18,904 research outputs found
Automated nose fairing design - Honeycomb sandwich construction
Computer program for near optimum structural designs of ring stiffened honeycomb sandwich nose fairing
Latent Acute Peritonitis of Idiopathic Origin; Large Amount of Pus in the Abdominal Cavity; Evacuation; Recovery
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Simulations of Fast X-Ray Detectors Based on Multichannel Plates
High-performance detectors with high spatial and time resolutions are required in applications such as imaging of fast processes, time-resolved coherent scattering, and time-resolved X-ray spectroscopy. Recently a new type of X-ray detector was proposed, based on microchannel plates (MCP) coated with resistive and emissive layers inside the pores by using atomic-layer deposition with better functional optimizations. Two microscopic Monte Carlo codes were used to calculate the characteristics of secondary electrons emitted from a photocathode irradiated by X-rays with energies of 1–15 keV and by electrons with energies in the interval of 0– -2 keV. WO3 was selected as the photocathode and the electron emissive material. The emissive characteristics obtained by the microscopic Monte Carlo codes were used as input data for a third, macroscopic MCP simulation Monte Carlo code, for calculating the gain and transit time spread of a MCP-based X-ray detector. Our simulation results showed that the X-ray detector should improve the spatial and time resolution and push the development of high-quantum-yield photocathodes based on MCPs
Experimental data on the single spin asymmetry and their interpretations by the chromo-magnetic string model
An attempt is made to interpret the various existing experimental data on the
single spin asymmetries in inclusive pion production by the polarized proton
and antiproton beams. As the basis of analysis the chromo-magnetic string model
is used. A whole measured kinematic region is covered. The successes and fails
of such approach are outlined. The possible improvements of model are
discussed.Comment: 17 pages, 3 figure
Transparent Nuclei and Deuteron-Gold Collisions at RHIC
The current normalization of the cross section of inclusive high-pT particle
production in deuteron-gold collisions measured RHIC relies on Glauber
calculations for the inelastic d-Au cross section. These calculations should be
corrected for diffraction. Moreover, they miss the Gribov's inelastic shadowing
which makes nuclei more transparent (color transparency). The magnitude of this
effect rises with energy and it may dramatically affect the normalization of
the RHIC data. We evaluate these corrections employing the light-cone dipole
formalism and found a rather modest corrections for the current normalization
of the d-Au data. The results of experiments insensitive to diffraction
(PHENIX, PHOBOS) should be renormalized by about 20% down, while those which
include diffraction (STAR), by only 10%. Such a correction completely
eliminates the Cronin enhancement in the PHENIX data for pions. The largest
theoretical uncertainty comes from the part of the inelastic shadowing which is
related to diffractive gluon radiation, or gluon shadowing. Our estimate is
adjusted to data for the triple-Pomeron coupling, however, other models do not
have such a restrictions and predict much stronger gluon shadowing. Therefore,
the current data for high-pT hadron production in d-Au collisions at RHIC
cannot exclude in a model independent way the possibility if initial state
suppression proposed by Kharzeev-Levin-McLerran. Probably the only way to
settle this uncertainty is a direct measurement of the inelastic d-Au cross
sections at RHIC. Also d-Au collisions with a tagged spectator nucleon may
serve as a sensitive probe for nuclear transparency and inelastic shadowing. We
found an illuminating quantum-mechanical effect: the nucleus acts like a lens
focusing spectators into a very narrow cone.Comment: Latex 50 pages. Based on lectures given by the author at Workshop on
High-pT Correlations at RHIC, Columbia University, May-June, 2003. The
version to appear in PR
Classicalization and Unitarity
We point out that the scenario for UV completion by "classicalization",
proposed recently is in fact Wilsonian in the classical Wilsonian sense. It
corresponds to the situation when a field theory has a nontrivial UV fixed
point governed by a higher dimensional operator. Provided the kinetic term is a
relevant operator around this point the theory will flow in the IR to the free
scalar theory. Physically, "classicalization", if it can be realized, would
correspond to a situation when the fluctuations of the field operator in the UV
are smaller than in the IR. As a result there exists a clear tension between
the "classicalization" scenario and constraints imposed by unitarity on a
quantum field theory, making the existence of classicalizing unitary theories
questionable.Comment: Some clarifications and refs added. Accepted as a JHEP publication;
12 page
Spin Waves in the Ferromagnetic Ground State of the Kagome Staircase System Co3V2O8
Inelastic neutron scattering measurements were performed on single crystal
Co3V2O8 wherein magnetic cobalt ions reside on distinct spine and cross-tie
sites within kagome staircase planes. This system displays a rich magnetic
phase diagram which culminates in a ferromagnetic ground state below Tc~6 K. We
have studied the low-lying magnetic excitations in this phase within the kagome
plane. Despite the complexity of the system at higher temperatures, linear
spin-wave theory describes most of the quantitative detail of the inelastic
neutron measurements. Our results show two spin-wave branches, the higher
energy of which displays finite spin-wave lifetimes well below Tc, and
negligible magnetic exchange coupling between Co moments on the spine sites.Comment: 4 pages and 4 figure
Magnetic, thermodynamic, and electrical transport properties of the noncentrosymmetric B20 germanides MnGe and CoGe
We present magnetization, specific heat, resistivity, and Hall effect
measurements on the cubic B20 phase of MnGe and CoGe and compare to
measurements of isostructural FeGe and electronic structure calculations. In
MnGe, we observe a transition to a magnetic state at K as identified
by a sharp peak in the ac magnetic susceptibility, as well as second phase
transition at lower temperature that becomes apparent only at finite magnetic
field. We discover two phase transitions in the specific heat at temperatures
much below the Curie temperature one of which we associate with changes to the
magnetic structure. A magnetic field reduces the temperature of this transition
which corresponds closely to the sharp peak observed in the ac susceptibility
at fields above 5 kOe. The second of these transitions is not affected by the
application of field and has no signature in the magnetic properties or our
crystal structure parameters. Transport measurements indicate that MnGe is
metal with a negative magnetoresistance similar to that seen in isostructural
FeGe and MnSi. Hall effect measurements reveal a carrier concentration of about
0.5 carriers per formula unit also similar to that found in FeGe and MnSi. CoGe
is shown to be a low carrier density metal with a very small, nearly
temperature independent diamagnetic susceptibility.Comment: 16 pages 23 figure
Far-infrared vibrational properties of linear C60 polymers: A comparison between neutral and charged materials
We report the far-infrared transmittance spectrum of a pure phase of the orthorhombic high-temperature and high-pressure C-60 polymer and compare the results with a previously published spectrum of the charged RbC60 orthorhombic polymer. Assignments for both spectra are made with the aid of first-principles quantum molecular dynamics simulations of the two materials. We find that the striking spectral differences between the neutral and charged linear fullerene polymers can be fully accounted for by charge effects on the C-60 ball
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