2,261 research outputs found
Reactor Neutrino Experiments with a Large Liquid Scintillator Detector
We discuss several new ideas for reactor neutrino oscillation experiments
with a Large Liquid Scintillator Detector. We consider two different scenarios
for a measurement of the small mixing angle with a mobile
source: a nuclear-powered ship, such as a submarine or an
icebreaker, and a land-based scenario with a mobile reactor. The former setup
can achieve a sensitivity to at the 90%
confidence level, while the latter performs only slightly better than Double
Chooz. Furthermore, we study the precision that can be achieved for the solar
parameters, and , with a mobile reactor
and with a conventional power station. With the mobile reactor, a precision
slightly better than from current global fit data is possible, while with a
power reactor, the accuracy can be reduced to less than 1%. Such a precision is
crucial for testing theoretical models, e.g. quark-lepton complementarity.Comment: 18 pages, 3 figures, 2 tables, revised version, to appear in JHEP,
Fig. 1 extended, Formula added, minor changes, results unchange
First-Order Melting and Dynamics of Flux Lines in a Model for YBaCuO
We have studied the statics and dynamics of flux lines in a model for YBCO,
using both Monte Carlo simulations and Langevin dynamics. For a clean system,
both approaches yield the same melting curve, which is found to be weakly first
order with a heat of fusion of about per vortex pancake at a
field of The time averaged magnetic field distribution
experienced by a fixed spin is found to undergo a qualitative change at
freezing, in agreement with NMR and experiments. Melting in the
clean system is accompanied by a proliferation of free disclinations which show
a clear B-dependent 3D-2D crossover from long disclination lines parallel to
the c-axis at low fields, to 2D ``pancake'' disclinations at higher fields.
Strong point pins produce a logarithmical relaxation which results from
slow annealing out of disclinations in disordered samples.Comment: 31 pages, latex, revtex, 12 figures available upon request, No major
changes to the original text, but some errors in the axes scale for Figures 6
and 7 were corrected(new figures available upon request), to be published in
Physical Review B, July 199
Geo-neutrinos: A systematic approach to uncertainties and correlations
Geo-neutrinos emitted by heat-producing elements (U, Th and K) represent a
unique probe of the Earth interior. The characterization of their fluxes is
subject, however, to rather large and highly correlated uncertainties. The
geochemical covariance of the U, Th and K abundances in various Earth
reservoirs induces positive correlations among the associated geo-neutrino
fluxes, and between these and the radiogenic heat. Mass-balance constraints in
the Bulk Silicate Earth (BSE) tend instead to anti-correlate the radiogenic
element abundances in complementary reservoirs. Experimental geo-neutrino
observables may be further (anti)correlated by instrumental effects. In this
context, we propose a systematic approach to covariance matrices, based on the
fact that all the relevant geo-neutrino observables and constraints can be
expressed as linear functions of the U, Th and K abundances in the Earth's
reservoirs (with relatively well-known coefficients). We briefly discuss here
the construction of a tentative "geo-neutrino source model" (GNSM) for the U,
Th, and K abundances in the main Earth reservoirs, based on selected
geophysical and geochemical data and models (when available), on plausible
hypotheses (when possible), and admittedly on arbitrary assumptions (when
unavoidable). We use then the GNSM to make predictions about several
experiments ("forward approach"), and to show how future data can constrain - a
posteriori - the error matrix of the model itself ("backward approach"). The
method may provide a useful statistical framework for evaluating the impact and
the global consistency of prospective geo-neutrino measurements and Earth
models.Comment: 17 pages, including 4 figures. To appear on "Earth, Moon, and
Planets," Special Issue on "Neutrino Geophysics," Proceedings of Neutrino
Science 2005 (Honolulu, Hawaii, Dec. 2005
Scientific basis for safely shutting in the Macondo Well after the April 20, 2010 Deepwater Horizon blowout
As part of the government response to the Deepwater Horizon blowout, a Well Integrity Team evaluated the geologic hazards of shutting in the Macondo Well at the seafloor and determined the conditions under which it could safely be undertaken. Of particular concern was the possibility that, under the anticipated high shut-in pressures, oil could leak out of the well casing below the seafloor. Such a leak could lead to new geologic pathways for hydrocarbon release to the Gulf of Mexico. Evaluating this hazard required analyses of 2D and 3D seismic surveys, seafloor bathymetry, sediment properties, geophysical well logs, and drilling data to assess the geological, hydrological, and geomechanical conditions around the Macondo Well. After the well was successfully capped and shut in on July 15, 2010, a variety of monitoring activities were used to assess subsurface well integrity. These activities included acquisition of wellhead pressure data, marine multichannel seismic pro- files, seafloor and water-column sonar surveys, and wellhead visual/acoustic monitoring. These data showed that the Macondo Well was not leaking after shut in, and therefore, it could remain safely shut until reservoir pressures were suppressed (killed) with heavy drilling mud and the well was sealed with cement
The ac magnetic response of mesoscopic type II superconductors
The response of mesoscopic superconductors to an ac magnetic field is
numerically investigated on the basis of the time-dependent Ginzburg-Landau
equations (TDGL). We study the dependence with frequency and dc
magnetic field of the linear ac susceptibility
in square samples with dimensions of the order of the London penetration depth.
At the behavior of as a function of agrees very well
with the two fluid model, and the imaginary part of the ac susceptibility,
, shows a dissipative a maximum at the frequency
. In the presence of a magnetic field a
second dissipation maximum appears at a frequency . The most
interesting behavior of mesoscopic superconductors can be observed in the
curves obtained at a fixed frequency. At a fixed number of
vortices, continuously increases with increasing . We
observe that the dissipation reaches a maximum for magnetic fields right below
the vortex penetration fields. Then, after each vortex penetration event, there
is a sudden suppression of the ac losses, showing discontinuities in
at several values of . We show that these
discontinuities are typical of the mesoscopic scale and disappear in
macroscopic samples, which have a continuos behavior of . We
argue that these discontinuities in are due to the effect of
{\it nascent vortices} which cause a large variation of the amplitude of the
order parameter near the surface before the entrance of vortices.Comment: 12 pages, 9 figures, RevTex
Density mismatch in thin diblock copolymer films
Thin films of diblock copolymer subject to gravitational field are simulated
by means of a cell dynamical system model. The difference in density of the two
sides of the molecule and the presence of the field causes the formation of
lamellar patterns with orientation parallel to the confining walls even when
they are neutral. The concentration profile of those films is analyzed in the
weak segregation regime and a functional form for the profile is proposed.Comment: 9 pages and 8 figures. Needs EPSF macros. Submitted to PR
CANGAROO-III Observation of TeV Gamma Rays from the vicinity of PSR B1 706-44
Observation by the CANGAROO-III stereoscopic system of the Imaging Cherenkov
Telescope has detected extended emission of TeV gamma rays in the vicinity of
the pulsar PSR B170644. The strength of the signal observed as
gamma-ray-like events varies when we apply different ways of emulating
background events. The reason for such uncertainties is argued in relevance to
gamma-rays embedded in the "off-source data", that is, unknown sources and
diffuse emission in the Galactic plane, namely, the existence of a complex
structure of TeV gamma-ray emission around PSR B170644.Comment: 10 pages, 13 figures, to be published in Ap
Evidence of TeV gamma-ray emission from the nearby starburst galaxy NGC 253
TeV gamma-rays were recently detected from the nearby normal spiral galaxy
NGC 253 (Itoh et al., 2002). Observations to detect the Cherenkov light images
initiated by gamma-rays from the direction of NGC 253 were carried out in 2000
and 2001 over a total period of 150 hours. The orientation of images in
gamma-ray--like events is not consistent with emission from a point source, and
the emission region corresponds to a size greater than 10 kpc in radius. Here,
detailed descriptions of the analysis procedures and techniques are given.Comment: 16 pages, 27 figures, aa.cl
Novel vortex lattice transition in d-wave superconductors
We study the vortex state in a magnetic field parallel to the axis in the
framework of the extended Ginzburg Landau equation. We find the vortex acquires
a fourfold modulation proportional to where is the angle
makes with the -axis. This term gives rise to an attractive
interaction between two vortices when they are aligned parallel to or
. We predict the first order vortex lattice transition at
from triangular into the square lattice
tilted by from the axis. This gives the critical field
a few Tesla for YBCO and Bi2212 monocrystals at low temperatures ().Comment: 6 pages, 4 figure
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