Gas chromatographic screening of cyclic alcohols as selective solvents for cyclohexane extraction

Summary Gas chromatography has been employed for screening cyclic alkanols as selective solvents for the extraction of cyclohexane from an aromatic-free cyclohexane-rich fraction (77–81°C). The relative volatilities for close boiling hydrocarbons in all three cyclic alcohol solvents have been compared. Activity coefficient data at infinite dilution for nine binary hydrocarbon systems at 25°C have also been presented.     

Crystallographic structure and defects in epitaxial bismuth films grown on mica

Atomic force microscopy is used to image the surface relief of epitaxial Bi films grown on mica substrates. Monatomic terrace steps are readily resolved, which provide detailed information on crystal growth and defect structures. The films grow from the coalescence of isolated three-dimensional islands, however, each island grows layer-by-layer. The islands are triangular in shape and when they coalesce to form a continuous film, their structures are either in-phase, and consequently large crystallites are formed, or they are out-of-phase and defect structures are formed. The most common defects observed are twinning and stacking faults. Images showing the microscopic details of stacking faults, twinning, and grain boundaries are observed as a result of islands coalescing to form a continuous film.     

Amperometric titration of mercury with a stationary platinum electrode in stirred solutions

Amperometric titration of mercury (in the range of 0-4 to 3.5 mg) has been carried out with 2-mercaptobenzoxazole with a stationary electrode in stirred solution in a sodium acetate-acetic acid medium.     

Wave propagation and vibration response of a periodically supported pipe conveying fluid

Propagation of free harmonic waves, in a periodically supported infinite pipe, has been studied. The presence of the Coriolis term in the equation of motion renders the phase velocity different for the positive and the negative going waves. Hence no classical normal modes (in the sense of standing modes) exist. Natural frequencies of a periodically supported finite pipe have been obtained by using the wave approach. The response of the infinite pipe to a convected harmonic pressure field has also been obtained. Owing to the difference in the phase velocities of the positive and the negative going free waves, the coincidence frequency depends on the direction of the convected loading. The static buckling or the divergence instability of such pipes has also been considered from the wave approach.     

Gravitational anomalies

The effective action for fermions moving in external gravitational and gauge fields is analyzed in terms of the corresponding external field propagator. The central object in our approach is the covariant energy-momentum tensor which is extracted from the regular part of the propagator at short distances. It is shown that the Lorentz anomaly, the conformal anomaly and the gauge anomaly can be expressed in terms of the local polynomials which determine the singular part of the propagator. (There are no coordinate anomalies.) Except for the conformal anomaly, for which we give explicit representations only ind<=4, we consider an arbitrary number of dimensions.     

Fixed angle dispersion relations and t-channel contribution in photo-pion production

We propose a method of evaluation of the contribution of t-channel singularities for the photon-pion production process on the basis of dispersion relations for invariant amplitudes in the s-plane at fixed angle (cos ? = ± 1). These dispersion relations are studied in the approximation scheme of retaining only the contributions from exchanges at low energy, viz., N, N^∗ (1237) in the s- and u-channels and π, ?, ω and A₁ in the t-channel. It is shown that the dispersion relations require more accurate evaluation in general than what the above approximation scheme can provide in order that the information obtained about the t-channel be reliable.     

Natural frequencies of a shaft with periodically placed rotors and bearings

Flexural and torsional natural frequencies of a shaft with periodically placed rotors and bearings are investigated by using a “wave approach”. By a judicious choice of parameters, it is possible to obtain ranges of operating speed that are free from both flexural and torsional resonances. Suggestions for widening such speed ranges are included.     

An approximate method of predicting the response of periodically supported beams subjected to random convected loading

The space-averaged response of an infinite, elastically supported, periodic beam subjected to convected random loading has been studied by using an approximate “assumed mode” method. The complex wave motion in the beam is represented by any number of suitably chosen complex modes. With a good, yet simple, choice of mode which satisfies certain boundary conditions on one periodic beam element, a “single mode approximation” can yield very accurate values of the average response. This has been verified for a wide range of the support stiffnesses and loading convection velocities. Consideration has also been given to the ratio of the maximum response in the beam to the space-averaged response. The method has been applied only to uniform beams in this paper, but it should be readily applicable to periodic systems consisting of non-uniform beam elements.     

Some exact solutions of stationary gas flows in a perpendicular magnetic field

The plane flow of a perfectly conducting gas subject to a perpendicular magnetic field is considered. Ladikov [1] has solved this problem as a special case of the more general solution for a specific condition. It is shown that, following the method of [2], this problem may be reduced to the determination of the unknown function which satisfies a partial differential equation. Since the equation for is very complex, we have considered only two interesting cases, namely: 1) when the motion is irrotational, and 2) when the pressure is constant along the streamlines.     

Weakly non-Hermitian square well

Inside a box of size L we contemplate the simplest -symmetric piece-wise constant potential of size ℓ < L and purely imaginary strength ig and describe all its bound states in closed form. Presented at the 3rd International Workshop “Pseudo-Hermitian Hamiltonians in Quantum Physics”, Istanbul, Turkey, June 20–22, 2005.