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.     

[18F]CuCF3: A [18F]Trifluoromethylating Agent for Arylboronic Acids and Aryl Iodides

Positron emission tomography has emerged as the leading method for medical imaging with fluorine‐18 as the most widely used radioactive isotope. Here we report a semi‐automated method for the preparation of valuable [¹⁸F]trifluoromethylcopper, as well as its use for the radiosynthesis of [¹⁸F]trifluoromethylarenes and heteroarenes. Mild conditions of [¹⁸F]trifluoromethylation make this method particularly useful for the radiosynthesis of pharmacologically relevant [¹⁸F]trifluoromethylarenes and heteroarenes.     

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.     

Light multiple scattering correction of laser-diffraction spray drop-size distribution measurements

This paper reports an experimental investigation on the practical use of a laser-diffraction instrument, the Malvern Spraytec 2007 to characterize sprays produced by a high-pressure GDI injector. The sprays are highly transient, large, composed of very small drops, dense and heterogeneously distributed in space. These characteristics are at the origin of undesirable effects (beam steering, vignetting and light multiple scattering) whose manifestations are experimentally identified. Ignoring the diodes concerned by beam steering erases the effect of this phenomenon but vignetting and light multiple scattering effects combine to bias the measurements and both require to be corrected. A nth order empirical correction procedure, based on the analysis of the light intensity distribution, is developed. It is a generalization of a second order procedure presented in a previous investigation. The increase of the correction order is demonstrated to be necessary when the injection pressure is greater than 11 MPa. The application of this correction procedure reported that light multiple scattering affects laser-diffraction when the transmission is less than 40%. This limit is in agreement with investigations of the literature and gives credit to the empirical correction procedure. Despite the correction procedure is applicable for the present operating conditions only, this work defines an experimental protocol to apprehend laser-diffraction spray characterization in severe operating conditions and that can be reproduced with ease. Furthermore, it is emphasized that the combination of the Spraytec and the correction procedure performances allows cycle-to-cycle spray drop-size distribution variations to be determined. Such information is of paramount importance and the Spraytec is probably the sole instrument able to provide it.     

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.     

Dynamic Hedging of Portfolio Credit Risk in a Markov Copula Model

We devise a bottom-up dynamic model of portfolio credit risk where instantaneous contagion is represented by the possibility of simultaneous defaults. Due to a Markovian copula nature of the model, calibration of marginals and dependence parameters can be performed separately using a two-step procedure, much like in a standard static copula setup. In this sense this solves the bottom-up top-down puzzle which the CDO industry had been trying to do for a long time. This model can be used for any dynamic portfolio credit risk issue, such as dynamic hedging of CDOs by CDSs, or CVA computations on credit portfolios.     

On Bernstein's Inequality and Kahane's Ultraflat Polynomials

The investigation of norm Bernstein inequalities for polynomials with unimodular coefficients, leads to unexpected results. Some phenomena here upset our intuition. This paper closely revisits the ultraflat polynomials whose existence was conjectured by Littlewood in 1966 and proved by Kahane in 1980. A major role in this study is also played by arbitrary ultraflat polynomials, that is, including those that are not necessarily obtained by variations or refinements of Kahane's method.