10,982 research outputs found
Moving frame technique for planar acoustic holography
No full textAcoustic holography is one of the best methods to visualize sound fields. The quality of the visualized sound is primarily determined by the size of the hologram, its microphone spacing, and the number of microphones. This paper describes a way to virtually increase the hologram size and the spatial resolution of the holograph. For a stationary sound field, the method continuously sweeps the sound field by a line array of microphones. For moving sound sources, radiating sound is measured by using a line array of microphones fixed in space. In both cases, the measured signals have Doppler effects. The theoretical formulation has been systematically addressed by employing a moving coordinate which has relative motion between the measurement coordinate and the hologram coordinate. Simulations and experiments support the proposed theory. The drawback is that the method is only applicable to discrete frequencies. (C) 1998 Acoustical Society of America
ANALYSIS OF THE HYDROSTATIC BULGING OF AN ELLIPTIC DIAPHRAGM BY THE ENERGY METHOD
No full textAn approach using the energy method is proposed for the analysis of three-dimensional sheet-metal forming. There are some limitations in analysis by the energy method, e.g., the analytical expression of the geometric configuration and the construction of a proper kinematically-admissible velocity field are very difficult and the estimation of strain rate at a point on the surface is very complicated. In the method suggested, the principal components of strain increment are calculated directly from the change of geometric profile for an arbitrary triangular element. The corresponding solution is found through optimization of the total energy consumption with respect to some parameters assumed in the kinematically-admissible velocity field and the geometric profile. In order to check the validity of the method proposed, the hydrostatic bulging of an elliptic diaphragm has been analyzed. In comparison of the computed results with existing experimental results, good agreement has been obtained for the pressure curve, the polar membrane strains and the strain distributions and it has thus been shown that the approach is applicable to the analysis of three-dimensional sheet-metal forming
AN ANALYSIS OF HEMISPHERICAL PUNCH STRETCHING BY THE ENERGY METHOD
No full textAn approach using the energy method in which the total deforming region is divided into several sections of different geometric shapes is suggested for the analysis of axisymmetric sheet metal forming with friction boundary condition. The corresponding solutions are found through optimization of the total energy dissipation with respect to some parameters assumed in the velocity field as well as in the corresponding geometric profile. Computations are carried out for hemispherical punch stretching of normal anisotropic work-hardening materials for several lubrication conditions. The punch load vs stroke relation, geometric configuration and strain components are determined from the computation. The comparison of the computed results with finite element solutions and corresponding experiments shows good agreements of solutions in load vs stroke, deformed profiles and strain distribution for various lubrication conditions. It is thus shown that the present simple approach can be effectively employed for the analysis of axisymmetric sheet metal working processes
MINIMIZATION OF BIAS ERROR DUE TO WINDOWS IN PLANAR ACOUSTIC HOLOGRAPHY USING A MINIMUM ERROR WINDOW
No full textBias errors in the prediction of a sound field using planar acoustic holography are due to aliasing and window effects. It is noteworthy that aliasing is negligible in the forward predictions if the sampling space is less than a quarter wavelength. However, bias error induced by a window is the major concern for accurate holographic prediction because of the small number of measurement points in the planar acoustic holography. For the reduction of this error, a new class of window, the MEW, is proposed and compared with Ham, Gaussian, and Kaiser-Bessel windows. It is built by modifying the method that Papoulis proposed by minimizing the second-order moment of the window spectrum. The characteristics of the MEW vary with the number of weighting values and the number of higher-order moment terms to be eliminated. The applicability of the MEW on planar acoustic holography is demonstrated. (C) 1995 Acoustical Society of America
Analysis of three-dimensional deep drawing by the energy method
No full textA systematic approach of the energy method is proposed for analysis of three-dimensional sheet metal forming of noncircular cups with complicated shape. In the proposed method, the whole deforming region is divided into several zones by considering the geometric characteristics and contact boundary condition. The geometric shape is expressed by sweeping the section curves defined on the boundary of each zone. Velocity fields are expressed in a similar manner by sweeping the boundary velocity functions. The solution is found through optimization of the total energy dissipation with respect to some parameters assumed in the kinematically admissible velocity field defined over each zone. In order to-check the effectiveness of the present method, three-dimensional deep drawing by the elliptic punch and the clover-type punch are analysed and compared with the corresponding experiments. In analysing the deep drawing process by the elliptic and clover-type punches, the total deforming region has been divided into five zones. The computed results are shown to be in good agreement with the experiment in punch load, deformed edge contour and distribution of thickness strain
A semantic basis for local reasoning
No full textWe present a semantic analysis of a recently proposed formalism for local reasoning, where a specification (and hence proof) can concentrate on only those cells that a program accesses. Our main results are the soundness and, in a sense, completeness of a rule that allows frame axioms, which describe invariant properties of portions of heap memory, to be inferred automatically; thus, these axioms can be avoided when writing specifications.
Monolayers of poly(alpha,beta-aspartic acid) with long alkyl chains and miscibility with L-alpha-phosphatidylcholine at air-water interface
No full textSurface pressure/area isotherms of polypeptides modified with long alkyl chains and their miscibility with DPPC were investigated. The modified polypeptides formed stable monolayers due to their hairy-rod structure and limiting area increased as the degree of substitution increased. Collapse pressure of mixed monolayers deviated from ideal mixture and the free energies of mixing were negative values in all composition
Sperm as a carrier to introduce an exogenous DNA fragment into the oocyte of Japanese abalone (Haliotis divorsicolor suportexta).
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