History, design and performance of the space shuttle hazardous gas detection system

The Hazardous Gas Detection System (HGDS) is designed to detect leaks hich could result in pre-launch or in-flight fires or explosions resulting from the presence of cryogenic rocket propellants. The historical development, design, and performance of the HGDS is discussed. Data for response time, detection limits, accuracy, and drift are presented. Finally, present and future applications are discussed, and some general conclusions are drawn

A portable hypergolic oxidizer vapor sensor for NASA's Space Shuttle program

The design and performance characteristics of an electrochemical NO2 sensor selected by NASA for the space shuttle program is described. The instrument consists of a sample pump, an electrochemical cell, and control and display electronics. The pump pushes the sample through the electrochemical cell where the vapors are analyzed and an output proportional to the NO2 concentration is produced. The output is displayed on a panel meter, and is also available at a recorder jack. The electrochemical cell is made up of a polypropylene chamber covered with teflon membrane faceplates. Plantinum electrodes are bonded to the faceplates, and the sensing and counter electrodes are potentiostatically controlled at -200 mV with respect to the reference electrode. The cell is filled with electrolyte, consisting of 13.5 cc of 23% solution of KOH

Orbit and Optics Improvement by Evaluating the Nonlinear BPM Response in CESR

We present an improved system for orbit and betatron phase measurement utilizing nonlinear models of BPM pickup response. We first describe the calculation of the BPM pickup signals as nonlinear functions of beam position using Green's reciprocity theorem with a two-dimensional formalism. We then describe the incorporation of these calculations in our beam position measurements by inverting the nonlinear functions, giving us beam position as a function of the pickup signals, and how this is also used to improve our measurement of the betatron phase advance. Measurements are presented comparing this system with the linearized pickup response used historically at CESR.Comment: 7 pages, 11 figure

Defining, Evaluating, and Removing Bias Induced by Linear Imputation in Longitudinal Clinical Trials with MNAR Missing Data

Missing not at random (MNAR) post-dropout missing data from a longitudinal clinical trial result in the collection of “biased data”, which leads to biased estimators and tests of corrupted hypotheses. In a full rank linear model analysis the model equation, E[Y] = Xβ, leads to the definition of the primary parameter β = (X′X)−1X′E[Y], and the definition of linear secondary parameters of the form θ = Lβ = L(X′X)−1X′E[Y], including for example, a parameter representing a “treatment effect”. These parameters depend explicitly on E[Y], which raises the questions: what is E[Y] when some elements of the incomplete random vector Y are not observed and MNAR, or when such a Y is “completed” via imputation? We develop a rigorous, readily interpretable definition of E[Y] in this context that leads directly to definitions of β,Bias(β^)=E[β^]−β,Bias(θ^)=E[θ^ ]−Lβ, and the extent of hypothesis corruption. These definitions provide a basis for evaluating, comparing, and removing biases induced by various linear imputation methods for MNAR incomplete data from longitudinal clinical trials. Linear imputation methods use earlier data from a subject to impute values for post-dropout missing values and include “Last Observation Carried Forward” (LOCF) and “Baseline Observation Carried Forward” (BOCF), among others. We illustrate the methods of evaluating, comparing, and removing biases and the effects of testing corresponding corrupted hypotheses via a hypothetical, but very realistic longitudinal analgesic clinical trial

TALKING TO ME? CREATING NETWORKS FROM ONLINE COMMUNITY LOGS

Online communities offer many potential sources of value to individuals and organisations. However, the effectiveness of online communities in delivering benefits such as knowledge sharing depends on the network of social relations within a community. Research in this area aims to understand and op-timize such networks. Researchers in this area employ diverse network creation methods, with little focus on the selection process, the fit of the selected method, or its relative accuracy. In this study we evaluate and compare the performance of four network creation methods. First we review the litera-ture to identify four network creation methods (algorithms) and their underlying assumptions. Using several data sets from an online community we test and compare the accuracy of each method against a baseline (‘actual’) network determined by content analysis. We use visual inspection, network cor-relation analysis and sensitivity analysis to highlight similarities and differences between the methods, and find some differences significant enough to impact study results. Based on our observations we argue for more careful selection of network creation methods. We propose two key guidelines for re-search into social networks that uses unstructured data from online communities. The study contrib-utes to the rigour of methodological decisions underpinning research in this area

Exploring barriers in expertise seeking : why don\u27t they ask an expert?

This paper reports findings from a research project that explores reasons why some employees prefer to seek expertise to resolve work-related problems from direct colleagues rather than designated internal experts. Several studies suggest that while an expert generally provides a higher quality solution in a shorter time, workers tend to ask friendly or proximate colleagues to help with knowledge-based problems at work. Prior research provides only fragmented insights into understanding the barriers to asking a designated internal expert for help at work. To address this gap, we asked post-graduate students enrolled in a knowledge management subject at a large Australian university to share their perspectives in an online discussion forum. Content analysis of the collected perspectives enabled identification of twenty-one factors that may limit the seeking of expertise from a designated internal expert. The factors are grouped in four categories: environment, accessibility, communication and personality. In addition one context variable is described, determining the extent to which the barriers are influential in a specific situation. By synthesising the results, we have proposed two models of expertise-seeking barriers. A literature review helps validate the barriers identified by the study. Key theoretical and practical implications are also discussed.<br /

ATTITUDE TOWARDS THE NEW WAY OF WORKING - A LONGITUDINAL STUDY

Information and communication technologies are rapidly transforming the work environment, providing flexibility of when and where to work. The New Way of Working (NWOW) is a relatively new phenomenon that provides the context for these developments. In this case research three reviews were performed over a one-year timeframe, evaluating the attitude of managers and employees towards the New Way of Working. Special attention was given to the relationship between personality traits (the ‘Big Five’) and satisfaction with NWOW. The case results show that, in general, managers and employees are and remain positive towards NWOW, though the actual effects of the implementation of NWOW on work and the work environment are often limited or hard to quantify. The personality survey shows there is a significant positive relationship between conscientiousness, being (self)disciplined, and satisfaction with NWOW. There is a negative relationship for neuroticism; sensitive employees. This leads to the conclusion that the New Way of Working is not beneficial to all. Where (self)disciplined employees may thrive well in the new work environment, high neuroticism (sensitive) persons may have problems to adapt to the newly gained freedom

Universal Chemomechanical Design Rules for Solid-Ion Conductors to Prevent Dendrite Formation in Lithium Metal Batteries

Dendrite formation during electrodeposition while charging lithium metal batteries compromises their safety. While high shear modulus solid-ion conductors (SICs) have been prioritized to resolve pressure-driven instabilities that lead to dendrite propagation and cell shorting, it is unclear whether these or alternatives are needed to guide uniform lithium electrodeposition, which is intrinsically density-driven. Here, we show that SICs can be designed within a universal chemomechanical paradigm to access either pressure-driven dendrite-blocking or density-driven dendrite-suppressing properties, but not both. This dichotomy reflects the competing influence of the SICs mechanical properties and partial molar volume of Li+ relative to those of the lithium anode on plating outcomes. Within this paradigm, we explore SICs in a previously unrecognized dendrite-suppressing regime that are concomitantly soft, as is typical of polymer electrolytes, but feature atypically low Li+ partial molar volume, more reminiscent of hard ceramics. Li plating mediated by these SICs is uniform, as revealed using synchrotron hard x-ray microtomography. As a result, cell cycle-life is extended, even when assembled with thin Li anodes and high-voltage NMC-622 cathodes, where 20 percent of the Li inventory is reversibly cycled