18,916 research outputs found
An alternative approach to the solution of a class of Wiener-Hopf and related problems Technical report no. 8
Alternative method to Weiner-Hopf approach for solving radiation and diffraction problem
A technique for solving certain Wiener-Hopf type boundary value problems Technical report no. 9
Technique for solving Weiner-Hopf type boundary value problem
Emergence of steady and oscillatory localized structures in a phytoplankton-nutrient model
Co-limitation of marine phytoplankton growth by light and nutrient, both of
which are essential for phytoplankton, leads to complex dynamic behavior and a
wide array of coherent patterns. The building blocks of this array can be
considered to be deep chlorophyll maxima, or DCMs, which are structures
localized in a finite depth interior to the water column. From an ecological
point of view, DCMs are evocative of a balance between the inflow of light from
the water surface and of nutrients from the sediment. From a (linear)
bifurcational point of view, they appear through a transcritical bifurcation in
which the trivial, no-plankton steady state is destabilized. This article is
devoted to the analytic investigation of the weakly nonlinear dynamics of these
DCM patterns, and it has two overarching themes. The first of these concerns
the fate of the destabilizing stationary DCM mode beyond the center manifold
regime. Exploiting the natural singularly perturbed nature of the model, we
derive an explicit reduced model of asymptotically high dimension which fully
captures these dynamics. Our subsequent and fully detailed study of this model
- which involves a subtle asymptotic analysis necessarily transgressing the
boundaries of a local center manifold reduction - establishes that a stable DCM
pattern indeed appears from a transcritical bifurcation. However, we also
deduce that asymptotically close to the original destabilization, the DCM
looses its stability in a secondary bifurcation of Hopf type. This is in
agreement with indications from numerical simulations available in the
literature. Employing the same methods, we also identify a much larger DCM
pattern. The development of the method underpinning this work - which, we
expect, shall prove useful for a larger class of models - forms the second
theme of this article
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Using airborne laser altimetry to improve river flood extents delineated from SAR data
Flood extent maps derived from SAR images are a useful source of data for validating hydraulic models of river flood flow. The accuracy of such maps is reduced by a number of factors, including changes in returns from the water surface caused by different meteorological conditions and the presence of emergent vegetation. The paper describes how improved accuracy can be achieved by modifying an existing flood extent delineation algorithm to use airborne laser altimetry (LiDAR) as well as SAR data. The LiDAR data provide an additional constraint that waterline (land-water boundary) heights should vary smoothly along the flooded reach. The method was tested on a SAR image of a flood for which contemporaneous aerial photography existed, together with LiDAR data of the un-flooded reach. Waterline heights of the SAR flood extent conditioned on both SAR and LiDAR data matched the corresponding heights from the aerial photo waterline significantly more closely than those from the SAR flood extent conditioned only on SAR data
Principle of scaling in a uniaxial medium scientific report no. 6
Solution to Maxwell equations for source currents in unbounded magnetoionic medium for which dielectric tensor is uniaxia
Methods of isolation and identification of pathogenic and potential pathogenic bacteria from skins and tannery effluents
Currently there is no standard protocol available within the leather industry to isolate and identify pathogenic bacteria from hides, skins or tannery effluent. This study was therefore carried out to identify simple but effective methods for isolation and identification of bacterial pathogens from the effluent and skins during leather processing. Identification methods based on both phenotypic and genotypic characteristics were investigated. Bacillus cereus and Pseudomonas aeruginosa were used as indicator bacteria to evaluate the isolation and identification methods. Decontaminated calfskins were inoculated with a pure culture of the above mentioned bacterial species followed by a pre-tanning and chromium tanning processes. Effluent samples were collected and skins were swabbed at the end of each processing stage. Bacterial identification was carried out based on the phenotypic characteristics; such as colony appearance on selective solid media, cell morphology following a standard Gram-staining and spore staining techniques, and biochemical reactions, e.g., the ability of a bacterial species to ferment particular sugars and ability to produce certain enzymes. Additionally, an identification system based on bacterial phenotypic characteristics, known as BiologĀ® system was applied. A pulsed-filed gel electrophoresis (PFGE) method for bacterial DNA fingerprinting was also evaluated and used for the identification of the inoculated bacteria. The methods described in the study were found to be effective for the identification of pathogenic bacteria from skins and effluent
Longtime behavior of nonlocal Cahn-Hilliard equations
Here we consider the nonlocal Cahn-Hilliard equation with constant mobility
in a bounded domain. We prove that the associated dynamical system has an
exponential attractor, provided that the potential is regular. In order to do
that a crucial step is showing the eventual boundedness of the order parameter
uniformly with respect to the initial datum. This is obtained through an
Alikakos-Moser type argument. We establish a similar result for the viscous
nonlocal Cahn-Hilliard equation with singular (e.g., logarithmic) potential. In
this case the validity of the so-called separation property is crucial. We also
discuss the convergence of a solution to a single stationary state. The
separation property in the nonviscous case is known to hold when the mobility
degenerates at the pure phases in a proper way and the potential is of
logarithmic type. Thus, the existence of an exponential attractor can be proven
in this case as well
Finite to infinite steady state solutions, bifurcations of an integro-differential equation
We consider a bistable integral equation which governs the stationary
solutions of a convolution model of solid--solid phase transitions on a circle.
We study the bifurcations of the set of the stationary solutions as the
diffusion coefficient is varied to examine the transition from an infinite
number of steady states to three for the continuum limit of the
semi--discretised system. We show how the symmetry of the problem is
responsible for the generation and stabilisation of equilibria and comment on
the puzzling connection between continuity and stability that exists in this
problem
An analysis of the global pharmacy workforce capacity trends from 2006 to 2012
Background: Human resources for health are at a critical low. The World Health Organization estimates that the
current shortage of health workers, including pharmacists, is in excess of 7.2 million worldwide and that, by 2035,the shortage will reach 12.9 million. Pharmacists, in particular, are lacking in the workforce in many countries. The International Pharmaceutical Federation (FIP) and academic partners have conducted periodic global pharmacy workforce surveys in 2006, 2009 and 2012 which have monitored and reported on the status of the pharmacy
workforce at the country and territory levels. This current analysis is a synthesis of workforce capacity data from
these date points to provide an overview of the global trends and changes to pharmacy workforce capacity over
this time period.
Methods: The methodology proceeded with accessing workforce capacity data collated in 2006, 2009 and 2012
held on file at the FIP Collaborating Centre. This data had previously been validated and made available to WHO
Human Resources for Health. The data focused (due to limitations from 2006 databank) on pharmacist workforce
capacity. Countries and territories were identified that had data available across at least two of the three time
points (2006, 2009 and 2012). Missing time-point data for some countries (data gaps) were subject, where possible,
to literature and online data searching to capture possible missing data. Country-level capacity data were plotted
against time to identify trends coupled with comparative analysis of the trends.
Results: The countries and territories identified as having valid data for each of the time points 2006, 2009 and
2012 were present in all WHO regions, with Europe having the most countries with data available and South East
Asia the fewest.
All WHO regions have experienced an increase in the density of pharmacists (measured as number of pharmacists
per 10 000 population) over the period 2006ā2012. However, some countries show a reduction in the density of
pharmacists. African countries show large relative increases in acceleration of capacity building but remain
significantly behind in terms of absolute capacity per capita. South East Asian and Middle Eastern countries also
show large proportional changes in pharmacist workforce.
Conclusion: The global trend is an increase in workforce across all nations and regions, and this is a move in the right
direction towards improved access to, and availability of, pharmaceutical expertise. However, there is still much to be
done, with some regions and low-income countries still displaying a disproportionately low number of pharmacists on
small overall capacity for delivering pharmacy service
Goals, Strategies and First Discoveries of AO327, the Arecibo All-Sky 327 MHz Drift Pulsar Survey
We report initial results from AO327, a drift survey for pulsars with the
Arecibo telescope at 327 MHz. The first phase of AO327 will cover the sky at
declinations of -1 to 28 degrees, excluding the region within 5 degrees of the
Galactic plane, where high scattering and dispersion make low-frequency surveys
sub-optimal. We record data from a 57 MHz bandwidth with 1024 channels and 125
us sampling time. The 60 s transit time through the AO327 beam means that the
survey is sensitive to very tight relativistic binaries even with no
acceleration searches. To date we have detected 44 known pulsars with periods
ranging from 3 ms to 2.21 s and discovered 24 new pulsars. The new discoveries
include three millisecond pulsars, three objects with periods of a few tens of
milliseconds typical of young as well as mildly recycled pulsars, a nuller, and
a rotating radio transient. Five of the new discoveries are in binary systems.
The second phase of AO327 will cover the sky at declinations of 28 to 38
degrees. We compare the sensitivity and search volume of AO327 to the Green
Bank North Celestial Cap survey and the GBT350 drift survey, both of which
operate at 350 MHz.Comment: Accepted for publication in Ap
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