensity heavy-ion flux of the galactic cosmic rays (GCR) since the missions are of long duration and the accumulated GCR exposures can be high. Because cancer induction rates increase behind low to rather large thicknesses of aluminum shielding, according to available biological data on mammalian exposures to GCR like ions, the shield requirements for a Mars mission are prohibitively expensive in terms of mission launch costs. Therefore, a critical issue in the Human Exploration and Development of Space enterprise is cost effective mitigation of risk associated with ionizing radiation exposure. In order to estimate astronaut risk to GCR exposure and associated cancer risks and health hazards, it is necessary to do shield material studies. To determine an optimum radiation shield material it is necessary to understand nuclear interaction processes such as fragmentation and secondary particle production which is a function of energy dependent cross sections. This requires knowledge of material transmission characteristics either through laboratory testing or improved theoretical modeling. Here ion beam transport theory is of importance in that testing of materials in the laboratory environment generated by particle accelerators is a necessary step in materials development and evaluation for space use. The approximations used in solving the Boltzmann transport equation for the space setting are often not sufficient for laboratory work and those issues are a major emphasis of the present work.

Tweed, J.

2005-01-01

63

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

64

On the effective electroelastic properties of microcracked generally anisotropic solids

In this study we first obtain the explicit expressions for the 15 effective reduced elastic compliances of an elastically\\u000a anisotropic solid containing multiple microcracks with an arbitrary degree of alignment under two-dimensional deformations\\u000a within the framework of the non-interaction approximation (NIA). Under special situations, our results can reduce to the classical\\u000a ones derived by Bristow (J Appl Phys 11: 81–85,

Xu Wang; George A. Gazonas; Michael H. Santare

2009-01-01

65

Imaging anisotropic and viscous properties of breast tissue by magnetic resonance-elastography

MR-elastography is a new technique for assessing the vis- coelastic properties of tissue. One current focus of elastogra- phy is the provision of new physical parameters for improving the specificity in breast cancer diagnosis. This analysis de- scribes a technique to extend the reconstruction to anisotropic elastic properties in terms of a so-called transversely isotropic model. Viscosity is treated as

R. Sinkus; M. Tanter; S. Catheline; J. Lorenzen; C. Kuhl; E. Sondermann; M. Fink

2005-01-01

66

Strong crystal anisotropy of magneto-transport property in Fe 3Si epitaxial film

NASA Astrophysics Data System (ADS)

This work reports the magneto-anisotropy property of epitaxial Fe 3Si film grown on GaAs (0 0 1) substrate by molecular beam epitaxy (MBE). We present a strong dependence of anisotropic magnetoresistance (MR) on field in the Fe 3Si film plane. The electron transport behavior is highly dependent on the direction of the current either parallel or perpendicular to the magnetic easy axis. By altering the direction of current from magnetic hard axis to magnetic easy axis, the unconventional behavior switches to normal anisotropic magnetoresistance (AMR). In addition, the anisotropic behaviors were also observed from the magneto-optic Kerr effect (MOKE) measurement, which demonstrates unusual anisotropic properties with the crystalline anisotropic constant K1=(3.8±0.2)×10 4 erg/cm 3 and uni-axial anisotropy Ku=(1.2±0.04)×10 4 erg/cm 3. The ratio K1/ Ku was used to account for the MR.

Hung, H. Y.; Huang, S. Y.; Chang, P.; Lin, W. C.; Liu, Y. C.; Lee, S. F.; Hong, M.; Kwo, J.

2011-05-01

67

Electronic Structure and Transport Properties of Intermetallics.

National Technical Information Service (NTIS)

The electronic interactions responsible for the unusual properties of several important classes of materials (including the highly anisotropic layered dichalcogenides, and network and cage structure materials and pseudobinary alloys) have been investigate...

A. J. Freeman D. E. Ellis L. B. Welsh

1975-01-01

68

The Isotropy Problem of Ultra-High Energy Cosmic Rays: The Effects of Anisotropic Transport

NASA Astrophysics Data System (ADS)

Time dependent anisotropic transport of ultra-high energy cosmic rays (UHECRs) from point-like sources in the Galaxy is calculated in various ways. To fully account for the discreteness of UHECR sources in space and time, the Monte Carlo method is used to randomly place sources in the Galaxy and calculate the anisotropy of UHECR flux, given specific realisations of source distribution. We show that reduction in the rate of cross-field transport reduces the anisotropy. However, if the crossfield transport is very small, drift of UHECRs in the Galactic magnetic field (GMF) becomes the dominant contributor to the anisotropy. Test particle simulations further illustrate the effect of drift and verify our analytical calculation. The surprisingly low anisotropy measured by Auger can be interpreted as intermittency of UHECR sources, without invoking a flat source distribution and/or a high source rate. Frequent events that follow star formation, such as hypernovae, imply an anisotropy that exceeds the Auger limit.

Kumar, Rahul; Eichler, David

2013-04-01

69

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

2014-01-01

70

TRANSPORT PROPERTIES OF CARTILAGINOUS TISSUES

Cartilaginous tissues, such as articular cartilage and intervertebral disc, are avascular tissues which rely on transport for cellular nutrition. Comprehensive knowledge of transport properties in such tissues is therefore necessary in the understanding of nutritional supply to cells. Furthermore, poor cellular nutrition in cartilaginous tissues is believed to be a primary source of tissue degeneration, which may result in osteoarthritis (OA) or disc degeneration. In this mini-review, we present an overview of the current status of the study of transport properties and behavior in cartilaginous tissues. The mechanisms of transport in these tissues, as well as experimental approaches to measuring transport properties and results obtained are discussed. The current status of bioreactors used in cartilage tissue engineering is also presented.

Jackson, AR; Gu, WY

2009-01-01

71

Transport of momentum and scalar in turbulent flows with anisotropic dispersive waves

NASA Astrophysics Data System (ADS)

Most geophysical flows encompass turbulence and internal and/or Rossby waves. We demonstrate that these two different classes of waves cause remarkably similar anomalies in the turbulent transport. While all scales in both types of flows contribute to the momentum diffusion, the vertical (diapycnal) scalar diffusion in stratified flows and lateral diffusion in ?-plane turbulence can be carried out only by turbulent eddies whose size is smaller than the thresholds of turbulence anisotropization. Beyond these thresholds, both flows become dominated by waves that provide no contribution to the scalar diffusion. Stably stratified flows exhibit enhanced isopycnal diffusion of both momentum and scalar. These results shed new light on the Osborn mixing model, diapycnal and isopycnal viscosity and diffusivity, absence of the critical gradient Richardson number, and large scale meridional transport.

Sukoriansky, Semion; Dikovskaya, Nadejda; Galperin, Boris

2009-07-01

72

Transport properties of holographic defects

We study the charge transport properties of fields confined to a (2+1)-dimensional defect coupled to (3+1)-dimensional super-Yang-Mills at large-Nc and strong coupling, using AdS\\/CFT techniques applied to linear response theory. The dual system is described by Nf probe D5- or D7-branes in the gravitational background of Nc black D3-branes. Surprisingly, the transport properties of both defect CFT's are essentially identical

Robert C. Myers; Matthias C. Wapler

2008-01-01

73

The unusual properties of anisotropic systems of quasiparticles in superfluid 4He

NASA Astrophysics Data System (ADS)

We discuss a number of unusual phenomena discovered recently in anisotropic quasiparticle systems in superfluid 4He. These include the creation of high-energy phonons by a pulse of low-energy phonons, the suprathermal distribution of high-energy phonons in long phonon pulses, the mesa shape of the angular distribution of low-energy phonons, and the creation of a ``hot line'' when two-phonon pulses cross. The thermodynamic properties of anisotropic quasiparticle systems of He II are derived for all degrees of anisotropy.

Adamenko, I. N.; Nemchenko, K. E.; Slipko, V. A.; Wyatt, A. F. G.

2007-09-01

74

The anisotropic mechanical properties of a Ti matrix composite reinforced with SiC fibers

NASA Astrophysics Data System (ADS)

The anisotropic mechanical properties of a Ti alloy composite reinforced with SiC fibers have been investigated and rationalized using analytical models. The appropriate material model for this composite involves the following features: an interface that debonds and slides, a flaw insensitive ductile matrix, and high-strength elastic fibers subject to residual compressive stress caused by thermal expansion mismatch. This, model is broadly consistent with the longitudinal, transverse, and shear properties of the composite.

Jansson, S.; Dève, H. E.; Evans, A. G.

1991-12-01

75

Transport Properties of Nanostructures

The current-voltage (I-V) properties of an InP nanowire and a CdS nanosheet are studied. Back to back metal semiconductor metal contacts are modeled based on thermionic emission theory and field emission theory. These are used to explain the I-V characteristics of these nanostructures which enables measurement of the important intrinsic properties including donor density and electrical conductivity of nanostructures. Photolithography

Amir Maharjan; H. E. Jackson; L. M. Smith; A. Kogan; J. Y. Rice; C. Jagadish

2008-01-01

76

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

77

Identifying the complete space of feasible anisotropic properties in polycrystalline microstructures

NASA Astrophysics Data System (ADS)

Current engineering design focuses mainly on the geometrical optimization of a component, while the material selection is often limited to picking a material based on a set of properties reported in handbooks. The inherent anisotropic behavior of materials is often ignored in the design process, and is usually assumed to be addressed by the safety factor employed. This simple treatment of material selection in the design and optimization process often leads to inefficient design. In this study, we present a rigorous and a comprehensive procedure that facilitates the treatment of material microstructure as a continuous design variable in the elastic-plastic design of structural components made from anisotropic polycrystalline metals. The mechanical behavior of a metal is influenced by several details of its microstructure, including chemical composition, grain size distribution, crystallographic texture, among others. Here, we focus on the crystallographic texture (also called Orientation Distribution Function or ODF) as the main microstructural parameter controlling the anisotropic elastic-plastic properties of interest. The property closures that we have delineated describe the complete set of feasible property combinations for a given polycrystalline material system, while accounting for all possible textures. The property closures are obtained here using a spectral representation of ODF and its relationship with rigorous first order bounds on the effective properties of interest in design. Using the proposed methodology, we successfully developed a few examples of property closures for face centered cubic (fcc) and hexagonal close-packed (hcp) metals. The mechanical anisotropic behavior at the single crystal level for face centered cubic metals has been characterized using the nanoindentation technique along with orientation imaging mapping. This methodology shows promising possibilities to extract fundamental elastic and plastic parameters. However, the methods proposed in the literature to extract data from the load-displacement curves cause discrepancy between the experimental and expected values. The discrepancy could be attributed to the induced plastic deformation among other factors.

Proust, Gwenaelle

78

Anisotropic nutrient transport in three-dimensional single species bacterial biofilms.

The ability for a biofilm to grow and function is critically dependent on the nutrient availability, and this in turn is dependent on the structure of the biofilm. This relationship is therefore an important factor influencing biofilm maturation. Nutrient transport in bacterial biofilms is complex; however, mathematical models that describe the transport of particles within biofilms have made three simplifying assumptions: the effective diffusion coefficient (EDC) is constant, the EDC is that of water, and/or the EDC is isotropic. Using a Monte Carlo simulation, we determined the EDC, both parallel to and perpendicular to the substratum, within 131 real, single species, three-dimensional biofilms that were constructed from confocal laser scanning microscopy images. Our study showed that diffusion within bacterial biofilms was anisotropic and depth dependent. The heterogeneous distribution of bacteria varied between and within species, reducing the rate of diffusion of particles via steric hindrance. In biofilms with low porosity, the EDCs for nutrient transport perpendicular to the substratum were significantly lower than the EDCs for nutrient transport parallel to the substratum. Here, we propose a reaction-diffusion model to describe the nutrient concentration within a bacterial biofilm that accounts for the depth dependence of the EDC. PMID:22124974

Van Wey, A S; Cookson, A L; Soboleva, T K; Roy, N C; McNabb, W C; Bridier, A; Briandet, R; Shorten, P R

2012-05-01

79

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

80

The diverse atomic configurations induce the anisotropic surface properties. For investigating anisotropic phenomena, we developed a rotational positioning system adapted to atomic force microscope (AFM). This rotational positioning system is applied to revolve the measured sample to defined angular direction, and it composed of an inertial rotational stepper and a visual angular measurement. The inertial rotational stepper with diameter 30 mm and height 7.6 mm can be easily attached to the AFM-system built in any general optical microscope. Based on a clearance less bearing and the inertial driving method, its bidirectional angular resolution reaches 0.005 deg. per step. For realizing a close-loop controlled angular positioning function, the visual measurement method is utilized. Through the feedback control, the angular positioning error is less than 0.01 deg. For verifying the system performance, we used it to investigate the anisotropic surface properties of graphite. Through a modified cantilever tip, the atomic-scale stick-slip, and the anisotropic friction phenomena can be distinctly detected.

Liao, H.-S.; Juang, B.-J. [Department of Mechanical Engineering, National Taiwan University, 10617, Taipei, Taiwan (China); Institute of Physics, Academia Sinica, 11529, Taipei, Taiwan (China); Chang, W.-C.; Lai, W.-C.; Chang, C.-S. [Institute of Physics, Academia Sinica, 11529, Taipei, Taiwan (China); Huang, K.-Y. [Department of Mechanical Engineering, National Taiwan University, 10617, Taipei, Taiwan (China)

2011-11-15

81

Anisotropic nanostructures with precise orientations or sharp corners display unique properties that may be useful in a variety of applications; however, precise control over the anisotropy of geometric features, using a simple and reproducible large-area fabrication technique, remains a challenge. Here, we report the fabrication of highly uniform polymeric and metallic nanostructure arrays prepared using prism holographic lithography (HL) in such a way that the isotropy that can be readily and continuously tuned. The prism position on the sample stage was laterally translated to vary the relative intensities of the four split beams, thereby tuning the isotropy of the resulting polymer nanostructures through the following shapes: circular nanoholes, elliptical nanoholes, and zigzag-shaped nanoarrays. Corresponding large-area, defect-free anisotropic metallic nanostructures could then be fabricated using an HL-featured porous polymer structure as a milling mask. Removal of the polymer mask left zigzag-shaped metallic nanostructure arrays in which nanogaps separated adjacent sharp edges. These structures displayed two distinct optical properties, depending on the direction along which the excitation beam was polarized (longitudinal and transverse modes) incident on the array. Furthermore, bidirectional anisotropic wetting was observed on the anisotropic polymer nanowall array surface. PMID:24020508

Jeon, Hwan Chul; Jeon, Tae Yoon; Yang, Seung-Man

2013-10-01

82

NASA Astrophysics Data System (ADS)

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.

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

2011-11-01

83

Imaging anisotropic and viscous properties of breast tissue by magnetic resonance-elastography.

MR-elastography is a new technique for assessing the viscoelastic properties of tissue. One current focus of elastography is the provision of new physical parameters for improving the specificity in breast cancer diagnosis. This analysis describes a technique to extend the reconstruction to anisotropic elastic properties in terms of a so-called transversely isotropic model. Viscosity is treated as being isotropic. The particular model chosen for the anisotropy is appealing because it is capable of describing elastic shear anisotropy of parallel fibers. The dependence of the reconstruction on the particular choice of Poisson's ratio is eliminated by extracting the compressional displacement contribution using the Helmholtz-Hodge decomposition. Results are presented for simulations, a polyvinyl alcohol breast phantom, excised beef muscle, and measurements in two patients with breast lesions (invasive ductal carcinoma and fibroadenoma). The results show enhanced anisotropic and viscous properties inside the lesions and an indication for preferred fiber orientation. PMID:15678538

Sinkus, R; Tanter, M; Catheline, S; Lorenzen, J; Kuhl, C; Sondermann, E; Fink, M

2005-02-01

84

NASA Astrophysics Data System (ADS)

Anisotropic polymeric materials are ubiquitous. They can form via self assembly, external mechanical deformation or by geometric confinement. Important examples of anisotropic polymeric materials include liquid crystalline polymers and elastomers, amorphous rubber networks, confined films and grafted polymer brushes. A common feature of these materials is the anisotropic conformation of the constituent polymer chains which leads to significant modification of interchain packing correlations and thermodynamics properties. Polymer liquid state statistical mechanical methods have been generalized to treat the structure, segmental orientation, thermodynamics and mechanical response of dense polymer fluids and crosslinked networks. The consequences of interchain repulsions and chain connectivity are explicitly taken into account. The strain-induced orientational order parameter of flexible chains is predicted to scale as the inverse of the square root of the degree of polymerization and increase in a supralinear manner with segmental concentration. Two nonclassical contributions to stress and linear modulus arise from the influence of anisotropic packing correlations on the excess free energy. Overall the theory is in good agreement with NMR and mechanical experiments and computer simulations. The thermomechanical properties of nematic elastomers have also been studied. Significant softening of the modulus is found as the isotropic-nematic transition is approached. The phenomenon of spontaneous distortion, relevant to artificial muscles, sensors and actuator applications, emerges in a manner correlated directly with the orientational order parameter. Comparison of our theoretical predictions with experiments on thermotropic liquid crystalline polymers shows good qualitative and semi-quantitative agreements. A dynamical theory has been developed for the onset or crossover temperature (Tc) to highly non-Arrenhius activated relaxation regime in deeply supercooled polymer liquids. Alignment and/or deformation modify thermodynamic and structural properties thereby inducing anisotropic segmental dynamics. Either suppression or elevation of ( Tc) is predicted depending on the nature of anisotropy. Results have been obtained for liquid crystalline polymers, thin films, rubber networks and grafted polymer brushes. The underlying mechanism for ( Tc) shifts is this theory is anisotropy of the degree of coil interpenetration.

Oyerokun, Folusho Taiwo

85

Search for anisotropic electrical properties in amorphous germanium.

NASA Technical Reports Server (NTRS)

Measurement of low-field and high-field resistivity in amorphous Ge in both the planar and transverse directions on the same samples, whose thickness ranged from 0.4 to 4 microns. No anisotropy was found, suggesting that the voids recently described by Galeener (1971) may not play a significant role in these transport processes.

Clark, A. H.; Burke, T. J.

1972-01-01

86

Transport properties of uranium dioxide

In order to provide reliable and consistent data on the thermophysical properties of reactor materials for reactor safety studies, this revision is prepared for the transport properties of the uranium dioxide portion of the fuel property section of the report Properties for LMFBR Safety Analysis. Since the original report was issued in 1976, measurements of thermal diffusivity and emissivity have been made. In addition to incorporating this new data, new equations have been derived to fit the thermal diffusivity and thermal conductivity data. This analysis is consistent with the analysis of enthalpy and heat capacity. A new form of equation for the emissivity is also given. The present report comprises the transport part of the UO/sub 2/ portion of section A of the planned complete revision of Properties for LMFBR Safety Analysis.

Fink, J.K.; Chasanov, M.G.; Leibowitz, L.

1981-04-01

87

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

88

Fast and highly anisotropic thermal transport through vertically aligned carbon nanotube arrays

NASA Astrophysics Data System (ADS)

This letter reports on fast and highly anisotropic thermal transport through millimeter-tall, vertically aligned carbon nanotube arrays (VANTAs) synthesized by chemical vapor deposition on Si substrates. Thermal diffusivity measurements were performed for both longitudinal and transverse to the nanotube alignment direction, with longitudinal values as large as 2.1+/-0.2 cm2/s and anisotropy ratios as large as 72. Longitudinal thermal conductivities of 15.3+/-1.8 W/(m K) for porous 8+/-1 vol % VANTAs in air and 5.5+/-0.7 W/(m K) for epoxy-infiltrated VANTAs already exceed those of phase-changing thermal interface materials used in microelectronics. Data suggest that further improvements are possible through optimization of density and defects in the arrays.

Ivanov, Ilia; Puretzky, Alexander; Eres, Gyula; Wang, Hsin; Pan, Zhengwei; Cui, Hongtao; Jin, Rongying; Howe, Jane; Geohegan, David B.

2006-11-01

89

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

An analytic theory of nonlinear pressure-induced magnetic island formation using a boundary layer analysis is presented. This theory extends previous work by including the effects of finite parallel heat transport and is applicable to general three dimensional magnetic configurations. In this work, particular attention is paid to the role of finite parallel heat conduction in the context of pressure-induced island physics. It is found that localized currents that require self-consistent deformation of the pressure profile, such as resistive interchange and bootstrap currents, are attenuated by finite parallel heat conduction when the magnetic islands are sufficiently small. However, these anisotropic effects do not change saturated island widths caused by Pfirsch-Schlueter current effects. Implications for finite pressure-induced island healing are discussed.

Schlutt, M. G.; Hegna, C. C. [University of Wisconsin-Madison, 1500 Engineering Drive, 510 ERB, Madison, Wisconsin 53706 (United States)

2012-08-15

90

The transport properties of graphene.

We review the transport properties of graphene, considering both the case of bulk graphene and that of nanoribbons of this material at zero magnetic field. We discuss: Klein tunneling, transport by evanescent waves when the chemical potential crosses the Dirac point, the conductance of narrow graphene ribbons, the optical conductivity of pristine graphene, and the effect of disorder on the DC conductivity of graphene. PMID:21693962

Peres, N M R

2009-08-12

91

Dimers of partially oxygen-bridged triarylamines were designed and synthesized as hole-transporting materials. X-ray structural analyses revealed that these compounds form on-top ?-stacking aggregates in the crystalline state. TRMC measurements showed that high levels of anisotropic charge transport were induced in the direction of the ?-stacking. Surprisingly, even in vacuum-deposited amorphous films, these compounds retained some of the face-on ?-stacking, thus facilitating an out-of-plane carrier mobility. PMID:24764307

Wakamiya, Atsushi; Nishimura, Hidetaka; Fukushima, Tatsuya; Suzuki, Furitsu; Saeki, Akinori; Seki, Shu; Osaka, Itaru; Sasamori, Takahiro; Murata, Michihisa; Murata, Yasujiro; Kaji, Hironori

2014-06-01

92

Systematic study of anisotropic properties of CeNiGe2

NASA Astrophysics Data System (ADS)

We have studied the anisotropic properties of CeNiGe2 by measuring the electrical resistivity, magnetic susceptibility, and magnetization. It is confirmed that CeNiGe2 undergoes two-step antiferromagnetic transition at TNI=4 K and TNII=3 K as reported earlier on polycrystalline samples. CeNiGe2 is found to exhibit highly anisotropic properties with an easy magnetization axis along the longest crystallographic b direction. The magnetization ratio M(H?b)/M(H?b) at 2 K is estimated to be about 15 at 5 T. The resistivity ratio ??b/??b increases from 5 to 65 on heating from 2 to 200 K. The in-plane resistivity ??b(T) shows double maxima typical of that expected when an interplay of crystal-field and Kondo effects plays a role.

Jung, M. H.; Lacerda, A. H.; Pagliuso, P. G.; Sarrao, J. L.; Thompson, J. D.

2002-05-01

93

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

94

Anisotropic magnetic properties of obliquely deposited Ni films

Magnetic properties of evaporated nickel films, deposited onto 75 µm thick 300 H Kapton substrates by evaporation at oblique off-normal angles of incidence, a were investigated by SQUID magnetometry. We found that, in the film plane, the direction of easy magnetization lay perpendicular to the incidence plane for films deposited at a s, the easy axis changed to the direction

T. Otiti

2004-01-01

95

Anisotropic Thermal Properties of Single-Wall Carbon Nanotube Reinforced Nanoceramics

Dense single-wall carbon nanotube (SWCNT) reinforced alumina nanocomposites have been fabricated by novel spark-plasma-sintering (SPS) technique. Anisotropic thermal properties have been found in the carbon nanotube composites. The introduction of ropes of SWCNT gives rise to a decrease of the transverse thermal diffusivity with increasing carbon nanotube content while it does not change the in-plane thermal diffusivity. This is scientifically interesting and technologically important for the development of materials for novel thermal barrier coatings.

Zhan, Guodong; Kuntz, Joshua D.; Wang, Hsin; Wang, Chong M.; Mukherjee, Amiya K.

2004-07-01

96

Anisotropic optical property of an asymmetric bideposition Ta2O5 film: fabrication and measurement

To develop diverse anisotropic thin films, asymmetric bideposition technique is introduced to fabricate tilt columnar Ta2O5 films with biaxial optical property. The asymmetric bideposition is achieved using two different opposite deposition angles (a+,a-) and two different thicknesses of opposite deposited subdeposits. The two sets of Ta2O5 columnar thin films associated with deposited subdeposits (d+,d-)=(5.2,2.8) are prepared at the opposite deposition

Yi-Jun Jen; Chia-Feng Lin; Tai-Hung Yu; Chun-Jung Lai

2011-01-01

97

Anisotropic etching and electrochemical etch-stop properties of single-crystal silicon in tetramethylammonium hydroxide (TMAH):\\u000a isopropyl alcohol (IPA) solutions containing pyrazine were investigated. With the addition of IPA to TMAH solution, an improvement\\u000a in flatness on the etching front and a reduction in undercutting were observed, but the etch rate on (100) silicon decreased.\\u000a However, the (100) silicon etch rate is improved

Gwiy-Sang Chung

2001-01-01

98

Analytical Approach to Predict Anisotropic Material Properties from Cup Drawings

Typical beverage can alloys have limited elongation (about 3–5%) under uniaxial tension. However, in order to obtain correct\\u000a material properties, it is recommended to have elongations over 10 percent. Thus, it is very difficult to predict stable r-value\\u000a and stress directionalities experimentally, which are essential for FE simulation of rigid-packing sheet forming operation.\\u000a An innovative simplified analytical approach that relates

J. W. Yoon; R. E. Dick; F. Barlat

2008-01-01

99

Anisotropic magnetic properties and crystal electric field studies on CePd2Ge2 single crystal.

The anisotropic magnetic properties of the antiferromagnetic compound CePd2Ge2, crystallizing in the tetragonal crystal structure have been investigated in detail on a single crystal grown by the Czochralski method. From the electrical transport, magnetization and heat capacity data, the Néel temperature is confirmed to be 5.1 K. Anisotropic behaviour of the magnetization and resistivity is observed along the two principal crystallographic directions-namely, [100] and [001]. The isothermal magnetization measured in the magnetically ordered state at 2 K exhibits a spin reorientation at 13.5 T for the field applied along the [100] direction, whereas the magnetization is linear along the [001] direction attaining a value of 0.94 ?(B)/Ce at 14 T. The reduced value of the magnetization is attributed to the crystalline electric field (CEF) effects. A sharp jump in the specific heat at the magnetic ordering temperature is observed. After subtracting the phononic contribution, the jump in the heat capacity amounts to 12.5 J K(-1)mol(-1) which is the expected value for a spin ½ system. From the CEF analysis of the magnetization data the excited crystal field split energy levels were estimated to be at 120 K and 230 K respectively, which quantitatively explains the observed Schottky anomaly in the heat capacity. A magnetic phase diagram has been constructed based on the field dependence of magnetic susceptibility and the heat capacity data. PMID:24097258

Maurya, Arvind; Kulkarni, R; Dhar, S K; Thamizhavel, A

2013-10-30

100

Anisotropic magnetic properties and crystal electric field studies on CePd2Ge2 single crystal

NASA Astrophysics Data System (ADS)

The anisotropic magnetic properties of the antiferromagnetic compound CePd2Ge2, crystallizing in the tetragonal crystal structure have been investigated in detail on a single crystal grown by the Czochralski method. From the electrical transport, magnetization and heat capacity data, the Néel temperature is confirmed to be 5.1 K. Anisotropic behaviour of the magnetization and resistivity is observed along the two principal crystallographic directions—namely, [100] and [001]. The isothermal magnetization measured in the magnetically ordered state at 2 K exhibits a spin reorientation at 13.5 T for the field applied along the [100] direction, whereas the magnetization is linear along the [001] direction attaining a value of 0.94 ?B/Ce at 14 T. The reduced value of the magnetization is attributed to the crystalline electric field (CEF) effects. A sharp jump in the specific heat at the magnetic ordering temperature is observed. After subtracting the phononic contribution, the jump in the heat capacity amounts to 12.5 J K-1mol-1 which is the expected value for a spin \\frac{1}{2} system. From the CEF analysis of the magnetization data the excited crystal field split energy levels were estimated to be at 120 K and 230 K respectively, which quantitatively explains the observed Schottky anomaly in the heat capacity. A magnetic phase diagram has been constructed based on the field dependence of magnetic susceptibility and the heat capacity data.

Maurya, Arvind; Kulkarni, R.; Dhar, S. K.; Thamizhavel, A.

2013-10-01

101

Determination of dynamically adapting anisotropic material properties of bone under cyclic loading.

Because bone tissue adapts to loading conditions, finite element simulations of remodelling bone require a precise prediction of dynamically changing anisotropic elastic parameters. We present a phenomenological theory that refers to the tissue in terms of the tendency of the structure to align with principal stress directions. We describe the material parameters of remodelling bone. This work follows findings by the same research group and independently by Danilov (1971) in the field of plasticity, where the dependencies of the components of the stiffness tensor in terms of time are based on Hill's anisotropy. We modify such an approach in this novel theory that addresses bone tissue that can regenerate. The computational assumption of the theory is that bone trabeculae have the tendency to orient along one of the principal stress directions but during remodelling the principal stresses change continuously and the resulting orientation of the trabeculae can differ from the principal stress direction at any given time. The novelty of this work consists in the limited number of parameters needed to compute the twenty-one anisotropic material parameters at any given location in the bone tissue. In addition to the theory, we present here two cases of simplified geometry, loading and boundary conditions to show the effect of (1) time on the material properties; and (2) change of loading conditions on the anisotropic parameters. The long term goal is to experimentally verify that the predictions generated by theory provide a reliable simulation of cancellous bone properties. PMID:21040919

Besdo, Silke

2011-01-11

102

NASA Astrophysics Data System (ADS)

Large single crystals of ?-NaxCoO2 ( x=0.91 , 0.92, and 0.93) have been successfully fabricated by using the traveling solvent floating zone method. Details on the crystal growth are discussed. The crystal structures were characterized using powder x-ray diffraction and Rietveld refinement. The magnetic susceptibility measurements show that the magnetic properties depend strongly on x . The compound was found to be antiferromagnetic at TN?20K for x=0.91 and x=0.92 , and paramagnetic for x=0.93 . The in-plane and out-of-plane anisotropies were observed for the x=0.91 crystals. In addition, the derived anisotropic g -factor ratios (gab/gc) from the anisotropic susceptibility along H?ab and H?c decreased significantly as the sodium composition increased from x=0.91 to x=0.93 .

Chen, D. P.; Wang, Xiaolin; Lin, C. T.; Dou, S. X.

2007-10-01

103

Optical properties of anisotropic polycrystalline Ce3+ activated LSO

NASA Astrophysics Data System (ADS)

Polycrystalline cerium activated lutetium oxyorthosilicate (LSO:Ce) is highly desirable technique to make cost effective and highly reproducible radiation detectors for medical imaging. In this article methods to improve transparency in polycrystalline LSO:Ce were explored. Two commercially available powders of different particulate sizes (average particle size 30 and 1500 nm) were evaluated for producing dense LSO:Ce by pressure assisted densification routes, such as hot pressing and hot isostatic pressing. Consolidation of the powders at optimum conditions produced three polycrystalline ceramics with average grain sizes of 500 nm, 700 nm and 2000 nm. Microstructural evolution studies showed that for grain sizes larger than 1 ?m, anisotropy in thermal expansion coefficient and elastic constants of LSO, resulted in residual stress at grain boundaries and triple points that led to intragranular microcracking. However, reducing the grain size below 1 ?m effectively avoids microcracking, leading to more favorable optical properties. The optical scattering profiles generated by a Stover scatterometer, measured by a He-Ne laser of wavelength 633 nm, showed that by reducing the grain size from 2 ?m to 500 nm, the in-line transmission increased by a factor of 103. Although these values were encouraging and showed that small changes in grain size could increase transmission by almost three orders of magnitude, even smaller grain sizes need to be achieved in order to get truly transparent material with high in-line transmission.

Roy, Sudesna; Lingertat, Helmut; Brecher, Charles; Sarin, Vinod

2013-03-01

104

Anisotropic magnetic properties of Co-doped SnO2 thin films

There is strong interest in oxide magnetic semiconductors, which show not only room-temperature ferromagnetism (FM), but also other interesting magnetic properties. Large magnetic moments and anisotropic FM have been observed in Co-doped SnO2 [1] and Co-doped ZnO [2], respectively. Here we report the preparation and magnetic properties of Co-doped SnO2 (Sn1-xCoxO2, x=0.05) thin films. Sn1-xCoxO2 thin films were grown on

Jun Zhang; Ralph Skomski; Yongfeng Lu; David Sellmyer

2006-01-01

105

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

106

Transport properties in the atmosphere of Jupiter

NASA Technical Reports Server (NTRS)

Activities reported include: (1) testing of the computer program used to obtain transport properties for the Hulburt-Hirschfelder potential; (2) calculation of transport properties for the C2-C interaction; (3) preliminary calculations for the C2-C2 interaction; (4) calculation of transport properties for the C2H-He interaction; (5) consideration of the effect of inelastic collisions on the transport properties; and (6) the use of the Hulburt-Hirschfelder potential to model ion-atom interactions.

Biolsi, L., Jr.

1979-01-01

107

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.

108

Anisotropic properties of the mid-lithospheric discontinuity beneath central North America

NASA Astrophysics Data System (ADS)

Several previous studies have observed a mid-lithospheric discontinuity beneath continental interiors, including beneath the North American craton. Various hypotheses have been proposed to explain the presence of a mid-lithospheric discontinuity, such as past lithospheric alteration from melt, stacking of oceanic plates originating from past subduction cycles, and a transition in the orientation of azimuthal anisotropy. We compute radial and transverse component P-to-S receiver functions from several long running stations in central North America using the multitaper correlation receiver function estimator (Park and Levin, 2000). Observations of coherent P-to-SV converted energy show a clear velocity decrease internal to the lithosphere, and are consistent with the expected depth of the mid-lithospheric discontinuity based on prior results. P-to-SH converted energy originating from conversions at approximately the same depth as the mid-lithospheric discontinuity show strong evidence for the presence of flat-layered anisotropic structure. We compute synthetic receiver functions using a forward modeling scheme to develop models for the depth to and anisotropic properties (i.e., trend and plunge of anisotropic symmetry axes, and strength of anisotropy) of the mid-lithospheric discontinuity beneath central North America. A better characterization of differences in anisotropy across the mid-lithospheric discontinuity will have important implications for our understanding of the internal structure of the lithosphere and lend insight into the processes associated craton formation.

Wirth, E. A.; Long, M. D.

2013-12-01

109

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

110

Transport properties in the atmosphere of Jupiter

NASA Technical Reports Server (NTRS)

The calculation of transport properties near the surface of a probe entering the atmosphere of Jupiter is discussed for (1) transport properties in the pure Jovian atmosphere, (2) transport properties for collisions between monatomic carbon atoms, including the effect of excited electronic states, (3) transport properties at the boundaries for mixing of the pure Jovian atmosphere and the atmosphere due to the injection of gaseous ablation products, and (4) transport properties for interactions involving some of the molecular ablation products. The transport properties were calculated using the kinetic theory of gases. Transport collision integrals were calculated for only a limited set of empirical and semiempirical interaction potentials. Since the accuracy of the fit of these empirical potentials to the true potential usually determines the accuracy of the calculation of the transport properties, the various interaction potentials used in these calculations are discussed.

Biolsi, L., Jr.

1978-01-01

111

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

112

Anisotropic Properties of Single-Crystalline CeNiGe2

NASA Astrophysics Data System (ADS)

The anisotropic properties of CeNiGe2 with a layered crystal structure have been studied by measurements of electrical resistivity, magnetic susceptibility and magnetization. It is confirmed that CeNiGe2 undergoes two-step antiferromagnetic transition at TNI = 4 K and TNII = 3 K as reported earlier on polycrystalline samples. CeNiGe2 is found to exhibit highly anisotropic properties with an easy magnetization axis along the longest crystallographic b direction. The magnetization ratio M(H//b)/M(H?b) is estimated to be about 15 at 5 T. The in-plane resistivity ??b(T) shows double maxima typical of that expected when an interplay of crystal-field and Kondo effects plays a role. The low-T maximum at 4-K in ??b(T) is strongly suppressed with increasing magnetic field. This negative magnetoresistance is a result of the strong reduction of magnetic scattering by the ferromagnetic alignment of Ce magnetic moments.

Jung, M. H.; Harrison, N.; Lacerda, A. H.; Pagliuso, P. G.; Sarrao, J. L.; Thompson, J. D.

113

Anisotropic Properties of Single-Crystalline CeNiGe2

NASA Astrophysics Data System (ADS)

The anisotropic properties of CeNiGe2 with a layered crystal structure have been studied by measurements of electrical resistivity, magnetic susceptibility and magnetization. It is confirmed that CeNiGe2 undergoes two-step antiferromagnetic transition at TNI = 4 K and TNII = 3 K as reported earlier on polycrystalline samples. CeNiGe2 is found to exhibit highly anisotropic properties with an easy magnetization axis along the longest crystallographic b direction. The magnetization ratio M(H//b)/M(H?b) is estimated to be about 15 at 5 T. The in-plane resistivity ?

Jung, M. H.; Harrison, N.; Lacerda, A. H.; Pagliuso, P. G.; Sarrao, J. L.; Thompson, J. D.

2002-07-01

114

Crossover in thermal transport properties of natural, perovskite-structured superlattices

NASA Astrophysics Data System (ADS)

Atomic-level simulations are used to analyze the thermal-transport properties of a naturally layered material: the Ruddlesden-Popper phase, formed by interleaving perovskite layers of strontium titanate with strontium oxide rocksalt layers. The thermal conductivity parallel to the plane of structural layering is found to be systematically greater than that perpendicular to the layering. With decreasing number of perovskite blocks in the structure, a transition is seen from the thermal-transport properties of a bulk solid containing interfaces to that of an anisotropic monolithic material. The exact transition point should be temperature dependent and might enable tuning of the thermal conductance properties of the material.

Chernatynskiy, Aleksandr; Grimes, Robin W.; Zurbuchen, Mark A.; Clarke, David R.; Phillpot, Simon R.

2009-10-01

115

A modified Landau-Devonshire phenomenological thermodynamic theory is used to describe the influence of in-plane anisotropic strains on the dielectric and pyroelectric properties of epitaxial Ba0.7Sr0.3TiO3 thin films grown on dissimilar tetragonal substrates. The in-plane anisotropic strain factor-temperature phase diagram is developed. The in-plane anisotropic strains play a crucial role in the dielectric and pyroelectric properties of BST thin films. The

Hai-Xia Cao; Veng Cheong Lo; Zhen-Ya Li

2007-01-01

116

The determination of elastic properties of plasma-sprayed ceramic and metallic coatings is difficult due to their complex microstructure, which involves a myriad array of pores, interfaces and other defects. Furthermore, the splat-based build-up of the coating results in transverse anisotropy in the elastic properties. In this paper, we report on the anisotropic elastic properties of these coatings determined by resonant ultrasound spectroscopy (RUS). This approach along with the analysis presented enables, for the first time, the determination of elastic properties as a function of direction and temperature for these complex systems with concomitant implications for design. The coating systems investigated included plasma-sprayed yttria-stabilized zirconia (YSZ) and nickel. An additional nickel coating deposited by high-velocity oxygen-fuel process was investigated and its elastic properties were compared to those of plasma-sprayed nickel. Average Young s moduli of the coatings were independently measured by using the instrumented indentation method. The elastic properties determined from the RUS and indentation methodologies allowed description of the microstructure elastic property relationships in the coatings.

Tan, Yang [Stony Brook University (SUNY); Shyam, Amit [ORNL; Choi, Wanhuk Brian [Stony Brook University (SUNY); Lara-Curzio, Edgar [ORNL; Sampath, Sanjay [Stony Brook University (SUNY)

2010-01-01

117

Anisotropic optical property of an asymmetric bideposition Ta2O5 film: fabrication and measurement

NASA Astrophysics Data System (ADS)

To develop diverse anisotropic thin films, asymmetric bideposition technique is introduced to fabricate tilt columnar Ta2O5 films with biaxial optical property. The asymmetric bideposition is achieved using two different opposite deposition angles (a+,a-) and two different thicknesses of opposite deposited subdeposits. The two sets of Ta2O5 columnar thin films associated with deposited subdeposits (d+,d-)=(5.2,2.8) are prepared at the opposite deposition angles (a+,a-)=(70,-40), (75,-40), (80,-40) and at the opposite deposition angles (a+,a-)=(70,-50), (75,-50), (80,-50). Columnar thin films with various column angle and biaxial properties are measured their planar birefringence and three principal indexes. The larger column angle leads to higher principal indices. It is demonstrated that the asymmetric bideposition can enhance the birefringence of a tilted columnar thin film.ntut.edu.tw

Jen, Yi-Jun; Lin, Chia-Feng; Yu, Tai-Hung; Lai, Chun-Jung

2011-09-01

118

Optical properties of composite systems based on anisotropic fibers with axisymmetric stacking

NASA Astrophysics Data System (ADS)

Simulation of optical properties of composite systems in the form of bundles consisting of anisotropic fibers with axisymmetric stacking is carried out in the ray-optics approximation. It is shown that such composite systems observed by the interference-polarization method for the case of crossed Nicol prisms produce figures in the form of a system of concentric light and dark rings, in the center of which there is a dark cross. The results of simulations applied to microsections of the human tooth taking into account the numerical values of the constituent components of the dentin (the sizes and optical properties of the dentinal tubules and of the matrix, etc.) are compared with the experiment. A good qualitative agreement between the calculation and the experiment for the observed patterns is found in the cases of some samples (molar and premolar).

Zolotarev, V. M.

2004-10-01

119

Large single crystals of {alpha}-Na{sub x}CoO{sub 2} (x=0.91, 0.92, and 0.93) have been successfully fabricated by using the traveling solvent floating zone method. Details on the crystal growth are discussed. The crystal structures were characterized using powder x-ray diffraction and Rietveld refinement. The magnetic susceptibility measurements show that the magnetic properties depend strongly on x. The compound was found to be antiferromagnetic at T{sub N}{approx_equal}20 K for x=0.91 and x=0.92, and paramagnetic for x=0.93. The in-plane and out-of-plane anisotropies were observed for the x=0.91 crystals. In addition, the derived anisotropic g-factor ratios (g{sub ab}/g{sub c}) from the anisotropic susceptibility along H parallel ab and H parallel c decreased significantly as the sodium composition increased from x=0.91 to x=0.93.

Chen, D. P. [Institute for Superconducting and Electronic Materials, University of Wollongong, New South Wales 2500 (Australia); Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Wang, Xiaolin; Dou, S. X. [Institute for Superconducting and Electronic Materials, University of Wollongong, New South Wales 2500 (Australia); Lin, C. T. [Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart (Germany)

2007-10-01

120

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

121

Anisotropic heat transport via monopoles in the spin-ice compound Dy2Ti2O7

NASA Astrophysics Data System (ADS)

We report a study of the thermal conductivity ? of the spin-ice material Dy2Ti2O7. From the anisotropic magnetic-field dependence of ? and by additional measurements on the phononic reference compounds Y2Ti2O7 and (Dy0.5Y0.5)2Ti2O7, we are able to separate the phononic and the magnetic contributions to the total heat transport, i.e., ?ph and ?mag, respectively, which both depend on the magnetic field. The field dependence of ?ph arises from the noncollinear magnetic moments of the Dy ions, which tend to align along the field direction. For ?mag, we observe a highly anisotropic magnetic-field dependence, which correlates with the corresponding magnetization data reflecting the different magnetic-field induced spin-ice ground states. The magnitude of ?mag increases with the degree of the ground-state degeneracy. This anisotropic field dependence as well as various hysteresis effects suggest that ?mag is essentially determined by the mobility of the magnetic monopole excitations in spin ice.

Kolland, G.; Valldor, M.; Hiertz, M.; Frielingsdorf, J.; Lorenz, T.

2013-08-01

122

The late-time macrodispersion coefficients are obtained for the case of flow in the presence of a small-scale deterministic transient in a three-dimensional anisotropic, heterogeneous medium. The transient is assumed to affect only the velocity component transverse to the mean flow direction and to take the form of a periodic function. For the case of a highly stratified medium, these late-time macrodispersion coefficients behave largely as the standard coefficients used in the transport equation. Only in the event that the medium is isotropic is it probable that significant deviations from the standard coefficients would occur.

Naff, R. L.

1998-01-01

123

Anisotropic photonic properties of III-V nanowires in the zinc-blende and wurtzite phase

NASA Astrophysics Data System (ADS)

Some critical aspects of the anisotropic absorption and emission properties of quasi one-dimensional structures are reviewed in the context of III-V compound semiconductor nanowires. The unique optical and electronic properties of III-V nanowires stem from the combination of dielectric effects due to their large aspect ratio, and their specific crystallographic structure which can differ significantly from the bulk case. The growth conditions leading to single-crystal nanowires with either zinc blende or wurtzite phase are first presented. Dipole selection rules for interband transitions in common III-V compounds are then summarized for the two different phases, and corroborated by ab initio Density Functional Theory calculations of the oscillator strength. The optical anisotropy is discussed considering both the effect of refractive index mismatch between the nanowire and its surroundings and the polarization of the emitting dipoles set by the nanowire crystallographic structure and orientation. Finite Difference Time Domain simulations are finally employed to illustrate the influence of the emitting dipole orientation and the nanowire diameter on the distribution of radiation in the far-field. The importance of the correlation between structural and optoelectronic properties is highlighted in view of potential applications in future nanowire photonics.Some critical aspects of the anisotropic absorption and emission properties of quasi one-dimensional structures are reviewed in the context of III-V compound semiconductor nanowires. The unique optical and electronic properties of III-V nanowires stem from the combination of dielectric effects due to their large aspect ratio, and their specific crystallographic structure which can differ significantly from the bulk case. The growth conditions leading to single-crystal nanowires with either zinc blende or wurtzite phase are first presented. Dipole selection rules for interband transitions in common III-V compounds are then summarized for the two different phases, and corroborated by ab initio Density Functional Theory calculations of the oscillator strength. The optical anisotropy is discussed considering both the effect of refractive index mismatch between the nanowire and its surroundings and the polarization of the emitting dipoles set by the nanowire crystallographic structure and orientation. Finite Difference Time Domain simulations are finally employed to illustrate the influence of the emitting dipole orientation and the nanowire diameter on the distribution of radiation in the far-field. The importance of the correlation between structural and optoelectronic properties is highlighted in view of potential applications in future nanowire photonics. This article was submitted as part of a collection highlighting papers on the `Recent Advances in Semiconductor Nanowires Research' from ICMAT 2011.

Wilhelm, Christophe; Larrue, Alexandre; Dai, Xing; Migas, Dmitri; Soci, Cesare

2012-02-01

124

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...

125

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...

126

The transport properties of activated carbon fibers

The transport properties of isotropic pitch-based carbon fibers with surface area 1000 m{sup 2}/g have been investigated. We report preliminary results on the electrical conductivity, the magnetoresistance, the thermal conductivity, and the thermopower of these fibers as a function of temperature. Comparisons are made to transport properties of other disordered carbons.

di Vittorio, S.L. (Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (USA)); Dresselhaus, M.S. (Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (USA) Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (USA)); Endo, M. (Department of Electrical Engineering, Faculty of Engineering, Shinshu University, Nagano 380, (Japan)); Issi, J.; Piraux, L.; Bayot, V. (Unite de Physico-Chimie et de Physique des Materiaux, Universite Catholique de Louvain, Louvain-la-Neuve, (Belgium))

1991-04-01

127

NASA Astrophysics Data System (ADS)

The Posidonia Shale Formation (PSF) is one of the possible resource shales for unconventional gas in Northern Europe and currently is of great interest to hydrocarbon exploration and production. Due to low permeability of shales, economically viable production requires hydraulic fracturing of the reservoir. The design of hydrofractures requires an estimate of stress state within the reservoir and geomechanical properties such as Young's modulus and Poisson's ratio. Shales are often highly anisotropic and the models which neglect shale anisotropy may fail to predict the behaviour of hydrofractures. Seismic attenuation anisotropy, on the other hand, can play a key role in quantitative rock characterization. Where the attenuation anisotropy can potentially be linked to anisotropic permeability of shales, its fluid/gas saturation and preferred development of anisotropic fracture orientations. In this research, by utilizing the so-called Thomsen's notations, the elastic anisotropy of our (fractured and unfractured) shales has been investigated using a pulse transmission technique in the ultrasonic frequency range (0.3-1 MHz). Assuming transverse isotropy of the shales, and taking the axis x3 as the axis of rotational symmetry, directional Young's moduli and Poisson's ratios were obtained. The Young's modulus measured parallel to bedding (E1) is found to be larger than the Young's modulus measured orthogonal to bedding (E3). In case of the Poisson's ratios, we found that ?31 is larger than ?12, where ?ijrelates elastic strain in xj direction to stress applied in xi direction. Finally, attenuation anisotropy in dry and layer-parallel fractured Posidonia shale samples has been studied in the same frequency range. The attenuation of compressional (QP-1) and shear (QS-1) waves increases substantially with a macro (or wavelength) fracture introduction, especially for P and S waves propagating orthogonal to the bedding. In non-fractured and fractured dry shales, QP-1 is always larger than QS-1. This inequality was also found for the fractured shale using different fluids (water, oil) on the fracture surface. A high-viscosity fluid decreases QP-1 and QS-1 in both (orthogonal and parallel to the bedding) directions, and the QP-1 to QS-1 ratio decreases with the increase of fluid viscosity.

Zhubayev, Alimzhan; Houben, Maartje; Smeulders, David; Barnhoorn, Auke

2014-05-01

128

Lately, neuromodulation of the brain is considered one of the promising applications of ultrasound technology in which low-intensity focused ultrasound (LIFU) is used noninvasively to excite or inhibit neuronal activity. In LIFU, one of critical barriers in the propagation of ultrasound wave is the skull, which is known to be highly anisotropic mechanically: this affects the ultrasound focusing, thereby neuromodulation effects. This study aims to investigate the influence of the anisotropic properties of the skull on the LIFU via finite element head models incorporating the anisotropic properties of the skull. We have examined the pressure and stress distributions within the head in LIFU. Our results show that though most of the pressure that reaches to the brain is due to the longitudinal wave propagation through the skull, the normal stress in the transverse direction of the wave propagation has the main role to control the pressure profile inside the brain more than the shear stress. The results also show that the anisotropic properties of skull contribute in broadening the focal zone in comparison to that of the isotropic skull. PMID:24110750

Metwally, Mohamed K; Han, Hee-Sok; Jeon, Hyun Jae; Khang, Gon; Kim, Tae-Seong

2013-01-01

129

Anisotropic photonic properties of III-V nanowires in the zinc-blende and wurtzite phase.

Some critical aspects of the anisotropic absorption and emission properties of quasi one-dimensional structures are reviewed in the context of III-V compound semiconductor nanowires. The unique optical and electronic properties of III-V nanowires stem from the combination of dielectric effects due to their large aspect ratio, and their specific crystallographic structure which can differ significantly from the bulk case. The growth conditions leading to single-crystal nanowires with either zinc blende or wurtzite phase are first presented. Dipole selection rules for interband transitions in common III-V compounds are then summarized for the two different phases, and corroborated by ab initio Density Functional Theory calculations of the oscillator strength. The optical anisotropy is discussed considering both the effect of refractive index mismatch between the nanowire and its surroundings and the polarization of the emitting dipoles set by the nanowire crystallographic structure and orientation. Finite Difference Time Domain simulations are finally employed to illustrate the influence of the emitting dipole orientation and the nanowire diameter on the distribution of radiation in the far-field. The importance of the correlation between structural and optoelectronic properties is highlighted in view of potential applications in future nanowire photonics. PMID:22327202

Wilhelm, Christophe; Larrue, Alexandre; Dai, Xing; Migas, Dmitri; Soci, Cesare

2012-03-01

130

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

131

Accurate material models and associated parameters of atherosclerotic plaques are crucial for reliable biomechanical plaque prediction models. These biomechanical models have the potential to increase our understanding of plaque progression and failure, possibly improving risk assessment of plaque rupture, which is the main cause of ischaemic strokes and myocardial infarction. However, experimental biomechanical data on atherosclerotic plaque tissue is scarce and shows a high variability. In addition, most of the biomechanical models assume isotropic behaviour of plaque tissue, which is a general over-simplification. This review discusses the past and the current literature that focus on mechanical properties of plaque derived from compression experiments, using unconfined compression, micro-indentation or nano-indentation. Results will be discussed and the techniques will be mutually compared. Thereafter, an in-house developed indentation method combined with an inverse finite element method is introduced, allowing analysis of the local anisotropic mechanical properties of atherosclerotic plaques. The advantages and limitations of this method will be evaluated and compared to other methods reported in literature. PMID:24480703

Chai, Chen-Ket; Speelman, Lambert; Oomens, Cees W J; Baaijens, Frank P T

2014-03-01

132

Pinning and the mixed-state thermomagnetic transport properties of YBaâCuâO{sub 7-Î´}

We have studied the role of pinning in the mixed-state thermomagnetic transport properties of YBaâCuâO{sub 7-Î´}. We demonstrate the pinning independence of the transport entropy {ital S}{sub Ï}, and its consequent scaling within an anisotropic mass model. Due to the anisotropy of YBaâCuâO{sub 7-Î´} the extrinsic pinning strength effectively decreases as we rotate the magnetic field into the {ital ab}

T. W. Clinton; W. Liu; X. Jiang; A. W. Smith; M. Rajeswari; R. L. Greene; C. J. Lobb

1996-01-01

133

Pinning and the mixed-state thermomagnetic transport properties of YBa2Cu3O7-delta

We have studied the role of pinning in the mixed-state thermomagnetic transport properties of YBa2Cu3O7-delta. We demonstrate the pinning independence of the transport entropy Sphi, and its consequent scaling within an anisotropic mass model. Due to the anisotropy of YBa2Cu3O7-delta the extrinsic pinning strength effectively decreases as we rotate the magnetic field into the ab plane. The Nernst (Ey\\/?xT) and

T. W. Clinton; Wu Liu; X. Jiang; A. W. Smith; M. Rajeswari; R. L. Greene; C. J. Lobb

1996-01-01

134

NASA Astrophysics Data System (ADS)

There has been a steady accumulation of observational evidence that the solar wind may be thought of as spaghetti: a network of individual magnetic flux tubes each with its own magnetic and plasma characteristics. As early as 1963, Parker referred to these tubes as magnetic and plasma ``filaments,'' and the picture has undergone several refinements since then [Bartley et al. 1966, Marliani et al. 1973, Tu and Marsch 1990, Bruno et al. 2001], culminating in the recent work of Borovsky [2008] who has suggested that these are fossil structures that originate at the solar surface. We use the weakly compressible MHD turbulence model [Bhattacharjee et al., 1998], which incorporates the effect of background spatial inhomogeneities, to describe such structures. We revisit the model equations, showing their relation to recent work by Hunana and Zank [2010]. For a model of interchange-instability driven turbulence, we then use the 1998 model equations to make predictions for the beta scaling of the anisotropic magnetic fluctuation spectra (the so-called variance anisotropy) observed by ACE, and show that the predictions bracket the observations well. We also predict the scaling of the anisotropic transport coefficients for particles and thermal energy.

Bhattacharjee, A.; Smith, C.; Vasquez, B.

2010-11-01

135

NASA Astrophysics Data System (ADS)

A modified Landau-Devonshire phenomenological thermodynamic theory is used to describe the influence of in-plane anisotropic strains on the dielectric and pyroelectric properties of epitaxial Ba0.7Sr0.3TiO3 thin films grown on dissimilar tetragonal substrates. The in-plane anisotropic strain factor-temperature phase diagram is developed. The in-plane anisotropic strains play a crucial role in the dielectric and pyroelectric properties of BST thin films. The theoretical maximum dielectric tunability approaching 100% can be attained at the critical anisotropic strain factor corresponding to the structural phase transformation from ca1 to a1 phase. Moreover, the anisotropic strain factor has an opposite effect on the figure of merit and pyroelectric coefficient, respectively. Furthermore, in the case of isotropic strains, our theoretical results are well consistent with the experimental results.

Cao, Hai-Xia; Lo, Veng Cheong; Li, Zhen-Ya

2007-01-01

136

Transport Properties of Biofluids in Micromachined Geometrics.

National Technical Information Service (NTIS)

The determination of transport properties of biological materials flowing in micron and sub-micron geometrics is discussed. The program goal was to develop techniques to identify anomalous viscous and diffusion effects due to complex biological materials....

K. Breuer

2002-01-01

137

Transport Properties of Dense Laser Plasmas.

National Technical Information Service (NTIS)

Generalized kinetic equations are used to investigate transport properties of dense plasmas in strong laser fields. Quantum statistical expressions are derived for, e.g., the collision frequency to account for nonlinear field phenomena as well as strong c...

D. Kremp M. Schlanges P. Hilse T. Bornath

2003-01-01

138

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

139

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

140

Structure and anisotropic properties of single crystals nickel doped barium iron arsenide

The crystal structure, anisotropic electrical resistivity and magnetic susceptibility, as well as specific heat results of the pure single crystals of BaFe{sub 2}As{sub 2}, BaFeNiAs{sub 2}, and BaNi{sub 2}As{sub 2} are surveyed. BaFe{sub 2}As{sub 2} properties demonstrate the equivalence of C(T), Fisher's d({chi}T)/dT and d{rho}/dT results in determining the antiferromagnetic transition at T{sub N} = 132(1) K. BaNi{sub 2}As{sub 2} shows a structural phase transition from a high-temperature tetragonal phase to a low-temperature triclinic pol symmetry at T{sub 0} 131 K, with superconducting critical temperature well below at {Tc} 0.69 K. BaFeNiAs{sub 2} does not show any sign of superconductivity and gives behavioral similarity to BaCo{sub 2}As{sub 2}, a renomalized paramagnetic metal.

Ronning, Filip [Los Alamos National Laboratory; Bauer, Eric D [Los Alamos National Laboratory; Sefat, A S [ORNL; Jin, R [ORNL; Mcguire, M A [ORNL; Sales, B C [ORNL; Mandrus, D [ORNL

2009-01-01

141

Anisotropic effective medium properties from interacting Ag nanoparticles in silicon dioxide.

Films containing a layer of Ag nanoparticles embedded in silicon dioxide were produced by RF magnetron sputtering. Optical transmittance measurements at several angles of incidence (from normal to 75°) revealed two surface plasmon resonance (SPR) peaks, which depend on electric field direction: one in the ultraviolet and another red-shifted from the dilute Ag/SiO? system resonance at 410 nm. In order to investigate the origin of this anisotropic behavior, the structural properties were determined by transmission electron microscopy, revealing the bidimensional plane distribution of Ag nanoparticles with nearly spherical shape as well as the filling factor of metal in the composite. A simple model linked to these experimental parameters allowed description of the most relevant features of the SPR positions, which, depending on the field direction, were distinctly affected by the coupling of oscillations between close nanoparticles, as described by a modified Drude-Lorentz dielectric function introduced into the Maxwell-Garnett relation. This approach allowed prediction of the resonance for light at 75° incidence from the SPR position for light at normal incidence, in good agreement with experimental observation. PMID:24921871

Menegotto, Thiago; Horowitz, Flavio

2014-05-01

142

Magnetic properties and Mott transition in the Hubbard model on the anisotropic triangular lattice

NASA Astrophysics Data System (ADS)

Magnetic properties and the Mott transition are studied in the Hubbard model on the anisotropic triangular lattice described by two hopping parameters t and t' in different spatial directions using the variational cluster approximation. Taking into account Néel (AF), 120? Néel (spiral), and collinear (AFC) orderings, the magnetic phase diagram is analyzed at zero temperature and half-filling. We found six phases, AF metal, AF insulator, spiral, AFC, paramagnetic metal, and nonmagnetic insulator, which is a candidate for a spin liquid. Direct transitions from a paramagnetic metal to an AF insulator take place for 0.6?t'/t?0.8, and a nonmagnetic insulator is realized between the paramagnetic metal and magnetic states for 0.8?t'/t?1.2. Around t'/t?1.2, the magnetic state (AFC or spiral) is realized above the paramagnetic metal, and as the on-site Coulomb repulsion U increases, it changes to a nonmagnetic insulator. Implications for the ?-(BEDT-TTF)2Cu2(CN)3 are discussed. As for the Mott transition, the structure of the self-energy in the spectral representation is studied in detail. As U increases around the Mott transition point, a single dispersion evolves in the spectral weights of the self-energy, which yields the Mott gap.

Yamada, A.

2014-05-01

143

Length-dependence of flexural rigidity as a result of anisotropic elastic properties of microtubules

Unexplained length-dependence of flexural rigidity and Young's modulus of microtubules is studied using an orthotropic elastic shell model. It is showed that vibration frequencies and buckling load predicted by the accurate orthotropic shell model are much lower than that given by the approximate isotropic beam model for shorter microtubules, although the two models give almost identical results for sufficiently long microtubules. It is this inaccuracy of the isotropic beam model used by all previous researchers that leads to reported lower flexural rigidity and Young's modulus for shorter microtubules. In particular, much lower shear modulus and circumferential Young's modulus, which only weaken flexural rigidity of shorter microtubules, are responsible for the observed length-dependence of the flexural rigidity. These results confirm that longitudinal Young's modulus of microtubules is length-independent, and the observed length-dependence of the flexural rigidity and Young's modulus is a result of strongly anisotropic elastic properties of microtubules which have a length-dependent weakening effect on flexural rigidity of shorter microtubules.

Li, C. [Department of Mechanical Engineering, University of Alberta, Edmonton, T6G 2G8 (Canada); Ru, C.Q. [Department of Mechanical Engineering, University of Alberta, Edmonton, T6G 2G8 (Canada)]. E-mail: c.ru@ualberta.ca; Mioduchowski, A. [Department of Mechanical Engineering, University of Alberta, Edmonton, T6G 2G8 (Canada)

2006-10-27

144

Magnetic properties of the anisotropic MnBi/Sm2Fe17Nx hybrid magnet

NASA Astrophysics Data System (ADS)

In order to improve the magnetic properties of MnBi compound, anisotropic MnBi/Sm2Fe17Nx hybrid magnet was prepared by grinding of high purity MnBi ribbons and Sm2Fe17Nx particles together. The smooth hysteresis loops of the hybrid magnets indicated that the mixture of the hard/hard phase magnetic components was well exchange coupled. As compared to the single MnBi phase magnet, the remanent magnetization and maximum energy product (BH)max of the composited magnets were improved. As an optimized result, the exchange coupled magnet of MnBi/Sm2Fe17Nx = 3/7 yielded both high remanence and coercivity from 250 K to 380 K. A maximum energy product (BH)max of 18 MGOe was achieved at 300 K, and remained 10 MGOe at 380 K, implying the MnBi/Sm2Fe17Nx magnets can be specially utilized in the high temperature environment.

Yang, Y. B.; Wei, J. Z.; Peng, X. L.; Xia, Y. H.; Chen, X. G.; Wu, R.; Du, H. L.; Han, J. Z.; Wang, C. S.; Yang, Y. C.; Yang, J. B.

2014-05-01

145

The room temperature magnetization, magnetoresistance and structural properties of soft magnetic Fe26Ni74 nanowires of 18nm diameter and various lengths electrodeposited in the pores of anodic alumina are investigated. Nanowires show perpendicular magnetic anisotropy, anisotropic crystallographic and magnetoresistance behaviour with a coercivity of 967Oe and a remanence value of 85%. It should be noted that an electrodeposited Fe26Ni74 layer (6?m) on

H. R Khan; K Petrikowski

2000-01-01

146

Transport properties of alumina nanofluids

NASA Astrophysics Data System (ADS)

Recent studies have showed that nanofluids have significantly greater thermal conductivity compared to their base fluids. Large surface area to volume ratio and certain effects of Brownian motion of nanoparticles are believed to be the main factors for the significant increase in the thermal conductivity of nanofluids. In this paper all three transport properties, namely thermal conductivity, electrical conductivity and viscosity, were studied for alumina nanofluid (aluminum oxide nanoparticles in water). Experiments were performed both as a function of volumetric concentration (3-8%) and temperature (2-50 °C). Alumina nanoparticles with a mean diameter of 36 nm were dispersed in water. The effect of particle size was not studied. The transient hot wire method as described by Nagaska and Nagashima for electrically conducting fluids was used to test the thermal conductivity. In this work, an insulated platinum wire of 0.003 inch diameter was used. Initial calibration was performed using de-ionized water and the resulting data was within 2.5% of standard thermal conductivity values for water. The thermal conductivity of alumina nanofluid increased with both increase in temperature and concentration. A maximum thermal conductivity of 0.7351 W m-1 K-1 was recorded for an 8.47% volume concentration of alumina nanoparticles at 46.6 °C. The effective thermal conductivity at this concentration and temperature was observed to be 1.1501, which translates to an increase in thermal conductivity by 22% when compared to water at room temperature. Alumina being a good conductor of electricity, alumina nanofluid displays an increasing trend in electrical conductivity as volumetric concentration increases. A microprocessor-based conductivity/TDS meter was used to perform the electrical conductivity experiments. After carefully calibrating the conductivity meter's glass probe with platinum tip, using a standard potassium chloride solution, readings were taken at various volumetric concentrations. A 3457.1% increase in the electrical conductivity was measured for a small 1.44% volumetric concentration of alumina nanoparticles in water. The highest value of electrical conductivity, 314 µS cm-1, was recorded for a volumetric concentration of 8.47%. In the determination of the kinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constant temperature bath was used. Calibrated capillary viscometers were used to measure flow under gravity at precisely controlled temperatures. The capillary viscometers were calibrated with de-ionized water at different temperatures, and the resulting kinematic viscosity values were found to be within 3% of the standard published values. An increase of 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration of alumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid, 2.901 42 mm2 s-1, was obtained at 0 °C for an 8.47% volumetric concentration of alumina nanoparticles. The experimental results of the present work will help researchers arrive at better theoretical models.

Wong, Kau-Fui Vincent; Kurma, Tarun

2008-08-01

147

Transport properties of alumina nanofluids.

Recent studies have showed that nanofluids have significantly greater thermal conductivity compared to their base fluids. Large surface area to volume ratio and certain effects of Brownian motion of nanoparticles are believed to be the main factors for the significant increase in the thermal conductivity of nanofluids. In this paper all three transport properties, namely thermal conductivity, electrical conductivity and viscosity, were studied for alumina nanofluid (aluminum oxide nanoparticles in water). Experiments were performed both as a function of volumetric concentration (3-8%) and temperature (2-50?°C). Alumina nanoparticles with a mean diameter of 36 nm were dispersed in water. The effect of particle size was not studied. The transient hot wire method as described by Nagaska and Nagashima for electrically conducting fluids was used to test the thermal conductivity. In this work, an insulated platinum wire of 0.003 inch diameter was used. Initial calibration was performed using de-ionized water and the resulting data was within 2.5% of standard thermal conductivity values for water. The thermal conductivity of alumina nanofluid increased with both increase in temperature and concentration. A maximum thermal conductivity of 0.7351 W m(-1) K(-1) was recorded for an 8.47% volume concentration of alumina nanoparticles at 46.6?°C. The effective thermal conductivity at this concentration and temperature was observed to be 1.1501, which translates to an increase in thermal conductivity by 22% when compared to water at room temperature. Alumina being a good conductor of electricity, alumina nanofluid displays an increasing trend in electrical conductivity as volumetric concentration increases. A microprocessor-based conductivity/TDS meter was used to perform the electrical conductivity experiments. After carefully calibrating the conductivity meter's glass probe with platinum tip, using a standard potassium chloride solution, readings were taken at various volumetric concentrations. A 3457.1% increase in the electrical conductivity was measured for a small 1.44% volumetric concentration of alumina nanoparticles in water. The highest value of electrical conductivity, 314 µS cm(-1), was recorded for a volumetric concentration of 8.47%. In the determination of the kinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constant temperature bath was used. Calibrated capillary viscometers were used to measure flow under gravity at precisely controlled temperatures. The capillary viscometers were calibrated with de-ionized water at different temperatures, and the resulting kinematic viscosity values were found to be within 3% of the standard published values. An increase of 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration of alumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid, 2.901?42 mm(2) s(-1), was obtained at 0?°C for an 8.47% volumetric concentration of alumina nanoparticles. The experimental results of the present work will help researchers arrive at better theoretical models. PMID:21730657

Wong, Kau-Fui Vincent; Kurma, Tarun

2008-08-27

148

Painleve Property for One-Dimensional Anisotropic Heisenberg Ferromagnetic Spin Chain.

National Technical Information Service (NTIS)

The classical one-dimensional anisotropic continuum Heisenberg ferromagnetic spin chain in the presence of a constant transverse magnetic field is considered. The evolution of the spin is expressed by the equation of motion in terms of a stereographic var...

M. Daniel

1983-01-01

149

National Technical Information Service (NTIS)

The present project focuses on the theoretical study of suspensions of nano-particles of different nature (ferroelectric, ferromagnetic, multiferroic) with size of 10-100nm in isotropic and anisotropic host. We shall investigate the effect of the disperse...

V. Y. Reshetnyak

2013-01-01

150

Conductivities and curing properties of electron-beam-irradiated anisotropic conductive films

NASA Astrophysics Data System (ADS)

Radiation-curable acrylated epoxy oligomer was irradiated by using an electron beam (E-beam) with dosages of 5, 10, 20, 40, 80, 200, 400, and 550 kGy to investigate the electrical and the physical properties of anisotropic conductive films (ACFs) and to evaluate the potential application of radiation technology to flip-chip package processing. An ACF is an insulating epoxy matrix containing conducting particles that keep the electrical conductivity along the out-of-plane direction and the insulation property along the in-plane direction. The contact resistance between ACF joints cured by using an E-beam irradiation of 80 kGy was measured under a constant bonding pressure of 2 kgf/cm2 to demonstrate the effects of pad pitch size and the number of added conductive particles in the epoxy resin. Three types of PCBs, 1000-, 500-, and 100-µm pad pitches, were employed while the E-beam curable epoxy resin was mixed with conductive particles in a weight ratio of 10:1. The measured average contact resistance was 0.24 ? with a minimum of 0.06 ? for the samples prepared with a 100-µm pad pitch size, which is compatible with or lower than the values obtained from thermally-cured commercial ACFs. Our results demonstrate that an E-beam is an effective radiation method for curing epoxy resins at low temperatures in a short time and can be employed as a new technique for bonding circuits in high-density electric devices.

Shin, Tae Gyu; Lee, Inhyuk; Kim, Jae yong

2012-07-01

151

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

152

Statistical anisotropy from anisotropic inflation

NASA Astrophysics Data System (ADS)

We review an inflationary scenario with the anisotropic expansion rate. An anisotropic inflationary universe can be realized by a vector field coupled with an inflaton, which can be regarded as a counter example to the cosmic no-hair conjecture. We show the generality of anisotropic inflation and derive a universal property. We formulate cosmological perturbation theory in anisotropic inflation. Using the formalism, we show that anisotropic inflation gives rise to the statistical anisotropy in primordial fluctuations. We also explain a method to test anisotropic inflation using the cosmic microwave background radiation.

Soda, Jiro

2012-04-01

153

NASA Astrophysics Data System (ADS)

SC-15 epoxy is used in many industrial applications and it is well known that the mechanical and viscoelastic properties of epoxy can be significantly enhanced when reinforced with nanofillers. In this work, SC-15 epoxy is reinforced by loading with magnetically-active nanofillers and cured in a modest magnetic field. Because of the significant magnetic response of the nanofillers, this is a low cost and relatively easy technique for imposing a strong magnetic anisotropy to the system without the need of a superconducting magnet. It is also found that this method is an effective way of enhancing the mechanical properties of epoxy. Three systems were prepared and studied. The first is a dilute system of various concentrations of Fe2O3 nanoparticles in SC-15 epoxy. The second systems is a combination of Fe2O3 nanoparticles and chemically-functionalized single-walled carbon nanotubes (SWCNT(COOH)s) in SC-15 epoxy. The third is a dilute system of SWCNT(COOH)s decorated with Fe3O4 particles through a sonochemical oxidation process in SC-15 epoxy. Samples have an initial cure of 6 hrs in a magnetic filed of 10 kOe followed by an additional 24 hrs of post curing at room temperature. These are compared to the control samples that do not have initial field curing. Tensile and compressive stress-strain analysis of the prepared systems shows that mechanical properties such as tensile strength, tensile modulus and compressive strength are enhanced with the inclusion of these nanofillers. It is also found that there is an anisotropic enhancement of these properties with respect to the imposed curing field. An interesting phenomenon is observed with the increase in modulus of toughness and fracture strain with nanotube inclusion. These parameters are drastically enhanced after curing the systems in a magnetic field. While there is a modest shift in glass transition temperature during viscoelastic analysis, the thermal stability of the created systems is not compromised. Results of these mechanical enhancements will be compared with other nanoloading techniques from literature.

Malkina, Olga

154

Anisotropic magnetotransport properties of MBE-grown LaAlO3/SrTiO3

NASA Astrophysics Data System (ADS)

The interface between the band insulators, LaAlO3 and SrTiO3, has been extensively explored by magnetotransport experiments probing its exciting properties including two-dimensional conductivity, superconductivity and magnetism. Here we report on the anisotropic magnetotransport properties observed in our Molecular Beam Epitaxy (MBE) grown LaAlO3/(100)SrTiO3 interfaces. We have observed Shubnikov-de Haas oscillations that depend on the direction of applied magnetic field and anisotropy in superconducting critical field -- clear signatures of two-dimensional conductivity at the interface. Similar observations have been reported by Caviglia et al., Shalom et al., and Reyren et al. on samples grown by pulsed laser deposition. We further observe a positive magnetoresistance (MR) cusp above superconducting TC at low magnetic fields due to weak antilocalization. Our measurements show that this cusp is anisotropic with applied magnetic field direction and for fields perpendicular to the interface we find a strong temperature dependence. We will discuss the temperature dependence of the characteristic relaxation time extracted from the MR data, which together with anisotropic behavior of MR provides important information about the various scattering mechanisms at play including spin-orbit interaction in these complex oxide interfaces.

Roy, P.; Ludwig, J. K.; Lee, M.; Warusawithana, M. P.; Kovalev, A.

2013-03-01

155

Coupled light transport-heat diffusion model for laser dosimetry with dynamic optical properties

NASA Astrophysics Data System (ADS)

The effect of dynamic optical properties on the spatial distribution of light in laser therapy is studied via numerical simulations. A 2D, time dependent computer program called LATIS is used. Laser light transport is simulated with a Monte Carlo technique including anisotropic scattering and absorption. Thermal heat transport is calculated with a finite difference algorithm. Material properties are specified on a 2D mesh and can be arbitrary functions of space and time. Arrhenius rate equations are solved for tissue damage caused by elevated temperatures. Optical properties are functions of tissue damage, as determined by previous measurements. Results are presented for the time variation of the light distribution and damage within the tissue as the optical properties of the tissue are altered.

London, Richard A.; Glinsky, Michael E.; Zimmerman, George B.; Eder, David C.; Jacques, Steven L.

1995-05-01

156

Coupled light transport-heat diffusion model for laser dosimetry with dynamic optical properties

The effect of dynamic optical properties on the spatial distribution of light in laser therapy is studied via numerical simulations. A two-dimensional, time dependent computer program called LATIS is used. Laser light transport is simulated with a Monte Carlo technique including anisotropic scattering and absorption. Thermal heat transport is calculated with a finite difference algorithm. Material properties are specified on a 2-D mesh and can be arbitrary functions of space and time. Arrhenius rate equations are solved for tissue damage caused by elevated temperatures. Optical properties are functions of tissue damage, as determined by previous measurements. Results are presented for the time variation of the light distribution and damage within the tissue as the optical properties of the tissue are altered.

London, R.A.; Glinsky, M.E.; Zimmerman, G.B.; Eder, D.C. [Lawrence Livermore National Lab., CA (United States); Jacques, S.L. [Texas Univ., Houston, TX (United States). M.D. Anderson Cancer Center

1995-03-01

157

Is the in-plane charge transport in the normal state of the cuprates anisotropic?

NASA Astrophysics Data System (ADS)

The doping dependence of the parameters of the cold-spot model of charge transport in the cuprates is studied. It is argued that the recently proposed test of the in-plane anisotropy of the charge transport in the cuprates by means of a nonlinear conductivity experiment should be feasible in underdoped cuprates, where electric fields ?10 V/cm should be sufficient in order to perform the test.

Hlubina, Richard

1999-06-01

158

NASA Astrophysics Data System (ADS)

While polymers are known as thermal insulators, recent studies show that stretched single chains of polymers have a very high thermal conductivity. In this work, our new simulation scheme for simulation of heat flow in nanoconfined fluids [H. Eslami, L. Mohammadzadeh, and N. Mehdipour, J. Chem. Phys. 135, 064703 (2011)] is employed to study the effect of chain ordering (stretching) on the rate of heat transfer in polyamide-6,6 nanoconfined between graphene surfaces. Our results for the heat flow in the parallel direction (the plane of surfaces) show that the coefficient of thermal conductivity depends on the intersurface distance and is much higher than that of the bulk polymer. A comparison of results in this work with our former findings on the heat flow in the perpendicular direction, with the coefficient of heat conductivity less than the bulk sample, reveal that well-organized polymer layers between the confining surfaces show an anisotropic heat conduction; the heat conduction in the direction parallel to the surfaces is much higher than that in the perpendicular direction. The origin of such anisotropy in nanometric heat flow is shown to be the dramatic anisotropy in chain conformations (chain stretching) beside the confining surfaces. The results indicate that the coefficients of heat conductivity in both directions, normal and parallel to the surfaces, depend on the degree of polymer layering between the surfaces and the pore width.

Eslami, Hossein; Mohammadzadeh, Laila; Mehdipour, Nargess

2012-03-01

159

Anisotropic magnetism in PrCrSb3 : Bulk properties of single crystals

NASA Astrophysics Data System (ADS)

We report anisotropic dc magnetic susceptibility ?(T) , isothermal magnetization M(H) , electrical resistivity ?(T) , and heat capacity C(T) measurements on a single crystalline sample of PrCrSb3 . The crystal exhibits ferromagnetic ordering below TC=112K due to ordering of Cr spins. The ferromagnetic phase is highly anisotropic. The anisotropy becomes even more evident at low temperatures at which the rare-earth ion gets magnetically ordered. Pr moments antiferromagnetically order at TN=12K . The magnetic interplay between these two species ( Cr3+ and Pr3+ ions) gives PrCrSb3 a complex magnetic phase diagram.

Inamdar, Manjusha; Thamizhavel, A.; Ramakrishnan, S.

2008-04-01

160

Anisotropic Silicon Etching Techniques.

National Technical Information Service (NTIS)

The main properties of anisotropic alkaline silicon etchants, such as anisotropy, influence of dopants, electrochemical, and photoelectrochemical behavior are summarized. A general unifying model is proposed, giving at least a qualitative explanation of a...

H. Seidel R. Voss

1991-01-01

161

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

162

An analytical model of anisotropic low-field electron mobility in wurtzite indium nitride

NASA Astrophysics Data System (ADS)

This paper presents a theoretical analysis of anisotropic transport properties and develops an anisotropic low-field electron analytical mobility model for wurtzite indium nitride (InN). For the different effective masses in the ?-A and ?-M directions of the lowest valley, both the transient and steady state transport behaviors of wurtzite InN show different transport characteristics in the two directions. From the relationship between velocity and electric field, the difference is more obvious when the electric field is low in the two directions. To make an accurate description of the anisotropic transport properties under low field, for the first time, we present an analytical model of anisotropic low-field electron mobility in wurtzite InN. The effects of different ionized impurity scattering models on the low-field mobility calculated by Monte Carlo method (Conwell-Weisskopf and Brooks-Herring method) are also considered.

Wang, Shulong; Liu, Hongxia; Song, Xin; Guo, Yulong; Yang, Zhaonian

2014-03-01

163

NASA Astrophysics Data System (ADS)

The sub-micrometer PbS with anisotropic microstructures including fishbone-like dendrites, multipods, cubes, corallines, and hopper cubes were successfully prepared by the solvothermal process. Different morphologies can be obtained by adjusting the reaction temperatures or using the nontoxic controlled reagents which can tune the relative growth rate in the <100> direction and the <111> direction of PbS nuclei. Based on the viewpoint of crystallography about face-centered cubic crystal structure, the possible formation mechanism for sub-micrometer anisotropic structures has been discussed. The difference between the enhanced growth rates on the {100} and {111} planes induced the change of ratio between the growth rates in the <100> and <111> directions, which resulted in the formation of the different PbS anisotropic microstructures. The PbS anisotropic structures exhibited the different visible emission with a peak in the red regions mainly attributed to the variation of shape, size, and the trap state of as-obtained PbS.

Cao, Yali; Hu, Pengfei; Jia, Dianzeng

2012-12-01

164

Properties of (311) planes anisotropically etched in (100) silicon by TMAH

This paper presents an investigation focused on the formation of (311) planes by wet anisotropic etching of (100) silicon in 5% TMAH etchant. Atomistic model of (311) plane formation is proposed, suggesting that (311) planes are composed of (111) and (100) steps. Surface roughness that is in most cases consequence of hillock formation at low concentrations of TMAH and etch

Drago Resnik; Danilo Vrtacnik; Uros Aljancic; Matej Mozek; Slavko Amon

2001-01-01

165

Slurry Transport Properties of Graded Coal Waste.

National Technical Information Service (NTIS)

The Bureau of Mines conducted laboratory tests to determine the slurry transport and deposition properties of coal waste. A 188.5-ft pipe test loop was constructed with instruments to measure density, flow, and power and discharge, suction, and differenti...

R. A. Busch R. R. Backer R. W. McKibbin

1983-01-01

166

Thermodynamic and transport properties of fluids

NASA Technical Reports Server (NTRS)

Computer program subroutine FLUID calculates thermodynamic and transport properties of pure fluids in liquid, gas, or two-phase (liquid/gas) conditions. Program determines thermodynamic state from assigned values for temperature and density, pressure and density, temperature and pressure, pressure and entropy, or pressure and enthalpy.

Fessler, T. E.

1980-01-01

167

Electronic transport properties in graphene oxide frameworks

NASA Astrophysics Data System (ADS)

The electronic transport properties in multiterminal graphene oxide framework (GOF) materials are investigated using a combination of theoretical and computational methods. GOFs make up four-terminal [origin=c]90H-shaped GNR-L-GNR junctions where sandwiched boronic acid molecules (L) are covalently linked to two graphene nanoribbons (GNRs) of different edge chiralities. The transport properties are governed by both tunneling and quasiresonant regimes. We determine how the presence of linker molecules affects the transport properties and establish that the through-molecule transport properties can be tuned by varying the chemical composition of the pillar molecules but are not significantly modified when changing the type of electrodes from zigzag GNRs to armchair GNRs. In addition, we find that in multilinker systems containing two parallel molecules in the device area, the coupling between the molecules can lead to both constructive and destructive quantum interferences. We also examine the inability of the classical Kirchhoff's superposition law to account for electron flow in multilinker GOF nanonetworks.

Zhu, P.; Cruz-Silva, E.; Meunier, V.

2014-02-01

168

Complex polarization ratio (CPR) in materials with birefringence and biattenuance is shown as a logarithmic spiral in the complex plane. A multi-state Levenberg-Marquardt nonlinear fitting algorithm using the CPR trajectory collected by polarization sensitive optical coherence tomography (PS-OCT) was developed to determine polarization properties of an anisotropic scattering medium. The Levenberg-Marquardt nonlinear fitting algorithm using the CPR trajectory is verified using simulated PS-OCT data with speckle noise. Birefringence and biattenuance of a birefringent film, ex-vivo rodent tail tendon and in-vivo primate retinal nerve fiber layer were determined using measured CPR trajectories and the Levenberg-Marquardt nonlinear fitting algorithm.

Park, Jesung; Kemp, Nate J.; Rylander, H. Grady; Milner, Thomas E.

2009-01-01

169

Transport properties in the Jovian atmosphere

NASA Technical Reports Server (NTRS)

Transport properties in a Jupiter-like atmosphere (89 mol % hydrogen and 11 mol % helium) are obtained by using the method of the kinetic theory of gases. The transport collision integrals are calculated by fitting various two-body semiempirical interaction potentials for which the collision integrals are tabulated to ab initio quantum mechanical calculations of the two-body interactions. The collision integrals are used to calculate the binary diffusion coefficients, viscosity, and 'total' thermal conductivity of the pure gases and the gas mixtures at 1-atm pressure from 1000 K to 25,000 K.

Biolsi, L.

1978-01-01

170

Some Properties of an Anisotropic Thin-Film-Waffle-Iron Memory Cell

A new mode of operation of the cubic waffle-iron memory cell in which an anisotropic, rather than isotropic, storage film is used has been investigated. When a conventional 1000-Å NiFe film is combined with a high-permeability ferrite baseplate a high-speed, low-current device is obtained. Typical operating parameters using a waffle baseplate containing 0.005-in. slots on 0.015-in. centers are:Iword=90 mA, Idigit=10

A. H. Bobeck; A. J. Perneski; J. P. Reekstin

1966-01-01

171

The issue of how to define and determine an optimal acoustical fit to a set\\u000aof anisotropic elastic constants is addressed. The optimal moduli are defined\\u000aas those which minimize the mean squared difference in the acoustical tensors\\u000abetween the given moduli and all possible moduli of a chosen higher material\\u000asymmetry. The solution is shown to be identical to

Andrew N. Norris

2006-01-01

172

NASA Astrophysics Data System (ADS)

It is well known that a tensor Stieltjes function f represents an effective transport coefficient q of an inhomogeneous medium consisting of two isotropic components. In this paper, we investigate multipoint matrix Padé approximants to matrix expansions of f. We prove that matrix Padé ones to f estimate f from the top and below. Consequently the Padé approximants to q form upper and lower bounds on q. The inequalities for matrix Padé bounds on f and q are established. They reduce to the inequalities for scalar Padé ones Tokarzewski (ZAMP 61:773-780, 2010). As an illustrative example, matrix Padé estimates of an effective conductivity of a specially laminated two-phase medium are computed.

Tokarzewski, S.

2013-02-01

173

Electronic transport properties of some liquid semiconductor

NASA Astrophysics Data System (ADS)

Electronic transport properties like electrical resistivity (?) and thermoelectric power (Q) of liquid semiconductor (Si, Ga, Ge, In, Sn, Tl and Bi) are calculated in the present study. Our well established single parametric model potential alongwith Percus Yevick hard sphere (PYHS) reference system are used to describe the structural information. To see the influence of exchange and correlation effect, Hartree, Taylor and Sarkar et al local field correlation functions are used. From present results, it is seen that good agreements between present results and experimental data have been achieved. Lastly we conclude that our model potential successfully produces the data of electronic transport properties for some liquid semiconductor (Si, Ga, Ge, In, Sn, Tl and Bi).

Sonvane, Y. A.; Thakor, P. B.; Jani, A. R.

2012-06-01

174

NASA Astrophysics Data System (ADS)

Spark plasma sintering technique had been applied to prepare bulk isotropic and anisotropic nanostructured Nd-Fe-B permanent magnets via hot pressing and subsequent hot deformation process. Influences of processing conditions and deformation height reduction on the structure and magnetic properties of the magnets were investigated. For the hot deformed magnet with 80% height reduction, XRD patterns of the anisotropic magnets show dominant (00l) diffraction peaks indicating evident c-axis crystallographic alignment in the magnet. Under the optimal processing conditions, the anisotropic magnet with 80% height reduction exhibits excellent magnetic properties as remanence (Br) of 1.492 T, coercive force (Hci) of 1004 kA/m, and the maximum energy product [(BH)max] of 400 kJ/m3, which are among the highest reported magnetic properties of nanostructured Nd-Fe-B permanent magnets.

Liu, W. Q.; Cui, Z. Z.; Yi, X. F.; Yue, M.; Jiang, Y. B.; Zhang, D. T.; Zhang, J. X.; Liu, X. B.

2010-05-01

175

Thermodynamic and Transport Properties of Gaseous Tetrafluoromethane in Chemical Equilibrium.

National Technical Information Service (NTIS)

Equations and in computer code are presented for the thermodynamic and transport properties of gaseous, undissociated tetrafluoromethane (CF4) in chemical equilibrium. The computer code calculates the thermodynamic and transport properties of CF4 when giv...

J. L. Hunt L. R. Boney

1973-01-01

176

Quantifying transport properties by exchange matrix method

NASA Astrophysics Data System (ADS)

The exchange matrix method is described to study of transport properties in chaotic geophysical flows. This study is important for applying in problems of pollutants transport (such as petroleum patches) in tidal flows and others. In order to construct this special exchange matrix (first suggested by Spencer & Wiley) we use an approximation of such flows made by Zimmerman, who adopted the idea of chaotic advection, first put forward by Aref. Then for a quantitative estimation of the transport properties we explore a coarse-grained density description introduced by Gibbs and Welander. Such coarse-grained representations over an investigation area, show a ``residence place'' for the pollutant material at any instant. The orbit expansion method, exploited an assumption that the contributions of tidal and residual currents are of different orders (the tidal is much stronger), does not give answers in many real situations. The exchange matrix can show transport of patches or particles from any place in the area under consideration to an arbitrary location in the tidal sea and time if it happens.

Krasnopolskaya, Tatyana; Meleshko, Vyacheslav

2005-11-01

177

Anisotropic Hydraulic Permeability Under Finite Deformation

The structural organization of biological tissues and cells often produces anisotropic transport properties. These tissues may also undergo large deformations under normal function, potentially inducing further anisotropy. A general framework for formulating constitutive relations for anisotropic transport properties under finite deformation is lacking in the literature. This study presents an approach based on representation theorems for symmetric tensor-valued functions and provides conditions to enforce positive semi-definiteness of the permeability or diffusivity tensor. Formulations are presented which describe materials that are orthotropic, transversely isotropic, or isotropic in the reference state, and where large strains induce greater anisotropy. Strain-induced anisotropy of the permeability of a solid-fluid mixture is illustrated for finite torsion of a cylinder subjected to axial permeation. It is shown that, in general, torsion can produce a helical flow pattern, rather than the rectilinear pattern observed when adopting a more specialized, unconditionally isotropic spatial permeability tensor commonly used in biomechanics. The general formulation presented in this study can produce both affine and non-affine reorientation of the preferred directions of material symmetry with strain, depending on the choice of material functions. This study addresses a need in the biomechanics literature by providing guidelines and formulations for anisotropic strain-dependent transport properties in porous-deformable media undergoing large deformations.

Ateshian, Gerard A.; Weiss, Jeffrey A.

2011-01-01

178

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

179

Anisotropic magnetic properties of Dy6Cr4Al43 single crystal

NASA Astrophysics Data System (ADS)

We have studied the anisotropic magnetic behavior of the rare earth intermetallic compound Dy6Cr4Al43. This compound crystallizes in the hexagonal symmetry and orders ferromagnetically at 8.3 K as confirmed by the magnetic susceptibility and heat capacity measurements. A significant anisotropy in the magnetization is observed between the c axis and the ab-plane. The easy axis liesin theab-plane at low temperatures; however it orients itselfalong the c-axis above 170 K as inferred from the susceptibility data.

Maurya, Arvind; Thamizhavel, A.; Dhar, S. K.

2014-04-01

180

In this paper we extend the theory of contact mechanics and rubber friction developed by one of us (B.N.J. Persson, J. Chem. Phys. 115, 3840 (2001)) to the case of surfaces with anisotropic surface roughness. As an application we calculate the viscoelastic contribution to the rubber friction. We show that the friction coefficient may depend significantly on the sliding direction, while the area of contact depends weakly on the sliding direction. We have carried out experiments for rubber blocks sliding on unidirectionally polished steel surfaces. The experimental data are in a good qualitative agreement with the theory. PMID:19578912

Carbone, G; Lorenz, B; Persson, B N J; Wohlers, A

2009-07-01

181

NASA Astrophysics Data System (ADS)

We designed, realized and tested a TE011-mode rectangular, high-permittivity, dielectric resonator, in order to obtain a measuring device capable of applying straight microwave currents to conductive samples. We characterized the prototype by means of extensive simulations that we compared to experimental results. Finally, we tested the device on a strongly anisotropic graphite sample. We found that the rotation of the sample produced significant changes in the response of the device. We conclude that the proposed rectangular dielectric resonator can be used as a device to detect the anisotropy of conductive samples.

Torokhtii, K.; Pompeo, N.; Silva, E.

2014-02-01

182

NMR properties of 3He-A in biaxially anisotropic aerogel

NASA Astrophysics Data System (ADS)

Theoretical model of G.E. Volovik for A-like phase of 3He in aerogel suggests formation of Larkin-Imry-Ma state of Anderson-Brinkmann-Morel order parameter. Most of results of NMR studies of A-like phase are in a good agreement with this model in assumption of uniaxial anisotropy, except for some of experiments in weakly anisotropic aerogel samples. We demonstrate that these results can be described in frames of the same model in assumption of biaxial anisotropy. Parameters of anisotropy in these experiments can be determined from the NMR data.

Dmitriev, V. V.; Krasnikhin, D. A.; Senin, A. A.; Yudin, A. N.

2012-12-01

183

Dielectric properties of highly anisotropic nematic liquid crystals for tunable microwave components

NASA Astrophysics Data System (ADS)

In this Letter, we report on measurements of the complex permittivity of highly anisotropic nematic liquid crystals at microwave frequencies as a function of the AC bias voltage. Permittivity measurements have been performed by the split post dielectric resonator technique. The experiments have shown that when the AC bias voltage increases from 0 to 8 V, the real part of the permittivity of these liquid crystals changes by up to 28%. The tunability and the relatively low dielectric losses observed in these liquid crystal mixtures mean that they are ideal materials for the design of tunable microwave components.

Kowerdziej, R.; Parka, J.; Krupka, J.; Olifierczuk, M.; Nowinowski-Kruszelnicki, E.; Jaroszewicz, L.; Chojnowska, O.

2013-10-01

184

NASA Astrophysics Data System (ADS)

Context: The Helios measurements of the angular momentum flux L of the fast solar wind lead to a tendency for the fluxes associated with individual ion angular momenta of protons and alpha particles, Lp and L_?, to be negative (i.e., in the sense of counter-rotation with the Sun). However, the opposite holds for the slow wind, and the overall particle contribution LP = L_p+L_? tends to exceed the magnetic contribution L_M. These two aspects are at variance with previous models. Aims: We examine whether introducing realistic ion temperature anisotropies can resolve this discrepancy. Methods: From a general set of multifluid transport equations with gyrotropic species pressure tensors, we derive the equations governing both the meridional and azimuthal dynamics of outflows from magnetized, rotating stars. The equations are not restricted to radial flows in the equatorial plane but valid for general axisymmetric winds that include two major ion species. The azimuthal dynamics are examined in detail, using the empirical meridional flow profiles for the solar wind, constructed mainly according to measurements made in situ. Results: The angular momentum flux L is determined by the requirement that the solution to the total angular momentum conservation law is unique and smooth in the vicinity of the Alfvén point, defined as where the combined Alfvénic Mach number M_T=1. MT has to consider the contributions from both protons and alpha particles. Introducing realistic ion temperature anisotropies may introduce a change of up to 10% in L and up to ~1.8 km~s-1 in azimuthal speeds of individual ions between 0.3 and 1 AU, compared with the isotropic case. The latter has strong consequences on the relative importance of LP and LM in the angular momentum budget. Conclusions: However, introducing ion temperature anisotropies cannot resolve the discrepancy between in situ measurements and model computations. For the fast-wind solutions, while in extreme cases LP may become negative, Lp never does. On the other hand, for the slow solar wind solutions examined, LP never exceeds L_M, even though LM may be less than the individual ion contribution, since Lp and L_? always have opposite signs for the slow and fast wind alike.

Li, B.; Li, X.

2009-01-01

185

Anisotropic charge transport in large single crystals of ?-conjugated organic molecules.

The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of ?-? stacking (along the long axis of the single crystal) with a mobility value in the order of 10(-3) cm(2) V(-1) s(-1), and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm(2) V(-1) s(-1). The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the ?-? stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility. PMID:24658783

Hourani, Wael; Rahimi, Khosrow; Botiz, Ioan; Koch, Felix Peter Vinzenz; Reiter, Günter; Lienerth, Peter; Heiser, Thomas; Bubendorff, Jean-Luc; Simon, Laurent

2014-05-01

186

Anisotropic charge transport in large single crystals of ?-conjugated organic molecules

NASA Astrophysics Data System (ADS)

The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of ?-? stacking (along the long axis of the single crystal) with a mobility value in the order of 10-3 cm2 V-1 s-1, and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm2 V-1 s-1. The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the ?-? stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility.

Hourani, Wael; Rahimi, Khosrow; Botiz, Ioan; Vinzenz Koch, Felix Peter; Reiter, Günter; Lienerth, Peter; Heiser, Thomas; Bubendorff, Jean-Luc; Simon, Laurent

2014-04-01

187

A novel blind inversion method using Lamb wave S(0) and A(0) mode velocities is proposed for the complete determination of elastic moduli, material symmetries, as well as principal plane orientations of anisotropic plates. The approach takes advantage of genetic algorithm, introduces the notion of "statistically significant" elastic moduli, and utilizes their sensitivities to velocity data to reconstruct the elastic moduli. The unknown material symmetry and the principal planes are then evaluated using the method proposed by Cowin and Mehrabadi [Q. J. Mech. Appl. Math. 40, 451-476 (1987)]. The blind inversion procedure was verified using simulated ultrasonic velocity data sets on materials with transversely isotropic, orthotropic, and monoclinic symmetries. A modified double ring configuration of the single transmitter and multiple receiver compact array was developed to experimentally validate the blind inversion approach on a quasi-isotropic graphite-epoxy composite plate. This technique finds application in the area of material characterization and structural health monitoring of anisotropic platelike structures. PMID:19206853

Vishnuvardhan, J; Krishnamurthy, C V; Balasubramaniam, Krishnan

2009-02-01

188

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

189

Electronic and transport properties of kinked graphene

Summary Local curvature, or bending, of a graphene sheet is known to increase the chemical reactivity presenting an opportunity for templated chemical functionalisation. Using first-principles calculations based on density functional theory (DFT), we investigate the reaction barrier reduction for the adsorption of atomic hydrogen at linear bends in graphene. We find a significant barrier lowering (?15%) for realistic radii of curvature (?20 Å) and that adsorption along the linear bend leads to a stable linear kink. We compute the electronic transport properties of individual and multiple kink lines, and demonstrate how these act as efficient barriers for electron transport. In particular, two parallel kink lines form a graphene pseudo-nanoribbon structure with a semimetallic/semiconducting electronic structure closely related to the corresponding isolated ribbons; the ribbon band gap translates into a transport gap for electronic transport across the kink lines. We finally consider pseudo-ribbon-based heterostructures and propose that such structures present a novel approach for band gap engineering in nanostructured graphene.

Rasmussen, Jesper Toft; Gunst, Tue; B?ggild, Peter; Jauho, Antti-Pekka

2013-01-01

190

Electrical and Thermoelectrical Transport Properties of Graphene

NASA Astrophysics Data System (ADS)

Graphene is a newly discovered material. It has many excellent properties, which make the research of this new material very important not only for the fundamental physics but also for the application. This thesis is a summary of our study in the electrical and thermoelectrical transport properties of graphene. In the first part of our work, we use a layer of molecules act as the charge reservoir to control the charge environment near or on graphene, we first obtained a mobility enhancement. By set the charge back and forth between graphene and the molecules, we found the graphene mobility can be widely tuned from 4000 to 19000 cm2/Vs. This strongly supports that charge impurities scattering is the main mechanism for graphene mobility. In addition, the charge neutral point in graphene can also be tuned independently over a wide gate voltage. A large memory effect is also found in the graphene device addressed with molecules, which makes this system potentially important for graphene application, such as graphene FLASH memory. In the second part of our work, we studied the thermopower of graphene with a wide range of mobility, i.e. varying degree of disorders, along with electrical conductivity at different temperatures. We have proved that the transport properties in graphene are indeed caused by the Dirac fermions particles. Moreover, we have found that the Mott relation fails in the vicinity of the Dirac point in high-mobility graphene. By properly taking account of high-temperature effects, we have obtained good agreement between the Boltzmann transport theory and our experimental data. In low-mobility graphene where the charged impurities induce relatively high residual carrier density, the Mott relation holds at all gate voltages.

Wang, Deqi

191

Quantum transport properties of zigzag graphene nanoribbons

NASA Astrophysics Data System (ADS)

We have studied the quantum transport properties of zigzag graphene nanoribbons under periodic or Möbius boundary conditions connected to one-dimensional leads using the nonequilibrium Green's function method with a tight-binding scheme. We reveal the existence of a current path originating from the edge states of the graphene nanoribbons. We have found that the conduction channel at the Fermi energy under the periodic boundary condition vanishes under the Möbius boundary condition, which is explained by the breaking of the AB-bipartite lattice symmetry.

Takaki, Hirokazu; Kobayashi, Nobuhiko

2011-01-01

192

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

193

Thermodynamics and magnetic properties of the anisotropic 3D Hubbard model.

We study the anisotropic 3D Hubbard model with increased nearest-neighbor tunneling amplitudes along one direction using the dynamical cluster approximation and compare the results to a quantum simulation experiment of ultracold fermions in an optical lattice. We find that the short-range spin correlations are significantly enhanced in the direction with stronger tunneling amplitudes. Our results agree with the experimental observations and show that the experimental temperature is lower than the strong tunneling amplitude. We characterize the system by examining the spin correlations beyond neighboring sites and determine the distribution of density, entropy, and spin correlation in the trapped system. We furthermore investigate the dependence of the critical entropy at the Néel transition on anisotropy. PMID:24702384

Imriška, Jakub; Iazzi, Mauro; Wang, Lei; Gull, Emanuel; Greif, Daniel; Uehlinger, Thomas; Jotzu, Gregor; Tarruell, Leticia; Esslinger, Tilman; Troyer, Matthias

2014-03-21

194

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

195

Investigation of carrier transport properties in semipolar (1122) GaN films with low defect density

NASA Astrophysics Data System (ADS)

We report on the anisotropic carrier transport properties of semipolar (1122) GaN films with low defect density. We utilized the asymmetric lateral epitaxy to obtain various semipolar (1122) GaN films having significantly reduced partial dislocations and basal-plane stacking faults (BPSFs). The directionally dependent carrier transport was observed with the lower sheet resistances (Rsh) along the [1100] direction. The Rsh ratios of semipolar (1122) GaN films were found to be relatively smaller than those of nonpolar a-plane GaN films, possibly due to low BPSF density and the reduced in-plane electric field induced by BPSF along the [1123] direction at wurtzite domain boundaries.

Jang, Soohwan; Kim, Hyonwoong; Soo Kim, Doo; Hwang, Sung-Min; Kim, Jihyun; Hyeon Baik, Kwang

2013-10-01

196

Electron Transport Properties of Ge nanowires

NASA Astrophysics Data System (ADS)

Electron Transport Properties of Ge nanowires Tobias Hanrath*, Saiful I. Khondaker, Zhen Yao, Brian A. Korgel* *Dept. of Chemical Engineering, Dept. of Physics, Texas Materials Institute, and Center for Nano- and Molecular Science and Technology University of Texas at Austin, Austin, Texas 78712-1062 e-mail: korgel@mail.che.utexas.edu Germanium (Ge) nanowires with diameters ranging from 6 to 50 nm and several micrometer in length were grown via a supercritical fluid-liquid-solid synthesis. Parallel electron energy loss spectroscopy (PEELS) was employed to study the band structure and electron density in the Ge nanowires. The observed increase in plasmon peak energy and peak width with decreasing nanowire diameter is attributed to quantum confinement effects. For electrical characterization, Ge nanowires were deposited onto a patterned Si/SiO2 substrate. E-beam lithography was then used to form electrode contacts to individual nanowires. The influence of nanowire diameter, surface chemistry and crystallographic defects on electron transport properties were investigated and the comparison of Ge nanowire conductivity with respect to bulk, intrinsic Ge will be presented.

Hanrath, Tobias; Khondaker, Saiful I.; Yao, Zhen; Korgel, Brian A.

2003-03-01

197

Electronic transport properties of assembled carbon nanoribbons.

Graphitic nanowiggles (GNWs) are 1D systems with segmented graphitic nanoribbon GNR edges of varying chiralities. They are characterized by the presence of a number of possible different spin distributions along their edges and by electronic band-gaps that are highly sensitive to the details of their geometry. These two properties promote these experimentally observed carbon nanostructures as some of the most promising candidates for developing high-performance nanodevices. Here, we highlight this potential with a detailed understanding of the electronic processes leading to their unique spin-state dependent electronic quantum transport properties. The three classes of GNWs containing at least one zigzag edge (necessary to the observation of multiple-magnetic states) are considered in two distinct geometries: a perfectly periodic system and in a one-GNW-cell system sandwiched between two semi-infinite terminals made up of straight GNRs. The present calculations establish a number of elementary rules to relate fundamental electronic transport functionality, electronic energy, the system geometry, and spin state. PMID:22735039

Girão, Eduardo Costa; Cruz-Silva, Eduardo; Meunier, Vincent

2012-07-24

198

Structure and charge transport properties in MEH-PPV

The charge carrier transport in MEH-PPV is investigated with respect to different molecular weight distributions and with different tetrahedral defect densities. The defect density influences the charge transport behaviors significantly. With smaller defect density, MEH-PPV exhibits better charge transport which further depends upon the morphology. Position disorder parameter which is due to the morphology difference dominates the charge transport properties

Anto Regis Inigo; Hsiang-Chih Chiu; Wunshain Fann; Ying-Sheng Huang; C. H. Hsu; Kang-Yung Peng; Show-An Chen

2003-01-01

199

Properties of (311) planes anisotropically etched in (100) silicon by TMAH

NASA Astrophysics Data System (ADS)

This paper presents an investigation focused on the formation of (311) planes by wet anisotropic etching of (100) silicon in 5% TMAH etchant. Atomistic model of (311) plane formation is proposed, suggesting that (311) planes are composed of (111) and (100) steps. Surface roughness that is in most cases consequence of hillock formation at low concentrations of TMAH and etch rates of (311) and (100) planes were studied as a function of etch temperature, time and addition of small amounts of ammonium peroxodisulfate (APODS). It was found that the smooth (311) planes without hillocks can be obtained only by etching in 5% TMAH with addition of 0,5% APODS. Due to obvious decomposition of APODS in the etching process determined by increased surface roughness, replenishing of additive is mandatory. Stirring experiments with 5%TMAH solution showed increased surface roughness and reduced etch rates of (100) and (311) plane. Dissolution rates of thermal oxide, LPCVD nitride and PECVD oxide and nitride were determined in temperature range from 60 degree(s)C-90 degree(s)C in 5% TMAH. APODS additive was found to have minor influence.

Resnik, Drago; Vrtacnik, Danilo; Aljancic, Uros; Mozek, Matej; Amon, Slavko

2001-09-01

200

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

201

Transport properties of epitaxial lift off films

NASA Technical Reports Server (NTRS)

Transport properties of epitaxially lifted-off (ELO) films were characterized using conductivity, Hall, and Shubnikov-de Haas measurements. A 10-15 percent increase in the 2D electron gas concentration was observed in these films as compared with adjacent conventional samples. We believe this result to be caused by a backgating effect produced by a charge build up at the interface of the ELO film and the quartz substrate. This increase results in a substantial decrease in the quantum lifetime in the ELO samples, by 17-30 percent, but without a degradation in carrier mobility. Under persistent photoconductivity, only one subband was populated in the conventional structure, while in the ELO films the population of the second subband was clearly visible. However, the increase of the second subband concentration with increasing excitation is substantially smaller than anticipated due to screening of the backgating effect.

Mena, R. A.; Schacham, S. E.; Young, P. G.; Haugland, E. J.; Alterovitz, S. A.

1993-01-01

202

Charge transport properties of spin crossover systems.

The study of spin crossover compounds by means of theoretical or experimental approaches has provided interesting results in recent decades. The main feature of such compounds is the change in the spin state induced by many different external stimuli, i.e. temperature, light, pressure, solvent coordination and the electric field. Spin crossover systems are potentially more useful than other magnetic molecules because their switching behaviour can occur closer to room temperature, and they are thus candidates for use in spintronic devices. Here, I review the state of the art in quantum chemical approaches to the study of such systems and discuss experiments that have focused on transport properties in single-molecule, nano-objects or thin-film spin crossover systems. PMID:24217339

Ruiz, Eliseo

2014-01-01

203

Transport Properties of the Universal Quantum Equation

NASA Astrophysics Data System (ADS)

The universal quantum equation (UQE) is found to describe the transport properties of the quantum particles. This equation describes a wave equation interacting with constant scalar and vector potentials propagating in spacetime. A new transformation that sends the Schrödinger equation with a potential energy to Dirac's equation is proposed. The Cattaneo telegraph equation as well as a one-dimensional UQE are compatible with our recently proposed generalized continuity equations. Furthermore, a new wave equation resulted from the invariance of the UQE under the post-Galilean transformations is derived. This equation is found to govern a Klein—Gordon's particle interacting with a photon-like vector field (ether) whose magnitude is proportional to the particle's mass.

I. Arbab, A.

2012-03-01

204

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

205

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

NASA Astrophysics Data System (ADS)

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.

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.

2013-02-01

206

Local anisotropic features method and its application

The local anisotropic features method is based on the analysis of anisotropy direction of energy Fourier spectrum of image points local neighborhood. Numbers of discrete anisotropic directions are chosen as features. In the features space the measure of images nearness is set. Thanks to its properties local anisotropic features (LAF) are invariant to a wide class of input images bright

Igor S. Gibin; Pavel G. Popov

1996-01-01

207

Electrical transport properties of silicon surfaces

NASA Astrophysics Data System (ADS)

The understanding and utilization of electronic transport phenomena in low-dimensional, quantum-confined structures is of enormous scientific and technological interest. We have studied the electrical transport properties of systems that are quantum confined in one dimension but periodic in the other two dimensions, namely surfaces and ultrathin film materials. The electrical conductance of atomically clean, reconstructed silicon surfaces and interfaces was measured as a function of temperature in ultrahigh vacuum using the classical four-point probe technique. We employed Silicon on Insulator (SOI) technology to enhance the surface sensitivity of the four-point probe measurements. High-quality ohmic contacts were fabricated using ion-implantation. The Si(100)2 x 1 surface reconstruction consists of a two-dimensional, anti-ferromagnetic c(4 x 2) array of buckled silicon dimers. The surface undergoes a c(4 x 2) ? 2 x 1 order-disorder transition near T = 200 K. Above 200 K, dimers fluctuate rapidly and the long-range c(4 x 2) ordering is destroyed. The conductance of this two-dimensional system has a temperature-dependence that is characteristic of a metal. The surface conductance appears closely correlated with the order parameter of the low-temperature c(4 x 2) structure. Thermally activated flip-flop motion of the Si dimers thus appears to be the dominant scattering mechanism. Recent high-resolution photoemission experiments indicate that the Si(111)7 x 7 surface reconstruction is a two-dimensional, correlated metal. The surface electrical conductivity decreases with increasing temperature, thus confirming metallic transport. However, conductivity measurements on ultrathin SOI indicate insulating behavior. The origin of this discrepancy is not understood and requires further investigation of the sheet conductance as a function of the SOI layer thickness. The Ga/Si(112) interface consists of a self-assembled, mesoscopic array of atomic Ga wires on a high-index Si(112) surface. The structural uniformity of this atomic-wire-or quantum-wire array is far superior to those created by nano-lithography or STM atom manipulation. Transport measurements reveal a strong conductance anisotropy as expected. However, the conduction channels are orthogonal to the crystallographic chains. This counterintuitive result is in excellent agreement with electronic structure calculations by Ortega and Flores. The theoretical band structure was confirmed independently with photoemission spectroscopy.

Yoo, Kwonjae

208

Transport properties of dimethyl sulfoxide aqueous solutions

NASA Astrophysics Data System (ADS)

The nonideal behavior of the transport properties of water-dimethyl sulfoxide (DMSO) mixtures has been studied through equilibrium and nonequilibrium molecular dynamic simulations. The shear viscosity and thermal conductivity of the mixture has been analyzed and compared with available experimental data at ambient conditions. The enhancement of shear viscosity at molar fractions xW=0.65 of water has been quantitatively reproduced in our simulations. In agreement with this fact, we have found an increase in the rigidity of the system reflected by an increase in the decay time of the survival probability of the H bonds. In addition, we compute the tetrahedral order parameter of water molecules in the solution at different molar fractions. This parameter indicates a reduction in the local tetrahedral order of water when the solute concentration is increased, followed by a clear minimum at the equimolar concentration near the locus of the maximum density of the mixture, probably due to the formation of water-DMSO complexes. We have obtained the thermal conductivity of the mixture for the first time. This property also presents a peculiar minimum at xW=0.4, precisely in the region of the minimum of the order parameter. However, no experimental confirmation of our results is available.

Nieto-Draghi, Carlos; Bonet Ávalos, Josep; Rousseau, Bernard

2003-09-01

209

Transport properties of supercooled confined water

NASA Astrophysics Data System (ADS)

This article presents an overview of recent experiments performed on transport properties of water in the deeply supercooled region, a temperature region of fundamental importance in the science of water. We report data of nuclear magnetic resonance, quasi-elastic neutron scattering, Fourier-transform infrared spectroscopy, and Raman spectroscopy, studying water confined in nanometer-scale environments. When contained within small pores, water does not crystallise, and can be supercooled well below its homogeneous nucleation temperature Th. On this basis it is possible to carry out a careful analysis of the well known thermodynamical anomalies of water. Studying the temperature and pressure dependencies of water dynamics, we show that the liquid-liquid phase transition (LLPT) hypothesis represents a reliable model for describing liquid water. In this model, water in the liquid state is a mixture of two different local structures, characterised by different densities, namely the low density liquid (LDL) and the high-density liquid (HDL). The LLPT line should terminate at a special transition point: a low-T liquid-liquid critical point. We discuss the following experimental findings on liquid water: (i) a crossover from non-Arrhenius behaviour at high T to Arrhenius behaviour at low T in transport parameters; (ii) a breakdown of the Stokes-Einstein relation; (iii) the existence of a Widom line, which is the locus of points corresponding to maximum correlation length in the p-T phase diagram and which ends in the liquid-liquid critical point; (iv) the direct observation of the LDL phase; (v) a minimum in the density at approximately 70 K below the temperature of the density maximum. In our opinion these results represent the experimental proofs of the validity of the LLPT hypothesis.

Mallamace, F.; Branca, C.; Broccio, M.; Corsaro, C.; Gonzalez-Segredo, N.; Spooren, J.; Stanley, H. E.; Chen, S.-H.

2008-07-01

210

Electronic transport properties of conducting polymers and carbon nanotubes

We review and compare electronic transport in different types of conducting polymer: conjugated organic polymers, the inorganic polymer polysulphur nitride, alkali-metal fulleride polymers, and carbon nanotubes. In each case, the transport properties show some unusual features compared to conventional metals. In conjugated organic conducting polymers, electronic transport shows a systematic pattern involving both metallic and non-metallic character. We discuss the

A. B. Kaiser

2001-01-01

211

NASA Astrophysics Data System (ADS)

In this study, we propose a new global procedure to perform optimization of semiempirical intermolecular potential parameters on the basis of a large reference database. To obtain transferable parameters, we used the original method proposed by Ungerer [Ungerer et al., J. Chem. Phys. 112, 5499 (2000)], based on the minimization of a dimensionless error criterion. This method allows the simultaneous optimization of several parameters from a large set of reference data. However, the computational cost of such a method limits its application, because it implies the calculation of an important number of partial derivatives, calculated by finite differences between the results of several different simulations. In this work, we propose a new method to evaluate partial derivatives, in order to reduce the computing time and to obtain more consistent derivatives. This method is based on the analysis of statistical fluctuations during a single simulation. To predict equilibrium properties of olefins, we optimize the Lennard-Jones potential parameters of the unsaturated hydrocarbon groups using the anisotropic united atoms description. The resulting parameters are consistent with those previously determined for linear and branched alkanes. Test simulations have been performed at temperatures ranging from 150 to 510 K for several ?-olefins (ethylene, propene, 1-butene, 1-pentene, 1-hexene, 1-octene), several ?-olefins (trans-2-butene, cis-2-butene, trans-2-pentene), isobutene, and butadiene. Equilibrium properties are well predicted, and critical properties can be evaluated with a good accuracy, despite the fact that most of the results constitute pure predictions. It is concluded that the AUA potential, due to a relevant physical meaning, can be transferred to a large range of olefins with good success.

Bourasseau, Emeric; Haboudou, Mehalia; Boutin, Anne; Fuchs, Alain H.; Ungerer, Philippe

2003-02-01

212

NASA Astrophysics Data System (ADS)

In this article we present recent developments regarding parameter estimation in sandwich structures with viscoelastic frequency dependent core and elastic laminated skin layers, with piezoelectric patch sensors and actuators bonded to the exterior surfaces of the sandwich. The frequency dependent viscoelastic properties of the core material are modelled using fractional derivative models, with unknown parameters that are to be estimated by an inverse technique, using experimentally measured natural frequencies and associated modal loss factors. The inverse problem is formulated as a constrained minimisation problem, and gradient based optimization techniques are employed. Applications are presented and discussed, focused on the identification of viscoelastic frequency dependent core material properties.

Araújo, Aurelio L.; Mota Soares, Cristovao M.; Mota Soares, Carlos A.; Herskovits, Jose

2010-10-01

213

Anisotropic flow and flow fluctuations for Au + Au at ?sNN =200 GeV in a multiphase transport model

NASA Astrophysics Data System (ADS)

Anisotropic flow coefficients and their fluctuations are investigated for Au + Au collisions at center-of-mass energy ?sNN = 200 GeV by using a multiphase transport model with string melting scenario. Experimental results of azimuthal anisotropies by means of the two- and four-particle cumulants are generally well reproduced by the model including both parton cascade and hadronic rescatterings. Event-by-event treatments of the harmonic flow coefficients vn (for n =2, 3, and 4) are performed, in which event distributions of vn for different orders are consistent with Gaussian shapes over all centrality bins. Systematic studies on centrality, transverse momentum (pT), and pseudorapidity (?) dependencies of anisotropic flows and quantitative estimations of the flow fluctuations are presented. The pT and ? dependencies of absolute fluctuations for both v2 and v3 follow trends similar to their flow coefficients. Relative fluctuation of triangular flow v3 is slightly centrality dependent, which is quite different from that of elliptic flow v2. It is observed that parton cascade has a large effect on the flow fluctuations, but hadronic scatterings make little contribution to the flow fluctuations, which indicates flow fluctuations are mainly modified during partonic evolution stage.

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

2014-04-01

214

Silver and gold nanoparticle superlattices with a layered structure were obtained via grafting of mesogenic molecules onto a metallic cluster surface. For the Ag superstructures unusual orientational order of the mesogenic ligands and anisotropy of the assembly afforded tunable plasmonic properties. PMID:23892425

Lewandowski, Wiktor; Constantin, Doru; Walicka, Kinga; Pociecha, Damian; Mieczkowski, Józef; Górecka, Ewa

2013-09-14

215

Anisotropic property of material arrangement in friction stir welding of dissimilar Mg alloys

Microstructure and mechanical properties of friction stir weld joints of dissimilar Mg alloys AZ31 and AZ80 were investigated in the present work. Several different welding parameters were adopted in the study, and the effects of rotation speed and welding speed on the joint quality were discussed comprehensively. In addition, material arrangement which means that AZ31 alloy was at advancing side

Duo Liu; Hiroyuki Nishio; Kazuhiro Nakata

2011-01-01

216

In this article we present recent developments regarding parameter estimation in sandwich structures with viscoelastic frequency dependent core and elastic laminated skin layers, with piezoelectric patch sensors and actuators bonded to the exterior surfaces of the sandwich. The frequency dependent viscoelastic properties of the core material are modelled using fractional derivative models, with unknown parameters that are to be estimated

Aurelio L. Araújo; Cristovao M. Mota Soares; Carlos A. Mota Soares; Jose Herskovits

2010-01-01

217

The physics of heterostructures is among the forefront problems in materials science. Composite materials also are attractive from the point of view of technological applications such as current-limiting thermistors, radar absorbers, and electromagnetic shields, because they exhibit a variety of interesting mechanical, electric and magnetic properties with the advantage of much reduced cost and weight. To quantify the dielectric response

A. Beroual; C. Brosseau

2001-01-01

218

A phenomenological Landau-Devonshine theory is used to describe the effects of external mechanical loading on equilibrium polarization states and dielectric properties in epitaxial ferroelectric thin films grown on dissimilar orthorhombic substrates which induce anisotropic misfit strains in the film plane. The calculation focuses on single-domain perovskite BaTiO3 and PbTiO3 thin films on the assumption that um1=-um2. Compared with the phase

J. H. Qiu; Q. Jiang

2007-01-01

219

Transport properties of fully screened Kondo models

NASA Astrophysics Data System (ADS)

We study the nonequilibrium transport properties of fully (exactly) screened Kondo quantum dots subject to a finite bias voltage or a finite temperature. First, we calculate the Fermi-liquid coefficients of the conductance for models with arbitrary spin, i.e., its leading behavior for small bias voltages or temperatures. Second, we determine the low-temperature behavior of the static susceptibility from the exactly known Bethe ansatz results for the magnetization. Third, we study the crossover from strong to weak coupling in the spin-1/2 and the spin-1 models coupled to one or two screening channels, respectively. Using a real-time renormalization group method we calculate the static and dynamical spin-spin correlation functions for the spin-1/2 model as well as the linear and differential conductance and the static susceptibility for the spin-1 model. We define various Kondo scales and discuss their relations. We assess the validity of the renormalization-group treatment by comparing with known results for the temperature dependence of the linear conductance and static susceptibility as well as the Fermi-liquid behavior at low energies.

Hörig, Christoph B. M.; Mora, Christophe; Schuricht, Dirk

2014-04-01

220

High-field transport properties of graphene

NASA Astrophysics Data System (ADS)

We present a theoretical investigation on the transport properties of graphene in the presence of high dc driving fields. Considering electron interactions with impurities and acoustic and optical phonons in graphene, we employ the momentum- and energy-balance equations derived from the Boltzmann equation to self-consistently evaluate the drift velocity and temperature of electrons in graphene in the linear and nonlinear response regimes. We find that the current-voltage relation exhibits distinctly nonlinear behavior, especially in the high electric field regime. Under the action of high-fields the large source-drain (sd) current density can be achieved and the current saturation in graphene is incomplete with increasing the sd voltage Vsd up to 3 V. Moreover, for high fields, Vsd>0.1 V, the heating of electrons in graphene occurs. It is shown that the sd current and electron temperature are sensitive to electron density and lattice temperature in the graphene device. This study is relevant to the application of graphene as high-field nano-electronic devices such as graphene field-effect transistors.

Dong, H. M.; Xu, W.; Peeters, F. M.

2011-09-01

221

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

222

In this article we present recent developments regarding parameter estimation in sandwich structures with viscoelastic frequency\\u000a dependent core and elastic laminated skin layers, with piezoelectric patch sensors and actuators bonded to the exterior surfaces\\u000a of the sandwich. The frequency dependent viscoelastic properties of the core material are modelled using fractional derivative\\u000a models, with unknown parameters that are to be estimated

Aurelio L. Araújo; Cristovao M. Mota Soares; Carlos A. Mota Soares; Jose Herskovits

2010-01-01

223

Polarization Properties of Synchrotron Radiation in the Study of Anisotropic Insulating Crystals

NASA Astrophysics Data System (ADS)

The optical properties of a wide series of the tungstates with the scheelite and wolframite crystal structure at the threshold of the fundamental absorption region were studied. New information about the influence of the electronic states forming the bottom of the conduction band and the top of the valence band on the formation of emission centers and mechanisms of energy transfer to these centers was obtained.

Kolobanov, V. N.; Kamenskikh, I. A.; Mikhailin, V. V.; Shpinkov, I. N.; Spassky, D. A.; Vasil'ev, A. N.; Zadneprovsky, B. I.; Potkin, L. I.; Zimmerer, G.

224

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

225

Anisotropic adhesion of micropillars with spatula pads.

Natural gecko adhesive structures consisting of angled setae, branched into thin spatulas, have remarkable properties including easily attachable and releasable anisotropic adhesion. The geometrically asymmetric structures lead to anisotropic adhesive properties. Inspired by the gecko, we fabricated an array of micropillars with asymmetric spatula pads from elastomeric materials. This paper describes the anisotropic properties of the micropillars with spatula pads as established by experimental measurements and observation together with finite element analysis. The results indicate that the structural difference of the spatula pad at one edge of the micropillar provides the anisotropic adhesive properties. PMID:24446878

Seo, Seungwan; Lee, Jehong; Kim, Kwang-Seop; Ko, Kwang Hee; Lee, Jong Hyun; Lee, Jongho

2014-02-12

226

ElAM: A computer program for the analysis and representation of anisotropic elastic properties

NASA Astrophysics Data System (ADS)

The continuum theory of elasticity has been used for more than a century and has applications in many fields of science and engineering. It is very robust, well understood and mathematically elegant. In the isotropic case elastic properties are easily represented, but for non-isotropic materials, even in the simple cubic symmetry, it can be difficult to visualise how properties such as Young's modulus or Poisson's ratio vary with stress/strain orientation. The ElAM ( Elastic Anisotropy Measures) code carries out the required tensorial operations (inversion, rotation, diagonalisation) and creates 3D models of an elastic property's anisotropy. It can also produce 2D cuts in any given plane, compute averages following diverse schemes and query a database of elastic constants to support meta-analyses. Program summaryProgram title: ElAM1.0 Catalogue identifier: AEHB_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEHB_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 43 848 No. of bytes in distributed program, including test data, etc.: 2 498 882 Distribution format: tar.gz Programming language: Fortran90 Computer: Any Operating system: Linux, Windows (XP, Vista) RAM: Depends chiefly on the size of the arrays representing elastic properties in 3D Classification: 7.7 Nature of problem: Representation of elastic moduli and ratios, and of wave velocities, in 3D; automatic discovery of unusual elastic properties. Solution method: Stiffness matrix (6×6) inversion and conversion to compliance tensor (3×3×3×3), tensor rotation, dynamic matrix diagonalisation, simple optimisation, postscript and VRML output preparation. Running time: Dependent on angular accuracy and size of elastic constant database (from a few seconds to a few hours). The tests provided take from a few seconds for test0 to approximately 1 hour for test4.

Marmier, Arnaud; Lethbridge, Zoe A. D.; Walton, Richard I.; Smith, Christopher W.; Parker, Stephen C.; Evans, Kenneth E.

2010-12-01

227

From Laplacian Transport to Dirichlet-to-Neumann (Gibbs) Semigroups

The paper gives a short account of some basic properties of \\\\textit{Dirichlet-to-Neumann} operators $\\\\Lambda_{\\\\gamma,\\\\partial\\\\Omega}$ including the corresponding semigroups motivated by the Laplacian transport in anisotropic media ($\\\\gamma \\\

Valentin A. Zagrebnov

2008-01-01

228

Neoclassical transport properties and their limits in NSTX

NASA Astrophysics Data System (ADS)

The low aspect ratio and low toroidal field of NSTX enhance its neoclassical transport properties, but also push the limits of standard neoclassical models. Particle and energy transport, plasma rotation, the radial electric field, and bootstrap current are examined for typical NSTX discharges. Regimes of inward and outward impurity transport driven by a combination of the inductive electric field (Ware pinch), inward transport on the deuterium density gradient, and outward transport on the ion temperature gradient are identified. Orbit losses and atomic physics effects near the plasma boundary lead to modifications in the bootstrap current and impurity transport properties in the H-mode pedestal. Potato orbit effects near the axis, included as a viscosity modification, can enhance the ion energy transport, but are reduced by orbit squeezing. The low aspect ratio and high beta of NSTX plasmas provide a critical test of the limits of neoclassical theory.

Houlberg, W. A.; Strand, P. I.; Shaing, K. C.

2001-10-01

229

Neoclassical Transport Properties of Tokamak Plasmas

The classical transport theory is strictly valid for a plasma in a homogeneous and stationary magnetic field. In the '60, experiments have shown that this theory does not apply as a local theory of transport in Tokamaks. It was shown that global geometric characteristics of the confining elements have a strong influence on the transport. Three regimes of collisionality are characteristic of the neoclassical transport theory: the banana regime (the electronic diffusion coefficient increases starting from zero), the plateau regime (the diffusion coefficient is almost independent of the collisionality) and the Pfirsch-Schlueter regime (the electronic diffusion coefficient again increases with the collisionality)

Weyssow, B. [Universite Libre de Bruxelles (Belgium)

2004-03-15

230

Anisotropic magnetic properties in Åkermanite Sr2 MSi2O7 ( M=Co, Mn) crystals

NASA Astrophysics Data System (ADS)

We have investigated the magnetic and the dielectric properties of åkermanite Sr2CoSi2O7 and Sr2MnSi2O7 single crystals. Sr2CoSi2O7 shows a canted antiferromagnetism with a large magnetic anisotropy at temperatures below 7 K. By applying a magnetic field along the [110] direction, an electric polarization emerges along the c axis at temperatures below the magnetic transition temperature. In high magnetic fields, the saturation magnetization becomes enhanced only when the electric polarization appears. In contrast, the magnetization of Sr2MnSi2O7 is isotropic at all temperatures, and its magnetic-field-induced electric polarization is very small. These results suggest that the electronic configuration of the transition-metal ion is of crucial importance for the appearance of electric polarization.

Akaki, Mitsuru; Tadokoro, Tomoya; Kuwahara, Hideki; Kihara, Takumi; Tokunaga, Masashi

2013-06-01

231

NASA Astrophysics Data System (ADS)

Dielectric property of epitaxial SrBi4Ti4O15 thin films with (001)-, (1110)-, (105)/(015)-, and (100)/(010)-orientations was investigated as a function of film thickness. As the tilting angle of c-axis from the surface normal is smaller, the relative dielectric constant begins to degrade at thinner thickness; eventually, the (001)-oriented films for which the c-axis is vertical to the substrate do not show noticeable degradation. The leakage current density also strongly depends of the tilting angle of the c-axis. The results indicate that the layer structure of SrBi4Ti4O15 exhibits a small size effect with high insulation performance.

Kojima, Takashi; Kimura, Junichi; Suzuki, Muneyasu; Takahashi, Kenji; Oikawa, Takahiro; Sakashita, Yukio; Kato, Kazumi; Watanabe, Takayuki; Takenaka, Tadashi; Yamada, Tomoaki; Funakubo, Hiroshi

2012-07-01

232

NASA Astrophysics Data System (ADS)

Magnetic properties of anisotropic and isotropic SmCo5/?-Fe nanocomposite magnets with a layered structure were computer-simulated with varying the stacking period, the ?-Fe fraction, and temperature. The (BH)max values of approximately 800 and 700 kJ/m3 were achieved for anisotropic magnets at 300 and 473 K, respectively. These values roughly agree with results for SmCo5/?-Fe with a core-shell structure, and the value at 473 K is much higher than that of Nd2Fe14B/?-Fe with a layered structure. For isotropic magnets, the largest Hc values were obtained for the stacking periods of approximately 20 and 25 nm at 300 and 473 K, respectively. The achieved (BH)max values were approximately 300 and 250 kJ/m3 at 300 and 473 K, respectively. The behavior of Hc was discussed in terms of the ratio of exchange energy to magnetic anisotropy one.

Horikawa, R.; Fukunaga, H.; Nakano, M.; Yanai, T.

2014-05-01

233

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 Vzz=-0.14% with an out-of-plane dilatation Vyy=0.38%. This anisotropic strain further separates the energy levels of top valence band at ? point. The energy splitting as 37 meV 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

234

Evaluating anisotropic properties in the porcine temporomandibular joint disc using nanoindentation.

The objective of this study was to determine the viscoelastic properties present within the intermediate zone of the porcine temporomandibular joint (TMJ) disc using nanoindentation. A 50-microm conospherical indenter tip using a displacement-controlled ramp function with a 600 nm/s loading and unloading rate, a 3000-nm peak displacement with a holding period of 30 s was used to indent the samples. Experimental load-relaxation tests were performed on the TMJ disc to determine the response in three different directions; the mediolateral, anteroposterior, and articular surface directions. The experimental data were analyzed using a generalized Maxwell model to obtain values for short- and long-time relaxation modulus and of material time constants. The short time relaxation modulus E ( I ) values were 180.92, 64.99, and 487.77 kPa for testing done on the articular surface, mediolateral, and anteroposterior directions, respectively. Corresponding values for the long-time relaxation modulus E (infinity) were 45.9, 14.97, and 133.5 kPa. The method confirmed anisotropy present within the central intermediate zone of the porcine TMJ disc due to the directional orientation of the collagen fibers. PMID:20195763

Yuya, P A; Amborn, E K; Beatty, M W; Turner, J A

2010-07-01

235

The precise nature of the material symmetry of articular cartilage in compression remains to be elucidated. The primary objective of this study was to determine the equilibrium compressive Young’s moduli and Poisson’s ratios of bovine cartilage along multiple directions (parallel and perpendicular to the split line direction, and normal to the articular surface) by loading small cubic specimens (0.9×0.9×0.8 mm, n=15) in unconfined compression, with the expectation that the material symmetry of cartilage could be determined more accurately with the help of a more complete set of material properties. The second objective was to investigate how the tension-compression nonlinearity of cartilage might alter the interpretation of material symmetry. Optimized digital image correlation was used to accurately determine the resultant strain fields within the specimens under loading. Experimental results demonstrated that neither the Young’s moduli nor the Poisson’s ratios exhibit the same values when measured along the three loading directions. The main findings of this study are that the framework of linear orthotropic elasticity (as well as higher symmetries of linear elasticity) is not suitable to describe the equilibrium response of articular cartilage nor characterize its material symmetry; a framework which accounts for the distinctly different responses of cartilage in tension and compression is more suitable for describing the equilibrium response of cartilage; within this framework, cartilage exhibits no lower than orthotropic symmetry.

Wang, Christopher C-B.; Chahine, Nadeen O.; Hung, Clark T.; Ateshian, Gerard A.

2010-01-01

236

Models of two level systems for anisotropic glassy materials

NASA Astrophysics Data System (ADS)

We use an extended version of the standard tunneling model to explain the sound absorption in anisotropic glassy materials and heat transport in mesoscopic slabs and bridges. The glassy properties are determined by an ensemble of two level systems (TLS). In our model a TLS is characterized by a 3x3 symmetric tensor, [T], which couples to the strain field, [S], through a 3x3x3x3 tensor of coupling constants, [[R

Anghel, Dragos-Victor; Dumitru, Irina Mihaela; Nemnes, Alexandru George; Churochkin, Dmitrii

2013-03-01

237

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

NASA Astrophysics Data System (ADS)

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 ridge axis. The seismic properties have been simulated at a temperature of 1200°C and pressure of 200 MPa so that the basalt melt is above its solidus. Various effective medium methods are discussed in the perspective of modelling rocks that have a strong background elastic anisotropy due to crystal preferred orientation (CPO) and an introduced anisotropy due to oriented melt filled inclusions. Calculations using various methods show a wide range of predicted melt fractions for a given seismic velocity. The self-consistent scheme (SCS) and differential effective medium (DEM) are compared in some detail. A tensorial model was developed using a poro-elastic method of Gassman at low seismic frequency and a standard DEM with isolated basalt inclusions at high frequency. At low frequency the basalt pore fluid is considered to be everywhere connected and the pressure uniform, whereas at high frequency basalt inclusions are isolated. Assuming the medium to be a standard linear solid the low and high frequency velocities were used to calculate the anisotropy of attenuation. Calculations with spherical basalt inclusions show that the seismic velocities decrease and attenuation increase with increasing melt fraction. The symmetry of the background anisotropy due to CPO is preserved, but gradually reduced with increasing melt fraction. For the seismic velocities observed for the axial magma chamber (AMC) with Vp of 3.5 to 4.7 km/s the model predicts 50-70% melt. For the low-velocity triangle (LVT) below the AMC with Vp of 4.8-5.6 km/s the model predicts 35-50% melt. Predictions from the observed attenuations ( Q-1) at the AMC of 0.05-0.02 and in the LVT of 0.02-0.01 are around 60% and 45% melt respectively. Seismic anisotropy has been modelled with ellipsoidal basalt 'pancake' shaped inclusions with their circular sections in the ( XY) foliation plane. Only a 2-3% of ellipsoidal basalt inclusions are required to over print the anisotropy of the background medium. There is a rapid decrease in Vp and increase of Q-1 for propagation normal to the foliation ( Z) with increasing axial ratio of the inclusions. With increasing axial ratio the model predicts decreasing amounts of melt for given velocity Vp in the Z direction. For the LVT only 15-25% melt is predicted for a 10:1 inclusion instead of the 35-50% of the spherical inclusion.

Mainprice, David

1997-09-01

238

Electronic transport properties of conducting polymers and carbon nanotubes

Abstract We review and compare,electronic transport in different types of conducting,polymer: conjugated organic polymers, the inorganic polymer polysulphur nitride, alkali-metal fulleride polymers, and carbon nanotubes. In each case, the transport properties show some unusual features compared,to conventional metals. In conjugated organic conducting polymers, electronic transport shows a systematic pattern involving both metallic and non-metallic character. We discuss the physical conduction

A B Kaiser

239

Analysis of bacterial cell properties and transport in porous media

The cell properties of Escherichia coli ATCC 11105 (gram-negative rod and motile) and Staphylococcus aureus ATCC 10537 (gram-positive coccus and immotile) and their transport in porous media were investigated in this study. Bacterial cell properties such as cell geometry, zeta potential, and hydrophobicity were analyzed using surface measurement and bio-imaging techniques. Transport of both bacteria was examined using column experiments

Seong-Jik Park; Song-Bae Kim; Ki-Woo Kim

2010-01-01

240

Issues with characterizing transport properties of graphene field effect transistors

NASA Astrophysics Data System (ADS)

The transport properties of graphene field effect transistors are typically characterized using a conventional test structure consisting of graphene on silicon dioxide with deposited metal contacts. Two of the primary parameters affecting the total resistance of this structure are the channel mobility and contact resistance. A simple model is used to describe the impact of these parameters on total device resistance and experimentally extract them. Important issues related to characterizing the transport properties of graphene field effect transistors are presented and discussed.

Venugopal, Archana; Colombo, Luigi; Vogel, Eric M.

2012-08-01

241

Anisotropic universe with anisotropic sources

NASA Astrophysics Data System (ADS)

We analyze the state space of a Bianchi-I universe with anisotropic sources. Here we consider an extended state space which includes null geodesics in this background. The evolution equations for all the state observables are derived. Dynamical systems approach is used to study the evolution of these equations. The asymptotic stable fixed points for all the evolution equations are found. We also check our analytic results with numerical analysis of these dynamical equations. The evolution of the state observables are studied both in cosmic time and using a dimensionless time variable. Then we repeat the same analysis with a more realistic scenario, adding the isotropic (dust like dark) matter and a cosmological constant (dark energy) to our anisotropic sources, to study their co-evolution. The universe now approaches a de Sitter space asymptotically dominated by the cosmological constant. The cosmic microwave background anisotropy maps due to shear are also generated in this scenario, assuming that the universe contains anisotropic matter along with the usual (dark) matter and vacuum (dark) energy since decoupling. We find that they contribute dominantly to the CMB quadrupole. We also constrain the current level of anisotropy and also search for any cosmic preferred axis present in the data. We use the Union 2 Supernovae data to this extent. An anisotropy axis close to the mirror symmetry axis seen in the cosmic microwave background data from Planck probe is found.

Aluri, Pavan K.; Panda, Sukanta; Sharma, Manabendra; Thakur, Snigdha

2013-12-01

242

Transport Properties: Conductivity, Viscosity, and Ultrasonic Relaxation.

National Technical Information Service (NTIS)

The paper considers the inter-relation of the various transport parameters in liquids. The structure of the liquid is considered arrested for most of the time. The discussion is limited to a comparison between the molten oxides and molten salts in which s...

P. B. Macedo R. A. Weiler

1968-01-01

243

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...

244

Early Collective Expansion: Relativistic Hydrodynamics and the Transport Properties of QCD Matter

NASA Astrophysics Data System (ADS)

This document is part of Volume 23 `Relativistic Heavy Ion Physics' of Landolt-Börnstein - Group I `Elementary Particles, Nuclei and Atoms'. It contains the Section `5.1 Hydrodynamics and Transport Properties of QCD Matter' of the Chapter `5 Primordial Bulk Plasma Dynamics in Nuclear Collisions at RHIC' with the content: 5.1 Hydrodynamics and Transport Properties of QCD Matter 5.1.1 Introduction 5.1.2 The equations of relativistic hydrodynamics 5.1.2.1 Ideal fluid dynamics for perfect fluids 5.1.2.2 Dissipative fluid dynamics for viscous relativistic fluids 5.1.2.3 Transport equations for the dissipative flows 5.1.2.3.1 Standard dissipative fluid dynamics (first-order or Navier-Stokes theory) 5.1.2.3.2 Second-order Israel-Stewart theory 5.1.3 The beginning and end of the hydrodynamic stage in heavy-ion collisions 5.1.3.1 Initialization 5.1.3.1.1 Glauber model 5.1.3.1.2 Color Glass Condensate theory and KLN model 5.1.3.1.3 Non-central collisions and initial fireball eccentricity 5.1.3.2 Decoupling and freeze-out 5.1.3.2.1 Two-stage decoupling 5.1.3.2.2 Final hadron momentum spectra 5.1.4 The nuclear equation of state 5.1.5 Phenomenology of the transverse expansion 5.1.5.1 Radial expansion in central collisions 5.1.5.2 Anisotropic flow in non-central collisions 5.1.6 Comparison with experiment 5.1.6.1 Azimuthally integrated momentum spectra 5.1.6.1.1 Rapidity distributions 5.1.6.1.2 Transverse momentum and transverse mass distributions at midrapidity 5.1.6.2 Anisotropic transverse momentum spectra from deformed fireballs 5.1.6.2.1 Elliptic flow as an early fireball signature 5.1.6.2.2 Elliptic flow at RHIC 5.1.6.2.3 Implications: Rapid thermalization and "strongly coupled quark-gluon plasma" (sQGP) 5.1.6.3 Signs of viscosity 5.1.6.3.1 Spectra and elliptic flow at midrapidity 5.1.6.3.2 Centrality and rapidity dependence of elliptic flow 5.1.6.3.3 Multiplicity scaling of elliptic flow 5.1.6.3.4 Towards extracting the QGP viscosity 5.1.7 Epilogue

Heinz, Ulrich

245

CET89 - CHEMICAL EQUILIBRIUM WITH TRANSPORT PROPERTIES, 1989

NASA Technical Reports Server (NTRS)

Scientists and engineers need chemical equilibrium composition data to calculate the theoretical thermodynamic properties of a chemical system. This information is essential in the design and analysis of equipment such as compressors, turbines, nozzles, engines, shock tubes, heat exchangers, and chemical processing equipment. The substantial amount of numerical computation required to obtain equilibrium compositions and transport properties for complex chemical systems led scientists at NASA's Lewis Research Center to develop CET89, a program designed to calculate the thermodynamic and transport properties of these systems. CET89 is a general program which will calculate chemical equilibrium compositions and mixture properties for any chemical system with available thermodynamic data. Generally, mixtures may include condensed and gaseous products. CET89 performs the following operations: it 1) obtains chemical equilibrium compositions for assigned thermodynamic states, 2) calculates dilute-gas transport properties of complex chemical mixtures, 3) obtains Chapman-Jouguet detonation properties for gaseous species, 4) calculates incident and reflected shock properties in terms of assigned velocities, and 5) calculates theoretical rocket performance for both equilibrium and frozen compositions during expansion. The rocket performance function allows the option of assuming either a finite area or an infinite area combustor. CET89 accommodates problems involving up to 24 reactants, 20 elements, and 600 products (400 of which may be condensed). The program includes a library of thermodynamic and transport properties in the form of least squares coefficients for possible reaction products. It includes thermodynamic data for over 1300 gaseous and condensed species and transport data for 151 gases. The subroutines UTHERM and UTRAN convert thermodynamic and transport data to unformatted form for faster processing. The program conforms to the FORTRAN 77 standard, except for some input in NAMELIST format. It requires about 423 KB memory, and is designed to be used on mainframe, workstation, and mini computers. Due to its memory requirements, this program does not readily lend itself to implementation on MS-DOS based machines.

Mcbride, B.

1994-01-01

246

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

247

NASA Astrophysics Data System (ADS)

We developed a quantitative approach for the determination of molecular arrangement and electronic structure in anisotropic organic ultrathin films based on the measurement of polarized reflectivity at the carbon K-edge. The reflectivity spectra were fitted to a parameterized model calculation. The method was applied to a self-assembled monolayer of 1,4-benzenedimethanethiol on gold. To simulate reflectivity, the organic anisotropic film was described by a dielectric tensor, obtained by ab initio calculations for the single molecule and suitable rotations to describe the molecular organization in film domains. Film structure was obtained though the best fit of the simulation to the experiment. Results were consistent with a monolayer-thick film composed of domains of molecules with in-plane isotropic distribution of orientations. In each domain, molecules adopted a standing configuration, with a tilt of 28° relative to the substrate normal. Information on the modification of the molecular electronic states due to chemical bonding was derived.

Pasquali, Luca; Mukherjee, Subhrangsu; Terzi, Fabio; Giglia, Angelo; Mahne, Nicola; Koshmak, Konstantin; Esaulov, Vladimir; Toccafondi, Chiara; Canepa, Maurizio; Nannarone, Stefano

2014-01-01

248

NASA Astrophysics Data System (ADS)

We have succeeded in growth of large high-quality single crystals of SmBaMn2O6 and measured their magnetism and electrical transport properties. The temperature dependence of the magnetization and resistivity exhibits anomalies at ˜375 and ˜200 K. The anomalies accompany hystereses and can be assigned to ordering and rearrangement transitions of charge and orbital of Mn ions, respectively. A broad peak in magnetic susceptibility at 250 K observed for pulverized samples is strongly suppressed in the case of single crystal. Magnetic susceptibility for a magnetic field parallel to the a-axis shows a kink at 175 K, below which a magnetic anisotropy emerges. The result indicates an antiferromagnetic transition of the Mn spin moments below the charge and orbital rearrangement transition, disagreeing with previous studies of polycrystalline samples.

Yamada, Shigeki; Maeda, Youichi; Arima, Taka-hisa

2012-11-01

249

Transport properties of single vacancies in nanotubes

NASA Astrophysics Data System (ADS)

We present density of states and electronic transport calculations of single vacancies in carbon nanotubes. We confirm that the defect reconstructs into a pentagon and a nonagon, following the removal of a single carbon atom. This leads to the formation of a dangling bond. Finally, we demonstrate that care must be taken when calculating the density of states of impurities in one-dimensional systems in general. Traditional treatments of these systems using periodic boundary conditions leads to the formation of minigaps even in the limit of large unit cells.

Rocha, A. R.; Padilha, J. E.; Fazzio, A.; da Silva, A. J. R.

2008-04-01

250

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

251

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

252

NASA Astrophysics Data System (ADS)

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 the score and the mean number of collisions per history in the nonanalog Monte Carlo simulations. Therefore, the solution of the BMC equation predicts the variance of the score and the figure of merit in the simulation. Also, by (i) using an angular biasing function that is closely related to the "asymptotic" solution of the linear Boltzmann equation and (ii) requiring isotropic weight changes at collisions, we derive a new angular biasing scheme. Using the BMC equation, we propose a universal "safe" upper limit of the transform parameter, valid for any type of exponential transform. In numerical calculations, we demonstrate that the behavior of the Monte Carlo simulations and the performance predicted by deterministically solving the BMC equation agree well, and that the new angular biasing scheme is always advantageous.

Ueki, Taro; Larsen, Edward W.

1998-09-01

253

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

254

Transport Properties of Semiconducting Phosphate Glasses

The temperature and frequency dependence of conductivity, dielectric properties, infrared absorption, and electron-paramagnetic-resonance data are presented for semiconducting phosphate glasses based on oxides of Ti, V, Mn, Fe, Co, Ni, Cu, Mo, and W. The vanadate system is examined in a range of compositions, most of the others in the composition 50 mol% oxide. A polaronic model is shown to

M. Sayer; A. Mansingh

1972-01-01

255

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

256

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

257

Charge transport properties of nanocrystals studied by electrostatic force microscopy

NASA Astrophysics Data System (ADS)

Charge transport in semiconductor and metal nanocrystal multilayers between two electrodes is probed by electrostatic force microscopy. The in-plane charge diffusion coefficients are deduced from the charge distribution imaged in real time. Temperature dependence of the transport properties and effects of photoionization and oxidation are also investigated. Implications of these results on the transport mechanisms will be discussed. This work was supported by the ONR Young Investigator Award N000140410489, the American Chemical Society (ACS) PRF award # 41256-G10, and the startup funds at the University of Pennsylvania. MF acknowledges funding from the NSF IGERT program (Grant #DGE-0221664) and SENS.

Hu, Zonghai

2005-03-01

258

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, J. D. Jr.; Caldas, I. L. [Instituto de Fisica, Universidade de Sao Paulo, Sao Paulo, 05315-970 Sao Paulo (Brazil); Lopes, S. R.; Viana, R. L. [Departamento de Fisica, Universidade Federal do Parana, Caixa Postal 19044, Curitiba, 81531-990 Parana (Brazil); Morrison, P. J. [Department of Physics and Institute for Fusion Studies, University of Texas at Austin, Austin, Texas 78712 (United States)

2009-12-15

259

Thermal transport properties of rolled graphene nanoribbons

NASA Astrophysics Data System (ADS)

Using nonequilibrium Green's function method, we investigate the influence of the curvature and edge effects on the thermal transport during the process of rolling graphene nanoribbons (GNRs) into carbon nanotubes (CNTs) in the transverse direction. The curvature effect results in a slight decrease in the thermal conductance of GNRs, which is remarkably different from that in the longitudinal direction. The curvature and edge effects show a strong size and chirality dependence, while the curvature effect is more sensitive to the size. When the size equals to 12.8 nm (49.2 nm) with the zigzag (armchair) edge, the edge effect results in the reduction of thermal conductance of 2.4% (13.0%) as compared to the corresponding CNT, but the curvature effect vanishes.

Li, Dengfeng; Li, Bolin; Luo, Min; Feng, Chunbao; Ouyang, Tao; Gao, Fei

2013-08-01

260

Transport properties of semi-Dirac

NASA Astrophysics Data System (ADS)

Recent theoretical works show the existence of a new type of dispersion relation in both VO2/TiO2 nanostructuresfootnotetextV. Pardo and W.E. Pickett, Phys.Rev. Let. 102, 166803 (2009) and in stressed graphene footnotetextG. Montambaux et al., PRB 80, 153412 (2009), where the electrons confined in a plane show a non-relativistic behavior along one direction, and relativistic in the other. This semi-Dirac dispersion E=?(vFpx)^2+(py^2/2m)^2 can be observed in graphene when the Dirac cones of different valleys touch each other because of stress. When stress is increased, a gap is opened, and the graphene turns from a semi-metal to an insulator. We propose to adress this topological phase transition through transport measurements.

Adroguer, Pierre

2013-03-01

261

A new anisotropic united atom (AUA4) force field is developed to predict the phase equilibrium and transport properties of different primary amines. The force field transferability was studied for an important set of molecules, including linear amines (methyl, ethyl, n-propyl, and n-hexylamine), branched amines (isopropyl and isobutylamine), and bifunctional amines (ethylenediamine, 1,3-propanediamine, and 1,5-pentanediamine). Monte Carlo simulations in the Gibbs ensemble were carried out to study thermodynamic properties such as equilibrium densities, vaporization enthalpies, and vapor pressures. Critical coordinates (critical density, critical temperature, and critical pressure) and normal boiling points were also calculated. The shear viscosity coefficients were studied for methyl, ethyl, and n-propylamine at different temperatures using molecular dynamics. Our results show a very good agreement with experimental values for thermodynamic properties and are an improvement on the models available in the literature, all of which are all-atom. Viscosity coefficients also show a good agreement compared with experimental data, demonstrating the transferability of our force field not only to predict thermodynamic properties but also to predict transport properties. PMID:22034922

Orozco, Gustavo A; Nieto-Draghi, Carlos; Mackie, Allan D; Lachet, Véronique

2011-12-15

262

Electronic and transport properties in graphene oxide frameworks

NASA Astrophysics Data System (ADS)

We report a detailed theoretical study of the electronic and transport properties of a series of graphene oxide frameworks (GOFs) using first-principles calculations based on density functional theory. The pillar molecular structure of GOFs determine that with various linear boronic acid pillars and different pillar concentrations, GOF structures can be fine tuned and exhibit various electronic properties. Based on ideal GOF structures, we predict that GOFs' electronic properties, such as band gap, can be modified controllobly by an appropriate choice of pillaring units and pillar concentration. The quantum transport properties of several systems with various linear boronic acid pillars are also evaluated. The variation of conductance arising from different pillar composition is shown to be potentially useful for practical applications.

Zhu, Pan; Meunier, Vincent

2013-03-01

263

Collective excitations and low-temperature transport properties of bismuth

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

P. Chudzinski; T. Giamarchi

2011-01-01

264

Electronic transport properties of an armchair boron-nitride nanotube

NASA Astrophysics Data System (ADS)

We present a theoretical study of electron transport properties through boron-nitride nanotube (BNNT) and contrast them to those of carbon nanotube (CNT). The work is based on a tight-binding Hamiltonian model within the framework of a generalized Green's function technique and relies on the Landauer-Bütikker formalism as the basis for studying the current-voltage characteristic of this system. We use an armchair single-walled BNNT in the CNT/BNNT/CNT structure. We numerically compute the transport properties in terms of transmission and current-voltage characteristic. Our calculations show that the electron transport can open a conduction gap in the CNT/BNNT/CNT structure.

Vahedi Fakhrabad, D.; Ashhadi, M.

2012-07-01

265

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

266

Investigation of mass transport properties of microfibrillated cellulose (MFC) films

The structure and transport properties of a four different films based on two different generations of microfibrillated cellulose (MFC), alone or in combination with glycerol as plasticizer, were investigated through FE-SEM analysis and sorption or permeation experiments. FE-SEM revealed the existence of complex structures in the different samples. A porous, closely packed fiber network, more homogeneous in the samples containing

Matteo Minelli; Marco Giacinti Baschetti; Ferruccio Doghieri; Mikael Ankerfors; Tom Lindström; István Siró; David Plackett

2010-01-01

267

Transport Properties of Bi-related Nanowire Systems.

National Technical Information Service (NTIS)

We present here an electrical transport property study of Te-doped Bi nanowires, and Bi(1-x)Sb(x) alloy nanowires embedded in a dielectric matrix. The crystal structure of the nanowires were characterized by X-ray diffraction measurements, indicating that...

Y. M. Lin S. B. Cronin J. Ying J. Heremans M. S. Dresselhaus

2001-01-01

268

The in-plane dielectric and ferroelectric properties of coherent anisotropically strained SrTiO{sub 3} thin films grown on orthorhombic (101) DyScO{sub 3} substrates were examined as a function of the angle between the applied electric field and the principal directions of the substrate. The dielectric permittivity revealed two distinct maxima as a function of temperature along the [100]{sub p} and [010]{sub p} SrTiO{sub 3} pseudocubic directions. These data, in conjunction with optical second-harmonic generation, show that the switchable ferroelectric polarization develops first predominantly along the in-plane axis with the larger tensile strain before developing a polarization component along the perpendicular direction with smaller strain as well, leading to domain twinning at the lower temperature. Finally, weak signatures in the dielectric and second-harmonic generation response were detected at the SrTiO{sub 3} tilt transition close to 165 K. These studies indicate that anisotropic biaxial strain can lead to new ferroelectric domain reorientation transitions that are not observed in isotropically strained films.

Biegalski, Michael D [ORNL; Trolier-McKinstry, Susan [Pennsylvania State University; Schlom, Darrell [Pennsylvania State University; Kumar, Amit [Pennsylvania State University; Sheng, Guang [Pennsylvania State University, University Park, PA; Vlahos, Eftihia [Pennsylvania State University, University Park, PA; Chen, Long-Qing [Pennsylvania State University; Uecker, Rinhold [Institute for Crystal Growth, Berlin, Germany; Streiffer, Stephen [Argonne National Laboratory (ANL); Gopalan, Venkatraman [ORNL

2009-01-01

269

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

270

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

271

Transport properties of silicate melts at high pressure

NASA Astrophysics Data System (ADS)

It is well appreciated that the transport properties (e.g., diffusion, viscosity) of silicate melts are intimately linked by melt structure and the time scales of structural relaxation. These linkages have been explored exten-sively at low pressure, but our understanding is more limited for high-pressure conditions relevant to the Earth's deep interior. Transport property models based on free-volume, activation energy and/or configurational entropy have merits, but their validity in extrapolation is uncertain. Moreover, the structural implications at high pressure are conflicting and lack experimental support. We examine these issues and review theoretical efforts to model transport properties at high pressure, as well as, those constraints provided by laboratory experiments and simulations. We emphasis the need to consider the properties of melt not only for high-pressure superheated conditions, but also for supercooled conditions in the vicinity of the glass transition. For example, the time scales for density relaxation traversing the glass transition at high pressure can be monitored using in situ X-ray miroctomography/absorption and ex vivo by the Archimedes' method combined with spectroscopy. These approaches are amenable to both strong and fragile liquids. Taken together with superliquidus data, we can greatly improve the interpolation of melt properties within the melting interval for refractory mantle compositions.

Lesher, C. E.; Gaudio, S. J.; Clark, A. N.; O'Dwyer-Brown, L.

2012-12-01

272

Wentzel-Bardeen singularity in coupled Luttinger liquids: Transport properties

The recent progress on 1 D interacting electrons systems and their applications to study the transport properties of quasi one dimensional wires is reviewed. We focus on strongly correlated elections coupled to low energy acoustic phonons in one dimension. The exponents of various response functions are calculated, and their striking sensitivity to the Wentzel-Bardeen singularity is discussed. For the Hubbard model coupled to phonons the equivalent of a phase diagram is established. By increasing the filling factor towards half filling the WB singularity is approached. This in turn suppresses antiferromagnetic fluctuations and drives the system towards the superconducting regime, via a new intermediate (metallic) phase. The implications of this phenomenon on the transport properties of an ideal wire as well as the properties of a wire with weak or strong scattering are analyzed in a perturbative renormalization group calculation. This allows to recover the three regimes predicted from the divergence criteria of the response functions.

Martin, T.

1994-08-26

273

NASA Astrophysics Data System (ADS)

With the help of the tensor method, the cross-spectral density matrix for the stochastic electromagnetic twist anisotropic Gaussian-Schell model (ETAGSM) beam truncated by a slit aperture propagating in turbulent atmosphere are derived. The spectral properties of this kind of beam are investigated in detail. It is shown by numerical results and analysis that the affection of the slit aperture on the spectral properties of the stochastic ETAGSM beam is obvious in the near field; while in the far field, the atmospheric turbulence plays an important role; the source beam's coherence can weaken the affection of the slit aperture and the atmospheric turbulence on the spectral properties of the stochastic ETAGSM beam truncated by a slit aperture propagating in turbulent atmosphere, while the twist properties of the source beam can strong the affection of the slit aperture on the spectral properties in the near field. Also, the spectral degree of polarization and normalized spectral density distributions and corresponding contour graphs of the stochastic ETAGSM beam truncated by a slit aperture propagating in turbulent atmosphere and free space at different propagation distances are investigated in detail.

Wang, Haiyan; Li, Xiangyin

2010-10-01

274

Iontophoretic transport pathways: dependence on penetrant physicochemical properties.

The objective of this work was to investigate how the preferred iontophoretic transport pathways of a molecule depend on its physicochemical properties. Laser scanning confocal microscopy (LSCM) was used to visualize in hairless mouse skin the distribution of two fluorescent penetrants: calcein, a multiply charged (-4), hydrophilic molecule; and nile red, a lipophilic, neutral compound. Iontophoresis and passive delivery of nile red showed that the percutaneous transport of this compound occurred via (inter- and intracellular) pathways that were clearly distinct from those followed by calcein. Although the distribution of nile red was influenced somewhat by the passage of current relative to the passive control, there was relatively little enhancement of the penetration of this compound into the skin. Calcein, on the other hand, did not passively enter the skin. However, with iontophoresis, greatly enhanced transport, with an important contribution from follicular structures, was observed. Sequential (dual) transport of the two fluorophores illustrated clearly the different pathways followed and reflected the transport and visualization studies of the individual species. It may be concluded, therefore, that the iontophoretic pathways followed across the skin are dictated by the physicochemical properties of the penetrant and by its affinity for the different environments available. PMID:9423151

Turner, N G; Guy, R H

1997-12-01

275

Microcrystalline silicon -- Relation of transport properties and microstructure

Understanding of transport in hydrogenated microcrystalline silicon ({micro}c-Si:H) is difficult due to its complicated microstructure (grains, grain boundaries, amorphous tissue). {micro}c-Si:H layers often exhibit preferential orientation leading to transport anisotropy. Furthermore, specific {micro}c-Si:H growth features lead to the thickness dependence of the structure and properties. {micro}c-Si:H incubation layer was studied by AFM with conductive cantilever measuring simultaneously morphology and local conductivity maps with submicron resolution. Clear identification of Si crystallites (with size of few tens of nanometers) is demonstrated. The crystalline fraction at the surface may be easily evaluated. For the charge collection in solar cells they need to study transport perpendicular to the substrate. Measurement of frequency spectra of A.C. conductivity is introduced as a new tool which can exclude the influence of contact barriers in sandwich geometry and can be used for finding the true conductivity perpendicular to the substrate. Using this technique transport anisotropy in some {micro}c-Si:H samples was clearly demonstrated. Finally, it is shown how the transport properties change with growing {micro}c-Si:H thickness and how these changes correlate with the structure observed by AFM.

Kocka, J.; Fejfar, A.; Vorlicek, V.; Stuchlikova, H.; Stuchlik, J.

1999-07-01

276

Evaluation of anisotropic thermoelectric power of ReSi 1.75

NASA Astrophysics Data System (ADS)

The highly anisotropic transport properties of ReSi 1.75 single crystals have been evaluated with the Boltzmann transport equation under the assumption that the deformation potential acoustic phonon scattering is dominant. There is a large difference between the calculated transport properties and the measured properties along [1 0 0], while there is little difference between the calculated and the measured along [0 0 1]. The intervalley scattering mechanism is proposed as the reason of the discrepancy in the transport properties along [1 0 0]. It is also shown that the large effective mass of holes along [0 0 1] restrict the contribution of the holes in transporting the energy induced by the Seebeck effect, resulting in good thermoelectric conversion efficiency.

Oh, Min-Wook; Gu, Jia-Jun; Inui, Haruyuki; Oh, Myung-Hoon; Wee, Dang-Moon

2007-02-01

277

Thermodynamic and anisotropic properties of single crystalline RCo2Ge2 (R = Y, La-Nd, Sm-Tm)

NASA Astrophysics Data System (ADS)

Single crystals of RCo2Ge2 (R = Y, La-Nd, Sm-Tm) were grown using a self-flux method and were characterized from 1.8-300 K by heat capacity, magnetization and in-plane resistivity measurements. Anisotropic metamagnetism was studied at 1.8 K up to 9 T. Due to a strong crystal electric field (CEF) effect, the magnetic ordering temperatures of the heavy rare earth members do not follow the de Gennes scaling, but rather a CEF modified trend. The RCo2Ge2 series offers an opportunity to study different types of magnetic anisotropy ranging from Heisenberg-like GdCo2Ge2 to Ising-like TbCo2Ge2. Correlation between the local moments and conduction electrons as well as the influence of interplay between CEF effect and long-range indirect exchange interaction (RKKY type) will also be discussed.

Kong, Tai; Buffon, Malinda; Lin, Xiao; Thaler, Alex; Cunningham, Charles; Bud'Ko, Sergey; Canfield, Paul

2013-03-01

278

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

279

Electronic properties and quantum transport in Graphene-based nanostructures

NASA Astrophysics Data System (ADS)

Carbon nanotubes (CNTs) and graphene nanoribbons (GNRs) represent a novel class of low-dimensional materials. All these graphene-based nanostructures are expected to display the extraordinary electronic, thermal and mechanical properties of graphene and are thus promising candidates for a wide range of nanoscience and nanotechnology applications. In this paper, the electronic and quantum transport properties of these carbon nanomaterials are reviewed. Although these systems share the similar graphene electronic structure, confinement effects are playing a crucial role. Indeed, the lateral confinement of charge carriers could create an energy gap near the charge neutrality point, depending on the width of the ribbon, the nanotube diameter, the stacking of the carbon layers regarding the different crystallographic orientations involved. After reviewing the transport properties of defect-free systems, doping and topological defects (including edge disorder) are also proposed as tools to taylor the quantum conductance in these materials. Their unusual electronic and transport properties promote these carbon nanomaterials as promising candidates for new building blocks in a future carbon-based nanoelectronics, thus opening alternatives to present silicon-based electronics devices.

Dubois, S. M.-M.; Zanolli, Z.; Declerck, X.; Charlier, J.-C.

2009-11-01

280

NASA Astrophysics Data System (ADS)

An anisotropic tunnel microporous crystal was prepared. Active transportation of anthracene as a guest molecule in the anisotropic tunnels was observed. The direction of anthracene movement implies that the anisotropic tunnel did not work as a flap-check valve. The direction of the movement was consistent with that caused by a Brownian ratchet.An anisotropic tunnel microporous crystal was prepared. Active transportation of anthracene as a guest molecule in the anisotropic tunnels was observed. The direction of anthracene movement implies that the anisotropic tunnel did not work as a flap-check valve. The direction of the movement was consistent with that caused by a Brownian ratchet. Electronic supplementary information (ESI) available. CCDC reference numbers 837539 and 837540. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2nr30880k

Kataoka, Keisuke; Yasumoto, Tetsuaki; Manabe, Yousuke; Sato, Hiroyasu; Yamano, Akihito; Katagiri, Toshimasa

2013-01-01

281

Nanoparticle decoration on carbon nanotubes was employed to modulate their electrical conductance and thermopower and thereby improved the thermoelectric power factor. Nanotubes were made into films by spraying nanotube solutions on glass substrates, and then the films were immersed in different concentrations of CuSO(4) or HAuCl(4) solutions for various time periods. Copper ions in the solutions were reduced on nanotubes by obtaining electrons from zinc electrodes, whose reduction potential is lower than that of copper (galvanic displacement). Gold ions were reduced on nanotubes by both silver counter electrodes and spontaneous reaction due to larger reduction potentials than those of nanotubes. These reactions made electrons donated to (copper incorporation) or withdrawn from (gold incorporation) nanotubes depending on the difference in their work functions and reduction potentials, resulting in considerable changes in electron transport. In this paper, a series of experiments at different ion concentrations and reaction time periods were systematically performed in order to find optimum nanoparticle formation conditions and corresponding electronic transport changes for better thermoelectric power factor. Transport measurement results show that electronic properties can be considerably altered and modulated, resulting in 2-fold improvement in the thermoelectric power factor with 1 mM/30 min reaction. Reactions with solutions of a low metal ion concentration, such as 1 mM, yielded well-distributed small particles over large surface areas, which strongly affected electron transfer between nanoparticles and nanotubes. Successive copper and gold decorations on nanotubes made electrical conductance (or thermopower) serially decreased and increased (or increased and decreased) upon precipitating different metal particles. This transport behavior is believed to be from the changes in the Fermi level as a result of electron exchanges between reduced metals and nanotubes. Thermopower improvement after copper decoration can be attributed to the enlarged gap between the Fermi level and the mean of differential electrical conductivity. Such behaviors often appear when the Fermi level is shifted toward the spike-shape density of states in nanotubes due to anisotropic differential electrical conductivity. Finally, this study demonstrates that the thermoelectric power factor can be considerably increased by properly locating the Fermi level of carbon nanotubes with nanoparticles, providing promising opportunities of developing efficient organic thermoelectric materials as well as various electronic materials of desired properties. PMID:21222461

Yu, Choongho; Ryu, Yeontack; Yin, Liang; Yang, Hongjoo

2011-02-22

282

Transport properties of a flexible fiber in cellular flows

NASA Astrophysics Data System (ADS)

Recent experiments by V. Steinberg and his collaborators have used ``low Reynolds turbulence'' in elastic flows to demonstrate coil-stretch transitions of fluorescently labelled DNA molecules. With this as motivation, we consider the much simpler problem of an elastic fiber that moves in a periodic cellular flow. Our numerical simulations show that such a fiber can act as a spatially extended test particle whose internal dynamics can lead to complex transport properties across space. In some parameter regimes, we find that space can be divided into regions of fiber entrapment and fiber transport, with fibers either trapped near elliptic points, or being transported along the connecting manifolds of the hyperbolic points. We also find that fiber buckling near hyperbolic points can yield random walk behavior over long times, with the effective diffusivity showing little dependence on the effective rigidity of the fiber.

Shelley, Michael; Young, Yuan-Nan

2006-11-01

283

The microgeometry and transport properties of sedimentary rock

NASA Astrophysics Data System (ADS)

This monograph describes recent progress in modelling the transport properties of sedimentary rock. Statistical descriptions are applied to the pore-space geometry and to the transport processes involving pore fluids. Fractals are used to quantify the pore geometry at length scales shorter than grain size. Percolation theory is applied to fluid flow. The permeability can be expressed in terms of a single effective pore diameter measured from mercury injection capillary pressure. This permeability relation is valid for essentially all porous rock and for a broad class of porous media. Mercury injection provides a powerful caliper of the geometry of a percolation cluster in a pore-space and supplies new information about pore space correlations and dynamics of fluid displacements. The statistical description of fluid transport in porous media has analogues in disordered electronic and magnetic materials. Future work may make substantial use of such analogues to solve more complex problems of direct relevance to petroleum exploration and production.

Thompson, A. H.; Katz, A. J.; Krohn, C. E.

1987-11-01

284

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.

2013-01-01

285

Electrical Transport Properties of Liquid Al-Cu Alloys

NASA Astrophysics Data System (ADS)

Electrical transport properties viz. electrical resistivity, thermoelectric power and thermal conductivity of liquid Al-Cu alloys as a function of Cu concentration have been studied in the present paper. Ashcroft empty core model potential has been used to incorporate the ion-electron interaction. To incorporate the exchange and correlation effects, five different forms of local field correction functions viz. Hartree, Taylor, Ichimaru et al., Farid et al. and Sarkar et al. have been used. The transport properties of binary system have been studied using Faber-Ziman formulation combined with Ashcroft-Langreth (AL) partial structure factor. The computed values of electrical resistivity are compared with experimental data and for low Cu concentration, good agreement has been observed. Further, thermoelectric power and thermal conductivity have also been predicted.

Thakore, B. Y.; Khambholja, S. G.; Suthar, P. H.; Jani, A. R.

2010-06-01

286

Low temperature transport properties of Ce-Al metallic glasses

NASA Astrophysics Data System (ADS)

The low temperature transport properties of Ce75-xAl25+x (x = 0, 10, and 15 at. %) metallic glasses were investigated. Magnetic field and composition tuned magnetoresistances changing from negative to positive values were observed at low temperature. It was suggested that these peculiar phenomena were caused by the tunable competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yoshida interaction in Ce-Al metallic glass with the variation in Ce content and magnetic field. Further magnetization and Ce-2p3d resonant inelastic x-ray scattering spectroscopy measurements supported this scenario. These Ce-Al metallic glasses could provide an interesting model system for the investigation of 4f electron behaviors in complex condensed matter with tunable transport properties.

Zeng, Q. S.; Rotundu, C. R.; Mao, W. L.; Dai, J. H.; Xiao, Y. M.; Chow, P.; Chen, X. J.; Qin, C. L.; Mao, H.-K.; Jiang, J. Z.

2011-06-01

287

Electrical and thermal transport properties of CdO ceramics

NASA Astrophysics Data System (ADS)

High temperature electrical and thermal transport properties, that is, electrical conductivity, Seebeck coefficient and thermal conductivity, of CdO ceramics have been investigated. Because of the good electrical properties and low thermal conductivity, the dimensionless figure-of-merit ZT of the CdO ceramics reaches 0.34 at 1023 K. This value is comparable to the best reported ZT for the n-type oxide ceramic thermoelectric materials and remains as potential to be further improved by porosity controlling or nanostructuring.

Lü, Qing; Wang, ShuFang; Li, LongJiang; Wang, JiangLong; Dai, ShouYu; Yu, Wei; Fu, GuangSheng

2014-03-01

288

Engineered microstructures and transport properties in YBCO coated conductors.

Each process used to deposit or make the bi-axially textured template, buffer layer(s), and the superconductor in a coated conductor creates interfaces along which defects or interfacial reactions may result. These defects can be additive and propagate through the entire film structure to affect the growth and properties of the superconducting film. Defects within the films and their corresponding transport properties have been correlated with the differences in the thickness of the underlying buffer layer material. This knowledge can be used to control and engineer the structure of the coated conductor to maximize critical current densities.

Holesinger, T. G. (Terry G.); Gibbons, B. J. (Brady J.); Coulter, J. Y. (James Y.); Foltyn, S. R. (Stephen R.); Arendt, P. N. (Paul N.)

2001-01-01

289

Transport properties of armchair graphene nanoribbon junctions between graphene electrodes.

The transmission properties of armchair graphene nanoribbon junctions between graphene electrodes are investigated by means of first-principles quantum transport calculations. First the dependence of the transmission function on the size of the nanoribbon has been studied. Two regimes are highlighted: for a small applied bias transport takes place via tunneling and the length of the ribbon is the key parameter that determines the junction conductance; at a higher applied bias resonant transport through the HOMO and LUMO starts to play a more determinant role, and the transport properties depend on the details of the geometry (width and length) of the carbon nanoribbon. In the case of the thinnest ribbon it has been verified that a tilted geometry of the central phenyl ring is the most stable configuration. As a consequence of this rotation the conductance decreases due to the misalignment of the ? orbitals between the phenyl ring and the remaining part of the junction. All the computed transmission functions have shown a negligible dependence on different saturations and reconstructions of the edges of the graphene leads, suggesting a general validity of the reported results. PMID:22743740

Motta, C; Sánchez-Portal, D; Trioni, M I

2012-08-14

290

Transport properties of a two impurity system: a theoretical approach.

NASA Astrophysics Data System (ADS)

Double magnetic-impurity systems have attracted great attention due to their rich physics and possible technological applications. A system of two interacting Co atoms has been studied in a recent STM experiments (Nature Physics 7, 901 (2011)). The precise control of the inter-impurity distance made it possible to explore in detail the transport properties of the system as a function of the impurities' interaction with each other. We explain, for all the parameter range studied, the physics observed in the experiments using a microscopic model, based on the two impurity Anderson model, including a two-path geometry for charge transport. The many-body system is treated in the finite-U Slave Boson Mean Field Approximation. Other results obtained using the Logarithmic Discretization Embedded Cluster Approximation are also discussed. We physically characterize the system and show that, as in the experiments, the features observed in the transport properties depend on the presence of two impurities but also on the existence of two conducting channels for electron transport. In particular, we obtain a splitting in the differential conductance, compatible with the one observed in the experiments, as a result of the superposition of the many-body Kondo states of each impurity.

Hamad, Ignacio J.; Costa Ribeiro, Laercio; Martins, George; Anda, Enrique V.

2013-03-01

291

Nonstoichiometry and transport properties of strontium-substituted lanthanum cobaltites

In La1?xSrxCoO3?? (LSC), the oxygen nonstoichiometry and transport properties change with variations in Sr content, temperature and oxygen partial pressure. The purpose of this study was to investigate and correlate these parameters. The extent of oxygen deficiency was investigated by oxygen exchange measurements over the range from 300 to 900 °C and 1.9×10?2?pO2?1.0×10?4 bar. The oxygen deficiency was found to

W. Sitte; E. Bucher; W. Preis

2002-01-01

292

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

293

Thermodynamic and Transport Properties of Superconducting Mg10B2

Transport and thermodynamic properties of a sintered pellet of the newly discovered MgB2 superconductor have been measured to determine the characteristic critical magnetic fields and critical current densities. Both resistive transition and magnetization data give similar values of the upper critical field, Hc2, with magnetization data giving dHc2\\/dT = 0.44 T\\/K at the transition temperature of Tc = 40.2 K.

D. K. Finnemore; J. E. Ostenson; S. L. Bud'Ko; G. Lapertot; P. C. Canfield

2001-01-01

294

Nonlinear transport properties of III-nitrides in electric field

We consider the transport properties of polar direct-gap semiconductors in an electric field, specializing the numerical calculation of the general theory to the case of n-doped III-nitrides, in particular, GaN, AlN, and InN. The nonequilibrium thermodynamic state of these materials-characterized by the variables so-called quasitemperature, quasichemical potential, and drift velocity of the carriers, and the quasitemperatures of longitudinal optical and

Clóves G. Rodrigues; Áurea R. Vasconcellos; Roberto Luzzi; Valder N. Freire

2005-01-01

295

The electron transport properties of pure liquid metals

Progress in the theory of the electrical conductivity and other ordinary transport properties of liquid metals since 1961 is reviewed. After a brief account of the basic nearly-free-electron diffraction formula, the quantitative comparison of this formula with experiment is discussed.For the alkali metals, the agreement is adequate, given the uncertainty of the pseudopotentials, although there is controversy about the calculation

J. M. Ziman

1967-01-01

296

Transport properties of antidot superlattices of graphene nanoribbons

In this work we show a theoretical study of the electronic and transport properties of superlattices formed by a periodic structure of vacancies (antidots) on graphene nanoribbons. The systems are described by a single-band tight-binding Hamiltonian and also by ab initio total energy density-functional theory calculations. The quantum conductance is determined within the Green's function formalism, calculated by real-space renormalization

L. Rosales; M. Pacheco; Z. Barticevic; A. León; A. Latgé; P. A. Orellana

2009-01-01

297

Magnetic and transport properties of oxide thin films

My dissertation research focuses on the investigation of the transport and magnetic properties of transition metal and rare earth doped oxides, particularly SnO2 and HfO2 thin films. Cr- and Fe-doped SnO 2 films were deposited on Al2O3 substrates by pulsed-laser deposition. X-ray-diffraction patterns (XRD) show that the films have rutile structure and grow epitaxially along the (101) plane. The diffraction

Yuanjia Hong

2007-01-01

298

Effects of antidots on the transport properties of graphene nanoribbons

Effects of magnetic antidots on the transport properties of zigzag-edged graphene nanoribbons ZGNRs are investigated by spin-polarized first-principles calculations combined with a nonequilibrium Green's-function technique. Specifically, the effects of antidots or holes with regular shapes rectangular and triangular are studied. It is found that rectangular holes with a zero total spin S0 and triangular holes with a finite spin S0

X. H. Zheng; G. R. Zhang; Z. Zeng; Víctor M. García-Suárez; Colin J. Lambert

2009-01-01

299

Effects of antidots on the transport properties of graphene nanoribbons

Effects of magnetic antidots on the transport properties of zigzag-edged graphene nanoribbons (ZGNRs) are investigated by spin-polarized first-principles calculations combined with a nonequilibrium Green's-function technique. Specifically, the effects of antidots (or holes) with regular shapes (rectangular and triangular) are studied. It is found that rectangular holes with a zero total spin S0 and triangular holes with a finite spin S0

X. H. Zheng; G. R. Zhang; Z. Zeng; Víctor M. García-Suárez; Colin J. Lambert

2009-01-01

300

Regional Differences in Ciliary Epithelial Cell Transport Properties

. Experiments were performed to determine whether the transport properties of the ciliary epithelium vary over different regions.\\u000a Rabbit iris-ciliary bodies were incubated under experimental or control conditions for 30 min before quick freezing, cryosectioning,\\u000a dehydration and electron probe X-ray microanalysis. Cryosections were cut from three regions along the major axis of the iris-ciliary\\u000a body, i.e., the anterior, middle and

C. W. McLaughlin; S. Zellhuber-McMillan; D. Peart; R. D. Purves; A. D. C. Macknight; M. M. Civan

2001-01-01

301

Transport properties of doped cuprate ladder compounds grown by MBE

Charge transfer was measured by X-ray absorption at the copper L3 edge in thin films of cuprate ladder compounds (Sr,Ca)Cu2O3+? grown by molecular beam epitaxy. Depending on the oxidation process, the charge transfer of the films varies in the range 0.07 to 0.26. Transport properties of the SrCu2O3 compounds show localization in agreement with variable range hopping, while some CaCu2O3

C. Partiot; M. Dorget; C. Deville Cavellin; F. Studer; X. Z. Xu; F. Beuran; M. Laguës

2000-01-01

302

The magnetic and transport properties of template-synthesized carbon-based and related nanomaterials

NASA Astrophysics Data System (ADS)

The porous alumina template-assisted method of nanoscale materials preparation provides a simple, relatively inexpensive, yet highly controllable and repeatable process for nanomaterial synthesis. Various nanostructures can then be made utilizing the porous structure as a scaffold. In this dissertation we study the porous alumina anodization process, the synthesis of porous alumina-assisted materials, and the basic physical properties of these materials, primarily concentrating on the magnetic and transport properties. First, we study the porous alumina formation process as a function of anodization voltage, acid type, and acid concentration. We find that while acid type strongly affects the growth characteristics of porous alumina, pH does not. We also study the stability of pore formation. We characterize the two- and three-dimensional stability of the growth process. We find that in three dimensions, an unstable formation region as a function of pH and voltage will cause the formation of dendrite structures. Next, we study the synthesis of materials in the porous alumina templates. Through chemical self-assembly, electrodeposition is able to make a wide variety of nanowires and nanotubes and we seek to optimize this process. Third, we study the optical properties Au and Ag nanowire arrays embedded in porous alumina. We find that such materials have use as negative index metamaterials owing to the existence of both transverse and longitudinal surface plasmon resonances. Next, we study the basic magnetic properties of new PAni-ferromagnet composite nanostructures and compare these properties to the magnetic properties of the nanotubes and the nanowires alone. We find the high dielectric properties of the PAni to strongly shield the ferromagnetic nanowires from magnetostatic interactions. Fifth, we make devices out of carbon nanotubes synthesized by CVD in the alumina templates. We investigate the transport properties of these carbon nanotubes. Further, we find that the contact resistances, which are normally on the order of mega-ohms for these tubes, can be lowered to the order of kilo-ohms by annealing in H 2/Ar atmosphere. We find that the disorder in these carbon nanotubes allows for the uptake of H during the annealing process. These H-complex hydrogen impurities, along with C and H adatoms, induce ferromagnetism in the carbon nanotubes. We carry out a magnetic study on the annealed carbon nanotubes. Moreover, the ferromagnetism of the carbon nanotubes results in hysteric magnetoresistance. We study this effect, attributing it to strong magneto-viscosity effects and anisotropic magnetoresistance. We also study the transport and magnetotransport properties of the annealed carbon nanotubes as a function of temperature and inner diameter. We find that there is an order-disorder transition that occurs at lower temperatures that resembles behavior predicted in disordered carbon fibers by the Bright model. We also find that the nanotubes behave as one-dimensional Luttinger liquids. Finally, as a means of comparison, we fabricate and study the properties of monolayer graphene devices.

Friedman, Adam Louis

303

Transport properties of polymer solutions. A comparative approach.

A variety of transport properties have been measured for solutions of the water soluble polymer poly(ethylene oxide)(PEO) with molecular weights ranging from 200 to 14,000, and volume fractions ranging from 0-80%. The transport properties are thermal conductivity, electrical conductivity at audio frequencies (in solutions containing dilute electrolyte), and water self-diffusion. These data, together with dielectric relaxation data previously reported, are amenable to analysis by the same mixture theory. The ionic conductivity and water self-diffusion coefficient, but not the thermal conductivity, are substantially smaller than predicted by the Maxwell and Hanai mixture relations, calculated using the known transport properties of pure liquid water. A 25% (by volume) solution of PEO exhibits an average dielectric relaxation frequency of the suspending water of one half that of pure water, with clear evidence of a distribution of relaxation times present. The limits of the cumulative distribution of dielectric relaxation times that are consistent with the data are obtained using a linear programming technique. The application of simple mixture theory, under appropriate limiting conditions, yields hydration values for the more dilute polymer solutions that are somewhat larger than values obtained from thermodynamic measurements.

Foster, K R; Cheever, E; Leonard, J B; Blum, F D

1984-01-01

304

NASA Astrophysics Data System (ADS)

Anisotropic cuprates La4Cu3MoO12 and La3Cu2VO9 crystallize in homeotypes of the YAlO3 structure with ordered transition metal cations that create a four times larger monoclinic supercell (? ~ 90) in the former, and a thirteen times larger hexagonal supercell in the latter. The magnetism of both exhibits distinct paramagnetic regimes owing to geometrically frustrated antiferromagnetic spin-coupling. Ln'2Ln '2Cu3MoO12 will form an analogous structure if rIXLn rIX Yb = 104 pm and DrIXLn< 14pm. (Ln'/Ln' )3Cu2VO9 will form if rIXLn rIX Tb = 110 pm. The phases with larger lanthanides ions are under- coordinated, but form in the proximity of an ``umbrella'' stoichiometry that promotes the formation of unconventional structures and complex compositions by destabilizing multiphase alternatives. Oxygen can even be removed from La4Cu 3MoO12 by shifting the composition, La4Cu 3.12Mo0.88O11.76, towards the ``umbrella'' stoichiometry La2Cu2O5. As many YAlO3-type compounds, La4Cu3MoO 12 transforms under pressure to perovskite. A magnetic transition at 280 K indicates the presence of pure copper-oxygen layers. Strontium substitutes for lanthanum, La4-xSrxCu3MoO 12-?, up to x = 1 with concurrent oxidation, and the resistivity drops considerably but the compound does not become metallic or superconducting. Pr, Nd and Sm analogues form layered perovskites only under pressure, and the buckling of the copper-oxygen planes increases with decreasing lanthanide size. La4Cu2MoNiO12 and La4Cu3MoO12 which also form under pressure, are layered double perovskites with considerably less structural distortion. La3Cu2VO9 transforms to perovskite under high-pressure conditions as well. LaYBa2CaCu2+xTi3-xO14-y is a perovskite system with constant A-cation composition, and the structural crossover from four to five layer perovskite as a function of x was shown to accommodate a layered structure rather than random oxygen defects. Specifically, the structure of the x = 0.40 sample is a five layer perovskite with some copper on the titanium site, rather than a four layer one with some titanium on the copper site. Finally, the experimental A-cation distributions of LaCa2Cu 2GaO7 and LaSr2CuGaO7 materials were used to calculate the enthalpy of cation switching reactions. Site distributions in materials with the same transition metal stoichiometry, (La/Ca/Sr) 3Cu2GaO7, can then be predicted. The model can be extended to include other lanthanide analogues of the Ga1212 family as well as other families altogether.

Vander Griend, Douglas Alan

2000-12-01

305

26 CFR 49.4271-1 - Tax on transportation of property by air.

Code of Federal Regulations, 2010 CFR

...2010-04-01 2010-04-01 true Tax on transportation of property by air. 49.4271-1...FACILITIES AND SERVICES EXCISE TAXES Transportation of Property Â§ 49.4271-1 Tax on transportation of property by air. (a)...

2010-04-01

306

Thermodynamic properties of the anisotropic frustrated spin-chain compound linarite PbCuSO4(OH)2

NASA Astrophysics Data System (ADS)

We present a comprehensive macroscopic thermodynamic study of the quasi-one-dimensional (1D) s=(1)/(2) frustrated spin-chain system linarite. Susceptibility, magnetization, specific heat, magnetocaloric effect, magnetostriction, and thermal-expansion measurements were performed to characterize the magnetic phase diagram. In particular, for magnetic fields along the b axis five different magnetic regions have been detected, some of them exhibiting short-range-order effects. The experimental magnetic entropy and magnetization are compared to a theoretical modeling of these quantities using density matrix renormalization group (DMRG) and transfer matrix renormalization group (TMRG) approaches. Within the framework of a purely 1D isotropic model Hamiltonian, only a qualitative agreement between theory and the experimental data can be achieved. Instead, it is demonstrated that a significant symmetric anisotropic exchange of about 10% is necessary to account for the basic experimental observations, including the three-dimensional (3D) saturation field, and which in turn might stabilize a triatic (three-magnon) multipolar phase.

Schäpers, M.; Wolter, A. U. B.; Drechsler, S.-L.; Nishimoto, S.; Müller, K.-H.; Abdel-Hafiez, M.; Schottenhamel, W.; Büchner, B.; Richter, J.; Ouladdiaf, B.; Uhlarz, M.; Beyer, R.; Skourski, Y.; Wosnitza, J.; Rule, K. C.; Ryll, H.; Klemke, B.; Kiefer, K.; Reehuis, M.; Willenberg, B.; Süllow, S.

2013-11-01

307

Dependence of zonal chondrocyte water transport properties on osmotic environment.

OBJECTIVE: The increasing concentration of proteoglycans from the surface to the deep zone of articular cartilage produces a depth-dependent gradient in fixed charge density, and therefore extracellular osmolarity, which may vary with loading conditions, growth and development, or disease. In this study we examine the relationship between in situ variations in osmolarity on chondrocyte water transport properties. Chondrocytes from the depth-dependent zones of cartilage, effectively preconditioned in varying osmolarities, were used to probe this relationship. DESIGN: First, depth variation in osmolarity of juvenile bovine cartilage under resting and loaded conditions was characterized using a combined experimental/theoretical approach. Zonal chondrocytes were isolated into two representative "baseline" osmolarities chosen from this analysis to reflect in situ conditions. Osmotic challenge was then used as a tool for determination of water transport properties at each of these baselines. Cell calcium signaling was monitored simultaneously as a preliminary examination of osmotic baseline effects on cell signaling pathways. RESULTS: Osmotic baseline exhibits a significant effect on the cell membrane hydraulic permeability of certain zonal subpopulations but not on cell water content or incidence of calcium signaling. CONCLUSIONS: Chondrocyte properties can be sensitive to changes in baseline osmolarity, such as those occurring during OA progression (decrease) and de novo tissue synthesis (increase). Care should be taken in comparing chondrocyte properties across zones when cells are tested in vitro in non-physiologic culture media. PMID:20011231

Oswald, Elizabeth S; Chao, Pen-Hsiu Grace; Bulinski, J Chloe; Ateshian, Gerard A; Hung, Clark T

2008-12-01

308

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

309

Linear elastic properties derivation from microstructures representative of transport parameters.

It is shown that three-dimensional periodic unit cells (3D PUC) representative of transport parameters involved in the description of long wavelength acoustic wave propagation and dissipation through real foam samples may also be used as a standpoint to estimate their macroscopic linear elastic properties. Application of the model yields quantitative agreement between numerical homogenization results, available literature data, and experiments. Key contributions of this work include recognizing the importance of membranes and properties of the base material for the physics of elasticity. The results of this paper demonstrate that a 3D PUC may be used to understand and predict not only the sound absorbing properties of porous materials but also their transmission loss, which is critical for sound insulation problems. PMID:24907783

Hoang, Minh Tan; Bonnet, Guy; Tuan Luu, Hoang; Perrot, Camille

2014-06-01

310

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

311

Charge-carrier transport properties of ultrathin Pb films

NASA Astrophysics Data System (ADS)

The charge-carrier transport properties of ultrathin metallic films are analysed with ab initio methods using the density functional theory (DFT) on free-standing single crystalline slabs in the thickness range between 1 and 8 monolayers and compared with experiments for Pb films on Si(111). A strong interplay between bandstructure, quantised in the direction normal to the ultrathin film, charge-carrier scattering mechanisms and magnetoconduction was found. Based on the bandstructure obtained from the DFT, we used standard Boltzmann transport theory in two dimensions to obtain results for the electronic transport properties of 2 to 8 monolayers thick Pb(111) slabs with and without magnetic field. Comparison of calculations and experiment for the thickness dependence of the dc conductivity shows that the dominant scattering mechanism of electrons is diffuse elastic interface scattering for which the assumption of identical scattering times for all subbands and directions, used in this paper, is a good approximation. Within this model we can explain the thickness dependences of the electric conductivity and of the Hall coefficient as well as the anomalous behaviour of the first Pb layer.

Vilfan, I.; Pfnür, H.

2003-11-01

312

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

313

Morphologic and transport properties of natural organic floc

NASA Astrophysics Data System (ADS)

The morphology, entrainment, and settling of suspended aggregates ("floc") significantly impact fluxes of organic carbon, nutrients, and contaminants in aquatic environments. However, transport properties of highly organic floc remain poorly understood. In this study detrital floc was collected in the Florida Everglades from two sites with different abundances of periphyton for use in a settling column and in racetrack flume entrainment experiments. Although Everglades flocs are similar to other organic aggregates in terms of morphology and settling rates, they tend to be larger and more porous than typical mineral flocs because of biostabilization processes and relatively low prevailing shear stresses typical of wetlands. Flume experiments documented that Everglades floc was entrained at a low bed shear stress of 1.0 × 10-2 Pa, which is considerably smaller than the typical entrainment threshold of mineral floc. Because of similarities between Everglades floc and other organic floc populations, floc transport characteristics in the Everglades typify the behavior of floc in other organic-rich shallow-water environments. Highly organic floc is more mobile than less organic floc, but because bed shear stresses in wetlands are commonly near the entrainment threshold, wetland floc dynamics are often transport-limited rather than supply limited. Organic floc transport in these environments is therefore governed by the balance between entrainment and settling fluxes, which has implications for ecosystem metabolism, materials cycling, and even landscape evolution.

Larsen, Laurel G.; Harvey, Judson W.; Crimaldi, John P.

2009-01-01

314

Rhamnolipid surface thermodynamic properties and transport in agricultural soil.

Rhamnolipid is a biosurfactant produced by several Pseudomonas species, which can wet hydrophobic soils by lowering the cohesive and/or adhesive surface tension. Because of its biodegradability, rhamnolipid applications bring minimal adverse impact on the soil and groundwater as compared with that of chemical wetting agents. Subsequently, rhamnolipid applications have more advantages when used to improve irrigation in the agricultural soil, especially under draught conditions. In the presence of rhamnolipid, water surface tension dropped linearly with the increase of rhamnolipid concentration until the rhamnolipid critical micelle concentration (CMC) of 30 mg/L was reached. Below the CMC, rhamnolipid had linear adsorption isotherms on the soil with a partition coefficient of 0.126 L/kg. Rhamnolipid transport breakthrough curves had a broad and diffuse infiltration front, indicating retention of rhamnolipid on the soil increased with time. Rhamnolipid transport was found to be well represented by the advection-dispersion equation based on a local equilibrium assumption. When applied at concentrations above the CMC, the formed rhamnolipid micelles prevented rhamnolipid adsorption (both equilibrium adsorption and kinetic adsorption) in the soil. It was discovered in this research that rhamnolipid surface thermodynamic properties played the key role in controlling rhamnolipid transport. The attractive forces between rhamnolipid molecules contributed to micelle formation and facilitated rhamnolipid transport. PMID:24394947

Renfro, Tyler Dillard; Xie, Weijie; Yang, Guang; Chen, Gang

2014-03-01

315

Nonlocal transport properties of nanoscale conductor-microwave cavity systems

NASA Astrophysics Data System (ADS)

Recent experimental progress in coupling nanoscale conductors to superconducting microwave cavities has opened up for transport investigations of the deep quantum limit of light-matter interactions, with tunneling electrons strongly coupled to individual cavity photons. We have investigated theoretically the most basic cavity-conductor system with strong, single photon induced nonlocal transport effects: two spatially separated double quantum dots (DQDs) resonantly coupled to the fundamental cavity mode. The system, described by a generalized Tavis-Cummings model, is investigated within a quantum master equation formalism, allowing us to account for both the electronic transport properties through the DQDs as well as the coherent, nonequilibrium cavity photon state. We find sizable nonlocally induced current and current cross-correlations mediated by individual photons. From a full statistical description of the electron transport we further reveal a dynamical channel blockade in one DQD lifted by photon emission due to tunneling through the other DQD. Moreover, large entanglement between the orbital states of electrons in the two DQDs is found for small DQD-lead temperatures.

Bergenfeldt, C.; Samuelsson, P.

2013-05-01

316

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

S. Gordon

1982-01-01

317

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

318

Transport properties of individual C{sub 60}-molecules

Electrical and thermal transport properties of C{sub 60} molecules are investigated with density-functional-theory based calculations. These calculations suggest that the optimum contact geometry for an electrode terminated with a single-Au atom is through binding to one or two C-atoms of C{sub 60} with a tendency to promote the ?sp{sup 2}-hybridization into an ?sp{sup 3}-type one. Transport in these junctions is primarily through an unoccupied molecular orbital that is partly hybridized with the Au, which results in splitting the degeneracy of the lowest unoccupied molecular orbital triplet. The transmission through these junctions, however, cannot be modeled by a single Lorentzian resonance, as our results show evidence of quantum interference between an occupied and an unoccupied orbital. The interference results in a suppression of conductance around the Fermi energy. Our numerical findings are readily analyzed analytically within a simple two-level model.

Géranton, G. [Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76128 Karlsruhe (Germany)] [Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76128 Karlsruhe (Germany); Seiler, C.; Evers, F. [Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76128 Karlsruhe (Germany) [Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76128 Karlsruhe (Germany); Center for Functional Nanostructures, Karlsruhe Institute of Technology, Campus South, D-76131 Karlsruhe (Germany); Institut für Theorie der Kondensierten Materie, Karlsruhe Institute of Technology, Campus South, D-76128 Karlsruhe (Germany); Bagrets, A. [Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76128 Karlsruhe (Germany) [Institute of Nanotechnology, Karlsruhe Institute of Technology, Campus North, D-76128 Karlsruhe (Germany); Steinbuch Center for Supercomputing, Karlsruhe Institute of Technology, D-76128 Karlsruhe (Germany); Venkataraman, L. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)] [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)

2013-12-21

319

Absorption and transport properties of ultra-fine cellulose webs.

Characterization of transport and absorption properties of nanofiber webs is a challenge, because in many cases the material is soft and cannot withstand the stresses exerted by the standard instruments. In this paper, we report on development of a new technique for materials characterization. We propose to conduct wicking and permeability experiments for full characterization of the nanowebs. As an example, we used electrospun cellulose acetate nanowebs. The wicking experiments showed very good reproducibility, demonstrating the square-root-of-time dependence of wetting front position vs time. The prefactor depends on a product of capillary pressure and materials permeability. We developed a technique to independently measure the permeability of small samples of nanowebs. Wicking and permeability data allow one to estimate the pore size; SEM micrographs confirmed the obtained estimates of pore radius. In general, the proposed method allows one to characterize the transport and absorption parameters of the nanofibrous materials for which the standard procedures are inapplicable. PMID:20932537

Callegari, Gerardo; Tyomkin, Ilya; Kornev, Konstantin G; Neimark, Alexander V; Hsieh, You-Lo

2011-01-01

320

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

321

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

322

Transport Properties for Biphenyl-Based Molecular Junction System

NASA Astrophysics Data System (ADS)

In the present study, the transport properties of an biphenyl-based molecule [X-BP-X (X: the end-group atom), X=O, S, Se, and Te] sandwiched between Au(111) electrodes are theoretically investigated using the non-equilibrium Green's function method based on the density functional theory. The end-group atom X has an influence on the interaction between the molecule and electrodes and the interaction between the two phenyl rings. For X =S, Se, and Te, similar transport properties are obtained, while the system with X =O exhibits much different properties from the other Xs. In case of X =O, the interaction between the molecule and electrodes becomes the weakest and that between ?-type orbitals of the two phenyl rings, which mainly contributes to the transmission around the Fermi energy, becomes the strongest. As a result, this system has a larger transmission around the Fermi energy. We also investigate the dependence on dihedral angle between the two phenyl rings for all Xs. This study was supported by the RISS project and a Grant-in-Aid for Scientific Research (No.17064017) of MEXT of the Japanese Government. The present calculations were performed by using the Numerical Materials Simulator in National Institute for Materials Science.

Kondo, Hisashi; Nara, Jun; Ohno, Takahisa

2009-03-01

323

Coefficients for calculating thermodynamic and transport properties of individual species

NASA Technical Reports Server (NTRS)

Libraries of thermodynamic data and transport properties are given for individual species in the form of least-squares coefficients. Values of C(sup 0)(sub p)(T), H(sup 0)(T), and S(sup 0)(T) are available for 1130 solid, liquid, and gaseous species. Viscosity and thermal conductivity data are given for 155 gases. The original C(sup 0)(sub p)(T) values were fit to a fourth-order polynomial with integration constants for H(sup 0)(T) and S(sup 0)(T). For each species the integration constant for H(sup 0)(T) includes the heat of formation. Transport properties have a different functional form. The temperature range for most of the data is 300 to 5000 K, although some of the newer thermodynamic data have a range of 200 to 6000 K. Because the species are mainly possible products of reaction, the data are useful for chemical equilibrium and kinetics computer codes. Much of the data has been distributed for several years with the NASA Lewis equilibrium program CET89. The thermodynamic properties of the reference elements were updated along with about 175 species that involve the elements carbon, hydrogen, oxygen, and nitrogen. These sets of data will be distributed with the NASA Lewis personal computer program for calculating chemical equilibria, CETPC.

Mcbride, Bonnie J.; Gordon, Sanford; Reno, Martin A.

1993-01-01

324

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

325

Directed Evolution Reveals Hidden Properties of VMAT, a Neurotransmitter Transporter*

The vesicular neurotransmitter transporter VMAT2 is responsible for the transport of monoamines into synaptic and storage vesicles. VMAT2 is the target of many psychoactive drugs and is essential for proper neurotransmission and survival. Here we describe a new expression system in Saccharomyces cerevisiae that takes advantage of the polyspecificity of VMAT2. Expression of rVMAT2 confers resistance to acriflavine and to the parkinsonian toxin 1-methyl-4-phenylpyridinium (MPP+) by their removal into the yeast vacuole. This expression system allowed identification of a new substrate, acriflavine, and isolation of mutants with modified affinity to tetrabenazine (TBZ), a non-competitive inhibitor of VMAT2 that is used in the treatment of various movement disorders including Tourette syndrome and Huntington chorea. Whereas one type of mutant obtained displayed decreased affinity to TBZ, a second type showed only a slight decrease in the affinity to TBZ, displayed a higher Km to the neurotransmitter serotonin, but conferred increased resistance to acriflavine and MPP+. A protein where both types of mutations were combined (with only three amino acid replacements) lost most of the properties of the neurotransmitter transporter (TBZ-insensitive, no transport of neurotransmitter) but displayed enhanced resistance to the above toxicants. The work described here shows that in the case of rVMAT2, loss of traits acquired in evolution of function (such as serotonin transport and TBZ binding) bring about an improvement in older functions such as resistance to toxic compounds. A process that has taken millions of years of evolution can be reversed by three mutations.

Gros, Yael; Schuldiner, Shimon

2010-01-01

326

Electrical tuning of transport properties of topological insulator ultrathin films

NASA Astrophysics Data System (ADS)

Considering that topological insulator (TI) ultrathin films (UTFs) provide an ideal platform for the transport measurement of topologically protected surface states, we have investigated the transport properties of the three-dimensional (3D) TI UTFs through an array of potential barriers. The 3D TI UTF was considered to be thin enough (5 nm) that the top and bottom surface states of the UTF can hybridize to create an energy gap at the Dirac point, which results in a hyperbola-like energy dispersion. It was found that the Klein tunneling effect disappears due to the interaction between the top and bottom surface states. By tuning the barrier strength or the incident energy, three kinds of transport processes can be realized, and the conditions of the transport processes were determined. The oscillatory characters of the transmission (conductance) spectra without a decaying envelope are due to the novel surface states of TIs, which are quite different from that observed for a conventional two-dimensional electron gas. For the structure consisting of two anti-parallel potential barriers, the conductance spectra exhibit a perfect on/off switching effect by tuning the barrier strength, which is favorable for electrically controllable device applications. In the case of a superlattice (SL) structure, due to the mini-gaps induced by the SL geometry, some additional resonant peaks and valleys can be observed in the transmission spectra, and similar characters are also reflected in the conductance spectra. Owing to the Dirac characters of the charge carriers therein, the transmission (conductance) spectra never decay with increasing barrier strength, which is distinguished from that observed for semiconductor SLs. These findings were not only meaningful for understanding the basic physical processes in the transport of TIs, but also useful for developing nanoscaled TI-based devices.

Li, H.; Shao, J. M.; Zhang, H. B.; Yang, G. W.

2014-02-01

327

Study of electronic transport properties of doped 8AGNR

NASA Astrophysics Data System (ADS)

The electronic and transport properties of 8-armchair graphene nanoribbon (8AGNR) with defect at different sites are investigated by performing first-principles calculations based on density functional theory (DFT). The calculated results show that the 8AGNR are semiconductor. The introduction of 3d transition metals, creates the nondegenerate states in the conduction band, makes 8AGNR metallic. The computed transmission spectrum confirms that AGNR are semiconducting in nature and their band gap remain unchanged and localized states appear when there is vacancy in their structures, and the conductance decreases due to defects compared with the pristine nanoribbon.

Sharma, Uma Shankar; Srivastava, Anurag; Verma, U. P.

2014-04-01

328

Effective Potential Energies and Transport Properties for Nitrogen and Oxygen

NASA Technical Reports Server (NTRS)

The results of recent theoretical studies for N--N2, O--O2, N2--N2 interactions are applied to the transport properties of nitrogen and oxygen gases. The theoretical results are used to select suitable oxygen interaction energies from previous work for determining the diffusion and viscosity coefficients at high temperatures. A universal formulation is applied to determine the collision integrals for O2--O2 interactions at high temperatures and to calculate certain ratios for determining higher-order collision integrals.

Stallcop, James R.; Partridge, Harry; Levin, Eugene; Kwak, Dochan (Technical Monitor)

2001-01-01

329

Structural and Transport Properties of Dielectrophoretically Assembled Interconnects

NASA Astrophysics Data System (ADS)

Dielectrophoresis was used to form ˜140nm diameter interconnects composed of gold nanorods between targeted points in a circuit. Cleanroom-based lithographic procedures were used to produce identical arrays of electrodes, improving the sample-to-sample reproducibility of the interconnect-conductances to ˜10%. Transmission electron microscopy and low temperature conductivity analyses indicate that the Coulomb Blockade associated with the individual nanorods is the primary conductance-limiting feature. To further improve the reproducibility of the structural and transport properties of dielectrophoretic interconnects, we investigate submicron wire formation in aqueous solutions of indium acetate. Our preliminary data show that single crystal wires with submicron diameters may be fabricated from such solutions.

Ozturk, Birol; Talukdar, Ishan; Thapa, Prem; Blackledge, Charles; Grischkowsky, Daniel; Flanders, Bret

2006-03-01

330

Oxygen nonstoichiometry and transport properties of strontium substituted lanthanum cobaltite

Oxygen nonstoichiometry, structure and transport properties of the two compositions (La0.6Sr0.4)0.99CoO3?? (LSC40) and La0.85Sr0.15CoO3?? (LSC15) were measured. It was found that the oxygen nonstoichiometry as a function of the temperature and oxygen partial pressure could be described using the itinerant electron model. The electrical conductivity, ?, of the materials is high (?>500 S cm?1) in the measured temperature range (650–1000 °C) and

Martin Søgaard; Peter Vang Hendriksen; Mogens Mogensen; Finn Willy Poulsen; Eivind Skou

2006-01-01

331

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

332

Transport properties of plastic separator for renewable energy applications

NASA Astrophysics Data System (ADS)

We report innovative results on optimization of intercalated polymer-clay nanocomposite endowed with desirable properties; (i) very high ionic conductivity (~10-3 S cm-1) at room temperature, (ii) tion~99% and cation transport number (tLi+)~67%: Intercalation of (PAN)8LiCF3SO3 complex into dodecylamine modified montmorillonite clay (DMMT) nanometric channels has been confirmed by Transmission electron microscopy (TEM) analysis. The optimized polymer film serves dual purpose of electrolyte and separator in energy storage devices.

Sharma, A. L.; Thakur, A. K.

2013-06-01

333

Transport properties of ZrN superconducting films

Superconductivity in nitrides presents intriguing aspects related to the role of optical phonons. In the present paper we report on high-quality superconducting zirconium nitride film preparation and characterization (including Raman scattering) as well as on both dc and microwave frequency transport properties. The high-temperature dc resistivity shows no evidence of saturation effects, possibly due to the low electron-phonon coupling. Surface impedance data can be well fitted by the standard BCS expressions. The data provide further evidence of the ''conventional'' nature of superconductivity in these compounds.

Cassinese, A.; Iavarone, M.; Vaglio, R.; Grimsditch, M.; Uran, S.

2000-12-01

334

Gas transport properties in thermally cured aromatic polyimide membranes

Aromatic polyimide derived from 2,2?-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 3,3?-diaminodiphenylsulfone (m-DDS) has been synthesized to facilitate the study of relationships between the polymer structure and the gas transport properties (permeability and selectivity). The gas permeability and selectivity of CO2, O2, N2, and CH4 for the 6FDA-m-DDS membranes cured at 150, 200, and 250°C have been determined at 35°C and at pressures

Hiroyoshi Kawakami; Masato Mikawa; Shoji Nagaoka

1996-01-01

335

Size effects on transport properties in topological Anderson insulators

NASA Astrophysics Data System (ADS)

We study the size effects on the transport properties in topological Anderson insulators (TAIs) by means of the Landauer-Büttiker formalism combined with the nonequilibrium Green function method. Conductances calculated for serval different widths of the nanoribbons reveal that there is no longer quantized plateaus for narrow nanoribbons. The local spin-resolved current distribution demonstrates that the edge states on the two sides can be coupled, leading to enhancement of backscattering as the width of the nanoribbon decreases, thus destroying the perfect quantization phenomena in the TAI. We also show that the main contribution to the nonquantized conductance also comes from edge states. Experiment proposals on TAI are discussed finally.

Li, Wei; Zang, Jiadong; Jiang, Yongjin

2011-07-01

336

Electron transport properties of ordered networks using carbon nanotubes

The electronic transport properties of ordered networks using carbon nanotubes as building blocks (ON-CNTs) are investigated within the framework of a multiterminal Landauer-Buttiker formalism using an s,p{sub x},p{sub y},p{sub z} parameterization of the tight-binding Hamiltonian for carbon. The networks exhibit electron pathway selectiveness, which is shown to depend on the atomic structure of the network nodes imposed by the specific architecture of the network and the distribution of its defects (non-hexagonal rings). This work represents the first understandings towards leading current through well-defined trajectories along an organic nanocircuit.

Romo Herrera, Jose M [ORNL; Terrones Maldonado, Humberto [ORNL; Terrones Maldonado, Mauricio [ORNL; Meunier, Vincent [ORNL

2008-01-01

337

Thermodynamic and transport properties of cryogenic propellants and related fluids

NASA Technical Reports Server (NTRS)

Significant advances have been made in recent years in the quality and range of thermophysical data for the cryogenic propellants, pressurants, and inertants. A review of recently completed and current data compilation projects for helium, hydrogen, argon, nitrogen, oxygen, fluorine, and methane is given together with recommended references for thermodynamic and transport property data tables for these fluids. Modern techniques in the plotting of thermodynamic charts from tabular data (or from functions such as the equation of state) have greatly improved their precision and value. A list of such charts is included.

Johnson, V. J.

1973-01-01

338

We have studied electron transport in n-AlGaAs/GaAs heterojunction FET channels, in which chains of InGaAs nano-islands are embedded along quasi-periodic steps. By using two samples, conductance G{sub para}(V{sub g}) parallel to the steps and G{sub perp}(V{sub g}) perpendicular to them were measured at 80 K as functions of gate voltage V{sub g}. At sufficiently high V{sub g}, G{sub para} at 80 K is several times as high as G{sub perp}, which manifests the anisotropic two-dimensional transport of electrons. When V{sub g} is reduced to -0.7 V, G{sub perp} almost vanishes, while {sub Gpara} stays sizable unless V{sub g} is set below -0.8 V. These results indicate that 'inter-chain' barriers play stronger roles than 'intra-chain' barriers.

Akiyama, Y.; Kawazu, T. [National Institute for Materials Science, Tsukuba-shi, Ibaraki 305-0047 (Japan); IIS, University of Tokyo, Meguro-ku, Tokyo 153-8505 (Japan); Noda, T. [National Institute for Materials Science, Tsukuba-shi, Ibaraki 305-0047 (Japan); Sakaki, H. [National Institute for Materials Science, Tsukuba-shi, Ibaraki 305-0047 (Japan); IIS, University of Tokyo, Meguro-ku, Tokyo 153-8505 (Japan); Toyota Technological Institute, Tempaku-ku, Nagoya 468-8511 (Japan)

2010-01-04

339

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

340

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

341

Anisotropic system of quasiparticles in superfluid helium.

The thermodynamic properties of anisotropic quasiparticle systems of He II are considered for all degrees of anisotropy. It is shown that the thermodynamic functions of a strongly anisotropic phonon-roton system are mainly determined by rotons at all temperatures. Analytical expressions for the roton thermodynamic functions are obtained for all degrees of anisotropy. The maximum anisotropy is limited by the criterion for thermodynamic stability, which is here derived for the whole temperature range. PMID:16606004

Adamenko, I N; Nemchenko, K E; Slipko, V A; Wyatt, A F G

2006-02-17

342

Anisotropic System of Quasiparticles in Superfluid Helium

NASA Astrophysics Data System (ADS)

The thermodynamic properties of anisotropic quasiparticle systems of He II are considered for all degrees of anisotropy. It is shown that the thermodynamic functions of a strongly anisotropic phonon-roton system are mainly determined by rotons at all temperatures. Analytical expressions for the roton thermodynamic functions are obtained for all degrees of anisotropy. The maximum anisotropy is limited by the criterion for thermodynamic stability, which is here derived for the whole temperature range.

Adamenko, I. N.; Nemchenko, K. E.; Slipko, V. A.; Wyatt, A. F. G.

2006-02-01

343

Highly anisotropic elements for acoustic pentamode applications.

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. PMID:23889408

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

2013-07-12

344

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

345

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

346

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

347

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

348

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

349

Right and left ventricle (RV/LV) combination models with three different patch materials (Dacron scaffold, treated pericardium, and contracting myocardium), two-layer construction, fiber orientation, and active anisotropic material properties were introduced to evaluate the effects of patch materials on RV function. A material-stiffening approach was used to model active heart contraction. Cardiac magnetic resonance (CMR) imaging was performed to acquire patient-specific ventricular geometries and cardiac motion from a patient with severe RV dilatation due to pulmonary regurgitation needing RV remodeling and pulmonary valve replacement operation. Computational models were constructed and solved to obtain RV stroke volume, ejection fraction, patch area variations, and stress/strain data for patch comparisons. Our results indicate that the patch model with contracting myocardium leads to decreased stress level in the patch area, improved RV function and patch area contractility. Maximum Stress-P1 (maximum principal stress) value at the center of the patch from the Dacron scaffold patch model was 350% higher than that from the other two models. Patch area reduction ratio was 0.3%, 3.1% and 27.4% for Dacron scaffold, pericardium, and contracting myocardium patches, respectively. These findings suggest that the contracting myocardium patch model may lead to improved recovery of RV function in patients with severe chronic pulmonary regurgitation.

Yang, Chun; Geva, Tal; Gaudette, Glenn; del Nido, Pedro J.

2010-01-01

350

NASA Astrophysics Data System (ADS)

Microstructure-sensitive design (MSD) is a novel mathematical framework that facilitates a rigorous consideration of the material microstructure as a continuous design variable in the engineering design enterprise [Adams, B.L., Henrie, A., Henrie, B., Lyon, M., Kalidindi, S.R., Garmestani, H., 2001. Microstructure-sensitive design of a compliant beam. J. Mech. Phys. Solids 49(8), 1639-1663; Adams, B.L., Lyon, M., Henrie, B., 2004. Microstructures by design: linear problems in elastic-plastic design. Int. J. Plasticity 20(8-9), 1577-1602; Kalidindi, S.R., Houskamp, J.R., Lyons, M., Adams, B.L., 2004. Microstructure sensitive design of an orthotropic plate subjected to tensile load. Int. J. Plasticity 20(8-9), 1561-1575]. MSD employs spectral representations of the local state distribution functions in describing the microstructure quantitatively, and these in turn enable development of invertible linkages between microstructure and effective properties using established homogenization (composite) theories. As a natural extension of the recent publications in MSD, we provide in this paper a detailed account of the methods that can be readily used by mechanical designers to construct first-order elastic-plastic property closures. The main focus in this paper is on the crystallographic texture (also called Orientation Distribution Function or ODF) as the main microstructural parameter controlling the elastic and yield properties of cubic (fcc and bcc) polycrystalline metals. The following specific advances are described in this paper: (i) derivation of rigorous first-order bounds for the off-diagonal terms of the effective elastic stiffness tensor and their incorporation in the MSD framework, (ii) delineation of the union of the property closures corresponding to both the upper and lower bound theories resulting in comprehensive first-order closures, (iii) development of generalized and readily usable expressions for effective anisotropic elastic-plastic properties that could be applied to all cubic polycrystals, and (iv) identification of the locations of readily available or easily processable ODFs (e.g. textures that are produced by rolling, drawing, etc.) on the property closures. It is anticipated that the advances communicated in this paper will make the mathematical framework of MSD highly accessible to the mechanical designers.

Proust, Gwénaëlle; Kalidindi, Surya R.

2006-08-01

351

Influence of ion properties on the equilibrium and transport properties of electrolyte solutions.

Strong electrolytes are described in the framework of the primitive model in which the solvent is regarded as a dielectric continuum, using the mean spherical approximation. The analytical solution of the equilibrium and transport properties is dependent on the ions' diameters and valencies. For hydrated or nonspherical ions, an effective diameter must be fitted. A sensitivity study of the osmotic coefficient and the transport coefficients is performed on theoretical 1-1, 2-1, and 3-1 electrolytes, up to a total ion concentration of 2 mol/L. PMID:16471636

Van Damme, Steven; Dufrêche, Jean-François; Deconinck, Johan

2006-01-19

352

Articular cartilage exhibits complex mechanical properties such as anisotropy, inhomogeneity and tension–compression nonlinearity. This study proposes and demonstrates that the application of compressive loading in the presence of osmotic swelling can be used to acquire a spectrum of incremental cartilage moduli (EYi) and Poisson's ratios (?ij) from tension to compression. Furthermore, the anisotropy of the tissue can be characterized in

Nadeen O. Chahine; Christopher C-B Wang; Clark T. Hung; Gerard A. Ateshian

2004-01-01

353

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

354

Quantifying Effective Flow and Transport Properties in Heterogeneous Porous Media

NASA Astrophysics Data System (ADS)

Spatial heterogeneity, the spatial variation in physical and chemical properties, exists at almost all scales and is an intrinsic property of natural porous media. It is important to understand and quantify how small-scale spatial variations determine large-scale "effective" properties in order to predict fluid flow and transport behavior in the natural subsurface. In this work, we aim to systematically understand and quantify the role of the spatial distribution of sand grains of different sizes in determining effective dispersivity and effective permeability using quasi-2D flow-cell experiments and numerical simulations. Two dimensional flow cells (20 cm by 20 cm) were packed with the same total amount of fine and coarse sands however with different spatial patterns. The homogeneous case has the completely mixed fine and coarse sands. The four zone case distributes the fine sand in four identical square zones within the coarse sand matrix. The one square case has all the fine sands in one square block. With the one square case pattern, two more experiments were designed in order to examine the effect of grain size contrast on effective permeability and dispersivity. Effective permeability was calculated based on both experimental and modeling results. Tracer tests were run for all cases. Advection dispersion equations were solved to match breakthrough data and to obtain average dispersivity. We also used Continuous Time Random Walk (CTRW) to quantify the non-Fickian transport behavior for each case. For the three cases with the same grain size contrast, the results show that the effective permeability does not differ significantly. The effective dispersion coefficient is the smallest for the homogeneous case (0.05 cm) and largest for the four zone case (0.27 cm). With the same pattern, the dispersivity value is the largest with the highest size contrast (0.28 cm), which is higher than the one with the lowest case by a factor of 2. The non-Fickian behavior was quantified by the ? value within the CTRW framework. Fickian transport will result in ? values larger than 2 while its deviation from 2 indicates the extent of non-Fickian behavior. Among the three cases with the same grain size contrast, the ? value is closest to 2 in the homogeneous case (1.95), while smallest in the four zone case (1.89). In the one square case, with the highest size contrast, the ? value was 1.57, indicating increasing extent of non-Fickian behavior with higher size contrast. This study is one step toward understanding how small-scale spatial variation in physical properties affect large-scale flow and transport behavior. This step is important in predicting subsurface transport processes that are relevant to earth sciences, environmental engineering, and petroleum engineering.

Heidari, P.; Li, L.

2012-12-01

355

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...

356

Optical and Transport Properties of Organic Molecules: Methods and Applications

NASA Astrophysics Data System (ADS)

Organic molecules are versatile and tunable building blocks for technology, in nanoscale and bulk devices. In this dissertation, I will consider some important applications for organic molecules involving optical and transport properties, and develop methods and software appropriate for theoretical calculations of these properties. Specifically, we will consider second-harmonic generation, a nonlinear optical process; photoisomerization, in which absorption of light leads to mechanical motion; charge transport in junctions formed of single molecules; and optical excitations in pentacene, an organic semiconductor with applications in photovoltaics, optoelectronics, and flexible electronics. In the Introduction (Chapter 1), I will give an overview of some phenomenology about organic molecules and these application areas, and discuss the basics of the theoretical methodology I will use: density-functional theory (DFT), time-dependent density-functional theory (TDDFT), and many-body perturbation theory based on the GW approximation. In the subsequent chapters, I will further discuss, develop, and apply this methodology. 2. I will give a pedagogical derivation of the methods for calculating response properties in TDDFT, with particular focus on the Sternheimer equation, as will be used in subsequent chapters. I will review the many different response properties that can be calculated (dynamic and static) and the appropriate perturbations used to calculate them. 3. Standard techniques for calculating response use either integer occupations (as appropriate for a system with an energy gap) or fractional occupations due to a smearing function, used to improve convergence for metallic systems. I will present a generalization which can be used to compute response for a system with arbitrary fractional occupations. 4. Chloroform (CHCl3) is a small molecule commonly used as a solvent in measurements of nonlinear optics. I computed its hyperpolarizability for second-harmonic generation with TDDFT with a real-space grid, finding good agreement with calculations using localized bases and with experimental measurements, and that the response is very long-ranged in space. 5. N C 60 is an endohedral fullerene, a sphere of carbon containing a single N atom inside, which is weakly coupled electronically. I show with TDDFT calculations that a laser pulse can excite the vibrational mode of this N atom, transiently turning on and off the system's ability to undergo second-harmonic generation. The calculated susceptibility is as large as some commercially used frequency-doubling materials. 6. A crucial question in understanding experimental measurements of nonlinear optics and their relation to device performance is the effect of the solution environment on the properties of the isolated molecules. I will consider possible explanations for the large enhancement of the hyperpolarizability of chloroform in solution, demonstrate an ab initio method of calculating electrostatic effects with local-field factors, and derive the equations necessary for a full calculation of liquid chloroform. 7. Many-body perturbation theory, in the GW approximation for quasiparticle band-structure and Bethe-Salpeter equation for optical properties, is a powerful method for calculations in solids, nanostructures, and molecules. The BerkeleyGW code is a freely available implementation of this methodology which has been extensively tested and efficiently parallelized for use on large systems. 8. Molecular junctions, in which a single molecule is contacted to two metallic leads, are interesting systems for studying nanoscale transport. I will present a method called DFT+Sigma which approximates many-body perturbation theory to enable accurate and efficient calculations of the conductance of these systems. 9. Azobenzene is a molecule with the unusual property that it can switch reversible between two different geometries, cis and trans, upon absorption of light. I have calculated the structures of these two forms when absorbed on the Au(111) surface, to understand scanning

Strubbe, David Alan

357

The effect of microporosity on transport properties in porous media

NASA Astrophysics Data System (ADS)

Sizeable amounts of connected microporosity with various origins can have a profound effect on important petrophysical properties of a porous medium such as (absolute/relative) permeability and capillary pressure relationships. We construct pore-throat networks that incorporate both intergranular porosity and microporosity. The latter originates from two separate mechanisms: partial dissolution of grains and pore fillings (e.g. clay). We then use the reconstructed network models to estimate the medium flow properties. In this work, we develop unique network construction algorithms and simulate capillary pressure-saturation and relative permeability-saturation curves for cases with inhomogeneous distributions of pores and micropores. Furthermore, we provide a modeling framework for variable amounts of cement and connectivity of the intergranular porosity and quantifying the conditions under which microporosity dominates transport properties. In the extreme case of a disconnected inter-granular network due to cementation a range of saturations within which neither fluid phase is capable of flowing emerges. To our knowledge, this is the first flexible pore scale model, from first principles, to successfully approach this behavior observed in tight reservoirs.

Mehmani, Ayaz; Prodanovi?, Maša

2014-01-01

358

NASA Astrophysics Data System (ADS)

Uniaxially aligned films of thiophene-based polymers were successfully fabricated by a novel film-forming method using the capillary action of polymer solutions without applying any mechanical or thermal stress to the polymers. Unique optical and electrical anisotropies were studied in the poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT) and poly(2,5-bis(3-alkylthiophene-2-yl)thieno[2,3-b]thiophene) (pBTCT) films fabricated by the method. Moreover, the improvements of the optical and electrical properties of the aligned polymer films by thermal annealing were also demonstrated.

Higashi, Takuya; Yamasaki, Naoyuki; Utsumi, Hideyuki; Yoshida, Hiroyuki; Fujii, Akihiko; Ozaki, Masanori

2011-09-01

359

Uniaxially aligned films of thiophene-based polymers were successfully fabricated by a novel film-forming method using the capillary action of polymer solutions without applying any mechanical or thermal stress to the polymers. Unique optical and electrical anisotropies were studied in the poly(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT) and poly(2,5-bis(3-alkylthiophene-2-yl)thieno[2,3-b]thiophene) (pBTCT) films fabricated by the method. Moreover, the improvements of the optical and electrical properties of

Takuya Higashi; Naoyuki Yamasaki; Hideyuki Utsumi; Hiroyuki Yoshida; Akihiko Fujii; Masanori Ozaki

2011-01-01

360

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

361

Theoretical study on transport properties of photo-reactive molecules

NASA Astrophysics Data System (ADS)

Azobenzene and stilbene molecules are powerful candidates for ultra-fast optical switches because of their ultra-fast photo-isomerization (trans-> cis and cis-> trans). These molecules have similar molecular structures. However, the isomerization mechanisms are completely different. In this work, we investigate the transport properties of both azobenzene and stilbene molecules based on the non-equilibrium green function (NEGF) method, and compare the results. This study was supported by RSS21 project and Grant-in-Aid for Scientific Research (No.17064017) of MEXT of the Japanese government. The calculations in this work were carried out partly using the Numerical Materials Simulator in National Institute for Materials Science (NIMS), and partly using the NEC-SX5 at Cybermedia Center, Osaka University.

Oyama, Norihisa; Kondo, Hisashi; Nara, Jun; Ohno, Takahisa

2007-03-01

362

Transport Properties Through Double Barrier Structure in Graphene

NASA Astrophysics Data System (ADS)

The mode-dependent transmission of relativistic ballistic massless Dirac fermion through a graphene based double barrier structure is being investigated for various barrier parameters. We compare our results with already published work and point out the relevance of these findings to a systematic study of the transport properties in double barrier structures. An interesting situation arises when we set the potential in the leads to zero, then our 2D problem reduces effectively to a 1D massive Dirac equation with an effective mass proportional to the quantized wave number along the transverse direction. Furthermore we have shown that the minimal conductivity and maximal Fano factor remain insensitive to the ratio between the two potentials (V2/V1=?).

Jellal, A.; Choubabi, E. B.; Bahlouli, H.; Aljaafari, A.

2012-07-01

363

Ab initio investigation of magnetic transport properties by Wannier interpolation

NASA Astrophysics Data System (ADS)

An efficient ab initio approach for the study of magnetic transport properties is developed based on the Boltzmann equation with the Wannier interpolation scheme. Using this method, we can investigate magnetoresistance [1], low field Hall coefficient, anomalous Hall effect, orbit magnetization, cyclotron motion and the effective mass, etc. As a typical application of this method, we present the band-resolved electric conductivities of MgB2 under finite magnetic fields, multiband characters for the individual bands are revealed. Combined with experimental result, fully band resolved scattering rate for each band was obtained for MgB2. It seems that the scattering from el-ph coupling or impurities affects the ?1 band more weakly [2]. [4pt] [1] Yi Liu, Hai-Jun Zhang, and Yugui Yao, Phys. Rev. B 79, 245123 (2009); [0pt] [2] H. Yang, et al. Phys. Rev. Lett 101, 067001 (2008).

Yao, Yugui; Liu, Yi

2010-03-01

364

Electronic and Transport Properties of DNA-based Nanowires

NASA Astrophysics Data System (ADS)

We study theoretically the transport properties through the quasi-one-dimensional (Q1D) one-channel DNA model and two-dimensional (2D) four-channel DNA model. We use a tight-binding (TB) technique to investigate the transmission, current-voltage characteristics, the differential conductance, and localization length as a function of incoming electron energy and magnetic flux. We find that the behavior of the transmission coefficients varies depending on the parameters of the backbone onsite energy, hopping integral from bases to backbone, and hydrogen bonds. Further, the fluctuations in the twisting angle from the temperature effects and the Aharonov-Bohm (AB) magnetic flux effect cause suppression and oscillations in the transmission.

Joe, Yong S.; Lee, Sun H.; Hedin, Eric R.

2011-12-01

365

Transport Properties of a Mott-like State of Molecules

NASA Astrophysics Data System (ADS)

In Ref. [1] we showed the preparation of a Mott-like state of molecules. This state is a quantum state with exactly one molecule at each site of an optical lattice. We now study the transport properties in the Mott-like state. A molecule can tunnel with an amplitude Jm to an adjacent site. If there is already another molecule at that site the molecules can collide inelastically [2], leading to loss of both molecules from the sample. This loss occurs with a rate coefficient ? which is typically much faster than Jm/. The fast on-site loss leads to a suppression of tunneling. Loss from the initial state effectively occurs with a rate ?eff Jm^2/?. This effect is studied experimentally at different lattice depths and the results are compared with theoretical predictions.[0ex] [1] T. Volz et al. Nature Physics 2, 692 (2006).[0ex] [2] N. Syassen et al. Phys. Rev. A 74, 062706 (2006).

Duerr, Stephan; Syassen, Niels; Bauer, Dominik; Volz, Thomas; Lettner, Matthias; Dietze, Daniel; Rempe, Gerhard

2007-06-01

366

Electronic transport properties through thiophenes on switchable domains

NASA Astrophysics Data System (ADS)

The electronic transport of electrons and holes through stacks of ?,? -dicyano- ?,?' -dibutyl-quaterthiophene (DCNDBQT) as part of a novel organic ferroic field-effect transistor is investigated. The novel application of a ferroelectric instead of a dielectric substrate provides the possibility to switch bitwise the ferroelectric domains and to employ the polarization of these domains as a gate field in an organic semiconductor. A device containing very thin DCNDBQT films of around 20-nm thickness is intended to be suitable for logical as well as optical applications. We investigate the device properties with the help of a phenomenological model called multilayer organic light-emitting diodes, which was extended to transverse fields. The results showed that space-charge and image-charge effects play a crucial role in these organic devices.

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

2010-03-01

367

Theoretical Predictions of Transport Properties of Oligoporphyrin Molecular Bridges

NASA Astrophysics Data System (ADS)

By theoretical calculations we investigated the dependence of the molecular shapes on the coherent transport properties of the molecular bridges, where oligoporphyrin molecular wires are bridged between two aluminum electrodes. We considered three types of differently conjugated molecular structures, i.e., the tape-porphyrins, the butadiyne-linked porphyrins, the edge-fused porphyrins. Among these molecular wires, the tape-porphyrins are found to be the most conductive because of their extremely small HOMO-LUMO energy gaps. The other two types of wires are found to form the semiconductive molecular bridges. Inside these molecular wires, the current is found to bypass the zinc atom sites, as the zinc energy level is away from the Fermi level.

Tagami, K.; Tsukada, M.

2003-12-01

368

Spin transport properties of triarylamine-based nanowires.

Triarylamine-derivatives can self-assemble upon light irradiation in one-dimensional nanowires with remarkable hole transport properties. We use a combination of density functional theory and Monte Carlo simulations to predict the nanowires spin-diffusion length. The orbital nature of the nanowires valence band, namely a singlet ?-like band localised on N, suggests that hyperfine coupling may be weak and that spin-orbit interaction is the primary source of intrinsic spin relaxation. Thus, we construct a model where the spin-orbit interaction mixes the spins of the valence band with that of three degenerate lower valence bands of sp(2) nature. The model includes also electron-phonon interaction with a single longitudinal mode. We find a room temperature spin-diffusion length of the order of 100 nm, which increases to 300 nm at 200 K. Our results indicate that triarylamine-based nanowires are attractive organic semiconductors for spintronics applications. PMID:24825819

Bhattacharya, Sandip; Akande, Akinlolu; Sanvito, Stefano

2014-06-25

369

Transport properties of graphene/metal planar junction

NASA Astrophysics Data System (ADS)

The transport properties of graphene/metal (Cu(111), Al(111), Ag(111), and Au(111)) planar junction are investigated using the first-principles nonequilibrium Green's function method. The planar junction induce second transmission minimum (TM2) below the Fermi level due to the existence of the Dirac point of clamped graphene. Interestingly, no matter the graphene is p- or n-type doped by the metal substrate, the TM2 always locates below the Fermi level. We find that the position of the TM2 is not only determined by the doping effect of metal lead on the graphene, but also influenced by the electrostatic potential of the metal substrate and the work function difference between the clamped and suspended graphene.

Shen, Caihua; Liu, Juan; Jiao, N.; Zhang, C. X.; Xiao, Huaping; Wang, R. Z.; Sun, L. Z.

2014-03-01

370

Magnetic and transport properties of MnBi/Bi nanocomposites

NASA Astrophysics Data System (ADS)

The magnetic and transport properties of a nanostructured Mn-Bi eutectic composition (~Mn5Bi95) produced by melt spinning and low-temperature/short time vacuum annealing were studied. A hysteretic magnetostructural transformation from low-temperature phase to high-temperature phase MnBi is confirmed at 520 K. The fact that the transition temperature is lower than that reported for bulk MnBi (633 K), is tentatively attributed to interfacial strain between MnBi and the Bi matrix. A positive temperature coefficient of coercivity is confirmed in the nanocomposites, with a maximum coercivity value of 36 kOe at 500 K. Magnetic field annealing the as-spun composites (525 K at 10 kOe) produces nanoparticle alignment. Annealed MnBi/Bi composites have a very large ordinary magnetoresistance (MR) ratio normal to the ribbon at 5 T, 275% at room temperature and 10 000% at 5 K.

Kang, Kyongha; Lewis, L. H.; Hu, Y. F.; Li, Qiang; Moodenbaugh, A. R.; Choi, Young-Suk

2006-04-01

371

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.

Phillips, J. C.

1997-01-01

372

Universal transport properties of three-dimensional topological insulator nanowires

NASA Astrophysics Data System (ADS)

We report theoretical calculations of electronic and transport properties mediated by topological helical states on the walls of three-dimensional topological insulator (TI) nanowires. A universal regime of quantized conductance and fluctuations is found that is induced by disorder. The average conductance of the disordered nanowire scales as a function of the number of transmission channels N in a universal form

Zhang, Lei; Zhuang, Jianing; Xing, Yanxia; Li, Jian; Wang, Jian; Guo, Hong

2014-06-01

373

Theory of magnetic and transport properties of double perovskites

NASA Astrophysics Data System (ADS)

We map out the finite temperature phase diagram of the generalized double exchange model for double perovskites A2BB^'O6 by self consistently solving the tight-binding Hamiltonian of the ``fast'' electrons moving in a background of ``slowly'' fluctuating classical spins. We investigate the stability of ferromagnetic and various antiferromagnetic phases as a function of electron density, the B-B^' charge transfer energy, the direct B^'-B^' hopping and various exchange interactions. We compute the temperature and doping dependence of the B-site magnetization and conduction electron polarization. We also investigate the effects of antisite (B/B^') disorder on magnetism and transport. We thus gain insight into material trends in the properties of A2Fe B^'O6 and A2Cr B^'O6 families, with B^'=Mo, W and A=La, Ca, Sr.

Nganba Meetei, Oinam; Mukherjee, Anamitra; Randeria, Mohit; Trivedi, Nandini; Woodward, Patrick

2010-03-01

374

Transport properties of antidot superlattices of graphene nanoribbons

NASA Astrophysics Data System (ADS)

In this work we show a theoretical study of the electronic and transport properties of superlattices formed by a periodic structure of vacancies (antidots) on graphene nanoribbons. The systems are described by a single-band tight-binding Hamiltonian and also by ab initio total energy density-functional theory calculations. The quantum conductance is determined within the Green’s function formalism, calculated by real-space renormalization techniques. A series of well defined gap structures on the conductance as a function of the Fermi energy is observed. This strongly depends on the period of the vacancies on the nanoribbon and on the internal geometrical structure of the supercell. Controlling these parameters could be possible to modulate the electronic response of the systems.

Rosales, L.; Pacheco, M.; Barticevic, Z.; León, A.; Latgé, A.; Orellana, P. A.

2009-08-01

375

Transport properties of doped cuprate ladder compounds grown by MBE

NASA Astrophysics Data System (ADS)

Charge transfer was measured by X-ray absorption at the copper L 3 edge in thin films of cuprate ladder compounds (Sr,Ca)Cu 2O 3+? grown by molecular beam epitaxy. Depending on the oxidation process, the charge transfer of the films varies in the range 0.07 to 0.26. Transport properties of the SrCu 2O 3 compounds show localization in agreement with variable range hopping, while some CaCu 2O 3 ladders are metallic for T>150K and show localization below 150K. The conductivity of CaCu 2O 3 increases with charge transfer. It increases more steeply if more than 0.2 hole per copper are transferred.

Partiot, C.; Dorget, M.; Cavellin, C. Deville; Studer, F.; Xu, X. Z.; Beuran, F.; Laguës, M.

376

Electrical Transport Properties of Liquid Sn-Sb Binary Alloys

NASA Astrophysics Data System (ADS)

The study of electrical transport properties viz. electrical resistivity, thermo electrical power and thermal conductivity of liquid Sn-Sb binary alloys have been made by our well recognized single parametric model potential. In the present work, screening functions due to Hartree, Taylor, Ichimaru et al.. Farid et al.. and Sarkar et al.. have been employed to incorporate the exchange and correlation effects. The liquid alloy is studied as a function of its composition at temperature 823 K according to the Faber-Ziman model. Further, thermoelectric power and thermal conductivity have been predicted. The values of electrical resistivity of binary alloys computed with Ichimaru et al. and Farid et al.. screening function are in good agreement with the experimental data.

Thakore, B. Y.; Suthar, P. H.; Khambholja, S. G.; Jani, A. R.

2010-06-01

377

Hole transporting properties of tris(8-hydroxyquinoline) aluminum (Alq3)

NASA Astrophysics Data System (ADS)

The hole transporting properties of tris (8-hydroxyquinoline) aluminum (Alq3) were investigated by time-of-flight (TOF) technique between 278 and 373 K, and under an applied field range of 0.6-1.3 MV/cm. At room temperature, the hole mobility has a value between 10-9 and 10-8 cm2 V-1 s-1. The hole mobility is at least two orders of magnitude less than electron under identical preparation and measurement conditions. Generally, all hole TOF transients of Alq3 exhibit a nondispersive behavior, with a clear plateau region and a dispersion tail. Two disorder transport models, namely, the Gaussian disorder model (GDM) and the correlated disorder model (CDM), were applied to analyze the temperature and field dependent hole mobility data. The GDM, however, is found to be invalid because it fails to produce a meaningful positional disorder parameter. The CDM gives a better fit to the data, yet the model is still not satisfactory.

Fong, H. H.; So, S. K.

2006-11-01

378

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

379

Transport properties of liquid metal hydrogen under high pressures

NASA Technical Reports Server (NTRS)

A theory is developed for the compressibility and transport properties of liquid metallic hydrogen, near to its melting point and under high pressure. The interionic force law is assumed to be of the screened Coulomb type, because hydrogen has no core electrons. The random phase approximation is used to obtain the structure factor S(k) of the system in terms of the Fourier transform of this force law. The long wavelenth limit of the structure factor S(o) is related to the compressibility, which is much lower than that of alkali metals at their melting points. The diffusion constant at the melting point is obtained in terms of the Debye frequency, using a frequency spectrum analogous with the phonon spectrum of a solid. A similar argument is used to obtain the combined shear and bulk viscosities, but these depend also on S(o). The transport coefficients are found to be about the same size as those of alkali metals at their melting points.

Brown, R. C.; March, N. H.

1972-01-01

380

Anisotropic Diffraction from Inclined Silver Nanorod Arrays on Grating Templates

Inclined silver nanorods (AgNRs) are highly anisotropic, with various applications in energy conversion, plasmonic and photonic devices, and sensing. So far, related studies have focused on the reflection or transmission, whereas studies on the diffraction and scattering from anisotropic AgNRs are still lacking. We investigate the anisotropic radiative properties of novel micro\\/nanoscale hybrid structures of inclined AgNRs deposited on compact

X. J. Wang; A. M. Haider; J. L. Abell; Y.-P. Zhao; Z. M. Zhang

2012-01-01

381

Predicting the transport properties of sedimentary rocks from microstructure

Understanding transport properties of sedimentary rocks, including permeability, relative permeability, and electrical conductivity, is of great importance for petroleum engineering, waste isolation, environmental restoration, and other applications. These transport properties axe controlled to a great extent by the pore structure. How pore geometry, topology, and the physics and chemistry of mineral-fluid and fluid-fluid interactions affect the flow of fluids through consolidated/partially consolidated porous media are investigated analytically and experimentally. Hydraulic and electrical conductivity of sedimentary rocks are predicted from the microscopic geometry of the pore space. Cross-sectional areas and perimeters of individual pores are estimated from two-dimensional scanning electron microscope (SEM) photomicrographs of rock sections. Results, using Berea, Boise, Massilon, and Saint-Gilles sandstones show close agreement between the predicted and measured permeabilities. Good to fair agreement is found in the case of electrical conductivity. In particular, good agreement is found for a poorly cemented rock such as Saint-Gilles sandstone, whereas the agreement is not very good for well-cemented rocks. The possible reasons for this are investigated. The surface conductance contribution of clay minerals to the overall electrical conductivity is assessed. The effect of partial hydrocarbon saturation on overall rock conductivity, and on the Archie saturation exponent, is discussed. The region of validity of the well-known Kozeny-Carman permeability formulae for consolidated porous media and their relationship to the microscopic spatial variations of channel dimensions are established. It is found that the permeabilities predicted by the Kozeny-Carman equations are valid within a factor of three of the observed values methods.

Schlueter, E.M.

1995-01-01

382

Calculation of the Anisotropic Diffusion Coefficient

The one-group anisotropic diffusion coefficient is calculated for slab and square lattice cells with use made of Benoist's formula. In utilizing the integral transport theory, only several collisions suffered by a neutron have hitherto been considered. In this paper, we adopt the integral theory and take into consideration the effect of an infinite number of collisions suffered by a neutron,

Toshikazu TAKEDA; Tamotsu SEKIYA

1972-01-01

383

Anisotropic nanomaterials: structure, growth, assembly, and functions

Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications.

Sajanlal, Panikkanvalappil R.; Sreeprasad, Theruvakkattil S.; Samal, Akshaya K.; Pradeep, Thalappil

2011-01-01

384

The use of an anisotropic material for the boundary truncation of the finite-element method is considered. The anisotropic material properties can be chosen such that a plane-wave incident from free space into the anisotropic halfspace has no reflection. Because there is no reflection, the material is referred to as a perfectly matched layer (PML). The relationship between the anisotropic PML

Jo-Yu Wu; David M. Kingsland; Jin-Fa Lee; Robert Lee

1997-01-01

385

Anisotropic thermal conductivity of MoS2 nanoribbons: Chirality and edge effects

NASA Astrophysics Data System (ADS)

Previous studies of the thermal transport in MoS2 are limited to the 0° (zigzag) and 30° (armchair) chiralities. We investigate the anisotropic thermal transport properties of MoS2 nanoribbons with various crystal chiralities by employing the full-band phonon dispersion relations obtained from first-principle calculations. The ribbons with chiralities other than 0° and 30° always have lower thermal conductivity, yet a local maximum at 19.1°. In addition, the thermal conductivity can be further decreased by increasing the edge roughness due to the largely degraded longitudinal phonons. These findings suggest possibilities of obtaining a higher thermoelectric efficiency in MoS2 nanoribbons.

Liu, Te-Huan; Chen, Yin-Chung; Pao, Chun-Wei; Chang, Chien-Cheng

2014-05-01

386

Electrical transport and thermodynamic properties of ?-Mo4O11

NASA Astrophysics Data System (ADS)

Low-dimensional systems have attracted a lot of attention during the last two decades because of their unusual chemical and physical properties [1]. ?-Mo4O11 is one such system exhibiting strong structural anisotropy, which is reflected in the electronic structure. This gives rise to uncommon features such as low-dimensional transport, metal- insulator and metal-metal transitions, and periodic lattice distortions and charge density waves (CDW) [2]. In this work the properties of ?-Mo4O11 single crystals are revisited. The single crystals were grown using a temperature- gradient flux method [3]. Electrical resistance as a function of temperature was determined with the Logan-Montgomery methods [4, 5] and was compared with reported measurements. We will report results of heat capacity and high-resolution thermal expansion measurements as well. [1] M.A.Valbuena, et al. Appl. Surf. Sci., 254, 40 (2007). [2] C. Schlenker, et al. Philos. Mag. B, 52, 643 (1985). [3] W. H. McCarroll and M. Greenblatt, J. Solid State Chem. 54, 282 (1984). [4] H. C. Montgomery, J. Appl. Phys. 42, 2971 (1971). [5] B. F. Logan, S. O. Rice, and R. F. Wick, J. Appl. Phys. 42, 2975 (1971). This material is based upon work supported by the Brazilian Agency CNPq (Grant No. 201439/2007-7), the NSF (Grant No. DMR- 0504769) and U.S. DOE Office of Basic Energy Sciences (Grant No. DE-FG-06ER46269).

de Campos, Ariana; da Luz, M. S.; White, B. D.; Neumeier, J. J.

2009-03-01

387

Generalized thermodynamic and transport properties. II. Molecular liquids

NASA Astrophysics Data System (ADS)

In the present paper, we extend the method described in paper I [D. Bertolini and A. Tani, preceding paper, Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.83.031201 83, 031201 (2011)] to molecular liquids, which allows us to solve the exact kinetic equation proposed by de Schepper [Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.38.271 38, 271 (1988)] without approximations. In particular, generalized thermodynamic properties (enthalpy, specific heat, and thermal expansion coefficient) and transport properties (longitudinal viscosity, thermal conductivity) have been calculated for three liquids of increasing complexity, namely dimethyl sulfoxide, hydrogen fluoride, and SPC/E water. All results have been obtained by the molecular formalism as well as the atomic one, corrected for intramolecular correlations that are due to the models adopted. As done for simple liquids, the coupling between the viscous stress tensor and the energy flux vector has been calculated exactly. We also show that the Markov assumption for the dynamics related to thermal conductivity can only be adopted with caution.

Bertolini, D.; Tani, A.

2011-03-01

388

NASA Astrophysics Data System (ADS)

We have systematically investigated the magnetic properties and magnetocaloric effect (MCE) in RMnO3 (R=Dy, Tb, Ho, and Yb) single crystals. Above a critical value of applied field (Hc), RMnO3 undergo a first-order antiferromagnetic (AFM) to ferromagnetic (FM) transition below the ordering temperature (TNR) of R3+ moment and a second-order FM to paramagnetic (PM) transition above TNR. Both H and T dependence of M shows that the system is highly anisotropic in the FM as well as PM states and, as a result, the magnetic entropy change (?SM) is extremely sensitive to the direction of applied field and can be negative (normal MCE) or positive (inverse MCE). For hexagonal HoMnO3 and YbMnO3 systems, a very small inverse MCE is observed only for H parallel to c axis and it decreases with increasing H and crosses over to normal one above Hc. On the other hand, for orthorhombic DyMnO3 and TbMnO3, though the inverse MCE disappears above Hc along easy axis of magnetization, it increases rapidly with H along hard axis of magnetization for T?TNR. Except for YbMnO3, the values of ?SM, relative cooling power and adiabatic temperature change along easy axis of magnetization are quite large in the field-induced FM state for a moderate field strength. The large values of these parameters, together with negligible hysteresis, suggest that the multiferroic manganites could be potential materials for magnetic refrigeration in the low-temperature region.

Midya, A.; Das, S. N.; Mandal, P.; Pandya, S.; Ganesan, V.

2011-12-01

389

Growth, morphology and anisotropic thermal properties of Nd-doped Sr3Y2(BO3)4 crystal

NASA Astrophysics Data System (ADS)

A high-quality Nd3+:Sr3Y2(BO3)4 laser crystal has been grown by the Czochralski method. The phase purity and accurate unit cell parameters were determined using X-ray powder diffraction; the unit cell parameters are calculated to be a=7.3933 (1) Å, b=15.9461 (2) Å, c=8.6967 (1) Å, and V=1025.29 (5) Å3. Effective segregation coefficients were measured and the optical homogeneity was further characterized by interferometry. A series of possible growth faces (hkl) were also deduced and compared with the as-grown crystal boules using the Bravais-Friedel-Donnay-Harker (BFDH) theory. A full set of thermal properties, including the thermal expansion, thermal diffusivity, specific heat, and thermal conductivity, were measured as a function of temperature. The average linear thermal expansion coefficients along different crystallographic directions were measured to be ?11=7.04×10-6 K-1, ?22=15.32×10-6 K-1 and ?33=14.35×10-6 K-1 over the temperature range 303.15-770.15 K. The specific heat was measured to be 0.573 J g-1 K-1 (92.64 cal mol-1 K-1) at 330 K. The thermal conductivity at room temperature was calculated to be 0.74 W m-1 K-1, 1.00 W m-1 K-1, and 0.67 W m-1 K-1 along the a-, b- and c-axis, respectively. It was found that thermal conductivity increases with increasing temperature, which indicates a glass-like behavior.

Pan, Zhongben; Cong, Hengjiang; Yu, Haohai; Zhang, Huaijin; Wang, Jiyang; Boughton, Robert I.

2013-01-01

390

Microstructure and water vapor transport properties of temperature sensitive polyurethanes

NASA Astrophysics Data System (ADS)

Temperature sensitive polyurethane (TS-PU) is one novel type of smart polymers. The water vapor permeability (WVP) of its membrane could undergo a significant increase as temperature increases within a predetermined temperature range. Such smart property enables this material to have a broad range of potential applications to textile industry, medicine, environmental fields and so on. However, based on the literature review, contradicting results were found on some TS-PUs. The aims of this project are to synthesize TS-PU with Tm in the broader temperature range including ambient temperature range, and then investigate systematically the relationships between microstructure and water vapor transport properties of TS-PU. For this purpose, in this project, a series of polyurethanes (PU) were synthesized using five different crystalline polyols with approximately similar molecule weight and three different hydrophilic contents, and dense membranes were prepared accordingly. The microstructure and properties of these PUs were investigated using DSC, WAXD, DMA, FTIR, GPC, POM, TEM, SEM and PALS. Their equilibrium water sorption and water vapor permeability were measured accordingly. Results show that crystal melting of these resulting PUs take place in the temperature range from -10--60°C as desired. Storage modulus (E') drops down quickly in the temperature range of crystal melting, suggesting a great transition in the predetermined temperature range. The decreased HSC as well as regular chemical structure of polyols results in the larger spherulites and higher melting end temperature, and the higher crystallinity induces the more obvious incompatibility of soft segment and hard segment in the PUs. These PUs are proved to have good enough tensile properties for textile application. The mean free volume size and fractional free volume increase more significantly in the temperature range of crystal melting than in other temperature intervals. Finally, as expected, the WVP of semi-crystalline PU membranes increases significantly in the temperature range of crystal melting. Equilibrium water sorption keeps approximately constant. The significant increase in WVP of semi-crystalline PU is obviously correlated with the sharp increase in the free volume in the predetermined temperature range.

Ding, Xuemei

391

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

392

Electromagnetic scattering by a wedge with anisotropic impedance faces

Electromagnetic scattering from the edge of an anisotropic impedance wedge, illuminated at oblique incidence, is addressed. In particular, the paper provides a review of existing solutions for this important topic in diffraction theory. Both numerical and analytical techniques, suitable to properly account for the scattering properties of the wedge's anisotropic impedance faces, are considered

Giuseppe Pelosi; Giuliano Manara; Paolo Nepa

1998-01-01

393

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

394

Status of the round robin on the transport properties of R134a

The paper contains a status report on an international project coordinated by the Subcommittee on Transport Properties of Commission 1.2 of the International Union of Pure and Applied Chemistry. The project has been conducted to investigate the large discrepancies between the results reported by various authors for the transport properties of R134a. The project has involved the remeasurement of the

M. J. Assael; Y. Nagasaka; C. A. Nieto de Castro; R. A. Perkins; K. Ström; E. Vogel; W. A. Wakeham

1995-01-01

395

The effects of vacancies on the transport properties of zigzag graphene nanoribbons

The transport properties of zigzag graphene nanoribbons (ZGNRs) with different patterns of vacancies are investigated by using density functional theory and nonequilibrium Green's function (NEGF) formalism. It is found that the transport properties are different with a different lattice type vacancy (A-type or B-type vacancy). The conductance of ZGNRs is more sensitive to an interior vacancy than an edge vacancy.

Yu Zhang; Lianqing Liu; Niandong Jiao; Ning Xi; Yuechao Wang; Zaili Dong

2010-01-01

396

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

397

Transport properties of multicomponent thermal plasmas: Grad method versus Chapman-Enskog method

Transport properties (thermal conductivity, viscosity, and electrical conductivity) for multicomponent Ar-Fe thermal plasmas at atmospheric pressure have been determined by means of two different methods. The transport coefficients set based on Grad's method is compared with the data obtained when using the Chapman-Enskog's method. Results from both applied methods are in good agreement. It is shown that the Grad method is suitable for the determination of transport properties of the thermal plasmas.

Porytsky, P. [Institute for Nuclear Research, 03680 Kyiv (Ukraine); Krivtsun, I.; Demchenko, V. [Paton Welding Institute, 03680 Kyiv (Ukraine); Reisgen, U.; Mokrov, O.; Zabirov, A. [RWTH Aachen University, ISF-Welding and Joining Institute, 52062 Aachen (Germany); Gorchakov, S.; Timofeev, A.; Uhrlandt, D. [Leibniz Institute for Plasma Science and Technology (INP Greifswald), 17489 Greifswald (Germany)

2013-02-15

398

Speckle reducing anisotropic diffusion

This paper provides the derivation of specklereducing anisotropic diffusion (SRAD), a diffusion method tailoredto ultrasonic and radar imaging applications. SRAD is theedge-sensitive diffusion for speckled images, in the same way thatconventional anisotropic diffusion is the edge-sensitive diffusionfor images corrupted with additive noise. We first show that theLee and Frost filters can be cast as partial differential equations,and then we derive

Yongjian Yu; Scott T. Acton

2002-01-01

399

NASA Astrophysics Data System (ADS)

Increasing energy demands and decreasing natural energy resources have sparked search for alternative clean and renewable energy sources. For instance, currently there is a tremendous interest in thermoelectric and photovoltaic solar energy production technologies. Half-Heusler (HH) alloys are among the most popular material systems presently under widespread investigations for high temperature thermoelectric energy conversion. Approaches to increase the thermoelectric figure of merit (ZT) of HH range from (1) chemical substitution of atoms with different masses within the same atomic position in the crystal structure to optimize carrier concentration and enhance phonon scattering via mass fluctuation and (2) embedding secondary phonon scattering centers in the matrix (nanostructuring) to further reduce thermal conductivity. This work focuses on three material systems. The first part describes the synthesis and properties (thermal conductivity, electrical conductivity, magnetic) of various oxide nanostructures (NiO, Co3O4) which were subsequently used as inclusion phases in a HH matrix to reduce the thermal conductivity. Detailed reviews of the past efforts along with the current effort to optimize synthetic routes are presented. The effects of the synthesis conditions on the thermoelectric properties of compacted pellets of NiO and Co3O4 are also discussed. The second part of the work discusses the development of synthetic strategies for the fabrication of p-type and n-type bulk nanostructured thermoelectric materials made of a half-Heusler matrix based on (Ti,Hf)CoSb, containing nanostructures with full-Heusler (FH) compositions and structures coherently embedded inside the half-Heusler matrix. The role of the nanostructures in the regulation of phonon and charge carrier transports within the half-heusler matrix is extensively discussed by combining transport data and electron microscopy images. It was found that the FH nanoinclusions form staggered heterojunctions with a valence band (VB) offset energy at the HH/FH phase boundaries. The resulting energy barrier discriminates existing holes with respect to their energy by trapping low energy holes, while promoting the transport of high energy holes through the VB of the FH-quantum dots. This "carrier culling" results in surprisingly large increase in the mobility and the effective mass of high energy holes contributing to electronic conduction. The simultaneous reduction in the density and the increase in the effective mass of holes resulted in large enhancements of the thermopower, whereas the increase in the mobility minimizes the drop in the electrical conductivity. In the third part, the application of this concept of nanostructuring on the Copper Selenide material system is described. Various synthetic approaches such as liquid assisted solid-state reaction and mechanical alloying are utilized for the fabrication of copper selenide compositions. We found that the mechanical alloying clearly decreases the thermal conductivity of the composition as well increases the Seebeck due to decrease in carrier concentrations.

Sahoo, Pranati

400

Thermodynamic and transport properties of superconducting Mg10B2.

Transport and thermodynamic properties of a sintered pellet of the newly discovered MgB2 superconductor have been measured to determine the characteristic critical magnetic fields and critical current densities. Both resistive transition and magnetization data give similar values of the upper critical field, Hc2, with magnetization data giving dHc2/dT = 0.44 T/K at the transition temperature of Tc = 40.2 K. Close to the transition temperature, magnetization curves are thermodynamically reversible, but at low temperatures the trapped flux can be on the order of 1 T. The value of dHc/dT at Tc is estimated to be about 12 mT/K, a value similar to classical superconductors like Sn. Hence, the Ginzburg-Landau parameter kappa approximately 26. Estimates of the critical supercurrent density, Jc, using hysteresis loops and the Bean model, give critical current densities on the order of 10(5) A/cm2. Hence the supercurrent coupling through the grain boundaries is comparable to intermetallics like Nb3Sn. PMID:11289944

Finnemore, D K; Ostenson, J E; Bud'ko, S L; Lapertot, G; Canfield, P C

2001-03-12

401

Thermodynamic and Transport Properties of Superconducting Mg10B2

NASA Astrophysics Data System (ADS)

Transport and thermodynamic properties of a sintered pellet of the newly discovered MgB2 superconductor have been measured to determine the characteristic critical magnetic fields and critical current densities. Both resistive transition and magnetization data give similar values of the upper critical field, Hc2, with magnetization data giving dHc2/dT = 0.44 T/K at the transition temperature of Tc = 40.2 K. Close to the transition temperature, magnetization curves are thermodynamically reversible, but at low temperatures the trapped flux can be on the order of 1 T. The value of dHc/dT at Tc is estimated to be about 12 mT/K, a value similar to classical superconductors like Sn. Hence, the Ginzburg-Landau parameter ?~26. Estimates of the critical supercurrent density, Jc, using hysteresis loops and the Bean model, give critical current densities on the order of 105 A/cm2. Hence the supercurrent coupling through the grain boundaries is comparable to intermetallics like Nb3Sn.

Finnemore, D. K.; Ostenson, J. E.; Bud'Ko, S. L.; Lapertot, G.; Canfield, P. C.

2001-03-01

402

Experimental investigation of electron transport properties of gallium nitride nanowires

NASA Astrophysics Data System (ADS)

We report transport properties of gallium nitride (GaN) nanowires grown using direct reaction of ammonia and gallium vapor. Reliable devices, such as four-terminal resistivity measuring structures and field-effect transistors, were realized by dielectrophoretically aligning the nanowires on an oxidized silicon substrate and subsequently applying standard microfabrication techniques. Room-temperature resistivity in the range of (1.0-6.2)×10-2 ? cm was obtained for the nanowires with diameters ranging from 200 to 90 nm. Temperature-dependent resistivity and mobility measurements indicated the possible sources for the n-type conductivity and high background charge carrier concentration in these nanowires. Specific contact resistance in the range of 5.0×10-5 ? cm2 was extracted for Ti/Al/Ti/Au metal contacts to GaN nanowires. Significant reduction in the activation energy of the dopants at low temperatures (<200 K) was observed in the temperature-dependent resistivity measurement of these nanowires, which is linked to the onset of degeneracy. Temperature-dependent field-effect mobility measurements indicated that the ionized impurity scattering is the dominant mechanism in these nanowires at all temperatures.

Motayed, Abhishek; Davydov, Albert V.; Mohammad, S. N.; Melngailis, John

2008-07-01

403

Magnetic and transport properties of PrRhSi3.

We have investigated the magnetic and transport properties of a noncentrosymmetric compound PrRhSi3 by dc magnetic susceptibility ?(T), isothermal magnetization M(H), thermoremanent magnetization M(t), specific heat Cp(T), electrical resistivity ?(T,H) and muon spin relaxation (?SR) measurements. At low fields ?(T) shows two anomalies near 15 and 7 K with an irreversibility between ZFC and FC data below 15 K. In contrast, no anomaly is observed in Cp(T) or ?(T) data. M(H) data at 2 K exhibit very sharp increase below 0.5 T and a weak hysteresis. M(t) exhibits very slow relaxation, typical for a spin-glass system. Even though the absence of any anomaly in Cp(T) is consistent with the spin-glass type behavior, there is no obvious origin of spin-glass behavior in this structurally well ordered compound. The crystal electric field (CEF) analysis of Cp(T) data indicates a CEF-split singlet ground state lying below a doublet at 81(1) K and a quasi-triplet at 152(2) K. The ?(T) data indicate a metallic behavior, and ?(H) exhibits a very high positive magnetoresistance, as high as ~300% in 9 T at 2 K. No long range magnetic order or spin-glass behavior was detected in a ?SR experiment down to 1.2 K. PMID:23604428

Anand, V K; Adroja, D T; Hillier, A D

2013-05-15

404

Magnetic and transport properties of PrRhSi3

NASA Astrophysics Data System (ADS)

We have investigated the magnetic and transport properties of a noncentrosymmetric compound PrRhSi3 by dc magnetic susceptibility ?(T), isothermal magnetization M(H), thermoremanent magnetization M(t), specific heat Cp(T), electrical resistivity ?(T,H) and muon spin relaxation (?SR) measurements. At low fields ?(T) shows two anomalies near 15 and 7 K with an irreversibility between ZFC and FC data below 15 K. In contrast, no anomaly is observed in Cp(T) or ?(T) data. M(H) data at 2 K exhibit very sharp increase below 0.5 T and a weak hysteresis. M(t) exhibits very slow relaxation, typical for a spin-glass system. Even though the absence of any anomaly in Cp(T) is consistent with the spin-glass type behavior, there is no obvious origin of spin-glass behavior in this structurally well ordered compound. The crystal electric field (CEF) analysis of Cp(T) data indicates a CEF-split singlet ground state lying below a doublet at 81(1) K and a quasi-triplet at 152(2) K. The ?(T) data indicate a metallic behavior, and ?(H) exhibits a very high positive magnetoresistance, as high as ?300% in 9 T at 2 K. No long range magnetic order or spin-glass behavior was detected in a ?SR experiment down to 1.2 K.

Anand, V. K.; Adroja, D. T.; Hillier, A. D.

2013-05-01

405

Transport properties of Sb-doped Si nanowires

NASA Astrophysics Data System (ADS)

We present a safe and cost-effective approach for synthesis of n-type Sb-doped Si nanowires. The nanowires were synthesized at ambient pressure using SiCl4 as Si source and pure Sb as the dopant source. Structural and compositional characterization using electron microscopy and X-ray spectroscopy show crystalline nanowires with lengths of 30-40 ?m and diameters of 40-100 nm. A 3-4 nm thick amorphous oxide shell covers the surface of the nanowire, post-growth. The composition of this shell was confirmed by Raman spectroscopy. Growth of Si nanowires, followed by low temperature annealing in Sb vapor, was shown to be an effective technique for synthesizing Sb-doped Si nanowires. The doping concentration of Sb was found to be dependent on temperature, with Sb re-evaporating from the Si nanowire at higher doping temperatures. Field effect transistors (FETs) were fabricated to investigate the electrical transport properties of these nanowires. The as-grown Si nanowires were found to be p-type with a channel mobility of 40 cm2 V-1 s-1. After doping with Sb, these nanowires exhibited n-type behavior. The channel mobility and carrier concentration of the Sb-doped Si nanowires were estimated to be 288 cm2 V-1 s-1 and 5.3×1018 cm-3 respectively.

Nukala, Prathyusha; Sapkota, Gopal; Gali, Pradeep; Philipose, U.

2012-08-01

406

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

407

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

408

Effects of antidots on the transport properties of graphene nanoribbons

NASA Astrophysics Data System (ADS)

Effects of magnetic antidots on the transport properties of zigzag-edged graphene nanoribbons (ZGNRs) are investigated by spin-polarized first-principles calculations combined with a nonequilibrium Green’s-function technique. Specifically, the effects of antidots (or holes) with regular shapes (rectangular and triangular) are studied. It is found that rectangular holes with a zero total spin S0 and triangular holes with a finite spin S0 cause different effects on the equilibrium conductance of ZGNRs. A rectangular hole with zigzag edges parallel to the ribbon edges blocks the transmission of the band edges of both the valence band and the conduction band from both the spin-up channel and the spin-down channel. Thus a much wider transmission gap than the pristine ZGNRs can be observed. However, a triangular hole with zigzag edges blocks transmission from only one spin channel in either the valence-band edge or the conduction-band edge. Thus the gap width in the total conductance is not affected in this case. The difference originates from the different energy shift of the valence band and conduction band relative to Fermi energy as a result of two effects: finite-size effect and spin splitting from the antidot-induced effective internal magnetic field.

Zheng, X. H.; Zhang, G. R.; Zeng, Z.; García-Suárez, Víctor M.; Lambert, Colin J.

2009-08-01

409

Effects of gemfibrozil on the oxygen transport properties of erythrocytes.

1. In the present study we have investigated the effects of the relatively low plasma concentrations of gemfibrozil (GFZ) found in clinical practice on the oxygen dissociation curve (ODC) of erythrocytes. 2. ODCs were measured at 30 degrees C and 37 degrees C and at pH 7.4: a) both on HbA solution and erythrocytes incubated in vitro with gemfibrozil and clofibric acid; b) on erythrocytes from healthy volunteers treated with a single oral dose of gemfibrozil. 3. These experiments showed a significant drug-induced shift of the ODC towards lower O2 affinity values without any significant modification of metabolic parameters of erythrocytes such as intracellular pH and intraerythrocytic levels of ATP and DPG. 4. In our experimental conditions gemfibrozil appears to lower both in vitro and in vivo, the partial pressure of oxygen required to give 50% of the haemes saturated with oxygen (P50) of erythrocytes from the control value of 24 +/- 0.5 mm Hg to 29 +/- 0.5 mm Hg (mean +/- s.d.; P < 0.02 by ANOVA). 5. These data clearly indicate that therapeutic doses of gemfibrozil may influence the oxygen transport properties of red cells. This effect could have relevant pharmacological and toxicological implications.

Scatena, R; Nocca, G; Messana, I; De Sole, P; Baroni, S; Zuppi, C; Castagnola, M; Giardina, B

1995-01-01

410

Microstructure, magnetic and transport properties of melt-spun Cu 60(Ni 0.8Fe 0.2) 40 alloys

NASA Astrophysics Data System (ADS)

The effect of annealing on the microstructure, magnetic and transport properties of melt-spun Cu 60(Ni 0.8Fe 0.2) 40 ribbons is reported. High-resolution analytical electron microscopy on as-spun ribbon shows a granular-like microstructure with the (Ni,Fe)-rich phase, which grows in its size after annealing, embedded in a Cu-rich matrix and a concentration gradient across the interface between the (Ni,Fe)-rich phase and Cu-rich matrix. By analyzing the magnetization curves, we found that the ferromagnetic contribution to the magnetization drastically increases from 11% for as-spun sample to 78% after annealing at 673 K for 240 min, which is clearly correlated to the microstructure modification. The ribbons show complex magnetoresistance behaviors: anisotropic magnetoresistance at low fields and giant magnetoresistance at higher fields.

Yang, Y. K.; Chen, L. H.; Chang, Y. H.; Yao, Y. D.

1998-11-01

411

Transport properties of two extremely thermophilic species of Thermus.

Thermus flavus and T. ruber grew optimally at 75 and 60 degrees C, respectively, but transport of monosaccharides (D-quinovose) and amino acids (2-aminoisobutyric acid) had optima about 20 degree C lower. Both transports were active, inhibited by 2,4-dinitrophenol but hardly at all by uranyl(2+) ions. Several transport systems are apparently involved with each class of compounds. Preincubation with glucose curtailed subsequent transport severely. Practical cessation of transport below 35 degrees C may be associated with the rather uniform composition of membrane lipids where iso- and anteiso-C15 and C17 acids are practically the only components. PMID:7262717

Michaljanicová, D; Kotyk, A; Loginova, L G; Yegorova, L A

1981-01-01

412

NASA Astrophysics Data System (ADS)

Micro-characterized variables are proposed to precisely characterize a micro-V-grooved Si surface through the 3D measured topography rather than the designed one. In this study, level and gradient micro-grooved surfaces with depth of 25–80 µm were precisely and smoothly fabricated using a new micro-grinding process rather than laser machining and chemical etching. The objective is to investigate how these accurate micro-characterized variables systematically influence anisotropic wetting and droplet self-movement on such regular micro-structured surfaces without surface chemical modification. First, the anisotropic wetting, droplet sliding, pinning effect and droplet impact were experimentally investigated; then, theoretical anisotropic wetting models were constructed to predict and design the anisotropic wetting. The experiments show that the level micro-V-grooved surface produces the anisotropic wetting and pinning effects. It not only approximates superhydrophobicity but also produces high surface free energy. Moreover, the gradient micro-V-grooved surface with large pitch may lead to much easier droplet sliding than the level one along the micro-groove. The droplet self-movement trend increases with increasing the micro-groove gradient and micro-V-groove ratio. The micro-groove pitch and depth also influence the droplet impact. Theoretical analyses show that the wetting anisotropy and the droplet anisotropy both reach their largest value and disappear for a sharp micro-groove top when the micro-V-groove ratio is equal to 0.70 and 2.58, respectively, which may change the wetting between the composite state and the non-composite state. It is confirmed that the wetting behavior may be designed and predicted by the accurate micro-characterized variables of a regular micro-structured surface.

Li, P.; Xie, J.; Cheng, J.; Wu, K. K.

2014-07-01

413

NASA Astrophysics Data System (ADS)

Leaching of solutes below the root zone has been identified as a main source of potential groundwater pollution. In structured soils, preferential flow paths can have a significant influence on rapid leaching of solutes. Dye tracer experiments have been frequently used to map the spatial distribution of macropore structures. However, the relative influence of the macropore network on solute leaching under field conditions and its correlation with physical properties of the matric soil (texture, density, mechanical strength) and land use effects have not been analyzed yet and require innovative sampling techniques. The objectives of the present study were to map the macropore network and analyze the leaching behaviour of a conservative tracer under two contrasting land uses. Ponded infiltration experiments with Potassiumbromide (KBr) and Brilliant Blue (BB) were conducted on a silt loam soil in Lexington, KY. Two land use systems, grassland and cropland (wheat), were tested. At soil water content close to field capacity, a total of 30 mm multi-tracer solution was infiltrated on an area of 1.2 × 0.7 m with a ponding head of 20 mm. The concentrations of KBr and BB were 10 and 5 g/L, respectively. After 24 hours, 10 profile sections (width: 100 cm, depth: 70 cm) were excavated in steps of 5 cm and sampled. Dye stained areas were mapped based on digital image analysis. The relative dye coverage was calculated as a function of depth. Vane shear resistance was measured as a proxy for soil mechanical strength. At every other profile section, the soil was sampled for soil water content at regular intervals along a 10 × 10 cm raster. X-ray fluorescence analysis was used to derive concentrations of Br, SiO2 and Al2O3, the latter two being used as proxy for soil particle size distribution. Anisotropic variance and covariance analysis was applied to derive direction-dependent correlations between physical, mechanical, and hydrological observations and to identify the relative influence of the macropore network and land use regime on solute leaching.

Schwen, Andreas; Backus, Jason; Walton, Riley J.; Wendroth, Ole

2014-05-01

414

Following the same philosophy of our previous force field for primary amines (J. Phys. Chem. B2011, 115, 14617), we present an extension for secondary and tertiary amines using the anisotropic united atom (AUA4) approach. The force field is developed to predict the phase equilibrium and transport properties of secondary and tertiary amines. The transferability was studied for an important set of molecules including as secondary amines dimethylamine, diethylamine, di-n-propylamine, di-iso-propylamine, and di-iso-butylamine. We have also tested diethylenetriamine, a multifunctional molecule which includes two primary and one secondary amino groups. For tertiary amines, we have included simulations for trimethylamine, triethylamine, tri-n-propylamine, and methyldiethylamine. Monte Carlo simulations in the Gibbs ensemble were carried out to study thermodynamic properties such as equilibrium densities, vaporization enthalpies, and vapor pressures. Critical coordinates (critical density and critical temperature) and normal boiling points were also calculated. The shear viscosity coefficients were studied for dimethyl, diethyl, di-n-propyl, trimethyl, triethyl, and tri-n-propylamine at different temperatures using molecular dynamics in the isothermal isobaric ensemble. Our results show a very good agreement with experimental values for all the studied molecules for both thermodynamic and transport properties, demonstrating the transferability of our force field. PMID:22551443

Orozco, Gustavo A; Nieto-Draghi, Carlos; Mackie, Allan D; Lachet, Véronique

2012-05-31

415

Evaluation of Baltic Sea transport properties using particle tracking

NASA Astrophysics Data System (ADS)

Particle tracking model (PTM) is an effective tool for quantifying transport properties of large water bodies such as the Baltic Sea. We have applied PTM to our fully calibrated and validated Baltic Sea 3D hydrodynamic model for a 10-years period (2000-9). One hundred particles were released at a constant rate during an initial 10-days period from all the Baltic Sea sub-basins, the major rivers, and the open boundary in the Arkona Basin. In each basin, the particles were released at two different depths corresponding to the deep water and middle water layers. The objectives of the PTM simulations were to analyse the intra-exchange processes between the Baltic Sea basins and to estimate the arrival times and the paths of particles released from the rivers. The novel contribution of this study is determining the paths and arrival times of deeper water masses rather than the surface masses. Advective and diffusive transport processes in the Bornholm and Arkona basins are both driven by the interacting flows of the northern basins of the Baltic Sea and the North Sea. Particles released from Arkona basin flows northwards along the Stople Channel. The Gotland basins are the major contributors to the exchange process in the Baltic Sea. We find high values of the advection ratio, indicative of a forced advective transport process. The Bay of Gdansk is probably the most vulnerable region in the Baltic Sea. This is despite the fact that the main exchanging basins are the Bornholm Sea and the Easter Gotland Basin. The main reason is the intensive supply of the particles from the northern basins that normally take about 3000 days to reach the Bay of Gdansk. The process maintains a high level of particle concentration (90%) along its coastlines even after the 10-years period. Comparing the particle paths in the Western and Eastern Gotland basins two interesting features were found. Particles travelled in all four directions in the former basin and the middle layer particles reached the surface flow in the eastern most part of the Gulf of Finland. This implies mixing of deeper waters of the Western Gotland Basin with the sub-surface waters of the Gulf of Finland. We believe strong density current and upwelling processes drive the process. Surprisingly, the two rivers Narva and Venta have the highest spreading in comparison to other rivers. This is despite the relatively low flow discharge values that rules out a correlation between high moment flows and the extent of spreading. We found the flow discharge to be correlated with the advection lengths. The lack of any correlation for the other rivers, signifies different hydrodynamic characteristics among the basins. The results of our PTM study may be used for a general environmental assessment in terms of sensitivity of the various coastlines and rick to the release of contaminants in the Baltic Sea.

Dargahi, Bijan; Cvetkovic, Vladimir

2014-05-01

416

<