Towards robust aero-thermodynamic predictions for re-usable single-stage to orbit vehicles

Re-usable single stage to orbit launch vehicles promise to reduce the cost of access to space, but their success will be particularly reliant on accurate and robust modelling of their aero-thermodynamic characteristics. For preliminary design and optimization studies, relatively simple numerical prediction techniques must perforce be used, but it is important that the uncertainty that is inherent in the predictions of these models be understood. Predictions of surface pressure and heat transfer obtained using a new reduced-order model that is based on the Newtonian flow assumption and the Reynolds analogy for heating are compared against those of a more physically-sophisticated Direct Simulation Monte Carlo method in order to determine the ability of the model to capture the aero-thermodynamics of vehicles with very complex configuration even when run at low enough resolution to be practical in the context of design optimization studies. Attention is focused on the high-altitude regime where lifting re-usable Single-Stage to Orbit configurations will experience their greatest thermal load during re-entry, but where non-continuum effects within the gas of the atmosphere might be important. It is shown that the reduced-order model is capable of reproducing the results of the more complex Monte Carlo formalism with surprising fidelity, but that residual uncertainties exist, particularly in the behaviour of the heating models and in the applicability of the continuum assumption given the onset of finite slip velocity on surface of vehicle. The results suggest thus that, if used with care, reduced-order models such as those described here can be used very effectively in the design and optimization of space-access vehicles with very complex configuration, as long as their predictions are adequately supported by the use of more sophisticated computational techniques

Non-AIDS defining cancers in the D:A:D Study-time trends and predictors of survival : a cohort study

BACKGROUND:Non-AIDS defining cancers (NADC) are an important cause of morbidity and mortality in HIV-positive individuals. Using data from a large international cohort of HIV-positive individuals, we described the incidence of NADC from 2004-2010, and described subsequent mortality and predictors of these.METHODS:Individuals were followed from 1st January 2004/enrolment in study, until the earliest of a new NADC, 1st February 2010, death or six months after the patient's last visit. Incidence rates were estimated for each year of follow-up, overall and stratified by gender, age and mode of HIV acquisition. Cumulative risk of mortality following NADC diagnosis was summarised using Kaplan-Meier methods, with follow-up for these analyses from the date of NADC diagnosis until the patient's death, 1st February 2010 or 6 months after the patient's last visit. Factors associated with mortality following NADC diagnosis were identified using multivariable Cox proportional hazards regression.RESULTS:Over 176,775 person-years (PY), 880 (2.1%) patients developed a new NADC (incidence: 4.98/1000PY [95% confidence interval 4.65, 5.31]). Over a third of these patients (327, 37.2%) had died by 1st February 2010. Time trends for lung cancer, anal cancer and Hodgkin's lymphoma were broadly consistent. Kaplan-Meier cumulative mortality estimates at 1, 3 and 5 years after NADC diagnosis were 28.2% [95% CI 25.1-31.2], 42.0% [38.2-45.8] and 47.3% [42.4-52.2], respectively. Significant predictors of poorer survival after diagnosis of NADC were lung cancer (compared to other cancer types), male gender, non-white ethnicity, and smoking status. Later year of diagnosis and higher CD4 count at NADC diagnosis were associated with improved survival. The incidence of NADC remained stable over the period 2004-2010 in this large observational cohort.CONCLUSIONS:The prognosis after diagnosis of NADC, in particular lung cancer and disseminated cancer, is poor but has improved somewhat over time. Modifiable risk factors, such as smoking and low CD4 counts, were associated with mortality following a diagnosis of NADC

Tuberculosis among European patients with AIDS.

Abstract OBJECTIVES: To describe the characteristics of acquired immune deficiency syndrome (AIDS) patients with tuberculosis in Europe; to assess the incidence and risk factors of tuberculosis after AIDS; to compare survival of AIDS patients with and without extra-pulmonary tuberculosis (EPTB) at the time of AIDS diagnosis. DESIGN: Multicentric retrospective cohort study of 6544 AIDS patients diagnosed in 52 clinical centres and 17 European countries. METHODS: Description of patient characteristics and comparisons of tuberculosis incidence and mortality after AIDS with multivariate Cox proportional hazard models. RESULTS: 14.6% of AIDS patients had tuberculosis and 78% of those with tuberculosis had EPTB. EPTB was the AIDS-defining condition in 8.7% of the patients. Tuberculosis incidence after AIDS was 3.1 per 100 person-years. Age, gender and HIV-transmission category were not significantly associated with an increased risk of tuberculosis and the strongest risk factor for both EPTB and pulmonary tuberculosis (PTB) was the region of origin. The adjusted hazard ratio of EPTB and PTB in Southern Europe compared to Northern Europe were 5.5 (95% confidence interval [CI]: 5.0-6.1) and 2.0 (CI: 1.4-2.7) respectively. The apparent survival advantage of AIDS patients with EPTB compared to patients diagnosed with other conditions (median survival time: 22 vs 16 months) was statistically not significant when confounding variables were adjusted for (Hazard ratio: 0.85; CI: 0.62-1.07). CONCLUSIONS: In Europe, there are large differences in the incidence of tuberculosis among AIDS patients in different countries. They do not seem to be due to differences in age or in the prevalence of injecting drug use and likely reflect differences in the prevalence of tuberculosis infection. The role of recent transmission should also be considered, and national tuberculosis control efforts and Europe-wide surveillance need to be reinforced accordingly

Dedicated launch of small satellites using scramjets

Reduced scale and improved responsiveness will be the technical and economic drivers of future satellite systems. Based on decades of practical experience with rocket-only expendable launch vehicles, current technology is operated close to theoretical limits. Scramjets have an advantage over rocket propulsion in terms of a significantly higher specific impulse. Other benefits of airbreathing propulsion for access-to-space are increased launch flexibility and the possibility of reusable aircraft-like operations. This article describes the use of a three-stage rocket-scramjet-rocket system for transporting payloads of the order of 100 kg to a Sun Synchronous Orbit. The reusable second stage is based on a winged-cone vehicle and is powered by hydrogen fueled scramjets. Analysis of the complete three-stage system was performed based around a fully trimmed trajectory simulation of the second stage. The scramjet powered second stage accelerated from Mach 6.0 to Mach 9.3 with an average net specific impulse of 923 seconds. As a result, the overall system showed a payload mass fraction of 1.26% to Sun Synchronous orbit, which is significantly higher than expendable rocket based systems of this scale