40,633 research outputs found
Surface interactions and high-voltage current collection
Spacecraft of the future will be larger and have higher power requirements than any flown to date. For several reasons, it is desirable to operate a high power system at high voltage. While the optimal voltages for many future missions are in the range 500 to 5000 volts, the highest voltage yet flown is approximately 100 volts. The NASCAP/LEO code is being developed to embody the phenomenology needed to model the environmental interactions of high voltage spacecraft. Some plasma environment are discussed. The treatment of the surface conductivity associated with emitted electrons and some simulations by NASCAP/LEO of ground based high voltage interaction experiments are described
Method for the preparation of thin-skinned asymmetric reverse osmosis membranes and products thereof
A method for preparing water insoluble asymmetric membranes from water soluble polymers is discussed. The process involves casting a film of the polymer, partially drying it, and then contacting it with a concentrated solution of a transition metal salt. The transition metal ions render the polymer insoluable and are believed to form a complex with it. Optionally, the polymer is crosslinked with heat or radiation. The most preferred polymer is poly(vinyl alcohol). The most preferred complexing salt is copper sulfate. The process and the metal ion linked membranes are discussed. The membranes are reverse osmosis membranes
Long and Short GRB
We report evidence from the 3B Catalogue that short (T_90 < 10 s) and long
(T_90 > 10 s) GRB represent different populations and processes: Their spectral
behavior is qualitatively different, with short bursts harder in the BATSE
range, but chiefly long bursts detected at higher photon energies; \langle
V/V_max \rangle = 0.385 \pm 0.019 for short GRB but \langle V/V_max \rangle =
0.282 \pm 0.014 for long GRB, differing by 0.103 \pm 0.024. Long GRB may be the
consequence of accretion-induced collapse, but this mechanism fails for short
GRB, for which we suggest colliding neutron stars.Comment: 5 pp., latex, no figures, revised to work around bug in latex
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A unified approach to computer analysis and modeling of spacecraft environmental interactions
A new, coordinated, unified approach to the development of spacecraft plasma interaction models is proposed. The objective is to eliminate the unnecessary duplicative work in order to allow researchers to concentrate on the scientific aspects. By streamlining the developmental process, the interchange between theories and experimentalists is enhanced, and the transfer of technology to the spacecraft engineering community is faster. This approach is called the UNIfied Spacecraft Interaction Model (UNISIM). UNISIM is a coordinated system of software, hardware, and specifications. It is a tool for modeling and analyzing spacecraft interactions. It will be used to design experiments, to interpret results of experiments, and to aid in future spacecraft design. It breaks a Spacecraft Ineraction analysis into several modules. Each module will perform an analysis for some physical process, using phenomenology and algorithms which are well documented and have been subject to review. This system and its characteristics are discussed
Implications of the Visible and X-Ray Counterparts to GRB970228
The gamma-ray burst source GRB970228 has been observed after a delay of 8--12
hours in X-rays and after one day in visible and near infrared light. This
marks the first detection of emission at lower frequencies following the
gamma-ray observation of a GRB and the first detection of any visible
counterpart to a GRB. We consider possible delayed visible and X-ray emission
mechanisms, and conclude that the intrinsic gamma-ray activity continued at a
much reduced intensity for at least a day. There are hints of such continued
activity in other GRB, and future observations can decide if this is true of
GRB in general. The observed multi-band spectrum of GRB970228 agrees with the
predictions of relativistic shock theory when the flux is integrated over a
time longer than that required for a radiating electron to lose its energy.Comment: 5 pp., tex, 1 figur
Gravitational energy
Observers at rest in a stationary spacetime flat at infinity can measure
small amounts of rest-mass+internal energies+kinetic energies+pressure energy
in a small volume of fluid attached to a local inertial frame. The sum of these
small amounts is the total "matter energy" for those observers. The total
mass-energy minus the matter energy is the binding gravitational energy.
Misner, Thorne and Wheeler evaluated the gravitational energy of a
spherically symmetric static spacetime. Here we show how to calculate
gravitational energy in any static and stationary spacetime for isolated
sources with a set of observers at rest.
The result of MTW is recovered and we find that electromagnetic and
gravitational 3-covariant energy densities in conformastatic spacetimes are of
opposite signs. Various examples suggest that gravitational energy is negative
in spacetimes with special symmetries or when the energy-momentum tensor
satisfies usual energy conditions.Comment: 12 pages. Accepted for publication in Class. Quantum Gra
Boydbolt, a positive-latch, simple-release fastener
Fastener /Boydbolt/ has recently been designed to furnish positive lock and release characteristics that positively prevent accidental adverse functions of lock or release
A New Generating Function for Calculating the Igusa Local Zeta Function
A new method is devised for calculating the Igusa local zeta function
of a polynomial over a -adic field. This involves a new
kind of generating function that is the projective limit of a family of
generating functions, and contains more data than . This resides in
an algebra whose structure is naturally compatible with operations on the
underlying polynomials, facilitating calculation of local zeta functions. This
new technique is used to expand significantly the set of quadratic polynomials
whose local zeta functions have been calculated explicitly. Local zeta
functions for arbitrary quadratic polynomials over -adic fields with odd
are presented, as well as for polynomials over unramified -adic fields of
the form where is a quadratic form and is a linear form where
and have disjoint variables. For a quadratic form over an arbitrary
-adic field with odd , this new technique makes clear precisely which of
the three candidate poles are actual poles.Comment: 54 page
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