Dichotomous Hamiltonians with Unbounded Entries and Solutions of Riccati Equations

An operator Riccati equation from systems theory is considered in the case that all entries of the associated Hamiltonian are unbounded. Using a certain dichotomy property of the Hamiltonian and its symmetry with respect to two different indefinite inner products, we prove the existence of nonnegative and nonpositive solutions of the Riccati equation. Moreover, conditions for the boundedness and uniqueness of these solutions are established.Comment: 31 pages, 3 figures; proof of uniqueness of solutions added; to appear in Journal of Evolution Equation

Rotations in isospace: a doorway to the understanding of neutron-proton superfluidity in N=Z nuclei

The $T$=2 excitations in even-even $N$=$Z$ nuclei are calculated within the isospin cranked mean-field approach. The response of pairing correlations to rotation in isospace is investigated. It is shown that whereas the isovector pairing rather modestly modifies the single-particle moment of inertia in isospace, the isoscalar pairing strongly reduces its value. This reduction of the moments of inertia in isospace with respect to its rigid body value is a strong indicator of collective isoscalar pairing correlations. Beautiful analogies between the role of isovector pairing for the case of spatial rotations and the role of isoscalar pairing for the case of iso-rotations are underlined

Nonlinear viscoelasticity of metastable complex fluids

Many metastable complex fluids such as colloidal glasses and gels show distinct nonlinear viscoelasticity with increasing oscillatory-strain amplitude; the storage modulus decreases monotonically as the strain amplitude increases whereas the loss modulus has a distinct peak before it decreases at larger strains. We present a qualitative argument to explain this ubiquitous behavior and use mode coupling theory (MCT) to confirm it. We compare theoretical predictions to the measured nonlinear viscoelasticity in a dense hard sphere colloidal suspensions; reasonable agreement is obtained. The argument given here can be used to obtain new information about linear viscoelasticity of metastable complex fluids from nonlinear strain measurements.Comment: 7 pages, 3 figures, accepted for publication in Europhys. Let

Displacement on the San Andreas fault subsequent to the 1966 Parkfield earthquake

Immediately following the 1966 Parkfield earthquake a continuing program of fault displacement measurements was undertaken, and several types of instruments were installed in the fault zone to monitor ground motion. In the year subsequent to the earthquake a maximum of at least 20 cm of displacement occurred on a 30 km section of the San Andreas fault, which far exceeded the surficial displacement at the time of the earthquake. The rate of displacement decreased logarithmically during this period in a manner similar to that of the decrease in aftershock activity. After the initial high rate of activity it could be seen that most of the displacement was occurring in 4–6 day epochs of rapid creep following local aftershocks. The variation of fault displacement along the surface trace was measured and shown to be consistent with a vertidal fault surface 44 km long and 14 km deep, along which a shear stress of 2.4 bars was relieved

Pairing in Nuclei

Simple generic aspects of nuclear pairing in homogeneous medium as well as in finite nuclei are discussed. It is argued that low-energy nuclear structure is not sensitive enough to resolve fine details of nuclear nucleon-nucleon (NN) interaction in general and pairing NN interaction in particular what allows for regularization of the ultraviolet (high-momentum) divergences and a consistent formulation of effective superfluid local theory. Some aspects of (dis)entanglement of pairing with various other effects as well as forefront ideas concerning isoscalar pairing are also briefly discussed.Comment: Invited talk presented at the International Conference on Finite Fermionic Systems, Nilsson Model 50 Years,Lund, Sweden, June 14-18, 2005, 7 LaTeX pages, 4 encapsulated postscript figure

Evaluation of the local physical activity and sport network in Nendaz: results of two cross-sectional population-based surveys

The aim of local physical activity and sport networks in Switzerland is to improve co-operation between different players in physical activity and sport promotion in a community, town or region. Nendaz has introduced such a network in 2004. Two postal questionnaire surveys were carried out in 2005 and 2007. The local network in Nendaz reached a high level of awareness, its utilisation in the population and satisfaction were generally good. Physical activity behaviour was high in both years compared to the general French-speaking population in Switzerland. In order to judge the effects of such an intervention on the population level, baseline surveys should be carried out before the start of the project and control communities should be studied simultaneously