34,954 research outputs found
Three-dimensional, transonic rotor flow field reconstructed from holographic interferogram data
Holographic interferometry and computer-assisted tomography (CAT) are used to determine the transonic flow field of a model rotor blade in hover. A pulsed ruby laser records 40 interferograms with a 61 cm-diam view field near the model rotor-blade tip operating at a tip Mach number of 0.90. After digitizing the interferograms and extracting fringe-order functions, the data are transferred to a CAT code. The CAT code then calculates pressure coefficients in several planes above the blade surface. The values from the holography-CAT method compare favorably with previously obtained numerical computations and laser velocimeter measurements at most locations near the blade tip. The results demonstrate the technique's potential for three-dimensional transonic rotor flow studies
Reconstruction of a 3-dimensional transonic rotor flow field from holographic interferogram data
Holographic interferometry and computer-assisted tomography (CAT) are used to determine the transonic velocity field of a model rotor blade in hover. A pulsed ruby laser recorded 40 interferograms with a 2-ft-diam view field near the model rotor-blade tip operating at a tip Mach number of 0.90. After digitizing the interferograms and extracting fringe-order functions, the data are transferred to a CAT code. The CAT code then calculates the perturbation velocity in seeral planes above the blade surface. The values from the holography-CAT method compare favorably with previously obtained numerical computations in most locations near the blade tip. The results demonstrate the technique's potential for three-dimensional transonic rotor flow studies
Exact Solution of Strongly Interacting Quasi-One-Dimensional Spinor Bose Gases
We present an exact analytical solution of the fundamental system of
quasi-one-dimensional spin-1 bosons with infinite delta-repulsion. The
eigenfunctions are constructed from the wave functions of non-interacting
spinless fermions, based on Girardeau's Fermi-Bose mapping, and from the wave
functions of distinguishable spins. We show that the spinor bosons behave like
a compound of non-interacting spinless fermions and non-interacting
distinguishable spins. This duality is especially reflected in the spin
densities and the energy spectrum. We find that the momentum distribution of
the eigenstates depends on the symmetry of the spin function. Furthermore, we
discuss the splitting of the ground state multiplet in the regime of large but
finite repulsion.Comment: Revised to discuss large but finite interaction
Status of neutrino astronomy
Astrophysical neutrinos can be produced in proton interactions of charged
cosmic rays with ambient photon or baryonic fields. Cosmic rays are observed in
balloon, satellite and air shower experiments every day, from below 1e9 eV up
to macroscopic energies of 1e21 eV. The observation of different photon fields
has been done ever since, today with detections ranging from radio wavelengths
up to very high-energy photons in the TeV range. The leading question for
neutrino astronomers is now which sources provide a combination of efficient
proton acceleration with sufficiently high photon fields or baryonic targets at
the same time in order to produce a neutrino flux that is high enough to exceed
the background of atmospheric neutrinos. There are only two confirmed
astrophysical neutrino sources up to today: the sun and SuperNova 1987A emit
and emitted neutrinos at MeV energies. The aim of large underground Cherenkov
telescopes like IceCube and KM3NeT is the detection of neutrinos at energies
above 100 GeV. In this paper, recent developments of neutrino flux modeling for
the most promising extragalactic sources, gamma ray bursts and active galactic
nuclei, are presented.Comment: Talk given at Neutrino 2008, Christchurch (New Zealand) 6 pages, 4
figures, 1 tabl
Status of neutrino astronomy
Astrophysical neutrinos can be produced in proton interactions of charged
cosmic rays with ambient photon or baryonic fields. Cosmic rays are observed in
balloon, satellite and air shower experiments every day, from below 1e9 eV up
to macroscopic energies of 1e21 eV. The observation of different photon fields
has been done ever since, today with detections ranging from radio wavelengths
up to very high-energy photons in the TeV range. The leading question for
neutrino astronomers is now which sources provide a combination of efficient
proton acceleration with sufficiently high photon fields or baryonic targets at
the same time in order to produce a neutrino flux that is high enough to exceed
the background of atmospheric neutrinos. There are only two confirmed
astrophysical neutrino sources up to today: the sun and SuperNova 1987A emit
and emitted neutrinos at MeV energies. The aim of large underground Cherenkov
telescopes like IceCube and KM3NeT is the detection of neutrinos at energies
above 100 GeV. In this paper, recent developments of neutrino flux modeling for
the most promising extragalactic sources, gamma ray bursts and active galactic
nuclei, are presented.Comment: Talk given at Neutrino 2008, Christchurch (New Zealand) 6 pages, 4
figures, 1 tabl
Status of neutrino astronomy
Astrophysical neutrinos can be produced in proton interactions of charged
cosmic rays with ambient photon or baryonic fields. Cosmic rays are observed in
balloon, satellite and air shower experiments every day, from below 1e9 eV up
to macroscopic energies of 1e21 eV. The observation of different photon fields
has been done ever since, today with detections ranging from radio wavelengths
up to very high-energy photons in the TeV range. The leading question for
neutrino astronomers is now which sources provide a combination of efficient
proton acceleration with sufficiently high photon fields or baryonic targets at
the same time in order to produce a neutrino flux that is high enough to exceed
the background of atmospheric neutrinos. There are only two confirmed
astrophysical neutrino sources up to today: the sun and SuperNova 1987A emit
and emitted neutrinos at MeV energies. The aim of large underground Cherenkov
telescopes like IceCube and KM3NeT is the detection of neutrinos at energies
above 100 GeV. In this paper, recent developments of neutrino flux modeling for
the most promising extragalactic sources, gamma ray bursts and active galactic
nuclei, are presented.Comment: Talk given at Neutrino 2008, Christchurch (New Zealand) 6 pages, 4
figures, 1 tabl
String vacua with flux from freely-acting obifolds
A precise correspondence between freely-acting orbifolds (Scherk-Schwarz
compactifications) and string vacua with NSNS flux turned on is established
using T-duality.
We focus our attention to a certain non-compact Z_2 heterotic freely-acting
orbifold with N=2 supersymmetry (SUSY). The geometric properties of the T-dual
background are studied. As expected, the space is non-Kahler with the most
generic torsion compatible with SUSY. All equations of motion are satisfied,
except the Bianchi identity for the NSNS field, that is satisfied only at
leading order in derivatives, i.e. without the curvature term. We point out
that this is due to unknown corrections to the standard heterotic T-duality
rules.Comment: 13 pages, no figures; v2: references added and rearranged, version to
appear in JHE
-Particle Spectrum in the Reaction p+B
Using a simple phenomenological parametrization of the reaction amplitude we
calculated -particle spectrum in the reaction p+B at the resonance proton energy 675 KeV. The parametrization
includes Breit-Wigner factor with an energy dependent width for intermediate
state and the Coulomb and the centrifugal factors in -particle
emission vertexes. The shape of the spectrum consists of a well defined peak
corresponding to emission of the primary and a flat shoulder going
down to very low energy. We found that below 1.5 MeV there are 17.5% of
's and below 1 MeV there are 11% of them.Comment: 6 pages, 3 figure
Linear Sigma Models with Torsion
Gauged linear sigma models with (0,2) supersymmetry allow a larger choice of
couplings than models with (2,2) supersymmetry. We use this freedom to find a
fully linear construction of torsional heterotic compactifications, including
models with branes. As a non-compact example, we describe a family of metrics
which correspond to deformations of the heterotic conifold by turning on
H-flux. We then describe compact models which are gauge-invariant only at the
quantum level. Our construction gives a generalization of symplectic reduction.
The resulting spaces are non-Kahler analogues of familiar toric spaces like
complex projective space. Perturbatively conformal models can be constructed by
considering intersections.Comment: 40 pages, LaTeX, 1 figure; references added; a new section on
supersymmetry added; quantization condition revisite
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