4,642 research outputs found
Role of interband scattering in neutron irradiated MgB thin films by Scanning Tunneling Spectroscopy measurements
A series of MgB thin films systematically disordered by neutron
irradiation have been studied by Scanning Tunneling Spectroscopy. The c-axis
orientation of the films allowed a reliable determination of local density of
state of the band. With increasing disorder, the conductance peak moves
towards higher voltages and becomes lower and broader, indicating a monotonic
increase of the gap and of the broadening parameter. These results are
discussed in the frame of two-band superconductivity.Comment: The text will be submitted in Latex format, and the corresponding pdf
file should take 6 pages. There are 5 figures (eps files submitted) and 1
tabl
High Momentum Probes of Nuclear Matter
We discuss how the chemical composition of QCD jets is altered by final state
interactions in surrounding nuclear matter. We describe this process through
conversions of leading jet particles. We find that conversions lead to an
enhancement of kaons at high transverse momentum in Au+Au collisions at RHIC,
while their azimuthal asymmetry v_2 is suppressed.Comment: Contribution to the 4th international workshop High-pT physics at LHC
09, Prague; 6 pages, 6 figure
SIMBOL-X : a new generation hard X-ray telescope
SIMBOL-X is a hard X-ray mission, operating in the 0.5-70 keV range, which is
proposed by a consortium of European laboratories for a launch around 2010.
Relying on two spacecraft in a formation flying configuration, SIMBOL-X uses a
30 m focal length X-ray mirror to achieve an unprecedented angular resolution
(30 arcsec HEW) and sensitivity (100 times better than INTEGRAL below 50 keV)
in the hard X-ray range. SIMBOL-X will allow to elucidate fundamental questions
in high energy astrophysics, such as the physics of accretion onto Black Holes,
of acceleration in quasar jets and in supernovae remnants, or the nature of the
hard X-ray diffuse emission. The scientific objectives and the baseline
concepts of the mission and hardware design are presented.Comment: 12 pages, 16 fig., Proc. SPIE conf. 5168, San Diego, Aug. 200
Science with Simbol-X
Simbol-X is a French-Italian mission, with a participation of German
laboratories, for X-ray astronomy in the wide 0.5-80 keV band. Taking advantage
of emerging technology in mirror manufacturing and spacecraft formation flying,
Simbol-X will push grazing incidence imaging up to ~80 keV, providing an
improvement of roughly three orders of magnitude in sensitivity and angular
resolution compared to all instruments that have operated so far above 10 keV.
This will open a new window in X-ray astronomy, allowing breakthrough studies
on black hole physics and census and particle acceleration mechanisms. We
describe briefly the main scientific goals of the Simbol-X mission, giving a
few examples aimed at highlighting key issues of the Simbol-X design.Comment: Proc. of the workshop "Simbol-X: The hard X-ray universe in focus",
Bologna 14-16 May, 200
Conversión de mezclas de amoniaco/dimetil éter a alta presión
Con el fin de mitigar las emisiones globales de CO2 y de buscar combustibles alternativos, en el presente trabajo se ha investigado la combustión de amoniaco (NH3) con dimetil éter (DME) a alta presión. Los resultados experimentales han sido simulados con un mecanismo cinético detallado de reacción
Systematic study of disorder induced by neutron irradiation in MgB2 thin films
The effects of neutron irradiation on normal state and superconducting
properties of epitaxial magnesium diboride thin films are studied up to
fluences of 1020 cm-2. All the properties of the films change systematically
upon irradiation. Critical temperature is suppressed and, at the highest
fluence, no superconducting transition is observed down to 1.8 K. Residual
resistivity progressively increases from 1 to 190 microohmcm; c axis expands
and then saturates at the highest damage level. We discuss the mechanism of
damage through the comparison with other damage procedures. The normal state
magnetoresistivity of selected samples measured up to high fields (28 and 45T)
allows to determine unambiguously the scattering rates in each band; the
crossover between the clean and dirty limit in each sample can be monitored.
This set of samples, with controlled amount of disorder, is suitable to study
the puzzling problem of critical field in magnesium diboride thin films. The
measured critical field values are extremely high (of the order of 50T in the
parallel direction at low fluences) and turns out to be rather independent on
the experimental resistivity, at least at low fluences. A simple model to
explain this phenomenology is presented.Comment: 29 pages, 6 figures, accepted for publication on J. of Applied
Physic
Inhomogeneous cosmologies, the Copernican principle and the cosmic microwave background: More on the EGS theorem
We discuss inhomogeneous cosmological models which satisfy the Copernican
principle. We construct some inhomogeneous cosmological models starting from
the ansatz that the all the observers in the models view an isotropic cosmic
microwave background. We discuss multi-fluid models, and illustrate how more
general inhomogeneous models may be derived, both in General Relativity and in
scalar-tensor theories of gravity. Thus we illustrate that the cosmological
principle, the assumption that the Universe we live in is spatially
homogeneous, does not necessarily follow from the Copernican principle and the
high isotropy of the cosmic microwave background.Comment: 17 pages; to appear in GR
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