25,801 research outputs found
Hot-water aquifer storage: A field test
The basic water injection cycle used in a large-scale field study of heat storage in a confined aquifer near Mobile, Alabama is described. Water was pumped from an upper semi-confined aquifer, passed through a boiler where it was heated to a temperature of about 55 C, and injected into a medium sand confined aquifer. The injection well has a 6-inch (15-cm) partially-penetrating steel screen. The top of the storage formation is about 40 meters below the surface and the formation thickness is about 21 meters. In the first cycle, after a storage period of 51 days, the injection well was pumped until the temperature of the recovered water dropped to 33 c. At that point 55,300 cubic meters of water had been withdrawn and 66 percent of the injected energy had been recovered. The recovery period for the second cycle continued until the water temperature was 27.5 C and 100,100 cubic meters of water was recovered. At the end of the cycle about 90 percent of the energy injected during the cycle had been recovered
Passive scalar intermittency in low temperature helium flows
We report new measurements of turbulent mixing of temperature fluctuations in
a low temperature helium gas experiment, spanning a range of microscale
Reynolds number, , from 100 to 650. The exponents of the
temperature structure functions
are shown to saturate to for the highest
orders, . This saturation is a signature of statistics dominated by
front-like structures, the cliffs. Statistics of the cliff characteristics are
performed, particularly their width are shown to scale as the Kolmogorov length
scale.Comment: 4 pages, with 4 figure
Phase transition in a spring-block model of surface fracture
A simple and robust spring-block model obeying threshold dynamics is
introduced to study surface fracture of an overlayer subject to stress induced
by adhesion to a substrate. We find a novel phase transition in the crack
morphology and fragment-size statistics when the strain and the substrate
coupling are varied. Across the transition, the cracks display in succession
short-range, power-law and long-range correlations. The study of stress release
prior to cracking yields useful information on the cracking process.Comment: RevTeX, 4 pages, 4 Postscript figures included using epsfi
Observation of Microlensing towards the Galactic Spiral Arms. EROS II 2 year survey
We present the analysis of the light curves of 8.5 million stars observed
during two seasons by EROS (Experience de Recherche d'Objets Sombres), in the
galactic plane away from the bulge. Three stars have been found that exhibit
luminosity variations compatible with gravitational microlensing effects due to
unseen objects. The corresponding optical depth, averaged over four directions,
is 0.38 (+0.53, -0.15) 10^{-6}. All three candidates have long Einstein radius
crossing times ( 70 to 100 days). For one of them, the lack of evidence
for a parallax or a source size effect enabled us to constrain the lens-source
% geometric configuration. Another candidate displays a modulation of the
magnification, which is compatible with the lensing of a binary source.
The interpretation of the optical depths inferred from these observations is
hindered by the imperfect knowledge of the distance to the target stars. Our
measurements are compatible with expectations from simple galactic models under
reasonable assumptions on the target distances.Comment: 11 pages, 13 figures, accepted by A&A in Aug 9
Some Applications of Thermal Field Theory to Quark-Gluon Plasma
The lecture provides a brief introduction of thermal field theory within
imaginary time formalism, the Hard Thermal Loop perturbation theory and some of
its application to the physics of the quark-gluon plasma, possibly created in
relativistic heavy ion collisions.Comment: 17 pages, 12 figures : Lectures given in "Workshop on Hadron Physics"
during March 7-17, 2005, Puri, Indi
Eta electroproduction on nuclei in the nucleon resonance region
We investigate eta electroproduction on nuclei for Q^2=2.4 and 3.6 GeV^2 in
the framework of a coupled-channel BUU transport model. We analyze the
importance of final state interactions and side feeding and compare with
findings drawn from eta photoproduction. It is shown that in contrast to
photoproduction the influence of etas stemming from secondary processes becomes
important at high Q^2.Comment: 5 pages, 5 figure
Screened Perturbation Theory to Three Loops
The thermal physics of a massless scalar field with a phi^4 interaction is
studied within screened perturbation theory (SPT). In this method the
perturbative expansion is reorganized by adding and subtracting a mass term in
the lagrangian. We consider several different mass prescriptions that
generalize the one-loop gap equation to two-loop order. We calculate the
pressure and entropy to three-loop order and the screening mass to two-loop
order. In contrast to the weak-coupling expansion, the SPT-improved
approximations appear to converge even for rather large values of the coupling
constant.Comment: 30 pages, 10 figure
Forward jets and forward -boson production at hadron colliders
In this talk we give a short review of forward jets and forward -boson
production at hadron colliders, in view of the extraction of footprints of BFKL
physics. We argue that at Tevatron energies, dijet production at large rapidity
intervals is still subasymptotic with respect to the BFKL regime, thus the
cross section is strongly dependent on the various cuts applied in the
experimental setup. In addition, the choice of equal transverse momentum cuts
on the tagging jets makes the cross section dependent on large logarithms of
non-BFKL origin, and thus may spoil the BFKL analysis. For vector boson
production in association with two jets, we argue that the configurations that
are kinematically favoured tend to have the vector boson forward in rapidity.
Thus jet production lends itself naturally to extensions to the
high-energy limit.Comment: LaTeX, JHEP style, 10 pages, 3 figures. Based on a talk at EPS2001,
Budapest, Hungar
Mass Expansions of Screened Perturbation Theory
The thermodynamics of massless phi^4-theory is studied within screened
perturbation theory (SPT). In this method the perturbative expansion is
reorganized by adding and subtracting a mass term in the Lagrangian. We
analytically calculate the pressure and entropy to three-loop order and the
screening mass to two-loop order, expanding in powers of m/T. The truncated
m/T-expansion results are compared with numerical SPT results for the pressure,
entropy and screening mass which are accurate to all orders in m/T. It is shown
that the m/T-expansion converges quickly and provides an accurate description
of the thermodynamic functions for large values of the coupling constant.Comment: 22 pages, 10 figure
Chiral Susceptibility in Hard Thermal Loop Approximation
The static and dynamic chiral susceptibilities in the quark-gluon plasma are
calculated within the lowest order perturbative QCD at finite temperature and
the Hard Thermal Loop resummation technique using an effective quark
propagator. After regularisation of ultraviolet divergences, the Hard Thermal
Loop results are compared to QCD lattice simulations.Comment: 12 pages, 4 figures, revised version, to be published in Phys. Rev.
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