Application of the wavelet transform for a channel flow in a mixed convection phenomenon

The aim of this paper is to investigate laminar-turbulent transition in a mixed convection phenomenon occurring in a horizontal rectangular duct. Indeed, laminar-turbulent transition is well known in the case of forced convection but the presence of secondary flow induced by natural convection on this transition is not well highlighted. In this study, we will not be concerned by determining a critical threshold value of a Reynolds number of transition but only to estimate the degree of turbulence in the transition regime, i.e. weak turbulence in the case of a mixed convection phenomenon. This is possible thanks to the application of the wavelet transform. The calculation of the Hölder exponent, associated with the maximum value of the singularity spectrum for various experimental conditions allows the degree of turbulence to be measured. The variation of the Hölder exponent versus heat flux and Reynolds number enables us to show that there are two ways to go towards turbulence: thermal by increasing heat flux and hydrodynamic by increasing fluid velocity.     

A New Method to Measure the Coupling Efficiency of Waveguide Photodetector

In this paper, a new method is outlined for the estimation of coupling efficiency between a source laser and a WGPD. Internal quantum efficiencies as high as 72% (for 0.15 μm device) and 86.5% (for 0.5 μm device) are achieved.     

Structure determination of bioactive galloyl derivatives by NMR spectroscopy

The investigation of the chemical constituents of Symplocos racemosa Roxb led to the isolation of two new glycosides, symcomoside A (1) and symcomoside B (2), together with one known glycoside, tortoside C (3), which is reported for the first time from this plant. The structures of the new compounds were determined by 1D and 2D homonuclear and heteronuclear NMR spectroscopy, from chemical evidence and by comparison with published data for closely related compounds. Symcomoside B (2) showed potent inhibitory activity against alpha-glucosidase in a concentration-dependent fashion with an IC50 value of 0.733 +/- 0.033 mM whereas symcomoside A (1) showed very weak inhibitory activity against alpha-glucosidase (9.90% in 0.70 mM).     

Supercapacitive admittance tomoscopy

A sensor for measuring adsorption on a substrate has been designed including a contactless detection scheme, called supercapacitive admittance tomoscopy (SCAT). The sensor comprises a thin dielectric layer with two parallel band electrodes on the one side and a chemically modified surface on the other onto which the adsorption of molecules occurs. Upon application of a high frequency ac voltage between the two electrodes, a capacitive coupling is established across the dielectric layer, and the admittance measured depends on the surface state of the chemically modified interface. On the basis of this principle, a flow sensor has been developed to measure sensorgrams to follow the dynamics of the adsorption and has been tested for the adsorption of IgG on the modified surface.     

Voltammetric determination of azithromycin at the carbon paste electrode

Azithromycin (AZ) is the first member of a class of macrolide azalides antibiotics called azolides. A simple and selective square-wave voltammetric (SWV) method has been developed for the determination of azithromycin in pure form, in pharmaceutical preparation and in biological samples. Determination of azithromycin was accomplished with hand-make carbon paste electrode (CPE) in oxidative screen mode. The counter and reference electrodes were a Pt wire and a Ag/AgCl, respectively. Various parameters that can influence the peak signal (effect of buffer, ionic strength, accumulation time, pH and the composition of the paste) have been scrutinized. The best results were obtained in acetonitrile—aqueous 1 M sodium acetate-acetic acid buffer (pH 4.6) containing 0.1 M KCl (1:9; v/v) using a 15% paraffin oil CPE. The limits of detection and quantification of the pure drug are 0.463 and 1.544 ppb (with the correlation coefficient, r=0.9785and the standard deviation, S.D.=0.1 (n=5), for the accumulation time of 60 s), respectively. The method was successfully applied to the determination of the drug in urine and two forms of pharmaceutical formulations. Recoveries were 99.2—100.5% with S.D.=0.1—and 0.8% (n=5).     

Ultrafast chemical interface scattering as an additional decay channel for nascent nonthermal electrons in small metal nanoparticles

The use of 4.2 nm gold nanoparticles wrapped in an adsorbates shell and embedded in a TiO2 metal oxide matrix gives the opportunity to investigate ultrafast electron-electron scattering dynamics in combination with electronic surface phenomena via the surface plasmon lifetimes. These gold nanoparticles (NPs) exhibit a large nonclassical broadening of the surface plasmon band, which is attributed to a chemical interface damping. The acceleration of the loss of surface plasmon phase coherence indicates that the energy and the momentum of the collective electrons can be dissipated into electronic affinity levels of adsorbates. As a result of the preparation process, gold NPs are wrapped in a shell of sulfate compounds that gives rise to a large density of interfacial molecules confined between Au and TiO2, as revealed by Fourier-transform-infrared spectroscopy. A detailed analysis of the transient absorption spectra obtained by broadband femtosecond transient absorption spectroscopy allows separating electron-electron and electron-phonon interaction. Internal thermalization times (electron-electron scattering) are determined by probing the decay of nascent nonthermal electrons (NNEs) and the build-up of the Fermi-Dirac electron distribution, giving time constants of 540 to 760 fs at 0.42 and 0.34 eV from the Fermi level, respectively. Comparison with literature data reveals that lifetimes of NNEs measured for these small gold NPs are more than four times longer than for silver NPs with similar sizes. The surprisingly long internal thermalization time is attributed to an additional decay mechanism (besides the classical e-e scattering) for the energy loss of NNEs, identified as the ultrafast chemical interface scattering process. NNEs experience an inelastic resonant scattering process into unoccupied electronic states of adsorbates, that directly act as an efficient heat bath, via the excitation of molecular vibrational modes. The two-temperature model is no longer valid for this system because of (i) the temporal overlap between the internal and external thermalization process is very important; (ii) a part of the photonic energy is directly transferred toward the adsorbates (not among "cold" conduction band electrons). These findings have important consequence for femtochemistry on metal surfaces since they show that reactions can be initiated by nascent nonthermal electrons (as photoexcited, out of a Fermi-Dirac distribution) besides of the hot electron gas.     

Studies on Azolylacetonitriles: The Reactivity of Thiazole-2-yl,Thiadiazol-2-yl Acetonitriles Toward Electrophilic Reagents

5-Acetyl-2-cyanomethyl-4-methylthiazole, 2-aminothiazole, and 5-N-benzoylamino-1,3,4-thiadiazole-2-yl-acetonitrile react with acetone, and malononitrile derivatives in the presence of sulfur to yield the corresponding thiophene derivatives. Also, 4-furylmethylene-2-phenyl-2-oxazolin-5-ones react with thiophenol, and/or thionaphthol to give the thiolester derivatives in one-pot synthesis. The structures of the products were based on IR, 1 H NMR, and elemental analysis.     

Divergent Synthesis of Molecular Winch Prototypes

We report the synthesis of conceptually new prototypes of molecular winches with the ultimate aim to investigate the work performed by a single ruthenium-based molecular motor anchored on a surface by probing its ability to pull a load upon electrically-driven directional rotation. According to a technomimetic design, the motor was embedded in a winch structure, with a long flexible polyethylene glycol chain terminated by an azide hook to connect a variety of molecular loads. The structure of the motor was first derivatized by means of two sequential cross-coupling reactions involving a penta(4-halogenophenyl)cyclopentadienyl hydrotris(indazolyl)borate ruthenium(II) precursor and the resulting benzylamine derivative was next exploited as key intermediate in the divergent synthesis of a family of nanowinch prototypes. A one-pot method involving sequential peptide coupling and Cu-catalyzed azide-alkyne cycloaddition was developed to yield four loaded nanowinches, with load fragments encompassing triptycene, fullerene and porphyrin moieties.     

Robustness in deterministic multi-objective linear programming with respect to the relative interior and angle deviation

This paper deals with the robustness issue in deterministic multi-objective linear programming from two new standpoints. It is shown that a robustness notion recently reported in the literature is equivalent to strict efficiency. Corresponding to an efficient solution, a new quantity, robustness order (RO) is defined with respect to the interiority order of the cost matrix in the binding cone. A linear programming problem is provided to calculate the RO of a given efficient solution. The second part of the paper is devoted to investigating the robustness with respect to the eligible angle deviation of the cost matrix in the binding cone. Theoretical results are given to obtain the maximum eligible angle deviation. Finally, the relationship between two above-mentioned robustness standpoints is established. To have a better geometrical view, we prove the results for single-objective LP problems at first, and then we extend them to the multi-objective case. In addition to the theoretical results, some clarifying examples are given.