Pseudo-Strong Regularity Around a Set

A generalization of strong regularity around a vertex subset C of a graph Γ, which makes sense even if Γis non-regular, is studied. Such a structure appears, together with a kind of distance-regularity around C , when an spectral bound concerning the so-called predistance polynomial of C is attained. As a main consequence of these results, it is shown that a regular (connected) graph Γwith d + 1 distinct eigenvalues is distance-regular, and its distance- d graph Γ d is strongly regular with parameters a = c , if and only if the number of vertices at distance d from each vertex satisfies an expression which depends only on the order of Γand the different eigenvalues of Γ.     

To the spectral theory of Krein systems

We consider the Krein systems. For the set of Stummel class coefficients, we establish the criterion in terms of these coefficients for the system to satisfy the Szegö-type estimate on the spectral measure.     

Laser writing techniques for photomask fabrication using a femtosecond laser

Photomasks are the backbone of microfabrication industries. Currently they are fabricated by a lithographic process, which is very expensive and time consuming since it is a multi-step process. These issues can be addressed by fabricating photomasks by direct femtosecond laser writing, which is a single-step process and comparatively cheaper and faster than lithography. In this paper we discuss our investigations on the effect of two types of laser writing techniques, namely front- and rear-side laser writing, with regard to the feature size and the edge quality of a feature. It is proved conclusively that for the patterning of masks, front-side laser writing is a better technique than rear-side laser writing with regard to smaller feature size and better edge quality. Moreover the energy required for front-side laser writing is considerably lower than that for rear-side laser writing. Received: 22 May 2001 / Accepted: 14 September 2001 / Published online: 17 October 2001     

Tablet disintegration monitored by magnetic resonance imaging

The disintegration of bromhexin tablets was monitored by magnetic resonance imaging. The fast imaging method FLASH with spoiling gradients was used to obtain images of the tablets in short time intervals. The rate of the disintegration depends on the preparation method, kind and percentage of the carrier (polyethylene glycol, lactose). Solid dispersion with slow evaporation of solvent yields materials with decreased dissolution rate. Increasing molecular mass of polyethylene glycol and its percentage content also hampers disintegration.     

Formation on field emitters coated with fullerenes of microformations producing ordered emission images

Field emission projector studies of fullerene coatings deposited on tungsten tip field emitters reveal specific ordered patterns in the form of doublets, quadruplets, rings, disks, and other forms in the emitter images. The ways in which these types of ordered emission patterns arise and their relation to C₆₀ microformations have been established. Possible causes of the emergence of the ordered emission images are analyzed on the basis of published data and experimental results obtained. A modification of the model of field emission from the surface of microformations taking into account internal reflection of the electronic waves from the formation boundaries has been proposed.     

Effect of amorphization on the electronic and lattice specific heat of an Ni2B alloy

The specific heats of the Ni₂B amorphous system and of its crystal analog were studied in the temperature range 3–270 K. The data obtained permitted us to isolate the contribution due to atomic vibrations from the experimentally measured specific heat, determine the electronic density of states at the Fermi level and the temperature dependence of the characteristic Debye parameter Θ, and to calculate some average frequencies (moments) of the vibrational spectrum. The electronic density of states at the Fermi level increases under amorphization. An analysis of the temperature dependence of the lattice specific heat showed that amorphization brings about a substantial growth in the density of vibrational states at low frequencies, whereas the spectrum-averaged and rms frequencies change very little, which is in good agreement with neutron diffraction measurements.     

The simulation of dendrite growth and partial discharges in epoxy resin

A self-consistent model of the development of dendrites and partial discharges in a dielectric solid under a variable voltage is suggested. Dendrites originate at sites with the enhanced local field strength and also where the dielectric is broken down under the action of partial discharges. The numerical simulation is used to quantitatively describe the space-time dynamics of the dendrites and partial discharges in epoxy resin for the tip-plane electrode configuration. The simulated data are compared with electrical measurements of partial discharges and with optical images of dendrite growth under the same conditions.     

Aspects of alpha-particle scattering and structure of the nuclear surface

The interaction of α particles above 5 MeV with a 2s-1d target is dominated by resonances. It cannot be described only in terms of a mean-field one-body potential. An analysis of the elastic α-particle scattering by ²⁸Si encourages the comprehension of the resonance states to be mainly fragments of a mixed-parity band. In the present article, the angular distributions of particles scattered by ³²S are analyzed in terms of such bands. The analysis of new data from an experiment made at Florida State University reveals the existence of states that do not belong to the above bands. This follows from a coupled-channel analysis of the elastic and inelastic (2⁺) cross sections. An α-particle structure at the nuclear surface is suggested.     

Switching kinetics of ferroelastic ferroelectrics

Switching kinetics of uniaxial ferroelastic ferroelectrics (FFs) in external electric and stress fields is studied using classical theory of nucleation and growth. The stage in which the polarization and deformation reversal involves the main body of the FF and the final stage (Ostwald ripening) of the FF switching are studied with allowance for the change in the repolarization and redeformation during the phase transition. The time dependences of the repolarization and redeformation are found, and equations are derived from which the polarization current and the deformation flux, as well as their time dependence, can be calculated. The calculated main characteristics of the FF switching are compared with the experimental data for switching of Rochelle salt single crystals.