Electrostatic charging of spacecraft in geosynchronous orbit

Any satellite whose orbit passes through the terrestrial magnetosphere will encounter several plasma regimes with widely differing temperatures, densities and compositions. The spacecraft itself will act as a plasma probe; each surface element changes its potential until no net current flows between it and the plasma. Differential charge build-up between adjacent surfaces (for example of different material or geometrical characteristics) can induce electrostatic discharges. The resulting current pulse, or RF interference gives rise to 'operational anomalies' (spurious switchings, telemetry drop-outs etc), or in extreme cases leads to permanent damage (eg short circuits in strings of solar cells). This thesis is a study of the spacecraft charging phenomenon applicable to satellites in geosynchronous orbit. Results are derived from three sources. Firstly, Meteosat F2 (a meteorological satellite launched by ESA in July 1981) which carried an electron spectrometer to make direct measurements of the geosynchronous orbit electron environment, and in addition, suffered a series of operational anomalies and surface charging events. Secondly, an experimental test programme was undertaken using a monoenergetic electron beam to irradiate some common spacecraft surface materials, and thereby examine their electrostatic charging properties. Thirdly, numerical simulation codes were written and employed to model several different situations, ranging from the electron beam experiment to a full three-dimensional simulation of Meteosat F2. Analysis of the electron beam irradiation data shows that the surface conductivity of some common insulating materials (Kapton and Teflon) plays a much greater role in the current balance equation than was thought previously. Furthermore, the process whereby bulk and surface conductivity is enhanced by large electric fields (deviations from pure Ohmic behaviour) is also shown to be a significant factor in the current balance equation. These results are of importance both to satellite surface design, and to high voltage insulating systems. Spacecraft charging simulation codes must accurately model the detailed interaction between plasma energy spectra and the energy dependent material surface properties (such as secondary electron emission). The thesis demonstrates that it is vital to use real, measured spectra (for example from the Meteosat spectrometer) rather than simple Maxwellian plasma definitions, if spacecraft charging is to be modelled successfully. Also, the need for an improved database of reliable secondary electron yield measurements is demonstrated

Peripheral arterial disease: diagnostic challenges and how photoplethysmography may help

Peripheral arterial disease (PAD) affects approximately 20% of patients aged ≥60 years.1 A GP with an average list size of 1800 patients can expect to have 50–60 patients with PAD. Ankle-brachial pressure index (ABPI), which is the ratio of the ankle to brachial systolic pressure measured by sphygmomanometer and hand-held Doppler ultrasound probe, is used to assess PAD in general practice. ABPI has been shown to have a sensitivity of 95% and specificity of 99% compared to angiographic imaging,2 however it is relatively time-consuming and requires adequately trained staff. There are limitations with ABPI in patients with diabetes, renal disease, and older people where an underestimation of disease can occur with a falsely high ratio due to the presence of incompressible calcified blood vessels

Novel Signal Noise Reduction Method through Cluster Analysis, Applied to Photoplethysmography

Physiological signals can often become contaminated by noise from a variety of origins. In this paper, an algorithm is described for the reduction of sporadic noise from a continuous periodic signal. The design can be used where a sample of a periodic signal is required, for example, when an average pulse is needed for pulse wave analysis and characterization. The algorithm is based on cluster analysis for selecting similar repetitions or pulses from a periodic single. This method selects individual pulses without noise, returns a clean pulse signal, and terminates when a sufficiently clean and representative signal is received. The algorithm is designed to be sufficiently compact to be implemented on a microcontroller embedded within a medical device. It has been validated through the removal of noise from an exemplar photoplethysmography (PPG) signal, showing increasing benefit as the noise contamination of the signal increases. The algorithm design is generalised to be applicable for a wide range of physiological (physical) signals

Nurses’ and patients’ experiences and preferences of the Ankle-Brachial Pressure Index and Multi-site Photoplethysmography for the diagnosis of peripheral arterial disease: A qualitative study

Peripheral arterial disease is a global health problem, affecting around 20% of people aged over 60 years. Whilst ankle-brachial pressure index (ABPI) is regularly used for diagnosis, it has a number of limitations, which have presented a need for alternative methods of diagnosis. Multi-site photoplethysmography (MPPG) is one such method, but evidence of acceptability of both methods is lacking. This study aims to describe and compare preferences and experiences amongst nurses and patients of ABPI and MPPG use in primary care. We used qualitative research methods in the context of a clinical diagnostic study comparing ABPI with MPPG. Use of ABPI and MPPG by 13 nurses were observed with 51 patients across general practice surgeries in North-East England in 2015/16. Follow-up semi-structured interviews were conducted with 12 nurses and 27 patients. Data were thematically analysed. Two major themes were identified: (1) device preferences; (2) test discomfort and anxiety. There was a compelling preference for MPPG due to ease of use, speed of the test, patient comfort, and perceived device accuracy/objectivity. However some patients struggled to identify a preference, describing ambivalence to medical testing. ABPI was deemed uncomfortable and painful, particularly when the blood pressure cuff was inflated at the lower limbs. There was also evidence of anxiety amongst patients when their foot pulses were not identified using ABPI. Whilst ABPI is a non-invasive and routine procedure it was associated with a number of drawbacks in clinical practice. Nurses required considerable dexterity to employ the test, and it resulted in anxiety amongst some patients. Conversely, MPPG was deemed to be easier and quicker to use, and perceived to be less subjective. Should diagnostic accuracy and cost be comparable to ABPI, then the findings of this study suggest MPPG would be preferable to ABPI for patients as well as nurses

CBFbeta is a facultative Runx partner in the sea urchin embryo

BACKGROUND: Runx proteins are developmentally important metazoan transcription factors that form a heterodimeric complex with the non-homologous protein Core Binding Factor beta (CBFbeta). CBFbeta allosterically enhances Runx DNA binding but does not bind DNA itself. We report the initial characterization of SpCBFbeta, the heterodimeric partner of SpRunt-1 from the sea urchin Stronylocentrotus purpuratus. RESULTS: SpCBFbeta is remarkably similar to its mammalian homologues, and like them it enhances the DNA binding of the Runt domain. SpCBFbeta is entirely of zygotic provenance and its expression is similar that of SpRunt-1, accumulating globally at late blastula stage then later localizing to endoderm and oral ectoderm. Unlike SpRunt-1, however, SpCBFbeta is enriched in the endodermal mid- and hindgut of the pluteus larva, and is not highly expressed in the foregut and ciliated band. We showed previously that morpholino antisense-mediated knockdown of SpRunt-1 leads to differentiation defects, as well as to extensive post-blastula stage apoptosis caused by under-expression of the Runx target gene SpPKC1. In contrast, we show here that knockdown of SpCBFbeta does not negatively impact cell survival or SpPKC1 expression, although it does lead to differentiation defects similar to those associated with SpRunt-1 deficiency. Moreover, SpRunt-1 containing a single amino acid substitution that abolishes its ability to interact with SpCBFbeta retains the ability to rescue cell survival in SpRunt-1 morphant embryos. Chromatin immunoprecipitation shows that while the CyIIIa promoter engages both proteins, the SpPKC1 promoter only engages SpRunt-1. CONCLUSION: SpCBFbeta is a facultative Runx partner that appears to be required specifically for cell differentiation

CBFbeta is a facultative Runx partner in the sea urchin embryo

BACKGROUND: Runx proteins are developmentally important metazoan transcription factors that form a heterodimeric complex with the non-homologous protein Core Binding Factor beta (CBFbeta). CBFbeta allosterically enhances Runx DNA binding but does not bind DNA itself. We report the initial characterization of SpCBFbeta, the heterodimeric partner of SpRunt-1 from the sea urchin Stronylocentrotus purpuratus. RESULTS: SpCBFbeta is remarkably similar to its mammalian homologues, and like them it enhances the DNA binding of the Runt domain. SpCBFbeta is entirely of zygotic provenance and its expression is similar that of SpRunt-1, accumulating globally at late blastula stage then later localizing to endoderm and oral ectoderm. Unlike SpRunt-1, however, SpCBFbeta is enriched in the endodermal mid- and hindgut of the pluteus larva, and is not highly expressed in the foregut and ciliated band. We showed previously that morpholino antisense-mediated knockdown of SpRunt-1 leads to differentiation defects, as well as to extensive post-blastula stage apoptosis caused by under-expression of the Runx target gene SpPKC1. In contrast, we show here that knockdown of SpCBFbeta does not negatively impact cell survival or SpPKC1 expression, although it does lead to differentiation defects similar to those associated with SpRunt-1 deficiency. Moreover, SpRunt-1 containing a single amino acid substitution that abolishes its ability to interact with SpCBFbeta retains the ability to rescue cell survival in SpRunt-1 morphant embryos. Chromatin immunoprecipitation shows that while the CyIIIa promoter engages both proteins, the SpPKC1 promoter only engages SpRunt-1. CONCLUSION: SpCBFbeta is a facultative Runx partner that appears to be required specifically for cell differentiation

Approaches towards expression profiling the response to treatment

Over the past 8 years there has been a wealth of breast cancer gene expression studies. The majority of these studies have focused upon characterising a tumour at presentation, before treatment, rather than looking at the effects of treatment on the tumour. More recently, a number of groups have moved from predicting prognosis based upon long-term follow-up to alternative approaches of using expression profiling to measure the effect of treatment on breast tumours and potentially predict response to therapy using either post-treatment samples or both pre-treatment and post-treatment samples. Whilst this provides great potential to further our understanding of the mode of action of treatments and to more accurately select which patients will benefit from a particular treatment, serious issues of experimental design must be considered

Systematic Review of Economic Models Used to Compare Techniques for Detecting Peripheral Arterial Disease

Background and objective Peripheral arterial disease (PAD) is a common condition, in which atherosclerotic narrowing in the arteries restricts blood supply to the leg muscles. In order to support future model-based economic evaluations comparing methods of diagnosis in this area, a systematic review of economic modelling studies was conducted. Methods A systematic literature review was performed in June 2017 to identify model-based economic evaluations of diagnostic tests to detect PAD, with six individual databases searched. The review was conducted in accordance with the methods outlined in the Centre for Reviews and Dissemination’s guidance for undertaking reviews in healthcare, and appropriate inclusion criteria were applied. Relevant data were extracted, and studies were quality assessed. Results Seven studies were included in the final review, all of which were published between 1995 and 2014. There was wide variation in the types of diagnostic test compared. The majority of the studies (six of seven) referenced the sources used to develop their model, and all studies stated and justified the structural assumptions. Reporting of the data within the included studies could have been improved. Only one identified study focused on the cost-effectiveness of a test typically used in primary care. Conclusions This review brings together all applied modelling methods for tests used in the diagnosis of PAD, which could be used to support future model-based economic evaluations in this field. The limited modelling work available on tests typically used for the detection of PAD in primary care, in particular, highlights the importance of future work in this area

Prospective assessment of the diagnostic accuracy of multi-site photoplethysmography pulse measurements for diagnosis of peripheral artery disease in primary care

Peripheral arterial disease (PAD) is associated with cerebral and coronary artery disease. Symptomatic PAD affects about 5% of people over 55 years; many more have asymptomatic PAD. Early detection enables modification of arterial disease risk factors. Diagnostically, assessment of symptoms or signs can be unreliable; ankle brachial pressure index (ABPI) testing is time-consuming and few healthcare professionals are properly trained. This study assessed the diagnostic accuracy of multi-site photoplethysmography (MPPG), an alternative non-invasive test for PAD, in primary care. PAD patients identified from general practice registers were age- and sex-matched with controls. Participants were assessed using MPPG, ABPI and duplex ultrasound (DUS). Outcome measures were sensitivity and specificity of MPPG and ABPI (relative to DUS) and concordance. MPPG test results were available in 249 of 298 eligible participants from 16 practices between May 2015 and November 2016. DUS detected PAD in 101/249 (40.6%). MPPG sensitivity was 79.8% (95% confidence interval [CI] 69.9-87.6%), with specificity 71.9% (95% CI 63.7-79.2%). ABPI sensitivity was 80.2% (95% CI 70.8-87.6%), with specificity 88.6% (95% CI 82-93.5%). With comparable sensitivity to ABPI, MPPG is quick, automated and simpler to do than ABPI; it offers the potential for rapid and accessible PAD assessments in primary care