Computer-aided design and analysis of mechanisms

An introduction to the computer programs developed to assist in the design and analysis of mechanisms is presented. A survey of the various types of programs which are available is given, and the most widely used programs are compared. The way in which the programs are used is discussed, and demonstrated with an example

The effect of pitch span on intonational plateaux

Previous research has indicated that the H (high) of a nuclear accent may be realized as a flat stretch of contour rather than as a single turning point. Both the duration of this plateau and its alignment within the accented syllable are affected by the segmental and prosodic structure of the utterance. The present work investigates whether a non-structural variable, namely pitch span, also affects the realization of the plateau. Speakers replicated all-sonorant utterances in different pitch spans. Results show that both the duration and alignment of the plateau vary with pitch span but in ways different from the way they vary with prosodic structure. Importantly, results also indicate that, when using a proportional measure of alignment, the end of the plateau is anchored within the syllable for each speaker and may be a marker of linguistic structure

In the Absence of Scrutiny: Narratives of Probable Cause

This Article reports on a set of roughly thirty interviews with federal magistrate judges. The focus of the interviews was the impact of the Supreme Court case, United States v. Leon, on the behavior of magistrate judges. Leon, famously, put in place the good faith exception for faulty warrants that were obtained by the officers in good faith. The insertion of this exception diminished significantly the incentive for defendants to challenge problematic warrant grants. That effect, in turn, could have diminished the incentive for magistrate judge scrutiny of the warrants at the front end of the process. We do not find any indication of diminished scrutiny. What we do find, however, is a highly ritualized and formalistic process for the evaluation of warrants where calculations of probabilities are viewed through a legalistic rather than a pragmatic lens

A study of pilot modeling in multi-controller tasks

A modeling approach, which utilizes a matrix of transfer functions to describe the human pilot in multiple input, multiple output control situations, is studied. The approach used was to extend a well established scalar Wiener-Hopf minimization technique to the matrix case and then study, via a series of experiments, the data requirements when only finite record lengths are available. One of these experiments was a two-controller roll tracking experiment designed to force the pilot to use rudder in order to coordinate and reduce the effects of aileron yaw. One model was computed for the case where the signals used to generate the spectral matrix are error and bank angle while another model was computed for the case where error and yaw angle are the inputs. Several anomalies were observed to be present in the experimental data. These are defined by the descriptive terms roll up, break up, and roll down. Due to these algorithm induced anomalies, the frequency band over which reliable estimates of power spectra can be achieved is considerably less than predicted by the sampling theorem

Error detection and control for nonlinear shell analysis

A problem-adaptive solution procedure for improving the reliability of finite element solutions to geometrically nonlinear shell-type problem is presented. The strategy incorporates automatic error detection and control and includes an iterative procedure which utilizes the solution at the same load step on a more refined model. Representative nonlinear shell problem are solved

Real closed exponential fields

In an extended abstract Ressayre considered real closed exponential fields and integer parts that respect the exponential function. He outlined a proof that every real closed exponential field has an exponential integer part. In the present paper, we give a detailed account of Ressayre's construction, which becomes canonical once we fix the real closed exponential field, a residue field section, and a well ordering of the field. The procedure is constructible over these objects; each step looks effective, but may require many steps. We produce an example of an exponential field $R$ with a residue field $k$ and a well ordering $<$ such that $D^c(R)$ is low and $k$ and $<$ are $\Delta^0_3$, and Ressayre's construction cannot be completed in $L_{\omega_1^{CK}}$.Comment: 24 page

Computational structural mechanics: A new activity at the NASA Langley Research Center

Complex structures considered for the late 1980's and early 1990's include composite primary aircraft structures and the space station. These structures are much more difficult to analyze than today's structures and necessitate a major upgrade in computerized structural analysis technology. A major research activity in computational structural mechanics (CSM) was initiated. The objective of the CSM activity is develop advanced structural analysis technology that will exploit modern and emerging computers such as computers with vector and/or parallel processing capabilities. The three main research activities underway in CSM include: (1) structural analysis methods development; (2) a software testbed for evaluating the methods; and (3) numerical techniques for parallel processing computers. The motivation and objectives of the CSM activity are presented and CSM activity is described. The current CSM research thrusts, and near and long term CSM research thrusts are outlined

Nonlinear transient analysis via energy minimization

The formulation basis for nonlinear transient analysis of finite element models of structures using energy minimization is provided. Geometric and material nonlinearities are included. The development is restricted to simple one and two dimensional finite elements which are regarded as being the basic elements for modeling full aircraft-like structures under crash conditions. The results indicate the effectiveness of the technique as a viable tool for this purpose