Particle dynamics associated with the space environment

A major factor in dust dynamics in a microgravity environment is the absence of settling; hence, Spacelab air will contain larger particles than a comparable laboratory on earth. In addition, the presence of low level acceleration fluctuations (thruster firings, crew motions, etc.) could inhibit dust removal by surface scavenging. Because of the presence of larger particles, aerosol dynamics at larger Reynolds numbers must be considered. An accurate drag coefficient for spherical particles was developed for the higher Reynolds number phenomena. A general graphic correlation for the drag coefficient as a function of Reynolds and Knudsen numbers was developed based on currently available drag data for spheres. The general equations that govern dust dynamics were reviewed

Measurements and a model for convective velocities in the turbulent boundary layer

A physical model is presented which describes convective velocities within a flat plate turbulent boundary layer. A production zone concept is used as a basis for the physical model. The production zone concept employs the idea that packets of turbulent fluid are generated near the viscous sublayer. These packets are found to be discernible from the mean motion and may move either outward from the production zone or inward depending on their circulation relative to the fluid surrounding the packet. The packets are predicted to travel with a convective velocity different from the local mean velocity throughout most of the boundary layer. The model also predicts that the convective velocities will be functions of wave number outside the production zone

Correlation between the outer flow and the turbulent production in a boundary layer

Space-time velocity correlation measurements between fluctuations occurring in the convoluting outer edge of a flat boundary layer with fluctuations occurring near the viscous subregion were made. The correlations indicate that information is propagated from the outer region to the inner region. The migration of turbulence away from the wall was previously studied in the open literature. The results presented here along with the migration results lend support to the limit cycle model for turbulence production

Evaluation of high Reynolds number flow in a 180 degree turn-around-duct

Mean and turbulent velocities were measured for the flow in a 180 degree turn-around-duct over a Reynolds number range from 600,000 to greater than 900,000. The measurements were made in water using a forward scattering laser velocimeter. A duct of 100 x 10 cm constant cross-section, with a mean radius of curvature (centerline) of 10 cm was employed for the study. The measurements are in agreement with previous studies in that the use of local bulk velocity to nondimensionalize the mean and turbulent velocities reduce the Reynolds number variations. The basic phenomenon of relaminarization along the inner surface at the exit of the turn are similar to the flow observed at low Reynolds numbers. The separation bubble region shows a systematic variation with Reynolds number, however the Reynolds number effect may be of second order in the calculation of the overall flow. Large tangential, radial, and lateral turbulent velocities are measured along the outer surface of the turn

Evaluation of mean and turbulent velocity measurements in subsonic accelerated boundary layers

Exploratory measurements of the mean and turbulent flow in the wall boundary layer of a 15.5- by 10.2-cm channel were obtained as part of an instrumentation development program for measurements in compressible flow. Mean surface and flow-field surveys were obtained at channel Mach numbers ranging from 0.2 to 0.9. The mean velocity distributions were obtained with total pressure probes and a laser velocimeter. At a channel Mach number of 0.2, several types of hot-wire probes were used to obtain both velocity fluctuations and Reynolds shear-stress results

Metrology of fluid mechanics

CER66VAS32.June 1966

Demonstration of a Response Time Based Remaining Useful Life (RUL) Prediction for Software Systems

Prognostic and Health Management (PHM) has been widely applied to hardware systems in the electronics and non-electronics domains but has not been explored for software. While software does not decay over time, it can degrade over release cycles. Software health management is confined to diagnostic assessments that identify problems, whereas prognostic assessment potentially indicates when in the future a problem will become detrimental. Relevant research areas such as software defect prediction, software reliability prediction, predictive maintenance of software, software degradation, and software performance prediction, exist, but all of these represent diagnostic models built upon historical data, none of which can predict an RUL for software. This paper addresses the application of PHM concepts to software systems for fault predictions and RUL estimation. Specifically, this paper addresses how PHM can be used to make decisions for software systems such as version update and upgrade, module changes, system reengineering, rejuvenation, maintenance scheduling, budgeting, and total abandonment. This paper presents a method to prognostically and continuously predict the RUL of a software system based on usage parameters (e.g., the numbers and categories of releases) and performance parameters (e.g., response time). The model developed has been validated by comparing actual data, with the results that were generated by predictive models. Statistical validation (regression validation, and k-fold cross validation) has also been carried out. A case study, based on publicly available data for the Bugzilla application is presented. This case study demonstrates that PHM concepts can be applied to software systems and RUL can be calculated to make system management decisions.Comment: This research methodology has opened up new and practical applications in the software domain. In the coming decades, we can expect a significant amount of attention and practical implementation in this area worldwid

Placebo response rate in clinical trials of fistulizing crohn's disease: systematic review and meta-analysis

Background & Aims: It is important to determine the magnitude and identify modifiers of the rate of response to placebo in clinical trials of fistulizing Crohn’s disease (CD), to understand disease progression, and to calculate sample size. We conducted a systematic review and meta-analysis of rates of response to placebo in trials of patients with fistulizing CD. Methods: We searched MEDLINE, EMBASE, EMBASE CLASSIC, and the Cochrane central register of controlled trials for randomized controlled trials (RCTs) comparing pharmacologic agents with placebo in adults with fistulizing CD. We identified studies that reported complete fistula closure, partial closure, or response. Data were extracted as intention-to-treat analyses and pooled by using a random-effects model. Proportions of patients who received placebo and had complete or partial fistula(e) closure were calculated, with 95% confidence intervals (CIs). The effects of trial characteristics on the magnitude of response to placebo were examined. Results: Thirteen RCTs were eligible for our analysis; these included 579 patients assigned to placebo groups. The pooled rate of response to placebo, among all RCTs, for complete fistula closure was 15.6% (95% CI, 10.9%–20.9%), with significant heterogeneity (I2 = 62.5%, P = .001). The pooled rate of response to placebo for partial fistula closure or response in 9 trials, comprising 423 patients, was 18.3% (95% CI, 14.8%–22.1%). Rates of response to placebo were significantly lower in trials with shorter durations of therapy and shorter intervals to assessment of fistula closure. Neither exposure to the pharmacologic agent during the induction phase of the same (or related) RCT nor concomitant medications had any effect. Conclusions: In a meta-analysis of rate of response to placebo in patients with fistulizing CD, we found that fistulae closed in almost 1/6 patients given placebo in RCTs of pharmacologic agents. Future research should identify characteristics of patients that predict response to placebo

Market Access Analysis of Biologics and Small-Molecule Inhibitors for Inflammatory Bowel Disease Among US Health Insurance Policies.

BACKGROUND AND AIMS:Treatment pathways for ulcerative colitis (UC) and Crohn's disease (CD) are shifting to a more individualized, risk-stratified approach. The perception is that insurance policies may not have implemented this paradigm shift, particularly regarding access to newer agents. We evaluated patient access to advanced therapies by analyzing policy information from the Managed Markets Insight and Technology database. METHODS:Coverage status as of December 2018 for all US lives was queried for adalimumab, infliximab, infliximab-dyyb, tofacitinib, ustekinumab, and vedolizumab by indication (UC and/or CD) and medical or pharmacy coverage benefit. Coverage status was classified by the number of biologic steps before access to specified drug as "No Biologic," "1 Prior Biologic," "2+ Prior Biologics," "Not Covered." Unknown lives were excluded from the analyses. RESULTS:Coverage analysis was available for approximately 302 million lives under each medical and pharmacy benefit. Our analysis indicates that approximately half of covered lives had access to all agents (except tofacitinib) as first-line therapy; two-thirds had access after one biologic exposure. Among newer agents, vedolizumab had the widest coverage. For indications of UC and CD, 81% of known lives had access to vedolizumab with no prior biologic exposure required ("No Biologic"), 95% after "No Biologic" + "1 prior Biologic." Geographic variations were identified for coverage patterns. CONCLUSIONS:This US-based healthcare policy analysis points to an increased access to advanced therapies for UC and CD. An individualized, risk-stratified treatment approach integrating advanced therapies, including those recently approved, into treatment pathways for UC and CD is feasible