Topological footprints of the Kitaev chain with long-range superconducting pairings at a finite temperature

NASA Astrophysics Data System (ADS)

Bhattacharya, Utso; Dutta, Amit

2018-06-01

We study the one-dimensional Kitaev chain with long-range superconductive pairing terms at a finite temperature where the system is prepared in a mixed state in equilibrium with a heat reservoir maintained at a constant temperature T . In order to probe the footprint of the ground-state topological behavior of the model at finite temperature, we look at two global quantities extracted out of two geometrical constructions: the Uhlmann and the interferometric phase. Interestingly, when the long-range effect dominates, the Uhlmann phase approach fails to reproduce the topological aspects of the model in the pure-state limit; on the other hand, the interferometric phase which has a proper pure state reduction, shows a behavior independent of the ambient temperature.

Effect of pairwise additivity on finite-temperature behavior of classical ideal gas

NASA Astrophysics Data System (ADS)

Shekaari, Ashkan; Jafari, Mahmoud

2018-05-01

Finite-temperature molecular dynamics simulations have been applied to inquire into the effect of pairwise additivity on the behavior of classical ideal gas within the temperature range of T = 250-4000 K via applying a variety of pair potentials and then examining the temperature dependence of a number of thermodynamical properties. Examining the compressibility factor reveals the most deviation from ideal-gas behavior for the Lennard-Jones system mainly due to the presence of both the attractive and repulsive terms. The systems with either attractive or repulsive intermolecular potentials are found to present no resemblance to real gases, but the most similarity to the ideal one as temperature rises.

Effect of quantum correction on nonlinear thermal wave of electrons driven by laser heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nafari, F.; Ghoranneviss, M., E-mail: ghoranneviss@gmail.com

2016-08-15

In thermal interaction of laser pulse with a deuterium-tritium (DT) plane, the thermal waves of electrons are generated instantly. Since the thermal conductivity of electron is a nonlinear function of temperature, a nonlinear heat conduction equation is used to investigate the propagation of waves in solid DT. This paper presents a self-similar analytic solution for the nonlinear heat conduction equation in a planar geometry. The thickness of the target material is finite in numerical computation, and it is assumed that the laser energy is deposited at a finite initial thickness at the initial time which results in a finite temperaturemore » for electrons at initial time. Since the required temperature range for solid DT ignition is higher than the critical temperature which equals 35.9 eV, the effects of quantum correction in thermal conductivity should be considered. This letter investigates the effects of quantum correction on characteristic features of nonlinear thermal wave, including temperature, penetration depth, velocity, heat flux, and heating and cooling domains. Although this effect increases electron temperature and thermal flux, penetration depth and propagation velocity are smaller. This effect is also applied to re-evaluate the side-on laser ignition of uncompressed DT.« less

NASTRAN thermal analyzer: A general purpose finite element heat transfer computer program

NASA Technical Reports Server (NTRS)

Lee, H.; Mason, J. B.

1972-01-01

The program not only can render temperature distributions in solids subjected to various thermal boundary conditions, including effects of diffuse-gray thermal radiation, but is fully compatible in capacity and in the finite-element model representation with that of its structural counterpart in the NASTRAN system. The development history of the finite-element approach for determining temperatures is summarized. The scope of analysis capability, program structure, features, and limitations are given with the objective of providing NASTRAN users with an overall veiw of the NASTRAN thermal analyzer.

Finite-density transition line for QCD with 695 MeV dynamical fermions

NASA Astrophysics Data System (ADS)

Greensite, Jeff; Höllwieser, Roman

2018-06-01

We apply the relative weights method to SU(3) gauge theory with staggered fermions of mass 695 MeV at a set of temperatures in the range 151 ≤T ≤267 MeV , to obtain an effective Polyakov line action at each temperature. We then apply a mean field method to search for phase transitions in the effective theory at finite densities. The result is a transition line in the plane of temperature and chemical potential, with an end point at high temperature, as expected, but also a second end point at a lower temperature. We cannot rule out the possibilities that a transition line reappears at temperatures lower than the range investigated, or that the second end point is absent for light quarks.

Fermionic halos at finite temperature in AdS/CFT

NASA Astrophysics Data System (ADS)

Argüelles, Carlos R.; Grandi, Nicolás E.

2018-05-01

We explore the gravitational backreaction of a system consisting in a very large number of elementary fermions at finite temperature, in asymptotically AdS space. We work in the hydrodynamic approximation, and solve the Tolman-Oppenheimer-Volkoff equations with a perfect fluid whose equation of state takes into account both the relativistic effects of the fermionic constituents, as well as its finite temperature effects. We find a novel dense core-diluted halo structure for the density profiles in the AdS bulk, similarly as recently reported in flat space, for the case of astrophysical dark matter halos in galaxies. We further study the critical equilibrium configurations above which the core undergoes gravitational collapse towards a massive black hole, and calculate the corresponding critical central temperatures, for two qualitatively different central regimes of the fermions: the diluted-Fermi case, and the degenerate case. As a probe for the dual CFT, we construct the holographic two-point correlator of a scalar operator with large conformal dimension in the worldline limit, and briefly discuss on the boundary CFT effects at the critical points.

Effects of Composite Pions on the Chiral Condensate within the PNJL Model at Finite Temperature

NASA Astrophysics Data System (ADS)

Blaschke, D.; Dubinin, A.; Ebert, D.; Friesen, A. V.

2018-05-01

We investigate the effect of composite pions on the behaviour of the chiral condensate at finite temperature within the Polyakov-loop improved NJL model. To this end we treat quark-antiquark correlations in the pion channel (bound states and scattering continuum) within a Beth-Uhlenbeck approach that uses medium-dependent phase shifts. A striking medium effect is the Mott transition which occurs when the binding energy vanishes and the discrete pion bound state merges the continuum. This transition is triggered by the lowering of the continuum edge due to the chiral restoration transition. This in turn also entails a modification of the Polyakov-loop so that the SU(3) center symmetry gets broken at finite temperature and dynamical quarks (and gluons) appear in the system, taking over the role of the dominant degrees of freedom from the pions. At low temperatures our model reproduces the chiral perturbation theory result for the chiral condensate while at high temperatures the PNJL model result is recovered. The new aspect of the current work is a consistent treatment of the chiral restoration transition region within the Beth-Uhlenbeck approach on the basis of mesonic phase shifts for the treatment of the correlations.

Collective many-body bounce in the breathing-mode oscillations of a finite-temperature Tonks-Girardeau gas

NASA Astrophysics Data System (ADS)

Kheruntsyan, Karen; Atas, Yasar; Bouchoule, Isabelle; Gangardt, Dimitri

2017-04-01

We analyse the breathing-mode oscillations of a harmonically quenched Tonks-Giradeau (TG) gas using an exact finite-temperature dynamical theory. We predict a striking collective manifestation of impenetrability-a collective many-body bounce effect. The effect, while being invisible in the evolution of the in situ density profile of the gas, can be revealed through a nontrivial periodic narrowing of its momentum distribution, taking place at twice the rate of the fundamental breathing-mode frequency of oscillations of the density profile. We identify physical regimes for observing the many-body bounce and construct the respective nonequilibrium phase diagram as a function of the quench strength and the initial equilibrium temperature of the gas. We also develop a finite-temperature hydrodynamic theory of the TG gas, wherein the many-body bounce is explained by an increased thermodynamic pressure during the isentropic compression cycle, which acts as a potential barrier for the particles to bounce off.

Role of electron-phonon coupling in finite-temperature dielectric functions of Au, Ag, and Cu

NASA Astrophysics Data System (ADS)

Xu, Meng; Yang, Jia-Yue; Zhang, Shangyu; Liu, Linhua

2017-09-01

Realistic representation of finite temperature dielectric functions of noble metals is crucial in describing the optical properties of advancing applications in plasmonics and optical metamaterials. However, the atomistic origins of the temperature dependence of noble metals' dielectric functions still lack full explanation. In this paper, we implement electronic structure calculations as well as ellipsometry experiments to study the finite temperature dielectric functions of noble metals Au, Ag, and Cu. Theoretically, the intraband dielectric function is described by the Drude model, of which the important quantity electron lifetime is obtained by considering the electron-phonon, electron-electron, and electron-surface scattering mechanism. The electron-phonon coupling is key to determining the temperature dependence of electron lifetime and intraband dielectric function. For the interband dielectric function, it arises from the electronic interband transition. Due to the limitation of incorporating electron-phonon coupling into the interband transition scheme, the temperature dependence of the interband dielectric function is mainly determined by the thermal expansion effect. Experimentally, variable angle spectroscopic ellipsometry measures the dielectric functions of Au and Ag over the temperature range of 300-700 K and spectral range of 2-20 µm. Those experimental measurements are consistent with theoretical results and thus verify the theoretical models for the finite temperature dielectric function.

Evaluation of the parameters affecting bone temperature during drilling using a three-dimensional dynamic elastoplastic finite element model.

PubMed

Chen, Yung-Chuan; Tu, Yuan-Kun; Zhuang, Jun-Yan; Tsai, Yi-Jung; Yen, Cheng-Yo; Hsiao, Chih-Kun

2017-11-01

A three-dimensional dynamic elastoplastic finite element model was constructed and experimentally validated and was used to investigate the parameters which influence bone temperature during drilling, including the drill speed, feeding force, drill bit diameter, and bone density. Results showed the proposed three-dimensional dynamic elastoplastic finite element model can effectively simulate the temperature elevation during bone drilling. The bone temperature rise decreased with an increase in feeding force and drill speed, however, increased with the diameter of drill bit or bone density. The temperature distribution is significantly affected by the drilling duration; a lower drilling speed reduced the exposure duration, decreases the region of the thermally affected zone. The constructed model could be applied for analyzing the influence parameters during bone drilling to reduce the risk of thermal necrosis. It may provide important information for the design of drill bits and surgical drilling powers.

Verification and rectification of the physical analogy of simulated annealing for the solution of the traveling salesman problem.

PubMed

Hasegawa, M

2011-03-01

The aim of the present study is to elucidate how simulated annealing (SA) works in its finite-time implementation by starting from the verification of its conventional optimization scenario based on equilibrium statistical mechanics. Two and one supplementary experiments, the design of which is inspired by concepts and methods developed for studies on liquid and glass, are performed on two types of random traveling salesman problems. In the first experiment, a newly parameterized temperature schedule is introduced to simulate a quasistatic process along the scenario and a parametric study is conducted to investigate the optimization characteristics of this adaptive cooling. In the second experiment, the search trajectory of the Metropolis algorithm (constant-temperature SA) is analyzed in the landscape paradigm in the hope of drawing a precise physical analogy by comparison with the corresponding dynamics of glass-forming molecular systems. These two experiments indicate that the effectiveness of finite-time SA comes not from equilibrium sampling at low temperature but from downward interbasin dynamics occurring before equilibrium. These dynamics work most effectively at an intermediate temperature varying with the total search time and thus this effective temperature is identified using the Deborah number. To test directly the role of these relaxation dynamics in the process of cooling, a supplementary experiment is performed using another parameterized temperature schedule with a piecewise variable cooling rate and the effect of this biased cooling is examined systematically. The results show that the optimization performance is not only dependent on but also sensitive to cooling in the vicinity of the above effec-tive temperature and that this feature is interpreted as a consequence of the presence or absence of the workable interbasin dynamics. It is confirmed for the present instances that the effectiveness of finite-time SA derives from the glassy relaxation dynamics occurring in the "landscape-influenced" temperature regime and that its naive optimization scenario should be rectified by considering the analogy with vitrification phenomena. A comprehensive guideline for the design of finite-time SA and SA-related algorithms is discussed on the basis of this rectified analogy.

Effective Tolman temperature induced by trace anomaly

NASA Astrophysics Data System (ADS)

Eune, Myungseok; Gim, Yongwan; Kim, Wontae

2017-04-01

Despite the finiteness of stress tensor for a scalar field on the four-dimensional Schwarzschild black hole in the Israel-Hartle-Hawking vacuum, the Tolman temperature in thermal equilibrium is certainly divergent on the horizon due to the infinite blue-shift of the Hawking temperature. The origin of this conflict is due to the fact that the conventional Tolman temperature was based on the assumption of a traceless stress tensor, which is, however, incompatible with the presence of the trace anomaly responsible for the Hawking radiation. Here, we present an effective Tolman temperature which is compatible with the presence of the trace anomaly by using the modified Stefan-Boltzmann law. Eventually, the effective Tolman temperature turns out to be finite everywhere outside the horizon, and so an infinite blue-shift of the Hawking temperature at the event horizon does not appear any more. In particular, it is vanishing on the horizon, so that the equivalence principle is exactly recovered at the horizon.

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.

Lack of a thermodynamic finite-temperature spin-glass phase in the two-dimensional randomly coupled ferromagnet

NASA Astrophysics Data System (ADS)

Zhu, Zheng; Ochoa, Andrew J.; Katzgraber, Helmut G.

2018-05-01

The search for problems where quantum adiabatic optimization might excel over classical optimization techniques has sparked a recent interest in inducing a finite-temperature spin-glass transition in quasiplanar topologies. We have performed large-scale finite-temperature Monte Carlo simulations of a two-dimensional square-lattice bimodal spin glass with next-nearest ferromagnetic interactions claimed to exhibit a finite-temperature spin-glass state for a particular relative strength of the next-nearest to nearest interactions [Phys. Rev. Lett. 76, 4616 (1996), 10.1103/PhysRevLett.76.4616]. Our results show that the system is in a paramagnetic state in the thermodynamic limit, despite zero-temperature simulations [Phys. Rev. B 63, 094423 (2001), 10.1103/PhysRevB.63.094423] suggesting the existence of a finite-temperature spin-glass transition. Therefore, deducing the finite-temperature behavior from zero-temperature simulations can be dangerous when corrections to scaling are large.

Analysis of intelligent hinged shell structures: deployable deformation and shape memory effect

NASA Astrophysics Data System (ADS)

Shi, Guang-Hui; Yang, Qing-Sheng; He, X. Q.

2013-12-01

Shape memory polymers (SMPs) are a class of intelligent materials with the ability to recover their initial shape from a temporarily fixable state when subjected to external stimuli. In this work, the thermo-mechanical behavior of a deployable SMP-based hinged structure is modeled by the finite element method using a 3D constitutive model with shape memory effect. The influences of hinge structure parameters on the nonlinear loading process are investigated. The total shape memory of the processes the hinged structure goes through, including loading at high temperature, decreasing temperature with load carrying, unloading at low temperature and recovering the initial shape with increasing temperature, are illustrated. Numerical results show that the present constitutive theory and the finite element method can effectively predict the complicated thermo-mechanical deformation behavior and shape memory effect of SMP-based hinged shell structures.

Polaronic effects at finite temperatures in the B850 ring of the LH2 complex.

PubMed

Chorošajev, Vladimir; Rancova, Olga; Abramavicius, Darius

2016-03-21

Energy transfer and relaxation dynamics in the B850 ring of LH2 molecular aggregates are described, taking into account the polaronic effects, by a stochastic time-dependent variational approach. We explicitly include the finite temperature effects in the model by sampling the initial conditions of the vibrational states randomly. This is in contrast to previous applications of the variational approach, which consider only the zero-temperature case. The method allows us to obtain both the microscopic dynamics at the single-wavefunction level and the thermally averaged picture of excitation relaxation over a wide range of temperatures. Spectroscopic observables such as temperature dependent absorption and time-resolved fluorescence spectra are calculated. Microscopic wavefunction evolution is quantified by introducing the exciton participation (localization) length and the exciton coherence length. Their asymptotic temperature dependence demonstrates that the environmental polaronic effects range from exciton self-trapping and excitonic polaron formation at low temperatures to thermally induced state delocalization and decoherence at high temperatures. While the transition towards the polaronic state can be observed on the wavefunction level, it does not produce a discernible effect on the calculated spectroscopic observables.

Effects of renormalizing the chiral SU(2) quark-meson model

NASA Astrophysics Data System (ADS)

Zacchi, Andreas; Schaffner-Bielich, Jürgen

2018-04-01

We investigate the restoration of chiral symmetry at finite temperature in the SU(2) quark-meson model, where the mean field approximation is compared to the renormalized version for quarks and mesons. In a combined approach at finite temperature, all the renormalized versions show a crossover transition. The inclusion of different renormalization scales leave the order parameter and the mass spectra nearly untouched but strongly influence the thermodynamics at low temperatures and around the phase transition. We find unphysical results for the renormalized version of mesons and the combined one.

The effective Tolman temperature in curved spacetimes

NASA Astrophysics Data System (ADS)

Kim, Wontae

We review a recently proposed effective Tolman temperature and present its applications to various gravitational systems. In the Unruh state for the evaporating black holes, the free-fall energy density is found to be negative divergent at the horizon, which is in contrast to the conventional calculations performed in the Kruskal coordinates. We resolve this conflict by invoking that the Kruskal coordinates could be no longer proper coordinates at the horizon. In the Hartle-Hawking-Israel state, despite the negative finite proper energy density at the horizon, the Tolman temperature is divergent there due to the infinite blueshift of the Hawking temperature. However, a consistent Stefan-Boltzmann law with the Hawking radiation shows that the effective Tolman temperature is eventually finite everywhere and the equivalence principle is surprisingly restored at the horizon. Then, we also show that the firewall necessarily emerges out of the Unruh vacuum, so that the Tolman temperature in the evaporating black hole is naturally divergent due to the infinitely blueshifted negative ingoing flux crossing the horizon, whereas the outgoing Hawking radiation characterized by the effective Tolman temperature indeed originates from the quantum atmosphere, not just at the horizon. So, the firewall and the atmosphere for the Hawking radiation turn out to be compatible, once we discard the fact that the Hawking radiation in the Unruh state originates from the infinitely blueshifted outgoing excitations at the horizon. Finally, as a cosmological application, the initial radiation energy density in warm inflation scenarios has been assumed to be finite when inflation starts. We successfully find the origin of the nonvanishing initial radiation energy density in the warm inflation by using the effective Tolman temperature.

Finite Volume Numerical Methods for Aeroheating Rate Calculations from Infrared Thermographic Data

NASA Technical Reports Server (NTRS)

Daryabeigi, Kamran; Berry, Scott A.; Horvath, Thomas J.; Nowak, Robert J.

2003-01-01

The use of multi-dimensional finite volume numerical techniques with finite thickness models for calculating aeroheating rates from measured global surface temperatures on hypersonic wind tunnel models was investigated. Both direct and inverse finite volume techniques were investigated and compared with the one-dimensional semi -infinite technique. Global transient surface temperatures were measured using an infrared thermographic technique on a 0.333-scale model of the Hyper-X forebody in the Langley Research Center 20-Inch Mach 6 Air tunnel. In these tests the effectiveness of vortices generated via gas injection for initiating hypersonic transition on the Hyper-X forebody were investigated. An array of streamwise orientated heating striations were generated and visualized downstream of the gas injection sites. In regions without significant spatial temperature gradients, one-dimensional techniques provided accurate aeroheating rates. In regions with sharp temperature gradients due to the striation patterns two-dimensional heat transfer techniques were necessary to obtain accurate heating rates. The use of the one-dimensional technique resulted in differences of 20% in the calculated heating rates because it did not account for lateral heat conduction in the model.

Pion properties at finite isospin chemical potential with isospin symmetry breaking

NASA Astrophysics Data System (ADS)

Wu, Zuqing; Ping, Jialun; Zong, Hongshi

2017-12-01

Pion properties at finite temperature, finite isospin and baryon chemical potentials are investigated within the SU(2) NJL model. In the mean field approximation for quarks and random phase approximation fpr mesons, we calculate the pion mass, the decay constant and the phase diagram with different quark masses for the u quark and d quark, related to QCD corrections, for the first time. Our results show an asymmetry between μI <0 and μI >0 in the phase diagram, and different values for the charged pion mass (or decay constant) and neutral pion mass (or decay constant) at finite temperature and finite isospin chemical potential. This is caused by the effect of isospin symmetry breaking, which is from different quark masses. Supported by National Natural Science Foundation of China (11175088, 11475085, 11535005, 11690030) and the Fundamental Research Funds for the Central Universities (020414380074)

An analysis of temperature effect in a finite journal bearing with spatial tilt and viscous dissipation

NASA Technical Reports Server (NTRS)

Braun, M. J.; Mullen, R. L.; Hendricks, R. C.

1984-01-01

The analysis presented herein deals with the evaluation of the pressure, velocity, and temperature profiles in a finite-length plane journal bearing. The geometry of the case under study consists of a spatially tilted shaft. The two-dimensional Reynolds equation accounts for the variation of the clearance gap h with x and z and is used to model the pressure field. The latter is solved for a variety of shaft tilt angles and then used to calculate the two-dimensional flow field. Finally, the flow field is used in the energy equation to solve for the film temperature profile, when the effect of viscous dissipation is taken into account.

Quantum Correlation in the XY Spin Model with Anisotropic Three-Site Interaction

NASA Astrophysics Data System (ADS)

Wang, Yao; Chai, Bing-Bing; Guo, Jin-Liang

2018-05-01

We investigate pairwise entanglement and quantum discord (QD) in the XY spin model with anisotropic three-site interaction at zero and finite temperatures. For both the nearest-neighbor spins and the next nearest-neighbor spins, special attention is paid to the dependence of entanglement and QD on the anisotropic parameter δ induced by the next nearest-neighbor spins. We show that the behavior of QD differs in many ways from entanglement under the influences of the anisotropic three-site interaction at finite temperatures. More important, comparing the effects of δ on the entanglement and QD, we find the anisotropic three-site interaction plays an important role in the quantum correlations at zero and finite temperatures. It is found that δ can strengthen the quantum correlation for both the nearest-neighbor spins and the next nearest-neighbor spins, especially for the nearest-neighbor spins at low temperature.

Dynamics of DNA breathing: weak noise analysis, finite time singularity, and mapping onto the quantum Coulomb problem.

PubMed

Fogedby, Hans C; Metzler, Ralf

2007-12-01

We study the dynamics of denaturation bubbles in double-stranded DNA on the basis of the Poland-Scheraga model. We show that long time distributions for the survival of DNA bubbles and the size autocorrelation function can be derived from an asymptotic weak noise approach. In particular, below the melting temperature the bubble closure corresponds to a noisy finite time singularity. We demonstrate that the associated Fokker-Planck equation is equivalent to a quantum Coulomb problem. Below the melting temperature, the bubble lifetime is associated with the continuum of scattering states of the repulsive Coulomb potential; at the melting temperature, the Coulomb potential vanishes and the underlying first exit dynamics exhibits a long time power law tail; above the melting temperature, corresponding to an attractive Coulomb potential, the long time dynamics is controlled by the lowest bound state. Correlations and finite size effects are discussed.

Two-dimensional finite element heat transfer model of softwood. Part II, Macrostructural effects

Treesearch

Hongmei Gu; John F. Hunt

2006-01-01

A two-dimensional finite element model was used to study the effects of structural features on transient heat transfer in softwood lumber with various orientations. Transient core temperature was modeled for lumber samples “cut” from various locations within a simulated log. The effects of ring orientation, earlywood to latewood (E/L) ratio, and ring density were...

Effects of the regularization on the restoration of chiral and axial symmetries

NASA Astrophysics Data System (ADS)

Costa, P.; Ruivo, M. C.; de Sousa, C. A.

2008-05-01

The effects of a type of regularization for finite temperatures on the restoration of chiral and axial symmetries are investigated within the SU(3) Nambu-Jona-Lasinio model. The regularization consists in using an infinite cutoff in the integrals that are convergent at finite temperature, a procedure that allows one to take into account the effects of high momentum quarks at high temperatures. It is found that the critical temperature for the phase transition is closer to lattice results than the one obtained with the conventional regularization, and the restoration of chiral and axial symmetries, signaled by the behavior of several observables, occurs simultaneously and at a higher temperature. The restoration of the axial symmetry appears as a natural consequence of the full recovering of the chiral symmetry that was dynamically broken. By using an additional ansatz that simulates instanton suppression effects, by means of a convenient temperature dependence of the anomaly coefficient, we found that the restoration of U(2) symmetry is shifted to lower values, but the dominant effect at high temperatures comes from the new regularization that enhances the decrease of quark condensates, especially in the strange sector.

Nuclear Deformation at Finite Temperature

NASA Astrophysics Data System (ADS)

Alhassid, Y.; Gilbreth, C. N.; Bertsch, G. F.

2014-12-01

Deformation, a key concept in our understanding of heavy nuclei, is based on a mean-field description that breaks the rotational invariance of the nuclear many-body Hamiltonian. We present a method to analyze nuclear deformations at finite temperature in a framework that preserves rotational invariance. The auxiliary-field Monte Carlo method is used to generate a statistical ensemble and calculate the probability distribution associated with the quadrupole operator. Applying the technique to nuclei in the rare-earth region, we identify model-independent signatures of deformation and find that deformation effects persist to temperatures higher than the spherical-to-deformed shape phase-transition temperature of mean-field theory.

Modeling the absorption spectrum of the permanganate ion in vacuum and in aqueous solution

NASA Astrophysics Data System (ADS)

Olsen, Jógvan Magnus Haugaard; Hedegård, Erik Donovan

The absorption spectrum of the MnO$_{4}$$^{-}$ ion has been a test-bed for quantum-chemical methods over the last decades. Its correct description requires highly-correlated multiconfigurational methods, which are incompatible with the inclusion of finite-temperature and solvent effects due to their high computational demands. Therefore, implicit solvent models are usually employed. Here we show that implicit solvent models are not sufficiently accurate to model the solvent shift of MnO$_{4}$$^{-}$, and we analyze the origins of their failure. We obtain the correct solvent shift for MnO$_{4}$$^{-}$ in aqueous solution by employing the polarizable embedding (PE) model combined with a range-separated complete active space short-range density functional theory method (CAS-srDFT). Finite-temperature effects are taken into account by averaging over structures obtained from ab initio molecular dynamics simulations. The explicit treatment of finite-temperature and solvent effects facilitates the interpretation of the bands in the low-energy region of the MnO$_{4}$$^{-}$ absorption spectrum, whose assignment has been elusive.

A simplified heat transfer model for predicting temperature change inside food package kept in cold room.

PubMed

Raval, A H; Solanki, S C; Yadav, Rajvir

2013-04-01

A simple analytical heat flow model for a closed rectangular food package containing fruits or vegetables is proposed for predicting time temperature distribution during transient cooling in a controlled environment cold room. It is based on the assumption of only conductive heat transfer inside a closed food package with effective thermal properties, and convective and radiative heat transfer at the outside of the package. The effective thermal conductivity of the food package is determined by evaluating its effective thermal resistance to heat conduction in the packages. Food packages both as an infinite slab and a finite slab have been investigated. The finite slab solution has been obtained as the product of three infinite slab solutions describe in ASHRAE guide and data book. Time temperature variation has been determined and is presented graphically. The cooling rate and the half cooling time were also obtained. These predicted values, are compared with the experimentally measured values for both the finite and infinite closed packages containing oranges. An excellent agreement between them validated the simple proposed model.

Adiabatic and nonadiabatic perturbation theory for coherence vector description of neutrino oscillations

NASA Astrophysics Data System (ADS)

Hollenberg, Sebastian; Päs, Heinrich

2012-01-01

The standard wave function approach for the treatment of neutrino oscillations fails in situations where quantum ensembles at a finite temperature with or without an interacting background plasma are encountered. As a first step to treat such phenomena in a novel way, we propose a unified approach to both adiabatic and nonadiabatic two-flavor oscillations in neutrino ensembles with finite temperature and generic (e.g., matter) potentials. Neglecting effects of ensemble decoherence for now, we study the evolution of a neutrino ensemble governed by the associated quantum kinetic equations, which apply to systems with finite temperature. The quantum kinetic equations are solved formally using the Magnus expansion and it is shown that a convenient choice of the quantum mechanical picture (e.g., the interaction picture) reveals suitable parameters to characterize the physics of the underlying system (e.g., an effective oscillation length). It is understood that this method also provides a promising starting point for the treatment of the more general case in which decoherence is taken into account.

The new finite temperature Schrödinger equations with strong or weak interaction

NASA Astrophysics Data System (ADS)

Li, Heling; Yang, Bin; Shen, Hongjun

2017-07-01

Implanting the thoughtway of thermostatistics into quantum mechanics, we formulate new Schrödinger equations of multi-particle and single-particle respectively at finite temperature. To get it, the pure-state free energies and the microscopic entropy operators are introduced and meantime the pure-state free energies take the places of mechanical energies at finite temperature. The definition of microscopic entropy introduced by Wu was also revised, and the strong or weak interactions dependent on temperature are considered in multi-particle Schrödinger Equations. Based on the new Schrödinger equation at finite temperature, two simple cases were analyzed. The first one is concerning some identical harmonic oscillators in N lattice points and the other one is about N unrelated particles in three dimensional in finite potential well. From the results gotten, we conclude that the finite temperature Schrödinger equation is particularly important for mesoscopic systems.

Validation of High Displacement Piezoelectric Actuator Finite Element Models

NASA Technical Reports Server (NTRS)

Taleghani, B. K.

2000-01-01

The paper presents the results obtained by using NASTRAN(Registered Trademark) and ANSYS(Regitered Trademark) finite element codes to predict doming of the THUNDER piezoelectric actuators during the manufacturing process and subsequent straining due to an applied input voltage. To effectively use such devices in engineering applications, modeling and characterization are essential. Length, width, dome height, and thickness are important parameters for users of such devices. Therefore, finite element models were used to assess the effects of these parameters. NASTRAN(Registered Trademark) and ANSYS(Registered Trademark) used different methods for modeling piezoelectric effects. In NASTRAN(Registered Trademark), a thermal analogy was used to represent voltage at nodes as equivalent temperatures, while ANSYS(Registered Trademark) processed the voltage directly using piezoelectric finite elements. The results of finite element models were validated by using the experimental results.

Improved method for detecting local discontinuities in CMB data by finite differencing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowyer, Jude; Jaffe, Andrew H.

2011-01-15

An unexpected distribution of temperatures in the CMB could be a sign of new physics. In particular, the existence of cosmic defects could be indicated by temperature discontinuities via the Kaiser-Stebbins effect. In this paper, we show how performing finite differences on a CMB map, with the noise regularized in harmonic space, may expose such discontinuities, and we report the results of this process on the 7-year Wilkinson Microwave Anisotropy Probe data.

A New Finite-Conductivity Droplet Evaporation Model Including Liquid Turbulence Effect

NASA Technical Reports Server (NTRS)

Balasubramanyam, M. S.; Chen, C. P.; Trinh, H. P.

2006-01-01

A new approach to account for finite thermal conductivity and turbulence effects within atomizing droplets of an evaporating spray is presented in this paper. The model is an extension of the T-blob and T-TAB atomization/spray model of Trinh and Chen [9]. This finite conductivity model is based on the two-temperature film theory in which the turbulence characteristics of the droplet are used to estimate the effective thermal diffusivity for the liquid-side film thickness. Both one-way and two-way coupled calculations were performed to investigate the performance cf this model against the published experimental data.

Kosterlitz-Thouless transition and vortex-antivortex lattice melting in two-dimensional Fermi gases with p - or d -wave pairing

NASA Astrophysics Data System (ADS)

Cao, Gaoqing; He, Lianyi; Huang, Xu-Guang

2017-12-01

We present a theoretical study of the finite-temperature Kosterlitz-Thouless (KT) and vortex-antivortex lattice (VAL) melting transitions in two-dimensional Fermi gases with p - or d -wave pairing. For both pairings, when the interaction is tuned from weak to strong attractions, we observe a quantum phase transition from the Bardeen-Cooper-Schrieffer (BCS) superfluidity to the Bose-Einstein condensation (BEC) of difermions. The KT and VAL transition temperatures increase during this BCS-BEC transition and approach constant values in the deep BEC region. The BCS-BEC transition is characterized by the nonanalyticities of the chemical potential, the superfluid order parameter, and the sound velocities as functions of the interaction strength at both zero and finite temperatures; however, the temperature effect tends to weaken the nonanalyticities compared to the zero-temperature case. The effect of mismatched Fermi surfaces on the d -wave pairing is also studied.

Finite-temperature H behaviors in tungsten and molybdenum: first-principles total energy and vibration spectrum calculations

NASA Astrophysics Data System (ADS)

Liu, Yue-Lin; Ding, Fang; Luo, G.-N.; Chen, Chang-An

2017-12-01

We have carried out systematic first-principles total energy and vibration spectrum calculations to investigate the finite-temperature H dissolution behaviors in tungsten and molybdenum, which are considered promising candidates for the first wall in nuclear fusion reactors. The temperature effect is considered by the lattice expansion and phonon vibration. We demonstrate that the H Gibbs energy of formation in both tetrahedral and octahedral interstitial positions depends strongly on the temperature. The H Gibbs energy of formation under one atmosphere of pressure increases significantly with increasing temperature. The phonon vibration contribution plays a decisive role in the H Gibbs energy of formation with the increasing temperature. Using the predicted H Gibbs energy of formation, our calculated H concentrations in both metals are about one or two orders of magnitude lower than the experimental data at temperature range from 900 to 2400 K. Such a discrepancy can be reasonably explained by the defect-capturing effect.

Dynamical phase transitions at finite temperature from fidelity and interferometric Loschmidt echo induced metrics

NASA Astrophysics Data System (ADS)

Mera, Bruno; Vlachou, Chrysoula; Paunković, Nikola; Vieira, Vítor R.; Viyuela, Oscar

2018-03-01

We study finite-temperature dynamical quantum phase transitions (DQPTs) by means of the fidelity and the interferometric Loschmidt echo (LE) induced metrics. We analyze the associated dynamical susceptibilities (Riemannian metrics), and derive analytic expressions for the case of two-band Hamiltonians. At zero temperature, the two quantities are identical, nevertheless, at finite temperatures they behave very differently. Using the fidelity LE, the zero-temperature DQPTs are gradually washed away with temperature, while the interferometric counterpart exhibits finite-temperature phase transitions. We analyze the physical differences between the two finite-temperature LE generalizations, and argue that, while the interferometric one is more sensitive and can therefore provide more information when applied to genuine quantum (microscopic) systems, when analyzing many-body macroscopic systems, the fidelity-based counterpart is a more suitable quantity to study. Finally, we apply the previous results to two representative models of topological insulators in one and two dimensions.

Effects of finite electron temperature on gradient drift instabilities in partially magnetized plasmas

NASA Astrophysics Data System (ADS)

Lakhin, V. P.; Ilgisonis, V. I.; Smolyakov, A. I.; Sorokina, E. A.; Marusov, N. A.

2018-01-01

The gradient-drift instabilities of partially magnetized plasmas in plasma devices with crossed electric and magnetic fields are investigated in the framework of the two-fluid model with finite electron temperature in an inhomogeneous magnetic field. The finite electron Larmor radius (FLR) effects are also included via the gyroviscosity tensor taking into account the magnetic field gradient. This model correctly describes the electron dynamics for k⊥ρe>1 in the sense of Padé approximants (here, k⊥ and ρe are the wavenumber perpendicular to the magnetic field and the electron Larmor radius, respectively). The local dispersion relation for electrostatic plasma perturbations with the frequency in the range between the ion and electron cyclotron frequencies and propagating strictly perpendicular to the magnetic field is derived. The dispersion relation includes the effects of the equilibrium E ×B electron current, finite ion velocity, electron inertia, electron FLR, magnetic field gradients, and Debye length effects. The necessary and sufficient condition of stability is derived, and the stability boundary is found. It is shown that, in general, the electron inertia and FLR effects stabilize the short-wavelength perturbations. In some cases, such effects completely suppress the high-frequency short-wavelength modes so that only the long-wavelength low-frequency (with respect to the lower-hybrid frequency) modes remain unstable.

Efimov effect for heteronuclear three-body systems at positive scattering length and finite temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Emmons, Samuel B.; Kang, Daekyoung; Acharya, Bijaya

2017-09-08

Here, we study the recombination process of three atoms scattering into an atom and diatomic molecule in heteronuclear mixtures of ultracold atomic gases with large and positive interspecies scattering length at finite temperature. We calculate the temperature dependence of the three-body recombination rates by extracting universal scaling functions that parametrize the energy dependence of the scattering matrix. We compare our results to experimental data for the 40K– 87Rb mixture and make a prediction for 6Li– 87Rb. We find that contributions from higher partial wave channels significantly impact the total rate and, in systems with particularly large mass imbalance, can evenmore » obliterate the recombination minima associated with the Efimov effect.« less

Finite-Length Line Source Superposition Model (FLLSSM)

NASA Astrophysics Data System (ADS)

1980-03-01

A linearized thermal conduction model was developed to economically determine media temperatures in geologic repositories for nuclear wastes. Individual canisters containing either high level waste or spent fuel assemblies were represented as finite length line sources in a continuous media. The combined effects of multiple canisters in a representative storage pattern were established at selected points of interest by superposition of the temperature rises calculated for each canister. The methodology is outlined and the computer code FLLSSM which performs required numerical integrations and superposition operations is described.

Flow adjustment inside large finite-size wind farms approaching the infinite wind farm regime

NASA Astrophysics Data System (ADS)

Wu, Ka Ling; Porté-Agel, Fernando

2017-04-01

Due to the increasing number and the growing size of wind farms, the distance among them continues to decrease. Thus, it is necessary to understand how these large finite-size wind farms and their wakes could interfere the atmospheric boundary layer (ABL) dynamics and adjacent wind farms. Fully-developed flow inside wind farms has been extensively studied through numerical simulations of infinite wind farms. The transportation of momentum and energy is only vertical and the advection of them is neglected in these infinite wind farms. However, less attention has been paid to examine the length of wind farms required to reach such asymptotic regime and the ABL dynamics in the leading and trailing edges of the large finite-size wind farms. Large eddy simulations are performed in this study to investigate the flow adjustment inside large finite-size wind farms in conventionally-neutral boundary layer with the effect of Coriolis force and free-atmosphere stratification from 1 to 5 K/km. For the large finite-size wind farms considered in the present work, when the potential temperature lapse rate is 5 K/km, the wind farms exceed the height of the ABL by two orders of magnitude for the incoming flow inside the farms to approach the fully-developed regime. An entrance fetch of approximately 40 times of the ABL height is also required for such flow adjustment. At the fully-developed flow regime of the large finite-size wind farms, the flow characteristics match those of infinite wind farms even though they have different adjustment length scales. The role of advection at the entrance and exit regions of the large finite-size wind farms is also examined. The interaction between the internal boundary layer developed above the large finite-size wind farms and the ABL under different potential temperature lapse rates are compared. It is shown that the potential temperature lapse rate plays a role in whether the flow inside the large finite-size wind farms adjusts to the fully-developed flow regime. The flow characteristics of the wake of these large finite-size wind farms are reported to forecast the effect of large finite-size wind farms on adjacent wind farms. A power deficit as large as 8% is found at a distance of 10 km downwind from the large finite-size wind farms.

Length and temperature dependence of the mechanical properties of finite-size carbyne

NASA Astrophysics Data System (ADS)

Yang, Xueming; Huang, Yanhui; Cao, Bingyang; To, Albert C.

2017-09-01

Carbyne is an ideal one-dimensional conductor and the thinnest interconnection in an ultimate nano-device and it requires an understanding of the mechanical properties that affect device performance and reliability. Here, we report the mechanical properties of finite-size carbyne, obtained by a molecular dynamics simulation study based on the adaptive intermolecular reactive empirical bond order potential. To avoid confusion in assigning the effective cross-sectional area of carbyne, the value of the effective cross-sectional area of carbyne (4.148 Å2) was deduced via experiment and adopted in our study. Ends-constraints effects on the ultimate stress (maximum force) of the carbyne chains are investigated, revealing that the molecular dynamics simulation results agree very well with the experimental results. The ultimate strength, Young's Modulus and maximum strain of carbyne are rather sensitive to the temperature and all decrease with the temperature. Opposite tendencies of the length dependence of the overall ultimate strength and maximum strain of carbyne at room temperature and very low temperature have been found, and analyses show that this originates in the ends effect of carbyne.

Frustrated magnetism and caloric effects in Mn-based antiperovskite nitrides: Ab initio theory

NASA Astrophysics Data System (ADS)

Zemen, J.; Mendive-Tapia, E.; Gercsi, Z.; Banerjee, R.; Staunton, J. B.; Sandeman, K. G.

2017-05-01

We model changes of magnetic ordering in Mn-based antiperovskite nitrides driven by biaxial lattice strain at zero and at finite temperature. We employ a noncollinear spin-polarized density functional theory to compare the response of the geometrically frustrated exchange interactions to a tetragonal symmetry breaking (the so called piezomagnetic effect) across a range of Mn3AN (A = Rh, Pd, Ag, Co, Ni, Zn, Ga, In, Sn) at zero temperature. Building on the robustness of the effect we focus on Mn3GaN and extend our study to finite temperature using the disordered local moment (DLM) first-principles electronic structure theory to model the interplay between the ordering of Mn magnetic moments and itinerant electron states. We discover a rich temperature-strain magnetic phase diagram with two previously unreported phases stabilized by strains larger than 0.75% and with transition temperatures strongly dependent on strain. We propose an elastocaloric cooling cycle crossing two of the available phase transitions to achieve simultaneously a large isothermal entropy change (due to the first-order transition) and a large adiabatic temperature change (due to the second-order transition).

Thermodynamic analysis of journal bearings operating under steady state loading in laminar regime. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Khonsari, M. M.

1983-01-01

Thermohydrodynamic effects in journal bearings operating under steady load in laminar regime are investigated. An analytical model for the finite and infinitely long journal bearings is formulated. The model includes correction factors for the cavitation effects in the unloaded region of the bearing and the mixing of the recirculating oil and supply oil at the oil inlet. A finite difference computer program is developed to numerically solve the governing equations of the continuity, Reynolds, energy, Laplace heat conduction, and a viscosity-temperature relation simultaneously. The program includes a numerical technique for obtaining an isothermal shaft temperature. The numerical results of temperature distribution and the heat effects on the bearing load carrying capacity agree closely with those of experimental findings. Several different sets of simpler boundary conditions for the energy equation are studied.

Magnetospheric Whistler Mode Raytracing with the Inclusion of Finite Electron and ion Temperature

NASA Astrophysics Data System (ADS)

Maxworth, Ashanthi S.

Whistler mode waves are a type of a low frequency (100 Hz - 30 kHz) wave, which exists only in a magnetized plasma. These waves play a major role in Earth's magnetosphere. Due to the impact of whistler mode waves in many fields such as space weather, satellite communications and lifetime of space electronics, it is important to accurately predict the propagation path of these waves. The method used to determine the propagation path of whistler waves is called numerical raytracing. Numerical raytracing determines the power flow path of the whistler mode waves by solving a set of equations known as the Haselgrove's equations. In the majority of the previous work, raytracing was implemented assuming a cold background plasma (0 K), but the actual magnetosphere is at a temperature of about 1 eV (11600 K). In this work we have modified the numerical raytracing algorithm to work at finite electron and ion temperatures. The finite temperature effects have also been introduced into the formulations for linear cyclotron resonance wave growth and Landau damping, which are the primary mechanisms for whistler mode growth and attenuation in the magnetosphere. Including temperature increases the complexity of numerical raytracing, but the overall effects are mostly limited to increasing the group velocity of the waves at highly oblique wave normal angles.

Stamping of Thin-Walled Structural Components with Magnesium Alloy AZ31 Sheets

NASA Astrophysics Data System (ADS)

Chen, Fuh-Kuo; Chang, Chih-Kun

2005-08-01

In the present study, the stamping process for manufacturing cell phone cases with magnesium alloy AZ31 sheets was studied using both the experimental approach and the finite element analysis. In order to determine the proper forming temperature and set up a fracture criterion, tensile tests and forming limit tests were first conducted to obtain the mechanical behaviors of AZ31 sheets at various elevated temperatures. The mechanical properties of Z31 sheets obtained from the experiments were then adopted in the finite element analysis to investigate the effects of the process parameters on the formability of the stamping process of cell phone cases. The finite element simulation results revealed that both the fracture and wrinkle defects could not be eliminated at the same time by adjusting blank-holder force or blank size. A drawbead design was then performed using the finite element simulations to determine the size and the location of drawbead required to suppress the wrinkle defect. An optimum stamping process, including die geometry, forming temperature, and blank dimension, was then determined for manufacturing the cell phone cases. The finite element analysis was validated by the good agreement between the simulation results and the experimental data. It confirms that the cell phone cases can be produced with magnesium alloy AZ31 sheet by the stamping process at elevated temperatures.

Critical scaling of the mutual information in two-dimensional disordered Ising models

NASA Astrophysics Data System (ADS)

Sriluckshmy, P. V.; Mandal, Ipsita

2018-04-01

Rényi mutual information, computed from second Rényi entropies, can identify classical phase transitions from their finite-size scaling at critical points. We apply this technique to examine the presence or absence of finite temperature phase transitions in various two-dimensional models on a square lattice, which are extensions of the conventional Ising model by adding a quenched disorder. When the quenched disorder causes the nearest neighbor bonds to be both ferromagnetic and antiferromagnetic, (a) a spin glass phase exists only at zero temperature, and (b) a ferromagnetic phase exists at a finite temperature when the antiferromagnetic bond distributions are sufficiently dilute. Furthermore, finite temperature paramagnetic-ferromagnetic transitions can also occur when the disordered bonds involve only ferromagnetic couplings of random strengths. In our numerical simulations, the ‘zero temperature only’ phase transitions are identified when there is no consistent finite-size scaling of the Rényi mutual information curves, while for finite temperature critical points, the curves can identify the critical temperature T c by their crossings at T c and 2 Tc .

Automatic control of finite element models for temperature-controlled radiofrequency ablation.

PubMed

Haemmerich, Dieter; Webster, John G

2005-07-14

The finite element method (FEM) has been used to simulate cardiac and hepatic radiofrequency (RF) ablation. The FEM allows modeling of complex geometries that cannot be solved by analytical methods or finite difference models. In both hepatic and cardiac RF ablation a common control mode is temperature-controlled mode. Commercial FEM packages don't support automating temperature control. Most researchers manually control the applied power by trial and error to keep the tip temperature of the electrodes constant. We implemented a PI controller in a control program written in C++. The program checks the tip temperature after each step and controls the applied voltage to keep temperature constant. We created a closed loop system consisting of a FEM model and the software controlling the applied voltage. The control parameters for the controller were optimized using a closed loop system simulation. We present results of a temperature controlled 3-D FEM model of a RITA model 30 electrode. The control software effectively controlled applied voltage in the FEM model to obtain, and keep electrodes at target temperature of 100 degrees C. The closed loop system simulation output closely correlated with the FEM model, and allowed us to optimize control parameters. The closed loop control of the FEM model allowed us to implement temperature controlled RF ablation with minimal user input.

Emergent Electronic and Dielectric Properties of Interacting Nanoparticles at Finite Temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Greenwood, Arin R.; Voros, Marton; Giberti, Federico

Lead chalcogenide nanoparticle solids have been successfully integrated into certified solar cells and represent promising platforms for the design of novel photoabsorbers for photoelectrochemical cells. While much attention has been drawn to improving efficiency and device performance through altering the character of the individual nanoparticles, the role of interactions between nanoparticles is not yet well-understood. Using first-principles molecular dynamics and electronic structure calculations, we investigated the combined effect of temperature and interaction on functionalized lead chalcogenide nanoparticles (NPs). Here, we show that at finite temperature, interacting NPs are dynamical dipolar systems, with the average values of dipole moments and polarizabilitiesmore » substantially increased with respect to those of the isolated building blocks. In addition, we show that the interacting NPs exhibit slightly smaller fundamental gaps that decrease as a function of temperature and that the radiative lifetimes of both the isolated NPs and the solids are greatly reduced at finite temperature compared to T = 0. Lastly, we present a critical discussion of various results reported in the literature for the values of dipole moments of nanoparticles.« less

Emergent Electronic and Dielectric Properties of Interacting Nanoparticles at Finite Temperature

DOE PAGES

Greenwood, Arin R.; Voros, Marton; Giberti, Federico; ...

2017-12-11

Lead chalcogenide nanoparticle solids have been successfully integrated into certified solar cells and represent promising platforms for the design of novel photoabsorbers for photoelectrochemical cells. While much attention has been drawn to improving efficiency and device performance through altering the character of the individual nanoparticles, the role of interactions between nanoparticles is not yet well-understood. Using first-principles molecular dynamics and electronic structure calculations, we investigated the combined effect of temperature and interaction on functionalized lead chalcogenide nanoparticles (NPs). Here, we show that at finite temperature, interacting NPs are dynamical dipolar systems, with the average values of dipole moments and polarizabilitiesmore » substantially increased with respect to those of the isolated building blocks. In addition, we show that the interacting NPs exhibit slightly smaller fundamental gaps that decrease as a function of temperature and that the radiative lifetimes of both the isolated NPs and the solids are greatly reduced at finite temperature compared to T = 0. Lastly, we present a critical discussion of various results reported in the literature for the values of dipole moments of nanoparticles.« less

Numerical simulation of one-dimensional heat transfer in composite bodies with phase change. M.S. Thesis, 1980 Final Report; [wing deicing pads

NASA Technical Reports Server (NTRS)

Dewitt, K. J.; Baliga, G.

1982-01-01

A numerical simulation was developed to investigate the one dimensional heat transfer occurring in a system composed of a layered aircraft blade having an ice deposit on its surface. The finite difference representation of the heat conduction equations was done using the Crank-Nicolson implicit finite difference formulation. The simulation considers uniform or time dependent heat sources, from heaters which can be either point sources or of finite thickness. For the ice water phase change, a numerical method which approximates the latent heat effect by a large heat capacity over a small temperature interval was applied. The simulation describes the temperature profiles within the various layers of the de-icer pad, as well as the movement of the ice water interface. The simulation could also be used to predict the one dimensional temperature profiles in any composite slab having different boundary conditions.

Pasta phases in core-collapse supernova matter

NASA Astrophysics Data System (ADS)

Pais, Helena; Chiacchiera, Silvia; Providência, Constança

2016-04-01

The pasta phase in core-collapse supernova matter (finite temperatures and fixed proton fractions) is studied within relativistic mean field models. Three different calculations are used for comparison, the Thomas-Fermi (TF), the Coexisting Phases (CP) and the Compressible Liquid Drop (CLD) approximations. The effects of including light clusters in nuclear matter and the densities at which the transitions between pasta configurations and to uniform matter occur are also investigated. The free energy and pressure, in the space of particle number densities and temperatures expected to cover the pasta region, are calculated. Finally, a comparison with a finite temperature Skyrme-Hartree-Fock calculation is drawn.

Numerical Modeling of Turbulence Effects within an Evaporating Droplet in Atomizing Sprays

NASA Technical Reports Server (NTRS)

Balasubramanyam, M. S.; Chen, C. P.; Trinh, H. P.

2006-01-01

A new approach to account for finite thermal conductivity and turbulence effects within atomizing liquid sprays is presented in this paper. The model is an extension of the T-blob and T-TAB atomization/spray model of Trinh and Chen (2005). This finite conductivity model is based on the two-temperature film theory, where the turbulence characteristics of the droplet are used to estimate the effective thermal diffhsivity within the droplet phase. Both one-way and two-way coupled calculations were performed to investigate the performance of this model. The current evaporation model is incorporated into the T-blob atomization model of Trinh and Chen (2005) and implemented in an existing CFD Eulerian-Lagrangian two-way coupling numerical scheme. Validation studies were carried out by comparing with available evaporating atomization spray experimental data in terms of jet penetration, temperature field, and droplet SMD distribution within the spray. Validation results indicate the superiority of the finite-conductivity model in low speed parallel flow evaporating spray.

Nonlinear temperature dependent failure analysis of finite width composite laminates

NASA Technical Reports Server (NTRS)

Nagarkar, A. P.; Herakovich, C. T.

1979-01-01

A quasi-three dimensional, nonlinear elastic finite element stress analysis of finite width composite laminates including curing stresses is presented. Cross-ply, angle-ply, and two quasi-isotropic graphite/epoxy laminates are studied. Curing stresses are calculated using temperature dependent elastic properties that are input as percent retention curves, and stresses due to mechanical loading in the form of an axial strain are calculated using tangent modulii obtained by Ramberg-Osgood parameters. It is shown that curing stresses and stresses due to tensile loading are significant as edge effects in all types of laminate studies. The tensor polynomial failure criterion is used to predict the initiation of failure. The mode of failure is predicted by examining individual stress contributions to the tensor polynomial.

Ab Initio Simulations of Temperature Dependent Phase Stability and Martensitic Transitions in NiTi

NASA Technical Reports Server (NTRS)

Haskins, Justin B.; Thompson, Alexander E.; Lawson, John W.

2016-01-01

For NiTi based alloys, the shape memory effect is governed by a transition from a low-temperature martensite phase to a high-temperature austenite phase. Despite considerable experimental and computational work, basic questions regarding the stability of the phases and the martensitic phase transition remain unclear even for the simple case of binary, equiatomic NiTi. We perform ab initio molecular dynamics simulations to describe the temperature-dependent behavior of NiTi and resolve several of these outstanding issues. Structural correlation functions and finite temperature phonon spectra are evaluated to determine phase stability. In particular, we show that finite temperature, entropic effects stabilize the experimentally observed martensite (B19') and austenite (B2) phases while destabilizing the theoretically predicted (B33) phase. Free energy computations based on ab initio thermodynamic integration confirm these results and permit estimates of the transition temperature between the phases. In addition to the martensitic phase transition, we predict a new transition between the B33 and B19' phases. The role of defects in suppressing these phase transformations is discussed.

Finite size effects on the experimental observables of the Glauber model: a theoretical and experimental investigation

NASA Astrophysics Data System (ADS)

Vindigni, A.; Bogani, L.; Gatteschi, D.; Sessoli, R.; Rettori, A.; Novak, M. A.

2004-05-01

We investigate the relaxation time, τ, of a dilute Glauber kinetic Ising chain obtained by ac susceptibility and SQUID magnetometry on a Co(II)-organic radical Ising 1D ferrimagnet doped with Zn(II). Theoretically we predicted a crossover in the temperature-dependence of τ, when the average segment is of the same order of the correlation length. Comparing the experimental results with theory we conclude that in the investigted temperature range the correlation length exceeds the finite length also in the pure sample.

The Overshoot Phenomenon in Geodynamics Codes

NASA Astrophysics Data System (ADS)

Kommu, R. K.; Heien, E. M.; Kellogg, L. H.; Bangerth, W.; Heister, T.; Studley, E. H.

2013-12-01

The overshoot phenomenon is a common occurrence in numerical software when a continuous function on a finite dimensional discretized space is used to approximate a discontinuous jump, in temperature and material concentration, for example. The resulting solution overshoots, and undershoots, the discontinuous jump. Numerical simulations play an extremely important role in mantle convection research. This is both due to the strong temperature and stress dependence of viscosity and also due to the inaccessibility of deep earth. Under these circumstances, it is essential that mantle convection simulations be extremely accurate and reliable. CitcomS and ASPECT are two finite element based mantle convection simulations developed and maintained by the Computational Infrastructure for Geodynamics. CitcomS is a finite element based mantle convection code that is designed to run on multiple high-performance computing platforms. ASPECT, an adaptive mesh refinement (AMR) code built on the Deal.II library, is also a finite element based mantle convection code that scales well on various HPC platforms. CitcomS and ASPECT both exhibit the overshoot phenomenon. One attempt at controlling the overshoot uses the Entropy Viscosity method, which introduces an artificial diffusion term in the energy equation of mantle convection. This artificial diffusion term is small where the temperature field is smooth. We present results from CitcomS and ASPECT that quantify the effect of the Entropy Viscosity method in reducing the overshoot phenomenon. In the discontinuous Galerkin (DG) finite element method, the test functions used in the method are continuous within each element but are discontinuous across inter-element boundaries. The solution space in the DG method is discontinuous. FEniCS is a collection of free software tools that automate the solution of differential equations using finite element methods. In this work we also present results from a finite element mantle convection simulation implemented in FEniCS that investigates the effect of using DG elements in reducing the overshoot problem.

Analysis of the transient behavior of rubbing components

NASA Technical Reports Server (NTRS)

Quezdou, M. B.; Mullen, R. L.

1986-01-01

Finite element equations are developed for studying deformations and temperatures resulting from frictional heating in sliding system. The formulation is done for linear steady state motion in two dimensions. The equations include the effect of the velocity on the moving components. This gives spurious oscillations in their solutions by Galerkin finite element methods. A method called streamline upwind scheme is used to try to deal with this deficiency. The finite element program is then used to investigate the friction of heating in gas path seal.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohanty, Subhasish; Majumdar, Saurindranath

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.

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.

Complex Langevin simulation of chiral symmetry restoration at finite baryonic density

NASA Astrophysics Data System (ADS)

Ilgenfritz, Ernst-Michael

1986-12-01

A recently proposed effective SU(3) spin model with chiral order parameter is studied by means of the complex Langevin equation. A first-order chiral symmetry restoring and deconfining transition is observed at sufficiently low temperature at finite baryonic density. Permanent address: Sektion Physik, Karl-Marx Universität, DDR-7010 Leipzig, German Democratic Republic.

Automatic control of finite element models for temperature-controlled radiofrequency ablation

PubMed Central

Haemmerich, Dieter; Webster, John G

2005-01-01

Background The finite element method (FEM) has been used to simulate cardiac and hepatic radiofrequency (RF) ablation. The FEM allows modeling of complex geometries that cannot be solved by analytical methods or finite difference models. In both hepatic and cardiac RF ablation a common control mode is temperature-controlled mode. Commercial FEM packages don't support automating temperature control. Most researchers manually control the applied power by trial and error to keep the tip temperature of the electrodes constant. Methods We implemented a PI controller in a control program written in C++. The program checks the tip temperature after each step and controls the applied voltage to keep temperature constant. We created a closed loop system consisting of a FEM model and the software controlling the applied voltage. The control parameters for the controller were optimized using a closed loop system simulation. Results We present results of a temperature controlled 3-D FEM model of a RITA model 30 electrode. The control software effectively controlled applied voltage in the FEM model to obtain, and keep electrodes at target temperature of 100°C. The closed loop system simulation output closely correlated with the FEM model, and allowed us to optimize control parameters. Discussion The closed loop control of the FEM model allowed us to implement temperature controlled RF ablation with minimal user input. PMID:16018811

Temperature Control and Numerical Analysis for Mass Concrete Pile Cap of Hai-huang Bridge

NASA Astrophysics Data System (ADS)

Shi, Han; Hao, Yang; Yong-liang, Wang

2018-05-01

In order to study the heat of hydration in massive concrete, this paper takes Hai-huang bridge for engineering background and uses the finite element analysis software of FEA to analyze the heat of hydration effect of the cushion cap. Comparing the measured data with the theory data, the results showed that the concrete crack was controlled effectively and ensure the construction quality by adopted reasonable temperature control measures. The results of the research prove that the measured data was consistent with calculation data, and it proves the accuracy of the finite element analysis. Finally, the study provides certain reference and guiding significance for similar project.

Finite grid radius and thickness effects on retarding potential analyzer measured suprathermal electron density and temperature

NASA Technical Reports Server (NTRS)

Knudsen, William C.

1992-01-01

The effect of finite grid radius and thickness on the electron current measured by planar retarding potential analyzers (RPAs) is analyzed numerically. Depending on the plasma environment, the current is significantly reduced below that which is calculated using a theoretical equation derived for an idealized RPA having grids with infinite radius and vanishingly small thickness. A correction factor to the idealized theoretical equation is derived for the Pioneer Venus (PV) orbiter RPA (ORPA) for electron gasses consisting of one or more components obeying Maxwell statistics. The error in density and temperature of Maxwellian electron distributions previously derived from ORPA data using the theoretical expression for the idealized ORPA is evaluated by comparing the densities and temperatures derived from a sample of PV ORPA data using the theoretical expression with and without the correction factor.

Electrosurgical vessel sealing tissue temperature: experimental measurement and finite element modeling.

PubMed

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.

Improved finite element methodology for integrated thermal structural analysis

NASA Technical Reports Server (NTRS)

Dechaumphai, P.; Thornton, E. A.

1982-01-01

An integrated thermal-structural finite element approach for efficient coupling of thermal and structural analysis is presented. New thermal finite elements which yield exact nodal and element temperatures for one dimensional linear steady state heat transfer problems are developed. A nodeless variable formulation is used to establish improved thermal finite elements for one dimensional nonlinear transient and two dimensional linear transient heat transfer problems. The thermal finite elements provide detailed temperature distributions without using additional element nodes and permit a common discretization with lower order congruent structural finite elements. The accuracy of the integrated approach is evaluated by comparisons with analytical solutions and conventional finite element thermal structural analyses for a number of academic and more realistic problems. Results indicate that the approach provides a significant improvement in the accuracy and efficiency of thermal stress analysis for structures with complex temperature distributions.

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.

Electronic part of the optical correlation function at finite temperature: the S-matrix expansion

NASA Astrophysics Data System (ADS)

Tavares, M.; Marques, G. E.; Tejedor, C.

1998-12-01

We present an extension to finite temperature of the Mahan-Nozières-De Dominicis framework to obtain the electronic part of the current-current correlation function. Its Fourier transform gives the absorption and emission spectra of doped low-dimensional semiconductors. We show the meaning of the new finite-temperature contributions characterizing the electronic part.

Kinetic description of finite-wall catalysis for monatomic molecular recombination

NASA Astrophysics Data System (ADS)

Yano, Ryosuke; Suzuki, Kojiro

2011-11-01

In our previous study on hypothetical diatomic molecular dissociation and monatomic molecular recombination, A2 + M ↔ A + A + M [Yano et al., Phys. Fluids 21, 127101 (2009)], the interaction between the wall and A2* intermediates was not formulated. In this paper, we consider the effect of finite-wall catalysis on recombination of a monatomic molecule A via the interaction between the wall and A2*. According to the proposed Boltzmann model equation, the catalytic recombination rate depends on two quantities; the vibrational temperature and the translational temperature of A2* intermediates that are emitted from the wall. In particular, the translational temperature of A2* is related to its lifetime. In this paper, we investigate the change in the catalytic recombination rate of A upon changing the vibrational temperature of A2* intermediates that are emitted from the wall. As an object of analysis, the rarefied hypersonic flow around a cylinder with a finite wall-catalysis is considered using the proposed Boltzmann model equation. Numerical results confirm that a decrease in the vibrational temperature of A2* intermediates that are emitted from the wall results in an increase in recombination of A near the wall.

Gradient corrections to the exchange-correlation free energy

DOE PAGES

Sjostrom, Travis; Daligault, Jerome

2014-10-07

We develop the first-order gradient correction to the exchange-correlation free energy of the homogeneous electron gas for use in finite-temperature density functional calculations. Based on this, we propose and implement a simple temperature-dependent extension for functionals beyond the local density approximation. These finite-temperature functionals show improvement over zero-temperature functionals, as compared to path-integral Monte Carlo calculations for deuterium equations of state, and perform without computational cost increase compared to zero-temperature functionals and so should be used for finite-temperature calculations. Furthermore, while the present functionals are valid at all temperatures including zero, non-negligible difference with zero-temperature functionals begins at temperatures abovemore » 10 000 K.« less

Three-loop hard-thermal-loop perturbation theory thermodynamics at finite temperature and finite baryonic and isospin chemical potential

NASA Astrophysics Data System (ADS)

Andersen, Jens O.; Haque, Najmul; Mustafa, Munshi G.; Strickland, Michael

2016-03-01

In a previous paper [N. Haque et al., J. High Energy Phys. 05 (2014) 27], we calculated the three-loop thermodynamic potential of QCD at finite temperature T and quark chemical potentials μq using the hard-thermal-loop perturbation theory (HTLpt) reorganization of finite temperature and density QCD. The result allows us to study the thermodynamics of QCD at finite temperature and finite baryon, strangeness, and isospin chemical potentials μB, μS, and μI. We calculate the pressure at nonzero μB and μI with μS=0 , and the energy density, the entropy density, the trace anomaly, and the speed of sound at nonzero μI with μB=μS=0 . The second- and fourth-order isospin susceptibilities are calculated at μB=μS=μI=0 . Our results can be directly compared to lattice QCD without Taylor expansions around μq=0 since QCD has no sign problem at μB=μS=0 and finite isospin chemical potential μI.

3D highly heterogeneous thermal model of pineal gland in-vitro study for electromagnetic exposure using finite volume method

NASA Astrophysics Data System (ADS)

Cen, Wei; Hoppe, Ralph; Lu, Rongbo; Cai, Zhaoquan; Gu, Ning

2017-08-01

In this paper, the relationship between electromagnetic power absorption and temperature distributions inside highly heterogeneous biological samples was accurately determinated using finite volume method. An in-vitro study on pineal gland that is responsible for physiological activities was for the first time simulated to illustrate effectiveness of the proposed method.

Finite-Temperature Relativistic Time-Blocking Approximation for Nuclear Strength Functions

NASA Astrophysics Data System (ADS)

Wibowo, Herlik; Litvinova, Elena

2017-09-01

This work presents an extension of the relativistic nuclear field theory (RNFT) developed throughout the last decade as an approach to the nuclear many-body problem, based on QHD meson-nucleon Lagrangian and relativistic field theory. The unique feature of RNFT is a consistent connection of the high-energy scale of heavy mesons, the medium-energy range of pion, and the low-energy domain of emergent collective vibrations (phonons). RNFT has demonstrated a very good performance in various nuclear structure calculations across the nuclear chart and, in particular, provides a consistent input for description of the two phases of r-process nucleosynthesis: neutron capture and beta decay. Further inclusion of finite temperature effects presented here allows for an extension of the method to highly excited compound nuclei. The covariant response theory in the relativistic time-blocking approximation (RTBA) is generalized for thermal effects, adopting the Matsubara Green's function formalism to the RNFT framework. The finite-temperature RTBA is implemented numerically to calculate multipole strength functions in medium-mass and heavy nuclei. The obtained results will be discussed in comparison to available experimental data and in the context of possible consequences for astrophysics.

Finite Element Simulations of Micro Turning of Ti-6Al-4V using PCD and Coated Carbide tools

NASA Astrophysics Data System (ADS)

Jagadesh, Thangavel; Samuel, G. L.

2017-02-01

The demand for manufacturing axi-symmetric Ti-6Al-4V implants is increasing in biomedical applications and it involves micro turning process. To understand the micro turning process, in this work, a 3D finite element model has been developed for predicting the tool chip interface temperature, cutting, thrust and axial forces. Strain gradient effect has been included in the Johnson-Cook material model to represent the flow stress of the work material. To verify the simulation results, experiments have been conducted at four different feed rates and at three different cutting speeds. Since titanium alloy has low Young's modulus, spring back effect is predominant for higher edge radius coated carbide tool which leads to the increase in the forces. Whereas, polycrystalline diamond (PCD) tool has smaller edge radius that leads to lesser forces and decrease in tool chip interface temperature due to high thermal conductivity. Tool chip interface temperature increases by increasing the cutting speed, however the increase is less for PCD tool as compared to the coated carbide tool. When uncut chip thickness decreases, there is an increase in specific cutting energy due to material strengthening effects. Surface roughness is higher for coated carbide tool due to ploughing effect when compared with PCD tool. The average prediction error of finite element model for cutting and thrust forces are 11.45 and 14.87 % respectively.

Finite-temperature behavior of a classical spin-orbit-coupled model for YbMgGaO4 with and without bond disorder

NASA Astrophysics Data System (ADS)

Parker, Edward; Balents, Leon

2018-05-01

We present the results of finite-temperature classical Monte Carlo simulations of a strongly spin-orbit-coupled nearest-neighbor triangular-lattice model for the candidate U (1 ) quantum spin liquid YbMgGaO4 at large system sizes. We find a single continuous finite-temperature stripe-ordering transition with slowly diverging heat capacity that completely breaks the sixfold ground-state degeneracy, despite the absence of a known conformal field theory describing such a transition. We also simulate the effect of random-bond disorder in the model, and find that even weak bond disorder destroys the transition by fragmenting the system into very large domains—possibly explaining the lack of observed ordering in the real material. The Imry-Ma argument only partially explains this fragility to disorder, and we extend the argument with a physical explanation for the preservation of our system's time-reversal symmetry even under a disorder model that preserves the same symmetry.

End point of a first-order phase transition in many-flavor lattice QCD at finite temperature and density.

PubMed

Ejiri, Shinji; Yamada, Norikazu

2013-04-26

Towards the feasibility study of the electroweak baryogenesis in realistic technicolor scenario, we investigate the phase structure of (2+N(f))-flavor QCD, where the mass of two flavors is fixed to a small value and the others are heavy. For the baryogenesis, an appearance of a first-order phase transition at finite temperature is a necessary condition. Using a set of configurations of two-flavor lattice QCD and applying the reweighting method, the effective potential defined by the probability distribution function of the plaquette is calculated in the presence of additional many heavy flavors. Through the shape of the effective potential, we determine the critical mass of heavy flavors separating the first-order and crossover regions and find it to become larger with N(f). We moreover study the critical line at finite density and the first-order region is found to become wider as increasing the chemical potential. Possible applications to real (2+1)-flavor QCD are discussed.

Concurrent design of an RTP chamber and advanced control system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spence, P.; Schaper, C.; Kermani, A.

1995-12-31

A concurrent-engineering approach is applied to the development of an axisymmetric rapid-thermal-processing (RTP) reactor and its associated temperature controller. Using a detailed finite-element thermal model as a surrogate for actual hardware, the authors have developed and tested a multi-input multi-output (MIMO) controller. Closed-loop simulations are performed by linking the control algorithm with the finite-element code. Simulations show that good temperature uniformity is maintained on the wafer during both steady and transient conditions. A numerical study shows the effect of ramp rate, feedback gain, sensor placement, and wafer-emissivity patterns on system performance.

Quantum statistical mechanics of nonrelativistic membranes: crumpling transition at finite temperature

NASA Astrophysics Data System (ADS)

Borelli, M. E. S.; Kleinert, H.; Schakel, Adriaan M. J.

2000-03-01

The effect of quantum fluctuations on a nearly flat, nonrelativistic two-dimensional membrane with extrinsic curvature stiffness and tension is investigated. The renormalization group analysis is carried out in first-order perturbative theory. In contrast to thermal fluctuations, which soften the membrane at large scales and turn it into a crumpled surface, quantum fluctuations are found to stiffen the membrane, so that it exhibits a Hausdorff dimension equal to two. The large-scale behavior of the membrane is further studied at finite temperature, where a nontrivial fixed point is found, signaling a crumpling transition.

Bi-stability resistant to fluctuations

NASA Astrophysics Data System (ADS)

Caruel, M.; Truskinovsky, L.

2017-12-01

We study a simple micro-mechanical device that does not lose its snap-through behavior in an environment dominated by fluctuations. The main idea is to have several degrees of freedom that can cooperatively resist the de-synchronizing effect of random perturbations. As an inspiration we use the power stroke machinery of skeletal muscles, which ensures at sub-micron scales and finite temperatures a swift recovery of an abruptly applied slack. In addition to hypersensitive response at finite temperatures, our prototypical Brownian snap spring also exhibits criticality at special values of parameters which is another potentially interesting property for micro-scale engineering applications.

Study of axial magnetic effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Braguta, Victor; School of Biomedicine, Far Eastern Federal University, Ajax 10 Building 25, Russian island, Vladivostok, 690922; Chernodub, M. N.

2016-01-22

The Axial Magnetic Effect manifests itself as an equilibrium energy flow of massless fermions induced by the axial (chiral) magnetic field. Here we study the Axial Magnetic Effect in the quenched SU(2) lattice gauge theory with massless overlap fermions at finite temperature. We numerically observe that in the low-temperature hadron phase the effect is absent due to the quark confinement. In the high-temperature deconfinement phase the energy flow is an increasing function of the temperature which reaches the predicted asymptotic T{sup 2} behavior at high temperatures. We find, however, that energy flow is about one order of magnitude lower comparedmore » to a theoretical prediction.« less

Toric-boson model: Toward a topological quantum memory at finite temperature

NASA Astrophysics Data System (ADS)

Hamma, Alioscia; Castelnovo, Claudio; Chamon, Claudio

2009-06-01

We discuss the existence of stable topological quantum memory at finite temperature. At stake here is the fundamental question of whether it is, in principle, possible to store quantum information for macroscopic times without the intervention from the external world, that is, without error correction. We study the toric code in two dimensions with an additional bosonic field that couples to the defects, in the presence of a generic environment at finite temperature: the toric-boson model. Although the coupling constants for the bare model are not finite in the thermodynamic limit, the model has a finite spectrum. We show that in the topological phase, there is a finite temperature below which open strings are confined and therefore the lifetime of the memory can be made arbitrarily (polynomially) long in system size. The interaction with the bosonic field yields a long-range attractive force between the end points of open strings but leaves closed strings and topological order intact.

Finite-temperature lattice dynamics and superionic transition in ceria from first principles

NASA Astrophysics Data System (ADS)

Klarbring, Johan; Skorodumova, Natalia V.; Simak, Sergei I.

2018-03-01

Ab initio molecular dynamics (AIMD) in combination with the temperature dependent effective potential (TDEP) method has been used to go beyond the quasiharmonic approximation and study the lattice dynamics in ceria, CeO2, at finite temperature. The results indicate that the previously proposed connection between the B1 u phonon mode turning imaginary and the transition to the superionic phase in fluorite structured materials is an artifact of the failure of the quasiharmonic approximation in describing the lattice dynamics at elevated temperatures. We instead show that, in the TDEP picture, a phonon mode coupling to the Eu mode prevents the B1 u mode from becoming imaginary. We directly observe the superionic transition at high temperatures in our AIMD simulations and find that it is initiated by the formation of oxygen Frenkel pairs (FP). These FP are found to form in a collective process involving simultaneous motion of two oxygen ions.

SPIREs: A Finite-Difference Frequency-Domain electromagnetic solver for inhomogeneous magnetized plasma cylinders

NASA Astrophysics Data System (ADS)

Melazzi, D.; Curreli, D.; Manente, M.; Carlsson, J.; Pavarin, D.

2012-06-01

We present SPIREs (plaSma Padova Inhomogeneous Radial Electromagnetic solver), a Finite-Difference Frequency-Domain (FDFD) electromagnetic solver in one dimension for the rapid calculation of the electromagnetic fields and the deposited power of a large variety of cylindrical plasma problems. The two Maxwell wave equations have been discretized using a staggered Yee mesh along the radial direction of the cylinder, and Fourier transformed along the other two dimensions and in time. By means of this kind of discretization, we have found that mode-coupling of fast and slow branches can be fully resolved without singularity issues that flawed other well-established methods in the past. Fields are forced by an antenna placed at a given distance from the plasma. The plasma can be inhomogeneous, finite-temperature, collisional, magnetized and multi-species. Finite-temperature Maxwellian effects, comprising Landau and cyclotron damping, have been included by means of the plasma Z dispersion function. Finite Larmor radius effects have been neglected. Radial variations of the plasma parameters are taken into account, thus extending the range of applications to a large variety of inhomogeneous plasma systems. The method proved to be fast and reliable, with accuracy depending on the spatial grid size. Two physical examples are reported: fields in a forced vacuum waveguide with the antenna inside, and forced plasma oscillations in the helicon radiofrequency range.

The effect of grid transparency and finite collector size on determining ion temperature and density by the retarding potential analyzer

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.

Collective many-body bounce in the breathing-mode oscillations of a Tonks-Girardeau gas

NASA Astrophysics Data System (ADS)

Atas, Y. Y.; Bouchoule, I.; Gangardt, D. M.; Kheruntsyan, K. V.

2017-10-01

We analyze the breathing-mode oscillations of a harmonically quenched Tonks-Giradeau (TG) gas using an exact finite-temperature dynamical theory. We predict a striking collective manifestation of impenetrability—a collective many-body bounce effect. The effect, although being invisible in the evolution of the in situ density profile of the gas, can be revealed through a nontrivial periodic narrowing of its momentum distribution, taking place at twice the rate of the fundamental breathing-mode frequency. We identify physical regimes for observing the many-body bounce and construct the respective nonequilibrium phase diagram as a function of the quench strength and the initial temperature of the gas. We also develop a finite-temperature hydrodynamic theory of the TG gas wherein the many-body bounce is explained by an increased thermodynamic pressure during the isentropic compression cycle, which acts as a potential barrier for the particles to bounce off.

The current-induced heat generation in a spin-flip quantum dot sandwiched between a ferromagnetic and a superconducting electrode

NASA Astrophysics Data System (ADS)

Jiang, Feng; Yan, Yonghong; Wang, Shikuan; Yan, Yijing

2017-12-01

Using non-equilibrium Green's functions' theory based on extended Nambu representation and small polaron transformation, we studied the current-induced heat generation in a spin-flip quantum dot sandwiched between a ferromagnetic and a superconducting electrode. We focused on moderate dot-leads coupling and relative small phonon energy, and derived the detailed expression of heat generation. The numerical results show (i) the heat generation decreases with polarization degree increasing, (ii) the intradot spin-flip can have a great effect on the heat generation at both zero temperature and finite temperature and (iii) at finite temperature an optimal workspace of keeping spin current and tuning heat generation by modulating the spin-flip intensity can be found.

Seebeck coefficient of one electron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Durrani, Zahid A. K., E-mail: z.durrani@imperial.ac.uk

2014-03-07

The Seebeck coefficient of one electron, driven thermally into a semiconductor single-electron box, is investigated theoretically. With a finite temperature difference ΔT between the source and charging island, a single electron can charge the island in equilibrium, directly generating a Seebeck effect. Seebeck coefficients for small and finite ΔT are calculated and a thermally driven Coulomb staircase is predicted. Single-electron Seebeck oscillations occur with increasing ΔT, as one electron at a time charges the box. A method is proposed for experimental verification of these effects.

Study of grid independence of finite element method on MHD free convective casson fluid flow with slip effect

NASA Astrophysics Data System (ADS)

Raju, R. Srinivasa; Ramesh, K.

2018-05-01

The purpose of this work is to study the grid independence of finite element method on MHD Casson fluid flow past a vertically inclined plate filled in a porous medium in presence of chemical reaction, heat absorption, an external magnetic field and slip effect has been investigated. For this study of grid independence, a mathematical model is developed and analyzed by using appropriate mathematical technique, called finite element method. Grid study discussed with the help of numerical values of velocity, temperature and concentration profiles in tabular form. avourable comparisons with previously published work on various special cases of the problem are obtained.

Experimentally validated finite element model of electrocaloric multilayer ceramic structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, N. A. S., E-mail: nadia.smith@npl.co.uk, E-mail: maciej.rokosz@npl.co.uk, E-mail: tatiana.correia@npl.co.uk; Correia, T. M., E-mail: nadia.smith@npl.co.uk, E-mail: maciej.rokosz@npl.co.uk, E-mail: tatiana.correia@npl.co.uk; Rokosz, M. K., E-mail: nadia.smith@npl.co.uk, E-mail: maciej.rokosz@npl.co.uk, E-mail: tatiana.correia@npl.co.uk

2014-07-28

A novel finite element model to simulate the electrocaloric response of a multilayer ceramic capacitor (MLCC) under real environment and operational conditions has been developed. The two-dimensional transient conductive heat transfer model presented includes the electrocaloric effect as a source term, as well as accounting for radiative and convective effects. The model has been validated with experimental data obtained from the direct imaging of MLCC transient temperature variation under application of an electric field. The good agreement between simulated and experimental data, suggests that the novel experimental direct measurement methodology and the finite element model could be used to supportmore » the design of optimised electrocaloric units and operating conditions.« less

Finite element modeling of temperature load effects on the vibration of local modes in multi-cable structures

NASA Astrophysics Data System (ADS)

Treyssède, Fabien

2018-01-01

Understanding thermal effects on the vibration of local (cable-dominant) modes in multi-cable structures is a complicated task. The main difficulty lies in the modification by temperature change of cable tensions, which are then undetermined. This paper applies a finite element procedure to investigate the effects of thermal loads on the linear dynamics of prestressed self-weighted multi-cable structures. Provided that boundary conditions are carefully handled, the discretization of cables with nonlinear curved beam elements can properly represent the thermoelastic behavior of cables as well as their linearized dynamics. A three-step procedure that aims to replace applied pretension forces with displacement continuity conditions is used. Despite an increase in the computational cost related to beam rotational degrees of freedom, such an approach has several advantages. Nonlinear beam finite elements are usually available in commercial codes. The overall method follows a thermoelastic geometrically non-linear analysis and hereby includes the main sources of non-linearities in multi-cable structures. The effects of cable bending stiffness, which can be significant, are also naturally accounted for. The accuracy of the numerical approach is assessed thanks to an analytical model for the vibration of a single inclined cable under temperature change. Then, the effects of thermal loads are investigated for two cable bridges, highlighting how natural frequencies can be affected by temperature. Although counterintuitive, a reverse relative change of natural frequency may occur for certain local modes. This phenomenon can be explained by two distinct mechanisms, one related to the physics intrinsic to cables and the other related to the thermal deflection of the superstructure. Numerical results show that cables cannot be isolated from the rest of the structure and the importance of modeling the whole structure for a quantitative analysis of temperature effects on the dynamics of cable bridges.

Finite Element Study into the effect of footwear temperature on the Forces transmitted to the foot during quasi- static compression loading

NASA Astrophysics Data System (ADS)

Shariatmadari, M. R.; English, R.; Rothwell, G.

2010-06-01

The determination of plantar stresses using computational footwear models which include temperature effects are crucial to predict foam performance in service and to aid material development and product design. Finite Element Method (FEM) provides an efficient computational framework to investigate the foot-footwear interaction. The aim of this research is to use FEM to investigate the effect of varying footwear temperature on plantar stresses. The results obtained will provide data which can be used to help optimise shoe design in terms of minimising damaging stresses in the foot particularly for individuals with diabetes who are susceptible to lower extremity complications. The FE simulation results showed significant reductions in foot stresses with the modifications from FE model (1) without footwear to model (2) with midsole only and to model (3) with midsole and insole. In summary, insole and midsole layers made from various foam materials aim to reduce the Ground Reaction Forces (GRF's) and foot stresses considerably and temperature variation can affect their cushioning and consequently the shock attenuation properties. The loss of footwear cushioning effect can have important clinical implications for those individuals with a history of lower limb overuse injuries or diabetes.

A three-dimensional thermal finite element analysis of AISI 304 stainless steel and copper dissimilar weldment

NASA Astrophysics Data System (ADS)

Singh, Gurdeep; Saxena, Ravindra K.; Pandey, Sunil

2018-04-01

The aim of this study to developed a 3-D thermal finite element model for dissimilar material welding of AISI-304 stainless steel and copper. Welding of similar material is widely studied using experimental and numerical methods but the problem becomes trivial for the welding of dissimilar materials especially in ferrous and nonferrous materials. Finite element analysis of dissimilar material welding is a cost-effective method for the understanding and analysis of the process. The finite element analysis has been performed to predict the heat affected zone and temperature distribution in AISI-304 stainless steel and copper dissimilar weldment using MSC Marc 2017®. Due to the difference in physical properties of these materials the behavior of heat affected zone and temperature distribution are perceived to be different. To verify the accuracy of the thermal finite element model, the welding process was simulated with butt-welded joints having same dimensions and parameters from Attarha and Far [1]. It is found from the study that the heat affected zone is larger in copper weld pads than in AISI 304 stainless steel due to large difference in thermal conductivity of these two weld pads.

Glassy phase in quenched disordered crystalline membranes

NASA Astrophysics Data System (ADS)

Coquand, O.; Essafi, K.; Kownacki, J.-P.; Mouhanna, D.

2018-03-01

We investigate the flat phase of D -dimensional crystalline membranes embedded in a d -dimensional space and submitted to both metric and curvature quenched disorders using a nonperturbative renormalization group approach. We identify a second-order phase transition controlled by a finite-temperature, finite-disorder fixed point unreachable within the leading order of ɛ =4 -D and 1 /d expansions. This critical point divides the flow diagram into two basins of attraction: that associated with the finite-temperature fixed point controlling the long-distance behavior of disorder-free membranes and that associated with the zero-temperature, finite-disorder fixed point. Our work thus strongly suggests the existence of a whole low-temperature glassy phase for quenched disordered crystalline membranes and, possibly, for graphene and graphene-like compounds.

A model to study finite-size and magnetic effects on the phase transition of a fermion interacting system

NASA Astrophysics Data System (ADS)

Corrêa, Emerson B. S.; Linhares, César A.; Malbouisson, Adolfo P. C.

2018-03-01

We present a model to study the effects from external magnetic field, chemical potential and finite size on the phase structures of a massive four- and six-fermion interacting systems. These effects are introduced by a method of compactification of coordinates, a generalization of the standard Matsubara prescription. Through the compactification of the z-coordinate and of imaginary time, we describe a heated system with the shape of a film of thickness L, at temperature β-1 undergoing first- or second-order phase transition. We have found a strong dependence of the temperature transition on the coupling constants λ and η. Besides inverse magnetic catalysis and symmetry breaking for both kinds of transition, we have found an inverse symmetry breaking phenomenon with respect to first-order phase transition.

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.

Novel Infrared Dynamics of Cold Atoms on Hot Graphene

NASA Astrophysics Data System (ADS)

Sengupta, Sanghita; Kotov, Valeri; Clougherty, Dennis

The low-energy dynamics of cold atoms interacting with macroscopic graphene membranes exhibits severe infrared divergences when treated perturbatively. These infrared problems are even more pronounced at finite temperature due to the (infinitely) many flexural phonons excited in graphene. We have devised a technique to take account (resummation) of such processes in the spirit of the well-known exact solution of the independent boson model. Remarkably, there is also similarity to the infrared problems and their treatment (via the Bloch-Nordsieck scheme) in finite temperature ``hot'' quantum electrodynamics and chromodynamics due to the long-range, unscreened nature of gauge interactions. The method takes into account correctly the strong damping provided by the many emitted phonons at finite temperature. In our case, the inverse membrane size plays the role of an effective low-energy scale, and, unlike the above mentioned field theories, there remains an unusual, highly nontrivial dependence on that scale due to the 2D nature of the problem. We present detailed results for the sticking (atomic damping rate) rate of cold atomic hydrogen as a function of the membrane temperature and size. We find that the rate is very strongly dependent on both quantities.

Finite Volume Numerical Methods for Aeroheating Rate Calculations from Infrared Thermographic Data

NASA Technical Reports Server (NTRS)

Daryabeigi, Kamran; Berry, Scott A.; Horvath, Thomas J.; Nowak, Robert J.

2006-01-01

The use of multi-dimensional finite volume heat conduction techniques for calculating aeroheating rates from measured global surface temperatures on hypersonic wind tunnel models was investigated. Both direct and inverse finite volume techniques were investigated and compared with the standard one-dimensional semi-infinite technique. Global transient surface temperatures were measured using an infrared thermographic technique on a 0.333-scale model of the Hyper-X forebody in the NASA Langley Research Center 20-Inch Mach 6 Air tunnel. In these tests the effectiveness of vortices generated via gas injection for initiating hypersonic transition on the Hyper-X forebody was investigated. An array of streamwise-orientated heating striations was generated and visualized downstream of the gas injection sites. In regions without significant spatial temperature gradients, one-dimensional techniques provided accurate aeroheating rates. In regions with sharp temperature gradients caused by striation patterns multi-dimensional heat transfer techniques were necessary to obtain more accurate heating rates. The use of the one-dimensional technique resulted in differences of 20% in the calculated heating rates compared to 2-D analysis because it did not account for lateral heat conduction in the model.

Possible ergodic-nonergodic regions in the quantum Sherrington-Kirkpatrick spin glass model and quantum annealing

NASA Astrophysics Data System (ADS)

Mukherjee, Sudip; Rajak, Atanu; Chakrabarti, Bikas K.

2018-02-01

We explore the behavior of the order parameter distribution of the quantum Sherrington-Kirkpatrick model in the spin glass phase using Monte Carlo technique for the effective Suzuki-Trotter Hamiltonian at finite temperatures and that at zero temperature obtained using the exact diagonalization method. Our numerical results indicate the existence of a low- but finite-temperature quantum-fluctuation-dominated ergodic region along with the classical fluctuation-dominated high-temperature nonergodic region in the spin glass phase of the model. In the ergodic region, the order parameter distribution gets narrower around the most probable value of the order parameter as the system size increases. In the other region, the Parisi order distribution function has nonvanishing value everywhere in the thermodynamic limit, indicating nonergodicity. We also show that the average annealing time for convergence (to a low-energy level of the model, within a small error range) becomes system size independent for annealing down through the (quantum-fluctuation-dominated) ergodic region. It becomes strongly system size dependent for annealing through the nonergodic region. Possible finite-size scaling-type behavior for the extent of the ergodic region is also addressed.

Superfluid transition of homogeneous and trapped two-dimensional Bose gases.

PubMed

Holzmann, Markus; Baym, Gordon; Blaizot, Jean-Paul; Laloë, Franck

2007-01-30

Current experiments on atomic gases in highly anisotropic traps present the opportunity to study in detail the low temperature phases of two-dimensional inhomogeneous systems. Although, in an ideal gas, the trapping potential favors Bose-Einstein condensation at finite temperature, interactions tend to destabilize the condensate, leading to a superfluid Kosterlitz-Thouless-Berezinskii phase with a finite superfluid mass density but no long-range order, as in homogeneous fluids. The transition in homogeneous systems is conveniently described in terms of dissociation of topological defects (vortex-antivortex pairs). However, trapped two-dimensional gases are more directly approached by generalizing the microscopic theory of the homogeneous gas. In this paper, we first derive, via a diagrammatic expansion, the scaling structure near the phase transition in a homogeneous system, and then study the effects of a trapping potential in the local density approximation. We find that a weakly interacting trapped gas undergoes a Kosterlitz-Thouless-Berezinskii transition from the normal state at a temperature slightly below the Bose-Einstein transition temperature of the ideal gas. The characteristic finite superfluid mass density of a homogeneous system just below the transition becomes strongly suppressed in a trapped gas.

A comprehensive model to determine the effects of temperature and species fluctuations on reaction rates in turbulent reacting flows

NASA Technical Reports Server (NTRS)

Chinitz, W.

1986-01-01

A computationally-viable model describing the interaction between fluid-mechanical turbulence and finite-rate combustion reactions, principally in high-speed flows was developed. Chemical kinetic mechanisms, complete and global, were developed describing the finite rate reaction of fuels of interest to NASA. These fuels included principally hydrogen and silane, although a limited amount of work involved hydrocarbon fuels as well.

Potential of energy harvesting in barium titanate based laminates from room temperature to cryogenic/high temperatures: measurements and linking phase field and finite element simulations

NASA Astrophysics Data System (ADS)

Narita, Fumio; Fox, Marina; Mori, Kotaro; Takeuchi, Hiroki; Kobayashi, Takuya; Omote, Kenji

2017-11-01

This paper studies the energy harvesting characteristics of piezoelectric laminates consisting of barium titanate (BaTiO3) and copper (Cu) from room temperature to cryogenic/high temperatures both experimentally and numerically. First, the output voltages of the piezoelectric BaTiO3/Cu laminates were measured from room temperature to a cryogenic temperature (77 K). The output power was evaluated for various values of load resistance. The results showed that the maximum output power density is approximately 2240 nW cm-3. The output voltages of the BaTiO3/Cu laminates were also measured from room temperature to a higher temperature (333 K). To discuss the output voltages of the BaTiO3/Cu laminates due to temperature changes, phase field and finite element simulations were combined. A phase field model for grain growth was used to generate grain structures. The phase field model was then employed for BaTiO3 polycrystals, coupled with the time-dependent Ginzburg-Landau theory and the oxygen vacancies diffusion, to calculate the temperature-dependent piezoelectric coefficient and permittivity. Using these properties, the output voltages of the BaTiO3/Cu laminates from room temperature to both 77 K and 333 K were analyzed by three dimensional finite element methods, and the results are presented for several grain sizes and oxygen vacancy densities. It was found that electricity in the BaTiO3 ceramic layer is generated not only through the piezoelectric effect caused by a thermally induced bending stress but also by the temperature dependence of the BaTiO3 piezoelectric coefficient and permittivity.

Reentry heat transfer analysis of the space shuttle orbiter

NASA Technical Reports Server (NTRS)

Ko, W. L.; Quinn, R. D.; Gong, L.

1982-01-01

A structural performance and resizing finite element thermal analysis computer program was used in the reentry heat transfer analysis of the space shuttle. Two typical wing cross sections and a midfuselage cross section were selected for the analysis. The surface heat inputs to the thermal models were obtained from aerodynamic heating analyses, which assumed a purely turbulent boundary layer, a purely laminar boundary layer, separated flow, and transition from laminar to turbulent flow. The effect of internal radiation was found to be quite significant. With the effect of the internal radiation considered, the wing lower skin temperature became about 39 C (70 F) lower. The results were compared with fight data for space transportation system, trajectory 1. The calculated and measured temperatures compared well for the wing if laminar flow was assumed for the lower surface and bay one upper surface and if separated flow was assumed for the upper surfaces of bays other than bay one. For the fuselage, good agreement between the calculated and measured data was obtained if laminar flow was assumed for the bottom surface. The structural temperatures were found to reach their peak values shortly before touchdown. In addition, the finite element solutions were compared with those obtained from the conventional finite difference solutions.

Proper time regularization and the QCD chiral phase transition

PubMed Central

Cui, Zhu-Fang; Zhang, Jin-Li; Zong, Hong-Shi

2017-01-01

We study the QCD chiral phase transition at finite temperature and finite quark chemical potential within the two flavor Nambu–Jona-Lasinio (NJL) model, where a generalization of the proper-time regularization scheme is motivated and implemented. We find that in the chiral limit the whole transition line in the phase diagram is of second order, whereas for finite quark masses a crossover is observed. Moreover, if we take into account the influence of quark condensate to the coupling strength (which also provides a possible way of how the effective coupling varies with temperature and quark chemical potential), it is found that a CEP may appear. These findings differ substantially from other NJL results which use alternative regularization schemes, some explanation and discussion are given at the end. This indicates that the regularization scheme can have a dramatic impact on the study of the QCD phase transition within the NJL model. PMID:28401889

Analysis and Calculation of the Fluid Flow and the Temperature Field by Finite Element Modeling

NASA Astrophysics Data System (ADS)

Dhamodaran, M.; Jegadeesan, S.; Kumar, R. Praveen

2018-04-01

This paper presents a fundamental and accurate approach to study numerical analysis of fluid flow and heat transfer inside a channel. In this study, the Finite Element Method is used to analyze the channel, which is divided into small subsections. The small subsections are discretized using higher number of domain elements and the corresponding number of nodes. MATLAB codes are developed to be used in the analysis. Simulation results showed that the analyses of fluid flow and temperature are influenced significantly by the changing entrance velocity. Also, there is an apparent effect on the temperature fields due to the presence of an energy source in the middle of the domain. In this paper, the characteristics of flow analysis and heat analysis in a channel have been investigated.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ozturk, Fahrettin; Toros, Serkan; Evis, Zafer

In this study, the diametral strength test of sintered hydroxyapatite was simulated by the finite element software, ABAQUS/Standard. Stress distributions on diametral test sample were determined. The effect of sintering temperature on stress distribution of hydroxyapatite was studied. It was concluded that high sintering temperatures did not reduce the stress on hydroxyapatite. It had a negative effect on stress distribution of hydroxyapatite after 1300 deg. C. In addition to the porosity, other factors (sintering temperature, presence of phases and the degree of crystallinity) affect the diametral strength of the hydroxyapatite.

Modeling heat transfer and inactivation of Escherichia coli O157:H7 in precooked meat products in Argentina using the finite element method.

PubMed

Santos, M V; Zaritzky, N; Califano, A

2008-07-01

The presence of Escherichia coli is linked with sanitary deficiencies and undercooking of meat products. Recent studies have detected E. coli O157:H7 in black blood sausages. Minimum time-temperature specifications to kill the bacteria were obtained by numerical simulations of the microscopic heat conduction equation using the finite element method, and calculating the temperature profile of the sausage and the population of E. coli at the coldest point during heating. The model was validated by heating sausages in a water-bath. The effects of heat transfer coefficients and water temperatures on the required time to achieve an inactivation value (IV) of 12(log) are reported. Macroscopic heat balances were simultaneously solved to consider the temperature drop in the water batch as a function of the ratio between the mass of thermally treated sausage and the heat capacity of the system.

An RF phased array applicator designed for hyperthermia breast cancer treatments

PubMed Central

Wu, Liyong; McGough, Robert J; Arabe, Omar Ali; Samulski, Thaddeus V

2007-01-01

An RF phased array applicator has been constructed for hyperthermia treatments in the intact breast. This RF phased array consists of four antennas mounted on a Lexan water tank, and geometric focusing is employed so that each antenna points in the direction of the intended target. The operating frequency for this phased array is 140 MHz. The RF array has been characterized both by electric field measurements in a water tank and by electric field simulations using the finite-element method. The finite-element simulations are performed with HFSS software, where the mesh defined for finite-element calculations includes the geometry of the tank enclosure and four end-loaded dipole antennas. The material properties of the water tank enclosure and the antennas are also included in each simulation. The results of the finite-element simulations are compared to the measured values for this configuration, and the results, which include the effects of amplitude shading and phase shifting, show that the electric field predicted by finite-element simulations is similar to the measured field. Simulations also show that the contributions from standing waves are significant, which is consistent with measurement results. Simulated electric field and bio-heat transfer results are also computed within a simple 3D breast model. Temperature simulations show that, although peak temperatures are generated outside the simulated tumour target, this RF phased array applicator is an effective device for regional hyperthermia in the intact breast. PMID:16357427

Phase transition for the system of finite volume in the ϕ4 theory in the Tsallis nonextensive statistics

NASA Astrophysics Data System (ADS)

Ishihara, Masamichi

2018-04-01

We studied the effects of nonextensivity on the phase transition for the system of finite volume V in the ϕ4 theory in the Tsallis nonextensive statistics of entropic parameter q and temperature T, when the deviation from the Boltzmann-Gibbs (BG) statistics, |q ‑ 1|, is small. We calculated the condensate and the effective mass to the order q ‑ 1 with the normalized q-expectation value under the free particle approximation with zero bare mass. The following facts were found. The condensate Φ divided by v, Φ/v, at q (v is the value of the condensate at T = 0) is smaller than that at q‧ for q > q‧ as a function of Tph/v which is the physical temperature Tph divided by v. The physical temperature Tph is related to the variation of the Tsallis entropy and the variation of the internal energies, and Tph at q = 1 coincides with T. The effective mass decreases, reaches minimum, and increases after that, as Tph increases. The effective mass at q > 1 is lighter than the effective mass at q = 1 at low physical temperature and heavier than the effective mass at q = 1 at high physical temperature. The effects of the nonextensivity on the physical quantity as a function of Tph become strong as |q ‑ 1| increases. The results indicate the significance of the definition of the expectation value, the definition of the physical temperature, and the constraints for the density operator, when the terms including the volume of the system are not negligible.

Validation of Finite-Element Models of Persistent-Current Effects in Nb 3Sn Accelerator Magnets

DOE PAGES

Wang, X.; Ambrosio, G.; Chlachidze, G.; ...

2015-01-06

Persistent magnetization currents are induced in superconducting filaments during the current ramping in magnets. The resulting perturbation to the design magnetic field leads to field quality degradation, in particular at low field where the effect is stronger relative to the main field. The effects observed in NbTi accelerator magnets were reproduced well with the critical-state model. However, this approach becomes less accurate for the calculation of the persistent-current effects observed in Nb 3Sn accelerator magnets. Here a finite-element method based on the measured strand magnetization is validated against three state-of-art Nb3Sn accelerator magnets featuring different subelement diameters, critical currents, magnetmore » designs and measurement temperatures. The temperature dependence of the persistent-current effects is reproduced. Based on the validated model, the impact of conductor design on the persistent current effects is discussed. The performance, limitations and possible improvements of the approach are also discussed.« less

Finite size effects in the thermodynamics of a free neutral scalar field

NASA Astrophysics Data System (ADS)

Parvan, A. S.

2018-04-01

The exact analytical lattice results for the partition function of the free neutral scalar field in one spatial dimension in both the configuration and the momentum space were obtained in the framework of the path integral method. The symmetric square matrices of the bilinear forms on the vector space of fields in both configuration space and momentum space were found explicitly. The exact lattice results for the partition function were generalized to the three-dimensional spatial momentum space and the main thermodynamic quantities were derived both on the lattice and in the continuum limit. The thermodynamic properties and the finite volume corrections to the thermodynamic quantities of the free real scalar field were studied. We found that on the finite lattice the exact lattice results for the free massive neutral scalar field agree with the continuum limit only in the region of small values of temperature and volume. However, at these temperatures and volumes the continuum physical quantities for both massive and massless scalar field deviate essentially from their thermodynamic limit values and recover them only at high temperatures or/and large volumes in the thermodynamic limit.

Numerical simulation of temperature field in K9 glass irradiated by ultraviolet pulse laser

NASA Astrophysics Data System (ADS)

Wang, Xi; Fang, Xiaodong

2015-10-01

The optical component of photoelectric system was easy to be damaged by irradiation of high power pulse laser, so the effect of high power pulse laser irradiation on K9 glass was researched. A thermodynamic model of K9 glass irradiated by ultraviolet pulse laser was established using the finite element software ANSYS. The article analyzed some key problems in simulation process of ultraviolet pulse laser damage of K9 glass based on ANSYS from the finite element models foundation, meshing, loading of pulse laser, setting initial conditions and boundary conditions and setting the thermal physical parameters of material. The finite element method (FEM) model was established and a numerical analysis was performed to calculate temperature field in K9 glass irradiated by ultraviolet pulse laser. The simulation results showed that the temperature of irradiation area exceeded the melting point of K9 glass, while the incident laser energy was low. The thermal damage dominated in the damage mechanism of K9 glass, the melting phenomenon should be much more distinct.

Thermocryogenic buckling and stress analyses of a partially filled cryogenic tank subjected to cylindrical strip heating

NASA Technical Reports Server (NTRS)

Ko, William L.

1994-01-01

Thermocryogenic buckling and stress analyses were conducted on a horizontally oriented cryogenic tank using the finite element method. The tank is a finite-length circular cylindrical shell with its two ends capped with hemispherical shells. The tank is subjected to cylindrical strip heating in the region above the liquid-cryogen fill level and to cryogenic cooling below the fill level (i.e., under thermocryogenic loading). The effects of cryogen fill level on the buckling temperature and thermocryogenic stress field were investigated in detail. Both the buckling temperature and stress magnitudes were relatively insensitive to the cryogen fill level. The buckling temperature, however, was quite sensitive to the radius-to-thickness ratio. A mechanical stress analysis of the tank also was conducted when the tank was under: (1) cryogen liquid pressure loading; (2) internal pressure loading; and (3) tank-wall inertia loading. Deformed shapes of the cryogenic tanks under different loading conditions were shown, and high-stress domains were mapped on the tank wall for the strain-gage installations. The accuracies of solutions from different finite element models were compared.

Switching times of nanoscale FePt: Finite size effects on the linear reversal mechanism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ellis, M. O. A.; Chantrell, R. W.

2015-04-20

The linear reversal mechanism in FePt grains ranging from 2.316 nm to 5.404 nm has been simulated using atomistic spin dynamics, parametrized from ab-initio calculations. The Curie temperature and the critical temperature (T{sup *}), at which the linear reversal mechanism occurs, are observed to decrease with system size whilst the temperature window T{sup *}

Nonperturbative finite-temperature Yang-Mills theory

NASA Astrophysics Data System (ADS)

Cyrol, Anton K.; Mitter, Mario; Pawlowski, Jan M.; Strodthoff, Nils

2018-03-01

We present nonperturbative correlation functions in Landau-gauge Yang-Mills theory at finite temperature. The results are obtained from the functional renormalisation group within a self-consistent approximation scheme. In particular, we compute the magnetic and electric components of the gluon propagator, and the three- and four-gluon vertices. We also show the ghost propagator and the ghost-gluon vertex at finite temperature. Our results for the propagators are confronted with lattice simulations and our Debye mass is compared to hard thermal loop perturbation theory.

REMARKS ON THE MAXIMUM ENTROPY METHOD APPLIED TO FINITE TEMPERATURE LATTICE QCD.

DOE Office of Scientific and Technical Information (OSTI.GOV)

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.

Explicit finite-volume time-marching calculations of total temperature distributions in turbulent flow

NASA Technical Reports Server (NTRS)

Nicholson, Stephen; Moore, Joan G.; Moore, John

1987-01-01

A method was developed which calculates two-dimensional, transonic, viscous flow in ducts. The finite volume, time-marching formulation is used to obtain steady flow solutions of the Reynolds-averaged form of the Navier-Stokes equations. The entire calculation is performed in the physical domain. This paper investigates the introduction of a new formulation of the energy equation which gives improved transient behavior as the calculation converges. The effect of variable Prandtl number on the temperature distribution through the boundary layer is also investigated. A turbulent boundary layer in an adverse pressure gradient (M = 0.55) is used to demonstrate the improved transient temperature distribution obtained when the new formulation of the energy equation is used. A flat plate turbulent boundary layer with a supersonic free-stream Mach number of 2.8 is used to investigate the effect of Prandtl number on the distribution of properties through the boundary layer. The computed total temperature distribution and recovery factor agree well with the measurements when a variable Prandtl number is used through the boundary layer.

Explicit finite-volume time-marching calculations of total temperature distributions in turbulent flow

NASA Technical Reports Server (NTRS)

Nicholson, Stephen; Moore, Joan G.; Moore, John

1986-01-01

A method was developed which calculates two-dimensional, transonic, viscous flow in ducts. The finite volume, time-marching formulation is used to obtain steady flow solutions of the Reynolds-averaged form of the Navier-Stokes equations. The entire calculation is performed in the physical domain. This paper investigates the introduction of a new formulation of the energy equation which gives improved transient behavior as the calculation converges. The effect of variable Prandtl number on the temperature distribution through the boundary layer is also investigated. A turbulent boundary layer in an adverse pressure gradient (M = 0.55) is used to demonstrate the improved transient temperature distribution obtained when the new formulation of the energy equation is used. A flat plate turbulent boundary layer with a supersonic free-stream Mach number of 2.8 is used to investigate the effect of Prandtl number on the distribution of properties through the boundary layer. The computed total temperature distribution and recovery factor agree well with the measurements when a variable Prandtl number is used through the boundary layer.

Ground state degeneracy, energy barriers, and molecular dynamics evidence for two-dimensional disorder in black phosphorus and monochalcogenide monolayers at finite temperature

NASA Astrophysics Data System (ADS)

Mehboudi, Mehrshad; Barraza-Lopez, Salvador; Dorio, Alex M.; Zhu, Wenjuan; van der Zande, Arend; Churchill, Hugh O. H.; Pacheco-Sanjuan, Alejandro A.; Harriss, Edmund O.; Kumar, Pradeep

Mono-layers of black phosphorus and other two dimensional materials such as mono-layers of SiSe, GeS, GeSe, GeTe, Sns, SnSe, and SnTe with a similar crystalline structure have a four-fold degenerate ground state that leads to two-dimensional disorder at finite temperature. Disorder happens when neighboring atoms gently re-accommodate bonds beyond a critical temperature. In this talk, the effect of atomic numbers on the transition temperature will be discussed. In addition Car-Parinello molecular dynamics calculations at temperatures 30, 300 and 1000 K were performed on supercells containing more than five hundred atoms and the results from these calculations confirm the transition onto a two-dimensional disordered structure past the critical temperature, which is close to room temperature for many of these compounds. References: M. Mehboudi, A.M. Dorio, W. Zhu, A. van der Zande, H.O.H. Churchill, A.A. Pacheco Sanjuan, E.O.H. Harris, P. Kumar, and S. Barraza-Lopez. arXiv:1510.09153.

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.

Electrostatic attraction of coupled Wigner crystals: finite temperature effects.

PubMed

Lau, A W; Pincus, P; Levine, D; Fertig, H A

2001-05-01

In this paper we present a unified physical picture for the electrostatic attraction between two coupled planar Wigner crystals at finite temperature. This model may facilitate our conceptual understanding of counterion-mediated attractions between (highly) similarly charged planes. By adopting an elastic theory, we show that the total attractive force between them can be (approximately) decomposed into a short-ranged and a long-ranged component. They are evaluated below the melting temperature of the Wigner crystals. In particular, we analyze the temperature dependence of the short-ranged attraction, arising from ground-state configuration, and we argue that thermal fluctuations may drastically reduce its strength. Also, the long-range force agrees exactly with that based on the charge-fluctuation approach. Furthermore, we take quantum contributions to the long-ranged (fluctuation-induced) attraction into account and show how the fractional power law, which scales as d(-7/2) for large interplanar distance d at zero temperature, crosses over to the classical regime d(-3) via an intermediate regime of d(-2).

Study of the temperature configuration of parallel tempering for the traveling salesman problem

NASA Astrophysics Data System (ADS)

Hasegawa, Manabu

The effective temperature configuration of parallel tempering (PT) in finite-time optimization is studied for the solution of the traveling salesman problem. An experimental analysis is conducted to decide the relative importance of the two characteristic temperatures, the specific-heat-peak temperature referred to in the general guidelines and the effective intermediate temperature identified in the recent study on simulated annealing (SA). The results show that the operation near the former has no notable significance contrary to the conventional belief but that the operation near the latter plays a crucial role in fulfilling the optimization function of PT. The method shares the same origin of effectiveness with the SA and SA-related algorithms.

Electric control of emergent magnonic spin current and dynamic multiferroicity in magnetic insulators at finite temperatures

NASA Astrophysics Data System (ADS)

Wang, Xi-guang; Chotorlishvili, L.; Guo, Guang-hua; Berakdar, J.

2018-04-01

Conversion of thermal energy into magnonic spin currents and/or effective electric polarization promises new device functionalities. A versatile approach is presented here for generating and controlling open circuit magnonic spin currents and an effective multiferroicity at a uniform temperature with the aid of spatially inhomogeneous, external, static electric fields. This field applied to a ferromagnetic insulator with a Dzyaloshinskii-Moriya type coupling changes locally the magnon dispersion and modifies the density of thermally excited magnons in a region of the scale of the field inhomogeneity. The resulting gradient in the magnon density can be viewed as a gradient in the effective magnon temperature. This effective thermal gradient together with local magnon dispersion result in an open-circuit, electric field controlled magnonic spin current. In fact, for a moderate variation in the external electric field the predicted magnonic spin current is on the scale of the spin (Seebeck) current generated by a comparable external temperature gradient. Analytical methods supported by full-fledge numerics confirm that both, a finite temperature and an inhomogeneous electric field are necessary for this emergent non-equilibrium phenomena. The proposal can be integrated in magnonic and multiferroic circuits, for instance to convert heat into electrically controlled pure spin current using for example nanopatterning, without the need to generate large thermal gradients on the nanoscale.

Effects of finite beam and plasma temperature on the growth rate of a two-stream free electron laser with background plasma

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mahdizadeh, N.; Aghamir, F. M.

2013-02-28

A fluid theory is used to derive the dispersion relation of two-stream free electron laser (TSFEL) with a magnetic planar wiggler pump in the presence of background plasma (BP). The effect of finite beams and plasma temperature on the growth rate of a TSFEL has been verified. The twelve order dispersion equation has been solved numerically. Three instabilities, FEL along with the TS and TS-FEL instabilities occur simultaneously. The analysis in the case of cold BP shows that when the effect of the beam temperature is taken into account, both instable bands of wave-number and peak growth rate in themore » TS instability increase, but peak growth of the FEL and TS-FEL instabilities decreases. Thermal motion of the BP causes to diminish the TS instability and it causes to decrease the FEL and TS-FEL instabilities. By increasing the beam densities and lowering initial velocities (in the collective Raman regime), growth rate of instabilities increases; however, it has opposite behavior in the Campton regime.« less

Finite-temperature effects in helical quantum turbulence

NASA Astrophysics Data System (ADS)

Clark Di Leoni, Patricio; Mininni, Pablo D.; Brachet, Marc E.

2018-04-01

We perform a study of the evolution of helical quantum turbulence at different temperatures by solving numerically the Gross-Pitaevskii and the stochastic Ginzburg-Landau equations, using up to 40963 grid points with a pseudospectral method. We show that for temperatures close to the critical one, the fluid described by these equations can act as a classical viscous flow, with the decay of the incompressible kinetic energy and the helicity becoming exponential. The transition from this behavior to the one observed at zero temperature is smooth as a function of temperature. Moreover, the presence of strong thermal effects can inhibit the development of a proper turbulent cascade. We provide Ansätze for the effective viscosity and friction as a function of the temperature.

Effects of large vessel on temperature distribution based on photothermal coupling interaction model

NASA Astrophysics Data System (ADS)

Li, Zhifang; Zhang, Xiyang; Li, Zuoran; Li, Hui

2016-10-01

This paper is based on the finite element analysis method for studying effects of large blood vessel on temperature based on photothermal coupling interaction model, and it couples the physical field of optical transmission with the physical field of heat transfer in biological tissue by using COMSOL Multiphysics 4.4 software. The results demonstrate the cooling effect of large blood vessel, which can be potential application for the treatment of liver tumors.

Finite quasiparticle lifetime in disordered superconductors.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zemlicka, M.; Neilinger, P.; Trgala, M

We investigate the complex conductivity of a highly disordered MoC superconducting film with k(F)l approximate to 1, where k(F) is the Fermi wave number and l is the mean free path, derived from experimental transmission characteristics of coplanar waveguide resonators in a wide temperature range below the superconducting transition temperature T-c. We find that the original Mattis-Bardeen model with a finite quasiparticle lifetime, tau, offers a perfect description of the experimentally observed complex conductivity. We show that iota is appreciably reduced by scattering effects. Characteristics of the scattering centers are independently found by scanning tunneling spectroscopy and agree with thosemore » determined from the complex conductivity.« less

Finite-β Split-weight Gyrokinetic Particle Simulation of Microinstabilities

NASA Astrophysics Data System (ADS)

Jenkins, Thomas G.; Lee, W. W.; Lewandowski, J. L. V.

2003-10-01

The finite-β split-weight gyrokinetic particle simulation scheme [1] has been implemented in two-dimensional slab geometry for the purpose of studying the effects of high temperature electrons on microinstabilities. Drift wave instabilities and ion temperature gradient modes are studied in both shearless slab and sheared slab geometries. The linear and nonlinear evolution of these modes, as well as the physics of microtearing, is compared with the results of Reynders [2] and Cummings [3]. [1] W. W. Lee, J. L. V. Lewandowski, T. S. Hahm, and Z. Lin, Phys. Plasmas 8, 4435 (2001). [2] J. V. W. Reynders, Ph.D. thesis, Princeton University (1992). [3] J. C. Cummings, Ph.D. thesis, Princeton University (1995).

Heat transfer analysis of the Bridgman-Stockbarger configuration for crystal growth. Part 1: Analytical treatment of the axial temperature distribution

NASA Technical Reports Server (NTRS)

Jasinski, T. J.; Rohsenow, W. M.; Witt, A. F.

1982-01-01

All first order effects on the axial temperature distribution in a solidifying charge in a Bridgman-Stockbarger configuration for crystal growth are analyzed on the basis of a one dimensional model whose validity can be verified through comparison with published finite difference ana;uses of two dimensional models. The model presented includes an insulated region between axially aligned heat pipes and considers the effects of charge diameter, charge motion, thickness, and thermal conductivity of a confining crucible, thermal conductivity change at the crystal-melt interface, generation of latent heat at the interface, and finite charge length. Results are primarily given in analytical form and can be used without recourse to computer work for both improve furnace design and optimization of growth conditions in a given thermal configuration.

Possible higher order phase transition in large-N gauge theory at finite temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nishimura, Hiromichi

2017-08-07

We analyze the phase structure of SU(¥) gauge theory at finite temperature using matrix models. Our basic assumption is that the effective potential is dominated by double-trace terms for the Polyakov loops. As a function of the temperature, a background field for the Polyakov loop, and a quartic coupling, it exhibits a universal structure: in the large portion of the parameter space, there is a continuous phase transition analogous to the third-order phase transition of Gross,Witten and Wadia, but the order of phase transition can be higher than third. We show that different confining potentials give rise to drastically differentmore » behavior of the eigenvalue density and the free energy. Therefore lattice simulations at large N could probe the order of phase transition and test our results. Critical« less

Evaluation of the finite element fuel rod analysis code (FRANCO)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, K.; Feltus, M.A.

1994-12-31

Knowledge of temperature distribution in a nuclear fuel rod is required to predict the behavior of fuel elements during operating conditions. The thermal and mechanical properties and performance characteristics are strongly dependent on the temperature, which can vary greatly inside the fuel rod. A detailed model of fuel rod behavior can be described by various numerical methods, including the finite element approach. The finite element method has been successfully used in many engineering applications, including nuclear piping and reactor component analysis. However, fuel pin analysis has traditionally been carried out with finite difference codes, with the exception of Electric Powermore » Research Institute`s FREY code, which was developed for mainframe execution. This report describes FRANCO, a finite element fuel rod analysis code capable of computing temperature disrtibution and mechanical deformation of a single light water reactor fuel rod.« less

The application of super wavelet finite element on temperature-pressure coupled field simulation of LPG tank under jet fire

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.

Universality of maximum-work efficiency of a cyclic heat engine based on a finite system of ultracold atoms.

PubMed

Ye, Zhuolin; Hu, Yingying; He, Jizhou; Wang, Jianhui

2017-07-24

We study the performance of a cyclic heat engine which uses a small system with a finite number of ultracold atoms as its working substance and works between two heat reservoirs at constant temperatures T h and T c (

Cranking of Nuclei at Finite Temperature:

NASA Astrophysics Data System (ADS)

Bartel, J.; Bencheikh, K.; Quentin, P.

We present a generalization of the Extended Thomas Fermi (ETF) theory to fermionic systems at finite temperature and finite angular momentum. In fact the present approach is more general in the sense that it is able to treat an excited system of fermions subject to an external vector field which in the case of nuclear rotations, developed more extensively here, is simply ěc{r}×ěc{ω }.

Finite-volume scheme for anisotropic diffusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Es, Bram van, E-mail: bramiozo@gmail.com; FOM Institute DIFFER, Dutch Institute for Fundamental Energy Research, The Netherlands"1; Koren, Barry

In this paper, we apply a special finite-volume scheme, limited to smooth temperature distributions and Cartesian grids, to test the importance of connectivity of the finite volumes. The area of application is nuclear fusion plasma with field line aligned temperature gradients and extreme anisotropy. We apply the scheme to the anisotropic heat-conduction equation, and compare its results with those of existing finite-volume schemes for anisotropic diffusion. Also, we introduce a general model adaptation of the steady diffusion equation for extremely anisotropic diffusion problems with closed field lines.

Meson properties at finite temperature in a three flavor nonlocal chiral quark model with Polyakov loop

DOE Office of Scientific and Technical Information (OSTI.GOV)

Contrera, G. A.; CONICET, Rivadavia 1917, 1033 Buenos Aires; Dumm, D. Gomez

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. Itmore » 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.« less

NiMnGa/Si Shape Memory Bimorph Nanoactuation

NASA Astrophysics Data System (ADS)

Lambrecht, Franziska; Lay, Christian; Aseguinolaza, Iván R.; Chernenko, Volodymyr; Kohl, Manfred

2016-12-01

The size dependences of thermal bimorph and shape memory effect of nanoscale shape memory alloy (SMA)/Si bimorph actuators are investigated in situ in a scanning electron microscope and by finite element simulations. By combining silicon nanomachining and magnetron sputtering, freestanding NiMnGa/Si bimorph cantilever structures with film/substrate thickness of 200/250 nm and decreasing lateral dimensions are fabricated. Electrical resistance and mechanical beam bending tests upon direct Joule heating demonstrate martensitic phase transformation and reversible thermal bimorph effect, respectively. Corresponding characteristics are strongly affected by the large temperature gradient in the order of 50 K/µm forming along the nano bimorph cantilever upon electro-thermal actuation, which, in addition, depends on the size-dependent heat conductivity in the Si nano layer. Furthermore, the martensitic transformation temperatures show a size-dependent decrease by about 40 K for decreasing lateral dimensions down to 200 nm. The effects of heating temperature and stress distribution on the nanoactuation performance are analyzed by finite element simulations revealing thickness ratio of SMA/Si of 90/250 nm to achieve an optimum SME. Differential thermal expansion and thermo-elastic effects are discriminated by comparative measurements and simulations on Ni/Si bimorph reference actuators.

Finite Atwood Number Effects on Deceleration-Phase Instability in Room-Temperature Direct-Drive Implosions

NASA Astrophysics Data System (ADS)

Miller, S.; Knauer, J. P.; Radha, P. B.; Goncharov, V. N.

2017-10-01

Performance degradation in direct-drive inertial confinement fusion implosions can be caused by several effects, one of which is Rayleigh-Taylor (RT) instability growth during the deceleration phase. In room-temperature plastic target implosions, this deceleration-phase RT growth is enhanced by the density discontinuity and finite Atwood numbers at the fuel-pusher interface. For the first time, an experimental campaign at the Omega Laser Facility systematically varied the ratio of deuterium-to-tritium (D-to-T) within the DT gas fill to change the Atwood number. The goal of the experiment was to understand the effects of Atwood number variation on observables like apparent ion temperature, yield, and variations in areal density and bulk fluid motion, which lead to broadening of neutron spectra along different lines of sight. Simulations by the hydrodynamic codes LILAC and DRACO were used to study growth rates for different D-to-T ratios and identify observable quantities effected by Atwood number variation. Results from simulations and the experiment are presented. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Sweeprate and temperature effects on crackling noise

NASA Astrophysics Data System (ADS)

White, Robert Allen

Crackling noise, defined as separate bursts characterized by power law behavior of the frequency histograms over many decades, is observed in many driven systems far from equilibrium. Examples of such systems pepper a remarkable range of length and energy scales from jerky domain wall motion of disordered magnets, to the sometimes devastating crackling of the earth to the bursty release of energy in the photosphere of the sun dwarfing that of our most horrible WMD. Typically, crackling noise is modeled in the infinitely slow driving rate limit at zero temperature. In this dissertation I investigate the effects of relaxing these limits. First I consider the crackling system at zero temperature and finite sweeprate. I discuss how the temporal overlap of power law bursts can account for a wide range of scaling behavior and provide a criterion for sweeprate controlled exponents based on exponents obtained in the infinitely slowly driven limit. I also discuss scaling arguments for hitherto unexplained results in the power spectrum of crackling response in disordered magnets, commonly referred to as Barkhausen noise. Scaling arguments and numerical results are compared to Barkhausen noise measurements in two materials representing distinct adiabatically driven universality classes. Relaxation of the zero temperature constraint cannot be done without considering finite sweeprates due to global relaxation timescales that arise at finite temperatures. We investigate the connection between sweeprate and thermal fluctuations in the far from equilibrium limit typical of crackling systems. Again, using scaling arguments and numerical simulations of the random field Ising model near a disorder-induced critical point we analyze interesting crossover phenomena in the power spectra which are also observed in Barkhausen noise but have yet to be explained.

Numerical renormalization group method for entanglement negativity at finite temperature

NASA Astrophysics Data System (ADS)

Shim, Jeongmin; Sim, H.-S.; Lee, Seung-Sup B.

2018-04-01

We develop a numerical method to compute the negativity, an entanglement measure for mixed states, between the impurity and the bath in quantum impurity systems at finite temperature. We construct a thermal density matrix by using the numerical renormalization group (NRG), and evaluate the negativity by implementing the NRG approximation that reduces computational cost exponentially. We apply the method to the single-impurity Kondo model and the single-impurity Anderson model. In the Kondo model, the negativity exhibits a power-law scaling at temperature much lower than the Kondo temperature and a sudden death at high temperature. In the Anderson model, the charge fluctuation of the impurity contributes to the negativity even at zero temperature when the on-site Coulomb repulsion of the impurity is finite, while at low temperature the negativity between the impurity spin and the bath exhibits the same power-law scaling behavior as in the Kondo model.

Heat capacity of the neutron star inner crust within an extended nuclear statistical equilibrium model

NASA Astrophysics Data System (ADS)

Burrello, S.; Gulminelli, F.; Aymard, F.; Colonna, M.; Raduta, Ad. R.

2015-11-01

Background: Superfluidity in the crust is a key ingredient for the cooling properties of proto-neutron stars. Present theoretical calculations employ the quasiparticle mean-field Hartree-Fock-Bogoliubov theory with temperature-dependent occupation numbers for the quasiparticle states. Purpose: Finite temperature stellar matter is characterized by a whole distribution of different nuclear species. We want to assess the importance of this distribution on the calculation of heat capacity in the inner crust. Method: Following a recent work, the Wigner-Seitz cell is mapped into a model with cluster degrees of freedom. The finite temperature distribution is then given by a statistical collection of Wigner-Seitz cells. We additionally introduce pairing correlations in the local density BCS approximation both in the homogeneous unbound neutron component, and in the interface region between clusters and neutrons. Results: The heat capacity is calculated in the different baryonic density conditions corresponding to the inner crust, and in a temperature range varying from 100 KeV to 2 MeV. We show that accounting for the cluster distribution has a small effect at intermediate densities, but it considerably affects the heat capacity both close to the outer crust and close to the core. We additionally show that it is very important to consider the temperature evolution of the proton fraction for a quantitatively reliable estimation of the heat capacity. Conclusions: We present the first modelization of stellar matter containing at the same time a statistical distribution of clusters at finite temperature, and pairing correlations in the unbound neutron component. The effect of the nuclear distribution on the superfluid properties can be easily added in future calculations of the neutron star cooling curves. A strong influence of resonance population on the heat capacity at high temperature is observed, which deserves to be further studied within more microscopic calculations.

Nonlinear heat transfer and structural analyses of SSME turbine blades

NASA Technical Reports Server (NTRS)

Abdul-Aziz, A.; Kaufman, A.

1987-01-01

Three-dimensional nonlinear finite-element heat transfer and structural analyses were performed for the first stage high-pressure fuel turbopump blade of the space shuttle main engine (SSME). Directionally solidified (DS) MAR-M 246 material properties were considered for the analyses. Analytical conditions were based on a typical test stand engine cycle. Blade temperature and stress-strain histories were calculated using MARC finite-element computer code. The study was undertaken to assess the structural response of an SSME turbine blade and to gain greater understanding of blade damage mechanisms, convective cooling effects, and the thermal-mechanical effects.

Finite Element Solution of Unsteady Mixed Convection Flow of Micropolar Fluid over a Porous Shrinking Sheet

PubMed Central

Gupta, Diksha; Singh, Bani

2014-01-01

The objective of this investigation is to analyze the effect of unsteadiness on the mixed convection boundary layer flow of micropolar fluid over a permeable shrinking sheet in the presence of viscous dissipation. At the sheet a variable distribution of suction is assumed. The unsteadiness in the flow and temperature fields is caused by the time dependence of the shrinking velocity and surface temperature. With the aid of similarity transformations, the governing partial differential equations are transformed into a set of nonlinear ordinary differential equations, which are solved numerically, using variational finite element method. The influence of important physical parameters, namely, suction parameter, unsteadiness parameter, buoyancy parameter and Eckert number on the velocity, microrotation, and temperature functions is investigated and analyzed with the help of their graphical representations. Additionally skin friction and the rate of heat transfer have also been computed. Under special conditions, an exact solution for the flow velocity is compared with the numerical results obtained by finite element method. An excellent agreement is observed for the two sets of solutions. Furthermore, to verify the convergence of numerical results, calculations are conducted with increasing number of elements. PMID:24672310

Keldysh approach for nonequilibrium phase transitions in quantum optics: Beyond the Dicke model in optical cavities

NASA Astrophysics Data System (ADS)

Torre, Emanuele G. Dalla; Diehl, Sebastian; Lukin, Mikhail D.; Sachdev, Subir; Strack, Philipp

2013-02-01

We investigate nonequilibrium phase transitions for driven atomic ensembles interacting with a cavity mode and coupled to a Markovian dissipative bath. In the thermodynamic limit and at low frequencies, we show that the distribution function of the photonic mode is thermal, with an effective temperature set by the atom-photon interaction strength. This behavior characterizes the static and dynamic critical exponents of the associated superradiance transition. Motivated by these considerations, we develop a general Keldysh path-integral approach that allows us to study physically relevant nonlinearities beyond the idealized Dicke model. Using standard diagrammatic techniques, we take into account the leading-order corrections due to the finite number N of atoms. For finite N, the photon mode behaves as a damped classical nonlinear oscillator at finite temperature. For the atoms, we propose a Dicke action that can be solved for any N and correctly captures the atoms’ depolarization due to dissipative dephasing.

Noisy bases in Hilbert space: A new class of thermal coherent states and their properties

NASA Technical Reports Server (NTRS)

Vourdas, A.; Bishop, R. F.

1995-01-01

Coherent mixed states (or thermal coherent states) associated with the displaced harmonic oscillator at finite temperature, are introduced as a 'random' (or 'thermal' or 'noisy') basis in Hilbert space. A resolution of the identity for these states is proved and used to generalize the usual coherent state formalism for the finite temperature case. The Bargmann representation of an operator is introduced and its relation to the P and Q representations is studied. Generalized P and Q representations for the finite temperature case are also considered and several interesting relations among them are derived.

Efficiencies of power plants, quasi-static models and the geometric-mean temperature

NASA Astrophysics Data System (ADS)

Johal, Ramandeep S.

2017-02-01

Observed efficiencies of industrial power plants are often approximated by the square-root formula: 1 - √ T -/ T +, where T +( T -) is the highest (lowest) temperature achieved in the plant. This expression can be derived within finite-time thermodynamics, or, by entropy generation minimization, based on finite rates for the processes. In these analyses, a closely related quantity is the optimal value of the intermediate temperature for the hot stream, given by the geometric-mean value: √ T +/ T -. In this paper, instead of finite-time models, we propose to model the operation of plants by quasi-static work extraction models, with one reservoir (source/sink) as finite, while the other as practically infinite. No simplifying assumption is made on the nature of the finite system. This description is consistent with two model hypotheses, each yielding a specific value of the intermediate temperature, say T 1 and T 2. The lack of additional information on validity of the hypothesis that may be actually realized, motivates to approach the problem as an exercise in inductive inference. Thus we define an expected value of the intermediate temperature as the equally weighted mean: ( T 1 + T 2)/2. It is shown that the expected value is very closely given by the geometric-mean value for almost all of the observed power plants.

The combined effects of longitudinal heat conduction, flow nonuniformity and temperature nonuniformity in crossflow plate-fin heat exchangers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ranganayakulu, C.; Seetharamu, K.N.

An analysis of a crossflow plate-fin compact heat exchanger, accounting for the combined effects of two-dimensional longitudinal heat conduction through the exchanger wall and nonuniform inlet fluid flow and temperature distribution is carried out using a finite element method. A mathematical equation is developed to generate different types of fluid flow/temperature maldistribution models considering the possible deviations in fluid flow. Using these models, the exchanger effectiveness and its deterioration due to the combined effects of longitudinal heat conduction, flow nonuniformity and temperature nonuniformity are calculated for various design and operating conditions of the exchanger. It was found that the performancemore » variations are quite significant in some typical applications.« less

Finite Element Simulation of Temperature and Strain Distribution during Friction Stir Welding of AA2024 Aluminum Alloy

NASA Astrophysics Data System (ADS)

Jain, Rahul; Pal, Surjya Kanta; Singh, Shiv Brat

2017-02-01

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.

Effects of transverse temperature field nonuniformity on stress in silicon sheet growth

NASA Technical Reports Server (NTRS)

Mataga, P. A.; Hutchinson, J. W.; Chalmers, B.; Bell, R. O.; Kalejs, J. P.

1987-01-01

Stress and strain rate distributions are calculated using finite element analysis for steady-state growth of thin silicon sheet temperature nonuniformities imposed in the transverse (sheet width) dimension. Significant reductions in residual stress are predicted to occur for the case where the sheet edge is cooled relative to its center provided plastic deformation with high creep rates is present.

Numerical investigation into thermal load responses of steel railway bridge

NASA Astrophysics Data System (ADS)

Saravana Raja Mohan, K.; Sreemathy, J. R.; Saravanan, U.

2017-07-01

Bridge design requires consideration of the effects produced by temperature variations and the resultant thermal gradients in the structure. Temperature fluctuation leads to expansion and contraction of bridges and these movements are taken care by providing expansion joints and bearings. Free movements of a member can be restrained by imposing certain boundary condition but at the same time considerable allowances should be made for the stresses resulting from this restrained condition since the additional deformations and stresses produced may affect the ultimate and serviceability limit states of the structure. If the reaction force generated by the restraints is very large, then its omission can lead to unsafe design. The principal objective of this research is to study the effects of temperature variation on stresses and deflection in a steel railway bridge. A numerical model, based on finite element analysis is presented for evaluating the thermal performance of the bridge. The selected bridge is analyzed and the temperature field distribution and the corresponding thermal stresses and strains are calculated using the finite element software ABAQUS. A thorough understanding of the thermal load responses of a structure will result in safer and dependable design practices.

Quantification of temperature effect on impedance monitoring via PZT interface for prestressed tendon anchorage

NASA Astrophysics Data System (ADS)

Huynh, Thanh-Canh; Kim, Jeong-Tae

2017-12-01

In this study, the quantification of temperature effect on impedance monitoring via a PZT interface for prestressed tendon-anchorage is presented. Firstly, a PZT interface-based impedance monitoring technique is selected to monitor impedance signatures by predetermining sensitive frequency bands. An analytical model is designed to represent coupled dynamic responses of the PZT interface-tendon anchorage system. Secondly, experiments on a lab-scaled tendon anchorage are described. Impedance signatures are measured via the PZT interface for a series of temperature and prestress-force changes. Thirdly, temperature effects on measured impedance responses of the tendon anchorage are estimated by quantifying relative changes in impedance features (such as RMSD and CCD indices) induced by temperature variation and prestress-force change. Finally, finite element analyses are conducted to investigate the mechanism of temperature variation and prestress-loss effects on the impedance responses of prestressed tendon anchorage. Temperature effects on impedance monitoring are filtered by effective frequency shift-based algorithm for distinguishing prestress-loss effects on impedance signatures.

Exploring connections between statistical mechanics and Green's functions for realistic systems: Temperature dependent electronic entropy and internal energy from a self-consistent second-order Green's function

NASA Astrophysics Data System (ADS)

Welden, Alicia Rae; Rusakov, Alexander A.; Zgid, Dominika

2016-11-01

Including finite-temperature effects from the electronic degrees of freedom in electronic structure calculations of semiconductors and metals is desired; however, in practice it remains exceedingly difficult when using zero-temperature methods, since these methods require an explicit evaluation of multiple excited states in order to account for any finite-temperature effects. Using a Matsubara Green's function formalism remains a viable alternative, since in this formalism it is easier to include thermal effects and to connect the dynamic quantities such as the self-energy with static thermodynamic quantities such as the Helmholtz energy, entropy, and internal energy. However, despite the promising properties of this formalism, little is known about the multiple solutions of the non-linear equations present in the self-consistent Matsubara formalism and only a few cases involving a full Coulomb Hamiltonian were investigated in the past. Here, to shed some light onto the iterative nature of the Green's function solutions, we self-consistently evaluate the thermodynamic quantities for a one-dimensional (1D) hydrogen solid at various interatomic separations and temperatures using the self-energy approximated to second-order (GF2). At many points in the phase diagram of this system, multiple phases such as a metal and an insulator exist, and we are able to determine the most stable phase from the analysis of Helmholtz energies. Additionally, we show the evolution of the spectrum of 1D boron nitride to demonstrate that GF2 is capable of qualitatively describing the temperature effects influencing the size of the band gap.

Impurity effects on electrical conductivity of doped bilayer graphene in the presence of a bias voltage

NASA Astrophysics Data System (ADS)

E, Lotfi; H, Rezania; B, Arghavaninia; M, Yarmohammadi

2016-07-01

We address the electrical conductivity of bilayer graphene as a function of temperature, impurity concentration, and scattering strength in the presence of a finite bias voltage at finite doping, beginning with a description of the tight-binding model using the linear response theory and Green’s function approach. Our results show a linear behavior at high doping for the case of high bias voltage. The effects of electron doping on the electrical conductivity have been studied via changing the electronic chemical potential. We also discuss and analyze how the bias voltage affects the temperature behavior of the electrical conductivity. Finally, we study the behavior of the electrical conductivity as a function of the impurity concentration and scattering strength for different bias voltages and chemical potentials respectively. The electrical conductivity is found to be monotonically decreasing with impurity scattering strength due to the increased scattering among electrons at higher impurity scattering strength.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mironov, Alexey Yu.; Silevitch, Daniel M.; Proslier, Thomas

Three decades after the prediction of charge-vortex duality in the critical vicinity of the two-dimensional superconductor-insulator transition (SIT), one of the fundamental implications of this duality-the charge Berezinskii-Kosterlitz-Thouless (BKT) transition that should occur on the insulating side of the SIT-has remained unobserved. The dual picture of the process points to the existence of a superinsulating state endowed with zero conductance at finite temperature. Here, we report the observation of the charge BKT transition on the insulating side of the SIT in 10 nm thick NbTiN films, identified by the BKT critical behavior of the temperature and magnetic field dependent resistance,more » and map out the magnetic-field dependence of the critical temperature of the charge BKT transition. Finally, we ascertain the effects of the finite electrostatic screening length and its divergence at the magnetic field-tuned approach to the superconductor-insulator transition.« less

Quantum phase slip phenomenon in ultra-narrow superconducting nanorings

NASA Astrophysics Data System (ADS)

Arutyunov, Konstantin Yu.; Hongisto, Terhi T.; Lehtinen, Janne S.; Leino, Leena I.; Vasiliev, Alexander L.

2012-02-01

The smaller the system, typically - the higher is the impact of fluctuations. In narrow superconducting wires sufficiently close to the critical temperature Tc thermal fluctuations are responsible for the experimentally observable finite resistance. Quite recently it became possible to fabricate sub-10 nm superconducting structures, where the finite resistivity was reported within the whole range of experimentally obtainable temperatures. The observation has been associated with quantum fluctuations capable to quench zero resistivity in superconducting nanowires even at temperatures T-->0. Here we demonstrate that in tiny superconducting nanorings the same phenomenon is responsible for suppression of another basic attribute of superconductivity - persistent currents - dramatically affecting their magnitude, the period and the shape of the current-phase relation. The effect is of fundamental importance demonstrating the impact of quantum fluctuations on the ground state of a macroscopically coherent system, and should be taken into consideration in various nanoelectronic applications.

Faithful state transfer between two-level systems via an actively cooled finite-temperature cavity

NASA Astrophysics Data System (ADS)

Sárkány, Lőrinc; Fortágh, József; Petrosyan, David

2018-03-01

We consider state transfer between two qubits—effective two-level systems represented by Rydberg atoms—via a common mode of a microwave cavity at finite temperature. We find that when both qubits have the same coupling strength to the cavity field, at large enough detuning from the cavity mode frequency, quantum interference between the transition paths makes the swap of the excitation between the qubits largely insensitive to the number of thermal photons in the cavity. When, however, the coupling strengths are different, the photon-number-dependent differential Stark shift of the transition frequencies precludes efficient transfer. Nevertheless, using an auxiliary cooling system to continuously extract the cavity photons, we can still achieve a high-fidelity state transfer between the qubits.

Elevated temperature crack growth

NASA Technical Reports Server (NTRS)

Kim, K. S.; Vanstone, R. H.; Malik, S. N.; Laflen, J. H.

1988-01-01

A study was performed to examine the applicability of path-independent (P-I) integrals to crack growth problems in hot section components of gas turbine aircraft engines. Alloy 718 was used and the experimental parameters included combined temperature and strain cycling, thermal gradients, elastic-plastic strain levels, and mean strains. A literature review was conducted of proposed P-I integrals, and those capable of analyzing hot section component problems were selected and programmed into the postprocessor of a finite element code. Detailed elastic-plastic finite element analyses were conducted to simulate crack growth and crack closure of the test specimen, and to evaluate the P-I integrals. It was shown that the selected P-I integrals are very effective for predicting crack growth for isothermal conditions.

Effect of thermal stresses on frequency band structures of elastic metamaterial plates

NASA Astrophysics Data System (ADS)

Wu, Ying; Yu, Kaiping; Yang, Linyun; Zhao, Rui; Shi, Xiaotian; Tian, Kuo

2018-01-01

We investigate the effect of thermal stresses on the band structure of elastic metamaterial plates by developing a useful finite-element based method. The thermal field is assumed to be uniform throughout the whole plate. Specifically, we find that the stiffness matrix of plate element is comprised of elastic and thermal stresses parts, which can be regarded as a linear function of temperature difference. We additionally demonstrate that the relative magnitudes between elastic properties and thermal stresses will lead to nonlinear effects on frequency band structures based on two different types of metamaterial plates made of single and double inclusions of square plates, respectively. Then, we validate the proposed approach by comparing the band structures with the frequency response curves obtained in finite periodic structures. We conduct sensitivity analysis and discuss in-depth the sensitivities of band structures with respect to temperature difference to quantitatively investigate the effect of thermal stresses on each band. In addition, the coupled effects of thermal stresses and temperature-dependent material properties on the band structure of Aluminum/silicone rubber plate have also been discussed. The proposed method and new findings in this paper extends the ability of existing metamaterial plates by enabling tunability over a wide range of frequencies in thermal environments.

Numerical analysis of ion temperature effects to the plasma wall transition using a one-dimensional two-fluid model. I. Finite Debye to ionization length ratio

NASA Astrophysics Data System (ADS)

Gyergyek, T.; Kovačič, J.

2017-06-01

A one-dimensional, two-fluid, steady state model is used for the analysis of ion temperature effects to the plasma-wall transition. In this paper, the model is solved for a finite ratio ɛ between the Debye and the ionization length, while in Part II [T. Gyergyek and J. Kovačič, Phys Plasmas 24, 063506 (2017)], the solutions for ɛ = 0 are presented. Ion temperature is treated as a given, independent parameter and it is included in the model as a boundary condition. It is shown that when the ion temperature larger than zero is selected, the ion flow velocity and the electric field at the boundary must be consistent with the selected ion temperature. A numerical procedure, how to determine such "consistent boundary conditions," is proposed, and a simple relation between the ion temperature and ion velocity at the boundary of the system is found. The effects of the ion temperature to the pre-sheath length, potential, ion temperature, and ion density drops in the pre-sheath and in the sheath are investigated. It is concluded that larger ion temperature results in a better shielding of the plasma from the wall. An attempt is made to include the ion heat flux qi into the model in its simplest form q i = - K ' /d T i d x , where K ' is a constant heat conduction coefficient. It is shown that inclusion of such a term into the energy transfer equation introduces an additional ion heating mechanism into the system and the ion flow then becomes isothermal instead of adiabatic even in the sheath.

Numerical analysis of ion temperature effects to the plasma wall transition using a one-dimensional two-fluid model. I. Finite Debye to ionization length ratio.

PubMed

Gyergyek, T; Kovačič, J

2017-06-01

A one-dimensional, two-fluid, steady state model is used for the analysis of ion temperature effects to the plasma-wall transition. In this paper, the model is solved for a finite ratio ε between the Debye and the ionization length, while in Part II [T. Gyergyek and J. Kovačič, Phys Plasmas 24, 063506 (2017)], the solutions for [Formula: see text] are presented. Ion temperature is treated as a given, independent parameter and it is included in the model as a boundary condition. It is shown that when the ion temperature larger than zero is selected, the ion flow velocity and the electric field at the boundary must be consistent with the selected ion temperature. A numerical procedure, how to determine such "consistent boundary conditions," is proposed, and a simple relation between the ion temperature and ion velocity at the boundary of the system is found. The effects of the ion temperature to the pre-sheath length, potential, ion temperature, and ion density drops in the pre-sheath and in the sheath are investigated. It is concluded that larger ion temperature results in a better shielding of the plasma from the wall. An attempt is made to include the ion heat flux q i into the model in its simplest form [Formula: see text], where [Formula: see text] is a constant heat conduction coefficient. It is shown that inclusion of such a term into the energy transfer equation introduces an additional ion heating mechanism into the system and the ion flow then becomes isothermal instead of adiabatic even in the sheath.

Empirical temperature-dependent intermolecular potentials determined by data mining from crystal data

NASA Astrophysics Data System (ADS)

Hofmann, D. W. M.; Kuleshova, L. N.

2018-05-01

Modern force fields are accurate enough to describe thermal effects in molecular crystals. Here, we have extended our earlier approach to discrete force fields for various temperatures to a force field with a continuous function. For the parametrisation of the force field, we used data mining on experimental structures with the temperature as an additional descriptor. The obtained force field can be used to minimise energy at a finite temperature and for molecular dynamics with zero-K potentials. The applicability of the method has been demonstrated for the prediction of crystal density, temperature density gradients and transition temperature.

Temperature Scaling Law for Quantum Annealing Optimizers.

PubMed

Albash, Tameem; Martin-Mayor, Victor; Hen, Itay

2017-09-15

Physical implementations of quantum annealing unavoidably operate at finite temperatures. We point to a fundamental limitation of fixed finite temperature quantum annealers that prevents them from functioning as competitive scalable optimizers and show that to serve as optimizers annealer temperatures must be appropriately scaled down with problem size. We derive a temperature scaling law dictating that temperature must drop at the very least in a logarithmic manner but also possibly as a power law with problem size. We corroborate our results by experiment and simulations and discuss the implications of these to practical annealers.

Quantitative magneto-optical analysis of the role of finite temperatures on the critical state in YBCO thin films

NASA Astrophysics Data System (ADS)

Albrecht, Joachim; Brück, Sebastian; Stahl, Claudia; Ruoß, Stephen

2016-11-01

We use quantitative magneto-optical microscopy to investigate the influence of finite temperatures on the critical state of thin YBCO films. In particular, temperature and time dependence of supercurrents in inhomogeneous and anisotropic films are analyzed to extract the role of temperature on the supercurrents themselves and the influence of thermally activated relaxation. We find that inhomogeneities and anisotropies of the current density distribution correspond to a different temperature dependence of local supercurrents. In addition, the thermally activated decay of supercurrents can be used to extract local vortex pinning energies. With these results the modification of vortex pinning introduced by substrate structures is studied. In summary the local investigation of supercurrent densities allows the full description of the vortex pinning landscape with respect to pinning forces and energies in superconducting films with complex properties under the influence of finite temperatures.

Realistic finite temperature simulations of magnetic systems using quantum statistics

NASA Astrophysics Data System (ADS)

Bergqvist, Lars; Bergman, Anders

2018-01-01

We have performed realistic atomistic simulations at finite temperatures using Monte Carlo and atomistic spin dynamics simulations incorporating quantum (Bose-Einstein) statistics. The description is much improved at low temperatures compared to classical (Boltzmann) statistics normally used in these kind of simulations, while at higher temperatures the classical statistics are recovered. This corrected low-temperature description is reflected in both magnetization and the magnetic specific heat, the latter allowing for improved modeling of the magnetic contribution to free energies. A central property in the method is the magnon density of states at finite temperatures, and we have compared several different implementations for obtaining it. The method has no restrictions regarding chemical and magnetic order of the considered materials. This is demonstrated by applying the method to elemental ferromagnetic systems, including Fe and Ni, as well as Fe-Co random alloys and the ferrimagnetic system GdFe3.

Finite-Temperature Hydrogen Adsorption/Desorption Thermodynamics Driven by Soft Vibration Modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Woo, Sung-Jae; Lee, Eui-Sup; Yoon, Mina

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-principlesmore » 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.« less

Heat transfer models for predicting Salmonella enteritidis in shell eggs through supply chain distribution.

PubMed

Almonacid, S; Simpson, R; Teixeira, A

2007-11-01

Egg and egg preparations are important vehicles for Salmonella enteritidis infections. The influence of time-temperature becomes important when the presence of this organism is found in commercial shell eggs. A computer-aided mathematical model was validated to estimate surface and interior temperature of shell eggs under variable ambient and refrigerated storage temperature. A risk assessment of S. enteritidis based on the use of this model, coupled with S. enteritidis kinetics, has already been reported in a companion paper published earlier in JFS. The model considered the actual geometry and composition of shell eggs and was solved by numerical techniques (finite differences and finite elements). Parameters of interest such as local (h) and global (U) heat transfer coefficient, thermal conductivity, and apparent volumetric specific heat were estimated by an inverse procedure from experimental temperature measurement. In order to assess the error in predicting microbial population growth, theoretical and experimental temperatures were applied to a S. enteritidis growth model taken from the literature. Errors between values of microbial population growth calculated from model predicted compared with experimentally measured temperatures were satisfactorily low: 1.1% and 0.8% for the finite difference and finite element model, respectively.

Finite element calculation of residual stress in dental restorative material

NASA Astrophysics Data System (ADS)

Grassia, Luigi; D'Amore, Alberto

2012-07-01

A finite element methodology for residual stresses calculation in dental restorative materials is proposed. The material under concern is a multifunctional methacrylate-based composite for dental restorations, activated by visible light. Reaction kinetics, curing shrinkage, and viscoelastic relaxation functions were required as input data on a structural finite element solver. Post cure effects were considered in order to quantify the residual stresses coming out from natural contraction with respect to those debited to the chemical shrinkage. The analysis showed for a given test case that residual stresses frozen in the dental restoration at uniform temperature of 37°C are of the same order of magnitude of the strength of the dental composite material per se.

White dwarfs and revelations

NASA Astrophysics Data System (ADS)

Saltas, Ippocratis D.; Sawicki, Ignacy; Lopes, Ilidio

2018-05-01

We use the most recent, complete and independent measurements of masses and radii of white dwarfs in binaries to bound the class of non-trivial modified gravity theories, viable after GW170817/GRB170817, using its effect on the mass-radius relation of the stars. We show that the uncertainty in the latest data is sufficiently small that residual evolutionary effects, most notably the effect of core composition, finite temperature and envelope structure, must now accounted for if correct conclusions about the nature of gravity are to be made. We model corrections resulting from finite temperature and envelopes to a base Hamada-Salpeter cold equation of state and derive consistent bounds on the possible modifications of gravity in the stars' interiors, finding that the parameter quantifying the strength of the modification Y< 0.14 at 95% confidence, an improvement of a factor of three with respect to previous bounds. Finally, our analysis reveals some fundamental degeneracies between the theory of gravity and the precise chemical makeup of white dwarfs.

Finite-size versus interface-proximity effects in thin-film epitaxial SrTiO3

NASA Astrophysics Data System (ADS)

De Souza, R. A.; Gunkel, F.; Hoffmann-Eifert, S.; Dittmann, R.

2014-06-01

The equilibrium electrical conductivity of epitaxial SrTiO3 (STO) thin films was investigated as a function of temperature, 950≤ T/K ≤1100, and oxygen partial pressure, 10-23≤ pO2/bar ≤1. Compared with single-crystal STO, nanoscale thin-film STO exhibited with decreasing film thickness an increasingly enhanced electronic conductivity under highly reducing conditions, with a corresponding decrease in the activation enthalpy of conduction. This implies substantial modification of STO's point-defect thermodynamics for nanoscale film thicknesses. We argue, however, against such a finite-size effect and for an interface-proximity effect. Indeed, assuming trapping of oxygen vacancies at the STO surface and concomitant depletion of oxygen vacancies—and accumulation of electrons—in an equilibrium surface space-charge layer, we are able to predict quantitatively the conductivity as a function of temperature, oxygen partial pressure, and film thickness. Particularly complex behavior is predicted for ultrathin films that are consumed entirely by space charge.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ferrario, Lorenzo, E-mail: lorenzo.ferrario@polimi.it; Little, Justin M., E-mail: jml@princeton.edu; Choueiri, Edgar Y., E-mail: choueiri@princeton.edu

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 ofmore » 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.« less

Rise of pairwise thermal entanglement for an alternating Ising and Heisenberg spin chain in an arbitrarily oriented magnetic field

NASA Astrophysics Data System (ADS)

Rojas, M.; de Souza, S. M.; Rojas, Onofre

2014-03-01

Typically two particles (spins) could be maximally entangled at zero temperature, and for a certain temperature the phenomenon of entanglement vanishes at the threshold temperature. For the Heisenberg coupled model or even the Ising model with a transverse magnetic field, one can observe some rise of entanglement even for a disentangled region at zero temperature. So we can understand this emergence of entanglement at finite temperature as being due to the mixing of some maximally entangled states with some other untangled states. Here, we present a simple one-dimensional Ising model with alternating Ising and Heisenberg spins in an arbitrarily oriented magnetic field, which can be mapped onto the classical Ising model with a magnetic field. This model does not show any evidence of entanglement at zero temperature, but surprisingly at finite temperature rise a pairwise thermal entanglement between two untangled spins at zero temperature when an arbitrarily oriented magnetic field is applied. This effect is a purely magnetic field, and the temperature dependence, as soon as the temperature increases, causes a small increase in concurrence, achieving its maximum at around 0.1. Even for long-range entanglement, a weak concurrence still survives. There are also some real materials that could serve as candidates that would exhibit this effect, such as Dy(NO3)(DMSO)2Cu(opba)(DMSO)2 [DMSO = dimethyl sulfoxide; opba = o-phenylenebis(oxamoto)] [J. Strečka, M. Hagiwara, Y. Han, T. Kida, Z. Honda, and M. Ikeda, Condens. Matter Phys. 15, 43002 (2012), 10.5488/CMP.15.43002].

Electron-phonon coupling from finite differences

NASA Astrophysics Data System (ADS)

Monserrat, Bartomeu

2018-02-01

The interaction between electrons and phonons underlies multiple phenomena in physics, chemistry, and materials science. Examples include superconductivity, electronic transport, and the temperature dependence of optical spectra. A first-principles description of electron-phonon coupling enables the study of the above phenomena with accuracy and material specificity, which can be used to understand experiments and to predict novel effects and functionality. In this topical review, we describe the first-principles calculation of electron-phonon coupling from finite differences. The finite differences approach provides several advantages compared to alternative methods, in particular (i) any underlying electronic structure method can be used, and (ii) terms beyond the lowest order in the electron-phonon interaction can be readily incorporated. But these advantages are associated with a large computational cost that has until recently prevented the widespread adoption of this method. We describe some recent advances, including nondiagonal supercells and thermal lines, that resolve these difficulties, and make the calculation of electron-phonon coupling from finite differences a powerful tool. We review multiple applications of the calculation of electron-phonon coupling from finite differences, including the temperature dependence of optical spectra, superconductivity, charge transport, and the role of defects in semiconductors. These examples illustrate the advantages of finite differences, with cases where semilocal density functional theory is not appropriate for the calculation of electron-phonon coupling and many-body methods such as the GW approximation are required, as well as examples in which higher-order terms in the electron-phonon interaction are essential for an accurate description of the relevant phenomena. We expect that the finite difference approach will play a central role in future studies of the electron-phonon interaction.

A combined experimental and finite element study to predict the failure mechanisms in SiC coated carbon/carbon composites at room and elevated temperatures under flexural loading

NASA Technical Reports Server (NTRS)

Mahfuz, Hassan; Das, Partha S.; Xue, Dongwei; Krishnagopalan, Jaya; Jeelani, Shaik

1993-01-01

Response of quasi-isotropic laminates of SiC coated Carbon/Carbon (C/C) composites have been investigated under flexural loading at various temperatures. Variation of load-deflection behavior with temperatures are studied. Increase in flexural strength and stiffness are observed with the rise in temperature. Extensive analyses through Optical Microscope (OM) and Non-Destructive Evaluation (NDE) have been performed to understand the failure mechanisms. Damage zone is found only within the neighborhood of the loading plane. Isoparametric layered shell elements developed on the basis of the first order shear deformation theory have been used to model the thin laminates of C/C under flexural loading. Large deformation behavior has been considered in the finite element analysis to account for the non-linearities encountered during the actual test. Data generated using finite element analysis are presented to corroborate the experimental findings, and a comparison in respect of displacement and stress-strain behavior are given to check the accuracy of the finite element analysis. Reasonable correlation between the experimental and finite element results have been established.

Simulation of Aluminum Micro-mirrors for Space Applications at Cryogenic Temperatures

NASA Technical Reports Server (NTRS)

Kuhn, J. L.; Dutta, S. B.; Greenhouse, M. A.; Mott, D. B.

2000-01-01

Closed form and finite element models are developed to predict the device response of aluminum electrostatic torsion micro-mirrors fabricated on silicon substrate for space applications at operating temperatures of 30K. Initially, closed form expressions for electrostatic pressure arid mechanical restoring torque are used to predict the pull-in and release voltages at room temperature. Subsequently, a detailed mechanical finite element model is developed to predict stresses and vertical beam deflection induced by the electrostatic and thermal loads. An incremental and iterative solution method is used in conjunction with the nonlinear finite element model and closed form electrostatic equations to solve. the coupled electro-thermo-mechanical problem. The simulation results are compared with experimental measurements at room temperature of fabricated micro-mirror devices.

Effect of electron-vibration interactions on the thermoelectric efficiency of molecular junctions.

PubMed

Hsu, Bailey C; Chiang, Chi-Wei; Chen, Yu-Chang

2012-07-11

From first-principles approaches, we investigate the thermoelectric efficiency of a molecular junction where a benzene molecule is connected directly to the platinum electrodes. We calculate the thermoelectric figure of merit ZT in the presence of electron-vibration interactions with and without local heating under two scenarios: linear response and finite bias regimes. In the linear response regime, ZT saturates around the electrode temperature T(e) = 25 K in the elastic case, while in the inelastic case we observe a non-saturated and a much larger ZT beyond T(e) = 25 K attributed to the tail of the Fermi-Dirac distribution. In the finite bias regime, the inelastic effects reveal the signatures of the molecular vibrations in the low-temperature regime. The normal modes exhibiting structures in the inelastic profile are characterized by large components of atomic vibrations along the current density direction on top of each individual atom. In all cases, the inclusion of local heating leads to a higher wire temperature T(w) and thus magnifies further the influence of the electron-vibration interactions due to the increased number of local phonons.

Coupled thermomechanical behavior of graphene using the spring-based finite element approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

Georgantzinos, S. K., E-mail: sgeor@mech.upatras.gr; Anifantis, N. K., E-mail: nanif@mech.upatras.gr; Giannopoulos, G. I., E-mail: ggiannopoulos@teiwest.gr

The prediction of the thermomechanical behavior of graphene using a new coupled thermomechanical spring-based finite element approach is the aim of this work. Graphene sheets are modeled in nanoscale according to their atomistic structure. Based on molecular theory, the potential energy is defined as a function of temperature, describing the interatomic interactions in different temperature environments. The force field is approached by suitable straight spring finite elements. Springs simulate the interatomic interactions and interconnect nodes located at the atomic positions. Their stiffness matrix is expressed as a function of temperature. By using appropriate boundary conditions, various different graphene configurations aremore » analyzed and their thermo-mechanical response is approached using conventional finite element procedures. A complete parametric study with respect to the geometric characteristics of graphene is performed, and the temperature dependency of the elastic material properties is finally predicted. Comparisons with available published works found in the literature demonstrate the accuracy of the proposed method.« less

Thermal analysis of underground power cable system

NASA Astrophysics Data System (ADS)

Rerak, Monika; Ocłoń, Paweł

2017-10-01

The paper presents the application of Finite Element Method in thermal analysis of underground power cable system. The computations were performed for power cables buried in-line in the ground at a depth of 2 meters. The developed mathematical model allows determining the two-dimensional temperature distribution in the soil, thermal backfill and power cables. The simulations studied the effect of soil and cable backfill thermal conductivity on the maximum temperature of the cable conductor. Also, the effect of cable diameter on the temperature of cable core was studied. Numerical analyses were performed based on a program written in MATLAB.

Gauge fields at finite temperatures—"Thermo field dynamics" and the KMS condition and their extension to gauge theories

NASA Astrophysics Data System (ADS)

Ojima, Izumi

1981-11-01

"Thermo field dynamics," allowing the Feynman diagram method to be applied to real-time causal Green's functions at finite temperatures ( not temperature Green's functions with imaginary times) expressed in the form of "vacuum" expectation values, is reconsidered in light of its connection with the algebraic formulation of statical machanics based upon the KMS condition. On the basis of so-obtained general basic formulae, the formalism is extended to the case of gauge theories, where the subsidiary condition specifying physical states, the notion of observables, and the structure of the physical subspace at finite temperatures are clarified.

Finite-temperature fluid–insulator transition of strongly interacting 1D disordered bosons

PubMed Central

Michal, Vincent P.; Aleiner, Igor L.; Altshuler, Boris L.; Shlyapnikov, Georgy V.

2016-01-01

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 → 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 7Li or 39K. PMID:27436894

Tunneling of Massive Flux Lines in a High Tc Superconductor at absolute Zero

NASA Astrophysics Data System (ADS)

Narahari Achar, B. N.; Waleed Gaber, M.

1997-11-01

Our previous study(M. W. Gaber and B. N. N. Achar, Phys. Rev. B52, 1314(1995)) of quantum tunneling of damped flux lines of finite mass has been extended over the temperature range from the crossover temperature T0 to T=0 with a view to investigate further the temperature dependence of the tunneling rate found earlier. It has been found that at T=0, for the case of the cubic pinning potential, the action can be evaluated in a closed form for a flux line of finite length. The only non-zero contribution arises from the dissipation term resulting in a finite action.

Improving the efficiency of the Finite Temperature Density Matrix Renormalization Group method

NASA Astrophysics Data System (ADS)

Nocera, Alberto; Alvarez, Gonzalo

I review the basics of the finite temperature DMRG method, and then show how its efficiency can be improved by working on reduced Hilbert spaces and by using canonical approaches. My talk explains the applicability of the ancilla DMRG method beyond spins systems to t-J and Hubbard models, and addresses the computation of static and dynamical observables at finite temperature. Finally, I discuss the features of and roadmap for our DMRG + + codebase. Work done at CNMS, sponsored by the SUF Division, BES, U.S. DOE under contract with UT-Battelle. Support by the early career research program, DSUF, BES, DOE.

[Finite element analysis of temperature field of retina by electrical stimulation with microelectrode array].

PubMed

Wang, Wei; Qiao, Qingli; Gao, Weiping; Wu, Jun

2014-12-01

We studied the influence of electrode array parameters on temperature distribution to the retina during the use of retinal prosthesis in order to avoid thermal damage to retina caused by long-term electrical stimulation. Based on real epiretinal prosthesis, a three-dimensional model of electrical stimulation for retina with 4 X 4 microelectrode array had been established using the finite element software (COMSOL Multiphysics). The steady-state temperature field of electrical stimulation of the retina was calculated, and the effects of the electrode parameters such as the distance between the electrode contacts, the materials and area of the electrode contact on temperature field were considered. The maximum increase in the retina steady temperature was about 0. 004 degrees C with practical stimulation current. When the distance between the electrode contacts was changed from 130 microm to 520 microm, the temperature was reduced by about 0.006 microC. When the contact radius was doubled from 130 microm to 260 microm, the temperature decrease was about 0.005 degrees C. It was shown that there were little temperature changes in the retina with a 4 x 4 epiretinal microelectrode array, reflecting the safety of electrical stimulation. It was also shown that the maximum temperature in the retina decreased with increasing the distance between the electrode contacts, as well as increasing the area of electrode contact. However, the change of the maximum temperature was very small when the distance became larger than the diameter of electrode contact. There was no significant difference in the effects of temperature increase among the different electrode materials. Rational selection of the distance between the electrode contacts and their area in electrode design can reduce the temperature rise induced by electrical stimulation.

A new thermal model for bone drilling with applications to orthopaedic surgery.

PubMed

Lee, JuEun; Rabin, Yoed; Ozdoganlar, O Burak

2011-12-01

This paper presents a new thermal model for bone drilling with applications to orthopaedic surgery. The new model combines a unique heat-balance equation for the system of the drill bit and the chip stream, an ordinary heat diffusion equation for the bone, and heat generation at the drill tip, arising from the cutting process and friction. Modeling of the drill bit-chip stream system assumes an axial temperature distribution and a lumped heat capacity effect in the transverse cross-section. The new model is solved numerically using a tailor-made finite-difference scheme for the drill bit-chip stream system, coupled with a classic finite-difference method for the bone. The theoretical investigation addresses the significance of heat transfer between the drill bit and the bone, heat convection from the drill bit to the surroundings, and the effect of the initial temperature of the drill bit on the developing thermal field. Using the new model, a parametric study on the effects of machining conditions and drill-bit geometries on the resulting temperature field in the bone and the drill bit is presented. Results of this study indicate that: (1) the maximum temperature in the bone decreases with increased chip flow; (2) the transient temperature distribution is strongly influenced by the initial temperature; (3) the continued cooling (irrigation) of the drill bit reduces the maximum temperature even when the tip is distant from the cooled portion of the drill bit; and (4) the maximum temperature increases with increasing spindle speed, increasing feed rate, decreasing drill-bit diameter, increasing point angle, and decreasing helix angle. The model is expected to be useful in determination of optimum drilling conditions and drill-bit geometries. Copyright © 2011. Published by Elsevier Ltd.

Two-dimensional thermal modeling of power monolithic microwave integrated circuits (MMIC's)

NASA Technical Reports Server (NTRS)

Fan, Mark S.; Christou, Aris; Pecht, Michael G.

1992-01-01

Numerical simulations of the two-dimensional temperature distributions for a typical GaAs MMIC circuit are conducted, aiming at understanding the heat conduction process of the circuit chip and providing temperature information for device reliability analysis. The method used is to solve the two-dimensional heat conduction equation with a control-volume-based finite difference scheme. In particular, the effects of the power dissipation and the ambient temperature are examined, and the criterion for the worst operating environment is discussed in terms of the allowed highest device junction temperature.

Thermal effects on current-related skyrmion formation in a nanobelt

NASA Astrophysics Data System (ADS)

Zhao, Xuebing; Wang, Shasha; Wang, Chao; Che, Renchao

2018-05-01

We report an in-situ Lorentz transmission electron microscopy (LTEM) investigation to study the thermal effects on the generation of magnetic skyrmions within a nanobelt. Under an action of a moderate current pulse, magnetic skyrmions appear even in the temperature range far below the critical temperature and even at zero field. Finite element simulation reveals that the Joule heating plays an essential role in this behavior. Our results also uncover the importance of the cooling conditions in the current-related in situ LTEM research.

Time-independent hybrid enrichment for finite element solution of transient conduction–radiation in diffusive grey media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mohamed, M. Shadi, E-mail: m.s.mohamed@durham.ac.uk; Seaid, Mohammed; Trevelyan, Jon

2013-10-15

We investigate the effectiveness of the partition-of-unity finite element method for transient conduction–radiation problems in diffusive grey media. The governing equations consist of a semi-linear transient heat equation for the temperature field and a stationary diffusion approximation to the radiation in grey media. The coupled equations are integrated in time using a semi-implicit method in the finite element framework. We show that for the considered problems, a combination of hyperbolic and exponential enrichment functions based on an approximation of the boundary layer leads to improved accuracy compared to the conventional finite element method. It is illustrated that this approach canmore » be more efficient than using h adaptivity to increase the accuracy of the finite element method near the boundary walls. The performance of the proposed partition-of-unity method is analyzed on several test examples for transient conduction–radiation problems in two space dimensions.« less

Finite difference modelling of the temperature rise in non-linear medical ultrasound fields.

PubMed

Divall, S A; Humphrey, V F

2000-03-01

Non-linear propagation of ultrasound can lead to increased heat generation in medical diagnostic imaging due to the preferential absorption of harmonics of the original frequency. A numerical model has been developed and tested that is capable of predicting the temperature rise due to a high amplitude ultrasound field. The acoustic field is modelled using a numerical solution to the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation, known as the Bergen Code, which is implemented in cylindrical symmetric form. A finite difference representation of the thermal equations is used to calculate the resulting temperature rises. The model allows for the inclusion of a number of layers of tissue with different acoustic and thermal properties and accounts for the effects of non-linear propagation, direct heating by the transducer, thermal diffusion and perfusion in different tissues. The effect of temperature-dependent skin perfusion and variation in background temperature between the skin and deeper layers of the body are included. The model has been tested against analytic solutions for simple configurations and then used to estimate temperature rises in realistic obstetric situations. A pulsed 3 MHz transducer operating with an average acoustic power of 200 mW leads to a maximum steady state temperature rise inside the foetus of 1.25 degrees C compared with a 0.6 degree C rise for the same transmitted power under linear propagation conditions. The largest temperature rise occurs at the skin surface, with the temperature rise at the foetus limited to less than 2 degrees C for the range of conditions considered.

Pion decay constant and the {rho}-meson mass at finite temperature in hidden local symmetry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harada, M.; Shibata, A.

1997-06-01

We study the temperature dependence of the pion decay constant and {rho}-meson mass in the hidden local symmetry model at one loop. Using the standard imaginary time formalism, we include the thermal effect of the {rho} meson as well as that of the pion. We show that the pion gives a dominant contribution to the pion decay constant and the {rho}-meson contribution slightly decreases the critical temperature. The {rho}-meson pole mass increases as T{sup 4}/m{sub {rho}}{sup 2} at low temperature, dominated by the pion-loop effect. At high temperature, although the pion-loop effect decreases the {rho}-meson mass, the {rho}-loop contribution overcomesmore » the pion-loop contribution and the {rho}-meson mass increases with temperature. We also show that the conventional parameter a is stable as the temperature increases. {copyright} {ital 1997} {ital The American Physical Society}« less

Improved boundary layer heat transfer calculations near a stagnation point

NASA Technical Reports Server (NTRS)

Ahn, Kyung Hwan

1990-01-01

A thermal design of a solar receiver has been developed for the solutions of problems involving phase-change thermal energy storage and natural convection loss. Two dimensional axisymmetrical solidification and melting of materials contained between two concentric cylinders of finite length has been studied for thermal energy storage analysis. For calculation of free convection loss inside receiver cavity, two dimensional axisymmetrical, laminar, transient free convection including radiation effects has been studied using integral/finite difference method. Finite difference equations are derived for the above analysis subject to constant or variable material properties, initial conditions, and boundary conditions. The validity of the analyses has been substantiated by comparing results of the present general method with available analytic solutions or numerical results reported in the literature. Both explicit and implicit schemes are tested in phase change analysis with different number of nodes ranging from 4 to 18. The above numerical methods have been applied to the existing solar receiver analyzing computer code as additional subroutines. The results were computed for one of the proposed Brayton cycle solar receiver models running under the actual environmental conditions. Effect of thermal energy storage on the thermal behavior of the receiver has been estimated. Due to the thermal energy storage, about 65% reduction on working gas outlet temperature fluctuation has been obtained; however, maximum temperature of thermal energy storage containment has been increased about 18%. Also, effect of natural convection inside a receiver cavity on the receiver heat transfer has been analyzed. The finding indicated that thermal stratification occurs during the sun time resulting in higher receiver temperatures at the outlet section of the gas tube, and lower temperatures at the inlet section of the gas tube when compared with the results with no natural convection. Due to heat supply from the air during the shade time, minimum temperature has been increased, while maximum temperature has been reduced due to convection loss to air. Consequently, cyclic temperature fluctuation has been reduced 29% for working gas and 16% for thermal energy storage containment. On the other hand, despite the presence of the natural convection the time-averaged temperatures for receiver components were found to be similar for two cases with/without natural convection (maximum difference was 1.8%).

A study on thermal damage during hyperthermia treatment based on DPL model for multilayer tissues using finite element Legendre wavelet Galerkin approach.

PubMed

Kumar, Dinesh; Rai, K N

2016-12-01

Hyperthermia is a process that uses heat from the spatial heat source to kill cancerous cells without damaging the surrounding healthy tissues. Efficacy of hyperthermia technique is related to achieve temperature at the infected cells during the treatment process. A mathematical model on heat transfer in multilayer tissues in finite domain is proposed to predict the control temperature profile at hyperthermia position. The treatment technique uses dual-phase-lag model of heat transfer in multilayer tissues with modified Gaussian distribution heat source subjected to the most generalized boundary condition and interface at the adjacent layers. The complete dual-phase-lag model of bioheat transfer is solved using finite element Legendre wavelet Galerkin approach. The present solution has been verified with exact solution in a specific case and provides a good accuracy. The effect of the variability of different parameters such as lagging times, external heat source, metabolic heat source and the most generalized boundary condition on temperature profile in multilayer tissues is analyzed and also discussed the effective approach of hyperthermia treatment. Furthermore, we studied the modified thermal damage model with regeneration of healthy tissues as well. For viewpoint of thermal damage, the least thermal damage has been observed in boundary condition of second kind. The article concludes with a discussion of better opportunities for future clinical application of hyperthermia treatment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Thermal-structural analyses of Space Shuttle Main Engine (SSME) hot section components

NASA Technical Reports Server (NTRS)

Abdul-Aziz, Ali; Thompson, Robert L.

1988-01-01

Three dimensional nonlinear finite element heat transfer and structural analyses were performed for the first stage high pressure fuel turbopump (HPFTP) blade of the space shuttle main engine (SSME). Directionally solidified (DS) MAR-M 246 and single crystal (SC) PWA-1480 material properties were used for the analyses. Analytical conditions were based on a typical test stand engine cycle. Blade temperature and stress strain histories were calculated by using the MARC finite element computer code. The structural response of an SSME turbine blade was assessed and a greater understanding of blade damage mechanisms, convective cooling effects, and thermal mechanical effects was gained.

Photothermal modeling of thulium fibre laser-tissue interactions

NASA Astrophysics Data System (ADS)

Warnaby, Catherine E.; Coleman, Daniel J.; King, Terence A.

2003-10-01

A one-dimensional finite difference model has been used to investigate the temperature distribution within thulium fibre laser-irradiated tissue. Temperature-time and temperature-depth profiles are presented for various laser stimulus parameters in the 2 micron region. These current calculations are aimed at determining theoretical temperature distributions in the application of relatively low power fibre lasers for thermal stimulation of cutaneous nerves in human pain processing. Theoretical skin surface temperatures are compared with those from thermal camera measurements during thulium fibre laser irradiation. The effectiveness of the thulium fibre laser for thermally stimulating cutaneous nerves is confirmed.

Evidence for a Finite-Temperature Insulator.

PubMed

Ovadia, M; Kalok, D; Tamir, I; Mitra, S; Sacépé, B; Shahar, D

2015-08-27

In superconductors the zero-resistance current-flow is protected from dissipation at finite temperatures (T) by virtue of the short-circuit condition maintained by the electrons that remain in the condensed state. The recently suggested finite-T insulator and the "superinsulating" phase are different because any residual mechanism of conduction will eventually become dominant as the finite-T insulator sets-in. If the residual conduction is small it may be possible to observe the transition to these intriguing states. We show that the conductivity of the high magnetic-field insulator terminating superconductivity in amorphous indium-oxide exhibits an abrupt drop, and seem to approach a zero conductance at T < 0.04 K. We discuss our results in the light of theories that lead to a finite-T insulator.

Frustrated honeycomb-lattice bilayer quantum antiferromagnet in a magnetic field

NASA Astrophysics Data System (ADS)

Krokhmalskii, Taras; Baliha, Vasyl; Derzhko, Oleg; Schulenburg, Jörg; Richter, Johannes

2018-05-01

Frustrated bilayer quantum magnets have attracted attention as flat-band spin systems with unconventional thermodynamic properties. We study the low-temperature properties of a frustrated honeycomb-lattice bilayer spin-1/2 isotropic (XXX) Heisenberg antiferromagnet in a magnetic field by means of an effective low-energy theory using exact diagonalizations and quantum Monte Carlo simulations. Our main focus is on the magnetization curve and the temperature dependence of the specific heat indicating a finite-temperature phase transition in high magnetic fields.

Superhigh moduli and tension-induced phase transition of monolayer gamma-boron at finite temperatures.

PubMed

Zhao, Junhua; Yang, Zhaoyao; Wei, Ning; Kou, Liangzhi

2016-03-16

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.

An analysis of thermal stress and gas bending effects on vibrations of compressor rotor stages. [blade torsional rigidity

NASA Technical Reports Server (NTRS)

Chen, L.-T.; Dugundji, J.

1979-01-01

A preliminary study conducted by Kerrebrock et al. (1976) has shown that the torsional rigidity of untwisted thin blades of a transonic compressor can be reduced significantly by transient thermal stresses. The aerodynamic loads have various effects on blade vibration. One effect is that gas bending loads may result in a bending-torsion coupling which may change the characteristics of the torsion and bending vibration of the blade. For a general study of transient-temperature distribution within a rotor stage, a finite-element heat-conduction analysis was developed. The blade and shroud are divided into annular elements. With a temperature distribution obtained from the heat-conduction analysis and a prescribed gas bending load distribution along the blade span, the static deformation and moment distributions of the blade can be solved iteratively using the finite-element method. The reduction of the torsional rigidity of pretwisted blades caused by the thermal stress effect is then computed. The dynamic behavior of the blade is studied by a modified Galerkin's method.

Two characteristic temperatures for a Bose-Einstein condensate of a finite number of particles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Idziaszek, Z.; Institut fuer Theoretische Physik, Universitaet Hannover, D-30167 Hannover,; Rzazewski, K.

2003-09-01

We consider two characteristic temperatures for a Bose-Einstein condensate, which are related to certain properties of the condensate statistics. We calculate them for an ideal gas confined in power-law traps and show that they approach the critical temperature in the limit of large number of particles. The considered characteristic temperatures can be useful in the studies of Bose-Einstein condensates of a finite number of atoms indicating the point of a phase transition.

Prediction of the effect of temperature on impact damage in carbon/epoxy laminates

NASA Astrophysics Data System (ADS)

Gómez del Río, T.; Zaera, R.; Navarro, C.

2003-09-01

The effect of temperature on impact damage in Carbon Fiber Reinforced Plastic (CFRP) tape laminates produced by low velocity impact was studied by numerical simulations made to model drop weight tower impact tests on carbon/epoxy laminate composites. The damage model was implemented into a user subroutine of the finite element code ABAQUS. The model takes into account the thermal stresses resulting form the different thermal expansion coefficients in each ply of the laminate. The tests and simulations show how temperature affects the propagation of each damage mode. Matrix cracking and delamination are greatly affected by low temperature, white matrix crushing and fibre failure appear only in a small region at all the impact energies and test temperatures.

Optimal parameters to avoid thermal necrosis during bone drilling: A finite element analysis.

PubMed

Mediouni, Mohamed; Schlatterer, Daniel R; Khoury, Amal; Von Bergen, Tobias; Shetty, Sunil H; Arora, Manit; Dhond, Amit; Vaughan, Neil; Volosnikov, Alexander

2017-11-01

The drilling bone may potentially cause excessive frictional heat, which can lead to local bone necrosis. This heat generation and local necrosis has been suggested to contribute to the resorption of bone around the placed screws, ending in loss of screw purchase in the bone and inadvertent loosening and/or the bone-implant construct. In vivo studies on this subject have inherent obstacles not the least of which is controlling the variables and real time bone temperature data acquisition. Theoretical models can be generated using computer software and the inclusion of known constants for the mechanical properties of metal and bone. These known Data points for the variables (drill bit and bone) enables finite element analysis of various bone drilling scenarios. An elastic-plastic three-dimensional (3D) acetabular bone mode was developed and finite element model analysis (FEA) was applied to various simulated drilling procedures. The FEA results clearly indicate that the depth of drilling and the drill speed both have a significant effect on the temperature during drilling procedures. The reduction of the feeding speed leads to a reduction in bone temperature. Our data suggests that reducing the feeding speed regardless of RPMs and pressure applied could be a simple useful and effective way to reduce drilling temperatures. This study is the first step in helping any surgeon who drills bone and places screws to better understand the ideal pressure to apply and drill speed to employ and advance rate to avoid osteonecrosis. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2386-2391, 2017. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

Comparative study of BCS-BEC crossover theories above T{sub c}: The nature of the pseudogap in ultracold atomic Fermi gases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chien, C.-C.; Guo Hao; He Yan

2010-02-15

This article presents a comparison of two finite-temperature BCS-Bose-Einstein condensation (BEC) crossover theories above the transition temperature: Nozieres-Schmitt-Rink (NSR) theory and finite-T extended BCS-Leggett theory. The comparison is cast in the form of numerical studies of the behavior of the fermionic spectral function both theoretically and as constrained by (primarily) radio frequency (rf) experiments. Both theories include pair fluctuations and exhibit pseudogap effects, although the nature of this pseudogap is very different. The pseudogap in finite-T extended BCS-Leggett theory is found to follow a BCS-like dispersion which, in turn, is associated with a broadened BCS-like self-energy, rather more similar tomore » what is observed in high-temperature superconductors (albeit, for a d-wave case). The fermionic quasiparticle dispersion is different in NSR theory and the damping is considerably larger. We argue that the two theories are appropriate in different temperature regimes with the BCS-Leggett approach being more suitable nearer to condensation. There should, in effect, be little difference at higher T as the pseudogap becomes weaker and where the simplifying approximations used in the BCS-Leggett approach break down. On the basis of momentum-integrated rf studies of unpolarized gases, it would be difficult to distinguish which theory is the better one. A full comparison for polarized gases is not possible since it is claimed that there are inconsistencies in the NSR approach (not found in the BCS-Leggett scheme). Future experiments along the lines of momentum-resolved experiments look to be very promising in distinguishing the two theories.« less

The assessment of nanofluid in a Von Karman flow with temperature relied viscosity

NASA Astrophysics Data System (ADS)

Tanveer, Anum; Salahuddin, T.; Khan, Mumtaz; Alshomrani, Ali Saleh; Malik, M. Y.

2018-06-01

This work endeavor to study the heat and mass transfer viscous nanofluid features in a Von Karman flow invoking the variable viscosity mechanism. Moreover, we have extended our study in view of heat generation and uniform suction effects. The flow triggering non-linear partial differential equations are inscribed in the non-dimensional form by manipulating suitable transformations. The resulting non-linear ordinary differential equations are solved numerically via implicit finite difference scheme in conjecture with the Newton's linearization scheme afterwards. The sought solutions are plotted graphically to present comparison between MATLAB routine bvp4c and implicit finite difference schemes. Impact of different parameters on the concentration/temperature/velocity profiles are highlighted. Further Nusselt number, skin friction and Sherwood number characteristics are discussed for better exposition.

Effect of element size on the solution accuracies of finite-element heat transfer and thermal stress analyses of space shuttle orbiter

NASA Technical Reports Server (NTRS)

Ko, William L.; Olona, Timothy

1987-01-01

The effect of element size on the solution accuracies of finite-element heat transfer and thermal stress analyses of space shuttle orbiter was investigated. Several structural performance and resizing (SPAR) thermal models and NASA structural analysis (NASTRAN) structural models were set up for the orbiter wing midspan bay 3. The thermal model was found to be the one that determines the limit of finite-element fineness because of the limitation of computational core space required for the radiation view factor calculations. The thermal stresses were found to be extremely sensitive to a slight variation of structural temperature distributions. The minimum degree of element fineness required for the thermal model to yield reasonably accurate solutions was established. The radiation view factor computation time was found to be insignificant compared with the total computer time required for the SPAR transient heat transfer analysis.

Evidence for phonon skew scattering in the spin Hall effect of platinum

NASA Astrophysics Data System (ADS)

Karnad, G. V.; Gorini, C.; Lee, K.; Schulz, T.; Lo Conte, R.; Wells, A. W. J.; Han, D.-S.; Shahbazi, K.; Kim, J.-S.; Moore, T. A.; Swagten, H. J. M.; Eckern, U.; Raimondi, R.; Kläui, M.

2018-03-01

We measure and analyze the effective spin Hall angle of platinum in the low-residual resistivity regime by second-harmonic measurements of the spin-orbit torques for a multilayer of Pt |Co | AlOx . An angular-dependent study of the torques allows us to extract the effective spin Hall angle responsible for the damping-like torque in the system. We observe a strikingly nonmonotonic and reproducible temperature dependence of the torques. This behavior is compatible with recent theoretical predictions which include both intrinsic and extrinsic (impurities and phonons) contributions to the spin Hall effect at finite temperatures.

Retrieving the ground state of spin glasses using thermal noise: Performance of quantum annealing at finite temperatures.

PubMed

Nishimura, Kohji; Nishimori, Hidetoshi; Ochoa, Andrew J; Katzgraber, Helmut G

2016-09-01

We study the problem to infer the ground state of a spin-glass Hamiltonian using data from another Hamiltonian with interactions disturbed by noise from the original Hamiltonian, motivated by the ground-state inference in quantum annealing on a noisy device. It is shown that the average Hamming distance between the inferred spin configuration and the true ground state is minimized when the temperature of the noisy system is kept at a finite value, and not at zero temperature. We present a spin-glass generalization of a well-established result that the ground state of a purely ferromagnetic Hamiltonian is best inferred at a finite temperature in the sense of smallest Hamming distance when the original ferromagnetic interactions are disturbed by noise. We use the numerical transfer-matrix method to establish the existence of an optimal finite temperature in one- and two-dimensional systems. Our numerical results are supported by mean-field calculations, which give an explicit expression of the optimal temperature to infer the spin-glass ground state as a function of variances of the distributions of the original interactions and the noise. The mean-field prediction is in qualitative agreement with numerical data. Implications on postprocessing of quantum annealing on a noisy device are discussed.

Volume dependence of baryon number cumulants and their ratios

DOE PAGES

Almási, Gábor A.; Pisarski, Robert D.; Skokov, Vladimir V.

2017-03-17

Here, we explore the influence of finite-volume effects on cumulants of baryon/quark number fluctuations in a nonperturbative chiral model. In order to account for soft modes, we use the functional renormalization group in a finite volume, using a smooth regulator function in momentum space. We compare the results for a smooth regulator with those for a sharp (or Litim) regulator, and show that in a finite volume, the latter produces spurious artifacts. In a finite volume there are only apparent critical points, about which we compute the ratio of the fourth- to the second-order cumulant of quark number fluctuations. Finally,more » when the volume is sufficiently small the system has two apparent critical points; as the system size decreases, the location of the apparent critical point can move to higher temperature and lower chemical potential.« less

Three dimensional finite temperature SU(3) gauge theory near the phase transition

NASA Astrophysics Data System (ADS)

Bialas, P.; Daniel, L.; Morel, A.; Petersson, B.

2013-06-01

We have measured the correlation function of Polyakov loops on the lattice in three dimensional SU(3) gauge theory near its finite temperature phase transition. Using a new and powerful application of finite size scaling, we furthermore extend the measurements of the critical couplings to considerably larger values of the lattice sizes, both in the temperature and space directions, than was investigated earlier in this theory. With the help of these measurements we perform a detailed finite size scaling analysis, showing that for the critical exponents of the two dimensional three state Potts model the mass and the susceptibility fall on unique scaling curves. This strongly supports the expectation that the gauge theory is in the same universality class. The Nambu-Goto string model on the other hand predicts that the exponent ν has the mean field value, which is quite different from the value in the abovementioned Potts model. Using our values of the critical couplings we also determine the continuum limit of the value of the critical temperature in terms of the square root of the zero temperature string tension. This value is very near to the prediction of the Nambu-Goto string model in spite of the different critical behaviour.

Symmetry Energy and Its Components in Finite Nuclei

NASA Astrophysics Data System (ADS)

Antonov, A. N.; Gaidarov, M. K.; Kadrev, D. N.; Sarriguren, P.; Moya de Guerra, E.

2018-05-01

We derive the volume and surface components of the nuclear symmetry energy (NSE) and their ratio within the coherent density fluctuation model. The estimations use the results of the model for the NSE in finite nuclei based on the Brueckner and Skyrme energy-density functionals for nuclear matter. The obtained values of the volume and surface contributions to the NSE and their ratio for the Ni, Sn, and Pb isotopic chains are compared with estimations of other approaches which have used available experimental data on binding energies, neutron-skin thicknesses, and excitation energies to isobaric analog states (IAS). Apart from the density dependence investigated in our previous works, we study also the temperature dependence of the symmetry energy in finite nuclei in the framework of the local density approximation combining it with the self-consistent Skyrme-HFB method using the cylindrical transformed deformed harmonic-oscillator basis. The results for the thermal evolution of the NSE in the interval T = 0–4 MeV show that its values decrease with temperature. The investigations of the T-dependence of the neutron and proton root-mean-square radii and the corresponding neutron skin thickness point out that the effect of temperature leads mainly to a substantial increase of the neutron radii and skins, especially in nuclei which are more rich of neutrons.

The quest for novel modes of excitation in exotic nuclei

NASA Astrophysics Data System (ADS)

Paar, N.

2010-06-01

This paper provides an insight into several open problems in the quest for novel modes of excitation in nuclei with isospin asymmetry, deformation and finite-temperature characteristics in stellar environments. Major unsolved problems include the nature of pygmy dipole resonances, the quest for various multipole and spin-isospin excitations both in neutron-rich and proton drip-line nuclei mainly driven by loosely bound nucleons, excitations in unstable deformed nuclei and evolution of their properties with the shape phase transition. Exotic modes of excitation in nuclei at finite temperatures characteristic of supernova evolution present open problems with a possible impact in modeling astrophysically relevant weak interaction rates. All these issues challenge self-consistent many-body theory frameworks at the frontiers of on-going research, including nuclear energy density functionals, both phenomenological and constrained by the strong interaction physics of QCD, models based on low-momentum two-nucleon interaction Vlow-k and correlated realistic nucleon-nucleon interaction VUCOM, supplemented by three-body force, as well as two-nucleon and three-nucleon interactions derived from the chiral effective field theory. Joined theoretical and experimental efforts, including research with radioactive isotope beams, are needed to provide insight into dynamical properties of nuclei away from the valley of stability, involving the interplay of isospin asymmetry, deformation and finite temperature.

Finite element procedures for time-dependent convection-diffusion-reaction systems

NASA Technical Reports Server (NTRS)

Tezduyar, T. E.; Park, Y. J.; Deans, H. A.

1988-01-01

New finite element procedures based on the streamline-upwind/Petrov-Galerkin formulations are developed for time-dependent convection-diffusion-reaction equations. These procedures minimize spurious oscillations for convection-dominated and reaction-dominated problems. The results obtained for representative numerical examples are accurate with minimal oscillations. As a special application problem, the single-well chemical tracer test (a procedure for measuring oil remaining in a depleted field) is simulated numerically. The results show the importance of temperature effects on the interpreted value of residual oil saturation from such tests.

Critical temperatures of hybrid laminates using finite elements

NASA Astrophysics Data System (ADS)

Chockalingam, S.; Mathew, T. C.; Singh, G.; Rao, G. V.

1992-06-01

Thermal buckling of antisymmetric cross-ply hybrid laminates is investigated. A one-dimensional finite element based on first-order shear deformation theory, having two nodes and six degrees of freedom per node, namely axial displacement, transverse displacements and rotation of the normal to the beam axis and their derivatives with respect to beam coordinate axis, is employed for this purpose. Various types of hybrid laminates with different combination of glass/epoxy, Kevlar/epoxy and carbon/epoxy are considered. Effects of slenderness ratio, boundary conditions and lay-ups are studied in detail.

User's manual for the one-dimensional hypersonic experimental aero-thermodynamic (1DHEAT) data reduction code

NASA Technical Reports Server (NTRS)

Hollis, Brian R.

1995-01-01

A FORTRAN computer code for the reduction and analysis of experimental heat transfer data has been developed. This code can be utilized to determine heat transfer rates from surface temperature measurements made using either thin-film resistance gages or coaxial surface thermocouples. Both an analytical and a numerical finite-volume heat transfer model are implemented in this code. The analytical solution is based on a one-dimensional, semi-infinite wall thickness model with the approximation of constant substrate thermal properties, which is empirically corrected for the effects of variable thermal properties. The finite-volume solution is based on a one-dimensional, implicit discretization. The finite-volume model directly incorporates the effects of variable substrate thermal properties and does not require the semi-finite wall thickness approximation used in the analytical model. This model also includes the option of a multiple-layer substrate. Fast, accurate results can be obtained using either method. This code has been used to reduce several sets of aerodynamic heating data, of which samples are included in this report.

TAP 1: A Finite Element Program for Steady-State Thermal Analysis of Convectively Cooled Structures

NASA Technical Reports Server (NTRS)

Thornton, E. A.

1976-01-01

The program has a finite element library of six elements: two conduction/convection elements to model heat transfer in a solid, two convection elements to model heat transfer in a fluid, and two integrated conduction/convection elements to represent combined heat transfer in tubular and plate/fin fluid passages. Nonlinear thermal analysis due to temperature dependent thermal parameters is performed using the Newton-Raphson iteration method. Program output includes nodal temperatures and element heat fluxes. Pressure drops in fluid passages may be computed as an option. A companion plotting program for displaying the finite element model and predicted temperature distributions is presented. User instructions and sample problems are presented in appendixes.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Delpassand, M.S.

The power section of a mud driven progressing cavity drill motors consists of a steel rotor shaped with an external helix rotating within a stationary tube with a molded helical elastomeric lining (stator). Operating temperature of the elastomer lining is an important parameter that affects the stator life. Motor operating conditions such as down hole temperature, torque, differential pressure, and speed determine the elastomer temperature. This paper presents an analysis technique to predict stator elastomer temperature as a function of the motor`s operating parameters. A non-linear finite element analysis technique is used to predict the stator temperature. Physical and mechanicalmore » properties of the elastomer are measured, using laboratory equipment such as Monsanto`s RPA2000 dynamic analyzer and BFGoodrich model (II) flexometer. Boundary conditions of the finite element model are defined based on the down hole temperature, differential pressure, and the motor`s speed. Results of the finite element analysis are compared with laboratory test data to verify the accuracy of the analysis.« less

Development of thermal models of footwear using finite element analysis.

PubMed

Covill, D; Guan, Z W; Bailey, M; Raval, H

2011-03-01

Thermal comfort is increasingly becoming a crucial factor to be considered in footwear design. The climate inside a shoe is controlled by thermal and moisture conditions and is crucial to attain comfort. Research undertaken has shown that thermal conditions play a dominant role in shoe climate. Development of thermal models that are capable of predicting in-shoe temperature distributions is an effective way forward to undertake extensive parametric studies to assist optimized design. In this paper, two-dimensional and three-dimensional thermal models of in-shoe climate were developed using finite element analysis through commercial code Abaqus. The thermal material properties of the upper shoe, sole, and air were considered. Dry heat flux from the foot was calculated on the basis of typical blood flow in the arteries on the foot. Using the thermal models developed, in-shoe temperatures were predicted to cover various locations for controlled ambient temperatures of 15, 25, and 35 degrees C respectively. The predicted temperatures were compared with multipoint measured temperatures through microsensor technology. Reasonably good correlation was obtained, with averaged errors of 6, 2, and 1.5 per cent, based on the averaged in-shoe temperature for the above three ambient temperatures. The models can be further used to help design shoes with optimized thermal comfort.

A comparison of two finite element models for the prediction of permafrost temperatures

DOT National Transportation Integrated Search

1986-01-01

In permafrost areas, the analysis of soil thermal and hydraulic regimes is complicated by phase change effects and by moisture migration. During freezing, mobile soil moisture is drawn toward the freezing front, increasing the available latent heat; ...

Biothermomechanics of skin tissues

NASA Astrophysics Data System (ADS)

Xu, F.; Lu, T. J.; Seffen, K. A.

Biothermomechanics of skin is highly interdisciplinary involving bioheat transfer, burn damage, biomechanics and neurophysiology. During heating, thermally induced mechanical stress arises due to the thermal denaturation of collagen, resulting in macroscale shrinkage. Thus, the strain, stress, temperature and thermal pain/damage are highly correlated; in other words, the problem is fully coupled. The aim of this study is to develop a computational approach to examine the heat transfer process and the heat-induced mechanical response, so that the differences among the clinically applied heating modalities can be quantified. Exact solutions for temperature, thermal damage and thermal stress for a single-layer skin model were first derived for different boundary conditions. For multilayer models, numerical simulations using the finite difference method (FDM) and finite element method (FEM) were used to analyze the temperature, burn damage and thermal stress distributions in the skin tissue. The results showed that the thermomechanical behavior of skin tissue is very complex: blood perfusion has little effect on thermal damage but large influence on skin temperature distribution, which, in turn, influences significantly the resulting thermal stress field; the stratum corneum layer, although very thin, has a large effect on the thermomechanical behavior of skin, suggesting that it should be properly accounted for in the modeling of skin thermal stresses; the stress caused by non-uniform temperature distribution in the skin may also contribute to the thermal pain sensation.

Optimization of tissue physical parameters for accurate temperature estimation from finite-element simulation of radiofrequency ablation.

PubMed

Subramanian, Swetha; Mast, T Douglas

2015-10-07

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.

Vibronic Boson Sampling: Generalized Gaussian Boson Sampling for Molecular Vibronic Spectra at Finite Temperature.

PubMed

Huh, Joonsuk; Yung, Man-Hong

2017-08-07

Molecular vibroic spectroscopy, where the transitions involve non-trivial Bosonic correlation due to the Duschinsky Rotation, is strongly believed to be in a similar complexity class as Boson Sampling. At finite temperature, the problem is represented as a Boson Sampling experiment with correlated Gaussian input states. This molecular problem with temperature effect is intimately related to the various versions of Boson Sampling sharing the similar computational complexity. Here we provide a full description to this relation in the context of Gaussian Boson Sampling. We find a hierarchical structure, which illustrates the relationship among various Boson Sampling schemes. Specifically, we show that every instance of Gaussian Boson Sampling with an initial correlation can be simulated by an instance of Gaussian Boson Sampling without initial correlation, with only a polynomial overhead. Since every Gaussian state is associated with a thermal state, our result implies that every sampling problem in molecular vibronic transitions, at any temperature, can be simulated by Gaussian Boson Sampling associated with a product of vacuum modes. We refer such a generalized Gaussian Boson Sampling motivated by the molecular sampling problem as Vibronic Boson Sampling.

Effect of ion temperature on ion-acoustic solitary waves in a magnetized plasma in presence of superthermal electrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, S. V.; Devanandhan, S.; Lakhina, G. S.

2013-01-15

Obliquely propagating ion-acoustic soliatry waves are examined in a magnetized plasma composed of kappa distributed electrons and fluid ions with finite temperature. The Sagdeev potential approach is used to study the properties of finite amplitude solitary waves. Using a quasi-neutrality condition, it is possible to reduce the set of equations to a single equation (energy integral equation), which describes the evolution of ion-acoustic solitary waves in magnetized plasmas. The temperature of warm ions affects the speed, amplitude, width, and pulse duration of solitons. Both the critical and the upper Mach numbers are increased by an increase in the ion temperature.more » The ion-acoustic soliton amplitude increases with the increase in superthermality of electrons. For auroral plasma parameters, the model predicts the soliton speed, amplitude, width, and pulse duration, respectively, to be in the range of (28.7-31.8) km/s, (0.18-20.1) mV/m; (590-167) m, and (20.5-5.25) ms, which are in good agreement with Viking observations.« less

A Riemann-Hilbert formulation for the finite temperature Hubbard model

NASA Astrophysics Data System (ADS)

Cavaglià, Andrea; Cornagliotto, Martina; Mattelliano, Massimo; Tateo, Roberto

2015-06-01

Inspired by recent results in the context of AdS/CFT integrability, we reconsider the Thermodynamic Bethe Ansatz equations describing the 1D fermionic Hubbard model at finite temperature. We prove that the infinite set of TBA equations are equivalent to a simple nonlinear Riemann-Hilbert problem for a finite number of unknown functions. The latter can be transformed into a set of three coupled nonlinear integral equations defined over a finite support, which can be easily solved numerically. We discuss the emergence of an exact Bethe Ansatz and the link between the TBA approach and the results by Jüttner, Klümper and Suzuki based on the Quantum Transfer Matrix method. We also comment on the analytic continuation mechanism leading to excited states and on the mirror equations describing the finite-size Hubbard model with twisted boundary conditions.

Numerical investigation of thermal and residual stress of sapphire during c-axis vertical Bridgman growth process considering the solidification history effect

NASA Astrophysics Data System (ADS)

Hwang, Ji Hoon; Lee, Young Cheol; Lee, Wook Jin

2018-01-01

Sapphire single crystals have been highlighted for epitaxial of gallium nitride films in high-power laser and light emitting diode industries. In this study, the evolution of thermally induced stress in sapphire during the vertical Bridgman crystal growth process was investigated using a finite element model that simplified the real Bridgman process. A vertical Bridgman process of cylindrical sapphire crystal with a diameter of 50 mm was considered for the model. The solidification history effect during the growth was modeled by the quite element technique. The effects of temperature gradient, seeding interface shape and seeding position on the thermal stress during the process were discussed based on the finite element analysis results.

Topological order, entanglement, and quantum memory at finite temperature

NASA Astrophysics Data System (ADS)

Mazáč, Dalimil; Hamma, Alioscia

2012-09-01

We compute the topological entropy of the toric code models in arbitrary dimension at finite temperature. We find that the critical temperatures for the existence of full quantum (classical) topological entropy correspond to the confinement-deconfinement transitions in the corresponding Z2 gauge theories. This implies that the thermal stability of topological entropy corresponds to the stability of quantum (classical) memory. The implications for the understanding of ergodicity breaking in topological phases are discussed.

Emergent kink statistics at finite temperature

DOE PAGES

Lopez-Ruiz, Miguel Angel; Yepez-Martinez, Tochtli; Szczepaniak, Adam; ...

2017-07-25

In this paper we use 1D quantum mechanical systems with Higgs-like interaction potential to study the emergence of topological objects at finite temperature. Two different model systems are studied, the standard double-well potential model and a newly introduced discrete kink model. Using Monte-Carlo simulations as well as analytic methods, we demonstrate how kinks become abundant at low temperatures. These results may shed useful insights on how topological phenomena may occur in QCD.

Overcoming the sign problem at finite temperature: Quantum tensor network for the orbital eg model on an infinite square lattice

NASA Astrophysics Data System (ADS)

Czarnik, Piotr; Dziarmaga, Jacek; Oleś, Andrzej M.

2017-07-01

The variational tensor network renormalization approach to two-dimensional (2D) quantum systems at finite temperature is applied to a model suffering the notorious quantum Monte Carlo sign problem—the orbital eg model with spatially highly anisotropic orbital interactions. Coarse graining of the tensor network along the inverse temperature β yields a numerically tractable 2D tensor network representing the Gibbs state. Its bond dimension D —limiting the amount of entanglement—is a natural refinement parameter. Increasing D we obtain a converged order parameter and its linear susceptibility close to the critical point. They confirm the existence of finite order parameter below the critical temperature Tc, provide a numerically exact estimate of Tc, and give the critical exponents within 1 % of the 2D Ising universality class.

Thermal effects on nonlinear vibration of a carbon nanotube-based mass sensor using finite element analysis

NASA Astrophysics Data System (ADS)

Kang, Dong-Keun; Kim, Chang-Wan; Yang, Hyun-Ik

2017-01-01

In the present study we carried out a dynamic analysis of a CNT-based mass sensor by using a finite element method (FEM)-based nonlinear analysis model of the CNT resonator to elucidate the combined effects of thermal effects and nonlinear oscillation behavior upon the overall mass detection sensitivity. Mass sensors using carbon nanotube (CNT) resonators provide very high sensing performance. Because CNT-based resonators can have high aspect ratios, they can easily exhibit nonlinear oscillation behavior due to large displacements. Also, CNT-based devices may experience high temperatures during their manufacture and operation. These geometrical nonlinearities and temperature changes affect the sensing performance of CNT-based mass sensors. However, it is very hard to find previous literature addressing the detection sensitivity of CNT-based mass sensors including considerations of both these nonlinear behaviors and thermal effects. We modeled the nonlinear equation of motion by using the von Karman nonlinear strain-displacement relation, taking into account the additional axial force associated with the thermal effect. The FEM was employed to solve the nonlinear equation of motion because it can effortlessly handle the more complex geometries and boundary conditions. A doubly clamped CNT resonator actuated by distributed electrostatic force was the configuration subjected to the numerical experiments. Thermal effects upon the fundamental resonance behavior and the shift of resonance frequency due to attached mass, i.e., the mass detection sensitivity, were examined in environments of both high and low (or room) temperature. The fundamental resonance frequency increased with decreasing temperature in the high temperature environment, and increased with increasing temperature in the low temperature environment. The magnitude of the shift in resonance frequency caused by an attached mass represents the sensing performance of a mass sensor, i.e., its mass detection sensitivity, and it can be seen that this shift is affected by the temperature change and the amount of electrostatic force. The thermal effects on the mass detection sensitivity are intensified in the linear oscillation regime and increase with increasing CNT length; this intensification can either improve or worsen the detection sensitivity.

Effective equilibrium picture in the x y model with exponentially correlated noise

NASA Astrophysics Data System (ADS)

Paoluzzi, Matteo; Marconi, Umberto Marini Bettolo; Maggi, Claudio

2018-02-01

We study the effect of exponentially correlated noise on the x y model in the limit of small correlation time, discussing the order-disorder transition in the mean field and the topological transition in two dimensions. We map the steady states of the nonequilibrium dynamics into an effective equilibrium theory. In the mean field, the critical temperature increases with the noise correlation time τ , indicating that memory effects promote ordering. This finding is confirmed by numerical simulations. The topological transition temperature in two dimensions remains untouched. However, finite-size effects induce a crossover in the vortices proliferation that is confirmed by numerical simulations.

Effective equilibrium picture in the xy model with exponentially correlated noise.

PubMed

Paoluzzi, Matteo; Marconi, Umberto Marini Bettolo; Maggi, Claudio

2018-02-01

We study the effect of exponentially correlated noise on the xy model in the limit of small correlation time, discussing the order-disorder transition in the mean field and the topological transition in two dimensions. We map the steady states of the nonequilibrium dynamics into an effective equilibrium theory. In the mean field, the critical temperature increases with the noise correlation time τ, indicating that memory effects promote ordering. This finding is confirmed by numerical simulations. The topological transition temperature in two dimensions remains untouched. However, finite-size effects induce a crossover in the vortices proliferation that is confirmed by numerical simulations.

Consequences of Part Temperature Variability in Electron Beam Melting of Ti-6Al-4V

NASA Astrophysics Data System (ADS)

Fisher, Brian A.; Mireles, Jorge; Ridwan, Shakerur; Wicker, Ryan B.; Beuth, Jack

2017-12-01

To facilitate adoption of Ti-6Al-4V (Ti64) parts produced via additive manufacturing (AM), the ability to ensure part quality is critical. Measuring temperatures is an important component of part quality monitoring in all direct metal AM processes. In this work, surface temperatures were monitored using a custom infrared camera system attached to an Arcam electron beam melting (EBM®) machine. These temperatures were analyzed to understand their possible effect on solidification microstructure based on solidification cooling rates extracted from finite element simulations. Complicated thermal histories were seen during part builds, and temperature changes occurring during typical Ti64 builds may be large enough to affect solidification microstructure. There is, however, enough time between fusion of individual layers for spatial temperature variations (i.e., hot spots) to dissipate. This means that an effective thermal control strategy for EBM® can be based on average measured surface temperatures, ignoring temperature variability.

Fluctuations and correlations of conserved charges in QCD at finite temperature with effective models

NASA Astrophysics Data System (ADS)

Fu, Wei-Jie; Liu, Yu-Xin; Wu, Yue-Liang

2010-01-01

We study fluctuations of conserved charges including baryon number, electric charge, and strangeness as well as the correlations among these conserved charges in the 2+1 flavor Polyakov-Nambu-Jona-Lasinio model at finite temperature. The calculated results are compared with those obtained from recent lattice calculations performed with an improved staggered fermion action at two values of the lattice cutoff with almost physical up and down quark masses and a physical value for the strange quark mass. We find that our calculated results are well consistent with those obtained in lattice calculations except for some quantitative differences for fluctuations related with strange quarks. Our calculations indicate that there is a pronounced cusp in the ratio of the quartic to quadratic fluctuations of baryon number, i.e. χ4B/χ2B, at the critical temperature during the phase transition, which confirms that χ4B/χ2B is a useful probe of the deconfinement and chiral phase transition.

Equation of state and QCD transition at finite temperature

NASA Astrophysics Data System (ADS)

Bazavov, A.; Bhattacharya, T.; Cheng, M.; Christ, N. H.; Detar, C.; Ejiri, S.; Gottlieb, Steven; Gupta, R.; Heller, U. M.; Huebner, K.; Jung, C.; Karsch, F.; Laermann, E.; Levkova, L.; Miao, C.; Mawhinney, R. D.; Petreczky, P.; Schmidt, C.; Soltz, R. A.; Soeldner, W.; Sugar, R.; Toussaint, D.; Vranas, P.

2009-07-01

We calculate the equation of state in 2+1 flavor QCD at finite temperature with physical strange quark mass and almost physical light quark masses using lattices with temporal extent Nτ=8. Calculations have been performed with two different improved staggered fermion actions, the asqtad and p4 actions. Overall, we find good agreement between results obtained with these two O(a2) improved staggered fermion discretization schemes. A comparison with earlier calculations on coarser lattices is performed to quantify systematic errors in current studies of the equation of state. We also present results for observables that are sensitive to deconfining and chiral aspects of the QCD transition on Nτ=6 and 8 lattices. We find that deconfinement and chiral symmetry restoration happen in the same narrow temperature interval. In an appendix we present a simple parametrization of the equation of state that can easily be used in hydrodynamic model calculations. In this parametrization we include an estimate of current uncertainties in the lattice calculations which arise from cutoff and quark mass effects.

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.

Probing α -RuCl3 Beyond Magnetic Order: Effects of Temperature and Magnetic Field

NASA Astrophysics Data System (ADS)

Winter, Stephen M.; Riedl, Kira; Kaib, David; Coldea, Radu; Valentí, Roser

2018-02-01

Recent studies have brought α -RuCl3 to the forefront of experimental searches for materials realizing Kitaev spin-liquid physics. This material exhibits strongly anisotropic exchange interactions afforded by the spin-orbit coupling of the 4 d Ru centers. We investigate the dynamical response at finite temperature and magnetic field for a realistic model of the magnetic interactions in α -RuCl3 . These regimes are thought to host unconventional paramagnetic states that emerge from the suppression of magnetic order. Using exact diagonalization calculations of the quantum model complemented by semiclassical analysis, we find a very rich evolution of the spin dynamics as the applied field suppresses the zigzag order and stabilizes a quantum paramagnetic state that is adiabatically connected to the fully polarized state at high fields. At finite temperature, we observe large redistributions of spectral weight that can be attributed to the anisotropic frustration of the model. These results are compared to recent experiments and provide a road map for further studies of these regimes.

Finite size induces crossover temperature in growing spin chains.

PubMed

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.

On the instability and energy flux of lower hybrid waves in the Venus plasma mantle

NASA Technical Reports Server (NTRS)

Strangeway, R. J.; Crawford, G. K.

1993-01-01

Waves generated near the lower hybrid resonance frequency by the modified two stream instability have been invoked as a possible source of energy flux into the topside ionosphere of Venus. These waves are observed above the ionopause in a region known as the plasma mantle. The plasma within the mantle appears to be a mixture of magnetosheath and ionospheric plasmas. Since the magnetosheath electrons and ions have temperatures of several tens of eV, any instability analysis of the modified two stream instability requires the inclusion of finite electron and ion temperatures. Finite temperature effects are likely to reduce the growth rate of the instability. Furthermore, the lower hybrid waves are only quasi-electrostatic, and the energy flux of the waves is mainly carried by parallel Poynting flux. The magnetic field in the mantle is draped over the ionopause. Lower hybrid waves therefore cannot transport any significant wave energy to lower altitudes, and so do not act as a source of additional heat to the topside ionosphere.

Chiral density wave versus pion condensation at finite density and zero temperature

NASA Astrophysics Data System (ADS)

Andersen, Jens O.; Kneschke, Patrick

2018-04-01

The quark-meson model is often used as a low-energy effective model for QCD to study the chiral transition at finite temperature T , baryon chemical potential μB , and isospin chemical potential μI . We determine the parameters of the model by matching the meson and quark masses, as well as the pion decay constant to their physical values using the on shell (OS) and modified minimal subtraction (MS ¯ ) schemes. In this paper, the existence of different phases at zero temperature is studied. In particular, we investigate the competition between an inhomogeneous chiral condensate and a homogeneous pion condensate. For the inhomogeneity, we use a chiral-density wave ansatz. For a sigma mass of 600 MeV, we find that an inhomogeneous chiral condensate exists only for pion masses below approximately 37 MeV. We also show that due to our parameter fixing, the onset of pion condensation takes place exactly at μIc=1/2 mπ in accordance with exact results.

Safety of High Speed Magnetic Levitation Transportation Systems : Thermal Effects and Related Safety Issues of Typical Maglev Steel Guideways

DOT National Transportation Integrated Search

1994-09-01

This report presents a theoretical analysis predicting the temperature distribution, thermal deflections, and thermal stresses that may occur in typical steel Maglev guideways under the proposed Orlando FL thermal environment. Transient, finite eleme...

Microstructural modeling of thermal conductivity of high burn-up mixed oxide fuel

NASA Astrophysics Data System (ADS)

Teague, Melissa; Tonks, Michael; Novascone, Stephen; Hayes, Steven

2014-01-01

Predicting the thermal conductivity of oxide fuels as a function of burn-up and temperature is fundamental to the efficient and safe operation of nuclear reactors. However, modeling the thermal conductivity of fuel is greatly complicated by the radially inhomogeneous nature of irradiated fuel in both composition and microstructure. In this work, radially and temperature-dependent models for effective thermal conductivity were developed utilizing optical micrographs of high burn-up mixed oxide fuel. The micrographs were employed to create finite element meshes with the OOF2 software. The meshes were then used to calculate the effective thermal conductivity of the microstructures using the BISON [1] fuel performance code. The new thermal conductivity models were used to calculate thermal profiles at end of life for the fuel pellets. These results were compared to thermal conductivity models from the literature, and comparison between the new finite element-based thermal conductivity model and the Duriez-Lucuta model was favorable.

Microstructural Modeling of Thermal Conductivity of High Burn-up Mixed Oxide Fuel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Melissa Teague; Michael Tonks; Stephen Novascone

2014-01-01

Predicting the thermal conductivity of oxide fuels as a function of burn-up and temperature is fundamental to the efficient and safe operation of nuclear reactors. However, modeling the thermal conductivity of fuel is greatly complicated by the radially inhomogeneous nature of irradiated fuel in both composition and microstructure. In this work, radially and temperature-dependent models for effective thermal conductivity were developed utilizing optical micrographs of high burn-up mixed oxide fuel. The micrographs were employed to create finite element meshes with the OOF2 software. The meshes were then used to calculate the effective thermal conductivity of the microstructures using the BISONmore » fuel performance code. The new thermal conductivity models were used to calculate thermal profiles at end of life for the fuel pellets. These results were compared to thermal conductivity models from the literature, and comparison between the new finite element-based thermal conductivity model and the Duriez–Lucuta model was favorable.« less

Properties of Localized Protons in Neutron Star Matter at Finite Temperatures

NASA Astrophysics Data System (ADS)

Szmaglinski, A.; Kubis, S.; Wójcik, W.

2014-02-01

We study properties of the proton component of neutron star matter for realistic nuclear models. Vanishing of the nuclear symmetry energy implies proton-neutron separation in dense nuclear matter. Protons which form admixture tend to be localized in potential wells. Here, we extend the description of proton localization to finite temperatures. It appears that the protons are still localized at temperatures typical for hot neutron stars. That fact has important astrophysical consequences. Moreover, the temperature inclusion leads to unexpected results for the behavior of the proton localized state.

Exchange-correlation approximations for reduced-density-matrix-functional theory at finite temperature: Capturing magnetic phase transitions in the homogeneous electron gas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baldsiefen, Tim; Cangi, Attila; Eich, F. G.

Here, we derive an intrinsically temperature-dependent approximation to the correlation grand potential for many-electron systems in thermodynamical equilibrium in the context of finite-temperature reduced-density-matrix-functional theory (FT-RDMFT). We demonstrate its accuracy by calculating the magnetic phase diagram of the homogeneous electron gas. We compare it to known limits from highly accurate quantum Monte Carlo calculations as well as to phase diagrams obtained within existing exchange-correlation approximations from density functional theory and zero-temperature RDMFT.

A Study on Aircraft Structure and Jet Engine

NASA Astrophysics Data System (ADS)

Park, Gil Moon; Park, Hwan Kyu; Kim, Jong Il; Kim, Jin Won; Kim, Jin Heung; Lee, Moo Seok; Chung, Nak Kyu

1985-12-01

The one of critical factor in gas turbine engine performance is high turbine inlet gas temperature. Therefore, the turbine rotor has so many problems which must be considered such as the turbine blade cooling, thermal stress of turbine disk due to severe temperature gradient, turbine rotor tip clearance, under the high operation temperature. The purpose of this study is to provide the temperature distribution and heat flux in turbine disk which is required to considered premensioned problem by the Finite Difference Method and the Finite Element Methods on the steady state condition.

Exchange-correlation approximations for reduced-density-matrix-functional theory at finite temperature: Capturing magnetic phase transitions in the homogeneous electron gas

DOE PAGES

Baldsiefen, Tim; Cangi, Attila; Eich, F. G.; ...

2017-12-18

Here, we derive an intrinsically temperature-dependent approximation to the correlation grand potential for many-electron systems in thermodynamical equilibrium in the context of finite-temperature reduced-density-matrix-functional theory (FT-RDMFT). We demonstrate its accuracy by calculating the magnetic phase diagram of the homogeneous electron gas. We compare it to known limits from highly accurate quantum Monte Carlo calculations as well as to phase diagrams obtained within existing exchange-correlation approximations from density functional theory and zero-temperature RDMFT.

Degenerate limit thermodynamics beyond leading order for models of dense matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Constantinou, Constantinos, E-mail: c.constantinou@fz-juelich.de; Muccioli, Brian, E-mail: bm956810@ohio.edu; Prakash, Madappa, E-mail: prakash@ohio.edu

2015-12-15

Analytical formulas for next-to-leading order temperature corrections to the thermal state variables of interacting nucleons in bulk matter are derived in the degenerate limit. The formalism developed is applicable to a wide class of non-relativistic and relativistic models of hot and dense matter currently used in nuclear physics and astrophysics (supernovae, proto-neutron stars and neutron star mergers) as well as in condensed matter physics. We consider the general case of arbitrary dimensionality of momentum space and an arbitrary degree of relativity (for relativistic models). For non-relativistic zero-range interactions, knowledge of the Landau effective mass suffices to compute next-to-leading order effects,more » but for finite-range interactions, momentum derivatives of the Landau effective mass function up to second order are required. Results from our analytical formulas are compared with the exact results for zero- and finite-range potential and relativistic mean-field theoretical models. In all cases, inclusion of next-to-leading order temperature effects substantially extends the ranges of partial degeneracy for which the analytical treatment remains valid. Effects of many-body correlations that deserve further investigation are highlighted.« less

Development of a Aerothermoelastic-Acoustics Simulation Capability of Flight Vehicles

NASA Technical Reports Server (NTRS)

Gupta, K. K.; Choi, S. B.; Ibrahim, A.

2010-01-01

A novel numerical, finite element based analysis methodology is presented in this paper suitable for accurate and efficient simulation of practical, complex flight vehicles. An associated computer code, developed in this connection, is also described in some detail. Thermal effects of high speed flow obtained from a heat conduction analysis are incorporated in the modal analysis which in turn affects the unsteady flow arising out of interaction of elastic structures with the air. Numerical examples pertaining to representative problems are given in much detail testifying to the efficacy of the advocated techniques. This is a unique implementation of temperature effects in a finite element CFD based multidisciplinary simulation analysis capability involving large scale computations.

Correlated Debye model for atomic motions in metal nanocrystals

NASA Astrophysics Data System (ADS)

Scardi, P.; Flor, A.

2018-05-01

The Correlated Debye model for the mean square relative displacement of atoms in near-neighbour coordination shells has been extended to include the effect of finite crystal size. This correctly explains the increase in Debye-Waller coefficient observed for metal nanocrystals. A good match with Molecular Dynamics simulations of Pd nanocrystals is obtained if, in addition to the phonon confinement effect of the finite domain size, proper consideration is also given to the static disorder component caused by the undercoordination of surface atoms. The new model, which addresses the analysis of the Pair Distribution Function and powder diffraction data collected at different temperatures, was preliminarily tested on recently published experimental data on nanocrystalline Pt powders.

Analytical YORP torques model with an improved temperature distribution function

NASA Astrophysics Data System (ADS)

Breiter, S.; Vokrouhlický, D.; Nesvorný, D.

2010-01-01

Previous models of the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect relied either on the zero thermal conductivity assumption, or on the solutions of the heat conduction equations assuming an infinite body size. We present the first YORP solution accounting for a finite size and non-radial direction of the surface normal vectors in the temperature distribution. The new thermal model implies the dependence of the YORP effect in rotation rate on asteroids conductivity. It is shown that the effect on small objects does not scale as the inverse square of diameter, but rather as the first power of the inverse.

Statistical properties and condensate fluctuation of attractive Bose gas with finite number of particles

NASA Astrophysics Data System (ADS)

Bera, Sangita; Lekala, Mantile Leslie; Chakrabarti, Barnali; Bhattacharyya, Satadal; Rampho, Gaotsiwe Joel

2017-09-01

'We study the condensate fluctuation and several statistics of weakly interacting attractive Bose gas of 7 Li atoms in harmonic trap. Using exact recursion relation we calculate canonical ensemble partition function and study the thermal evolution of the condensate. As 7 Li condensate is associated with collapse, the number of condensate atom is truly finite and it facilitates to study the condensate in mesoscopic region. Being highly correlated, we utilize the two-body correlated basis function to get the many-body effective potential which is further used to calculate the energy levels. Taking van der Waals interaction as interatomic interaction we calculate several quantities like condensate fraction N, root-mean-square fluctuation δn0 and different orders of central moments. We observe the effect of finite size on the calculation of condensate fluctuations and the effect of attractive interaction over the noninteracting limit. We observe the depletion of the condensate with increase in temperature. The calculated moments nicely exhibit the mesoscopic effect. The sharp fall in the root-mean-square fluctuation near the critical point signifies the possibility of phase transition.

Lepton effects on the protoneutron stars with the hadron-quark mixed phase in the Nambu-Jona-Lasinio model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yasutake, Nobutoshi; Kashiwa, Kouji

2009-02-15

We study the structures of hybrid stars with leptons at finite temperature under beta equilibrium. For the quark phase, we use the three flavor Nambu-Jona-Lasinio (NJL) model. For the hadron phase, we adopt the nuclear equation of state (EOS) by Shen et al.. This EOS is in the framework of the relativistic mean field theory including the tree body effects. For the hadron-quark phase transition, we impose the bulk Gibbs construction or the Maxwell construction to take into account uncertainties by finite-size effects. We find that the pure quark phase does not appear in stable star cores in all cases.more » With the phase transition, the maximum masses increase {approx}10% for high lepton fraction. On the contrary, without the transition, they decrease {approx}10%. We also find that, in the NJL model, the lepton fraction is more important for structures of unstable stars than the temperature. This result is important for many astrophysical phenomena such as the core collapse of massive stars.« less

Designing Two-Dimensional Dirac Heterointerfaces of Few-Layer Graphene and Tetradymite-Type Sb2Te3 for Thermoelectric Applications.

PubMed

Jang, Woosun; Lee, Jiwoo; In, Chihun; Choi, Hyunyong; Soon, Aloysius

2017-12-06

Despite the ubiquitous nature of the Peltier effect in low-dimensional thermoelectric devices, the influence of finite temperature on the electronic structure and transport in the Dirac heterointerfaces of the few-layer graphene and layered tetradymite, Sb 2 Te 3 (which coincidently have excellent thermoelectric properties) are not well understood. In this work, using the first-principles density-functional theory calculations, we investigate the detailed atomic and electronic structure of these Dirac heterointerfaces of graphene and Sb 2 Te 3 and further re-examine the effect of finite temperature on the electronic band structures using a phenomenological temperature-broadening model based on Fermi-Dirac statistics. We then proceed to understand the underlying charge redistribution process in this Dirac heterointerfaces and through solving the Boltzmann transport equation, we present the theoretical evidence of electron-hole asymmetry in its electrical conductivity as a consequence of this charge redistribution mechanism. We finally propose that the hexagonal-stacked Dirac heterointerfaces are useful as efficient p-n junction building blocks in the next-generation thermoelectric devices where the electron-hole asymmetry promotes the thermoelectric transport by "hot" excited charge carriers.

Finite Element Analysis of Interaction of Laser Beam with Material in Laser Metal Powder Bed Fusion Process.

PubMed

Fu, Guang; Zhang, David Z; He, Allen N; Mao, Zhongfa; Zhang, Kaifei

2018-05-10

A deep understanding of the laser-material interaction mechanism, characterized by laser absorption, is very important in simulating the laser metal powder bed fusion (PBF) process. This is because the laser absorption of material affects the temperature distribution, which influences the thermal stress development and the final quality of parts. In this paper, a three-dimensional finite element analysis model of heat transfer taking into account the effect of material state and phase changes on laser absorption is presented to gain insight into the absorption mechanism, and the evolution of instantaneous absorptance in the laser metal PBF process. The results showed that the instantaneous absorptance was significantly affected by the time of laser radiation, as well as process parameters, such as hatch space, scanning velocity, and laser power, which were consistent with the experiment-based findings. The applicability of this model to temperature simulation was demonstrated by a comparative study, wherein the peak temperature in fusion process was simulated in two scenarios, with and without considering the effect of material state and phase changes on laser absorption, and the simulated results in the two scenarios were then compared with experimental data respectively.

Thermo-mechanical analysis of an internal cooling system with various configurations of a combustion liner after shell

NASA Astrophysics Data System (ADS)

Moon, Hokyu; Kim, Kyung Min; Park, Jun Su; Kim, Beom Seok; Cho, Hyung Hee

2015-12-01

The after-shell section, which is part of the gas turbine combustion liner, is exposed to the hottest combustion gas. Various cooling schemes have been applied to protect against severe thermal load. However, there is a significant discrepancy in the thermal expansion with large temperature differences, resulting in thermo-mechanical crack formation. In this study, to reduce combustion liner damage, thermo-mechanical analysis was conducted on three after-shell section configurations: inline-discrete divider wall, staggered divider wall, and swirler wall arrays. These array components are well-known heat-transfer enhancement structures in the duct. In the numerical analyses, the heat transfer characteristics, temperature and thermo-mechanical stress distribution were evaluated using finite volume method and finite element method commercial codes. As a result, we demonstrated that the temperature and the thermo-mechanical stress distribution were readily dependent on the structural array for cooling effectiveness and structural support in each modified cooling system. Compared with the reference model, the swirler wall array was most effective in diminishing the thermo-mechanical stress concentration, especially on the inner ring that is vulnerable to crack formation.

Quantum dynamics at finite temperature: Time-dependent quantum Monte Carlo study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Christov, Ivan P., E-mail: ivan.christov@phys.uni-sofia.bg

2016-08-15

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 realmore » time propagation can be a challenge.« less

Three-dimensional vector modeling and restoration of flat finite wave tank radiometric measurements

NASA Technical Reports Server (NTRS)

Truman, W. M.; Balanis, C. A.; Holmes, J. J.

1977-01-01

In this paper, a three-dimensional Fourier transform inversion method describing the interaction between water surface emitted radiation from a flat finite wave tank and antenna radiation characteristics is reported. The transform technique represents the scanning of the antenna mathematically as a correlation. Computation time is reduced by using the efficient and economical fast Fourier transform algorithm. To verify the inversion method, computations have been made and compared with known data and other available results. The technique has been used to restore data of the finite wave tank system and other available antenna temperature measurements made at the Cape Cod Canal. The restored brightness temperatures serve as better representations of the emitted radiation than the measured antenna temperatures.

Quantum field theory on toroidal topology: Algebraic structure and applications

NASA Astrophysics Data System (ADS)

Khanna, F. C.; Malbouisson, A. P. C.; Malbouisson, J. M. C.; Santana, A. E.

2014-05-01

The development of quantum theory on a torus has a long history, and can be traced back to the 1920s, with the attempts by Nordström, Kaluza and Klein to define a fourth spatial dimension with a finite size, being curved in the form of a torus, such that Einstein and Maxwell equations would be unified. Many developments were carried out considering cosmological problems in association with particle physics, leading to methods that are useful for areas of physics, in which size effects play an important role. This interest in finite size effect systems has been increasing rapidly over the last decades, due principally to experimental improvements. In this review, the foundations of compactified quantum field theory on a torus are presented in a unified way, in order to consider applications in particle and condensed matter physics. The theory on a torus ΓDd=(S1)d×RD-d is developed from a Lie-group representation and c*c*-algebra formalisms. As a first application, the quantum field theory at finite temperature, in its real- and imaginary-time versions, is addressed by focusing on its topological structure, the torus Γ41. The toroidal quantum-field theory provides the basis for a consistent approach of spontaneous symmetry breaking driven by both temperature and spatial boundaries. Then the superconductivity in films, wires and grains are analyzed, leading to some results that are comparable with experiments. The Casimir effect is studied taking the electromagnetic and Dirac fields on a torus. In this case, the method of analysis is based on a generalized Bogoliubov transformation, that separates the Green function into two parts: one is associated with the empty space-time, while the other describes the impact of compactification. This provides a natural procedure for calculating the renormalized energy-momentum tensor. Self interacting four-fermion systems, described by the Gross-Neveu and Nambu-Jona-Lasinio models, are considered. Then finite size effects on the hadronic phase structure are investigated, taking into account density and temperature. As a final application, effects of extra spatial dimensions are addressed, by developing a quantum electrodynamics in a five-dimensional space-time, where the fifth-dimension is compactified on a torus. The formalism, initially developed for particle physics, provides results compatible with other trials of probing the existence of extra-dimensions.

Highlighting non-uniform temperatures close to liquid/solid surfaces

NASA Astrophysics Data System (ADS)

Noirez, L.; Baroni, P.; Bardeau, J. F.

2017-05-01

The present experimental measurements reveal that similar to external fields such as electric, magnetic, or flow fields, the vicinity of a solid surface can preclude the liquid molecules from relaxing to equilibrium, generating located non-uniform temperatures. The non-uniform temperature zone extends up to several millimeters within the liquid with a lower temperature near the solid wall (reaching ΔT = -0.15 °C ± 0.02 °C in the case of liquid water) counterbalanced at larger distances by a temperature rise. These effects highlighted by two independent methods (thermistor measurement and infra-red emissivity) are particularly pronounced for highly wetting surfaces. The scale over which non-uniform temperatures are extended indicates that the effect is assisted by intermolecular interactions, in agreement with recent developments showing that liquids possess finite shear elasticity and theoretical approaches integrating long range correlations.

Experimental investigations and finite element simulation of cutting heat in vibrational and conventional drilling of cortical bone.

PubMed

Wang, Yu; Cao, Meng; Zhao, Xiangrui; Zhu, Gang; McClean, Colin; Zhao, Yuanyuan; Fan, Yubo

2014-11-01

Heat generated during bone drilling could cause irreversible thermal damage, which can lead to bone necrosis or even osteomyelitis. In this study, vibrational drilling was applied to fresh bovine bones to investigate the cutting heat in comparison with conventional drilling through experimental investigation and finite element analysis (FEA). The influence of vibrational frequency and amplitude on cutting heat generation and conduction were studied. The experimental results showed that, compared with the conventional drilling, vibrational drilling could significantly reduce the cutting temperature in drilling of cortical bone (P<0.05): the cutting temperature tended to decrease with increasing vibrational frequency and amplitude. The FEA results also showed that the vibrational amplitude holds a significant effect on the cutting heat conduction. Copyright © 2014 IPEM. Published by Elsevier Ltd. All rights reserved.

Scaling laws and bulk-boundary decoupling in heat flow.

PubMed

del Pozo, Jesús J; Garrido, Pedro L; Hurtado, Pablo I

2015-03-01

When driven out of equilibrium by a temperature gradient, fluids respond by developing a nontrivial, inhomogeneous structure according to the governing macroscopic laws. Here we show that such structure obeys strikingly simple scaling laws arbitrarily far from equilibrium, provided that both macroscopic local equilibrium and Fourier's law hold. Extensive simulations of hard disk fluids confirm the scaling laws even under strong temperature gradients, implying that Fourier's law remains valid in this highly nonlinear regime, with putative corrections absorbed into a nonlinear conductivity functional. In addition, our results show that the scaling laws are robust in the presence of strong finite-size effects, hinting at a subtle bulk-boundary decoupling mechanism which enforces the macroscopic laws on the bulk of the finite-sized fluid. This allows one to measure the marginal anomaly of the heat conductivity predicted for hard disks.

Temperature nonuniformity occurring during the cooling process of a KDP crystal and its effects on second-harmonic generation.

PubMed

Liang, Yingchun; Su, Ruifeng; Lu, Lihua; Liu, Haitao

2014-08-10

The temperature nonuniformity occurring during the cooling process of a KDP crystal is studied, along with its effects on the second-harmonic generation (SHG) of a high-average-power laser. A comprehensive model is proposed incorporating principles of thermodynamics, mechanics, and optics, and it is applied to investigate the temperature nonuniformity and its effects. The temperature rise caused by linear absorption is calculated, while the temperature nonuniformity occurring during the cooling process is analyzed using the finite-element method (FEM). The stress induced by the nonuniformity is then studied using the FEM, and the trend of its change is determined. Moreover, the changes in refractive index caused by the stress are calculated, the results of which are used to determine the variations in the induced phase mismatch. The SHG efficiency considering the phase mismatch is eventually obtained by solving the coupling wave equations. The results demonstrate that the temperature nonuniformity has negative effects on the SHG efficiency.

Phonon Confinement Effect in TiO2 Nanoparticles as Thermosensor Materials

DTIC Science & Technology

2018-01-24

TiO2 or ZnO nanoparticles (NPs) have a very strong finite-size dependency in their Raman spectra or photoluminescence (PL) spectra due to the phonon...spectrometers were used to establish the particle size versus the Raman/PL peak position master curves. Systematic isothermal and temperature- dependent heat...Thermosensor Materials", Workshop on Time- Dependent Temperature Measurements in Energy Release Processes, Chicago, IL, 2012. 11 3) Ashish Kumar Mishra

Pressure Effects on the Temperature Sensitivity of Fiber Bragg Gratings

NASA Technical Reports Server (NTRS)

Wu, Meng-Chou

2012-01-01

A 3-dimensional physical model was developed to relate the wavelength shifts resulting from temperature changes of fiber Bragg gratings (FBGs) to the thermal expansion coefficients, Young s moduli of optical fibers, and thicknesses of coating polymers. Using this model the Bragg wavelength shifts were calculated and compared with the measured wavelength shifts of FBGs with various coating thickness for a finite temperature range. There was a discrepancy between the calculated and measured wavelength shifts. This was attributed to the refractive index change of the fiber core by the thermally induced radial pressure. To further investigate the pressure effects, a small diametric load was applied to a FBG and Bragg wavelength shifts were measured over a temperature range of 4.2 to 300K.

Finite element thermal analysis of multispectral coatings for the ABL

NASA Astrophysics Data System (ADS)

Shah, Rashmi S.; Bettis, Jerry R.; Stewart, Alan F.; Bonsall, Lynn; Copland, James; Hughes, William; Echeverry, Juan C.

1999-04-01

The thermal response of a coated optical surface is an important consideration in the design of any high average power system. Finite element temperature distribution were calculated for both coating witness samples and calorimetry wafers and were compared to actual measured data under tightly controlled conditions. Coatings for ABL were deposited on various substrates including fused silica, ULE, Zerodur, and silicon. The witness samples were irradiate data high power levels at 1.315micrometers to evaluate laser damage thresholds and study absorption levels. Excellent agreement was obtained between temperature predictions and measured thermal response curves. When measured absorption values were not available, the code was used to predict coating absorption based on the measured temperature rise on the back surface. Using the finite element model, the damaging temperature rise can be predicted for a coating with known absorption based on run time, flux, and substrate material.

Dynamical transition for a particle in a squared Gaussian potential

NASA Astrophysics Data System (ADS)

Touya, C.; Dean, D. S.

2007-02-01

We study the problem of a Brownian particle diffusing in finite dimensions in a potential given by ψ = phi2/2 where phi is Gaussian random field. Exact results for the diffusion constant in the high temperature phase are given in one and two dimensions and it is shown to vanish in a power-law fashion at the dynamical transition temperature. Our results are confronted with numerical simulations where the Gaussian field is constructed, in a standard way, as a sum over random Fourier modes. We show that when the number of Fourier modes is finite the low temperature diffusion constant becomes non-zero and has an Arrhenius form. Thus we have a simple model with a fully understood finite size scaling theory for the dynamical transition. In addition we analyse the nature of the anomalous diffusion in the low temperature regime and show that the anomalous exponent agrees with that predicted by a trap model.

Effect of quantum dispersion on the radial distribution function of a one-component sticky-hard-sphere fluid

NASA Astrophysics Data System (ADS)

Fantoni, Riccardo

2018-04-01

In this short communication we present a possible scheme to study the radial distribution function of the quantum slightly polydisperse Baxter sticky hard sphere liquid at finite temperature thorugh a semi-analytical method devised by Chandler and Wolynes.

Finite element calculations of the time dependent thermal fluxes in the laser-heated diamond anvil cell

NASA Astrophysics Data System (ADS)

Montoya, Javier A.; Goncharov, Alexander F.

2012-06-01

The time-dependent temperature distribution in the laser-heated diamond anvil cell (DAC) is examined using finite element simulations. Calculations are carried out for the practically important case of a surface-absorbing metallic plate (coupler) surrounded by a thermally insulating transparent medium. The time scales of the heat transfer in the DAC cavity are found to be typically on the order of tens of microseconds depending on the geometrical and thermochemical parameters of the constituent materials. The use of much shorter laser pulses (e.g., on the order of tens of nanoseconds) creates sharp radial temperature gradients, which result in a very intense and abrupt axial conductive heat transfer that exceeds the radiative heat transfer by several orders of magnitude in the practically usable temperature range (<12 000 K). In contrast, the use of laser pulses with several μs duration provides sufficiently uniform spatial heating conditions suitable for studying the bulk sample. The effect of the latent heat of melting on the temperature distribution has been examined in the case of iron and hydrogen for both pulsed and continuous laser heating. The observed anomalies in temperature-laser power dependencies cannot be due to latent heat effects only. Finally, we examine the applicability of a modification to the plate geometry Ångström method for measurements of the thermal diffusivity in the DAC. The calculations show substantial effects of the thermochemical parameters of the insulating medium on the amplitude change and phase shift between the surface temperature variations of the front and back of the sample, which makes this method dependent on the precise knowledge of the properties of the medium.

Transition in coupled replicas may not imply a finite-temperature ideal glass transition in glass-forming systems.

PubMed

Garrahan, Juan P

2014-03-01

A key open question in the glass transition field is whether a finite temperature thermodynamic transition to the glass state exists or not. Recent simulations of coupled replicas in atomistic models have found signatures of a static transition as a function of replica coupling. This can be viewed as evidence of an associated thermodynamic glass transition in the uncoupled system. We demonstrate here that a different interpretation is possible. We consider the triangular plaquette model, an interacting spin system which displays (East model-like) glassy dynamics in the absence of any static transition. We show that when two replicas are coupled, there is a curve of equilibrium phase transitions, between phases of small and large overlap, in the temperature-coupling plane (located on the self-dual line of an exact temperature-coupling duality of the system) which ends at a critical point. Crucially, in the limit of vanishing coupling the finite temperature transition disappears, and the uncoupled system is in the disordered phase at all temperatures. We discuss an interpretation of atomistic simulations in light of this result.

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.

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Analysis and finite element simulation of electromagnetic heating in the nitride MOCVD reactor

NASA Astrophysics Data System (ADS)

Li, Zhi-Ming; Hao, Yue; Zhang, Jin-Cheng; Xu, Sheng-Rui; Ni, Jin-Yu; Zhou, Xiao-Wei

2009-11-01

Electromagnetic field distribution in the vertical metal organic chemical vapour deposition (MOCVD) reactor is simulated by using the finite element method (FEM). The effects of alternating current frequency, intensity, coil turn number and the distance between the coil turns on the distribution of the Joule heat are analysed separately, and their relations to the value of Joule heat are also investigated. The temperature distribution on the susceptor is also obtained. It is observed that the results of the simulation are in good agreement with previous measurements.

Thermal finite-element analysis of space shuttle main engine turbine blade

NASA Technical Reports Server (NTRS)

Abdul-Aziz, Ali; Tong, Michael T.; Kaufman, Albert

1987-01-01

Finite-element, transient heat transfer analyses were performed for the first-stage blades of the space shuttle main engine (SSME) high-pressure fuel turbopump. The analyses were based on test engine data provided by Rocketdyne. Heat transfer coefficients were predicted by performing a boundary-layer analysis at steady-state conditions with the STAN5 boundary-layer code. Two different peak-temperature overshoots were evaluated for the startup transient. Cutoff transient conditions were also analyzed. A reduced gas temperature profile based on actual thermocouple data was also considered. Transient heat transfer analyses were conducted with the MARC finite-element computer code.

Solidification of a binary mixture

NASA Technical Reports Server (NTRS)

Antar, B. N.

1982-01-01

The time dependent concentration and temperature profiles of a finite layer of a binary mixture are investigated during solidification. The coupled time dependent Stefan problem is solved numerically using an implicit finite differencing algorithm with the method of lines. Specifically, the temporal operator is approximated via an implicit finite difference operator resulting in a coupled set of ordinary differential equations for the spatial distribution of the temperature and concentration for each time. Since the resulting differential equations set form a boundary value problem with matching conditions at an unknown spatial point, the method of invariant imbedding is used for its solution.

Evaporating Spray in Supersonic Streams Including Turbulence Effects

NASA Technical Reports Server (NTRS)

Balasubramanyam, M. S.; Chen, C. P.

2006-01-01

Evaporating spray plays an important role in spray combustion processes. This paper describes the development of a new finite-conductivity evaporation model, based on the two-temperature film theory, for two-phase numerical simulation using Eulerian-Lagrangian method. The model is a natural extension of the T-blob/T-TAB atomization/spray model which supplies the turbulence characteristics for estimating effective thermal diffusivity within the droplet phase. Both one-way and two-way coupled calculations were performed to investigate the performance of this model. Validation results indicate the superiority of the finite-conductivity model in low speed parallel flow evaporating sprays. High speed cross flow spray results indicate the effectiveness of the T-blob/T-TAB model and point to the needed improvements in high speed evaporating spray modeling.

Three-dimensional Simulation and Prediction of Solenoid Valve Failure Mechanism Based on Finite Element Model

NASA Astrophysics Data System (ADS)

Li, Jianfeng; Xiao, Mingqing; Liang, Yajun; Tang, Xilang; Li, Chao

2018-01-01

The solenoid valve is a kind of basic automation component applied widely. It’s significant to analyze and predict its degradation failure mechanism to improve the reliability of solenoid valve and do research on prolonging life. In this paper, a three-dimensional finite element analysis model of solenoid valve is established based on ANSYS Workbench software. A sequential coupling method used to calculate temperature filed and mechanical stress field of solenoid valve is put forward. The simulation result shows the sequential coupling method can calculate and analyze temperature and stress distribution of solenoid valve accurately, which has been verified through the accelerated life test. Kalman filtering algorithm is introduced to the data processing, which can effectively reduce measuring deviation and restore more accurate data information. Based on different driving current, a kind of failure mechanism which can easily cause the degradation of coils is obtained and an optimization design scheme of electro-insulating rubbers is also proposed. The high temperature generated by driving current and the thermal stress resulting from thermal expansion can easily cause the degradation of coil wires, which will decline the electrical resistance of coils and result in the eventual failure of solenoid valve. The method of finite element analysis can be applied to fault diagnosis and prognostic of various solenoid valves and improve the reliability of solenoid valve’s health management.

Homogeneous hydride formation path in α-Zr: Molecular dynamics simulations with the charge-optimized many-body potential

DOE PAGES

Zhang, Yongfeng; Bai, Xian-Ming; Yu, Jianguo; ...

2016-06-01

A formation path for homogeneous γ hydride formation in hcp α-Zr, from solid solution to the ζ and then the γ hydride, was demonstrated using molecular static calculations and molecular dynamic simulations with the charge-optimized many-body (COMB) potential. Hydrogen has limited solubility in α-Zr. Once the solubility limit is exceeded, the stability of solid solution gives way to that of coherent hydride phases such as the ζ hydride by planar precipitation of hydrogen. At finite temperatures, the ζ hydride goes through a partial hcp-fcc transformation via 1/3 <1¯100> slip on the basal plane, and transforms into a mixture of γmore » hydride and α-Zr. In the ζ hydride, slip on the basal plane is favored thermodynamically with negligible barrier, and is therefore feasible at finite temperatures without mechanical loading. The transformation process involves slips of three equivalent shear partials, in contrast to that proposed in the literature where only a single shear partial was involved. The adoption of multiple slip partials minimizes the macroscopic shape change of embedded hydride clusters and the shear strain accumulation in the matrix, and thus reduces the overall barrier needed for homogeneous γ hydride formation. In conclusion, this formation path requires finite temperatures for hydrogen diffusion without mechanical loading. Therefore, it should be effective at the cladding operating conditions.« less

Effect of influx on the free surface transport within a hollow ampule

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, S.C.; Vafai, K.

1994-07-01

A numerical investigation of free surface transport within a hollow glass ampule with feed-in boundary conditions is presented. The glass ampule is treated as a vertical film with a finite pressure difference across the film, with applied influx on the upper boundary, and with applied heat flux at the outer free surface. Two different sizes of glass ampules, along with different influx values are investigated. A finite element method with full consideration of surface tension and viscosity effects is used to solve the transient Navier-Stokes equations in cylindrical coordinates. Radiative and convective boundary conditions are incorporated when solving the energymore » equation. The movement of the inner and outer free surfaces with the specified feed-in velocity for different dimensions and temporal temperature distribution are analyzed. It is found that the feed-in mechanism rather than the pressure difference provides the more dominant driving forces. Also studied is the effect of using different feed-in velocities on the flow and temperature fields. The results presented in this work illustrate the basic effects of the feed-in mechanism of the free surface transport phenomenon.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gim, Yongwan; Kim, Wontae, E-mail: yongwan89@sogang.ac.kr, E-mail: wtkim@sogang.ac.kr

In warm inflation scenarios, radiation always exists, so that the radiation energy density is also assumed to be finite when inflation starts. To find out the origin of the non-vanishing initial radiation energy density, we revisit thermodynamic analysis for a warm inflation model and then derive an effective Stefan-Boltzmann law which is commensurate with the temperature-dependent effective potential by taking into account the non-vanishing trace of the total energy-momentum tensors. The effective Stefan-Boltzmann law shows that the zero energy density for radiation at the Grand Unification epoch increases until the inflation starts and it becomes eventually finite at the initialmore » stage of warm inflation. By using the above effective Stefan-Boltzmann law, we also study the cosmological scalar perturbation, and obtain the sufficient radiation energy density in order for GUT baryogenesis at the end of inflation.« less

Finite-size effects on the dynamic susceptibility of CoPhOMe single-chain molecular magnets in presence of a static magnetic field

NASA Astrophysics Data System (ADS)

Pini, M. G.; Rettori, A.; Bogani, L.; Lascialfari, A.; Mariani, M.; Caneschi, A.; Sessoli, R.

2011-09-01

The static and dynamic properties of the single-chain molecular magnet Co(hfac)2NITPhOMe (CoPhOMe) (hfac = hexafluoroacetylacetonate, NITPhOMe = 4'-methoxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) are investigated in the framework of the Ising model with Glauber dynamics, in order to take into account both the effect of an applied magnetic field and a finite size of the chains. For static fields of moderate intensity and short chain lengths, the approximation of a monoexponential decay of the magnetization fluctuations is found to be valid at low temperatures; for strong fields and long chains, a multiexponential decay should rather be assumed. The effect of an oscillating magnetic field, with intensity much smaller than that of the static one, is included in the theory in order to obtain the dynamic susceptibility χ(ω). We find that, for an open chain with N spins, χ(ω) can be written as a weighted sum of N frequency contributions, with a sum rule relating the frequency weights to the static susceptibility of the chain. Very good agreement is found between the theoretical dynamic susceptibility and the ac susceptibility measured in moderate static fields (Hdc≤2 kOe), where the approximation of a single dominating frequency for each segment length turns out to be valid. For static fields in this range, data for the relaxation time, τ versus Hdc, of the magnetization of CoPhOMe at low temperature are also qualitatively reproduced by theory, provided that finite-size effects are included.

3DHYDROGEOCHEM: A 3-DIMENSIONAL MODEL OF DENSITY-DEPENDENT SUBSURFACE FLOW AND THERMAL MULTISPECIES-MULTICOMPONENT HYDROGEOCHEMICAL TRANSPORT

EPA Science Inventory

This report presents a three-dimensional finite-element numerical model designed to simulate chemical transport in subsurface systems with temperature effect taken into account. The three-dimensional model is developed to provide (1) a tool of application, with which one is able...

Finite Element Models, Validation, and Results for Wheel Temperature and Elastic Thermal Stress Distributions

DOT National Transportation Integrated Search

1993-09-01

The report is the third of a series on the results of an engineering study of the effects of service loads on railroad vehicle wheels. The study was initiated in September 1991, in response to a request for assessment of contributing factors and corr...

Dynamical mean field theory equations on nearly real frequency axis

NASA Astrophysics Data System (ADS)

Fathi, M. B.; Jafari, S. A.

2010-03-01

The iterated perturbation theory (IPT) equations of the dynamical mean field theory (DMFT) for the half-filled Hubbard model are solved on nearly real frequencies at various values of the Hubbard parameters, U, to investigate the nature of metal-insulator transition (MIT) at finite temperatures. This method avoids the instabilities associated with the infamous Padé analytic continuation and reveals fine structures across the MIT at finite temperatures, which cannot be captured by conventional methods for solving DMFT-IPT equations on Matsubara frequencies. Our method suggests that at finite temperatures, there is a crossover from a bad metal to a bad insulator in which the height of the quasi-particle (Kondo) peak decreases to a non-zero small bump, which gradually suppresses as one moves deeper into the bad insulating regime.

Orbital selective directional conductor in the two-orbital Hubbard model

DOE PAGES

Mukherjee, Anamitra; Patel, Niravkumar D.; Moreo, Adriana; ...

2016-02-29

Recently, we employed a developed many-body technique that allows for the incorporation of thermal effects, the rich phase diagram of a two-dimensional two-orbital (degenerate d xz and d yz) Hubbard model is presented varying temperature and the repulsion U. The main result is the finding at intermediate U of an antiferromagnetic orbital selective state where an effective dimensional reduction renders one direction insulating and the other metallic. Possible realizations of this state are discussed. Additionally, we also study nematicity above the N eel temperature. After a careful finite-size scaling analysis, the nematicity temperature window appears to survive in the bulkmore » limit, although it is very narrow.« less

Electronic correlation effects and the Coulomb gap at finite temperature.

PubMed

Sandow, B; Gloos, K; Rentzsch, R; Ionov, A N; Schirmacher, W

2001-02-26

We have investigated the effect of the long-range Coulomb interaction on the one-particle excitation spectrum of n-type germanium, using tunneling spectroscopy on mechanically controllable break junctions. At low temperatures, the tunnel conductance shows a minimum at zero bias voltage due to the Coulomb gap. Above 1 K, the gap is filled by thermal excitations. This behavior is reflected in the variable-range hopping resistivity measured on the same samples: up to a few degrees Kelvin the Efros-Shklovskii lnR infinity T(-1/2) law is obeyed, whereas at higher temperatures deviations from this law occur. The type of crossover differs from that considered previously in the literature.

Hall viscosity of a chiral two-orbital superconductor at finite temperatures

NASA Astrophysics Data System (ADS)

Yazdani-Hamid, Meghdad; Shahzamanian, Mohammad Ali

2018-06-01

The Hall viscosity known as the anti-symmetric part of the viscosity fourth-rank tensor. Such dissipationless response which appears for systems with broken time reversal symmetry. We calculate this non-dissipative quantity for a chiral two-orbital superconductor placed in a viscoelastic magnetic field using the linear response theory and apply our calculations to the putative multiband chiral superconductor Sr2RuO4. The chirality origin of a multiband superconductor arises from the interorbital coupling of the superconducting state. This feature leads to the robustness of the Hall viscosity against temperature and impurity effects. We study the temperature effect on the Hall viscosity at the one-loop approximation.

Finite-Length Diocotron Modes in a Non-neutral Plasma Column

NASA Astrophysics Data System (ADS)

Walsh, Daniel; Dubin, Daniel

2017-10-01

Diocotron modes are 2D distortions of a non-neutral plasma column that propagate azimuthally via E × B drifts. While the infinite-length theory of diocotron modes is well-understood for arbitrary azimuthal mode number l, the finite-length mode frequency is less developed (with some exceptions), and is naturally of relevance to experiments. In this poster, we present an approach to address finite length effects, such as temperature dependence of the mode frequency. We use a bounce-averaged solution to the Vlasov Equation, in which the Vlasov Equation is solved using action-angle variables of the unperturbed Hamiltonian. We write the distribution function as a Fourier series in the bounce-angle variable ψ, keeping only the bounce-averaged term. We demonstrate a numerical solution to this equation for a realistic plasma with a finite Debye Length, compare to the existing l = 1 theory, and discuss possible extensions of the existing theory to l ≠ 1 . Supported by NSF/DOE Partnership Grants PHY1414570 and DESC0002451.

Effects of Process Parameters on Copper Powder Compaction Process Using Multi-Particle Finite Element Method

NASA Astrophysics Data System (ADS)

Güner, F.; Sofuoğlu, H.

2018-01-01

Powder metallurgy (PM) has been widely used in several industries; especially automotive and aerospace industries and powder metallurgy products grow up every year. The mechanical properties of the final product that is obtained by cold compaction and sintering in powder metallurgy are closely related to the final relative density of the process. The distribution of the relative density in the die is affected by parameters such as compaction velocity, friction coefficient and temperature. Moreover, most of the numerical studies utilizing finite element approaches treat the examined environment as a continuous media with uniformly homogeneous porosity whereas Multi-Particle Finite Element Method (MPFEM) treats every particles as an individual body. In MPFEM, each of the particles can be defined as an elastic- plastic deformable body, so the interactions of the particles with each other and the die wall can be investigated. In this study, each particle was modelled and analyzed as individual deformable body with 3D tetrahedral elements by using MPFEM approach. This study, therefore, was performed to investigate the effects of different temperatures and compaction velocities on stress distribution and deformations of copper powders of 200 µm-diameter in compaction process. Furthermore, 3-D MPFEM model utilized von Mises material model and constant coefficient of friction of μ=0.05. In addition to MPFEM approach, continuum modelling approach was also performed for comparison purposes.

Finite-size effects in simulations of electrolyte solutions under periodic boundary conditions

NASA Astrophysics Data System (ADS)

Thompson, Jeffrey; Sanchez, Isaac

The equilibrium properties of charged systems with periodic boundary conditions may exhibit pronounced system-size dependence due to the long range of the Coulomb force. As shown by others, the leading-order finite-size correction to the Coulomb energy of a charged fluid confined to a periodic box of volume V may be derived from sum rules satisfied by the charge-charge correlations in the thermodynamic limit V -> ∞ . In classical systems, the relevant sum rule is the Stillinger-Lovett second-moment (or perfect screening) condition. This constraint implies that for large V, periodicity induces a negative bias of -kB T(2 V) - 1 in the total Coulomb energy density of a homogeneous classical charged fluid of given density and temperature. We present a careful study of the impact of such finite-size effects on the calculation of solute chemical potentials from explicit-solvent molecular simulations of aqueous electrolyte solutions. National Science Foundation Graduate Research Fellowship Program, Grant No. DGE-1610403.

An approach to parameter estimation for breast tumor by finite element method

NASA Astrophysics Data System (ADS)

Xu, A.-qing; Yang, Hong-qin; Ye, Zhen; Su, Yi-ming; Xie, Shu-sen

2009-02-01

The temperature of human body on the surface of the skin depends on the metabolic activity, the blood flow, and the temperature of the surroundings. Any abnormality in the tissue, such as the presence of a tumor, alters the normal temperature on the skin surface due to increased metabolic activity of the tumor. Therefore, abnormal skin temperature profiles are an indication of diseases such as tumor or cancer. This study is to present an approach to detect the female breast tumor and its related parameter estimations by combination the finite element method with infrared thermography for the surface temperature profile. A 2D simplified breast embedded a tumor model based on the female breast anatomical structure and physiological characteristics was first established, and then finite element method was used to analyze the heat diffuse equation for the surface temperature profiles of the breast. The genetic optimization algorithm was used to estimate the tumor parameters such as depth, size and blood perfusion by minimizing a fitness function involving the temperature profiles simulated data by finite element method to the experimental data obtained by infrared thermography. This preliminary study shows it is possible to determine the depth and the heat generation rate of the breast tumor by using infrared thermography and the optimization analysis, which may play an important role in the female breast healthcare and diseases evaluation or early detection. In order to develop the proposed methodology to be used in clinical, more accurate anatomy 3D breast geometry should be considered in further investigations.

Possible Many-Body Localization in a Long-Lived Finite-Temperature Ultracold Quasineutral Molecular Plasma

NASA Astrophysics Data System (ADS)

Sous, John; Grant, Edward

2018-03-01

We argue that the quenched ultracold plasma presents an experimental platform for studying the quantum many-body physics of disordered systems in the long-time and finite energy-density limits. We consider an experiment that quenches a plasma of nitric oxide to an ultracold system of Rydberg molecules, ions, and electrons that exhibits a long-lived state of arrested relaxation. The qualitative features of this state fail to conform with classical models. Here, we develop a microscopic quantum description for the arrested phase based on an effective many-body spin Hamiltonian that includes both dipole-dipole and van der Waals interactions. This effective model appears to offer a way to envision the essential quantum disordered nonequilibrium physics of this system.

Magnetic fields end-face effect investigation of HTS bulk over PMG with 3D-modeling numerical method

NASA Astrophysics Data System (ADS)

Qin, Yujie; Lu, Yiyun

2015-09-01

In this paper, the magnetic fields end-face effect of high temperature superconducting (HTS) bulk over a permanent magnetic guideway (PMG) is researched with 3D-modeling numerical method. The electromagnetic behavior of the bulk is simulated using finite element method (FEM). The framework is formulated by the magnetic field vector method (H-method). A superconducting levitation system composed of one rectangular HTS bulk and one infinite long PMG is successfully investigated using the proposed method. The simulation results show that for finite geometrical HTS bulk, even the applied magnetic field is only distributed in x-y plane, the magnetic field component Hz which is along the z-axis can be observed interior the HTS bulk.

Magnetic Chern bands and triplon Hall effect in an extended Shastry-Sutherland model

NASA Astrophysics Data System (ADS)

Malki, M.; Schmidt, K. P.

2017-05-01

We study topological properties of one-triplon bands in an extended Shastry-Sutherland model relevant for the frustrated quantum magnet SrCu2(BO3)2 . To this end perturbative continuous unitary transformations are applied about the isolated dimer limit allowing us to calculate the one-triplon dispersion up to high order in various couplings including intra- and interdimer Dzyaloshinskii-Moriya interactions and a general uniform magnetic field. We determine the Berry curvature and the Chern number of the different one-triplon bands. We demonstrate the occurrence of Chern numbers ±1 and ±2 for the case that two components of the magnetic field are finite. Finally, we also calculate the triplon Hall effect arising at finite temperatures.

Finite-Size Effects on the Behavior of the Susceptibility in van der Waals Films Bounded by Strongly Absorbing Substrates

NASA Technical Reports Server (NTRS)

Dantchev, Daniel; Rudnick, Joseph; Barmatz, M.

2007-01-01

We study critical point finite-size effects in the case of the susceptibility of a film in which interactions are characterized by a van der Waals-type power law tail. The geometry is appropriate to a slab-like system with two bounding surfaces. Boundary conditions are consistent with surfaces that both prefer the same phase in the low temperature, or broken symmetry, state. We take into account both interactions within the system and interactions between the constituents of the system and the material surrounding it. Specific predictions are made with respect to the behavior of 3He and 4He films in the vicinity of their respective liquid-vapor critical points.

Interaction effects in Aharonov-Bohm-Kondo rings

NASA Astrophysics Data System (ADS)

Komijani, Yashar; Yoshii, Ryosuke; Affleck, Ian

2013-12-01

We study the conductance through an Aharonov-Bohm ring, containing a quantum dot in the Kondo regime in one arm, at finite temperature and arbitrary electronic density. We develop a general method for this calculation based on changing the basis to the screening and nonscreening channels. We show that an unusual term appears in the conductance, involving the connected four-point Green's function of the conduction electrons. However, this term and the terms quadratic in the T matrix can be eliminated at sufficiently low temperatures, leading to an expression for the conductance linear in the Kondo T matrix. Explicit results are given for temperatures that are high compared to the Kondo temperature.

PLIF Temperature and Velocity Distributions in Laminar Hypersonic Flat-plate Flow

NASA Technical Reports Server (NTRS)

OByrne, S.; Danehy, P. M.; Houwing, A. F. P.

2003-01-01

Rotational temperature and velocity distributions have been measured across a hypersonic laminar flat-plate boundary layer, using planar laser-induced fluorescence. The measurements are compared to a finite-volume computation and a first-order boundary layer computation, assuming local similarity. Both computations produced similar temperature distributions and nearly identical velocity distributions. The disagreement between calculations is ascribed to the similarity solution not accounting for leading-edge displacement effects. The velocity measurements agreed to within the measurement uncertainty of 2 % with both calculated distributions. The peak measured temperature was 200 K lower than the computed values. This discrepancy is tentatively ascribed to vibrational relaxation in the boundary layer.

On Pokrovskii's anisotropic gap equations in superconductivity theory

NASA Astrophysics Data System (ADS)

Yang, Yisong

2003-11-01

An existence and uniqueness theorem for Pokrovskii's zero-temperature anisotropic gap equation is proved. Furthermore, it is shown that Pokrovskii's finite-temperature equation is inconsistent with the Bardeen-Cooper-Schrieffer (BCS) theory. A reformulation of the anisotropic gap equation is presented along the line of Pokrovskii and it is shown that the new equation is consistent with the BCS theory for the whole temperature range. As an application, the Markowitz-Kadanoff model for anisotropic superconductivity is considered and a rigorous proof of the half-integer-exponent isotope effect is obtained. Furthermore, a sharp estimate of the gap solution near the transition temperature is established.

Transport phenomena in the micropores of plug-type phase separators

NASA Technical Reports Server (NTRS)

Fazah, M. M.

1995-01-01

This study numerically investigates the transport phenomena within and across a porous-plug phase separator. The effect of temperature differential across a single pore and of the sidewall boundary conditions, i.e., isothermal or linear thermal gradient, are presented and discussed. The effects are quantified in terms of the evaporation mass flux across the boundary and the mean surface temperature. A two-dimensional finite element model is used to solve the continuity, momentum, and energy equations for the liquid. Temperature differentials across the pore interface of 1.0, and 1.5 K are examined and their effect on evaporation flux and mean surface temperature is shown. For isothermal side boundary conditions, the evaporation flux across the pore is directly proportional and linear with Delta T. For the case of an imposed linear thermal gradient on the side boundaries, Biot numbers of 0.0, 0.15, and 0.5 are examined. The most significant effect of Biot number is to lower the overall surface temperature and evaporation flux.

Direct Numerical Simulation of Fingering Instabilities in Coating Flows

NASA Astrophysics Data System (ADS)

Eres, Murat H.; Schwartz, Leonard W.

1998-11-01

We consider stability and finger formation in free surface flows. Gravity driven downhill drainage and temperature gradient driven climbing flows are two examples of such problems. The former situation occurs when a mound of viscous liquid on a vertical wall is allowed to flow. Constant surface shear stress due to temperature gradients (Marangoni stress) can initiate the latter problem. The evolution equations are derived using the lubrication approximation. We also include the effects of finite-contact angles in the evolution equations using a disjoining pressure model. Evolution equations for both problems are solved using an efficient alternating-direction-implicit method. For both problems a one-dimensional base state is established, that is steady in a moving reference frame. This base state is unstable to transverse perturbations. The transverse wavenumbers for the most rapidly growing modes are found through direct numerical solution of the nonlinear evolution equations, and are compared with published experimental results. For a range of finite equilibrium contact angles, the fingers can grow without limit leading to semi-finite steady fingers in a moving coordinate system. A computer generated movie of the nonlinear simulation results, for several sets of input parameters, will be shown.

Determination of female breast tumor and its parameter estimation by thermal simulation

NASA Astrophysics Data System (ADS)

Chen, Xin-guang; Xu, A.-qing; Yang, Hong-qin; Wang, Yu-hua; Xie, Shu-sen

2010-02-01

Thermal imaging is an emerging method for early detection of female breast tumor. The main challenge for thermal imaging used in breast clinics lies in how to detect or locate the tumor and obtain its related parameters. The purpose of this study is to apply an improved method which combined a genetic algorithm with finite element thermal analysis to determine the breast tumor and its parameters, such as the size, location, metabolic heat generation and blood perfusion rate. A finite element model for breast embedded a tumor was used to investigate the temperature distribution, and then the influences of tumor metabolic heat generation, tumor location and tumor size on the temperature were studied by use of an improved genetic algorithm. The results show that thermal imaging is a potential and effective detection tool for early breast tumor, and thermal simulation may be helpful for the explanation of breast thermograms.

Effects of Thermal Resistance on One-Dimensional Thermal Analysis of the Epidermal Flexible Electronic Devices Integrated with Human Skin

NASA Astrophysics Data System (ADS)

Li, He; Cui, Yun

2017-12-01

Nowadays, flexible electronic devices are increasingly used in direct contact with human skin to monitor the real-time health of human body. Based on the Fourier heat conduction equation and Pennes bio-heat transfer equation, this paper deduces the analytical solutions of one - dimensional heat transfer for flexible electronic devices integrated with human skin under the condition of a constant power. The influence of contact thermal resistance between devices and skin is considered as well. The corresponding finite element model is established to verify the correctness of analytical solutions. The results show that the finite element analysis agrees well with the analytical solution. With bigger thermal resistance, temperature increase of skin surface will decrease. This result can provide guidance for the design of flexible electronic devices to reduce the negative impact that exceeding temperature leave on human skin.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stubblefield, M.A.; Yang, C.; Lea, R.H.

The use of heat-activated thermal couplings is a quick and cost-effective joining method for composite-to-composite materials. In this study, a prepreg laminate which contains thermoset resins and fiberglass reinforcements is wrapped around the ends of components which are to be joined. A shrink tape, made of thermoplastic material, is placed over the prepreg laminate. When curing the shrink tape and the prepreg laminate, the shrink tape shrinks and compresses the prepreg to obtain good adhesion and the required mechanical properties. The mechanical strength of the heat coupling joint in bending increased by 29% over the currently used butt-weld method. Tomore » optimize the curing process, a finite element model was also developed to show the temperature distribution of the heat coupling joint during the curing process. Based on the tested prepreg material properties and model, the finite analysis temperature distribution differed less than 10% from that of the experimental data.« less

A two-dimensional finite-difference solution for the temperature distribution in a radial gas turbine guide vane blade

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.

An investigation into the impact of cryogenic environment on mechanical stresses in FRP composites

NASA Astrophysics Data System (ADS)

Fifo, O.; Basu, B.

2015-07-01

Fibre reinforced polymer (FRP) composites are fast becoming a highly utilised engineering material for high performance applications due to their light weight and high strength. Carbon fibre and other high strength fibres are commonly used in design of aerospace structures, wind turbine blades, etc. and potentially for propellant tanks of launch vehicles. For the aforementioned fields of application, stability of the material is essential over a wide range of temperature particularly for structures in hostile environments. Many studies have been conducted, experimentally, over the last decade to investigate the mechanical behaviour of FRP materials at varying subzero temperature. Likewise, tests on aging and cycling effect (room to low temperature) on the mechanical response of FRP have been reported. However, a relatively lesser focused area has been the mechanical behaviour of FRP composites under cryogenic environment. This article reports a finite element method of investigating the changes in the mechanical characteristics of an FRP material when temperature based analysis falls below zero. The simulated tests are carried out using a finite element package with close material properties used in the cited literatures. Tensile test was conducted and the results indicate that the mechanical responses agree with those reported in the literature sited.

Detecting temperature fluctuations at equilibrium.

PubMed

Dixit, Purushottam D

2015-05-21

The Gibbs and the Boltzmann definition of temperature agree only in the macroscopic limit. The ambiguity in identifying the equilibrium temperature of a finite-sized 'small' system exchanging energy with a bath is usually understood as a limitation of conventional statistical mechanics. We interpret this ambiguity as resulting from a stochastically fluctuating temperature coupled with the phase space variables giving rise to a broad temperature distribution. With this ansatz, we develop the equilibrium statistics and dynamics of small systems. Numerical evidence using an analytically tractable model shows that the effects of temperature fluctuations can be detected in the equilibrium and dynamical properties of the phase space of the small system. Our theory generalizes statistical mechanics to small systems relevant in biophysics and nanotechnology.

Simulation of one-sided heating of boiler unit membrane-type water walls

NASA Astrophysics Data System (ADS)

Kurepin, M. P.; Serbinovskiy, M. Yu.

2017-03-01

This study describes the results of simulation of the temperature field and the stress-strain state of membrane-type gastight water walls of boiler units using the finite element method. The methods of analytical and standard calculation of one-sided heating of fin-tube water walls by a radiative heat flux are analyzed. The methods and software for input data calculation in the finite-element simulation, including thermoelastic moments in welded panels that result from their one-sided heating, are proposed. The method and software modules are used for water wall simulation using ANSYS. The results of simulation of the temperature field, stress field, deformations and displacement of the membrane-type panel for the boiler furnace water wall using the finite-element method, as well as the results of calculation of the panel tube temperature, stresses and deformations using the known methods, are presented. The comparison of the known experimental results on heating and bending by given moments of membrane-type water walls and numerical simulations is performed. It is demonstrated that numerical results agree with high accuracy with the experimental data. The relative temperature difference does not exceed 1%. The relative difference of the experimental fin mutual turning angle caused by one-sided heating by radiative heat flux and the results obtained in the finite element simulation does not exceed 8.5% for nondisplaced fins and 7% for fins with displacement. The same difference for the theoretical results and the simulation using the finite-element method does not exceed 3% and 7.1%, respectively. The proposed method and software modules for simulation of the temperature field and stress-strain state of the water walls are verified and the feasibility of their application in practical design is proven.

Decisive role of nuclear quantum effects on surface mediated water dissociation at finite temperature.

PubMed

Litman, Yair; Donadio, Davide; Ceriotti, Michele; Rossi, Mariana

2018-03-14

Water molecules adsorbed on inorganic substrates play an important role in several technological applications. In the presence of light atoms in adsorbates, nuclear quantum effects (NQEs) influence the structural stability and the dynamical properties of these systems. In this work, we explore the impact of NQEs on the dissociation of water wires on stepped Pt(221) surfaces. By performing ab initio molecular dynamics simulations with van der Waals corrected density functional theory, we note that several competing minima for both intact and dissociated structures are accessible at finite temperatures, making it important to assess whether harmonic estimates of the quantum free energy are sufficient to determine the relative stability of the different states. We thus perform ab initio path integral molecular dynamics (PIMD) in order to calculate these contributions taking into account the conformational entropy and anharmonicities at finite temperatures. We propose that when adsorption is weak and NQEs on the substrate are negligible, PIMD simulations can be performed through a simple partition of the system, resulting in considerable computational savings. We then calculate the full contribution of NQEs to the free energies, including also anharmonic terms. We find that they result in an increase of up to 20% of the quantum contribution to the dissociation free energy compared with the harmonic estimates. We also find that the dissociation process has a negligible contribution from tunneling but is dominated by zero point energies, which can enhance the rate of dissociation by three orders of magnitude. Finally we highlight how both temperature and NQEs indirectly impact dipoles and the redistribution of electron density, causing work function changes of up to 0.4 eV with respect to static estimates. This quantitative determination of the change in the work function provides a possible approach to determine experimentally the most stable configurations of water oligomers on the stepped surfaces.

Decisive role of nuclear quantum effects on surface mediated water dissociation at finite temperature

NASA Astrophysics Data System (ADS)

Litman, Yair; Donadio, Davide; Ceriotti, Michele; Rossi, Mariana

2018-03-01

Water molecules adsorbed on inorganic substrates play an important role in several technological applications. In the presence of light atoms in adsorbates, nuclear quantum effects (NQEs) influence the structural stability and the dynamical properties of these systems. In this work, we explore the impact of NQEs on the dissociation of water wires on stepped Pt(221) surfaces. By performing ab initio molecular dynamics simulations with van der Waals corrected density functional theory, we note that several competing minima for both intact and dissociated structures are accessible at finite temperatures, making it important to assess whether harmonic estimates of the quantum free energy are sufficient to determine the relative stability of the different states. We thus perform ab initio path integral molecular dynamics (PIMD) in order to calculate these contributions taking into account the conformational entropy and anharmonicities at finite temperatures. We propose that when adsorption is weak and NQEs on the substrate are negligible, PIMD simulations can be performed through a simple partition of the system, resulting in considerable computational savings. We then calculate the full contribution of NQEs to the free energies, including also anharmonic terms. We find that they result in an increase of up to 20% of the quantum contribution to the dissociation free energy compared with the harmonic estimates. We also find that the dissociation process has a negligible contribution from tunneling but is dominated by zero point energies, which can enhance the rate of dissociation by three orders of magnitude. Finally we highlight how both temperature and NQEs indirectly impact dipoles and the redistribution of electron density, causing work function changes of up to 0.4 eV with respect to static estimates. This quantitative determination of the change in the work function provides a possible approach to determine experimentally the most stable configurations of water oligomers on the stepped surfaces.

An Exponential Finite Difference Technique for Solving Partial Differential Equations. M.S. Thesis - Toledo Univ., Ohio

NASA Technical Reports Server (NTRS)

Handschuh, Robert F.

1987-01-01

An exponential finite difference algorithm, as first presented by Bhattacharya for one-dimensianal steady-state, heat conduction in Cartesian coordinates, has been extended. The finite difference algorithm developed was used to solve the diffusion equation in one-dimensional cylindrical coordinates and applied to two- and three-dimensional problems in Cartesian coordinates. The method was also used to solve nonlinear partial differential equations in one (Burger's equation) and two (Boundary Layer equations) dimensional Cartesian coordinates. Predicted results were compared to exact solutions where available, or to results obtained by other numerical methods. It was found that the exponential finite difference method produced results that were more accurate than those obtained by other numerical methods, especially during the initial transient portion of the solution. Other applications made using the exponential finite difference technique included unsteady one-dimensional heat transfer with temperature varying thermal conductivity and the development of the temperature field in a laminar Couette flow.

exponential finite difference technique for solving partial differential equations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Handschuh, R.F.

1987-01-01

An exponential finite difference algorithm, as first presented by Bhattacharya for one-dimensianal steady-state, heat conduction in Cartesian coordinates, has been extended. The finite difference algorithm developed was used to solve the diffusion equation in one-dimensional cylindrical coordinates and applied to two- and three-dimensional problems in Cartesian coordinates. The method was also used to solve nonlinear partial differential equations in one (Burger's equation) and two (Boundary Layer equations) dimensional Cartesian coordinates. Predicted results were compared to exact solutions where available, or to results obtained by other numerical methods. It was found that the exponential finite difference method produced results that weremore » more accurate than those obtained by other numerical methods, especially during the initial transient portion of the solution. Other applications made using the exponential finite difference technique included unsteady one-dimensional heat transfer with temperature varying thermal conductivity and the development of the temperature field in a laminar Couette flow.« less

Ab initio calculation of finite-temperature charmonium potentials

NASA Astrophysics Data System (ADS)

Evans, P. W. M.; Allton, C. R.; Skullerud, J.-I.

2014-04-01

The interquark potential in charmonium states is calculated in both the zero and nonzero temperature phases from a first-principles lattice QCD calculation. Simulations with two dynamical quark flavors are used with temperatures T in the range 0.4Tc≲T≲1.7Tc, where Tc is the deconfining temperature. The correlators of point-split operators are analyzed to gain spatial information about the charmonium states. A method introduced by the HAL QCD Collaboration and based on the Schrödinger equation is applied to obtain the interquark potential. We find a clear temperature dependence with the central potential agreeing with the Cornell potential in the confined phase and becoming flatter (more screened) as the temperature increases past the deconfining temperature. This is the first time the interquark potential has been calculated for realistic quarks at finite temperature.

Finite temperature magnon spectra in yttrium iron garnet from a mean field approach in a tight-binding model

NASA Astrophysics Data System (ADS)

Shen, Ka

2018-04-01

We study magnon spectra at finite temperature in yttrium iron garnet using a tight-binding model with nearest-neighbor exchange interaction. The spin reduction due to thermal magnon excitation is taken into account via the mean field approximation to the local spin and is found to be different at two sets of iron atoms. The resulting temperature dependence of the spin wave gap shows good agreement with experiment. We find that only two magnon modes are relevant to the ferromagnetic resonance.

Transient conduction-radiation analysis of an absolute active cavity radiometer using finite elements

NASA Technical Reports Server (NTRS)

Mahan, J. R.; Kowsary, F.; Tira, N.; Gardiner, B. D.

1987-01-01

A NASA-developed finite element-based model of a generic active cavity radiometer (ACR) has been developed in order to study the dependence on operating temperature of the closed-loop and open-loop transient response of the instrument. Transient conduction within the sensing element is explored, and the transient temperature distribution resulting from the application of a time-varying radiative boundary condition is calculated. The results verify the prediction that operation of an ACR at cryogenic temperatures results in large gains in frequency response.

Complex heavy-quark potential at finite temperature from lattice QCD.

PubMed

Rothkopf, Alexander; Hatsuda, Tetsuo; Sasaki, Shoichi

2012-04-20

We calculate for the first time the complex potential between a heavy quark and antiquark at finite temperature across the deconfinement transition in lattice QCD. The real and imaginary part of the potential at each separation distance r is obtained from the spectral function of the thermal Wilson loop. We confirm the existence of an imaginary part above the critical temperature T(C), which grows as a function of r and underscores the importance of collisions with the gluonic environment for the melting of heavy quarkonia in the quark-gluon plasma.

Lorentz violation, gravitoelectromagnetism and Bhabha scattering at finite temperature

NASA Astrophysics Data System (ADS)

Santos, A. F.; Khanna, Faqir C.

2018-04-01

Gravitoelectromagnetism (GEM) is an approach for the gravitation field that is described using the formulation and terminology similar to that of electromagnetism. The Lorentz violation is considered in the formulation of GEM that is covariant in its form. In practice, such a small violation of the Lorentz symmetry may be expected in a unified theory at very high energy. In this paper, a non-minimal coupling term, which exhibits Lorentz violation, is added as a new term in the covariant form. The differential cross-section for Bhabha scattering in the GEM framework at finite temperature is calculated that includes Lorentz violation. The Thermo Field Dynamics (TFD) formalism is used to calculate the total differential cross-section at finite temperature. The contribution due to Lorentz violation is isolated from the total cross-section. It is found to be small in magnitude.

The Effect of Temperature Dependent Material Nonlinearities on the Response of Piezoelectric Composite Plates

NASA Technical Reports Server (NTRS)

Lee, Ho-Jun; Saravanos, Dimitris A.

1997-01-01

Previously developed analytical formulations for piezoelectric composite plates are extended to account for the nonlinear effects of temperature on material properties. The temperature dependence of the composite and piezoelectric properties are represented at the material level through the thermopiezoelectric constitutive equations. In addition to capturing thermal effects from temperature dependent material properties, this formulation also accounts for thermal effects arising from: (1) coefficient of thermal expansion mismatch between the various composite and piezoelectric plies and (2) pyroelectric effects on the piezoelectric material. The constitutive equations are incorporated into a layerwise laminate theory to provide a unified representation of the coupled mechanical, electrical, and thermal behavior of smart structures. Corresponding finite element equations are derived and implemented for a bilinear plate element with the inherent capability to model both the active and sensory response of piezoelectric composite laminates. Numerical studies are conducted on a simply supported composite plate with attached piezoceramic patches under thermal gradients to investigate the nonlinear effects of material property temperature dependence on the displacements, sensory voltages, active voltages required to minimize thermal deflections, and the resultant stress states.

Temperature dependence of the fundamental optical absorption edge in crystals and disordered semiconductors

NASA Astrophysics Data System (ADS)

Grein, C. H.; John, Sajeev

1989-04-01

We present a first principles theory of the temperature dependence of the Urbach optical absorption edge in crystals and disordered semiconductors which incorporates the effects of short range correlated static disorder and the non-adiabatic quantum dynamics of the coupled electron-phonon system. At finite temperatures the dominant features of the Urbach tail are accounted for by multiple phonon absorption and emission side bands which accompany the optically induced electronic transition and which provide a dynamic polaronic potential well that localizes the electron. Excellent agreement is found with experimental data on both crystalline and amorphous silicon.

Enhancing the nonlinear thermoelectric response of a correlated quantum dot in the Kondo regime by asymmetrical coupling to the leads

NASA Astrophysics Data System (ADS)

Pérez Daroca, Diego; Roura-Bas, Pablo; Aligia, Armando A.

2018-04-01

We study the low-temperature properties of the differential response of the current to a temperature gradient at finite voltage in a single-level quantum dot including electron-electron interaction, nonsymmetric couplings to the leads, and nonlinear effects. The calculated response is significantly enhanced in setups with large asymmetries between the tunnel couplings. In the investigated range of voltages and temperatures with corresponding energies up to several times the Kondo energy scale, the maximum response is enhanced nearly an order of magnitude with respect to symmetric coupling to the leads.

Quantum size effects in the size-temperature phase diagram of gallium: structural characterization of shape-shifting clusters.

PubMed

Steenbergen, Krista G; Gaston, Nicola

2015-02-09

Finite temperature analysis of cluster structures is used to identify signatures of the low-temperature polymorphs of gallium, based on the results of first-principle Born-Oppenheimer molecular dynamics simulations. Pre-melting structural transitions proceed from either the β- and/or the δ-phase to the γ- or δ-phase, with a size- dependent phase progression. We relate the stability of each isomer to the electronic structures of the different phases, giving new insight into the origin of polymorphism in this complicated element. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Analytical study of temperature distribution in a rectangular porous fin considering both insulated and convective tip

NASA Astrophysics Data System (ADS)

Deshamukhya, Tuhin; Bhanja, Dipankar; Nath, Sujit; Maji, Ambarish; Choubey, Gautam

2017-07-01

The following study is concerned with determination of temperature distribution of porous fins under convective and insulated tip conditions. The authors have made an effort to study the effect of various important parameters involved in the transfer of heat through porous fins as well as the temperature distribution along the fin length subjected to both convective as well as insulated ends. The non-linear equation obtained has been solved by Adomian Decomposition method and validated with a numerical scheme called Finite Difference method by using a central difference scheme and Gauss Siedel Iterative method.

On finite element implementation and computational techniques for constitutive modeling of high temperature composites

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.

Prediction of the Grain-Microstructure Evolution Within a Friction Stir Welding (FSW) Joint via the Use of the Monte Carlo Simulation Method

NASA Astrophysics Data System (ADS)

Grujicic, M.; Ramaswami, S.; Snipes, J. S.; Avuthu, V.; Galgalikar, R.; Zhang, Z.

2015-09-01

A thermo-mechanical finite element analysis of the friction stir welding (FSW) process is carried out and the evolution of the material state (e.g., temperature, the extent of plastic deformation, etc.) monitored. Subsequently, the finite-element results are used as input to a Monte-Carlo simulation algorithm in order to predict the evolution of the grain microstructure within different weld zones, during the FSW process and the subsequent cooling of the material within the weld to room temperature. To help delineate different weld zones, (a) temperature and deformation fields during the welding process, and during the subsequent cooling, are monitored; and (b) competition between the grain growth (driven by the reduction in the total grain-boundary surface area) and dynamic-recrystallization grain refinement (driven by the replacement of highly deformed material with an effectively "dislocation-free" material) is simulated. The results obtained clearly revealed that different weld zones form as a result of different outcomes of the competition between the grain growth and grain refinement processes.

First-principles calculations of finite temperature Sc and O NMR parameters in Pb(Sc2/3W1/3)O3

NASA Astrophysics Data System (ADS)

Krakauer, Henry; Walter, Eric J.; Ellden, Jeremy; Hoatson, Gina L.; Vold, Robert L.

2012-02-01

Understanding the dynamics of complex relaxor ferroelectrics is important to characterizing their large electromechanical coupling. Preliminary NMR measurements of Sc electric-field-gradients (EFG) in Pb(Sc2/3W1/3)O3 (PSW) show a strong temperature dependence in the range T = 250 - 330 K. To understand this behavior, we use the first-principles GIPAWootnotetextC. J. Pickard and F. Mauri, Phys. Rev. B 63, 245101 (2001); method within the Quantum Espresso (QE) packageootnotetextP. Giannozzi et al., Journal of Physics: Condensed Matter 21, 395502 (2009) to calculate ^45Sc and ^17O chemical-shifts and EFG tensors. To study finite temperature effects, we incorporate the thermal expansion of the lattice and sample thermal disorder, using the phonon degrees of freedom. As in our previous studies of perovksites,ootnotetextD. L. Pechkis, E. J. Walter, and H. Krakauer. J. Chem. Phys. 135, 114507 (2011); ibid. 131, 184511 (2009) we show that the ^17O chemical shifts in PSW also exhibit a linear correlation with the nearest-neighbor B-O bond length.

Fermionic spectral functions in backreacting p-wave superconductors at finite temperature

NASA Astrophysics Data System (ADS)

Giordano, G. L.; Grandi, N. E.; Lugo, A. R.

2017-04-01

We investigate the spectral function of fermions in a p-wave superconducting state, at finite both temperature and gravitational coupling, using the AdS/CF T correspondence and extending previous research. We found that, for any coupling below a critical value, the system behaves as its zero temperature limit. By increasing the coupling, the "peak-dip-hump" structure that characterizes the spectral function at fixed momenta disappears. In the region where the normal/superconductor phase transition is first order, the presence of a non-zero order parameter is reflected in the absence of rotational symmetry in the fermionic spectral function at the critical temperature.

One-shot calculation of temperature-dependent optical spectra and phonon-induced band-gap renormalization

NASA Astrophysics Data System (ADS)

Zacharias, Marios; Giustino, Feliciano

Electron-phonon interactions are of fundamental importance in the study of the optical properties of solids at finite temperatures. Here we present a new first-principles computational technique based on the Williams-Lax theory for performing predictive calculations of the optical spectra, including quantum zero-point renormalization and indirect absorption. The calculation of the Williams-Lax optical spectra is computationally challenging, as it involves the sampling over all possible nuclear quantum states. We develop an efficient computational strategy for performing ''one-shot'' finite-temperature calculations. These require only a single optimal configuration of the atomic positions. We demonstrate our methodology for the case of Si, C, and GaAs, yielding absorption coefficients in good agreement with experiment. This work opens the way for systematic calculations of optical spectra at finite temperature. This work was supported by the UK EPSRC (EP/J009857/1 and EP/M020517/) and the Leverhulme Trust (RL-2012-001), and the Graphene Flagship (EU-FP7-604391).

Bubble Dynamics on a Heated Surface

NASA Technical Reports Server (NTRS)

Kassemi, Mohammad; Rashidnia, Nasser

1996-01-01

In this work, we study the combined thermocapillary and natural convective flow generated by a bubble on a heated solid surface. The interaction between gas and vapor bubbles with the surrounding fluid is of interest for both space and ground-based processing. On earth, the volumetric forces are dominant, especially, in apparatuses with large volume to surface ratio. But in the reduced gravity environment of orbiting spacecraft, surface forces become more important and the effects of Marangoni convection are easily unmasked. In order to delineate the roles of the various interacting phenomena, a combined numerical-experimental approach is adopted. The temperature field is visualized using Mach-Zehnder interferometry and the flow field is observed by a laser sheet flow visualization technique. A finite element numerical model is developed which solves the two-dimensional momentum and energy equations and includes the effects of bubble surface deformation. Steady state temperature and velocity fields predicted by the finite element model are in excellent qualitative agreement with the experimental results. A parametric study of the interaction between Marangoni and natural convective flows including conditions pertinent to microgravity space experiments is presented. Numerical simulations clearly indicate that there is a considerable difference between 1-g and low-g temperature and flow fields induced by the bubble.

Thermodynamics and structural transition of binary atomic Bose-Fermi mixtures in box or harmonic potentials: A path-integral study

NASA Astrophysics Data System (ADS)

Kim, Tom; Chien, Chih-Chun

2018-03-01

Experimental realizations of a variety of atomic binary Bose-Fermi mixtures have brought opportunities for studying composite quantum systems with different spin statistics. The binary atomic mixtures can exhibit a structural transition from a mixture into phase separation as the boson-fermion interaction increases. By using a path-integral formalism to evaluate the grand partition function and the thermodynamic grand potential, we obtain the effective potential of binary Bose-Fermi mixtures. Thermodynamic quantities in a broad range of temperatures and interactions are also derived. The structural transition can be identified as a loop of the effective potential curve, and the volume fraction of phase separation can be determined by the lever rule. For 6Li-7Li and 6Li-41K mixtures, we present the phase diagrams of the mixtures in a box potential at zero and finite temperatures. Due to the flexible densities of atomic gases, the construction of phase separation is more complicated when compared to conventional liquid or solid mixtures where the individual densities are fixed. For harmonically trapped mixtures, we use the local density approximation to map out the finite-temperature density profiles and present typical trap structures, including the mixture, partially separated phases, and fully separated phases.

Elastoviscoplastic snap-through behavior of shallow arches subjected to thermomechanical loads

NASA Technical Reports Server (NTRS)

Simitses, George J.; Song, Yuzhao; Sheinman, Izhak

1991-01-01

The problem of snap-through buckling of clamped shallow arches under thermomechanical loads is investigated. The analysis is based on nonlinear kinematic relations and nonlinear rate-dependent unified constitutive equations. A finite element approach is employed to predict the, in general, inelastic buckling behavior. The construction material is alloy B1900 + Hf, which is commonly utilized in high-temperature environments. The effect of several parameters is assessed. These parameters include the rise parameter and temperature. Comparison between elastic and elastoviscoplastic responses is also presented.

Computation of the temperature distribution in cooled radial inflow turbine guide vanes

NASA Technical Reports Server (NTRS)

Tabakoff, W.; Hosny, W.; Hamed, A.

1977-01-01

A two-dimensional finite-difference numerical technique is presented to determine the temperature distribution of an internally-cooled blade of radial turbine guide vanes. A simple convection cooling is assumed inside the guide vane. Such an arrangement results in relatively small cooling effectiveness at the leading edge and at the trailing edge. Heat transfer augmentation in these critical areas may be achieved by using impingement jets and film cooling. A computer program is written in Fortran IV for IBM 370/165 computer.

Physics based calculation of the fine structure constant

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lestone, John Paul

2009-01-01

We assume that the coupling between particles and photons is defined by a surface area and a temperature, and that the square of the temperature is the inverse of the surface area ({Dirac_h}=c= 1). By making assumptions regarding stimulated emission and effects associated with the finite length of a string that forms the particle surface, the fine structure constant is calculated to be {approx}1/137.04. The corresponding calculated fundamental unit of charge is 1.6021 x 10{sup -19} C.

Spectral function of few electrons in quantum wires and carbon nanotubes as a signature of Wigner localization

NASA Astrophysics Data System (ADS)

Secchi, Andrea; Rontani, Massimo

2012-03-01

We demonstrate that the profile of the space-resolved spectral function at finite temperature provides a signature of Wigner localization for electrons in quantum wires and semiconducting carbon nanotubes. Our numerical evidence is based on the exact diagonalization of the microscopic Hamiltonian of few particles interacting in gate-defined quantum dots. The minimal temperature required to suppress residual exchange effects in the spectral function image of (nanotubes) quantum wires lies in the (sub)kelvin range.

Explicit formula of finite difference method to estimate human peripheral tissue temperatures during exposure to severe cold stress.

PubMed

Khanday, M A; Hussain, Fida

2015-02-01

During cold exposure, peripheral tissues undergo vasoconstriction to minimize heat loss to preserve the maintenance of a normal core temperature. However, vasoconstricted tissues exposed to cold temperatures are susceptible to freezing and frostbite-related tissue damage. Therefore, it is imperative to establish a mathematical model for the estimation of tissue necrosis due to cold stress. To this end, an explicit formula of finite difference method has been used to obtain the solution of Pennes' bio-heat equation with appropriate boundary conditions to estimate the temperature profiles of dermal and subdermal layers when exposed to severe cold temperatures. The discrete values of nodal temperature were calculated at the interfaces of skin and subcutaneous tissues with respect to the atmospheric temperatures of 25 °C, 20 °C, 15 °C, 5 °C, -5 °C and -10 °C. The results obtained were used to identify the scenarios under which various degrees of frostbite occur on the surface of skin as well as the dermal and subdermal areas. The explicit formula of finite difference method proposed in this model provides more accurate predictions as compared to other numerical methods. This model of predicting tissue temperatures provides researchers with a more accurate prediction of peripheral tissue temperature and, hence, the susceptibility to frostbite during severe cold exposure. Copyright © 2014 Elsevier Ltd. All rights reserved.

Finite temperature grand canonical ensemble study of the minimum electrophilicity principle.

PubMed

Miranda-Quintana, Ramón Alain; Chattaraj, Pratim K; Ayers, Paul W

2017-09-28

We analyze the minimum electrophilicity principle of conceptual density functional theory using the framework of the finite temperature grand canonical ensemble. We provide support for this principle, both for the cases of systems evolving from a non-equilibrium to an equilibrium state and for the change from one equilibrium state to another. In doing so, we clearly delineate the cases where this principle can, or cannot, be used.

Dynamics and Melting of Finite Plasma Crystals

NASA Astrophysics Data System (ADS)

Ludwig, Patrick; K"Ahlert, Hanno; Baumgartner, Henning; Thomsen, Hauke; Bonitz, Michael

2009-11-01

Interacting few-particle systems in external trapping potentials are of strong current interest since they allow to realize and control strong correlation and quantum effects [1]. Here, we present our recent results on the structural and thermodynamic properties of the crystal-like Wigner phase of complex plasma confined in a 3D harmonic potential. We discuss the linear response of the strongly correlated system to external excitations, which can be described in terms of normal modes [2]. By means of first-principle simulations the details of the melting phase transitions of these mesoscopic systems are systematically analysed with the melting temperatures being determined by a modified Lindemann parameter for the pair distance fluctuations [3]. The critical temperatures turn out to be utmost sensitive to finite size effects (i.e., the exact particle number), and form of the (screened) interaction potential.[4pt] [1] PhD Thesis, P. Ludwig, U Rostock (2008)[0pt] [2] C. Henning et al., J. Phys. A 42, 214023 (2009)[0pt] [3] B"oning et al., Phys. Rev. Lett. 100, 113401 (2008)

Finite Element Analysis of Active and Sensory Thermopiezoelectric Composite Materials. Degree awarded by Northwestern Univ., Dec. 2000

NASA Technical Reports Server (NTRS)

Lee, Ho-Jun

2001-01-01

Analytical formulations are developed to account for the coupled mechanical, electrical, and thermal response of piezoelectric composite materials. The coupled response is captured at the material level through the thermopiezoelectric constitutive equations and leads to the inherent capability to model both the sensory and active responses of piezoelectric materials. A layerwise laminate theory is incorporated to provide more accurate analysis of the displacements, strains, stresses, electric fields, and thermal fields through-the-thickness. Thermal effects which arise from coefficient of thermal expansion mismatch, pyroelectric effects, and temperature dependent material properties are explicitly accounted for in the formulation. Corresponding finite element formulations are developed for piezoelectric beam, plate, and shell elements to provide a more generalized capability for the analysis of arbitrary piezoelectric composite structures. The accuracy of the current formulation is verified with comparisons from published experimental data and other analytical models. Additional numerical studies are also conducted to demonstrate additional capabilities of the formulation to represent the sensory and active behaviors. A future plan of experimental studies is provided to characterize the high temperature dynamic response of piezoelectric composite materials.

TORO II simulations of induction heating in ferromagnetic materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adkins, D.R.; Gartling, D.K.; Kelley, J.B.

TORO II is a finite element computer program that is used in the simulation of electric and magnetic fields. This code, which was developed at Sandia National Laboratories, has been coupled with a finite element thermal code, COYOTE II, to predict temperature profiles in inductively heated parts. The development of an effective technique to account for the nonlinear behavior of the magnetic permeability in ferromagnetic parts is one of the more difficult aspects of solving induction heating problems. In the TORO II code, nonlinear, spatially varying magnetic permeability is approximated by an effective permeability on an element-by-element basis that effectivelymore » provides the same energy deposition that is produced when the true permeability is used. This approximation has been found to give an accurate estimate of the volumetric heating distribution in the part, and predicted temperature distributions have been experimentally verified using a medium carbon steel and a 10kW industrial induction heating unit. Work on the model was funded through a Cooperative Research and Development Agreement (CRADA) between the Department of Energy and General Motors` Delphi Saginaw Steering Systems.« less

A mixed pseudospectral/finite difference method for a thermally driven fluid in a nonuniform gravitational field

NASA Technical Reports Server (NTRS)

Macaraeg, M. G.

1985-01-01

A numerical study of the steady, axisymmetric flow in a heated, rotating spherical shell is conducted to model the Atmospheric General Circulation Experiment (AGCE) proposed to run aboard a later Shuttle mission. The AGCE will consist of concentric rotating spheres confining a dielectric fluid. By imposing a dielectric field across the fluid a radial body force will be created. The numerical solution technique is based on the incompressible Navier-Stokes equations. In the method a pseudospectral technique is used in the latitudinal direction, and a second-order accurate finite difference scheme discretizes time and radial derivatives. This paper discusses the development and performance of this numerical scheme for the AGCE which has been modeled in the past only by pure FD formulations. In addition, previous models have not investigated the effect of using a dielectric force to simulate terrestrial gravity. The effect of this dielectric force on the flow field is investigated as well as a parameter study of varying rotation rates and boundary temperatures. Among the effects noted are the production of larger velocities and enhanced reversals of radial temperature gradients for a body force generated by the electric field.

Fluctuations in non-ideal pion gas with dynamically fixed particle number

NASA Astrophysics Data System (ADS)

Kolomeitsev, E. E.; Voskresensky, D. N.

2018-05-01

We consider a non-ideal hot pion gas with the dynamically fixed number of particles in the model with the λϕ4 interaction. The effective Lagrangian for the description of such a system is obtained after dropping the terms responsible for the change of the total particle number. Reactions π+π- ↔π0π0, which determine the isospin balance of the medium, are permitted. Within the self-consistent Hartree approximation we compute the effective pion mass, thermodynamic characteristics of the system and the variance of the particle number at temperatures above the critical point of the induced Bose-Einstein condensation when the pion chemical potential reaches the value of the effective pion mass. We analyze conditions for the condensate formation in the process of thermalization of an initially non-equilibrium pion gas. The normalized variance of the particle number increases with a temperature decrease but remains finite in the critical point of the Bose-Einstein condensation. This is due to the non-perturbative account of the interaction and is in contrast to the ideal-gas case. In the kinetic regime of the condensate formation the variance is shown to stay finite also.

Prediction of ground effects on aircraft noise

NASA Technical Reports Server (NTRS)

Pao, S. P.; Wenzel, A. R.; Oncley, P. B.

1978-01-01

A unified method is recommended for predicting ground effects on noise. This method may be used in flyover noise predictions and in correcting static test-stand data to free-field conditions. The recommendation is based on a review of recent progress in the theory of ground effects and of the experimental evidence which supports this theory. It is shown that a surface wave must be included sometimes in the prediction method. Prediction equations are collected conveniently in a single section of the paper. Methods of measuring ground impedance and the resulting ground-impedance data are also reviewed because the recommended method is based on a locally reactive impedance boundary model. Current practice of estimating ground effects are reviewed and consideration is given to practical problems in applying the recommended method. These problems include finite frequency-band filters, finite source dimension, wind and temperature gradients, and signal incoherence.

Temporal and spatiotemporal correlation functions for trapped Bose gases

NASA Astrophysics Data System (ADS)

Kohnen, M.; Nyman, R. A.

2015-03-01

Density correlations unambiguously reveal the quantum nature of matter. Here, we study correlations between measurements of density in cold-atom clouds at different times at one position, and also at two separated positions. We take into account the effects of finite-size and -duration measurements made by light beams passing through the atom cloud. We specialize to the case of Bose gases in harmonic traps above critical temperature, for weakly perturbative measurements. For overlapping measurement regions, shot-noise correlations revive after a trap oscillation period. For nonoverlapping regions, bosonic correlations dominate at long times, and propagate at finite speeds. Finally, we give a realistic measurement protocol for performing such experiments.

Rotational Diffusion Depends on Box Size in Molecular Dynamics Simulations.

PubMed

Linke, Max; Köfinger, Jürgen; Hummer, Gerhard

2018-06-07

We show that the rotational dynamics of proteins and nucleic acids determined from molecular dynamics simulations under periodic boundary conditions suffer from significant finite-size effects. We remove the box-size dependence of the rotational diffusion coefficients by adding a hydrodynamic correction k B T/6 ηV with k B Boltzmann's constant, T the absolute temperature, η the solvent shear viscosity, and V the box volume. We show that this correction accounts for the finite-size dependence of the rotational diffusion coefficients of horse-heart myoglobin and a B-DNA dodecamer in aqueous solution. The resulting hydrodynamic radii are in excellent agreement with experiment.

How hot? Systematic convergence of the replica exchange method using multiple reservoirs.

PubMed

Ruscio, Jory Z; Fawzi, Nicolas L; Head-Gordon, Teresa

2010-02-01

We have devised a systematic approach to converge a replica exchange molecular dynamics simulation by dividing the full temperature range into a series of higher temperature reservoirs and a finite number of lower temperature subreplicas. A defined highest temperature reservoir of equilibrium conformations is used to help converge a lower but still hot temperature subreplica, which in turn serves as the high-temperature reservoir for the next set of lower temperature subreplicas. The process is continued until an optimal temperature reservoir is reached to converge the simulation at the target temperature. This gradual convergence of subreplicas allows for better and faster convergence at the temperature of interest and all intermediate temperatures for thermodynamic analysis, as well as optimizing the use of multiple processors. We illustrate the overall effectiveness of our multiple reservoir replica exchange strategy by comparing sampling and computational efficiency with respect to replica exchange, as well as comparing methods when converging the structural ensemble of the disordered Abeta(21-30) peptide simulated with explicit water by comparing calculated Rotating Overhauser Effect Spectroscopy intensities to experimentally measured values. Copyright 2009 Wiley Periodicals, Inc.

Entropic Barriers for Two-Dimensional Quantum Memories

NASA Astrophysics Data System (ADS)

Brown, Benjamin J.; Al-Shimary, Abbas; Pachos, Jiannis K.

2014-03-01

Comprehensive no-go theorems show that information encoded over local two-dimensional topologically ordered systems cannot support macroscopic energy barriers, and hence will not maintain stable quantum information at finite temperatures for macroscopic time scales. However, it is still well motivated to study low-dimensional quantum memories due to their experimental amenability. Here we introduce a grid of defect lines to Kitaev's quantum double model where different anyonic excitations carry different masses. This setting produces a complex energy landscape which entropically suppresses the diffusion of excitations that cause logical errors. We show numerically that entropically suppressed errors give rise to superexponential inverse temperature scaling and polynomial system size scaling for small system sizes over a low-temperature regime. Curiously, these entropic effects are not present below a certain low temperature. We show that we can vary the system to modify this bound and potentially extend the described effects to zero temperature.

One-shot calculation of temperature-dependent optical spectra and phonon-induced band-gap renormalization

NASA Astrophysics Data System (ADS)

Zacharias, Marios; Giustino, Feliciano

2016-08-01

Recently, Zacharias et al. [Phys. Rev. Lett. 115, 177401 (2015), 10.1103/PhysRevLett.115.177401] developed an ab initio theory of temperature-dependent optical absorption spectra and band gaps in semiconductors and insulators. In that work, the zero-point renormalization and the temperature dependence were obtained by sampling the nuclear wave functions using a stochastic approach. In the present work, we show that the stochastic sampling of Zacharias et al. can be replaced by fully deterministic supercell calculations based on a single optimal configuration of the atomic positions. We demonstrate that a single calculation is able to capture the temperature-dependent band-gap renormalization including quantum nuclear effects in direct-gap and indirect-gap semiconductors, as well as phonon-assisted optical absorption in indirect-gap semiconductors. In order to demonstrate this methodology, we calculate from first principles the temperature-dependent optical absorption spectra and the renormalization of direct and indirect band gaps in silicon, diamond, and gallium arsenide, and we obtain good agreement with experiment and with previous calculations. In this work we also establish the formal connection between the Williams-Lax theory of optical transitions and the related theories of indirect absorption by Hall, Bardeen, and Blatt, and of temperature-dependent band structures by Allen and Heine. The present methodology enables systematic ab initio calculations of optical absorption spectra at finite temperature, including both direct and indirect transitions. This feature will be useful for high-throughput calculations of optical properties at finite temperature and for calculating temperature-dependent optical properties using high-level theories such as G W and Bethe-Salpeter approaches.

Dynamic gas temperature measurement system

NASA Technical Reports Server (NTRS)

Elmore, D. L.; Robinson, W. W.; Watkins, W. B.

1983-01-01

A gas temperature measurement system with compensated frequency response of 1 KHz and capability to operate in the exhaust of a gas turbine combustor was developed. Environmental guidelines for this measurement are presented, followed by a preliminary design of the selected measurement method. Transient thermal conduction effects were identified as important; a preliminary finite-element conduction model quantified the errors expected by neglecting conduction. A compensation method was developed to account for effects of conduction and convection. This method was verified in analog electrical simulations, and used to compensate dynamic temperature data from a laboratory combustor and a gas turbine engine. Detailed data compensations are presented. Analysis of error sources in the method were done to derive confidence levels for the compensated data.

The acoustic radiation force on a heated (or cooled) rigid sphere - Theory

NASA Technical Reports Server (NTRS)

Lee, C. P.; Wang, T. G.

1984-01-01

A finite amplitude sound wave can exert a radiation force on an object due to second-order effect of the wave field. The radiation force on a rigid small sphere (i.e., in the long wavelength limit), which has a temperature different from that of the environment, is presently studied. This investigation assumes no thermally induced convection and is relevant to material processing in the absence of gravity. Both isotropic and nonisotropic temperature profiles are considered. In this calculation, the acoustic effect and heat transfer process are essentially decoupled because of the long wavelength limit. The heat transfer information required for determining the force is contained in the parameters, which are integrals over the temperature distribution.

Topics in QCD at Nonzero Temperature and Density

NASA Astrophysics Data System (ADS)

Pangeni, Kamal

Understanding the behavior of matter at ultra-high density such as neutron stars require the knowledge of ground state properties of Quantum chromodynamics (QCD) at finite chemical potential. However, this task has turned out to be very difficult because of two main reasons: 1) QCD may still be strongly coupled at those regimes making perturbative calculations unreliable and 2) QCD at finite density suffers from the sign problem that makes the use of lattice simulation problematic and it even affects phenomenological models. In the first part of this thesis, we show that the sign problem in analytical calculations of finite density models can be solved by considering the CK-symmetric, where C is charge conjugation and K is complex conjugation, complex saddle points of the effective action. We then explore the properties and consequences of such complex saddle points at non-zero temperature and density. Due to CK symmetry, the mass matrix eigenvalues in these models are not always real but can be complex, which results in damped oscillation of the density-density correlation function, a new feature of finite density models. To address the generality of such behavior, we next consider a lattice model of QCD with static quarks at strong-coupling. Computation of the mass spectrum confirms the existence of complex eigenvalues in much of temperature-chemical potential plane. This provides an independent confirmation of our results obtained using phenomenological models of QCD. The existence of regions in parameter space where density-density correlation function exhibit damped oscillation is one of the hallmarks of typical liquid-gas system. The formalism developed to tackle the sign problem in QCD models actually gives a simple understanding for the existence of such behavior in liquid-gas system. To this end, we develop a generic field theoretic model for the treatment of liquid-gas phase transition. An effective field theory at finite density derived from a fundamental four dimensional field theory turns out to be complex but CK symmetric. The existence of CK symmetry results in complex mass eigenvalues, which in turn leads to damped oscillatory behavior of the density-density correlation function. In the last part of this thesis, we study the effect of large amplitude density oscillations on the transport properties of superfluid nuclear matter. In nuclear matter at neutron-star densities and temperature, Cooper pairing leads to the formations of a gap in the nucleon excitation spectra resulting in exponentially strong Boltzmann suppression of many transport coefficients. Previous calculations have shown evidence that density oscillations of sufficiently large amplitude can overcome this suppression for flavor-changing beta processes via the mechanism of "gap-bridging". We address the simplifications made in that initial work, and show that gap bridging can counteract Boltzmann suppression of neutrino emissivity for the realistic case of modified Urca processes in matter with 3 P2 neutron pairing.

Real time evolution at finite temperatures with operator space matrix product states

NASA Astrophysics Data System (ADS)

Pižorn, Iztok; Eisler, Viktor; Andergassen, Sabine; Troyer, Matthias

2014-07-01

We propose a method to simulate the real time evolution of one-dimensional quantum many-body systems at finite temperature by expressing both the density matrices and the observables as matrix product states. This allows the calculation of expectation values and correlation functions as scalar products in operator space. The simulations of density matrices in inverse temperature and the local operators in the Heisenberg picture are independent and result in a grid of expectation values for all intermediate temperatures and times. Simulations can be performed using real arithmetics with only polynomial growth of computational resources in inverse temperature and time for integrable systems. The method is illustrated for the XXZ model and the single impurity Anderson model.

Semiclassical theory for liquidlike behavior of the frustrated magnet Ca10Cr7O28

NASA Astrophysics Data System (ADS)

Biswas, Sounak; Damle, Kedar

2018-03-01

We identify the low energy effective Hamiltonian that is expected to describe the low temperature properties of the frustrated magnet Ca10Cr7O28 . Motivated by the fact that this effective Hamiltonian has S =3 /2 effective moments as its degrees of freedom, we use semiclassical spin-wave theory to study the T =0 physics of this effective model and argue that singular spin-wave fluctuations destabilize the spiral order favored by the exchange couplings of this effective Hamiltonian. We also use a combination of classical Monte-Carlo simulations and molecular dynamics, as well as analytical approximations, to study the physics at low, nonzero temperatures. The results of these nonzero temperature calculations capture the liquidlike structure factors observed in the temperature range accessed by recent experiments. Additionally, at still lower temperatures, they predict that a transition to nematic order in the bond energies reflects itself in the spin channel in the form of a crossover to a regime with large but finite correlation length for spiral spin correlations and a corresponding slowing down of spin dynamics.

Effect of substrate preheating temperature and coating thickness on residual stress in plasma sprayed hydroxyapatite coating

NASA Astrophysics Data System (ADS)

Tang, Dapei

2015-07-01

A thermal-mechanical coupling model was developed based on thermal-elastic- plastic theory according the special process of plasma spraying Hydroxyapatite (HA) coating upon Ti-6Al-4V substrate. On the one hand, the classical Fourier transient heat conduction equation was modified by introducing the effect item of deformation on temperature, on the other hand, the Johnson-Cook model, suitable for high temperature and high strain rate conditions, was used as constitutive equation after considering temperature softening effect, strain hardening effect and strain rate reinforcement effect. Based on the above coupling model, the residual stress field within the HA coating was simulated by using finite element method (FEM). Meanwhile, the substrate preheating temperature and coating thickness on the influence of residual stress components were calculated, respectively. The failure modes of coating were also preliminary analyzed. In addition, in order to verify the reliability of calculation, the material removal measurement technique was applied to determine the residual stress of HA coating near the interface. Some important conclusions are obtained.

Analysis of temperature rise for piezoelectric transformer using finite-element method.

PubMed

Joo, Hyun-Woo; Lee, Chang-Hwan; Rho, Jong-Seok; Jung, Hyun-Kyo

2006-08-01

Analysis of heat problem and temperature field of a piezoelectric transformer, operated at steady-state conditions, is described. The resonance frequency of the transformer is calculated from impedance and electrical gain analysis using a finite-element method. Mechanical displacement and electric potential of the transformer at the calculated resonance frequency are used to calculate the loss distribution of the transformer. Temperature distribution using discretized heat transfer equation is calculated from the obtained losses of the transformer. Properties of the piezoelectric material, dependent on the temperature field, are measured to recalculate the losses, temperature distribution, and new resonance characteristics of the transformer. Iterative method is adopted to recalculate the losses and resonance frequency due to the changes of the material constants from temperature increase. Computed temperature distributions and new resonance characteristics of the transformer at steady-state temperature are verified by comparison with experimental results.

Residual stress and damage-induced critical fracture on CO2 laser treated fused silica

NASA Astrophysics Data System (ADS)

Matthews, M. J.; Stolken, J. S.; Vignes, R. M.; Norton, M. A.; Yang, S.; Cooke, J. D.; Guss, G. M.; Adams, J. J.

2009-10-01

Localized damage repair and polishing of silica-based optics using mid- and far-IR CO2 lasers has been shown to be an effective method for increasing optical damage threshold in the UV. However, it is known that CO2 laser heating of silicate surfaces can lead to a level of residual stress capable of causing critical fracture either during or after laser treatment. Sufficient control of the surface temperature as a function of time and position is therefore required to limit this residual stress to an acceptable level to avoid critical fracture. In this work we present the results of 351 nm, 3ns Gaussian damage growth experiments within regions of varying residual stress caused by prior CO2 laser exposures. Thermally stressed regions were non-destructively characterized using polarimetry and confocal Raman microscopy to measure the stress induced birefringence and fictive temperature respectively. For 1~40s square pulse CO2 laser exposures created over 0.5-1.25kW/cm2 with a 1-3mm 1/e2 diameter beam (Tmax~1500-3000K), the critical damage site size leading to fracture increases weakly with peak temperature, but shows a stronger dependence on cooling rate, as predicted by finite element hydrodynamics simulations. Confocal micro-Raman was used to probe structural changes to the glass over different thermal histories and indicated a maximum fictive temperature of 1900K for Tmax>=2000K. The effect of cooling rate on fictive temperature caused by CO2 laser heating are consistent with finite element calculations based on a Tool-Narayanaswamy relaxation model.

Vanishing spin stiffness in the spin-1/2 Heisenberg chain for any nonzero temperature

NASA Astrophysics Data System (ADS)

Carmelo, J. M. P.; Prosen, T.; Campbell, D. K.

2015-10-01

Whether at the zero spin density m =0 and finite temperatures T >0 the spin stiffness of the spin-1 /2 X X X chain is finite or vanishes remains an unsolved and controversial issue, as different approaches yield contradictory results. Here we explicitly compute the stiffness at m =0 and find strong evidence that it vanishes. In particular, we derive an upper bound on the stiffness within a canonical ensemble at any fixed value of spin density m that is proportional to m2L in the thermodynamic limit of chain length L →∞ , for any finite, nonzero temperature, which implies the absence of ballistic transport for T >0 for m =0 . Although our method relies in part on the thermodynamic Bethe ansatz (TBA), it does not evaluate the stiffness through the second derivative of the TBA energy eigenvalues relative to a uniform vector potential. Moreover, we provide strong evidence that in the thermodynamic limit the upper bounds on the spin current and stiffness used in our derivation remain valid under string deviations. Our results also provide strong evidence that in the thermodynamic limit the TBA method used by X. Zotos [Phys. Rev. Lett. 82, 1764 (1999), 10.1103/PhysRevLett.82.1764] leads to the exact stiffness values at finite temperature T >0 for models whose stiffness is finite at T =0 , similar to the spin stiffness of the spin-1 /2 Heisenberg chain but unlike the charge stiffness of the half-filled 1D Hubbard model.

Hyperbolic heat conduction, effective temperature, and third law for nonequilibrium systems with heat flux

NASA Astrophysics Data System (ADS)

Sobolev, S. L.

2018-02-01

Some analogies between different nonequilibrium heat conduction models, particularly random walk, the discrete variable model, and the Boltzmann transport equation with the single relaxation time approximation, have been discussed. We show that, under an assumption of a finite value of the heat carrier velocity, these models lead to the hyperbolic heat conduction equation and the modified Fourier law with relaxation term. Corresponding effective temperature and entropy have been introduced and analyzed. It has been demonstrated that the effective temperature, defined as a geometric mean of the kinetic temperatures of the heat carriers moving in opposite directions, acts as a criterion for thermalization and is a nonlinear function of the kinetic temperature and heat flux. It is shown that, under highly nonequilibrium conditions when the heat flux tends to its maximum possible value, the effective temperature, heat capacity, and local entropy go to zero even at a nonzero equilibrium temperature. This provides a possible generalization of the third law to nonequilibrium situations. Analogies and differences between the proposed effective temperature and some other definitions of a temperature in nonequilibrium state, particularly for active systems, disordered semiconductors under electric field, and adiabatic gas flow, have been shown and discussed. Illustrative examples of the behavior of the effective temperature and entropy during nonequilibrium heat conduction in a monatomic gas and a strong shockwave have been analyzed.

The analysis of temperature effect and temperature compensation of MOEMS accelerometer based on a grating interferometric cavity

NASA Astrophysics Data System (ADS)

Han, Dandan; Bai, Jian; Lu, Qianbo; Lou, Shuqi; Jiao, Xufen; Yang, Guoguang

2016-08-01

There is a temperature drift of an accelerometer attributed to the temperature variation, which would adversely influence the output performance. In this paper, a quantitative analysis of the temperature effect and the temperature compensation of a MOEMS accelerometer, which is composed of a grating interferometric cavity and a micromachined sensing chip, are proposed. A finite-element-method (FEM) approach is applied in this work to simulate the deformation of the sensing chip of the MOEMS accelerometer at different temperature from -20°C to 70°C. The deformation results in the variation of the distance between the grating and the sensing chip of the MOEMS accelerometer, modulating the output intensities finally. A static temperature model is set up to describe the temperature characteristics of the accelerometer through the simulation results and the temperature compensation is put forward based on the temperature model, which can improve the output performance of the accelerometer. This model is permitted to estimate the temperature effect of this type accelerometer, which contains a micromachined sensing chip. Comparison of the output intensities with and without temperature compensation indicates that the temperature compensation can improve the stability of the output intensities of the MOEMS accelerometer based on a grating interferometric cavity.

Recasting a model atomistic glassformer as a system of icosahedra

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pinney, Rhiannon; Bristol Centre for Complexity Science, University of Bristol, Bristol BS8 1TS; Liverpool, Tanniemola B.

2015-12-28

We consider a binary Lennard-Jones glassformer whose super-Arrhenius dynamics are correlated with the formation of icosahedral structures. Upon cooling, these icosahedra organize into mesoclusters. We recast this glassformer as an effective system of icosahedra which we describe with a population dynamics model. This model we parameterize with data from the temperature regime accessible to molecular dynamics simulations. We then use the model to determine the population of icosahedra in mesoclusters at arbitrary temperature. Using simulation data to incorporate dynamics into the model, we predict relaxation behavior at temperatures inaccessible to conventional approaches. Our model predicts super-Arrhenius dynamics whose relaxation timemore » remains finite for non-zero temperature.« less

Thermal response of Space Shuttle wing during reentry heating

NASA Technical Reports Server (NTRS)

Gong, L.; Ko, W. L.; Quinn, R. D.

1984-01-01

A structural performance and resizing (SPAR) finite element thermal analysis computer program was used in the heat transfer analysis of the space shuttle orbiter that was subjected to reentry aerodynamic heatings. One wing segment of the right wing (WS 240) and the whole left wing were selected for the thermal analysis. Results showed that the predicted thermal protection system (TPS) temperatures were in good agreement with the space transportation system, trajectory 5 (STS-5) flight-measured temperatures. In addition, calculated aluminum structural temperatures were in fairly good agreement with the flight data up to the point of touchdown. Results also showed that the internal free convection had a considerable effect on the change of structural temperatures after touchdown.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mensah, P.F.; Stubblefield, M.A.; Pang, S.S.

Thermal characterization of a prepreg fabric used as the bonding material to join composite pipes has been modeled and solved using finite difference modeling (FDM) numerical analysis technique for one dimensional heat transfer through the material. Temperature distributions within the composite pipe joint are predicted. The prepreg material has temperature dependent thermal properties. Thus the resulting boundary value equations are non linear and analytical solutions cannot be obtained. This characterization is pertinent in determining the temperature profile in the prepreg layer during the manufacturing process for optimization purposes. In addition, in order to assess the effects of induced thermal stressmore » in the joint, the temperature profile is needed. The methodology employed in this analysis compares favorably with data from experimentation.« less

Quantum Discord Preservation for Two Quantum-Correlated Qubits in Two Independent Reserviors

NASA Astrophysics Data System (ADS)

Xu, Lan

2018-03-01

We investigate the dynamics of quantum discord using an exactly solvable model where two qubits coupled to independent thermal environments. The quantum discord is employed as a non-classical correlation quantifier. By studying the quantum discord of a class of initial states, we find discord remains preserve for a finite time. The effects of the temperature, initial-state parameter, system-reservoir coupling constant and temperature difference parameter of the two independent reserviors are also investigated. We discover that the quantum nature loses faster in high temperature, however, one can extend the time of quantum nature by choosing smaller system-reservoir coupling constant, larger certain initial-state parameter and larger temperature difference parameter.

Finite temperature corrections to tachyon mass in intersecting D-branes

NASA Astrophysics Data System (ADS)

Sethi, Varun; Chowdhury, Sudipto Paul; Sarkar, Swarnendu

2017-04-01

We continue with the analysis of finite temperature corrections to the Tachyon mass in intersecting branes which was initiated in [1]. In this paper we extend the computation to the case of intersecting D3 branes by considering a setup of two intersecting branes in flat-space background. A holographic model dual to BCS superconductor consisting of intersecting D8 branes in D4 brane background was proposed in [2]. The background considered here is a simplified configuration of this dual model. We compute the one-loop Tachyon amplitude in the Yang-Mills approximation and show that the result is finite. Analyzing the amplitudes further we numerically compute the transition temperature at which the Tachyon becomes massless. The analytic expressions for the one-loop amplitudes obtained here reduce to those for intersecting D1 branes obtained in [1] as well as those for intersecting D2 branes.

A study of the diffusional behavior of a two-phase metal matrix composite exposed to a high temperature environment

NASA Technical Reports Server (NTRS)

Tenney, D. R.

1974-01-01

The progress of diffusion-controlled filament-matrix interaction in a metal matrix composite where the filaments and matrix comprise a two-phase binary alloy system was studied by mathematically modeling compositional changes resulting from prolonged elevated temperature exposure. The analysis treats a finite, diffusion-controlled, two-phase moving-interface problem by means of a variable-grid finite-difference technique. The Ni-W system was selected as an example system. Modeling was carried out for the 1000 to 1200 C temperature range for unidirectional composites containing from 6 to 40 volume percent tungsten filaments in a Ni matrix. The results are displayed to show both the change in filament diameter and matrix composition as a function of exposure time. Compositional profiles produced between first and second nearest neighbor filaments were calculated by superposition of finite-difference solutions of the diffusion equations.

Finite-temperature dynamic structure factor of the spin-1 XXZ chain with single-ion anisotropy

NASA Astrophysics Data System (ADS)

Lange, Florian; Ejima, Satoshi; Fehske, Holger

2018-02-01

Improving matrix-product state techniques based on the purification of the density matrix, we are able to accurately calculate the finite-temperature dynamic response of the infinite spin-1 XXZ chain with single-ion anisotropy in the Haldane, large-D , and antiferromagnetic phases. Distinct thermally activated scattering processes make a significant contribution to the spectral weight in all cases. In the Haldane phase, intraband magnon scattering is prominent, and the on-site anisotropy causes the magnon to split into singlet and doublet branches. In the large-D phase response, the intraband signal is separated from an exciton-antiexciton continuum. In the antiferromagnetic phase, holons are the lowest-lying excitations, with a gap that closes at the transition to the Haldane state. At finite temperatures, scattering between domain-wall excitations becomes especially important and strongly enhances the spectral weight for momentum transfer π .

Correlation of predicted and measured thermal stresses on an advanced aircraft structure with dissimilar materials. [hypersonic heating simulation

NASA Technical Reports Server (NTRS)

Jenkins, J. M.

1979-01-01

Additional information was added to a growing data base from which estimates of finite element model complexities can be made with respect to thermal stress analysis. The manner in which temperatures were smeared to the finite element grid points was examined from the point of view of the impact on thermal stress calculations. The general comparison of calculated and measured thermal stresses is guite good and there is little doubt that the finite element approach provided by NASTRAN results in correct thermal stress calculations. Discrepancies did exist between measured and calculated values in the skin and the skin/frame junctures. The problems with predicting skin thermal stress were attributed to inadequate temperature inputs to the structural model rather than modeling insufficiencies. The discrepancies occurring at the skin/frame juncture were most likely due to insufficient modeling elements rather than temperature problems.

Superconducting surface impedance under radiofrequency field

DOE PAGES

Xiao, Binping P.; Reece, Charles E.; Kelley, Michael J.

2013-04-26

Based on BCS theory with moving Cooper pairs, the electron states distribution at 0K and the probability of electron occupation with finite temperature have been derived and applied to anomalous skin effect theory to obtain the surface impedance of a superconductor under radiofrequency (RF) field. We present the numerical results for Nb and compare these with representative RF field-dependent effective surface resistance measurements from a 1.5 GHz resonant structure.

Application of mass spectrometer-inverse gas chromatography to study polymer-solvent diffusivity and solubility.

PubMed

Galdámez, J Román; Danner, Ronald P; Duda, J Larry

2007-07-20

The application of a mass spectrometer detector in capillary column inverse gas chromatography is shown to be a valuable tool in the measurement of diffusion and solubility in polymer-solvent systems. The component specific detector provides excellent results for binary polymer-solvent systems, but it is particularly valuable because it can be readily applied to multicomponent systems. Results for a number of infinitely dilute solvents in poly(vinyl acetate) (PVAc) are reported over a range of temperature from 60 to 150 degrees C. Results are also reported for finite concentrations of toluene and methanol in PVAc from 60 to 110 degrees C. Finally, the technique was applied to study the effect of finite concentrations of toluene on the diffusion coefficients of THF and cyclohexane in PVAc. The experimental data compare well with literature values for both infinite and finite concentrations, indicating that the experimental protocol described in this work is sound.

Predicting Print-thru for the Sub-scale Beryllium Mirror Demonstrator (SBMD)

NASA Technical Reports Server (NTRS)

Craig, Larry; J. Kevin Russell (Technical Monitor)

2002-01-01

This document presents a finite element method for predicting print-thru or quilting for a lightweight mirror in a low temperature environment. The mirror is represented with quadrilateral and triangular plate finite elements. The SBMD (Sub-scale Beryllium Mirror Demonstrator) is circular with a diameter of 50 cm and one flat side. The mirror structure is a thin-wall triangular cell core with a single facesheet. There is a 4 mm radius fillet between the facesheet and cell walls. It is made entirely of Beryllium. It is assumed that polishing the mirror surface creates a thin surface layer with different material properties. Finite element results are compared with measured values at cryogenic temperatures.

Transition to Quantum Turbulence and the Propagation of Vortex Loops at Finite Temperatures

NASA Astrophysics Data System (ADS)

Yamamoto, Shinji; Adachi, Hiroyuki; Tsubota, Makoto

2011-02-01

We performed numerical simulation of the transition to quantum turbulence and the propagation of vortex loops at finite temperatures in order to understand the experiments using vibrating wires in superfluid 4He by Yano et al. We injected vortex rings to a finite volume in order to simulate emission of vortices from the wire. When the injected vortices are dilute, they should decay by mutual friction. When they are dense, however, vortex tangle are generated through vortex reconnections and emit large vortex loops. The large vortex loops can travel a long distance before disappearing, which is much different from the dilute case. The numerical results are consistent with the experimental results.

Discontinuous Galerkin (DG) Method for solving time dependent convection-diffusion type temperature equation : Demonstration and Comparison with Other Methods in the Mantle Convection Code ASPECT

NASA Astrophysics Data System (ADS)

He, Y.; Puckett, E. G.; Billen, M. I.; Kellogg, L. H.

2016-12-01

For a convection-dominated system, like convection in the Earth's mantle, accurate modeling of the temperature field in terms of the interaction between convective and diffusive processes is one of the most common numerical challenges. In the geodynamics community using Finite Element Method (FEM) with artificial entropy viscosity is a popular approach to resolve this difficulty, but introduce numerical diffusion. The extra artificial viscosity added into the temperature system will not only oversmooth the temperature field where the convective process dominates, but also change the physical properties by increasing the local material conductivity, which will eventually change the local conservation of energy. Accurate modeling of temperature is especially important in the mantle, where material properties are strongly dependent on temperature. In subduction zones, for example, the rheology of the cold sinking slab depends nonlinearly on the temperature, and physical processes such as slab detachment, rollback, and melting all are sensitively dependent on temperature and rheology. Therefore methods that overly smooth the temperature may inaccurately represent the physical processes governing subduction, lithospheric instabilities, plume generation and other aspects of mantle convection. Here we present a method for modeling the temperature field in mantle dynamics simulations using a new solver implemented in the ASPECT software. The new solver for the temperature equation uses a Discontinuous Galerkin (DG) approach, which combines features of both finite element and finite volume methods, and is particularly suitable for problems satisfying the conservation law, and the solution has a large variation locally. Furthermore, we have applied a post-processing technique to insure that the solution satisfies a local discrete maximum principle in order to eliminate the overshoots and undershoots in the temperature locally. To demonstrate the capabilities of this new method we present benchmark results (e.g., falling sphere), and a simple subduction models with kinematic surface boundary condition. To evaluate the trade-offs in computational speed and solution accuracy we present results for the same benchmarks using the Finite Element entropy viscosity method available in ASPECT.

Superfluid density and condensate fraction in the BCS-BEC crossover regime at finite temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fukushima, N.; Ohashi, Y.; Faculty of Science and Technology, Keio University, Hiyoshi, Yokohama 223

2007-03-15

The superfluid density is a fundamental quantity describing the response to a rotation as well as in two-fluid collisional hydrodynamics. We present extensive calculations of the superfluid density {rho}{sub s} in the BCS-BEC crossover regime of a uniform superfluid Fermi gas at finite temperatures. We include strong-coupling or fluctuation effects on these quantities within a Gaussian approximation. We also incorporate the same fluctuation effects into the BCS single-particle excitations described by the superfluid order parameter {delta} and Fermi chemical potential {mu}, using the Nozieres-Schmitt-Rink approximation. This treatment is shown to be necessary for consistent treatment of {rho}{sub s} over themore » entire BCS-BEC crossover. We also calculate the condensate fraction N{sub c} as a function of the temperature, a quantity which is quite different from the superfluid density {rho}{sub s}. We show that the mean-field expression for the condensate fraction N{sub c} is a good approximation even in the strong-coupling BEC regime. Our numerical results show how {rho}{sub s} and N{sub c} depend on temperature, from the weak-coupling BCS region to the BEC region of tightly bound Cooper pair molecules. In a companion paper [Phys. Rev. A 74, 063626 (2006)], we derive an equivalent expression for {rho}{sub s} from the thermodynamic potential, which exhibits the role of the pairing fluctuations in a more explicit manner.« less

Dark-soliton dynamics in Bose-Einstein condensates at finite temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jackson, B.; Proukakis, N. P.; Barenghi, C. F.

2007-05-15

The dynamics of a dark soliton in an elongated Bose-Einstein condensate is studied at finite temperatures. In addition to accurately reproducing all stages of the decay of the soliton observed in the experiment of Burger et al. [Phys. Rev. Lett. 83, 5198 (1999)], our numerical simulations reveal the existence of an experimentally accessible parameter regime for which phase-imprinted dark solitons can execute at least one full axial oscillation prior to their decay. The dependence of the decay time scale on temperature and initial soliton depth is analyzed and the role of interatomic collisions quantified.

Charmonium ground and excited states at finite temperature from complex Borel sum rules

NASA Astrophysics Data System (ADS)

Araki, Ken-Ji; Suzuki, Kei; Gubler, Philipp; Oka, Makoto

2018-05-01

Charmonium spectral functions in vector and pseudoscalar channels at finite temperature are investigated through the complex Borel sum rules and the maximum entropy method. Our approach enables us to extract the peaks corresponding to the excited charmonia, ψ‧ and ηc‧ , as well as those of the ground states, J / ψ and ηc, which has never been achieved in usual QCD sum rule analyses. We show the spectral functions in vacuum and their thermal modification around the critical temperature, which leads to the almost simultaneous melting (or peak disappearance) of the ground and excited states.

Properties of highly frustrated magnetic molecules studied by the finite-temperature Lanczos method

NASA Astrophysics Data System (ADS)

Schnack, J.; Wendland, O.

2010-12-01

The very interesting magnetic properties of frustrated magnetic molecules are often hardly accessible due to the prohibitive size of the related Hilbert spaces. The finite-temperature Lanczos method is able to treat spin systems for Hilbert space sizes up to 109. Here we first demonstrate for exactly solvable systems that the method is indeed accurate. Then we discuss the thermal properties of one of the biggest magnetic molecules synthesized to date, the icosidodecahedron with antiferromagnetically coupled spins of s = 1/2. We show how genuine quantum features such as the magnetization plateau behave as a function of temperature.

Chiral symmetry restoration at finite temperature and chemical potential in the improved ladder approximation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taniguchi, Y.; Yoshida, Y.

1997-02-01

The chiral symmetry of QCD is studied at finite temperature and chemical potential using the Schwinger-Dyson equation in the improved ladder approximation. We calculate three order parameters: the vacuum expectation value of the quark bilinear operator, the pion decay constant, and the quark mass gap. We have a second order phase transition at the temperature T{sub c}=169 MeV along the zero chemical potential line, and a first order phase transition at the chemical potential {mu}{sub c}=598 MeV along the zero temperature line. We also calculate the critical exponents of the three order parameters. {copyright} {ital 1997} {ital The American Physicalmore » Society}« less

Temperature distribution of thick thermoset composites

NASA Astrophysics Data System (ADS)

Guo, Zhan-Sheng; Du, Shanyi; Zhang, Boming

2004-05-01

The development of temperature distribution of thick polymeric matrix laminates during an autoclave vacuum bag process was measured and compared with numerically calculated results. The finite element formulation of the transient heat transfer problem was carried out for polymeric matrix composite materials from the heat transfer differential equations including internal heat generation produced by exothermic chemical reactions. Software based on the general finite element software package was developed for numerical simulation of the entire composite process. From the experimental and numerical results, it was found that the measured temperature profiles were in good agreement with the numerical ones, and conventional cure cycles recommended by prepreg manufacturers for thin laminates should be modified to prevent temperature overshoot.

Some Finite Difference Solutions of the Laminar Compressible Boundary Layer Showing the Effects of Upstream Transpiration Cooling

NASA Technical Reports Server (NTRS)

Howe, John T.

1959-01-01

Three numerical solutions of the partial differential equations describing the compressible laminar boundary layer are obtained by the finite difference method described in reports by I. Flugge-Lotz, D.C. Baxter, and this author. The solutions apply to steady-state supersonic flow without pressure gradient, over a cold wall and over an adiabatic wall, both having transpiration cooling upstream, and over an adiabatic wall with upstream cooling but without upstream transpiration. It is shown that for a given upstream wall temperature, upstream transpiration cooling affords much better protection to the adiabatic solid wall than does upstream cooling without transpiration. The results of the numerical solutions are compared with those of approximate solutions. The thermal results of the finite difference solution lie between the results of Rubesin and Inouye, and those of Libby and Pallone. When the skin-friction results of one finite difference solution are used in the thermal analysis of Rubesin and Inouye, improved agreement between the thermal results of the two methods of solution is obtained.

Durability of Structural Adhesively Bonded System.

DTIC Science & Technology

1981-06-01

Composites , Finite Element Method. II DURABILITY OF STRUCTURAL ADHESIVELY BONDED SYSTEMS TABLE OF CONTENTS 1. Introduction...That investigation was mainly devoted to the temperature effects in time on the mechanical behavior of fiber-reinforced plastic (FRP) composites and...ervironmental-loading history on the mechanical performance of similar FRP composites (which may serve as adherends in structural bcnded systems). That

3DHYDROGEOCHEM: A 3-DIMENSIONAL MODEL OF DENSITY-DEPENDENT SUBSURFACE FLOW AND THERMAL MULTISPECIES-MULTICOMPONENT HYDROGEOCHEMICAL TRANSPORT (EPA/600/SR-98/159)

EPA Science Inventory

This report presents a three-dimensional finite-element numerical model designed to simulate chemical transport in subsurface systems with temperature effect taken into account. The three-dimensional model is developed to provide (1) a tool of application, with which one is able ...

Photoacoustic and luminescence spectroscopy of benzil crystals

NASA Astrophysics Data System (ADS)

Bonno, B.; Laporte, J. L.; Rousset, Y.

1991-06-01

In the present work, both photoacoustic and luminescence techniques were employed to study molecular crystals. This paper presents an extension of the standard Rosencwaig-Gersho photoacoustic model to molecular crystals, which includes finite-deexcitation-time effects and excited-state populations. In the temperature range 100-300 K, the phosphorescence quantum yield and thermal diffusivity of benzil crystals were determined.

New Flexible Channels for Room Temperature Tunneling Field Effect Transistors.

PubMed

Hao, Boyi; Asthana, Anjana; Hazaveh, Paniz Khanmohammadi; Bergstrom, Paul L; Banyai, Douglas; Savaikar, Madhusudan A; Jaszczak, John A; Yap, Yoke Khin

2016-02-05

Tunneling field effect transistors (TFETs) have been proposed to overcome the fundamental issues of Si based transistors, such as short channel effect, finite leakage current, and high contact resistance. Unfortunately, most if not all TFETs are operational only at cryogenic temperatures. Here we report that iron (Fe) quantum dots functionalized boron nitride nanotubes (QDs-BNNTs) can be used as the flexible tunneling channels of TFETs at room temperatures. The electrical insulating BNNTs are used as the one-dimensional (1D) substrates to confine the uniform formation of Fe QDs on their surface as the flexible tunneling channel. Consistent semiconductor-like transport behaviors under various bending conditions are detected by scanning tunneling spectroscopy in a transmission electron microscopy system (in-situ STM-TEM). As suggested by computer simulation, the uniform distribution of Fe QDs enable an averaging effect on the possible electron tunneling pathways, which is responsible for the consistent transport properties that are not sensitive to bending.

The Effect of Spray Initial Conditions on Heat Release and Emissions in LDI CFD Calculations

NASA Technical Reports Server (NTRS)

Iannetti, Anthony C.; Liu, Nan-Suey; Davoudzadeh, Farhad

2008-01-01

The mass and velocity distribution of liquid spray has a primary effect on the combustion heat release process. This heat release process then affects emissions like nitrogen oxides (NOx) and carbon monoxide (CO). Computational Fluid Dynamics gives the engineer insight into these processes, but various setup options exist (number of droplet groups, and initial droplet temperature) for spray initial conditions. This paper studies these spray initial condition options using the National Combustion Code (NCC) on a single swirler lean direct injection (LDI) flame tube. Using laminar finite rate chemistry, comparisons are made against experimental data for velocity measurements, temperature, and emissions (NOx, CO).

First principles calculation of finite temperature magnetism in Fe and Fe3C

NASA Astrophysics Data System (ADS)

Eisenbach, M.; Nicholson, D. M.; Rusanu, A.; Brown, G.

2011-04-01

Density functional calculations have proven to be a useful tool in the study of ground state properties of many materials. The investigation of finite temperature magnetism, on the other hand, has to rely usually on the usage of empirical models that allow the large number of evaluations of the systems Hamiltonian that are required to obtain the phase space sampling needed to obtain the free energy, specific heat, magnetization, susceptibility, and other quantities as function of temperature. We have demonstrated a solution to this problem that harnesses the computational power of today's large massively parallel computers by combining a classical Wang-Landau Monte-Carlo calculation [F. Wang and D. P. Landau, Phys. Rev. Lett. 86, 2050 (2001)] with our first principles multiple scattering electronic structure code [Y. Wang et al., Phys. Rev. Lett. 75, 2867 (1995)] that allows the energy calculation of constrained magnetic states [M. Eisenbach et al., Proceedings of the Conference on High Performance Computing, Networking, Storage and Analysis (ACM, New York, 2009)]. We present our calculations of finite temperature properties of Fe and Fe3C using this approach and we find the Curie temperatures to be 980 and 425K, respectively.

Ground State and Finite Temperature Lanczos Methods

NASA Astrophysics Data System (ADS)

Prelovšek, P.; Bonča, J.

The present review will focus on recent development of exact- diagonalization (ED) methods that use Lanczos algorithm to transform large sparse matrices onto the tridiagonal form. We begin with a review of basic principles of the Lanczos method for computing ground-state static as well as dynamical properties. Next, generalization to finite-temperatures in the form of well established finite-temperature Lanczos method is described. The latter allows for the evaluation of temperatures T>0 static and dynamic quantities within various correlated models. Several extensions and modification of the latter method introduced more recently are analysed. In particular, the low-temperature Lanczos method and the microcanonical Lanczos method, especially applicable within the high-T regime. In order to overcome the problems of exponentially growing Hilbert spaces that prevent ED calculations on larger lattices, different approaches based on Lanczos diagonalization within the reduced basis have been developed. In this context, recently developed method based on ED within a limited functional space is reviewed. Finally, we briefly discuss the real-time evolution of correlated systems far from equilibrium, which can be simulated using the ED and Lanczos-based methods, as well as approaches based on the diagonalization in a reduced basis.

On the ab initio calculation of vibrational formation entropy of point defect: the case of the silicon vacancy

NASA Astrophysics Data System (ADS)

Seeberger, Pia; Vidal, Julien

2017-08-01

Formation entropy of point defects is one of the last crucial elements required to fully describe the temperature dependence of point defect formation. However, while many attempts have been made to compute them for very complicated systems, very few works have been carried out such as to assess the different effects of finite size effects and precision on such quantity. Large discrepancies can be found in the literature for a system as primitive as the silicon vacancy. In this work, we have proposed a systematic study of formation entropy for silicon vacancy in its 3 stable charge states: neutral, +2 and -2 for supercells with size not below 432 atoms. Rationalization of the formation entropy is presented, highlighting importance of finite size error and the difficulty to compute such quantities due to high numerical requirement. It is proposed that the direct calculation of formation entropy of VSi using first principles methods will be plagued by very high computational workload (or large numerical errors) and finite size dependent results.

Analysis of turbulent free jet hydrogen-air diffusion flames with finite chemical reaction rates

NASA Technical Reports Server (NTRS)

Sislian, J. P.

1978-01-01

The nonequilibrium flow field resulting from the turbulent mixing and combustion of a supersonic axisymmetric hydrogen jet in a supersonic parallel coflowing air stream is analyzed. Effective turbulent transport properties are determined using the (K-epsilon) model. The finite-rate chemistry model considers eight reactions between six chemical species, H, O, H2O, OH, O2, and H2. The governing set of nonlinear partial differential equations is solved by an implicit finite-difference procedure. Radial distributions are obtained at two downstream locations of variables such as turbulent kinetic energy, turbulent dissipation rate, turbulent scale length, and viscosity. The results show that these variables attain peak values at the axis of symmetry. Computed distributions of velocity, temperature, and mass fraction are also given. A direct analytical approach to account for the effect of species concentration fluctuations on the mean production rate of species (the phenomenon of unmixedness) is also presented. However, the use of the method does not seem justified in view of the excessive computer time required to solve the resulting system of equations.

On the formulation and assessment of flamelet-generated manifolds applied to two-phase turbulent combustion

NASA Astrophysics Data System (ADS)

Bojko, Brian T.

Accounting for the effects of finite rate chemistry in reacting flows is intractable when considering the number of species and reactions to be solved for during a large scale flow simulation. This is especially complicated when solid/liquid fuels are also considered. While modeling the reacting boundary layer with the use of finite-rate chemistry may allow for a highly accurate description of the coupling between the flame and fuel surface, it is not tractable in large scale simulations when considering detailed chemical kinetics. It is the goal of this research to investigate a Flamelet-Generated Manifold (FGM) method in order to reduce the finite rate chemistry to a lookup table cataloged by progress variables and queried during runtime. In this study, simplified unsteady 1D flames with mass blowing are considered for a solid biomass fuel where the FGM method is employed as a model reduction strategy for potential application to multidimensional calculations. Two types of FGM are considered. The first are a set of steady-state flames differentiated by their scalar dissipation rate. Results show the use of steady flames produce unacceptable errors compared to the finite-rate chemistry solution, with temperature errors in excess of 45%. To avoid these errors, a new methodology for developing an unsteady FGM (UFGM) is presented that accounts for unsteady diffusion effects and greatly reduces errors in temperature with differences that are under 10%. The FGM modeling is then extended to individual droplet combustion with the development of a Droplet Flamelet-Generated Manifold (DFGM) to account for the effects of finite-rate chemistry of individual droplets. A spherically symmetric droplet model is developed for methanol and aluminum. The inclusion of finite-rate chemistry allows the capturing of the transition from diffusion to kinetically controlled combustion as the droplet diameter decreases. The droplet model is then used to create a DFGM by successively solving the 1D flame equations at varying drop sizes, where the source terms for energy, mixture fraction, and progress variable are cataloged as a function of normalized diameter. A unique coupling of the DFGM and planar UFGM is developed and is used to account for individual and gas phase combustion processes in turbulent combustion situations, such as spray flames, particle laden blasts, etc. The DFGM for the methanol and aluminum droplets are used in mixed Eulerian and Eulerian-Lagrangian formulations of compressible multiphase flows. System level simulations are conducted and compared experimental data for a methanol spray flame and an aluminized blast studied at the Explosives Components Facility (ECF) at Sandia National Laboratories.

Surface thermochemical effects on TPS-coupled aerothermodynamics in hypersonic Martian gas flow

NASA Astrophysics Data System (ADS)

Yang, Xiaofeng; Gui, Yewei; Tang, Wei; Du, Yanxia; Liu, Lei; Xiao, Guangming; Wei, Dong

2018-06-01

This paper deals with the surface thermochemical effects on TPS-coupled aerothermodynamics in hypersonic Martian gas flow. An interface condition with finite-rate thermochemistry was established to balance the three-dimensional Navier-Stokes solver and TPS thermal response solver, and a series of coupled simulations of chemical non-equilibrium aerothermodynamics and structure heat transfer with various surface catalycities were performed for hypersonic Mars entries. The analysis of surface thermochemistry reveals that the surface chemical reactions have great contribution to aerodynamic heating, and the temperature-dependence of finite-rate catalysis highly influences the evolution of the coupling aerodynamic heating in the coupling process. For fixed free stream parameters with proper catalytic excitation energy, a "leap" phenomenon of the TPS-coupled heat flux with the coupling time appears in the initial stage of the coupling process, due to the strong thermochemical effects on the TPS surface.

Thermo-mechanically coupled fracture analysis of shape memory alloys using the extended finite element method

NASA Astrophysics Data System (ADS)

Hatefi Ardakani, S.; Ahmadian, H.; Mohammadi, S.

2015-04-01

In this paper, the extended finite element method is used for fracture analysis of shape memory alloys for both cases of super elastic and shape memory effects. Heat generation during the forward and reverse phase transformations can lead to temperature variation in the material because of strong thermo-mechanical coupling, which significantly influences the SMA mechanical behavior. First, the stationary crack mode is studied and the effects of loading rate on material behavior in the crack tip are examined. Then, the crack propagation analysis is performed in the presence of an initial crack by adopting a weighted averaging criterion, where the direction of crack propagation is determined by weighted averaging of effective stresses at all the integration points in the vicinity of the crack tip. Finally, several numerical examples are analyzed and the obtained results are compared with the available reference results.

Effects of variable electrical conductivity and thermal conductivity on unsteady MHD free convection flow past an exponential accelerated inclined plate

NASA Astrophysics Data System (ADS)

Rana, B. M. Jewel; Ahmed, Rubel; Ahmmed, S. F.

2017-06-01

An analysis is carried out to investigate the effects of variable viscosity, thermal radiation, absorption of radiation and cross diffusion past an inclined exponential accelerated plate under the influence of variable heat and mass transfer. A set of suitable transformations has been used to obtain the non-dimensional coupled governing equations. Explicit finite difference technique has been used to solve the obtained numerical solutions of the present problem. Stability and convergence of the finite difference scheme have been carried out for this problem. Compaq Visual Fortran 6.6a has been used to calculate the numerical results. The effects of various physical parameters on the fluid velocity, temperature, concentration, coefficient of skin friction, rate of heat transfer, rate of mass transfer, streamlines and isotherms on the flow field have been presented graphically and discussed in details.

Histological and Finite Element Analysis of Cell Death due to Irreversible Electroporation

PubMed Central

Long, G.; Bakos, G.; Shires, P. K.; Gritter, L.; Crissman, J. W.; Harris, J. L.; Clymer, J. W.

2014-01-01

Irreversible electroporation (IRE) has been shown to be an effective method of killing cells locally. In contrast to radiofrequency ablation, the mechanism by which cells are thought to die via IRE is the creation of pores in cell membranes, without substantial increase in tissue temperature. To determine the degree to which cell death is non-thermal, we evaluated IRE in porcine hepatocytes in vivo. Using pulse widths of 10μs, bursts of 3 kV square-wave pulses were applied through a custom probe to the liver of an anesthetized pig. Affected tissue was evaluated histologically via stainings of hematoxylin & eosin (H&E), nitroblue tetrazolium (NBT) to monitor cell respiration and TUNEL to gauge apoptosis. Temperature was measured during the application of electroporation, and heat transfer was modeled via finite element analysis. Cell death was calculated via Arrhenius kinetics. Four distinct zones were observed within the ring return electrode; heat-fixed tissue, coagulation, necrotic, and viable. The Arrhenius damage integral estimated complete cell death only in the first zone, where the temperature exceeded 70°C, and partial or no cell death in the other zones, where maximum temperature was approximately 45°C. Except for a limited area near the electrode tip, cell death in IRE is predominantly due to a non-thermal mechanism. PMID:24000980

Non-linear dual-phase-lag model for analyzing heat transfer phenomena in living tissues during thermal ablation.

PubMed

Kumar, P; Kumar, Dinesh; Rai, K N

2016-08-01

In this article, a non-linear dual-phase-lag (DPL) bio-heat transfer model based on temperature dependent metabolic heat generation rate is derived to analyze the heat transfer phenomena in living tissues during thermal ablation treatment. The numerical solution of the present non-linear problem has been done by finite element Runge-Kutta (4,5) method which combines the essence of Runge-Kutta (4,5) method together with finite difference scheme. Our study demonstrates that at the thermal ablation position temperature predicted by non-linear and linear DPL models show significant differences. A comparison has been made among non-linear DPL, thermal wave and Pennes model and it has been found that non-linear DPL and thermal wave bio-heat model show almost same nature whereas non-linear Pennes model shows significantly different temperature profile at the initial stage of thermal ablation treatment. The effect of Fourier number and Vernotte number (relaxation Fourier number) on temperature profile in presence and absence of externally applied heat source has been studied in detail and it has been observed that the presence of externally applied heat source term highly affects the efficiency of thermal treatment method. Copyright © 2016 Elsevier Ltd. All rights reserved.

First-principles thermodynamics study of phase stability in inorganic halide perovskite solid solutions

NASA Astrophysics Data System (ADS)

Bechtel, Jonathon S.; Van der Ven, Anton

2018-04-01

Halide substitution gives rise to a tunable band gap as a function of composition in halide perovskite materials. However, photoinduced phase segregation, observed at room temperature in mixed halide A Pb (IxBr1-x) 3 systems, limits open circuit voltages and decreases photovoltaic device efficiencies. We investigate equilibrium phase stability of orthorhombic P n m a γ -phase CsM (XxY1-x) 3 perovskites where M is Pb or Sn, and X and Y are Br, Cl, or I. Finite-temperature phase diagrams are constructed using a cluster expansion effective Hamiltonian parameterized from first-principles density-functional-theory calculations. Solid solution phases for CsM (IxBr1-x) 3 and CsM (BrxCl1-x) 3 are predicted to be stable well below room temperature while CsM (IxCl1-x) 3 systems have miscibility gaps that extend above 400 K. The height of the miscibility gap correlates with the difference in volume between end members. Also layered ground states are found on the convex hull at x =2 /3 for CsSnBr2Cl ,CsPbI2Br , and CsPbBrCl2. The impact of these ground states on the finite temperature phase diagram is discussed in the context of the experimentally observed photoinduced phase segregation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ryabov, E.G.; Adeev, G.D.

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, ismore » 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.« less

The effect of temporary reductions in incubation temperature on growth characteristics and lipid utilisation in the chick embryo

PubMed Central

FEAST, M.; NOBLE, R. C.; SPEAKE, B. K.; FERGUSON, M. W. J.

1998-01-01

The effect(s) of finite exposure(s) to 22.0 °C on embryo weight gain, 3rd tarsus length, transfer of lipid from the yolk and uptake of specific lipid components by the liver, were measured in the chick embryo. Embryo growth was completely suspended over the period of temperature reduction, but resumed unimpaired when the optimum temperature of 37.5 °C was restored. Two successive periods of embryonic exposure to 22.0 °C (36 h at d 3 followed by 24 at d 10) were additive in their effect on growth retardation. Embryos subjected to temperature reductions on d 3 of incubation displayed significant changes in lipid concentrations and polyunsaturated fatty acid profiles within the liver when measured at d 18 of incubation. Yolk lipid uptake was significantly reduced but not suspended by embryonic exposure to 22.0 °C. It is suggested that the observed suspension of embryonic development was the result of a temperature dependent reduction in metabolism according to a Q10∼2, which is typical of an ectothermic organism. PMID:9877293

The effects of chemical kinetics and wall temperature on performance of porous media burners

NASA Astrophysics Data System (ADS)

mohammadi, Iman; Hossainpour, Siamak

2013-06-01

This paper reports a two-dimensional numerical prediction of premixed methane-air combustion in inert porous media burner by using of four multi-step mechanisms: GRI-3.0 mechanism, GRI-2.11 mechanism and the skeletal and 17 Species mechanisms. The effects of these models on temperature, chemical species and pollutant emissions are studied. A two-dimensional axisymmetric model for premixed methane-air combustion in porous media burner has developed. The finite volume method has used to solve the governing equations of methane-air combustion in inert porous media burner. The results indicate that the present four models have the same accuracy in predicting temperature profiles and the difference between these profiles is not more than 2 %. In addition, the Gri-3.0 mechanism shows the best prediction of NO emission in comparison with experimental data. The 17 Species mechanism shows good agreement in prediction of temperature and pollutant emissions with GRI-3.0, GRI-2.11 and the skeletal mechanisms. Also the effects of wall temperature on the gas temperature and mass fraction of species such as NO and CH4 are studied.

Thermal-Mechanical Response of Cracked Satin Weave CFRP Composites at Cryogenic Temperatures

NASA Astrophysics Data System (ADS)

Watanabe, S.; Shindo, Y.; Narita, F.; Takeda, T.

2008-03-01

This paper examines the thermal-mechanical response of satin weave carbon fiber reinforced polymer (CFRP) laminates with internal and/or edge cracks subjected to uniaxial tension load at cryogenic temperatures. Cracks are considered to occur in the transverse fiber bundles and extend through the entire thickness of the fiber bundles. Two-dimentional generalized plane strain finite element models are developed to study the effects of residual thermal stresses and cracks on the mechanical behavior of CFRP woven laminates. A detailed examination of the Young's modulus and stress distributions near the crack tip is carried out which provides insight into material behavior at cryogenic temperatures.

Designing shape-memory Heusler alloys from first-principles

NASA Astrophysics Data System (ADS)

Siewert, M.; Gruner, M. E.; Dannenberg, A.; Chakrabarti, A.; Herper, H. C.; Wuttig, M.; Barman, S. R.; Singh, S.; Al-Zubi, A.; Hickel, T.; Neugebauer, J.; Gillessen, M.; Dronskowski, R.; Entel, P.

2011-11-01

The phase diagrams of magnetic shape-memory Heusler alloys, in particular, ternary Ni-Mn-Z and quarternary (Pt, Ni)-Mn-Z alloys with Z = Ga, Sn, have been addressed by density functional theory and Monte Carlo simulations. Finite temperature free energy calculations show that the phonon contribution stabilizes the high-temperature austenite structure while at low temperatures magnetism and the band Jahn-Teller effect favor the modulated monoclinic 14M or the nonmodulated tetragonal structure. The substitution of Ni by Pt leads to a series of magnetic shape-memory alloys with very similar properties to Ni-Mn-Ga but with a maximal eigenstrain of 14%.

Thermal corrections to the Casimir energy in a general weak gravitational field

NASA Astrophysics Data System (ADS)

Nazari, Borzoo

2016-12-01

We calculate finite temperature corrections to the energy of the Casimir effect of a two conducting parallel plates in a general weak gravitational field. After solving the Klein-Gordon equation inside the apparatus, mode frequencies inside the apparatus are obtained in terms of the parameters of the weak background. Using Matsubara’s approach to quantum statistical mechanics gravity-induced thermal corrections of the energy density are obtained. Well-known weak static and stationary gravitational fields are analyzed and it is found that in the low temperature limit the energy of the system increases compared to that in the zero temperature case.

The effect of numerical methods on the simulation of mid-ocean ridge hydrothermal models

NASA Astrophysics Data System (ADS)

Carpio, J.; Braack, M.

2012-01-01

This work considers the effect of the numerical method on the simulation of a 2D model of hydrothermal systems located in the high-permeability axial plane of mid-ocean ridges. The behavior of hot plumes, formed in a porous medium between volcanic lava and the ocean floor, is very irregular due to convective instabilities. Therefore, we discuss and compare two different numerical methods for solving the mathematical model of this system. In concrete, we consider two ways to treat the temperature equation of the model: a semi-Lagrangian formulation of the advective terms in combination with a Galerkin finite element method for the parabolic part of the equations and a stabilized finite element scheme. Both methods are very robust and accurate. However, due to physical instabilities in the system at high Rayleigh number, the effect of the numerical method is significant with regard to the temperature distribution at a certain time instant. The good news is that relevant statistical quantities remain relatively stable and coincide for the two numerical schemes. The agreement is larger in the case of a mathematical model with constant water properties. In the case of a model with nonlinear dependence of the water properties on the temperature and pressure, the agreement in the statistics is clearly less pronounced. Hence, the presented work accentuates the need for a strengthened validation of the compatibility between numerical scheme (accuracy/resolution) and complex (realistic/nonlinear) models.

Bose-Einstein condensation in atomic alkali gases

NASA Astrophysics Data System (ADS)

Dodd, Robert J.

1998-05-01

I present a review of the time-independent Gross-Pitaevskii (GP), Bogoliubov, and finite-temperature Hartree-Fock-Bogoliubov (HFB) mean-field theories used to study trapped, Bose-Einstein condensed alkali gases. Numerical solutions of the (zero-temperature) GP equation are presented for attractive (negative scattering length) and repulsive (positive scattering length) interactions. Comparison is made with the Thomas-Fermi and (variational) trial wavefunction appr oximations that are used in the literature to study condensed gases. Numerical calculations of the (zero-temperature) Bogoliubov quasi-particle excitation frequencies are found to be in excellent agreement with the experimental results. The finite-temperature properties of condensed gases are examined using the Popov approximation (of the HFB theory) and a simple two-gas model. Specific, quantitative comparisons are made with experimental results for finite-temperature excitation frequencies. Qualitative comparisons are made between the results of the Popov approximation, two-gas model, and other published models for condensate fraction and thermal density distribution. The time-independent mean-field theories are found to be in excellent agreement with experimental results at relatively low temperatures (high condensate fractions). However, at higher temperatures (and condensate fractions of less than 50%) there are significant discrepancies between experimental data and theoretical calculations. This work was undertaken at the University of Maryland at College Park and was supported in part by the National Science Foundation (PHY-9601261) and the U.S. Office of Naval Research.

Size effects and realiability of barium strontium titanate thin films

NASA Astrophysics Data System (ADS)

Parker, Charles Bernard

Thin films of (Ba,Sr)TiO3 (BST) deposited by Liquid Source MOCVD were investigated. BST is a candidate dielectric for future-generation DRAM and as a tunable dielectric. Two areas of both scientific and commercial interest were investigated. The first area is the effect of decreasing dimension on ferroelectric properties. Several theories of size effects in ferroelectrics were evaluated. The dielectric response of a set of BST films of thicknesses from 15 to 580 nm was measured from 85 to 580 K. These films were extensively characterized and the boundary conditions that often influence size effects measurements were considered, including strain, finite screening length in the electrode, depolarization fields in the ferroelectric, atmospheric effects, control of stochiometry, and others. The data set was compared to the theoretical predictions and it was determined that Finite Size Scaling provided the best fit to the data. Using this theory, the predicted dielectric response was compared to the requirements of future generations of DRAM and was found to be sufficient, if film strain can be controlled. The second area is reliability. The types of lifetime-limiting electrical failure observed in BST are resistance degradation, time dependant dielectric breakdown (tddb), and noisy breakdown. Previous work on BST reliability has largely focused on resistance degradation at high temperature. This condition is only a small subset of experimental space. This work extends the understanding of BST failure into the low temperature regime and evaluates the effects of both DC and AC stress. It was found that tddb is the dominant failure mode at low temperature and resistance degradation is the dominant failure modes at high temperature. Synthesizing this work with previous work on resistance degradation allowed a failure framework to be developed. Rigorous extrapolation of resistance degradation and tddb lifetimes was compared to the requirements of future generations of DRAM and was found that while resistance degradation will not limit device lifetimes, tddb will. Refinement of BST processing will be necessary to reduce the defect causing tddb failure.

Transient thermal, hydraulic, and mechanical analysis of a counter flow offset strip fin intermediate heat exchanger using an effective porous media approach

NASA Astrophysics Data System (ADS)

Urquiza, Eugenio

This work presents a comprehensive thermal hydraulic analysis of a compact heat exchanger using offset strip fins. The thermal hydraulics analysis in this work is followed by a finite element analysis (FEA) to predict the mechanical stresses experienced by an intermediate heat exchanger (IHX) during steady-state operation and selected flow transients. In particular, the scenario analyzed involves a gas-to-liquid IHX operating between high pressure helium and liquid or molten salt. In order to estimate the stresses in compact heat exchangers a comprehensive thermal and hydraulic analysis is needed. Compact heat exchangers require very small flow channels and fins to achieve high heat transfer rates and thermal effectiveness. However, studying such small features computationally contributes little to the understanding of component level phenomena and requires prohibitive computational effort using computational fluid dynamics (CFD). To address this issue, the analysis developed here uses an effective porous media (EPM) approach; this greatly reduces the computation time and produces results with the appropriate resolution [1]. This EPM fluid dynamics and heat transfer computational code has been named the Compact Heat Exchanger Explicit Thermal and Hydraulics (CHEETAH) code. CHEETAH solves for the two-dimensional steady-state and transient temperature and flow distributions in the IHX including the complicating effects of temperature-dependent fluid thermo-physical properties. Temperature- and pressure-dependent fluid properties are evaluated by CHEETAH and the thermal effectiveness of the IHX is also calculated. Furthermore, the temperature distribution can then be imported into a finite element analysis (FEA) code for mechanical stress analysis using the EPM methods developed earlier by the University of California, Berkeley, for global and local stress analysis [2]. These simulation tools will also allow the heat exchanger design to be improved through an iterative design process which will lead to a design with a reduced pressure drop, increased thermal effectiveness, and improved mechanical performance as it relates to creep deformation and transient thermal stresses.

Measurement of Temperature and Soil Properties for Finite Element Model Verification

DOT National Transportation Integrated Search

2012-08-01

In recent years, ADOT&PF personnel have used TEMP/W, a commercially available two-dimensional finite element program, to conduct thermal modeling of various : embankment configurations in an effort to reduce the thawing of ice-rich permafrost through...

Excitations in the Yang–Gaudin Bose gas

DOE PAGES

Robinson, Neil J.; Konik, Robert M.

2017-06-01

Here, we study the excitation spectrum of two-component delta-function interacting bosons confined to a single spatial dimension, the Yang–Gaudin Bose gas. We show that there are pronounced finite-size effects in the dispersion relations of excitations, perhaps best illustrated by the spinon single particle dispersion which exhibits a gap at 2k F and a finite-momentum roton-like minimum. Such features occur at energies far above the finite volume excitation gap, vanish slowly as 1/L for fixed spinon number, and can persist to the thermodynamic limit at fixed spinon density. Features such as the 2k F gap also persist to multi-particle excitation continua. Our results show that excitations in the finite system can behave in a qualitatively different manner to analogous excitations in the thermodynamic limit. The Yang–Gaudin Bose gas is also host to multi-spinon bound states, known asmore » $$\\Lambda$$ -strings. We study these excitations both in the thermodynamic limit under the string hypothesis and in finite size systems where string deviations are taken into account. In the zero-temperature limit we present a simple relation between the length n $$\\Lambda$$-string dressed energies $$\\epsilon_n(\\lambda)$$ and the dressed energy $$\\epsilon(k)$$. We solve the Yang–Yang–Takahashi equations numerically and compare to the analytical solution obtained under the strong couple expansion, revealing that the length n $$\\Lambda$$ -string dressed energy is Lorentzian over a wide range of real string centers λ in the vicinity of $$\\lambda = 0$$ . We then examine the finite size effects present in the dispersion of the two-spinon bound states by numerically solving the Bethe ansatz equations with string deviations.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robinson, Neil J.; Konik, Robert M.

Here, we study the excitation spectrum of two-component delta-function interacting bosons confined to a single spatial dimension, the Yang–Gaudin Bose gas. We show that there are pronounced finite-size effects in the dispersion relations of excitations, perhaps best illustrated by the spinon single particle dispersion which exhibits a gap at 2k F and a finite-momentum roton-like minimum. Such features occur at energies far above the finite volume excitation gap, vanish slowly as 1/L for fixed spinon number, and can persist to the thermodynamic limit at fixed spinon density. Features such as the 2k F gap also persist to multi-particle excitation continua. Our results show that excitations in the finite system can behave in a qualitatively different manner to analogous excitations in the thermodynamic limit. The Yang–Gaudin Bose gas is also host to multi-spinon bound states, known asmore » $$\\Lambda$$ -strings. We study these excitations both in the thermodynamic limit under the string hypothesis and in finite size systems where string deviations are taken into account. In the zero-temperature limit we present a simple relation between the length n $$\\Lambda$$-string dressed energies $$\\epsilon_n(\\lambda)$$ and the dressed energy $$\\epsilon(k)$$. We solve the Yang–Yang–Takahashi equations numerically and compare to the analytical solution obtained under the strong couple expansion, revealing that the length n $$\\Lambda$$ -string dressed energy is Lorentzian over a wide range of real string centers λ in the vicinity of $$\\lambda = 0$$ . We then examine the finite size effects present in the dispersion of the two-spinon bound states by numerically solving the Bethe ansatz equations with string deviations.« less

Cyclic fatigue analysis of rocket thrust chambers. Volume 1: OFHC copper chamber low cycle fatigue

NASA Technical Reports Server (NTRS)

Miller, R. W.

1974-01-01

A three-dimensional finite element elasto-plastic strain analysis was performed for the throat section of a regeneratively cooled rocket combustion chamber. The analysis employed the RETSCP finite element computer program. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the chamber operating cycle. The analysis was performed for chamber configuration and operating conditions corresponding to a hydrogen-oxygen combustion chamber which was fatigue tested to failure. The computed strain range at typical chamber operating conditions was used in conjunction with oxygen-free, high-conductivity (OHFC) copper isothermal fatigue test data to predict chamber low-cycle fatigue life.

An adaptive approach to the physical annealing strategy for simulated annealing

NASA Astrophysics Data System (ADS)

Hasegawa, M.

2013-02-01

A new and reasonable method for adaptive implementation of simulated annealing (SA) is studied on two types of random traveling salesman problems. The idea is based on the previous finding on the search characteristics of the threshold algorithms, that is, the primary role of the relaxation dynamics in their finite-time optimization process. It is shown that the effective temperature for optimization can be predicted from the system's behavior analogous to the stabilization phenomenon occurring in the heating process starting from a quenched solution. The subsequent slow cooling near the predicted point draws out the inherent optimizing ability of finite-time SA in more straightforward manner than the conventional adaptive approach.

Numerical solution for the temperature distribution in a cooled guide vane blade of a radial gas turbine

NASA Technical Reports Server (NTRS)

Hosny, W. M.; Tabakoff, W.

1977-01-01

A two dimensional finite difference numerical technique is presented to determine the temperature distribution of an internal cooled blade of radial turbine guide vanes. A simple convection cooling is assumed inside the guide vane blade. Such cooling has relatively small cooling effectiveness at the leading edge and at the trailing edge. Heat transfer augmentation in these critical areas may be achieved by using impingement jets and film cooling. A computer program is written in FORTRAN IV for IBM 370/165 computer.

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.

Solution accuracies of finite element reentry heat transfer and thermal stress analyses of Space Shuttle Orbiter

NASA Technical Reports Server (NTRS)

Ko, William L.

1988-01-01

Accuracies of solutions (structural temperatures and thermal stresses) obtained from different thermal and structural FEMs set up for the Space Shuttle Orbiter (SSO) are compared and discussed. For studying the effect of element size on the solution accuracies of heat-transfer and thermal-stress analyses of the SSO, five SPAR thermal models and five NASTRAN structural models were set up for wing midspan bay 3. The structural temperature distribution over the wing skin (lower and upper) surface of one bay was dome shaped and induced more severe thermal stresses in the chordwise direction than in the spanwise direction. The induced thermal stresses were extremely sensitive to slight variation in structural temperature distributions. Both internal convention and internal radiation were found to have equal effects on the SSO.

Optimization of bone drilling parameters using Taguchi method based on finite element analysis

NASA Astrophysics Data System (ADS)

Rosidi, Ayip; Lenggo Ginta, Turnad; Rani, Ahmad Majdi Bin Abdul

2017-05-01

Thermal necrosis results fracture problems and implant failure if temperature exceeds 47 °C for one minute during bone drilling. To solve this problem, this work studied a new thermal model by using three drilling parameters: drill diameter, feed rate and spindle speed. Effects of those parameters to heat generation were studied. The drill diameters were 4 mm, 6 mm and 6 mm; the feed rates were 80 mm/min, 100 mm/min and 120 mm/min whereas the spindle speeds were 400 rpm, 500 rpm and 600 rpm then an optimization was done by Taguchi method to which combination parameter can be used to prevent thermal necrosis during bone drilling. The results showed that all the combination of parameters produce confidence results which were below 47 °C and finite element analysis combined with Taguchi method can be used for predicting temperature generation and optimizing bone drilling parameters prior to clinical bone drilling. All of the combination parameters can be used for surgeon to achieve sustainable orthopaedic surgery.

First-principles theory of cation and intercalation ordering in Li xCoO 2

NASA Astrophysics Data System (ADS)

Wolverton, C.; Zunger, Alex

Several types of cation- and vacancy-ordering are of interest in the Li xCoO 2 battery cathode material since they can have a profound effect on the battery voltage. We present a first-principles theoretical approach which can be used to calculate both cation- and vacancy-ordering patterns at both zero and finite temperatures. This theory also provides quantum-mechanical predictions (i.e., without the use of any experimental input) of battery voltages of both ordered and disordered Li xCoO 2/Li cells from the energetics of the Li intercalation reactions. Our calculations allow us to search the entire configurational space to predict the lowest-energy ground-state structures, search for large voltage cathodes, explore metastable low-energy states, and extend our calculations to finite temperatures, thereby searching for order-disorder transitions and states of partial disorder. We present the first prediction of the stable spinel structure LiCo 2O 4 for the 50% delithiated Li 0.5CoO 2.

Numerical Simulation of a Solar Domestic Hot Water System

NASA Astrophysics Data System (ADS)

Mongibello, L.; Bianco, N.; Di Somma, M.; Graditi, G.; Naso, V.

2014-11-01

An innovative transient numerical model is presented for the simulation of a solar Domestic Hot Water (DHW) system. The solar collectors have been simulated by using a zerodimensional analytical model. The temperature distributions in the heat transfer fluid and in the water inside the tank have been evaluated by one-dimensional models. The reversion elimination algorithm has been used to include the effects of natural convection among the water layers at different heights in the tank on the thermal stratification. A finite difference implicit scheme has been implemented to solve the energy conservation equation in the coil heat exchanger, and the energy conservation equation in the tank has been solved by using the finite difference Euler implicit scheme. Energy conservation equations for the solar DHW components models have been coupled by means of a home-made implicit algorithm. Results of the simulation performed using as input data the experimental values of the ambient temperature and the solar irradiance in a summer day are presented and discussed.

An analysis of a charring ablator with thermal nonequilibrium, chemical kinetics, and mass transfer

NASA Technical Reports Server (NTRS)

Clark, R. K.

1973-01-01

The differential equations governing the transient response of a one-dimensional ablative thermal protection system are presented for thermal nonequilibrium between the pyrolysis gases and the char layer and with finite rate chemical reactions occurring. The system consists of three layers (the char layer, the uncharred layer, and an optical insulation layer) with concentrated heat sinks at the back surface and between the second and third layers. The equations are solved numerically by using a modified implicit finite difference scheme to obtain solutions for the thickness of the charred and uncharred layers, surface recession and pyrolysis rates, solid temperatures, porosity profiles, and profiles of pyrolysis-gas temperature, pressure, composition, and flow rate. Good agreement is obtained between numerical results and exact solutions for a number of simplified cases. The complete numerical analysis is used to obtain solutions for an ablative system subjected to a constant heating environment. Effects of thermal, chemical, and mass transfer processes are shown.

Thermal Analysis of the NASA Integrated Vehicle Health Monitoring Experiment Technology for X-Vehicles (NITEX)

NASA Technical Reports Server (NTRS)

Hegab, Hisham E.

2002-01-01

The purpose of this project was to perform a thermal analysis for the NASA Integrated Vehicle Health Monitoring (IVHM) Technology Experiment for X-vehicles (NITEX). This electronics package monitors vehicle sensor information in flight and downlinks vehicle health summary information via telemetry. The experiment will be tested on the X-34 in an unpressurized compartment, in the vicinity of one of the vehicle's liquid oxygen tanks. The transient temperature profile for the electronics package has been determined using finite element analysis for possible mission profiles that will most likely expose the package to the most extreme hot and cold environmental conditions. From the analyses, it was determined that temperature limits for the electronics would be exceeded for the worst case cold environment mission profile. The finite element model used for the analyses was modified to examine the use of insulation to address this problem. Recommendations for insulating the experiment for the cold environment are presented, and were analyzed to determine their effect on a nominal mission profile.

Thermal Analysis Of The NASA Integrated Vehicle Health Monitoring Experiment Technology For X-Vehicles (NITEX)

NASA Technical Reports Server (NTRS)

Hegab, Hisham E.

2001-01-01

The purpose of this project was to perform a thermal analysis for the NASA Integrated Vehicle Health Monitoring (IVHM) Technology Experiment for X-vehicles (NITEX). This electronics package monitors vehicle sensor information in flight and downlinks vehicle health summary information via telemetry. The experiment will be tested on the X-34 in an unpressurized compartment, in the vicinity of one of the vehicle's liquid oxygen tanks. The transient temperature profile for the electronics package has been determined using finite element analysis for possible mission profiles that will most likely expose the package to the most extreme hot and cold environmental conditions. From the analyses, it was determined that temperature limits for the electronics would be exceeded for the worst case cold environment mission profile. The finite element model used for the analyses was modified to examine the use of insulation to address this problem. Recommendations for insulating the experiment for the cold environment are presented, and were analyzed to determine their effect on a nominal mission profile.

Computer simulation of the relationship between selected properties of laser remelted tool steel surface layer

NASA Astrophysics Data System (ADS)

Bonek, Mirosław; Śliwa, Agata; Mikuła, Jarosław

2016-12-01

Investigations >The language in this paper has been slightly changed. Please check for clarity of thought, and that the meaning is still correct, and amend if necessary.include Finite Element Method simulation model of remelting of PMHSS6-5-3 high-speed steel surface layer using the high power diode laser (HPDL). The Finite Element Method computations were performed using ANSYS software. The scope of FEM simulation was determination of temperature distribution during laser alloying process at various process configurations regarding the laser beam power and method of powder deposition, as pre-coated past or surface with machined grooves. The Finite Element Method simulation was performed on five different 3-dimensional models. The model assumed nonlinear change of thermal conductivity, specific heat and density that were depended on temperature. The heating process was realized as heat flux corresponding to laser beam power of 1.4, 1.7 and 2.1 kW. Latent heat effects are considered during solidification. The molten pool is composed of the same material as the substrate and there is no chemical reaction. The absorptivity of laser energy was dependent on the simulated materials properties and their surface condition. The Finite Element Method simulation allows specifying the heat affected zone and the temperature distribution in the sample as a function of time and thus allows the estimation of the structural changes taking place during laser remelting process. The simulation was applied to determine the shape of molten pool and the penetration depth of remelted surface. Simulated penetration depth and molten pool profile have a good match with the experimental results. The depth values obtained in simulation are very close to experimental data. Regarding the shape of molten pool, the little differences have been noted. The heat flux input considered in simulation is only part of the mechanism for heating; thus, the final shape of solidified molten pool will depend on more variables.

Estimating the composition of hydrates from a 3D seismic dataset near Penghu Canyon on Chinese passive margin offshore Taiwan

NASA Astrophysics Data System (ADS)

Chi, Wu-Cheng

2016-04-01

A bottom-simulating reflector (BSR), representing the base of the gas hydrate stability zone, can be used to estimate geothermal gradients under seafloor. However, to derive temperature estimates at the BSR, the correct hydrate composition is needed to calculate the phase boundary. Here we applied the method by Minshull and Keddie to constrain the hydrate composition and the pore fluid salinity. We used a 3D seismic dataset offshore SW Taiwan to test the method. Different from previous studies, we have considered the effects of 3D topographic effects using finite element modelling and also depth-dependent thermal conductivity. Using a pore water salinity of 2% at the BSR depth as found from the nearby core samples, we successfully used 99% methane and 1% ethane gas hydrate phase boundary to derive a sub-bottom depth vs. temperature plot which is consistent with the seafloor temperature from in-situ measurements. The results are also consistent with geochemical analyses of the pore fluids. The derived regional geothermal gradient is 40.1oC/km, which is similar to 40oC/km used in the 3D finite element modelling used in this study. This study is among the first documented successful use of Minshull and Keddie's method to constrain seafloor gas hydrate composition.

Finite Element Analysis of the Random Response Suppression of Composite Panels at Elevated Temperatures using Shape Memory Alloy Fibers

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.

Natural convection with evaporation in a vertical cylindrical cavity under the effect of temperature-dependent surface tension

NASA Astrophysics Data System (ADS)

Kozhevnikov, Danil A.; Sheremet, Mikhail A.

2018-01-01

The effect of surface tension on laminar natural convection in a vertical cylindrical cavity filled with a weak evaporating liquid has been analyzed numerically. The cylindrical enclosure is insulated at the bottom, heated by a constant heat flux from the side, and cooled by a non-uniform evaporative heat flux from the top free surface having temperature-dependent surface tension. Governing equations with corresponding boundary conditions formulated in dimensionless stream function, vorticity, and temperature have been solved by finite difference method of the second-order accuracy. The influence of Rayleigh number, Marangoni number, and aspect ratio on the liquid flow and heat transfer has been studied. Obtained results have revealed that the heat transfer rate at free surface decreases with Marangoni number and increases with Rayleigh number, while the average temperature inside the cavity has an opposite behavior; namely, it growths with Marangoni number and reduces with Rayleigh number.

Nonlinear mesomechanics of composites with periodic microstructure

NASA Technical Reports Server (NTRS)

Walker, Kevin P.; Jordan, Eric H.; Freed, Alan D.

1989-01-01

This work is concerned with modeling the mechanical deformation or constitutive behavior of composites comprised of a periodic microstructure under small displacement conditions at elevated temperature. A mesomechanics approach is adopted which relates the microimechanical behavior of the heterogeneous composite with its in-service macroscopic behavior. Two different methods, one based on a Fourier series approach and the other on a Green's function approach, are used in modeling the micromechanical behavior of the composite material. Although the constitutive formulations are based on a micromechanical approach, it should be stressed that the resulting equations are volume averaged to produce overall effective constitutive relations which relate the bulk, volume averaged, stress increment to the bulk, volume averaged, strain increment. As such, they are macromodels which can be used directly in nonlinear finite element programs such as MARC, ANSYS and ABAQUS or in boundary element programs such as BEST3D. In developing the volume averaged or efective macromodels from the micromechanical models, both approaches will require the evaluation of volume integrals containing the spatially varying strain distributions throughout the composite material. By assuming that the strain distributions are spatially constant within each constituent phase-or within a given subvolume within each constituent phase-of the composite material, the volume integrals can be obtained in closed form. This simplified micromodel can then be volume averaged to obtain an effective macromodel suitable for use in the MARC, ANSYS and ABAQUS nonlinear finite element programs via user constitutive subroutines such as HYPELA and CMUSER. This effective macromodel can be used in a nonlinear finite element structural analysis to obtain the strain-temperature history at those points in the structure where thermomechanical cracking and damage are expected to occur, the so called damage critical points of the structure.

Temperature Dependence Of Elastic Constants Of Polymers

NASA Technical Reports Server (NTRS)

Simha, Robert; Papazoglou, Elisabeth

1989-01-01

Two papers extend theory of elastic constants of disordered solids to finite temperatures below glass-transition temperatures. First paper, entitled "Elastic Constants of Disordered Solids II: Temperature Dependence," applies to cryogenic temperatures. Second paper, entitled "Theory of Thermoelastic Properties for Polymer Glasses," develops unified treatment for static compressional and elongational properties at temperatures up to glass-transition temperatures.

The effect of nonlinear propagation on heating of tissue: A numerical model of diagnostic ultrasound beams

NASA Astrophysics Data System (ADS)

Cahill, Mark D.; Humphrey, Victor F.; Doody, Claire

2000-07-01

Thermal safety indices for diagnostic ultrasound beams are calculated under the assumption that the sound propagates under linear conditions. A non-axisymmetric finite difference model is used to solve the KZK equation, and so to model the beam of a diagnostic scanner in pulsed Doppler mode. Beams from both a uniform focused rectangular source and a linear array are considered. Calculations are performed in water, and in attenuating media with tissue-like characteristics. Attenuating media are found to exhibit significant nonlinear effects for finite-amplitude beams. The resulting loss of intensity by the beam is then used as the source term in a model of tissue heating to estimate the maximum temperature rises. These are compared with the thermal indices, derived from the properties of the water-propagated beams.

Finite Element Simulation and Experimental Verification of Internal Stress of Quenched AISI 4140 Cylinders

NASA Astrophysics Data System (ADS)

Liu, Yu; Qin, Shengwei; Hao, Qingguo; Chen, Nailu; Zuo, Xunwei; Rong, Yonghua

2017-03-01

The study of internal stress in quenched AISI 4140 medium carbon steel is of importance in engineering. In this work, the finite element simulation (FES) was employed to predict the distribution of internal stress in quenched AISI 4140 cylinders with two sizes of diameter based on exponent-modified (Ex-Modified) normalized function. The results indicate that the FES based on Ex-Modified normalized function proposed is better consistent with X-ray diffraction measurements of the stress distribution than FES based on normalized function proposed by Abrassart, Desalos and Leblond, respectively, which is attributed that Ex-Modified normalized function better describes transformation plasticity. Effect of temperature distribution on the phase formation, the origin of residual stress distribution and effect of transformation plasticity function on the residual stress distribution were further discussed.

Finite size effects in ferroelectric-semiconductor thin films under open-circuit electric boundary conditions

DOE PAGES

Eliseev, Eugene A.; Kalinin, Sergei V.; Morozovska, Anna N.

2015-01-21

General features of finite size effects in the ferroelectric-semiconductor film under open-circuit electric boundary conditions are analyzed using Landau-Ginzburg-Devonshire theory and continuum media electrostatics. The temperature dependence of the film critical thickness, spontaneous polarization and depolarization field profiles of the open-circuited films are found to be significantly different from the characteristics of short-circuited ones. In particular, we predict the re-entrant type transition boundary between the mono-domain and poly-domain ferroelectric states due to reduced internal screening efficiency and analyzed possible experimental scenarios created by this mechanism. Performed analysis is relevant for the quantitative description of free-standing ferroelectric films phase diagrams andmore » polar properties. Also our results can be useful for the explanation of the scanning-probe microscopy experiments on free ferroelectric surfaces.« less

User-defined Material Model for Thermo-mechanical Progressive Failure Analysis

NASA Technical Reports Server (NTRS)

Knight, Norman F., Jr.

2008-01-01

Previously a user-defined material model for orthotropic bimodulus materials was developed for linear and nonlinear stress analysis of composite structures using either shell or solid finite elements within a nonlinear finite element analysis tool. Extensions of this user-defined material model to thermo-mechanical progressive failure analysis are described, and the required input data are documented. The extensions include providing for temperature-dependent material properties, archival of the elastic strains, and a thermal strain calculation for materials exhibiting a stress-free temperature.

Spectral functions at small energies and the electrical conductivity in hot quenched lattice QCD.

PubMed

Aarts, Gert; Allton, Chris; Foley, Justin; Hands, Simon; Kim, Seyong

2007-07-13

In lattice QCD, the maximum entropy method can be used to reconstruct spectral functions from Euclidean correlators obtained in numerical simulations. We show that at finite temperature the most commonly used algorithm, employing Bryan's method, is inherently unstable at small energies and gives a modification that avoids this. We demonstrate this approach using the vector current-current correlator obtained in quenched QCD at finite temperature. Our first results indicate a small electrical conductivity above the deconfinement transition.

Finite-temperature Gutzwiller approximation from the time-dependent variational principle

NASA Astrophysics Data System (ADS)

Lanatà, Nicola; Deng, Xiaoyu; Kotliar, Gabriel

2015-08-01

We develop an extension of the Gutzwiller approximation to finite temperatures based on the Dirac-Frenkel variational principle. Our method does not rely on any entropy inequality, and is substantially more accurate than the approaches proposed in previous works. We apply our theory to the single-band Hubbard model at different fillings, and show that our results compare quantitatively well with dynamical mean field theory in the metallic phase. We discuss potential applications of our technique within the framework of first-principle calculations.

Finite Element Modeling of Reheat Stretch Blow Molding of PET

NASA Astrophysics Data System (ADS)

Krishnan, Dwarak; Dupaix, Rebecca B.

2004-06-01

Poly (ethylene terephthalate) or PET is a polymer used as a packaging material for consumer products such as beverages, food or other liquids, and in other applications including drawn fibers and stretched films. Key features that make it widely used are its transparency, dimensional stability, gas impermeability, impact resistance, and high stiffness and strength in certain preferential directions. These commercially useful properties arise from the fact that PET crystallizes upon deformation above the glass transition temperature. Additionally, this strain-induced crystallization causes the deformation behavior of PET to be highly sensitive to processing conditions. It is thus crucial for engineers to be able to predict its performance at various process temperatures, strain rates and strain states so as to optimize the manufacturing process. In addressing these issues; a finite element analysis of the reheat blow molding process with PET has been carried out using ABAQUS. The simulation employed a constitutive model for PET developed by Dupaix and Boyce et al.. The model includes the combined effects of molecular orientation and strain-induced crystallization on strain hardening when the material is deformed above the glass transition temperature. The simulated bottles were also compared with actual blow molded bottles to evaluate the validity of the simulation.

The Master Equation for Two-Level Accelerated Systems at Finite Temperature

NASA Astrophysics Data System (ADS)

Tomazelli, J. L.; Cunha, R. O.

2016-10-01

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.

Finite element model of the temperature increase in excised porcine cadaver iris during direct illumination by femtosecond laser pulses

PubMed Central

Sun, Hui; Kurtz, Ronald M.

2012-01-01

Abstract. In order to model the thermal effect of laser exposure of the iris during laser corneal surgery, we simulated the temperature increase in porcine cadaver iris. The simulation data for the 60 kHz FS60 Laser showed that the temperature increased up to 1.23°C and 2.45°C (at laser pulse energy 1 and 2 µJ, respectively) by the 24 second procedure time. Calculated temperature profiles show good agreement with data obtained from ex vivo experiments using porcine cadaver iris. Simulation results of different types of femtosecond lasers indicate that the Laser in situ keratomileusis procedure does not present a safety hazard to the iris. PMID:22894525

A mixed pseudospectral/finite difference method for a thermally driven fluid in a nonuniform gravitational field

NASA Technical Reports Server (NTRS)

Macaraeg, M. G.

1985-01-01

A numerical study of the steady, axisymmetric flow in a heated, rotating spherical shell is conducted to model the Atmospheric General Circulation Experiment (AGCE) proposed to run aboard a later shuttle mission. The AGCE will consist of concentric rotating spheres confining a dielectric fluid. By imposing a dielectric field across the fluid a radial body force will be created. The numerical solution technique is based on the incompressible Navier-Stokes equations. In the method a pseudospectral technique is based on the incompressible Navier-Stokes equations. In the method a pseudospectral technique is used in the latitudinal direction, and a second-order accurate finite difference scheme discretizes time and radial derivatives. This paper discusses the development and performance of this numerical scheme for the AGCE which has been modelled in the past only by pure FD formulations. In addition, previous models have not investigated the effect of using a dielectric force to simulate terrestrial gravity. The effect of this dielectric force on the flow field is investigated as well as a parameter study of varying rotation rates and boundary temperatures. Among the effects noted are the production of larger velocities and enhanced reversals of radial temperature gradients for a body force generated by the electric field.

Local structural ordering in surface-confined liquid crystals

NASA Astrophysics Data System (ADS)

Śliwa, I.; Jeżewski, W.; Zakharov, A. V.

2017-06-01

The effect of the interplay between attractive nonlocal surface interactions and attractive pair long-range intermolecular couplings on molecular structures of liquid crystals confined in thin cells with flat solid surfaces has been studied. Extending the McMillan mean field theory to include finite systems, it has been shown that confining surfaces can induce complex orientational and translational ordering of molecules. Typically, local smectic A, nematic, and isotropic phases have been shown to coexist in certain temperature ranges, provided that confining cells are sufficiently thick, albeit finite. Due to the nonlocality of surface interactions, the spatial arrangement of these local phases can display, in general, an unexpected complexity along the surface normal direction. In particular, molecules located in the vicinity of surfaces can still be organized in smectic layers, even though nematic and/or isotropic order can simultaneously appear in the interior of cells. The resulting surface freezing of smectic layers has been confirmed to occur even for rather weak surface interactions. The surface interactions cannot, however, prevent smectic layers from melting relatively close to system boundaries, even when molecules are still arranged in layers within the central region of the system. The internal interfaces, separating individual liquid-crystal phases, are demonstrated here to form fronts of local finite-size transitions that move across cells under temperature changes. Although the complex molecular ordering in surface confined liquid-crystal systems can essentially be controlled by temperature variations, specific thermal properties of these systems, especially the nature of the local transitions, are argued to be strongly conditioned to the degree of molecular packing.

Analyzing the effect of tool edge radius on cutting temperature in micro-milling process

NASA Astrophysics Data System (ADS)

Liang, Y. C.; Yang, K.; Zheng, K. N.; Bai, Q. S.; Chen, W. Q.; Sun, G. Y.

2010-10-01

Cutting heat is one of the important physical subjects in the cutting process. Cutting heat together with cutting temperature produced by the cutting process will directly have effects on the tool wear and the life as well as on the workpiece processing precision and surface quality. The feature size of the workpiece is usually several microns. Thus, the tiny changes of cutting temperature will affect the workpiece on the surface quality and accuracy. Therefore, cutting heat and temperature generated in micro-milling will have significantly different effect than the one in the traditional tools cutting. In this paper, a two-dimensional coupled thermal-mechanical finite element model is adopted to determine thermal fields and cutting temperature during the Micro-milling process, by using software Deform-2D. The effect of tool edge radius on effective stress, effective strain, velocity field and cutting temperature distribution in micro-milling of aluminum alloy Al2024-T6 were investigated and analyzed. Also, the transient cutting temperature distribution was simulated dynamically. The simulation results show that the cutting temperature in Micro-milling is lower than those occurring in conventional milling processes due to the small loads and low cutting velocity. With increase of tool edge radius, the maximum temperature region gradually occurs on the contact region between finished surfaced and flank face of micro-cutter, instead of the rake face or the corner of micro-cutter. And this phenomenon shows an obvious size effect.

Chiral interface at the finite temperature transition point of QCD

NASA Technical Reports Server (NTRS)

Frei, Z.; Patkos, A.

1990-01-01

The domain wall between coexisting chirally symmetric and broken symmetry regions is studied in a saddle point approximation to the effective three-flavor sigma model. In the chiral limit the surface tension varies in the range ((40 to -50)MeV)(exp 3). The width of the domain wall is estimated to be approximately or equal to 4.5 fm.

A thermo-fluid analysis in magnetic hyperthermia

NASA Astrophysics Data System (ADS)

Iordana, Astefanoaei; Ioan, Dumitru; Alexandra, Stancu; Horia, Chiriac

2014-04-01

In the last years, hyperthermia induced by the heating of magnetic nanoparticles (MNPs) in an alternating magnetic field received considerable attention in cancer therapy. The thermal effects could be automatically controlled by using MNPs with selective magnetic absorption properties. In this paper, we analyze the temperature field determined by the heating of MNPs, injected in a malignant tissue, subjected to an alternating magnetic field. The main parameters which have a strong influence on temperature field are analyzed. The temperature evolution within healthy and tumor tissues are analyzed by finite element method (FEM) simulations in a thermo-fluid model. The cooling effect produced by blood flow in blood vessels from the tumor is considered. A thermal analysis is conducted under different distributions of MNP injection sites. The interdependence between the optimum dose of the nanoparticles and various types of tumors is investigated in order to understand their thermal effect on hyperthermia therapy. The control of the temperature field in the tumor and healthy tissues is an important step in the healing treatment.

Studying the effects of the heat stress on the various layers of human skin using damage function

NASA Astrophysics Data System (ADS)

Aijaz, Mir; Khanday, M. A.

2016-03-01

This paper develops a model to identify the effects of thermal stress on temperature distribution and damage in human dermal regions. The design and selection of the model takes into account many factors effecting the temperature distribution of skin, e.g., thermal conductance, perfusion, metabolic heat generation and thermal protective capabilities of the skin. The transient temperature distribution within the region is simulated using a two-dimensional finite element model of the Pennes’ bioheat equation. The relationship between temperature and time is integrated to view the damage caused to human skin by using Henriques’ model Henriques, F. C., Arch. Pathol. 43 (1947) 489-502]. The Henriques’ damage model is found to be more desirable for use in predicting the threshold of thermal damage. This work can be helpful in both emergency medicines as well as to plastic surgeon in deciding upon a course of action for the treatment of different burn injuries.

Counting states and the Hadron Resonance Gas: Does X(3872) count?

NASA Astrophysics Data System (ADS)

Ortega, Pablo G.; Entem, David R.; Fernández, Francisco; Ruiz Arriola, Enrique

2018-06-01

We analyze how the renowned X(3872), a weakly bound state right below the DDbar* threshold, should effectively be included in a hadronic representation of the QCD partition function. This can be decided by analyzing the DDbar* scattering phase-shifts in the JPC =1++ channel and their contribution to the level density in the continuum from which the abundance in a hot medium can be determined. We show that in a purely molecular picture the bound state contribution cancels the continuum providing a vanishing occupation number density at finite temperature and the X (3872) does not count below the Quark-Gluon Plasma crossover happening at T ∼ 150 MeV. In contrast, within a coupled-channels approach, for a non vanishing c c bar content the cancellation does not occur due to the onset of the X (3940) which effectively counts as an elementary particle for temperatures above T ≳ 250 MeV. Thus, a direct inclusion of the X (3872) in the Hadron Resonance Gas is not justified. We also estimate the role of this cancellation in X(3872) production in heavy-ion collision experiments in terms of the corresponding pT distribution due to a finite energy resolution.

Thermal analysis of epidermal electronic devices integrated with human skin considering the effects of interfacial thermal resistance

NASA Astrophysics Data System (ADS)

Li, Yuhang; Zhang, Jianpeng; Xing, Yufeng; Song, Jizhou

2018-05-01

Epidermal electronic devices (EEDs) have similar mechanical properties as those of human skin such that they can be integrated with human skin for potential applications in monitoring of human vital signs for diagnostic, therapeutic or surgical functions. Thermal management is critical for EEDs in these applications since excessive heating may cause discomfort. Comprehensive analytical studies, finite element analysis and experiments are carried out to study the effects of interfacial thermal resistance between EEDs and human skin on thermal properties of the EED/skin system in this paper. The coupling between the Fourier heat transfer in EEDs and the bio-heat transfer in human skin is accounted in the analytical model based on the transfer matrix method to give accurate predictions on temperatures, which agree well with finite element analysis and experimental measurements. It is shown that the maximum temperature increase of the EED for the case of imperfect bonding between EED and skin is much higher than that of perfect bonding. These results may help the design of EEDs in bi-integrated applications and suggest a valuable route to evaluate the bonding condition between EEDs and biological tissues.

Early-Stage Aggregation of Human Islet Amyloid Polypeptide

NASA Astrophysics Data System (ADS)

Guo, Ashley; de Pablo, Juan

Human islet amyloid polypeptide (hIAPP, or human amylin) is implicated in the development of type II diabetes. hIAPP is known to aggregate into amyloid fibrils; however, it is prefibrillar oligomeric species, rather than mature fibrils, that are proposed to be cytotoxic. In order to better understand the role of hIAPP aggregation in the onset of disease, as well as to design effective diagnostics and therapeutics, it is crucial to understand the mechanism of early-stage hIAPP aggregation. In this work, we use atomistic molecular dynamics simulations combined with multiple advanced sampling techniques to examine the formation of the hIAPP dimer and trimer. Metadynamics calculations reveal a free energy landscape for the hIAPP dimer, which suggest multiple possible transition pathways. We employ finite temperature string method calculations to identify favorable pathways for dimer and trimer formation, along with relevant free energy barriers and intermediate structures. Results provide valuable insights into the mechanisms and energetics of hIAPP aggregation. In addition, this work demonstrates that the finite temperature string method is an effective tool in the study of protein aggregation. Funded by National Institute of Standards and Technology.

Correlation of analytical and experimental hot structure vibration results

NASA Technical Reports Server (NTRS)

Kehoe, Michael W.; Deaton, Vivian C.

1993-01-01

High surface temperatures and temperature gradients can affect the vibratory characteristics and stability of aircraft structures. Aircraft designers are relying more on finite-element model analysis methods to ensure sufficient vehicle structural dynamic stability throughout the desired flight envelope. Analysis codes that predict these thermal effects must be correlated and verified with experimental data. Experimental modal data for aluminum, titanium, and fiberglass plates heated at uniform, nonuniform, and transient heating conditions are presented. The data show the effect of heat on each plate's modal characteristics, a comparison of predicted and measured plate vibration frequencies, the measured modal damping, and the effect of modeling material property changes and thermal stresses on the accuracy of the analytical results at nonuniform and transient heating conditions.

Effect of thermal and mechanical parameter’s damage numerical simulation cycling effects on defects in hot metal forming processes

NASA Astrophysics Data System (ADS)

El Amri, Abdelouahid; el yakhloufi Haddou, Mounir; Khamlichi, Abdellatif

2017-10-01

Damage mechanisms in hot metal forming processes are accelerated by mechanical stresses arising during Thermal and mechanical properties variations, because it consists of the materials with different thermal and mechanical loadings and swelling coefficients. In this work, 3D finite element models (FEM) are developed to simulate the effect of Temperature and the stresses on the model development, using a general purpose FE software ABAQUS. Explicit dynamic analysis with coupled Temperature displacement procedure is used for a model. The purpose of this research was to study the thermomechanical damage mechanics in hot forming processes. The important process variables and the main characteristics of various hot forming processes will also be discussed.

Hot Strange Hadronic Matter in an Effective Model

NASA Astrophysics Data System (ADS)

Qian, Wei-Liang; Su, Ru-Keng; Song, Hong-Qiu

2003-10-01

An effective model used to describe the strange hadronic matter with nucleons, Λ-hyperons, and Ξ-hyperons is extended to finite temperature. The extended model is used to study the density, temperature, and strangeness fraction dependence of the effective masses of baryons in the matter. The thermodynamical quantities, such as free energy and pressure, as well as the equation of state of the matter, are given. The project supported in part by National Natural Science Foundation of China under Grant Nos. 10075071, 10047005, 19947001, 19975010, and 10235030, and the CAS Knowledge Innovation Project No. KJCX2-N11. Also supported by the State Key Basic Research Development Program under Grant No. G200077400 and the Exploration Project of Knowledge Innovation Program of the Chinese Academy of Sciences

Screening effects due to carrier doping on valley relaxation in transition metal dichalcogenide monolayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Konabe, Satoru

2016-08-15

This work theoretically investigated the mechanism of valley polarization relaxation in monolayers of transition metal dichalcogenides, focusing on the exchange interactions between electrons and holes. In particular, we elucidated the effects of screening resulting from carrier doping on valley depolarization dynamics. The results show that the valley relaxation time is highly dependent on the extent of carrier doping. In addition, a finite degree of doping is predicted to induce additional valley relaxation temperature dependence at low temperatures, an effect that is absent at zero doping. Our calculation results suggest the possibility of increasing the valley relaxation time by tuning carriermore » doping, which could present a means of manipulating the valley degrees of freedom.« less

Finite-temperature spin dynamics in a perturbed quantum critical Ising chain with an E₈ symmetry.

PubMed

Wu, Jianda; Kormos, Márton; Si, Qimiao

2014-12-12

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.

Investigation on the Crack Behaviour in Kevlar 49 Based Composite Materials using Extended Finite Element Method for Aerospace Applications

NASA Astrophysics Data System (ADS)

Handa, Danish; Sekhar Dondapati, Raja; Kumar, Abhinav

2017-08-01

Ductile to brittle transition (DTBT) is extensively observed in materials under cryogenic temperatures, thereby observing brittle failure due to the non-resistance of crack propagation. Owing to its outstanding mechanical and thermal properties, Kevlar 49 composites are widely used in aerospace applications under cryogenic temperatures. Therefore, in this paper, involving the assumption of linear elastic fracture mechanics (LEFM), mechanical characterization of Kevlar 49 composite is done using Extended Finite Element Method (X-FEM) technique in Abaqus/CAE software. Further, the failure of Kevlar 49 composites due to the propagation of crack at room temperature and the cryogenic temperature is investigated. Stress, strain and strain energy density as a function of the width of the Kevlar specimen is predicted, indicates that Kevlar 49 composites are suitable for use under cryogenic temperatures.

A finite-temperature Hartree-Fock code for shell-model Hamiltonians

NASA Astrophysics Data System (ADS)

Bertsch, G. F.; Mehlhaff, J. M.

2016-10-01

The codes HFgradZ.py and HFgradT.py find axially symmetric minima of a Hartree-Fock energy functional for a Hamiltonian supplied in a shell model basis. The functional to be minimized is the Hartree-Fock energy for zero-temperature properties or the Hartree-Fock grand potential for finite-temperature properties (thermal energy, entropy). The minimization may be subjected to additional constraints besides axial symmetry and nucleon numbers. A single-particle operator can be used to constrain the minimization by adding it to the single-particle Hamiltonian with a Lagrange multiplier. One can also constrain its expectation value in the zero-temperature code. Also the orbital filling can be constrained in the zero-temperature code, fixing the number of nucleons having given Kπ quantum numbers. This is particularly useful to resolve near-degeneracies among distinct minima.

Non-Fermi Liquid Behavior and Continuously Tunable Resistivity Exponents in the Anderson-Hubbard Model at Finite Temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Patel, Niravkumar D.; Mukherjee, Anamitra; Kaushal, Nitin

Here, we employ a recently developed computational many-body technique to study for the first time the half-filled Anderson-Hubbard model at finite temperature and arbitrary correlation U and disorder V strengths. Interestingly, the narrow zero temperature metallic range induced by disorder from the Mott insulator expands with increasing temperature in a manner resembling a quantum critical point. Our study of the resistivity temperature scaling T α for this metal reveals non-Fermi liquid characteristics. Moreover, a continuous dependence of α on U and V from linear to nearly quadratic is observed. We argue that these exotic results arise from a systematic changemore » with U and V of the “effective” disorder, a combination of quenched disorder and intrinsic localized spins.« less

High-Temperature Nonequilibrium Bose Condensation Induced by a Hot Needle.

PubMed

Schnell, Alexander; Vorberg, Daniel; Ketzmerick, Roland; Eckardt, André

2017-10-06

We investigate theoretically a one-dimensional ideal Bose gas that is driven into a steady state far from equilibrium via the coupling to two heat baths: a global bath of temperature T and a "hot needle," a bath of temperature T_{h}≫T with localized coupling to the system. Remarkably, this system features a crossover to finite-size Bose condensation at temperatures T that are orders of magnitude larger than the equilibrium condensation temperature. This counterintuitive effect is explained by a suppression of long-wavelength excitations resulting from the competition between both baths. Moreover, for sufficiently large needle temperatures ground-state condensation is superseded by condensation into an excited state, which is favored by its weaker coupling to the hot needle. Our results suggest a general strategy for the preparation of quantum degenerate nonequilibrium steady states with unconventional properties and at large temperatures.

BEC-BCS crossover and the liquid-gas phase transition in hot and dense nuclear matter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jin Meng; Urban, Michael; Schuck, Peter

2010-08-15

The effect of nucleon-nucleon correlations in symmetric nuclear matter at finite temperature is studied beyond BCS theory. Starting from a Hartree-Fock description of nuclear matter with the Gogny effective interaction, we add correlations corresponding to the formation of preformed pairs and scattering states above the superfluid critical temperature within the in-medium T-matrix approach, which is analogous to the Nozieres-Schmitt-Rink theory. We calculate the critical temperature for a BEC superfluid of deuterons, of a BCS superfluid of nucleons, and in the crossover between these limits. The effect of the correlations on thermodynamic properties (equation of state, energy, entropy) and the liquid-gasmore » phase transition is discussed. Our results show that nucleon-nucleon correlations beyond BCS play an important role for the properties of nuclear matter, especially in the low-density region.« less

A multi-scale model of dislocation plasticity in α-Fe: Incorporating temperature, strain rate and non-Schmid effects

DOE PAGES

Lim, H.; Hale, L. M.; Zimmerman, J. A.; ...

2015-01-05

In this study, we develop an atomistically informed crystal plasticity finite element (CP-FE) model for body-centered-cubic (BCC) α-Fe that incorporates non-Schmid stress dependent slip with temperature and strain rate effects. Based on recent insights obtained from atomistic simulations, we propose a new constitutive model that combines a generalized non-Schmid yield law with aspects from a line tension (LT) model for describing activation enthalpy required for the motion of dislocation kinks. Atomistic calculations are conducted to quantify the non-Schmid effects while both experimental data and atomistic simulations are used to assess the temperature and strain rate effects. The parameterized constitutive equationmore » is implemented into a BCC CP-FE model to simulate plastic deformation of single and polycrystalline Fe which is compared with experimental data from the literature. This direct comparison demonstrates that the atomistically informed model accurately captures the effects of crystal orientation, temperature and strain rate on the flow behavior of siangle crystal Fe. Furthermore, our proposed CP-FE model exhibits temperature and strain rate dependent flow and yield surfaces in polycrystalline Fe that deviate from conventional CP-FE models based on Schmid's law.« less

Competition between Chaotic and Nonchaotic Phases in a Quadratically Coupled Sachdev-Ye-Kitaev Model.

PubMed

Chen, Xin; Fan, Ruihua; Chen, Yiming; Zhai, Hui; Zhang, Pengfei

2017-11-17

The Sachdev-Ye-Kitaev (SYK) model is a concrete solvable model to study non-Fermi liquid properties, holographic duality, and maximally chaotic behavior. In this work, we consider a generalization of the SYK model that contains two SYK models with a different number of Majorana modes coupled by quadratic terms. This model is also solvable, and the solution shows a zero-temperature quantum phase transition between two non-Fermi liquid chaotic phases. This phase transition is driven by tuning the ratio of two mode numbers, and a nonchaotic Fermi liquid sits at the critical point with an equal number of modes. At a finite temperature, the Fermi liquid phase expands to a finite regime. More intriguingly, a different non-Fermi liquid phase emerges at a finite temperature. We characterize the phase diagram in terms of the spectral function, the Lyapunov exponent, and the entropy. Our results illustrate a concrete example of the quantum phase transition and critical behavior between two non-Fermi liquid phases.

Principal component analysis for fermionic critical points

NASA Astrophysics Data System (ADS)

Costa, Natanael C.; Hu, Wenjian; Bai, Z. J.; Scalettar, Richard T.; Singh, Rajiv R. P.

2017-11-01

We use determinant quantum Monte Carlo (DQMC), in combination with the principal component analysis (PCA) approach to unsupervised learning, to extract information about phase transitions in several of the most fundamental Hamiltonians describing strongly correlated materials. We first explore the zero-temperature antiferromagnet to singlet transition in the periodic Anderson model, the Mott insulating transition in the Hubbard model on a honeycomb lattice, and the magnetic transition in the 1/6-filled Lieb lattice. We then discuss the prospects for learning finite temperature superconducting transitions in the attractive Hubbard model, for which there is no sign problem. Finally, we investigate finite temperature charge density wave (CDW) transitions in the Holstein model, where the electrons are coupled to phonon degrees of freedom, and carry out a finite size scaling analysis to determine Tc. We examine the different behaviors associated with Hubbard-Stratonovich auxiliary field configurations on both the entire space-time lattice and on a single imaginary time slice, or other quantities, such as equal-time Green's and pair-pair correlation functions.

Portevin-Le Chatelier effect under cyclic loading: experimental and numerical investigations

NASA Astrophysics Data System (ADS)

Mazière, M.; Pujol d'Andrebo, Q.

2015-10-01

The Portevin-Le Chatelier (PLC) effect is generally evidenced by the apparition of serrated yielding under monotonic tensile loading conditions. It appears at room temperature in some aluminium alloys, around ? in some steels and in many other metallic materials. This effect is associated with the propagation of bands of plastic deformation in tensile specimens and can in some cases lead to unexpected failures. The PLC effect has been widely simulated under monotonic conditions using finite elements and an appropriate mechanical model able to reproduce serrations and strain localization. The occurrence of serrations can be predicted using an analytical stability analysis. Recently, this serrated yielding has also been observed in specimens made of Cobalt-based superalloy under cyclic loading, after a large number of cycles. The mechanical model has been identified in this case to accurately reproduce this critical number of cycle where serrations appear. The associated apparition of localized bands of deformation in specimens and their influence on its failure has also been investigated using finite element simulations.

Effects of implant drilling parameters for pilot and twist drills on temperature rise in bone analog and alveolar bones.

PubMed

Chen, Yung-Chuan; Hsiao, Chih-Kun; Ciou, Ji-Sih; Tsai, Yi-Jung; Tu, Yuan-Kun

2016-11-01

This study concerns the effects of different drilling parameters of pilot drills and twist drills on the temperature rise of alveolar bones during dental implant procedures. The drilling parameters studied here include the feed rate and rotation speed of the drill. The bone temperature distribution was analyzed through experiments and numerical simulations of the drilling process. In this study, a three dimensional (3D) elasto-plastic dynamic finite element model (DFEM) was proposed to investigate the effects of drilling parameters on the bone temperature rise. In addition, the FE model is validated with drilling experiments on artificial human bones and porcine alveolar bones. The results indicate that 3D DFEM can effectively simulate the bone temperature rise during the drilling process. During the drilling process with pilot drills or twist drills, the maximum bone temperature occurred in the region of the cancellous bones close to the cortical bones. The feed rate was one of the important factors affecting the time when the maximum bone temperature occurred. Our results also demonstrate that the elevation of bone temperature was reduced as the feed rate increased and the drill speed decreased, which also effectively reduced the risk region of osteonecrosis. These findings can serve as a reference for dentists in choosing drilling parameters for dental implant surgeries. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

Finite temperature m=0 upper-hybrid modes in a non-neutral plasma, theory and simulation.

NASA Astrophysics Data System (ADS)

Hart, Grant W.; Takeshi Nakata, M.; Spencer, Ross L.

2007-11-01

Axisymmetric upper-hybrid oscillations have been known to exist in non-neutral plasmas and FTICR/MS devices for a number of years^1,2. However, because they are electrostatic in nature and axisymmetric, they are self-shielding and therefore difficult to detect in long systems. Previous theoretical studies have assumed a zero temperature plasma. In the zero temperature limit these oscillations are not properly represented as a mode, because the frequency at a given radius depends only on the local density and is not coupled to neighboring radii, much like the zero temperature plasma oscillation. Finite temperature provides the coupling which links the oscillation into a coherent mode. We have analyzed the finite-temperature theory of these modes and find that they form an infinite set of modes with frequencies above 2̂c- 2̂p. For a constant density plasma the eigenmodes are Bessel functions. For a more general plasma the eigenmodes must be numerically calculated. We have simulated these modes in our r-θ particle-in-cell code that includes a full Lorentz-force mover^3 and find that the eigenmodes correspond well with the theory.^1 J.J. Bollinger, et al., Phys. Rev. A 48, 525 (1993).^2 S.E. Barlow, et al., Int. J. Mass Spectrom. Ion Processes 74, 97 (1986).^3 M. Takeshi Nakata, et al., Bull. Am. Phys. Soc. 51, 245 (2006).

Finite temperature m=0 Bernstein modes in a non-neutral plasma, theory and simulation

NASA Astrophysics Data System (ADS)

Hart, Grant W.; Spencer, Ross L.; Takeshi Nakata, M.

2008-11-01

Axisymmetric upper-hybrid oscillations have been known to exist in non-neutral plasmas and FTICR/MS devices for a number of years. However, because they are electrostatic in nature and axisymmetric, they are self-shielding and therefore difficult to detect in long systems. Previous theoretical studies have assumed a zero temperature plasma. In the zero temperature limit these oscillations are not properly represented as a mode, because the frequency at a given radius depends only on the local density and is not coupled to neighboring radii, much like the zero temperature plasma oscillation. Finite temperature provides the coupling which links the oscillation into a coherent mode. We have analyzed the finite-temperature theory of these modes and find that they form an infinite set of modes with frequencies above 2̂c- 2̂p. We have simulated these modes in our r-θ particle-in-cell code that includes a full Lorentz-force mover and find that in a mostly flat-top plasma there are two eigenmodes that have essentially the same shape in the bulk of the plasma, but different frequencies. It appears likely that they have different boundary conditions in the boundary region. J.J. Bollinger, et al., Phys. Rev. A 48, 525 (1993). S.E. Barlow, et al., Int. J. Mass Spectrom. Ion Processes 74, 97 (1986). M. Takeshi Nakata, et al., Bull. Am. Phys. Soc. 51, 245 (2006).

Effects of plume afterburning on infrared spectroscopy

NASA Astrophysics Data System (ADS)

Zhu, Xijuan; Xu, Ying; Ma, Jing; Duan, Ran; Wu, Jie

2017-10-01

Contains H2, CO and unburned components of high-temperature plume of rocket engine, then injected into the atmosphere, continue to carry out the oxidation reaction in the plume near field region with the volume in the plume of oxygen in the air, two times burning. The afterburning is an important cause of infrared radiation intensification of propellant plume, which increases the temperature of the flame and changes the components of the gas, thus enhancing the infrared radiation intensity of the flame. [1]. Two the combustion numerical using chemical reaction mechanism involving HO2 intermediate reaction, the study confirmed that HO2 is a key intermediate, plays a decisive role to trigger early response, on afterburning temperature and flow concentration distribution effect. A finite rate chemical reaction model is used to describe the two burning phenomenon in high temperature plume[2]. In this paper, a numerical simulation of the flame flow field and radiative transfer is carried out for the afterburning phenomenon. The effects of afterburning on the composition, temperature and infrared radiation of the plume are obtained by comparison.

Bose–Einstein condensation temperature of finite systems

NASA Astrophysics Data System (ADS)

Xie, Mi

2018-05-01

In studies of the Bose–Einstein condensation of ideal gases in finite systems, the divergence problem usually arises in the equation of state. In this paper, we present a technique based on the heat kernel expansion and zeta function regularization to solve the divergence problem, and obtain the analytical expression of the Bose–Einstein condensation temperature for general finite systems. The result is represented by the heat kernel coefficients, where the asymptotic energy spectrum of the system is used. Besides the general case, for systems with exact spectra, e.g. ideal gases in an infinite slab or in a three-sphere, the sums of the spectra can be obtained exactly and the calculation of corrections to the critical temperatures is more direct. For a system confined in a bounded potential, the form of the heat kernel is different from the usual heat kernel expansion. We show that as long as the asymptotic form of the global heat kernel can be found, our method works. For Bose gases confined in three- and two-dimensional isotropic harmonic potentials, we obtain the higher-order corrections to the usual results of the critical temperatures. Our method can also be applied to the problem of generalized condensation, and we give the correction of the boundary on the second critical temperature in a highly anisotropic slab.

Analytical Predictions of Thermal Stress in the Stardust PICA Heatshield Under Reentry Flight Conditions

NASA Technical Reports Server (NTRS)

Squire, Thomas; Milos, Frank; Agrawal, Parul

2009-01-01

We performed finite element analyses on a model of the Phenolic Impregnated Carbon Ablator (PICA) heatshield from the Stardust sample return capsule (SRC) to predict the thermal stresses in the PICA material during reentry. The heatshield on the Stardust SRC was a 0.83 m sphere cone, fabricated from a single piece of 5.82 cm-thick PICA. The heatshield performed successfully during Earth reentry of the SRC in January 2006. Material response analyses of the full, axisymmetric PICA heatshield were run using the Two-Dimensional Implicit Ablation, Pyrolysis, and Thermal Response Program (TITAN). Peak surface temperatures were predicted to be 3385K, while the temperature at the PICA backface remained at the estimated initial cold-soak temperature of 278K. Surface recession and temperature distribution results from TITAN, at several points in the reentry trajectory, were mapped onto an axisymmetric finite element model of the heatshield. We used the finite element model to predict the thermal stresses in the PICA from differential thermal expansion. The predicted peak compressive stress in the PICA heatshield was 1.38 MPa. Although this level of stress exceeded the chosen design limit for compressive stresses in PICA tiles for the design of the Orion crew exploration vehicle heatshield, the Stardust heatshield exhibited no obvious mechanical failures from thermal stress. The analyses of the Stardust heatshield were used to assess and adjust the level of conservatism in the finite element analyses in support of the Orion heatshield design.

Effects of finite wall thickness and sinusoidal heating on convection in nanofluid-saturated local thermal non-equilibrium porous cavity

NASA Astrophysics Data System (ADS)

Alsabery, A. I.; Chamkha, A. J.; Saleh, H.; Hashim, I.; Chanane, B.

2017-03-01

The effects of finite wall thickness and sinusoidal heating on convection in a nanofluid-saturated local thermal non-equilibrium (LTNE) porous cavity are studied numerically using the finite difference method. The finite thickness vertical wall of the cavity is maintained at a constant temperature and the right wall is heated sinusoidally. The horizontal insulated walls allow no heat transfer to the surrounding. The Darcy law is used along with the Boussinesq approximation for the flow. Water-based nanofluids with Cu nanoparticles are chosen for investigation. The results of this study are obtained for various parameters such as the Rayleigh number, periodicity parameter, nanoparticles volume fraction, thermal conductivity ratio, ratio of wall thickness to its height and the modified conductivity ratio. Explanation for the influence of the various above-mentioned parameters on the streamlines, isotherms, local Nusselt number and the weighted average heat transfer is provided with regards to the thermal conductivities of nanoparticles suspended in the pure fluid and the porous medium. It is shown that the overall heat transfer is significantly increased with the relative non-uniform heating. Further, the convection heat transfer is shown to be inhibited by the presence of the solid wall. The results have possible applications in the heat-storage fluid-saturated porous systems and the applications of the high power heat transfer.

Finite-Size Effects in Non-neutral Two-Dimensional Coulomb Fluids

NASA Astrophysics Data System (ADS)

Šamaj, Ladislav

2017-07-01

Thermodynamic potential of a neutral two-dimensional (2D) Coulomb fluid, confined to a large domain with a smooth boundary, exhibits at any (inverse) temperature β a logarithmic finite-size correction term whose universal prefactor depends only on the Euler number of the domain and the conformal anomaly number c=-1. A minimal free boson conformal field theory, which is equivalent to the 2D symmetric two-component plasma of elementary ± e charges at coupling constant Γ =β e^2, was studied in the past. It was shown that creating a non-neutrality by spreading out a charge Qe at infinity modifies the anomaly number to c(Q,Γ ) = - 1 + 3Γ Q^2. Here, we study the effect of non-neutrality on the finite-size expansion of the free energy for another Coulomb fluid, namely the 2D one-component plasma (jellium) composed of identical pointlike e-charges in a homogeneous background surface charge density. For the disk geometry of the confining domain we find that the non-neutrality induces the same change of the anomaly number in the finite-size expansion. We derive this result first at the free-fermion coupling Γ ≡ β e^2=2 and then, by using a mapping of the 2D one-component plasma onto an anticommuting field theory formulated on a chain, for an arbitrary even coupling constant.

Thermal Effects on the Bearing Behavior of Composite Joints

NASA Technical Reports Server (NTRS)

Walker, Sandra Polesky

2001-01-01

Thermal effects on the pin-bearing behavior of an IM7/PET15 composite laminate are studied comprehensively. A hypothesis presents factors influencing a change in pin-bearing strength with a change in temperature for a given joint design. The factors include the change in the state of residual cure stress, the material properties, and the fastener fit with a change in temperature. Experiments are conducted to determine necessary lamina and laminate material property data for the IM7/PET15 being utilized in this study. Lamina material properties are determined between the assumed stress free temperature of 460 F down to -200 F. Laminate strength properties are determined for several lay-ups at the operating temperatures of 350 F, 70 F, and -200 F. A three-dimensional finite element analysis model of a composite laminate subject to compressive loading is developed. Both the resin rich layer located between lamina and the thermal residual stresses present in the laminate due to curing are determined to influence the state of stress significantly. Pin-bearing tests of several lay-ups were conducted to develop an understanding on the effect of temperature changes on the pin-bearing behavior of the material. A computational study investigating the factors influencing pin-bearing strength was performed. A finite element model was developed and used to determine the residual thermal cure stresses in the laminate containing a hole. Very high interlaminar stress concentrations were observed two elements away from the hole boundary at all three operating temperatures. The pin-bearing problem was modeled assuming a rigid frictionless pin and restraining only radial displacements at the hole boundary. A uniform negative pressure load was then applied to the straight end of the model. A solution, where thermal residual stresses were combined with the state of stress due to pin-bearing loads was evaluated. The presence of thermal residual stresses intensified the interlaminar stresses predicted at the hole boundary in the pin-bearing problem. This dissertation shows that changes in material properties drives pin-bearing strength degradation with increasing temperature.

Free energy and phase transition of the matrix model on a plane wave

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hadizadeh, Shirin; Ramadanovic, Bojan; Semenoff, Gordon W.

2005-03-15

It has recently been observed that the weakly coupled plane-wave matrix model has a density of states which grows exponentially at high energy. This implies that the model has a phase transition. The transition appears to be of first order. However, its exact nature is sensitive to interactions. In this paper, we analyze the effect of interactions by computing the relevant parts of the effective potential for the Polyakov loop operator in the finite temperature plane-wave matrix model to three-loop order. We show that the phase transition is indeed of first order. We also compute the correction to the Hagedornmore » temperature to order two loops.« less

Spin Nernst effect of magnons in collinear antiferromagnets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheng, Ran; Okamoto, Satoshi; Xiao, Di

2016-11-15

In a collinear antiferromagnet with easy-axis anisotropy, symmetry guarantees that the spin wave modes are doubly degenerate. The two modes carry opposite spin angular momentum and exhibit opposite chirality. Using a honeycomb antiferromagnet in the presence of the Dzyaloshinskii-Moriya interaction, we show that a longitudinal temperature gradient can drive the two modes to opposite transverse directions, realizing a spin Nernst effect of magnons with vanishing thermal Hall current. We find that magnons around themore » $$\\Gamma$$ point and the $K$ point contribute oppositely to the transverse spin transport, and their competition leads to a sign change of the spin Nernst coefficient at finite temperature. As a result, possible material candidates are discussed.« less

Finite-element simulation of ceramic drying processes

NASA Astrophysics Data System (ADS)

Keum, Y. T.; Jeong, J. H.; Auh, K. H.

2000-07-01

A finite-element simulation for the drying process of ceramics is performed. The heat and moisture movements in green ceramics caused by the temperature gradient, moisture gradient, conduction, convection and evaporation are considered. The finite-element formulation for solving the temperature and moisture distributions, which not only change the volume but also induce the hygro-thermal stress, is carried out. Employing the internally discontinuous interface elements, the numerical divergence problem arising from sudden changes in heat capacity in the phase zone is solved. In order to verify the reliability of the formulation, the drying process of a coal and the wetting process of a graphite epoxy are simulated and the results are compared with the analytical solution and another investigator's result. Finally, the drying process of a ceramic electric insulator is simulated.

FINITE-DIFFERENCE ELECTROMAGNETIC DEPOSITION/THERMOREGULATORY MODEL: COMPARISON BETWEEN THEORY AND MEASUREMENTS (JOURNAL VERSION)

EPA Science Inventory

The rate of the electromagnetic energy deposition and the resultant thermoregulatory response of a block model of a squirrel monkey exposed to plane-wave fields at 350 MHz were calculated using a finite-difference procedure. Noninvasive temperature measurements in live squirrel m...

Experimental Determination of η/s for Finite Nuclear Matter.

PubMed

Mondal, Debasish; Pandit, Deepak; Mukhopadhyay, S; Pal, Surajit; Dey, Balaram; Bhattacharya, Srijit; De, A; Bhattacharya, Soumik; Bhattacharyya, S; Roy, Pratap; Banerjee, K; Banerjee, S R

2017-05-12

We present, for the first time, simultaneous determination of shear viscosity (η) and entropy density (s) and thus, η/s for equilibrated nuclear systems from A∼30 to A∼208 at different temperatures. At finite temperature, η is estimated by utilizing the γ decay of the isovector giant dipole resonance populated via fusion evaporation reaction, while s is evaluated from the nuclear level density parameter (a) and nuclear temperature (T), determined precisely by the simultaneous measurements of the evaporated neutron energy spectra and the compound nuclear angular momenta. The transport parameter η and the thermodynamic parameter s both increase with temperature, resulting in a mild decrease of η/s with temperature. The extracted η/s is also found to be independent of the neutron-proton asymmetry at a given temperature. Interestingly, the measured η/s values are comparable to that of the high-temperature quark-gluon plasma, pointing towards the fact that strong fluidity may be the universal feature of the strong interaction of many-body quantum systems.

Ground-state factorization and correlations with broken symmetry

NASA Astrophysics Data System (ADS)

Tomasello, B.; Rossini, D.; Hamma, A.; Amico, L.

2011-10-01

We show how the phenomenon of factorization in a quantum many-body system is of collective nature. To this aim we study the quantum discord Q in the one-dimensional XY model in a transverse field. We analyze the behavior of Q at both the critical point and at the non-critical factorizing field. The factorization is found to be governed by an exponential scaling law for Q. We also address the thermal effects fanning out from the anomalies occurring at zero temperature. Close to the quantum phase transition, Q exhibits a finite-temperature crossover with universal scaling behavior, while the factorization phenomenon results in a non-trivial pattern of correlations present at low temperature.

Unified constitutive models for high-temperature structural applications

NASA Technical Reports Server (NTRS)

Lindholm, U. S.; Chan, K. S.; Bodner, S. R.; Weber, R. M.; Walker, K. P.

1988-01-01

Unified constitutive models are characterized by the use of a single inelastic strain rate term for treating all aspects of inelastic deformation, including plasticity, creep, and stress relaxation under monotonic or cyclic loading. The structure of this class of constitutive theory pertinent for high temperature structural applications is first outlined and discussed. The effectiveness of the unified approach for representing high temperature deformation of Ni-base alloys is then evaluated by extensive comparison of experimental data and predictions of the Bodner-Partom and the Walker models. The use of the unified approach for hot section structural component analyses is demonstrated by applying the Walker model in finite element analyses of a benchmark notch problem and a turbine blade problem.

Disentangling nonradiative recombination processes in Ge micro-crystals on Si substrates

NASA Astrophysics Data System (ADS)

Pezzoli, Fabio; Giorgioni, Anna; Gallacher, Kevin; Isa, Fabio; Biagioni, Paolo; Millar, Ross W.; Gatti, Eleonora; Grilli, Emanuele; Bonera, Emiliano; Isella, Giovanni; Paul, Douglas J.; Miglio, Leo

2016-06-01

We address nonradiative recombination pathways by leveraging surface passivation and dislocation management in μm-scale arrays of Ge crystals grown on deeply patterned Si substrates. The time decay photoluminescence (PL) at cryogenic temperatures discloses carrier lifetimes approaching 45 ns in band-gap engineered Ge micro-crystals. This investigation provides compelling information about the competitive interplay between the radiative band-edge transitions and the trapping of carriers by dislocations and free surfaces. Furthermore, an in-depth analysis of the temperature dependence of the PL, combined with capacitance data and finite difference time domain modeling, demonstrates the effectiveness of GeO2 in passivating the surface of Ge and thus in enhancing the room temperature PL emission.

Characteristics of Mach 10 transitional and turbulent boundary layers

NASA Technical Reports Server (NTRS)

Watson, R. D.

1978-01-01

Measurements of the mean flow properties of transitional and turbulent boundary layers in helium on 4 deg and 5 deg wedges were made for flows with edge Mach numbers from 9.5 to 11.3, ratios of wall temperature to total temperature of 0.4 to 0.95, and maximum length Reynolds numbers of one hundred million. The data include pitot and total temperature surveys and measurements of heat transfer and surface shear. In addition, with the assumption of local similarity, turbulence quantities such as the mixing length were derived from the mean flow profiles. Low Reynolds number and precursor transition effects were significant factors at these test conditions and were included in finite difference boundary layer predictions.

Non-Markovian Quantum State Diffusion for temperature-dependent linear spectra of light harvesting aggregates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ritschel, Gerhard; Möbius, Sebastian; Eisfeld, Alexander, E-mail: eisfeld@mpipks-dresden.mpg.de

2015-01-21

Non-Markovian Quantum State Diffusion (NMQSD) has turned out to be an efficient method to calculate excitonic properties of aggregates composed of organic chromophores, taking into account the coupling of electronic transitions to vibrational modes of the chromophores. NMQSD is an open quantum system approach that incorporates environmental degrees of freedom (the vibrations in our case) in a stochastic way. We show in this paper that for linear optical spectra (absorption, circular dichroism), no stochastics is needed, even for finite temperatures. Thus, the spectra can be obtained by propagating a single trajectory. To this end, we map a finite temperature environmentmore » to the zero temperature case using the so-called thermofield method. The resulting equations can then be solved efficiently by standard integrators.« less

Path integral Monte Carlo and the electron gas

NASA Astrophysics Data System (ADS)

Brown, Ethan W.

Path integral Monte Carlo is a proven method for accurately simulating quantum mechanical systems at finite-temperature. By stochastically sampling Feynman's path integral representation of the quantum many-body density matrix, path integral Monte Carlo includes non-perturbative effects like thermal fluctuations and particle correlations in a natural way. Over the past 30 years, path integral Monte Carlo has been successfully employed to study the low density electron gas, high-pressure hydrogen, and superfluid helium. For systems where the role of Fermi statistics is important, however, traditional path integral Monte Carlo simulations have an exponentially decreasing efficiency with decreased temperature and increased system size. In this thesis, we work towards improving this efficiency, both through approximate and exact methods, as specifically applied to the homogeneous electron gas. We begin with a brief overview of the current state of atomic simulations at finite-temperature before we delve into a pedagogical review of the path integral Monte Carlo method. We then spend some time discussing the one major issue preventing exact simulation of Fermi systems, the sign problem. Afterwards, we introduce a way to circumvent the sign problem in PIMC simulations through a fixed-node constraint. We then apply this method to the homogeneous electron gas at a large swatch of densities and temperatures in order to map out the warm-dense matter regime. The electron gas can be a representative model for a host of real systems, from simple medals to stellar interiors. However, its most common use is as input into density functional theory. To this end, we aim to build an accurate representation of the electron gas from the ground state to the classical limit and examine its use in finite-temperature density functional formulations. The latter half of this thesis focuses on possible routes beyond the fixed-node approximation. As a first step, we utilize the variational principle inherent in the path integral Monte Carlo method to optimize the nodal surface. By using a ansatz resembling a free particle density matrix, we make a unique connection between a nodal effective mass and the traditional effective mass of many-body quantum theory. We then propose and test several alternate nodal ansatzes and apply them to single atomic systems. Finally, we propose a method to tackle the sign problem head on, by leveraging the relatively simple structure of permutation space. Using this method, we find we can perform exact simulations this of the electron gas and 3He that were previously impossible.

Finite element analysis of heat generation from different light-polymerization sources during cementation of all-ceramic crowns.

PubMed

Tunc, Elif Pak

2007-06-01

Exothermic composite resin chemical reactions and visible light generators can produce heat during a restorative polymerization process. These thermal changes in restored teeth may cause pain and irreversible pulpitis. The purpose of this study was to analyze the temperature distribution and heat flow patterns of a crowned mandibular second premolar tooth model using 3 different light-polymerization technologies and a finite element technique. A 2-dimensional finite element model was used to simulate a clinical condition. Heat flow and thermal stress distribution in a tooth during cementation of an all-ceramic crown using 4 commercially available light-polymerization units (LPUs), each with different wavelengths (Elipar TriLight, Elipar Freelight, Apollo 95 E, and ADT 1000 PAC), were investigated. The temperature values were measured at 3, 10, 12, and 40 seconds for each light-polymerizing unit (LPU) at 6 different finite element nodes. Two-dimensional temporal and spatial distribution of the thermal stress within the tooth, including the thermal coefficients and boundary conditions of the dental materials, were obtained and evaluated. The temperature at the nodal points did not exceed 42 degrees C, which is a threshold value for tissue vitality within the recommended operating periods at the dentin and pulp surface for all LPUs, except for Elipar TriLight. In the case of Elipar TriLlight, the temperatures at the dentin and pulp surfaces were 47 degrees C and 42 degrees C, respectively. When the light-polymerization units were used according to the manufacturers' operating procedures and without prolonged operating periods, with the exception of Elipar TriLight, the investigated LPUs did not produce significant heat. However, when the operating periods were prolonged, unacceptable temperature increases were observed, especially with the high-intensity LPUs.

Determining the Gaussian Modulus and Edge Properties of 2D Materials: From Graphene to Lipid Bilayers

NASA Astrophysics Data System (ADS)

Zelisko, Matthew; Ahmadpoor, Fatemeh; Gao, Huajian; Sharma, Pradeep

2017-08-01

The dominant deformation behavior of two-dimensional materials (bending) is primarily governed by just two parameters: bending rigidity and the Gaussian modulus. These properties also set the energy scale for various important physical and biological processes such as pore formation, cell fission and generally, any event accompanied by a topological change. Unlike the bending rigidity, the Gaussian modulus is, however, notoriously difficult to evaluate via either experiments or atomistic simulations. In this Letter, recognizing that the Gaussian modulus and edge tension play a nontrivial role in the fluctuations of a 2D material edge, we derive closed-form expressions for edge fluctuations. Combined with atomistic simulations, we use the developed approach to extract the Gaussian modulus and edge tension at finite temperatures for both graphene and various types of lipid bilayers. Our results possibly provide the first reliable estimate of this elusive property at finite temperatures and appear to suggest that earlier estimates must be revised. In particular, we show that, if previously estimated properties are employed, the graphene-free edge will exhibit unstable behavior at room temperature. Remarkably, in the case of graphene, we show that the Gaussian modulus and edge tension even change sign at finite temperatures.

Dependence of Coulomb Sum Rule on the Short Range Correlation by Using Av18 Potential

NASA Astrophysics Data System (ADS)

Modarres, M.; Moeini, H.; Moshfegh, H. R.

The Coulomb sum rule (CSR) and structure factor are calculated for inelastic electron scattering from nuclear matter at zero and finite temperature in the nonrelativistic limit. The effect of short-range correlation (SRC) is presented by using lowest order constrained variational (LOCV) method and the Argonne Av18 and Δ-Reid soft-core potentials. The effects of different potentials as well as temperature are investigated. It is found that the nonrelativistic version of Bjorken scaling approximately sets in at the momentum transfer of about 1.1 to 1.2 GeV/c and the increase of temperature makes it to decrease. While different potentials do not significantly change CSR, the SRC improves the Coulomb sum rule and we get reasonably close results to both experimental data and others theoretical predictions.

Equation of state of the one- and three-dimensional Bose-Bose gases

NASA Astrophysics Data System (ADS)

Chiquillo, Emerson

2018-06-01

We calculate the equation of state of Bose-Bose gases in one and three dimensions in the framework of an effective quantum field theory. The beyond-mean-field approximation at zero temperature and the one-loop finite-temperature results are obtained performing functional integration on a local effective action. The ultraviolet divergent zero-point quantum fluctuations are removed by means of dimensional regularization. We derive the nonlinear Schrödinger equation to describe one- and three-dimensional Bose-Bose mixtures and solve it analytically in the one-dimensional scenario. This equation supports self-trapped brightlike solitonic droplets and self-trapped darklike solitons. At low temperature, we also find that the pressure and the number of particles of symmetric quantum droplets have a nontrivial dependence on the chemical potential and the difference between the intra- and the interspecies coupling constants.

An Analysis of the Effect of Surface Heat Exchange on the Thermal Behavior of an Idealized Aquifer Thermal Energy Storage System

NASA Astrophysics Data System (ADS)

Güven, O.; Melville, J. G.; Molz, F. J.

1983-06-01

Analytical expressions are derived for the temperature distribution and the mean temperature of an idealized aquifer thermal energy storage (ATES) system, taking into account the heat exchange at the ground surface and the finite thickness of the overlying layer above the storage aquifer. The analytical expressions for the mean temperature may be used to obtain rough estimates of first-cycle recovery factors for preliminary evaluations of shallow confined or unconfined ATES systems. The results, which are presented in nondimensional plots, indicate that surface heat exchange may have a significant influence on the thermal behavior of shallow ATES systems. Thus it is suggested that the effects of surface heat exchange should be considered carefully and included in the detailed analyses of such ATES systems.

Unusual Thermal Hall Effect in a Kitaev Spin Liquid Candidate α -RuCl3

NASA Astrophysics Data System (ADS)

Kasahara, Y.; Sugii, K.; Ohnishi, T.; Shimozawa, M.; Yamashita, M.; Kurita, N.; Tanaka, H.; Nasu, J.; Motome, Y.; Shibauchi, T.; Matsuda, Y.

2018-05-01

The Kitaev quantum spin liquid displays the fractionalization of quantum spins into Majorana fermions. The emergent Majorana edge current is predicted to manifest itself in the form of a finite thermal Hall effect, a feature commonly discussed in topological superconductors. Here we report on thermal Hall conductivity κx y measurements in α -RuCl3 , a candidate Kitaev magnet with the two-dimensional honeycomb lattice. In a spin-liquid (Kitaev paramagnetic) state below the temperature characterized by the Kitaev interaction JK/kB˜80 K , positive κx y develops gradually upon cooling, demonstrating the presence of highly unusual itinerant excitations. Although the zero-temperature property is masked by the magnetic ordering at TN=7 K , the sign, magnitude, and T dependence of κx y/T at intermediate temperatures follows the predicted trend of the itinerant Majorana excitations.

Ionization competition effects on population distribution and radiative opacity of mixture plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Yongjun; Gao, Cheng; Tian, Qinyun

2015-11-15

Ionization competition arising from the electronic shell structures of various atomic species in the mixture plasmas was investigated, taking SiO{sub 2} as an example. Using a detailed-level-accounting approximation, we studied the competition effects on the charge state population distribution and spectrally resolved and Planck and Rosseland mean radiative opacities of mixture plasmas. A set of coupled equations for ionization equilibria that include all components of the mixture plasmas are solved to determine the population distributions. For a given plasma density, competition effects are found at three distinct temperature ranges, corresponding to the ionization of M-, L-, and K-shell electrons ofmore » Si. Taking the effects into account, the spectrally resolved and Planck and Rosseland mean opacities are systematically investigated over a wide range of plasma densities and temperatures. For a given mass density, the Rosseland mean decreases monotonically with plasma temperature, whereas Planck mean does not. Although the overall trend is a decrease, the Planck mean increases over a finite intermediate temperature regime. A comparison with the available experimental and theoretical results is made.« less

Finite-element analysis of scattering parameters of surface acoustic wave bandpass filter formed on barium titanate thin film

NASA Astrophysics Data System (ADS)

Timoshenko; Kalinchuk; Shirokov

2018-04-01

The frequency dependence of scattering parameters of interdigital surface acoustic wave transducers placed on ferroelectric barium titanate (BaTiO3) epitaxial film in c-phase coated over magnesium oxide has been studied using the finite-element method (FEM) approach along with the perfectly matched layer (PML) technique. The interdigital transducer which has a comb-like structure with aluminum electrodes excites the mechanical wave. The distance between the fingers allows tuning the frequency properties of the wave propagation. The magnesium oxide is taken as the substrate. The two-dimensional model of two-port surface acoustic wave filter is created to calculate scattering parameters and to show how to design the fixture in COMSOLTM. Some practical computational challenges of finite element modeling of SAW devices in COMSOLTM are shown. The effect of lattice misfit strain on acoustic properties of heterostructures of BaTiO3 epitaxial film in c-phase at room temperature is discussed in present article for two low-frequency surface acoustic resonances.

Mass Efficiency Considerations for Thermally Insulated Structural Skin of an Aerospace Vehicle

NASA Technical Reports Server (NTRS)

Blosser, Max L.

2012-01-01

An approximate equation was derived to predict the mass of insulation required to limit the maximum temperature reached by an insulated structure subjected to a transient heating pulse. In the course of the derivation two figures of merit were identified. One figure of merit correlates to the effectiveness of the heat capacity of the underlying structural material in reducing the amount of required insulation. The second figure of merit provides an indicator of the mass efficiency of the insulator material. An iterative, one dimensional finite element analysis was used to size the external insulation required to protect the structure at a single location on the Space Shuttle Orbiter and a reusable launch vehicle. Required insulation masses were calculated for a range of different materials for both structure and insulator. The required insulation masses calculated using the approximate equation were shown to typically agree with finite element results within 10 to 20 percent over the range of parameters studied. Finite element results closely followed the trends indicated by both figures of merit.

Analysis of turbulent free-jet hydrogen-air diffusion flames with finite chemical reaction rates

NASA Technical Reports Server (NTRS)

Sislian, J. P.; Glass, I. I.; Evans, J. S.

1979-01-01

A numerical analysis is presented of the nonequilibrium flow field resulting from the turbulent mixing and combustion of an axisymmetric hydrogen jet in a supersonic parallel ambient air stream. The effective turbulent transport properties are determined by means of a two-equation model of turbulence. The finite-rate chemistry model considers eight elementary reactions among six chemical species: H, O, H2O, OH, O2 and H2. The governing set of nonlinear partial differential equations was solved by using an implicit finite-difference procedure. Radial distributions were obtained at two downstream locations for some important variables affecting the flow development, such as the turbulent kinetic energy and its dissipation rate. The results show that these variables attain their peak values on the axis of symmetry. The computed distribution of velocity, temperature, and mass fractions of the chemical species gives a complete description of the flow field. The numerical predictions were compared with two sets of experimental data. Good qualitative agreement was obtained.

Effect of curvature squared corrections to gravitational action on viscosity-to-entropy ratio of the dual gauge theory

NASA Astrophysics Data System (ADS)

Petrov, Pavel

In this thesis we study the properties of strongly-coupled large-N conformal field theories (CFT's) using AdS/CFT correspondence. Chapter 1 serves as an introduction. In Chapter 2 we study the shear viscosity of strongly-coupled large-N conformal field theories. We find that it is affected by R2 corrections to the AdS action and present an example of 4D theory in which the the conjectured universal lower bound on viscosity-to-entropy ratio η/s > 1/4π is violated by 1/N corrections. This fact proves that there is no universal lower bound of 1/4π on viscosity-to-entropy ratio and may be relevant for the studies of QCD quark-gluon plasma for which this ratio is experimentally found to be close to 1/4π. In Chapter 3 we study the formation of the electron star in 4D AdS space. We show that in a gravity theory with charged fermions a layer of charged fermion fluid may form at a finite distance from the charged black hole. We show that these “electron stars” are candidate gravity duals for strongly interacting fermion systems at finite density and finite temperature. Entropy density for such systems scales as s ˜ T2/z at low temperatures as expected from IR criticality of electron stars solutions.

Residual stress prediction in a powder bed fusion manufactured Ti6Al4V hip stem

NASA Astrophysics Data System (ADS)

Barrett, Richard A.; Etienne, Titouan; Duddy, Cormac; Harrison, Noel M.

2017-10-01

Powder bed fusion (PBF) is a category of additive manufacturing (AM) that is particularly suitable for the production of 3D metallic components. In PBF, only material in the current build layer is at the required melt temperature, with the previously melted and solidified layers reducing in temperature, thus generating a significant thermal gradient within the metallic component, particularly for laser based PBF components. The internal thermal stresses are subsequently relieved in a post-processing heat-treatment step. Failure to adequately remove these stresses can result in cracking and component failure. A prototype hip stem was manufactured from Ti6Al4V via laser PBF but was found to have fractured during over-seas shipping. This study examines the evolution of thermal stresses during the laser PBF manufacturing and heat treatment processes of the hip stem in a 2D finite element analysis (FEA) and compares it to an electron beam PBF process. A custom written script for the automatic conversion of a gross geometry finite element model into a thin layer- by-layer finite element model was developed. The build process, heat treatment (for laser PBF) and the subsequent cooling were simulated at the component level. The results demonstrate the effectiveness of the heat treatment in reducing PBF induced thermal stresses, and the concentration of stresses in the region that fractured.

The use of supercomputer modelling of high-temperature failure in pipe weldments to optimize weld and heat affected zone materials property selection

NASA Astrophysics Data System (ADS)

Wang, Z. P.; Hayhurst, D. R.

1994-07-01

The creep deformation and damage evolution in a pipe weldment has been modeled by using the finite-element continuum damage mechanics (CDM) method. The finite-element CDM computer program DAMAGE XX has been adapted to run with increased speed on a Cray XMP/416 supercomputer. Run times are sufficiently short (20 min) to permit many parametric studies to be carried out on vessel lifetimes for different weld and heat affected zone (HAZ) materials. Finite-element mesh sensitivity was studied first in order to select a mesh capable of correctly predicting experimentally observed results using at least possible computer time. A study was then made of the effect on the lifetime of a butt welded vessel of each of the commomly measured material parameters for the weld and HAZ materials. Forty different ferritic steel welded vessels were analyzed for a constant internal pressure of 45.5 MPa at a temperature of 565 C; each vessel having the same parent pipe material but different weld and HAZ materials. A lifetime improvement has been demonstrated of 30% over that obtained for the initial materials property data. A methodology for weldment design has been established which uses supercomputer-based CDM analysis techniques; it is quick to use, provides accurate results, and is a viable design tool.

Assessment of crack growth in a space shuttle main engine first-stage, high-pressure fuel turbopump blade

NASA Technical Reports Server (NTRS)

Abdul-Aziz, Ali

1993-01-01

A two-dimensional finite element fracture mechanics analysis of a space shuttle main engine (SSME) turbine blade firtree was performed using the MARC finite element code. The analysis was conducted under combined effects of thermal and mechanical loads at steady-state conditions. Data from a typical engine stand cycle of the SSME were used to run a heat transfer analysis and, subsequently, a thermal structural fracture mechanics analysis. Temperature and stress contours for the firtree under these operating conditions were generated. High stresses were found at the firtree lobes where crack initiation was triggered. A life assessment of the firtree was done by assuming an initial and a final crack size.