均质旋转面绕旋转轴转动的转动惯量

根据转动惯量的定义推得任意形状均质旋转面对旋转轴的转动惯量的计算公式,文中讨论了鼓形面、花瓶形面、圆台面、圆锥面、圆柱面等特殊形状均质旋转面对旋转轴的转动惯量.     

Surface analysis by means of photoemission and other photon‐stimulated processes

In the decades after World War 11, there was an explosion of fundamental research in solids and practical applications thereof. Although surfaces were not ignored in this work, until recently they were not strongly emphasized. In the last few years there has been a growing emphasis on the study of surfaces and related interfaces. There are several reasons for hs. First, as knowledge regarding the bulk properties of solids became increasingly complete, it became more and more evident how little was known about the surfaces. Thus, the study of surfaces is an exciting new frontier of scientific knowledge. Secondly, the development of devices and processes that depend on surfaces has been increasingly hindered by the lack of knowledge about surfaces, interfaces, and interactions that take place on surfaces. As a result, new techniques for experimental studies of surfaces have recently been developed.^1,2 These show great promise for allowing examination of surfaces and interfaces on a microscopic and even atomic level, and for the gathering of detded information impossible to obtain in the past. Finally, theoretical methods³ are being rapidly developed, which provide increasingly detailed insight into surfaces and interactions on surfaces.     

LEED studies of clean high Miller index surfaces of silicon

Clean high Miller index surfaces of silicon were studied by LEED at different temperatures. Three types of surfaces were observed depending on orientation: flat surfaces, stepped ones with the (100) and (111) terraces and with the step heights of one or two interplanar distances, and “hill and valley” or facetted surfaces. All clean surfaces of silicon are reconstructed and contain surface structures with the periodicities different from the periodicities in the bulk. At certain temperatures the reversible order-order and order-disorder transitions take place on clean surfaces of silicon.     

Scattering by two-dimensional rough surfaces: comparison between the method of moments,Kirchhoff and small-slope approximations

Abstract

We use a rigorous numerical code based on the method of moments to test the accuracy and validity domains of two popular first-order approximations, namely the Kirchhoff and the small-slope approximation(SSA), in the case of two-dimensional rough surfaces. The experiment is performed on two representative types of surfaces: surfaces with Gaussian spectrum, which are the paradigm of single-scale surfaces, and ocean-like surfaces, which belong to the family of multi-scale surfaces. The main outcome of these computations in the former case is that the SSA is outperformed by the Kirchhoff approximation(KA) outside the near-perturbative domain and in fact is quite unpredictable in that its accuracy does not depend only on the slope. For ocean-like surfaces, however, SSA behaves surprisingly well and is more accurate than the KA.     

Scattering by two-dimensional rough surfaces: comparison between the method of moments, Kirchhoff and small-slope approximations

We use a rigorous numerical code based on the method of moments to test the accuracy and validity domains of two popular first-order approximations, namely the Kirchhoff and the small-slope approximation(SSA), in the case of two-dimensional rough surfaces. The experiment is performed on two representative types of surfaces: surfaces with Gaussian spectrum, which are the paradigm of single-scale surfaces, and ocean-like surfaces, which belong to the family of multi-scale surfaces. The main outcome of these computations in the former case is that the SSA is outperformed by the Kirchhoff approximation(KA) outside the near-perturbative domain and in fact is quite unpredictable in that its accuracy does not depend only on the slope. For ocean-like surfaces, however, SSA behaves surprisingly well and is more accurate than the KA.     

Geometric propagation of acoustic phonons in monocrystals within anisotropic continuum acoustics

A detailed study of anisotropic phonon propagation in sapphire and quartz is made by means of energy surfaces, group-velocity surfaces and intensity surfaces which were all determined numerically from published elastic constants. For convenience these surfaces are presented in threedimensional representations.Work supported by Bundesministerium für Forschung und Technologie     

Stability of twistor lifts for surfaces in four-dimensional manifolds as harmonic sections

We prove that the twistor lifts of certain twistor holomorphic surfaces in four-dimensional manifolds are weakly stable harmonic sections. As a corollary, if ambient spaces are self-dual Einstein manifolds with nonnegative scalar curvature, then the twistor lifts of twistor holomorphic surfaces are weakly stable. Moreover, for certain surfaces in four-dimensional hyperkähler manifolds, we show that the surfaces are twistor holomorphic if their twistor lifts are weakly stable harmonic sections. In particular, we characterize twistor holomorphic surfaces in four-dimensional Euclidean space by weak stability of the twistor lifts.     

Enhanced static evaporation heat transfer surfaces for compact two-phase heat exchangers

In the frame of the JOULE 1 R&D programme of the Commission of the European Communities this project has been carried out on enhanced evaporation heat transfer surfaces. The main goal of the project was to develop and investigate enhanced evaporation heat transfer surfaces for industrial compact two-phase heat exchangers. Planar and tubular surfaces have been investigated by IKE (structured planar and tubular surfaces), GRETh (covered planar surfaces) and NEL (covered tubular surfaces).     

Brewster's scattering angle in scattered waves from slightly rough metal surfaces

Brewster's scattering angle in electromagnetic wave scattering from slightly random metal surfaces is investigated by means of the stochastic functional approach. While there are dips due to Brewster's scattering angle in scattering profiles from dielectric surfaces, Brewster's scattering angle does not exist in scattering from metal surfaces. However, the dips can exist in scattering from rough metal surfaces with the optically denser medium to convert evanescent wave into radiative wave.     

Atomistic simulation of mineral surfaces: Studies of surface stability and growth

Atomistic simulation represents a valuable methodology for interpreting and predicting surface structures. The emphasis of our work is to develop and apply this approach to understanding the role of surface defects and additives in modifying the structure and stability of mineral surfaces. The basis of our approach is energy minimisation which allows us to evaluate the most stable surface configurations. The utility and limitations of this approach will be illustrated via a number of examples. These include describing the factors governing the stability of mineral surfaces and applying these considerations to understanding the surfaces of olivine and spinel. In addition, we are beginning to address the water-solid interface. We find a wide variation in the reactivity of the different surfaces of rock-salt oxides from (100) which show only physisorption, through stepped surfaces which show dissociative adsorption to (111) which forms the hydroxide. One way of determining the interaction between surfaces and additives is the modification of crystal growth thus we are also concerned with attempting to model the growth process. However, the low index surfaces often grow via screw dislocations. Therefore preliminary work on modelling the interaction of screw dislocations with surfaces of MgO will be described.     

Wetting behaviour of plasma sprayed oxide coatings

Wetting behaviour of several plasma sprayed oxide surfaces were characterised using contact angle measurements. Since surfaces contained pores and cracks, the evaluation of wetting angles led only to rough estimation of surface free energies. In order to find out the effect of atmospheric contamination the wetting behaviour of plasma-etched surfaces was followed as a function of time.It was found out that the sample preparation method had great influence on the contact angle of plasma sprayed oxide surfaces. The contact angle of plasma-etched surfaces increased when the surfaces were exposed to air. The probable reason for that was adsorption of low surface free energy contaminants to the sample surfaces.     

DLC nano-dot surfaces for tribological applications in MEMS devices

With the invention of miniaturized devices like micro-electro-mechanical systems (MEMS), tribological studies at micro/nano-scale have gained importance. These studies are directed towards understanding the interactions between surfaces at micro/nano-scales, under relative motion. In MEMS devices, the critical forces, namely adhesion and friction restrict the smooth operation of the elements that are in relative motion. These miniaturized devices are traditionally made from silicon (Si), whose tribological properties are not good. In this paper, we present a short investigation of nano- and micro-tribological properties of diamond-like carbon (DLC) nano-dot surfaces. The investigation was undertaken to evaluate the potential of these surfaces for their possible application to the miniaturized devices. The tribological evaluation of the DLC nano-dot surfaces was done in comparison with bare Si (1 0 0) surfaces and DLC coated silicon surfaces. A commercial atomic force microscope (AFM) was used to measure adhesion and friction properties of the test materials at the nano-scale, whereas a custom-built micro-tribotester was used to measure their micro-friction property. Results showed that the DLC nano-dot surfaces exhibited superior tribological properties with the lowest values of adhesion force, and friction force both at the nano- and micro-scales, when compared to the bare Si (1 0 0) surfaces and DLC coated silicon surfaces. In addition, the DLC nano-dot surfaces showed no observable wear at the micro-scale, unlike the other two test materials. The superior tribological performance of the DLC nano-dot surfaces is attributed to their hydrophobic nature and the reduced area of contact projected by them.     

Bio-inspired water repellent surfaces produced by ultrafast laser structuring of silicon

We report here an efficient method for preparing stable superhydrophobic and highly water repellent surfaces by irradiating silicon wafers with femtosecond laser pulses and subsequently coating them with chloroalkylsilane monolayers. By varying the laser pulse fluence on the surface one can successfully control its wetting properties via a systematic and reproducible variation of roughness at micro- and nano-scale, which mimics the topology of natural superhydrophobic surfaces. The self-cleaning and water repellent properties of these artificial surfaces are investigated. It is found that the processed surfaces are among the most water repellent surfaces ever reported. These results may pave the way for the implementation of laser surface microstructuring techniques for the fabrication of superhydrophobic and self-cleaning surfaces in different kinds of materials as well.     

IR Properties of Randomly Sea Surfaces

Sea surfaces should be considered as randomly rough surfaces at the infrared(IR) and optical bands. The geometric model of sea surfaces has been obtained by using image processing. Based on the electromagnetic scattering theory, the Laser Radar Cross Section(LRCS) for the sea surfaces is analyzed at IR band and the scattering properties of the sea surfaces have been gotten.     

Transient radiation and conduction heat transfer inside a plane-parallel participating gray medium with boundaries having different reflecting characteristics

A hybrid ray-tracing method is developed for the solution to the radiative transfer in a plane-parallel participating medium having one specular surface and another diffuse surface. By this method, radiative transfer coefficients (RTCs) for specular–diffuse (S–D) surfaces are deduced. The medium surfaces are considered to be semitransparent. The effects of convection–radiation parameter, conduction–radiation parameter and refractive index on transient coupled heat transfer are investigated. Results show that the temperature curves of the medium having S–D surfaces is higher than those of the medium having S–S surfaces (two specular surfaces); the total heat flux at steady state for the S–D surfaces is lower than that for the S–S surfaces.     

The structure and dynamics of crystal surfaces at high temperatures

After a brief review of the historical evolution of the understanding of crystal surfaces at high temperatures in general the subject is narrowed down to fcc metal surfaces, in particular to (110) surfaces. The recent work on these surfaces is reviewed, with emphasis on Pb, and the interpretation of the results in terms of various kinds of disordering such as surface melting, surface roughening, anharmonic vibrations and other processes is critically examined. While some of the results are now well established, others are contradictory, so that no unambiguous picture of metal surfaces at high temperatures can be given at present.     

The Rayleigh hypothesis in scattering off photonic crystal interfaces

We examine the Rayleigh hypothesis in the context of scattering of light off photonic crystal interfaces. First, the hypothesis - which was initially suggested for scattering of waves off rough surfaces between homogeneous media - is rephrased to apply to photonic crystal interfaces. Next, an exact and explicit functional form is presented that maps plane photonic crystal surfaces to periodic rough surfaces in free space, so that known criteria for the validity of the Rayleigh hypothesis for scattering at rough surfaces can be applied directly to scattering at the photonic crystal surfaces. The same map also allows the scattering problem to be solved exactly.