A Simulation Study of the Single Moving Dipole Representation of Cardiac Electrical Activity

A simulation study of the accuracy of the single moving dipole (SMD) cardiac representation was done using a realistic computer model of the human torso. This model included regions of different electrical conductivities such as the lungs and the intraventricular blood masses. Dipolar potential distributions generated on the surface of this model were sampled with different electrode arrangements and were subsequently contaminated with random noise. The location, magnitude, and orientation of the SMD which optimally fitted these potentials were then compared to those of the original dipole source in order to assess the errors in the SMD parameters. The SMD computations were based on a least squares estimation of a variable number of multipolar components recovered inside a torso model which was either finite and homogeneous or finite with lungs. The results showed that the SMD accuracy can be significantly improved by adding higher order multipolar components, e.g., with 120 electrodes and the absence of noise, the rms position error was 15.5 mm with eight multipoles and 0.6 mm with 24 multipoles when the same homogeneous model was used for both the simulation and the recovery. It was also shown that the addition of lungs in the recovery model permitted a higher accuracy when either the lungs, or the lungs with blood masses, were present when the dipolar potential distributions were generated; for these two cases, the rms position errors were thus 1.7 and 4 mm, respectively, using 120 electrodes and 24 multipoles in the absence of noise.     

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Modeling and Multiobjective Optimization of A Fed-Batch Emulsion Copolymerization Process to Control the Resulting Particles Core-Shell Morphology

Summary: This paper deals with the design and control of the morphology of core-shell nanoparticles elaborated by fed-batch emulsion copolymerization of styrene and butyl-acrylate in the presence of a chain transfer agent (n-dodecyl mercaptan). A mathematical model was elaborated and validated. It consists of a system of differential algebraic equations involving 49 unknown kinetic and thermodynamic parameters, many of them being impossible to be accurately estimated, due to the lack of experimental data. A method based on the sensitivity analysis allowed us to determine a subset of the 21 most influential parameters. The 28 non estimable parameters were taken from the literature. The validated model was then used in a dynamic multiobjective optimization to optimize the best profile of the pre-emulsion feed rate to control (i) the composition and average molar masses of the copolymer, (ii) the instantaneous glass transition temperature, corresponding to a core-shell morphology suited for special end-use properties.     

Magnetic nanoparticles with hybrid shape

Co₅₀Ni₅₀ particles with very unusual shapes, resembling dumbbells or diabolos, are obtained by reducing mixtures of cobalt and nickel acetates in sodium hydroxide solution in 1,2-propane diol. These particles consist of a central column richer in cobalt than the overall composition, capped with two terminal platelets that are richer in nickel. These hybrid shapes are the result of a two-step growth mechanism due to a difference in reactivity of the two metal ions. The sodium hydroxide concentration controls the length and diameter of the column, in the ranges 50–250 nm and 5–15 nm, respectively, and the diameter of the platelets in the range 25–50 nm. The X-ray diffraction patterns show a mixture of hcp and fcc phases in various proportions depending on the particle shape. High-resolution electron microscopy shows that the hcp phase is located mainly in the central column and the fcc phase mainly in the terminal platelets. The particles are ferromagnetic at room temperature. When the volume fraction of the central column is high enough and the hcp phase is predominant and not much faulted, high coercivity (up to 1900 Oe) is observed.     

Positive cooperative mechanistic binding of proteins at low concentrations: a comparison of poly (sodium N-undecanoyl sulfate) and sodium dodecyl sulfate

The interactions of the negatively charged achiral molecular micelle, poly (sodium N-undecanoyl sulfate) (poly-SUS), with four different proteins using intrinsic and extrinsic fluorescence spectroscopic probes, are studied. A comparison of poly-SUS with the conventional surfactant, sodium dodecyl sulfate (SDS), and the monomeric species, SUS, is also reported. In this work, we observed that poly-SUS preferentially binds to acidic proteins, exhibiting positive cooperativity at concentrations less than 1 mM for all proteins studied. Moreover, it appears that the hydrophobic microdomain formed through polymerization of the terminal vinyl group of the monomer, SUS, is largely responsible for the superior binding capacity of poly-SUS. From these results, we conclude that the interactions of poly-SUS with the acidic proteins are predominantly hydrophobic and postulate that poly-SUS would produce superior interactions relative to SDS at low concentrations in polyacrylamide gel electrophoresis (PAGE). As predicted, use of poly-SUS allowed separation of the His-tagged tumor suppressor protein, p53, at sample buffer concentrations as low as 0.08% w/v (2.9 mM), which is 24 times lower than required for SDS in the standard reducing PAGE protocol. This work highlights the use of poly-SUS as an effective surfactant in 1D biochemical analysis.     

Comments on: ’Non-symmetrical coupled lines in an inhomogeneous dielectric medium’

Many magnetic multi-level counters count in an upward sequence, but not in reverse sequence, and the counting cores have readouts in the form of analogue displays. This paper shows how to construct a reversible decimal counter with a non-destructive read-out by a toroidal core.     

Stereoselective Syntheses of Tetrahydrolipstatin and of an Analogue,Potent Pancreatic-Lipase Inhibitors Containing a β-Lactone Moiety

Tetrahydrolipstatin ( 1 ) and itsanalogue 2 are representatives of a new class of pancreatic-lipase inhibtors. Two stereoselective synthetic approaches are described.