Évaluation de l'influence de sources acoustiques secondaires sur la puissance acoustique rayonnée

The boundary element method and equivalent sources method are currently used in vibroacoustic. While designing the model, we have to know if it is necessary or not to model some geometric “details”. In order to determine the acoustic part of these “details” as vibrating sources, we propose to study a simplified model of two point sources in opposite phase. We determine, on the one hand, the conditions of distance between sources, and, on the other hand, the output ratio for which the secondary source can be neglected when calculating the acoustic power radiated.     

Fabrication of regular mesoscopic networks of GaAs wires

A novel and simple approach to nanolithography has been developed as a technique for fabricating two-dimensional periodic mesoscopic (submicrometre) networks of semiconductor wires with a feature size down to about 20 nm. The etching mask is made by coating the material's surface with an initially structured polymer network . This is obtained by self-organized patterning in a complex liquid (nitrocellulose solution). Reactive ion etching is used for GaAs surface patterning. This technique can find potential applications in many areas of science and technology which use low-dimensional and mesoscopic devices.     

A note on the use of PROMETHEE multicriteria methods

The PROMETHEE methods are rather popular in the world of outranking methods. One of the reasons for this popularity is the existence of the very userfriendly software, called PROMCALC-PROMethee CALCulation. More and more practitioners are using PROMCALC to handle their multiple criteria problems. However, not all users are aware of the consequences of the model assumptions made in PROMETHEE methods. A short overview of some drawbacks of PROMETHEE methods that users must know and avoid are described in this paper.     

Use of a multi-tube Nafion® membrane dryer for desolvation with thermospray sample introduction to inductively coupled plasma-atomic emission spectrometry

A multi-tube Nafion^® membrane dryer used as a part of a desolvation system in conjunction with thermospray nebulization was optimized and characterized with inductively coupled plasma-atomic emission spectrometry (ICP-AES). Either argon or nitrogen could be used as the sweep gas, and optimum conditions were found to be at low temperature and low sweep gas flow rate. Analyte sensitivity was not significantly affected by placing the membrane between the plasma and the nebulizer, although about 20% of the analyte entering the dryer is lost within the dryer. A dual role of the membrane dryer was demonstrated. As a secondary step within the desolvation system, it enabled a high desolvation efficiency of 99.94% for aerosols from 1% (v/v) nitric acid. Plasma solvent load could be reduced to 0.9 mg min⁻¹ with a tap water cooled condenser combined with the membrane dryer, compared to 21 mg min⁻¹ with the normal chilled condenser desolvation system. Meanwhile, the membrane was also found to act as a pulse dampener, eliminating the plasma pulsation in the central channel caused by thermospray nebulization and thus improving the analytical performance of the system. The average relative standard deviations (RSD) with the optimized membrane/thermospray system were 0.83% and 0.60% for the background and analyte signals, respectively, which were reduced by a factor of 1.9 and 2.7 for the background and analyte signals, respectively, compared to thermospray without the membrane desolvation, and were essentially identical to those obtained with pneumatic nebulization sample introduction. The improvements in detection limits with the membrane/thermospray system were 1.2–3.0 times with an average factor of 1.8 compared to thermospray without the membrane dryer, and 18–68 times with an average factor of 39 compared to the standard pneumatic nebulization sample introduction system without a desolvation unit. The detection limits for Mn, Mg, Cr and Cd with the present thermospray/membrane system were comparable to those reported for pneumatic nebulization ICP mass spectrometry.     

Transmission dynamics of COVID-19 in Wuhan,China: effects of lockdown and medical resources

Nonlinear Dynamics - Due to the strong infectivity of COVID-19, it spread all over the world in about three months and thus has been studied from different aspects including its source of...     

Inhibitive detection of benzoic acid using a novel phenols biosensor based on polyaniline–polyacrylonitrile composite matrix

A novel sensitive and stable phenols amperometric biosensor, based on polyaniline–polyacrylonitrile composite matrix, was applied for determination of benzoic acid. The electrochemical biosensor functioning was based on the inhibition effect of benzoic acid on the biocatalytic activity of the polyphenol oxidase (PPO) to its substrate (catechol) in 0.1 M phosphate buffer solution (pH 6.5). A potential value of −50 mV versus SCE, and a constant catechol concentration of 20 μM were selective to carry out the amperometric inhibition measurement. The kinetic parameters Michaelis-Menten constant and maximum current (I_max) in the absence and in the presence of benzoic acid were also evaluated and the possible inhibition mechanism was deduced. The inhibiting action of benzoic acid on the polyphenol oxidase electrode was reversible and of the typical competitive type, with an apparent inhibition constant of 38 μM. This proposed biosensor detected levels of benzoic acid as low as 2 × 10⁻⁷ M in solution. In addition, the effects of temperature, pH value of solution on the inhibition and the interferences were investigated and discussed herein. Inhibition studies revealed that the proposed electrochemical biosensor was applicable for monitoring benzoic acid in real sample such as milk, yoghurt, sprite and cola.     

An unexpected generation of magnetically separable Se/Fe3O4 for catalytic degradation of polyene contaminants with molecular oxygen

Selenization of Fe₂O₃ with NaHSe led to Se/Fe₃O₄. The unexpected generation of Fe₃O₄ attributed to the reduction conditions of the reaction, and the resulted magnetic features of the material facilitated its separation in practical applications. Owning to the synergistic effect of Se with Fe, the material was especially active to catalyze the oxidative C=C scission using O₂ as mild oxidant. The technique has been successfully applied in polyene degradation project, which is of profound practical values for the treatment of the polyene pigment pollution and may be applied in the food and pharmaceutical industry.     

Solubility and solution thermodynamics of 2,3,4,5-tetrabromothiophene in (ethanol + tetrahydrofuran) binary solvent mixtures

The solubility of 2,3,4,5-tetrabromothiophene in (ethanol + tetrahydrofuran) binary solvent mixtures was measured within the temperature range from (278.15 to 322.15) K. The solubility increases with the rise of temperature, while it decreases with increasing ethanol content at constant temperature. The experimental data were fitted using the two variants of the combined nearly ideal binary solvent/Redlich–Kister (CNIBS/R–K) equation and the Jouyban–Acree equation, respectively. All the three equations were proven to give good representations of the experimental values. Computational results showed that the variant two of CNIBS/R–K equation was superior to the other two equations. The thermodynamic properties of the solution process, including the Gibbs free energy, enthalpy, and entropy, were calculated by the van’t Hoff analysis. The values of both the enthalpy change and the standard molar Gibbs free energy change of solution were positive, which indicated that the process was endothermic.