977 research outputs found
Inclusive versus Exclusive EM Processes in Relativistic Nuclear Systems
Connections are explored between exclusive and inclusive electron scattering
within the framework of the relativistic plane-wave impulse approximation,
beginning with an analysis of the model-independent kinematical constraints to
be found in the missing energy--missing momentum plane. From the interplay
between these constraints and the spectral function basic features of the
exclusive and inclusive nuclear responses are seen to arise. In particular, the
responses of the relativistic Fermi gas and of a specific hybrid model with
confined nucleons in the initial state are compared in this work. As expected,
the exclusive responses are significantly different in the two models, whereas
the inclusive ones are rather similar. By extending previous work on the
relativistic Fermi gas, a reduced response is introduced for the hybrid model
such that it fulfills the Coulomb and the higher-power energy-weighted sum
rules. While incorporating specific classes of off-shellness for the struck
nucleons, it is found that the reducing factor required is largely
model-independent and, as such, yields a reduced response that is useful for
extracting the Coulomb sum rule from experimental data. Finally, guided by the
difference between the energy-weighted sum rules of the two models, a version
of the relativistic Fermi gas is devised which has the 0, 1 and 2 moments of the charge response which agree rather well
with those of the hybrid model: this version thus incorporates {\em a priori}
the binding and confinement effects of the stuck nucleons while retaining the
simplicity of the original Fermi gas.Comment: LaTex file with 15 .ps figure
Section Extension from Hyperbolic Geometry of Punctured Disk and Holomorphic Family of Flat Bundles
The construction of sections of bundles with prescribed jet values plays a
fundamental role in problems of algebraic and complex geometry. When the jet
values are prescribed on a positive dimensional subvariety, it is handled by
theorems of Ohsawa-Takegoshi type which give extension of line bundle valued
square-integrable top-degree holomorphic forms from the fiber at the origin of
a family of complex manifolds over the open unit 1-disk when the curvature of
the metric of line bundle is semipositive. We prove here an extension result
when the curvature of the line bundle is only semipositive on each fiber with
negativity on the total space assumed bounded from below and the connection of
the metric locally bounded, if a square-integrable extension is known to be
possible over a double point at the origin. It is a Hensel-lemma-type result
analogous to Artin's application of the generalized implicit function theorem
to the theory of obstruction in deformation theory. The motivation is the need
in the abundance conjecture to construct pluricanonical sections from flatly
twisted pluricanonical sections. We also give here a new approach to the
original theorem of Ohsawa-Takegoshi by using the hyperbolic geometry of the
punctured open unit 1-disk to reduce the original theorem of Ohsawa-Takegoshi
to a simple application of the standard method of constructing holomorphic
functions by solving the d-bar equation with cut-off functions and additional
blowup weight functions
Vortex precession in Bose-Einstein condensates: observations with filled and empty cores
We have observed and characterized the dynamics of singly quantized vortices
in dilute-gas Bose-Einstein condensates. Our condensates are produced in a
superposition of two internal states of 87Rb, with one state supporting a
vortex and the other filling the vortex core. Subsequently, the state filling
the core can be partially or completely removed, reducing the radius of the
core by as much as a factor of 13, all the way down to its bare value. The
corresponding superfluid rotation rates, evaluated at the core radius, vary by
a factor of 150, but the precession frequency of the vortex core about the
condensate axis changes by only a factor of two.Comment: 4 pages, 3 figure
Casimir Forces for Robin Scalar Field on Cylindrical Shell in de Sitter Space
The Casimir stress on a cylinderical shell in background of conformally flat
space-time for massless scalar field is investigated. In the general case of
Robin (mixed) boundary condition formulae are derived for the vacuum
expectation values of the energy-momentum tensor and vacuum forces acting on
boundaries. The special case of the dS bulk is considered then different
cosmological constants are assumed for the space inside and outside of the
shell to have general results applicable to the case of cylindrical domain wall
formations in the early universe.Comment: 10 pages, no figur
Parity Violating Measurements of Neutron Densities
Parity violating electron nucleus scattering is a clean and powerful tool for
measuring the spatial distributions of neutrons in nuclei with unprecedented
accuracy. Parity violation arises from the interference of electromagnetic and
weak neutral amplitudes, and the of the Standard Model couples primarily
to neutrons at low . The data can be interpreted with as much confidence
as electromagnetic scattering. After briefly reviewing the present theoretical
and experimental knowledge of neutron densities, we discuss possible parity
violation measurements, their theoretical interpretation, and applications. The
experiments are feasible at existing facilities. We show that theoretical
corrections are either small or well understood, which makes the interpretation
clean. The quantitative relationship to atomic parity nonconservation
observables is examined, and we show that the electron scattering asymmetries
can be directly applied to atomic PNC because the observables have
approximately the same dependence on nuclear shape.Comment: 38 pages, 7 ps figures, very minor changes, submitted to Phys. Rev.
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Chemical composition of air masses transported from Asia to the U.S. West coast during ITCT 2K2: Fossil fuel combustion versus biomass-burning signatures
As part of the Intercontinental Transport and Chemical Transformation experiment in 2002 (ITCT 2K2), a National Oceanic and Atmospheric Administration (NOAA) WP-3D research aircraft was used to study the long-range transport of Asian air masses toward the west coast of North America. During research flights on 5 and 17 May, strong enhancements of carbon monoxide (CO) and other species were observed in air masses that had been transported from Asia. The hydrocarbon composition of the air masses indicated that the highest CO levels were related to fossil fuel use. During the flights on 5 and 17 May and other days, the levels of several biomass-buming indicators increased with altitude. This was true for acetonitrile (CH3CN), methyl chloride (CH3Cl), the ratio of acetylene (C2H2) to propane (C3H8), and, on May 5, the percentage of particles measured by the particle analysis by laser mass spectrometry (PALMS) instrument that were attributed to biomass burning based on their carbon and potassium content. An ensemble of back-trajectories, calculated from the U.S. west coast over a range of latitudes and altitudes for the entire ITCT 2K2 period, showed that air masses from Southeast Asia and China were generally observed at higher altitudes than air from Japan and Korea. Emission inventories estimate the contribution of biomass burning to the total emissions to be low for Japan and Korea, higher for China, and the highest for Southeast Asia. Combined with the origin of the air masses versus altitude, this qualitatively explains the increase with altitude, averaged over the whole ITCT 2K2 period, of the different biomass-burning indicators. Copyright 2004 by the American Geophysical Union
Local Cattle and Badger Populations Affect the Risk of Confirmed Tuberculosis in British Cattle Herds
Background: The control of bovine tuberculosis (bTB) remains a priority on the public health agenda in Great Britain, after launching in 1998 the Randomised Badger Culling Trial (RBCT) to evaluate the effectiveness of badger (Meles meles) culling as a control strategy. Our study complements previous analyses of the RBCT data (focusing on treatment effects) by presenting analyses of herd-level risks factors associated with the probability of a confirmed bTB breakdown in herds within each treatment: repeated widespread proactive culling, localized reactive culling and no culling (survey-only). Methodology/Principal Findings: New cases of bTB breakdowns were monitored inside the RBCT areas from the end of the first proactive badger cull to one year after the last proactive cull. The risk of a herd bTB breakdown was modeled using logistic regression and proportional hazard models adjusting for local farm-level risk factors. Inside survey-only and reactive areas, increased numbers of active badger setts and cattle herds within 1500 m of a farm were associated with an increased bTB risk. Inside proactive areas, the number of M. bovis positive badgers initially culled within 1500 m of a farm was the strongest predictor of the risk of a confirmed bTB breakdown. Conclusions/Significance: The use of herd-based models provide insights into how local cattle and badger populations affect the bTB breakdown risks of individual cattle herds in the absence of and in the presence of badger culling. These measures of local bTB risks could be integrated into a risk-based herd testing programme to improve the targeting o
Simulations of Vortex Evolution and Phase Slip in Oscillatory Potential Flow of the Superfluid Component of Helium-4 Through an Aperture
The evolution of semicircular quantum vortex loops in oscillating potential
flow emerging from an aperture is simulated in some highly symmetrical cases.
As the frequency of potential flow oscillation increases, vortex loops that are
evolving so as eventually to cross all of the streamlines of potential flow are
drawn back toward the aperture when the flow reverses. As a result, the escape
size of the vortex loops, and hence the net energy transferred from potential
flow to vortex flow in such 2 Pi phase-slip events, decreases as the
oscillation frequency increases. Above some aperture-dependent and
flow-dependent threshold frequency, vortex loops are drawn back into the
aperture. Simulations are preformed using both radial potential flow and
oblate-spheroidal potential flow.Comment: 18 pages, 6 figures, sequel to cond-mat/050203
Revision and Update of the Consensus Definitions of Invasive Fungal Disease From the European Organization for Research and Treatment of Cancer and the Mycoses Study Group Education and Research Consortium.
BACKGROUND: Invasive fungal diseases (IFDs) remain important causes of morbidity and mortality. The consensus definitions of the Infectious Diseases Group of the European Organization for Research and Treatment of Cancer and the Mycoses Study Group have been of immense value to researchers who conduct clinical trials of antifungals, assess diagnostic tests, and undertake epidemiologic studies. However, their utility has not extended beyond patients with cancer or recipients of stem cell or solid organ transplants. With newer diagnostic techniques available, it was clear that an update of these definitions was essential. METHODS: To achieve this, 10 working groups looked closely at imaging, laboratory diagnosis, and special populations at risk of IFD. A final version of the manuscript was agreed upon after the groups' findings were presented at a scientific symposium and after a 3-month period for public comment. There were several rounds of discussion before a final version of the manuscript was approved. RESULTS: There is no change in the classifications of "proven," "probable," and "possible" IFD, although the definition of "probable" has been expanded and the scope of the category "possible" has been diminished. The category of proven IFD can apply to any patient, regardless of whether the patient is immunocompromised. The probable and possible categories are proposed for immunocompromised patients only, except for endemic mycoses. CONCLUSIONS: These updated definitions of IFDs should prove applicable in clinical, diagnostic, and epidemiologic research of a broader range of patients at high-risk
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