The actual impedance of non-reflecting boundary conditions : implications for the computation of resonators

Non-reflecting boundary conditions are essential elements in the computation of many compressible flows: such simulations are very sensitive to the treatment of acoustic waves at boundaries. Non-reflecting conditions allow acoustic waves to propagate through boundaries with zero or small levels of reflection into the domain. However, perfectly non-reflecting conditions must be avoided because they can lead to ill-posed problems for the mean flow. Various methods have been proposed to construct boundary conditions which can be sufficiently non-reflecting for the acoustic field while still making the mean-flow problem well posed. This paper analyses a widely-used technique for non-reflecting outlets (Rudy and Strikwerda, Poinsot and Lele). It shows that the correction introduced by these authors can lead to large reflection levels and non-physical resonant behaviors. A simple scaling is proposed to evaluate the relaxation coefficient used in theses methods for a non-reflecting outlet. The proposed scaling is tested for simple cases (ducts) both theoretically and numerically

ISGRI: the INTEGRAL Soft Gamma-Ray Imager

For the first time in the history of high energy astronomy, a large CdTe gamma-ray camera is operating in space. ISGRI is the low-energy camera of the IBIS telescope on board the INTEGRAL satellite. This paper details its design and its in-flight behavior and performances. Having a sensitive area of 2621 cm$^2$ with a spatial resolution of 4.6 mm, a low threshold around 12 keV and an energy resolution of $\sim$ 8% at 60 keV, ISGRI shows absolutely no signs of degradation after 9 months in orbit. All aspects of its in-flight behavior and scientific performance are fully nominal, and in particular the observed background level confirms the expected sensitivity of 1 milliCrab for a 10$^6$s observation.Comment: INTEGRAL A&A special issu

Enhancing backcross programs through increased recombination

International audienceBackground; Introgression of a quantitative trait locus (QTL) by successive backcrosses is used to improve elite lines (recurrent parent) by introducing alleles from exotic material (donor parent). In the absence of selection, the proportion of the donor genome decreases by half at each generation. However, since selection is for the donor allele at the QTL, elimination of the donor genome around that QTL will be much slower than in the rest of the genome (i.e. linkage drag). Using markers to monitor the genome around the QTL and in the genetic background can accelerate the return to the recurrent parent genome. Successful introgression of a locus depends partly on the occurrence of crossovers at favorable positions. However, the number of crossovers per generation is limited and their distribution along the genome is heterogeneous. Recently, techniques have been developed to modify these two recombination parameters.Results: In this paper, we assess, by simulations in the context of Brassicaceae, the effect of increased recombination on the efficiency of introgression programs by studying the decrease in linkage drag and the recovery of the recurrent genome. The simulated selection schemes begin by two generations of foreground selection and continue with one or more generations of background selection. Our results show that, when the QTL is in a region that initially lacked crossovers, an increase in recombination rate can decrease linkage drag by nearly ten-fold after the foreground selection and improves the return to the recurrent parent. However, if the QTL is in a region that is already rich in crossovers, an increase in recombination rate is detrimental.Conclusions: Depending on the recombination rate in the region targeted for introgression, increasing it can be beneficial or detrimental. Thus, the simulations analysed in this paper help us understand how an increase in recombination rate can be beneficial. They also highlight the best methods that can be used to increase recombination rate, depending on the situation

Assessing by Modeling the Consequences of Increased Recombination in Recurrent Selection of Oryza sativa and Brassica rapa

Meiotic recombination generates genetic diversity but in most species the number of crossovers per meiosis is limited. Previous modeling studies showed that increasing recombination can enhance response to selection. However, such studies did not assume a specific method of modifying recombination. Our objective was to test whether two methods used to increase recombination in plants could increase genetic gain in a population undergoing recurrent selection such as in genomic selection programs. The first method, in Oryza sativa, used a mutant of anti-crossover genes, increasing global recombination without affecting the recombination landscape shape. The second one used the ploidy level of a cross between Brassica rapa and Brassica napus, increasing recombination especially in pericentromeric regions. Our modeling framework used these recombination landscapes and sampled quantitative trait loci positions from the actual gene distributions. We simulated selection programs with initially a cross between two inbred lines, for two species. Increased recombination enhanced the response to selection. The amount of enhancement in the cumulative gain largely depended on the species and the number of quantitative trait loci (2, 10, 20, 50, 200 or 1000 per chromosome). Genetic gains were increased up to 30% after 20 generations. Furthermore, increasing recombination in cold regions was the most effective: the gain was larger by 25% with the first method and 34% with the second one in B. rapa, and 12% compared to 16% in O. sativa. In summary, increased recombination enhances the genetic gain in long-term selection programs, with visible effects after four to five generations

Application of temperature and pH responsive microhydrogels for functional finishing of cotton fabric

This paper discusses the developing of an innovative strategy for functional finishing of cotton by application of surface modifying systems based on stimuli responsive microparticulate hydrogels. Dual responsive hydrogels in the microscale were prepared using a temperature responsive synthetic polymer (poly-NiPAAm) and a pH responsive biopolymer (chitosan). The physicochemical characterisation and the stimuli responsiveness of the microparticulate systems have been investigated by microscopy and spectrophotometric techniques, and dynamic light scattering. In an attempt to enhance the incorporation of microparticulate hydrogel to cotton surface, carboxymethylation and aminisation methods for cotton activation have been assessed. Surface modified textile material with incorporated microparticles has been characterised by SEM and XPS techniques in order to determine surface morphology and chemical structure. The capability of the material to respond to different stimuli (pH, temperature, humidity) was studied through swelling/shrinking or hydration/dehydration kinetics and equilibrium using a gravimetric method

Attachment of beta-Cyclodextrins on Cotton and Influence of beta-Cyclodextrin on Ester Formation with BTCA on Cotton

Cotton was treated with beta-cyclodextrin (BCD) and two derivatives of beta-cyclodextrin (2-hydroxypropyl-beta-cyclodextrin and monochlorotriazinyl-beta-cyclodextrin) to assess the optimal type for fixation with cotton. The experimental results showed that treatment of cotton with BCD using the crosslinker BTCA resulted in higher fixation than the treatments with the other two derivatives. The concentration of BTCA used did not significantly influence the amount of fixation of BCD on cotton. FTIR-ATR spectroscopic analysis showed that the amount of ester formed on the fabric was influenced by the addition of BCD on cotton with BTCA in comparison to crosslinking of only BTCA with cotton. The laundering tests showed relatively poor washfastness of the beta-cyclodextrins on the fabrics

Hierarchical macroporosity induced by constrained syneresis in core-shell polysaccharide composites

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