2,146 research outputs found
Numerical Study of the Ghost-Ghost-Gluon Vertex on the Lattice
It is well known that, in Landau gauge, the renormalization function of the
ghost-ghost-gluon vertex \widetilde{Z}_1(p^2) is finite and constant, at least
to all orders of perturbation theory. On the other hand, a direct
non-perturbative verification of this result using numerical simulations of
lattice QCD is still missing. Here we present a preliminary numerical study of
the ghost-ghost-gluon vertex and of its corresponding renormalization function
using Monte Carlo simulations in SU(2) lattice Landau gauge. Data were obtained
in 4 dimensions for lattice couplings beta = 2.2, 2.3, 2.4 and lattice sides N
= 4, 8, 16.Comment: 3 pages, 1 figure, presented by A. Mihara at the IX Hadron Physics
and VII Relativistic Aspects of Nuclear Physics Workshops, Angra dos Reis,
Rio de Janeiro, Brazil (March 28--April 3, 2004
Guia para a captura e o aproveitamento artesanal do tubarão em Moçambique
A summary is given of practical recommendations on materials and methods for the capture and main utilization of shark in Mozambique
ASCA Observations of the Seyfert 2 Galaxy NGC 7582: An Obscured and Scattered View of the Hidden Nucleus
ASCA observations of the Seyfert 2 galaxy NGC 7582 revealed it was highly
variable on the timescale of s in the hard X-ray (2-10 keV)
band, while the soft X-ray (0.5-2 keV) flux remained constant during the
observations.
The spectral analysis suggests that this object is seen through an obscuring
torus with the thickness of N. The
hard X-ray is an absorbed direct continuum from a hidden Seyfert 1 nucleus; the
soft X-ray is dominated by the scattered central continuum from an extended
spatial region. Thus we have an obscured/absorbed and a scattered view of this
source as expected from the unification model for Seyfert galaxies.
More interestingly, the inferred X-ray column was observed to increase by
from 1994 to 1996, suggesting a ``patchy''
torus structure, namely the torus might be composed of many individual clouds.
The observed iron line feature near 6.4 keV with the equivalent width of 170 eV
is also consistent with the picture of the transmission of nuclear X-ray
continuum through a non-uniform torus.Comment: 10 pages, 6 figures. To be appear in PASJ 50 No.5 (1998 Oct.25 issue
Energy-Dependent Harmonic Ratios of the Cyclotron Features of X0331+53 in the 2004-2005 Outburst
We report on changes of the cyclotron resonance energies of the recurrent
transient pulsar, X0331+53 (V0332+53). The whole RXTE data acquired in the
2004-2005 outburst were utilized. The 3-80 keV source luminosity varied between
1.7x10^36 and 3.5x10^38 ers/s, assuming a distance of 7 kpc. We confirmed that
the fundamental cyclotron resonance energy changed from ~22 to ~27 keV in a
clear anti-correlation to the source luminosity, and without any hysteresis
effects between the rising and declining phases of the outburst. In contrast,
the second harmonic energy changed from ~49 to ~54 keV, implying a weaker
fractional change as a function of the luminosity. As a result, the observed
resonance energy ratio between the second harmonic and the fundamental was ~2.2
when the source was most luminous, whereas the ratio decreased to the nominal
value of 2.0 at the least luminous state. Although the significance of this
effect is model dependent, these results suggest that the fundamental and
second harmonic resonances represent different heights in the accretion column,
depending on the mass accretion rate.Comment: 39 pages, 15 figures, 4 tables. Accepted for publication in
Astrophysical Journa
High Quality Factor Silicon Cantilever Driven by PZT Actuator for Resonant Based Mass Detection
A high quality factor (Q-factor) piezoelectric lead zirconat titanate (PZT)
actuated single crystal silicon cantilever was proposed in this paper for
resonant based ultra-sensitive mass detection. Energy dissipation from
intrinsic mechanical loss of the PZT film was successfully compressed by
separating the PZT actuator from resonant structure. Excellent Q-factor, which
is several times larger than conventional PZT cantilever, was achieved under
both atmospheric pressure and reduced pressures. For a 30 micrometer-wide 100
micrometer-long cantilever, Q-factor was measured as high as 1113 and 7279
under the pressure of 101.2 KPa and 35 Pa, respectively. Moreover, it was found
that high-mode vibration can be realized by the cantilever for the pursuit of
great Q-factor, while support loss became significant because of the increased
vibration amplitude at the actuation point. An optimized structure using
node-point actuation was suggested then to suppress corresponding energy
dissipation.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/handle/2042/16838
Warm absorber, reflection and Fe K line in the X-ray spectrum of IC 4329A
Results from the X-ray spectral analysis of the ASCA PV phase observation of
the Seyfert 1 galaxy IC 4329A are presented. We find that the 0.4 - 10 keV
spectrum of IC 4329A is best described by the sum of a steep () power-law spectrum passing through a warm absorber plus a strong
reflection component and associated Fe K line, confirming recent results
(Madejski et al. 1995, Mushotsky et al. 1995). Further cold absorption in
excess of the Galactic value and covering the entire source is also required by
the data, consistent with the edge-on galactic disk and previous X-ray
measurements. The effect of the warm absorber at soft X-ray energies is best
parameterized by two absorption edges, one consistent with OVI, OVII or NVII,
the other consistent with OVIII. A description of the soft excess in terms of
blackbody emission, as observed in some other Seyfert 1 galaxies, is ruled out
by the data. A large amount of reflection is detected in both the GIS and SIS
detectors, at similar intensities. We find a strong correlation between the
amount of reflection and the photon index, but argue that the best solution
with the present data is that given by the best statistical fit. The model
dependence of the Fe K line parameters is also discussed. Our best fit gives a
slightly broad ( keV) and redshifted (E keV) Fe K line, with equivalent width 89 33 eV.
The presence of a weak Fe K line with a strong reflection can be reconciled if
one assumes iron underabundances or ionized reflection. We also have modeled
the line with a theoretical line profile produced by an accretion disk. This
yields results in better agreement with the constraints obtained from the
reflection component.Comment: Accepted for publication in The Astrophysical Journal, 10th February
1996 issue; 24 pages and 8 figures + 1 table tared, compressed and uuencoded
(with uufiles
Probing the stellar wind environment of Vela X-1 with MAXI
Vela X-1 is among the best studied and most luminous accreting X-ray pulsars.
The supergiant optical companion produces a strong radiatively-driven stellar
wind, which is accreted onto the neutron star producing highly variable X-ray
emission. A complex phenomenology, due to both gravitational and radiative
effects, needs to be taken into account in order to reproduce orbital spectral
variations. We have investigated the spectral and light curve properties of the
X-ray emission from Vela X-1 along the binary orbit. These studies allow to
constrain the stellar wind properties and its perturbations induced by the
compact object. We took advantage of the All Sky Monitor MAXI/GSC data to
analyze Vela X-1 spectra and light curves. By studying the orbital profiles in
the and keV energy bands, we extracted a sample of orbital light
curves (% of the total) showing a dip around the inferior
conjunction, i.e., a double-peaked shape. We analyzed orbital phase-averaged
and phase-resolved spectra of both the double-peaked and the standard sample.
The dip in the double-peaked sample needs cm to
be explained by absorption solely, which is not observed in our analysis. We
show how Thomson scattering from an extended and ionized accretion wake can
contribute to the observed dip. Fitted by a cutoff power-law model, the two
analyzed samples show orbital modulation of the photon index, hardening by
around the inferior conjunction, compared to earlier and later
phases, hinting a likely inadequacy of this model. On the contrary, including a
partial covering component at certain orbital phase bins allows a constant
photon index along the orbital phases, indicating a highly inhomogeneous
environment. We discuss our results in the framework of possible scenarios.Comment: 10 pages, 9 figures, accepted for publication in A&
Temperature dependence of the ohmic conductivity and activation energy of Pb1+y(Zr0.3Ti0.7)O3 thin films
The ohmic conductivity of the sol-gel derived Pb1+y(Zr0.3Ti0.7)O3 thin films
(with the excess lead y=0.0 to 0.4) are investigated using low frequency small
signal alternate current (AC) and direct current (DC) methods. Its temperature
dependence shows two activation energies of 0.26 and 0.12 eV depending on
temperature range and excess Pb levels. The former is associated with Pb3+
acceptor centers, while the latter could be due to a different defect level yet
to be identified.Comment: 13 pages, 3 figures, PostScript. Submitted to Applied Physics Letter
Orbital phase resolved spectroscopy of 4U1538-52 with MAXI
4U 1538-52, an absorbed high mass X-ray binary with an orbital period of 3.73
days, shows moderate orbital intensity modulations with a low level of counts
during the eclipse. Several models have been proposed to explain the accretion
at different orbital phases by a spherically symmetric stellar wind from the
companion. The aim of this work is to study both the light curve and orbital
phase spectroscopy of this source in the long term. Particularly, the folded
light curve and the changes of the spectral parameters with orbital phase to
analyse the stellar wind of QV Nor, the mass donor of this binary system. We
used all the observations made from the Gas Slit Camera on board MAXI of 4U
1538-52 covering many orbits continuously. We obtained the good interval times
for every orbital phase range which were the input to extract our data. We
estimated the orbital period of the system and then folded the light curves and
we fitted the X-ray spectra with the same model for every orbital phase
spectrum. We also extracted the averaged spectrum of all the MAXI data
available. The MAXI spectra in the 2-20 keV energy range were fitted with an
absorbed Comptonization of cool photons on hot electrons. We found a strong
orbital dependence of the absorption column density but neither the
fluorescence iron emission line nor low energy excess were needed to fit the
MAXI spectra. The variation of the spectral parameters over the binary orbit
were used to examine the mode of accretion onto the neutron star in 4U 1538-52.
We deduce a best value of for QV Nor.Comment: 12 pages, 5 figures, accepted to be published by A&A, corrected typos
(changing bold font to normal one
- …