Simple technique for the generation of plane surface normal to optic axis direction of uniaxial crystal

What we believe to be a new experimental technique for the generation of a plane crystal surface perpendicular to the optic axis direction of a transparent birefringent uniaxial crystal is presented. A simple setup has been described for the initial optic axis alignment of a raw uniaxial crystal blank. Error correction methods have been illustrated. A technique for producing high optical quality surfaces by block polishing plane parallel crystal surfaces normal to the direction of the optic axis, in one setting, is discussed. The block with angular graduations facilitates the correction of angular error. A new conoscopy setup has been coupled to a Fizeau interferometer for high accuracy testing of the optic axis alignment with respect to the surface normal of the relevant polished surface of the uniaxial crystal. The results obtained for a quartz crystal blank are presented.     

The application of self adjusting interfaces to the design of fibrous composites

In the case of orthodox fibre composite materials the mechanical properties of the interfaces are fixed at an almost constant level by a choice of materials and manufacturing techniques. In such systems semi-continuous reinforcing elements fail when the tensile strain in the composite becomes comparable with the failing strain of the fibres. It is shown that the reinforcing elements can be prevented from failing, whatever the tensile strain in the composite material, if the shear strength of the interface between the reinforcing elements and the rest of the composite structure is self adjusting and is reduced locally as the local tensile stress carried by a reinforcing element increases. The characteristics of experimental reinforcing elements possessing these features have been investigated and the properties of composites utilizing such fibres are discussed.     

Beam dynamics of two modes propagating along the optic axis in a uniaxial crystal

The Gaussian beam propagation in the direction of the optic axis of a uniaxial crystal is treated by the complex-source-point technique. At the input plane the electric field is linearly polarized. A particular superposition of the ordinary-mode and the extraordinary-mode beams is generated. The electrodynamics of the composite beam has features that are different from those of the two constituent beams. As a result of the anisotropy, on propagation, the cross-polarized component of the electric field is generated except along the beam axis; the cross section of the beam, which is circular at the input plane, becomes elliptical; and the mean squared width of the beam departs from the usual quadratic dependence on the distance from the waist in the direction of propagation.     

Morphological stability of a crystal with respect to arbitrary boundary perturbations

The morphological stability of a growing round crystal with respect to harmonic perturbations of arbitrary amplitudes has been studied. The critical crystal size with respect to stable growth decreases with increasing amplitude of perturbations and tends to a value that was previously analytically determined proceeding from the principle of maximum entropy production. This result offers new important evidence for the validity of a hypothesis concerning the possibility of using entropy production instead of a thermodynamic potential in the analysis of nonequilibrium phase transitions.     

含负折射率材料的一维光子晶体带隙及应用

研究了含负折射率材料的一维光子晶体中一种特殊的带隙,这种带隙最适合的用途是做新型光子晶体滤波器.     

遗传算法的改进策略及其在桥梁抗震优化设计中的应用效果

本文论述了采用遗传算法进行结构优化设计时遇到的诸如计算量大、早熟收敛和边界探索不足等棘手问题，提出了三个解决对策，编制了计算程序，其在桥梁抗震代化设计中的应用效果表明，改进后的遗传算法不但提高了计算速度，而且在尽可能短的时间内找到最好的优化解。     

Out-of-plane reflection and refraction of light by anisotropic optical antenna metasurfaces with phase discontinuities

Experiments on ultrathin anisotropic arrays of subwavelength optical antennas display out-of-plane refraction. A powerful three-dimensional (3D) extension of the recently demonstrated generalized laws of refraction and reflection shows that the interface imparts a tangential wavevector to the incident light leading to anomalous beams, which in general are noncoplanar with the incident beam. The refracted beam direction can be controlled by varying the angle between the plane of incidence and the antenna array.     

Scattering of a gaussian beam by an infinite cylinder with arbitrary location and arbitrary orientation: numerical results

We present numerical results concerning the properties of the electromagnetic field scattered by an infinite circular cylinder illuminated by a circular Gaussian beam. The cylinder is arbitrarily located and arbitrarily oriented with respect to the illuminating Gaussian beam. Numerical evaluations are provided within the framework of a rigorous electromagnetic theory, the generalized Lorenz-Mie theory, for infinite cylinders. This theory provides new insights that could not be obtained from older formulations, i.e., geometrical optics and plane-wave scattering. In particular, some emphasis is laid on the waveguiding effect and on the rainbow phenomenon whose fine structure is hardly predictable by use of geometrical optics.     

Focusing properties of a photonic crystal slab with multiple mechanisms in addition to negative refraction

A brief review of imaging by a photonic crystal (PC) slab with negative refraction is given. The focusing properties of the PC with multiple mechanisms in addition to negative refraction are studied by the finite-difference time-domain method. In addition to the effect of negative refraction, there are multiple mechanisms that are all attributed to the PC focusing properties, including Bragg diffraction, excitation of the surface mode, and self-collimation. The resulting field pattern is the total result of these factors. Bragg diffraction occurs in the high-frequency domain and mainly influences the quality of focusing in the optical axis direction. The excitation of the surface mode improves the resolution of focusing. Self-collimation makes the focusing position deviate from Snell's law.     

Evolution of the spread of crystal orientation with plastic deformation in a cold-rolled Cu single crystal

Using scanning electron microscopy, we investigated how the microstructure of a Cu single crystal with a {15 12 9}〈9 10 3〉 orientation evolved from cold rolling. The first 50 % rolling caused its crystal orientation to rotate to {211}〈111〉. Although orientation splitting occurred near the surface of the single crystal, band-like regions with near-{211}〈111〉 orientations were still present after the fourth 50 % rolling. We measured the spread of crystal orientation in the near-{211}〈111〉 regions as a function of the total plastic equivalent strain induced by all rolling steps. When 50 % rolling was performed less than twice, the spread of crystal orientation was proportional to the square root of the plastic equivalent strain. Based on our results, we discussed the relationship between the spread of crystal orientation and the plastic equivalent strain generated by rolling.     

Neuroadaptive technologies: Applying neuroergonomics to the design of advanced interfaces

This article describes an emerging approach to the design of human-machine systems referred to as 'neuroadaptive interface technology'. A neuroadaptive interface is an ensemble of computer-based displays and controls whose functional characteristics change in response to meaningful variations in the user's cognitive and/or emotional states. Variations in these states are indexed by corresponding central nervous system activity, which control functionally adaptive modifications to the interface. The purpose of these modifications is to promote safer and more effective human-machine system performance. While fully functional adaptive interfaces of this type do not currently exist, there are promising steps being taken toward their development, and great potential value in doing so--value that corresponds directly to and benefits from a neuroergonomic approach to systems development. Specifically, it is argued that the development of these systems will greatly enhance overall human-machine system performance by providing more symmetrical communications between users and computer-based systems than currently exist. Furthermore, their development will promote a greater understanding of the relationship between nervous system activity and human behaviour (specifically work-related behaviour), and as such may serve as an exemplary paradigm for neuroergonomics. A number of current research and development areas related to neuroadaptive interface design are discussed, and challenges associated with the development of this technology are described.     

Three-dimensional analysis of multi-layer composite plates of arbitrary shape and boundary conditions with shear slip interfaces

An accurate semi-analytical method for three-dimensional static analysis of composite plates consisting of several anisotropic layers with shear slip imperfection is presented. The geometry and boundary conditions of the composite plate are arbitrary. At given interfaces, the imperfections are modeled via linear springs. The in-plane displacements are represented by appropriate expressions such that their discontinuity across the interfaces is incorporated accordingly. Also, the out-of-plane displacement normal to the interface must be continuous while the out-of-plane normal strain is discontinuous across the interface. In this approach, the essential boundary conditions are satisfied exactly, and the continuity of the inter-layer traction is captured with high accuracy.     

Dynamic motion analysis of optically trapped nonspherical particles with off-axis position and arbitrary orientation

We present a general computational method of determining radiation pressure forces and torques exerted on small particles by a converging beam of light. This method, based on a ray optics model of optical trapping, allows time-series dynamic motion analysis to be performed on nonspherical objects that are initially positioned off the optical axis with arbitrary orientation. Comparison tests of computer simulation with experimental results prove that the proposed model can be used to predict complicated trapping behavior of microfabricated objects.     

Application of non-linear programming to optimum grillage design with non-convex sets of variables

The application of non-linear programming methods for the optimum design of statically indeterminate structures is discussed, with special emphasis on the design of elastic grillages loaded laterally and in plane. Some features of SUMT (sequential unconstrained minimization technique) are demonstrated by means of numerous examples of varying complexity. The Variable Metric method of search is discussed and compared to Powell's Direct Method. It is shown that non-convex sets of design variables are often encountered in structural problems of the grillage type. SUMT may still be used, but the choice of starting value and initial response factor decisively influences the chance of finding the global optimum. It is demonstrated that a fully stressed design may not necessarily correspond to the minimum weight design. Optimum design of grillages which are simultaneously subjected to lateral and in-plane loads may be performed efficiently by means of non-linear programming.     

Calculation of multilayer plates and shells of different geometry with arbitrary orientation of layer material

Relationships that take geometric nonlinearity, transverse-shear deformation, and lack of inclination into account are derived. The principal directions of layer elasticity in multilayer plates and shells form a certain angle with the coordinate lines. The conditions of layer contact are satisfactory with respect to displacements. The three-dimensional problem is reduced to a two-dimensional one, The problems are solved by the finite-element method in displacements. The stiffness matrix and vectors of geometrically nonlinear terms for various shells as parts of a torus, cone, sphere and out-of-round cylinder are presented. The results are given in the form of diagrams. The stiffness matrix and vectors of geometrically nonlinear terms are derived for a N-angle element. Conversion from one form of shell to another is achieved by varying the quadratic-shape factors and their derivatives using subroutines for each type of shell.Translated from Problemy Prochnosti, No. 11, pp. 34–44, November, 1993.     

Beta tricalcium phosphate ceramics with controlled crystal orientation fabricated by application of external magnetic field during the slip casting process

Beta tricalcium phosphate (β-TCP) is a resorbable bioceramic that has hitherto been utilized in the medical field. Since it crystallizes in the anisotropic hexagonal system, properties such as chemical and physical ones are expected to depend on its crystal axis direction and/or on its crystal plane (anisotropy). Control of crystal orientation is thus important when used in polycrystalline form. Meanwhile, application of a strong magnetic field has been found to be a promising technique to control crystal orientation of anisotropic shape or structured crystals. In this work, we attempted to fabricate β-TCP ceramics with controlled crystal orientation by applying an external magnetic field during the slip casting process and subsequently sintering them at 1050 °C, below the β–α transition temperature. Application of a vertical magnetic field increased intensities of planes perpendicular to c-plane on the top surface, while a horizontal one with simultaneous mechanical mold rotation decreased it. These results indicated that crystal orientation of β-TCP ceramics were successfully controlled by the external magnetic field and together that the magnetic susceptibility of β-TCP is χ_c⊥ > χ_c//.     

Extremes of random fields over arbitrary domains with application to concrete rupture stresses

To find the exact probability distribution of the global maximum or minimum of a random field within a bounded domain is a pending problem even for Gaussian fields. Except for very special examples of fields, recourse must be taken to approximate reasoning or asymptotic considerations to be judged with respect to accuracy by simulations. In this paper, the problem is addressed through a functional equation that leads to the definition of a class of distribution functions that depend solely on process or field characteristics and domain quantities that can be calculated explicitly. This distribution function class is studied for Gaussian processes in earlier works by the author and it has been obtained explicitly for Gaussian fields on rectangular domains in the plane. Simulation studies show that rather good predictions are obtained for sufficiently smooth wide band Gaussian processes and fields. In this paper, the distribution function is obtained in general for Gaussian fields over arbitrary bounded domains with piecewise continuous and differentiable boundaries, and as in earlier works the distribution function is tested against empirical distribution functions obtained by simulation of sample functions of a smooth approximately Gaussian field, herein called a broken line Hino field. For completeness this particular field type is defined in appendix a and appendix b. The paper concludes with a statistical application on data for plain concrete tensile strength.