Studying anomalous scaling and heat transport of turbulent thermal convection using a dynamical model

Turbulent thermal convection is a well-studied problem with various issues of interest. In this paper, we review our work which shows the nature and origin of anomalous scaling and heat transport in the limit of very strong thermal forcing, can be gained by studying a dynamical model, known as shell model, of homogeneous turbulent thermal convection in which buoyancy acts directly at most scales. Specifically, we have obtained two results. The first result is that when buoyancy acts directly at most scales such that the dynamics are governed by a cascade of entropy, the scaling behavior is described by Bolgiano and Obukhov scaling plus corrections that are due to the variations of the local entropy transfer rate. This result indicates the validity of the extension of refined similarity hypothesis to turbulent thermal convection. The second result is that when buoyancy is acting directly at most scales, a damping term acting on the largest scale, which has to be added for the system to achieve stationarity, plays a crucial role in heat transport, and that the heat transport depends on the strength of thermal forcing in the same manner as that predicted for the ultimate state of very strong thermal forcing. With our interpretation of the damping term representing the effect of the boundaries, this result indicates that in the ultimate state of turbulent thermal convection, when buoyancy is acting at most scales, boundaries would play a significant role in heat transport.     

Particle Acceleration by Shocks in Supernova Remnants

Particle acceleration occurs on a range of scales from AU in the heliosphere to Mpc in clusters of galaxies and to energies ranging from MeV to exaelectronvolt (EeV). A number of acceleration processes have been proposed, but diffusive shock acceleration (DSA) is widely invoked as the predominant mechanism. DSA operates on all these scales and probably to the highest energies. DSA is simple, robust and predicts a universal spectrum. However, there are still many unknowns regarding particle acceleration. This paper focuses on the particular question of whether supernova remnants (SNR) can produce the Galactic cosmic ray (CR) spectrum up to the knee at a few petaelectronvolt (PeV). The answer depends in large part on the detailed physics of diffusive shock acceleration.     

Solid-oxide fuel cells with hydrocarbon fuels

Solid-oxide fuel cells can directly use hydrocarbon or hydrocarbon-derived fuels. Conversion efficiencies can be considerably greater than those of heat engines, with hybrid cycles in combination with heat engines and co-generation promising conversion efficiencies as high as 70%. This paper discusses the fundamental concepts of fuel cells, concentrating on the underlying chemical and electrochemical processes. Fully understanding fuel cell function requires attention to physical and chemical processes that span length scales ranging from atomistic to meter-scale systems. Beyond the electrochemistry that is responsible for electrical energy production, fuel cell function relies on chemically reacting flow, porous-media transport, and heterogeneous thermal chemistry. Especially with hydrocarbon and hydrocarbon-derived fuels, there are interesting scientific and engineering connections, and analogies with combustion science and technology.     

Wavelet-analysis of polarization maps of human blood plasma

Possibilities of local wavelet-analysis of coordinate distributions of polarization azimuths and ellipticity of laser images of blood plasma in healthy and cancer patients are considered. The set of statistical, correlation, and fractal parameters of distributions of wavelet-coefficients characterizing different scales of geometric dimensions of amino acid polycrystalline networks is determined. The criteria for the differentiation of transformation processes of birefringence of optically anisotropic structures of blood plasma at different scales are established.     

Adiabatic Theorems and Reversible Isothermal Processes

Isothermal processes of a finitely extended, driven quantum system in contact with an infinite heat bath are studied from the point of view of quantum statistical mechanics. Notions like heat flux, work and entropy are defined for trajectories of states close to, but distinct from states of joint thermal equilibrium. A theorem characterizing reversible isothermal processes as quasi-static processes (“isothermal theorem”) is described. Corollaries concerning the changes of entropy and free energy in reversible isothermal processes and on the 0th law of thermodynamics are outlined.*Supported by the Swiss National Foundation.     

Dissipative processes in peripheral heavy ion collisions at Fermi energies

Peripheral heavy ion reactions are of interest for the production of new isotopes. In this contribution we present an investigation of reactions of light projectiles O and Ne on Be and Ta targets at Fermi energies in the framework of transport theory. Transport theory describes dissipative (deep-inelastic) processes, where considerable amounts of mass and energy are exchanged. The data, on the other hand, also seem to include a more direct component with small energy loss. We separate the two components on the basis of the velocity distribution and compare the dissipative component to the transport calculations. The primary fragments of the transport calculation still have considerable excitation energies. For the comparison with experiment we take into account the secondary evaporation in a statistical model. This improves the qualitative agreement with the data.     

Torque scaling in turbulent Taylor-Couette flow with co- and counterrotating cylinders

We analyze the global transport properties of turbulent Taylor-Couette flow in the strongly turbulent regime for independently rotating outer and inner cylinders, reaching Reynolds numbers of the inner and outer cylinders of Re(i) = 2×10(6) and Re(o) = ±1.4×10(6), respectively. For all Re(i), Re(o), the dimensionless torque G scales as a function of the Taylor number Ta (which is proportional to the square of the difference between the angular velocities of the inner and outer cylinders) with a universal effective scaling law G ∝ Ta(0.88), corresponding to Nu(ω) ∝ Ta(0.38) for the Nusselt number characterizing the angular velocity transport between the inner and outer cylinders. The exponent 0.38 corresponds to the ultimate regime scaling for the analogous Rayleigh-Bénard system. The transport is most efficient for the counterrotating case along the diagonal in phase space with ω(o) ≈ -0.4ω(i).     

金原子纳米团簇的负热容现象的分子动力学模拟研究

文中采用微正则分子动力学方法模拟研究了原子数N=60到675之间的6种金原子纳米团簇从固态到液态的熔解过程,得到了势能和热容量随温度的变化关系.其结果表明,所模拟的6种团簇在熔点附近出现负热容,通过对这些团簇熔解前后的势能以及结构变化的分析,探讨了产生负热容的微观机制.     

Collider physics at HERA

From 1992 to 2007, HERA, the first electron-proton collider, operated at cms energies of about 320 GeV and allowed the investigation of deep-inelastic and photoproduction processes at the highest energy scales accessed thus far. This review is an introduction to, and a summary of, the main results obtained at HERA during its operation.     

Low-magnetic-field divergence of the electronic g factor obtained from the cyclotron spin-flip mode of the nu=1 quantum Hall ferromagnet

We report an inelastic light scattering study of the cyclotron spin-flip mode in the two-dimensional electron system at filling nu=1. The energy of this mode can serve as a probe of the many-body exchange interaction on short length scales. Its magnetic field dependence is compared with predictions based on Hartree-Fock theory. They agree well when including the nonzero width of the electron system. From the measured energies, the exchange enhanced g factor is extracted. It diverges at small fields and differs largely from g factors obtained via transport activation studies.     

非均一多孔介质中的水热迁移研究

孔隙裂隙非均一多孔介质中水热迁移的研究，国际上只是近年来才开始取得明显的进展。在发育裂隙的孔隙岩层中同时存在着两种渗流系统：孔隙总体积较大、渗透性相对弱的多孔岩块和总体积较小、渗透性却相对较强的分割多孔块体的裂隙。从而提出了“孔隙一裂隙二重性”假定，即地下水主要贮存在孔隙中，而水的运动主要在裂隙中进行，用一个一阶量描述孔隙裂隙间水流（热流）的传递耦合项。本文导出描述孔隙─裂隙岩层中的水流和热迁移的基本微分方程，建立起相应的数学模型，并成功地用于我国西藏羊八井热田分布参数模型的水热迁移研究。     

Spin-polarized transient electron trapping in phosphorus-doped silicon

Experimental evidence of electron spin precession during travel through the phosphorus-doped Si channel of an all-electrical device simultaneously indicates two distinct processes: (i) short time scales (≈50 ps) due to purely conduction-band transport from injector to detector and (ii) long time scales (≈1 ns) originating from delays associated with capture or reemission in shallow impurity traps. The origin of this phenomenon, examined via temperature, voltage, and electron density dependence measurements, is established by means of a comparison to a numerical model and is shown to reveal the participation of metastable excited states in the phosphorus-impurity spectrum. This work therefore demonstrates the potential to make the study of macroscopic spin transport relevant to the quantum regime of individual spin interactions with impurities as envisioned for quantum information applications.     

Thermal Transport in One-Dimensional FPU-FK Lattices

Thermal transport in the FPU model with FK on-site potential is studied by using fourth-order Runge-Kutta algorithm. The heat flux, local temperature profile, and heat conductivity are simulated and analyzed. It is found that temperature gradient scales behave as N^-1 linearly. The divergence of heatconductivity κ with system size N is in term of κ∝ N^α with α=0.44. It is shown that thermal transport is mainly dependent on the FPU nonlinear and the FK interactions.     

Radio-frequency single-electron refrigerator

We propose a cyclic refrigeration principle based on mesoscopic electron transport. Synchronous sequential tunneling of electrons in a Coulomb-blockaded device, a normal metal-superconductor single-electron box, results in a cooling power of approximately k(B)T x f at temperature T over a wide range of cycle frequencies f. Electrostatic work, done by the gate voltage source, removes heat from the Coulomb island with an efficiency of approximately k(B)T/Delta, where Delta is the superconducting gap parameter. The performance is not affected significantly by nonidealities, for instance by offset charges. We propose ways of characterizing the system and of its practical implementation.     

Collider physics at high energies and low luminosities

While very high acceleration gradients are expected in novel accelerating schemes such as those discussed by IZEST, generating high luminosities will be extremely challenging and will likely require a separate technology revolution. It is important to determine if a low-luminosity but high energy collider would have serious interest from a particle physics perspective. We consider a process involving physics beyond the Standard Model that would be detectable at high energies without requiring the types of luminosities normally quoted for future colliders, “classicalization”. In this example, scattering cross sections grow with a power of the center-of-mass energy, thereby reducing the luminosity requirement at high energies. Another process discussed is deep-inelastic-scattering of electrons on protons, where a precision measurement of the energy dependence of the scattering cross section could yield information about physics processes at much higher scales.     

Energy scales and the non-Fermi liquid behavior in YbRh<Subscript>2</Subscript>Si<Subscript>2</Subscript>

Multiple energy scales are detected in measurements of the thermodynamic and transport properties in heavy fermion metals. We demonstrate that the experimental data on the energy scales can be well described by the scaling behavior of the effective mass at the fermion condensation quantum phase transition, and show that the dependence of the effective mass on temperature and applied magnetic fields gives rise to the non-Fermi liquid behavior. Our analysis is placed in the context of recent salient experimental results. Our calculations of the non-Fermi liquid behavior, of the scales and thermodynamic and transport properties are in good agreement with the heat capacity, magnetization, longitudinal magnetoresistance and magnetic entropy obtained in remarkable measurements on the heavy fermion metal YbRh₂Si₂.