Effet sterique sur les vitesses de transfert protonique: cyclohexanols substitues dans le dimethylsulfoxyde

Steric effects on proton transfer from, and to, hydroxylic oxygen have been studied in a series of seventeen α-methyl and a-benzyl cyclohexanols in anhydrous DMSO, under both acid and base catalysed conditions, using dynamic MNR techniques. The protonation rate constants (k₁ ? 10⁶ M^-1 s^-1 at 25°C) obey a Taft-Ingold relationship, containing only a steric contribution E_s = E_s^OH + E_s^α, where: E_s^OH = 0 or 0.15 for an axial or equatorial hydroxyl respectively and E_s^α = ?0.070 (or ?0.115) for substituting an α-hydrogen by a methyl (or benzyl) group. An equatorial hydroxylic function is therefore 40% more reactive than its axial homologue. These kinetic data are fairly consistent with structural information resulting from IR spectroscopy (v_co and v_OH vibrations) and from NMR (hydroxylic chemical shifts and coupling constants).     

Microwave spectroscopy and nuclear magnetic resonance study of the molecular geometry of 2-fluorophenylisocyanate

Analysis of the microwave spectra of the vibrational ground state of 2-fluorophenyl-isocyanate in the gaseous state shows the existence of a single planar cis conformer. Rotational spectra of the excited torsional states out of the plane and spectra of in-plane vibrations have also been studied. MINDO III type theoretical calculations corroborate the experimental results. Similarly, the configuration of 2-fluorophenylisocyanate in the liquid phase has been studied by NMR using the chemical shift reagent, Eu(fod)₃. Induced paramagnetic shifts have been measured on the ¹³C spectra, for different quantities of the reagent. The results clearly show a higher paramagnetic shift for the carbon bonded to the fluorine atom than for the other nuclei of the aromatic cycle (with the exception of the quaternary carbon), indicating the probable presence of the cis isomer.     

Beyond the diffusing-wave spectroscopy model for the temporal fluctuations of scattered light

We extend the theory of diffusing-wave spectroscopy using a random-walk approach and a numerical solution of the radiative transfer equation. The theory is not restricted to the diffusive regime and allows one to describe the crossover between the single-scattering and the diffusive regimes, which has been observed experimentally. It also predicts a lower bound of the scattered-field correlation time at long paths. This extended theory should have broad experimental applications in the field of imaging through biological tissues.     

Gas chromatography/mass spectrometric identification of dopaminergic metabolites in striata of rats treated with L-DOPA

The ex vivo identification of dopaminergic metabolites present in rat striata after (L-DOPA + benserazide) treatment is reported. The different metabolites have been identified as the trimethylsilyl derivatives in the striatal extracts by gas chromatography/mass spectrometry.     

A comparative study of the structures, NMR properties and magnetic behaviour of complexes of cobalt(II) with octamethylpyrophosphoramide and nonamethylimidodiphosphoramide

The structure of the complex Co(NIPA)₃(ClO₄)₂ has been determined by X-ray diffraction analysis and found to be very close to that of the corresponding OMPA complex. The magnetic susceptibilities of the OMPA and NIPA complexes have been measured by a thermomagnetic method and have allowed the calculation of χ_| and χ, the susceptibilities along the principal axes of the complex. The magnetic properties of the isomorphous nickel compounds have been studied for comparison. Results give evidence for the greater magnetic anisotropy of the NIPA complexes.     

Onset of Surface Damage in Modular Orthopedic Implants: Influence of Normal Contact Loading and Stress-assisted Dissolution

Surface damage at interfaces of modular implants results from repeated fretting contacts between metallic surfaces in a corrosive environment. As a first step in understanding this complex process, multi-asperity contact experiments were conducted to characterize roughness evolution due to action of contact loads and exposure to a reactive environment. Cobalt–chromium specimens with surface roughness similar to modular implant were first subjected to only contact loading and subsequently, to alternating contact loads and exposure to reactive environment. During repeated normal contact loading, amplitude of surface roughness reached a steady value after decreasing during the first few cycles. However during the second phase surface roughness amplitude continuously evolved—decreasing during contact loading and increasing on exposure to corrosive environment. The increase in roughness amplitude during surface reaction depended on the magnitude of applied contact loads. A damage mechanism that incorporates contact-induced residual stress development and stress-assisted dissolution is proposed to elucidate the measured surface roughness evolution.     

Characterization of Ce(3+) -tributyl phosphate coordination complexes produced by fused droplet electrospray ionization with a target capillary

Coordination complexes containing Ce(III) and tri-n-butyl phosphate (TBP) in the 1+, 2+ and 3+ charge states were generated using both direct infusion electrospray ionization (ESI) and fused droplet (FD) ESI using a target capillary, in which the analyte solutions are impinged by the ESI droplets. The same coordination complexes were produced in each experiment, and their relative abundances were also very close, suggesting that similar processes are occurring in both experiments. The ion species formed in both experiments have the general formula [Ce(NO(3) )(m=0-2) (TBP)(n=3-7) ]((3-m)+) . The appearance of abundant 1+ and 2+ ion pair complexes indicated that the ESI process was modifying the ion populations in the original solutions, which contain predominantly 3+ and 2+ species. The FD ESI experiments were less sensitive for coordination complexes compared to direct infusion ESI; however, mid-picomolar quantities of coordination complexes were measured using the target capillary, indicating that sensitivity would be sufficient for measuring species in many industrial separations processes.     

Parallel machines scheduling with a deteriorating maintenance activity

In this paper, we consider parallel identical machines scheduling problems with a deteriorating maintenance activity. In this model, each machine has a deteriorating maintenance activity, that is, delaying the maintenance increases the time required to perform it. We need to make a decision on when to schedule the deteriorating maintenance activities and the sequence of jobs to minimize total completion time. We provide a polynomial time algorithm to solve the total completion time minimization problem.     

Choosing best alliance partners and allocating optimal alliance resources using the fuzzy multi-objective dummy programming model

Synergy effects are the motives to enter into strategic alliances; however due to lack of adequate preparation or planning, these alliances often fail. It is of no doubt that a successful strategic alliance depends on choosing the correct alliance partners and appropriate resource allocation. In this paper, the fuzzy multi-objective dummy programming model is proposed to overcome the above-mentioned problems. Two types of strategic alliances, joint ventures and mergers and acquisitions (M&A), are demonstrated to choose the best alliance partners and allocate the optimal alliance resources in a numerical example. Based on the results, our method can provide the optimal alliance cluster and satisfaction in strategic alliances.