Pulsed power modeling of very-large-aperture,transverse-discharge CO2 lasers

Discharge behavior of large-aperture (10–70 cm) CO₂ lasers is computed using a coupled particle kinetics-equivalent circuit model. Pulsed power systems that produce a single excitation pulse are only able to satisfy the preionization, ignition, and impedance matching conditions for interelectrode gaps 40–50 cm. Double-pulse systems are required for larger gaps, not only to optimize electrical efficiency, but to avoid oscillatory behavior which can lead to arc formation during the second cycle.     

Dynamical precursor of nematic order in a dense fluid of hard ellipsoids of revolution

We investigate hard ellipsoids of revolution in a parameter regime where no long range nematic order is present but already finite-size domains are formed which show orientational order. Domain formation leads to a substantial slowing down of a collective rotational mode which separates well from the usual microscopic frequency regime. A dynamic coupling of this particular mode into all other modes provides a general mechanism which explains an excess peak in spectra of molecular fluids. Using molecular dynamics simulation on up to 4096 particles and on solving the molecular mode coupling equation we investigate dynamic properties of the peak and prove its orientational origin. Received 19 September 2001 and Received in final form 19 March 2002     

Light scattering by longitudinal acoustic modes in supercooled molecular liquids II: microscopic derivation of the phenomenological equations

The constitutive equations for the orientational dynamics of a liquid formed of linear molecules are derived microscopically. The resulting generalised Langevin equations coincide with the phenomenological approach of Dreyfus et al. [1]. Formally exact expressions are given for the phenomenological coefficients and various constraints are shown to be consequences of this microscopic approach. Received 14 August 2002 Published online 4 February 2003 RID="a" ID="a"e-mail: franosch@hmi.de     

On spectral radii of matrices governing some numerical estimating algorithms with incomplete data

Summary Many estimating procedures are carried out with incomplete data by means of different types of EM algorithms. They allow us to obtain maximum likelihood parameter estimates in classical inference and also estimates based on the posterior mode in Bayesian inference. This paper analyzes in detail the spectral radii of the Jacobian matrices algorithm as a possible way to evaluate convergence rates. The eigenvalues of such matrices are explicitly obtained in some cases and, in all of them, a geometric convergence rate is, at least, guaranteed near the optimum. Finally, a comparison between the leading eigenvalues of EM and direct and approximate EM-Bayes algorithms may suggest the efficiency of each case.     

Fast intramolecular dynamics of triphenyl phosphite investigated by <Emphasis Type="Bold">2</Emphasis>H NMR

The first analysis of rapid intramolecular motions of triphenyl phosphite by ²H NMR is presented. The fragile slowing down of the primary relaxation is followed by a solid-echo method. The occurrence of a fast reorientation of the phenyl side groups is demonstrated in the supercooled liquid state, identified as a two-fold flip on the basis of simple lineshape simulations. Coexistence of both static and motionally averaged components in “two phase” spectra indicate a broad distribution of correlation times for this relaxation. This dynamical behavior is shown to persist in the glacial phase. Received 28 May 2002 / Received in final form 1st October 2002 Published online 31 December 2002     

Static observables of relativistic three-fermion systems with instantaneous interactions

We show that static properties like the charge radius and the magnetic moment of relativistic three-fermion bound states with instantaneous interactions can be formulated as expectation values with respect to intrinsically defined wave functions. The resulting operators can be given a natural physical interpretation in accordance with relativistic covariance. We also indicate how the formalism may be generalized to arbitrary moments. The method is applied to the computation of static baryon properties with numerical results for the nucleon charge radii and the baryon octet magnetic moments. In addition, we make predictions for the magnetic moments of some selected nucleon resonances and discuss the decomposition of the nucleon magnetic moments in contributions of spin and angular momentum, as well as the evolution of these contributions with decreasing quark mass.     

Photoemission Spectroscopy and Electronic Structures of LiMn2O4

We study the electronic structures of LiMn2O4 by x-ray and ultraviolet photoelectron spectroscopy （XPS, UPS） and resonant photoelectron spectroscopy （RPES）. XPS data suggest that the average oxidation state of Mn ions is 3.55, probably due to the small amount of lithium oxides on the surface. UPS and RPES data imply that Mn ions are in a high spin state, and RPES results show strong Mn3d-O2p hybridization in the LiMn2O4 valence band.     

Nucleon form factors in a relativistic quark model

Electromagnetic form factors of protons and neutrons are investigated based on a relativistic quark model with the inclusion of a pion cloud. Pseudo-scalar π-quark interaction is employed to study the coupling between the nucleon and the π. The results show the important role of the pion cloud for the neutron charge form factor. Moreover, our numerical analysis indicates a difference between the relativistic and the nonrelativistic treatments. Received: 10 March 1999 / Revised version: 14 June 1999     

Evidence of a two-state picture for supercooled water and its connections with glassy dynamics

The picture of liquid water as consisting of a mixture of molecules of two different structural states (structured, low-density molecules and unstructured, high-density ones) represents a belief that has been around for long time awaiting for a conclusive validation. While in the last years some indicators have indeed provided certain evidence for the existence of structurally different “species”, a more definite bimodality in the distribution function of a sound structural quantity would be desired. In this context, our present work combines the use of a structural parameter with a minimization technique to yield neat bimodal distributions in a temperature range within the supercooled liquid regime, thus clearly revealing the presence of two populations of differently structured water molecules. Furthermore, we elucidate the role of the inter-conversion between the identified two kinds of states for the dynamics of structural relaxation, thus linking structural information to dynamics, a long-standing issue in glassy physics.     

Theoretical investigation of the electronic structure of 1-(3,4; 3,5 and 3,6-bis-selenocyanato-phenyl) pyrrolidinofullerenes

The electronic structures and geometries of 1-(3,4; 3,5 and 3,6-bis-Selenocyanato-phenyl) pyrrolidinofullerenes were investigated theoretically using Density Functional theory at the B3LYP/3-21G∗ and B3LYP/6-31G∗ levels of theory. On all levels of theory the ortho isomer is predicted to be the most stable. The obtained optimized geometries, electronic properties and energetics of structural variables are discussed.