Optical diffraction by three-dimensional quasi-repetitive structures : some aspects of thick holograms

Imperial Users onl

Cell model of a fluid with hard-core repulsive long-range attractive potential

A model of a one-dimensional fluid is investigated in which the praticles [sic] are embedded in a cellular space grid and interact with a modified Lennart-Jones potential. It is shown that with an appropriate change in the potential function the model is also suitable for a two- or three-dimensional fluid with more restricted interactions. The man-fermion-like nature of the system resulting from the hard-rod repulsive part of the modified Lennard-Jones potential makes possible an isomorphism between occupation numbers (number operators) and spin states (spin operators) of an Ising ferromagnet, permitting a convenient mathematical formulation of the problem in terms of the Ising model formalism. While the spinor-algebraic method of Onsager and Kaufman is seen not to lead to a solution of this problem, a method is found for linearizing the partition function which results in a useful series solution. The validity of the solution is first proved by applying it to a one-dimensional model with nearest-neighbor interactions for which the exact partition function is known in closed form. The series solution is shown to offer a convenient and unified method for obtaining, algebraically, correct low-temperature expansions of the partition function for two- and three-dimensional fluids with nearest-neighbor interactions and similar potentials incorporating only a limited number of bonds. Application of the solution to several infinite systems produced consistent and realistic results in various limits and leas to a correct picture of a phase transition under certain conditions without recourse to the Maxwell construction. A numerical evaluation and analysis of the series solution, by means of high-speed computer, for small one-, two-, and three-dimensional systems shows realistic thermodynamic behavior and confirms other estimates of the critical temperature of the three-dimensional system --Abstract, pages ii-iii

A Framework for Size-dependent Structural Analysis of Smart Micro/nanoplates

This age has witnessed a proliferation of technological advancements that affected all facets of civilisation. Driven by the joint force of the evolution of sophisticated design tools, tailored material characteristics, and robust mechanics-based analyses, smart composite materials are widely used in high-performance engineering applications. Meanwhile, there is a growing interest in micro/nanoscopic structures in academia and industry due to the overwhelming trend toward portability, miniaturisation and integration in engineering. Therefore, the theoretical, computational, and experimental research communities have developed various effective methodologies to understand the structural behaviour of smart small-scale structures comprehensively. This dissertation introduces two size-dependent continuum theories, modified strain gradient and nonlocal strain gradient theories, to build the analytical framework for exploring application-driven micro/nanoplates made of smart composite materials. As examples of promising candidates for power supply and nano/microelectromechanical systems, organic solar cells and thermo-magneto-elastic sandwich nanoplates are studied. Size-dependent continuum models combined with various shear deformation plate theories are adopted to derive the governing equations. The size-sensitive static and dynamic mechanical responses, including bending, buckling, and free vibration behaviours of these ultra-fine-size structures, are predicted by capturing the size effect with material length scale or nonlocal parameters. The numerical results underlying size-dependent theories pose a new insight into the structural analysis of functional micro/nanoscopic plate-like structures. Some typical size-involving mechanical characteristics are revealed by comparing the present estimation with those from size-independent models. Moreover, the simulation outcomes thoroughly investigate several practical factors, such as boundary conditions, geometric configuration, and elastic foundation modelling parameters. In this endeavour, taking advantage of the computational efficiency and accessible operation of nonclassical continuum-based theories, the current analytical framework is suitable for exploring the size-tendency of the smart micro-/nanosized structures. The present work may serve as a benchmark for following numerical simulations and as a guide for evolving new engineering tools for modelling relevant responses by designers and manufacturers

Publications of Goddard Space Flight Center, 1964. Volume I - Space sciences

This publication is a collection of articles, papers, talks, and reports generated by the scientific and engineering staff of Goddard Space Flight Center in the year 1964. Many of these articles were originally published in scientific or engineering Journals or as official NASA technical publications, while other are documents of a more informal nature. All are reprinted here as nearly verbatim as typography and format will permit. These articles are grouped into broad subject categories, but no detailed subdivision has been made. Within each category, the articles are arranged alphabetically by author. An overall author index is given in the back of the volume. The years 1963, 1964, and 1965 are being published as whole-year issues, and the resulting size dictates the use of two volumes; the first volume is titled Space Sciences, and the second Space Technology. It is anticipated, however, that future issues will be quarterly single volumes