8,749 research outputs found
On Lyapunov-Krasovskii Functionals for Switched Nonlinear Systems with Delay
We present a set of results concerning the existence of Lyapunov-Krasovskii
functionals for classes of nonlinear switched systems with time-delay. In
particular, we first present a result for positive systems that relaxes
conditions recently described in \cite{SunWang} for the existence of L-K
functionals. We also provide related conditions for positive coupled
differential-difference positive systems and for systems of neutral type that
are not necessarily positive. Finally, corresponding results for discrete-time
systems are described.Comment: 19 Page
Production of radioactive aerosols in the radiation field of the synchro-cyclotron at the Leningrad Nuclear Physics Institute
The Stabilization of Superconductivity by Magnetic Field in Out-of-Equilibrium Nanowires
A systematic study has been carried out on the previously reported
"magnetic-field-induced superconductivity" of Zn nanowires. By varying
parameters such as magnetic field orientation and wire length, the results
provide evidence that the phenomenon is a nonequilibrium effect associated with
the boundary electrodes. They also suggest there are two length scales
involved, the superconducting coherence length and quasiparticle relaxation
length. As wire lengths approach either of these length scales, the effect
weakens. We demonstrate that it is appropriate to consider the effect to be a
stabilization of superconductivity, that has been suppressed by an applied
current.Comment: (Updated Version) 9 pages, 8 figure
Profiles of inflated surfaces
We study the shape of inflated surfaces introduced in \cite{B1} and
\cite{P1}. More precisely, we analyze profiles of surfaces obtained by
inflating a convex polyhedron, or more generally an almost everywhere flat
surface, with a symmetry plane. We show that such profiles are in a
one-parameter family of curves which we describe explicitly as the solutions of
a certain differential equation.Comment: 13 pages, 2 figure
Non-equilibrium statistical mechanics of classical nuclei interacting with the quantum electron gas
Kinetic equations governing time evolution of positions and momenta of atoms
in extended systems are derived using quantum-classical ensembles within the
Non-Equilibrium Statistical Operator Method (NESOM). Ions are treated
classically, while their electrons quantum mechanically; however, the
statistical operator is not factorised in any way and no simplifying
assumptions are made concerning the electronic subsystem. Using this method, we
derive kinetic equations of motion for the classical degrees of freedom (atoms)
which account fully for the interaction and energy exchange with the quantum
variables (electrons). Our equations, alongside the usual Newtonian-like terms
normally associated with the Ehrenfest dynamics, contain additional terms,
proportional to the atoms velocities, which can be associated with the
electronic friction. Possible ways of calculating the friction forces which are
shown to be given via complicated non-equilibrium correlation functions, are
discussed. In particular, we demonstrate that the correlation functions are
directly related to the thermodynamic Matsubara Green's functions, and this
relationship allows for the diagrammatic methods to be used in treating
electron-electron interaction perturbatively when calculating the correlation
functions. This work also generalises previous attempts, mostly based on model
systems, of introducing the electronic friction into Molecular Dynamics
equations of atoms.Comment: 18 page
Nucleon polarizabilities in the perturbative chiral quark model
The nucleon polarizabilities alpha(E) and beta(M) are studied in the context
of the perturbative chiral quark model. We demonstrate that meson cloud effects
are sufficient to explain the electric polarizability of nucleon. Contributions
of excite quark states to the paramagnetic polarizability are dominant and
cancel the diamagnetic polarizability arising from the chiral field. The
obtained results are compared to data and other theoretical predictions.Comment: 25 pages, 18 figures, 2 table
Role of the mean curvature in the geometry of magnetic confinement configurations
Examples are presented of how the geometric notion of the mean curvature is
used for general magnetic field configurations and magnetic surfaces. It is
shown that the mean magnetic curvature is related to the variation of the
absolute value of the magnetic field along its lines. Magnetic surfaces of
constant mean curvature are optimum for plasma confinement in multimirror open
confinement systems and rippled tori.Comment: PDFLaTeX, 10 pages, 5 figure
The Effect of Air Density on Atmospheric Electric Fields Required for Lightning Initiation from a Long Airborne Object
The purpose of the work was to determine minimum atmospheric electric fields required for lightning initiation from an airborne vehicle at various altitudes up to 10 km. The problem was reduced to the determination of a condition for initiation of a viable positive leader from a conductive object in an ambient electric field. It was shown that, depending on air density and shape and dimensions of the object, critical atmospheric fields are governed by the condition for leader viability or that for corona onset. To establish quantitative criteria for reduced air densities, available observations of spark discharges in long laboratory gaps were analyzed, the effect of air density on leader velocity was discussed and evolution in time of the properties of plasma in the leader channel was numerically simulated. The results obtained were used to evaluate the effect of pressure on the quantitative relationships between the potential difference near the leader tip, leader current and its velocity; based on these relationships, criteria for steady development of a leader were determined for various air pressures. Atmospheric electric fields required for lightning initiation from rods and ellipsoidal objects of various dimensions were calculated at different air densities. It was shown that there is no simple way to extend critical ambient fields obtained for some given objects and pressures to other objects and pressures
Compton Scattering from the Deuteron and Extracted Neutron Polarizabilities
Differential cross sections for Compton scattering from the deuteron were
measured at MAX-lab for incident photon energies of 55 MeV and 66 MeV at
nominal laboratory angles of , , and . Tagged
photons were scattered from liquid deuterium and detected in three NaI
spectrometers. By comparing the data with theoretical calculations in the
framework of a one-boson-exchange potential model, the sum and difference of
the isospin-averaged nucleon polarizabilities, and (in units of fm),
have been determined. By combining the latter with the global-averaged value
for and using the predictions of the Baldin sum rule for
the sum of the nucleon polarizabilities, we have obtained values for the
neutron electric and magnetic polarizabilities of (total) (model) and (total) (model), respectively.Comment: 4 pages, 2 figures, revtex. The text is substantially revised. The
cross sections are slightly different due to improvements in the analysi
- …