A mathematical model of a flexible manufacturing system with limited in-process inventory

This paper describes a computationally simple, asymptotic model of a flexible job shop, especially designed for estimating the influence of limited in-process inventory level on the production rate. Its main features make it very similar to the one by Solberg. While Solberg's model consists of a closed queuing network, we propose an open queuing network with a limited amount of inprocess customers; a single customer class is assumed, the various actual processing routes being accounted for by routing probabilities. For such a queuing network, the product form of state probabilities is valid, and the normalization constant can be very simply obtained by a convolution algorithm, close to the one used by Solberg. Various performance indices are calculated, regarding the job shop behaviour over a long period of time. Comparison of analytical results of the model and simulation results are provided in order to estimate the amount of error introduced by assuming exponentially distributed processing times and Poisson inputs in the mathematical representation. Simulations were carried out in FORTRAN-based SLAM language.     

Calcul fonctionnel sur les opérateurs admissibles et application

Let $\text{H}{}_{\mathrm{v}}\text{(h) = ?(}\text{h}{}^2\text{2}\text{) · Δ + V,}\text{lim}{}_{\mathrm{¦x¦\; \to \; +\infty }}\text{V(x) = + ∞}$. Under suitable conditions we prove that $\text{?(H}{}_{\mathrm{v}}\text{(h))}$ is a pseudodifferential operator whose symbol has an asymptotic: $\text{a}{}_{\mathrm{?}}\text{(h) ~∑}{}_{\mathrm{j\; ?\; 0}}\text{h}{}^{\mathrm{j}}\text{a}{}_{\mathrm{?,j}}$. More general pseudodifferential operator's classes are also considered. We apply this result to study the semi-classical behaviour of the spectrum of H_v as h → 0. So, we improve recent results obtained by J. Chazarain and by the author in collaboration with B. Helffer. Furthermore we give a precise meaning to the formal development considered in B. Grammaticos and A. Voros' work (Ann. Physics123 (1979), 359–380).     

Catalytic oxidation of weakly acidic carbon compounds by air in the presence of potassium fluoride on alumina

Oxidation of weakly acidic carbon compounds was achieved with air in presence of KF-Al₂O₃ as catalyst. A carbanion process is proposed.     

Trichlorosilane isocyanate as coupling agent for mild conditions functionalization of silica-coated surfaces

Despite the importance of the isocyanate group in chemistry, very few examples of isocyanate-modified silicas have been reported, and all of the strategies described so far led to partial or total hydrolysis or condensation of the isocyanate group. By synthesizing trichlorosilane isocyanate as the coupling reagent, we show that oxidized silicon wafers are successfully modified with the isocyanate group. Our method is achieved in mild conditions, at low temperature, without side-reactions and allows the formation of a self-assembled monolayer (SAM) of isocyanates. The isocyanate group then offers a flexible way to further functionalize silica substrates with different nucleophiles, due to its high and specific reactivity.     

First structural characterization of a protactinium(V) single oxo bond in aqueous media

The present work describes the first structural studies of protactinium(V) in sulfuric and hydrofluoric acid media using X-ray absorption spectroscopy. The results show unambiguously the absence of the trans-dioxo bond that characterizes the other early actinide elements such as U and Np. In concentrated sulfuric acid (13 M), Pa(V) is proved to exhibit a single oxo bond as postulated in the literature for species in more dilute media. In a 0.5 M HF medium, XANES and EXAFS spectra indicate the absence of any oxo bond: Pa(V) exists in the form of a pure fluoro complex.     

Inhibition of the electrochemistry of ferrocenes by polyamine dendrimers and the key role of hydrogen-bonding with hydroxy groups

Commercial DSM polyamine dendrimers inhibit the observation of the cyclic voltammetry (CV) of simple ferrocenes all the more as they are larger (marked dendritic effect); the CV is re-established, however, if a OH-containing group is present in the ferrocene derivative.     

Surface characterizations of fluorescent-functionalized silica nanoparticles: from the macroscale to the nanoscale

Journal of Nanoparticle Research - Fluorescent silica nanoparticles are widely used for various applications from mechanical reinforcement to biology. In many cases, their surface has to be...