Monte Carlo modeling of underwater-image formation: validity of the linear and small-angle approximations

A Monte Carlo model has been used to compute a set of point-spread functions (PSF's) and modulation transfer functions (MTF's) that determine underwater-image quality in a range of different environments. The results have been used to analyze the range of application under which a linear-approximation theory holds. Conclusions of the study are that the linear-approximation theory Seems to hold quite well over a broad range of applications. The ramifications of the Wells small-angle-scattering theory that predicts the PSF from a knowledge of the volume-scattering function (VSF) are also considered.

Discrepancies are noted between a predicted and a computationally obtained MTF; these discrepancies increase with range. Therefore, the results of the simulations indicate that the small-angle-scattering theory is more valid at a limited number of attenuation lengths. The results of the simulations indicate that the theory is valid to approximately three attenuation lengths.

     

Experimental assessment of mixed-mode partition theories

The propagation of mixed-mode interlaminar fractures is investigated using existing experimental results from the literature and various partition theories. These are (i) a partition theory by Williams (1988) based on Euler beam theory; (ii) a partition theory by Suo (1990) and Hutchinson and Suo (1992) based on 2D elasticity; and (iii) the Wang–Harvey partition theories of the authors based on the Euler and Timoshenko beam theories. The Wang–Harvey Euler beam partition theory seems to offer the best and most simple explanation for all the experimental observations. No recourse to fracture surface roughness or new failure criteria is required. It is in excellent agreement with the linear failure locus and is significantly closer than other partition theories. It is also demonstrated that the global partition of energy release rate when using the Wang–Harvey Timoshenko beam or averaged partition theories or 2D elasticity exactly corresponds with the partition from the Wang–Harvey Euler beam partition theory. It is therefore concluded that the excellent performance of the Wang–Harvey Euler beam partition theory is either due to the failure of materials generally being based on global partitions or that for the specimens tested, the through-thickness shear effect is negligibly small. Further experimental investigations are definitely required.     

Lipopolymer gradient diffusion in supported bilayer membranes

We measure the gradient diffusion coefficient of a model lipopolymer in supported lipid bilayer membranes from Fourier-transform post-electrophoresis relaxation. The experiments and accompanying quantitative interpretation furnish the concentration dependence of the gradient diffusion coefficient. In striking contrast to the recent measurements of the self-diffusion coefficient from fluorescence recovery after photobleaching, the lipopolymer gradient diffusion coefficient increases with concentration. We interpret the enhancement at small but finite concentrations using the Scalettar–Abney–Owicki (SAO) statistical mechanical theory (1988) and the Bussell–Koch–Hammer (BKH) hydrodynamic theory (1995), which are customarily adopted to model membrane protein dynamics. The SAO theory furnishes an effective disc radius and soft repulsive interaction radius that are comparable to the Flory radius of the unperturbed polyethylene glycol chains. On the other hand, the BKH theory predicts a gradient diffusion coefficient that decreases with disc/membrane protein concentration. Thus, in contrast to membrane proteins, we conclude that lipopolymer hydrodynamic interactions are weak because the principal disturbances are in the low-viscosity aqueous phase. Accordingly, lipopolymer interactions are dominated by thermodynamic interactions among polymer chains. Interestingly, our experiments suggest that increasing (decreasing) the polymer molecular weight should increase (decrease) the relaxation rate of lipopolymer concentration fluctuations.     

On the moment theory of elasticity. Plane deformation. Part I

We propose a model of the moment theory of elasticity in which equations of the classical (momentless) theory of elasticity are supplemented with equilibrium equations (momental equations) and boundary conditions for couple stresses and shear strains are determined by tangential and couple stresses. As a result, the basic relationships between strains and displacements and, hence, the continuity equations for strains preserve the same form as in the momentless theory. The proposed moment theory of elasticity completely includes all basic postulates of the classical theory and supplements it in the case where the law of parity of tangential stresses is not valid. We obtain solutions of some problems which cannot be solved within the framework of the classical theory of elasticity. Moscow State Postal-Tuition Institute of the Food Industry, Moscow, Russia. Translated from Problemy Prochnosti, No. 3, pp. 103–113, May–June, 1998.     

热致液晶共聚酯酰胺／PET共混物的相容性和形态结构

用溶解度参数预测热致液晶共聚酯酰胺（ＰＥＡ）与聚对苯二甲酸乙二酯（ＰＥＴ）共混物的相容性。采用偏光显微镜、扫描电镜研究其形态结构。结果表明：ＰＥＡ／ＰＥＴ共混物虽然在理论上是热力学相容的，但因ＰＥＡ的热致液晶性，从液晶有序相变为各向同性存在热效应，致使理论预测与实验结果产生偏差。ＰＥＡ／ＰＥＴ共混物呈两相结构，当ＰＥＡ含量少时，两相之间具有一定的相容性。共混物熔体在剪切力作用下，液晶相形成取向微纤     

Item Response Theory: Past Performance,Present Developments,and Future Expectations

We give a historical introduction to item response theory, which places the work of Thurstone, Lord, Guttman and Coombs in a present-day perspective. The general assumptions of modern item response theory, local independence and monotonicity of response functions, are discussed, followed by a general framework for estimating item response models. Six classes of well-known item response models and recent developments are discussed: (1) models for dichotomous item scores; (2) models for polytomous item scores; (3) nonparametric models; (4) unfolding models; (5) multidimensional models; and (6) models with restrictions on the parameters. Finally, it is noted that item response theory has evolved from unidimensional scaling of items and measurement of persons to data analysis tools for complicated research designs.

     

Bending of a bimodulus laminated plate based on a higher-order shear deformation theory

This paper presents an exact flexural analysis of rectangular simply supported single-layer and two-layer cross-ply plates of bimodulus materials. The governing equations of a bimodulus plate based on a higherorder shear deformation theory are simplified from the composite plate. The present analysis of displacements in flexure is compared with Bert's results and Turvey's results which are based on Mindlin plate theory. The in-plane stress and bending stress are included in the present study. All the present numerical results are compared with the Mindlin plate theory (first-order plate theory) results. From those comparisons, the effects of higher-order shear deformation terms on the neutral surface locations and the flexure displacements can be observed.     

An upscale theory of particle simulation for two‐dimensional quasi‐static problems

An upscale theory of the particle simulation, which is based on the distinct element method, is presented for two‐dimensional quasi‐static problems. Since the present upscale theory is comprised of four similarity criteria between different length‐scale particle‐simulation models, it reveals the intrinsic relationship between the particle‐simulation solution obtained from a small length‐scale (e.g. a laboratory length‐scale) model and that obtained from a large length‐scale (e.g. a geological length‐scale) one. The present upscale theory is of significant theoretical value in the particle simulation of two‐dimensional systems, at least from the following two points of view. (1) If the mechanical response of a particle model of a small length‐scale is used to indirectly investigate that of a large length‐scale, then the present upscale theory provides the necessary conditions, under which the particle model of the small length‐scale needs to be satisfied so that a similarity between the mechanical responses of two different length‐scale particle models can be maintained. (2) If a particle model of a large length‐scale is used to directly investigate the mechanical response of the model, then the present upscale theory can be used to determine the necessary particle‐scale mechanical properties from the macroscopic mechanical properties that are obtained from either a laboratory test or an in situ measurement. The related simulation results from two typical examples of significantly different length‐scales (i.e. a metre‐scale and a kilometre‐scale) have demonstrated the usefulness and correctness of the proposed upscale theory for simulating different length‐scale problems in quasi‐static geological systems. Copyright © 2007 John Wiley & Sons, Ltd.     

Theory of High Temperature Superconductivity Beyond BCS with Realistic Coulomb and Fröhlich Interactions

Along with some other researches we have realised that the true origin of high-temperature superconductivity is found in the strong Coulomb repulsion combined with a significant electron–phonon interaction. Both interactions are strong (on the order of 1 eV) compared with the low Fermi energy of doped carriers which makes the conventional BCS-Eliashberg theory inapplicable in cuprates and related doped insulators. Based on our recent analytical and numerical results we argue that high-temperature superconductivity from repulsion alone is impossible for any strength of the Coulomb interaction. Major steps of the alternative polaron theory are outlined starting from the generic Hamiltonian including the unscreened (bare) Coulomb and electron–phonon interactions. The theory accounts for high superconducting critical temperatures, unconventional isotope effects and reconciles tunnelling, photoemission and quantum oscillation data.     

Attenuation and velocity of first sound in a saturated 3He-4He mixture at very low temperatures and high magnetic field

We present experimental results on the attenuation and velocity of first sound in a saturated (X = 0.064) ³He-⁴He mixture. The measurements were performed at very low temperature (3.5 <T< 20 mK) with relatively low frequencies (around 1 MHz) at saturated vapor pressure, using a CW technique. Though the results are found to be in qualitative agreement with the theory for acoustic transmission in degenerate mixtures, they are not quantitatively consistent with theory. A phenomenological explanation is offered for this discrepancy. We compare our data with recent measurements at higher temperatures and frequency. We have also performed the measurements in a magnetic field of 9 T. Within our experimental accuracy we cannot detect any systematic difference from the measurements in zero field. This is expected from theory.     

An Overview of Complexity Theory in Discrete Optimizations: Part I. Concepts

Over the past decade, complexity theory has emerged from a branch of computer science almost unknown to the operations research community into a topic of widespread interest and research. The goals of the theory are to broadly classify problems and algorithms according to their convenience for solution by digital computers. Very considerable progress has been achieved, but some of the concepts in the theory are so subtle that their implications are as often misunderstood as grasped correctly. In this and the succeeding paper, we will present an elementary tutorial review of the important concepts and results in complexity theory. Emphasis is placed on constructs and implications for persons interested in discrete optimization—especially scheduling theory. The present Part I develops background concepts and definitions. Part II (in the June 1982 TRANSACTIONS) will cover results and implications.     

Angular responses of the first diffracted order in over-modulated volume diffraction gratings

Abstract

Kogelnik's coupled-wave (CW) theory has been used for decades to predict the diffraction efficiency of volume diffraction gratings. Although this theory has been applied with success to volume diffraction gratings recorded under a great variety of experimental conditions, its predictions deviate from the actual behaviour whenever the hologram is thin or the refractive index is high. In these cases, it is necessary to use a more general CW theory or the rigorous coupled-wave (RCW) theory. Both of these theories allow for more than two orders to propagate inside the hologram. The difference between them is that in the CW theory the second derivatives that appear in the coupled equations are disregarded. The RCW theory does not incorporate any approximation and thus, since it is rigorous, permits judging the accuracy of the approximations included in Kogelnik's CW theory and the more general CW theory. In this article a comparison between the predictions of the three theories for phase transmission diffraction gratings is carried out. Over-modulated diffraction gratings are also recorded in photographic emulsions in order to study the applicability of Kogelnik's theory in this case. Good agreement between theory and experiment is found for both Kogelnik's theory and the RCW theory formulations in the particular experimental cases studied.     

A two-dimensional theory for the analysis of laminated plates

A new displacement-based two-dimensional theory for the analysis of multilayered plates is presented. The theory is based on the only kinematic constraint of transverse inextensibility, whereas no restrictions are imposed on the representation of the in-plane displacement components. A governing system of integral-differential equations is obtained which can be given a closed-form solution for a number of problems where no boundary layer are present. It is also shown that most of the 2-D plate models can be directly derived from the presented theory. The possibility of developing asymptotic solutions in the boundary layers is discussed with reference to the problem of a plate in cylindrical bending. Finally some numerical solutions are compared with those given by the plate model by Lo et al. (1977) and with F.E.M. solutions.The authors gratefully acknowledge the financial support of the (Italian) Ministry of University and Scientific and Technological Research (MURST) and of the National Council of Research (CNR, contr. 92.03045.07)     

Transport properties of Freon-152a and Freon-142b in the temperature range of 280–510 K

The thermal conductivity of 1,1 difluoroethane (Freon-152a) and 1 chloro-1 difluoroethane (Freon-142b) are measured at several pressures in the range 29.7–75.8 kPa and as a function of temperature in the range 280–510 K. The thermal conductivity column instrument is employed, and the experimental values are estimated to be accurate within a maximum uncertainty of ±5.6% at the lowest temperature, which reduces to ±2.4% at the highest temperature. These conductivity values are compared with the predictions of Chapman-Enskog kinetic theory, with the correction factor for the internal energy transport estimated from Hirschfelder's theory, and the Lennard-Jones (12-6) potential. The experimental conductivity data are also utilized to generate the values for the two other transport properties in conjunction with the interrelations obtained between different properties on the basis of kinetic theory. The data on transport properties are employed to give the best possible estimates of Prandtl and Schmidt numbers as a function of temperature.     

The Theory of International Business: The Role of Economic Models

This paper reviews the scope for economic modelling in international business. It argues for a multi-level theory based on classical internalisation theory. The theory extends the ‘systems approach’ to the multinational enterprise in which modular activities, such as production, marketing and R&D, are linked by flows of semi-processed products and proprietary knowledge. It is shown how this theory can be extended from the firm level to the industry level in order to analyse inter-firm co-operation and rivalry. The theory can be extended to higher levels (e.g., the global economy) and lower levels (e.g., personal relationships within plants and offices).     

Fabrication and characterization of transducer elements in two-dimensional arrays for medical ultrasound imaging

Some of the problems of developing a two-dimensional (2-D) transducer array for medical imaging are examined. The fabrication of a 2-D array material consisting of lead zirconate titanate (PZT) elements separated by epoxy is discussed. Ultrasound pulses and transmitted radiation patterns from individual elements in the arrays are measured. A diffraction theory for the continuous wave pressure field of a 2-D array element is generalized to include both electrical and acoustical cross-coupling between elements. This theory can be fit to model the measured radiation patterns of 2-D array elements, giving an indication of the level of cross-coupling in the array, and the velocity of the acoustic cross-coupling wave. Improvements in bandwidth and cross-coupling resulting from the inclusion of a front acoustic matching layer are demonstrated, and the effects of including a lossy backing material on the array are discussed. A broadband electrical matching network is described, and pulse-echo waveforms and insertion loss from a 2-D array element are measured.     

INTERLAMINAR STRESSES IN SHELLS OF REVOLUTION

SUMMARY

A comparative study of the interlaminar stresses in shells of revolution has been made between first order shear deformation theory (FSDT), higher order shear deformation theory with thickness stretch (HSDT7), higher order shear deformation theory with higher order inplane displacement terms (HSDT9) and three-dimensional finite element (3D) models. A semi-analytical approach is used for all the models. Interlaminar stresses are evaluated using equilibrium equations in the cases of FSDT, HSDT7 and HSDT9 models as interlaminar stresses obtained from constitutive equations are not correct. For the 3D model an eight-noded quadratic quadrilateral semi-analytic solid element is used whereas for equivalent single layer (ESL) theories a three-noded isoparametric curved element is used. Crossply parabolic and hyperbolic caps subjected to uniform external pressure and a simply supported cylindrical shell subjected to an internal sinusoidal pressure are considered in the present study.