界面羟基对碳纳米管摩擦行为和能量耗散的影响

本文采用分子动力学模拟研究了羟基对碳纳米管摩擦和能量耗散方式的影响.研究结果表明:由于界面间氢键的形成,碳纳米管所受的平均摩擦力明显增大;随着羟基比例的改变,界面间氢键的数量与摩擦力的变化趋势一致;碳纳米管的手性角对摩擦力有一定的影响,扶手椅型碳纳米管所受的摩擦力比其他类型的碳纳米管的大;直径对摩擦力的影响较大,直径越大界面间的摩擦力越大,其原因是大直径的碳纳米管底部变平导致界面接触面积增大;界面接枝羟基后,体系的声子态密度中出现羟基的振动峰;随羟基比例的增加,羟基的振动在能量耗散中起到更为重要的作用,当碳纳米管和硅基底的羟基比例为10%/20%时,体系能量耗散的主要途径由碳纳米管和硅基底的振动转变为羟基的振动.     

Fission with microscopic energy dissipation

We calculate the non-adiabatic excitations of pair states in a BCS formalism for a fissioning²³⁶U nucleus. The single-particle spectrum is calculated for a folded-Yukawa potential along a deformation path that is determined classically for one-body dissipation. The resulting microscopic energy dissipation is compared to that due to one- and two-body dissipation.     

Casimir energy dissipation in media at rest

From classical electrodynamics the energy dissipation per unit volume in a dispersive nonmagnetic medium is known to be equal to ωϵ″(ω) 〈E²〉, where ϵ″ denotes the imaginary part of the permittivity. The present work calculates the energy dissipation per unit surface area when two semi-infinite homogenous slabs are separated by a gap a. Only the gap-induced part of the dissipation is taken into account, so that the effect may be called a Casimir dissipative effect. Subtracting off the formal T = 0 expression the net dissipation is found to be negative. This reflects the fact that the dissipation in the presence of a gap is less than it would be in the case of a single homogeneous medium (i.e., a = ∞).     

Dynamical behavior of entanglement, purity and energy for two atoms in the presence of dissipation

Entanglement, purity and energy of two isolated two-level atoms which are initially prepared in Bell state and each interacts with a dissipative thermal cavity field are investigated with considering the atomic motion and the field-mode structure. We give the analytical solution of the atomic state by using the algebraic dynamics approach. The influences of the field-mode structure, the dissipation of the cavities, the strength of the thermal field and the detuning on the entanglement, purity and energy are discussed. We also study the evolution of the atomic state using the entanglement-purity-energy diagrams. Our results suggest that the disentanglement process of the atomic state accompanies with the excitations transferring from atoms to the cavity field modes and with the state converting from a pure one to the mixed ones. When the two atoms become separable, they must be in the mixed states, and their energy decreases with the increase of the purity.     

Stick-slip friction and energy dissipation in boundary lubrication

Shearing of a simple nonpolar film, right after the liquid-to-solid phase transition under nanometer confinement, is studied by using a liquid-vapor molecular dynamics simulation method. We find that, in contrast with the shear melting and recrystallization behavior of the solidlike phase during the stick-slip motion, interlayer slips within the film and wall slips at the wall-film interface are often observed. The ordered solidified film is well maintained during the slip. Through the time variations of the frictional force and potential energy change within the film, we find that both the friction dissipation during the slip and the potential energy decay after the slip in the solidified film take a fairly large portion of the total energy dissipation.     

Onset of energy dissipation in ballistic atomic wires

Electronic transport at finite voltages in free-standing gold atomic chains of up to seven atoms in length is studied at low temperatures using a scanning tunneling microscope. The conductance vs voltage curves show that transport in these single-mode ballistic atomic wires is nondissipative up to a finite voltage threshold of the order of several mV. The onset of dissipation and resistance within the wire corresponds to the excitation of the atomic vibrations by the electrons traversing the wire and is very sensitive to strain.     

Bonding and energy dissipation in a nanohook assembly

Combining total energy and molecular dynamics calculations, we explore the suitability of nanotube-based hooks for bonding. Our results indicate that a large force of 3.0 nN is required to disengage two hooks, which are formed by the insertion of pentagon-heptagon pairs in a (7,0) carbon nanotube. Nanohooks based on various nanotubes are resilient and keep their structural integrity during the opening process. Arrays of hooks, which are permanently anchored in solid surfaces, are a nanoscale counterpart of velcro fasteners, forming tough bonds with a capability of self-repair.     

Mechanism of energy dissipation in a droplet cluster

It has been shown that thermocapillary processes on the surface of the drops in a drop cluster that appears above a locally heated liquid ensure additional energy transfer. Thus, the drop cluster is a typical dissipative structure. The energy dissipated by an individual drop of the cluster has been estimated.     

Critical behavior in type-II superconductors

The high-field critical behavior of type-II superconductors with weak disorder is dominated by the Landau levels of Cooper pairs. The macroscopic degeneracy of Landau manifolds suppresses phase coherence and eliminates the Abrikosov transition in dimensions two and three. A novel phase transition, unrelated to the conventional Abrikosov transition, is predicted to take its place. At this transition the normal state is unstable to the charge-density wave of Cooper pairs. The nature of this new state is discussed. This phase should be most readily observable in layered materials at fields > 1–10T.     

Effects of energy dissipation on anisotropic materials

A model and its simulations are presented to describe the effects of energy dissipation on anisotropic systems. When the current electromigration is constant, energy dissipation depends on lattice constants, resistivity, and the angles along the longitudinal and transversal directions. It is shown that an orientation variation of the grain can significantly influence the energy dissipation for some anisotropic materials. Based on calculations for the grain model, the mechanism of grain growth and microstructure evolution under electromigration is explained. Theoretical implications about material selection and reliability are derived.     

Structure functions in a model of turbulent energy dissipation

A stochastic activity-transfer model, previously proposed to apply to turbulence, is studied and simulated on a 256×256 lattice. Introduction of random self-activation does not allow stable fronts to develop in the limit of small growth probability. By assigning discrete density values equal to the threshold values in a related continuous and deterministic model, the structure functions for distancesr in the lattice are calculated. They have a functional form different from the power behavior which in the case of the deterministic version was interpreted as another sign of self-organized criticality. Future studies of these and other models may be facilitated by the algorithm developed for structure function calculations.     

Uncertainty principle and minimal energy dissipation in the computer

Reversible computation is briefly reviewed, utilizing a refined version of the Bennett-Fredkin-Turing machine, invoked in an earlier paper. A dissipationless classical version of this machine, which has no internal frietion, and where the computational velocity is determined by the initial kinetic energy, is also described. Such a machine requires perfect parts and also requires the unrealisstic assumption that the many extraneous degrees of freedom, which contribute to the physical structure, do not couple to the information-bearing degrees of freedom, and thus cause no friction Quantum mechanical computation is discussed at two levels. First of all we deplore the assertion. repcatedly found in the literature, that the uncertainty principle. Eth, with t equated to a switching time, yields any information about energydissipation. Similarly we point out that computation is not an iterated transmission and receiving process, and that considerations, which avoid the uncertainty principle, and instead use quantum mechanical channel capacity considerations, are equally unfounded. At a more constructive level we ask whether there is a quantum mechanical version of the dissipationless computer. Benioff has proposed one possible answer Quantum mechanical versions of dissipationless computers may suffer from the problems found in electron transport in disordered one-dimensional periodic potentials. The buildup of internal reflections may give a transmission coefficient. through the whole computation, which decreases exponentially with the length of the computation.     

Temperature dependence of energy dissipation in type I superconductors

Energy dissipation due to the movement of the magnetic flux in superconducting tin was studied by means of the torsion pendulum technique. The study was made as a function of the mean velocity of vortices, applied magnetic field and temperature. A phenomenological expression for the energy dissipation is proposed. This model explained our experimental results as well as these obtained previously by Houston and Smith.     

On the energy dissipation in a convective well-mixed layer

Summary Energy dissipation in a convective atmospheric mixed layer and its parametrization are discussed. A formulation of energy dissipation based on the results of Zeman and Tennekes and Kitaigoroskii is proposed.

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Riassunto In questo lavoro si discutono il ruolo e la parametrizzazione dell'energia dissipata nei moti convettivi che generano lo strato rimescolato in atmosfera. Si propone una possibile parametrizzazione basata sui precedenti lavori di Kitaigoroskii e di Zeman e Tennekes.

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Резюме Обсуждается диссипация энергии в конвективном атмосферном перемешанном слое и параметризация диссипации. Предлагается формулировка диссипации энергии, основанная на результатах Земана и Тенекеса (1976) и Китайгородского (1978).

     

Critical behavior in radiation damaged systems

Perturbed angular distribution (PAD) measurements of Bleck et al. of the critical behavior of⁶³NiNi,⁶⁶CuNi, and⁶⁷ZnNi have been reanalyzed, and shown to be insufficiently asymptotic to permit deduction of meaningful critical exponents. Via experiments on implanted¹¹¹InNi, done with and without annealing of radiation damage, and by comparison to diffused¹¹¹InNi, it is suggested that unannealed radiation damage can produce serious systematic errors in critical exponents.This work has been supported in part by DMR 01250 from the U.S. National Science Foundation to Clark University, and in part by the Stichting voor Fundamenteel Onderzoek der Materie, the Netherlands     

不同材料回旋管输出窗的临界热耗散功率

 从陶瓷介质材料的临界温度差出发,研究了不同材料的回旋管输出窗的临界热耗散功率。针对TE₀₁,TE11和TE₀₂模式的电磁波通过窗片时发生的不同加热模式进行分析,比较了氧化铝窗片、氧化铍窗片、氮化硼窗片和蓝宝石窗片的热功率承受能力。另外,研究了窗片厚度变化时,不同材料窗片的临界热耗散功率的变化情况。研究表明：蓝宝石和氧化铍窗片表现出较好的热功率耗散能力,其中以蓝宝石窗片最为出色;氧化铝和氮化硼窗片的热功率耗散能力相对较弱;随着窗片厚度的增加,4种材料的临界热耗散功率均有不同程度的变大,其中以蓝宝石和氧化铍窗片更为明显。     

不同材料回旋管输出窗的临界热耗散功率

从陶瓷介质材料的临界温度差出发,研究了不同材料的回旋管输出窗的临界热耗散功率。针对TE01,TE11和TE02模式的电磁波通过窗片时发生的不同加热模式进行分析,比较了氧化铝窗片、氧化铍窗片、氮化硼窗片和蓝宝石窗片的热功率承受能力。另外,研究了窗片厚度变化时,不同材料窗片的临界热耗散功率的变化情况。研究表明：蓝宝石和氧化铍窗片表现出较好的热功率耗散能力,其中以蓝宝石窗片最为出色;氧化铝和氮化硼窗片的热功率耗散能力相对较弱;随着窗片厚度的增加,4种材料的临界热耗散功率均有不同程度的变大,其中以蓝宝石和氧化铍窗片更为明显。     

界面摩擦过程非连续能量耗散机理研究

结合无磨损界面摩擦微观能量耗散机理的复合振子模型,运用量子理论建立了微观能量耗散的量子力学模型.分析表明：在滑动过程中,当界面原子从一种平衡态跳跃至另一种平衡态时,摩擦功以离散形式耗散为界面原子热振子,且界面吸收能量的能力是离散的;高能态界面较低能态界面吸收能量的能力强,表现为易于吸收界面势能.界面原子吸收和释放能量的离散性在宏观上表现为摩擦功耗散的非连续性,为从微观角度解释无磨损界面摩擦状态周期性变化提供了理论基础. 关键词： 摩擦 非连续能量耗散 复合振子模型