A Degenerate Birdcage with Integrated Tx/Rx Switches and Butler Matrix for the Human Limbs at 7 T

The theoretically known degeneracy condition of the band-pass birdcage coil has rarely been exploited in transmit coil designs. We have created an eight-channel degenerate birdcage for the human limbs at 7 T, with dedicated Tx/Rx switches and a Butler matrix. The coil can be split into two half cylinders, as required for its application to patients with limited mobility. The design of the coil, the Butler matrix, and Tx/Rx switches relied on a combination of analytical, circuital, and numerical simulations. The birdcage theory was extended to the degenerate case. The theoretical and practical aspects of the design and construction of the coil are presented. The performance of the coil was demonstrated by simulations, workbench, and scanner measurements. The fully assembled prototype presents good performance in terms of efficiency, B₁ homogeneity, and signal-to-noise ratio, despite the asymmetry introduced by the splittable design. The first in vivo images of the knee are also shown. A novel RF coil design consisting of an eight-channel splittable degenerate birdcage has been developed, and it is now available for 7 T MRI applications of the human lower limbs, including high-resolution imaging of the knee cartilages and of the patellar trabecular structure.     

A mesoscopic model of the intermixing during nanoenergetic materials processing

A general mesoscopic model for the simulation of thin-film vapor deposition applied to energetic materials, specifically bimetallic multilayers, is presented. We describe the setup of this mesoscopic simulator developed in the frame of a multiscale study by implementing ab initio data into a set of differential equations. We present numerical results relative to the formation of barrier layers as a result of interdiffusion between successive bimetallic AlNi multilayers. The key role of the vacancies species created during deposition is highlighted.     

Statistical mechanics of combinatorial auctions

Combinatorial auctions are formulated as frustrated lattice gases on sparse random graphs, allowing the determination of the optimal revenue by methods of statistical physics. Transitions between computationally easy and hard regimes are found and interpreted in terms of the geometric structure of the space of solutions. We introduce an iterative algorithm to solve intermediate and large instances, and discuss competing states of optimal revenue and maximal number of satisfied bidders. The algorithm can be generalized to the hard phase and to more sophisticated auction protocols.     

Numerical and experimental exploration of phase control of chaos

A well-known method to suppress chaos in a periodically forced chaotic system is to add a harmonic perturbation. The phase control of chaos scheme uses the phase difference between a small added harmonic perturbation and the main driving to suppress chaos, leading the system to different periodic orbits. Using the Duffing oscillator as a paradigm, we present here an in-depth study of this technique. A thorough numerical exploration has been made focused in the important role played by the phase, from which new interesting patterns in parameter space have appeared. On the other hand, our novel experimental implementation of phase control in an electronic circuit confirms both the well-known features of this method and the new ones detected numerically. All this may help in future implementations of phase control of chaos, which is globally confirmed here to be robust and easy to implement experimentally.     

Acute stress alters transcript expression pattern and reduces processing of proBDNF to mature BDNF in <Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>

Background  

Stress involves alterations of brain functioning that may precipitate to mood disorders. The neurotrophin Brain Derived Neurotrophic Factor (BDNF) has recently been involved in stress-induced adaptation. BDNF is a key regulator of neuronal plasticity and adaptive processes. Regulation of BDNF is complex and may reflect not only stress-specific mechanisms but also hormonal and emotional responses. For this reason we used, as an animal model of stress, a fish whose brain organization is very similar to that of higher vertebrates, but is generally considered free of emotional reactions.     

Indole Synthesis Using Silver Catalysis

Indoles are amongst the most important classes of heteroaromatics in organic chemistry, commonly found in biologically active natural products and therapeutically useful compounds. The synthesis of indoles is therefore important and several methods for their synthesis that make use of silver(I) catalysts and reagents have been developed in recent years. This Minireview contains, to the best of our knowledge, a comprehensive coverage of silver‐mediated indole forming reactions since the first reaction of this type was reported in 2004.     

Applications of a Cole–Hopf transform to the 3D Navier–Stokes equations

The Navier–Stokes equations written in the vector potential can be recast as non-linear Schrödinger equations at imaginary times, i.e. heat equations with a potential term, using the Cole–Hopf transform. On this basis, we study two kinds of Navier–Stokes flows by means of direct numerical simulations. In an experiment on vortex reconnection, it is found that the potential term takes large negative values in regions where intensive reconnection takes place, whereas the signature of the non-linear term is more broadly spread. For decaying turbulence starting from a random initial condition, such a correspondence is also observed in the early stage when the flow is dominated by vorticity layers. At later times, when the flow features several tubular vortices, this correspondence becomes weaker. Finally, a similar set of transformations is presented for the magneto–hydrodynamic equations, which reduces them to a set of heat equations with suitable potential terms, thereby obtaining new criteria for the regularity of their solutions.     

Reactivity of the insecticide chlorpyrifos‐methyl toward hydroxyl and perhydroxyl ion. Effect of cyclodextrins

The reactivity of Chlorpyrifos‐Methyl ( 1 ) toward hydroxyl ion and the α‐nucleophile, perhydroxyl ion was investigated in aqueous basic media. The hydrolysis of 1 was studied at 25 °C in water containing 10% ACN or 7% 1,4‐dioxane at NaOH concentrations between 0.01 and 0.6 M ; the second‐order rate constant is 1.88 × 10^?2 M ^?1 s^?1 in 10% ACN and 1.70 × 10^?2 M ^?1 s^?1 in 7% 1,4‐dioxane. The reaction with H₂O₂ was studied in a pH range from 9.14 to 12.40 in 7% 1,4‐dioxane/H₂O; the second‐order rate constant for the reaction of HOO^? ion is 7.9 M ^?1 s^?1 whereas neutral H₂O₂ does not compete as nucleophile. In all cases quantitative formation of 3,5,6‐trichloro‐2‐pyridinol ( 3 ) was observed indicating an S_N2(P) pathway. The hydrolysis reaction is inhibited by α‐, β‐, and γ‐cyclodextrin showing saturation kinetics; the greater inhibition is produced by γ‐cyclodextrin. The reaction with hydrogen peroxide is weakly inhibited by α‐ and β‐cyclodextrin (β‐CD), whereas γ‐cyclodextrin produces a greater inhibition and saturation kinetics. The kinetic data obtained in the presence of β‐ or γ‐cyclodextrin for the reaction with hydroxyl or perhydroxyl ion indicate that the main reaction pathway for the cyclodextrin‐mediated reaction is the reaction of HO^? or HOO^? ion with the substrate complexed with the anion of the cyclodextrin. The inhibition is attributed to the inclusion of the substrate with the reaction center far from the ionized secondary OH groups of the cyclodextrin and protected from external attack of the nucleophile. Sucrose also inhibits the hydrolysis reaction but the effect is independent of its concentration. Copyright © 2008 John Wiley & Sons, Ltd.     

Temperature and potential-dependent structural changes in a Pt cathode electrocatalyst viewed by in situ XAFS

The paper presents an X-ray absorption fine structure (XAFS) investigation of Pt supported on Vulcan XC-72 operating as a cathode catalyst in a polymer electrolyte membrane fuel cell (PEM FC). XAFS spectroscopy was performed in situ using a cell developed by the authors and optimized for absorption measurements. Low-noise spectra were obtained using the transmission mode over the Pt L₃ XAFS range, enabling multiple-scattering XAFS data-analysis for the Pt nanocrystalline system under operating conditions. Accurate measurements of the local structure were performed at various potentials and working temperatures. Changes in the near-edge structures reflecting variations in the Pt electronic structure were observed for various potential values in the cathode activation region. The Pt average local geometric structure was found to be practically potential-independent. The increase in structural disorder caused by the higher working FC temperature was not found to affect the catalyst’s performance in the kinetically controlled region.