Projective homogeneous varieties birational to quadrics

We will consider an explicit birational map between a quadric and the projective variety X(J) of traceless rank one elements in a simple reduced Jordan algebra J. X(J) is a homogeneous G-variety for the automorphism group G=Aut(J). We will show that the birational map is a blow up followed by a blow down. This will allow us to use the blow up formula for motives together with Vishik's work on the motives of quadrics to give a motivic decomposition of X(J).Comment: 20 pages, 1 figur

Lack of agreement between measured and self-reported distance from public green parks in Glasgow, Scotland

<p><b>Background:</b></p> <p>Reviews have reported mixed findings for associations between physical activity and proximity to a range of environmental resources. Initially most studies used self reported proximity, but more are now using GIS techniques to measure proximity objectively. We know little about the extent of agreement between self reported and directly measured proximity of the same resource.</p> <p><b>Methods:</b></p> <p>We used previously collected data in a community survey in Glasgow in which 658 respondents aged around 40 and 60 were asked whether they lived within half a mile of a public park. We compared their answers with GIS measures of whether there was a park within a half mile service area of their home (and whether their home was within a half mile crow fly buffer of a park).</p> <p><b>Results:</b></p> <p>Agreement was poor; percentage agreement between measured network distance and reported residence within 0.5 miles of a park was 62.0%, and the kappa value was 0.095. Agreement was no higher than poor in any socio-demographic subgroup, or when using crow fly buffers instead of service areas.</p> <p><b>Conclusion:</b></p> <p>One should be cautious about assuming that respondents' self reports of proximity to a resource are a valid proxy for actual distance, or vice versa. Further research is needed to establish whether actual or self-reported proximity predict physical activity or other behaviours, and if so which is the strongest predictor. Further, qualitative study, also needs to examine the basis of people's judgements about the location of resources, and the possibility that these are shaped by their social and personal significance.</p&gt

The food retail environment and area deprivation in Glasgow City

It has previously been suggested that deprived neighbourhoods within modern cities have poor access to general amenities, for example, fewer food retail outlets. Here we examine the distribution of food retailers by deprivation in the City of Glasgow, UK.We obtained a list of 934 food retailers in Glasgow, UK, in 2007, and mapped these at address level. We categorised small areas (data zones) into quintiles of area deprivation using the 2006 Scottish Index of Multiple Deprivation Income sub-domain score. We computed mean number of retailers per 1000 residents per data zone, and mean network distance to nearest outlet from data zone centroid, for all retailers combined and for each of seven categories of retailer separately (i.e. bakers, butchers, fruit and vegetable sellers, fishmongers, convenience stores, supermarkets and delicatessens).The most deprived quintile (of areas) had the greatest mean number of total food retailers per 1000 residents while quintile 1 (least deprived) had the least, and this difference was statistically significant (Chi-square p < 0.01). The closest mean distance to the nearest food retailer was within quintile 3 while the furthest distance was within quintile 1, and this was also statistically significant (Chi-square p < 0.01). There was variation in the distribution of the seven different types of food retailers, and access to amenities depended upon the type of food retailer studied and whether proximity or density was measured. Overall the findings suggested that deprived neighbourhoods within the City of Glasgow did not necessarily have fewer food retail outlets

Are housing tenure and car access still associated with health? A repeat cross-sectional study of UK adults over a 13-year period

Background: It is usually assumed that housing tenure and car access are associated with health simply because they are acting as markers for social class or income and wealth. However, previous studies conducted in the late 1990s found that these household assets were associated with health independently of social class and income. Here, we set out to examine if this is still the case. Methods: We use data from our 2010 postal survey of a random sample of adults (n=2092) in 8 local authority areas in the West of Scotland. Self-reported health measures included limiting longstanding illness (LLSI), general health over the last year and the Hospital Anxiety and Depression Scale. Results: We found a statistically significant relationship between housing tenure and all 4 health measures, regardless of the inclusion of social class or income as controls. Compared with owner occupiers, social renters were more likely to report ill-health (controlling for social class—LLSI OR: 3.24, general health OR: 2.82, anxiety η2: 0.031, depression η2: 0.048, controlling for income—LLSI OR: 3.28, general health OR: 2.82, anxiety η2: 0.033, depression η2: 0.057) (p<0.001 for all models). Car ownership was independently associated with depression and anxiety, with non-owners at higher risk of both (controlling for income—anxiety η2: 0.010, depression η2: 0.023, controlling for social class—anxiety η2: 0.013, depression η2: 0.033) (p<0.001 for all models). Conclusions: Our results show that housing tenure and car ownership are still associated with health, after taking known correlates (age, sex, social class, income) into account. Further research is required to unpack some of the features of these household assets such as the quality of the dwelling and access to and use of different forms of transport to determine what health benefits or disbenefits they may be associated with in different contexts

Measuring dopant concentrations in compensated p-type crystalline silicon via iron-acceptor pairing

We present a method for measuring the concentrations of ionized acceptors and donors in compensated p-type silicon at room temperature.Carrier lifetimemeasurements on silicon wafers that contain minute traces of iron allow the iron-acceptor pair formation rate to be determined, which in turn allows the acceptor concentration to be calculated. Coupled with an independent measurement of the resistivity and a mobility model that accounts for majority and minority impurity scatterings of charge carriers, it is then possible to also estimate the total concentration of ionized donors. The method is valid for combinations of different acceptor and donor species.D.M. is supported by an Australian Research Council fellowship. L.J.G. would like to acknowledge SenterNovem for support

Novel orbits of Mercury and Venus enabled using low-thrust propulsion

Exploration of the inner planets of the Solar System is vital to significantly enhance the understanding of the formulation of Earth and other planets. This paper therefore considers the development of novel orbits of both Mercury and Venus to enhance the opportunities for remote sensing. Continuous low-thrust propulsion is used to extend the critical inclination of highly elliptical orbits at each planet, which are shown to require very small acceleration magnitudes. Unlike other bodies in the Solar System, natural sun-synchronous orbits do not exist at Mercury or Venus. This research therefore also uses continuous acceleration to enable both circular and elliptical sun-synchronous orbits, which could significantly simplify the spacecraft thermal environment. Considerably high thrust levels are however required to enable these orbits, which could not be provided by current propulsion systems

Extension of Martian orbits using continuous low-thrust propulsion

There has recently been significant interest in exploration of the Martian surface and atmosphere with a view to future human exploration. Thus missions must be developed which are responsive to these scientific goals. This work therefore develops novel orbits around Mars using continuous low-thrust propulsion to enable new and unique investigations of the red planet. This paper considers the use of continuous acceleration, using Solar Electric Propulsion, to alter the critical inclination of Highly Elliptical Orbits away from the conventional values, to any inclination required to optimally fulfill the mission objectives. This allows the spacecraft to spend a large amount of time over a region of interest as a result of apoareion dwell, thus allowing enhanced opportunities for remote sensing. In addition to this, the extension of existing circular Sun-synchronous orbits is considered as well as the development of Sun-synchronous Highly Elliptical Orbits, which force the ascending node angle to rotate at the same rate as the mean rotation of the Sun, whilst maintaining a constant argument of perihelion over the orbit. Thus, allowing simplification of the spacecraft thermal environment. Notably, we can enable these orbits using existing Electric Propulsion technology

Application of parallel distributed processing to space based systems

The concept of using Parallel Distributed Processing (PDP) to enhance automated experiment monitoring and control is explored. Recent very large scale integration (VLSI) advances have made such applications an achievable goal. The PDP machine has demonstrated the ability to automatically organize stored information, handle unfamiliar and contradictory input data and perform the actions necessary. The PDP machine has demonstrated that it can perform inference and knowledge operations with greater speed and flexibility and at lower cost than traditional architectures. In applications where the rule set governing an expert system's decisions is difficult to formulate, PDP can be used to extract rules by associating the information an expert receives with the actions taken