33,203 research outputs found
Centaur propellant acquisition system study
A study was performed to determine the desirability of replacing the hydrogen peroxide settling system on the Centaur D-1S with a capillary acquisition system. A comprehensive screening was performed to select the most promising capillary device fluid acquisition, thermal conditioning, and fabrication techniques. Refillable start baskets and bypass feed start tanks were selected for detailed design. Critical analysis areas were settling and refilling, start sequence development with an initially dry boost pump, and cooling the fluid delivered to the boost pump in order to provide necessary net position suction head (NPSH). Design drawings were prepared for the start basket and start tank concepts for both LO2 and LH2 tanks. System comparisons indicated that the start baskets using wicking for thermal conditioning, and thermal subcooling for boost pump NPSH, are the most desirable systems for future development
Leptonic origin of the 100 MeV gamma-ray emission from the Galactic Centre
The Galactic centre is a bright gamma-ray source with the GeV-TeV band
spectrum composed of two distinct components in the 1-10 GeV and 1-10 TeV
energy ranges. The nature of these two components is not clearly understood. We
investigate the gamma-ray properties of the Galactic centre to clarify the
origin of the observed emission. We report imaging, spectral, and timing
analysis of data from 74 months of observations of the Galactic centre by
FERMI/LAT gamma-ray telescope complemented by sub-MeV data from approximately
ten years of INTEGRAL/PICsIT observations. We find that the Galactic centre is
spatially consistent with the point source in the GeV band. The tightest 3
sigma upper limit on its radius is 0.13 degree in the 10-300 GeV energy band.
The spectrum of the source in the 100 MeV energy range does not have a
characteristic turnover that would point to the pion decay origin of the
signal. Instead, the source spectrum is consistent with a model of inverse
Compton scattering by high-energy electrons. In this a model, the GeV bump in
the spectrum originates from an episode of injection of high-energy particles,
which happened ~300 years ago. This injection episode coincides with the known
activity episode of the Galactic centre region, previously identified using
X-ray observations. The hadronic model of source activity could be still
compatible with the data if bremsstrahlung emission from high-energy electrons
was present in addition to pion decay emission.Comment: To match the accepted versio
Incorporation of amino acids into the outer and inner membrane of isolated rat liver mitochondria II
Light scalar at LHC: the Higgs or the dilaton?
It is likely that the LHC will observe a color- and charge-neutral scalar
whose decays are consistent with those of the Standard Model (SM) Higgs boson.
The Higgs interpretation of such a discovery is not the only possibility. For
example, electroweak symmetry breaking (EWSB) could be triggered by a
spontaneously broken, nearly conformal sector. The spectrum of states at the
electroweak scale would then contain a narrow scalar resonance, the
pseudo-Goldstone boson of conformal symmetry breaking, with Higgs-like
properties. If the conformal sector is strongly coupled, this pseudo-dilaton
may be the only new state accessible at high energy colliders. We discuss the
prospects for distinguishing this mode from a minimal Higgs boson at the LHC
and ILC. The main discriminants between the two scenarios are (1) cubic
self-interactions and (2) a potential enhancement of couplings to massless SM
gauge bosons. A particularly interesting situation arises when the scale f of
conformal symmetry breaking is approximately the electroweak scale v~246 GeV.
Although in this case the LHC may not be able to tell apart a pseudo-dilaton
from the Higgs boson, the self-interactions differ in a way that depends only
on the scaling dimension of certain operators in the conformal sector. This
opens the possibility of using dilaton pair production at future colliders as a
probe of EWSB induced by nearly conformal new physics.Comment: 7 pages, LaTe
Comprehensive Spectral Analysis of Human EEG GENERATORS in Posterior Cerebral Regions
Human electroencephalogram generator spectral analysis in posterior cerebral region
The X-ray Spectrum of the z=6.30 QSO SDSS J1030+0524
We present a deep XMM-Newton observation of the z=6.30 QSO SDSS J1030+0524,
the second most distant quasar currently known. The data contain sufficient
counts for spectral analysis, demonstrating the ability of XMM-Newton to
measure X-ray spectral shapes of z~6 QSOs with integration times >100ks. The
X-ray spectrum is well fit by a power law with index Gamma=2.12 +/- 0.11, an
optical-X-ray spectral slope of a_{ox}=-1.80, and no absorption excess to the
Galactic value, though our data are also consistent with a power law index in
the range 2.02 < Gamma < 2.5 and excess absorption in the range 0 < N_H(cm^-2)
< 8x10^22. There is also a possible detection (2 sigma) of FeKa emission. The
X-ray properties of this QSO are, overall, similar to those of lower-redshift
radio-quiet QSOs. This is consistent with the statement that the X-ray
properties of radio-quiet QSOs show no evolution over 0<z<6.3. Combined with
previous results, this QSO appears indistinguishable in any way from lower
redshift QSOs, indicating that QSOs comparable to those seen locally existed
less than one Gyr after the Big Bang.Comment: ApJ Letters, accepte
Pseudogap at hot spots in the two-dimensional Hubbard model at weak coupling
We analyze the interaction-induced renormalization of single-particle
excitations in the two-dimensional Hubbard model at weak coupling using the
Wick-ordered version of the functional renormalization group. The self energy
is computed for real frequencies by integrating a flow equation with
renormalized two-particle interactions. In the vicinity of hot spots, that is
points where the Fermi surface intersects the umklapp surface, self energy
effects beyond the usual quasi-particle renormalizations and damping occur near
instabilities of the normal, metallic phase. Strongly enhanced renormalized
interactions between particles at different hot spots generate a pronounced
low-energy peak in the imaginary part of the self energy, leading to a
pseudogap-like double-peak structure in the spectral function for
single-particle excitations.Comment: 14 pages, 7 figure
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