66,719 research outputs found
Nature of Decoupling in the Mixed Phase of Extremely Type-II Layered Superconductors
The uniformly frustrated layered XY model is analyzed in its Villain form. A
decouple pancake vortex liquid phase is identified. It is bounded by both
first-order and second-order decoupling lines in the magnetic field versus
temperature plane. These transitions, respectively, can account for the
flux-lattice melting and for the flux-lattice depinning observed in the mixed
phase of clean high-temperature superconductors.Comment: 11 pages of PLAIN TeX, 1 postscript figure, published version, many
change
Double fluctuations on the attractive Hubbard model: ladder approximation
We explore, for the first time, the effect of double fluctuations on both the
diagonal and off-diagonal self-energy. We use the T-Matrix equations below
, developed recently by the Z\"urich group (M.H. Pedersen et al) for the
local pair attraction Hamiltonian. Here, we include as well the effect of
fluctuations on the order parameter (beyond the BCS solution) up to second
order in . This is equivalent to approximating the effective interaction
by in the off-diagonal self-energy. For , , and , we find four peaks both for the diagonal,
, and off-diagonal, ,
spectral functions. These peaks are not symmetric in pairs as previously found.
In addition: (a) in , the far left peak has a
vanishing small weight; (b) in the far left and
far right peaks have very small weights. The physical picture is, then, that
the pair physics in the normal phase () is still valid below .
However, the condensation of the e-h pairs produces an additional gap around
the chemical potential as in BCS, in other words, superconductivity opens a gap
in the lower branch of a Hubbard-type-I solution.Comment: LaTeX, 7 pages. 8 figures available on request. To appear in Z.
Physik
Optimal design of pipes in series: An explicit approximation
This paper introduces a new methodology for the optimum design of pipes in series, named Optimum Hydraulic Grade Line (OHGL). This methodology is explicit and is based on the knowledge of the series topology and the geometrical distribution of water demands on nodes, i.e. the way in which the pipe in series delivers water mass as function of the distance from the entrance. OHGL consists in the pre-determination of that hydraulic grade line which gives the minimum construction cost, in an explicit way. Once this line has been established, calculation of the pipe’s continuous diameters is direct; after a round up to commercial diameters is developed. To validate the proposed methodology, several pipes in series were designed both using GA and OHGL. Four hundred series were used in total, each with different topological characteristics and demands. Keywords: Pipe in series, optimum design, genetic algorithms, optimum hydraulic grade line
The faint 2005 hard state outburst of Aquila X-1 seen by INTEGRAL and RXTE
We report on the spectral analysis of RXTE and INTEGRAL data of the 2005
April outburst of the transient Atoll source Aql X-1. Although this outburst is
one of the faintest ever detected for this source in the soft X-rays
(RXTE/ASM), one of our INTEGRAL observations, taken close to the soft X-ray
peak, shows that the source flux was quite high, with a 20-200 keV flux of 2.05
x 10^-9 erg cm^-2 s^-1. On this occasion we detect the source up to 150 keV for
the first time. We compare and discuss the similarity of the source behavior
with that of black hole transients especially XTE J1550-564.Comment: 4 pages 2 figures, Accepted for publication in A&A as a RESEARCH NOT
Spectral evolution of the microquasar XTE J1550-564 over its entire 2000 outburst
We report on RXTE observations of the microquasar XTE J1550-564 during a ~70
day outburst in April-June 2000. We study the evolution of the PCA+HEXTE
spectra over the outburst. The source transited from an initial Low Hard State
(LS), to an Intermediate State (IS), and then back to the LS. The source shows
an hysteresis effect similar to what is observed in other sources, favoring a
common origin for the state transitions in soft X-ray transients. The first
transition occurs at a ~ constant 2-200 keV flux, which probably indicates a
change in the relative importance of the emitting media. The second transition
is more likely driven by a drop in the mass accretion rate.
In both LS, the spectra are characterized by the presence of a strong
power-law tail (Compton corona) with a variable high energy cut-off. During the
IS, the spectra show the presence of a ~0.8 keV thermal component (accretion
disk). We discuss the apparently independent evolution of the two media, and
show that right after the X-ray maximum on MJD 51662, the decrease of the
source luminosity is due to a decrease of the power-law luminosity, at a
constant disk luminosity. This, together with the detection of radio emission
(with a spectrum typical of optically thin synchrotron emission), may suggest
that the corona is ejected and further detected as a discrete radio ejection.Comment: Accepted for publication in ApJ. 9 pages, 4 figures, abstract
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Area Littlewood-Paley functions associated with Hermite and Laguerre operators
In this paper we study Lp-boundedness properties for area Littlewood-Paley
functions associated with heat semigroups for Hermite and Laguerre operator
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