Investigation of nickel hydrogen battery technology for the RADARSAT spacecraft

The low Earth orbit (LEO) operations of the RADARSAT spacecraft require high performance batteries to provide energy to the payload and platform during eclipse period. Nickel Hydrogen cells are currently competing with the more traditional Nickel Cadmium cells for high performance spacecraft applications at geostationary Earth orbit (GEO) and Leo. Nickel Hydrogen cells appear better suited for high power applications where high currents and high Depths of Discharge are required. Although a number of GEO missions have flown with Nickel Hydrogen batteries, it is not readily apparent that the LEO version of the Nickel Hydrogen cell is able to withstand the extended cycle lifetime (5 years) of the RADARSAT mission. The problems associated with Nickel Hydrogen cells are discussed in the contex of RADARSAT mission and a test program designed to characterize cell performance is presented

Stress relaxation and mechanical properties of RL-1973 and PD-200-16 silicone resin sponge materials

Stress relaxation tests were conducted by loading specimens in double-lap shear to a preselected strain level and monitoring the decay of stress with time. The stress relaxation response characteristics were measured over a temperature range of 100 to 300 K and four strain levels. It is concluded that only a slight amount of stress relaxation was observed, and the stiffness increased approximately two orders of magnitude over the range of temperatures

Five-Year Growth of Rock Lichens in a Low-Arctic Mountain Environment, Northern Labrador

In 1978, three lichen growth stations were established for Rhizocarpon section Rhizocarpon species and one for Alectoria miniscula in the Cirque Mountain area of the Torngat mountains. Five years later, in 1983, the lichens were remeasured. The five-year growth represented by the change in the theoretical diameter is very variable, between 0.10 and 0.54 mm per year. These rates are larger than expected and exceed rates previously determined for an eastern Arctic area, the Northern Cumberland Peninsula of Baffin Island, by more than 3 to more than 20 times. Similar rates are known for 'great period' growth outside Arctic regions. If the growth rates represent long-term growth, the ages of recessional moraines in the Torngat Mountains should be recalculated. Moraines formerly described as Late Wisconsin to mid-Holocene may be of Neoglacial age. Variability of growth rates from one individual to another precludes using these data for constructing growth curves which may be used, even locally, in lichenometric dating.En 1978, on a établi quatre sites de croissance du lichen dans la région du mont du Cirque dans les monts Torngat: trois sites des espèces Rhizocarpon de la section Rhizocarpon et un site de Alectoria miniscula. Cinq ans plus tard, en 1983, on a mesuré de nouveau les lichens pour constater que le diamètre moyen, qui témoigne de la croissance, a crû de manière très variable, soit de 0,10 à 0,54 mm par année. Ces taux de croissance sont plus élevés que prévu puisqu'ils dépassent de 3 à 20 fois les taux déjà mesurés dans le nord de la péninsule de Cumberland, île de Baffin. De tels taux de croissance du lichen s'apparentent davantage à ceux que l'on a observé dans les régions non arctiques au cours de sa période dite de grande croissance. Si ces taux s'appliquent à de longues périodes, il faudrait réévaluer la date de dépôt des moraines de récession dans les monts Torngat. Les moraines, que l'on croit dater de la période s'étendant du Wisconsinien supérieur à l'Holocène moyen, pourraient en fait dater du néoglaciaire. Toutefois, les variations observées entre les taux de croissance ne permettent pas d'utiliser ces données, même à l'échelle locale, pour tracer des courbes de croissance qui serviraient à établir des datations lichénométriques.1978 wurden im Cirque-Mountain-Gebiet der Torngat mountains vier Stationen zur Beobachtung des Flechten-Wachstums eingerichtet : drei Stationen fur Rhizocarpon-Arten der Sektion Rhizocarpon und eine Station fur Alectoria miniscula. Fùnf Jahre spâter, 1983, wurden die Flechten wieder gemessen. Der Fùnfjahreswuchs, der sich im Wechsel des durchschnittlichen Durchmessers ablesen IaBt, ist sehr unterschiedlich, zwischen 0.10 und 0.54 mm pro Jahr. Dièse Wachstumsraten sind grôfîer als erwartet und gehen ùber die zuvor fur ein ôstliches arktisches Gebiet, die Nord-Cumberland HaIbinsel der lnsel Baffin, bestimmten Raten mehr als dreifach bis zu mehr als zwanzigfach hinaus. Àhnliche Wachstumsraten sind fur die "groBe Periode" des Flechten-Wachstums auBerhalb der arktischen Gebiete bekannt. Wenn die Wachstumsraten Langzeit-Wachstum reprâsentieren, mûfite das Alter der Rùckzugs-Morànen in den Torngat-Bergen neu berechnet werden. Morànen, die zuvor dem spàten Wisconsin bis mittleren Holozân zugeschrieben wurden, kônnten aus der Neoglazialzeit stammen. Die Variationen der Wachstumsraten von einer Person zur anderen schlieBen eine Nutzung dieser Daten zum Aufbau von Wachstumskurven aus, welche, selbst lokal, zur Datierung auf der Basis der Flechten benutzt werden kônnten

Finite Temperature and Dynamical Properties of the Random Transverse-Field Ising Spin Chain

We study numerically the paramagnetic phase of the spin-1/2 random transverse-field Ising chain, using a mapping to non-interacting fermions. We extend our earlier work, Phys. Rev. 53, 8486 (1996), to finite temperatures and to dynamical properties. Our results are consistent with the idea that there are ``Griffiths-McCoy'' singularities in the paramagnetic phase described by a continuously varying exponent $z(\delta)$, where $\delta$ measures the deviation from criticality. There are some discrepancies between the values of $z(\delta)$ obtained from different quantities, but this may be due to corrections to scaling. The average on-site time dependent correlation function decays with a power law in the paramagnetic phase, namely $\tau^{-1/z(\delta)}$, where $\tau$ is imaginary time. However, the typical value decays with a stretched exponential behavior, $\exp(-c\tau^{1/\mu})$, where $\mu$ may be related to $z(\delta)$. We also obtain results for the full probability distribution of time dependent correlation functions at different points in the paramagnetic phase.Comment: 10 pages, 14 postscript files included. The discussion of the typical time dependent correlation function has been greatly expanded. Other papers of APY are available on-line at http://schubert.ucsc.edu/pete

Tetramethylenedisulfotetramine alters Ca²⁺ dynamics in cultured hippocampal neurons: mitigation by NMDA receptor blockade and GABA(A) receptor-positive modulation.

Tetramethylenedisulfotetramine (TETS) is a potent convulsant that is considered a chemical threat agent. We characterized TETS as an activator of spontaneous Ca²⁺ oscillations and electrical burst discharges in mouse hippocampal neuronal cultures at 13-17 days in vitro using FLIPR Fluo-4 fluorescence measurements and extracellular microelectrode array recording. Acute exposure to TETS (≥ 2 µM) reversibly altered the pattern of spontaneous neuronal discharges, producing clustered burst firing and an overall increase in discharge frequency. TETS also dramatically affected Ca²⁺ dynamics causing an immediate but transient elevation of neuronal intracellular Ca²⁺ followed by decreased frequency of Ca²⁺ oscillations but greater peak amplitude. The effect on Ca²⁺ dynamics was similar to that elicited by picrotoxin and bicuculline, supporting the view that TETS acts by inhibiting type A gamma-aminobutyric acid (GABA(A)) receptor function. The effect of TETS on Ca²⁺ dynamics requires activation of N-methyl-D-aspartic acid (NMDA) receptors, because the changes induced by TETS were prevented by MK-801 block of NMDA receptors, but not nifedipine block of L-type Ca²⁺ channels. Pretreatment with the GABA(A) receptor-positive modulators diazepam and allopregnanolone partially mitigated TETS-induced changes in Ca²⁺ dynamics. Moreover, low, minimally effective concentrations of diazepam (0.1 µM) and allopregnanolone (0.1 µM), when administered together, were highly effective in suppressing TETS-induced alterations in Ca²⁺ dynamics, suggesting that the combination of positive modulators of synaptic and extrasynaptic GABA(A) receptors may have therapeutic potential. These rapid throughput in vitro assays may assist in the identification of single agents or combinations that have utility in the treatment of TETS intoxication

Effect of hydrogen additive on the evolution of beam divergence incopper bromide lasers

©2001 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.We present a systematic study of the effect of hydrogen additive on the beam quality of copper bromide lasers. It is a well-established fact that the addition of small amounts of hydrogen to the neon buffer gas of this class of laser will dramatically increase their average output power and efficiency. Our results show that the partial pressure of hydrogen used to maximize the total output power is not the same as that which optimizes the power density in the drilling plane of a copper bromide laser based micro-machining systemPeter Graham Foster, Peter Eric Davis, Donald McCoy, and Jesper Munc

Implications of AlphaFold2 for crystallographic phasing by molecular replacement.

The AlphaFold2 results in the 14th edition of Critical Assessment of Structure Prediction (CASP14) showed that accurate (low root-mean-square deviation) in silico models of protein structure domains are on the horizon, whether or not the protein is related to known structures through high-coverage sequence similarity. As highly accurate models become available, generated by harnessing the power of correlated mutations and deep learning, one of the aspects of structural biology to be impacted will be methods of phasing in crystallography. Here, the data from CASP14 are used to explore the prospects for changes in phasing methods, and in particular to explore the prospects for molecular-replacement phasing using in silico models