Design, construction and testing of the Communications Technology Satellite protection against spacecraft charging

Detailed discussions are presented of the measures taken on the Communications Technology Satellite (CTS or Hermes) which provide protection against the effects of spacecraft charging. These measures include: a comprehensive grounding philosophy and implementation; provision of command and data line transmitters and receivers for transient noise immunity; and a fairly restrictive EMI specification. Ground tests were made on materials and the impact of these tests on the CTS spacecraft is described. Hermes, launched on 17 January 1976 on a 2914 Delta vehicle, has successfully completed 10 months of operations. Anomalies observed are being assessed in relation to spacecraft charging, but no definite correlations have yet been established. A list of conclusions with regard to the CTS experience is given and recommendations for future spacecraft are also listed

Design and analysis considerations for deployment mechanisms in a space environment

On the second flight of the INTELSAT V spacecraft the time required for successful deployment of the north solar array was longer than originally predicted. The south solar array deployed as predicted. As a result of the difference in deployment times a series of experiments was conducted to locate the cause of the difference. Deployment rate sensitivity to hinge friction and temperature levels was investigated. A digital computer simulation of the deployment was created to evaluate the effects of parameter changes on deployment. Hinge design was optimized for nominal solar array deployment time for future INTELSAT V satellites. The nominal deployment times of both solar arrays on the third flight of INTELSAT V confirms the validity of the simulation and design optimization

Reconstructing 3D x-ray CT images of polymer gel dosimeters using the zero-scan method

In this study x-ray CT has been used to produce a 3D image of an irradiated PAGAT gel sample, with noise-reduction achieved using the ‘zero-scan’ method. The gel was repeatedly CT scanned and a linear fit to the varying Hounsfield unit of each pixel in the 3D volume was evaluated across the repeated scans, allowing a zero-scan extrapolation of the image to be obtained. To minimise heating of the CT scanner’s x-ray tube, this study used a large slice thickness (1 cm), to provide image slices across the irradiated region of the gel, and a relatively small number of CT scans (63), to extrapolate the zero-scan image. The resulting set of transverse images shows reduced noise compared to images from the initial CT scan of the gel, without being degraded by the additional radiation dose delivered to the gel during the repeated scanning. The full, 3D image of the gel has a low spatial resolution in the longitudinal direction, due to the selected scan parameters. Nonetheless, important features of the dose distribution are apparent in the 3D x-ray CT scan of the gel. The results of this study demonstrate that the zero-scan extrapolation method can be applied to the reconstruction of multiple x-ray CT slices, to provide useful 2D and 3D images of irradiated dosimetry gels

HypTrails: A Bayesian Approach for Comparing Hypotheses About Human Trails on the Web

When users interact with the Web today, they leave sequential digital trails on a massive scale. Examples of such human trails include Web navigation, sequences of online restaurant reviews, or online music play lists. Understanding the factors that drive the production of these trails can be useful for e.g., improving underlying network structures, predicting user clicks or enhancing recommendations. In this work, we present a general approach called HypTrails for comparing a set of hypotheses about human trails on the Web, where hypotheses represent beliefs about transitions between states. Our approach utilizes Markov chain models with Bayesian inference. The main idea is to incorporate hypotheses as informative Dirichlet priors and to leverage the sensitivity of Bayes factors on the prior for comparing hypotheses with each other. For eliciting Dirichlet priors from hypotheses, we present an adaption of the so-called (trial) roulette method. We demonstrate the general mechanics and applicability of HypTrails by performing experiments with (i) synthetic trails for which we control the mechanisms that have produced them and (ii) empirical trails stemming from different domains including website navigation, business reviews and online music played. Our work expands the repertoire of methods available for studying human trails on the Web.Comment: Published in the proceedings of WWW'1

Time history of the magnetospheric cavity

Laboratory scale model simulation of effect of solar wind on magnetosphere by propelling plasma stream into dipole magnetic field - time history of magnetospheric cavit

Kolektivne i jednočestične strukture u jezgrama bogatim neutronima

The neutron-rich nuclei of 104,106Mo, 139,141Ba, 139Xe, 115,117Ag and 133,135Te have been studied by using the spontaneous fission source of 252Cf with the Gammasphere array. In the present work, the collective and single particle structures in these neutron-rich nuclei have been reported. Gamma type vibrational bands in 104,106Mo, particle and hole states, including candidates for tilted rotor bands in 133,135Te and a 7/2[413] rotational band in both 115,117Ag have been observed. The N = 83 135Te and 139Ba show marked differences associated with differences in their particle and hole states. New levels in 141Ba and 139Xe extend evidence for two opposite parity doublets characteristic of stable octupole deformation.Proučavali smo neutronima bogate jezgre 104,106Mo, 139,141Ba, 139Xe, 115,117Ag i 133,135Te pomoću izvora spontane fisije 252Cf, primjenom uređaja Gammasphere. Prikazujemo njihove kolektivne i jednočestične strukture. Opazili smo γ-vibracijske vrpce u 104,106Mo, čestična i šupljinska stanja, uključivši kandidate za nagnutu rotorsku vrpcu u 133,135Te i rotacijsku vrpcu 7/2[413] u 115,117Ag. Jezgre 135Te i 139Ba s N = 83 su izrazito različite zbog razlika u njihovim čestičnim i šupljinskim stanjima. Novi nivoi jezgara 141Ba i 139Xe daju dodatni dokaz za postojanje dvaju dubleta suprotne parnosti koji su karakteristični za stabilnu oktupolnu deformaciju

Kolektivne i jednočestične strukture u jezgrama bogatim neutronima

The neutron-rich nuclei of 104,106Mo, 139,141Ba, 139Xe, 115,117Ag and 133,135Te have been studied by using the spontaneous fission source of 252Cf with the Gammasphere array. In the present work, the collective and single particle structures in these neutron-rich nuclei have been reported. Gamma type vibrational bands in 104,106Mo, particle and hole states, including candidates for tilted rotor bands in 133,135Te and a 7/2[413] rotational band in both 115,117Ag have been observed. The N = 83 135Te and 139Ba show marked differences associated with differences in their particle and hole states. New levels in 141Ba and 139Xe extend evidence for two opposite parity doublets characteristic of stable octupole deformation.Proučavali smo neutronima bogate jezgre 104,106Mo, 139,141Ba, 139Xe, 115,117Ag i 133,135Te pomoću izvora spontane fisije 252Cf, primjenom uređaja Gammasphere. Prikazujemo njihove kolektivne i jednočestične strukture. Opazili smo γ-vibracijske vrpce u 104,106Mo, čestična i šupljinska stanja, uključivši kandidate za nagnutu rotorsku vrpcu u 133,135Te i rotacijsku vrpcu 7/2[413] u 115,117Ag. Jezgre 135Te i 139Ba s N = 83 su izrazito različite zbog razlika u njihovim čestičnim i šupljinskim stanjima. Novi nivoi jezgara 141Ba i 139Xe daju dodatni dokaz za postojanje dvaju dubleta suprotne parnosti koji su karakteristični za stabilnu oktupolnu deformaciju