4,437 research outputs found
Asymptotic behaviour of multiple scattering on infinite number of parallel demi-planes
The exact solution for the scattering of electromagnetic waves on an infinite
number of parallel demi-planes has been obtained by J.F. Carlson and A.E. Heins
in 1947 using the Wiener-Hopf method. We analyze their solution in the
semiclassical limit of small wavelength and find the asymptotic behaviour of
the reflection and transmission coefficients. The results are compared with the
ones obtained within the Kirchhoff approximation
Dual production of polyhydroxyalkanoates and antibacterial/antiviral gold nanoparticles
Gold nanoparticles (AuNPs) have been explored for their use in medicine. Here, we report a sustainable, and cost-effective method to produce AuNPs using a bacterial strain such as Pseudomonas mendocina CH50 which is also known to be a polyhydroxyalkanoate (PHA) producer. A cell-free bacterial supernatant, which is typically discarded after PHA extraction, was used to produce spherical AuNPs of 3.5 ± 1.5 nm in size as determined by Transmission Electron Microscopy (TEM) analysis. The AuNPs/PHA composite coating demonstrated antibacterial activity against Staphylococcus aureus 6538P, and antiviral activity, with a 75% reduction in viral infectivity against SARS-CoV-2 pseudotype virus
Detection of the heavy Higgs boson at colliders
We consider the possibility of detecting a heavy Higgs boson () in
proposed colliders through the semi-leptonic mode . We show that
due to the non-monochromatic nature of the photon beams produced by the
laser-backscattering method, the resultant cross section for Higgs production
is much smaller than the on-resonance cross section and generally {\it
decreases} with increasing collider energy. Although continuum production
is expected to be negligible, we demonstrate the presence of and calculate
sizeable backgrounds from ,
with , respectively, and
.
This channel may be used to detect a Higgs of mass up to around 350~GeV
at a 0.5~TeV collider, assuming a nominal yearly luminosity of
10--20~fb.Comment: 18 pages (in RevTeX) plus Postscript figures (available by email or
FAX), NUHEP-TH-92-29 and DOE-309-CPP-47. (Revised version: NO CHANGES to the
manuscript, simply removed corrupted figure files
Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations
Ongoing millimeter VLBI observations with the Event Horizon Telescope allow
unprecedented study of the innermost portion of black hole accretion flows.
Interpreting the observations requires relativistic, time-dependent physical
modeling. We discuss the comparison of radiative transfer calculations from
general relativistic MHD simulations of Sagittarius A* and M87 with current and
future mm-VLBI observations. This comparison allows estimates of the viewing
geometry and physical conditions of the Sgr A* accretion flow. The viewing
geometry for M87 is already constrained from observations of its large-scale
jet, but, unlike Sgr A*, there is no consensus for its millimeter emission
geometry or electron population. Despite this uncertainty, as long as the
emission region is compact, robust predictions for the size of its jet
launching region can be made. For both sources, the black hole shadow may be
detected with future observations including ALMA and/or the LMT, which would
constitute the first direct evidence for a black hole event horizon.Comment: 8 pages, 2 figures, submitted to the proceedings of AHAR 2011: The
Central Kiloparse
Analysis of exchange terms in a projected ERPA Theory applied to the quasi-elastic (e,e') reaction
A systematic study of the influence of exchange terms in the longitudinal and
transverse nuclear response to quasi-elastic (e,e') reactions is presented. The
study is performed within the framework of the extended random phase
approximation (ERPA), which in conjuction with a projection method permits a
separation of various contributions tied to different physical processes. The
calculations are performed in nuclear matter up to second order in the residual
interaction for which we take a (pi+rho)-model with the addition of the
Landau-Migdal g'-parameter. Exchange terms are found to be important only for
the RPA-type contributions around the quasielastic peak.Comment: 29 pages, 6 figs (3 in postscript, 3 faxed on request), epsf.st
Upstream passage of adult sea trout (Salmo trutta) at a low-head weir with an Archimedean screw hydropower turbine and co-located fish pass
© 2018 CSIRO. The exploitation of riverine systems for renewable energy has resulted in large numbers of small-scale hydropower schemes on low-head weirs. Although considered a clean and 'green' energy source in terms of emissions, hydropower can affect upstream migrating species by diverting flow away from viable routes over the impoundment and attract fish towards the turbine outfall. In an attempt to reduce this negative effect, hydropower outfalls with co-located fish-passage entrances are recommended, utilising turbine flows to attract fish towards the fish pass. The present study used acoustic telemetry to understand the performance of a co-located Larinier fish pass at a low-head hydropower scheme at a weir on the tidal Yorkshire Esk, England. The majority of the sea trout (anadromous Salmo trutta L) individuals that approached the impediment were attracted to the hydropower and the co-located fish pass. Fish ascended through the pass under a wide range of river flows, tide heights, downstream river levels and hydropower flows, and there was no evidence that the hydropower operation affected fish-pass ascent. The information presented is urgently required to inform management decisions on the operation of hydropower schemes during the migratory period of salmonid fish, and help determine best-practice designs and operation at these facilities
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Development of an ultrasound training curriculum in a limited resource international setting: successes and challenges of ultrasound training in rural Rwanda
Background: Over the last decade, the diffusion of ultrasound technology to nontraditional users has been rapid and far-reaching. Much research and effort has been focused on developing an ultrasound curriculum and training and practice guidelines for these users. The potential for this diagnostic tool is not limited to the developed world and in many respects ultrasound is adaptable to limited resource international settings. However, needs-based curriculum development, training guidelines, impact on resource utilization, and sustainability are not well studied in the developing world setting. Aims: We review one method of introducing applicable curriculum, training local providers, and sustaining a comprehensive ultrasound program. Methods: Two rural Rwandan hospitals affiliated with a US nongovernmental organization participated in a pilot ultrasound training program. Prior to introduction of ultrasound, local physicians completed a survey to determine the perceived importance of various ultrasound scan types. Hospital records were also reviewed to determine disease and presenting complaint prevalence as part of an initial needs assessment and to define our curriculum. We hypothesized certain studies would be more utilized and have a greater impact given available treatment resources. Results: We review here the choice of curriculum, the training plan, helpful equipment specifications, and implementation of ongoing measures of quality assessment and sustainability. Our 9-week lecture and practice-based ultrasound curriculum included obstetrics, abdominal, renal, hepatobiliary, cardiac, pleural, vascular, and procedural ultrasound. Conclusions: While ultrasound as a diagnostic modality for resource-poor parts of the world has generated interest for years, recent advances in technology have brought ultrasound again to the forefront as a sustainable and high impact technology for resource-poor developing world nations. From our experience in rural Rwanda, we conclude that ultrasound remains helpful in patient care and the diagnostic impact is enhanced by choosing the correct applications to implement. We also conclude that ultrasound is a teachable skill, with a several week intensive training period involving hands-on practice skills and plans for long-term learning and have begun a second phase of evaluating knowledge retention for this introductory program
Astrochemical models of interstellar ices: History matters
Ice is ubiquitous in the interstellar medium. We model the formation of the
main constituents of interstellar ices, including H2O, CO2 , CO, and CH3 OH. We
strive to understand what physical or chemical parameters influence the final
composition of the ice and how they benchmark to what has already been
observed, with the aim of applying these models to the preparation and analysis
of JWST observations. We used the Nautilus gas-grain model, which computes the
gas and ice composition as a function of time for a set of physical conditions,
starting from an initial gas phase composition. All important processes
(gas-phase reactions, gas-grain interactions, and grain surface processes) are
included and solved with the rate equation approximation. We first ran an
astrochemical code for fixed conditions of temperature and density mapped in
the cold core L429-C to benchmark the chemistry. One key parameter was revealed
to be the dust temperature. When the dust temperature is higher than 12 K, CO2
will form efficiently at the expense of H2O, while at temperatures below 12 K,
it will not form. Whatever hypothesis we assumed for the chemistry (within
realistic conditions), the static simulations failed to reproduce the observed
trends of interstellar ices in our target core. In a second step, we simulated
the chemical evolution of parcels of gas undergoing different physical and
chemical situations throughout the molecular cloud evolution and starting a few
1e7 yr prior to the core formation (dynamical simulations). Our dynamical
simulations satisfactorily reproduce the main trends already observed for
interstellar ices. Moreover, we predict that the apparent constant ratio of
CO2/H2O observed to date is probably not true for regions of low AV , and that
the history of the evolution of clouds plays an essential role, even prior to
their formation.Comment: Accepted for publication in A&
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