568 research outputs found
Field theoretic calculation of the surface tension for a model electrolyte system
We carry out the calculation of the surface tension for a model electrolyte
to first order in a cumulant expansion about a free field theory equivalent to
the Debye-H\"uckel approximation. In contrast with previous calculations, the
surface tension is calculated directly without recourse to integrating
thermodynamic relations. The system considered is a monovalent electrolyte with
a region at the interface, of width h, from which the ionic species are
excluded. In the case where the external dielectric constant epsilon_0 is
smaller than the electrolyte solution's dielectric constant epsilon we show
that the calculation at this order can be fully regularized. In the case where
h is taken to be zero the Onsager-Samaras limiting law for the excess surface
tension of dilute electrolyte solutions is recovered, with corrections coming
from a non-zero value of epsilon_0/epsilon.Comment: LaTeX, 14 pages, 3 figures, 1 tabl
Curvature-Induced Defect Unbinding in Toroidal Geometries
Toroidal templates such as vesicles with hexatic bond orientational order are
discussed. The total energy including disclination charges is explicitly
computed for hexatic order embedded in a toroidal geometry. Related results
apply for tilt or nematic order on the torus in the one Frank constant
approximation. Although there is no topological necessity for defects in the
ground state, we find that excess disclination defects are nevertheless
energetically favored for fat torii or moderate vesicle sizes. Some
experimental consequences are discussed.Comment: 12 pages, 15 eps figure
Molecular Diagnostics of Histoplasmosis
Histoplasmosis is a systemic fungal disease that occurs worldwide. The highest incidence of the disease is reported on the American continent. It also occurs in China, India, South-Eastern Asia, Africa, Australia and Europe. Clinical syndromes of histoplasmosis are not specific and in most cases immunocompetent individuals are asymptomatic or present mild influenza-like disease. Immunocompromised patients especially individuals with AIDS, can develop a severe and fatal disease due to fungal dissemination to many organs. Etiological agent of histoplasmosis is the dimorphic fungus Histoplasma capsulatum, which inhabits the soils contaminated with bird or bat droppings. Three biological varieties are considered for this fungus: H. capsulatum var. capsulatum, H. capsulatum var. duboissii and H. capsulatum var. farciminosum. Genetic differences are observed among H. capsulatum strains from diverse regions of the world. The main molecular methodologies for genetic typing of fungi are based on DNA fingerprinting. They have been an important instrument to identify possible sources of infection in outbreaks of histoplasmosis. Genetic profiles of H. capsulatum, isolated from bats and humans, helped to understand the distribution of the disease in certain endemic regions. The con-ventional diagnosis of histoplasmosis is performed by means of cultural and microscopic examination of samples from the respiratory tract and biologic fluids. However, these techniques yield positive results in only 50 % of cases. In the last two decades, approaches for the detecting of H. capsulatum in clinical samples, using different molecular targets, based on PCR assay have been developed. Their use can shorten the time span of analysis for diagnosis confirmation. Molecular methods have high specificity and sensitivity and reduce the risk of infection for the laboratory personnel. In this study we reviewed the recently published data on the use of main molecular methods for diagnosis of histoplasmosis
How to obtain division algebras used for fast-decodable space-time block codes
We present families of unital algebras obtained through a doubling process from a cyclic central simple algebra D, employing a K-automorphism tau and an invertible element d in D. These algebras appear in the construction of iterated space-time block codes. We give conditions when these iterated algebras are division which can be used to construct fully diverse iterated codes. We also briefly look at algebras (and codes) obtained from variations of this method
Behavior of Metallic Inclusions in Uranium Dioxide
The mobility of micron-size powders of refractory and noble metals in UO{sub 2} was investigated under isothermal and temperature gradient conditions, The metal particles were initially placed between two polished surfaces of UO{sub 2} and any movement which occurred during high temperature annealing was determined microscopically. Tungsten and molybdenum particles 1 to 10 {micro}m in diameter were immobile in UO{sub 2} at 2500°C in a temperature gradient of 1400°C/cm. Ruthenium, however, dissolved into and spread through hypostoichiometric, polycrystalline urania and was found after isothermal annealing as the U-Ru intermetallic compound in the grain boundaries of the oxide. The mechanism does not involve bodily motion of the metal particles. Rather, ruthenium dissolves in the grain bmmdaries of the oxide, migrates as atoms via the same pathway, and reacts while migrating to form URu{sub 3}, This product grows as layers in the grain boundaries. Isothermal ruthenium spreading followed simple diffusion theory, and apparent solubilities and effective diffusivities were obtained from the data for the temperature nmge 2000 to 2300°C. In a temperature gradient, ruthenium moves to the hot zones of UO{sub 2}; the mechanism appears to be the same as found for isothermal spreading, but the extent of movement up the temperature gradient cannot be explained by simple diffusion theory, even with an appreciable Soret effect
Pion and proton showers in the CALICE scintillator-steel analogue hadron calorimeter
Showers produced by positive hadrons in the highly granular CALICE
scintillator-steel analogue hadron calorimeter were studied. The experimental
data were collected at CERN and FNAL for single particles with initial momenta
from 10 to 80 GeV/c. The calorimeter response and resolution and spatial
characteristics of shower development for proton- and pion-induced showers for
test beam data and simulations using Geant4 version 9.6 are compared.Comment: 26 pages, 16 figures, JINST style, changes in the author list, typos
corrected, new section added, figures regrouped. Accepted for publication in
JINS
The Time Structure of Hadronic Showers in highly granular Calorimeters with Tungsten and Steel Absorbers
The intrinsic time structure of hadronic showers influences the timing
capability and the required integration time of hadronic calorimeters in
particle physics experiments, and depends on the active medium and on the
absorber of the calorimeter. With the CALICE T3B experiment, a setup of 15
small plastic scintillator tiles read out with Silicon Photomultipliers, the
time structure of showers is measured on a statistical basis with high spatial
and temporal resolution in sampling calorimeters with tungsten and steel
absorbers. The results are compared to GEANT4 (version 9.4 patch 03)
simulations with different hadronic physics models. These comparisons
demonstrate the importance of using high precision treatment of low-energy
neutrons for tungsten absorbers, while an overall good agreement between data
and simulations for all considered models is observed for steel.Comment: 24 pages including author list, 9 figures, published in JINS
Shower development of particles with momenta from 15 GeV to 150 GeV in the CALICE scintillator-tungsten hadronic calorimeter
We present a study of showers initiated by electrons, pions, kaons, and
protons with momenta from 15 GeV to 150 GeV in the highly granular CALICE
scintillator-tungsten analogue hadronic calorimeter. The data were recorded at
the CERN Super Proton Synchrotron in 2011. The analysis includes measurements
of the calorimeter response to each particle type as well as measurements of
the energy resolution and studies of the longitudinal and radial shower
development for selected particles. The results are compared to Geant4
simulations (version 9.6.p02). In the study of the energy resolution we include
previously published data with beam momenta from 1 GeV to 10 GeV recorded at
the CERN Proton Synchrotron in 2010.Comment: 35 pages, 21 figures, 8 table
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