Maximal efficiency versus the amplification factor in double-cavity klystrons

The dependence of the maximal efficiency on the amplification factor is studied for double-cavity klystrons simulated based on real electron-optical systems and real electrodynamic parameters of cavities. Simulation uses a mathematical model of electron beam transformation in a narrow tube and a KlypWin software suite. It is shown that the maximal efficiency of such klystrons, 46–47%, is achieved at an amplification factor of 16–18 dB.     

Letter: Classical and Quantum Evolution of Non-Isentropic Hot Singular Layers in Finite-Temperature General Relativity

The spherically symmetric layer of matter isconsidered within the frame-works of general relativity.We perform a generalization of the already known theoryfor the case of nonconstant surface entropy and finite temperature. We also propose theminisuperspace model to determine the behavior of thetemperature field and perform the Wheeler-DeWittquantization.     

Harmonic Crystal on the Wall: A Microscopic Approach

A three dimensional Winterbottom type construction in the regime of partial wetting is derived in a scaling limit of a gas of microscopic Gaussian SOS droplets under the fixed volume constraint. The proof is based on a coarse graining of the random microscopic region “wetted” by the crystal, random walk representations of various quantities related to free massless fields and a stability analysis of the torsional rigidity problem. Received: 28 August 1996 / Accepted: 23 December 1996     

Collapse of a Bose gas: Kinetic approach

We have analytically explored the temperature dependence of critical number of particles for the collapse of a harmonically trapped attractively interacting Bose gas below the condensation point by introducing a kinetic approach within the Hartree?CFock approximation. The temperature dependence obtained by this easy approach is consistent with that obtained from the scaling theory.     

Gravitational Collapse: A Case for Thermal Relaxation

Two relativistic models for collapsing spheres at different stages of evolution, which include pre-relaxation processes, are presented. The influence of relaxation time on the outcome of evolution in both cases is exhibited and established. It is shown that relaxation processes can drastically change the final state of the collapsing system. In particular, there are cases in which the value of the relaxation time determines the bounce or the collapse of the sphere.     

Maximal lensing: mass constraints on point lens configurations

We set constraints and an upper bound on the masses required for a configuration of n point lenses to produce the maximum of 5n − 5 images of a distant source. We show how this result can be used to detect and constrain the mass of planets or brown dwarfs in multiple-star systems.     

Collapse of polyelectrolyte brushes: Scaling theory and simulations

We investigate polyelectrolyte brushes using both scaling arguments and molecular dynamics simulations. As a main result, we find a novel collapsed brush phase. In this phase, the height of the brush results from a competition between steric repulsion between ions and monomers and an attractive force due to electrostatic correlations. As a result, the monomer density inside the brush is independent of the grafting density and the polymerization index. For small ionic and monomer radii (or for large Bjerrum length) the brush undergoes a first-order phase transition from the osmotic into the collapsed state. Received 26 September 2000     

Harmonic confinement: A fully relativistic approximation to the meson spectrum

We propose a pair of covariant wave equations describing mesons as confined q$\text{q}$ pairs and realizing a spontaneously broken chiral symmetry. The system is Hamiltonian and does not contain unphysical solutions. The force is harmonic. The hyperfine splitting is given by the universal slope of the linear Regge trajectories.     

Collapse temperature of bacterial suspensions: the effect of cell type and concentration

The characterisation of the physical state of frozen and freeze dried biological products delivers powerful information for freeze-drying process optimisation. The influence of lactic acid bacterial cell size, shape and concentration on collapse temperature of concentrated bacterial suspensions was investigated. Lactobacillus bulgaricus (long rods), and Streptococcus thermophilus (small spherical cells) were used as cellular models for this study. Whatever the strain, when lactic acid bacterial cells were added to protective solutions, the collapse temperature increased, thus allowing the use of higher sublimation temperatures during primary drying than expected from the protective medium alone. Moreover, the higher the cell concentration, the greater the effect, linear relationships existing between the collapse temperatures and the total dried matter. Cells of both strains gave a kind of robustness to the freeze-dried product, but the increase observed in collapse temperature was considerably higher (3 - 5 degree C) for L. bulgaricus compared to S. thermophilus. This result was ascribed to the different size and shape of the strains.     

Second Harmonic Generation Measurements for Biomacromolecules: Celluloses

The molecular chain orientation of mercerized cellulose II was examined by optical second harmonic generation (SHG) measurements. The SHG intensities of several kinds of mercerized cellulose II were found to be much larger than those expected for a structural model with an antiparallel molecular chain orientation as proposed by X-ray studies. This result suggests that the orientation of mercerized cellulose II is parallel as suggested by molecular dynamics simulation. © 2004 The Optical Society of Japan     

Stellar Collapse in the Time Dependent Hartree-Fock Approximation

We prove blow-up in finite time for radially symmetric solutions to the pseudo-relativistic Hartree-Fock equation with negative energy. The non-linear Hartree-Fock equation is commonly used in the physics literature to describe the dynamics of white dwarfs. We extend thereby recent results by Fröhlich and Lenzmann, who established in [3,4] blow-up for solutions to the pseudo-relativistic Hartree equation. As key ingredient for handling the exchange term we use the conservation of the expectation of the square of the angular momentum operator.     

Letter: Self-Similar Collapse of Scalar Field with Plane Symmetry

Plane symmetric self-similar solutions to Einstein's four-dimensional theory of gravity are studied and all such solutions are given analytically in closed form. The local and global properties of these solutions are investigated and it is shown that some of the solutions can be interpreted as representing gravitational collapse of the scalar field. During the collapse, trapped surfaces are never developed. As a result, no black hole is formed. Although the collapse always ends with spacetime singularities, it is found that these singularities are spacelike and not naked.     

Letter: Junction Conditions of Spherically Symmetric Collapse with Dissipation

A spherically symmetric collapse of a fluid with bulk viscosity and heat conduction is investigated. It is found that the junction conditions of the limited region of a radiation zone require a faster decay of a collapsing star.