Survivable Failure Data Recorders for Spacecraft

A spacecraft may be unable to communicate critical data associated with a serious or catastrophic failure. A brief report proposes a system, somewhat like a commercial aircraft "black box," for retrieving these data. A microspacecraft attached to the prime spacecraft would continually store recent critical data from that spacecraft. If either spacecraft detected certain serious conditions of the prime spacecraft, the microspacecraft would separate from the prime spacecraft and independently transmit the stored data to Earth. Supplemental data, acquired from sensors onboard the microspacecraft, could be added to this transmission. For example, the orientation and angular rates of the prime spacecraft immediately before separation as well as pictures taken of the prime spacecraft after separation could be included. Functional enhancements over aircraft black boxes include the separation from the prime vehicle (which gains independence from the fate of that vehicle), wireless transmission of data (making physical black box recovery unnecessary), and the optional acquisition of supplemental sensor data

A model for the simultaneous inference of attribute nonattendance and taste heterogeneity

An extensive literature has recognised that when travel choices are made, only a subset of the attributes of the choice alternatives may be considered or attended to by each decision maker. This paper introduces the random parameters attribute nonattendance (RPANA) model. Attribute nonattendance (ANA) is estimated through the model, which does not rely on stated ANA, although the latter can be introduced as a covariate, in recognition that whilst concerns have been raised about the reliability of stated ANA, it may provide the analyst with valuable information. The model employs a latent class structure to capture an elevated mass of taste coefficients at zero; a technique widely employed in the literature. However, preference heterogeneity can additionally be captured as a continuous distribution, with random parameters. The latent class component introduced in this model is highly flexible and parsimonious, and can exploit any independence of ANA across the attributes, whilst also handling correlation in ANA across subsets of attributes, as needed. Results are presented from a stated choice experiment investigating short haul flights. Non-zero probabilities of ANA are estimated for all attributes, and the RPANA model represents an improvement on the random parameters logit model in terms of model fit. Specific issues with model identification are discussed, and some potential pitfalls noted

The Removal of Numerical Drift from Scientific Models

Computer programs often behave differently under different compilers or in different computing environments. Relative debugging is a collection of techniques by which these differences are analysed. Differences may arise because of different interpretations of errors in the code, because of bugs in the compilers or because of numerical drift, and all of these were observed in the present study. Numerical drift arises when small and acceptable differences in values computed by different systems are integrated, so that the results drift apart. This is well understood and need not degrade the validity of the program results. Coding errors and compiler bugs may degrade the results and should be removed. This paper describes a technique for the comparison of two program runs which removes numerical drift and therefore exposes coding and compiler errors. The procedure is highly automated and requires very little intervention by the user. The technique is applied to the Weather Research and Forecasting model, the most widely used weather and climate modelling code.Comment: 12 page

Far infrared studies of radiation damaged and annealed GaAs and GaP

Far infrared absorption spectra (20-700cm-1) have been recorded using either a modified Grubb-Parsons/NPL cube interferometer with a maximum resolution of 0.1cm-1, or a Bruker 113V FTIR interferometer with a maximum resolution of 0.03cm-1, with samples mounted on a wheel inside a liquid helium cryostat close to the bolometer. Nominally pure GaAs and GaP samples and GaAs containing Al, B, C and Si impurities, were studied. The GaAs samples had either been irradiated with fast neutrons or 2MeV electrons with a range of doses varying from the minimum required to produce detectable changes in the infrared spectrum , up to a maximum corresponding to saturation of the damage produced. The only GaP sample to be studied was nominally pure and was irradiated with a dose of 2MeV electrons. All the samples were subsequently annealed in 30&deg;C stages up to about 550&deg;C at which temperature the recovery from the effects of theradiation damage was essentially complete and in many cases free carrier absorption had returned.The damage produced in the samples caused a relaxation of the selection rules, which normally forbid certain absorption processes, so that pronounced structure wasdetected which corresponded to features in the one-phonon density of states of the pure crystal. On annealing thesamples, the damage and hence this structure, was progressively removed. In addition, in GaAs irradiated with fast neutrons, new lines at 45cm 119cm-1 and328cm-1 were observed which first grew in strength withincreasing anneal temperature and then disappeared at higher temperatures. These lines were present in all samples given a sufficiently large dose of neutrons and hence were attributed to in-band resonances arising from intrinsic defect centres. However, in GaAs irradiated with 2MeV electrons only the feature at 45cm-l was observed, showing that the features at 119cm-l and 328cm-1 are produced only by neutron irradiation. In electron irradiated and annealed GaP a resonant mode at 149cm-1 was observed together with four gap mode lines which were all attributed to intrinsic radiation damage centres. In order to identify the defect centres responsible, these results were compared with a) the observations of local modes in doped samples which had undergone similar treatment and for which site switching of impurity atoms was observed during the annealing process and b) EPR data for similar annealing studies on the Asga antisite defect in irradiated GaAs.High resolution studies of neutron irradiated GaAs doped with carbon showed that the previously reported C(l) lines at 577.5cm-1 and 606cm-l show structure consistent with the centre responsible for these lines being Cas bonded to an interstitial As atom, surrounded by four Ga atoms.<p

A qualitative investigation of elite golf coaches knowledge and the epistemological chain

The aim of the study was to explore the existence and application of the epistemological chain (EC) construct in the decision making of elite golf coaches. Eight male expert golf coaches were recruited for the study. Employing a qualitative methodology, semi-structured interviews were conducted to gain understanding of the participants‟ perceptions and application of the EC and to determine its overall effect on their knowledge development. Data were analysed to identify themes using interpretive phenomenological analysis (IPA). Results indicate the EC is indeed present in the coaching of elite golfers and implemented in a structured and coherent form. This raises a number of interesting issues regarding coach and player development that may impact upon future pedagogical provision