Properties of dipolar bosonic quantum gases at finite temperatures
NASA Astrophysics Data System (ADS)
Boudjemâa, Abdelâali
2016-07-01
The properties of ultracold quantum gases of bosons with dipole–dipole interaction are investigated at finite temperature in the frame of representative ensembles theory. Self-consistent coupled equations of motion are derived for the condensate and the non-condensate components. Corrections due to the dipolar interaction to condensate depletion, the anomalous density and thermodynamic quantities such as the ground state energy, the equation of state, the compressibility and the presure are calculated in the homogeneous case at both zero and finite temperatures. Effects of interaction and temperature on the structure factor are also discussed. Within the realm of the local density approximation, we generalize our results to the case of a trapped dipolar gas.
Finite-Temperature Properties of Three-Dimensional Chiral Helimagnets
NASA Astrophysics Data System (ADS)
Shinozaki, Misako; Hoshino, Shintaro; Masaki, Yusuke; Kishine, Jun-ichiro; Kato, Yusuke
2016-07-01
We study a three-dimensional (3d) classical chiral helimagnet at finite temperatures through analysis of a spin Hamiltonian, which is defined on a simple cubic lattice and consists of the Heisenberg exchange, monoaxial Dzyaloshinskii-Moriya interactions, and the Zeeman energy due to a magnetic field applied in the plane perpendicular to the helical axis. We take account of the quasi-two-dimensionality of the known monoaxial chiral helimagnet CrNb3S6 and we adopt three methods: (i) a conventional mean-field (MF) analysis, which we call the 3dMF method, (ii) a hybrid method called the 2dMC-1dMF method, which is composed of a classical Monte Carlo (MC) simulation and a MF approximation applied respectively to the intra- and interlayer interactions, and (iii) a simple-MC simulation (3dMC) at zero field. The temperature dependence of the magnetization calculated by the 3dMF method shows a cusp-like structure similar to that observed in experiments. In the absence of a magnetic field, both 2dMC-1dMF and 3dMC yield similar values of the transition temperature. The 2dMC-1dMF method provides a quantitative description of the thermodynamic properties, even under an external field, at an accessible numerical cost.
Spectral properties of Shiba subgap states at finite temperatures
NASA Astrophysics Data System (ADS)
Žitko, Rok
2016-05-01
Using the numerical renormalization group (NRG), we analyze the temperature dependence of the spectral function of a magnetic impurity described by the single-impurity Anderson model with a superconducting host. With increasing temperature the spectral weight is gradually transferred from the δ peak to the continuous subgap background, and both spectral features coexist at finite temperatures: the δ peak persists to temperatures of order Δ . The continuous background is due to inelastic exchange scattering of Bogoliubov quasiparticles off the impurity, and it is thermally activated since it requires a finite thermal population of quasiparticles above the gap. In the singlet regime for strong hybridization or away from the particle-hole symmetric point (charge-fluctuation regime) an additional subgap structure is observed just below the gap edges. It has thermally activated behavior with an activation energy equal to the Shiba state excitation energy.
Properties of the sigma meson at finite temperature
NASA Astrophysics Data System (ADS)
Ibarra, J. R. Morones; Aguirre, A. J. Garza; Flores-Baez, Francisco V.
2015-12-01
We study the changes of the mass and width of the sigma meson in the framework of the Linear Sigma Model at finite temperature, in the one-loop approximation. We have found that as the temperature increases, the mass of sigma shifts down. We have also analyzed the σ-spectral function and we observe an enhancement at the threshold which is a signature of partial restoration of chiral symmetry, also interpreted as a tendency to chiral phase transition. Additionally, we studied the width of the sigma, when the threshold enhancement takes place, for different values of the sigma mass. We found that there is a brief enlargement followed by an abrupt fall in the width as the temperature increases, which is also related with the restoration of chiral symmetry and an indication that the sigma is a bound state of two pions.
Meson properties in a nonlocal SU(3) chiral quark model at finite temperature
Contrera, G. A.; Gomez Dumm, D.; Scoccola, N. N.
2010-11-12
Finite temperature meson properties are studied in the context of a nonlocal SU(3) quark model which includes flavor mixing and the coupling of quarks to the Polyakov loop (PL). We analyze the behavior of scalar and pseudoscalar meson masses and mixing angles, as well as quark-meson couplings and pseudoscalar meson decay constants.
Finite Temperature Properties of Three-Component Fermion Systems in Optical Lattice
NASA Astrophysics Data System (ADS)
Yanatori, Hiromasa; Koga, Akihisa
2016-01-01
We investigate finite temperature properties in the half-filled three-component (colors) fermion systems. It is clarified that a color density-wave (CDW) state is more stable than a color-selective "antiferromagnetic" (CSAF) state against thermal fluctuations. The reentrant behavior in the phase boundary for the CSAF state is found. We also address the maximum critical temperature of the translational symmetry breaking states in the multicomponent fermionic systems.
Quark matter and meson properties in a Nonlocal SU(3) chiral quark model at finite temperature
Gomez Dumm, D.; Contrera, G. A.
2012-06-15
We study the finite temperature behavior of light scalar and pseudoscalar meson properties in the context of a three-flavor nonlocal chiral quark model. The model includes mixing with active strangeness degrees of freedom, and takes care of the effect of gauge interactions by coupling the quarks with a background color field. We analyze the chiral restoration and deconfinement transitions, as well as the temperature dependence of meson masses, mixing angles, and decay constants.
Mechanical properties and fracture behavior of single-layer phosphorene at finite temperatures
NASA Astrophysics Data System (ADS)
Sha, Zhen-Dong; Pei, Qing-Xiang; Ding, Zhiwei; Jiang, Jin-Wu; Zhang, Yong-Wei
2015-10-01
Phosphorene, a new two-dimensional (2D) material beyond graphene, has attracted great attention in recent years due to its superior physical and electrical properties. However, compared to graphene and other 2D materials, phosphorene has a relatively low Young’s modulus and fracture strength, which may limit its applications due to possible structure failures. For the mechanical reliability of future phosphorene-based nanodevices, it is necessary to have a deep understanding of the mechanical properties and fracture behaviors of phosphorene. Previous studies on the mechanical properties of phosphorene were based on first principles calculations at 0 K. In this work, we employ molecular dynamics simulations to explore the mechanical properties and fracture behaviors of phosphorene at finite temperatures. It is found that temperature has a significant effect on the mechanical properties of phosphorene. The fracture strength and strain reduce by more than 65% when the temperature increases from 0 K to 450 K. Moreover, the fracture strength and strain in the zigzag direction is more sensitive to the temperature rise than that in the armchair direction. More interestingly, the failure crack propagates preferably along the groove in the puckered structure when uniaxial tension is applied in the armchair direction. In contrast, when the uniaxial tension is applied in the zigzag direction, multiple cracks are observed with rough fracture surfaces. Our present work provides useful information about the mechanical properties and failure behaviors of phosphorene at finite temperatures.
NASA Astrophysics Data System (ADS)
Sun, Kaipeng; Zhao, Yonghui; Hu, Haiyan
2015-02-01
The objective of this study is to develop a strategy to identify the temperature-dependent properties of a thermo-elastic structure in an unsteady temperature environment, where time-varying material properties and thermal stresses are taken into account. The identification problem is formulated as an updating procedure of the finite element model. Due to the unsteady temperature environment, this procedure is based on a time-variant finite element model because the system matrices change over time. The temperature-dependent properties are expressed as low-order polynomials first. Then, an integrated objective function is established by using errors of the instantaneous frequencies and the sum of the highest order of the polynomials for all the parameters. Subsequently, the particle swarm optimisation is performed to minimise the above objective function to simultaneously determine the coefficient and the order of the polynomials. To demonstrate the effectiveness of the proposed procedure, the identification of a simply supported beam with an axially movable boundary subjected to an unsteady, uniformly distributed temperature field is presented. The numerical verification shows that the identified temperature-dependent properties well track the trends of the true values with high accuracy.
Finite temperature effect on mechanical properties of graphene sheets with various grain boundaries
NASA Astrophysics Data System (ADS)
Yong, Ge; Hong-Xiang, Sun; Yi-Jun, Guan; Gan-He, Zeng
2016-06-01
The mechanical properties of graphene sheets with various grain boundaries are studied by molecular dynamics method at finite temperatures. The finite temperature reduces the ultimate strengths of the graphenes with different types of grain boundaries. More interestingly, at high temperatures, the ultimate strengths of the graphene with the zigzag-orientation grain boundaries at low tilt angles exhibit different behaviors from those at lower temperatures, which is determined by inner initial stress in grain boundaries. The results indicate that the finite temperature, especially the high one, has a significant effect on the ultimate strength of graphene with grain boundaries, which gives a more in-depth understanding of their mechanical properties and could be useful for potential graphene applications. Project supported by the Nation Natural Science Foundation of China (Grant Nos. 11347219 and 11404147), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK20140519), the Training Project of Young Backbone Teacher of Jiangsu University, the Advanced Talents of Jiangsu University, China (Grant No. 11JDG118), the Practice Innovation Training Program Projects for Industrial Center of Jiangsu University, China, and the State Key Laboratory of Acoustics, Chinese Academy of Sciences (Grant No. SKLOA201308).
Finite-temperature properties of strongly correlated fermions in the honeycomb lattice
NASA Astrophysics Data System (ADS)
Tang, Baoming; Paiva, Thereza; Khatami, Ehsan; Rigol, Marcos
2013-09-01
We study finite-temperature properties of strongly interacting fermions in the honeycomb lattice using numerical linked-cluster expansions and determinantal quantum Monte Carlo simulations. We analyze a number of thermodynamic quantities, including the entropy, the specific heat, uniform and staggered spin susceptibilities, short-range spin correlations, and the double occupancy at and away from half filling. We examine the viability of adiabatic cooling by increasing the interaction strength for homogeneous as well as for trapped systems. For the homogeneous case, this process is found to be more efficient at finite doping than at half filling. That, in turn, leads to an efficient adiabatic cooling in the presence of a trap, which, starting with even relatively high entropies, can drive the system to have a Mott insulating phase with substantial antiferromagnetic correlations.
QUARKONIUM AT FINITE TEMPERATURE.
UMEDA, T.
2006-06-09
Lattice QCD studies on charmonium at finite temperature are presented After a discussion about problems for the Maximum Entropy Method applied to finite temperature lattice QCD, I show several results on charmonium spectral functions. The 'wave function' of charmonium is also discussed to study the spatial correlation between quark and anti-quark in deconfinement phase.
Contrera, G. A.; Dumm, D. Gomez; Scoccola, Norberto N.
2010-03-01
We study the finite temperature behavior of light scalar and pseudoscalar meson properties in the context of a three-flavor nonlocal chiral quark model. The model includes mixing with active strangeness degrees of freedom, and takes care of the effect of gauge interactions by coupling the quarks with the Polyakov loop. We analyze the chiral restoration and deconfinement transitions, as well as the temperature dependence of meson masses, mixing angles and decay constants. The critical temperature is found to be T{sub c{approx_equal}}202 MeV, in better agreement with lattice results than the value recently obtained in the local SU(3) PNJL model. It is seen that above T{sub c} pseudoscalar meson masses get increased, becoming degenerate with the masses of their chiral partners. The temperatures at which this matching occurs depend on the strange quark composition of the corresponding mesons. The topological susceptibility shows a sharp decrease after the chiral transition, signalling the vanishing of the U(1){sub A} anomaly for large temperatures.
Finite-Temperature Micromagnetism
Skomski, R; Kumar, P; Hadjipanayis, GC; Sellmyer, DJ
2013-07-01
It is investigated how magnetic hysteresis is affected by finite-temperature excitations, using soft regions in hard-magnetic matrices as model systems. In lowest order, magnetization processes are described by the traditional approach of using finite-temperature materials constants such as K-1(T). Nanoscale excitations are usually small perturbations. For example, a Bloch summation over all magnon wave vectors shows that remanence is slightly enhanced, because long-wavelength excitations are suppressed. However, a reverse magnetic field enhances the effect of thermal excitations and causes a small reduction of the coercivity. To describe such effects, we advocate micromagnetic calculations where finite-temperature fluctuations are treated as small corrections to the traditional approach, as contrasted to full-scale Monte Carlo simulations.
NASA Astrophysics Data System (ADS)
Abu-Shady, M.; Abu-Nab, A.
2015-12-01
The logarithmic quark sigma model is applied to study the nucleon properties at finite temperature and chemical potential. The field equations have been solved numerically in the mean-field approximation by using the extended iteration method at finite temperature and baryon chemical potential. Baryon properties are investigated, such as the hedgehog mass, the magnetic moments of the proton and neutron, and the pion-nucleon coupling constant. We find that the hedgehog mass and the magnetic moments of the proton and neutron increase with increasing temperature and chemical potential, while the pion-nucleon coupling constant decreases. A comparison with the original sigma model and QCD sum rules is presented. We conclude that the logarithmic quark sigma model successfully describes baryon properties of a hot and dense medium.
Lu Xiancong; Yu Yue; Li Jinbin
2006-04-15
By using slave particle (slave boson and slave fermion) techniques on the Bose-Hubbard model, we study the finite temperature properties of ultracold Bose gases in optical lattices. The phase diagrams at finite temperature are depicted by including different types of slave particles and the effect of the finite types of slave particles is estimated. The superfluid density is evaluated using the Landau second order phase transition theory. The atom density, excitation spectrum, and dispersion curve are also computed at various temperatures, and how the Mott-insulator evolves as the temperature increases is demonstrated. For most quantities to be calculated, we find that there are no qualitative differences in using the slave boson or the slave fermion approaches. However, when studying the stability of the mean field state, we find that in contrast to the slave fermion approach, the slave boson mean field state is not stable. Although the slave boson mean field theory gives a qualitatively correct phase boundary, it corresponds to a local maximum of Landau free energy and cannot describe the second order phase transition because the coefficient a{sub 4} of the fourth order term is always negative in the free energy expansion.
Thermodynamic Properties of 4f- and 5f-SHELL Metals at Finite Temperatures:
NASA Astrophysics Data System (ADS)
Bhatt, N. K.; Vyas, P. R.; Jani, A. R.; Gohel, V. B.
The thermodynamic properties of 4f- and 5f-shell metals have been studied at high temperatures using mean-field potential approach. The MFP seen by the lattice ion is constructed in terms of the total energy-volume relation using local pseudopotentials due to Pandya et al. [Physica B 307, 138 (2001)]. We have calculated static compression, shock-wave compression, volume thermal expansion, isothermal and adiabatic bulk moduli (BT and BS), specific heats (CV and CP), thermodynamic Grüneisen parameter (γth), anharmonic contribution to the specific heat and temperature along shock Hugoniot for 4f (γ-Ce)- and 5f (fcc-Th)-shell metals. The results are well compared with the other theoretical and experimental findings, which ensure the use of pseudopotentials for studying thermodynamic properties at higher temperatures in case of lanthanides and actinides.
Supersymmetry at Finite Temperature Revisited
NASA Astrophysics Data System (ADS)
Paranjape, M. B.; Taormina, A.; Wijewardhana, L. C. R.
1983-05-01
The authors have formulated supersymmetry at finite temperature, generalizing the recent observations by Van Hove. They find that in a two-dimensional model broken supersymmetry is not restored at high temperature.
Browning, R.V.; Anderson, C.A.
1982-02-01
The finite element method is used to determine the temperatures, displacements, stresses, and strains in axisymmetric solids with orthotropic, temperature-dependent material properties under axisymmetric thermal and mechanical loads. The mechanical loads can be surface pressures, surface shears, and nodal point forces as well as an axial or centripetal acceleration. The continuous solid is replaced by a system of ring elements with triangular or quadrilateral cross sections. Accordingly, the method is valid for solids that are composed of many different materials and that have complex geometry. Nonlinear mechanical behavior as typified by plastic, locking, or creeping materials can be approximated. Two dimensional mesh generation, plotting, and editing features allow the computer program to be readily used. In addition to a stress analysis program that is based on a modified version of the SAAS code, TSAAS can carry out a transient thermal analysis with the finite element mesh used in stress analysis. An implicit time differencing scheme allows the use of arbitrary time steps with consequent fast running times. At specified times, the program will return to SAAS for thermal stress analysis. Nonlinear thermal properties and Arrhenius reaction kinetics are also incorporated into TSAAS. Several versions of TSAAS are in use at Los Alamos, running on CDC-7600, CRAY-1 and VAX 11/780 computers. This report describes the nominal TSAAS; other versions may have some unique features.
Magnetic insulation at finite temperatures
Goedecke, G. H.; Davis, Brian T.; Chen, Chiping
2006-08-15
A finite-temperature non-neutral plasma (FTNNP) theory of magnetically insulated (MI) electron flows in crossed-field vacuum devices is developed and applied in planar geometry. It is shown that, in contrast to the single type of MI flow predicted by traditional cold-plasma treatments, the nonlinear FTNNP equations admit five types of steady flow, of which three types are MI flows, including flows in which the electric field and/or the tangential velocity at the cathode may be zero or nonzero. It is also shown that finite-temperature Vlasov-Poisson treatments yield solutions for electron number densities and electrostatic potentials that are a subset of the FTNNP solutions. The algorithms that are used to solve the FTNNP equations numerically are discussed, and the numerical results are presented for several examples of the three types of MI flow. Results include prediction of the existence, boundaries, number density profiles, and other properties of sheaths of electrons in the anode-cathode gap.
Finite temperature magnetic properties of small Fe chains and clusters on Pt(111)
NASA Astrophysics Data System (ADS)
Riemer, S.; Dorantes-Dávila, J.; Pastor, G. M.
2016-04-01
The magnetic properties of Fe chains and clusters on Pt(111) are investigated in the framework of a functional-integral theory of itinerant magnetism. The considered nanostructures show a ferromagnetic (FM) ground state with nearly saturated Fe local magnetic moments μFe0≃3.15 μB . In addition, small moments μPt0≃0.1 -0.3 μB are induced at the Pt substrate, which depend sensitively on the number of Fe atoms in their nearest-neighbor (NN) shell. The spin-fluctuation (SF) energies Δ Fl(ξ ) at the different atoms l are calculated as a function of the local exchange fields ξl, by using a real-space recursive expansion of the local Green's functions. Results for the temperature dependence of the average magnetization per atom μ¯N, local magnetic moments μl, and spin correlation functions γl k are derived. At the Fe atoms the dominant magnetic excitations are fluctuations of the local-moment orientations. The spin-flip energies Δ Fl(ξ ) in the deposited Fe clusters are found to be about 50 % smaller than in free-standing clusters of comparable size. This results in flatter SF-energy landscapes and in a weaker stability of the FM order at T >0 . The effective exchange interactions between the Fe local moments, which are derived from the electronic calculations, reveal competing FM and antiferromagnetic couplings at different distances. In contrast to Fe, the main spin excitations at the Pt atoms are fluctuations of the size of the induced local magnetic moments. The interplay between the different types of spin excitations and their effect on the temperature-dependent magnetic properties is discussed.
Arago C. de; Bazeia, D.; Eboli, O.J.P.; Marques, G.C.
1985-12-15
We obtain a semiclassical evaluation of the temperature for which the free energy of the strings of spontaneously broken scalar electrodynamics vanishes. We argue that, above this temperature, these objects should play a significant physical role.
Ryabov, E.G.; Adeev, G.D.
2005-09-01
A macroscopic temperature-dependent model that takes into account nuclear forces of finite range is used to calculate the static and statistical properties of hot rotating compound nuclei. The level-density parameter is approximated by an expression of the leptodermous type. The resulting expansion coefficients are in good agreement with their counterparts proposed previously by A.V. Ignatyuk and his colleagues. The effect of taking simultaneously into account the temperature of a nucleus and its angular momentum on the quantities under study, such as the heights and positions of fission barriers and the effective moments of inertia of nuclei at the barrier, is considered, and the importance of doing this is demonstrated. The fissility parameter (Z{sup 2}/A){sub crit} and the position of the Businaro-Gallone point are studied versus temperature. It is found that, with increasing temperature, both parameters are shifted to the region of lighter nuclei. It is shown that the inclusion of temperature leads to qualitatively the same effects as the inclusion of the angular momentum of a nucleus, but, quantitatively, thermal excitation leads to smaller effects than rotational excitation.
Quasiparticle properties of the nonlinear Holstein model at finite doping and temperature
NASA Astrophysics Data System (ADS)
Li, Shaozhi; Nowadnick, Beth; Johnston, Steven
Models with linear electron-phonon (e-ph) interactions often predict the formation of small polarons with large lattice displacements. This directly violates the approximations made in deriving the linear model, which implies that one should consider higher order terms in the interaction. Previously we have shown that even small positive nonlinear e-ph interactions dramatically suppress charge-density-wave formation and s-wave superconductivity relative to the linear model [EPL. 109, 27007 (2015)]. In this talk, we present a determinant quantum Monte Carlo study of thesingle-particle properties of quasiparticles and phonons in a two-dimensional Holstein model that includes an additional nonlinear e-ph interaction. We show that a small positive nonlinear e-ph interaction reduces the effective coupling between electrons and phonons and hardens the effective phonon frequency. Conversely, a small negative nonlinear interaction can enhance e-ph coupling resulting in heavier quasiparticles. In addition, we find that an effective linear model fails to simultaneously capture the quantitative effects of the nonlinearity of both the electronic and phononic degrees of freedom, even though it can qualitatively reproduce properties.
Topological defects at finite temperature
Bazeia, D.; Eboli, O.J.P.; Guerra, J.M. Jr.; Marques, G.C.
1987-11-15
We obtain the phase diagram of gauge theories by studying the influence of topologically nontrivial boundary conditions. For this reason, we develop a scheme for computing the free energy of topological defects at finite temperature. As an application, the free energy of topological defects for the minimal SU(5) model are evaluated in the semiclassical approximation.
Quasiparticle properties of the nonlinear Holstein model at finite doping and temperature
NASA Astrophysics Data System (ADS)
Li, Shaozhi; Nowadnick, E. A.; Johnston, S.
2015-08-01
We use determinant quantum Monte Carlo to study the single-particle properties of quasiparticles and phonons in a variant of the two-dimensional Holstein model that includes an additional nonlinear electron-phonon (e-ph) interaction. We find that a small positive nonlinear interaction reduces the effective coupling between the electrons and the lattice, suppresses charge-density-wave (CDW) correlations, and hardens the effective phonon frequency. Conversely, a small negative nonlinear interaction can enhance the e-ph coupling resulting in heavier quasiparticles, an increased tendency towards a CDW phase at all fillings, and a softened phonon frequency. An effective linear model with a renormalized interaction strength and phonon frequency can qualitatively capture this physics; however, the quantitative effects of the nonlinearity on both the electronic and phononic degrees of freedom cannot be captured by such a model. These results are significant for typical nonlinear coupling strengths found in real materials, indicating that nonlinearity can have an important influence on the physics of many e-ph coupled systems.
Finite-temperature properties of the triangular lattice t-J model and applications to NaxCoO2
NASA Astrophysics Data System (ADS)
Haerter, Jan O.; Peterson, Michael R.; Shastry, B. Sriram
2006-12-01
We present a finite temperature (T) study of the t-J model on the two-dimensional triangular lattice for the negative hopping t , as relevant for the electron-doped NaxCoO2 (NCO). We study several thermodynamic and transport properties in this study: the T -dependent chemical potential, specific heat, magnetic susceptibility, and the dynamic Hall coefficient across the entire doping range. We show systematically how this simplest model for strongly correlated electrons describes a crossover as function of doping (x) from a Pauli-like weakly spin-correlated metal close to the band limit (density n=2 ) to the Curie-Weiss metallic phase (1.5
Electroweak relaxation from finite temperature
NASA Astrophysics Data System (ADS)
Hardy, Edward
2015-11-01
We study theories which naturally select a vacuum with parametrically small Electroweak Scale due to finite temperature effects in the early universe. In particular, there is a scalar with an approximate shift symmetry broken by a technically natural small coupling to the Higgs, and a temperature dependent potential. As the temperature of the universe drops, the scalar follows the minimum of its potential altering the Higgs mass squared parameter. The scalar also has a periodic potential with amplitude proportional to the Higgs expectation value, which traps it in a vacuum with a small Electroweak Scale. The required temperature dependence of the potential can occur through strong coupling effects in a hidden sector that are suppressed at high temperatures. Alternatively, it can be generated perturbatively from a one-loop thermal potential. In both cases, for the scalar to be displaced, a hidden sector must be reheated to temperatures significantly higher than the visible sector. However this does not violate observational constraints provided the hidden sector energy density is transferred to the visible sector without disrupting big bang nucleosynthesis. We also study how the mechanism can be implemented when the visible sector is completed to the Minimal Supersymmetric Standard Model at a high scale. Models with a UV cutoff of 10 TeV and no fields taking values over a range greater than 1012 GeV are possible, although the scalar must have a range of order 108 times the effective decay constant in the periodic part of its potential.
Costa, R. S.; Duarte, S. B.; Oliveira, J. C. T.; Chiapparini, M.
2010-05-21
We study the nuclear matter properties in the regime of high temperatures using a relativistic mean-field theory. Contrasting with the usual linear Walecka model, we include the sigma-omega meson coupling in order to investigate the role of this interaction in the nucleon effective mass behavior. Some numerical results are presented and discussed.
Dynamical properties of the sine-Gordon quantum spin magnet Cu-PM at zero and finite temperature
NASA Astrophysics Data System (ADS)
Tiegel, Alexander C.; Honecker, Andreas; Pruschke, Thomas; Ponomaryov, Alexey; Zvyagin, Sergei A.; Feyerherm, Ralf; Manmana, Salvatore R.
2016-03-01
The material copper pyrimidine dinitrate (Cu-PM) is a quasi-one-dimensional spin system described by the spin-1/2 X X Z Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interactions. Based on numerical results obtained by the density-matrix renormalization group, exact diagonalization, and accompanying electron spin resonance (ESR) experiments we revisit the spin dynamics of this compound in an applied magnetic field. Our calculations for momentum and frequency-resolved dynamical quantities give direct access to the intensity of the elementary excitations at both zero and finite temperature. This allows us to study the system beyond the low-energy description by the quantum sine-Gordon model. We find a deviation from the Lorentz invariant dispersion for the single-soliton resonance. Furthermore, our calculations only confirm the presence of the strongest boundary bound state previously derived from a boundary sine-Gordon field theory, while composite boundary-bulk excitations have too low intensities to be observable. Upon increasing the temperature, we find a temperature-induced crossover of the soliton and the emergence of new features, such as interbreather transitions. The latter observation is confirmed by our ESR experiments on Cu-PM over a wide range of the applied field.
Anomalies in curved spacetime at finite temperature
Boschi-Filho, H. Departamento de Fisica e Quimica, Universidade Estadual Paulista, Campus de Guaratingueta, 12500 Guaratingueta, Caixa Postal 205 Sao Paulo ); Natividade, C.P. )
1992-12-15
We discuss the problem of the breakdown of conformal and gauge symmetries at finite temperature in curved-spacetime background, when the changes in the background are gradual, in order to have a well-defined quantum field theory at finite temperature. We obtain the expressions for Seeley's coefficients and the heat-kernel expansion in this regime. As applications, we consider the self-interacting [lambda][phi][sup 4] and chiral Schwinger models in curved backgrounds at finite temperature.
Strange stars at finite temperature
NASA Astrophysics Data System (ADS)
Ray, Subharthi; Bagchi, Manjari; Dey, Jishnu; Dey, Mira
2006-03-01
We calculate strange star properties, using large Nc approximation with built-in chiral symmetry restoration (CSM). We used a relativistic Hartree Fock meanfield approximation method, using a modi.ed Richardson potential with two scale parameters Λ and Λ', to find a new set of equation of state (EOS) for strange quark matter. We take the effect of temperature (T) on gluon mass, in addition to the usual density dependence, and find that the transition T from hadronic matter to strange matter is 80 MeV. Therefore formation of strange stars may be the only signal for formation of QGP with asymptotic freedom (AF) and CSM.
LATTICE QCD AT FINITE TEMPERATURE AND DENSITY.
BLUM,T.; CREUTZ,M.; PETRECZKY,P.
2004-02-24
temperature for three different lattice spacings and performed a continuum extrapolation of T{sub tr} for the first time. Lattice calculations of the meson spectral functions were presented by M. Asakawa, S. Datta, E. Laermann and H. Matsufuru. These show that charmonia ground states ({eta}{sub c} and J/{psi}) continue to exist in the plasma at least up to a temperature of 1.7 T{sub tr}. At what temperature charmonia states cease to exist is not yet clear. Calculations presented by M. Asakawa show dissolution of the J/{psi} at T = 1.7 T{sub tr}, while the analysis presented H. Matsufuru provided evidence that ground state charmonia still exist at this temperature. S. Datta argued that the ground state charmonia is likely to dissolve only for temperatures T > 2.25 T{sub tr}, while the P-states are dissociated at, 1.1 T{sub tr}. It is also very interesting that, even in the case of light quarks, meson spectral functions show a resonance-like structure in the plasma phase (talk by E. Laermann). Finally attempts to calculate transport properties in the Quark Gluon Plasma were presented by S. Gupta. The workshop devoted special attention to the finite temperature modification of inter-quark forces and color screening, another area where considerable progress has been made in recent years (talks by 0. Kaczmarek, K. Petrov, O. Philipsen and F. Zantow). Many other new theoretical developments which cannot be discussed here were also presented on the workshop. Altogether the workshop was a great success, for which we thank all the participants.
Single-electron coherence: Finite temperature versus pure dephasing
NASA Astrophysics Data System (ADS)
Moskalets, Michael; Haack, Géraldine
2016-01-01
We analyze a coherent injection of single electrons on top of the Fermi sea in two situations, at finite-temperature and in the presence of pure dephasing. Both finite-temperature and pure dephasing change the property of the injected quantum states from pure to mixed. However, we show that the temperature-induced mixedness does not alter the coherence properties of these single-electron states. In particular two such mixed states exhibit perfect antibunching while colliding at an electronic wave splitter. This is in striking difference with the dephasing-induced mixedness which suppresses antibunching. On the contrary, a single-particle shot noise is suppressed at finite temperatures but is not affected by pure dephasing. This work therefore extends the investigation of the coherence properties of single-electron states to the case of mixed states and clarifies the difference between different types of mixedness.
Flux tubes at finite temperature
NASA Astrophysics Data System (ADS)
Cea, Paolo; Cosmai, Leonardo; Cuteri, Francesca; Papa, Alessandro
2016-06-01
The chromoelectric field generated by a static quark-antiquark pair, with its peculiar tube-like shape, can be nicely described, at zero temperature, within the dual superconductor scenario for the QCD confining vacuum. In this work we investigate, by lattice Monte Carlo simulations of the SU (3) pure gauge theory, the fate of chromoelectric flux tubes across the deconfinement transition. We find that, if the distance between the static sources is kept fixed at about 0.76 fm˜eq 1.6/√{σ } and the temperature is increased towards and above the deconfinement temperature T c , the amplitude of the field inside the flux tube gets smaller, while the shape of the flux tube does not vary appreciably across deconfinement. This scenario with flux-tube "evaporation" above T c has no correspondence in ordinary (type-II) superconductivity, where instead the transition to the phase with normal conductivity is characterized by a divergent fattening of flux tubes as the transition temperature is approached from below. We present also some evidence about the existence of flux-tube structures in the magnetic sector of the theory in the deconfined phase.
Finite temperature error-correcting codes
NASA Astrophysics Data System (ADS)
Ruján, Pál
1993-05-01
The correspondence between error-correcting convolution codes and gauge invariant spin-glass models is used to show that the optimal way to recover the original message is by decoding at a finite temperature TN(p)>0, where p is the strength of the channel noise and TN(p) the Nishimori temperature. This improves upon the retrieval performance of the T=0 maximal likelihood Viterbi decoding algorithm without increasing its computational complexity. Numerical simulations support the theory.
Gauge bosons at zero and finite temperature
NASA Astrophysics Data System (ADS)
Maas, Axel
2013-03-01
Gauge theories of the Yang-Mills type are the single most important building block of the standard model of particle physics and beyond. They are an integral part of the strong and weak interactions, and in their Abelian version of electromagnetism. Since Yang-Mills theories are gauge theories their elementary particles, the gauge bosons, cannot be described without fixing a gauge. Therefore, to obtain their properties a quantized and gauge-fixed setting is necessary. Beyond perturbation theory, gauge-fixing in non-Abelian gauge theories is obstructed by the Gribov-Singer ambiguity, which requires the introduction of non-local constraints. The construction and implementation of a method-independent gauge-fixing prescription to resolve this ambiguity is the single most important first step to describe gauge bosons beyond perturbation theory. Proposals for such a procedure, generalizing the perturbative Landau gauge, are described here. Their implementation are discussed for two example methods, lattice gauge theory and the quantum equations of motion. After gauge-fixing, it is possible to study gauge bosons in detail. The most direct access is provided by their correlation functions. The corresponding two- and three-point correlation functions are presented at all energy scales. These give access to the properties of the gauge bosons, like their absence from the asymptotic physical state space, particle-like properties at high energies, and the running coupling. Furthermore, auxiliary degrees of freedom are introduced during gauge-fixing, and their properties are discussed as well. These results are presented for two, three, and four dimensions, and for various gauge algebras. Finally, the modifications of the properties of gauge bosons at finite temperature are presented. Evidence is provided that these reflect the phase structure of Yang-Mills theory. However, it is found that the phase transition is not deconfining the gauge bosons, although the bulk
Bimetallic nanostructures. II. Finite temperature and applications
NASA Astrophysics Data System (ADS)
Montejano-Carrizales, J. M.; Morán-López, J. L.
1990-12-01
A systematic study of ordering and segregation at finite temperatures in bimetallic nanoclusters is presented. Icosahedral and cubo-octahedral clusters, with a total number of atoms, N = 13, 55 and 147, are studied. The equilibrium configuration is obtained by calculating the free energy within the regular solution model. The theory is applied to CuPd, NiPt and CuNi nanoclusters. We present results for the temperature dependence of the concentrations at the different shells around the central atom. In most of the cases a strong segregation is found.
Multiquark baryons and color screening at finite temperature
Ghoroku, Kazuo; Ishihara, Masafumi; Nakamura, Akihiro; Toyoda, Fumihiko
2009-03-15
We study baryons in SU(N) gauge theories at finite temperature according to the gauge/string correspondence based on IIB string theory. The baryon is constructed out of the D5-brane and N fundamental strings to form a color singlet N-quark bound state. At finite temperature and in the deconfining phase, we could find k(
U(1) problem at finite temperature
Janik, Romuald A.; Nowak, Maciej A.; Papp, Gabor; Zahed, Ismail
1999-11-22
We model the effects of a large number of zero and near-zero modes in the QCD partition function by using sparse chiral matrix models with an emphasis on the quenched topological susceptibility in the choice of the measure. At finite temperature, the zero modes are not affected by temperature but are allowed to pair into topologically neutral near-zero modes which are gapped at high temperature. In equilibrium, chiral and U(1) symmetry are simultaneously restored for total pairing, evading mean-field arguments. We analyze a number of susceptibilities versus the light quark masses. At the transition point the topological susceptibility vanishes, and the dependence on the vacuum angle {theta} drops out. Our results are briefly contrasted with recent lattice simulations.
Finite Temperature Quasicontinuum: Molecular Dynamics without all the Atoms
Dupuy, L; Tadmor, E B; Miller, R E; Phillips, R
2005-02-02
Using a combination of statistical mechanics and finite-element interpolation, the authors develop a coarse-grained (CG) alternative to molecular dynamics (MD) for crystalline solids at constant temperature. The new approach is significantly more efficient than MD and generalizes earlier work on the quasi-continuum method. The method is validated by recovering equilibrium properties of single crystal Ni as a function of temperature. CG dynamical simulations of nanoindentation reveal a strong dependence on temperature of the critical stress to nucleate dislocations under the indenter.
Thermal geometry from CFT at finite temperature
NASA Astrophysics Data System (ADS)
Gan, Wen-Cong; Shu, Fu-Wen; Wu, Meng-He
2016-09-01
We present how the thermal geometry emerges from CFT at finite temperature by using the truncated entanglement renormalization network, the cMERA. For the case of 2d CFT, the reduced geometry is the BTZ black hole or the thermal AdS as expectation. In order to determine which spacetimes prefer to form, we propose a cMERA description of the Hawking-Page phase transition. Our proposal is in agreement with the picture of the recent proposed surface/state correspondence.
Ferromagnetism in metals at finite temperatures
Gyorffy, B.L.; Staunton, J.B.; Stocks, G.M.
1984-01-01
The conventional spin-polarized band theory is well known to give a reasonable description of the magnetic ground states of metals. Here it is generalized to finite temperatures. The resulting theory is the first first-principles theory of the ferromagnetic phase transition in metals. It is a mean-field theory. For iron we find T/sub c/ = 1250 K and chi/sup -1/(q = 0) follows a Curie-Weiss law. We also report on our results for the wave-vector dependent susceptibility chi(q) which is a measure of magnetic short-range order above T/sub c/.
Damping of Bogoliubov excitations at finite temperatures
NASA Astrophysics Data System (ADS)
Pastukhov, Volodymyr
2015-10-01
We present a simple and efficient method to calculate the damping for the excitation spectrum of a uniform D-dimensional Bose gas. Starting from the original Popov’s hydrodynamic description and integrating out phase variables, we obtained the effective action of amplitude fluctuations. Within this approach, the lifetime of quasi-particles with a finite momentum is calculated at a wide temperature range. It is shown that the correct use of the hydrodynamic approach leads to the damping rate, which coincides with results obtained by means of the perturbation theory.
LARGE volume string compactifications at finite temperature
NASA Astrophysics Data System (ADS)
Anguelova, Lilia; Calò, Vincenzo; Cicoli, Michele
2009-10-01
We present a detailed study of the finite-temperature behaviour of the LARGE Volume type IIB flux compactifications. We show that certain moduli can thermalise at high temperatures. Despite that, their contribution to the finite-temperature effective potential is always negligible and the latter has a runaway behaviour. We compute the maximal temperature Tmax, above which the internal space decompactifies, as well as the temperature T*, that is reached after the decay of the heaviest moduli. The natural constraint T* < Tmax implies a lower bound on the allowed values of the internal volume Script V. We find that this restriction rules out a significant range of values corresponding to smaller volumes of the order Script V ~ 104ls6, which lead to standard GUT theories. Instead, the bound favours values of the order Script V ~ 1015ls6, which lead to TeV scale SUSY desirable for solving the hierarchy problem. Moreover, our result favours low-energy inflationary scenarios with density perturbations generated by a field, which is not the inflaton. In such a scenario, one could achieve both inflation and TeV-scale SUSY, although gravity waves would not be observable. Finally, we pose a two-fold challenge for the solution of the cosmological moduli problem. First, we show that the heavy moduli decay before they can begin to dominate the energy density of the Universe. Hence they are not able to dilute any unwanted relics. And second, we argue that, in order to obtain thermal inflation in the closed string moduli sector, one needs to go beyond the present EFT description.
Convexity at finite temperature and non-extensive thermodynamics
NASA Astrophysics Data System (ADS)
Alexandre, J.
2016-09-01
Assuming that tunnel effect between two degenerate bare minima occurs, in a scalar field theory at finite volume, this article studies the consequences for the effective potential, to all loop orders. Convexity is achieved only if the two bare minima are taken into account in the path integral, and a new derivation of the effective potential is given, in the large volume limit. The effective potential then has a universal form, it is suppressed by the space time volume, and does not feature spontaneous symmetry breaking as long as the volume is finite. The finite temperature analysis leads to surprising thermal properties, following from the non-extensive expression for the free energy. Although the physical relevance of these results is not clear, the potential application to ultra-light scalar particles is discussed.
Envisioning the Infinite by Projecting Finite Properties
ERIC Educational Resources Information Center
Ely, Robert
2011-01-01
We analyze interviews with 24 post-secondary students as they reason about infinite processes in the context of the tricky Tennis Ball Problem. By metaphorically projecting various properties from the finite states such as counting and indexing, participants envisioned widely varying final states for the infinite process. Depending on which…
Finite element simulation of temperature dependent free surface flows
NASA Technical Reports Server (NTRS)
Engelman, M. S.; Sani, R. L.
1985-01-01
The method of Engelman and Sani (1984) for a finite-element simulation of incompressible surface flows with a free and/or moving fluid interface, such as encountered in crystal growth and coating and polymer technology, is extended to temperature-dependent flows, including the effect of temperature-dependent surface tension. The basic algorithm of Saito and Scriven (1981) and Ruschak (1980) has been generalized and implemented in a robust and versatile finite-element code that can be employed with relative ease for the simulation of free-surface problems in complex geometries. As a result, the costly dependence on the Newton-Raphson algorithm has been eliminated by replacing it with a quasi-Newton iterative method, which nearly retains the superior convergence properties of the Newton-Raphson method.
Entropic uncertainty relation at finite temperature
NASA Technical Reports Server (NTRS)
Abe, Sumiyoshi; Suzuki, Norikazu
1992-01-01
We discussed how much information is lost when a particle is in equilibrium with the thermal reservoir of temperature T = 1/beta. The universal temperature correction to the r.h.s. of U(X,P:psi) greater than or = 1 + ln(pi) is determined. For this purpose, it is convenient to employ the framework of thermo-field dynamics (TFD). This formulation of finite-temperature (T not = 0) quantum theory utilizes the doubled Hilbert space, the normal operator (A) acting on the objective space, and its corresponding tildian operator on the fictitious space. The physical probability density associated with the measurement of the normal operator, A, is given, and the information entropy at T not = 0 is defined. The results describe how the thermal disturbance effects in S sub X or S sub P (delta X or delta P) can be suppressed by squeezing with keeping U = S sub X + S sub P (delta X x delta P) its minimum value.
Finite temperature static charge screening in quantum plasmas
NASA Astrophysics Data System (ADS)
Eliasson, B.; Akbari-Moghanjoughi, M.
2016-07-01
The shielding potential around a test charge is calculated, using the linearized quantum hydrodynamic formulation with the statistical pressure and Bohm potential derived from finite temperature kinetic theory, and the temperature effects on the force between ions is assessed. The derived screening potential covers the full range of electron degeneracy in the equation of state of the plasma electrons. An attractive force between shielded ions in an arbitrary degenerate plasma exists below a critical temperature and density. The effect of the temperature on the screening potential profile qualitatively describes the ion-ion bound interaction strength and length variations. This may be used to investigate physical properties of plasmas and in molecular-dynamics simulations of fermion plasma. It is further shown that the Bohm potential including the kinetic corrections has a profound effect on the Thomson scattering cross section in quantum plasmas with arbitrary degeneracy.
Optimization of finite-size errors in finite-temperature calculations of unordered phases
NASA Astrophysics Data System (ADS)
Iyer, Deepak; Srednicki, Mark; Rigol, Marcos
2015-06-01
It is common knowledge that the microcanonical, canonical, and grand-canonical ensembles are equivalent in thermodynamically large systems. Here, we study finite-size effects in the latter two ensembles. We show that contrary to naive expectations, finite-size errors are exponentially small in grand canonical ensemble calculations of translationally invariant systems in unordered phases at finite temperature. Open boundary conditions and canonical ensemble calculations suffer from finite-size errors that are only polynomially small in the system size. We further show that finite-size effects are generally smallest in numerical linked cluster expansions. Our conclusions are supported by analytical and numerical analyses of classical and quantum systems.
Optimization of finite-size errors in finite-temperature calculations of unordered phases
NASA Astrophysics Data System (ADS)
Iyer, Deepak; Srednicki, Mark; Rigol, Marcos
It is common knowledge that the microcanonical, canonical, and grand canonical ensembles are equivalent in thermodynamically large systems. Here, we study finite-size effects in the latter two ensembles. We show that contrary to naive expectations, finite-size errors are exponentially small in grand canonical ensemble calculations of translationally invariant systems in unordered phases at finite temperature. Open boundary conditions and canonical ensemble calculations suffer from finite-size errors that are only polynomially small in the system size. We further show that finite-size effects are generally smallest in numerical linked cluster expansions. Our conclusions are supported by analytical and numerical analyses of classical and quantum systems.
Holographic zero sound at finite temperature
NASA Astrophysics Data System (ADS)
Davison, Richard A.; Starinets, Andrei O.
2012-01-01
We use gauge-gravity duality to study the temperature dependence of the zero sound mode and the fundamental matter diffusion mode in the strongly coupled N=4 SU(Nc) supersymmetric Yang-Mills theory with Nf N=2 hypermultiplets in the Nc≫1, Nc≫Nf limit, which is holographically realized via the D3/D7 brane system. In the high density limit μ≫T, three regimes can be identified in the behavior of these modes, analogous to the collisionless quantum, collisionless thermal, and hydrodynamic regimes of a Landau Fermi liquid. The transitions between the three regimes are characterized by the parameters T/μ and (T/μ)2, respectively, and in each of these regimes the modes have a distinctively different temperature and momentum dependence. The collisionless-hydrodynamic transition occurs when the zero sound poles of the density-density correlator in the complex frequency plane collide on the imaginary axis to produce a hydrodynamic diffusion pole. We observe that the properties characteristic of a Landau Fermi-liquid zero sound mode are present in the D3/D7 system despite the atypical T6/μ3 temperature scaling of the specific heat and an apparent lack of a directly identifiable Fermi surface.
Two-dimensional finite-element temperature variance analysis
NASA Technical Reports Server (NTRS)
Heuser, J. S.
1972-01-01
The finite element method is extended to thermal analysis by forming a variance analysis of temperature results so that the sensitivity of predicted temperatures to uncertainties in input variables is determined. The temperature fields within a finite number of elements are described in terms of the temperatures of vertices and the variational principle is used to minimize the integral equation describing thermal potential energy. A computer calculation yields the desired solution matrix of predicted temperatures and provides information about initial thermal parameters and their associated errors. Sample calculations show that all predicted temperatures are most effected by temperature values along fixed boundaries; more accurate specifications of these temperatures reduce errors in thermal calculations.
Correlation effects on a topological insulator at finite temperatures
NASA Astrophysics Data System (ADS)
Yoshida, Tsuneya; Fujimoto, Satoshi; Kawakami, Norio
2012-03-01
We analyze the effects of the local Coulomb interaction on a topological band insulator (TBI) by applying the dynamical mean-field theory to a generalized Bernevig-Hughes-Zhang model having electron correlations. It is elucidated how the correlation effects modify electronic properties in the TBI phase at finite temperatures. In particular, the band inversion character of the TBI inevitably leads to the large reduction of the spectral gap via the renormalization effect, which results in the strong temperature dependence of the spin Hall conductivity. We clarify that a quantum phase transition from the TBI to a trivial Mott insulator, if it is nonmagnetic, is of first order with a hysteresis. This is confirmed via the interaction dependence of the double occupancy and the spectral function. A magnetic instability is also addressed. All these results imply that the spectral gap does not close at the transition.
Lowest order constrained variational calculation of polarized neutron matter at finite temperature
Bordbar, G. H.; Bigdeli, M.
2008-11-15
Some properties of polarized neutron matter at finite temperature have been studied using the lowest order constrained variational (LOCV) method with the Argonne V18 (AV18) potential. Our results indicate that a spontaneous transition to the ferromagnetic phase does not occur. Effective mass, free energy, magnetic susceptibility, entropy, and the equation of state of polarized neutron matter at finite temperature are also calculated. A comparison is also made between our results and those of other many-body techniques.
Finite ion temperature effects on scrape-off layer turbulence
NASA Astrophysics Data System (ADS)
Mosetto, Annamaria; Halpern, Federico D.; Jolliet, Sébastien; Loizu, Joaquim; Ricci, Paolo
2015-01-01
Ion temperature has been measured to be of the same order, or higher, than the electron temperature in the scrape-off layer (SOL) of tokamak machines, questioning its importance in determining the SOL turbulent dynamics. Here, we present a detailed analysis of finite ion temperature effects on the linear SOL instabilities, such as the resistive and inertial branches of drift waves and ballooning modes, and a discussion of the properties of the ion temperature gradient (ITG) instability in the SOL, identifying the η i = L n / L Ti threshold necessary to drive the mode unstable. The non-linear analysis of the SOL turbulent regimes by means of the gradient removal theory is performed, revealing that the ITG plays a negligible role in limited SOL discharges, since the ion temperature gradient is generally below the threshold for driving the mode unstable. It follows that the resistive ballooning mode is the prevailing turbulence regime for typical limited SOL parameters. The theoretical estimates are confirmed by non-linear flux-driven simulations of SOL plasma dynamics.
Finite ion temperature effects on scrape-off layer turbulence
Mosetto, Annamaria Halpern, Federico D.; Jolliet, Sébastien; Loizu, Joaquim; Ricci, Paolo
2015-01-15
Ion temperature has been measured to be of the same order, or higher, than the electron temperature in the scrape-off layer (SOL) of tokamak machines, questioning its importance in determining the SOL turbulent dynamics. Here, we present a detailed analysis of finite ion temperature effects on the linear SOL instabilities, such as the resistive and inertial branches of drift waves and ballooning modes, and a discussion of the properties of the ion temperature gradient (ITG) instability in the SOL, identifying the η{sub i}=L{sub n}/L{sub T{sub i}} threshold necessary to drive the mode unstable. The non-linear analysis of the SOL turbulent regimes by means of the gradient removal theory is performed, revealing that the ITG plays a negligible role in limited SOL discharges, since the ion temperature gradient is generally below the threshold for driving the mode unstable. It follows that the resistive ballooning mode is the prevailing turbulence regime for typical limited SOL parameters. The theoretical estimates are confirmed by non-linear flux-driven simulations of SOL plasma dynamics.
Recent progress in lattice QCD at finite temperature
Petreczky,P.
2009-02-01
I review recent progress in finite temperature lattice calculations,including the study of the nature of the deconfinement transition in QCD, equation of state, screening of static quarks and meson spectral functions.
Reprint of : Single-electron coherence: Finite temperature versus pure dephasing
NASA Astrophysics Data System (ADS)
Moskalets, Michael; Haack, Géraldine
2016-08-01
We analyze a coherent injection of single electrons on top of the Fermi sea in two situations, at finite-temperature and in the presence of pure dephasing. Both finite-temperature and pure dephasing change the property of the injected quantum states from pure to mixed. However, we show that the temperature-induced mixedness does not alter the coherence properties of these single-electron states. In particular two such mixed states exhibit perfect antibunching while colliding at an electronic wave splitter. This is in striking difference with the dephasing-induced mixedness which suppresses antibunching. On the contrary, a single-particle shot noise is suppressed at finite temperatures but is not affected by pure dephasing. This work therefore extends the investigation of the coherence properties of single-electron states to the case of mixed states and clarifies the difference between different types of mixedness.
Coarse-grained molecular dynamics: Nonlinear finite elements and finite temperature
Rudd, R E; Broughton, J Q
2005-05-30
Coarse-grained molecular dynamics (CGMD) is a technique developed as a concurrent multiscale model that couples conventional molecular dynamics (MD) to a more coarse-grained description of the periphery. The coarse-grained regions are modeled on a mesh in a formulation that generalizes conventional finite element modeling (FEM) of continuum elasticity. CGMD is derived solely from the MD model, however, and has no continuum parameters. As a result, it provides a coupling that is smooth and provides control of errors that arise at the coupling between the atomistic and coarse-grained regions. In this article, we elaborate on the formulation of CGMD, describing in detail how CGMD is applied to anharmonic solids and finite temperature simulations. As tests of CGMD, we present in detail the calculation of the phonon spectra for solid argon and tantalum in 3D, demonstrating how CGMD provides a better description of the elastic waves than that provided by FEM. We also present elastic wave scattering calculations that show the elastic wave scattering is more benign in CGMD than FEM. We also discuss the dependence of scattering on the properties of the mesh. We introduce a rigid approximation to CGMD that eliminates internal relaxation, similar to the Quasicontinuum technique, and compare it to the full CGMD.
Sudden change of geometric quantum discord in finite temperature reservoirs
Hu, Ming-Liang Sun, Jian
2015-03-15
We investigate sudden change (SC) behaviors of the distance-based measures of geometric quantum discords (GQDs) for two non-interacting qubits subject to the two-sided and the one-sided thermal reservoirs. We found that the GQDs defined by different distances exhibit different SCs, and thus the SCs are the combined result of the chosen discord measure and the property of a state. We also found that the thermal reservoir may generate states having different orderings related to different GQDs. These inherent differences of the GQDs reveal that they are incompatible in characterizing quantum correlations both quantitatively and qualitatively. - Highlights: • Comparable study of different distance-based geometric quantum discords. • Evolution of the geometric quantum discords in finite temperature reservoirs. • Different geometric quantum discords exhibit distinct sudden changes. • Nonunique states ordering imposed by different geometric quantum discords.
THE TWO-LEVEL MODEL AT FINITE-TEMPERATURE
Goodman, A.L.
1980-07-01
The finite-temperature HFB cranking equations are solved for the two-level model. The pair gap, moment of inertia and internal energy are determined as functions of spin and temperature. Thermal excitations and rotations collaborate to destroy the pair correlations. Raising the temperature eliminates the backbending effect and improves the HFB approximation.
Quantum entanglement of localized excited states at finite temperature
NASA Astrophysics Data System (ADS)
Caputa, Pawel; Simón, Joan; Štikonas, Andrius; Takayanagi, Tadashi
2015-01-01
In this work we study the time evolutions of (Renyi) entanglement entropy of locally excited states in two dimensional conformal field theories (CFTs) at finite temperature. We consider excited states created by acting with local operators on thermal states and give both field theoretic and holographic calculations. In free field CFTs, we find that the growth of Renyi entanglement entropy at finite temperature is reduced compared to the zero temperature result by a small quantity proportional to the width of the localized excitations. On the other hand, in finite temperature CFTs with classical gravity duals, we find that the entanglement entropy approaches a characteristic value at late time. This behaviour does not occur at zero temperature. We also study the mutual information between the two CFTs in the thermofield double (TFD) formulation and give physical interpretations of our results.
Comparison between microscopic methods for finite-temperature Bose gases
Cockburn, S. P.; Proukakis, N. P.; Negretti, A.; Henkel, C.
2011-04-15
We analyze the equilibrium properties of a weakly interacting, trapped quasi-one-dimensional Bose gas at finite temperatures and compare different theoretical approaches. We focus in particular on two stochastic theories: a number-conserving Bogoliubov (NCB) approach and a stochastic Gross-Pitaevskii equation (SGPE) that have been extensively used in numerical simulations. Equilibrium properties like density profiles, correlation functions, and the condensate statistics are compared to predictions based upon a number of alternative theories. We find that due to thermal phase fluctuations, and the corresponding condensate depletion, the NCB approach loses its validity at relatively low temperatures. This can be attributed to the change in the Bogoliubov spectrum, as the condensate gets thermally depleted, and to large fluctuations beyond perturbation theory. Although the two stochastic theories are built on different thermodynamic ensembles (NCB, canonical; SGPE, grand-canonical), they yield the correct condensate statistics in a large Bose-Einstein condensate (BEC) (strong enough particle interactions). For smaller systems, the SGPE results are prone to anomalously large number fluctuations, well known for the grand-canonical, ideal Bose gas. Based on the comparison of the above theories to the modified Popov approach, we propose a simple procedure for approximately extracting the Penrose-Onsager condensate from first- and second-order correlation functions that is both computationally convenient and of potential use to experimentalists. This also clarifies the link between condensate and quasicondensate in the Popov theory of low-dimensional systems.
Optimized Perturbation Theory:. Finite Temperature Applications
NASA Astrophysics Data System (ADS)
Pinto, Marcus Benghi
2001-09-01
We review the optimized perturbation theory (or linear δ-expansion) illustrating with an application to the anharmonic oscillator. We then apply the method to multi-field O(N1) × O(N2) scalar theories at high temperatures to investigate the possibility of inverse symmetry breaking (or symmetry non restoration). Our results support inverse symmetry breaking and reveal the possibility of other high temperature symmetry breaking patterns for which the last term in the breaking sequence is O(N1 - 1) × O(N2 - 1).
The Big Bang nucleosynthesis and finite temperature field theory
NASA Astrophysics Data System (ADS)
Johansson, Anders E. I.; Peressutti, Giorgio; Skagerstam, Bo-Sture
1982-11-01
We consider electromagnetic corrections at finite temperature and their effect on the nucleosynthesis in the standard Big Bang scenario. This requires discussing the finite, temperature dependent correction to the neutron-proton mass difference as well as making use of a previous result on the temperature correction to the mass of the electron. We find that these corrections do not affect the conventional results of e.g. the helium abundance to any appreciable extent. Research supported by the Swedish Natural Science Research Council, contract no. 7310-108.
Modified random phase approximation for multipole excitations at finite temperature
Dang, N.D. )
1992-03-01
The modified finite-temperature random phase approximation (FT-RPA) has been constructed by taking the influence of thermostat on the structure of quasiparticles into account. The modified FT-RPA linear response for electric quadrupole ({lambda}{sup {pi}}=2{sup +}) and octupole ({lambda}{sup {pi}}=3{sup {minus}}) excitations in {sup 58}Ni has been calculated as a function of the nuclear temperature. As compared to the conventional FT-RPA, the modified FT-RPA has given a stronger spreading for the strength distribution of quadrupole excitations at finite temperature {ital T}{le}3 MeV.
Simplified Quantum Transport Theory for Finite Bias and Temperature
NASA Astrophysics Data System (ADS)
Zhang, Xiaoguang; Wu, Yuning; Pantelides, Sokrates
We reformulate the Landauer-Buttiker formula for quantum transport by explicitly accounting for the energy and bias voltage dependence of the transmission probability. Under the assumption of a constant electric field, a simple formula for the differential conductance under a finite bias and at a finite temperature is derived that does not require a nonequilibrium self-consistent calculation. Calculation for the tunneling current through Au-Benzendithiol-Au molecular junction shows excellent agreement with the nonequilibrium Green's function (NEGF) method at zero temperature. Temperature dependent I-V curves for a number of devices are demonstrated. Supported by NSF Grant 1508898.
Exotic modes of excitation and weak interaction rates at finite temperature
Paar, N.
2011-10-28
The interplay of isospin asymmetry and finite temperature in nuclei plays an important role on properties of nuclear excitations and weak interaction rates in stellar environment. Recently a fully self-consistent microscopic framework, based on Hartree-Fock plus random phase approximation using Skyrme functionals, has been introduced for description of excitations and weak-interaction cross sections at finite temperature. Another self-consistent framework involving nuclei at finite temperature has also been developed within relativistic mean field theory using effective Lagrangians with density dependent meson-nucleon vertex functions. Nuclear excitations are studied using finite temperature random phase approximation for the range of temperatures T = 0-2 MeV, as well as in nuclei far from stability. In the focus of research are the structure properties of exotic modes of excitation (e.g. pygmy dipole resonances) and charge-exchange modes (e.g. Gamow-Teller resonances and forbidden transitions). It is shown that finite temperature effects include novel low-energy multipole excitations and modifications of the Gamow-Teller transition spectra. Using a representative set of Skyrme functionals, as well as covariant energy density functional with DD-ME2 parameterization, both theory frameworks have been applied in calculations of electron-capture cross sections relevant in the stage of supernova precollapse.
The gamma decay of the giant dipole resonance: from zero to finite temperature
NASA Astrophysics Data System (ADS)
Bracco, Angela; Camera, Franco
2016-08-01
This paper is intended to give a selected and rather brief overview of the work made in the last thirty years to study the properties of the giant dipole resonance focusing in particular on nuclei formed at finite temperatures using heavy ion reactions. The physical problems that are discussed (using examples of particular results) in this paper can be grouped into 3 major topics: (i) the temperature dependence of the GDR width; (ii) the dipole oscillation in reaction dynamics; (iii) the isospin mixing at finite temperature.
Casimir force at both nonzero temperature and finite conductivity.
Bordag, M; Geyer, B; Klimchitskaya, G L; Mostepanenko, V M
2000-07-17
We find the combined effect of nonzero temperature and finite conductivity onto the Casimir force between real metals. Configurations of two parallel plates and a sphere (lens) above a plate are considered. Perturbation theory in two parameters (the relative temperature and the relative penetration depth of zero-point oscillations into the metal) is developed. Perturbative results are compared with computations. Recent improper computations based on the Lifshitz formula for the temperature Casimir force are discussed. PMID:10991326
Variational Equation for Quantum Number Projection at Finite Temperature
NASA Astrophysics Data System (ADS)
Tanabe, Kosai; Nakada, Hitoshi
2008-04-01
To describe phase transitions in a finite system at finite temperature, we develop a formalism of the variation-after-projection (VAP) of quantum numbers based on the thermofield dynamics (TFD). We derive a new Bardeen-Cooper-Schrieffer (BCS)-type equation by variating the free energy with approximate entropy without violating Peierls inequality. The solution to the new BCS equation describes the S-shape in the specific heat curve and the superfluid-to-normal phase transition caused by the temperature effect. It simulates the exact quantum Monte Carlo results well.
Finite sample effect in temperature gradient focusing.
Lin, Hao; Shackman, Jonathan G; Ross, David
2008-06-01
Temperature gradient focusing (TGF) is a new and promising equilibrium gradient focusing method which can provide high concentration factors for improved detection limits in combination with high-resolution separation. In this technique, temperature-dependent buffer chemistry is employed to generate a gradient in the analyte electrophoretic velocity. By the application of a convective counter-flow, a zero-velocity point is created within a microchannel, at which location the ionic analytes accumulate or focus. In general, the analyte concentration is small when compared with buffer ion concentrations, such that the focusing mechanism works in the ideal, linearized regime. However, this presumption may at times be violated due to significant sample concentration growth or the use of a low-concentration buffer. Under these situations the sample concentration becomes non-negligible and can induce strong nonlinear interactions with buffer ions, which eventually lead to peak shifting and distortion, and the loss of detectability and resolution. In this work we combine theory, simulation, and experimental data to present a detailed study on nonlinear sample-buffer interactions in TGF. One of the key results is the derivation of a generalized Kohlrausch regulating function (KRF) that is valid for systems in which the electrophoretic mobilities are not constant but vary spatially. This generalized KRF greatly facilitates analysis, allowing reduction of the problem to a single equation describing sample concentration evolution, and is applicable to other problems with heterogeneous electrophoretic mobilities. Using this sample evolution equation we have derived an understanding of the nonlinear peak deformation phenomenon observed experimentally in TGF. We have used numerical simulations to validate our theory and to quantitatively predict TGF. Our simulation results demonstrate excellent agreement with experimental data, and also indicate that the proper inclusion of
Equilibrium structure of white dwarfs at finite temperatures
NASA Astrophysics Data System (ADS)
Boshkayev, K. A.; Rueda, J. A.; Zhami, B. A.; Kalymova, Zh. A.; Balgymbekov, G. Sh.
2016-03-01
Recently, it has been shown by S. M. de Carvalho et al. (2014) that the deviations between the degenerate case and observations were already evident for 0.7-0.8 M⊙ white dwarfs. Such deviations were related to the neglected effects of finite temperatures on the structure of a white dwarf. Therefore, in this work by employing the Chandrasekhar equation of state taking into account the effects of temperature we show how the total pressure of the white dwarf matter depends on the mass density at different temperatures. Afterwards we construct equilibrium configurations of white dwarfs at finite temperatures. We obtain the mass-radius relations of white dwarfs for different temperatures by solving the Tolman-Oppenheimer-Volkoff equation, and compare them with the estimated masses and radii inferred from the Sloan Digital Sky Survey Data Release 4.
Finite temperature effects in Bose-Einstein condensed dark matter halos
Harko, Tiberiu; Madarassy, Enikö J.M. E-mail: eniko.madarassy@physics.uu.se
2012-01-01
Once the critical temperature of a cosmological boson gas is less than the critical temperature, a Bose-Einstein Condensation process can always take place during the cosmic history of the universe. Zero temperature condensed dark matter can be described as a non-relativistic, Newtonian gravitational condensate, whose density and pressure are related by a barotropic equation of state, with barotropic index equal to one. In the present paper we analyze the effects of the finite dark matter temperature on the properties of the dark matter halos. We formulate the basic equations describing the finite temperature condensate, representing a generalized Gross-Pitaevskii equation that takes into account the presence of the thermal cloud. The static condensate and thermal cloud in thermodynamic equilibrium is analyzed in detail, by using the Hartree-Fock-Bogoliubov and Thomas-Fermi approximations. The condensed dark matter and thermal cloud density and mass profiles at finite temperatures are explicitly obtained. Our results show that when the temperature of the condensate and of the thermal cloud are much smaller than the critical Bose-Einstein transition temperature, the zero temperature density and mass profiles give an excellent description of the dark matter halos. However, finite temperature effects may play an important role in the early stages of the cosmological evolution of the dark matter condensates.
Heavy quark scattering and quenching in a QCD medium at finite temperature and chemical potential
NASA Astrophysics Data System (ADS)
Berrehrah, H.; Bratkovskaya, E.; Cassing, W.; Gossiaux, P. B.; Aichelin, J.
2015-05-01
The heavy quark collisional scattering on partons of the quark gluon plasma (QGP) is studied in a quantum chromodynamics medium at finite temperature and chemical potential. We evaluate the effects of finite parton masses and widths, finite temperature T , and quark chemical potential μq on the different elastic cross sections for dynamical quasiparticles (on- and off-shell particles in the QGP medium as described by the dynamical quasiparticle model "DQPM") using the leading order Born diagrams. Our results show clearly the decrease of the q Q and g Q total elastic cross sections when the temperature and the quark chemical potential increase. These effects are amplified for finite μq at temperatures lower than the corresponding critical temperature Tc(μq) . Using these cross sections we, furthermore, estimate the energy loss and longitudinal and transverse momentum transfers of a heavy quark propagating in a finite temperature and chemical potential medium. Accordingly, we have shown that the transport properties of heavy quarks are sensitive to the temperature and chemical potential variations. Our results provide some basic ingredients for the study of charm physics in heavy-ion collisions at Beam Energy Scan at RHIC and CBM experiment at FAIR.
Displacement properties of the product of two finite recursive matrices
NASA Astrophysics Data System (ADS)
Barnabei, Marilena; Montefusco, Laura B.
2002-12-01
We study the displacement properties, with respect to a suitable displacement operator, of the product of two finite sections of recursive matrices, and we give an explicit evaluation of the displacement rank of such a product in the case when the second matrix is a finite Toeplitz or Hankel matrix.
Resummation methods at finite temperature: The tadpole way
Boyd, C.G. ); Brahm, D.E. ); Hsu, S.D.H. )
1993-11-15
We examine several resummation methods for computing higher order corrections to the finite temperature effective potential, in the context of a scalar [phi][sup 4] theory. We show by explicit calculation to four loops that dressing the propagator, not the vertex, of the one-loop tadpole correctly counts daisy'' and superdaisy'' diagrams.
Finite-Temperature Gauge Theory from the Transverse Lattice
Dalley, S.; Sande, B. van de
2005-10-14
Numerical computations are performed and analytic bounds are obtained on the excited spectrum of glueballs in SU({infinity}) gauge theory, by transverse lattice Hamiltonian methods. We find an exponential growth of the density of states, implying a finite critical (Hagedorn) temperature. It is argued that the Nambu-Goto string model lies in a different universality class.
Finite temperature quantum field theory in the functional Schroedinger picture
Lee, H. ); Na, K.; Yee, J.H. )
1995-03-15
We calculate the finite temperature Gaussian effective potential of scalar [phi][sup 4] theory in the functional Schroedinger picture. Our method is the direct generalization of the variational method proposed by Eboli, Jackiw, and Pi for quantum-mechanical systems, and gives the same result as that of Amelino-Camelia and Pi who used the self-consistent composite operator method.
Pairing and thermodynamics properties of finite-systems with fixed number of particles
NASA Astrophysics Data System (ADS)
Gambacurta, D.; Lacroix, D.
2012-12-01
A canonical description of the thermodynamical pairing properties of small systems is achieved by using the Variation After Projection approach at finite temperature. The minimization of the free energy is made by a direct evaluation of the energy and full diagonalization of the entropy. We use the Richardson - pairing model whose exact solution allows to study the reliability of different approaches. We show that the Projection After Variation approach, that is usually performed at zero temperature with rather good success, provides a quite poor description at finite temperature. On the contrary, the Variation After Projection applied at finite temperature provides a perfect reproduction of the exact canonical properties of odd or even systems from very low to high temperature.
An adaptive finite element method for convective heat transfer with variable fluid properties
NASA Astrophysics Data System (ADS)
Pelletier, Dominique; Ilinca, Florin; Hetu, Jean-Francois
1993-07-01
This paper presents an adaptive finite element method based on remeshing to solve incompressible viscous flow problems for which fluid properties present a strong temperature dependence. Solutions are obtained in primitive variables using a highly accurate finite element approximation on unstructured grids. Two general purpose error estimators, that take into account fluid properties variations, are presented. The methodology is applied to a problem of practical interest: the thermal convection of corn syrup in an enclosure with localized heating. Predictions are in good agreement with experimental measurements. The method leads to improved accuracy and reliability of finite element predictions.
Kaon condensation in the linear sigma model at finite density and temperature
Tran Huu Phat; Nguyen Van Long; Nguyen Tuan Anh; Le Viet Hoa
2008-11-15
Basing on the Cornwall-Jackiw-Tomboulis effective action approach we formulate a theoretical formalism for studying kaon condensation in the linear sigma model at finite density and temperature. We derive the renormalized effective potential in the Hartree-Fock approximation, which preserves the Goldstone theorem. This quantity is then used to consider physical properties of kaon matter.
Finite difference program for calculating hydride bed wall temperature profiles
Klein, J.E.
1992-10-29
A QuickBASIC finite difference program was written for calculating one dimensional temperature profiles in up to two media with flat, cylindrical, or spherical geometries. The development of the program was motivated by the need to calculate maximum temperature differences across the walls of the Tritium metal hydrides beds for thermal fatigue analysis. The purpose of this report is to document the equations and the computer program used to calculate transient wall temperatures in stainless steel hydride vessels. The development of the computer code was motivated by the need to calculate maximum temperature differences across the walls of the hydrides beds in the Tritium Facility for thermal fatigue analysis.
First principles calculation of finite temperature magnetism in Ni
NASA Astrophysics Data System (ADS)
Eisenbach, Markus; Yin, Junqi; Nicholson, Don M.; Li, Ying Wai
2013-03-01
We harnesses the computational power of massively parallel computers to calculate finite temperature magnetic properties by combining classical Monte-Carlo calculations with our first principles multiple scattering electronic structure code (LSMS) for constrained magnetic states. Our previous calculations of Fe and Fe3 C [J. Appl. Phys. 109, 07E138 (2011)] only considered fluctuations in the local moment directions. Recent advances, both in the understanding of the Wang-Landau method used in our calculations [Phys. Rev. E 84, 065702(R) (2011)] and more powerful computing resources have enabled us to investigate Ni where the fluctuation in the magnitude of the local magnetic moments is of importance equal to their directional fluctuations. Here we will present our recent results for Ni that axpands our method to an even wider class of 3d element based ferromagnets. This research was sponsored by the Offices of Basic Energy Science (M.E. and D.M.N) and the Office of Advanced Computing Research (J.Y. and Y.W.L) of the US Department of Energy. This research used resources of the Oak Ridge Leadership Computing Facility at Oak Ridge National Laboratory, which is supported by the Office of Science of the Department of Energy under contract DE-AC05-00OR22725.
Ground-state and finite-temperature energetics and topologies of germanium microclusters
Antonio, G.A.; Feuston, B.P.; Kalia, R.K.; Vashishta, P.
1988-06-15
We have investigated the ground-state and finite-temperature properties of Ge microclusters (N = 2 to 14) using molecular dynamics (MD) simulation along with the method of steepest-descent quench (SDQ). The interaction potential adopted is the three-body Stillinger--Weber potential as modified by Ding and Andersen for amorphous Ge. Our results indicate that the experimentally observed greater stability of certain cluster sizes can be explained by the topology and energetics of the clusters at finite temperature rather than by the binding energies of the ground-state structures.
Nuclear pairing at finite temperature and angular momentum
Dang, N. Dinh; Hung, N. Quang
2009-01-28
We propose an approach to nuclear pairing at finite temperature and angular momentum. This approach includes the effects due to the quasiparticle-number fluctuation and dynamic coupling to pair vibrations within the self-consistent quasiparticle random-phase approximation. The pairing gaps, total energies, and heat capacities are calculated within a doubly folded multilevel model as well as several realistic nuclei. The results obtained show that, in the region of moderate and strong couplings, the sharp transition between the superconducting and normal phases is smoothed out. This is manifested in a thermal pairing gap, which does not collapse at a critical temperature predicted by the conventional Bardeen-Cooper-Schrieffer's (BCS) theory, but has a tail extended to high temperatures. Moreover, this approach also predicts the appearance of a thermally assisted pairing at finite angular momentum. The effect of backbending of the momentum of inertia as a function of the square of angular velocity is also discussed.
Diagrammatic algorithm for evaluating finite-temperature reaction rates
NASA Astrophysics Data System (ADS)
Ashida, Naoki; Nakkagawa, Hisao; Niégawa, Akira; Yokota, Hiroshi
1992-05-01
In this paper, by following the procedure of statistical mechanics we present the systematic calculational rules for evaluating the reaction rate of a generic dynamical process taking place in a heat bath. These rules are formulated within the framework of real-time thermal field theory (RTFT), in terms of the Feynman-like diagrams, the so-called circled diagrams. With the machinery developed in this paper we can establish the finite temperature generalization of the Cutkosky, or the cutting rules in quantum field theory at zero temperature. We have also studied the relation between the imaginary part of forward RTFT amplitude and the reaction rates; the imaginary part consists of various reaction rates. This is a finite temperature generalization of the optical theorem.
A note on the pulay force at finite temperatures
Niklasson, Anders M N
2008-01-01
Pulay's original expression for the basis-set dependent adjustment term to the Hellmann-Feynman force in electronic structure theory, which occurs for nonorthogonal local basis-set representations, is based on the idempotency condition of a pure ensemble. At finite electronic temperatures with a fractional occupation of the states, the conventional expression of the Pulay force is therefore no longer valid. Here we derive a simple and computationally efficient expression for a generalized Pulay force, which is suitable for large-scale ab initio simulations at finite electronic temperatures using local nonorthogonal basis-set representations. The generalized Pulay force expression is given in terms of the temperature-dependent density matrix. For the construction of the density matrix, we propose a recursive Fermi operator expansion algorithm that automatically converges to the correct chemical potential.
Phase transition in finite density and temperature lattice QCD
NASA Astrophysics Data System (ADS)
Wang, Rui; Chen, Ying; Gong, Ming; Liu, Chuan; Liu, Yu-Bin; Liu, Zhao-Feng; Ma, Jian-Ping; Meng, Xiang-Fei; Zhang, Jian-Bo
2015-06-01
We investigate the behavior of the chiral condensate in lattice QCD at finite temperature and finite chemical potential. The study was done using two flavors of light quarks and with a series of β and ma at the lattice size 24 × 122 × 6. The calculation was done in the Taylor expansion formalism. We are able to calculate the first and second order derivatives of ≤ft< {\\bar{\\psi} \\psi } \\right> in both isoscalar and isovector channels. With the first derivatives being small, we find that the second derivatives are sizable close to the phase transition and that the magnitude of \\bar{\\psi} \\psi decreases under the influence of finite chemical potential in both channels. Supported by National Natural Science Foundation of China (11335001, 11105153, 11405178), Projects of International Cooperation and Exchanges NSFC (11261130311)
Excitation spectrum of TTF-TCNQ: a finite temperature calculation
NASA Astrophysics Data System (ADS)
Lošić, Željana Bonačić
2013-01-01
In this paper we study the excitation spectrum of the organic conductor tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) using finite temperature calculations. The effect of electronelectron interaction is considered within the random phase approximation (RPA). Our results show the temperature dependent plasmon and dipolar mode corresponding qualitatively to the modes obtained previously using zero temperature formalism assigned to the observed excitations at 10 meV and 0.75 eV. These modes have an essential influence on the energy-loss function. The obtained results are in good qualitative agreement with the optical and EELS data of TTF-TCNQ.
Quarkonium correlators and spectral functions at zero and finite temperature
Jakovac, A.; Petreczky, P.; Petrov, K.; Velytsky, A.
2007-01-01
We study quarkonium correlators and spectral functions at zero and finite temperature using the anisotropic Fermilab lattice formulation with anisotropy {xi}=2 and 4. To control cut-off effects we use several different lattice spacings. The spectral functions were extracted from lattice correlators with maximum entropy method based on a new algorithm. We find evidence for the survival of 1S quarkonium states in the deconfined medium till relatively high temperatures as well as for dissolution of 1P quarkonium states right above the deconfinement temperature.
Zero finite-temperature charge stiffness within the half-filled 1D Hubbard model
Carmelo, J.M.P.; Gu, Shi-Jian; Sacramento, P.D.
2013-12-15
Even though the one-dimensional (1D) Hubbard model is solvable by the Bethe ansatz, at half-filling its finite-temperature T>0 transport properties remain poorly understood. In this paper we combine that solution with symmetry to show that within that prominent T=0 1D insulator the charge stiffness D(T) vanishes for T>0 and finite values of the on-site repulsion U in the thermodynamic limit. This result is exact and clarifies a long-standing open problem. It rules out that at half-filling the model is an ideal conductor in the thermodynamic limit. Whether at finite T and U>0 it is an ideal insulator or a normal resistor remains an open question. That at half-filling the charge stiffness is finite at U=0 and vanishes for U>0 is found to result from a general transition from a conductor to an insulator or resistor occurring at U=U{sub c}=0 for all finite temperatures T>0. (At T=0 such a transition is the quantum metal to Mott–Hubbard-insulator transition.) The interplay of the η-spin SU(2) symmetry with the hidden U(1) symmetry beyond SO(4) is found to play a central role in the unusual finite-temperature charge transport properties of the 1D half-filled Hubbard model. -- Highlights: •The charge stiffness of the half-filled 1D Hubbard model is evaluated. •Its value is controlled by the model symmetry operator algebras. •We find that there is no charge ballistic transport at finite temperatures T>0. •The hidden U(1) symmetry controls the U=0 phase transition for T>0.
Finite temperature quasiparticle self-consistent GW approximation
Vanschilfgaarde, Mark; Leonard, Francois; Desjarlais, Michael Paul; Kotani, Takao; Faleev, Sergey V
2005-10-01
We present a new ab initio method for electronic structure calculations of materials at finite temperature (FT) based on the all-electron quasiparticle self-consistent GW (QPscGW) approximation and Keldysh time-loop Green's function approach. We apply the method to Si, Ge, GaAs, InSb, and diamond and show that the band gaps of these materials universally decrease with temperature in contrast with the local density approximation (LDA) of density functional theory (DFT) where the band gaps universally increase. At temperatures of a few eV the difference between quasiparticle energies obtained in FT-QPscGW and FT-LDA approaches significantly reduces. This result suggests that existing simulations of very high temperature materials based on the FT-LDA are more justified then it might appear from well-known LDA band gap errors at zero-temperature.
B to D(D*)e{nu}{sub e} transitions at finite temperature in QCD
Azizi, K.; Er, N.
2010-05-01
In this article, we work out the properties of the B, D, and D* mesons as well as the B{yields}D(D*)e{nu}{sub e} decay properties at finite temperature QCD. The behavior of the masses, decay constants and widths of the B, D, and D* mesons in terms of the temperature is studied. The temperature dependency of the form factors responsible for such decays are also obtained. These temperature-dependent form factors are used to investigate the variation of the branching ratios with respect to the temperature. It is shown that the branching ratios do not change up to T/T{sub c}=0.3, however they start to diminish with increasing the temperature after this region and vanish at the critical or deconfinement temperature.
Spotlighting quantum critical points via quantum correlations at finite temperatures
Werlang, T.; Ribeiro, G. A. P.; Rigolin, Gustavo
2011-06-15
We extend the program initiated by T. Werlang et al. [Phys. Rev. Lett. 105, 095702 (2010)] in several directions. Firstly, we investigate how useful quantum correlations, such as entanglement and quantum discord, are in the detection of critical points of quantum phase transitions when the system is at finite temperatures. For that purpose we study several thermalized spin models in the thermodynamic limit, namely, the XXZ model, the XY model, and the Ising model, all of which with an external magnetic field. We compare the ability of quantum discord, entanglement, and some thermodynamic quantities to spotlight the quantum critical points for several different temperatures. Secondly, for some models we go beyond nearest neighbors and also study the behavior of entanglement and quantum discord for second nearest neighbors around the critical point at finite temperature. Finally, we furnish a more quantitative description of how good all these quantities are in spotlighting critical points of quantum phase transitions at finite T, bridging the gap between experimental data and those theoretical descriptions solely based on the unattainable absolute zero assumption.
Zhao, Junhua; Yang, Zhaoyao; Wei, Ning; Kou, Liangzhi
2016-01-01
Two dimensional (2D) gamma-boron (γ-B28) thin films have been firstly reported by the experiments of the chemical vapor deposition in the latest study. However, their mechanical properties are still not clear. Here we predict the superhigh moduli (785 ± 42 GPa at 300 K) and the tension-induced phase transition of monolayer γ-B28 along a zigzag direction for large deformations at finite temperatures using molecular dynamics (MD) simulations. The new phase can be kept stable after unloading process at these temperatures. The predicted mechanical properties are reasonable when compared with our results from density functional theory. This study provides physical insights into the origins of the new phase transition of monolayer γ-B28 at finite temperatures. PMID:26979283
Zhao, Junhua; Yang, Zhaoyao; Wei, Ning; Kou, Liangzhi
2016-01-01
Two dimensional (2D) gamma-boron (γ-B28) thin films have been firstly reported by the experiments of the chemical vapor deposition in the latest study. However, their mechanical properties are still not clear. Here we predict the superhigh moduli (785 ± 42 GPa at 300 K) and the tension-induced phase transition of monolayer γ-B28 along a zigzag direction for large deformations at finite temperatures using molecular dynamics (MD) simulations. The new phase can be kept stable after unloading process at these temperatures. The predicted mechanical properties are reasonable when compared with our results from density functional theory. This study provides physical insights into the origins of the new phase transition of monolayer γ-B28 at finite temperatures. PMID:26979283
NASA Astrophysics Data System (ADS)
Zhao, Junhua; Yang, Zhaoyao; Wei, Ning; Kou, Liangzhi
2016-03-01
Two dimensional (2D) gamma-boron (γ-B28) thin films have been firstly reported by the experiments of the chemical vapor deposition in the latest study. However, their mechanical properties are still not clear. Here we predict the superhigh moduli (785 ± 42 GPa at 300 K) and the tension-induced phase transition of monolayer γ-B28 along a zigzag direction for large deformations at finite temperatures using molecular dynamics (MD) simulations. The new phase can be kept stable after unloading process at these temperatures. The predicted mechanical properties are reasonable when compared with our results from density functional theory. This study provides physical insights into the origins of the new phase transition of monolayer γ-B28 at finite temperatures.
Orientational order at finite temperature on curved surfaces
NASA Astrophysics Data System (ADS)
Brito, Carolina; Vitelli, Vincenzo; Dauchot, Olivier
2016-03-01
We study the effect of thermal fluctuations in the XY model on surfaces with unequal principal curvatures. Unlike Gaussian curvature that typically frustrates orientational order, the extrinsic curvature of the surface can act as a local field that promotes long-range order at low temperature. We find numerically that the transition from the high temperature isotropic phase to the true long-range ordered phase is characterized by critical exponents consistent with those of the flat space Ising model in two dimensions, up to finite size effects. Our results suggest a versatile strategy to achieve geometric control of liquid crystal order by suitable design of the underlying curvature of a substrate.
On the fate of the Standard Model at finite temperature
NASA Astrophysics Data System (ADS)
Rose, Luigi Delle; Marzo, Carlo; Urbano, Alfredo
2016-05-01
In this paper we revisit and update the computation of thermal corrections to the stability of the electroweak vacuum in the Standard Model. At zero temperature, we make use of the full two-loop effective potential, improved by three-loop beta functions with two-loop matching conditions. At finite temperature, we include one-loop thermal corrections together with resummation of daisy diagrams. We solve numerically — both at zero and finite temperature — the bounce equation, thus providing an accurate description of the thermal tunneling. Assuming a maximum temperature in the early Universe of the order of 1018 GeV, we find that the instability bound excludes values of the top mass M t ≳ 173 .6 GeV, with M h ≃ 125 GeV and including uncertainties on the strong coupling. We discuss the validity and temperature-dependence of this bound in the early Universe, with a special focus on the reheating phase after inflation.
QCD nature of dark energy at finite temperature: Cosmological implications
NASA Astrophysics Data System (ADS)
Azizi, K.; Katırcı, N.
2016-05-01
The Veneziano ghost field has been proposed as an alternative source of dark energy, whose energy density is consistent with the cosmological observations. In this model, the energy density of the QCD ghost field is expressed in terms of QCD degrees of freedom at zero temperature. We extend this model to finite temperature to search the model predictions from late time to early universe. We depict the variations of QCD parameters entering the calculations, dark energy density, equation of state, Hubble and deceleration parameters on temperature from zero to a critical temperature. We compare our results with the observations and theoretical predictions existing at different eras. It is found that this model safely defines the universe from quark condensation up to now and its predictions are not in tension with those of the standard cosmology. The EoS parameter of dark energy is dynamical and evolves from -1/3 in the presence of radiation to -1 at late time. The finite temperature ghost dark energy predictions on the Hubble parameter well fit to those of Λ CDM and observations at late time.
Plasma shape and finite {beta} effects on stability thresholds of the ion temperature gradient modes
Jhowry, B.; Andersson, J.; Dastgeer, S.
2004-12-01
The stability of electromagnetic ion temperature gradient driven modes with emphasis on the lower and upper stability thresholds is investigated by a collisionless magnetized plasma in both circular and noncircular geometry. The stability properties are discussed and the results are compared for finite {beta} effects, arbitrary elongation, and Shafranov shift rate parameters. It has been found that the lower stability thresholds are weakly dependent on the (combined) effects of Shafranov shift rate, finite {beta}, and elongation whereas the second (upper) stability regime shows substantial dependence depending on parameter regimes.
FAST TRACK COMMUNICATION: Finite-temperature magnetism in bcc Fe under compression
NASA Astrophysics Data System (ADS)
Sha, Xianwei; Cohen, R. E.
2010-09-01
We investigate the contributions of finite-temperature magnetic fluctuations to the thermodynamic properties of bcc Fe as functions of pressure. First, we apply a tight-binding total-energy model parameterized to first-principles linearized augmented plane-wave computations to examine various ferromagnetic, anti-ferromagnetic, and noncollinear spin spiral states at zero temperature. The tight-binding data are fit to a generalized Heisenberg Hamiltonian to describe the magnetic energy functional based on local moments. We then use Monte Carlo simulations to compute the magnetic susceptibility, the Curie temperature, heat capacity, and magnetic free energy. Including the finite-temperature magnetism improves the agreement with experiment for the calculated thermal expansion coefficients.
Finite Element Estimation of Meteorite Structural Properties
NASA Technical Reports Server (NTRS)
Hart, Kenneth Arthur
2015-01-01
The goal of the project titled Asteroid Threat Assessment at NASA Ames Research Center is to develop risk assessment tools. The expertise in atmospheric entry in the Entry Systems and Technology Division is being used to describe the complex physics of meteor breakup in the atmosphere. The breakup of a meteor is dependent on its structural properties, including homogeneity of the material. The present work describes an 11-week effort in which a literature survey was carried for structural properties of meteoritic material. In addition, the effect of scale on homogeneity isotropy was studied using a Monte Carlo approach in Nastran. The properties were then in a static structural response simulation of an irregularly-shape meteor (138-scale version of Asteroid Itokawa). Finally, an early plan was developed for doctoral research work at Georgia Tech. in the structural failure fragmentation of meteors.
Occupation number and fluctuations in the finite-temperature Bose-Hubbard model
Plimak, L.I.; Fleischhauer, M.; Olsen, M.K.
2004-07-01
We study the occupation numbers and number fluctuations of ultracold atoms in deep optical lattices for finite-temperatures within the Bose-Hubbard model. Simple analytical expressions for the mean occupation number and number fluctuations are obtained in the weak-hopping regime using an interpolation between results from different perturbation approaches in the Mott-insulator and superfluid phases. With this approach the magnitude of number fluctuations under a wide range of experimental conditions can be estimated and the properties of the finite-temperature phase diagram can be studied. These analytical results are compared to exact one-dimensional numerical calculations using a finite temperature variant of the density-matrix renormalization group (DMRG) method and found to have a high degree of accuracy. We find very good agreement, also in the crossover 'thermal' region. We also analyze the influence of finite temperature on the behavior of the system in the vicinity of the zero-temperature phase transition, in one, two, and three dimensions.
Temperature dependent phonon properties of thermoelectric materials
NASA Astrophysics Data System (ADS)
Hellman, Olle; Broido, David; Fultz, Brent
2015-03-01
We present recent developments using the temperature dependent effective potential technique (TDEP) to model thermoelectric materials. We use ab initio molecular dynamics to generate an effective Hamiltonian that reproduce neutron scattering spectra, thermal conductivity, phonon self energies, and heat capacities. Results are presented for (among others) SnSe, Bi2Te3, and Cu2Se proving the necessity of careful modelling of finite temperature properties for strongly anharmonic materials. Supported by the Swedish Research Council (VR) Project Number 637-2013-7296.
Quarkonium at finite temperature: towards realistic phenomenology from first principles
NASA Astrophysics Data System (ADS)
Burnier, Yannis; Kaczmarek, Olaf; Rothkopf, Alexander
2015-12-01
We present the finite temperature spectra of both bottomonium and charmonium, obtained from a consistent lattice QCD based potential picture. Starting point is the complex in-medium potential extracted on full QCD lattices with dynamical u,d and s quarks, generated by the HotQCD collaboration. Using the generalized Gauss law approach, vetted in a previous study on quenched QCD, we fit Re[ V] with a single temperature dependent parameter m D , the Debye screening mass, and confirm the up to now tentative values of Im[ V]. The obtained analytic expression for the complex potential allows us to compute quarkonium spectral functions by solving an appropriate Schrödinger equation. These spectra exhibit thermal widths, which are free from the resolution artifacts that plague direct reconstructions from Euclidean correlators using Bayesian methods. In the present adiabatic setting, we find clear evidence for sequential melting and derive melting temperatures for the different bound states. Quarkonium is gradually weakened by both screening (Re[ V]) and scattering (Im[ V]) effects that in combination lead to a shift of their in-medium spectral features to smaller frequencies, contrary to the mass gain of elementary particles at finite temperature.
Finite-temperature free fermions and the Kardar-Parisi-Zhang equation at finite time.
Dean, David S; Le Doussal, Pierre; Majumdar, Satya N; Schehr, Grégory
2015-03-20
We consider the system of N one-dimensional free fermions confined by a harmonic well V(x)=mω(2)x(2)/2 at finite inverse temperature β=1/T. The average density of fermions ρ(N)(x,T) at position x is derived. For N≫1 and β∼O(1/N), ρ(N)(x,T) is given by a scaling function interpolating between a Gaussian at high temperature, for β≪1/N, and the Wigner semicircle law at low temperature, for β≫N(-1). In the latter regime, we unveil a scaling limit, for βℏω=bN(-1/3), where the fluctuations close to the edge of the support, at x∼±√[2ℏN/(mω)], are described by a limiting kernel K(b)(ff)(s,s') that depends continuously on b and is a generalization of the Airy kernel, found in the Gaussian unitary ensemble of random matrices. Remarkably, exactly the same kernel K(b)(ff)(s,s') arises in the exact solution of the Kardar-Parisi-Zhang equation in 1+1 dimensions at finite time t, with the correspondence t=b(3). PMID:25839245
Conservative properties of finite difference schemes for incompressible flow
NASA Technical Reports Server (NTRS)
Morinishi, Youhei
1995-01-01
The purpose of this research is to construct accurate finite difference schemes for incompressible unsteady flow simulations such as LES (large-eddy simulation) or DNS (direct numerical simulation). In this report, conservation properties of the continuity, momentum, and kinetic energy equations for incompressible flow are specified as analytical requirements for a proper set of discretized equations. Existing finite difference schemes in staggered grid systems are checked for satisfaction of the requirements. Proper higher order accurate finite difference schemes in a staggered grid system are then proposed. Plane channel flow is simulated using the proposed fourth order accurate finite difference scheme and the results compared with those of the second order accurate Harlow and Welch algorithm.
Sideband Rabi spectroscopy of finite-temperature trapped Bose gases
NASA Astrophysics Data System (ADS)
Allard, Baptiste; Fadel, Matteo; Schmied, Roman; Treutlein, Philipp
2016-04-01
We use Rabi spectroscopy to explore the low-energy excitation spectrum of a finite-temperature Bose gas of rubidium atoms across the phase transition to a Bose-Einstein condensate (BEC). To record this spectrum, we coherently drive the atomic population between two spin states. A small relative displacement of the spin-specific trapping potentials enables sideband transitions between different motional states. The intrinsic nonlinearity of the motional spectrum, mainly originating from two-body interactions, makes it possible to resolve and address individual excitation lines. Together with sensitive atom counting, this constitutes a feasible technique to count single excited atoms of a BEC and to determine the temperature of nearly pure condensates. As an example, we show that for a nearly pure BEC of N =800 atoms the first excited state has a population of less than five atoms, corresponding to an upper bound on the temperature of 30 nK .
Towards quantum turbulence in finite temperature Bose-Einstein condensates
NASA Astrophysics Data System (ADS)
Lan, Shanquan; Tian, Yu; Zhang, Hongbao
2016-07-01
Motivated by the various indications that holographic superfluid is BCS like at the standard quantization but BEC like at the alternative quantization, we have implemented the alternative quantization in the dynamical holographic superfluid for the first time. With this accomplishment, we further initiate the detailed investigation of quantum turbulence in finite temperature BEC by a long time stable numerical simulation of bulk dynamics, which includes the two body decay of vortex number caused by vortex pair annihilation, the onset of superfluid turbulence signaled by Kolmogorov scaling law, and a direct energy cascade demonstrated by injecting energy to the turbulent superfluid. All of these results share the same patterns as the holographic superfluid at the standard quantization, thus suggest that these should be universal features for quantum turbulence at temperatures order of the critical temperature.
A minimal model for finite temperature superfluid dynamics
NASA Astrophysics Data System (ADS)
Andersson, N.; Krüger, C.; Comer, G. L.; Samuelsson, L.
2013-12-01
Building on a recently improved understanding of the problem of heat flow in general relativity, we develop a hydrodynamical model for coupled finite temperature superfluids. The formalism is designed with the dynamics of the outer core of a mature neutron star (where superfluid neutrons are coupled to a conglomerate of protons and electrons) in mind, but the main ingredients are relevant for a range of analogous problems. The entrainment between material fluid components (the condensates) and the entropy (the thermal excitations) plays a central role in the development. We compare and contrast the new model to previous results in the literature, and provide estimates for the relevant entrainment coefficients that should prove useful in future applications. Finally, we consider the sound-wave propagation in the system in two simple limits, demonstrating the presence of second sound if the temperature is sub-critical, but absence of this phenomenon above the critical temperature for superfluidity.
Transport properties of finite-beta microturbulence
Pueschel, M. J.; Jenko, F.
2010-06-15
Via nonlinear gyrokinetic simulations, microturbulent transport is investigated for electromagnetic trapped electron mode (TEM) and ion temperature gradient (ITG) tokamak core turbulence with beta up to and beyond the kinetic ballooning mode threshold. Deviations from linear expectations are explained by zonal flow activity in the TEM case. For the ITG scenario, beta-induced changes are observed in the nonlinear critical gradient upshift--from a certain beta, a strong increase is observed in the Dimits shift. Additionally, a Rechester-Rosenbluth-type model for magnetic transport is applied, and the amplitudes of magnetic field fluctuations are quantified for different types of turbulence.
Ferromagnetic instabilities in neutron matter at finite temperature with the Gogny interaction
Lopez-Val, D.; Rios, A.; Polls, A.; Vidana, I.
2006-12-15
The properties of spin-polarized neutron matter are studied both at zero and finite temperature using the D1 and the D1P parametrizations of the Gogny interaction. The results show two different behaviors: whereas the D1P force exhibits a ferromagnetic transition at a density of {rho}{sub c}{approx}1.31 fm{sup -3} whose onset increases with temperature, no sign of such a transition is found for D1 at any density and temperature, in agreement with recent microscopic calculations.
An improved classical mapping method for homogeneous electron gases at finite temperature
Liu, Yu; Wu, Jianzhong
2014-08-14
We introduce a modified classical mapping method to predict the exchange-correlation free energy and the structure of homogeneous electron gases (HEG) at finite temperature. With the classical map temperature parameterized on the basis of the quantum Monte Carlo simulation data for the correlation energy and exact results at high and low temperature limits, the new theoretical procedure greatly improves the classical mapping method for correlating the energetic properties HEG over a broad range of thermodynamic conditions. Improvement can also be identified in predicting the long-range components of the spin-averaged pair correlation functions.
Disentangling the imaginary-time formalism at finite temperature
Wong, S. M. H.
2001-07-15
We rewrite the imaginary-time formalism of finite temperature field theory in a form that all graphs used in calculating physical processes do not have any loops. Any production of a particle from a heat bath which is itself not thermalized or the decay and absorption of a similar particle in the bath is expressed entirely in terms of the sum of particle interaction processes. These are themselves very general in meaning. They can be straightforward interactions or the more subtle and less well-known purely interference processes that do not have a counterpart in the vacuum.
Nonlocal microscopic theory of Casimir forces at finite temperature
Despoja, V.; Marusic, L.
2011-04-15
The interaction energy between two metallic slabs in the retarded limit at finite temperature is expressed in terms of surface polariton propagators for separate slabs, avoiding the usual matching procedure, with both diamagnetic and paramagnetic excitations included correctly. This enables appropriate treatment of arbitrary electron density profiles and fully nonlocal electronic response, including both collective and single-particle excitations. The results are verified by performing the nonretarded and long-wavelength (local) limits and showing that they reduce to the previously obtained expressions. Possibilities for practical use of the theory are explored by applying it to calculation of various contributions to the Casimir energy between two silver slabs.
Pairing phase transition: A finite-temperature relativistic Hartree-Fock-Bogoliubov study
NASA Astrophysics Data System (ADS)
Li, Jia Jie; Margueron, Jérôme; Long, Wen Hui; Van Giai, Nguyen
2015-07-01
Background: The relativistic Hartree-Fock-Bogoliubov (RHFB) theory has recently been developed and it provides a unified and highly predictive description of both nuclear mean-field and pairing correlations. Ground-state properties of finite nuclei can accurately be reproduced without neglecting exchange (Fock) contributions. Purpose: Finite-temperature RHFB (FT-RHFB) theory has not yet been developed, leaving yet unknown its predictions for phase transitions and thermal excitations in both stable and weakly bound nuclei. Method: FT-RHFB equations are solved in a Dirac Woods-Saxon (DWS) basis considering two kinds of pairing interactions: finite or zero range. Such a model is appropriate for describing stable as well as loosely bound nuclei since the basis states have correct asymptotic behavior for large spatial distributions. Results: Systematic FT-RH(F)B calculations are performed for several semimagic isotopic/isotonic chains comparing the predictions of a large number of Lagrangians, among which are PKA1, PKO1, and DD-ME2. It is found that the critical temperature for a pairing transition generally follows the rule Tc=0.60 Δ (0 ) for a finite-range pairing force and Tc=0.57 Δ (0 ) for a contact pairing force, where Δ (0 ) is the pairing gap at zero temperature. Two types of pairing persistence are analyzed: type I pairing persistence occurs in closed subshell nuclei while type II pairing persistence can occur in loosely bound nuclei strongly coupled to the continuum states. Conclusions: This FT-RHFB calculation shows very interesting features of the pairing correlations at finite temperature and in finite systems such as pairing re-entrance and pairing persistence.
Gluonic profile of the static baryon at finite temperature
NASA Astrophysics Data System (ADS)
Bakry, Ahmed S.; Leinweber, Derek B.; Williams, Anthony G.
2015-05-01
The gluon flux distribution of a static three quark system has been revealed at finite temperature in the pure SU(3) Yang-Mills theory. An action density operator is correlated with three Polyakov loops representing the baryonic state at temperatures near the end of the QCD plateau, T /Tc≈0.8 , and another just before the deconfinement point, T /Tc≈0.9 . The flux distributions at short distance separations between the quarks display an action-density profile consistent with a rounded filled Δ shape iso surface. However the Δ shape action iso-surface distributions are found to persist even at large interquark separations. The action density distribution in the quark plane exhibits a nonuniform pattern for all quark separations considered. This result contrasts with the Y-shaped uniform action density gluonic-flux profile obtained using the Wilson loop as a quark source operator at zero temperature. We systematically measure and compare the main aspects of the profile of the flux distribution at the two considered temperature scales for three sets of isosceles triangle quark configurations. In this paper, we present major characteristics of the gluonic profile including radii, amplitudes, and rate of change of the width of the flux distribution. These aspects show significant changes as the temperature changes from the end of the QCD plateau towards the deconfinement point. In particular, we found the flux tube is exhibiting a linear divergence at some planes of the gluonic pattern for the temperature close to the deconfinement point.
NASA Technical Reports Server (NTRS)
Saleeb, A. F.; Chang, T. Y. P.; Wilt, T.; Iskovitz, I.
1989-01-01
The research work performed during the past year on finite element implementation and computational techniques pertaining to high temperature composites is outlined. In the present research, two main issues are addressed: efficient geometric modeling of composite structures and expedient numerical integration techniques dealing with constitutive rate equations. In the first issue, mixed finite elements for modeling laminated plates and shells were examined in terms of numerical accuracy, locking property and computational efficiency. Element applications include (currently available) linearly elastic analysis and future extension to material nonlinearity for damage predictions and large deformations. On the material level, various integration methods to integrate nonlinear constitutive rate equations for finite element implementation were studied. These include explicit, implicit and automatic subincrementing schemes. In all cases, examples are included to illustrate the numerical characteristics of various methods that were considered.
Scaling law for topologically ordered systems at finite temperature
Iblisdir, S.; Perez-Garcia, D.; Aguado, M.; Pachos, J.
2009-04-01
Understanding the behavior of topologically ordered lattice systems at finite temperature is a way of assessing their potential as fault-tolerant quantum memories. We compute the natural extension of the topological entanglement entropy for T>0, namely, the subleading correction I{sub topo} to the area law for mutual information. Its dependence on T can be written, for Abelian Kitaev models, in terms of information-theoretical functions and readily identifiable scaling behavior, from which the interplay between volume, temperature, and topological order, can be read. These arguments are extended to non-Abelian quantum double models, and numerical results are given for the D(S{sub 3}) model, showing qualitative agreement with the Abelian case.
Baryon number dissipation at finite temperature in the standard model
Mottola, E. ); Raby, S. . Dept. of Physics); Starkman, G. . Dept. of Astronomy)
1990-01-01
We analyze the phenomenon of baryon number violation at finite temperature in the standard model, and derive the relaxation rate for the baryon density in the high temperature electroweak plasma. The relaxation rate, {gamma} is given in terms of real time correlation functions of the operator E{center dot}B, and is directly proportional to the sphaleron transition rate, {Gamma}: {gamma} {preceq} n{sub f}{Gamma}/T{sup 3}. Hence it is not instanton suppressed, as claimed by Cohen, Dugan and Manohar (CDM). We show explicitly how this result is consistent with the methods of CDM, once it is recognized that a new anomalous commutator is required in their approach. 19 refs., 2 figs.
Dynamical structure factor of magnetic Bloch oscillations at finite temperatures
NASA Astrophysics Data System (ADS)
Syljuåsen, Olav F.
2015-10-01
Domain-walls in one-dimensional Ising ferromagnets can undergo Bloch oscillations when subjected to a skew magnetic field. Such oscillations imply finite temperature non-dispersive low-frequency peaks in the dynamical structure factor which can be probed in neutron scattering. We study in detail the spectral weight of these peaks. Using an analytical approach based on an approximate treatment of a gas of spin-cluster excitations we give an explicit expression for the momentum- and temperature-dependence of the spectral weights. Generally the spectral weights increase with temperature T and approaches the same order of magnitude as the spin-wave spectral weights at high temperatures. We compare the analytical expression to numerical exact diagonalizations and find that it can, without any adjustable parameters, account for the T and momentum-transfer dependence of the numerically obtained spectral weights in the parameter regime where the ratio of magnetic fields h x / h z ≪ 1 and the temperature is h x < T < ˜ J z /2. We also carry out numerical calculations pertinent to the material CoNb2O6, and find qualitatively similar results.
Finite-Temperature Variational Monte Carlo Method for Strongly Correlated Electron Systems
NASA Astrophysics Data System (ADS)
Takai, Kensaku; Ido, Kota; Misawa, Takahiro; Yamaji, Youhei; Imada, Masatoshi
2016-03-01
A new computational method for finite-temperature properties of strongly correlated electrons is proposed by extending the variational Monte Carlo method originally developed for the ground state. The method is based on the path integral in the imaginary-time formulation, starting from the infinite-temperature state that is well approximated by a small number of certain random initial states. Lower temperatures are progressively reached by the imaginary-time evolution. The algorithm follows the framework of the quantum transfer matrix and finite-temperature Lanczos methods, but we extend them to treat much larger system sizes without the negative sign problem by optimizing the truncated Hilbert space on the basis of the time-dependent variational principle (TDVP). This optimization algorithm is equivalent to the stochastic reconfiguration (SR) method that has been frequently used for the ground state to optimally truncate the Hilbert space. The obtained finite-temperature states allow an interpretation based on the thermal pure quantum (TPQ) state instead of the conventional canonical-ensemble average. Our method is tested for the one- and two-dimensional Hubbard models and its accuracy and efficiency are demonstrated.
Energy spectra of finite temperature superfluid helium-4 turbulence
Kivotides, Demosthenes
2014-10-15
A mesoscopic model of finite temperature superfluid helium-4 based on coupled Langevin-Navier-Stokes dynamics is proposed. Drawing upon scaling arguments and available numerical results, a numerical method for designing well resolved, mesoscopic calculations of finite temperature superfluid turbulence is developed. The application of model and numerical method to the problem of fully developed turbulence decay in helium II, indicates that the spectral structure of normal-fluid and superfluid turbulence is significantly more complex than that of turbulence in simple-fluids. Analysis based on a forced flow of helium-4 at 1.3 K, where viscous dissipation in the normal-fluid is compensated by the Lundgren force, indicate three scaling regimes in the normal-fluid, that include the inertial, low wavenumber, Kolmogorov k{sup −5/3} regime, a sub-turbulence, low Reynolds number, fluctuating k{sup −2.2} regime, and an intermediate, viscous k{sup −6} range that connects the two. The k{sup −2.2} regime is due to normal-fluid forcing by superfluid vortices at high wavenumbers. There are also three scaling regimes in the superfluid, that include a k{sup −3} range that corresponds to the growth of superfluid vortex instabilities due to mutual-friction action, and an adjacent, low wavenumber, k{sup −5/3} regime that emerges during the termination of this growth, as superfluid vortices agglomerate between intense normal-fluid vorticity regions, and weakly polarized bundles are formed. There is also evidence of a high wavenumber k{sup −1} range that corresponds to the probing of individual-vortex velocity fields. The Kelvin waves cascade (the main dynamical effect in zero temperature superfluids) appears to be damped at the intervortex space scale.
Radial convection of finite ion temperature, high amplitude plasma blobs
Wiesenberger, M. Kendl, A.; Madsen, J.
2014-09-15
We present results from simulations of seeded blob convection in the scrape-off-layer of magnetically confined fusion plasmas. We consistently incorporate high fluctuation amplitude levels and finite Larmor radius (FLR) effects using a fully nonlinear global gyrofluid model. This is in line with conditions found in tokamak scrape-off-layers (SOL) regions. Varying the ion temperature, the initial blob width, and the initial amplitude, we found an FLR dominated regime where the blob behavior is significantly different from what is predicted by cold-ion models. The transition to this regime is very well described by the ratio of the ion gyroradius to the characteristic gradient scale length of the blob. We compare the global gyrofluid model with a partly linearized local model. For low ion temperatures, we find that simulations of the global model show more coherent blobs with an increased cross-field transport compared to blobs simulated with the local model. The maximal blob amplitude is significantly higher in the global simulations than in the local ones. When the ion temperature is comparable to the electron temperature, global blob simulations show a reduced blob coherence and a decreased cross-field transport in comparison with local blob simulations.
Finite Larmor radius effects on the coupled trapped electron and ion temperature gradient modes
Sandberg, I.; Isliker, H.; Pavlenko, V. P.
2007-09-15
The properties of the coupled trapped electron and toroidal ion temperature gradient modes are investigated using the standard reactive fluid model and taking rigorously into account the effects attributed to the ion polarization drift and to the drifts associated with the lowest-order finite ion Larmor radius effects. In the flat density regime, where the coupling between the modes is relatively weak, the properties of the unstable modes are slightly modified through these effects. For the peak density regions, where the coupling of the modes is rather strong, these second-order drifts determine the spectra of the unstable modes near the marginal conditions.
Density-matrix Chern insulators: Finite-temperature generalization of topological insulators
NASA Astrophysics Data System (ADS)
Rivas, A.; Viyuela, O.; Martin-Delgado, M. A.
2013-10-01
Thermal noise can destroy topological insulators (TI). However, we demonstrate how TIs can be made stable in dissipative systems. To that aim, we introduce the notion of band Liouvillian as the dissipative counterpart of band Hamiltonian, and show a method to evaluate the topological order of its steady state. This is based on a generalization of the Chern number valid for general mixed states (referred to as density-matrix Chern value), which witnesses topological order in a system coupled to external noise. Additionally, we study its relation with the electrical conductivity at finite temperature, which is not a topological property. Nonetheless, the density-matrix Chern value represents the part of the conductivity which is topological due to the presence of quantum mixed edge states at finite temperature. To make our formalism concrete, we apply these concepts to the two-dimensional Haldane model in the presence of thermal dissipation, but our results hold for arbitrary dimensions and density matrices.
Finite temperature holographic duals of 2-dimensional BCFTs
NASA Astrophysics Data System (ADS)
Estes, J.
2015-07-01
We consider holographic duals of 2-dimensional conformal field theories in the presence of a boundary, interface, defect and/or junction, referred to collectively as BCFTs. In general, the presence of a boundary reduces the SO(2, 2) conformal symmetry to SO(2, 1) and the dual geometry is realized as a warped product of the form , where is not compact. In particular, it will contain points where the warp factor of the AdS 2 space diverges, leading to asymptotically AdS 3 regions. We show that the AdS 2 space-time may always be replaced with an AdS 2-"black-hole" space-time. We argue the resulting geometry describes the BCFT at finite temperature. To motivate this claim, we compute the entanglement entropy holographically for a segment centered around the defect or ending on the boundary and find agreement with a known universal formula.
Containerless high temperature property measurements
NASA Technical Reports Server (NTRS)
Nordine, Paul C.; Weber, J. K. Richard; Krishnan, Shankar; Anderson, Collin D.
1991-01-01
Containerless processing in the low gravity environment of space provides the opportunity to increase the temperature at which well controlled processing of and property measurements on materials is possible. This project was directed towards advancing containerless processing and property measurement techniques for application to materials research at high temperatures in space. Containerless high temperature material property studies include measurements of the vapor pressure, melting temperature, optical properties, and spectral emissivities of solid boron. The reaction of boron with nitrogen was also studied by laser polarimetric measurement of boron nitride film growth. The optical properties and spectral emissivities were measured for solid and liquid silicon, niobium, and zirconium; liquid aluminum and titanium; and liquid Ti-Al alloys of 5 to 60 atomic pct. titanium. Alternative means for noncontact temperature measurement in the absence of material emissivity data were evaluated. Also, the application of laser induced fluorescence for component activity measurements in electromagnetic levitated liquids was studied, along with the feasibility of a hybrid aerodynamic electromagnetic levitation technique.
Finite size induces crossover temperature in growing spin chains
NASA Astrophysics Data System (ADS)
Sienkiewicz, Julian; Suchecki, Krzysztof; Hołyst, Janusz A.
2014-01-01
We introduce a growing one-dimensional quenched spin model that bases on asymmetrical one-side Ising interactions in the presence of external field. Numerical simulations and analytical calculations based on Markov chain theory show that when the external field is smaller than the exchange coupling constant J there is a nonmonotonous dependence of the mean magnetization on the temperature in a finite system. The crossover temperature Tc corresponding to the maximal magnetization decays with system size, approximately as the inverse of the Lambert W function. The observed phenomenon can be understood as an interplay between the thermal fluctuations and the presence of the first cluster determined by initial conditions. The effect exists also when spins are not quenched but fully thermalized after the attachment to the chain. By performing tests on real data we conceive the model is in part suitable for a qualitative description of online emotional discussions arranged in a chronological order, where a spin in every node conveys emotional valence of a subsequent post.
Finite-temperature phase transitions in the SU (N ) Hubbard model
NASA Astrophysics Data System (ADS)
Yanatori, Hiromasa; Koga, Akihisa
2016-07-01
We investigate the SU (N ) Hubbard model for the multicomponent fermionic optical lattice system, combining dynamical mean-field theory with the continuous-time quantum Monte Carlo method. We obtain the finite-temperature phase diagrams with N ≤6 and find that low-temperature properties depend on the parity of the components. The magnetically ordered state competes with the correlated metallic state in the system with an even number of components (N ≥4 ) , yielding the first-order phase transition. It is also clarified that in the odd-component system, the ordered state is realized at relatively lower temperatures and the critical temperature is constant in the strong coupling limit.
Light-front QED1+1 at finite temperature.
Strauss, S; Beyer, M
2008-09-01
We investigate the thermodynamic properties of quantum electrodynamics in 1+1 dimensions. We derive the partition function of the canonical ensemble in discrete light cone quantization and calculate the thermodynamical potential. This central quantity is evaluated for different system sizes and coupling strengths. We investigate the continuum limit and the thermodynamical limit and present basic thermodynamical quantities as a function of temperature for the interacting system. The results are compared to the idealized cases. PMID:18851196
NASA Technical Reports Server (NTRS)
Caruso, J. J.; Trowbridge, D.; Chamis, C. C.
1989-01-01
The mechanics of materials approach (definition of E, G, Nu, and Alpha) and the finite element method are used to explore the effects of partial bonding and fiber fracture on the behavior of high temperature metal matrix composites. Composite ply properties are calculated for various degrees of disbonding to evaluate the sensitivity of these properties to the presence of fiber/matrix disbonding and fiber fracture. The mechanics of materials approach allows for the determination of the basic ply material properties needed for design/analysis of composites. The finite element method provides the necessary structural response (forces and displacements) for the mechanics of materials equations. Results show that disbonding of fractured fibers affect only E sub (111) and alpha sub (111) significantly.
NASA Technical Reports Server (NTRS)
Caruso, J. J.; Chamis, C. C.; Trowbridge, D.
1989-01-01
The mechanics of materials approach (definition of E, G, nu, and alpha) and the finite element method are used to explore the effects of partial bonding and fiber fracture on the behavior of high temperature metal matrix composites. Composite ply properties are calculated for various degrees of disbonding to evaluate the sensitivity of these properties to the presence of fiber/matrix disbonding and fiber fracture. The mechanics of materials approach allows for the determination of the basic ply material properties needed for design/analysis of composites. The finite element method provides the necessary structural response (forces and displacements) for the mechanics of materials equations. Results show that disbonding of fractured fibers affect only E-l(11) and alpha-l(11) significantly.
Chiral restoration at finite temperature with meson loop corrections
Nam, Seung-il; Kao, Chung-Wen
2010-11-01
We investigate the pattern of chiral-symmetry restoration of QCD for N{sub c}=3 and N{sub f}=2 at finite temperature (T) beyond the chiral limit. To this end, we employ the instanton-vacuum configuration for the flavor SU(2) sector and the Harrington-Shepard caloron for modifying relevant instanton parameters as functions of T. The meson loop corrections (MLC), which correspond to 1/N{sub c} corrections, are also taken into account to reproduce appropriate m{sub q} dependences of chiral order parameters. We compute the chiral condensate as a function of T and/or m{sub q}. We observe that MLC play an important role to have a correct universality-class behavior of chiral-restoration patterns in this framework, depending on m{sub q}: Second-order phase transition in the chiral limit m{sub q}=0 and cross-over for m{sub q{ne}}0. Without MLC, all the restoration patterns are crossover, due to simple saddle-point approximations. It turns out that T{sub c}{sup {chi}=}159 MeV in the chiral limit and T{sub c}{sup {chi}=}(177,186,196) MeV for m{sub q}=(5,10,15) MeV, using the phenomenological choices for the instanton parameters at T=0.
Chiral restoration at finite temperature with meson loop corrections
NASA Astrophysics Data System (ADS)
Nam, Seung-Il; Kao, Chung-Wen
2010-11-01
We investigate the pattern of chiral-symmetry restoration of QCD for Nc=3 and Nf=2 at finite temperature (T) beyond the chiral limit. To this end, we employ the instanton-vacuum configuration for the flavor SU(2) sector and the Harrington-Shepard caloron for modifying relevant instanton parameters as functions of T. The meson loop corrections (MLC), which correspond to 1/Nc corrections, are also taken into account to reproduce appropriate mq dependences of chiral order parameters. We compute the chiral condensate as a function of T and/or mq. We observe that MLC play an important role to have a correct universality-class behavior of chiral-restoration patterns in this framework, depending on mq: Second-order phase transition in the chiral limit mq=0 and cross-over for mq≠0. Without MLC, all the restoration patterns are crossover, due to simple saddle-point approximations. It turns out that Tcχ=159MeV in the chiral limit and Tcχ=(177,186,196)MeV for mq=(5,10,15)MeV, using the phenomenological choices for the instanton parameters at T=0.
Equation of State of Structured Matter at Finite Temperature
NASA Astrophysics Data System (ADS)
Maruyama, T.; Yasutake, N.; Tatsumi, T.
We investigate the properties of nuclear matter at the first-order phase transitions such as liquid-gas phase transition and hadron-quark phase transition. As a general feature of the first-order phase transitions of matter consisting of many species of charged particles, there appears a mixed phases with geometrical structures called ``pasta'' due to the balance of the Coulomb repulsion and the surface tension between two phases [G.~D.~Ravenhall, C.~J.~Pethick and J.~R.~Wilson, Phys. Rev. Lett. 50 (1983), 2066. M.~Hashimoto, H.~Seki and M.~Yamada, Prog. Theor. Phys. 71 (1984), 320.] The equation of state (EOS) of mixed phase is different from the one obtained by a bulk application of the Gibbs conditions or by the Maxwell construction due to the effects of the non-uniform structure. We show that the charge screening and strong surface tension make the EOS close to that of the Maxwell construction. The thermal effects are elucidated as well as the above finite-size effects.
Symbolic derivation of material property matrices in finite element analysis
NASA Technical Reports Server (NTRS)
Tan, H. Q.
1988-01-01
The principles and operation of MMAX, a symbolic-computation program which automates the process of generating property matrices for structural materials, are briefly described and illustrated with sample analyses of a rubberlike material and an elastoplastic material. MMAX is written in LISP under the symbolic finite-element generator FINGER and the general symbolic manipulator MACSYMA; it first derives the formulas required by mathematical manipulation, and then translates the formulas into FORTRAN code, adapted to the particular type of machine to be used for the numerical calculations. This approach is shown to combine efficiently the advantages of symbolic and numerical computation for engineering applications.
Finite temperature spin-dynamics and phase transitions in spin-orbital models
Chen, C.-C.
2010-04-29
We study finite temperature properties of a generic spin-orbital model relevant to transition metal compounds, having coupled quantum Heisenberg-spin and Ising-orbital degrees of freedom. The model system undergoes a phase transition, consistent with that of a 2D Ising model, to an orbitally ordered state at a temperature set by short-range magnetic order. At low temperatures the orbital degrees of freedom freeze-out and the model maps onto a quantum Heisenberg model. The onset of orbital excitations causes a rapid scrambling of the spin spectral weight away from coherent spin-waves, which leads to a sharp increase in uniform magnetic susceptibility just below the phase transition, reminiscent of the observed behavior in the Fe-pnictide materials.
T2 can be greater than 2T1 even at finite temperature
NASA Astrophysics Data System (ADS)
Laird, Brian B.; Skinner, James L.
1991-03-01
The relaxation of a nondegenerate two-level quantum system linearly and off-diagonally coupled to a thermal bath of quantum-mechanical harmonic oscillators is studied. The population and phase relaxation times, T1 and T2, are calculated to fourth order in the system/bath interaction. Focus is on a specific model of the bath spectral density that is both Ohmic (proportional to frequency at low frequency) and Lorentzian, and which has the property that, in the semiclassical or high-temperature limit, it reproduces the stochastic model studied previously by Budimir and Skinner [J. Stat. Phys. 49, 1029 (1987)]. For this fully quantum-mechanical model, it is found that under certain conditions the standard inequality, T2≤2T1, is violated, demonstrating that this unusual result, which was originally derived from the (infinite-temperature) stochastic model, is valid at finite temperature as well.
Exchange-correlations in a dilute quasi-two-dimensional electron gas at finite temperature
NASA Astrophysics Data System (ADS)
Bhukal, Nisha; Moudgil, R. K.
2012-06-01
We have studied the extent to which temperature and finite transversal confinement can influence the exchange-correlations in a dilute two-dimensional electron gas as realized in a narrow GaAs-based single quantum well. The correlations are treated within the self-consistent mean-field theory of Singwi et al. Numerical results are presented for the local-field correction factor at experimentally realized electron densities and temperature, choosing a harmonic confinement model. We find that the local-field correction factor, which is a direct measure of exchange-correlation correction to the bare Coulomb interaction potential, becomes less (at least over the currently accessible wave vector region to experiments) with increasing T/TF and/or decreasing confinement; TF is the Fermi temperature. These findings are expected to be useful in the theoretical understanding of dynamical excitation spectra and transport properties of a two-dimensional electron system.
An atomistic J-integral at finite temperature based on Hardy estimates of continuum fields
NASA Astrophysics Data System (ADS)
Jones, R. E.; Zimmerman, J. A.; Oswald, J.; Belytschko, T.
2011-01-01
In this work we apply a material-frame, kernel-based estimator of continuum fields to atomic data in order to estimate the J-integral for the analysis of an atomically sharp crack at finite temperatures. Instead of the potential energy appropriate for zero temperature calculations, we employ the quasi-harmonic free energy as an estimator of the Helmholtz free energy required by the Eshelby stress in isothermal conditions. We employ the simplest of the quasi-harmonic models, the local harmonic model of LeSar and co-workers, and verify that it is adequate for correction of the zero temperature J-integral expression for various deformation states for our Lennard-Jones test material. We show that this method has the properties of: consistency among the energy, stress and deformation fields; path independence of the contour integrals of the Eshelby stress; and excellent correlation with linear elastic fracture mechanics theory.
NASA Astrophysics Data System (ADS)
Schunck, N.; Duke, D.; Carr, H.
2015-03-01
Understanding the mechanisms of induced nuclear fission for a broad range of neutron energies could help resolve fundamental science issues, such as the formation of elements in the universe, but could have also a large impact on societal applications in energy production or nuclear waste management. The goal of this paper is to set up the foundations of a microscopic theory to study the static aspects of induced fission as a function of the excitation energy of the incident neutron, from thermal to fast neutrons. To account for the high excitation energy of the compound nucleus, we employ a statistical approach based on finite temperature nuclear density functional theory with Skyrme energy densities, which we benchmark on the 239Pu(n ,f ) reaction. We compute the evolution of the least-energy fission pathway across multidimensional potential energy surfaces with up to five collective variables as a function of the nuclear temperature and predict the evolution of both the inner and the outer fission barriers as a function of the excitation energy of the compound nucleus. We show that the coupling to the continuum induced by the finite temperature is negligible in the range of neutron energies relevant for many applications of neutron-induced fission. We prove that the concept of quantum localization introduced recently can be extended to T >0 , and we apply the method to study the interaction energy and total kinetic energy of fission fragments as a function of the temperature for the most probable fission. While large uncertainties in theoretical modeling remain, we conclude that a finite temperature nuclear density functional may provide a useful framework to obtain accurate predictions of fission fragment properties.
Finite temperature quantum critical transport near the Mott transition
NASA Astrophysics Data System (ADS)
Terletska, Hanna; Dobrosavljevic, Vladimir
2010-03-01
We use Dynamical Mean-Field Theory to study incoherent transport above the critical end-point temperature Tc of the single band Hubbard model at half-filling. By employing an eigenvalue analysis for the free energy functional, we are able to precisely identify the crossover temperature T*(U) separating the Fermi liquid and the Mott insulating regimes. Our calculations demonstrate that a broad parameter range exist around the crossover line, where the family of resistivity curves displays simple scaling behavior. This is interpreted as a manifestation of quantum criticality controlled by the T=0 Mott transition, which is ``interrupted'' by the emergence of the coexistence dome at T < Tc . We argue that in situations where the critical temperature Tc is significantly reduced, so that the coexistence region is reduced or even absent (as in two-band, particle-hole asymmetric models, where this is found even in the clean d->∞ limit [1, 2]), similar critical scaling properties should persist down to much lower temperatures, resembling quantum critical transport similar to that found in a number of experiments [2]. [1] A. Amaricci, G. Sordi, and M. J. Rosenberg, Phys. Rev. Lett. 101, 146403 (2008) [2] A. Camjayi, K. Haule, V. Dobrosavljevic, and G. Kotliar, Nature Physics, 4, 932 (2008)
Finite-temperature elasticity of fcc Al: Atomistic simulations and ultrasonic measurements
NASA Astrophysics Data System (ADS)
Pham, Hieu H.; Williams, Michael E.; Mahaffey, Patrick; Radovic, Miladin; Arroyave, Raymundo; Cagin, Tahir
2011-08-01
Though not very often, there are some cases in the literature where discrepancies exist in the temperature dependence of elastic constants of materials. A particular example of this case is the behavior of C12 coefficient of a simple metal, aluminum. In this paper we attempt to provide insight into various contributions to temperature dependence in elastic properties by investigating the thermoelastic properties of fcc aluminum as a function of temperature through the use of two computational techniques and experiments. First, ab initio calculations based on density functional theory (DFT) are used in combination with quasiharmonic theory to calculate the elastic constants at finite temperatures through a strain-free energy approach. Molecular dynamics (MD) calculations using tight-binding potentials are then used to extract the elastic constants through a fluctuation-based formalism. Through this dynamic approach, the different contributions (Born, kinetic, and stress fluctuations) to the elastic constants are isolated and the underlying physical basis for the observed thermally induced softening is elucidated. The two approaches are then used to shed light on the relatively large discrepancies in the reported temperature dependence of the elastic constants of fcc aluminum. Finally, the polycrystalline elastic constants (and their temperature dependence) of fcc aluminum are determined using resonant ultrasound spectroscopy (RUS) and compared to previously published data as well as the atomistic calculations performed in this work.
Structural Properties of Finite MoS2 Nanowires
NASA Astrophysics Data System (ADS)
Clark, Shaylyn; Salgado, Andres; Fernandez-Seivane, Lucas; Lopez-Lozano, Xochitl
2015-03-01
Molybdenum disulfide (MoS2) has been one of the most important catalysts used in refineries worldwide for hydrodesulfurization over the past century. In the last decade, and with the advent of nanotechnology, there has been a special interest in MoS2 nanostructures due to their high potential as novel nanocatalysts. The study of the properties of these systems is of fundamental interest for the experimental design of their catalytic activity and efficiency. In this work, we have performed ab initio density-functional calculations (DFT) to investigate the structural properties of finite MoS2 nanostrutures. All the models here presented were based on newly experimentally observed morphologies in MoS2 industrial catalysts using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) images. We simulated STEM images of the theoretical models to compare it with the experimental ones. In contrast with infinite models, the finite models prefer a rippled/twisted structure morphology over the planar or helical ones. The rippled/twisted models appear to be structurally more stable.
Transport properties of two finite armchair graphene nanoribbons.
Rosales, Luis; González, Jhon W
2013-01-01
: In this work, we present a theoretical study of the transport properties of two finite and parallel armchair graphene nanoribbons connected to two semi-infinite leads of the same material. Using a single Π-band tight binding Hamiltonian and based on Green's function formalisms within a real space renormalization techniques, we have calculated the density of states and the conductance of these systems considering the effects of the geometric confinement and the presence of a uniform magnetic field applied perpendicularly to the heterostructure. Our results exhibit a resonant tunneling behaviour and periodic modulations of the transport properties as a function of the geometry of the considered conductors and as a function of the magnetic flux that crosses the heterostructure. We have observed Aharonov-Bohm type of interference representing by periodic metal-semiconductor transitions in the DOS and conductance curves of the nanostructures. PMID:23279756
Transport properties of two finite armchair graphene nanoribbons
2013-01-01
In this work, we present a theoretical study of the transport properties of two finite and parallel armchair graphene nanoribbons connected to two semi-infinite leads of the same material. Using a single Π-band tight binding Hamiltonian and based on Green’s function formalisms within a real space renormalization techniques, we have calculated the density of states and the conductance of these systems considering the effects of the geometric confinement and the presence of a uniform magnetic field applied perpendicularly to the heterostructure. Our results exhibit a resonant tunneling behaviour and periodic modulations of the transport properties as a function of the geometry of the considered conductors and as a function of the magnetic flux that crosses the heterostructure. We have observed Aharonov-Bohm type of interference representing by periodic metal-semiconductor transitions in the DOS and conductance curves of the nanostructures. PMID:23279756
Test of finite temperature random-phase approximation on a Lipkin model
Hagino, K.; Minato, F.
2009-10-15
We investigate the applicability of the finite temperature random phase approximation (RPA) using a solvable Lipkin model. We show that the finite temperature RPA reproduces reasonably well the temperature dependence of total strength, both for the positive energy (i.e., the excitation) and the negative energy (i.e., the de-excitation) parts. This is the case even at very low temperatures, which may be relevant to astrophysical purposes.
Behaviour of `free-standing' hollow Au nanocages at finite temperatures: a BOMD study
NASA Astrophysics Data System (ADS)
Joshi, Krati; Krishnamurty, Sailaja
2015-10-01
Finite-temperature behaviour of a hollow golden cage (HGC) plays a crucialrole in its potential applications as a catalyst, drug delivery agent, contrasting agent and so on. This physico-chemical property of HGCs is not well understood so far. In that context, Born-Oppenheimer molecular dynamics (BOMD) simulations are performed on a well-known 'free-standing' HGC. The cluster considered in this study is the ground state Au18 cluster (a cage with a diameter of about >5.5 Å). The results thus obtained are compared with the BOMD simulation results reported earlier on Au32 icosahedron cage, a conformation with a diameter of nearly. The sphericity of both the clusters is studied using a shape deformation parameter as a function of time and temperature. These results are supplemented by radial distribution function at various temperatures. The observations and analysis of results indicate that, both the clusters retain an HGC conformation from 300 to 400 K, admitting structural fluxionality by the Au18 cluster. Remarkably, the Au18 cluster is able to maintain its hollowness and sphericity up to a high temperature of 1000 K. Underlying structural and electronic properties influencing the individualistic behaviour of cages are highlighted. Composition of the frontier molecular orbitals and the charge distribution play a crucial role in the finite-temperature behaviour of the Au cages. The conclusions are supplemented by supporting calculations on another degenerate ground state Au18 hollow cage and a well-known pyramidal Au18 cage at 300 and 400 K.
Finite-Temperature Entanglement Dynamics in an Anisotropic Two-Qubit Heisenberg Spin Chain
NASA Astrophysics Data System (ADS)
Chen, Tao; Shan, Chuanjia; Li, Jinxing; Liu, Tangkun; Huang, Yanxia; Li, Hong
2010-07-01
This paper investigates the entanglement dynamics of an anisotropic two-qubit Heisenberg spin chain in the presence of decoherence at finite temperature. The time evolution of the concurrence is studied for different initial Werner states. The influences of initial purity, finite temperature, spontaneous decay and Hamiltonian on the entanglement evolution are analyzed in detail. Our calculations show that the finite temperature restricts the evolution of the entanglement all the time when the Hamiltonian improves it and the spontaneous decay to the reservoirs can produce quantum entanglement with the anisotropy of spin-spin interaction. Finally, the steady-state concurrence which may remain non-zero for low temperature is also given.
Finite temperature QCD with two flavors of nonperturbatively improved Wilson fermions
Bornyakov, V.G.; Chernodub, M.N.; Ichie, H.; Mori, Y.; Nakamura, Y.; Suzuki, T.; Koma, Y.; Polikarpov, M.I.; Uvarov, P.V.; Veselov, A.I.; Schierholz, G.; Slavnov, A. A.; Stueben, H.
2005-06-01
We study QCD with two flavors of nonperturbatively improved Wilson fermions at finite temperature on the 16{sup 3}8 lattice. We determine the transition temperature at lattice spacing as small as a{approx}0.12 fm, and study string breaking below the finite temperature transition. We find that the static potential can be fitted by a two-state ansatz, including a string state and a two-meson state. We investigate the role of Abelian monopoles at finite temperature.
Fermionic path-integral Monte Carlo results for the uniform electron gas at finite temperature.
Filinov, V S; Fortov, V E; Bonitz, M; Moldabekov, Zh
2015-03-01
The uniform electron gas (UEG) at finite temperature has recently attracted substantial interest due to the experimental progress in the field of warm dense matter. To explain the experimental data, accurate theoretical models for high-density plasmas are needed that depend crucially on the quality of the thermodynamic properties of the quantum degenerate nonideal electrons and of the treatment of their interaction with the positive background. Recent fixed-node path-integral Monte Carlo (RPIMC) data are believed to be the most accurate for the UEG at finite temperature, but they become questionable at high degeneracy when the Brueckner parameter rs=a/aB--the ratio of the mean interparticle distance to the Bohr radius--approaches 1. The validity range of these simulations and their predictive capabilities for the UEG are presently unknown. This is due to the unknown quality of the used fixed nodes and of the finite-size scaling from N=33 simulated particles (per spin projection) to the macroscopic limit. To analyze these questions, we present alternative direct fermionic path integral Monte Carlo (DPIMC) simulations that are independent from RPIMC. Our simulations take into account quantum effects not only in the electron system but also in their interaction with the uniform positive background. Also, we use substantially larger particle numbers (up to three times more) and perform an extrapolation to the macroscopic limit. We observe very good agreement with RPIMC, for the polarized electron gas, up to moderate densities around rs=4, and larger deviations for the unpolarized case, for low temperatures. For higher densities (high electron degeneracy), rs≲1.5, both RPIMC and DPIMC are problematic due to the increased fermion sign problem. PMID:25871225
Fermionic path-integral Monte Carlo results for the uniform electron gas at finite temperature
NASA Astrophysics Data System (ADS)
Filinov, V. S.; Fortov, V. E.; Bonitz, M.; Moldabekov, Zh.
2015-03-01
The uniform electron gas (UEG) at finite temperature has recently attracted substantial interest due to the experimental progress in the field of warm dense matter. To explain the experimental data, accurate theoretical models for high-density plasmas are needed that depend crucially on the quality of the thermodynamic properties of the quantum degenerate nonideal electrons and of the treatment of their interaction with the positive background. Recent fixed-node path-integral Monte Carlo (RPIMC) data are believed to be the most accurate for the UEG at finite temperature, but they become questionable at high degeneracy when the Brueckner parameter rs=a /aB —the ratio of the mean interparticle distance to the Bohr radius—approaches 1. The validity range of these simulations and their predictive capabilities for the UEG are presently unknown. This is due to the unknown quality of the used fixed nodes and of the finite-size scaling from N =33 simulated particles (per spin projection) to the macroscopic limit. To analyze these questions, we present alternative direct fermionic path integral Monte Carlo (DPIMC) simulations that are independent from RPIMC. Our simulations take into account quantum effects not only in the electron system but also in their interaction with the uniform positive background. Also, we use substantially larger particle numbers (up to three times more) and perform an extrapolation to the macroscopic limit. We observe very good agreement with RPIMC, for the polarized electron gas, up to moderate densities around rs=4 , and larger deviations for the unpolarized case, for low temperatures. For higher densities (high electron degeneracy), rs≲1.5 , both RPIMC and DPIMC are problematic due to the increased fermion sign problem.
Finite-temperature scaling of quantum coherence near criticality in a spin chain
NASA Astrophysics Data System (ADS)
Cheng, Weiwen; Zhang, Zhijun; Gong, Longyan; Zhao, Shengmei
2016-06-01
We explore quantum coherence, inherited from Wigner-Yanase skew information, to analyze quantum criticality in the anisotropic XY chain model at finite temperature. Based on the exact solutions of the Hamiltonian, the quantum coherence contained in a nearest-neighbor spin pairs reduced density matrix ρ is obtained. The first-order derivative of the quantum coherence is non-analytic around the critical point at sufficient low temperature. The finite-temperature scaling behavior and the universality are verified numerically. In particular, the quantum coherence can also detect the factorization transition in such a model at sufficient low temperature. We also show that quantum coherence contained in distant spin pairs can characterize quantum criticality and factorization phenomena at finite temperature. Our results imply that quantum coherence can serve as an efficient indicator of quantum criticality in such a model and shed considerable light on the relationships between quantum phase transitions and quantum information theory at finite temperature.
Prediction of high temperature metal matrix composite ply properties
NASA Technical Reports Server (NTRS)
Caruso, J. J.; Chamis, C. C.
1988-01-01
The application of the finite element method (superelement technique) in conjunction with basic concepts from mechanics of materials theory is demonstrated to predict the thermomechanical behavior of high temperature metal matrix composites (HTMMC). The simulated behavior is used as a basis to establish characteristic properties of a unidirectional composite idealized an as equivalent homogeneous material. The ply properties predicted include: thermal properties (thermal conductivities and thermal expansion coefficients) and mechanical properties (moduli and Poisson's ratio). These properties are compared with those predicted by a simplified, analytical composite micromechanics model. The predictive capabilities of the finite element method and the simplified model are illustrated through the simulation of the thermomechanical behavior of a P100-graphite/copper unidirectional composite at room temperature and near matrix melting temperature. The advantage of the finite element analysis approach is its ability to more precisely represent the composite local geometry and hence capture the subtle effects that are dependent on this. The closed form micromechanics model does a good job at representing the average behavior of the constituents to predict composite behavior.
Bosonic D-branes at finite temperature with an external field
NASA Astrophysics Data System (ADS)
Abdalla, M. C. B.; Gadelha, A. L.; Vancea, I. V.
2001-10-01
Bosonic boundary states at finite temperature are constructed as solutions of boundary conditions at T≠0 for bosonic open strings with a constant gauge field Fab coupled to the boundary. The construction is done in the framework of thermo field dynamics where a thermal Bogoliubov transformation maps states and operators to finite temperature. Boundary states are given in terms of states from the direct product space between the Fock space of the closed string and another identical copy of it. By analogy with zero temperature, the boundary states have the interpretation of Dp-branes at finite temperature. The boundary conditions admit two different solutions. The entropy of the closed string in a Dp-brane state is computed and analyzed. It is interpreted as the entropy of the Dp-brane at finite temperature.
Franco-Pérez, Marco E-mail: jlgm@xanum.uam.mx; Gázquez, José L. E-mail: jlgm@xanum.uam.mx; Ayers, Paul W.; Vela, Alberto
2015-10-21
We extend the definition of the electronic chemical potential (μ{sub e}) and chemical hardness (η{sub e}) to finite temperatures by considering a reactive chemical species as a true open system to the exchange of electrons, working exclusively within the framework of the grand canonical ensemble. As in the zero temperature derivation of these descriptors, the response of a chemical reagent to electron-transfer is determined by the response of the (average) electronic energy of the system, and not by intrinsic thermodynamic properties like the chemical potential of the electron-reservoir which is, in general, different from the electronic chemical potential, μ{sub e}. Although the dependence of the electronic energy on electron number qualitatively resembles the piecewise-continuous straight-line profile for low electronic temperatures (up to ca. 5000 K), the introduction of the temperature as a free variable smoothens this profile, so that derivatives (of all orders) of the average electronic energy with respect to the average electron number exist and can be evaluated analytically. Assuming a three-state ensemble, well-known results for the electronic chemical potential at negative (−I), positive (−A), and zero values of the fractional charge (−(I + A)/2) are recovered. Similarly, in the zero temperature limit, the chemical hardness is formally expressed as a Dirac delta function in the particle number and satisfies the well-known reciprocity relation with the global softness.
NASA Astrophysics Data System (ADS)
Franco-Pérez, Marco; Gázquez, José L.; Ayers, Paul W.; Vela, Alberto
2015-10-01
We extend the definition of the electronic chemical potential (μe) and chemical hardness (ηe) to finite temperatures by considering a reactive chemical species as a true open system to the exchange of electrons, working exclusively within the framework of the grand canonical ensemble. As in the zero temperature derivation of these descriptors, the response of a chemical reagent to electron-transfer is determined by the response of the (average) electronic energy of the system, and not by intrinsic thermodynamic properties like the chemical potential of the electron-reservoir which is, in general, different from the electronic chemical potential, μe. Although the dependence of the electronic energy on electron number qualitatively resembles the piecewise-continuous straight-line profile for low electronic temperatures (up to ca. 5000 K), the introduction of the temperature as a free variable smoothens this profile, so that derivatives (of all orders) of the average electronic energy with respect to the average electron number exist and can be evaluated analytically. Assuming a three-state ensemble, well-known results for the electronic chemical potential at negative (-I), positive (-A), and zero values of the fractional charge (-(I + A)/2) are recovered. Similarly, in the zero temperature limit, the chemical hardness is formally expressed as a Dirac delta function in the particle number and satisfies the well-known reciprocity relation with the global softness.
Thermal properties of hot and dense matter with finite range interactions
NASA Astrophysics Data System (ADS)
Constantinou, Constantinos; Muccioli, Brian; Prakash, Madappa; Lattimer, James M.
2015-08-01
We explore the thermal properties of hot and dense matter using a model that reproduces the empirical properties of isospin symmetric and asymmetric bulk nuclear matter, optical-model fits to nucleon-nucleus scattering data, heavy-ion flow data in the energy range 0.5-2 GeV/A , and the largest well-measured neutron star mass of 2 M⊙ . This model, which incorporates finite range interactions through a Yukawa-type finite range force, is contrasted with a conventional zero range Skyrme model. Both models predict nearly identical zero-temperature properties at all densities and proton fractions, including the neutron star maximum mass, but differ in their predictions for heavy-ion flow data. We contrast their predictions of thermal properties, including their specific heats, and provide analytical formulas for the strongly degenerate and nondegenerate limits. We find significant differences in the results of the two models for quantities that depend on the density derivatives of nucleon effective masses. We show that a constant value for the ratio of the thermal components of pressure and energy density expressed as Γth=1 +(Pth/ɛth) , often used in simulations of proto-neutron stars and merging compact object binaries, fails to adequately describe results of either nuclear model. The region of greatest discrepancy extends from subsaturation densities to a few times the saturation density of symmetric nuclear matter. Our results suggest alternate approximations for the thermal properties of dense matter that are more realistic.
Deformation properties with a finite-range simple effective interaction
NASA Astrophysics Data System (ADS)
Behera, B.; Viñas, X.; Routray, T. R.; Robledo, L. M.; Centelles, M.; Pattnaik, S. P.
2016-08-01
Deformed and spherical even-even nuclei are studied using a finite-range simple effective interaction within the Hartree-Fock-Bogoliubov mean-field approach. Different parameter sets of the interaction, corresponding to different incompressibility, are constructed by varying the exponent γ of the density in the traditional density-dependent term. Ten of the 12 parameters of these interactions are determined from properties of asymmetric nuclear matter and spin-polarized pure neutron matter. The two remaining parameters are fitted to reproduce the experimental binding energies known in 620 even-even nuclei using several variants of the rotational energy correction. The rms deviations for the binding energy depend on the value of γ and the way the rotational energy correction is treated but they can be as low as 1.56 MeV, a value competitive with other renowned effective interactions of Skyrme and Gogny type. Charge radii are compared to the experimental values of 313 even-even nuclei and the rms deviation is again comparable and even superior to the one of popular Skyrme and Gogny forces. Emphasis is given to the deformation properties predicted with these interactions by analyzing the potential energy surfaces for several well deformed nuclei and the fission barriers of some nuclei. Comparison of the results with the experimental information, where available, as well as with the results of the Gogny D1S force, shows satisfactory agreement.
REMARKS ON THE MAXIMUM ENTROPY METHOD APPLIED TO FINITE TEMPERATURE LATTICE QCD.
UMEDA, T.; MATSUFURU, H.
2005-07-25
We make remarks on the Maximum Entropy Method (MEM) for studies of the spectral function of hadronic correlators in finite temperature lattice QCD. We discuss the virtues and subtlety of MEM in the cases that one does not have enough number of data points such as at finite temperature. Taking these points into account, we suggest several tests which one should examine to keep the reliability for the results, and also apply them using mock and lattice QCD data.
Finite-size effects on the Bose-Einstein condensation critical temperature in a harmonic trap
NASA Astrophysics Data System (ADS)
Noronha, J. M. B.
2016-01-01
We obtain second and higher order corrections to the shift of the Bose-Einstein critical temperature due to finite-size effects. The confinement is that of a harmonic trap with general anisotropy. Numerical work shows the high accuracy of our expressions. We draw attention to a subtlety involved in the consideration of experimental values of the critical temperature in connection with analytical expressions for the finite-size corrections.
Parity-odd and CPT-even electrodynamics of the standard model extension at finite temperature
Casana, Rodolfo; Ferreira, Manoel M. Jr.; Silva, Madson R. O.
2010-05-15
This work examines the finite temperature properties of the CPT-even and parity-odd electrodynamics of the standard model extension. The starting point is the partition function computed for an arbitrary and sufficiently small tensor (k{sub F}){sub {alpha}{nu}{rho}{phi}} [see R. Casana, M. M. Ferreira, Jr., J. S. Rodrigues, and M. R. O. Silva, Phys. Rev. D 80, 085026 (2009).]. After specializing the Lorentz-violating tensor (k{sub F}){sub {alpha}{nu}{rho}{phi}}for the leading-order-nonbirefringent and parity-odd coefficients, the partition function is explicitly carried out, showing that it is a power of the Maxwell partition function. Also, it is observed that the Lorentz invariance violation coefficients induce an anisotropy in the black-body angular energy density distribution. Planck's radiation law retains its usual frequency dependence and the Stefan-Boltzmann law keeps the same form, except for a global proportionality constant.
Finite-temperature mobility of a particle coupled to a fermionic environment
Castella, H.; Zotos, X.
1996-08-01
We study numerically the finite-temperature and frequency mobility of a particle coupled by a local interaction to a system of spinless fermions in one dimension. We find that when the model is integrable (particle mass equal to the mass of fermions) the static mobility diverges. Further, an enhanced mobility is observed over a finite parameter range away from the integrable point. We present an analysis of the finite-temperature static mobility based on a random matrix theory description of the many-body Hamiltonian. {copyright} {ital 1996 The American Physical Society.}
Infrared features of unquenched finite temperature lattice Landau gauge QCD
Furui, Sadataka; Nakajima, Hideo
2007-09-01
The color diagonal and color antisymmetric ghost propagators slightly above T{sub c} of N{sub f}=2 MILC 24{sup 3}x12 lattices are measured and compared with zero-temperature unquenched N{sub f}=2+1 MILC{sub c} 20{sup 3}x64 and MILC{sub f} 28{sup 3}x96 lattices and zero-temperature quenched 56{sup 4} {beta}=6.4 and 6.45 lattices. The expectation value of the color antisymmetric ghost propagator {phi}{sup c}(q) is zero, but its Binder cumulant, which is consistent with that of N{sub c}{sup 2}-1 dimensional Gaussian distribution below T{sub c}, decreases above T{sub c}. Although the color diagonal ghost propagator is temperature independent, the l{sup 1} norm of the color antisymmetric ghost propagator is temperature dependent. The expectation value of the ghost condensate observed at zero-temperature unquenched configuration is consistent with 0 in T>T{sub c}. We also measure transverse, magnetic, and electric gluon propagator and extract gluon screening masses. The running coupling measured from the product of the gluon dressing function and the ghost dressing function are almost temperature independent, but the effect of A{sup 2} condensate observed at zero temperature is consistent with 0 in T>T{sub c}. The transverse gluon dressing function at low temperature has a peak in the infrared at low temperature, but it becomes flatter at high temperature. The magnetic gluon propagator at high momentum depends on the temperature. These data imply that the magnetic gluon propagator and the color antisymmetric ghost propagator are affected by the presence of dynamical quarks, and there are strong nonperturbative effects through the temperature-dependent color antisymmetric ghost propagator.
Heit, Yonaton N; Beran, Gregory J O
2016-08-01
Molecular crystals expand appreciably upon heating due to both zero-point and thermal vibrational motion, yet this expansion is often neglected in molecular crystal modeling studies. Here, a quasi-harmonic approximation is coupled with fragment-based hybrid many-body interaction calculations to predict thermal expansion and finite-temperature thermochemical properties in crystalline carbon dioxide, ice Ih, acetic acid and imidazole. Fragment-based second-order Möller-Plesset perturbation theory (MP2) and coupled cluster theory with singles, doubles and perturbative triples [CCSD(T)] predict the thermal expansion and the temperature dependence of the enthalpies, entropies and Gibbs free energies of sublimation in good agreement with experiment. The errors introduced by neglecting thermal expansion in the enthalpy and entropy cancel somewhat in the Gibbs free energy. The resulting ∼ 1-2 kJ mol(-1) errors in the free energy near room temperature are comparable to or smaller than the errors expected from the electronic structure treatment, but they may be sufficiently large to affect free-energy rankings among energetically close polymorphs. PMID:27484373
Collector and source sheaths of a finite ion temperature plasma
Schwager, L.A.; Birdsall, C.K. )
1990-05-01
The region between a Maxwellian plasma source and an absorbing surface is described theoretically with a static, kinetic plasma--sheath model and modeled numerically with a dynamic, electrostatic particle simulation. In the kinetic theory, Poisson's equation and Vlasov equations govern the non-Maxwellian velocity distribution of the ions and electrons. The results in this paper for collector potential and plasma transport agree with the bounded model of Emmert {ital et} {ital al}. (Phys. Fluids {bold 23}, 803 (1980)). However, this approach differs from those using traditional Bohm sheath analysis by {plus minus}0.25 (in units of electron temperature) for potential drop through the collector sheath of a hydrogen plasma. In both the theory and simulation, the plasma source injects equal fluxes of ions and electrons with half-Maxwellian velocities and various mass and temperature ratios and is assumed to have a zero electric field. The potential change within a spatially distributed, full Maxwellian source region is represented with the source sheath potential drop that depends primarily on temperature ratio. This source sheath evolves over a few Debye lengths from the source to neutralize the injected plasma. The plasma flows to an electrically floating collector where the more familiar electron-repelling collector sheath appears. The collector potential {psi}{sub {ital C}} and source sheath potential drop {psi}{sub {ital P}} (in units of electron temperature) are evaluated as a function of mass and temperature ratio. The velocity moments of density, drift velocity, temperature, kinetic energy flux, and heat flux are also derived as a function of {psi}{sub {ital C}} and {psi}{sub {ital P}}. Comparisons with electrostatic particle simulations are shown for the ion/electron mass ratios of 40 and 100 and temperature ratios of 0.1, 1, and 10.
NASA Astrophysics Data System (ADS)
Xin, Xian-yin; Qin, Si-xue; Liu, Yu-xin
2014-10-01
We investigate the quark number fluctuations up to the fourth order in the matter composed of two light flavor quarks with isospin symmetry and at finite temperature and finite chemical potential using the Dyson-Schwinger equation approach of QCD. In order to solve the quark gap equation, we approximate the dressed quark-gluon vertex with the bare one and adopt both the Maris-Tandy model and the infrared constant (Qin-Chang) model for the dressed gluon propagator. Our results indicate that the second, third, and fourth order fluctuations of net quark number all diverge at the critical endpoint (CEP). Around the CEP, the second order fluctuation possesses obvious pump while the third and fourth order ones exhibit distinct wiggles between positive and negative. For the Maris-Tandy model and the Qin-Chang model, we give the pseudocritical temperature at zero quark chemical potential as Tc=146 MeV and 150 MeV, and locate the CEP at (μEq,TE)=(120,124) MeV and (124,129) MeV, respectively. In addition, our results manifest that the fluctuations are insensitive to the details of the model, but the location of the CEP shifts to low chemical potential and high temperature as the confinement length scale increases.
Finite temperature quark matter under strong magnetic fields
Avancini, S. S.; Menezes, D. P.; Providencia, C.
2011-06-15
In this paper, we use the mean-field approximation to investigate quark matter described by both SU(2) and SU(3) versions of the Nambu-Jona-Lasinio model at temperatures below 150 MeV and subject to a strong magnetic field. This kind of matter is possibly present in the early stages of heavy-ion collisions and in the interior of protoneutron stars. We have studied symmetric and asymmetric quark matter. The effect of the magnetic field on the effective quark masses and chemical potentials is only felt for quite strong magnetic fields, above 5x10{sup 18} G, with larger effects for the lower densities. Spin polarizations are more sensitive to weaker magnetic fields and are larger for lower temperatures and lower densities. Temperature tends to wash out the magnetic field effects.
Breakdown of nonlinear elasticity in amorphous solids at finite temperatures
NASA Astrophysics Data System (ADS)
Procaccia, Itamar; Rainone, Corrado; Shor, Carmel A. B. Z.; Singh, Murari
2016-06-01
It is known [H. G. E. Hentschel et al., Phys. Rev. E 83, 061101 (2011), 10.1103/PhysRevE.83.061101] that amorphous solids at zero temperature do not possess a nonlinear elasticity theory: besides the shear modulus, which exists, none of the higher order coefficients exist in the thermodynamic limit. Here we show that the same phenomenon persists up to temperatures comparable to that of the glass transition. The zero-temperature mechanism due to the prevalence of dangerous plastic modes of the Hessian matrix is replaced by anomalous stress fluctuations that lead to the divergence of the variances of the higher order elastic coefficients. The conclusion is that in amorphous solids elasticity can never be decoupled from plasticity: the nonlinear response is very substantially plastic.
Finite-temperature magnetism of FeRh compounds
NASA Astrophysics Data System (ADS)
Polesya, S.; Mankovsky, S.; Ködderitzsch, D.; Minár, J.; Ebert, H.
2016-01-01
The temperature dependent stability of the magnetic phases of FeRh were investigated by means of total energy calculations with magnetic disorder treated within the uncompensated disordered local moment approach. In addition, Monte Carlo simulations based on the extended Heisenberg model have been performed, using exchange coupling parameters obtained from first principles. The crucial role and interplay of two factors in the metamagnetic transition in FeRh has been revealed, namely the dependence of the Fe-Fe exchange coupling parameters on the temperature-governed degree of magnetic disorder in the system and the stabilizing nature of the induced magnetic moment on Rh-sites. An important observation is the temperature dependence of these two competing factors.
Finite-Temperature Conductivity and Magnetoconductivity of Topological Insulators
NASA Astrophysics Data System (ADS)
Lu, Hai-Zhou; Shen, Shun-Qing
2014-04-01
The electronic transport experiments on topological insulators exhibit a dilemma. A negative cusp in magnetoconductivity is widely believed as a quantum transport signature of the topological surface states, which are immune from localization and exhibit the weak antilocalization. However, the measured conductivity drops logarithmically when lowering temperature, showing a typical feature of the weak localization as in ordinary disordered metals. Here, we present a conductivity formula for massless and massive Dirac fermions as a function of magnetic field and temperature, by taking into account the electron-electron interaction and quantum interference simultaneously. The formula reconciles the dilemma by explicitly clarifying that the temperature dependence of the conductivity is dominated by the interaction, while the magnetoconductivity is mainly contributed by the quantum interference. The theory paves the road to quantitatively study the transport in topological insulators, and can be extended to other two-dimensional Dirac-like systems, such as graphene, transition metal dichalcogenides, and silicene.
Mobility of Holstein Polaron at Finite Temperature: An Unbiased Approach
NASA Astrophysics Data System (ADS)
Mishchenko, A. S.; Nagaosa, N.; De Filippis, G.; de Candia, A.; Cataudella, V.
2015-04-01
We present the first unbiased results for the mobility μ of a one-dimensional Holstein polaron obtained by numerical analytic continuation combined with diagrammatic and worldline Monte Carlo methods in the thermodynamic limit. We have identified for the first time several distinct regimes in the λ -T plane including a band conduction region, incoherent metallic region, an activated hopping region, and a high-temperature saturation region. We observe that although mobilities and mean free paths at different values of λ differ by many orders of magnitude at small temperatures, their values at T larger than the bandwidth become very close to each other.
Extension of Nelson's stochastic quantization to finite temperature using thermo field dynamics
NASA Astrophysics Data System (ADS)
Kobayashi, K.; Yamanaka, Y.
2011-08-01
We present an extension of Nelson's stochastic quantum mechanics to finite temperature. Utilizing the formulation of Thermo Field Dynamics (TFD), we can show that Ito's stochastic equations for tilde and non-tilde particle positions reproduce the TFD-type Schrödinger equation which is equivalent to the Liouville-von Neumann equation. In our formalism, the drift terms in the Ito's stochastic equation have the temperature dependence and the thermal fluctuation is induced through the correlation of the non-tilde and tilde particles. We show that our formalism satisfies the position-momentum uncertainty relation at finite temperature.
Decay of a Yukawa fermion at finite temperature and applications to leptogenesis
Kiessig, Clemens P.; Pluemacher, Michael; Thoma, Markus H.
2010-08-01
We calculate the decay rate of a Yukawa fermion in a thermal bath using finite-temperature cutting rules and effective Green's functions according to the hard thermal loop resummation technique. We apply this result to the decay of a heavy Majorana neutrino in leptogenesis. Compared to the usual approach where thermal masses are inserted into the kinematics of final states, we find that deviations arise through two different leptonic dispersion relations. The decay rate differs from the usual approach by more than 1 order of magnitude in the temperature range which is interesting for the weak washout regime. We discuss how to arrive at consistent finite-temperature treatments of leptogenesis.
Finite Temperature Response of a 2D Dipolar Bose Gas at Different Dipolar Tilt Angles
NASA Astrophysics Data System (ADS)
Shen, Pengtao; Quader, Khandker
We calculate finite temperature (T) response of a 2D Bose gas, subject to dipolar interaction, within the random phase approximation (RPA). We evaluate the appropriate 2D finite-T pair bubble diagram needed in RPA, and explore ranges of density and temperature for various dipolar tilt angles. We find the system to exhibit a collapse transition and a finite momentum instability, signaling a density wave or striped phase. We construct phase diagrams depicting these instabilities and resulting phases, including a normal Bose gas phase. We also consider the finite-T response of a quasi-2D dipolar Bose gas. We discuss how our results may apply to ultracold dense Bose gas of polar molecules, such as 41K87Rb, that has been realized experimentally. Acknowledge partial support from Institute for Complex Adaptive Matter (ICAM).
Isospin Mixing in 80Zr: From Finite to Zero Temperature
NASA Astrophysics Data System (ADS)
Ceruti, S.; Camera, F.; Bracco, A.; Avigo, R.; Benzoni, G.; Blasi, N.; Bocchi, G.; Bottoni, S.; Brambilla, S.; Crespi, F. C. L.; Giaz, A.; Leoni, S.; Mentana, A.; Million, B.; Morales, A. I.; Nicolini, R.; Pellegri, L.; Pullia, A.; Riboldi, S.; Wieland, O.; Birkenbach, B.; Bazzacco, D.; Ciemala, M.; Désesquelles, P.; Eberth, J.; Farnea, E.; Görgen, A.; Gottardo, A.; Hess, H.; Judson, D. S.; Jungclaus, A.; Kmiecik, M.; Korten, W.; Maj, A.; Menegazzo, R.; Mengoni, D.; Michelagnoli, C.; Modamio, V.; Montanari, D.; Myalski, S.; Napoli, D.; Quintana, B.; Reiter, P.; Recchia, F.; Rosso, D.; Sahin, E.; Salsac, M. D.; Söderström, P.-A.; Stezowski, O.; Theisen, Ch.; Ur, C.; Valiente-Dobón, J. J.; Zieblinski, M.
2015-11-01
The isospin mixing was deduced in the compound nucleus 80Zr at an excitation energy of E*=54 MeV from the γ decay of the giant dipole resonance. The reaction 40Ca + 40Ca at Ebeam=136 MeV was used to form the compound nucleus in the isospin I =0 channel, while the reaction 37Cl + 44Ca at Ebeam=95 MeV was used as the reference reaction. The γ rays were detected with the AGATA demonstrator array coupled with LaBr3 :Ce detectors. The temperature dependence of the isospin mixing was obtained and the zero-temperature value deduced. The isospin-symmetry-breaking correction δC used for the Fermi superallowed transitions was extracted and found to be consistent with β -decay data.
One-point functions in finite volume/temperature: a case study
NASA Astrophysics Data System (ADS)
Szécsényi, I. M.; Takács, G.; Watts, G. M. T.
2013-08-01
We consider finite volume (or equivalently, finite temperature) expectation values of local operators in integrable quantum field theories using a combination of numerical and analytical approaches. It is shown that the truncated conformal space approach, when supplemented with a recently proposed renormalization group, can be sufficiently extended to the low-energy regime that it can be matched with high precision by the low-temperature expansion proposed by Leclair and Mussardo. Besides verifying the consistency of the two descriptions, their combination leads to an evaluation of expectation values which is valid to a very high precision for all volume/temperature scales. As a side result of the investigation, we also discuss some unexpected singularities in the framework recently proposed by Pozsgay and Takács for the description of matrix elements of local operators in finite volume, and show that while some of these singularities are resolved by the inclusion of the class of exponential finite size corrections known as μ-terms, these latter corrections themselves lead to the appearance of new singularities. We point out that a fully consistent description of finite volume matrix elements is expected to be free of singularities, and therefore a more complete and systematic understanding of exponential finite size corrections is necessary.
Collector and source sheaths of a finite ion temperature plasma
Schwager, L.A.; Birdsall, C.K.
1988-04-13
The region between a Maxwellian plasma source and an absorbing surface is modeled with an electrostatic particle simulation and with a kinetic plasma-sheath model. In the kinetic model, Poisson's equation and Vlasov equations govern the velocity distribution of the ions and electrons. Our numerical and theoretical results for collector potential and plasma transport agree with the bounded model of Emmert et al., but differ somewhat from those using traditional Bohm sheath analysis. The plasma source injects equal fluxes of half-Maxwellian ions and electrons with specified mass and temperature ratios and is assumed to have a zero electric field. Representing the potential change within a distributed full-Maxwellian source region, the source potential drop depends primarily on temperature ratio and evolves a few Debye lengths from the source to neutralize the injected plasma. The plasma flows to an electrically floating collector where the more familiar electron-repelling collector sheath appears. Profiles of potential, density, drift velocity, temperature, kinetic energy flux, and heat flux are shown from simulation; all compare very well with theory. 24 refs., 7 figs., 1 tab.
Finite-temperature stability of a trapped dipolar Bose gas
Bisset, R. N.; Baillie, D.; Blakie, P. B.
2011-06-15
We calculate the stability diagram for a trapped normal Bose gas with dipole-dipole interactions. Our study characterizes the roles of trap geometry, temperature, and short-range interactions on the stability. We predict a robust double instability feature in oblate trapping geometries arising from the interplay of thermal gas saturation and the anisotropy of the interaction. Our results are relevant to current experiments with polar molecules and will be useful in developing strategies to obtain a polar molecule Bose-Einstein condensate.
The simulation of electron diffusion in solids at finite temperature
NASA Astrophysics Data System (ADS)
Carter, J.; Michez, L. A.; Hickey, B. J.; Morgan, G. J.
2001-01-01
We show how the transport of properties of electrons in disordered solids can be simulated taking into account atomic motion. The time-dependent Schrödinger equation and the molecular dynamics equation are solved in tandem for electronic diffusion and as a test of the methods we obtain metallic behaviour and variable range hopping in appropriate circumstances. We also describe a stable algorithm which introduces dissipation into the Schrödinger equation via imaginary components for the energy levels enabling electrons to be removed from a system as is necessary in device simulation. This is important because the often used leap frog method becomes unstable in this situation.
Finite-temperature Casimir force between perfectly metallic corrugated surfaces
Sarabadani, Jalal; Miri, MirFaez
2011-09-15
We study the Casimir force between two corrugated plates due to thermal fluctuations of a scalar field. For arbitrary corrugations and temperature T, we provide an analytical expression for the Casimir force, which is exact to second order in the corrugation amplitude. We study the specific case of two sinusoidally corrugated plates with corrugation wavelength {lambda}, lateral displacement b, and mean separation H. We find that the lateral Casimir force is F{sub l}(T,H)sin(2{pi}b/{lambda}). In other words, at all temperatures, the lateral force is a sinusoidal function of the lateral shift. In the limit {lambda}>>H, F{sub l}(T{yields}{infinity},H){proportional_to}k{sub B}TH{sup -4}{lambda}{sup -1}. In the opposite limit {lambda}<
Evidence for a finite-temperature phase transition in a bilayer quantum Hall system.
Champagne, A R; Eisenstein, J P; Pfeiffer, L N; West, K W
2008-03-01
We study the Josephson-like interlayer tunneling signature of the strongly correlated nuT=1 quantum Hall phase in bilayer two-dimensional electron systems as a function of the layer separation, temperature, and interlayer charge imbalance. Our results offer strong evidence that a finite temperature phase transition separates the interlayer coherent phase from incoherent phases which lack strong interlayer correlations. The transition temperature is dependent on both the layer spacing and charge imbalance between the layers. PMID:18352740
Evidence for a Finite-Temperature Phase Transition in a Bilayer Quantum Hall System
NASA Astrophysics Data System (ADS)
Champagne, A. R.; Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.
2008-03-01
We study the Josephson-like interlayer tunneling signature of the strongly correlated νT=1 quantum Hall phase in bilayer two-dimensional electron systems as a function of the layer separation, temperature, and interlayer charge imbalance. Our results offer strong evidence that a finite temperature phase transition separates the interlayer coherent phase from incoherent phases which lack strong interlayer correlations. The transition temperature is dependent on both the layer spacing and charge imbalance between the layers.
Single-bubble sonoluminescence as Dicke superradiance at finite temperature
NASA Astrophysics Data System (ADS)
Aparicio Alcalde, M.; Quevedo, H.; Svaiter, N. F.
2014-12-01
Sonoluminescence is a process in which a strong sound field is used to produce light in liquids. We explain sonoluminescence as a phase transition from ordinary fluorescence to a superradiant phase. We consider a spin-boson model composed of a single bosonic mode and an ensemble of N identical two-level atoms. We assume that the whole system is in thermal equilibrium with a reservoir at temperature β-1. We show that, in a ultrastrong-coupling regime, between the two-level atoms and the electromagnetic field it is possible to have a cooperative interaction of the molecules of the gas in the interior of the bubble with the field, generating sonoluminescence.
EXACT SOLUTION TO FINITE TEMPERATURE SFDM: NATURAL CORES WITHOUT FEEDBACK
Robles, Victor H.; Matos, T. E-mail: tmatos@fis.cinvestav.mx
2013-01-20
Recent high-quality observations of low surface brightness (LSB) galaxies have shown that their dark matter (DM) halos prefer flat central density profiles. However, the standard cold dark matter model simulations predict a more cuspy behavior. One mechanism used to reconcile the simulations with the observed data is the feedback from star formation. While this mechanism may be successful in isolated dwarf galaxies, its success in LSB galaxies remains unclear. Additionally, the inclusion of too much feedback in the simulations is a double-edged sword-in order to obtain a cored DM distribution from an initially cuspy one, the feedback recipes usually require one to remove a large quantity of baryons from the center of the galaxies; however, some feedback recipes produce twice the number of satellite galaxies of a given luminosity and with much smaller mass-to-light ratios from those that are observed. Therefore, one DM profile that produces cores naturally and that does not require large amounts of feedback would be preferable. We find both requirements to be satisfied in the scalar field dark matter model. Here, we consider that DM is an auto-interacting real scalar field in a thermal bath at temperature T with an initial Z {sub 2} symmetric potential. As the universe expands, the temperature drops so that the Z {sub 2} symmetry is spontaneously broken and the field rolls down to a new minimum. We give an exact analytic solution to the Newtonian limit of this system, showing that it can satisfy the two desired requirements and that the rotation curve profile is no longer universal.
Exact Solution to Finite Temperature SFDM: Natural Cores without Feedback
NASA Astrophysics Data System (ADS)
Robles, Victor H.; Matos, T.
2013-01-01
Recent high-quality observations of low surface brightness (LSB) galaxies have shown that their dark matter (DM) halos prefer flat central density profiles. However, the standard cold dark matter model simulations predict a more cuspy behavior. One mechanism used to reconcile the simulations with the observed data is the feedback from star formation. While this mechanism may be successful in isolated dwarf galaxies, its success in LSB galaxies remains unclear. Additionally, the inclusion of too much feedback in the simulations is a double-edged sword—in order to obtain a cored DM distribution from an initially cuspy one, the feedback recipes usually require one to remove a large quantity of baryons from the center of the galaxies; however, some feedback recipes produce twice the number of satellite galaxies of a given luminosity and with much smaller mass-to-light ratios from those that are observed. Therefore, one DM profile that produces cores naturally and that does not require large amounts of feedback would be preferable. We find both requirements to be satisfied in the scalar field dark matter model. Here, we consider that DM is an auto-interacting real scalar field in a thermal bath at temperature T with an initial Z 2 symmetric potential. As the universe expands, the temperature drops so that the Z 2 symmetry is spontaneously broken and the field rolls down to a new minimum. We give an exact analytic solution to the Newtonian limit of this system, showing that it can satisfy the two desired requirements and that the rotation curve profile is no longer universal.
Importance of finite-temperature exchange correlation for warm dense matter calculations
NASA Astrophysics Data System (ADS)
Karasiev, Valentin V.; Calderín, Lázaro; Trickey, S. B.
2016-06-01
The effects of an explicit temperature dependence in the exchange correlation (XC) free-energy functional upon calculated properties of matter in the warm dense regime are investigated. The comparison is between the Karasiev-Sjostrom-Dufty-Trickey (KSDT) finite-temperature local-density approximation (TLDA) XC functional [Karasiev et al., Phys. Rev. Lett. 112, 076403 (2014), 10.1103/PhysRevLett.112.076403] parametrized from restricted path-integral Monte Carlo data on the homogeneous electron gas (HEG) and the conventional Monte Carlo parametrization ground-state LDA XC [Perdew-Zunger (PZ)] functional evaluated with T -dependent densities. Both Kohn-Sham (KS) and orbital-free density-functional theories are used, depending upon computational resource demands. Compared to the PZ functional, the KSDT functional generally lowers the dc electrical conductivity of low-density Al, yielding improved agreement with experiment. The greatest lowering is about 15% for T =15 kK. Correspondingly, the KS band structure of low-density fcc Al from the KSDT functional exhibits a clear increase in interband separation above the Fermi level compared to the PZ bands. In some density-temperature regimes, the deuterium equations of state obtained from the two XC functionals exhibit pressure differences as large as 4% and a 6% range of differences. However, the hydrogen principal Hugoniot is insensitive to the explicit XC T dependence because of cancellation between the energy and pressure-volume work difference terms in the Rankine-Hugoniot equation. Finally, the temperature at which the HEG becomes unstable is T ≥7200 K for the T -dependent XC, a result that the ground-state XC underestimates by about 1000 K.
Importance of finite-temperature exchange correlation for warm dense matter calculations.
Karasiev, Valentin V; Calderín, Lázaro; Trickey, S B
2016-06-01
The effects of an explicit temperature dependence in the exchange correlation (XC) free-energy functional upon calculated properties of matter in the warm dense regime are investigated. The comparison is between the Karasiev-Sjostrom-Dufty-Trickey (KSDT) finite-temperature local-density approximation (TLDA) XC functional [Karasiev et al., Phys. Rev. Lett. 112, 076403 (2014)PRLTAO0031-900710.1103/PhysRevLett.112.076403] parametrized from restricted path-integral Monte Carlo data on the homogeneous electron gas (HEG) and the conventional Monte Carlo parametrization ground-state LDA XC [Perdew-Zunger (PZ)] functional evaluated with T-dependent densities. Both Kohn-Sham (KS) and orbital-free density-functional theories are used, depending upon computational resource demands. Compared to the PZ functional, the KSDT functional generally lowers the dc electrical conductivity of low-density Al, yielding improved agreement with experiment. The greatest lowering is about 15% for T=15 kK. Correspondingly, the KS band structure of low-density fcc Al from the KSDT functional exhibits a clear increase in interband separation above the Fermi level compared to the PZ bands. In some density-temperature regimes, the deuterium equations of state obtained from the two XC functionals exhibit pressure differences as large as 4% and a 6% range of differences. However, the hydrogen principal Hugoniot is insensitive to the explicit XC T dependence because of cancellation between the energy and pressure-volume work difference terms in the Rankine-Hugoniot equation. Finally, the temperature at which the HEG becomes unstable is T≥7200 K for the T-dependent XC, a result that the ground-state XC underestimates by about 1000 K. PMID:27415377
Finite-temperature fluid-insulator transition of strongly interacting 1D disordered bosons.
Michal, Vincent P; Aleiner, Igor L; Altshuler, Boris L; Shlyapnikov, Georgy V
2016-08-01
We consider the many-body localization-delocalization transition for strongly interacting one-dimensional disordered bosons and construct the full picture of finite temperature behavior of this system. This picture shows two insulator-fluid transitions at any finite temperature when varying the interaction strength. At weak interactions, an increase in the interaction strength leads to insulator [Formula: see text] fluid transition, and, for large interactions, there is a reentrance to the insulator regime. It is feasible to experimentally verify these predictions by tuning the interaction strength with the use of Feshbach or confinement-induced resonances, for example, in (7)Li or (39)K. PMID:27436894
Role of barrier layer on dielectric function of graphene double layer system at finite temperature
NASA Astrophysics Data System (ADS)
Patel, Digish K.; Ambavale, Sagar K.; Prajapati, Ketan; Sharma, A. C.
2016-05-01
We have theoretically investigated the static dielectric function of graphene double layer system (GDLS) at finite temperatures within the random phase approximation. GDLS has been suspended on a substrate and barrier layer of three different materials; h-BN, Al2O3 and HfO2 has been introduced between two graphene sheets of GDLS. We have reported dependence of the overall dielectric function of GDLS on interlayer distance and the effect of the dielectric environment at finite temperatures. Results show close relation between changing environment and behavior of dielectric constant of GDLS.
Dissipative soliton protocols in semiconductor microcavities at finite temperatures
NASA Astrophysics Data System (ADS)
Karpov, D. V.; Savenko, I. G.; Flayac, H.; Rosanov, N. N.
2015-08-01
We consider exciton polaritons in a semiconductor microcavity with a saturable absorber in the growth direction of the heterostructure. This feature promotes additional nonlinear losses of the system with the emergence of bistability of the condensate particles number on the nonresonant (electrical or optical) excitation intensity. Furthermore, we demonstrate a new type of bright spatial dissipative exciton-polariton soliton which emerges in the equilibrium between the regions with different particle density. We develop protocols of soliton creation and destruction. The switch to a solitonlike behavior occurs if the cavity is exposed by a short strong laser pulse with certain energy and duration. We estimate the characteristic times of soliton switch on and off and the time of return to the initial cycle. In particular, we demonstrate surprising narrowing of the spatial profile of the soliton and its vanishing at certain temperature due to interaction of the system with the thermal bath of acoustic phonons. We also address the role of polariton-polariton interaction (Kerr-like nonlinearity) on formation of dissipative solitons and show that the soliton may exist both in its presence and its absence.
On the finite-temperature quantum electrodynamics of gravitational acceleration
NASA Astrophysics Data System (ADS)
Barton, G.
1989-12-01
The temperature-dependent quantum-electrodynamic corrections to the Helmholtz free energy F of a particle at rest, and to its inertial mass minert, are the same: ΔF=Δminert=πe2(kT)2/3m. By contrast, the correction to the total energy U=F+TS is ΔU=-ΔF. Donoghue, Holstein, and Robinett have pointed out that if (as the equivalence principle appears to imply) weight is proportional to total energy, then the gravitational acceleration of a particle inside a blackbody cavity becomes g(m+ΔU)/(m+ΔF)~=g(1-2ΔF/m)
Değer, Yalçın; Adigüzel, Özkan; Özer, Senem Yiğit; Kaya, Sadullah; Polat, Zelal Seyfioğlu; Bozyel, Bejna
2015-01-01
Background The mouth is exposed to thermal irritation from hot and cold food and drinks. Thermal changes in the oral cavity produce expansions and contractions in tooth structures and restorative materials. The aim of this study was to investigate the effect of temperature and stress distribution on 2 different post systems using the 3-dimensional (3D) finite element method. Material/Methods The 3D finite element model shows a labio-lingual cross-sectional view of the endodontically treated upper right central incisor and supporting periodontal ligament with bone structures. Stainless steel and glass fiber post systems with different physical and thermal properties were modelled in the tooth restored with composite core and ceramic crown. We placed 100 N static vertical occlusal loading onto the center of the incisal surface of the tooth. Thermal loads of 0°C and 65°C were applied on the model for 5 s. Temperature and thermal stresses were determined on the labio-lingual section of the model at 6 different points. Results The distribution of stress, including thermal stress values, was calculated using 3D finite element analysis. The stainless steel post system produced more temperature and thermal stresses on the restorative materials, tooth structures, and posts than did the glass fiber reinforced composite posts. Conclusions Thermal changes generated stresses in the restorative materials, tooth, and supporting structures. PMID:26615495
Finite-Temperature Hydrogen Adsorption/Desorption Thermodynamics Driven by Soft Vibration Modes
Woo, Sung-Jae; Lee, Eui-Sup; Yoon, Mina; Yong-Hyun, Kim
2013-01-01
It is widely accepted that room-temperature hydrogen storage on nanostructured or porous materials requires enhanced dihydrogen adsorption. In this work we reveal that room-temperature hydrogen storage is possible not only by the enhanced adsorption, but also by making use of the vibrational free energy from soft vibration modes. These modes exist for example in the case of metallo-porphyrin-incorporated graphenes (M-PIGs) with out-of-plane ( buckled ) metal centers. There, the in-plane potential surfaces are flat because of multiple-orbital-coupling between hydrogen molecules and the buckled-metal centers. This study investigates the finite-temperature adsorption/desorption thermodynamics of hydrogen molecules adsorbed on M-PIGs by employing first-principles total energy and vibrational spectrum calculations. Our results suggest that the current design strategy for room-temperature hydrogen storage materials should be modified by explicitly taking finite-temperature vibration thermodynamics into account.
Finite element study of plate buckling induced by spatial temperature gradients
Thornton, E.A.; Kolenski, J.D.; Marino, R.P.
1993-01-01
Finite element analyses of thermal buckling of thin metallic plates with prescribed spatial temperature distributions are described. Thermally induced compressive membrane stresses and transverse plate displacement imperfections initiate plates buckling. A finite element formulation based on von Karman plate theory is presented. The resulting nonlinear equations are solved for incremental temperature increases by Newton-Raphson iteration. The computational method is used to investigate the buckling response of rectangular plates with steady and unsteady spatially varying temperature distributions. The role of initial plate imperfections and temperature distributions on the nonlinear response of plate displacements and stresses is described. The relatively high levels of stress induced by spatial temperature gradients should be considered carefully in the postbuckling design of panels for aerospace vehicles subjected to combined mechanical and thermal loads. 31 refs.
Finite element study of plate buckling induced by spatial temperature gradients
NASA Technical Reports Server (NTRS)
Thornton, Earl A.; Kolenski, James D.; Marino, Robert P.
1993-01-01
Finite element analyses of thermal buckling of thin metallic plates with prescribed spatial temperature distributions are described. Thermally induced compressive membrane stresses and transverse plate displacement imperfections initiate plates buckling. A finite element formulation based on von Karman plate theory is presented. The resulting nonlinear equations are solved for incremental temperature increases by Newton-Raphson iteration. The computational method is used to investigate the buckling response of rectangular plates with steady and unsteady spatially varying temperature distributions. The role of initial plate imperfections and temperature distributions on the nonlinear response of plate displacements and stresses is described. The relatively high levels of stress induced by spatial temperature gradients should be considered carefully in the postbuckling design of panels for aerospace vehicles subjected to combined mechanical and thermal loads.
Kulkarni, Y; Knap, J; Ortiz, M
2007-04-26
The aim of this paper is the development of equilibrium and non-equilibrium extensions of the quasicontinuum (QC) method. We first use variational mean-field theory and the maximum-entropy formalism for deriving approximate probability distribution and partition functions for the system. The resulting probability distribution depends locally on atomic temperatures defined for every atom and the corresponding thermodynamic potentials are explicit and local in nature. The method requires an interatomic potential as the sole empirical input. Numerical validation is performed by simulating thermal equilibrium properties of selected materials using the Lennard-Jones pair potential and the EAM potential and comparing with molecular dynamics results as well as experimental data. The max-ent variational approach is then taken as a basis for developing a three-dimensional non-equilibrium finite temperature extension of the quasicontinuum method. This extension is accomplished by coupling the local temperature-dependent free energy furnished by the max-ent approximation scheme to the heat equation in a joint thermo-mechanical variational setting. Results for finite-temperature nanoindentation tests demonstrate the ability of the method to capture non-equilibrium transport properties and differentiate between slow and fast indentation.
Asymmetry of the dimension-two gluon condensate: The finite temperature case
Vercauteren, David; Verschelde, Henri
2010-10-15
In this paper, we continue the work begun in a previous article. We compute, in the formalism of local composite operators, the value of the asymmetry in the dimension two condensate for finite temperatures. We find a positive value for the asymmetry, which disappears when the temperature is increased. We also compute the value of the full dimension two condensate for higher temperatures, and we find that it decreases in absolute value, finally disappearing for sufficiently high temperature. We also comment on the temperature dependence of the electric and magnetic components of the condensate separately. We compare our results with the corresponding lattice date found by Chernodub and Ilgenfritz.
NASA Astrophysics Data System (ADS)
Umar Alkali, Adam; Lenggo Ginta, Turnad; Majdi Abdul-Rani, Ahmad
2015-04-01
This paper presents a 3D transient finite element modelling of the workpiece temperature field produced during the travelling heat sourced from oxyacetylene flame. The proposed model was given in terms of preheat-only test applicable during thermally enhanced machining using the oxyacetylene flame as a heat source. The FEA model as well as the experimental test investigated the surface temperature distribution on 316L stainless steel at scanning speed of 100mm/min, 125mm/min 160mm/min, 200mm/min and 250mm/min. The parametric properties of the heat source maintained constant are; lead distance Ld =10mm, focus height Fh=7.5mm, oxygen gas pressure Poxy=15psi and acetylene gas pressure Pacty=25psi. An experimental validation of the temperature field induced on type 316L stainless steel reveal that temperature distribution increases when the travelling speed decreases.
Mostafa, Salwa; Lavrik, Nickolay V; Bannuru, Thirumalesh; Rajic, Slobodan; Islam, Syed K; Datskos, Panos G; Hunter, Scott Robert
2011-01-01
A self resonating bimorph cantilever structure for fast temperature cycling in a pyroelectric energy harvester has been modeled using a finite element method. The effect of constituting material properties and system parameters on the frequency and magnitude of temperature cycling and the efficiency of energy recycling using the proposed structure has been investigated. Results show that thermal contact conductance and heat source temperature play a key role in dominating the cycling frequency and efficiency of energy recycling. An optimal solution for the most efficient energy scavenging process has been sought by studying the performance trend with different variable parameters such as thermal contact conductance, heat source temperature, device aspect ratio and constituent materials of varying thermal conductivity and expansion coefficients.
Chang, Isaac
2003-01-01
Background Few finite element models (FEM) have been developed to describe the electric field, specific absorption rate (SAR), and the temperature distribution surrounding hepatic radiofrequency ablation probes. To date, a coupled finite element model that accounts for the temperature-dependent electrical conductivity changes has not been developed for ablation type devices. While it is widely acknowledged that accounting for temperature dependent phenomena may affect the outcome of these models, the effect has not been assessed. Methods The results of four finite element models are compared: constant electrical conductivity without tissue perfusion, temperature-dependent conductivity without tissue perfusion, constant electrical conductivity with tissue perfusion, and temperature-dependent conductivity with tissue perfusion. Results The data demonstrate that significant errors are generated when constant electrical conductivity is assumed in coupled electrical-heat transfer problems that operate at high temperatures. These errors appear to be closely related to the temperature at which the ablation device operates and not to the amount of power applied by the device or the state of tissue perfusion. Conclusion Accounting for temperature-dependent phenomena may be critically important in the safe operation of radiofrequency ablation device that operate near 100°C. PMID:12780939
BCS instability and finite temperature corrections to tachyon mass in intersecting D1-branes
NASA Astrophysics Data System (ADS)
Chowdhury, Sudipto Paul; Sarkar, Swarnendu; Sathiapalan, B.
2014-09-01
A holographic description of BCS superconductivity is given in [1]. This model was constructed by insertion of a pair of D8-branes on a D4-background. The spectrum of intersecting D8-branes has tachyonic modes indicating an instability which is identified with the BCS instability in superconductors. Our aim is to study the stability of the intersecting branes under finite temperature effects. Many of the technical aspects of this problem are captured by a simpler problem of two intersecting D1-branes on flat background. In the simplified set-up we compute the one-loop finite temperature corrections to the tree-level tachyon mass-squared-squared using the frame-work of SU(2) Yang-Mills theory in (1 + 1)-dimensions. We show that the one-loop two-point functions are ultraviolet finite due to cancellation of ultraviolet divergence between the amplitudes containing bosons and fermions in the loop. The amplitudes are found to be infrared divergent due to the presence of massless fields in the loops. We compute the finite temperature mass-squared correction to all the massless fields and use these temperature dependent masses-squared to compute the tachyonic mass-squared correction. We show numerically the existence of a transition temperature at which the effective mass-squared of the tree-level tachyons becomes zero, thereby stabilizing the brane configuration.
Midinfrared thermal emission properties of finite arrays of gold dipole nanoantennas
NASA Astrophysics Data System (ADS)
Centini, M.; Benedetti, A.; Larciprete, M. C.; Belardini, A.; Li Voti, R.; Bertolotti, M.; Sibilia, C.
2015-11-01
We studied the far-field thermal emission properties of finite arrays of resonant gold dipole nanoantennas at equilibrium temperature. We numerically investigated the transition from the super-Planckian emission of the single resonant antenna to the sub-Planckian emission inherent to infinite periodic arrays. Increasing the number of unit cells of the array, the overall size of the system increases, and the relative emissivity quickly converges to values lower than the unity. Nevertheless, if the separation between nanoantennas in the array is small compared to the wavelength, the near-field interaction makes the emission of each unit cell multipolar. This opens the doors for additional tailoring of the emitted power and directionality of thermal radiation.
Electronic chemical response indexes at finite temperature in the canonical ensemble
NASA Astrophysics Data System (ADS)
Franco-Pérez, Marco; Gázquez, José L.; Vela, Alberto
2015-07-01
Assuming that the electronic energy is given by a smooth function of the number of electrons and within the extension of density functional theory to finite temperature, the first and second order chemical reactivity response functions of the Helmholtz free energy with respect to the temperature, the number of electrons, and the external potential are derived. It is found that in all cases related to the first or second derivatives with respect to the number of electrons or the external potential, there is a term given by the average of the corresponding derivative of the electronic energy of each state (ground and excited). For the second derivatives, including those related with the temperature, there is a thermal fluctuation contribution that is zero at zero temperature. Thus, all expressions reduce correctly to their corresponding chemical reactivity expressions at zero temperature and show that, at room temperature, the corrections are very small. When the assumption that the electronic energy is given by a smooth function of the number of electrons is replaced by the straight lines behavior connecting integer values, as required by the ensemble theorem, one needs to introduce directional derivatives in most cases, so that the temperature dependent expressions reduce correctly to their zero temperature counterparts. However, the main result holds, namely, at finite temperature the thermal corrections to the chemical reactivity response functions are very small. Consequently, the present work validates the usage of reactivity indexes calculated at zero temperature to infer chemical behavior at room and even higher temperatures.
Electronic chemical response indexes at finite temperature in the canonical ensemble
Franco-Pérez, Marco E-mail: jlgm@xanum.uam.mx Gázquez, José L. E-mail: jlgm@xanum.uam.mx; Vela, Alberto E-mail: jlgm@xanum.uam.mx
2015-07-14
Assuming that the electronic energy is given by a smooth function of the number of electrons and within the extension of density functional theory to finite temperature, the first and second order chemical reactivity response functions of the Helmholtz free energy with respect to the temperature, the number of electrons, and the external potential are derived. It is found that in all cases related to the first or second derivatives with respect to the number of electrons or the external potential, there is a term given by the average of the corresponding derivative of the electronic energy of each state (ground and excited). For the second derivatives, including those related with the temperature, there is a thermal fluctuation contribution that is zero at zero temperature. Thus, all expressions reduce correctly to their corresponding chemical reactivity expressions at zero temperature and show that, at room temperature, the corrections are very small. When the assumption that the electronic energy is given by a smooth function of the number of electrons is replaced by the straight lines behavior connecting integer values, as required by the ensemble theorem, one needs to introduce directional derivatives in most cases, so that the temperature dependent expressions reduce correctly to their zero temperature counterparts. However, the main result holds, namely, at finite temperature the thermal corrections to the chemical reactivity response functions are very small. Consequently, the present work validates the usage of reactivity indexes calculated at zero temperature to infer chemical behavior at room and even higher temperatures.
Finite Element Models and Properties of a Stiffened Floor-Equipped Composite Cylinder
NASA Technical Reports Server (NTRS)
Grosveld, Ferdinand W.; Schiller, Noah H.; Cabell, Randolph H.
2010-01-01
Finite element models were developed of a floor-equipped, frame and stringer stiffened composite cylinder including a coarse finite element model of the structural components, a coarse finite element model of the acoustic cavities above and below the beam-supported plywood floor, and two dense models consisting of only the structural components. The report summarizes the geometry, the element properties, the material and mechanical properties, the beam cross-section characteristics, the beam element representations and the boundary conditions of the composite cylinder models. The expressions used to calculate the group speeds for the cylinder components are presented.
Thomas, Edward Jr.; Fisher, Ross; Merlino, Robert L.
2007-12-15
An experiment has been performed to study the behavior of dust acoustic waves driven at high frequencies (f>100 Hz), extending the range of previous work. In this study, two previously unreported phenomena are observed--interference effects between naturally excited dust acoustic waves and driven dust acoustic waves, and the observation of finite dust temperature effects on the dispersion relation.
Self-consistently improved finite temperature effective potential for gauge theories
Amelino-Camelia, G. )
1994-03-15
The finite temperature effective potential of the Abelian Higgs model is studied using the self-consistent composite operator method, which can be used to sum up the contributions of daisy and superdaisy diagrams. The effect of the momentum dependence of the effective masses is estimated by using a Rayleigh-Ritz variational approximation.
Calculation of equation of state of QCD at zero temperature and finite chemical potential
NASA Astrophysics Data System (ADS)
Jiang, Yu; Li, Ning; Sun, Wei-Min; Zong, Hong-Shi
2010-09-01
In this paper we calculate the equation of state (EOS) of QCD at zero temperature and finite chemical potential by using several models of quark propagators including the Dyson-Schwinger equations (DSEs) model, the hard-dense-loop (HDL) approximation and the quasi-particle model. The results are analyzed and compared with the known results in the literature.
Ion currents to cylindrical Langmuir probes for finite ion temperature values: Theory
Ballesteros, J.; Palop, J.I.F.; Colomer, V.; Hernandez, M.A.
1995-12-31
As it is known, the experimental ion currents to a cylindrical Langmuir probe fit quite well to the radial motion theory, developed by Allen, Boyd and Reynolds (ABR Model) and generalized by Chen for the cylindrical probe case. In this paper, we are going to develop a generalization of the ABR theory, taking into account the influence of a finite ion temperature value.
Observations of vertically propagating driven dust acoustic waves: Finite temperature effects
Williams, Jeremiah D.; Thomas, Edward Jr.; Marcus, Lydia
2008-04-15
In this study, the first measurement of the dispersion relationship for a vertically propagating (i.e., parallel to gravity), driven dust acoustic wave is reported. Finite dust temperature effects were observed in the dispersion relation of the dust acoustic wave.
Finite temperature quantum field theory in the functional Schrödinger picture
NASA Astrophysics Data System (ADS)
Lee, Hyuk-Jae; Na, Kyunghyun; Yee, Jae Hyung
1995-03-01
We calculate the finite temperature Gaussian effective potential of scalar φ4 theory in the functional Schrödinger picture. Our method is the direct generalization of the variational method proposed by Eboli, Jackiw, and Pi for quantum-mechanical systems, and gives the same result as that of Amelino-Camelia and Pi who used the self-consistent composite operator method.
Finite-temperature behavior of an interspecies fermionic superfluid with population imbalance
Guo Hao; Chien, C.-C.; He Yan; Levin, K.; Chen Qijin
2009-07-15
We determine the superfluid transition temperature T{sub c} and related finite temperature phase diagrams for the entire BCS-Bose-Einstein-condensation crossover in a three-dimensional homogeneous mixture of {sup 6}Li and {sup 40}K atoms with population imbalance. Our work is motivated by the recent observation of an interspecies Feshbach resonance. Pairing fluctuation effects, which significantly reduce T{sub c} from the onset temperature for pairing (T*), provide reasonable estimates of T{sub c} and indicate that the interspecies superfluid phase should be accessible in future experiments. Although a homogeneous polarized superfluid is not stable in the ground state near unitarity, our phase diagrams show that it stabilizes at finite temperature.
He, Qi-Liang; Xu, Jing-Bo; Yao, Dao-Xin; Department of Physics and Astronomy, University of Tennessee, Knoxville, TN 37996 ; Zhang, Ye-Qi
2013-07-15
We investigate the dynamics of quantum correlation between two noninteracting qubits each inserted in its own finite-temperature environment with 1/f spectral density. It is found that the phenomenon of sudden transition between classical and quantum decoherence exists in the system when two qubits are initially prepared in X-type quantum states, and the transition time depends on the initial-state of two qubits, the qubit–environment coupling constant and the temperature of the environment. Furthermore, we explore the influence of dynamical decoupling pulses on the transition time and show that it can be prolonged by applying the dynamical decoupling pulses. -- Highlights: •The sudden transition phenomenon from finite-temperature environments is studied. •The transition time depends on the environment temperature and the system parameters. •The transition time can be prolonged by applying the dynamical decoupling pulses.
String effects and the distribution of the glue in static mesons at finite temperature
Bakry, A. S.; Leinweber, D. B.; Moran, P. J.; Williams, A. G.; Sternbeck, A.
2010-11-01
The distribution of the gluon action density in mesonic systems is investigated at finite temperature. The simulations are performed in quenched QCD for two temperatures below the deconfinement phase. Unlike the gluonic profiles displayed at T=0, the action-density isosurfaces display a prolate-spheroid-like shape. The curved width profile of the flux tube is found to be consistent with the prediction of the free bosonic string model at large distances.
Finite temperature solitons in nonlocal field theories from p-adic strings
Biswas, Tirthabir; Cembranos, Jose A. R.; Kapusta, Joseph I.
2010-10-15
Nonlocal field theories which arise from p-adic string theories have vacuum soliton solutions. We find the soliton solutions at finite temperature. These solutions become important for the partition function when the temperature exceeds m{sub s}/g{sub o}{sup 2}, where m{sub s} is the string mass scale and g{sub o} is the open string coupling.
Ion currents to cylindrical Langmuir probes for finite ion temperature values: Experimental
Ballesteros, J.; Palop, J.I.F.; Colomer, V.; Hernandez, M.A.
1995-12-31
A new theoretical model about the ion currents to a cylindrical probe has been developed which takes into account the influence of a finite ion temperature value. The ABR (Allen, Boyd and Reynolds) model, which considers only radial motion for the positive ions, is recovered in the limit of cold ions. In this paper we axe going to show the experimental ion currents obtained in a plasma in which the positive ion temperature effect cannot be neglected.
Critical velocity for vortex nucleation in a finite-temperature Bose gas
NASA Astrophysics Data System (ADS)
Stagg, G. W.; Pattinson, R. W.; Barenghi, C. F.; Parker, N. G.
2016-02-01
We use classical field simulations of the homogeneous Bose gas to study the breakdown of superflow due to vortex nucleation past a cylindrical obstacle at finite temperature. Thermal fluctuations modify the vortex nucleation from the obstacle, turning antiparallel vortex lines (which would be nucleated at zero temperature) into wiggly lines, vortex rings, and even vortex tangles. We find that the critical velocity for vortex nucleation decreases with increasing temperature and scales with the speed of sound of the condensate, becoming zero at the critical temperature for condensation.
NASA Astrophysics Data System (ADS)
Konar, G.; Chakraborty, N.; Das, J.
Hysteresis motors being capable of producing a steady torque at low speeds and providing good starting properties at loaded condition became popular among different fractional horse power electrical motors. High temperature superconducting materials being intrinsically hysteretic are suitable for this type of motor. In the present work, performance study of a 2-pole, 50 Hz HTS hysteresis motor with conventional stator and HTS rotor has been carried out numerically using finite element method. The simulation results confirm the ability of the segmented HTS rotor with glued circular sectors to trap the magnetic field as high as possible compared to the ferromagnetic rotor. Also the magnetization loops in the HTS hysteresis motor are obtained and the corresponding torque and AC losses are calculated. The motor torque thus obtained is linearly proportional to the current which is the common feature of any hysteresis motor. Calculations of torques, current densities etc are done using MATLAB program developed in-house and validated using COMSOL Multiphysics software. The simulation result shows reasonable agreement with the published results.
Role of external fields in enhancing long-distance entanglement at finite temperatures
NASA Astrophysics Data System (ADS)
Kuwahara, Tomotaka
2013-04-01
We investigate the end-to-end entanglement of a general XYZ-spin chain at the non-zero temperatures. The entanglement usually vanishes at a certain critical temperature Tc, but external fields can make Tc higher. We obtain a general statement on the increase of the critical temperature Tc by the external fields. We prove that if the two end spins are separated by two spins or more, then the critical temperature cannot be higher than a certain finite temperature \\bar{T}_c (T_c\\le \\bar{T}_c), that is, the entanglement must vanish above the temperature \\bar{T}_c for any values of the external fields. On the other hand, if the two end spins are separated by one spin, then the entanglement maximized by the external fields exhibits a power-law decay of the temperature, being finite at any temperatures. In order to demonstrate the former case, we numerically calculate the temperature \\bar{T}_c in XX and XY four-spin chains. We find that the temperature \\bar{T}_c shows qualitatively different behavior, depending on the conservation of the angular momentum in the z direction.
NASA Astrophysics Data System (ADS)
Nghiem, H. T. M.; Costi, T. A.
2014-02-01
The time-dependent numerical renormalization group (TDNRG) method [Anders et al., Phys. Rev. Lett. 95, 196801 (2005), 10.1103/PhysRevLett.95.196801] offers the prospect of investigating in a nonperturbative manner the time dependence of local observables of interacting quantum impurity models at all time scales following a quantum quench. Here, we present a generalization of this method to arbitrary finite temperature by making use of the full density matrix approach [Weichselbaum et al., Phys. Rev. Lett. 99, 076402 (2007), 10.1103/PhysRevLett.99.076402]. We show that all terms in the projected full density matrix ρi →f=ρ+++ρ--+ρ+-+ρ-+ appearing in the time evolution of a local observable may be evaluated in closed form at finite temperature, with ρ+-=ρ-+=0. The expression for ρ-- is shown to be finite at finite temperature, becoming negligible only in the limit of vanishing temperatures. We prove that this approach recovers the short-time limit for the expectation value of a local observable exactly at arbitrary temperatures. In contrast, the corresponding long-time limit is recovered exactly only for a continuous bath, i.e., when the logarithmic discretization parameter Λ →1+. Since the numerical renormalization group approach breaks down in this limit, and calculations have to be carried out at Λ >1, the long-time behavior following an arbitrary quantum quench has a finite error, which poses an obstacle for the method, e.g., in its application to the scattering-states numerical renormalization group method for describing steady-state nonequilibrium transport through correlated impurities [Anders, Phys. Rev. Lett. 101, 066804 (2008), 10.1103/PhysRevLett.101.066804]. We suggest a way to overcome this problem by noting that the time dependence, in general, and the long-time limit, in particular, become increasingly more accurate on reducing the size of the quantum quench. This suggests an improved generalized TDNRG approach in which the system is time
Hard thermal loops and beyond in the finite temperature world-line formulation of QED
Venugopalan, R.; Wirstam, J.
2001-06-15
We derive the hard thermal loop action for soft electromagnetic fields in the finite temperature world-line formulation at imaginary time by first integrating out the hard fermion modes from the microscopic QED action. Further, using the finite T world-line method, we calculate all static higher order terms in the soft electromagnetic field. At high T, the leading non-linear terms are independent of the temperature and, except for a term quartic in the time component of the vector potential, they cancel exactly against the vacuum contribution. The remaining T-dependent non-linear terms become more strongly suppressed by the temperature as the number of soft fields increases, thus making the expansion reliable.
Finite-temperature Dynamics and Quantum Criticality in a Model for Insulating Magnets
NASA Astrophysics Data System (ADS)
Wu, Jianda; Yang, Wang; Wu, Congjun; Si, Qimiao
Theoretical understanding of the finite-temperature dynamics in quantum critical systems is a challenging problem, due to the mixing of thermal and quantum fluctuations. Recently, neutron scattering experiments in the three-dimensional quantum dimmer material TlCuCl3 under pressure tuning have mapped out the magnetic dynamics at finite temperatures in the quantum critical regime, thereby providing the opportunity for systematic understandings. In this work, we calculate the spin spectral function of an O (n) symmetric field theory using a field-theory procedure to two loops. We calculate the temperature dependence of the energy and damping rate of the spin excitations in the quantum critical regime, demonstrate a good agreement with the experimental results, and determine the parameter regime of the field theory that is appropriate for TlCuCl3. From our calculations we can also suggest further experimental means to test the applicability of the underlying field theory in this and related systems.
Finite element model of iron powder compaction at above room temperature
NASA Astrophysics Data System (ADS)
Rahman, M. M.; Ariffin, A. K.
2015-05-01
This paper presents the finite element modelling of iron powder compaction process at above ambient temperature. The deformation behaviour of powder mass at elevated temperature was assumed to be rate independent thermo-elastoplastic material where the material constitutive laws were derived based on a continuum mechanics approach by considering a large displacement based finite element formulation. The temperature dependent material parameters were established through experimentation. Two constitutive relations namely Mohr-Coulomb and Elliptical Cap yield models were used to represent the deformation behaviour of the powder mass during the compaction process. These yield models were tested, however an Elliptical Cap model was shown to be the most appropriate to represent the compaction process. The staggered-incremental-iterative solution strategy was established to solve the non-linearity in the systems of equations. Some numerical simulation results were validated through experimentation, where a good agreement was observed.
Simultaneous Measurement of Temperature Dependent Thermophysical Properties
NASA Astrophysics Data System (ADS)
Czél, Balázs; Gróf, Gyula; Kiss, László
2011-11-01
A new evaluation method for a transient measurement of thermophysical properties is presented in this paper. The aim of the research was to couple a new automatic evaluation procedure to the BICOND thermophysical property measurement method to enhance the simultaneous determination of the temperature dependent thermal conductivity and volumetric heat capacity. The thermophysical properties of two different polymers were measured and compared with the literature data and with the measurement results that were done by well-known, traditional methods. The BICOND method involves a step-down cooling, recording the temperature histories of the inner and the outer surfaces of a hollow cylindrical sample and the thermophysical properties are evaluated from the solution of the corresponding inverse heat conduction using a genetic algorithm-based method (BIGEN) developed by the authors. The BIGEN is able to find the material properties with any kind of temperature dependency, that is illustrated through the measurement results of poly(tetrafluoroethylene) (PTFE) and polyamide (PA) samples.
Finite Element Analysis of Thermo-Mechanical Properties of 3D Braided Composites
NASA Astrophysics Data System (ADS)
Jiang, Li-li; Xu, Guo-dong; Cheng, Su; Lu, Xia-mei; Zeng, Tao
2014-04-01
This paper presents a modified finite element model (FEM) to investigate the thermo-mechanical properties of three-dimensional (3D) braided composite. The effective coefficients of thermal expansion (CTE) and the meso-scale mechanical response of 3D braided composites are predicted. The effects of the braiding angle and fiber volume fraction on the effective CTE are evaluated. The results are compared to the experimental data available in the literature to demonstrate the accuracy and reliability of the present method. The tensile stress distributions of the representative volume element (RVE) are also outlined. It is found that the stress of the braiding yarn has a significant increase with temperature rise; on the other hand, the temperature change has an insignificant effect on the stress of the matrix. In addition, a rapid decrease in the tensile strength of 3D braided composites is observed with the increase in temperature. It is revealed that the thermal conditions have a significant effect on the strength of 3D braided composites. The present method provides an effective tool to predict the stresses of 3D braided composites under thermo-mechanical loading.
Linear and nonlinear finite-element analysis of laminated composite structures at high temperatures
Wilt, T.E.
1992-01-01
A simple robust finite element which can effectively model the multilayer composite material is developed. This will include thermal gradient capabilities necessary for a complete thermomechanical analysis. In order to integrate the numerically stiff rate-dependent viscoplastic equations, efficient, stable numerical algorithms are developed. In addition, consistent viscoplastic/plastic tangent matrices are also formulated. The finite element is formulated based upon a generalized mixed variational principle with independently assumed displacements and layer-number independent strains. A unique scheme utilizing nodal temperatures is used to model a linear thermal gradient through the thickness of the composite. The numerical-integration algorithms are formulated in the context of a fully implicit backward Euler scheme. The consistent tangent matrices arise directly from the formulation. The multi-layer composite finite element demonstrates good performance in terms of static displacement and stress predictions, and dynamic response.
Butz, Kent D; Chan, Deva D; Nauman, Eric A; Neu, Corey P
2011-10-13
The noninvasive measurement of finite strains in biomaterials and tissues by magnetic resonance imaging (MRI) enables mathematical estimates of stress distributions and material properties. Such methods allow for non-contact and patient-specific modeling in a manner not possible with traditional mechanical testing or finite element techniques. Here, we employed three constitutive (i.e. linear Hookean, and nonlinear Neo-Hookean and Mooney-Rivlin) relations with known loading conditions and MRI-based finite strains to estimate stress patterns and material properties in the articular cartilage of tibiofemoral joints. Displacement-encoded MRI was used to determine two-dimensional finite strains in juvenile porcine joints, and an iterative technique estimated stress distributions and material properties with defined constitutive relations. Stress distributions were consistent across all relations, although the stress magnitudes varied. Material properties for femoral and tibial cartilage were found to be consistent with those reported in literature. Further, the stress estimates from Hookean and Neo-Hookean, but not Mooney-Rivlin, relations agreed with finite element-based simulations. A nonlinear Neo-Hookean relation provided the most appropriate model for the characterization of complex and spatially dependent stresses using two-dimensional MRI-based finite strain. These results demonstrate the feasibility of a new and computationally efficient technique incorporating MRI-based deformation with mathematical modeling to non-invasively evaluate the mechanical behavior of biological tissues and materials. PMID:21920526
Sequences with M-Bonacci Property and Their Finite Sums
ERIC Educational Resources Information Center
Asiru, Muniru A.
2008-01-01
The note introduces sequences having M-bonacci property. Two summation formulas for sequences with M-bonacci property are derived. The formulas are generalizations of corresponding summation formulas for both M-bonacci numbers and Fibonacci numbers that have appeared previously in the literature. Applications to the Arithmetic series, "m"th "g -…
Anagnostopoulos, Konstantinos N; Hanada, Masanori; Nishimura, Jun; Takeuchi, Shingo
2008-01-18
We present the first Monte Carlo results for supersymmetric matrix quantum mechanics with 16 supercharges at finite temperature. The recently proposed nonlattice simulation enables us to include the effects of fermionic matrices in a transparent and reliable manner. The internal energy nicely interpolates the weak coupling behavior obtained by the high temperature expansion, and the strong coupling behavior predicted from the dual black-hole geometry. The Polyakov line asymptotes at low temperature to a characteristic behavior for a deconfined theory, suggesting the absence of a phase transition. These results provide highly nontrivial evidence for the gauge-gravity duality. PMID:18232852
Wu, H.W.; Shii, Sheng Hwa . Dept. of Naval Architecture and Marine Engineering)
1994-06-01
A new method, involving the combined use of analysis and the finite-element method, is applicable to the heat conduction problem with isolated heat sources. Unlike the finite-element method the analysis/finite-element combined method is able to discretize the distributed sources with discontinuities into course elements, and the solution is still calculated accurately. The results are compared in tables with exact solutions and other numerical data, and the agreement is found to be good.
NASA Astrophysics Data System (ADS)
Majka; Staszel, P.; Natowitz, J. B.; Cibor, J.; Hagel, K.; Li, J.; Mdeiwayeh, N.; Wada, R.; Zhao, Y.
1996-10-01
Quantum statistical thermodynamics has been used to calculate the number of available states and their occupation for fermions and bosons at temperature, T_in, of finite nuclear sytems. An apparent temperature of these systems, T_app, has been calculated from double yield ratios of two isotope pairs. The importance of employing the quantum statistics when high densities and/or low temperatures are involved is shown. However, at high temperatures and low densities, the system behaves as a Maxwell-Boltzmann gas. Sequental decays of fragments from excited states influence the double yield ratio observable, causing problems with the temperature extraction. The model has been applied to study the high temperature branch of the "caloric curve".
Magnetospheric Whistler Mode Ray Tracing with the Inclusion of Finite Electron and Ion Temperature
NASA Astrophysics Data System (ADS)
Maxworth, A. S.; Golkowski, M.
2015-12-01
Ray tracing is an important technique for the study of whistler mode wave propagation in the Earth's magnetosphere. In numerical ray tracing the trajectory of a wave packet is calculated at each point in space by solving the Haselgrove equations, assuming a smooth, loss-less medium with no mode coupling. Previous work on ray tracing has assumed a cold plasma environment with negligible electron and ion temperatures. In this work we present magnetospheric whistler mode wave ray tracing results with the inclusion of finite ion and electron temperature. The inclusion of finite temperature effects makes the fourth order dispersion relation become sixth order. We compare our results with the work done by previous researchers for cold plasma environments, using two near earth space models (NGO and GCPM). Inclusion of finite temperature closes the otherwise open refractive index surface near the lower hybrid resonance frequency and affects the magnetospheric reflection of whistler waves. We also asses the main changes in the ray trajectory and implications for cyclotron resonance wave particle interactions including energetic particle precipitation.
NASA Astrophysics Data System (ADS)
Eckmann, Jean-Pierre; Procaccia, Itamar
2008-07-01
The aim of this paper is to discuss some basic notions regarding generic glass-forming systems composed of particles interacting via soft potentials. Excluding explicitly hard-core interaction, we discuss the so-called glass transition in which a supercooled amorphous state is formed, accompanied by a spectacular slowing down of relaxation to equilibrium, when the temperature is changed over a relatively small interval. Using the classical example of a 50-50 binary liquid of N particles with different interaction length scales, we show the following. (i) The system remains ergodic at all temperatures. (ii) The number of topologically distinct configurations can be computed, is temperature independent, and is exponential in N . (iii) Any two configurations in phase space can be connected using elementary moves whose number is polynomially bounded in N , showing that the graph of configurations has the small world property. (iv) The entropy of the system can be estimated at any temperature (or energy), and there is no Kauzmann crisis at any positive temperature. (v) The mechanism for the super-Arrhenius temperature dependence of the relaxation time is explained, connecting it to an entropic squeeze at the glass transition. (vi) There is no Vogel-Fulcher crisis at any finite temperature T>0 .
A finite-temperature density functional study of electron self-trapping in 3He and 4He.
Jin, Dafei; Guo, Wei
2012-06-28
We introduce a compact finite-temperature density functional model to study electron self-trapping in both liquid and vapor (3)He and (4)He. This model can quantitatively reproduce the most essential thermodynamic properties of (3)He and (4)He along their liquid-vapor coexistence lines. The structures and energetics of self-trapped electron bubbles on the 1S ground state and 1P excited state are particularly investigated. Our results show that 1S and 1P bubbles exist in liquid at any temperature, whereas 1S bubbles exist in vapor only above 1.6 K in (3)He and above 2.8 K in (4)He, 1P bubbles exist in vapor only above 2.5 K in (3)He and 4.0 K in (4)He. An initially spherical 1P bubble is unstable against deformation towards a peanut shape. In liquid, a peanut-shaped 1P bubble is held from fission by surface tension until reaching the liquid-vapor critical point, whereas in vapor it always splits into two smaller bubbles. The existence of 1P bubbles in finite-temperature liquid helium and their fission instability in helium vapor reveal interesting physics in this system. PMID:22755590
NASA Astrophysics Data System (ADS)
Mirnov, V. V.; Ding, W. X.; Brower, D. L.; Van Zeeland, M. A.; Carlstrom, T. N.
2007-10-01
Finite electron temperature effects on interferometry and polarimetry measurements for burning plasma are considered with particular focus on analytically understanding the role of weakly relativistic effects. Development of a new iterative technique, in the limit when the probing wave frequency is much higher than the electron cyclotron frequency, yields the dispersion relation to lowest (linear) order in Te/mec2≪1. Perturbative treatment of the wave phase and polarization is presented in a form suitable for interpretation of experimental data. Previous analysis of the problem included nonrelativistic calculations only. Herein, it is shown that relativistic effects are equally important. Theoretical results are in agreement with computations and can be used for benchmarking of ray tracing codes. The implication of finite temperature effects on future burning plasma interferometer diagnostics is discussed.
Spin Transport in the XXZ Chain at Finite Temperature and Momentum
NASA Astrophysics Data System (ADS)
Brenig, Wolfram; Steinigeweg, Robin
2012-02-01
We investigate the role of momentum for the transport of magnetization in the spin-1/2 Heisenberg chain above the isotropic point at finite temperature and momentum [1]. Using numerical and analytical approaches, we analyze the autocorrelations of density and current and observe a finite region of the Brillouin zone with diffusive dynamics below a cut-off momentum, and a diffusion constant independent of momentum and time, which scales inversely with anisotropy. Lowering the temperature over a wide range, starting from infinity, the diffusion constant is found to increase strongly while the cut-off momentum for diffusion decreases. Above the cut-off momentum diffusion breaks down completely.[4pt] [1] Robin Steinigeweg and Wolfram Brenig, arXiv:1107.3103
Niu, Y. F.; Paar, N.; Vretenar, D.; Meng, J.
2011-04-15
We introduce a self-consistent microscopic theoretical framework for modeling the process of electron capture on nuclei in stellar environment, based on relativistic energy density functionals. The finite-temperature relativistic mean-field model is used to calculate the single-nucleon basis and the occupation factors in a target nucleus, and J{sup {pi}}=0{sup {+-}}, 1{sup {+-}}, and 2{sup {+-}} charge-exchange transitions are described by the self-consistent finite-temperature relativistic random-phase approximation. Cross sections and rates are calculated for electron capture on {sup 54,56}Fe and {sup 76,78}Ge in stellar environment, and results compared with predictions of similar and complementary model calculations.
Finite temperature dynamics of spin-1/2 chains with symmetry breaking interactions
NASA Astrophysics Data System (ADS)
Manmana, Salvatore R.; Tiegel, Alexander C.; Pruschke, Thomas; Honecker, Andreas
I will discuss recent developments for flexible matrix product state (MPS) approaches to calculate finite-temperature spectral functions of low-dimensional strongly correlated quantum systems. The main focus will be on a Liouvillian formulation. The resulting algorithm does not specifically depend on the MPS formulation, but is applicable for any wave function based approach which can provide a purification of the density matrix, opening the way for further developments of numerical methods. Based on MPS results for various spin chains, in particular systems with Dzyaloshinskii-Moriya interactions caused by spin-orbit coupling and dimerized chains, I will discuss how symmetry breaking interactions change the nature of the finite-temperature dynamic spin structure factor obtained in ESR and neutron scattering experiments. We acknowledge funding by the Helmholtz Virtual Institute ``New States of Matter and Their Excitations''.
Quantum dynamics at finite temperature: Time-dependent quantum Monte Carlo study
NASA Astrophysics Data System (ADS)
Christov, Ivan P.
2016-08-01
In this work we investigate the ground state and the dissipative quantum dynamics of interacting charged particles in an external potential at finite temperature. The recently devised time-dependent quantum Monte Carlo (TDQMC) method allows a self-consistent treatment of the system of particles together with bath oscillators first for imaginary-time propagation of Schrödinger type of equations where both the system and the bath converge to their finite temperature ground state, and next for real time calculation where the dissipative dynamics is demonstrated. In that context the application of TDQMC appears as promising alternative to the path-integral related techniques where the real time propagation can be a challenge.
Finite element nonlinear flutter and fatigue life of 2-D panels with temperature effects
NASA Technical Reports Server (NTRS)
Mei, Chuh; Xue, David Y.
1991-01-01
A frequency domain method for two-dimensional nonlinear panel flutter with thermal effects obtained from a consistent finite element formulation is presented. The von Karman nonlinear strain-displacement relation is used to account for large deflections, and the quasi-steady first-order piston theory is employed for aerodynamic loading. The finite element frequency domain results are compared with analytical time domain solutions. In a limit-cycle motion, the panel frequency and stress can be determined, thus fatigue life can be predicted. The influence of temperature and dynamic pressure on panel fatigue life is presented. An endurance dynamic pressure can be established at a given temperature from the present method.
Bicudo, P.
2010-08-01
We study the string tension as a function of temperature, fitting the SU(3) lattice QCD finite temperature free energy potentials computed by the Bielefeld group. We compare the string tension points with order parameter curves of ferromagnets, superconductors, or string models, all related to confinement. We also compare the SU(3) string tension with the one of SU(2) lattice QCD. With the curve providing the best fit to the finite temperature string tensions, the spontaneous magnetization curve, we then show how to include finite temperature, in the state of the art confining and chiral invariant quark models.
Wu, Wei; Luo, Da-Wei; Xu, Jing-Bo
2014-06-28
We investigate the phenomenon of double sudden transitions in geometric quantum correlations for a system consisting of a bare qubit and a qubit locally coupled to its finite-temperature heat environment with an Ohmic spectrum in the framework of stochastic description. Moreover, we explore the possibility of protecting the geometric discord between the two qubits and prolonging the time during which the geometric discord remains constant by applying Bang-Bang pulses.
Two-loop self-energy and multiple scattering at finite temperature
Kapusta, J. I.; Wong, S. M. H.
2001-08-15
One- and two-loop self-energies are worked out explicitly for a heavy scalar field interacting weakly with a light self-interacting scalar field at finite temperature. The ring or daisy diagrams and a set of necklace diagrams can be summed simultaneously. This simple model serves to illustrate the connection between multiloop self-energy diagrams and multiple scattering in a medium.
NASA Astrophysics Data System (ADS)
Guo, You-neng; Fang, Mao-fa; Wang, Guo-you; Zeng, Ke
2016-07-01
Distillability sudden death and sudden birth in a two-qutrit system locally subject to amplitude damping channel at a finite temperature have been studied in detail. By using the negativity and the realignment criterion, the results show that certain initially prepared free entangled states under amplitude damping channel at a finite temperature may become bound entangled or separable states in a finite time. Moreover, we have also demonstrated initially prepared bound entangled or separable states may also become distillable entangled states in a finite time.
Chen, Roland K; Chastagner, Matthew W; Dodde, Robert E; Shih, Albert J
2013-02-01
The temporal and spatial tissue temperature profile in electrosurgical vessel sealing was experimentally measured and modeled using finite element modeling (FEM). Vessel sealing procedures are often performed near the neurovascular bundle and may cause collateral neural thermal damage. Therefore, the heat generated during electrosurgical vessel sealing is of concern among surgeons. Tissue temperature in an in vivo porcine femoral artery sealed using a bipolar electrosurgical device was studied. Three FEM techniques were incorporated to model the tissue evaporation, water loss, and fusion by manipulating the specific heat, electrical conductivity, and electrical contact resistance, respectively. These three techniques enable the FEM to accurately predict the vessel sealing tissue temperature profile. The averaged discrepancy between the experimentally measured temperature and the FEM predicted temperature at three thermistor locations is less than 7%. The maximum error is 23.9%. Effects of the three FEM techniques are also quantified. PMID:23192471
Finite-temperature exchange-correlation theory for dense, partially ionized matter
Ritchie, A B
2006-12-21
The importance of exchange-correlation in dense, partially-ionized matter at elevated temperatures is demonstrated using ab initio theoretical methods. Good agreement with the Kohn-Sham exchange model, as extended to finite temperatures by Gupta and Rajagopal, is obtained for the Be Hugoniot at maximum compression. Exchange correlation is achieved by calculating the quantum average of the electron-electron interaction using the spectral solution of the time-dependent Schrodinger equation, which is a superposition of eigenfunctions. The quantum average of the electron-electron interaction has strong temporal fluctuations about a stationary time average. The eigenfunctions calculated in the temporally fluctuating potential are sensibly stationary.
Superradiant Raman scattering in an ultracold Bose gas at finite temperature
NASA Astrophysics Data System (ADS)
Uys, H.; Meystre, P.
2008-06-01
We study superradiant Raman scattering from an ultracold, but finite, temperature Bose gas in a harmonic trap. Numerical simulations indicate the existence of distinct time scales associated with the decoherence of the condensed versus thermal fractions, and the concomitant preferred scattering from atoms in low-lying trap states in the regime where superradiance takes place on a time scale comparable to an inverse trap frequency. As a consequence the scattered atoms experience a modest reduction in temperature as compared to the unscattered atoms.
NASA Astrophysics Data System (ADS)
Abbas, Ibrahim A.; Youssef, Hamdy M.
2012-07-01
In this article, a general finite element method (FEM) is proposed to analyze transient phenomena in a thermoelastic model in the context of the theory of generalized thermoelasticity with one relaxation time. The exact solution of the nonlinear model of the thermal shock problem of a generalized thermoelastic half-space of temperature-dependent materials exists only for very special and simple initial- and boundary problems. In view of calculating general problems, a numerical solution technique is to be used. For this reason, the FEM is chosen. The results for the temperature increment, the stress components, and the displacement component are illustrated graphically with some comparisons.
Finite-temperature charge transport in the one-dimensional Hubbard model
NASA Astrophysics Data System (ADS)
Jin, F.; Steinigeweg, R.; Heidrich-Meisner, F.; Michielsen, K.; De Raedt, H.
2015-11-01
We study the charge conductivity of the one-dimensional repulsive Hubbard model at finite temperature using the method of dynamical quantum typicality, focusing at half filling. This numerical approach allows us to obtain current autocorrelation functions from systems with as many as 18 sites, way beyond the range of standard exact diagonalization. Our data clearly suggest that the charge Drude weight vanishes with a power law as a function of system size. The low-frequency dependence of the conductivity is consistent with a finite dc value and thus with diffusion, despite large finite-size effects. Furthermore, we consider the mass-imbalanced Hubbard model for which the charge Drude weight decays exponentially with system size, as expected for a nonintegrable model. We analyze the conductivity and diffusion constant as a function of the mass imbalance and we observe that the conductivity of the lighter component decreases exponentially fast with the mass-imbalance ratio. While in the extreme limit of immobile heavy particles, the Falicov-Kimball model, there is an effective Anderson-localization mechanism leading to a vanishing conductivity of the lighter species, we resolve finite conductivities for an inverse mass ratio of η ≳0.25 .
Lattice QCD at finite temperature and density in the phase-quenched approximation.
Kogut, J. B.; Sinclair, D. K.; High Energy Physics; Univ Maryland
2008-06-01
QCD at a finite quark-number chemical potential {mu} has a complex fermion determinant, which precludes its study by standard lattice QCD simulations. We therefore simulate lattice QCD at finite {mu} in the phase-quenched approximation, replacing the fermion determinant with its magnitude. (The phase-quenched approximation can be considered as simulating at finite isospin chemical potential 2{mu} for N{sub f}/2 u-type and N{sub F}/2 d-type quark flavors.) These simulations are used to study the finite-temperature transition for small {mu}, where there is some evidence that the position (and possibly the nature) of this transition is unchanged by this approximation. We look for the expected critical endpoint for 3-flavor QCD. Here, it has been argued that the critical point at zero {mu} would become the critical endpoint at small {mu}, for quark masses just above the critical mass. Our simulations indicate that this does not happen, and there is no such critical endpoint for small {mu}. We discuss how we might adapt techniques used for imaginary {mu} to improve the signal/noise ratio and strengthen our conclusions, using results from relatively low statistics studies.
Lattice QCD at finite temperature and density in the phase-quenched approximation
Kogut, J. B.; Sinclair, D. K.
2008-06-01
QCD at a finite quark-number chemical potential {mu} has a complex fermion determinant, which precludes its study by standard lattice QCD simulations. We therefore simulate lattice QCD at finite {mu} in the phase-quenched approximation, replacing the fermion determinant with its magnitude. (The phase-quenched approximation can be considered as simulating at finite isospin chemical potential 2{mu} for N{sub f}/2 u-type and N{sub f}/2 d-type quark flavors.) These simulations are used to study the finite-temperature transition for small {mu}, where there is some evidence that the position (and possibly the nature) of this transition is unchanged by this approximation. We look for the expected critical endpoint for 3-flavor QCD. Here, it has been argued that the critical point at zero {mu} would become the critical endpoint at small {mu}, for quark masses just above the critical mass. Our simulations indicate that this does not happen, and there is no such critical endpoint for small {mu}. We discuss how we might adapt techniques used for imaginary {mu} to improve the signal/noise ratio and strengthen our conclusions, using results from relatively low statistics studies.
Unified treatment of subsaturation stellar matter at zero and finite temperature
NASA Astrophysics Data System (ADS)
Gulminelli, F.; Raduta, Ad. R.
2015-11-01
The standard variational derivation of stellar-matter structure in the Wigner-Seitz approximation is generalized to the finite-temperature situation where a wide distribution of different nuclear species can coexist in the same density and proton fraction condition, possibly out of β equilibrium. The same theoretical formalism is shown to describe on one side the single-nucleus approximation (SNA), currently used in most core-collapse supernova simulations and on the other side the nuclear statistical equilibrium (NSE) approach, routinely employed in r - and p -process explosive nucleosynthesis problems. In particular, we show that in-medium effects have to be accounted for in NSE to have a theoretical consistency between the zero-temperature and the finite-temperature modeling. The bulk part of these in-medium effects is analytically calculated in the local density approximation and shown to be different from a Van der Waals excluded-volume term. This unified formalism allows controlling quantitatively the deviations from the SNA in the different thermodynamic conditions, as well as having a NSE model which is reliable at any arbitrarily low value of the temperature, with potential applications for neutron-star cooling and accretion problems. We present different illustrative results with several mass models and effective interactions, showing the importance of accounting for the nuclear species distribution even at temperatures lower than 1 MeV.
Optical properties of water at high temperature
French, Martin; Redmer, Ronald
2011-04-15
We calculate optical properties of water along the principal Hugoniot curve from ambient conditions up to temperatures of 130 000 K with density functional theory (DFT) and the Kubo-Greenwood formula. The effect of the exchange correlation functional is examined by comparing the generalized gradient approximation with a hybrid functional that contains Fock exchange. We find noticeable but moderate differences between the respective results which decrease rapidly above 80 000 K. The reflectivity along the principal Hugoniot is calculated and a good qualitative but fair quantitative agreement with available experimental data is found. Our results are of general relevance for calculations of optical properties with DFT at zero and elevated temperature.
NASA Astrophysics Data System (ADS)
Wang, Zhiyuan; Ma, Bo-Qiang
2016-05-01
We propose a unified approach to study meson, nucleon and Δ -baryon properties at zero and finite temperatures in the context of hard-wall AdS/QCD model. We first combine some previous works dealing with mesons and baryons separately, and introduce a new parameter ξ so that the model could give a universal description of spectrum and couplings of both sectors in a self-consistent way. All observables calculated numerically show reasonable agreement with experimental data. We then study these observables at nonzero temperature by modifying the AdS space-time into AdS-Schwartzchild space-time. Numerically solving the model, we find an interesting temperature dependence of the spectrum and the couplings. We also make a prediction on the finite-temperature decay width of some nucleon and Δ excited states.
U(1) slave-particle study of the finite-temperature doped Hubbard model in one and two dimensions
Ribeiro, P.; Sacramento, P.D.; Araujo, M.A.N.
2011-05-15
Research Highlights: > Mean-field U(1) slave-particle description of Hubbard model. > Fractionalized phases at finite-temperature in Hubbard model. > Spectral function of 1d and 2d Hubbard model. - Abstract: One-dimensional systems have unusual properties such as fractionalization of degrees of freedom. The occurrence of similar phenomena in higher dimensional systems has been considered in the literature for the description of quantum spin liquids and some non-fermi liquid phases. In this work we construct a mean field (MF) theory of the Hubbard model which is based on a representation of the electronic fields that explicitly introduces a separation of the charge and spin degrees of freedom (the so-called Zou-Anderson transformation) and study the finite-temperature phase diagram for the Hubbard chain and square lattice. The mean field variables are defined along the links of the underlying lattice. We obtain the spectral function and identify the regions of higher spectral weight with the fractionalized fermionic (spin) and bosonic (charge) excitations.
Lach, Joanna; Goclon, Jakub; Rodziewicz, Pawel
2016-04-01
Sulfur mustard (SM) is one of the most dangerous chemical compounds used against humans, mostly at war conditions but also in terrorist attacks. Even though the sulfur mustard has been synthesized over a hundred years ago, some of its molecular properties are not yet resolved. We investigate the structural flexibility of the SM molecule in the gas phase by Car-Parrinello molecular dynamics simulations. Thorough conformation analysis of 81 different SM configurations using density functional theory is performed to analyze the behavior of the system at finite temperature. The conformational diversity is analyzed with respect to the formation of intramolecular blue-shifting CH⋯S and CH⋯Cl hydrogen bonds. Molecular dynamics simulations indicate that all structural rearrangements between SM local minima are realized either in direct or non-direct way, including the intermediate structure in the last case. We study the lifetime of the SM conformers and perform the population analysis. Additionally, we provide the anharmonic dynamical finite temperature IR spectrum from the Fourier Transform of the dipole moment autocorrelation function to mimic the missing experimental IR spectrum. PMID:26774981
Temperature of a small quantum system as an internal property
NASA Astrophysics Data System (ADS)
Wang, Jiaozi; Wang, Wenge
Equilibration of small quantum systems is a topic of current interest both theoretically and experimentally. In this work, we study the extent to which a temperature can be assigned to a small quantum (chaotic) system as an internal property, but not as a property of any large environment. Specifically, we study a total system, which is composed of an Ising chain in a nonhomogeneous transverse field and an additional spin coupled to one of the spins in the chain. The additional spin can be used as a probe to detect local temperature of the chain. The total system lies in a pure state under unitary evolution and initial state of the chain is prepared in a typical state within an energy shell. Our numerical simulations show that the reduced density matrix of the probe spin approaches canonical states with similar temperatures at different locations of the chain beyond a relaxation time, and the results are close to the theoretical prediction given by the statistical mechanics in the thermodynamic limit, namely β =∂lnρ/(E) ∂E with ρ (E) being the density of states. We also study effects due to finite size of the chain, including the dependence on initial state of the probe and difference of numerically-obtain temperature from theoretical results.
NASA Astrophysics Data System (ADS)
Zhou, Li-Juan; Zheng, Bo; Zhong, Hong-Wei; Ma, Wei-Xing
2015-03-01
Based on the Dyson-Schwinger Equations (DSEs), the two-quark vacuum condensate, the four-quark vacuum condensate, and the quark gluon mixed vacuum condensate in the non-perturbative QCD vacuum state are investigated by solving the DSEs with rainbow truncation at zero- and finite- temperature, respectively. These condensates are important input parameters in QCD sum rule with zero and finite temperature, and in studying hadron physics, as well as predicting the quark mean squared momentum m20- also called quark virtuality in the QCD vacuum state. The present calculated results show that these physical quantities are almost independent of the temperature below the critical point temperature Tc = 131 MeV, and above Tc the chiral symmetry is restored. For comparison we calculate the temperature dependence of the “in-hadron condensate” for pion. At the same time, we also calculate the ratio of the quark gluon mixed vacuum condensate to the two-quark vacuum condensate by using these condensates, and the unknown quark mean squared momentum in the QCD vacuum state has been obtained. The results show that the ratio m20(T) is almost flat in the temperature region from 0 to Tc, although there are drastic changes of the quark vacuum condensate and the quark gluon mixed vacuum condensate at the region. Our predicted ratio comes out to be m20(T)=2.41 GeV2 at the Chiral limit, which is consistent with other theory model predictions, and strongly indicates the significance that the quark gluon mixed vacuum condensate has played in the virtuality calculations. Supported by National Natural Science Foundation of China (11365002), Guangxi Natural Science Foundation for Young Researchers (2013GXNSFBB053007, 2011GXNSFA018140), Guangxi Education Department (2013ZD049), Guangxi Grant for Excellent Researchers (2011-54), and Guangxi University of Science and Technology Foundation for PhDs (11Z16)
NASA Astrophysics Data System (ADS)
Garbrecht, Björn; Glowna, Frank; Herranen, Matti
2013-04-01
The production and decay rate of massive sterile neutrinos at finite temperature receives next-to-leading order corrections from the gauge interactions of lepton and Higgs doublets. Using the Closed-Time-Path approach, we demonstrate that the perturbatively obtained inclusive rate is finite. For this purpose, we show that soft, collinear and Bose divergences cancel when adding the tree-level rates from 1 ↔ 3 and 2 ↔ 2 processes to vertex and wave-function corrections to 1 ↔ 2 processes. These results hold for a general momentum of the sterile neutrino with respect to the plasma frame. Moreover, they do not rely on non-relativistic approximations, such that the full quantum-statistical effects are accounted for to the given order in perturbation theory. While the neutrino production rate is of relevance for Leptogenesis, the proposed methods may as well be suitable for application to a more general class of relativistic transport phenomena.
Finite-size effects and percolation properties of Poisson geometries.
Larmier, C; Dumonteil, E; Malvagi, F; Mazzolo, A; Zoia, A
2016-07-01
Random tessellations of the space represent a class of prototype models of heterogeneous media, which are central in several applications in physics, engineering, and life sciences. In this work, we investigate the statistical properties of d-dimensional isotropic Poisson geometries by resorting to Monte Carlo simulation, with special emphasis on the case d=3. We first analyze the behavior of the key features of these stochastic geometries as a function of the dimension d and the linear size L of the domain. Then, we consider the case of Poisson binary mixtures, where the polyhedra are assigned two labels with complementary probabilities. For this latter class of random geometries, we numerically characterize the percolation threshold, the strength of the percolating cluster, and the average cluster size. PMID:27575099
Finite-size effects and percolation properties of Poisson geometries
NASA Astrophysics Data System (ADS)
Larmier, C.; Dumonteil, E.; Malvagi, F.; Mazzolo, A.; Zoia, A.
2016-07-01
Random tessellations of the space represent a class of prototype models of heterogeneous media, which are central in several applications in physics, engineering, and life sciences. In this work, we investigate the statistical properties of d -dimensional isotropic Poisson geometries by resorting to Monte Carlo simulation, with special emphasis on the case d =3 . We first analyze the behavior of the key features of these stochastic geometries as a function of the dimension d and the linear size L of the domain. Then, we consider the case of Poisson binary mixtures, where the polyhedra are assigned two labels with complementary probabilities. For this latter class of random geometries, we numerically characterize the percolation threshold, the strength of the percolating cluster, and the average cluster size.
Entanglement and topological entropy of the toric code at finite temperature
NASA Astrophysics Data System (ADS)
Castelnovo, Claudio; Chamon, Claudio
2007-11-01
We calculate exactly the von Neumann and topological entropies of the toric code as a function of system size and temperature. We do so for systems with infinite energy scale separation between magnetic and electric excitations, so that the magnetic closed loop structure is fully preserved while the electric loop structure is tampered with by thermally excited electric charges. We find that the entanglement entropy is a singular function of temperature and system size, and that the limit of zero temperature and the limit of infinite system size do not commute. The two orders of limit differ by a term that does not depend on the size of the boundary between the partitions of the system, but instead depends on the topology of the bipartition. From the entanglement entropy we obtain the topological entropy, which is shown to drop to half its zero-temperature value for any infinitesimal temperature in the thermodynamic limit, and remains constant as the temperature is further increased. Such discontinuous behavior is replaced by a smooth decreasing function in finite-size systems. If the separation of energy scales in the system is large but finite, we argue that our results hold at small enough temperature and finite system size, and a second drop in the topological entropy should occur as the temperature is raised so as to disrupt the magnetic loop structure by allowing the appearance of free magnetic charges. We discuss the scaling of these entropies as a function of system size, and how the quantum topological entropy is shaved off in this two-step process as a function of temperature and system size. We interpret our results as an indication that the underlying magnetic and electric closed loop structures contribute equally to the topological entropy (and therefore to the topological order) in the system. Since each loop structure per se is a classical object, we interpret the quantum topological order in our system as arising from the ability of the two
Pairing within the self-consistent quasiparticle random-phase approximation at finite temperature
Dang, N. Dinh; Hung, N. Quang
2008-06-15
An approach to pairing in finite nuclei at nonzero temperature is proposed, which incorporates the effects due to the quasiparticle-number fluctuation (QNF) around Bardeen-Cooper-Schrieffer (BCS) mean field and dynamic coupling to quasiparticle-pair vibrations within the self-consistent quasiparticle random-phase approximation (SCQRPA). The numerical calculations of pairing gap, total energy, and heat capacity were carried out within a doubly folded multilevel model as well as realistic nuclei {sup 56}Fe and {sup 120}Sn. The results obtained show that, under the effect of QNF, in the region of moderate and strong couplings, the sharp transition between the superconducting and normal phases is smoothed out, resulting in a thermal pairing gap, which does not collapse at the BCS critical temperature, but has a tail, which extends to high temperature. The dynamic coupling of quasiparticles to SCQRPA vibrations significantly improves the agreement with the results of exact calculations and those obtained within the finite-temperature quantal Monte Carlo method for the total energy and heat capacity. It also causes a deviation of the quasiparticle occupation numbers from the Fermi-Dirac distributions for free fermions.
Finite temperature bosonic charge and current densities in compactified cosmic string spacetime
NASA Astrophysics Data System (ADS)
Mohammadi, A.; Bezerra de Mello, E. R.
2016-06-01
In this paper, we study the expectation values of the induced charge and current densities for a massive bosonic field with nonzero chemical potential in the geometry of a higher-dimensional compactified cosmic string with magnetic fluxes along the string core and also enclosed by the compactified direction in thermal equilibrium at finite temperature T . These densities are calculated by decomposing them into the vacuum expectation values and finite temperature contributions coming from the particles and antiparticles. The only nonzero components correspond to the charge, azimuthal, and axial current densities. By using the Abel-Plana formula, we decompose the components of the densities into the part induced by the cosmic string and the one by the compactification. The charge density is an odd function of the chemical potential and even periodic function of the magnetic flux with a period equal to the quantum flux. Moreover, the azimuthal (axial) current density is an even function of the chemical potential and an odd (even) periodic function of the magnetic flux with the same period. In this paper, our main concern is the thermal effect on the charge and current densities, including some limiting cases, the low- and high-temperature approximations. We show that in all cases, the temperature enhances the induced densities.
Y-stringlike behavior of a static baryon at finite temperature
NASA Astrophysics Data System (ADS)
Bakry, Ahmed S.; Chen, Xurong; Zhang, Peng-Ming
2015-06-01
We look into the signatures of the effective Y-bosonic strings in the gluonic profile due to a system of three static quarks on the lattice. The color field is calculated in pure SU(3) Yang-Mills lattice gauge theory at finite temperature with Polyakov loop operators. The analysis of the action density unveils a filled-Δ distribution. However, we found that these Δ -shaped action density profiles are structured from three Y-shaped Gaussian-like flux tubes. The geometry of the Y-shaped Gaussian flux tubes changes according to the quark configuration and temperature. The lattice data for the mean-square width of the gluonic action density have been compared to the corresponding width calculated based on the string model at finite temperature. We assume Y-string configuration with minimal length. The growth pattern of the action density of the gluonic field fits to junction fluctuations of the Y-baryonic string model for large quark separation at the considered temperatures.
Real-time finite-temperature correlators from AdS/CFT
NASA Astrophysics Data System (ADS)
Barnes, Edwin; Vaman, Diana; Wu, Chaolun; Arnold, Peter
2010-07-01
In this paper we use anti-de Sitter/conformal field theory correspondence ideas in conjunction with insights from finite-temperature real-time field theory formalism to compute 3-point correlators of N=4 super Yang-Mills operators, in real time and at finite temperature. To this end, we propose that the gravity field action is integrated only over the right and left quadrants of the Penrose diagram of the anti-de Sitter-Schwarzschild background, with a relative sign between the two terms. For concreteness we consider the case of a scalar field in the black hole background. Using the scalar field Schwinger-Keldysh bulk-to-boundary propagators, we give the general expression of a 3-point real-time Green’s correlator. We then note that this particular prescription amounts to adapting the finite-temperature analog of Veltman’s circling rules to tree-level Witten diagrams, and comment on the retarded and Feynman scalar bulk-to-boundary propagators. We subject our prescription to several checks: Kubo-Martin-Schwinger identities, the largest time equation, and the zero-temperature limit. When specializing to a particular retarded (causal) 3-point function, we find a very simple answer: the momentum-space correlator is given by three causal (two advanced and one retarded) bulk-to-boundary propagators, meeting at a vertex point which is integrated from spatial infinity to the horizon only. This result is expected based on analyticity, since the retarded n-point functions are obtained by analytic continuation from the imaginary-time Green’s function, and based on causality considerations.
NASA Astrophysics Data System (ADS)
Arahata, Emiko; Nikuni, Tetsuro
2008-03-01
We study damping of the dipole oscillation in a Bose-condensed gas in a combined cigar-shaped harmonic trap and one-dimensional (1D) optical lattice potential at finite temperatures. In order to include the effect of thermal excitations in the radial direction, we derive a quasi-1D model of the Gross-Pitaevskii equation and the Bogoliubov equations. We use the Popov approximation to calculate the temperature dependence of the condensate fraction with varying lattice depth. We then calculate the Landau damping rate of the dipole oscillation as a function of the lattice depth and temperature. The damping rate increases with increasing lattice depth, which is consistent with experimental observations. The magnitude of the damping rate is in reasonable agreement with experimental data. We also find that the damping rate has a strong temperature dependence, showing a sharp increase with increasing temperature. Finally, we emphasize the importance of the radial thermal excitations in both equilibrium properties and the Landau damping.
NASA Astrophysics Data System (ADS)
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Lee, Ting-Kuo; Mou, Chung-Yu
The energy gap in Dirac materials controls the topology and critical behaviors of the quantum phase transition associated with the critical point when the gap vanishes. However, it is often difficult to access the critical point as it requires tunablity of electronic structures. Here by exploiting the many-body screening interaction of localized spins and conduction electrons in a Kondo lattice, we demonstrate that the electronic band structures in a Kondo lattice are tunable in temperature. When spin-orbit interactions are included, we find that below the Kondo temperature, the Kondo lattice is a strong topological insulator at low temperature and undergoes a topological transition to a weak topological insulator at a higher temperature TD. At TD, Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our results indicate that the topological phase transition though a Dirac semi-metallic phase at finite temperatures also manifests profound physics and results in critical-like behavior both in magnetic and transport properties near TD. We acknowledge support from NCTS and Ministry of Science and Technology (MoST), Taiwan.
Properties of a finite fully spin-polarized free homogeneous one-dimensional electron gas
Ciftja, Orion
2015-01-15
The homogeneous electron gas model has been quite successful to predict the bulk properties of systems of electrons at various densities. In many occasions, a simplified free homogeneous electron gas model represents a powerful first approximation to a real system. Despite our considerable knowledge on the bulk properties of a homogeneous electron gas, advances in nanoscience and nanotechnology call for a greater effort to understand the opposite limit of small finite systems of electrons with size-dependent properties. In this work, we provide a detailed description of the properties of a finite fully spin-polarized (spinless) free homogeneous one-dimensional electron gas, the simplest of the free homogeneous electron gases. We derive exact analytical results for various quantities such as the one-particle density function, two-particle density function, one-particle density matrix, pair correlation function and energy of finite systems with an arbitrary number of electrons. The results obtained provide a detailed view on how various quantities corresponding to a finite system approach their bulk (thermodynamic limit) value.
Stability Properties of Underdominance in Finite Subdivided Populations
Altrock, Philipp M.; Traulsen, Arne; Reed, Floyd A.
2011-01-01
In isolated populations underdominance leads to bistable evolutionary dynamics: below a certain mutant allele frequency the wildtype succeeds. Above this point, the potentially underdominant mutant allele fixes. In subdivided populations with gene flow there can be stable states with coexistence of wildtypes and mutants: polymorphism can be maintained because of a migration-selection equilibrium, i.e., selection against rare recent immigrant alleles that tend to be heterozygous. We focus on the stochastic evolutionary dynamics of systems where demographic fluctuations in the coupled populations are the main source of internal noise. We discuss the influence of fitness, migration rate, and the relative sizes of two interacting populations on the mean extinction times of a group of potentially underdominant mutant alleles. We classify realistic initial conditions according to their impact on the stochastic extinction process. Even in small populations, where demographic fluctuations are large, stability properties predicted from deterministic dynamics show remarkable robustness. Fixation of the mutant allele becomes unlikely but the time to its extinction can be long. PMID:22072956
Finite Volume Dependence of Hadron Properties and Lattice QCD
Anthony W. Thomas; Jonathan D. Ashley; Derek B. Leinweber; Ross D. Young
2005-02-01
Because the time needed for a simulation in lattice QCD varies at a rate exceeding the fourth power of the lattice size, it is important to understand how small one can make a lattice without altering the physics beyond recognition. It is common to use a rule of thumb that the pion mass times the lattice size should be greater than (ideally much greater than) four (i.e., m{sub {pi}} L >> 4). By considering a relatively simple chiral quark model we are led to suggest that a more realistic constraint would be m{sub {pi}} (L - 2R) >> 4, where R is the radius of the confinement region, which for these purposes could be taken to be around 0.8-1.0 fm. Within the model we demonstrate that violating the second condition can lead to unphysical behavior of hadronic properties as a function of pion mass. In particular, the axial charge of the nucleon is found to decrease quite rapidly as the chiral limit is approached.
Zeta-function regularization approach to finite temperature effects in Kaluza-Klein space-times
Bytsenko, A.A. ); Vanzo, L.; Zerbini, S. )
1992-09-21
In the framework of heat-kernel approach to zeta-function regularization, in this paper the one-loop effective potential at finite temperature for scalar and spinor fields on Kaluza-Klein space-time of the form M[sup p] [times] M[sub c][sup n], where M[sup p] is p-dimensional Minkowski space-time is evaluated. In particular, when the compact manifold is M[sub c][sup n] = H[sup n]/[Gamma], the Selberg tracer formula associated with discrete torsion-free group [Gamma] of the n-dimensional Lobachevsky space H[sup n] is used. An explicit representation for the thermodynamic potential valid for arbitrary temperature is found. As a result a complete high temperature expansion is presented and the roles of zero modes and topological contributions is discussed.
Some exact results for a trapped quantum gas at finite temperature
Zyl, Brandon P. van; Bhaduri, Rajat K.; Suzuki, Akira; Brack, Matthias
2003-02-01
We present closed analytical expressions for the particle and kinetic-energy spatial densities at finite temperatures for a system of noninteracting fermions (bosons) trapped in a d-dimensional harmonic-oscillator potential. For d=2 and 3, exact expressions for the N-particle densities are used to calculate perturbatively the temperature dependence of the splittings of the energy levels in a given shell due to a very weak interparticle interaction in a dilute Fermi gas. In two dimensions, we obtain analytically the surprising result that the l degeneracy in a harmonic-oscillator shell is not lifted in the lowest order even when the exact, rather than the Thomas-Fermi expression for the particle density is used. We also demonstrate rigorously (in two dimensions) the reduction of the exact zero-temperature fermionic expressions to the Thomas-Fermi form in the large-N limit.
Finite-temperature Wigner solid and other phases of ripplonic polarons on a helium film
NASA Astrophysics Data System (ADS)
Klimin, Serghei N.; Tempere, Jacques; Misko, Vyacheslav R.; Wouters, Michiel
2016-07-01
Electrons on liquid helium can form different phases depending on density, and temperature. Also the electron-ripplon coupling strength influences the phase diagram, through the formation of so-called "ripplonic polarons", that change how electrons are localized, and that shifts the transition between the Wigner solid and the liquid phase. We use an all-coupling, finite-temperature variational method to study the formation of a ripplopolaron Wigner solid on a liquid helium film for different regimes of the electron-ripplon coupling strength. In addition to the three known phases of the ripplopolaron system (electron Wigner solid, polaron Wigner solid, and electron fluid), we define and identify a fourth distinct phase, the ripplopolaron liquid. We analyse the transitions between these four phases and calculate the corresponding phase diagrams. This reveals a reentrant melting of the electron solid as a function of temperature. The calculated regions of existence of the Wigner solid are in agreement with recent experimental data.
Singh, Rameswar; Brunner, S.; Ganesh, R.; Jenko, F.
2014-03-15
This paper presents effects of finite ballooning angles on linear ion temperature gradient (ITG) driven mode and associated heat and momentum flux in Gyrokinetic flux tube simulation GENE. It is found that zero ballooning angle is not always the one at which the linear growth rate is maximum. The ITG mode acquires a short wavelength (SW) branch (k{sub ⊥}ρ{sub i} > 1) when growth rates maximized over all ballooning angles are considered. However, the SW branch disappears on reducing temperature gradient showing characteristics of zero ballooning angle SWITG in case of extremely high temperature gradient. Associated heat flux is even with respect to ballooning angle and maximizes at nonzero ballooning angle while the parallel momentum flux is odd with respect to the ballooning angle.
Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice
NASA Astrophysics Data System (ADS)
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Mou, Chung-Yu; Lee, Ting-Kuo
2016-04-01
The underlying Dirac point is central to the profound physics manifested in a wide class of materials. However, it is often difficult to drive a system with Dirac points across the massless fermionic critical point. Here by exploiting screening of local moments under spin-orbit interactions in a Kondo lattice, we show that below the Kondo temperature, the Kondo lattice undergoes a topological transition from a strong topological insulator to a weak topological insulator at a finite temperature TD. At TD, massless Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis indicates that the emergent relativistic symmetry dictates nontrivial thermal responses over large parameter and temperature regimes. In particular, it yields critical scaling behaviors both in magnetic and transport responses near TD.
Emergence of a Fermionic Finite-Temperature Critical Point in a Kondo Lattice.
Chou, Po-Hao; Zhai, Liang-Jun; Chung, Chung-Hou; Mou, Chung-Yu; Lee, Ting-Kuo
2016-04-29
The underlying Dirac point is central to the profound physics manifested in a wide class of materials. However, it is often difficult to drive a system with Dirac points across the massless fermionic critical point. Here by exploiting screening of local moments under spin-orbit interactions in a Kondo lattice, we show that below the Kondo temperature, the Kondo lattice undergoes a topological transition from a strong topological insulator to a weak topological insulator at a finite temperature T_{D}. At T_{D}, massless Dirac points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis indicates that the emergent relativistic symmetry dictates nontrivial thermal responses over large parameter and temperature regimes. In particular, it yields critical scaling behaviors both in magnetic and transport responses near T_{D}. PMID:27176534
NASA Astrophysics Data System (ADS)
Czarnik, Piotr; Dziarmaga, Jacek; Oleś, Andrzej M.
2016-05-01
Progress in describing thermodynamic phase transitions in quantum systems is obtained by noticing that the Gibbs operator e-β H for a two-dimensional (2D) lattice system with a Hamiltonian H can be represented by a three-dimensional tensor network, the third dimension being the imaginary time (inverse temperature) β . Coarse graining the network along β results in a 2D projected entangled-pair operator (PEPO) with a finite bond dimension D . The coarse graining is performed by a tree tensor network of isometries. The isometries are optimized variationally, taking into account full tensor environment, to maximize the accuracy of the PEPO. The algorithm is applied to the isotropic quantum compass model on an infinite square lattice near a symmetry-breaking phase transition at finite temperature. From the linear susceptibility in the symmetric phase and the order parameter in the symmetry-broken phase, the critical temperature is estimated at Tc=0.0606 (4 ) J , where J is the isotropic coupling constant between S =1/2 pseudospins.
Magnetic susceptibility of QCD at zero and at finite temperature from the lattice
NASA Astrophysics Data System (ADS)
Bali, G. S.; Bruckmann, F.; Constantinou, M.; Costa, M.; Endrődi, G.; Katz, S. D.; Panagopoulos, H.; Schäfer, A.
2012-11-01
The response of the QCD vacuum to a constant external (electro)magnetic field is studied through the tensor polarization of the chiral condensate and the magnetic susceptibility at zero and at finite temperature. We determine these quantities using lattice configurations generated with the tree-level Symanzik improved gauge action and Nf=1+1+1 flavors of stout smeared staggered quarks with physical masses. We carry out the renormalization of the observables under study and perform the continuum limit both at T>0 and at T=0, using different lattice spacings. Finite size effects are studied by using various spatial lattice volumes. The magnetic susceptibilities χf reveal a spin-diamagnetic behavior; we obtain at zero temperature χu=-(2.08±0.08)GeV-2, χd=-(2.02±0.09)GeV-2 and χs=-(3.4±1.4)GeV-2 for the up, down and strange quarks, respectively, in the MS¯ scheme at a renormalization scale of 2 GeV. We also find the polarization to change smoothly with the temperature in the confinement phase and then to drastically reduce around the transition region.
Finite-temperature local protein sequence alignment: percolation and free-energy distribution.
Wolfsheimer, S; Melchert, O; Hartmann, A K
2009-12-01
Sequence alignment is a tool in bioinformatics that is used to find homological relationships in large molecular databases. It can be mapped on the physical model of directed polymers in random media. We consider the finite-temperature version of local sequence alignment for proteins and study the transition between the linear phase and the biologically relevant logarithmic phase, where the free energy grows linearly or logarithmically with the sequence length. By means of numerical simulations and finite-size-scaling analysis, we determine the phase diagram in the plane that is spanned by the gap costs and the temperature. We use the most frequently used parameter set for protein alignment. The critical exponents that describe the parameter-driven transition are found to be explicitly temperature dependent. Furthermore, we study the shape of the (free-) energy distribution close to the transition by rare-event simulations down to probabilities on the order 10(-64). It is well known that in the logarithmic region, the optimal score distribution (T=0) is described by a modified Gumbel distribution. We confirm that this also applies for the free-energy distribution (T>0). However, in the linear phase, the distribution crosses over to a modified Gaussian distribution. PMID:20365196
Magnetic field corrections to the repulsive Casimir effect at finite temperature
NASA Astrophysics Data System (ADS)
Erdas, Andrea
2016-02-01
I investigate the finite temperature Casimir effect for a charged and massless scalar field satisfying mixed (Dirichlet-Neumann) boundary conditions on a pair of plane parallel plates of infinite size. The effect of a uniform magnetic field, perpendicular to the plates, on the Helmholtz free energy and Casimir pressure is studied. The ζ-function regularization technique is used to obtain finite results. Simple analytic expressions are obtained for the zeta function and the free energy, in the limits of small plate distance, high temperature and strong magnetic field. The Casimir pressure is obtained in each of the three limits and the situation of a magnetic field present between and outside the plates, as well as that of a magnetic field present only between the plates is examined. It is discovered that, in the small plate distance and high temperature limits, the repulsive pressure is less when the magnetic field is present between the plates but not outside, than it is when the magnetic field is present between and outside the plates.
A holographic model for QCD in the Veneziano limit at finite temperature and density
NASA Astrophysics Data System (ADS)
Alho, T.; Järvinen, M.; Kajantie, K.; Kiritsis, E.; Rosen, C.; Tuominen, K.
2014-04-01
A holographic model of QCD in the limit of large number of colors, N c , and massless fermion flavors, N f , but constant ratio x f = N f /N c is analyzed at finite temperature and chemical potential. The five dimensional gravity model contains three bulk fields: a scalar dilaton sourcing Tr F 2, a scalar tachyon dual to and a 4-vector dual to the baryon current γ μ q. The main result is the μ, T phase diagram of the holographic theory. A first order deconfining transition along T h ( μ) and a chiral transition at T χ ( μ) > T h ( μ) are found. The chiral transition is of second order for small μ and becomes of first order at larger μ. The two regimes are separated by a tricritical point. The dependence of thermodynamical quantities including the speed of sound and susceptibilities on the chemical potential and temperature is computed. A new quantum critical regime is found at zero temperature and finite chemical potential. It is controlled by an AdS2 × R 3 geometry and displays semi-local criticality.
Calculation of the equation of state of QCD at finite chemical and zero temperature
Zong Hongshi; Sun Weimin
2008-09-01
In this paper, we give a direct method for calculating the partition function, and hence the equation of state (EOS) of quantum chromodynamics (QCD) at finite chemical potential and zero temperature. In the EOS derived in this paper the pressure density is the sum of two terms: the first term P({mu})|{sub {mu}}{sub =0} (the pressure density at {mu}=0) is a {mu}-independent constant; the second term, which is totally determined by G{sub R}[{mu}](p) (the renormalized dressed quark propagator at finite {mu}), contains all the nontrivial {mu}-dependence. By applying a general result in the rainbow-ladder approximation of the Dyson-Schwinger approach obtained in our previous study [Phys. Rev. C 71, 015205 (2005)], G{sub R}[{mu}](p) is calculated from the meromorphic quark propagator proposed in [Phys. Rev. D 70, 014014 (2004)]. From this the full analytic expression of the EOS of QCD at finite {mu} and zero T is obtained (apart from the constant term P({mu})|{sub {mu}}{sub =0} which can in principle be calculated from the Cornwall-Jackiw-Tomboulis effective action). A comparison between our EOS and the cold, perturbative EOS of QCD of Fraga, Pisarski, and Schaffner-Bielich is made. It is expected that our EOS can provide a possible new approach for the study of neutron stars.
A finite element thermal analysis procedure for several temperature-dependent parameters
NASA Technical Reports Server (NTRS)
Thornton, E. A.; Wieting, A. R.
1978-01-01
A finite-element thermal analysis procedure for elements with several temperature-dependent thermal parameters is presented. The procedure, based on an application of the Newton-Raphson iteration technique, is formulated by resolving element matrices into component matrices, one component for each thermal parameter. Component conductance matrices are evaluated by assuming constant thermal parameters within an element and are computed once per unit thermal parameter. Significant savings in computer time result from the unit thermal parameter concept. The solution procedure applied to a convectively cooled structure with significantly varying thermal parameters converged in four iterations.
The equation of state at finite temperature: Structure and composition of protoneutron stars
NASA Astrophysics Data System (ADS)
Burgio, G. F.; Baldo, M.; Chen, H.; Schulze, H.-J.
2016-01-01
We study the hadron-quark phase transition at finite temperature in the interior of protoneutron stars, combining the equation of state obtained within the Brueckner-Hartree-Fock approach for hadronic matter with the MIT bag and the Dyson-Schwinger models for quark matter. We discuss the dependence of the results on different nuclear three-body forces and on details of the quark model. We find that a maximum mass exceeding two solar masses can be obtained with a strong three-body force and suitable parameter values in the Dyson-Schwinger model.
Sound Modes of a Bose-Fermi Mixture Superfluid at Finite Temperatures
NASA Astrophysics Data System (ADS)
Ono, Yosuke; Sakamoto, Ryohei; Mori, Hiroyuki; Arahata, Emiko
2016-06-01
We study the sound modes of a Bose-Fermi mixture superfluid at finite temperatures in the collisional hydrodynamic regime. We extend Landau's hydrodynamic theory to deal with a Bose-Fermi mixture superfluid and show the existence of three sound modes. We calculate the hydrodynamic sound velocities numerically using the Nozières and Schmitt-Rink theory at unitarity. The three-sound-modes hybrid in Bose-Fermi mixture superfluids contrasts with the two sound modes exhibited by 3He and 4He superfluids.
NASA Astrophysics Data System (ADS)
Hu, Yao-Hua; Tong, Lei; Tan, Yong-Gang; Fang, Mao-Fa
2016-03-01
We demonstrate methods of enhancing robustness of entanglement of two-qubit systems undergoing generalized amplitude damping decoherence using weak measurement and measurement reversal. The results show that the local action of generalized amplitude damping noise can cause sudden death of entanglement, and the weak measurement and measurement reversal is useful for combating generalized amplitude damping decoherence and recovering the entanglement of two entangled qubits. In addition, the results indicate that it would be much more easily implemented by applying quantum measurement reversal on a single-qubit to enhance robustness of entanglement in finite temperature environment, than on both qubits.
Finite-temperature scaling at the quantum critical point of the Ising chain in a transverse field
NASA Astrophysics Data System (ADS)
Haelg, Manuel; Huvonen, Dan; Guidi, Tatiana; Quintero-Castro, Diana Lucia; Boehm, Martin; Regnault, Louis-Pierre; Zheludev, Andrey
2015-03-01
Inelastic neutron scattering is used to study the finite-temperature scaling behavior of spin correlations at the quantum critical point in an experimental realization of the one-dimensional Ising model in a transverse field. The target compound is the well-characterized, anisotropic and bond-alternating Heisenberg spin-1 chain material NTENP. The validity and the limitations of the dynamic structure factor scaling are tested, discussed and compared to theoretical predictions. For this purpose neutron data have been collected on the three-axes spectrometers IN14 at ILL and FLEXX at HZB as well as on the time of flight multi-chopper spectrometer LET at ISIS. In addition to the general statement about quantum criticality and universality, present study also reveals new insight into the properties of the spin chain compound NTENP in particular.
NASA Astrophysics Data System (ADS)
Madaras, E. I.; Kline, R. A.; Cruse, G.; Striz, A. G.
1991-07-01
In this work, the use of ultrasonic property measurements as the basis for finite element analysis of full scale composite components is presented. The approach utilizes multiple velocity measurements at oblique angles of incidence and quantitative analysis of radiographic images for the local determination of each of the nine orthotropic moduli in a woven carbon-carbon composite. These values were then used as input into a finite element code (NASTRAN) to analyze the response of the material to load: here, diametric compression. The predicted response was then compared with strain gage results at several locations to validate the approach.
NASA Technical Reports Server (NTRS)
Madaras, E. I.; Kline, R. A.; Cruse, G.; Striz, A. G.
1991-01-01
In this work, the use of ultrasonic property measurements as the basis for finite element analysis of full scale composite components is presented. The approach utilizes multiple velocity measurements at oblique angles of incidence and quantitative analysis of radiographic images for the local determination of each of the nine orthotropic moduli in a woven carbon-carbon composite. These values were then used as input into a finite element code (NASTRAN) to analyze the response of the material to load: here, diametric compression. The predicted response was then compared with strain gage results at several locations to validate the approach.
NASA Astrophysics Data System (ADS)
Uezu, Tatsuya
2011-04-01
In the problem of learning under external disturbance, there is a possibility that the existence of some tolerance or flexibility in the system weakens the effect of noise and helps the system to perform more efficiently. In a previous letter, we gave one example of such phenomena in learning from stochastic rules by spherical perceptrons adopting the Gibbs algorithm using statistical mechanical methods. By the replica method, we showed that, in the output noise model, there exists an optimal temperature at which the generalization error takes its minimum for the stable replica symmetric (RS) solution. On the other hand, for other types of noise including input noise, it was shown that no such temperature exists up to the one-step replica symmetry breaking (1RSB) solution. That is, it was shown that for the asymptotic region of a large number of training sets, the RS solution becomes unstable, and the asymptotic behavior is determined by the 1RSB solution, The asymptotic expressions for learning curves were derived, and it turned out that, within the 1RSB solution, the learning curve does not depend on temperature. In this study, we give a detailed derivation of these results and also the results obtained by simulated annealing and exchange Monte Carlo simulation. The numerical results support the theoretical predictions.
Temperature Dependent Electrical Properties of PZT Wafer
NASA Astrophysics Data System (ADS)
Basu, T.; Sen, S.; Seal, A.; Sen, A.
2016-04-01
The electrical and electromechanical properties of lead zirconate titanate (PZT) wafers were investigated and compared with PZT bulk. PZT wafers were prepared by tape casting technique. The transition temperature of both the PZT forms remained the same. The transition from an asymmetric to a symmetric shape was observed for PZT wafers at higher temperature. The piezoelectric coefficient (d 33) values obtained were 560 pc/N and 234 pc/N, and the electromechanical coupling coefficient (k p) values were 0.68 and 0.49 for bulk and wafer, respectively. The reduction in polarization after fatigue was only ~3% in case of PZT bulk and ~7% for PZT wafer.
NASA Astrophysics Data System (ADS)
Dai, Qingli; Ng, Kenny
2013-04-01
This paper presents the combined micromechanics analysis and finite element modeling of the electromechanical properties of piezoelectric structural fiber (PSF) composites. The active piezoelectric materials are widely used due to their high stiffness, voltage-dependent actuation capability, and broadband electro-mechanical interactions. However, the fragile nature of piezoceramics limits their sensing and actuating applications. In this study, the active PSF composites were made by deploying the longitudinally poled PSFs into a polymer matrix. The PSF itself consists a silicon carbide (SiC) or carbon core fiber as reinforcement to the fragile piezoceramic shell. To predict the electromechanical properties of PSF composites, the micromechanics analysis was firstly conducted with the dilute approximation model and the Mori-Tanaka approach. The extended Rule of Mixtures was also applied to accurately predict the transverse properties by considering the effects of microstructure including inclusion sizes and geometries. The piezoelectric finite element (FE) modeling was developed with the ABAQUS software to predict the detailed mechanical and electrical field distribution within a representative volume element (RVE) of PSF composites. The simulated energy or deformation under imposed specific boundary conditions was used to calculate each individual property with constitutive laws. The comparison between micromechanical analysis and finite element modeling indicates the combination of the dilute approximation model, the Mori-Tanaka approach and the extended Rule of Mixtures can favorably predict the electromechanical properties of three-phase PSF composites.
NASA Astrophysics Data System (ADS)
Imani Yengejeh, Sadegh; Kazemi, Seyedeh Alieh; Ivasenko, Oleksandr; Öchsner, Andreas
2016-04-01
Different types of degenerated nanostructures were simulated and their eigenfrequencies and corresponding eigenmodes were evaluated by applying the well-established finite element method. In addition, the structural and vibrational stability of these nanoparticles was examined under the influence of microscopic modifications. For this purpose, four common types of atomic defects (i.e. different types of vacancy defects, perturbation, pentagon-heptagon pair defect and chemical doping) were introduced to the finite element models and their vibrational properties were obtained and finally compared to those of perfect, i.e. defect-free, structures. The detailed geometry around a defected area was calculated based on density functional theory and implemented in the finite element model. Based on the results, it was shown that all these structural modifications changes the natural frequency and as a result, reduce the vibrational stability of degenerated nano-materials.
NASA Astrophysics Data System (ADS)
Caparica, A. A.; DaSilva, Cláudio J.
2015-12-01
In this work, we discuss the behavior of the microcanonical temperature {partial S(E)}/{partial E} obtained by means of numerical entropic sampling studies. It is observed that in almost all cases, the slope of the logarithm of the density of states S( E) is not infinite in the ground state, since as expected it should be directly related to the inverse temperature {1}/{T}. Here, we show that these finite slopes are in fact due to finite-size effects and we propose an analytic expression aln( bL) for the behavior of {\\varDelta S}/{\\varDelta E} when L→ ∞. To test this idea, we use three distinct two-dimensional square lattice models presenting second-order phase transitions. We calculated by exact means the parameters a and b for the two-states Ising model and for the q = 3 and 4 states Potts model and compared with the results obtained by entropic sampling simulations. We found an excellent agreement between exact and numerical values. We argue that this new set of parameters a and b represents an interesting novel issue of investigation in entropic sampling studies for different models.
Chiral phase transition in QED3 at finite temperature and impurity potential
NASA Astrophysics Data System (ADS)
Yin, Pei-Lin; Wei, Wei; Xiao, Hai-Xiao; Feng, Hong-Tao; Liu, Xiao-Jun; Zong, Hong-Shi
2016-01-01
In a realistic interacting system described by (2 +1 )-dimensional quantum electrodynamics (QED3 ), there is always a certain number of impurities by which fermions are scattered. In general, impurity scattering can generate a finite density of states at the Fermi level, which screens the temporal component of the gauge field. This effect is expected to weaken dynamical fermion mass generation. Within the Born approximation, by introducing a damping term in the energy component of the fermion propagator, the influences of finite temperature and impurity scattering on the chiral phase transition in QED3 are investigated. Pursuing this aim, we solve the Dyson-Schwinger equations for the fermion and boson propagators to the leading order in 1 /Nf expansion at zero frequency and then calculate the chiral condensate, the chiral susceptibility, and the thermal susceptibility within a range of the impurity scattering rates Γ and the numbers of fermion flavors Nf. It is found that impurity scattering leads to an obvious suppression of the dynamical fermion mass generation and critical temperature Tc.
Gluon scattering in N = 4 Super Yang-Mills at finite temperature
Ito, Katsushi; Iwasaki, Koh; Nastase, Horatiu
2008-11-23
We extend the AdS/CFT prescription of Alday and Maldacena to finite temperature T, defining an amplitude for gluon scattering in N = 4 Super Yang-Mills at strong coupling from string theory. It is defined by a lightlike 'Wilson loop' living at the horizon of the T-dual to the black hole in AdS space. Unlike the zero temperature case, this is different from the Wilson loop contour defined at the boundary of the AdS black hole metric, thus at nonzero T there is no relation between gluon scattering amplitudes and the Wilson loop. We calculate a gauge theory observable that can be interpreted as the amplitude at strong coupling in both cut-off and generalized dimensional regularization.
NASA Astrophysics Data System (ADS)
Jang, S.
1991-07-01
Within the framework of the quantum dynamical description of Brownian motion, a closed expression for the density operator is extracted from the master equation based on the dynamics of the second random phase approximation (RPA) at finite temperature. The second RPA theory is an extension of the usual RPA theory up to next higher order. The entropy and effective temperature of the system of collective RPA phonons are subsequently calculated by exploiting the analogy with the quantum optics damped oscillator, and their temporal behavior is surveyed by showing how these quantities relax to their equilibrium values. The calculation is carried out without invoking the so-called the resonant approximation, which amounts to ignoring the rapidly oscillating coupling terms. Particular attention is paid to the effect of these coupling terms.
The Casimir Effect at Finite Temperature in a Six-Dimensional Vortex Scenario
NASA Astrophysics Data System (ADS)
Cheng, Hongbo
2016-03-01
The Casimir effect for parallel plates satisfying the Dirichlet boundary condition in the context of effective QED coming from a six-dimensional Nielsen-Olesen vortex solution of the Abelian Higgs model with fermions coupled to gravity is studied at finite temperature. We find that the sign of the Casimir energy remains negative under the thermal influence. It is also shown that the Casimir force between plates will be weaker in the higher-temperature surroundings while keeps attractive. This Casimir effect involving the thermal influence is still inconsistent with the known experiments. We find that the thermal correction can not compensate or even reduce the modification from this kind of vortex model to make the Casimir force to be in less conflict with the measurements.
Bloch-Nordsieck thermometers: one-loop exponentiation in finite temperature QED
NASA Astrophysics Data System (ADS)
Gupta, Sourendu; Indumathi, D.; Mathews, Prakash; Ravindran, V.
1996-02-01
We study the scattering of hard external particles in a heat bath in a real-time formalism for finite temperature QED. We investigate the distribution of the 4-momentum difference of initial and final hard particles in a fully covariant manner when the scale of the process, Q, is much larger than the temperature, T. Our computations are valid for all T subject to this constraint. We exponentiate the leading infra-red term at one-loop order through a resummation of soft (thermal) photon emissions and absorptions. For T > 0, we find that tensor structures arise which are not present at T = 0. These cant' thermal signatures. As a result, external particles can serve as thermometers introduced into the heat bath. We investigate the phase space origin of log( Q/ m) and log ( Q/ T) teens.
Thermoelectric properties by high temperature annealing
NASA Technical Reports Server (NTRS)
Ren, Zhifeng (Inventor); Chen, Gang (Inventor); Kumar, Shankar (Inventor); Lee, Hohyun (Inventor)
2009-01-01
The present invention generally provides methods of improving thermoelectric properties of alloys by subjecting them to one or more high temperature annealing steps, performed at temperatures at which the alloys exhibit a mixed solid/liquid phase, followed by cooling steps. For example, in one aspect, such a method of the invention can include subjecting an alloy sample to a temperature that is sufficiently elevated to cause partial melting of at least some of the grains. The sample can then be cooled so as to solidify the melted grain portions such that each solidified grain portion exhibits an average chemical composition, characterized by a relative concentration of elements forming the alloy, that is different than that of the remainder of the grain.
Variational density matrices in quantum field theory at finite temperature and chemical potential
Nadeau, H.
1996-07-01
I evaluate the Helmholtz free energy of finite temperature {lambda}{var_phi}{sup 4} theory, both real and complex, using a variational quadratic {ital ansatz} for the density matrix. Minimizing with respect to the variational parameters produces results identical to those obtained by summing the daisy and superdaisy diagrams. In the nonrelativistic limit this is equivalent to a Hartree-Fock mean field with an effective mass. Quartic terms are then included by means of a relativistic generalization of the hypernetted-chain approximation without exchange terms, called the {open_quote}{open_quote}direct approximation.{close_quote}{close_quote} In this way infinite groups of rings and ladders are summed, giving nonperturbative expressions for the internal energy and four-point function in terms of a small number of Dyson-like integral equations. An expression is obtained for the internal energy of a zero-temperature system in terms of only two variational parameters. Because the hypernetted-chain approximation preserves the Euler-Lagrange variational principle, minimizing the internal energy with respect to these parameters should provide a semiquantitative upper bound on the ground state energy of an interacting relativistic system at zero temperature. For the full finite temperature theory in the direct approximation, there are now three variational parameters and it is necessary to obtain the entropy in a approximation comparable to that for the internal energy. This is done in an analogous manner to the separability approximation of nonrelativistic hypernetted-chain theory. Finally, an improvement on the direct approximation is attained by including exchange terms of all types. This proceeds along the lines of parquet summations, resulting in a set of integral equations that, when solved self-consistently, includes all series and parallel connections of direct and exchange diagrams. {copyright} {ital 1996 The American Physical Society.}
Evidence for a finite temperature phase transition in a bilayer quantum Hall system
NASA Astrophysics Data System (ADS)
Champagne, A. R.; Eisenstein, J. P.; Pfeiffer, L. N.; West, K. W.
2008-03-01
We study the Joshepson-like interlayer tunneling signature of the quantum Hall bilayer excitonic state at total filling factor νT= 1 as a function of the layer separation, interlayer charge imbalance and temperature. The tunneling amplitude collapses to zero as either the temperature or interlayer spacing is increased. The interlayer tunneling amplitude dependences on the layer spacing at various temperatures are very similar, but the layer separations where the tunneling disappears scale linearly with temperature. Our results offer evidence [1] that a finite temperature phase transition separates the interlayer coherent phase from incoherent phases which lack strong interlayer correlations. The phase boundary is found to be re-entrant as a function of charge imbalance thus suggesting an intricate competition between the interlayer coherent phase and various independent layer states. This work was supported by the NSF and the DOE. [1] A.R. Champagne, J.P. Eisenstein, L.N. Pfeiffer, K.W. West, Cond-mat/0709.0718
Finite-temperature quantum fluctuations in two-dimensional Fermi superfluids
NASA Astrophysics Data System (ADS)
Bighin, G.; Salasnich, L.
2016-01-01
In two-dimensional systems with a continuous symmetry, the Mermin-Wagner-Hohenberg theorem precludes spontaneous symmetry breaking and condensation at finite temperature. The Berezinskii-Kosterlitz-Thouless critical temperature marks the transition from a superfluid phase characterized by quasicondensation and algebraic long-range order, to a normal phase in which vortex proliferation completely destroys superfluidity. As opposed to conventional off-diagonal long-range order typical of three-dimensional superfluid systems, algebraic long-range order is driven by quantum and thermal fluctuations strongly enhanced in reduced dimensionality. Motivated by this unique scenario and by the very recent experimental realization of trapped quasi-two-dimensional fermionic clouds, we include one-loop Gaussian fluctuations in the theoretical description of resonant Fermi superfluids in two dimensions demonstrating that first sound, second sound, and also critical temperature are strongly renormalized, away from their mean-field values. In particular, we prove that in the intermediate- and strong-coupling regimes, these quantities are radically different when Gaussian fluctuations are taken into account. Our one-loop theory shows good agreement with very recent experimental data on the Berezinskii-Kosterlitz-Thouless critical temperature [Phys. Rev. Lett. 115, 010401 (2015)], 10.1103/PhysRevLett.115.010401 and on the first sound velocity, giving predictions for the second sound as a function of interaction strength and temperature that are open for experimental verification.
NASA Astrophysics Data System (ADS)
Kvíčala, M.; Frydrýšek, K.; Štamborská, M.
2015-03-01
This paper deals with the comparison of experimentally measured temperature gradients and finite-element-method (FEM) simulations of two heating strategies that were used for continuously cast bloom soaking. The temperature gradient between the bloom surface and center was measured by two thermocouples incorporated directly into the bloom. Scanning electron microscopy equipped by energy dispersive X-ray spectroscopy analysis, hot tensile tests, and interdendritic solidification software was used for modeling of steel thermophysical properties with respect to the alloying-elements macrosegregation. The model of the bloom was programmed in the Fortran language. The FEM software MARC/MENTAT 2012 was used for simulation of two heating strategies (plane strain formulation). The first heating model was fitted to the commonly used heating strategy when internal defects grew above the critical limit. The second heating model was a newly proposed strategy that consisted of slower heating up to 1073 K when the first warming-through period occurred. The FEM simulations included determinations of the temperature gradient, the equivalent of stress, the equivalent of elastic strain, the equivalent of plastic strain, and the equivalent of total strain. The simulation results were in good agreement with experimental observations. The new heating strategy based on the FEM simulations led to significantly lower occurrence of internal defects in hot-rolled billets that are used for cylinder production.
NASA Astrophysics Data System (ADS)
Deák, A.; Simon, E.; Balogh, L.; Szunyogh, L.; dos Santos Dias, M.; Staunton, J. B.
2014-06-01
We develop a self-consistent relativistic disordered local moment (RDLM) scheme aimed at describing finite-temperature magnetism of itinerant metals from first principles. Our implementation in terms of the Korringa-Kohn-Rostoker multiple-scattering theory and the coherent potential approximation allows us to relate the orientational distribution of the spins to the electronic structure, thus a self-consistent treatment of the distribution is possible. We present applications for bulk bcc Fe, L10-FePt, and FeRh ordered in the CsCl structure. The calculations for Fe show significant variation of the local moments with temperature, whereas according to the mean-field treatment of the spin fluctuations the Curie temperature is overestimated. The magnetic anisotropy of FePt alloys is found to depend strongly on intermixing between nominally Fe and Pt layers, and it shows a power-law behavior as a function of magnetization for a broad range of chemical disorder. In the case of FeRh we construct a lattice constant vs temperature phase diagram and determine the phase line of metamagnetic transitions based on self-consistent RDLM free-energy curves.
Finite-temperature electron correlations in the framework of a dynamic local-field correction
Schweng, H.K.; Boehm, H.M. )
1993-07-15
The quantum-mechanical version of the Singwi-Tosi-Land-Sjoelander (STLS) approximation is applied to finite temperatures. This approximation has two main advantages. First, it includes a dynamic local-field correction and second, it gives positive values for the pair-distribution function in the short-range region at zero temperature. This is even valid for rather low densities. After a description of the numerical difficulties arising with the use of a dynamic approximation, the results for the static-structure factor and the pair-distribution function are discussed thoroughly. Detailed work is performed on the static part of the local-field correction, with special emphasis put on the investigation of its structure. A peak is found at a wave vector [ital q][approx]2.8 (in units of the Fermi wave vector) for small temperatures, which tends towards higher values of [ital q] with increasing temperature. This peak causes an attractive particle-hole interaction in a certain [ital q] region and thus gives rise to the appearance of a charge-density wave. A parametric description is given for the static local-field correction in order to simplify further applications. Furthermore, the exchange-and-correlation free energy is considered. The results are compared with the STLS results and with the modified convolution approach.
NASA Astrophysics Data System (ADS)
Sadiek, Gehad; Almalki, Samaher
2016-07-01
We consider a finite one-dimensional Heisenberg XYZ spin chain under the influence of a dissipative Lindblad environment obeying the Born-Markovian constraint in presence of an external magnetic field with closed and open boundary conditions. We present an exact numerical solution for the Lindblad master equation of the system in the Liouville space. The dynamics and asymptotic behavior of the nearest-neighbor and beyond-nearest-neighbor pairwise entanglements in the system are investigated under the effect of spatial anisotropy, temperature, system size, and different initial states. The entanglements in the free spin system exhibit nonuniform oscillatory behavior that varies significantly depending on the system size, anisotropy, and initial state. The x y spatial anisotropy dictates the asymptotic behavior of the different entanglements in the system under the influence of the environment regardless of the initial state. Higher anisotropy yields higher steady-state value of the nearest-neighbor entanglement whereas a complete isotropy wipes it out. The longer range entanglements respond differently to the anisotropy variation. The anisotropy in the z direction may enhance the entanglements depending on the interplay with the magnetic field applied in the same direction. As the temperature is raised, the steady state of the short-range entanglements is found to be robust within very small nonzero temperature range that depends critically on the spatial anisotropy. Moreover, the end to end entanglement transfer time and speed through the open boundary chain vary considerably based on the degree of anisotropy and temperature of the environment.
Properties of finite difference models of non-linear conservative oscillators
NASA Technical Reports Server (NTRS)
Mickens, R. E.
1988-01-01
Finite-difference (FD) approaches to the numerical solution of the differential equations describing the motion of a nonlinear conservative oscillator are investigated analytically. A generalized formulation of the Duffing and modified Duffing equations is derived and analyzed using several FD techniques, and it is concluded that, although it is always possible to contstruct FD models of conservative oscillators which are themselves conservative, caution is required to avoid numerical solutions which do not accurately reflect the properties of the original equation.
NASA Technical Reports Server (NTRS)
Kim, H. Alicia; Hardie, Robert; Yamakov, Vesselin; Park, Cheol
2015-01-01
This paper is the second part of a two-part series where the first part presents a molecular dynamics model of a single Boron Nitride Nanotube (BNNT) and this paper scales up to multiple BNNTs in a polymer matrix. This paper presents finite element (FE) models to investigate the effective elastic and piezoelectric properties of (BNNT) nanocomposites. The nanocomposites studied in this paper are thin films of polymer matrix with aligned co-planar BNNTs. The FE modelling approach provides a computationally efficient way to gain an understanding of the material properties. We examine several FE models to identify the most suitable models and investigate the effective properties with respect to the BNNT volume fraction and the number of nanotube walls. The FE models are constructed to represent aligned and randomly distributed BNNTs in a matrix of resin using 2D and 3D hollow and 3D filled cylinders. The homogenisation approach is employed to determine the overall elastic and piezoelectric constants for a range of volume fractions. These models are compared with an analytical model based on Mori-Tanaka formulation suitable for finite length cylindrical inclusions. The model applies to primarily single-wall BNNTs but is also extended to multi-wall BNNTs, for which preliminary results will be presented. Results from the Part 1 of this series can help to establish a constitutive relationship for input into the finite element model to enable the modeling of multiple BNNTs in a polymer matrix.
NASA Astrophysics Data System (ADS)
Zhao, Bin
2015-02-01
Temperature-pressure coupled field analysis of liquefied petroleum gas (LPG) tank under jet fire can offer theoretical guidance for preventing the fire accidents of LPG tank, the application of super wavelet finite element on it is studied in depth. First, review of related researches on heat transfer analysis of LPG tank under fire and super wavelet are carried out. Second, basic theory of super wavelet transform is studied. Third, the temperature-pressure coupled model of gas phase and liquid LPG under jet fire is established based on the equation of state, the VOF model and the RNG k-ɛ model. Then the super wavelet finite element formulation is constructed using the super wavelet scale function as interpolating function. Finally, the simulation is carried out, and results show that the super wavelet finite element method has higher computing precision than wavelet finite element method.
Silicon photomultiplier properties at cryogenic temperatures
NASA Astrophysics Data System (ADS)
Biroth, M.; Achenbach, P.; Downie, E.; Thomas, A.
2015-07-01
The properties of different types of silicon photomultipliers (SiPMs) were studied at cryogenic temperatures. In liquid nitrogen at 77 K, problems with quenching in Hamamatsu SiPMs and with the protective epoxy layer, covering Zecotek SiPMs, were observed. Tests with one Zecotek SiPM were successful after removal of the epoxy layer. In liquid helium at 4 K, fast signals with pulse lengths shorter than 50 ns were observed, the dark count rate was below 10 Hz and no after-pulses were detected. The gain, as a function of over-voltage, was comparable to room temperature. The SiPM's response to photons was found to be linear with intensity for low light levels and single-photon detection was possible at 4 K.
Fuzzy Modal Finite Element Analysis of Structures with Imprecise Material Properties
NASA Astrophysics Data System (ADS)
Lallemand, B.; Cherki, A.; Tison, T.; Level, P.
1999-02-01
This paper extends the fuzzy set theory to a dynamic finite element analysis of engineering systems which have uncertainties in material properties. A general algorithm which resolves the uncertain eigenvalue problem by using a reanalysis approach is considered. This algorithm is applied to the study of the modal behaviour of structures presenting uncertain material properties. Some indexes which determine the more sensitive eigenvalue to several uncertainty sources are also put forward. Finally, a plate structure as numerical path-test is analysed. The results of such a calculation determine the sensitivity of the modal behaviour to multiple simultaneous material parameters.
On a strong dense periodicity property of shifts of finite type
Dzul-Kifli, Syahida Che; Al-Muttairi, Hassan
2015-10-22
There are various definitions of chaotic dynamical systems. The most utilized definition of chaos is Devaney chaos which isolates three components as being the essential features of chaos; transitivity, dense periodic points and sensitive dependence on initial conditions. In this paper, we focus on a strong dense periodicity property i.e. the set of points with prime period at least n is dense for each n. On shift of finite type over two symbols Σ{sub 2}, we show that the strong dense periodicity property implies another strong chaotic notions; locally everywhere onto (also called exact) and totally transitive.
NASA Astrophysics Data System (ADS)
Resapu, Rajeswara Reddy
The most common approaches to determining mechanical material properties of materials are tension and compression tests. However, tension and compression testing cannot be implemented under certain loading conditions (immovable object, not enough space to hold object for testing, etc). Similarly, tensile and compression testing cannot be performed on certain types of materials (delicate, bulk, non-machinable, those that cannot be separated from a larger structure, etc). For such cases, other material testing methods need to be implemented. Indentation testing is one such method; this approach is often non-destructive and can be used to characterize regions that are not compatible with other testing methods. However, indentation testing typically leads to force-displacement data as opposed to the direct stress-strain data normally used for the mechanical characterization of materials; this data needs to be analyzed using a suitable approach to determine the associated material properties. As such, methods to establish material properties from force-displacement indentation data need to be identified. In this work, a finite element approach using parameter optimization is developed to determine the mechanical properties from the experimental indentation data. Polymers and tissues tend to have time-dependent mechanical behavior; this means that their mechanical response under load changes with time. This dissertation seeks to characterize the properties of these materials using indentation testing under the assumption that they are linear viscoelastic. An example of a material of interest is the polymer poly vinyl chloride (PVC) that is used as the insulation of some aircraft wiring. Changes in the mechanical properties of this material over years of service can indicate degradation and a potential hazard to continued use. To investigate the validity of using indentation testing to monitor polymer insulation degradation, PVC film and PVC-insulated aircraft wiring are
Analysis of quarkonia at finite temperature from complex Borel sum rules
NASA Astrophysics Data System (ADS)
Araki, Ken-Ji; Suzuki, Kei; Guber, Phillip; Oka, Makoto
2014-09-01
Recently, we proposed a new type of QCD sum rules i.e. the complex Borel sum rules (CBSR). It has been found that the CBSR is superior to the conventional QCD sum rules from the point of view of the maximum entropy method (MEM) analysis. Specifically, we have demonstrated that our novel method can be used to study the excited states of hadrons. The suppression of quarkonium states (e.g. J/psi and upsilon) is an important signature of the hot matter produced in relativistic heavy-ion collisions at RHIC and LHC. Recently, the behavior of the excited states at finite temperature, which can be different from the ground state, has attracted much attention. The suppression of the charmonium and bottomonium ground states has already been analyzed by conventional QCD sum rules with MEM. In this talk, we report on the results of a reanalysis by CBSR with MEM to investigate the thermal behavior of the quarkonium excited states.
Approximation to the quantum planar rotor coupled to a finite temperature bath
NASA Astrophysics Data System (ADS)
López Vázquez, P. C.; García, A.
2016-05-01
An approximation to the description of the dynamics of a quantum planar rotor coupled to a finite temperature bath is derived by considering a microscopic model of interaction based on an angular momentum exchange with two different environments coupled independently to the positive and negative angular momentum spectrum. A non-Lindblad master equation is derived for this microscopic model by using the Born–Markov approximation in the weak coupling limit. We show that under this approximation the rotor dynamics presents the correct damping behavior of the motion and the thermal state reached by the rotor is in the form of Boltzmann distribution. The case of the quantum rotor in an external uniform field and the quantum kicked rotor are briefly discussed as exemplification.
Holographic geometry of cMERA for quantum quenches and finite temperature
NASA Astrophysics Data System (ADS)
Mollabashi, Ali; Naozaki, Masahiro; Ryu, Shinsei; Takayanagi, Tadashi
2014-03-01
We study the time evolution of cMERA (continuous MERA) under quantum quenches in free field theories. We calculate the corresponding holographic metric using the proposal in arXiv:1208.3469 and confirm that it qualitatively agrees with its gravity dual given by a half of the AdS black hole spacetime, argued by Hartman and Maldacena in arXiv:1303.1080. By doubling the cMERA for the quantum quench, we give an explicit construction of finite temperature cMERA. We also study cMERA in the presence of chemical potential and show that there is an enhancement of metric in the infrared region corresponding to the Fermi energy.
Induced fermionic current by a magnetic flux in a cosmic string spacetime at finite temperature
NASA Astrophysics Data System (ADS)
Bezerra de Mello, Eugênio R.; Saharian, Aram A.; Mohammadi, Azadeh
2016-01-01
Here we analyze the finite temperature expectation values of the charge and current densities for a massive fermionic quantum field with nonzero chemical potential μ, induced by a magnetic flux running along the axis of an idealized cosmic string. These densities are decomposed into the vacuum expectation values and contributions coming from the particles and antiparticles. Specifically the charge density is an even periodic function of the magnetic flux with the period equal to the quantum flux and an odd function of the chemical potential. The only nonzero component of the current density corresponds to the azimuthal current and it is an odd periodic function of the magnetic flux and an even function of the chemical potential. Both analyzed are developed for the cases where |μ| is smaller than the mass of the field quanta m.
Filion, Laura; Marechal, Matthieu; van Oorschot, Bas; Pelt, Daniël; Smallenburg, Frank; Dijkstra, Marjolein
2009-10-30
We present an efficient and robust method based on Monte Carlo simulations for predicting crystal structures at finite temperature. We apply this method, which is surprisingly easy to implement, to a variety of systems, demonstrating its effectiveness for hard, attractive, and anisotropic interactions, binary mixtures, semi-long-range soft interactions, and truly long-range interactions where the truly long-range interactions are treated using Ewald sums. In the case of binary hard-sphere mixtures, star polymers, and binary Lennard-Jones mixtures, the crystal structures predicted by this algorithm are consistent with literature, providing confidence in the method. Finally, we predict new crystal structures for hard asymmetric dumbbell particles, bowl-like particles and hard oblate cylinders and present the phase diagram for the oblate cylinders based on full free energy calculations. PMID:19905838
NASA Astrophysics Data System (ADS)
Albright, M.; Kapusta, J. I.
2016-01-01
We develop a flexible quasiparticle theory of transport coefficients of hot hadronic matter at finite baryon density. We begin with a hadronic quasiparticle model which includes a scalar and a vector mean field. Quasiparticle energies and the mean fields depend on temperature and baryon chemical potential. Starting with the quasiparticle dispersion relation, we derive the Boltzmann equation and use the Chapman-Enskog expansion to derive formulas for the shear and bulk viscosities and thermal conductivity. We obtain both relaxation-time approximation formulas and more general integral equations. Throughout the work, we explicitly enforce the Landau-Lifshitz conditions of fit and ensure the theory is thermodynamically self-consistent. The derived formulas should be useful for predicting the transport coefficients of the hadronic phase of matter produced in heavy-ion collisions at the Relativistic Heavy Ion Collider and at other accelerators.
Angle dependence of the switching field of recording media at finite temperatures
NASA Astrophysics Data System (ADS)
Saharan, L.; Morrison, C.; Miles, J. J.; Thomson, T.; Schrefl, T.; Hrkac, G.
2011-11-01
A combined micromagnetic and nudged elastic band method was used to investigate the utility of a one-grain model in describing the switching field of CoCrPt perpendicular recording media as a function of applied field angle at finite temperatures of 150 K, 292 K and 350 K. The effect of grain diameter, attempt frequency, and thermal activation on the switching field were investigated. The results of the simulations show good agreement with vector vibrating sample magnetometer measurements on well segregated, single layer CoCrPt-SiOx recording media and demonstrate that thermal activation modifies the Stoner-Wohlfarth angle dependency of the switching field by reducing the depth of the minimum that occurs at 45°.
Accurate force fields and methods for modelling organic molecular crystals at finite temperatures.
Nyman, Jonas; Pundyke, Orla Sheehan; Day, Graeme M
2016-06-21
We present an assessment of the performance of several force fields for modelling intermolecular interactions in organic molecular crystals using the X23 benchmark set. The performance of the force fields is compared to several popular dispersion corrected density functional methods. In addition, we present our implementation of lattice vibrational free energy calculations in the quasi-harmonic approximation, using several methods to account for phonon dispersion. This allows us to also benchmark the force fields' reproduction of finite temperature crystal structures. The results demonstrate that anisotropic atom-atom multipole-based force fields can be as accurate as several popular DFT-D methods, but have errors 2-3 times larger than the current best DFT-D methods. The largest error in the examined force fields is a systematic underestimation of the (absolute) lattice energy. PMID:27230942
Formation of Vortex Lattices in Superfluid Bose Gases at Finite Temperatures
NASA Astrophysics Data System (ADS)
Arahata, E.; Nikuni, T.
2016-05-01
We study the dynamics of a rotating trapped Bose-Einstein condensate (BEC) at finite temperatures. Using the Zaremba-Nikuni-Griffin formalism, based on a generalized Gross-Pitaevskii equation for the condensate coupled to a semiclassical kinetic equation for a thermal cloud, we numerically simulate vortex lattice formation in the presence of a time-dependent rotating trap potential. At low rotation frequency, the thermal cloud undergoes rigid body rotation, while the condensate exhibits irrotational flow. Above a certain threshold rotation frequency, vortices penetrate into the condensate and form a vortex lattice. Our simulation result clearly indicates a crucial role for the thermal cloud, which triggers vortex lattice formation in the rotating BEC.
Binary 3-D Markov Chain Random Fields: Finite-size Scaling Analysis of Percolation Properties
NASA Astrophysics Data System (ADS)
Harter, T.
2004-12-01
Percolation phenomena in random media have been extensively studied in a wide variety of fields in physics, chemistry, engineering, bio-, earth-, and environmental sciences. Most work has focused on uncorrelated random fields. The critical behavior in media with short-range correlations is thought to be identical to that in uncorrelated systems. However, the percolation threshold, pc, which is 0.3116 in uncorrelated media, has been observed to vary with the correlation scale and also with the random field type. Here, we present percolation properties and finite-size scaling effects in three-dimensional binary cubic lattices represented by correlated Markov-chain random fields and compare them to those in sequential Gaussian and sequential indicator random fields. We find that the computed percolation threshold in correlated random fields is significantly lower than in the uncorrelated lattice and decreases with increasing correlation scale. The rate of decrease rapidly flattens out for correlation lengths larger than 2-3 grid-blocks. At correlation scales of 5-6 grid blocks, pc is found to be 0.126 for the Markov chain random fields and slightly higher for sequential Gaussian and indicator random fields. The universal scaling constants for mean cluster size, backbone fraction, and connectivity are found to be consistent with results on uncorrelated lattices. For numerical studies, it is critical to understand finite-size effects on the percolation and associated phase connectivity properties of lattices. We present detailed statistical results on the percolation properties in finite sized lattice and their dependence on correlation scale. We show that appropriate grid resolution and choice of simulation boundaries is critical to properly simulate correlated natural geologic systems, which may display significant finite-size effects.
Finite element analysis and simulation of rheological properties of bulk molding compound (BMC)
NASA Astrophysics Data System (ADS)
Ergin, M. Fatih; Aydin, Ismail
2013-12-01
Bulk molding compound (BMC) is one of the important composite materials with various engineering applications. BMC is a thermoset plastic resin blend of various inert fillers, fiber reinforcements, catalysts, stabilizers and pigments that form a viscous, molding compound. Depending on the end-use application, bulk molding compounds are formulated to achieve close dimensional control, flame and scratch resistance, electrical insulation, corrosion and stain resistance, superior mechanical properties, low shrink and color stability. Its excellent flow characteristics, dielectric properties, and flame resistance make this thermoset material well-suited to a wide variety of applications requiring precision in detail and dimensions as well as high performance. When a BMC is used for these purposes, the rheological behavior and properties of the BMC is the main concern. In this paper, finite element analysis of rheological properties of bulk molding composite material was studied. For this purpose, standard samples of composite material were obtained by means of uniaxial hot pressing. 3 point flexural tests were then carried out by using a universal testing machine. Finite element analyses were then performed with defined material properties within a specific constitutive material behavior. Experimental and numerical results were then compared. Good correlation between the numerical simulation and the experimental results was obtained. It was expected with this study that effects of various process parameters and boundary conditions on the rheological behavior of bulk molding compounds could be determined by means of numerical analysis without detailed experimental work.
Motion of a single hole in a quantum antiferromagnet at finite temperatures
Igarashi, J. ); Fulde, P. )
1993-07-01
Motion of a single hole is studied at finite temperatures in the [ital t]-[ital J] model on a slave-fermion Schwinger-boson representation. The spin fluctuation is treated with the mean-field theory of Arovas and Auerbach. The Green's function for the slave fermion is calculated within the self-consistent Born approximation. A sharp quasiparticle peak is found to be separated from a broad spectrum of incoherence in the spectral function for low temperatures. The Green's function for the physical hole is calculated by taking account of the multiple scattering between the slave fermion and the Schwinger boson. A bound state of the slave fermion and the Schwinger boson is found at low temperatures, suggesting that the spin and the charge cannot be separated into a simple form. The energy of the bound state is minimized at momenta ([plus minus][pi]/2, [plus minus][pi]/2), indicating that a small pocketlike Fermi surface is formed around the momenta for low concentrations of dopant holes.
Dornheim, Tobias; Schoof, Tim; Groth, Simon; Filinov, Alexey; Bonitz, Michael
2015-11-28
The uniform electron gas (UEG) at finite temperature is of high current interest due to its key relevance for many applications including dense plasmas and laser excited solids. In particular, density functional theory heavily relies on accurate thermodynamic data for the UEG. Until recently, the only existing first-principle results had been obtained for N = 33 electrons with restricted path integral Monte Carlo (RPIMC), for low to moderate density, rs=r¯/aB≳1. These data have been complemented by configuration path integral Monte Carlo (CPIMC) simulations for rs ≤ 1 that substantially deviate from RPIMC towards smaller rs and low temperature. In this work, we present results from an independent third method-the recently developed permutation blocking path integral Monte Carlo (PB-PIMC) approach [T. Dornheim et al., New J. Phys. 17, 073017 (2015)] which we extend to the UEG. Interestingly, PB-PIMC allows us to perform simulations over the entire density range down to half the Fermi temperature (θ = kBT/EF = 0.5) and, therefore, to compare our results to both aforementioned methods. While we find excellent agreement with CPIMC, where results are available, we observe deviations from RPIMC that are beyond the statistical errors and increase with density. PMID:26627944
Finite-temperature excitations of a trapped Bose-Fermi mixture
Liu, Xia-Ji; Hu, Hui
2003-09-01
We present a detailed study of the low-lying collective excitations of a spherically trapped Bose-Fermi mixture at finite temperature in the collisionless regime. The excitation frequencies of the condensate are calculated self-consistently using the static Hartree-Fock-Bogoliubov theory within the Popov approximation. The frequency shifts and damping rates due to the coupled dynamics of the condensate, noncondensate, and degenerate Fermi gas are also taken into account by means of the random-phase approximation and linear-response theory. In our treatment, the dipole excitation remains close to the bare trapping frequency for all temperatures considered, and thus is consistent with the generalized Kohn theorem. We discuss in some detail the behavior of monopole and quadrupole excitations as a function of the Bose-Fermi coupling. At nonzero temperatures we find that, as the mixture moves towards spatial separation with increasing Bose-Fermi coupling, the damping rate of the monopole (quadrupole) excitation increases (decreases). This provides us a useful signature to identify the phase transition of spatial separation.
Unusual Finite-Temperature Phase Diagram for Semi-hard-core Bosons in Two Dimensions
NASA Astrophysics Data System (ADS)
Konev, V. V.; Panov, Yu. D.; Korolev, A. V.; Moskvin, A. S.
2016-04-01
The extended bosonic Hubbard model (EBHM) is a paradigmatic model for the highly topical field of ultracold gases in optical lattices. Using quantum Monte Carlo simulations, we have determined the finite-temperature phase diagram of the EBHM with truncation of the on-site Hilbert space to the three lowest occupation states: n = 0, 1, 2 (semi-hard-core boson Hubbard model) given nearest-neighbor repulsion, however, both positive and negative values of the on-site boson-boson coupling U. This model is equivalent to an anisotropic spin-1 XXZ model (n=S_z+1 ) in a magnetic field. In the limit of large negative U (the boson-boson attraction), the model turns into the well-known model of hard-core bosons whose rich phase diagram demonstrates several puzzling features, in particular, signatures of an unusual reentrant behavior with a charge ordering upon increasing the temperature. We have shown that the rise of the correlation parameter U to positive values (the boson-boson repulsion) expectedly leads to a lowering of the temperature of the superfluid transition and unexpectedly to the more and more pronounced "reentrance" effect.
Bawolin, Nahshon K; Dolovich, Allan T; Chen, Daniel X B; Zhang, Chris W J
2015-08-01
In tissue engineering, the cell and scaffold approach has shown promise as a treatment to regenerate diseased and/or damaged tissue. In this treatment, an artificial construct (scaffold) is seeded with cells, which organize and proliferate into new tissue. The scaffold itself biodegrades with time, leaving behind only newly formed tissue. The degradation qualities of the scaffold are critical during the treatment period, since the change in the mechanical properties of the scaffold with time can influence cell behavior. To observe in time the scaffold's mechanical properties, a straightforward method is to deform the scaffold and then characterize scaffold deflection accordingly. However, experimentally observing the scaffold deflection is challenging. This paper presents a novel study on characterization of mechanical properties of scaffolds by phase contrast imaging and finite element modeling, which specifically includes scaffold fabrication, scaffold imaging, image analysis, and finite elements (FEs) modeling of the scaffold mechanical properties. The innovation of the work rests on the use of in-line phase contrast X-ray imaging at 20 KeV to characterize tissue scaffold deformation caused by ultrasound radiation forces and the use of the Fourier transform to identify movement. Once deformation has been determined experimentally, it is then compared with the predictions given by the forward solution of a finite element model. A consideration of the number of separate loading conditions necessary to uniquely identify the material properties of transversely isotropic and fully orthotropic scaffolds is also presented, along with the use of an FE as a form of regularization. PMID:25902011
Corneal Viscoelastic Properties from Finite-Element Analysis of In Vivo Air-Puff Deformation
Kling, Sabine; Bekesi, Nandor; Dorronsoro, Carlos; Pascual, Daniel; Marcos, Susana
2014-01-01
Biomechanical properties are an excellent health marker of biological tissues, however they are challenging to be measured in-vivo. Non-invasive approaches to assess tissue biomechanics have been suggested, but there is a clear need for more accurate techniques for diagnosis, surgical guidance and treatment evaluation. Recently air-puff systems have been developed to study the dynamic tissue response, nevertheless the experimental geometrical observations lack from an analysis that addresses specifically the inherent dynamic properties. In this study a viscoelastic finite element model was built that predicts the experimental corneal deformation response to an air-puff for different conditions. A sensitivity analysis reveals significant contributions to corneal deformation of intraocular pressure and corneal thickness, besides corneal biomechanical properties. The results show the capability of dynamic imaging to reveal inherent biomechanical properties in vivo. Estimates of corneal biomechanical parameters will contribute to the basic understanding of corneal structure, shape and integrity and increase the predictability of corneal surgery. PMID:25121496
NASA Astrophysics Data System (ADS)
Isaenkova, M. G.; Perlovich, Yu A.; Krymskaya, O. A.; Zhuk, D. I.
2016-04-01
3D finite element model of indentation process with Berkovich tip was created. Using this model with different type of test materials, several series of calculations were made. These calculations lead to determination of material behavior features during indentation. Relations between material properties and its behavior during instrumented indentation were used for construction of dimensionless functions required for development the calculation algorithm, suitable to determine mechanical properties of materials by results of the depth-sensing indentation. Results of mechanical properties determination using elaborated algorithm for AISI 1020 steel grade were compared to properties obtained with standard compression tests. These two results differ by less than 10% for yield stress that evidence of a good accuracy of the proposed technique.
NASA Astrophysics Data System (ADS)
Barbadikar, Dipika R.; Ballal, A. R.; Peshwe, D. R.; Mathew, M. D.
2015-08-01
Ball indentation (BI) technique has been effectively used to evaluate the tensile properties with minimal volume of material. In the present investigation, BI test carried out on P92 steel (9Cr-0.5Mo-1.8W), using 0.76 mm diameter silicon nitride ball indenter was modeled using finite element (FE) method and analyzed. The effect of test temperature [300 K and 923 K (27 °C and 650 °C)], tempering temperature [1013 K, 1033 K, and 1053 K (740 °C, 760 °C, and 780 °C)], and coefficient of friction of steel (0.0 to 0.5) on the tensile strength and material pile-up was investigated. The stress and strain distributions underneath the indenter and along the top elements of the model have been studied to understand the deformation behavior. The tensile strength was found to decrease with increase in tempering and test temperatures. The increased pile-up around the indentation was attributed to the decrease in strain hardening exponent ( n) with increase in the test temperature. The pile-up height determined from profilometry studies and FE analysis as well as the load depth curve from BI and FE analysis was in agreement. The maximum strain location below the indentation changes with the test temperature. Stress-strain curves obtained by conventional tensile, BI test, and representative stress-strain concepts of FE model were found exactly matching.
NASA Astrophysics Data System (ADS)
Wang, Xiu-Xia
2016-02-01
By employing the generalized Hellmann-Feynman theorem, the quantization of mesoscopic complicated coupling circuit is proposed. The ensemble average energy, the energy fluctuation and the energy distribution are investigated at finite temperature. It is shown that the generalized Hellmann-Feynman theorem plays the key role in quantizing a mesoscopic complicated coupling circuit at finite temperature, and when the temperature is lower than the specific temperature, the value of (\\vartriangle {hat {H}})2 is almost zero and the values of
NASA Astrophysics Data System (ADS)
Suárez, Abril; Matos, Tonatiuh
2014-02-01
In this paper, the thermal evolution of scalar field dark matter (SFDM) particles at finite cosmological temperatures is studied. Starting with a real SF in a thermal bath and using the one-loop quantum corrections potential, we rewrite Klein-Gordon’s equation in its hydrodynamical representation and study the phase transition of this SF due to a Z2 symmetry breaking of its potential. A very general version of a nonlinear Schrödinger equation is obtained. When introducing Madelung’s representation, the continuity and momentum equations for a non-ideal SFDM fluid are formulated, and the cosmological scenario with the SFDM described in analogy to an imperfect fluid is then considered where dissipative contributions are obtained in a natural way. Additional terms appear in the results compared to those in the classical version commonly used to describe the ΛCDM model, i.e., the ideal fluid. The equations and parameters that characterize the physical properties of the system such as its energy, momentum and viscous flow are related to the temperature of the system, scale factor, Hubble’s expansion parameter and the matter energy density. Finally, some details on how galaxy halos and smaller structures might be able to form by condensation of this SF are given.
Finite-temperature Gutzwiller approximation and the phase diagram of a toy model for V2O3
NASA Astrophysics Data System (ADS)
Sandri, Matteo; Capone, Massimo; Fabrizio, Michele
2013-05-01
We exploit exact inequalities that refer to the entropy of a distribution to derive a simple variational principle at finite temperature for trial density matrices of Gutzwiller and Jastrow type. We use the result to extend at finite temperature the Gutzwiller approximation, which we apply to study a two-orbital model that we believe captures some essential features of V2O3. We indeed find that the phase diagram of the model bears many similarities to that of real vanadium sesquioxide. In addition, we show that in a Bethe lattice, where the finite-temperature Gutzwiller approximation provides a rigorous upper bound of the actual free energy, the results compare well with the exact phase diagram obtained by dynamical mean-field theory.
Application of finite element techniques in predicting the acoustic properties of turbofan inlets
NASA Technical Reports Server (NTRS)
Majjigi, R. K.; Sigman, R. K.; Zinn, B. T.
1978-01-01
An analytical technique was developed for predicting the acoustic performance of turbofan inlets carrying a subsonic axisymmetric steady flow. The finite element method combined with the method of weighted residuals is used in predicting the acoustic properties of variable area, annular ducts with or without acoustic treatments along their walls. An approximate solution for the steady inviscid flow field is obtained using an integral method for calculating the incompressible potential flow field in the inlet with a correction to account for compressibility effects. The accuracy of the finite element technique was assessed by comparison with available analytical solutions for the problems of plane and spinning wave propagation through a hard walled annular cylinder with a constant mean flow.
Material Models and Properties in the Finite Element Analysis of Knee Ligaments: A Literature Review
Galbusera, Fabio; Freutel, Maren; Dürselen, Lutz; D’Aiuto, Marta; Croce, Davide; Villa, Tomaso; Sansone, Valerio; Innocenti, Bernardo
2014-01-01
Knee ligaments are elastic bands of soft tissue with a complex microstructure and biomechanics, which are critical to determine the kinematics as well as the stress bearing behavior of the knee joint. Their correct implementation in terms of material models and properties is therefore necessary in the development of finite element models of the knee, which has been performed for decades for the investigation of both its basic biomechanics and the development of replacement implants and repair strategies for degenerative and traumatic pathologies. Indeed, a wide range of element types and material models has been used to represent knee ligaments, ranging from elastic unidimensional elements to complex hyperelastic three-dimensional structures with anatomically realistic shapes. This paper systematically reviews literature studies, which described finite element models of the knee, and summarizes the approaches, which have been used to model the ligaments highlighting their strengths and weaknesses. PMID:25478560
The Master Equation for Two-Level Accelerated Systems at Finite Temperature
NASA Astrophysics Data System (ADS)
Tomazelli, J. L.; Cunha, R. O.
2016-07-01
In this work, we study the behaviour of two weakly coupled quantum systems, described by a separable density operator; one of them is a single oscillator, representing a microscopic system, while the other is a set of oscillators which perform the role of a reservoir in thermal equilibrium. From the Liouville-Von Neumann equation for the reduced density operator, we devise the master equation that governs the evolution of the microscopic system, incorporating the effects of temperature via Thermofield Dynamics formalism by suitably redefining the vacuum of the macroscopic system. As applications, we initially investigate the behaviour of a Fermi oscillator in the presence of a heat bath consisting of a set of Fermi oscillators and that of an atomic two-level system interacting with a scalar radiation field, considered as a reservoir, by constructing the corresponding master equation which governs the time evolution of both sub-systems at finite temperature. Finally, we calculate the energy variation rates for the atom and the field, as well as the atomic population levels, both in the inertial case and at constant proper acceleration, considering the two-level system as a prototype of an Unruh detector, for admissible couplings of the radiation field.
Conserving and gapless approximations for an inhomogeneous Bose gas at finite temperatures
Griffin, A.
1996-04-01
We derive and discuss the equations of motion for the condensate and its fluctuations for a dilute, weakly interacting Bose gas in an external potential within the self-consistent Hartree-Fock-Bogoliubov (HFB) approximation. Account is taken of the depletion of the condensate and the anomalous Bose correlations, which are important at finite temperatures. We give a critical analysis of the self-consistent HFB approximation in terms of the Hohenberg-Martin classification of approximations (conserving vs gapless) and point out that the Popov approximation to the full HFB gives a gapless single-particle spectrum at all temperatures. The Beliaev second-order approximation is discussed as the spectrum generated by functional differentiation of the HFB single-particle Green{close_quote}s function. We emphasize that the problem of determining the excitation spectrum of a Bose-condensed gas (homogeneous or inhomogeneous) is difficult because of the need to satisfy several different constraints. {copyright} {ital 1996 The American Physical Society.}
NASA Astrophysics Data System (ADS)
Ami, I.; Fellah, M.; Allal, N. H.; Benhamouda, N.; Belabbas, M.; Oudih, M. R.
Expressions of temperature-dependent perpendicular (ℑ⊥) and parallel (ℑ‖) moments of inertia, including isovector pairing effects, have been established using the cranking method. They are derived from recently proposed temperature-dependent gap equations. The obtained expressions generalize the conventional finite-temperature BCS (FTBCS) ones. Numerical calculations have been carried out within the framework of the schematic Richardson model as well as for nuclei such as N = Z, using the single-particle energies and eigenstates of a deformed Woods-Saxon mean-field. ℑ⊥ and ℑ‖ have been studied as a function of the temperature. It has been shown that the isovector pairing effect on both the perpendicular and parallel moments of inertia is non-negligible at finite temperature. These correlations must thus be taking into account in studies of warm rotating nuclei in the N ≃ Z region.
Gusakov, Mikhail E.; Kantor, Elena M.; Haensel, Pawel
2009-07-15
We calculate the important quantity of superfluid hydrodynamics, the relativistic entrainment matrix for a nucleon-hyperon mixture at arbitrary temperature. In the nonrelativistic limit this matrix is also termed the Andreev-Bashkin or mass-density matrix. Our results can be useful for modeling the pulsations of massive neutron stars with superfluid nucleon-hyperon cores and for studies of the kinetic properties of superfluid baryon matter.
Light-Front QED{sub 1+1} at Finite Temperature
Strauss, S.; Beyer, M.
2008-09-05
We investigate the thermodynamic properties of quantum electrodynamics in 1+1 dimensions. We derive the partition function of the canonical ensemble in discrete light cone quantization and calculate the thermodynamical potential. This central quantity is evaluated for different system sizes and coupling strengths. We investigate the continuum limit and the thermodynamical limit and present basic thermodynamical quantities as a function of temperature for the interacting system. The results are compared to the idealized cases.
Three-dimensional finite element analysis of the mechanical properties of helical thread connection
NASA Astrophysics Data System (ADS)
Yang, Guoqing; Hong, Jun; Zhu, Linbo; Li, Baotong; Xiong, Meihua; Wang, Fei
2013-05-01
Conventional analytical and numerical methods for the mechanical properties of helical threads are relied on many assumptions and approximations and thus hardly yield satisfied results. A parameterized 3D finite element model of bolted joints with real helical thread geometry is established and meshed with refined hexahedral elements. The Von Mises plasticity criterion, kinematic hardening rule of materials and interfacial contacts are employed to make it possible for the suggested model be able to approach real assembly conditions. Then, the mechanical properties of bolted joints with different thread pitches, thread numbers and modular ratios are investigated, including the contact pressure distribution at joint interfaces, the axial load distribution and stress concentration in screw threads during the loading and unloading process. Simulation results indicate that the load distribution in screw threads produced by the suggested model agrees well the results from CHEN's photoelastic tests. In addition, an interesting phenomenon is found that tightening the bolt with a large preload first and then adjusting the clamping force by unloading can make the load distribution more uniform and reduce the maximum residual equivalent stress in thread roots by up to 40%. This research provides a simple and practical approach to constructing the 3D finite element model and predicting the mechanical properties of helical thread connection.
Thermal monopole condensation and confinement in finite temperature Yang-Mills theories
D'Alessandro, Alessio; D'Elia, Massimo; Shuryak, Edward V.
2010-05-01
We investigate the connection between color confinement and thermal Abelian monopoles populating the deconfined phase of SU(2) Yang-Mills theory, by studying how the statistical properties of the monopole ensemble change as the confinement/deconfinement temperature is approached from above. In particular, we study the distribution of monopole currents with multiple wrappings in the Euclidean time direction, corresponding to two or more particle permutations, and show that multiple wrappings increase as the deconfinement temperature is approached from above, in a way compatible with a condensation of such objects happening right at the deconfining transition. We also address the question of the thermal monopole mass, showing that different definitions give consistent results only around the transition, where the monopole mass goes down and becomes of the order of the critical temperature itself.
NASA Astrophysics Data System (ADS)
Farengo, R.; Guzdar, P. N.; Lee, Y. C.
1989-08-01
The effect of finite parallel wavenumber and electron temperature gradients on the lower hybrid drift instability is studied in the parameter regime corresponding to the TRX-2 device [Fusion Technol. 9, 48 (1986)]. Perturbations in the electrostatic potential and all three components of the vector potential are considered and finite beta electron orbit modifications are included. The electron temperature gradient decreases the growth rate of the instability but, for kz=0, unstable modes exist for ηe(=T'en0/Ten0)>6. Since finite kz effects completely stabilize the mode at small values of kz/ky(≂5×10-3), magnetic shear could be responsible for stabilizing the lower hybrid drift instability in field-reversed configurations.
Structural properties and magic structures in hydrogenated finite and infinite silicon nanowires
NASA Astrophysics Data System (ADS)
Zdetsis, A. D.; Koukaras, E. N.; Garoufalis, C. S.
2007-11-01
Unusual effects such as bending and "canting," related with the stability, have been identified by ab initio real-space calculations for hydrogenated silicon nanowires. We have examined in detail the electronic and structural properties of finite and infinite nanowires as a function of length (and width) and have developed stability and bending rules, demonstrating that "magic" wires do not bend. Reconstructed 2×1 nanowires are practically as stable as the magic ones. Our calculations are in good agreement with the experimental data of Ma et al. [Science 299, 1874 (2003).].
Wouters, Sebastian; Limacher, Peter A; Van Neck, Dimitri; Ayers, Paul W
2012-04-01
We have implemented the sweep algorithm for the variational optimization of SU(2) U(1) (spin and particle number) invariant matrix product states (MPS) for general spin and particle number invariant fermionic Hamiltonians. This class includes non-relativistic quantum chemical systems within the Born-Oppenheimer approximation. High-accuracy ab initio finite field results of the longitudinal static polarizabilities and second hyperpolarizabilities of one-dimensional hydrogen chains are presented. This allows to assess the performance of other quantum chemical methods. For small basis sets, MPS calculations in the saturation regime of the optical response properties can be performed. These results are extrapolated to the thermodynamic limit. PMID:22482543
NASA Technical Reports Server (NTRS)
Hosny, W. M.; Tabakoff, W.
1975-01-01
A two-dimensional finite difference numerical technique is presented to determine the temperature distribution in a solid blade of a radial guide vane. A computer program is written in Fortran IV for IBM 370/165 computer. The computer results obtained from these programs have a similar behavior and trend as those obtained by experimental results.
Chung, Chen-Yuan; Mansour, Joseph M.
2014-01-01
The feasibility of determining biphasic material properties using a finite element model of stress relaxation coupled with two types of constrained optimization to match measured data was investigated. Comparison of these two approaches, a zero-order method and a gradient-based algorithm, validated the predicted material properties. Optimizations were started from multiple different initial guesses of material properties (design variables) to establish the robustness of the optimization. Overall, the optimal values are close to those found by Cohen et al., (1998), but these small differences produced a marked improvement in the fit to the measured stress relaxation. Despite the greater deviation in the optimized values obtained from the zero-order method, both optimization procedures produced material properties that gave equally good overall fits to the measured data. Furthermore, optimized values were all within the expected range of material properties. Modeling stress relaxation using the optimized material properties showed an excellent fit to the entire time history of the measured data. PMID:25460921
Chung, Chen-Yuan; Mansour, Joseph M
2015-02-01
The feasibility of determining biphasic material properties using a finite element model of stress relaxation coupled with two types of constrained optimization to match measured data was investigated. Comparison of these two approaches, a zero-order method and a gradient-based algorithm, validated the predicted material properties. Optimizations were started from multiple different initial guesses of material properties (design variables) to establish the robustness of the optimization. Overall, the optimal values are close to those found by Cohen et al. (1998) but these small differences produced a marked improvement in the fit to the measured stress relaxation. Despite the greater deviation in the optimized values obtained from the zero-order method, both optimization procedures produced material properties that gave equally good overall fits to the measured data. Furthermore, optimized values were all within the expected range of material properties. Modeling stress relaxation using the optimized material properties showed an excellent fit to the entire time history of the measured data. PMID:25460921
A finite element model for temperature induced electrohydrodynamic pumping horizontal pipes
Kuo, B.S.; Chato, J.C.; Crowley, J.M.
1984-02-01
The electrohydrodynamic (EHD) pumping created by an axially traveling electric wave superimposed on a dielectric fluid with a transverse temperature field has abeen investigated using a finite element technique. Both forward wave (cooled wall) and backward wave (heated wall) modes of operation have been considered. The secondary flow generated by buoyancy effects in the cross section were included in the calculations. The driving effects of the traveling wave were calculated by assuming that only the average electric shear stress produced movement while the sinusoidally varying transient effects cancelled out. The results show that effective pumping can be achieved without the use of a grounding electrode along the axis of the tube but the design parameters have to be carefully selected. Increasing the diameter-to-wavelength ratios increases the velocities. The flow rate is maximum at an optimum frequency, about 0.8 Hz in our typical cases, but it drops off rather quickly as he frequency is either decreased or increased. The velocities were much less sensitive to heating/cooling rates (i.e., Rayleigh numbers) or changes in the magnitude of the electrical conductivity values. Although the pumping effect increases approximately as the square of the maximum applied electric potential, in practice, the electric gradients are limited by the dielectric strength of the fluid. The results indicate the EHD heat exchanger/pumps can be feasible alternatives to mechanical pumps in certain circumstances when dielectric liquids require both heat transfer and circulation.
Theory of the dissociation dynamics of small molecules on metal surfaces: Finite temperature studies
Jackson, B.E.
1992-02-01
The goal of this study is to gain a better understanding of metal- catalyzed reactions via a detailed examination of the dynamics of molecule-metal interactions. Much effort has focused on treating the molecule as quantum mechanically as possible, and including the effects of finite surface temperature. Recently developed time dependent quantum techniques have been used to compute the dissociative sticking probability of H{sub 2} on various metal surfaces. All molecular degrees of freedom are included either quantum mechanically or classically. The dependence upon translational and internal molecular energy, the angle and site of the surface impact, and the details of the molecule-metal interaction potential were examined. Similar techniques have been used to study the Eley-Rideal mechanism for the recombinative desorption of adsorbed H atoms with gas phase H atoms. Extremely accurate methods for coupling the molecule to the thermal vibrations of the solid have been developed. They are being used in a general study of sticking, as well as to examine the trapping of H{sub 2} and other diatomics in weakly bound molecular precursors to dissociative adsorption.
Enhancement of the critical temperature in iron pnictide superconductors by finite-size effects
NASA Astrophysics Data System (ADS)
Araújo, M. A. N.; García-García, Antonio M.; Sacramento, P. D.
2011-11-01
Recent experiments have shown that in agreement with previous theoretical predictions, superconductivity in nanostructures can be enhanced with respect to the bulk (L→∞) limit. Motivated by these results, we study finite size effects (FSEs) in iron pnictide superconductors. We employ a five-band mean-field approach that reproduces quantitatively the band structure of these materials around the Fermi energy. For realistic values of the bulk critical temperature Tcbulk˜20-50 K, we find that Tc(L) has a complicated oscillating pattern as a function of the system size L. For a simplified two-band model we show analytically that these oscillations are caused by fluctuations of the spectral density around the Fermi energy. We identify a scale L˜10 nm for which deviations from mean fields, not included in our model, are small but still Tc(L) is higher than Tcbulk. Similar results are obtained for different boundary conditions and geometries. Finally we show that the differential conductance, an experimental observable, is also very sensitive to FSE.
Martins, R. A.
2007-08-15
The recent extension of the standard model to include massive neutrinos in the framework of noncommutative geometry and the spectral action principle involves new scalar fields and their interactions with the usual complex scalar doublet. After ensuring that they bring no unphysical consequences, we address the question of how these fields affect the physics predicted in the Weinberg-Salam theory, particularly in the context of the electroweak phase transition. Applying the Dolan-Jackiw procedure, we calculate the finite temperature corrections, and find that the phase transition is first order. The new scalar interactions significantly improve the stability of the electroweak Z string, through the 'bag' phenomenon described by Vachaspati and Watkins ['Bound states can stabilize electroweak strings', Phys. Lett. B 318, 163-168 (1993)]. (Recently, cosmic strings have climbed back into interest due to a new evidence.) Sourced by static embedded strings, an internal space analogy of Cartan's torsion is drawn, and a possible Higgs-force-like 'gravitational' effect of this nonpropagating torsion on the fermion masses is described. We also check that the field generating the Majorana mass for the {nu}{sub R} is nonzero in the physical vacuum.
Massive Yang-Mills for vector and axial-vector spectral functions at finite temperature
NASA Astrophysics Data System (ADS)
Hohler, Paul M.; Rapp, Ralf
2016-05-01
The hadronic mechanism which leads to chiral symmetry restoration is explored in the context of the ρπa1 system using Massive Yang-Mills, a hadronic effective theory which governs their microscopic interactions. In this approach, vector and axial-vector mesons are implemented as gauge bosons of a local chiral gauge group. We have previously shown that this model can describe the experimentally measured vector and axial-vector spectral functions in vacuum. Here, we carry the analysis to finite temperatures by evaluating medium effects in a pion gas and calculating thermal spectral functions. We find that the spectral peaks in both channels broaden along with a noticeable downward mass shift in the a1 spectral peak and negligible movement of the ρ peak. The approach toward spectral function degeneracy is accompanied by a reduction of chiral order parameters, i.e., the pion decay constant and scalar condensate. Our findings suggest a mechanism where the chiral mass splitting induced in vacuum is burned off. We explore this mechanism and identify future investigations which can further test it.
Casana, Rodolfo; Ferreira, Manoel M. Jr; Rodrigues, Josberg S.; Silva, Madson R. O.
2009-10-15
In this work, we examine the finite temperature properties of the CPT-even and Lorentz-invariance-violating (LIV) electrodynamics of the standard model extension, represented by the term W{sub {alpha}}{sub {nu}}{sub {rho}}{sub {phi}}F{sup {alpha}}{sup {nu}}F{sup {rho}}{sup {phi}}. We begin analyzing the Hamiltonian structure following the Dirac's procedure for constrained systems and construct a well-defined and gauge invariant partition function in the functional integral formalism. Next, we specialize for the nonbirefringent coefficients of the tensor W{sub {alpha}}{sub {nu}}{sub {rho}}{sub {phi}}. In the sequel, the partition function is explicitly carried out for the parity-even sector of the tensor W{sub {alpha}}{sub {nu}}{sub {rho}}{sub {phi}}. The modified partition function is a power of the Maxwell's partition function. It is observed that the LIV coefficients induce an anisotropy in the black body angular energy density distribution. The Planck's radiation law, however, retains its frequency dependence and the Stefan-Boltzmann law keeps the usual form, except for a change in the Stefan-Boltzmann constant by a factor containing the LIV contributions.
Deformable spin- (1)/(2) XX chain with three-site interactions at zero and finite temperatures
NASA Astrophysics Data System (ADS)
Derzhko, Oleg; Krokhmalskii, Taras; Stolze, Joachim; Verkholyak, Taras
2009-03-01
We study spin-Peierls structural lattice instabilities for a spin-1/2 isotropic XY chain with three-site interactions of (XZX+YZY) type. Within the adopted adiabatic treatment we have to examine the ground-state energy or the Helmholtz free energy of the spin chain with exchange couplings varying coherently with a possible static lattice distortion pattern. Since the considered spin model can be converted into a system of noninteracting spinless fermions the required ground-state energy or the Helmholtz free energy can be calculated accurately without making any approximations. We examine rigorously several lattice distortion patterns focusing on dimerized and trimerized ones, which owe their presence to the spin-Peierls mechanism. We present phase diagrams illustrating the effect of the three-site interaction on the spin-Peierls lattice distortions. Finally we discuss some properties of the deformable spin chain in the ground state and at finite temperatures. In particular, we examine the transverse magnetization, the static transverse susceptibility and the specific heat illustrating the changes in these quantities due to lattice instabilities.
Moduli stabilization in type II Calabi-Yau compactifications at finite temperature
NASA Astrophysics Data System (ADS)
Liu, Lihui; Partouche, Hervé
2012-11-01
We consider the type II superstring compactified on Calabi-Yau threefolds, at finite temperature. The latter is implemented at the string level by a free action on the Euclidean time circle. We show that all Kähler and complex structure moduli involved in the gauge theories geometrically engineered in the vicinity of singular loci are lifted by the stringy thermal effective potential. The analysis is based on the effective gauged super-gravity at low energy, without integrating out the non-perturbative BPS states becoming massless at the singular loci. The universal form of the action in the weak coupling regime and at low enough temperature is determined in two cases. Namely, the conifold locus, as well as a locus where the internal space develops a genus- g curve of A N -1 singularities, thus realizing an SU( N ) gauge theory coupled to g hypermultiplets in the adjoint. In general, we argue that the favored points of stabilization sit at the intersection of several such loci. As a result, the entire vector multiplet moduli space is expected to be lifted, together with hypermultiplet moduli. The scalars are dynamically stabilized during the cosmological evolution induced by the back-reaction of the thermal effective potential on the originally static background. When the universe expands and the temperature T drops, the scalars converge to minima, with damped oscillations. Moreover, they store an energy density that scales as T 4, which never dominates over radiation. The reason for this is that the mass they acquire at one-loop is of order the temperature scale, which is time-dependent rather than constant. As an example, we analyze the type IIA compactification on a hy-persurface {P}_{{( {1,1,2,2,6} )}}^4 [12], with Hodge numbers h 11 = 2 and h 12 = 128. In this case, both Kähler moduli are stabilized at a point, where the internal space develops a node and an enhanced SU(2) gauge theory coupled to 2 adjoint hypermultiplets. This shows that in the dual thermal
NASA Astrophysics Data System (ADS)
Lankinen, Juho; Lyyra, Henri; Sokolov, Boris; Teittinen, Jose; Ziaei, Babak; Maniscalco, Sabrina
2016-05-01
We present a general model of qubit dynamics which entails pure dephasing and dissipative time-local master equations. This allows us to describe the combined effect of thermalization and dephasing beyond the usual Markovian approximation. We investigate the complete positivity conditions and introduce a heuristic model that is always physical and provides the correct Markovian limit. We study the effects of temperature on the non-Markovian behavior of the system and show that the noise additivity property discussed by Yu and Eberly [Phys. Rev. Lett. 97, 140403 (2006), 10.1103/PhysRevLett.97.140403] holds beyond the Markovian limit.
NASA Astrophysics Data System (ADS)
Wu, Jianda; Kormos, Marton; Si, Qimiao
2013-03-01
When the transverse field Ising chain at its quantum critical point is subjected to a small longitudinal field, the perturbed conformal field theory led to a field theory with an exotic E8 symmetry. Recent neutron scattering experiments have provided evidence for the lightest two particles in this E8 model in the quasi-1D Ising ferromagnet CoNb2O6. While the zero temperature dynamics of the model is well known, its finite-temperature counterpart has not yet been systematically studied. We study the low-frequency dynamical structure factor at finite temperatures using the form-factor method. We show that the dominant contribution to the dynamical structure factor comes from the scattering between two lightest particles, and discuss the implications of our results for the NMR relaxation rate.
NASA Astrophysics Data System (ADS)
Park, Sung-Been; Cha, Min-Chul
2015-11-01
We investigate the finite-size scaling properties of the quantum phase transition in the one-dimensional quantum Ising model with periodic boundary conditions by representing the ground state in matrix product state forms. The infinite time-evolving block decimation technique is used to optimize the states. A trace over a product of the matrices multiplied as many times as the number of sites yields the finite-size effects. For sufficiently large Schmidt ranks, the finite-size scaling behavior determines the critical point and the critical exponents whose values are consistent with the analytical results.
Study of the multi-orbital Hubbard model at finite temperature
NASA Astrophysics Data System (ADS)
Mukherjee, Anamitra; Dong, Shuai; Alvarez, Gonzalo; Dagotto, Elbio
2014-03-01
Research in pnictide superconductors have clearly established the need for the study of multi-orbital Hubbard models. With this motivation, here we apply a combination of the real-space Exact Diagonalization and Classical Monte Carlo (ED+MC) method, widely used in manganites, with the standard Hartree-Fock mean field (MF) theory to investigate the properties of multiorbital models as a function of temperature. In this approach the MF parameters are treated via a classical MC and the fermions moving in the MF background are solved by exact diagonalization. The temperature dependence of the dynamical spin susceptibility S(q --> , ω) , orbital resolved single particle spectral function A(k --> , ω) , optical conductivity, and real space charge/spin/orbital density maps are calculated at different dopings. These results are relevant in understanding the role of the multiple degrees of freedom in governing the magnetic and transport properties of the Fe based superconductor materials. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Finite Element Study of the Effect of Substrate Properties in Micro-cutting Thin Workpiece Materials
NASA Astrophysics Data System (ADS)
Saptaji, K.; Subbiah, S.
2016-02-01
The cutting mechanism and residual stress profile of the micro-cutting thin workpiece are affected by the interaction of the thin workpiece and the fixture (substrate) underneath it similar to that observed in the nano-indentation and nano-scratching of thin film. The appropriate substrate properties are necessary especially to avoid detachment during machining and to minimize deformation and warping of the machined thin workpiece. Thus, the investigations of the influence of substrate properties on micro-cutting thin workpiece are essentially to be conducted. The finite element study of orthogonal micro-cutting of thin Al6061-T6 is presented here. The simulations were conducted to study the residual stress profile across the thickness of the machined thin workpiece at various workpiece thicknesses and various substrate (adhesive) elastic properties. Simulations results show that as the machined workpiece become thinner, the stress is more significant not only on the machined surface but also it can reach the bottom of the workpiece. The stiffer substrate produces less variation of the stress across the workpiece thickness while more compliant substrate produces broader stress variation as the workpiece become thinner. The results show the significant effect of the workpiece thickness and the substrate properties on the stress profiles in the micro-cutting of thin workpiece.
Spanos, P; Elsbernd, P; Ward, B; Koenck, T
2013-06-28
This paper reviews and enhances numerical models for determining thermal, elastic and electrical properties of carbon nanotube-reinforced polymer composites. For the determination of the effective stress-strain curve and thermal conductivity of the composite material, finite-element analysis (FEA), in conjunction with the embedded fibre method (EFM), is used. Variable nanotube geometry, alignment and waviness are taken into account. First, a random morphology of a user-defined volume fraction of nanotubes is generated, and their properties are incorporated into the polymer matrix using the EFM. Next, incremental and iterative FEA approaches are used for the determination of the nonlinear properties of the nanocomposite. For the determination of the electrical properties, a spanning network identification algorithm is used. First, a realistic nanotube morphology is generated from input parameters defined by the user. The spanning network algorithm then determines the connectivity between nanotubes in a representative volume element. Then, interconnected nanotube networks are converted to equivalent resistor circuits. Finally, Kirchhoff's current law is used in conjunction with FEA to solve for the voltages and currents in the system and thus calculate the effective electrical conductivity of the nanocomposite. The model accounts for electrical transport mechanisms such as electron hopping and simultaneously calculates percolation probability, identifies the backbone and determines the effective conductivity. Monte Carlo analysis of 500 random microstructures is performed to capture the stochastic nature of the fibre generation and to derive statistically reliable results. The models are validated by comparison with various experimental datasets reported in the recent literature. PMID:23690646
Vanden-Eijnden, Eric; Venturoli, Maddalena
2009-05-21
An improved and simplified version of the finite temperature string (FTS) method [W. E, W. Ren, and E. Vanden-Eijnden, J. Phys. Chem. B 109, 6688 (2005)] is proposed. Like the original approach, the new method is a scheme to calculate the principal curves associated with the Boltzmann-Gibbs probability distribution of the system, i.e., the curves which are such that their intersection with the hyperplanes perpendicular to themselves coincides with the expected position of the system in these planes (where perpendicular is understood with respect to the appropriate metric). Unlike more standard paths such as the minimum energy path or the minimum free energy path, the location of the principal curve depends on global features of the energy or the free energy landscapes and thereby may remain appropriate in situations where the landscape is rough on the thermal energy scale and/or entropic effects related to the width of the reaction channels matter. Instead of using constrained sampling in hyperplanes as in the original FTS, the new method calculates the principal curve via sampling in the Voronoi tessellation whose generating points are the discretization points along this curve. As shown here, this modification results in greater algorithmic simplicity. As a by-product, it also gives the free energy associated with the Voronoi tessellation. The new method can be applied both in the original Cartesian space of the system or in a set of collective variables. We illustrate FTS on test-case examples and apply it to the study of conformational transitions of the nitrogen regulatory protein C receiver domain using an elastic network model and to the isomerization of solvated alanine dipeptide. PMID:19466817
Low temperature thermophysical properties of lunar soil
NASA Technical Reports Server (NTRS)
Cremers, C. J.
1973-01-01
The thermal conductivity and thermal diffusivity of lunar fines samples from the Apollo 11 and Apollo 12 missions, determined at low temperatures as a function of temperature and various densities, are reviewed. It is shown that the thermal conductivity of lunar soil is nearly the same as that of terrestrial basaltic rock under the same temperature and pressure conditions.
NASA Technical Reports Server (NTRS)
Turner, Travis L.; Zhong, Z. W.; Mei, Chuh
1994-01-01
A feasibility study on the use of shape memory alloys (SMA) for suppression of the random response of composite panels due to acoustic loads at elevated temperatures is presented. The constitutive relations for a composite lamina with embedded SMA fibers are developed. The finite element governing equations and the solution procedures for a composite plate subjected to combined acoustic and thermal loads are presented. Solutions include: 1) Critical buckling temperature; 2) Flat panel random response; 3) Thermal postbuckling deflection; 4) Random response of a thermally buckled panel. The preliminary results demonstrate that the SMA fibers can completely eliminate the thermal postbuckling deflection and significantly reduce the random response at elevated temperatures.
NASA Astrophysics Data System (ADS)
Vukovic, Mirko
2008-10-01
Differential transport equations for plasma are most commonly discretized using the finite difference formalism. More recently, discretizations based on the finite element method have also been used. An alternate method is the finite volume method which discretizes the integral conservation equations.ootnotetextNumerical Heat Transfer and Fluid Flow, Suhas V. Patankar, McGraw-Hill, 1980 This method conserves flux across the grid cell interfaces. In this presentation, we present the discretization of plasma transport equations based on the finite volume formalism. We will discuss the discretization of the drift-diffusion, momentum, and electron kinetic equations based on this formalism. A one-dimensional problem will be solved for several DC and time-dependent cases.
Directional anisotropy, finite size effect and elastic properties of hexagonal boron nitride
NASA Astrophysics Data System (ADS)
Thomas, Siby; Ajith, K. M.; Valsakumar, M. C.
2016-07-01
Classical molecular dynamics simulations have been performed to analyze the elastic and mechanical properties of two-dimensional (2D) hexagonal boron nitride (h-BN) using a Tersoff-type interatomic empirical potential. We present a systematic study of h-BN for various system sizes. Young’s modulus and Poisson’s ratio are found to be anisotropic for finite sheets whereas they are isotropic for the infinite sheet. Both of them increase with system size in accordance with a power law. It is concluded from the computed values of elastic constants that h-BN sheets, finite or infinite, satisfy Born’s criterion for mechanical stability. Due to the the strong in-plane sp2 bonds and the small mass of boron and nitrogen atoms, h-BN possesses high longitudinal and shear velocities. The variation of bending rigidity with system size is calculated using the Foppl–von Karman approach by coupling the in-plane bending and out-of-plane stretching modes of the 2D h-BN.
Statistical Properties of a DNA Sample under the Finite-Sites Model
Yang, Z.
1996-01-01
Statistical properties of a DNA sample from a random-mating population of constant size are studied under the finite-sites model. It is assumed that there is no migration and no recombination occurs within the locus. A Markov process model is used for nucleotide substitution, allowing for multiple substitutions at a single site. The evolutionary rates among sites are treated as either constant or variable. The general likelihood calculation using numerical integration involves intensive computation and is feasible for three or four sequences only; it may be used for validating approximate algorithms. Methods are developed to approximate the probability distribution of the number of segregating sites in a random sample of n sequences, with either constant or variable substitution rates across sites. Calculations using parameter estimates obtained for human D-loop mitochondrial DNAs show that among-site rate variation has a major effect on the distribution of the number of segregating sites; the distribution under the finite-sites model with variable rates among sites is quite different from that under the infinite-sites model. PMID:8978077
NASA Astrophysics Data System (ADS)
Carmelo, J. M. P.; Gu, Shi-Jian; Sampaio, M. J.
2014-06-01
Finite-temperature T > 0 transport properties of integrable and nonintegrable one-dimensional (1D) many-particle quantum systems are rather different, showing ballistic and diffusive behavior, respectively. The repulsive 1D Hubbard model is a prominent example of an integrable correlated system. For electronic densities n ≠ 1 (and spin densities m ≠ 0) it is an ideal charge (and spin) conductor, with ballistic charge (and spin) transport for T ⩾ 0. In spite of the fact that it is solvable by the Bethe ansatz, at n = 1 (and m = 0) its T > 0 charge (and spin) transport properties are an issue that remains poorly understood. Here we combine this solution with symmetry and the explicit calculation of current-operator matrix elements between energy eigenstates to show that for on-site repulsion U > 0 and at n = 1 the charge stiffness Dη(T) vanishes for T > 0 in the thermodynamic limit. A similar behavior is found by such methods for the spin stiffness Ds(T) for U > 0 and T > 0, which vanishes at m = 0. This absence of finite temperature n = 1 ballistic charge transport and m = 0 ballistic spin transport are exact results that clarify long-standing open problems.
Slaboch, Constance L; Alber, Mark S; Rosen, Elliot D; Ovaert, Timothy C
2012-06-01
Deep vein thrombosis, pulmonary embolism, and abdominal aortic aneurysms are blood-related diseases that represent a major public health problem. These diseases are characterized by the formation of a thrombus (i.e., blood clot) that either blocks a major artery or causes an aortic rupture. Identifying the mechanical properties of thrombi can help determine when these incidents will occur. In this investigation, a murine thrombus, formed from platelet-rich plasma, calcium, and thrombin, was nanoindented and the elastic modulus was estimated via elastic contact theory. This information was used as input to an inverse finite element simulation, which determined optimal values for the elastic modulus and viscosity of the thrombus using a viscoelastic material model. A sensitivity analysis was also performed to determine which material parameters have the greatest affect on the simulation. Results from this investigation demonstrate the feasibility of the mechanical characterization of a murine thrombus using nanoindentation. PMID:22520420
Statistical properties of record-breaking temperatures.
Newman, William I; Malamud, Bruce D; Turcotte, Donald L
2010-12-01
A record-breaking temperature is the highest or lowest temperature at a station since the period of time considered began. The temperatures at a station constitute a time series. After the removal of daily and annual periodicities, the primary considerations are trends (i.e., global warming) and long-range correlations. We first carry out Monte Carlo simulations to determine the influence of trends and long-range correlations on record-breaking statistics. We take a time series that is a Gaussian white noise and give the classic record-breaking theory results for an independent and identically distributed process. We then carry out simulations to determine the influence of long-range correlations and linear temperature trends. For the range of fractional Gaussian noises that are observed to be applicable to temperature time series, the influence on the record-breaking statistics is less than 10%. We next superimpose a linear trend on a Gaussian white noise and extend the theory to include the effect of an additive trend. We determine the ratios of the number of maximum to the number of minimum record-breaking temperatures. We find the single governing parameter to be the ratio of the temperature change per year to the standard deviation of the underlying white noise. To test our approach, we consider a 30 yr record of temperatures at the Mauna Loa Observatory for 1977-2006. We determine the temperature trends by direct measurements and use our simulations to infer trends from the number of record-breaking temperatures. The two approaches give values that are in good agreement. We find that the warming trend is primarily due to an increase in the (overnight) minimum temperatures, while the maximum (daytime) temperatures are approximately constant. PMID:21230709
Models for predicting temperature dependence of material properties of aluminum
NASA Astrophysics Data System (ADS)
Marla, Deepak; Bhandarkar, Upendra V.; Joshi, Suhas S.
2014-03-01
A number of processes such as laser ablation, laser welding, electric discharge machining, etc involve high temperatures. Most of the processes involve temperatures much higher than the target melting and normal boiling point. Such large variation in target temperature causes a significant variation in its material properties. Due to the unavailability of experimental data on material properties at elevated temperatures, usually the data at lower temperatures is often erroneously extrapolated during modelling of these processes. Therefore, this paper attempts to evaluate the variation in material properties with temperature using some general and empirical theories, along with the available experimental data for aluminum. The evaluated properties of Al using the proposed models show a significant variation with temperature. Between room temperature and near-critical temperature (0.9Tc), surface reflectivity of Al varies from more than 90% to less than 50%, absorption coefficient decreases by a factor of 7, thermal conductivity decreases by a factor of 5, density decreases by a factor of 4, specific heat and latent heat of vapourization vary by a factor between 1.5 and 2. Applying these temperature-dependent material properties for modelling laser ablation suggest that optical properties have a greater influence on the process than thermophysical properties. The numerical predictions of the phase explosion threshold in laser ablation are within 5% of the experimental values.
Rémond, Agnès; Naïli, Salah; Lemaire, Thibault
2008-12-01
Bone remodelling is the process that maintains bone structure and strength through adaptation of bone tissue mechanical properties to applied loads. Bone can be modelled as a porous deformable material whose pores are filled with cells, organic material and interstitial fluid. Fluid flow is believed to play a role in the mechanotransduction of signals for bone remodelling. In this work, an osteon, the elementary unit of cortical bone, is idealized as a hollow cylinder made of a deformable porous matrix saturated with an interstitial fluid. We use Biot's poroelasticity theory to model the mechanical behaviour of bone tissue taking into account transverse isotropic mechanical properties. A finite element poroelastic model is developed in the COMSOL Multiphysics software. Elasticity equations and Darcy's law are implemented in this software; they are coupled through the introduction of an interaction term to obtain poroelasticity equations. Using numerical simulations, the investigation of the effect of spatial gradients of permeability or Poisson's ratio is performed. Results are discussed for their implication on fluid flow in osteons: (i) a permeability gradient affects more the fluid pressure than the velocity profile; (ii) focusing on the fluid flow, the key element of loading is the strain rate; (iii) a Poisson's ratio gradient affects both fluid pressure and fluid velocity. The influence of textural and mechanical properties of bone on mechanotransduction signals for bone remodelling is also discussed. PMID:17990014
Zhang, Jingzhou; Niebur, Glen L.; Ovaert, Timothy C.
2009-01-01
Measurement of the mechanical properties of bone is important for estimating the stresses and strains exerted at the cellular level due to loading experienced on a macro-scale. Nano- and micro-mechanical properties of bone are also of interest to the pharmaceutical industry when drug therapies have intentional or non-intentional effects on bone mineral content and strength. The interactions that can occur between nano- and micro-indentation creep test condition parameters were considered in this study, and average hardness and elastic modulus were obtained as a function of indentation testing conditions (maximum load, load/unload rate, load-holding time, and indenter shape). The results suggest that bone reveals different mechanical properties when loading increases from the nano- to the micro-scale range (μN to N), which were measured using low- and high-load indentation testing systems. A four-parameter visco-elastic/plastic constitutive model was then applied to simulate the indentation load vs. depth response over both load ranges. Good agreement between the experimental data and finite element model was obtained when simulating the visco-elastic/plastic response of bone. The results highlight the complexity of bone as a biological tissue and the need to understand the impact of testing conditions on the measured results. PMID:17961578
Homogenized mechanical properties of auxetic composite materials in finite-strain elasticity
NASA Astrophysics Data System (ADS)
Kochmann, Dennis M.; Venturini, Gabriela N.
2013-08-01
Careful microstructural design can result in materials with counterintuitive effective (macroscale) mechanical properties such as a negative Poisson’s ratio, commonly referred to as auxetic behavior. One specific approach to achieving auxetic behavior is to elastically connect structural elements with rotational degrees of freedom to result in elastic structures that unfold under uniaxial loading in specific directions, thereby giving rise to bi- or triaxial expansion, i.e. auxetic behavior (transverse expansion under uniaxial extension). This concept has been applied successfully to elastically coupled two-dimensional rigid rotational elements (such as rotating rectangles and triangles) which exhibit a negative effective in-plane Poisson’s ratio under uniaxial (ex)tension. Here, we adopt this fundamental design principle but take it to the next level by achieving auxetic behavior in finitely strained composites made of stiff inclusions in a hyperelastic matrix, and we study the resulting elastic properties under in-plane strain by numerical homogenization. Our results highlight the emergence of auxetic behavior based on geometric arrangement and properties of the base material and demonstrate a path towards simple inclusion-matrix composites with auxetic behavior.
D* and B* mesons in strange hadronic medium at finite temperature
NASA Astrophysics Data System (ADS)
Chhabra, Rahul; Kumar, Arvind
2016-03-01
We calculate the effect of density and temperature of isospin symmetric strange medium on the shift in masses and decay constants of vector D and B mesons using chiral SU(3) model and QCD sum rule approach. In the present investigation the values of quark and gluon condensates are calculated from the chiral SU(3) model and these condensatesare further used as input in the QCD Sum rule framework to calculate the in-medium masses and decay constants of vector D and B mesons. These in medium properties of vector D and B mesons may be helpful to understand the experimental observables of the experiments like CBM and PANDA under FAIR project at GSI, Germany. The results which are observed in present work are also compared with the previous predictions.
Huang, Chen
2016-03-28
A key element in the density functional embedding theory (DFET) is the embedding potential. We discuss two major issues related to the embedding potential: (1) its non-uniqueness and (2) the numerical difficulty for solving for it, especially for the spin-polarized systems. To resolve the first issue, we extend DFET to finite temperature: all quantities, such as the subsystem densities and the total system's density, are calculated at a finite temperature. This is a physical extension since materials work at finite temperatures. We show that the embedding potential is strictly unique at T > 0. To resolve the second issue, we introduce an efficient iterative embedding potential solver. We discuss how to relax the magnetic moments in subsystems and how to equilibrate the chemical potentials across subsystems. The solver is robust and efficient for several non-trivial examples, in all of which good quality spin-polarized embedding potentials were obtained. We also demonstrate the solver on an extended periodic system: iron body-centered cubic (110) surface, which is related to the modeling of the heterogeneous catalysis involving iron, such as the Fischer-Tropsch and the Haber processes. This work would make it efficient and accurate to perform embedding simulations of some challenging material problems, such as the heterogeneous catalysis and the defects of complicated spin configurations in electronic materials. PMID:27036426
NASA Astrophysics Data System (ADS)
Huang, Chen
2016-03-01
A key element in the density functional embedding theory (DFET) is the embedding potential. We discuss two major issues related to the embedding potential: (1) its non-uniqueness and (2) the numerical difficulty for solving for it, especially for the spin-polarized systems. To resolve the first issue, we extend DFET to finite temperature: all quantities, such as the subsystem densities and the total system's density, are calculated at a finite temperature. This is a physical extension since materials work at finite temperatures. We show that the embedding potential is strictly unique at T > 0. To resolve the second issue, we introduce an efficient iterative embedding potential solver. We discuss how to relax the magnetic moments in subsystems and how to equilibrate the chemical potentials across subsystems. The solver is robust and efficient for several non-trivial examples, in all of which good quality spin-polarized embedding potentials were obtained. We also demonstrate the solver on an extended periodic system: iron body-centered cubic (110) surface, which is related to the modeling of the heterogeneous catalysis involving iron, such as the Fischer-Tropsch and the Haber processes. This work would make it efficient and accurate to perform embedding simulations of some challenging material problems, such as the heterogeneous catalysis and the defects of complicated spin configurations in electronic materials.
Subramanian, Swetha; Mast, T Douglas
2015-10-01
Computational finite element models are commonly used for the simulation of radiofrequency ablation (RFA) treatments. However, the accuracy of these simulations is limited by the lack of precise knowledge of tissue parameters. In this technical note, an inverse solver based on the unscented Kalman filter (UKF) is proposed to optimize values for specific heat, thermal conductivity, and electrical conductivity resulting in accurately simulated temperature elevations. A total of 15 RFA treatments were performed on ex vivo bovine liver tissue. For each RFA treatment, 15 finite-element simulations were performed using a set of deterministically chosen tissue parameters to estimate the mean and variance of the resulting tissue ablation. The UKF was implemented as an inverse solver to recover the specific heat, thermal conductivity, and electrical conductivity corresponding to the measured area of the ablated tissue region, as determined from gross tissue histology. These tissue parameters were then employed in the finite element model to simulate the position- and time-dependent tissue temperature. Results show good agreement between simulated and measured temperature. PMID:26352462
NASA Astrophysics Data System (ADS)
Subramanian, Swetha; Mast, T. Douglas
2015-09-01
Computational finite element models are commonly used for the simulation of radiofrequency ablation (RFA) treatments. However, the accuracy of these simulations is limited by the lack of precise knowledge of tissue parameters. In this technical note, an inverse solver based on the unscented Kalman filter (UKF) is proposed to optimize values for specific heat, thermal conductivity, and electrical conductivity resulting in accurately simulated temperature elevations. A total of 15 RFA treatments were performed on ex vivo bovine liver tissue. For each RFA treatment, 15 finite-element simulations were performed using a set of deterministically chosen tissue parameters to estimate the mean and variance of the resulting tissue ablation. The UKF was implemented as an inverse solver to recover the specific heat, thermal conductivity, and electrical conductivity corresponding to the measured area of the ablated tissue region, as determined from gross tissue histology. These tissue parameters were then employed in the finite element model to simulate the position- and time-dependent tissue temperature. Results show good agreement between simulated and measured temperature.
Tensile and fatigue properties of Inconel 718 at cryogenic temperatures
NASA Technical Reports Server (NTRS)
Malin, C. O.; Schmidt, E. H.
1969-01-01
Tests to determine the tensile and fatigue properties of Inconel 718 at cryogenic temperatures show that the alloy increases in strength at low temperatures, with very little change in toughness. The effect of surface finish and grain size on the fatigue properties was also determined.
Dillenschneider, Raoul; Richert, Jean
2006-10-01
We study the role played by a Chern-Simons contribution to the action in the QED{sub 3} formulation of a two-dimensional Heisenberg model of quantum spin systems with a strictly fixed site occupation at finite temperature. We show how this contribution affects the screening of the potential that acts between spinons and contributes to the restoration of chiral symmetry in the spinon sector. The constant that characterizes the Chern-Simons term can be related to the critical temperature T{sub c} above which the dynamical mass goes to zero.
First- and second-sound-like modes at finite temperature in trapped Fermi gases from BCS to BEC
He Yan; Chen Qijin; Chien, C.-C.; Levin, K.
2007-11-15
We determine the temperature (T) dependence of first- and second-sound-like mode frequencies for trapped Fermi gases undergoing the BCS to Bose-Einstein condensation (BEC) crossover. Our results are based on numerical solution of the two-fluid equations in conjunction with a microscopic calculation of thermodynamical variables. As in experiment and at unitarity, we show that the lowest radial breathing mode is T independent. At finite T, higher-order breathing modes strongly mix with second sound. Their complex T dependence should provide an alternative way of measuring the transition temperature T{sub c}.
Zhang, Jing; Tian, Jiabin; Ta, Na; Huang, Xinsheng; Rao, Zhushi
2016-08-01
Finite element method was employed in this study to analyze the change in performance of implantable hearing devices due to the consideration of soft tissues' viscoelasticity. An integrated finite element model of human ear including the external ear, middle ear and inner ear was first developed via reverse engineering and analyzed by acoustic-structure-fluid coupling. Viscoelastic properties of soft tissues in the middle ear were taken into consideration in this model. The model-derived dynamic responses including middle ear and cochlea functions showed a better agreement with experimental data at high frequencies above 3000 Hz than the Rayleigh-type damping. On this basis, a coupled finite element model consisting of the human ear and a piezoelectric actuator attached to the long process of incus was further constructed. Based on the electromechanical coupling analysis, equivalent sound pressure and power consumption of the actuator corresponding to viscoelasticity and Rayleigh damping were calculated using this model. The analytical results showed that the implant performance of the actuator evaluated using a finite element model considering viscoelastic properties gives a lower output above about 3 kHz than does Rayleigh damping model. Finite element model considering viscoelastic properties was more accurate to numerically evaluate implantable hearing devices. PMID:27276992
Žvátora, Pavel; Veverka, Miroslav; Veverka, Pavel; Knížek, Karel; Závěta, Karel; Pollert, Emil; Goglio, Graziella; Duguet, Etienne; Kaman, Ondřej
2013-08-15
Syntheses of nanocrystalline perovskite phases of the general formula La{sub 1−x}Sr{sub x}MnO{sub 3+δ} were carried out employing sol–gel technique followed by thermal treatment at 700–900 °C under oxygen flow. The prepared samples exhibit a rhombohedral structure with space group R3{sup ¯}c in the whole investigated range of composition 0.20≤x≤0.45. The studies were aimed at the chemical composition including oxygen stoichiometry and extrinsic properties, i.e. size of the particles, both influencing the resulting structural and magnetic properties. The oxygen stoichiometry was determined by chemical analysis revealing oxygen excess in most of the studied phases. The excess was particularly high for the samples with the smallest crystallites (12–28 nm) while comparative bulk materials showed moderate non-stoichiometry. These differences are tentatively attributed to the surface effects in view of the volume fraction occupied by the upper layer whose atomic composition does not comply with the ideal bulk stoichiometry. - Graphical abstract: Evolution of the particle size with annealing temperature in the nanocrystalline La{sub 0.70}Sr{sub 0.30}MnO{sub 3+δ} phase. Display Omitted - Highlights: • The magnetic behaviour of nanocrystalline La{sub 1−x}Sr{sub x}MnO{sub 3+δ} phases was analyzed on the basis of their crystal structure, chemical composition and size of the particles. • Their Curie temperature and magnetization are markedly affected by finite size and surface effects. • The oxygen excess observed in the La{sub 1−x}Sr{sub x}MnO{sub 3+δ} nanoparticles might be generated by the surface layer with deviated oxygen stoichiometry.
Equilibrium and non-equilibrium properties of finite-volume crystallites
NASA Astrophysics Data System (ADS)
Degawa, Masashi
Finite volume effects on equilibrium and non-equilibrium properties of nano-crystallites are studied theoretically and compared to both experiment and simulation. When a system is isolated or its size is small compared to the correlation length, all equilibrium and close-to-equilibrium properties will depend on the system boundary condition. Specifically for solid nano-crystallites, their finite size introduces global curvature to the system, which alters its equilibrium properties compared to the thermodynamic limit. Also such global curvature leads to capillary-induced morphology changes of the surface. Interesting dynamics can arise when the crystallite is supported on a substrate, with crossovers of the dominant driving force from the capillary force and crystallite-substrate interactions. To address these questions, we introduce thermodynamic functions for the boundary conditions, which can be derived from microscopic models. For nano-crystallites, the boundary is the surface (including interfaces), the thermodynamic description is based on the steps that define the shape of the surface, and the underlying microscopic model includes kinks. The global curvature of the surface introduces metastable states with different shapes governed by a constant of integration of the extra boundary condition, which we call the shape parameter c. The discrete height of the steps introduces transition states in between the metastable states, and the lowest energy accessible structure (energy barrier less 10k BT) as a function of the volume has been determined. The dynamics of nano-crystallites as they relax from a non-equilibrium structure is described quantitatively in terms of the motion of steps in both capillary-induced and interface-boundary-induced regimes. The step-edge fluctuations of the top facet are also influenced by global curvature and volume conservation and the effect yields different dynamic scaling exponents from a pure 1D system. Theoretical results are
2+1 flavor Polyakov Nambu Jona-Lasinio model at finite temperature and nonzero chemical potential
NASA Astrophysics Data System (ADS)
Fu, Wei-Jie; Zhang, Zhao; Liu, Yu-Xin
2008-01-01
We extend the Polyakov-loop improved Nambu Jona-Lasinio model to 2+1 flavor case to study the chiral and deconfinement transitions of strongly interacting matter at finite temperature and nonzero chemical potential. The Polyakov loop, the chiral susceptibility of light quarks (u and d), and the strange quark number susceptibility as functions of temperature at zero chemical potential are determined and compared with the recent results of lattice QCD simulations. We find that there is always an inflection point in the curve of strange quark number susceptibility accompanying the appearance of the deconfinement phase, which is consistent with the result of lattice QCD simulations. Predictions for the case at nonzero chemical potential and finite temperature are made as well. We give the phase diagram in terms of the chemical potential and temperature and find that the critical end point moves down to low temperature and finally disappears with the decrease of the strength of the ’t Hooft flavor-mixing interaction.
Shiomi, Masanori; Mori, Kenichiro; Osakada, Kozo
1995-12-31
Non-steady-state metal flow and temperature distribution in twin roll strip casting are simulated by the finite element method. In the present simulation, the viscoplastic finite element method is combined with that for heat conduction to calculate the metal flow and the temperature distribution during the casting process. The solid, mushy and liquid phases are assumed to be viscoplastic materials with individual flow stresses. In the temperature analysis, the latent heat due to solidification of the molten metal is taken into account by using the temperature recovery method. Since the metal flow and temperature distribution do not often attain to steady states, they are simulated by the stepwise calculation. To examine the accuracy of the calculated results, physical simulation of plane-strain twin roll strip casting is carried out by use of paraffin wax as a model material. The calculated profiles of the solid region agree qualitatively well with the experimental ones. Twin roll strip casting processes for stainless steel are also simulated. An optimum roll speed for obtaining a strip without a liquid zone under a minimum rolling load is obtained from the results of the simulation.
Material properties assignment to finite element models of bone structures: a new method.
Zannoni, C; Mantovani, R; Viceconti, M
1998-12-01
Finite element analysis (FEA) is widely adopted to investigate the mechanical behaviour of bone structures. Computed tomography (CT) data are frequently used to generate FE models of bone. If properly calibrated, CT images are capable of providing accurate information about the bone morphology and tissue density. The aim of this work was to develop a special program able to read a CT data set as well as the FEA mesh generated from it, and to assign to each element of the mesh the material properties derived from the bone tissue density at the element location. The program was tested on phantom data sets and was adopted to evaluate the effects of the discrete description of the bone material properties. A three-dimensional FE model was generated automatically from a 16 bit CT data set of a distal femur acquired in vivo. The strain energy density (SED) was evaluated for each model element for increasing model complexity (number of different material cards assigned to the model). The computed SED were strongly dependent on the material mapping strategy. PMID:10223642
Finite-difference time-domain studies of the optical properties of nanoshell dimers.
Oubre, C; Nordlander, P
2005-05-26
The optical properties of metallic nanoshell dimers are investigated using the finite difference time domain (FDTD) method. We discuss issues of numerical convergence specific for the dimer system. We present results for both homodimers and heterodimers. The results show that retardation effects must be taken into account for an accurate description of realistic size nanoparticle dimers. The optical properties of the nanoshell dimer are found to be strongly polarization dependent. Maximal coupling between the nanoshells in a dimer occurs when the electric field of the incident pulse is aligned parallel to the dimer axis. The wavelengths of the peaks in the extinction cross section of the dimer are shown to vary by more than 100 nm, depending on the incident electric field polarization. The calculations show that electric field enhancements in the dimer junctions depend strongly on dimer separation. The maximum field enhancements occur in the dimer junction and at the expense of a reduced electric field enhancement in other regions of space. We investigate the usefulness of nanoshell dimers substrates for SERS by integrating the fourth power of the electric field enhancements around the surfaces of the nanoparticles as a function of dimer separation and wavelength. The SERS efficiency is shown to depend strongly on dimer separation but much weaker than the fourth power of the maximum electric field enhancement at a particular point. The SERS efficiency is also found to depend strongly on the wavelength of the incident light. Maximum SERS efficiency occurs for resonant excitation of the dimer plasmons. PMID:16852215
Effects of Phase Lags on Three-Dimensional Wave Propagation with Temperature-Dependent Properties
NASA Astrophysics Data System (ADS)
Kalkal, Kapil Kumar; Deswal, Sunita
2014-05-01
A three-dimensional model of equations for a homogeneous and isotropic medium with temperature-dependent mechanical properties is established under the purview of two-phase-lag thermoelasticity theory. The modulus of elasticity is taken as a linear function of the reference temperature. The resulting non-dimensional coupled equations are applied to a specific problem of a half-space whose surface is traction-free and is subjected to a time-dependent thermal shock. The analytical expressions for the displacement component, stress, temperature field, and strain are obtained in the physical domain by employing normal mode analysis. These expressions are also calculated numerically for a copper-like material and depicted graphically. Discussions have been made to highlight the joint effects of the temperature-dependent modulus of elasticity and time on these physical fields. The phenomenon of a finite speed of propagation is observed graphically for each field.
Finite-Temperature Spin Dynamics in a Perturbed Quantum Critical Ising Chain with an E8 Symmetry
NASA Astrophysics Data System (ADS)
Wu, Jianda; Kormos, Márton; Si, Qimiao
2014-12-01
A spectrum exhibiting E8 symmetry is expected to arise when a small longitudinal field is introduced in the transverse-field Ising chain at its quantum critical point. Evidence for this spectrum has recently come from neutron scattering measurements in cobalt niobate, a quasi-one-dimensional Ising ferromagnet. Unlike its zero-temperature counterpart, the finite-temperature dynamics of the model has not yet been determined. We study the dynamical spin structure factor of the model at low frequencies and nonzero temperatures, using the form factor method. Its frequency dependence is singular, but differs from the diffusion form. The temperature dependence of the nuclear magnetic resonance (NMR) relaxation rate has an activated form, whose prefactor we also determine. We propose NMR experiments as a means to further test the applicability of the E8 description for CoNb2O6 .
NASA Astrophysics Data System (ADS)
Danchev, Daniel M.; Tonchev, Nicholay S.
1999-10-01
The behaviour of the finite-temperature C-function, defined by Neto and Fradkin (1993 Nucl. Phys. B 400 525), is analysed within a d -dimensional exactly solvable lattice model, recently considered by Vojta (1996 Phys. Rev. B 53 710), which is of the same universality class as the quantum nonlinear O(n) sigma model in the limit nicons/Journals/Common/rightarrow" ALT="rightarrow" ALIGN="TOP"/>icons/Journals/Common/infty" ALT="infty" ALIGN="TOP"/>. The scaling functions of C for the cases d = 1 (absence of long-range order), d = 2 (existence of a quantum critical point), d = 4 (existence of a line of finite-temperature critical points that ends up with a quantum critical point) are derived and analysed. The locations of regions where C is monotonically increasing (which depend significantly on d) are exactly determined. The results are interpreted within the finite-size scaling theory that has to be modified for d = 4.
NASA Astrophysics Data System (ADS)
Li, Dian-Sen; Fang, Dai-Ning; Lu, Zi-Xing; Yang, Zhen-Yu; Jiang, Nan
2010-08-01
In the first part of the work, we have established a new parameterized three-dimensional (3D) finite element model (FEM) which precisely simulated the spatial configuration of the braiding yarns and considered the cross-section deformation as well as the surface contact relationship between the yarns. This paper presents a prediction of the effective elastic properties and the meso-scale mechanical response of 3D braided composites to verify the validation of the FEM. The effects of the braiding parameters on the mechanical properties are investigated in detail. By analyzing the deformation and stress nephogram of the model, a reasonable overall stress field is provided and the results well support the strength prediction. The results indicate it is convenient to predict all the elastic constants of 3D braided composites with different parameters simultaneously using the FEM. Moreover, the FEM can successfully predict the meso-scale mechanical response of 3D braided composites containing periodical structures.
ERIC Educational Resources Information Center
Song, Hairong; Ferrer, Emilio
2009-01-01
This article presents a state-space modeling (SSM) technique for fitting process factor analysis models directly to raw data. The Kalman smoother via the expectation-maximization algorithm to obtain maximum likelihood parameter estimates is used. To examine the finite sample properties of the estimates in SSM when common factors are involved, a…
Polyurethane adhesive with improved high temperature properties
NASA Technical Reports Server (NTRS)
Stuckey, J. M.
1977-01-01
A polyurethane resin with paste activator, capable of providing useful bond strengths over the temperature range of -184 C to 149 C, is described. The adhesive system has a pot life of over one hour. Tensile shear strength ratings are given for various adhesive formulations.
NASA Astrophysics Data System (ADS)
Kormos, Márton; Wu, Jianda; Si, Qimiao
2014-03-01
When the transverse-field Ising chain at its quantum critical point is subjected to a small longitudinal field, the perturbed conformal field theory led to a field theory with an exotic E8 symmetry. Recent neutron scattering experiments have provided evidence for the lightest two particles in this E8 model in the quasi-1D Ising ferromagnet CoNb2O6. While the zero temperature dynamic of the model is well known, its finite-temperature counterpart has not yet been systematically studied. We study the low-frequency dynamical spin structure factor at finite temperatures using the form-factor method. We show that the dominant contribution to the spin dynamics comes from the channel between two lightest particles, and demonstrate how the spin dynamics differ from a diffusion form. Using these results, we determine the temperature dependence of the NMR relaxation rate. We suggest that, for CoNb2O6, measurements of the NMR relaxation rate provide a means to further test the applicability of the E8 model.
Temperature dependent terahertz properties of energetic materials
NASA Astrophysics Data System (ADS)
Azad, Abul K.; Whitley, Von H.; Brown, Kathryn E.; Ahmed, Towfiq; Sorensen, Christian J.; Moore, David S.
2016-04-01
Reliable detection of energetic materials is still a formidable challenge which requires further investigation. The remote standoff detection of explosives using molecular fingerprints in the terahertz spectral range has been an evolving research area for the past two decades. Despite many efforts, identification of a particular explosive remains difficult as the spectral fingerprints often shift due to the working conditions of the sample such as temperature, crystal orientation, presence of binders, etc. In this work, we investigate the vibrational spectrum of energetic materials including RDX, PETN, AN, and 1,3-DNB diluted in a low loss PTFE host medium using terahertz time domain spectroscopy (THz-TDS) at cryogenic temperatures. The measured absorptions of these materials show spectral shifts of their characteristic peaks while changing their operating temperature from 300 to 7.5 K. We have developed a theoretical model based on first principles methods, which is able to predict most of the measured modes in 1, 3-DNB between 0.3 to 2.50 THz. These findings may further improve the security screening of explosives.
Low temperature properties of boron carbides
NASA Astrophysics Data System (ADS)
de Rooy, J. C. J. M.; Reefman, D.; van der Putten, D.; Brom, H. B.; Aselage, T.; Emin, D.
1991-07-01
We have investigated boron carbides, B1-xCx with x=0.1, 0.13, and 0.2, especially below 1 K. The samples were characterized by ESR. The integrated intensities are roughly sample independent and correspond to about 1020 spins per gram. The temperature (T) dependences are Curie like. The line shapes were lorentzian and for x=0.1 and 0.13 are strongly temperature dependent, which is suggestive for a coupling of linewidths and charge carriers. The room temperature linewidths are 0.38 mT, 32.6 mT, and 23.5 mT for resp. x=0.2, 0.13 and 0.1. Also the AC susceptibility (χ) measured down to 100 mK points to a similar small number spins. There is no sign of a Pauli susceptibility within experimental error. No phase transition (e.g., to a superconducting state) is observed. For x=0.13 and 0.1 a very small specific heat, C is seen. The T dependence of C can be described by a Tα plus a small cubic term, α about 0.26. The relation between C and χ can be explained with a random exchange model. The C-value for x=0.2 is below the limit of our experimental accuracy.
Electrical properties of teflon and ceramic capacitors at high temperatures
NASA Technical Reports Server (NTRS)
Hammoud, A. N.; Baumann, E. D.; Myers, I. T.; Overton, E.
1992-01-01
Space power systems and components are often required to operate efficiently and reliably in harsh environments where stresses, such as high temperature, are encountered. These systems must, therefore, withstand exposure to high temperature while still providing good electrical and other functional properties. Experiments were carried out to evaluate Teflon and ceramic capacitors for potential use in high temperature applications. The capacitors were characterized in terms of their capacitance and dielectric loss as a function of temperature, up to 200 C. At a given temperature, these properties were obtained in a frequency range of 50 Hz to 100 kHz. DC leakage current measurements were also performed in a temperature range from 25 to 200 C. The results obtained are discussed and conclusions are made concerning the suitability of the capacitors studied for high temperature applications.
Finite temperature effect in infrared-improved AdS/QCD model with back reaction of bulk vacuum
NASA Astrophysics Data System (ADS)
Cui, Ling-Xiao; Fang, Zhen; Wu, Yue-Liang
2016-06-01
Based on an IR-improved soft-wall AdS/QCD model for mesons, which provides a consistent prediction for the mass spectra of resonance scalar, pseudoscalar, vector and axial-vector mesons, we investigate its finite temperature effect. By analyzing the spectral function of mesons and fitting it with a Breit-Wigner form, we perform an analysis for the critical temperature of mesons. The back-reaction effects of bulk vacuum are considered and the thermal mass spectral function of resonance mesons is calculated based on the back-reaction improved action. A reasonable melting temperature is found to be T c ≈ 150 ± 7 MeV, which is consistent with the recent results from lattice QCD simulations. Supported by National Nature Science Foundation of China (NSFC)(10975170, 10905084, 10821504), and Project of Knowledge Innovation Program (PKIP) of Chinese Academy of Science
Drummond, Liana; Sun, Da-Wen
2008-11-01
A finite difference model was developed to describe and predict the temperature and mass loss evolution in reconstructed beef joints during immersion vacuum cooling. Fast cooling is obtained within beef pores and at beef surface when evaporation in the surrounding liquid is high. The cooling rate diminishes as the vacuum chamber pressure stabilizes and the liquid temperature reaches its lower value. The maximum deviation between measured and calculated temperatures was within 5°C for the beef (core and surface) and within 7°C for the surrounding liquid (measured at the bottom of the container). Absolute differences between predicted and experimental mass losses for the liquid and beef sample were around 2% and 1%, respectively. Mass losses are higher during the first period when evaporation is the main mode of heat transfer. Mechanical agitation in the surrounding liquid is suggested as a way to further reduce cooling times and to prevent uneven cooling. PMID:22063613
NASA Astrophysics Data System (ADS)
Ashhab, Sahel
2015-03-01
The Landau-Zener (LZ) problem is a standard paradigm for studying energy transfer and adiabatic passage protocols. We consider the LZ problem for a two level system when this system interacts with one harmonic oscillator mode that is initially set to a finite-temperature thermal equilibrium state. The oscillator could represent an external mode that is strongly coupled to the system, e.g. an ionic oscillation mode in a molecule, or it could represent a prototypical uncontrolled environment. We analyze the system's occupation probabilities at the final time in a number of different regimes, varying the system and oscillator frequencies, their coupling strength and the temperature. In particular we find some surprising non-monotonic dependence on the coupling strength and temperature.
Shim, Sang Hoon; Jang, Jae-il; Pharr, George Mathews
2008-01-01
A method is presented for estimating the plastic flow behavior of single crystal silicon carbide by nanoindentation experiments using a series of triangular pyramidal indenters with different centerline-to-face angles (35.3?to 75?in this work) in combination with 2-dimensional axisymmetric finite element (FE) simulations. The method is based on Tabor's concepts of characteristic strain, e_char, and constraint factor, C_q, which allow indentation hardness values obtained with indenters of different angles to be related to the flow properties of the indented material. The procedure utilizes FE simulations applied in an iterative manner in order to establish the yield strength and work hardening exponent from the experimentally measured dependence of the hardness on indenter angle. The methodology is applied to a hard, brittle ceramic material, 6H SiC, whose flow behavior cannot be determined by conventional tension or compression testing. It is shown that the friction between the indenter and the material plays a significant role, especially for very sharp indenters.
Abbasi, Mostafa; Barakat, Mohammed S; Vahidkhah, Koohyar; Azadani, Ali N
2016-09-01
Computational modeling has an important role in design and assessment of medical devices. In computational simulations, considering accurate constitutive models is of the utmost importance to capture mechanical response of soft tissue and biomedical materials under physiological loading conditions. Lack of comprehensive three-dimensional constitutive models for soft tissue limits the effectiveness of computational modeling in research and development of medical devices. The aim of this study was to use inverse finite element (FE) analysis to determine three-dimensional mechanical properties of bovine pericardial leaflets of a surgical bioprosthesis under dynamic loading condition. Using inverse parameter estimation, 3D anisotropic Fung model parameters were estimated for the leaflets. The FE simulations were validated using experimental in-vitro measurements, and the impact of different constitutive material models was investigated on leaflet stress distribution. The results of this study showed that the anisotropic Fung model accurately simulated the leaflet deformation and coaptation during valve opening and closing. During systole, the peak stress reached to 3.17MPa at the leaflet boundary while during diastole high stress regions were primarily observed in the commissures with the peak stress of 1.17MPa. In addition, the Rayleigh damping coefficient that was introduced to FE simulations to simulate viscous damping effects of surrounding fluid was determined. PMID:27173827
Kim, Jeongnim; Reboredo, Fernando A
2014-01-01
The self-healing diffusion Monte Carlo method for complex functions [F. A. Reboredo J. Chem. Phys. {\\bf 136}, 204101 (2012)] and some ideas of the correlation function Monte Carlo approach [D. M. Ceperley and B. Bernu, J. Chem. Phys. {\\bf 89}, 6316 (1988)] are blended to obtain a method for the calculation of thermodynamic properties of many-body systems at low temperatures. In order to allow the evolution in imaginary time to describe the density matrix, we remove the fixed-node restriction using complex antisymmetric trial wave functions. A statistical method is derived for the calculation of finite temperature properties of many-body systems near the ground state. In the process we also obtain a parallel algorithm that optimizes the many-body basis of a small subspace of the many-body Hilbert space. This small subspace is optimized to have maximum overlap with the one expanded by the lower energy eigenstates of a many-body Hamiltonian. We show in a model system that the Helmholtz free energy is minimized within this subspace as the iteration number increases. We show that the subspace expanded by the small basis systematically converges towards the subspace expanded by the lowest energy eigenstates. Possible applications of this method to calculate the thermodynamic properties of many-body systems near the ground state are discussed. The resulting basis can be also used to accelerate the calculation of the ground or excited states with Quantum Monte Carlo.
NASA Astrophysics Data System (ADS)
Dave, Eshan V.
Asphalt concrete pavements are inherently graded viscoelastic structures. Oxidative aging of asphalt binder and temperature cycling due to climatic conditions being the major cause of non-homogeneity. Current pavement analysis and simulation procedures dwell on the use of layered approach to account for these non-homogeneities. The conventional finite-element modeling (FEM) technique discretizes the problem domain into smaller elements, each with a unique constitutive property. However the assignment of unique material property description to an element in the FEM approach makes it an unattractive choice for simulation of problems with material non-homogeneities. Specialized elements such as "graded elements" allow for non-homogenous material property definitions within an element. This dissertation describes the development of graded viscoelastic finite element analysis method and its application for analysis of asphalt concrete pavements. Results show that the present research improves efficiency and accuracy of simulations for asphalt pavement systems. Some of the practical implications of this work include the new technique's capability for accurate analysis and design of asphalt pavements and overlay systems and for the determination of pavement performance with varying climatic conditions and amount of in-service age. Other application areas include simulation of functionally graded fiber-reinforced concrete, geotechnical materials, metal and metal composites at high temperatures, polymers, and several other naturally existing and engineered materials.
Thermodynamic properties of UF6 at high temperatures
NASA Technical Reports Server (NTRS)
Hassan, H. A.; Deese, J. E.
1974-01-01
The equilibrium composition and the thermodynamic properties of the mixture resulting from the decomposition of uranium hexafluoride is calculated for temperatures ranging from 600 K to 4000 K at pressures from 0.01 atmospheres to 10 atmospheres.
Susan, Anju; Joshi, Kavita
2014-04-21
Melting in finite size systems is an interesting but complex phenomenon. Many factors affect melting and owing to their interdependencies it is a challenging task to rationalize their roles in the phase transition. In this work, we demonstrate how structural motif of the ground state influences melting transition in small clusters. Here, we report a case with clusters of aluminum and gallium having same number of atoms, valence electrons, and similar structural motif of the ground state but drastically different melting temperatures. We have employed Born-Oppenheimer molecular dynamics to simulate the solid-like to liquid-like transition in these clusters. Our simulations have reproduced the experimental trends fairly well. Further, the detailed analysis of isomers has brought out the role of the ground state structure and underlying electronic structure in the finite temperature behavior of these clusters. For both clusters, isomers accessible before cluster melts have striking similarities and does have strong influence of the structural motif of the ground state. Further, the shape of the heat capacity curve is similar in both the cases but the transition is more spread over for Al{sub 36} which is consistent with the observed isomerization pattern. Our simulations also suggest a way to characterize transition region on the basis of accessibility of the ground state at a specific temperature.
Shape memory polymers with high and low temperature resistant properties
Xiao, Xinli; Kong, Deyan; Qiu, Xueying; Zhang, Wenbo; Liu, Yanju; Zhang, Shen; Zhang, Fenghua; Hu, Yang; Leng, Jinsong
2015-01-01
High temperature shape memory polymers that can withstand the harsh temperatures for durable applications are synthesized, and the aromatic polyimide chains with flexible linkages within the backbone act as reversible phase. High molecular weight (Mn) is demanded to form physical crosslinks as fixed phase of thermoplastic shape memory polyimide, and the relationship between Mn and glass transition temperature (Tg) is explored. Thermoset shape memory polyimide shows higher Tg and storage modulus, better shape fixity than thermoplastic counterpart due to the low-density covalent crosslinking, and the influence of crosslinking on physical properties are studied. The mechanism of high temperature shape memory effects based on chain flexibility, molecular weight and crosslink density is proposed. Exposure to thermal cycling from +150 °C to −150 °C for 200 h produces negligible effect on the properties of the shape memory polyimide, and the possible mechanism of high and low temperature resistant property is discussed. PMID:26382318
Shape memory polymers with high and low temperature resistant properties
NASA Astrophysics Data System (ADS)
Xiao, Xinli; Kong, Deyan; Qiu, Xueying; Zhang, Wenbo; Liu, Yanju; Zhang, Shen; Zhang, Fenghua; Hu, Yang; Leng, Jinsong
2015-09-01
High temperature shape memory polymers that can withstand the harsh temperatures for durable applications are synthesized, and the aromatic polyimide chains with flexible linkages within the backbone act as reversible phase. High molecular weight (Mn) is demanded to form physical crosslinks as fixed phase of thermoplastic shape memory polyimide, and the relationship between Mn and glass transition temperature (Tg) is explored. Thermoset shape memory polyimide shows higher Tg and storage modulus, better shape fixity than thermoplastic counterpart due to the low-density covalent crosslinking, and the influence of crosslinking on physical properties are studied. The mechanism of high temperature shape memory effects based on chain flexibility, molecular weight and crosslink density is proposed. Exposure to thermal cycling from +150 °C to -150 °C for 200 h produces negligible effect on the properties of the shape memory polyimide, and the possible mechanism of high and low temperature resistant property is discussed.
NASA Technical Reports Server (NTRS)
Tauchert, T. R.
1976-01-01
Rayleigh-Ritz and modified Rayleigh-Ritz procedures are used to construct approximate solutions for the response of a thick-walled sphere to uniform pressure loads and an arbitrary radial temperature distribution. The thermoelastic properties of the sphere are assumed to be transversely isotropic and nonhomogeneous; variations in the elastic stiffness and thermal expansion coefficients are taken to be an arbitrary function of the radial coordinate and temperature. Numerical examples are presented which illustrate the effect of the temperature-dependence upon the thermal stress field. A comparison of the approximate solutions with a finite element analysis indicates that Ritz methods offer a simple, efficient, and relatively accurate approach to the problem.
Correlation functions of the energy-momentum tensor in SU(2) gauge theory at finite temperature
Huebner, K.; Pica, C.; Karsch, F.
2008-11-01
We calculate correlation functions of the energy-momentum tensor in the vicinity of the deconfinement phase transition of (3+1)-dimensional SU(2) gauge theory and discuss their critical behavior in the vicinity of the second order deconfinement transition. We show that correlation functions of the trace of the energy-momentum tensor diverge uniformly at the critical point in proportion to the specific heat singularity. Correlation functions of the pressure, on the other hand, stay finite at the critical point. We discuss the consequences of these findings for the analysis of transport coefficients, in particular, the bulk viscosity, in the vicinity of a second order phase transition point.
Containerless high temperature property measurements by atomic fluorescence
NASA Technical Reports Server (NTRS)
Schiffman, R. A.; Walker, C. A.
1984-01-01
Laser induced fluorescence (LIF) techniques for containerless study of high temperature processes and material properties was studied. Gas jet and electromagnetic levitation and electromagnetic and laser heating techniques are used with LIF in earth-based containerless high temperature experiments. Included are the development of an apparatus and its use in the studies of (1) chemical reactions on Al2O3, molybdenum, tungsten and LaB6 specimens, (2) methods for noncontact specimen temperature measurement, (3) levitation jet properties and (4) radiative lifetime and collisional energy transfer rates for electronically excited atoms.
Containerless high temperature property measurements by atomic fluorescence
NASA Technical Reports Server (NTRS)
1983-01-01
The use of laser induced fluorescence (LIF) techniques for containerless study of high temperature processes and material properties is studied. Gas jet and electromagnetic levitation and electromagnetic and laser heating techniques are used with LIF in Earth-based containerless high temperature experiments. The work to date includes development of an apparatus and its use in studies of chemical reactions on Al2O3, molybdenum, and tungsten specimens, novel methods for noncontact specimen temperature measurement, and levitation jet properties. Brief summaries of these studies are given. The apparatus is described and detailed results for the current reporting period are presented.
Temperature-dependent elastic properties of Ti1-xAlxN alloys
NASA Astrophysics Data System (ADS)
Shulumba, Nina; Hellman, Olle; Rogström, Lina; Raza, Zamaan; Tasnádi, Ferenc; Abrikosov, Igor A.; Odén, Magnus
2015-12-01
Ti1-xAlxN is a technologically important alloy that undergoes a process of high temperature age-hardening that is strongly influenced by its elastic properties. We have performed first principles calculations of the elastic constants and anisotropy using the symmetry imposed force constant temperature dependent effective potential method, which include lattice vibrations and therefore the effects of temperature, including thermal expansion and intrinsic anharmonicity. These are compared with in situ high temperature x-ray diffraction measurements of the lattice parameter. We show that anharmonic effects are crucial to the recovery of finite temperature elasticity. The effects of thermal expansion and intrinsic anharmonicity on the elastic constants are of the same order, and cannot be considered separately. Furthermore, the effect of thermal expansion on elastic constants is such that the volume change induced by zero point motion has a significant effect. For TiAlN, the elastic constants soften non-uniformly with temperature: C11 decreases substantially when the temperature increases for all compositions, resulting in an increased anisotropy. These findings suggest that an increased Al content and annealing at higher temperatures will result in a harder alloy.
Ferrario, Lorenzo; Little, Justin M. Choueiri, Edgar Y.
2014-11-15
The plasma flow in a finite-electron-temperature magnetic nozzle, under the influence of an applied azimuthal current at the throat, is modeled analytically to assess its propulsive performance. A correction to the nozzle throat boundary conditions is derived by modifying the radial equilibrium of a magnetized infinite two-population cylindrical plasma column with the insertion of an external azimuthal body force for the electrons. Inclusion of finite-temperature effects, which leads to a modification of the radial density profile, is necessary for calculating the propulsive performance, which is represented by nozzle divergence efficiency and thrust coefficient. The solutions show that the application of the azimuthal current enhances all the calculated performance parameters through the narrowing of the radial density profile at the throat, and that investing power in this beam focusing effect is more effective than using the same power to pre-heat the electrons. The results open the possibility for the design of a focusing stage between the plasma source and the nozzle that can significantly enhance the propulsive performance of electron-driven magnetic nozzles.
Phase lamination in a t-J bilayer at finite temperature
NASA Astrophysics Data System (ADS)
Voo, Khee-Kyun
2016-05-01
A bilayered t- J model is investigated with a slave boson mean field theory. A spontaneous phase lamination (PL) into a layer dominated by antiferromagnetism (AFM) and a layer dominated by superconductivity (SC) is found at a low doping density and low temperature regime. Raising the temperature removes the PL and SC, turns the system into a homogeneously antiferromagnetic (AF) bilayer, and eventually a homogeneously paramagnetic bilayer at high temperature. The PL circumvents the competition between AFM and SC, and may result in a higher superconducting transition temperature. The density of states of low energy single particle excitation in the homogeneously AF state at intermediate temperature is reduced by the AF scattering. The relation between this study and the bilayered superconducting cuprates is discussed.
Tan, L B; Webb, D C; Kormi, K; Al-Hassani, S T
2001-03-01
The proliferation of stent designs poses difficult problems to clinicians, who have to learn the relative merits of all stents to ensure optimal selection for each lesion, and also to regulatory authorities who have the dilemma of preventing the inappropriate marketing of substandard stents while not denying patients the benefits of advanced technology. Of the major factors influencing long-term results, those of patency and restenosis are being actively studied whereas the mechanical characteristics of devices influencing the technical results of stenting remain under-investigated. Each different stent design has its own particular features. A robust method for the independent objective comparison of the mechanical performance of each design is required. To do this by experimental measurement alone may be prohibitively expensive. A less costly option is to combine computer analysis, employing the standard numerical technique of the finite element method (FEM), with targeted experimental measurements of the specific mechanical behaviour of stents. In this paper the FEM technique is used to investigate the structural behaviour of two different stent geometries: Freedom stent geometry and Palmaz-Schatz (P-S) stent geometry. The effects of altering the stent geometry, the stent wire diameter and contact with (and material properties of) a hard eccentric intravascular lesion (simulating a calcified plaque) on stent mechanical performance were investigated. Increasing the wire diameter and the arterial elastic modulus by 150% results in the need to increase the balloon pressure to expand the stent by 10-fold. Increasing the number of circumferential convolutions increases the pressure required to initiate radial expansion of mounted stents. An incompressible plaque impinging on the mid portion of a stent causes a gross distortion of the Freedom stent and an hour-glass deformity in the P-S stent. These findings are of relevance for future comparative studies of the
NASA Technical Reports Server (NTRS)
Troy, B. E., Jr.; Maier, E. J.
1973-01-01
The analysis of ion data from retarding potential analyzers (RPA's) is generally done under the planar approximation, which assumes that the grid transparency is constant with angle of incidence and that all ions reaching the plane of the collectors are collected. These approximations are not valid for situations in which the ion thermal velocity is comparable to the vehicle velocity, causing ions to enter the RPA with high average transverse velocity. To investigate these effects, the current-voltage curves for H+ at 4000 K were calculated, taking into account the finite collector size and the variation of grid transparency with angle. These curves are then analyzed under the planar approximation. The results show that only small errors in temperature and density are introduced for an RPA with typical dimensions; and that even when the density error is substantial for non-typical dimensions, the temperature error remains minimal.
Dynamical simulations of QCD at finite temperature with a truncated perfect action
NASA Astrophysics Data System (ADS)
Shcheredin, Stanislav
2006-12-01
The Hypercube operator determines a variant of the approximate, truncated perfect fermion ac- tion. In this pilot study we are going to report on first experiences in dynamical QCD simulations with the Hypercube fermions. We apply this formulation in an investigation of the finite tempera- ture transition for two flavours. On lattices of size 83 × 4 we explore the phase diagram. Physical scales are estimated from pseudoscalar and vector meson masses obtained on 83 × 16 lattices. We observe the presence of a metastability region but do not find evidence for an Aoki phase. The Hypercube operator allows us to simulate at ratios of pseudoscalar to vector meson masses at least as small as 0.8 at the thermal crossover at Nt = 4, which renders this formulation cheaper than the Wilson like fermions.
Ruderman-Kittel-Kasuya-Yosida interaction at finite temperature: Graphene and bilayer graphene
NASA Astrophysics Data System (ADS)
Klier, N.; Shallcross, S.; Sharma, S.; Pankratov, O.
2015-11-01
We investigate the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between magnetic impurities in both single layer and Bernal stacked bilayer graphene, finding a number of striking anomalies in the temperature dependence of this interaction. In undoped single layer graphene the strength of the RKKY interaction for substitutional impurities anomalously increases upon increasing temperature, an effect that persists up to and beyond room temperature. For impurities intercalated in the Bernal stacked bilayer and a doping that places the chemical potential near the antibonding band edge, a qualitative change of the RKKY interaction with temperature occurs: a low-temperature oscillatory interaction develops into a high-temperature antiferromagnetic coupling, accompanied by an overall increase of the interaction strength. The origin of the temperature anomalies can be traced back to specific features of the density of states: the vanishing density of states at the apex of the Dirac cone in single layer graphene, and the "kink" in the density of states at the antibonding band edge in the case of the Bernal bilayer.
NASA Astrophysics Data System (ADS)
Mozafari, E.; Shulumba, N.; Steneteg, P.; Alling, B.; Abrikosov, Igor A.
2016-08-01
We present a theoretical scheme to calculate the elastic constants of magnetic materials in the high-temperature paramagnetic state. Our approach is based on a combination of disordered local moments picture and ab initio molecular dynamics (DLM-MD). Moreover, we investigate a possibility to enhance the efficiency of the simulations of elastic properties using the recently introduced method: symmetry imposed force constant temperature-dependent effective potential (SIFC-TDEP). We have chosen cubic paramagnetic CrN as a model system. This is done due to its technological importance and its demonstrated strong coupling between magnetic and lattice degrees of freedom. We have studied the temperature-dependent single-crystal and polycrystalline elastic constants of paramagentic CrN up to 1200 K. The obtained results at T = 300 K agree well with the experimental values of polycrystalline elastic constants as well as the Poisson ratio at room temperature. We observe that the Young's modulus is strongly dependent on temperature, decreasing by ˜14 % from T = 300 K to 1200 K. In addition we have studied the elastic anisotropy of CrN as a function of temperature and we observe that CrN becomes substantially more isotropic as the temperature increases. We demonstrate that the use of Birch law may lead to substantial errors for calculations of temperature induced changes of elastic moduli. The proposed methodology can be used for accurate predictions of mechanical properties of magnetic materials at temperatures above their magnetic order-disorder phase transition.
Implication-based fuzzy semiautomaton of a finite group and its properties
NASA Astrophysics Data System (ADS)
Selva Rathi, M.; Michael Anna Spinneli, J.
2016-06-01
Implication-based fuzzy semiautomaton (IBFSA) of a finite group is defined. The ideas of an implication-based fuzzy kernel and implication-based fuzzy subsemiautomaton of an IBFSA over a finite group are developed using the concept of implication-based fuzzy subgroup and implication-based fuzzy normal subgroup. The necessary and sufficient condition for the implication-based fuzzy kernel and implication-based fuzzy subsemiautomaton of an IBFSA and few other results are proved in this paper.
Sedlacik, Michal; Pavlinek, Vladimir; Peer, Petra; Filip, Petr
2014-05-14
Magnetic nanoparticles of spinel nanocrystalline cobalt ferrite were synthesized via the sol-gel method and subsequent annealing. The influence of the annealing temperature on the structure, magnetic properties, and magnetorheological effect was investigated. The finite crystallite size of the particles, determined by X-ray diffraction and the particle size observed via transmission electron microscopy, increased with the annealing temperature. The magnetic properties observed via a vibrating sample magnetometer showed that an increase in the annealing temperature leads to the increase in the magnetization saturation and, in contrast, a decrease in the coercivity. The effect of annealing on the magnetic properties of ferrite particles has been explained by the recrystallization process at high temperatures. This resulted in grain size growth and a decrease in an imposed stress relating to defects in the crystal lattice structure of the nanoparticles. The magnetorheological characteristics of suspensions of ferrite particles in silicone oil were measured using a rotational rheometer equipped with a magnetic field generator in both steady shear and small-strain oscillatory regimes. The magnetorheological performance expressed as a relative increase in the magnetoviscosity appeared to be significantly higher for suspensions of particles annealed at 1000 °C. PMID:24668306
Temperature dependence of optical properties of GaAs
NASA Technical Reports Server (NTRS)
Yao, Huade; Snyder, Paul G.; Woollam, John A.
1991-01-01
The effect of temperature on the optical properties of GaAs was investigated using spectroscopic ellipsometry measurements, between room temperature and about 610 C in increments of 50 C, of pseudodielectric functions and related optical constants of GaAs. A quantitative analysis of the pseudodielectric function spectrum was carried out using a harmonic-oscillator approximation (HOA) to fit the measured dielectric functions. Good fits were obtained with this model, which provides a convenient means of reproducing the GaAs dielectric function at any temperature, by using the temperature-dependent oscillator parameters. The HOA analysis also provides information about band-gap variation with temperature. Using the measured optical constants at a number of fixed temperatures, an algorithm was developed for computing the dielectric function spectrum at an arbitrary temperature in the range 22-610 C.
NASA Astrophysics Data System (ADS)
Xu, Xing-Lei; Xu, Shi-Min; Li, Hong-Qi
2008-06-01
The quantization of mesoscopic damped circuit involving capacitance-inductance coupling is proposed by the method of thrice linear transformation and damped harmonic oscillator quantization. The quantum fluctuations of the charges and current of each loop are calculated by thermo-field dynamics (TFD) in thermal vacuum state, thermal coherent state and thermal squeezed state, respectively. It is shown that the quantum fluctuations of the charges and current not only depend on circuit inherent parameter and coupled magnitude, but also rely on squeezed coefficients, squeezed angle, environmental temperature and damped resistance. And, because of influence of environmental temperature and damped resistance, the quantum fluctuations increase with increasing temperature and decrease with prolonging time.
Majka, Z.; Staszel, P.; Cibor, J.; Natowitz, J.B.; Hagel, K.; Li, J.; Mdeiwayeh, N.; Wada, R.; Zhao, Y.
1997-06-01
We investigate the importance of the quantum statistics and deexcitation of primary fragments on the isotope yield ratio temperature determination. A phenomenological formula is presented which allows derivation of the temperature of the decaying nuclear system at the freeze-out time from the measured double yield ratios of two isotope pairs. This prescription is applied to the recent ALADIN and EOS Collaboration data. {copyright} {ital 1997} {ital The American Physical Society}
Deconfinement and hadron properties at extremes of temperature and density
Blaschke, D.; Roberts, C.D.
1998-08-01
After introducing essential, qualitative concepts and results, the authors discuss the application of Dyson-Schwinger equations to QCD at finite T and {mu}. They summarize the calculation of the critical exponents of two-light-flavor QCD using the chiral and thermal susceptibilities; and an algebraic model that elucidates the origin of an anticorrelation between the {mu}- and T-dependence of a range of meson properties. That model also provides an algebraic understanding of why the finite-T behavior of bulk thermodynamic properties is mirrored in their {mu}-dependence, and why meson masses decrease with {mu} even though f{sub {pi}} and {minus}<{anti q}q> increase. The possibility of diquark condensation is canvassed. Its realization is uncertain because it is contingent upon an assumption abut the quark-quark scattering kernel that is demonstrably false in some applications; e.g., it predicts the existence of colored diquarks in the strong interaction spectrum, which are not observed.
Containerless high temperature property measurements by atomic fluorescence
NASA Technical Reports Server (NTRS)
Nordine, Paul C.; Shiffman, Robert A.
1987-01-01
Containerless high temperature processing and material property measurements are discussed. Researchers developed methods for non-contact suspension, heating, and property measurement for materials at temperatures up to 3,680K, the melting point of tungsten. New, scientifically interesting results were obtained in Earth-based research. These results and the demonstration of new methods and techniques form a basis for further advances under the low gravity environment of space where containerless conditions are more easily achieved. Containerless high temperature material property investigations that have been completed in this and our earlier projects include measurements of fluorine LaB sub 6 reaction kinetics at 1,000 to 1,500K; optical property measurements on sapphire (Al2O3) at temperatures up to the melting point (2,327K); and vapor pressure measurements for LaB sub 6 at 2,000 to 2,500K, for molybdenum up to 2,890K and for tungsten up to 3,680K. Gas jet levitation which is applicable to any solid material, and electromagnetic levitation of electrical conductors were used to suspend the materials of interest. Non-contact heating and property measurements were achieved by optical techniques, i.e., laser heating, laser induced fluorescence measurements of vapor concentrations, and optical pyrometry for specimen temperatures.
Temperature-Dependent Dielectric Properties of Al/Epoxy Nanocomposites
NASA Astrophysics Data System (ADS)
Wang, Zijun; Zhou, Wenying; Sui, Xuezhen; Dong, Lina; Cai, Huiwu; Zuo, Jing; Chen, Qingguo
2016-01-01
Broadband dielectric spectroscopy was carried out to study the transition in electrical properties of Al/epoxy nanocomposites over the frequency range of 1-107 Hz and the temperature range of -20°C to 200°C. The dielectric permittivity, dissipation factor, and electrical conductivity of the nanocomposites increased with temperature and showed an abrupt increase around the glass transition temperature (T g). The results clearly reveal an interesting transition of the electrical properties with increasing temperature: insulator below 70°C, conductor at about 70°C. The behavior of the transition in electrical properties of the nanocomposites was explored at different temperatures. The presence of relaxation peaks in the loss tangent and electric modulus spectra of the nanocomposites confirms that the chain segmental dynamics of the polymer is accompanied by the absorption of energy given to the system. It is suggested that the temperature-dependent transition of the electric properties in the nanocomposite is closely associated with the α-relaxation. The large increase in the dissipation factor and electric conductivity depends on the direct current conduction of thermally activated charge carriers resulting from the epoxy matrix above T g.
Challenges in Characterizing Low-Temperature Regolith Properties
NASA Technical Reports Server (NTRS)
Swanger, Adam Michael; Mantovani, James G.
2014-01-01
The success or failure of in-situ resource utilization for planetary surface exploration--be it for scientific, colonization or commercialization purposes--relies heavily on the ability to design and implement systems which effectively process the associated regolith and exploit its benefits. In most cases this challenge necessarily includes the characterization of low-temperature (cryogenic) properties; as many celestial destinations of interest, such as the moon, Mars and asteroids, have little or no atmosphere to help sustain the consistently "high" surface temperatures seen on planets such as Earth, and therefore can experience permanent cryogenic temperatures or dramatic cyclical changes. Characterization of physical properties (such as specific heat, thermal and electrical conductivity, etc.) over the entire temperature profile is undoubtedly an important piece of the puzzle; however, the impact on mechanical properties due to the introduction of icy deposit must also be explored in order to devise effective and robust excavation technologies. Currently the Granular Mechanics and Regolith Operations Lab and the Cryogenics Test Lab at NASA Kennedy Space Center are developing technologies and experimental methods to address these challenges and aid in the characterization of physical and mechanical properties of regolith at cryogenic temperatures. This presentation will review the current state of knowledge concerning lunar regolith at low temperature including that of icy regolith.
Temperature-Dependent Dielectric Properties of Al/Epoxy Nanocomposites
NASA Astrophysics Data System (ADS)
Wang, Zijun; Zhou, Wenying; Sui, Xuezhen; Dong, Lina; Cai, Huiwu; Zuo, Jing; Chen, Qingguo
2016-06-01
Broadband dielectric spectroscopy was carried out to study the transition in electrical properties of Al/epoxy nanocomposites over the frequency range of 1-107 Hz and the temperature range of -20°C to 200°C. The dielectric permittivity, dissipation factor, and electrical conductivity of the nanocomposites increased with temperature and showed an abrupt increase around the glass transition temperature ( T g). The results clearly reveal an interesting transition of the electrical properties with increasing temperature: insulator below 70°C, conductor at about 70°C. The behavior of the transition in electrical properties of the nanocomposites was explored at different temperatures. The presence of relaxation peaks in the loss tangent and electric modulus spectra of the nanocomposites confirms that the chain segmental dynamics of the polymer is accompanied by the absorption of energy given to the system. It is suggested that the temperature-dependent transition of the electric properties in the nanocomposite is closely associated with the α-relaxation. The large increase in the dissipation factor and electric conductivity depends on the direct current conduction of thermally activated charge carriers resulting from the epoxy matrix above T g.
Role of temperature on static correlational properties in a spin-polarized electron gas
NASA Astrophysics Data System (ADS)
Arora, Priya; Kumar, Krishan; Moudgil, R. K.
2016-05-01
We have studied the effect of temperature on the static correlational properties of a spin-polarized three-dimensional electron gas (3DEG) over a wide coupling and temperature regime. This problem has been very recently studied by Brown et al. using the restricted path-integral Monte Carlo (RPIMC) technique in the warm-dense regime. To this endeavor, we have used the finite temperature version of the dynamical mean-field theory of Singwi et al, the so-called quantum STLS (qSTLS) approach. The static density structure factor and the static pair-correlation function are calculated, and compared with the RPIMC simulation data. We find an excellent agreement with the simulation at high temperature over a wide coupling range. However, the agreement is seen to somewhat deteriorate with decreasing temperature. The pair-correlation function is found to become small negative for small electron separation. This may be attributed to the inadequacy of the mean-field theory in dealing with the like spin electron correlations in the strong-coupling domain. A nice agreement with RPIMC data at high temperature seems to arise due to weakening of both the exchange and coulomb correlations with rising temperature.
High-Temperature Properties of Piezoelectric Langatate Single Crystals
NASA Technical Reports Server (NTRS)
Sehirlioglu, Alp; Sayir, Ali; Klemenz, Christine
2007-01-01
Langasite type crystals belong to non-polar point group of 32 and do not show any phase transformations up to the melting temperature. Langatate (La3Ga(5.5)Ta(0.5)O14) demonstrates piezoelectric activity better than quartz and possesses attractive properties for high temperature sensors, resonators and filter applications. High-quality and colorless langatate crystals were grown by the Czochralski technique. The electromechanical and electrical properties of langatate crystals in different crystallographic directions were characterized at elevated temperature. The piezoelectric coefficient along x-axis was 7 pC/N as measured by a Berlincourt meter for a plate geometry with an aspect ratio of 10:1. The dielectric constant did not exhibit any significant temperature dependence (K33 approx. 21 at 30 C and K33 approx. 23 at 600 C). Loss tangent at 100 kHz remained <0.003 up to 300 C and <0.65 at 600 C. The dielectric properties along the y-axis were similar and its temperature dependence was analogous to the x-axis. Electromechanically, the inactive z-axis exhibited no resonance with K33 approx. 84 at room temperature, decreasing down to approx. 49 at 600 C. Resistivity of these crystals along x-axis decreased from approx. 6x10(exp 11) omega-cm at room temperature, to approx. 1.6x10(exp 6) omega-cm at 600 C.
Eab, C. H.; Lim, S. C.; Teo, L. P.
2007-08-15
This paper studies the Casimir effect due to fractional massless Klein-Gordon field confined to parallel plates. A new kind of boundary condition called fractional Neumann condition which involves vanishing fractional derivatives of the field is introduced. The fractional Neumann condition allows the interpolation of Dirichlet and Neumann conditions imposed on the two plates. There exists a transition value in the difference between the orders of the fractional Neumann conditions for which the Casimir force changes from attractive to repulsive. Low and high temperature limits of Casimir energy and pressure are obtained. For sufficiently high temperature, these quantities are dominated by terms independent of the boundary conditions. Finally, validity of the temperature inversion symmetry for various boundary conditions is discussed.
Properties and potential of high-temperature niobium beryllides
Bruemmer, S.M.; Brimhall, J.L.; Henager, C.H. Jr.; Hirth, J.P.
1992-12-01
Recent research on the low- and high-temperature properties of two beryllium-niobium intermetallic compounds, Be{sub l2}Nb and Be{sub l7}Nb{sub 2}, is reviewed and discussed. Strength (bend and compression), hardness and fracture toughness has been mapped as a function of test temperature up to 1200C. Results for hot-isostatically-pressed Be{sub 12}Nb and Be{sub l7}Nb{sub 2} are highlighted illustrating the potential for reasonable strength at both low and high temperatures. Limitations for structural use of the beryllides are identified and discussed including low-temperature toughness, intermediate-temperature embrittlement, high-temperature creep strength and composite compatability.
Dynamic properties of human tympanic membrane based on frequency-temperature superposition.
Zhang, Xiangming; Gan, Rong Z
2013-01-01
The human tympanic membrane (TM) transfers sound in the ear canal into the mechanical vibration of the ossicles in the middle ear. The dynamic properties of TM directly affect the middle ear transfer function. The static or quasi-static mechanical properties of TM were reported in the literature, but the dynamic properties of TM over the auditory frequency range are very limited. In this paper, a new method was developed to measure the dynamic properties of human TM using the Dynamic-Mechanical Analyzer (DMA). The test was conducted at the frequency range of 1-40 Hz at three different temperatures: 5, 25, and 37 °C. The frequency-temperature superposition was applied to extend the testing frequency range to a much higher level (at least 3800 Hz). The generalized linear solid model was employed to describe the constitutive relation of the TM. The storage modulus E' and the loss modulus E″ were obtained from 11 specimens. The mean storage modulus was 15.1 MPa at 1 Hz and 27.6 MPa at 3800 Hz. The mean loss modulus was 0.28 MPa at 1 Hz and 4.1 MPa at 3800 Hz. The results show that the frequency-temperature superposition is a feasible approach to study the dynamic properties of the ear soft tissues. The dynamic properties of human TM obtained in this study provide a better description of the damping behavior of ear tissues. The properties can be transferred into the finite element model of the human ear to replace the Rayleigh type damping. The data reported here contribute to the biomechanics of the middle ear and improve the accuracy of the FE model for the human ear. PMID:22820983
Final-state effects on photoemission line shapes at finite temperature
S {o}ndergaard, Ch.; Hofmann, Ph.; Schultz, Ch.; Moreno, M. S.; Gayone, J. E.; Vicente Alvarez, M. A.; Zampieri, G.; Lizzit, S.; Baraldi, A.
2001-06-15
We have measured angle-resolved photoemission spectra from Al(001) over a large range of temperatures and photon energies. These data were analyzed using a model that allows one to calculate the photoemission intensity for transitions with the simultaneous excitation/absorption of 0, 1, 2, etc., phonons. By making a simple simulation of the line shape, we show that the so-called direct transition (or quasiparticle) peaks always contain a significant contribution from photoemission events with a simultaneous excitation and/or absorption of 1 and 2 phonons, i.e., from transitions that are actually indirect. At low photon energies and/or low temperatures these contributions are small; but as the photon energy or the temperature is raised they increase relative to the elastic or zero-phonon contribution and eventually become the dominant contribution to the so-called direct transition peak. The effect of these phonon-assisted transitions is a significant change of the photoemission line shape. Our model gives a good description of the temperature dependence in the experimental data but only if the phonon-assisted contributions to the photoemission peak are taken into account.
Franco-Pérez, Marco; Ayers, Paul W; Gázquez, José L; Vela, Alberto
2015-12-28
We explore the local and nonlocal response functions of the grand canonical potential density functional at nonzero temperature. In analogy to the zero-temperature treatment, local (e.g., the average electron density and the local softness) and nonlocal (e.g., the softness kernel) intrinsic response functions are defined as partial derivatives of the grand canonical potential with respect to its thermodynamic variables (i.e., the chemical potential of the electron reservoir and the external potential generated by the atomic nuclei). To define the local and nonlocal response functions of the electron density (e.g., the Fukui function, the linear density response function, and the dual descriptor), we differentiate with respect to the average electron number and the external potential. The well-known mathematical relationships between the intrinsic response functions and the electron-density responses are generalized to nonzero temperature, and we prove that in the zero-temperature limit, our results recover well-known identities from the density functional theory of chemical reactivity. Specific working equations and numerical results are provided for the 3-state ensemble model. PMID:26723661
Franco-Pérez, Marco E-mail: ayers@mcmaster.ca E-mail: avela@cinvestav.mx; Ayers, Paul W. E-mail: ayers@mcmaster.ca E-mail: avela@cinvestav.mx; Gázquez, José L. E-mail: ayers@mcmaster.ca E-mail: avela@cinvestav.mx; Vela, Alberto E-mail: ayers@mcmaster.ca E-mail: avela@cinvestav.mx
2015-12-28
We explore the local and nonlocal response functions of the grand canonical potential density functional at nonzero temperature. In analogy to the zero-temperature treatment, local (e.g., the average electron density and the local softness) and nonlocal (e.g., the softness kernel) intrinsic response functions are defined as partial derivatives of the grand canonical potential with respect to its thermodynamic variables (i.e., the chemical potential of the electron reservoir and the external potential generated by the atomic nuclei). To define the local and nonlocal response functions of the electron density (e.g., the Fukui function, the linear density response function, and the dual descriptor), we differentiate with respect to the average electron number and the external potential. The well-known mathematical relationships between the intrinsic response functions and the electron-density responses are generalized to nonzero temperature, and we prove that in the zero-temperature limit, our results recover well-known identities from the density functional theory of chemical reactivity. Specific working equations and numerical results are provided for the 3-state ensemble model.
Role of N defects in paramagnetic CrN at finite temperatures from first principles
NASA Astrophysics Data System (ADS)
Mozafari, E.; Alling, B.; Steneteg, P.; Abrikosov, Igor A.
2015-03-01
Simulations of defects in paramagnetic materials at high temperature constitute a formidable challenge to solid-state theory due to the interaction of magnetic disorder, vibrations, and structural relaxations. CrN is a material where these effects are particularly large due to a strong magnetolattice coupling and a tendency for deviations from the nominal 1:1 stoichiometry. In this work, we present a first-principles study of nitrogen vacancies and nitrogen interstitials in CrN at elevated temperature. We report on formation energetics, the geometry of interstitial nitrogen dimers, and the impact on the electronic structure caused by the defects. We find a vacancy formation energy of 2.28 eV with a small effect of temperature, i.e., a formation energy for N interstitial in the form of a <111 > -oriented split bond of 3.77 eV with an increase to 3.97 at 1000 K. Vacancies are found to add three electrons, while split-bond interstitial adds one electron to the conduction band. The band gap of defect-free CrN is smeared out due to vibrations, although it is difficult to draw a conclusion about the exact temperature at which the band gap closes from our calculations. However, it is clear that at 900 K there is a nonzero density of electronic states at the Fermi level. At 300 K, our results indicate a border case where the band gap is about to close.
RECENT LATTICE RESULTS ON FINITE TEMPERATURE AND DENSITY QCD, PART II.
KARSCH,F.
2007-07-09
We discuss recent progress in studies of QCD thermodynamics with almost physical light quark masses and a physical value of the strange quark mass. We summarize results on the transition temperature in QCD and analyze the relation between deconfinement and chiral symmetry restoration.
Electrical Insulation Paper and Its Physical Properties at Cryogenic Temperatures
Tuncer, Enis; Polyzos, Georgios; Sauers, Isidor; James, David Randy
2011-01-01
Paper is widely used in various engineering applications due to its physical properties and ease of manufacture. As a result paper has been selected or designed as an electrical insulation material for parts and components in high voltage technology. In the current study we select a paper employed in conventional transformers as the electrical insulation material. The potential of this paper is investigated at cryogenic temperatures to determine its physical properties for high temperature superconducting power applications. Dielectric measurements were performed using impedance spectroscopy at a constant frequency. Dielectric breakdown tests were performed on samples at 77 K using a liquid nitrogen bath.
Controllable Fluids:. the Temperature Dependence of Post-Yield Properties
NASA Astrophysics Data System (ADS)
Weiss, Keith D.; Duclos, Theodore G.
This paper represents the first detailed description of the affect of temperature on the properties exhibited by state-of-the-art electrorheological (ER) and magnetorheological (MR) fluids. In particular, shear stress versus shear strain rate curves, dynamic and static yield stress values, zero-field viscosity data, and current density measurements are discussed. Specific comments concerning the stability of both mechanical and electrical properties over broad temperature ranges are provided. Finally, insight into the advantages associated with using electrorheological and magnetorheological fluids in a controllable device is provided.
NASA Astrophysics Data System (ADS)
Huang, Xu-Guang; Koide, Tomoi
2012-09-01
The microscopic formulas for the shear viscosity η, the bulk viscosity ζ, and the corresponding relaxation times τπ and τΠ of causal dissipative relativistic fluid-dynamics are obtained at finite temperature and chemical potential by using the projection operator method. The non-triviality of the finite chemical potential calculation is attributed to the arbitrariness of the operator definition for the bulk viscous pressure. We show that, when the operator definition for the bulk viscous pressure Π is appropriately chosen, the leading-order result of the ratio, ζ over τΠ, coincides with the same ratio obtained at vanishing chemical potential. We further discuss the physical meaning of the time-convolutionless (TCL) approximation to the memory function, which is adopted to derive the main formulas. We show that the TCL approximation violates the time reversal symmetry appropriately and leads results consistent with the quantum master equation obtained by van Hove. Furthermore, this approximation can reproduce an exact relation for transport coefficients obtained by using the f-sum rule derived by Kadanoff and Martin. Our approach can reproduce also the result in Baier et al. (2008) [8] by taking into account the next-order correction to the TCL approximation, although this correction causes several problems.
Mohanty, Subhasish; Majumdar, Saurindranath
2015-01-01
Irradiation creep plays a major role in the structural integrity of the graphite components in high temperature gas cooled reactors. Finite element procedures combined with a suitable irradiation creep model can be used to simulate the time-integrated structural integrity of complex shapes, such as the reactor core graphite reflector and fuel bricks. In the present work a comparative study was undertaken to understand the effect of linear and nonlinear irradiation creep on results of finite element based stress analysis. Numerical results were generated through finite element simulations of a typical graphite reflector.
High temperature structural and magnetic properties of cobalt nanorods
Ait Atmane, Kahina; Zighem, Fatih; Soumare, Yaghoub; Ibrahim, Mona; Boubekri, Rym; Maurer, Thomas; Margueritat, Jeremie; Piquemal, Jean-Yves; Ott, Frederic; Chaboussant, Gregory; Schoenstein, Frederic; Jouini, Noureddine; Viau, Guillaume
2013-01-15
We present in this paper the structural and magnetic properties of high aspect ratio Co nanoparticles ({approx}10) at high temperatures (up to 623 K) using in-situ X ray diffraction (XRD) and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. The coercivity can be modelled by {mu}{sub 0}H{sub C}=2(K{sub MC}+K{sub shape})/M{sub S} with K{sub MC} the magnetocrystalline anisotropy constant, K{sub shape} the shape anisotropy constant and M{sub S} the saturation magnetization. H{sub C} decreases linearly when the temperature is increased due to the loss of the Co magnetocrystalline anisotropy contribution. At 500 K, 50% of the room temperature coercivity is preserved corresponding to the shape anisotropy contribution only. We show that the coercivity drop is reversible in the range 300-500 K in good agreement with the absence of particle alteration. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation. - Graphical abstract: We present in this paper the structural and magnetic properties of high aspect ratio Co nanorods ({approx}10) at high temperatures (up to 623 K) using in-situ X-ray diffraction and SQUID characterizations. We show that the anisotropic shapes, the structural and texture properties are preserved up to 500 K. Above 525 K, the magnetic properties are irreversibly altered either by sintering or by oxidation. Highlights: Black-Right-Pointing-Pointer Ferromagnetic Co nanorods are prepared using the polyol process. Black-Right-Pointing-Pointer The structural and texture properties of the Co nanorods are preserved up to 500 K. Black-Right-Pointing-Pointer The magnetic properties of the Co nanorods are irreversibly altered above 525 K.
Microstructure and water vapor transport properties of temperature sensitive polyurethanes
NASA Astrophysics Data System (ADS)
Ding, Xuemei
Temperature sensitive polyurethane (TS-PU) is one novel type of smart polymers. The water vapor permeability (WVP) of its membrane could undergo a significant increase as temperature increases within a predetermined temperature range. Such smart property enables this material to have a broad range of potential applications to textile industry, medicine, environmental fields and so on. However, based on the literature review, contradicting results were found on some TS-PUs. The aims of this project are to synthesize TS-PU with Tm in the broader temperature range including ambient temperature range, and then investigate systematically the relationships between microstructure and water vapor transport properties of TS-PU. For this purpose, in this project, a series of polyurethanes (PU) were synthesized using five different crystalline polyols with approximately similar molecule weight and three different hydrophilic contents, and dense membranes were prepared accordingly. The microstructure and properties of these PUs were investigated using DSC, WAXD, DMA, FTIR, GPC, POM, TEM, SEM and PALS. Their equilibrium water sorption and water vapor permeability were measured accordingly. Results show that crystal melting of these resulting PUs take place in the temperature range from -10--60°C as desired. Storage modulus (E') drops down quickly in the temperature range of crystal melting, suggesting a great transition in the predetermined temperature range. The decreased HSC as well as regular chemical structure of polyols results in the larger spherulites and higher melting end temperature, and the higher crystallinity induces the more obvious incompatibility of soft segment and hard segment in the PUs. These PUs are proved to have good enough tensile properties for textile application. The mean free volume size and fractional free volume increase more significantly in the temperature range of crystal melting than in other temperature intervals. Finally, as expected, the
NASA Astrophysics Data System (ADS)
Tarighi Ahmadpour, Mahdi; Hashemifar, S. Javad; Rostamnejadi, Ali
2016-07-01
We use density functional computations to study the zero temperature structural, electronic, magnetic, and optical properties of (5,0) finite carbon nanotubes (FCNT), with length in the range of 4-44 Å. It is found that the structural and electronic properties of (5,0) FCNTs, in the ground state, converge at a length of about 30 Å, while the excited state properties exhibit long-range edge effects. We discuss that curvature effects enhance energy gap of FCNTs, in contrast to the known trend in the periodic limit. It is seen that compensation of curvature effects in two special small sizes may give rise to spontaneous magnetization. The obtained cohesive energies provide some insights into the effects of environment on the growth of FCNTs. The second-order difference of the total energies reveals an important magic size of about 15 Å. The optical and dynamical magnetic responses of the FCNTs to polarized electromagnetic pulses are studied by time dependent density functional theory. The results show that the static and dynamic magnetic properties mainly come from the edge carbon atoms. The optical absorption properties are described in terms of local field effects and characterized by Casida linear response method.
CP asymmetry in heavy Majorana neutrino decays at finite temperature: the nearly degenerate case
NASA Astrophysics Data System (ADS)
Biondini, S.; Brambilla, N.; Escobedo, M. A.; Vairo, A.
2016-03-01
In a model where Majorana neutrinos heavier than the electroweak scale couple to Standard Model Higgs bosons and leptons, we compute systematically thermal corrections to the direct and indirect CP asymmetries in the Majorana neutrino decays. These are key ingredients entering the equations that describe the thermodynamic evolution of the induced lepton-number asymmetry eventually leading to the baryon asymmetry in the universe. We compute the thermal corrections in an effective field theory framework that assumes the temperature smaller than the masses of the Majorana neutrinos and larger than the electroweak scale, and we provide the leading corrections in an expansion of the temperature over the mass. In this work, we consider the case of two Majorana neutrinos with nearly degenerate masses.
Finite-temperature interatomic exchange and magnon softening in Fe overlayers on Ir(001)
NASA Astrophysics Data System (ADS)
Rodrigues, D. C. M.; Szilva, A.; Klautau, A. B.; Bergman, A.; Eriksson, O.; Etz, C.
2016-07-01
We evaluate how thermal effects soften the magnon dispersion in 6 layers of Fe(001) on top of Ir(001). We perform a systematic study considering noncollinear spin arrangement and calculate configuration-dependent exchange parameters Jij n c following the methodology described by Szilva et al. [Phys. Rev. Lett. 111, 127204 (2013)], 10.1103/PhysRevLett.111.127204. In addition, Monte Carlo simulations were performed in order to estimate the noncollinear spin arrangement as a function of temperature. Hence the Jij n c's related to these configurations were calculated and used in an atomistic spin dynamics approach to evaluate the magnon spectra. Our results show good agreement with recent room-temperature measurements, and highlights how thermal effects produce magnon softening in this, and similar, systems.
Liu, Yu; Wu, Jianzhong
2014-02-28
Efficient and accurate prediction of the correlation functions of uniform electron gases is of great importance for both practical and theoretical applications. This paper presents a bridge-functional-based classical mapping method for calculating the correlation functions of uniform spin-unpolarized electron gases at finite temperature. The bridge functional is formulated by following Rosenfeld's universality ansatz in combination with the modified fundamental measure theory. The theoretical predictions are in good agreement with recent quantum Monte Carlo results but with negligible computational cost, and the accuracy is better than a previous attempt based on the hypernetted-chain approximation. We find that the classical mapping method is most accurate if the effective mass of electrons increases as the density falls.
Anomalous Hall conductivity of clean Sr2RuO4 at finite temperatures
NASA Astrophysics Data System (ADS)
Taylor, Edward; Kallin, Catherine
2013-07-01
Building on previous work, we calculate the temperature- and frequency-dependent anomalous Hall conductivity for the putative multiband chiral superconductor Sr2RuO4 using a simple microscopic two-orbital model without impurities. A Hall effect arises in this system without the application of an external magnetic field due to the time-reversal-symmetry breaking chiral superconducting state. The anomalous Hall conductivity is nonzero only when there is more than one superconducting order parameter, involving inter- as well as intra-band Cooper pairing. We find that such a multiband superconducting state gives rise to a distinctive resonance in the frequency-dependence of the Hall conductivity at a frequency close to the inter-orbital hopping energy scale that describes hopping between Ru dxz and dyz orbitals. The detection of this feature, robust to temperature and impurity effects in the superconducting phase, would thus constitute compelling evidence in favour of a multiband origin of superconductivity in Sr2RuO4, with strong superconductivity on the α and β bands. The temperature dependence of the Hall conductivity and Kerr rotation angle are studied within this model at the one-loop approximation.
Liquidus temperature and optical properties measurement by containerless techniques
NASA Technical Reports Server (NTRS)
Anderson, Collin D.
1993-01-01
Reactive alloy liquidus temperatures measured by conventional, contained techniques are often in error due to reactions with containers and gaseous impurities. This paper describes a new liquidus temperature measurement technique that avoids these problems by employing containerless processing. This technique relies on precise and accurate noncontact temperature measurements (NCTM), which are made possible by spectral emissivity values. The spectral emissivities, epsilon(sub lambda), are measured along with the optical properties (real, n, and imaginary, k, components of the index of refraction) using polarimetric techniques on electromagnetically levitated specimens. Results from work done at Vanderbilt University and Intersonics on the Ti-Al system are presented to demonstrate the above techniques.
NASA Astrophysics Data System (ADS)
Jain, Rahul; Pal, Surjya Kanta; Singh, Shiv Brat
2016-06-01
Friction Stir Welding (FSW) is a solid state joining process and is handy for welding aluminum alloys. Finite Element Method (FEM) is an important tool to predict state variables of the process but numerical simulation of FSW is highly complex due to non-linear contact interactions between tool and work piece and interdependency of displacement and temperature. In the present work, a three dimensional coupled thermo-mechanical method based on Lagrangian implicit method is proposed to study the thermal history, strain distribution and thermo-mechanical process in butt welding of Aluminum alloy 2024 using DEFORM-3D software. Workpiece is defined as rigid-visco plastic material and sticking condition between tool and work piece is defined. Adaptive re-meshing is used to tackle high mesh distortion. Effect of tool rotational and welding speed on plastic strain is studied and insight is given on asymmetric nature of FSW process. Temperature distribution on the workpiece and tool is predicted and maximum temperature is found in workpiece top surface.
Sabaeian, Mohammad; Shahzadeh, Mohammadreza
2015-02-01
The authors report the simulation of temperature distribution and thermally induced stresses of human tooth under CO2 pulsed laser beam. A detailed tooth structure comprising enamel, dentin, and pulp with realistic shapes and thicknesses were considered, and a numerical method of finite element was adopted to solve time-dependent bio-heat and stress equations. The realistic boundary conditions of constant temperature for those parts embedded in the gingiva and heat flux condition for those parts out of the gingiva were applied. The results which were achieved as a function of energy density (J/cm(2)) showed when laser beam is irradiated downward (from the top of the tooth), the temperature and thermal stresses decrease quickly as a function of depth that is a result of strong absorption of CO2 beams by enamel. This effect is so influential that one can use CO2 beams to remove micrometer layers while underlying tissues, especially the pulp, are safe from thermal effects. PMID:23868367
NASA Technical Reports Server (NTRS)
Mickens, R. E.
1984-01-01
Work on the construction of finite difference models of differential equations having zero truncation errors is summarized. Both linear and nonlinear unidirectional wave equations are discussed. Results regarding the construction of zero truncation error schemes for the full wave equation and Burger's equation are also briefly reported.
Structure and properties of a high-temperature austenitic steel at high temperatures
NASA Astrophysics Data System (ADS)
Kostina, M. V.; Skorobogatykh, V. N.; Tykochinskaya, T. V.; Nakhabina, M. S.; Nemov, V. V.; Bannykh, I. O.; Korneev, A. E.
2010-11-01
The structure of a high-temperature austenitic 12Kh15N16M2TR steel, which is promising for manufacturing steam superheater tubes, is studied after long-term thermal holding under stress. The type, morphology, and matrix arrangement of excess-phase particles that form during thermal holding are found. The structure of the alloy correlates with its high-temperature strength, and the mechanical properties obtained during short-time tensile tests in the temperature range 20-730°C are compared to the results of high-temperature strength tests.
NASA Astrophysics Data System (ADS)
Rouhi, S.; Alizadeh, Y.; Ansari, R.; Aryayi, M.
2015-09-01
Molecular dynamics simulations are used to study the mechanical behavior of single-walled carbon nanotube reinforced composites. Polyethylene and polyketone are selected as the polymer matrices. The effects of nanotube atomic structure and diameter on the mechanical properties of polymer matrix nanocomposites are investigated. It is shown that although adding nanotube to the polymer matrix raises the longitudinal elastic modulus significantly, the transverse tensile and shear moduli do not experience important change. As the previous finite element models could not be used for polymer matrices with the atom types other than carbon, molecular dynamics simulations are used to propose a finite element model which can be used for any polymer matrices. It is shown that this model can predict Young’s modulus with an acceptable accuracy.
Mechanical properties of polyimide coated optical fibers at elevated temperatures
NASA Astrophysics Data System (ADS)
Huang, Lei; Dyer, Robert S.; Lago, Ralph J.; Stolov, Andrei A.; Li, Jie
2016-03-01
High temperature mechanical strength and reliability of optical fibers have become important subjects as optical fibers are increasingly used for harsher environments. Theories and models of fiber mechanical properties established for traditional telecommunications applications may need to be validated for applications at elevated temperatures. In this paper, we describe the test setup for high temperature tensile strength of fiber and report initial results of dynamic tensile strength of polyimide coated optical fiber at 300 and 350ºC for different heating time intervals. The results are compared with room temperature strength data, data available in the literature, and our earlier work on thermogravimetric analysis (TGA) weight loss of the polyimide coating and the observations on surface morphology at elevated temperatures. Interesting observations are discussed and possible explanations are proposed.
Ni, Xiao-Yu; Pan, Chang-Wang; Gangadhara Prusty, B
2015-08-01
This paper discusses various issues relating to the mechanical properties of a braided non-vascular stent made of a Ni-Ti alloy. The design of the stent is a major factor which determines its reliability after implantation into a stenosed non-vascular cavity. This paper presents the effect of the main structural parameters on the mechanical properties of braided stents. A parametric analysis of a commercial stent model is developed using the commercial finite element code ANSYS. As a consequence of the analytical results that the pitch of wire has a greater effect than other structural parameters, a new design of a variable pitch stent is presented to improve mechanical properties of these braided stents. The effect of structural parameters on mechanical properties is compared for both stent models: constant and variable pitches. When the pitches of the left and right quarters of the stent are 50% larger and 100% larger than that of the central portion, respectively, the radial stiffness in the central portion increases by 10% and 38.8%, while the radial stiffness at the end portions decreases by 128% and 164.7%, the axial elongation by 25.6% and 56.6% and the bending deflection by 3.96% and 10.15%. It has been demonstrated by finite element analysis that the variable pitch stent can better meet the clinical requirements. PMID:24867297
Gubser, Steven S.; Nellore, Abhinav; Pufu, Silviu S.; Rocha, Fabio D.
2008-09-26
We consider classes of translationally invariant black hole solutions whose equations of state closely resemble that of QCD at zero chemical potential. We use these backgrounds to compute the ratio {zeta}/s of bulk viscosity to entropy density. For a class of black holes that exhibits a first-order transition, we observe a sharp rise in {zeta}/s near T{sub c}. For constructions that exhibit a smooth crossover, like QCD does, the rise in {zeta}/s is more modest. We conjecture that divergences in {zeta}/s for black hole horizons are related to extrema of the entropy density as a function of temperature.
NASA Astrophysics Data System (ADS)
McGann, Mark Robert
Molecular simulations are used to examine and elucidate the thermophysical properties of polyethylene and n-alkane crystals. The n-alkane crystals serve as models of semi-crystalline polyethylene, which is composed of nanoscale crystallites. These simulations emphasize the vibrational dynamics when interpreting the properties of these crystals. The unit cell dimensions, thermal expansion coefficients, heat capacities and melting temperatures of n-alkane crystals are shown to depend strongly on chain length. The results presented here are expected to be qualitatively similar to the effects of lamellar thickness in semi-crystalline polymers. Monte Carlo simulations are carried out on model n-alkane crystals to investigate the chain length dependence of the interlamellar spacing, which has implications with regard to the Raman spectra of n-alkane crystals. The results of these simulations show there to be no significant chain length dependence of the interlamellar spacing. Compression of perfect polyethylene crystals is shown to give rise to a long wavelength Euler buckling instability. The critical stress necessary to produce this buckling instability decreases as the wavelength of the instability increases, and it approaches the value of the lowest shear modulus in the limit of very long wavelength. The role of defects and the lamellar structure on the compressive failure mechanism of real polyethylene fibers is qualitatively addressed by simulations of n-alkane crystals. Heating crystalline polyethylene is shown to lead to an entropically-induced Euler buckling instability, associated with the softening of the long wavelength transverse acoustic vibrational modes propagating along the chain axis. This entropic effect is augmented by axial compressive stress, leading to a decrease in the instability temperature with applied stress. The stability limits of orthorhombic polyethylene crystals under compression, tension or shear are examined. In all cases, except shear
Evaluation of low temperature properties of warm mix asphalt
NASA Astrophysics Data System (ADS)
Wen, Jin; Liu, Zhifei; Wu, Shaopeng
2010-03-01
Warm mix asphalt (WMA), which reduces the mixing and compaction temperature of conventional hot mix asphalt (HMA), is becoming an attractive paving material. It is critical to identify the low temperature properties of warm mix asphalt. In this study, the three-point bending, bending creep tests and indirect tensile tests were conducted to test the low-temperature properties of warm mix asphalt as well as the conventional hot mix asphalt, which was used as the control mixture. Sasobit and Aspha-min were used as additives for warm mix asphalt, which was mixed and compacted lower than the traditional hot mix asphalt about 25°C dosages accounted for 3% of asphalt, and 0.3% of mixture, respectively. The results of bending strength, bending modulus, and creep rate indicate that warm mix asphalt using Sasobit and Aspha-min slightly affects the resistance property to cracking compared with the conventional hot mix asphalt. The results suggest that the warm mix asphalt can maintain the low temperature properties of hot mix asphalt.
Evaluation of low temperature properties of warm mix asphalt
NASA Astrophysics Data System (ADS)
Wen, Jin; Liu, Zhifei; Wu, Shaopeng
2009-12-01
Warm mix asphalt (WMA), which reduces the mixing and compaction temperature of conventional hot mix asphalt (HMA), is becoming an attractive paving material. It is critical to identify the low temperature properties of warm mix asphalt. In this study, the three-point bending, bending creep tests and indirect tensile tests were conducted to test the low-temperature properties of warm mix asphalt as well as the conventional hot mix asphalt, which was used as the control mixture. Sasobit and Aspha-min were used as additives for warm mix asphalt, which was mixed and compacted lower than the traditional hot mix asphalt about 25°C dosages accounted for 3% of asphalt, and 0.3% of mixture, respectively. The results of bending strength, bending modulus, and creep rate indicate that warm mix asphalt using Sasobit and Aspha-min slightly affects the resistance property to cracking compared with the conventional hot mix asphalt. The results suggest that the warm mix asphalt can maintain the low temperature properties of hot mix asphalt.
Low Temperature Properties and Thermal Stability of Oligomerized Soybean Oil
Technology Transfer Automated Retrieval System (TEKTRAN)
Soybean oil polymers with lower molecular weight prepared in supercritical carbon dioxide (scCO2) by cationic polymerization were investigated for their applications as lubricants and hydraulic fluids. The low-temperature properties were studied by measuring their cloud and pour points; while therm...
NASA Astrophysics Data System (ADS)
Khanh, Nguyen Quoc; Totsuji, Hiroo
2004-01-01
Applying the classical-map hypernetted-chain method (CHNC) developed recently by Dharma-wardana and Perrot, we have studied the temperature and spin-polarization effects on electron correlation in the uniform quantum two-dimensional gas (2DEG) over a wide range of temperature T and spin-polarization ζ. The quantum fluid at the temperature T is mapped to a classical fluid at the temperature Tcf given by Tcf2= T2+ Tq2, where the quantum temperature Tq is determined by comparing the calculated correlation energy to that of Monte Carlo results for the fully spin-polarized quantum system at zero temperature. By the iterative solution of the modified HNC equation and the Ornstein-Zernike equation, we have obtained the pair distribution function (PDF) and correlation energy for the two-component classical 2DEG with a classical fluid temperature Tcf. The anti-parallel bridge function B12( r) appearing in the modified HNC equation is determined by using the Monte Carlo correlation energy at T=0 or STLS (Singwi-Tosi-Land-Sjölander) result at T>0 and the numerical solution to the Percus-Yevick (PY) equation for the system of hard disks. By calculating the Pauli potential, the bridge function, PDFs, structure factors and correlation energy, we have shown that in some cases, the properties of the uniform quantum 2DEG depend remarkably on the temperature and spin-polarization.
NASA Astrophysics Data System (ADS)
Klyushina, E. S.; Tiegel, A. C.; Fauseweh, B.; Islam, A. T. M. N.; Park, J. T.; Klemke, B.; Honecker, A.; Uhrig, G. S.; Manmana, S. R.; Lake, B.
2016-06-01
Unlike most quantum systems which rapidly become incoherent as temperature is raised, strong correlations persist at elevated temperatures in S =1/2 dimer magnets, as revealed by the unusual asymmetric line shape of their excitations at finite temperatures. Here, we quantitatively explore and parametrize the strongly correlated magnetic excitations at finite temperatures using high-resolution inelastic neutron scattering of the model compound BaCu2V2O8 which we show to be an alternating antiferromagnetic-ferromagnetic spin -1/2 chain. Comparison to state of the art computational techniques shows excellent agreement over a wide temperature range. Our findings hence demonstrate the possibility to quantitatively predict coherent behavior at elevated temperatures in quantum magnets.
Low temperature self-cleaning properties of superhydrophobic surfaces
NASA Astrophysics Data System (ADS)
Wang, Fajun; Shen, Taohua; Li, Changquan; Li, Wen; Yan, Guilong
2014-10-01
Outdoor surfaces are usually dirty surfaces. Ice accretion on outdoor surfaces could lead to serious accidents. In the present work, the superhydrophobic surface based on 1H, 1H, 2H, 2H-Perfluorodecanethiol (PFDT) modified Ag/PDMS composite was prepared to investigate the anti-icing property and self-cleaning property at temperatures below freezing point. The superhydrophobic surface was deliberately polluted with activated carbon before testing. It was observed that water droplet picked up dusts on the cold superhydrophobic surface and took it away without freezing at a measuring temperature of -10 °C. While on a smooth PFDT surface and a rough surface base on Ag/PDMS composite without PFDT modification, water droplets accumulated and then froze quickly at the same temperature. However, at even lower temperature of -12 °C, the superhydrophobic surface could not prevent the surface water from icing. In addition, it was observed that the frost layer condensed from the moisture pay an important role in determining the low temperature self-cleaning properties of a superhydrophobic surface.
Study of the electrical conductivity at finite temperature in 2D Si- MOSFETs
Limouny, L. Kaaouachi, A. El Tata, O.; Daoudi, E.; Errai, M.; Dlimi, S.; Idrissi, H. El; Zatni, A.
2014-01-27
We investigate the low temperature density dependent conductivity of two dimensional electron systems in zero magnetic field for sample Si-15 MOSFETs. The first purpose of this paper is to establish that the knee of the conductivity σ{sub 0} (σ{sub 0} is the T = 0.3 conductivity obtained by linear extrapolation of the curves of σ (T) for different values of electron density, n{sub s}) as a function of the carrier densities n{sub s} for T = 0.3 K, observed by Lai et al. and Limouny et al. in previous work for two different samples, is independent of temperature. The second aim is the determination of the critical density, n{sub c}, of the metal-insulator transition. Many methods are used in this investigation of n{sub c} which have been already used for other samples. The motivation behind this last study is the observation of many values of n{sub c} that have been obtained from different methods and that are slightly different. We will use in this study three methods with the intention to infer which one is more appropriate to obtain n{sub c}.
Symmetry breaking patterns of the 3-3-1 model at finite temperature
NASA Astrophysics Data System (ADS)
Borges, J. Sá; Ramos, Rudnei O.
2016-06-01
We consider the minimal version of an extension of the standard electroweak model based on the SU(3)_c × SU(3)_L × U(1)_X gauge symmetry (the 3-3-1 model). We analyze the most general potential constructed from three scalars in the triplet representation of SU(3)_L, whose neutral components develop nonzero vacuum expectation values, giving mass for all the model's massive particles. For different choices of parameters, we obtain the particle spectrum for the two symmetry breaking scales: one where the SU(3)_L × U(1)_X group is broken down to SU(2)_L× U(1)_Y and a lower scale similar to the standard model one. Within the considerations used, we show that the model encodes two first-order phase transitions, respecting the pattern of symmetry restoration. The last transition, corresponding to the standard electroweak one, is found to be very weak first-order, most likely turning second-order or a crossover in practice. However, the first transition in this model can be strongly first-order, which might happen at a temperature not too high above the second one. We determine the respective critical temperatures for symmetry restoration for the model.
General properties of the acoustic plate modes at different temperatures.
Anisimkin, V I; Anisimkin, I V; Voronova, N V; Puсhkov, Yu V
2015-09-01
Using acoustic plate modes with SH-polarization and quartz crystal with Euler angles 0°, 132.75°, 90°, as an example, general properties of the acoustic plate modes at different temperatures are studied theoretically and experimentally in the range from -40 to +80°C. It is shown that in addition to well-known parameters responsible for temperature characteristics of acoustic waves the temperature coefficients of the acoustic plate modes depend on the mode order n, plate thickness h/λ, and expansion of the plate in direction of its thickness (h - thickness, λ - acoustic wavelength). These properties permit the mode sensitivity to be increased or decreased without replacing plate material and orientation. PMID:26002698
Temperature dependent mechanical property testing of nitrate thermal storage salts.
Iverson, Brian DeVon; Broome, Scott Thomas; Siegel, Nathan Phillip
2010-08-01
Three salt compositions for potential use in trough-based solar collectors were tested to determine their mechanical properties as a function of temperature. The mechanical properties determined were unconfined compressive strength, Young's modulus, Poisson's ratio, and indirect tensile strength. Seventeen uniaxial compression and indirect tension tests were completed. It was found that as test temperature increases, unconfined compressive strength and Young's modulus decreased for all salt types. Empirical relationships were developed quantifying the aforementioned behaviors. Poisson's ratio tends to increase with increasing temperature except for one salt type where there is no obvious trend. The variability in measured indirect tensile strength is large, but not atypical for this index test. The average tensile strength for all salt types tested is substantially higher than the upper range of tensile strengths for naturally occurring rock salts.
Hydrologic property alterations due to elevated temperatures at Yucca Mountain
Flint, A.L.; Nash, M.H.; Nash, M.S.
1994-12-31
Yucca Mountain is currently being evaluated as a potential site for a high level nuclear waste repository. The pre-emplacement hydrologic properties of the rock are important in determining the suitability of the site; however, post emplacement thermal loads and associated drying may permanently alter the character of the rock. A preliminary study was undertaken to determine the effects of elevated temperatures on hydrologic properties of the welded Topopah Spring member of the Paintbrush Tuff and a zeolitic, nonwelded tuff from the Tuffaceous Beds of Calico Hills. Rock outcrop samples were collected and dried in the laboratory at different temperatures (up to 400 degrees C). Hydrologic and physical properties -were tested before and after each of the drying cycles.
Elevated temperature properties of boron/aluminum composites
NASA Technical Reports Server (NTRS)
Sullivan, P. G.
1978-01-01
The high temperature properties of boron/aluminum composites, fabricated by an air diffusion bonding technique utilizing vacuum-bonded monolayer tape are reported. Seventeen different combinations of matrix alloy, reinforcement diameter, reinforcement volume percent, angle-ply and matrix enhancement (i.e. titanium cladding and interleaves) were fabricated, inspected, and tested. It is shown that good to excellent mechanical properties could be obtained for air-bonded boron/aluminum composites and that these properties did not decrease significantly up to a test temperature of at least 260 C. Composites made with 8 mil B/W fiber show a much greater longitudinal strength dependence on volume percent fiber than composites made with 5.6 mil fiber. The addition of titanium caused difficulties in composite bonding and yielded composites with reduced strength.
Effects of Temperature and CSSX Organics on Saltstone Processing Properties
Harbour, J
2006-02-06
This task was performed to determine whether the two variables, ''mix temperature'' and ''quantity of organics'' introduced into the decontaminated salt solution by the caustic side solvent extraction (CSSX) process, need to be included in the upcoming Saltstone Variability Study. Because the amount and types of organics introduced through the CSSX process do not significantly impact the fresh properties of Saltstone, the ''quantity of organics'' variable will not be included in the Saltstone Variability Study. The Saltstone Variability Study should include the variable of ''mix temperature'' in the experimental design. Examples are presented in this report that clearly demonstrate a pronounced dependence of the fresh grout properties on ''mix temperature''. One example, using mixes made with the Deliquification, Dissolution and Adjustment (DDA) simulant, shows that the properties of gel time and bleed water are highly mix temperature dependent. The gel time increased from 15 minutes at 10 C to 90 minutes at 35 C with most of the change occurring between 20 and 30 C. That is, gel time is highly sensitive to mix temperature, especially in the temperature range over which processing is most likely. The volume percent bleed water for these mixes increased from {approx}1 % at 10 C to 13 % at 35 C. The gel times and volume percent bleed water are correlated such that the longer the gel time, the greater the amount of bleed water. In another example, and in contrast to the DDA results, gel times decreased with increasing temperatures for mixes made using the Modular CSSX Unit (MCU) simulants. In this case the gel time decreased from 150 minutes at 10 C to 20 minutes at 38 C. The rheological properties of these mixes were shown to be dependent on temperature over the range of 10 to 40 C. The plastic viscosity increased from 35 cP at 40 C to values between 60 to 70 cP at 10 C for these mixes. Yield stress values for these mixes increased slightly with increasing
Microscopic derivation of the finite-temperature Josephson relation in operator form
Rieckers, A.; Ullrich, M.
1986-04-01
As a microscopic description of the Josephson junction, two BCS models, are studied in the strict pair formulation with quite an arbitrary weak coupling potential. The modular formalism, the separate gauge transformations, and the limiting dynamics are analyzed for the interacting system in terms of the GNS representation of the uncoupled limiting Gibbs state. By means of the Connes theory the condensed Cooper pair and the quasiparticle spectrum is shown to be stable against weak perturbations. The modular formalism is used to construct a local approximation to the renormalized particle number operator and, by this, its time dependence, in spite of this observable not being affiliated with the von Neumann algebra of the temperature representation. The time derivation from this unbounded operator-valued function coincides with the limit of the local currents and splits under a natural assumption into a sum of the Josephson and the quasiparticle current operator extending the two-fluid picture also to the coupled model.
Modelling interfacial coupling in thin film magnetic exchange springs at finite temperature
NASA Astrophysics Data System (ADS)
Saharan, L.; Morrison, C.; Miles, J. J.; Thomson, T.; Schrefl, T.; Hrkac, G.
2013-10-01
We report a numerical study that demonstrates the interface layer between a soft and hard magnetic phase, the exchange transition layer, is the dominant factor that influences the magnetization reversal process at room temperature and long measurement times. It is found that the exchange transition layer thickness affects the magnetization reversal and the coupling of a bi-layer system by lowering the switching field and changing the angle dependent magnetization reversal. We show that the change in angle dependence of reversal is due to an increased incoherency in the lateral spin behavior. Changing the value of exchange coupling in the exchange transition layer affects only the angle dependent behavior and does not lower the switching field.
Thermodynamics of hydrogen-helium mixtures at high pressure and finite temperature
NASA Technical Reports Server (NTRS)
Hubbard, W. B.
1972-01-01
A technique is reviewed for calculating thermodynamic quantities for mixtures of light elements at high pressure, in the metallic state. Ensemble averages are calculated with Monte Carlo techniques and periodic boundary conditions. Interparticle potentials are assumed to be coulombic, screened by the electrons in dielectric function theory. This method is quantitatively accurate for alloys at pressures above about 10 Mbar. An alloy of equal parts hydrogen and helium by mass appears to remain liquid and mixed for temperatures above about 3000 K, at pressures of about 15 Mbar. The additive volume law is satisfied to within about 10%, but the Gruneisen equation of state gives poor results. A calculation at 1300 K shows evidence of a hydrogen-helium phase separation.
Effects of trapping and finite temperature in a relativistic degenerate plasma
Shah, H. A.; Qureshi, M. N. S.; Masood, W.; Tsintsadze, N. L.
2011-10-15
In the present work, we have undertaken, for the first time, investigation on the effect of trapping on the formation of solitary structures in relativistic degenerate plasmas. Such plasmas have been observed in dense astrophysical objects, and in laboratory these may result due to the interaction of intense lasers with matter. We have used the relativistic Fermi-Dirac distribution to describe the dynamics of the degenerate trapped electrons by solving the kinetic equation. The Sagdeev potential approach has been employed to obtain the arbitrary amplitude solitary structures both when the plasma has been considered cold and when small temperature effects have been taken into account. The theoretical results obtained have been analyzed numerically for different parameter values, and the results have been presented graphically.
Elevated temperature mechanical properties of line pipe steels
NASA Astrophysics Data System (ADS)
Jacobs, Taylor Roth
The effects of test temperature on the tensile properties of four line pipe steels were evaluated. The four materials include a ferrite-pearlite line pipe steel with a yield strength specification of 359 MPa (52 ksi) and three 485 MPa (70 ksi) yield strength acicular ferrite line pipe steels. Deformation behavior, ductility, strength, strain hardening rate, strain rate sensitivity, and fracture behavior were characterized at room temperature and in the temperature range of 200--350 °C, the potential operating range for steels used in oil production by the steam assisted gravity drainage process. Elevated temperature tensile testing was conducted on commercially produced as-received plates at engineering strain rates of 1.67 x 10 -4, 8.33 x 10-4, and 1.67 x 10-3 s-1. The acicular ferrite (X70) line pipe steels were also tested at elevated temperatures after aging at 200, 275, and 350 °C for 100 h under a tensile load of 419 MPa. The presence of serrated yielding depended on temperature and strain rate, and the upper bound of the temperature range where serrated yielding was observed was independent of microstructure between the ferrite-pearlite (X52) steel and the X70 steels. Serrated yielding was observed at intermediate temperatures and continuous plastic deformation was observed at room temperature and high temperatures. All steels exhibited a minimum in ductility as a function of temperature at testing conditions where serrated yielding was observed. At the higher temperatures (>275 °C) the X52 steel exhibited an increase in ductility with an increase in temperature and the X70 steels exhibited a maximum in ductility as a function of temperature. All steels exhibited a maximum in flow strength and average strain hardening rate as a function of temperature. The X52 steel exhibited maxima in flow strength and average strain hardening rate at lower temperatures than observed for the X70 steels. For all steels, the temperature where the maximum in both flow
Su, Yukun; Kluess, Daniel; Mittelmeier, Wolfram; van Rienen, Ursula; Bader, Rainer
2016-09-01
The dielectric properties of human bone are one of the most essential inputs required by electromagnetic stimulation for improved bone regeneration. Measuring the electric properties of bone is a difficult task because of the complexity of the bone structure. Therefore, an automatic approach is presented to calibrate the electric properties of bone. The numerical method consists of three steps: generating input from experimental data, performing the numerical simulation, and calibrating the bone dielectric properties. As an example, the dielectric properties at 20 Hz of a rabbit distal femur were calibrated. The calibration process was considered as an optimization process with the aim of finding the optimum dielectric bone properties that match most of the numerically calculated simulation and experimentally measured data sets. The optimization was carried out automatically by the optimization software tool iSIGHT in combination with the finite-element solver COMSOL Multiphysics. As a result, the optimum conductivity and relative permittivity of the rabbit distal femur at 20 Hz were found to be 0.09615 S/m and 19522 for cortical bone and 0.14913 S/m and 1561507 for cancellous bone, respectively. The proposed method is a potential tool for the identification of realistic dielectric properties of the entire bone volume. The presented approach combining iSIGHT with COMSOL is applicable to, amongst others, designing implantable electro-stimulative devices or the optimization of electrical stimulation parameters for improved bone regeneration. PMID:26777343
Role of initial state and final quench temperature on aging properties in phase-ordering kinetics
NASA Astrophysics Data System (ADS)
Corberi, Federico; Villavicencio-Sanchez, Rodrigo
2016-05-01
We study numerically the two-dimensional Ising model with nonconserved dynamics quenched from an initial equilibrium state at the temperature Ti≥Tc to a final temperature Tf below the critical one. By considering processes initiating both from a disordered state at infinite temperature Ti=∞ and from the critical configurations at Ti=Tc and spanning the range of final temperatures Tf∈[0 ,Tc[ we elucidate the role played by Ti and Tf on the aging properties and, in particular, on the behavior of the autocorrelation C and of the integrated response function χ . Our results show that for any choice of Tf, while the autocorrelation function exponent λC takes a markedly different value for Ti=∞ [λC(Ti=∞ ) ≃5 /4 ] or Ti=Tc [λC(Ti=Tc) ≃1 /8 ] the response function exponents are unchanged. Supported by the outcome of the analytical solution of the solvable spherical model we interpret this fact as due to the different contributions provided to autocorrelation and response by the large-scale properties of the system. As changing Tf is considered, although this is expected to play no role in the large-scale and long-time properties of the system, we show important effects on the quantitative behavior of χ . In particular, data for quenches to Tf=0 are consistent with a value of the response function exponent λχ=1/2 λC(Ti=∞ ) =5 /8 different from the one [λχ∈(0.5 -0.56 ) ] found in a wealth of previous numerical determinations in quenches to finite final temperatures. This is interpreted as due to important preasymptotic corrections associated to Tf>0 .
Zero and finite temperature phase diagram of the spinless fermion model in infinite dimensions
NASA Astrophysics Data System (ADS)
Uhrig, G. S.; Vlaming, R.
The phase diagram of the model of spinless fermions with repulsive nearest neighbour interaction is calculated analytically on a hypercubic lattice in infinite dimensions (d ). In spite of its simplicity the model displays a rich phase diagram depending on the doping , the interaction U and the temperature T. The system can be in the homogeneous phase (HOM), the nonsegregated AB charge density wave (AB-CDW), the AB phase separation region (PS-AB/HOM; coexistence of AB-CDW and HOM), the incommensurate phase (IP) or the IP phase separation region (PS-AB/IP; coexistence of AB-CDW and IP). We identify three important values of the interaction UIPL = 0.572 < UIPH = 1.914 < UIP/PS = 4.212 which distinguish four intervals of U. These imply four different types of phase diagrams. In all the three phase diagrams with U below UIP/PS the IP appears. We propose a new general ansatz for the order parameter of this phase. A competition between the IP, the PS-AB/IP and the PS-AB/HOM is found. The relevance of our findings for the phase scenario of the Hubbard model is shown.
Does finite-temperature decoding deliver better optima for noisy Hamiltonians?
NASA Astrophysics Data System (ADS)
Ochoa, Andrew J.; Nishimura, Kohji; Nishimori, Hidetoshi; Katzgraber, Helmut G.
The minimization of an Ising spin-glass Hamiltonian is an NP-hard problem. Because many problems across disciplines can be mapped onto this class of Hamiltonian, novel efficient computing techniques are highly sought after. The recent development of quantum annealing machines promises to minimize these difficult problems more efficiently. However, the inherent noise found in these analog devices makes the minimization procedure difficult. While the machine might be working correctly, it might be minimizing a different Hamiltonian due to the inherent noise. This means that, in general, the ground-state configuration that correctly minimizes a noisy Hamiltonian might not minimize the noise-less Hamiltonian. Inspired by rigorous results that the energy of the noise-less ground-state configuration is equal to the expectation value of the energy of the noisy Hamiltonian at the (nonzero) Nishimori temperature [J. Phys. Soc. Jpn., 62, 40132930 (1993)], we numerically study the decoding probability of the original noise-less ground state with noisy Hamiltonians in two space dimensions, as well as the D-Wave Inc. Chimera topology. Our results suggest that thermal fluctuations might be beneficial during the optimization process in analog quantum annealing machines.
Finite temperature effects and the validity of the Weinberg sum rules
NASA Astrophysics Data System (ADS)
Ayala, Alejandro; Dominguez, C. A.; Loewe, M.; Zhang, Y.
2016-05-01
Using resent independent results from QCD sum rules for the thermal evolution of hadronic parameters in the vector and the axial-vector channels, we discuss the saturation of the two Weinberg sum rules. It turn out that both sum rules are quite well satisfied in a wide range from T = 0 up to T/T c ≃ 0.7 — 0.8. At higher temperatures, coming closer to Tc , there is an asymmetry between both channels since in the vector case there is a leading order effect, proportional to T2 , due to a one loop pion contribution in the space-like region, which is absent in the axial-vector case. This leads then to a small deviation. More important, though, in this region the QCD sum rules for the hadronic parameters begin to have no solutions since the widths of the ρ and the a1-mesons diverge signaling the occurrence of deconfinement. Close to and at Tc there are no pions left in the medium and chiral symmetry is restored so that the Weinberg sum rules are trivially satisfied.
The rate dependent response of a bistable chain at finite temperature
NASA Astrophysics Data System (ADS)
Benichou, Itamar; Zhang, Yaojun; Dudko, Olga K.; Givli, Sefi
2016-10-01
We study the rate dependent response of a bistable chain subjected to thermal fluctuations. The study is motivated by the fact that the behavior of this model system is prototypical to a wide range of nonlinear processes in materials physics, biology and chemistry. To account for the stochastic nature of the system response, we formulate a set of governing equations for the evolution of the probability density of meta-stable configurations. Based on this approach, we calculate the behavior for a wide range of parametric values, such as rate, temperature, overall stiffness, and number of elements in the chain. Our results suggest that fundamental characteristics of the response, such as average transition stress and hysteresis, can be captured by a simple law which folds the influence of all these factors into a single non-dimensional quantity. We also show that the applicability of analytical results previously obtained for single-well systems can be extended to systems having multiple wells by proper definition of rate and of the transition stress.
Nuclear Pasta at Finite Temperature with the Time-Dependent Hartree-Fock Approach
NASA Astrophysics Data System (ADS)
Schuetrumpf, B.; Klatt, M. A.; Iida, K.; Maruhn, J. A.; Mecke, K.; Reinhard, P.-G.
2016-01-01
We present simulations of neutron-rich matter at sub-nuclear densities, like supernova matter. With the time-dependent Hartree-Fock approximation we can study the evolution of the system at temperatures of several MeV employing a full Skyrme interaction in a periodic three-dimensional grid [1]. The initial state consists of α particles randomly distributed in space that have a Maxwell-Boltzmann distribution in momentum space. Adding a neutron background initialized with Fermi distributed plane waves the calculations reflect a reasonable approximation of astrophysical matter. The matter evolves into spherical, rod-like, connected rod-like and slab-like shapes. Further we observe gyroid-like structures, discussed e.g. in [2], which are formed spontaneously choosing a certain value of the simulation box length. The ρ-T-map of pasta shapes is basically consistent with the phase diagrams obtained from QMD calculations [3]. By an improved topological analysis based on Minkowski functionals [4], all observed pasta shapes can be uniquely identified by only two valuations, namely the Euler characteristic and the integral mean curvature. In addition we propose the variance in the cell-density distribution as a measure to distinguish pasta matter from uniform matter.
NASA Astrophysics Data System (ADS)
Blanco, R.; Pesquera, L.; Santos, E.
1987-08-01
An oscillator with a small, but otherwise arbitrary, perturbing potential is considered immersed in a random cavity radiation. Classical (stochastic) calculations are done when the radiation has a Rayleigh-Jeans spectrum and a complete Planck spectrum (i.e., with zero point). These are compared with the results obtained by a quantum calculation. First, a comparison is made of stationary values, in particular, the energy. Then the emission and the absorption spectra are calculated, in particular, the absorption spectrum for an arbitrary incoming radiation. Finally, a detailed comparison is made of the absorption bands when the perturbing potential has the form λx2K (K=2,3,...). In all cases, it is explicitly shown that the quantum and the classical behavior agree in the limit of high temperatures. It is also shown that the classical system immersed in a radiation with complete Planck spectrum is much closer to the quantum system than the fully classical system (with a Rayleigh-Jeans spectrum).