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101.
For the transient dynamic analysis of structural systems, the direct numerical integration of the equations of motion may be regarded as an alternative to the mode superposition method for linear problems and a necessity for nonlinear problems. When compared to a modal superposition solution, the direct integration approach is attractive in that the eigenvalue problem is avoided. Depending on the amount of information required from the dynamic analysis, e.g. frequencies, frequencies and mode shapes, and/or a complete time history, a direct integration scheme may prove to be more efficient than a modal superposition solution for some linear problems as well.The purpose of this study is to develop and demonstrate a direct integration algorithm which is compatible with an existing high-precision rotational shell finite element. Excellent comparative efficiency for static problems was achieved with this element by the incorporation of the exact geometry, the utilization of high-order interpolation polynomials and, yet, the retention of only a minimum number of nodal variables in the global formulation. Likewise, accurate and efficient results for the free vibration analysis of rotational shells were facilitated by the inclusion of a consistent mass matrix and the utilization of a rationally justified kinematic condensation procedure. The approach to the direct integration stage is strongly tempered by the established characteristics of this element which enable a given shell to be modeled accurately in the spatial domain with a comparatively coarse discretization.The equations of motion for a shell of revolution under conservative loading are derived from Hamilton's variational principle and specialized for the discretization of a rotational shell into curved shell elements. Degrees of freedom in excess of those required to establish minimum (C°) continuity at the nodal circles are eliminated through kinematic condensation. Some guidance as to the proper order of the polynominal approximations for a dynamic analysis is provided by earlier free vibration studies. Whereas the condensation is exact for static problems, it is only approximate for dynamic response and it was found that the accuracy of the eigenvalues obtained for the reduced problem decreases with increasing order of the condensed functions. This tendency is counted by the desirability of using sufficiently high-order interpolations so as to permit accurate stress computations, both at the nodal circles and between nodes since a coarse discretization is necessary to realize maximum efficiency. It was found that cubic polynomials were generally satisfactory from both standpoints, except in localized regions of high stress gradients where quintic polynomials were employed. The finite element discretizations for the direct integration studies were selected on this basis.For the high-precision finite element at hand, the efficiencies achieved in the space domain are demonstrated by the ability to achieve precise solutions with relatively coarse discretization patterns. The resulting comparatively large elements are not subject to accurate representation by diagonal mass matrices so that an implicit, consistent mass approach is followed. Efficiency in the time domain as well rests on the successful modeling of rotational shells subject to dynamic loading using coarse discretitations in space and large increments in time. Computational efficiency and accuracy are demonstrated for various problems documented in the literature, including a shallow spherical cap subject to a step pulse and a hyperboloidal shell under a simulated dynamic wind pressure. 相似文献
102.
Decisions on organizational arrangements for MIS units comprise location in the organization, rank of responsible executive, organization of MIS implementators, degree of centralization, the user interface, the study group, the steering committee, the data base administrator, the corporate computer staff, and external assistance. Based on a wide-ranging survey of papers in the field of MIS, the authors have formulated guidelines which derive from the impact of organizational decisions on the success or failure or MIS and MIS projects. 相似文献
103.
James P. Schaffer Edward J. Shaughnessy Phillip L. Jones 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》1984,5(1):75-79
A deconvolution procedure which corrects Doppler-broadened positron annihilation spectra for instrument resolution is described. The method employs fast Fourier transforms, is model independent, and does not require iteration. The mathematical difficulties associated with the incorrectly posed first order Fredholm integral equation are overcome by using power spectral analysis to select a limited number of low frequency Fourier coefficients. The FFT/power spectrum method is then demonstrated for an irradiated high purity single crystal sapphire sample. 相似文献
104.
A 53-year-old female rheumatoid arthritis (RA) patient endured 2 unexpected family deaths during a 12-week study investigating the prospective relationships between stressful small life events, negative affect, and disease activity. Her disease went into temporary remission the same week as the deaths. She was identified as a case study participant, and weekly data collection was extended to 1 year. Clinical exams verified a large decrease in disease status immediately after the major losses. In addition to major events, negative affect and small events were found to serve as independent arthritis symptom predictors within this patient. Major events were associated with decreased symptoms. Negative affect and small events related to symptom increased. Subsequent between-subjects analyses conducted on 25 participants from the parent project probed for generalizability. The substantive findings from the case study were supported: Major life events and small life events functioned as opposing predictors of RA disease states. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
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107.
Cholesterol levels of both plasma and liver of cholesterol-fed rats are lowered by feeding linoleyl and oleyl esters of p-toluenesulfonic
acid. A structural specificity exists, since the effect is not observed with similar amounts of sodium p-toluenesulfonate
nor with linoleyl methanesulfonate. Effective levels of these arylsulfonates do not alter liver to body weight ratios and
maturation, nor reduce plasma cholesterol in normocholesterolemic rats.
Published as Journal Paper No. 6696, AES, Purdue University 相似文献
108.
This paper describes an experimental evaluation of the execution speed of object programs produced by six PL/I compilers. A set of 139 representative PL/I statements were compiled and executed under the PL/I Optimizing, PL/I(F), PL/C, PL/I Checkout, SP/k and PLUTO compilers. An analysis is made of the relative speed of the object code produced by each compiler and also of the relative execution speed of each statement. 相似文献
109.
Copolymers of vinylidene chloride, SARAN* resins, can be fabricated into films which have excellent barrier to mass transport. They are useful for making packages which must keep oxygen out or prevent moisture from entering or leaving. The oxygen barrier properties of SARAN films have been recently published (8). The purpose of this paper is to describe the moisture barrier properties of SARAN films as functions of temperature, humidity, and film composition. This information will aid packaging engineers design better barrier packaging. 相似文献
110.
Godding Phillip R.; Fitterling James M.; Schmitz Joy M.; Seville Janette L.; Parisi Sharon A. 《Canadian Metallurgical Quarterly》1992,6(1):34
Assessed the discriminative utility of a brief assessment procedure for quantifying cognitive status in alcoholics and the impact of existing cognitive status on acquisition of information presented during treatment. 112 male patients (aged 20–77 yrs), consecutively admitted to an inpatient alcohol treatment program, were assessed at admission and discharge. The 30-min assessment protocol included the Rey Auditory Verbal Learning Task (M. D. Lezak, 1983), portions of the Wechsler Memory Scale, and a brief structured interview that assessed treatment-relevant knowledge. These measures were able to differentiate performance levels related to age and drinking history. Recent drinking behavior and cognitive function may only moderately influence acquisition of treatment program content. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献