In this paper, we study the time-harmonic scalar equation describing the propagation of acoustic waves in the Sun’s atmosphere under ideal atmospheric assumptions. We use the Liouville change of unknown to conjugate the original problem to a Schrödinger equation with a Coulomb-type potential. This transformation makes appear a new wavenumber, k, and the link with the Whittaker’s equation. We consider two different problems: in the first one, with the ideal atmospheric assumptions extended to the whole space, we construct explicitly the Schwartz kernel of the resolvent, starting from a solution given by Hostler and Pratt in punctured domains, and use this to construct outgoing solutions and radiation conditions. In the second problem, we construct exact Dirichlet-to-Neumann map using Whittaker functions, and new radiation boundary conditions (RBC), using gauge functions in terms of k. The new approach gives rise to simpler RBC for the same precision compared to existing ones. The robustness of our new RBC is corroborated by numerical experiments.

We prove Weyl type of asymptotic formulas for the real and the complex internal transmission eigenvalues when the domain is a ball and the index of refraction is constant.

| on behalf of the VIZIONS consortium †This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. The detection of HEV RNA in pigs indicates that HEV may be a zoonotic disease risk in this location, although a larger sample size is required to infer an association between HEV positivity in pigs and seroprevalence in humans. K E Y W O R D Shepatitis E virus, human, pigs, prevalence, seroprevalence, Vietnam, zoonosis

We investigate numerically the inverse problem of locating small circular obstacles in a homogeneous medium from multi-frequency back-scattered data limited to four angles of incidence. The main novelty of our paper is working with the position of the obstacles as parameter space in the frame work of full-waveform inversion (FWI) procedure. The computational cost of FWI is lowered by using a method based on single-layer potential. Reconstruction results are shown up to twenty-four obstacles, from initial guesses allowed to be far from the target. In experiments with six obstacles, we supplement the reconstruction with an analysis of the performance of the nonlinear conjugate gradient and quasi-Newton methods, in used with various line search algorithms.

We investigate efficient methods to simulate the multiple scattering of obstacles in homogeneous media. With a large number of small obstacles on a large domain, optimized pieces of software based on spatial discretization such as Finite Element Method (FEM) or Finite Difference lose their robustness. As an alternative, we work with an integral equation method, which uses singlelayer potentials and truncation of Fourier series to describe the approximate scattered field. In the theoretical part of the paper, we describe in detail the linear systems generated by the method for impenetrable obstacles, accompanied by a well-posedness study. For the numerical performance study, we limit ourselves to the case of circular obstacles. We first compare and validate our codes with the highly optimized FEM-based software Montjoie. Secondly, we investigate the efficiency of different solver types (direct and iterative of type GMRES) in solving the dense linear system generated by the method. We observe the robustness of direct solvers over iterative ones for closely-spaced obstacles, and that of GMRES with Lower-Upper Symmetric Gauss-Seidel and Symmetric Gauss-Seidel preconditioners for far-apart obstacles.

Background MDR bacteria including carbapenem-resistant Pseudomonas aeruginosa are recognized as an important cause of hospital-acquired infections worldwide. This investigation seeks to determine the molecular characterization and antibiotic resistance genes associated with carbapenem-resistant P. aeruginosa. Methods We conducted WGS and phylogenetic analysis of 72 carbapenem-resistant P. aeruginosa isolated from hospital-acquired infection patients from August 2011 to March 2015 in three major hospitals in Hanoi, Vietnam. Results We identified three variants of IMP gene, among which blaIMP-15 was the most frequent (n = 34) in comparison to blaIMP-26 (n = 2) and blaIMP-51 (n = 12). We observed two isolates with imipenem MIC >128 mg/L that co-harboured blaIMP-15 and blaDIM-1 genes and seven isolates (imipenem MIC > 128 mg/L) with a blaKPC-1 gene from the same hospital. MLST data shows that these 72 isolates belong to 18 STs and phylogenetic tree analysis has divided these isolates into nine groups. Conclusions Our results provide evidence that not only blaIMP-26 but other IMP variants such as blaIMP-15 and blaIMP-51 genes and several STs (ST235, ST244, ST277, ST310, ST773 and ST3151) have been disseminating in healthcare settings in Vietnam. In addition, we report the emergence of two isolates belonging to ST1240 and ST3340 that harboured two important carbapenemase genes (blaIMP-15 and blaDIM-1) and seven isolates belonging to ST3151 of P. aeruginosa that carried the blaKPC-1 gene in Vietnam, which could potentially cause serious restricted availability of treatment options in healthcare settings.

A Gram-stain-negative, non-motile, facultatively anaerobic and rod-shaped bacterial strain, designated PAMC 28131T, was isolated from a sea surface microlayer sample in the open water of the Pacific Ocean. Phylogenetic analysis of the 16S rRNA gene sequence of strain PAMC 28131T revealed an affiliation to the genus Sandaracinobacter with the closest species Sandaracinobacter sibiricus RB16-17T (sequence similarity of 98.2 %). Strain PAMC 28131T was able to grow optimally with 0.5–1.0 % NaCl and at pH 6.5–7.0 and 30 °C. The polar lipids were phosphatidylglycerol, phosphatidylethanolamine, two unidentified phospholipids, an unidentified aminolipid, an unidentified glycolipid and an unidentified lipid. The major cellular fatty acids (>10 %) were C18 : 1  ω6c and/or C18 : 1  ω7c, (42.6 %), C17 : 1  ω6c (19.3 %) and C16 : 1  ω6c and/or C16 : 1  ω7c (15.8 %), and the respiratory quinone was Q-10. The genomic DNA G+C content was 65.3 mol%. The phylogenetic, phenotypic and chemotaxonomic data showed that strain PAMC 28131T could be clearly distinguished from S. sibiricus RB16-17T. Thus, strain PAMC 28131T should be classified as representing a novel species in the genus Sandaracinobacter , for which the name Sandaracinobacter neustonicus sp. nov. is proposed. The type strain is PAMC 28131T (=KCCM 43127T=JCM 30734T).

For a fluid-solid interaction problem with Lipschitz interface, we investigate the partial Fréchet differentiability of the solutions and the approximate far-fieldpattern with respect to solid material parameters. Differentiability is shown in standard Sobolev framework, and the derivatives are characterized as solutions to inhomogeneous fluid-solid transmission problems. To validate the accuracy of the characterization, we compare analytical values with numerical ones given by Interior Penalty Discontinuous Galerkin (IPDG) in a setting with circular obstacles. Our comparisons also show that IPDG gives results with high precision and incurs almost no effect of discretization error accumulation.