355 research outputs found
Space Station and Space Cabin Testing
For Earth Orbiting Space Stations neither expandable, extensible, nor converted propellant tanks appear as suitable for manned operations as a specially designed cabin regardless of the mission to be performed. While an interesting possibility, use of converted propellant tanks offer little advantage when viewed in the light of the overall space station system problem.
During the past two years studies have been conducted in some depth of the cabins associated with space station systems suitable for launch by Titan III C, Saturn IB, and Saturn 5 boosters. These studies have considered various crew complements, supporting ferries f and the effects of rotation for the generation of artificial G .
Considering the requirements for integrating power supplies, thermal control* life support, attitude control, orbit propulsion, specific mission equipment, rendezvous, docking, communications, navigation, and crew creature comforts, the development of an efficient usable cabin becomes a task of significant proportions. Applying the constraints of removable and storable equipment to the fixed sizes and shapes of booster tankage makes the problem more difficult, the results less than optimum, and the increased cost substantial
Reversible skew laurent polynomial rings and deformations of poisson automorphisms
A skew Laurent polynomial ring S = R[x(+/- 1); alpha] is reversible if it has a reversing automorphism, that is, an automorphism theta of period 2 that transposes x and x(-1) and restricts to an automorphism gamma of R with gamma = gamma(-1). We study invariants for reversing automorphisms and apply our methods to determine the rings of invariants of reversing automorphisms of the two most familiar examples of simple skew Laurent polynomial rings, namely a localization of the enveloping algebra of the two-dimensional non-abelian solvable Lie algebra and the coordinate ring of the quantum torus, both of which are deformations of Poisson algebras over the base field F. Their reversing automorphisms are deformations of Poisson automorphisms of those Poisson algebras. In each case, the ring of invariants of the Poisson automorphism is the coordinate ring B of a surface in F-3 and the ring of invariants S-theta of the reversing automorphism is a deformation of B and is a factor of a deformation of F[x(1), x(2), x(3)] for a Poisson bracket determined by the appropriate surface
Irreducible actions and compressible modules
Any finite set of linear operators on an algebra yields an operator
algebra and a module structure on A, whose endomorphism ring is isomorphic
to a subring of certain invariant elements of . We show that if is
a critically compressible left -module, then the dimension of its
self-injective hull over the ring of fractions of is bounded by the
uniform dimension of and the number of linear operators generating .
This extends a known result on irreducible Hopf actions and applies in
particular to weak Hopf action. Furthermore we prove necessary and sufficient
conditions for an algebra A to be critically compressible in the case of group
actions, group gradings and Lie actions
Nilpotent maximal subgroups of GLn(D)
AbstractIn [S. Akbari, J. Algebra 217 (1999) 422–433] it has been conjectured that if D is a noncommutative division ring, then D∗ contains no nilpotent maximal subgroup. In connection with this conjecture we show that if GLn(D) contains a nilpotent maximal subgroup, say M, then M is abelian, provided D is infinite. This extends one of the main results appeared in [S. Akbari, J. Algebra 259 (2003) 201–225, Theorem 4]
Duplex Ultrasound Graft Limb Velocity Asymmetry Predicts Endoleak After Endovascular Aneurysm Repair
Lie bialgebras of generalized Witt type
In a paper by Michaelis a class of infinite-dimensional Lie bialgebras
containing the Virasoro algebra was presented. This type of Lie bialgebras was
classified by Ng and Taft. In this paper, all Lie bialgebra structures on the
Lie algebras of generalized Witt type are classified. It is proved that, for
any Lie algebra of generalized Witt type, all Lie bialgebras on are
coboundary triangular Lie bialgebras. As a by-product, it is also proved that
the first cohomology group is trivial.Comment: 14 page
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Meeting on flows of granular materials in complex geometries
The International Energy Agency Fossil Fuel Multiphase Flow Sciences Agreement has been in effect since 1986. The traditional mechanism for the effort has been information exchange, effected by the inclusion of scientists in annual Executive committee meetings, by exchange of reports and papers, and by visits of scientists to one another`s institutions. In a sequence of informal meetings and at the 1993 Executive committee meeting, held in Pittsburgh, US in March 1994, it was decided that more intensive interactions could be productive. A candidate for such interactions would be specific projects. Each of these would be initiated through a meeting of scientists in which feasibility of the particular project was decided, followed by relatively intense international co-operation in which the work would be done. This is a report of the first of these meetings. Official or unofficial representatives from Canada, italy, japan, mexico, the United Kingdom, and the US met in Albuquerque, New Mexico, US, to consider the subject Flows of Granular Materials in Complex Geometries. Representatives of several other countries expressed interest but were unable to attend this meeting. Sixteen lectures were given on aspects of this topic. It was decided that a co-operative effort was desirable and possible. The most likely candidate for the area of study would be flows in bins and hoppers. Each of the countries wishing to co-operate will pursue funding for its effort. This report contains extended abstracts of the sixteen presentations and a transcription of the final discussion
Branch Rings, Thinned Rings, Tree Enveloping Rings
We develop the theory of ``branch algebras'', which are infinite-dimensional
associative algebras that are isomorphic, up to taking subrings of finite
codimension, to a matrix ring over themselves. The main examples come from
groups acting on trees.
In particular, for every field k we construct a k-algebra K which (1) is
finitely generated and infinite-dimensional, but has only finite-dimensional
quotients;
(2) has a subalgebra of finite codimension, isomorphic to ;
(3) is prime;
(4) has quadratic growth, and therefore Gelfand-Kirillov dimension 2;
(5) is recursively presented;
(6) satisfies no identity;
(7) contains a transcendental, invertible element;
(8) is semiprimitive if k has characteristic ;
(9) is graded if k has characteristic 2;
(10) is primitive if k is a non-algebraic extension of GF(2);
(11) is graded nil and Jacobson radical if k is an algebraic extension of
GF(2).Comment: 35 pages; small changes wrt previous versio
Del Pezzo surfaces of degree 1 and jacobians
We construct absolutely simple jacobians of non-hyperelliptic genus 4 curves,
using Del Pezzo surfaces of degree 1. This paper is a natural continuation of
author's paper math.AG/0405156.Comment: 24 page
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