1,952 research outputs found
Ultracold homonuclear and heteronuclear collisions in metastable helium
Scattering and ionizing cross sections and rates are calculated for ultracold
collisions between metastable helium atoms using a fully quantum-mechanical
close-coupled formalism. Homonuclear collisions of the bosonic HeHe and fermionic HeHe systems, and
heteronuclear collisions of the mixed HeHe system,
are investigated over a temperature range 1 K to 1 K. Carefully
constructed Born-Oppenheimer molecular potentials are used to describe the
electrostatic interaction between the colliding atoms, and complex optical
potentials used to represent loss through ionization from the
states. Magnetic spin-dipole mediated transitions from the
state are included and results reported for spin-polarized and unpolarized
systems. Comparisons are made with experimental results, previous
semi-classical models, and a perturbed single channel model.Comment: 14 pages, 9 figure
Border parasites: schistosomiasis control among Uganda's fisherfolk
Copyright @ 2012 Taylor & Francis. This article has been made publically available through the Brunel Open Access Publishing Fund.It is recognized that the control of schistosomisais in Uganda requires a focus on
fisherfolk. Large numbers suffer from this water-borne parasitic disease; notably along the shores of lakes Albert and Victoria and along the River Nile. Since 2004, a policy has been adopted of providing drugs, free of charge, to all those at risk. The strategy has been reported to be successful, but closer investigation reveals serious problems. This paper draws upon long-term research undertaken at three locations in northwestern and southeastern Uganda. It highlights consequences of not engaging with the day to day realities of fisherfolk
livelihoods; attributable, in part, to the fact that so many fisherfolk live and work in places located at the country’s international borders, and to a related
tendency to treat them as "feckless" and "ungovernable". Endeavours to roll out
treatment end up being haphazard, erratic and location-specific. In some places,
concerted efforts have been made to treat fisherfolk; but there is no effective
monitoring, and it is difficult to gauge what proportion have actually swallowed
the tablets. In other places, fisherfolk are, in practice, largely ignored, or are
actively harassed in ways that make treatment almost impossible. At all sites, the current reliance upon resident "community" drug distributors or staff based at static clinics and schools was found to be flawed.The Schistosomiasis Control Initiative, Imperial College, under the auspices of the Bill and Melinda Gates Foundation
Ultracold collisions in tight harmonic traps: Quantum defect model and application to metastable helium atoms
We analyze a system of two colliding ultracold atoms under strong harmonic
confinement from the viewpoint of quantum defect theory and formulate a
generalized self-consistent method for determining the allowed energies. We
also present two highly efficient computational methods for determining the
bound state energies and eigenfunctions of such systems. The perturbed harmonic
oscillator problem is characterized by a long asymptotic region beyond the
effective range of the interatomic potential. The first method, which is based
on quantum defect theory and is an adaptation of a technique developed by one
of the authors (GP) for highly excited states in a modified Coulomb potential,
is very efficient for integrating through this outer region. The second method
is a direct numerical solution of the radial Schr\"{o}dinger equation using a
discrete variable representation of the kinetic energy operator and a scaled
radial coordinate grid. The methods are applied to the case of trapped
spin-polarized metastable helium atoms. The calculated eigenvalues agree very
closely for the two methods, and with those computed self-consistently using
the generalized self-consistent method.Comment: 11 pages,REVTEX, text substantially revised, title modifie
Ultracold collisions in metastable helium
Photoassociation processes are studied in ultracold collisions between different isotopes of metastable
He(2^3S) and He(2^3P) atoms; Penning and associative ionization rates for collisions between two He(2^3S) atoms are also obtained. Comparisons are made with data from existing experiments
Hot DQ White Dwarfs: Something Different
We present a detailed analysis of all the known Hot DQ white dwarfs in the
Fourth Data Release of the Sloan Digital Sky Survey (SDSS) recently found to
have carbon dominated atmospheres. Our spectroscopic and photometric analysis
reveals that these objects all have effective temperatures between ~18,000 and
24,000 K. The surface composition is found to be completely dominated by
carbon, as revealed by the absence of Hbeta and HeI 4471 lines (or
determination of trace amount in a few cases). We find that the surface gravity
of all objects but one seems to be ''normal'' and around log g = 8.0 while one
is likely near log g = 9.0. The presence of a weak magnetic field is directly
detected by spectropolarimetry in one object and is suspected in two others. We
propose that these strange stars could be cooled down versions of the weird
PG1159 star H1504+65 and form a new family of hydrogen and helium deficient
objects following the post-AGB phase. Finally, we present the results of full
nonadiabatic calculations dedicated specifically to each of the Hot DQ that
show that only SDSS J142625.70+575218.4 is expected to exhibit luminosity
variations. This result is in excellent agreement with recent observations by
Montgomery et al. who find that J142625.70+575218.4 is the only pulsator among
6 Hot DQ white dwarfs surveyed in February 2008.Comment: 33 pages, 7 figures, accepted for publication in Ap
Civil and forensic patients : comparing demographics, risk factors, and negative life events
OBJECTIVES: This investigation centres on how the mentally ill with a forensic admission compare to the mentally ill with a civil admission, and investigates who inpatients with a forensic and civil admission are, and how the risk factors and negative historical events they have experienced compare or differ. THEORETICAL BASE: Using a risk and resilience framework, risk factors that are deleterious to healthy development are used as variables.
METHODS: The records of all adult inpatients both forensic and civil, aged 18 to 89 at admission in two U.S. mountain region public psychiatric hospitals were included in the sample (n=1768). All patients are assessed using the Colorado Clinical Assessment Record (CCAR) which, measures a diverse set of variables including Current Issues, History of Issues, Demographics, and Disabilities.
OUTCOMES: Civil and forensic patients have more in common than differences. Both samples compare more closely to risk factors and negative historical events than they do to the general population. However, this begins to break down once the sample is separated by gender.
SOCIAL WORK IMPLICATIONS: Social Workers who work in prison systems need to become more familiar with mental illness interventions. Additionally, social workers should both educate law enforcement about de-escalation tactics with the mentally ill and intervene on mental health related police calls. On the macro level, social workers should advocate for the mentally ill to be housed in psychiatric hospitals rather than be imprisoned where they will often not receive inpatient psychiatric care
Use of seasonal trend decomposition to understand groundwater behaviour in the Permo-Triassic Sandstone aquifer, Eden Valley, UK
The daily groundwater level (GWL) response in the Permo-Triassic Sandstone aquifers in the Eden Valley, England (UK), has been studied using the seasonal trend decomposition by LOESS (STL) technique. The hydrographs from 18 boreholes in the Permo-Triassic Sandstone were decomposed into three components: seasonality, general trend and remainder. The decomposition was analysed first visually, then using tools involving a variance ratio, time-series hierarchical clustering and correlation analysis. Differences and similarities in decomposition pattern were explained using the physical and hydrogeological information associated with each borehole. The Penrith Sandstone exhibits vertical and horizontal heterogeneity, whereas the more homogeneous St Bees Sandstone groundwater hydrographs characterize a well-identified seasonality; however, exceptions can be identified. A stronger trend component is obtained in the silicified parts of the northern Penrith Sandstone, while the southern Penrith, containing Brockram (breccias) Formation, shows a greater relative variability of the seasonal component. Other boreholes drilled as shallow/deep pairs show differences in responses, revealing the potential vertical heterogeneities within the Penrith Sandstone. The differences in bedrock characteristics between and within the Penrith and St Bees Sandstone formations appear to influence the GWL response. The de-seasonalized and de-trended GWL time series were then used to characterize the response, for example in terms of memory effect (autocorrelation analysis). By applying the STL method, it is possible to analyse GWL hydrographs leading to better conceptual understanding of the groundwater flow. Thus, variation in groundwater response can be used to gain insight into the aquifer physical properties and understand differences in groundwater behaviour
Modeling the adiabatic connection in Hâ‚‚
Full configuration interaction (FCI) data are used to quantify the accuracy of approximate adiabatic connection (AC) forms in describing the ground state potential energy curve of H2, within spin-restricted density functional theory (DFT). For each internuclear separation R, accurate properties of the AC are determined from large basis set FCI calculations. The parameters in the approximate AC form are then determined so as to reproduce these FCI values exactly, yielding an exchange-correlation energy expressed entirely in terms of FCI-derived quantities. This is combined with other FCI-derived energy components to give the total electronic energy; comparison with the FCI energy quantifies the accuracy of the AC form. Initial calculations focus on a [1/1]-Padé-based form. The potential energy curve determined using the procedure is a notable improvement over those from existing DFT functionals. The accuracy near equilibrium is quantified by calculating the bond length and vibrational wave numbers; errors in the latter are below 0.5%. The molecule dissociates correctly, which can be traced to the use of virtual orbital eigenvalues in the slope in the noninteracting limit, capturing static correlation. At intermediate R, the potential energy curve exhibits an unphysical barrier, similar to that noted previously using the random phase approximation. Alternative forms of the AC are also considered, paying attention to size extensivity and the behavior in the strong-interaction limit; none provide an accurate potential energy curve for all R, although good accuracy can be achieved near equilibrium. The study demonstrates how data from correlated ab initio calculations can provide valuable information about AC forms and highlight areas where further theoretical progress is required
Charge Exchange Processes between Excited Helium and Fully Stripped Ions
We made a classical trajectory Monte Carlo (CTMC) calculation of state
selective cross sections for processes between some light ions and excited
helium. The results, useful for analysis of spectroscopic data of fusion
devices, are in good agreement with theoretical predictions of scaling laws.Comment: LaTex, 8 pages, 4 figures (available on request to the authors),
DFPD/94/TH/57, to be published in Phys. Rev.
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