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Sample records for compounds lattice thermal

  1. Lattice thermal expansion for normal tetrahedral compound semiconductors

    SciTech Connect

    Omar, M.S. . E-mail: dr_m_s_omar@yahoo.com

    2007-02-15

    The cubic root of the deviation of the lattice thermal expansion from that of the expected value of diamond for group IV semiconductors, binary compounds of III-V and II-VI, as well as several ternary compounds from groups I-III-VI{sub 2}, II-IV-V{sub 2} and I-IV{sub 2}V{sub 3} semiconductors versus their bonding length are given straight lines. Their slopes were found to be 0.0256, 0.0210, 0.0170, 0.0259, 0.0196, and 0.02840 for the groups above, respectively. Depending on the valence electrons of the elements forming these groups, a formula was found to correlate all the values of the slopes mentioned above to that of group IV. This new formula which depends on the melting point and the bonding length as well as the number of valence electrons for the elements forming the compounds, will gives best calculated values for lattice thermal expansion for all compounds forming the groups mentioned above. An empirical relation is also found between the mean ionicity of the compounds forming the groups and their slopes mentioned above and that gave the mean ionicity for the compound CuGe{sub 2}P{sub 3} in the range of 0.442.

  2. Compressed sensing approach for calculating lattice thermal conductivity of complex thermoelectric compounds

    NASA Astrophysics Data System (ADS)

    Ozolins, Vidvuds; Xia, Yi; Nielson, Weston; Zhou, Fei

    2015-03-01

    Earth-abundant minerals such as tetrahedrite Cu12Sb4S13 have recently received attention as promising thermoelectrics due to a combination of a relatively high figure of merit (ZT > 1 at T = 700 K in tetrahedrite), good mechanical properties and inexpensive bulk processing methods. Like many large unit-cell thermoelectrics, these compounds often have complex chemical formulas with very large unit cells that pose challenges to our ability to study their lattice dynamical properties theoretically. Here we show that a recently introduced approach, compressive sensing lattice dynamics (CSLD) [F. Zhou et al., Phys. Rev. Lett. 113, 185501 (2014)] provides an accurate and computationally efficient platform for investigating anharmonic lattice dynamics in complex materials. We will discuss the basic ideas and illustrate the performance of CSLD for the lattice thermal conductivity κL of tetrahedrite, collusite, pyrite, and other earth-abundant mineral compounds.

  3. Prediction of Low-Thermal-Conductivity Compounds with First-Principles Anharmonic Lattice-Dynamics Calculations and Bayesian Optimization.

    PubMed

    Seko, Atsuto; Togo, Atsushi; Hayashi, Hiroyuki; Tsuda, Koji; Chaput, Laurent; Tanaka, Isao

    2015-11-13

    Compounds of low lattice thermal conductivity (LTC) are essential for seeking thermoelectric materials with high conversion efficiency. Some strategies have been used to decrease LTC. However, such trials have yielded successes only within a limited exploration space. Here, we report the virtual screening of a library containing 54,779 compounds. Our strategy is to search the library through Bayesian optimization using for the initial data the LTC obtained from first-principles anharmonic lattice-dynamics calculations for a set of 101 compounds. We discovered 221 materials with very low LTC. Two of them even have an electronic band gap <1 eV, which makes them exceptional candidates for thermoelectric applications. In addition to those newly discovered thermoelectric materials, the present strategy is believed to be powerful for many other applications in which the chemistry of materials is required to be optimized. PMID:26613454

  4. Prediction of Low-Thermal-Conductivity Compounds with First-Principles Anharmonic Lattice-Dynamics Calculations and Bayesian Optimization

    NASA Astrophysics Data System (ADS)

    Seko, Atsuto; Togo, Atsushi; Hayashi, Hiroyuki; Tsuda, Koji; Chaput, Laurent; Tanaka, Isao

    2015-11-01

    Compounds of low lattice thermal conductivity (LTC) are essential for seeking thermoelectric materials with high conversion efficiency. Some strategies have been used to decrease LTC. However, such trials have yielded successes only within a limited exploration space. Here, we report the virtual screening of a library containing 54 779 compounds. Our strategy is to search the library through Bayesian optimization using for the initial data the LTC obtained from first-principles anharmonic lattice-dynamics calculations for a set of 101 compounds. We discovered 221 materials with very low LTC. Two of them even have an electronic band gap <1 eV , which makes them exceptional candidates for thermoelectric applications. In addition to those newly discovered thermoelectric materials, the present strategy is believed to be powerful for many other applications in which the chemistry of materials is required to be optimized.

  5. Thermal expansion and lattice dynamics of RB66 compounds at low temperatures

    SciTech Connect

    Novikov, V V; Avdashchenko, D V; Mitroshenkov, N V; Matovnikov, A V; Budko, Serguei L

    2014-10-01

    Thermal characteristics of the phonon and magnon subsystems of icosahedral borides RB66 (R = Gd, Tb, Dy, Ho, Eu, or Lu) have been studied based on the obtained experimental data on the thermal expansion of the borides and the earlier results on their heat capacity in the range of 2–300 K. The contribution to the expansion of borides containing paramagnetic R 3+ ions, which is characteristic of transition to the spin-glass state, has been revealed. The phonon spectrum moments of RB66 compounds and the Grüneisen parameters have been calculated.

  6. Reducing Lattice Thermal Conductivity of the Thermoelectric Compound AgSbTe2 (P4/mmm) by Lanthanum Substitution: Computational and Experimental Approaches

    NASA Astrophysics Data System (ADS)

    Amouyal, Yaron

    2014-10-01

    In this study we performed lattice dynamics first-principles calculations for the promising thermoelectric (TE) compound AgSbTe2, and estimated the stability of its three polymorphs over a wide temperature range from 0 to 600 K. We calculated the vibrational density of states of the AgSbTe2 (P4/mmm) phase. The results suggested that formation of substitutional defects at Ag-sublattice sites impedes lattice vibrations, thereby reducing lattice thermal conductivity. We focused on calculations based on the Debye approximation for the compound La0.125Ag0.875SbTe2, and predicted reduction of the average sound velocity from 1684 to 1563 m s-1 as a result of La doping. This is manifested as a ca. 14% reduction in thermal conductivity. To confirm the results from computation we produced two Ag-Sb-Te-based alloys, a ternary alloy without La addition and a quaternary alloy containing La. We measured the thermal conductivity of both alloys by use of the laser flash analysis method, and, as a result of La alloying, observed a reduction in thermal conductivity from 0.92 to 0.71 W m-1 K-1 at 573 K, as calculated from first principles.

  7. A Robust Approach to Lattice Thermal Conductivity

    NASA Astrophysics Data System (ADS)

    Nielson, Weston; Fei Zhou Team; Yi Xia Team; Vidvuds Ozolins Team

    2015-03-01

    Thermal conductivity is a key parameter in designing high performance thermoelectric materials. A multitude of computational methods have been developed to calculate lattice thermal conductivity. Molecular dynamics (MD) based techniques, including equilibrium and non-equilibrium methods, in addition to non MD-based solutions, such as the Boltzmann Transport Equation (BTE), are all capable of calculating thermal conductivity, but each comes with different sets of limitations and difficulties. After extensive use of these different methods, we have developed a robust set of tools for obtaining high-quality lattice thermal conductivity values of crystalline solids. The crux of our method involves a novel compressive sensing (CS) based approach for efficiently calculating high quality force constants for crystalline materials. The result is a technique for building lattice dynamical models that can treat compounds with large, complex unit cells and strong anharmonicity, including those with harmonically unstable phonon modes.

  8. Colossal negative thermal expansion induced by magnetic phase competition on frustrated lattices in Laves phase compound (Hf,Ta)Fe2

    NASA Astrophysics Data System (ADS)

    Li, B.; Luo, X. H.; Wang, H.; Ren, W. J.; Yano, S.; Wang, C.-W.; Gardner, J. S.; Liss, K.-D.; Miao, P.; Lee, S.-H.; Kamiyama, T.; Wu, R. Q.; Kawakita, Y.; Zhang, Z. D.

    2016-06-01

    Competition between ferromagnetic and antiferromagnetic phases on frustrated lattices in hexagonal Laves phase compound Hf0.86Ta0.14Fe2 is investigated by using neutron diffraction as a function of temperature and magnetic fields and density-functional-theory calculations. At 325 K, the compound orders into the 120° frustrated antiferromagnetic state with a well-reduced magnetic moment, and an in-plane lattice contraction simultaneously sets in. With further cooling down, however, the accumulated distortion in turn destabilizes this susceptible frustrated structure. The frustration is completely relieved at 255 K when the first-order transition to the ferromagnetic state takes place, where a colossal negative volumetric thermal expansion, -123 ×10-6 /K, is obtained. Meanwhile, the antiferromagnetic state can be suppressed by few-tesla magnetic fields, which results in a colossal positive magnetostriction. Such delicate competition is attributed to the giant magnetic fluctuation inherent in the frustrated antiferromagnetic state. Therefore, the magnetoelastic instability is approached even under a small perturbation.

  9. A modified model for calculating lattice thermal expansion of I{sub 2}-IV-VI{sub 3} and I{sub 3}-V-VI{sub 4} tetrahedral compounds

    SciTech Connect

    Omar, M.S. . E-mail: dr_m_s_omar@yahoo.com

    2007-05-03

    A general empirical formula was found for calculating lattice thermal expansion for compounds having their properties extended for compound groups having different mean ionicity as well as more than one type of cation atoms with that of different numbers of them such as I{sub 2}-IV-VI{sub 3} and I{sub 3}-V-VI{sub 4}. The difference in the valence electrons for cations and anions in the compound was used to correlate the deviations caused by the compound ionicity. The ionicity effects, which are due to their different numbers for their types, were also added to the correlation equation. In general, the lattice thermal expansion for a compound semiconductor can be calculated from a relation containing melting point, mean atomic distance and number of valence electrons for the atoms forming the compound. The mean ionicity for the group compounds forming I{sub 2}-IV-VI{sub 3} was found to be 0.323 and 0.785 for the ternary group compounds of I{sub 3}-V-VI{sub 4}.

  10. Structure and thermoelectric properties of the quaternary compound Cs2[PdCl4]I2 with ultralow lattice thermal conductivity

    NASA Astrophysics Data System (ADS)

    Li, Wenfeng; Yang, Gui

    2016-03-01

    We study the electronic structure and thermoelectric properties of Cs2[PdCl4]I2 with ultralow lattice thermal conductivity using first-principles calculations and the semi-classical Boltzmann transport theory. The coexistence of several ionic and covalent bonds in Cs2[PdCl4]I2 indicates a similar Zintl phase crystal structure. Cs2[PdCl4]I2 is an indirect-band semiconductor with high density of states near the valence band maximum, which leads to high Seebeck coefficients even at high carrier concentrations. The calculated transport properties of p-type Cs2[PdCl4]I2 are higher than that of the known high-performance thermoelectric material CuGaTe2. The combination of good transport properties and ultralow lattice thermal conductivity suggests that Cs2[PdCl4]I2 can be a promising p-type thermoelectric material.

  11. Diverse lattice dynamics in ternary Cu-Sb-Se compounds

    PubMed Central

    Qiu, Wujie; Wu, Lihua; Ke, Xuezhi; Yang, Jihui; Zhang, Wenqing

    2015-01-01

    Searching and designing materials with extremely low lattice thermal conductivity (LTC) has attracted considerable attention in material sciences. Here we systematically demonstrate the diverse lattice dynamics of the ternary Cu-Sb-Se compounds due to the different chemical-bond environments. For Cu3SbSe4 and CuSbSe2, the chemical bond strength is nearly equally distributed in crystalline bulk, and all the atoms are constrained to be around their equilibrium positions. Their thermal transport behaviors are well interpreted by the perturbative phonon-phonon interactions. While for Cu3SbSe3 with obvious chemical-bond hierarchy, one type of atoms is weakly bonded with surrounding atoms, which leads the structure to the part-crystalline state. The part-crystalline state makes a great contribution to the reduction of thermal conductivity that can only be effectively described by including a rattling-like scattering process in addition to the perturbative method. Current results may inspire new approaches to designing materials with low lattice thermal conductivities for high-performance thermoelectric conversion and thermal barrier coatings. PMID:26328765

  12. Diverse lattice dynamics in ternary Cu-Sb-Se compounds

    NASA Astrophysics Data System (ADS)

    Qiu, Wujie; Wu, Lihua; Ke, Xuezhi; Yang, Jihui; Zhang, Wenqing

    2015-09-01

    Searching and designing materials with extremely low lattice thermal conductivity (LTC) has attracted considerable attention in material sciences. Here we systematically demonstrate the diverse lattice dynamics of the ternary Cu-Sb-Se compounds due to the different chemical-bond environments. For Cu3SbSe4 and CuSbSe2, the chemical bond strength is nearly equally distributed in crystalline bulk, and all the atoms are constrained to be around their equilibrium positions. Their thermal transport behaviors are well interpreted by the perturbative phonon-phonon interactions. While for Cu3SbSe3 with obvious chemical-bond hierarchy, one type of atoms is weakly bonded with surrounding atoms, which leads the structure to the part-crystalline state. The part-crystalline state makes a great contribution to the reduction of thermal conductivity that can only be effectively described by including a rattling-like scattering process in addition to the perturbative method. Current results may inspire new approaches to designing materials with low lattice thermal conductivities for high-performance thermoelectric conversion and thermal barrier coatings.

  13. Lattice dynamics and lattice thermal conductivity of thorium dicarbide

    NASA Astrophysics Data System (ADS)

    Liao, Zongmeng; Huai, Ping; Qiu, Wujie; Ke, Xuezhi; Zhang, Wenqing; Zhu, Zhiyuan

    2014-11-01

    The elastic and thermodynamic properties of ThC2 with a monoclinic symmetry have been studied by means of density functional theory and direct force-constant method. The calculated properties including the thermal expansion, the heat capacity and the elastic constants are in a good agreement with experiment. Our results show that the vibrational property of the C2 dimer in ThC2 is similar to that of a free standing C2 dimer. This indicates that the C2 dimer in ThC2 is not strongly bonded to Th atoms. The lattice thermal conductivity for ThC2 was calculated by means of the Debye-Callaway model. As a comparison, the conductivity of ThC was also calculated. Our results show that the ThC and ThC2 contributions of the lattice thermal conductivity to the total conductivity are 29% and 17%, respectively.

  14. Thermal lattice Boltzmann method for complex microflows

    NASA Astrophysics Data System (ADS)

    Yasuoka, Haruka; Kaneda, Masayuki; Suga, Kazuhiko

    2016-07-01

    A methodology to simulate thermal fields in complex microflow geometries is proposed. For the flow fields, the regularized multiple-relaxation-time lattice Boltzmann method (LBM) is applied coupled with the diffusive-bounce-back boundary condition for wall boundaries. For the thermal fields, the regularized lattice Bhatnagar-Gross-Krook model is applied. For the thermal wall boundary condition, a newly developed boundary condition, which is a mixture of the diffuse scattering and constant temperature conditions, is applied. The proposed set of schemes is validated by reference data in the Fourier flows and square cylinder flows confined in a microchannel. The obtained results confirm that it is essential to apply the regularization to the thermal LBM for avoiding kinked temperature profiles in complex thermal flows. The proposed wall boundary condition is successful to obtain thermal jumps at the walls with good accuracy.

  15. Low lattice thermal conductivity of stanene

    PubMed Central

    Peng, Bo; Zhang, Hao; Shao, Hezhu; Xu, Yuchen; Zhang, Xiangchao; Zhu, Heyuan

    2016-01-01

    A fundamental understanding of phonon transport in stanene is crucial to predict the thermal performance in potential stanene-based devices. By combining first-principle calculation and phonon Boltzmann transport equation, we obtain the lattice thermal conductivity of stanene. A much lower thermal conductivity (11.6 W/mK) is observed in stanene, which indicates higher thermoelectric efficiency over other 2D materials. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. Detailed analysis of phase space for three-phonon processes shows that phonon scattering channels LA + LA/TA/ZA ↔ TA/ZA are restricted, leading to the dominant contributions of high-group-velocity LA phonons to the thermal conductivity. The size dependence of thermal conductivity is investigated as well for the purpose of the design of thermoelectric nanostructures. PMID:26838731

  16. Low lattice thermal conductivity of stanene.

    PubMed

    Peng, Bo; Zhang, Hao; Shao, Hezhu; Xu, Yuchen; Zhang, Xiangchao; Zhu, Heyuan

    2016-01-01

    A fundamental understanding of phonon transport in stanene is crucial to predict the thermal performance in potential stanene-based devices. By combining first-principle calculation and phonon Boltzmann transport equation, we obtain the lattice thermal conductivity of stanene. A much lower thermal conductivity (11.6 W/mK) is observed in stanene, which indicates higher thermoelectric efficiency over other 2D materials. The contributions of acoustic and optical phonons to the lattice thermal conductivity are evaluated. Detailed analysis of phase space for three-phonon processes shows that phonon scattering channels LA + LA/TA/ZA ↔ TA/ZA are restricted, leading to the dominant contributions of high-group-velocity LA phonons to the thermal conductivity. The size dependence of thermal conductivity is investigated as well for the purpose of the design of thermoelectric nanostructures. PMID:26838731

  17. Lattice Boltzmann approach to thermal transpiration

    SciTech Connect

    Sofonea, Victor

    2006-11-15

    Diffuse reflection boundary conditions are introduced in a thermal lattice Boltzmann model to allow for variable fluid density and temperature along the walls. The capability of this model to capture the main characteristics of the thermal transpiration phenomenon in a box at nonvanishing Knudsen numbers is demonstrated. The thermal creep velocity is found to be proportional to the temperature gradient imposed at the wall, whereas the accuracy of the simulation results are found to be of first or second order, depending on the numerical scheme.

  18. The Lattice and Thermal Radiation Conductivity of Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Spuckler, Charles M.

    2008-01-01

    The lattice and radiation conductivity of thermal barrier coatings was evaluated using a laser heat flux approach. A diffusion model has been established to correlate the apparent thermal conductivity of the coating to the lattice and radiation conductivity. The radiation conductivity component can be expressed as a function of temperature and the scattering and absorption properties of the coating material. High temperature scattering and absorption of the coating systems can also be derived based on the testing results using the modeling approach. The model prediction is found to have good agreement with experimental observations.

  19. Higher Order Thermal Lattice Boltzmann Model

    NASA Astrophysics Data System (ADS)

    Sorathiya, Shahajhan; Ansumali, Santosh

    2013-03-01

    Lattice Boltzmann method (LBM) modelling of thermal flows, compressible and micro flows requires an accurate velocity space discretization. The sub optimality of Gauss-Hermite quadrature in this regard is well known. Most of the thermal LBM in the past have suffered from instability due to lack of proper H-theorem and accuracy. Motivated from these issues, the present work develops along the two works and and imposes an eighth higher order moment to get correct thermal physics. We show that this can be done by adding just 6 more velocities to D3Q27 model and obtain a ``multi-speed on lattice thermal LBM'' with 33 velocities in 3D and calO (u4) and calO (T4) accurate fieq with a consistent H-theorem and inherent numerical stability. Simulations for Rayleigh-Bernard as well as velocity and temperature slip in micro flows matches with analytical results. Lid driven cavity set up for grid convergence is studied. Finally, a novel data structure is developed for HPC. The authors express their gratitude for computational resources and financial support provide by Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bangalore, India.

  20. Lattice thermal conductivity crossovers in semiconductor nanowires.

    PubMed

    Mingo, N; Broido, D A

    2004-12-10

    For binary compound semiconductor nanowires, we find a striking relationship between the nanowire's thermal conductivity kappa(nwire), the bulk material's thermal conductivity kappa(bulk), and the mass ratio of the material's constituent atoms, r, as kappa(bulk)/kappa(nwire) (alpha) (1+1/r)(-3/2). A significant consequence is the presence of crossovers in which a material with higher bulk thermal conductivity than the rest is no longer the best nanowire thermal conductor. We show that this behavior stems from a change in the dominant phonon scattering mechanism with decreasing nanowire size. The results have important implications for nanoscale heat dissipation, thermoelectricity, and thermal conductivity of nanocomposites. PMID:15697834

  1. Multifunctional Lattices with Low Thermal Expansion and Low Thermal Conductivity

    NASA Astrophysics Data System (ADS)

    Xu, Hang; Liu, Lu; Pasini, Damiano

    Systems in space are vulnerable to large temperature changes when travelling into and out of the Earth's shadow. Variations in temperature can lead to undesired geometric changes in susceptible applications requiring very fine precision. In addition, temperature-sensitive electronic equipment hosted in a satellite needs adequate thermal-control to guarantee a moderate ambient temperature. To address these specifications, materials with low coefficient of thermal expansion (CTE) and low coefficient of thermal conductivity (CTC) over a wide range of temperatures are often sought, especially for bearing components in satellites. Besides low CTE and low CTC, these materials should also provide desirable stiffness, strength and extraordinarily low mass. This work presents ultralightweight bi-material lattices with tunable CTE and CTC, besides high stiffness and strength. We show that the compensation of the thermal expansion and joint rotation at the lattice joints can be used as an effective strategy to tailor thermomechanical performance. Proof-of-concept lattices are fabricated from Al and Ti alloy sheets via a simple snap-fit technique and vacuum brazing, and their CTE and CTC are assessed via a combination of experiments and theory. Corresponding Author.

  2. A photonic thermalization gap in disordered lattices

    NASA Astrophysics Data System (ADS)

    Kondakci, H. Esat; Abouraddy, Ayman F.; Saleh, Bahaa E. A.

    2015-11-01

    The formation of gaps--forbidden ranges in the values of a physical parameter--is common to a variety of physical systems: from energy bandgaps of electrons in periodic lattices and their analogues in photonic, phononic and plasmonic systems to pseudo-energy gaps in aperiodic quasicrystals. Here, we predict a thermalization gap for light propagating in finite disordered structures characterized by disorder-immune chiral symmetry--the appearance of the eigenvalues and eigenvectors in skew-symmetric pairs. In these systems, the span of sub-thermal photon statistics is inaccessible to input coherent light, which--once the steady state is reached--always emerges with super-thermal statistics no matter how small the disorder level. We formulate an independent constraint of the input field for the chiral symmetry to be activated and the gap to be observed. This unique feature enables a new form of photon-statistics interferometry: the deterministic tuning of photon statistics via controlled excitation symmetry breaking realized by sculpting the amplitude or phase of the input coherent field.

  3. Multi-Species Thermal Lattice Boltzmann Models

    NASA Astrophysics Data System (ADS)

    Wah, Darren; Vahala, George; Vahala, Linda; Pavlo, Pavol; Carter, Jonathan

    1998-11-01

    Thermal Lattice Boltzmann models (TLBM) are ideal for simulating nonlinear macroscopic conservation systems because of their inherent parallelizeability (nearly all operations are purely local). The TLBM solves a linear BGK-like kinetic equation so that the standard nonlinear convective terms in the standard fluid codes are now replaced by a simple shift operator (linear advection) at the kinetic level. Here we extend our previous TLBM to handle a two-species system, utilizing the models of Morse (1964),Greene (1973) and Kotelnikov & Montgomery (1997). Each kinetic equation now has 2 BGK-like relaxation terms : the first is due to self-collisions and the other is due to different- species collisions. The relaxation rates used are appropriate for electron-ion collisions. Certain constraints can be imposed on the relaxed distribution functions so that the cross-species momentum and energy evolutions relax at the rate determined from the full nonlinear Boltzmann integral collision operator. Ionization and recombination processes will also be examined. Both hexagonal and octagonal lattices are studied.

  4. Lattice dynamics study of bismuth III V compounds

    NASA Astrophysics Data System (ADS)

    Belabbes, A.; Zaoui, A.; Ferhat, M.

    2008-10-01

    We present first-principles calculations of the structural and lattice-dynamical properties for cubic bismuth III-V compounds: BBi, AlBi and GaBi. The ground-state properties, i.e., the lattice constant and the bulk modulus, are calculated using a plane wave pseudopotential method within density functional theory. A linear-response approach to density functional theory is used to derive the phonon frequencies. The effect of pressure on the dynamical charges and the longitudinal optical-transverse optical splitting is also examined.

  5. Thermal expansion of compounds of zircon structure

    SciTech Connect

    Subbarao, E.C.; Agrawal, D.K.; McKinstry, H.A.; Sallese, C.W.; Roy, R. . Materials Research Lab.)

    1990-05-01

    The thermal expansion behavior of 13 members of ABO{sub 4} compounds of the zircon family is examined in terms of crystal chemical (size, charge, and mass of cations) and crystallographic (a and c) parameters. The systematic trend in the thermal expansion coefficients {alpha}{sub a} and {alpha}{sub c}, with the ionic radii, r{sub A} and R{sub B}, can be explained in terms of the unique arrangement of M-O polyhedra along a and c directions of this lattice. In the zircon structure, edge-sharing ZrO{sub 8} dodecahedra form a chain along the a direction while the chain along the c direction consists of alternate edge-sharing SiO{sub 4} tetrahedra and ZrO{sub 8} triangular dodecahedra. Substitution in the A sites affects a and {alpha}{sub a} more than c and {alpha}{sub c} and the reverse is true for replacements in the B sites. Unequal valencies on the A and B sites affect thermal expansion coefficients, particularly {alpha}{sub c}.

  6. Lattice-structures and constructs with designed thermal expansion coefficients

    SciTech Connect

    Spadaccini, Christopher; Hopkins, Jonathan

    2014-10-28

    A thermal expansion-managed lattice structure having a plurality of unit cells each having flexure bearing-mounted tabs supported on a base and actuated by thermal expansion of an actuator having a thermal expansion coefficient greater than the base and arranged so that the tab is inwardly displaced into a base cavity. The flexure bearing-mounted tabs are connected to other flexure-bearing-mounted tabs of adjacent unit cells so that the adjacent unit cells are spaced from each other to accommodate thermal expansion of individual unit cells while maintaining a desired bulk thermal expansion coefficient of the lattice structure as a whole.

  7. Thermal equation of state for lattice Boltzmann gases

    NASA Astrophysics Data System (ADS)

    Ran, Zheng

    2009-06-01

    The Galilean invariance and the induced thermo-hydrodynamics of the lattice Boltzmann Bhatnagar-Gross-Krook model are proposed together with their rigorous theoretical background. From the viewpoint of group invariance, recovering the Galilean invariance for the isothermal lattice Boltzmann Bhatnagar-Gross-Krook equation (LBGKE) induces a new natural thermal-dynamical system, which is compatible with the elementary statistical thermodynamics.

  8. Lattice thermal conductivity of nanograined half-Heusler solid solutions

    SciTech Connect

    Geng, Huiyuan Meng, Xianfu; Zhang, Hao; Zhang, Jian

    2014-05-19

    We report a phenomenological model of atomic weight, lattice constant, temperature, and grain size to calculate the high-temperature lattice thermal conductivity of nanograined solid solutions. The theoretical treatment developed here is reasonably consistent with the experimental results of n-type MNiSn and p-type MCoSb alloys, where M is the combination of Hf, Zr, and Ti. For disordered half-Heusler alloys with moderated grain sizes, we predict that the reduction in lattice thermal conductivity due to grain boundary scattering is independent of the scattering parameter, which characterizes the phonon scattering cross section of point defects. In addition, the lattice thermal conductivity falls off with temperature as T{sup –1∕2} around the Debye temperature.

  9. The S=1 Underscreened Anderson Lattice model for Uranium compounds

    NASA Astrophysics Data System (ADS)

    Thomas, C.; Simões, A. S. R.; Iglesias, J. R.; Lacroix, C.; Perkins, N. B.; Coqblin, B.

    2011-01-01

    Magnetic properties of uranium and neptunium compounds showing coexistence of the Kondo effect and ferromagnetic order are investigated within the degenerate Anderson Lattice Hamiltonian, describing a 5f2 electronic configuration with S = 1 spins. Through the Schrieffer-Wolff transformation, both an exchange Kondo interaction for the S = 1 f-spins and an effective f-band term are obtained, allowing to describe the coexistence of Kondo effect and ferromagnetic ordering and a weak delocalization of the 5f-electrons. We calculate the Kondo and Curie temperatures and we can account for the pressure dependence of the Curie temperature of UTe.

  10. Accurate measurements of thermal radiation from a tungsten photonic lattice

    SciTech Connect

    Seager, C.H.; Sinclair, M.B.; Fleming, J.G.

    2005-06-13

    Recently, photonic lattice structures have become available that are fabricated from refractory materials such as tungsten and thus stable in vacuo at high temperatures. Such structures can be tailored to exhibit optical properties that are not achievable with ordinary optical materials. In particular, photonic lattices can be designed to suppress thermal emission in undesired spectral regions, and can thereby enhance the overall energy efficiency of emission at useful wavelengths. We report measurements of the thermal emission spectra of tungsten photonic lattices in the wavelength range 3 to 24 {mu}m. Suppression of thermal emission at wavelengths longer than the photonic bandedge ({approx}6 {mu}m) is observed, along with significant emission at shorter wavelengths. We show that from 404 to 546 K the spectral emissivity E({lambda}) is temperature independent and approaches [1-R({lambda})], where R({lambda}) is the measured specular reflectance spectrum. These results are in accord with Kirchhoff's law.

  11. Dynamical thermal conductivity of the spin Lieb lattice

    NASA Astrophysics Data System (ADS)

    Yarmohammadi, Mohsen

    2016-05-01

    In the ferromagnetic insulator with the Dzyaloshinskii-Moriya interaction (DMI), we have theoretically investigated the dynamical thermal conductivity (DTC). In other words, we have investigated the frequency dependence of thermal conductivity, κ, of the Lieb lattice, a face-centered square lattice, subjected to a time dependence temperature gradient. Using linear response theory and Green's function approach, DTC has been obtained in the context of Heisenberg Hamiltonian. At low frequencies, DTC is found to be monotonically increasing with DMI strength (DMIS), temperature and next-nearest-neighbor (NNN) coupling. Also we have found that DTC includes a peak for different values of temperature, DMIS and NNN coupling. Furthermore we study the temperature dependence of thermal conductivity of Lieb lattice for different values of DMIS, NNN coupling and external magnetic filed. We witness a decrease in DTC with temperature due to the quantum effects in the system.

  12. Predicting lattice thermal conductivity with help from ab initio methods

    NASA Astrophysics Data System (ADS)

    Broido, David

    2015-03-01

    The lattice thermal conductivity is a fundamental transport parameter that determines the utility a material for specific thermal management applications. Materials with low thermal conductivity find applicability in thermoelectric cooling and energy harvesting. High thermal conductivity materials are urgently needed to help address the ever-growing heat dissipation problem in microelectronic devices. Predictive computational approaches can provide critical guidance in the search and development of new materials for such applications. Ab initio methods for calculating lattice thermal conductivity have demonstrated predictive capability, but while they are becoming increasingly efficient, they are still computationally expensive particularly for complex crystals with large unit cells . In this talk, I will review our work on first principles phonon transport for which the intrinsic lattice thermal conductivity is limited only by phonon-phonon scattering arising from anharmonicity. I will examine use of the phase space for anharmonic phonon scattering and the Grüneisen parameters as measures of the thermal conductivities for a range of materials and compare these to the widely used guidelines stemming from the theory of Liebfried and Schölmann. This research was supported primarily by the NSF under Grant CBET-1402949, and by the S3TEC, an Energy Frontier Research Center funded by the US DOE, office of Basic Energy Sciences under Award No. DE-SC0001299.

  13. Lattice constraints on the thermal photon rate

    NASA Astrophysics Data System (ADS)

    Ghiglieri, J.; Kaczmarek, O.; Laine, M.; Meyer, F.

    2016-07-01

    We estimate the photon production rate from an SU(3) plasma at temperatures of about 1.1 Tc and 1.3 Tc . Lattice results for the vector current correlator at spatial momenta k ˜(2 -6 )T are extrapolated to the continuum limit and analyzed with the help of a polynomial interpolation for the corresponding spectral function, which vanishes at zero frequency and matches to high-precision perturbative results at large invariant masses. For small invariant masses the interpolation is compared with the next-to-leading-order (NLO) weak-coupling result, hydrodynamics, and a holographic model. At vanishing invariant mass we extract the photon rate which for k ≳3 T is found to be close to the NLO weak-coupling prediction. For k ≲2 T uncertainties remain large but the photon rate is likely to fall below the NLO prediction, in accordance with the onset of a strongly interacting behavior characteristic of the hydrodynamic regime.

  14. A three dimensional lattice model for thermal compressible flow on standard lattices

    NASA Astrophysics Data System (ADS)

    Feng, Yongliang; Sagaut, Pierre; Tao, Wenquan

    2015-12-01

    A three-dimensional double distribution function thermal lattice Boltzmann model has been developed for simulation of thermal compressible flows in the low Mach number limit. Both the flow field and energy conservation equation are solved by LB approach. A higher order density distribution function on standard lattices is used to solve the flow field, while an energy distribution function is employed to compute the temperature field. The equation of state of thermal perfect gas is recovered by higher order Hermite polynomial expansions in Navier-Stokes-Fourier equations. The equilibrium distribution functions of D3Q15, D3Q19 and D3Q27 lattices are obtained from the Hermite expansion. They exhibit slight differences originating in differences in the discrete lattice symmetries. The correction terms in LB models for third order derivation are added using an external force in orthogonal polynomials form. Present models are successfully assessed considering several test cases, namely the thermal Couette flow, Rayleigh-Bénard convection, natural convection in square cavity and a spherical explosion in a 3D enclosed box. The numerical results are in good agreement with both analytical solution and results given by previous authors.

  15. Lattice thermal conductance of quantum wires with disorder

    NASA Astrophysics Data System (ADS)

    Vyhmeister, Erik; Hershfield, Selman

    We model the lattice thermal conductance in long quantum wires connected to two large heat baths at different temperatures in the harmonic approximation. The thermal conductance is computed with the Landauer formula for phonons, where it is related to the sum over all transmission probabilities for phonons through the wire. The net transmission probability is computed using a recursive Green function technique, which allows one to study long wires efficiently. We consider several different kinds of disorder to reduce the lattice thermal conductivity: periodic rectangular holes of varying sizes and shapes, periodic triangular holes, and narrow bands, averaged over randomness to account for variance in manufacturing. Depending on the model, the thermal conductance was reduced by 80 percent or more from the perfectly ordered wire case. Funded by NSF grant DMR-1461019.

  16. Calculation of the lattice thermal conductivity in granular crystals

    SciTech Connect

    Kazan, M.; Volz, S.

    2014-02-21

    This paper provides a general model for the lattice thermal conductivity in granular crystals. The key development presented in this model is that the contribution of surface phonons to the thermal conductivity and the interplay between phonon anharmonic scattering and phonon scattering by boundaries are considered explicitly. Exact Boltzmann equation including spatial dependence of phonon distribution function is solved to yield expressions for the rates at which phonons scatter by the grain boundaries in the presence of intrinsic phonon scattering mechanisms. The intrinsic phonon scattering rates are calculated from Fermi's golden rule, and the vibration parameters of the model are derived as functions of temperature and crystallographic directions by using a lattice dynamics approach. The accuracy of the model is demonstrated with reference to experimental measurements regarding the effects of surface orientation and isotope composition on the thermal conductivity in single crystals, and the effect of grains size and shape on the thermal conductivity tensor in granular crystals.

  17. More Efficient Thermalization of Gauge Fields in Lattice QCD Simulations

    SciTech Connect

    Frigori, R.B.; Cucchieri, A.; Mendes, T.; Mihara, A.

    2004-12-02

    We introduce a new thermalization algorithm for pure SU(2) lattice gauge theory by combining heat-bath and micro-canonical updates in a single step, while preserving ergodicity. We test the new algorithm in the two-dimensional case and compare its performance with the standard heat-bath method.

  18. Lattice thermal conductivity of dense silicate glass at high pressures

    NASA Astrophysics Data System (ADS)

    Chang, Y. Y.; Hsieh, W. P.

    2015-12-01

    The layered structure of the Earth's interior is generally believed to develop through the magma ocean differentiation in the early Earth. Previous seismic studies revealed the existence of ultra low velocity zones above the core mantle boundary (CMB) which was inferred to be associated with the remnant of a deep magma ocean. The heat flux through the core mantle boundary therefore would strongly depend on the thermal conductivity, both lattice (klat) and radiative (krad) of dense silicate melts and major constituent minerals of the lower mantle. Recent experimental results on the radiative thermal conductivity of dense silicate glasses and lower-mantle minerals suggest that krad of dense silicate glasses could be remarkably lower than krad of the surrounding solid mantle phases. In this case, the dense silicate melts will act as a trap for heat from the Earth's outer core. However, this conclusion remains uncertain because of the lack of direct measurements on lattice thermal conductivities of silicate glasses/melts under lower mantle pressures up to date. Here we report experimental results on lattice thermal conductivities of dense silicate glass with basaltic composition under pressures relevant to the Earth's lower mantle in a diamond-anvil cell using time-domain thermoreflectance method. The study will assist the comprehension of thermal transport properties of silicate melts in the Earth's deep interior and is crucial for understanding the dynamic and thermal evolution of the Earth's internal structure.

  19. Application of the underscreened Kondo lattice model to neptunium compounds

    NASA Astrophysics Data System (ADS)

    Thomas, Christopher; da Rosa Simoes, Acirete S.; Iglesias, J. R.; Lacroix, C.; Coqublin, B.

    2012-12-01

    The coexistence of Kondo effect and ferromagnetic order has been observed in many uranium and neptunium compounds such as UTe or Np2PdGa3. This coexistence can be described within the underscreened Anderson lattice model with two f-electrons and S = 1 spins on each site. After performing the Schrieffer-Wolff transformation on this model, we have obtained an effective Hamiltonian with a f-band term in addition to the Kondo interaction for S = 1 spins. The results indicate a coexistence of Kondo effect and ferromagnetic order, with different relative values of the Kondo TK and Curie TC temperatures. We emphasize here especially the case TK < TC where there is a Kondo behavior below TC and a clear decrease of the magnetization below TK. Such a behavior has been observed in the magnetization curves of NpNiSi2 at low temperatures.

  20. Effect of partial void filling on the lattice thermal conductivity of skutterudites

    NASA Astrophysics Data System (ADS)

    Nolas, G. S.; Cohn, J. L.; Slack, G. A.

    1998-07-01

    Polycrystalline samples of antimonides with the skutterudite crystal structure with La partially filling the voids have been prepared in an effort to quantify the impact of partial void filling on the lattice thermal conductivity of these compounds. It is observed that a relatively small concentration of La in the voids results in a relatively large decrease in the lattice thermal conductivity. In addition, the largest decrease in the lattice thermal conductivity, compared to ``unfilled'' CoSb3 is not observed near 100% filling of the voids with La, as was previously believed. This suggests a point-defect-type phonon scattering effect due to the partial, random distribution of La in the voids as well as the ``rattling'' effect of the La ions, resulting in the scattering of a larger spectrum of phonons than in the case of 100% filling. An additional benefit of partial filling in thermoelectric materials is that it may be one way of adjusting the electronic properties of these compounds. Seebeck, resistivity, Hall effect and structural data for these skutterudite compounds are also presented.

  1. Method of simultaneous measurement of radiative and lattice thermal conductivity.

    NASA Technical Reports Server (NTRS)

    Schatz, J. F.; Simmons, G.

    1972-01-01

    A new technique of high-temperature thermal-conductivity measurement is described. A CO2 gas laser is used to generate a low-frequency temperature wave at one face of a small disk-shaped sample, and an infrared detector views the opposite face to detect the phase of the emerging radiation. A mathematical expression is derived which enables phase data at several frequencies to be used for the simultaneous determination of thermal diffusivity and mean extinction coefficient. Lattice and radiative thermal conductivities are then calculated. Test results for sintered aluminum oxide at temperatures from 530 to 1924 K are within the range of error of previously existing data.

  2. THERMAL DECOMPOSITION OF URANIUM COMPOUNDS

    DOEpatents

    Magel, T.T.; Brewer, L.

    1959-02-10

    A method is presented of preparing uranium metal of high purity consisting contacting impure U metal with halogen vapor at between 450 and 550 C to form uranium halide vapor, contacting the uranium halide vapor in the presence of H/sub 2/ with a refractory surface at about 1400 C to thermally decompose the uranium halides and deposit molten U on the refractory surface and collecting the molten U dripping from the surface. The entire operation is carried on at a sub-atmospheric pressure of below 1 mm mercury.

  3. Biodegradable compounds: Rheological, mechanical and thermal properties

    NASA Astrophysics Data System (ADS)

    Nobile, Maria Rossella; Lucia, G.; Santella, M.; Malinconico, M.; Cerruti, P.; Pantani, R.

    2015-12-01

    Recently great attention from industry has been focused on biodegradable polyesters derived from renewable resources. In particular, PLA has attracted great interest due to its high strength and high modulus and a good biocompatibility, however its brittleness and low heat distortion temperature (HDT) restrict its wide application. On the other hand, Poly(butylene succinate) (PBS) is a biodegradable polymer with a low tensile modulus but characterized by a high flexibility, excellent impact strength, good thermal and chemical resistance. In this work the two aliphatic biodegradable polyesters PBS and PLA were selected with the aim to obtain a biodegradable material for the industry of plastic cups and plates. PBS was also blended with a thermoplastic starch. Talc was also added to the compounds because of its low cost and its effectiveness in increasing the modulus and the HDT of polymers. The compounds were obtained by melt compounding in a single screw extruder and the rheological, mechanical and thermal properties were investigated. The properties of the two compounds were compared and it was found that the values of the tensile modulus and elongation at break measured for the PBS/PLA/Talc compound make it interesting for the production of disposable plates and cups. In terms of thermal resistance the compounds have HDTs high enough to contain hot food or beverages. The PLA/PBS/Talc compound can be, then, considered as biodegradable substitute for polystyrene for the production of disposable plates and cups for hot food and beverages.

  4. Thermal expansion of noble metals using improved lattice dynamical model

    NASA Astrophysics Data System (ADS)

    Kumar, Priyank; Bhatt, N. K.; Vyas, P. R.; Gohel, V. B.

    2013-06-01

    Isothermal bulk modulus and volume thermal expansion for noble metals have been studied on the basis of improved lattice dynamical model proposed by Pandya et al [Physica B 307, 138-149 (2001)]. The present study shows that for all three noble metals the approach gives satisfactory results, when they are compared with experimental findings. The present study thus confirms the use of improved model to study anharmonic property, and can be extended to study temperature dependent properties in high temperature range.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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.

  6. 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.

  7. Thermal expansion and lattice misfit in two-phase superalloys

    NASA Astrophysics Data System (ADS)

    Gornostyrev, Yu. N.; Kontsevoi, O. Yu.; Freeman, A. J.; Khromov, K. Yu.; Maksyutov, A. F.; Trefilov, A. V.; Katsnelson, M. I.; Lichtenstein, A. I.

    2004-03-01

    The magnitude of the lattice misfit between the γ and γ' phases is one of the key parameters determining the mechanical behavior, microstructure morphology and stability of γ/γ' high temperature superalloys. For the first time, the γ and γ' thermal expansion coefficients α(T) and the temperature dependence of the unconstrained lattice misfit parameter δ (T) for Ni-, Ir-, and Pt-based superalloys is obtained by means of ab initio full-potential electron and phonon spectrum calculations. We demonstrate that, in contrast with traditional beliefs, the electronic contribution to the misfit parameter dominates due to the strong compensation of the phonon contributions to α(T) from γ and γ'. The calculated results are in a good agreement with available experimental data for temperatures up to 0.8T_melt; at higher temperatures the effect of the redistribution of alloying elements between the γ, and γ' phases on δ (T) becomes essential.

  8. Local lattice distortions and thermal transport in perovskite manganites

    SciTech Connect

    Cohn, J.L.; Neumeier, J.J.; Popoviciu, C.P.; McClellan, K.J.; Leventouri, T.

    1997-10-01

    Measurements of thermal conductivity versus temperature and magnetic field are reported for perovskite manganites that exhibit ferromagnetic (FM), charge-ordering (CO), antiferromagnetic, and/or structural phase transitions. The data reveal a dominant lattice contribution to the heat conductivity with {kappa}{approximately}1{minus}2 W/mK near room temperature. The rather low values, implying a phonon mean free path on the order of a lattice spacing, are shown to correlate with static local distortions of the MnO{sub 6} octahedra. Modifications of the local structure are responsible for abrupt anomalies in the zero-field {kappa} at the FM, CO, and structural transitions, and for colossal magnetothermal resistance near the FM transition. {copyright} {ital 1997} {ital The American Physical Society}

  9. Lattice thermal transport in large-area polycrystalline graphene

    NASA Astrophysics Data System (ADS)

    Aksamija, Z.; Knezevic, I.

    2014-07-01

    We study lattice thermal transport in large-area polycrystalline graphene, such as the samples grown by chemical vapor deposition (CVD) of carbon on Cu. These systems are composed of single-crystalline grains with a broad range of sizes and crystal orientations, separated by atomically rough grain boundaries. We solve the phonon Boltzmann transport equation and calculate the thermal conductivity in each grain, including scattering from the grain boundary roughness. Thermal transport in the large-area sample is considered in the Corbino-membrane geometry, with heat flowing through a network of thermal resistors and away from a pointlike heat source. The thermal transport in polycrystalline graphene is shown to be highly anisotropic, depending on the individual properties of the grains (their size and boundary roughness), as well as on grain connectivity. Strongest heat conduction occurs along large-grain filaments, while the heat flow is blocked through regions containing predominantly small grains. We discuss how thermal transport in CVD graphene can be tailored by controlling grain disorder.

  10. The Coulombic Lattice Potential of Ionic Compounds: The Cubic Perovskites.

    ERIC Educational Resources Information Center

    Francisco, E.; And Others

    1988-01-01

    Presents coulombic models representing the particles of a system by point charges interacting through Coulomb's law to explain coulombic lattice potential. Uses rubidium manganese trifluoride as an example of cubic perovskite structure. Discusses the effects on cluster properties. (CW)

  11. Lattice thermal conductivity of Bi, Sb, and Bi-Sb alloy from first principles

    NASA Astrophysics Data System (ADS)

    Lee, Sangyeop; Esfarjani, Keivan; Mendoza, Jonathan; Dresselhaus, Mildred S.; Chen, Gang

    2014-02-01

    Using first principles, we calculate the lattice thermal conductivity of Bi, Sb, and Bi-Sb alloys, which are of great importance for thermoelectric and thermomagnetic cooling applications. Our calculation reveals that the ninth-neighbor harmonic and anharmonic force constants are significant; accordingly, they largely affect the lattice thermal conductivity. Several features of the thermal transport in these materials are studied: (1) the relative contributions from phonons and electrons to the total thermal conductivity as a function of temperature are estimated by comparing the calculated lattice thermal conductivity to the measured total thermal conductivity, (2) the anisotropy of the lattice thermal conductivity is calculated and compared to that of the electronic contribution in Bi, and (3) the phonon mean free path distributions, which are useful for developing nanostructures to reduce the lattice thermal conductivity, are calculated. The phonon mean free paths are found to range from 10 to 100 nm for Bi at 100 K.

  12. High thermopower and ultra low thermal conductivity in Cd-based Zintl phase compounds.

    PubMed

    Pandey, Tribhuwan; Singh, Abhishek K

    2015-07-14

    By combining first principles density functional theory and electronic as well as lattice Boltzmann transport calculations, we unravel the excellent thermoelectric properties of Zintl phase compounds ACd2Sb2 (where, A = Ca, Ba, Sr). The calculated electronic structures of these compounds show charge carrier pockets and heavy light bands near the band edge, which lead to a large power factor. Furthermore, we report large Grüneisen parameters and low phonon group velocity indicating essential strong anharmonicity in these compounds, which resulted in low lattice thermal conductivity. The combination of low thermal conductivity and the excellent transport properties give a high ZT value of ∼1.4-1.9 in CaCd2Sb2 and BaCd2Sb2 at moderate p and n-type doping. Our results indicate that well optimized Cd-based Zintl phase compounds have the potential to match the performance of conventional thermoelectric materials. PMID:26060054

  13. The Lattice and Thermal Radiation Conductivity of Thermal Barrier Coatings: Models and Experiments

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Spuckler, Charles M.

    2010-01-01

    The lattice and radiation conductivity of ZrO2-Y2O3 thermal barrier coatings was evaluated using a laser heat flux approach. A diffusion model has been established to correlate the coating apparent thermal conductivity to the lattice and radiation conductivity. The radiation conductivity component can be expressed as a function of temperature, coating material scattering, and absorption properties. High temperature scattering and absorption of the coating systems can be also derived based on the testing results using the modeling approach. A comparison has been made for the gray and nongray coating models in the plasma-sprayed thermal barrier coatings. The model prediction is found to have a good agreement with experimental observations.

  14. Demystifying umklapp vs normal scattering in lattice thermal conductivity

    NASA Astrophysics Data System (ADS)

    Maznev, A. A.; Wright, O. B.

    2014-11-01

    We discuss the textbook presentation of the concept of umklapp vs normal phonon-phonon scattering processes in the context of lattice thermal conductivity. A simplistic picture, in which the "momentum conservation" in a normal process leads to the conservation of the heat flux, is only valid within the single-velocity Debye model of phonon dispersion. Outside this model, the simple "momentum conservation" argument is demonstrably inaccurate and leads to conceptual confusion. Whether or not an individual scattering event changes the direction of the energy flow is determined by the phonon group velocity, which, unlike the quasimomentum, is a uniquely defined quantity independent of the choice of the primitive cell in reciprocal space. Furthermore, the statement that normal processes do not lead to a finite thermal conductivity when umklapp processes are absent is a statistical statement that applies to a phonon distribution rather than to individual scattering events. It is also important to understand that once umklapp processes are present, both normal and umklapp processes contribute to thermal resistance. A nuanced explanation of the subject would help avoid confusion of the student and establish a connection with cutting edge research.

  15. Lattice thermal conduction in ultra-thin nanocomposites

    NASA Astrophysics Data System (ADS)

    Thomas, Iorwerth O.; Srivastava, G. P.

    2016-06-01

    We have studied the lattice thermal conductivity of Si/Ge periodic nanocomposites (superlattice, nanowire, and nanodot structures) of sample sizes in the range of 30 nm-30 μm, periodicities 1.1 nm and 2.2 nm, with reasonably dirty interfaces, and n-type doping concentration in the range of 1023-1026 m-3. Our calculations employ a judicious combination of ab initio and physically sound semi-empirical methods for detailed calculations of estimates of phonon scattering rates due to anharmonicity and interface formation. Based upon our results we conclude that the formation of ultra-thin nanocomposites in any of the three structures is capable of reducing the conductivity below the alloy limit. This can be explained as a result of combination of the sample length dependence, the on-set of mini-Umklapp three-phonon processes, mass mixing at the interfaces between Si and Ge regions, and the sample doping level.

  16. Compound Refractive Lenses for Thermal Neutron Applications

    SciTech Connect

    Gary, Charles K.

    2013-11-12

    This project designed and built compound refractive lenses (CRLs) that are able to focus, collimate and image using thermal neutrons. Neutrons are difficult to manipulate compared to visible light or even x rays; however, CRLs can provide a powerful tool for focusing, collimating and imaging neutrons. Previous neutron CRLs were limited to long focal lengths, small fields of view and poor resolution due to the materials available and manufacturing techniques. By demonstrating a fabrication method that can produce accurate, small features, we have already dramatically improved the focal length of thermal neutron CRLs, and the manufacture of Fresnel lens CRLs that greatly increases the collection area, and thus efficiency, of neutron CRLs. Unlike a single lens, a compound lens is a row of N lenslets that combine to produce an N-fold increase in the refraction of neutrons. While CRLs can be made from a variety of materials, we have chosen to mold Teflon lenses. Teflon has excellent neutron refraction, yet can be molded into nearly arbitrary shapes. We designed, fabricated and tested Teflon CRLs for neutrons. We demonstrated imaging at wavelengths as short as 1.26 ? with large fields of view and achieved resolution finer than 250 μm which is better than has been previously shown. We have also determined designs for Fresnel CRLs that will greatly improve performance.

  17. Thermal multicomponent lattice Boltzmann model for catalytic reactive flows.

    PubMed

    Kang, Jinfen; Prasianakis, Nikolaos I; Mantzaras, John

    2014-06-01

    Catalytic reactions are of great interest in many applications related to power generation, fuel reforming and pollutant abatement, as well as in various biochemical processes. A recently proposed lattice Boltzmann model for thermal binary-mixture gas flows [J. Kang, N. I. Prasianakis, and J. Mantzaras, Phys. Rev. E. 87, 053304 (2013)] is revisited and extended for the simulation of multispecies flows with catalytic reactions. The resulting model can handle flows with large temperature and concentration gradients. The developed model is presented in detail and validated against a finite volume Navier-Stokes solver in the case of channel-flow methane catalytic combustion. The surface chemistry is treated with a one-step global reaction for the catalytic total oxidation of methane on platinum. In order to take into account thermal effects, the catalytic boundary condition of S. Arcidiacono, J. Mantzaras, and I. V. Karlin [Phys. Rev. E 78, 046711 (2008)] is adapted to account for temperature variations. Speed of sound simulations further demonstrate the physical integrity and unique features of the model. PMID:25019915

  18. Multiblock approach for the passive scalar thermal lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Huang, Rongzong; Wu, Huiying

    2014-04-01

    A multiblock approach for the passive scalar thermal lattice Boltzmann method (TLBM) with multiple-relaxation-time collision scheme is proposed based on the Chapman-Enskog analysis. The interaction between blocks is executed in the moment space directly and an external force term is considered. Theoretical analysis shows that all the nonequilibrium parts of the nonconserved moments should be rescaled, while the nonequilibrium parts of the conserved moments can be calculated directly. Moreover, a local scheme based on the pseudoparticles for computing heat flux is proposed with no need to calculate temperature gradient based on the finite-difference scheme. In order to validate the multiblock approach and local scheme for computing heat flux, thermal Couette flow with wall injection is simulated and good results are obtained, which show that the adoption of the multiblock approach does not deteriorate the convergence rate of TLBM and the local scheme for computing heat flux has second-order convergence rate. Further application of the present approach is the simulation of natural convection in a square cavity with the Rayleigh number up to 109.

  19. Thermal multicomponent lattice Boltzmann model for catalytic reactive flows

    NASA Astrophysics Data System (ADS)

    Kang, Jinfen; Prasianakis, Nikolaos I.; Mantzaras, John

    2014-06-01

    Catalytic reactions are of great interest in many applications related to power generation, fuel reforming and pollutant abatement, as well as in various biochemical processes. A recently proposed lattice Boltzmann model for thermal binary-mixture gas flows [J. Kang, N. I. Prasianakis, and J. Mantzaras, Phys. Rev. E. 87, 053304 (2013), 10.1103/PhysRevE.87.053304] is revisited and extended for the simulation of multispecies flows with catalytic reactions. The resulting model can handle flows with large temperature and concentration gradients. The developed model is presented in detail and validated against a finite volume Navier-Stokes solver in the case of channel-flow methane catalytic combustion. The surface chemistry is treated with a one-step global reaction for the catalytic total oxidation of methane on platinum. In order to take into account thermal effects, the catalytic boundary condition of S. Arcidiacono, J. Mantzaras, and I. V. Karlin [Phys. Rev. E 78, 046711 (2008), 10.1103/PhysRevE.78.046711] is adapted to account for temperature variations. Speed of sound simulations further demonstrate the physical integrity and unique features of the model.

  20. Anomalous pressure dependence of thermal conductivities of large mass ratio compounds

    DOE PAGESBeta

    Lindsay, Lucas R; Broido, David A.; Carrete, Jesus; Mingo, Natalio; Reinecke, Tom L.

    2015-03-27

    The lattice thermal conductivities (k) of binary compound materials are examined as a function of hydrostatic pressure P using a first-principles approach. Compound materials with relatively small mass ratios, such as MgO, show an increase in k with P, consistent with measurements. Conversely, compounds with large mass ratios (e.g., BSb, BAs, BeTe, BeSe) exhibit decreasing with increasing P, a behavior that cannot be understood using simple theories of k. This anomalous P dependence of k arises from the fundamentally different nature of the intrinsic scattering processes for heat-carrying acoustic phonons in large mass ratio compounds compared to those with smallmore » mass ratios. We find this work demonstrates the power of first principles methods for thermal properties and advances the understanding of thermal transport in non-metals.« less

  1. Anomalous pressure dependence of thermal conductivities of large mass ratio compounds

    SciTech Connect

    Lindsay, Lucas R; Broido, David A.; Carrete, Jesus; Mingo, Natalio; Reinecke, Tom L.

    2015-03-27

    The lattice thermal conductivities (k) of binary compound materials are examined as a function of hydrostatic pressure P using a first-principles approach. Compound materials with relatively small mass ratios, such as MgO, show an increase in k with P, consistent with measurements. Conversely, compounds with large mass ratios (e.g., BSb, BAs, BeTe, BeSe) exhibit decreasing with increasing P, a behavior that cannot be understood using simple theories of k. This anomalous P dependence of k arises from the fundamentally different nature of the intrinsic scattering processes for heat-carrying acoustic phonons in large mass ratio compounds compared to those with small mass ratios. We find this work demonstrates the power of first principles methods for thermal properties and advances the understanding of thermal transport in non-metals.

  2. Classial lattice gauge fields with hard thermal loops

    NASA Astrophysics Data System (ADS)

    Hu, Chaoran

    We design, implement, and test a novel lattice program which is aimed at the study of long-range physics in either an electroweak or a quark-gluon plasma at high temperatures. Our approach starts from a separation of short-range (hard) and long-range (soft) modes. Hard modes are represented as particles, while soft modes are represented as lattice fields. Such a treatment is motivated by the dual classical limits of quantum fields as waves and particles in the infrared and ultraviolet limits, respectively. By including these charged particles, we are able to simulate their influence, by the name of 'hard thermal loops' (HTL), on the soft modes. Our investigations are based on two sets of coupled differential equations: Wong equation and Yang- Mills equation. The former describes the evolution of charged particles in the background of a mean field; the latter is the equation of motion of the mean field. The numerical implementation uses a modified leap-frog algorithm with time-centered evaluations. The validity of our approach is evaluated and verified by evidences from both analytical calculations and numerical measurements. Extensive tests have been done by using the U(1) plasma as a test ground. These include the measurement of plasma frequencies, damping rates, dispersion relation, and linear responses. Similar investigations are also performed in the SU(2) case. The results agree very well with those from perturbative calculations. An application where the method developed here has proved to be successful is the study of Chern-Simons number diffusion, which has to do with the baryon number violation responsible for the observed matter-antimatter asymmetry in the Universe. We have measured the diffusion rate and verified a newly proposed scaling law. Other applications such as the study of energy loss, color diffusion in a quark-gluon plasma await further development.

  3. Maximum hardness and minimum polarizability principles through lattice energies of ionic compounds

    NASA Astrophysics Data System (ADS)

    Kaya, Savaş; Kaya, Cemal; Islam, Nazmul

    2016-03-01

    The maximum hardness (MHP) and minimum polarizability (MPP) principles have been analyzed using the relationship among the lattice energies of ionic compounds with their electronegativities, chemical hardnesses and electrophilicities. Lattice energy, electronegativity, chemical hardness and electrophilicity values of ionic compounds considered in the present study have been calculated using new equations derived by some of the authors in recent years. For 4 simple reactions, the changes of the hardness (Δη), polarizability (Δα) and electrophilicity index (Δω) were calculated. It is shown that the maximum hardness principle is obeyed by all chemical reactions but minimum polarizability principles and minimum electrophilicity principle are not valid for all reactions. We also proposed simple methods to compute the percentage of ionic characters and inter nuclear distances of ionic compounds. Comparative studies with experimental sets of data reveal that the proposed methods of computation of the percentage of ionic characters and inter nuclear distances of ionic compounds are valid.

  4. Thermal resistances of solder-boss/potting compound combinations

    NASA Technical Reports Server (NTRS)

    Veilleux, E. D.

    1968-01-01

    Formulas, which can be used as a design tool, are derived to calculate the thermal resistance of solder-boss/potting compound combinations, for different depths of a solder boss, in electronic cordwood modules. Since the solder boss is the heat source, its shape and position will affect the thermal resistance of the surrounding potting compound.

  5. Adaptive bimaterial lattices to mitigate thermal expansion mismatch stresses in satellite structures

    NASA Astrophysics Data System (ADS)

    Toropova, Marina M.; Steeves, Craig A.

    2015-08-01

    Earth-orbiting satellites regularly pass from sunlight to shade and back; these transitions are typically accompanied by significant temperature changes. When adjoining parts of a satellite that are made of different materials are subjected to large temperature changes, thermal mismatch stresses arise that are a function of the temperature change and the difference in coefficients of thermal expansion (CTEs) between the two materials. These thermal stresses are linked to undesirable deformation and, through long-term cycling, fatigue and failure of the structure. This paper describes a type of anisotropic lattice that can serve as a stress-free adaptor between two materials, eliminating thermal mismatch stresses and their concomitant consequences. The lattices consist of planar nonidentical anisotropic bimaterial cells, each designed based on a virtual triangle. Physically the cells consist of a triangle made of material with higher CTE surrounded by a hexagon made of material with lower CTE. Different skew angles of the hexagon make a particular cell and the whole lattice anisotropic. The cells can be designed and combined in a lattice in such a way that one edge of the lattice has CTE that coincides with the CTE of the first part of the structure (substrate 1), while the other edge of the lattice has CTE equal to the CTE of the second part of the structure (substrate 2). If all joints between the parts of each cell, neighbouring cells, and the lattice and the substrates are pinned, the whole structure will be free of thermal stresses. This paper will discuss the fundamental principles governing such lattices, their refinement for special circumstances, and opportunities for improving the structural performance of the lattices. This will be presented coupled to a rational strategy for lattice design.

  6. Lattice anharmonicity and thermal properties of strongly correlated Fe1- x Co x Si alloys

    NASA Astrophysics Data System (ADS)

    Povzner, A. A.; Nogovitsyna, T. A.; Filanovich, A. N.

    2015-10-01

    The temperature dependences of the thermal and elastic properties of strongly correlated metal alloys Fe1- x Co x Si ( x = 0.1, 0.3, 0.5) with different atomic chiralities have been calculated in the framework of the self-consistent thermodynamic model taking into account the influence of lattice anharmonicity. The lattice contributions to the heat capacity and thermal expansion coefficient of the alloys have been determined using the experimental data. It has been demonstrated that the invar effect in the thermal expansion of the lattice observed in the magnetically ordered region of Fe0.7Co0.3Si and Fe0.5Co0.5Si is not related to the lattice anharmonicity, even though its appearance correlates with variations in the atomic chirality.

  7. Ab initio studies on the lattice thermal conductivity of silicon clathrate frameworks II and VIII

    NASA Astrophysics Data System (ADS)

    Härkönen, Ville J.; Karttunen, Antti J.

    2016-01-01

    The lattice thermal conductivities of silicon clathrate frameworks II and VIII are investigated by using ab initio lattice dynamics and an iterative solution of the linearized Boltzmann transport equation (BTE) for phonons. Within the temperature range 100-350 K, the clathrate structures II and VIII were found to have lower lattice thermal conductivity values than the silicon diamond structure (d -Si) by factors of 1/2 and 1/3, respectively. The main reason for the lower lattice thermal conductivity of the clathrate structure II in comparison to d -Si was found to be the harmonic phonon spectra, while in the case of the clathrate structure VIII, the difference is mainly due to the harmonic phonon spectra and partly due to the shorter relaxation times of phonons. In the studied clathrate frameworks, the anharmonic effects have larger impact on the lattice thermal conductivity than the size of the unit cell. For the structure II, the predicted lattice thermal conductivity differs approximately by a factor of 20 from the previous experimental results obtained for a polycrystalline sample at room temperature.

  8. First-principles study of lattice thermal conductivity of Td-WTe2

    NASA Astrophysics Data System (ADS)

    Liu, Gang; Sun, Hong Yi; Zhou, Jian; Li, Qing Fang; Wan, Xian-Gang

    2016-03-01

    The structural and thermal properties of bulk Td-WTe2 have been studied by using first-principles calculations based on the simple Klemens model and an iterative self-consistent method. Both methods show that lattice thermal conductivity is anisotropic, with the highest value in the (001) plane, and lowest one along the c-axis at 300 K. The calculated average thermal conductivity of WTe2 is in agreement with the experimental measurement. The size dependent thermal conductivity shows that nanostructuring of WTe2 can possibly further decrease the lattice thermal conductivity, which can improve the thermoelectric efficiency. Such extremely low thermal conductivity, even much lower than WSe2, makes WTe2 having many potential applications in thermal insulation and thermoelectric materials.

  9. Competing orbital ordering in RVO{sub 3} compounds: High-resolution x-ray diffraction and thermal expansion

    SciTech Connect

    Sage, M. H.; Blake, G. R.; Palstra, T. T. M.; Marquina, C.

    2007-11-15

    We report evidence for the phase coexistence of orbital orderings of different symmetry in RVO{sub 3} compounds with intermediate-size rare earths. Through a study by high-resolution x-ray powder diffraction and thermal expansion, we show that the competing orbital orderings are associated with the magnitude of the VO{sub 6} octahedral tilting and magnetic exchange striction in these compounds and that the phase-separated state is stabilized by lattice strains.

  10. First principles study of lattice thermal conductivity and large isotope effect in materials

    NASA Astrophysics Data System (ADS)

    Broido, David; Lindsay, Lucas; Reinecke, Tom

    2014-03-01

    The isotope effect--the percent enhancement to a material's lattice thermal conductivity, k, with isotopic purification--depends on the interplay between phonon-isotope and phonon-phonon scattering. Diamond is known to have the largest measured room temperature (RT) isotope effect of any bulk crystal, achieving a k enhancement of 50%. Using an ab initioBoltzmann transport equation approach, we have identified several other materials with far larger RT isotope effects. In particular, we find that germanium carbide (GeC) and beryllium selenide (BeSe) have RT isotope effects of 450%, almost an order of magnitude higher than that in diamond. Isotopic purification in these materials gives surprisingly high intrinsic RT k values, over 1500 Wm-1K-1 for GeC and over 600 Wm-1 K-1 for BeSe, well above those of the best metals. These large values stem from fundamental material properties that give both enhanced phonon scattering by isotopes and weak anharmonic phonon-phonon scattering. The physical insights discussed in this work provide guidance for efficient manipulation of thermal transport properties of compound semiconductors through isotopic modification. This work was supported by ONR, DARPA and NSF.

  11. Lattice Thermal Conductivity from Atomistic Simulations: ZrB2 and HfB2

    NASA Technical Reports Server (NTRS)

    Lawson, John W.; Daw, Murray S.; Bauschlicher, Charles W.

    2012-01-01

    Ultra high temperature ceramics (UHTC) including ZrB2 and HfB2 have a number of properties that make them attractive for applications in extreme environments. One such property is their high thermal conductivity. Computational modeling of these materials will facilitate understanding of fundamental mechanisms, elucidate structure-property relationships, and ultimately accelerate the materials design cycle. Progress in computational modeling of UHTCs however has been limited in part due to the absence of suitable interatomic potentials. Recently, we developed Tersoff style parameterizations of such potentials for both ZrB2 and HfB2 appropriate for atomistic simulations. As an application, Green-Kubo molecular dynamics simulations were performed to evaluate the lattice thermal conductivity for single crystals of ZrB2 and HfB2. The atomic mass difference in these binary compounds leads to oscillations in the time correlation function of the heat current, in contrast to the more typical monotonic decay seen in monoatomic materials such as Silicon, for example. Results at room temperature and at elevated temperatures will be reported.

  12. Lattice thermal conductivity of UO2 using ab-initio and classical molecular dynamics

    NASA Astrophysics Data System (ADS)

    Kim, Hyoungchul; Kim, Moo Hwan; Kaviany, Massoud

    2014-03-01

    We applied the non-equilibrium ab-initio molecular dynamics and predict the lattice thermal conductivity of the pristine uranium dioxide for up to 2000 K. We also use the equilibrium classical molecular dynamics and heat-current autocorrelation decay theory to decompose the lattice thermal conductivity into acoustic and optical components. The predicted optical phonon transport is temperature independent and small, while the acoustic component follows the Slack relation and is in good agreement with the limited single-crystal experimental results. Considering the phonon grain-boundary and pore scatterings, the effective lattice thermal conductivity is reduced, and we show it is in general agreement with the sintered-powder experimental results. The charge and photon thermal conductivities are also addressed, and we find small roles for electron, surface polaron, and photon in the defect-free structures and for temperatures below 1500 K.

  13. Lattice thermal conductivity of UO{sub 2} using ab-initio and classical molecular dynamics

    SciTech Connect

    Kim, Hyoungchul; Kim, Moo Hwan; Kaviany, Massoud

    2014-03-28

    We applied the non-equilibrium ab-initio molecular dynamics and predict the lattice thermal conductivity of the pristine uranium dioxide for up to 2000 K. We also use the equilibrium classical molecular dynamics and heat-current autocorrelation decay theory to decompose the lattice thermal conductivity into acoustic and optical components. The predicted optical phonon transport is temperature independent and small, while the acoustic component follows the Slack relation and is in good agreement with the limited single-crystal experimental results. Considering the phonon grain-boundary and pore scatterings, the effective lattice thermal conductivity is reduced, and we show it is in general agreement with the sintered-powder experimental results. The charge and photon thermal conductivities are also addressed, and we find small roles for electron, surface polaron, and photon in the defect-free structures and for temperatures below 1500 K.

  14. Elastic and Thermal Properties of Silicon Compounds from First-Principles Calculations

    NASA Astrophysics Data System (ADS)

    Hou, Haijun; Zhu, H. J.; Cheng, W. H.; Xie, L. H.

    2016-07-01

    The structural and elastic properties of V-Si (V3Si, VSi2, V5Si3, and V6Si5) compounds are studied by using first-principles method. The calculated equilibrium lattice parameters and formation enthalpy are in good agreement with the available experimental data and other theoretical results. The calculated results indicate that the V-Si compounds are mechanically stable. Elastic properties including bulk modulus, shear modulus, Young's modulus, and Poisson's ratio are also obtained. The elastic anisotropies of V-Si compounds are investigated via the three-dimensional (3D) figures of directional dependences of reciprocals of Young's modulus. Finally, based on the quasi-harmonic Debye model, the internal energy, Helmholtz free energy, entropy, heat capacity, thermal expansion coefficient, Grüneisen parameter, and Debye temperature of V-Si compounds have been calculated.

  15. First-principles calculation of the lattice thermal conductivity of the lower mantle

    NASA Astrophysics Data System (ADS)

    Stackhouse, S.; Stixrude, L. P.; Karki, B. B.; Liu, T.; Todd, B.

    2015-12-01

    The thermal conductivity of the lower mantle has important implications for the thermal structure of the Earth's interior. Estimates of the thermal conductivity of the most abundant phases, at core-mantle boundary conditions vary widely. We performed ab initio simulations to determine the lattice thermal conductivity of MgSiO3 perovskite, finding a value of about 7 ± 1 W m-1 K-1 at core-mantle boundary conditions, consistent with geophysical constraints for the thermal state at the base of the mantle. We find that lattice thermal conductivity depends strongly on pressure, explaining the dynamical stability of super-plumes, but weakly with temperature and composition. Our results show evidence of saturation, at lower mantle temperatures, as the phonon mean free path approaches the interatomic spacing. Combining our results with seismic tomography, we predict large lateral variations in the heat-flux from the core that could have important implications for core dynamics.

  16. Lattice dynamics and thermal conductivity of calcium fluoride via first-principles investigation

    NASA Astrophysics Data System (ADS)

    Qi, Yuan-Yuan; Zhang, Tian; Cheng, Yan; Chen, Xiang-Rong; Wei, Dong-Qing; Cai, Ling-Cang

    2016-03-01

    The lattice thermal conductivity of CaF2 is accurately computed from a first-principles theoretical approach based on an iterative solution of the Boltzmann transport equation. The second- and third-order interatomic force constants are generated from a real-space finite-difference supercell approach. Then, the force constants for both the second- and third-order potential interactions are used to calculate the lattice thermal conductivity and related physical quantities of CaF2 at temperatures ranging from 30 K to 1500 K. The obtained lattice thermal conductivity 8.6 W/(m.K) for CaF2 at room temperature agrees better with the experimental value than other theoretical data, demonstrating the promise of this parameter-free approach in providing precise descriptions of the lattice thermal conductivity of materials. The obtained dielectric parameters and phonon spectrum of CaF2 accord well with available data. Meanwhile, the temperature dependence curves of the lattice thermal conductivity, heat capacity, and phonon mean free path are presented.

  17. Size and Temperature Effect on Thermal Expansion Coefficient and Lattice Parameter of Nanomaterials

    NASA Astrophysics Data System (ADS)

    Kumar, Raghuvesh; Sharma, Geeta; Kumar, Munish

    2013-10-01

    A simple theoretical model is developed to study the effect of size and temperature on the coefficient of thermal expansion and lattice parameter of nanomaterials. We have studied the size dependence of thermal expansion coefficient of Pb, Ag and Zn in different shape viz. spherical, nanowire and nanofilm. A good agreement between theory and available experimental data confirmed the model predictions. We have used these results to study the temperature dependence of lattice parameter for different size and also included the results of bulk materials. The temperature dependence of lattice parameter of Zn nanowire and Ag nanowire are found to present a good agreement with the experimental data. We have also computed the temperature and size dependence of lattice parameter of Se and Pb for different shape viz. spherical, nanowire and nanofilm. The results are discussed in the light of recent research on nanomaterials.

  18. Impact of Lone-Pair Electrons on Thermal Conductivity in CuSbS2 Compound

    NASA Astrophysics Data System (ADS)

    Du, Baoli; Zhang, Ruizhi; Chen, Kan; Reece, Michael; Material research institute Team

    Compounds with intrinsically low lattice thermal conductivity are of practical importance for thermoelectric energy conversion. Recent studies suggest that s2 lone pair orbital electrons are a key contributing factor to the anomalously low lattice thermal conductivity of chalcogenide compounds that contain a nominally trivalent group VA element. CuSbS2 has an orthorhombic structure with space group Pnma. The pyramidal SbS5 units are separated by CuS4 tetrahedron so that the base of the square pyramidal units are aligned to face one another, thus directing the Sb lone pair electron density into the void separating the SbS5 units. Different from tetrahedrite, all the Cu atoms are bonded in the CuS4 tetrahedron. So, it has a perfect structure to study the influence of electron lone pair on thermal conductivity without the impact from trigonal coordinated Cu. In this work, the trivalent transition metal atom Fe and IIIA atom Ga without lone-pair electrons were chosen to substitute Sb in CuSbS2. The changes in the bonding environment by foreign atoms and their influences on the thermal properties have been studied and correlated. Marie Curie International Incoming Fellowship of the European Community Human Potential Program under Contract No. PIIF-GA-2013-622847.

  19. Nanoscale size dependence parameters on lattice thermal conductivity of Wurtzite GaN nanowires

    SciTech Connect

    Mamand, S.M.; Omar, M.S.; Muhammad, A.J.

    2012-05-15

    Graphical abstract: Temperature dependence of calculated lattice thermal conductivity of Wurtzite GaN nanowires. Highlights: Black-Right-Pointing-Pointer A modified Callaway model is used to calculate lattice thermal conductivity of Wurtzite GaN nanowires. Black-Right-Pointing-Pointer A direct method is used to calculate phonon group velocity for these nanowires. Black-Right-Pointing-Pointer 3-Gruneisen parameter, surface roughness, and dislocations are successfully investigated. Black-Right-Pointing-Pointer Dislocation densities are decreases with the decrease of wires diameter. -- Abstract: A detailed calculation of lattice thermal conductivity of freestanding Wurtzite GaN nanowires with diameter ranging from 97 to 160 nm in the temperature range 2-300 K, was performed using a modified Callaway model. Both longitudinal and transverse modes are taken into account explicitly in the model. A method is used to calculate the Debye and phonon group velocities for different nanowire diameters from their related melting points. Effect of Gruneisen parameter, surface roughness, and dislocations as structure dependent parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the experimentally measured curves. It was observed that Gruneisen parameter will decrease with decreasing nanowire diameters. Scattering of phonons is assumed to be by nanowire boundaries, imperfections, dislocations, electrons, and other phonons via both normal and Umklapp processes. Phonon confinement and size effects as well as the role of dislocation in limiting thermal conductivity are investigated. At high temperatures and for dislocation densities greater than 10{sup 14} m{sup -2} the lattice thermal conductivity would be limited by dislocation density, but for dislocation densities less than 10{sup 14} m{sup -2}, lattice thermal conductivity would be independent of that.

  20. Impact of internal crystalline boundaries on lattice thermal conductivity: Importance of boundary structure and spacing

    SciTech Connect

    Aghababaei, Ramin Anciaux, Guillaume; Molinari, Jean-François

    2014-11-10

    The low thermal conductivity of nano-crystalline materials is commonly explained via diffusive scattering of phonons by internal boundaries. In this study, we have quantitatively studied phonon-crystalline boundaries scattering and its effect on the overall lattice thermal conductivity of crystalline bodies. Various types of crystalline boundaries such as stacking faults, twins, and grain boundaries have been considered in FCC crystalline structures. Accordingly, the specularity coefficient has been determined for different boundaries as the probability of the specular scattering across boundaries. Our results show that in the presence of internal boundaries, the lattice thermal conductivity can be characterized by two parameters: (1) boundary spacing and (2) boundary excess free volume. We show that the inverse of the lattice thermal conductivity depends linearly on a non-dimensional quantity which is the ratio of boundary excess free volume over boundary spacing. This shows that phonon scattering across crystalline boundaries is mainly a geometrically favorable process rather than an energetic one. Using the kinetic theory of phonon transport, we present a simple analytical model which can be used to evaluate the lattice thermal conductivity of nano-crystalline materials where the ratio can be considered as an average density of excess free volume. While this study is focused on FCC crystalline materials, where inter-atomic potentials and corresponding defect structures have been well studied in the past, the results would be quantitatively applicable for semiconductors in which heat transport is mainly due to phonon transport.

  1. Reduced thermal conductivity in niobium-doped calcium-manganate compounds for thermoelectric applications

    SciTech Connect

    Graff, Ayelet; Amouyal, Yaron

    2014-11-03

    Reduction of thermal conductivity is essential for obtaining high energy conversion efficiency in thermoelectric materials. We report on significant reduction of thermal conductivity in niobium-doped CaO(CaMnO{sub 3}){sub m} compounds for thermoelectric energy harvesting due to introduction of extra CaO-planes in the CaMnO{sub 3}-base material. We measure the thermal conductivities of the different compounds applying the laser flash analysis at temperatures between 300 and 1000 K, and observe a remarkable reduction in thermal conductivity with increasing CaO-planar density, from a value of 3.7 W·m{sup −1}K{sup −1} for m = ∞ down to 1.5 W·m{sup −1}K{sup −1} for m = 1 at 400 K. This apparent correlation between thermal conductivity and CaO-planar density is elucidated in terms of boundary phonon scattering, providing us with a practical way to manipulate lattice thermal conductivity via microstructural modifications.

  2. Lattice thermal conductivity of disordered NiPd and NiPt alloys

    NASA Astrophysics Data System (ADS)

    Alam, Aftab; Mookerjee, Abhijit

    2006-05-01

    Numerical calculations of lattice thermal conductivity are reported for the binary alloys NiPd and NiPt. The present work is a continuation of an earlier paper by us (Alam and Mookerjee 2005 Phys. Rev. B 72 214207), which developed a theoretical framework for the calculation of configuration-averaged lattice thermal conductivity and thermal diffusivity in disordered alloys. The formulation was based on the augmented space theorem (Mookerjee 1973 J. Phys. C: Solid State Phys. 6 L205) combined with a scattering diagram technique. In this paper we shall show the dependence of the lattice thermal conductivity on a series of variables like phonon frequency, temperature and alloy composition. The temperature dependence of κ(T) and its relation to the measured thermal conductivity is discussed. The concentration dependence of κ appears to justify the notion of a minimum thermal conductivity as discussed by Kittel, Slack and others (Kittel 1948 Phys. Rev. 75 972, Brich and Clark 1940 Am. J. Sci. 238 613; Slack 1979 Solid State Physics vol 34, ed H Ehrenreich, F Seitz and D Turnbull (New York: Academic) p 1). We also study the frequency and composition dependence of the thermal diffusivity averaged over modes. A numerical estimate of this quantity gives an idea about the location of the mobility edge and the fraction of states in the frequency spectrum which is delocalized.

  3. Estimation of the isotope effect on the lattice thermal conductivity of group IV and group III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Morelli, D. T.; Heremans, J. P.; Slack, G. A.

    2002-11-01

    The isotope effect on the lattice thermal conductivity for group IV and group III-V semiconductors is calculated using the Debye-Callaway model modified to include both transverse and longitudinal phonon modes explicitly. The frequency and temperature dependences of the normal and umklapp phonon-scattering rates are kept the same for all compounds. The model requires as adjustable parameters only the longitudinal and transverse phonon Grüneisen constants and the effective sample diameter. The model can quantitatively account for the observed isotope effect in diamond and germanium but not in silicon. The magnitude of the isotope effect is predicted for silicon carbide, boron nitride, and gallium nitride. In the case of boron nitride the predicted increase in the room-temperature thermal conductivity with isotopic enrichment is in excess of 100%. Finally, a more general method of estimating normal phonon-scattering rate coefficients for other types of solids is presented.

  4. Positron spectroscopy of point defects in the skyrmion-lattice compound MnSi

    PubMed Central

    Reiner, Markus; Bauer, Andreas; Leitner, Michael; Gigl, Thomas; Anwand, Wolfgang; Butterling, Maik; Wagner, Andreas; Kudejova, Petra; Pfleiderer, Christian; Hugenschmidt, Christoph

    2016-01-01

    Outstanding crystalline perfection is a key requirement for the formation of new forms of electronic order in a vast number of widely different materials. Whereas excellent sample quality represents a standard claim in the literature, there are, quite generally, no reliable microscopic probes to establish the nature and concentration of lattice defects such as voids, dislocations and different species of point defects on the level relevant to the length and energy scales inherent to these new forms of order. Here we report an experimental study of the archetypical skyrmion-lattice compound MnSi, where we relate the characteristic types of point defects and their concentration to the magnetic properties by combining different types of positron spectroscopy with ab-initio calculations and bulk measurements. We find that Mn antisite disorder broadens the magnetic phase transitions and lowers their critical temperatures, whereas the skyrmion lattice phase forms for all samples studied underlining the robustness of this topologically non-trivial state. Taken together, this demonstrates the unprecedented sensitivity of positron spectroscopy in studies of new forms of electronic order. PMID:27388948

  5. Positron spectroscopy of point defects in the skyrmion-lattice compound MnSi

    NASA Astrophysics Data System (ADS)

    Reiner, Markus; Bauer, Andreas; Leitner, Michael; Gigl, Thomas; Anwand, Wolfgang; Butterling, Maik; Wagner, Andreas; Kudejova, Petra; Pfleiderer, Christian; Hugenschmidt, Christoph

    2016-07-01

    Outstanding crystalline perfection is a key requirement for the formation of new forms of electronic order in a vast number of widely different materials. Whereas excellent sample quality represents a standard claim in the literature, there are, quite generally, no reliable microscopic probes to establish the nature and concentration of lattice defects such as voids, dislocations and different species of point defects on the level relevant to the length and energy scales inherent to these new forms of order. Here we report an experimental study of the archetypical skyrmion-lattice compound MnSi, where we relate the characteristic types of point defects and their concentration to the magnetic properties by combining different types of positron spectroscopy with ab-initio calculations and bulk measurements. We find that Mn antisite disorder broadens the magnetic phase transitions and lowers their critical temperatures, whereas the skyrmion lattice phase forms for all samples studied underlining the robustness of this topologically non-trivial state. Taken together, this demonstrates the unprecedented sensitivity of positron spectroscopy in studies of new forms of electronic order.

  6. Ultralow lattice thermal conductivity in topological insulator TlBiSe2

    NASA Astrophysics Data System (ADS)

    Ding, Guangqian; Carrete, Jesús; Li, Wu; Gao, G. Y.; Yao, Kailun

    2016-06-01

    We present ab-initio calculations of the phonon thermal transport properties of topological insulator TlBiSe2. Our results point to a very low lattice thermal conductivity, comparable or lower than those of some popular good thermoelectric materials. Furthermore, we find a slight thermal anisotropy between the in-plane and cross-plane directions in TlBiSe2, markedly smaller than those of van-der-Waals topological insulators explored so far. These conclusions are confirmed and explained by comprehensive analysis of the phonon spectrum of TlBiSe2. The combination of ultralow lattice thermal conductivity and small anisotropy makes TlBiSe2 a promising candidate for thermoelectric applications.

  7. Models for mean bonding length, melting point and lattice thermal expansion of nanoparticle materials

    SciTech Connect

    Omar, M.S.

    2012-11-15

    Graphical abstract: Three models are derived to explain the nanoparticles size dependence of mean bonding length, melting temperature and lattice thermal expansion applied on Sn, Si and Au. The following figures are shown as an example for Sn nanoparticles indicates hilly applicable models for nanoparticles radius larger than 3 nm. Highlights: ► A model for a size dependent mean bonding length is derived. ► The size dependent melting point of nanoparticles is modified. ► The bulk model for lattice thermal expansion is successfully used on nanoparticles. -- Abstract: A model, based on the ratio number of surface atoms to that of its internal, is derived to calculate the size dependence of lattice volume of nanoscaled materials. The model is applied to Si, Sn and Au nanoparticles. For Si, that the lattice volume is increases from 20 Å{sup 3} for bulk to 57 Å{sup 3} for a 2 nm size nanocrystals. A model, for calculating melting point of nanoscaled materials, is modified by considering the effect of lattice volume. A good approach of calculating size-dependent melting point begins from the bulk state down to about 2 nm diameter nanoparticle. Both values of lattice volume and melting point obtained for nanosized materials are used to calculate lattice thermal expansion by using a formula applicable for tetrahedral semiconductors. Results for Si, change from 3.7 × 10{sup −6} K{sup −1} for a bulk crystal down to a minimum value of 0.1 × 10{sup −6} K{sup −1} for a 6 nm diameter nanoparticle.

  8. Mode dependent lattice thermal conductivity of single layer graphene

    SciTech Connect

    Wei, Zhiyong; Yang, Juekuan; Bi, Kedong; Chen, Yunfei

    2014-10-21

    Molecular dynamics simulation is performed to extract the phonon dispersion and phonon lifetime of single layer graphene. The mode dependent thermal conductivity is calculated from the phonon kinetic theory. The predicted thermal conductivity at room temperature exhibits important quantum effects due to the high Debye temperature of graphene. But the quantum effects are reduced significantly when the simulated temperature is as high as 1000 K. Our calculations show that out-of-plane modes contribute about 41.1% to the total thermal conductivity at room temperature. The relative contribution of out-of-plane modes has a little decrease with the increase of temperature. Contact with substrate can reduce both the total thermal conductivity of graphene and the relative contribution of out-of-plane modes, in agreement with previous experiments and theories. Increasing the coupling strength between graphene and substrate can further reduce the relative contribution of out-of-plane modes. The present investigations also show that the relative contribution of different mode phonons is not sensitive to the grain size of graphene. The obtained phonon relaxation time provides useful insight for understanding the phonon mean free path and the size effects in graphene.

  9. CH4 dissociation on Ni(111): a quantum dynamics study of lattice thermal motion.

    PubMed

    Shen, Xiangjian; Zhang, Zhaojun; Zhang, Dong H

    2015-10-14

    Lattice thermal motion is of great importance because it has a significant effect on molecule activation on metal surfaces. Here, we present an in-depth quantum dynamics study of lattice thermal motion for methane dissociation on some static distorted Ni(111) surfaces based on an accurate, fourteen-dimensional potential energy surface fitted to ∼10(5)ab initio energy points. Our study reproduces the tendency that the sticking probability of ground state methane increases (decreases) as the lattice atom moves upward (downward), and thus represents the first validation of the applicability of the energy-shifting scheme to polyatomic molecular gas-surface reactions. Furthermore, we improve on the linear model proposed by Jackson's group and introduce a new model that is applicable to a broad range of surface temperatures. PMID:26364792

  10. Insight into lattice thermal impedance via equilibrium molecular dynamics: case study on Al

    NASA Astrophysics Data System (ADS)

    Evteev, Alexander V.; Levchenko, Elena V.; Momenzadeh, Leila; Belova, Irina V.; Murch, Graeme E.

    2016-02-01

    Using results of equilibrium molecular dynamics simulation in conjunction with the Green-Kubo formalism, we present a general treatment of thermal impedance of a crystal lattice with a monatomic unit cell. The treatment is based on an analytical expression for the heat current autocorrelation function which reveals, in a monatomic lattice, an energy gap between the origin of the phonon states and the beginning of the energy spectrum of the so-called acoustic short-range phonon modes. Although, we consider here the f.c.c. Al model as a case example, the analytical expression is shown to be consistent for different models of elemental f.c.c. crystals over a wide temperature range. Furthermore, we predict a frequency 'window' where the thermal waves can be generated in a monatomic lattice by an external periodic temperature perturbation.

  11. Lattice dynamics of the mixed-conducting intermetallic compound,. beta. -LiAl

    SciTech Connect

    Brun, T.O.; Robinson, J.E.; Susman, S.; Mildner, D.F.R.; Dejus, R.; Skoeld K.

    1983-04-01

    The intermetallic compound, ..beta..-LiAl, that crystallizes in the uncommon Zintl structure is a mixed-conducting electrode and has many unusual properties pointing to the existence of unusual bonding in the semi-metallic compound. In order to elucidate the nature of the bonding in LiAl, we have studied the lattice dynamics of ..beta..-LiAl by inelastic neutron scattering. Results for the phonon dispersion curves have been obtained for the principal symmetry directions. A force constant fit to the results indicates that the Al-Al force constants are unusually large. Pair potentials were constructed by conventional pseudopotential calculations. The pair interactions favoring the Zintl structure were used to compute phonon dispersion curves. Good agreement between theory and experiment can be obtained for the acoustic branches.

  12. Thermal diffusivity of oxide perovskite compounds at elevated temperature

    NASA Astrophysics Data System (ADS)

    Hofmeister, Anne M.

    2010-05-01

    The phonon component of thermal diffusivity (D) for eleven compounds (synthetic SrTiO3, SrTiO3:Fe3+, BaTiO3, KTaO3, KNbO3, NdGaO3, YAlO3, YAlO3:Tm, LaAlO3, La0.29Sr0.66Al0.65Ta0.35O3, and natural Ca1.01Mn0.001Fe0.007Ti0.99O3) with various perovskite structures was measured from ambient temperature (T) up to ˜2000 K using contact-free, laser-flash analysis, from which effects of ballistic radiative transfer were removed. Structural transitions (e.g., orthorhombic to tetragonal) below 800 K were manifest as sharp steps in 1/D. Above 800 K, structural transitions occur over intervals of ˜150 K. Similarly broad peaks accompany changes from colorless to black, attributable to partial reduction in Ti, Nb, or Ta from contact with graphite coatings. Otherwise, D decreases with increasing T and, if substitutional disorder exists, approaches a constant (Dsat) near 1600 K. Our data are best described as D-1 following a low order polynomial in T. Ordered, cubic perovskites occupy a single trend for D(T )-1, defining the contribution of the ideal lattice. Distortion, disorder, and polymorphism affect D-1 in a manner that is consistent with the damped harmonic oscillator-phonon gas model which relates phonon lifetimes to infrared peak widths. Calculated D-values at ambient and high T agree with measurements. The behavior of D is simple compared to that of thermal conductivity, k =ρCPD, where ρ is density and CP is heat capacity. Combining our data with cryogenic measurements of YAlO3 and LaAlO3 shows that D-1 depends on T similarly to CP, consistent with phonon lifetime depending on the density of states but, the best description for D-1(T) is a proportionality to αT from ˜0 K up to the limit of measurements, where α is thermal expansivity, a strongly anharmonic property. At low T, D-1 due to phonon scattering follows that of CP, generally∝T3, so klat=k0+k1T. Defects being present preclude scattering at sample walls, adding a small constant D0-1 ˜0.0001 mm-2 s as T

  13. Understanding Nanostructuring Processes in Thermoelectrics and Their Effects on Lattice Thermal Conductivity.

    PubMed

    Wu, Di; Zhao, Li-Dong; Zheng, Fengshan; Jin, Lei; Kanatzidis, Mercouri G; He, Jiaqing

    2016-04-01

    Cooling rates of molten PbTe-CdTe compositions play a determinant role in defining the nanoscale precipitate size distribution and the corresponding number densities, resulting in distinct trends of lattice thermal conductivity evolution with varying CdTe fractions. PMID:26848933

  14. Iodine doping effects on the lattice thermal conductivity of oxidized polyacetylene nanofibers

    SciTech Connect

    Bi, Kedong E-mail: kedongbi@seu.edu.cn; Weathers, Annie; Pettes, Michael T.; Shi, Li E-mail: kedongbi@seu.edu.cn; Matsushita, Satoshi; Akagi, Kazuo; Goh, Munju

    2013-11-21

    Thermal transport in oxidized polyacetylene (PA) nanofibers with diameters in the range between 74 and 126 nm is measured with the use of a suspended micro heater device. With the error due to both radiation and contact thermal resistance corrected via a differential measurement procedure, the obtained thermal conductivity of oxidized PA nanofibers varies in the range between 0.84 and 1.24 W m{sup −1} K{sup −1} near room temperature, and decreases by 40%–70% after iodine doping. It is also found that the thermal conductivity of oxidized PA nanofibers increases with temperature between 100 and 350 K. Because of exposure to oxygen during sample preparation, the PA nanofibers are oxidized to be electrically insulating before and after iodine doping. The measurement results reveal that iodine doping can result in enhanced lattice disorder and reduced lattice thermal conductivity of PA nanofibers. If the oxidation issue can be addressed via further research to increase the electrical conductivity via doping, the observed suppressed lattice thermal conductivity in doped polymer nanofibers can be useful for the development of such conducting polymer nanostructures for thermoelectric energy conversion.

  15. Application of the S=1 underscreened Anderson lattice model to Kondo uranium and neptunium compounds

    NASA Astrophysics Data System (ADS)

    Thomas, Christopher; da Rosa Simões, Acirete S.; Iglesias, J. R.; Lacroix, C.; Perkins, N. B.; Coqblin, B.

    2011-01-01

    Magnetic properties of uranium and neptunium compounds showing the coexistence of the Kondo screening effect and ferromagnetic order are investigated within the Anderson lattice Hamiltonian with a two-fold degenerate f level in each site, corresponding to 5f2 electronic configuration with S=1 spins. A derivation of the Schrieffer-Wolff transformation is presented and the resulting Hamiltonian has an effective f-band term, in addition to the regular exchange Kondo interaction between the S=1 f spins and the s=1/2 spins of the conduction electrons. The resulting effective Kondo lattice model can describe both the Kondo regime and a weak delocalization of the 5f electrons. Within this model we compute the Kondo and Curie temperatures as a function of model parameters, namely the Kondo exchange interaction constant JK, the magnetic intersite exchange interaction JH, and the effective f bandwidth. We deduce, therefore, a phase diagram of the model which yields the coexistence of the Kondo effect and ferromagnetic ordering and also accounts for the pressure dependence of the Curie temperature of uranium compounds such as UTe.

  16. Decomposition model for phonon thermal conductivity of a monatomic lattice

    NASA Astrophysics Data System (ADS)

    Evteev, Alexander V.; Momenzadeh, Leila; Levchenko, Elena V.; Belova, Irina V.; Murch, Graeme E.

    2014-12-01

    An analytical treatment of decomposition of the phonon thermal conductivity of a crystal with a monatomic unit cell is developed on the basis of a two-stage decay of the heat current autocorrelation function observed in molecular dynamics simulations. It is demonstrated that the contributions from the acoustic short- and long-range phonon modes to the total phonon thermal conductivity can be presented in the form of simple kinetic formulas, consisting of products of the heat capacity and the average relaxation time of the considered phonon modes as well as the square of the average phonon velocity. On the basis of molecular dynamics calculations of the heat current autocorrelation function, this treatment allows for a self-consistent numerical evaluation of the aforementioned variables. In addition, the presented analysis allows, within the Debye approximation, for the identification of the temperature range where classical molecular dynamics simulations can be employed for the prediction of phonon thermal transport properties. As a case example, Cu is considered.

  17. Lattice thermal conductivity of multi-component alloys

    DOE PAGESBeta

    Caro, Magdalena; Béland, Laurent K.; Samolyuk, German D.; Stoller, Roger E.; Caro, Alfredo

    2015-06-12

    High entropy alloys (HEA) have unique properties including the potential to be radiation tolerant. These materials with extreme disorder could resist damage because disorder, stabilized by entropy, is the equilibrium thermodynamic state. Disorder also reduces electron and phonon conductivity keeping the damage energy longer at the deposition locations, eventually favoring defect recombination. In the short time-scales related to thermal spikes induced by collision cascades, phonons become the relevant energy carrier. In this paper, we perform a systematic study of phonon thermal conductivity in multiple component solid solutions represented by Lennard-Jones (LJ) potentials. We explore the conditions that minimize phonon meanmore » free path via extreme alloy complexity, by varying the composition and the elements (differing in mass, atomic radii, and cohesive energy). We show that alloy complexity can be tailored to modify the scattering mechanisms that control energy transport in the phonon subsystem. Finally, our analysis provides a qualitative guidance for the selection criteria used in the design of HEA alloys with low phonon thermal conductivity.« less

  18. Lattice thermal conductivity of multi-component alloys

    SciTech Connect

    Caro, Magdalena; Béland, Laurent K.; Samolyuk, German D.; Stoller, Roger E.; Caro, Alfredo

    2015-06-12

    High entropy alloys (HEA) have unique properties including the potential to be radiation tolerant. These materials with extreme disorder could resist damage because disorder, stabilized by entropy, is the equilibrium thermodynamic state. Disorder also reduces electron and phonon conductivity keeping the damage energy longer at the deposition locations, eventually favoring defect recombination. In the short time-scales related to thermal spikes induced by collision cascades, phonons become the relevant energy carrier. In this paper, we perform a systematic study of phonon thermal conductivity in multiple component solid solutions represented by Lennard-Jones (LJ) potentials. We explore the conditions that minimize phonon mean free path via extreme alloy complexity, by varying the composition and the elements (differing in mass, atomic radii, and cohesive energy). We show that alloy complexity can be tailored to modify the scattering mechanisms that control energy transport in the phonon subsystem. Finally, our analysis provides a qualitative guidance for the selection criteria used in the design of HEA alloys with low phonon thermal conductivity.

  19. Thermal decomposition studies of halogenated organic compounds

    SciTech Connect

    Michael, J.V.; Kumaran, S.S.

    1997-06-01

    Thermal decomposition results for CCl{sub 4}, CHCl{sub 3}, CH{sub 2}Cl{sub 2}, CH{sub 3}Cl, C{sub 3}H{sub 3}Cl, CFCl{sub 3}, CF{sub 2}Cl{sub 2}, CF{sub 3}Cl, CF{sub 2}HCl, CF{sub 3}I, CH{sub 3}I, C{sub 2}H{sub 5}I, C{sub 6}H{sub 5}I, and CCl{sub 2}O are presented. The results were obtained by shock tube techniques coupled with optical spectroscopic detection of transient species formed from dissociation. The method is illustrated with the CH{sub 3}I (+ Kr) {yields} CH{sub 3} + I (+ Kr) reaction where decomposition was monitored using I-atomic resonance absorption spectrometry (ARAS). Modern unimolecular rate theoretical analysis has been carried out on the present cases, and the conclusions from these calculations are discussed. Lastly, the possible destruction of halo-organics by incineration is considered and some implications are discussed.

  20. Lattice thermal conductivity of MgO at conditions of Earth’s interior

    PubMed Central

    Tang, Xiaoli; Dong, Jianjun

    2010-01-01

    Thermal conductivity of the Earth’s lower mantle greatly impacts the mantle convection style and affects the heat conduction from the core to the mantle. Direct laboratory measurement of thermal conductivity of mantle minerals remains a technical challenge at the pressure-temperature (P-T) conditions relevant to the lower mantle, and previously estimated values are extrapolated from low P-T data based on simple empirical thermal transport models. By using a numerical technique that combines first-principles electronic structure theory and Peierls–Boltzmann transport theory, we predict the lattice thermal conductivity of MgO, previously used to estimate the thermal conductivity in the Earth, at conditions from ambient to the core-mantle boundary (CMB). We show that our first-principles technique provides a realistic model for the P-T dependence of lattice thermal conductivity of MgO at conditions from ambient to the CMB, and we propose thermal conductivity profiles of MgO in the lower mantle based on geotherm models. The calculated conductivity increases from 15 –20 W/K-m at the 670 km seismic discontinuity to 40 –50 W/K-m at the CMB. This large depth variation in calculated thermal conductivity should be included in models of mantle convection, which has been traditionally studied based on the assumption of constant conductivity. PMID:20176973

  1. Inelastic neutron scattering studies of the spin and lattice dynamics in iron arsenide compounds.

    SciTech Connect

    Osborn, R.; Rosenkranz, S.; Goremychkin, E. A.; Christianson, A. D.

    2009-03-20

    Although neutrons do not couple directly to the superconducting order parameter, they have nevertheless played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Measurements of the spin and lattice dynamics have been performed on non-superconducting 'parent' compounds based on the LaFeAsO ('1111') and BaFe{sub 2}As{sub 2} ('122') crystal structures, and on electron and hole-doped superconducting compounds, using both polycrystalline and single crystal samples. Neutron measurements of the phonon density-of-state, subsequently supported by single crystal inelastic X-ray scattering, are in good agreement with ab initio calculations, provided the magnetism of the iron atoms is taken into account. However, when combined with estimates of the electron-phonon coupling, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order and a large anisotropy gap. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below T{sub c}, there is evidence in three '122' compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with T{sub c}. Such resonances have been observed in the high-T{sub c} copper oxides and a number of heavy fermion superconductors, where they are considered to be evidence of d-wave symmetry. In the iron arsenides, they also provide evidence of unconventional superconductivity, but a comparison with ARPES and other measurements, which indicate that the gaps are isotropic, suggests that the symmetry is more likely

  2. Inelastic Neutron Scattering Studies of the Spin and Lattice Dynamics inIron Arsenide Compounds

    SciTech Connect

    Christianson, Andrew D; Osborn, R.; Rosenkranz, Stephen; Goremychkin, E. A.

    2009-01-01

    Although neutrons do not couple directly to the superconducting order parameter, they have nevertheless played an important role in advancing our understanding of the pairing mechanism and the symmetry of the superconducting energy gap in the iron arsenide compounds. Measurements of the spin and lattice dynamics have been performed on non-superconducting 'parent' compounds based on the LaFeAsO ('1111') and BaFe{sub 2}As{sub 2} ('122') crystal structures, and on electron and hole-doped superconducting compounds, using both polycrystalline and single crystal samples. Neutron measurements of the phonon density-of-state, subsequently supported by single crystal inelastic X-ray scattering, are in good agreement with ab initio calculations, provided the magnetism of the iron atoms is taken into account. However, when combined with estimates of the electron-phonon coupling, the predicted superconducting transition temperatures are less than 1 K, making a conventional phononic mechanism for superconductivity highly unlikely. Measurements of the spin dynamics within the spin density wave phase of the parent compounds show evidence of strongly dispersive spin waves with exchange interactions consistent with the observed magnetic order and a large anisotropy gap. Antiferromagnetic fluctuations persist in the normal phase of the superconducting compounds, but they are more diffuse. Below T{sub c}, there is evidence in three '122' compounds that these fluctuations condense into a resonant spin excitation at the antiferromagnetic wavevector with an energy that scales with T{sub c}. Such resonances have been observed in the high-T{sub c} copper oxides and a number of heavy fermion superconductors, where they are considered to be evidence of d-wave symmetry. In the iron arsenides, they also provide evidence of unconventional superconductivity, but a comparison with ARPES and other measurements, which indicate that the gaps are isotropic, suggests that the symmetry is more likely

  3. Precise realization of the thermal radiation environment for an optical lattice clock

    NASA Astrophysics Data System (ADS)

    Beloy, Kyle; Sherman, Jeff; Phillips, Nathaniel; Hinkley, Nathan; Oates, Chris; Ludlow, Andrew

    2013-05-01

    The Stark shift due to thermal radiation contributes one of the largest known perturbations to the clock transition frequency of optical lattice clocks. Consequently, the uncertainty stemming from this shift has played a dominant role in the total uncertainty of these standards. Following recent works focused on atomic response factors (e.g., the differential polarizability), uncertainty in this perturbation is now limited by imprecise knowledge of the environment itself. Here we present progress towards precise realization of the thermal radiation environment in a Yb optical lattice clock by trapping the atoms in a highly uniform radiation shield at a well-known temperature. We characterize the non-ideal aspects of this approach, including less than unit emissivity, contamination of the blackbody environment from the ambient environment, and thermal non-uniformities.

  4. Lattice dynamics and thermal expansion behavior in the metal cyanides M CN (M =Cu , Ag, Au): Neutron inelastic scattering and first-principles calculations

    NASA Astrophysics Data System (ADS)

    Gupta, M. K.; Singh, Baltej; Mittal, R.; Rols, S.; Chaplot, S. L.

    2016-04-01

    We report measurement of temperature dependence of phonon spectra in quasi-one-dimensional metal cyanides M CN (M =Cu , Ag, Au). Ab initio lattice dynamics calculations have been performed to interpret the phonon spectra as well as to understand the anomalous anisotropic thermal expansion behavior in these compounds. We bring out the differences in the phonon mode behavior to explain the differences in the thermal expansion behavior among the three compounds. The chain-sliding modes are found to contribute maximum to the negative thermal expansion along the "c " axis in the Cu and Ag compounds, while the same modes contribute to positive thermal expansion in the Au compound. Several low-energy transverse modes lead to positive thermal expansion in the a -b plane in all the compounds. The calculated Born-effective charges show that AuCN has a covalent nature of bonding, which results in least distortion as well as the least number of unstable modes among the three cyanides. This result is well correlated with the fact that the coefficient of negative thermal expansion along the c axis in AuCN is the smallest.

  5. Lattice Mismatch Dominant Yet Mechanically Tunable Thermal Conductivity in Bilayer Heterostructures.

    PubMed

    Gao, Yuan; Liu, Qingchang; Xu, Baoxing

    2016-05-24

    Heterostructures that are assembled by interfacing two-dimensional (2D) materials offer a unique platform for the emerging devices with unprecedented functions. The attractive functions in heterostructures that are usually absent and beyond the single layer 2D materials are largely affected by the inherent lattice mismatch between layers. Using nonequilibrium molecular dynamics simulations, we show that the phonon thermal transport in the graphene-MoS2 bilayer heterostructure is reduced by the lattice mismatch, and the reduction can be mitigated well by an external tension, weakening the effect of inherent mismatch-induced strain on thermal conductivity. Mechanical analysis in each layered component indicates that the external tension will alleviate the lattice mismatch-induced deformation. The phonon spectra are also softened by the applied tension with a significant shift of frequency from high to low modes. A universal theory is proposed to quantitatively predict the role of the lattice mismatch in thermal conductivity of various bilayer heterostructures and shows good agreement with simulations. PMID:27093571

  6. Anisotropic lattice thermal diffusivity in olivines and pyroxenes to high temperatures

    NASA Astrophysics Data System (ADS)

    Harrell, Michael Damian

    The anisotropic lattice thermal diffusivity of three olivines (Fo 0, Fo78, and Fo91), one orthopyroxene (En 91), and one clinopyroxene (Di72He9Jd3Cr 3Ts12) have been measured via impulsive stimulated light scattering, permitting the calculation of their lattice thermal diffusivity tensors to high temperatures. For Fo0 olivine, measurements extend from room temperature to 600°C, for Fo78 to 900°C, and for Fo91 to 1000°C, all in steps of 100°C. The orthopyroxene also was taken in steps to 1000°C, while the clinopyroxene was measured at room temperature. A limited set of room-temperature measurements to 5 GPa on a fourth olivine (Fo89) is also included. Diffusivities have been combined with calculations of density and specific heat to determine the lattice thermal conductivity tensors. An earlier theory that explains the observed behavior in terms of a positive lower bound on the phonon mean free path is discussed, and the data are used to constrain a model of thermal conductivity at high temperature. The relative contributions of optic and acoustic modes are evaluated from analysis of published dispersion curves. Five conclusions are reached: First, the anisotropy of lattice thermal conductivity remains essentially unchanged over the observed range of temperatures, indicating that anisotropy remains significant under upper-mantle conditions, and, in regions displaying preferred alignment, may account for observed lateral variations in the geotherm. Second, thermal conductivity departs significantly from earlier predictions of its temperature dependence; this may be understood in terms of a phonon mean free path that cannot diminish below 1.75 times the mean interatomic spacing. Third, for olivine, the optic modes have group velocities that are approximately one-third those of the acoustic modes, and do not dominate lattice conduction despite their greater number. Fourth, impurity scattering is significant along the olivine Fe-Mg solid solution series, but is not

  7. Lattice dynamics of BaFe2X3(X=S,Se) compounds

    DOE PAGESBeta

    Popović, Z. V.; Šćepanović, M.; Lazarević, N.; Opačić, M.; Radonjić, M. M.; Tanasković, D.; Lei, Hechang; Petrovic, C.

    2015-02-27

    We present the Raman scattering spectra of the S=2 spin ladder compounds BaFe₂X₃ (X=S,Se) in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe₂S₃ (BaFe₂Se₃) is base-centered Cmcm (primitive Pnma), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe₂S(Se)₃ is supported by themore » lattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe₂Se₃ below TN=255K leaves a fingerprint both in the A1g and B3g phonon mode linewidth and energy.« less

  8. Magnetic structure of the Kondo lattice compound CeZn0.6Sb2

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Lynn, J. W.; Lee, H.; Klavins, P.; Fisk, Z.; Nakatsuji, S.; Bao, W.; Thompson, J.; Park, T.; Macaluso, R.; Chan, J.; Carter, B.

    2006-03-01

    The new Kondo lattice compound CeZn0.6Sb2 has a tetragonal structure with space group P4/nmm and shows ferromagnetic behavior below 2.5 K. The Curie-Weiss temperature is 22 K along the tetragonal ab plane, indicating ferromagnetic interactions in the plane. Along the c axis, however, the Curie-Weiss temperature is -145 K, suggesting antiferromagnetic exchange interaction in this direction [1]. We determined the magnetic structure of CeZn0.6Sb2 using single crystal neutron diffraction. (h,0,l) and (h,h,l) scattering planes were investigated. We found CeZn0.6Sb2 orders ferromagnetically at TC=2.5 K. The magnetic structure is collinear with a low temperature ordered Ce moment of 1.3 (1) μB that lies in the ab plane. In addition, we measured the order parameter of the ferromagnetic transition. [1] Studies of the ferromagnetic Kondo lattice system of single crystal CeZnSb2, H. Lee, S. Nakatsuji, Y. Chen, W. Bao, R. Macaluso, J. Chan, T. Park, B. Carter, P. Klavins, J. Thompson, Z. Fisk, BAPS, Session L41, 2005.

  9. Lattice Anharmonicity and Thermal Conductivity from Compressive Sensing of First-Principles Calculations

    SciTech Connect

    Zhou, Fei; Nielson, Weston; Xia, Yi; Ozolins, Vidvuds

    2014-10-27

    First-principles prediction of lattice thermal conductivity KL of strongly anharmonic crystals is a long-standing challenge in solid state physics. Using recent advances in information science, we propose a systematic and rigorous approach to this problem, compressive sensing lattice dynamics (CSLD). Compressive sensing is used to select the physically important terms in the lattice dynamics model and determine their values in one shot. Non-intuitively, high accuracy is achieved when the model is trained on first-principles forces in quasi-random atomic configurations. The method is demonstrated for Si, NaCl, and Cu12Sb4S13, an earth-abundant thermoelectric with strong phononphonon interactions that limit the room-temperature KL to values near the amorphous limit.

  10. Lattice Anharmonicity and Thermal Conductivity from Compressive Sensing of First-Principles Calculations

    SciTech Connect

    Zhou, Fei; Nielson, Weston; Xia, Yi; Ozoliņš, Vidvuds

    2014-10-01

    First-principles prediction of lattice thermal conductivity κL of strongly anharmonic crystals is a long-standing challenge in solid-state physics. Making use of recent advances in information science, we propose a systematic and rigorous approach to this problem, compressive sensing lattice dynamics. Compressive sensing is used to select the physically important terms in the lattice dynamics model and determine their values in one shot. Nonintuitively, high accuracy is achieved when the model is trained on first-principles forces in quasirandom atomic configurations. The method is demonstrated for Si, NaCl, and Cu12Sb4S13, an earth-abundant thermoelectric with strong phonon-phonon interactions that limit the room-temperature κL to values near the amorphous limit.

  11. Lattice Anharmonicity and Thermal Conductivity from Compressive Sensing of First-Principles Calculations

    DOE PAGESBeta

    Zhou, Fei; Nielson, Weston; Xia, Yi; Ozolins, Vidvuds

    2014-10-27

    First-principles prediction of lattice thermal conductivity KL of strongly anharmonic crystals is a long-standing challenge in solid state physics. Using recent advances in information science, we propose a systematic and rigorous approach to this problem, compressive sensing lattice dynamics (CSLD). Compressive sensing is used to select the physically important terms in the lattice dynamics model and determine their values in one shot. Non-intuitively, high accuracy is achieved when the model is trained on first-principles forces in quasi-random atomic configurations. The method is demonstrated for Si, NaCl, and Cu12Sb4S13, an earth-abundant thermoelectric with strong phononphonon interactions that limit the room-temperature KLmore » to values near the amorphous limit.« less

  12. Thermal phase transitions in a honeycomb lattice gas with three-body interactions.

    PubMed

    Lohöfer, Maximilian; Bonnes, Lars; Wessel, Stefan

    2013-11-01

    We study the thermal phase transitions in a classical (hard-core) lattice gas model with nearest-neighbor three-body interactions on the honeycomb lattice, based on parallel tempering Monte Carlo simulations. This system realizes incompressible low-temperature phases at fractional fillings of 9/16, 5/8, and 3/4 that were identified in a previous study of a related quantum model. In particular, both the 9/16 and the 5/8 phase exhibit an extensive ground-state degeneracy reflecting the frustrated nature of the three-body interactions on the honeycomb lattice. The thermal melting of the 9/16 phase is found to be a first-order, discontinuous phase transition. On the other hand, from the thermodynamic behavior we obtain indications for a four-states Potts-model thermal transition out of the 5/8 phase. We find that this thermal Potts-model transition relates to the selection of one out of four extensive sectors within the low-energy manifold of the 5/8 phase, which we obtain via an exact mapping of the ground-state manifold to a hard-core dimer model on an embedded honeycomb superlattice. PMID:24329242

  13. Lattice dynamics investigations of phonon thermal conductivity of Si /Ge superlattices with rough interfaces

    NASA Astrophysics Data System (ADS)

    Ren, Shang-Fen; Cheng, Wei; Chen, Gang

    2006-11-01

    Phonon thermal conductivities in both growth and in-plane directions of Si /Ge superlattices (SLs) with perfect and rough interfaces are calculated by using a lattice dynamics model. In addition to the general trend, the results show that there exist fluctuations of thermal conductivity in both directions for SLs with even or odd number of layers when the layer thickness is small. Thermal conductivities in both directions of Si /Ge SLs with rough interfaces are shown to be much lower than those of SLs with perfect interfaces. To understand the influences of rough interfaces, thermal conductivities of homogeneous alloy are further calculated and compared. The results show that along the in-plane direction, the thermal conductivity of SLs with rough interfaces is about the same as that of random alloy, while in the growth direction it is lower than that of the random alloy.

  14. Phonon-mediated Thermal Conductivity in Ionic Solids by Lattice Dynamics-based Methods

    SciTech Connect

    Chernatynskiy, Aleksandr; Turney, Joseph E.; McGaughey, Alan J. H.; Amon, Christina H.; Phillpot, Simon R.

    2011-07-22

    Phonon properties predicted from lattice dynamics calculations and the Boltzmann Transport Equation (BTE) are used to elucidate the thermal-transport properties of ionic materials. It is found that a rigorous treatment of the Coulombic interactions within the harmonic analysis is needed for the analysis of the phonon structure of the solid, while a short-range approximation is sufficient for the third-order force constants. The effects on the thermal conductivity of the relaxation time approximation, the classical approximation to the phonon statistics, the direct summation method for the electrostatic interactions, and the quasi-harmonic approximation to lattice dynamics are quantified. Quantitative agreement is found between predictions from molecular dynamics simulations (a method valid at temperatures above the Debye temperature) and the BTE result within quasi-harmonic approximation over a wide temperature range.

  15. Effect of phonon confinement on lattice thermal conductivity of lead Telluride quantum well structure

    SciTech Connect

    Tripathi, Madhvendra Nath

    2014-04-24

    The paper examines the effect of spatial confinement of acoustic phonons on average group velocity and consequently the lattice thermal conductivity of a free-standing PbTe quantum well structure and their temperature dependence. The average group velocity at 100 Å decreases 30% to the bulk value and falls more rapidly on reducing the width of quantum well. Moreover, the lattice thermal conductivity of 100 Å wide PbTe quantum well with value of 0.60 W/mK shows considerable decrease of 70% compared to it’s bulk value. It is observed that the effect of reduction in well width is less pronounce as temperature increases. This appears mainly due to dominance of umklapp processes over the confinement effects.

  16. First-principles Study of Lattice Thermal Conductivity of Cu3SbS4andCu3SbSe4

    NASA Astrophysics Data System (ADS)

    Xia, Yi; Zhou, Fei; Nielson, Weston; Ozolins, Vidvuds

    2015-03-01

    Linearized self-consistent Boltzmann transport equation (BTE), utilizing interatomic force constants (IFCs) obtained via compressive sensing lattice dynamics (CSLD), is used to study the lattice thermal conductivity (κl) of Cu3SbS4, Cu3SbSe4 and their solid solutions. With these IFCs we obtain bulk lattice thermal conductivity in good agreement with experimental measurements. We also compare Cu3SbS4andCu3SbSe4 with respect to Grüneisen parameter, group velocity, phonon lifetime, mean free path and cumulative κl. All the analysis indicates that (1) slightly larger group velocity and lifetime of acoustic modes found in Cu3SbS4 lead to larger κl compared with Cu3SbSe4 over the whole temperature range. Contributions from optical modes to κl for both compounds are about 25% at temperature higher than 300K. This large portion of κl can not be neglected if one aims to predict accurate κl; (2) Nanostructures with length less than 10nm can effectively reduce κl by about 80% for both of the compounds; (3) solid solution of two compounds can effectively reduce κl as much as 40% at room temperature.

  17. From quantum to thermal topological-sector fluctuations of strongly interacting Bosons in a ring lattice

    NASA Astrophysics Data System (ADS)

    Roscilde, Tommaso; Faulkner, Michael F.; Bramwell, Steven T.; Holdsworth, Peter C. W.

    2016-07-01

    Inspired by recent experiments on Bose–Einstein condensates in ring traps, we investigate the topological properties of the phase of a one-dimensional Bose field in the presence of both thermal and quantum fluctuations—the latter ones being tuned by the depth of an optical lattice applied along the ring. In the regime of large filling of the lattice, quantum Monte Carlo simulations give direct access to the full statistics of fluctuations of the Bose-field phase, and of its winding number W along the ring. At zero temperature the winding-number (or topological-sector) fluctuations are driven by quantum phase slips localized around a Josephson link between two lattice wells, and their susceptibility is found to jump at the superfluid-Mott insulator transition. At finite (but low) temperature, on the other hand, the winding number fluctuations are driven by thermal activation of nearly uniform phase twists, whose activation rate is governed by the superfluid fraction. A quantum-to-thermal crossover in winding-number fluctuations is therefore exhibited by the system, and it is characterized by a conformational change in the topologically non-trivial configurations, from localized to uniform phase twists, which can be experimentally observed in ultracold Bose gases via matter–wave interference.

  18. Analytical insight into the lattice thermal conductivity and heat capacity of monolayer MoS2

    NASA Astrophysics Data System (ADS)

    Saha, Dipankar; Mahapatra, Santanu

    2016-09-01

    We report, a detailed theoretical study on the lattice thermal conductivity of a suspended monolayer MoS2, far beyond its ballistic limit. The analytical approach adopted in this work mainly relies on the use of Boltzmann transport equation (BTE) within the relaxation time approximation (RTA), along with the first-principles calculations. Considering the relative contributions from the various in-plane and out-of-plane acoustic modes, we derive the closed-form expressions of the mode specific heat capacities, which we later use to obtain the phonon thermal conductivities of the monolayer MoS2. Besides finding the intrinsic thermal conductivity, we also analyse the effect of the phonon-boundary scattering, for different dimensions and edge roughness conditions. The viability of the semi-analytic solution of lattice thermal conductivity reported in this work ranges from a low temperature (T∼30 K) to a significantly high temperature (T∼550 K), and the room temperature (RT) thermal conductivity value has been obtained as 34.06 Wm-1K-1 which is in good agreement with the experimental result.

  19. Effect of some nitrogen compounds thermal stability of jet A

    NASA Technical Reports Server (NTRS)

    Antoine, A. C.

    1982-01-01

    The effect of known concentrations of some nitrogen containing compounds on the thermal stability of a conventional fuel, namely, Jet A was investigated. The concentration range from 0.01 to 0.1 wt% nitrogen was examined. Solutions were made containing, individually, pyrrole, indole, quinoline, pyridine, and 4 ethylpyridine at 0.01, 0.03, 0.06, and 0.1 wt% nitrogen concentrations in Jet A. The measurements were all made by using a standard ASTM test for evaluating fuel thermal oxidation behavior, namely, ASTM D3241, 'thermal oxidation stability of turbine fuels (JFTOT procedure).' Measurements were made at two temperature settings, and 'breakpoint temperatures' were determined. The results show that the pyrrole and indole solutions have breakpoint temperatures substantially lower than those of the Jet A used.

  20. Real space visualization of thermal fluctuations in a triangular flux-line lattice

    NASA Astrophysics Data System (ADS)

    Schwarz, A.; Liebmann, M.; Pi, U. H.; Wiesendanger, R.

    2010-03-01

    The temperature-dependent properties of a triangular flux-line lattice (FLL) in the low-flux density regime were investigated by evaluating the imaged flux-line (FL) size and the lattice regularity observed in real space utilizing magnetic force microscopy (MFM). At low temperatures, pinning by randomly distributed point defects in the anisotropic type-II superconductor Bi2Sr2CaCu2O8+δ results in curved FLs and lateral disorder within the FLL (Bragg glass). Above 30 K, depinning of pancake vortices (PVs) leads to straightening of FLs and a better-ordered lattice. Evaluation of the temperature-dependent imaged FL size allows us to determine the stiffness of the potential, in which FLs in the lattice are caged due to mutual repulsion between them. At 54.1 K, far below melting temperatures reported so far, thermal fluctuations plus the lateral force exerted by the scanning tip facilitate decoupling of PVs near the surface and the image contrast exhibit a liquid-like behavior. Our analysis demonstrates the ability of MFM to obtain three-dimensional information on the arrangement of PVs.

  1. Macroscopic Artificial Magnetic Honeycomb Lattice of Thermally Controlled Ultra-Small Bonds

    NASA Astrophysics Data System (ADS)

    Summers, Brock; Dahal, Ashutosh; Debeer-Schitt, Lisa; Gunasekera, Jagath; Singh, Deepak

    The two-dimensional artificial magnetic honeycomb lattice system is evolving into a new research arena to explore a plethora of novel magnetism that are predicted to occur as functions of temperature and magnetic field: a long-range spin ice, spin liquid, an entropy-driven magnetic charge-ordered state involving topological vortex pairs and a spin-order due to the spin chirality. We have created macroscopic samples of artificial magnetic honeycomb lattices of Cobalt and Permalloy having connected ultra-small elements (bonds), with length scales of sub-10 nm to 30 nm, which have never before been possible. The equivalent energy of the resulting systems is 10-100 K and is thus amenable to both temperature- and field-dependent exploration of novel magnetic phenomena. We have performed detailed magnetic and small angle neutron scattering measurements (SANS) on the newly fabricated honeycomb lattice of Permalloy that show the thermal character of the system. Furthermore, the experimental data reveals the onset of magnetic ordered regimes in temperature that are consistent with the predicted novel phase diagram in artificial honeycomb lattice. Research is supported by U.S. Department of Energy, Office of Basic Energy Sciences under Grant No. DE-SC0014461.

  2. Planar lattices with tailorable coefficient of thermal expansion and high stiffness based on dual-material triangle unit

    NASA Astrophysics Data System (ADS)

    Wei, Kai; Chen, Haosen; Pei, Yongmao; Fang, Daining

    2016-01-01

    The unexpected thermal distortions and failures in engineering raise the big concern about thermal expansion controlling. Thus, design of tailorable coefficient of thermal expansion (CTE) is urgently needed for the materials used in large temperature variation circumstance. Here, inspired by multi-fold rotational symmetry in crystallography, we have devised six kinds of periodic planar lattices, which incorporate tailorable CTE and high specific biaxial stiffness. Fabrication process, which overcame shortcomings of welding or adhesion connection, was developed for the dual-material planar lattices. The analytical predictions agreed well with the CTE measurements. It is shown that the planar lattices fabricated from positive CTE constituents, can give large positive, near zero and even negative CTEs. Furthermore, a generalized stationary node method was proposed for aperiodic lattices and even arbitrary structures with desirable thermal expansion. As an example, aperiodic quasicrystal lattices were designed and exhibited zero thermal expansion property. The proposed method for the lattices of lightweight, robust stiffness, strength and tailorable thermal expansion is useful in the engineering applications.

  3. Robust thermal quantum correlation and quantum phase transition of spin system on fractal lattices

    NASA Astrophysics Data System (ADS)

    Xu, Yu-Liang; Zhang, Xin; Liu, Zhong-Qiang; Kong, Xiang-Mu; Ren, Ting-Qi

    2014-06-01

    We investigate the quantum correlation measured by quantum discord (QD) for thermalized ferromagnetic Heisenberg spin systems in one-dimensional chains and on fractal lattices using the decimation renormalization group approach. It is found that the QD between two non-nearest-neighbor end spins exhibits some interesting behaviors which depend on the anisotropic parameter Δ, the temperature T, and the size of system L. With increasing Δ continuously, the QD possesses a cuspate change at Δ = 0 which is a critical point of quantum phase transition (QPT). There presents the "regrowth" tendency of QD with increasing T at Δ < 0, in contrast to the "growth" of QD at Δ > 0. As the size of the system L becomes large, there still exists considerable thermal QD between long-distance end sites in spin chains and on the fractal lattices even at unentangled states, and the long-distance QD can spotlight the presence of QPT. The robustness of QD on the diamond-type hierarchical lattices is stronger than that in spin chains and Koch curves, which indicates that the fractal can affect the behaviors of quantum correlation.

  4. Thermal expansion and self-irradiation damage in curium nitride lattice

    NASA Astrophysics Data System (ADS)

    Takano, Masahide; Hayashi, Hirokazu; Minato, Kazuo

    2014-05-01

    A powder sample of curium nitride (CmN) containing 0.35%-Pu and 3.59%-Am as actinide impurities was prepared by carbothermic nitridation of the oxide. The lattice expansion induced by self-irradiation damage at room temperature was measured as a function of time. The saturated Δa/ao value was 0.43%, which is greater than those for transuranium dioxides available in literature. The undamaged lattice parameter at 297 ± 1 K was determined to be 0.50261 ± 0.00006 nm. Temperature dependence of the lattice parameter was measured by a high temperature X-ray diffractometer in the temperature range up to 1375 K. The linear thermal expansion from 293 to 1273 K was 0.964% and the corresponding thermal expansion coefficient was 9.84 × 10-6 K-1. Comparing with the other actinide nitrides, it was found that CmN lies between the higher expansion nitrides (PuN and AmN) and the lower expansion nitrides (UN and NpN).

  5. Manipulating graphene's lattice to create pseudovector potentials, discover anomalous friction, and measure strain dependent thermal conductivity

    NASA Astrophysics Data System (ADS)

    Kitt, Alexander Luke

    Graphene is a single atomic sheet of graphite that exhibits a diverse range of unique properties. The electrons in intrinsic graphene behave like relativistic Dirac fermions; graphene has a record high Young's modulus but extremely low bending rigidity; and suspended graphene exhibits very high thermal conductivity. These properties are made more intriguing because with a thickness of only a single atomic layer, graphene is both especially affected by its environment and readily manipulated. In this dissertation the interaction between graphene and its environment as well as the exciting new physics realized by manipulating graphene's lattice are investigated. Lattice manipulations in the form of strain cause alterations in graphene's electrical dispersion mathematically analogous to the vector potential associated with a magnetic field. We complete the standard description of the strain-induced vector potential by explicitly including the lattice deformations and find new, leading order terms. Additionally, a strain engineered device with large, localized, plasmonically enhanced pseudomagnetic fields is proposed to couple light to pseudomagnetic fields. Accurate strain engineering requires a complete understanding of the interactions between a two dimensional material and its environment, particularly the adhesion and friction between graphene and its supporting substrate. We measure the load dependent sliding friction between mono-, bi-, and trilayer graphene and the commonly used silicon dioxide substrate by analyzing Raman spectra of circular, graphene sealed microchambers under variable external pressure. We find that the sliding friction for trilayer graphene behaves normally, scaling with the applied load, whereas the friction for monolayer and bilayer graphene is anomalous, scaling with the inverse of the strain in the graphene. Both strain and graphene's environment are expected to affect the quadratically dispersed out of plane acoustic phonon. Although

  6. Application of the multi distribution function lattice Boltzmann approach to thermal flows

    NASA Astrophysics Data System (ADS)

    Parmigiani, A.; Huber, C.; Chopard, B.; Latt, J.; Bachmann, O.

    2009-04-01

    Numerical methods able to model high Rayleigh ( Ra) and high Prandtl ( Pr) number thermal convection are important to study large-scale geophysical phenomena occuring in very viscous fluids such as magma chamber dynamics (104 < Pr < 107 and 107 < Ra < 1011). The important variable to quantify the thermal state of a convective fluid is a generalized dimensionless heat transfer coefficient (the Nusselt number) whose measure indicates the relative efficiency of the thermal convection. In this paper we test the ability of Multi-distribution Function approach (MDF) Thermal Lattice Boltzmann method to study the well-established scaling result for the Nusselt number ( Nu ∝ Ra 1/3) in Rayleigh Bénard convection for 104 ≤ Ra ≤ 109 and 101 ≤ Pr ≤ 104. We explore its main drawbacks in the range of Pr and Ra number under investigation: (1) high computational time N c required for the algorithm to converge and (2) high spatial accuracy needed to resolve the thickness of thermal plumes and both thermal and velocity boundary layer. We try to decrease the computational demands of the method using a multiscale approach based on the implicit dependence of the Pr number on the relaxation time, the spatial and temporal resolution characteristic of the MDF thermal model.

  7. Molecular simulations and lattice dynamics determination of Stillinger-Weber GaN thermal conductivity

    SciTech Connect

    Liang, Zhi; Jain, Ankit; McGaughey, Alan J. H.; Keblinski, Pawel

    2015-09-28

    The bulk thermal conductivity of Stillinger-Weber (SW) wurtzite GaN in the [0001] direction at a temperature of 300 K is calculated using equilibrium molecular dynamics (EMD), non-equilibrium MD (NEMD), and lattice dynamics (LD) methods. While the NEMD method predicts a thermal conductivity of 166 ± 11 W/m·K, both the EMD and LD methods predict thermal conductivities that are an order of magnitude greater. We attribute the discrepancy to significant contributions to thermal conductivity from long-mean free path phonons. We propose that the Grüneisen parameter for low-frequency phonons is a good predictor of the severity of the size effects in NEMD thermal conductivity prediction. For weakly anharmonic crystals characterized by small Grüneisen parameters, accurate determination of thermal conductivity by NEMD is computationally impractical. The simulation results also indicate the GaN SW potential, which was originally developed for studying the atomic-level structure of dislocations, is not suitable for prediction of its thermal conductivity.

  8. Investigation of Oxygen Transfer Enhancement in Thermally Driven Cavities By Lattice Boltzmann Simulation.

    NASA Astrophysics Data System (ADS)

    Yu, Huidan; Zhang, Jinsuo; Li, Ning

    2006-03-01

    We investigate the enhancement of mass transfer in 2D thermally driven cavities using lattice Boltzmann equation (LBE) method. The computational technique integrates three coupled LBEs for solving velocity, temperature, and concentration fields simultaneously. Simulation is performed for oxygen transfer in lead/lead-bismuth eutectic with variations of temperature boundary, Schmidt number, and field aspect ratio to investigate the effects on enhancement of oxygen transfer. Interested characteristics include oxygen concentration, Sherwood number, and velocity profiles, etc. Our results clearly indicate that oxygen transfer is dominated by convection while diffusion also plays a role on it. Comparative studies demonstrate that side heating and top cooling device is more efficient to transfer oxygen than side heating and cooling device and oxygen transfers more rapidly in square cavity than in rectangular cavity. This work establishes a reliable thermal LBE model for thermally driven heat and mass transfer.

  9. Heavy fermion compounds on the geometrically frustrated Shastry-Sutherland lattice.

    PubMed

    Kim, M S; Aronson, M C

    2011-04-27

    We present measurements of the basic properties of Ce(2)Ge(2)Mg, Yb(2)Pt(2)Pb and Ce(2)Pt(2)Pb, which are members of a new class of geometrically frustrated magnets R(2)T(2)X (R = rare earth, T = transition metal, X = main group). Here, the moment-bearing R atoms are confined to layers where they are arranged in the Shastry-Sutherland lattice. Magnetic susceptibility and specific heat measurements indicate that Ce(2)Ge(2)Mg orders antiferromagnetically at 9.4 K and Yb(2)Pt(2)Pb at 2.07 K. No long ranged order is observed in Ce(2)Pt(2)Pb above 0.05 K. Analysis of Schottky peaks in the specific heat indicates that all three compounds have doublet ground states that are well separated in energy from the excited states of the crystal-field-split manifold. Electrical resistivity measurements show that Ce(2)Ge(2)Mg and Yb(2)Pt(2)Pb are excellent metals with small residual resistivities. However, the measured resistivity of Ce(2)Pt(2)Pb is large and almost temperature-independent, suggesting that strong disorder or perhaps strong quantum critical fluctuations saturate the quasiparticle scattering in this compound. The magnetic entropy develops very slowly above the onset of antiferromagnetic order and we discuss the possibility that a nonordered fluid of dimerized moments exists above T(N) in Ce(2)Ge(2)Mg and Yb(2)Pt(2)Pb, and for a wide range of temperatures in Ce(2)Pt(2)Pb, which appears to be close to a frustration-driven quantum critical point. PMID:21471619

  10. Heavy fermion compounds on the geometrically frustrated Shastry-Sutherland lattice

    NASA Astrophysics Data System (ADS)

    Kim, M. S.; Aronson, M. C.

    2011-04-01

    We present measurements of the basic properties of Ce2Ge2Mg, Yb2Pt2Pb and Ce2Pt2Pb, which are members of a new class of geometrically frustrated magnets R2T2X (R = rare earth, T = transition metal, X = main group). Here, the moment-bearing R atoms are confined to layers where they are arranged in the Shastry-Sutherland lattice. Magnetic susceptibility and specific heat measurements indicate that Ce2Ge2Mg orders antiferromagnetically at 9.4 K and Yb2Pt2Pb at 2.07 K. No long ranged order is observed in Ce2Pt2Pb above 0.05 K. Analysis of Schottky peaks in the specific heat indicates that all three compounds have doublet ground states that are well separated in energy from the excited states of the crystal-field-split manifold. Electrical resistivity measurements show that Ce2Ge2Mg and Yb2Pt2Pb are excellent metals with small residual resistivities. However, the measured resistivity of Ce2Pt2Pb is large and almost temperature-independent, suggesting that strong disorder or perhaps strong quantum critical fluctuations saturate the quasiparticle scattering in this compound. The magnetic entropy develops very slowly above the onset of antiferromagnetic order and we discuss the possibility that a nonordered fluid of dimerized moments exists above TN in Ce2Ge2Mg and Yb2Pt2Pb, and for a wide range of temperatures in Ce2Pt2Pb, which appears to be close to a frustration-driven quantum critical point.

  11. Thermal conductivities of one-dimensional anharmonic/nonlinear lattices: renormalized phonons and effective phonon theory

    NASA Astrophysics Data System (ADS)

    Li, Nianbei; Li, Baowen

    2012-12-01

    Heat transport in low-dimensional systems has attracted enormous attention from both theoretical and experimental aspects due to its significance to the perception of fundamental energy transport theory and its potential applications in the emerging field of phononics: manipulating heat flow with electronic anologs. We consider the heat conduction of one-dimensional nonlinear lattice models. The energy carriers responsible for the heat transport have been identified as the renormalized phonons. Within the framework of renormalized phonons, a phenomenological theory, effective phonon theory, has been developed to explain the heat transport in general one-dimensional nonlinear lattices. With the help of numerical simulations, it has been verified that this effective phonon theory is able to predict the scaling exponents of temperature-dependent thermal conductivities quantitatively and consistently.

  12. Topology optimization in thermal-fluid flow using the lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Yaji, Kentaro; Yamada, Takayuki; Yoshino, Masato; Matsumoto, Toshiro; Izui, Kazuhiro; Nishiwaki, Shinji

    2016-02-01

    This paper proposes a topology optimization method for thermal-fluid flow problems using the lattice Boltzmann method (LBM). The design sensitivities are derived based on the adjoint lattice Boltzmann method (ALBM), whose basic idea is that the adjoint problem is first formulated using a continuous adjoint approach, and the adjoint problem is then solved using the LBM. In this paper, the discrete velocity Boltzmann equation, in which only the particle velocities are discretized, is introduced to the ALBM to deal with the various boundary conditions in the LBM. The novel sensitivity analysis is applied in two flow channel topology optimization problems: 1) a pressure drop minimization problem, and 2) a heat exchange maximization problem. Several numerical examples are provided to confirm the utility of the proposed method.

  13. Lattice Thermal Transport in Si-based Nanocomposites for Thermoelectric Applications

    NASA Astrophysics Data System (ADS)

    Aksamija, Zlatan

    2015-06-01

    Silicon-germanium (SiGe) superlattices (SLs) have been studied for application as efficient thermoelectrics because of their low thermal conductivity, below that of bulk SiGe alloys. However, the cost of growing SLs is prohibitive, so Si-based nanocomposites, made by a ball-milling and sintering, have been proposed as a cost-effective replacement with similar properties. Because the lattice thermal conductivity of SiGe SLs is reduced by scattering from rough boundaries between layers, it is expected that grain boundary properties, for example roughness, orientation, and composition, will also substantially effect thermal transport in nanocomposites, resulting in many ways of adjusting their thermal conductivity by manipulation of grain size, shape, and crystal angle distributions. A model of phonon transport in nanocomposites was developed on the basis of the phonon Boltzmann transport equation. When nanocomposite structures were modeled by using a Voronoi tessellation to mimic the grains and their distribution, agreement with experimentally observed structures was excellent. To accurately treat phonon scattering from a series of atomically rough interfaces between the grains in the nanocomposite, we used a momentum-dependent specularity variable. Our results revealed thermal transport in Si-based nanocomposites is highly anisotropic and suggest further utilization of grain morphology to minimize thermal conductivity.

  14. Development of magneto-thermal lattice Boltzmann heat and fluid flow simulation

    NASA Astrophysics Data System (ADS)

    Kaneda, Masayuki; Kano, Hironori; Suga, Kazuhiko

    2015-09-01

    In this study, magneto-thermal lattice Boltzmann model is developed and heat transfer enhancement is investigated for a porous media heat exchanger. First, two models of thermal LBM are discussed in terms of its precision and applicability to magneto-thermal LBM including tolerance range of computational parameter. The implemented magneto-thermal LBM is then validated by convection in a cubic enclosure comparing with finite difference computation. The incompressibility limit of magneto-thermal LBM is additionally discussed. Finally, the effect of magnetic field on a flow through heated porous media is numerically investigated. It is found that, the magneto-thermal force is effective at the stagnant region inside the porous media to enhance the heat transfer. In a macroscopic view, the heat transfer enhancement is found in overall region. The effect becomes remarkable at low Reynolds number flow. Since its effect is aligned on a curve of Nusselt-Reynolds relation, the magnetic effect obviously found to assist the main flow.

  15. Thermal hydraulic design analysis of ternary carbide fueled square-lattice honeycomb nuclear rocket engine

    SciTech Connect

    Furman, Eric M.; Anghaie, Samim

    1999-01-22

    A computational analysis is conducted to determine the optimum thermal-hydraulic design parameters for a square-lattice honeycomb nuclear rocket engine core that will incorporate ternary carbide based uranium fuels. Recent studies at the Innovative Nuclear Space Power and Propulsion Institute (INSPI) have demonstrated the feasibility of processing solid solution, ternary carbide fuels such as (U, Zr, Nb)C, (U, Zr, Ta)C, (U, Zr, Hf)C and (U, Zr, W)C. The square-lattice honeycomb design provides high strength and is amenable to the processing complexities of these ultrahigh temperature fuels. A parametric analysis is conducted to examine how core geometry, fuel thickness and the propellant flow area effect the thermal performance of the nuclear rocket engine. The principal variables include core size (length and diameter) and fuel element dimensions. The optimum core configuration requires a balance between high specific impulse and thrust level performance, and maintaining the temperature and strength limits of the fuel. A nuclear rocket engine simulation code is developed and used to examine the system performance as well as the performance of the main reactor core components. The system simulation code was originally developed for analysis of NERVA-Derivative and Pratt and Whitney XNR-2000 nuclear thermal rockets. The code is modified and adopted to the square-lattice geometry of the new fuel design. Thrust levels ranging from 44,500 to 222,400 N (10,000 to 50,000 lbf) are considered. The average hydrogen exit temperature is kept at 2800 K, which is well below the melting point of these fuels. For a nozzle area ratio of 300 and a thrust chamber pressure of 4.8 Mpa (700 psi), the specific impulse is 930 s. Hydrogen temperature and pressure distributions in the core and the fuel maximum temperatures are calculated.

  16. Phase separation in thermal systems: a lattice Boltzmann study and morphological characterization.

    PubMed

    Gan, Yanbiao; Xu, Aiguo; Zhang, Guangcai; Li, Yingjun; Li, Hua

    2011-10-01

    We investigate thermal and isothermal symmetric liquid-vapor separations via a fast Fourier transform thermal lattice Boltzmann (FFT-TLB) model. Structure factor, domain size, and Minkowski functionals are employed to characterize the density and velocity fields, as well as to understand the configurations and the kinetic processes. Compared with the isothermal phase separation, the freedom in temperature prolongs the spinodal decomposition (SD) stage and induces different rheological and morphological behaviors in the thermal system. After the transient procedure, both the thermal and isothermal separations show power-law scalings in domain growth, while the exponent for thermal system is lower than that for isothermal system. With respect to the density field, the isothermal system presents more likely bicontinuous configurations with narrower interfaces, while the thermal system presents more likely configurations with scattered bubbles. Heat creation, conduction, and lower interfacial stresses are the main reasons for the differences in thermal system. Different from the isothermal case, the release of latent heat causes the changing of local temperature, which results in new local mechanical balance. When the Prandtl number becomes smaller, the system approaches thermodynamical equilibrium much more quickly. The increasing of mean temperature makes the interfacial stress lower in the following way: σ=σ(0)[(T(c)-T)/(T(c)-T(0))](3/2), where T(c) is the critical temperature and σ(0) is the interfacial stress at a reference temperature T(0), which is the main reason for the prolonged SD stage and the lower growth exponent in the thermal case. Besides thermodynamics, we probe how the local viscosities influence the morphology of the phase separating system. We find that, for both the isothermal and thermal cases, the growth exponents and local flow velocities are inversely proportional to the corresponding viscosities. Compared with the isothermal case, the

  17. Porous Substrate Effects on Thermal Flows Through a Rev-Scale Finite Volume Lattice Boltzmann Model

    NASA Astrophysics Data System (ADS)

    Zarghami, Ahad; Francesco, Silvia Di; Biscarini, Chiara

    2014-09-01

    In this paper, fluid flows with enhanced heat transfer in porous channels are investigated through a stable finite volume (FV) formulation of the thermal lattice Boltzmann method (LBM). Temperature field is tracked through a double distribution function (DDF) model, while the porous media is modeled using Brinkman-Forchheimer assumptions. The method is tested against flows in channels partially filled with porous media and parametric studies are conducted to evaluate the effects of various parameters, highlighting their influence on the thermo-hydrodynamic behavior.

  18. Entropic Lattice Boltzmann Methods for Fluid Mechanics: Thermal, Multi-phase and Turbulence

    NASA Astrophysics Data System (ADS)

    Chikatamarla, Shyam; Boesch, F.; Frapolli, N.; Mazloomi, A.; Karlin, I.

    2014-11-01

    With its roots in statistical mechanics and kinetic theory, the lattice Boltzmann method (LBM) is a paradigm-changing innovation, offering for the first time an intrinsically parallel CFD algorithm. Over the past two decades, LBM has achieved numerous results in the field of CFD and is now in a position to challenge state-of-the art CFD techniques. Major restyling of LBM resulted in an unconditionally stable entropic LBM which restored Second Law (Boltzmann H theorem) in the LBM kinetics and thus enabled affordable direct simulations of fluid turbulence. In this talk, we shall review recent advances in ELBM as a practical, modeling-free tool for simulation of complex flow phenomenon. We shall present recent simulations of fluid turbulence including turbulent channel flow, flow past a circular cylinder, creation and dynamics of vortex tubes, and flow past a surface mounted cube. Apart from its achievements in turbulent flow simulations, ELBM has also presented us the opportunity to extend lattice Boltzmann method to higher order lattices which shall be employed for turbulent, multi-phase and thermal flow simulations. A new class of entropy functions are proposed to handle non-ideal equation of state and surface tension terms in multi-phase flows. It is shown the entropy principle brings unconditional stability and thermodynamic consistency to all the three flow regimes considered here. Acknowledgements: ERC Advanced Grant ``ELBM'' and CSCS grant s437 are deeply acknowledged. References:

  19. Final Design and Experimental Validation of the Thermal Performance of the LHC Lattice Cryostats

    NASA Astrophysics Data System (ADS)

    Bourcey, N.; Capatina, O.; Parma, V.; Poncet, A.; Rohmig, P.; Serio, L.; Skoczen, B.; Tock, J.-P.; Williams, L. R.

    2004-06-01

    The recent commissioning and operation of the LHC String 2 have given a first experimental validation of the global thermal performance of the LHC lattice cryostat at nominal cryogenic conditions. The cryostat designed to minimize the heat inleak from ambient temperature, houses under vacuum and thermally protects the cold mass, which contains the LHC twin-aperture superconducting magnets operating at 1.9 K in superfluid helium. Mechanical components linking the cold mass to the vacuum vessel, such as support posts and insulation vacuum barriers are designed with efficient thermalisations for heat interception to minimise heat conduction. Heat inleak by radiation is reduced by employing multilayer insulation (MLI) wrapped around the cold mass and around an aluminium thermal shield cooled to about 60 K. Measurements of the total helium vaporization rate in String 2 gives, after substraction of supplementary heat loads and end effects, an estimate of the total thermal load to a standard LHC cell (107 m) including two Short Straight Sections and six dipole cryomagnets. Temperature sensors installed at critical locations provide a temperature mapping which allows validation of the calculated and estimated thermal performance of the cryostat components, including efficiency of the heat interceptions.

  20. Diameter Dependence of Lattice Thermal Conductivity of Single-Walled Carbon Nanotubes: Study from Ab Initio.

    PubMed

    Yue, Sheng-Ying; Ouyang, Tao; Hu, Ming

    2015-01-01

    The effects of temperature, tube length, defects, and surface functionalization on the thermal conductivity (κ) of single-walled carbon nanotubes (SWCNTs) were well documented in literature. However, diameter dependence of thermal conductivity of SWCNTs received less attentions. So far, diverse trends of the diameter dependence have been discussed by different methods and all the previous results were based on empirical interatomic potentials. In this paper, we emphasize to clarify accurate κ values of SWCNTs with different diameters and in-plane κ of graphene. All the studies were under the framework of anharmonic lattice dynamics and Boltzmann transport equation (BTE) based on first principle calculations. We try to infer the right trend of diameter dependent thermal conductivity of SWCNTs. We infer that graphene is the limitation as SWCNT with an infinite diameter. We analyzed the thermal conductivity contributions from each phonon mode in SWCNTs to explain the trend. Meanwhile, we also identify the extremely low thermal conductivity of ultra-thin SWCNTs. PMID:26490342

  1. Diameter Dependence of Lattice Thermal Conductivity of Single-Walled Carbon Nanotubes: Study from Ab Initio

    PubMed Central

    Yue, Sheng-Ying; Ouyang, Tao; Hu, Ming

    2015-01-01

    The effects of temperature, tube length, defects, and surface functionalization on the thermal conductivity (κ) of single-walled carbon nanotubes (SWCNTs) were well documented in literature. However, diameter dependence of thermal conductivity of SWCNTs received less attentions. So far, diverse trends of the diameter dependence have been discussed by different methods and all the previous results were based on empirical interatomic potentials. In this paper, we emphasize to clarify accurate κ values of SWCNTs with different diameters and in-plane κ of graphene. All the studies were under the framework of anharmonic lattice dynamics and Boltzmann transport equation (BTE) based on first principle calculations. We try to infer the right trend of diameter dependent thermal conductivity of SWCNTs. We infer that graphene is the limitation as SWCNT with an infinite diameter. We analyzed the thermal conductivity contributions from each phonon mode in SWCNTs to explain the trend. Meanwhile, we also identify the extremely low thermal conductivity of ultra-thin SWCNTs. PMID:26490342

  2. Dispersion relations of externally and thermally excited dust lattice modes in 2D complex plasma crystals

    SciTech Connect

    Yang Xuefeng; Cui Jian; Zhang Yuan; Liu Yue

    2012-07-15

    The dispersion relations of the externally and thermally (naturally) excited dust lattice modes (both longitudinal and transverse) in two-dimensional Debye-Yukawa complex plasma crystals are investigated. The dispersion relations are calculated numerically by taking the neutral gas damping effects into account and the numerical results are in agreement with the experimental data given by Nunomura et al.[Phys. Rev. E 65, 066402 (2002)]. It is found that for the mode excited by an external disturbance with a real frequency, the dispersion properties are changed at a critical frequency near where the group velocity of the mode goes to zero. Therefore, the high frequency branch with negative dispersion cannot be reached. In contrast, for the thermally excited mode, the dispersion curve can extend all the way to the negative dispersion region, while a 'cut-off' wave number exists at the long wavelength end of the dispersion in the transverse mode.

  3. Lattice Thermal Conductivity of Superlattices from an Adiabatic Bond Charge Model

    NASA Astrophysics Data System (ADS)

    Ward, Alistair; Broido, David

    2007-03-01

    The adiabatic bond charge model (ABCM) has successfully rendered phonon dispersions of a host of bulk semiconductors [1,2] and has also been used to calculate the phonon dispersions in quantum well superlattices [3]. We have developed an ABCM for superlattices and combined it with a symmetry-based representation of the anharmonic interatomic forces to calculate the lattice thermal conductivity of short-period superlattices, using an iterative solution to the Boltzmann-Peierls equation [4]. We compare our ABCM results with those obtained from some commonly used models for the interatomic forces in semiconductors to assess the importance of accurate descriptions of the phonon dispersions in thermal conductivity calculations. [1] W. Weber, Physical Review B 15, 4789 (1977). [2] K. C. Rustagi and W. Weber, Solid State Communications 18, 673 (1976). [3] S. K. Yip and Y. C. Chang, Physical Review B 30 7037 (1984). [4] D. A. Broido, A. Ward, and N. Mingo, Physical Review B 72, 014308 (2005).

  4. Orbital thermal analysis of lattice structured spacecraft using color video display techniques

    NASA Technical Reports Server (NTRS)

    Wright, R. L.; Deryder, D. D.; Palmer, M. T.

    1983-01-01

    A color video display technique is demonstrated as a tool for rapid determination of thermal problems during the preliminary design of complex space systems. A thermal analysis is presented for the lattice-structured Earth Observation Satellite (EOS) spacecraft at 32 points in a baseline non Sun-synchronous (60 deg inclination) orbit. Large temperature variations (on the order of 150 K) were observed on the majority of the members. A gradual decrease in temperature was observed as the spacecraft traversed the Earth's shadow, followed by a sudden rise in temperature (100 K) as the spacecraft exited the shadow. Heating rate and temperature histories of selected members and color graphic displays of temperatures on the spacecraft are presented.

  5. Theory of the lattice Boltzmann method: acoustic and thermal properties in two and three dimensions.

    PubMed

    Lallemand, Pierre; Luo, Li-Shi

    2003-09-01

    The focus of the present work is to provide an analysis for the acoustic and thermal properties of the energy-conserving lattice Boltzmann models, and a solution to the numerical defects and instability associated with these models in two and three dimensions. We discover that a spurious algebraic coupling between the shear and energy modes of the linearized evolution operator is a defect universal to the energy-conserving Boltzmann models in two and three dimensions. This spurious mode coupling is highly anisotropic and may occur at small values of wave number k along certain directions, and it is a direct consequence of the following key features of the lattice Boltzmann equation: (1) its simple spatial-temporal dynamics, (2) the linearity of the relaxation modeling for collision operator, and (3) the energy-conservation constraint. To eliminate the spurious mode coupling, we propose a hybrid thermal lattice Boltzmann equation (HTLBE) in which the mass and momentum conservation equations are solved by using the multiple-relaxation-time model due to d'Humières, whereas the diffusion-advection equation for the temperature is solved separately by using finite-difference technique (or other means). Through the Chapman-Enskog analysis we show that the hydrodynamic equations derived from the proposed HTLBE model include the equivalent effect of gamma=C(P)/C(V) in both the speed and attenuation of sound. Appropriate coupling between the energy and velocity field is introduced to attain correct acoustics in the model. The numerical stability of the HTLBE scheme is analyzed by solving the dispersion equation of the linearized collision operator. We find that the numerical stability of the lattice Boltzmann scheme improves drastically once the spurious mode coupling is removed. It is shown that the HTLBE scheme is far superior to the existing thermal LBE schemes in terms of numerical stability, flexibility, and possible generalization for complex fluids. We also present

  6. Lattice Thermal Conductivity of Ultra High Temperature Ceramics (UHTC) ZrB2 and HfB2 from Atomistic Simulations

    NASA Technical Reports Server (NTRS)

    Lawson, JOhn W.; Daw, Murray S.; Bauschlicher, Charles W.

    2011-01-01

    Ultra high temperature ceramics (UHTC) including ZrB2 and HfB2 are candidate materials for applications in extreme environments because of their high melting point, good mechanical properties and reasonable oxidation resistance. Unlike many ceramics, these materials have high thermal conductivity which can be advantageous, for example, to reduce thermal shock. Recently, we developed Tersoff style interatomic potentials for both ZrB2 and HfB2 appropriate for atomistic simulations. As an application, Green-Kubo molecular dynamics simulations were performed to evaluate the lattice thermal conductivity for single crystals of ZrB2 and HfB2. The atomic mass difference in these binary compounds leads to oscillations in the time correlation function of the heat current. Results at room temperature and at elevated temperatures will be reported.

  7. Influence of asperities on fluid and thermal flow in a fracture: A coupled lattice Boltzmann study

    NASA Astrophysics Data System (ADS)

    Neuville, A.; Flekkøy, E. G.; Toussaint, R.

    2013-07-01

    The characteristics of the hydro-thermal flow which occurs when a cold fluid is injected into a hot fractured bedrock depend on the morphology of the fracture. We consider a sharp triangular asperity, invariant in one direction, perturbing an otherwise flat fracture. We investigate its influence on the macroscopic hydraulic transmissivity and heat transfer efficiency, at fixed low Reynolds number. In this study, numerical simulations are done with a coupled lattice Boltzmann method that solves both the complete Navier-Stokes and advection-diffusion equations in three dimensions. The results are compared with those obtained under lubrication approximations which rely on many hypotheses and neglect the three-dimensional (3-D) effects. The lubrication results are obtained by analytically solving the Stokes equation and a two-dimensional (integrated over the thickness) advection-diffusion equation. We use a lattice Boltzmann method with a double distribution (for mass and energy transport) on hypercubic and cubic lattices. Beyond some critical slope for the boundaries, the velocity profile is observed to be far from a quadratic profile in the vicinity of the sharp asperity: the fluid within the triangular asperity is quasi-static. We find that taking account of both the 3-D effects and the cooling of the rock, are important for the thermal exchange. Neglecting these effects with lubrication approximations results in overestimating the heat exchange efficiency. The evolution of the temperature over time, toward steady state, also shows complex behavior: some sites alternately reheat and cool down several times, making it difficult to forecast the extracted heat.

  8. Nernst and magneto-thermal conductivity in a lattice model of Weyl fermions

    NASA Astrophysics Data System (ADS)

    Sharma, Girish; Goswami, Pallab; Tewari, Sumanta

    Weyl semimetals (WSM) are topologically protected three dimensional materials whose low energy excitations are linearly dispersing massless Dirac fermions, possessing a non-trivial Berry curvature. Using semi-classical Boltzmann dynamics in the relaxation time approximation for a lattice model of time reversal (TR) symmetry broken WSM, we compute both magnetic field dependent and anomalous contributions to the Nernst coefficient. In addition to the magnetic field dependent Nernst response, which is present in both Dirac and Weyl semimetals, we show that, contrary to previous reports, the TR-broken WSM also has an anomalous Nernst response due to a non-vanishing Berry curvature. We also compute the thermal conductivities of a WSM in the Nernst (∇T ⊥ B) and the longitudinal (∇T ∥ B) set-up and confirm from our lattice model that in the parallel set-up, the Wiedemann-Franz law is violated between the longitudinal thermal and electrical conductivities due to chiral anomaly. G.S and S.T are supported by AFOSR (FA9550-13-1-0045). P.G was supported by NSF-JQI-PFC and and LPS-CMTC.

  9. Ab initio lattice dynamical studies of silicon clathrate frameworks and their negative thermal expansion

    NASA Astrophysics Data System (ADS)

    Härkönen, Ville J.; Karttunen, Antti J.

    2014-01-01

    The thermal and lattice dynamical properties of seven silicon clathrate framework structures are investigated with ab initio density functional methods (frameworks I, II, IV, V, VII, VIII, and H). The negative thermal expansion (NTE) phenomenon is investigated by means of quasiharmonic approximation and applying it to equal time displacement correlation functions. The thermal properties of the studied clathrate frameworks, excluding the VII framework, resemble those of the crystalline silicon diamond structure. The clathrate framework VII was found to have an anomalous NTE temperature range up to 300 K and it is suitable for further studies of the mechanisms of NTE. Investigation of the displacement correlation functions revealed that in NTE, the volume derivatives of the mean square displacements and mean square relative displacements of atoms behave similarly to the vibrational entropy volume derivatives and consequently to the coefficients of thermal expansion as a function of temperature. All studied clathrate frameworks, excluding the VII framework, possess a phonon band gap or even two in the case of framework V.

  10. Thermalization and Canonical Typicality in Translation-Invariant Quantum Lattice Systems

    NASA Astrophysics Data System (ADS)

    Müller, Markus P.; Adlam, Emily; Masanes, Lluís; Wiebe, Nathan

    2015-12-01

    It has previously been suggested that small subsystems of closed quantum systems thermalize under some assumptions; however, this has been rigorously shown so far only for systems with very weak interaction between subsystems. In this work, we give rigorous analytic results on thermalization for translation-invariant quantum lattice systems with finite-range interaction of arbitrary strength, in all cases where there is a unique equilibrium state at the corresponding temperature. We clarify the physical picture by showing that subsystems relax towards the reduction of the global Gibbs state, not the local Gibbs state, if the initial state has close to maximal population entropy and certain non-degeneracy conditions on the spectrumare satisfied.Moreover,we showthat almost all pure states with support on a small energy window are locally thermal in the sense of canonical typicality. We derive our results from a statement on equivalence of ensembles, generalizing earlier results by Lima, and give numerical and analytic finite size bounds, relating the Ising model to the finite de Finetti theorem. Furthermore, we prove that global energy eigenstates are locally close to diagonal in the local energy eigenbasis, which constitutes a part of the eigenstate thermalization hypothesis that is valid regardless of the integrability of the model.

  11. First principles lattice thermal conductivity of Li2Se, Li2Te and alloys: phase space guidelines for thermal transport

    NASA Astrophysics Data System (ADS)

    Lindsay, Lucas; Mukhopadhyay, Saikat; Parker, David

    The lattice thermal conductivities (k) of Li2Se, Li2Te and alloys are examined using a first-principles Peierls-Boltzmann transport methodology. The dominant resistance to heat-carrying acoustic phonons in Li2Se and Li2Te comes from the interactions of these modes with two optic phonons, aoo scattering. In typical cubic and hexagonal materials (e . g . , Si, GaAs, AlN) aoo scattering does not play a considerable role in determining k, as it requires significant bandwidth and dispersion of the optic phonon branches, both present in Li2Se and Li2Te. We discuss how these properties and other features of the phonon dispersion (e . g . , bunching of the acoustic branches and an acoustic-optic frequency gap) combine to determine the overall conductivity of a material. Thus, microscopic scattering phase space arguments are generalized to give a more comprehensive view of intrinsic thermal transport in crystalline solids. We note that these general considerations are important for the discovery and design of new `high k' and `low k' materials for thermal management applications. L. L., S. M. and D. S. P. acknowledge support from the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division.

  12. On elliptic Lax systems on the lattice and a compound theorem for hyperdeterminants

    NASA Astrophysics Data System (ADS)

    Delice, N.; Nijhoff, F. W.; Yoo-Kong, S.

    2015-01-01

    A general elliptic N × N matrix Lax scheme is presented, leading to two classes of elliptic lattice systems, one which we interpret as the higher-rank analogue of the Landau-Lifschitz equations, while the other class we characterize as the higher-rank analogue of the lattice Krichever-Novikov equation (or Adler's lattice). We present the general scheme, but focus mainly on the latter type of models. In the case N = 2 we obtain a novel Lax representation of Adler's elliptic lattice equation in its so-called 3-leg form. The case of rank N = 3 is analyzed using Cayley's hyperdeterminant of format 2× 2× 2, yielding a multi-component system of coupled 3-leg quad-equations.

  13. Importance of local force fields on lattice thermal conductivity reduction in PbTe1-xSex alloys

    NASA Astrophysics Data System (ADS)

    Murakami, Takuru; Shiga, Takuma; Hori, Takuma; Esfarjani, Keivan; Shiomi, Junichiro

    2013-05-01

    Lattice thermal conductivity of PbTe1-xSex alloyed crystals has been calculated by molecular-dynamics simulations with anharmonic interatomic force constants (a-IFCs) obtained from first principles. The a-IFCs of pure PbTe and PbSe were calculated by the real-space displacement method with care of the stability for molecular-dynamics simulations. An empirical mixing rule of a-IFCs has been developed to account for both mass and local force-field differences in alloys. The obtained alloy-fraction dependence of lattice thermal conductivity reduction agrees well with the experiments. The comparative study shows that the local force-field difference significantly impacts the lattice thermal conductivity.

  14. Thermal Lattice Expansion in Epitaxial SrTiO3(100) on Si(100)

    SciTech Connect

    McCready, David E.; Liang, Yong; Shutthanandan, V.; Wang, Chong M.; Thevuthasan, Suntharampillai

    2006-10-01

    Thermal lattice expansion in epitaxial SrTiO3(100) grown on Si(100) by molecular beam epitaxy was examined by in situ x-ray diffraction (XRD) at temperatures ranging from 25 C to 1000 C. The SrTiO3 layer thickness ({approx}400 ?) was determined a priori by ex situ x-ray reflectivity (XRR). In addition, the SrTiO3(100) film was further characterized before and after thermal treatment by Rutherford backscattering spectroscopy in channeling geometry (RBS/C) and transmission electron microscopy (TEM). The XRD results showed that the rate of thermal expansion in epitaxial SrTiO3 in the out-of-plane direction is approximately 1.5-2.0 times the bulk value. In addition, the SrTiO3 film was seen to relax after heating. RBS/C and TEM also revealed the formation of a thick ({approx}1000 ?), amorphous silica layer at the SrTiO3/Si interface. Interestingly, the SrTiO3 film retained its epitaxial form atop this non-templating surface while its crystalline quality improved with annealing. These results will be further discussed in the context of their potential application toward silicon-on-insulator (SOI) semiconductor architecture.

  15. Measurement-induced disturbance and thermal negativity in 1D optical lattice chain

    SciTech Connect

    Guo, Jin-Liang; Lin-Wang; Long, Gui-Lu

    2013-03-15

    We study the measurement-induced disturbance (MID) in a 1D optical lattice chain with nonlinear coupling. Special attention is paid to the difference between the thermal entanglement and MID when considering the influences of the linear coupling constant, nonlinear coupling constant and external magnetic field. It is shown that MID is more robust than thermal entanglement against temperature T and external magnetic field B, and MID may reveal more properties about quantum correlations of the system, which can be seen from the point of view that MID can be nonzero when there is no thermal entanglement and MID can detect the critical point of quantum phase transition at finite temperature. - Highlights: Black-Right-Pointing-Pointer The nonlinear coupling constant can strengthen the quantum correlation. Black-Right-Pointing-Pointer MID is more robust than entanglement against temperature and magnetic field. Black-Right-Pointing-Pointer MID exhibits more information about quantum correlation than entanglement. Black-Right-Pointing-Pointer MID can detect the critical point of quantum phase transition at finite temperature.

  16. Electrical Conductivity, Thermal Stability, and Lattice Defect Evolution During Cyclic Channel Die Compression of OFHC Copper

    NASA Astrophysics Data System (ADS)

    Satheesh Kumar, S. S.; Raghu, T.

    2015-02-01

    Oxygen-free high-conductivity (OFHC) copper samples are severe plastically deformed by cyclic channel die compression (CCDC) technique at room temperature up to an effective plastic strain of 7.2. Effect of straining on variation in electrical conductivity, evolution of deformation stored energy, and recrystallization onset temperatures are studied. Deformation-induced lattice defects are quantified using three different methodologies including x-ray diffraction profile analysis employing Williamson-Hall technique, stored energy based method, and electrical resistivity-based techniques. Compared to other severe plastic deformation techniques, electrical conductivity degrades marginally from 100.6% to 96.6% IACS after three cycles of CCDC. Decrease in recrystallization onset and peak temperatures is noticed, whereas stored energy increases and saturates at around 0.95-1.1J/g after three cycles of CCDC. Although drop in recrystallization activation energy is observed with the increasing strain, superior thermal stability is revealed, which is attributed to CCDC process mechanics. Low activation energy observed in CCDC-processed OFHC copper is corroborated to synergistic influence of grain boundary characteristics and lattice defects distribution. Estimated defects concentration indicated continuous increase in dislocation density and vacancy with strain. Deformation-induced vacancy concentration is found to be significantly higher than equilibrium vacancy concentration ascribed to hydrostatic stress states experienced during CCDC.

  17. Superconducting gap and vortex lattice of the heavy-fermion compound CeCu2Si2

    NASA Astrophysics Data System (ADS)

    Enayat, Mostafa; Sun, Zhixiang; Maldonado, Ana; Suderow, Hermann; Seiro, Silvia; Geibel, Christoph; Wirth, Steffen; Steglich, Frank; Wahl, Peter

    2016-01-01

    The order parameter and pairing mechanism for superconductivity in heavy-fermion compounds are still poorly understood. Scanning tunneling microscopy and spectroscopy at ultralow temperatures can yield important information about the superconducting order parameter and the gap structure. Here, we study the first heavy-fermion superconductor, CeCu2Si2 . Our data show the superconducting gap which is not fully formed and exhibits features that point to a multigap order parameter. Spatial mapping of the zero-bias conductance in magnetic field reveals the vortex lattice, which allows us to unequivocally link the observed conductance gap to superconductivity in CeCu2Si2 . The vortex lattice is found to be predominantly triangular with distortions at fields close to ˜0.7 Hc 2 .

  18. Tinselenidene: a Two-dimensional Auxetic Material with Ultralow Lattice Thermal Conductivity and Ultrahigh Hole Mobility.

    PubMed

    Zhang, Li-Chuan; Qin, Guangzhao; Fang, Wu-Zhang; Cui, Hui-Juan; Zheng, Qing-Rong; Yan, Qing-Bo; Su, Gang

    2016-01-01

    By means of extensive ab initio calculations, a new two-dimensional (2D) atomic material tin selenide monolayer (coined as tinselenidene) is predicted to be a semiconductor with an indirect gap (~1.45 eV) and a high hole mobility (of order 10000 cm(2)V(-1)S(-1)), and will bear an indirect-direct gap transition under a rather low strain (<0.5 GPa). Tinselenidene has a very small Young's modulus (20-40 GPa) and an ultralow lattice thermal conductivity (<3 Wm(-1)K(-1) at 300 K), making it probably the most flexible and most heat-insulating material in known 2D atomic materials. In addition, tinseleniden has a large negative Poisson's ratio of -0.17, thus could act as a 2D auxetic material. With these intriguing properties, tinselenidene could have wide potential applications in thermoelectrics, nanomechanics and optoelectronics. PMID:26830330

  19. An immersed boundary-thermal lattice Boltzmann method for solid-liquid phase change

    NASA Astrophysics Data System (ADS)

    Huang, Rongzong; Wu, Huiying

    2014-11-01

    In this work, an immersed boundary-thermal lattice Boltzmann method (IB-TLBM) is proposed to simulate solid-liquid phase change problems. To treat the velocity and temperature boundary conditions on the solid-liquid interface, immersed boundary method (IBM) is adopted, in which the solid-liquid interface is represented as a sharp interface rather than a diffusive interface and is tracked explicitly by Lagrangian grid. The surface forces along the immersed boundary, including the “momentum force” for velocity boundary condition and the “energy force” for temperature boundary condition, are calculated by the direct-forcing scheme. The moving velocity of solid-liquid interface induced by phase change is calculated by the amount of latent heat absorbed or released in a time step directly, with no need to compute temperature gradients in solid and liquid phases separately. The temperature on the solid-liquid interface is specified as the melting temperature, which means phase change happens at a constant temperature. As the solid-liquid interface evolves with time, the identification of phase of Eulerian points and the rearrangement of Lagrangian points are also considered. With regard to the velocity and temperature fields, passive scalar thermal lattice Boltzmann method (TLBM) with multiple-relaxation-time (MRT) collision schemes is adopted. Numerical examples, including conduction-induced melting in a semi-infinite space and melting in a square cavity, are carried out to verify the present method and good results are obtained. As a further application, melting in a circular cylinder with considering the motion of solid phase is simulated successfully by the present method; numerical results show that the motion of solid phase accelerates the melting process obviously.

  20. Lattice structure transformation and change in surface hardness of Ni3Nb and Ni3Ta intermetallic compounds induced by energetic ion beam irradiation

    NASA Astrophysics Data System (ADS)

    Kojima, H.; Yoshizaki, H.; Kaneno, Y.; Semboshi, S.; Hori, F.; Saitoh, Y.; Okamoto, Y.; Iwase, A.

    2016-04-01

    Ni3Nb and Ni3Ta intermetallic compounds, which show the complicated lattice structures were irradiated with 16 MeV Au5+ ions at room temperature. The X-ray diffraction measurement revealed that the lattice structure of these intermetallic compounds changed from the ordered structures to the amorphous state by the ion irradiation. The irradiation-induced amorphization caused the increase in Vickers hardness. The result was compared with our previous results for Ni3Al and Ni3V, and was discussed in terms of the intrinsic lattice structures of the samples.

  1. Lattice thermal conductivity of crystalline and amorphous silicon with and without isotopic effects from the ballistic to diffusive thermal transport regime

    SciTech Connect

    Park, Minkyu; Lee, In-Ho; Kim, Yong-Sung

    2014-07-28

    Thermal conductivity of a material is an important physical parameter in electronic and thermal devices, and as the device size shrinks down, its length-dependence becomes unable to be neglected. Even in micrometer scale devices, materials having a long mean free path of phonons, such as crystalline silicon (Si), exhibit a strong length dependence of the thermal conductivities that spans from the ballistic to diffusive thermal transport regime. In this work, through non-equilibrium molecular-dynamics (NEMD) simulations up to 17 μm in length, the lattice thermal conductivities are explicitly calculated for crystalline Si and up to 2 μm for amorphous Si. The Boltzmann transport equation (BTE) is solved within a frequency-dependent relaxation time approximation, and the calculated lattice thermal conductivities in the BTE are found to be in good agreement with the values obtained in the NEMD. The isotopic effects on the length-dependent lattice thermal conductivities are also investigated both in the crystalline and amorphous Si.

  2. Phase stability and lattice thermal conductivity reduction in CoSb3 skutterudites, doped with chalcogen atoms

    NASA Astrophysics Data System (ADS)

    Battabyal, M.; Priyadarshini, B.; Pradipkanti, L.; Satapathy, Dillip K.; Gopalan, R.

    2016-07-01

    We report a significant reduction in the lattice thermal conductivity of the CoSb3 skuttertudites, doped with chalcogen atoms. Te/Se chalcogen atoms doped CoSb3 skutterudite samples (Te0.1Co4Sb12, Se0.1Co4Sb12, Te0.05Se0.05Co4Sb12) are processed by ball milling and spark plasma sintering. X-ray diffraction data combined with energy dispersive X-ray spectra indicate the doping of Te/Se chalcogen atoms in the skutterudite. The temperature dependent X-ray diffraction confirms the stability of the Te/Se doped CoSb3 skutterudite phase and absence of any secondary phase in the temperature range starting from 300 K to 773 K. The Raman spectroscopy reveals that different chalcogen dopant atoms cause different resonant optical vibrational modes between the dopant atom and the host CoSb3 skutterudite lattice. These optical vibrational modes do scatter heat carrying acoustic phonons in a different spectral range. It was found that among the Te/Se chalcogen atoms, Te atoms alter the host CoSb3 skutterudite lattice vibrations to a larger extent than Se atoms, and can potentially scatter more Sb related acoustic phonons. The Debye model of lattice thermal conductivity confirms that the resonant phonon scattering has important contributions to the reduction of lattice thermal conductivity in CoSb3 skutterudites doped with Te/Se chalcogen atoms. Lattice thermal conductivity ˜ 0.9 W/mK at 773 K is achieved in Te0.1Co4Sb12 skutterudites, which is the lowest value reported so far in CoSb3 skutterudites, doped with single Te chalcogen atom.

  3. Topological Metal of NaBi with Ultralow Lattice Thermal Conductivity and Electron-phonon Superconductivity

    PubMed Central

    Li, Ronghan; Cheng, Xiyue; Xie, Qing; Sun, Yan; Li, Dianzhong; Li, Yiyi; Chen, Xing-Qiu

    2015-01-01

    By means of first-principles and ab initio tight-binding calculations, we found that the compound of NaBi is a three-dimensional non-trivial topological metal. Its topological feature can be confirmed by the presence of band inversion, the derived effective Z2 invariant and the non-trivial surface states with the presence of Dirac cones. Interestingly, our calculations further demonstrated that NaBi exhibits the uniquely combined properties between the electron-phonon coupling superconductivity in nice agreement with recent experimental measurements and the obviously anisotropic but extremely low thermal conductivity. The spin-orbit coupling effects greatly affect those properties. NaBi may provide a rich platform to study the relationship among metal, topology, superconductivity and thermal conductivity. PMID:25676863

  4. Transition to and from the skyrmion lattice phase by electric fields in a magnetoelectric compound.

    PubMed

    Okamura, Y; Kagawa, F; Seki, S; Tokura, Y

    2016-01-01

    Dissipation-less electric control of magnetic state variable is an important target of contemporary spintronics. The non-volatile control of magnetic skyrmions, nanometre-sized spin-swirling objects, with electric fields may exemplify this goal. The skyrmion-hosting magnetoelectric chiral magnet Cu2OSeO3 provides a unique platform for the implementation of such control; however, the hysteresis that accompanies the first-order transition associated with the skyrmion phase is negligibly narrow in practice. Here we demonstrate another method that functions irrespective of the transition boundary. Combination of magnetic-susceptibility measurements and microwave spectroscopy reveals that although the metastable skyrmion lattice is normally hidden behind a more thermodynamically stable conical phase, it emerges under electric fields and persists down to the lowest temperature. Once created, this metastable skyrmion lattice remains without electric fields, establishing a bistability distinct from the transition hysteresis. This bistability thus enables non-volatile electric-field control of the skyrmion lattice even in temperature/magnetic-field regions far from the transition boundary. PMID:27580648

  5. Thermal oxidation of 3-5 compound semiconductors

    NASA Astrophysics Data System (ADS)

    Monteironeto, Othon Derego

    1988-11-01

    Thermal oxidation of 3-5 compound semiconductors has been studied in the temperature range of 300 to 600 C. Two members of this class of materials, namely InP and GaAs, were the object of the experimental work carried out here. The main analytical tools used were transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS). TEM was employed to access microstructural changes and SIMS to access the composition redistribution that takes place as a consequence of the oxidation reaction. Below 400 C oxidation of both materials led to the formation of amorphous scales, which consisted of a mixture of gallium and arsenic oxides in the case of GaAs, and indium phosphate and oxide in the case of InP. The oxidation kinetics of InP was found to be slower than that of GaAs. In the high temperature regime, i.e., above 400 C, the oxidation of both materials resulted in crystalline products. Precipitation of the group 5 element at the scale/semiconductor interface took place during oxidation. At the GaAs/Ga2O3interface, As precipitates were formed with a truncated square pyramid shape bound by (111) sub GaAs planes. The precipitates found at the InPO4/InP interface were either a phosphorus rich phase or red phosphorus. Strong vaporization under the electron beam prohibited a more accurate determination. The morphology of those precipitates were very similar to the As ones in GaAs.

  6. Effects of Lattice Defects and Niobium Doping on Thermoelectric Properties of Calcium Manganate Compounds for Energy Harvesting Applications

    NASA Astrophysics Data System (ADS)

    Graff, Ayelet; Amouyal, Yaron

    2016-03-01

    We have investigated the thermoelectric (TE) properties of Ruddlesden-Popper (RP) CaO(CaMnO3) m n-type compounds, to be applied for TE waste heat recovery at elevated temperatures. We prepared several Nb-doped and undoped CaO(CaMnO3) m compounds having different CaO planar densities by controlling the Ca content via solid-state reaction, and characterized the resulting microstructures by x-ray diffraction analysis and high-resolution scanning electron microscopy. The thermal conductivity, electrical conductivity, and TE thermopower of the different compounds were measured in the range from 300 K through 1000 K. We observed a remarkable reduction in thermal conductivity as a result of increasing the CaO planar density for the Nb-doped RP compounds, from a value of 2.9 W m-1 K-1 for m = ∞ down to 1.3 W m-1 K-1 for m = 1 at 1000 K. This trend was, however, accompanied by a corresponding reduction in electrical conductivity from 76 Ω-1 cm-1 to 2.9 Ω-1 cm-1, which is associated with electron scattering. Finally, we propose an approach that enables optimization of the TE performance of these RP compounds.

  7. Reduction of the temperature jump in the immersed boundary-thermal lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Seta, Takeshi; Hayashi, Kosuke; Tomiyama, Akio

    2015-11-01

    We analytically and numerically investigate the boundary errors computed by the immersed boundary-thermal lattice Boltzmann method (IB-TLBM) with the two-relaxation-time (TRT) collision operator. In the linear collision operator of the TRT, we decompose the distribution function into symmetric and antisymmetric components and define the relaxation parameters for each part. We derive the theoretical relation between the relaxation parameters for the symmetric and antisymmetric parts of the distribution function so as to eliminate the temperature jump. The simple TRT collision operator succeeds in reducing the temperature jump occurring at the high relaxation time in the IB-TLBM calculation. The porous plate problem numerically and analytically demonstrate that the velocity squared terms should be neglected in the equilibrium distribution function in order to eliminate the effect of the advection velocity on the temperature jump in the IB-TLBMs. The passive scalar model without the velocity squared terms more accurately calculates the incompressible temperature equation in the IB-TLBMs, compared to the double distribution model, which is based on the relation of the distribution function gk = (ek - u)2fk / 2 . We apply the passive scalar model without the velocity squared terms to the simulation of the natural convection between a hot circular cylinder and a cold square enclosure. The proposed method adequately sets the boundary values and provides reasonable average Nusselt numbers and maximum absolute values of the stream function.

  8. Tinselenidene: a Two-dimensional Auxetic Material with Ultralow Lattice Thermal Conductivity and Ultrahigh Hole Mobility

    PubMed Central

    Zhang, Li-Chuan; Qin, Guangzhao; Fang, Wu-Zhang; Cui, Hui-Juan; Zheng, Qing-Rong; Yan, Qing-Bo; Su, Gang

    2016-01-01

    By means of extensive ab initio calculations, a new two-dimensional (2D) atomic material tin selenide monolayer (coined as tinselenidene) is predicted to be a semiconductor with an indirect gap (~1.45 eV) and a high hole mobility (of order 10000 cm2V−1S−1), and will bear an indirect-direct gap transition under a rather low strain (<0.5 GPa). Tinselenidene has a very small Young’s modulus (20–40 GPa) and an ultralow lattice thermal conductivity (<3 Wm−1K−1 at 300 K), making it probably the most flexible and most heat-insulating material in known 2D atomic materials. In addition, tinseleniden has a large negative Poisson’s ratio of −0.17, thus could act as a 2D auxetic material. With these intriguing properties, tinselenidene could have wide potential applications in thermoelectrics, nanomechanics and optoelectronics. PMID:26830330

  9. Intrinsic ultralow lattice thermal conductivity of the unfilled skutterudite FeSb3

    NASA Astrophysics Data System (ADS)

    Fu, Yuhao; Singh, David J.; Li, Wu; Zhang, Lijun

    2016-08-01

    It is generally accepted that unfilled skutterudites process high lattice thermal conductivity κl that can be efficiently reduced upon filling. Here by using first-principles Boltzmann-Peierls transport calculations, we find pure skutterudite of FeSb3 with no filler in fact has an intrinsic ultralow κl smaller than that of CoSb3 by one order of magnitude. The value is even smaller than those of most of the fully filled skutterudites. This finding means that with FeSb3 as a reference, filling does not necessarily lower κl. The ultralow κl of FeSb3 is a consequence of the overall softening of phonon spectrum, especially the lowering in frequency of optical phonon branches associated with the weakly bonded Sb4 rings. They overlap more with heat-carrying acoustic phonons and significantly increase the phase space for three-phonon anharmonic scattering processes. This provides an alternative non-filling-related mechanism for lowering the κl of skutterudites.

  10. Lattice thermal conductivity of nanostructured thermoelectric materials based on PbTe

    NASA Astrophysics Data System (ADS)

    Koh, Yee Kan; Vineis, C. J.; Calawa, S. D.; Walsh, M. P.; Cahill, David G.

    2009-04-01

    We report the through-thickness lattice thermal conductivity Λl of (PbTe)1-x/(PbSe)x nanodot superlattices (NDSLs) over a wide range of periods 5 nm≤h≤50 nm, compositions 0.15≤x≤0.25, growth temperatures 550 K≤Tg≤620 K, and growth rates 1 μm h-1≤R≤4 μm h-1. All of our measurements approach Λl of bulk homogenous PbTe1-xSex alloys with the same average composition. For 5 nm≤h≤50 nm, Λl is independent of h; a result we attribute to short mean-free paths of phonons in PbTe and small acoustic impedance mismatch between PbTe/PbSe. We alloyed the PbTe layers of four NDSLs with SnTe up to a mole fraction y =18%; Λl is reduced by <25%.

  11. Massively parallel sampling of lattice proteins reveals foundations of thermal adaptation.

    PubMed

    Venev, Sergey V; Zeldovich, Konstantin B

    2015-08-01

    Evolution of proteins in bacteria and archaea living in different conditions leads to significant correlations between amino acid usage and environmental temperature. The origins of these correlations are poorly understood, and an important question of protein theory, physics-based prediction of types of amino acids overrepresented in highly thermostable proteins, remains largely unsolved. Here, we extend the random energy model of protein folding by weighting the interaction energies of amino acids by their frequencies in protein sequences and predict the energy gap of proteins designed to fold well at elevated temperatures. To test the model, we present a novel scalable algorithm for simultaneous energy calculation for many sequences in many structures, targeting massively parallel computing architectures such as graphics processing unit. The energy calculation is performed by multiplying two matrices, one representing the complete set of sequences, and the other describing the contact maps of all structural templates. An implementation of the algorithm for the CUDA platform is available at http://www.github.com/kzeldovich/galeprot and calculates protein folding energies over 250 times faster than a single central processing unit. Analysis of amino acid usage in 64-mer cubic lattice proteins designed to fold well at different temperatures demonstrates an excellent agreement between theoretical and simulated values of energy gap. The theoretical predictions of temperature trends of amino acid frequencies are significantly correlated with bioinformatics data on 191 bacteria and archaea, and highlight protein folding constraints as a fundamental selection pressure during thermal adaptation in biological evolution. PMID:26254668

  12. Tinselenidene: a Two-dimensional Auxetic Material with Ultralow Lattice Thermal Conductivity and Ultrahigh Hole Mobility

    NASA Astrophysics Data System (ADS)

    Zhang, Li-Chuan; Qin, Guangzhao; Fang, Wu-Zhang; Cui, Hui-Juan; Zheng, Qing-Rong; Yan, Qing-Bo; Su, Gang

    2016-02-01

    By means of extensive ab initio calculations, a new two-dimensional (2D) atomic material tin selenide monolayer (coined as tinselenidene) is predicted to be a semiconductor with an indirect gap (~1.45 eV) and a high hole mobility (of order 10000 cm2V-1S-1), and will bear an indirect-direct gap transition under a rather low strain (<0.5 GPa). Tinselenidene has a very small Young’s modulus (20-40 GPa) and an ultralow lattice thermal conductivity (<3 Wm-1K-1 at 300 K), making it probably the most flexible and most heat-insulating material in known 2D atomic materials. In addition, tinseleniden has a large negative Poisson’s ratio of -0.17, thus could act as a 2D auxetic material. With these intriguing properties, tinselenidene could have wide potential applications in thermoelectrics, nanomechanics and optoelectronics.

  13. Significant reduction of lattice thermal conductivity due to phonon confinement in graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Nissimagoudar, A. S.; Sankeshwar, N. S.

    2014-06-01

    Lattice thermal conductivity, κp, of suspended and supported graphene nanoribbons (GNRs) is studied over a wide temperature range, taking into account the dispersive nature of confined acoustic phonon modes. Employing a modified Callaway model, an expression for κp is developed, considering the explicit contributions from in-plane longitudinal, transverse, and torsional acoustic, and out-of-plane flexural acoustic phonon modes. Numerical calculations of κp(T) are presented assuming the confined acoustic phonons to be scattered by sample boundaries, impurities, and other phonons via both normal and umklapp processes. The effect of phonon confinement is to modify the phonon group velocities and the temperature dependence of κp. In a suspended 5-nm-wide GNR at room temperature, a decrease in κp by ˜70% is predicted. Our study brings out the relative importance of the contributing phonon modes and reveals the influence of flexural phonons on κp as a marked shoulder at low temperatures. The role of the various sample-dependent scattering mechanisms is examined. The substrate, in supported GNRs, is shown to curtail the phonon mean free path and suppress the low-temperature κp. Our results are in good agreement with recent experimental data of Bae et al. [M. H. Bae, Z. Li, Z. Aksamija, P. N. Martin, F. Xiong, Z. Y. Ong, I. Knezevic, and E. Pop, Nat. Commun. 4, 1734 (2013), 10.1038/ncomms2755] for supported GNRs.

  14. Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3Sb7–xTex

    DOE PAGESBeta

    Bansal, Dipanshu; Li, Chen W.; Said, Ayman H.; Abernathy, Douglas L.; Yan, Jiaqiang; Delaire, Olivier A.

    2015-12-07

    Phonon properties of Mo3Sb7–xTex (x = 0, 1.5, 1.7), a potential high-temperature thermoelectric material, have been studied with inelastic neutron and x-ray scattering, and with first-principles simulations. The substitution of Te for Sb leads to pronounced changes in the electronic struc- ture, local bonding, phonon density of states (DOS), dispersions, and phonon lifetimes. Alloying with tellurium shifts the Fermi level upward, near the top of the valence band, resulting in a strong suppression of electron-phonon screening, and a large overall stiffening of interatomic force- constants. The suppression in electron-phonon coupling concomitantly increases group velocities and suppresses phonon scattering rates, surpassingmore » the effects of alloy-disorder scattering, and re- sulting in a surprising increased lattice thermal conductivity in the alloy. We also identify that the local bonding environment changes non-uniformly around different atoms, leading to variable perturbation strengths for different optical phonon branches. The respective roles of changes in phonon group velocities and phonon lifetimes on the lattice thermal conductivity are quantified. Lastly, our results highlight the importance of the electron-phonon coupling on phonon mean-free-paths in this compound, and also estimates the contributions from boundary scattering, umklapp scattering, and point-defect scattering.« less

  15. Study on effective thermal conductivity of silicone/phosphor composite and its size effect by Lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Li, Lan; Zheng, Huai; Yuan, Chao; Hu, Run; Luo, Xiaobing

    2016-02-01

    The silicone/phosphor composite is widely used in light emitting diode (LED) packaging. The composite thermal properties, especially the effective thermal conductivity, strongly influence the LED performance. In this paper, a lattice Boltzmann model was presented to predict the silicone/phosphor composite effective thermal conductivity. Based on the present lattice Boltzmann model, a random generation method was established to describe the phosphor particle distribution in composite. Benchmarks were conducted by comparing the simulation results with theoretical solutions for simple cases. Then the model was applied to analyze the effective thermal conductivity of the silicone/phosphor composite and its size effect. The deviations between simulation and experimental results are <7 %, when the phosphor volume fraction varies from 0.038 to 0.45. The simulation results also indicate that effective thermal conductivity of the composite with larger particles is higher than that with small particles at the same volume fraction. While mixing these two sizes of phosphor particles provides an extra enhancement for the effective thermal conductivity.

  16. Thermal lattice expansion effect on reactive scattering of H2 from Cu(111) at T(s) = 925 K.

    PubMed

    Mondal, Arobendo; Wijzenbroek, Mark; Bonfanti, Matteo; Díaz, Cristina; Kroes, Geert-Jan

    2013-09-12

    Surface phonons and surface temperature may have important effects on reactions of molecules at surfaces, and at present much remains unknown about these effects. A question addressed here, which has received little attention so far, is how reaction at elevated temperature is affected by thermal lattice expansion. To answer this question for the benchmark reaction of H2 and D2 with Cu(111), we have performed quantum and quasi-classical dynamics calculations. The specific reaction parameter (SRP) approach to density functional theory (DFT) has been used to compute the required six-dimensional potential energy surfaces (PES). Computed reaction probabilities and rotational quadrupole alignment parameters have been compared for surface temperatures Ts = 0 and 925 K. Surface thermal expansion of the lattice leads to a considerable decrease of reaction barrier heights and thereby to increased reaction probabilities as well as decreased rotational quadrupole alignment parameter values in associative desorption. PMID:23763274

  17. Lattice Thermal Conductivity of Ultra High Temperature Ceramics ZrB2 and HfB2 from Atomistic Simulations

    NASA Technical Reports Server (NTRS)

    Lawson, John W.; Murray, Daw S.; Bauschlicher, Charles W., Jr.

    2011-01-01

    Atomistic Green-Kubo simulations are performed to evaluate the lattice thermal conductivity for single crystals of the ultra high temperature ceramics ZrB2 and HfB2 for a range of temperatures. Recently developed interatomic potentials are used for these simulations. Heat current correlation functions show rapid oscillations which can be identified with mixed metal-Boron optical phonon modes. Agreement with available experimental data is good.

  18. Ba-filled Ni-Sb-Sn based skutterudites with anomalously high lattice thermal conductivity.

    PubMed

    Paschinger, W; Rogl, G; Grytsiv, A; Michor, H; Heinrich, P R; Müller, H; Puchegger, S; Klobes, B; Hermann, R P; Reinecker, M; Eisenmenger-Sitter, Ch; Broz, P; Bauer, E; Giester, G; Zehetbauer, M; Rogl, P F

    2016-07-01

    Novel filled skutterudites BayNi4Sb12-xSnx (ymax = 0.93) have been prepared by arc melting followed by annealing at 250, 350 and 450 °C up to 30 days in vacuum-sealed quartz vials. Extension of the homogeneity region, solidus temperatures and structural investigations were performed for the skutterudite phase in the ternary Ni-Sn-Sb and in the quaternary Ba-Ni-Sb-Sn systems. Phase equilibria in the Ni-Sn-Sb system at 450 °C were established by means of Electron Probe Microanalysis (EPMA) and X-ray Powder Diffraction (XPD). With rather small cages Ni4(Sb,Sn)12, the Ba-Ni-Sn-Sb skutterudite system is perfectly suited to study the influence of filler atoms on the phonon thermal conductivity. Single-phase samples with the composition Ni4Sb8.2Sn3.8, Ba0.42Ni4Sb8.2Sn3.8 and Ba0.92Ni4Sb6.7Sn5.3 were used to measure their physical properties, i.e. temperature dependent electrical resistivity, Seebeck coefficient and thermal conductivity. The resistivity data demonstrate a crossover from metallic to semiconducting behaviour. The corresponding gap width was extracted from the maxima in the Seebeck coefficient data as a function of temperature. Single crystal X-ray structure analyses at 100, 200 and 300 K revealed the thermal expansion coefficients as well as Einstein and Debye temperatures for Ba0.73Ni4Sb8.1Sn3.9 and Ba0.95Ni4Sb6.1Sn5.9. These data were in accordance with the Debye temperatures obtained from the specific heat (4.4 K < T < 140 K) and Mössbauer spectroscopy (10 K < T < 290 K). Rather small atom displacement parameters for the Ba filler atoms indicate a severe reduction in the "rattling behaviour" consistent with the high levels of lattice thermal conductivity. The elastic moduli, collected from Resonant Ultrasonic Spectroscopy ranged from 100 GPa for Ni4Sb8.2Sn3.8 to 116 GPa for Ba0.92Ni4Sb6.7Sn5.3. The thermal expansion coefficients were 11.8 × 10(-6) K(-1) for Ni4Sb8.2Sn3.8 and 13.8 × 10(-6) K(-1) for Ba0.92Ni4Sb6.7Sn5.3. The room temperature Vickers

  19. Ba-filled Ni–Sb–Sn based skutterudites with anomalously high lattice thermal conductivity

    DOE PAGESBeta

    Paschinger, W.; Rogl, Gerda; Grytsiv, A.; Michor, H.; Heinrich, P. R.; Mueller, H.; Puchegger, S.; Klobes, B.; Hermann, Raphael P.; Reinecker, M.; et al

    2016-06-21

    Here, in this study, novel filled skutterudites BayNi4Sb12-xSnx (ymax = 0.93) have been prepared by arc melting followed by annealing at 250, 350 and 450°C up to 30 days in vacuum-sealed quartz vials. Extension of the homogeneity region, solidus temperatures and structural investigations were performed for the skutterudite phase in the ternary Ni–Sn–Sb and in the quaternary Ba–Ni–Sb–Sn systems. Phase equilibria in the Ni–Sn–Sb system at 450°C were established by means of Electron Probe Microanalysis (EPMA) and X-ray Powder Diffraction (XPD). With rather small cages Ni4(Sb,Sn)12, the Ba–Ni–Sn–Sb skutterudite system is perfectly suited to study the influence of filler atomsmore » on the phonon thermal conductivity. Single-phase samples with the composition Ni4Sb8.2Sn3.8, Ba0.42Ni4Sb8.2Sn3.8 and Ba0.92Ni4Sb6.7Sn5.3 were used to measure their physical properties, i.e. temperature dependent electrical resistivity, Seebeck coefficient and thermal conductivity. The resistivity data demonstrate a crossover from metallic to semiconducting behaviour. The corresponding gap width was extracted from the maxima in the Seebeck coefficient data as a function of temperature. Single crystal X-ray structure analyses at 100, 200 and 300 K revealed the thermal expansion coefficients as well as Einstein and Debye temperatures for Ba0.73Ni4Sb8.1Sn3.9 and Ba0.95Ni4Sb6.1Sn5.9. These data were in accordance with the Debye temperatures obtained from the specific heat (4.4 K < T < 140 K) and Mössbauer spectroscopy (10 K < T < 290 K). Rather small atom displacement parameters for the Ba filler atoms indicate a severe reduction in the “rattling behaviour” consistent with the high levels of lattice thermal conductivity. The elastic moduli, collected from Resonant Ultrasonic Spectroscopy ranged from 100 GPa for Ni4Sb8.2Sn3.8 to 116 GPa for Ba0.92Ni4Sb6.7Sn5.3. The thermal expansion coefficients were 11.8 × 10-6 K-1 for Ni4Sb8.2Sn3.8 and 13.8 × 10-6 K-1 for Ba0.92Ni4

  20. Ba-filled Ni Sb Sn based skutterudites with anomalously high lattice thermal conductivity

    DOE PAGESBeta

    Paschinger, W; Rogl, Gerda; Grytsiv, A; Michor, H.; Heinrich, P. R.; Mueller, H; Puchegger, S; Klobes, B.; Hermann, Raphael P; Reinecker, M; et al

    2016-01-01

    Novel filled skutterudites BayNi4Sb12 xSnx (ymax = 0.93) have been prepared by arc melting followed by annealing at 250, 350 and 450 C up to 30 days in vacuum-sealed quartz vials. Extension of the homogeneity region, solidus temperatures and structural investigations were performed for the skutterudite phase in the ternary Ni Sn Sb and in the quaternary Ba Ni Sb Sn systems. Phase equilibria in the Ni Sn Sb system at 450 C were established by means of Electron Probe Microanalysis (EPMA) and X-ray Powder Diffraction (XPD). With rather small cages Ni4(Sb,Sn)12, the Ba Ni Sn Sb skutterudite system ismore » perfectly suited to study the influence of filler atoms on the phonon thermal conductivity. Single-phase samples with the composition Ni4Sb8.2Sn3.8, Ba0.42Ni4Sb8.2Sn3.8 and Ba0.92Ni4Sb6.7Sn5.3 were used to measure their physical properties, i.e. temperature dependent electrical resistivity, Seebeck coefficient and thermal conductivity. The resistivity data demonstrate a crossover from metallic to semiconducting behaviour. The corresponding gap width was extracted from the maxima in the Seebeck coefficient data as a function of temperature. Single crystal X-ray structure analyses at 100, 200 and 300 K revealed the thermal expansion coefficients as well as Einstein and Debye temperatures for Ba0.73Ni4Sb8.1Sn3.9 and Ba0.95Ni4Sb6.1Sn5.9. These data were in accordance with the Debye temperatures obtained from the specific heat (4.4 K < T < 140 K) and M ssbauer spectroscopy (10 K < T < 290 K). Rather small atom displacement parameters for the Ba filler atoms indicate a severe reduction in the rattling behaviour consistent with the high levels of lattice thermal conductivity. The elastic moduli, collected from Resonant Ultrasonic Spectroscopy ranged from 100 GPa for Ni4Sb8.2Sn3.8 to 116 GPa for Ba0.92Ni4Sb6.7Sn5.3. The thermal expansion coefficients were 11.8 10 6 K 1 for Ni4Sb8.2Sn3.8 and 13.8 10 6 K 1 for Ba0.92Ni4Sb6.7Sn5.3. The room temperature Vickers hardness values

  1. Electron-phonon interaction and thermal boundary resistance at the crystal-amorphous interface of the phase change compound GeTe

    SciTech Connect

    Campi, Davide; Bernasconi, Marco; Donadio, Davide; Sosso, Gabriele C.; Behler, Jörg

    2015-01-07

    Phonon dispersion relations and electron-phonon coupling of hole-doped trigonal GeTe have been computed by density functional perturbation theory. This compound is a prototypical phase change material of interest for applications in phase change non-volatile memories. The calculations allowed us to estimate the electron-phonon contribution to the thermal boundary resistance at the interface between the crystalline and amorphous phases present in the device. The lattice contribution to the thermal boundary resistance has been computed by non-equilibrium molecular dynamics simulations with an interatomic potential based on a neural network scheme. We find that the electron-phonon term contributes to the thermal boundary resistance to an extent which is strongly dependent on the concentration and mobility of the holes. Further, for measured values of the holes concentration and electrical conductivity, the electron-phonon term is larger than the contribution from the lattice. It is also shown that the presence of Ge vacancies, responsible for the p-type degenerate character of the semiconductor, strongly affects the lattice thermal conductivity of the crystal.

  2. Electron-phonon interaction and thermal boundary resistance at the crystal-amorphous interface of the phase change compound GeTe

    NASA Astrophysics Data System (ADS)

    Campi, Davide; Donadio, Davide; Sosso, Gabriele C.; Behler, Jörg; Bernasconi, Marco

    2015-01-01

    Phonon dispersion relations and electron-phonon coupling of hole-doped trigonal GeTe have been computed by density functional perturbation theory. This compound is a prototypical phase change material of interest for applications in phase change non-volatile memories. The calculations allowed us to estimate the electron-phonon contribution to the thermal boundary resistance at the interface between the crystalline and amorphous phases present in the device. The lattice contribution to the thermal boundary resistance has been computed by non-equilibrium molecular dynamics simulations with an interatomic potential based on a neural network scheme. We find that the electron-phonon term contributes to the thermal boundary resistance to an extent which is strongly dependent on the concentration and mobility of the holes. Further, for measured values of the holes concentration and electrical conductivity, the electron-phonon term is larger than the contribution from the lattice. It is also shown that the presence of Ge vacancies, responsible for the p-type degenerate character of the semiconductor, strongly affects the lattice thermal conductivity of the crystal.

  3. Relationship between changes in the crystal lattice strain and thermal conductivity of high burnup UO 2 pellets

    NASA Astrophysics Data System (ADS)

    Amaya, Masaki; Nakamura, Jinichi; Fuketa, Toyoshi; Kosaka, Yuji

    2010-01-01

    Two kinds of disk-shaped UO 2 samples (4 mm in diameter and 1 mm in thickness) were irradiated in a test reactor up to about 60 and 130 GWd/t, respectively. The microstructures of the samples were investigated by means of optical microscopy, scanning electron microscopy/ electron probe micro-analysis (SEM/EPMA) and micro-X-ray diffractometry. The measured lattice parameters tended to be considerably smaller than the reported values, and the typical cauliflower structure which is often observed in high burnup fuel pellet is hardly seen in these samples. Thermal diffusivities of the samples were also measured by using a laser flash method, and their thermal conductivities were evaluated by multiplying the heat capacity of unirradiated UO 2 and sample densities. While the thermal conductivities of sample 2 showed recovery after being annealed at 1500 K, those of sample 4 were not clearly observed even after being annealed at 1500 K. These trends suggest that the amount of accumulated irradiation-induced defects depends on the irradiation condition of each sample. From the comparison of the changes in the lattice parameter and strain energy density before and after the thermal diffusivity measurements, it is likely that the thermal conductivity recovery in the temperature region from 1200 to 1500 K is related to the migration of dislocation.

  4. First-Principles Prediction of Ultralow Lattice Thermal Conductivity of Dumbbell Silicene: A Comparison with Low-Buckled Silicene.

    PubMed

    Peng, Bo; Zhang, Hao; Shao, Hezhu; Xu, Yuanfeng; Zhang, Rongjun; Lu, Hongliang; Zhang, David Wei; Zhu, Heyuan

    2016-08-17

    The dumbbell structure of two-dimensional group IV material offers alternatives to grow thin films for diverse applications. Thermal properties are important for these applications. We obtain the lattice thermal conductivity of low-buckled (LB) and dumbbell (DB) silicene by using first-principles calculations and the Boltzmann transport equation for phonons. For LB silicene, the calculated lattice thermal conductivity with naturally occurring isotope concentrations is 27.72 W/mK. For DB silicene, the calculated value is 2.86 W/mK. The thermal conductivity for DB silicene is much lower than LB silicene due to stronger phonon scattering. Our results will induce further theoretical and experimental investigations on the thermoelectric (TE) properties of DB silicene. The size-dependent thermal conductivity in both LB and DB silicene is investigated as well for designing TE devices. This work sheds light on the manipulation of phonon transport in two-dimensional group IV materials by dumbbell structure formed from the addition of adatoms. PMID:27460331

  5. Massively parallel sampling of lattice proteins reveals foundations of thermal adaptation

    NASA Astrophysics Data System (ADS)

    Venev, Sergey V.; Zeldovich, Konstantin B.

    2015-08-01

    Evolution of proteins in bacteria and archaea living in different conditions leads to significant correlations between amino acid usage and environmental temperature. The origins of these correlations are poorly understood, and an important question of protein theory, physics-based prediction of types of amino acids overrepresented in highly thermostable proteins, remains largely unsolved. Here, we extend the random energy model of protein folding by weighting the interaction energies of amino acids by their frequencies in protein sequences and predict the energy gap of proteins designed to fold well at elevated temperatures. To test the model, we present a novel scalable algorithm for simultaneous energy calculation for many sequences in many structures, targeting massively parallel computing architectures such as graphics processing unit. The energy calculation is performed by multiplying two matrices, one representing the complete set of sequences, and the other describing the contact maps of all structural templates. An implementation of the algorithm for the CUDA platform is available at http://www.github.com/kzeldovich/galeprot and calculates protein folding energies over 250 times faster than a single central processing unit. Analysis of amino acid usage in 64-mer cubic lattice proteins designed to fold well at different temperatures demonstrates an excellent agreement between theoretical and simulated values of energy gap. The theoretical predictions of temperature trends of amino acid frequencies are significantly correlated with bioinformatics data on 191 bacteria and archaea, and highlight protein folding constraints as a fundamental selection pressure during thermal adaptation in biological evolution.

  6. Anderson lattice in the intermediate valence compound Ce3Ni2B2N3-δ

    NASA Astrophysics Data System (ADS)

    Ali, Tahir; Bauer, Ernst; Hilscher, Gerfried; Michor, Herwig

    2011-03-01

    We have studied magnetic, thermodynamic, and transport properties of Ce3Ni2B2N3-δ and its solid solution with the Tc≃13 K superconductor La3Ni2B2N3-δ. The solid solution (La,Ce)3Ni2B2N3-δ reveals a rapid reduction of Tc by increasing the Ce content with a complete suppression of superconductivity at the composition La2.85Ce0.15Ni2B2N3-δ. The low-temperature properties characterize Ce3Ni2B2N3-δ as an intermediate valence system with a moderately enhanced Sommerfeld value γ≃54 mJ/mol K2 and a susceptibility χ0≃1.6×10-3 emu/mol, increased by about one order of magnitude as compared to the respective value χ0≃0.2×10-3 emu/mol of superconducting La3Ni2B2N3-δ (γ=26 mJ/mol K2) which serves as reference with a nonmagnetic rare earth ion. The electrical resistivity and thermoelectric power of Ce3Ni2B2N3-δ are analyzed in terms of the degenerate Anderson lattice model revealing a characteristic Kondo temperature TKALM~1100 K.

  7. A nonlocal Fourier's law and its application to the heat conduction of one-dimensional and two-dimensional thermal lattices

    NASA Astrophysics Data System (ADS)

    Challamel, Noël; Grazide, Cécile; Picandet, Vincent; Perrot, Arnaud; Zhang, Yingyan

    2016-06-01

    This study focuses on heat conduction in unidimensional lattices also known as microstructured rods. The lattice thermal properties can be representative of concentrated thermal interface phases in one-dimensional segmented rods. The exact solution of the linear time-dependent spatial difference equation associated with the lattice problem is presented for some given initial and boundary conditions. This exact solution is compared to the quasicontinuum approximation built by continualization of the lattice equations. A rational-based asymptotic expansion of the pseudo-differential problem leads to an equivalent nonlocal-type Fourier's law. The differential nonlocal Fourier's law is analysed with respect to thermodynamic models available in the literature, such as the Guyer-Krumhansl-type equation. The length scale of the nonlocal heat law is calibrated with respect to the lattice spacing. An error analysis is conducted for quantifying the efficiency of the nonlocal model to capture the lattice evolution problem, as compared to the local model. The propagation of error with the nonlocal model is much slower than that in its local counterpart. A two-dimensional thermal lattice is also considered and approximated by a two-dimensional nonlocal heat problem. It is shown that nonlocal and continualized heat equations both approximate efficiently the two-dimensional thermal lattice response. These extended continuous heat models are shown to be good candidates for approximating the heat transfer behaviour of microstructured rods or membranes.

  8. Giant Phonon Anharmonicity and Anomalous Pressure Dependence of Lattice Thermal Conductivity in Y2Si2O7 silicate

    PubMed Central

    Luo, Yixiu; Wang, Jiemin; Li, Yiran; Wang, Jingyang

    2016-01-01

    Modification of lattice thermal conductivity (κL) of a solid by means of hydrostatic pressure (P) has been a crucially interesting approach that targets a broad range of advanced materials from thermoelectrics and thermal insulators to minerals in mantle. Although it is well documented knowledge that thermal conductivity of bulk materials normally increase upon hydrostatic pressure, such positive relationship is seriously challenged when it comes to ceramics with complex crystal structure and heterogeneous chemical bonds. In this paper, we predict an abnormally negative trend dκL/dP < 0 in Y2Si2O7 silicate using density functional theoretical calculations. The mechanism is disclosed as combined effects of slightly decreased group velocity and significantly augmented scattering of heat-carrying acoustic phonons in pressured lattice, which is originated from pressure-induced downward shift of low-lying optic and acoustic phonons. The structural origin of low-lying optic phonons as well as the induced phonon anharmonicity is also qualitatively elucidated with respect to intrinsic bonding heterogeneity of Y2Si2O7. The present results are expected to bring deeper insights for phonon engineering and modulation of thermal conductivity in complex solids with diverging structural flexibility, enormous bonding heterogeneity, and giant phonon anharmonicity. PMID:27430670

  9. Giant Phonon Anharmonicity and Anomalous Pressure Dependence of Lattice Thermal Conductivity in Y2Si2O7 silicate

    NASA Astrophysics Data System (ADS)

    Luo, Yixiu; Wang, Jiemin; Li, Yiran; Wang, Jingyang

    2016-07-01

    Modification of lattice thermal conductivity (κL) of a solid by means of hydrostatic pressure (P) has been a crucially interesting approach that targets a broad range of advanced materials from thermoelectrics and thermal insulators to minerals in mantle. Although it is well documented knowledge that thermal conductivity of bulk materials normally increase upon hydrostatic pressure, such positive relationship is seriously challenged when it comes to ceramics with complex crystal structure and heterogeneous chemical bonds. In this paper, we predict an abnormally negative trend dκL/dP < 0 in Y2Si2O7 silicate using density functional theoretical calculations. The mechanism is disclosed as combined effects of slightly decreased group velocity and significantly augmented scattering of heat-carrying acoustic phonons in pressured lattice, which is originated from pressure-induced downward shift of low-lying optic and acoustic phonons. The structural origin of low-lying optic phonons as well as the induced phonon anharmonicity is also qualitatively elucidated with respect to intrinsic bonding heterogeneity of Y2Si2O7. The present results are expected to bring deeper insights for phonon engineering and modulation of thermal conductivity in complex solids with diverging structural flexibility, enormous bonding heterogeneity, and giant phonon anharmonicity.

  10. Giant Phonon Anharmonicity and Anomalous Pressure Dependence of Lattice Thermal Conductivity in Y2Si2O7 silicate.

    PubMed

    Luo, Yixiu; Wang, Jiemin; Li, Yiran; Wang, Jingyang

    2016-01-01

    Modification of lattice thermal conductivity (κL) of a solid by means of hydrostatic pressure (P) has been a crucially interesting approach that targets a broad range of advanced materials from thermoelectrics and thermal insulators to minerals in mantle. Although it is well documented knowledge that thermal conductivity of bulk materials normally increase upon hydrostatic pressure, such positive relationship is seriously challenged when it comes to ceramics with complex crystal structure and heterogeneous chemical bonds. In this paper, we predict an abnormally negative trend dκL/dP < 0 in Y2Si2O7 silicate using density functional theoretical calculations. The mechanism is disclosed as combined effects of slightly decreased group velocity and significantly augmented scattering of heat-carrying acoustic phonons in pressured lattice, which is originated from pressure-induced downward shift of low-lying optic and acoustic phonons. The structural origin of low-lying optic phonons as well as the induced phonon anharmonicity is also qualitatively elucidated with respect to intrinsic bonding heterogeneity of Y2Si2O7. The present results are expected to bring deeper insights for phonon engineering and modulation of thermal conductivity in complex solids with diverging structural flexibility, enormous bonding heterogeneity, and giant phonon anharmonicity. PMID:27430670

  11. Some properties of correlations of quantum lattice systems in thermal equilibrium

    SciTech Connect

    Fröhlich, Jürg; Ueltschi, Daniel

    2015-05-15

    Simple proofs of uniqueness of the thermodynamic limit of KMS states and of the decay of equilibrium correlations are presented for a large class of quantum lattice systems at high temperatures. New quantum correlation inequalities for general Heisenberg models are described. Finally, a simplified derivation of a general result on power-law decay of correlations in 2D quantum lattice systems with continuous symmetries is given, extending results of McBryan and Spencer for the 2D classical XY model.

  12. Thermal properties of quaternary ammonium and pyridinium compounds

    SciTech Connect

    Aksenova, V.P.; Khar'kov, S.N.; Logovotovskaya, V.D.; Belotserkovets, N.I.; Chegolya, A.S.

    1982-12-10

    In the present work an attempt was made at a comprehensive investigation of the influence of the chemical structure of a whole series of cation-active surfactants on the stability to temperature influences, and the general directions of the irreversible transformations at high temperature were established. As a result of a study of processes of thermal decomposition of quaternary ammonium and syridinium salts, quantitative correlations were established according to the influence of the chemical structure of the salts on the limits of thermal stability. On the basis of a detailed analysis of volatile pyrolysis products, concrete schemes of the conversions in the objects studied were proposed.

  13. Generalized Debye-Peierls/Allen-Feldman model for the lattice thermal conductivity of low-dimensional and disordered materials

    NASA Astrophysics Data System (ADS)

    Zhu, Taishan; Ertekin, Elif

    2016-04-01

    We present a generalized model to describe the lattice thermal conductivity of low-dimensional (low-D) and disordered systems. The model is a straightforward generalization of the Debye-Peierls and Allen-Feldman schemes to arbitrary dimensions, accounting for low-D effects such as differences in dispersion, density of states, and scattering. Similar in spirit to the Allen-Feldman approach, heat carriers are categorized according to their transporting capacity as propagons, diffusons, and locons. The results of the generalized model are compared to experimental results when available, and equilibrium molecular dynamics simulations otherwise. The results are in very good agreement with our analysis of phonon localization in disordered low-D systems, such as amorphous graphene and glassy diamond nanothreads. Several unique aspects of thermal transport in low-D and disordered systems, such as milder suppression of thermal conductivity and negligible diffuson contributions, are captured by the approach.

  14. The relationship between bond ionicity, lattice energy, coefficient of thermal expansion and microwave dielectric properties of Nd(Nb(1-x)Sb(x))O4 ceramics.

    PubMed

    Zhang, Ping; Zhao, Yonggui; Wang, Xiuyu

    2015-06-28

    The crystalline structure refinement, chemical bond ionicity, lattice energy and coefficient of thermal expansion were carried out for Nd(Nb(1-x)Sb(x))O4 ceramics with a monoclinic fergusonite structure to investigate the correlations between the crystalline structure, phase stability, bond ionicity, lattice energy, coefficient of thermal expansion, and microwave dielectric properties. The bond ionicity, lattice energy, and coefficient of thermal expansion of Nd(Nb(1-x)Sb(x))O4 ceramics were calculated using a semiempirical method based on the complex bond theory. The phase structure stability varied with the lattice energy which was resulted by the substitution constant of Sb(5+). With the increasing of the Sb(5+) contents, the decrease of Nb/Sb-O bond ionicity was observed, which could be contributed to the electric polarization. The ε(r) had a close relationship with the Nb/Sb-O bond ionicity. The increase of the Q×f and |τ(f)| values could be attributed to the lattice energy and the coefficient of thermal expansion. The microwave dielectric properties of Nd(Nb(1-x)Sb(x))O4 ceramics with the monoclinic fergusonite structure were strongly dependent on the chemical bond ionicity, lattice energy and coefficient of thermal expansion. PMID:25997635

  15. Friction, wear, and thermal stability studies of some organotin and organosilicon compounds

    NASA Technical Reports Server (NTRS)

    Jones, W. R., Jr.

    1973-01-01

    Thermal decomposition temperatures were determined for a number of organotin and organosilicon compounds. A ball-on-disk sliding friction apparatus was used to determine the friction and wear characteristics of two representative compounds, (1) 3-tri-n-butylstannyl (diphenyl) and (2) 3-tri-n-butylsilyl (diphenyl). Friction and wear test conditions included a 1-kg load, 25 to 225 C disk temperatures, and a dry air atmosphere. The tin and silicon compounds yielded friction and wear results either lower than or similar to those obtained with a polyphenyl ether and a C-ether. The maximum thermal decomposition temperatures obtained in the silicon and tin series were 358 and 297 C, respectively. Increasing the steric hindrance around the silicon or tin atoms increased the thermal stability. Future work with these compounds will emphasize their use as antiwear additives rather than base fluids.

  16. The Role of Lattice Dynamics on The Thermal Properties of Cu-Ni Alloys

    NASA Astrophysics Data System (ADS)

    Onat, Berk; Durukanoglu, Sondan

    2014-03-01

    We have investigated Cu-Ni alloys with both disorder and order phases in fcc structures to analyze the effect of temperature dependent vibrational thermodynamical properties. The interactions between the atoms in the model systems are defined using an EAM type potential, specifically developed for Cu-Ni alloys. Vibrational thermodynamic functions are determined within the harmonic approximation of lattice dynamics and the vibrational densities of states are calculated using real space Green's function technique. In addition, through ab-initio calculations we have estimated the electronic contributions to set the ground for a comparative discussion. Our results show that the overall characteristics of thermodynamic functions of Cu-Ni alloys of varying concentrations are governed by the lattice vibrations. We will present our results for free energy, heat capacity and entropy of ordered/disordered Cu-Ni alloys with the experimental findings and discuss the electronic, anharmonic and lattice dynamic contributions.

  17. Spin-glass-like behavior and negative thermal expansion in antiperovskite Mn{sub 3}Ni{sub 1−x}Cu{sub x}N compounds

    SciTech Connect

    Ding, Lei; Wang, Cong Sun, Ying; Colin, Claire V.; Chu, Lihua

    2015-06-07

    The Cu-doping effect on the lattice and magnetic properties in Mn{sub 3}Ni{sub 1−x}Cu{sub x}N (x = 0, 0.3, 0.5, 0.7, 1.0) was extensively investigated. We observed that the Cu-doping at the Ni site complicated the magnetic ground states, which induced the competition of antiferromagnetic and ferromagnetic interactions. Spin-glass-like behavior, arising from possible site-randomness and competing interactions of magnetism, was observed in compounds with x = 0.3, 0.5, and 0.7, and typically discussed by means of the measurement of ac magnetic susceptibility for x = 0.7. The negative thermal expansion (NTE) behavior, due to the magnetic ordering transition, was observed in Mn{sub 3}Ni{sub 1−x}Cu{sub x}N compounds using variable temperature x-ray diffraction. It reveals that the introduction of Cu effectively broadens the temperature range displaying negative thermal expansion. The relationship between the local lattice distortion and the competing magnetic ground states might play an important role in broadening the NTE temperature range in this antiperovskite compound.

  18. Characterization of radiation-induced lattice vacancies in intermetallic compounds by means of positron-lifetime studies

    NASA Astrophysics Data System (ADS)

    Würschum, R.; Badura-Gergen, K.; Kümmerle, E. A.; Grupp, C.; Schaefer, H.-E.

    1996-07-01

    In the present paper a characterization of atomic vacancies in intermetallic compounds is given by means of positron-lifetime measurements after electron irradiation and comparison with the states after preparation, after long-time annealing, or in high-temperature equilibrium. In TiAl, Ti3Al, and Ni3Al no structural vacancies (detection limit CV=10-6) are observed at ambient temperature. This confirms that in these compounds slight deviations from stoichiometry are compensated by antisite atoms. In the Al-poor B2 alloys FeAl and NiAl, on the other hand, remnant vacancies exist due to the high thermal equilibrium vacancy concentrations and their slow diffusivities. The kinetics of vacancy elimination in FeAl and NiAl is discussed. A substantial temperature dependence of the positron lifetime in vacancies is detected in close-packed intermetallics which is attributed to an increased atomic relaxation or partial positron detrapping at high temperatures. In contrast to that, the temperature dependence of the positron lifetime in vacancies is small in the open-structured B2 aluminides. The lifetimes τf of free delocalized positrons in transition-metal aluminides and in NiZr and NiTi can be correlated to those of the pure components, taking into account the densities of valence electrons. For the positron lifetimes τ1 of vacancies in intermetallic compounds, values of τ1/τf=1.5-1.7 are observed similar as in the pure metals. Annealing studies of B2-FeAl after electron irradiation yield time constants for the disappearance of vacancies identical to those deduced recently for the equilibration of thermal vacancies. In electron-irradiated Ti aluminides annealing processes at 250 K and 450 K are observed where the latter process is tentatively attributed to long-range migration of vacancies.

  19. Antiferromagnetic Kondo lattice in the layered compounds Re2NiGa9Ge2 (Re =Ce, Pr, Sm)

    NASA Astrophysics Data System (ADS)

    Zhu, Yanglin; Liu, Jinyu; Hu, Jin; Adams, Daniel; Spinu, Leonard; Mao, Zhiqiang

    Intermetallic compounds containing rare-earth/actinide elements with 4f/5f electrons have formed a special family of strongly correlated materials, i.e. heavy fermion systems. We have recently found a new layered rare earth intermetallic system showing moderate heavy fermion behavior: Re2NiGa9Ge2 (Re =Ce, Sm, Pr). The Re =Ce and Sm members were previously synthesized, while their electronic properties have not been reported. We have recently grown single crystals of Re2NiGa9Ge2 (Re =Ce, Sm, Pr) and characterized their electronic and magnetic properties. We find all these materials are antiferromagnetic, with TN = 2.5 K, 5 K, 3.4 K respectively for Re =Ce, Pr and Sm. Moreover, they also exhibit large values of electronic specific coefficient: γ ~ 101 mJ mol-Ce-1 K-2 for Re =Ce, 368 mJ mol-Pr-1 K-2 for Re =Pr, and 196.4 mJ mol-Sm-1 K-2 for Re =Sm, indicating enhanced Kondo effect and the presence of AFM Kondo lattice. Our findings suggest that Re2NiGa9Ge2 (Re =Ce, Pr, Sm) could be interesting candidate materials for exploring novel exotic properties of correlated electrons through external parameter tuning such as chemical substitution and pressure.

  20. Effects of molecular and lattice structure on the thermal behaviours of some long chain length potassium(I) n-alkanoates

    NASA Astrophysics Data System (ADS)

    Nelson, Peter N.; Ellis, Henry A.; Taylor, Richard A.

    2014-01-01

    Lattice structures and thermal behaviours for some long chain potassium carboxylates (nc = 8-18, inclusive) are investigated using Fourier Transform Infrared spectroscopy, X-ray Powder Diffraction, Solid State spin decoupled 13C NMR spectroscopy, Differential Scanning Calorimetry and Thermogravimetry. The measurements show that the carboxyl groups are coordinated to potassium atoms via asymmetric chelating bidentate bonding, with extensive carboxyl intermolecular interactions to yield tetrahedral metal centers, irrespective of chain length. Furthermore, the hydrocarbon chains are crystallized in the fully extended all-trans configuration and are arranged as non-overlapping lamellar bilayer structures with closely packed methyl groups from opposite layers. Additionally, odd-even alternation, observed in density and methyl group chemical shift, is ascribed to the relative vertical distances between layers in the bilayer, that are not in the same plane. Therefore, for even chain homologues, where this distances is less than for odd chain adducts, more intimate packing is indicated. The phase sequences for all compounds show several reversible crystal-crystal transition associated with kinetically controlled gauche-trans isomerism of the polymethylene chains which undergo incomplete fusion when heated to the melt. The compounds degrade above 785 K to yield carbon dioxide, water, potassium oxide and an alkene.

  1. Lattice Thermal Conductivity of Ultra High Temperature Ceramics (UHTC) ZrB2 and HfB2 from Atomistic Simulations

    NASA Technical Reports Server (NTRS)

    Lawson, John W.; Daw, Murray S.; Bauschlicher, Charles W.

    2012-01-01

    Ultra high temperature ceramics (UHTC) including ZrB2 and HfB2 have a number of properties that make them attractive for applications in extreme environments. One such property is their high thermal conductivity. Computational modeling of these materials will facilitate understanding of fundamental mechanisms, elucidate structure-property relationships, and ultimately accelerate the materials design cycle. Progress in computational modeling of UHTCs however has been limited in part due to the absence of suitable interatomic potentials. Recently, we developed Tersoff style parameterizations of such potentials for both ZrB2 and HfB2 appropriate for atomistic simulations. As an application, Green-Kubo molecular dynamics simulations were performed to evaluate the lattice thermal conductivity for single crystals of ZrB2 and HfB2. The atomic mass difference in these binary compounds leads to oscillations in the time correlation function of the heat current, in contrast to the more typical monotonic decay seen in monoatomic materials such as Silicon, for example. Results at room temperature and at elevated temperatures will be reported.

  2. Non-Newtonian unconfined flow and heat transfer over a heated cylinder using the direct-forcing immersed boundary-thermal lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Amiri Delouei, A.; Nazari, M.; Kayhani, M. H.; Succi, S.

    2014-05-01

    In this study, the immersed boundary-thermal lattice Boltzmann method has been used to simulate non-Newtonian fluid flow over a heated circular cylinder. The direct-forcing algorithm has been employed to couple the off-lattice obstacles and on-lattice fluid nodes. To investigate the effect of boundary sharpness, two different diffuse interface schemes are considered to interpolate the velocity and temperature between the boundary and computational grid points. The lattice Boltzmann equation with split-forcing term is applied to consider the effects of the discrete lattice and the body force to the momentum flux, simultaneously. A method for calculating the Nusselt number based on diffuse interface schemes is developed. The rheological and thermal properties of non-Newtonian fluids are investigated under the different power-law indices and Reynolds numbers. The effect of numerical parameters on the accuracy of the proposed method has been investigated in detail. Results show that the rheological and thermal properties of non-Newtonian fluids in the presence of a heated immersed body can be suitably captured using the immersed boundary thermal lattice Boltzmann method.

  3. Thermal Cycling Effects on the Thermoelectric Properties of n-Type In, Ce based Skutterudite Compounds

    SciTech Connect

    Biswas, Krishnendu; Subramanian, Mas A.; Good, Morris S.; Roberts, Kamandi C.; Hendricks, Terry J.

    2012-06-14

    N-type In-filled CoSb3 are known skutterudite compounds that have shown promising thermoelectric (TE) properties resulting in high dimensionless figure of merit values at elevated temperatures. Their use in various waste heat recovery applications will require that they survive and operate after exposure to harsh thermal cycling environments. This research focused on uncovering the thermal cycling effects on thermoelectric properties of n-type In0.2Co4Sb12 and In0.2Ce0.15Co4Sb12 skutterudite compositions as well as quantifying their temperature-dependent structural properties (elastic modulus, shear modulus, and Poisson's ratio). It was observed that the Seebeck coefficient and resistivity increased only slightly in the double-filled In,Ce skutterudite materials upon thermal cycling. In the In-filled skutterudites the Seebeck coefficient remained approximately the same on thermal cycling, while electrical resistivity increased significantly after thermal cycling. Results also show that thermal conductivity marginally decreases in the case of In-filled skutterudites, whereas the reduction is more pronounced in In, Ce-based skutterudite compounds. The possible reason for this kind of reduction can be attributed to grain pinning effects due to formation of nano inclusions. High temperature structural property measurements (i.e., Young's modulus and shear modulus) are also reported and the results show that these structural properties decrease slowly as temperature increases and the compounds are structurally stable after numerous thermal cycles.

  4. Coupled theoretical interpretation and experimental investigation of the lattice thermal conductivity of Bi2Te3 single crystal

    NASA Astrophysics Data System (ADS)

    Jacquot, A.; Bayer, B.; Winkler, M.; Jaegle, M.

    2012-06-01

    An essential challenge in thermoelectric material research is the selection of materials having potentially a high figure-of-merit and their improvement by the reduction of their lattice thermal conductivity. In the present article the Debye model is modified for the calculation of the lattice thermal conductivity and used to gain insight into the anisotropy of single crystalline bismuth telluride (Bi2Te3). In this article the minimum wavelength of phonons that moved, which is closely related to the concept of cutoff frequency, is not taken twice the atoms separation. The Debye temperature is in fact not used to estimate the cutoff frequencies of the phonons that carry heat. The cutoff frequencies are defined in this work by setting an upper limit to the energy of acoustic phonons using the complete dispersion relations. Our work indicates that the cutoff frequencies of acoustic phonons are anisotropic in Bi2Te3. The anisotropy of the thermal conductivity is surprisingly found to be unrelated to the anisotropy of the sound velocities that are calculated as a function of the tensor of the elastic constants. The sound velocity is in fact almost isotropic when the longitudinal and two transversal waves are added together. In addition it is suggested that the relaxation time is also a function of the cutoff frequencies and that this may counterbalance the anisotropy arising from the variation of the number of acoustic phonons traveling in various directions. Finally, the anisotropy of the thermal conductivity of Bi2Te3 single crystal is found to be mostly related to the Grüneisen's constant if the main scattering mechanism is a phonon-phonon interaction.

  5. Cryogenic abnormal thermal expansion properties of carbon-doped La(Fe,Si)13 compounds.

    PubMed

    Li, Shaopeng; Huang, Rongjin; Zhao, Yuqiang; Wang, Wei; Li, Laifeng

    2015-12-14

    Recently, La(Fe,Si)13-based compounds have attracted much attention due to their isotropic and tunable abnormal thermal expansion (ATE) properties as well as bright prospects for practical applications. In this research, we have prepared cubic NaZn13-type carbon-doped La(Fe,Si)13 compounds by the arc-melting method, and their ATE and magnetic properties were investigated by means of variable-temperature X-ray diffraction, strain gauge and the physical property measurement system (PPMS). The experimental results indicate that both micro and macro negative thermal expansion (NTE) behaviors gradually weaken with the increase of interstitial carbon atoms. Moreover, the temperature region with the most remarkable NTE properties has been broadened and near zero thermal expansion (NZTE) behavior occurs in the bulk carbon-doped La(Fe,Si)13 compounds. PMID:26549525

  6. The impact of milling and thermal processing on phenolic compounds in cereal grains.

    PubMed

    Ragaee, Sanaa; Seetharaman, Koushik; Abdel-Aal, El-Sayed M

    2014-01-01

    Consumption of wholegrain foods has been recommended for healthy diets. The beneficial health properties of wholegrain products have been associated with the presence of higher amounts of dietary fiber and antioxidants and lower calories as compared to their respective refined ones. Phenolic compounds are mainly attributed to antioxidant properties of wholegrain foods. This review article provides a single comprehensive source that describes effects of milling and thermal processing on phenolic compounds and antioxidant properties in cereals. In general, milling and pearling processes affect the distribution of phenolic, compounds and thus antioxidant properties vary among the milling fractions. Thermal processes such as baking and extrusion could cause negative or positive effects on phenolic compounds and antioxidant properties of the end product subject to grain type and processing conditions. Thus factors that enhance health benefits of wholegrain cereal products have been discussed. PMID:24499063

  7. Nematic order by thermal disorder in a three-dimensional lattice spin model with dipolarlike interactions.

    PubMed

    Chamati, Hassan; Romano, Silvano

    2014-08-01

    At low temperatures, some lattice spin models with simple ferromagnetic or antiferromagnetic interactions (for example, nearest-neighbor interaction being isotropic in spin space on a bipartite three-dimensional lattice) produce orientationally ordered phases exhibiting nematic (second-rank) order, in addition to the primary first-rank one; on the other hand, in the literature, they have been rather seldom investigated in this respect. Here we study the thermodynamic properties of a three-dimensional model with dipolar-like interaction. Its ground state is found to exhibit full orientational order with respect to a suitably defined staggered magnetization (polarization), but no nematic second-rank order. Extensive Monte Carlo simulations, in conjunction with finite-size scaling analysis, have been used for characterizing its critical behavior; on the other hand, it has been found that nematic order does indeed set in at low temperatures, via a mechanism of order by disorder. PMID:25215748

  8. Application of Artificial Neural Networks in Differential Thermal Analysis of Inorganic Compounds

    NASA Astrophysics Data System (ADS)

    Ilgun, Ozlem; Beken, Murat; Alekberov, Vilayet; Ozcanli, Yesim

    2010-01-01

    Thermal decomposition of inorganic compounds have been analyzed by simultaneous differential thermal analysis (DTA) method. Also phase transitions and critical points have been investigated. Additionally a computer model based on backpropagation multilayer feed-forward artificial neural networks (ANNs) have been used for the stimulation and prediction of critical points and phase transitions of inorganic compounds. Experimental data and output values of artificial neural networks have been compared and ANN predictions showed a considerably good result due to some unjustified data values and ANN predictions concurred with each other.

  9. First principles calculation of lattice thermal conductivity of metals considering phonon-phonon and phonon-electron scattering

    NASA Astrophysics Data System (ADS)

    Wang, Yan; Lu, Zexi; Ruan, Xiulin

    2016-06-01

    The effect of phonon-electron (p-e) scattering on lattice thermal conductivity is investigated for Cu, Ag, Au, Al, Pt, and Ni. We evaluate both phonon-phonon (p-p) and p-e scattering rates from first principles and calculate the lattice thermal conductivity (κL). It is found that p-e scattering plays an important role in determining the κL of Pt and Ni at room temperature, while it has negligible effect on the κL of Cu, Ag, Au, and Al. Specifically, the room temperature κLs of Cu, Ag, Au, and Al predicted from density-functional theory calculations with the local density approximation are 16.9, 5.2, 2.6, and 5.8 W/m K, respectively, when only p-p scattering is considered, while it is almost unchanged when p-e scattering is also taken into account. However, the κL of Pt and Ni is reduced from 7.1 and 33.2 W/m K to 5.8 and 23.2 W/m K by p-e scattering. Even though Al has quite high electron-phonon coupling constant, a quantity that characterizes the rate of heat transfer from hot electrons to cold phonons in the two-temperature model, p-e scattering is not effective in reducing κL owing to the relatively low p-e scattering rates in Al. The difference in the strength of p-e scattering in different metals can be qualitatively understood by checking the amount of electron density of states that is overlapped with the Fermi window. Moreover, κL is found to be comparable to the electronic thermal conductivity in Ni.

  10. Thermal properties of carbon-boron-titanium compounds as plasma facing materials

    NASA Astrophysics Data System (ADS)

    Tanabe, T.; Baba, T.; Ono, A.; Fujitsuka, M.; Shikama, T.; Shinno, H.

    1992-09-01

    The carbon-boron-titanium compounds were synthesized by hot press and subsequent HIP (high temperature isostatic press) treatment. The thermal diffusivity of the compounds was measured by the advanced laser-flash technique, and the heat-load shock resistance was evaluated with a low energy and high current electron beam. The obtained results were analyzed as a function of chemical composition of the compounds. The so-called gradient material was formed to attempt to improve the heat-load shock resistance.

  11. Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics--a Comparative Study with Gallium Nitride.

    PubMed

    Wu, Xufei; Lee, Jonghoon; Varshney, Vikas; Wohlwend, Jennifer L; Roy, Ajit K; Luo, Tengfei

    2016-01-01

    Wurtzite Zinc-Oxide (w-ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w-ZnO. In this paper, we determine the thermal conductivity of w-ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride (w-GaN)--another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w-ZnO. However, the thermal conductivity values show large differences (400 W/mK of w-GaN vs. 50 W/mK of w-ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w-GaN, w-ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering, and the weaker interatomic bonds in w-ZnO leads to smaller phonon group velocities. The thermal conductivity of w-ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w-ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w-ZnO-based electronics. PMID:26928396

  12. Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics – a Comparative Study with Gallium Nitride

    PubMed Central

    Wu, Xufei; Lee, Jonghoon; Varshney, Vikas; Wohlwend, Jennifer L.; Roy, Ajit K.; Luo, Tengfei

    2016-01-01

    Wurtzite Zinc-Oxide (w-ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w-ZnO. In this paper, we determine the thermal conductivity of w-ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride (w-GaN) – another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w-ZnO. However, the thermal conductivity values show large differences (400 W/mK of w-GaN vs. 50 W/mK of w-ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w-GaN, w-ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering, and the weaker interatomic bonds in w-ZnO leads to smaller phonon group velocities. The thermal conductivity of w-ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w-ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w-ZnO-based electronics. PMID:26928396

  13. Thermal Conductivity of Wurtzite Zinc-Oxide from First-Principles Lattice Dynamics - a Comparative Study with Gallium Nitride

    NASA Astrophysics Data System (ADS)

    Wu, Xufei; Lee, Jonghoon; Varshney, Vikas; Wohlwend, Jennifer L.; Roy, Ajit K.; Luo, Tengfei

    2016-03-01

    Wurtzite Zinc-Oxide (w-ZnO) is a wide bandgap semiconductor that holds promise in power electronics applications, where heat dissipation is of critical importance. However, large discrepancies exist in the literature on the thermal conductivity of w-ZnO. In this paper, we determine the thermal conductivity of w-ZnO using first-principles lattice dynamics and compare it to that of wurtzite Gallium-Nitride (w-GaN) - another important wide bandgap semiconductor with the same crystal structure and similar atomic masses as w-ZnO. However, the thermal conductivity values show large differences (400 W/mK of w-GaN vs. 50 W/mK of w-ZnO at room temperature). It is found that the much lower thermal conductivity of ZnO originates from the smaller phonon group velocities, larger three-phonon scattering phase space and larger anharmonicity. Compared to w-GaN, w-ZnO has a smaller frequency gap in phonon dispersion, which is responsible for the stronger anharmonic phonon scattering, and the weaker interatomic bonds in w-ZnO leads to smaller phonon group velocities. The thermal conductivity of w-ZnO also shows strong size effect with nano-sized grains or structures. The results from this work help identify the cause of large discrepancies in w-ZnO thermal conductivity and will provide in-depth understanding of phonon dynamics for the design of w-ZnO-based electronics.

  14. Thermal lens and all optical switching of new organometallic compound doped polyacrylamide gel

    NASA Astrophysics Data System (ADS)

    Badran, Hussain Ali

    In this work thermal lens spectrometry (TLS) is applied to investigate the thermo-optical properties of new organometallic compound containing azomethine group, Dichloro bis [2-(2-hydroxybenzylideneamino)-5-methylphenyl] telluride platinum(II), doped polyacrylamide gel using transistor-transistor logic (TTL) modulated cw 532 nm laser beam as an excitation beam modulated at 10 Hz frequency and probe beam wavelength 635 nm at 14 mW. The technique is applied to determine the thermal diffusivities, ds/dT and the linear thermal expansion coefficient of the sample. All-optical switching effects with low background and high stability are demonstrated.

  15. Effects of guest atomic species on the lattice thermal conductivity of type-I silicon clathrate studied via classical molecular dynamics

    NASA Astrophysics Data System (ADS)

    Kumagai, Tomohisa; Nakamura, Kaoru; Yamada, Susumu; Ohnuma, Toshiharu

    2016-08-01

    The effects of guest atomic species in Si clathrates on the lattice thermal conductivity were studied using classical molecular dynamics calculations. The interaction between a host atom and a guest atom was described by the Morse potential function while that between host atoms was described by the Tersoff potential. The parameters of the potentials were newly determined for this study such that the potential curves obtained from first-principles calculations for the insertion of a guest atom into a Si cage were successfully reproduced. The lattice thermal conductivities were calculated by using the Green-Kubo method. The experimental lattice thermal conductivity of Ba8Ga16Si30 can be successfully reproduced using the method. As a result, the lattice thermal conductivities of type-I Si clathrates, M8Si46 (M = Na, Mg, K, Ca Rb, Sr, Cs, or Ba), were obtained. It is found that the lattice thermal conductivities of M8Si46, where M is IIA elements (i.e., M = Mg, Ca, Sr, or Ba) tend to be lower than those of M8Si46, where M is IA elements (i.e., M = Na, K, Rb, or Cs). Those of mM8Si46, where m was artificially modified atomic weight were also obtained. The obtained lattice thermal conductivity can be regarded as a function of a characteristic frequency, fc. That indicates minimum values around fc=2-4 THz, which corresponds to the center of the frequencies of the transverse acoustic phonon modes associated with Si cages.

  16. Large tunability of lattice thermal conductivity of monolayer silicene via mechanical strain

    NASA Astrophysics Data System (ADS)

    Xie, Han; Ouyang, Tao; Germaneau, Éric; Qin, Guangzhao; Hu, Ming; Bao, Hua

    2016-02-01

    Strain engineering is one of the most promising and effective routes toward continuously tuning the electronic and optic properties of materials, while thermal properties are generally believed to be insensitive to mechanical strain. In this paper, the strain-dependent thermal conductivity of monolayer silicene under uniform biaxial tension is computed by solving the phonon Boltzmann transport equation with interatomic force constants extracted from first-principles calculations. Unlike the commonly believed understanding that thermal conductivity only slightly decreases with increased tensile strain for bulk materials, it is found that the thermal conductivity of silicene can increase dramatically with strain. Depending on the size, the maximum thermal conductivity of strained silicene can be a few times higher than that of the unstrained case. Such an unusual strain dependence is mainly attributed to the dramatic enhancement in the acoustic phonon lifetime. Such enhancement plausibly originates from the flattening of the buckling of the silicene structure upon stretching, which is unique for silicene as compared with other common two-dimensional materials. Our findings offer perspectives on modulating the thermal properties of low-dimensional structures for applications such as thermoelectrics, thermal circuits, and nanoelectronics.

  17. Thermal expansion of supported and freestanding graphene: lattice constant versus interatomic distance.

    PubMed

    Pozzo, Monica; Alfè, Dario; Lacovig, Paolo; Hofmann, Philip; Lizzit, Silvano; Baraldi, Alessandro

    2011-04-01

    By using ab initio molecular dynamics calculations, we show that even where the graphene lattice constant contracts, as previously reported for freestanding graphene below room temperature, the average carbon-carbon distance increases with temperature, in both free and supported graphene. This results in a larger corrugation at higher temperature, which can affect the interaction between graphene and the supporting substrate. For a weakly interacting system as graphene/Ir(111), we confirm the results using an experimental approach which gives direct access to interatomic distances. PMID:21517393

  18. GC/FT-IR ANALYSIS OF THE THERMALLY LABILE COMPOUND TRIS (2,3-DIBROMOPROPYL) PHOSPHATE

    EPA Science Inventory

    A fast and convenient GC method has been developed for a compound [tris(2,3-dibromopropyl)phosphate] that poses a difficult analytical problem for both GC (thermal instability/low volatility) and LC (not amenable to commonly available, sensitive detectors) analysis. his method em...

  19. Thermoelectric Properties of Silicon Germanium: An Investigation of the Reduction of Lattice Thermal Conductivity and Enhancement of Power Factor

    NASA Astrophysics Data System (ADS)

    Lahwal, Ali Sadek

    Thermoelectric materials are of technological interest owing to their ability of direct thermal-to-electrical energy conversion. In thermoelectricity, thermal gradients can be used to generate an electrical power output. Recent efforts in thermoelectrics are focused on developing higher efficient power generation materials. In this dissertation, the overall goal is to investigate both the n-type and p-type of the state of the art thermoelectric material, silicon germanium (SiGe), for high temperature power generation. Further improvement of thermoelectric performance of Si-Ge alloys hinges upon how to significantly reduce the as yet large lattice thermal conductivity, and optimizing the thermoelectric power factor PF. Our methods, in this thesis, will be into two different approaches as follow: The first approach is manipulating the lattice thermal conductivity of n and p-type SiGe alloys via direct nanoparticle inclusion into the n-type SiGe matrix and, in a different process, using a core shell method for the p-type SiGe. This approach is in line with the process of in-situ nanocomposites. Nanocomposites have become a new paradigm for thermoelectric research in recent years and have resulted in the reduction of thermal conductivity via the nano-inclusion and grain boundary scattering of heat-carrying phonons. To this end, a promising choice of nano-particle to include by direct mixing into a SiGe matrix would be Yttria Stabilized Zirconia ( YSZ). In this work we report the preparation and thermoelectric study of n-type SiGe + YSZ nanocomposites prepared by direct mechanical mixing followed by Spark Plasma Sintering (SPS) processing. Specifically, we experimentally investigated the reduction of lattice thermal conductivity (kappaL) in the temperature range (30--800K) of n-type Si 80Ge20P2 alloys with the incorporation of YSZ nanoparticles (20 ˜ 40 nm diameter) into the Si-Ge matrix. These samples synthesized by SPS were found to have densities > 95% of the

  20. Optic phonon bandwidth and lattice thermal conductivity: The case of L i2X (X =O , S, Se, Te)

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, S.; Lindsay, L.; Parker, D. S.

    2016-06-01

    We examine the lattice thermal conductivities (κl) of L i2X (X =O ,S ,Se ,Te ) using a first-principles Peierls-Boltzmann transport methodology. We find low κl values ranging between 12 and 30 W m-1K-1 despite light Li atoms, a large mass difference between constituent atoms, and tightly bunched acoustic branches, all features that give high κl in other materials including BeSe (630 W m-1K-1 ), BeTe (370 W m-1K-1 ), and cubic BAs (3170 W m-1K-1 ). Together these results suggest a missing ingredient in the basic guidelines commonly used to understand and predict κl. Unlike typical simple systems (e.g., Si, GaAs, SiC), the dominant resistance to heat-carrying acoustic phonons in L i2Se and L i2Te comes from interactions of these modes with two optic phonons. These interactions require significant bandwidth and dispersion of the optic branches, both present in L i2X materials. These considerations are important for the discovery and design of new materials for thermal management applications and give a more comprehensive understanding of thermal transport in crystalline solids.

  1. Optic phonon bandwidth and lattice thermal conductivity: The case of Li2X ( X=O , S, Se, Te)

    DOE PAGESBeta

    Mukhopadhyay, S.; Lindsay, L.; Parker, D. S.

    2016-06-07

    Here, we examine the lattice thermal conductivities ( l) of Li2X (X=O, S, Se, Te) using a first-principles Peierls-Boltzmann transport methodology. We find low l values ranging between 12 and 30 W/m-K despite light Li atoms, a large mass difference between constituent atoms and tightly bunched acoustic branches, all features that give high l in other materials including BeSe (630 W/m-1K-1), BeTe (370 W/m-1K-1) and cubic BAs (3150 W/m-1K-1). Together these results suggest a missing ingredient in the basic guidelines commonly used to understand and predict l. Unlike typical simple systems (e.g., Si, GaAs, SiC), the dominant resistance to heat-carryingmore » acoustic phonons in Li2Se and Li2Te comes from interactions of these modes with two optic phonons. These interactions require significant bandwidth and dispersion of the optic branches, both present in Li2X materials. Finally, these considerations are important for the discovery and design of new materials for thermal management applications, and give a more comprehensive understanding of thermal transport in crystalline solids.« less

  2. Optimization of Norbornadiene Compounds for Solar Thermal Storage by First-Principles Calculations.

    PubMed

    Kuisma, Mikael; Lundin, Angelica; Moth-Poulsen, Kasper; Hyldgaard, Per; Erhart, Paul

    2016-07-21

    Molecular photoswitches capable of storing solar energy are interesting candidates for future renewable energy applications. Here, using quantum mechanical calculations, we carry out a systematic screening of crucial optical (solar spectrum match) and thermal (storage energy density) properties of 64 such compounds based on the norbornadiene-quadricyclane system. Whereas a substantial number of these molecules reach the theoretical maximum solar power conversion efficiency, this requires a strong red-shift of the absorption spectrum, which causes undesirable absorption by the photoisomer as well as reduced thermal stability. These compounds typically also have a large molecular mass, leading to low storage densities. By contrast, single-substituted systems achieve a good compromise between efficiency and storage density, while avoiding competing absorption by the photo-isomer. This establishes guiding principles for the future development of molecular solar thermal storage systems. PMID:27254282

  3. Electrical and thermal transport properties of RECu4 Au compounds, RE=Nd, Gd

    NASA Astrophysics Data System (ADS)

    Bashir, Aiman Kamal; Tchokonté, Moise Bertin Tchoula; Strydom, A. M.

    2016-09-01

    We report the electrical and thermal transport properties of NdCu4 Au and GdCu4 Au compounds, crystallizing in the cubic MgCu4 Sn - type crystal structure, with space group F 4 bar 3 m (no. 216).These properties are reported through measurements of electrical resistivity, ρ(T) , thermoelectric power, S(T) and thermal conductivity, λ(T) . ρ(T) and S(T) data indicate an antiferromagnetic (AFM)-like anomaly associated with a N e ´ el temperature TN=3.9 K and 10.9 K for NdCu4 Au and GdCu4 Au compounds, respectively. ρ(T) data for both compounds shows a sudden drop at TN. Above TN, ρ(T) results are characteristic of an electron-phonon interaction in the presence of s - d scattering. Application of magnetic field slightly suppresses TN value in GdCu4 Au compound from TN=10.9 K in a field of 0 T to 10.1 K in a field of 6 T. S(T) data at low temperatures for both compounds shows a minimum at TN. Critical analysis of S(T) in terms of the phenomenological resonance model yield the positions (Ef) and bandwidths (Wf) of the 4 f - band in both compounds: Ef=3.81(6)K, Wf=329(58) K for the Nd compound and Ef=18.2(4) K, Wf=306(5) K for the Gd compound. λ(T) for both compounds decreases linearly upon cooling from room temperature. The reduced Lorentz number L /L0 deviates from the Wiedmann-Franz at low temperature with a strong increase in L /L0 upon cooling the samples from room temperature.

  4. Boundary condition-enforced immersed boundary-lattice Boltzmann flux solver for thermal flows with Neumann boundary conditions

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Shu, C.; Yang, L. M.

    2016-02-01

    A boundary condition-enforced-immersed boundary-lattice Boltzmann flux solver is proposed in this work for effective simulation of thermal flows with Neumann boundary conditions. In this method, two auxiliary layers of Lagrangian points are introduced and respectively placed inside and outside of the solid body, on which the temperature corrections (related to the heat source) are set as unknowns. To effectively consider the fluid-boundary interaction, these unknowns are expressed as algebraic summations of the temperature correction on Eulerian points, which are in turn obtained from biased distributions of unknown temperature corrections on the immersed boundary. By enforcing the temperature gradient at the solid boundary being equal to that approximated by the corrected temperature field, a set of algebraic equations are formed and solved to obtain all the unknowns simultaneously. They are then distributed biasedly to the inner region of the auxiliary layer so that the diffusion from the smooth delta function can be reduced substantially. In addition, the solutions of the flow and temperature fields are obtained by the thermal lattice Boltzmann flux solver with the second order of accuracy. The proposed method is well validated through its applications to simulate several benchmarks of natural, forced and mixed convection problems. It has been demonstrated that the present solver has about 1.724 order of accuracy and the error between the present result and theoretical value for the temperature gradient on the solid surface is in the order of 10-13, which indicates that the proposed method is able to satisfy the Neumann boundary condition accurately.

  5. Lattice location and thermal stability of implanted Fe in ZnO

    SciTech Connect

    Rita, E.; Wahl, U.; Correia, J.G.; Alves, E.; Soares, J.C.

    2004-11-22

    The emission channeling technique was applied to evaluate the lattice location of implanted {sup 59}Fe in single-crystalline ZnO. The angular distribution of {beta}{sup -} particles emitted by {sup 59}Fe was monitored with a position-sensitive electron detector, following 60 keV low dose (2.0x10{sup 13} cm{sup -2}) room-temperature implantation of the precursor isotope {sup 59}Mn. The emission patterns around the [0001], [1102],[1101], and [2113] directions revealed that following annealing at 800 deg. C, 95(8)% of the Fe atoms occupy ideal substitutional Zn sites with rms displacements of 0.06-0.09 A.

  6. Probing the lower limit of lattice thermal conductivity in an ordered extended solid: Gd117Co56Sn112, a phonon glass-electron crystal system.

    PubMed

    Schmitt, Devin C; Haldolaarachchige, Neel; Xiong, Yimin; Young, David P; Jin, Rongying; Chan, Julia Y

    2012-04-01

    The discovery of novel materials with low thermal conductivity is paramount to improving the efficiency of thermoelectric devices. As lattice thermal conductivity is inversely linked to unit cell complexity, we set out to synthesize a highly complex crystalline material with glasslike thermal conductivity. Here we present the structure, transport properties, heat capacity, and magnetization of single-crystal Gd(117)Co(56)Sn(112), a complex material with a primitive unit cell volume of ~6858 Å(3) and ~285 atoms per primitive unit cell (1140 atoms per face-centered cubic unit cell). The room temperature lattice thermal conductivity of this material is κ(L) = 0.28 W/(m·K) and represents one of the lowest ever reported for a nonglassy or nonionically conducting bulk solid. Furthermore, this material exhibits low resistivity at room temperature, and thus represents a true physical system that approaches the ideal phonon glass-electron crystal. PMID:22375963

  7. NaKV4O9·2H2O: a new 2D magnetic compound with a 1/5-depleted square lattice.

    PubMed

    Cui, Meiyan; He, Zhangzhen; Wang, Nannan; Tang, Yingying; Guo, Wenbin; Zhang, Suyun; Wang, Lin; Xiang, Hongping

    2016-03-15

    A new vanadate compound NaKV4O9·2H2O is successfully synthesized by a conventional hydrothermal method. This compound crystallizes in the monoclinic system with the space group C2/c, showing a typical 2D layered structure built from VO5 pyramids, in which the layers are separated by Na(+), K(+), and H2O. The topology structure of magnetic V(4+) ions shows a quite interesting 1/5-depleted square lattice, which is quite similar to that of a famous low-dimensional quantum spin system CaV4O9. A structural and magnetic comparison confirmed that the title compound may exhibit a more pronounced 2D character with a large spin gap. PMID:26892907

  8. Evaluation of thermal contact conductance between mold compound and heat spreader materials

    SciTech Connect

    Peterson, G.P.; Fletcher, L.S. )

    1988-11-01

    The need to develop microelectronic devices capable of operating at increased performance levels with high reliability requires a better understanding of the factors that govern the thermal performance of semiconductor packages. With the recent trend toward increased miniaturization and component density, thermal management wtihin these packages has become the primary factor that limits the physical size of both individual components and multichip modules. Although extensive testing and analysis of the thermal conductivity of various mold compound materials have been performed by several different manufacturers, presently no experimental information is available on the contact conductance occurring at the interface between mold compounds and substrate or heat spreader materials. From a modeling perspective, numerous standard thermal modeling techniques, which have been modified to accomodate electronic packages, are currently in use. In addition, a number of numerical models have been developed specifically for electronic packages by Pogson and Franklin Buchanan and Reeber, Andrews et al., and Chyu and Aghazadeh. However, none of these existing models incorporates the effects of the contact conductance present at the mold compound and heat spreader interface.

  9. Determination of the thermal and physical properties of black tattoo ink using compound analysis.

    PubMed

    Humphries, Alexander; Lister, Tom S; Wright, Philip A; Hughes, Michael P

    2013-07-01

    Despite the widespread use of laser therapy in the removal of tattoos, comparatively little is known about its mechanism of action. There is a need for an improved understanding of the composition and thermal properties of the tattoo ink in order that simulations of laser therapy may be better informed and treatment parameters optimised. Scanning electron microscopy and time-of-flight secondary ion mass spectrometry identified that the relative proportions of the constituent compounds of the ink likely to exist in vivo are the following: carbon black pigment (89 %), carvacrol (5 %), eugenol (2 %), hexenol (3 %) and propylene glycol (1 %). Chemical compound property tables identify that changes in phase of these compounds lead to a considerable reduction in the density and thermal conductivity of the ink and an increase in its specific heat as temperature increases. These temperature-dependent values of density, thermal conductivity and specific heat are substantially different to the constant values, derived from water or graphite at a fixed temperature, which have been applied in the simulations of laser therapy as previously described in the literature. Accordingly, the thermal properties of black tattoo ink described in this study provide valuable information that may be used to improve simulations of tattoo laser therapy. PMID:22983425

  10. Length divergence of the lattice thermal conductivity in suspended graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Majee, Arnab K.; Aksamija, Zlatan

    2016-06-01

    Thermal properties of graphene have attracted much attention, culminating in a recent measurement of its length dependence in ribbons up to 9 μ m long. In this paper, we use the improved Callaway model to solve the phonon Boltzmann transport equation while capturing both the resistive (umklapp, isotope, and edge roughness) and nonresistive (normal) contributions. We show that for lengths smaller than 100 μ m , scaling the ribbon length while keeping the width constant leads to a logarithmic divergence of thermal conductivity. The length dependence is driven primarily by a ballistic-to-diffusive transition in the in-plane (LA and TA) branches, while in the hydrodynamic regime when 10 μ m thermal conductivity converges beyond L >100 μ m due to the coupling between in-plane and flexural modes. This coupling leads to renormalization of ZA phonon dispersion in the long-wavelength range, preventing further divergence of thermal conductivity. We also uncover a strong dependence on sample width, which we attribute to the interplay between nonresistive normal and diffusive edge scattering in the Poisseuille flow regime. We conclude that normal processes play a crucial role in the length and width dependence of thermal transport in graphene in the hydrodynamic regime and dictate the relative in-plane (LA+TA) to out-of-plane (ZA) contribution to transport.

  11. Effect of disorder on the dimer transition of the honeycomb-lattice compound Li2RuO3

    NASA Astrophysics Data System (ADS)

    Jimenez-Segura, Marco-Polo; Ikeda, Atsutoshi; Yonezawa, Shingo; Maeno, Yoshiteru

    2016-02-01

    We report the dependence of magnetic properties on the crystalline disorder in Li2RuO3 with Ru honeycomb lattice. This oxide exhibits unconventional Ru-dimer transition below Td˜540 K. We demonstrate that the cell parameters, related to the coherence of the dimer formation, are strongly dependent on the synthesis procedure. We show that the magnetic behavior at the dimer transition is closely related to the lattice parameters. In particular, we revealed that samples with well-ordered dimers exhibit a first-order magnetic transition with the onset exceeding 550 K, higher than that reported previously. We discuss possible dimer configurations leading to this magnetolattice coupling.

  12. Effectiveness and Mechanisms of Defluorination of Perfluorinated Alkyl Substances by Calcium Compounds during Waste Thermal Treatment.

    PubMed

    Wang, Fei; Lu, Xingwen; Li, Xiao-yan; Shih, Kaimin

    2015-05-01

    The mineralization of perfluorinated alkyl substances (PFASs) by calcium compounds during the waste thermal treatment was systemically studied. Different calcium compounds showed different mineralization efficiencies of PFASs during the thermal process, owing to the different reaction mechanisms. Calcium hydroxide was recommended as the most effective Ca reagent for PFAS defluorination because the carbon-fluorine bonds in PFASs can be converted to carbon-hydrogen bonds via the hydrodefluorination reaction. PFASs with different chain lengths and functional groups were further investigated for their potentially different mineralization behavior. The results showed that the chain length of PFASs had an insignificant effect on the mineralization efficiency by calcium hydroxide. The thermogravimetric analysis-differential thermal analysis (TGA-DTA) also revealed that perfluorooctanesulfonate (PFOS) and perfluorohexanesulfonate (PFHxS) (with different chain lengths) had a similar thermal behavior. However, PFASs with different functional groups showed different mineralization behavior with calcium hydroxide in relation to their different thermal decomposition temperatures. Finally, the mineralization ratio of polytetrafluoroethylene (PTFE) particles by calcium hydroxide could reach 80% or higher when the temperature was above 400 °C. The gas chromatography/mass spectrometry (GC/MS) results demonstrated much reduced production of gaseous fluorocarbon fragments during PTFE decomposition when coexisting with calcium hydroxide. PMID:25850557

  13. An Improved Momentum-Exchanged Immersed Boundary-Based Lattice Boltzmann Method for Incompressible Viscous Thermal Flows

    NASA Astrophysics Data System (ADS)

    Chen, Mufeng; Niu, Xiaodong

    2016-06-01

    An improved momentum-exchanged immersed boundary-based lattice Boltzmann method (MEIB-LBM) for incompressible viscous thermal flows is presented here. MEIB-LBM was first proposed by Niu et al, which has been shown later that the non-slip boundary condition is not satisfied. Wang. et al. and Hu. et al overcome this drawback by iterative method. But it needs to give an appropriate relaxation parameter. In this work, we come back to the intrinsic feature of LBM, which uses the density distribution function as a dependent variable to evolve the flow field, and uses the density distribution function correction at the neighboring Euler mesh points to satisfy the non-slip boundary condition on the immersed boundary. The same idea can also be applied to the thermal flows with fluid-structure interference. The merits of present improvements for the original MEIB-LBM are that the intrinsic feature of LBM is kept and the flow penetration across the immersed boundaries is avoided. To validate the present method, examples, including forced convection over a stationary heated circular cylinder for heat flux condition, and natural convection with a suspended circle particle in viscous fluid, are simulated. The streamlines, isothermal contours, the drag coefficients and Nusselt numbers are calculated and compared to the benchmark results to demonstrate the effective of the present method.

  14. Role of ions in thermal diffusion of DNA: Lattice Boltzmann based simulations

    NASA Astrophysics Data System (ADS)

    Hammack, Audrey; Rana, Daharsh; May, Karl; Bledsoe, Matthew; Kreft Pearce, Jennifer; Chen, Yeng-Long

    2008-11-01

    The Ludwig-Soret effect, the migrarion of a species as a consequence of a temperature gradient, has been a factor in the development of microfluidic laboratory instrumentation. In a system consisting of DNA in a buffered salt solution exposed to a temperature gradient in micro channels, it has previously been observed that DNA will migrate to the colder regions, yielding an irregular density profile. We present a computational model in order to quantify the motion of the particles and describe the causes of this migration. In this construct, the salt ions are modeled as charged point particles and DNA as charged beads connected by springs. The motions of particles is calculated by using a combination of Brownian dynamics and the lattice Boltzmann method. We observe that the salt are also affected by the temperature gradient, creating a density profile. By varying the number of ions, the charge of the ions and the length of the DNA chain, we observe that the accumulation of ions in the cold region enhances the migration of the DNA to those regions of the channel.

  15. Simple microscope using a compound refractive lens and a wide-bandwidth thermal neutron beam

    SciTech Connect

    Cremer, J. T.; Park, H.; Piestrup, M. A.; Gary, C. K.; Pantell, R. H.; Flocchini, R. G.; Egbert, H. P.; Kloh, M. D.; Walker, R. B.

    2007-04-02

    The results of imaging experiments using biconcave, spherical compound refractive lenses (CRLs) and a wide-bandwidth thermal neutron beam are presented. Two CRLs were used, consisting of 155 beryllium and 120 copper lenses. The experiments were performed using a thermal neutron beam line at McClellan Nuclear Radiation Center reactor. The authors obtained micrographs of cadmium slits with up to 5x magnification and 0.3 mm resolution. The CRL resolution was superior to a pinhole camera with the same aperture diameter. The modulation transfer function (MTF) of the CRL was calculated and compared with the measured MTF at five spatial frequencies, showing good agreement.

  16. Abnormal thermal expansion properties of cubic NaZn13-type La(Fe,Al)13 compounds.

    PubMed

    Li, Wen; Huang, Rongjin; Wang, Wei; Zhao, Yuqiang; Li, Shaopeng; Huang, Chuanjun; Li, Laifeng

    2015-02-28

    The cubic NaZn13-type La(Fe,Al)13 compounds were synthesized, and their linear thermal expansion properties were investigated in the temperature range of 4.2-300 K. It was found that these compounds exhibit abnormal thermal expansion behavior, i.e., pronounced negative thermal expansion (NTE) or zero thermal expansion (ZTE) behavior, below the Curie temperature due to the magnetovolume effect (MVE). Moreover, in the La(Fe,Al)13 compounds, the modification of the coefficient of thermal expansion (CTE) as well as the abnormal thermal expansion (ATE) temperature-window is achieved through optimizing the proportion of Fe and Al. Typically, the average CTE of the LaFe13-xAlx compounds with x = 1.8 reaches as large as -10.47 × 10(-6) K(-1) between 100 and 225 K (ΔT = 125 K). Also, the ZTE temperature-window of the LaFe13-xAlx compounds with x = 2.5 and x = 2.7 could be broadened to 245 K (from 5 to 250 K). Besides, the magnetic properties of these compounds were measured and correlated with the abnormal thermal expansion behavior. The present results highlight the potential application of such La(Fe,Al)13 compounds with abnormal thermal expansion properties in cryogenic engineering. PMID:25642468

  17. Thermal properties of a new dye compound measured by thermal lens effect and Z-scan technique

    NASA Astrophysics Data System (ADS)

    Badran, Hussain A.

    2015-05-01

    A new dye compound containing azomethine groups has been synthesized and characterized by FT-IR, 13C NMR, and an UV-visible spectrometer. Measurements of the thermally induced optical nonlinearity of dichloro bis[2-(2-hydroxybenzylideneamino)-5-methylphenyl] telluride platinum(II) in a chloroform solvent were studied using a cw diode laser at 487 nm as the source of excitation, both in solution and as a poly methyl methacrylate solid film, respectively. The optical response was characterized by measuring the intensity-dependent refractive index n 2 of the medium using the Z-scan technique. The sample showed negative and large nonlinear refractive index values of the order of 10-7 cm2/W and reverse saturable absorption with high values of the nonlinear absorption coefficient of the order of 10-3 cm/W. The nonlinear refractive index was found to vary with the concentration. These results indicate that the dye is a promising candidate for applications in the nonlinear optic field. Thermal lens spectrometry was applied to investigate the thermo-optical properties and the nonlinear refractive index. In this technique, a pump and a probe beam were aligned collinearly. A localized change in the refractive index of the sample due to the thermal heating produced a thermal lens, which was then detected by studying the focusing and defocusing of the pump and probe beam.

  18. Comparative Ab-Initio Study of Substituted Norbornadiene-Quadricyclane Compounds for Solar Thermal Storage

    PubMed Central

    2016-01-01

    Molecular photoswitches that are capable of storing solar energy, so-called molecular solar thermal storage systems, are interesting candidates for future renewable energy applications. In this context, substituted norbornadiene-quadricyclane systems have received renewed interest due to recent advances in their synthesis. The optical, thermodynamic, and kinetic properties of these systems can vary dramatically depending on the chosen substituents. The molecular design of optimal compounds therefore requires a detailed understanding of the effect of individual substituents as well as their interplay. Here, we model absorption spectra, potential energy storage, and thermal barriers for back-conversion of several substituted systems using both single-reference (density functional theory using PBE, B3LYP, CAM-B3LYP, M06, M06-2x, and M06-L functionals as well as MP2 calculations) and multireference methods (complete active space techniques). Already the diaryl substituted compound displays a strong red-shift compared to the unsubstituted system, which is shown to result from the extension of the conjugated π-system upon substitution. Using specific donor/acceptor groups gives rise to a further albeit relatively smaller red-shift. The calculated storage energy is found to be rather insensitive to the specific substituents, although solvent effects are likely to be important and require further study. The barrier for thermal back-conversion exhibits strong multireference character and as a result is noticeably correlated with the red-shift. Two possible reaction paths for the thermal back-conversion of diaryl substituted quadricyclane are identified and it is shown that among the compounds considered the path via the acceptor side is systematically favored. Finally, the present study establishes the basis for high-throughput screening of norbornadiene-quadricyclane compounds as it provides guidelines for the level of accuracy that can be expected for key properties from

  19. Electron-phonon coupling and thermal transport in the thermoelectric compound Mo3Sb7–xTex

    SciTech Connect

    Bansal, Dipanshu; Li, Chen W.; Said, Ayman H.; Abernathy, Douglas L.; Yan, Jiaqiang; Delaire, Olivier A.

    2015-12-07

    Phonon properties of Mo3Sb7–xTex (x = 0, 1.5, 1.7), a potential high-temperature thermoelectric material, have been studied with inelastic neutron and x-ray scattering, and with first-principles simulations. The substitution of Te for Sb leads to pronounced changes in the electronic struc- ture, local bonding, phonon density of states (DOS), dispersions, and phonon lifetimes. Alloying with tellurium shifts the Fermi level upward, near the top of the valence band, resulting in a strong suppression of electron-phonon screening, and a large overall stiffening of interatomic force- constants. The suppression in electron-phonon coupling concomitantly increases group velocities and suppresses phonon scattering rates, surpassing the effects of alloy-disorder scattering, and re- sulting in a surprising increased lattice thermal conductivity in the alloy. We also identify that the local bonding environment changes non-uniformly around different atoms, leading to variable perturbation strengths for different optical phonon branches. The respective roles of changes in phonon group velocities and phonon lifetimes on the lattice thermal conductivity are quantified. Lastly, our results highlight the importance of the electron-phonon coupling on phonon mean-free-paths in this compound, and also estimates the contributions from boundary scattering, umklapp scattering, and point-defect scattering.

  20. Thermoelectric Properties of Silicon Germanium: An In-depth Study to the Reduction of Lattice Thermal Conductivity

    NASA Astrophysics Data System (ADS)

    Thompson, Daniel Ross

    properties of the resulting materials were investigated. Based on the densities, x-ray diffraction patterns, derived lattice constants, and Vegard's law it will be shown that the SE SPS method does successfully alloy multiple compositions of undoped SiGe. The third and most important study demonstrated that SiGe alloyed using the SE SPS synthesis technique can be successfully doped to a n and p type thermoelectric (TE) material. This required an investigation of all of the TE transport properties of these materials. A significant investigation and commentary will be provided for the lattice thermal conductivity of SiGe. The need for this investigation arises from the difference in synthesis processes between the traditional MA and the novel SE SPS techniques. The MA powder is already alloyed into micron sized powders that are consolidated by the HP for an extended time (>1 hour), which allows for grain growth. The SE SPS method relies on diffusion being promoted by the electric field assisted sintering technique and occurs over a very short period of time (<30 minutes). Therefore it can not be assumed that grain growth is not affected by the time dependent processes of sintering and diffusion with the SE SPS process. As will be discussed grain size plays a role in the lattice thermal conductivity of SiGe. It is surprising and physically interesting that the MA+HP standards and the SE SPS samples have lattice thermal conductivities that indicate the dominant scattering mechanism is the same. The physical insight provided by the fourth study is made possible by the existence of the new SE SPS synthesis method for SiGe. The MA method is optimized by the addition of GaP to the n-type SiGe materials during processing. The explanation for this optimization is a subject of debate within the community. Although, a staunch conclusion can not be made due to the need for more samples and carrier concentration data, this initial study does indicate that one physical explanation within

  1. Electronic and thermal properties of compounds bearing diimide, azomethine and triphenylamine units

    NASA Astrophysics Data System (ADS)

    Grucela-Zajac, Marzena; Bijak, Katarzyna; Zaleckas, Ernestas; Grigalevicius, Saulius; Wiacek, Malgorzata; Janeczek, Henryk; Schab-Balcerzak, Ewa

    2014-11-01

    New triphenylamine containing azomethine diimides and two kinds of poly(azomethine imide)s, i.e., linear and branched were synthesized. These compounds were prepared from two diamines, that is, N,N‧-bis(4-amino-2,3,5,6-tetramethylphenyl)phtalene-1,2,4,5-dicarboximide (DAPhDI), N,N‧-bis(5-aminonaphtalen)naphthalene-1,4,5,8-dicarboxyimide (DANDI-2) and 4-formyltriphenylamine, 4,4‧-diformyltriphenylamine and 4,4‧,4″-triformyltriphenylamine. The structures of the compounds were characterized by means of FTIR, 1H NMR spectroscopy and elemental analysis; the results show an agreement with the proposed structure. Thermal properties of prepared azomethine diimides and polymers were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Obtained compounds exhibited high thermal stability with 5% weight-loss temperatures above 390 °C. Azomethine diimides exhibited glass-forming properties with high glass-transition temperatures 216 and 308 °C. Optical properties of the prepared compounds were investigated by UV-vis and photoluminescence (PL) measurements. All compounds emitted blue light in NMP solution and in solid state as blend with PMMA. The electrochemical properties, that is, orbital energies and resulting energy gap were estimated based on cyclic voltammetry (CV). All synthesized material showed reversible reduction process, furthermore AzPhDI and AzNDI showed partially reversible oxidation process. Electrochemical band gap was found in the range 1.23-1.70 eV. Low molecular weight model compounds were tested as bipolar host materials in blue phosphorescent organic light emitting diodes (OLEDs). The devices exhibited turn-on voltages of about 5.5 V and maximum brightness of 40-220 cd/m2.

  2. Nanostructure and thermal properties of melt compounded PE/clay nanocomposites filled with an organosilylated montmorillonite

    SciTech Connect

    Scarfato, Paola; Incarnato, Loredana; Di Maio, Luciano; Dittrich, Bettina; Niebergall, Ute; Böhning, Martin; Schartel, Bernhard

    2015-12-17

    In this work we report on the functionalization of a natural sodium montmorillonite (MMT) with (3-glycidyloxypropyl)trimethoxysilane by a silylation procedure and on its use as nanofiller in melt compounding of polyethylene nanocomposites. The obtained organosilylated clay showed higher interlayer spacing than the original MMT and higher thermal stability with respect to most of commercial organoclays modified with alkylammonium salts. Its addition (at 5wt%) to two different polyethylene matrices (a low density polyethylene, LDPE, and a high density polyethylene, HDPE), processed in a pilot-scale twin-screw extruder, allowed to produce hybrids with nanoscale dispersion of the filler, as demonstrated by X-ray diffraction. Thermogravimetric and differential scanning thermal analyses point out that the obtained nanocomposites do not show noticeable changes in the thermal behavior of both LDPE and HDPE, even if a slight reduction in the overall bulk crystallinity was observed in presence of the nanofillers.

  3. Nanostructure and thermal properties of melt compounded PE/clay nanocomposites filled with an organosilylated montmorillonite

    NASA Astrophysics Data System (ADS)

    Scarfato, Paola; Incarnato, Loredana; Di Maio, Luciano; Dittrich, Bettina; Niebergall, Ute; Böhning, Martin; Schartel, Bernhard

    2015-12-01

    In this work we report on the functionalization of a natural sodium montmorillonite (MMT) with (3-glycidyloxypropyl)trimethoxysilane by a silylation procedure and on its use as nanofiller in melt compounding of polyethylene nanocomposites. The obtained organosilylated clay showed higher interlayer spacing than the original MMT and higher thermal stability with respect to most of commercial organoclays modified with alkylammonium salts. Its addition (at 5wt%) to two different polyethylene matrices (a low density polyethylene, LDPE, and a high density polyethylene, HDPE), processed in a pilot-scale twin-screw extruder, allowed to produce hybrids with nanoscale dispersion of the filler, as demonstrated by X-ray diffraction. Thermogravimetric and differential scanning thermal analyses point out that the obtained nanocomposites do not show noticeable changes in the thermal behavior of both LDPE and HDPE, even if a slight reduction in the overall bulk crystallinity was observed in presence of the nanofillers.

  4. Correlation of lattice defects and thermal processing in the crystallization of titania nanotube arrays

    NASA Astrophysics Data System (ADS)

    Hosseinpour, Pegah M.; Yung, Daniel; Panaitescu, Eugen; Heiman, Don; Menon, Latika; Budil, David; Lewis, Laura H.

    2014-12-01

    Titania nanotubes have the potential to be employed in a wide range of energy-related applications such as solar energy-harvesting devices and hydrogen production. As the functionality of titania nanostructures is critically affected by their morphology and crystallinity, it is necessary to understand and control these factors in order to engineer useful materials for green applications. In this study, electrochemically-synthesized titania nanotube arrays were thermally processed in inert and reducing environments to isolate the role of post-synthesis processing conditions on the crystallization behavior, electronic structure and morphology development in titania nanotubes, correlated with the nanotube functionality. Structural and calorimetric studies revealed that as-synthesized amorphous nanotubes crystallize to form the anatase structure in a three-stage process that is facilitated by the creation of structural defects. It is concluded that processing in a reducing gas atmosphere versus in an inert environment provides a larger unit cell volume and a higher concentration of Ti3+ associated with oxygen vacancies, thereby reducing the activation energy of crystallization. Further, post-synthesis annealing in either reducing or inert atmospheres produces pronounced morphological changes, confirming that the nanotube arrays thermally transform into a porous morphology consisting of a fragmented tubular architecture surrounded by a network of connected nanoparticles. This study links explicit data concerning morphology, crystallization and defects, and shows that the annealing gas environment determines the details of the crystal structure, the electronic structure and the morphology of titania nanotubes. These factors, in turn, impact the charge transport and consequently the functionality of these nanotubes as photocatalysts.

  5. Magnetic structure of the antiferromagnetic Kondo lattice compounds CeRhAl4Si2 and CeIrAl4Si2

    DOE PAGESBeta

    Ghimire, N. J.; Calder, S.; Janoschek, M.; Bauer, E. D.

    2015-06-01

    In this article, we have investigated the magnetic ground state of the antiferromagnetic Kondo-lattice compounds CeMAl4Si2(M = Rh, Ir) using neutron powder diffraction. Although both of these compounds show two magnetic transitions TN1 and TN2 in the bulk properties measurements, evidence for magnetic long-range order was only found below the lower transition TN2. Analysis of the diffraction profiles reveals a commensurate antiferromagnetic structure with a propagation vector k = (0, 0, 1/2). The magnetic moment in the ordered state of CeRhAl4Si2 and CeIrAl4Si2 were determined to be 1.14(2) and 1.41(3) μB/Ce, respectively, and are parallel to the crystallographic c-axis inmore » agreement with magnetic susceptibility measurements.« less

  6. Lattice specific heat for the RMIn5 (R=Gd, La, Y; M=Co, Rh) compounds: Non-magnetic contribution subtraction

    NASA Astrophysics Data System (ADS)

    Facio, Jorge I.; Betancourth, D.; Cejas Bolecek, N. R.; Jorge, G. A.; Pedrazzini, Pablo; Correa, V. F.; Cornaglia, Pablo S.; Vildosola, V.; García, D. J.

    2016-06-01

    We analyze theoretically a common experimental process used to obtain the magnetic contribution to the specific heat of a given magnetic material. In the procedure, the specific heat of a non-magnetic analog is measured and used to subtract the non-magnetic contributions, which are generally dominated by the lattice degrees of freedom in a wide range of temperatures. We calculate the lattice contribution to the specific heat for the magnetic compounds GdMIn5 (M=Co, Rh) and for the non-magnetic YMIn5 and LaMIn5 (M=Co, Rh), using density functional theory based methods. We find that the best non-magnetic analog for the subtraction depends on the magnetic material and on the range of temperatures. While the phonon specific heat contribution of YRhIn5 is an excellent approximation to the one of GdCoIn5 in the full temperature range, for GdRhIn5 we find a better agreement with LaCoIn5, in both cases, as a result of an optimum compensation effect between masses and volumes. We present measurements of the specific heat of the compounds GdMIn5 (M=Co, Rh) up to room temperature where it surpasses the value expected from the Dulong-Petit law. We obtain a good agreement between theory and experiment when we include anharmonic effects in the calculations.

  7. Effects of monovalent cation doping on the structure, microstructure, lattice distortion and magnetic behavior of single crystalline NdMnO3 compounds.

    PubMed

    Nandy, Anshuman; Pradhan, S K

    2015-10-21

    Pure and 15 mol% Na, K-doped NdMnO3 compounds with perovskite structures are prepared by sol-gel method. Tiny single crystals are formed after sintering the compounds at 1000 °C. The effect of Na and K doping as well as the effect of sintering temperature on the formation and microstructure of NdMnO3 are studied in detail by the Rietveld refinement technique using X-ray powder diffraction data. Single phase formation and single crystalline growth are also confirmed by high resolution transmission electron microscopy (HRTEM). Bond angles and bond lengths are calculated and shown by 3D diagrams. Monovalent doping induces noticeable changes in the microstructure and yields better structural stability in these compounds. Doping results in the change of Mn-O, Nd-O and Mn-O-Mn bond lengths which in turn reduces the lattice and octahedral distortion in the system along with an increase in the tolerance factor. The magnetic properties of these compounds are also modified as a result of doping. The temperature dependent magnetization results show that the Neel temperature of antiferromagnetic NdMnO3 compound is 67.2 K and the Curie temperatures of ferromagnetic Nd0.85Na0.15MnO3 and Nd0.85K0.15MnO3 compounds are 99.1 K and 98.6 K respectively. Both 15% Na and K doping results in a similar TC in doped NdMnO3 compounds. PMID:26373986

  8. Thermal dilepton rates and electrical conductivity of the QGP from the lattice

    NASA Astrophysics Data System (ADS)

    Ding, Heng-Tong; Kaczmarek, Olaf; Meyer, Florian

    2016-08-01

    We investigate the temperature dependence of the thermal dilepton rate and the electrical conductivity of the gluon plasma at temperatures of 1.1, 1.3, and 1.5 Tc in quenched QCD. Making use of nonperturbatively clover-improved Wilson valence quarks allows for a clean extrapolation of the vector meson correlation function to the continuum limit. We found that the vector correlation function divided by T3 is almost temperature independent in the current temperature window. The spectral functions are obtained by χ2 fitting of phenomenologically inspired Ansätze for the spectral function to the continuum extrapolated correlator data, where the correlations between the data points have been included. Systematic uncertainties arising from varying the Ansätze motivated from strong coupling theory as well as perturbation theory are discussed and estimated. We found that the electrical conductivity of the hot medium, related to the slope of the vector spectral function at zero frequency and momentum, is 0.2 Ce m≲σ /T ≲0.7 Ce m for T =1.1 Tc and 0.2 Ce m≲σ /T ≲0.4 Ce m for the higher temperatures. The dilepton rates and soft photon rates, resulting from the obtained spectral functions, show no significant temperature dependence, either.

  9. Effect of AlN content on the lattice site location of terbium ions in Al x Ga1-x N compounds

    NASA Astrophysics Data System (ADS)

    Fialho, M.; Rodrigues, J.; Magalhães, S.; Correia, M. R.; Monteiro, T.; Lorenz, K.; Alves, E.

    2016-03-01

    Terbium lattice site location and optical emission in Tb implanted Al x Ga1-x N (0 ≤ x ≤ 1) samples grown by halide vapour phase epitaxy on (0001) sapphire substrates are investigated as a function of AlN content. The samples were implanted with a fluence of 5 × 1014 cm-2 of terbium ions and an energy of 150 keV. Lattice implantation damage is reduced using channelled ion implantation performed along the <0001> axis, normal to the sample surface. Afterwards, thermal annealing treatments at 1400 °C for GaN and 1200 °C for samples with x > 0 were performed to reduce the damage and to activate the optical emission of Tb3+ ions. The study of lattice site location is achieved measuring detailed angular ion channelling scans across the <0001>, < 10\\bar{1}1> and < \\bar{2}113> axial directions. The precise location of the implanted Tb ions is obtained by combining the information of these angular scans with simulations using the Monte Carlo code FLUX. In addition to a Ga/Al substitutional fraction and a random fraction, a fraction of Tb ions occupying a site displaced by 0.2 Å along c-axis from the Ga/Al substitutional site was considered, giving a good agreement between the experimental results and the simulation. Photoluminescence studies proved the optical activation of Tb3+ after thermal annealing and the enhancement of the 5D4 to 7F6 transition intensity with increasing AlN content.

  10. Time-resolved observation of band-gap shrinking and electron-lattice thermalization within X-ray excited gallium arsenide

    PubMed Central

    Ziaja, Beata; Medvedev, Nikita; Tkachenko, Victor; Maltezopoulos, Theophilos; Wurth, Wilfried

    2015-01-01

    Femtosecond X-ray irradiation of solids excites energetic photoelectrons that thermalize on a timescale of a few hundred femtoseconds. The thermalized electrons exchange energy with the lattice and heat it up. Experiments with X-ray free-electron lasers have unveiled so far the details of the electronic thermalization. In this work we show that the data on transient optical reflectivity measured in GaAs irradiated with femtosecond X-ray pulses can be used to follow electron-lattice relaxation up to a few tens of picoseconds. With a dedicated theoretical framework, we explain the so far unexplained reflectivity overshooting as a result of band-gap shrinking. We also obtain predictions for a timescale of electron-lattice thermalization, initiated by conduction band electrons in the temperature regime of a few eVs. The conduction and valence band carriers were then strongly non-isothermal. The presented scheme is of general applicability and can stimulate further studies of relaxation within X-ray excited narrow band-gap semiconductors. PMID:26655671

  11. Time-resolved observation of band-gap shrinking and electron-lattice thermalization within X-ray excited gallium arsenide

    NASA Astrophysics Data System (ADS)

    Ziaja, Beata; Medvedev, Nikita; Tkachenko, Victor; Maltezopoulos, Theophilos; Wurth, Wilfried

    2015-12-01

    Femtosecond X-ray irradiation of solids excites energetic photoelectrons that thermalize on a timescale of a few hundred femtoseconds. The thermalized electrons exchange energy with the lattice and heat it up. Experiments with X-ray free-electron lasers have unveiled so far the details of the electronic thermalization. In this work we show that the data on transient optical reflectivity measured in GaAs irradiated with femtosecond X-ray pulses can be used to follow electron-lattice relaxation up to a few tens of picoseconds. With a dedicated theoretical framework, we explain the so far unexplained reflectivity overshooting as a result of band-gap shrinking. We also obtain predictions for a timescale of electron-lattice thermalization, initiated by conduction band electrons in the temperature regime of a few eVs. The conduction and valence band carriers were then strongly non-isothermal. The presented scheme is of general applicability and can stimulate further studies of relaxation within X-ray excited narrow band-gap semiconductors.

  12. Time-resolved observation of band-gap shrinking and electron-lattice thermalization within X-ray excited gallium arsenide.

    PubMed

    Ziaja, Beata; Medvedev, Nikita; Tkachenko, Victor; Maltezopoulos, Theophilos; Wurth, Wilfried

    2015-01-01

    Femtosecond X-ray irradiation of solids excites energetic photoelectrons that thermalize on a timescale of a few hundred femtoseconds. The thermalized electrons exchange energy with the lattice and heat it up. Experiments with X-ray free-electron lasers have unveiled so far the details of the electronic thermalization. In this work we show that the data on transient optical reflectivity measured in GaAs irradiated with femtosecond X-ray pulses can be used to follow electron-lattice relaxation up to a few tens of picoseconds. With a dedicated theoretical framework, we explain the so far unexplained reflectivity overshooting as a result of band-gap shrinking. We also obtain predictions for a timescale of electron-lattice thermalization, initiated by conduction band electrons in the temperature regime of a few eVs. The conduction and valence band carriers were then strongly non-isothermal. The presented scheme is of general applicability and can stimulate further studies of relaxation within X-ray excited narrow band-gap semiconductors. PMID:26655671

  13. Negative thermal expansion and associated anomalous physical properties: review of the lattice dynamics theoretical foundation

    NASA Astrophysics Data System (ADS)

    Dove, Martin T.; Fang, Hong

    2016-06-01

    Negative thermal expansion (NTE) is the phenomenon in which materials shrink rather than expand on heating. Although NTE had been previously observed in a few simple materials at low temperature, it was the realisation in 1996 that some materials have NTE over very wide ranges of temperature that kick-started current interest in this phenomenon. Now, nearly two decades later, a number of families of ceramic NTE materials have been identified. Increasingly quantitative studies focus on the mechanism of NTE, through techniques such as high-pressure diffraction, local structure probes, inelastic neutron scattering and atomistic simulation. In this paper we review our understanding of vibrational mechanisms of NTE for a range of materials. We identify a number of different cases, some of which involve a small number of phonons that can be described as involving rotations of rigid polyhedral groups of atoms, others where there are large bands of phonons involved, and some where the transverse acoustic modes provide the main contribution to NTE. In a few cases the elasticity of NTE materials has been studied under pressure, identifying an elastic softening under pressure. We propose that this property, called pressure-induced softening, is closely linked to NTE, which we can demonstrate using a simple model to describe NTE materials. There has also been recent interest in the role of intrinsic anharmonic interactions on NTE, particularly guided by calculations of the potential energy wells for relevant phonons. We review these effects, and show how anhamonicity affects the response of the properties of NTE materials to pressure.

  14. Degradation of pharmaceutical compounds in water by non-thermal plasma treatment.

    PubMed

    Magureanu, Monica; Mandache, Nicolae Bogdan; Parvulescu, Vasile I

    2015-09-15

    Pharmaceutical compounds became an important class of water pollutants due to their increasing consumption over the last years, as well as due to their persistence in the environment. Since conventional waste water treatment plants are unable to remove certain non-biodegradable pharmaceuticals, advanced oxidation processes was extensively studied for this purpose. Among them, non-thermal plasma was also recently investigated and promising results were obtained. This work reviews the recent research on the oxidative degradation of pharmaceuticals using non-thermal plasma in contact with liquid. As target compounds, several drugs belonging to different therapeutic groups were selected: antibiotics, anticonvulsants, anxiolytics, lipid regulators, vasodilatators, contrast media, antihypertensives and analgesics. It was found that these compounds were removed from water relatively fast, partly degraded, and partly even mineralized. In order to ensure the effluent is environmentally safe it is important to identify the degradation intermediates and to follow their evolution during treatment, which requires complex chemical analysis of the solutions. Based on this analysis, degradation pathways of the investigated pharmaceuticals under plasma conditions were suggested. After sufficient plasma treatment the final organic by-products present in the solutions were mainly small molecules in an advanced oxidation state. PMID:26057260

  15. Analysis of organic compounds in water by direct adsorption and thermal desorption. [Dissertation

    SciTech Connect

    Ryan, J.P. Jr.

    1980-03-01

    An instrument was designed and constructed that makes it possible to thermally desorb organic compounds from wet adsorption traps to a gas chromatograph in an efficient and reproducible manner. Based on this device, a method of analyzing organics in water was developed that is rapid, sensitive, and of broader scope than previously published methods. The system was applied to the analysis of compounds with a wide range of volatilities. Temperature and flow parameters were investigated and specific procedures for quantitation were established. Real samples, including tap water and well water, were also analyzed with this system. Depending on the analysis requirements, the thermal desorption instrument can be used with either packed column or high resolution open-tubular column gas chromatography. The construction plans of normal and high-resolution systems are presented along with chromatograms and data produced by each. Finally, an improved thermal desorption instrument is described. Modifications to the basic system, including splitless injection onto a capillary column, automation, dual cryogenic trapping, reduction of scale, and effluent splitting to dual detection are discussed at length as they relate to the improved instrument.

  16. Thermal Solitons in 1d and 2d Anharmonic Lattices - Solectrons and the Organization of Non-Linear Fluctuations in Long-Living Dynamical Structures

    NASA Astrophysics Data System (ADS)

    Velarde, M. G.; Ebeling, W.; Chetverikov, A. P.

    2013-01-01

    We study the thermal excitation of intrinsic localized modes in the form of solitons in 1d and 2d anharmonic lattices at moderately high temperatures. Such finite-amplitude fluctuations form long-living dynamical structures with life-time in the pico-second range thus surviving a relatively long time in comparison to other thermal fluctuations. Further we discuss the influence of such long-living fluctuations on the dynamics of added excess free electrons. The atomic lattice units are treated as quasi-classical objects interacting by Morse forces and stochastically moving according to Langevin equations. In 2d the atoms are initially organized in a triangular lattice. The electron distributions are in a first estimate represented by equilibrium adiabatic distributions in the actual polarization fields. Computer simulations show that in 2d systems such excitations are moving with supersonic velocities along lattice rows oriented with the cristallographic axes. By following the electron distributions we have also been able to study the excitations of solectron type (electron-soliton dynamic bound states) and estimate their life times.

  17. Vibrational spectra and lattice thermal conductivity of kesterite-structured Cu2ZnSnS4 and Cu2ZnSnSe4

    NASA Astrophysics Data System (ADS)

    Skelton, Jonathan M.; Jackson, Adam J.; Dimitrievska, Mirjana; Wallace, Suzanne K.; Walsh, Aron

    2015-04-01

    Cu2ZnSnS4 (CZTS) is a promising material for photovoltaic and thermoelectric applications. Issues with quaternary semiconductors include chemical disorder (e.g., Cu-Zn antisites) and disproportionation into secondary phases (e.g., ZnS and Cu2SnS3). To provide a reference for the pure kesterite structure, we report the vibrational spectra—including both infra-red and Raman intensities—from lattice-dynamics calculations using first-principles force constants. Three-phonon interactions are used to estimate phonon lifetimes (spectral linewidths) and thermal conductivity. CZTS exhibits a remarkably low lattice thermal conductivity, competitive with high-performance thermoelectric materials. Transition from the sulfide to selenide (Cu2ZnSnSe4) results in softening of the phonon modes and an increase in phonon lifetimes.

  18. Abatement of mixture of volatile organic compounds (VOCs) in a catalytic non-thermal plasma reactor.

    PubMed

    Karuppiah, J; Reddy, E Linga; Reddy, P Manoj Kumar; Ramaraju, B; Karvembu, R; Subrahmanyam, Ch

    2012-10-30

    Total oxidation of mixture of dilute volatile organic compounds was carried out in a dielectric barrier discharge reactor with various transition metal oxide catalysts integrated in-plasma. The experimental results indicated the best removal efficiencies in the presence of metal oxide catalysts, especially MnO(x), whose activity was further improved with AgO(x) deposition. It was confirmed water vapor improves the efficiency of the plasma reactor, probably due to the formation of hydroxyl species, whereas, in situ decomposition of ozone on the catalyst surface may lead to nascent oxygen. It may be concluded that non-thermal plasma approach is beneficial for the removal of mixture of volatile organic compounds than individual VOCs, probably due to the formation of reactive intermediates like aldehydes, peroxides, etc. PMID:22975253

  19. Magnetic phase transitions in heavy-fermion compounds studied by thermal-expansion measurements

    NASA Astrophysics Data System (ADS)

    de Visser, A.; Lacerda, A.; Franse, J. J. M.; Flouquet, J.

    1990-12-01

    On alloying the heavy-fermion compounds CeRu 2Si 2 and UPt 3 with small amounts of La and Pd, respectively, long-range antiferromagnetic order develops with Néel temperatures in the order of a few kelvin. In order to study the volume effects that are involved with the evolution into the long-range ordered state, we have performed thermal-expansion measurements on the pure and doped systems. The results are compared with data on antiferromagnetic URu 2Si 2. Subsequently, we discuss thermal-expansion measurements in high-magnetic fields, in particular on CeRu 2Si 2, where a metamagnetic-like transition occurs as the intersite-correlations collapse in a field of 7.8 T. Most of the measurements have been performed on single-crystalline samples, revealing a pronounced anisotropy.

  20. Lattice thermal conductivity of ultra high temperature ceramics ZrB{sub 2} and HfB{sub 2} from atomistic simulations

    SciTech Connect

    Lawson, John W.; Daw, Murray S.; Bauschlicher, Charles W. Jr.

    2011-10-15

    Atomistic Green-Kubo simulations are performed to evaluate the lattice thermal conductivity for single crystals of the ultra high temperature ceramics ZrB{sub 2} and HfB{sub 2}. Recently developed interatomic potentials are used for these simulations. Heat current correlation functions show rapid oscillations, which can be identified with mixed metal-Boron optical phonon modes. Results for temperatures from 300K to 1000K are presented.

  1. Electronic and thermal properties of TiFe{sub 2} compound: An ab initio study

    SciTech Connect

    Sathyakumari, V. S.; Sankar, S. Mahalakshmi, K.; Subashree, G.; Krithiga, R.

    2015-06-24

    A systematic study of electronic, and thermal properties such as the Density of states, Fermi energy, Debye temperature and specific heat coefficient, has been carried out using the results of electronic bandstructure and related characteristics of the Laves phase compound, TiFe{sub 2}. Computation of electronic bandstructure and associated properties has been carried out using the tight-binding-linear-muffin-tin-orbital (TB-LMTO) method within atomic sphere approximation (ASA). The calculated values are compared with the available results of literature.

  2. Thermal reaction studies of organic model compound-mineral matter interactions in solids

    SciTech Connect

    Buchanan, A.C. III; Britt, P.F.; Thomas, K.B.

    1995-07-01

    The solid-state chemistry of silica-immobilized phenethyl phenyl ethers is being investigated in the presence of interdispersed aluininosilicates at temperatures relevant to coal processing to gain a better understanding of the impact of mineral matter on pyrolysis and liquefaction mechanisms. Results demonstrate the dramatic effect that aluminosilicates can have in altering the normal thermal reaction pathways for these models of ether linkages in lignin and low rank coals. An investigation of the chemistry of these model compounds at low temperatures (ca. 150-200{degrees}C) in the presence of aluminosilicates, including montmorillonite, is currently being investigated to delineate the chemical transformations that can occur during lignin maturation.

  3. Competing anisotropies on 3d sub-lattice of YNi{sub 4–x}Co{sub x}B compounds

    SciTech Connect

    Caraballo Vivas, R. J.; Rocco, D. L.; Reis, M. S.; Caldeira, L.; Coelho, A. A.

    2014-08-14

    The magnetic anisotropy of 3d sub-lattices has an important rule on the overall magnetic properties of hard magnets. Intermetallics alloys with boron (R-Co/Ni-B, for instance) belong to those hard magnets family and are useful objects to help to understand the magnetic behavior of 3d sub-lattice, specially when the rare earth ions R do not have magnetic nature, like YCo{sub 4}B ferromagnetic material. Interestingly, YNi{sub 4}B is a paramagnetic material and Ni ions do not contribute to the magnetic anisotropy. We focused therefore our attention to YNi{sub 4–x}Co{sub x}B series, with x = 0, 1, 2, 3, and 4. The magnetic anisotropy of these compounds is deeper described using statistical and preferential models of Co occupation among the possible Wyckoff positions into the CeCo{sub 4}B type hexagonal structure. We found that the preferential model is the most suitable to explain the magnetization experimental data.

  4. Measurement of Organic Compounds in Diesel and Gasoline Engine Exhaust using Thermal Desorption PTR-MS

    NASA Astrophysics Data System (ADS)

    Jobson, B. T.; Gueneron, M.; Erickson, M. H.; Vanderschelden, G. S.

    2013-12-01

    A proton transfer reaction mass spectrometer modified with a thermal desorption sampler was used to measure organic compounds in diesel and gasoline engine exhaust in a laboratory setting. The drift tube was operated at 80 Td, providing an M+1 and M-1 mass spectrum for the most abundant constituents of the exhaust including alkenes, cycloalkanes, bicycloalkanes, monoaromatics, and naphthenic monoaromatic compounds. Alkanes were observed to fragment to a common set of ions. Use of the thermal desorption sampler enabled the total concentration of C10-C17 alkanes to be determined. The abundance of higher molecular weight cycloalkanes, bicycloalkanes, napthenic monoaromatics, and larger C10-C17 alkanes was much greater in diesel exhaust, allowing for a distinct source fingerprint pattern to distinguish diesel from gasoline exhaust. Use of the finger print source profiles allowed us to quantify the relative amounts of diesel and gasoline exhaust in mixtures, suggesting its utility to determine the relative contributions of gasoline and diesel engine exhaust to hydrocarbon concentrations in urban areas.

  5. Coupled theoretical interpretation and experimental investigation of the anisotropy of the lattice thermal conductivity of Bi{sub 2}Te{sub 3} single crystal

    SciTech Connect

    Jacquot, A.; Bayer, B.; Winkler, M.; Boettner, H.; Jaegle, M.

    2012-09-15

    The Debye model is modified for the calculation of the lattice thermal conductivity and used to gain insight into the anisotropy of Bi{sub 2}Te{sub 3}. In this work, the Debye temperature is not used to estimate the cutoff frequencies of the phonons that carry heat. The cutoff frequencies are defined by setting an upper limit to the energy of acoustic phonons using the complete dispersion relations. The anisotropy of the thermal conductivity is found to be unrelated to the anisotropy of the sound velocities. It is found that the sound velocity is almost isotropic when the longitudinal and two transversal waves are added together. In addition the relaxation time must be a function of the cutoff frequencies and counterbalances the anisotropy arising from the variation of the number of acoustic phonons traveling in various directions. It is concluded that the anisotropy of the thermal conductivity is mostly related to the Grueneisen's constant. - Graphical abstract: Dispersion relations of Bi{sub 2}Te{sub 3} along c-axis. The cutoff frequencies are found to be anisotropic and are defined exactly in this article where the acoustic branch crosses the optical branch. This affects both the number of phonons that carry heat in a given direction and the number of phonons that can scatter them. This is decisive for understanding the lattice thermal conductivity. Highlights: Black-Right-Pointing-Pointer Prediction of the anisotropy of the lattice thermal conductivity. Black-Right-Pointing-Pointer Provide a definition of the cutoff frequencies that makes sense. Black-Right-Pointing-Pointer Reduction of the number of frees parameter in phenomenological model. Black-Right-Pointing-Pointer Prediction that the anisotropy is a function of the scattering mechanism. Black-Right-Pointing-Pointer Means of experimental verification of theory.

  6. Thermal and oxidation stability of organo-fluorine compound-mixed electrolyte solutions for lithium ion batteries

    NASA Astrophysics Data System (ADS)

    Nishikawa, Daiki; Nakajima, Tsuyoshi; Ohzawa, Yoshimi; Koh, Meiten; Yamauchi, Akiyoshi; Kagawa, Michiru; Aoyama, Hirokazu

    2013-12-01

    Thermal and oxidation stability of fluorine compound-mixed electrolyte solutions have been investigated. Charge/discharge behavior of natural graphite electrode has been also examined in the same electrolyte solutions. Fluorine compounds demonstrate much lower reactivity with metallic Li than ethylene carbonate/dimethyl carbonate. Fluorine compound-mixed electrolyte solutions show the lower reactivity with LiC6 and the smaller exothermic peaks due to decomposition of electrolyte solutions and surface films than original solutions without fluorine compound. Oxidation currents are also smaller in fluorine compound-mixed electrolyte solutions than in original ones. First coulombic efficiencies in fluorine compound-mixed electrolyte solutions are similar to those in original ethylene carbonate-based solutions except one case. Mixing of fluorine compounds highly increase first coulombic efficiencies of natural graphite electrode in propylene carbonate-containing solution.

  7. Production of films of uranium and americium compounds by thermal decomposition of volatile β-diketonates

    NASA Astrophysics Data System (ADS)

    Danilin, I. D.; Kartushin, V. D.; Pilipenko, N. V.; Abramycheva, I. D.; Vesnovskii, S. P.

    2002-03-01

    The production of films containing uranium and americium through thermal decomposition of diketonates and their adducts is described. It is demonstrated that for substrate temperatures in the range 300-400°C and at a residual reactor pressure of 1.3 Pa, stable uranium-containing layers up to several milligrams per square centimetre can be produced, with yields of up to 90%. A variety of metal backings were investigated, including aluminium and its alloys, stainless steel and titanium. Similar results were obtained for americium, but with a strong influence of backing material on the yield. X-ray diffraction identified the chemical form of the uranium deposits as dioxide, with crystal lattice parameters varying from 5.4338 to 5.4871 Å, while the density determined by X-rays lies within the range from 10920 to 11255 kg/m 3. In the case of Am (Cm) hexafluoroacetyl acetonate decomposition, the deposit is most probably AmF 3 (CmF 3). The gases released from the pyrolytic uranium dioxide layers heated in vacuum to 470°C were studied. The volume of gas released varied between 10 and 40 cm 3 per gram of UO 2 depending on the initial β-diketonate preparation and reagent purity. The released gases were mainly hydrogen, carbon monoxide, carbon dioxide, water and a small amount of methane. The films of uranium and americium obtained by thermal decomposition show good adhesion to backings and are suitable for use in a number of fields, for example in nuclear physics research and instrument engineering.

  8. Lattice thermal expansion of the solid solutions (La{sub 1−x}Sm{sub x}){sub 2}Ce{sub 2}O{sub 7}

    SciTech Connect

    Wu, Hongdan; Lei, Xinrong; Zhang, Jinhua; Yu, Jishun; Zhang, Suxin

    2014-09-15

    Highlights: • Sm-doped La{sub 2}Ce{sub 2}O{sub 7} was prepared by the coprecipitation–calcination method. • In situ HT-XRD measurements revealed that is much stable than 8YSZ. • Its thermal expansion is better than 8YSZ. - Abstract: A series of solid solutions with the general formula (La{sub 1−x}Sm{sub x}){sub 2}Ce{sub 2}O{sub 7} (0.0 ≤ x ≤ 1.0) were prepared by the coprecipitation–calcination method. The products obtained were characterized by powder X-ray diffraction for phase purity. It was observed that La{sup 3+} and Sm{sup 3+} can form complete solid solution in (La,Sm){sub 2}Ce{sub 2}O{sub 7} with defect-fluorite-type phase. The unit cell parameters of these solutions were calculated by a least squares method and the lattice parameters decreased linearly as x increased. The lattice thermal expansion behavior of (La{sub 1−x}Sm{sub x}){sub 2}Ce{sub 2}O{sub 7} (0.0 ≤ x ≤ 1.0) was investigated by high-temperature X-ray diffraction in the temperature range 298–1623 K. The lattice parameters a{sub T} of all the solutions at different temperature can be expressed as a{sub T} = a + bT + cT{sup 2}. As x < 1, the thermal expansion has a sudden decrease at ca. 473 K. The coefficients of lattice thermal expansion of Sm{sub 2}Ce{sub 2}O{sub 7} were 10.2–13.6 × 10{sup −6} K{sup −1} from 298 to 1623 K, and without the thermal contraction at low temperature. The materials show positive or negative thermal expansion due to the asymmetric anharmonic vibration.

  9. Thermal characterization of ZnBeMnSe mixed compounds by means of photopyroelectric and lock-in thermography methods

    NASA Astrophysics Data System (ADS)

    Strzałkowski, K.; Dadarlat, D.; Streza, M.; Zakrzewski, J.

    2015-06-01

    In this work, a thermal characterization (measurement of dynamic thermal parameters) of quaternary Zn1-x-yBexMnySe mixed crystals was carried out. The crystals under investigation were grown from the melt by the modified high-pressure Bridgman method with different Be and Mn contents. The effect of Be and Mn contents on thermal properties of Zn1-x-yBexMnySe compounds was analyzed, by using the photopyroelectric (PPE) method in the back configuration (BPPE) for thermal diffusivity measurements and the PPE technique in the front configuration for thermal effusivity investigations. Infrared lock-in thermography was used in order to validate the BPPE results. The measured thermal effusivity and diffusivity allowed the calculation of thermal conductivity of the investigated materials.

  10. Thermal stability of inorganic and organic compounds in atmospheric particulate matter

    NASA Astrophysics Data System (ADS)

    Perrino, Cinzia; Marconi, Elisabetta; Tofful, Luca; Farao, Carmela; Materazzi, Stefano; Canepari, Silvia

    2012-07-01

    The thermal behaviour of atmospheric particulate matter (PM) has been investigated by using different analytical approaches to explore the added value offered by these technique in environmental studies. The thermogravimetric analysis (TGA), carried out on both certified material and real PM samples, has shown that several mass losses can be detected starting from 80 °C up to above 500 °C, when pyrolysis occur. Thermo-optical analysis of PM and ion chromatographic analysis of the residual have shown that the mass losses in the temperature range 80-180 °C are not justified by the release of either organic or inorganic compounds; it can be thus attributed to the release of weakly and strongly bound water. Release of water has also been evidenced in the temperature range 225-275 °C. The release of ammonium chloride and nitrate has been detected only above 80 °C. This indicates that the release of nitric acid, hydrochloric acid and ammonia, which is observed downstream of the filters during the sampling of atmospheric PM at ambient temperature, cannot be reproduced off-line, after the end of the sampling. We successfully explored one of the possible explanations, that is the desorption of HNO3, HCl and NH3 adsorbed on collected particles. NH4NO3 and NH4Cl, which can be thermally released by the filter, exhibit a different thermal behaviour from NaNO3 and NaCl, which are thermally stable up to 370 °C. This different behaviour can be used to discriminate between natural and secondary sources of atmospheric inorganic salts, as the interconversion that is observed when heating mixtures of pure salts resulted to be not relevant when heating real PM samples.

  11. Ionothermal synthesis of open-framework metal phosphates with a Kagomé lattice network exhibiting canted anti-ferromagnetism† †Electronic supplementary information (ESI) available: Cif files, atomic parameters, X-ray diffraction patterns, IR spectra, TG curves, and thermal ellipsoid plot and atomic label schemes of compound 1–4. See DOI: 10.1039/c4tc00290c Click here for additional data file.

    PubMed Central

    Wang, Guangmei; Valldor, Martin; Mallick, Bert

    2014-01-01

    Four open-framework transition-metal phosphates; (NH4)2Co3(HPO4)2F4 (1), (NH4)Co3(HPO4)2(H2PO4)F2 (2), KCo3(HPO4)2(H2PO4)F2 (3), and KFe3(HPO4)2(H2PO4)F2 (4); are prepared by ionothermal synthesis using pyridinium hexafluorophosphate as the ionic liquid. Single-crystal X-ray diffraction analyses reveal that the four compounds contain cobalt/iron–oxygen/fluoride layers with Kagomé topology composed of interlinked face-sharing MO3F3/MO4F2 octahedra. PO3OH pseudo-tetrahedral groups augment the [M3O6F4] (1)/[M3O8F2] layers on both sides to give M3(HPO4)2F4 (1) and M3(HPO4)2F2 (2–4) layers. These layers are stacked along the a axis in a sequence AA…, resulting in the formation of a layer structure for (NH4)2Co3(HPO4)2F4(1). In NH4Co3(HPO4)2(H2PO4)F2 and KM3(HPO4)2(H2PO4)F2, the M3(HPO4)2F2 layers are stacked along the a axis in a sequence AAi… and are connected by [PO3(OH)] tetrahedra, giving rise to a 3-D open framework structure with 10-ring channels along the [001] direction. The negative charges of the inorganic framework are balanced by K+/NH4 + ions located within the channels. The magnetic transition metal cations themselves form layers with stair-case Kagomé topology. Magnetic susceptibility and magnetization measurements reveal that all four compounds exhibit a canted anti-ferromagnetic ground state (T c = 10 or 13 K for Co and T c = 27 K for Fe) with different canting angles. The full orbital moment is observed for both Co2+ and Fe2+. PMID:25580250

  12. Thermal Decomposition Mechanisms of Lignin Model Compounds: From Phenol to Vanillin

    NASA Astrophysics Data System (ADS)

    Scheer, Adam Michael

    Lignin is a complex, aromatic polymer abundant in cellulosic biomass (trees, switchgrass etc.). Thermochemical breakdown of lignin for liquid fuel production results in undesirable polycyclic aromatic hydrocarbons that lead to tar and soot byproducts. The fundamental chemistry governing these processes is not well understood. We have studied the unimolecular thermal decomposition mechanisms of aromatic lignin model compounds using a miniature SiC tubular reactor. Products are detected and characterized using time-of-flight mass spectrometry with both single photon (118.2 nm; 10.487 eV) and 1 + 1 resonance-enhanced multiphoton ionization (REMPI) as well as matrix isolation infrared spectroscopy. Gas exiting the heated reactor (300 K--1600 K) is subject to a free expansion after a residence time of approximately 100 micros. The expansion into vacuum rapidly cools the gas mixture and allows the detection of radicals and other highly reactive intermediates. By understanding the unimolecular fragmentation patterns of phenol (C6H5OH), anisole (C6H 5OCH3) and benzaldehyde (C6H5CHO), the more complicated thermocracking processes of the catechols (HO-C 6H4-OH), methoxyphenols (HO-C6H4-OCH 3) and hydroxybenzaldehydes (HO-C6H4-CHO) can be interpreted. These studies have resulted in a predictive model that allows the interpretation of vanillin, a complex phenolic ether containing methoxy, hydroxy and aldehyde functional groups. This model will serve as a guide for the pyrolyses of larger systems including lignin monomers such as coniferyl alcohol. The pyrolysis mechanisms of the dimethoxybenzenes (H3C-C 6H4-OCH3) and syringol, a hydroxydimethoxybenzene have also been studied. These results will aid in the understanding of the thermal fragmentation of sinapyl alcohol, the most complex lignin monomer. In addition to the model compound work, pyrolyisis of biomass has been studied via the pulsed laser ablation of poplar wood. With the REMPI scheme, aromatic lignin decomposition

  13. Effect of lattice constant on pseudo Jahn-Teller polar distortion: Application to search for new multiferroic compounds

    NASA Astrophysics Data System (ADS)

    Song, Guang; Zhang, Weiyi

    2016-08-01

    By analog to Maxwell construction for the first-order phase transition, the pseudo Jahn-Teller polar distortion arises naturally once the local bond length of transition-metal oxygen octahedra is enhanced beyond the inflexion point of pair potential into the concave-down dominated region. This concept is applied to search for the new multiferroic compounds for which we specifically choose the (BaMnO3)1/(BaFeO3)1 superlattice as a candidate. The large Ba radius favors the polar distortion in a BaMnO3 layer, while the orbital-ordering-induced superexchange ferromagnetic coupling among Fe-Fe and double-exchange mediated ferromagnetic coupling among Fe-Mn ions stabilize the overall ferromagnetic insulator. A large magnetic moment of 7 μB per unit cell and electric polarization of 14.4 μ Ccm -2 are obtained. Our study offers an important insight for designing robust multiferroic compounds in the future.

  14. Evolution of a double-front Rayleigh-Taylor system using a graphics-processing-unit-based high-resolution thermal lattice-Boltzmann model.

    PubMed

    Ripesi, P; Biferale, L; Schifano, S F; Tripiccione, R

    2014-04-01

    We study the turbulent evolution originated from a system subjected to a Rayleigh-Taylor instability with a double density at high resolution in a two-dimensional geometry using a highly optimized thermal lattice-Boltzmann code for GPUs. Our investigation's initial condition, given by the superposition of three layers with three different densities, leads to the development of two Rayleigh-Taylor fronts that expand upward and downward and collide in the middle of the cell. By using high-resolution numerical data we highlight the effects induced by the collision of the two turbulent fronts in the long-time asymptotic regime. We also provide details on the optimized lattice-Boltzmann code that we have run on a cluster of GPUs. PMID:24827347

  15. Degradation of volatile organic compounds in a non-thermal plasma air purifier.

    PubMed

    Schmid, Stefan; Jecklin, Matthias C; Zenobi, Renato

    2010-03-01

    The degradation of volatile organic compounds in a commercially available non-thermal plasma based air purifying system was investigated. Several studies exist that interrogate the degradation of VOCs in closed air systems using a non-thermal plasma combined with a heterogeneous catalyst. For the first time, however, our study was performed under realistic conditions (normal indoor air, 297.5K and 12.5 g m(-3) water content) on an open system, in the absence of an auxiliary catalyst, and using standard operating air flow rates (up to 320 L min(-1)). Cyclohexene, benzene, toluene, ethylbenzene and the xylene isomers were nebulized and guided through the plasma air purifier. The degradation products were trapped by activated charcoal tubes or silica gel tubes, and analyzed using gas chromatography mass spectrometry. Degradation efficiencies of 11+/-1.6% for cyclohexene, <2% for benzene, 11+/-2.4% for toluene, 3+/-1% for ethylbenzene, 1+/-1% for sigma-xylene, and 3+/-0.4% for m-/rho-xylene were found. A fairly wide range of degradation products could be identified. On both trapping media, various oxidized species such as alcohols, aldehydes, ketones and one epoxide were observed. The formation of adipaldehyde from nebulized cyclohexene clearly indicates an ozonolysis reaction. Other degradation products observed suggests reactions with OH radicals. We propose that mostly ozone and OH radicals are responsible for the degradation of organic molecules in the plasma air purifier. PMID:20167347

  16. Pyrolysis of surface-immobilized model compounds: Mechanistic implications for the thermal chemistry of coal

    SciTech Connect

    Britt, P F; Poutsma, M L

    1990-01-01

    Our research has been investigating the potential role that the cross-linked network structure of coal may play in perturbing free-radical reactions associated with coal thermolysis. This may be particularly important in the thermal conversion of coal at low temperatures, e.g., 350--400{degree}C, where bonds begin to break but most of the residual framework is retained. In order to assess the potential impact of restricted transport on thermal reaction pathways, we have modeled the phenomenon experimentally by studying organic model compounds that are covalently linked to an inert silica surface. The experimental methodology and significant results from studies of the thermolysis of surface-attached Ph(CH{sub 2}){sub n}Ph (n = 0--4) at 345--400{degree}C will be briefly surveyed. Initial results from studies of two-component surfaces will also be presented that reveal the role of radical migration, via facile hydrogen shuttling, in modifying the effects of diffusional constraints. 13 refs., 5 figs.

  17. Synthesis and Thermal Decomposition Mechanism of the Energetic Compound 3,5-Dinitro-4-nitroxypyrazole

    NASA Astrophysics Data System (ADS)

    Feng, Xiao-Qin; Cao, Duan-Lin; Cui, Jian-Lan

    2016-07-01

    A novel energetic material, 3,5-dinitro-4-nitroxypyrazole (DNNP), was synthesized via nitration and nucleophilic substitution reaction using 4-chloropyrazole as raw material. The structure of DNNP was characterized by Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR), and elemental analysis. Its detonation properties were calculated and compared with those of other commonly used energetic compounds. The thermal decomposition mechanism of DNNP was studied by means of thermogravimetry and differential scanning calorimetry coupled with a mass spectrometry (DSC-MS). The results show that the detonation properties of DNNP were better than those of TNT and comparable to those of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). In addition, the thermal decomposition mechanism of DNNP was supposed. Initially, the O-NO2 bond was broken, thereby producing a nitropyrazole oxygen radical. Subsequently, the nitropyrazole oxygen radical was decomposed by free radical cleavage of nitro or isomerized to nitritepyrazole and subsequently decomposed by free radical cleavage of the nitroso group. Finally, pyrazole ring fission occurred and produced N2, NO, N2O, and CO2.

  18. Impact of organic-mineral matter interactions on thermal reaction pathways for coal model compounds

    SciTech Connect

    Buchanan, A.C. III; Britt, P.F.; Struss, J.A.

    1995-07-01

    Coal is a complex, heterogeneous solid that includes interdispersed mineral matter. However, knowledge of organic-mineral matter interactions is embryonic, and the impact of these interactions on coal pyrolysis and liquefaction is incomplete. Clay minerals, for example, are known to be effective catalysts for organic reactions. Furthermore, clays such as montmorillonite have been proposed to be key catalysts in the thermal alteration of lignin into vitrinite during the coalification process. Recent studies by Hatcher and coworkers on the evolution of coalified woods using microscopy and NMR have led them to propose selective, acid-catalyzed, solid state reaction chemistry to account for retained structural integrity in the wood. However, the chemical feasibility of such reactions in relevant solids is difficult to demonstrate. The authors have begun a model compound study to gain a better molecular level understanding of the effects in the solid state of organic-mineral matter interactions relevant to both coal formation and processing. To satisfy the need for model compounds that remain nonvolatile solids at temperatures ranging to 450 C, model compounds are employed that are chemically bound to the surface of a fumed silica (Si-O-C{sub aryl}linkage). The organic structures currently under investigation are phenethyl phenyl ether (C{sub 6}H{sub 5}CH{sub 2}CH{sub 2}OC{sub 6}H{sub 5}) derivatives, which serve as models for {beta}-alkyl aryl ether units that are present in lignin and lignitic coals. The solid-state chemistry of these materials at 200--450 C in the presence of interdispersed acid catalysts such as small particle size silica-aluminas and montmorillonite clay will be reported. Initial focus will be on defining the potential impact of these interactions on coal pyrolysis and liquefaction.

  19. Evaluation of bioactive compounds of black mulberry juice after thermal, microwave, ultrasonic processing, and storage at different temperatures.

    PubMed

    Jiang, Bo; Mantri, Nitin; Hu, Ya; Lu, Jiayin; Jiang, Wu; Lu, Hongfei

    2015-07-01

    The effect of different sterilization methods (thermal, microwave, and ultrasonic processing) on the main bioactive compounds and antioxidant activity of black mulberry juice during selected storage time (8 days) and temperatures (5, 15, and 25 ℃) was investigated. The antioxidant activity of thermal-treated juice depleted with storage time, whilst both ultrasound- and microwave-treated juices showed transient increase in antioxidant activity during the first 2 days that later decreased with storage time. Lower temperature storage preserved more bioactive compounds and antioxidant activity, especially in ultrasound sterilized samples. The activation energy values were 15.99, 13.07, and 12.81 kJ/mol for ultrasonic, microwave, and thermal pasteurization processes, respectively. In general, ultrasound-sterilized samples showed higher total phenolics, anthocyanin, and antioxidant activity compared to the microwave- and thermal-processed juice during the storage time especially at lower temperatures. PMID:24917651

  20. Development of Design Technology on Thermal-Hydraulic Performance in Tight-Lattice Rod Bundles: II - Rod Bowing Effect on Boiling Transition under Transient Conditions

    NASA Astrophysics Data System (ADS)

    Liu, Wei; Tamai, Hidesada; Kureta, Masatoshi; Ohnuki, Akira; Akimoto, Hajime

    A thermal-hydraulic feasibility project for an Innovative Water Reactor for Flexible fuel cycle (FLWR) has been performed since 2002. In this R&D project, large-scale thermal-hydraulic tests, several model experiments and development of advanced numerical analysis codes have been carried out. In this paper, we describe the critical power characteristics in a 37-rod tight-lattice bundle with rod bowing under transient states. It is observed that transient Boiling Transition (BT) always occurs axially at exit elevation of upper high-heat-flux region and transversely in the central area of the bundle, which is same as that under steady state. For the postulated power increase and flow decrease cases that may be possibly met in a normal operation of the FLWR, it is confirmed that no BT occurs when Initial Critical Power Ratio (ICPR) is 1.3. Moreover, when the transients are run under severer ICPR that causes BT, the transient critical powers are generally same as the steady ones. The experiments are analyzed with a modified TRAC-BFI code, where Japan Atomic Energy Agency (JAEA) newest critical power correlation is implemented for the BT judgement. The code shows good prediction for the occurrence or the non occurrence of the BT and predicts the BT starting time conservatively. Traditional quasi-steady state prediction of the transient BT is confirmed being applicable for the postulated abnormal transient processes in the tight-lattice bundle with rod bowing.

  1. Modeling of gas transport with electrochemical reaction in nickel-yttria-stabilized zirconia anode during thermal cycling by Lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Guo, Pengfei; Guan, Yong; Liu, Gang; Liang, Zhiting; Liu, Jianhong; Zhang, Xiaobo; Xiong, Ying; Tian, Yangchao

    2016-09-01

    This work reports an investigation of the impact of microstructure on the performance of solid oxide fuel cells (SOFC) composed of nickel yttria-stabilized zirconia (Ni YSZ). X-ray nano computed tomography (nano-CT) was used to obtain three-dimensional (3D) models of Ni-YSZ composite anode samples subjected to different thermal cycles. Key parameters, such as triple phase boundary (TPB) density, were calculated using 3D reconstructions. The electrochemical reaction occurring at active-TPB was modeled by the Lattice Boltzmann Method for simulation of multi-component mass transfer in porous anodes. The effect of different electrode geometries on the mass transfer and the electrochemical reaction in anodes was studied by TPB distributions measured by nano CT for samples subjected to different thermal cycles. The concentration polarization and the activation polarization were estimated respectively. The results demonstrate that a combined approach involving nano-CT experiments in conjunction with simulations of gas transport and electrochemical reactions using the Lattice Boltzmann method can be used to better understand the relationship between electrode microstructure and performance of nickel yttria-stabilized zirconia anodes.

  2. Thermoelectric properties of monolayer MSe2 (M = Zr, Hf): low lattice thermal conductivity and a promising figure of merit

    NASA Astrophysics Data System (ADS)

    Ding, Guangqian; Gao, G. Y.; Huang, Zhishuo; Zhang, Wenxu; Yao, Kailun

    2016-09-01

    Monolayer transition-metal dichalcogenides (TMDCs) MX2 (M = Mo, W, Zr, Hf, etc; X = S, Se, Te) have become well-known in recent times for their promising applications in thermoelectrics and field effect transistors. In this work, we perform a systematic study on the thermoelectric properties of monolayer ZrSe2 and HfSe2 using first-principles calculations combined with Boltzmann transport equations. Our results point to a competitive thermoelectric figure of merit (close to 1 at optimal doping) in both monolayer ZrSe2 and HfSe2, which is markedly higher than previous explored monolayer TMDCs such as MoS2 and MoSe2. We also reveal that the higher figure of merits arise mainly from their low lattice thermal conductivity, and this is partly due to the strong coupling of acoustic modes with low frequency optical modes. It is found that the figure of merits can be better optimized in n-type than in p-type. In particular, the performance of HfSe2 is superior to ZrSe2 at a higher temperature. Our results suggest that monolayer ZrSe2 and HfSe2 with lower lattice thermal conductivity than usual monolayer TMDCs are promising candidates for thermoelectric applications.

  3. Thermoelectric properties of monolayer MSe2 (M = Zr, Hf): low lattice thermal conductivity and a promising figure of merit.

    PubMed

    Ding, Guangqian; Gao, G Y; Huang, Zhishuo; Zhang, Wenxu; Yao, Kailun

    2016-09-16

    Monolayer transition-metal dichalcogenides (TMDCs) MX2 (M = Mo, W, Zr, Hf, etc; X = S, Se, Te) have become well-known in recent times for their promising applications in thermoelectrics and field effect transistors. In this work, we perform a systematic study on the thermoelectric properties of monolayer ZrSe2 and HfSe2 using first-principles calculations combined with Boltzmann transport equations. Our results point to a competitive thermoelectric figure of merit (close to 1 at optimal doping) in both monolayer ZrSe2 and HfSe2, which is markedly higher than previous explored monolayer TMDCs such as MoS2 and MoSe2. We also reveal that the higher figure of merits arise mainly from their low lattice thermal conductivity, and this is partly due to the strong coupling of acoustic modes with low frequency optical modes. It is found that the figure of merits can be better optimized in n-type than in p-type. In particular, the performance of HfSe2 is superior to ZrSe2 at a higher temperature. Our results suggest that monolayer ZrSe2 and HfSe2 with lower lattice thermal conductivity than usual monolayer TMDCs are promising candidates for thermoelectric applications. PMID:27487270

  4. Suppression of temperature hysteresis in negative thermal expansion compound BiNi1-xFexO3 and zero-thermal expansion composite

    NASA Astrophysics Data System (ADS)

    Nabetani, K.; Muramatsu, Y.; Oka, K.; Nakano, K.; Hojo, H.; Mizumaki, M.; Agui, A.; Higo, Y.; Hayashi, N.; Takano, M.; Azuma, M.

    2015-02-01

    Negative thermal expansion (NTE) of BiNi1-xFexO3 is investigated. All x = 0.05, 0.075, 0.10, and 0.15 samples shows large NTE with the coefficient of linear thermal expansion (CTE) αL exceeding -150 ppm K-1 induced by charge transfer between Bi5+ and Ni2+ in the controlled temperature range near room temperature. Compared with Bi1-xLnxNiO3 (Ln: rare-earth elements), the thermal hysteresis that causes a problem for practical application is suppressed because random distribution of Fe in the Ni site changes the first order transition to second order-like transition. The CTE of BiNi0.85Fe0.15O3 reaches -187 ppm K-1 and it is demonstrated that 18 vol. % addition of the present compound compensates for the thermal expansion of epoxy resin.

  5. Scoring function for DNA-drug docking of anticancer and antiparasitic compounds based on spectral moments of 2D lattice graphs for molecular dynamics trajectories.

    PubMed

    Pérez-Montoto, Lázaro G; Santana, Lourdes; González-Díaz, Humberto

    2009-11-01

    We introduce here a new class of invariants for MD trajectories based on the spectral moments pi(k)(L) of the Markov matrix associated to lattice network-like (LN) graph representations of Molecular Dynamics (MD) trajectories. The procedure embeds the MD energy profiles on a 2D Cartesian coordinates system using simple heuristic rules. At the same time, we associate the LN with a Markov matrix that describes the probabilities of passing from one state to other in the new 2D space. We construct this type of LNs for 422 MD trajectories obtained in DNA-drug docking experiments of 57 furocoumarins. The combined use of psoralens+ultraviolet light (UVA) radiation is known as PUVA therapy. PUVA is effective in the treatment of skin diseases such as psoriasis and mycosis fungoides. PUVA is also useful to treat human platelet (PTL) concentrates in order to eliminate Leishmania spp. and Trypanosoma cruzi. Both are parasites that cause Leishmaniosis (a dangerous skin and visceral disease) and Chagas disease, respectively; and may circulate in blood products collected from infected donors. We included in this study both lineal (psoralens) and angular (angelicins) furocoumarins. In the study, we grouped the LNs on two sets; set1: DNA-drug complex MD trajectories for active compounds and set2: MD trajectories of non-active compounds or no-optimal MD trajectories of active compounds. We calculated the respective pi(k)(L) values for all these LNs and used them as inputs to train a new classifier that discriminate set1 from set2 cases. In training series the model correctly classifies 79 out of 80 (specificity=98.75%) set1 and 226 out of 238 (Sensitivity=94.96%) set2 trajectories. In independent validation series the model correctly classifies 26 out of 26 (specificity=100%) set1 and 75 out of 78 (sensitivity=96.15%) set2 trajectories. We propose this new model as a scoring function to guide DNA-docking studies in the drug design of new coumarins for anticancer or antiparasitic

  6. Charge transport and vector meson dissociation across the thermal phase transition in lattice QCD with two light quark flavors

    NASA Astrophysics Data System (ADS)

    Brandt, Bastian B.; Francis, Anthony; Jäger, Benjamin; Meyer, Harvey B.

    2016-03-01

    We compute and analyze correlation functions in the isovector vector channel at vanishing spatial momentum across the deconfinement phase transition in lattice QCD. The simulations are carried out at temperatures T /Tc=0.156 , 0.8, 1.0, 1.25 and 1.67 with Tc≃203 MeV for two flavors of Wilson-Clover fermions with a zero-temperature pion mass of ≃270 MeV . Exploiting exact sum rules and applying a phenomenologically motivated Ansatz allows us to determine the spectral function ρ (ω ,T ) via a fit to the lattice correlation function data. From these results we estimate the electrical conductivity across the deconfinement phase transition via a Kubo formula and find evidence for the dissociation of the ρ meson by resolving its spectral weight at the available temperatures. We also apply the Backus-Gilbert method as a model-independent approach to this problem. At any given frequency, it yields a local weighted average of the true spectral function. We use this method to compare kinetic theory predictions and previously published phenomenological spectral functions to our lattice study.

  7. Novel negative resists using thermally stable crosslinkers based on phenolic compounds

    NASA Astrophysics Data System (ADS)

    Kajita, Toru; Kobayashi, Eiichi; Ota, Toshiyuki; Miura, Takao

    1993-09-01

    This is a preliminary report on a family of crosslinkers based on phenolic compounds for negative-working photoresists which are suitable for KrF excimer laser exposure using poly(hydroxystyrene) (PHS) as a base resin. The crosslinkers are benzylic derivatives having etherificated or esterificated phenolic hydroxyl group. Several effects upon the resist performances of chemically amplified (CA) resist systems comprising onium salt, PHS, and the crosslinkers are mainly discussed: i.e., sort of substituent, sort of mother molecular structure, sort of crosslinkable group, baking conditions, PHS's molecular weight, additives, and so on. The CA resist gives quarter-micron line and space pairs without swelling using a KrF excimer laser exposure. Moreover, in this report another effective method for inhibiting the swelling is proposed. Finally, a unique negative resist, which is not a CA resist, is also presented. It gives negative-tone images by thermal crosslinking reaction following photo- induced dissociation of the protective group of crosslinker.

  8. Using a melanin granule lattice model to study the thermal effects of pulsed and scanning light irradiations through a measurement aperture

    NASA Astrophysics Data System (ADS)

    Kim, Do-Hyun

    2011-12-01

    Optical radiation hazards of scanning light sources are often evaluated using pulsed light source criteria, with the relevant pulse parameter equivalent to the scanning light source determined by the energy delivered through a measurement aperture. However, physical equivalence has not been completely understood: a pulsed light source is temporally dynamic but spatially stationary, while a scanning light source is temporally stationary but spatially dynamic. This study introduces a numerical analysis based upon the melanin granule lattice model to investigate the equivalence of scanning and pulsed light sources through a measurement aperture and their respective thermal effects in the pigmented retinal layer. The numerical analysis calculates the thermal contribution of individual melanin granules with varying temporal sequence, and finds that temperature changes and thermal damage thresholds for the two different types of light sources were not equal. However, dwell times of 40 to 200 μsec did not produce significant differences between pulsed and scanning light sources in temperature change and thermal damage thresholds to the sample tissue.

  9. Multiscale Modeling of Ultra High Temperature Ceramics (UHTC) ZrB2 and HfB2: Application to Lattice Thermal Conductivity

    NASA Technical Reports Server (NTRS)

    Lawson, John W.; Daw, Murray S.; Squire, Thomas H.; Bauschlicher, Charles W.

    2012-01-01

    We are developing a multiscale framework in computational modeling for the ultra high temperature ceramics (UHTC) ZrB2 and HfB2. These materials are characterized by high melting point, good strength, and reasonable oxidation resistance. They are candidate materials for a number of applications in extreme environments including sharp leading edges of hypersonic aircraft. In particular, we used a combination of ab initio methods, atomistic simulations and continuum computations to obtain insights into fundamental properties of these materials. Ab initio methods were used to compute basic structural, mechanical and thermal properties. From these results, a database was constructed to fit a Tersoff style interatomic potential suitable for atomistic simulations. These potentials were used to evaluate the lattice thermal conductivity of single crystals and the thermal resistance of simple grain boundaries. Finite element method (FEM) computations using atomistic results as inputs were performed with meshes constructed on SEM images thereby modeling the realistic microstructure. These continuum computations showed the reduction in thermal conductivity due to the grain boundary network.

  10. Comparison of phenolic compounds of orange juice processed by pulsed electric fields (PEF) and conventional thermal pasteurisation.

    PubMed

    Agcam, E; Akyıldız, A; Akdemir Evrendilek, G

    2014-01-15

    Processing of orange juice by pulsed electric fields (PEF) and thermal pasteurisation was carried out to compare changes in total phenolic concentration, hydroxybenzoic acid, hydroxycinnamic acids, flavonols, flavones and flavonones before and after being stored at 4°C for 180days. Changes in the initial total phenolic concentration of the samples varied depending on the applied electric field intensity and thermal pasteurisation. Hesperidin and chlorogenic acids were detected as the most abounded flavonoid and phenolic acids in the orange juice, respectively. Except for syringic acid and neoeriocitrin, the concentration of the phenolic compounds indentified in the orange juice samples enhanced after the PEF or thermal pasteurisation. The samples treated with PEF had more stable flavonoids and phenolic acids than those treated with the thermal pasteurisation. The PEF-treated samples had higher sensory scores than the heat-treated samples. PMID:24054251

  11. Thermal decomposition of high-nitrogen energetic compounds: TAGzT and GUzT

    NASA Astrophysics Data System (ADS)

    Hayden, Heather F.

    The U.S. Navy is exploring high-nitrogen compounds as burning-rate additives to meet the growing demands of future high-performance gun systems. Two high-nitrogen compounds investigated as potential burning-rate additives are bis(triaminoguanidinium) 5,5-azobitetrazolate (TAGzT) and bis(guanidinium) 5,5'-azobitetrazolate (GUzT). Small-scale tests showed that formulations containing TAGzT exhibit significant increases in the burning rates of RDX-based gun propellants. However, when GUzT, a similarly structured molecule was incorporated into the formulation, there was essentially no effect on the burning rate of the propellant. Through the use of simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) and Fourier-Transform ion cyclotron resonance (FTICR) mass spectrometry methods, an investigation of the underlying chemical and physical processes that control the thermal decomposition behavior of TAGzT and GUzT alone and in the presence of RDX, was conducted. The objective was to determine why GUzT is not as good a burning-rate enhancer in RDX-based gun propellants as compared to TAGzT. The results show that TAGzT is an effective burning-rate modifier in the presence of RDX because the decomposition of TAGzT alters the initial stages of the decomposition of RDX. Hydrazine, formed in the decomposition of TAGzT, reacts faster with RDX than RDX can decompose itself. The reactions occur at temperatures below the melting point of RDX and thus the TAGzT decomposition products react with RDX in the gas phase. Although there is no hydrazine formed in the decomposition of GUzT, amines formed in the decomposition of GUzT react with aldehydes, formed in the decomposition of RDX, resulting in an increased reaction rate of RDX in the presence of GUzT. However, GUzT is not an effective burning-rate modifier because its decomposition does not alter the initial gas-phase decomposition of RDX. The decomposition of GUzT occurs at temperatures above the melting point

  12. Performance evaluation of a sorbent tube sampling method using short path thermal desorption for volatile organic compounds.

    PubMed

    Peng, C Y; Batterman, S

    2000-08-01

    Air sampling, using sorbents, thermal desorption and gas chromatography, is a versatile method for identifying and quantifying trace levels of volatile organic compounds (VOCs). Thermal desorption can provide high sensitivity, appropropriate choices of sorbents and method parameters can accommodate a wide range of compounds and high humidity, and automated short-path systems can minimize artifacts, losses and carry-over effects. This study evaluates the performance of a short-path thermal desorption method for 77 VOCs using laboratory and field tests and a dual sorbent system (Tenax GR, Carbosieve SIII). Laboratory tests showed that the method requirements for ambient air sampling were easily achieved for most compounds, e.g., using the average and standard deviation across target compounds, blank emissions were < or = 0.3 ng per sorbent tube for all target compounds except benzene, toluene and phenol; the method detection limit was 0.05 +/- 0.08 ppb, reproducibility was 12 +/- 6%, linearity, as the relative standard deviation of relative response factors, was 16 +/- 9%, desorption efficiency was 99 +/- 28%, samples stored for 1-6 weeks had recoveries of 87 +/- 9%, and high humidity samples had recoveries of 102 +/- 12%. Due to sorbent, column and detector characteristics, performance was somewhat poorer for phenol groups, ketones, and nitrogen containing compounds. The laboratory results were confirmed in an analysis of replicate samples collected in two field studies that sampled ambient air along roadways and indoor air in a large office building. Replicates collected under field conditions demonstrated good agreement except for very low concentrations or large (> 41 volume) samples of high humidity air. Overall, the method provides excellent performance and satisfactory throughput for many applications. PMID:11249785

  13. Headspace sorptive extraction for the analysis of organotin compounds using thermal desorption and gas chromatography with mass spectrometry.

    PubMed

    Cacho, J I; Campillo, N; Viñas, P; Hernández-Córdoba, M

    2013-03-01

    A method based on headspace sorptive extraction (HSSE) in combination with thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) has been developed for the simultaneous determination of six organotin compounds (OTCs), corresponding to mono- and di-substituted methyltin, butyltin and octyltin species. Several parameters affecting both the headspace extraction and thermal desorption steps were carefully optimized using multivariate designs. Analytes were derivatized by in situ ethylation with sodium tetraethylborate. The optimized method was applied to the analysis of water samples of different origins, as well as to checking the migration of the studied compounds from commercially available plastic containers to the adequate liquid simulant. Quantification was carried out against aqueous calibration curves using diphenyltin as internal standard, providing detection limits of between 1.7 and 7.0 ng(Sn) L(-1), depending on the compound, and repeatabilities lower than 10% in terms of relative standard deviation. The applicability of the method was assessed by means of recovery studies and satisfactory values for all compounds were attained. The release of OTCs from the tested packages to the liquid simulant was confirmed, concentrations as high as 2.4 μg(Sn) L(-1) being found for dioctyltin. Even though the proposed method was developed for organotin halides, its application to an organotin ester shows its suitability for determining these compounds in migration assays. PMID:23357745

  14. Magnetic and thermal properties of RCu9In2 (R=La, Ce, Pr, Nd, Sm and Eu) compounds

    NASA Astrophysics Data System (ADS)

    Baran, S.; Przewoźnik, J.; Kalychak, Ya. M.; Tyvanchuk, Yu.; Szytuła, A.

    2016-07-01

    The RCu9In2 intermetallics with R=La, Ce, Pr, Nd, Sm, Eu have been synthesized and characterized with regards to their crystal structure as well as magnetic and thermal properties. The compounds have tetragonal structure of the YNi9In2-type (space group P4/mbm). Except for LaCu8.25In2.75, they exhibit localized magnetism due to the presence of magnetic moments on the respective trivalent rare-earth ions. The Nd-, Sm- and Eu- based compounds order antiferromagnetically below 4.6, 11.0 and 23.2 K, respectively.

  15. The role of spontaneous polarization in the negative thermal expansion of tetragonal PbTiO3-based compounds.

    PubMed

    Chen, Jun; Nittala, Krishna; Forrester, Jennifer S; Jones, Jacob L; Deng, Jinxia; Yu, Ranbo; Xing, Xianran

    2011-07-27

    PbTiO(3)-based compounds are well-known ferroelectrics that exhibit a negative thermal expansion more or less in the tetragonal phase. The mechanism of negative thermal expansion has been studied by high-temperature neutron powder diffraction performed on two representative compounds, 0.7PbTiO(3)-0.3BiFeO(3) and 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3), whose negative thermal expansion is contrarily enhanced and weakened, respectively. With increasing temperature up to the Curie temperature, the spontaneous polarization displacement of Pb/Bi (δz(Pb/Bi)) is weakened in 0.7PbTiO(3)-0.3BiFeO(3) but well-maintained in 0.7PbTiO(3)-0.3Bi(Zn(1/2)Ti(1/2))O(3). There is an apparent correlation between tetragonality (c/a) and spontaneous polarization. Direct experimental evidence indicates that the spontaneous polarization originating from Pb/Bi-O hybridization is strongly associated with the negative thermal expansion. This mechanism can be used as a guide for the future design of negative thermal expansion of phase-transforming oxides. PMID:21696173

  16. Lattice Thermal Conductivity of the Binary and Ternary Group-IV Alloys Si-Sn, Ge-Sn, and Si-Ge-Sn

    NASA Astrophysics Data System (ADS)

    Khatami, S. N.; Aksamija, Z.

    2016-07-01

    Efficient thermoelectric (TE) energy conversion requires materials with low thermal conductivity and good electronic properties. Si-Ge alloys, and their nanostructures such as thin films and nanowires, have been extensively studied for TE applications; other group-IV alloys, including those containing Sn, have not been given as much attention as TEs, despite their increasing applications in other areas including optoelectronics. We study the lattice thermal conductivity of binary (Si-Sn and Ge-Sn) and ternary (Si-Ge-Sn) alloys and their thin films in the Boltzmann transport formalisms, including a full phonon dispersion and momentum-dependent boundary-roughness scattering. We show that Si-Sn alloys have the lowest conductivity (3 W /mK ) of all the bulk alloys, more than 2 times lower than Si-Ge, attributed to the larger difference in mass between the two constituents. In addition, we demonstrate that thin films offer an additional reduction in thermal conductivity, reaching around 1 W /mK in 20-nm-thick Si-Sn, Ge-Sn, and ternary Si-Ge-Sn films, which is near the conductivity of amorphous SiO2 . We conclude that group-IV alloys containing Sn have the potential for high-efficiency TE energy conversion.

  17. Anisotropic lattice thermal expansion of PbFeBO4: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations

    DOE PAGESBeta

    Murshed, M. Mangir; Mendive, Cecilia B.; Curti, Mariano; Nénert, Gwilherm; Kalita, Patricia E.; Lipinska, Kris; Cornelius, Andrew L.; Huq, Ashfia; Gesing, Thorsten M.

    2014-11-01

    We present the lattice thermal expansion of mullite-type PbFeBO4 in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modeled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. Moreover, the unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations. Harmonic frequencies ofmore » the optical Raman modes at the Γ-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low-temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO4, FeO6 and BO3 polyhedra as a function of temperature.« less

  18. Anisotropic lattice thermal expansion of PbFeBO4: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations

    SciTech Connect

    Murshed, M. Mangir; Mendive, Cecilia B.; Curti, Mariano; Nénert, Gwilherm; Kalita, Patricia E.; Lipinska, Kris; Cornelius, Andrew L.; Huq, Ashfia; Gesing, Thorsten M.

    2014-11-01

    We present the lattice thermal expansion of mullite-type PbFeBO4 in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modeled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. Moreover, the unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations. Harmonic frequencies of the optical Raman modes at the Γ-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low-temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO4, FeO6 and BO3 polyhedra as a function of temperature.

  19. Optimization of conditions for thermal treatment of rice bran using an accelerator including an organo-iron compound.

    PubMed

    Kanno, Hikari; Tachibana, Naoya; Fukushima, Masami

    2011-02-01

    A method for thermal conversion of raw organic waste (ROW) to a compost-like material (CLM) with higher levels of unsaturated carbohydrates, nitrogen- and oxygen-containing compounds was developed, in which rice bran and an organo-iron compound were employed as a model ROW and the accelerator, respectively. To evaluate the qualities of CLMs, organic substances of an acid insoluble fraction of alkaline extracts (AIAEs) from a CLM were structurally characterized by elemental analysis, pyrolysis-gas chromatography/mass spectrometry and FT-IR. The levels of unsaturated carbohydrates, and nitrogen- and oxygen-containing compounds in the CLM samples were increased by long-term treatment (60°C for 5 days, 170°C for 3 days). In particular, the high lipid content of the AIAEs, which was indicative of inadequate digestion of CLM components, was dramatically reduced in the presence of the accelerator. PMID:21044838

  20. Fast volatile organic compound recovery from soil standards for analysis by thermal desorption gas chromatography.

    PubMed

    Meniconi, Maria de Fátima Guadalupe; Parris, R; Thomas, C L P

    2003-10-01

    The development of high-throughput environmental screening assays are needed to meet high-specification data quality objectives (DQOs) that require large numbers of samples to be taken and analysed rapidly. The acquisition and stabilisation of the sample is a key technical and operational challenge in analytical sequences associated with the determination of volatile organic compound (VOC) contamination of soils. Further the development of miniaturised and embedded analytical systems for environmental conditioning monitoring requires the development of new sampling techniques. A proof-of-concept study is described that shows how pressurised gas, in this case carbon dioxide, may be used to recover reversibly-bound VOCs from soil into an adsorbent sampler, and then analysed by thermal desorption-gas chromatography. The effects of the volume of the pressurised gas, the gas flow rate and the mass of the soil sample on the recovery efficiency and breakthrough from the adsorbent trap were investigated in a preliminary characterisation study. Two distinct approaches were identified. The first involved ventilation of the voids within the soil matrix to displace the soil-gas headspace, a rapid screening approach. The second involved a more prolonged purge of the matrix to strip reversibly bound species into the gas phase and hence pass them into the adsorbent trap, a purge and trap approach. The shortest possible sample processing time required to yield analytically useful responses was 5 s with the use of the headspace approach. In this case n-octane, benzene and toluene were recovered from conditioned spiked soil samples at concentrations in the range 42 to 1690 mg kg(-1). The limit of detection for the system was estimated to be no greater than 1.2 mg kg(-1). Using the purge and trap variant enabled recovery efficiencies greater than 93% to be achieved with liquid spikes of n-octane onto soil samples. These preliminary studies showed that a system based on this approach

  1. Competition between the Direct Exchange Interaction and Superexchange Interaction in Layered Compounds LiCrSe2, LiCrTe2, and NaCrTe2 with a Triangular Lattice.

    PubMed

    Kobayashi, Shintaro; Ueda, Hiroaki; Michioka, Chishiro; Yoshimura, Kazuyoshi

    2016-08-01

    Physical properties of new S = 3/2 triangular-lattice compounds LiCrSe2, LiCrTe2, and NaCrTe2 have been investigated by X-ray diffraction and magnetic measurements. These compounds crystallize in the ordered NiAs-type structure, where alkali metal ions and Cr atoms stack alternately. Despite their isomorphic structures, magnetic properties of these three compounds are different; NaCrTe2 has an A-type spin structure with ferromagnetic layers, LiCrTe2 is likely to exhibit a helical spin structure, and LiCrSe2 shows a first-order-like phase transition from the paramagnetic trigonal phase to the antiferromagnetic monoclinic phase. In these compounds and the other chromium chalcogenides with a triangular lattice, we found a general relationship between the Curie-Weiss temperature and magnetic structures. This relation indicates that the competition between the antiferromagnetic direct d-d exchange interaction and the ferromagnetic superexchange interaction plays an important role in determining the ground state of chromium chalcogenides. PMID:27400024

  2. Extended lattice Boltzmann method for numerical simulation of thermal phase change in two-phase fluid flow

    NASA Astrophysics Data System (ADS)

    Safari, Hesameddin; Rahimian, Mohammad Hassan; Krafczyk, Manfred

    2013-07-01

    In this article, a method based on the multiphase lattice Boltzmann framework is presented which is applicable to liquid-vapor phase-change phenomena. Both liquid and vapor phases are assumed to be incompressible. For phase changes occurring at the phase interface, the divergence-free condition of the velocity field is no longer satisfied due to the gas volume generated by vaporization or fluid volume generated by condensation. Thus, we extend a previous model by a suitable equation to account for the finite divergence of the velocity field within the interface region. Furthermore, the convective Cahn-Hilliard equation is extended to take into account vaporization effects. In a first step, a D1Q3 LB model is constructed and validated against the analytical solution of a one-dimensional Stefan problem for different density ratios. Finally the model is extended to two dimensions (D2Q9) to simulate droplet evaporation. We demonstrate that the results obtained by this approach are in good agreement with theory.

  3. Measurement of volatile plant compounds in field ambient air by thermal desorption-gas chromatography-mass spectrometry.

    PubMed

    Cai, Xiao-Ming; Xu, Xiu-Xiu; Bian, Lei; Luo, Zong-Xiu; Chen, Zong-Mao

    2015-12-01

    Determination of volatile plant compounds in field ambient air is important to understand chemical communication between plants and insects and will aid the development of semiochemicals from plants for pest control. In this study, a thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) method was developed to measure ultra-trace levels of volatile plant compounds in field ambient air. The desorption parameters of TD, including sorbent tube material, tube desorption temperature, desorption time, and cold trap temperature, were selected and optimized. In GC-MS analysis, the selected ion monitoring mode was used for enhanced sensitivity and selectivity. This method was sufficiently sensitive to detect part-per-trillion levels of volatile plant compounds in field ambient air. Laboratory and field evaluation revealed that the method presented high precision and accuracy. Field studies indicated that the background odor of tea plantations contained some common volatile plant compounds, such as (Z)-3-hexenol, methyl salicylate, and (E)-ocimene, at concentrations ranging from 1 to 3400 ng m(-3). In addition, the background odor in summer was more abundant in quality and quantity than in autumn. Relative to previous methods, the TD-GC-MS method is more sensitive, permitting accurate qualitative and quantitative measurements of volatile plant compounds in field ambient air. PMID:26493981

  4. Giant negative thermal expansion in NaZn13-type La(Fe, Si, Co)13 compounds.

    PubMed

    Huang, Rongjin; Liu, Yanying; Fan, Wei; Tan, Jie; Xiao, Furen; Qian, Lihe; Li, Laifeng

    2013-08-01

    La(Fe, Si)13-based compounds are well-known magnetocaloric materials, which show a pronounced negative thermal expansion (NTE) around the Curie temperature but have not been considered as NTE materials for industrial applications. The NaZn13-type LaFe13-xSix and LaFe11.5-xCoxSi1.5 compounds were synthesized, and their linear NTE properties were investigated. By optimizing the chemical composition, the sharp volume change in La(Fe, Si)13-based compounds was successfully modified into continuous expansion. By increasing the amount of Co dopant in LaFe11.5-xCoxSi1.5, the NTE shifts toward a higher temperature region, and also the NTE operation-temperature window becomes broader. Typically, the linear NTE coefficient identified in the LaFe10.5Co1.0Si1.5 compound reaches as much as -26.1 × 10(-6) K(-1), with an operation-temperature window of 110 K from 240 to 350 K, which includes room temperature. Such control of the specific composition and the NTE properties of La(Fe, Si)13-based compounds suggests their potential application as NTE materials. PMID:23885928

  5. Effects of hydrogen impurities on the lattice thermal diffusivity of quartz and quartzites up to 1000\\deg C

    NASA Astrophysics Data System (ADS)

    Branlund, J. M.; Hofmeister, A. M.

    2004-12-01

    The phonon contribution to thermal diffusivity (Dlat) in quartz single-crystals was measured using a laser flash apparatus between room temperature and 1000\\deg C. Our measurements revealed differences in Dlat between samples which most likely result from hydroxyl impurities. Variations in Dlat between wet and dry samples persist above the α to β transition. For all samples, Dlat follows a 1/T trend. Unlike previous measurements, thermal diffusivity of β -quartz remains constant or decreases slightly with increasing temperature, showing that the technique removes radiative transfer effects. The difference between samples is of greatest interest. The two orientations of a quartz single-crystal containing 171 H/106 Si as OH defects have Dlat vales at room temperature that are 22% and 41% lower than equivalent orientations for a dry sample. The effect of defects on Dlat is amplified when the OH-dipole is parallel to the electromagnetic vector of the diffusing heat. Oriented milky quartz samples with 1260 to 2100 H/6 Si have Dlat 12-15% lower than dry quartz values, suggesting that fluid inclusions slow thermal diffusion to a smaller degree. Room temperature Dlat of 5 different quartzite samples vary up to 24% from the highest quartzite value of 4.04 mm2/s. For all samples, Dlat is lower than that expected for randomly oriented, dry quartz. In quartzites, differences in Dlat between samples decrease with temperature, such that little variation is seen for the β phase. This behavior is expected if porosity, which ranges from 5% to 19%, hinders thermal transport in quartzite. Grain size does not appear to affect Dlat. If water plays an important role in heat transport, we should see it, since quartzite contains much more water than the single crystals. Because of the small number of samples examined, the dual speciation as silanol complexes on grain surfaces of some quartzites (up to 420 H/6 Si) and as molecular water in all samples (ranging from 328 to 5103 H/6 Si

  6. Electronic Band Structure, Optical, Thermal and Bonding Properties of XMg2O4(X = Si, Ge) Spinel Compounds

    NASA Astrophysics Data System (ADS)

    Semari, F.; Ouahrani, T.; Khachai, H.; Khenata, R.; Rabah, M.; Bouhemadou, A.; Murtaza, G.; Amin, B.; Rached, D.

    2013-07-01

    Bonding nature as well as structural, optoelectronic and thermal properties of the cubic XMg2O4(X = Si, Ge) spinel compounds have been calculated using a full-potential augmented plane-wave plus local orbitals (FP-APW+lo) method within the density functional theory. The exchange-correlation potential was treated with the PBE-GGA approximation to calculate the total energy. Moreover, the modified Becke-Johnson potential (TB-mBJ) was also applied to improve the electronic band structure calculations. The computed ground-state parameters (a, B, B‧ and u) are in excellent agreements with the available theoretical data. Calculations of the electronic band structure and bonding properties show that these compounds have a direct energy band gap (Γ-Γ) with a dominated ionic character and the TB-mBJ approximation yields larger fundamental band gaps compared to those obtained using the PBE-GGA. Optical properties such as the complex dielectric function ɛ(ω), reflectivity R(ω) and energy loss function L(ω), for incident photon energy up to 40 eV, have been predicted. Through the quasi-harmonic Debye model, in which the phononic effects are considered, the effects of pressure P and temperature T on the thermal expansion coefficient, Debye temperature and heat capacity for the considered compounds are investigated for the first time.

  7. Thermal noise and optomechanical features in the emission of a membrane-coupled compound cavity laser diode

    PubMed Central

    Baldacci, Lorenzo; Pitanti, Alessandro; Masini, Luca; Arcangeli, Andrea; Colangelo, Francesco; Navarro-Urrios, Daniel; Tredicucci, Alessandro

    2016-01-01

    We demonstrate the use of a compound optical cavity as linear displacement detector, by measuring the thermal motion of a silicon nitride suspended membrane acting as the external mirror of a near-infrared Littrow laser diode. Fluctuations in the laser optical power induced by the membrane vibrations are collected by a photodiode integrated within the laser, and then measured with a spectrum analyzer. The dynamics of the membrane driven by a piezoelectric actuator is investigated as a function of air pressure and actuator displacement in a homodyne configuration. The high Q-factor (~3.4 · 104 at 8.3 · 10−3 mbar) of the fundamental mechanical mode at ~73 kHz guarantees a detection sensitivity high enough for direct measurement of thermal motion at room temperature (~87 pm RMS). The compound cavity system here introduced can be employed as a table-top, cost-effective linear displacement detector for cavity optomechanics. Furthermore, thanks to the strong optical nonlinearities of the laser compound cavity, these systems open new perspectives in the study of non-Markovian quantum properties at the mesoscale. PMID:27538586

  8. Thermal noise and optomechanical features in the emission of a membrane-coupled compound cavity laser diode.

    PubMed

    Baldacci, Lorenzo; Pitanti, Alessandro; Masini, Luca; Arcangeli, Andrea; Colangelo, Francesco; Navarro-Urrios, Daniel; Tredicucci, Alessandro

    2016-01-01

    We demonstrate the use of a compound optical cavity as linear displacement detector, by measuring the thermal motion of a silicon nitride suspended membrane acting as the external mirror of a near-infrared Littrow laser diode. Fluctuations in the laser optical power induced by the membrane vibrations are collected by a photodiode integrated within the laser, and then measured with a spectrum analyzer. The dynamics of the membrane driven by a piezoelectric actuator is investigated as a function of air pressure and actuator displacement in a homodyne configuration. The high Q-factor (~3.4 · 10(4) at 8.3 · 10(-3) mbar) of the fundamental mechanical mode at ~73 kHz guarantees a detection sensitivity high enough for direct measurement of thermal motion at room temperature (~87 pm RMS). The compound cavity system here introduced can be employed as a table-top, cost-effective linear displacement detector for cavity optomechanics. Furthermore, thanks to the strong optical nonlinearities of the laser compound cavity, these systems open new perspectives in the study of non-Markovian quantum properties at the mesoscale. PMID:27538586

  9. A micro gas chromatography column with a micro thermal conductivity detector for volatile organic compound analysis.

    PubMed

    Sun, J H; Cui, D F; Chen, X; Zhang, L L; Cai, H Y; Li, H

    2013-02-01

    In this paper, a micro gas chromatography (μGC) system contained a μGC column and a micro thermal conductivity detector (μTCD) was proposed. In order to reduce the volume of the system, some micro heaters were integrated on the surface and backside of the GC column, which could provide a robust temperature programming capability and rapidly increase the temperature of the μGC column. In addition, a silicon-glass μTCD with four-thermistor thermal conductivity cells that can offer significant advantages over previously reported designs including low dead volume, good thermal isolation, and elimination of the thermal noise was proposed in this paper. Experimental results have indicated that the μGC system with a detection limit of several ppm concentration levels separated and detected the benzene, toluene, and styrene in less than 3 min, and the μGC system also exhibited a good linear response in the test range. PMID:23464240

  10. A micro gas chromatography column with a micro thermal conductivity detector for volatile organic compound analysis

    NASA Astrophysics Data System (ADS)

    Sun, J. H.; Cui, D. F.; Chen, X.; Zhang, L. L.; Cai, H. Y.; Li, H.

    2013-02-01

    In this paper, a micro gas chromatography (μGC) system contained a μGC column and a micro thermal conductivity detector (μTCD) was proposed. In order to reduce the volume of the system, some micro heaters were integrated on the surface and backside of the GC column, which could provide a robust temperature programming capability and rapidly increase the temperature of the μGC column. In addition, a silicon-glass μTCD with four-thermistor thermal conductivity cells that can offer significant advantages over previously reported designs including low dead volume, good thermal isolation, and elimination of the thermal noise was proposed in this paper. Experimental results have indicated that the μGC system with a detection limit of several ppm concentration levels separated and detected the benzene, toluene, and styrene in less than 3 min, and the μGC system also exhibited a good linear response in the test range.

  11. X-rays structural analysis and thermal stability studies of the ternary compound {alpha}-AlFeSi

    SciTech Connect

    Roger, J.; Bosselet, F.; Viala, J.C.

    2011-05-15

    From literature data presently available, the decomposition temperature and the nature of the decomposition reaction of the ternary compound {alpha}-AlFeSi (also designated as {alpha}{sub H} or {tau}{sub 5}) are not clearly identified. Moreover, some uncertainties remain concerning its crystal structure. The crystallographic structure and thermochemical behaviour of the ternary compound {alpha}-AlFeSi were meticulously studied. The crystal structure of {alpha}-AlFeSi was examined at room temperature from X-ray single crystal intensity data. It presents hexagonal symmetry, space group P6{sub 3}/mmc with unit cell parameters (293 K) a=12.345(2) A and c=26.210(3) A (V=3459 A{sup 3}). The average chemical formula obtained from refinement is Al{sub 7.1}Fe{sub 2}Si. From isothermal reaction-diffusion experiments and Differential Thermal Analysis, the title compound decomposes peritectically upon heating into {theta}-Fe{sub 4}Al{sub 13}(Si), {gamma}-Al{sub 3}FeSi and a ternary Al-rich liquid. Under atmospheric pressure, the temperature of this reversible transformation has been determined to be 772{+-}12 {sup o}C. -- Graphical abstract: Partial representation of the crystal structure of the {alpha}-Al{sub 7.1}Fe{sub 2}Si compound. Display Omitted Highlights: The main findings of our work are: {yields} a detailed X-rays crystal structure determination of the ternary compound {alpha}-AlFeSi. {yields} The precision of the silicon atoms positions in the crystal structure. {yields} A precised determination of the decomposition temperature of this compound.

  12. Generation of Maillard compounds from inulin during the thermal processing of Agave tequilana Weber Var. azul.

    PubMed

    Mancilla-Margalli, Norma A; López, Mercedes G

    2002-02-13

    During the cooking process of Agave tequilana Weber var. azul to produce tequila, besides the hydrolysis of inulin to generate fermentable sugars, many volatiles, mainly Maillard compounds, are produced, most of which may have a significant impact on the overall flavor of tequila. Exudates (agave juice) from a tequila company were collected periodically, and color, Brix, fructose concentration, and reducing sugars were determined as inulin breakdown took place. Maillard compounds were obtained by extraction with CH(2)Cl(2), and the extracts were analyzed by GC-MS. Increments in color, Brix, and reducing sugars were observed as a function of time, but a decrease in fructose concentration was found. Many Maillard compounds were identified in the exudates, including furans, pyrans, aldehydes, and nitrogen and sulfur compounds. The most abundant Maillard compounds were methyl-2-furoate, 2,3-dihydroxy-3,5-dihydro-6-methyl-4(H)-pyran-4-one, and 5-(hydroxymethyl)furfural. In addition, a series of short- and long-chain fatty acids was also found. A large number of the volatiles in A. tequilana Weber var. azul were also detected in tequila extracts, and most of these have been reported as a powerful odorants, responsible for the unique tequila flavor. PMID:11829648

  13. Surfactant-thermal method to prepare two novel two-dimensional Mn–Sb–S compounds for photocatalytic applications

    SciTech Connect

    Nie, Lina; Xiong, Wei-Wei; Li, Peizhou; Han, Jianyu; Zhang, Guodong; Yin, Shengming; Zhao, Yanli; Xu, Rong; Zhang, Qichun

    2014-12-15

    Two novel two-dimensional crystalline chalcogenidoantimonates, [MnSb{sub 2}S{sub 4}(N{sub 2}H{sub 4}){sub 2}] (1) and [Mn(tepa)Sb{sub 6}S{sub 10}] (2) (tepa=tetraethylenepentamine), have been successfully synthesized under surfactant-thermal conditions through using PEG-400 and sodium dodecyl sulfate as reaction media, respectively. In compound 1, [MnS{sub 2}N{sub 4}]{sub n}{sup 2n−} species connect [SbS{sub 2}]{sub n}{sup n−} chains via vertex-sharing S atoms to form neutral layered frameworks, while in compound 2, 8-membered windows [Sb{sub 4}S{sub 8}]{sub n}{sup 4n−}, 24-membered windows [Sb{sub 12}S{sub 24}]{sub n}{sup 12n−} and Mn atoms are connected together to form neutral 2D-[MnSb{sub 6}S{sub 10}] layers. All Sb atoms in both complexes form [Sb{sup ⍰}S{sub 3}]{sup 3−} trigonal-pyramid by coordinating with three S atoms. The steep UV–vis absorption edges indicate that 1 and 2 have the band gaps of 1.96 eV and 2.12 eV, respectively. Both compound 1 and 2 show active visible-light-driven photocatalytic properties for hydrogen production. - Graphiacl abstract: Two novel 2D framework sulfides, [MnSb{sub 2}S{sub 4}(N{sub 2}H{sub 4}){sub 2}] (1) and [Mn(tepa)Sb{sub 6}S{sub 10}] (2) (tepa=tetraethylenepentamine), have been successfully synthesized under surfactant-thermal conditions and show active visible-light-driven photocatalytic properties for hydrogen production. - Highlights: • Two novel two-dimensional Mn–Sb–sulfide frameworks. • Synthesis through surfactant-thermal condition. • Photocatalytic properties for hydrogen generation.

  14. Lattice QCD

    SciTech Connect

    Bornyakov, V.G.

    2005-06-01

    Possibilities that are provided by a lattice regularization of QCD for studying nonperturbative properties of QCD are discussed. A review of some recent results obtained from computer calculations in lattice QCD is given. In particular, the results for the QCD vacuum structure, the hadron mass spectrum, and the strong coupling constant are considered.

  15. Electrical and thermal transport properties of Nb- and Ru-substituted Mo3Al2C superconducting compounds

    NASA Astrophysics Data System (ADS)

    Ramachandran, B.; Jhiang, J. Y.; Kuo, Y. K.; Kuo, C. N.; Lue, C. S.

    2016-03-01

    Partial substitution effects of Nb and Ru on the superconducting and normal-state properties of Mo3Al2C-based compounds, namely Mo3-x Nb x Al2C (x = 0.00-0.25) and Mo3-x Ru x Al2C (x = 0.00-0.15), were investigated by means of electrical, magnetic, and thermoelectric studies. From the resistivity and magnetization data, we noted that the superconducting transition temperature of Mo3Al2C decreases gradually with increasing the dopant content of Nb and Ru, and the superconducting volume fraction also decreases significantly upon the substitution. The electrons dominate the thermoelectric transport in the studied compounds. Moreover, a change of curvature near 50 K in the transport properties of the parent Mo3Al2C compound was observed, prior to the superconducting transition. This is most likely due to the strong electron-phonon interaction which could have originated from the distortions near the Al sites. Finally, it was found that electronic carriers contribute considerably to heat conduction of the Mo3Al2C-based compounds near room temperature, whereas the phonons dominate the low-temperature thermal transport.

  16. Fracture Behaviors of Sn-Cu Intermetallic Compound Layer in Ball Grid Array Induced by Thermal Shock

    NASA Astrophysics Data System (ADS)

    Shen, Jun; Zhai, Dajun; Cao, Zhongming; Zhao, Mali; Pu, Yayun

    2014-02-01

    In this work, thermal shock reliability testing and finite-element analysis (FEA) of solder joints between ball grid array components and printed circuit boards with Cu pads were used to investigate the failure mechanism of solder interconnections. The morphologies, composition, and thickness of Sn-Cu intermetallic compounds (IMC) at the interface of Sn-3.0Ag-0.5Cu lead-free solder alloy and Cu substrates were investigated by scanning electron microscopy and transmission electron microscopy. Based on the experimental observations and FEA results, it can be recognized that the origin and propagation of cracks are caused primarily by the difference between the coefficient of thermal expansion of different parts of the packaged products, the growth behaviors and roughness of the IMC layer, and the grain size of the solder balls.

  17. Thermal engine driven heat pump for recovery of volatile organic compounds

    DOEpatents

    Drake, Richard L.

    1991-01-01

    The present invention relates to a method and apparatus for separating volatile organic compounds from a stream of process gas. An internal combustion engine drives a plurality of refrigeration systems, an electrical generator and an air compressor. The exhaust of the internal combustion engine drives an inert gas subsystem and a heater for the gas. A water jacket captures waste heat from the internal combustion engine and drives a second heater for the gas and possibly an additional refrigeration system for the supply of chilled water. The refrigeration systems mechanically driven by the internal combustion engine effect the precipitation of volatile organic compounds from the stream of gas.

  18. Effect of PEF, HHP and Thermal Treatment on PME Inactivation and Volatile Compounds Concentration of an Orange Juice-Milk Based Beverage

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The effects of thermal, pulsed electric field (PEF) and high hydrostatic pressure (HHP) processing on pectin methyl esterase (PME) activity and concentrations of volatile compounds in an orange juice-milk beverage were studied. Thermal treatment (85 C for 1 min), PEF treatment (25 kV/cm at 65 C init...

  19. First Principles Investigation of the Elastic, Optoelectronic and Thermal Properties of XRuSb: (X = V, Nb, Ta) Semi-Heusler Compounds Using the mBJ Exchange Potential

    NASA Astrophysics Data System (ADS)

    Bencherif, K.; Yakoubi, A.; Della, N.; Miloud Abid, O.; Khachai, H.; Ahmed, R.; Khenata, R.; Bin Omran, S.; Gupta, S. K.; Murtaza, G.

    2016-07-01

    Semi-Heusler materials are intensively investigated due to their potential use in diverse applications, such as in spintronics and green energy applications. In this work, we employ the density functional theory to calculate the structural, electronic, elastic, thermal and optical properties of the VRuSb, NbRuSb and TaRuSb semi-Heusler compounds. The calculated results for the lattice constants, bulk moduli and their corresponding pressure derivative values are in fairly good agreement with previous works. In addition, besides the local density approximation, the modified Becke-Johnson exchange potential is also used to improve the value of the band gaps. The bonding nature reveals a mixture of covalent and ionic bonding character of the VRuSb, NbRuSb and TaRuSb compounds. Furthermore, the elastic constants ( C ij) and the related elastic moduli confirm their stability in the cubic phase and demonstrate their ductile nature. We also analyze the influence of the pressure and temperature on the primitive cell volume, heat capacity, volume expansion coefficient, and Debye temperature of the semi-Heusler compounds. Additionally, we investigate the optical properties, such as the complex dielectric function, refractive index, reflectivity, and the energy loss function.

  20. First Principles Investigation of the Elastic, Optoelectronic and Thermal Properties of XRuSb: (X = V, Nb, Ta) Semi-Heusler Compounds Using the mBJ Exchange Potential

    NASA Astrophysics Data System (ADS)

    Bencherif, K.; Yakoubi, A.; Della, N.; Miloud Abid, O.; Khachai, H.; Ahmed, R.; Khenata, R.; Bin Omran, S.; Gupta, S. K.; Murtaza, G.

    2016-04-01

    Semi-Heusler materials are intensively investigated due to their potential use in diverse applications, such as in spintronics and green energy applications. In this work, we employ the density functional theory to calculate the structural, electronic, elastic, thermal and optical properties of the VRuSb, NbRuSb and TaRuSb semi-Heusler compounds. The calculated results for the lattice constants, bulk moduli and their corresponding pressure derivative values are in fairly good agreement with previous works. In addition, besides the local density approximation, the modified Becke-Johnson exchange potential is also used to improve the value of the band gaps. The bonding nature reveals a mixture of covalent and ionic bonding character of the VRuSb, NbRuSb and TaRuSb compounds. Furthermore, the elastic constants (C ij) and the related elastic moduli confirm their stability in the cubic phase and demonstrate their ductile nature. We also analyze the influence of the pressure and temperature on the primitive cell volume, heat capacity, volume expansion coefficient, and Debye temperature of the semi-Heusler compounds. Additionally, we investigate the optical properties, such as the complex dielectric function, refractive index, reflectivity, and the energy loss function.

  1. Thermal treatment and leaching of biochar alleviates plant growth inhibition from mobile organic compounds

    PubMed Central

    Sackett, Tara E.; Thomas, Sean C.

    2016-01-01

    Recent meta-analyses of plant responses to biochar boast positive average effects of between 10 and 40%. Plant responses, however, vary greatly across systems, and null or negative biochar effects are increasingly reported. The mechanisms responsible for such responses remain unclear. In a glasshouse experiment we tested the effects of three forestry residue wood biochars, applied at five dosages (0, 5, 10, 20, and 50 t/ha) to a temperate forest drystic cambisol as direct surface applications and as complete soil mixes on the herbaceous pioneers Lolium multiflorum and Trifolium repens. Null and negative effects of biochar on growth were found in most cases. One potential cause for null and negative plant responses to biochar is plant exposure to mobile compounds produced during pyrolysis that leach or evolve following additions of biochars to soil. In a second glasshouse experiment we examined the effects of simple leaching and heating techniques to ameliorate potentially phytotoxic effects of volatile and leachable compounds released from biochar. We used Solid Phase Microextraction (SPME)–gas chromatography–mass spectrometry (GC-MS) to qualitatively describe organic compounds in both biochar (through headspace extraction), and in the water leachates (through direct injection). Convection heating and water leaching of biochar prior to application alleviated growth inhibition. Additionally, growth was inhibited when filtrate from water-leached biochar was applied following germination. SPME-GC-MS detected primarily short-chained carboxylic acids and phenolics in both the leachates and solid chars, with relatively high concentrations of several known phytotoxic compounds including acetic acid, butyric acid, 2,4-di-tert-butylphenol and benzoic acid. We speculate that variable plant responses to phytotoxic organic compounds leached from biochars may largely explain negative plant growth responses and also account for strongly species-specific patterns of plant

  2. Abiotic formation of hydrocarbons and oxygenated compounds during thermal decomposition of iron oxalate

    NASA Technical Reports Server (NTRS)

    McCollom, T. M.; Simoneit, B. R.

    1999-01-01

    The formation of organic compounds during the decomposition of iron oxalate dihydrate (IOD) was investigated as a possible analog for abiotic organic synthesis in geological systems. After heating at 330 degrees C for 2-4 days, IOD decomposed to a mixture of the minerals siderite and magnetite plus gas and non-volatile organic compounds. The organic products included an extremely large variety of compounds, making identification of individual reaction products difficult. However, the non-volatile products were dominated by several homologous series of alkylated cyclic compounds mostly containing a single aromatic ring, including alkylphenols, alkylbenzenes, alkyltetrahydronaphthols, and alkyltetrahydronaphthalenes. Traces of n-alkanols, n-alkanoic acids, n-alkanones, and n-alkanes were also identified. Carbon in the gas phase was predominantly CO2 (+CO?), with lesser amounts of light hydrocarbons to > C6 including all possible branched and normal isomers of the alkanes and alkenes. The organic products were apparently the result of two concurrent reaction processes: (1) condensation of the two-carbon units present in the initial oxalate moiety, and (2) Fischer-Tropsch-type synthesis from CO2 or CO generated during the experiment. Compounds produced by the former process may not be characteristic of synthesis from the single-carbon precursors which predominate in geologic systems, suggesting iron oxalate decomposition may not provide a particularly suitable analog for investigation of abiotic organic synthesis. When water was included in the reaction vessels, CO2 and traces of methane and light hydrocarbon gases were the only carbon products observed (other than siderite), suggesting that the presence of water allowed the system to proceed rapidly towards equilibrium and precluded the formation of metastable organic intermediates.

  3. Anomalous thermal expansion in orthorhombic perovskite SrIrO3: Interplay between spin-orbit coupling and the crystal lattice

    NASA Astrophysics Data System (ADS)

    Blanchard, Peter E. R.; Reynolds, Emily; Kennedy, Brendan J.; Kimpton, Justin A.; Avdeev, Maxim; Belik, Alexei A.

    2014-06-01

    The structure of the orthorhombic (Pbnm) polytype of SrIrO3 has been investigated between 3 and 1100 K using a combination of synchrotron and neutron diffraction methods. The orthorhombic structure persists to 1100 K, the highest temperature available in this work. This is a consequence of the larger than expected octahedral tilting estimated from the neutron diffraction studies. We postulate that the strong spin-orbit coupling of the Ir4+ cation, which splits the t2g band, introduces additional strain on the lattice. This introduces unusual thermal expansion of the cell. SrIrO3 was characterized by resistivity, magnetization, and specific heat measurements. Metallic conductivity was observed between 2 and 300 K without indication of the previously reported metal-insulator transition. The Sommerfeld constant γ was 3.12(2) mJ mol-1 K-2, and a Fermi-liquid behavior was observed between 2 and 30 K with positive magnetoresistence of up to 2% (at 70 kOe and between 2 and 50 K).

  4. [Determination of volatile organic compounds in ambient air by thermal desorption-gas chromatography-triple quadrupole tandem mass spectrometry].

    PubMed

    Feng, Lili; Hu, Xiaofang; Yu, Xiaojuan; Zhang, Wenying

    2016-02-01

    A method was established for the simultaneous determination of 23 volatile organic compounds (VOCs) in ambient air with combination of thermal desorption (TD) and gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS). The air samples were collected by active sampling method using Tenax-TA sorbent tubes, and desorbed by thermal desorption. The analytes were determined by GC-MS/MS in selected reaction monitoring (SRM) mode, and internal standard method was applied to quantify the VOCs. The results of all the 23 VOCs showed good linearities in low level (0. 01-1 ng) and high level (1-100 ng) with all the correlation coefficients (r2) more than 0. 99. The method quantification limits were between 0. 000 08-1 µg/m3. The method was validated by means of recovery experiments (n = 6) at three spiked levels of 2, 10 and 50 ng. The recoveries between 77% and 124% were generally obtained. The relative standard deviations (RSDs) in all cases were lower than 20%, except for chlorobenzene at the low spiked level. The developed method was applied to determine VOCs in ambient air collected at three sites in Shanghai. Several compounds, like benzene, toluene, ethylbenzene, m-xylenes, p-xylenes, styrene, 1, 2, 4-trimethylbenzene and hexachlorobutadiene were detected and confirmed in all the samples analyzed. The method is highly accurate, reliable and sensitive for monitoring the VOCs in ambient air. PMID:27382728

  5. General Route for Preparing β-Nitrocarbonyl Compounds Using Copper Thermal Redox Catalysis

    PubMed Central

    2015-01-01

    Using a simple copper catalyst, the alkylation of nitroalkanes with α-bromocarbonyls is now possible. This method provides a general, functional group tolerant route to β-nitrocarbonyl compounds, including nitro amides, esters, ketones, and aldehydes. The highly sterically dense, functional group rich products from these reactions can be readily elaborated into a range of complex nitrogen-containing molecules, including highly substituted β-amino acids. PMID:24870052

  6. Fabrication of Porous Copper with Directional Pores through Thermal Decomposition of Compounds

    NASA Astrophysics Data System (ADS)

    Nakajima, Hideo; Ide, Takuya

    2008-02-01

    Lotus-type porous copper with aligned long cylindrical pores was fabricated by unidirectional solidification in an argon atmosphere. The hydrogen dissolved in molten copper through thermal decomposition of titanium hydride contained in the mold, which then formed hydrogen gas that evolved into the gas pores in the solidified copper. On the other hand, titanium may form oxides in the melt that serve as nucleation sites for insoluble hydrogen. The porosity and pore size decreased with increasing atmospheric argon pressure during the solidification, which can be explained by the Boyle-Charles law and the possible suppression of the decomposition due to external pressure. The addition of titanium hydride was more effective when it was added just before the melt solidified than when it was added to the melt. Moreover, the thermal decomposition method (TDM) is superior to the conventional fabrication method, which requires high pressure hydrogen gas. Thus, TDM is a promising fabrication technique for various lotus metals.

  7. Phosphorescence versus thermally activated delayed fluorescence. Controlling singlet-triplet splitting in brightly emitting and sublimable Cu(I) compounds.

    PubMed

    Leitl, Markus J; Krylova, Valentina A; Djurovich, Peter I; Thompson, Mark E; Yersin, Hartmut

    2014-11-12

    Photophysical properties of two highly emissive three-coordinate Cu(I) complexes, (IPr)Cu(py2-BMe2) (1) and (Bzl-3,5Me)Cu(py2-BMe2) (2), with two different N-heterocyclic (NHC) ligands were investigated in detail (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; Bzl-3,5Me = 1,3-bis(3,5-dimethylphenyl)-1H-benzo[d]imidazol-2-ylidene; py2-BMe2 = di(2-pyridyl)dimethylborate). The compounds exhibit remarkably high emission quantum yields of more than 70% in the powder phase. Despite similar chemical structures of both complexes, only compound 1 exhibits thermally activated delayed blue fluorescence (TADF), whereas compound 2 shows a pure, yellow phosphorescence. This behavior is related to the torsion angles between the two ligands. Changing this angle has a huge impact on the energy splitting between the first excited singlet state S1 and triplet state T1 and therefore on the TADF properties. In addition, it was found that, in both compounds, spin-orbit coupling (SOC) is particularly effective compared to other Cu(I) complexes. This is reflected in short emission decay times of the triplet states of only 34 μs (1) and 21 μs (2), respectively, as well as in the zero-field splittings of the triplet states amounting to 4 cm(-1) (0.5 meV) for 1 and 5 cm(-1) (0.6 meV) for 2. Accordingly, at ambient temperature, compound 1 exhibits two radiative decay paths which are thermally equilibrated: one via the S1 state as TADF path (62%) and one via the T1 state as phosphorescence path (38%). Thus, if this material is applied in an organic light-emitting diode, the generated excitons are harvested mainly in the singlet state, but to a significant portion also in the triplet state. This novel mechanism based on two separate radiative decay paths reduces the overall emission decay time distinctly. PMID:25260042

  8. Surfactant-thermal method to prepare two novel two-dimensional Mn-Sb-S compounds for photocatalytic applications

    NASA Astrophysics Data System (ADS)

    Nie, Lina; Xiong, Wei-Wei; Li, Peizhou; Han, Jianyu; Zhang, Guodong; Yin, Shengming; Zhao, Yanli; Xu, Rong; Zhang, Qichun

    2014-12-01

    Two novel two-dimensional crystalline chalcogenidoantimonates, [MnSb2S4(N2H4)2] (1) and [Mn(tepa)Sb6S10] (2) (tepa=tetraethylenepentamine), have been successfully synthesized under surfactant-thermal conditions through using PEG-400 and sodium dodecyl sulfate as reaction media, respectively. In compound 1, [MnS2N4]n2n- species connect [SbS2]nn- chains via vertex-sharing S atoms to form neutral layered frameworks, while in compound 2, 8-membered windows [Sb4S8]n4n-, 24-membered windows [Sb12S24]n12n- and Mn atoms are connected together to form neutral 2D-[MnSb6S10] layers. All Sb atoms in both complexes form [SbшS3]3- trigonal-pyramid by coordinating with three S atoms. The steep UV-vis absorption edges indicate that 1 and 2 have the band gaps of 1.96 eV and 2.12 eV, respectively. Both compound 1 and 2 show active visible-light-driven photocatalytic properties for hydrogen production.

  9. Rapid characterization of chemical compounds in liquid and solid states using thermal desorption electrospray ionization mass spectrometry.

    PubMed

    Huang, Min-Zong; Zhou, Chi-Chang; Liu, De-Lin; Jhang, Siou-Sian; Cheng, Sy-Chyi; Shiea, Jentaie

    2013-10-01

    Rapid characterization of thermally stable chemical compounds in solid or liquid states is achieved through thermal desorption electrospray ionization mass spectrometry (TD-ESI/MS). A feature of this technique is that sampling, desorption, ionization, and mass spectrometric detection are four separate events with respect to time and location. A metal probe was used to sample analytes in their solid or liquid states. The probe was then inserted in a preheated oven to thermally desorb the analytes on the probe. The desorbed analytes were carried by a nitrogen gas stream into an ESI plume, where analyte ions were formed via interactions with charged solvent species generated in the ESI plume. The analyte ions were subsequently detected by a mass analyzer attached to the TD-ESI source. Quantification of acetaminophen in aqueous solutions using TD-ESI/MS was also performed in which a linear response for acetaminophen was obtained between 25 and 500 ppb (R(2) = 0.9978). The standard deviation for a reproducibility test for ten liquid samples was 9.6%. Since sample preparation for TD-ESI/MS is unnecessary, a typical analysis can be completed in less than 10 s. Analytes such as the active ingredients in over-the-counter drugs were rapidly characterized regardless of the different physical properties of said drugs, which included liquid eye drops, viscous cold syrup solution, ointment cream, and a drug tablet. This approach was also used to detect trace chemical compounds in illicit drugs and explosives, in which samples were obtained from the surfaces of a cell phone, piece of luggage made from hard plastic, business card, and wooden desk. PMID:24050317

  10. Wet thermal oxidation of Al(x)Ga(1-x)As compounds

    NASA Astrophysics Data System (ADS)

    Burton, R. S.; Schlesinger, T. E.

    1994-11-01

    Results are presented on the wet thermal oxidation of Al(x)Ga(1-x)As. The growth of wet thermal oxides of Al(x)Ga(1-x)As is shown to be linear with time. An O2 carrier gas was found to form a self-terminating oxide for compositions investigated (x greater than 0.4), but required elevated temperature for substantial growth. The use of a medium oxygen concentration (about 20%) in a N2 carrier formed nonuniform oxides for all compositions investigated. A low O2 concentration (0.1%) in the N2 carrier was found to reduce the activation energy of the oxidation process for Al(0.6)Ga(0.4)As from 1.9 to 1.0 eV while increasing the activation energy of Al(0.8)Ga(0.2)As from 1.6 to 1.75 eV. For these wet thermal oxides it is observed that lateral oxidation at heterojunction interfaces is enhanced. This enhanced lateral oxidation can be attributed to local stress due to the smaller volume of the growing oxide compared to the volume of the consumed semiconductor.

  11. Lattice Cubes

    ERIC Educational Resources Information Center

    Parris, Richard

    2011-01-01

    Given a segment that joins two lattice points in R[superscript 3], when is it possible to form a lattice cube that uses this segment as one of its twelve edges? A necessary and sufficient condition is that the length of the segment be an integer. This paper presents an algorithm for finding such a cube when the prime factors of the length are…

  12. Role of volatile compounds on the thermal evolution of Pluto and Charon

    NASA Astrophysics Data System (ADS)

    Mitri, G.; Tobie, G.; Bellino, G.; Yao, C.; Deschamps, F.; Cadek, O.; Mège, D.

    2015-12-01

    The first images taken by New Horizons suggest that the dwarf planet Pluto and its moon Charon are much more active than previously anticipated, with possible recent resurfacing events. This is unexpected for bodies the sizes of Pluto and Charon several billions after their formation. Radiogenic heating is expected to be rather low at present, and tidal heating due to the interaction between the two companions may have played a role but only during the early stage of the evolution before the system reached dual synchronization (Robuchon and Nimmo, Icarus 2011; Barr and Collins, Icarus 2015). Recent resurfacings may suggests a slow cooling of the interior associated with recent activation of dynamical processes in the interior, possibly helped by the presence of anti-freezing compounds, such as ammonia and methanol, and low-conductivity gas clathrates. In order to determine in which conditions Pluto and Charon may be active several billions after their formation, we investigate the role of anti-freezing compounds (ammonia and methanol) and gas compounds on the formation and evolution of an internal ocean. Using a parameterized model initially developed for Titan (Tobie et al. Icarus, 2005), we model the thermo-chemical evolution of Pluto's and Charon's interior, including the formation of an internal ocean and its subsequent crystallization, the formation/dissociation of gas clathrates and their feedback on the internal cooling rate, by assuming various initial compositions. A particular attention will be paid on the conditions under which convective instabilities may initiate in the outer ice shell, on the coupling between ocean crystallization and surface deformation, and on their consequences for the geological activity of Pluto and Charon.

  13. Synthesis, characterization, thermal properties and antiproliferative potential of copper(ii) 4'-phenyl-terpyridine compounds.

    PubMed

    Ma, Zhen; Zhang, Bian; Guedes da Silva, M Fátima C; Silva, Joana; Mendo, Ana Soraia; Baptista, Pedro Viana; Fernandes, Alexandra R; Pombeiro, Armando J L

    2016-03-15

    Reactions between 4'-phenyl-terpyridine (L) and several Cu(ii) salts (p-toluenesulfonate, benzoate and o-, m- or p-hydroxybenzoate) led to the formation of [Cu(p-SO3C6H4CH3)L(H2O)2](p-SO3C6H4CH3) (), [Cu(OCOPh)2L] (), [Cu(o-OCOC6H4OH)2L] (), [Cu(m-OCOC6H4OH)2L]·MeOH (·MeOH) and [Cu(p-OCOC6H4OH)2L]·2H2O (·2H2O), which were characterized by elemental and TG-DTA analyses, ESI-MS, IR spectroscopy and single crystal X-ray diffraction, as well as by conductivimetry. In all structures the Cu atoms present N3O3 octahedral coordination geometries, which, in , are highly distorted as a result of the chelating-bidentate mode of one of the carboxylate ligands. Intermolecular ππ stacking interactions could also be found in (in the 3.569-3.651 Å range and involving solely the pyridyl rings). Medium-strong hydrogen bond interactions lead to infinite 1D chains (in and ) and to an infinite 2D network (in ). Compounds and show high in vitro cytotoxicity towards HCT116 colorectal carcinoma and HepG2 hepatocellular carcinoma cell lines. The antiproliferative potential of compound is due to an increase of the apoptotic process that was confirmed by Hoechst staining, flow cytometry and RT-qPCR. All compounds able to non-covalently intercalate the DNA helix and induce in vitro pDNA double-strand breaks in the absence of H2O2. Concerning compound , the hydroxyl radical and singlet oxygen do not appear to be involved in the pDNA cleavage process and the fact that this cleavage also occurs in the absence of molecular oxygen points to a hydrolytic mechanism of cleavage. PMID:26905013

  14. Effect of solvents on thermal cracking of model compounds typical of coal

    SciTech Connect

    Chiba, K.; Tagaya, H.; Yamauchi, T.; Sato, S. )

    1992-06-01

    Conversions of bibenzyl and dibenzyl ether as coal models depend on the nature of the solvent. When solvents that were poor hydrogen donors, but their dehydrogenated radicals were more stable than donors, were used, bibenzyl and dibenzyl ether conversion were markedly enhanced. Positive effects wee observed by the mixing of tetralin with nondonor solvents. However, negative effects by such mixing were observed in the case of dibenzyl ether. In this paper, the importance of radical-induced decomposition on cracking of coal model compounds is suggested.

  15. Low-Temperature Magnetic and Thermal Properties of Some Low-Dimensional Compounds

    NASA Astrophysics Data System (ADS)

    Lukin, Jonathan Allen

    Heat capacity and A.C. susceptibility measurements of powdered alpha-rm MnC_2O_4cdot2H_2O have led to its description as a Heisenberg chain antiferromagnet with exchange J/k = -1.17(2) K. Anomalies in C_{p} signal the onset of long-range order at T_{N} = 2.4 K and an order-order transition at T_2 = 1.5 K. For T_2lattice were deduced. The powder susceptibility and heat capacity of alpha- rm CoC_2O_4cdot2H_2O delineate a 2D Ising antiferromagnet with J/k = -30+/- 2 K, | J^'/J |~ 3times 10^{-3}, and an ordering temperature T_{N }=6.23(2) K. The measured susceptibility above 20 K of alpha-rm NiC _2O_4cdot2H_2O agrees with that of a spin-1 Heisenberg chain with J/k = -19.5+/- 1 K; a peak in C_{p } indicates magnetic ordering at T _{N} = 6.33(2) K. X-ray diffraction, heat capacity, and magnetic susceptibility measurements of rm ErBa_2Cu _3O_{x} with 6.12 <= x<=6.91 revealed several effects correlated with the oxygen concentration x. The fully -oxygenated orthorhombic material, with a superconducting transition temperature T_{c} = 92 K, exhibits a 2D Ising-like peak corresponding to magnetic ordering of the Er^{3+} moments at T_{m} = 0.604 K. Removal of oxygen reduces the lattice orthorhombicity and depresses both T_{c} and T_{m}, until in the 2 = 6.12, 6.23 tetragonal phases superconductivity and long-range magnetic order are quenched. These

  16. Characterization of thermal desorption with the Deans-switch technique in gas chromatographic analysis of volatile organic compounds.

    PubMed

    Ou-Yang, Chang-Feng; Huang, Ying-Xue; Huang, Ting-Jyun; Chen, Yong-Shen; Wang, Chieh-Heng; Wang, Jia-Lin

    2016-09-01

    This study presents a novel application based on the Deans-switch cutting technique to characterize the thermal-desorption (TD) properties for gas chromatographic (GC) analysis of ambient volatile organic compounds (VOCs). Flash-heating of the sorbent bed at high temperatures to desorb trapped VOCs to GC may easily produce severe asymmetric or tailing GC peaks affecting resolution and sensitivity if care is not taken to optimize the TD conditions. The TD peak without GC separation was first examined for the quality of the TD peak by analyzing a standard gas mixture from C2 to C12 at ppb level. The Deans switch was later applied in two different stages. First, it was used to cut the trailing tail of the TD peak, which, although significantly improved the GC peak symmetry, led to more loss of the higher boiling compounds than the low boiling ones, thus suggesting compound discrimination. Subsequently, the Deans switch was used to dissect the TD peak into six 30s slices in series, and an uneven distribution in composition between the slices were found. A progressive decrease in low boiling compounds and increase in higher boiling ones across the slices indicated severe inhomogeneity in the TD profile. This finding provided a clear evidence to answer the discrimination problem found with the tail cutting approach to improve peak symmetry. Through the use of the innovated slicing method based on the Deans-switch cutting technique, optimization of TD injection for highly resolved, symmetric and non-discriminated GC peaks can now be more quantitatively assessed and guided. PMID:27492597

  17. Spectral studies and thermal analysis of new vanadium complexes of ethanolamine and related compounds

    NASA Astrophysics Data System (ADS)

    Masoud, Mamdouh S.; Ali, Alaa E.; Ahmed, Hytham M.; Mohamed, Essam A.

    2013-10-01

    The electronic absorption spectral behaviors of newly synthesized complexes of VIII, VIV and VO2+ with Ethanolamine, Diethanolamine and Triethanolamine were described. The complexes have been characterized by elemental analyses, magnetic moment measurements, IR and UV-Vis spectroscopy. Absorption spectra in seven different solvents were recorded. The solvatochromism was examined and discussed. Dipolar interactions between the solvent and the complexes were used to correlate the observed spectral shifts to solvent polarity. Some of the obtained complexes were studied by thermal analysis using DTA and TG techniques.

  18. Comparison of Sn-Ag-Cu Solder Alloy Intermetallic Compound Growth Under Different Thermal Excursions for Fine-Pitch Flip-Chip Assemblies

    NASA Astrophysics Data System (ADS)

    Tian, Ye; Liu, Xi; Chow, Justin; Wu, Yi Ping; Sitaraman, Suresh K.

    2013-08-01

    The intermetallic compound (IMC) evolution in Cu pad/Sn-Ag-Cu solder interface and Sn-Ag-Cu solder/Ni pad interface was investigated using thermal shock experiments with 100- μm-pitch flip-chip assemblies. The experiments show that low standoff height of solder joints and high thermomechanical stress play a great role in the interfacial IMC microstructure evolution under thermal shock, and strong cross-reaction of pad metallurgies is evident in the intermetallic growth. Furthermore, by comparing the IMC growth during thermal aging and thermal shock, it was found that thermal shock accelerates IMC growth and that kinetic models based on thermal aging experiments underpredict IMC growth in thermal shock experiments. Therefore, new diffusion kinetic parameters were determined for the growth of (Cu,Ni)6Sn5 using thermal shock experiments, and the Cu diffusion coefficient through the IMC layer was calculated to be 0.2028 μm2/h under thermal shock. Finite-element models also show that the solder stresses are higher under thermal shock, which could explain why the IMC growth is faster and greater under thermal shock cycling as opposed to thermal aging.

  19. Degradation mechanisms of sulfur and nitrogen containing compounds during thermal stability testing of model fuels

    NASA Technical Reports Server (NTRS)

    Reddy, K. T.; Cernansky, N. P.; Cohen, R. S.

    1987-01-01

    The degradation behavior of n-dodecane (singly or in combination with S- and N-containing dopants) was studied using a modified Jet Fuel Thermal Oxidation Tester facility between 200 and 400 C. The products were analyzed by gas chromatography and mass spectrometry. The soluble products consisted mainly of n-alkanes and 1-alkenes, aldehydes, tetrahydrofuran derivatives, dodecanol and dodecanone isomers, C21-C24 alkane isomers, and dodecylhydroperoxide (ROOH) decomposition products. The major products were always the same, with and without dopants, but their distributions varied considerably. The 3,4-dimercaptotoluene and dibutylsulfide dopants added individually to n-dodecane interferred with the hydrocarbon oxidation at the alkylperoxy radical and the alkylhydroperoxide link, respectively, while the 2,5-dimethylpyrrole dopant inhibited ROOH formation. Pyridine, pyrrole, and dibenzothiophene added individually showed few significant effects.

  20. Synthesis, characterization and thermal studies on metal complexes of new azo compounds derived from sulfa drugs

    NASA Astrophysics Data System (ADS)

    Mohamed, Gehad G.; Gad-Elkareem, Mohamed A. M.

    2007-12-01

    Four new azo ligands, L1 and HL2-4, of sulfa drugs have been prepared and characterized. [MX 2(L1)(H 2O) m]· nH 2O; [(MX 2) 2(HL2 or HL3)(H 2O) m]· nH 2O and [M 2X 3(L4)(H 2O)]· nH 2O; M = Co(II), Ni(II) and Cu(II) (X = Cl) and Zn(II) (X = AcO); m = 0-4 and n = 0-3, complexes were prepared. Elemental and thermal analyses (TGA and DTA), IR, solid reflectance spectra, magnetic moment and molar conductance measurements have accomplished characterization of the complexes. The IR data reveal that HL1 and HL2-3 ligands behave as a bidentate neutral ligands while HL4 ligand behaves as a bidentate monoionic ligand. They coordinated to the metal ions via the carbonyl O, enolic sulfonamide sbnd S(O)OH, pyrazole or thiazole N and azo N groups. The molar conductance data reveal that the chelates are non-electrolytes. From the solid reflectance spectra and magnetic moment data, the complexes were found to have octahedral, tetrahedral and square planar geometrical structures. The thermal behaviour of these chelates shows that the water molecules (hydrated and coordinated) and the anions are removed in a successive two steps followed immediately by decomposition of the ligand in the subsequent steps. The activation thermodynamic parameters, such as, E*, Δ H*, Δ S* and Δ G* are calculated from the TG curves applying Coats-Redfern method.

  1. Heat conduction of symmetric lattices

    NASA Astrophysics Data System (ADS)

    Nie, Linru; Yu, Lilong; Zheng, Zhigang; Shu, Changzheng

    2013-06-01

    Heat conduction of symmetric Frenkel-Kontorova (FK) lattices with a coupling displacement was investigated. Through simplifying the model, we derived analytical expression of thermal current of the system in the overdamped case. By means of numerical calculations, the results indicate that: (i) As the coupling displacement d equals to zero, temperature oscillations of the heat baths linked with the lattices can control magnitude and direction of the thermal current; (ii) Whether there is a temperature bias or not, the thermal current oscillates periodically with d, whose amplitudes become greater and greater; (iii) As d is not equal to zero, the thermal current monotonically both increases and decreases with temperature oscillation amplitude of the heat baths, dependent on values of d; (iv) The coupling displacement also induces nonmonotonic behaviors of the thermal current vs spring constant of the lattice and coupling strength of the lattices; (v) These dynamical behaviors come from interaction of the coupling displacement with periodic potential of the FK lattices. Our results have the implication that the coupling displacement plays a crucial role in the control of heat current.

  2. Identification of Oxidation Compounds of 1-Stearoyl-2-linoleoyl-sn-glycero-3-phosphoethanolamine during Thermal Oxidation.

    PubMed

    Zhou, Li; Zhao, Minjie; Bindler, Françoise; Marchioni, Eric

    2015-11-01

    Heat-induced oxidative modification of phosphatidylethanolamine molecular species as potential functional food components was investigated. 1-Stearoyl-2-linoleoyl-sn-glycero-3-phosphoethanolamine (SLPE) was chosen as a model. The optimal temperature for hydroperoxide formation was determined by mass spectrometry. The maximal level of formation of this compound was obtained at 125 °C. The structures of nonvolatile organic compounds (non-VOCs) were identified using liquid chromatography-electrospray ionization mass spectrometry combined with an acid treatment. Kinetics of formation of non-VOCs was monitored over time. Results showed that the level of the SLPE precursor rapidly decreased during thermal oxidation and oxygenated products, such as hydroxyl, oxo, or epoxy groups, were formed. The VOCs formed from oxidized SLPE were determined by headspace solid-phase microextraction followed by gas chromatography-mass spectrometry analysis. The result showed that a saturated methyl ketone (2-heptanone) was the most predominant VOC of SLPE. Kinetics indicated that the formation of VOCs was related not only to the decomposition of hydroperoxides but also to the further decomposition of non-VOCs. PMID:26478449

  3. Improving breakdown, conductive, and thermal performances for SOI high voltage LDMOS using a partial compound buried layer

    NASA Astrophysics Data System (ADS)

    Hu, Shengdong; Luo, Jun; Jiang, YuYu; Cheng, Kun; Chen, Yinhui; Jin, Jingjing; Wang, Jian'an; Zhou, Jianlin; Tang, Fang; Zhou, Xichuan; Gan, Ping

    2016-03-01

    A novel SOI LDMOS with a partial compound buried layer structure (P-CBL SOI) is proposed in this paper. The buried oxide layer at the source-side is replaced by a compound buried layer (CBL) of "top oxide-middle polysilicon-bottom oxide", and the buried oxide layer at the drain-side is just as the conventional SOI LDMOS (C-SOI). Firstly, a new peak of electric field is introduced at the interface and the whole lateral electric field in the top silicon layer is modulated, resulting in a higher lateral BV. Secondly, impurity doping meeting the RESURF effect in the top silicon layer is higher because the top oxide is thinner than the conventional buried oxide layer, leading to a lower Ron,sp at the on-state and an enhanced vertical BV at the off-state. Finally, thermal conductivity of polysilicon is higher than that of SiO2, offering a lower self-heating effect. The influences of structure parameters on the devices performances are investigated. Compared with those of C-SOI LDMOS on the same top silicon layer of 4 μm, buried dielectric layer of 4 μm, and drift region of 40 μm, BV of P-CBL SOI LDMOS is enhanced by 33.4%, Ron,sp is reduced by 37.4%, and the maximum temperature at the power of 1 mW/μm is depressed by 13.3 K, respectively.

  4. Testing and linearity calibration of films of phenol compounds exposed to thermal neutron field for EPR dosimetry.

    PubMed

    Gallo, S; Panzeca, S; Longo, A; Altieri, S; Bentivoglio, A; Dondi, D; Marconi, R P; Protti, N; Zeffiro, A; Marrale, M

    2015-12-01

    This paper reports the preliminary results obtained by Electron Paramagnetic Resonance (EPR) measurements on films of IRGANOX® 1076 phenols with and without low content (5% by weight) of gadolinium oxide (Gd2O3) exposed in the thermal column of the Triga Mark II reactor of LENA (Laboratorio Energia Nucleare Applicata) of Pavia (Italy). Thanks to their size, the phenolic films here presented are good devices for the dosimetry of beams with high dose gradient and which require accurate knowledge of the precise dose delivered. The dependence of EPR signal as function of neutron dose was investigated in the fluence range between 10(11) cm(-2) and 10(14) cm(-2). Linearity of EPR response was found and the signal was compared with that of commercial alanine films. Our analysis showed that gadolinium oxide (5% by weight) can enhance the thermal neutron sensitivity more than 18 times. Irradiated dosimetric films of phenolic compound exhibited EPR signal fading of about 4% after 10 days from irradiation. PMID:26242561

  5. Secondary and compound concentrators for parabolic dish solar thermal power systems

    NASA Technical Reports Server (NTRS)

    Jaffe, L. D.; Poon, P. T.

    1981-01-01

    A secondary optical element may be added to a parabolic dish solar concentrator to increase the geometric concentration ratio attainable at a given intercept factor. This secondary may be a Fresnel lens or a mirror, such as a compound elliptic concentrator or a hyperbolic trumpet. At a fixed intercept factor, higher overall geometric concentration may be obtainable with a long focal length primary and a suitable secondary matched to it. Use of a secondary to increase the geometric concentration ratio is more likely to e worthwhile if the receiver temperature is high and if errors in the primary are large. Folding the optical path with a secondary may reduce cost by locating the receiver and power conversion equipment closer to the ground and by eliminating the heavy structure needed to support this equipment at the primary focus. Promising folded-path configurations include the Ritchey-Chretien and perhaps some three element geometries. Folding the optical path may be most useful in systems that provide process heat.

  6. Adsorption and desorption characteristics of semiconductor volatile organic compounds on the thermal swing honeycomb zeolite concentrator.

    PubMed

    Chang, Feng-Tang; Lin, Yu-Chih; Bai, Hsunling; Pei, Bau-Shei

    2003-11-01

    The use of a honeycomb zeolite concentrator and an oxidation process is one of the most popular methods demonstrated to control volatile organic compound (VOCs) emissions from waste gases in semiconductor manufacturing plants. This study attempts to characterize the performance of a concentrator in terms of the removal efficiencies of semiconductor VOCs (isopropyl alcohol [IPA], acetone, propylene glycol methyl ether [PGME], and propylene glycol monomethyl ether acetate [PGMEA]) under several parameters that govern the actual operations. Experimental results indicated that at inlet temperatures of under 40 degrees C and a relative humidity of under 80%, the removal efficiency of a zeolite concentrator can be maintained well over 90%. The optimal rotation speed of the concentrator is between 3 and 4.5 rph in this study. The optimal rotation speed increases with the VOCs inlet concentration. Furthermore, reducing the concentration ratio helps to increase the removal efficiency, but it also increases the incineration cost. With reference to competitive adsorption, PGMEA and PGME are more easily adsorbed on a zeolite concentrator than are IPA and acetone because of their high boiling points and molecular weights. PMID:14649758

  7. Inelastic neutron scattering, lattice dynamics, and high-pressure phase stability of zircon-structured lanthanide orthophosphates

    SciTech Connect

    Bose, Preyoshi P.; Mittal, R; Chaplot, S L; Loong, C. K.; Boatner, Lynn A

    2010-01-01

    Inelastic neutron-scattering experiments and lattice-dynamical calculations are reported on a series of rareearth orthophosphates RPO4 R=Tm, Er, Ho, and Tb. The experimental phonon spectra for the compounds are in good agreement with our model calculations. The lattice-dynamical model is found useful for the calculation of various thermodynamic properties such as the lattice specific heat, thermal expansion, and equation of state of these compounds. The RPO4 compounds are known to transform to the scheelite body-centered tetragonal, I41 /a or monoclinic phase P21 /n at high pressures. Our calculations show that while the scheelite phase stabilizes at high pressure due to its lower volume, the monoclinic phase may occur as an intermediate phase depending on the ionic size of the R atom. The latter phase is stabilized at higher temperature at high pressure due to its high vibrational entropy. A pressure-temperature phase diagram is proposed.

  8. Treatment of malignant melanoma by selective thermal neutron capture therapy using melanoma-seeking compound

    SciTech Connect

    Mishima, Y.; Ichihashi, M.; Tsuji, M.; Hatta, S.; Ueda, M.; Honda, C.; Suzuki, T.

    1989-05-01

    As pigment cells undergo melanoma genesis, accentuated melanogenesis concurrently occurs in principle. Subsequent to the understanding of intrinsic factors controlling both processes, we found our selective melanoma neutron capture therapy (NCT) using 10B-dopa (melanin substrate) analogue, 10B1-p-boronophenylalanine (10B1-BPA), followed by 10B(n, alpha)7Li reaction, induced by essentially harmless thermal neutrons, which releases energy of 2.33 MeV to 14 mu, the diameter of melanoma cells. In vitro/in vivo radiobiological analysis revealed the highly enhanced melanoma killing effect of 10B1-BPA. Chemical and prompt gamma ray spectrometry assays of 10B accumulated within melanoma cells after 10B1-BPA administration in vitro and in vivo show high affinity, e.g., 10B melanoma/blood ratio of 11.5. After successfully eradicating melanoma transplanted into hamsters with NCT, we advanced to preclinical studies using spontaneously occurring melanoma in Duroc pig skin. We cured three melanoma cases, 4.6 to 12 cm in diameter, by single neutron capture treatment. Complete disappearance of melanoma was obtained without substantial side effects. Acute and subacute toxicity as well as pharmacodynamics of 10B1-BPA have been studied in relation to therapeutic dosage requirements. Clinical radiation dosimetry using human phantom has been carried out. Further preclinical studies using human melanoma transplanted into nude mouse have been a useful model for obtaining optimal results for each melanoma type. We recently treated the first human melanoma patient with our NCT, using essentially the method for Duroc pig melanoma, and obtained similar regression time course leading to cure.

  9. Determination of off-flavor compounds, 2-methylisoborneol and geosmin, in salmon fillets using stir bar sorptive extraction–thermal desorption coupled with gas chromatography–mass spectrometry

    Technology Transfer Automated Retrieval System (TEKTRAN)

    A sensitive and solvent-less method for the determination of musty and earthy off-flavor compounds, 2-methylisoborneol (MIB) and geosmin (GSM), in salmon tissue was developed using stir bar sorptive extraction -thermal desorption coupled with gas chromatography -mass spectrometry (SBSE -TD -GCMS). M...

  10. Low-dimensional compounds containing cyano groups. XIV. Crystal structure, spectroscopic, thermal and magnetic properties of [CuL {sub 2}][Pt(China){sub 4}] complexes (L=ethylenediamine or N,N-dimethylethylenediamine)

    SciTech Connect

    Potocnak, Ivan . E-mail: ivan.potocnak@upjs.sk; Vavra, Martin; Cizmar, Erik; Tibenska, Katarina; Orendacova, Alzbeta; Steinborn, Dirk; Wagner, Christoph; Dusek, Michal; Fejfarova, Karla; Schmidt, Harry; Muller, Thomas; Orendac, Martin; Feher, Alexander

    2006-07-15

    Violet crystals of [Cu(en){sub 2}][Pt(China){sub 4}] and blue crystals of [Cu(dmen){sub 2}][Pt(China){sub 4}] were crystallized from the water-methanol solution containing CuCl{sub 2}.2H{sub 2}O, ethylenediamine (en) or N,N-dimethylethylenediamine (dmen) and K{sub 2}[Pt(China){sub 4}].3H{sub 2}O. Both compounds were characterized using elemental analysis, infrared and UV-VIS spectroscopy, magnetic measurements, specific heat measurements and thermal analysis. X-ray structure analysis revealed chain-like structure in both compounds. The covalent chains are built of Cu(II) ions linked by [Pt(China){sub 4}]{sup 2-} anions in the [111] and [101] direction, respectively. The Cu(II) atoms are hexacoordinated by four nitrogen atoms in the equatorial plane from two molecules of bidentate ligands L with average Cu-N distance of 2.022(2) and 2.049(4) A, respectively. Axial positions are occupied by two nitrogen atoms from bridging [Pt(China){sub 4}]{sup 2-} anions at longer Cu-N distance of 2.537(2) and 2.600(5) A, respectively. Both materials are characterized by the presence of weak antiferromagnetic exchange coupling. Despite the one-dimensional (1D) character of the structure, the analysis of magnetic properties and specific heat at very low temperatures shows that [Cu(en){sub 2}][Pt(China){sub 4}] behaves as two-dimensional (2D) spatially anisotropic square lattice Heisenberg magnet, while more pronounced influence of interlayer coupling is observed in [Cu(dmen){sub 2}][Pt(China){sub 4}]. - Graphical abstract: Chain-like structure in [Cu(en){sub 2}][Pt(China){sub 4}] (R=H) and [Cu(dmen){sub 2}][Pt(China){sub 4}] (R=CH{sub 3}) compounds.

  11. Pyrolysis reaction networks for lignin model compounds: unraveling thermal deconstruction of β-O-4 and α-O-4 compounds

    SciTech Connect

    Choi, Yong S.; Singh, Rahul; Zhang, Jing; Balasubramanian, Ganesh; Sturgeon, Matthew R.; Katahira, Rui; Chupka, Gina; Beckham, Gregg T.; Shanks, Brent H.

    2016-01-01

    Although lignin is one of the main components of biomass, its pyrolysis chemistry is not well understood due to complex heterogeneity. To gain insights into this chemistry, the pyrolysis of seven lignin model compounds (five ..beta..-O-4 and two ..alpha..-O-4 linked molecules) was investigated in a micropyrolyzer connected to GC-MS/FID. According to quantitative product mole balance for the reaction networks, concerted retro-ene fragmentation and homolytic dissociation were strongly suggested as the initial reaction step for ..beta..-O-4 compounds and ..alpha..-O-4 compounds, respectively. The difference in reaction pathway between compounds with different linkages was believed to result from thermodynamics of the radical initiation. The rate constants for the different reaction pathways were predicted from ab initio density functional theory calculations and pre-exponential literature values. The computational findings were consistent with the experiment results, further supporting the different pyrolysis mechanisms for the ..beta..-ether linked and ..alpha..-ether linked compounds. A combination of the two pathways from the dimeric model compounds was able to describe qualitatively the pyrolysis of a trimeric lignin model compound containing both ..beta..-O-4 and ..alpha..-O-4 linkages.

  12. Magnetic structure of the antiferromagnetic Kondo lattice compounds CeRhAl4Si2 and CeIrAl4Si2

    SciTech Connect

    Ghimire, N. J.; Calder, S.; Janoschek, M.; Bauer, E. D.

    2015-06-01

    In this article, we have investigated the magnetic ground state of the antiferromagnetic Kondo-lattice compounds CeMAl4Si2(M = Rh, Ir) using neutron powder diffraction. Although both of these compounds show two magnetic transitions TN1 and TN2 in the bulk properties measurements, evidence for magnetic long-range order was only found below the lower transition TN2. Analysis of the diffraction profiles reveals a commensurate antiferromagnetic structure with a propagation vector k = (0, 0, 1/2). The magnetic moment in the ordered state of CeRhAl4Si2 and CeIrAl4Si2 were determined to be 1.14(2) and 1.41(3) μB/Ce, respectively, and are parallel to the crystallographic c-axis in agreement with magnetic susceptibility measurements.

  13. A model to predict the adsorber thermal behavior during treatment of volatile organic compounds onto wet activated carbon.

    PubMed

    Pré, P; Delage, F; Le Cloirec, P

    2002-11-01

    A model for adsorption of volatile organic compounds (VOCs) onto a wet activated carbon bed was proposed in this study. This model accounts for temperature changes induced by the reversed and coupled mass-transfer processes of both organic species adsorption and water desorption. Indeed, it was experimentally pointed out that temperature rises, which result from the exothermal nature of the energetic interactions between the organic molecule and the activated carbon surface, are notably reduced when the adsorbent contains an initial moisture of approximately 10% in weight. Moreover, it was shown that water rate desorption was enhanced in the presence of organic vapor. This phenomenon may be explained by the displacement of sorbed water bythe organic molecules, owing to more intensive interactions with the activated carbon surface. The model proposed was elaborated from a previous comprehensive analysis of the diffusion mechanisms governing VOC adsorption at high concentrations onto a dry activated carbon bed. In a similar way, a theoretical approach was developed to model water desorption during drying of a wet activated carbon bed under pure flowing air. At last, a theoretical depiction of both competitive and reverse processes was outlined. The final model fits reasonably with experimental data relative to both breakthrough curves and thermal wave shape along the bed, even if local temperature change calculation may require some further improvement. PMID:12433182

  14. Determination of volatile organic compounds in workplace air by multisorbent adsorption/thermal desorption-GC/MS.

    PubMed

    Wu, Chien-Hou; Feng, Chien-Tai; Lo, Yu-Shiu; Lin, Tsai-Yin; Lo, Jiunn-Guang

    2004-07-01

    Investigation of volatile organic compounds (VOCs) was first conducted in the air of class-100 cleanrooms at liquid crystal display (LCD) fabrication facilities. Air samples were collected on multisorbent tubes (including Carbopack B, Carbopack C, and Carbosieve S-III) and analyzed using adsorption/thermal desorption coupled with gas chromatography-mass spectrometry (GC-MS). Optimal conditions lead to average recoveries in the range of 96.2-98.2%, and method detection limits between 0.38 and 0.78 ppb, under the condition of 1-l sampling volume and 80% relative humidity. The method appears to be accurate, sensitive, simple and well-suited for determining VOC distributions from various stages of LCD manufacturing process and temporal variations of the analyte concentrations. About 15 VOCs were identified in workplace air. The major pollutants such as propylene glycol methyl ether acetate (PGMEA), butyl acetate, and acetone that are commonly used in the opto-electronics industry were detected and accurately quantified with the established method. PMID:15109881

  15. Performance of a high flow rate, thermally extractable multicapillary denuder for atmospheric semivolatile organic compound concentration measurement.

    PubMed

    Rowe, Mark D; Perlinger, Judith A

    2010-03-15

    A high flow rate (300 L min(-1)) multicapillary denuder was designed to collect trace atmospheric semivolatile organic compounds (SOCs). The denuder is coated with a reusable, polydimethylsiloxane stationary phase as a nonselective absorbent for SOCs. A solvent-free thermal desorption method was developed, including sample cleanup, that is selective for nonpolar SOCs, and has low consumables cost per sample. The entire sample is transferred into the gas chromatograph to minimize the sampling time required to collect detectable analyte mass. Trace concentrations (0.1-100 pg m(-3)) of polychlorinated biphenyls and hexachlorobenzene were measured in the atmosphere near Lake Superior in sample times of 3.2-6.2 h. Overall method precision was determined using field duplicates and compared to the conventional high-volume sampler method. Method precision (coefficient of variation) of 16% was found for the high-flow denuder compared to 21% for the high-volume method. The relative difference between the two methods was 25%, with the high-flow denuder method giving generally lower concentrations. The high-flow denuder is an alternative to high-volume or passive samplers when it is desirable to separate gaseous from particle-associated SOCs upstream of a filter. The method is advantageous for studies that require high temporal resolution. PMID:20148550

  16. Highly efficient luminescence of Cu(I) compounds: thermally activated delayed fluorescence combined with short-lived phosphorescence.

    PubMed

    Hofbeck, Thomas; Monkowius, Uwe; Yersin, Hartmut

    2015-01-14

    Luminescent materials showing thermally activated delayed fluorescence (TADF) have gained high attractiveness as emitters in organic light emitting diodes (OLEDs) and other photonic applications. Nevertheless, even utilization of TADF can be further improved, introducing a novel concept. This is demonstrated by a new class of brightly luminescent low-cost Cu(I) compounds, for which the emission stems from both the lowest excited triplet T1 and singlet S1 state. At T = 300 K, these materials exhibit quantum yields of more than ΦPL = 90% at short emission decay times. About 80% of the emission intensity stems from the singlet due to TADF, but importantly, an additional 20% is contributed by the lower lying triplet state according to effective spin-orbit coupling (SOC). SOC induces also a relatively large zero-field splitting of the triplet being unusual for Cu(I) complexes. Thus, the overall emission decay time is distinctly reduced. Combined use of both decay paths opens novel photonic applications, in particular, for OLEDs. PMID:25486064

  17. Multistage symmetry breaking in the breathing pyrochlore lattice Li(Ga ,In )Cr 4O8

    NASA Astrophysics Data System (ADS)

    Lee, S.; Do, S.-H.; Lee, W.-J.; Choi, Y. S.; Lee, M.; Choi, E. S.; Reyes, A. P.; Kuhns, P. L.; Ozarowski, A.; Choi, K.-Y.

    2016-05-01

    We present magnetic susceptibility, dielectric constant, high-frequency electron spin resonance, 7Li nuclear magnetic resonance, and zero-field muon spin relaxation measurements of LiACr4O8 (A =Ga , In), towards realizing a breathing pyrochlore lattice. Unlike the uniform pyrochlore ZnCr2O4 lattice, both the In and the Ga compounds feature two-stage symmetry breaking: a magnetostructural phase transition with subsequent antiferromagnetic ordering. We find a disparate symmetry breaking process between the In and the Ga compounds, having different degrees of bond alternation. Our data reveal that the Ga compound with moderate bond alternation shows the concomitant structural and magnetic transition at TS=15.2 K, followed by the magnetic ordering at Tm=12.9 K. In contrast, the In compound with strong bond alternation undergoes a thermal crossover at T*≈20.1 K from a tetramer singlet to a dimer singlet or a correlated paramagnet with a separate weak magnetostructural transition at TS=17.6 K and the second antiferromagnetic ordering at Tm=13.7 K. This suggests that the magnetic phases and correlations of the breathing pyrochlore lattice can be determined from the competition between bond alternation and spin-lattice coupling, thus stabilizing long-range magnetic ordering against a nonmagnetic singlet.

  18. Lattice kinetic simulation of nonisothermal magnetohydrodynamics.

    PubMed

    Chatterjee, Dipankar; Amiroudine, Sakir

    2010-06-01

    In this paper, a lattice kinetic algorithm is presented to simulate nonisothermal magnetohydrodynamics in the low-Mach number incompressible limit. The flow and thermal fields are described by two separate distribution functions through respective scalar kinetic equations and the magnetic field is governed by a vector distribution function through a vector kinetic equation. The distribution functions are only coupled via the macroscopic density, momentum, magnetic field, and temperature computed at the lattice points. The novelty of the work is the computation of the thermal field in conjunction with the hydromagnetic fields in the lattice Boltzmann framework. A 9-bit two-dimensional (2D) lattice scheme is used for the numerical computation of the hydrodynamic and thermal fields, whereas the magnetic field is simulated in a 5-bit 2D lattice. Simulation of Hartmann flow in a channel provides excellent agreement with corresponding analytical results. PMID:20866540

  19. Construction of a cryogen-free thermal desorption gas chromatographic system with off-the-shelf components for monitoring ambient volatile organic compounds.

    PubMed

    Ou-Yang, Chang-Feng; Liao, Wei-Cheng; Wang, Pei-Chieh; Fan, Gang-Jei; Hsiao, Chien-Cheng; Chuang, Ming-Tung; Chang, Chih-Chung; Lin, Neng-Huei; Wang, Jia-Lin

    2016-04-01

    An automated gas chromatographic system aimed at performing unattended measurements of ambient volatile organic compounds was configured and tested. By exploiting various off-the-shelf components, the thermal desorption unit was easily assembled and can be connected with any existing commercial gas chromatograph in the laboratory to minimize cost. The performance of the complete thermal desorption gas chromatographic system was assessed by analyzing a standard mixture containing 56 target nonmethane hydrocarbons from C2 -C12 at sub-ppb levels. Particular attention was given to the enrichment efficiency of the C2 compounds, such as ethane (b.p. = -88.6°C) and ethylene (b.p. = -104.2°C), due to their extremely high volatilities. Quality assurance was performed in terms of the linearity, precision and limits of detection of the target compounds. To further validate the system, field measurements of target compounds in ambient air were compared with those of a commercial total hydrocarbon analyzer and a carbon monoxide analyzer. Highly coherent results from the three instruments were observed during a two-month period of synchronized measurements. Moreover, the phenomenon of opposite diurnal variations between the biogenic isoprene and anthropogenic species was exploited to help support the field applicability of the thermal desorption gas chromatographic method. PMID:26924196

  20. Influence of nanoparticle addition on the formation and growth of intermetallic compounds (IMCs) in Cu/Sn-Ag-Cu/Cu solder joint during different thermal conditions

    NASA Astrophysics Data System (ADS)

    Tan, Ai Ting; Tan, Ai Wen; Yusof, Farazila

    2015-06-01

    Nanocomposite lead-free solders are gaining prominence as replacements for conventional lead-free solders such as Sn-Ag-Cu solder in the electronic packaging industry. They are fabricated by adding nanoparticles such as metallic and ceramic particles into conventional lead-free solder. It is reported that the addition of such nanoparticles could strengthen the solder matrix, refine the intermetallic compounds (IMCs) formed and suppress the growth of IMCs when the joint is subjected to different thermal conditions such as thermal aging and thermal cycling. In this paper, we first review the fundamental studies on the formation and growth of IMCs in lead-free solder joints. Subsequently, we discuss the effect of the addition of nanoparticles on IMC formation and their growth under several thermal conditions. Finally, an outlook on the future growth of research in the fabrication of nanocomposite solder is provided.

  1. Antiferromagnetic Kondo lattice in the layered compound CePd1 -xBi2 and comparison to the superconductor LaPd1 -xBi2

    NASA Astrophysics Data System (ADS)

    Han, Fei; Wan, Xiangang; Phelan, Daniel; Stoumpos, Constantinos C.; Sturza, Mihai; Malliakas, Christos D.; Li, Qing'an; Han, Tian-Heng; Zhao, Qingbiao; Chung, Duck Young; Kanatzidis, Mercouri G.

    2015-07-01

    The layered compound CePd1 -xBi2 with the tetragonal ZrCuSi2-type structure was obtained from excess Bi flux. Magnetic susceptibility data of CePd1 -xBi2 show an antiferromagnetic ordering below 6 K and are anisotropic along the c axis and the a b plane. The anisotropy is attributed to crystal-electric-field (CEF) effects and a CEF model which is able to describe the susceptibility data is given. An enhanced Sommerfeld coefficient γ of 0.191 J mol Ce -1 K -2 obtained from specific-heat measurement suggests a moderate Kondo effect in CePd1 -xBi2. Other than the antiferromagnetic peak at 6 K, the resistivity curve shows a shoulderlike behavior around 75 K which could be attributed to the interplay between Kondo and CEF effects. Magnetoresistance and Hall-effect measurements suggest that the interplay reconstructs the Fermi-surface topology of CePd1 -xBi2 around 75 K. Electronic structure calculations reveal that the Pd vacancies are important to the magnetic structure and enhance the CEF effects which quench the orbital moment of Ce at low temperatures.

  2. Antiferromagnetic Kondo lattice in the layered compound CePd1–xBi₂ and comparison to the superconductor LaPd1–xBi₂

    DOE PAGESBeta

    Han, Fei; Wan, Xiangang; Phelan, Daniel; Stoumpos, Constantinos C.; Sturza, Mihai; Malliakas, Christos D.; Li, Qing'an; Han, Tian-Heng; Zhao, Qingbiao; Chung, Duck Young; et al

    2015-07-13

    The layered compound CePd1–xBi₂ with the tetragonal ZrCuSi₂-type structure was obtained from excess Bi flux. Magnetic susceptibility data of CePd1–xBi₂ show an antiferromagnetic ordering below 6 K and are anisotropic along the c axis and the ab plane. The anisotropy is attributed to crystal-electric-field (CEF) effects and a CEF model which is able to describe the susceptibility data is given. An enhanced Sommerfeld coefficient γ of 0.191 J mol Ce⁻¹ K⁻² obtained from specific-heat measurement suggests a moderate Kondo effect in CePd1–xBi₂. Other than the antiferromagnetic peak at 6 K, the resistivity curve shows a shoulderlike behavior around 75 Kmore » which could be attributed to the interplay between Kondo and CEF effects. Magnetoresistance and Hall-effect measurements suggest that the interplay reconstructs the Fermi-surface topology of CePd1–xBi₂ around 75 K. Electronic structure calculations reveal that the Pd vacancies are important to the magnetic structure and enhance the CEF effects which quench the orbital moment of Ce at low temperatures.« less

  3. Submicron Magnetite Grains and Carbon Compounds in Martian Meteorite ALH84001: Inorganic, Abiotic Formation by Shock and Thermal Metamorphism

    NASA Astrophysics Data System (ADS)

    Treiman, Allan H.

    2003-06-01

    Purported biogenic features of the ALH84001 Martian meteorite (the carbonate globules, their submicron magnetite grains, and organic matter) have reasonable inorganic origins, and a comprehensive hypothesis is offered here. The carbonate globules were deposited from hydrothermal water, without biological mediation. Thereafter, ALH84001 was affected by an impact shock event, which raised its temperature nearly instantaneously to 500-700K, and induced iron-rich carbonate in the globules to decompose to magnetite and other minerals. The rapidity of the temperature increase caused magnetite grains to nucleate in abundance; hence individual crystals were very small. Nucleation and growth of magnetite crystals were fastest along edges and faces of the precursor carbonate grains, forcing the magnetite grains to be platy or elongated, including the "truncated hexa-octahedra" shape. ALH84001 had formed at some depth within Mars where the lithostatic pressure was significantly above that of Mars' surface. Also, because the rock was at depth, the impact heat dissipated slowly. During this interval, magnetite crystals approached chemical equilibria with surrounding minerals and gas. Their composition, nearly pure Fe3O4, reflects those of equilibria; elements that substitute into magnetite are either absent from iron-rich carbonate (e.g., Ti, Al, Cr), or partitioned into other minerals during magnetite formation (Mg, Mn). Many microstructural imperfections in the magnetite grains would have annealed out as the rock cooled. In this post-shock thermal regime, carbon-bearing gas from the decomposition of iron carbonates reacted with water in the rock (or from its surroundings) to produce organic matter via Fischer-Tropschlike reactions. Formation of such organic compounds like polycyclic aromatic hydrocarbons would have been catalyzed by the magnetite (formation of graphite, the thermochemically stable phase, would be kinetically hindered).

  4. Submicron magnetite grains and carbon compounds in Martian meteorite ALH84001: inorganic, abiotic formation by shock and thermal metamorphism.

    PubMed

    Treiman, Allan H

    2003-01-01

    Purported biogenic features of the ALH84001 Martian meteorite (the carbonate globules, their submicron magnetite grains, and organic matter) have reasonable inorganic origins, and a comprehensive hypothesis is offered here. The carbonate globules were deposited from hydrothermal water, without biological mediation. Thereafter, ALH84001 was affected by an impact shock event, which raised its temperature nearly instantaneously to 500-700K, and induced iron-rich carbonate in the globules to decompose to magnetite and other minerals. The rapidity of the temperature increase caused magnetite grains to nucleate in abundance; hence individual crystals were very small. Nucleation and growth of magnetite crystals were fastest along edges and faces of the precursor carbonate grains, forcing the magnetite grains to be platy or elongated, including the "truncated hexa-octahedra" shape. ALH84001 had formed at some depth within Mars where the lithostatic pressure was significantly above that of Mars' surface. Also, because the rock was at depth, the impact heat dissipated slowly. During this interval, magnetite crystals approached chemical equilibria with surrounding minerals and gas. Their composition, nearly pure Fe(3)O(4), reflects those of equilibria; elements that substitute into magnetite are either absent from iron-rich carbonate (e.g., Ti, Al, Cr), or partitioned into other minerals during magnetite formation (Mg, Mn). Many microstructural imperfections in the magnetite grains would have annealed out as the rock cooled. In this post-shock thermal regime, carbon-bearing gas from the decomposition of iron carbonates reacted with water in the rock (or from its surroundings) to produce organic matter via Fischer-Tropschlike reactions. Formation of such organic compounds like polycyclic aromatic hydrocarbons would have been catalyzed by the magnetite (formation of graphite, the thermochemically stable phase, would be kinetically hindered). PMID:14577885

  5. Lattice gas and lattice Boltzmann computational physics

    SciTech Connect

    Chen, S.

    1993-05-01

    Recent developments of the lattice gas automata method and its extension to the lattice Boltzmann method have provided new computational schemes for solving a variety of partial differential equations and modeling different physics systems. The lattice gas method, regarded as the simplest microscopic and kinetic approach which generates meaningful macroscopic dynamics, is fully parallel and can be easily programmed on parallel machines. In this talk, the author will review basic principles of the lattice gas and lattice Boltzmann method, its mathematical foundation and its numerical implementation. A detailed comparison of the lattice Boltzmann method with the lattice gas technique and other traditional numerical schemes, including the finite-difference scheme and the pseudo-spectral method, for solving the Navier-Stokes hydrodynamic fluid flows, will be discussed. Recent achievements of the lattice gas and the the lattice Boltzmann method and their applications in surface phenomena, spinodal decomposition and pattern formation in chemical reaction-diffusion systems will be presented.

  6. Area of Lattice Polygons

    ERIC Educational Resources Information Center

    Scott, Paul

    2006-01-01

    A lattice is a (rectangular) grid of points, usually pictured as occurring at the intersections of two orthogonal sets of parallel, equally spaced lines. Polygons that have lattice points as vertices are called lattice polygons. It is clear that lattice polygons come in various shapes and sizes. A very small lattice triangle may cover just 3…

  7. Thermal conductivity of halide solid solutions: measurement and prediction.

    PubMed

    Gheribi, Aïmen E; Poncsák, Sándor; St-Pierre, Rémi; Kiss, László I; Chartrand, Patrice

    2014-09-14

    The composition dependence of the lattice thermal conductivity in NaCl-KCl solid solutions has been measured as a function of composition and temperature. Samples with systematically varied compositions were prepared and the laser flash technique was used to determine the thermal diffusivity from 373 K to 823 K. A theoretical model, based on the Debye approximation of phonon density of state (which contains no adjustable parameters) was used to predict the thermal conductivity of both stoichiometric compounds and fully disordered solid solutions. The predictions obtained with the model agree very well with our measurement. A general method for predicting the thermal conductivity of different halide systems is discussed. PMID:25217938

  8. On-line derivatization for hourly measurements of gas- and particle-phase Semi-Volatile oxygenated organic compounds by Thermal desorption Aerosol Gas chromatography (SV-TAG)

    NASA Astrophysics Data System (ADS)

    Isaacman, G.; Kreisberg, N. M.; Yee, L. D.; Worton, D. R.; Chan, A. W. H.; Moss, J. A.; Hering, S. V.; Goldstein, A. H.

    2014-07-01

    Laboratory oxidation studies have identified a large number of oxygenated organic compounds that can be used as tracers to understand sources and oxidation chemistry of atmospheric particulate matter. Quantification of these compounds in ambient environments has traditionally relied on low time-resolution collection of filter samples followed by offline sample treatment with a derivatizing agent to allow analysis by gas chromatography of otherwise non-elutable organic chemicals with hydroxyl groups. We present here an automated in situ instrument for the measurement of highly polar organic semi-volatile and low-volatility compounds in both the gas- and particle-phase with hourly time-resolution. The dual-cell Semi-Volatile Thermal desorption Aerosol Gas chromatograph (SV-TAG) with derivatization collects particle-only and combined particle-plus-vapor samples on two parallel sampling cells that are analyzed in series by thermal desorption into helium saturated with derivatizing agent. Introduction of MSTFA, a silylating agent, yields complete derivatization of all tested compounds, including alkanoic acids, polyols, diacids, sugars, and multifunctional compounds. In laboratory tests, derivatization is found to be highly reproducible (< 3% variability). During field deployment, a regularly injected internal standard is used to correct for variability in detector response, derivatization efficiency, desorption efficiency, and transfer efficiency. Error in quantification from instrument fluctuations is found to be less than 10% for hydrocarbons and less than 15% for all oxygenates for which a functionally similar internal standard is available. After internal standard corrections, calibration curves are found to be linear for all compounds over the span of one month with comparable response on both of the parallel sampling cells.

  9. Online derivatization for hourly measurements of gas- and particle-phase semi-volatile oxygenated organic compounds by thermal desorption aerosol gas chromatography (SV-TAG)

    NASA Astrophysics Data System (ADS)

    Isaacman, G.; Kreisberg, N. M.; Yee, L. D.; Worton, D. R.; Chan, A. W. H.; Moss, J. A.; Hering, S. V.; Goldstein, A. H.

    2014-12-01

    Laboratory oxidation studies have identified a large number of oxygenated organic compounds that can be used as tracers to understand sources and oxidation chemistry of atmospheric particulate matter. Quantification of these compounds in ambient environments has traditionally relied on low-time-resolution collection of filter samples followed by offline sample treatment with a derivatizing agent to allow analysis by gas chromatography of otherwise non-elutable organic chemicals with hydroxyl groups. We present here an automated in situ instrument for the measurement of highly polar organic semi-volatile and low-volatility compounds in both the gas- and particle-phase with hourly quantification of mass concentrations and gas-particle partitioning. The dual-cell semi-volatile thermal desorption aerosol gas chromatograph (SV-TAG) with derivatization collects particle-only and combined particle-plus-vapor samples on two parallel sampling cells that are analyzed in series by thermal desorption into helium saturated with derivatizing agent. Introduction of MSTFA (N-methyl-N-(trimethylsilyl)trifluoroacetamide), a silylating agent, yields complete derivatization of all tested compounds, including alkanoic acids, polyols, diacids, sugars, and multifunctional compounds. In laboratory tests, derivatization is found to be highly reproducible (< 3% variability). During field deployment, a regularly injected internal standard is used to correct for variability in detector response, consumption of the derivatization agent, desorption efficiency, and transfer losses. Error in quantification from instrument fluctuations is found to be less than 10% for hydrocarbons and less than 15% for all oxygenates for which a functionally similar internal standard is available, with an uncertainty of 20-25% in measurements of particle fraction. After internal standard corrections, calibration curves are found to be linear for all compounds over the span of 1 month, with comparable response on

  10. Chaos in the honeycomb optical-lattice unit cell

    NASA Astrophysics Data System (ADS)

    Porter, Max D.; Reichl, L. E.

    2016-01-01

    Natural and artificial honeycomb lattices are of great interest because the band structure of these lattices, if properly constructed, contains a Dirac point. Such lattices occur naturally in the form of graphene and carbon nanotubes. They have been created in the laboratory in the form of semiconductor 2DEGs, optical lattices, and photonic crystals. We show that, over a wide energy range, gases (of electrons, atoms, or photons) that propagate through these lattices are Lorentz gases and the corresponding classical dynamics is chaotic. Thus honeycomb lattices are also of interest for understanding eigenstate thermalization and the conductor-insulator transition due to dynamic Anderson localization.

  11. Lattice Instability of 2H-TaSe2

    NASA Astrophysics Data System (ADS)

    John Bosco Balaguru, R.; Lawrence, N.; Alfred Cecil Raj, S.

    The charge density wave (CDW) in the layered compound 2H-TaSe2 at low temperatures has a commensurate phase, which causes super lattice points to appear in the Brillöuin zone of the undistorted phase. A Born-von Karman formalism has been employed for the calculation of phonon frequency distribution curves of 2H-TaSe2 both in the normal and in the commensurate charge density wave (CCDW) phases. A folding technique has been adopted for the calculation in the CCDW phase. The phonon distribution for both the phases have been reported. With these distributions the thermal properties such as specific heat capacity, Debye Waller factor W(k) and thermal conductivity have been worked out, and compared with the available experimental results.

  12. Lattice constants and expansivities of gas hydrates from 10 K up to the stability limit.

    PubMed

    Hansen, T C; Falenty, A; Kuhs, W F

    2016-02-01

    The lattice constants of hydrogenated and deuterated CH4-, CO2-, Xe- (clathrate structure type I) and N2-hydrates (clathrate structure type II) from 10 K up to the stability limit were established in neutron- and synchrotron diffraction experiments and were used to derive the related thermal expansivities. The following results emerge from this analysis: (1) The differences of expansivities of structure type I and II hydrates are fairly small. (2) Despite the larger guest-size of CO2 as compared to methane, CO2-hydrate has the smaller lattice constants at low temperatures, which is ascribed to the larger attractive guest-host interaction of the CO2-water system. (3) The expansivity of CO2-hydrate is larger than for CH4-hydrate which leads to larger lattice constants for the former at temperatures above ∼150 K; this is likely due to the higher motional degrees of freedom of the CO2 guest molecules. (4) The cage occupancies of Xe- and CO2-hydrates affect significantly the lattice constants. (5) Similar to ice Ih, the deuterated compounds have generally slightly larger lattice constants which can be ascribed to the somewhat weaker H-bonding. (6) Compared to ice Ih, the high temperature expansivities are about 50% larger; in contrast to ice Ih and the empty hydrate, there is no negative thermal expansion at low temperature. (7) A comparison of the experimental results with lattice dynamical work, with models based on an Einstein oscillator model, and results from inelastic neutron scattering suggest that the contribution of the guest atoms' vibrational energy to thermal expansion is important, most prominently for CO2- and Xe-hydrates. PMID:26851915

  13. Lattice constants and expansivities of gas hydrates from 10 K up to the stability limit

    NASA Astrophysics Data System (ADS)

    Hansen, T. C.; Falenty, A.; Kuhs, W. F.

    2016-02-01

    The lattice constants of hydrogenated and deuterated CH4-, CO2-, Xe- (clathrate structure type I) and N2-hydrates (clathrate structure type II) from 10 K up to the stability limit were established in neutron- and synchrotron diffraction experiments and were used to derive the related thermal expansivities. The following results emerge from this analysis: (1) The differences of expansivities of structure type I and II hydrates are fairly small. (2) Despite the larger guest-size of CO2 as compared to methane, CO2-hydrate has the smaller lattice constants at low temperatures, which is ascribed to the larger attractive guest-host interaction of the CO2-water system. (3) The expansivity of CO2-hydrate is larger than for CH4-hydrate which leads to larger lattice constants for the former at temperatures above ˜150 K; this is likely due to the higher motional degrees of freedom of the CO2 guest molecules. (4) The cage occupancies of Xe- and CO2-hydrates affect significantly the lattice constants. (5) Similar to ice Ih, the deuterated compounds have generally slightly larger lattice constants which can be ascribed to the somewhat weaker H-bonding. (6) Compared to ice Ih, the high temperature expansivities are about 50% larger; in contrast to ice Ih and the empty hydrate, there is no negative thermal expansion at low temperature. (7) A comparison of the experimental results with lattice dynamical work, with models based on an Einstein oscillator model, and results from inelastic neutron scattering suggest that the contribution of the guest atoms' vibrational energy to thermal expansion is important, most prominently for CO2- and Xe-hydrates.

  14. Detection of gaseous compounds by needle trap sampling and direct thermal-desorption photoionization mass spectrometry: concept and demonstrative application to breath gas analysis.

    PubMed

    Kleeblatt, Juliane; Schubert, Jochen K; Zimmermann, Ralf

    2015-02-01

    A fast detection method to analyze gaseous organic compounds in complex gas mixtures was developed, using a needle trap device (NTD) in conjunction with thermal-desorption photoionization time-of-flight mass spectrometry (TD-PI-TOFMS). The mass spectrometer was coupled via a deactivated fused silica capillary to an injector of a gas chromatograph. In the hot injector, the analytes collected on the NTD were thermally desorbed and directly transferred to the PI-TOFMS ion source. The molecules are softly ionized either by single photon ionization (SPI, 118 nm) or by resonance enhanced multiphoton ionization (REMPI, 266 nm), and the molecular ion signals are detected in the TOF mass analyzer. Analyte desorption and the subsequent PI-TOFMS detection step only lasts ten seconds. The specific selectivity of REMPI (i.e., aromatic compounds) and universal ionization characteristics render PI-MS as a promising detection system. As a first demonstrative application, the alveolar phase breath gas of healthy, nonsmoking subjects was sampled on NTDs. While smaller organic compounds such as acetone, acetaldehyde, isoprene, or cysteamine can be detected in the breath gas with SPI, REMPI depicts the aromatic substances phenol and indole at 266 nm. In the breath gas of a healthy, smoking male subject, several xenobiotic substances such as benzene, toluene, styrene, and ethylbenzene can be found as well. Furthermore, the NTD-REMPI-TOFMS setup was tested for breath gas taken from a mechanically ventilated pig under continuous intravenous propofol (2,6-diisopropylphenol, narcotic drug) infusion. PMID:25517186

  15. Subwavelength Lattice Optics by Evolutionary Design

    PubMed Central

    2015-01-01

    This paper describes a new class of structured optical materials—lattice opto-materials—that can manipulate the flow of visible light into a wide range of three-dimensional profiles using evolutionary design principles. Lattice opto-materials are based on the discretization of a surface into a two-dimensional (2D) subwavelength lattice whose individual lattice sites can be controlled to achieve a programmed optical response. To access a desired optical property, we designed a lattice evolutionary algorithm that includes and optimizes contributions from every element in the lattice. Lattice opto-materials can exhibit simple properties, such as on- and off-axis focusing, and can also concentrate light into multiple, discrete spots. We expanded the unit cell shapes of the lattice to achieve distinct, polarization-dependent optical responses from the same 2D patterned substrate. Finally, these lattice opto-materials can also be combined into architectures that resemble a new type of compound flat lens. PMID:25380062

  16. Subwavelength lattice optics by evolutionary design.

    PubMed

    Huntington, Mark D; Lauhon, Lincoln J; Odom, Teri W

    2014-12-10

    This paper describes a new class of structured optical materials--lattice opto-materials--that can manipulate the flow of visible light into a wide range of three-dimensional profiles using evolutionary design principles. Lattice opto-materials are based on the discretization of a surface into a two-dimensional (2D) subwavelength lattice whose individual lattice sites can be controlled to achieve a programmed optical response. To access a desired optical property, we designed a lattice evolutionary algorithm that includes and optimizes contributions from every element in the lattice. Lattice opto-materials can exhibit simple properties, such as on- and off-axis focusing, and can also concentrate light into multiple, discrete spots. We expanded the unit cell shapes of the lattice to achieve distinct, polarization-dependent optical responses from the same 2D patterned substrate. Finally, these lattice opto-materials can also be combined into architectures that resemble a new type of compound flat lens. PMID:25380062

  17. Built-in-polarization field effect on lattice thermal conductivity of AlxGa1-xN/GaN heterostructure

    NASA Astrophysics Data System (ADS)

    Pansari, Anju; Gedam, Vikas; Kumar Sahoo, Bijaya

    2015-12-01

    The built-in-polarization field at the interface of AlxGa1-xN/GaN heterostructure enhances elastic constant, phonon velocity, Debye temperature and their bowing constants of barrier material AlxGa1-xN. The combined phonon relaxation time of acoustics phonons has been computed for with and without built-in-polarization field at room temperature for different aluminum (Al) content (x). Our result shows that the built-in-polarization field suppresses the scattering mechanisms and enhances the combined relaxation time. The thermal conductivity of AlxGa1-xN has been estimated as a function of temperature for x=0, 0.1, 0.5 and 1 for with and without polarization field. Minimum thermal conductivity has been observed for x=0.1 and 0.5. Analysis shows that up to a certain temperature (different for different x) the polarization field acts as negative effect and reduces the thermal conductivity and after this temperature thermal conductivity is significantly contributed by polarization field. This signifies pyroelectric character of AlxGa1-xN. The pyroelectric transition temperature of AlxGa1-xN alloy has been predicted for different x. Our study reports that room temperature thermal conductivity of AlxGa1-xN/GaN heterostructure is enhanced by built-in-polarization field. The temperature dependence of thermal conductivity for x=0.1 and 0.5 are in line with prior experimental studies. The method we have developed can be used for the simulation of heat transport in nitride devices to minimize the self heating processes and in polarization engineering strategies to optimize the thermoelectric performance of AlxGa1-xN/GaN heterostructures.

  18. Three interesting coordination compounds based on metalloligand and alkaline-earth ions: Syntheses, structures, thermal behaviors and magnetic property

    NASA Astrophysics Data System (ADS)

    Zhou, Qiang; Qian, Jun; Zhang, Chi

    2016-09-01

    Based on metalloligand LCu ([Cu(2,4-pydca)2]2-, 2,4-pydca2- = pyridine-2,4-dicarboxylate) and alkaline-earth ions (Ca2+, Sr2+, and Ba2+), three interesting coordination compounds, [Ca(H2O)7][LCu·H2O]·H2O (1), {Sr[LCu·H2O]·4H2O}n (2), and {Ba[LCu·H2O]·8H2O}n (3), have been synthesized and well-characterized by elemental analysis, infrared spectroscopy, thermogravimetric and single-crystal X-ray diffraction analysis. X-ray crystallographic studies reveal that 1 features a discrete 0D coordination compound, while 2 and 3 exhibit the 2D network and 1D chain structures, respectively. Compound 2 is constructed from {LCu}2 dimers connected with {Sr2} units, which is fabricated by two Sr2+ ions bridged via two μ2-O bridges, while compound 3 is formed by 1D {Ba}n chain linked with metalloligands LCu and exhibits an interesting sandwich like chain structure. It is noted that the coordination numbers of alkaline-earth ions are in positive correlation with their radiuses. Moreover, the magnetic property of compound 2 has been studied.

  19. Anomalous thermal expansion in the square-net compounds RE{sub 4}TGe{sub 8} (RE = Yb, Gd; T = Cr-Ni, Ag).

    SciTech Connect

    Peter, S. C.; Chondroudi, M.; Malliakas, C. D.; Balasubramanian, M.; Kanatzidis, M. G.

    2011-01-01

    The family of materials RE{sub 4}TGe{sub 8} (RE = Yb, Gd; T = transition metal) exhibits directional zero thermal expansion (ZTE) via a process that is associated with the linking of planar square nets in the third dimension. The Ge square nets in these compounds exhibit commensurate long-range modulations similar to those observed in charge-density-wave compounds. The ZTE is manifested in the plane of the square nets from 10 to 300 K with negligible volume expansion below {approx}160 K. The specific atomic arrangement in RE{sub 4}TGe{sub 8} enables a Poisson-like mechanism that allows the structure to contract along one direction as it expands only slightly in the perpendicular direction.

  20. Evaluation of an in-injection port thermal desorption-gas chromatography/mass spectrometry method for analysis of non-polar organic compounds in ambient aerosol samples.

    PubMed

    Ho, Steven Sai Hang; Yu, Jian Zhen; Chow, Judith C; Zielinska, Barbara; Watson, John G; Sit, Elber Hoi Leung; Schauer, James J

    2008-07-25

    Thermal desorption coupled with gas chromatography/mass spectrometry (TD-GC/MS) is an alternative to solvent extraction (SE)-based GC/MS (SE-GC/MS) for the analysis of non-polar organic compounds in filter or impactor-collected aerosols. TD-GC/MS has no sample pretreatment and requires a small filter aliquot for detecting individual organic compounds. The performance of an in-injection port TD-GC/MS is evaluated for polycyclic aromatic hydrocarbons (PAHs), n-alkanes, iso-/anteiso-alkanes, hopanes, steranes, branched alkanes, cyclohexanes, alkenes, and phthalates in standards and ambient air samples. Replicate analysis for 132 organic compounds showed relative standard deviations <10%, with the majority <5%. Accuracy for 15 PAHs, determined with NIST standard reference material (SRM) 1649a urban dust, was within +/-5% of the certified values. TD-GC/MS and SE-GC/MS method comparisons for 14 Hong Kong ambient samples agreed within 11% for 106 non-polar compounds. For 19 Tong Liang, China samples, agreement was within 13% for 23 PAHs. PMID:18556009

  1. Dibenzo[a,j]phenazine-Cored Donor-Acceptor-Donor Compounds as Green-to-Red/NIR Thermally Activated Delayed Fluorescence Organic Light Emitters.

    PubMed

    Data, Przemyslaw; Pander, Piotr; Okazaki, Masato; Takeda, Youhei; Minakata, Satoshi; Monkman, Andrew P

    2016-05-01

    A new family of thermally activated delayed fluorescence (TADF) emitters based on U-shaped D-A-D architecture with a novel accepting unit has been developed. All investigated compounds have small singlet-triplet energy splitting (ΔEST ) ranging from 0.02 to 0.20 eV and showed efficient TADF properties. The lowest triplet state of the acceptor unit plays the key role in the TADF mechanism. OLEDs fabricated with these TADF emitters achieved excellent efficiencies up to 16 % external quantum efficiency (EQE). PMID:27060474

  2. Thermal and Electric Properties of the FeAs2‑xSbx (x=0, 1, or 2) Marcasite Compounds from First Principles

    NASA Astrophysics Data System (ADS)

    Bang, Semi; Orabi, Rabih Al Rahal Al; Wee, Daehyun

    2016-04-01

    Thermoelectric energy conversion has been considered as one piece of the future solution to the energy crisis for a long time. In thermoelectric energy conversion, thermoelectric materials, which exhibit strong coupling between heat flow and electric current, are used to convert thermal energy into electrical energy and vice versa. Hence, thermoelectric devices can be potential and present applications for both thermoelectric generation and cooling system. There are significant demands for thermoelectric materials that can be used for environment-friendly cooling applications that need to be met. A few recent studies reported thermoelectric properties of the FeAs2‑xSbx (x=0, 1, or 2) marcasite compounds, which has a potential for becoming a good thermoelectric material for low-temperature cooling applications. The compound can be more environment-friendly and more economically viable than other competing materials, for the composition does not involve rare and expensive element like Te or Pt. In this study, we investigate thermoelectric properties of the FeAs2‑xSbx (x=0, 1, or 2) marcasite compounds by first-principles calculations in order to demonstrate the feasibility for the use in practical cooling applications. Electronic band structures and density of states are constructed from DFT (density functional theory) calculations, from which electrical properties, including the Seebeck coefficient and the electrical conductivity, are estimated. At the same time, vibrational characteristics are investigated through DFPT (density functional perturbation theory) calculations, from which the thermal conductivity is estimated using semiempirical formulae and the Grüneissen parameters of the compound obtained at the level of the QHA (quasi-harmonic approximation).

  3. Lattice vibrations in lead bromide and chloride

    NASA Astrophysics Data System (ADS)

    Carabatos-Nédelec, C.; Bréhat, F.; Wyncke, B.

    Lead bromide and lead chloride lattice dynamics studies by polarized IR reflectivity and Raman scattering are reported at room temperature and at 10 K. Reflectivity spectra from 20 to 300 cm -1 have been fitted with a model of the factorized form of the dielectric function. The lattice modes frequencies, damping factors and oscillators strengths are given, as well as the effective charges of the polar modes. The study concludes the ionic character of the compounds.

  4. Fabrication of glass-ceramics containing spin-chain compound SrCuO{sub 2} and its high thermal conductivity

    SciTech Connect

    Terakado, Nobuaki Watanabe, Kouki; Kawamata, Takayuki; Yokochi, Yuudai; Takahashi, Yoshihiro; Koike, Yoji; Fujiwara, Takumi

    2015-04-06

    High thermal conductivity materials are in great demand for heat-flow control and heat dissipation in electronic devices. In this study, we have produced a glass-ceramics that contains spin-chain compound SrCuO{sub 2} and have found that the glass-ceramics yields high thermal conductivity of ∼5 W K{sup −1} m{sup −1} even at room temperature. The glass-ceramics is fabricated through crystallization of inhomogeneous melt-quenched oxides made from SrCO{sub 3}, CuO, Li{sub 2}CO{sub 3}, Ga{sub 2}O{sub 3}, and Al{sub 2}O{sub 3}. Transmission electron microscopy and X-ray and electron diffraction reveal that SrCuO{sub 2} crystallites with a size of 100–200 nm are precipitated in the glass-ceramics. The highness of the thermal conductivity is attributable to two sources: one is elongation of phonon mean free path due to the crystallization of the inhomogeneous structure or structural ordering. The other is emergence of the heat carriers, spinons, in the SrCuO{sub 2}. This highly thermal conductive glass-ceramics is expected to be utilized as base materials for heat-flow control devices.

  5. Preparation and structure of BiCrTeO{sub 6}: A new compound in Bi–Cr–Te–O system. Thermal expansion studies of Cr{sub 2}TeO{sub 6}, Bi{sub 2}TeO{sub 6} and BiCrTeO{sub 6}

    SciTech Connect

    Vats, Bal Govind; Phatak, Rohan; Krishnan, K.; Kannan, S.

    2013-09-01

    Graphical abstract: A new compound BiCrTeO{sub 6} in the Bi–Cr–Te–O system was prepared by solid state route and characterized by X-ray diffraction method. The crystal structure of BiCrTeO{sub 6} shows that there is one distinct site for bismuth (Bi) atom (pink color), one chromium rich (Cr/Te = 68/32) (blue/green color), one tellurium rich (Te/Cr = 68/32) sites (green/blue color), and one distinct site for oxygen (O) atom (red color) in the unit cell. All cations in this structure show an octahedral coordination with oxygen atoms at the corners. The thermogram (TG) of the compound in air shows that it is stable up to 1103 K and decomposes thereafter. The thermal expansion behaviour of BiCrTeO{sub 6} was studied using high temperature X-ray diffraction method from room temperature to 923 K under vacuum of 10{sup −8} atmosphere and showed positive thermal expansion with the average volume thermal expansion coefficients of 16.0 × 10{sup −6}/K. - Highlights: • A new compound BiCrTeO{sub 6} in Bi–Cr–Te–O system was prepared and characterized. • The crystal structure of BiCrTeO{sub 6} was determined by Rietveld refinement method. • The structure of BiCrTeO{sub 6} shows an octahedral coordination for all the metal ions. • The thermal expansion behavior of BiCrTeO{sub 6} from room temperature to 923 K showed a positive thermal expansion. • The average volume thermal expansion coefficient for BiCrTeO{sub 6} is 16.0 × 10{sup −6}/K. - Abstract: A new compound BiCrTeO{sub 6} in Bi–Cr–Te–O system was prepared by solid state reaction of Bi{sub 2}O{sub 3}, Cr{sub 2}O{sub 3} and H{sub 6}TeO{sub 6} in oxygen and characterized by X-ray diffraction (XRD) method. It could be indexed on a trigonal lattice, with the space group P-31c, unit cell parameters a = 5.16268(7) Å and c = 9.91861(17) Å. The crystal structure of BiCrTeO{sub 6} was determined by Rietveld refinement method using the powder XRD data. Structure shows that there is one distinct

  6. Development of Design Technology on Thermal-Hydraulic Performance in Tight-Lattice Rod Bundles: III - Numerical Evaluation of Fluid Mixing Phenomena using Advanced Interface-Tracking Method -

    NASA Astrophysics Data System (ADS)

    Yoshida, Hiroyuki; Nagayoshi, Takuji; Takase, Kazuyuki; Akimoto, Hajime

    Thermal-hydraulic design of the current boiling water reactor (BWR) is performed by correlations with empirical results of actual-size tests. However, for the Innovative Water Reactor for Flexible Fuel Cycle (FLWR) core, an actual size test of an embodiment of its design is required to confirm or modify such correlations. Development of a method that enables the thermal-hydraulic design of nuclear reactors without these actual size tests is desired, because these tests take a long time and entail great cost. For this reason we developed an advanced thermal-hydraulic design method for FLWRs using innovative two-phase flow simulation technology. In this study, detailed Two-Phase Flow simulation code using advanced Interface Tracking method: TPFIT is developed to calculate the detailed information of the two-phase flow. We tried to verify the TPFIT code by comparing it with the 2-channel air-water and steam-water mixing experimental results. The predicted result agrees well the observed results and bubble dynamics through the gap and cross flow behavior could be effectively predicted by the TPFIT code, and pressure difference between fluid channels is responsible for the fluid mixing.

  7. Ultralow Thermal Conductivity in Full Heusler Semiconductors.

    PubMed

    He, Jiangang; Amsler, Maximilian; Xia, Yi; Naghavi, S Shahab; Hegde, Vinay I; Hao, Shiqiang; Goedecker, Stefan; Ozoliņš, Vidvuds; Wolverton, Chris

    2016-07-22

    Semiconducting half and, to a lesser extent, full Heusler compounds are promising thermoelectric materials due to their compelling electronic properties with large power factors. However, intrinsically high thermal conductivity resulting in a limited thermoelectric efficiency has so far impeded their widespread use in practical applications. Here, we report the computational discovery of a class of hitherto unknown stable semiconducting full Heusler compounds with ten valence electrons (X_{2}YZ, X=Ca, Sr, and Ba; Y=Au and Hg; Z=Sn, Pb, As, Sb, and Bi) through high-throughput ab initio screening. These new compounds exhibit ultralow lattice thermal conductivity κ_{L} close to the theoretical minimum due to strong anharmonic rattling of the heavy noble metals, while preserving high power factors, thus resulting in excellent phonon-glass electron-crystal materials. PMID:27494488

  8. Ultralow Thermal Conductivity in Full Heusler Semiconductors

    NASA Astrophysics Data System (ADS)

    He, Jiangang; Amsler, Maximilian; Xia, Yi; Naghavi, S. Shahab; Hegde, Vinay I.; Hao, Shiqiang; Goedecker, Stefan; OzoliĆš, Vidvuds; Wolverton, Chris

    2016-07-01

    Semiconducting half and, to a lesser extent, full Heusler compounds are promising thermoelectric materials due to their compelling electronic properties with large power factors. However, intrinsically high thermal conductivity resulting in a limited thermoelectric efficiency has so far impeded their widespread use in practical applications. Here, we report the computational discovery of a class of hitherto unknown stable semiconducting full Heusler compounds with ten valence electrons (X2Y Z , X =Ca , Sr, and Ba; Y =Au and Hg; Z =Sn , Pb, As, Sb, and Bi) through high-throughput ab initio screening. These new compounds exhibit ultralow lattice thermal conductivity κL close to the theoretical minimum due to strong anharmonic rattling of the heavy noble metals, while preserving high power factors, thus resulting in excellent phonon-glass electron-crystal materials.

  9. Determination of a wide range of volatile organic compounds in ambient air using multisorbent adsorption/thermal desorption and gas chromatography/mass spectrometry

    USGS Publications Warehouse

    Pankow, J.F.; Luo, W.; Isabelle, L.M.; Bender, D.A.; Baker, R.J.

    1998-01-01

    Adsorption/thermal desorption with multisorbent air-sampling cartridges was developed for the determination of 87 method analytes including halogenated alkanes, halogenated alkenes, ethers, alcohols, nitriles, esters, ketones, aromatics, a disulfide, and a furan. The volatilities of the compounds ranged from that of dichlorofluoromethane (CFC12) to that of 1,2,3- trichlorobenzene. The eight most volatile compounds were determined using a 1.5-L air sample and a sample cartridge containing 50 mg of Carbotrap B and 280 mg of Carboxen 1000; the remaining 79 compounds were determined using a 5-L air sample and a cartridge containing 180 mg of Carbotrap B and 70 mg of Carboxen 1000. Analysis and detection were by gas chromatography/mass spectrometry. The minimum detectable level (MDL) concentration values ranged from 0.01 parts per billion by volume (ppbv) for chlorobenzene to 0.4 ppbv for bromomethane; most of the MDL values were in the range 0.02-0.06 ppbv. No breakthrough was detected with the prescribed sample volumes. Analyte stability on the cartridges was very good. Excellent recoveries were obtained with independent check standards. Travel spike recoveries ranged from 90 to 110% for 72 of the 87 compounds. The recoveries were less than 70% for bromomethane and chloroethene and for a few compounds such as methyl acetate that are subject to losses by hydrolysis; the lowest travel spike recovery was obtained for bromomethane (62%). Blank values for all compounds were either below detection or very low. Ambient atmospheric sampling was conducted in New Jersey from April to December, 1997. Three sites characterized by low, moderate, and high densities of urbanization/traffic were sampled. The median detected concentrations of the compounds were either similar at all three sites (as with the chlorofluorocarbon compounds) or increased with the density of urbanization/traffic (as with dichloromethane, MTBE, benzene, and toluene). For toluene, the median detected

  10. Thermometry via Light Shifts in Optical Lattices

    NASA Astrophysics Data System (ADS)

    McDonald, M.; McGuyer, B. H.; Iwata, G. Z.; Zelevinsky, T.

    2015-01-01

    For atoms or molecules in optical lattices, conventional thermometry methods are often unsuitable due to low particle numbers or a lack of cycling transitions. However, a differential spectroscopic light shift can map temperature onto the line shape with a low sensitivity to trap anharmonicity. We study narrow molecular transitions to demonstrate precise frequency-based lattice thermometry, as well as carrier cooling. This approach should be applicable down to nanokelvin temperatures. We also discuss how the thermal light shift can affect the accuracy of optical lattice clocks.

  11. Thermoelectric materials ternary penta telluride and selenide compounds

    DOEpatents

    Sharp, Jeffrey W.

    2001-01-01

    Ternary tellurium compounds and ternary selenium compounds may be used in fabricating thermoelectric devices with a thermoelectric figure of merit (ZT) of 1.5 or greater. Examples of such compounds include Tl.sub.2 SnTe.sub.5, Tl.sub.2 GeTe.sub.5, K.sub.2 SnTe.sub.5 and Rb.sub.2 SnTe.sub.5. These compounds have similar types of crystal lattice structures which include a first substructure with a (Sn, Ge) Te.sub.5 composition and a second substructure with chains of selected cation atoms. The second substructure includes selected cation atoms which interact with selected anion atoms to maintain a desired separation between the chains of the first substructure. The cation atoms which maintain the desired separation between the chains occupy relatively large electropositive sites in the resulting crystal lattice structure which results in a relatively low value for the lattice component of thermal conductivity (.kappa..sub.g). The first substructure of anion chains indicates significant anisotropy in the thermoelectric characteristics of the resulting semiconductor materials.

  12. Thermoelectric materials: ternary penta telluride and selenide compounds

    DOEpatents

    Sharp, Jeffrey W.

    2002-06-04

    Ternary tellurium compounds and ternary selenium compounds may be used in fabricating thermoelectric devices with a thermoelectric figure of merit (ZT) of 1.5 or greater. Examples of such compounds include Tl.sub.2 SnTe.sub.5, Tl.sub.2 GeTe.sub.5, K.sub.2 SnTe.sub.5 and Rb.sub.2 SnTe.sub.5. These compounds have similar types of crystal lattice structures which include a first substructure with a (Sn, Ge) Te.sub.5 composition and a second substructure with chains of selected cation atoms. The second substructure includes selected cation atoms which interact with selected anion atoms to maintain a desired separation between the chains of the first substructure. The cation atoms which maintain the desired separation between the chains occupy relatively large electropositive sites in the resulting crystal lattice structure which results in a relatively low value for the lattice component of thermal conductivity (.kappa..sub.g). The first substructure of anion chains indicates significant anisotropy in the thermoelectric characteristics of the resulting semiconductor materials.

  13. Polybenzimidazole compounds

    DOEpatents

    Klaehn, John R.; Peterson, Eric S.; Wertsching, Alan K.; Orme, Christopher J.; Luther, Thomas A.; Jones, Michael G.

    2010-08-10

    A PBI compound that includes imidazole nitrogens, at least a portion of which are substituted with an organic-inorganic hybrid moiety. At least 85% of the imidazole nitrogens may be substituted. The organic-inorganic hybrid moiety may be an organosilane moiety, for example, (R)Me.sub.2SiCH.sub.2--, where R is selected from among methyl, phenyl, vinyl, and allyl. The PBI compound may exhibit similar thermal properties in comparison to the unsubstituted PBI. The PBI compound may exhibit a solubility in an organic solvent greater than the solubility of the unsubstituted PBI. The PBI compound may be included in separatory media. A substituted PBI synthesis method may include providing a parent PBI in a less than 5 wt % solvent solution. Substituting may occur at about room temperature and/or at about atmospheric pressure. Substituting may use at least five equivalents in relation to the imidazole nitrogens to be substituted or, preferably, about fifteen equivalents.

  14. Thermal conductivity studies of a polyurea cross-linked silica aerogel-RTV 655 compound for cryogenic propellant tank applications in space

    NASA Astrophysics Data System (ADS)

    Sabri, F.; Marchetta, J.; Smith, K. M.

    2013-10-01

    Silica-based aerogel is an ideal thermal insulator with a makeup of up to 99% air associated with the highly porous nature of this material. Polyurea cross-linked silica aerogel (PCSA) has superior mechanical properties compared to the native aerogels yet retains the highly porous open pore network and functions as an ideal thermal insulator with added load-bearing capability necessary for some applications. Room temperature vulcanizing rubber-RTV 655—is a space qualified elastomeric thermal insulator and encapsulant with high radiation and temperature tolerance as well as chemical resistance. Storage and transport of cryogenic propellant liquids is an integral part of the success of future space exploratory missions and is an area under constant development. Limitations and shortcomings of current cryogenic tank materials and insulation techniques such as non-uniform insulation layers, self-pressurization, weight and durability issues of the materials used, has motivated the quest for alternative materials. Both RTV 655 and PCSA are promising space qualified materials with unique and tunable microscopic and macroscopic properties making them attractive candidates for this study. In this work, the effect of PCSA geometry and volume concentration on the thermal behavior of RTV 655—PCSA compound material has been investigated at room temperature and at a cryogenic temperature. Macroscopic and microscopic PCSA material was encapsulated at increasing concentrations in an RTV 655 elastomeric matrix. The effect of pulverization on the nanopores of PCSA as a method for creating large quantities of homogeneous PCSA microparticles has also been investigated and is reported. The PCSA volume concentrations ranged between 22% and 75% for both geometries. Thermal conductivity measurements were performed based on the steady state transient plane source method.

  15. Some new nano-structure zinc(II) coordination compounds of an imidazolidine Schiff base: Spectral, thermal, antimicrobial properties and DNA interaction

    NASA Astrophysics Data System (ADS)

    Montazerozohori, Morteza; Musavi, Sayed Alireza; Naghiha, Asghar; Zohour, Mostafa Montazer

    2014-08-01

    Some novel nano-sized structure zinc complexes of a new Schiff base ligand entitled as (3-nitro-benzylidene)-{2-[2-(3-nitro-phenyl)-imidazolidine-1-yl]-ethyl}-amine(L) with general formula of ZnLX2 wherein X = Cl-, Br-, I-, SCN- and N3- have been synthesized under ultrasonic conditions. The ligand and its complexes have been characterized by elemental analysis, molar conductance measurements, FT-IR, 1H and 13C NMR and UV-Visible spectroscopy. The resulting data from spectral investigation especially 1H and 13C NMR well confirmed formation of an imidazolidine ring in the ligand structure. Transmission electron microscopy (TEM) showed nano-size structures with average particle sizes of 21.80-78.10 nm for the zinc(II) Schiff base complexes. The free Schiff base and its Zn(II) complexes have been screened in vitro both for antibacterial activity against some gram-positive and gram-negative bacteria and also for antifungal activity. The metal complexes were found to be more active than the free Schiff base ligand. The results showed that ZnL(N3)2 is the most effective inhibitor against Escherichia coli, Pseudomonas aereuguinosa, Staphylococcus aureus and Candida albicans while ZnLBr2 was found to be more effective against Bacillus subtillis than other compounds. Moreover, DNA cleavage potential of all compounds with plasmid DNA was investigated. The results showed that the ligand and ZnLCl2 complex cleave DNA more efficiently than others. In final, thermal analysis of ligand and its complexes revealed that they are decomposed via 2-3 thermal steps in the range of room temperature to 1000 °C. Furthermore some activation kinetic parameters such as A, E*, ΔH*, ΔS* and ΔG* were calculated based on TG/DTA plots by use of coats - Redfern relation. Positive values of activation energy evaluated for the compounds confirmed the thermal stability of them. In addition to, the positive ΔH*, and ΔG* values suggested endothermic character for the thermal decomposition steps.

  16. Phonon scattering due to van der Waals forces in the lattice thermal conductivity of Bi{sub 2}Te{sub 3} thin films

    SciTech Connect

    Park, Kyeong Hyun Mohamed, Mohamed; Ravaioli, Umberto; Aksamija, Zlatan

    2015-01-07

    In this work, we calculate the thermal conductivity of layered bismuth telluride (Bi{sub 2}Te{sub 3}) thin films by solving the Boltzmann transport equation in the relaxation-time approximation using full phonon dispersion and compare our results with recently published experimental data and molecular dynamics simulation. The group velocity of each phonon mode is readily extracted from the full phonon dispersion obtained from first-principle density-functional theory calculation and is used along with the phonon frequency to compute the various scattering terms. Our model incorporates the typical interactions impeding thermal transport (e.g., umklapp, isotope, and boundary scatterings) and introduces a new interaction capturing the reduction of phonon transmission through van der Waals interfaces of adjacent Bi{sub 2}Te{sub 3} quintuple layers forming the virtual superlattice thin film. We find that this novel approach extends the empirical Klemens-Callaway relaxation model in such anisotropic materials and recovers the experimental anisotropy while using a minimal set of parameters.

  17. Simple theories of complex lattices

    NASA Astrophysics Data System (ADS)

    Peyrard, Michel

    1998-11-01

    While the theory of solitons has been very successful for continuous systems, very few nonlinear discrete lattices are amenable to an exact analytical treatment. In these “complex lattices” discreteness can be hostile to the solitons, preventing them to move due to the lack of translational invariance or even to exist as localized excitations. On the other hand, lattice discreteness can sometimes be very helpful. It can stabilize solutions that otherwise would split apart as in the discrete sine-Gordon lattice, or even allow the existence of localized oscillatory modes as exact solutions in systems where they would decay in the continuum limit. It is interesting that many of these phenomena can be understood qualitatively, and sometimes quantitatively, with very simple theories that rely on the usual concepts of linear wave propagation, resonances, linear stability of waves, for instance. There are, however, phenomena specific to discrete nonlinear lattices which allow the build up of large amplitude localized excitations, sometimes out of thermal fluctuations, which are more resistant to simple approaches and could deserve further interest because they may be relevant for various physical systems.

  18. Measurement of the stable carbon isotope ratio of atmospheric volatile organic compounds using chromatography, combustion, and isotope ratio mass spectrometry coupled with thermal desorption

    NASA Astrophysics Data System (ADS)

    Kawashima, Hiroto; Murakami, Mai

    2014-06-01

    The isotopic analysis of atmospheric volatile organic compounds (VOCs), and in particular of their stable carbon isotope ratio (δ13C), could potentially be used as an effective tool for identifying the sources of VOCs. However, to date, there have been very few such analyses. In this work, we analyze the δ13C values of VOCs using thermal desorption coupled with chromatography, combustion, and isotope ratio mass spectrometry (TD-GC/C/IRMS). The measured peak shapes were of high quality and 36 compounds in a standard gas containing 58 VOCs (C5-C11) were detected. The measured δ13C varied widely, from -49.7‰ to -22.9‰, while the standard deviation of the δ13C values varied from 0.07‰ to 0.85‰ (n = 5). We then measured samples from two passenger cars in hot and cold modes, three gas stations, roadside air, and ambient air. In comparison with existing studies, the analytical precision for the 36 compounds in this study was reasonable. By comparing the δ13C values obtained from the cars and gas stations, we could identify some degree of the sources of VOCs in the roadside and ambient air samples.

  19. Use of thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) on identification of odorant emission focus by volatile organic compounds characterisation.

    PubMed

    Rodríguez-Navas, Carlos; Forteza, Rafael; Cerdà, Víctor

    2012-11-01

    Volatile organic compounds (VOCs) from several different municipal solid wastes' treatment plants in Mallorca (Spain) have been analysed by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). Ambient (immission) air was collected during February and March 2011 by active sampling onto sorbents Tenax™ TA and Carboxen™ 1000. The study presents the chemical characterisation of 93 volatile organic compounds (VOCs) from an overall set of 84 immission air samples. 70 VOCs were positively identified. The linear fit for all 93 external standard calibration, from 10 mg L(-1) to 150 mg L(-1) (n=4), was within the range 0.974compounds (RSCs) and municipal solid wastes show contribution of a wide sort of VOCs. The use of a chemometric approach for variable's reduction to 12 principal components enables evaluation of similarities and dissimilarities between facilities. PCA clearly related samples to its corresponding facility on the basis of their VOCs composition and the ambient temperature. PMID:22776256

  20. Determination of off-flavor compounds, 2-methylisoborneol and geosmin, in salmon fillets using stir bar sorptive extraction-thermal desorption coupled with gas chromatography-mass spectrometry.

    PubMed

    Ruan, E D; Aalhus, J L; Summerfelt, S T; Davidson, J; Swift, B; Juárez, M

    2013-12-20

    A sensitive and solvent-less method for the determination of musty and earthy off-flavor compounds, 2-methylisoborneol (MIB) and geosmin (GSM), in salmon tissue was developed using stir bar sorptive extraction-thermal desorption coupled with gas chromatography-mass spectrometry (SBSE-TD-GCMS). MIB and GSM were solid phase extracted using polydimethylsiloxane (PDMS) coated stir bars, analyzed by gas chromatography, and detected in full scan mode of mass selective detector (MSD). Using this method, the calibration curves of MIB and GSM were linear in the range of 0.3-100ng/L, with a correlation coefficient above 0.999 and RSDs less than 4% (n=4). The limit of detection (LOD, S/N=3, n=6) and limit of quantification (LOQ, S/N=10, n=6) of MIB and GSM were both ∼0.3 and 1ng/L, respectively. The recoveries of MIB and GSM were 22% and 29% by spike in 30ng/L standard compounds, 23% and 30% by spike-in 100ng/L standard compounds in salmon tissue samples with good precision (<8% of RSDs, n=6), respectively. The recoveries of MIB and GSM were better than reported methodologies using SPME fibres (<10%) in fish tissue samples. This method was successfully applied to monitor and characterize depurated salmon fillet samples (0, 3, 6 and 10 days). PMID:24252650

  1. Synthesis, crystal structure, thermal analysis and dielectric properties of [(C4H9)4N]3Bi2Cl9 compound

    NASA Astrophysics Data System (ADS)

    Trigui, W.; Oueslati, A.; Chaabane, I.; Hlel, F.

    2015-07-01

    A new organic-inorganic tri-tetrabutylammonium nonachlorobibismuthate(III) compound was prepared. It was found to crystallize in the monoclinic system (P21/n space group) with the following lattice parameters: a=11.32(2) Å, b=22.30(3) Å, c=28.53(2) Å and β=96.52(0)°. The [Bi2Cl9]3- anions are surrounded by six [(C4H9)N]+ cations, forming an octahedral configuration. These octahedra are sharing corners in order to provide the tri-dimensional network cohesion. The differential scanning calorimetry reveals four order-disorder reversible phase transitions located at 214, 238, 434 and 477 K. The Raman and infrared spectra confirm the presence of both cationic [(C4H9)N]+ and anionic [Bi2Cl9]3- parts. The dielectric parameters, real and imaginary dielectric permittivity (ε‧ and ε″), and dielectric loss tangent (tg δ), were measured in the frequency range of 209 kHz-5 MHz at different temperatures. The variations of dielectric dispersion (ε') and dielectric absorption (ε″) with frequency show a distribution of relaxation times, which is probably related to the change in the dynamical state of the [(C4H9)4N]+ cations and the [Bi2Cl9]3- anions.

  2. Exotic damping ring lattices

    SciTech Connect

    Palmer, R.B.

    1987-05-01

    This paper looks at, and compares three types of damping ring lattices: conventional, wiggler lattice with finite ..cap alpha.., wiggler lattice with ..cap alpha.. = 0, and observes the attainable equilibrium emittances for the three cases assuming a constraint on the attainable longitudinal impedance of 0.2 ohms. The emittance obtained are roughly in the ratio 4:2:1 for these cases.

  3. Population-imbalanced lattice fermions near the BCS-BEC crossover: Thermal physics of the breached pair and Fulde-Ferrell-Larkin-Ovchinnikov phases

    NASA Astrophysics Data System (ADS)

    Karmakar, Madhuparna; Majumdar, Pinaki

    2016-05-01

    We study s -wave superconductivity in the two-dimensional attractive Hubbard model in an applied magnetic field, assume the extreme Pauli limit, and examine the role of spatial fluctuations in the coupling regime corresponding to BCS-BEC crossover. We use a decomposition of the interaction in terms of an auxiliary pairing field, retain the static mode, and sample the pairing field via a Monte Carlo approach. The method requires iterative solution of the Bogoliubov-de-Gennes equations for amplitude- and phase-fluctuating configurations of the pairing field. We establish the full thermal phase diagram of this strong-coupling problem. At low field we observe the magnetized but homogeneous "breached pair" superfluid phase. It reveals that Tc scales an order of magnitude below the mean-field estimate, spontaneous inhomogeneity in the field-induced magnetization, and a strong nonmonotonicity in the temperature dependence of the low-energy density of states. We compare our results to the experimental phase diagram of the imbalanced Fermi gas at unitarity. At higher field we obtain the modulated Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases. The thermal transition from the FFLO phases to the normal state is strongly first order. We track the fermionic momentum distribution, the density of states, and the pairing structure factor deep into the normal state. The pairing structure factor retains weak signature of finite momentum pairing to a high temperature despite the low Tc itself, while the spin-resolved density of states changes from the "pseudogapped" FFLO character to gapless and pseudogapped again with increasing temperature.

  4. Characterization of Key Aroma Compounds in Raw and Thermally Processed Prawns and Thermally Processed Lobsters by Application of Aroma Extract Dilution Analysis.

    PubMed

    Mall, Veronika; Schieberle, Peter

    2016-08-24

    Application of aroma extract dilution analysis (AEDA) to an aroma distillate of blanched prawn meat (Litopenaeus vannamei) (BPM) revealed 40 odorants in the flavor dilution (FD) factor range from 4 to 1024. The highest FD factors were assigned to 2-acetyl-1-pyrroline, 3-(methylthio)propanal, (Z)-1,5-octadien-3-one, trans-4,5-epoxy-(E)-2-decenal, (E)-3-heptenoic acid, and 2-aminoacetophenone. To understand the influence of different processing conditions on odorant formation, fried prawn meat was investigated by means of AEDA in the same way, revealing 31 odorants with FD factors between 4 and 2048. Also, the highest FD factors were determined for 2-acetyl-1-pyrroline, 3-(methylthio)propanal, and (Z)-1,5-octadien-3-one, followed by 4-hydroxy-2,5-dimethyl-3(2H)-furanone, (E)-3-heptenoic acid, and 2-aminoacetophenone. As a source of the typical marine, sea breeze-like odor attribute of the seafood, 2,4,6-tribromoanisole was identified in raw prawn meat as one of the contributors. Additionally, the aroma of blanched prawn meat was compared to that of blanched Norway and American lobster meat, respectively (Nephrops norvegicus and Homarus americanus). Identification experiments revealed the same set of odorants, however, with differing FD factors. In particular, 3-hydroxy-4,5-dimethyl-2(5H)-furanone was found as the key aroma compound in blanched Norway lobster, whereas American lobster contained 3-methylindole with a high FD factor. PMID:27486834

  5. Growth mechanism and properties of the thermal and anodic oxides of the 3-5 compound semiconductors

    NASA Astrophysics Data System (ADS)

    Wilmsen, C. W.

    1985-03-01

    The mechanisms of oxide growth on InP, GaP, GaAs, and InGaAs were investigated and their electrical properties measured. Islands were observed as the initial stage of anodization of InP and GaAs, but the details of the growth on the two materials are different. The thermal oxides of InP and GaP also differ in composition and surface topography. InP forms bubbles and GaP has pits under the oxide. Traps at the deposited insulator/InP interface were also investigated.

  6. Characterization of nitrogen-bridged 1,2,4,5-tetrazine-, furazan-, and 1H-tetrazole-based polyheterocyclic compounds: heats of formation, thermal stability, and detonation properties.

    PubMed

    Wei, Tao; Wu, Jianzhang; Zhu, Weihua; Zhang, Chenchen; Xiao, Heming

    2012-08-01

    The heats of formation (HOFs), thermal stability, and detonation properties for a series of nitrogen-bridged 1,2,4,5-tetrazine-, furazan-, and 1H-tetrazole-based polyheterocyclic compounds (3,6-bis(1H-1,2,3,4-tetrazole-5-ylamino)-1,2,4,5- tetrazine (TST), 3,6-bis(furazan-5-ylamino)-1,2,4,5-tetrazine (FSF), 3,4-bis(1,2,4,5- tetrazine-3-ylamino)-furazan (SFS), 3,4-bis(1H-1,2,3,4-tetrazole-5-ylamino)-furazan (TFT), 1,5-bis(1,2,4,5-tetrazine-3-ylamino)-1H-1,2,3,4-tetrazole (STS), and 1,5-bis(furazan-3-ylamino)-1H-1,2,3,4-tetrazole (FTF) derivatives) were systematically studied by using density functional theory. The results show that the -N(3) or -NHNH(2) group plays a very important role in increasing the HOF values of the derivatives. Among these series, the SFS derivatives have lower energy gaps, while the TFT derivatives have higher ones. Incorporation of the -NH(2) group into the FSF, SFS, STS, or FTF ring is favorable for enhancing its thermal stability, whereas the substitution of the -NHNH(2) group could increase the thermal stability of the TST, SFS, STS, or FTF ring. The calculated detonation properties indicate that the -NO(2) or -NF(2) is very helpful for enhancing the detonation performance for these derivatives. Considering the detonation performance and thermal stability, six derivatives may be regarded as promising candidates of high-energy density materials (HEDMs). These results provide basic information for the molecular design of novel HEDMs. PMID:22281812

  7. Multigroup Reactor Lattice Cell Calculation

    Energy Science and Technology Software Center (ESTSC)

    1990-03-01

    The Winfrith Improved Multigroup Scheme (WIMS), is a general code for reactor lattice cell calculations on a wide range of reactor systems. In particular, the code will accept rod or plate fuel geometries in either regular arrays or in clusters, and the energy group structure has been chosen primarily for thermal calculations. The basic library has been compiled with 14 fast groups, 13 resonance groups and 42 thermal groups, but the user is offered themore » choice of accurate solutions in many groups or rapid calculations in few groups. Temperature dependent thermal scattering matrices for a variety of scattering laws are available in the library for the principal moderators which include hydrogen, deuterium, graphite, beryllium and oxygen. WIMSD5 is a succesor version of WIMS-D/4.« less

  8. Orbital optical lattices with bosons

    NASA Astrophysics Data System (ADS)

    Kock, T.; Hippler, C.; Ewerbeck, A.; Hemmerich, A.

    2016-02-01

    This article provides a synopsis of our recent experimental work exploring Bose-Einstein condensation in metastable higher Bloch bands of optical lattices. Bipartite lattice geometries have allowed us to implement appropriate band structures, which meet three basic requirements: the existence of metastable excited states sufficiently protected from collisional band relaxation, a mechanism to excite the atoms initially prepared in the lowest band with moderate entropy increase, and the possibility of cross-dimensional tunneling dynamics, necessary to establish coherence along all lattice axes. A variety of bands can be selectively populated and a subsequent thermalization process leads to the formation of a condensate in the lowest energy state of the chosen band. As examples the 2nd, 4th and 7th bands in a bipartite square lattice are discussed. The geometry of the 2nd and 7th bands can be tuned such that two inequivalent energetically degenerate energy minima arise at the X ±-points at the edge of the 1st Brillouin zone. In this case even a small interaction energy is sufficient to lock the phase between the two condensation points such that a complex-valued chiral superfluid order parameter can emerge, which breaks time reversal symmetry. In the 4th band a condensate can be formed at the Γ-point in the center of the 1st Brillouin zone, which can be used to explore topologically protected band touching points. The new techniques to access orbital degrees of freedom in higher bands greatly extend the class of many-body scenarios that can be explored with bosons in optical lattices.

  9. Towards a predictive route for selection of doping elements for the thermoelectric compound PbTe from first-principles

    NASA Astrophysics Data System (ADS)

    Joseph, Elad; Amouyal, Yaron

    2015-05-01

    Striving for improvements of the thermoelectric (TE) properties of the technologically important lead telluride (PbTe) compound, we investigate the influence of different doping elements on the thermal conductivity, Seebeck coefficient, and electrical conductivity applying density functional theory calculations. Our approach combines total-energy calculations yielding lattice vibrational properties with the Boltzmann transport theory to obtain electronic transport properties. We find that doping with elements from the 1st and 3rd columns of the periodic table reduces the sound velocity and, consequently, the lattice thermal conductivity, while 2nd column dopants have no such influence. Furthermore, 1.6 at. % doping with 4th and 5th column elements provides the highest reduction of lattice thermal conductivity. Out of this group, Hf doping results in maximum reduction of the sound velocity from 2030 m s-1 for pure PbTe to 1370 m s-1, which is equivalent to ca. 32% reduction of lattice thermal conductivity. The highest power factor values calculated for 1.6 at. % doping range between 40 and 56 μW cm-1 K-2, and are obtained for substitution with dopants having the same valence as Pb or Te, such as those located at the 2nd, 14th, and 16th columns of the periodic table. We demonstrate how this method may be generalized for dopant-selection-oriented materials design aimed at improving TE performance of other compounds.

  10. Thermally-induced single-crystal-to-single-crystal transformations from a 2D two-fold interpenetrating square lattice layer to a 3D four-fold interpenetrating diamond framework and its application in dye-sensitized solar cells.

    PubMed

    Gao, Song; Fan, Rui Qing; Wang, Xin Ming; Wei, Li Guo; Song, Yang; Du, Xi; Xing, Kai; Wang, Ping; Yang, Yu Lin

    2016-07-28

    In this work, a rare 2D → 3D single-crystal-to-single-crystal transformation (SCSC) is observed in metal-organic coordination complexes, which is triggered by thermal treatment. The 2D two-fold interpenetrating square lattice layer [Cd(IBA)2]n (1) is irreversibly converted into a 3D four-fold interpenetrating diamond framework {[Cd(IBA)2(H2O)]·2.5H2O}n (2) (HIBA = 4-(1H-imidazol-1-yl)benzoic acid). Consideration is given to these two complexes with different interpenetrating structures and dimensionality, and their influence on photovoltaic properties are studied. Encouraged by the UV-visible absorption and HOMO-LUMO energy states matched for sensitizing TiO2, the two complexes are employed in combination with N719 in dye-sensitized solar cells (DSSCs) to compensate absorption in the ultraviolet and blue-violet region, offset competitive visible light absorption of I3(-) and reducing charge the recombination of injected electrons. After co-sensitization with 1 and 2, the device co-sensitized by 1/N719 and 2/N719 to yield overall efficiencies of 7.82% and 8.39%, which are 19.94% and 28.68% higher than that of the device sensitized only by N719 (6.52%). Consequently, high dimensional interpenetrating complexes could serve as excellent co-sensitizers and have application in DSSCs. PMID:27356177

  11. Speciation of inorganic and organometallic compounds in solid biological samples by thermal vaporization and plasma emission spectrometry

    SciTech Connect

    Hanamura, S.; Smith, B.W.; Winefordner, J.D.

    1983-11-01

    By means of thermal vaporization, inorganic, organic, and metallorganic species are separated and elemental emission in a microwave plasma is detected as a function of vaporization temperature. Solid samples of 250 mg or more are used to avoid problems with sample heterogeneity. The precision of characteristic appearance temperatures is +/-2/sup 0/C. The single electrode atmosphere pressure microwave plasma system is extremely tolerant to the introduction of water, organic solvents, and air. The measurement system contained a repetition wavelength scan device to allow background correction. The plasma temperature was 5500 K. The system was used to measure C, H, N, O, and Hg in orchard leaves and in tuna fish. 9 figures, 5 tables.

  12. Impact of high pressure and pulsed electric fields on bioactive compounds and antioxidant activity of orange juice in comparison with traditional thermal processing.

    PubMed

    Sánchez-Moreno, Concepción; Plaza, Lucía; Elez-Martínez, Pedro; De Ancos, Begoña; Martín-Belloso, Olga; Cano, M Pilar

    2005-06-01

    Bioactive compounds (vitamin C, carotenoids, and flavanones) and DPPH* radical scavenging capacity (RSC) were measured in orange juice (OJ) subjected to different technologies. High pressure (HP) (400 MPa/40 degrees C/1 min), pulsed electric fields (PEF) (35 kVcm(-1)/750 micros), low pasteurization (LPT) (70 degrees C/30 s), high pasteurization (HPT) (90 degrees C/1 min), HPT plus freezing (HPT+F) (-38 degrees C/15 min), and freezing (F) were studied. Among the treatments assayed, even though the losses in total vitamin C were < 9%, treatments with the higher temperatures tended to show the higher decrease in the content of both forms of vitamin C. HP treatment led to an increased (P < 0.05) carotenoid release (53.88%) and vitamin A value (38.74%). PEF treatment did not modify individual or total carotenoids content. Traditional thermal treatments did not exert any effect on total carotenoid content or vitamin A value. With regard to individual carotenoid extraction, HPT and HPT+F led to different releases of carotenoids. With respect to flavanones, HP treatment led to increased (P < 0.05) naringenin (20.16%) and hesperetin (39.88%) contents, whereas PEF treatment did not modify flavanone content. In general, pasteurization and freezing process led to a diminished (P < 0.05) naringenin content (16.04%), with no modification in hesperetin. HP and PEF treatments did not modify DPPH* RSC. In the case of traditional thermal technologies, HPT treatment showed a decrease (P < 0.05) in RSC (6.56%), whereas LPT, HPT+F, and F treatments did not modify RSC. Vitamin C modulated RSC, in terms of antioxidant concentration (EC50) and kinetics (AE = 1/EC50TEC50), in the treated and untreated OJ. In summary, HP and PEF technologies were more effective than HPT treatment in preserving bioactive compounds and RSC of freshly squeezed orange juice. PMID:15913302

  13. Synthesis, structure, and thermally stable luminescence of Eu(2+)-doped Ba2Ln(BO3)2Cl (Ln = Y, Gd and Lu) host compounds.

    PubMed

    Xia, Zhiguo; Wang, Xiaoming; Wang, Yingxia; Liao, Libing; Jing, Xiping

    2011-10-17

    A new family of chloroborate compounds, which was investigated from the viewpoint of rare earth ion activated phosphor materials, have been synthesized by a conventional high temperature solid-state reaction. The crystal structure and thermally stable luminescence of chloroborate phosphors Ba(2)Ln(BO(3))(2)Cl:Eu(2+) (Ln = Y, Gd, and Lu) have been reported in this paper. X-ray diffraction studies verify the successful isomorphic substitution for Ln(3+) sites in Ba(2)Ln(BO(3))(2)Cl by other smaller trivalent rare earth ions, such as Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb. The detailed structure information for Ba(2)Ln(BO(3))(2)Cl (Ln = Y, Gd, and Lu) by Rietveld analysis reveals that they all crystallize in a monoclinic P2(1)/m space group. These compounds display interesting and tunable photoluminescence (PL) properties after Eu(2+)-doping. Ba(2)Ln(BO(3))(2)Cl:Eu(2+) phosphors exhibit bluish-green/greenish-yellow light with peak wavelengths at 526, 548, and 511 nm under 365 UV light excitation for Ba(2)Y(BO(3))(2)Cl:Eu(2+), Ba(2)Gd(BO(3))(2)Cl:Eu(2+), and Ba(2)Lu(BO(3))(2)Cl:Eu(2+), respectively. Furthermore, they possess a high thermal quenching temperature. With the increase of temperature, the emission bands show blue shifts with broadening bandwidths and slightly decreasing emission intensities. It is expected that this series of chloroborate phosphors can be used in white-light UV-LEDs as a good wavelength-conversion phosphor. PMID:21919480

  14. Antioxidant Activity and Thermal Stability of Oleuropein and Related Phenolic Compounds of Olive Leaf Extract after Separation and Concentration by Salting-Out-Assisted Cloud Point Extraction

    PubMed Central

    Stamatopoulos, Konstantinos; Katsoyannos, Evangelos; Chatzilazarou, Arhontoula

    2014-01-01

    A fast, clean, energy-saving, non-toxic method for the stabilization of the antioxidant activity and the improvement of the thermal stability of oleuropein and related phenolic compounds separated from olive leaf extract via salting-out-assisted cloud point extraction (CPE) was developed using Tween 80. The process was based on the decrease of the solubility of polyphenols and the lowering of the cloud point temperature of Tween 80 due to the presence of elevated amounts of sulfates (salting-out) and the separation from the bulk solution with centrifugation. The optimum conditions were chosen based on polyphenols recovery (%), phase volume ratio (Vs/Vw) and concentration factor (Fc). The maximum recovery of polyphenols was in total 95.9%; Vs/Vw was 0.075 and Fc was 15 at the following conditions: pH 2.6, ambient temperature (25 °C), 4% Tween 80 (w/v), 35% Na2SO4 (w/v) and a settling time of 5 min. The total recovery of oleuropein, hydroxytyrosol, luteolin-7-O-glucoside, verbascoside and apigenin-7-O-glucoside, at optimum conditions, was 99.8%, 93.0%, 87.6%, 99.3% and 100.0%, respectively. Polyphenolic compounds entrapped in the surfactant-rich phase (Vs) showed higher thermal stability (activation energy (Ea) 23.8 kJ/mol) compared to non-entrapped ones (Ea 76.5 kJ/mol). The antioxidant activity of separated polyphenols remained unaffected as determined by the 1,1-diphenyl-2-picrylhydrazyl method. PMID:26784869

  15. Influence of surface modification of LiCoO2 by organic compounds on electrochemical and thermal properties of Li/LiCoO2 rechargeable cells

    NASA Astrophysics Data System (ADS)

    Takeuchi, Takashi; Kyuna, Tomohiro; Morimoto, Hideyuki; Tobishima, Shin-ichi

    2011-03-01

    LiCoO2 is the most famous positive electrode (cathode) for lithium ion cells. When LiCoO2 is charged at high charge voltages far from 4.2 V, cycleability of LiCoO2 becomes worse. Causes for this deterioration are instability of pure LiCoO2 crystalline structure and an oxidation of electrolyte solutions LiCoO2 at higher charge voltages. This electrolyte oxidation accompanies with the partial reduction of LiCoO2. We think more important factor is the oxidation of electrolyte solutions. In this work, influence of 10 organic compounds on electrochemical and thermal properties of LiCoO2 cells was examined as electrolyte additives. As a base electrolyte solution, 1 M (M: mol L-1) LiPF6-ethylene carbonate (EC)/ethylmethyl carbonate (EMC) (mixing volume ratio = 3:7) was used. These compounds are o-terphenyl (o-TP), Ph-X (CH3)n (n = 1 or 2, X = N, O or S) compounds, adamantyl toluene compounds, furans and thiophenes. These additives had the oxidation potentials (Eox) between 3.4 and 4.7 V vs. Li/Li+. These Eox values were lower than that (6.30 V vs. Li/Li+) of the base electrolyte. These additives are oxidized on LiCoO2 during charge of the LiCoO2 cells. Oxidation products suppress the excess oxidation of electrolyte solutions on LiCoO2. As a typical example of these organic compounds, o-TP (Eox: 4.52 V) was used to check the fundamental properties of these organic additives. Charge-discharge cycling tests were carried out for the Li/LiCoO2 cells with and without o-TP. Constant current charge at 4.5 V is mainly used as a charge method. Cells with 0.1 wt.% o-TP exhibited slightly better cycling performance and lower polarization than those without additives. Lower polarization arises from a decrease in a resistance of interface between electrolyte solutions and LiCoO2 by surface film formation resulted from oxidation of o-TP. Oxidation products were found by mass spectroscopy analysis to be mixture of several polycondensation compounds made from two to four terphenly

  16. Synthesis of Nanocrystals and Particle Size Effects Studies on the Thermally Induced Spin Transition of the Model Spin Crossover Compound [Fe(phen)2(NCS)2].

    PubMed

    Valverde-Muñoz, Francisco Javier; Gaspar, Ana B; Shylin, Sergii I; Ksenofontov, Vadim; Real, José A

    2015-08-17

    Surfactant-free nanocrystals of the model spin-crossover compound [Fe(phen)2(NCS)2] (phen: 1,10-phenanthroline) have been synthesized applying the reverse micelle technique. The morphology of the nanocrystals, characterized by scanning electronic microscopy, corresponds to rhombohedric platelets with dimensions ranging from 203 × 203 × 106 nm to 142 × 142 × 74 nm. Variation of the concentration of the Fe(BF4)2·6H2O salt in the synthesis has been found to have little influence on the crystallite size. In contrast, the solvent-surfactant ratio (ω) is critical for a good particle growth. The spin transition of the nanocrystals has been characterized by magnetic susceptibility measurements and Mössbauer spectroscopy. The nanocrystals undergo an abrupt and more cooperative spin transition in comparison with the bulk compound. The spin transition is centered in the interval of temperature of 175-185 K and is accompanied by 8 K of thermal hysteresis width. The crystallite quality more than the crystallite size is responsible for the higher cooperativity. The magnetic properties of the nanocrystals embedded in organic polymers such as polyethylene glycol, nujol, glycerol, and triton have been studied as well. The spin transition in the nanocrystals is affected by the polymer coating. The abrupt and first-order spin transition transforms into a more continuous spin transition as a result of the chemical pressure asserted by the organic polymers on the Fe(II) centers. PMID:26208031

  17. Analysis of the Thermal Degradation of the Individual Anthocyanin Compounds of Black Carrot (Daucus carota L.): A New Approach Using High-Resolution Proton Nuclear Magnetic Resonance Spectroscopy.

    PubMed

    Iliopoulou, Ioanna; Thaeron, Delphine; Baker, Ashley; Jones, Anita; Robertson, Neil

    2015-08-12

    The black carrot dye is a mixture of cyanidin molecules, the nuclear magnetic resonance (NMR) spectrum of which shows a highly overlapped aromatic region. In this study, the (1)H NMR (800 MHz) aromatic chemical shifts of the mixture were fully assigned by overlaying them with the characterized (1)H NMR chemical shifts of the separated compounds. The latter were isolated using reverse-phase high-performance liquid chromatography (RP-HPLC), and their chemical shifts were identified using (1)H and two-dimensional (2D) correlation spectroscopy (COSY) NMR spectroscopy. The stability of the black carrot mixture to heat exposure was investigated at pH 3.6, 6.8, and 8.0 by heat-treating aqueous solutions at 100 °C and the powdered material at 180 °C. From integration of high-resolution (1)H NMR spectra, it was possible to follow the relative degradation of each compound, offering advantages over the commonly used ultraviolet/visible (UV/vis) and HPLC approaches. UV/vis spectroscopy and CIE color measurements were used to determine thermally induced color changes, under normal cooking conditions. PMID:26160425

  18. Broad Negative Thermal Expansion Operation-Temperature Window Achieved by Adjusting Fe-Fe Magnetic Exchange Coupling in La(Fe,Si)13 Compounds.

    PubMed

    Li, Shaopeng; Huang, Rongjin; Zhao, Yuqiang; Li, Wen; Wang, Wei; Huang, Chuanjun; Gong, Pifu; Lin, Zheshuai; Li, Laifeng

    2015-08-17

    Cubic La(Fe,Si)13-based compounds have been recently developed as promising negative thermal expansion(NTE) materials, but the narrow NTE operation-temperature window(∼110 K) restricts their actual applications. In this work, we demonstrate that the NTE operation-temperature window of LaFe(13-x)Si(x) can be significantly broadened by adjusting Fe-Fe magnetic exchange coupling as x ranges from 2.8 to 3.1. In particular, the NTE operation-temperature window of LaFe10.1Si2.9 is extended to 220 K. More attractively, the coefficients of thermal expansion of LaFe10.0Si3.0 and LaFe9.9Si3.1 are homogeneous in the NTE operation-temperature range of about 200 K, which is much valuable for the stability of fabricating devices. The further experimental characterizations combined with first-principles studies reveal that the tetragonal phase is gradually introduced into the cubic phase as the Si content increases, hence modifies the Fe-Fe interatomic distance. The reduction of the overall Fe-Fe magnetic exchange interactions contributes to the broadness of NTE operation-temperature window for LaFe(13-x)Si(x). PMID:26196377

  19. Crystallization Kinetics Study on Orthogonal Ordering in N-(p-n-Alkyoxybenzylidene)-p-n-Alkylanilines (nO.m Compounds) by Thermal and Electrical Techniques. Part I

    NASA Astrophysics Data System (ADS)

    Chitravel, Thangaiyan; Madhu Mohan, Mathukumalli Lakshmi Nasayana; Krishnakumar, Varadarajan

    2009-06-01

    A systematic kinetic study of crystallization among two smectogens of higher homologues of the benzylidene aniline series nO.m, viz. 4O.12 and 8O.12, has been carried out by thermal microscopy, differential scanning calorimetry (DSC), and dielectric studies. The crystallization kinetics was studied by two techniques, viz. the traditional thermal analysis, i. e. DSC, and electrical studies, i. e. capacitance and dielectric loss variation measurements with temperature. The DSC thermograms were run from the crystallization temperature to the isotropic melting temperature for different time intervals. The liquid crystalline behaviour together with the rate of crystallization of smectic ordering in newly synthesized nO.m compounds were discussed in relation to the kinetophase (which occurs prior to crystallization). The molecular mechanism and dimensionality of crystal growth were computed using the Avrami equation. The characteristic crystallization time (t∗) at each crystallization temperature was deduced from the individual plots of logt and ΔH. Further, it was observed that the data obtained from DSC and dielectric studies were in good agreement.

  20. Entanglement scaling in classical and quantum harmonic oscillator lattices

    SciTech Connect

    Audenaert, K.; Eisert, J.; Plenio, M. B.; Cramer, M.

    2006-11-15

    We consider entanglement properties of ground and thermal states of harmonic lattice systems. A theorem connecting entanglement between a region and the rest of the lattice with the surface area of the boundary between the two regions is presented for systems in arbitrary spatial dimensions. The behavior of the block entanglement in the field limit is analysed and a logarithmic divergence is recovered.

  1. Erosion-corrosion of cooled thermal sprayed coatings impacted by mixtures of quartz and chemically active compounds

    SciTech Connect

    Wang, B.; Luer, K.

    1996-08-01

    A series of erosion-corrosion tests was carried out on AISI 1018 steel and four thermal sprayed coatings using a nozzle type elevated temperature erosion tester. The erodent particles were mechanical mixtures of SiO{sub 2} (quartz) with 1--4% NaCl or 1--4% KCl. The specimens were water-cooled on the backside. Test conditions attempted to simulate erosion-corrosion (E-C) conditions at the tubes in the convection pass of FBC boilers. The effect of Cl-bearing salt/quartz mixtures on the E-C wastage mechanisms of these materials were investigated. It was found that the E-C wastage of 1018 steel and carbide coating specimens increased with increasing amounts of NaCl and KCl doped in the quartz. Among the four coatings tested, a WC-17CoCr coating demonstrated the lowest thickness loss of all of the quartz/salt mixtures while the Cr{sub 3}C{sub 2}-25NiCr coating exhibited the highest E-C wastage. Meanwhile, quartz doped with NaCl or KCl had no effect on the E-C wastage of an HVOF Ni20Cr15Mo metal coating. The accelerating effect of doping alkali chlorides increased with both specimen surface temperature and environmental temperature.

  2. Carboxylate-modulated two novel Ag(I) coordination compounds with benzoguanamine ligand: Syntheses, structures, thermal stability and photoluminescent properties

    NASA Astrophysics Data System (ADS)

    Hao, Hong-Jun; Sun, Di; Liu, Fu-Jing; Huang, Rong-Bin; Zheng, Lan-Sun

    2012-03-01

    Two mixed-ligand coordination complexes (CCs) of the formula [Ag2(bga)2(pnba)2(H2O)]·(bga)2 (1) and {[Ag3(bga)3(dnb)3(H2O)]·(CH3OH)·(C2H5OH)}n (2) (bga = benzoguanamine, Hpnba = 4-nitrobenzoic acid, Hdnb = 3,5-dinitrobenzoic acid) were synthesized by reactions of AgNO3 and bga in the presence of different carboxylates under the ammoniacal condition. Both CCs have been characterized by element analysis, powder X-ray diffraction (PXRD), IR and X-ray single-crystal diffraction. Complex 1 is 0D discrete molecule which is extended to 1D supramolecular chains through intermolecular N-H···N complementary hydrogen bonds. Complex 2 is a 1D infinite chain containing monodentate and bidentate bga ligands. Analogously, the presence of complementary N-H···N hydrogen bonds drives the 1D chains to form 2D supramolecular sheet. In addition, the thermal stabilities and the photoluminescence properties of them were also investigated.

  3. Lattice invariants for knots

    SciTech Connect

    Janse Van Rensburg, E.J.

    1996-12-31

    The geometry of polygonal knots in the cubic lattice may be used to define some knot invariants. One such invariant is the minimal edge number, which is the minimum number of edges necessary (and sufficient) to construct a lattice knot of given type. In addition, one may also define the minimal (unfolded) surface number, and the minimal (unfolded) boundary number; these are the minimum number of 2-cells necessary to construct an unfolded lattice Seifert surface of a given knot type in the lattice, and the minimum number of edges necessary in a lattice knot to guarantee the existence of an unfolded lattice Seifert surface. In addition, I derive some relations amongst these invariants. 8 refs., 5 figs., 2 tabs.

  4. Anthraquinone-based intramolecular charge-transfer compounds: computational molecular design, thermally activated delayed fluorescence, and highly efficient red electroluminescence.

    PubMed

    Zhang, Qisheng; Kuwabara, Hirokazu; Potscavage, William J; Huang, Shuping; Hatae, Yasuhiro; Shibata, Takumi; Adachi, Chihaya

    2014-12-31

    Red fluorescent molecules suffer from large, non-radiative internal conversion rates (k(IC)) governed by the energy gap law. To design efficient red thermally activated delayed fluorescence (TADF) emitters for organic light-emitting diodes (OLEDs), a large fluorescence rate (k(F)) as well as a small energy difference between the lowest singlet and triplet excited states (ΔE(ST)) is necessary. Herein, we demonstrated that increasing the distance between donor (D) and acceptor (A) in intramolecular-charge-transfer molecules is a promising strategy for simultaneously achieving small ΔE(ST) and large k(F). Four D-Ph-A-Ph-D-type molecules with an anthraquinone acceptor, phenyl (Ph) bridge, and various donors were designed, synthesized, and compared with corresponding D-A-D-type molecules. Yellow to red TADF was observed from all of them. The k(F) and ΔE(ST) values determined from the measurements of quantum yield and lifetime of the fluorescence and TADF components are in good agreement with those predicted by corrected time-dependent density functional theory and are approximatively proportional to the square of the cosine of the theoretical twisting angles between each subunit. However, the introduction of a Ph-bridge was found to enhance k(F) without increasing ΔE(ST). Molecular simulation revealed a twisting and stretching motion of the N-C bond in the D-A-type molecules, which is thought to lower ΔE(ST) and k(F) but raise k(IC), that was experimentally confirmed in both solution and doped film. OLEDs containing D-Ph-A-Ph-D-type molecules with diphenylamine and bis(4-biphenyl)amine donors demonstrated maximum external quantum efficiencies of 12.5% and 9.0% with emission peaks at 624 and 637 nm, respectively. PMID:25469624

  5. Mass-dependent and Mass-independent Sulphur Isotope Fractionation Accompanying Thermal- and Photo-chemical Decomposition of Sulphur Bearing Organic Compounds

    NASA Astrophysics Data System (ADS)

    Oduro, Harry; Izon, Gareth; Ono, Shuhei

    2014-05-01

    The bimodal S-isotope record, specifically the transition from mass independent (MIF) to mass dependent fractionation (MDF), is perhaps the most widely cited line of evidence for an irreversible rise in atmospheric oxygen at ca. 2.4Ga. The production and preservation of S-MIF, manifested in both Δ33S and Δ36S, within the geological record are linked to atmospheric O2 via a number of arguments. However, to date, the only mechanism capable of generating S-MIF consistent with the Archaean sedimentary records involves gas-phase ultraviolet irradiation of SO21 photolysis. More recently, Δ33S S-MIF trends have been reported from en vitro thermochemical sulphate reduction (TSR) experiments, prompting authors to question the importance of S-MIF as a proxy for Earth oxidation2. Importantly, whilst emerging TSR experiments3,4 affirm the reported Δ33S trends2, these experiments fail to identify correlated S-MIF between Δ33S and Δ36S values3,4. Realization that S-MIF is confined to Δ33S during TSR, precludes TSR as a mechanism responsible for the origin of the Archaean S-MIF record but strongly suggests the effect originating from a magnetic isotope effect (MIE) associated with 33S nucleus3,4. Clearly, photochemical and thermochemical processes impart different Δ36S/Δ33S trends with significant variation in δ34S; however, a complete experimental elucidation of mechanisms responsible for the S-MIF and S-MIE signatures is lacking. Interestingly, a complete understanding of the S-isotope chemistry during thermal- and photo-chemical decomposition may reveal wavelength and thermal dependence archived in the sedimentary record. Here we extend the experimental database to explore the magnitude and sign of Δ36S/Δ33S and δ34S produced during both photo- and thermochemical processes. Here the organic sulphur compounds (OSC) utilized in these experiments carries diagnostic Δ36S/Δ33S patterns that differ from those reported from photolysis experiment SO2 and from the

  6. δD and δ13C analyses of atmospheric volatile organic compounds by thermal desorption gas chromatography isotope ratio mass spectrometry.

    PubMed

    von Eckstaedt, Christiane Vitzthum; Grice, Kliti; Ioppolo-Armanios, Marisa; Chidlow, Geoff; Jones, Mark

    2011-09-16

    This paper describes the establishment of a robust method to determine compound specific δD and δ(13)C values of volatile organic compounds (VOCs) in a standard mixture ranging between C(6) and C(10) and was applied to various complex emission samples, e.g. from biomass combustion and car exhaust. A thermal desorption (TD) unit was linked to a gas chromatography isotope ratio mass spectrometer (GC-irMS) to enable compound specific isotope analysis (CSIA) of gaseous samples. TenaxTA was used as an adsorbent material in stainless steel TD tubes. We determined instrument settings to achieve a minimal water background level for reliable δD analysis and investigated the impact of storage time on δD and δ(13)C values of collected VOCs (176 days and 40 days of storage, respectively). Most of the standard compounds investigated showed standard deviations (SD)<6‰ (δD) when stored for 148 days at 4 °C. However, benzene revealed occasionally D depleted values (21‰ SD) for unknown reasons. δ(13)C analysis demonstrated that storage of 40 days had no effect on VOCs investigated. We also showed that breakthrough (benzene and toluene, 37% and 7%, respectively) had only a negligible effect (0.7‰ and 0.4‰, respectively) on δ(13)C values of VOCs on the sample tube. We established that the sample portion collected at the split flow effluent of the TD unit can be used as a replicate sample for isotope analysis saving valuable sampling time and resources. We also applied TD-GC-irMS to different emission samples (biomass combustion, petrol and diesel car engines exhaust) and for the first time δD values of atmospheric VOCs in the above range are reported. Significant differences in δD of up to 130‰ were observed between VOCs in emissions from petrol car engine exhaust and biomass combustion (Karri tree). However, diesel car emissions showed a high content of highly complex unresolved mixtures thus a baseline separation of VOCs was not achieved for stable hydrogen

  7. Atomic Layer Epitaxy of III-V compound semiconductors by thermal and laser-assisted metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    DenBaars, Steven P.

    A new parallel implicit adaptive mesh refinement (AMR) algorithm is developed for the prediction of unsteady behaviour of laminar flames. The scheme is applied to the solution of the system of partial-differential equations governing time-dependent, two- and three-dimensional, compressible laminar flows for reactive thermally perfect gaseous mixtures. A high-resolution finite-volume spatial discretization procedure is used to solve the conservation form of these equations on body-fitted multi-block hexahedral meshes. A local preconditioning technique is used to remove numerical stiffness and maintain solution accuracy for low-Mach-number, nearly incompressible flows. A flexible block-based octree data structure has been developed and is used to facilitate automatic solution-directed mesh adaptation according to physics-based refinement criteria. The data structure also enables an efficient and scalable parallel implementation via domain decomposition. The parallel implicit formulation makes use of a dual-time-stepping like approach with an implicit second-order backward discretization of the physical time, in which a Jacobian-free inexact Newton method with a preconditioned generalized minimal residual (GMRES) algorithm is used to solve the system of nonlinear algebraic equations arising from the temporal and spatial discretization procedures. An additive Schwarz global preconditioner is used in conjunction with block incomplete LU type local preconditioners for each sub-domain. The Schwarz preconditioning and block-based data structure readily allow efficient and scalable parallel implementations of the implicit AMR approach on distributed-memory multi-processor architectures. The scheme was applied to solutions of steady and unsteady laminar diffusion and premixed methane-air combustion and was found to accurately predict key flame characteristics. For a premixed flame under terrestrial gravity, the scheme accurately predicted the frequency of the natural

  8. Analysis of a GC/MS thermal desorption system with simultaneous sniffing for determination of off-odor compounds and VOCs in fumes formed during extrusion coating of low-density polyethylene.

    PubMed

    Villberg, K; Veijanen, A

    2001-03-01

    A thermal desorption equipment introducing volatile organic compounds (VOCs) into the gas chromatographic/ mass spectrometric system (GC/MS) with simultaneous sniffing (SNIFF) is a suitable method for identifying the volatile organic off-odor compounds formed during the extrusion coating process of low-density polyethylene. Fumes emitted during the extrusion coating process of three different plastic materials were collected at two different temperatures (285 and 315 degrees C) from an outgoing pipe and near an extruder. The VOCs of fumes were analyzed by drawing a known volume of air through the adsorbent tube filled with a solid adsorbent (Tenax GR). The air samples were analyzed by using a special thermal desorption device and GC/MS determination. The simultaneous sniffing was carried out to detect off-odors and to assist in the identification of those compounds that contribute to tainting and smelling. The amounts of off-odor carbonyl compounds and the total content of the volatile organic compounds were determined. The most odorous compounds were identified as carboxylic acids while the majority of the volatile compounds were hydrocarbons. The detection and quantification of carboxylic acids were based on the characteristic ions of their mass spectra. The higher the extrusion temperature the more odors were detected. An important observation was that the total concentration of volatiles was dependent not only on the extrusion temperature but also on the plastic material. PMID:11289444

  9. Supersymmetry on the lattice

    NASA Astrophysics Data System (ADS)

    Bergner, Georg; Catterall, Simon

    2016-08-01

    We discuss the motivations, difficulties and progress in the study of supersymmetric lattice gauge theories focusing in particular on 𝒩 = 1 and 𝒩 = 4 super-Yang-Mills in four dimensions. Brief reviews of the corresponding lattice formalisms are given and current results are presented and discussed. We conclude with a summary of the main aspects of current work and prospects for the future.

  10. Flat Band Quastiperiodic Lattices

    NASA Astrophysics Data System (ADS)

    Bodyfelt, Joshua; Flach, Sergej; Danieli, Carlo

    2014-03-01

    Translationally invariant lattices with flat bands (FB) in their band structure possess irreducible compact localized flat band states, which can be understood through local rotation to a Fano structure. We present extension of these quasi-1D FB structures under incommensurate lattices, reporting on the FB effects to the Metal-Insulator Transition.

  11. Laterally closed lattice homomorphisms

    NASA Astrophysics Data System (ADS)

    Toumi, Mohamed Ali; Toumi, Nedra

    2006-12-01

    Let A and B be two Archimedean vector lattices and let be a lattice homomorphism. We call that T is laterally closed if T(D) is a maximal orthogonal system in the band generated by T(A) in B, for each maximal orthogonal system D of A. In this paper we prove that any laterally closed lattice homomorphism T of an Archimedean vector lattice A with universal completion Au into a universally complete vector lattice B can be extended to a lattice homomorphism of Au into B, which is an improvement of a result of M. Duhoux and M. Meyer [M. Duhoux and M. Meyer, Extended orthomorphisms and lateral completion of Archimedean Riesz spaces, Ann. Soc. Sci. Bruxelles 98 (1984) 3-18], who established it for the order continuous lattice homomorphism case. Moreover, if in addition Au and B are with point separating order duals (Au)' and B' respectively, then the laterally closedness property becomes a necessary and sufficient condition for any lattice homomorphism to have a similar extension to the whole Au. As an application, we give a new representation theorem for laterally closed d-algebras from which we infer the existence of d-algebra multiplications on the universal completions of d-algebras.

  12. Continuous partition lattice

    PubMed Central

    Björner, Anders

    1987-01-01

    A continuous analogue to the partition lattices is presented. This is the metric completion of the direct limit of a system of embeddings of the finite partition lattices. The construction is analogous to von Neumann's construction of a continuous geometry over a field F from the finite-dimensional projective geometries over F. PMID:16593874

  13. Electric and magnetic investigations of the new layered compound bis(DL-alaninium) tetrachlorocuperate

    NASA Astrophysics Data System (ADS)

    Mostafa, M. F.; Arafat, S.; Mansour-Gabr, M.

    1996-02-01

    Powder X-ray diffraction at room temperature, magnetic and electric properties in the temperature range between liquid nitrogen and room temperature have been investigated for the compound (DL-alaninium) 2CuCl 4. At room temperature it has a tetragonal unit cell with lattice constants a = b = 0.556 nm and c = 1.665 nm. The compound is found to be thermochromic, changing color from a low temperature green phase to a high temperature yellow phase at Ttr = 285 K. The dielectric constant reflects this order-disorder phase transition. The conductivity shows three thermally activated regions with different activation energies. Possible conduction mechanisms are discussed.

  14. LaPtSb: a half-Heusler compound with high thermoelectric performance.

    PubMed

    Xue, Q Y; Liu, H J; Fan, D D; Cheng, L; Zhao, B Y; Shi, J

    2016-07-21

    The electronic and transport properties of the half-Heusler compound LaPtSb are investigated by performing first-principles calculations combined with semi-classical Boltzmann theory and deformation potential theory. Compared with many typical half-Heusler compounds, LaPtSb exhibits an obviously larger power factor at room temperature, especially for the n-type system. Together with the very low lattice thermal conductivity, the thermoelectric figure of merit (ZT) of LaPtSb can be optimized to a record high value of 2.2 by fine tuning the carrier concentration. PMID:27321233

  15. Measurement of aerosol organic compounds during TexAQS 2006 using a novel collection/thermal-desorption PTR-ITMS instrument

    NASA Astrophysics Data System (ADS)

    Thornberry, T.; Murphy, D. M.; Thomson, D. S.; Welsh-Bon, D.; Warneke, C.; Bates, T. S.; Coffman, D.; Lerner, B.; Williams, E. J.

    2007-12-01

    Knowledge of the organic species present in atmospheric aerosols is needed in order to understand their effect on aerosol microphysical and optical properties, to resolve outstanding questions about important organic aerosol sources and formation mechanisms, and to elucidate the role of aerosols in the chemistry of the atmosphere through their interaction with gas-phase compounds. The measurement of aerosol organic compounds poses a significant experimental challenge due to the complexity and large number of organic species and the low concentration at which individual species are present. A new instrument that utilizes proton- transfer-reaction mass spectrometry (PTR-MS) to probe the organic composition of atmospheric aerosols has been developed to investigate semi-volatile and condensed-phase organic species in the atmosphere. Aerosols are collected by impaction and then thermally desorbed into a carrier gas that transports the organic analyte molecules into a drift tube where they are ionized by reaction with H3O+ ions. Analyte ions are detected using an ion trap mass spectrometer. The instrument was deployed for the first time during summer 2006 in the Texas Air Quality Study (TexAQS 2006) aboard NOAA R.V. Ronald H. Brown. Signals significantly above detection limit were observed at a number of masses during periods of elevated photochemical activity when aerosol loading increased in the 0.5-1 μm size range and aerosol mass spectrometer (AMS) measurements indicated increased organic mass. Different masses exhibited different temporal behaviors, indicating varying composition of the aerosol organic fraction even during periods when the AMS organic mass (OA) loading was relatively constant. Plumes of aerosol-phase pyridine were observed during sampling near the entrance to the Houston Ship Channel, indicating a relatively local source and rapid partitioning to the aerosol phase. These field results and results of laboratory instrument performance experiments

  16. The effect of mineral fillers on the rheological, mechanical and thermal properties of halogen-free flame-retardant polypropylene/expandable graphite compounds

    NASA Astrophysics Data System (ADS)

    Mattausch, Hannelore; Laske, Stephan; Hohenwarter, Dieter; Holzer, Clemens

    2015-05-01

    In many polyolefin applications, such as electrical cables or automotive applications, the fire protection is a very important task. Unfortunately flame-retardant polymeric materials are often halogenated and form toxic substances in case of fire, which explains the general requirement to reduce the halogen content to zero. Non-halogenated, state-of-the-art flame retardants must be incorporated into the polymer in very high grades (> 40 wt%) leading to massive decrease in mechanical properties and/or processability. In this research work halogen-free flame-retardant polypropylene (PP) /expandable graphite (EG) were filled with minerals fillers such as layered silicates (MMT), magnesium hydroxide (MgOH), zeolite (Z) and expanded perlite (EP) in order to enhance the flame-retardant effect. The rheological, mechanical and thermal properties of these materials were investigated to gain more fundamental knowledge about synergistic combinations of flame-retardants and other additives. The rheological properties were characterized with a rotational rheometer with plate-plate setup. The EG/EP/PP compound exhibited the highest increase in viscosity (˜ 37 %). As representative value for the mechanical properties the Young's modulus was chosen. The final Young's modulus values of the twofold systems gained higher values than the single ones. Thermo gravimetric analysis (TGA) was utilized to investigate the material with respect to volatile substances and combustion behavior. All materials decomposed in one-step degradation. The EG filled compounds showed a significant increase in sample weight due to the expansion of EG. The combustion behavior of these materials was characterized by cone calorimeter tests. Especially combinations of expandable graphite with mineral fillers exhibit a reduction of the peak heat release rate during cone calorimeter measurements of up to 87% compared to pure PP.

  17. Honeycomb lattices with defects

    NASA Astrophysics Data System (ADS)

    Spencer, Meryl A.; Ziff, Robert M.

    2016-04-01

    In this paper, we introduce a variant of the honeycomb lattice in which we create defects by randomly exchanging adjacent bonds, producing a random tiling with a distribution of polygon edges. We study the percolation properties on these lattices as a function of the number of exchanged bonds using an alternative computational method. We find the site and bond percolation thresholds are consistent with other three-coordinated lattices with the same standard deviation in the degree distribution of the dual; here we can produce a continuum of lattices with a range of standard deviations in the distribution. These lattices should be useful for modeling other properties of random systems as well as percolation.

  18. An Approach for Measuring the Sorptive Behavior of Odorants Using a Multifunction Thermal Desorber Unit: Preliminary Tests on Reduced Sulfur Compounds

    PubMed Central

    Kim, Ki-Hyun; Choi, Ye-Jin; Yang, Hye-Soon; Joo, Sang-Woo

    2008-01-01

    In this study, the sorptive behavior of reduced sulfur compounds (RSC) was investigated using a combination of thermal desorber (TD) unit and gas chromatography (GC). To examine the sorptive properties of RSC on textile materials, two types of experiments were conducted under experimental conditions favorable for sorptive processes. In all the experiments, gaseous standards of hydrogen sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide were supplied to initiate the adsorption processes on textile pieces. The textile pieces were then forced to release those adsorbed RSC under a fixed condition. It was found that the extent of adsorption, if evaluated quantitatively, occurred at approximately 1/1000 to 1/100 of the level of RSC standards supplied originally to induce adsorption. It also indicated that RSC adsorption was affected very sensitively by the initial exposure durations to induce RSC adsorption with an exponential decrease in relative recovery (RR) values with increasing exposure time. The relative sorptive patterns, when compared between different RSCs, were affected most sensitively by such factors as molecular weight and/or physical contact conditions.

  19. Nonpolar organic compounds in fine particles: quantification by thermal desorption-GC/MS and evidence for their significant oxidation in ambient aerosols in Hong Kong.

    PubMed

    Yu, Jian Zhen; Huang, X H Hilda; Ho, Steven S H; Bian, Qijing

    2011-12-01

    Nonpolar organic compounds (NPOCs) in ambient particulate matter (PM) commonly include n-alkanes, branched alkanes, hopanes and steranes, and polycyclic aromatic hydrocarbons (PAHs). The recent development of thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) has greatly reduced time and labor in their quantification by eliminating the laborious solvent extraction and sample concentration steps in the traditional approach that relies on solvent extraction. The simplicity of the TD-GCMS methods has afforded us concentration data of NPOCs in more than 90 aerosol samples in two aerosol field studies and 20 vehicular emissions-dominated source samples in Hong Kong over the past few years. In this work, we examine the interspecies relationships between select NPOCs and their concentration ratios to elemental carbon (EC) among the ambient samples and among the source samples. Our analysis indicates that hopanes were mainly from vehicular emissions and they were significantly oxidized in ambient PM. The hopane/EC ratio in ambient samples was on average less than half of the ratio in vehicular emissions-dominated source samples. This highlights the necessity in considering oxidation loss in applying organic tracer data in source apportionment studies. Select PAH/EC ratio-ratio plots reveal that PAHs had diverse sources and vehicular emissions were unlikely a dominant source for PAHs in Hong Kong. Biomass burning and other regional sources likely dominated ambient PAHs in Hong Kong. PMID:21983947

  20. Theoretical studies on the crystal structure, thermodynamic properties, detonation performance and thermal stability of cage-tetranitrotetraazabicyclooctane as a novel high energy density compound.

    PubMed

    Zhao, Guo-zheng; Lu, Ming

    2013-01-01

    The B3LYP/6-31G (d) method of density functional theory (DFT) was used to study molecular geometry, electronic structure, infrared spectrum (IR) and thermodynamic properties. The heat of formation (HOF) and calculated density were estimated to evaluate the detonation properties using Kamlet-Jacobs equations. Thermal stability of 3,5,7,10,12,14,15,16-octanitro- 3,5,7,10,12,14,15,16-octaaza-heptacyclo[7.5.1.1(2,8).0(1,11).0(2,6).0(4,13).0(6,11)]hexadecane (cage-tetranitrotetraazabicyclooctane) was investigated by calculating the bond dissociation energy (BDE) at unrestricted B3LYP/6-31G (d) level. The calculated results show that the N-NO2 bond is a trigger bond during thermolysis initiation process. The crystal structure obtained by molecular mechanics (MM) methods belongs to Pna2(1) space group, with cell parameters a=12.840 Å, b=9.129 Å, c=14.346 Å, Z=6 and ρ=2.292 g·cm(-3). Both the detonation velocity of 9.96 km·s(-1) and the detonation pressure of 47.47 GPa are better than those of CL-20. According to the quantitative standard of energetics and stability, as a high energy density compound (HEDC), cage-tetranitrotetraazabicyclooctane essentially satisfies this requirement. PMID:22790340

  1. Phase transitions and electrical conduction in thermal energy storage compound (n-C12H25NH3)2CdCl4

    NASA Astrophysics Data System (ADS)

    Mahmoud Abdelkader, Mohamed; Aboud, Aboud Ibrahim; Gamal, Wafia Mohamed

    2015-05-01

    Differential scanning calorimetry (DSC) and differential thermal analysis (DTA) are performed for the compound (n-C12H25NH3)2CdCl4. The ac conductivity σ(ω,T), and the complex dielectric permittivity ɛ*(ω,T) are measured as a function of temperature (100 K < T < 375 K) and at some selected frequencies (3 → 100 kHz). Two structural phase transitions are detected at T = (330 ± 1) K and T = (343 ± 1) K as minor and major transitions, respectively. The analysis of the measured electrical parameters reveals that the frequency-dependent conductivity obeys the power law, and the quantum mechanical tunneling (QMT) model is the main conduction mechanism in the low-temperature phase (LTP; phase III). The role of hydrogen bond N-H…Cl as a trigger force for phase transitions has been discussed. While the LTP is of the order-disorder type, the high-temperature phase (HTP) or phase I seems to be conformational and represents the main transition.

  2. Crystallization kinetics study on tilted ordering in N-(p-n-alkyoxybenzylidene)-p-n-alkylanilines (nO.m compounds) by thermal and electrical techniques. Part I

    NASA Astrophysics Data System (ADS)

    Chitravel, T.; Madhu Mohan, M. L. N.; Krishnakumar, V.

    2009-05-01

    A systematic kinetic study of crystallization among two smectogens of higher homologues of the benzylidene aniline nO.m series viz. 15O.12 and 15O.16 has been carried out by polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and dielectric studies. The crystallization kinetics was studied by two techniques viz. the traditional thermal analysis (DSC) and dielectric technique viz. capacitance and dielectric loss variation with temperature. The DSC thermograms were run from crystallization temperature to the isotropic melt for different time intervals. The liquid crystalline behaviour together with the rate of crystallization of smectic ordering in newly synthesized nO.m compounds were discussed in relation to the kinetophase (which occurs prior to the crystallization). The molecular mechanism and dimensionality in the crystal growth were computed from the Avrami equation. The characteristic crystallization time ( t*) at each crystallization temperature was deduced from the individual plots of log t and Δ H. Further, it was observed that the data obtained from DSC, POM and dielectric studies were in good agreement with one another.

  3. A realistic lattice example

    SciTech Connect

    Courant, E.D.; Garren, A.A.

    1985-10-01

    A realistic, distributed interaction region (IR) lattice has been designed that includes new components discussed in the June 1985 lattice workshop. Unlike the test lattices, the lattice presented here includes utility straights and the mechanism for crossing the beams in the experimental straights. Moreover, both the phase trombones and the dispersion suppressors contain the same bending as the normal cells. Vertically separated beams and 6 Tesla, 1-in-1 magnets are assumed. Since the cells are 200 meters long, and have 60 degree phase advance, this lattice has been named RLD1, in analogy with the corresponding test lattice, TLD1. The quadrupole gradient is 136 tesla/meter in the cells, and has similar values in other quadrupoles except in those in the IR`s, where the maximum gradient is 245 tesla/meter. RLD1 has distributed IR`s; however, clustered realistic lattices can easily be assembled from the same components, as was recently done in a version that utilizes the same type of experimental and utility straights as those of RLD1.

  4. High-resolution x-ray diffraction study of the heavy-fermion compound YbBiPt

    NASA Astrophysics Data System (ADS)

    Ueland, B. G.; Saunders, S. M.; Bud'ko, S. L.; Schmiedeshoff, G. M.; Canfield, P. C.; Kreyssig, A.; Goldman, A. I.

    2015-11-01

    YbBiPt is a heavy-fermion compound possessing significant short-range antiferromagnetic correlations below a temperature of T*=0.7 K , fragile antiferromagnetic order below TN=0.4 K , a Kondo temperature of TK≈1 K , and crystalline-electric-field splitting on the order of E /kB=1 -10 K . Whereas the compound has a face-centered-cubic lattice at ambient temperature, certain experimental data, particularly those from studies aimed at determining its crystalline-electric-field scheme, suggest that the lattice distorts at lower temperature. Here, we present results from high-resolution, high-energy x-ray diffraction experiments which show that, within our experimental resolution of ≈6 -10 ×10-5Å , no structural phase transition occurs between T =1.5 and 50 K . In combination with results from dilatometry measurements, we further show that the compound's thermal expansion has a minimum at ≈18 K and a region of negative thermal expansion for 9 ≲T ≲18 K . Despite diffraction patterns taken at 1.6 K which indicate that the lattice is face-centered cubic and that the Yb resides on a crystallographic site with cubic point symmetry, we demonstrate that the linear thermal expansion may be modeled using crystalline-electric-field level schemes appropriate for Yb3 + residing on a site with either cubic or less than cubic point symmetry.

  5. Josephson vortex lattice in layered superconductors

    SciTech Connect

    Koshelev, A. E.; Dodgson, M. J. W.

    2013-09-15

    Many superconducting materials are composed of weakly coupled conducting layers. Such a layered structure has a very strong influence on the properties of vortex matter in a magnetic field. This review focuses on the properties of the Josephson vortex lattice generated by the magnetic field applied in the direction of the layers. The theoretical description is based on the Lawrence-Doniach model in the London limit, which takes only the phase degree of freedom of the superconducting order parameter into account. In spite of its simplicity, this model leads to an amazingly rich set of phenomena. We review in detail the structure of an isolated vortex line and various properties of the vortex lattice, in both dilute and dense limits. In particular, we extensively discuss the influence of the layered structure and thermal fluctuations on the selection of lattice configurations at different magnetic fields.

  6. Intermetallic Compounds

    NASA Astrophysics Data System (ADS)

    Takagiwa, Y.; Matsuura, Y.; Kimura, K.

    2014-06-01

    We have focused on the binary narrow-bandgap intermetallic compounds FeGa3 and RuGa3 as thermoelectric materials. Their crystal structure is FeGa3-type (tetragonal, P42/ mnm) with 16 atoms per unit cell. Despite their simple crystal structure, their room temperature thermal conductivity is in the range 4-5-W-m-1-K-1. Both compounds have narrow-bandgaps of approximately 0.3-eV near the Fermi level. Because their Seebeck coefficients are quite large negative values in the range 350-<-| S 373K|-<-550- μV-K-1 for undoped samples, it should be possible to obtain highly efficient thermoelectric materials both by adjusting the carrier concentration and by reducing the thermal conductivity. Here, we report the effects of doping on the thermoelectric properties of FeGa3 and RuGa3 as n and p-type materials. The dimensionless figure of merit, ZT, was significantly improved by substitution of Sn for Ga in FeGa3 (electron-doping) and by substitution of Zn for Ga in RuGa3 (hole-doping), mainly as a result of optimization of the electronic part, S 2 σ.

  7. Shaken lattice interferometry

    NASA Astrophysics Data System (ADS)

    Weidner, Carrie; Yu, Hoon; Anderson, Dana

    2016-05-01

    In this work, we report on progress towards performing interferometry using atoms trapped in an optical lattice. That is, we start with atoms in the ground state of an optical lattice potential V(x) =V0cos [ 2 kx + ϕ(t) ] , and by a prescribed phase function ϕ(t) , transform from one atomic wavefunction to another. In this way, we implement the standard interferometric sequence of beam splitting, propagation, reflection, reverse propagation, and recombination. Through the use of optimal control techniques, we have computationally demonstrated a scalable accelerometer that provides information on the sign of the applied acceleration. Extension of this idea to a two-dimensional shaken-lattice-based gyroscope is discussed. In addition, we report on the experimental implementation of the shaken lattice system.

  8. SPIN ON THE LATTICE.

    SciTech Connect

    ORGINOS,K.

    2003-01-07

    I review the current status of hadronic structure computations on the lattice. I describe the basic lattice techniques and difficulties and present some of the latest lattice results; in particular recent results of the RBC group using domain wall fermions are also discussed. In conclusion, lattice computations can play an important role in understanding the hadronic structure and the fundamental properties of Quantum Chromodynamics (QCD). Although some difficulties still exist, several significant steps have been made. Advances in computer technology are expected to play a significant role in pushing these computations closer to the chiral limit and in including dynamical fermions. RBC has already begun preliminary dynamical domain wall fermion computations [49] which we expect to be pushed forward with the arrival of QCD0C. In the near future, we also expect to complete the non-perturbative renormalization of the relevant derivative operators in quenched QCD.

  9. Superalloy Lattice Block Structures

    NASA Technical Reports Server (NTRS)

    Nathal, M. V.; Whittenberger, J. D.; Hebsur, M. G.; Kantzos, P. T.; Krause, D. L.

    2004-01-01

    Initial investigations of investment cast superalloy lattice block suggest that this technology will yield a low cost approach to utilize the high temperature strength and environmental resistance of superalloys in lightweight, damage tolerant structural configurations. Work to date has demonstrated that relatively large superalloy lattice block panels can be successfully investment cast from both IN-718 and Mar-M247. These castings exhibited mechanical properties consistent with the strength of the same superalloys measured from more conventional castings. The lattice block structure also accommodates significant deformation without failure, and is defect tolerant in fatigue. The potential of lattice block structures opens new opportunities for the use of superalloys in future generations of aircraft applications that demand strength and environmental resistance at elevated temperatures along with low weight.

  10. Automated Lattice Perturbation Theory

    SciTech Connect

    Monahan, Christopher

    2014-11-01

    I review recent developments in automated lattice perturbation theory. Starting with an overview of lattice perturbation theory, I focus on the three automation packages currently "on the market": HiPPy/HPsrc, Pastor and PhySyCAl. I highlight some recent applications of these methods, particularly in B physics. In the final section I briefly discuss the related, but distinct, approach of numerical stochastic perturbation theory.

  11. Lattice vibrations of the charge-transfer salt κ -(BEDT-TTF)2Cu2(CN )3: Comprehensive explanation of the electrodynamic response in a spin-liquid compound

    NASA Astrophysics Data System (ADS)

    Dressel, M.; Lazić, P.; Pustogow, A.; Zhukova, E.; Gorshunov, B.; Schlueter, J. A.; Milat, O.; Gumhalter, B.; Tomić, S.

    2016-02-01

    The dimer Mott insulator κ -(BEDT-TTF)2Cu2(CN )3 exhibits unusual electrodynamic properties. Numerical investigations of the electronic ground state and the molecular and lattice vibrations reveal the importance of the Cu2(CN )3- anion network coupled to the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) molecules: The threefold cyanide coordination of copper and linkage isomerism in the anion structure cause a loss of symmetry, frustration, disorder, and domain formation. Our findings consistently explain the temperature and polarization-dependent THz and infrared measurements, reinforce the understanding of dielectric properties, and have important implications for the quantum spin-liquid state, which should be treated beyond two-dimensional, purely electronic models.

  12. Lattice dynamics of BaFe2X3(X=S,Se) compounds

    SciTech Connect

    Popović, Z. V.; Šćepanović, M.; Lazarević, N.; Opačić, M.; Radonjić, M. M.; Tanasković, D.; Lei, Hechang; Petrovic, C.

    2015-02-27

    We present the Raman scattering spectra of the S=2 spin ladder compounds BaFe₂X₃ (X=S,Se) in a temperature range between 20 and 400 K. Although the crystal structures of these two compounds are both orthorhombic and very similar, they are not isostructural. The unit cell of BaFe₂S₃ (BaFe₂Se₃) is base-centered Cmcm (primitive Pnma), giving 18 (36) modes to be observed in the Raman scattering experiment. We have detected almost all Raman active modes, predicted by factor group analysis, which can be observed from the cleavage planes of these compounds. Assignment of the observed Raman modes of BaFe₂S(Se)₃ is supported by the lattice dynamics calculations. The antiferromagnetic long-range spin ordering in BaFe₂Se₃ below TN=255K leaves a fingerprint both in the A1g and B3g phonon mode linewidth and energy.

  13. Legless locomotion in lattices

    NASA Astrophysics Data System (ADS)

    Schiebel, Perrin; Dai, Jin; Gong, Chaohui; Serrano, Miguel M.; Mendelson, Joseph R., III; Choset, Howie; Goldman, Daniel I.

    2015-03-01

    By propagating waves from head to tail, limbless organisms like snakes can traverse terrain composed of rocks, foliage, soil and sand. Previous research elucidated how rigid obstacles influence snake locomotion by studying a model terrain-symmetric lattices of pegs placed in hard ground. We want to understand how different substrate-body interaction modes affect performance in desert-adapted snakes during transit of substrates composed of both rigid obstacles and granular media (GM). We tested Chionactis occipitalis, the Mojave shovel-nosed snake, in two laboratory treatments: lattices of 0 . 64 cm diameter obstacles arrayed on both a hard, slick substrate and in a GM of ~ 0 . 3 mm diameter glass particles. For all lattice spacings, d, speed through the hard ground lattices was less than that in GM lattices. However, maximal undulation efficiencies ηu (number of body lengths advanced per undulation cycle) in both treatments were comparable when d was intermediate. For other d, ηu was lower than this maximum in hard ground lattices, while on GM, ηu was insensitive to d. To systematically explore such locomotion, we tested a physical robot model of the snake; performance depended sensitively on base substrate, d and body wave parameters.

  14. Investigating the Structural, Thermal, and Electronic Properties of the Zircon-Type ZrSiO4, ZrGeO4 and HfSiO4 Compounds

    NASA Astrophysics Data System (ADS)

    Chiker, Fafa; Boukabrine, Fatiha; Khachai, H.; Khenata, R.; Mathieu, C.; Bin Omran, S.; Syrotyuk, S. V.; Ahmed, W. K.; Murtaza, G.

    2016-07-01

    In the present study, the structural, thermal, and electronic properties of some important orthosilicate dielectrics, such as the ZrSiO4, ZrGeO4, and HfSiO4 compounds, have been investigated theoretically with the use of first-principle calculations. We attribute the application of the modified Becke-Johnson exchange potential, which is basically an improvement over the local density approximation and the Perdew-Burke-Ernzerhof exchange-correlation functional, for a better description of the band gaps of the compounds. This resulted in a good agreement with our estimated values in comparison with the reported experimental data, specifically for the ZrSiO4, and HfSiO4 compounds. Conversely, for the ZrGeO4 compound, the calculated electronic band structure shows a direct band gap at the Γ point with the value of 5.79 eV. Furthermore, our evaluated thermal properties that are calculated by using the quasi-harmonic Debye model indicated that the volume variation with temperature is higher in the ZrGeO4 compound as compared to both the ZrSiO4 and HfSiO4 compounds, which is ascribed to the difference between the electron shells of the Si and Ge atoms. Therefore, these results also indicate that while the entropy (S) and enthalpy (U) parameters increase monotonically, the free energy (G), in contrast, decreases monotonically with increasing temperature, respectively. Moreover, the pressure and temperature dependencies of the Debye temperature Θ, thermal expansion coefficient, and heat capacities C V were also predicted in our study.

  15. Preparation of uranium compounds

    DOEpatents

    Kiplinger, Jaqueline L; Montreal, Marisa J; Thomson, Robert K; Cantat, Thibault; Travia, Nicholas E

    2013-02-19

    UI.sub.3(1,4-dioxane).sub.1.5 and UI.sub.4(1,4-dioxane).sub.2, were synthesized in high yield by reacting turnings of elemental uranium with iodine dissolved in 1,4-dioxane under mild conditions. These molecular compounds of uranium are thermally stable and excellent precursor materials for synthesizing other molecular compounds of uranium including alkoxide, amide, organometallic, and halide compounds.

  16. X-231A demonstration of in-situ remediation of DNAPL compounds in low permeability media by soil fracturing with thermally enhanced mass recovery or reactive barrier destruction

    SciTech Connect

    Siegrist, R.L. |; Lowe, K.S.; Murdoch, L.D. |; Slack, W.W.; Houk, T.C.

    1998-03-01

    The overall goal of the program of activities is to demonstrate robust and cost-effective technologies for in situ remediation of DNAPL compounds in low permeability media (LPM), including adaptations and enhancements of conventional technologies to achieve improved performance for DNAPLs in LPM. The technologies sought should be potential for application at simple, small sites (e.g., gasoline underground storage tanks) as well as at complex, larger sites (e.g., DOE land treatment units). The technologies involved in the X-231A demonstration at Portsmouth Gaseous Diffusion Plant (PORTS) utilized subsurface manipulation of the LPM through soil fracturing with thermally enhanced mass recovery or horizontal barrier in place destruction. To enable field evaluation of these approaches, a set of four test cells was established at the X-231A land treatment unit at the DOE PORTS plant in August 1996 and a series of demonstration field activities occurred through December 1997. The principal objectives of the PORTS X-231A demonstration were to: determine and compare the operational features of hydraulic fractures as an enabling technology for steam and hot air enhanced soil vapor extraction and mass recovery, in situ interception and reductive destruction by zero valent iron, and in situ interception and oxidative destruction by potassium permanganate; determine the interaction of the delivered agents with the LPM matrix adjacent to the fracture and within the fractured zone and assess the beneficial modifications to the transport and/or reaction properties of the LPM deposit; and determine the remediation efficiency achieved by each of the technology strategies.

  17. Effects of post-reflow cooling rate and thermal aging on growth behavior of interfacial intermetallic compound between SAC305 solder and Cu substrate

    NASA Astrophysics Data System (ADS)

    Hu, Xiaowu; Xu, Tao; Jiang, Xiongxin; Li, Yulong; Liu, Yi; Min, Zhixian

    2016-04-01

    The interfacial reactions between Cu and Sn3Ag0.5Cu (SAC305) solder reflowed under various cooling rates were investigated. It is found that the cooling rate is an important parameter in solder reflow process because it influences not only microstructure of solder alloy but also the morphology and growth of intermetallic compounds (IMCs) formed between solder and Cu substrate. The experimental results indicate that only scallop-like Cu6Sn5 IMC layer is observed between solder and Cu substrate in case of water cooling and air cooling, while bilayer composed of scallop-like Cu6Sn5 and thin layer-like Cu3Sn is detected under furnace cooling due to sufficient reaction time to form Cu3Sn between Cu6Sn5 IMC and Cu substrate which resulted from slow cooling rate. Samples with different reflow cooling rates were further thermal-aged at 423 K. And it is found that the thickness of IMC increases linearly with square root of aging time. The growth constants of interfacial IMC layer during aging were obtained and compared for different cooling rates, indicating that the IMC layer thickness increased faster in samples under low cooling rate than in the high cooling rate under the same aging condition. The long prismatic grains were formed on the existing interfacial Cu6Sn5 grains to extrude deeply into solder matrix with lower cooling rate and long-term aging, and the Cu6Sn5 grains coarsened linearly with cubic root of aging time.

  18. Magnetic Frustration in an Iron-Based Cairo Pentagonal Lattice

    NASA Astrophysics Data System (ADS)

    Ressouche, E.; Simonet, V.; Canals, B.; Gospodinov, M.; Skumryev, V.

    2009-12-01

    The Fe3+ lattice in the Bi2Fe4O9 compound is found to materialize the first analogue of a magnetic pentagonal lattice. Because of its odd number of bonds per elemental brick, this lattice, subject to first neighbor antiferromagnetic interactions, is prone to geometric frustration. The Bi2Fe4O9 magnetic properties have been investigated by macroscopic magnetic measurements and neutron diffraction. The observed noncollinear magnetic arrangement is related to the one stabilized on a perfect tiling as obtained from a mean field analysis with direct space magnetic configuration calculations. The peculiarity of this structure arises from the complex connectivity of the pentagonal lattice, a novel feature compared to the well-known case of triangle-based lattices.

  19. Enhanced negative thermal expansion in La(1-x)Pr(x)Fe10.7Co0.8Si1.5 compounds by doping the magnetic rare-earth element praseodymium.

    PubMed

    Li, Wen; Huang, Rongjin; Wang, Wei; Tan, Jie; Zhao, Yuqiang; Li, Shaopeng; Huang, Chuanjun; Shen, Jun; Li, Laifeng

    2014-06-01

    Experiments have been performed to enhance negative thermal expansion (NTE) in the La(Fe,Co,Si)13-based compounds by optimizing the chemical composition, i.e., proper substitution of La by magnetic element Pr. It is found that increasing the absolute value of the average coefficient of thermal expansion (CTE) in the NTE temperature region (200-300 K) attributes to enhancement of the spontaneous magnetization and its growth rate with increasing Pr content. Typically, the average CTE of La(1-x)Pr(x)Fe10.7Co0.8Si1.5 with x = 0.5 reaches as large as -38.5 × 10(-6) K(-1) between 200 and 300 K (ΔT = 100 K), which is 18.5% larger than that of x = 0. The present results highlight the potential applications of La(Fe,Co,Si)13-based compounds with a larger NTE coefficient. PMID:24848739

  20. Measuring on Lattices

    NASA Astrophysics Data System (ADS)

    Knuth, Kevin H.

    2009-12-01

    Previous derivations of the sum and product rules of probability theory relied on the algebraic properties of Boolean logic. Here they are derived within a more general framework based on lattice theory. The result is a new foundation of probability theory that encompasses and generalizes both the Cox and Kolmogorov formulations. In this picture probability is a bi-valuation defined on a lattice of statements that quantifies the degree to which one statement implies another. The sum rule is a constraint equation that ensures that valuations are assigned so as to not violate associativity of the lattice join and meet. The product rule is much more interesting in that there are actually two product rules: one is a constraint equation arises from associativity of the direct products of lattices, and the other a constraint equation derived from associativity of changes of context. The generality of this formalism enables one to derive the traditionally assumed condition of additivity in measure theory, as well introduce a general notion of product. To illustrate the generic utility of this novel lattice-theoretic foundation of measure, the sum and product rules are applied to number theory. Further application of these concepts to understand the foundation of quantum mechanics is described in a joint paper in this proceedings.

  1. Thermal and vibrational properties of thermoelectric ZnSb: Exploring the origin of low thermal conductivity

    NASA Astrophysics Data System (ADS)

    Fischer, A.; Scheidt, E.-W.; Scherer, W.; Benson, D. E.; Wu, Y.; Eklöf, D.; Häussermann, U.

    2015-06-01

    The intermetallic compound ZnSb is an interesting thermoelectric material largely due to its low lattice thermal conductivity. The origin of the low thermal conductivity has so far been speculative. Using multitemperature single crystal x-ray diffraction (9-400 K) and powder x-ray diffraction (300-725 K) measurements, we characterized the volume expansion and the evolution of structural properties with temperature and identified an increasingly anharmonic behavior of the Zn atoms. From a combination of Raman spectroscopy and first principles calculations of phonons, we consolidate the presence of low-energy optic modes with wave numbers below 60 cm-1 . Heat capacity measurements between 2 and 400 K can be well described by a Debye-Einstein model containing one Debye and two Einstein contributions with temperatures ΘD=195 K , ΘE 1=78 K , and ΘE 2=277 K as well as a significant contribution due to anharmonicity above 150 K. The presence of a multitude of weakly dispersed low-energy optical modes (which couple with the acoustic, heat carrying phonons) combined with anharmonic thermal behavior provides an effective mechanism for low lattice thermal conductivity. The peculiar vibrational properties of ZnSb are attributed to its chemical bonding properties, which are characterized by multicenter bonded structural entities. We argue that the proposed mechanism to explain the low lattice thermal conductivity of ZnSb might also control the thermoelectric properties of other electron poor semiconductors, such as Zn4Sb3 , CdSb, Cd4Sb3 , Cd13 -xInyZn10 , and Zn5Sb4In2 -δ .

  2. Instrumentation for Measuring Thermodynamic Properties of Rare-Earth Compounds

    NASA Astrophysics Data System (ADS)

    Urbina, Ulises I.; Thompson, Jonathon; Ho, Pei-Chun

    2010-03-01

    Current models on some Rare-Earth compounds cannot fully account for their strongly correlated electron behavior, which give rise to phenomenon such as unconventional superconductivity, heavy Fermion, and quantum critical behavior. The specific heat, thermopower, and thermal conductivity measurements give important thermodynamic properties, such as effective electronic mass, stiffness of the lattice (Debye temperature), entropy, density of states of charge carriers, and phase transitions which are crucial in characterizing these materials of interest in our laboratory. A calorimeter and a thermopower-thermal conductivity probe, which are using a modified relaxation method and standard steady-state heat flow technique, respectively, are constructed for the above purpose. Detailed schematic diagram and operating principles will be discussed in the report.

  3. Lattice Boltzmann Stokesian dynamics.

    PubMed

    Ding, E J

    2015-11-01

    Lattice Boltzmann Stokesian dynamics (LBSD) is presented for simulation of particle suspension in Stokes flows. This method is developed from Stokesian dynamics (SD) with resistance and mobility matrices calculated using the time-independent lattice Boltzmann algorithm (TILBA). TILBA is distinguished from the traditional lattice Boltzmann method (LBM) in that a background matrix is generated prior to the calculation. The background matrix, once generated, can be reused for calculations for different scenarios, thus the computational cost for each such subsequent calculation is significantly reduced. The LBSD inherits the merits of the SD where both near- and far-field interactions are considered. It also inherits the merits of the LBM that the computational cost is almost independent of the particle shape. PMID:26651812

  4. Latticed pentamode acoustic cloak

    PubMed Central

    Chen, Yi; Liu, Xiaoning; Hu, Gengkai

    2015-01-01

    We report in this work a practical design of pentamode acoustic cloak with microstructure. The proposed cloak is assembled by pentamode lattice made of a single-phase solid material. The function of rerouting acoustic wave round an obstacle has been demonstrated numerically. It is also revealed that shear related resonance due to weak shear resistance in practical pentamode lattices punctures broadband feature predicted based on ideal pentamode cloak. As a consequence, the latticed pentamode cloak can only conceal the obstacle in segmented frequency ranges. We have also shown that the shear resonance can be largely reduced by introducing material damping, and an improved broadband performance can be achieved. These works pave the way for experimental demonstration of pentamode acoustic cloak. PMID:26503821

  5. Lattice Boltzmann Stokesian dynamics

    NASA Astrophysics Data System (ADS)

    Ding, E. J.

    2015-11-01

    Lattice Boltzmann Stokesian dynamics (LBSD) is presented for simulation of particle suspension in Stokes flows. This method is developed from Stokesian dynamics (SD) with resistance and mobility matrices calculated using the time-independent lattice Boltzmann algorithm (TILBA). TILBA is distinguished from the traditional lattice Boltzmann method (LBM) in that a background matrix is generated prior to the calculation. The background matrix, once generated, can be reused for calculations for different scenarios, thus the computational cost for each such subsequent calculation is significantly reduced. The LBSD inherits the merits of the SD where both near- and far-field interactions are considered. It also inherits the merits of the LBM that the computational cost is almost independent of the particle shape.

  6. Exact Lattice Supersymmetry

    SciTech Connect

    Catterall, Simon; Kaplan, David B.; Unsal, Mithat

    2009-03-31

    We provide an introduction to recent lattice formulations of supersymmetric theories which are invariant under one or more real supersymmetries at nonzero lattice spacing. These include the especially interesting case of N = 4 SYM in four dimensions. We discuss approaches based both on twisted supersymmetry and orbifold-deconstruction techniques and show their equivalence in the case of gauge theories. The presence of an exact supersymmetry reduces and in some cases eliminates the need for fine tuning to achieve a continuum limit invariant under the full supersymmetry of the target theory. We discuss open problems.

  7. Effect of mechanical treatment on the silicate lattice of kaolinite

    NASA Astrophysics Data System (ADS)

    Zulumyan, N. H.; Papakhchyan, L. R.; Isahakyan, A. R.; Beglaryan, H. A.; Aloyan, S. G.

    2012-12-01

    X-ray diffraction, differential thermal and chemical analysis have been used to investigate the effect of mechanical treatment on the crystalline lattice of kaolinite. It was established that mechanical treatment leads to amorphization of the mineral and the release of hydroxyl water, but the continuity of kaolinite's silicate lattice remains intact despite certain deformations, and the phase transformations of the mineral thus occur without any noticeable change in temperature.

  8. Potts ferromagnet: Transformations and critical exponents in planar hierarchical lattices

    NASA Astrophysics Data System (ADS)

    Hauser, Paulo R.; Curado, Evaldo M. F.

    1988-07-01

    We prove that the duality transformation for a Potts ferromagnet on two-rooted planar hierarchical lattices (HL) preserves the thermal eigenvalue. This leads to a relation between the correlation length critical exponents υ of a HL and its corresponding dual lattice. Using hyperscaling, we show that their specific heat critical exponents α coincide. For a smaller class of HL—namely of diamond and tress types—we prove that another transformation also preserves υ and α.

  9. Anomalous thermal expansion with infrared spectroscopy.

    PubMed

    Plendl, J N; Mansur, L C

    1972-05-01

    Anomalous thermal expansion is treated through an analytical approach, based on the anharmonic behavior of lattice vibrations of the solids CuCl and CuBr of which complete ir spectroscopic data were available for the low temperature region. In the two cases examined here, anomalous thermal expansion as well as change of anharmonic factor, as a function of temperature, show a mirrorlike proportionality. In addition, drastic changes of ir energy absorption take place within the temperature region of reexpansion, suggesting a substantial increase of the ionic fraction of binding, coupled with a corresponding decrease of the covalent fraction, within the re-expansion period. These striking events appear to be the basic reason for the re-expansion phenomenon, since the sum value of the ionic radii of the compounds in question is greater than the sum value of the covalent radii, thus enlarging the interatomic distance, instead of contracting it. PMID:20119115

  10. Single-crystal growth, crystallography, magnetic susceptibility, heat capacity, and thermal expansion of the antiferromagnetic S=1 chain compound CaV[subscript 2]O[subscript 4

    SciTech Connect

    Niazi, A.; Bud'ko, S.L.; Schlagel, D.L.; Yan, J.Q.; Lograsso, T.A.; Kreyssig, A.; Das, S.; Nandi, S.; Goldman, A.I.; Honecker, A.; McCallum, R.W.; Reehuis, M.; Pieper, O.; Lake, B.; Johnston, D.C.

    2009-05-01

    The compound CaV{sub 2}O{sub 4} contains V{sup +3} cations with spin S=1 and has an orthorhombic structure at room temperature containing zigzag chains of V atoms running along the c axis. We have grown single crystals of CaV{sub 2}O{sub 4} and report crystallography, static magnetization, magnetic susceptibility x, ac magnetic susceptibility, heat capacity C{sub p}, and thermal expansion measurements in the temperature T range of 1.8--350 K on the single crystals and on polycrystalline samples. An orthorhombic-to-monoclinic structural distortion and a long-range antiferromagnetic (AF) transition were found at sample-dependent temperatures T{sub S}{approx}108--145 K and T{sub N}{approx}51--76 K, respectively. In two annealed single crystals, another transition was found at {approx}200 K. In one of the crystals, this transition is mostly due to V{sub 2}O{sub 3} impurity phase that grows coherently in the crystals during annealing. However, in the other crystal the origin of this transition at 200 K is unknown. The x(T) shows a broad maximum at {approx}300 K associated with short-range AF ordering and the anisotropy of x above T{sub N} is small. The anisotropic x(T{yields}0) data below T{sub N} show that the (average) easy axis of the AF magnetic structure is the b axis. The C{sub p}(T) data indicate strong short-range AF ordering above T{sub N}, consistent with the x(T) data. We fitted our x data by a J{sub 1}-J{sub 2} S=1 Heisenberg chain model, where J{sub 1}(J{sub 2}) is the (next)-nearest-neighbor exchange interaction. We find J{sub 1}{approx}230 K and surprisingly, J{sub 2}/J{sub 1}{approx}0 (or J{sub 1}/J{sub 2}{approx}0). The interaction J{sub {perpendicular}} between these S=1 chains leading to long-range AF ordering at T{sub N} is estimated to be J{sub {perpendicular}}/J{sub 1}{approx_equal}0.04.

  11. Effects of thermal fluctuations on thermal inflation

    SciTech Connect

    Hiramatsu, Takashi; Miyamoto, Yuhei; Yokoyama, Jun’ichi

    2015-03-12

    The mechanism of thermal inflation, a relatively short period of accelerated expansion after primordial inflation, is a desirable ingredient for a certain class of particle physics models if they are not to be in contention with the cosmology of the early Universe. Though thermal inflation is most simply described in terms of a thermal effective potential, a thermal environment also gives rise to thermal fluctuations that must be taken into account. We numerically study the effects of these thermal fluctuations using lattice simulations. We conclude that though they do not ruin the thermal inflation scenario, the phase transition at the end of thermal inflation proceeds through phase mixing and is therefore not accompanied by the formations of bubbles nor appreciable amplitude of gravitational waves.

  12. Effects of thermal fluctuations on thermal inflation

    NASA Astrophysics Data System (ADS)

    Hiramatsu, Takashi; Miyamoto, Yuhei; Yokoyama, Jun'ichi

    2015-03-01

    The mechanism of thermal inflation, a relatively short period of accelerated expansion after primordial inflation, is a desirable ingredient for a certain class of particle physics models if they are not to be in contention with the cosmology of the early Universe. Though thermal inflation is most simply described in terms of a thermal effective potential, a thermal environment also gives rise to thermal fluctuations that must be taken into account. We numerically study the effects of these thermal fluctuations using lattice simulations. We conclude that though they do not ruin the thermal inflation scenario, the phase transition at the end of thermal inflation proceeds through phase mixing and is therefore not accompanied by the formations of bubbles nor appreciable amplitude of gravitational waves.

  13. Strongly Correlated Quantum Gases Trapped in 3D Spin-Dependent Optical Lattices

    NASA Astrophysics Data System (ADS)

    Demarco, Brian

    2011-03-01

    Optical lattices have emerged as ideal systems for exploring Hubbard model physics, since the equivalent of material parameters such as the ratio of tunneling to interaction energy are easily and widely tunable. In this talk I will discuss our recent measurements using novel lattice potentials to realize more complex Hubbard models for bosonic 87 Rb atoms. In these experiments, we adjust the polarization of the lattice laser beams to realize fully three-dimensional, spin-dependent cubic optical lattices. We demonstrate that atoms can be trapped in combinations of spin states for which superfluid and Mott-insulator phases exist simultaneously in the lattice. We also co-trap states that experience a strong lattice potential and no lattice potential whatsoever. I will discuss recent measurements revealing a mechanism similar to Kapitza resistance that leads to thermal decoupling in this latter combination. The implications for sympathetic cooling and thermometry using species-dependent lattices will be outlined.

  14. Variation of magnetism and half-metallicity in Ru{sub 2}VSi with lattice expansion

    SciTech Connect

    Bhat, Idris Hamid; Gupta, Dinesh C.

    2015-06-24

    Full-potential linearized augmented plane wave method has been employed to investigate the electronic and magnetic properties of Ru{sub 2}VSi Heusler alloy at optimized lattice parameter and in expanded lattice. Present computations predict that Ru{sub 2}VSi has a ferromagnetic ground state with an optimized lattice constant 5.952 Å. The compound in ambient conditions was found to have metallic character. However, increased value of lattice parameter induces 100% spin-polarization in the material at Fermi energy. Further, the band gap tends to increase and the material behaves as pure half-metallic at an increased value of lattice constant.

  15. Advanced thermoelectric materials with enhanced crystal lattice structure and methods of preparation

    NASA Technical Reports Server (NTRS)

    Fleurial, Jean-Pierre (Inventor); Caillat, Thierry F. (Inventor); Borshchevsky, Alexander (Inventor)

    1998-01-01

    New skutterudite phases including Ru.sub.0.5 Pd.sub.0.5 Sb.sub.3, RuSb.sub.2 Te, and FeSb.sub.2 Te, have been prepared having desirable thermoelectric properties. In addition, a novel thermoelectric device has been prepared using skutterudite phase Fe.sub.0.5 Ni.sub.0.5 Sb.sub.3. The skutterudite-type crystal lattice structure of these semiconductor compounds and their enhanced thermoelectric properties results in semiconductor materials which may be used in the fabrication of thermoelectric elements to substantially improve the efficiency of the resulting thermoelectric device. Semiconductor materials having the desired skutterudite-type crystal lattice structure may be prepared in accordance with the present invention by using powder metallurgy techniques. Measurements of electrical and thermal transport properties of selected semiconductor materials prepared in accordance with the present invention, demonstrated high Hall mobilities and good Seebeck coefficients. These materials have low thermal conductivity and relatively low electrical resistivity, and are good candidates for low temperature thermoelectric applications.

  16. Fibonacci Optical Lattices

    NASA Astrophysics Data System (ADS)

    Singh, Kevin; Geiger, Zachary; Senaratne, Ruwan; Rajagopal, Shankari; Fujiwara, Kurt; Weld, David; Weld Group Team

    2015-05-01

    Quasiperiodicity is intimately involved in quantum phenomena from localization to the quantum Hall effect. Recent experimental investigation of quasiperiodic quantum effects in photonic and electronic systems have revealed intriguing connections to topological phenomena. However, such experiments have been limited by the absence of techniques for creating tunable quasiperiodic structures. We propose a new type of quasiperiodic optical lattice, constructed by intersecting a Gaussian beam with a 2D square lattice at an angle with an irrational tangent. The resulting potential, a generalization of the Fibonacci lattice, is a physical realization of the mathematical ``cut-and-project'' construction which underlies all quasiperiodic structures. Calculation of the energies and wavefunctions of atoms loaded into the proposed quasiperiodic lattice demonstrate a fractal energy spectrum and the existence of edge states. We acknowledge support from the ONR (award N00014-14-1-0805), the ARO and the PECASE program (award W911NF-14-1-0154), the AFOSR (award FA9550-12-1-0305), and the Alfred P. Sloan foundation (grant BR2013-110).

  17. Progress in lattice QCD

    SciTech Connect

    Andreas S. Kronfeld

    2002-09-30

    After reviewing some of the mathematical foundations and numerical difficulties facing lattice QCD, I review the status of several calculations relevant to experimental high-energy physics. The topics considered are moments of structure functions, which may prove relevant to search for new phenomena at the LHC, and several aspects of flavor physics, which are relevant to understanding CP and flavor violation.

  18. Random lattice superstrings

    SciTech Connect

    Feng Haidong; Siegel, Warren

    2006-08-15

    We propose some new simplifying ingredients for Feynman diagrams that seem necessary for random lattice formulations of superstrings. In particular, half the fermionic variables appear only in particle loops (similarly to loop momenta), reducing the supersymmetry of the constituents of the type IIB superstring to N=1, as expected from their interpretation in the 1/N expansion as super Yang-Mills.

  19. Convex Lattice Polygons

    ERIC Educational Resources Information Center

    Scott, Paul

    2006-01-01

    A "convex" polygon is one with no re-entrant angles. Alternatively one can use the standard convexity definition, asserting that for any two points of the convex polygon, the line segment joining them is contained completely within the polygon. In this article, the author provides a solution to a problem involving convex lattice polygons.

  20. Supersymmetry on the Lattice

    NASA Astrophysics Data System (ADS)

    Schaich, David

    2016-03-01

    Lattice field theory provides a non-perturbative regularization of strongly interacting systems, which has proven crucial to the study of quantum chromodynamics among many other theories. Supersymmetry plays prominent roles in the study of physics beyond the standard model, both as an ingredient in model building and as a tool to improve our understanding of quantum field theory. Attempts to apply lattice techniques to supersymmetric field theories have a long history, but until recently these efforts have generally encountered insurmountable difficulties related to the interplay of supersymmetry with the lattice discretization of spacetime. In recent years these difficulties have been overcome for a class of theories that includes the particularly interesting case of maximally supersymmetric Yang-Mills (N = 4 SYM) in four dimensions, which is a cornerstone of AdS/CFT duality. In combination with computational advances this progress enables practical numerical investigations of N = 4 SYM on the lattice, which can address questions that are difficult or impossible to handle through perturbation theory, AdS/CFT duality, or the conformal bootstrap program. I will briefly review some of the new ideas underlying this recent progress, and present some results from ongoing large-scale numerical calculations, including comparisons with analytic predictions.

  1. Shaken Lattice Interferometry

    NASA Astrophysics Data System (ADS)

    Weidner, Carrie; Yu, Hoon; Anderson, Dana

    2015-05-01

    This work introduces a method to perform interferometry using atoms trapped in an optical lattice. Starting at t = 0 with atoms in the ground state of a lattice potential V(x) =V0cos [ 2 kx + ϕ(t) ] , we show that it is possible to transform from one atomic wavefunction to another by a prescribed shaking of the lattice, i.e., by an appropriately tailored time-dependent phase shift ϕ(t) . In particular, the standard interferometer sequence of beam splitting, propagation, reflection, reverse propagation, and recombination can be achieved via a set of phase modulation operations {ϕj(t) } . Each ϕj(t) is determined using a learning algorithm, and the split-step method calculates the wavefunction dynamics. We have numerically demonstrated an interferometer in which the shaken wavefunctions match the target states to better than 1 % . We carried out learning using a genetic algorithm and optimal control techniques. The atoms remain trapped in the lattice throughout the full interferometer sequence. Thus, the approach may be suitable for use in an dynamic environment. In addition to the general principles, we discuss aspects of the experimental implementation. Supported by the Office of Naval Research (ONR) and Northrop Grumman.

  2. Thermal decomposition of energetic materials; 65: Conversion of insensitive explosives (NTO, ANTA) and related compounds to polymeric melon-like cyclic azine burn-rate suppressants

    SciTech Connect

    Williams, G.K.; Palopoli, S.F.; Brill, T.B. . Dept. of Chemistry)

    1994-08-01

    Selected triazole, tetrazole, triazine, tetrazine, furazan, and acyclic backbone compounds are shown by IR spectroscopy to convert to polymeric, melon-like, cyclic azine residues upon heating to T [ge] 500 C. These compounds include the insensitive explosives 3-nitro-1,2,4-triazol-5-one (NTO), 3-amino-5-nitro-1,2,4-triazole (ANTA), and nitroguanidine. The melon-like residue could suppress the burn rate if these compounds are formulated into solid rocket propellants. The IR-active gaseous products from thermolysis are determined as a function of pressure and are related to the atom connectivity in the parent molecules.

  3. Antiferromagnetic Kondo lattice in the layered compound CePd1–xBi₂ and comparison to the superconductor LaPd1–xBi₂

    SciTech Connect

    Han, Fei; Wan, Xiangang; Phelan, Daniel; Stoumpos, Constantinos C.; Sturza, Mihai; Malliakas, Christos D.; Li, Qing'an; Han, Tian-Heng; Zhao, Qingbiao; Chung, Duck Young; Kanatzidis, Mercouri G.

    2015-07-13

    The layered compound CePd1–xBi₂ with the tetragonal ZrCuSi₂-type structure was obtained from excess Bi flux. Magnetic susceptibility data of CePd1–xBi₂ show an antiferromagnetic ordering below 6 K and are anisotropic along the c axis and the ab plane. The anisotropy is attributed to crystal-electric-field (CEF) effects and a CEF model which is able to describe the susceptibility data is given. An enhanced Sommerfeld coefficient γ of 0.191 J mol Ce⁻¹ K⁻² obtained from specific-heat measurement suggests a moderate Kondo effect in CePd1–xBi₂. Other than the antiferromagnetic peak at 6 K, the resistivity curve shows a shoulderlike behavior around 75 K which could be attributed to the interplay between Kondo and CEF effects. Magnetoresistance and Hall-effect measurements suggest that the interplay reconstructs the Fermi-surface topology of CePd1–xBi₂ around 75 K. Electronic structure calculations reveal that the Pd vacancies are important to the magnetic structure and enhance the CEF effects which quench the orbital moment of Ce at low temperatures.

  4. Towards a predictive route for selection of doping elements for the thermoelectric compound PbTe from first-principles

    SciTech Connect

    Joseph, Elad; Amouyal, Yaron

    2015-05-07

    Striving for improvements of the thermoelectric (TE) properties of the technologically important lead telluride (PbTe) compound, we investigate the influence of different doping elements on the thermal conductivity, Seebeck coefficient, and electrical conductivity applying density functional theory calculations. Our approach combines total-energy calculations yielding lattice vibrational properties with the Boltzmann transport theory to obtain electronic transport properties. We find that doping with elements from the 1st and 3rd columns of the periodic table reduces the sound velocity and, consequently, the lattice thermal conductivity, while 2nd column dopants have no such influence. Furthermore, 1.6 at. % doping with 4th and 5th column elements provides the highest reduction of lattice thermal conductivity. Out of this group, Hf doping results in maximum reduction of the sound velocity from 2030 m s{sup −1} for pure PbTe to 1370 m s{sup −1}, which is equivalent to ca. 32% reduction of lattice thermal conductivity. The highest power factor values calculated for 1.6 at. % doping range between 40 and 56 μW cm{sup −1} K{sup −2}, and are obtained for substitution with dopants having the same valence as Pb or Te, such as those located at the 2nd, 14th, and 16th columns of the periodic table. We demonstrate how this method may be generalized for dopant-selection-oriented materials design aimed at improving TE performance of other compounds.

  5. Synthesis, crystal structure, thermal analysis and vibrational spectroscopy accomplished with DFT calculation of new hybrid compound [2-CH3C6H4NH3]HSO4.H2O

    NASA Astrophysics Data System (ADS)

    Ben Hassen, C.; Boujelbene, M.; Marweni, S.; Bahri, M.; Mhiri, T.

    2015-10-01

    The present paper undertakes the study of a new organic/inorganic hybrid compound [2-CH3C6H4NH3]HSO4.H2O characterized by the X-ray diffraction, TG-DTA, IR and Raman spectroscopy accomplished with DFT calculation. It is crystallized in the monoclinic system with the centrosymmetric space group P 21/c, with a = 9.445 (5) Å, b = 10.499 Å, c = 10.073 Å, β = 90.627 (5)° and Z = 4. The atomic arrangement can be described as inorganic layers built by infinite chains, parallel to the (a c) planes between which the organic cations are inserted. In this atomic arrangement, hydrogen bonds and π-π interactions between the different species have an important role in the tri-dimensional network cohesion. Besides, the X-ray powder diffraction of the title compound confirms the existence of only one phase at room temperature. The thermal decomposition of precursors studied by thermo gravimetric analysis (TGA), the differential thermal analysis (DTA) and the temperature-dependent X-ray diffraction, show crystalline anhydrous compounds upon dehydration. DFT/BHHLYP calculations were performed, using the DZV (d,p) basis set, to determine the harmonic frequencies of the vibrational modes of an optimized cluster structure. The calculated modes were animated using the Molden graphical package to give tentative assignments of the observed IR and Raman spectra.

  6. Determination of free and bound phenolic compounds in buckwheat spaghetti by RP-HPLC-ESI-TOF-MS: effect of thermal processing from farm to fork.

    PubMed

    Verardo, Vito; Arraez-Roman, David; Segura-Carretero, Antonio; Marconi, Emanuele; Fernandez-Gutierrez, Alberto; Caboni, Maria Fiorenza

    2011-07-27

    Nowadays there is considerable interest in the consumption of alternative crops as potential recipes for gluten-free products production. Therefore, the use of buckwheat for the production of gluten-free pasta has been investigated in the present study. RP-HPLC-ESI-TOF-MS has been applied for the separation and characterization of free and bound phenolic compounds in buckwheat flour and buckwheat spaghetti. Thus, 32 free and 24 bound phenolic compounds in buckwheat flour and spaghetti have been characterized and quantified. To the authors' knowledge, protochatechuic-4-O-glucoside acid and procyanidin A have been detected in buckwheat for the first time. The results have demonstrated a decrease of total free phenolic compounds from farm to fork (from flour to cooked spaghetti) of about 74.5%, with a range between 55.3 and 100%, for individual compounds. The decrease in bound phenols was 80.9%, with a range between 46.2 and 100%. The spaghetti-making process and the cooking caused losses of 46.1 and 49.4% of total phenolic compounds, respectively. Of the total phenolic compounds present in dried spaghetti, 11.6% were dissolved in water after cooking. PMID:21678994

  7. Statistics of lattice animals

    NASA Astrophysics Data System (ADS)

    Hsu, Hsiao-Ping; Nadler, Walder; Grassberger, Peter

    2005-07-01

    The scaling behavior of randomly branched polymers in a good solvent is studied in two to nine dimensions, modeled by lattice animals on simple hypercubic lattices. For the simulations, we use a biased sequential sampling algorithm with re-sampling, similar to the pruned-enriched Rosenbluth method (PERM) used extensively for linear polymers. We obtain high statistics of animals with up to several thousand sites in all dimension 2⩽d⩽9. The partition sum (number of different animals) and gyration radii are estimated. In all dimensions we verify the Parisi-Sourlas prediction, and we verify all exactly known critical exponents in dimensions 2, 3, 4, and ⩾8. In addition, we present the hitherto most precise estimates for growth constants in d⩾3. For clusters with one site attached to an attractive surface, we verify the superuniversality of the cross-over exponent at the adsorption transition predicted by Janssen and Lyssy.

  8. Lattice Boltzmann morphodynamic model

    NASA Astrophysics Data System (ADS)

    Zhou, Jian Guo

    2014-08-01

    Morphological change due to sediment transport is a common natural phenomenon in real flows. It involves complex processes of erosion and deposition such as those along beaches and in river beds, imposing a strong strain on human beings. Studying and understanding morphodynamic evolution are essential to protect living environment. Although there are conventional numerical methods like finite difference method and finite volume method for forecast of morphological change by solving flow and morphodynamic equations, the methods are too complex/inefficient to be applied to a real large scale problem. To overcome this, a lattice Boltzmann method is developed to simulate morphological evolution under flows. It provides an alternative way of studying morphodynamics at the full advantages of the lattice Boltzmann methodology. The model is verified by applications to the evolution of one and two dimensional sand dunes under shallow water flows.

  9. Introduction to lattice QCD

    SciTech Connect

    Gupta, R.

    1998-12-31

    The goal of the lectures on lattice QCD (LQCD) is to provide an overview of both the technical issues and the progress made so far in obtaining phenomenologically useful numbers. The lectures consist of three parts. The author`s charter is to provide an introduction to LQCD and outline the scope of LQCD calculations. In the second set of lectures, Guido Martinelli will discuss the progress they have made so far in obtaining results, and their impact on Standard Model phenomenology. Finally, Martin Luescher will discuss the topical subjects of chiral symmetry, improved formulation of lattice QCD, and the impact these improvements will have on the quality of results expected from the next generation of simulations.

  10. Predictions from lattice QCD

    SciTech Connect

    Kronfeld, A.S.; Allison, I.F.; Aubin, C.; Bernard, C.; Davies, C.T.H.; DeTar, C.; Di Pierro, M.; Freeland, E.D.; Gottlieb, Steven; Gray, A.; Gregor, E.; Heller, U.M.; Hetrick, J.E.; El-Khadra, Aida X.; Levkova, L.; Mackenzie, P.B.; Maresca, F.; Menscher, D.; Nobes, M.; Okamoto, M.; Oktay, M.B.; /Fermilab /Glasgow U. /Columbia U. /Washington U., St. Louis /Utah U. /DePaul U. /Art Inst. of Chicago /Indiana U. /Ohio State U. /Arizona U. /APS, New York /U. Pacific, Stockton /Illinois U., Urbana /Cornell U., LEPP /Simon Fraser U. /UC, Santa Barbara

    2005-09-01

    In the past year, we calculated with lattice QCD three quantities that were unknown or poorly known. They are the q{sup 2} dependence of the form factor in semileptonic D {yields} K/{nu} decay, the decay constant of the D meson, and the mass of the B{sub c} meson. In this talk, we summarize these calculations, with emphasis on their (subsequent) confirmation by experiments.

  11. Multipole plasmonic lattice solitons

    SciTech Connect

    Kou Yao; Ye Fangwei; Chen Xianfeng

    2011-09-15

    We theoretically demonstrate a variety of multipole plasmonic lattice solitons, including dipoles, quadrupoles, and necklaces, in two-dimensional metallic nanowire arrays with Kerr-type nonlinearities. Such solitons feature complex internal structures with an ultracompact mode size approaching or smaller than one wavelength. Their mode sizes and the stability characteristics are studied in detail within the framework of coupled mode theory. The conditions to form and stabilize these highly confined solitons are within the experimentally achievable range.

  12. Nucleon Structure from Lattice QCD

    SciTech Connect

    David Richards

    2007-09-05

    Recent advances in lattice field theory, in computer technology and in chiral perturbation theory have enabled lattice QCD to emerge as a powerful quantitative tool in understanding hadron structure. I describe recent progress in the computation of the nucleon form factors and moments of parton distribution functions, before proceeding to describe lattice studies of the Generalized Parton Distributions (GPDs). In particular, I show how lattice studies of GPDs contribute to building a three-dimensional picture of the proton, I conclude by describing the prospects for studying the structure of resonances from lattice QCD.

  13. Crystallographic Lattice Boltzmann Method.

    PubMed

    Namburi, Manjusha; Krithivasan, Siddharth; Ansumali, Santosh

    2016-01-01

    Current approaches to Direct Numerical Simulation (DNS) are computationally quite expensive for most realistic scientific and engineering applications of Fluid Dynamics such as automobiles or atmospheric flows. The Lattice Boltzmann Method (LBM), with its simplified kinetic descriptions, has emerged as an important tool for simulating hydrodynamics. In a heterogeneous computing environment, it is often preferred due to its flexibility and better parallel scaling. However, direct simulation of realistic applications, without the use of turbulence models, remains a distant dream even with highly efficient methods such as LBM. In LBM, a fictitious lattice with suitable isotropy in the velocity space is considered to recover Navier-Stokes hydrodynamics in macroscopic limit. The same lattice is mapped onto a cartesian grid for spatial discretization of the kinetic equation. In this paper, we present an inverted argument of the LBM, by making spatial discretization as the central theme. We argue that the optimal spatial discretization for LBM is a Body Centered Cubic (BCC) arrangement of grid points. We illustrate an order-of-magnitude gain in efficiency for LBM and thus a significant progress towards feasibility of DNS for realistic flows. PMID:27251098

  14. Crystallographic Lattice Boltzmann Method

    PubMed Central

    Namburi, Manjusha; Krithivasan, Siddharth; Ansumali, Santosh

    2016-01-01

    Current approaches to Direct Numerical Simulation (DNS) are computationally quite expensive for most realistic scientific and engineering applications of Fluid Dynamics such as automobiles or atmospheric flows. The Lattice Boltzmann Method (LBM), with its simplified kinetic descriptions, has emerged as an important tool for simulating hydrodynamics. In a heterogeneous computing environment, it is often preferred due to its flexibility and better parallel scaling. However, direct simulation of realistic applications, without the use of turbulence models, remains a distant dream even with highly efficient methods such as LBM. In LBM, a fictitious lattice with suitable isotropy in the velocity space is considered to recover Navier-Stokes hydrodynamics in macroscopic limit. The same lattice is mapped onto a cartesian grid for spatial discretization of the kinetic equation. In this paper, we present an inverted argument of the LBM, by making spatial discretization as the central theme. We argue that the optimal spatial discretization for LBM is a Body Centered Cubic (BCC) arrangement of grid points. We illustrate an order-of-magnitude gain in efficiency for LBM and thus a significant progress towards feasibility of DNS for realistic flows. PMID:27251098

  15. Crystallographic Lattice Boltzmann Method

    NASA Astrophysics Data System (ADS)

    Namburi, Manjusha; Krithivasan, Siddharth; Ansumali, Santosh

    2016-06-01

    Current approaches to Direct Numerical Simulation (DNS) are computationally quite expensive for most realistic scientific and engineering applications of Fluid Dynamics such as automobiles or atmospheric flows. The Lattice Boltzmann Method (LBM), with its simplified kinetic descriptions, has emerged as an important tool for simulating hydrodynamics. In a heterogeneous computing environment, it is often preferred due to its flexibility and better parallel scaling. However, direct simulation of realistic applications, without the use of turbulence models, remains a distant dream even with highly efficient methods such as LBM. In LBM, a fictitious lattice with suitable isotropy in the velocity space is considered to recover Navier-Stokes hydrodynamics in macroscopic limit. The same lattice is mapped onto a cartesian grid for spatial discretization of the kinetic equation. In this paper, we present an inverted argument of the LBM, by making spatial discretization as the central theme. We argue that the optimal spatial discretization for LBM is a Body Centered Cubic (BCC) arrangement of grid points. We illustrate an order-of-magnitude gain in efficiency for LBM and thus a significant progress towards feasibility of DNS for realistic flows.

  16. Group-IV semiconductor compounds

    SciTech Connect

    Berding, M.A.; Sher, A.; van Schilfgaarde, M.

    1997-08-01

    Properties of ordered group-IV compounds containing carbon, silicon, and germanium are calculated within the local density approximation. Twenty-seven fully relaxed compounds represented by seven different compound structures are compared and, with the exception of SiC, all compounds are found to be metastable. Two trends emerge: carbon-germanium bonds are disfavored, and compounds that have carbon on a common sublattice are the least unbound because of their relatively low strain. When carbon shares a sublattice with silicon or germanium, the large strain results in a narrowing of the band gap, and in some cases the compound is metallic. The most promising structures with the lowest excess energy contain carbon on one sublattice and although they do not lattice match to silicon, they match rather well to silicon carbide. {copyright} {ital 1997} {ital The American Physical Society}

  17. Cr and Ru substituted defect manganese silicides MnSiδ (δ˜ 1.72-1.74) as low thermal conductivity thermoelectrics*

    NASA Astrophysics Data System (ADS)

    Ponnambalam, Vijayabarathi; Morelli, Donald T.

    2013-03-01

    Defect manganese silicides MnSiδ (δ ~ 1.72-1.74) belong to a large family of compounds known as Nowotny chimney-ladder (NCL) phases and are closely related to an orthorhombic NCL compound TiSi2. One interesting feature is the low lattice thermal conductivity (κL ~ 2.5 W/m K) which may be due to several reasons: Since δ doesn't exceed 1.75 in MnSiδ, a considerable concentration of random vacancies exists on the Si-sublattice and can give rise to a low thermal conductivity. In addition, as synthesized MnSiδ is a mixture of many phases including Mn4Si7, Mn11Si19,Mn15Si26 and Mn27Si47 and in all these phases, while a-lattice parameter is closely matched, the c-lattice parameter substantially varies with δ. Such a closely matched a-lattice parameter can cause lattice strain and potentially reduce κL. Ru2Si3 forms solid solutions and Cr can be substituted as much as 20% in MnSiδ. These substitutions can favorably modify the lattice strain and reduce the thermal conductivity further. Hence manganese silicides substituted with small amounts of Cr and Ru have been synthesized. Thermoelectric properties including resistivity, Seebeck and Hall coefficients and thermal conductivity will be studied and presented. *This work was supported as part of the Center for Revolutionary Materials for Solid State Energy Conversion, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001054.

  18. Lattice QCD for parallel computers

    NASA Astrophysics Data System (ADS)

    Quadling, Henley Sean

    Lattice QCD is an important tool in the investigation of Quantum Chromodynamics (QCD). This is particularly true at lower energies where traditional perturbative techniques fail, and where other non-perturbative theoretical efforts are not entirely satisfactory. Important features of QCD such as confinement and the masses of the low lying hadronic states have been demonstrated and calculated in lattice QCD simulations. In calculations such as these, non-lattice techniques in QCD have failed. However, despite the incredible advances in computer technology, a full solution of lattice QCD may still be in the too-distant future. Much effort is being expended in the search for ways to reduce the computational burden so that an adequate solution of lattice QCD is possible in the near future. There has been considerable progress in recent years, especially in the research of improved lattice actions. In this thesis, a new approach to lattice QCD algorithms is introduced, which results in very significant efficiency improvements. The new approach is explained in detail, evaluated and verified by comparing physics results with current lattice QCD simulations. The new sub-lattice layout methodology has been specifically designed for current and future hardware. Together with concurrent research into improved lattice actions and more efficient numerical algorithms, the very significant efficiency improvements demonstrated in this thesis can play an important role in allowing lattice QCD researchers access to much more realistic simulations. The techniques presented in this thesis also allow ambitious QCD simulations to be performed on cheap clusters of commodity computers.

  19. Alkaline earth lead and tin compounds Ae2Pb, Ae2Sn, Ae=Ca,Sr,Ba, as thermoelectric materials

    SciTech Connect

    Parker, David S; Singh, David J

    2013-01-01

    We present a detailed theoretical study of three alkaline earth compounds Ca2Pb, Sr2Pb and Ba2Pb, which have undergone little previous study, calculating electronic band structures and Boltzmann transport and bulk moduli using density functional theory. We also study the corresponding tin compounds Ca2 Sn, Sr2 Sn and Ba2 Sn. We find that these are all narrow band gap semiconductors with an electronic structure favorable for thermoelectric performance, with substantial thermopowers for the lead compounds at temperature ranges from 300 to 800 K. For the lead compounds, we further find very low calculated bulk moduli - roughly half of the values for the lead chalcogenides, suggestive of soft phonons and hence low lattice thermal conductivity. All these facts indicate that these materials merit experimental investigation as potential high performance thermoelectrics. We find good potential for thermoelectric performance in the environmentally friendly stannide materials, particularly at high temperature.

  20. Toward lattice fractional vector calculus

    NASA Astrophysics Data System (ADS)

    Tarasov, Vasily E.

    2014-09-01

    An analog of fractional vector calculus for physical lattice models is suggested. We use an approach based on the models of three-dimensional lattices with long-range inter-particle interactions. The lattice analogs of fractional partial derivatives are represented by kernels of lattice long-range interactions, where the Fourier series transformations of these kernels have a power-law form with respect to wave vector components. In the continuum limit, these lattice partial derivatives give derivatives of non-integer order with respect to coordinates. In the three-dimensional description of the non-local continuum, the fractional differential operators have the form of fractional partial derivatives of the Riesz type. As examples of the applications of the suggested lattice fractional vector calculus, we give lattice models with long-range interactions for the fractional Maxwell equations of non-local continuous media and for the fractional generalization of the Mindlin and Aifantis continuum models of gradient elasticity.