Spectral-kinetic relationships for the room-temperature phosphorescence of polycyclic aromatic hydrocarbons in micellar solutions

Lifetimes of triplet sates of molecules of different polycyclic aromatic hydrocarbons are measured in the system 0.1 M sodium dodecyl sulfate-0.025 M thallium nitrate-0.01 M sodium sulfite are measured, and the dependences of these quantities on the spectral luminescence characteristics are determined. Based on the obtained results, the application range of room-temperature phosphorimetry with time and spectral selection for the determination of individual polycyclic aromatic hydrocarbons in mixtures is determined.     

Measurements of the np total cross section difference DsL\Delta \sigma_L at 1.59, 1.79 and 2.20 GeV

New results of the neutron-proton spin-dependent total cross section difference at the neutron beam kinetic energies 1.59, 1.79 and 2.20 GeV are presented. Measurements were performed at the Synchrophasotron of the Laboratory of High Energies of the Joint Institute for Nuclear Research in Dubna. A quasi-monochromatic neutron beam was produced by break-up of extracted polarized deuterons. Neutrons were transmitted through a large polarized proton target. Measurements were performed either with a parallel or an antiparallel beam and target polarizations, both oriented along the beam momentum. The results at the two higher energies were measured with two opposite beam and target polarization directions. Only one target polarization direction was available at 1.59 GeV. The present measurements agree well with existing data. A fast decrease of the values with increasing energy above 1.1 GeV was confirmed. The new results are also compared with model predictions and with phase shift analysis fits. The quantities for isosinglet state I=0, deduced from the measured values and known data, are given. Received: 19 August 1999 / Published online: 3 February 2000     

Flexoelectric polarization in nematic liquid crystals measured by a field on-off pyroelectric technique

A novel technique based on the pyroelectric effect is developed for making direct measurements of the flexoelectric polarization P _f in hybrid aligned nematic cells. The pyroelectric response is measured first in the field-off regime and then with the bias field applied. The latter allows a direct comparison of P _f with the field-induced polarization over the whole range of the nematic phase of the standard compound 5CB. The sum of the flexoelectric coefficients (e ₁+e ₃) is shown to be negative, and its dependence on the nematic order parameter does not follow a simple law (linear or quadratic), as has been predicted theoretically. The dynamics of P _f is discussed in terms of the order parameter fluctuations. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 220–225 (10 February 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.     

High-Current Electron-Beam Transport in the LIA-5 Linear Induction Accelerator

Physics of Particles and Nuclei Letters - The issue of high-current electron-beam transport in the LIA-5 accelerator is discussed. The results of numerical simulation of beam transport in the...     

Electro-Optic Effect in Thin Films of a Dielectric and a Ferroelectric with Subwavelength Aluminum Grating

The electro-optic effect in three nanoscale heterostructures, in each of which a thin layer of dielectric or ferroelectric material is inserted between two planar metal electrodes, has been studied. Each structure has one aluminum layer, containing a subwavelength grating with a period of 400 nm, contacting with either the glass substrate or air. The light transmission spectra of structures with subwavelength grating contain characteristic plasmon dips. Short external-voltage pulses affect the change in the refractive index of the corresponding active layer. Significant values of these changes may be useful for designing optical modulators.     

Stabilization of the equilibria of dynamical systems

Based on Rumyantsev's method, a procedure is developed for stabilizing stable and unstable equilibria of dynamical systems by continuous and modulus-constrained control actions. It is shown that, when modulus constraints are imposed on the controls, and when the quadratic-form coefficients are reduced in modulus, the optimal stabilization, in terms of this method, approximates to time-optimal stabilization. A solution is obtained of the problem of stabilizing unstable equilibrium positions at which the potential energy of the system has neither a maximum nor a minimum (or, in particular, at which the potential energy is identically equal to zero).     

Synthesis of polyphilic compounds Evidence for ferroelectricity in a non-chiral mesophase

The synthesis and properties of new mesomorphic ferroelectrics composed of nonchiral polyphilic molecules are described. Polyphilic molecular units are made up of a sequence of chemical fragments differing by their chemical nature. The segregation between unlike species is used to favour a polar packing. Ferroelectricity is demonstrated by the measurement of an acoustically induced piezoelectric response and the determination of repolarization currents. It is the first time that a ferroelectric repolarizable mesophase is obtained with non-chiral molecular units. The mechanism of ferroelectricity is therefore different from that found in conventional chiral smectic C.     

Oxidative destruction of polymers under stress

The effect of stresses on the reactivity of macromolecules in chemical reactions has been studied. This effect may be a promoting, inhibiting or neutral effect. Experimental results are satisfactorily explained in terms of a transition complex approach and conformation analysis, by comparison of the energy changes in the initial and transition states under structural strain in a reacting fragment. Our concept, based on the reactivity change, has shed new light on the well-known ‘critical’ strain phenomenon in the ozone corrosion of rubbers. In the case of saturated polyolefins (polyethylene and polypropylene) it was found that the oxidation rate is proportional to exp σ, where σ is the stress, applied to uniaxially oriented films.     

The motion of a point mass along a string

An equation for the trajectory of a point mass (a particle) when it moves (slides) in a plane by inertia along a weightless elastic thread (string), stretched between two fixed points is obtained. The time dependence of the trajectory parameter is established. An equation of the trajectory of the particle when it suddenly decelerates is obtained. Forced motion of the particle along a straight string (as a model of the swinging of a lift on an elastic tether in zero gravity) is considered.