Guidance and Control strategies for aerospace vehicles

A neighboring optimal guidance scheme was devised for a nonlinear dynamic system with stochastic inputs and perfect measurements as applicable to fuel optimal control of an aeroassisted orbital transfer vehicle. For the deterministic nonlinear dynamic system describing the atmospheric maneuver, a nominal trajectory was determined. Then, a neighboring, optimal guidance scheme was obtained for open loop and closed loop control configurations. Taking modelling uncertainties into account, a linear, stochastic, neighboring optimal guidance scheme was devised. Finally, the optimal trajectory was approximated as the sum of the deterministic nominal trajectory and the stochastic neighboring optimal solution. Numerical results are presented for a typical vehicle. A fuel-optimal control problem in aeroassisted noncoplanar orbital transfer is also addressed. The equations of motion for the atmospheric maneuver are nonlinear and the optimal (nominal) trajectory and control are obtained. In order to follow the nominal trajectory under actual conditions, a neighboring optimum guidance scheme is designed using linear quadratic regulator theory for onboard real-time implementation. One of the state variables is used as the independent variable in reference to the time. The weighting matrices in the performance index are chosen by a combination of a heuristic method and an optimal modal approach. The necessary feedback control law is obtained in order to minimize the deviations from the nominal conditions

Second-line antiretroviral therapy in a workplace and community-based treatment programme in South Africa: determinants of virological outcome.

: Background: As antiretroviral treatment (ART) programmes in resource-limited settings mature, more patients are experiencing virological failure. Without resistance testing, deciding who should switch to second-line ART can be difficult. The consequences for second-line outcomes are unclear. In a workplace- and community-based multi-site programme, with 6-monthly virological monitoring, we describe outcomes and predictors of viral suppression on second-line, protease inhibitor-based ART.Methods: We used prospectively collected clinic data from patients commencing first-line ART between 1/1/03 and 31/12/08 to construct a study cohort of patients switched to second-line ART in the presence of a viral load (VL) ?400 copies/ml. Predictors of VL<400 copies/ml within 15 months of switch were assessed using modified Poisson regression to estimate risk ratios.Results: 205 workplace patients (91.7% male; median age 43 yrs) and 212 community patients (38.7% male; median age 36 yrs) switched regimens. At switch compared to community patients, workplace patients had a longer duration of viraemia, higher VL, lower CD4 count, and higher reported non-adherence on first-line ART. Non-adherence was the reported reason for switching in a higher proportion of workplace patients. Following switch, 48.3% (workplace) and 72.0% (community) achieved VL<400, with non-adherence (17.9% vs. 1.4%) and virological rebound (35.6% vs. 13.2% with available measures) reported more commonly in the workplace programme. In adjusted analysis of the workplace programme, lower switch VL and younger age were associated with VL<400. In the community programme, shorter duration of viraemia, higher CD4 count and transfers into programme on ART were associated with VL<400.Conclusion: High levels of viral suppression on second-line ART can be, but are not always, achieved in multi-site treatment programmes with both individual- and programme-level factors influencing outcomes. Strategies to support both healthcare workers and patients during this switch period need to be evaluated; sub-optimal adherence, particularly in the workplace programme must be addressed

Resource Provisioning for Multi-Tier Virtualized Server Applications

Virtualizing the x86-based data center creates a dynamic environment for server application deployment and resource sharing. Resource management in this environment is challenging as applications are under fluctuating workloads causing diverse resource demands across their tiers. Resource allocation adaptation is essential for high performance machine utilization. This paper presents feedback controllers that dynamically adjust the CPU allocations of multi-tier applications in order to adapt to workload changes by considering the resource coupling between utilizations of application components. Our experimental evaluation on a virtualized 3-tier Rubis server application shows that our techniques work effectively

Assessing the performance of symmetric and assymetric implied volatility functions

This study examines several alternative symmetric and asymmetric model specifications of regression-based deterministic volatility models to identify the one that best characterizes the implied volatility functions of S&P 500 Index options in the period 1996–2009. We find that estimating the models with nonlinear least squares, instead of ordinary least squares, always results in lower pricing errors in both in- and out-of-sample comparisons. In-sample, asymmetric models of the moneyness ratio estimated separately on calls and puts provide the overall best performance. However, separating calls from puts violates the put-call-parity and leads to severe model mis-specification problems. Out-of-sample, symmetric models that use the logarithmic transformation of the strike price are the overall best ones. The lowest out-of-sample pricing errors are observed when implied volatility models are estimated consistently to the put-call-parity using the joint data set of out-of-the-money options. The out-of-sample pricing performance of the overall best model is shown to be resilient to extreme market conditions and compares quite favorably with continuous-time option pricing models that admit stochastic volatility and random jump risk factors

Visibility analysis, spatial experience and EEG recordings in virtual reality environments: The experience of ‘knowing where one is’ and isovist properties as a means to assess the related brain activity

Virtual Reality environments in combination with brain activity recordings using electroencephalography (EEG) offer a fruitful method to investigate the emergence of specific experiential events in response to the built environment. However, real-world experimental settings involve dynamic and complex conditions which are difficult to be controlled in order to test specific hypothesis that are related to neurophysiology. We discuss here several factors that should be taking into account when designing ecological EEG experiments such as a reflective approach on the human spatial experience, consideration of first-person perspectives and a quantitative analysis of the spatial context. The focus of this paper is to propose a methodology that may facilitate the design of virtual reality EEG experiments that aim to investigate the human experience and cognition within and of the built environment. A pilot virtual reality case study is presented to illustrate how the experience of 'suddenly knowing where one is' could be approached. In this case the isovist measurements of area and revelation along participants' paths offer a useful 'tool' that allows us to isolate and study with further analysis of the EEG signal, the moment that this experience might be manifested as neuronal firing patterns in the human brain

Ethnicity and prosperity in east London: How racial inequalities impact experiences of the good life

This working paper explores the London Prosperity Index survey data through an ethnicity lens and provides some preliminary findings concerning on the relation between racial inequality and prosperity. The quantitative data analysis is framed around three thematic issues, identified in qualitative research as critical to experiences of prosperity in east London: livelihoods, feelings about the local area and feelings about the future

Synthesis of bacteriophage lytic proteins against Streptococcus pneumoniae in the chloroplast of Chlamydomonas reinhardtii.

There is a pressing need to develop novel antibacterial agents given the widespread antibiotic resistance among pathogenic bacteria and the low specificity of the drugs available. Endolysins are antibacterial proteins that are produced by bacteriophage-infected cells to digest the bacterial cell wall for phage progeny release at the end of the lytic cycle. These highly efficient enzymes show a considerable degree of specificity for the target bacterium of the phage. Furthermore, the emergence of resistance against endolysins appears to be rare as the enzymes have evolved to target molecules in the cell wall that are essential for bacterial viability. Taken together, these factors make recombinant endolysins promising novel antibacterial agents. The chloroplast of the green unicellular alga Chlamydomonas reinhardtii represents an attractive platform for production of therapeutic proteins in general, not least due to the availability of established techniques for foreign gene expression, a lack of endotoxins or potentially infectious agents in the algal host, and low cost of cultivation. The chloroplast is particularly well suited to the production of endolysins as it mimics the native bacterial expression environment of these proteins while being devoid of their cell wall target. In this study the endolysins Cpl-1 and Pal, specific to the major human pathogen Streptococcus pneumoniae, were produced in the C. reinhardtii chloroplast. The antibacterial activity of cell lysates and the isolated endolysins was demonstrated against different serotypes of S. pneumoniae, including clinical isolates and total recombinant protein yield was quantified at ~1.3 mg/g algal dry weight. This article is protected by copyright. All rights reserved

Ultra-high-Q optoelectronic oscillator based on bilaterally coupled loops

An optoelectronic oscillator (OEO) based on bilateral coupling between two individual optoelectronic loops is demonstrated. The resulting OEO has two modes of operation, in which the individual loops either oscillate or act as IIR filters. A Q-factor greater than 1010 at 5.8 GHz is observed