Resurgence in quasiclassical scattering

In quasiclassical spectral theory, "resurgence" means that long periodic orbits can be expressed by short ones in such a way that the spectral determinant is real. The question has thus long been posed whether long scattering orbits can be expressed by short orbits in such a way as to make the quasiclassical scattering matrix unitary. We here find a resurgent and manifestly Hermitean expression for Wigner's R matrix, implying a unitary scattering matrix. The result is particularly important if the average resonance width is comparable with the average resonance spacing.     

Lineshape and moment analysis of the dynamic susceptibility in ferromagnets. Iron above Tc

A method is described for separating the magnetic response function of ferromagnets into magnon creation and annihilation parts, even above the Curie temperature. In the simplest approximation the lineshape is Gaussian in the magnitude of the momentum transfer at constant energy, and this is observed in iron. The magnitude, energy dependence, and temperature dependence of the line width and peak position are as predicted. An exact moment analysis lends support to the approximate expression.     

Etude par RMN 1H des effets de solvant sur les déplacements chimiques et les couplages vincinaux des benzothiénopyridines

The solvent/solute interactions of four isomeric benzothienopyridines (parent compounds) have been investigated by ¹H n.m.r. A close study of the second-order spectra shows: (i) a preferential orientation of the solvent molecules (acetone) surrounding the pyridine ring; (ii) large variations in the coupling constants of the benzenic part of the benzothienopyridines as a function of the solvent; (iii) a preferential interaction of the pyridine ring in collision complexes with benzene. These results can be applied to a comparative study of the complexes between DNA base pairs and intercalating derivatives.     

In-line concentration measurement in complex liquids using ultrasonic sensors

Recently there has been increased demand for chemical sensors measuring in-line the concentration of selected substances in complex liquids in order to guarantee a high product quality in the process industry. At present there is a great interest in acoustic sensor systems for concentration measurements. This article presents a new ultrasonic sensor system consisting of a miniaturized multi-sensor arrangement for the comprehensive acoustic characterization of liquid mixtures. The sensor system measures sound velocity, impedance coefficient, attenuation coefficient and temperature.     

Gas-phase deprotonation of arylalkylamines. A collision-induced dissociation study

The collision-induced dissociation (CID) of deprotonated arylalkylamines of general formula R(1)C(6)H(4)CHR(2)CH(2)NR(3)(2) (where R(1) = H, OH, F or NO(2); R(2) = H or OH; R(3) = H or CH(3)) generated by negative chemical ionization with H(2)O and D(2)O as ionizing reagents, is discussed. The negative chemical ionization mass spectra show that, in the absence of a hydroxy group in the aromatic ring, deprotonation takes place at the benzylic position whereas the proton is lost from the OH group when present. The nitro compound forms only M(-.) ions. The CID spectra of the deprotonated molecules show that fragmentations are strongly dependent on the structural features of the molecules, namely the presence or absence of substituents in the aromatic ring or aliphatic chain. Copyright 1999 John Wiley & Sons, Ltd.     

Quantifying uncertainty in NMR T2 spectra using Monte Carlo inversion

Relaxation and diffusion data are often analyzed using a Laplace inversion algorithm that incorporates regularization. Regularization is used because Laplace inversion with finite and noisy data is an ill-conditioned problem for which many solutions exist for a given data set. This paper reports a different approach. Instead of finding a "best" solution by some ad hoc criterion, we developed an efficient Monte Carlo algorithm that generates thousands of probable solutions from which the statistical properties of the solution can be analyzed. We find that although all of the individual solutions are spiky, the mean solution spectrum is smooth and similar to the regularized solution. From the Monte Carlo solutions we obtain probability distributions for quantities derived from the spectrum, such as porosity and bound fluid. This ability to characterize the uncertainty of such quantities is novel.     

Direct comparison of capillary electrophoresis and capillary liquid chromatography hyphenated to collision-cell inductively coupled plasma mass spectrometry for the investigation of Cd-, Cu- and Zn-containing metalloproteins

Capillary liquid chromatography (cLC) and capillary electrophoresis (CE) have been critically compared for the separation of metalloproteins when using collision-cell inductively coupled plasma mass spectrometry (ICP-CC-MS) as detection system. For cLC separation, the selected column was a C8 (0.3 mm I.D.) and the separation conditions involved a gradient up to 80% methanol in 10mM ammonium acetate buffer (pH 7.4). The low flow rate used (3 microL min(-1)) permitted the utilization of a high methanol content maintaining the sensitivity along the whole chromatographic run. For this purpose, a new low-flow interface has been developed based on a total consumption nebulizer. Similarly, CE has been studied as separation technique using a 75 microm I.D. fused silica capillary and a running buffer of 20 mM Tris-HNO3 (pH 7.4) and working at 30 kV. Metallothionein (mixture of MT-I and -II) and superoxide dismutase (SOD) have been used as protein models in order to evaluate the separation/detection capabilities using the same injection volumes in both systems (20 nL). For both hybrid systems, separation parameters such as retention factor, numbers of theoretical plates, tailing factor and resolution have been critically compared. Also, the analytical performance characteristics of both hybrid systems have been evaluated and tested by analyzing the Cu-, Zn-species present in red blood cell extracts in order to explore more adequate separation methodology for the analysis of metalloproteins in complex matrices.     

Steering in computational science: Mesoscale modelling and simulation

This paper outlines the benefits of computational steering for high performance computing applications. Lattice-Boltzmann mesoscale fluid simulations of binary and ternary amphiphilic fluids in two and three dimensions are used to illustrate the substantial improvements which computational steering offers in terms of resource efficiency and time to discover new physics. We discuss details of our current steering implementations and describe their future outlook with the advent of computational grids.