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Sample records for anisotropic conduction properties

  1. Anisotropic properties of the fluctuational conductivity in YBCO

    NASA Astrophysics Data System (ADS)

    Sarti, S.; Boffa, V.; Fastampa, R.; Giura, M.; Marcon, R.; Silva, E.

    1996-03-01

    We report on resisitive transitions in YBCO films as a function of strength and orientation of the applied magnetic field. Angular behaviour is found to be markedly different in the upper and lower part of the transition. At high dissipation level, and angular scaling behaviour is observed, following the anisotropic Lawerence-Doniach expression for the upper critical field. The scaling breaks down at the midpoint of the transition. No scaling is observed at lower temperatures, even if different angular scaling functions are used. The results are very well interpreted in terms of superconducting fluctuations above ρ/ρn=0.5 and pinning phenomena below.

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

    NASA Astrophysics Data System (ADS)

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

    2012-07-01

    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 Ω with a minimum of 0.06 Ω 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.

  3. Large anisotropic thermal conductivity and excellent thermoelectric properties observed in carbon foam

    NASA Astrophysics Data System (ADS)

    Tan, Ting; Chen, Shi-Zhang; Cao, Xuan-Hao; Zhou, Wu-Xing; Xie, Fang; Chen, Ke-Qiu

    2017-07-01

    Using first-principles calculations in combination with the Boltzmann transport equation and empirical potential models, we investigate the thermal transport and thermoelectric properties of carbon foam. The results show that large anisotropic thermal conductivity can be observed in carbon foam. The Z direction of carbon foam has the highest thermal conductivity of 22.97 W/m K at room temperature, which is about 25 times greater than that of the Y direction. This is due to the lower phonon group velocity and stronger anharmonic interaction in the Y direction than those in the Z direction. Moreover, we find that the carbon form has excellent thermoelectric properties in the Y direction, the ZT can reach 0.5 at room temperature, and the ZT can be further improved to 0.84 at 800 K, which is two orders of magnitude higher than that in the Z direction. This results from the large power factor and ultralow thermal conductivity in the Y direction.

  4. Mechanical Properties of Anisotropic Conductive Adhesive Film Under Hygrothermal Aging and Thermal Cycling

    NASA Astrophysics Data System (ADS)

    Gao, Li-Lan; Chen, Xu; Gao, Hong

    2012-07-01

    Mechanical properties of anisotropic conductive adhesive film (ACF) were investigated experimentally under various environmental conditions. The temperature sweep test was conducted to investigate the effects of temperature on dynamical mechanical properties of the ACF. The ACF exhibited transitions to the glass state, viscoelastic state, and rubber state with increasing temperature, and its glass-transition temperature ( T g) was determined to be 149°C. The creep-recovery behaviors of the ACF were investigated, and it was found that the initial strains, instantaneous strains, and creep or recovery rates increased with increasing temperature. No obvious creep phenomenon was observed at low temperatures (≤0°C). The creep strain and creep rates at any time decreased with increasing hygrothermal aging time. The uniaxial tensile behaviors of the ACF were also investigated under hygrothermal aging and thermal cycling. The results show that the Young's modulus and tensile strength of the ACF decrease with increasing hygrothermal aging time; however, they increase at first and then decrease with increasing thermal cycling time. T g decreases slightly for the ACF after hygrothermal aging; however, it increases after thermal cycling.

  5. Conductivity in an anisotropic background

    SciTech Connect

    Lee, Bum-Hoon; Nam, Siyoung; Pang, Da-Wei; Park, Chanyong

    2011-03-15

    By using the gauge/gravity duality, we investigate the dual field theories of the anisotropic backgrounds, which are exact solutions of Einstein-Maxwell-dilaton theory with a Liouville potential. When we turn on the bulk gauge field fluctuation A{sub x} with a nontrivial dilaton coupling, the AC conductivity of this dual field theory is proportional to the frequency with an exponent depending on parameters of the anisotropic background. In some parameter regions, we find that this conductivity can have the negative exponent like the strange metal. In addition, we also investigate another U(1) gauge field fluctuation, which is not coupled with a dilaton field. We classify all possible conductivities of this system and find that the exponent of the conductivity is always positive.

  6. Tunable anisotropic thermal conduction in graphane nanoribbons

    NASA Astrophysics Data System (ADS)

    Li, Dengfeng; Xu, Yong; Chen, Xiaobin; Li, Bolin; Duan, Wenhui

    2014-04-01

    Graphane and graphene are both two-dimensional materials but of different bonding configurations, which can result in distinct thermal conduction properties. We simulate thermal conduction in graphane nanoribbons (GANRs) using the nonequilibrium Green's function method. We find anisotropic thermal conduction in GANRs, with zigzag GANRs giving higher thermal conductance than armchair ones. Compared to the graphene counterparts, GANRs show lower ballistic thermal conductance and stronger thermal conductance anisotropy. Furthermore, hydrogen vacancies of GANRs considerably suppress thermal conduction, accompanied by enhanced thermal conductance anisotropy. The tunable thermal conduction, realized by controlling the ribbon width, edge shape, and hydrogen vacancy concentration of GANRs, could be useful for thermal management and thermoelectric applications.

  7. Retrieval procedure of effective conductivity for plasmonic resonant anisotropic metasurface

    NASA Astrophysics Data System (ADS)

    Yermakov, O. Y.; Porubaev, F.; Bogdanov, A. A.; Samusev, A. K.; Iorsh, I. V.

    2017-09-01

    In this work we introduce the effective surface conductivity retrieval procedure in order to describe the properties of plasmonic resonant anisotropic metasurface consisting of plasmonic elliptical nanodisks.

  8. Simultaneous Measurement of Thermal Diffusivity and Thermal Conductivity by Means of Inverse Solution for One-Dimensional Heat Conduction (Anisotropic Thermal Properties of CFRP for FCEV)

    NASA Astrophysics Data System (ADS)

    Kosaka, Masataka; Monde, Masanori

    2015-11-01

    For safe and fast fueling of hydrogen in a fuel cell electric vehicle at hydrogen fueling stations, an understanding of the heat transferred from the gas into the tank wall (carbon fiber reinforced plastic (CFRP) material) during hydrogen fueling is necessary. Its thermal properties are needed in estimating heat loss accurately during hydrogen fueling. The CFRP has anisotropic thermal properties, because it consists of an adhesive agent and layers of the CFRP which is wound with a carbon fiber. In this paper, the thermal diffusivity and thermal conductivity of the tank wall material were measured by an inverse solution for one-dimensional unsteady heat conduction. As a result, the thermal diffusivity and thermal conductivity were 2.09 × 10^{-6}{ m}2{\\cdot }{s}^{-1} and 3.06{ W}{\\cdot }{m}{\\cdot }^{-1}{K}^{-1} for the axial direction, while they were 6.03 × 10^{-7} {m}2{\\cdot }{s}^{-1} and 0.93 {W}{\\cdot }{m}^{-1}{\\cdot }{K}^{-1} for the radial direction. The thermal conductivity for the axial direction was about three times higher than that for the radial direction. The thermal diffusivity shows the same trend in both directions because the thermal capacity, ρ c, is independent of direction, where ρ is the density and c is the heat capacity.

  9. Anisotropic heat conduction in diacetylenes

    NASA Astrophysics Data System (ADS)

    Morelli, D. T.; Heremans, J.; Sakamoto, M.; Uher, C.

    1986-08-01

    Measurements of the low-temperature thermal conductivity of diacetylene single crystals are reported. Monomer samples show little anisotropy and display the temperature dependence of a crystalline dielectric. In polymerized samples, heat is conducted up to 60 times better parallel to the chains than perpendicular to them. Dislocations can account for this anisotropy at the lowest temperatures. Quasi one dimensionality of the polymer crystals induces anisotropy at higher temperatures and strongly suppresses anharmonic phonon interactions.

  10. Anisotropic Thermal Conductivity of Exfoliated Black Phosphorus.

    PubMed

    Jang, Hyejin; Wood, Joshua D; Ryder, Christopher R; Hersam, Mark C; Cahill, David G

    2015-12-22

    The anisotropic thermal conductivity of passivated black phosphorus (BP), a reactive two-dimensional material with strong in-plane anisotropy, is ascertained. The room-temperature thermal conductivity for three crystalline axes of exfoliated BP is measured by time-domain thermo-reflectance. The thermal conductivity along the zigzag direction is ≈2.5 times higher than that of the armchair direction.

  11. Anisotropic electronic conduction in stacked two-dimensional titanium carbide

    PubMed Central

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-01-01

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I−V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane. PMID:26548439

  12. Anisotropic electronic conduction in stacked two-dimensional titanium carbide

    NASA Astrophysics Data System (ADS)

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-11-01

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I-V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane.

  13. Anisotropic electronic conduction in stacked two-dimensional titanium carbide.

    PubMed

    Hu, Tao; Zhang, Hui; Wang, Jiemin; Li, Zhaojin; Hu, Minmin; Tan, Jun; Hou, Pengxiang; Li, Feng; Wang, Xiaohui

    2015-11-09

    Stacked two-dimensional titanium carbide is an emerging conductive material for electrochemical energy storage which requires an understanding of the intrinsic electronic conduction. Here we report the electronic conduction properties of stacked Ti3C2T2 (T = OH, O, F) with two distinct stacking sequences (Bernal and simple hexagonal). On the basis of first-principles calculations and energy band theory analysis, both stacking sequences give rise to metallic conduction with Ti 3d electrons contributing most to the conduction. The conduction is also significantly anisotropic due to the fact that the effective masses of carriers including electrons and holes are remarkably direction-dependent. Such an anisotropic electronic conduction is evidenced by the I-V curves of an individual Ti3C2T2 particulate, which demonstrates that the in-plane electrical conduction is at least one order of magnitude higher than that vertical to the basal plane.

  14. Anisotropic conducting films for electromagnetic radiation applications

    SciTech Connect

    Cavallo, Francesca; Lagally, Max G.; Rojas-Delgado, Richard

    2015-06-16

    Electronic devices for the generation of electromagnetic radiation are provided. Also provided are methods for using the devices to generate electromagnetic radiation. The radiation sources include an anisotropic electrically conducting thin film that is characterized by a periodically varying charge carrier mobility in the plane of the film. The periodic variation in carrier mobility gives rise to a spatially varying electric field, which produces electromagnetic radiation as charged particles pass through the film.

  15. Effects of anisotropic heat conduction on solidification

    NASA Technical Reports Server (NTRS)

    Weaver, J. A.; Viskanta, R.

    1989-01-01

    Two-dimensional solidification influenced by anisotropic heat conduction has been considered. The interfacial energy balance was derived to account for the heat transfer in one direction (x or y) depending on the temperature gradient in both the x and y directions. A parametric study was made to determine the effects of the Stefan number, aspect ratio, initial superheat, and thermal conductivity ratios on the solidification rate. Because of the imposed boundary conditions, the interface became skewed and sometimes was not a straight line between the interface position at the upper and lower adiabatic walls (spatially nonlinear along the height). This skewness depends on the thermal conductivity ratio k(yy)/k(yx). The nonlinearity of the interface is influenced by the solidification rate, aspect ratio, and k(yy/k(yx).

  16. Anisotropic Thermal Conduction in Polymers and its Molecular Origins

    NASA Astrophysics Data System (ADS)

    Nieto Simavilla, David; Venerus, David; Schieber, Jay; uCoSm Team

    2014-03-01

    Anisotropy in thermal conductivity has a significant impact on both processing and final properties of materials. Simple molecular arguments suggest that Fourier?s law must be generalized to allow for anisotropic thermal conductivity. We present two complementary experimental methods to obtain quantitative measurements of the thermal diffusivity (conductivity) tensor. We report anisotropic thermal diffusivity and stress in molten, cross-linked and solid polymers under several types of flows. Our results support the validity of a linear relationship between stress and anisotropy in thermal conductivity. When the proportionality constant, the stress-thermal coefficient, is made dimensionless by the plateau modulus of the polymer melt, a universal value of approximately 0.03 is observed for all chemistries. Such a universality is surprising, since phonon transport mechanisms are sensitive to chemical structure. For instance, the analogous stress-optic coefficient depends strongly on chemistry, and can even change sign. Connecting these measurements with current theories for thermal transport in amorphous materials, such as Minimum Thermal Conductivity (MTC) model, is crucial to understand the molecular origins of anisotropic thermal conduction in polymers.

  17. Anisotropic Thermal Conduction in Polymers and its Molecular Origins

    NASA Astrophysics Data System (ADS)

    Schieber, Jay; Venerus, David; Gupta, Sahil

    2013-03-01

    The strong coupling of mechanical and thermal effects in polymer flows have a significant impact on both the processing and final properties of the material. Simple molecular arguments suggest that Fourier's law must be generalized to allow for anisotropic thermal conductivity in polymers subjected to deformation. In our laboratory we have developed a novel application of the optical technique known as Forced Rayleigh Scattering to obtain quantitative measurements of components of the thermal diffusivity (conductivity) tensor in polymers subjected to deformations. We report measurements of anisotropic thermal diffusivity and stress in molten, cross-linked and solid polymers subjected to several types of flows. The deformed samples have significant anisotropy in polymer chain orientation that results in significant anisotropy in thermal conductivity. Stress and thermal conductivity data support the validity of the stress-thermal rule, which is analogous to the well-known stress-optic rule. We also report measurements on solid polymers with isotropic polymer chain orientation that are under stress, which display rather unexpected behavior. These measurements are used to develop an understanding of the molecular origins of anisotropic thermal conduction in polymeric material NSF-DMR-706582

  18. Anisotropic thermal conductivity in epoxy-bonded magnetocaloric composites

    NASA Astrophysics Data System (ADS)

    Weise, Bruno; Sellschopp, Kai; Bierdel, Marius; Funk, Alexander; Bobeth, Manfred; Krautz, Maria; Waske, Anja

    2016-09-01

    Thermal management is one of the crucial issues in the development of magnetocaloric refrigeration technology for application. In order to ensure optimal exploitation of the materials "primary" properties, such as entropy change and temperature lift, thermal properties (and other "secondary" properties) play an important role. In magnetocaloric composites, which show an increased cycling stability in comparison to their bulk counterparts, thermal properties are strongly determined by the geometric arrangement of the corresponding components. In the first part of this paper, the inner structure of a polymer-bonded La(Fe, Co, Si)13-composite was studied by X-ray computed tomography. Based on this 3D data, a numerical study along all three spatial directions revealed anisotropic thermal conductivity of the composite: Due to the preparation process, the long-axis of the magnetocaloric particles is aligned along the xy plane which is why the in-plane thermal conductivity is larger than the thermal conductivity along the z-axis. Further, the study is expanded to a second aspect devoted to the influence of particle distribution and alignment within the polymer matrix. Based on an equivalent ellipsoids model to describe the inner structure of the composite, numerical simulation of the thermal conductivity in different particle arrangements and orientation distributions were performed. This paper evaluates the possibilities of microstructural design for inducing and adjusting anisotropic thermal conductivity in magnetocaloric composites.

  19. Anisotropic conductivity imaging with MREIT using equipotential projection algorithm.

    PubMed

    Değirmenci, Evren; Eyüboğlu, B Murat

    2007-12-21

    Magnetic resonance electrical impedance tomography (MREIT) combines magnetic flux or current density measurements obtained by magnetic resonance imaging (MRI) and surface potential measurements to reconstruct images of true conductivity with high spatial resolution. Most of the biological tissues have anisotropic conductivity; therefore, anisotropy should be taken into account in conductivity image reconstruction. Almost all of the MREIT reconstruction algorithms proposed to date assume isotropic conductivity distribution. In this study, a novel MREIT image reconstruction algorithm is proposed to image anisotropic conductivity. Relative anisotropic conductivity values are reconstructed iteratively, using only current density measurements without any potential measurement. In order to obtain true conductivity values, only either one potential or conductivity measurement is sufficient to determine a scaling factor. The proposed technique is evaluated on simulated data for isotropic and anisotropic conductivity distributions, with and without measurement noise. Simulation results show that the images of both anisotropic and isotropic conductivity distributions can be reconstructed successfully.

  20. Textured silicon nitride: processing and anisotropic properties

    PubMed Central

    Zhu, Xinwen; Sakka, Yoshio

    2008-01-01

    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 β-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 β-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 β-Si3N4 single crystals are presented. Various anisotropic properties of textured Si3N4 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 β-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 α-Sialon is also reviewed, because the presence of elongated α-Sialon grains allows the production of textured α-Sialon using the

  1. Textured silicon nitride: processing and anisotropic properties.

    PubMed

    Zhu, Xinwen; Sakka, Yoshio

    2008-07-01

    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 β-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 β-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 β-Si3N4 single crystals are presented. Various anisotropic properties of textured Si3N4 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 β-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 α-Sialon is also reviewed, because the presence of elongated α-Sialon grains allows the production of textured α-Sialon using the

  2. On the anisotropic elastic properties of hydroxyapatite.

    NASA Technical Reports Server (NTRS)

    Katz, J. L.; Ukraincik, K.

    1971-01-01

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

  3. Anisotropic conductivity of magnetic carbon nanotubes embedded in epoxy matrices

    PubMed Central

    Kim, Il Tae; Tannenbaum, Allen; Tannenbaum, Rina

    2010-01-01

    Maghemite (γ-Fe2O3)/multi-walled carbon nanotubes (MWCNTs) hybrid-materials were synthesized and their anisotropic electrical conductivities as a result of their alignment in a polymer matrix under an external magnetic field were investigated. The tethering of γ-Fe2O3 nanoparticles on the surface of MWCNT was achieved by a modified sol-gel reaction, where sodium dodecylbenzene sulfonate (NaDDBS) was used in order to inhibit the formation of a 3D iron oxide gel. These hybrid-materials, specifically, magnetized multi-walled carbon nanotubes (m-MWCNTs) were readily aligned parallel to the direction of a magnetic field even when using a relatively weak magnetic field. The conductivity of the epoxy composites formed in this manner increased with increasing m-MWCNT mass fraction in the polymer matrix. Furthermore, the conductivities parallel to the direction of magnetic field were higher than those in the perpendicular direction, indicating that the alignment of the m-MWCNT contributed to the enhancement of the anisotropic electrical properties of the composites in the direction of alignment. PMID:23019381

  4. Anisotropic ionic conductivities in lyotropic supramolecular liquid crystals.

    PubMed

    Huang, Youju; Cong, Yuanhua; Li, Junjun; Wang, Daoliang; Zhang, Jingtuo; Xu, Lu; Li, Weili; Li, Liangbin; Pan, Guoqiang; Yang, Chuanlu

    2009-12-28

    The designed aromatic amide discotic molecule with sulfonic acid groups at its periphery exhibits a hexagonal supramolecular columnar liquid crystalline phase, which leads to the achievement of anisotropic ionic conductivity through macroscopically aligning the ionic channels.

  5. Anisotropic Tuning of Graphite Thermal Conductivity by Lithium Intercalation.

    PubMed

    Qian, Xin; Gu, Xiaokun; Dresselhaus, Mildred S; Yang, Ronggui

    2016-11-17

    Understanding thermal transport in lithium intercalated layered materials is not only important for managing heat generation and dissipation in lithium ion batteries but also the understanding potentially provides a novel way to design materials with reversibly tunable thermal conductivity. In this work, the thermal conductivity of lithium-graphite intercalation compounds (LixC6) is calculated using molecular dynamics simulations as a function of the amount of lithium intercalated. We found that intercalation of lithium has an anisotropic effect on tuning the thermal conductivity: the thermal conductivity in the basal plane decreases monotonically from 1232 W/m·K of pristine graphite to 444 W/m·K of the fully lithiated LiC6, while the thermal conductivity along the c-axis decreases first from 6.5 W/m·K for graphite to 1.3 W/m·K for LiC18 and then increases to 5.0 W/m·K for LiC6 as the lithium composition increases. More importantly, we provide the very first atomic-scale insight into the effect of lithium intercalation on the spectral phonon properties of graphite. The intercalated lithium ions are found to suppress the phonon lifetime and to reduce the group velocity of phonons parallel to the basal plane but significantly to increase the phonon group velocity along the c-axis, which anisotropically tunes the thermal conductivity of lithiated graphite compounds. This work could shed some light on the search for tunable thermal conductivity materials and might have strong impacts on the thermal management of lithium ion batteries.

  6. Elastic properties of spherically anisotropic piezoelectric composites

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

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

  7. Anisotropic subvoxel-smooth conduction model for bioelectromagnetism analysis

    NASA Astrophysics Data System (ADS)

    He, Zhi Zhu; Liu, Jing

    2016-01-01

    The bioelectric conduction model plays a key role in bioelectromagnetism analysis, such as solving electromagnetic forward and inverse problems. This paper is aimed to develop an anisotropic subvoxel-smooth conduction model (ASCM) to characterize the electrical conductivity tensor jump across the tissue interface, which is derived based on the interfacial continuity condition with asymptotic analysis method. This conduction model is furthermore combined with finite volume method to improve the numerical accuracy for solving electromagnetic forward problem. The performance of ASCM for electrical potential analysis is verified by comparison with analytic solution. The method is also applied to investigate the effect of anisotropic conduction on EEG analysis in a realistic human head model.

  8. Thermal conduction in single-layer black phosphorus: highly anisotropic?

    PubMed

    Jiang, Jin-Wu

    2015-02-06

    The single-layer black phosphorus is characteristic for its puckered structure, which has led to distinct anisotropy in its optical, electronic, and mechanical properties. We use the non-equilibrium Green's function approach and the first-principles method to investigate the thermal conductance for single-layer black phosphorus in the ballistic transport regime, in which the phonon-phonon scattering is neglected. We find that the anisotropy in the thermal conduction is very weak for the single-layer black phosphorus--the difference between two in-plane directions is less than 4%. Our phonon calculations disclose that the out-of-plane acoustic phonon branch has lower group velocities in the direction perpendicular to the pucker, as the black phosphorus is softer in this direction, leading to a weakening effect for the thermal conductance in the perpendicular direction. However, the longitudinal acoustic phonon branch behaves abnormally; i.e., the group velocity of this phonon branch is higher in the perpendicular direction, although the single-layer black phosphorus is softer in this direction. The abnormal behavior of the longitudinal acoustic phonon branch is closely related to the highly anisotropic Poisson's ratio in the single-layer black phosphorus. As a result of the counteraction between the out-of-plane phonon mode and the in-plane phonon modes, the thermal conductance in the perpendicular direction is weaker than the parallel direction, but the anisotropy is pretty small.

  9. Anisotropic thermal conductivity in uranium dioxide

    NASA Astrophysics Data System (ADS)

    Gofryk, K.; Du, S.; Stanek, C. R.; Lashley, J. C.; Liu, X.-Y.; Schulze, R. K.; Smith, J. L.; Safarik, D. J.; Byler, D. D.; McClellan, K. J.; Uberuaga, B. P.; Scott, B. L.; Andersson, D. A.

    2014-08-01

    The thermal conductivity of uranium dioxide has been studied for over half a century, as uranium dioxide is the fuel used in a majority of operating nuclear reactors and thermal conductivity controls the conversion of heat produced by fission events to electricity. Because uranium dioxide is a cubic compound and thermal conductivity is a second-rank tensor, it has always been assumed to be isotropic. We report thermal conductivity measurements on oriented uranium dioxide single crystals that show anisotropy from 4 K to above 300 K. Our results indicate that phonon-spin scattering is important for understanding the general thermal conductivity behaviour, and also explains the anisotropy by coupling to the applied temperature gradient and breaking cubic symmetry.

  10. Anisotropic thermal conduction with magnetic fields in galaxy clusters

    NASA Astrophysics Data System (ADS)

    Arth, Alexander; Dolag, Klaus; Beck, Alexander; Petkova, Margarita; Lesch, Harald

    2015-08-01

    Magnetic fields play an important role for the propagation and diffusion of charged particles, which are responsible for thermal conduction. In this poster, we present an implementation of thermal conduction including the anisotropic effects of magnetic fields for smoothed particle hydrodynamics (SPH). The anisotropic thermal conduction is mainly proceeding parallel to magnetic fields and suppressed perpendicular to the fields. We derive the SPH formalism for the anisotropic heat transport and solve the corresponding equation with an implicit conjugate gradient scheme. We discuss several issues of unphysical heat transport in the cases of extreme ansiotropies or unmagnetized regions and present possible numerical workarounds. We implement our algorithm into the cosmological simulation code GADGET and study its behaviour in several test cases. In general, we reproduce the analytical solutions of our idealised test problems, and obtain good results in cosmological simulations of galaxy cluster formations. Within galaxy clusters, the anisotropic conduction produces a net heat transport similar to an isotropic Spitzer conduction model with low efficiency. In contrast to isotropic conduction our new formalism allows small-scale structure in the temperature distribution to remain stable, because of their decoupling caused by magnetic field lines. Compared to observations, strong isotropic conduction leads to an oversmoothed temperature distribution within clusters, while the results obtained with anisotropic thermal conduction reproduce the observed temperature fluctuations well. A proper treatment of heat transport is crucial especially in the outskirts of clusters and also in high density regions. It's connection to the local dynamical state of the cluster also might contribute to the observed bimodal distribution of cool core and non cool core clusters. Our new scheme significantly advances the modelling of thermal conduction in numerical simulations and overall gives

  11. An Engineered Anisotropic Nanofilm with Unidirectional Wetting Properties

    DTIC Science & Technology

    2010-01-01

    ARTICLES PUBLISHED ONLINE: 10 OCTOBER 2010 | DOI: 10.1038/NMAT2864 An engineered anisotropic nanofilm with unidirectional wetting properties Niranjan...body3. Engineering synthetic materials with such anisotropic adhesive properties has led to advances in digitalmicrofluidic devices5,6 andmedicine7,8...The anisotropic wetting properties of existing engineered surfaces are derived either from spatial gradients (for example, temperature, surface

  12. Anisotropic thermal conductivity of thin polycrystalline oxide samples

    SciTech Connect

    Tiwari, A.; Boussois, K.; Nait-Ali, B.; Smith, D. S.; Blanchart, P.

    2013-11-15

    This paper reports about the development of a modified laser-flash technique and relation to measure the in-plane thermal diffusivity of thin polycrystalline oxide samples. Thermal conductivity is then calculated with the product of diffusivity, specific heat and density. Design and operating features for evaluating in-plane thermal conductivities are described. The technique is advantageous as thin samples are not glued together to measure in-plane thermal conductivities like earlier methods reported in literature. The approach was employed to study anisotropic thermal conductivity in alumina sheet, textured kaolin ceramics and montmorillonite. Since it is rare to find in-plane thermal conductivity values for such anisotropic thin samples in literature, this technique offers a useful variant to existing techniques.

  13. Anisotropic properties of tracheal smooth muscle tissue.

    PubMed

    Sarma, P A; Pidaparti, R M; Meiss, R A

    2003-04-01

    The anisotropic (directional-dependent) properties of contracting tracheal smooth muscle tissue are estimated from a computational model based on the experimental data of length-dependent stiffness. The area changes are obtained at different muscle lengths from experiments in which stimulated muscle undergoes unrestricted shortening. Then, through an interative process, the anisotropic properties are estimated by matching the area changes obtained from the finite element analysis to those derived from the experiments. The results obtained indicate that the anisotropy ratio (longitudinal stiffness to transverse stiffness) is about 4 when the smooth muscle undergoes 70% strain shortening, indicating that the transverse stiffness reduces as the longitudinal stiffness increases. It was found through a sensitivity analysis from the simulation model that the longitudinal stiffness and the in-plane shear modulus are not very sensitive as compared to major Poisson's ratio to the area changes of the muscle tissue. Copyright 2003 Wiley Periodicals, Inc.

  14. Anisotropic frictional properties in snakes

    NASA Astrophysics Data System (ADS)

    Benz, Martina J.; Kovalev, Alexander E.; Gorb, Stanislav N.

    2012-04-01

    Since the ventral body side of snakes is in almost continuous contact with the substrate during locomotion, their skin is presumably adapted to generate propulsion (high friction) and simultaneously slide along the substrate at rather low friction. In this study, the microstructure of ventral scales is shown and its influence on frictional properties was investigated by the use of scanning electron microscopy and microtribometry. To analyze the role of the system stiffness on the frictional anisotropy, two different types of sample cushioning (hard and soft) were tested while sliding in four different directions. Frictional anisotropy for both types of sample cushioning was demonstrated, however, the anisotropy was much stronger expressed in the soft cushioned sample. This effect is explained by the stronger ability of the soft-cushioned microstructure to slip along (or resist) the micro- and nanoscale features of the substrate, if compared with the hard-cushioned one.

  15. Anisotropic charge transport in ion-conductive photoresponsive polyethylene oxide-based mesomorphic materials

    NASA Astrophysics Data System (ADS)

    Binet, Corinne; Allart, Alexandre; Judeinstein, Patrick; Roussel, Frédérick

    2017-01-01

    The mechanism of charge motion in conductive and photosensitive mesogenic block copolymers containing polyethylene oxide (PEO) segments is investigated over a wide frequency and temperature range with the broadband dielectric spectroscopy technique. It is found that the ultraviolet (UV) irradiation, the UV intensity, and the anchoring conditions of mesogenic unit in the cells produce changes in conductivity properties and in the molecular arrangement. The anisotropic nature of the conductivity is established.

  16. Anisotropic charge transport in ion-conductive photoresponsive polyethylene oxide-based mesomorphic materials.

    PubMed

    Binet, Corinne; Allart, Alexandre; Judeinstein, Patrick; Roussel, Frédérick

    2017-01-01

    The mechanism of charge motion in conductive and photosensitive mesogenic block copolymers containing polyethylene oxide (PEO) segments is investigated over a wide frequency and temperature range with the broadband dielectric spectroscopy technique. It is found that the ultraviolet (UV) irradiation, the UV intensity, and the anchoring conditions of mesogenic unit in the cells produce changes in conductivity properties and in the molecular arrangement. The anisotropic nature of the conductivity is established.

  17. Identifying heterogeneous anisotropic properties in cerebral aneurysms: a pointwise approach.

    PubMed

    Zhao, Xuefeng; Raghavan, Madhavan L; Lu, Jia

    2011-04-01

    The traditional approaches of estimating heterogeneous properties in a soft tissue structure using optimization-based inverse methods often face difficulties because of the large number of unknowns to be simultaneously determined. This article proposes a new method for identifying the heterogeneous anisotropic nonlinear elastic properties in cerebral aneurysms. In this method, the local properties are determined directly from the pointwise stress-strain data, thus avoiding the need for simultaneously optimizing for the property values at all points/regions in the aneurysm. The stress distributions needed for a pointwise identification are computed using an inverse elastostatic method without invoking the material properties in question. This paradigm is tested numerically through simulated inflation tests on an image-based cerebral aneurysm sac. The wall tissue is modeled as an eight-ply laminate whose constitutive behavior is described by an anisotropic hyperelastic strain energy function containing four parameters. The parameters are assumed to vary continuously in the sac. Deformed configurations generated from forward finite element analysis are taken as input to inversely establish the parameter distributions. The delineated and the assigned distributions are in excellent agreement. A forward verification is conducted by comparing the displacement solutions obtained from the delineated and the assigned material parameters at a different pressure. The deviations in nodal displacements are found to be within 0.2% in most part of the sac. The study highlights some distinct features of the proposed method, and demonstrates the feasibility of organ level identification of the distributive anisotropic nonlinear properties in cerebral aneurysms.

  18. A Method for Measuring the Specific Electrical Conductivity of an Anisotropically Conductive Medium

    NASA Astrophysics Data System (ADS)

    Ašmontas, S.; Kleiza, V.; Kleiza, J.

    2008-06-01

    The paper deals with the ways of finding an electrical conductivity tensor of a plane and anisotropically conductive sample. Application of the Van der Pauw method to investigate the conductivity of anisotropically conductive media makes the basis of research. Several models of distribution of the electric field potential are presented, their merits and demerits are discussed, and the necessary physical measurements are indicated. On the basis of these models, the respective calculation expressions of the specific conductivity tensor are derived and algorithms for their realization and error calculation are developed.

  19. Strong anisotropic thermal conductivity of monolayer WTe2

    NASA Astrophysics Data System (ADS)

    Ma, Jinlong; Chen, Yani; Han, Zheng; Li, Wu

    2016-12-01

    Tungsten ditelluride (WTe2) has attracted increasing attention due to its large magnetoresistance and pressure-induced superconductivity. In this work, we investigate the thermal conductivity (κ) of monolayer WTe2 by performing first-principles calculations, and find strong anisotropic κ with predicted room-temperature values of 9 and 20 W m-1 K-1 along two principal lattice directions, respectively. Such strong anisotropy suggests the importance of orientation when engineering thermal-related applications based on WTe2. The anisotropy of κ is attributed to the in-plane linear acoustic phonon branches, while the out-of-plane quadratic acoustic phonon branch is almost isotropic. The size dependence of κ shows that the size effect can persists up to 10 μm, and the anisotropy decreases with decreasing sample size due to the suppression of low-frequency anisotropic phonons by boundary scattering.

  20. Elliptical silicon arrays with anisotropic optical and wetting properties.

    PubMed

    Wang, Tieqiang; Li, Xiao; Zhang, Junhu; Wang, Xianzhe; Zhang, Xuemin; Zhang, Xun; Zhu, Difu; Hao, Yudong; Ren, Zhiyu; Yang, Bai

    2010-08-17

    We demonstrate a facile etching method to fabricate silicon elliptical pillar arrays (Si-EPAs) with unique anisotropic optical and wetting characters using polystyrene elliptical hemisphere arrays (EHAs) as mask. The EHAs were fabricated via a modified micromolding method. By varying the experimental conditions in the fabrication process, the morphology of the resulting microstructures can be controlled exactly. Because of the anisotropic morphology of the elliptical pillar, the Si-EPA shows unique anisotropic properties, such as anisotropic surface reflection and anisotropic wetting property. Additionally, through oblique evaporation deposition of Au and selective chemical modification to turn the elliptical pillars into "Janus" elliptical pillars, the "Janus" Si-EPA shows more peculiar anisotropic properties owing to the further increased asymmetry. We believe that the Si-EPAs will have potential applications in anisotropic optical and electronic devices.

  1. Anisotropic thermal conduction in cosmological cluster formation simulations

    NASA Astrophysics Data System (ADS)

    Ruszkowski, Mateusz; Parrish, Ian; Brueggen, Marcus

    2009-05-01

    We investigate the role of the magnetothermal instability (MTI) in the cosmological cluster formation simulations. Our simulations self-consistently incorporate the effects of the field amplification by the structure formation (i.e., gravitational collapse and shearing) and by anisotropic thermal conduction, as well as the effects of violent sloshing motions (e.g., due to mergers) that tend to slow down the field growth. We quantify the effects of these processes on the temperature and density profiles, the strength and topology of the magnetic fields as well as the effective thermal conduction in the intarcluster medium.

  2. Magnetotelluric inversion for anisotropic conductivities in layered media

    NASA Astrophysics Data System (ADS)

    Pek, Josef; Santos, Fernando A. M.

    2006-10-01

    Electrical anisotropy in the Earth's crust and upper mantle has recently gained attention as a significant linking factor between electrical models and underlying structural and tectonic patterns. This interest has also motivated new methodological studies into the modelling and inversion for electrically anisotropic structures. We present an algorithm for the inversion of magnetotelluric data over layered anisotropic conductors which is a straightforward extension of the standard Occam 1-D inversion to anisotropic models. Owing to the essential limitation of magnetotellurics to resolve the complete conductivity tensor, we formulate the inversion for azimuthal anisotropy only. We treat the non-linear inverse problem as a multi-criterion minimization of the structure complexity, data misfit and anisotropy. To constrain the structure complexity, we employ the standard roughness penalty as well as non-quadratic penalties of the total variation and gradient support type that produce more focused model sections and thus conform better to the idea about sharp, non-diffuse boundaries of anisotropic structures in the Earth. Application of the anisotropy penalty is crucial for suppressing spurious anisotropy in the inverse models. We use a 2-D extension of the heuristic L-curve method to estimate the quasi-optimal penalty weights. With two non-linear iteration solvers, specifically the reweighted conjugate gradient method and the lagged diffusivity iteration, we can arrive at the minimum of the target functional, for one selected pair of regularization weights, typically after a few tens of iteration steps. To demonstrate the inverse solution, we present two simple yet not completely trivial synthetic examples, the first one based on data generated by a model with two anisotropic layers with discordant strikes, and the other showing possible misinterpretations in case a 1-D inversion with anisotropy is formally applied to data produced by simple 2-D block structures. Field

  3. Anisotropic ion diffusivity in intervertebral disc: an electrical conductivity approach.

    PubMed

    Jackson, Alicia; Yao, Hai; Brown, Mark D; Yong Gu, Wei

    2006-11-15

    Investigation of the transport behavior of ions in intervertebral disc using an electrical conductivity method. To determine the electrical conductivity and ion diffusivity of nucleus pulposus and anulus fibrosus in 3 major directions (axial, circumferential, and radial). Knowledge of diffusivity of small molecules is important for understanding nutrition supply in intervertebral disc and disc degeneration. However, little is known on the anisotropic behaviors of ion diffusivity and of electrical conductivity in intervertebral disc. Electrical conductivity measurement was performed on 24 axial, circumferential, and radial anulus fibrosus specimens and 24 axial nucleus pulposus specimens from bovine coccygeal discs. The diffusivity of Na and Cl were estimated by the analysis of conductivity data. The electrical conductivity (mean +/- standard deviation; n = 24) of the bovine anulus fibrosus was 4.70 +/- 1.08 mS/cm in the axial, 2.86 +/- 0.83 mS/cm in the radial, and 4.38 +/- 1.25 mS/cm in the circumferential direction. For nucleus pulposus, the electrical conductivity (mean +/- standard deviation; n = 24) was 8.95 +/- 0.89 mS/cm. The mean value for nucleus pulposus was significantly higher than that of anulus fibrosus (t test, P < 0.05). For anulus fibrosus, the conductivity in the radial direction was significantly lower than in axial or circumferential directions. Similar trends were found for both Na and Cl diffusivities. Both electrical conductivity and ion diffusivity were highly sensitive to water content. Electrical conductivity and ion diffusivity of anulus fibrosus are anisotropic.

  4. Anisotropic thermal property of magnetically oriented carbon nanotube polymer composites

    NASA Astrophysics Data System (ADS)

    Li, Bin; Dong, Shuai; Wang, Caiping; Wang, Xiaojie; Fang, Jun

    2016-04-01

    This paper proposes a method for preparing multi-walled carbon nanotubea/polydimethylsiloxane (MWCNTs/PDMS) composites with enhanced thermal properties by using a high magnetic field (up to 10T). The MWCNT are oriented magnetically inside a silicone by in-situ polymerization method. The anisotropic structure would be expected to produce directional thermal conductivity. This study will provide a new approach to the development of anisotropic thermal-conductive polymer composites. Systematic studies with the preparation of silicone/graphene composites corresponding to their thermal and mechanical properties are carried out under various conditions: intensity of magnetic field, time, temperature, fillings. The effect of MWCNT/graphene content and preparation procedures on thermal conductivity of composites is investigated. Dynamic mechanical analysis (DMA) is used to reveal the mechanical properties of the composites in terms of the filling contents and magnetic field strength. The scanning electron microscope (SEM) is used to observe the micro-structure of the MWCNT composites. The alignment of MWCNTs in PDMS matrix is also studied by Raman spectroscopy. The thermal conductivity measurements show that the magnetically aligned CNT-composites feature high anisotropy in thermal conductivity.

  5. Accurately simulating anisotropic thermal conduction on a moving mesh

    NASA Astrophysics Data System (ADS)

    Kannan, Rahul; Springel, Volker; Pakmor, Rüdiger; Marinacci, Federico; Vogelsberger, Mark

    2016-05-01

    We present a novel implementation of an extremum preserving anisotropic diffusion solver for thermal conduction on the unstructured moving Voronoi mesh of the AREPO code. The method relies on splitting the one-sided facet fluxes into normal and oblique components, with the oblique fluxes being limited such that the total flux is both locally conservative and extremum preserving. The approach makes use of harmonic averaging points and a simple, robust interpolation scheme that works well for strong heterogeneous and anisotropic diffusion problems. Moreover, the required discretization stencil is small. Efficient fully implicit and semi-implicit time integration schemes are also implemented. We perform several numerical tests that evaluate the stability and accuracy of the scheme, including applications such as point explosions with heat conduction and calculations of convective instabilities in conducting plasmas. The new implementation is suitable for studying important astrophysical phenomena, such as the conductive heat transport in galaxy clusters, the evolution of supernova remnants, or the distribution of heat from black hole-driven jets into the intracluster medium.

  6. Reciprocal relations for effective conductivities of anisotropic media

    NASA Astrophysics Data System (ADS)

    Nevard, John; Keller, Joseph B.

    1985-11-01

    Any pair of two-dimensional anisotropic media with local conductivity tensors that are functions of position and that are related to one another in a certain reciprocal way are considered. It is proved that their effective conductivity tensors are related to each other in the same way for both spatially periodic media and statistically stationary random media. An inequality involving the effective conductivity tensors of two three-dimensional media that are reciprocally related is also proved. These results extend the corresponding results for locally isotropic media obtained by Keller, Mendelsohn, Hansen, Schulgasser, and Kohler and Papanicolau. They also yield a relation satisfied by the effective conductivity tensor of a medium reciprocal to a translated or rotated copy of itself.

  7. A Controllably Anisotropic Conductivity or Diffusion Phantom Constructed from Isotropic Layers

    PubMed Central

    Sadleir, Rosalind J.; Neralwala, Farida; Te, Tang; Tucker, Aaron

    2009-01-01

    Phantoms with controllable and well-defined anisotropy are needed to test methods for imaging electrical anisotropy. We developed and tested a phantom that had properties similar to a homogeneous anisotropic conductive medium. The phantom was constructed with alternate slices of isotropic gel having different conductivities. The degree of anisotropy in the phantom could be varied easily by changing the relative conductivity of the two gels. We tested the stability of several phantoms and found their properties were maintained for approximately 8 h following construction. The phantom has application to electrical impedance tomography, magnetic resonance electrical impedance tomography, EEG and ECG source imaging and diffusion tensor imaging. PMID:19760146

  8. Anisotropic heat conduction in silicon nanowire network revealed by Raman scattering

    NASA Astrophysics Data System (ADS)

    Isaiev, Mykola; Didukh, Oles; Nychyporuk, Tetyana; Timoshenko, Victor; Lysenko, Vladimir

    2017-01-01

    Anisotropic nanomaterials possess interesting thermal transport properties because they allow orientation of heat fluxes along preferential directions due to a high ratio (up to three orders of magnitude) between their in-plane and cross-plane thermal conductivities. Among different techniques allowing thermal conductivity evaluation, micro-Raman scattering is known to be one of the most efficient contactless measurement approaches. In this letter, an experimental approach based on Raman scattering measurements with variable laser spot sizes is reported. Correlation between experimental and calculated thermal resistances of one-dimensional nanocrystalline solids allows a simultaneous estimation of their in-plane and cross-plane thermal conductivities. In particular, our measurement approach is illustrated to be applied for anisotropic thermal conductivity evaluation of silicon nanowire arrays.

  9. Thermal Conductivity Measurement of Anisotropic Biological Tissue In Vitro

    NASA Astrophysics Data System (ADS)

    Yue, Kai; Cheng, Liang; Yang, Lina; Jin, Bitao; Zhang, Xinxin

    2017-06-01

    The accurate determination of the thermal conductivity of biological tissues has implications on the success of cryosurgical/hyperthermia treatments. In light of the evident anisotropy in some biological tissues, a new modified stepwise transient method was proposed to simultaneously measure the transverse and longitudinal thermal conductivities of anisotropic biological tissues. The physical and mathematical models were established, and the analytical solution was derived. Sensitivity analysis and experimental simulation were performed to determine the feasibility and measurement accuracy of simultaneously measuring the transverse and longitudinal thermal conductivities. The experimental system was set up, and its measurement accuracy was verified by measuring the thermal conductivity of a reference standard material. The thermal conductivities of the pork tenderloin and bovine muscles were measured using the traditional 1D and proposed methods, respectively, at different temperatures. Results indicate that the thermal conductivities of the bovine muscle are lower than those of the pork tenderloin muscle, whereas the bovine muscle was determined to exhibit stronger anisotropy than the pork tenderloin muscle. Moreover, the longitudinal thermal conductivity is larger than the transverse thermal conductivity for the two tissues and all thermal conductivities increase with the increase in temperature. Compared with the traditional 1D method, results obtained by the proposed method are slightly higher although the relative deviation is below 5 %.

  10. COSMOLOGICAL MAGNETOHYDRODYNAMIC SIMULATIONS OF CLUSTER FORMATION WITH ANISOTROPIC THERMAL CONDUCTION

    SciTech Connect

    Ruszkowski, M.; Lee, D.; Parrish, I.; Oh, S. Peng E-mail: dongwook@flash.uchicago.edu E-mail: iparrish@astro.berkeley.edu

    2011-10-20

    The intracluster medium (ICM) has been suggested to be buoyantly unstable in the presence of magnetic field and anisotropic thermal conduction. We perform first cosmological simulations of galaxy cluster formation that simultaneously include magnetic fields, radiative cooling, and anisotropic thermal conduction. In isolated and idealized cluster models, the magnetothermal instability (MTI) tends to reorient the magnetic fields radially whenever the temperature gradient points in the direction opposite to gravitational acceleration. Using cosmological simulations of cluster formation we detect radial bias in the velocity and magnetic fields. Such radial bias is consistent with either the inhomogeneous radial gas flows due to substructures or residual MTI-driven field rearrangements that are expected even in the presence of turbulence. Although disentangling the two scenarios is challenging, we do not detect excess bias in the runs that include anisotropic thermal conduction. The anisotropy effect is potentially detectable via radio polarization measurements with LOFAR and the Square Kilometer Array and future X-ray spectroscopic studies with the International X-ray Observatory. We demonstrate that radiative cooling boosts the amplification of the magnetic field by about two orders of magnitude beyond what is expected in the non-radiative cases. This effect is caused by the compression of the gas and frozen-in magnetic field as it accumulates in the cluster center. At z = 0 the field is amplified by a factor of about 10{sup 6} compared to the uniform magnetic field that evolved due to the universal expansion alone. Interestingly, the runs that include both radiative cooling and thermal conduction exhibit stronger magnetic field amplification than purely radiative runs. In these cases, buoyant restoring forces depend on the temperature gradients rather than the steeper entropy gradients. Thus, the ICM is more easily mixed and the winding up of the frozen-in magnetic

  11. Variable Anisotropic Brain Electrical Conductivities in Epileptogenic Foci

    PubMed Central

    Mandelkern, M.; Bui, D.; Salamon, N.; Vinters, H. V.; Mathern, G. W.

    2010-01-01

    Source localization models assume brain electrical conductivities are isotropic at about 0.33 S/m. These assumptions have not been confirmed ex vivo in humans. This study determined bidirectional electrical conductivities from pediatric epilepsy surgery patients. Electrical conductivities perpendicular and parallel to the pial surface of neocortex and subcortical white matter (n = 15) were measured using the 4-electrode technique and compared with clinical variables. Mean (±SD) electrical conductivities were 0.10 ± 0.01 S/m, and varied by 243% from patient to patient. Perpendicular and parallel conductivities differed by 45%, and the larger values were perpendicular to the pial surface in 47% and parallel in 40% of patients. A perpendicular principal axis was associated with normal, while isotropy and parallel principal axes were linked with epileptogenic lesions by MRI. Electrical conductivities were decreased in patients with cortical dysplasia compared with non-dysplasia etiologies. The electrical conductivity values of freshly excised human brain tissues were approximately 30% of assumed values, varied by over 200% from patient to patient, and had erratic anisotropic and isotropic shapes if the MRI showed a lesion. Understanding brain electrical conductivity and ways to non-invasively measure them are probably necessary to enhance the ability to localize EEG sources from epilepsy surgery patients. PMID:20440549

  12. Anisotropic conductivity tensor imaging in MREIT using directional diffusion rate of water molecules.

    PubMed

    Kwon, Oh In; Jeong, Woo Chul; Sajib, Saurav Z K; Kim, Hyung Joong; Woo, Eung Je

    2014-06-21

    Magnetic resonance electrical impedance tomography (MREIT) is an emerging method to visualize electrical conductivity and/or current density images at low frequencies (below 1 KHz). Injecting currents into an imaging object, one component of the induced magnetic flux density is acquired using an MRI scanner for isotropic conductivity image reconstructions. Diffusion tensor MRI (DT-MRI) measures the intrinsic three-dimensional diffusion property of water molecules within a tissue. It characterizes the anisotropic water transport by the effective diffusion tensor. Combining the DT-MRI and MREIT techniques, we propose a novel direct method for absolute conductivity tensor image reconstructions based on a linear relationship between the water diffusion tensor and the electrical conductivity tensor. We first recover the projected current density, which is the best approximation of the internal current density one can obtain from the measured single component of the induced magnetic flux density. This enables us to estimate a scale factor between the diffusion tensor and the conductivity tensor. Combining these values at all pixels with the acquired diffusion tensor map, we can quantitatively recover the anisotropic conductivity tensor map. From numerical simulations and experimental verifications using a biological tissue phantom, we found that the new method overcomes the limitations of each method and successfully reconstructs both the direction and magnitude of the conductivity tensor for both the anisotropic and isotropic regions.

  13. Measurement of the anisotropic thermal conductivity of the porcine cornea.

    PubMed

    Barton, Michael D; Trembly, B Stuart

    2013-10-01

    Accurate thermal models for the cornea of the eye support the development of thermal techniques for reshaping the cornea and other scientific purposes. Heat transfer in the cornea must be quantified accurately so that a thermal treatment does not destroy the endothelial layer, which cannot regenerate, and yet is responsible for maintaining corneal transparency. We developed a custom apparatus to measure the thermal conductivity of ex vivo porcine corneas perpendicular to the surface and applied a commercial apparatus to measure thermal conductivity parallel to the surface. We found that corneal thermal conductivity is 14% anisotropic at the normal state of corneal hydration. Small numbers of ex vivo feline and human corneas had a thermal conductivity perpendicular to the surface that was indistinguishable from the porcine corneas. Aqueous humor from ex vivo porcine, feline, and human eyes had a thermal conductivity nearly equal to that of water. Including the anisotropy of corneal thermal conductivity will improve the predictive power of thermal models of the eye.

  14. Pulse accumulation, radial heat conduction, and anisotropic thermal conductivity in pump-probe transient thermoreflectance.

    PubMed

    Schmidt, Aaron J; Chen, Xiaoyuan; Chen, Gang

    2008-11-01

    The relationship between pulse accumulation and radial heat conduction in pump-probe transient thermoreflectance (TTR) is explored. The results illustrate how pulse accumulation allows TTR to probe two thermal length scales simultaneously. In addition, the conditions under which radial transport effects are important are described. An analytical solution for anisotropic heat flow in layered structures is given, and a method for measuring both cross-plane and in-plane thermal conductivities of thermally anisotropic thin films is described. As verification, the technique is used to extract the cross-plane and in-plane thermal conductivities of highly ordered pyrolytic graphite. Results are found to be in good agreement with literature values.

  15. Stable determination of an inclusion for a class of anisotropic conductivities

    NASA Astrophysics Data System (ADS)

    Di Cristo, Michele; Ren, Yong

    2017-09-01

    We deal with the inverse problem of determining an inclusion within an electrical conductor from electrostatic boundary measurements. We consider an anisotropic conductivity and provide logarithmic type stability.

  16. High field dielectric properties of anisotropic polymer-ceramic composites

    SciTech Connect

    Tomer, V.; Randall, C. A.

    2008-10-01

    Using dielectrophoretic assembly, we create anisotropic composites of BaTiO{sub 3} particles in a silicone elastomer thermoset polymer. We study a variety of electrical properties in these composites, i.e., permittivity, dielectric breakdown, and energy density as function of ceramic volume fraction and connectivity. The recoverable energy density of these electric-field-structured composites is found to be highly dependent on the anisotropy present in the system. Our results indicate that x-y-aligned composites exhibit higher breakdown strengths along with large recoverable energy densities when compared to 0-3 composites. This demonstrates that engineered anisotropy can be employed to control dielectric breakdown strengths and nonlinear conduction at high fields in heterogeneous systems. Consequently, manipulation of anisotropy in high-field dielectric properties can be exploited for the development of high energy density polymer-ceramic systems.

  17. Measuring In-Plane Thermal Conductivity of Anisotropic Thin-films

    NASA Astrophysics Data System (ADS)

    Rodin, Misha; Yee, Shannon

    2014-03-01

    Polymer thermoelectrics (TEs) are a promising alternative to traditional TEs due to low cost and scalability. Higher efficiency polymer TEs can be realized by control of in-plane electrical and thermal properties. This specifically requires a non-contact technique that can probe the thermal conductivity of highly anisotropic films. Current conductivity measurements of thin-films rely on periodic heating of a semi-infinite solid. The periodic heating causes surface temperature fluctuations, which depend on the thermal and physical properties of the material. Presented here is our progress in developing a frequency-domain thermoreflectance (FDTR) technique to measure in-plane thermal conductivity of highly anisotropic films. Traditional FDTR uses a circular laser spot for heating and is insensitive to the effects of lateral heat flow. By modifying the heating laser spot from a circle to an annulus, the temperature fluctuations inside the annulus perimeter are significantly influenced by lateral heat flow. The probe laser can scan within the annulus, making this technique sensitive to both the in-plane and through-plane properties. Additionally, this technique can be used at high heating frequencies to measure phonon MFP contributions to the thermal conductivity in both directions.

  18. Unusually High and Anisotropic Thermal Conductivity in Amorphous Silicon Nanostructures.

    PubMed

    Kwon, Soonshin; Zheng, Jianlin; Wingert, Matthew C; Cui, Shuang; Chen, Renkun

    2017-02-02

    Amorphous Si (a-Si) nanostructures are ubiquitous in numerous electronic and optoelectronic devices. Amorphous materials are considered to possess the lower limit to the thermal conductivity (κ), which is ∼1 W·m(-1) K(-1) for a-Si. However, recent work suggested that κ of micrometer-thick a-Si films can be greater than 3 W·m(-1) K(-1), which is contributed to by propagating vibrational modes, referred to as "propagons". However, precise determination of κ in a-Si has been elusive. Here, we used structures of a-Si nanotubes and suspended a-Si films that enabled precise in-plane thermal conductivity (κ∥) measurement within a wide thickness range of 5 nm to 1.7 μm. We showed unexpectedly high κ∥ in a-Si nanostructures, reaching ∼3.0 and 5.3 W·m(-1) K(-1) at ∼100 nm and 1.7 μm, respectively. Furthermore, the measured κ∥ is significantly higher than the cross-plane κ on the same films. This unusually high and anisotropic thermal conductivity in the amorphous Si nanostructure manifests the surprisingly broad propagon mean free path distribution, which is found to range from 10 nm to 10 μm, in the disordered and atomically isotropic structure. This result provides an unambiguous answer to the century-old problem regarding mean free path distribution of propagons and also sheds light on the design and performance of numerous a-Si based electronic and optoelectronic devices.

  19. Computational Study of Subdural Cortical Stimulation: Effects of Simulating Anisotropic Conductivity on Activation of Cortical Neurons

    PubMed Central

    Seo, Hyeon; Kim, Donghyeon; Jun, Sung Chan

    2015-01-01

    Subdural cortical stimulation (SuCS) is an appealing method in the treatment of neurological disorders, and computational modeling studies of SuCS have been applied to determine the optimal design for electrotherapy. To achieve a better understanding of computational modeling on the stimulation effects of SuCS, the influence of anisotropic white matter conductivity on the activation of cortical neurons was investigated in a realistic head model. In this paper, we constructed pyramidal neuronal models (layers 3 and 5) that showed primary excitation of the corticospinal tract, and an anatomically realistic head model reflecting complex brain geometry. The anisotropic information was acquired from diffusion tensor magnetic resonance imaging (DT-MRI) and then applied to the white matter at various ratios of anisotropic conductivity. First, we compared the isotropic and anisotropic models; compared to the isotropic model, the anisotropic model showed that neurons were activated in the deeper bank during cathodal stimulation and in the wider crown during anodal stimulation. Second, several popular anisotropic principles were adapted to investigate the effects of variations in anisotropic information. We observed that excitation thresholds varied with anisotropic principles, especially with anodal stimulation. Overall, incorporating anisotropic conductivity into the anatomically realistic head model is critical for accurate estimation of neuronal responses; however, caution should be used in the selection of anisotropic information. PMID:26057524

  20. Infrared properties of an anisotropically stirred fluid

    NASA Technical Reports Server (NTRS)

    Rubinstein, Robert; Barton, J. Michael

    1987-01-01

    A renormalization group is developed for the Navier-Stokes equations driven by an anisotropically correlated random stirring force. The stirring force generates homogeneous turbulence with a preferred direction. The force correlation is the sum of a small anisotropic perturbation and an isotropic correlation chosen, so that the fixed point of renormalization group has a k exp -5/3 energy spectrum. Fixed points for the anisotropic correlation are found near this isotropic fixed point. Two types of anisotropy are analyzed. when the additional stirring is in the plane perpendicular to the preferred direction, the renormalized viscosity is increased. When it is aligned with the preferred direction, the viscosity is decreased. A possible connection with the inverse energy cascade of two-dimensional turbulence is discussed.

  1. Measurements of anisotropic thermoelectric properties in superlattices

    NASA Astrophysics Data System (ADS)

    Yang, B.; Liu, W. L.; Liu, J. L.; Wang, K. L.; Chen, G.

    2002-11-01

    Thermoelectric properties, i.e., thermal conductivity, electrical conductivity, and the Seebeck coefficient, have been measured in the directions parallel (in-plane) and perpendicular to the interface of an n-type Si(80 A)/Ge(20 A) superlattice. A two-wire 3omega method is employed to measure the in-plane and cross-plane thermal conductivities. The cross-plane Seebeck coefficient is deduced by using a differential measurement between the superlattice and reference samples and the cross-plane electrical conductivity is determined through a modified transmission-line method. The in-plane thermal conductivity of the Si/Ge superlattice is 5-6 times higher than the cross-plane one, and the electrical conductivity shows a similar anisotropy. The anisotropy of the Seebeck coefficients is smaller in comparison to electrical and thermal conductivities in the temperature range from 150 to 300 K. However, the cross-plane Seebeck coefficient rises faster with increasing temperature than that of the in-plane direction.

  2. Effects of anisotropic conduction and heat pipe interaction on minimum mass space radiators

    NASA Technical Reports Server (NTRS)

    Baker, Karl W.; Lund, Kurt O.

    1991-01-01

    Equations are formulated for the two dimensional, anisotropic conduction of heat in space radiator fins. The transverse temperature field was obtained by the integral method, and the axial field by numerical integration. A shape factor, defined for the axial boundary condition, simplifies the analysis and renders the results applicable to general heat pipe/conduction fin interface designs. The thermal results are summarized in terms of the fin efficiency, a radiation/axial conductance number, and a transverse conductance surface Biot number. These relations, together with those for mass distribution between fins and heat pipes, were used in predicting the minimum radiator mass for fixed thermal properties and fin efficiency. This mass is found to decrease monotonically with increasing fin conductivity. Sensitivities of the minimum mass designs to the problem parameters are determined.

  3. Nanofiber Anisotropic Conductive Films (ACF) for Ultra-Fine-Pitch Chip-on-Glass (COG) Interconnections

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Hoon; Kim, Tae-Wan; Suk, Kyung-Lim; Paik, Kyung-Wook

    2015-11-01

    Nanofiber anisotropic conductive films (ACF) were invented, by adapting nanofiber technology to ACF materials, to overcome the limitations of ultra-fine-pitch interconnection packaging, i.e. shorts and open circuits as a result of the narrow space between bumps and electrodes. For nanofiber ACF, poly(vinylidene fluoride) (PVDF) and poly(butylene succinate) (PBS) polymers were used as nanofiber polymer materials. For PVDF and PBS nanofiber ACF, conductive particles of diameter 3.5 μm were incorporated into nanofibers by electrospinning. In ultra-fine-pitch chip-on-glass assembly, insulation was significantly improved by using nanofiber ACF, because nanofibers inside the ACF suppressed the mobility of conductive particles, preventing them from flowing out during the bonding process. Capture of conductive particles was increased from 31% (conventional ACF) to 65%, and stable electrical properties and reliability were achieved by use of nanofiber ACF.

  4. Cellulose-Templated Graphene Monoliths with Anisotropic Mechanical, Thermal, and Electrical Properties.

    PubMed

    Zhang, Rujing; Chen, Qiao; Zhen, Zhen; Jiang, Xin; Zhong, Minlin; Zhu, Hongwei

    2015-09-02

    Assembling particular building blocks into composites with diverse targeted structures has attracted considerable interest for understanding its new properties and expanding the potential applications. Anisotropic organization is considered as a frequently used targeted architecture and possesses many peculiar properties because of its unusual shapes. Here, we show that anisotropic graphene monoliths (AGMs), three-dimensional architectures of well-aligned graphene sheets obtained by a dip-coating method using cellulose acetate fibers as templates show thermal-insulating, fire-retardant, and anisotropic properties. They exhibit a feature of higher mechanical strength and thermal/electrical conductivities in the axial direction than in the radial direction. Elastic polymer resins are then introduced into the pores of the AGMs to form conductive and flexible composites. The composites, as AGMs, retain the unique anisotropic properties, revealing opposite resistance change under compressions in different directions. The outstanding anisotropic properties of AGMs make them possible to be applied in the fields of thermal insulation, integrated circuits, and electromechanical devices.

  5. Hybrid hydrogels containing vertically aligned carbon nanotubes with anisotropic electrical conductivity for muscle myofiber fabrication

    NASA Astrophysics Data System (ADS)

    Ahadian, Samad; Ramón-Azcón, Javier; Estili, Mehdi; Liang, Xiaobin; Ostrovidov, Serge; Shiku, Hitoshi; Ramalingam, Murugan; Nakajima, Ken; Sakka, Yoshio; Bae, Hojae; Matsue, Tomokazu; Khademhosseini, Ali

    2014-03-01

    Biological scaffolds with tunable electrical and mechanical properties are of great interest in many different fields, such as regenerative medicine, biorobotics, and biosensing. In this study, dielectrophoresis (DEP) was used to vertically align carbon nanotubes (CNTs) within methacrylated gelatin (GelMA) hydrogels in a robust, simple, and rapid manner. GelMA-aligned CNT hydrogels showed anisotropic electrical conductivity and superior mechanical properties compared with pristine GelMA hydrogels and GelMA hydrogels containing randomly distributed CNTs. Skeletal muscle cells grown on vertically aligned CNTs in GelMA hydrogels yielded a higher number of functional myofibers than cells that were cultured on hydrogels with randomly distributed CNTs and horizontally aligned CNTs, as confirmed by the expression of myogenic genes and proteins. In addition, the myogenic gene and protein expression increased more profoundly after applying electrical stimulation along the direction of the aligned CNTs due to the anisotropic conductivity of the hybrid GelMA-vertically aligned CNT hydrogels. We believe that platform could attract great attention in other biomedical applications, such as biosensing, bioelectronics, and creating functional biomedical devices.

  6. Hybrid hydrogels containing vertically aligned carbon nanotubes with anisotropic electrical conductivity for muscle myofiber fabrication

    PubMed Central

    Ahadian, Samad; Ramón-Azcón, Javier; Estili, Mehdi; Liang, Xiaobin; Ostrovidov, Serge; Shiku, Hitoshi; Ramalingam, Murugan; Nakajima, Ken; Sakka, Yoshio; Bae, Hojae; Matsue, Tomokazu; Khademhosseini, Ali

    2014-01-01

    Biological scaffolds with tunable electrical and mechanical properties are of great interest in many different fields, such as regenerative medicine, biorobotics, and biosensing. In this study, dielectrophoresis (DEP) was used to vertically align carbon nanotubes (CNTs) within methacrylated gelatin (GelMA) hydrogels in a robust, simple, and rapid manner. GelMA-aligned CNT hydrogels showed anisotropic electrical conductivity and superior mechanical properties compared with pristine GelMA hydrogels and GelMA hydrogels containing randomly distributed CNTs. Skeletal muscle cells grown on vertically aligned CNTs in GelMA hydrogels yielded a higher number of functional myofibers than cells that were cultured on hydrogels with randomly distributed CNTs and horizontally aligned CNTs, as confirmed by the expression of myogenic genes and proteins. In addition, the myogenic gene and protein expression increased more profoundly after applying electrical stimulation along the direction of the aligned CNTs due to the anisotropic conductivity of the hybrid GelMA-vertically aligned CNT hydrogels. We believe that platform could attract great attention in other biomedical applications, such as biosensing, bioelectronics, and creating functional biomedical devices. PMID:24642903

  7. Anisotropic Tribological Properties of Silicon Carbide

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1980-01-01

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

  8. Identification of current density distribution in electrically conducting subject with anisotropic conductivity distribution.

    PubMed

    Pyo, Hyun Chan; Kwon, Ohin; Seo, Jin Keun; Woo, Eung Je

    2005-07-07

    Current density imaging (CDI) is able to visualize a three-dimensional current density distribution J inside an electrically conducting subject caused by an externally applied current. CDI may use a magnetic resonance imaging (MRI) scanner to measure the induced magnetic flux density B and compute J via the Ampere law [Formula: see text]. However, measuring all three components of B = (B(x), B(y), B(z)) has a technical difficulty due to the requirement of orthogonal rotations of the subject inside the MRI scanner. In this work, we propose a new method of reconstructing a current density image using only B(z) data so that we can avoid the subject rotation procedure. The method utilizes an auxiliary injection current to compensate the missing information of B(x) and B(y). The major advantage of the method is its applicability to a subject with an anisotropic conductivity distribution. Numerical experiments show the feasibility of the new technique.

  9. INTERPLAY AMONG COOLING, AGN FEEDBACK, AND ANISOTROPIC CONDUCTION IN THE COOL CORES OF GALAXY CLUSTERS

    SciTech Connect

    Karen Yang, H.-Y.; Reynolds, Christopher S.

    2016-02-20

    Feedback from the active galactic nuclei (AGNs) is one of the most promising heating mechanisms to circumvent the cooling-flow problem in galaxy clusters. However, the role of thermal conduction remains unclear. Previous studies have shown that anisotropic thermal conduction in cluster cool cores (CCs) could drive the heat-flux-driven buoyancy instabilities (HBIs) that reorient the field lines in the azimuthal directions and isolate the cores from conductive heating from the outskirts. However, how the AGN interacts with the HBI is still unknown. To understand these interwined processes, we perform the first 3D magnetohydrodynamic simulations of isolated CC clusters that include anisotropic conduction, radiative cooling, and AGN feedback. We find the following: (1) For realistic magnetic field strengths in clusters, magnetic tension can suppress a significant portion of HBI-unstable modes, and thus the HBI is either completely inhibited or significantly impaired, depending on the unknown magnetic field coherence length. (2) Turbulence driven by AGN jets can effectively randomize magnetic field lines and sustain conductivity at ∼1/3 of the Spitzer value; however, the AGN-driven turbulence is not volume filling. (3) Conductive heating within the cores could contribute to ∼10% of the radiative losses in Perseus-like clusters and up to ∼50% for clusters twice the mass of Perseus. (4) Thermal conduction has various impacts on the AGN activity and intracluster medium properties for the hottest clusters, which may be searched by future observations to constrain the level of conductivity in clusters. The distribution of cold gas and the implications are also discussed.

  10. Modeling anisotropic Maxwell-Jüttner distributions: derivation and properties

    NASA Astrophysics Data System (ADS)

    Livadiotis, George

    2016-12-01

    In this paper we develop a model for the anisotropic Maxwell-Jüttner distribution and examine its properties. First, we provide the characteristic conditions that the modeling of consistent and well-defined anisotropic Maxwell-Jüttner distributions needs to fulfill. Then, we examine several models, showing their possible advantages and/or failures in accordance to these conditions. We derive a consistent model, and examine its properties and its connection with thermodynamics. We show that the temperature equals the average of the directional temperature-like components, as it holds for the classical, anisotropic Maxwell distribution. We also derive the internal energy and Boltzmann-Gibbs entropy, where we show that both are maximized for zero anisotropy, that is, the isotropic Maxwell-Jüttner distribution.

  11. Three-dimensional forward modeling and inversion of marine CSEM data in anisotropic conductivity structures

    NASA Astrophysics Data System (ADS)

    Han, B.; Li, Y.

    2016-12-01

    We present a three-dimensional (3D) forward and inverse modeling code for marine controlled-source electromagnetic (CSEM) surveys in anisotropic media. The forward solution is based on a primary/secondary field approach, in which secondary fields are solved using a staggered finite-volume (FV) method and primary fields are solved for 1D isotropic background models analytically. It is shown that it is rather straightforward to extend the isotopic 3D FV algorithm to a triaxial anisotropic one, while additional coefficients are required to account for full tensor conductivity. To solve the linear system resulting from FV discretization of Maxwell' s equations, both iterative Krylov solvers (e.g. BiCGSTAB) and direct solvers (e.g. MUMPS) have been implemented, makes the code flexible for different computing platforms and different problems. For iterative soloutions, the linear system in terms of electromagnetic potentials (A-Phi) is used to precondition the original linear system, transforming the discretized Curl-Curl equations to discretized Laplace-like equations, thus much more favorable numerical properties can be obtained. Numerical experiments suggest that this A-Phi preconditioner can dramatically improve the convergence rate of an iterative solver and high accuracy can be achieved without divergence correction even for low frequencies. To efficiently calculate the sensitivities, i.e. the derivatives of CSEM data with respect to tensor conductivity, the adjoint method is employed. For inverse modeling, triaxial anisotropy is taken into account. Since the number of model parameters to be resolved of triaxial anisotropic medias is twice or thrice that of isotropic medias, the data-space version of the Gauss-Newton (GN) minimization method is preferred due to its lower computational cost compared with the traditional model-space GN method. We demonstrate the effectiveness of the code with synthetic examples.

  12. Anisotropic in-Plane Thermal Conductivity Observed in Few-Layer Black Phosphorus

    DTIC Science & Technology

    2015-10-16

    consists of puckered honeycomb atomic sheets bonded by van der Waals force and therefore can be mechanically exfo- liated into atomically thin layers ...ARTICLE Received 25 Mar 2015 | Accepted 7 Sep 2015 | Published 16 Oct 2015 Anisotropic in-plane thermal conductivity observed in few- layer black...report the anisotropic in-plane thermal conductivity of suspended few- layer black phosphorus measured by micro-Raman spectroscopy. The armchair and

  13. Strain-engineering the anisotropic electrical conductance in ReS{sub 2} monolayer

    SciTech Connect

    Yu, Sheng Eshun, Kwesi; Shi, Chen; Zeng, Min; Li, Qiliang; Zhu, Hao

    2016-05-09

    Rhenium disulfide (ReS{sub 2}) is a semiconducting layered transition metal dichalcogenide that exhibits a stable distorted 1 T (Re in octahedral coordination) phase. The reduced symmetry in ReS{sub 2} leads to in-plane anisotropy in various material properties. In this work, we performed a comprehensive first-principle computational study of strain effect on the anisotropic mechanical and electronic properties of ReS{sub 2} monolayers. We found that the anisotropic ratio in electron mobility along two principle axes is 2.36 while the ratio in hole mobility reaches 7.76. The study of strain applied along different directions shows that the elastic modulus is largest for out-of-plane direction, and the strain along a-direction induces indirect bandgap while strain along b- or c-direction does not. In addition, the carrier mobility can be significantly improved by the c-direction tensile strain. This study indicates that the ReS{sub 2} monolayer has promising applications in nanoscale strain sensor and conductance-switch FETs.

  14. Strain-engineering the anisotropic electrical conductance in ReS2 monolayer

    NASA Astrophysics Data System (ADS)

    Yu, Sheng; Zhu, Hao; Eshun, Kwesi; Shi, Chen; Zeng, Min; Li, Qiliang

    2016-05-01

    Rhenium disulfide (ReS2) is a semiconducting layered transition metal dichalcogenide that exhibits a stable distorted 1 T (Re in octahedral coordination) phase. The reduced symmetry in ReS2 leads to in-plane anisotropy in various material properties. In this work, we performed a comprehensive first-principle computational study of strain effect on the anisotropic mechanical and electronic properties of ReS2 monolayers. We found that the anisotropic ratio in electron mobility along two principle axes is 2.36 while the ratio in hole mobility reaches 7.76. The study of strain applied along different directions shows that the elastic modulus is largest for out-of-plane direction, and the strain along a-direction induces indirect bandgap while strain along b- or c-direction does not. In addition, the carrier mobility can be significantly improved by the c-direction tensile strain. This study indicates that the ReS2 monolayer has promising applications in nanoscale strain sensor and conductance-switch FETs.

  15. Anisotropic intrinsic lattice thermal conductivity of borophane from first-principles calculations.

    PubMed

    Liu, Gang; Wang, Haifeng; Gao, Yan; Zhou, Jian; Wang, Hui

    2017-01-25

    Borophene (boron sheet) as a new type of two-dimensional (2D) material was grown successfully recently. Unfortunately, the structural stability of freestanding borophene is still an open issue. Theoretical research has found that full hydrogenation can remove such instability, and the product is called borophane. In this paper, using first-principles calculations we investigate the lattice dynamics and thermal transport properties of borophane. The intrinsic lattice thermal conductivity and the relaxation time of borophane are investigated by solving the phonon Boltzmann transport equation (BTE) based on first-principles calculations. We find that the intrinsic lattice thermal conductivity of borophane is anisotropic, as the higher value (along the zigzag direction) is about two times of the lower one (along the armchair direction). The contributions of phonon branches to the lattice thermal conductivities along different directions are evaluated. It is found that both the anisotropy of thermal conductivity and the different phonon branches which dominate the thermal transport along different directions are decided by the group velocity and the relaxation time of phonons with very low frequency. In addition, the size dependence of thermal conductivity is investigated using cumulative thermal conductivity. The underlying physical mechanisms of these unique properties are also discussed in this paper.

  16. Properties and evolution of anisotropic structures in collisionless plasmas

    NASA Astrophysics Data System (ADS)

    Karimov, A. R.; Yu, M. Y.; Stenflo, L.

    2016-10-01

    A new class of exact electrostatic solutions of the Vlasov-Maxwell equations based on the Jeans's theorem is proposed for studying the evolution and properties of two-dimensional anisotropic plasmas that are far from thermodynamic equilibrium. In particular, the free expansion of a slab of electron-ion plasma into vacuum is investigated.

  17. Measurement of Anisotropic Mechanical Properties of the Tectorial Membrane

    NASA Astrophysics Data System (ADS)

    Gavara, N.; Chadwick, R. S.

    2009-02-01

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

  18. Extracellular measurement of anisotropic bidomain myocardial conductivities. I. Theoretical analysis.

    PubMed

    Le Guyader, P; Trelles, F; Savard, P

    2001-10-01

    The passive electrical properties of cardiac tissue, such as the intracellular and interstitial conductivities along the longitudinal and transverse axes, have not been often measured because intracellular electrodes are usually needed for these measurements. In this paper, we present a theoretical analysis of two myocardial models developed to estimate these properties by analyzing potentials recorded with a pair of extracellular electrodes while injecting alternating current between another pair of electrodes. First, the cardiac tissue is represented by a standard bidomain model which includes a membrane capacitance; second, this model is modified by adding an intracellular capacitance representing the intercalated disks. Numerical solutions are computed with a fast Fourier transform algorithm without constraining the anisotropy ratios of the interstitial and intracellular domains. We systematically investigate the effects of changes in the bidomain parameters on the voltage-to-current ratio curves. We also demonstrate how the bidomain parameters can be theoretically estimated by fitting, with a modified Shor's r algorithm, the simulated potentials along the longitudinal and transverse axes for different frequencies between 10 and 10,000 Hz. An important finding is that the interelectrode distance must be similar to the myocardial space constant so as to obtain frequency dependent measurements.

  19. Anisotropic Electroless Deposition on DNA Origami Templates To Form Small Diameter Conductive Nanowires.

    PubMed

    Uprety, Bibek; Westover, Tyler; Stoddard, Michael; Brinkerhoff, Kamron; Jensen, John; Davis, Robert C; Woolley, Adam T; Harb, John N

    2017-01-24

    An improved method for the metallization of DNA origami is examined in this work. DNA origami, a simple and robust method for creating a wide variety of nanostructured shapes and patterns, provides an enabling template for bottom-up fabrication of next-generation nanodevices. Selective metallization of these DNA templates is needed to make nanoelectronic devices. Here, we demonstrate a metallization process that uses gold nanorod seeds followed by anisotropic plating to provide improved morphology and greater control of the final metallized width of the structure. In our approach, gold nanorods are attached to an origami template to create a seed layer. Electroless gold deposition is then used to fill the gaps between seeds in order to create continuous, conductive nanowires. Importantly, growth during electroless deposition occurs preferentially in the length direction at a rate that is approximately 4 times the growth rate in the width direction, which enables fabrication of narrow, continuous wires. The electrical properties of 49 nanowires with widths ranging from 13 to 29 nm were characterized, and resistivity values as low as 8.9 × 10(-7) Ω·m were measured. The anisotropic metallization process presented here represents important progress toward the creation of nanoelectronic devices by molecularly directed placement of functional components onto self-assembled biological templates.

  20. Geometric tuning of thermal conductivity in three-dimensional anisotropic phononic crystals.

    PubMed

    Wei, Zhiyong; Wehmeyer, Geoff; Dames, Chris; Chen, Yunfei

    2016-10-07

    Molecular dynamics simulations are performed to investigate the thermal transport properties of a three-dimensional (3D) anisotropic phononic crystal consisting of silicon nanowires and films. The calculation shows that the in-plane thermal conductivity is negatively correlated with the out-of-plane thermal conductivity upon making geometric changes, whether varying the nanowire diameter or the film thickness. This enables the anisotropy ratio of thermal conductivity to be tailored over a wide range, in some cases by more than a factor of 20. Similar trends in thermal conductivity are also observed from an independent phonon ray tracing simulation considering only diffuse boundary scattering effects, though the range of anisotropy ratios is smaller than that obtained in MD simulation. By analyzing the phonon dispersion relation with varied geometric parameters, it is found that increasing the nanowire diameter increases the out-of-plane acoustic phonon group velocities, but reduces the in-plane longitudinal and fast transverse acoustic phonon group velocities. The calculated phonon irradiation further verified the negative correlation between the in-plane and the out-of-plane thermal conductivity. The proposed 3D phononic crystal may find potential application in thermoelectrics, energy storage, catalysis and sensing applications owing to its widely tailorable thermal conductivity.

  1. Lattice thermal conductivity evaluated using elastic properties

    NASA Astrophysics Data System (ADS)

    Jia, Tiantian; Chen, Gang; Zhang, Yongsheng

    2017-04-01

    Lattice thermal conductivity is one of the most important thermoelectric parameters in determining the energy conversion efficiency of thermoelectric materials. However, the lattice thermal conductivity evaluation requires time-consuming first-principles (quasi)phonon calculations, which limits seeking high-performance thermoelectric materials through high-throughput computations. Here, we establish a methodology to determine the Debye temperature Θ , Grüneisen parameter γ , and lattice thermal conductivity κ using computationally feasible elastic properties (the bulk and shear moduli). For 39 compounds with three different prototypes (the cubic isotropic rocksalt and zinc blende, and the noncubic anisotropic wurtzite), the theoretically calculated Θ ,γ , and κ are in reasonable agreement with those determined using (quasi)harmonic phonon calculations or experimental measurements. Our results show that the methodology is an efficient tool to predict the anharmonicity and the lattice thermal conductivity.

  2. Anisotropic optical response of optically opaque elastomers with conductive fillers as revealed by terahertz polarization spectroscopy

    NASA Astrophysics Data System (ADS)

    Okano, Makoto; Watanabe, Shinichi

    2016-12-01

    Elastomers are one of the most important materials in modern society because of the inherent viscoelastic properties due to their cross-linked polymer chains. Their vibration-absorbing and adhesive properties are especially useful and thus utilized in various applications, for example, tires in automobiles and bicycles, seismic dampers in buildings, and seals in a space shuttle. Thus, the nondestructive inspection of their internal states such as the internal deformation is essential in safety. Generally, industrial elastomers include various kinds of additives, such as carbon blacks for reinforcing them. The additives make most of them opaque in a wide spectral range from visible to mid-infrared, resulting in that the nondestructive inspection of the internal deformation is quite difficult. Here, we demonstrate transmission terahertz polarization spectroscopy as a powerful technique for investigating the internal optical anisotropy in optically opaque elastomers with conductive additives, which are transparent only in the terahertz frequency region. The internal deformation can be probed through the polarization changes inside the material due to the anisotropic dielectric response of the conductive additives. Our study about the polarization-dependent terahertz response of elastomers with conductive additives provides novel knowledge for in situ, nondestructive evaluation of their internal deformation.

  3. Anisotropic optical response of optically opaque elastomers with conductive fillers as revealed by terahertz polarization spectroscopy.

    PubMed

    Okano, Makoto; Watanabe, Shinichi

    2016-12-23

    Elastomers are one of the most important materials in modern society because of the inherent viscoelastic properties due to their cross-linked polymer chains. Their vibration-absorbing and adhesive properties are especially useful and thus utilized in various applications, for example, tires in automobiles and bicycles, seismic dampers in buildings, and seals in a space shuttle. Thus, the nondestructive inspection of their internal states such as the internal deformation is essential in safety. Generally, industrial elastomers include various kinds of additives, such as carbon blacks for reinforcing them. The additives make most of them opaque in a wide spectral range from visible to mid-infrared, resulting in that the nondestructive inspection of the internal deformation is quite difficult. Here, we demonstrate transmission terahertz polarization spectroscopy as a powerful technique for investigating the internal optical anisotropy in optically opaque elastomers with conductive additives, which are transparent only in the terahertz frequency region. The internal deformation can be probed through the polarization changes inside the material due to the anisotropic dielectric response of the conductive additives. Our study about the polarization-dependent terahertz response of elastomers with conductive additives provides novel knowledge for in situ, nondestructive evaluation of their internal deformation.

  4. Anisotropic optical response of optically opaque elastomers with conductive fillers as revealed by terahertz polarization spectroscopy

    PubMed Central

    Okano, Makoto; Watanabe, Shinichi

    2016-01-01

    Elastomers are one of the most important materials in modern society because of the inherent viscoelastic properties due to their cross-linked polymer chains. Their vibration-absorbing and adhesive properties are especially useful and thus utilized in various applications, for example, tires in automobiles and bicycles, seismic dampers in buildings, and seals in a space shuttle. Thus, the nondestructive inspection of their internal states such as the internal deformation is essential in safety. Generally, industrial elastomers include various kinds of additives, such as carbon blacks for reinforcing them. The additives make most of them opaque in a wide spectral range from visible to mid-infrared, resulting in that the nondestructive inspection of the internal deformation is quite difficult. Here, we demonstrate transmission terahertz polarization spectroscopy as a powerful technique for investigating the internal optical anisotropy in optically opaque elastomers with conductive additives, which are transparent only in the terahertz frequency region. The internal deformation can be probed through the polarization changes inside the material due to the anisotropic dielectric response of the conductive additives. Our study about the polarization-dependent terahertz response of elastomers with conductive additives provides novel knowledge for in situ, nondestructive evaluation of their internal deformation. PMID:28008942

  5. Use of the correct heat conduction-convection equation as basis for heat-pulse sap flow methods in anisotropic wood.

    PubMed

    Vandegehuchte, Maurits W; Steppe, Kathy

    2012-05-01

    Heat-pulse methods to determine sap flux density in trees are founded on the theory of heat conduction and heat convection in an isotropic medium. However, sapwood is clearly anisotropic, implying a difference in thermal conductivity along and across the grain, and hence necessitates the theory for an anisotropic medium. This difference in thermal conductivities, which can be up to 50%, is, however, not taken into account in the key equation leading to the currently available heat-pulse methods. Despite this major flaw, the methods remain theoretically correct as they are based on derivations of the key equation, ruling out any anisotropic aspects. The importance of specifying the thermal characteristics of the sapwood according to axial, tangential or radial direction is revealed as well as referring to and using the proper anisotropic theory in order to avoid confusion and misinterpretation of thermal properties when dealing with sap flux density measurements or erroneous results when modelling heat transport in sapwood.

  6. CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES: Effective Anisotropic Dielectric Properties of Crystal Composites

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

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

  7. Anisotropic lattice thermal conductivity in chiral tellurium from first principles

    SciTech Connect

    Peng, Hua; Kioussis, Nicholas; Stewart, Derek A.

    2015-12-21

    Using ab initio based calculations, we have calculated the intrinsic lattice thermal conductivity of chiral tellurium. We show that the interplay between the strong covalent intrachain and weak van der Waals interchain interactions gives rise to the phonon band gap between the lower and higher optical phonon branches. The underlying mechanism of the large anisotropy of the thermal conductivity is the anisotropy of the phonon group velocities and of the anharmonic interatomic force constants (IFCs), where large interchain anharmonic IFCs are associated with the lone electron pairs. We predict that tellurium has a large three-phonon scattering phase space that results in low thermal conductivity. The thermal conductivity anisotropy decreases under applied hydrostatic pressure.

  8. Strain-Engineering the Anisotropic Electrical Conductance of Few-Layer Black Phosphorus

    NASA Astrophysics Data System (ADS)

    Fei, Ruixiang; Yang, Li

    2014-05-01

    Newly fabricated monolayer phosphorene and its few-layer structures are expected to be promising for electronic and optical applications because of their finite direct band gaps and sizable but anisotropic electronic mobility. By first-principles simulations, we show that this unique anisotropic conductance can be controlled by using simple strain conditions. With the appropriate biaxial or uniaxial strain, we can rotate the preferred conducting direction by 90 degrees. This will be of useful for exploring quantum Hall effects, and exotic electronic and mechanical applications based on phosphorene.

  9. The Effect of Anisotropic Conduction on the Thermal Instability in the Interstellar Medium

    NASA Astrophysics Data System (ADS)

    Choi, Ena; Stone, James M.

    2012-03-01

    Thermal instability (TI) can strongly affect the structure and dynamics of the interstellar medium (ISM) in the Milky Way and other disk galaxies. Thermal conduction plays an important role in the TI by stabilizing small scales and limiting the size of the smallest condensates. In the magnetized ISM, however, heat is conducted anisotropically (primarily along magnetic field lines). We investigate the effects of anisotropic thermal conduction on the nonlinear regime of the TI by performing two-dimensional magnetohydrodynamic simulations. We present models with magnetic fields of different initial geometries and strengths, and compare them to hydrodynamic models with isotropic conduction. We find that anisotropic conduction does not significantly alter the overall density and temperature statistics in the saturated state of the TI. However, it can strongly affect the shapes and sizes of cold clouds formed by the TI. For example, for uniform initial fields long filaments of cold gas are produced that are reminiscent of some observed H I clouds. For initially tangled fields, such filaments are not produced. We also show that anisotropic conduction suppresses turbulence generated by evaporative flows from the surfaces of cold blobs, which may have implications for mechanisms for driving turbulence in the ISM.

  10. Anisotropic Ionic Conductivity of Lithium-Doped Sulfonated PBI.

    NASA Astrophysics Data System (ADS)

    Spry, R. J.; Arnold, F. E.; Dean, D. R.; Alexander, M. D., Jr.; Bai, S. J.; Dang, T. D.; Price, G. E.; Solomon, J. S.

    1997-03-01

    We report the conductivity study results of lithium-doped sulfonated PBI, a conjugated rigid rod polymer, poly[(1,7-dihydrobenzo[1,2-d:4,5-d']dimidazole-2,6-diyl)-2-(2-sulfo)-p- phenylene], derivatized with pendants of propane sulfonate Li^+ ionomer. The DC four-probe conductivity parallel to the surface of cast films was as large as 8.3× 10-3 S/cm. Similar measurements in an eight-probe configuration showed no difference between bulk and surface conductivity. The ionic nature of the conductivity was indicated by constant voltage depletion experiments and by secondary ion mass spectroscopy measurements of the residues near the electrodes. Both the AC and DC two-probe conductivities measured transverse to the sample surface were ~ 10-8 S/cm. Electron microscopy indicated that the films has a layered structure parallel to the surfaces. This structural anisotropy was confirmed by refractive index values obtained from wave-guide experiments. The polymer morphology was also investigated by X-ray scattering.

  11. 3D Anisotropic Thermal Conductivity of Exfoliated Rhenium Disulfide.

    PubMed

    Jang, Hyejin; Ryder, Christopher R; Wood, Joshua D; Hersam, Mark C; Cahill, David G

    2017-07-19

    ReS2 represents a different class of 2D materials, which is characterized by low symmetry having 1D metallic chains within the planes and extremely weak interlayer bonding. Here, the thermal conductivity of single-crystalline ReS2 in a distorted 1T phase is determined at room temperature for the in-plane directions parallel and perpendicular to the Re-chains, and the through-plane direction using time-domain thermoreflectance. ReS2 is prepared in the form of flakes having thicknesses of 60-450 nm by micromechanical exfoliation, and their crystalline orientations are identified by polarized Raman spectroscopy. The in-plane thermal conductivity is higher along the Re-chains, (70 ± 18) W m(-1) K(-1) , as compared to transverse to the chains, (50 ± 13) W m(-1) K(-1) . As expected from the weak interlayer bonding, the through-plane thermal conductivity is the lowest observed to date for 2D materials, (0.55 ± 0.07) W m(-1) K(-1) , resulting in a remarkably high anisotropy of (130 ± 40) and (90 ± 30) for the two in-plane directions. The thermal conductivity and interface thermal conductance of ReS2 are discussed relative to the other 2D materials. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Anisotropic linear elastic properties of fractal-like composites.

    PubMed

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

    2010-11-01

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

  13. Anisotropic linear elastic properties of fractal-like composites

    NASA Astrophysics Data System (ADS)

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

    2010-11-01

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

  14. Magneto-optical conductivity of anisotropic two-dimensional Dirac-Weyl materials

    NASA Astrophysics Data System (ADS)

    Oliva-Leyva, M.; Wang, Chumin

    2017-09-01

    In the presence of an external magnetic field, the optical response of two-dimensional materials, whose charge carriers behave as massless Dirac fermions with arbitrary anisotropic Fermi velocity, is investigated. Using Kubo formalism, we obtain the magneto-optical conductivity tensor for these materials, which allows to address the magneto-optical response of anisotropic Dirac fermions from the well known magneto-optical conductivity of isotropic Dirac fermions. As an application, we analyse the combined effects of strain-induced anisotropy and magnetic field on the transmittance, as well as on the Faraday rotation, of linearly polarized light after passing strained graphene. The reported analytical expressions can be a useful tool to predict the absorption and the Faraday angle of strained graphene under magnetic field. Finally, our study is extended to anisotropic two-dimensional materials with Dirac fermions of arbitrary pseudospin.

  15. Theoretical determination of anisotropic thermal conductivity for initially defect-free and defective TATB single crystals

    NASA Astrophysics Data System (ADS)

    Kroonblawd, Matthew P.; Sewell, Thomas D.

    2014-11-01

    The anisotropic thermal conductivity was determined for initially defect-free and defective crystals of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a material that exhibits a graphitic-like packing structure with stacked single-molecule-thick layers, using the reverse non-equilibrium molecular dynamics method and an established TATB molecular dynamics force field. Thermal conduction in TATB is predicted to be substantially higher and more anisotropic than in other related organic molecular explosives, with conduction along directions nominally in the plane of the molecular layers at least 68% greater than conduction along the direction exactly perpendicular to the layers. Finite-size effects along the conduction directions were assessed. The conductivity along directions nominally in the plane of the molecular layers was found to be insensitive to the supercell length along the conduction direction—a result commensurate with the estimated phonon mean free path, ˜6 Å. A small decrease in the conductivity normal to the layers was found for longer supercells and is likely due to increased phonon scattering as a result of dynamic structural transitions in the crystal. The thermal conductivity of TATB crystals containing vacancy defects was also determined and the variation of conductivity with crystal density was found to be both linear and anisotropic, with the introduction of vacancy defects leading to a greater percentage reduction in conduction for the direction perpendicular to the molecular layers.

  16. Theoretical determination of anisotropic thermal conductivity for initially defect-free and defective TATB single crystals.

    PubMed

    Kroonblawd, Matthew P; Sewell, Thomas D

    2014-11-14

    The anisotropic thermal conductivity was determined for initially defect-free and defective crystals of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), a material that exhibits a graphitic-like packing structure with stacked single-molecule-thick layers, using the reverse non-equilibrium molecular dynamics method and an established TATB molecular dynamics force field. Thermal conduction in TATB is predicted to be substantially higher and more anisotropic than in other related organic molecular explosives, with conduction along directions nominally in the plane of the molecular layers at least 68% greater than conduction along the direction exactly perpendicular to the layers. Finite-size effects along the conduction directions were assessed. The conductivity along directions nominally in the plane of the molecular layers was found to be insensitive to the supercell length along the conduction direction-a result commensurate with the estimated phonon mean free path, ∼6 Å. A small decrease in the conductivity normal to the layers was found for longer supercells and is likely due to increased phonon scattering as a result of dynamic structural transitions in the crystal. The thermal conductivity of TATB crystals containing vacancy defects was also determined and the variation of conductivity with crystal density was found to be both linear and anisotropic, with the introduction of vacancy defects leading to a greater percentage reduction in conduction for the direction perpendicular to the molecular layers.

  17. Prediction of Two-Dimensional Phase of Boron with Anisotropic Electric Conductivity.

    PubMed

    Cui, Zhi-Hao; Jimenez-Izal, Elisa; Alexandrova, Anastassia N

    2017-03-03

    Two-dimensional (2D) phases of boron are rare and unique. Here we report a new 2D all-boron phase (named the π phase) that can be grown on a W(110) surface. The π phase, composed of four-membered rings and six-membered rings filled with an additional B atom, is predicted to be the most stable on this support. It is characterized by an outstanding stability upon exfoliation off of the W surface, and unusual electronic properties. The chemical bonding analysis reveals the metallic nature of this material, which can be attributed to the multicentered π-bonds. Importantly, the calculated conductivity tensor is anisotropic, showing larger conductivity in the direction of the sheet that is in-line with the conjugated π-bonds, and diminished in the direction where the π-subsystems are connected by single σ-bonds. The π-phase can be viewed as an ultrastable web of aligned conducting boron wires, possibly of interest to applications in electronic devices.

  18. Sheet resistance characterization of locally anisotropic transparent conductive films made of aligned metal-enriched single-walled carbon nanotubes.

    PubMed

    Kang, Hosung; Kim, Duckjong; Baik, Seunghyun

    2014-09-21

    One-dimensional conductive fillers such as single-walled carbon nanotubes (SWNTs) can be aggregated and aligned during transparent conductive film (TCF) formation by the vacuum filtration method. The potential error of analysing the average sheet resistance of these anisotropic films, using the four-point probe in-line method and the conversion formula developed assuming uniform isotropic material properties, was systematically investigated by finite element analysis and experiments. The finite element analysis of anisotropic stripe-patterned TCFs with alternating low (ρ1) and high (ρ2) resistivities revealed that the estimated average sheet resistance approached ρ1/t when the probes were parallel to the aligned nanotubes. The thickness of the film is t. It was more close to ρ2/t when the probes were perpendicular to the aligned tubes. Indeed, TCFs fabricated by the vacuum filtration method using metal-enriched SWNTs exhibited highly anisotropic local regions where tubes were aggregated and aligned. The local sheet resistances of randomly oriented, aligned, and perpendicular tube regions of the TCF at a transmittance of 89.9% were 5000, 2.4, and 12 300 Ω □(-1), respectively. Resistivities of the aggregated and aligned tube region (ρ1 = 1.2 × 10(-5) Ω cm) and the region between tubes (ρ2 = 6.2 × 10(-2) Ω cm) could be approximated with the aid of finite element analysis. This work demonstrates the potential error of characterizing the average sheet resistance of anisotropic TCFs using the four-point probe in-line method since surprisingly high or low values could be obtained depending on the measurement angle. On the other hand, a better control of aggregation and alignment of nanotubes would realize TCFs with a very small anisotropic resistivity and a high transparency.

  19. Electromagnetic characterization of the CFRPs anisotropic conductivity: modeling and measurements

    NASA Astrophysics Data System (ADS)

    Menana, H.; Féliachi, M.

    2011-02-01

    This work deals with the characterization of the conductivity tensor of a carbon fiber reinforced polymer composite (CFRP) thin plate. We propose a contactless method based on the eddy current non destructive testing technique. The used eddy current sensor consists of a ferrite torus on which a winding is wound. The torus is of a rectangular section and contains a thin air-gap in which the thin CFRP plate is inserted. We developed analytical relations giving the longitudinal and transversal conductivities of the CFRP plate as functions of the impedances variations of the eddy current sensor, corresponding to the orientations of the carbon fibers parallel and transverse to the direction of the torus width which is much greater than its thickness. The analytical relations are developed by inverting interpolation functions of curves giving the variations of the sensor impedances as functions of the longitudinal and transversal conductivities of the CFRP plate. These curves are obtained by a numerical model based on a simplified integro-differential formulation in terms of the electric vector potential in the CFRP plate, coupled to the magnetic circuit equations in the ferrite torus. The modeling results are supported by measurements.

  20. Highly Anisotropic Thermal Conductivity of Layer-by-Layer Assembled Nanofibrillated Cellulose/Graphene Nanosheets Hybrid Films for Thermal Management.

    PubMed

    Song, Na; Jiao, Dejin; Cui, Siqi; Hou, Xingshuang; Ding, Peng; Shi, Liyi

    2017-01-25

    An anisotropic thermally conductive film with tailorable microstructures and macroproperties is fabricated using a layer-by-layer (LbL) assembly of graphene oxide (GO) and nanofibrillated cellulose (NFC) on a flexible NFC substrate driven by hydrogen bonding interactions, followed by chemical reduction process. The resulting NFC/reduced graphene oxide (RGO) hybrid film reveals an orderly hierarchical structure in which the RGO nanosheets exhibit a high degree of orientation along the in-plane direction. The assembly cycles dramatically increase the in-plane thermal conductivity (λX) of the hybrid film to 12.6 W·m(-1)·K(-1), while the cross-plane thermal conductivity (λZ) shows a lower value of 0.042 W·m(-1)·K(-1) in the hybrid film with 40 assembly cycles. The thermal conductivity anisotropy reaches up to λX/λZ = 279, which is substantially larger than that of similar polymeric nanocomposites, indicating that the LbL assembly on a flexible NFC substrate is an efficient technique for the preparation of polymeric nanocomposites with improved heat conducting property. Moreover, the layered hybrid film composed of 1D NFC and 2D RGO exhibits synergetic mechnical properties with outstanding flexibility and a high tensile strength (107 MPa). The combination of anisotropic thermal conductivity and superior mechanical performance may facilitate the applications in thermal management.

  1. Strain-engineering the anisotropic electrical conductance of few-layer black phosphorus.

    PubMed

    Fei, Ruixiang; Yang, Li

    2014-05-14

    Newly fabricated few-layer black phosphorus and its monolayer structure, phosphorene, are expected to be promising for electronic and optical applications because of their finite direct band gaps and sizable but anisotropic electronic mobility. By first-principles simulations, we show that this unique anisotropic free-carrier mobility can be controlled by using simple strain conditions. With the appropriate biaxial or uniaxial strain (4-6%), we can rotate the preferred conducting direction by 90°. This will be useful for exploring unusual quantum Hall effects and exotic electronic and mechanical applications based on phosphorene.

  2. Conductivity tensor for anisotropic plasma in gyrokinetic theory

    DOE PAGES

    Porazik, Peter; Johnson, Jay R.

    2017-05-18

    Comprehensive non-invasive spectroscopic techniques and electrical measurements of the carbon arc revealed two distinguishable plasma synthesis regions in the radial direction normal to the arc axis. These regions, which are defined as the arc core and the arc periphery, are shown to have very different compositions of carbon species with different densities and temperatures. The colder arc periphery is dominated by carbon diatomic molecules (C-2), which are in the minority in the composition of the hot arc core. These differences are due to a highly non-uniform distribution of the arc current, which is mainly conducted through the arc core populatedmore » with carbon atoms and ions. Therefore, the ablation of the graphite anode is governed by the arc core, while the formation of carbon molecules occurs in the colder arc periphery. This result is consistent with previous predictions that the plasma environment in the arc periphery is suitable for synthesis of carbon nanotubes.« less

  3. Anisotropic conduction block and reentry in neonatal rat ventricular myocyte monolayers

    PubMed Central

    de Diego, Carlos; Chen, Fuhua; Xie, Yuanfang; Pai, Rakesh K.; Slavin, Leonid; Parker, John; Lamp, Scott T.; Qu, Zhilin; Valderrábano, Miguel

    2011-01-01

    Anisotropy can lead to unidirectional conduction block that initiates reentry. We analyzed the mechanisms in patterned anisotropic neonatal rat ventricular myocyte monolayers. Voltage and intracellular Ca (Cai) were optically mapped under the following conditions: extrastimulus (S1S2) testing and/or tetrodotoxin (TTX) to suppress Na current availability; heptanol to reduce gap junction conductance; and incremental rapid pacing. In anisotropic monolayers paced at 2 Hz, conduction velocity (CV) was faster longitudinally than transversely, with an anisotropy ratio [AR = CVL/CVT, where CVL and CVT are CV in the longitudinal and transverse directions, respectively], averaging 2.1 ± 0.8. Interventions decreasing Na current availability, such as S1S2 pacing and TTX, slowed CVL and CVT proportionately, without changing the AR. Conduction block preferentially occurred longitudinal to fiber direction, commonly initiating reentry. Interventions that decreased gap junction conductance, such as heptanol, decreased CVT more than CVL, increasing the AR and causing preferential transverse conduction block and reentry. Rapid pacing resembled the latter, increasing the AR and promoting transverse conduction block and reentry, which was prevented by the Cai chelator 1,2-bis oaminophenoxy ethane-N,N,N′,N′-tetraacetic acid (BAPTA). In contrast to isotropic and uniformly anisotropic monolayers, in which reentrant rotors drifted and self-terminated, bidirectional anisotropy (i.e., an abrupt change in fiber direction exceeding 45°) caused reentry to anchor near the zone of fiber direction change in 77% of monolayers. In anisotropic monolayers, unidirectional conduction block initiating reentry can occur longitudinal or transverse to fiber direction, depending on whether the experimental intervention reduces Na current availability or decreases gap junction conductance, agreeing with theoretical predictions. PMID:21037233

  4. Anisotropic Thermal Conduction in a Polymer Liquid Subjected to Shear Flow

    NASA Astrophysics Data System (ADS)

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

    2004-08-01

    Flow-induced anisotropic thermal conduction in a polymer liquid is studied using force Rayleigh scattering. Time-dependent measurements of the complete thermal diffusivity tensor, which includes one off-diagonal and three diagonal components, are reported on an entangled polymer melt subjected to a uniform shear deformation. These data, in conjunction with mechanical measurements of the stress, provide the first direct evidence that the thermal conductivity tensor and the stress tensor are linearly related in a deformed polymer liquid.

  5. Anisotropic Conductivity Tensor Imaging of In Vivo Canine Brain Using DT-MREIT.

    PubMed

    Jeong, Woo Chul; Sajib, Saurav Z K; Katoch, Nitish; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

    2017-01-01

    We present in vivo images of anisotropic electrical conductivity tensor distributions inside canine brains using diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT). The conductivity tensor is represented as a product of an ion mobility tensor and a scale factor of ion concentrations. Incorporating directional mobility information from water diffusion tensors, we developed a stable process to reconstruct anisotropic conductivity tensor images from measured magnetic flux density data using an MRI scanner. Devising a new image reconstruction algorithm, we reconstructed anisotropic conductivity tensor images of two canine brains with a pixel size of 1.25 mm. Though the reconstructed conductivity values matched well in general with those measured by using invasive probing methods, there were some discrepancies as well. The degree of white matter anisotropy was 2 to 4.5, which is smaller than previous findings of 5 to 10. The reconstructed conductivity value of the cerebrospinal fluid was about 1.3 S/m, which is smaller than previous measurements of about 1.8 S/m. Future studies of in vivo imaging experiments with disease models should follow this initial trial to validate clinical significance of DT-MREIT as a new diagnostic imaging modality. Applications in modeling and simulation studies of bioelectromagnetic phenomena including source imaging and electrical stimulation are also promising.

  6. Five-layer realistic head model based on inhomogeneous and anisotropic conductivity distribution of different tissues

    NASA Astrophysics Data System (ADS)

    Yan, Dandan; Zhang, Jianwei; Wu, Weijuan; Ying, Xiaoyan; Wu, Xiangping

    2009-10-01

    This paper is focused on the sophisticated realistic head modeling based on inhomogeneous and anisotropic conductivity distribution of the head tissues. The finite element method (FEM) was used to model the five-layer head volume conductor models with hexahedral elements from segmentation and mapping of DT-MRI data. Then the inhomogeneous conductivities of the scalp, CSF and gray matter tissue were distributed according a normal distribution based on the mean value of respective tissues. The electric conductivity of the brain tissues dictates different inhomogeneous and anisotropic at some different microscopic levels. Including the inhomogeneous and anisotropy of the tissue would improve the accuracy of the MREIT, EEG and MEG problems in the simulation research.

  7. The Dynamics of Rayleigh-Taylor Stable and Unstable Contact Discontinuities with Anisotropic Thermal Conduction

    NASA Astrophysics Data System (ADS)

    Lecoanet, Daniel; Parrish, Ian; Quataert, Eliot

    2012-11-01

    We study the effects of anisotropic thermal conduction along magnetic field lines on an accelerated contact discontinuity in a weakly collisional plasma. Anisotropic conduction can result in doubly-diffusive instabilities, including the magnetothermal instability (MTI) and the heat flux driven buoyancy instability (HBI). We run fully non-linear numerical simulations of a contact discontinuity with anisotropic conduction. The non-linear evolution can be described as a superposition of three physical effects: temperature diffusion due to vertical conduction, the Rayleigh-Taylor instability (RTI) and the HBI. In simulations with RTI-stable contact discontinuities, the temperature discontinuity spreads due to vertical heat conduction. The HBI slows this temperature diffusion by reorienting initially vertical magnetic field lines to a more horizontal geometry, eventually stopping vertical temperature diffusion. In simulations with RTI-unstable contact discontinuities, the dynamics are initially governed by temperature diffusion, but the RTI becomes increasingly important at late times. These results could be important in various astrophysical contexts including supernova remnants, solar prominences and cold fronts in galaxy clusters. DL is supported by the Hertz Foundation and NSF Grant DGE 1106400; IP & EQ are supported in part by NASA Grant ATP09-0125, NSF-DOE Grant PHY-0812811, and by the David and Lucille Packard Foundation.

  8. MHD Simulations of Coronal Supra-arcade Downflows Including Anisotropic Thermal Conduction

    NASA Astrophysics Data System (ADS)

    Zurbriggen, E.; Costa, A.; Esquivel, A.; Schneiter, M.; Cécere, M.

    2016-11-01

    Coronal supra-arcade downflows (SADs) are observed as dark trails descending toward hot turbulent-fan-shaped regions. Due to the large temperature values and gradients in these fan regions, the thermal conduction (TC) should be very efficient. While several models have been proposed to explain the triggering and the evolution of SADs, none of these scenarios address a systematic consideration of TC. Thus, we accomplish this task numerically simulating the evolution of SADs within this framework. That is, SADs are conceived as voided (subdense) cavities formed by nonlinear waves triggered by downflowing bursty localized reconnection events in a perturbed hot fan. We generate a properly turbulent fan, obtained by a stirring force that permits control of the energy and vorticity input in the medium where SADs develop. We include anisotropic TC and consider plasma properties consistent with observations. Our aim is to study whether it is possible to prevent SADs from vanishing by thermal diffusion. We find that this will be the case, depending on the turbulence parameters, in particular if the magnetic field lines are able to envelope the voided cavities, thermally isolating them from the hot environment. Velocity shear perturbations that are able to generate instabilities of the Kelvin-Helmholtz type help to produce magnetic islands, extending the lifetime of SADs.

  9. Rectangular waveguide material characterization: anisotropic property extraction and measurement validation

    NASA Astrophysics Data System (ADS)

    Crowgey, Benjamin Reid

    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

  10. Anisotropic thermal transport property of defect-free GaN

    SciTech Connect

    Ju, Wenjing; Zhou, Zhongyuan E-mail: zywei@seu.edu.cn; Wei, Zhiyong E-mail: zywei@seu.edu.cn

    2016-06-15

    Non-equilibrium molecular dynamics (MD) simulation is performed to calculate the thermal conductivity of defect-free GaN along three high-symmetry directions. It is found that the thermal conductivity along [001] direction is about 25% higher than that along [100] or [120] direction. The calculated phonon dispersion relation and iso-energy surface from lattice dynamics show that the difference of the sound speeds among the three high-symmetry directions is quite small for the same mode. However, the variation of phonon irradiation with direction is qualitatively consistent with that of the calculated thermal conductivity. Our results indicate that the anisotropic thermal conductivity may partly result from the phonons in the low-symmetry region of the first Brillouin zone due to phonon focus effects, even though the elastic properties along the three high-symmetry directions are nearly isotropic. Thus, the phonon irradiation is able to better describe the property of thermal conductivity as compared to the commonly used phonon dispersion relation. The present investigations uncover the physical origin of the anisotropic thermal conductivity in defect-free GaN, which would provide an important guide for optimizing the thermal management of GaN-based device.

  11. Investigation of Anisotropic Thermal Conductivity of GaAs/AlAs Superlattices

    NASA Astrophysics Data System (ADS)

    Li, Ran

    The thermal conductivities of superlattices are essential to improve the properties of thermoelectrics and optoelectronics; however, limited results in relation to both the in-plane and cross-plane thermal conductivities have been reported. A convenient, effective, and accurate experimental method is required to improve the current research on the thermal properties of superlattices. We conducted an experimental research study on two GaAs/AlAs superlattice samples with a total superlattice layer thickness of 2 microm using a combination of the 2-omega and 3-omega techniques. The samples have period thicknesses of 4 nm and 10 nm, respectively. To explore the thermal conductivities of the substrate and insulation layer of the superlattice samples indirectly, a controlled sample with the same structure, but without a superlattice layer, is used. We obtained the thermal conductivities of the GaAs substrate and insulation layer (SiO2 thin film) using the 3-omega technique and FEM simulation model. We also explored the deviation of the experimental results of the 2-omega technique from the Fourier's Law through the controlled sample. These parameters obtained from the controlled sample are used in the data analysis in the following superlattice research. In the superlattice study, we combine the 3-omega and 2-omega techniques to characterize the anisotropic thermal conductivity of GaAs/AlAs superlattice from the same wafer. The in-plane thermal conductivity, cross-plane thermal conductivity, and anisotropy are obtained from the same wafer by comparing the experimental results with the FEM simulated results. This combination works fine in general and demonstrates a significant reduction in thermal conductivity compared to that of equivalent bulk materials. Superlattices with different period thicknesses but the same total superlattice thickness present a significant difference in both the in-plane and cross-plane thermal conductivities of the superlattices. However, we

  12. Influence of heterogeneous and anisotropic tissue conductivity on electric field distribution in deep brain stimulation.

    PubMed

    Aström, Mattias; Lemaire, Jean-Jacques; Wårdell, Karin

    2012-01-01

    The aim was to quantify the influence of heterogeneous isotropic and heterogeneous anisotropic tissue on the spatial distribution of the electric field during deep brain stimulation (DBS). Three finite element tissue models were created of one patient treated with DBS. Tissue conductivity was modelled as (I) homogeneous isotropic, (II) heterogeneous isotropic based on MRI, and (III) heterogeneous anisotropic based on diffusion tensor MRI. Modelled DBS electrodes were positioned in the subthalamic area, the pallidum, and the internal capsule in each tissue model. Electric fields generated during DBS were simulated for each model and target-combination and visualized with isolevels at 0.20 (inner), and 0.05 V mm(-1) (outer). Statistical and vector analysis was used for evaluation of the distribution of the electric field. Heterogeneous isotropic tissue altered the spatial distribution of the electric field by up to 4% at inner, and up to 10% at outer isolevel. Heterogeneous anisotropic tissue influenced the distribution of the electric field by up to 18 and 15% at each isolevel, respectively. The influence of heterogeneous and anisotropic tissue on the electric field may be clinically relevant in anatomic regions that are functionally subdivided and surrounded by multiple fibres of passage.

  13. Intrinsic left-handed electromagnetic properties in anisotropic superconductors

    NASA Astrophysics Data System (ADS)

    Lin, Shi-Zeng; Chen, Hou-Tong

    2017-04-01

    Left-handed materials usually are realized in artificial subwavelength structures. Here, we show that some anisotropic superconductors such as Bi 2 Sr 2 CaCu 2 O 8 + δ , YBa 2 Cu x O y , and La 2 - x Sr x CuO 4 , are intrinsic left-handed materials. The condition is that the plasma frequency in the c axis, ωc, and in the ab plane, ωab, and the operating angular frequency, ω, satisfy ω c < ω < ω a b . In addition, ω should be smaller than the superconducting energy gap to sustain superconductivity. We study the reflection and transmission of electromagnetic waves and reveal negative refraction and the backward wave with the phase velocity opposite to the direction of energy flux propagation. We also discuss possible approaches for improvement, making these properties feasible for experimental validation. Being intrinsic left-hand materials, the anisotropic superconductors are promising for applications in functional electromagnetic devices in the terahertz frequency band.

  14. Anisotropic Elastic Properties of Muscle-like Nematic Elastomers

    NASA Astrophysics Data System (ADS)

    Ratna, Banahalii; Thomseniii, Donald L.; Shenoy, Devanand; Srinivasan, Amritha; Keller, Patrick

    2001-03-01

    De Gennes suggested in 1997 that the liquid crystal elastomers are an excellent framework to mimic muscular action. We have prepared anisotropic freestanding films of nematic elastomers from laterally attached side-chain polymers that show muscle-like mechanical properties. The orientational order of the liquid crystal side groups imposes a conformational anisotropy in the polymer backbone. When the order parameter drops at the nematic-isotropic phase transition, there is a concomitant loss of order in the backbone which results in a contraction of the film in the direction of the director orientation. Dynamic mechanical data along directions parallel and perpendicular to the optic axis, show anisotropic stress-strain behavior. The film exhibits soft elasticity when strained in the perpendicular direction when the liquid crystal mesogens reorient without appreciable stress build up. Thermostrictive studies in the parallel direction show 40constriction at the nematic-isotropic phase transition. Isometric studies show that the elastic energy stored is purely entropic in origin and the elastomer acts like a spring with unusually large spring constant at the NI transition. The maximum stress measured is 300kPa. A strain rate of 5s-1 is estimated from shear relaxation studies.

  15. Temperature and Thickness Dependences of the Anisotropic In-Plane Thermal Conductivity of Black Phosphorus.

    PubMed

    Smith, Brandon; Vermeersch, Bjorn; Carrete, Jesús; Ou, Eric; Kim, Jaehyun; Mingo, Natalio; Akinwande, Deji; Shi, Li

    2017-02-01

    The anisotropic basal-plane thermal conductivities of thin black phosphorus obtained from a new four-probe measurement exhibit much higher peak values at low temperatures than previous reports. First principles calculations reveal the important role of crystal defects and weak thickness dependence that is opposite to the case of graphene and graphite due to the absence of reflection symmetry in puckered phosphorene. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Anisotropic thermal conductivity of Ge quantum-dot and symmetrically strained Si/Ge superlattices.

    PubMed

    Liu, W L; Borca-Tasciuc, T; Chen, G; Liu, J L; Wang, K L

    2001-03-01

    We report the first experimental results on the temperature dependent in-plane and cross-plane thermal conductivities of a symmetrically strained Si/Ge superlattice and a Ge quantum-dot superlattice measured by the two-wire 3 omega method. The measured thermal conductivity values are highly anisotropic and are significantly reduced compared to the bulk thermal conductivity of the structures. The results can be explained by using heat transport models based on the Boltzmann transport equation with partially diffusive scattering of the phonons at the superlattice interfaces.

  17. Strong anisotropic optical conductivity in two-dimensional puckered structures: The role of the Rashba effect

    NASA Astrophysics Data System (ADS)

    Saberi-Pouya, S.; Vazifehshenas, T.; Salavati-fard, T.; Farmanbar, M.; Peeters, F. M.

    2017-08-01

    We calculate the optical conductivity of an anisotropic two-dimensional system with Rashba spin-flip excitation within the Kubo formalism. We show that the anisotropic Rashba effect caused by an external field significantly changes the magnitude of the spin splitting. Furthermore, we obtain an analytical expression for the longitudinal optical conductivity associated with interband transitions as a function of the frequency for arbitrary polarization angle. We find that the diagonal components of the optical conductivity tensor are direction dependent and the optical absorption spectrum exhibits a strongly anisotropic absorption window. The height and width of this absorption window are very sensitive to the anisotropy of the system. While the height of absorption peak increases with increasing effective mass anisotropy ratio, the peak intensity is larger when the light polarization is along the armchair direction. Moreover, the absorption peak width becomes broader as the density-of-states mass or Rashba interaction is enhanced. These features in the optical absorption spectrum can be used to determine parameters relevant for spintronics.

  18. Anisotropic in-plane thermal conductivity observed in few-layer black phosphorus

    PubMed Central

    Luo, Zhe; Maassen, Jesse; Deng, Yexin; Du, Yuchen; Garrelts, Richard P.; Lundstrom, Mark S; Ye, Peide D.; Xu, Xianfan

    2015-01-01

    Black phosphorus has been revisited recently as a new two-dimensional material showing potential applications in electronics and optoelectronics. Here we report the anisotropic in-plane thermal conductivity of suspended few-layer black phosphorus measured by micro-Raman spectroscopy. The armchair and zigzag thermal conductivities are ∼20 and ∼40 W m−1 K−1 for black phosphorus films thicker than 15 nm, respectively, and decrease to ∼10 and ∼20 W m−1 K−1 as the film thickness is reduced, exhibiting significant anisotropy. The thermal conductivity anisotropic ratio is found to be ∼2 for thick black phosphorus films and drops to ∼1.5 for the thinnest 9.5-nm-thick film. Theoretical modelling reveals that the observed anisotropy is primarily related to the anisotropic phonon dispersion, whereas the intrinsic phonon scattering rates are found to be similar along the armchair and zigzag directions. Surface scattering in the black phosphorus films is shown to strongly suppress the contribution of long mean-free-path acoustic phonons. PMID:26472191

  19. A small-plane heat source method for measuring the thermal conductivities of anisotropic materials

    NASA Astrophysics Data System (ADS)

    Cheng, Liang; Yue, Kai; Wang, Jun; Zhang, Xinxin

    2017-07-01

    A new small-plane heat source method was proposed in this study to simultaneously measure the in-plane and cross-plane thermal conductivities of anisotropic insulating materials. In this method the size of the heat source element is smaller than the sample size and the boundary condition is thermal insulation due to no heat flux at the edge of the sample during the experiment. A three-dimensional model in a rectangular coordinate system was established to exactly describe the heat transfer process of the measurement system. Using the Laplace transform, variable separation, and Laplace inverse transform methods, the analytical solution of the temperature rise of the sample was derived. The temperature rises calculated by the analytical solution agree well with the results of numerical calculation. The result of the sensitivity analysis shows that the sensitivity coefficients of the estimated thermal conductivities are high and uncorrelated to each other. At room temperature and in a high-temperature environment, experimental measurements of anisotropic silica aerogel were carried out using the traditional one-dimensional plane heat source method and the proposed method, respectively. The results demonstrate that the measurement method developed in this study is effective and feasible for simultaneously obtaining the in-plane and cross-plane thermal conductivities of the anisotropic materials.

  20. Anisotropic surface hole-transport property of triphenylamine-derivative single crystal prepared by solution method

    NASA Astrophysics Data System (ADS)

    Umeda, Minoru; Katagiri, Mitsuhiko; Shironita, Sayoko; Nagayama, Norio

    2016-12-01

    This paper reports the anisotropic hole transport at the triphenylamine-derivative single crystal surface prepared by a solution method. Triphenylamine derivatives are commonly used in a hole-transport material for organic photoconductors of laser-beam printers, in which the materials are used as an amorphous form. For developing organic photovoltaics using the photoconductor's technology, preparation of a single crystal seems to be a specific way by realizing the high mobility of an organic semiconductor. In this study, a single crystal of 4-(2,2-diphenylethenyl)-N,N-bis(4-methylphenyl)-benzenamine (TPA) was prepared and its anisotropic hole-transport property measured. First, the hole-transport property of the TPA was investigated based on its chemical structure and electrochemical redox characteristics. Next, a large-scale single crystal formation at a high rate was developed by employing a solution method based on its solubility and supersolubility curves. The grown TPA was found to be a single crystal based on the polarization micrograph observation and crystallographic analysis. For the TPA single crystal, an anisotropic surface conduction was found, which was well explained by its molecular stack structure. The measured current in the long-axis direction is one order of magnitude greater than that of amorphous TPA.

  1. Shape-Dependent Nonlinear Optical Properties of Anisotropic Gold Nanoparticles.

    PubMed

    Hua, Yi; Chandra, Kavita; Dam, Duncan Hieu M; Wiederrecht, Gary P; Odom, Teri W

    2015-12-17

    This Letter reports the shape-dependent third-order nonlinear optical properties of anisotropic gold nanoparticles. We characterized the nonlinear absorption coefficients of nanorods, nanostars, and nanoshells using femtosecond Z-scan measurements. By comparing nanoparticle solutions with a similar linear extinction at the laser excitation wavelength, we separated shape effects from that of the localized surface plasmon wavelength. We found that the nonlinear response depended on particle shape. Using pump-probe spectroscopy, we measured the ultrafast transient response of nanoparticles, which supported the strong saturable absorption observed in nanorods and weak nonlinear response in nanoshells. We found that the magnitude of saturable absorption as well as the ultrafast spectral responses of nanoparticles were affected by the linear absorption of the nanoparticles.

  2. Hyperhoneycomb boron nitride with anisotropic mechanical, electronic, and optical properties

    NASA Astrophysics Data System (ADS)

    Yu, Jin; Qu, Lihua; van Veen, Edo; Katsnelson, Mikhail I.; Yuan, Shengjun

    2017-09-01

    Boron nitride structures have excellent thermal and chemical stabilities. Based on state-of-art theoretical calculations, we propose a wide-gap semiconducting BN crystal with a three-dimensional hyperhoneycomb structure (Hp-BN), which is both mechanically and thermodynamically stable. Our calculated results show that Hp-BN has a higher bulk modulus and a smaller energy gap as compared to c-BN. Moreover, due to the unique bonding structure, Hp-BN exhibits anisotropic electronic and optical properties. It has great adsorption in the ultraviolet region, but it is highly transparent in the visible and infrared region, suggesting that the Hp-BN crystal could have potential applications in electronic and optical devices.

  3. Measurement of anisotropic thermophysical properties of cylindrical Li-ion cells

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  4. Graphics processing unit (GPU)-based computation of heat conduction in thermally anisotropic solids

    NASA Astrophysics Data System (ADS)

    Nahas, C. A.; Balasubramaniam, Krishnan; Rajagopal, Prabhu

    2013-01-01

    Numerical modeling of anisotropic media is a computationally intensive task since it brings additional complexity to the field problem in such a way that the physical properties are different in different directions. Largely used in the aerospace industry because of their lightweight nature, composite materials are a very good example of thermally anisotropic media. With advancements in video gaming technology, parallel processors are much cheaper today and accessibility to higher-end graphical processing devices has increased dramatically over the past couple of years. Since these massively parallel GPUs are very good in handling floating point arithmetic, they provide a new platform for engineers and scientists to accelerate their numerical models using commodity hardware. In this paper we implement a parallel finite difference model of thermal diffusion through anisotropic media using the NVIDIA CUDA (Compute Unified device Architecture). We use the NVIDIA GeForce GTX 560 Ti as our primary computing device which consists of 384 CUDA cores clocked at 1645 MHz with a standard desktop pc as the host platform. We compare the results from standard CPU implementation for its accuracy and speed and draw implications for simulation using the GPU paradigm.

  5. Increasing Black Hole Feedback-induced Quenching with Anisotropic Thermal Conduction

    NASA Astrophysics Data System (ADS)

    Kannan, Rahul; Vogelsberger, Mark; Pfrommer, Christoph; Weinberger, Rainer; Springel, Volker; Hernquist, Lars; Puchwein, Ewald; Pakmor, Rüdiger

    2017-03-01

    Feedback from central supermassive black holes is often invoked to explain the low star formation rates (SFRs) in the massive galaxies at the centers of galaxy clusters. However, the detailed physics of the coupling of the injected feedback energy with the intracluster medium (ICM) is still unclear. Using high-resolution magnetohydrodynamic cosmological simulations of galaxy cluster formation, we investigate the role of anisotropic thermal conduction in shaping the thermodynamic structure of clusters, and in particular, in modifying the impact of black hole feedback. Stratified anisotropically conducting plasmas are formally always unstable, and thus more prone to mixing, an expectation borne out by our results. The increased mixing efficiently isotropizes the injected feedback energy, which in turn significantly improves the coupling between the feedback energy and the ICM. This facilitates an earlier disruption of the cool-core, reduces the SFR by more than an order of magnitude, and results in earlier quenching despite an overall lower amount of feedback energy injected into the cluster core. With conduction, the metallicity gradients and dispersions are lowered, aligning them better with observational constraints. These results highlight the important role of thermal conduction in establishing and maintaining the quiescence of massive galaxies.

  6. Anisotropic electrical conductivity of surface-roughened semipolar (11\\bar{2}2) GaN films by photochemical etching

    NASA Astrophysics Data System (ADS)

    Jang, Soohwan; Lee, Sohyun; Baik, Kwang Hyeon

    2017-05-01

    We studied the anisotropy of electrical conductivity in surface-roughened semipolar (11\\bar{2}2) GaN (s-GaN) films. Highly crystalline s-GaN films were obtained using asymmetric lateral epitaxy on oxide-patterned m-plane sapphire substrates. The in-plane structural anisotropy of the s-GaN films was confirmed by anisotropic peak broadening in X-ray rocking curves (XRC) with the in-beam orientations. The XRC full-width at half maximum (FWHM) values were measured to be 454 and 615 arcsec along the [11\\bar{2}3] GaN and [1\\bar{1}00] GaN directions, respectively. The s-GaN surface was roughened using photo-chemical etching, and the electrical anisotropy was then investigated as a function of azimuth angles with the transmission line method. The Ohmic contact properties on the roughened s-GaN surface did not depend on the azimuth angle or annealing temperatures between 750 and 950 °C. The sheet resistances parallel to the [1\\bar{1}00] GaN direction on roughened s-GaN were found to be approximately half of the resistance parallel to the [11\\bar{2}3] GaN direction, showing that anisotropic electrical conductivity is maintained for surface-roughened s-GaN due to charged carrier scattering induced by basal-plane stacking faults.

  7. Anisotropic properties of high permeability grain-oriented 3.25% Si-Fe electrical steel

    SciTech Connect

    Shirkoohi, G.H.; Arikat, M.A.M.

    1994-03-01

    Anisotropic magnetic properties of two grades of 0.27 mm thick 3.25% silicon grain-oriented electrical steels are investigated using Epstein size samples cut at 10{degree} intervals between the direction of rolling and its transverse. The global anisotropic variation of the steels is shown to be directly proportionality that of the intrinsic anisotropy energy of the cubic single crystal.

  8. Linking elastic, mechanical and transport properties in anisotropically cracked rocks

    NASA Astrophysics Data System (ADS)

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

    2007-12-01

    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, average crack aspect ratio and mean crack fabric orientation using the solid grains and fluid elastic properties. Using the same tool, we show that the anisotropy, the shear wave splitting and the dispersion of elastic waves can be derived for anisotropic crack fabrics. Mechanically, the existence of embedded microcrack fabrics in rocks also significantly influences the fracture toughness (KIC) of rocks. We show that KIC can show large amounts of anisotropy as well, the degree and orientation of which being largely constrained once again by the microcrack fabric. NIC can predict relatively well KIC at high crack density, by simply using dimensionless crack densities inverted from velocities. A decrease of 50% for crack densities larger than 1, 80% for crack densities larger than 5 is predicted, in close agreement with our observed experimental variation of KIC. At the microscale, this can be interpreted by the fact that the main fracture is strongly interacting with the pre-existing microcrack fabric. Finally, and above the percolation threshold, macroscopic fluid flow also depends on the porosity, crack density and aspect ratio. Using the permeability model of Guéguen and Dienes (1989) and the crack density and aspect ratio recovered from the elastic wave velocity inversion, we successfully predict the evolution of permeability with pressure for direct comparison with the laboratory measurements. These combined experimental and modelling results illustrate the importance of understanding the details of how rock microstructures change in response to an external stimulus in predicting the

  9. Effect of anisotropic thermal conductivity on the morphological stability of a binary alloy

    NASA Technical Reports Server (NTRS)

    Coriell, S. R.; Mcfadden, G. B.; Sekerka, R. F.

    1990-01-01

    A linear morphological stability analysis is presented for a planar interface during unidirectional solidification of a binary alloy, in the case of a crystal having an anisotropic thermal conductivity. A dispersion relation shows that the onset of instability depends on the orientation of the growth direction with respect to principal crystallographic axes and on the orientation of the wavevector of the perturbation. The onset of instability can be either oscillatory (traveling waves) or nonoscillatory in time. For growth along a principal axis of the crystal there is an exchange of stabilities, and the onset of instability is nonoscillatory.

  10. Optic phonons and anisotropic thermal conductivity in hexagonal Ge2Sb2Te5

    DOE PAGES

    Mukhopadhyay, Saikat; Lindsay, Lucas R.; Singh, David

    2016-11-16

    The lattice thermal conductivity ($κ$) of hexagonal Ge2Sb2Tesub>5 (h-GST) is studied via direct first-principles calculations. We find significant intrinsic anisotropy of ( $κ$a/$κ$c~2) of $κ$ in bulk h-GST along different transport directions. The dominant contribution to$κ$ is from optic phonons, ~75%. This is extremely unusual as the acoustic phonon modes carry most of the heat in typical semiconductors and insulators with small unit cells. Very recently, Lee et. al. observed anisotropic in GST thin films and attributed this to thermal resistance of amorphous regions near grain boundaries. However, our results suggest an additional strong intrinsic anisotropy for the pure hexagonalmore » phase. This derives from bonding anisotropy along different crystal directions, specifically from weak interlayer coupling, which gives anisotropic phonon dispersions. The phonon spectrum of h-GST has very dispersive optic branches with higher group velocities along the a-axis as compared to flat optic bands along the c-axis. The importance of optic mode contributions for the thermal conductivity in low-$κ$ h-GST is unusual, and development of fundamental physical understanding of these contributions may be critical to better understanding of thermal conduction in other complex layered materials.« less

  11. Heat transfer due to electroconvulsive therapy: Influence of anisotropic thermal and electrical skull conductivity.

    PubMed

    Menezes de Oliveira, Marilia; Wen, Peng; Ahfock, Tony

    2016-09-01

    This paper focuses on electroconvulsive therapy (ECT) and head models to investigate temperature profiles arising when anisotropic thermal and electrical conductivities are considered in the skull layer. The aim was to numerically investigate the threshold for which this therapy operates safely to the brain, from the thermal point of view. A six-layer spherical head model consisting of scalp, fat, skull, cerebro-spinal fluid, grey matter and white matter was developed. Later on, a realistic human head model was also implemented. These models were built up using the packages from COMSOL Inc. and Simpleware Ltd. In these models, three of the most common electrode montages used in ECT were applied. Anisotropic conductivities were derived using volume constraint and included in both spherical and realistic head models. The bio-heat transferring problem governed by Laplace equation was solved numerically. The results show that both the tensor eigenvalues of electrical conductivity and the electrode montage affect the maximum temperature, but thermal anisotropy does not have a significant influence. Temperature increases occur mainly in the scalp and fat, and no harm is caused to the brain by the current applied during ECT. The work assures the thermal safety of ECT and also provides a numerical method to investigate other non-invasive therapies. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

  12. Electrical conductivity of a two-dimensional model for a structurally anisotropic composite

    SciTech Connect

    Balagurov, B. Ya.

    2010-02-15

    The electrical conductivity of a two-dimensional structurally anisotropic model for a composite is considered. The model represents an isotropic matrix with a system of nonconducting inclusions in the form of infinitely thin straight line segments (scratches). The scratches make an angle {theta} or -{theta} with a preferred axis (for definiteness, axis y) at the same probability, and their centers are chaotically distributed. An approximate effective medium method is used to obtain a general expression for the effective conductivity tensor of this model that is valid over a wide concentration range. In this approximation, both components of tensor are shown to vanish at the same percolation threshold, which is expressed explicitly. The conductivity of the model in a critical region is considered in terms of the similarity hypothesis.

  13. Anisotropic vanadium dioxide sculptured thin films with superior thermochromic properties

    PubMed Central

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

    2013-01-01

    VO2 (M) STF through reduction of V2O5 STF was prepared. The results illustrate that V2O5 STF can be successfully obtained by oblique angle thermal evaporation technique. After annealing at 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 ΔTsol 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

  14. Anisotropic vanadium dioxide sculptured thin films with superior thermochromic properties.

    PubMed

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

    2013-09-25

    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 ΔTsol 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.

  15. Anisotropic properties of the enamel organic extracellular matrix.

    PubMed

    do Espírito Santo, Alexandre R; Novaes, Pedro D; Line, Sérgio R P

    2006-05-01

    Enamel biosynthesis is initiated by the secretion, processing, and self-assembly of a complex mixture of proteins. This supramolecular ensemble controls the nucleation of the crystalline mineral phase. The detection of anisotropic properties by polarizing microscopy has been extensively used to detect macromolecular organizations in ordinary histological sections. The aim of this work was to study the birefringence of enamel organic matrix during the development of rat molar and incisor teeth. Incisor and molar teeth of rats were fixed in 2% paraformaldehyde/0.5% glutaraldehyde in 0.2 M phosphate-buffered saline (PBS), pH 7.2, and decalcified in 5% nitric acid/4% formaldehyde. After paraffin embedding, 5-microm-thick sections were obtained, treated with xylene, and hydrated. Form birefringence curves were obtained after measuring optical retardations in imbibing media, with different refractive indices. Our observations showed that enamel organic matrix of rat incisor and molar teeth is strongly birefringent, presenting an ordered supramolecular structure. The birefringence starts during the early secretion phase and disappears at the maturation phase. The analysis of enamel organic matrix birefringence may be used to detect the effects of genetic and environmental factors on the supramolecular orientation of enamel matrix and their effects on the structure of mature enamel.

  16. Anisotropic Energy Transport Properties of 1,3,5-Triamino-2,4,6-Trinitrobenzene (TATB)

    NASA Astrophysics Data System (ADS)

    Kroonblawd, Matthew P.

    Anisotropic energy transport properties were determined theoretically for crystals of the insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) using molecular dynamics simulations. Determination of these properties is necessary for the analysis and interpretation of molecular dynamics predictions of transient processes such as shock response and hot spot formation/relaxation and is similarly important for the accurate parameterization of meso- and continuum-scale engineering models aimed at understanding complex processes such as ignition and growth leading to detonation. TATB crystal exhibits a graphitic-like layered packing structure with a two-dimensional hydrogen-bonding network that forms within, but not between, the molecule-thick layers that comprise the crystal. This structure is thought to be the primary factor behind the significant anisotropy in many physical properties of TATB crystals. Anisotropic thermal conductivity coefficients were determined for initially defect-free and defective TATB crystals and isotropic values were determined for the liquid at temperatures and pressures up to (1800 K, 2.0 GPa). The room temperature, atmospheric pressure thermal conductivity for TATB is predicted to be generally greater and more anisotropic than the thermal conductivities of other molecular explosives; conduction within the layers is approximately 70% greater than conduction between the layers. The conductivity is predicted to decrease with temperature approximately as λ ∝ 1/T over the interval 200 K ≤ T ≤ 700 K and to linearly increase with pressure up to 2.5 GPa. Direction-dependent relaxation of idealized one-dimensional hot spots was studied. Results from hot spot relaxation simulations were compared with and fit to solutions for the one-dimensional diffusive heat equation by treating the thermal di.usivity as a parameter to assess the validity of using continuum models to describe heat transport in TATB on length scales below 10 nm. A

  17. Field determination of the three dimensional hydraulic conductivity tensor of anisotropic media: 1. Theory

    USGS Publications Warehouse

    Hsieh, Paul A.; Neuman, Shlomo P.

    1985-01-01

    A field method is proposed for determining the three-dimensional hydraulic conductivity tensor and specific storage of an anisotropic porous or fractured medium. The method, known as cross-hole testing (to distinguish it from conventional single-hole packer tests), consists of injecting fluid into (or withdrawing fluid from) packed-off intervals in a number of boreholes and monitoring the transient head response in similar intervals in neighboring boreholes. The directions of the principal hydraulic conductivities need not be known prior to the test, and the boreholes may have arbitrary orientations (e.g., they can all be vertical). An important aspect of the proposed method is that it provides direct field information on whether it is proper to regard the medium as being uniform and anisotropic on the scale of the test. The first paper presents theoretical expressions describing transient and steady state head response in monitoring intervals of arbitrary lengths and orientations, to constant-rate injection into (or withdrawal from) intervals having similar or different lengths and orientations. The conditions under which these intervals can be treated mathematically as points are investigated by an asymptotic analysis. The effect of planar no-flow and constant-head boundaries on the response is analyzed by the theory of images. The second paper describes the field methodology and shows how the proposed approach works in the case of fractured granitic rocks.

  18. An engineered anisotropic nanofilm with unidirectional wetting properties

    NASA Astrophysics Data System (ADS)

    Malvadkar, Niranjan A.; Hancock, Matthew J.; Sekeroglu, Koray; Dressick, Walter J.; Demirel, Melik C.

    2010-12-01

    Anisotropic textured surfaces allow water striders to walk on water, butterflies to shed water from their wings and plants to trap insects and pollen. Capturing these natural features in biomimetic surfaces is an active area of research. Here, we report an engineered nanofilm, composed of an array of poly(p-xylylene) nanorods, which demonstrates anisotropic wetting behaviour by means of a pin-release droplet ratchet mechanism. Droplet retention forces in the pin and release directions differ by up to 80μN, which is over ten times greater than the values reported for other engineered anisotropic surfaces. The nanofilm provides a microscale smooth surface on which to transport microlitre droplets, and is also relatively easy to synthesize by a bottom-up vapour-phase technique. An accompanying comprehensive model successfully describes the film's anisotropic wetting behaviour as a function of measurable film morphology parameters.

  19. An engineered anisotropic nanofilm with unidirectional wetting properties.

    PubMed

    Malvadkar, Niranjan A; Hancock, Matthew J; Sekeroglu, Koray; Dressick, Walter J; Demirel, Melik C

    2010-12-01

    Anisotropic textured surfaces allow water striders to walk on water, butterflies to shed water from their wings and plants to trap insects and pollen. Capturing these natural features in biomimetic surfaces is an active area of research. Here, we report an engineered nanofilm, composed of an array of poly(p-xylylene) nanorods, which demonstrates anisotropic wetting behaviour by means of a pin-release droplet ratchet mechanism. Droplet retention forces in the pin and release directions differ by up to 80 μN, which is over ten times greater than the values reported for other engineered anisotropic surfaces. The nanofilm provides a microscale smooth surface on which to transport microlitre droplets, and is also relatively easy to synthesize by a bottom-up vapour-phase technique. An accompanying comprehensive model successfully describes the film's anisotropic wetting behaviour as a function of measurable film morphology parameters.

  20. Uncertainty and sensitivity analysis for anisotropic inhomogeneous head tissue conductivity in human head modelling.

    PubMed

    Bashar, M R; Li, Y; Wen, P

    2010-06-01

    The accuracy of an electroencephalography (EEG) forward problem partially depends on the head tissue conductivities. These conductivities are anisotropic and inhomogeneous in nature. This paper investigates the effects of conductivity uncertainty and analyses its sensitivity on an EEG forward problem for a spherical and a realistic head models. We estimate the uncertain conductivities using an efficient constraint based on an optimization method and perturb it by means of the volume and directional constraints. Assigning the uncertain conductivities, we construct spherical and realistic head models by means of a stochastic finite element method for fixed dipolar sources. We also compute EEG based on the constructed head models. We use a probabilistic sensitivity analysis method to determine the sensitivity indexes. These indexes characterize the conductivities with the most or the least effects on the computed outputs. These results demonstrate that conductivity uncertainty has significant effects on EEG. These results also show that the uncertain conductivities of the scalp, the radial direction of the skull and transversal direction in the white matter are more sensible.

  1. Cold Fronts and Gas Sloshing in Galaxy Clusters with Anisotropic Thermal Conduction

    NASA Astrophysics Data System (ADS)

    ZuHone, J. A.; Markevitch, M.; Ruszkowski, M.; Lee, D.

    2013-01-01

    Cold fronts in cluster cool cores should be erased on short timescales by thermal conduction, unless protected by magnetic fields that are "draped" parallel to the front surfaces, suppressing conduction perpendicular to the sloshing fronts. We present a series of MHD simulations of cold front formation in the core of a galaxy cluster with anisotropic thermal conduction, exploring a parameter space of conduction strengths parallel and perpendicular to the field lines. Including conduction has a strong effect on the temperature distribution of the core and the appearance of the cold fronts. Though magnetic field lines are draping parallel to the front surfaces, preventing conduction directly across them, the temperature jumps across the fronts are nevertheless reduced. The geometry of the field is such that the cold gas below the front surfaces can be connected to hotter regions outside via field lines along directions perpendicular to the plane of the sloshing motions and along sections of the front that are not perfectly draped. This results in the heating of this gas below the front on a timescale of a Gyr, but the sharpness of the density and temperature jumps may nevertheless be preserved. By modifying the gas density distribution below the front, conduction may indirectly aid in suppressing Kelvin-Helmholtz instabilities. If conduction along the field lines is unsuppressed, we find that the characteristic sharp jumps seen in Chandra observations of cold front clusters do not form. Therefore, the presence of cold fronts in hot clusters is in contradiction with our simulations with full Spitzer conduction. This suggests that the presence of cold fronts in hot clusters could be used to place upper limits on conduction in the bulk of the intracluster medium. Finally, the combination of sloshing and anisotropic thermal conduction can result in a larger flux of heat to the core than either process in isolation. While still not sufficient to prevent a cooling

  2. COLD FRONTS AND GAS SLOSHING IN GALAXY CLUSTERS WITH ANISOTROPIC THERMAL CONDUCTION

    SciTech Connect

    ZuHone, J. A.; Markevitch, M.; Lee, D.

    2013-01-10

    Cold fronts in cluster cool cores should be erased on short timescales by thermal conduction, unless protected by magnetic fields that are 'draped' parallel to the front surfaces, suppressing conduction perpendicular to the sloshing fronts. We present a series of MHD simulations of cold front formation in the core of a galaxy cluster with anisotropic thermal conduction, exploring a parameter space of conduction strengths parallel and perpendicular to the field lines. Including conduction has a strong effect on the temperature distribution of the core and the appearance of the cold fronts. Though magnetic field lines are draping parallel to the front surfaces, preventing conduction directly across them, the temperature jumps across the fronts are nevertheless reduced. The geometry of the field is such that the cold gas below the front surfaces can be connected to hotter regions outside via field lines along directions perpendicular to the plane of the sloshing motions and along sections of the front that are not perfectly draped. This results in the heating of this gas below the front on a timescale of a Gyr, but the sharpness of the density and temperature jumps may nevertheless be preserved. By modifying the gas density distribution below the front, conduction may indirectly aid in suppressing Kelvin-Helmholtz instabilities. If conduction along the field lines is unsuppressed, we find that the characteristic sharp jumps seen in Chandra observations of cold front clusters do not form. Therefore, the presence of cold fronts in hot clusters is in contradiction with our simulations with full Spitzer conduction. This suggests that the presence of cold fronts in hot clusters could be used to place upper limits on conduction in the bulk of the intracluster medium. Finally, the combination of sloshing and anisotropic thermal conduction can result in a larger flux of heat to the core than either process in isolation. While still not sufficient to prevent a cooling

  3. Current-dependent anisotropic conductivity of locally assembled silver nanoparticles in hybrid polymer films.

    PubMed

    Goel, Pooja; Vinokur, Rostislav; Weichold, Oliver

    2010-12-15

    The electrical behaviour of hybrid poly(ethylene terephthalate) films containing localised, percolating networks of silver nanoparticles separated by pure polymer is studied. The films resemble an array of parallel wires in the submicron range and, thus, exhibit anisotropic conductivity. In the high-conductivity direction at low amplitudes, the films show Ohmic behaviour, while at moderate voltage, non-linearity and a decreasing resistance is observed. The samples were found to heat up during the measurements and the deviation from Ohm's law coincides with the Tg of the polymer. Microstructural analysis of the samples revealed an irreversible agglomeration of the particles at moderate voltages leading to the formation of filaments with higher metallic character than the random particle network.

  4. Anisotropic hopping conduction in spin-coated PEDOT:PSS thin films

    NASA Astrophysics Data System (ADS)

    Nardes, A. M.; Kemerink, M.; Janssen, R. A. J.

    2007-08-01

    The charge transport in spin-coated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been investigated as a function of temperature and electric field. Both the magnitude and the transport mechanism are found to be strongly anisotropic. This striking behavior is quantitatively explained in terms of a morphological model in which flattened, quasimetallic PEDOT-rich grains are organized in horizontal layers that are separated by continuous insulating PSS lamellas. In this model, the in-plane conductivity is described by three-dimensional variable range hopping between ˜25nm sized PEDOT-rich particles separated by subnanometer PSS barriers, while the out-of-plane conductivity is described by nearest-neighbor hopping between more widely spaced molecular sites. These length scales are supported by previously reported scanning probe measurements.

  5. ANISOTROPIC THERMAL CONDUCTION AND THE COOLING FLOW PROBLEM IN GALAXY CLUSTERS

    SciTech Connect

    Parrish, Ian J.; Sharma, Prateek; Quataert, Eliot

    2009-09-20

    We examine the long-standing cooling flow problem in galaxy clusters with three-dimensional magnetohydrodynamics simulations of isolated clusters including radiative cooling and anisotropic thermal conduction along magnetic field lines. The central regions of the intracluster medium (ICM) can have cooling timescales of {approx}200 Myr or shorter-in order to prevent a cooling catastrophe the ICM must be heated by some mechanism such as active galactic nucleus feedback or thermal conduction from the thermal reservoir at large radii. The cores of galaxy clusters are linearly unstable to the heat-flux-driven buoyancy instability (HBI), which significantly changes the thermodynamics of the cluster core. The HBI is a convective, buoyancy-driven instability that rearranges the magnetic field to be preferentially perpendicular to the temperature gradient. For a wide range of parameters, our simulations demonstrate that in the presence of the HBI, the effective radial thermal conductivity is reduced to {approx}<10% of the full Spitzer conductivity. With this suppression of conductive heating, the cooling catastrophe occurs on a timescale comparable to the central cooling time of the cluster. Thermal conduction alone is thus unlikely to stabilize clusters with low central entropies and short central cooling timescales. High central entropy clusters have sufficiently long cooling times that conduction can help stave off the cooling catastrophe for cosmologically interesting timescales.

  6. Anisotropic nanomaterials: Synthesis, optical and magnetic properties, and applications

    NASA Astrophysics Data System (ADS)

    Banholzer, Matthew John

    As nanoscience and nanotechnology mature, anisotropic metal nanostructures are emerging in a variety of contexts as valuable class of nanostructures due to their distinctive attributes. With unique properties ranging from optical to magnetic and beyond, these structures are useful in many new applications. Chapter two discusses the nanodisk code: a linear array of metal disk pairs that serve as surface-enhanced Raman scattering substrates. These multiplexing structures employ a binary encoding scheme, perform better than previous nanowires designs (in the context of SERS) and are useful for both convert encoding and tagging of substrates (based both on spatial disk position and spectroscopic response) as well as biomolecule detection (e.g. DNA). Chapter three describes the development of improved, silver-based nanodisk code structures. Work was undertaken to generate structures with high yield and reproducibility and to reoptimize the geometry of each disk pair for maximum Raman enhancement. The improved silver structures exhibit greater enhancement than Au structures (leading to lower DNA detection limits), convey additional flexibility, and enable trinary encoding schemes where far more unique structures can be created. Chapter four considers the effect of roughness on the plasmonic properties of nanorod structures and introduces a novel method to smooth the end-surfaces of nanorods structures. The smoothing technique is based upon a two-step process relying upon diffusion control during nanowires growth and selective oxidation after each step of synthesis is complete. Empirical and theoretical work show that smoothed nanostructures have superior and controllable optical properties. Chapter five concerns silica-encapsulated gold nanoprisms. This encapsulation allows these highly sensitive prisms to remain stable and protected in solution, enabling their use as class-leading sensors. Theoretical study complements the empirical work, exploring the effect of

  7. Thermoelectric Properties of Conducting Polymers

    DTIC Science & Technology

    1994-07-01

    polyphenylene sulfide , all of which are made conductive by addition of carbon. Polymers made conductive in this way do not have a high Seebeck...merit. KEYWORDS: Polyaniline, conducting polymer, conductive vinyl, conductive nylon, conductive polyphenylene sulfide , polyoctylthiophene, Schiff’s...directions. Polyphenylene sulfide (Ryton) A conductive form of this material, which is commercially available, is made conductive by the presence of carbon

  8. Anisotropic and inhomogeneous thermal conduction in suspended thin-film polycrystalline diamond

    NASA Astrophysics Data System (ADS)

    Sood, Aditya; Cho, Jungwan; Hobart, Karl D.; Feygelson, Tatyana I.; Pate, Bradford B.; Asheghi, Mehdi; Cahill, David G.; Goodson, Kenneth E.

    2016-05-01

    While there is a great wealth of data for thermal transport in synthetic diamond, there remains much to be learned about the impacts of grain structure and associated defects and impurities within a few microns of the nucleation region in films grown using chemical vapor deposition. Measurements of the inhomogeneous and anisotropic thermal conductivity in films thinner than 10 μm have previously been complicated by the presence of the substrate thermal boundary resistance. Here, we study thermal conduction in suspended films of polycrystalline diamond, with thicknesses ranging between 0.5 and 5.6 μm, using time-domain thermoreflectance. Measurements on both sides of the films facilitate extraction of the thickness-dependent in-plane ( κ r ) and through-plane ( κ z ) thermal conductivities in the vicinity of the coalescence and high-quality regions. The columnar grain structure makes the conductivity highly anisotropic, with κ z being nearly three to five times as large as κ r , a contrast higher than that reported previously for thicker films. In the vicinity of the high-quality region, κ r and κ z range from 77 ± 10 W/m-K and 210 ± 50 W/m-K for the 1 μm thick film to 130 ± 20 W/m-K and 710 ± 120 W/m-K for the 5.6 μm thick film, respectively. The data are interpreted using a model relating the anisotropy to the scattering on the boundaries of columnar grains and the evolution of the grain size considering their nucleation density and spatial rate of growth. This study aids in the reduction in the near-interfacial resistance of diamond films and efforts to fabricate diamond composites with silicon and GaN for power electronics.

  9. Anisotropic Elastography for Local Passive Properties and Active Contractility of Myocardium from Dynamic Heart Imaging Sequence

    PubMed Central

    Wang, Ge; Sun, L. Z.

    2006-01-01

    Major heart diseases such as ischemia and hypertrophic myocardiopathy are accompanied with significant changes in the passive mechanical properties and active contractility of myocardium. Identification of these changes helps diagnose heart diseases, monitor therapy, and design surgery. A dynamic cardiac elastography (DCE) framework is developed to assess the anisotropic viscoelastic passive properties and active contractility of myocardial tissues, based on the chamber pressure and dynamic displacement measured with cardiac imaging techniques. A dynamic adjoint method is derived to enhance the numerical efficiency and stability of DCE. Model-based simulations are conducted using a numerical left ventricle (LV) phantom with an ischemic region. The passive material parameters of normal and ischemic tissues are identified during LV rapid/reduced filling and artery contraction, and those of active contractility are quantified during isovolumetric contraction and rapid/reduced ejection. It is found that quasistatic simplification in the previous cardiac elastography studies may yield inaccurate material parameters. PMID:23165032

  10. Effective Heat and Mass Transport Properties of Anisotropic Porous Ceria for Solar Thermochemical Fuel Generation

    PubMed Central

    Haussener, Sophia; Steinfeld, Aldo

    2012-01-01

    High-resolution X-ray computed tomography is employed to obtain the exact 3D geometrical configuration of porous anisotropic ceria applied in solar-driven thermochemical cycles for splitting H2O and CO2. The tomography data are, in turn, used in direct pore-level numerical simulations for determining the morphological and effective heat/mass transport properties of porous ceria, namely: porosity, specific surface area, pore size distribution, extinction coefficient, thermal conductivity, convective heat transfer coefficient, permeability, Dupuit-Forchheimer coefficient, and tortuosity and residence time distributions. Tailored foam designs for enhanced transport properties are examined by means of adjusting morphologies of artificial ceria samples composed of bimodal distributed overlapping transparent spheres in an opaque medium. PMID:28817039

  11. Effective Heat and Mass Transport Properties of Anisotropic Porous Ceria for Solar Thermochemical Fuel Generation.

    PubMed

    Haussener, Sophia; Steinfeld, Aldo

    2012-01-19

    High-resolution X-ray computed tomography is employed to obtain the exact 3D geometrical configuration of porous anisotropic ceria applied in solar-driven thermochemical cycles for splitting H2O and CO2. The tomography data are, in turn, used in direct pore-level numerical simulations for determining the morphological and effective heat/mass transport properties of porous ceria, namely: porosity, specific surface area, pore size distribution, extinction coefficient, thermal conductivity, convective heat transfer coefficient, permeability, Dupuit-Forchheimer coefficient, and tortuosity and residence time distributions. Tailored foam designs for enhanced transport properties are examined by means of adjusting morphologies of artificial ceria samples composed of bimodal distributed overlapping transparent spheres in an opaque medium.

  12. Anisotropic elastography for local passive properties and active contractility of myocardium from dynamic heart imaging sequence.

    PubMed

    Liu, Yi; Wang, Ge; Sun, L Z

    2006-01-01

    Major heart diseases such as ischemia and hypertrophic myocardiopathy are accompanied with significant changes in the passive mechanical properties and active contractility of myocardium. Identification of these changes helps diagnose heart diseases, monitor therapy, and design surgery. A dynamic cardiac elastography (DCE) framework is developed to assess the anisotropic viscoelastic passive properties and active contractility of myocardial tissues, based on the chamber pressure and dynamic displacement measured with cardiac imaging techniques. A dynamic adjoint method is derived to enhance the numerical efficiency and stability of DCE. Model-based simulations are conducted using a numerical left ventricle (LV) phantom with an ischemic region. The passive material parameters of normal and ischemic tissues are identified during LV rapid/reduced filling and artery contraction, and those of active contractility are quantified during isovolumetric contraction and rapid/reduced ejection. It is found that quasistatic simplification in the previous cardiac elastography studies may yield inaccurate material parameters.

  13. A Study on the Nanofiber-Sheet Anisotropic Conductive Films (NS-ACFs) for Ultra-Fine-Pitch Interconnection Applications

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Hoon; Paik, Kyung-Wook

    2017-01-01

    Nanofiber-sheet anisotropic conductive films (NS-ACFs) were invented to overcome the limitations of high joint resistance and short-circuit issues of ultra-fine-pitch interconnections. The NS-ACFs have great advantages in terms of suppressing conductive particle movement during the flip-chip bonding process. In a 20-μm ultra-fine-pitch with 7-μm bump spacing ultra-fine-pitch chip-on-glass assembly, suppression effects of conductive particle movement were significantly improved by using the NS-ACFs because an unmelted NS inside the ACFs suppressed the mobility of conductive particles so that they would not flow out during the bonding process. The NS-ACFs could significantly increase the capture rate of conductive particles from 31% up to 81% compared to conventional ACFs. Moreover, excellent electrical contact properties were obtained without melting the nanofiber material which was essential for the conventional nanofiber ACFs. The NS-ACFs are promising interconnection materials for ultra-fine-pitch packaging applications.

  14. Dielectric properties of conductive ionomers

    NASA Astrophysics Data System (ADS)

    Klein, Robert James

    plasticized PEO-based ionomer were also studied in comparison to conductivity, with the conclusion that the glass transition temperature (a manifestation of the segmental segments) is the primary property governing conduction behavior in single-phase ionomers. Consideration of the solvent quality parameters yielded a similar result, that the plasticization effect on the glass transition is far stronger than the dielectric constant, donor number, or viscosity of the solvents.

  15. Reflection and refraction properties of plane waves on the interface of uniaxially anisotropic chiral media

    NASA Astrophysics Data System (ADS)

    Cheng, Qiang; Cui, Tie Jun

    2006-12-01

    We have investigated the reflection and refraction properties of plane waves incident from free space into a uniaxially anisotropic chiral medium, where the chirality appears only in one direction and the host medium can be either an isotropic dielectric or an anisotropic electric plasma. We show that the reflection and refraction properties are closely related to the dispersion relation of the chiral medium and that negative phase refractions and/or negative group refractions may occur. We further demonstrate that the two eigenwaves within the uniaxially anisotropic chiral medium behave differently with respect to the incident angle, and in some cases only one of them can be supported and transmitted. We have studied the critical angle and Brewster's angle with some special properties. We have also discussed the potential application of the uniaxially anisotropic chiral medium for the polarization beam splitter. Numerical results are given to validate our analysis.

  16. Reflection and refraction properties of plane waves on the interface of uniaxially anisotropic chiral media.

    PubMed

    Cheng, Qiang; Cui, Tie Jun

    2006-12-01

    We have investigated the reflection and refraction properties of plane waves incident from free space into a uniaxially anisotropic chiral medium, where the chirality appears only in one direction and the host medium can be either an isotropic dielectric or an anisotropic electric plasma. We show that the reflection and refraction properties are closely related to the dispersion relation of the chiral medium and that negative phase refractions and/or negative group refractions may occur. We further demonstrate that the two eigenwaves within the uniaxially anisotropic chiral medium behave differently with respect to the incident angle, and in some cases only one of them can be supported and transmitted. We have studied the critical angle and Brewster's angle with some special properties. We have also discussed the potential application of the uniaxially anisotropic chiral medium for the polarization beam splitter. Numerical results are given to validate our analysis.

  17. Field determination of the three-dimensional hydraulic conductivity tensor of anisotropic media 2. Methodology and application to fractured rocks.

    USGS Publications Warehouse

    Hsieh, P.A.; Neuman, S.P.; Stiles, G.K.; Simpson, E.S.

    1985-01-01

    The analytical solutions developed in the first paper can be used to interpret the results of cross-hole tests conducted in anisotropic porous or fractured media. Test results from a granitic rock near Oracle in southern Arizona are presented to illustrate how the method works for fractured rocks. At the site, the Oracle granite is shown to respond as a near-uniform, anisotropic medium, the hydraulic conductivity of which is strongly controlled by the orientations of major fracture sets. The cross-hole test results are shown to be consistent with the results of more than 100 single- hole packer tests conducted at the site. -from Authors

  18. Low-Temperature Curable Photo-Active Anisotropic Conductive Films (PA-ACFs)

    NASA Astrophysics Data System (ADS)

    Kim, Il; Paik, Kyung-Wook

    2014-09-01

    Photo-active anisotropic conductive films (PA-ACFs) with curing temperatures below 120°C were introduced using photo-active curing agents. The PA-ACFs showed no curing before UV activation, and the crosslinking systems of the PA-ACFs were not activated under fluorescent light exposure. However, after UV activation, the PA-ACFs were completely cured at 120°C within 10 s. Flex-on-board (FOB) assembly using PA-ACFs had adhesion strength and joint resistances similar to those of the FOB assemblies using conventional epoxy-based ACFs. This study demonstrates that PA-ACFs provide reliable interconnection and minimal thermal deformation among all the commercially available ACFs, especially for low T g substrate applications.

  19. Automated optical inspection of liquid crystal display anisotropic conductive film bonding

    NASA Astrophysics Data System (ADS)

    Ni, Guangming; Du, Xiaohui; Liu, Lin; Zhang, Jing; Liu, Juanxiu; Liu, Yong

    2016-10-01

    Anisotropic conductive film (ACF) bonding is widely used in the liquid crystal display (LCD) industry. It implements circuit connection between screens and flexible printed circuits or integrated circuits. Conductive microspheres in ACF are key factors that influence LCD quality, because the conductive microspheres' quantity and shape deformation rate affect the interconnection resistance. Although this issue has been studied extensively by prior work, quick and accurate methods to inspect the quality of ACF bonding are still missing in the actual production process. We propose a method to inspect ACF bonding effectively by using automated optical inspection. The method has three steps. The first step is that it acquires images of the detection zones using a differential interference contrast (DIC) imaging system. The second step is that it identifies the conductive microspheres and their shape deformation rate using quantitative analysis of the characteristics of the DIC images. The final step is that it inspects ACF bonding using a back propagation trained neural network. The result shows that the miss rate is lower than 0.1%, and the false inspection rate is lower than 0.05%.

  20. Layered Black Phosphorus: Strongly Anisotropic Magnetic, Electronic, and Electron-Transfer Properties.

    PubMed

    Sofer, Zdeněk; Sedmidubský, David; Huber, Štěpán; Luxa, Jan; Bouša, Daniel; Boothroyd, Chris; Pumera, Martin

    2016-03-01

    Layered elemental materials, such as black phosphorus, exhibit unique properties originating from their highly anisotropic layered structure. The results presented herein demonstrate an anomalous anisotropy for the electrical, magnetic, and electrochemical properties of black phosphorus. It is shown that heterogeneous electron transfer from black phosphorus to outer- and inner-sphere molecular probes is highly anisotropic. The electron-transfer rates differ at the basal and edge planes. These unusual properties were interpreted by means of calculations, manifesting the metallic character of the edge planes as compared to the semiconducting properties of the basal plane. This indicates that black phosphorus belongs to a group of materials known as topological insulators. Consequently, these effects render the magnetic properties highly anisotropic, as both diamagnetic and paramagnetic behavior can be observed depending on the orientation in the magnetic field.

  1. Optic phonons and anisotropic thermal conductivity in hexagonal Ge2Sb2Te5

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Saikat; Lindsay, Lucas; Singh, David J.

    2016-11-01

    The lattice thermal conductivity (κ) of hexagonal Ge2Sb2Te5 (h-GST) is studied via direct first-principles calculations. We find significant intrinsic anisotropy (κa/κc~2) of κ in bulk h-GST, with the dominant contribution to κ from optic phonons, ~75%. This is extremely unusual as the acoustic phonon modes are the majority heat carriers in typical semiconductors and insulators. The anisotropy derives from varying bonding along different crystal directions, specifically from weak interlayer bonding along the c-axis, which gives anisotropic phonon dispersions. The phonon spectrum of h-GST has very dispersive optic branches with higher group velocities along the a-axis as compared to flat optic bands along the c-axis. The large optic mode contributions to the thermal conductivity in low-κ h-GST is unusual, and development of fundamental physical understanding of these contributions may be critical to better understanding of thermal conduction in other complex layered materials.

  2. Optic phonons and anisotropic thermal conductivity in hexagonal Ge2Sb2Te5

    PubMed Central

    Mukhopadhyay, Saikat; Lindsay, Lucas; Singh, David J.

    2016-01-01

    The lattice thermal conductivity (κ) of hexagonal Ge2Sb2Te5 (h-GST) is studied via direct first-principles calculations. We find significant intrinsic anisotropy (κa/κc~2) of κ in bulk h-GST, with the dominant contribution to κ from optic phonons, ~75%. This is extremely unusual as the acoustic phonon modes are the majority heat carriers in typical semiconductors and insulators. The anisotropy derives from varying bonding along different crystal directions, specifically from weak interlayer bonding along the c-axis, which gives anisotropic phonon dispersions. The phonon spectrum of h-GST has very dispersive optic branches with higher group velocities along the a-axis as compared to flat optic bands along the c-axis. The large optic mode contributions to the thermal conductivity in low-κ h-GST is unusual, and development of fundamental physical understanding of these contributions may be critical to better understanding of thermal conduction in other complex layered materials. PMID:27848985

  3. Measurement of the anisotropic thermal conductivity of molybdenum disulfide by the time-resolved magneto-optic Kerr effect

    SciTech Connect

    Liu, Jun Choi, Gyung-Min; Cahill, David G.

    2014-12-21

    We use pump-probe metrology based on the magneto-optic Kerr effect to measure the anisotropic thermal conductivity of (001)-oriented MoS{sub 2} crystals. A ≈20 nm thick CoPt multilayer with perpendicular magnetization serves as the heater and thermometer in the experiment. The low thermal conductivity and small thickness of the CoPt transducer improve the sensitivity of the measurement to lateral heat flow in the MoS{sub 2} crystal. The thermal conductivity of MoS{sub 2} is highly anisotropic with basal-plane thermal conductivity varying between 85–110 W m{sup -1} K{sup -1} as a function of laser spot size. The basal-plane thermal conductivity is a factor of ≈50 larger than the c-axis thermal conductivity, 2.0±0.3 W m{sup -1} K{sup -1}.

  4. Three discontinuous Galerkin schemes for the anisotropic heat conduction equation on non-aligned grids

    NASA Astrophysics Data System (ADS)

    Held, M.; Wiesenberger, M.; Stegmeir, A.

    2016-02-01

    We present and discuss three discontinuous Galerkin (dG) discretizations for the anisotropic heat conduction equation on non-aligned cylindrical grids. Our non-aligned scheme relies on a self-adjoint local dG (LDG) discretization of the elliptic operator. It conserves the energy exactly and converges with arbitrary order. The pollution by numerical perpendicular heat fluxes decreases with superconvergence rates. We compare this scheme with aligned schemes that are based on the flux-coordinate independent approach for the discretization of parallel derivatives. Here, the dG method provides the necessary interpolation. The first aligned discretization can be used in an explicit time-integrator. However, the scheme violates conservation of energy and shows up stagnating convergence rates for very high resolutions. We overcome this partly by using the adjoint of the parallel derivative operator to construct a second self-adjoint aligned scheme. This scheme preserves energy, but reveals unphysical oscillations in the numerical tests, which result in a decreased order of convergence. Both aligned schemes exhibit low numerical heat fluxes into the perpendicular direction and are superior for flute-modes with finite parallel gradients. We build our argumentation on various numerical experiments on all three schemes for a general axisymmetric magnetic field, which is closed by a comparison to the aligned finite difference (FD) schemes of Stegmeir et al. (2014) and Stegmeir et al. (submitted for publication).

  5. A novel finite element model of the ovine lumbar intervertebral disc with anisotropic hyperelastic material properties

    PubMed Central

    Galbusera, Fabio; Jonas, René; Schlager, Benedikt; Wilke, Hans-Joachim; Villa, Tomaso

    2017-01-01

    The Ovine spine is an accepted model to investigate the biomechanical behaviour of the human lumbar one. Indeed, the use of animal models for in vitro studies is necessary to investigate the mechanical behaviour of biological tissue, but needs to be reduced for ethical and social reasons. The aim of this study was to create a finite element model of the lumbar intervertebral disc of the sheep that may help to refine the understanding of parallel in vitro experiments and that can be used to predict when mechanical failure occurs. Anisotropic hyperelastic material properties were assigned to the annulus fibrosus and factorial optimization analyses were performed to find out the optimal parameters of the ground substance and of the collagen fibers. For the ground substance of the annulus fibrosus the investigation was based on experimental data taken from the literature, while for the collagen fibers tensile tests on annulus specimens were conducted. Flexibility analysis in flexion-extension, lateral bending and axial rotation were conducted. Different material properties for the anterior, lateral and posterior regions of the annulus were found. The posterior part resulted the stiffest region in compression whereas the anterior one the stiffest region in tension. Since the flexibility outcomes were in a good agreement with the literature data, we considered this model suitable to be used in conjunction with in vitro and in vivo tests to investigate the mechanical behaviour of the ovine lumbar disc. PMID:28472100

  6. Dipole estimation errors due to differences in modeling anisotropic conductivities in realistic head models for EEG source analysis.

    PubMed

    Hallez, Hans; Vanrumste, Bart; Van Hese, Peter; Delputte, Steven; Lemahieu, Ignace

    2008-04-07

    To improve the EEG source localization in the brain, the conductivities used in the head model play a very important role. In this study, we focus on the modeling of the anisotropic conductivity of the white matter. The anisotropic conductivity profile can be derived from diffusion weighted magnetic resonance images (DW-MRI). However, deriving these anisotropic conductivities from diffusion weighted MR images of the white matter is not straightforward. In the literature, two methods can be found for calculating the conductivity from the diffusion weighted images. One method uses a fixed value for the ratio of the conductivity in different directions, while the other method uses a conductivity profile obtained from a linear scaling of the diffusion ellipsoid. We propose a model which can be used to derive the conductivity profile from the diffusion tensor images. This model is based on the variable anisotropic ratio throughout the white matter and is a combination of the linear relationship as stated in the literature, with a constraint on the magnitude of the conductivity tensor (also known as the volume constraint). This approach is stated in the paper as approach A. In our study we want to investigate dipole estimation differences due to using a more simplified model for white matter anisotropy (approach B), while the electrode potentials are derived using a head model with a more realistic approach for the white matter anisotropy (approach A). We used a realistic head model, in which the forward problem was solved using a finite difference method that can incorporate anisotropic conductivities. As error measures we considered the dipole location error and the dipole orientation error. The results show that the dipole location errors are all below 10 mm and have an average of 4 mm in gray matter regions. The dipole orientation errors ranged up to 66.4 degrees, and had a mean of, on average, 11.6 degrees in gray matter regions. In a qualitative manner, the results

  7. Anisotropic Thermal Properties of Nanostructured Magnetic, Carbon and Hybrid Magnetic - Carbon Materials

    NASA Astrophysics Data System (ADS)

    Ramirez, Sylvester

    anisotropy of the thermal conductivity, K/K ⊥ ˜ 675, which is substantially larger even than in the high-quality graphite. The strongly anisotropic heat conduction properties of these films can be useful for the thermal filler applications. The results obtained for the nanostructured magnetic and hybrid materials are important for the renewable energy and electronic applications of permanent magnets.

  8. Hexagonal superlattice of chiral conducting polymers self-assembled by mimicking beta-sheet proteins with anisotropic electrical transport.

    PubMed

    Yan, Yong; Wang, Rui; Qiu, Xiaohui; Wei, Zhixiang

    2010-09-01

    An ordered superlattice self-assembled from monodispersed nanostructures can exhibit collective effects of its individual building blocks, a desirable property that gives rise to potential applications. However, no general method for the direct fabrication of superstructures yet exists, especially for superlattices that start from rational-designed functional molecules. Noncovalent interactions are widely used for the self-assembly of biomolecules in nature, such as various superstructures of proteins. Instead of using hydrogen bonds as driving force for the self-assembly of beta-sheet structures of peptides, pi-pi stacking interactions were used in this study to self-assemble conducting polyaniline (PANI) nanostructures and superstructures. Monodispersed crystalline PANI nanorices were prepared by using homochiral PANI as building blocks; these nanorices can further self-assemble into hexagonal microplates aligned shoulder to shoulder. PANI molecules were organized into nanorices via single-handed helical pi-pi stacking, in which the molecular plane was normal to the long axis of the nanorices. Electrical transport measurements showed the anisotropic characteristics of self-assembled nanorices and their superstructures, which were due to the directional transport barrier in the nanorices and the structural defects at the interfaces between neighboring nanorices. As chiral PANI and peptides have similar self-assembly behaviors, the method used in this study is greatly expected to be applicable to other chemical and biochemical building blocks.

  9. Ionic Intercalation in Two-Dimensional van der Waals Materials: In Situ Characterization and Electrochemical Control of the Anisotropic Thermal Conductivity of Black Phosphorus.

    PubMed

    Kang, Joon Sang; Ke, Ming; Hu, Yongjie

    2017-03-08

    Two-dimensional van der Waals materials have shown novel fundamental properties and promise for wide applications. Here, we report for the first time an experimental demonstration of the in situ characterization and highly reversible control of the anisotropic thermal conductivity of black phosphorus. We develop a novel platform based on lithium ion batteries that integrates ultrafast optical spectroscopy and electrochemical control to investigate the interactions between lithium ions and the lattices of the black phosphorus electrode. We discover a strong dependence of the thermal conductivity on battery charge states (lithium concentrations) during the discharge/charge process. The thermal conductivity of black phosphorus is reversibly tunable over a wide range of 2.45-3.86, 62.67-85.80, and 21.66-27.58 W·m(-1)·K(-1) in the cross-plan, zigzag, and armchair directions, respectively. The modulation in thermal conductivity is attributed to phonon scattering introduced by the ionic intercalation in between the interspacing layers and shows anisotropic phonon scattering mechanism based on semiclassical model. At the fully discharged state (x ∼ 3 in LixP), a dramatic reduction of thermal conductivity by up to 6 times from that of the pristine crystal has been observed. This study provides a unique approach to explore the fundamental energy transport involving lattices and ions in the layered structures and may open up new opportunities in controlling energy transport based on novel operation mechanisms and the rational design of nanostructures.

  10. Time-resolved measurements of the optical properties of fibrous media using the anisotropic diffusion equation

    NASA Astrophysics Data System (ADS)

    Simon, Emanuel; Krauter, Philipp; Kienle, Alwin

    2014-07-01

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

  11. Properties of solid and gaseous hydrogen, based upon anisotropic pair interactions

    NASA Technical Reports Server (NTRS)

    Etters, R. D.; Danilowicz, R.; England, W.

    1975-01-01

    Properties of H2 are studied on the basis of an analytic anisotropic potential deduced from atomic orbital and perturbation calculations. The low-pressure solid results are based on a spherical average of the anisotropic potential. The ground state energy and the pressure-volume relation are calculated. The metal-insulator phase transition pressure is predicted. Second virial coefficients are calculated for H2 and D2, as is the difference in second virial coefficients between ortho and para H2 and D2.

  12. Thermal conductivity of layered borides: The effect of building defects on the thermal conductivity of TmAlB{sub 4} and the anisotropic thermal conductivity of AlB{sub 2}

    SciTech Connect

    Wang, X. J. E-mail: xwang58@illinois.edu; Mori, T. E-mail: xwang58@illinois.edu; Kuzmych-Ianchuk, I.; Michiue, Y.; Yubuta, K.; Shishido, T.; Grin, Y.; Okada, S.; Cahill, D. G.

    2014-04-01

    Rare earth metal borides have attracted great interest due to their unusual properties, such as superconductivity and f-electron magnetism. A recent discovery attributes the tunability of magnetism in rare earth aluminoborides to the effect of so-called “building defects.” In this paper, we report data for the effect of building defects on the thermal conductivities of α-TmAlB{sub 4} single crystals. Building defects reduce the thermal conductivity of α-TmAlB{sub 4} by ≈30%. At room temperature, the thermal conductivity of AlB{sub 2} is nearly a factor of 5 higher than that of α-TmAlB{sub 4}. AlB{sub 2} single crystals are thermally anisotropic with the c-axis thermal conductivity nearly twice the thermal conductivity of the a-b plane. Temperature dependence of the thermal conductivity near and above room temperature reveals that both electrons and phonons contribute substantially to thermal transport in AlB{sub 2} with electrons being the dominant heat carriers.

  13. Strong tendency of homeotropic alignment and anisotropic lithium ion conductivity of sulfonate functionalized zwitterionic imidazolium ionic liquid crystals.

    PubMed

    Rondla, Rohini; Lin, Joseph C Y; Yang, C T; Lin, Ivan J B

    2013-09-17

    Here, we report the first attempt to investigate the liquid crystal (LC) behavior of SO3(-) functionalized imidazolium zwitterionic (SO3(-)ImZI) salts, which display homeotropic alignment on a glass slide without the aid of any aligning approach. Doping lithium salt to ImZI salts lowers the melting temperatures and raises the clearing temperatures substantially to form room temperature ImZILCs. Excellent anisotropic lithium ion conductivity is achieved; which is strengthened by their tendency for homeotropic alignment.

  14. Synthesis and optical properties of anisotropic metal nanoparticles.

    PubMed

    Hao, Encai; Schatz, George C; Hupp, Joseph T

    2004-07-01

    In this paper we overview our recent studies of anisotropic noble metal (e.g. gold and silver) nanoparticles, in which a combination of theory and experiment has been used to elucidate the extinction spectra of the particles, as well as information related to their surface enhanced Raman spectroscopy. We used wet-chemical methods to generate several structurally well-defined nanostructures other than solid spheres, including silver nanodisks and triangular nanoprisms, and gold nanoshells and multipods. When solid spheres are transformed into one of these shapes, the surface plasmon resonances in these particles are strongly affected, typically red-shifting and even splitting into distinctive dipole and quadrupole plasmon modes. In parallel, we have developed computational electrodynamics methods based on the discrete dipole approximation (DDA) method to determine the origins of these intriguing optical features. This has resulted in considerable insight concerning the variation of plasmon wavelength with nanoparticle size, shape and dielectric environment, as well as the use of these particles for optical sensing applications.

  15. 75 FR 78915 - Conduct on Postal Property

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-17

    ... in 39 CFR 232.1. 1. Paragraph (f) Gambling: The prohibition of lottery ticket sales contains an... Conduct on postal property. * * * * * (f) Gambling. Participating in games for money or other personal property, the operation of gambling devices, the conduct of a lottery or pool, or the selling or purchasing...

  16. Nanoindentation study of electrodeposited Ag thin coating: An inverse calculation of anisotropic elastic-plastic properties

    SciTech Connect

    Cheng, Guang; Sun, Xin; Wang, Yuxin; Tay, See Leng; Gao, Wei

    2017-01-01

    A new inverse method was proposed to calculate the anisotropic elastic-plastic properties (flow stress) of thin electrodeposited Ag coating utilizing nanoindentation tests, previously reported inverse method for isotropic materials and three-dimensional (3-D) finite element analyses (FEA). Indentation depth was ~4% of coating thickness (~10 μm) to avoid substrate effect and different indentation responses were observed in the longitudinal (L) and the transverse (T) directions. The estimated elastic-plastic properties were obtained in the newly developed inverse method by matching the predicted indentation responses in the L and T directions with experimental measurements considering indentation size effect (ISE). The results were validated with tensile flow curves measured from free-standing (FS) Ag film. The current method can be utilized to characterize the anisotropic elastic-plastic properties of coatings and to provide the constitutive properties for coating performance evaluations.

  17. Resolution of anisotropic and shielded highly conductive layers using 2-D electromagnetic modelling in the Rhine Graben and Black Forest

    NASA Astrophysics Data System (ADS)

    Tezkan, Bülent; Červ, Václav; Pek, Josef

    1992-12-01

    Anisotropy in magnetotelluric (MT) data has been found very often and has been explained as the result of local structures of different conductivities. In this paper, an observed anisotropy in MT data is not interpreted qualitatively in terms of local structures but is modelled quantitatively by a quasi-anisotropic layer. Besides the MT transfer functions, measurements of the vertical magnetic component are required. The second goal of this paper is to describe a method which permits the resolution of mid-crustal conductive layers in the presence of an additional high-conductivity layer at the surface. This method is possible in a two-dimensional (2-D) situation that limits the spatial extension of the surface structure. Again, vertical magnetic field recordings are necessary, but the phase of the E-polarization with respect to the 2-D structure is the most sensitive parameter. Using two field sites in Southern Germany, it has been possible to give a quantitative explanation of anisotropy and an improved depth resolution, and to derive an integrated conductivity of the highly conductive mid-crustal layers using MT and geomagnetic depth sounding data. The anisotropic highly conductive layer is located 12 km beneath the poorly conductive Black Forest crystalline rocks, whereas it is at a depth of 6 km beneath the highly conductive Rhine Graben sediments.

  18. Anisotropic properties of RFe_2Ge2 single crystals

    NASA Astrophysics Data System (ADS)

    Avila, M. A.; Bud'Ko, S. L.; Canfield, P. C.

    2003-03-01

    We have grown RFe_2Ge2 single crystals for R = Y and ten members of the lanthanide series (Pr, Nd, Sm, Gd-Tm, Lu) using Sn flux as the solvent. The method yields clean, high quality crystal plates as evidenced by residual resistivities and RRR values in the range of 3-12 μΩ cm and 20-70 respectively. The crystals are also virtually free of magnetic impurities or secondary phases, allowing the study of the intrinsic anisotropic magnetic behavior of each compound. Characterization was made with X-Ray diffraction, temperature and field dependent magnetization, specific heat and resistivity. Strong anisotropies arising mostly from CEF effects were observed for all magnetic rare earths except Gd. Anti-ferromagnetic ordering occurred at temperatures between 16.5 K (Nd) and 1.25 K (Ho) and for some members there are further well-defined metamagnetic transitions. The calculated effective moments per rare earth atom tend to be larger than the expected values at high temperatures while smaller at low temperatures, probably indicating temperature-dependent contributions of d-band electrons to the magnetic behavior. We acknowledge the help of R. A. Ribeiro and C. Petrovic in the X-Ray diffraction measurements, and K. Myers in the early development and characterization of the crystals. Ames Laboratory is operated for the US Department of Energy by Iowa State University under Contract No. W-7405-Eng-82. This work was supported by the Director for Energy Research, Office of Basic Energy Sciences.

  19. Anisotropic magnetic properties of the KMo4O6

    NASA Astrophysics Data System (ADS)

    Andrade, M.; Maffei, M. L.; Dos Santos, C. A. M.; Ferreira, B.; Sartori, A. F.

    2012-02-01

    Electrical resistivity measurements in the tetragonal KMo4O6 single crystals show a metal-insulator transition (MIT) near 100K. Magnetization measurements as a function of temperature show no evidence of magnetic ordering at this MIT [1]. Single crystals of KMo4O6 were obtained by electrolysis of a melt with a molar ratio of K2MoO4:MoO3 = 6:1. The process were carried out at 930 C with a current of 20-25mA for 52h in argon atmosphere. After that, electrodes were removed from the melt alloying the crystals to cool down to room temperature rapidly. Scanning Electron Microscopy (SEM) showed that the black single crystals were grown on the platinum cathode. Typical dimensions of the single crystals are 1x0.2x0.2mm^3. X-ray diffractometry confirmed that the single crystals have KMo4O6 tetragonal crystalline structure with space group P4. Magnetization measurements were performed parallel and perpendicular to the c-axis from 2 to 300K. The results show anisotropic behavior between both directions. Furthermore, the temperature independence of the magnetization at high temperature and the upturn at low temperature are observed in agreement with previous results [1]. MxH curves measured at several temperatures show nonlinear behavior and a small magnetic ordering. The magnetic ordering seems to be related to the MIT near 100K. This material is based upon support by FAPESP (2009/14524-6 and 2009/54001-6) and CNPq/NSF (490182/2009-7). M. Andrade is CAPES fellow and C.A.M. dos Santos is CNPq fellow. [4pt] [1] K. V. Ramanujachary et al., J. Sol. State Chem.102 (1993) 69.

  20. Analysis of optically anisotropic properties of biological tissues under stretching based on differential Mueller matrix formalism

    NASA Astrophysics Data System (ADS)

    Chen, Hao-Wei; Huang, Chih-Ling; Lo, Yu-Lung; Chang, You-Ren

    2017-03-01

    The optical properties of biological tissues under stretching are investigated using a full-field ellipsometry technique based on a differential Mueller matrix formalism. Traditional photoelastic-based formalism for extracting the linear birefringence (LB) properties of stretched anisotropic optical samples ignores the effects of the other optical properties of the sample. By contrast, in the formalism proposed in this study, the LB, linear dichroism (LD), circular birefringence (CB), circular dichroism (CD), and depolarization (Dep) properties are fully decoupled. Simulations are performed to evaluate the performance of the two formalisms in extracting the LB properties of optically anisotropic samples with different degrees of Dep, CB, LD, and CD. The practical feasibility of the proposed all-parameter decoupled formalism is then demonstrated using chicken breast muscle tissue. In general, the results show that both formalisms provide a reliable LB measurement performance for healthy chicken breast tissue under stretching. However, while the LB-only formalism has good robustness toward scattering, its measurement performance is seriously degraded for samples with high CB. Thus, of the two formalisms, the proposed all-parameter decoupled formalism provides a more effective approach for examining the anisotropic properties of biological tissues under stretching.

  1. Probing Anisotropic Thermal Conductivity of Transition Metal Dichalcogenides MX2 (M = Mo, W and X = S, Se) using Time-Domain Thermoreflectance.

    PubMed

    Jiang, Puqing; Qian, Xin; Gu, Xiaokun; Yang, Ronggui

    2017-09-01

    Transition metal dichalcogenides (TMDs) are a group of layered 2D semiconductors that have shown many intriguing electrical and optical properties. However, the thermal transport properties in TMDs are not well understood due to the challenges in characterizing anisotropic thermal conductivity. Here, a variable-spot-size time-domain thermoreflectance approach is developed to simultaneously measure both the in-plane and the through-plane thermal conductivity of four kinds of layered TMDs (MoS2 , WS2 , MoSe2 , and WSe2 ) over a wide temperature range, 80-300 K. Interestingly, it is found that both the through-plane thermal conductivity and the Al/TMD interface conductance depend on the modulation frequency of the pump beam for all these four compounds. The frequency-dependent thermal properties are attributed to the nonequilibrium thermal resistance between the different groups of phonons in the substrate. A two-channel thermal model is used to analyze the nonequilibrium phonon transport and to derive the intrinsic thermal conductivity at the thermal equilibrium limit. The measurements of the thermal conductivities of bulk TMDs serve as an important benchmark for understanding the thermal conductivity of single- and few-layer TMDs. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Anisotropic in-plane thermal conductivity of black phosphorus nanoribbons at temperatures higher than 100 K

    DOE PAGES

    Lee, Sangwook; Yang, Fan; Suh, Joonki; ...

    2015-10-16

    Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing thermal conductivity anisotropy, up to a factor of two, with temperatures above 100 K. A size effect in thermal conductivity was also observed in which thinner nanoribbons show lower thermal conductivity. Analysed with the relaxation time approximation model using phononmore » dispersions obtained based on density function perturbation theory, the high anisotropy is attributed mainly to direction-dependent phonon dispersion and partially to phonon–phonon scattering. Lastly, our results revealing the intrinsic, orientation-dependent thermal conductivity of black phosphorus are useful for designing devices, as well as understanding fundamental physical properties of layered materials.« less

  3. Anisotropic in-plane thermal conductivity of black phosphorus nanoribbons at temperatures higher than 100 K

    SciTech Connect

    Lee, Sangwook; Yang, Fan; Suh, Joonki; Yang, Sijie; Lee, Yeonbae; Li, Guo; Sung Choe, Hwan; Suslu, Aslihan; Chen, Yabin; Ko, Changhyun; Park, Joonsuk; Liu, Kai; Li, Jingbo; Hippalgaonkar, Kedar; Urban, Jeffrey J.; Tongay, Sefaattin; Wu, Junqiao

    2015-10-16

    Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing thermal conductivity anisotropy, up to a factor of two, with temperatures above 100 K. A size effect in thermal conductivity was also observed in which thinner nanoribbons show lower thermal conductivity. Analysed with the relaxation time approximation model using phonon dispersions obtained based on density function perturbation theory, the high anisotropy is attributed mainly to direction-dependent phonon dispersion and partially to phonon–phonon scattering. Lastly, our results revealing the intrinsic, orientation-dependent thermal conductivity of black phosphorus are useful for designing devices, as well as understanding fundamental physical properties of layered materials.

  4. Anisotropic in-plane thermal conductivity of black phosphorus nanoribbons at temperatures higher than 100 K

    NASA Astrophysics Data System (ADS)

    Lee, Sangwook; Yang, Fan; Suh, Joonki; Yang, Sijie; Lee, Yeonbae; Li, Guo; Sung Choe, Hwan; Suslu, Aslihan; Chen, Yabin; Ko, Changhyun; Park, Joonsuk; Liu, Kai; Li, Jingbo; Hippalgaonkar, Kedar; Urban, Jeffrey J.; Tongay, Sefaattin; Wu, Junqiao

    2015-10-01

    Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing thermal conductivity anisotropy, up to a factor of two, with temperatures above 100 K. A size effect in thermal conductivity was also observed in which thinner nanoribbons show lower thermal conductivity. Analysed with the relaxation time approximation model using phonon dispersions obtained based on density function perturbation theory, the high anisotropy is attributed mainly to direction-dependent phonon dispersion and partially to phonon-phonon scattering. Our results revealing the intrinsic, orientation-dependent thermal conductivity of black phosphorus are useful for designing devices, as well as understanding fundamental physical properties of layered materials.

  5. Evolution, Interaction, and Intrinsic Properties of Dislocations in Intermetallics: Anisotropic 3D Dislocation Dynamics Approach

    SciTech Connect

    Chen, Qian

    2008-01-01

    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.

  6. Evolution, interaction, and intrinsic properties of dislocations in intermetallics: Anisotropic three-dimensional dislocation dynamics approach

    NASA Astrophysics Data System (ADS)

    Chen, Qian

    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.

  7. Scale Properties of Anisotropic and Isotropic Turbulence in the Urban Surface Layer

    NASA Astrophysics Data System (ADS)

    Liu, Hao; Yuan, Renmin; Mei, Jie; Sun, Jianning; Liu, Qi; Wang, Yu

    2017-06-01

    The scale properties of anisotropic and isotropic turbulence in the urban surface layer are investigated. A dimensionless anisotropic tensor is introduced and the turbulent tensor anisotropic coefficient, defined as C, where C = 3d3 + 1 (d3 is the minimum eigenvalue of the tensor) is used to characterize the turbulence anisotropy or isotropy. Turbulence is isotropic when C ≈ 1 , and anisotropic when C ≪ 1 . Three-dimensional velocity data collected using a sonic anemometer are analyzed to obtain the anisotropic characteristics of atmospheric turbulence in the urban surface layer, and the tensor anisotropic coefficient of turbulent eddies at different spatial scales calculated. The analysis shows that C is strongly dependent on atmospheric stability ξ = (z-zd)/L_{MO} , where z is the measurement height, zd is the displacement height, and L_{MO} is the Obukhov length. The turbulence at a specific scale in unstable conditions (i.e., ξ < 0 ) is closer to isotropic than that at the same scale under stable conditions. The maximum isotropic scale of turbulence is determined based on the characteristics of the power spectrum in three directions. Turbulence does not behave isotropically when the eddy scale is greater than the maximum isotropic scale, whereas it is horizontally isotropic at relatively large scales. The maximum isotropic scale of turbulence is compared to the outer scale of temperature, which is obtained by fitting the temperature fluctuation spectrum using the von Karman turbulent model. The results show that the outer scale of temperature is greater than the maximum isotropic scale of turbulence.

  8. Evaluation of the Anisotropic Radiative Conductivity of a Low-Density Carbon Fiber Material from Realistic Microscale Imaging

    NASA Technical Reports Server (NTRS)

    Nouri, Nima; Panerai, Francesco; Tagavi, Kaveh A.; Mansour, Nagi N.; Martin, Alexandre

    2015-01-01

    The radiative heat transfer inside a low-density carbon fiber insulator is analyzed using a three-dimensional direct simulation model. A robust procedure is presented for the numerical calculation of the geometric configuration factor to compute the radiative energy exchange processes among the small discretized surface areas of the fibrous material. The methodology is applied to a polygonal mesh of a fibrous insulator obtained from three-dimensional microscale imaging of the real material. The anisotropic values of the radiative conductivity are calculated for that geometry. The results yield both directional and thermal dependence of the radiative conductivity.

  9. Numerical computation of lightning transfer functions for layered, anisotropically conducting shielding structures by the method of moments

    NASA Astrophysics Data System (ADS)

    Happ, Fabian; Brüns, Heinz-D.; Mavraj, Gazmend; Gronwald, Frank

    2016-09-01

    A formalism for the computation of lightning transfer functions by the method of moments, which involves shielding structures that may consist of layered, anisotropically conducting composite materials, is presented in this contribution. The composite materials, being of a type that is widely used in space- and aircraft design, are electrically characterized by an equivalent conductivity. As basis for the quantitative analysis the method of moments is used where shielding surfaces can be treated by a thin layer technique which utilizes analytical solutions inside the layer. Also the effect of an extended lightning channel can be taken into account. The method is applied to geometries that resemble an actual airplane fuselage.

  10. Magnetotelluric Transfer Functions: Phase Tensor and Tipper Vector above a Simple Anisotropic Three-Dimensional Conductivity Anomaly and Implications for 3D Isotropic Inversion

    NASA Astrophysics Data System (ADS)

    Löwer, Alexander; Junge, Andreas

    2017-05-01

    The influence of anisotropic conductivity structures on magnetotelluric transfer functions is not easy to analyse in its entire complexity. In this study, we investigate the spatial and frequency-dependent behaviour of phase tensors and tipper vectors above a 3D anisotropic conductivity anomaly. The anomaly consists of a simple cubic block embedded in a homogeneous half space. Using a 3D FD code, we compare an isotropic, 2 anisotropic models with an anisotropy factor of 10 and one anisotropic model with the anisotropy factor of 100. The results show characteristic differences between the isotropic and anisotropic cases. For the anisotropic anomalies, the tipper vectors are parallel over the entire area despite the 3D geometry of the anomalous body. The size of the tipper vectors depends on the position of the site relative to the anomaly's boundaries and the direction of the anisotropic strike. Above the anomalous anisotropic body, the main diagonal elements of the phase tensor show the well-known split. Outside the anomaly, the phase tensor principal axis rotates according to the site position in contrast to the constant tipper direction. The 3D inversion of the forward data using an isotropic 3D code (ModEM) yields a very good fit for all cases. Whereas the inversion result matches the isotropic model, wave-like structures with high conductivity contrast occur for the anisotropic models. These structures extend far beyond the extension of the original anomalous body. Thus, the study reveals important indications of the existence of anisotropic conductivity structures for observed magnetotelluric transfer functions.

  11. Picosecond Acoustic Measurement of Anisotropic Properties of Thin Films

    SciTech Connect

    Perton, M.; Rossignol, C.; Chigarev, N.; Audoin, B.

    2007-03-21

    Properties of thin metallic films have been studied extensively by means of laser-picosecond ultrasonics. Generation of longitudinal and shear waves via thermoelastic mechanism and large source has been only demonstrated for waves vectors along the normal to the interface. However, such measurements cannot provide complete information about elastic properties of films. As it has been already shown for nanosecond ultrasonics, the knowledge of group or phase velocities in several directions for sources with small lateral size allows determining the stiffness tensor coefficients of a sample. The experimental set-up was prepared to obtain the thinnest size for the source to achieve acoustic diffraction. The identification of the stiffness tensor components, based on the inversion of the bulk waves phase velocities, is applied to signals simulated and experimentally recorded for a material with hexagonal properties. First estimation of stiffness tensor coefficients for thin metallic film 2.1 {mu}m has been performed.

  12. Single-layer nanosheets with exceptionally high and anisotropic hydroxyl ion conductivity

    PubMed Central

    Sun, Pengzhan; Ma, Renzhi; Bai, Xueyin; Wang, Kunlin; Zhu, Hongwei; Sasaki, Takayoshi

    2017-01-01

    When the dimensionality of layered materials is reduced to the physical limit, an ultimate two-dimensional (2D) anisotropy and/or confinement effect may bring about extraordinary physical and chemical properties. Layered double hydroxides (LDHs), bearing abundant hydroxyl groups covalently bonded within 2D host layers, have been proposed as inorganic anion conductors. However, typical hydroxyl ion conductivities for bulk or lamellar LDHs, generally up to 10−3 S cm−1, are considered not high enough for practical applications. We show that single-layer LDH nanosheets exhibited exceptionally high in-plane conductivities approaching 10−1 S cm−1, which were the highest among anion conductors and comparable to proton conductivities in commercial proton exchange membranes (for example, Nafion). The in-plane conductivities were four to five orders of magnitude higher than the cross-plane or cross-membrane values of restacked LDH nanosheets. This 2D superionic transport characteristic might have great promises in a variety of applications including alkaline fuel cells and water electrolysis. PMID:28439551

  13. Anisotropic adhesion properties of triangular-tip-shaped micropillars.

    PubMed

    Kwak, Moon Kyu; Jeong, Hoon Eui; Bae, Won Gyu; Jung, Ho-Sup; Suh, Kahp Y

    2011-08-22

    Directional dry adhesive microstructures consisting of high-density triangular-tip-shaped micropillars are described. The wide-tip structures allow for unique directional shear adhesion properties with respect to the peeling direction, along with relatively high normal adhesion. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Mechanical Anisotropic and Electronic Properties of Amm2-carbon under Pressure*

    NASA Astrophysics Data System (ADS)

    Xing, Meng-Jiang; Li, Xiao-Zhen; Yu, Shao-Jun; Wang, Fu-Yan

    2017-09-01

    Structural, electronic properties and mechanical anisotropy of Amm2-carbon are investigated utilizing frist-principles calculations by Cambridge Serial Total Energy Package (CASTEP) code. The work is performed with the generalized gradient approximation in the form of Perdew–Burke–Ernzerhof (PBE), PBEsol, Wu and Cohen (WC) and local density approximation in the form of Ceperley and Alder data as parameterized by Perdew and Zunger (CA-PZ). The mechanical anisotropy calculations show that Amm2-carbon exhibit large anisotropy in elastic moduli, such as Poisson’s ratio, shear modulus and Young’s modulus, and other anisotropy factors, such as the shear anisotropic factor and the universal anisotropic index AU. It is interestingly that the anisotropy in shear modulus and Young’s modulus, universal anisotropic index and the shear anisotropic factor all increases with increasing pressure, but the anisotropy in Poisson’s ratio decreases. The band structure calculations reveal that Amm2-carbon is a direct-band-gap semiconductor at ambient pressure, but with the pressure increasing, it becomes an indirect-band-gap semiconductor.

  15. Linear and nonlinear optical properties of anisotropic quantum dots in a magnetic field

    NASA Astrophysics Data System (ADS)

    Xie, Wenfang

    2013-05-01

    We have investigated the linear and nonlinear optical properties of a two-dimensional anisotropic quantum dot in a magnetic field. Based on the computed energies and wave functions, the linear, third-order nonlinear and total optical absorption coefficients as well as the refractive index changes have been examined. The results are presented as a function of the incident photon energy for the different cases of anisotropy, dot size and external magnetic field. The results show that the linear and nonlinear optical properties of anisotropic quantum dots are strongly affected by the degree of anisotropy, the dot size, the external magnetic field and the polarized direction of the incident electromagnetic wave. The result also shows that the size effect of anisotropy quantum dots on the optical absorptions is different from that of isotropic quantum dots.

  16. Molecular Organization Induced Anisotropic Properties of Perylene - Silica Hybrid Nanoparticles.

    PubMed

    Sriramulu, Deepa; Turaga, Shuvan Prashant; Bettiol, Andrew Anthony; Valiyaveettil, Suresh

    2017-08-10

    Optically active silica nanoparticles are interesting owing to high stability and easy accessibility. Unlike previous reports on dye loaded silica particles, here we address an important question on how optical properties are dependent on the aggregation-induced segregation of perylene molecules inside and outside the silica nanoparticles. Three differentially functionalized fluorescent perylene - silica hybrid nanoparticles are prepared from appropriate ratios of perylene derivatives and tetraethyl orthosilicate (TEOS) and investigated the structure property correlation (P-ST, P-NP and P-SF). The particles differ from each other on the distribution, organization and intermolecular interaction of perylene inside or outside the silica matrix. Structure and morphology of all hybrid nanoparticles were characterized using a range of techniques such as electron microscope, optical spectroscopic measurements and thermal analysis. The organizations of perylene in three different silica nanoparticles were explored using steady-state fluorescence, fluorescence anisotropy, lifetime measurements and solid state polarized spectroscopic studies. The interactions and changes in optical properties of the silica nanoparticles in presence of different amines were tested and quantified both in solution and in vapor phase using fluorescence quenching studies. The synthesized materials can be regenerated after washing with water and reused for sensing of amines.

  17. Blow-up properties in the parabolic problems with anisotropic nonstandard growth conditions

    NASA Astrophysics Data System (ADS)

    Liu, Bingchen; Yang, Jie

    2016-03-01

    In this paper, we study the parabolic problems with anisotropic nonstandard growth nonlinearities. We first give the existence and uniqueness of weak solutions in variable Sobolev spaces. Second, we use the energy methods to show the existence of blow-up solutions with negative or positive initial energy, respectively. Both the variable exponents and the coefficients make important roles in Fujita blow-up phenomena. Moreover, asymptotic properties of the blow-up solutions are determined.

  18. The paramagnetic properties of one-dimensional spin-1 single-ion anisotropic ferromagnet

    NASA Astrophysics Data System (ADS)

    Wang, Hai-Jun; Chen, Yuan; Fu, Liang-Jie; Lin, Rui-Na; Song, Chuang-Chuang

    2009-06-01

    One-dimensional single-ion anisotropic ferromagnet with spin-1 is investigated by means of Green's function treatment in this paper. The model Hamiltonian includes a Heisenberg ferromagnetic term, an external magnetic field, and a second-order single-ion anisotropy. The magnetic properties of the system are treated by the random phase approximation for the exchange interaction term and the Anderson-Callen approximation for the anisotropy term. Our paramagnetic results are in agreement with the other theoretical results.

  19. Towards p × n transverse thermoelectrics: extreme anisotropic conduction in bulk doped semiconductor thin films via proton implantation

    NASA Astrophysics Data System (ADS)

    Tang, Yang; Koblmüller, G.; Riedl, H.; Grayson, M.

    2016-03-01

    Transverse thermoelectrics promise entirely new strategies for integrated cooling elements for optoelectronics. The recently introduced p × n-type transverse thermoelectric paradigm indicates that the most important step to engineering artificial transverse thermoelectrics is to create alternate p- and n-doped layers with orthogonally oriented anisotropic conductivity. This paper studies an approach to creating extreme anisotropic conductivity in bulk-doped semiconductor thin films via ion implantation. This approach defines an array of parallel conduction channels with photolithographic patterning of an SiO2 mask layer, followed by proton implantation. With a 10 μm channel width and 20 μm pitch, both n-type and p-type Al0.42 Ga0.58As thin films demonstrate a conductivity anisotropy ratio σ /σ⊥ > 104 at room temperature, while the longitudinal resistivity along the channel direction after implantation only increased by a factor of 3.3 ˜ 3.6. This approach can be readily adapted to other semiconductor materials for artificial p × n-type transverse thermoelectrics as other applications.

  20. Commensurability Oscillations in the Radio-Frequency Conductivity of Unidirectional Lateral Superlattices: Measurement of Anisotropic Conductivity by Coplanar Waveguide

    NASA Astrophysics Data System (ADS)

    Endo, Akira; Kajioka, Toshiyuki; Iye, Yasuhiro

    2013-05-01

    We have measured the rf magnetoconductivity of unidirectional lateral superlattices (ULSLs) by detecting the attenuation of microwave through a coplanar waveguide placed on the surface. ULSL samples with the principal axis of the modulation perpendicular (S\\bot) and parallel (S\\|) to the microwave electric field are examined. For low microwave power, we observe expected anisotropic behavior of the commensurability oscillations (CO), with CO in samples S\\bot and S\\| dominated by the diffusion and the collisional contributions, respectively. Amplitude modulation of the Shubnikov--de Haas oscillations is observed to be more prominent in sample S\\|. The difference between the two samples is washed out with the increase of the microwave power, letting the diffusion contribution govern the CO in both samples. The dominance of the diffusion contribution even in sample S\\| in the CO measured with high microwave power is interpreted in terms of large-angle electron--phonon scattering.

  1. High-aspect ratio fillers: fiber-reinforced composites and their anisotropic properties.

    PubMed

    Vallittu, Pekka K

    2015-01-01

    To present an overview of fiber-reinforced composites (FRCs) that are a group of non-metallic dental biomaterials used in several fields of dentistry. A range of relevant publications from the past half century are surveyed, with emphasis upon recent publications. FRCs vary according to the type of fiber fillers and orientation of fibers, the latter being responsible for several properties which can vary from isotropic to anisotropic. The length of the fibers, i.e. the aspect ratio of the filler, is another factor or variable that contributes to the properties and the development of new types of composite resins for restorative and prosthetic dentistry, as well as to reconstructive medicine. Understanding the anisotropic nature of FRCs from the perspective of dental applications has increased in recent years. This review describes some fiber orientation related anisotropic properties of FRCs which contribute to the increased use of FRCs in clinical dentistry. Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

  2. An inverse finite element method for determining the anisotropic properties of the cornea.

    PubMed

    Nguyen, T D; Boyce, B L

    2011-06-01

    An inverse finite element method was developed to determine the anisotropic properties of bovine cornea from an in vitro inflation experiment. The experiment used digital image correlation (DIC) to measure the three-dimensional surface geometry and displacement field of the cornea at multiple pressures. A finite element model of a bovine cornea was developed using the DIC measured surface geometry of the undeformed specimen. The model was applied to determine five parameters of an anisotropic hyperelastic model that minimized the error between the measured and computed surface displacement field and to investigate the sensitivity of the measured bovine inflation response to variations in the anisotropic properties of the cornea. The results of the parameter optimization revealed that the collagen structure of bovine cornea exhibited a high degree of anisotropy in the limbus region, which agreed with recent histological findings, and a transversely isotropic central region. The parameter study showed that the bovine corneal response to the inflation experiment was sensitive to the shear modulus of the matrix at pressures below the intraocular pressure, the properties of the collagen lamella at higher pressures, and the degree of anisotropy in the limbus region. It was not sensitive to a weak collagen anisotropy in the central region.

  3. Computational Study on Subdural Cortical Stimulation - The Influence of the Head Geometry, Anisotropic Conductivity, and Electrode Configuration

    PubMed Central

    Kim, Donghyeon; Seo, Hyeon; Kim, Hyoung-Ihl; Jun, Sung Chan

    2014-01-01

    Subdural cortical stimulation (SuCS) is a method used to inject electrical current through electrodes beneath the dura mater, and is known to be useful in treating brain disorders. However, precisely how SuCS must be applied to yield the most effective results has rarely been investigated. For this purpose, we developed a three-dimensional computational model that represents an anatomically realistic brain model including an upper chest. With this computational model, we investigated the influence of stimulation amplitudes, electrode configurations (single or paddle-array), and white matter conductivities (isotropy or anisotropy). Further, the effects of stimulation were compared with two other computational models, including an anatomically realistic brain-only model and the simplified extruded slab model representing the precentral gyrus area. The results of voltage stimulation suggested that there was a synergistic effect with the paddle-array due to the use of multiple electrodes; however, a single electrode was more efficient with current stimulation. The conventional model (simplified extruded slab) far overestimated the effects of stimulation with both voltage and current by comparison to our proposed realistic upper body model. However, the realistic upper body and full brain-only models demonstrated similar stimulation effects. In our investigation of the influence of anisotropic conductivity, model with a fixed ratio (1∶10) anisotropic conductivity yielded deeper penetration depths and larger extents of stimulation than others. However, isotropic and anisotropic models with fixed ratios (1∶2, 1∶5) yielded similar stimulation effects. Lastly, whether the reference electrode was located on the right or left chest had no substantial effects on stimulation. PMID:25229673

  4. Anisotropic compressive properties of passive porcine muscle tissue.

    PubMed

    Pietsch, Renee; Wheatley, Benjamin B; Haut Donahue, Tammy L; Gilbrech, Ryan; Prabhu, Rajkumar; Liao, Jun; Williams, Lakiesha N

    2014-11-01

    The body has approximately 434 muscles, which makes up 40-50% of the body by weight. Muscle is hierarchical in nature and organized in progressively larger units encased in connective tissue. Like many soft tissues, muscle has nonlinear visco-elastic behavior, but muscle also has unique characteristics of excitability and contractibility. Mechanical testing of muscle has been done for crash models, pressure sore models, back pain, and other disease models. The majority of previous biomechanical studies on muscle have been associated with tensile properties in the longitudinal direction as this is muscle's primary mode of operation under normal physiological conditions. Injury conditions, particularly high rate injuries, can expose muscle to multiple stress states. Compressive stresses can lead to tissue damage, which may not be reversible. In this study, we evaluate the structure-property relationships of porcine muscle tissue under compression, in both the transverse and longitudinal orientations at 0.1 s-1, 0.01 s-1, or 0.001 s-1. Our results show an initial toe region followed by an increase in stress for muscle in both the longitudinal and transverse directions tested to 50% strain. Strain rate dependency was also observed with the higher strain rates showing significantly more stress at 50% strain. Muscle in the transverse orientation was significantly stiffer than in the longitudinal orientation indicating anisotropy. The mean area of fibers in the longitudinal orientation shows an increasing mean fiber area and a decreasing mean fiber area in the transverse orientation. Data obtained in this study can help provide insight on how muscle injuries are caused, ranging from low energy strains to high rate blast events, and can also be used in developing computational injury models.

  5. Electrospun PCL nanofibers with anisotropic mechanical properties as a biomedical scaffold.

    PubMed

    Kim, Geun Hyung

    2008-06-01

    To design an ideal scaffold, various factors should be considered, such as pore size and morphology, mechanical properties versus porosity, surface properties and appropriate biodegradability. Of these factors, the importance of mechanical properties on cell growth is particularly obvious in tissues such as bone, cartilage, blood vessels, tendons and muscles. Although electrospun nanofibers provide easily applicable nano-sized structures which could be used as biomedical scaffolds, the mechanical properties are poor since an increased pore size and porosity are generally accompanied by a decrease in mechanical properties. In addition, the general electrospinning has been limited to the fabrication of a variety of anisotropic mechanical properties, which are extremely important parameters for designing a musculoskeletal system. In this study, scaffolds consisting of variously oriented nanofibers were produced using an electrospinning process modified with an auxiliary electrode and a two-axis robot collecting system. Using an auxiliary electrode, a stable Taylor cone and initial spun jets were obtained. The influence of the electrode was evaluated with electric field simulation. Using the modified electrospinning process, various directions of orientation of electrospun fibers could be acquired and the fabricated oriented nanofiber webs showed a mechanically anisotropic behavior and a higher hydrophilic property compared to randomly distributed fibrous mats.

  6. Simultaneous inversion for anisotropic and structural crustal properties by stacking of radial and transverse receiver functions

    NASA Astrophysics Data System (ADS)

    Link, Frederik; Rümpker, Georg; Kaviani, Ayoub; Singh, Manvendra

    2016-04-01

    The well-known H-κ-stacking method of Zhu and Kanamori (2000) has developed into a standard tool to infer the thickness of the crust, H, and the average P to S-wave velocity ratio, κ. The stacking approach allows for the largely automated analysis of teleseismic waveforms recorded in the distance range between 30° and 95° . Here, we present an extension of the method to include the inversion for anisotropic crustal properties. For a single anisotropic crustal layer, this involves the computation of delay times and amplitudes for 20 P-to-S converted phases and their crustal reverberations, instead of (up to) five phases in the isotropic case (Kaviani and Rümpker, 2015). The delay times and amplitudes exhibit a complex dependency on slowness and backazimuth. They can be calculated semi-analytically from the eigenvalues and eigenvectors of the system matrix, as defined by Woodhouse (1974). A comparison of the calculated delay times and amplitudes with those obtained by similar methods (Frederiksen and Bostock, 2000) shows a very good agreement between the results. In our approach, the crust exhibits hexagonal anisotropy with a horizontal symmetry axis, such that the anisotropic properties are defined by two parameters: the orientation of the symmetry axis w.r.t. North, φ, and the percentage of anisotropy, a. The inversion, thus, involves a grid search in a 4-dimensional parameter space (H, κ, φ, a) and the stacking of both radial and transverse receiver functions. Known input parameters are the average P-wave velocity of the crust, and the slowness vector (as given by the event-receiver configuration and a global 1D-velocity model). The computations are performed by the new software package AnStack which is based on MATLAB. Synthetic test show that the extended anisotropic stacking has advantages compared to the conventional H-κ stacking as it may allow for inversions at even higher noise levels. We further test for the effect of the azimuthal distribution of

  7. Anisotropic dc conductivity in stretch-oriented iodine-doped poly[3-(4-octylphenyl)-2,2script]-bithiophene

    NASA Astrophysics Data System (ADS)

    Dyreklev, P.; Inganäs, O.

    1994-12-01

    A square four-point probe is constructed to measure anisotropic conductivity of small samples. The method is applied to measurements of the anisotropic conductivity of a conjugated polymer. The polymer poly[3-(4-octylphenyl)-2,2'-bithiophene] is stretch oriented to various elongations and doped with I2 vapor. The conductivity anisotropy is dependent on the degree of orientation and the absolute conductivity. An anisotropy value of 2.4 is obtained for an elongation of four times. For a given elongation the conductivity anisotropy decreases during the spontaneous undoping. The experimental results are discussed in terms of varying charge hopping distances.

  8. Mechanical, Anisotropic, and Electronic Properties of XN (X = C, Si, Ge): Theoretical Investigations.

    PubMed

    Ma, Zhenyang; Liu, Xuhong; Yu, Xinhai; Shi, Chunlei; Wang, Dayun

    2017-08-08

    The structural, mechanical, elastic anisotropic, and electronic properties of Pbca-XN (X = C, Si, Ge) are investigated in this work using the Perdew-Burke-Ernzerhof (PBE) functional, Perdew-Burke-Ernzerhof for solids (PBEsol) functional, and Ceperly and Alder, parameterized by Perdew and Zunger (CA-PZ) functional in the framework of density functional theory. The achieved results for the lattice parameters and band gap of Pbca-CN with the PBE functional in this research are in good accordance with other theoretical results. The band structures of Pbca-XN (X = C, Si, Ge) show that Pbca-SiN and Pbca-GeN are both direct band gap semiconductor materials with a band gap of 3.39 eV and 2.22 eV, respectively. Pbca-XN (X = C, Si, Ge) exhibits varying degrees of mechanical anisotropic properties with respect to the Poisson's ratio, bulk modulus, shear modulus, Young's modulus, and universal anisotropic index. The (001) plane and (010) plane of Pbca-CN/SiN/GeN both exhibit greater elastic anisotropy in the bulk modulus and Young's modulus than the (100) plane.

  9. Dielectric Properties of Aligned Conducting Polymers

    DTIC Science & Technology

    1991-10-01

    It has been demonstrated that aligned polyacetylene and polyaniline possess remarkably enhanced conductivities. The increase in crystallinity and...and thermal stability compared to other CPs such as polyacetylenes, polythiophenes, and polyaniline . These favorable properties and the commercial...stretch-orientation of BF4- doped PPy films electrochemically deposited at -30,C, 7 pyrrole electropolymerization at a xylene/water interface, 8 and

  10. Anisotropic physical properties of myocardium characterized by ultrasonic measurements of backscatter, attenuation, and velocity

    NASA Astrophysics Data System (ADS)

    Baldwin, Steven L.

    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.

  11. Black Arsenic-Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties

    NASA Astrophysics Data System (ADS)

    Liu, Bilu; Zhou, Chongwu

    2D layered materials with diverse properties have attracted significant interest in the past decade. The layered materials discovered so far have covered a wide, yet discontinuous electromagnetic spectral range from semimetallic graphene, insulating boron nitride, to semiconductors with bandgaps from middle infrared to visible light. Here, we introduce new layered semiconductors, black arsenic-phosphorus (b-AsP), with highly tunable chemical compositions and electronic and optical properties. Transport and infrared absorption studies demonstrate the semiconducting nature of b-AsP with tunable bandgaps, ranging from 0.3 to 0.15 eV. These bandgaps fall into long-wavelength infrared (LWIR) regime and cannot be readily reached by other layered materials. Moreover, polarization-resolved infrared absorption and Raman studies reveal in-plane anisotropic properties of b-AsP. This family of layered b-AsP materials extend the electromagnetic spectra covered by 2D layered materials to the LWIR regime, and may find unique applications for future all 2D layered material based devices. Ref. Liu, B., et al., Black Arsenic-Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties. Adv. Mater., 2015, 27, 4423-4429.

  12. Anisotropic Effective Mass, Optical Property, and Enhanced Band Gap in BN/Phosphorene/BN Heterostructures.

    PubMed

    Hu, Tao; Hong, Jisang

    2015-10-28

    Phosphorene is receiving great research interests because of its peculiar physical properties. Nonetheless, the phosphorus has a trouble of degradation due to oxidation. Hereby, we propose that the electrical and optical anisotropic properties can be preserved by encapsulating into hexagonal boron nitride (h-BN). We found that the h-BN contributed to enhancing the band gap of the phosphorene layer. Comparing the band gap of the pristine phosphorene layer, the band gap of the phosphorene/BN(1ML) system was enhanced by 0.15 eV. It was further enhanced by 0.31 eV in the BN(1ML)/phosphorene/BN(1ML) trilayer structure. However, the band gap was not further enhanced when we increased the thickness of the h-BN layers even up to 4 MLs. Interestingly, the anisotropic effective mass and optical property were still preserved in BN/phosphorene/BN heterostructures. Overall, we predict that the capping of phosphorene by the h-BN layers can be an excellent solution to protect the intrinsic properties of the phosphorene.

  13. Mesoscale Effective Property Simulations Incorporating Conductive Binder

    DOE PAGES

    Trembacki, Bradley L.; Noble, David R.; Brunini, Victor E.; ...

    2017-07-26

    Lithium-ion battery electrodes are composed of active material particles, binder, and conductive additives that form an electrolyte-filled porous particle composite. The mesoscale (particle-scale) interplay of electrochemistry, mechanical deformation, and transport through this tortuous multi-component network dictates the performance of a battery at the cell-level. Effective electrode properties connect mesoscale phenomena with computationally feasible battery-scale simulations. We utilize published tomography data to reconstruct a large subsection (1000+ particles) of an NMC333 cathode into a computational mesh and extract electrode-scale effective properties from finite element continuum-scale simulations. We present a novel method to preferentially place a composite binder phase throughout the mesostructure,more » a necessary approach due difficulty distinguishing between non-active phases in tomographic data. We compare stress generation and effective thermal, electrical, and ionic conductivities across several binder placement approaches. Isotropic lithiation-dependent mechanical swelling of the NMC particles and the consideration of strain-dependent composite binder conductivity significantly impact the resulting effective property trends and stresses generated. Lastly, our results suggest that composite binder location significantly affects mesoscale behavior, indicating that a binder coating on active particles is not sufficient and that more accurate approaches should be used when calculating effective properties that will inform battery-scale models in this inherently multi-scale battery simulation challenge.« less

  14. Anisotropic dielectric properties of two-dimensional matrix in pseudo-spin ferroelectric system

    NASA Astrophysics Data System (ADS)

    Kim, Se-Hun

    2016-10-01

    The anisotropic dielectric properties of a two-dimensional (2D) ferroelectric system were studied using the statistical calculation of the pseudo-spin Ising Hamiltonian model. It is necessary to delay the time for measurements of the observable and the independence of the new spin configuration under Monte Carlo sampling, in which the thermal equilibrium state depends on the temperature and size of the system. The autocorrelation time constants of the normalized relaxation function were determined by taking temperature and 2D lattice size into account. We discuss the dielectric constants of a two-dimensional ferroelectric system by using the Metropolis method in view of the Slater-Takagi defect energies.

  15. Realistic Electric Field Mapping of Anisotropic Muscle During Electrical Stimulation Using a Combination of Water Diffusion Tensor and Electrical Conductivity.

    PubMed

    Choi, Bup Kyung; Oh, Tong In; Sajib, Saurav Zk; Kim, Jin Woong; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

    2017-04-01

    To realistically map the electric fields of biological tissues using a diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) method to estimate tissue response during electrical stimulation. Imaging experiments were performed using chunks of bovine muscle. Two silver wire electrodes were positioned inside the muscle tissue for electrical stimulation. Electric pulses were applied with a 100-V amplitude and 100-μs width using a voltage stimulator. During electrical stimulation, we collected DT-MREIT data from a 3T magnetic resonance imaging scanner. We adopted the projected current density method to calculate the electric field. Based on the relation between the water diffusion tensor and the conductivity tensor, we computed the position-dependent scale factor using the measured magnetic flux density data. Then, a final conductivity tensor map was reconstructed using the multiplication of the water diffusion tensor and the scale factor. The current density images from DT-MREIT data represent the internal current flows that exist not only in the electrodes but also in surrounding regions. The reconstructed electric filed map from our anisotropic conductivity tensor with the projected current density shows coverage that is more than 2 times as wide, and higher signals in both the electrodes and surrounding tissues, than the previous isotropic method owing to the consideration of tissue anisotropy. An electric field map obtained by an anisotropic reconstruction method showed different patterns from the results of the previous isotropic reconstruction method. Since accurate electric field mapping is important to correctly estimate the coverage of the electrical treatment, future studies should include more rigorous validations of the new method through in vivo and in situ experiments.

  16. Realistic Electric Field Mapping of Anisotropic Muscle During Electrical Stimulation Using a Combination of Water Diffusion Tensor and Electrical Conductivity

    PubMed Central

    2017-01-01

    Purpose To realistically map the electric fields of biological tissues using a diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) method to estimate tissue response during electrical stimulation. Methods Imaging experiments were performed using chunks of bovine muscle. Two silver wire electrodes were positioned inside the muscle tissue for electrical stimulation. Electric pulses were applied with a 100-V amplitude and 100-μs width using a voltage stimulator. During electrical stimulation, we collected DT-MREIT data from a 3T magnetic resonance imaging scanner. We adopted the projected current density method to calculate the electric field. Based on the relation between the water diffusion tensor and the conductivity tensor, we computed the position-dependent scale factor using the measured magnetic flux density data. Then, a final conductivity tensor map was reconstructed using the multiplication of the water diffusion tensor and the scale factor. Results The current density images from DT-MREIT data represent the internal current flows that exist not only in the electrodes but also in surrounding regions. The reconstructed electric filed map from our anisotropic conductivity tensor with the projected current density shows coverage that is more than 2 times as wide, and higher signals in both the electrodes and surrounding tissues, than the previous isotropic method owing to the consideration of tissue anisotropy. Conclusions An electric field map obtained by an anisotropic reconstruction method showed different patterns from the results of the previous isotropic reconstruction method. Since accurate electric field mapping is important to correctly estimate the coverage of the electrical treatment, future studies should include more rigorous validations of the new method through in vivo and in situ experiments. PMID:28446015

  17. Stability of grain boundary texture during isothermal grain growth in UO2 considering anisotropic grain boundary properties

    NASA Astrophysics Data System (ADS)

    Hallberg, Håkan; Zhu, Yaochan

    2015-10-01

    In the present study, mesoscale simulations of grain growth in UO2 are performed using a 2D level set representation of the polycrystal grain boundary network, employed in a finite element setting. Anisotropic grain boundary properties are considered by evaluating how grain boundary energy and mobility varies with local grain boundary character. This is achieved by considering different formulations of the anisotropy of grain boundary properties, for example in terms of coincidence site lattice (CSL) correspondence. Such modeling approaches allow tracing of the stability of a number of characteristic low-Σ boundaries in the material during grain growth. The present simulations indicate that anisotropic grain boundary properties have negligible influence on the grain growth rate. However, considering the evolution of grain boundary character distribution and the grain size distribution, it is found that neglecting anisotropic boundary properties will strongly bias predictions obtained from numerical simulations.

  18. Properties of conductive thick-film inks

    NASA Technical Reports Server (NTRS)

    Holtze, R. F.

    1972-01-01

    Ten different conductive inks used in the fabrication of thick-film circuits were evaluated for their physical and handling properties. Viscosity, solid contents, and spectrographic analysis of the unfired inks were determined. Inks were screened on ceramic substrates and fired for varying times at specified temperatures. Selected substrates were given additional firings to simulate the heat exposure received if thick-film resistors were to be added to the same substrate. Data are presented covering the (1) printing characteristics, (2) solderability using Sn-63 and also a 4 percent silver solder, (3) leach resistance, (4) solder adhesion, and (5) wire bonding properties. Results obtained using different firing schedules were compared. A comparison was made between the various inks showing general results obtained for each ink. The changes in firing time or the application of a simulated resistor firing had little effect on the properties of most inks.

  19. The thermal instability in a sheared magnetic field - Filament condensation with anisotropic heat conduction. [solar physics

    NASA Technical Reports Server (NTRS)

    Van Hoven, G.; Mok, Y.

    1984-01-01

    The condensation-mode growth rate of the thermal instability in an empirically motivated sheared field is shown to depend upon the existence of perpendicular thermal conduction. This typically very small effect (perpendicular conductivity/parallel conductivity less than about 10 to the -10th for the solar corona) increases the spatial-derivative order of the compressible temperature-perturbation equation, and thereby eliminates the singularities which appear when perpendicular conductivity = 0. The resulting growth rate is less than 1.5 times the controlling constant-density radiation rate, and has a clear maximum at a cross-field length of order 100 times and a width of about 0.1 the magnetic shear scale for solar conditions. The profiles of the observable temperature and density perturbations are independent of the thermal conductivity, and thus agree with those found previously. An analytic solution to the short-wavelength incompressible case is also given.

  20. Characterization of anisotropic acoustic metamaterial slabs

    NASA Astrophysics Data System (ADS)

    Park, Jun Hyeong; Lee, Hyung Jin; Kim, Yoon Young

    2016-01-01

    In an anisotropic acoustic metamaterial, the off-diagonal components of its effective mass density tensor should be considered in order to describe the anisotropic behavior produced by arbitrarily shaped inclusions. However, few studies have been carried out to characterize anisotropic acoustic metamaterials. In this paper, we propose a method that uses the non-diagonal effective mass density tensor to determine the behavior of anisotropic acoustic metamaterials. Our method accurately evaluates the effective properties of anisotropic acoustic metamaterials by separately dealing with slabs made of single and multiple unit cells along the thickness direction. To determine the effective properties, the reflection and transmission coefficients of an acoustic metamaterial slab are calculated, and then the wave vectors inside of the slab are determined using these coefficients. The effective material properties are finally determined by utilizing the spatial dispersion relation of the anisotropic acoustic metamaterial. Since the dispersion relation of an anisotropic acoustic metamaterial is explicitly used, its effective properties can be easily determined by only using a limited number of normal and oblique plane wave incidences into a metamaterial slab, unlike existing approaches requiring a large number of wave incidences. The validity of the proposed method is verified by conducting wave simulations for anisotropic acoustic metamaterial slabs with Z-shaped elastic inclusions of tilted principal material axes.

  1. Highly Anisotropic intrinsic electronic transport properties of monolayer and bilayer phosphorene from first principles1

    NASA Astrophysics Data System (ADS)

    Jin, Zhenghe; Mullen, Jeffrey; Kim, Ki Wook

    We present an analysis of the electron(hole)-phonon scattering in monolayer and bilayer phosphorene using first principles. Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) are used to calculate the scattering matrix elements and full band Monte Carlo carrier transport simulation is employed to obtain the intrinsic electron/hole mobility. Room temperature mobility and saturation velocity in monolayer and bilayer phosphorene are extracted and significant layer number dependence in the mobility is revealed which results from the carrier-phonon interaction matrix elements. The transport properties are also varied with the crystal orientation with anisotropy mobility mostly attributed to the anisotropic band structure and effective masses. Our calculation reveals monolayer phosphorene has anisotropic hole transport property with the room temperature mobility in the armchair direction (458 cm2/Vs) about five times larger than in the zigzag direction (90 cm2/Vs). For bilayer phosphorene, the mobility on both directions increases to 1610 cm2/Vs and 760 cm2/Vs along armchair and zigzag direction respectively. The increased mobility in bilayer is consistent with the experiments which revealed low field mobility of over one thousand in multiple layer phosphorene structure, which provides optimal material for channel in field-effect transistor and a good opportunity for high-performance p-type device. 1This work was supported, in part, by SRC/NRI SWAN.

  2. Imaging Anisotropic Elastic Properties of an Orthotropic Paper Sheet Using Photorefractive Dynamic Holography

    SciTech Connect

    Telschow, Kenneth Louis; Deason, Vance Albert

    2002-12-01

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

  3. On the Anisotropic Mechanical Properties of Selective Laser-Melted Stainless Steel.

    PubMed

    Hitzler, Leonhard; Hirsch, Johann; Heine, Burkhard; Merkel, Markus; Hall, Wayne; Öchsner, Andreas

    2017-09-26

    The thorough description of the peculiarities of additively manufactured (AM) structures represents a current challenge for aspiring freeform fabrication methods, such as selective laser melting (SLM). These methods have an immense advantage in the fast fabrication (no special tooling or moulds required) of components, geometrical flexibility in their design, and efficiency when only small quantities are required. However, designs demand precise knowledge of the material properties, which in the case of additively manufactured structures are anisotropic and, under certain circumstances, inhomogeneous in nature. Furthermore, these characteristics are highly dependent on the fabrication settings. In this study, the anisotropic tensile properties of selective laser-melted stainless steel (1.4404, 316L) are investigated: the Young's modulus ranged from 148 to 227 GPa, the ultimate tensile strength from 512 to 699 MPa, and the breaking elongation ranged, respectively, from 12% to 43%. The results were compared to related studies in order to classify the influence of the fabrication settings. Furthermore, the influence of the chosen raw material was addressed by comparing deviations on the directional dependencies reasoned from differing microstructural developments during manufacture. Stainless steel was found to possess its maximum strength at a 45° layer versus loading offset, which is precisely where AlSi10Mg was previously reported to be at its weakest.

  4. Nanostructured SnS with inherent anisotropic optical properties for high photoactivity

    NASA Astrophysics Data System (ADS)

    Patel, Malkeshkumar; Chavda, Arvind; Mukhopadhyay, Indrajit; Kim, Joondong; Ray, Abhijit

    2016-01-01

    In view of the worldwide energy challenge in the 21st century, the technology of semiconductor-based photoelectrochemical (PEC) water splitting has received considerable attention as an alternative approach for solar energy harvesting and storage. Two-dimensional (2D) structures such as nanosheets have the potential to tap the solar energy by unlocking the functional properties at the nanoscale. Tin(ii) sulfide is a fascinating solar energy material due to its anisotropic material properties. In this manuscript, we report on exploiting the 2D structure modulated optical properties of nanocrystalline SnS thin film synthesized by chemical spray pyrolysis using ambient transport in the harvesting of solar energy. We obtained the nanostructured SnS with well-preserved dimensions and morphologies with one step processing. The work demonstrates that the intrinsically ordered SnS nanostructure on FTO coated glass can tap the incident radiation in an efficient manner. The structure-property relationship to explain the photo-response in nanocrystalline-SnS is verified experimentally and theoretically. The novel design scheme for antireflection coating along with the anisotropic properties of SnS is conceived for realizing a PEC cell. The developed PEC cell consists of a SnS photoanode which shows considerably high photocurrent density of 7 mA cm-2 with aqueous media under AM 1.5G, 100 mW cm-2 exposure with notably stable operation. Electrochemical impedance spectroscopy revealed that a non-ideal capacitive behavior as well as drift assisted transport across the solid-state interface is responsible for such a high photo-current density in the nanocrystalline-SnS photoanode.In view of the worldwide energy challenge in the 21st century, the technology of semiconductor-based photoelectrochemical (PEC) water splitting has received considerable attention as an alternative approach for solar energy harvesting and storage. Two-dimensional (2D) structures such as nanosheets have the

  5. Conduction Properties Of Decellularized Nerve Biomaterials

    PubMed Central

    Urbanchek, M.G.; Shim, B.S.; Baghmanli, Z.; Wei, B.; Schroeder, K.; Langhals, N.B.; Miriani, R.M.; Egeland, B.M.; Kipke, D.R.; Martin, D.C.; Cederna, P.S.

    2011-01-01

    The purpose of this study is to optimize poly(3,4,-ethylenedioxythiophene) (PEDOT) polymerization into decellular nerve scaffolding for interfacing to peripheral nerves. Our ultimate aim is to permanently implant highly conductive peripheral nerve interfaces between amputee, stump, nerve fascicles and prosthetic electronics. Decellular nerve (DN) scaffolds are an FDA approved biomaterial (Axogen ) with the flexible tensile properties needed for successful permanent coaptation to peripheral nerves. Biocompatible, electroconductive, PEDOT facilitates electrical conduction through PEDOT coated acellular muscle. New electrochemical methods were used to polymerize various PEDOT concentrations into DN scaffolds without the need for a final dehydration step. DN scaffolds were then tested for electrical impedance and charge density. PEDOT coated DN scaffold materials were also implanted as 15–20mm peripheral nerve grafts. Measurement of in-situ nerve conduction immediately followed grafting. DN showed significant improvements in impedance for dehydrated and hydrated, DN, polymerized with moderate and low PEDOT concentrations when they were compared with DN alone (a ≤ 0.05). These measurements were equivalent to those for DN with maximal PEDOT concentrations. In-situ, nerve conduction measurements demonstrated that DN alone is a poor electro-conductor while the addition of PEDOT allows DN scaffold grafts to compare favorably with the “gold standard”, autograft (Table 1). Surgical handling characteristics for conductive hydrated PEDOT DN scaffolds were rated 3 (pliable) while the dehydrated models were rated 1 (very stiff) when compared with autograft ratings of 4 (normal). Low concentrations of PEDOT on DN scaffolds provided significant increases in electro active properties which were comparable to the densest PEDOT coatings. DN pliability was closely maintained by continued hydration during PEDOT electrochemical polymerization without compromising

  6. Research of the electrical anisotropic characteristics of water-conducting fractured zones in coal seams

    NASA Astrophysics Data System (ADS)

    Su, Ben-Yu; Yue, Jian-Hua

    2017-06-01

    Water flooding disasters are one of the five natural coal-mining disasters that threaten the lives of coal miners. The main causes of this flooding are water-conducting fractured zones within coal seams. However, when resistivity methods are used to detect water-conducting fractured zones in coal seams, incorrect conclusions can be drawn because of electrical anisotropy within the water-conducting fractured zones. We present, in this paper, a new geo-electrical model based on the geology of water-conducting fractured zones in coal seams. Factors that influence electrical anisotropy were analyzed, including formation water resistivity, porosity, fracture density, and fracture surface roughness, pressure, and dip angle. Numerical simulation was used to evaluate the proposed electrical method. The results demonstrate a closed relationship between the shape of apparent resistivity and the strike and dip of a fracture. Hence, the findings of this paper provide a practical resistivity method for coal-mining production.

  7. Tunneling conductivity in anisotropic nanofiber composites: a percolation-based model.

    PubMed

    Chatterjee, Avik P; Grimaldi, Claudio

    2015-04-15

    The critical path approximation ('CPA') is integrated with a lattice-based approach to percolation to provide a model for conductivity in nanofiber-based composites. Our treatment incorporates a recent estimate for the anisotropy in tunneling-based conductance as a function of the relative angle between the axes of elongated nanoparticles. The conductivity is examined as a function of the volume fraction, degree of clustering, and of the mean value and standard deviation of the orientational order parameter. Results from our calculations suggest that the conductivity can depend strongly upon the standard deviation in the orientational order parameter even when all the other variables (including the mean value of the order parameter 〈S〉) are held invariant.

  8. Experimental evaluation of electrical conductivity imaging of anisotropic brain tissues using a combination of diffusion tensor imaging and magnetic resonance electrical impedance tomography

    NASA Astrophysics Data System (ADS)

    Sajib, Saurav Z. K.; Jeong, Woo Chul; Kyung, Eun Jung; Kim, Hyun Bum; Oh, Tong In; Kim, Hyung Joong; Kwon, Oh In; Woo, Eung Je

    2016-06-01

    Anisotropy of biological tissues is a low-frequency phenomenon that is associated with the function and structure of cell membranes. Imaging of anisotropic conductivity has potential for the analysis of interactions between electromagnetic fields and biological systems, such as the prediction of current pathways in electrical stimulation therapy. To improve application to the clinical environment, precise approaches are required to understand the exact responses inside the human body subjected to the stimulated currents. In this study, we experimentally evaluate the anisotropic conductivity tensor distribution of canine brain tissues, using a recently developed diffusion tensor-magnetic resonance electrical impedance tomography method. At low frequency, electrical conductivity of the biological tissues can be expressed as a product of the mobility and concentration of ions in the extracellular space. From diffusion tensor images of the brain, we can obtain directional information on diffusive movements of water molecules, which correspond to the mobility of ions. The position dependent scale factor, which provides information on ion concentration, was successfully calculated from the magnetic flux density, to obtain the equivalent conductivity tensor. By combining the information from both techniques, we can finally reconstruct the anisotropic conductivity tensor images of brain tissues. The reconstructed conductivity images better demonstrate the enhanced signal intensity in strongly anisotropic brain regions, compared with those resulting from previous methods using a global scale factor.

  9. Experimental evaluation of electrical conductivity imaging of anisotropic brain tissues using a combination of diffusion tensor imaging and magnetic resonance electrical impedance tomography

    SciTech Connect

    Sajib, Saurav Z. K.; Jeong, Woo Chul; Oh, Tong In; Kim, Hyung Joong E-mail: ejwoo@khu.ac.kr; Woo, Eung Je E-mail: ejwoo@khu.ac.kr; Kyung, Eun Jung; Kim, Hyun Bum; Kwon, Oh In

    2016-06-15

    Anisotropy of biological tissues is a low-frequency phenomenon that is associated with the function and structure of cell membranes. Imaging of anisotropic conductivity has potential for the analysis of interactions between electromagnetic fields and biological systems, such as the prediction of current pathways in electrical stimulation therapy. To improve application to the clinical environment, precise approaches are required to understand the exact responses inside the human body subjected to the stimulated currents. In this study, we experimentally evaluate the anisotropic conductivity tensor distribution of canine brain tissues, using a recently developed diffusion tensor-magnetic resonance electrical impedance tomography method. At low frequency, electrical conductivity of the biological tissues can be expressed as a product of the mobility and concentration of ions in the extracellular space. From diffusion tensor images of the brain, we can obtain directional information on diffusive movements of water molecules, which correspond to the mobility of ions. The position dependent scale factor, which provides information on ion concentration, was successfully calculated from the magnetic flux density, to obtain the equivalent conductivity tensor. By combining the information from both techniques, we can finally reconstruct the anisotropic conductivity tensor images of brain tissues. The reconstructed conductivity images better demonstrate the enhanced signal intensity in strongly anisotropic brain regions, compared with those resulting from previous methods using a global scale factor.

  10. Impact of magnetic properties on the Casimir torque between anisotropic metamaterial plates

    SciTech Connect

    Deng Gang; Liu Zhongzhu; Luo Jun

    2009-12-15

    The quantized surface mode technique is used to calculate the Casimir torque between two parallel anisotropic metamaterial plates with in-plane optical axes, and our main concern is focused on the impact of the magnetic properties of the plates on the Casimir torque. Our result shows that at small separation, the Casimir torque between the two plates with frequency dependent permeabilities is larger than that between two nonmagnetic plates, while at large separation it is smaller. This can be explained as a result of the impact of both magnetic properties and material dispersion of the plates. The impact of the Drude background in connected metallic metamaterial is also discussed. These phenomena provide us with new understanding about the Casimir effect and show great potential in application.

  11. Anisotropic Poly(Vinyl Alcohol) Hydrogel: Connection Between Structure and Bulk Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Hudson, Stephen; Hutter, Jeffrey; Millon, Leonardo; Wan, Wankei; Nieh, Mu-Ping

    2009-03-01

    Poly(vinyl alcohol) (PVA) hydrogels are formed from PVA solution by creation of physical cross-links during freeze/thaw cycling. By choosing a suitable freeze/thaw protocol and applying a strain during thermal processing, gels with permanent, anisotropic bulk mechanical properties matching those of cardiovascular tissues can be made, making them useful for applications ranging from artificial heart valves to vascular grafts. We have performed small- and ultra small-angle neutron scattering (SANS and USANS) measurements covering length scales from 2 nm to 10 μm, and modeled the structure as interconnected PVA blobs of size 20 to 50 nm arranged in fractal aggregates extending to at least 10 μm. Here, we discuss the relationship between the microstructure and bulk mechanical properties. Strength increases with the number of thermal cycles due to reinforcement of the small-scale gel phase, while anisotropy is due to elongation of the much larger fractal aggregates.

  12. Dispersion properties of transverse anisotropic liquid crystal core photonic crystal fibers

    NASA Astrophysics Data System (ADS)

    Karasawa, Naoki

    2016-04-01

    The dispersion properties of liquid crystal core photonic crystal fibers for different core diameters have been calculated by a full vectorial finite difference method. In calculations, air holes are assumed to be arranged in a regular hexagonal array in fused silica and a central hole is filled with liquid crystal to create a core. In this study, three types of transverse anisotropic configurations, where liquid crystal molecules are oriented in a transverse plane, and a planar configuration, where liquid crystal molecules are oriented in a propagation direction, are considered. The large changes of the dispersion properties are found when the orientation of the liquid crystal molecules is changed from a planar configuration to a uniform configuration, where all molecules are oriented in the same direction in a transverse plane. Since the orientation of liquid crystal molecules may be controlled by applying an electric field, it could be utilized for various applications including the spectral control of supercontinuum generation.

  13. Anisotropic mechanical properties of the MA956 ODS steel characterized by the small punch testing technique

    NASA Astrophysics Data System (ADS)

    Turba, K.; Hurst, R. C.; Hähner, P.

    2012-09-01

    The small punch testing technique was used to assess both creep and fracture properties of the MA956 oxide dispersion strengthened ferritic steel. The anisotropy in mechanical properties was addressed, as well as the alloy's susceptibility to thermal embrittlement. Strong anisotropy was found in the material's creep resistance at 725 °C for longer rupture times. Anisotropic behavior was also observed for the ductile-brittle transition temperature (DBTT). The origin of the anisotropy can be related to the strongly directional microstructure which enables a large amount of intergranular cracking during straining at both high and low temperatures. The DBTT of the alloy is very high, and can be further increased by at least 200 °C after 1000 h of ageing at 475 °C, due to the formation of the Cr-rich α' phase. The particularly high susceptibility of the MA956 to thermal embrittlement is mainly a consequence of its high chromium content.

  14. A study of phonon anisotropic scattering effect on silicon thermal conductivity at nanoscale

    SciTech Connect

    Bong, Victor N-S; Wong, Basil T.

    2015-08-28

    Previous studies have shown that anisotropy in phonon transport exist because of the difference in phonon dispersion relation due to different lattice direction, as observed by a difference in in-plane and cross-plane thermal conductivity. The directional preference (such as forward or backward scattering) in phonon propagation however, remains a relatively unexplored frontier. Our current work adopts a simple scattering probability in radiative transfer, which is called Henyey and Greenstein probability density function, and incorporates it into the phonon Monte Carlo simulation to investigate the effect of directional scattering in phonon transport. In this work, the effect of applying the anisotropy scattering is discussed, as well as its impact on the simulated thermal conductivity of silicon thin films. While the forward and backward scattering will increase and decrease thermal conductivity respectively, the extent of the effect is non-linear such that forward scattering has a more obvious effect than backward scattering.

  15. Anisotropic Magnetoresistance of Nano-conductive Filament in Co/HfO2/Pt Resistive Switching Memory

    NASA Astrophysics Data System (ADS)

    Li, Leilei; Liu, Yang; Teng, Jiao; Long, Shibing; Guo, Qixun; Zhang, Meiyun; Wu, Yu; Yu, Guanghua; Liu, Qi; Lv, Hangbing; Liu, Ming

    2017-03-01

    Conductive bridge random access memory (CBRAM) has been extensively studied as a next-generation non-volatile memory. The conductive filament (CF) shows rich physical effects such as conductance quantization and magnetic effect. But so far, the study of filaments is not very sufficient. In this work, Co/HfO2/Pt CBRAM device with magnetic CF was designed and fabricated. By electrical manipulation with a partial-RESET method, we controlled the size of ferromagnetic metal filament. The resistance-temperature characteristics of the ON-state after various partial-RESET behaviors have been studied. Using two kinds of magnetic measurement methods, we measured the anisotropic magnetoresistance (AMR) of the CF at different temperatures to reflect the magnetic structure characteristics. By rotating the direction of the magnetic field and by sweeping the magnitude, we obtained the spatial direction as well as the easy-axis of the CF. The results indicate that the easy-axis of the CF is along the direction perpendicular to the top electrode plane. The maximum magnetoresistance was found to appear when the angle between the direction of magnetic field and that of the electric current in the CF is about 30°, and this angle varies slightly with temperature, indicating that the current is tilted.

  16. Anisotropic conductivity and charge ordering in (TMTTF)2X salts probed by ESR

    NASA Astrophysics Data System (ADS)

    Coulon, Claude; Lalet, Grégory; Pouget, Jean Paul; Foury-Leylekian, Pascale; Moradpour, Alec; Fabre, Jean Marc

    2007-08-01

    Single crystal ESR data on (TMTTF)2X salts are presented. Taking advantage of the large dimensions of the crystals, skin effect is studied through the asymmetry of the ESR resonance lines. When the microwave magnetic field is perpendicular to the stacking axis, a very rich temperature dependence of this asymmetry is found although the three components of the conductivity tensor often exhibit a semiconducting behavior. In particular, we show that anomalies are present when the TMTTF chains experience a Mott localization or a charge ordering. The whole set of data is discussed theoretically in relation with the anisotropy of the electrical conductivity. We show that the crystal orientation and crystal shape are crucial parameters in explaining the experimental results. More precisely, we found that at the charge ordering transition, the largest conductivity anomaly occurs along the transverse b direction, and we provide evidence, through ESR measurements of the conductivity in this direction, of a charge ordering transition at about 50K in (TMTTF)2Br . With the same method, we also show that irradiation kills the charge ordering transition, while deuteration enhances its critical temperature.

  17. Highly anisotropic conductivity of tablets pressed from polyaniline-montmorillonite nanocomposite

    SciTech Connect

    Tokarský, Jonáš

    2016-03-15

    Highlights: • Montmorillonite (MMT) can be intercalated with polyaniline (PANI) chains. • Tablets pressed from PANI/MMT exhibit high anisotropy in electrical conductivity. • Pressure 28MPa is sufficient to reach the anisotropy. • Tablets pressed from pure PANI also exhibit anisotropy in electrical conductivity. - Abstract: Polyaniline-montmorillonite nanocomposite was prepared from anilinium sulfate (precursor) and ammonium peroxodisulfate (oxidizing agent) using simple one-step method. The resulting nanocomposite obtained in powder form has been pressed into tablets using various compression pressures (28–400 MPa). Electrical conductivities of tablets in two perpendicular directions, i.e. direction parallel with the main surface of tablet (σ=) and in orthogonal direction (σ⊥), and corresponding anisotropy factors (i.e., the ratio σ=/σ⊥) have been studied in dependence on compression pressure used during the preparation. Polyaniline-montmorillonite nanocomposite was characterized using X-ray diffraction analysis, raman spectroscopy, transmission electron microscopy, thermogravimetric analysis and molecular modeling which led to the understanding of the internal structure. Measurement of hardness performed on pressed tablets has been also involved. Taking into account the highest value of anisotropy factor reached (σ=/σ⊥ = 490), present study shows a chance to design conductors with nearly two-dimensional conductivity.

  18. Anisotropic Lithium Ion Conductivity in Single-Ion Diblock Copolymer Electrolyte Thin Films.

    PubMed

    Aissou, Karim; Mumtaz, Muhammad; Usluer, Özlem; Pécastaings, Gilles; Portale, Giuseppe; Fleury, Guillaume; Cloutet, Eric; Hadziioannou, Georges

    2016-02-01

    Well-defined single-ion diblock copolymers consisting of a Li-ion conductive poly(styrenesulfonyllithium(trifluoromethylsulfonyl)imide) (PSLiTFSI) block associated with a glassy polystyrene (PS) block have been synthesized via reversible addition fragmentation chain transfer polymerization. Conductivity anisotropy ratio up to 1000 has been achieved from PS-b-PSLiTFSI thin films by comparing Li-ion conductivities of out-of-plane (aligned) and in-plane (antialigned) cylinder morphologies at 40 °C. Blending of PS-b-PSLiTFSI thin films with poly(ethylene oxide) homopolymer (hPEO) enables a substantial improvement of Li-ion transport within aligned cylindrical domains, since hPEO, preferentially located in PSLiTFSI domains, is an excellent lithium-solvating material. Results are also compared with unblended and blended PSLiTFSI homopolymer (hPSLiTFSI) homologues, which reveals that ionic conductivity is improved when thin films are nanostructured. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Time-domain thermoreflectance (TDTR) measurements of anisotropic thermal conductivity using a variable spot size approach

    NASA Astrophysics Data System (ADS)

    Jiang, Puqing; Qian, Xin; Yang, Ronggui

    2017-07-01

    It is challenging to characterize thermal conductivity of materials with strong anisotropy. In this work, we extend the time-domain thermoreflectance (TDTR) method with a variable spot size approach to simultaneously measure the in-plane (Kr) and the through-plane (Kz) thermal conductivity of materials with strong anisotropy. We first determine Kz from the measurement using a larger spot size, when the heat flow is mainly one-dimensional along the through-plane direction, and the measured signals are only sensitive to Kz. We then extract the in-plane thermal conductivity Kr from a second measurement using the same modulation frequency but with a smaller spot size, when the heat flow becomes three-dimensional, and the signal is sensitive to both Kr and Kz. By choosing the same modulation frequency for the two sets of measurements, we can avoid potential artifacts introduced by the frequency-dependent Kz, which we have found to be non-negligible, especially for some two-dimensional layered materials like MoS2. After careful evaluation of the sensitivity of a series of hypothetical samples, we provided guidelines on choosing the most appropriate laser spot size and modulation frequency that yield the smallest uncertainty, and established a criterion for the range of thermal conductivity that can be measured reliably using our proposed variable spot size TDTR approach. We have demonstrated this variable spot size TDTR approach on samples with a wide range of in-plane thermal conductivity, including fused silica, rutile titania (TiO2 [001]), zinc oxide (ZnO [0001]), molybdenum disulfide (MoS2), hexagonal boron nitride (h-BN), and highly ordered pyrolytic graphite.

  20. Time-domain thermoreflectance (TDTR) measurements of anisotropic thermal conductivity using a variable spot size approach.

    PubMed

    Jiang, Puqing; Qian, Xin; Yang, Ronggui

    2017-07-01

    It is challenging to characterize thermal conductivity of materials with strong anisotropy. In this work, we extend the time-domain thermoreflectance (TDTR) method with a variable spot size approach to simultaneously measure the in-plane (Kr) and the through-plane (Kz) thermal conductivity of materials with strong anisotropy. We first determine Kz from the measurement using a larger spot size, when the heat flow is mainly one-dimensional along the through-plane direction, and the measured signals are only sensitive to Kz. We then extract the in-plane thermal conductivity Kr from a second measurement using the same modulation frequency but with a smaller spot size, when the heat flow becomes three-dimensional, and the signal is sensitive to both Kr and Kz. By choosing the same modulation frequency for the two sets of measurements, we can avoid potential artifacts introduced by the frequency-dependent Kz, which we have found to be non-negligible, especially for some two-dimensional layered materials like MoS2. After careful evaluation of the sensitivity of a series of hypothetical samples, we provided guidelines on choosing the most appropriate laser spot size and modulation frequency that yield the smallest uncertainty, and established a criterion for the range of thermal conductivity that can be measured reliably using our proposed variable spot size TDTR approach. We have demonstrated this variable spot size TDTR approach on samples with a wide range of in-plane thermal conductivity, including fused silica, rutile titania (TiO2 [001]), zinc oxide (ZnO [0001]), molybdenum disulfide (MoS2), hexagonal boron nitride (h-BN), and highly ordered pyrolytic graphite.

  1. Anisotropic superconducting property studies of single crystal PbTaSe2

    NASA Astrophysics Data System (ADS)

    Sankar, Raman; Narsinga Rao, G.; Panneer Muthuselvam, I.; Chang, Tay-Rong; Jeng, H. T.; Senthil Murugan, G.; Lee, Wei-Li; Chou, F. C.

    2017-03-01

    The anisotropic superconducting properties of PbTaSe2 single crystal is reported. Superconductivity with T c  =  3.83  ±  0.02 K has been characterized fully with electrical resistivity ρ(T), magnetic susceptibility χ(T), and specific heat C p (T) measurements using single crystal samples. The superconductivity is type-II with lower critical field H c1 and upper critical field H c2 of 65 and 450 Oe (H⊥  to the ab-plane), 140 and 1500 Oe (H|| to the ab-plane), respectively. These results indicate that the superconductivity of PbTaSe2 is anisotropic. The superconducting anisotropy, electron-phonon coupling λ ep, superconducting energy gap Δ0, and the specific heat jump ΔC/γT c at T c confirms that PbTaSe2 can be categorized as a bulk superconductor.

  2. Anisotropic linear and nonlinear optical properties from anisotropy-controlled metallic nanocomposites.

    PubMed

    Reyes-Esqueda, Jorge Alejandro; Rodríguez-Iglesias, Vladimir; Silva-Pereyra, Héctor-Gabriel; Torres-Torres, Carlos; Santiago-Ramírez, Ana-Laura; Cheang-Wong, Juan Carlos; Crespo-Sosa, Alejandro; Rodríguez-Fernández, Luis; López-Suárez, Alejandra; Oliver, Alicia

    2009-07-20

    High-energy metallic ions were implanted in silica matrices, obtaining spherical-like metallic nanoparticles (NPs) after a proper thermal treatment. These NPs were then deformed by irradiation with Si ions, obtaining an anisotropic metallic nanocomposite. An average large birefringence of 0.06 was measured for these materials in the 300-800 nm region. Besides, their third order nonlinear optical response was measured using self-diffraction and P-scan techniques at 532 nm with 26 ps pulses. By adjusting the incident light's polarization and the angular position of the nanocomposite, the measurements could be directly related to, at least, two of the three linear independent components of its third order susceptibility tensor, finding a large, but anisotropic, response of around 10(-7) esu with respect to other isotropic metallic systems. For the nonlinear optical absorption, we were able to shift from saturable to reverse saturable absorption depending on probing the Au NP's major or minor axes, respectively. This fact could be related to local field calculations and NP's electronic properties. For the nonlinear optical refraction, we passed from self-focusing to self-defocusing, when changing from Ag to Au.

  3. Optimum condition of anisotropic plasma etching for improving bending properties of ionic polymer-metal composites.

    PubMed

    Choi, N J; Lee, H K; Jung, S; Park, K H

    2010-05-01

    We presented an anisotropic plasma etching technique by reactive ion etcher (RIE) as a new pretreatment method of fabrication of ionic polymer-metal composite (IPMC). We already found that the new technique provided large displacement to the fabricated IPMC in the presence of low applied voltage. However, we did not examine the optimum condition for the anisotropic plasma etching. In this research, we tried to figure out optimum treatment condition of film in etcher. Nafion (by DuPont) films were etched using various etching time and shadow masks with various slit and space sizes. The etched samples were plated with Pt at top and bottom side by Oguro's reduction method. The surface morphology of fabricated IPMCs was characterized by SEM. And, we've measured surface resistance, bending displacement, and driving force in order to check the IPMC properties out. Here, we found that optimum condition for pre-treatment of Nafion was 1 min for etching time under shadow mask with 200 microm slit and 100 microm space.

  4. Anisotropic superconducting property studies of single crystal PbTaSe2.

    PubMed

    Sankar, Raman; Rao, G Narsinga; Muthuselvam, I Panneer; Chang, Tay-Rong; Jeng, H T; Murugan, G Senthil; Lee, Wei-Li; Chou, F C

    2017-03-08

    The anisotropic superconducting properties of PbTaSe2 single crystal is reported. Superconductivity with T c  =  3.83  ±  0.02 K has been characterized fully with electrical resistivity ρ(T), magnetic susceptibility χ(T), and specific heat C p (T) measurements using single crystal samples. The superconductivity is type-II with lower critical field H c1 and upper critical field H c2 of 65 and 450 Oe (H⊥  to the ab-plane), 140 and 1500 Oe (H|| to the ab-plane), respectively. These results indicate that the superconductivity of PbTaSe2 is anisotropic. The superconducting anisotropy, electron-phonon coupling λ ep, superconducting energy gap Δ0, and the specific heat jump ΔC/γT c at T c confirms that PbTaSe2 can be categorized as a bulk superconductor.

  5. Polymeric and Organic Light-Emitting Diodes and Field-Effect Transistors with Anisotropic Electrical Properties

    NASA Astrophysics Data System (ADS)

    Lovinger, Andrew J.; Bao, Zhenan; Chen, X. Linda

    2001-03-01

    There has been great progress and interest recently in polymeric and organic light-emitting diodes (LEDs) and field-effect transistors (FETs) for ``plastic electronics". These hold promise for versatile, low-cost applications such as electronic price tags, disposable cell phones, and flexible computer screens (2). We have obtained anisotropic electrical properties for such LEDs and FETs by deposition of the active materials on aligned polymeric or organic substrates. These could be polytetrafluoroethylene (PTFE) or the same compounds as the electrically active layers. The LED materials consist of poly(p-phenylene vinylene)s with a large variety of dendritic side chains, which we have synthesized and characterized, while the FET materials are sexithienyl, sexiphenyl, pentacene, and a number of phthalocyanines. The resulting morphologies, examined by transmission electron microscopy, electron diffraction, and atomic-force microscopy, exhibit high orientations of the deposited materials. In addition, many of these materials adopt additional remarkable morphologies such as edge-on crystallites with or without twinning about the direction of molecular alignment. As a result of their special morphologies, films prepared in this manner exhibit polarized absorption and luminescence with dichroic ratios around 5 or anisotropic carrier mobilities with ratios greater than 15. (1) Now at Infineon Technologies (2) Nature, 407, 442 (2000)

  6. Anisotropic Thermal Conductivity Measurements on Cross-Linked Polybutadienes in Uniaxial Elongation

    NASA Astrophysics Data System (ADS)

    Venerus, David C.; Kolev, Dimitre

    2008-07-01

    Cross-linked elastomers have numerous applications including automobiles, sporting goods, and biomedical devices. During both their processing and application, these materials experience large mechanical stresses and thermal gradients. In this study, we investigate the mechanical and thermal transport behavior of cross-linked polybutadienes. These materials have been prepared by cross linking well-entangled polybutadienes using an organic peroxide cross-linking agent at low concentration. Samples obtained after nearly complete conversion of the cross-linking agent, which can be characterized as lightly cross-linked (i.e., more than 10 entanglements per cross-link), were subjected to a series of large strain, uniaxial deformations. Measurements of the tensile stress and two components of the thermal conductivity tensor will be reported as a function of elongation. These data are also used to examine the stress-thermal rule in which the stress and thermal conductivity tensors are linearly related.

  7. The value and cost of complexity in predictive modelling: role of tissue anisotropic conductivity and fibre tracts in neuromodulation

    NASA Astrophysics Data System (ADS)

    Salman Shahid, Syed; Bikson, Marom; Salman, Humaira; Wen, Peng; Ahfock, Tony

    2014-06-01

    Objectives. Computational methods are increasingly used to optimize transcranial direct current stimulation (tDCS) dose strategies and yet complexities of existing approaches limit their clinical access. Since predictive modelling indicates the relevance of subject/pathology based data and hence the need for subject specific modelling, the incremental clinical value of increasingly complex modelling methods must be balanced against the computational and clinical time and costs. For example, the incorporation of multiple tissue layers and measured diffusion tensor (DTI) based conductivity estimates increase model precision but at the cost of clinical and computational resources. Costs related to such complexities aggregate when considering individual optimization and the myriad of potential montages. Here, rather than considering if additional details change current-flow prediction, we consider when added complexities influence clinical decisions. Approach. Towards developing quantitative and qualitative metrics of value/cost associated with computational model complexity, we considered field distributions generated by two 4 × 1 high-definition montages (m1 = 4 × 1 HD montage with anode at C3 and m2 = 4 × 1 HD montage with anode at C1) and a single conventional (m3 = C3-Fp2) tDCS electrode montage. We evaluated statistical methods, including residual error (RE) and relative difference measure (RDM), to consider the clinical impact and utility of increased complexities, namely the influence of skull, muscle and brain anisotropic conductivities in a volume conductor model. Main results. Anisotropy modulated current-flow in a montage and region dependent manner. However, significant statistical changes, produced within montage by anisotropy, did not change qualitative peak and topographic comparisons across montages. Thus for the examples analysed, clinical decision on which dose to select would not be altered by the omission of anisotropic brain conductivity

  8. Probing anisotropic surface properties and interaction forces of chrysotile rods by atomic force microscopy and rheology.

    PubMed

    Yang, Dingzheng; Xie, Lei; Bobicki, Erin; Xu, Zhenghe; Liu, Qingxia; Zeng, Hongbo

    2014-09-16

    Understanding the surface properties and interactions of nonspherical particles is of both fundamental and practical importance in the rheology of complex fluids in various engineering applications. In this work, natural chrysotile, a phyllosilicate composed of 1:1 stacked silica and brucite layers which coil into cylindrical structure, was chosen as a model rod-shaped particle. The interactions of chrysotile brucite-like basal or bilayered edge planes and a silicon nitride tip were measured using an atomic force microscope (AFM). The force-distance profiles were fitted using the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which demonstrates anisotropic and pH-dependent surface charge properties of brucite-like basal plane and bilayered edge surface. The points of zero charge (PZC) of the basal and edge planes were estimated to be around pH 10-11 and 6-7, respectively. Rheology measurements of 7 vol % chrysotile (with an aspect ratio of 14.5) in 10 mM NaCl solution showed pH-dependent yield stress with a local maximum around pH 7-9, which falls between the two PZC values of the edge and basal planes of the rod particles. On the basis of the surface potentials of the edge and basal planes obtained from AFM measurements, theoretical analysis of the surface interactions of edge-edge, basal-edge, and basal-basal planes of the chrysotile rods suggests the yield stress maximum observed could be mainly attributed to the basal-edge attractions. Our results indicate that the anisotropic surface properties (e.g., charges) of chrysotile rods play an important role in the particle-particle interaction and rheological behavior, which also provides insight into the basic understanding of the colloidal interactions and rheology of nonspherical particles.

  9. Theoretical determination of anisotropic thermal conductivity for crystalline 1,3,5-triamino-2,4,6-trinitrobenzene (TATB).

    PubMed

    Kroonblawd, Matthew P; Sewell, Thomas D

    2013-08-21

    Bond stretching and three-center angle bending potentials have been developed to extend an existing rigid-bond 1,3,5-triamino-2,4,6-trinitrobenzene molecular dynamics force field [D. Bedrov, O. Borodin, G. D. Smith, T. D. Sewell, D. M. Dattelbaum, and L. L. Stevens, J. Chem. Phys. 131, 224703 (2009)] for simulations requiring fully flexible molecules. The potentials were fit to experimental vibrational spectra and electronic structure predictions of vibrational normal modes using a combination of zero kelvin eigenmode analysis for the isolated molecule and power spectra for the isolated molecule and crystal. A reverse non-equilibrium molecular dynamics method [F. Müller-Plathe, J. Chem. Phys. 106, 6082 (1997)] was used to obtain the room temperature, atmospheric pressure thermal conductivity along three directions in a well-defined, non-orthogonal basis. The thermal conductivity was found to be significantly anisotropic with values 1.13 ± 0.07, 1.07 ± 0.07, and 0.65 ± 0.03 W m(-1) K(-1) for directions nominally parallel to the a, b, and c lattice vectors, respectively.

  10. Theoretical determination of anisotropic thermal conductivity for crystalline 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)

    NASA Astrophysics Data System (ADS)

    Kroonblawd, Matthew P.; Sewell, Thomas D.

    2013-08-01

    Bond stretching and three-center angle bending potentials have been developed to extend an existing rigid-bond 1,3,5-triamino-2,4,6-trinitrobenzene molecular dynamics force field [D. Bedrov, O. Borodin, G. D. Smith, T. D. Sewell, D. M. Dattelbaum, and L. L. Stevens, J. Chem. Phys. 131, 224703 (2009), 10.1063/1.3264972] for simulations requiring fully flexible molecules. The potentials were fit to experimental vibrational spectra and electronic structure predictions of vibrational normal modes using a combination of zero kelvin eigenmode analysis for the isolated molecule and power spectra for the isolated molecule and crystal. A reverse non-equilibrium molecular dynamics method [F. Müller-Plathe, J. Chem. Phys. 106, 6082 (1997), 10.1063/1.473271] was used to obtain the room temperature, atmospheric pressure thermal conductivity along three directions in a well-defined, non-orthogonal basis. The thermal conductivity was found to be significantly anisotropic with values 1.13 ± 0.07, 1.07 ± 0.07, and 0.65 ± 0.03 W m-1 K-1 for directions nominally parallel to the a, b, and c lattice vectors, respectively.

  11. Theoretical determination of anisotropic thermal conductivity for crystalline 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)

    NASA Astrophysics Data System (ADS)

    Kroonblawd, Matthew; Sewell, Thomas

    2013-06-01

    Bond stretching and three-center angle bending potentials have been developed to extend an existing rigid-bond TATB molecular dynamics (MD) force field (FF) for simulations requiring fully flexible molecules. The FF potentials were fit to experimental vibrational spectra and electronic structure predictions of vibrational normal modes and frequencies using a combination of zero Kelvin eigenmode analysis for the isolated molecule and finite-temperature power spectra for the isolated molecule and bulk crystal. Crystal structures computed using the revised FF are in good agreement with results from other computational models and experimental data. A non-equilibrium MD method was used to obtain the room temperature, atmospheric pressure thermal conductivity along three directions in a well-defined, non-orthogonal basis. The thermal conductivity was found to be significantly anisotropic with values of 1.13 +/- 0.07, 1.07 +/- 0.07 and 0.65 +/- 0.03 W m-1 K-1 for directions nominally parallel to the a, b, and c crystal directions, respectively. The U.S. Air Force Office of Scientific Research supported this research.

  12. Remote cooling by a novel thermal lens with anisotropic positive thermal conductivity

    PubMed Central

    Sun, Fei; He, Sailing

    2017-01-01

    A novel thermal lens that can achieve a remote cooling effect is designed by transformation thermodynamics. The effective distance between the separate hot source and cold source is shortened by our shelled thermal lens without any negative thermal conductivity. Numerical simulations verify the performance of our thermal lens. Based on the effective medium theory, we also propose a practical way to realize our lens using two-layered isotropic thermal media that are both found in nature. The proposed thermal lens will have potential applications in remote temperature control and in creating other thermal illusions. PMID:28098221

  13. Remote cooling by a novel thermal lens with anisotropic positive thermal conductivity

    NASA Astrophysics Data System (ADS)

    Sun, Fei; He, Sailing

    2017-01-01

    A novel thermal lens that can achieve a remote cooling effect is designed by transformation thermodynamics. The effective distance between the separate hot source and cold source is shortened by our shelled thermal lens without any negative thermal conductivity. Numerical simulations verify the performance of our thermal lens. Based on the effective medium theory, we also propose a practical way to realize our lens using two-layered isotropic thermal media that are both found in nature. The proposed thermal lens will have potential applications in remote temperature control and in creating other thermal illusions.

  14. Anisotropic layered Bi2Te3-In2Te3 composites: control of interface density for tuning of thermoelectric properties

    PubMed Central

    Liu, Dongmei; Li, Xinzhong; Borlido, Pedro Miguel de Castro; Botti, Silvana; Schmechel, Roland; Rettenmayr, Markus

    2017-01-01

    Layered (Bi1−xInx)2Te3-In2Te3 (x = 0.075) composites of pronounced anisotropy in structure and thermoelectric properties were produced by zone melting and subsequent coherent precipitation of In2Te3 from a (Bi1−xInx)2Te3 (x > 0.075) matrix. Employing solid state phase transformation, the Bi2Te3/In2Te3 interface density was tuned by modifying the driving force for In2Te3 precipitation. The structure-property relationship in this strongly anisotropic material is characterized thoroughly and systematically for the first time. Unexpectedly, with increasing Bi2Te3/In2Te3 interface density, an increase in electrical conductivity and a decrease in the absolute Seebeck coefficient were found. This is likely to be due to electron accumulation layers at the Bi2Te3/In2Te3 interfaces and the interplay of bipolar transport in Bi2Te3. Significantly improved thermoelectric properties of Bi2Te3-In2Te3 composites as compared to the single phase (Bi1−xInx)2Te3 solid solution are obtained. PMID:28272541

  15. Anisotropic layered Bi2Te3-In2Te3 composites: control of interface density for tuning of thermoelectric properties.

    PubMed

    Liu, Dongmei; Li, Xinzhong; Borlido, Pedro Miguel de Castro; Botti, Silvana; Schmechel, Roland; Rettenmayr, Markus

    2017-03-08

    Layered (Bi1-xInx)2Te3-In2Te3 (x = 0.075) composites of pronounced anisotropy in structure and thermoelectric properties were produced by zone melting and subsequent coherent precipitation of In2Te3 from a (Bi1-xInx)2Te3 (x > 0.075) matrix. Employing solid state phase transformation, the Bi2Te3/In2Te3 interface density was tuned by modifying the driving force for In2Te3 precipitation. The structure-property relationship in this strongly anisotropic material is characterized thoroughly and systematically for the first time. Unexpectedly, with increasing Bi2Te3/In2Te3 interface density, an increase in electrical conductivity and a decrease in the absolute Seebeck coefficient were found. This is likely to be due to electron accumulation layers at the Bi2Te3/In2Te3 interfaces and the interplay of bipolar transport in Bi2Te3. Significantly improved thermoelectric properties of Bi2Te3-In2Te3 composites as compared to the single phase (Bi1-xInx)2Te3 solid solution are obtained.

  16. Anisotropic layered Bi2Te3-In2Te3 composites: control of interface density for tuning of thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Liu, Dongmei; Li, Xinzhong; Borlido, Pedro Miguel De Castro; Botti, Silvana; Schmechel, Roland; Rettenmayr, Markus

    2017-03-01

    Layered (Bi1-xInx)2Te3-In2Te3 (x = 0.075) composites of pronounced anisotropy in structure and thermoelectric properties were produced by zone melting and subsequent coherent precipitation of In2Te3 from a (Bi1-xInx)2Te3 (x > 0.075) matrix. Employing solid state phase transformation, the Bi2Te3/In2Te3 interface density was tuned by modifying the driving force for In2Te3 precipitation. The structure-property relationship in this strongly anisotropic material is characterized thoroughly and systematically for the first time. Unexpectedly, with increasing Bi2Te3/In2Te3 interface density, an increase in electrical conductivity and a decrease in the absolute Seebeck coefficient were found. This is likely to be due to electron accumulation layers at the Bi2Te3/In2Te3 interfaces and the interplay of bipolar transport in Bi2Te3. Significantly improved thermoelectric properties of Bi2Te3-In2Te3 composites as compared to the single phase (Bi1-xInx)2Te3 solid solution are obtained.

  17. Characterization of a random anisotropic conductivity field with Karhunen-Loeve methods

    SciTech Connect

    Cherry, Matthew R.; Sabbagh, Harold S.; Pilchak, Adam L.; Knopp, Jeremy S.

    2014-02-18

    While parametric uncertainty quantification for NDE models has been addressed in recent years, the problem of stochastic field parameters such as spatially distributed electrical conductivity has only been investigated minimally in the last year. In that work, the authors treated the field as a one-dimensional random process and Karhunen-Loeve methods were used to discretize this process to make it amenable to UQ methods such as ANOVA expansions. In the present work, we will treat the field as a two dimensional random process, and the eigenvalues and eigenfunctions of the integral operator will be determined via Galerkin methods. The Karhunen-Loeve methods is extended to two dimensions and implemented to represent this process. Several different choices for basis functions will be discussed, as well as convergence criteria for each. The methods are applied to correlation functions collected over electron backscatter data from highly micro textured Ti-7Al.

  18. Anisotropic transport properties in the phase-separated La0.67Ca0.33MnO3/NdGaO3 (001) films

    NASA Astrophysics Data System (ADS)

    Hong-Rui, Zhang; Yuan-Bo, Liu; Shuan-Hu, Wang; De-Shun, Hong; Wen-Bin, Wu; Ji-Rong, Sun

    2016-07-01

    The anisotropic transport property was investigated in a phase separation La0.67Ca0.33MnO3 (LCMO) film grown on (001)-oriented NdGaO3 (NGO) substrate. It was found that the resistivity along the b-axis is much higher than that along the a-axis. Two resistivity peaks were observed in the temperature dependent measurement along the b-axis, one located at 91 K and the other centered at 165 K. Moreover, we also studied the response of the resistivities along the two axes to various electric currents, magnetic fields, and light illuminations. The resistivities along the two axes are sensitive to the magnetic field. However, the electric current and light illumination can influence the resistivity along the b-axis obviously, but have little effect on the resistivity along the a-axis. Based on these results, we believe that an anisotropic-strain-controlled MnO6 octahedra shear-mode deformation may provide a mechanism of conduction filaments paths along the a-axis, which leads to the anisotropic transport property. Project supported by the National Basic Research Program of China (Grant Nos. 2011CB921801, 2012CB921403, and 2013CB921701) and the National Natural Science Foundation of China (Grant Nos. 11074285, 51372064, and 11134007).

  19. Synthesis and anisotropic magnetic and transport properties of cubic SrCoO3 single crystal

    NASA Astrophysics Data System (ADS)

    Long, Youwen; Kaneko, Yoshio; Ishiwata, Shintaro; Taguchi, Yasujiro; Tokura, Yoshinori

    2011-03-01

    Solid state oxides containing transition metals with unusually high valence states exhibit interesting physical properties. However, due to the unstableness of these high valence states, high pressure is often needed to stabilize such high valence states. We were successful in growing a large-size SrCo O3 single crystal by using high-pressure technique. This material shows good metallic behavior with high ferromagnetic Curie temperature about 305 K, and the easy magnetization axis is 111 > direction . ThespinmomentofCo 4+ ionmeasuredat 2 Kand 7 Tisabout 2.50 μB , suggesting an spin configuration as predicted by theoretical calculations. Although SrCoO3 has a highly symmetric cubic crystal structure (Pm-3m), it exhibits significant anisotropic magnetoresistance at low temperatures.

  20. Solidification of Anisotropic Semiconductor Tellurium Samples in Microgravity and Their Properties

    NASA Astrophysics Data System (ADS)

    Parfeniev, R. V.; Farbshtein, I. I.; Yakimov, S. V.; Shalimov, V. P.; Turchaninov, A. M.

    A research program was partly completed to determine the influence of microgravity on the crystallization and electrical properties of tellurium, as a semiconductor with both anisotropic crystal lattice and energy spectrum. Three different tellurium samples were solidified in space by a modified Bridgman method in the Crystallizator ChSK-1 furnace aboard the MIR space station. The variation of the crystal structure, charge carrier concentration and mobility along the sample length was investigated and compared with material solidified on earth. The lowest impurity and defect concentrations were obtained in partially melted single crystals resolidified by the Bridgman method. The distribution of electric active and neutral defects along the samples with a concentration as small as 10 -5 at% were measured by a galvanomagnetic method at low temperatures. Some peculiarities of the remelting process connected with microgravity were observed.

  1. High Tg and fast curing epoxy-based anisotropic conductive paste for electronic packaging

    NASA Astrophysics Data System (ADS)

    Keeratitham, Waralee; Somwangthanaroj, Anongnat

    2016-03-01

    Herein, our main objective is to prepare the fast curing epoxy system with high glass transition temperature (Tg) by incorporating the multifunctional epoxy resin into the mixture of diglycidyl ether of bisphenol A (DGEBA) as a major epoxy component and aromatic diamine as a hardener. Furthermore, the curing behavior as well as thermal and thermomechanical properties were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA). It was found that Tg obtained from tan δ of DGEBA/aromatic diamine system increased from 100 °C to 205 °C with the presence of 30 percentage by weight of multifunctional epoxy resin. Additionally, the isothermal DSC results showed that the multifunctional epoxy resin can accelerate the curing reaction of DGEBA/aromatic diamine system. Namely, a high degree of curing (˜90%) was achieved after a few minutes of curing at low temperature of 130 °C, owing to a large number of epoxy ring of multifunctional epoxy resin towards the active hydrogen atoms of aromatic diamine.

  2. Revisiting HOPG superlattices: Structure and conductance properties

    NASA Astrophysics Data System (ADS)

    Patil, Sumati; Kolekar, Sadhu; Deshpande, Aparna

    2017-04-01

    Superlattices observed on highly oriented pyrolytic graphite (HOPG) have been studied extensively by scanning tunnelling microscopy (STM). The interest in the study of graphite superlattices has seen a resurgence since the discovery of graphene. Single layer graphene, bilayer graphene, and few layer graphene can now be grown on different substrates. The adherence of graphene to various substrates often leads to a periodic out-of-plane modulation and superlattices due to lattice mismatch. In this paper, we report STM imaging and scanning tunnelling spectroscopy (STS) of different kinds of superlattices on HOPG characterized by a variation in lattice periodicities. Our study also shows evidence of the displacement of the topmost HOPG layer by scanning different areas of the same superlattice. A correlation between the lattice periodicity with its conductance properties is derived. The results of this work are important for understanding the origin of the superlattice structure on HOPG. Investigation of such superlattices may open up possible ways to modify two dimensional electron systems to create materials with tailored electronic properties.

  3. Anisotropic mechanical properties of zircon and the effect of radiation damage

    SciTech Connect

    Beirau, Tobias; Nix, William D.; Bismayer, Ulrich; Boatner, Lynn A.; Isaacson, Scott G.; Ewing, Rodney C.

    2016-06-02

    Our study provides new insights into the relationship between radiation-dose-dependent structural damage, due to natural U and Th impurities, and the anisotropic mechanical properties (Poisson s ratio, elastic modulus and hardness) of zircon. Natural zircon samples from Sri Lanka (see Muarakami et al. 1991) and synthetic samples, covering a dose range of zero up to 6.8 x 1018 -decays/g, have been studied by nanoindentation. Measurements along the [100] crystallographic direction and calculations, based on elastic stiffness constants determined by zkan (1976), revealed a general radiation-induced decrease in stiffness (~ 54 %) and hardness (~ 48 %) and an increase of the Poisson s ratio (~ 54 %) with increasing dose. Additional indentations on selected samples along the [001] allowed one to follow the amorphization process to the point that the mechanical properties are isotropic. This work shows that the radiation-dose-dependent changes of the mechanical properties of zircon can be directly correlated with the amorphous fraction as determined by previous investigations with local and global probes (Rios et al. 2000a; Farnan and Salje 2001; Zhang and Salje 2001). This agreement, revealed by the different methods, indicates a huge influence of structural and even local phenomena on the macroscopic mechanical properties.

  4. Anisotropic mechanical properties of zircon and the effect of radiation damage

    DOE PAGES

    Beirau, Tobias; Nix, William D.; Bismayer, Ulrich; ...

    2016-06-02

    Our study provides new insights into the relationship between radiation-dose-dependent structural damage, due to natural U and Th impurities, and the anisotropic mechanical properties (Poisson s ratio, elastic modulus and hardness) of zircon. Natural zircon samples from Sri Lanka (see Muarakami et al. 1991) and synthetic samples, covering a dose range of zero up to 6.8 x 1018 -decays/g, have been studied by nanoindentation. Measurements along the [100] crystallographic direction and calculations, based on elastic stiffness constants determined by zkan (1976), revealed a general radiation-induced decrease in stiffness (~ 54 %) and hardness (~ 48 %) and an increase ofmore » the Poisson s ratio (~ 54 %) with increasing dose. Additional indentations on selected samples along the [001] allowed one to follow the amorphization process to the point that the mechanical properties are isotropic. This work shows that the radiation-dose-dependent changes of the mechanical properties of zircon can be directly correlated with the amorphous fraction as determined by previous investigations with local and global probes (Rios et al. 2000a; Farnan and Salje 2001; Zhang and Salje 2001). This agreement, revealed by the different methods, indicates a huge influence of structural and even local phenomena on the macroscopic mechanical properties.« less

  5. Anisotropic mechanical properties of zircon and the effect of radiation damage

    SciTech Connect

    Beirau, Tobias; Nix, William D.; Bismayer, Ulrich; Boatner, Lynn A.; Isaacson, Scott G.; Ewing, Rodney C.

    2016-06-02

    Our study provides new insights into the relationship between radiation-dose-dependent structural damage, due to natural U and Th impurities, and the anisotropic mechanical properties (Poisson s ratio, elastic modulus and hardness) of zircon. Natural zircon samples from Sri Lanka (see Muarakami et al. 1991) and synthetic samples, covering a dose range of zero up to 6.8 x 1018 -decays/g, have been studied by nanoindentation. Measurements along the [100] crystallographic direction and calculations, based on elastic stiffness constants determined by zkan (1976), revealed a general radiation-induced decrease in stiffness (~ 54 %) and hardness (~ 48 %) and an increase of the Poisson s ratio (~ 54 %) with increasing dose. Additional indentations on selected samples along the [001] allowed one to follow the amorphization process to the point that the mechanical properties are isotropic. This work shows that the radiation-dose-dependent changes of the mechanical properties of zircon can be directly correlated with the amorphous fraction as determined by previous investigations with local and global probes (Rios et al. 2000a; Farnan and Salje 2001; Zhang and Salje 2001). This agreement, revealed by the different methods, indicates a huge influence of structural and even local phenomena on the macroscopic mechanical properties.

  6. Mechanical properties of cancellous bone in the human mandibular condyle are anisotropic.

    PubMed

    Giesen, E B; Ding, M; Dalstra, M; van Eijden, T M

    2001-06-01

    The objective of the present study was (1) to test the hypothesis that the elastic and failure properties of the cancellous bone of the mandibular condyle depend on the loading direction, and (2) to relate these properties to bone density parameters. Uniaxial compression tests were performed on cylindrical specimens (n=47) obtained from the condyles of 24 embalmed cadavers. Two loading directions were examined, i.e., a direction coinciding with the predominant orientation of the plate-like trabeculae (axial loading) and a direction perpendicular to the plate-like trabeculae (transverse loading). Archimedes' principle was applied to determine bone density parameters. The cancellous bone was in axial loading 3.4 times stiffer and 2.8 times stronger upon failure than in transverse loading. High coefficients of correlation were found among the various mechanical properties and between them and the apparent density and volume fraction. The anisotropic mechanical properties can possibly be considered as a mechanical adaptation to the loading of the condyle in vivo.

  7. Geomechanical and anisotropic acoustic properties of Lower Jurassic Posidonia shales from Whitby (UK)

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The Posidonia Shale Formation (PSF) is one of the possible resource shales for unconventional gas in Northern Europe and currently is of great interest to hydrocarbon exploration and production. Due to low permeability of shales, economically viable production requires hydraulic fracturing of the reservoir. The design of hydrofractures requires an estimate of stress state within the reservoir and geomechanical properties such as Young's modulus and Poisson's ratio. Shales are often highly anisotropic and the models which neglect shale anisotropy may fail to predict the behaviour of hydrofractures. Seismic attenuation anisotropy, on the other hand, can play a key role in quantitative rock characterization. Where the attenuation anisotropy can potentially be linked to anisotropic permeability of shales, its fluid/gas saturation and preferred development of anisotropic fracture orientations. In this research, by utilizing the so-called Thomsen's notations, the elastic anisotropy of our (fractured and unfractured) shales has been investigated using a pulse transmission technique in the ultrasonic frequency range (0.3-1 MHz). Assuming transverse isotropy of the shales, and taking the axis x3 as the axis of rotational symmetry, directional Young's moduli and Poisson's ratios were obtained. The Young's modulus measured parallel to bedding (E1) is found to be larger than the Young's modulus measured orthogonal to bedding (E3). In case of the Poisson's ratios, we found that ν31 is larger than ν12, where νijrelates 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

  8. Influence of the anisotropic mechanical properties of the skull in low-intensity focused ultrasound towards neuromodulation of the brain.

    PubMed

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

    2013-01-01

    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.

  9. Regional electric field induced by electroconvulsive therapy in a realistic finite element head model: Influence of white matter anisotropic conductivity

    PubMed Central

    Lee, Won Hee; Deng, Zhi-De; Kim, Tae-Seong; Laine, Andrew F.; Lisanby, Sarah H.; Peterchev, Angel V.

    2012-01-01

    We present the first computational study investigating the electric field (E-field) strength generated by various electroconvulsive therapy (ECT) electrode configurations in specific brain regions of interest (ROIs) that have putative roles in the therapeutic action and/or adverse side effects of ECT. This study also characterizes the impact of the white matter (WM) conductivity anisotropy on the E-field distribution. A finite element head model incorporating tissue heterogeneity and WM anisotropic conductivity was constructed based on structural magnetic resonance imaging (MRI) and diffusion tensor MRI data. We computed the spatial E-field distributions generated by three standard ECT electrode placements including bilateral (BL), bifrontal (BF), and right unilateral (RUL) and an investigational electrode configuration for focal electrically administered seizure therapy (FEAST). The key results are that (1) the median E-field strength over the whole brain is 3.9, 1.5, 2.3, and 2.6 V/cm for the BL, BF, RUL, and FEAST electrode configurations, respectively, which coupled with the broad spread of the BL E-field suggests a biophysical basis for observations of superior efficacy of BL ECT compared to BF and RUL ECT; (2) in the hippocampi, BL ECT produces a median E-field of 4.8 V/cm that is 1.5–2.8 times stronger than that for the other electrode configurations, consistent with the more pronounced amnestic effects of BL ECT; and (3) neglecting the WM conductivity anisotropy results in E-field strength error up to 18% overall and up to 39% in specific ROIs, motivating the inclusion of the WM conductivity anisotropy in accurate head models. This computational study demonstrates how the realistic finite element head model incorporating tissue conductivity anisotropy provides quantitative insight into the biophysics of ECT, which may shed light on the differential clinical outcomes seen with various forms of ECT, and may guide the development of novel stimulation

  10. Chest conduction properties and ECG equalization.

    PubMed

    Delle Cave, G; Fabricatore, G; Nolfe, G; Petrosino, M; Pizzuti, G P

    2000-01-01

    In common practice of detecting and recording biomedical signals, it is often implicitly assumed that the propagation, through the whole circuit human body-electrodes recording devices, is frequency and voltage independent. As a consequence, clinicians are not aware that recorded signals do not correspond faithfully to the original electrical activity of organs under investigation. We have studied the transmission of electrical signals in human body at various voltages and frequencies to understand if and to which extent the most diffused stimulating and recording techniques used in medicine are affected by global body conduction properties. Our results show that, in order to obtain a more faithful detection of electrical activity produced or evoked by human organs (e.g. EGG, electromyography, etc.), it is convenient to 'equalize'' recorded signals. To this purpose, two equalization techniques are proposed, based, respectively, on a simple hardware filtering during acquisition, or FFT post-processing of the acquired signals. As an application, we have studied the transmission of electrical signal in human chest and have compared equalized high frequency ECG signals with raw (original) recordings.

  11. Smart Optical Composite Materials: Dispersions of Metal-Organic Framework@Superparamagnetic Microrods for Switchable Isotropic-Anisotropic Optical Properties.

    PubMed

    Mandel, Karl; Granath, Tim; Wehner, Tobias; Rey, Marcel; Stracke, Werner; Vogel, Nicolas; Sextl, Gerhard; Müller-Buschbaum, Klaus

    2017-01-24

    A smart optical composite material with dynamic isotropic and anisotropic optical properties by combination of luminescence and high reflectivity was developed. This combination enables switching between luminescence and angle-dependent reflectivity by changing the applied wavelength of light. The composite is formed as anisotropic core/shell particles by coating superparamagnetic iron oxide-silica microrods with a layer of the luminescent metal-organic framework (MOF) (3)∞[Eu2(BDC)3]·2DMF·2H2O (BDC(2-) = 1,4-benzenedicarboxylate). The composite particles can be rotated by an external magnet. Their anisotropic shape causes changes in the reflectivity and diffraction of light depending on the orientation of the composite particle. These rotation-dependent optical properties are complemented by an isotropic luminescence resulting from the MOF shell. If illuminated by UV light, the particles exhibit isotropic luminescence while the same sample shows anisotropic optical properties when illuminated with visible light. In addition to direct switching, the optical properties can be tailored continuously between isotropic red emission and anisotropic reflection of light if the illuminating light is tuned through fractions of both UV and visible light. The integration and control of light emission modes within a homogeneous particle dispersion marks a smart optical material, addressing fundamental directions for research on switchable multifunctional materials. The material can function as an optic compass or could be used as an optic shutter that can be switched by a magnetic field, e.g., for an intensity control for waveguides in the visible range.

  12. Liquid crystal self-assembly of halloysite nanotubes in ionic liquids: a novel soft nanocomposite ionogel electrolyte with high anisotropic ionic conductivity and thermal stability

    NASA Astrophysics Data System (ADS)

    Zhao, Ningning; Liu, Yulin; Zhao, Xiaomeng; Song, Hongzan

    2016-01-01

    We report a novel class of liquid crystalline (LC) nanohybrid ionogels fabricated via self-assembly of natural halloysite nanotubes (HNTs) in ionic liquids (ILs). The obtained ionogels are very stable and nonvolatile and show LC phases over a wide temperature range. Remarkably, the nanocomposite ionogels exhibit high anisotropic ionic conductivity after shear, and their room temperature ionic conductivity can reach 3.8 × 10-3 S cm-1 for aligned nanotubes perpendicular to the electrode even when the HNTs content increases to 40 wt%, which is 380 times higher than that obtained for aligned nanotubes parallel to the electrode, which is 1.0 × 10-5 S cm-1. Crucially, the obtained LC nanocomposite ionogels have very high thermal stability, which can sustain 400 °C thermal treatment. The findings will promote the development of novel nanocomposite ionogel electrolytes with faster ion transport and larger anisotropic conductivity.We report a novel class of liquid crystalline (LC) nanohybrid ionogels fabricated via self-assembly of natural halloysite nanotubes (HNTs) in ionic liquids (ILs). The obtained ionogels are very stable and nonvolatile and show LC phases over a wide temperature range. Remarkably, the nanocomposite ionogels exhibit high anisotropic ionic conductivity after shear, and their room temperature ionic conductivity can reach 3.8 × 10-3 S cm-1 for aligned nanotubes perpendicular to the electrode even when the HNTs content increases to 40 wt%, which is 380 times higher than that obtained for aligned nanotubes parallel to the electrode, which is 1.0 × 10-5 S cm-1. Crucially, the obtained LC nanocomposite ionogels have very high thermal stability, which can sustain 400 °C thermal treatment. The findings will promote the development of novel nanocomposite ionogel electrolytes with faster ion transport and larger anisotropic conductivity. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06888f

  13. Anisotropic optical properties of few-layer transition metal dichalcogenide ReS2

    NASA Astrophysics Data System (ADS)

    Li, Zhenglu; Cao, Ting; da Jornada, Felipe H.; Wu, Meng; Louie, Steven G.

    We present first-principles (DFT, GW and GW-BSE) calculations of the electronic and optical properties of few-layer rhenium disulfide (ReS2). Monolayer ReS2 shows strong many-electron effects with a fundamental quasiparticle band gap of 2.38 eV based on G0W0 calculation and a large exciton binding energy of 690 meV based on solving the Bethe-Salpeter equation. Highly anisotropic linear-polarized optical absorptions are revealed for few-layer and bulk ReS2. The band gap shows a decreasing trend with the optical polarization direction near the absorption edge gradually rotating from around 67 degree in the monolayer to 85 degree in the bulk, referencing to the Re-chain. Our calculations are consistent with recent experimental data and theoretical studies, and provide a systematic understanding of the electronic and optical properties in few-layer ReS2. This work was supported by National Science Foundation Grant No. DMR15-1508412 and the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Computational resources have been provided by DOE at Lawrence Berkeley National Laboratory's NERSC facility.

  14. Can anisotropic conductivity in the lower ionosphere and in the Earth's crust be studied by Schumann resonance transients?

    NASA Astrophysics Data System (ADS)

    Ludván, Brigitta; Bór, József; Steinbach, Péter; Novák, Attila; Sátori, Gabriella

    2015-04-01

    to anisotropic conductivity in the Earth's crust below the observatory. On the other hand, the diurnal variation of source azimuth deviations is rather due to different conductivities in the upper waveguide boundary (i.e. in the lower ionosphere) above the detection site during day and night.

  15. Influence of anisotropic electrical conductivity in white matter tissue on the EEG/MEG forward and inverse solution. A high-resolution whole head simulation study.

    PubMed

    Güllmar, Daniel; Haueisen, Jens; Reichenbach, Jürgen R

    2010-05-15

    To investigate the influence of anisotropic electrical conductivity in white matter on the forward and inverse solution in electroencephalography (EEG) and magnetoencephalography (MEG) numerical simulation studies were performed. A high-resolution (1 mm3 isotropic) finite element model of a human head was implemented to study the sensitivity of EEG and MEG source localization. In vivo information on the anisotropy was obtained from magnetic resonance diffusion tensor imaging and included into the model, whereas both a direct transformation and a direct transformation with volume normalization were used to obtain conductivity tensors. Additionally, fixed artificial anisotropy ratios were also used, while considering only the orientation information from DTI, to generate conductivity tensors. Analysis was performed using over 25,000 single dipolar sources covering the full neocortex. Major findings of the study include that EEG is more sensitive to anisotropic conductivities in white matter compared to MEG. Especially with the inverse analysis, we found that sources placed deep in sulci are located more laterally if anisotropic conductivity of white matter tissue is neglected. Overall, the single-source localization errors resulting from a neglect of anisotropy were found to be smaller compared to errors associated with other modeling errors, like misclassified tissue or the use of nonrealistic head models. In contrast to the small localization error we observed significant changes in magnitude and orientation. The latter is important since dipole orientation might be more important than absolute dipole localization in assigning, e.g., epileptic activity to the wall of the affected brain sulcal area. If high-resolution finite element models are used to perform source localization in EEG and MEG experiments and the quality of the measured data permits localization accuracy of 1 mm and below, the influence of anisotropic compartments has to be taken into account

  16. Anisotropic mechanical properties of zircon and the effect of radiation damage

    NASA Astrophysics Data System (ADS)

    Beirau, Tobias; Nix, William D.; Bismayer, Ulrich; Boatner, Lynn A.; Isaacson, Scott G.; Ewing, Rodney C.

    2016-10-01

    This study provides new insights into the relationship between radiation-dose-dependent structural damage due to natural U and Th impurities and the anisotropic mechanical properties (Poisson's ratio, elastic modulus and hardness) of zircon. Natural zircon samples from Sri Lanka (see Muarakami et al. in Am Mineral 76:1510-1532, 1991) and synthetic samples, covering a dose range of zero up to 6.8 × 1018 α-decays/g, have been studied by nanoindentation. Measurements along the [100] crystallographic direction and calculations, based on elastic stiffness constants determined by Özkan (J Appl Phys 47:4772-4779, 1976), revealed a general radiation-induced decrease in stiffness (~54 %) and hardness (~48 %) and an increase in the Poisson's ratio (~54 %) with increasing dose. Additional indentations on selected samples along the [001] allowed one to follow the amorphization process to the point that the mechanical properties are isotropic. This work shows that the radiation-dose-dependent changes of the mechanical properties of zircon can be directly correlated with the amorphous fraction as determined by previous investigations with local and global probes (Ríos et al. in J Phys Condens Matter 12:2401-2412, 2000a; Farnan and Salje in J Appl Phys 89:2084-2090, 2001; Zhang and Salje in J Phys Condens Matter 13:3057-3071, 2001). The excellent agreement, revealed by the different methods, indicates a large influence of structural and even local phenomena on the macroscopic mechanical properties. Therefore, this study indicates the importance of acquiring better knowledge about the mechanical long-term stability of radiation-damaged materials.

  17. Optical conductivity of a 2DEG with anisotropic Rashba interaction at the interface of LaAlO3/SrTiO3

    NASA Astrophysics Data System (ADS)

    Mawrie, Alestin; Kanti Ghosh, Tarun

    2016-10-01

    We study optical conductivity of a two-dimensional electron gas with anisotropic k-cubic Rashba spin-orbit interaction formed at the LaAlO3/SrTiO3 interface. The anisotropic spin splitting energy gives rise to different features of the optical conductivity in comparison to the isotropic k-cubic Rashba spin-orbit interaction. For large carrier density and strong spin-orbit couplings, the density dependence of Drude weight deviates from the linear behavior. The charge and optical conductivities remain isotropic despite anisotropic nature of the Fermi contours. An infinitesimally small photon energy would suffice to initiate inter-band optical transitions due to degeneracy along certain directions in momentum space. The optical conductivity shows a single peak at a given photon energy depending on the system parameters and then falls off to zero at higher photon energy. These features are lacking for systems with isotropic k-cubic Rashba spin-orbit coupling. These striking features can be used to extract the information about nature of the spin-orbit interaction experimentally and illuminate some light on the orbital origin of the two-dimensional electron gas.

  18. Optical conductivity of a 2DEG with anisotropic Rashba interaction at the interface of LaAlO3/SrTiO3.

    PubMed

    Mawrie, Alestin; Kanti Ghosh, Tarun

    2016-10-26

    We study optical conductivity of a two-dimensional electron gas with anisotropic k-cubic Rashba spin-orbit interaction formed at the LaAlO3/SrTiO3 interface. The anisotropic spin splitting energy gives rise to different features of the optical conductivity in comparison to the isotropic k-cubic Rashba spin-orbit interaction. For large carrier density and strong spin-orbit couplings, the density dependence of Drude weight deviates from the linear behavior. The charge and optical conductivities remain isotropic despite anisotropic nature of the Fermi contours. An infinitesimally small photon energy would suffice to initiate inter-band optical transitions due to degeneracy along certain directions in momentum space. The optical conductivity shows a single peak at a given photon energy depending on the system parameters and then falls off to zero at higher photon energy. These features are lacking for systems with isotropic k-cubic Rashba spin-orbit coupling. These striking features can be used to extract the information about nature of the spin-orbit interaction experimentally and illuminate some light on the orbital origin of the two-dimensional electron gas.

  19. When do fractured media become seismically anisotropic? Some implications on quantifying fracture properties

    NASA Astrophysics Data System (ADS)

    Yousef, B. M.; Angus, D. A.

    2016-06-01

    Fractures are pervasive features within the Earth's crust and they have a significant influence on the multi-physical response of the subsurface. The presence of coherent fracture sets often leads to observable seismic anisotropy enabling seismic techniques to remotely locate and characterise fracture systems. In this study, we confirm the general scale-dependence of seismic anisotropy and provide new results specific to shear-wave splitting (SWS). We find that SWS develops under conditions when the ratio of wavelength to fracture size (λS / d) is greater than 3, where Rayleigh scattering from coherent fractures leads to an effective anisotropy such that effective medium model (EMM) theory is qualitatively valid. When 1 <λS / d < 3 there is a transition from Rayleigh to Mie scattering, where no effective anisotropy develops and hence the SWS measurements are unstable. When λS / d < 1 we observe geometric scattering and begin to see behaviour similar to transverse isotropy. We find that seismic anisotropy is more sensitive to fracture density than fracture compliance ratio. More importantly, we observe that the transition from scattering to an effective anisotropic regime occurs over a propagation distance between 1 and 2 wavelengths depending on the fracture density and compliance ratio. The existence of a transition zone means that inversion of seismic anisotropy parameters based on EMM will be fundamentally biased. More importantly, we observe that linear slip EMM commonly used in inverting fracture properties is inconsistent with our results and leads to errors of approximately 400% in fracture spacing (equivalent to fracture density) and 60% in fracture compliance. Although EMM representations can yield reliable estimates of fracture orientation and spatial location, our results show that EMM representations will systematically fail in providing quantitatively accurate estimates of other physical fracture properties, such as fracture density and compliance

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

    SciTech Connect

    Ronning, Filip; Bauer, Eric D; Sefat, A S; Jin, R; Mcguire, M A; Sales, B C; Mandrus, D

    2009-01-01

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

  1. Anisotropic physical properties of single-crystal U2Rh2Sn in high magnetic fields

    NASA Astrophysics Data System (ADS)

    Prokeš, K.; Gorbunov, D. I.; Reehuis, M.; Klemke, B.; Gukasov, A.; Uhlířová, K.; Fabrèges, X.; Skourski, Y.; Yokaichiya, F.; Hartwig, S.; Andreev, A. V.

    2017-05-01

    We report on the crystal and magnetic structures, magnetic, transport, and thermal properties of U2Rh2Sn single crystals studied in part in high magnetic fields up to 58 T. The material adopts a U3Si2 -related tetragonal crystal structure and orders antiferromagnetically below TN=25 K. The antiferromagnetic structure is characterized by a propagation vector k =(00 1/2 ) . The magnetism in U2Rh2Sn is found to be associated mainly with 5 f states. However, both unpolarized and polarized neutron experiments reveal at low temperatures in zero field non-negligible magnetic moments also on Rh sites. U moments of 0.50(2) μB are directed along the tetragonal axis while Rh moments of 0.06(4) μB form a noncollinear arrangement confined to the basal plane. The response to applied magnetic field is highly anisotropic. Above ˜15 K the easy magnetization direction is along the tetragonal axis. At lower temperatures, however, a stronger response is found perpendicular to the c axis. While for the a axis no magnetic phase transition is observed up to 58 T, for the field applied at 1.8 K along the tetragonal axis we observe above 22.5 T a field-polarized state. A magnetic phase diagram for the field applied along the c axis is presented.

  2. Optical properties of phase shift on reflection and/or transmission through biaxial anisotropic thin films

    NASA Astrophysics Data System (ADS)

    Hou, Yongqiang; Qi, Hongji; Li, Xu; He, Kai; Fang, Ming; Yi, Kui; Shao, Jianda

    2013-07-01

    On the basis of theoretical analysis of biaxial birefringent thin films, this study investigates the optical properties of phase shift on reflection and/or transmission through slanted columnar TiO2 sculptured anisotropic thin film (ATF) deposited with glancing angle deposition (GLAD) technique via reactive electron-beam evaporation. The tilted nanocolumn microstructures of thin film induce the optical anisotropy. The optical constants dispersion equations of TiO2 ATF are determined from fitting the transmittance spectra for s- and p-polarized waves measured at normal and oblique incidence within 400-1200nm. With the extracted structure parameters, the phase shifts of polarized light are analyzed with the characteristic matrix and then measured with spectroscopic ellipsometry in the deposition plane. A reasonably good agreement between the theoretical studies and experimental measurements is obtained. In addition, the dependence of the phase shift on oblique incidence angle is also discussed. The results show a greater generality and superiority of the characteristic matrix method. Birefringence of the biaxial ATF performed a sophisticated phase modulation with varied incidence angles over a broad range to have a wide-angle phase shift.

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

    PubMed

    Denny, William J; Walsh, Michael T

    2014-01-03

    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. © 2013 Published by Elsevier Ltd.

  4. Asymptotic analysis of solution to the nonlinear problem of non-stationary heat conductivity of layered anisotropic non-uniform shells at low Biot numbers on the front surfaces

    NASA Astrophysics Data System (ADS)

    Yankovskii, A. P.

    2017-03-01

    The nonlinear problem of non-stationary heat conductivity of the layered anisotropic heat-sensitive shells was formulated taking into account the linear dependence of thermal-physical characteristics of the materials of phase compositions on the temperature. The initial-boundary-value problem is formulated in the dimensionless form, and four small parameters are identified: thermal-physical, characterizing the degree of heat sensitivity of the layer material; geometric, characterizing the relative thickness of the thin-walled structure, and two small Biot numbers on the front surfaces of shells. A sequential recursion of dimensionless equations is carried out, at first, using the thermalphysical small parameter, then, small Biot numbers and, finally, geometrical small parameter. The first type of recursion allowed us to linearize the problem of heat conductivity, and on the basis of two latter types of recursion, the outer asymptotic expansion of solution to the problem of non-stationary heat conductivity of the layered anisotropic non-uniform shells and plates under boundary conditions of the II and III kind and small Biot numbers on the facial surfaces was built, taking into account heat sensitivity of the layer materials. The resulting two-dimensional boundary problems were analyzed, and asymptotic properties of solutions to the heat conductivity problem were studied. The physical explanation was given to some aspects of asymptotic temperature decomposition.

  5. Multi-phase-field study of the effects of anisotropic grain-boundary properties on polycrystalline grain growth

    NASA Astrophysics Data System (ADS)

    Miyoshi, Eisuke; Takaki, Tomohiro

    2017-09-01

    Numerical studies of the effects of anisotropic (misorientation-dependent) grain-boundary energy and mobility on polycrystalline grain growth have been carried out for decades. However, conclusive knowledge has yet to be obtained even for the simplest two-dimensional case, which is mainly due to limitations in the computational accuracy of the grain-growth models and computer resources that have been employed to date. Our study attempts to address these problems by utilizing a higher-order multi-phase-field (MPF) model, which was developed to accurately simulate grain growth with anisotropic grain-boundary properties. In addition, we also employ general-purpose computing on graphics processing units to accelerate MPF grain-growth simulations. Through a series of simulations of anisotropic grain growth, we succeeded in confirming that both the anisotropies in grain-boundary energy and mobility affect the morphology formed during grain growth. On the other hand, we found the grain growth kinetics in anisotropic systems to follow parabolic law similar to isotropic growth, but only after an initial transient period.

  6. Synthesizing metamaterials with angularly independent effective medium properties based on an anisotropic parameter retrieval technique coupled with a genetic algorithm

    NASA Astrophysics Data System (ADS)

    Jiang, Zhi Hao; Bossard, Jeremy A.; Wang, Xiande; Werner, Douglas H.

    2011-01-01

    In this paper, we present a method to retrieve the effective electromagnetic parameters of a slab of anisotropic metamaterial from reflection and transmission coefficients (or scattering parameters). In this retrieval method, calculated or measured scattering parameters are employed for plane waves incident obliquely on a metamaterial slab at different angles. Useful analytical expressions are derived for extracting the homogeneous anisotropic medium parameters of a metamaterial. To validate the method, the effective permittivity and permeability tensor parameters for a composite split-ring resonator-wire array are retrieved and shown to be consistent with observations previously reported in the literature. This retrieval method is further incorporated into a genetic algorithm (GA) to synthesize an infrared zero-index-metamaterial with a wide field-of-view, demonstrating the utility of the new design approach. The anisotropic parameter retrieval algorithm, when combined with a robust optimizer such as GA, can provide a powerful design tool for exploiting the anisotropic properties in metamaterials to achieve specific angle dependant or independent responses.

  7. Anisotropic in-plane thermal conductivity of black phosphorus nanoribbons at temperatures higher than 100 K.

    PubMed

    Lee, Sangwook; Yang, Fan; Suh, Joonki; Yang, Sijie; Lee, Yeonbae; Li, Guo; Sung Choe, Hwan; Suslu, Aslihan; Chen, Yabin; Ko, Changhyun; Park, Joonsuk; Liu, Kai; Li, Jingbo; Hippalgaonkar, Kedar; Urban, Jeffrey J; Tongay, Sefaattin; Wu, Junqiao

    2015-10-16

    Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing thermal conductivity anisotropy, up to a factor of two, with temperatures above 100 K. A size effect in thermal conductivity was also observed in which thinner nanoribbons show lower thermal conductivity. Analysed with the relaxation time approximation model using phonon dispersions obtained based on density function perturbation theory, the high anisotropy is attributed mainly to direction-dependent phonon dispersion and partially to phonon-phonon scattering. Our results revealing the intrinsic, orientation-dependent thermal conductivity of black phosphorus are useful for designing devices, as well as understanding fundamental physical properties of layered materials.

  8. Anisotropic in-plane thermal conductivity of black phosphorus nanoribbons at temperatures higher than 100 K

    PubMed Central

    Lee, Sangwook; Yang, Fan; Suh, Joonki; Yang, Sijie; Lee, Yeonbae; Li, Guo; Sung Choe, Hwan; Suslu, Aslihan; Chen, Yabin; Ko, Changhyun; Park, Joonsuk; Liu, Kai; Li, Jingbo; Hippalgaonkar, Kedar; Urban, Jeffrey J.; Tongay, Sefaattin; Wu, Junqiao

    2015-01-01

    Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing thermal conductivity anisotropy, up to a factor of two, with temperatures above 100 K. A size effect in thermal conductivity was also observed in which thinner nanoribbons show lower thermal conductivity. Analysed with the relaxation time approximation model using phonon dispersions obtained based on density function perturbation theory, the high anisotropy is attributed mainly to direction-dependent phonon dispersion and partially to phonon–phonon scattering. Our results revealing the intrinsic, orientation-dependent thermal conductivity of black phosphorus are useful for designing devices, as well as understanding fundamental physical properties of layered materials. PMID:26472285

  9. Relation of thermal conductivity with process induced anisotropic void system in EB-PVD PYSZ thermal barrier coatings.

    SciTech Connect

    Renteria, A. F.; Saruhan, B.; Ilavsky, J.; German Aerospace Center

    2007-01-01

    Thermal barrier coatings (TBCs) deposited by Electron-beam physical deposition (EB-PVD) protect the turbine blades situated at the high pressure sector of the aircraft and stationary turbines. It is an important task to uphold low thermal conductivity in TBCs during long-term service at elevated temperatures. One of the most promising methods to fulfil this task is to optimize the properties of PYSZ-based ,TBC by tailoring its microstructure. Thermal conductivity of the EB-PVD produced PYSZ TBCs is influenced mainly by the size, shape, orientation and volume of the various types of porosity present in the coatings. These pores can be classified as open (inter-columnar and between feather arms gaps) and closed (intra-columnar pores). Since such pores are located within the three-dimensionally deposited columns and enclose large differences in their sizes, shapes, distribution and anisotropy, the accessibility for their characterization is very complex and requires the use of sophisticated methods. In this work, three different EB-PVD TBC microstructures were manufactured by varying the process parameters, yielding various characteristics of their pores. The corresponding thermal conductivities in as-coated state and after ageing at 1100C/1h and 100h were measured via Laser Flash Analysis Method (LFA). The pore characteristics and their individual effect on the thermal conductivity are analysed by USAXS which is supported by subsequent modelling and LFA methods, respectively. Evident differences in the thermal conductivity values of each microstructure were found in as-coated and aged conditions. In summary, broader columns introduce higher values in thermal conductivity. In general, thermal conductivity increases after ageing for all three investigated microstructures, although those with initial smaller pore surface area show smaller changes.

  10. Relation of Thermal Conductivity with Process Induced Anisotropic Void Systems in EB-PVD PYSZ Thermal Barrier Coatings

    SciTech Connect

    Renteria, A. Flores; Saruhan-Brings, B.; Ilavsky, J.

    2008-03-03

    Thermal barrier coatings (TBCs) deposited by Electron-beam physical deposition (EB-PVD) protect the turbine blades situated at the high pressure sector of the aircraft and stationary turbines. It is an important task to uphold low thermal conductivity in TBCs during long-term service at elevated temperatures. One of the most promising methods to fulfil this task is to optimize the properties of PYSZ-based TBC by tailoring its microstructure. Thermal conductivity of the EB-PVD produced PYSZ TBCs is influenced mainly by the size, shape, orientation and volume of the various types of porosity present in the coatings. These pores can be classified as open (inter-columnar and between feather arms gaps) and closed (intra-columnar pores). Since such pores are located within the three-dimensionally deposited columns and enclose large differences in their sizes, shapes, distribution and anisotropy, the accessibility for their characterization is very complex and requires the use of sophisticated methods. In this work, three different EB-PVD TBC microstructures were manufactured by varying the process parameters, yielding various characteristics of their pores. The corresponding thermal conductivities in as-coated state and after ageing at 11000C/1h and 100h were measured via Laser Flash Analysis Method (LFA). The pore characteristics and their individual effect on the thermal conductivity are analysed by USAXS which is supported by subsequent modelling and LFA methods, respectively. Evident differences in the thermal conductivity values of each microstructure were found in as-coated and aged conditions. In summary, broader columns introduce higher values in thermal conductivity. In general, thermal conductivity increases after ageing for all three investigated microstructures, although those with initial smaller pore surface area show smaller changes.

  11. Calculation of effective conductivity of 2D and 3D composite materials with anisotropic constituents and different inclusion shapes in Mathematica

    NASA Astrophysics Data System (ADS)

    Gómez-Muñoz, José Luis; Bravo-Castillero, Julián

    2008-08-01

    The study of the effective properties of composite materials with anisotropic constituents and different inclusion shapes has motivated the development of the Mathematica 6.0 package "CompositeMaterials". This package can be used to calculate the effective anisotropic conductivity tensor of two-phase composites. Any fiber cross section, even percolating ones, can be studied in the 2D composites. "Rectangular Prism" and "Ellipsoidal" inclusion shapes with arbitrary orientations can be investigated in the 3D composites. This package combines the Asymptotic Homogenization Method and the Finite Element Method in order to obtain the effective conductivity tensor. The commands and options of the package are illustrated with two sample applications for two- and three-dimensional composites. Program summaryProgram title:CompositeMaterials Catalogue identifier:AEAU_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEAU_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.:132 183 No. of bytes in distributed program, including test data, etc.:1 334 908 Distribution format:tar.gz Programming language:Mathematica 6.0 Computer:Any that can run Mathematica 6.0 and where the open-source free C-programs Triangle ( http://www.cs.cmu.edu/ quake/triangle.html) and TetGen ( http://tetgen.berlios.de/) can be compiled and executed. Tested in Intel Pentium computers. Operating system:Any that can run Mathematica 6.0 and where the open-source free C-programs Triangle ( http://www.cs.cmu.edu/ quake/triangle.html) and TetGen ( http://tetgen.berlios.de/) can be compiled and executed. Tested in Windows XP. RAM:Small two-dimensional calculations require less than 100 MB. Large three-dimensional calculations require 500 MB or more. Classification:7.9 External routines:One Mathematica Add-on and

  12. Mechanical property and conductivity of a flax fibre weave strengthened magnetorheological elastomer

    NASA Astrophysics Data System (ADS)

    Gong, Xinglong; Wang, Yu; Hu, Tao; Xuan, Shouhu

    2017-07-01

    This work reported a novel flax-fibre-weaves (FFWs) incorporated magnetorheological elastomer (MRE), whose shear properties, compressive properties, tensile properties, and electrical performance were critically increased by the FFWs. In comparison to the pure MRE, the plastic deformation of the FFW-MRE was smaller and it absorbed more energy under the quasi-static compression and tension. With increasing of the FFW from 1 to 2 and 3 layers, the tensile strength of the MRE increased by 500%, 1300% and 3200% approximately. Because the carbonyl iron particles can form chain-like aggregation structure along the fibre directions, the conductivity of the FFW-MRE showed a typical anisotropic characteristic and it was sensitive to the external stimulus. When the compressive direction was parallel to the fibre weaves, the resistance of the FFW-MRE reduced to 2.7 kΩ, which was only 1/71 of the pure MRE. A possible mechanism was proposed to investigate in detail mechanical and electrical properties of the FFW-MRE. This method provides an economical, effective and environmentally friendly way to improve shear properties, compressive properties, tensile properties and conductivity of MREs.

  13. Anisotropic magnetic properties and superzone gap formation in CeGe single crystal.

    PubMed

    Das, Pranab Kumar; Kumar, Neeraj; Kulkarni, R; Dhar, S K; Thamizhavel, A

    2012-04-11

    Single crystals of CeGe and its non-magnetic analog LaGe have been grown by the Czochralski method. The CeGe compound crystallizes in the orthorhombic FeB-type crystal structure with the space group Pnma (#62). The anisotropic magnetic properties have been investigated for well oriented single crystals by measuring the magnetic susceptibility, electrical resistivity and heat capacity. It has been found that CeGe orders antiferromagnetically at 10.5 K. Both transport and magnetic studies have revealed large anisotropy, reflecting the orthorhombic crystal structure. The magnetization data at 1.8 K reveal metamagnetic transitions along the [010] direction at 4.8 and 6.4 T and along the [100] direction at a critical field of 10.7 T, while the magnetization along the [001] direction increases linearly without any anomaly up to a field of 16 T. From the magnetic susceptibility and the magnetization measurements it has been found that the [010] direction is the easy axis of magnetization. The electrical resistivity along the three crystallographic directions exhibits an upturn at T(N), indicating superzone gap formation below T(N) in this compound. We have performed crystal electric field analysis on the magnetic susceptibility and the heat capacity data and found that the ground state is a doublet, and the energies of splitting from the ground state to the first and second excited doublet states were estimated to be 39 and 111 K, respectively.

  14. Size dependent anisotropic strain and optical properties of strained Si nanocrystals.

    PubMed

    Dhara, Soumen; Giri, P K

    2011-10-01

    We report on the growth of strained Si nanocrystals (NCs) of sizes in the range 5-43 nm and analyze the detailed nature of strain and its influence on the optical properties of the NCs as a function of size. Freestanding Si NPs were prepared in a controlled way using a contamination free mechanical ball milling for duration 2-40 hrs. Structural analysis based on X-ray diffraction (XRD) pattern and high resolution transmission electron microscopy (HRTEM) confirms the good crystalline nature of these Si NCs. A detailed analysis of XRD line profile reveals that nature of the strain is anisotropic and the screw type dislocations are the main contributors to the lattice strain. The dislocation density and corresponding strain changes non-monotonically, while the crystallite size changes monotonically with milling time. Direct evidence of dislocations is shown from HRTEM images. The UV-vis-NIR absorption spectra of the Si NCs show an enhanced absorption band in the visible region that shows a systematic blue shift with reduced NC sizes. Si NCs with size approximately 5-10 nm exhibits a distinct photoluminescence (PL) band in the visible region at 580-585 nm at room temperature, while higher size NCs does not exhibit any visible emission. PL excitation measurement shows a very small Stokes shift for the visible emission band indicating no involvement of defects/interface in the emission. We argue that the observed absorption and emission can be explained based on the enhanced confinement effect on the strained Si NCs due to the combined effect of strain and size quantization.

  15. Thermal conductivity calculation in anisotropic crystals by molecular dynamics: Application to α-Fe2O3.

    PubMed

    Severin, Jonathan; Jund, Philippe

    2017-02-07

    In this work, we aim to study the thermal properties of materials using classical molecular dynamics simulations and specialized numerical methods. We focus primarily on the thermal conductivity κ using non-equilibrium molecular dynamics (NEMD) to study the response of a crystalline solid, namely hematite (α-Fe2O3), to an imposed heat flux as is the case in real life applications. We present a methodology for the calculation of κ as well as an adapted potential for hematite. Taking into account the size of the simulation box, we show that not only the longitudinal size (in the direction of the heat flux) but also the transverse size plays a role in the determination of κ and should be converged properly in order to have reliable results. Moreover we propose a comparison of thermal conductivity calculations in two different crystallographic directions to highlight the spatial anisotropy and we investigate the non-linear temperature behavior typically observed in NEMD methods.

  16. Thermal conductivity calculation in anisotropic crystals by molecular dynamics: Application to α-Fe2O3

    NASA Astrophysics Data System (ADS)

    Severin, Jonathan; Jund, Philippe

    2017-02-01

    In this work, we aim to study the thermal properties of materials using classical molecular dynamics simulations and specialized numerical methods. We focus primarily on the thermal conductivity κ using non-equilibrium molecular dynamics (NEMD) to study the response of a crystalline solid, namely hematite (α -Fe2O3 ), to an imposed heat flux as is the case in real life applications. We present a methodology for the calculation of κ as well as an adapted potential for hematite. Taking into account the size of the simulation box, we show that not only the longitudinal size (in the direction of the heat flux) but also the transverse size plays a role in the determination of κ and should be converged properly in order to have reliable results. Moreover we propose a comparison of thermal conductivity calculations in two different crystallographic directions to highlight the spatial anisotropy and we investigate the non-linear temperature behavior typically observed in NEMD methods.

  17. Anisotropic lattice thermal conductivity in three-fold degeneracy topological semimetal MoP: a first-principles study.

    PubMed

    Guo, San-Dong

    2017-08-30

    Recently, three-component new fermions in topological semimetal MoP are experimentally observed (2017 Nature 546 627), which may have potential applications like topological qubits, low-power electronics and spintronics. These are closely related to thermal transport properties of MoP. In this work, the phonon transport of MoP is investigated by solving the linearized phonon Boltzmann equation within the single-mode relaxation time approximation (RTA). The calculated room-temperature lattice thermal conductivity is 18.41 [Formula: see text] and 34.71 [Formula: see text] along the in- and cross-plane directions, exhibiting very strong anisotropy. The isotope and size effects on the lattice thermal conductivity are also considered. It is found that isotope scattering produces little effect, and phonon has little contribution to the lattice thermal conductivity, when phonon mean free path (MFP) is larger than 0.15 [Formula: see text] at 300 K. It is noted that average room-temperature lattice thermal conductivity of MoP is lower than that of representative Weyl semimetal TaAs, which is due to smaller group velocities and larger Grüneisen parameters. Our works provide valuable informations for the thermal management of MoP-based nano-electronics devices, and motivate further experimental works to study thermal transport of MoP.

  18. Macroscopic properties of isotropic and anisotropic fracture networks from the percolation threshold to very large densities

    NASA Astrophysics Data System (ADS)

    Adler, P. M.; Thovert, J.; Mourzenko, V.

    2011-12-01

    The main purpose of this review paper is to summarize some recent studies of fracture networks. Progress has been made possible thanks to a very versatile numerical technique based on a three-dimensional discrete description of the fracture networks. Any network geometry, any boundary condition, and any distribution of the fractures can be addressed. The first step is to mesh the fracture network as it is by triangles of a controlled size. The second step consists in the discretization of the conservation equations by the finite volume technique. Two important properties were systematically studied, namely the percolation threshold rho_c and the macroscopic permeability K_n of the fracture network. Dimensionless quantities are denoted by a prime. The numerical results are interpreted in a systematic way with the concept of excluded volume which enables us to define a dimensionless fracture density rho' equal in the average to the average number of intersections per fracture. 1. Isotropic networks of identical fractures The dimensionless percolation threshold rho'_c of such networks was systematically studied for fractures of various shapes. rho'_c was shown to be almost independent of the shape except when one has very elongated rectangles. A formula is proposed for rho'_c. The permeability of these networks was calculated for a wide range of fracture densities and shapes. K'_n(rho') is almost independent of the fracture shape; an empirical formula is proposed for any value of rho' between rho'_c and infinity. For large rho', K_n is well approximated by the Snow formula initially derived for infinite fractures. 2. Anisotropic networks of identical fractures The fracture orientations are supposed to follow a Fisher distribution characterized by the parameter kappa; when kappa=0, the fractures are isotropic; when kappa=infinity, the fractures are perpendicular to a given direction. rho'_c does not depend significantly on kappa and the general formula proposed in 1

  19. Anisotropic temperature-dependent thermal conductivity by an Al2O3 interlayer in Al2O3/ZnO superlattice films

    NASA Astrophysics Data System (ADS)

    Lee, Won-Yong; Lee, Jung-Hoon; Ahn, Jae-Young; Park, Tae-Hyun; Park, No-Won; Kim, Gil-Sung; Park, Jin-Seong; Lee, Sang-Kwon

    2017-03-01

    The thermal conductivity of superlattice films is generally anisotropic and should be studied separately in the in-plane and cross-plane directions of the films. However, previous works have mostly focused on the cross-plane thermal conductivity because the electrons and phonons in the cross-plane direction of superlattice films may result in much stronger interface scattering than that in the in-plane direction. Nevertheless, it is highly desirable to perform systematic studies on the effect of interface formation in semiconducting superlattice films on both in-plane and cross-plane thermal conductivities. In this study, we determine both the in-plane and cross-plane thermal conductivities of Al2O3 (AO)/ZnO superlattice films grown by atomic layer deposition (ALD) on SiO2/Si substrates in the temperature range of 50-300 K by the four-point-probe 3-ω method. Our experimental results indicate that the formation of an atomic AO layer (0.82 nm) significantly contributes to the decrease of the cross-plane thermal conductivity of the AO/ZnO superlattice films compared with that of AO/ZnO thin films. The cross-plane thermal conductivity (0.26-0.63 W m-1 K-1 of the AO/ZnO superlattice films (with an AO layer of ˜0.82 nm thickness) is approximately ˜150%-370% less than the in-plane thermal conductivity (0.96-1.19 W m-1 K-1) of the corresponding film, implying significant anisotropy. This indicates that the suppression of the cross-plane thermal conductivity is mainly attributed to the superlattice, rather than the nanograin columnar structure in the films. In addition, we theoretically analyzed strong anisotropic behavior of the in-plane and cross-plane thermal conductivities of the AO/ZnO superlattice films in terms of temperature dependence.

  20. Anisotropic temperature-dependent thermal conductivity by an Al2O3 interlayer in Al2O3/ZnO superlattice films.

    PubMed

    Lee, Won-Yong; Lee, Jung-Hoon; Ahn, Jae-Young; Park, Tae-Hyun; Park, No-Won; Kim, Gil-Sung; Park, Jin-Seong; Lee, Sang-Kwon

    2017-03-10

    The thermal conductivity of superlattice films is generally anisotropic and should be studied separately in the in-plane and cross-plane directions of the films. However, previous works have mostly focused on the cross-plane thermal conductivity because the electrons and phonons in the cross-plane direction of superlattice films may result in much stronger interface scattering than that in the in-plane direction. Nevertheless, it is highly desirable to perform systematic studies on the effect of interface formation in semiconducting superlattice films on both in-plane and cross-plane thermal conductivities. In this study, we determine both the in-plane and cross-plane thermal conductivities of Al2O3 (AO)/ZnO superlattice films grown by atomic layer deposition (ALD) on SiO2/Si substrates in the temperature range of 50-300 K by the four-point-probe 3-ω method. Our experimental results indicate that the formation of an atomic AO layer (0.82 nm) significantly contributes to the decrease of the cross-plane thermal conductivity of the AO/ZnO superlattice films compared with that of AO/ZnO thin films. The cross-plane thermal conductivity (0.26-0.63 W m(-1) K(-1) of the AO/ZnO superlattice films (with an AO layer of ∼0.82 nm thickness) is approximately ∼150%-370% less than the in-plane thermal conductivity (0.96-1.19 W m(-1) K(-1)) of the corresponding film, implying significant anisotropy. This indicates that the suppression of the cross-plane thermal conductivity is mainly attributed to the superlattice, rather than the nanograin columnar structure in the films. In addition, we theoretically analyzed strong anisotropic behavior of the in-plane and cross-plane thermal conductivities of the AO/ZnO superlattice films in terms of temperature dependence.

  1. An anisotropically and heterogeneously aligned patterned electrospun scaffold with tailored mechanical property and improved bioactivity for vascular tissue engineering.

    PubMed

    Xu, He; Li, Haiyan; Ke, Qinfei; Chang, Jiang

    2015-04-29

    The development of vascular scaffolds with controlled mechanical properties and stimulatory effects on biological activities of endothelial cells still remains a significant challenge to vascular tissue engineering. In this work, we reported an innovative approach to prepare a new type of vascular scaffolds with anisotropically and heterogeneously aligned patterns using electrospinning technique with unique wire spring templates, and further investigated the structural effects of the patterned electrospun scaffolds on mechanical properties and angiogenic differentiation of human umbilical vein endothelial cells (HUVECs). Results showed that anisotropically aligned patterned nanofibrous structure was obtained by depositing nanofibers on template in a structurally different manner, one part of nanofibers densely deposited on the embossments of wire spring and formed cylindrical-like structures in the transverse direction, while others loosely suspended and aligned along the longitudinal direction, forming a three-dimensional porous microstructure. We further found that such structures could efficiently control the mechanical properties of electrospun vascular scaffolds in both longitudinal and transverse directions by altering the interval distances between the embossments of patterned scaffolds. When HUVECs were cultured on scaffolds with different microstructures, the patterned scaffolds distinctively promoted adhesion of HUVECs at early stage and proliferation during the culture period. Most importantly, cells experienced a large shape change associated with cell cytoskeleton and nuclei remodeling, leading to a stimulatory effect on angiogenesis differentiation of HUVECs by the patterned microstructures of electrospun scaffolds, and the scaffolds with larger distances of intervals showed a higher stimulatory effect. These results suggest that electrospun scaffolds with the anisotropically and heterogeneously aligned patterns, which could efficiently control the

  2. Anisotropic thermoelectric properties of layered compounds in SnX2 (X = S, Se): a promising thermoelectric material.

    PubMed

    Sun, Bao-Zhen; Ma, Zuju; He, Chao; Wu, Kechen

    2015-11-28

    Thermoelectrics interconvert heat to electricity and are of great interest in waste heat recovery, solid-state cooling and so on. Here we assessed the potential of SnS2 and SnSe2 as thermoelectric materials at the temperature gradient from 300 to 800 K. Reflecting the crystal structure, the transport coefficients are highly anisotropic between a and c directions, in particular for the electrical conductivity. The preferred direction for both materials is the a direction in TE application. Most strikingly, when 800 K is reached, SnS2 can show a peak power factor (PF) of 15.50 μW cm(-1) K(-2) along the a direction, while a relatively low value (11.72 μW cm(-1) K(-2)) is obtained in the same direction of SnSe2. These values are comparable to those observed in thermoelectrics such as SnSe and SnS. At 300 K, the minimum lattice thermal conductivity (κmin) along the a direction is estimated to be about 0.67 and 0.55 W m(-1) K(-1) for SnS2 and SnSe2, respectively, even lower than the measured lattice thermal conductivity of Bi2Te3 (1.28 W m(-1) K(-1) at 300 K). The reasonable PF and κmin suggest that both SnS2 and SnSe2 are potential thermoelectric materials. Indeed, the estimated peak ZT can approach 0.88 for SnSe2 and a higher value of 0.96 for SnS2 along the a direction at a carrier concentration of 1.94 × 10(19) (SnSe2) vs. 2.87 × 10(19) cm(-3) (SnS2). The best ZT values in SnX2 (X = S, Se) are comparable to that in Bi2Te3 (0.8), a typical thermoelectric material. We hope that this theoretical investigation will provide useful information for further experimental and theoretical studies on optimizing the thermoelectric properties of SnX2 materials.

  3. Anisotropic Mechanical Properties of Plasma-Sprayed Thermal Barrier Coatings at High Temperature Determined by Ultrasonic Method

    NASA Astrophysics Data System (ADS)

    Wei, Qin; Zhu, Jianguo; Chen, Wei

    2016-02-01

    The mechanical properties of plasma-sprayed thermal barrier coatings (TBC) are of great scientific and technological significance for the design and fabrication of TBC systems. The ultrasonic method combined with a sing-around method for mechanical properties measurement of TBC is deduced and the elastic modulus can be determined in the spray, or longitudinal, direction, and the transverse direction. Tested specimens of plasma-sprayed TBC are detached from the substrate and treated with thermal exposure at 1400 °C. The elastic moduli along the longitudinal and transverse directions of the TBCs are measured by different types of ultrasonic waves combined with a sing-around method, while the Poisson's ratio is also obtained simultaneously. The experimental results indicate that the magnitude of longitudinal elastic modulus is larger than that of the transverse one, and thus the plasma-sprayed TBC has an anisotropic mechanical property. Moreover, the elastic moduli along both longitudinal and transverse directions change with high-temperature exposure time, which consists of a rapid increasing stage followed by a slow decreasing stage. In addition, the magnitude of Poisson's ratio increases slightly from 0.05 to 0.2 with the high-temperature exposure time. Generally, the microstructures in the plasma-sprayed coatings and their evolution in a high-temperature environment are the main causes of the varying anisotropic mechanical properties.

  4. Optic phonons and anisotropic thermal conductivity in hexagonal Ge2Sb2Te5

    SciTech Connect

    Mukhopadhyay, Saikat; Lindsay, Lucas R.; Singh, David

    2016-11-16

    The lattice thermal conductivity ($κ$) of hexagonal Ge2Sb2Tesub>5 (h-GST) is studied via direct first-principles calculations. We find significant intrinsic anisotropy of ( $κ$a/$κ$c~2) of $κ$ in bulk h-GST along different transport directions. The dominant contribution to$κ$ is from optic phonons, ~75%. This is extremely unusual as the acoustic phonon modes carry most of the heat in typical semiconductors and insulators with small unit cells. Very recently, Lee et. al. observed anisotropic in GST thin films and attributed this to thermal resistance of amorphous regions near grain boundaries. However, our results suggest an additional strong intrinsic anisotropy for the pure hexagonal phase. This derives from bonding anisotropy along different crystal directions, specifically from weak interlayer coupling, which gives anisotropic phonon dispersions. The phonon spectrum of h-GST has very dispersive optic branches with higher group velocities along the a-axis as compared to flat optic bands along the c-axis. The importance of optic mode contributions for the thermal conductivity in low-$κ$ h-GST is unusual, and development of fundamental physical understanding of these contributions may be critical to better understanding of thermal conduction in other complex layered materials.

  5. Tensile and electrical properties of high-strength high-conductivity copper alloys

    SciTech Connect

    Zinkle, S.J.; Eatherly, W.S.

    1998-09-01

    Electrical conductivity and tensile properties have been measured on an extruded and annealed CuCrNb dispersion strengthened copper alloy which has been developed for demanding aerospace high heat flux applications. The properties of this alloy are somewhat inferior to GlidCop dispersion strengthened copper and prime-aged CuCrZr over the temperature range of 20--500 C. However, if the property degradation in CuCrZr due to joining operations and the anisotropic properties of GlidCop in the short transverse direction are taken into consideration, CuCrNb may be a suitable alternative material for high heat flux structural applications in fusion energy devices. The electrical conductivity and tensile properties of CuCrZr that was solution annealed and then simultaneously aged and diffusion bonded are also summarized. A severe reduction in tensile elongation is observed in the diffusion bonded joint, particularly if a thin copper shim is not placed in the diffusion bondline.

  6. Pulse transient hot strip technique adapted for slab sample geometry to study anisotropic thermal transport properties of μm-thin crystalline films.

    PubMed

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

    2014-04-01

    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 μm) 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-μm 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 μm, 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.

  7. Anisotropic electrical and thermal conductivity in Bi2AE2Co2O8+δ [AE = Ca, Sr1-xBax (x = 0.0, 0.25, 0.5, 0.75, 1.0)] single crystals

    NASA Astrophysics Data System (ADS)

    Dong, Song-Tao; Zhang, Bin-Bin; Xiong, Ye; Lv, Yang-Yang; Yao, Shu-Hua; Chen, Y. B.; Zhou, Jian; Zhang, Shan-Tao; Chen, Yan-Feng

    2015-09-01

    Bi2AE2Co2O8+δ (AE represents alkaline earth), constructed by stacking of rock-salt Bi2AE2O4 and triangle CoO2 layers alternatively along c-axis, is one of promising thermoelectric oxides. The most impressive feature of Bi2AE2Co2O8+δ, as reported previously, is their electrical conductivity mainly lying along CoO2 plane, adjusting Bi2AE2O4 layer simultaneously manipulates both thermal conductivity and electrical conductivity. It in turn optimizes thermoelectric performance of these materials. In this work, we characterize the anisotropic thermal and electrical conductivity along both ab-plane and c-direction of Bi2AE2Co2O8+δ (AE = Ca, Sr, Ba, Sr1-xBax) single crystals. The results substantiate that isovalence replacement in Bi2AE2Co2O8+δ remarkably modifies their electrical property along ab-plane; while their thermal conductivity along ab-plane only has a slightly difference. At the same time, both the electrical conductivity and thermal conductivity along c-axis of these materials also have dramatic changes. Certainly, the electrical resistance along c-axis is too high to be used as thermoelectric applications. These results suggest that adjusting nano-block Bi2AE2O4 layer in Bi2AE2Co2O8+δ cannot modify the thermal conductivity along high electrical conductivity plane (ab-plane here). The evolution of electrical property is discussed by Anderson localization and electron-electron interaction U. And the modification of thermal conductivity along c-axis is attributed to the microstructure difference. This work sheds more light on the manipulation of the thermal and electrical conductivity in the layered thermoelectric materials.

  8. Magnetic Cellulose Nanocrystal Based Anisotropic Polylactic Acid Nanocomposite Films: Influence on Electrical, Magnetic, Thermal, and Mechanical Properties.

    PubMed

    Dhar, Prodyut; Kumar, Amit; Katiyar, Vimal

    2016-07-20

    This paper reports a single-step co-precipitation method for the fabrication of magnetic cellulose nanocrystals (MGCNCs) with high iron oxide nanoparticle content (∼51 wt % loading) adsorbed onto cellulose nanocrystals (CNCs). X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman spectroscopic studies confirmed that the hydroxyl groups on the surface of CNCs (derived from the bamboo pulp) acted as anchor points for the adsorption of Fe3O4 nanoparticles. The fabricated MGCNCs have a high magnetic moment, which is utilized to orient the magnetoresponsive nanofillers in parallel or perpendicular orientations inside the polylactic acid (PLA) matrix. Magnetic-field-assisted directional alignment of MGCNCs led to the incorporation of anisotropic mechanical, thermal, and electrical properties in the fabricated PLA-MGCNC nanocomposites. Thermomechanical studies showed significant improvement in the elastic modulus and glass-transition temperature for the magnetically oriented samples. Differential scanning calorimetry (DSC) and XRD studies confirmed that the alignment of MGCNCs led to the improvement in the percentage crystallinity and, with the absence of the cold-crystallization phenomenon, finds a potential application in polymer processing in the presence of magnetic field. The tensile strength and percentage elongation for the parallel-oriented samples improved by ∼70 and 240%, respectively, and for perpendicular-oriented samples, by ∼58 and 172%, respectively, in comparison to the unoriented samples. Furthermore, its anisotropically induced electrical and magnetic properties are desirable for fabricating self-biased electronics products. We also demonstrate that the fabricated anisotropic PLA-MGCNC nanocomposites could be laminated into films with the incorporation of directionally tunable mechanical properties. Therefore, the current study provides a novel noninvasive approach of orienting nontoxic bioderived CNCs in the presence of low

  9. Entropy-Driven Pt3Co Nanocube Assembles and Thermally Mediated Electrical Conductivity with Anisotropic Variation of the Rhombohedral Superlattice.

    PubMed

    Zhang, Jun; Zhu, Jinlong; Li, Ruipeng; Fang, Jiye; Wang, Zhongwu

    2017-01-11

    Understanding the shape-dependent superlattices and resultant anisotropies of both structure and property allows for rational design of materials processing and engineering to fabricate transformative materials with useful properties for applications. This work shows the structural evolution from square lattice of two-dimensional (2D) thin film to rhombic lattice of large three-dimensional (3D) assembles of Pt3Co nanocubes (NCs). Synchrotron-based X-ray supercrystallography determines the superlattice of large 3D supercrystal into an obtuse rhombohedral (Rh) symmetry, which holds a long-range coherence of both NC translation and atomic crystallographic orientation. The Rh superlattice has a trigonal cell angle of 104°, and the constitute NCs orient their atomic Pt3Co(111) planes to the superlattice Rh[111] direction. The temperature-dependent in situ small and wide-angle X-ray scattering (SAXS/WAXS) measurements reveal a thermally induced superlattice contraction of supercrystal, which maintains translational ordering but slightly develops orientational disordering. The observed increases of both the packing density and the rotation magnitude of NCs indicate a rational compromise between configurational and rotational entropies of NCs. The resultant minimization of the total free energy is responsible for the formation and stability of the obtuse Rh superlattice. The temperature-dependent in situ measurements of SAXS and electrical resistance reveal that, in conjunction with the thermally induced sharp contraction of superlattice at 160 °C, the supercrystal becomes measurable of electrical resistance, which was followed by a temperature-dependent linear increase. Upon rapid annealing from 250 °C, the supercrystal remains almost constant in both structure and electrical resistance. The heating-enabled electrical conductivity of the supercrystal at high temperature implies the formation of a NC-interconnected architecture. The experiments and overall analysis

  10. Chemical Vapor Deposition Synthesis of Ultrathin Hexagonal ReSe2 Flakes for Anisotropic Raman Property and Optoelectronic Application.

    PubMed

    Hafeez, Muhammad; Gan, Lin; Li, Huiqiao; Ma, Ying; Zhai, Tianyou

    2016-10-01

    Hexagonal crystalline ultrathin ReSe2 flakes are synthesized for the first time by a chemical vapor deposition (CVD) method. The as-synthesized ReSe2 flake is revealed as a novel structure, which has mirror-symmetric single-crystal domains inside, by polarization incident Raman and HRTEM. The successful development of the CVD method will facilitate research on the novel anisotropic electronic/optoelectronic properties of ReSe2 in the future. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Anisotropic Thermal and Electrical Properties of Thin Thermal Interface Layers of Graphite Nanoplatelet-Based Composites

    PubMed Central

    Tian, Xiaojuan; Itkis, Mikhail E.; Bekyarova, Elena B.; Haddon, Robert C.

    2013-01-01

    Thermal interface materials (TIMs) are crucial components of high density electronics and the high thermal conductivity of graphite makes this material an attractive candidate for such applications. We report an investigation of the in-plane and through-plane electrical and thermal conductivities of thin thermal interface layers of graphite nanoplatelet (GNP) based composites. The in-plane electrical conductivity exceeds its through-plane counterpart by three orders of magnitude, whereas the ratio of the thermal conductivities is about 5. Scanning electron microscopy reveals that the anisotropy in the transport properties is due to the in-plane alignment of the GNPs which occurs during the formation of the thermal interface layer. Because the alignment in the thermal interface layer suppresses the through-plane component of the thermal conductivity, the anisotropy strongly degrades the performance of GNP-based composites in the geometry required for typical thermal management applications and must be taken into account in the development of GNP-based TIMs.

  12. Blind inversion method using Lamb waves for the complete elastic property characterization of anisotropic plates.

    PubMed

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

    2009-02-01

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

  13. First-principles investigation on vibrational, anisotropic elastic and thermodynamic properties for L12 structure of Al3Er and Al3Yb under high pressure

    NASA Astrophysics Data System (ADS)

    Zhang, Xudong; Jiang, Wei

    2016-02-01

    To better clarify the physical properties for Al3RE precipitates, first-principles calculations are performed to investigate the vibrational, anisotropic elastic and thermodynamic properties of Al3Er and Al3Yb. The calculated results agree well with available experimental and theoretical ones. The vibrational properties indicate that Al3Er and Al3Yb will keep their dynamical stabilities with L12 structure up to 100 GPa. The elastic constants are satisfied with mechanical stability criteria up to the external pressure of 100 GPa. The mechanical anisotropy is predicted by anisotropic constants AG, AU, AZ and 3D curved surface of Young's modulus. The calculated results show that both Al3Er and Al3Yb are isotropic at zero pressure and obviously anisotropic under high pressure. Further, we systematically investigate the thermodynamic properties and provide the relationships between thermal parameters and pressure. Finally, the pressure-dependent behaviours of density of states, Mulliken charge and bond length are discussed.

  14. First-principle studies on the influence of anisotropic pressure on the physical properties of aluminum nitride

    NASA Astrophysics Data System (ADS)

    Wang, Zhifan; Zhao, Junwu; Gao, Yang; Zhang, Yanning

    2017-01-01

    In this work, we performed extensive first-principle studies to discuss the effect of uniaxial and biaxial mechanical pressure on the structural and physical properties of AlN piezoelectric material, including the longitudinal elastic constant (C 33), piezoelectric constant (e 33), static dielectric constant (ε 33), and mass density (ρ). In particular, we give the relationship between the paramters mentioned above and the longitudinal acoustic wave velocity (V) under anisotropic pressure. Our results show that the applied uniaxial or biaxial pressure in the basal plane has a more obvious influence on physical properties of AlN than the uniaxial pressure along hexagonal axis. The pressure-induced variations of C 33, e 33 and ρ significantly change the V value, whereas the effect of ε 33 on V is negligible. Our theoretical results provide useful information for the performance predictions of electro-acoustic mechanics sensors, such as FBAR mechanical sensors, based on the intrinsic properties of piezoelectric materials.

  15. Inverse estimation of the elastic and anelastic properties of the porous frame of anisotropic open-cell foams.

    PubMed

    Cuenca, Jacques; Göransson, Peter

    2012-08-01

    This paper presents a method for simultaneously identifying both the elastic and anelastic properties of the porous frame of anisotropic open-cell foams. The approach is based on an inverse estimation procedure of the complex stiffness matrix of the frame by performing a model fit of a set of transfer functions of a sample of material subjected to compression excitation in vacuo. The material elastic properties are assumed to have orthotropic symmetry and the anelastic properties are described using a fractional-derivative model within the framework of an augmented Hooke's law. The inverse estimation problem is formulated as a numerical optimization procedure and solved using the globally convergent method of moving asymptotes. To show the feasibility of the approach a numerically generated target material is used here as a benchmark. It is shown that the method provides the full frequency-dependent orthotropic complex stiffness matrix within a reasonable degree of accuracy.

  16. In vivo anisotropic mechanical properties of dystrophic skeletal muscles measured by anisotropic MR elastographic imaging: the mdx mouse model of muscular dystrophy.

    PubMed

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

    2014-12-01

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

  17. Thermophysical Properties of Polymer Materials with High Thermal Conductivity

    NASA Astrophysics Data System (ADS)

    Lebedev, S. M.; Gefle, O. S.; Dneprovskii, S. N.; Amitov, E. T.

    2015-06-01

    Results of studies on the main thermophysical properties of new thermally conductive polymer materials are presented. It is shown that modification of polymer dielectrics by micron-sized fillers allows thermally conductive materials with thermal conductivity not less than 2 W/(m K) to be produced, which makes it possible to use such materials as cooling elements of various electrical engineering and semiconductor equipment and devices.

  18. Thermoelectric SnS and SnS-SnSe solid solutions prepared by mechanical alloying and spark plasma sintering: Anisotropic thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Asfandiyar; Wei, Tian-Ran; Li, Zhiliang; Sun, Fu-Hua; Pan, Yu; Wu, Chao-Feng; Farooq, Muhammad Umer; Tang, Huaichao; Li, Fu; Li, Bo; Li, Jing-Feng

    2017-02-01

    P–type SnS compound and SnS1‑xSex solid solutions were prepared by mechanical alloying followed by spark plasma sintering (SPS) and their thermoelectric properties were then studied in different compositions (x = 0.0, 0.2, 0.5, 0.8) along the directions parallel (//) and perpendicular (⊥) to the SPS–pressurizing direction in the temperature range 323–823 Κ. SnS compound and SnS1‑xSex solid solutions exhibited anisotropic thermoelectric performance and showed higher power factor and thermal conductivity along the direction ⊥ than the // one. The thermal conductivity decreased with increasing contents of Se and fell to 0.36 W m‑1 K‑1 at 823 K for the composition SnS0.5Se0.5. With increasing selenium content (x) the formation of solid solutions substantially improved the electrical conductivity due to the increased carrier concentration. Hence, the optimized power factor and reduced thermal conductivity resulted in a maximum ZT value of 0.64 at 823 K for SnS0.2Se0.8 along the parallel direction.

  19. Thermoelectric SnS and SnS-SnSe solid solutions prepared by mechanical alloying and spark plasma sintering: Anisotropic thermoelectric properties

    PubMed Central

    Asfandiyar; Wei, Tian-Ran; Li, Zhiliang; Sun, Fu-Hua; Pan, Yu; Wu, Chao-Feng; Farooq, Muhammad Umer; Tang, Huaichao; Li, Fu; Li, Bo; Li, Jing-Feng

    2017-01-01

    P–type SnS compound and SnS1−xSex solid solutions were prepared by mechanical alloying followed by spark plasma sintering (SPS) and their thermoelectric properties were then studied in different compositions (x = 0.0, 0.2, 0.5, 0.8) along the directions parallel (//) and perpendicular (⊥) to the SPS–pressurizing direction in the temperature range 323–823 Κ. SnS compound and SnS1−xSex solid solutions exhibited anisotropic thermoelectric performance and showed higher power factor and thermal conductivity along the direction ⊥ than the // one. The thermal conductivity decreased with increasing contents of Se and fell to 0.36 W m−1 K−1 at 823 K for the composition SnS0.5Se0.5. With increasing selenium content (x) the formation of solid solutions substantially improved the electrical conductivity due to the increased carrier concentration. Hence, the optimized power factor and reduced thermal conductivity resulted in a maximum ZT value of 0.64 at 823 K for SnS0.2Se0.8 along the parallel direction. PMID:28240324

  20. Thermoelectric SnS and SnS-SnSe solid solutions prepared by mechanical alloying and spark plasma sintering: Anisotropic thermoelectric properties.

    PubMed

    Asfandiyar; Wei, Tian-Ran; Li, Zhiliang; Sun, Fu-Hua; Pan, Yu; Wu, Chao-Feng; Farooq, Muhammad Umer; Tang, Huaichao; Li, Fu; Li, Bo; Li, Jing-Feng

    2017-02-27

    P-type SnS compound and SnS1-xSex solid solutions were prepared by mechanical alloying followed by spark plasma sintering (SPS) and their thermoelectric properties were then studied in different compositions (x = 0.0, 0.2, 0.5, 0.8) along the directions parallel (//) and perpendicular (⊥) to the SPS-pressurizing direction in the temperature range 323-823 Κ. SnS compound and SnS1-xSex solid solutions exhibited anisotropic thermoelectric performance and showed higher power factor and thermal conductivity along the direction ⊥ than the // one. The thermal conductivity decreased with increasing contents of Se and fell to 0.36 W m(-1) K(-1) at 823 K for the composition SnS0.5Se0.5. With increasing selenium content (x) the formation of solid solutions substantially improved the electrical conductivity due to the increased carrier concentration. Hence, the optimized power factor and reduced thermal conductivity resulted in a maximum ZT value of 0.64 at 823 K for SnS0.2Se0.8 along the parallel direction.

  1. Contact mechanics and rubber friction for randomly rough surfaces with anisotropic statistical properties

    NASA Astrophysics Data System (ADS)

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

    2009-07-01

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

  2. Changes in the statistical properties of stochastic anisotropic electromagnetic beams on propagation in the turbulent atmosphere.

    PubMed

    Du, Xinyue; Zhao, Daomu; Korotkova, Olga

    2007-12-10

    We report analytic formulas for the elements of the e 2 X2 cross-spectral density matrix of a stochastic electromagnetic anisotropic beam propagating through the turbulent atmosphere with the help of vector integration. From these formulas the changes in the spectral density (spectrum), in the spectral degree of polarization, and in the spectral degree of coherence of such a beam on propagation are determined. As an example, these quantities are calculated for a so-called anisotropic electromagnetic Gaussian Schell-model beam propagating in the isotropic and homogeneous atmosphere. In particular, it is shown numerically that for a beam of this class, unlike for an isotropic electromagnetic Gaussian Schell-model beam, its spectral degree of polarization does not return to its value in the source plane after propagating at sufficiently large distances in the atmosphere. It is also shown that the spectral degree of coherence of such a beam tends to zero with increasing distance of propagation through the turbulent atmosphere, in agreement with results previously reported for isotropic beams.

  3. P(VDF-TrFE) nanorod assemblies with anisotropic piezoelectric properties investigated by piezoelectric response microscopy

    NASA Astrophysics Data System (ADS)

    Chen, Xiaosui; Wang, Yunli; Cai, Kai; Bai, Yang; Bo, Shuhui; Guo, Dong

    2014-08-01

    Highly ordered assemblies of the copolymer of vinylidene fluoride and trifluoroethylene P(VDF-TrFE) nanorods with anisotropic piezoelectric response were fabricated on different substrates by using a template-free self-organization method. The significant difference in vertical and lateral piezoelectric responses of the nanorods in piezoresponse force microscopy (PFM) revealed that their molecular dipoles were preferentially oriented parallel to the substrate plane. In addition, dipole orientation distribution map in the nanorods was derived by analyzing the vertical and lateral PFM amplitude and phase images. Infrared reflection spectra further showed that the macromolecular backbones were oriented perpendicularly relative to the substrate. A flat-on lamellar structure and a confined crystallization of dewetted melt phase nanorod formation mechanism were proposed. The highly anisotropic piezoelectric response of the assemblies of nanorods may be promising for nanoscale devices for application in energy harvesting, etc. More importantly, the results demonstrated that self organization could be used for fabricating P(VDF-TrFE) nanostructures by controlling the surface energy of the substrates.

  4. Effect of strain-path change on the anisotropic mechanical properties of a commercially pure aluminum

    NASA Astrophysics Data System (ADS)

    Sun, P. L.; Huang, S. J.

    2017-07-01

    Samples of commercially pure aluminum were subjected to equal channel angular extrusion (ECAE) using a 90° square die by routes A and C, where the specimens are not rotated and are rotated 180° between extrusion passes, respectively. Qualitatively similar anisotropic responses under compressive loading along the three orthogonal directions of the ECAE billet are seen in both cases. The plastic anisotropy is related to the effect of strain-path change, namely that different slip activities are induced for specimens loaded along different directions with respect to the last ECAE pass. The anisotropic mechanical behavior is more evident in the sample deformed by route C. Considering the shear patterns imposed in each ECAE route, the characteristics of dislocations introduced in ECAE should affect the mechanical response in post-ECAE loading. It is suggested that during the ECAE process, dislocations on fewer slip systems are activated in route C than in route A, and therefore, a stronger plastic anisotropy results in this sample. The as-ECAE specimens were also heat treated to achieve a recovery-annealed state. The plastic anisotropy persists in the annealed specimens to slightly reduced extent, which can be ascribed to partial annihilation of preexisting dislocations.

  5. Phase transformations, anisotropic pyroelectric energy harvesting and electrocaloric properties of (Pb,La)(Zr,Sn,Ti)O3 single crystals.

    PubMed

    Zhuo, Fangping; Li, Qiang; Gao, Jinghan; Yan, Qingfeng; Zhang, Yiling; Xi, Xiaoqing; Chu, Xiangcheng

    2017-05-31

    (Pb,La)(Zr,Sn,Ti)O3 (PLZST) single crystals with their chemical composition located at the tetragonal antiferroelectric region are grown via the flux method in a PbO-PbF2-B2O3 mixture. Segregation of the Ti(4+) component in the as-grown crystals is observed due to the strong affinity between the oxygen anion and Ti(4+) ions. The critical electric field of the antiferroelectric to ferroelectric phase transition is determined to be about 0.5 kV mm(-1). The electric field induced ferroelectric phase transforms back into the antiferroelectric phase at a depolarization temperature of 125 °C. Anisotropy of the harvested energy density and electrocaloric behaviors are achieved for the [100], [110] and [111]-oriented PLZST crystals. Based on the thermodynamic theory approach, all the abovementioned behaviors originate from the anisotropic total entropy change. Enhanced electrocaloric strength (0.3 K mm kV(-1)) and the harvested energy density of 0.62 J cm(-3) are obtained in the [111]-oriented PLZST crystals. Our results demonstrate the competence of PLZST single crystals for cooling devices and pyroelectric energy harvesting and provide new opportunities to improve energy harvesting density and electrocaloric properties via the anisotropic structural layout, which make the PLZST crystals attractive for solid state cooling devices and energy conversion technologies.

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

    PubMed

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

    2013-10-30

    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 μ(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.

  7. A comparison of anisotropic statistical properties of CMB maps based on the WMAP and planck space mission data

    NASA Astrophysics Data System (ADS)

    Verkhodanov, O. V.; Naiden, Ya. V.

    2016-10-01

    We compare the anisotropic properties of the cosmic microwave background (CMB) maps constructed based on the data of NASA's WMAP (9th year of observations) and ESA's Planck (2015 release) space missions. In our analysis, we use two two-dimensional estimators of the scatter of the signal on a sphere, which amount to algorithms of mapping the ratio of the scatter in the Northern and Southern hemispheres depending on the method of dividing (specifically, rotating and cutting) the sky into hemispheres. The scatter is computed either as a standard deviation σ, or as the difference between the minimum and maximum values on a given hemisphere. Applying both estimators to the CMB anisotropy datameasured by two spacemissions, Planck and WMAP, we compared the variations of the background at different angular scales.Maps with a resolution of l ≤ 100 show that the division into regions with different levels of statistical anisotropy lies close to the ecliptic plane, and after preliminary removal of the l ≤ 20 harmonics from the CMB data, the anisotropic signal related to the Galaxy begins to dominate.

  8. Anisotropic thermal conductivity of β-Ga2O3 at elevated temperatures: Effect of Sn and Fe dopants

    NASA Astrophysics Data System (ADS)

    Slomski, M.; Blumenschein, N.; Paskov, P. P.; Muth, J. F.; Paskova, T.

    2017-06-01

    The thermal conductivity of undoped, Sn-doped, and Fe-doped β-Ga2O3 bulk crystals was measured by the 3ω technique in the temperature range of 295-410 K. A unique approach for extracting the thermal conductivity along the lateral and transverse heat flow directions was used in order to determine the thermal conductivity along different crystallographic directions. The data analysis at room temperature confirmed the expected anisotropy of the thermal conductivity of β-Ga2O3, revealing the highest value of ˜29 W/m K in the [010] direction. The thermal conductivity of the Sn-doped and Fe-doped β-Ga2O3 samples was found to be lower than that of the undoped samples due to the enhanced phonon-impurity scattering contribution, which reduces the thermal conductivity. This tendency was maintained for the thermal conductivity at elevated temperatures. The thermal conductivity in all samples decreased with increasing temperature, but the slope of the temperature dependence was found to depend on both the doping and the crystallographic orientation.

  9. Effect of mechanical boundary conditions on the dynamic and static properties of a strongly anisotropic ferromagnet

    SciTech Connect

    Gorelikov, G. A.; Fridman, Yu. A.

    2013-07-15

    The spectra of coupled magnetoelastic waves in a semi-infinite strongly anisotropic easy-plane ferromagnet with a rigidly fixed face are analyzed for two variants of fixation (in the basal plane and perpendicularly to it). The phase states of the system are determined. Differences in the phase diagrams and elementary excitation spectra depending on the choice of the sample fixation plane are considered. When rotational invariance is taken into account, the nonreciprocity effect for the velocities of sound in a crystal appears. It is shown that the velocity of sound in the sample considerably depends on the symmetry of the imposed mechanical boundary conditions. The phase diagrams of the system under investigation are presented.

  10. Effect of specimen-specific anisotropic material properties in quantitative computed tomography-based finite element analysis of the vertebra.

    PubMed

    Unnikrishnan, Ginu U; Barest, Glenn D; Berry, David B; Hussein, Amira I; Morgan, Elise F

    2013-10-01

    Intra- and inter-specimen variations in trabecular anisotropy are often ignored in quantitative computed tomography (QCT)-based finite element (FE) models of the vertebra. The material properties are typically estimated solely from local variations in bone mineral density (BMD), and a fixed representation of elastic anisotropy ("generic anisotropy") is assumed. This study evaluated the effect of incorporating specimen-specific, trabecular anisotropy on QCT-based FE predictions of vertebral stiffness and deformation patterns. Orthotropic material properties estimated from microcomputed tomography data ("specimen-specific anisotropy"), were assigned to a large, columnar region of the L1 centrum (n = 12), and generic-anisotropic material properties were assigned to the remainder of the vertebral body. Results were compared to FE analyses in which generic-anisotropic properties were used throughout. FE analyses were also performed on only the columnar regions. For the columnar regions, the axial stiffnesses obtained from the two categories of material properties were uncorrelated with each other (p = 0.604), and the distributions of minimum principal strain were distinctly different (p ≤ 0.022). In contrast, for the whole vertebral bodies in both axial and flexural loading, the stiffnesses obtained using the two categories of material properties were highly correlated (R2 > 0.82, p < 0.001) with, and were no different (p > 0.359) from, each other. Only moderate variations in strain distributions were observed between the two categories of material properties. The contrasting results for the columns versus vertebrae indicate a large contribution of the peripheral regions of the vertebral body to the mechanical behavior of this bone. In companion analyses on the effect of the degree of anisotropy (DA), the axial stiffnesses of the trabecular column (p < 0.001) and vertebra (p = 0.007) increased with increasing DA. These findings

  11. Properties of polymer blends filled with mixtures of conductive fillers

    NASA Astrophysics Data System (ADS)

    Thongruang, Wiriya

    2001-11-01

    High-density polyethylene (HDPE), ultrahigh molecular weight polyethylene (UHMWPE) and blends thereof are used to produce ternary and quaternary conductive polymer composites (CPCs) containing carbon black (CB), carbon graphite (G), carbon fiber (CF) and selected mixtures thereof to discern if polymer blends and mixed fillers yield appreciable advantages over CPCs composed of single polymers and/or single fillers. The effects of polymer blend composition and filler type, concentration and composition on electrical conductivity, composite morphology, mechanical properties and thermal behavior have been examined and correlated to establish meaningful structure-property relationships that can facilitate the rational design of efficient CPCs. Enhanced conductivity due to double-percolation is observed in ternary CPCs containing CB or G, whereas the concept of bridged double percolation is proposed to explain substantial conductivity increases in quaternary composites.

  12. Multifunctional Nanostructured Conductive Polymer Gels: Synthesis, Properties, and Applications.

    PubMed

    Zhao, Fei; Shi, Ye; Pan, Lijia; Yu, Guihua

    2017-07-18

    Conductive polymers have attracted significant interest over the past few decades because they synergize the advantageous features of conventional polymeric materials and organic conductors. With rationally designed nanostructures, conductive polymers can further exhibit exceptional mechanical, electrical, and optical properties because of their confined dimensions at the nanoscale level. Among various nanostructured conductive polymers, conductive polymer gels (CPGs) with synthetically tunable hierarchical 3D network structures show great potential for a wide range of applications, such as bioelectronics, and energy storage/conversion devices owing to their structural features. CPGs retain the properties of nanosized conductive polymers during the assembly of the nanobuilding blocks into a monolithic macroscopic structure while generating structure-derived features from the highly cross-linked network. In this Account, we review our recent progress on the synthesis, properties, and novel applications of dopant cross-linked CPGs. We first describe the synthetic strategies, in which molecules with multiple functional groups are adopted as cross-linkers to cross-link conductive polymer chains into a 3D molecular network. These cross-linking molecules also act as dopants to improve the electrical conductivity of the gel network. The microstructure and physical/chemical properties of CPGs can be tuned by controlling the synthetic conditions such as species of monomers and cross-linkers, reaction temperature, and solvents. By incorporating other functional polymers or particles into the CPG matrix, hybrid gels have been synthesized with tailored structures. These hybrid gel materials retain the functionalities from each component, as well as enable synergic effects to improve mechanical and electrical properties of CPGs. We then introduce the unique structure-derived properties of the CPGs. The network facilitates both electronic and ionic transport owing to the

  13. Ellipsometric characterization and density-functional theory analysis of anisotropic optical properties of single-crystal α-SnS

    SciTech Connect

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

    2014-07-07

    We report on the anisotropic optical properties of single-crystal tin monosulfide (SnS). The components ε{sub a}, ε{sub b}, and ε{sub c} of the pseudodielectric-function tensor (ε)=(ε₁)+i(ε₂) spectra are taken from 0.73 to 6.45 eV by spectroscopic ellipsometry. The measured (ε) spectra are in a good agreement with the results of the calculated dielectric response from hybrid density functional theory. The (ε) spectra show the direct band-gap onset and a total of eight above-band-gap optical structures that are associated with the interband-transition critical points (CPs). We obtain accurate CP energies by fitting analytic CP expressions to second-energy-derivatives of the (ε) data. Their probable electronic origins and implications for photovoltaic applications are discussed.

  14. Complex polarization ratio to determine polarization properties of anisotropic tissue using polarization-sensitive optical coherence tomography

    PubMed Central

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

    2009-01-01

    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. PMID:19654746

  15. Experimental Investigation of the Anisotropic Mechanical Properties of a Columnar Jointed Rock Mass: Observations from Laboratory-Based Physical Modelling

    NASA Astrophysics Data System (ADS)

    Ji, H.; Zhang, J. C.; Xu, W. Y.; Wang, R. B.; Wang, H. L.; Yan, L.; Lin, Z. N.

    2017-07-01

    Because of the complex geological structure, determination of the field mechanical parameters of the columnar jointed rock mass (CJRM) was a challenging task in the design and construction of the Baihetan hydropower plant. To model the mechanical behaviour of the CJRM, uniaxial compression tests were conducted on artificial CJRM specimens with geological structure similar to that found in the actual CJRM. Based on the test results, the anisotropic deformation and strength were mainly analysed. The empirical correlations of evaluating the field mechanical parameters were derived based on the joint factor approach and the modulus reduction factor method. The findings of the physical model tests were then used to estimate the field moduli and unconfined compressive strengths of the Baihetan CJRM. The results predicted by physical model tests were compared with those obtained from the field tests and the RMR classification system. It is concluded that physical model tests were capable of providing valuable estimations on the field mechanical parameters of the CJRM.

  16. Drastic changes in electronic properties of Kondo semiconductor CeRu2Al10 induced by Rh doping: Anisotropic transport properties in the antiferromagnetic ordered state

    NASA Astrophysics Data System (ADS)

    Tanida, H.; Nohara, H.; Nakagawa, F.; Yoshida, K.; Sera, M.; Nishioka, T.

    2016-10-01

    Electrical resistivity (ρ ), thermopower, and specific heat measurements have been performed on the novel Kondo semiconductor Ce (Ru1-xRhx) 2Al10 (x =0 , 0.02, 0.03, and 0.05), which has been attracting a great deal of interest due to an unusual antiferromagnetic (AFM) order below T0, in order to clarify the Rh doping effect on the anisotropy of the electronic properties in the ordered state. In CeRu2Al10 , ρ shows an anisotropic increase below T0 independently of the electric current direction. We propose the existence of two different mechanisms to explain the anisotropic increase of ρ . One is an isotropic charge gap which enhances ρ below T0 isotropically, although its origin is not known at present. The other is an anisotropic suppression of ρ which originates from the anisotropic c-f hybridization and is largest along the orthorhombic a axis. By the Rh doping, the anisotropic temperature dependence of ρ below T0 is drastically changed. For I ∥b , the increase is almost completely suppressed and a metallic-like behavior is observed, whereas it is small and isotropic for I ∥a and c . From these results, we propose that as a result of the destruction of the spin-gap excitation by the Rh doping, a metallic-like electronic state is formed along the b axis and the small isotropic charge gap is opened in the a c plane. By taking into account the present results and the still high T0 even in x =0.05 , we conclude that the AFM order in the Rh-doped CeRu2Al10 should be viewed as unusual as the AFM order in CeRu2Al10 although the localized character of the Ce-4 f electron is apparently enhanced by the Rh doping. We have also examined the evolution of the AFM ordered state from x =0 to x =0.05 , where the AFM ordered moment (mAF) is aligned along the c axis in x =0 and a axis in x =0.05 . From the results of those experiments in magnetic field, we have revealed that the spin reorientation from mAF∥c to mAF∥a takes place quite abruptly just at xc˜0

  17. Thermal conductivity and other properties of cementitious grouts

    SciTech Connect

    Allan, M.

    1998-08-01

    The thermal conductivity and other properties cementitious grouts have been investigated in order to determine suitability of these materials for grouting vertical boreholes used with geothermal heat pumps. The roles of mix variables such as water/cement ratio, sand/cement ratio and superplasticizer dosage were measured. In addition to thermal conductivity, the cementitious grouts were also tested for bleeding, permeability, bond to HDPE pipe, shrinkage, coefficient of thermal expansion, exotherm, durability and environmental impact. This paper summarizes the results for selected grout mixes. Relatively high thermal conductivities were obtained and this leads to reduction in predicted bore length and installation costs. Improvements in shrinkage resistance and bonding were achieved.

  18. THERMAL CONDUCTIVITY AND OTHER PROPERTIES OF CEMENTITIOUS GROUTS

    SciTech Connect

    ALLAN,M.

    1998-05-01

    The thermal conductivity and other properties cementitious grouts have been investigated in order to determine suitability of these materials for grouting vertical boreholes used with geothermal heat pumps. The roles of mix variables such as water/cement ratio, sand/cement ratio and superplasticizer dosage were measured. In addition to thermal conductivity, the cementitious grouts were also tested for bleeding, permeability, bond to HDPE pipe, shrinkage, coefficient of thermal expansion, exotherm, durability and environmental impact. This paper summarizes the results for selected grout mixes. Relatively high thermal conductivities were obtained and this leads to reduction in predicted bore length and installation costs. Improvements in shrinkage resistance and bonding were achieved.

  19. Electromechanical and conductance switching properties of single oligothiophene molecules.

    PubMed

    Xu, Bingqian Q; Li, Xiulan L; Xiao, Xiaoyin Y; Sakaguchi, Hiroshi; Tao, Nongjian J

    2005-07-01

    We have studied the electron transport and electromechanical properties of single oligothiophenes with three and four thiophene repeating units covalently linked to two Au electrodes. The four-repeating unit molecule is found to be more conductive than the three-repeating unit molecule. This unusual length dependence is due to the different electronic states of the molecules. Both molecules can be switched reversibly between a high and low conducting state by oxidizing and reducing the molecules using an electrochemical gate. The conductance of the molecules decreases upon stretching, which is attributed to a force-induced increase in the HOMO-LUMO gap.

  20. Phase behavior of 1-dodecyl-3-methylimidazolium fluorohydrogenate salts (C12MIm(FH)(n)F, n = 1.0-2.3) and their anisotropic ionic conductivity as ionic liquid crystal electrolytes.

    PubMed

    Xu, Fei; Matsumoto, Kazuhiko; Hagiwara, Rika

    2012-08-23

    The effects of the HF composition, n, in 1-dodecyl-3-methylimidazolium fluorohydrogenate salts (C(12)MIm(FH)(n)F, n = 1.0-2.3) on their physicochemical and structural properties have been investigated using infrared spectroscopy, thermal analysis, polarized optical microscopy, X-ray diffraction, and anisotropic ionic conductivity measurements. The phase diagram of C(12)MIm(FH)(n)F (n vs transition temperature) suggests that C(12)MIm(FH)(n)F is a mixed crystal system that has a boundary around n = 1.9. For all compositions, a liquid crystalline mesophase with a smectic A interdigitated bilayer structure is observed. The temperature range of the mesophase decreases with increasing n value (from 61.8 °C for C(12)MIm(FH)(1.0)F to 37.0 °C for C(12)MIm(FH)(2.3)F). The layer spacing of the smectic structure decreases with increasing n value or increasing temperature. Two structural types with different layer spacings are observed in the crystalline phase (type I, 1.0 ≤ n ≤ 1.9, and type II, 1.9 ≤ n ≤ 2.3). Ionic conductivities parallel and perpendicular to the smectic layers (σ(||) and σ([perpendicular])) increase with increasing n value, whereas the anisotropy of the ionic conductivities (σ(||)/σ([perpendicular])) is independent of the n value, since the thickness of the insulating sheet formed by the dodecyl group remains nearly unchanged.

  1. Anisotropic thermodynamic and transport properties of single-crystalline CaKFe4As4

    NASA Astrophysics Data System (ADS)

    Meier, W. R.; Kong, T.; Kaluarachchi, U. S.; Taufour, V.; Jo, N. H.; Drachuck, G.; Böhmer, A. E.; Saunders, S. M.; Sapkota, A.; Kreyssig, A.; Tanatar, M. A.; Prozorov, R.; Goldman, A. I.; Balakirev, Fedor F.; Gurevich, Alex; Bud'ko, S. L.; Canfield, P. C.

    2016-08-01

    Single-crystalline, single-phase CaKFe4As4 has been grown out of a high-temperature, quaternary melt. Temperature-dependent measurements of x-ray diffraction, anisotropic electrical resistivity, elastoresistivity, thermoelectric power, Hall effect, magnetization, and specific heat, combined with field-dependent measurements of electrical resistivity and field and pressure-dependent measurements of magnetization indicate that CaKFe4As4 is an ordered, stoichiometric, Fe-based superconductor with a superconducting critical temperature, Tc=35.0 ±0.2 K. Other than superconductivity, there is no indication of any other phase transition for 1.8 K≤T ≤300 K. All of these thermodynamic and transport data reveal striking similarities to those found for optimally or slightly overdoped (Ba1 -xKx )Fe2As2 , suggesting that stoichiometric CaKFe4As4 is intrinsically close to what is referred to as "optimal-doped" on a generalized, Fe-based superconductor, phase diagram. The anisotropic superconducting upper critical field, Hc 2(T ) , of CaKFe4As4 was determined up to 630 kOe. The anisotropy parameter γ (T ) =Hc2 ⊥/Hc2 ∥ , for H applied perpendicular and parallel to the c axis, decreases from ≃2.5 at Tc to ≃1.5 at 25 K, which can be explained by interplay of paramagnetic pair breaking and orbital effects. The slopes of d Hc2 ∥/d T ≃-44 kOe/K and d Hc2 ⊥/d T ≃-109 kOe/K at Tc yield an electron mass anisotropy of m⊥/m∥≃1 /6 and short Ginzburg-Landau coherence lengths ξ∥(0 ) ≃5.8 Å and ξ⊥(0 ) ≃14.3 Å . The value of Hc2 ⊥(0 ) can be extrapolated to ≃920 kOe, well above the BCS paramagnetic limit.

  2. Anisotropic thermodynamic and transport properties of single-crystalline CaKFe4As4

    DOE PAGES

    Meier, W. R.; Kong, T.; Kaluarachchi, U. S.; ...

    2016-08-01

    We grew single-crystalline, single-phase CaKFe4As4 out of a high-temperature, quaternary melt. Temperature-dependent measurements of x-ray diffraction, anisotropic electrical resistivity, elastoresistivity, thermoelectric power, Hall effect, magnetization, and specific heat, combined with field-dependent measurements of electrical resistivity and field and pressure-dependent measurements of magnetization indicate that CaKFe4As4 is an ordered, stoichiometric, Fe-based superconductor with a superconducting critical temperature, Tc=35.0±0.2 K. Other than superconductivity, there is no indication of any other phase transition for 1.8K≤T≤300 K. All of these thermodynamic and transport data reveal striking similarities to those found for optimally or slightly overdoped (Ba1-xKx)Fe2As2, suggesting that stoichiometric CaKFe4As4 is intrinsically close to what is referred to as “optimal-doped” on a generalized, Fe-based superconductor, phase diagram. Furthermore, the anisotropic superconducting upper critical field, Hc2(T), of CaKFe4As4 was determined up to 630 kOe. The anisotropy parameter γ(T)=Hmore » $$⊥\\atop{c2}$$/H$$∥\\atop{c2}$$, for H applied perpendicular and parallel to the c axis, decreases from ≃2.5 at Tc to ≃1.5 at 25 K, which can be explained by interplay of paramagnetic pair breaking and orbital effects. The slopes of dH$$∥\\atop{c2}$$/dT≃-44 kOe/K and dH$$⊥\\atop{c2}$$/dT≃-109 kOe/K at Tc yield an electron mass anisotropy of m⊥/m∥≃1/6 and short Ginzburg-Landau coherence lengths ξ∥(0)≃5.8Å and ξ⊥(0)≃14.3Å. Finally, the value of H$$⊥\\atop{c2}$$(0) can be extrapolated to ≃920 kOe, well above the BCS paramagnetic limit.« less

  3. Mechanical property determination of high conductivity metals and alloys

    NASA Technical Reports Server (NTRS)

    Harrod, D. L.; Vandergrift, E.; France, L.

    1973-01-01

    Pertinent mechanical properties of three high conductivity metals and alloys; namely, vacuum hot pressed grade S-200E beryllium, OFHC copper and beryllium-copper alloy no. 10 were determined. These materials were selected based on their possible use in rocket thrust chamber and nozzle hardware. They were procured in a form and condition similar to that which might be ordered for actual hardware fabrication. The mechanical properties measured include (1) tension and compression stress strain curves at constant strain rate (2) tensile and compressive creep, (3) tensile and compressive stress-relaxation behavior and (4) elastic properties. Tests were conducted over the temperature range of from 75 F to 1600 F. The resulting data is presented in both graphical and tabular form.

  4. Molecular anisotropic magnetoresistance

    NASA Astrophysics Data System (ADS)

    Otte, Fabian; Heinze, Stefan; Mokrousov, Yuriy

    2015-12-01

    Using density functional theory calculations, we demonstrate that the effect of anisotropic magnetoresistance (AMR) can be enhanced by orders of magnitude with respect to conventional bulk ferromagnets in junctions containing molecules sandwiched between ferromagnetic leads. We study ballistic transport in metal-benzene complexes contacted by 3 d transition-metal wires. We show that a gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symmetry filtering properties of the molecules. We further discuss how this molecular anisotropic magnetoresistance (MAMR) can be tuned by the proper choice of materials and their electronic properties.

  5. Anisotropic Artificial Impedance Surfaces

    NASA Astrophysics Data System (ADS)

    Quarfoth, Ryan Gordon

    Anisotropic artificial impedance surfaces are a group of planar materials that can be modeled by the tensor impedance boundary condition. This boundary condition relates the electric and magnetic field components on a surface using a 2x2 tensor. The advantage of using the tensor impedance boundary condition, and by extension anisotropic artificial impedance surfaces, is that the method allows large and complex structures to be modeled quickly and accurately using a planar boundary condition. This thesis presents the theory of anisotropic impedance surfaces and multiple applications. Anisotropic impedance surfaces are a generalization of scalar impedance surfaces. Unlike the scalar version, anisotropic impedance surfaces have material properties that are dependent on the polarization and wave vector of electromagnetic radiation that interacts with the surface. This allows anisotropic impedance surfaces to be used for applications that scalar surfaces cannot achieve. Three of these applications are presented in this thesis. The first is an anisotropic surface wave waveguide which allows propagation in one direction, but passes radiation in the orthogonal direction without reflection. The second application is a surface wave beam shifter which splits a surface wave beam in two directions and reduces the scattering from an object placed on the surface. The third application is a patterned surface which can alter the scattered radiation pattern of a rectangular shape. For each application, anisotropic impedance surfaces are constructed using periodic unit cells. These unit cells are designed to give the desired surface impedance characteristics by modifying a patterned metallic patch on a grounded dielectric substrate. Multiple unit cell geometries are analyzed in order to find the setup with the best performance in terms of impedance characteristics and frequency bandwidth.

  6. Preparation, characterization and properties of new ion-conducting ORMOLYTES

    SciTech Connect

    Dahmouche, K.; Atik, M.; Mello, N.C.; Bonagamba, T.J.; Panepucci, H.; Aegerter, M.; Judeinstein, P.

    1996-12-31

    Two families of hybrid organic-inorganic composites exhibiting ionic conduction properties, so called ORMOLYTES (organically modified electrolytes), have been prepared by the sol-gel process. The first family has been prepared for a mixture of 3-isocyanatopropyltriethoxysilane (IsoTrEOS), O,O{prime} Bis (2-aminopropyl)polyethyleneglycol and lithium salt. These materials present chemical bonds between the organic (polymer) and the inorganic (silica) phases. The second family has been prepared by an ultrasonic method from a mixture of tetraethoxysilane (TEOS), polyethyleneglycol and lithium salt. The organic and inorganic phases are not chemically bonded. The Li{sup +} ionic conductivity has been studied by AC impedance spectroscopy up to 100 C. Values of {sigma} up to 10{sup {minus}4} Scm{sup {minus}1} have been found at room temperature. The conduction properties have been related to the materials structure using linewidth and relaxation times NMR measurements of {sup 7}Li between {minus}100 C and 90 C. A systematic study has been done changing the lithium concentration, the polymer chain length and the polymer to silica weight ratio. The structures and the ionic conduction properties of both families are compared with emphasis on the nature of the bonds between the organic and inorganic components.

  7. On the relativistic anisotropic configurations

    NASA Astrophysics Data System (ADS)

    Shojai, F.; Kohandel, M.; Stepanian, A.

    2016-06-01

    In this paper we study anisotropic spherical polytropes within the framework of general relativity. Using the anisotropic Tolman-Oppenheimer-Volkov equations, we explore the relativistic anisotropic Lane-Emden equations. We find how the anisotropic pressure affects the boundary conditions of these equations. Also we argue that the behavior of physical quantities near the center of star changes in the presence of anisotropy. For constant density, a class of exact solution is derived with the aid of a new ansatz and its physical properties are discussed.

  8. Investigation of thermal conductivity and tribological properties of nanofluids

    NASA Astrophysics Data System (ADS)

    Gara, Luan

    Nanofluids are engineered by dispersing and stably suspending nanoparticles with typical length on the order of 1--50 nm in traditional fluids. In the past decade, scientists and engineers have made great progresses in finding that a very small amount (< 1 vol %) of dispersed nanoparticles can provide dramatic improvement in the thermal properties of the base fluids. Therefore, numerous mechanisms and models have been proposed to account for the thermal enhancement of nanofluids. The molecular dynamics (MD) simulation has become an important tool in the study of dynamic properties of liquids, molecular solutions, and macromolecules. Therefore, MD simulation is a very helpful tool to model the enhanced thermal conduction and predict thermal conductivities of nanofluids. In recent years, investigations on the tribological properties of nanofluids have also been carried out. Some papers have reported that nanofluids are effective in reducing wear and friction. The mechanisms of friction reduction and anti-wear of nanoparticles in lubricants have been reported as colloidal effect, rolling effect, protective film, and third body. The objective of this research is to study the thermal conductivity and tribological properties of nanofluids. The thermal conductivity of nanofluids was investigated theoretically through MD simulation. Nanodiamond was selected as the nanoparticle and octane as the base oil. The Large-scale Atomic-Molecular Massively Parallel Simulator (LAMMPS) was used. The effects of the particle size, shape and concentration on the thermal conductivity of nanofluids was investigated. The thermal conductivity of oil based nanofluids with nanodiamond particles was also measured experimentally using transient hot-wire method. The tribological properties of nanofluids were studied through experimental investigation using commercially available nanopowders and nanofluids. Both water based and oil based nanofluids were investigated. A Universal Micro

  9. Soil hydraulic properties near saturation, an improved conductivity model

    NASA Astrophysics Data System (ADS)

    Børgesen, Christen D.; Jacobsen, Ole H.; Hansen, Søren; Schaap, Marcel G.

    2006-06-01

    The hydraulic properties near saturation can change dramatically due to the presence of macropores that are usually difficult to handle in traditional pore size models. The purpose of this study is to establish a data set on hydraulic conductivity near saturation, test the predictive capability of commonly used hydraulic conductivity models and give suggestions for improved models. Water retention and near saturated and saturated hydraulic conductivity were measured for a variety of 81 top and subsoils. The hydraulic conductivity models by van Genuchten [ van Genuchten, 1980. A closed-form equation for predicting the hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44, 892-898.] (vGM) and Brooks and Corey, modified by Jarvis [ Jarvis, 1991. MACRO—A Model of Water Movement and Solute Transport in Macroporous Soils. Swedish University of Agricultural Sciences. Department of Soil Sciences. Reports and Dissertations 9.] were optimised to describe the unsaturated hydraulic conductivity in the range measured. Different optimisation procedures were tested. Using the measured saturated hydraulic conductivity in the vGM model tends to overestimate the unsaturated hydraulic conductivity. Optimising a matching factor ( k0) improved the fit considerably whereas optimising the l-parameter in the vGM model improved the fit only slightly. The vGM was improved with an empirical scaling function to account for the rapid increase in conductivity near saturation. Using the improved models, it was possible to describe both the saturated and the unsaturated hydraulic conductivity better than a previously published model by Jarvis. The pore size boundary of the macropores was found at a capillary pressure of -4 hPa corresponding to a circular pore diameter of 750 μm.

  10. Conductive elastomers with autonomic self-healing properties.

    PubMed

    Guo, Kun; Zhang, Da-Li; Zhang, Xiao-Mei; Zhang, Jian; Ding, Li-Sheng; Li, Bang-Jing; Zhang, Sheng

    2015-10-05

    Healable, electrically conductive materials are highly desirable and valuable for the development of various modern electronics. But the preparation of a material combining good mechanical elasticity, functional properties, and intrinsic self-healing ability remains a great challenge. Here, we design composites by connecting a polymer network and single-walled carbon nanotubes (SWCNTs) through host-guest interactions. The resulting materials show bulk electrical conductivity, proximity sensitivity, humidity sensitivity and are able to self-heal without external stimulus under ambient conditions rapidly. Furthermore, they also possess elasticity comparable to commercial rubbers. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. Electrical conductivity, thermal conductivity, and rheological properties of graphene oxide-based nanofluids

    NASA Astrophysics Data System (ADS)

    Hadadian, Mahboobeh; Goharshadi, Elaheh K.; Youssefi, Abbas

    2014-12-01

    Highly stable graphene oxide (GO)-based nanofluids were simply prepared by dispersing graphite oxide with the average crystallite size of 20 nm, in polar base fluids without using any surfactant. Electrical conductivity, thermal conductivity, and rheological properties of the nanofluids were measured at different mass fractions and various temperatures. An enormous enhancement, 25,678 %, in electrical conductivity of distilled water was observed by loading 0.0006 mass fraction of GO at 25 °C. GO-ethylene glycol nanofluids exhibited a non-Newtonian shear-thinning behavior followed by a shear-independent region. This shear-thinning behavior became more pronounced at higher GO concentrations. The maximum ratio of the viscosity of nanofluid to that of the ethylene glycol as a base fluid was 3.4 for the mass fraction of 0.005 of GO at 20 °C under shear rate of 27.5 s-1. Thermal conductivity enhancement of 30 % was obtained for GO-ethylene glycol nanofluid for mass fraction of 0.07. The measurement of the transport properties of this new kind of nanofluid showed that it could provide an ideal fluid for heat transfer and electronic applications.

  12. High T{sub g} and fast curing epoxy-based anisotropic conductive paste for electronic packaging

    SciTech Connect

    Keeratitham, Waralee Somwangthanaroj, Anongnat

    2016-03-09

    Herein, our main objective is to prepare the fast curing epoxy system with high glass transition temperature (T{sub g}) by incorporating the multifunctional epoxy resin into the mixture of diglycidyl ether of bisphenol A (DGEBA) as a major epoxy component and aromatic diamine as a hardener. Furthermore, the curing behavior as well as thermal and thermomechanical properties were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA). It was found that T{sub g} obtained from tan δ of DGEBA/aromatic diamine system increased from 100 °C to 205 °C with the presence of 30 percentage by weight of multifunctional epoxy resin. Additionally, the isothermal DSC results showed that the multifunctional epoxy resin can accelerate the curing reaction of DGEBA/aromatic diamine system. Namely, a high degree of curing (∼90%) was achieved after a few minutes of curing at low temperature of 130 °C, owing to a large number of epoxy ring of multifunctional epoxy resin towards the active hydrogen atoms of aromatic diamine.

  13. Microwave conductance properties of aligned multiwall carbon nanotube textile sheets

    NASA Astrophysics Data System (ADS)

    Brown, Brian L.; Martinez, Patricia; Zakhidov, Anvar A.; Shaner, Eric A.; Lee, Mark

    2015-07-01

    Understanding the conductance properties of multi-walled carbon nanotube (MWNT) textile sheets in the microwave regime is essential for their potential use in high-speed and high-frequency applications. To expand current knowledge, complex high-frequency conductance measurements from 0.01 to 50 GHz and across temperatures from 4.2 K to 300 K and magnetic fields up to 2 T were made on textile sheets of highly aligned MWNTs with strand alignment oriented both parallel and perpendicular to the microwave electric field polarization. Sheets were drawn from 329 and 520 μm high MWNT forests that resulted in different DC resistance anisotropy. For all samples, the microwave conductance can be modeled approximately by a shunt capacitance in parallel with a frequency-independent conductance, but with no inductive contribution. This is consistent with diffusive Drude conduction as the primary transport mechanism up to 50 GHz. Further, it is found that the microwave conductance is essentially independent of both temperature and magnetic field.

  14. Thermophysical Properties of Liquid Te: Density, Electrical Conductivity, and Viscosity

    NASA Technical Reports Server (NTRS)

    Li, C.; Su, C.; Lehoczky, S. L.; Scripa, R. N.; Ban, H.; Lin, B.

    2004-01-01

    The thermophysical properties of liquid Te, namely, density, electrical conductivity, and viscosity, were determined using the pycnometric and transient torque methods from the melting point of Te (723 K) to approximately 1150 K. A maximum was observed in the density of liquid Te as the temperature was increased. The electrical conductivity of liquid Te increased to a constant value of 2.89 x 10(exp 5 OMEGA-1m-1) as the temperature was raised above 1000 K. The viscosity decreased rapidly upon heating the liquid to elevated temperatures. The anomalous behaviors of the measured properties are explained as caused by the structural transitions in the liquid and discussed in terms of Eyring's and Bachiskii's predicted behaviors for homogeneous liquids. The Properties were also measured as a function of time after the liquid was coded from approximately 1173 or 1123 to 823 K. No relaxation phenomena were observed in the properties after the temperature of liquid Te was decreased to 823 K, in contrast to the relaxation behavior observed for some of the Te compounds.

  15. Thermophysical Properties of Liquid Te: Density, Electrical Conductivity, and Viscosity

    NASA Technical Reports Server (NTRS)

    Li, C.; Su, C.; Lehoczky, S. L.; Scripa, R. N.; Ban, H.; Lin, B.

    2004-01-01

    The thermophysical properties of liquid Te, namely, density, electrical conductivity, and viscosity, were determined using the pycnometric and transient torque methods from the melting point of Te (723 K) to approximately 1150 K. A maximum was observed in the density of liquid Te as the temperature was increased. The electrical conductivity of liquid Te increased to a constant value of 2.89 x 10(exp 5 OMEGA-1m-1) as the temperature was raised above 1000 K. The viscosity decreased rapidly upon heating the liquid to elevated temperatures. The anomalous behaviors of the measured properties are explained as caused by the structural transitions in the liquid and discussed in terms of Eyring's and Bachiskii's predicted behaviors for homogeneous liquids. The Properties were also measured as a function of time after the liquid was coded from approximately 1173 or 1123 to 823 K. No relaxation phenomena were observed in the properties after the temperature of liquid Te was decreased to 823 K, in contrast to the relaxation behavior observed for some of the Te compounds.

  16. Thermal conductivity and combustion properties of wheat gluten foams.

    PubMed

    Blomfeldt, Thomas O J; Nilsson, Fritjof; Holgate, Tim; Xu, Jianxiao; Johansson, Eva; Hedenqvist, Mikael S

    2012-03-01

    Freeze-dried wheat gluten foams were evaluated with respect to their thermal and fire-retardant properties, which are important for insulation applications. The thermal properties were assessed by differential scanning calorimetry, the laser flash method and a hot plate method. The unplasticised foam showed a similar specific heat capacity, a lower thermal diffusivity and a slightly higher thermal conductivity than conventional rigid polystyrene and polyurethane insulation foams. Interestingly, the thermal conductivity was similar to that of closed cell polyethylene and glass-wool insulation materials. Cone calorimetry showed that, compared to a polyurethane foam, both unplasticised and glycerol-plasticised foams had a significantly longer time to ignition, a lower effective heat of combustion and a higher char content. Overall, the unplasticised foam showed better fire-proof properties than the plasticized foam. The UL 94 test revealed that the unplasticised foam did not drip (form droplets of low viscous material) and, although the burning times varied, self-extinguished after flame removal. To conclude both the insulation and fire-retardant properties were very promising for the wheat gluten foam. © 2012 American Chemical Society

  17. Structural, ac conductivity and dielectric properties of 3-formyl chromone

    NASA Astrophysics Data System (ADS)

    Ali, H. A. M.

    2017-07-01

    The structure for the powder of 3-formyl chromone was examined by X-ray diffraction technique in the 2θ° range ( 4° - 60° . The configuration of Al/3-formyl chromone/Al samples was designed. The electrical and dielectric properties were studied as a function of frequency (42- 5 × 106 Hz) and temperature (298-408K). The ac conductivity data of bulk of 3-formyl chromone varies as a power law with the frequency at different temperatures. The predominant mechanism for ac conduction was deduced. The ac conductivity shows a thermally activated process at different frequencies. The dielectric constant and dielectric loss were determined using the capacitance and dissipation factor measurements at different temperatures. The dielectric loss shows a peak of relaxation time that shifted to higher frequency with an increase in the temperature. The activation energy of the relaxation process was estimated.

  18. Near-field investigations of the anisotropic properties of supported lipid bilayers

    NASA Astrophysics Data System (ADS)

    Johnson, Merrell A.

    2011-12-01

    The details of Polarization Modulation Near-Field Scanning Optical Microscopy (PM-NSOM) are presented. How to properly calibrate and align the system is also introduced. A measurement of Muscovite crystal is used to display the capabilities of the setup. Measurements of supported gel state 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers are presented, emphasizing how it was tooled in exploiting the anisotropic nature of the acyl chains. A discussion of how the effective retardance (DeltaS = 2 pi (ne-no) t /lambda) and the direction of the projection of the acyl chains (φ) are measured simultaneously is given, (where t is the thickness of the bilayer and lambda is the wavelength of light used). It is shown from DeltaS the birefringence (ne-n o) of the bilayer is determined, by assuming the acyl chain tilt with respect to the membrane's normal to be approximately φ ≈ 32 degrees. Time varying experiments show lateral diffusions of ˜ 2x10 -12 (cm2)/s. Temperature controlled PM-NSOM is shown to be a viable way to determine the main phase transition temperature (Tm) for going from the gel to liquid disorder state of supported DPPC bilayers. A change DeltaS ˜ (3.8+/-0.3 mrad) at the main phase transition temperature Tm (≈ 41°C) is observed. This agrees well with previous values of ( ne-no) and translates to an assumed φ ˜ 32 degrees, when T < Tm and 0 when T > Tm. Evidence of supper heating and supper cooling will be presented, along with a discussion of the fluctuations that occur around Tm. Finally it is shown how physical parameters such as the polarizability are extracted from the data. Values of the transverse (alpha t) and longitudinal (alphal) polarizabilites of the acyl chains are shown to be, alphat = 44.2A3 and alphal = 94.4 A3, which correspond well with the theoretical values of a single palmitic acid (C16) alpha t = 25.14 A3 and alpha l = 45.8 A3.

  19. Anisotropic Nanoparticles and Anisotropic Surface Chemistry.

    PubMed

    Burrows, Nathan D; Vartanian, Ariane M; Abadeer, Nardine S; Grzincic, Elissa M; Jacob, Lisa M; Lin, Wayne; Li, Ji; Dennison, Jordan M; Hinman, Joshua G; Murphy, Catherine J

    2016-02-18

    Anisotropic nanoparticles are powerful building blocks for materials engineering. Unusual properties emerge with added anisotropy-often to an extraordinary degree-enabling countless new applications. For bottom-up assembly, anisotropy is crucial for programmability; isotropic particles lack directional interactions and can self-assemble only by basic packing rules. Anisotropic particles have long fascinated scientists, and their properties and assembly behavior have been the subjects of many theoretical studies over the years. However, only recently has experiment caught up with theory. We have begun to witness tremendous diversity in the synthesis of nanoparticles with controlled anisotropy. In this Perspective, we highlight the synthetic achievements that have galvanized the field, presenting a comprehensive discussion of the mechanisms and products of both seed-mediated and alternative growth methods. We also address recent breakthroughs and challenges in regiospecific functionalization, which is the next frontier in exploiting nanoparticle anisotropy.

  20. Intricate Short-Range Ordering and Strongly Anisotropic Transport Properties of Li1–x Sn 2+x As2

    DOE PAGES

    Lee, Kathleen; Kaseman, Derrick; Sen, Sabyasachi; ...

    2015-02-22

    A new ternary compound, Li1-xSn2+xAs2, 0.2 < x < 0.4, was synthesized via solid-state reaction of elements. The compound crystallizes in a layered structure in the Rmore » $$\\overline{3}m$$ space group (No. 166) with Sn-As layers separated by layers of jointly occupied Li/Sn. The Sn-As layers are comprised of Sn3As3 puckered hexagons in a chair conformation that share all edges. Li/Sn atoms in the interlayer space are surrounded by a regular As6 octahedron. Thorough investigations by synchrotron x-ray and neutron powder diffraction indicate no long-range Li/Sn ordering. In contrast, local Sn/Li ordering was revealed by synergistic investigations via solid-state 6,7Li NMR spectroscopy, HR-TEM, and neutron and X-ray pair distribution function analyses. Due to their different chemical natures, Li and Sn atoms tend to segregate into Li-rich and Sn-rich regions creating substantial inhomogeneity on the nanoscale. Inhomogeneous local structure has high impact on the physical properties of the synthesized compounds: local Li/Sn ordering and multiple nanoscale interfaces result in unexpectedly low thermal conductivity and highly anisotropic resistivity in Li1-xSn2+xAs2.« less

  1. New optimization method for intermolecular potentials: Optimization of a new anisotropic united atoms potential for olefins: Prediction of equilibrium properties

    NASA Astrophysics Data System (ADS)

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

    2003-02-01

    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 α-olefins (ethylene, propene, 1-butene, 1-pentene, 1-hexene, 1-octene), several β-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.

  2. Understanding anisotropic mechanical properties of shales at different length scales: In situ micropillar compression combined with finite element calculations

    NASA Astrophysics Data System (ADS)

    Keller, Lukas M.; Schwiedrzik, Jakob J.; Gasser, Philippe; Michler, Johann

    2017-08-01

    From microstructural observations and experimental work it is known that shales consist of a mechanically weak porous fine-grained clay matrix with embedded and mechanically strong silt/sand grains. Thereby, the respective contents of weak and strong constituents control bulk mechanical properties. In addition, the clay matrix is characterized by a preferred orientation of clay platelets, which are a major control on the bulk anisotropy of shales. To date, little is known about the micromechanical properties of the fine-grained porous clay matrix, which is particularly true in case of its micromechanical anisotropy. Such information can, however, only be assessed on the microscale. Therefore, the drained micromechanical properties parallel and perpendicular to bedding were investigated by means of compressing micropillars with a flat punch indenter in a scanning electron microscope. Microscopic failure mechanism was found to be anisotropic: (i) in case loading was parallel to bedding it occurred by a combination of localized shearing, kinking/buckling of elongated clay aggregates, and bedding parallel splitting and (ii) for loading perpendicular to bedding failure occurred mainly by localized shearing. The measured stiffness of the drained porous clay matrix perpendicular (Ev) and parallel (Eh) to bedding was about 8 GPa and 30 GPa, respectively. Using these stiffness values as input in voxel-based finite element modeling and in combination with realistic microstructures, which are characterized with different contents of "soft" and "hard" constituents, revealed that the measured high microscale anisotropy Eh/Ev = 3.75 is crucial in understanding the bulk anisotropy of clay rocks.

  3. Applying distributions of hydraulic conductivity for anisotropic systems and applications to Tc Transport at the U.S. Department of Energy Hanford Site

    SciTech Connect

    Allen G Hunt

    2008-06-09

    43Tc99 is spreading mostly laterally through the U.S. Department of Energy Hanford site sediments. At higher tensions in the unsaturated zone, the hydraulic conductivity may be strongly anisotropic as a consequence of finer soils to retain more water than coarser ones, and for these soils to have been deposited primarily in horizontal structures. We have tried to develop a consistent modeling procedure that could predict the behavior of Tc plumes. Our procedure consists of: (1) Adapting existing numerical recipes based on critical path analysis to calculate the hydraulic conductivity, K, as a function of tension, h, (2) Statistically correlating the predicted K at various values of the tension with fine content, (3) Seeking a tension value, for which the anisotropy and the horizontal K values are both sufficiently large to accommodate multi-kilometer spreading, (4) Predicting the distribution of K values for vertical flow as a function of system support volume, (5) Comparing the largest likely K value in the vertical direction with the expected K in the horizontal direction, (6) Finding the length scale at which the two K values are roughly equal, (7) Comparing that length scale with the horizontal spreading of the plume. We find that our predictions of the value of the tension at which the principle spreading is likely occurring compares very well with experiment. However, we seem to underestimate the physical length scale at which the predominantly horizontal spreading begins to take on significant vertical characteristics. Our data and predictions would seem to indicate that this should happen after horizontal transport of somewhat over a km, but the chiefly horizontal transport appears to continue out to scales of 10km or so.

  4. Anisotropic properties of unconventional superconductors in a magnetic field: testing the nodal stucture

    NASA Astrophysics Data System (ADS)

    Vorontsov, Anton; Vekhter, Ilya

    2006-03-01

    We present a calculation of electronic specific heat and heat conductivity in a vortex state of quasi-two dimensional d-wave superconductors. We employ quasiclassical theory and use the Brand-Pesch-Tewordt approximation to model the superconducting state at moderate to high magnetic fields. Within this framework we investigate the dependence of heat capacity and heat conductivity on the angle of rotation of magnetic field with respect to the nodal directions. We find that the fourfold anisotropy due to nodal structure in both quantities changes sign in the temperature-field plane. This result helps resolve the apparent disagreement about the gap symmetry reached from the specific heat and the thermal conductivity measurements in CeCoIn5. We comment on the physics behind the difference between our results and those obtained in the Doppler shift approximation.

  5. Anisotropic Effects on the Thermoelectric Properties of Highly Oriented Electrodeposited Bi2Te3 Films

    PubMed Central

    Manzano, Cristina V.; Abad, Begoña; Muñoz Rojo, Miguel; Koh, Yee Rui; Hodson, Stephen L.; Lopez Martinez, Antonio M.; Xu, Xianfan; Shakouri, Ali; Sands, Timothy D.; Borca-Tasciuc, Theodorian; Martin-Gonzalez, Marisol

    2016-01-01

    Highly oriented [1 1 0] Bi2Te3 films were obtained by pulsed electrodeposition. The structure, composition, and morphology of these films were characterized. The thermoelectric figure of merit (zT), both parallel and perpendicular to the substrate surface, were determined by measuring the Seebeck coefficient, electrical conductivity, and thermal conductivity in each direction. At 300 K, the in-plane and out-of-plane figure of merits of these Bi2Te3 films were (5.6 ± 1.2)·10−2 and (10.4 ± 2.6)·10−2, respectively. PMID:26776726

  6. Anisotropic ray trace

    NASA Astrophysics Data System (ADS)

    Lam, Wai Sze Tiffany

    Optical components made of anisotropic materials, such as crystal polarizers and crystal waveplates, are widely used in many complex optical system, such as display systems, microlithography, biomedical imaging and many other optical systems, and induce more complex aberrations than optical components made of isotropic materials. The goal of this dissertation is to accurately simulate the performance of optical systems with anisotropic materials using polarization ray trace. This work extends the polarization ray tracing calculus to incorporate ray tracing through anisotropic materials, including uniaxial, biaxial and optically active materials. The 3D polarization ray tracing calculus is an invaluable tool for analyzing polarization properties of an optical system. The 3x3 polarization ray tracing P matrix developed for anisotropic ray trace assists tracking the 3D polarization transformations along a ray path with series of surfaces in an optical system. To better represent the anisotropic light-matter interactions, the definition of the P matrix is generalized to incorporate not only the polarization change at a refraction/reflection interface, but also the induced optical phase accumulation as light propagates through the anisotropic medium. This enables realistic modeling of crystalline polarization elements, such as crystal waveplates and crystal polarizers. The wavefront and polarization aberrations of these anisotropic components are more complex than those of isotropic optical components and can be evaluated from the resultant P matrix for each eigen-wavefront as well as for the overall image. One incident ray refracting or reflecting into an anisotropic medium produces two eigenpolarizations or eigenmodes propagating in different directions. The associated ray parameters of these modes necessary for the anisotropic ray trace are described in Chapter 2. The algorithms to calculate the P matrix from these ray parameters are described in Chapter 3 for

  7. Magnetic properties and anisotropic coercivity in nanogranular films of Co/Al2O3 above the percolation limit

    NASA Astrophysics Data System (ADS)

    Kulyk, M. M.; Kalita, V. M.; Lozenko, A. F.; Ryabchenko, S. M.; Stognei, O. V.; Sitnikov, A. V.; Korenivski, V.

    2014-08-01

    Magnetic properties of nanogranular ferromagnetic Co/Al2O3 films with 74.5 at% Co, which is above the percolation limit, are investigated. It is established that the films have perpendicular magnetic anisotropy and a weaker in-plane anisotropy. The magnetization curves show that the film consists of two magnetic components: a dominating contribution from magneto-anisotropic isolated grains with the anisotropy axis perpendicular to the film plane and a weaker contribution from the percolated part of the film. This two-component magnetic composition of the films, with the dominating contribution from the nanograins, is confirmed by transmission electron microscopy as well as by ferromagnetic resonance spectroscopy. It is further established that the coercive field of the film is almost entirely determined by the percolated part of the film. In this, the angular dependence of the coercive force, Hc (θH), is essentially proportional to sin-1θH, where θH is the angle between the applied field and the film's normal. However, for θH → 0, Hc (θH) there is a narrow minimum with Hc approaching zero. Such non-linear dependence agrees well with our modelling results for a two-component magnetic system of the film, where the non-percolated nanograins have a distinct perpendicular anisotropy. The reported results should be important for in-depth characterization and understanding the magnetism and anisotropy in inhomogeneous systems as well as for applications, specifically in perpendicular magnetic recording.

  8. Analysis on the anisotropic electromechanical properties of lead magnoniobate titanate single crystal for ring type ultrasonic motors

    NASA Astrophysics Data System (ADS)

    Shi, Xiang; Huang, Wenbin; Li, Fei; Li, Zhenrong; Xu, Zhuo; Jiang, Xiaoning; Wei, Xiaoyong

    2016-11-01

    This work discussed the optimized cut of single crystal lead magnoniobate titanate (PMNT) for use of ring type travelling wave ultrasonic motors (USMs), according to anisotropic analysis on electromechanical properties. The selection criterion of crystal orientation relies on the circular uniformity of the induced travelling wave amplitude on the stator surface. By calculating the equivalent elastic coefficient c11 and lateral piezoelectric constant d31, the optimal crystal orientations were proposed for PMNT single crystals poled along different directions. For single crystal poled along <001>c directions, the optimal orientation lies along [001]c with d31=-1335pC/N and k31=0.87. The crystallographic orientation [025]c is the optimized orientation for single crystals poled along <011>c direction with d31=199pC/N and k31=0.55. The optimal orientation of 1R configuration is [332 ¯ ] c with a large enhancement of d31 = 1201 and k31=0.92.

  9. Investigating linkages between atmospheric and terrain properties and spatial anisotropic multiscaling in orographic convective precipitation

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  10. Multifunctional and biomimicking electrochemical properties of conducting polymers

    NASA Astrophysics Data System (ADS)

    Otero, Toribio

    2005-06-01

    Electrochemical oxidation and reduction taking place in films of a conducting polymer involve: generation and annihilation of positive charges on the polymeric chains, conformational changes along the polymeric chains, coulombic repulsions and generation of free volume with interchange of ions and water molecules between the polymer and the solution. So, electric pulses, conformational changes, ionic and aqueous interchanges are involved, as it occurs during most of the biological functions. Those changes induce, simultaneously, different electrochemical properties: electrochemomechanical by swelling and shrinking processes, electrochromic by change of the molecular orbitals, charge storage by accumulation of positive or negative charges, electron-ion transduction between an electronic conductor and an electrolyte. All those properties mimic biological functions: muscles, mimicking skins, electric organs or nervous pulses. Some of the developed devices as sensing actuators (muscles), or smart membranes are presented.

  11. Anisotropic local physical properties of human dental enamel in comparison to properties of some common dental filling materials.

    PubMed

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

    2014-11-01

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

  12. Physical properties of Li ion conducting polyphosphazene based polymer electrolytes

    SciTech Connect

    Sanderson, S.; Zawodzinski, T.; Hermes, R.; Davey, J.; Dai, Hongli

    1996-12-31

    We report a systematic study of the transport properties and the underlying physical chemistry of some polyphosphazene (PPhz)-based polymer electrolytes. We synthesized MEEP and variants which employed mixed combinations of different length oxyethylene side-chains. We compare the conductivity and ion-ion interactions in polymer electrolytes obtained with lithium triflate and lithium bis(trifluoromethanesulfonyl)imide (TFSI) salts added to the polymer. The combination of the lithium imide salt and MEEP yields a maximum conductivity of 8 x 10{sup -5} {Omega}{sup -1} cm{sup -1} at room temperature at a salt loading of 8 monomers per lithium. In one of the mixed side-chain variations, a maximum conductivity of 2 x 10{sup -4} {Omega}{sup -1} cm{sup -1} was measured at the same molar ratio. Raman spectral analysis shows some ion aggregation and some polymer - ion interactions in the PPhz-LiTFSI case but much less than observed with Li CF{sub 3}SO{sub 3}. A sharp increase in the Tg as salt is added corresponds to concentrations above which the conductivity significantly decreases and ion associations appear.

  13. Investigation of Thermal and Electrical Properties for Conductive Polymer Composites

    NASA Astrophysics Data System (ADS)

    Juwhari, Hassan K.; Abuobaid, Ahmad; Zihlif, Awwad M.; Elimat, Ziad M.

    2017-10-01

    This study addresses the effects of temperature ranging from 300 K to 400 K on thermal ( κ) and electrical ( σ) conductivities, and Lorenz number ( L) for different conductive polymeric composites (CPCs), as tailoring the ratios between both conductivities of the composites can be influential in the design optimization of certain thermo-electronic devices. Both κ and σ were found to have either a linear or a nonlinear (2nd and 3rd degree polynomial function) increasing behavior with increased temperatures, depending on the conduction mechanism occurring in the composite systems studied. Temperature-dependent behavior of L tends to show decreasing trends above 300 K, where at 300 K the highest and the lowest values were found to be 3 × 103 W Ω/K2 for CPCs containing iron particles and 3 × 10-2 W Ω/K2 for CPCs-containing carbon fibers respectively. Overall, temperature-dependent behavior of κ/ σ and L can be controlled by heterogeneous structures produced via mechanical-molding-compression. These structures are mainly responsible for energy-transfer processes or transport properties that take place by electrons and phonons in the CPCs' bulks. Hence, the outcome is considered significant in the development process of high performing materials for the thermo-electronic industry.

  14. Local electric conductive property of Si nanowire models

    NASA Astrophysics Data System (ADS)

    Ikeda, Yuji; Senami, Masato; Tachibana, Akitomo

    2012-12-01

    Local electric conductive properties of Si nanowire models are investigated by using two local electric conductivity tensors, {{σ }limits^{leftrArr }}_{ext}(r) and {{σ }limits^{leftrArr }}_{int}(r), defined in Rigged QED. It is emphasized that {{σ }limits^{leftrArr }}_{int}(r) is defined as the response of electric current to the actual electric field at a specific point and does not have corresponding macroscopic physical quantity. For the Si nanowire models, there are regions which show complicated response of electric current density to electric field, in particular, opposite and rotational ones. Local conductivities are considered to be available for the study of a negative differential resistance (NDR), which may be related to this opposite response. It is found that {{σ }limits^{leftrArr }}_{int}(r) shows quite different pattern from {{σ }limits^{leftrArr }}_{ext}(r), local electric conductivity defined for the external electric field. The effects of impurities are also studied by using the model including a Ge atom, in terms of the local response to electric field. It is found that the difference from the pristine model is found mainly around the Ge atom.

  15. 3D Printing Biocompatible Polyurethane/Poly(lactic acid)/Graphene Oxide Nanocomposites: Anisotropic Properties.

    PubMed

    Chen, Qiyi; Mangadlao, Joey Dacula; Wallat, Jaqueline; De Leon, Al; Pokorski, Jonathan K; Advincula, Rigoberto C

    2017-02-01

    Blending thermoplastic polyurethane (TPU) with poly(lactic acid) (PLA) is a proven method to achieve a much more mechanically robust material, whereas the addition of graphene oxide (GO) is increasingly applied in polymer nanocomposites to tailor further their properties. On the other hand, additive manufacturing has high flexibility of structure design which can significantly expand the application of materials in many fields. This study demonstrates the fused deposition modeling (FDM) 3D printing of TPU/PLA/GO nanocomposites and its potential application as biocompatible materials. Nanocomposites are prepared by solvent-based mixing process and extruded into filaments for FDM printing. The addition of GO largely enhanced the mechanical property and thermal stability of the nanocomposites. Interestingly, we found that the mechanical response is highly dependent on printing orientation. Furthermore, the 3D printed nanocomposites exhibit good biocompatibility with NIH3T3 cells, indicating promise as biomaterials scaffold for tissue engineering applications.

  16. Magnetic properties of cubic FeCo nanoparticles with anisotropic long chain structure

    NASA Astrophysics Data System (ADS)

    Liu, Jinming; Wu, Kai; Wang, Jian-Ping

    2016-05-01

    Cubic FeCo alloy nanoparticles (NPs) with body-centered cubic (bcc) phase were prepared using sputter based gas-condensation method. When the NPs formed long chain assemblies, the magnetic properties were quite different from that of well-dispersed NPs. Most of the well-dispersed NPs were superparamagnetic at room temperature while the long chain NP assemblies were ferromagnetic with coercivities around 765 Oe, which displayed quite different magnetic properties. The ferromagnetism of long chain NPs was from the exchange coupling between NPs, which eventually led to the transition from superparamagnetism (SPM) to superferromagetism (SFM). Zero-field-cooled (ZFC) and field-cooled (FC) curves were obtained and long chain NP assemblies displayed ferromagnetism at the temperature ranging from 10 K to 400 K. Time-dependent remanent magnetic moment curves also indicated that the long chain structure had better thermal stability due to the strong exchange coupling.

  17. Rationalization of anisotropic mechanical properties of Al-6061 fabricated using ultrasonic additive manufacturing

    SciTech Connect

    Sridharan, Niyanth; Gussev, Maxim; Seibert, Rachel; Parish, Chad; Norfolk, Mark; Terrani, Kurt; Babu, Sudarsanam Suresh

    2016-09-01

    Ultrasonic additive manufacturing (UAM) is a solid-state process, which uses ultrasonic vibrations at 20 kHz along with mechanized tape layering and intermittent milling operation, to build fully functional three-dimensional parts. In the literature, UAM builds made with low power (1.5 kW) exhibited poor tensile properties in Z-direction, i.e., normal to the interfaces. This reduction in properties is often attributed to the lack of bonding at faying interfaces. The generality of this conclusion is evaluated further in 6061 aluminum alloy builds made with very high power UAM (9 kW). Tensile deformation behavior along X and Z directions were evaluated with small-scale in-situ mechanical testing equipped with high-resolution digital image correlation, as well as, multi-scale characterization of builds. Interestingly, even with complete metallurgical bonding across the interfaces without any discernable voids, poor Z-direction properties were observed. This reduction is correlated to coalescence of pre-existing shear bands at interfaces into micro voids, leading to strain localization and spontaneous failure on tensile loading.

  18. Rationalization of anisotropic mechanical properties of Al-6061 fabricated using ultrasonic additive manufacturing

    DOE PAGES

    Sridharan, Niyanth; Gussev, Maxim; Seibert, Rachel; ...

    2016-09-01

    Ultrasonic additive manufacturing (UAM) is a solid-state process, which uses ultrasonic vibrations at 20 kHz along with mechanized tape layering and intermittent milling operation, to build fully functional three-dimensional parts. In the literature, UAM builds made with low power (1.5 kW) exhibited poor tensile properties in Z-direction, i.e., normal to the interfaces. This reduction in properties is often attributed to the lack of bonding at faying interfaces. The generality of this conclusion is evaluated further in 6061 aluminum alloy builds made with very high power UAM (9 kW). Tensile deformation behavior along X and Z directions were evaluated with small-scalemore » in-situ mechanical testing equipped with high-resolution digital image correlation, as well as, multi-scale characterization of builds. Interestingly, even with complete metallurgical bonding across the interfaces without any discernable voids, poor Z-direction properties were observed. This reduction is correlated to coalescence of pre-existing shear bands at interfaces into micro voids, leading to strain localization and spontaneous failure on tensile loading.« less

  19. Field-dependent anisotropic microrheological and microstructural properties of dilute ferrofluids.

    PubMed

    Yendeti, Balaji; Thirupathi, G; Vudaygiri, Ashok; Singh, R

    2014-08-01

    We have measured microrheological and microstructural properties of a superparamagnetic ferrofluid made of Mn0.75Zn0.25Fe2O4 (MZF) nanoparticles, using passive microrheology in a home-built inverted microscope. Thermal motion of a probe microsphere was measured for different values of an applied external magnetic field and analysed. The analysis shows anisotropy in magneto-viscous effect. Additional microrheological properties, such as storage modulus and loss modulus and their transition are also seen. We have also obtained microstructural properties such as elongational flow coefficient [Formula: see text] , relaxation time constant [Formula: see text] , coefficient of dissipative magnetization [Formula: see text] , etc., using the analysis given in Oliver Muller et al., J. Phys.: Condens. Matter 18, S2623, (2006) and Stefan Mahle et al., Phys. Rev. E 77, 016305 (2008) over our measured viscosity data. Our values for the above parameters are in agreement with earlier theoretical calculations and macro-rheological experimental measurements. These theoretical calculations consider an ideal situation of zero-shear limit, which is best approximated only in the passive microrheology technique described here and a first time measurement of all these parameters with passive microrheology.

  20. Influence of anisotropic grain boundary properties on the evolution of grain boundary character distribution during grain growth—a 2D level set study

    NASA Astrophysics Data System (ADS)

    Hallberg, Håkan

    2014-12-01

    The present study elaborates on a 2D level set model of polycrystal microstructures that was recently established by adding the influence of anisotropic grain boundary energy and mobility on microstructure evolution. The new model is used to trace the evolution of grain boundary character distribution during grain growth. The employed level set formulation conveniently allows the grain boundary characteristics to be quantified in terms of coincidence site lattice (CSL) type per unit of grain boundary length, providing a measure of the distribution of such boundaries. In the model, both the mobility and energy of the grain boundaries are allowed to vary with misorientation. In addition, the influence of initial polycrystal texture is studied by comparing results obtained from a polycrystal with random initial texture against results from a polycrystal that initially has a cube texture. It is shown that the proposed level set formulation can readily incorporate anisotropic grain boundary properties and the simulation results further show that anisotropic grain boundary properties only have a minor influence on the evolution of CSL boundary distribution during grain growth. As anisotropic boundary properties are considered, the most prominent changes in the CSL distributions are an increase of general low-angle Σ1 boundaries as well as a more stable presence of Σ3 boundaries. The observations also hold for the case of an initially cube-textured polycrystal. The presence of this kind of texture has little influence over the evolution of the CSL distribution. Taking into consideration the anisotropy of grain boundary properties, grain growth alone does not seem to be sufficient to promote any significantly increased overall presence of CSL boundaries.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  2. Anisotropic transport properties of PrBa 2Cu 3O 7

    NASA Astrophysics Data System (ADS)

    Goto, M.; Takenaka, K.; Eisaki, H.; Uchida, S.

    1997-08-01

    The in-plane resitivity is measured on the twin-free PrBa 2Cu 3O 7 crystals. The observal anisotropy indicates that dominant carrier conduction takes place in the CuO one-dimensional chain. By applying the pressure, ϱa, containing CuO 2 plane contribution increases more rapidly than ϱa, containing both and plane contributions. This is considered to be due to the increased the hybridization between Pr4f and O2p orbital at the plane site, consistent with the scenario proposed by Fehrenbacher and Rice.

  3. Non-destructive determination of anisotropic mechanical properties of pharmaceutical solid dosage forms.

    PubMed

    Akseli, I; Hancock, B C; Cetinkaya, C

    2009-07-30

    The mechanical property anisotropy of compacts made from four commercially available pharmaceutical excipient powders (microcrystalline cellulose, lactose monohydrate, ascorbic acid, and aspartame) was evaluated. The speed of pressure (longitudinal) waves in the uni-axially compressed cubic compacts of each excipient in the three principle directions was determined using a contact ultrasonic method. Average Young's moduli of each compact in the axial (x) and radial (y and z) directions were characterized. The contact ultrasonic measurements revealed that average Young's modulus values vary with different testing orientations which indicate Young's modulus anisotropy in the compacts. The extent of Young's modulus anisotropy was quantified by using a dimensionless ratio and was found to be significantly different for each material (microcrystalline cellulose>lactose>aspartame>ascorbic acid). It is also observed that using the presented contact method, compacts at high solid fraction (0.857-0.859) could be differentiated than those at the solid fraction of 0.85 in their groups. The presented contact ultrasonic method is an attractive tool since it has the advantages of being sensitive to solid fraction ratio, non-destructive, requiring small amount of material and rapid. It is noteworthy that, since the approach provides insight into the performance of common pharmaceutical materials and fosters increased process knowledge, it can be applied to broaden the understanding of the effect of the mechanical properties on the performance (e.g., disintegration profiles) of solid oral dosage forms.

  4. Electrical Conductivity and Dielectrical Properties of Bulk Methylene Green

    NASA Astrophysics Data System (ADS)

    El-Menyawy, E. M.; Zedan, I. T.; Mansour, A. M.

    2017-03-01

    Thermal stability, direct current electrical conductivity (σ DC), alternating current electrical conductivity (σ AC) and dielectric properties of bulk methylene green (MG) have been investigated. The thermal stability of MG was studied by differential scanning calorimetry and thermogravimetry techniques. Temperature dependence of σ DC showed that the MG has semiconductor behavior with two activation energies determined as 0.12 eV and 0.31 eV in the temperature range 303-343 K and 363-463 K, respectively. The σ AC of bulk MG was performed in the frequency range 150 Hz-5 MHz and temperature range 303-463 K. The dependence of AC conductivity on frequency for MG is found to satisfy Jonscher's universal power law, especially at high frequencies. The correlated barrier hopping model is found to be applicable in which the density of localized states is determined. The σ AC is thermally activated and the activation energy decreases with the increases in frequency. The variation of the real and imaginary parts of the dielectric constant with the frequency and temperature is explained.

  5. Electrical Conductivity and Dielectrical Properties of Bulk Methylene Green

    NASA Astrophysics Data System (ADS)

    El-Menyawy, E. M.; Zedan, I. T.; Mansour, A. M.

    2017-07-01

    Thermal stability, direct current electrical conductivity ( σ DC), alternating current electrical conductivity ( σ AC) and dielectric properties of bulk methylene green (MG) have been investigated. The thermal stability of MG was studied by differential scanning calorimetry and thermogravimetry techniques. Temperature dependence of σ DC showed that the MG has semiconductor behavior with two activation energies determined as 0.12 eV and 0.31 eV in the temperature range 303-343 K and 363-463 K, respectively. The σ AC of bulk MG was performed in the frequency range 150 Hz-5 MHz and temperature range 303-463 K. The dependence of AC conductivity on frequency for MG is found to satisfy Jonscher's universal power law, especially at high frequencies. The correlated barrier hopping model is found to be applicable in which the density of localized states is determined. The σ AC is thermally activated and the activation energy decreases with the increases in frequency. The variation of the real and imaginary parts of the dielectric constant with the frequency and temperature is explained.

  6. Anisotropic and Hierarchical Porosity in Multifunctional Ceramics

    NASA Astrophysics Data System (ADS)

    Lichtner, Aaron Zev

    The performance of multifunctional porous ceramics is often hindered by the seemingly contradictory effects of porosity on both mechanical and non-structural properties and yet a sufficient body of knowledge linking microstructure to these properties does not exist. Using a combination of tailored anisotropic and hierarchical materials, these disparate effects may be reconciled. In this project, a systematic investigation of the processing, characterization and properties of anisotropic and isotropic hierarchically porous ceramics was conducted. The system chosen was a composite ceramic intended as the cathode for a solid oxide fuel cell (SOFC). Comprehensive processing investigations led to the development of approaches to make hierarchical, anisotropic porous microstructures using directional freeze-casting of well dispersed slurries. The effect of all the important processing parameters was investigated. This resulted in an ability to tailor and control the important microstructural features including the scale of the microstructure, the macropore size and total porosity. Comparable isotropic porous ceramics were also processed using fugitive pore formers. A suite of characterization techniques including x-ray tomography and 3-D sectional scanning electron micrographs (FIB-SEM) was used to characterize and quantify the green and partially sintered microstructures. The effect of sintering temperature on the microstructure was quantified and discrete element simulations (DEM) were used to explain the experimental observations. Finally, the comprehensive mechanical properties, at room temperature, were investigated, experimentally and using DEM, for the different microstructures.

  7. Anisotropic magneto-optical properties of vanadium in Bi4Ge3O12

    NASA Astrophysics Data System (ADS)

    Petkova, P.

    2016-07-01

    The paper deals with the investigation of the magneto-optical effect and photochromism in vanadium doped Bi4Ge3O12 (BGO) single crystals in a wide spectral range. It has been found out that the photosensitivity of doped crystals is significantly shifted to the visible wavelengths. This investigation reports the experimental results of Faraday rotation in the case of vanadium doped Bi4Ge3O12. The rotation angle of the polarization plane of the crystal plate has been investigated in the magnetic field in an illuminated state, obtained by exposure with ultraviolet (UV) light and an annealed state developed after annealing at 400 °C. We have observed the strong appearance of vanadium impurity in the spectral range 380-700 nm. The experimental determination of magneto-optical properties of V4+ ions gives us an opportunity for calculation of the refractive index n of the doped BGO.

  8. Optical Determination of Anisotropic Material Properties of Bovine Articular Cartilage in Compression

    PubMed Central

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

    2010-01-01

    The precise nature of the material symmetry of articular cartilage in compression remains to be elucidated. The primary objective of this study was to determine the equilibrium compressive Young’s moduli and Poisson’s ratios of bovine cartilage along multiple directions (parallel and perpendicular to the split line direction, and normal to the articular surface) by loading small cubic specimens (0.9×0.9×0.8 mm, n=15) in unconfined compression, with the expectation that the material symmetry of cartilage could be determined more accurately with the help of a more complete set of material properties. The second objective was to investigate how the tension-compression nonlinearity of cartilage might alter the interpretation of material symmetry. Optimized digital image correlation was used to accurately determine the resultant strain fields within the specimens under loading. Experimental results demonstrated that neither the Young’s moduli nor the Poisson’s ratios exhibit the same values when measured along the three loading directions. The main findings of this study are that the framework of linear orthotropic elasticity (as well as higher symmetries of linear elasticity) is not suitable to describe the equilibrium response of articular cartilage nor characterize its material symmetry; a framework which accounts for the distinctly different responses of cartilage in tension and compression is more suitable for describing the equilibrium response of cartilage; within this framework, cartilage exhibits no lower than orthotropic symmetry. PMID:12594982

  9. Anisotropic physical properties and pressure dependent magnetic ordering of CrAuTe4

    SciTech Connect

    Jo, Na Hyun; Kaluarachchi, Udhara S.; Wu, Yun; Mou, Daixiang; Huang, Lunan; Taufour, Valentin; Kaminski, Adam; Bud'ko, Sergey L.; Canfield, Paul C.

    2016-11-11

    Systematic measurements of temperature-dependent magnetization, resistivity, and angle-resolved photoemission spectroscopy (ARPES) at ambient pressure as well as resistivity under pressures up to 5.25 GPa were conducted on single crystals of CrAuTe4. Magnetization data suggest that magnetic moments are aligned antiferromagnetically along the crystallographic c axis below TN = 255 K. ARPES measurements show band reconstruction due to the magnetic ordering. Magnetoresistance data show clear anisotropy, and, at high fields, quantum oscillations. The Néel temperature decreases monotonically under pressure, decreasing to TN = 236 K at 5.22 GPa. The pressure dependencies of (i) TN, (ii) the residual resistivity ratio, and (iii) the size and power-law behavior of the low-temperature magnetoresistance all show anomalies near 2 GPa suggesting that there may be a phase transition (structural, magnetic, and/or electronic) induced by pressure. Lastly, for pressures higher than 2 GPa a significantly different quantum oscillation frequency emerges, consistent with a pressure induced change in the electronic states.

  10. Anisotropic physical properties and pressure dependent magnetic ordering of CrAuTe4

    DOE PAGES

    Jo, Na Hyun; Kaluarachchi, Udhara S.; Wu, Yun; ...

    2016-11-11

    Systematic measurements of temperature-dependent magnetization, resistivity, and angle-resolved photoemission spectroscopy (ARPES) at ambient pressure as well as resistivity under pressures up to 5.25 GPa were conducted on single crystals of CrAuTe4. Magnetization data suggest that magnetic moments are aligned antiferromagnetically along the crystallographic c axis below TN = 255 K. ARPES measurements show band reconstruction due to the magnetic ordering. Magnetoresistance data show clear anisotropy, and, at high fields, quantum oscillations. The Néel temperature decreases monotonically under pressure, decreasing to TN = 236 K at 5.22 GPa. The pressure dependencies of (i) TN, (ii) the residual resistivity ratio, and (iii)more » the size and power-law behavior of the low-temperature magnetoresistance all show anomalies near 2 GPa suggesting that there may be a phase transition (structural, magnetic, and/or electronic) induced by pressure. Lastly, for pressures higher than 2 GPa a significantly different quantum oscillation frequency emerges, consistent with a pressure induced change in the electronic states.« less

  11. Anisotropic physical properties and pressure dependent magnetic ordering of CrAuTe4

    DOE PAGES

    Jo, Na Hyun; Kaluarachchi, Udhara S.; Wu, Yun; ...

    2016-11-11

    Systematic measurements of temperature-dependent magnetization, resistivity, and angle-resolved photoemission spectroscopy (ARPES) at ambient pressure as well as resistivity under pressures up to 5.25 GPa were conducted on single crystals of CrAuTe4. Magnetization data suggest that magnetic moments are aligned antiferromagnetically along the crystallographic c axis below TN = 255 K. ARPES measurements show band reconstruction due to the magnetic ordering. Magnetoresistance data show clear anisotropy, and, at high fields, quantum oscillations. The Néel temperature decreases monotonically under pressure, decreasing to TN = 236 K at 5.22 GPa. The pressure dependencies of (i) TN, (ii) the residual resistivity ratio, and (iii)more » the size and power-law behavior of the low-temperature magnetoresistance all show anomalies near 2 GPa suggesting that there may be a phase transition (structural, magnetic, and/or electronic) induced by pressure. Lastly, for pressures higher than 2 GPa a significantly different quantum oscillation frequency emerges, consistent with a pressure induced change in the electronic states.« less

  12. Pristine Basal- and Edge-Plane-Oriented Molybdenite MoS2 Exhibiting Highly Anisotropic Properties.

    PubMed

    Tan, Shu Min; Ambrosi, Adriano; Sofer, Zdenĕk; Huber, Štěpán; Sedmidubský, David; Pumera, Martin

    2015-05-04

    The layered structure of molybdenum disulfide (MoS2 ) is structurally similar to that of graphite, with individual sheets strongly covalently bonded within but held together through weak van der Waals interactions. This results in two distinct surfaces of MoS2 : basal and edge planes. The edge plane was theoretically predicted to be more electroactive than the basal plane, but evidence from direct experimental comparison is elusive. Herein, the first study comparing the two surfaces of MoS2 by using macroscopic crystals is presented. A careful investigation of the electrochemical properties of macroscopic MoS2 pristine crystals with precise control over the exposure of one plane surface, that is, basal plane or edge plane, was performed. These crystals were characterized thoroughly by AFM, Raman spectroscopy, X-ray photoelectron spectroscopy, voltammetry, digital simulation, and DFT calculations. In the Raman spectra, the basal and edge planes show anisotropy in the preferred excitation of E2g and A1g phonon modes, respectively. The edge plane exhibits a much larger heterogeneous electron transfer rate constant k(0) of 4.96×10(-5) and 1.1×10(-3)  cm s(-1) for [Fe(CN)6 ](3-/4-) and [Ru(NH3 )6 ](3+/2+) redox probes, respectively, compared to the basal plane, which yielded k(0) tending towards zero for [Fe(CN)6 ](3-/4-) and about 9.3×10(-4)  cm s(-1) for [Ru(NH3 )6 ](3+/2+) . The industrially important hydrogen evolution reaction follows the trend observed for [Fe(CN)6 ](3-/4-) in that the basal plane is basically inactive. The experimental comparison of the edge and basal planes of MoS2 crystals is supported by DFT calculations.

  13. Anisotropic Kepler and anisotropic two fixed centres problems

    NASA Astrophysics Data System (ADS)

    Maciejewski, Andrzej J.; Przybylska, Maria; Szumiński, Wojciech

    2017-02-01

    In this paper we show that the anisotropic Kepler problem is dynamically equivalent to a system of two point masses which move in perpendicular lines (or planes) and interact according to Newton's law of universal gravitation. Moreover, we prove that generalised version of anisotropic Kepler problem as well as anisotropic two centres problem are non-integrable. This was achieved thanks to investigation of differential Galois groups of variational equations along certain particular solutions. Properties of these groups yield very strong necessary integrability conditions.

  14. Dependence of the magnetic properties on the alignment magnetic field for NdFeB bonded magnets made from anisotropic HDDR powders

    NASA Astrophysics Data System (ADS)

    Gao, R. W.; Zhang, J. C.; Zhang, D. H.; Dai, Y. Y.; Meng, X. H.; Wang, Z. M.; Zhang, Y. J.; Liu, H. Q.

    1999-01-01

    The dependence of the hard magnetic properties on the alignment magnetic field for Nd(Fe,Co)B bonded magnets made from anisotropic HDDR powders is studied. The experimental results demonstrate that addition of a little Ga can induce a strong magnetic anisotropy in the HDDR magnetic powders. The application of an alignment magnetic field while the powders are bonded can increase the remanence, the coercivity and the maximum energy product in different degrees and the hard magnetic properties of the magnet are obviously improved with increasing alignment field.

  15. Theoretical studies of anisotropic energy transport in TATB crystals

    NASA Astrophysics Data System (ADS)

    Kroonblawd, Matthew; Sewell, Thomas

    2015-06-01

    Anisotropic thermal transport properties were determined theoretically for single crystals of the insensitive explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) using molecular dynamics. TATB exhibits a graphitic-like layered packing structure with a two-dimensional hydrogen-bonding network within, but not between, the molecule-thick layers that comprise the crystal. Anisotropic thermal conductivity coefficients were determined for initially defect-free and defective TATB crystals at various temperatures and pressures, and direction-dependent relaxation of idealized hot spots was studied. The room temperature, atmospheric pressure thermal conductivity for TATB is predicted to be generally greater and more anisotropic than the thermal conductivities of other molecular explosives; conduction within the layers is at least 68% greater than conduction between them. The phonon mean free path length is predicted to be less than 1 nm. Decreases in thermal conductivity induced by molecular vacancy defects are also anisotropic and exhibit a linear dependence on defect density. Results from the hot-spot relaxation simulations were compared with and fit to an analytical solution for the one-dimensional continuum heat equation by treating the thermal diffusivity as a parameter. Validity of the continuum heat equation predictions for TATB is assessed for length scales below 20 nm.

  16. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Tunable Anisotropic Absorption of Ag-Embedded SiO2 Thin Films by Oblique Angle Deposition

    NASA Astrophysics Data System (ADS)

    Xiao, Xiu-Di; Dong, Guo-Ping; Shao, Jian-Da; Fan, Zheng-Xiu; He, Hong-Bo; Qi, Hong-Ji

    2009-08-01

    Ag-embedded SiO2 thin films are prepared by oblique angle deposition. Through field emission scanning electron microscopy (SEM), an orientated slanted columnar structure is observed. Energy-dispersive x-ray (EDX) analysis shows the Ag concentration is about 3% in the anisotropic SiO2 matrix. Anisotropic surface plasma resonance (SPR) absorption is observed in the Ag-embedded SiO2 thin films, which is dependent on polarization state and incidence angle of two orthogonal polarized lights and the deposition angle. This means that optical properties and anisotropic SPR absorption can be tunable in Ag-embedded SiO2 thin films. Broadband polarization splitting is also observed and the transmission ratio Tp/Ts between p- and s-polarized lights is up to 2.7 for thin films deposited at α = 70°, which means that Ag-embedded SiO2 thin films are a promising candidate for thin film polarizers.

  17. Interpreting equilibrium-conductivity and conductivity-relaxation measurements to establish thermodynamic and transport properties for multiple charged defect conducting ceramics.

    PubMed

    Zhu, Huayang; Ricote, Sandrine; Coors, W Grover; Kee, Robert J

    2015-01-01

    A model-based interpretation of measured equilibrium conductivity and conductivity relaxation is developed to establish thermodynamic, transport, and kinetics parameters for multiple charged defect conducting (MCDC) ceramic materials. The present study focuses on 10% yttrium-doped barium zirconate (BZY10). In principle, using the Nernst-Einstein relationship, equilibrium conductivity measurements are sufficient to establish thermodynamic and transport properties. However, in practice it is difficult to establish unique sets of properties using equilibrium conductivity alone. Combining equilibrium and conductivity-relaxation measurements serves to significantly improve the quantitative fidelity of the derived material properties. The models are developed using a Nernst-Planck-Poisson (NPP) formulation, which enables the quantitative representation of conductivity relaxations caused by very large changes in oxygen partial pressure.

  18. Combining MR elastography and diffusion tensor imaging for the assessment of anisotropic mechanical properties: a phantom study.

    PubMed

    Qin, Eric C; Sinkus, Ralph; Geng, Guangqiang; Cheng, Shaokoon; Green, Michael; Rae, Caroline D; Bilston, Lynne E

    2013-01-01

    To investigate the anisotropic elasticity of soft tissues using MR elastography (MRE) combined with diffusion tensor imaging (DTI). The storage moduli parallel (μ(‖)) and perpendicular (μ(⊥)) to the local fiber orientation were calculated assuming a transversely isotropic model. The local fiber orientation was provided by DTI. The proposed technique was validated against rheometry using anisotropic viscoelastic phantoms with various fiber volume fractions (V(f) = 0%, 15%, and 35%) and bovine skeletal muscle samples. The anisotropic ratio (μ(‖)/μ(⊥)) as measured by MRE correlated well with rheometry for all samples (R(2) = 0.809). The combined MRE/DTI technique was also able to differentiate different levels of mechanical anisotropy with the mechanical anisotropy (μ(‖)/μ(⊥)) of the V(f) = 35% phantoms being significantly higher than the V(f) = 15% and the isotropic (V(f) = 0%) phantoms. The bovine muscle samples showed significantly higher mechanical anisotropy than all phantoms. This study has demonstrated the feasibility of the proposed imaging technique for characterizing mechanical anisotropy of anisotropic materials and biological tissues, and validated the mechanical anisotropy results. Copyright © 2012 Wiley-Liss, Inc.

  19. Crystal growth and anisotropic thermal properties of the nonlinear and polar oxide Cs{sub 2}TeW{sub 3}O{sub 12}

    SciTech Connect

    Feng, Jiang-He; Xiang Xu; Mao, Jiang-Gao

    2015-12-15

    Large crystal of the nonlinear optical and polar oxide Cs{sub 2}TeW{sub 3}O{sub 12} with a size of 20×15×4 mm{sup 3} has been grown by the top-seeded solution growth (TSSG) method. This crystal can be thermally stable up to 808 °C and melts incongruently. It possesses a large transparent range of 0.415–5.250 μm. Thermal properties, including thermal expansion, specific heat, thermal diffusivity and thermal conductivity were investigated. The average linear thermal expansion coefficients were calculated based on the measurement in the temperature range of 30–390 °C. It exhibits strong anisotropic thermal expansion which was discussed according to the relationships between the structure and thermal properties. Furthermore, laser-induced damage threshold has been estimated to be 591.28 MW/cm{sup 2} with a laser wavelength of 1064 nm and pulse duration of 8 ns. - Graphical abstract: The crystallization region of Cs{sub 2}TeW{sub 3}O{sub 12} single-phase in the quasi-ternary Cs{sub 2}TeW{sub 3}O{sub 12}–TeO{sub 2}–Cs{sub 2}O system has been investigated. And Cs{sub 2}TeW{sub 3}O{sub 12} large crystal has been grown by the top-seeded solution growth method. - Highlights: • The crystallization region of Cs{sub 2}TeW{sub 3}O{sub 12} in Cs{sub 2}TeW{sub 3}O{sub 12}–TeO{sub 2}–Cs{sub 2}O system has been investigated. • Large Cs{sub 2}TeW{sub 3}O{sub 12} crystal has been grown. • Cs{sub 2}TeW{sub 3}O{sub 12} possesses a large transparent range of 0.415–5.250 μm. • Cs{sub 2}TeW{sub 3}O{sub 12} possesses large laser-induced damage threshold of 591.28 MW/cm{sup 2}. • Detialed thermal properties have been investigated.

  20. Anisotropic universe with anisotropic sources

    SciTech Connect

    Aluri, Pavan K.; Panda, Sukanta; Sharma, Manabendra; Thakur, Snigdha E-mail: sukanta@iiserb.ac.in E-mail: snigdha@iiserb.ac.in

    2013-12-01

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

  1. Inferring Single Neuron Properties in Conductance Based Balanced Networks

    PubMed Central

    Pool, Román Rossi; Mato, Germán

    2011-01-01

    Balanced states in large networks are a usual hypothesis for explaining the variability of neural activity in cortical systems. In this regime the statistics of the inputs is characterized by static and dynamic fluctuations. The dynamic fluctuations have a Gaussian distribution. Such statistics allows to use reverse correlation methods, by recording synaptic inputs and the spike trains of ongoing spontaneous activity without any additional input. By using this method, properties of the single neuron dynamics that are masked by the balanced state can be quantified. To show the feasibility of this approach we apply it to large networks of conductance based neurons. The networks are classified as Type I or Type II according to the bifurcations which neurons of the different populations undergo near the firing onset. We also analyze mixed networks, in which each population has a mixture of different neuronal types. We determine under which conditions the intrinsic noise generated by the network can be used to apply reverse correlation methods. We find that under realistic conditions we can ascertain with low error the types of neurons present in the network. We also find that data from neurons with similar firing rates can be combined to perform covariance analysis. We compare the results of these methods (that do not requite any external input) to the standard procedure (that requires the injection of Gaussian noise into a single neuron). We find a good agreement between the two procedures. PMID:22016730

  2. Laser properties of luminescent conducting polymers in open resonators

    NASA Astrophysics Data System (ADS)

    Eradat Oskouei, Nayer; Gellermann, Werner; Shkunov, Maxim N.; Frolov, Sergey V.; Osaki, M.; Yoshino, Katsumi; Vardeny, Z. Valy

    1997-12-01

    We have investigated the lasing properties of several luminescent conducting polymers, i.e. DOO-PPV and the bi- substituted polyacetylenes PDPA-nBu, and PHxPA, dissolved in various polar and non-polar solvents. PPV polymers emit with high quantum efficiencies in broad emission bands cantered in the orange/red region of the spectrum, depending on the solvent, and the PDPA polymers emit in the blue/green region. Our tested laser resonators include polymer solutions excited with 100 ps pulses from a regeneratively amplified mode-locked Nd:YAG laser. We obtain pulsed, low-threshold laser operation with repetition rate of up to 1 kHz. Resulting mainly from recent reported originally in the literature. The dependencies of threshold pump energy and output versus input power characteristics on material parameters are investigated for a fixed optical gain length. The results are compared with the standard Rhodamine 590 organic dye system used in the same wavelength regions. We have observed that the well know phenomenon of 'concentration quenching' in dye molecules does not happen in polymers. Spectral narrowing in PDPA-nBu solution, emitting near 500 nm, is also obtained for the first time.

  3. Novel 18650 lithium-ion battery surrogate cell design with anisotropic thermophysical properties for studying failure events

    NASA Astrophysics Data System (ADS)

    Spinner, Neil S.; Hinnant, Katherine M.; Mazurick, Ryan; Brandon, Andrew; Rose-Pehrsson, Susan L.; Tuttle, Steven G.

    2016-04-01

    Cylindrical 18650-type surrogate cells were designed and fabricated to mimic the thermophysical properties and behavior of active lithium-ion batteries. An internal jelly roll geometry consisting of alternating stainless steel and mica layers was created, and numerous techniques were used to estimate thermophysical properties. Surrogate cell density was measured to be 1593 ± 30 kg/m3, and heat capacity was found to be 727 ± 18 J/kg-K. Axial thermal conductivity was determined to be 5.1 ± 0.6 W/m-K, which was over an order of magnitude higher than radial thermal conductivity due to jelly roll anisotropy. Radial heating experiments were combined with numerical and analytical solutions to the time-dependent, radial heat conduction equation, and from the numerical method an additional estimate for heat capacity of 805 ± 23 J/kg-K was found. Using both heat capacities and analysis techniques, values for radial thermal conductivity were between 0.120 and 0.197 W/m-K. Under normal operating conditions, relatively low radial temperature distributions were observed; however, during extreme battery failure with a hexagonal cell package, instantaneous radial temperature distributions as high as 43-71 °C were seen. For a vertical cell package, even during adjacent cell failure, similar homogeneity in internal temperatures were observed, demonstrating thermal anisotropy.

  4. Ion jelly conductive properties using dicyanamide-based ionic liquids.

    PubMed

    Carvalho, Tânia; Augusto, Vera; Rocha, Ângelo; Lourenço, Nuno M T; Correia, Natália T; Barreiros, Susana; Vidinha, Pedro; Cabrita, Eurico J; Dionísio, Madalena

    2014-08-07

    The thermal behavior and transport properties of several ion jellys (IJs), a composite that results from the combination of gelatin with an ionic liquid (IL), were investigated by dielectric relaxation spectroscopy (DRS), differential scanning calorimetry (DSC), and pulsed field gradient nuclear magnetic resonance spectroscopy (PFG NMR). Four different ILs containing the dicyanamide anion were used: 1-butyl-3-methylimidazolium dicyanamide (BMIMDCA), 1-ethyl-3-methylimidazolium dicyanamide (EMIMDCA), 1-butyl-1-methylpyrrolidinium dicyanamide (BMPyrDCA), and 1-butylpyridinium dicyanamide (BPyDCA); the bulk ILs were also investigated for comparison. A glass transition was detected by DSC for all materials, ILs and IJs, allowing them to be classified as glass formers. Additionally, an increase in the glass transition temperature upon dehydration was observed with a greater extent for IJs, attributed to a greater hindrance imposed by the gelatin matrix after water removal, rendering the IL less mobile. While crystallization is observed for some ILs with negligible water content, it was never detected for any IJ upon thermal cycling, which persist always as fully amorphous materials. From DRS measurements, conductivity and diffusion coefficients for both cations (D+) and anions (D-) were extracted. D+ values obtained by DRS reveal excellent agreement with those obtained from PFG NMR direct measurements, obeying the same VFTH equation over a large temperature range (ΔT ≈ 150 K) within which D+ varies around 10 decades. At temperatures close to room temperature, the IJs exhibit D values comparable to the most hydrated (9%) ILs. The IJ derived from EMIMDCA possesses the highest conductivity and diffusion coefficient, respectively, ∼10(-2) S·cm(-1) and ∼10(-10) m(2)·s(-1). For BMPyrDCA the relaxational behavior was analyzed through the complex permittivity and modulus formalism allowing the assignment of the detected secondary relaxation to a Johari

  5. Theoretical aspects for estimating anisotropic saturated hydraulic conductivity from in-well or direct-push probe injection tests in uniform media

    NASA Astrophysics Data System (ADS)

    Klammler, Harald; Layton, Leif; Nemer, Bassel; Hatfield, Kirk; Mohseni, Ana

    2017-06-01

    Hydraulic conductivity and its anisotropy are fundamental aquifer properties for groundwater flow and transport modeling. Current in-well or direct-push field measurement techniques allow for relatively quick determination of general conductivity profiles with depth. However, capabilities for identifying local scale conductivities in the horizontal and vertical directions are very limited. Here, we develop the theoretical basis for estimating horizontal and vertical conductivities from different types of steady-state single-well/probe injection tests under saturated conditions and in the absence of a well skin. We explore existing solutions and a recent semi-analytical solution approach to the flow problem under the assumption that the aquifer is locally homogeneous. The methods are based on the collection of an additional piece of information in the form of a second injection (or recirculation) test at a same location, or in the form of an additional head or flow observation along the well/probe. Results are represented in dimensionless charts for partial validation against approximate solutions and for practical application to test interpretation. The charts further allow for optimization of a test configuration to maximize sensitivity to anisotropy ratio. The two methods most sensitive to anisotropy are found to be (1) subsequent injection from a lateral screen and from the bottom of an otherwise cased borehole, and (2) single injection from a lateral screen with an additional head observation along the casing. Results may also be relevant for attributing consistent divergences in conductivity measurements from different testing methods applied at a same site or location to the potential effects of anisotropy. Some practical aspects are discussed and references are made to existing methods, which appear easily compatible with the proposed procedures.

  6. Fractures in anisotropic media

    NASA Astrophysics Data System (ADS)

    Shao, Siyi

    Rocks may be composed of layers and contain fracture sets that cause the hydraulic, mechanical and seismic properties of a rock to be anisotropic. Coexisting fractures and layers in rock give rise to competing mechanisms of anisotropy. For example: (1) at low fracture stiffness, apparent shear-wave anisotropy induced by matrix layering can be masked or enhanced by the presence of a fracture, depending on the fracture orientation with respect to layering, and (2) compressional-wave guided modes generated by parallel fractures can also mask the presence of matrix layerings for particular fracture orientations and fracture specific stiffness. This report focuses on two anisotropic sources that are widely encountered in rock engineering: fractures (mechanical discontinuity) and matrix layering (impedance discontinuity), by investigating: (1) matrix property characterization, i.e., to determine elastic constants in anisotropic solids, (2) interface wave behavior in single-fractured anisotropic media, (3) compressional wave guided modes in parallel-fractured anisotropic media (single fracture orientation) and (4) the elastic response of orthogonal fracture networks. Elastic constants of a medium are required to understand and quantify wave propagation in anisotropic media but are affected by fractures and matrix properties. Experimental observations and analytical analysis demonstrate that behaviors of both fracture interface waves and compressional-wave guided modes for fractures in anisotropic media, are affected by fracture specific stiffness (controlled by external stresses), signal frequency and relative orientation between layerings in the matrix and fractures. A fractured layered medium exhibits: (1) fracture-dominated anisotropy when the fractures are weakly coupled; (2) isotropic behavior when fractures delay waves that are usually fast in a layered medium; and (3) matrix-dominated anisotropy when the fractures are closed and no longer delay the signal. The

  7. Synthesis and anisotropic properties of single crystalline Ln{sub 2}Ru{sub 3}Al{sub 15+x} (Ln=Gd, Tb)

    SciTech Connect

    Morrison, Gregory; Prestigiacomo, Joseph; Haldolaarachchige, Neel; Rai, Binod K.; Young, David P.; Stadler, Shane; Morosan, Emilia; Chan, Julia Y.

    2016-04-15

    Single crystals of Ln{sub 2}Ru{sub 3}Al{sub 15+x} (Ln=Gd, Tb) have been grown using the self-flux method under Ru-poor conditions. The structure of the Gd analog is found to be highly dependent on the synthesis method. Gd{sub 2}Ru{sub 3}Al{sub 15.08} orders antiferromagnetically at 17.5 K. Tb{sub 2}Ru{sub 3}Al{sub 15.05} enters an antiferromagnetic state at 16.6 K followed by a likely incommensurate-to-commensurate transition at 14.9 K for crystals oriented with H//ab. For crystals oriented with H//c, a broad maximum is observed in the temperature dependent M/H, indicative of a highly anisotropic magnetic system with the hard axis in the c-direction. The magnetization as a function of field and magnetoresistance along the ab-direction of Tb{sub 2}Ru{sub 3}Al{sub 15.05} display a stepwise behavior and indicate strong crystalline electric field effects. - Graphical abstract: Single crystal, structure, and highly anisotropic magnetoresistance due to strong crystalline electric field effects of Tb{sub 2}Ru{sub 3}Al{sub 15.05}. - Highlights: • Single crystals of Ln{sub 2}Ru{sub 3}Al{sub 15+x} were grown for the first time via flux growth. • The structure of Gd{sub 2}Ru{sub 3}Al{sub 15.09} differs from that of arc melted Gd{sub 2}Ru{sub 3.08}Al{sub 15}. • Tb{sub 2}Ru{sub 3}Al{sub 15.05} exhibits highly anisotropic magnetic and transport properties. • The properties of Tb{sub 2}Ru{sub 3}Al{sub 15.05} arise due to crystalline electric field effects.

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

    SciTech Connect

    Zhang, Junjie; Zhang, Zhonghan; Sun, Youxuan; Zhang, Chengqian; Tao, Xutang

    2012-11-15

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

  9. Synthesis of Conductive Nanofillers/Nanofibers and Electrical Properties of their Conductive Polymer Composites

    NASA Astrophysics Data System (ADS)

    Sarvi, Ali

    Thanks to their corrosion resistance, light weight, low cost, and ease of processing, electrically conducting polymer composites (CPCs) have received significant attention for the replacement of metals and inorganic materials for sensors, actuators, supercapacitors, and electromagnetic interference (EMI) shields. In this PhD thesis, high aspect ratio conductive nanofillers namely copper nanowires (CuNWs) and multiwall carbon nanotubes (MWCNTs) were coated with polyaniline (PANi) using solution mixing and in-situ polymerization method, respectively. Transmission electron microscopy (TEM) showed a smooth polyaniline nano-coating between 5--18 nm in thickness on the nanofillers' surface. The coating thickness and; consequently, electrical conductivity was controlled and tuned by polyaniline/aniline concentration in solution. Composites with tunable conductivity may be used as chemisensors, electronic pressure sensors and switches. Coated nanofillers demonstrated better dispersion in polystyrene (PS) and provided lower electrical percolation threshold. Dispersion of nanofillers in PS was investigated using rheological measurements and confirmed with electron micrographs and nano-scale images of CPCs. Polyaniline (PANi), when used as a coating layer, was able to attenuate electromagnetic (EM) waves via absorption and store electrical charges though pseudocapacitance mechanism. The dielectric measurements of MWCNT-PANi/PS composites showed one order of magnitude increase in real electrical permittivity compared to that of MWCNT/PS composites making them suitable for charge storage purposes. Incorporation of PANi also brought a new insight into conductive network formation mechanism in electrospun mats where the orientation of conductive high aspect ratio nanofillers is a major problem. Conductive nanofibers of poly(vinylidene fluoride) (PVDF) filled with coated multiwall carbon nanotubes (MWCNTs) were fabricated using electrospinning. These highly oriented PVDF

  10. Conductive magnetorheological elastomer: fatigue dependent impedance-mechanic coupling properties

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Xuan, Shouhu; Ge, Lin; Wen, Qianqian; Gong, Xinglong

    2017-01-01

    This work investigated the relationship between the impedance properties and dynamic mechanical properties of magnetorheological elastomers (MREs) under fatigue loading. The storage modulus and the impedance properties of MREs were highly influenced by the pressure and magnetic field. Under the same experimental condition, the two characteristics exhibited similar fatigue dependent change trends. When pressure was smaller than 10 N, the capacitance of MRE could be divided into four sections with the increase of the cyclic numbers. The relative equivalent circuit model was established to fit the experimental results of the impedance spectra. Each parameter of circuit element reflected the change of fatigue loading, relative microstructure of MRE, MRE-electrode interface layer, respectively. Based on the above analysis, the real-time and nondestructive impedance method was demonstrated to be high potential on detecting the fatigue of the MRE device.

  11. Structure and Properties of Amorphous Transparent Conducting Oxides

    NASA Astrophysics Data System (ADS)

    Medvedeva, Julia

    Driven by technological appeal, the research area of amorphous oxide semiconductors has grown tremendously since the first demonstration of the unique properties of amorphous indium oxide more than a decade ago. Today, amorphous oxides, such as a-ITO, a-IZO, a-IGZO, or a-ZITO, exhibit the optical, electrical, thermal, and mechanical properties that are comparable or even superior to those possessed by their crystalline counterparts, pushing the latter out of the market. Large-area uniformity, low-cost low-temperature deposition, high carrier mobility, optical transparency, and mechanical flexibility make these materials appealing for next-generation thin-film electronics. Yet, the structural variations associated with crystalline-to-amorphous transition as well as their role in carrier generation and transport properties of these oxides are far from being understood. Although amorphous oxides lack grain boundaries, factors like (i) size and distribution of nanocrystalline inclusions; (ii) spatial distribution and clustering of incorporated cations in multicomponent oxides; (iii) formation of trap defects; and (iv) piezoelectric effects associated with internal strains, will contribute to electron scattering. In this work, ab-initio molecular dynamics (MD) and accurate density-functional approaches are employed to understand how the properties of amorphous ternary and quaternary oxides depend on quench rates, cation compositions, and oxygen stoichiometries. The MD results, combined with thorough experimental characterization, reveal that interplay between the local and long-range structural preferences of the constituent oxides gives rise to a complex composition-dependent structural behavior in the amorphous oxides. The proposed network models of metal-oxygen polyhedra help explain the observed intriguing electrical and optical properties in In-based oxides and suggest ways to broaden the phase space of amorphous oxide semiconductors with tunable properties. The

  12. Anisotropic structural and magnetic properties of the field-aligned superconducting system SmFeAsO1-xFx (x = 0, 0.1, 0.2, 0.25 and 0.3)

    NASA Astrophysics Data System (ADS)

    You, Y. B.; Hsiao, T. K.; Chang, B. C.; Tai, M. F.; Hsu, Y. Y.; Ku, H. C.; Wei, Z.; Ruan, K. Q.; Li, X. G.

    2011-01-01

    Anisotropic structural and magnetic properties of the field-aligned superconducting system SmFeAsO1-xFx (x = 0, 0.1, 0.2, 0.25 and 0.3) are reported. Due to the Fe spin-orbital related anisotropic exchange coupling, all the tetragonal microcrystalline powders in epoxy were aligned at room temperature using the field-rotation method where the tetragonal ab-plane is parallel to the magnetic alignment field Ba of 0.9 T and the c-axis parallels to the rotating axis. Anisotropic magnetic properties are studied through low temperature magnetic measurements along the c-axis and paralleled to the ab-plane of aligned samples in both zero-field-cooled (ZFC) and field-cooled (FC) modes. The under-doped compound (x = 0.1) is not superconducting with an antiferromagnetic Néel temperature TN ~ 40 K, while the two optimum-doped compounds (x = 0.2 and 0.25) show high superconducting transition temperatures Tc of 49K and 50K, respectively. The variation of anisotropic structural and magnetic properties for this system are discussed and compared with the previously reported 52 K anisotropic superconductor Sm0.95La0.05FeAsO0.85F0.15.

  13. Physical and conductivity properties of poly (vinyl chloride) ionomers

    NASA Astrophysics Data System (ADS)

    Misra, Nira; Panda, H. S.; Kapusetti, Govinda; Jaiswal, Shilpa; Bhattacharya, Subhratanu

    2011-02-01

    Poly (vinyl chloride)(PVC) is a cheapest plastic. Importance of PVC based ionomer has been gradually being popularizing due to compatibility of PVC with a number of salts to replace polyethylene oxide based ionomer. Under present investigation few of chloride group of PVC chain have been replaced by basic thiouronium group and these thiouronium groups are further oxidized to sulfonate group. Introduction of thiouronium group in PVC is confirmed through FTIR and further its oxidation to sulfonate group is also confirmed by FTIR. Conductivity in different stoichiometric ratio of PVCTU and PVCSO3H was studied and found that PVCTU: PVCSO3H in 1:1 ratio has conductivity near to pure PVC (10-9 Ohm-1 cm-1) and increases with proportion of PVCSO3Na in the mixture (10-6 Ohm-1 cm-1) for pure PVC, PVCTU has less conductivity not much significant.

  14. 39 CFR 232.1 - Conduct on postal property.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... brought upon postal property for other than official purposes. (k) Vehicular and pedestrian traffic. (1... signals and directions of security force personnel, other authorized individuals, and all posted traffic... head from time to time by the issuance and posting of specific traffic directives as may be...

  15. 39 CFR 232.1 - Conduct on postal property.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... brought upon postal property for other than official purposes. (k) Vehicular and pedestrian traffic. (1... signals and directions of security force personnel, other authorized individuals, and all posted traffic... head from time to time by the issuance and posting of specific traffic directives as may be...

  16. 39 CFR 232.1 - Conduct on postal property.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... brought upon postal property for other than official purposes. (k) Vehicular and pedestrian traffic. (1... signals and directions of security force personnel, other authorized individuals, and all posted traffic... head from time to time by the issuance and posting of specific traffic directives as may be...

  17. 39 CFR 232.1 - Conduct on postal property.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... brought upon postal property for other than official purposes. (k) Vehicular and pedestrian traffic. (1... signals and directions of security force personnel, other authorized individuals, and all posted traffic... head from time to time by the issuance and posting of specific traffic directives as may be...

  18. AC Conductivity and Dielectric Properties of Borotellurite Glass

    NASA Astrophysics Data System (ADS)

    Taha, T. A.; Azab, A. A.

    2016-10-01

    Borotellurite glasses with formula 60B2O3-10ZnO-(30 - x)NaF- xTeO2 ( x = 0 mol.%, 5 mol.%, 10 mol.%, and 15 mol.%) have been synthesized by thermal melting. X-ray diffraction (XRD) analysis confirmed that the glasses were amorphous. The glass density ( ρ) was determined by the Archimedes method at room temperature. The density ( ρ) and molar volume ( V m) were found to increase with increasing TeO2 content. The direct-current (DC) conductivity was measured in the temperature range from 473 K to 623 K, in which the electrical activation energy of ionic conduction increased from 0.27 eV to 0.48 eV with increasing TeO2 content from 0 mol.% to 15 mol.%. The dielectric parameters and alternating-current (AC) conductivity ( σ ac) were investigated in the frequency range from 1 kHz to 1 MHz and temperature range from 300 K to 633 K. The AC conductivity and dielectric constant decreased with increasing TeO2 content from 0 mol.% to 15 mol.%.

  19. Effects of anisotropic interaction-induced properties of hydrogen-rare gas compounds on rototranslational Raman scattering spectra: Comprehensive theoretical and numerical analysis.

    PubMed

    Głaz, Waldemar; Bancewicz, Tadeusz; Godet, Jean-Luc; Gustafsson, Magnus; Haskopoulos, Anastasios; Maroulis, George

    2016-07-21

    A comprehensive study is presented of many aspects of the depolarized anisotropic collision induced (CI) component of light scattered by weakly bound compounds composed of a dihydrogen molecule and a rare gas (Rg) atom, H2-Rg. The work continues a series of earlier projects marking the revival of interest in linear light scattering following the development of new highly advanced tools of quantum chemistry and other theoretical, computational, and experimental means of spectral analyses. Sophisticated ab initio computing procedures are applied in order to obtain the anisotropic polarizability component's dependence on the H2-Rg geometry. These data are then used to evaluate the CI spectral lines for all types of Rg atoms ranging from He to Xe (Rn excluded). Evolution of the properties of CI spectra with growing polarizability/masses of the complexes studied is observed. Special attention is given to the heaviest, Kr and Xe based, scatterers. The influence of specific factors shaping the spectral lines (e.g., bound and metastable contribution, potential anisotropy) is discussed. Also the share of pressure broadened allowed rotational transitions in the overall spectral profile is taken into account and the extent to which it is separable from the pure CI contribution is discussed. We finish with a brief comparison between the obtained results and available experimental data.

  20. Anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using double AlN buffer layers

    PubMed Central

    Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

    2016-01-01

    We report the anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11–22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1–100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting. PMID:26861595

  1. Effects of anisotropic interaction-induced properties of hydrogen-rare gas compounds on rototranslational Raman scattering spectra: Comprehensive theoretical and numerical analysis

    NASA Astrophysics Data System (ADS)

    Głaz, Waldemar; Bancewicz, Tadeusz; Godet, Jean-Luc; Gustafsson, Magnus; Haskopoulos, Anastasios; Maroulis, George

    2016-07-01

    A comprehensive study is presented of many aspects of the depolarized anisotropic collision induced (CI) component of light scattered by weakly bound compounds composed of a dihydrogen molecule and a rare gas (Rg) atom, H2-Rg. The work continues a series of earlier projects marking the revival of interest in linear light scattering following the development of new highly advanced tools of quantum chemistry and other theoretical, computational, and experimental means of spectral analyses. Sophisticated ab initio computing procedures are applied in order to obtain the anisotropic polarizability component's dependence on the H2-Rg geometry. These data are then used to evaluate the CI spectral lines for all types of Rg atoms ranging from He to Xe (Rn excluded). Evolution of the properties of CI spectra with growing polarizability/masses of the complexes studied is observed. Special attention is given to the heaviest, Kr and Xe based, scatterers. The influence of specific factors shaping the spectral lines (e.g., bound and metastable contribution, potential anisotropy) is discussed. Also the share of pressure broadened allowed rotational transitions in the overall spectral profile is taken into account and the extent to which it is separable from the pure CI contribution is discussed. We finish with a brief comparison between the obtained results and available experimental data.

  2. A general methodology for inverse estimation of the elastic and anelastic properties of anisotropic open-cell porous materials—with application to a melamine foam

    SciTech Connect

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

    2014-02-28

    This paper proposes an inverse estimation method for the characterisation of the elastic and anelastic properties of the frame of anisotropic open-cell foams used for sound absorption. A model of viscoelasticity based on a fractional differential constitutive equation is used, leading to an augmented Hooke's law in the frequency domain, where the elastic and anelastic phenomena appear as distinctive terms in the stiffness matrix. The parameters of the model are nine orthotropic elastic moduli, three angles of orientation of the material principal directions and three parameters governing the anelastic frequency dependence. The inverse estimation consists in numerically fitting the model on a set of transfer functions extracted from a sample of material. The setup uses a seismic-mass measurement repeated in the three directions of space and is placed in a vacuum chamber in order to remove the air from the pores of the sample. The method allows to reconstruct the full frequency-dependent complex stiffness matrix of the frame of an anisotropic open-cell foam and in particular it provides the frequency of maximum energy dissipation by viscoelastic effects. The characterisation of a melamine foam sample is performed and the relation between the fractional-derivative model and other types of parameterisations of the augmented Hooke's law is discussed.

  3. A general methodology for inverse estimation of the elastic and anelastic properties of anisotropic open-cell porous materials—with application to a melamine foam

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

    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.

  4. Fabrication, Conductive Properties and Photocatalytic Application of Silver Nanorods

    NASA Astrophysics Data System (ADS)

    Chen, Yi-Hsun; Liu, Pai-Chung; Lin, C. B.

    2017-07-01

    This study proposes a process for fabricating silver nanorods used in conductive circuits and photocatalytic applications. In this process, UV-irradiated silver chloride nanoparticles are added to ethylene glycol solution containing polyvinyl pyrrolidone (PVP) and silver nitrate at 120 °C. With the seed crystal synthesis method, this process yielded a solution containing silver nanowires with an aspect ratio (AR) of approximately 1055 after 12 h. Aluminum foam was then placed in this solution, and the solution was stirred using a magnetic stirrer at 400 rpm. After 4 days, this process yielded a solution of silver nanorods with an AR of approximately 130. After completely washing away any PVP on the surface of the silver nanorods, a conductive ethanol ink containing 25 wt.% silver nanorods was prepared, and a conductive layer approximately 3 μm thick was applied on a glass slide. Measurements obtained using a four-point probe indicated that this layer had a sheet resistance of approximately 0.012 Ω/sq. Furthermore, a conductive ethanol ink containing 26 wt.% silver nanorods was used in a pen to draw conductive circuits on Bristol board and matte paper; the resulting sheet resistances were 132 and 0.018 Ω/sq, respectively. Finally, a visible-light-responsive photocatalyst consisting of silver nanorods dispersed over the Ag@AgCl film (Ag@AgCl/Ag nanorods; AR = 25) was synthesized through heterogeneous precipitation. The photocatalytic activity of the Ag@AgCl film can be further improved by the addition of silver nanorods.

  5. Understanding hopping transport and thermoelectric properties of conducting polymers

    NASA Astrophysics Data System (ADS)

    Ihnatsenka, S.; Crispin, X.; Zozoulenko, I. V.

    2015-07-01

    We calculate the conductivity σ and the Seebeck coefficient S for the phonon-assisted hopping transport in conducting polymers poly(3,4-ethylenedioxythiophene) or PEDOT, experimentally studied by Bubnova et al. [J. Am. Chem. Soc. 134, 16456 (2012)], 10.1021/ja305188r. We use the Monte Carlo technique as well as the semianalytical approach based on the transport energy concept. We demonstrate that both approaches show a good qualitative agreement for the concentration dependence of σ and S . At the same time, we find that the semianalytical approach is not in a position to describe the temperature dependence of the conductivity. We find that both Gaussian and exponential density of states (DOS) reproduce rather well the experimental data for the concentration dependence of σ and S giving similar fitting parameters of the theory. The obtained parameters correspond to a hopping model of localized quasiparticles extending over 2-3 monomer units with typical jumps over a distance of 3-4 units. The energetic disorder (broadening of the DOS) is estimated to be 0.1 eV. Using the Monte Carlo calculation we reproduce the activation behavior of the conductivity with the calculated activation energy close to the experimentally observed one. We find that for a low carrier concentration a number of free carriers contributing to the transport deviates strongly from the measured oxidation level. Possible reasons for this behavior are discussed. We also study the effect of the dimensionality on the charge transport by calculating the Seebeck coefficient and the conductivity for the cases of three-, two-, and one-dimensional motion.

  6. In situ studies of strain dependent transport properties of conducting polymers on elastomeric substrates

    NASA Astrophysics Data System (ADS)

    Vijay, Venugopalan; Rao, Arun D.; Narayan, K. S.

    2011-04-01

    We report the changes in the surface electrical resistance, R, of conducting polymer, Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) films coated on appropriate flexible substrates in stretched conditions. These studies are important in the context of flexible organic electronic applications. In situ conductivity measurements on pristine PEDOT:PSS thin films on elastomeric substrates upon stretching reveal a minima in R as a function of strain, x, prior to the expected increase at higher strain levels. The studies emphasize (i) role of substrates, (ii) stress-induced anisotropic features, and temperature dependence of R (iii) in comparison of R(x) in polymer films to that of conventional metal films. The stress induced changes is modeled in terms of effective medium approximation.

  7. Ground State Properties and Localized Excited States around a Magnetic Impurity Described by the Anisotropic s- d Interaction in Superconductivity

    NASA Astrophysics Data System (ADS)

    Yoshioka, Tomoki; Ohashi, Yoji

    1998-04-01

    We investigate the electronic state around a magnetic impurity in thesuperconductivity in order to clarify how the anisotropy of thes-d interaction works in the presence of the superconductingenergy gap. Using the numerical renormalization group method, weobtain regions induced by the anisotropy where two localizedexcited states with different energies appear at the same time; theycannot obtain as far as the isotropic interaction is considered. Thismeans that the anisotropy of the s-d interaction works relevantlyin some cases in the superconducting state. We also examine whether ornot the bound state energy for the anisotropic and antiferromagnetics-d interaction is scaled by T K/Δ (T K: Kondotemperature, Δ: superconducting order parameter), and find thatit does not hold in the regions with two bound states.

  8. Synthesis of cubic SrCoO3 single crystal and its anisotropic magnetic and transport properties

    NASA Astrophysics Data System (ADS)

    Long, Youwen; Kaneko, Yoshio; Ishiwata, Shintaro; Taguchi, Yasujiro; Tokura, Yoshinori

    2011-06-01

    A large-size single crystal of nearly stoichiometric SrCoO3 was prepared with a two-step method combining the floating-zone technique and subsequent high oxygen pressure treatment. SrCoO3 crystallizes in a cubic perovskite structure with space group Pm\\bar {3}m , and displays an itinerant ferromagnetic behavior with the Curie temperature of 305 K. The easy magnetization axis is found to be along the [111] direction, and the saturation moment is 2.5 µB/f.u., in accord with the picture of the intermediate spin state. The resistivity at low temperatures (T) is proportional to T2, indicative of the possible effect of orbital fluctuation in the intermediate spin ferromagnetic metallic state. Unusual anisotropic magnetoresistance is also observed and its possible origin is discussed.

  9. The magnetic properties of three-dimensional spin-1 easy-axis single-ion anisotropic antiferromagnets

    NASA Astrophysics Data System (ADS)

    Hu, Ai-Yuan; Wang, Qin

    2010-05-01

    The ordered and disordered phases of spin-1 Heisenberg and Ising antiferromagnets with easy-axis single-ion anisotropy on a three-dimensional lattice are studied. By using of the double-time Green's function method within the Tyablikov decoupling for the exchange anisotropy and Callen's approximation for the single-ion anisotropy, the Néel temperature, magnetization and susceptibility are investigated. Their relations with the temperature and anisotropic parameter are analyzed over the entire range of temperature. It is found that our results agree well with spin wave theory results at low temperature, agree with the high temperature series results at high temperature, and compare reasonably well with the linked-cluster series approach and ratio method results at intermediate temperature.

  10. Anisotropic thermoelectric properties of Sr5Sn2As6 compound under pressure by PBE-GGA and mBJ approaches

    NASA Astrophysics Data System (ADS)

    Abareshi, A.; Rahnamaye Aliabad, H. A.

    2017-09-01

    We have investigated the effect of pressure on the structural, electronic and thermoelectric properties of Sr5Sn2As6 zintl compound using the full potential linearized augmented plane wave method and the Perdew– Burke– Ernzerhof-generalized gradient approximation and modified Becke–Johnson exchange correlation potentials. The anisotropic crystal structure is observed in the z-direction. The results show that the lattice parameters decrease and the size of the band gap increases with increasing pressure. The thermoelectric efficiency along the z-direction is better than the x-and y-directions with a maximum ZT value of 0.993 in 7.1 GPa. P-type doping of Sr5Sn2As6 has better ZT than n-type doping.

  11. Peculiarities of spectral properties of a one-dimensional photonic crystal with an anisotropic defect layer of the nanocomposite with resonant dispersion

    SciTech Connect

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

    2014-09-30

    We have studied the spectral properties of a one-dimensional photonic crystal with a structure defect that represents an anisotropic nanocomposite layer sandwiched between two multilayer dielectric mirrors. The nanocomposite consists of metallic nanoscale inclusions of orientationally ordered spheroidal shape, dispersed in a transparent matrix, and is characterised by an effective resonant permittivity. Each of the two orthogonal polarisations of probe radiation corresponds to a particular plasmon resonant frequency of the nanocomposite. The problem of calculating the transmittance spectrum of the waves with s- and p-polarisations for such structures is solved. Spectral manifestation of splitting of the defect mode depending on the structure parameters and volumetric fraction of the nanospheroids is studied. The essential dependence of the position of maxima of the defect modes in the bandgap of the photonic crystal and their splitting on the incidence angle, polarisation, and the ratio of lengths of the polar and equatorial semi-axes of the spheroidal nanoparticles is shown. (photonic crystals)

  12. Peculiarities of spectral properties of a one-dimensional photonic crystal with an anisotropic defect layer of the nanocomposite with resonant dispersion

    NASA Astrophysics Data System (ADS)

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

    2014-09-01

    We have studied the spectral properties of a one-dimensional photonic crystal with a structure defect that represents an anisotropic nanocomposite layer sandwiched between two multilayer dielectric mirrors. The nanocomposite consists of metallic nanoscale inclusions of orientationally ordered spheroidal shape, dispersed in a transparent matrix, and is characterised by an effective resonant permittivity. Each of the two orthogonal polarisations of probe radiation corresponds to a particular plasmon resonant frequency of the nanocomposite. The problem of calculating the transmittance spectrum of the waves with s- and p-polarisations for such structures is solved. Spectral manifestation of splitting of the defect mode depending on the structure parameters and volumetric fraction of the nanospheroids is studied. The essential dependence of the position of maxima of the defect modes in the bandgap of the photonic crystal and their splitting on the incidence angle, polarisation, and the ratio of lengths of the polar and equatorial semi-axes of the spheroidal nanoparticles is shown.

  13. Configurational temperature and local properties of the anisotropic Gay-Berne liquid crystal model: Applications to the isotropic liquid/vapor interface and isotropic/nematic transition

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

    Molecular simulations in the isothermal statistical ensembles require that the macroscopic thermal and mechanical equilibriums are respected and that the local values of these properties are constant at every point in the system. The thermal equilibrium in Monte Carlo simulations can be checked through the calculation of the configurational temperature, {k_BT_{conf}={< |nabla _r U({r}^N)|2>}/{< nabla _r{^2} U({r}^N) >}}, where nabla _r is the nabla operator of position vector r. As far as we know, T_{conf} was never calculated with the anisotropic Gay-Berne potential, whereas the calculation of T_{conf} is much more widespread with more common potentials (Lennard Jones, electrostatic, …). We establish here an operational expression of the macroscopic and local configurational temperatures, and we investigate locally the isotropic liquid phase, the liquid / vapor interface, and the isotropic-nematic transition by Monte Carlo simulations.

  14. Magnetic properties and anisotropic magnetoresistance of antiperovskite nitride Mn{sub 3}GaN/Co{sub 3}FeN exchange-coupled bilayers

    SciTech Connect

    Sakakibara, H. Ando, H.; Kuroki, Y.; Kawai, S.; Ueda, K.; Asano, H.

    2015-05-07

    Epitaxial bilayers of antiferromagnetic Mn{sub 3}GaN/ferromagnetic Co{sub 3}FeN with an antiperovskite structure were grown by reactive magnetron sputtering, and their structural, magnetic, and electrical properties were investigated. Exchange coupling with an exchange field H{sub ex} of 0.4 kOe at 4 K was observed for Mn{sub 3}GaN (20 nm)/Co{sub 3}FeN (5 nm) bilayers. Negative anisotropic magnetoresistance (AMR) effect in Co{sub 3}FeN was observed and utilized to detect magnetization reversal in exchange-coupled Mn{sub 3}GaN/Co{sub 3}FeN bilayers. The AMR results showed evidence for current-induced spin transfer torque in antiferromagnetic Mn{sub 3}GaN.

  15. Structure and magnetic properties of bulk anisotropic SmCo5/α-Fe nanocomposite permanent magnets with different α-Fe content

    NASA Astrophysics Data System (ADS)

    Liu, W. Q.; Zuo, J. H.; Yue, M.; Cui, Z. Z.; Zhang, D. T.; Zhang, J. X.; Zhang, P. Y.; Ge, H. L.; Guo, Z. H.; Li, W.

    2011-04-01

    Chemical coating, hot compaction, and hot deformation techniques have been applied to prepare bulk anisotropic SmCo5/α-Fe nanocomposite magnets. The effects of α-Fe content on the structure and magnetic properties of the magnets were studied. With the increase of the α-Fe content, both the saturation magnetization (Ms) and remanence (Mr) of the magnets rise first, peak at 10 vol. % α-Fe content and then fall while the coercivity (Hci) of the magnets drops simultaneously. Crystal structure analysis shows that the magnets exhibit a strong c-axis crystal texture of the SmCo5 phase, which, however, weakens gradually as the α-Fe content increases. Microstructure observation also shows that there are many SmCo5 equiaxial grains even after hot deformation in the magnets with 15 vol. % α-Fe.

  16. Ligand substitution effect on optical properties in conducting tetraazaporphyrines

    SciTech Connect

    Guo, L.; Ellis, D.E.; Gubanova, O.V.; Hoffman, B.M.

    1995-12-31

    Self-consistent Density Functional calculations have been performed on a variety of planar conjugated Ni-centered macrocycles with a basic tetraazaporphyrinic core and dithiolene groups (PZ) or fused-benzo groups (PC). Theoretical energy diagrams, charge and spin distributions and densities of states have been obtained in order to understand the electronic structure modifications due to peripheral ligand substitution. The substituents role in altering electronic properties and charge distribution of the porphyrazine macrocycles has been used to interpret the observed variations in optical absorption profiles. In the Q-band ({approximately} 680 nm) region, a single peak is seen for high symmetry (D{sub 4h}) macrocycles and a double peak for lower symmetry (D{sub 2h} and C{sub 2v}) systems. Calculated intensities and band splittings are compared in detail with qualitative molecular orbital models and experiment in the visible and UV regions. Predictions are made for the infrared absorption and semiconducting band gap.

  17. Corrosion properties of second-generation conductive materials

    NASA Technical Reports Server (NTRS)

    Groshart, E.

    1984-01-01

    Since the introduction of silver-filled epoxy adhesives and silver-filled nitrocellulose lacquer as RFI control materials, a number of new materials have been introduced. The resin carriers have been changed in an effort to make the materials more usable or more EPA acceptable and the fillers have been varied in an effort to make the materials less costly. The corrosion-related properties of second-generation materials were assessed, including adhesives, caulks, and greases. Aluminum 2024 was used as the only substrate material. Ten days of salt fog was used as the corrosive environment. If a noble material such as silver, nickel, or carbon is sandwiched with aluminum an increase in dc resistance results given enough time. If this is unsatisfactory electrically it should either not be used or have all corrosive environments excluded.

  18. Synthesis of polymer nanostructures with conductance switching properties

    DOEpatents

    Su, Kai; Nuraje, Nurxat; Zhang, Lingzhi; Matsui, Hiroshi; Yang, Nan Loh

    2015-03-03

    The present invention is directed to crystalline organic polymer nanoparticles comprising a conductive organic polymer; wherein the crystalline organic polymer nanoparticles have a size of from 10 nm to 200 nm and exhibits two current-voltage states: (1) a high resistance current-voltage state, and (2) a low resistance current-voltage state, wherein when a first positive threshold voltage (V.sub.th1) or higher positive voltage, or a second negative threshold voltage (V.sub.th2) or higher negative voltage is applied to the nanoparticle, the nanoparticle exhibits the low-resistance current-voltage state, and when a voltage less positive than the first positive threshold voltage or a voltage less negative than the second negative threshold voltage is applied to the nanoparticle, the nanoparticle exhibits the high-resistance current-voltage state. The present invention is also directed methods of manufacturing the nanoparticles using novel interfacial oxidative polymerization techniques.

  19. Anisotropic modulation of magnetic properties and the memory effect in a wide-band (011)-Pr0.7Sr0.3MnO3/PMN-PT heterostructure

    PubMed Central

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Liu, Yao; Wu, Rong-Rong; Zhang, Xi-Xiang; Sun, Ji-Rong; Shen, Bao-Gen

    2015-01-01

    Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories. PMID:25909177

  20. Anisotropic modulation of magnetic properties and the memory effect in a wide-band (011)-Pr0.7Sr0.3MnO3/PMN-PT heterostructure

    NASA Astrophysics Data System (ADS)

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Liu, Yao; Wu, Rong-Rong; Zhang, Xi-Xiang; Sun, Ji-Rong; Shen, Bao-Gen

    2015-04-01

    Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories.

  1. Anisotropic modulation of magnetic properties and the memory effect in a wide-band (011)-Pr0.7Sr0.3MnO3/PMN-PT heterostructure.

    PubMed

    Zhao, Ying-Ying; Wang, Jing; Kuang, Hao; Hu, Feng-Xia; Liu, Yao; Wu, Rong-Rong; Zhang, Xi-Xiang; Sun, Ji-Rong; Shen, Bao-Gen

    2015-04-24

    Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories.

  2. Anisotropic rheology of a polycrystalline aggregate and convection in planetary mantles

    NASA Astrophysics Data System (ADS)

    Pouilloux, L. S.; Labrosse, S.; Kaminski, E.

    2011-12-01

    Observations of seismic anisotropy in the Earth mantle is often related to the crystal preferred orientation of polycrystalline aggregates. In this case, the physical properties depends on the direction and require the use of tensors to be fully described. In particular, the viscosity must be defined as a fourth order tensor whereas the thermal conductivity is a 2nd order tensor. However, the dynamical implications of such physical properties have received little attention until now. In this work, we present the mathematical formulation for an anisotropic medium and the relationship with dislocation creep deformation. We explore extensively the problem of the onset of Rayleigh-Bénard convection with such anisotropic properties. We finally presents some numerical results on the time-dependent problem using an orthotropic law for an ice polycrystal. Geophysical implications of this work related to the dynamics of planetary mantles are discussed, especially the potential of anisotropic rheology to localize deformation.

  3. Anisotropically structured magnetic aerogel monoliths

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture.Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture. Electronic supplementary information (ESI) available: Digital photographs of dispersions and gels with different water-to-ethanol ratios; magnetic measurements of an anatase aerogel containing 0.25 mol% Fe3O4 nanoparticles; XRD patterns of the iron oxide and

  4. Effects of external mechanical loading on phase diagrams and dielectric properties in epitaxial ferroelectric thin films with anisotropic in-plane misfit strains

    NASA Astrophysics Data System (ADS)

    Qiu, J. H.; Jiang, Q.

    2007-02-01

    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 diagrams without external loading, the characteristic features of "misfit strain-misfit strain" phase diagrams at room temperature are the presence of paraelectric phase and the strain-induced ferroelectric to paraelectric phase transition. Due to the external loading, the "misfit strain-stress" and "stress-temperature" phase diagrams also have drastic changes, especially for the vanishing of paraelectric phase in "misfit strain-stress" phase map and the appearance of possible ferroelectric phases. We also investigate the dielectric properties and the tunability of both BaTiO3 and PbTiO3 thin films. We find that the external stress dependence of phase diagrams and dielectric properties largely depends on strain anisotropy as well.

  5. Anisotropic Particles in Turbulence

    NASA Astrophysics Data System (ADS)

    Voth, Greg A.; Soldati, Alfredo

    2017-01-01

    Anisotropic particles are common in many industrial and natural turbulent flows. When these particles are small and neutrally buoyant, they follow Lagrangian trajectories while exhibiting rich orientational dynamics from the coupling of their rotation to the velocity gradients of the turbulence field. This system has proven to be a fascinating application of the fundamental properties of velocity gradients in turbulence. When particles are not neutrally buoyant, they experience preferential concentration and very different preferential alignment than neutrally buoyant tracer particles. A vast proportion of the parameter range of anisotropic particles in turbulence is still unexplored, with most existing research focusing on the simple foundational cases of axisymmetric ellipsoids at low concentrations in homogeneous isotropic turbulence and in turbulent channel flow. Numerical simulations and experiments have recently developed a fairly comprehensive picture of alignment and rotation in these cases, and they provide an essential foundation for addressing more complex problems of practical importance. Macroscopic effects of nonspherical particle dynamics include preferential concentration in coherent structures and drag reduction by fiber suspensions. We review the models used to describe nonspherical particle motion, along with numerical and experimental methods for measuring particle dynamics.

  6. Electrical and Hydraulic Properties of Humified Bog Peat as a Function of Pore-fluid Conductivity

    NASA Astrophysics Data System (ADS)

    Comas, X.; Slater, L.

    2003-12-01

    The electrical properties of organic sediments and their relationship to physical properties are poorly understood. A simple approach to relate electrical properties to physical properties commonly applied to inorganic sediments is to model the electrolytic conductivity and the surface conductivity as parallel conduction paths. Low-frequency electrical measurements were made in conjunction with hydraulic conductivity measurements on peat samples from an 11 m section collected in a large freshwater peatland. The electrical and hydraulic measurements were made as a function of NaCl concentration and depth of burial. In all cases, the electrical conductivity of the peat was not well modeled by the parallel conduction path model, with the model yielding formation factor values close to one. Sample measurements along the section suggest a slight increase in the formation factor and surface conductivity values with depth. Hydraulic conductivity measured by constant head method shows a marked increase with increasing NaCl concentration, which we believe results from expansion of macropore porosity by chemical dilation as proposed by others. Attempts to return the samples to their original conditions by decreasing the salinity only partially restored the hydraulic conductivity values, indicating a permanent disruption of the hydraulic properties of the peat. The increase of surface electrical conductivity and hydraulic conductivity with depth may indicate a close correlation with the high cation exchange capacity of organic matter and its tendency for chemical dilation as decomposition of organic matter increases with depth. We propose that the electrical conductivity of peat cannot be modeled by an electrolytic and a surface conduction path in parallel. The increase in the electrolytic conduction causes ionic accumulation and dispersion processes, expanding the macropore porosity and hence inducing a decrease in the formation factor values. A proper electrical model for

  7. Effects of surface modification of Nd-Fe-B powders using parylene C by CVDP method on the properties of anisotropic bonded Nd-Fe-B magnets

    NASA Astrophysics Data System (ADS)

    Ma, Bin; Sun, Aizhi; Lu, Zhenwen; Cheng, Chuan; Xu, Chen

    2016-10-01

    This paper presents effects of surface modification of Nd-Fe-B powders using parylene C by means of chemical vapor deposition polymerization (CVDP) on the properties of anisotropic bonded Nd-Fe-B magnets. It can be well verified from SEM images and EDS analysis that the surface of Nd-Fe-B powder is coated with thin parylene C films. The maximum energy product ((BH)max), degree of alignment (DOA), actual density and corrosion resistance of parylene Nd-Fe-B magnets prepared at room temperature are much higher than that of non-parylene Nd-Fe-B magnets. (BH)max, DOA and actual density of parylene Nd-Fe-B magnets (70 kJ/m3, 0.342, 5.82 g/cm3) prepared at room temperature under 578 MPa are improved by 18.6%, 4.6%, 2.1% and 27.3%, 29.1%, 7.8% compared with non-parylene Nd-Fe-B magnets prepared at 140 °C (59 kJ/m3, 0327, 5.70 g/cm3) and room temperature (55 kJ/m3, 0.265, 5.40 g/cm3), respectively. Additional, the improvement of actual density and the room temperature process also solve problems such as powders' sticking wall, non-uniform powder filling, non-uniform magnetic properties, seriously mould damage, short life cycle of mould and so on, which exists during warm compaction process. Parylene Nd-Fe-B magnets have better corrosion resistance and worse mechanical properties than that of non-parylene Nd-Fe-B magnets. The reason for the improvement of magnetic properties and actual density is the low friction cofficient of parylene C films, which results in lower frictional resistance and better lubricating property of parylene Nd-Fe-B powders.

  8. Anisotropic characterization of magnetorheological materials

    NASA Astrophysics Data System (ADS)

    Dohmen, E.; Modler, N.; Gude, M.

    2017-06-01

    For the development of energy efficient lightweight parts novel function integrating materials are needed. Concerning this field of application magnetorheological (MR) fluids, MR elastomers and MR composites are promising materials allowing the adjustment of mechanical properties by an external magnetic field. A key issue for operating such structures in praxis is the magneto-mechanical description. Most rheological properties are gathered at laboratory conditions for high magnetic flux densities and a single field direction, which does not correspond to real praxis conditions. Although anisotropic formation of superstructures can be observed in MR suspensions (Fig. 1) or experimenters intentionally polymerize MR elastomers with anisotropic superstructures these MR materials are usually described in an external magnetic field as uniform, isotropic materials. This is due to missing possibilities for experimentally measuring field angle dependent properties and ways of distinguishing between material properties and frictional effects. Just a few scientific works experimentally investigated the influence of different field angles (Ambacher et al., 1992; Grants et al., 1990; Kuzhir et al., 2003) [1-3] or the influence of surface roughness on the shear behaviour of magnetic fluids (Tang and Conrad, 1996) [4]. The aim of this work is the introduction of a novel field angle cell allowing the determination of anisotropic mechanical properties for various MR materials depending on the applied magnetic field angle.

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

    SciTech Connect

    Safa-Sefat, Athena; Jin, Rongying; McGuire, Michael A; Sales, Brian C; Mandrus, David; Ronning, F.; Bauer, E D; Mozharivskyj, Yurij

    2009-01-01

    The crystal structure, anisotropic electrical resistivity and magnetic susceptibility, as well as specific heat results from single crystals of BaFe2As2, BaNi2As2, and BaFeNiAs2 are surveyed. BaFe2As2 properties demonstrate the equivalence of C(T), Fisher s d(T)/dT, and d/dT results in determining the antiferromagnetic transition at TN = 132(1) K. BaNi2As2 shows a structural phase transition from a high-temperature tetragonal phase to a low-temperature triclinic (Pī) phase at T0 = 131 K. The superconducting critical temperature for BaNi2As2 is well below T0 and at Tc = 0.69 K. BaFeNiAs2 does not show any sign of superconductivity to 0.4 K and exhibits properties similar to BaCo2As2, a renormalized paramagnetic metal.

  10. Polarization distribution control of anisotropic electromagnetic Gaussian-Schell model beams on free propagation by exploiting correlation properties at the source plane.

    PubMed

    Zhang, Rong; Wang, Xiangzhao; Cheng, Xin; Qiu, Zicheng

    2010-11-01

    When propagating in free space, the transversal distribution of the degree of polarization of an anisotropic electromagnetic Gaussian-Schell model (AEGSM) beam will generally undergo a complex evolution process. We find that this transversal distribution of the degree of polarization of an AEGSM beam can be controlled by exploiting the partial correlation properties of the source. The main research of our paper falls into two parts. First, the concept of analogical propagation of the transversal distribution of the degree of polarization is proposed, and the condition for an AEGSM beam having an analogical propagation is obtained. When an AEGSM beam is on analogical propagation, the distribution of the degree of polarization on any cross section of the beam is always similar to that on the source plane, except that the size of the distribution pattern will expand continuously as the propagation distance increases. Second, the far-field transversal distribution of the degree of polarization is considered, and the condition for the far-field transversal polarization distribution of an AEGSM beam to be always of circularly symmetric shape, no matter how complicated it is on the source, is obtained. Our research is expected to find applications in areas that make use of the polarization properties of random electromagnetic beams.

  11. Anisotropic optical properties of an oriented-emeraldine-base polymer and an emeraldine-hydrochloride-salt polymer

    NASA Astrophysics Data System (ADS)

    McCall, R. P.; Scherr, E. M.; MacDiarmid, A. G.; Epstein, A. J.

    1994-08-01

    We present results of polarized reflectance measurements for unstretched and stretched films of polyaniline in the insulating emeraldine-base (EB) and conducting emeraldine-salt (ES) forms. The reflectance data and the resulting optical conductivity, obtained from a Kramers-Kronig transform of the reflectance data, of unstretched films agree well with optical data reported by S. Stafström et al. [Phys. Rev. Lett. 59, 1464 (1987)]. The stretched films (400% elongation) show significant anisotropy in the reflectance and the other optical constants. The frequency-dependent conductivity in ES exhibits a large shift in oscillator strength to lower energies compared to that of EB and compared to that of unstretched films of ES, which demonstrates delocalization of conduction electrons in the ``polaron band.'' The dielectric constant of stretched ES indicates that ES is metal-like, with maximum conductivity greater than ten times the dc conductivity. These results indicate that the dc conductivity is likely dominated by interchain processes and that higher values for conductivity are possible.

  12. Electrical and morphological properties of conducting layers formed from the silver-glass composite conducting powders prepared by spray pyrolysis.

    PubMed

    Jung, D S; Koo, H Y; Kang, Y C

    2010-03-01

    Ag-glass composite powders with various glass contents and excellent conducting properties were prepared by spray pyrolysis. Irrespective of the glass content, all the prepared powders were found to comprise spherical particles with nonaggregation characteristics. The crystal structure of the powder particles resembled that of pure Ag particles, irrespective of the glass content. Conducting layers formed from pure Ag did not melt even when sintered at 400 degrees C. On the other hand, conducting layers formed from composite powders containing 3 and 5 wt% glass melted when sintered at 400 degrees C. The optimum glass content of the composite powders was 3 wt% at sintering temperatures of 400 and 450 degrees C. However, the optimum glass content decreased to 1 wt% when the sintering temperature was increased to 550 degrees C. The lowest specific resistances of the conducting layers formed from the composite powders were 5.3 and 2.3 microohms-cm at sintering temperatures of 400 and 550 degrees C, respectively.

  13. Anisotropic and heterogeneous mechanical properties of a stratified shale/limestone sequence at Nash Point, South Wales: A case study for hydraulic fracture propagation through a layered medium

    NASA Astrophysics Data System (ADS)

    Forbes Inskip, Nathaniel; Meredith, Philip; Gudmundsson, Agust

    2016-04-01

    While considerable effort has been expended on the study of fracture propagation in rocks in recent years, our understanding of how fractures propagate through layered sedimentary rocks with different mechanical and elastic properties remains poorly constrained. Yet this is a key issue controlling the propagation of both natural and anthropogenic hydraulic fractures in layered sequences. Here we report measurements of the contrasting mechanical and elastic properties of the Lower Lias at Nash Point, South Wales, which comprises an interbedded sequence of shale and limestone layers, and how those properties may influence fracture propagation. Elastic properties of both materials have been characterised via ultrasonic wave velocity measurements as a function of azimuth on samples cored both normal and parallel to bedding. The shale is highly anisotropic, with P-wave velocities varying from 2231 to 3890 m s-1, giving an anisotropy of ~55%. By contrast, the limestone is essentially isotropic, with a mean P-wave velocity of 5828 m s-1 and an anisotropy of ~2%. The dynamic Young's modulus of the shale, calculated from P- and S-wave velocity data, is also anisotropic with a value of 36 GPa parallel to bedding and 12 GPa normal to bedding. The modulus of the limestone is again isotropic with a value of 80 GPa. It follows that for a vertical fracture propagating (i.e. normal to bedding) the modulus contrast is 6.6. This is important because the contrast in elastic properties is a key factor in controlling whether fractures arrest, deflect, or propagate across interfaces between layers in a sequence. There are three principal mechanisms by which a fracture may deflect across or along an interface, namely: Cook-Gordon debonding, stress barrier, and elastic mismatch. Preliminary numerical modelling results (using a Finite Element Modelling software) of induced fractures at Nash Point suggest that all three are important. The results demonstrate a rotation of the maximum

  14. Intricate Short-Range Ordering and Strongly Anisotropic Transport Properties of Li1–x Sn 2+x As2

    SciTech Connect

    Lee, Kathleen; Kaseman, Derrick; Sen, Sabyasachi; Hung, Ivan; Gan, Zhehong; Gerke, Birgit; Pöttgen, Rainer; Feygenson, Mikhail; Neuefeind, Jörg; Lebedev, Oleg I.; Kovnir, Kirill

    2015-02-22

    A new ternary compound, Li1-xSn2+xAs2, 0.2 < x < 0.4, was synthesized via solid-state reaction of elements. The compound crystallizes in a layered structure in the R$\\overline{3}m$ space group (No. 166) with Sn-As layers separated by layers of jointly occupied Li/Sn. The Sn-As layers are comprised of Sn3As3 puckered hexagons in a chair conformation that share all edges. Li/Sn atoms in the interlayer space are surrounded by a regular As6 octahedron. Thorough investigations by synchrotron x-ray and neutron powder diffraction indicate no long-range Li/Sn ordering. In contrast, local Sn/Li ordering was revealed by synergistic investigations via solid-state 6,7Li NMR spectroscopy, HR-TEM, and neutron and X-ray pair distribution function analyses. Due to their different chemical natures, Li and Sn atoms tend to segregate into Li-rich and Sn-rich regions creating substantial inhomogeneity on the nanoscale. Inhomogeneous local structure has high impact on the physical properties of the synthesized compounds: local Li/Sn ordering and multiple nanoscale interfaces result in unexpectedly low thermal conductivity and highly anisotropic resistivity in Li1-xSn2+xAs2.

  15. Shaped beam scattering by an anisotropic particle

    NASA Astrophysics Data System (ADS)

    Chen, Zhenzhen; Zhang, Huayong; Huang, Zhixiang; Wu, Xianliang

    2017-03-01

    An exact semi-analytical solution to the electromagnetic scattering from an optically anisotropic particle illuminated by an arbitrarily shaped beam is proposed. The scattered fields and fields within the anisotropic particle are expanded in terms of spherical vector wave functions. The unknown expansion coefficients are determined by using the boundary conditions and the method of moments scheme. For incidence of a Gaussian beam, zero-order Bessel beam and Hertzian electric dipole radiation, numerical results of the normalized differential scattering cross section are given to a uniaxial, gyrotropic anisotropic spheroid and circular cylinder of finite length. The scattering properties are analyzed concisely.

  16. Anisotropic electrical and thermal conductivity in Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} [AE = Ca, Sr{sub 1−x}Ba{sub x} (x = 0.0, 0.25, 0.5, 0.75, 1.0)] single crystals

    SciTech Connect

    Dong, Song-Tao; Zhang, Bin-Bin; Lv, Yang-Yang; Zhou, Jian; Zhang, Shan-Tao; Xiong, Ye; Yao, Shu-Hua E-mail: ybchen@nju.edu.cn; Chen, Y. B. E-mail: ybchen@nju.edu.cn; Chen, Yan-Feng

    2015-09-28

    Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} (AE represents alkaline earth), constructed by stacking of rock-salt Bi{sub 2}AE{sub 2}O{sub 4} and triangle CoO{sub 2} layers alternatively along c-axis, is one of promising thermoelectric oxides. The most impressive feature of Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ}, as reported previously, is their electrical conductivity mainly lying along CoO{sub 2} plane, adjusting Bi{sub 2}AE{sub 2}O{sub 4} layer simultaneously manipulates both thermal conductivity and electrical conductivity. It in turn optimizes thermoelectric performance of these materials. In this work, we characterize the anisotropic thermal and electrical conductivity along both ab-plane and c-direction of Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} (AE = Ca, Sr, Ba, Sr{sub 1−x}Ba{sub x}) single crystals. The results substantiate that isovalence replacement in Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} remarkably modifies their electrical property along ab-plane; while their thermal conductivity along ab-plane only has a slightly difference. At the same time, both the electrical conductivity and thermal conductivity along c-axis of these materials also have dramatic changes. Certainly, the electrical resistance along c-axis is too high to be used as thermoelectric applications. These results suggest that adjusting nano-block Bi{sub 2}AE{sub 2}O{sub 4} layer in Bi{sub 2}AE{sub 2}Co{sub 2}O{sub 8+δ} cannot modify the thermal conductivity along high electrical conductivity plane (ab-plane here). The evolution of electrical property is discussed by Anderson localization and electron-electron interaction U. And the modification of thermal conductivity along c-axis is attributed to the microstructure difference. This work sheds more light on the manipulation of the thermal and electrical conductivity in the layered thermoelectric materials.

  17. Determination of all relevant conduction electron scattering times in an exceptionally anisotropic arene conductor, the 12:7 pyrene hexafluoroantimonate radical cation salt

    NASA Astrophysics Data System (ADS)

    Kaiser, A.; Wokrina, T.; Pongs, B.; Dormann, E.

    2003-10-01

    For (pyrene)12(SbF6)7 a 104:1 anisotropy of the microwave conductivity is observed. We show that the timescale for the end of the one-dimensional motion of the conduction electron spins derived by analysis of the frequency and temperature dependence of the proton spin-lattice relaxation and of the electron spin resonance linewidth and relaxation times is governed to a comparable degree by perpendicular-to-stack hopping and by interaction with intrastack paramagnetic localized defects in these crystals. The electron spin self-diffusion coefficient derived for the magnetic field gradient parallel to the pyrene stacking direction is therefore influenced by perpendicular-to-stack motion as well.

  18. Reconstructing material properties by deconvolution of full-field measurement images: The conductivity case

    NASA Astrophysics Data System (ADS)

    Bellis, Cédric; Trabelsi, Manel; Frémy, Flavien

    2017-03-01

    This study concerns the reconstruction of material parameters from full-field measurements. In this context the typical available data is a set of digital images that is seldom handled as such when solving the inverse problem. Therefore, this work investigates a direct method to compute constitutive parameter maps from full-field measurement images. Within the prototypical framework of the periodic conductivity model, the starting point for the proposed approach is the Lippmann–Schwinger equation, which is satisfied by the fields measured internally. This integral equation is reinterpreted as a linear convolution model for the sought conductivity field. Considering that multiple experiments might be available and then combined, this problem is solved in the least-square sense. To do so, the Krylov subspace-based LSQR algorithm is employed. Full advantage is taken of the convenient expression of the featured Green’s function in Fourier space and of the intensive use of the fast Fourier transform (FFT). Moreover, a spectral-based filtering regularization scheme is implemented to tackle noisy data. Overall, the proposed reconstruction algorithm only handles image-like quantities in an efficient mesh-free approach. The performance of the method is assessed on a set of synthetic 2D numerical examples both for isotropic and anisotropic material configurations.

  19. Finite-volume scheme for anisotropic diffusion

    SciTech Connect

    Es, Bram van; Koren, Barry; Blank, Hugo J. de

    2016-02-01

    In this paper, we apply a special finite-volume scheme, limited to smooth temperature distributions and Cartesian grids, to test the importance of connectivity of the finite volumes. The area of application is nuclear fusion plasma with field line aligned temperature gradients and extreme anisotropy. We apply the scheme to the anisotropic heat-conduction equation, and compare its results with those of existing finite-volume schemes for anisotropic diffusion. Also, we introduce a general model adaptation of the steady diffusion equation for extremely anisotropic diffusion problems with closed field lines.

  20. The Study of Simulated Space Radiation Environment Effect on Conductive Properties of ITO Thermal Control Materials

    NASA Astrophysics Data System (ADS)

    Wei-Quan, Feng; Chun-Qing, Zhao; Zi-Cai, Shen; Yi-Gang, Ding; Fan, Zhang; Yu-Ming, Liu; Hui-Qi, Zheng; Xue, Zhao

    In order to prevent detrimental effects of ESD caused by differential surface charging of spacecraft under space environments, an ITO transparent conductive coating is often deposited on the thermal control materials outside spacecraft. Since the ITO coating is exposed in space environment, the environment effects on electrical property of ITO coatings concern designers of spacecraft deeply. This paper introduces ground tests to simulate space radiation environmental effects on conductive property of ITO coating. Samples are made of ITO/OSR, ITO/Kapton/Al and ITO/FEP/Ag thermal control coatings. Simulated space radiation environment conditions are NUV of 500ESH, 40 keV electron of 2 × 1016 е/cm2, 40 keV proton of 2.5 × 1015 p/cm2. Conductive property is surface resistivity measured in-situ in vacuum. Test results proved that the surface resistivity for all ITO coatings have a sudden decrease in the beginning of environment test. The reasons for it may be the oxygen vacancies caused by vacuum and decayed RIC caused by radiation. Degradation in conductive properties caused by irradiation were found. ITO/FEP/Ag exhibits more degradation than other two kinds. The conductive property of ITO/kapton/Al is stable for vacuum irradiation. The analysis of SEM and XPS found more crackers and less Sn and In concentration after irradiation which may be the reason for conductive property degradation.

  1. Anisotropic ripple deformation in phosphorene

    SciTech Connect

    Kou, Liangzhi; Ma, Yandong; Smith, Sean C.; Chen, Changfeng

    2015-04-07

    Here, two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS2. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticity theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications.

  2. Anisotropic ripple deformation in phosphorene

    DOE PAGES

    Kou, Liangzhi; Ma, Yandong; Smith, Sean C.; ...

    2015-04-07

    Here, two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS2. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticitymore » theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications.« less

  3. Anisotropic Ripple Deformation in Phosphorene.

    PubMed

    Kou, Liangzhi; Ma, Yandong; Smith, Sean C; Chen, Changfeng

    2015-05-07

    Two-dimensional materials tend to become crumpled according to the Mermin-Wagner theorem, and the resulting ripple deformation may significantly influence electronic properties as observed in graphene and MoS2. Here, we unveil by first-principles calculations a new, highly anisotropic ripple pattern in phosphorene, a monolayer black phosphorus, where compression-induced ripple deformation occurs only along the zigzag direction in the strain range up to 10%, but not the armchair direction. This direction-selective ripple deformation mode in phosphorene stems from its puckered structure with coupled hinge-like bonding configurations and the resulting anisotropic Poisson ratio. We also construct an analytical model using classical elasticity theory for ripple deformation in phosphorene under arbitrary strain. The present results offer new insights into the mechanisms governing the structural and electronic properties of phosphorene crucial to its device applications.

  4. 75 FR 28204 - Conduct on Postal Property; Penalties and Other Law

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-05-20

    ... Authority delegations (Government agencies), Crime, Federal buildings and facilities, Government property... From the Federal Register Online via the Government Publishing Office POSTAL SERVICE 39 CFR Part 232 Conduct on Postal Property; Penalties and Other Law AGENCY: Postal Service. ACTION: Final rule...

  5. Anisotropic surface properties of micro/nanostructured a-C:H:F thin films with self-assembly applications

    NASA Astrophysics Data System (ADS)

    Freire, V.-M.; Corbella, C.; Bertran, E.; Portal-Marco, S.; Rubio-Roy, M.; Andújar, J.-L.

    2012-06-01

    The singular properties of hydrogenated amorphous carbon (a-C:H) thin films deposited by pulsed DC plasma enhanced chemical vapor deposition (PECVD), such as hardness and wear resistance, make it suitable as protective coating with low surface energy for self-assembly applications. In this paper, we designed fluorine-containing a-C:H (a-C:H:F) nanostructured surfaces and we characterized them for self-assembly applications. Sub-micron patterns were generated on silicon through laser lithography while contact angle measurements, nanotribometer, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the surface. a-C:H:F properties on lithographied surfaces such as hydrophobicity and friction were improved with the proper relative quantity of CH4 and CHF3 during deposition, resulting in ultrahydrophobic samples and low friction coefficients. Furthermore, these properties were enhanced along the direction of the lithography patterns (in-plane anisotropy). Finally, self-assembly properties were tested with silica nanoparticles, which were successfully assembled in linear arrays following the generated patterns. Among the main applications, these surfaces could be suitable as particle filter selector and cell colony substrate.

  6. Anisotropic optical properties of free and bound excitons in highly strained A-plane ZnO investigated with polarized photoreflectance and photoluminescence spectroscopy

    NASA Astrophysics Data System (ADS)

    Nam, Yoon Sung; Lee, Sang Wook; Baek, K. S.; Chang, S. K.; Song, Jae-Ho; Song, Jung-Hoon; Han, Seok Kyu; Hong, Soon-Ku; Yao, Takafumi

    2008-05-01

    We have investigated the polarization dependence of the near-band-edge photoluminescence and photoreflectance spectra in nonpolar (A-plane) ZnO films under strong biaxial compressive strain. We show that anisotropic strain and the orientation of the nonpolar plane play an important role in determining the polarization selectivity and properties of excitonic transitions. We identified four distinct band-edge transitions at 3.449, 3.420, 3.386, and 3.326eV. They were identified as E2 and E1 free excitons, E1 excitons bound to a donor, and free-electron-to-bound-hole transition, respectively. Unlike previously reported results on relatively thick nonpolar films, the E1 exciton (lowest energy) was mainly polarized to E ⊥c and weakly polarized to E ∥c under strong biaxial compressive strain in the 100nm thick film. The E2 exciton (next higher energy) was exclusively polarized to E ∥c. The localization energy of DX is 34meV, which is much larger than that in polar ZnO, and the DX was not thermally delocalized even at room temperature.

  7. Turbulent properties of a deep-sea hydrothermal plume in a time-variable cross flow using anisotropic mixing parameterizations in LES

    NASA Astrophysics Data System (ADS)

    Adams, I. G.; Di Iorio, D.; Lavelle, J. W.

    2016-02-01

    A large eddy simulation of a deep-sea hydrothermal plume in a time-variable cross flow, parameterized with anisotropic eddy viscosities and diffusivities, is developed to simulate turbulent flow characteristics. The turbulent dissipation rates for kinetic energy (ɛ) and thermal variance (ɛθ) is approximated by computing the Reynolds averaged sub-grid scale turbulent production from shear and buoyancy (ɛ=P-B) and from temperature fluxes (ɛθ=Pθ) respectively. The model is tuned to represent the mean flow and turbulent observations of the hydrothermal plume properties at Dante within the Main Endeavour vent field (MEF) at the Endeavour segment of the Juan de Fuca Ridge using specialized acoustic instrumentation. The model takes into account realistic background stratification, and vent exit fluid heat and flow transport. The turbulent kinetic energy and thermal dissipation rates reach their maximum near the vent. Shear production dominates over buoyancy production of turbulent kinetic energy. The model is used to derive several important scalings with cross flows that are relevant to understanding plume impact on the ocean. These scalings include maximum plume rise height and turbulent diffusivity and their variability with cross flow speeds.

  8. Anisotropic superconducting and normal state magnetic properties of single crystals of RNi*2*B*2*C compounds (R = Y, Gd, Dy, Ho, Er, and Tm)

    SciTech Connect

    Cho, Beongki

    1995-09-26

    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 RNi2B2C (R = rare earth, Y) offers a new system to study this interaction. The wide ranges of superconducting transition (Tc) and antiferromagnetic (AF) ordering temperatures (TN) (0 K ≤ Tc ≤ 16 K, 0 K ≤ TN ≤ 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.

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

    SciTech Connect

    Qasrawi, A.F.; Gasanly, N.M.

    2009-10-15

    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.

  10. Procedures for construction of anisotropic elastic plastic property closures for face-centered cubic polycrystals using first-order bounding relations

    NASA Astrophysics Data System (ADS)

    Proust, Gwénaëlle; Kalidindi, Surya R.

    2006-08-01

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

  11. The electrical, thermal conductivity, microstructure and mechanical properties of Al-Sn-Pb ternary alloys

    NASA Astrophysics Data System (ADS)

    Alper Billur, C.; Gerçekcioglu, E.; Bozoklu, M.; Saatçi, B.; Ari, M.; Nair, F.

    2015-08-01

    The structural, thermal, electrical and mechanical properties and micro-hardness of four different samples of Al-Sn-Pb ternary alloys (Al-[x] wt. % Sn-10 wt. % Pb) (x = 40, 30, 20 and 10) with constant lead concentrations were investigated for four different samples. Electrical resistivity and conductivity were measured by using (four-point probe measurement techniques) 4PPT techniques. The variations of thermal conductivity were determined by Wiedemann-Franz law (W-F) and Smith-Palmer (S-P) equation using the data obtained from electrical properties. The mechanical properties of the same alloys were obtained by the tensile test and the Vickers micro-hardness test.

  12. Correlation of electrical conductivity, dielectric properties, microwave absorption, and matrix properties of composites filled with graphene nanoplatelets and carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Khurram, A. A.; Rakha, Sobia A.; Zhou, Peiheng; Shafi, M.; Munir, Arshad

    2015-07-01

    The DC electrical conductivity, percolation threshold, and dielectric properties of Graphene Nanoplatelets (GNPs) filled epoxy composites are studied and correlated with microwave absorption. The properties of GNPs filled composites are also compared with multiwalled carbon nanotubes (MWCNTs) composites, and GNPs are observed to have superior conductivity than MWCNTs. In all batches, the nanofillers have 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 wt. %. All composites irrespective of the type of nanofiller and viscosity of the matrix have shown electrical percolation threshold at 3.0 wt. %. The dielectric properties, i.e., complex permittivity, tan loss, and AC conductivity, are studied in 100 Hz-5.5 MHz. The DC and AC electrical conductivities (at and below the percolation) measured in 100 Hz-5.5 MHz are correlated to the GNPs and MWCNTs epoxy composites in the microwave frequency range (11-17 GHz). The maximum return loss of -12 dB and -6 dB was determined for MWCNTs and GNPs, respectively. The effects of nanofiller shape and the viscosity of the matrix on the dispersion and interparticle spacing of the conductive fillers within the polymer matrix have been discussed based on the results of conductivity, dielectric, and absorption properties.

  13. Ab initio study of anisotropic mechanical properties of LiCoO{sub 2} during lithium intercalation and deintercalation process

    SciTech Connect

    Wu, Linmin; Zhang, Jing

    2015-12-14

    The mechanical properties of Li{sub x}CoO{sub 2} under various Li concentrations and associated anisotropy have been systematically studied using the first principles method. During the lithium intercalation process, the Young's modulus, bulk modulus, shear modulus, and ultimate strength increase with increasing lithium concentration. Strong anisotropy of mechanical properties between a-axis and c-axis in Li{sub x}CoO{sub 2} is identified at low lithium concentrations, and the anisotropy decreases with increasing lithium concentration. The observed lithium concentration dependence and anisotropy are explained by analyzing the charge transfer using Bader charge analysis, bond order analysis, and bond strength by investigating partial density of states and charge density difference. With the decrease of Li concentration, the charge depletion in the bonding regions increases, indicating a weaker Co-O bond strength. Additionally, the Young's modulus, bulk modulus, shear modulus, and toughness are obtained by simulating ab initio tensile tests. From the simulated stress-strain curves, Li{sub x}CoO{sub 2} shows the highest toughness, which is in contraction with Pugh criterion prediction based on elastic properties only.

  14. A review of properties and potential aerospace applications of electrically conducting polymers

    NASA Technical Reports Server (NTRS)

    Meador, Mary Ann B.; Gaier, James R.; Good, Brian S.; Sharp, G. Richard; Meador, Michael A.

    1990-01-01

    An overview of current research in conducting polymers is presented. Emphasis is placed on development of materials useful for aeronautic and space applications. Research on organic conducting polymers began in the early 1970s with the discovery of polyacetylene. Since then, many polymers which share structural characteristics with polyacetylene have been prepared which conduct electricity, especially when they are doped with suitable agents. Problems with environmental instability, difficult processing, poor mechanical properties and high cost have slowed the development of conducting polymers. However, practical use of these materials is imminent, based on recent refinements in understanding how polymers conduct, more systematic approaches to the development of new materials, and significant improvements in both the processing and properties.

  15. Boron behavior induced lamellar structure and anisotropic magnetic properties of Nd2Fe14B during HDDR process

    NASA Astrophysics Data System (ADS)

    Choi, Moonhee; Cho, Seungchan; Jo, Ilguk; Song, Yeonghwan; Kim, Chiho; Yu, Jihun; Kim, Yangdo

    2017-08-01

    The anisotropy of the Nd2Fe14B powder is originated during the creation of a fine Fe2B lamellar structure in the disproportionation step. The aspect ratio (A/R) of Fe2B structure increased from 3.37 ± 1.5 to 6.69 ± 3.2 during phase decomposition for 0 60 min at 820 ° C (P H2 = 10 kPa). The Fe2B having high A/R ratio recombined Nd2Fe14B, which is close to the single domain, and the magnetic properties are also improved with increasing A/R ratio.

  16. Antegrade and retrograde decremental conduction properties of an accessory pathway associated with the coronary sinus musculature.

    PubMed

    Nakamura, Kohki; Naito, Shigeto; Kaseno, Kenichi; Oshima, Shigeru

    2015-01-01

    A 32-year-old man underwent catheter ablation of an orthodromic atrioventricular reentrant tachycardia. The sinus rhythm electrocardiogram exhibited a normal PQ interval and no delta waves, but atrial pacing produced a prolonged PQ interval and wide QRS morphology with right bundle-branch block due to antegrade accessory pathway (AP) conduction. During the tachycardia, atrial double potentials consisting of the coronary sinus musculature (CSM) and left atrial (LA) potentials were observed. Ventricular extrastimulation exhibited retrograde decremental conduction with an identical atrial activation sequence as during the tachycardia. A radiofrequency application within the posterolateral CS during ventricular pacing eliminated the CSM-LA conduction and concomitantly the ventriculoatrial conduction via the AP was abolished. In this case, the CSM was associated with the bidirectional decremental conduction properties of the AP, and the antegrade slow conduction resulted in the absence of a shortening of the PQ interval and delta waves during sinus rhythm despite the continuous presence of antegrade AP conduction.

  17. Thermal conductive and radiative properties of solid foams: Traditional and recent advanced modelling approaches

    NASA Astrophysics Data System (ADS)

    Randrianalisoa, Jaona; Baillis, Dominique

    2014-10-01

    The current paper presents an overview of traditional and recent models for predicting the thermal properties of solid foams with open- and closed-cells. Their effective thermal conductivity has been determined analytically by empirical or thermal-resistance-network-based models. Radiative properties crucial to obtain the radiative conductivity have been determined analytically by models based on the independent scattering theory. Powerful models combine three-dimensional (3D) foam modelling (by X-ray tomography, Voronoi tessellation method, etc.) and numerical solution of transport equations. The finite-element method (FEM) has been used to compute thermal conductivity due to solid network for which the computation cost remains reasonable. The effective conductivity can be determined from FEM results combined with the conductivity due to the fluid, which can be accurately evaluated by a simple formula for air or weakly conducting gas. The finite volume method seems well appropriate for solving the thermal problem in both the solid and fluid phases. The ray-tracing Monte Carlo method constitutes the powerful model for radiative properties. Finally, 3D image analysis of foams is useful to determine topological information needed to feed analytical thermal and radiative properties models. xml:lang="fr"

  18. Investigation of anisotropic thermal transport in polymers using infrared thermography

    NASA Astrophysics Data System (ADS)

    Nieto Simavilla, David; Venerus, David; Schieber, Jay

    2014-03-01

    During manufacturing, the anisotropic nature of thermal transport in flowing polymers plays an important role in the final properties of materials. In our laboratory, we have investigated anisotropic thermal conductivity in polymers subjected to deformation using an optical technique based on Forced Rayleigh Scattering (FRS). For over a decade, our setup has been the only one capable of testing the linear relationship between anisotropy in thermal conductivity and stress, known as the stress-thermal rule. In order to overcome some of the limitations in the optical properties of materials inherent to FRS, we have recently developed a complementary technique based on infrared thermography (IRT). We validate IRT technique by comparing measurements of anisotropy in thermal conductivity on crosslinked networks against those obtained with FRS. The main advantage of IRT method is that, it allows us to study optically thick materials, including polymers that are prone to strain induced crystallization. Additionally, examination of IRT transient state experiments enables us to study the effect of deformation on other properties such as specific heat capacity.

  19. Structural properties of highly conductive ultra-nanocrystalline diamond films grown by hot-filament CVD

    NASA Astrophysics Data System (ADS)

    Mertens, M.; Lin, I.-N.; Manoharan, D.; Moeinian, A.; Brühne, K.; Fecht, H. J.

    2017-01-01

    In this work we show the correlation of the electrical conductivity of ultra-nanocrystalline (UNCD) diamond films grown by hot filament chemical vapor deposition (HFCVD) with their structural properties. The substrate temperature, the methane to hydrogen ratio and the pressure are the main factor influencing the growth of conductive UNCD films, which extends from electrical resistive diamond films (<10-4 S/cm) to highly conductive diamond films with a specific conductivity of 300 S/cm. High-resolution-transmission-electron-microscopy (HRTEM) and electron-energy-loss-spectroscopy (EELS) have been done on the highly conductive diamond films, to show the origin of the high electrical conductivity. The HRTEM results show random oriented diamond grains and a large amount of nano-graphite between the diamond crystals. EELS investigations are confirming these results. Raman measurements are correlated with the specific conductivity, which shows structural changes of sp2 carbons bonds as function of conductivity. Hall experiments complete the results, which lead to a model of an electron mobility based conductivity, which is influenced by the structural properties of the grain boundary regions in the ultra-nanocrystalline diamond films.

  20. Anisotropic viscoelastic properties of quartz and quartzite in the vicinity of the α-β phase transition

    NASA Astrophysics Data System (ADS)

    Klumbach, Steffen; Schilling, Frank R.

    2017-04-01

    In this study we performed high-temperature, dynamic (i.e. sinusoidal), three-point bending experiments of quartz single crystals and quartzite samples within the frequency range of seismic surveys (i.e. 0.1-20 Hz). At constant temperature close to the α-β phase transition we observed a unique complex elastic behaviour of both quartz and quartzite. We find a frequency dependence of the complex Young's modulus of α-quartz, including a dissipation maximum at ≈1 Hz supposedly related to the formation and variation of Dauphiné twin domains. Based on our experimental results for different crystallographic directions and additional modelling, we are able to describe the complex Young's modulus of quartz at its α-β phase transition in a 3D diagram. We derive a frequency-dependent elasticity tensor, using a three-element equivalent circuit, composed of two springs E 1 and E 2 as well as a dashpot η. E 1 and η are connected parallel to each other, E 2 is added in series. Compliance coefficients yield (S 11) E 1 = 572 GPa, E 2 = 70.0 GPa, η = 64.6 GPa·s, (S 33) E 1 = 127 GPa, E 2 = 52.1 GPa, η = 22.9 GPa·s, (S 44) E 1 = 204 GPa, E 2 = 37.5 GPa, η = 26.4 GPa·s, (S 12) E 1 = 612 GPa, E 2 = 106.7 GPa, η = 78.5 GPa·s, (S 13) E 1 = 1546 GPa, E 2 = 284 GPa, η = 200 GPa·s; S 14 ≈-0.0024 GPa-1. We use the derived direction-dependent coefficients to predict the frequency-dependent complex elastic properties of isotropic polycrystalline quartz. These predictions agree well with the experimental results of the investigated quartzite. Finally, we explore the potential of using the anomalous frequency-dependent complex elastic properties of quartz at the α-β phase transition that we observed as an in situ temperature probe for seismic studies of the Earth's continental crust.

  1. Consequences of Ca multisite occupation for the conducting properties of BaTiO3

    NASA Astrophysics Data System (ADS)

    Zulueta, Y. A.; Dawson, J. A.; Leyet, Y.; Anglada-Rivera, J.; Guerrero, F.; Silva, R. S.; Nguyen, Minh Tho

    2016-11-01

    In combination with the dielectric modulus formalism and theoretical calculations, a newly developed defect incorporation mode, which is a combination of the standard A- and B-site doping mechanisms, is used to explain the conducting properties in 5 mol% Ca-doped BaTiO3. Simulation results for Ca solution energies in the BaTiO3 lattice show that the new oxygen vacancy inducing mixed mode exhibits low defect energies. A reduction in dc conductivity compared with undoped BaTiO3 is witnessed for the incorporation of Ca. The conducting properties of 5 mol% Ca-doped BaTiO3 are analyzed using molecular dynamics and impedance spectroscopy. The ionic conductivity activation energies for each incorporation mode are calculated and good agreement with experimental data for oxygen migration is observed. The likely existence of the proposed defect configuration is also analyzed on the basis of these methods.

  2. Electrical properties of transparent conductive ATO coatings obtained by spray pyrolysis

    NASA Astrophysics Data System (ADS)

    Zinchenko, T. O.; Kondrashin, V. I.; Pecherskaya, E. A.; Kozlyakov, A. S.; Nikolaev, K. O.; Shepeleva, J. V.

    2017-08-01

    Transparent conductive coatings based on thin films of metal oxides have been widely spread in various optoelectronic devices and appliances. It is necessary to determine the influence of preparation conditions on coatings properties for their use in the solution of certain tasks. Thin films of tin dioxide were obtained by the method of spray pyrolysis on glass substrates. Surface resistance and resistivity, concentration and mobility of charge carriers, the conductivity were measured, and the dependences showing the effect of preparation conditions on electrical properties of optically transparent coatings.

  3. Study on Ion-Conducting Properties of Ionic Liquid Containing Carbonate Electrolytes Against Carbon Electrode.

    PubMed

    Choi, Bo-Ra; Park, Soo-Jin; Kim, Seok

    2016-03-01

    The ionic performances for the mixture of ethylene carbonate (EC) and dimethylcarbonate (DMC) were investigated for supercapacitor electrolyte. The usage of ethylene carbonate (EC) and dimethylcarbonate (DMC) as organic solvent could solve some problems of acetonitrile (AN). The general aim of present paper is compare to properties of electrochemical properties based on two mixed organic electrolytes. The ionic conductivity, viscosity, and electrochemical performances of EC/DMC+0.1 M TEABF4 mixtures were determined. The ionic conductivity of the electrolytes was measured by AC impedance, and the capacitative performances of the electrolytes were evaluated by using cyclic voltammetry.

  4. Physical properties of madocite: A quaternary chalcogenide with very low thermal conductivity

    NASA Astrophysics Data System (ADS)

    Wei, Kaya; Martin, Joshua; Maruyama, Satofumi; Mori, Takao; Nolas, George S.

    2017-07-01

    The madocite Pb17(Sb0.75As0.25)16S41 was synthesized by reaction of binary compounds and densified using hot pressing. The optical band-gap, thermal stability, and temperature-dependent heat capacity and thermal conductivity are reported for the first time. The thermal properties are evaluated using the Debye model. The findings in this work lay the foundation for a more detailed understanding of the physical properties of this material, and is part of the continuing effort in investigating materials with new compositions that possess low thermal conductivity for potential low-cost thermal barrier coating and energy-related applications.

  5. Salient material properties and haptic volume perception: the influences of surface texture, thermal conductivity, and compliance.

    PubMed

    Bergmann Tiest, Wouter M; Kahrimanovic, Mirela; Niemantsverdriet, Ilona; Bogale, Kassahun; Kappers, Astrid M L

    2012-11-01

    We investigated the influences of surface texture, thermal conductivity, and compliance on the haptic perception of the volume of small cubes. It was hypothesized that an object containing highly salient material properties would be perceived as larger in volume than the same object without these properties. Blindfolded subjects were asked to explore pairs of cubes differing in their material properties and to select the one with the larger volume. The results showed that, counterintuitively, a smooth cube was perceived as being significantly larger than a rough cube of the same physical volume, with average biases of about 19 %. Furthermore, cubes with a higher thermal conductivity were perceived as significantly larger than cubes with a lower thermal conductivity (average bias of about 7 %). In addition, the magnitude of the bias in this condition was not changed by increasing or decreasing the temperature of the test objects, suggesting that the effect of thermal conductivity could not be attributed directly to the heat flow. Finally, a hard cube was perceived as significantly larger than a soft cube of equal physical volume, with an average bias of about 25 %. These results reveal that the studied material properties have significant and consistent influences on the haptic perception of volume. The observed biases provide an indication of the levels at which the processing of haptic information on volume and material properties occurs.

  6. Phase stability, single crystal growth, and anisotropic magnetic properties of Ca-La magnetoplumbite-type ferrite

    NASA Astrophysics Data System (ADS)

    Uji, K.; Waki, T.; Tabata, Y.; Nakamura, H.

    2017-01-01

    The cation compositions in the Ca-La magnetoplumbite-type (M-type) ferrite, CaxLayFezO19, prepared from various initial fractions of reagents, were analyzed by wavelength-dispersive X-ray (WDX) spectroscopy. The reliability of the WDX composition analysis was confirmed by a crosscheck using inductively coupled plasma atomic emission spectrometry (ICP-AES). For particular polycrystalline samples furnace-cooled from 1250 ° C , the solubility ranges of Ca, La, and Fe were found to be 0.45 ≤ x ≤ 0.70 , 0.39 ≤ y ≤ 0.66 , and 11.82 ≤ z ≤ 11.92 , respectively, assuming x + y + z = 13 . Despite that the samples were synthesized from various starting compositions, the values of z / (x + y) of the matrix M phase are smaller than the M-type regular value, 12, for all the samples and comes in a very limited range at ∼ 11 , suggesting most probably Ca occupation at particular Fe sites or Fe deficiency due to insertion of stacking fault to Ca/La/O packing. Single crystals of CaxLayFezO19 with various x / y ratios were synthesized successfully by the self-flux method, followed by the characterization of their magnetic properties. The saturation magnetization and the Curie temperature were found to be almost independent of the cation composition. In contrast, the hard-axis magnetization process at low temperature depended significantly on the Ca/La ratio, and showed a sharp jump at ≲ 10 kOe, which can be attributed to a spin reorientation transition associated with the appearance of Fe2+.

  7. Electrochemical evaluation of the p-Si/conducting polymer interfacial properties

    NASA Technical Reports Server (NTRS)

    Nagasubramanian, G.; Distefano, S.; Moacanin, J.

    1988-01-01

    Results are presented from an experimental investigation of the contact resistance and interfacial properties of a p-Si/conducting polymer interface for solar cell applications. The electronic character of the polymer/semiconductor function is determined by studying the electrochemical behavior of both poly(isothianapthene) (PITN) and polypyrrole (PP) in an acetonitrile solution on p-silicon electrodes. The results obtained indicate that while PITN is intrinsically more conductive than PP, neither passivates surface states nor forms ohmic contact.

  8. AC conductivity and dielectric properties of Co-doped TiO 2

    NASA Astrophysics Data System (ADS)

    Okutan, Mustafa; Basaran, Engin; Bakan, Halil I.; Yakuphanoglu, Fahrettin

    2005-07-01

    The alternating current (AC) conductivity and dielectric properties of the Co-doped TiO 2 were investigated. The temperature dependence of AC conductivity and the parameter s, is reasonably well interpreted by the correlated barrier hopping (CBH) model. The activation energy ( E), and the density of states at Fermi level, N( EF) were determined. The dielectric constant decreases with frequency at low frequencies and increases at high frequencies.

  9. Electrochemical evaluation of the p-Si/conducting polymer interfacial properties

    NASA Technical Reports Server (NTRS)

    Nagasubramanian, G.; Distefano, S.; Moacanin, J.

    1988-01-01

    Results are presented from an experimental investigation of the contact resistance and interfacial properties of a p-Si/conducting polymer interface for solar cell applications. The electronic character of the polymer/semiconductor function is determined by studying the electrochemical behavior of both poly(isothianapthene) (PITN) and polypyrrole (PP) in an acetonitrile solution on p-silicon electrodes. The results obtained indicate that while PITN is intrinsically more conductive than PP, neither passivates surface states nor forms ohmic contact.

  10. Anisotropic nanomaterials: structure, growth, assembly, and functions

    PubMed Central

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

    2011-01-01

    Comprehensive knowledge over the shape of nanomaterials is a critical factor in designing devices with desired functions. Due to this reason, systematic efforts have been made to synthesize materials of diverse shape in the nanoscale regime. Anisotropic nanomaterials are a class of materials in which their properties are direction-dependent and more than one structural parameter is needed to describe them. Their unique and fine-tuned physical and chemical properties make them ideal candidates for devising new applications. In addition, the assembly of ordered one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) arrays of anisotropic nanoparticles brings novel properties into the resulting system, which would be entirely different from the properties of individual nanoparticles. This review presents an overview of current research in the area of anisotropic nanomaterials in general and noble metal nanoparticles in particular. We begin with an introduction to the advancements in this area followed by general aspects of the growth of anisotropic nanoparticles. Then we describe several important synthetic protocols for making anisotropic nanomaterials, followed by a summary of their assemblies, and conclude with major applications. PMID:22110867

  11. Anisotropic nanomaterials: structure, growth, assembly, and functions.

    PubMed

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

    2011-01-01

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

  12. Anisotropic electronic states in the fractional quantum Hall regime

    NASA Astrophysics Data System (ADS)

    Ciftja, Orion

    2017-05-01

    Recent experiments indicate the presence of new anisotropic fractional quantum Hall states at regimes not anticipated before. These experiments raise many fundamental questions regarding the inner nature of the electronic system that leads to such anisotropic states. Interplay between electron mass anisotropy and electron-electron correlation effects in a magnetic field can create a rich variety of possibilities. Several anisotropic electronic states ranging from anisotropic quantum Hall liquids to anisotropic Wigner solids may stabilize due to such effe