2,489 research outputs found
Geometric and Radiometric Correction of Multibeam Backscatter Derived from Reson 8101 Systems
A common by-product of multibeam surveys is a measure of the backscattered acoustic intensity from the seafloor. These data are of immense interest to geologists and geoscientists since maps of the acoustic backscatter strength can be used to infer physical properties of the sea bottom, such as impedance, roughness and volume inhomogeneity. Before such maps can be created from multibeam acoustic backscatter data, however, two tasks must be performed.
1. The data must be geographically registered using the bathymetric profile collected by the multibeam (which accounts for full orientation and refraction), as opposed to using the traditional flat-seafloor assumption. This allows us to additionally calculate the true grazing angle. 2. The signal intensities must be reduced to as close a measure of the backscatter strength of the seafloor as possible by radiometrically correcting the data on a ping-by-ping basis for variables such as transmission power, beam pattern, receiver gain, and pulse length.
The purpose of this research project is to develop software tools to perform the above corrections for a massive backlog of RESON SeaBat 8101 multibeam data, as collected by the NOAA ship Rainier. While the backscatter logged by the multibeam systems is not of prime importance to NOAAâs hydrographic charting mandate, they recognize the potential value of this data to the work of other sister agencies such as the U.S. Geological Survey (who is funding this project). The particular problems encountered with these data are that.
Up to the end of 2001 field season, the backscatter data acquired by this system were collected from dedicated receiver beams, separate from those used for bathymetry. This receive beam is broad in the elevation plane (similar to a sidescan sonar) so that the variation in elevation angle with time must be indirectly inferred from the corresponding bathymetric profile.
As some backscatter data are collected from slant-ranges beyond which bathymetric data are acquired, for that case the imaging geometry must be either inferred using a simple slope model, or derived from neighbouring swaths.
Results of the application of full geometric and radiometric corrections will be presented
Validated Numerical Approximation of Stable Manifolds for Parabolic Partial Differential Equations
This paper develops validated computational methods for studying infinite dimensional stable manifolds at equilibrium solutions of parabolic PDEs, synthesizing disparate errors resulting from numerical approximation. To construct our approximation, we decompose the stable manifold into three components: a finite dimensional slow component, a fast-but-finite dimensional component, and a strongly contracting infinite dimensional âtailâ. We employ the parameterization method in a finite dimensional projection to approximate the slow-stable manifold, as well as the attached finite dimensional invariant vector bundles. This approximation provides a change of coordinates which largely removes the nonlinear terms in the slow stable directions. In this adapted coordinate system we apply the Lyapunov-Perron method, resulting in mathematically rigorous bounds on the approximation errors. As a result, we obtain significantly sharper bounds than would be obtained using only the linear approximation given by the eigendirections. As a concrete example we illustrate the technique for a 1D Swift-Hohenberg equation.</p
Phase behaviour of binary mixtures of diamagnetic colloidal platelets in an external magnetic field
Using fundamental measure density functional theory we investigate
paranematic-nematic and nematic-nematic phase coexistence in binary mixtures of
circular platelets with vanishing thicknesses. An external magnetic field
induces uniaxial alignment and acts on the platelets with a strength that is
taken to scale with the platelet area. At particle diameter ratio lambda=1.5
the system displays paranematic-nematic coexistence. For lambda=2, demixing
into two nematic states with different compositions also occurs, between an
upper critical point and a paranematic-nematic-nematic triple point. Increasing
the field strength leads to shrinking of the coexistence regions. At high
enough field strength a closed loop of immiscibility is induced and phase
coexistence vanishes at a double critical point above which the system is
homogeneously nematic. For lambda=2.5, besides paranematic-nematic coexistence,
there is nematic-nematic coexistence which persists and hence does not end in a
critical point. The partial orientational order parameters along the binodals
vary strongly with composition and connect smoothly for each species when
closed loops of immiscibility are present in the corresponding phase diagram.Comment: 9 pages, to appear in J.Phys:Condensed Matte
Quantum horizons and black hole entropy: Inclusion of distortion and rotation
Equilibrium states of black holes can be modelled by isolated horizons. If
the intrinsic geometry is spherical, they are called type I while if it is
axi-symmetric, they are called type II. The detailed theory of geometry of
\emph{quantum} type I horizons and the calculation of their entropy can be
generalized to type II, thereby including arbitrary distortions and rotations.
The leading term in entropy of large horizons is again given by 1/4th of the
horizon area for the \emph{same} value of the Barbero-Immirzi parameter as in
the type I case. Ideas and constructions underlying this extension are
summarized.Comment: 9 page
Effect of mineralocorticoid receptor antagonists on proteinuria and progression of chronic kidney disease: a systematic review and meta-analysis
Background:
Hypertension and proteinuria are critically involved in the progression of chronic kidney disease. Despite treatment with renin angiotensin system inhibition, kidney function declines in many patients. Aldosterone excess is a risk factor for progression of kidney disease. Hyperkalaemia is a concern with the use of mineralocorticoid receptor antagonists. We aimed to determine whether the renal protective benefits of mineralocorticoid antagonists outweigh the risk of hyperkalaemia associated with this treatment in patients with chronic kidney disease.
Methods:
We conducted a meta-analysis investigating renoprotective effects and risk of hyperkalaemia in trials of mineralocorticoid receptor antagonists in chronic kidney disease. Trials were identified from MEDLINE (1966â2014), EMBASE (1947â2014) and the Cochrane Clinical Trials Database. Unpublished summary data were obtained from investigators. We included randomised controlled trials, and the first period of randomised cross over trials lasting â„4Â weeks in adults.
Results:
Nineteen trials (21 study groups, 1 646 patients) were included. In random effects meta-analysis, addition of mineralocorticoid receptor antagonists to renin angiotensin system inhibition resulted in a reduction from baseline in systolic blood pressure (â5.7 [â9.0, â2.3] mmHg), diastolic blood pressure (â1.7 [â3.4, â0.1] mmHg) and glomerular filtration rate (â3.2 [â5.4, â1.0] mL/min/1.73Â m2). Mineralocorticoid receptor antagonism reduced weighted mean protein/albumin excretion by 38.7Â % but with a threefold higher relative risk of withdrawing from the trial due to hyperkalaemia (3.21, [1.19, 8.71]). Death, cardiovascular events and hard renal end points were not reported in sufficient numbers to analyse.
Conclusions:
Mineralocorticoid receptor antagonism reduces blood pressure and urinary protein/albumin excretion with a quantifiable risk of hyperkalaemia above predefined study upper limit
Multipole Moments of Isolated Horizons
To every axi-symmetric isolated horizon we associate two sets of numbers,
and with , representing its mass and angular
momentum multipoles. They provide a diffeomorphism invariant characterization
of the horizon geometry. Physically, they can be thought of as the `source
multipoles' of black holes in equilibrium. These structures have a variety of
potential applications ranging from equations of motion of black holes and
numerical relativity to quantum gravity.Comment: 25 pages, 1 figure. Minor typos corrected, reference adde
Disentangling the role of environmental processes in galaxy clusters
In this work we present the results of a novel approach devoted to
disentangle the role of the environmental processes affecting galaxies in
clusters. This is based on the analysis of the NUV-r' distributions of a large
sample of star-forming galaxies in clusters spanning more than four absolute
magnitudes. The galaxies inhabit three distinct environmental regions: virial
regions, cluster infall regions and field environment. We have applied rigorous
statistical tests in order to analyze both, the complete NUV-r' distributions
and their averages for three different bins of r'-band galaxy luminosity down
to M_r' ~ -18, throughout the three environmental regions considered. We have
identified the environmental processes that significantly affect the
star-forming galaxies in a given luminosity bin by using criteria based on the
characteristics of these processes: their typical time-scales, the regions
where they operate and the galaxy luminosity range for which their effects are
more intense. We have found that the high-luminosity (M_r'<=-20) star-forming
galaxies do not show significant signs in their star formation activity neither
of being affected by the environment in the last ~10^8 yr nor of a sudden
quenching in the last 1.5 Gyr. The intermediate-luminosity (-20<M_r'<=-19)
star-forming galaxies appear to be affected by starvation in the virial regions
and by the harassment both, in the virial and infall regions. Low-luminosity
(-19<M_r'<=-18.2) star-forming galaxies seem to be affected by the same
environmental processes as intermediate-luminosity star-forming galaxies in a
stronger way, as it would be expected for their lower luminosities.Comment: 42 pages, 7 figures, 5 tables; accepted for publication in Ap
The effect of dicyclohexylamine and fumagillin on Nosema ceranae-infected honey bee (Apis mellifera) mortality in cage trial assays
International audienceAbstractBoth commercially available fumagillin-based treatments for honey bees (Apis mellifera), Fumagilin-BÂź as well as Fumidil-BÂź, contain the reportedly genotoxic and tumorigenic compound dicyclohexylamine (DCH) as the counter ion in the fumagillin-DCH salt. The effect of DCH, purified fumagillin (containing no DCH), and the commercial formulation Fumagilin-BÂź (containing both fumagillin as well as DCH) on the mortality of caged Nosema ceranae-infected honey bees was investigated. A statistically significant risk of bee mortality associated with oral exposure to DCH was observed. DCH is also known to be significantly more stable than fumagillin in honey under a variety of temperature conditions, both in the presence and absence of light. The presence of DCH in the hive is therefore a potential concern for bee health and also for food safety
Evaluation of Fumagilin-BÂź and other potential alternative chemotherapies against Nosema ceranae-infected honeybees (Apis mellifera) in cage trial assays
International audienceAbstractFumagilin-BÂź is the only currently registered chemical treatment available to combat nosema disease in apiculture. Fumagillol, the basic hydrolysis product of fumagillin, two semisynthetic fumagillin analogues, and four in-house purely synthetic compounds which were designed to mimic the mode of action of fumagillin against the methionine aminopeptidase type 2 (MetAP-2) enzyme, was observed to exhibit statistically significant biological activity against Nosema ceranae-infected caged bees. None of these compounds were, however, as effective as Fumagilin-BÂź. The commercially available thymol and enilconazole also exhibited activity against N. ceranae, with thymol being the most promising chemical treatment other than Fumagilin-BÂź. High cumulative bee mortality was associated with the therapeutic dosage of Fumagilin-BÂź during our study, suggesting the need for continued investigation
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