411 research outputs found
Wave scattering by small bodies and creating materials with a desired refraction coefficient
Asymptotic solution to many-body wave scattering problem is given in the case
of many small scatterers. The small scatterers can be particles whose physical
properties are described by the boundary impedances, or they can be small
inhomogeneities, whose physical properties are described by their refraction
coefficients. Equations for the effective field in the limiting medium are
derived. The limit is considered as the size of the particles or
inhomogeneities tends to zero while their number tends to infinity.
These results are applied to the problem of creating materials with a desired
refraction coefficient. For example, the refraction coefficient may have
wave-focusing property, or it may have negative refraction, i.e., the group
velocity may be directed opposite to the phase velocity. This paper is a review
of the author's results presented in MR2442305 (2009g:78016), MR2354140
(2008g:82123), MR2317263 (2008a:35040), MR2362884 (2008j:78010), and contains
new results.Comment: In this paper the author's invited plenary talk at the 7-th PACOM
(PanAfrican Congress of Mathematicians), is presente
High frequency limit of the Transport Cross Section and boundedness of the Total Cross Section in scattering by an obstacle with impedance boundary conditions
The scalar scattering of the plane wave by a strictly convex obstacle with
impedance boundary conditions is considered. The uniform boundedness of the
Total Cross Section for all values of frequencies is proved. The high frequency
limit of the Transport Cross Section is founded and presented as a classical
functional of the variational theory
Spectral properties of the Dirichlet-to-Neumann operator for exterior Helmholtz problem and its applications to scattering theory
We prove that the Dirichlet-to-Neumann operator (DtN) has no spectrum in the
lower half of the complex plane. We find several application of this fact in
scattering by obstacles with impedance boundary conditions. In particular, we
find an upper bound for the gradient of the scattering amplitude and for the
total cross section. We justify numerical approximations by providing bounds on
difference between theoretical and approximated solutions without using any a
priory unknown constants
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Implementation of passive samplers for monitoring volatile organic compounds in ground water at the Kansas City Plant
Passive sampling for monitoring volatile organic compounds (VOCs) has been suggested as a possible replacement to the traditional bailer method used at the Department of Energy Kansas City Plant (KCP) for routine groundwater monitoring. To compare methods, groundwater samples were collected from 19 KCP wells with VOC concentrations ranging from non-detectable to > 100,000 {micro}g/L. Analysis of the data was conducted using means and medians of multiple measurements of TCE, 1,2-DCE, 1,1-DCE and VC. All 95% confidence intervals of these VOCs overlap, providing evidence that the two methods are similar. The study also suggests that elimination of purging and decontamination of sampling equipment reduces the labor required to sample by approximately 32%. Also, because the passive method generates no waste water, there are no associated disposal costs. The results suggest evidence to continue studies and efforts to replace traditional bailer methods with passive sampling at KCP based on cost and the similarity of the methods
Time-resolved single-particle x-ray scattering reveals electron-density as coherent plasmonic-nanoparticle-oscillation source
Dynamics of optically-excited plasmonic nanoparticles are presently
understood as a series of sequential scattering events, involving
thermalization processes after pulsed optical excitation. One important step is
the initiation of nanoparticle breathing oscillations. According to established
experiments and models, these are caused by the statistical heat transfer from
thermalized electrons to the lattice. An additional contribution by hot
electron pressure has to be included to account for phase mismatches that arise
from the lack of experimental data on the breathing onset. We used optical
transient-absorption spectroscopy and time-resolved single-particle
x-ray-diffractive imaging to access the excited electron system and lattice.
The time-resolved single-particle imaging data provided structural information
directly on the onset of the breathing oscillation and confirmed the need for
an additional excitation mechanism to thermal expansion, while the observed
phase-dependence of the combined structural and optical data contrasted
previous studies. Therefore, we developed a new model that reproduces all our
experimental observations without using fit parameters. We identified
optically-induced electron density gradients as the main driving source.Comment: 32 pages, 5 figures, 1 supporting information document include
Carbon States in Carbon-Encapsulated Nickel Nanoparticles Studied by Means of X-Ray Absorption, Emission, and Photoelectron Spectroscopies
Electronic structure of nickel nanoparticles encapsulated in carbon was
characterized by photoelectron, X-ray absorption, and X-ray emission
spectroscopies. Experimental spectra are compared with the density of states
calculated in the frame of the density functional theory. The carbon shell of
Ni nanoparticles has been found to be multilayer graphene with significant
(about 6%) amount of Stone--Wales defects. Results of the experiments evidence
protection of the metallic nanoparticles from the environmental degradation by
providing a barrier against oxidation at least for two years. Exposure in air
for 2 years leads to oxidation only of the carbon shell of Ni@C nanoparticles
with coverage of functional groups.Comment: 16 pages, 6 figures, accepted in J. Phys. Chem.
Lectin-like bacteriocins from pseudomonas spp. utilise D-rhamnose containing lipopolysaccharide as a cellular receptor
Lectin-like bacteriocins consist of tandem monocot mannose-binding domains and display a genus-specific killing activity. Here we show that pyocin L1, a novel member of this family from Pseudomonas aeruginosa, targets susceptible strains of this species through recognition of the common polysaccharide antigen (CPA) of P. aeruginosa lipopolysaccharide that is predominantly a homopolymer of d-rhamnose. Structural and biophysical analyses show that recognition of CPA occurs through the C-terminal carbohydrate-binding domain of pyocin L1 and that this interaction is a prerequisite for bactericidal activity. Further to this, we show that the previously described lectin-like bacteriocin putidacin L1 shows a similar carbohydrate-binding specificity, indicating that oligosaccharides containing d-rhamnose and not d-mannose, as was previously thought, are the physiologically relevant ligands for this group of bacteriocins. The widespread inclusion of d-rhamnose in the lipopolysaccharide of members of the genus Pseudomonas explains the unusual genus-specific activity of the lectin-like bacteriocins
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Temporal Expression of Chemokines Dictates the Hepatic Inflammatory Infiltrate in a Murine Model of Schistosomiasis
Schistosomiasis continues to be an important cause of parasitic morbidity and mortality world-wide. Determining the molecular mechanisms regulating the development of granulomas and fibrosis will be essential for understanding how schistosome antigens interact with the host environment. We report here the first whole genome microarray analysis of the murine liver during the progression of Schistosoma japonicum egg-induced granuloma formation and hepatic fibrosis. Our results reveal a distinct temporal relationship between the expression of chemokine subsets and the recruitment of cells to the infected liver. Genes up-regulated earlier in the response included T- and B-cell chemoattractants, reflecting the early recruitment of these cells illustrated by flow cytometry. The later phases of the response corresponded with peak recruitment of eosinophils, neutrophils, macrophages and myofibroblasts/hepatic stellate cells (HSCs) and the expression of chemokines with activity for these cells including CCL11 (eotaxin 1), members of the Monocyte-chemoattractant protein family (CCL7, CCL8, CCL12) and the Hepatic Stellate Cell/Fibrocyte chemoattractant CXCL1. Peak expression of macrophage chemoattractants (CCL6, CXCL14) and markers of alternatively activated macrophages (e.g. Retnla) during this later phase provides further evidence of a role for these cells in schistosome-induced pathology. Additionally, we demonstrate that CCL7 immunolocalises to the fibrotic zone of granulomas. Furthermore, striking up-regulation of neutrophil markers and the localisation of neutrophils and the neutrophil chemokine S100A8 to fibrotic areas suggest the involvement of neutrophils in S. japonicum-induced hepatic fibrosis. These results further our understanding of the immunopathogenic and, especially, chemokine signalling pathways that regulate the development of S. japonicum-induced granulomas and fibrosis and may provide correlative insight into the pathogenesis of other chronic inflammatory diseases of the liver where fibrosis is a common feature
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