4,053 research outputs found
IAC user manual
The User Manual for the Integrated Analysis Capability (IAC) Level 1 system is presented. The IAC system currently supports the thermal, structures, controls and system dynamics technologies, and its development is influenced by the requirements for design/analysis of large space systems. The system has many features which make it applicable to general problems in engineering, and to management of data and software. Information includes basic IAC operation, executive commands, modules, solution paths, data organization and storage, IAC utilities, and module implementation
Disentanglement and decoherence in two-spin and three-spin systems under dephasing
We compare disentanglement and decoherence rates within two-spin and
three-spin entangled systems subjected to all possible combinations of local
and collective pure dephasing noise combinations. In all cases, the bipartite
entanglement decay rate is found to be greater than or equal to the
dephasing-decoherence rates and often significantly greater. This sharpens
previous results for two-spin systems [T. Yu and J. H. Eberly Phys. Rev. B 68,
165322 (2003)] and extends them to the three-spin context.Comment: 17 page
Developmental design, fabrication, and test of acoustic suppressors for fans of high bypass turbofan engines
An analysis procedure was developed for design of acoustically treated nacelles for high bypass turbofan engines. The plan was applied to the conceptual design of a nacelle for the quiet engine typical of a 707/DC-8 airplane installation. The resultant design was modified to a test nacelle design for the NASA Lewis quiet fan. The acoustic design goal was a 10 db reduction in effective perceived fan noise levels during takoff and approach. Detailed nacelle designs were subsequently developed for both the quiet engine and the quiet fan. The acoustic design goal for each nacelle was 15 db reductions in perceived fan noise levels from the inlet and fan duct. Acoustically treated nacelles were fabricated for the quiet engine and quiet fan for testing. Performance of selected inlet and fan duct lining configurations was experimentally evaluated in a flow duct. Results of the tests show that the linings perform as designed
Interaction between Mn Ions and Free Carriers in Quantum Wells with Asymmetrical Semimagnetic Barriers
Investigations of photoluminescence (PL) in the magnetic field of quantum
structures based on the ZnSe quantum well with asymmetrical ZnBeMnSe and ZnBeSe
barriers reveal that the introduction of Be into semimagnetic ZnMnSe causes a
decrease of the exchange integrals for conductive and valence bands as well as
the forming of a complex based on Mn, degeneration of an energy level of which
with the energy levels of the V band of ZnBeMnSe or ZnSe results in spin-flip
electron transitions.Comment: Accepted to Europhys. Let
Oscillatory Energy Exchange Between Waves Coupled by a Dynamic Artificial Crystal
We describe a general mechanism of controllable energy exchange between waves
propagating in a dynamic artificial crystal. We show that if a spatial
periodicity is temporarily imposed on the transmission properties of a
wave-carrying medium whilst a wave is inside, this wave is coupled to a
secondary counter-propagating wave and energy oscillates between the two. The
oscillation frequency is determined by the width of the spectral band gap
created by the periodicity and the frequency difference between the coupled
waves. The effect is demonstrated with spin waves in a dynamic magnonic
crystal.Comment: 5 pages, 4 figure
Fourier, Gauss, Fraunhofer, Porod and the Shape from Moments Problem
We show how the Fourier transform of a shape in any number of dimensions can
be simplified using Gauss's law and evaluated explicitly for polygons in two
dimensions, polyhedra three dimensions, etc. We also show how this combination
of Fourier and Gauss can be related to numerous classical problems in physics
and mathematics. Examples include Fraunhofer diffraction patterns, Porods law,
Hopfs Umlaufsatz, the isoperimetric inequality and Didos problem. We also use
this approach to provide an alternative derivation of Davis's extension of the
Motzkin-Schoenberg formula to polygons in the complex plane.Comment: 21 pages, no figure
The Compact Structure of Radio-Loud Broad Absorption Line Quasars
We present the results of EVN+MERLIN VLBI polarization observations of 8
Broad Absorption Line (BAL) quasars at 1.6 GHz, including 4 LoBALs and 4 HiBALs
with either steep or flat spectra on VLA scales. Only one steep-spectrum
source, J1122+3124, shows two-sided structure on the scale of 2 kpc. The other
four steep-spectrum sources and three flat-spectrum sources display either an
unresolved image or a core-jet structure on scales of less than three hundred
parsecs. In all cases the marginally resolved core is the dominant radio
component. Linear polarization in the cores has been detected in the range of a
few to 10 percent. Polarization, together with high brightness temperatures
(from 2*10^9-5*10^10 K), suggest a synchrotron origin for the radio emission.
There is no apparent difference in the radio orphologies or polarization
between low-ionization and high-ionization BAL QSOs nor between flat- and
steep-spectrum sources. We discuss the orientation of BAL QSOs with both flat
and steep spectra, and consider a possible evolutionary scenario for BAL QSOs.
In this scenario, BAL QSOs are probably the young population of radio sources,
which are Compact Steep Spectrum or GHz peaked radio source analog at the low
end of radio power.Comment: 16 pages, 3 figures, 4 tables; accepted for publication in MNRA
Discovery of a Classic FR-II Broad Absorption Line Quasar from the FIRST Survey
We have discovered a remarkable quasar, FIRST J101614.3+520916, whose optical
spectrum shows unambiguous broad absorption features while its double-lobed
radio morphology and luminosity clearly indicate a classic Fanaroff-Riley Type
II radio source. Its radio luminosity places it at the extreme of the recently
established class of radio-loud broad absorption line quasars (Becker et al.
1997, 2000; Brotherton et al. 1998). Because of its hybrid nature, we speculate
that FIRST J101614.3+520916 is a typical FR-II quasar which has been
rejuvenated as a broad absorption line (BAL) quasar with a Compact Steep
Spectrum core. The direction of the jet axis of FIRST J101614.3+520916 can be
estimated from its radio structure and optical brightness, indicating that we
are viewing the system at a viewing angle of > 40 degrees. The position angles
of the radio jet and optical polarization are not well-aligned, differing by 20
to 30 degrees. When combined with the evidence presented by Becker et al.
(2000) for a sample of 29 BAL quasars showing that at least some BAL quasars
are viewed along the jet axis, the implication is that no preferred viewing
orientation is necessary to observe BAL systems in a quasar's spectrum. This,
and the probable young nature of compact steep spectrum sources, leads
naturally to the alternate hypothesis that BALs are an early stage in the lives
of quasars.Comment: 14 pages, 6 postscript figures; accepted for publication in the
Astrophysical Journa
The Intrinsic Absorber in QSO 2359-1241: Keck and HST Observations
We present detailed analyses of the absorption spectrum seen in QSO 2359-1241
(NVSS J235953-124148). Keck HIRES data reveal absorption from twenty
transitions arising from: He I, Mg I, Mg II, Ca II, and Fe II. HST data show
broad absorption lines (BALs) from Al III 1857, C IV 1549, Si IV 1397, and N V
1240. Absorption from excited Fe II states constrains the temperature of the
absorber to 2000K < T < 10,000K and puts a lower limit of 10^5 cm^{-3} on the
electron number density. Saturation diagnostics show that the real column
densities of He I and Fe II can be determined, allowing to derive meaningful
constraints on the ionization equilibrium and abundances in the flow. The
ionization parameter is constrained by the iron, helium and magnesium data to
-3.0 < log(U) < -2.5 and the observed column densities can be reproduced
without assuming departure from solar abundances. From comparison of the He I
and Fe II absorption features we infer that the outflow seen in QSO 2359-1241
is not shielded by a hydrogen ionization front and therefore that the existence
of low-ionization species in the outflow (e.g., Mg II, Al III, Fe II) does not
necessitate the existence of such a front. We find that the velocity width of
the absorption systematically increases as a function of ionization and to a
lesser extent with abundance. Complementary analyses of the radio and
polarization properties of the object are discussed in a companion paper
(Brotherton et al. 2000).Comment: 30 pages, 9 figures, in press with the Ap
- …