100 research outputs found
The behaviour of metal contaminants in silty sand and gravel
An investigative study is reported to determine the behaviour of metal contaminants in silty sand and gravel. A soil box experiment was conducted with a silty sand of permeability, k =
3.9242x10-5 m/s. The sand was placed on a bedding of 6 mm peagravel, inside the test box. Copper Nitrate, Chromium Nitrate, Nickel Sulphate and Lead Nitrate were dissolved, mixed with RO (reverse
osmosis) water for use in four separate experiments. Column tests were conducted with the same silty sand and gravel and under similar experimental conditions. Copper flushing was very slow, it was
strongly absorbed to the silty sand and gravel. Chromium was entirely retained (34mg/Kg) within the experimental system, and its released concentrations were very low. Nickel was shown to have a good aqueous solubility thus it was freely mobile in the sand. There was some minor adsorption of Nickel though lower than that of Copper and Chromium
Beam Cooling with ionisation losses
A novel type of particle "cooling", called Ionization Cooling, is applicable
to slow (v of the order of 0.1c) ions stored in a small ring. The many
traversals through a thin foil enhance the nuclear reaction probability, in a
steady configuration in which ionisation losses are recovered at each turn by a
RF-cavity. For a uniform target "foil" the longitudinal momentum spread
diverges exponentially since faster (slower) particles ionise less (more) than
the average. In order to "cool" also longitudinally, a chromaticity has to be
introduced with a wedge shaped "foil". Multiple scattering and straggling are
then "cooled" in all three dimensions, with a method similar to the one of
synchrotron cooling, but valid for low energy ions. Particles then stably
circulate in the beam indefinitely, until they undergo for instance nuclear
processes in the thin target foil. This new method is under consideration for
the nuclear production of a few MeV/A ion beams. Simple reactions, for instance
Li 7 + D Li 8 + p, are more favourably exploited with the heavier ion colliding
against a gas-jet D2 target. Kinematics is generally very favourable, with
emission angles in a narrow angular cone and a relatively concentrated outgoing
energy spectrum which allows an efficient collection as a neutral gas in a tiny
volume with a technology at high temperatures perfected at ISOLDE. It is
however of a much more general applicability. The method appears capable of
producing a "table top" storage ring with an accumulation rate in excess of
10**14 Li-8 radioactive ion/s for possible use for radioactive beams for
physics studies (for example for beta-beams) or for therapy.Comment: 27 pages, 11 figure
Muon Collider
Both e+e- and {\mu}+{\mu}- colliders have been proposed as possible
candidates for a lepton collider to complement and extend the reach of the
Large Hadron Collider (LHC) at CERN. The physics program that could be pursued
by a new lepton collider (e+e- or {\mu}+{\mu}-) with sufficient luminosity
would include understanding the mechanism behind mass generation and
electroweak symmetry breaking; searching for, and possibly discovering,
supersymmetric particles; and hunting for signs of extra spacetime dimensions
and quantum gravity. However, the appropriate energy reach for such a collider
is currently unknown, and will only be determined following initial physics
results at the LHC. It is entirely possible that such results will indicate
that a lepton collider with a collision energy well in excess of 1 TeV will be
required to illuminate the physics uncovered at LHC. Such a requirement would
require consideration of muons as the lepton of choice for such a collider.Comment: v.2., 6 pp. To appear in the 2nd edition of the book Elementary
Particles, Landolt-Boernstein Series published by Springer. arXiv admin note:
text overlap with arXiv:physics/9901022 by other autho
Rising trend and indications of caesarean section at the university of Maiduguri teaching hospital, Nigeria
Objective : To determine the trend and indications for the use of
caesarean delivery in our environment. Method : A retrospective review
of the caesarean sections performed at University of Maiduguri Teaching
Hospital from January 2000 to December 2005 inclusive. Results :
During the study period, there were 10,097 deliveries and 1192
caesarean sections giving a caesarean section rate of 11.8%. The major
maternal indications were cephalopelvic disproportion (15.5%), previous
caesarean section (14.7%), eclampsia (7.2%), failed induction of labor
(5.5%), and placenta previa (5.1%). Fetal distress (9.6%), breech
presentation (4.7%), fetal macrosomia (4.3%), and pregnancy complicated
by multiple fetuses (4.2%) were the major fetal indications. The
caesarean section rate showed a steady increase over the years (7.20%
in 2000-13.95% in 2005), but yearly analysis of the demographic
characteristics, type of caesarean section, and the major indications
did not reveal any consistent changes to account for the rising trend
except for the increasing frequency of fetal distress as an indication
of caesarean section over the years, which was also not statistically
significant (\u3c7[2] =8.08; P=0.12). The overall perinatal mortality
in the study population was found to be 72.7/1000 birth and despite the
rising rate of caesarean section, the perinatal outcomes did not
improve over the years. Conclusion : Trial of vaginal birth after
caesarean section in appropriate cases and use of cardiotocography for
continuous fetal heart rate monitoring in labor with confirmation of
suspected fetal distress through fetal blood acid--base study are
recommended. A prospective study may reveal some of the other reasons
for the increasing caesarean section rate
Status of Muon Collider Research and Development and Future Plans
The status of the research on muon colliders is discussed and plans are
outlined for future theoretical and experimental studies. Besides continued
work on the parameters of a 3-4 and 0.5 TeV center-of-mass (CoM) energy
collider, many studies are now concentrating on a machine near 0.1 TeV (CoM)
that could be a factory for the s-channel production of Higgs particles. We
discuss the research on the various components in such muon colliders, starting
from the proton accelerator needed to generate pions from a heavy-Z target and
proceeding through the phase rotation and decay ()
channel, muon cooling, acceleration, storage in a collider ring and the
collider detector. We also present theoretical and experimental R & D plans for
the next several years that should lead to a better understanding of the design
and feasibility issues for all of the components. This report is an update of
the progress on the R & D since the Feasibility Study of Muon Colliders
presented at the Snowmass'96 Workshop [R. B. Palmer, A. Sessler and A.
Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics
(Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].Comment: 95 pages, 75 figures. Submitted to Physical Review Special Topics,
Accelerators and Beam
Asteroseismology and Interferometry
Asteroseismology provides us with a unique opportunity to improve our
understanding of stellar structure and evolution. Recent developments,
including the first systematic studies of solar-like pulsators, have boosted
the impact of this field of research within Astrophysics and have led to a
significant increase in the size of the research community. In the present
paper we start by reviewing the basic observational and theoretical properties
of classical and solar-like pulsators and present results from some of the most
recent and outstanding studies of these stars. We centre our review on those
classes of pulsators for which interferometric studies are expected to provide
a significant input. We discuss current limitations to asteroseismic studies,
including difficulties in mode identification and in the accurate determination
of global parameters of pulsating stars, and, after a brief review of those
aspects of interferometry that are most relevant in this context, anticipate
how interferometric observations may contribute to overcome these limitations.
Moreover, we present results of recent pilot studies of pulsating stars
involving both asteroseismic and interferometric constraints and look into the
future, summarizing ongoing efforts concerning the development of future
instruments and satellite missions which are expected to have an impact in this
field of research.Comment: Version as published in The Astronomy and Astrophysics Review, Volume
14, Issue 3-4, pp. 217-36
Understanding how immigrant entrepreneurs view business opportunity formation through ethnicity
Given that international research is now consistently showing higher rates of entrepreneurial activity from immigrants above native people, research regarding our understanding of how immigrant entrepreneurs view business opportunity formation remains underdeveloped. Based upon a review of the literature, this chapter examines how ethnicity relates to business opportunity formation through constant interactions. It also introduces the Visual Mixed Embeddedness Framework as an empirical lens for understanding the differences in the business opportunity formation process models between immigrant and native entrepreneurs. By explaining how factors and traits from both home and host countries impact upon the immigrant entrepreneurial business activity process, the framework clearly identifies how the concept of ethnicity influences immigrant entrepreneurial opportunity formation activities in different ways. The framework contributes to existing knowledge by offering a novel method for examining the influence on business opportunity formation of ethnicity, the role of home and host countries and variations between immigrant and native entrepreneurs
Next generation sequencing analysis of nine Corynebacterium ulcerans isolates reveals zoonotic transmission and a novel putative diphtheria toxin-encoding pathogenicity island
Background: Toxigenic Corynebacterium ulcerans can cause a diphtheria-like illness in humans and have been found in domestic animals, which were suspected to serve as reservoirs for a zoonotic transmission. Additionally, toxigenic C. ulcerans were reported to take over the leading role in causing diphtheria in the last years in many industrialized countries. Methods: To gain deeper insights into the tox gene locus and to understand the transmission pathway in detail, we analyzed nine isolates derived from human patients and their domestic animals applying next generation sequencing and comparative genomics. Results: We provide molecular evidence for zoonotic transmission of C. ulcerans in four cases and demonstrate the superior resolution of next generation sequencing compared to multi-locus sequence typing for epidemiologic research. Additionally, we provide evidence that the virulence of C. ulcerans can change rapidly by acquisition of novel virulence genes. This mechanism is exemplified by an isolate which acquired a prophage not present in the corresponding isolate from the domestic animal. This prophage contains a putative novel virulence factor, which shares high identity with the RhuM virulence factor from Salmonella enterica but which is unknown in Corynebacteria so far. Furthermore, we identified a putative pathogenicity island for C. ulcerans bearing a diphtheria toxin gene. Conclusion: The novel putative diphtheria toxin pathogenicity island could provide a new and alternative pathway for Corynebacteria to acquire a functional diphtheria toxin-encoding gene by horizontal gene transfer, distinct from the previously well characterized phage infection model. The novel transmission pathway might explain the unexpectedly high number of toxigenic C. ulcerans
First-principles quantum transport modeling of spin-transfer and spin-orbit torques in magnetic multilayers
We review a unified approach for computing: (i) spin-transfer torque in
magnetic trilayers like spin-valves and magnetic tunnel junction, where
injected charge current flows perpendicularly to interfaces; and (ii)
spin-orbit torque in magnetic bilayers of the type
ferromagnet/spin-orbit-coupled-material, where injected charge current flows
parallel to the interface. Our approach requires to construct the torque
operator for a given Hamiltonian of the device and the steady-state
nonequilibrium density matrix, where the latter is expressed in terms of the
nonequilibrium Green's functions and split into three contributions. Tracing
these contributions with the torque operator automatically yields field-like
and damping-like components of spin-transfer torque or spin-orbit torque
vector, which is particularly advantageous for spin-orbit torque where the
direction of these components depends on the unknown-in-advance orientation of
the current-driven nonequilibrium spin density in the presence of spin-orbit
coupling. We provide illustrative examples by computing spin-transfer torque in
a one-dimensional toy model of a magnetic tunnel junction and realistic
Co/Cu/Co spin-valve, both of which are described by first-principles
Hamiltonians obtained from noncollinear density functional theory calculations;
as well as spin-orbit torque in a ferromagnetic layer described by a
tight-binding Hamiltonian which includes spin-orbit proximity effect within
ferromagnetic monolayers assumed to be generated by the adjacent monolayer
transition metal dichalcogenide.Comment: 22 pages, 9 figures, PDFLaTeX; prepared for Springer Handbook of
Materials Modeling, Volume 2 Applications: Current and Emerging Material
Wastewater dephosphorization using crude clays
The present work aims to establish the possibility of using local clays
to treat wastewater. Thus, three clay samples extracted from two
localities in the south of Côte d Ivoire have been studied in
their crude state. The qualitative physicochemical study that consisted
in measurement of pH variation and argillaceous particles zeta
potential showed that the Nieki-Agneby clay and the Beige Anyama clay
presented disposal to uptake phosphate ions in solution at pH 5. For
each clay, it is shown that the tension accompanying the sorption of a
phosphate ion could be estimated to -5 mV. Differences in their
composition and in the number of hydrating molecules of water were also
accessible. The quantitative study performed with the Nieki-Agneby clay
thereafter consisted following the sorption kinetic. The adsorption was
found to reach the maximum after 5 h. of exchange, and almost 400
μg phosphate ions in per gram of clay were fixed. Future studies
will focus on the modification of these materials in order to increase
their sorption capacity
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