Rechargeable sodium batteries—VI. Cycling behavior of VS2, ‘VCl3 + nS’ and NbS2Cl2 cathodes in molten NaAlCl4

The electrochemistry of VS₂ in molten NaAlCl₄ has been investigated in relation to its usefulness as a reversible positive electrode for sodium batteries operating in the moderate temperature range of 160–200°C. VS₂ reacted with NaAlCl₄ during early stages of cell cycling, and became VS₂Cl showing a reversible capacity of 2.8 electrons/vanadium. The electrochemistry of mixtures of VCl₃ and S in molten NaAlCl₄ showed similarities to that of VS₂Cl. The VS_xCl_y cathodes obtained via the two different routes exhibited excellent rechargeability as evidenced by the long-term cycling behavior of cells of the configuration, Na_(l)/β″-Al₂O₃/NaAlCl_4(l), cathode material. When NbS₂Cl₂ was used as the cathode material it underwent a structural change in the first cycle to form what appeared to be NbS₂Cl₂, the Nb analog of VS_xCl_y. The structurally modified niobium sulfur chloride cathode exhibited excellent rechargeability.     

Performance dependence of InGaP/InGaAs/GaAs pHEMTs on gatemetallization

The performance of InGaP-based pHEMTs as a function of gate metallization is examined for Mo/Au, Ti/Au, and Pt/Au gates. DC and microwave performance of pHEMT's with 0.7-μm gate lengths is evaluated. Transconductance, threshold voltage, f_t, and f_max are found to depend strongly on gate metallization. High-speed performance is achieved, with f_t of 41.3 GHz and f _max of 101 GHz using Mo/Au gates. The difference in performance between devices with different gate metallizations is postulated to be due to a combination of the difference in Schottky barrier heights and different gate-to-channel spacings due to penetration of the gate metal into the InGaP barrier layer     

Doping efficiency and energy-level scheme in C60F48-doped zinc–tetraphenylporphyrin films

High resolution synchrotron-based core level spectroscopy was used to examine the energy level alignment at the interface of zinc–tetraphenylporphyrin films doped by the surface acceptor C₆₀F₄₈. Two distinct fluorofullerene charge states were identified, corresponding to ionized and neutral molecules, and their relative concentration as a function of coverage was used to evaluate the probability of occupation of the acceptor lowest unoccupied molecular orbital (LUMO). From an initial acceptor energy of ?0.25 eV, the C₆₀F₄₈ LUMO shifts upwards with coverage due to a doping-induced interfacial dipole potential, and stabilization of the LUMO at an energy 0.45 eV above the Fermi energy was obtained. While the energy difference upon saturation is consistent with the results obtained for other donor–acceptor systems that have been interpreted as Fermi level pinning, the present work shows that the energy offset is a direct consequence of the interplay between Fermi–Dirac statistics in combination with the interfacial dipole potential.     

Analysis and optimisation of the HIPERLAN Channel Access Contention Scheme

This paper analyses the HIPERLAN channel access mechanism. Both a purely mathematical and a simulation model are built in order to evaluate the two successive phases of the contention scheme. Several optimisations, based on the choice of parametric values, are proposed, evaluated and compared.     

Respiratory motion of the heart from free breathing coronary angiograms

Respiratory motion compensation for cardiac imaging requires knowledge of the heart's motion and deformation during breathing. This paper presents a method for measuring the natural tidal respiratory motion of the heart from free breathing coronary angiograms. A three-dimensional (3-D) deformation field describing the cardiac and respiratory motion of the coronary arteries is recovered from a biplane acquisition. A cardiac respiratory parametric model is formulated and used to decompose the deformation field into cardiac and respiratory components. Angiograms from ten patients were analyzed. A 3-D translation motion model was sufficient for describing the motion of the heart in only two patients. For all patients, the heart translated caudally (mean, 4.9+/-1.9 mm; range, 2.4 to 8.0 mm) and underwent a cranio-dorsal rotation (mean, 1.5 degrees+/-0.9 degrees; range, 0.2 degrees to 3.5 degrees) during inspiration. In eight patients, the heart also translated anteriorly (mean, 1.3+/-1.8 mm; range, -0.4 to 5.1 mm) and rotated in a caudo-dextral direction (mean, 1.2 degrees+/-1.3 degrees; range, -1.9 degrees to 3.2 degrees).     

Gate length scaling in high performance InGaP/InGaAs/GaAs pHEMTs

The performance of InGaP-based pHEMTs as a function of gate length has been examined experimentally. The direct-current and microwave performance of pHEMTs with gate lengths ranging from 1.0-0.2 μm has been evaluated. Extrinsic transconductances from 341 mS/mm for 1.0 μm gate lengths to 456 mS/mm for 0.5 μm gate lengths were obtained. High-speed device operation has been verified, with f_t of 93 GHz and f_max of 130 GHz for 0.2 μm gate lengths. The dependence of DC and small-signal device parameters on gate length has been examined, and scaling effects in InGaP-based pHEMT's are examined and compared to those for AlGaAs/InGaAs/GaAs pHEMTs. High-field transport in InGaP/InGaAs heterostructures is found to be similar to that of AlGaAs/InGaAs heterostructures. The lower ϵ_r of InGaP relative to AlGaAs is shown to be responsible for the early onset of short-channel effects in InGaP-based devices     

Building maps of local apparent conductivity of the epicardium with a 2-D electrophysiological model of the heart

In this paper, we address the problem of estimating the parameters of an electrophysiological model of the heart from a set of electrical recordings. The chosen model is the reaction-diffusion model on the transmembrane potential proposed by Aliev and Panfilov. For this model of the transmembrane, we estimate a local apparent two-dimensional conductivity from a measured depolarization time distribution. First, we perform an initial adjustment including the choice of initial conditions and of a set of global parameters. We then propose a local estimation by minimizing the quadratic error between the depolarization time computed by the model and the measures. As a first step we address the problem on the epicardial surface in the case of an isotropic version of the Aliev and Panfilov model. The minimization is performed using Brent method without computing the derivative of the error. The feasibility of the approach is demonstrated on synthetic electrophysiological measurements. A proof of concept is obtained on real electrophysiological measures of normal and infarcted canine hearts.     

Regioselective Alkoxylation of 2,2,4-Trimethyl-1,3-pentanediol

An efficient procedure for the regioselective synthesis of secondary alcohol alkoxylates from 2,2,4-trimethyl-1,3-pentanediol (TMPD) is described. TMPD was reacted with propylene oxide followed by ethylene oxide in the presence of a catalytic amount of alkali metal hydroxide to form secondary alcohol alkoxylates. Instead of a mixture of compounds resulting from the reaction of TMPD and propylene oxide, the primary hydroxyl group of the TMPD reacted to form predominantly 2,2,4-trimethyl-3-hydroxypentylpropoxylate as the major product. On further ethoxylation the less hindered secondary hydroxyl group of the 2,2,4-trimethyl-3-hydroxypentylpropoxylate reacted predominantly. ¹³C NMR indicated that the secondary hydroxyl group (96.2 mol%) of TMPD remained unreacted during alkoxylation.