Ultrasound to Enhance a Liquid–Liquid Reaction

Liquid–liquid mass transfer with ultrasound was investigated experimentally during the hydrolysis of n-amyl acetate. Power ultrasound is supposed to improve the yield and kinetics of such multiphase chemical reactions thanks to the mechanical effects of cavitation. Indeed, implosion of micro-bubbles at the vicinity of the liquid– liquid interface generates disruption of this surface, and enhances mixing in the liquid around the inclusion, thus improving mass transfer between the two phases. This effect has been demonstrated here on the hydrolysis of n-amyl acetate by sodium hydroxide, a rather slow reaction but influenced by mass transfer; the reaction is carried out in a glass jacketed reactor, 500 mL of volume, equipped with a Rushton turbine and a 20 kHz sonotrode dipping in the solution. The ester is initially pure in the organic dispersed phase, and sodium hydroxide has an initial concentration of 300 mol/m3; one of the products, pentanol partitions between the two phases and the sodium salt stays in the aqueous phase. The initial apparent reaction rate is measured from the record of the conductivity giving the concentration of alkali versus time. The reaction rate was always found to increase when ultrasound is superimposed to mechanical stirring (at 600 rpm), with a positive influence of input power (20 and 50 W). When varying initial concentration (300 and 600 mol/m3), temperature (36 and 45°C) and ultrasound emitter (sonotrode or cuphorn), the benefit of ultrasound over mechanical agitation was systematic. The only case of a weak influence of ultrasound was the sonication of a dense medium, containing 23% of organic phase and impeding the propagation of ultrasound

D-brane Models with Non-Linear Supersymmetry

We study a class of type I string models with supersymmetry broken on the world-volume of some D-branes and vanishing tree-level potential. Despite the non-supersymmetric spectrum, supersymmetry is non-linearly realized on these D-branes, while it is spontaneously broken in the bulk by Scherk-Schwarz boundary conditions. These models can easily accommodate 3-branes with interesting gauge groups and chiral fermions. We also study the effective field theory and in particular we compute the four-fermion couplings of the localized Goldstino with the matter fermions on the brane.We study a class of type I string models with supersymmetry broken on the world-volume of some D-branes and vanishing tree-level potential. Despite the non-supersymmetric spectrum, supersymmetry is non-linearly realized on these D-branes, while it is spontaneously broken in the bulk by Scherk-Schwarz boundary conditions. These models can easily accommodate 3-branes with interesting gauge groups and chiral fermions. We also study the effective field theory and in particular we compute the four-fermion couplings of the localized Goldstino with the matter fermions on the brane.We study a class of type I string models with supersymmetry broken on the world-volume of some D-branes and vanishing tree-level potential. Despite the non-supersymmetric spectrum, supersymmetry is non-linearly realized on these D-branes, while it is spontaneously broken in the bulk by Scherk–Schwarz boundary conditions. These models can easily accommodate 3-branes with interesting gauge groups and chiral fermions. We also study the effective field theory and in particular we compute the four-fermion couplings of the localized goldstino with the matter fermions on the brane

Stability in multi-skill workforce scheduling

This paper analyzes stability in multi-skill workforce schedules. In our stability analysis, we extend the notion of blocking pairs as stated in the Marriage model of Gale-Shapley. It is shown that finding stable schedules is NP-Hard. In some special cases stable schedules can be constructed in polynomial time. An integer linear programming model is proposed to decrease the instability of schedules

Contact interactions in D-brane models

We compute the tree-level four-point scattering amplitudes in string models where matter fields live on D-brane intersections. Extracting the contribution of massless modes, we are left with dimension-six four-fermion operators which in general receive contributions from three different sources: exchange of massive Kaluza--Klein excitations, winding modes and string oscillator states. We compute their coefficients and extract new bounds on the string scale in the brane-world scenario. This is contrasted with the situation where matter fields arise from open strings with both ends confined on the same collection of D-branes, in which case the exchange of massive string modes leads to dimension-eight operators that have been studied in the past. When matter fields live on brane intersections, the presence of dimension-six operators increases the lower bound on the string scale to 2--3 TeV, independently of the number of large extra dimensions.Comment: 27 pages, 1 eps figure, uses JHEP.cls. One reference added. Use of low energy precision electroweak data increased the bounds on the string scale to 2--3 Te

The temperature dependence of the isothermal bulk modulus at 1 bar pressure

It is well established that the product of the volume coefficient of thermal expansion and the bulk modulus is nearly constant at temperatures higher than the Debye temperature. Using this approximation allows predicting the values of the bulk modulus. The derived analytical solution for the temperature dependence of the isothermal bulk modulus has been applied to ten substances. The good correlations to the experiments indicate that the expression may be useful for substances for which bulk modulus data are lacking

A modern Fizeau experiment for education and outreach purposes

On the occasion of the laser's 50th anniversary, we performed a modern Fizeau experiment, measuring the speed of light with a laser beam passing over the city centre of Marseille. For a round trip distance of almost five kilometers, the measurement has reached an uncertainty of about 10$^{-4}$, mainly due to atmospheric fluctuations. We present the experimental and pedagogical challenges of this brilliant outreach experiment.Comment: accepted by Eur J Phys in november 201

PULSED LASER AND ELECTRON BEAM INDUCED DIFFUSION OF ANTIMONY IN SILICON

The aim of this work is to compare the diffusion into silicon of a thin film (~ 100 Å) of deposited antimony induced either by a pulsed laser irradiation or electron beam and to interpret the different experimental behaviours as observed by Rutherford backscattering spectrometry, by using the calculated temperature distributions obtained by solving the heat flow equation for the two different annealing processes

PULSED ELECTRON BEAM ANNEALING OF As AND B IMPLANTED SILICON

p-type (100) silicon wafers have been implanted either by As or B ions at 20 and 200 keV energies and doses of 1016cm-2. Pulsed electron beam annealing has been performed with fluences of 1.1 and 1.4 J/cm2 using a mean electron energy of 15 keV. The pulse duration was 50 ns. The annealed layers have been investigated by Rutherford backscattering under random and channeling conditions and by S.I.M.S. profiling. Good crystal regrowth and high dopant activation occur in all cases except for the 200 keV Boron implant. Impurities redistribution is observed but no significant segregation effects appear. The experimental profiles are in good agreement with a diffusion model using a modified green function solution and taking into account dopant diffusion in liquid phase and the computed melt front location. The deduced diffusion coefficient are in the 5.10-5cm2/s range for boron and 2.10-4cm2/s range for arsenic

Effect of articular cartilage proteoglycan depletion on high frequency ultrasound backscatter

AbstractObjective To study the effect of variations of articular cartilage proteoglycans (PG) on high-frequency ultrasound backscatter.Design The study was performed on patellar cartilages of immature and mature rats (N=36). The variation of PG content was induced by enzyme digestion. Control and treated cartilages were explored in vitro using a 55MHz scanning acoustic microscopy, then assessed by histology for the fibrillar collagen organization analysis. The variations of proteoglycan and collagen content were evaluated. Thickness measurements performed on both B-scan images and histologic sections were compared. Ultrasonic radio-frequency signals reflected by the cartilage surface and backscattered from its internal matrix were processed to estimate the integrated reflection coefficient (IRC) and apparent integrated backscatter (AIB).Results Although hyaluronidase treatment of immature and mature cartilages removed approximately 50% of the proteoglycans, the echogenicity level of ultrasound images of degraded cartilages was similar to that of controls. IRC and AIB parameters did not significantly vary. Histologic sections of degraded cartilage displayed no change in collagen fiber organization. The thickness mean values measured by ultrasound in PG-depleted groups were significantly higher than in controls, whereas no significant difference in thickness was detected by histological measurement. The increase in cartilage thickness may potentially be explained by a decrease of speed of sound in PG-depleted cartilages that is more likely subsequent to an increase of water content.ConclusionCurrent results indicate that PG depletion has no significant effect on high frequency ultrasound backscattered from rat patellar cartilage. Ultrasound may provide information about variations of PG content via speed of sound measurement. Copyright 2002 OsteoArthritis Research Society International. Published by Elsevier Science Ltd. All rights reserved

Comparison between SiN x :H and hydrogen passivation of electromagnetically casted multicrystalline silicon material

International audienceThis work intends to compare two different passivation methods for electromagnetically continuous pulling silicon (EMCP): remote plasma hydrogenation and remote plasma enhanced CVD of SiN followed by high-temperature sintering. All experiments are carried out on textured and non-textured EMCP samples from the same ingot. To check the effect of high-temperature diffusion on EMCP, a n +-emitter is formed on one group of the samples using POCl 3 diffusion. Passivation capabilities of both techniques are checked using measurements of minority carrier lifetime by means of microwave photoconductance decay mapping. Solar cells are made to compare lifetime measurement with cell parameters.