Three isoparametric solid elements for NASTRAN

Linear, quadratic, and cubic isoparametric hexahedral solid elements have been added to the element library of NASTRAN. These elements are available for static, dynamic, buckling, and heat-transfer analyses. Because the isoparametric element matrices are generated by direct numerical integration over the volume of the element, variations in material properties, temperatures, and stresses within the elements are represented in the computations. In order to compare the accuracy of the new elements, three similar models of a slender cantilever were developed, one for each element. All elements performed well. As expected, however, the linear element model yielded excellent results only when shear behavior predominated. In contrast, the results obtained from the quadratic and cubic element models were excellent in both shear and bending

Addition of three-dimensional isoparametric elements to NASA structural analysis program (NASTRAN)

Implementation is made of the three-dimensional family of linear, quadratic and cubic isoparametric solid elements into the NASA Structural Analysis program, NASTRAN. This work included program development, installation, testing, and documentation. The addition of these elements to NASTRAN provides a significant increase in modeling capability particularly for structures requiring specification of temperatures, material properties, displacements, and stresses which vary throughout each individual element. Complete program documentation is presented in the form of new sections and updates for direct insertion to the three NASTRAN manuals. The results of demonstration test problems are summarized. Excellent results are obtained with the isoparametric elements for static, normal mode, and buckling analyses

Persistent junk solutions in time-domain modeling of extreme mass ratio binaries

In the context of metric perturbation theory for non-spinning black holes, extreme mass ratio binary (EMRB) systems are described by distributionally forced master wave equations. Numerical solution of a master wave equation as an initial boundary value problem requires initial data. However, because the correct initial data for generic-orbit systems is unknown, specification of trivial initial data is a common choice, despite being inconsistent and resulting in a solution which is initially discontinuous in time. As is well known, this choice leads to a "burst" of junk radiation which eventually propagates off the computational domain. We observe another unintended consequence of trivial initial data: development of a persistent spurious solution, here referred to as the Jost junk solution, which contaminates the physical solution for long times. This work studies the influence of both types of junk on metric perturbations, waveforms, and self-force measurements, and it demonstrates that smooth modified source terms mollify the Jost solution and reduce junk radiation. Our concluding section discusses the applicability of these observations to other numerical schemes and techniques used to solve distributionally forced master wave equations.Comment: Uses revtex4, 16 pages, 9 figures, 3 tables. Document reformatted and modified based on referee's report. Commentary added which addresses the possible presence of persistent junk solutions in other approaches for solving master wave equation

On the Coherence of Ground Motion in the San Fernando Valley

We present an analysis of the coherence of seismic ground motion recorded on alluvial sediments in the San Fernando Valley, California. Using aftershocks of the 17 January 1994 M_w6.7 earthquake recorded at a quasi-dense array of portable stations, we analyze the coherence of three well-recorded magnitude 3.7 to 4.0 events over the frequency range 0.5 to 15 Hz and a distance range of 0.5 to 5.3 km. All stations are located at sites with broadly similar near-site geology, characterized by medium to fine-grain Quaternary alluvial sediments. On average, relatively high values of coherence are observed for distances up to 3 to 4 km and frequencies up to 2 to 3 Hz; coherence drops sharply at frequencies near and above 3 Hz. Although average coherence functions are described reasonably well by a log-linear relationship with frequency, the curves at all distances exhibit a flattening at low frequencies that is not consistent with previous observations of coherence at hardrock sites. The distance decay of coherence is also markedly less strong, with high coherence values observed over station separations corresponding to multiple wavelengths. This may reflect fundamental differences in shallow-wave propagation in the two environments, with high-frequency scattering relatively more dominant in regions of hard-rock near-surface geology. Within a sedimentary basin or valley, the site response itself generally reflects a resonance phenomenon that may tend to give rise to more uniform ground motions. However, previous studies have demonstrated the existence of pathological focusing and amplification effects within complex sedimentary basin environments such as the greater Los Angeles region; our results undoubtedly do not quantify the full range of ground-motion variability at all sites, but rather represent the level of that variability that can be expected, and quantified, for typical source/receiver paths

Fast prediction and evaluation of gravitational waveforms using surrogate models

[Abridged] We propose a solution to the problem of quickly and accurately predicting gravitational waveforms within any given physical model. The method is relevant for both real-time applications and in more traditional scenarios where the generation of waveforms using standard methods can be prohibitively expensive. Our approach is based on three offline steps resulting in an accurate reduced-order model that can be used as a surrogate for the true/fiducial waveform family. First, a set of m parameter values is determined using a greedy algorithm from which a reduced basis representation is constructed. Second, these m parameters induce the selection of m time values for interpolating a waveform time series using an empirical interpolant. Third, a fit in the parameter dimension is performed for the waveform's value at each of these m times. The cost of predicting L waveform time samples for a generic parameter choice is of order m L + m c_f online operations where c_f denotes the fitting function operation count and, typically, m << L. We generate accurate surrogate models for Effective One Body (EOB) waveforms of non-spinning binary black hole coalescences with durations as long as 10^5 M, mass ratios from 1 to 10, and for multiple harmonic modes. We find that these surrogates are three orders of magnitude faster to evaluate as compared to the cost of generating EOB waveforms in standard ways. Surrogate model building for other waveform models follow the same steps and have the same low online scaling cost. For expensive numerical simulations of binary black hole coalescences we thus anticipate large speedups in generating new waveforms with a surrogate. As waveform generation is one of the dominant costs in parameter estimation algorithms and parameter space exploration, surrogate models offer a new and practical way to dramatically accelerate such studies without impacting accuracy.Comment: 20 pages, 17 figures, uses revtex 4.1. Version 2 includes new numerical experiments for longer waveform durations, larger regions of parameter space and multi-mode model

Bidirectional ventricular tachycardia in cardiac sarcoidosis.

A 73-year-old man with history of pulmonary sarcoidosis was found to have runs of non-sustained bidirectional ventricular tachycardia (BVT) with two different QRS morphologies on a Holter monitor. Cardiac magnetic resonance delayed gadolinium imaging revealed a region of patchy mid-myocardial enhancement within the left ventricular basal inferolateral myocardium. An 18-fluorodeoxyglucose positron emission tomography (FDG-PET) showed increased uptake in the same area, consistent with active sarcoid, with no septal involvement. Follow-up FDG-PET one year later showed disease progression with new septal involvement. Cardiac sarcoidosis, characterized by myocardial inflammation and interstitial fibrosis that can lead to conduction system disturbance and macro re-entrant arrhythmias, should be considered in differential diagnosis of BVT. BVT may indicate septal involvement with sarcoidosis before the lesions are large enough to be detected radiologically

Determination of polarized parton distribution functions with recent data on polarization asymmetries

Global analysis has been performed within the next-to-leading order in Quantum Chromodynamics (QCD) to determine polarized parton distributions with new experimental data in spin asymmetries. The new data set includes JLab, HERMES, and COMPASS measurements on spin asymmetry A_1 for the neutron and deuteron in lepton scattering. Our new analysis also utilizes the double-spin asymmetry for pi^0 production in polarized pp collisions, A_{LL}^{pi^0}, measured by the PHENIX collaboration. Because of these new data, uncertainties of the polarized PDFs are reduced. In particular, the JLab, HERMES, and COMPASS measurements are valuable for determining Delta d_v(x) at large x and Delta qbar(x) at x~0.1. The PHENIX pi^0 data significantly reduce the uncertainty of Delta g(x). Furthermore, we discuss a possible constraint on Delta g(x) at large x by using the HERMES data on g_1^d in comparison with the COMPASS ones at x~0.05.Comment: 11 pages, REVTeX, 13 eps files, Phys. Rev. D in pres

Measuring public perceptions of sex offenders: reimagining the Community Attitudes Toward Sex Offenders (CATSO) scale

The Community Attitudes Toward Sex Offenders (CATSO) scale is an 18-item self-report questionnaire designed to measure respondents’ attitudes toward sex offenders. Its original factor structure has been questioned by a number of previous studies, and so this paper sought to reimagine the scale as an outcome measure, as opposed to a scale of attitudes. A face validity analysis produced a provisional three-factor structure underlying the CATSO: ‘punitiveness,’ ‘stereotype endorsement,’ and ‘risk perception.’ A sample of 400 British members of the public completed a modified version of the CATSO, the Attitudes Toward Sex Offenders scale, the General Punitiveness Scale, and the Rational-Experiential Inventory. A three-factor structure of a 22-item modified CATSO was supported using half of the sample, with factors being labeled ‘sentencing and management,’ ‘stereotype endorsement,’ and ‘risk perception.’ Confirmatory factor analysis on data from the other half of the sample endorsed the three-factor structure; however, two items were removed in order to improve ratings of model fit. This new 20-item ‘Perceptions of Sex Offenders scale’ has practical utility beyond the measurement of attitudes, and suggestions for its future use are provided