62,321 research outputs found
The Segal--Bargmann transform for odd-dimensional hyperbolic spaces
We develop isometry and inversion formulas for the Segal--Bargmann transform
on odd-dimensional hyperbolic spaces that are as parallel as possible to the
dual case of odd-dimensional spheres.Comment: To appear in Mathematic
Coherent states for a 2-sphere with a magnetic field
We consider a particle moving on a 2-sphere in the presence of a constant
magnetic field. Building on earlier work in the nonmagnetic case, we construct
coherent states for this system. The coherent states are labeled by points in
the associated phase space, the (co)tangent bundle of S^2. They are constructed
as eigenvectors for certain annihilation operators and expressed in terms of a
certain heat kernel. These coherent states are not of Perelomov type, but
rather are constructed according to the "complexifier" approach of T. Thiemann.
We describe the Segal--Bargmann representation associated to the coherent
states, which is equivalent to a resolution of the identity.Comment: 23 pages. To appear in Journal of Physics A, Special Issue on
Coherent State
Influence of structure and material research on advanced launch systems' weight, performance, and cost Summary report, May 25, 1965 - Jun. 30, 1967
Influence of structure and materials research on weight, performance, and cost of advanced launch vehicle system
The Segal-Bargmann transform for noncompact symmetric spaces of the complex type
We consider the generalized Segal-Bargmann transform, defined in terms of the
heat operator, for a noncompact symmetric space of the complex type. For radial
functions, we show that the Segal-Bargmann transform is a unitary map onto a
certain L^2 space of meromorphic functions. For general functions, we give an
inversion formula for the Segal-Bargmann transform, involving integration
against an "unwrapped" version of the heat kernel for the dual compact
symmetric space. Both results involve delicate cancellations of singularities.Comment: 28 pages. Minor corrections made. To appear in J. Functional Analysi
One Controller at a Time (1-CAT): A mimo design methodology
The One Controller at a Time (1-CAT) methodology for designing digital controllers for Large Space Structures (LSS's) is introduced and illustrated. The flexible mode problem is first discussed. Next, desirable features of a LSS control system design methodology are delineated. The 1-CAT approach is presented, along with an analytical technique for carrying out the 1-CAT process. Next, 1-CAT is used to design digital controllers for the proposed Space Based Laser (SBL). Finally, the SBL design is evaluated for dynamical performance, noise rejection, and robustness
Formation of Supermassive Black Holes by Direct Collapse in Pregalactic Halos
We describe a mechanism by which supermassive black holes can form directly
in the nuclei of protogalaxies, without the need for seed black holes left over
from early star formation. Self-gravitating gas in dark matter halos can lose
angular momentum rapidly via runaway, global dynamical instabilities, the
so-called "bars within bars" mechanism. This leads to the rapid buildup of a
dense, self-gravitating core supported by gas pressure - surrounded by a
radiation pressure-dominated envelope - which gradually contracts and is
compressed further by subsequent infall. These conditions lead to such high
temperatures in the central region that the gas cools catastrophically by
thermal neutrino emission, leading to the formation and rapid growth of a
central black hole.
We estimate the initial mass and growth rate of the black hole for typical
conditions in metal-free halos with T_vir ~ 10^4 K, which are the most likely
to be susceptible to runaway infall. The initial black hole should have a mass
of <~20 solar masses, but in principle could grow at a super-Eddington rate
until it reaches ~ 10^4-10^6 solar masses. Rapid growth may be limited by
feedback from the accretion process and/or disruption of the mass supply by
star formation or halo mergers. Even if super-Eddington growth stops at
\~10^3-10^4 solar masses, this process would give black holes ample time to
attain quasar-size masses by a redshift of 6, and could also provide the seeds
for all supermassive black holes seen in the present universe.Comment: 11 pages, 2 figures, Monthly Notices of the Royal Astronomical
Society, in press. Minor revision
LOGSIM programmer's manual
A programmer's manual is reported for a Logic Simulator (LOGSIM) computer program that is a large capacity event simulator with the capability to accurately simulate the effects of certain unknown states, rise and fall times, and floating nodes in large scale metal oxide semiconductor logic circuits. A detailed description of the software with flow charts is included within the report
Advanced expander test bed program
The Advanced Expander Test Bed (AETB) is a key element in NASA's Space Chemical Engine Technology Program for development and demonstration of expander cycle oxygen/hydrogen engine and advanced component technologies applicable to space engines as well as launch vehicle upper stage engines. The AETB will be used to validate the high-pressure expander cycle concept, investigate system interactions, and conduct investigations of advanced mission focused components and new health monitoring techniques in an engine system environment. The split expander cycle AETB will operate at combustion chamber pressures up to 1200 psia with propellant flow rates equivalent to 20,000 lbf vacuum thrust. Contract work began 27 Apr. 1990. During 1992, a major milestone was achieved with the review of the final design of the oxidizer turbopump in Sep. 1992
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