3,681 research outputs found
The Viking surface sampler
A surface sampler subsystem for the Viking Lander has been designed, fabricated, cleaned, and successfully tested. Testing has included component level tests to qualification environment and subsystem level tests. This development hardware has also been integrated into a System Test Bed (STB) for the lander system. In addition to the normal dynamic and thermal environments the surface sampler hardware has been tested in an aircraft to simulate the effects of the reduced Martian gravity. Although problems have been encountered with the first-build and integration, the basic design appears to be sound and hardware qualification is scheduled for late 1973
Fermion Pair Production From an Electric Field Varying in Two Dimensions
The Hamiltonian describing fermion pair production from an arbitrarily
time-varying electric field in two dimensions is studied using a
group-theoretic approach. We show that this Hamiltonian can be encompassed by
two, commuting SU(2) algebras, and that the two-dimensional problem can
therefore be reduced to two one-dimensional problems. We compare the group
structure for the two-dimensional problem with that previously derived for the
one-dimensional problem, and verify that the Schwinger result is obtained under
the appropriate conditions.Comment: Latex, 14 pages of text. Full postscript version available via the
worldwide web at http://nucth.physics.wisc.edu/ or by anonymous ftp from
ftp://nucth.physics.wisc.edu:/pub/preprints
A variational approach to the stochastic aspects of cellular signal transduction
Cellular signaling networks have evolved to cope with intrinsic fluctuations,
coming from the small numbers of constituents, and the environmental noise.
Stochastic chemical kinetics equations govern the way biochemical networks
process noisy signals. The essential difficulty associated with the master
equation approach to solving the stochastic chemical kinetics problem is the
enormous number of ordinary differential equations involved. In this work, we
show how to achieve tremendous reduction in the dimensionality of specific
reaction cascade dynamics by solving variationally an equivalent quantum field
theoretic formulation of stochastic chemical kinetics. The present formulation
avoids cumbersome commutator computations in the derivation of evolution
equations, making more transparent the physical significance of the variational
method. We propose novel time-dependent basis functions which work well over a
wide range of rate parameters. We apply the new basis functions to describe
stochastic signaling in several enzymatic cascades and compare the results so
obtained with those from alternative solution techniques. The variational
ansatz gives probability distributions that agree well with the exact ones,
even when fluctuations are large and discreteness and nonlinearity are
important. A numerical implementation of our technique is many orders of
magnitude more efficient computationally compared with the traditional Monte
Carlo simulation algorithms or the Langevin simulations.Comment: 15 pages, 11 figure
Partition Functions in Statistical Mechanics, Symmetric Functions, and Group Representations
Partition functions for non-interacting particles are known to be symmetric
functions. It is shown that powerful group-theoretical techniques can be used
not only to derive these relationships, but also to significantly simplify
calculation of the partition functions for particles that carry internal
quantum numbers. The partition function is shown to be a sum of one or more
group characters. The utility of character expansions in calculating the
partition functions is explored. Several examples are given to illustrate these
techniques.Comment: 16 pages of RevTe
Nodding syndrome in Tanzania may not be associated with circulating anti-NMDA- and anti-VGKC receptor antibodies or decreased pyridoxal phosphate serum levels-a pilot study
Background: Nodding syndrome (NS) is a seemingly progressive epilepsy disorder of unknown underlying cause. We investigated association of pyridoxal-phosphate serum levels and occurrence of anti-neuronal antibodies against N-methyl-D-aspartate (NMDA) receptor and voltage gated potassium channel (VGKC) complex in NS patients.Methods: Sera of a Tanzanian cohort of epilepsy and NS patients and community controls were tested for the presence of anti-NMDA-receptor and anti-VGKC complex antibodies by indirect immunofluorescence assay. Furthermore pyridoxal-phosphate levels were measured.Results: Auto-antibodies against NMDA receptor or VGKC (LG1 or Caspr2) complex were not detected in sera of patients suffering from NS (n=6), NS plus other seizure types (n=16), primary generalized epilepsy (n=1) and community controls without epilepsy (n=7). Median Pyridoxal-phosphate levels in patients with NS compared to patients with primary generalized seizures and community controls were not significantly different. However, these median pyridoxal-phosphate levels are significantly lower compared to the range considered normal in Europeans.Conclusions: In this pilot study NS was not associated with serum anti-NMDA receptor or anti-VGKC complex antibodies and no association to pyridoxal-phosphate serum levels was found.Key words: nodding syndrome, epilepsy, anti-neuronal antibodies, pyridoxal-phosphat
Determinants of E-Learning Implementation Success In The Iraqi MoHE
The aim of this paper is to investigate the determinants of implementation success of the E-Learning in the Iraqi Ministry of Higher Education (IMoHE) and put a work plan to make the E-Learning widely implemented in the IMoHE. The Technology-Organization- Environment (TOE) framework and the E-Learning literature were used to analyze the factors which may influence this implementation and adoption. A questionnaire which consists of twenty nine questions divided into three parts: Technological factors (Information Systems (IS) infrastructure and IS expertise), Organizational factors (organizational compatibility and organizational benefits), and Environmental factors (competitive pressure and educational partner readiness) were written. The implementation success is characterized by two dimensions Internal Integration and External Diffusion. This questionnaire data gathered from 120 faculty members in the IMoHE were employed to test the relationships between the research models constructs using a structural equation modeling (SEM) approach. The results reveal that IS expertise, and Expected Benefits are key determinants of E-Learning implementation success in terms of Internal Integration and External Diffusion
Handreichung Anrechnung Teil 1. Ein theoretischer Ăśberblick
Diese Handreichung gibt in neun Kapiteln einen theoretischen Einblick in das Thema Anrechnung. Dabei werden u. a. Anrechnungsverfahren, zentrale Konzepte und Bezugsrahmen sowie die Qualitätssicherung in Anrechnungsprozessen in den Blick genommen. Die Handreichung wird ergänzt durch einen zweiten Teil, der Praxiserfahrungen mit Anrechnung einbezieht. Diese Publikation ist im Rahmen der wissenschaftlichen Begleitung des Bund-Länder-Wettbewerbs „Aufstieg durch Bildung: offene Hochschulen“ entstanden. (Hrgs.
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