2,211 research outputs found
Hard-wall Potential Function for Transport Properties of Alkali Metals Vapor
This study demonstrates that the transport properties of alkali metals are
determined principally by the repulsive wall of the pair interaction potential
function. The (hard-wall) Lennard-Jones(15-6) effective pair potential function
is used to calculate transport collision integrals. Accordingly, reduced
collision integrals of K, Rb, and Cs metal vapors are obtained from
Chapman-Enskog solution of the Boltzman equation. The law of corresponding
states based on the experimental-transport reduced collision integral is used
to verify the validity of a LJ(15-6) hybrid potential in describing the
transport properties. LJ(8.5-4) potential function and a simple thermodynamic
argument with the input PVT data of liquid metals provide the required
molecular potential parameters. Values of the predicted viscosity of monatomic
alkali metals vapor are in agreement with typical experimental data with the
average absolute deviation 2.97% for K in the range 700-1500 K, 1.69% for Rb,
and 1.75% for Cs in the range 700-2000 K. In the same way, the values of
predicted thermal conductivity are in agreement with experiment within 2.78%,
3.25%, and 3.63% for K, Rb, and Cs, respectively. The LJ(15-6) hybrid potential
with a hard-wall repulsion character conclusively predicts best transport
properties of the three alkali metals vapor.Comment: 21 pages, 5 figures, 41 reference
Classical gravitational spin-spin interaction
I obtain an exact, axially symmetric, stationary solution of Einstein's
equations for two massless spinning particles. The term representing the
spin-spin interaction agrees with recently published approximate work. The
spin-spin force appears to be proportional to the inverse fourth power of the
coordinate distance between the particles.Comment: six pages, no figures, journal ref:accepted for Classical and Quantum
Gravit
Risk Factors associated with Intestinal Parasitic Infections on School Children in Thika District, Central Kenya
The effective prevention and control of intestinal parasitic infections requires the identification of risk factors that contribute to their transmission, among high risk groups.
Objectives: To determine the prevalence and associated risk factors of intestinal parasitic infections among school children in public primary schools in Thika district.
Methods: A cross-sectional study, involving 377 schoolchildren, was conducted in Thika District Central Kenya. Interviews, observation, and anthropometric indices assessment were used to identify the risk factors predisposing the children to infections with parasites. Stool specimens were examined using Katz method for helminthes and formal ether concentration techniques for protozoan infections. Data was analysed using SPSS version.
Results: Ten species of intestinal parasites were identified. Ascaris lumbricoides 74 (19.6%) and hookworm 50 (13.3%) while Entamoeba histolytica and Entamoeba coli were the common protozoa in the study area. A higher prevalence of Ascaris lumbricoides was reported among children in the slums. Entamoeba histolytica infection was associated with eating raw tubers and fruits (p< 0.001) in rural children. Iodamoeba bustchili infection was significantly associated with stunted children in rural children. Several factors contribute to high prevalence of intestinal parasites in school going children in Thika District.
Keywords: Risk factors, school-age, children, Anthropometrics indice
Transmission of Information in Active Networks
Shannon's Capacity Theorem is the main concept behind the Theory of
Communication. It says that if the amount of information contained in a signal
is smaller than the channel capacity of a physical media of communication, it
can be transmitted with arbitrarily small probability of error. This theorem is
usually applicable to ideal channels of communication in which the information
to be transmitted does not alter the passive characteristics of the channel
that basically tries to reproduce the source of information. For an {\it active
channel}, a network formed by elements that are dynamical systems (such as
neurons, chaotic or periodic oscillators), it is unclear if such theorem is
applicable, once an active channel can adapt to the input of a signal, altering
its capacity. To shed light into this matter, we show, among other results, how
to calculate the information capacity of an active channel of communication.
Then, we show that the {\it channel capacity} depends on whether the active
channel is self-excitable or not and that, contrary to a current belief,
desynchronization can provide an environment in which large amounts of
information can be transmitted in a channel that is self-excitable. An
interesting case of a self-excitable active channel is a network of
electrically connected Hindmarsh-Rose chaotic neurons.Comment: 15 pages, 5 figures. submitted for publication. to appear in Phys.
Rev.
Three-dimensional antiferromagnetic q-state Potts models: application of the Wang-Landau algorithm
We apply a newly proposed Monte Carlo method, the Wang-Landau algorithm, to
the study of the three-dimensional antiferromagnetic q-state Potts models on a
simple cubic lattice. We systematically study the phase transition of the
models with q=3, 4, 5 and 6. We obtain the finite-temperature phase transition
for q= 3 and 4, whereas the transition temperature is down to zero for q=5. For
q=6 there exists no order for all the temperatures. We also study the
ground-state properties. The size-dependence of the ground-state entropy is
investigated. We find that the ground-state entropy is larger than the
contribution from the typical configurations of the broken-sublattice-symmetry
state for q=3. The same situations are found for q = 4, 5 and 6.Comment: 9 pages including 9 eps figures, RevTeX, to appear in J. Phys.
Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer for the Radiation Belt Storm Probes Mission
The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 %. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance
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