Interaction Mechanisms Between Ar–O<Subscript>2</Subscript> Post-Discharge and Stearic Acid II: Behaviour of Thick Films

We study the interaction of thick films (~4 mm) of stearic acid (SA), a C₁₈ alkane skeleton with an acid function, with late Ar–O₂ post-discharge. Contrary to what is observed with thin films of SA (~2–3 μm) which are efficiently etched (part I), only functionalization is observed over the first 2 h of treatment with a plasma source operated in the continuous mode, whatever the temperature. The heat released by surface reactions affects non-linearly the temperature of the substrate. Pulsing the source at a frequency ranging from 0.1 to 1 kHz slows down the functionalization process but does not allow any etching of the material. On the contrary, the SA can be etched as thick films by pulsing the oxygen flow rate at a frequency below 50 mHz. By pulsing the reactive gas, the time averaged value of the [O]/[O₂] ratio is decreased, limiting the functionalization processes due to oxygen atoms, and the mean temperature is lowered, decreasing the diffusion length of O₂ (and/or possibly O₂*) species in the SA which are responsible for the scission of C–C bonds of radicals.     

QSAR modeling of in vitro inhibition of cytochrome P450 3A4

We report the QSAR modeling of cytochrome P450 3A4 (CYP3A4) enzyme inhibition using four large data sets of in vitro data. These data sets consist of marketed drugs and drug-like compounds all tested in four assays measuring the inhibition of the metabolism of four different substrates by the CYP3A4 enzyme. The four probe substrates are benzyloxycoumarin, testosterone, benzyloxyresorufin, and midazolam. We first show that using state-of-the-art QSAR modeling approaches applied to only one of these four data sets does not lead to predictive models that would be useful for in silico filtering of chemical libraries. We then present the development and the testing of a multiple pharmacophore hypothesis (MPH) that is formulated as a conceptual extension of the traditional QSAR approach to modeling the promiscuous binding of a large variety of drugs to CYP3A4. In the simplest form, the MPH approach takes advantage of the multiple substrate data sets and identifies the binding of test compounds as either proximal or distal relative to that of a given substrate. Application of the approach to the in silico filtering of test compounds for potential inhibitors of CYP3A4 is also presented. In addition to an improvement in the QSAR modeling for the inhibition of CYP3A4, the results from this modeling approach provide structural insights into the drug-enzyme interactions. The existence of multiple inhibition data sets in the BioPrint database motivates the original development of the concept of a multiple pharmacophore hypothesis and provides a unique opportunity for formulating alternative strategies of QSAR modeling of the inhibition of the in vitro metabolism of CYP3A4.     

Neutral cesium deposition prior to SIMS analysis of inorganic and organic samples

The enhancement of negative secondary ions yields in SIMS by the use of electropositive primary ions is well known. In previous papers, the authors of this article have reported on the simultaneous use of primary ion bombardment coupled with neutral cesium deposition to optimize the useful yields of negative secondary ions in the steady‐state regime. For electronegative elements, total ionization was achieved while the gain for the other elements attained two orders of magnitude. In this paper, we study the enhancement of negative secondary ion yields in the pre‐equilibrium regime by depositing neutral cesium onto the sample surface prior to the SIMS analysis. The main areas of application of this technique lie in the field of secondary ion imaging of sample surfaces. Of particular interest is the analysis of organic and biological samples on the Cameca NanoSIMS50 instrument. Both inorganic and organic samples will be investigated in this paper. Copyright © 2010 John Wiley & Sons, Ltd.     

Accumulations of Ca/P in the core of hairs from Taklamakan desert mummies

Hairs from mummies discovered in the west China Taklamakan desert are investigated by NanoSIMS, ToF-SIMS, Auger and TEM. Intra-medullar accumulations of calcium and phosphorus are described. The present study is an attempt to understand the significance of these accumulations. Their possible exogenous or endogenous origin is debated. Moreover, TEM revealed a particular nature of the accumulation that decorates a fibrilar structure of the medullar. To what extent did molecular control govern the particle growth and does such an accumulation represent a step toward the mineralization of the keratinized fiber?     

The free energy of a reaction coordinate at multiple constraints: a concise formulation

The free energy as a function of the reaction coordinate (rc) is the key quantity for the computation of equilibrium and kinetic quantities. When it is considered as the potential of mean force, the problem is the calculation of the mean force for given values of the rc. We reinvestigate the PMCF (potential of mean constraint force) method which applies a constraint to the rc to compute the mean force as the mean negative constraint force and a metric tensor correction. The latter allows for the constraint imposed to the rc and possible artefacts due to multiple constraints of other variables which for practical reasons are often used in numerical simulations. Two main results are obtained that are of theoretical and practical interest. First, the correction term is given a very concise and simple shape which facilitates its interpretation and evaluation. Secondly, a theorem describes various rcs and possible combinations with constraints that can be used without introducing any correction to the constraint force. The results facilitate the computation of free energy by molecular dynamics simulations.     

Three-dimensional analysis of trace elements with the CAMECA IMS 4F

Summary The CAMECA IMS 4F operates in the microprobe and microscope modes with submicron lateral resolutions. The high useful yields obtained via the appropriate primary ion beam species and high transmission ion optical system give access to trace analysis in small structures. As an example, a depth profile of arsenic in silicon performed at 5,000 mass resolution in a 8 m² area allows detection of 1.10¹⁶ at/cm³ (0.2 ppm).

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Dreidimensionale Analyse von Spurenelementen mit dem CAMECA IMS 4F

     

Electrodeposition of composite Ni–B coatings in a stirred heterogeneous system

The formation of composite electrochemical coatings of a nickel matrix with boron microparticles was investigated. Electrolytical nickel–boron layers were deposited on a paraffin-impregnated graphite electrode in a stirred heterogeneous system formed by a Watts-type nickel plating bath and dispersed boron powder particles. The polarisation behaviour of the composite plating bath as a function of the boron particle loading was examined. The effect of deposition conditions, as well as of the amount of boron powder in the plating bath on the boron content in the composite Ni–B coatings, was examined. The composite coating structure was established using scanning electron microscopy and light optical microscopy. The distribution of boron particles in the composite deposits was investigated by dynamic secondary ion mass spectrometry. The boron particles content was determined gravimetrically. The obtained results suggest that the content of incorporated boron particles increases with an increasing amount of boron in the plating bath. The potentiodynamic deposition method is demonstrated to be more suitable for production of composite coatings with a high content of boron particles than the potentiostatic one. Homogeneous distribution of boron particles in the nickel matrix without coagulation or sedimentation was associated with the electrochemical fabrication method in stirred heterogeneous systems.     

Particulars of the cross- and spanwise near-wake development of a short Semicircular-section Shell, through the TransitionRe-range (60 ≤Re ≤ 600)

Within the fundamental context of quasi-2D bluff-body near-wake investigation, we analyse the way the initial wake vortices (primary and secondary vortices) form and develop with time behind a short (5.2∶1) cylindrical semicircular shell (hollow at the back), after an impulsive start in translation. The study includes the transition regime and non-usual cross-sectional shapes. The structure of the vortices is examined by means of precise visualizations both in the mid-cross and mid-span planes. The particulars induced by the hollow face are deduced from a comparison with the cases of analogous solid cylinders and more particularly with the full semicircular cylinder (Boisaubert et al., 1996; Coutanceau et al., 1998).     

Details on the start-up development of the Taylor-Gortler-like vortices inside a square-section lid-driven cavity for 1,000≤<Emphasis Type="Italic">Re</Emphasis>≤3,200

The time development of counter-rotating vortices, which are formed in the early stages of impulsively started laminar lid-driven cavity flows, is investigated by experimental visualizations using the particle streak technique with the aim of explaining the successive phases of their establishment. The standard square-section cavity of aspect ratio 1:1:2 has been selected for this study and the results presented are for the Reynolds numbers 1,000, 2,000, and 3,200. A detailed analysis of streamline fields evolution clearly shows, for the first time, that the transient appearance of the Taylor-Gortler-type counter-rotating vortices succeeds four main phases. Each of them has been associated to a critical value of a Taylor-Gortler control parameter.