Power penalty of cascaded Bragg gratings in the presence of PMD and PDL

Considering the presence of birefringence in Bragg gratings, the spectral polarization mode dispersion (PMD) and polarization dependent loss (PDL) induced power penalty of eye opening is examined for a network with cascaded Bragg gratings. It is shown that when the birefringence in the grating is less than 10⁻⁵, the induced power penalty is less than 0.1 dB for a network with up to 30 cascaded Bragg gratings. However, when the grating birefringence is on the order of 10⁻⁴, the induced power penalty can be as high as 5.6 dB for a network with 14 cascaded Bragg gratings.     

Effect of pressure on soot formation in the pyrolysis of <Emphasis Type="Italic">n</Emphasis>-hexane and the oxidation of fuel-rich mixtures of <Emphasis Type="Italic">n</Emphasis>-heptane behind reflected shock waves

The results of detailed kinetic simulations of the formation of soot particles in the pyrolysis of n-hexane–argon mixtures and in the oxidation of fuel-rich (φ = 5) n-heptane–oxygen–argon mixtures behind reflected shock waves at pressures of 20–100 bar and a constant concentration of carbon atoms or a constant fraction of argon in the initial mixture within the framework of a modified reaction mechanism are reported. The choice of n-hexane and n-heptane for examining the effect of pressure on the process of soot formation was motivated by the availability for these hydrocarbons of experimental measurements in reflected shock waves at high pressures (up to ~100 bar). The temperature dependences of the yield of soot particles formed in the pyrolysis of n-hexane are found to be very weakly dependent on pressure and slightly shifting to lower temperatures with increasing pressure. In general, pressure produces a very weak effect on the soot formation in the pyrolysis of n-hexane. The effect of pressure and concentration of carbon atoms in the initial mixture on the process of soot formation during the oxidation of fuel-rich n-heptane mixtures behind reflected shock waves is studied. The results of our kinetic simulations show that, for both the pyrolysis of n-hexane and the oxidation of fuel-rich n-heptane–oxygen mixtures, the influence of pressure on the process of soot formation is negligible. By contrast, the concentration of carbon atoms in the initial reaction mixture produces a much more pronounced effect.     

Excited singlet-state absorption in laser dyes at the XeCl wavelength

The transmission properties of the laser dyes BBQ, PBD, BPBD, -NPO,p-Quarterphenyl and PPO have been measured using a XeCl (308 nm) excimer laser. A model for the dye saturation which incorporates excited-state absorption was used to estimate the lifetime and the absorption cross section of the first excited singlet-state for each dye.     

Properties and structure of compositions of polyethylene and san-copolymer

Some strength-deformation and rheological properties of compositions of PE and SAN-copolymer obtained by three methods were studied. Light-microscopy analyses were made. It was established that the structural characteristics and the properties of the mixtures depend on the method of production rather than on composition.     

Crystallization of systems of water and polyoxyethylene

The thermal behaviour of systems of water and polyoxyethylenes (POE) of different molecular weights was investigated by differential scanning calorimetry at a cooling rate of 5 deg/min^–1. In the narrow concentration range 55–60 wt% POE, the systems showed a reduced crystallization ability or no crystallization at all. The tendency to supercooling in the water/POE systems is highest at eutectic and slightly higher POE concentrations, and rises with increasing POE molecular weight.

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Zusammenfassung Das thermische Verhalten der Systeme von Wasser und Polyäthylenen (POE) verschiedenen Molekulargewichts wurde mittels DSC bei einer Abkühlgeschwindigkeit von 5° min^–1 untersucht. In dem engen Konzentrationsbereich von 55–60 Gew.-% POE weisen die Systeme eine verminderte oder überhaupt keine Neigung zur Kristallisation auf. Die Tendenz der Wasser/POE-Systeme zur Unterkühlung ist bei eutektischen und etwas höheren POE-Konzentrationen am größten und wird mit ansteigendem POE-Molekulargewicht ausgeprägter.

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5°/ — () . (55–60 . %) . — .

     

Low temperature acoustic properties in YBa2Cu3O7−δ

Temperature dependencies of acoustic lossesQ ^–1 and of relative sound velocity change v/v in YBa₂Cu₃O_7– up to 60 K are calculated by the tunneling model theory. The tunneling systems are related to the off-centered positions of the apical oxygen atoms O(A) and are described through the pseudo-Jahn-Teller effect. Tunneling systems' parameters are distributed in narrow range of values and are in correspondence with the experimentally observed infrared phonon spectra and thermal ellipsoids of O(A). Respective relaxation times are calculated by the adapted reaction rate method. The calculatedQ ^–1(T) and v(T)/v dependencies are in good agreement with the experimental data, which is an additional support to the conclusion about the existence of tunneling systems in YBa₂Cu₃O_7– due to the pseudo Jahn-Teller effect.     

Non-Resonant Photoionization Optogal Vanic Effect in Hollow Cathode Glow Discharge

Abstract

This non-resonant optogalvanic effect caused by photoionization of the atoms lying at high excited levels is investigated in this work on the base of Neatoms in a hollow cathode glow discharge.     

Vibrational spectra of hexagonal crystalline polyoxymethylene

Infrared and Raman spectra of two hexagonal crystalline forms of polyoxymethylene were measured, and the characteristic infrared bands have been determined. The Raman spectra of these two forms do not differ. The vibrational spectra of both forms can be explained by the occurrence of defects in the helical structure of one of them.