Coverage Options for a Low cost, High Resolution Optical Constellation

This paper presents the range of coverage options available to TopSat like small satellites, both singly and in a small constellation. TopSat is a low-cost, high resolution and image quality, optical small satellite, due for launch in October 2004. In particular, the paper considers the use of tuned, repeat ground track orbits to improve coverage for selected ground targets, at the expense of global coverage. TopSat is designed to demonstrate the capabilities of small satellites for high value remote sensing missions. It is a 108kg, sun-synchronous satellite, designed to provide 2.5m resolution imagery direct to users in the vicinity of the imaged area. Its objectives are to demonstrate the capability to cost performance available from small satellites, the utility of direct reception of remotely sensed imagery, and the affordability of constellations and individually owned assets. A description of the satellite, and update on the development and flight build of the satellite is given, as of June 2003. Two coverage improving augmentations to the TopSat satellite are discussed, namely the addition of a propulsion system and more capable attitude actuators. With limited orbit control, achievement and maintenance of tuned orbits, and phasing of a constellation within orbits, become practicable. TopSat is an agile small satellite, allowing boresight reorientation required for slews during imaging. The capability for performing multiple images in a single target pass is considered, with the existing and improved torque actuator implementations. Similar options for performing stereo imaging with 2 formation flying TopSats are outlined. Reconfiguration of repeat ground track orbits for a single satellite is analysed in terms of fuel cost and drift orbit options. A one day repeat orbit case is presented which would allow daily coverage of a fixed target, with orbit reconfiguration required to allow global access. A typical mission for such a satellite is summarised, along with practical requirements for the propulsion system. Coverage options for constellations of between 2 and 4 satellites are then also scrutinised, with fuel estimates for the most promising options explored. Again, the benefits that could be achieved by using repeat ground track orbits are weighed against the fuel requirements, to maintain and reconfigure such a constellation. The TopSat mission is a collaboration between four UK partners. QinetiQ are leading the mission and providing data handling and ground segment elements. Rutherford Appleton Laboratory (RAL) are developing the camera, Surrey Satellite Technology Limited (SSTL) are providing the bus, and InfoTerra are responsible for developing potential data markets. The programme is jointly funded by the UK Ministry of Defence (MoD) and by the British National Space Centre (BNSC)

Pharmacokinetic profile and quantitation of protection against soman poisoning by the antinicotinic compound MB327 in the guinea-pig

Current organophosphorus nerve agent medical countermeasures do not directly address the nicotinic effects of poisoning. A series of antinicotinic bispyridinium compounds has been synthesized in our laboratory and screened in vitro. Their actions can include open-channel block at the nicotinic receptor which may contribute to their efficacy. The current lead compound from these studies, MB327 1,1′-(propane-1,3-diyl)bis(4-tert-butylpyridinium) as either the diiodide (I2) or dimethanesulfonate (DMS) has been examined in vivo for efficacy against nerve agent poisoning. MB327 I2 (0–113 mg kg−1) or the oxime HI-6 DMS (0–100 mg kg− 1), in combination with atropine and avizafone (each at 3 mg kg−1) was administered to guinea-pigs 1 min following soman poisoning. Treatment increased the LD50 of soman in a dose-dependent manner. The increase was statistically significant (p < 0.01) at the 33.9 mg kg−1 (MB327) or 30 mg kg−1 (HI-6) dose with a comparable degree of protection obtained for both compounds. Following administration of 10 mg kg−1 (i.m.), MB327 DMS reached plasma Cmax of 22 μM at 12 min with an elimination t1/2 of 22 min. In an adverse effect study, in the absence of nerve agent poisoning, a dose of 100 mg kg−1 or higher of MB327 DMS was lethal to the guinea-pigs. A lower dose of MB327 DMS (30 mg kg−1) caused flaccid paralysis accompanied by respiratory impairment. Respiration normalised by 30 min, although the animals remained incapacitated to 4 h. MB327 or related compounds may be of utility in treatment of nerve agent poisoning as a component of therapy with atropine, anticonvulsant and oxime, or alternatively as an infusion under medical supervision

Characterization of the luminescence center in photo- and electroluminescent amorphous silicon oxynitride films

We have studied the photoluminescence (PL) mechanism of photo- and electroluminescent amorphous silicon oxynitride films grown by plasma enhanced chemical vapor deposition. The composition of the films was determined by Rutherford backscattering spectrometry and monitored by the index of refraction with single-wavelength ellipsometry. Two sets of samples were grown, each with different reactant gas residence times in the deposition chamber. For samples grown with a residence time of about 5 s, the energy of the PL peak for 2.54 eV excitation is 2.3 eV for stoichiometric films and redshifts with increasing silicon content to 1.7 eV for the most silicon-rich films. The energy of the PL peak for 3.8 eV excitation is 2.8 eV for stoichiometric films and 2.1 eV for the most silicon-rich films. For stoichiometric films, the PL intensity is independent of temperature between 80 and 300 K using 2.54 eV excitation, but the PL intensity decreases by a factor of two over the same temperature range for 3.8 eV excitation. The authors interpret these aspects of the PL as consistent with tail-state recombination. Other results imply the PL is due to a specific luminescence center related to Si-Si or Si-H bonding. A 450°C anneal reduces the paramagnetic defect density in the films, as detected by electron paramagnetic resonance, by an order of magnitude, but does not increase the PL intensity, while a 950°C anneal increases both the defect density and the PL intensity. In addition, films in a second set of samples, grown with a residence time of 1.8 s, display very different PL behavior than samples in the first set with the same composition. Samples near stoichiometry in the second set have a PL peak at 2.06 eV and are 20 times less intense than stoichiometric samples in the first set. Optical absorption measurements indicate both types of samples contain Si-Si bonds, with the second set containing many more Si-Si bonds than the first. Fourier-transform infrared measurements indicate the presence of a Si-H bond that is stable at temperatures of 950°C in the first set, but not in the second set. Thus, the study as a whole suggests a complete picture of luminescence in our silicon oxynitride films must incorporate elements of both tail-state and luminescence center models. The relation of the results to other PL studies in silicon alloys and porous silicon is discussed

Displaying the Heterogeneity of the SN 2002cx-like Subclass of Type Ia Supernovae with Observations of the Pan-STARRS-1 Discovered SN2009ku

SN2009ku, discovered by Pan-STARRS-1, is a Type Ia supernova (SNIa), and a member of the distinct SN2002cx-like class of SNeIa. Its light curves are similar to the prototypical SN2002cx, but are slightly broader and have a later rise to maximum in g. SN2009ku is brighter (~0.6 mag) than other SN2002cx-like objects, peaking at M_V = -18.4 mag - which is still significantly fainter than typical SNeIa. SN2009ku, which had an ejecta velocity of ~2000 kms^-1 at 18 days after maximum brightness is spectroscopically most similar to SN2008ha, which also had extremely low-velocity ejecta. However, SN2008ha had an exceedingly low luminosity, peaking at M_V = -14.2 mag, ~4 mag fainter than SN2009ku. The contrast of high luminosity and low ejecta velocity for SN2009ku is contrary to an emerging trend seen for the SN2002cx class. SN2009ku is a counter-example of a previously held belief that the class was more homogeneous than typical SNeIa, indicating that the class has a diverse progenitor population and/or complicated explosion physics. As the first example of a member of this class of objects from the new generation of transient surveys, SN2009ku is an indication of the potential for these surveys to find rare and interesting objects.Comment: 7 pages, 3 figure

Stability and Instability of Extreme Reissner-Nordstr\"om Black Hole Spacetimes for Linear Scalar Perturbations I

We study the problem of stability and instability of extreme Reissner-Nordstrom spacetimes for linear scalar perturbations. Specifically, we consider solutions to the linear wave equation on a suitable globally hyperbolic subset of such a spacetime, arising from regular initial data prescribed on a Cauchy hypersurface crossing the future event horizon. We obtain boundedness, decay and non-decay results. Our estimates hold up to and including the horizon. The fundamental new aspect of this problem is the degeneracy of the redshift on the event horizon. Several new analytical features of degenerate horizons are also presented.Comment: 37 pages, 11 figures; published version of results contained in the first part of arXiv:1006.0283, various new results adde

The Structure and Stellar Content of the Outer Disks of Galaxies: A New View from the Pan-STARRS1 Medium Deep Survey

We present the results of an analysis of Pan-STARRS1 Medium Deep Survey multi-band (grizy) images of a sample of 698 low-redshift disk galaxies that span broad ranges in stellar mass, star-formation rate, and bulge/disk ratio. We use population synthesis spectral energy distribution fitting techniques to explore the radial distribution of the light, color, surface mass density, mass/light ratio, and age of the stellar populations. We characterize the structure and stellar content of the galaxy disks out to radii of about twice Petrosian r 90, beyond which the halo light becomes significant. We measure normalized radial profiles for sub-samples of galaxies in three bins each of stellar mass and concentration. We also fit radial profiles to each galaxy. The majority of galaxies have down-bending radial surface brightness profiles in the bluer bands with a break radius at roughly r 90. However, they typically show single unbroken exponentials in the reddest bands and in the stellar surface mass density. We find that the mass/light ratio and stellar age radial profiles have a characteristic "U" shape. There is a good correlation between the amplitude of the down-bend in the surface brightness profile and the rate of the increase in the M/L ratio in the outer disk. As we move from late- to early-type galaxies, the amplitude of the down-bend and the radial gradient in M/L both decrease. Our results imply a combination of stellar radial migration and suppression of recent star formation can account for the stellar populations of the outer disk

Pan-STARRS Pixel Analysis: Source Detection and Characterization

Over 3 billion astronomical sources have been detected in the more than 22 million orthogonal transfer CCD images obtained as part of the Pan-STARRS1 3π survey. Over 85 billion instances of those sources have been automatically detected and characterized by the Pan-STARRS Image Processing Pipeline photometry software, psphot. This fast, automatic, and reliable software was developed for the Pan-STARRS project but is easily adaptable to images from other telescopes. We describe the analysis of the astronomical sources by psphot in general as well as for the specific case of the third processing version used for the first two public releases of the Pan-STARRS 3π Survey data

Detailed electronic structure studies on superconducting MgB2_2 and related compounds

In order to understand the unexpected superconducting behavior of MgB$_2$ compound we have made electronic structure calculations for MgB$_2$ and closely related systems. Our calculated Debye temperature from the elastic properties indicate that the average phonon frequency is very large in MgB$_2$ compared with other superconducting intermetallics and the exceptionally high $T_c$ in this material can be explained through BCS mechanism only if phonon softening occurs or the phonon modes are highly anisotropic. We identified a doubly-degenerate quasi-two dimensional key-energy band in the vicinity of $E_{F}$ along $\Gamma$-A direction of BZ which play an important role in deciding the superconducting behavior of this material. Based on this result, we have searched for similar kinds of electronic feature in a series of isoelectronic compounds such as BeB$_2$, CaB$_2$, SrB$_2$, LiBC and MgB$_2$C$_2$ and found that MgB$_2$C$_2$ is one potential material from the superconductivity point of view. There are contradictory experimental results regarding the anisotropy in the elastic properties of MgB$_2$ ranging from isotropic, moderately anisotropic to highly anisotropic. In order to settle this issue we have calculated the single crystal elastic constants for MgB$_2$ by the accurate full-potential method and derived the directional dependent linear compressibility, Young's modulus, shear modulus and relevant elastic properties. We have observed large anisotropy in the elastic properties. Our calculated polarized optical dielectric tensor shows highly anisotropic behavior even though it possesses isotropic transport property. MgB$_2$ possesses a mixed bonding character and this has been verified from density of states, charge density and crystal orbital Hamiltonian population analyses