Acoustic fatigue: Overview of activities at NASA Langley

A number of aircraft and spacecraft configurations are being considered for future development. These include high-speed turboprop aircraft, advanced vertical take-off and landing fighter aircraft, and aerospace planes for hypersonic intercontinental cruise or flight to orbit and return. Review of the acoustic environment expected for these vehicles indicates levels high enough that acoustic fatigue must be considered. Unfortunately, the sonic fatique design technology used for current aircraft may not be adequate for these future vehicles. This has resulted in renewed emphasis on acoustic fatigue research at the NASA Langley Research Center. The overall objective of the Langley program is to develop methods and information for design of aerospace vehicles that will resist acoustic fatigue. The program includes definition of the acoustic loads acting on structures due to exhaust jets of boundary layers, and subsequent determination of the stresses within the structure due to these acoustic loads. Material fatigue associated with the high frequency structural stress reversal patterns resulting from acoustic loadings is considered to be an area requiring study, but no activity is currently underway

Noise Transmission Loss of a Rectangular Plate in an Infinite Baffle

An improved analytical procedure was developed that allows for the efficient calculation of the noise transmission characteristics of a finite rectangular plate. Both isotropic and symmetrically laminated composite plates are considered. The plate is modeled with classic thin-plate theory and is assumed to be simply supported on all four sides. The incident acoustic pressure is assumed to be a plane wave impinging on the plate at an arbitrary angle. The reradiated pressure is assumed to be negligible compared with the blocked pressure, and the plate vibrations are calculated by a normal-mode approach. A Green's function integral equation is used to link the plate vibrations to be transmitted far-field sound waves, and transmission loss is calculated from the ratio of incident to transmitted acoustic powers. The result is a versatile research and engineering analysis tool that predicts noise transmission loss and enables the determination of the modal behavior of the plate

Dissecting the Shared Genetic Architecture of Suicide Attempt, Psychiatric Disorders, and Known Risk Factors

Background Suicide is a leading cause of death worldwide, and nonfatal suicide attempts, which occur far more frequently, are a major source of disability and social and economic burden. Both have substantial genetic etiology, which is partially shared and partially distinct from that of related psychiatric disorders. Methods We conducted a genome-wide association study (GWAS) of 29,782 suicide attempt (SA) cases and 519,961 controls in the International Suicide Genetics Consortium (ISGC). The GWAS of SA was conditioned on psychiatric disorders using GWAS summary statistics via multitrait-based conditional and joint analysis, to remove genetic effects on SA mediated by psychiatric disorders. We investigated the shared and divergent genetic architectures of SA, psychiatric disorders, and other known risk factors. Results Two loci reached genome-wide significance for SA: the major histocompatibility complex and an intergenic locus on chromosome 7, the latter of which remained associated with SA after conditioning on psychiatric disorders and replicated in an independent cohort from the Million Veteran Program. This locus has been implicated in risk-taking behavior, smoking, and insomnia. SA showed strong genetic correlation with psychiatric disorders, particularly major depression, and also with smoking, pain, risk-taking behavior, sleep disturbances, lower educational attainment, reproductive traits, lower socioeconomic status, and poorer general health. After conditioning on psychiatric disorders, the genetic correlations between SA and psychiatric disorders decreased, whereas those with nonpsychiatric traits remained largely unchanged. Conclusions Our results identify a risk locus that contributes more strongly to SA than other phenotypes and suggest a shared underlying biology between SA and known risk factors that is not mediated by psychiatric disorders.Peer reviewe

A new dimensionality estimation tool for multiple-item tests and a new DIF analysis paradigm based on multidimensionality and construct validity

This thesis is concerned with two critical issues facing the testing industry today: dimensionality analysis and DIF (Differential Item Functioning) analysis. Chapter 1 develops the use of new dimensionally-sensitive proximity measures with Hierarchical Cluster Analysis and DIMTEST to estimate the dimensionality structure of tests. The results of simulation studies and real data analyses indicate that the new tool represents a significant step forward in the ability of dimensionality assessment tools to identify reliably the latent dimensionality structure of a set of items. Chapter 2 of the thesis develops a new DIF analysis paradigm that unifies the substantive and statistical DIF research camps by linking both camps to a theoretically sound and mathematically rigorous multidimensional conceptualization of DIF. The new paradigm is shown to have the potential to improve the understanding of the root causes of DIF through the testing of substantive DIF hypotheses, to reduce Type 1 error through a better understanding of the dimensionality of the matching criterion, and to increase power through the testing of bundles of items with similar content. Two new paradigm-based DIF analysis methods, one of which employed the new dimensionality estimation tool of Chapter 1, were described and applied to real data. The analyses demonstrated that the new paradigm-based methods offered insights that cannot be obtained from the standard one-item-at-a-time DIF analysis.U of I OnlyETDs are only available to UIUC Users without author permissio

Determining targets for multi-stage adaptive tests using integer programming

This paper considers a multi-stage adaptive test (MST) where the testlets at each stage are determined prior to the administration. The assembly of a MST requires target information and target response functions for the MST design. The targets are chosen to create tests with accurate scoring and high utilization of items in an operational pool. Forcing all MSTs to have information and response function plots to be within an interval about the targets will yield parallel MSTs, in the sense that standardized paper-and-pencil tests are considered parallel. The objective of this paper is to present a method to determine targets for the MST design based on an item pool and an assumed distribution of examinee ability. The approach is applied to a Skills Readiness Inventory test designed to identify logical reasoning deficiencies of examinees. This method can be applied to obtain item response theory targets for a linear test as this is a special case of a MST.Integer programming Simulation Testing Item response theory Poisson trials

The influence of biphasic positive airway pressure vs. sham biphasic positive airway pressure on pulmonary function in morbidly obese patients after bariatric surgery

Background: The effect of biphasic positive airway pressure (BPAP) at individualized pressures on the postoperative pulmonary recovery of morbidly obese patients (MOP) undergoing open bariatric surgery (OBS) and possible placebo device-related effects (sham BPAP) were investigated. Methods: Forty-eight MOP scheduled for OBS were initially enrolled. Subjects were randomly assigned to: A) the BPAP group in which BPAP, at individualized inspiratory positive airway pressure/expiratory positive airway pressure (IPAP/EPAP), was applied for 3 days postoperatively and B) the sham BPAP group in which sham BPAP was applied for the same time. Pulmonary function was assessed by spirometry 24 h prior to surgery and at 24, 48 and 72 h postoperatively and respiratory complications were recorded. Results: Thirty-five subjects, 21 in the BPAP group and 14 in the sham BPAP group, completed the study. Baseline characteristics and pulmonary function were similar between groups preoperatively. Subjects in the BPAP group showed in general better spirometric performance and SpO2 values postoperatively and expedited pulmonary recovery. Atelectasis combined with respiratory distress syndrome (RDS) symptoms was observed in 21% of subjects in the sham BPAP group and one of these subjects developed lower respiratory tract infection. No respiratory complications were recorded in the BPAP group. Use of higher BPAP pressures was not associated with anastomosis leakage or disruption in any patient. Conclusion: Use of BPAP, at individualized pressures, expedites postoperative pulmonary recovery and eliminates respiratory complications in MOP who have undergone OBS. © 2019 Via Medica. All rights reserved