Asphaltene adsorption mechanism under shear flow probed by in situ neutron reflectivity measurements

We propose here a method to adapt a rheometer with a cone/plate geometry to a neutron reflectometer in order to perform in situ reflectivity measurements. This study allowed us to probe the influence of the shear rate on the mechanism of asphaltenes adsorption, the heaviest and most polar compounds of crude oil, using bad solvent conditions. Such experiment aims at describing at a local scale the surface modifications induced by flowing crude oils (pipe transportation or production through porous media). Without shearing, in a 34%/66% xylene/dodecane mixture for which the asphaltenes flocculation is achieved in bulk, the nanoaggregates are able to be adsorbed on a hydrophilic surface as multilayers, with a surface excess much larger than for good solvent conditions. Moreover, the thickness of these multilayers increases almost linearly with time, in accordance with QCM experiments. In shear rate conditions, the adsorption process is however strongly limited since the surface excess of the adsorbed layers is around twice lower at 2600 s^?1 than at 1200 s^?1.     

Managing an integrated production inventory system with information on the production and demand status and multiple non-unitary demand classes

In this paper, we study a system consisting of a manufacturer or supplier serving several retailers or clients. The manufacturer produces a standard product in a make-to-stock fashion in anticipation of orders emanating from n retailers with different contractual agreements hence ranked/prioritized according to their importance. Orders from the retailers are non-unitary and have sizes that follow a discrete distribution. The total production time is assumed to follow a k₀-Erlang distribution. Order inter-arrival time for class l demand is assumed to follow a k_l-Erlang distribution. Work-in-process as well as the finished product incur a, per unit per unit of time, carrying cost. Unsatisfied units from an order from a particular demand class are assumed lost and incur a class specific lost sale cost. The objective is to determine the optimal production and inventory allocation policies so as to minimize the expected total (discounted or average) cost. We formulate the problem as a Markov decision process and show that the optimal production policy is of the base-stock type with base-stock levels non-decreasing in the demand stages. We also show that the optimal inventory allocation policy is a rationing policy with rationing levels non-decreasing in the demand stages. We also study several important special cases and provide, through numerical experiments, managerial insights including the effect of the different sources of variability on the operating cost and the benefits of such contracts as Vendor Managed Inventory or Collaborative Planning, Forecasting, and Replenishment. Also, we show that a heuristic that ignores the dependence of the base-stock and rationing levels on the demands stages can perform very poorly compared to the optimal policy.     

Adsorption structures of water in NaX studied by DRIFT spectroscopy and neutron powder diffraction

Diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) measurements (4000-1500 cm(-1)) and the results of neutron powder diffraction have been combined to study the structure of adsorption complexes of water in a NaX zeolite at different water loadings (25, 48, 72, and 120 water molecules per unit cell, respectively). Sharp bands corresponding to non-hydrogen-bonded OH groups of water molecules and broad associate bands due to hydrogen-bonded molecules are observed in the DRIFT spectra. We observe a remarkable downshift of the high-frequency associate band in a narrow temperature interval when the water amount decreases from 120 to 72 molecules per unit cell, which could signify some kind of "phase transition" for the water inside the zeolite cavities. Neutron powder diffraction results show that water molecules are predominantly localized in or near the 12-ring windows. Water molecules with hydrogen-bonded and non-hydrogen-bonded OH groups were found, in agreement with the observation of sharp and broad bands in the DRIFT spectra. We find strong evidence for the formation of cyclic hexamers of water molecules localized in the 12-ring windows, which are further stabilized by hydrogen bonds to framework oxygen atoms.     

What tunes the structural anisotropy of magnetic fluids under a magnetic field?

In the present study, the structure of monophasic ionic magnetic fluids under a static magnetic field is explored. In these aqueous electrostatically stabilized ferrofluids, we vary both the isotropic interparticle interactions and the anisotropic dipolar magnetic interaction by tuning the ionic strength and the size of the nanoparticles. Small angle neutron scattering measurements carried out on nanoparticles dispersed in light water exhibit miscellaneous 2D nuclear patterns under a magnetic field with various q-dependent anisotropies. In this nondeuterated solvent where the magnetic scattering is negligible, this anisotropy originates from an anisotropy of the structure of the dispersions. Both the low q region and the peak of the structure factor can be anisotropic. On the scale of the interparticle distance, the structure is better defined in the direction perpendicular to the field. In the thermodynamic limit (q-->0), the model previously described in ref 10 matches the data without any fitting parameters: the interparticle interaction is more repulsive in the direction parallel to the magnetic field. At low q, the amplitude of the anisotropy of the pattern is governed by the ratio of two interaction parameters: the reduced parameter of the anisotropic magnetic dipolar interaction, gamma/Phi, over the isotropic interaction parameter, , in zero field, which is proportional to the second virial coefficient.     

An examination of specific interactions of esters and polyesters with chlorinated solvents by infrared and nuclear magnetic resonance spectroscopies

Poly(?-caprolactone) and low-molecular-weight esters (methyl acetate and propyl propionate) were dissolved in binary solvent mixtures. The relative ability of the two solvents to associate with the ester group was then determined by examining the equilibrium between the two solvation states of the ester using infrared and nuclear magnetic resonance spectroscopies. The ability of the solvents to associate with the chosen esters was found to be in the sequence α-hydrogenated chlorocarbons > β-hydrogenated chlorocarbon > carbon tetrachloride ≈ aliphatic hydrocarbons. The association-state equilibrium was also shown to be concentration dependent and the polyester was shown to become involved in specific interactions to a lesser degree than the model esters. The relevance of these results to the nature of the specific interactions in polyester/halogenated polymer blends is discussed.     

The design of a high voltage scr pulse generator for ultrasonic pulse echo applications

This paper presents the design of a high voltage scr pulse generator that is useful for testing highly attenuative materials in the pulse echo mode. Electrical and ultrasonic considerations are discussed in detail followed by an example of a practical circuit design that can operate from a supply voltage of 1000 V at a pulse repetition frequency of 1000 Hz.     

Dispositif de prelevement microanalytique de produits alterables

A small glass device is described for microanalytical or submicroanalytical sampling of unstable solid or liquid substances, in an argon atmosphere.

Zusammenfassung

Ein kleines Glasgerät wird beschrieben, das die Probenahme für die Mikrooder Submikroanalyse instabiler fester oder flüssiger Substanzen in Argonatmosphäre erlaubt.