8,024 research outputs found
Estimation of C II and C II* column densities along Galactic sight-lines
We present interstellar C II (1334.5323 \AA) and C II* (1335.7077 \AA) column
density measurements along 14 Galactic sight-lines. These sight-lines sample a
variety of Galactic disk environments and include paths that range nearly two
orders of magnitude in average hydrogen densities () along the lines of
sight. Five of the sight-lines show super-Solar gas phase abundances of carbon.
Our results show that the excess carbon along these sight-lines may result from
different mechanisms taking place in the regions associated with these stars.Comment: 9 pages, 3 figures; Accepted for publication in BAS
High Temperature Composite Analyzer (HITCAN) demonstration manual, version 1.0
This manual comprises a variety of demonstration cases for the HITCAN (HIgh Temperature Composite ANalyzer) code. HITCAN is a general purpose computer program for predicting nonlinear global structural and local stress-strain response of arbitrarily oriented, multilayered high temperature metal matrix composite structures. HITCAN is written in FORTRAN 77 computer language and has been configured and executed on the NASA Lewis Research Center CRAY XMP and YMP computers. Detailed description of all program variables and terms used in this manual may be found in the User's Manual. The demonstration includes various cases to illustrate the features and analysis capabilities of the HITCAN computer code. These cases include: (1) static analysis, (2) nonlinear quasi-static (incremental) analysis, (3) modal analysis, (4) buckling analysis, (5) fiber degradation effects, (6) fabrication-induced stresses for a variety of structures; namely, beam, plate, ring, shell, and built-up structures. A brief discussion of each demonstration case with the associated input data file is provided. Sample results taken from the actual computer output are also included
Current-Voltage Characteristics of Long-Channel Nanobundle Thin-Film Transistors: A Bottom-up Perspective
By generalizing the classical linear response theory of stick percolation to
nonlinear regime, we find that the drain current of a Nanobundle Thin Film
Transistor (NB-TFT) is described under a rather general set of conditions by a
universal scaling formula ID = A/LS g(LS/LC, rho_S * LS * LS) f(VG, VD), where
A is a technology-specific constant, g is function of geometrical factors like
stick length (LS), channel length (LC), and stick density (rho_S) and f is a
function of drain (VD) and gate (VG) biasing conditions. This scaling formula
implies that the measurement of full I-V characteristics of a single NB-TFT is
sufficient to predict the performance characteristics of any other transistor
with arbitrary geometrical parameters and biasing conditions
High temperature composite analyzer (HITCAN) user's manual, version 1.0
This manual describes 'how-to-use' the computer code, HITCAN (HIgh Temperature Composite ANalyzer). HITCAN is a general purpose computer program for predicting nonlinear global structural and local stress-strain response of arbitrarily oriented, multilayered high temperature metal matrix composite structures. This code combines composite mechanics and laminate theory with an internal data base for material properties of the constituents (matrix, fiber and interphase). The thermo-mechanical properties of the constituents are considered to be nonlinearly dependent on several parameters including temperature, stress and stress rate. The computation procedure for the analysis of the composite structures uses the finite element method. HITCAN is written in FORTRAN 77 computer language and at present has been configured and executed on the NASA Lewis Research Center CRAY XMP and YMP computers. This manual describes HlTCAN's capabilities and limitations followed by input/execution/output descriptions and example problems. The input is described in detail including (1) geometry modeling, (2) types of finite elements, (3) types of analysis, (4) material data, (5) types of loading, (6) boundary conditions, (7) output control, (8) program options, and (9) data bank
On supersymmetry breaking in string theory from gauge theory in a throat
We embed the supersymmetry breaking mechanism in N=1 SQCD of hep-th/0602239
in a smooth superstring theory using D-branes in the background R^4 \times
SL(2)_{k=1}/U(1) which smoothly captures the throat region of an intersecting
NS5-brane configuration. A controllable deformation of the supersymmetric
branes gives rise to the mass deformation of the magnetic SQCD theory on the
branes. The consequent instability on the open string worldsheet can be
followed onto a stable non-supersymmetric configuration of D-branes which
realize the metastable vacuum configuration in the field theory. The new brane
configuration is shown to backreact onto the background such as to produce
different boundary conditions for the string fields in the radial direction
compared to the supersymmetric configuration. In the string theory, this is
interpreted to mean that the supersymmetry breaking is explicit rather than
spontaneous.Comment: 29 pages, harvmac, 8 figures; v2 typos corrected, reference adde
Planetary Nebulae with Ultra-Violet Imaging Telescope (UVIT): Far Ultra-violet halo around the Bow Tie nebula (NGC 40)
Context. NGC 40 is a planetary nebula with diffuse X-ray emission, suggesting
an interaction of the high speed wind from WC8 central star (CS) with the
nebula. It shows strong Civ 1550 {\AA} emission that cannot be explained by
thermal processes alone. We present here the first map of this nebula in C IV
emission, using broad band filters on the UVIT.
Aims. To map the hot C IV emitting gas and its correspondence with soft X-ray
(0.3-8 keV) emitting regions, in order to study the shock interaction with the
nebula and the ISM. This also illustrates the potential of UVIT for nebular
studies.
Methods. Morphological study of images of the nebula obtained at an angular
resolution of about 1.3" in four UVIT filter bands that include C IV 1550 {\AA}
and C II] 2326 {\AA} lines and UV continuum. Comparisons with X-ray, optical,
and IR images from literature.
Results. The C II] 2326 {\AA} images show the core of the nebula with two
lobes on either side of CS similar to [N II]. The C IV emission in the core
shows similar morphology and extant as that of diffuse X-ray emission
concentrated in nebular condensations. A surprising UVIT discovery is the
presence of a large faint FUV halo in FUV Filter with {\lambda}eff of 1608
{\AA}. The UV halo is not present in any other UV filter. FUV halo is most
likely due to UV fluorescence emission from the Lyman bands of H2 molecules.
Unlike the optical and IR halo, FUV halo trails predominantly towards
south-east side of the nebular core, opposite to the CS's proper motion
direction.
Conclusions. Morphological similarity of C IV 1550 {\AA} and X-ray emission
in the core suggests that it results mostly from interaction of strong CS wind
with the nebula. The FUV halo in NGC 40 highlights the existence of H2
molecules extensively in the regions even beyond the optical and IR halos.Comment: 4 pages, 5 figures, accepted for publication as a letter in Astronomy
& Astrophysic
Three dimensional flow field inside compressor rotor, including blade boundary layers
The flow in a turbomachinery blade passage has a predominant flow direction. The viscous diffusion in the streamwise direction is usually small and the elliptic influence is transmitted upstream through the pressure field. Starting with a guessed pressure field, it is possible to converge on the full elliptic solution by iterating between a parabolic solution and an iteration of the pressure field. The main steps of the calculation are given. The blade boundary layers which are three dimensional with laminar, transitional, turbulent, and separation zones are investigated. The kinetic energy is analyzed, and the dissipation equation is presented. Measurements were made of the three dimensional flow inside an axial flow compressor passage
Finite Temperature Magnetism in Fractional Quantum Hall Systems: Composite Fermion Hartree-Fock and Beyond
Using the Hamiltonian formulation of Composite Fermions developed recently,
the temperature dependence of the spin polarization is computed for the
translationally invariant fractional quantum Hall states at and
in two steps. In the first step, the effect of particle-hole
excitations on the spin polarization is computed in a Composite Fermion
Hartree-Fock approximation. The computed magnetization for lies above
the experimental results for intermediate temperatures indicating the
importance of long wavelength spin fluctuations which are not correctly treated
in Hartree-Fock. In the second step, spin fluctuations beyond Hartree-Fock are
included for by mapping the problem on to the coarse-grained
continuum quantum ferromagnet. The parameters of the effective continuum
quantum ferromagnet description are extracted from the preceding Hartree-Fock
analysis. After the inclusion of spin fluctuations in a large-N approach, the
results for the finite-temperature spin polarization are in quite good
agreement with the experiments.Comment: 10 pages, 8 eps figures. Two references adde
Aerothermal modeling program, phase 2
The main objectives of the Aerothermal Modeling Program, Phase 2 are: to develop an improved numerical scheme for incorporation in a 3-D combustor flow model; to conduct a benchmark quality experiment to study the interaction of a primary jet with a confined swirling crossflow and to assess current and advanced turbulence and scalar transport models; and to conduct experimental evaluation of the air swirler interaction with fuel injectors, assessments of current two-phase models, and verification the improved spray evaporation/dispersion models
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