4,860 research outputs found
RF multicoupler design techniques to minimize problems of corona, multipaction, and stability
A mathematical expression was derived describing multipacting and corona effects in a coaxial cavity. Both mechanical and electrical design techniques were investigated to minimize the susceptibility of coaxial cavity to corona and multipacting-type breakdown. To assist in the design of a multicoupler free from corona and multipactor breakdown, a flow chart obtained from the derived mathematical expression is included
The Interplanetary Network Supplement to the BeppoSAX Gamma-Ray Burst Catalogs
Between 1996 July and 2002 April, one or more spacecraft of the
interplanetary network detected 787 cosmic gamma-ray bursts that were also
detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera
experiments aboard the BeppoSAX spacecraft. During this period, the network
consisted of up to six spacecraft, and using triangulation, the localizations
of 475 bursts were obtained. We present the localization data for these events.Comment: 89 pages, 3 figures. Submitted to the Astrophysical Journal
Supplement Serie
Real time localization of Gamma Ray Bursts with INTEGRAL
The INTEGRAL satellite has been successfully launched in October 2002 and has
recently started its operational phase. The INTEGRAL Burst Alert System (IBAS)
will distribute in real time the coordinates of the GRBs detected with
INTEGRAL. After a brief introduction on the INTEGRAL instruments, we describe
the main IBAS characteristics and report on the initial results. During the
initial performance and verification phase of the INTEGRAL mission, which
lasted about two months, two GRBs have been localized with accuracy of about
2-4 arcmin. These observations have allowed us to validate the IBAS software,
which is now expected to provide quick (few seconds delay) and precise (few
arcmin) localization for about 10-15 GRBs per year.Comment: 6 pages, latex, 3 figures, submitted to Adv. Sp. Res., Proceedings of
the 34th COSPAR Scientific Assembly, Houston, 10-19 October 200
De-blending Deep Herschel Surveys: A Multi-wavelength Approach
Cosmological surveys in the far infrared are known to suffer from confusion.
The Bayesian de-blending tool, XID+, currently provides one of the best ways to
de-confuse deep Herschel SPIRE images, using a flat flux density prior. This
work is to demonstrate that existing multi-wavelength data sets can be
exploited to improve XID+ by providing an informed prior, resulting in more
accurate and precise extracted flux densities. Photometric data for galaxies in
the COSMOS field were used to constrain spectral energy distributions (SEDs)
using the fitting tool CIGALE. These SEDs were used to create Gaussian prior
estimates in the SPIRE bands for XID+. The multi-wavelength photometry and the
extracted SPIRE flux densities were run through CIGALE again to allow us to
compare the performance of the two priors. Inferred ALMA flux densities
(F), at 870m and 1250m, from the best fitting SEDs from the
second CIGALE run were compared with measured ALMA flux densities (F) as an
independent performance validation. Similar validations were conducted with the
SED modelling and fitting tool MAGPHYS and modified black body functions to
test for model dependency. We demonstrate a clear improvement in agreement
between the flux densities extracted with XID+ and existing data at other
wavelengths when using the new informed Gaussian prior over the original
uninformed prior. The residuals between F and F were calculated. For
the Gaussian prior, these residuals, expressed as a multiple of the ALMA error
(), have a smaller standard deviation, 7.95 for the Gaussian
prior compared to 12.21 for the flat prior, reduced mean, 1.83
compared to 3.44, and have reduced skew to positive values, 7.97
compared to 11.50. These results were determined to not be significantly model
dependent. This results in statistically more reliable SPIRE flux densities.Comment: 8 pages, 7 figures, 3 tables. Accepted for publication in A&
INTEGRAL discovery of persistent hard X-ray emission from the Soft Gamma Ray Repeater SGR 1806-20
We report the discovery of persistent hard X-ray emission extending up to 150
keV from the soft gamma-ray repeater SGR 1806-20 using data obtained with the
INTEGRAL satellite in 2003-2004. Previous observations of hard X-rays from
objects of this class were limited to short duration bursts and rare transient
episodes of strongly enhanced luminosity (``flares''). The emission observed
with the IBIS instrument above 20 keV has a power law spectrum with photon
index in the range 1.5-1.9 and a flux of 3 milliCrabs, corresponding to a
20-100 keV luminosity of ~10^36 erg s^-1 (for a distance of 15 kpc). The
spectral hardness and the luminosity correlate with the level of source
activity as measured from the number of emitted bursts.Comment: 5 pages, 3 figures, Revised version accepted for publication in
Astronomy and Astrophysics Letter
A pertubative approach to the Kondo effect in magnetic atoms on nonmagnetic substrates
Recent experimental advances in scanning tunneling microscopy make the
measurement of the conductance spectra of isolated and magnetically coupled
atoms on nonmagnetic substrates possible. Notably these spectra are
characterized by a competition between the Kondo effect and spin-flip inelastic
electron tunneling. In particular they include Kondo resonances and a
logarithmic enhancement of the conductance at voltages corresponding to
magnetic excitations, two features that cannot be captured by second order
perturbation theory in the electron-spin coupling. We have now derived a third
order analytic expression for the electron-spin self-energy, which can be
readily used in combination with the non-equilibrium Green's function scheme
for electron transport at finite bias. We demonstrate that our method is
capable of quantitative description the competition between Kondo resonances
and spin-flip inelastic electron tunneling at a computational cost
significantly lower than that of other approaches. The examples of Co and Fe on
CuN are discussed in detail
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