On the electronic contribution to the surface energy of metals

An expression for the exchange and correlation contributions to the surface energy of metals is derived using the dielectric formulation of the electron gas. The result which is obtained in the infinite barrier model for the surface is exact within the RPA and include the off-diagonal character of the response function.     

On the plasmon contribution to the surface energy of metals

The agreement between a recently propounded theory of metallic surface energies and experiment is a consequence of the arbitrary choice of the same plasmon cut-off wave-vector, k_c, for both bulk and surface plasmons. With a more reasonable choice of k_c's, the ‘plasmon theory’ predicts negative surface energies.     

On the relation between monovacancy formation energy and surface energy for metals

An empirical relation between vacancy formation energy, surface energy and nearest-neighbor separation for metals is presented and the basis for this correlation is discussed.     

On the collective contribution to the surface energy of simple metals

A recent analysis by Feibelman of the contribution of collective modes to the surface energy is re-examined. When sum rule considerations are studied, his negative energy results are found to be spurious.     

On the origin of optics

The first optical devices in animals evolved in the Cambrian period. The first reflector known dates from around 508 million years ago (Ma); the first eyes with lenses evolved at around 521 Ma. Consideration of the introduction of vision leads to a hypothesis for the cause of evolution's Big Bang—the Cambrian explosion. Suddenly, and for no obvious reason, the range and variety of life-forms erupted somewhere between 520 and 515 Ma (as limited by of our dating techniques). At no other time in Earth's history there has been such a profusion, such an exuberance, and such an overwhelming diversity in so short time, within one million years. Prior to this Cambrian explosion event, all animals were soft-bodied and mainly worm-like, as they had been for millions of years before that. But during the Cambrian explosion many of the major animal groups on Earth today independently evolved their hard body parts for the first time. Following the appearance of the first trilobites, some animals evolved shells and spines, some with bright colours, to visually warn of their new armour. Others evolved streamlined appearances and swimming oars to advise trilobites that they could not be caught. The Light Switch Theory provides an explanation for what triggered this event—that it was the development of vision (in trilobites); the introduction of optics. Once visual capability arose, it allowed predators to identify prey, triggering an arms race. From here on, vision became a dominant force of evolution and resulted in the eyes and reflecting optics that we have in nature today. This paper provides a summary of the first optical devices to evolve in animals, along with the implications of these in their relevance to the Big Bang of evolution, written for the physical sciences.     

Hand-held laser welding of metals using fibre optics

A fibre optic delivery system has for the first time been used in laser welding of metals. The optical fibre is flexible and has a length of 140 cm. It can transmit pulsed energies from a Nd-YAG laser in excess of 25 J with an efficiency of 85%. Potential applications in industry and in dentistry are discussed.     

On the asymptotic behaviour of solutions of a stochastic energy balance climate model

We prove the existence of a random global attractor for the multivalued random dynamical system associated to a nonlinear multivalued parabolic equation with a stochastic term of amplitude of the order of $\epsilon$. The equation was initially suggested by North and Cahalan (following a previous deterministic model proposed by M.I. Budyko), for the modeling of some non-deterministic variability (as, for instance, the cyclones which can be treated as a fast varying component and are represented as a white-noise process) in the context of energy balance climate models. We also prove the convergence (in some sense) of the global attractors, when $\epsilon \to 0$, i.e., the convergence to the global attractor for the associated deterministic case ($\epsilon =0$).     

Correlation effects in the surface energy of metals

It is argued that the correlation energy plays a minor role in the surface energy of metals, compared to kinetic, electrostatic and exchange energies. Recent work in which the surface energy is attributed primarily to changes in plasmon zero point energy during the creation of the surface is criticized.     

Physics of the Earth's radiative energy balance

Clusters are aggregates of atoms or molecules in the form of microscopic and submicroscopic particles. They are of practical interest in many diflerent contexts. At the same time they represent an inroad to the understanding of condensed matter in bulk, much as embryology is important for the understanding of full-grown organisms. But just as embryonic development illuminates biological laws in peculiar and often unique ways, so recent research on clusters has uncovered a number of laws that are speciJic to submicroscopic particles. As a particularly striking example, one jinds that the conduction electrons in a small drop of sodium, or some other simple metal, form an ordered quantum state in analogy with the ordered electron structure in atoms. As a consequence, small metal clusters form a periodic system like the system of chemical elements—only much larger.     

On the nonlinear optics of few-cycle pulses

A brief review of the development of the nonlinear optics of few-cycle optical laser pulses is presented. Emphasis is placed on analyzing the soliton propagation modes of such pulses in the context of possible applications in optical data transmission systems.     

Optical energy balance in laser-produced plasmas

Optical energy balance in plasmas produced by irradiating solid targets by highpower laser pulses, has been experimentally determined. The total light scattered has been measured as a function of the laser intensity and the irratiated spot diameter. It has been found that the net light absorption does not depend on the laser intensity alone, but is also affected by the irradiated spot area. It has also been observed that diffuse back reflection becomes a dominant loss mechanism at high incident flux and small irradiated spot area.     

Multiple-wave diffraction in high energy resolution back-reflecting x-ray optics

We have studied the effects of multiple-wave diffraction in a novel optical scheme recently published by Shvyd'ko et?al. utilizing Bragg diffraction of x?rays in backscattering geometry from asymmetrically cut crystals for achieving energy resolutions beyond the intrinsic width of the Bragg reflection. By numerical simulations based on dynamic x-ray diffraction and by experimentation involving two-dimensional angular scans of the back-reflecting crystal, multiple-wave diffraction was found to contribute up to several tens percent loss of efficiency but can be avoided without degrading the energy resolution of the original scheme by careful choice of azimuthal orientation of the diffracting crystal surface and by tilting of the crystal perpendicular to the dispersion plane.     

On optics of human meridians

A new concept and its methodology for studying human meridians are presented based on rigorous and scientific observation on the objective existence of human meridians in view of biomedical optics. According to this methodology, the infrared radiant characteristics of acupuncture meridians over human body and the optical transport properties of light propagating along the meridian are reported. This study, thus, confirms the existence of acupuncture meridians, sheds new light on an approach to investigation of human meridians and offers a new perspective in understanding the potential meridian functions such as energy and information transfer and physiological regulation. Supported by the National Key Basic Research Program of China (Grant No. 2006CB504505), the National Natural Science Foundation of China (Grant Nos. 60578056 and 30572309), the Science Research Foundation of Ministry of Health & United Fujian Provincial Health and Education Project for Tackling the Key Research of China (Grant No. WKJ2005-2-004), the Young Scientists and Technicians Innovation Project of Fujian Province (Grant No. 2007F3026), and the Fund from Fujian Normal University (Grant No. 2008100218)     

On negative refraction in electron optics

Negative refraction is investigated within the context of both relativistic and non-relativistic electron optics. In fact, starting from the de Broglie wave-particle dualism, the negative refractive index as a function of wavelength is determined for both relativistic and non-relativistic electrons. Comparison with photon optics is done. Negative refractive index averaged over both sufficiently small and sufficiently large wavelength ranges is found to be tending to minus unity and minus infinity, respectively. In addition, the sensitivity to wavelength of the negative refractive index is evaluated.     

The peierls energy and kink energy in fcc metals

In fcc crystals, dislocations are dissociated on the {111} glide plane into pairs of partial dislocations. Since each partial interacts individually with the Peierls potential and is coupled to its neighbour by a stacking fault, periodic variations in the separation distance d of the partials occur when dislocations running along closed packed lattice directions are displaced. This can drastically reduce the effective Peierls stress. By using the Peierls model the structure of 0°, 30°, 60° and 90° dislocations in a typical fcc metal with the elastic properties of Cu and a stacking-fault energy γ₀ in the interval 0.04?≤?γ₀?≤?0.05?J/m² was studied, and the magnitude of the Peierls energy ΔE _P and the resulting kink energies E _K were determined. Since the energies involved are of the order of 10^?3?eV/b or less, their magnitude cannot be asserted with high confidence, considering the simplifying assumptions in the model. The difference in the changes of the core configuration during displacement of dislocations of different orientations should, however, be of physical significance. It is found that a dissociated 60° dislocation generally has a higher effective Peierls energy than a screw dislocation, but the reverse is true for the kink energy, at least in Cu.     

On the origin of the integral representations in quantum optics

In Abelian subalgebras of observables it is shown that the integral representations of states in terms of coherent states result from the indistinguishability of the quanta of the harmonic oscillator under consideration. It is argued that these integral representations contain a quantum de Finetti theorem on Bose-Fock space.     

Low energy excitations in amorphous metals

The low temperature properties of amorphous metals pertinent to the existence of low energy excitations are reviewed. In an introductory section, the currently accepted model for low energy excitations, i.e. the model of two level systems (TLS), is discussed. The treatment of amorphous metals focuses on the specific heat C, thermal conductivity κ, ultrasonic properties and electrical resistivity ?. Measurements of C and κ are often performed on amorphous superconductors in order to exclude the effect of conduction electrons. The TLS density of states and the TLS-phonon coupling in these materials as determined from C and κ respectively are surprisingly close to values for insulating glasses. Ultrasonic experiments carried out mostly on normal amorphous metals reveal a strongly enhanced TLS relaxation rate with respect to insulators. This can be attributed to TLS-electron coupling. The effect of this coupling on ? is uncertain at present. In order to obtain more insight into the microscopic origin of TLS in metallic and insulating glasses some examples of TLS in crystalline disordered solids are discussed. Finally, some formal analogies are drawn between spin glasses and real glasses.     

Simulating high energy cascades in metals

Abstract

The processes of radiation damage, from initial defect production to microstructure evolution, occur over a wide spectrum of time and size scales. An understanding of the fundamental aspects of these processes requires a spectrum of theoretical models, each applicable in its own time and distance scales. As elements of this multi-model approach, molecular dynamics and binary collision simulations play complementary roles in the characterization of the primary damage state of high energy collision cascades. Molecular dynamics is needed to describe the individual point defects in the primary damage state with the requisite physical reality. The binary collision approximation is needed to model the gross structure of statistically significant numbers of high energy cascades. Information provided by both models is needed for connecting the defect production in the primary damage state with the appropriate models of defect diffusion and interaction describing the microstructure evolution. Results of binary collision simulations of high energy cascade morphology are reviewed. The energy dependence of freely migrating defect fractions calculated in recent molecular dynamics simulations are compared to results obtained much earlier with a binary collision/annealing simulation approach. The favorable agreement demonstrates the viability of the multi-model approach to defect production in high energy cascades.