Thermal buckling and natural vibration of the beam with an axial stick–slip–stop boundary

As a first attempt to study the dynamics of a heated structure with complicated boundaries, this paper deals with the thermal buckling and the natural vibration of a simply supported slender beam, which is subject to a uniformly distributed heating and has a frictional sliding end within a clearance. This sliding end is initially at a stick status under the friction force, but may be slightly slipping due to the thermal expansion of the beam until the sliding end contacts a stop, i.e., the bound of the clearance. The material properties of the beam are temperature-independent for low temperature, but temperature-dependent for high temperature. For each case, the analytic solutions for the critical buckling temperature and the natural frequencies of the heated beam are derived first. Then, discussions are made to reveal the effects of beam parameters, such as the ratio of beam length to beam thickness, the ratio of clearance to beam length and the temperature-dependent material properties, on the critical buckling temperature and the fundamental natural frequency of the heated beam. The study shows that both friction force and clearance have significant influences on the critical buckling temperature and the fundamental natural frequency of the beam. When the friction force is not very large, the clearance can greatly increase the critical buckling temperature. These conclusions enable one to properly design the stick–slip–stop boundary so as to improve the mechanical performance of the beam in thermal environments.     

The structure of the thermal explosion limit with variable pre-exponential factor

An approximate critical explosion parameter, which separates the slow and explosive reactions is determined with respect to the initial data, using the asymptotic technique to analyze a one step reaction mechanism with temperature dependent pre-exponential factor. We obtained and analysed the effect of the variable pre-exponential factor on the critical temperature, critical parameter for thermal explosion and the first order approximation of the slow curve. By introducing a new coordinate and using the Method of Invariant Manifold (MIM), we obtained corrections on the critical temperature. The results obtained are not only general; they also reveal some salient properties of the system hitherto unknown.     

Quantum critical end point for the Kondo volume collapse model

The Kondo volume collapse describes valence transitions in f-electron metals and is characterized by a line of first order transitions in the pressure-temperature phase plane terminated at critical end points. We analyze the quantum critical end point, when the lower end point is tuned to T=0, and determine the specific heat, thermal expansion, and compressibility. We find that the inclusion of quantum critical fluctuations leads to a novel bifurcation of the first order phase line. Finally, we show that critical strain fluctuations can cause both, superconductivity and non-Fermi liquid behavior near the critical point.     

Advances of phononics in 2012—2022

Due to its great potential applications in thermal management, heat control, and quantum information, phononics has gained increasing attentions since the first publication in Rev. Mod. Phys. 84 1045 (2012). Many theoretical and experimental progresses have been achieved in the past decade. In this paper, we first give a critical review of the progress in thermal diodes and transistors, especially in classical regime. Then, we give a brief introduction to the new developing research directions such as topological phononics and quantum phononics. In the third part, we discuss the potential applications. Last but not least, we point out the outlook and challenges ahead.     

MnFeP_(0.45)As_(0.55)材料中的相变研究

利用不同的测量方法,研究了MnFeP1-xAsx(0·32相似文献   

Generation and detection of quantum turbulence in superfluid 3He-B

We describe the first direct observations of turbulence in superfluid 3He-B. The turbulence is generated by a vibrating-wire resonator driven at velocities exceeding the pair-breaking critical velocity. It is detected by the resulting decrease in the thermal damping on a neighboring "detector" vibrating-wire resonator. The superfluid flow field associated with the turbulence Andreev reflects thermal quasiparticle excitations, effectively screening the detector wire, resulting in a decrease in the thermal damping.     

Evaluating the effects of loading parameters on single-crystal slip in tantalum using molecular mechanics

This study is aimed at developing a physics-based crystal plasticity finite element model for body-centred cubic (BCC) metals, through the introduction of atomic-level deformation information from molecular dynamics (MD) investigations of dislocation motion at the onset of plastic flow. In this study, three critical variables governing crystal plasticity mediated by dislocation motion are considered. MD simulations are first performed across a range of finite temperatures up to 600K to quantify the temperature dependence of critical stress required for slip initiation. An important feature of slip in BCC metals is that it is not solely dependent on the Schmid law measure of resolved shear stress, commonly employed in crystal plasticity models. The configuration of a screw dislocation and its subsequent motion is studied under different load orientations to quantify these non-Schmid effects. Finally, the influence of strain rates on thermal activation is studied by inducing higher stresses during activation at higher applied strain rates. Functional dependence of the critical resolved shear stress on temperature, loading orientation and strain rate is determined from the MD simulation results. The functional forms are derived from the thermal activation mechanisms that govern the plastic behaviour and quantification of relevant deformation variables. The resulting physics-based rate-dependent crystal plasticity model is implemented in a crystal plasticity finite element code. Uniaxial simulations reveal orientation-dependent tension–compression asymmetry of yield that more accurately represents single-crystal experimental results than standard models.     

Universal Biot number determining stress duration and susceptibility of ceramic cylinders to quenching

A universal Biot number, which not only describes the susceptibility of ceramic cylinders to quenching but also determines the duration that ceramic cylinders are subjected to thermal stress during thermal shock, is theoretically obtained. The analysis proves that thermal shock failure of ceramic cylinders with a Biot number greater than the critical value is a rapid process, which only occurs in the initial heat conduction regime. The results provide a guide to the selection of ceramic materials for thermostructural engineering, with particular reference to thermal shock.     

MnFeP0.45As0.55材料中的相变研究

利用不同的测量方法，研究了MnFeP_１-xAs_x（0.32关键词： MnFePAs 磁致伸缩 巡游电子变磁性 一级磁相变     

Effects of size and surface anisotropy on thermal magnetization and hysteresis in the magnetic clusters

Based on Monte Carlo simulation, the spin configurations, thermal magnetization and hysteresis loops of the clusters coated by the surface shell with radial anisotropy are studied. Interestingly, a new multidomain containing a few of subdomains whose easy directions are along those of the configurational anisotropy, a magnetization curve in steps and a first order phase transition from the single domain to the multidomain in the thermal and field magnetization processes, are found, which is as a result of the interplay of the configurational anisotropy, the size effect, the surface anisotropy, the applied field and the thermal fluctuation. In this first order transition, we find a critical temperature, a critical surface anisotropy and a critical size. The simulated temperature dependence of the coercivity of the cluster with the surface anisotropy can be fitted by H_c (T)=H_c (0)(1-C_αT^α) with low value of α, which explains well the experimental results of the nanoparticles. Moreover, it is found that the hysteresis loops and coercivity are strongly affected by the cluster size and the thickness of the surface layer.     

Peltier-effect-induced correction to ohmic resistance

The standard ohmic measurements by means of two extra leads contain an additional thermal correction to resistance. The current results in heating (cooling) at the first (second) sample contact because of the Peltier effect. The contact temperatures are different. The measured voltage is the sum of the ohmic voltage swing and the Peltier-effect-induced thermoelectromotive force that is linear in the current. As a result, the thermal correction to the resistance measured exists as I→0. The correction could be comparable with the ohmic resistance. Above some critical frequency depending on thermal inertial effects, the thermal correction disappears.     

Thermal conductivity of an alloy in relation to the observed cooling rate and glass-forming ability

The glass-forming ability (GFA) of an alloy in this case is the largest diameter of a rod which can be cast fully glassy. The present work shows that the thermal conductivity of a liquid alloy has a strong effect on GFA by influencing the cooling rate upon mould casting. The initial cooling rates (for the first 70–100?K of temperature decrease), obtained for Cu-, Zr- and Au-based bulk glass-forming alloys in the liquid state, are found to scale linearly with the thermal conductivities of the liquid base elements. However the low cooling rate found for Ni-based alloy suggests that the heat transfer at the melt–mould interface may also influence the cooling rate. The low thermal conductivity of Ni-based alloys and the correspondingly low cooling rate obtained compared to Cu-based counterparts explains their lower GFA. In the literature, many factors influencing the GFA of alloys have been discussed. To these factors, the present study adds the thermal conductivity of the molten alloy and the melt–mould heat-transfer coefficient. Moreover, the cooling rate depends on temperature and, thus, the critical cooling rate itself is not a suitable parameter for indicating GFA. The cooling can be better described by an appropriate fitting of the cooling curve to an exponential temperature decay function.     

Possible Fulde-Ferrell-Larkin-Ovchinnikov inhomogeneous superconducting state in CeCoIn5

We present specific heat and thermal conductivity of the heavy fermion superconductor CeCoIn5 in the vicinity of the superconducting critical fieldH _c2, measured with magnetic field in the plane of this quasi-2D compound and at temperatures down to 50 mK. The superconducting phase diagram and the first order nature of the superconducting phase transition at high fields close to a critical fieldH _c2 indicate the importance of the Pauli limiting effect in CeCoIn₅. In the same range of magnetic field we observe a second specific heat anomaly within the superconducting state, and interpret it as a signature of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) inhomogeneous superconducting state. In addition, the thermal conductivity data as a function of field display a kink at a fieldH _k below the superconducting critical field, which closely coincides with the low temperature anomaly in specific heat tentatively identified with the appearance of the FFLO superconducting state. The enhancement of thermal conductivity within the FFLO state calls for further theoretical investigations of the real space structure of the order parameter (and in particular, the structure of vortices) and of the thermal transport within the inhomogeneous FFLO state.     

The magnetic critical exponent in the three-state three-dimensional Potts model

We perform a numerical study of the Potts model q=3 in three dimensions with nearest neighbour and next to nearest neighbour couplings by means of the finite-size renormalization group method. The analysis of the magnetic critical exponents is complementary to the one of the thermal critical exponent already presented by us and confirms our conclusions that the transition from the disordered phase to the low-temperature ordered phase is first order.     

Wilson renormalization group formulation of real time thermal field theories

We apply Renormalization Group techniques to the Real Time formulation of thermal field theory. Due to the separation between the T = 0 and the T ≠ 0 parts of the propagator in this formalism, one can derive exact evolution equations for the Green functions describing the effect of integrating out thermal fluctuations of increasing wavelengths, the initial conditions being the renormalized Green functions of the T = 0 theory. As a first application, we study the phase transition for the real scalar theory, computing the order of the transition, the critical temperature, and critical exponents, in different approximations to the evolution equations for the scalar potential.     

The effect of temperature on generic stable periodic structures in the parameter space of dissipative relativistic standard map

In this work, we have characterized changes in the dynamics of a two-dimensional relativistic standard map in the presence of dissipation and specially when it is submitted to thermal effects modeled by a Gaussian noise reservoir. By the addition of thermal noise in the dissipative relativistic standard map (DRSM) it is possible to suppress typical stable periodic structures (SPSs) embedded in the chaotic domains of parameter space for large enough temperature strengths. Smaller SPSs are first affected by thermal effects, starting from their borders, as a function of temperature. To estimate the necessary temperature strength capable to destroy those SPSs we use the largest Lyapunov exponent to obtain the critical temperature (T _C ) diagrams. For critical temperatures the chaotic behavior takes place with the suppression of periodic motion, although the temperature strengths considered in this work are not so large to convert the deterministic features of the underlying system into a stochastic ones.     

Theory of the vortex matter transformations in high-Tc superconductor YBCO

Flux line lattice in type II superconductors undergoes a transition into a "disordered" phase such as vortex liquid or vortex glass, due to thermal fluctuations and random quenched disorder. We quantitatively describe the competition between the thermal fluctuations and the disorder using the Ginzburg-Landau approach. The following T-H phase diagram of YBCO emerges. There are just two distinct thermodynamical phases, the homogeneous and the crystalline one, separated by a single first order transition line. The line, however, makes a wiggle near the experimentally claimed critical point at 12 T. The "critical point" is reinterpreted as a (noncritical) Kauzmann point in which the latent heat vanishes and the line is parallel to the T axis. The magnetization, the entropy, and the specific heat discontinuities at melting compare well with experiments.     

The thermal conductivity of argon,carbon dioxide and nitrous oxide

The paper presents new, absolute measurements of the thermal conductivity of three gases: argon (Ar), carbon dioxide (CO₂) and nitrous oxide (N₂O). The measurements have been carried out with a transient hot-wire instrument in the temperature range 308 to 430 K and at pressures up to 11 MPa. For most of the range of thermodynamic states covered by the measurements it is estimated that the accuracy of the thermal conductivity data is one of ±0.3%. However, for carbon dioxide and nitrous oxide near their critical conditions the accuracy is degraded and the uncertainty may be as much as ±2%. The new experimental data for argon confirm the accuracy claimed for the thermal conductivity in the limit of zero-density.The thermal conductivity of the polyatomic gases in the limit of zero-density is used in conjunction with information on other transport cross-sections for the same systems, to extract a consistent set of cross-sections sensitive to the anisotropy of the intermolecular pair potential for use in the testing of proposed potential surfaces. Cross-sections for both of the available formulations of the thermal conductivity of a polyatomic gas due to Wang Chang and Uhlenbeck and Thijsse et al. are derived. For both gases it is shown that the Mason-Monchick approximation breaks down in either formulation. However, the effect of the failure on the formulation of Thijsse et al. is smaller and it is possible to represent the data with the aid of a single cross-section which has a very simple temperature dependence. The analysis also demonstrates that all available high-temperature thermal conductivity data for carbon dioxide are in substantial error.In the moderately dense gas the concept of a temperature-independent excess thermal conductivity is confirmed to a high degree of precision for carbon dioxide and argon when due allowance is made for the critical enhancement. A generalized correlation of the temperature dependence of the first density coefficient of thermal conductivity is broadly confirmed.     

Opposed-flow flame spread in microgravity-theoretical prediction of spread rate and flammability map

The spread rate formulas of de Ris in the thermal regime of opposed-flow flame spread are inarguably the most well-known formulas in the flame spread literature. Similar easy-to-use formulas are lacking in all other regimes of flame spread. This paper presents a simplified analysis leading to the development of closed-form expressions for spread rate for both thin and thick fuels in the microgravity regime of opposed-flow flame spread. The resulting formulas, expressed in terms of the thermal limit of spread rate and a radiation number that can be evaluated from the known parameters of the problem, are shown to reproduce the experimentally and numerically observed trends quite well at both limits of fuel thickness. These formulas are utilized to develop quantitative criterion to delineate thin and thick fuels in the microgravity and thermal regimes. The transition between the microgravity and thermal regimes is also explored. The flammability maps, derived from the spread rate expressions, are the first of their kind, establishing fuel thickness as one of the critical parameters.     

Thermal stabilization of the resistive states of superconducting composites: Quasilinear approximation

The conditions of the occurrence and development of thermal instabilities in the composite superconductor with a continuously increasing current-voltage characteristic, which is described by the power equation, have been studied. The conditions for thermal stabilization have been analyzed in the general form using dimensionless variables that keep their invariance when varying. For the local temperature disturbance, the critical energies and velocities of its irreversible propagation have been calculated. It has been proved that composites superconductors can have stable states, when the ultimate currents can be higher or lower of the conventionally preset critical current of the composite. Furthermore, superconductivity destruction at supercritical currents takes place not in the form of a stepwise transition from the superconducting to normal state, but due to the formation of thermal and electric switching waves that propagate along the composite superconductor with a constant speed. The condition for full thermal stabilization has been formulated for the superconducting composites with a power current–voltage characteristic. The results of the numerical experiments have proved that the existing theory of thermal stabilization, which assumes a stepwise superconducting–normal transition, leads to the considerable limitation of the range of the stable currents, at which a superconducting state can be kept.