Mission and space vehicle sizing data for a chemical propulsion/aerobraking option

Sizing data is presented for various combinations of Mars missions and chemical-propulsion/aerobraking vehicles. Data is compared for vehicles utilizing opposition (2-year mission) and conjunction (3-year mission) trajectories for 1999 and 2001 opportunities, for various sizes of vehicles. Payload capabilities for manned and unmanned missions vehicles and for propulsive-braking and aerobraking cases are shown. The effect of scaling up a reference vehicle is compared to the case of utilizing two identical vehicles, for growth in payload capability. The rate of cumulative build up of weight on the surface of Mars is examined for various mission/vehicle combinations, and is compared to the landed-weight requirements for sortie missions, moving-base missions, and fixed-base missions. Also, the required buildup of weight in low Earth orbit (LEO) for various mission/vehicle combinations is presented and discussed

Influence of a thermal denuder on diesel exhaust particle size distributions

Particle size distributions in diesel exhaust were studied using a thermal desorption technique to determine the volatile and non-volatile fractions. A thermal denuder was designed and characterized for optimal operating parameters and its influence on the exhaust chemistries studied using diesel engine exhaust. The study was conducted on a 1992 DDC Series 60 engine mounted on a heavy-duty direct current dynamometer and exercised over steady state and transient cycles. The particle size distributions were recorded upstream and downstream of the denuder maintained at different temperatures to determine the behavior of the volatile fraction. The volatilization technique was also applied to the crankcase emissions in light of the 2007/2010 EPA regulations. The SMPS was used to obtain the particle size distributions from the sample gases diluted by an ejector diluter system. With the removal of the volatile fraction from the sample exhaust a shift in the size distribution towards the lower end of the spectrum was observed. (Abstract shortened by UMI.)

Gust Generator for a Supersonic Wind Tunnel

The effectiveness was investigated of a flat plate gust generator that was located in the nozzle throat of the Lewis 10- by 10-foot supersonic wind tunnel. Gust plates were tested at nozzle wall Mach numbers of 3.1, 2.4, and 2.0. Test results show that the flat plate concept may be used as a gust generator for a wind tunnel; however, more extensive investigation is required to completely define its capabilities and limitations. For the single transient data point recorded, a gust amplitude (decrement) of 0.15 in Mach number was obtained. Analysis of these transient data indicates a response with a corner frequency of at least 8 hertz

Optimal control with mixed H_2 and H∞ performance objectives

This paper considers the analysis and synthesis of control systems subject to two types of disturbance signals: signals with bounded power spectral density and signals with bounded power. The resulting control problem involves minimizing a mixed H_2 and H∞ norm of the system. It is shown that the controller shares a separation property similar to those of pare H_2 or H∞. controller. It is also shown that the mixed problem reduces naturally to H_2 and H∞ problem in special cases. Some necessary and sufficient conditions are obtained for the existence of a solution to the mixed problem. Explicit state space formulae are given for the optimal controllers

Thermally isolated deployable shield for spacecraft

A thermally isolated deployable shield for spacecraft is provided utilizing a plurality of lattice panels stowable generally against the craft and deployable to some fixed distance from the craft. The lattice panels are formed from replaceable shield panels affixed to lattice structures. The lattice panels generally encircle the craft providing 360 degree coverage therearound. Actuation means are provided from translating the shield radially outward from the craft and thermally isolating the shield from the craft. The lattice panels are relatively flexible, allowing the shield to deploy to variable diameters while retaining uniform curvature thereof. Restraining means are provided for holding the shield relatively tight in its stowed configuration. Close-out assemblies provide light sealing and protection of the annular spaces between the deployed shield and the crafts end structure

What Factors Do Players Perceive as Methods of Retention in Battle Royale Games?

Battle Royale (BR) games are well known for their ability to not only attract but also retain a large number of players. In this paper, we attempt to identify the common themes which BR players identify as methods of retention through a qualitative thematic analysis with 11 participants. Data was gathered using semi-structured interviews and analysed through thematic analysis. Seven common themes were identified, where (1) draw of new content, (2) mechanics and action of BR games, and (3) reward systems were suggested to impact retention. Additionally, (4) social dynamics and (5) mastery were external factors outside the game that may impact retention in BR games. However, the other themes of (6) aesthetic preference and (7) unique selling points were not contributing factors in our sample. Further work is needed to understand the impact of these retention factors and how to design for these factors in game development

Mixed H_2 and H∞ control

Mixed H_2 and H∞ norm analysis and synthesis problems are considered in this paper. It is shown that the mixed norm analysis combined with structured uncertainty can be used to give bounds on robust H_2 and H∞ performance. It is also shown that the mixed norm controller shares a separation property similar to those of pure H_2 or H∞ controllers. The obvious advantage for a mixed norm is that it gives a natural trade-off between H_2 performance and H∞ performance, and provides a potential framework for extending the μ-synthesis framework to address robust H_2 performance. A simple example is used to motivate the possible advantages such a framework might have over a pure H∞ theory

Mixed H_2 and H∞ performance objectives. II. Optimal control

This paper considers the analysis and synthesis of control systems subject to two types of disturbance signals: white signals and signals with bounded power. The resulting control problem involves minimizing a mixed H_2 and H∞ norm of the system. It is shown that the controller shares a separation property similar to those of pure H_2 or H∞ controllers. Necessary conditions and sufficient conditions are obtained for the existence of a solution to the mixed problem. Explicit state-space formulas are also given for the optimal controller

Bloodborne viral infection in Irish injecting drug users.

The aim of this study was to determine the prevalence of, and factors associated with, hepatitis C (HCV), hepatitis B (HBV) and HIV infections among injecting drug users (IDUs) against this background. A cross-sectional survey of participants in an addiction treatment clinic was carried out on seven hundred and thirty-five people IDU tested for antibody to HCV (anti-HCV) between September 1992 and September 1997. Socio-demographic and drug use characteristics were measured. Serology tests for anti-HCV, HBV surface antigen (HBsAg) and HIV. The vast majority (89%) commenced injecting since 1990. Prevalence of anti-HCV was 61.8% (453/733), of HBsAg was 1.0% (7/729) and of HIV was 1.2% (7/600). Logistic regression analyses indicated that longer history of injecting and increased daily drug expenditure were the only independent variables associated with significantly increased risk of HCV. The only characteristic associated with increased prevalence of HBsAg was a history of injecting prior to 1990 (3.8%, 3/80). HIV prevalence was significantly higher when aged over 24 years (3.7%, 6/162), when injecting commenced prior to 1990 (6.3%, 4/64) and when injecting over 5 years (6.5%, 4/62). The study concluded that HIV prevalence has sustained a low level in this population. Interventions which aim to halt transmission of HCV are necessary and will need to target IDU very early in their injecting careers and also those at risk of commencing to inject