Structural and spectroscopic studies of silylated cyclo- and bicyclosilanes

A number of cyclo-and bicyclosilanes have been prepared and structurally characterized by X-ray crystallography and Raman spectroscopy. 1,1,4,4- and 1,1,3,3-tetrakis(trimethylsilyl)octamethylcyclohexasilanes were found to exhibit unusual twist- and twisted boat-conformations. The UV absorption properties of all compounds were studied and found to show absorption maxima red shifted compared to the parent compound dodecamethylcyclohexasilane. Dedicated to Prof. Mitsuo Kira on the occasion of his reception of the Wacker Silicon Award 2005 and in recongnition of his numerous outstanding achievements in organosilicon chemistry.     

Scheduling unit-time tasks in renewable resource constrained flowshops

In this paper we address the problem of scheduling unit time jobs in a flowshop to minimize makespan under a discrete renewable resource constraint. We propose algorithms having complexityO(n) for special cases of two machine and three machine problems. For the three machineN P-hard problem we develop a branch and bound procedure and several upper and lower bounds. We test the efficiency of the procedure and report our computational experience.Suna Kondakci was a visiting assistant professor at the Industrial Engineering Department, Purdue University, when the paper was revised.     

Two- and three-dimensional analysis of bose-einstein correlations inπ +/K+p interactions at 250 GeV/c

The NA22 data onπ ^? π ^? correlations are analyzed in terms of a number of two- and three-dimensional parametrizations (Gaussian space-time, Goldhaber, Bowler string-like, Bertsch hydrodynamical, Kopylov-Podgoretskii, etc.). Contrary to the results obtained for e⁺e^? andµp collisions, the Goldhaber parametrization, as well as string-like models, fail in describing the hadron-hadron data. Better fits are obtained in the framework of surface-emitting fireball-like models, both when including and excluding hydrodynamical expansion of nuclear matter. Our results indicate that pion radiation occurs at earlier stages of matter evolution than in nuclear collisions.     

Oblique impingement of a circular jet in a cross flow

The distributions of temperature and dye concentration produced by a cross flow jet impinging on a flat surface are examined experimentally. Measurements show that for sufficiently high jet injection speeds, a ground vortex region upstream of the jet develops. The dimensionless gross geometrical features of this recirculating region are related by a simple linear law and are independent of the jet — surface spacing or the injection speed ratio.     

Coaxial Discharge and Transverse Magnetic Field

The study deals with the effect of an applied transverse magnetic field on the dynamics and parameters of the focused and expanded plasma in a coaxial discharge. The experimental results were found with a 3 kJ Plasma focus device of a Mather geometry. The discharge takes place in hydrogen gas with base pressure of 0.5 Torr. The experiments are conducted with a 10 kV bank voltage, which corresponds to 100 kA peak discharge current with rise time 8 μs. Helmholtz magnetic coils are placed outside the expansions chamber to produce a transverse magnetic field with intensity 280 G perpendicular to the plasma expanded from the coaxial electrodes. The investigations have shown that the plasma flow along the expansion chamber axis is restricted when applying the externally transverse magnetic field and the maximum axial velocity of the expanded plasma is decreased by 33%. X-ray probe has been used to measure the focused plasma electron temperature (T_e). The experimental results and the calculations showed that T_e is decreased from 2.2 keV to 800 eV with the application of a transverse magnetic field. The expanded plasma electron temperature and density have been measured by an electric double probe, the results cleared that the expanded plasma electron temperature is decreased by 2.6 times while its density is increased by 9 times, when a transverse magnetic field is applied.     

A method for investigating the orientational behaviour of fibrous particles in gaseous flow

A method is described by which the angular orientation distribution of fibrous particles carried in a gaseous stream may be investigated. The method is based upon the interpretation of the spatial intensity distribution or scattering profile of laser light scattered by individual fibres. The scattering instrument used to capture the profiles is described, and the mathematical computation required to ascertain the orientation of each particle at the measurement point is detailed. Illustrative results are given for a study of airborne micromachined silicon particles of 12 μm length and 1.0 μm by 1.5 μm cross-section. The method is currently being employed by the authors to investigate ways of improving the orientation control over nonspherical particles in systems such as aerodynamic particle sizers and particle shape classifiers, since lack of particle orientation control is known to adversely affect the measurement accuracy of both these types of instrument.