Tricarbonylchromium-complexed phenylsiloxane polymers as stereoselective hydrogenation catalysts: Preparation and properties

Soluble tricarbonylchromium complexes were made by reacting Cr(CO)₆ with a ladder polyphenylsilsesquioxane and a linear polydiphenylsiloxane. These new polymer Cr(CO)₃ complexes were characterized by elemental Cr, infrared (IR), gel permeation chromatography (GPC), viscosity, and thermal analyses and were evaluated as stereoselective hydrogenation catalysts. Thermogravimetry studies demonstrated that the new complexes were more stable at 180–200°C in N₂ than the corresponding complex from crosslinked polystyrene. These silicone polymer complexes catalyzed stereoselective hydrogenation of methyl sorbate to cis-3-hexenoate in cyclohexane and tetrahydrofuran (THF) and could be recovered from THF for recycling by precipitation-fiItration. Catalytic activity and recyclability, however, were highly influenced by the solvent. Loss of catalytic activity associated with loss of Cr(CO)₃ was observed on recycling. These results support a mechanisim that involves dissociation of Cr(CO)₃, a significant portion of which cannot become reassociated with the polymer phenyl groups.     

Predicted new electromagnetic precursors and altered signal velocity in dispersive media

New optical precursors are predicted in media exhibiting “non-conventional” dispersion characteristics such as spatial dispersion, surface polaritons and surface plasmons. Numerical estimates are given for the exciton and surface polariton precursors in CdS, and surface plasmon in Al. The signal velocity increases in spatially dispersive media and is essentially constant throughout the “stop” gap. Measurement of these effects may provide new spectroscopic information regarding “non-conventional” dispersion.     

Far infrared absorption of Fe2+ in KMgF3

Far infrared absorption in cubic KMgF₃ doped with Fe²⁺ is reported . A line is observed at 87cm^?1, which is assigned to the (Γ_5g → Γ_3g, Γ_4g) transition in the Fe²⁺. The reduction in the spin-orbit coupling from the free ion value has been predicted by Ham, Schwarz and O'Brien.     

Sound generation by steady flow through glottis-shaped orifices

Although the signature of human voice is mostly tonal, it also includes a significant broadband component. Quadrupolelike sources due to turbulence in the region downstream of the glottis, and dipolelike sources due to the force applied by the vocal folds onto the surrounding fluid are the two primary broadband sound generating mechanisms. In this study, experiments were conducted to characterize the broadband sound emissions of confined stationary jets through rubber orifices formed to imitate the approximate shape of the human glottis at different stages during one cycle of vocal fold vibrations. The radiated sound pressure spectra downstream of the orifices were measured for varying flow rates, orifice shapes, and gas mixtures. The nondimensional sound pressure spectra were decomposed into the product of three functions: a source function F, a radiation efficiency function M, and an acoustic response function G. The results show that, as for circular jets, the quadrupole source contributions dominated for straight and convergent orifices. For divergent jets, whistling tonal sounds were emitted at low flow rates. At high flow rates for the same geometry, dipole contributions dominated the sound radiated by free jets. However, possible source-load acoustic feedback may have hampered accurate source identification in confined flows.     

Shape and stability of a liquid drop moving at low Weber numbers

The equilibrium cross sectional shape and stability of a liquid drop moving in a gaseous medium is studied analytically. Such liquid drops appear as the final product in numerous industrial spraying and atomisation processes. Raindrops falling at their terminal speed can also be described by the present model. The equilibrium shape is formed by the interaction of two main factors; the dynamic pressure distribution in the gaseous medium which tends to deform the liquid drop into an oblate shape and the surface tension which tends to restore the spherical shape. The meridional shape of the liquid drop is obtained as a power series in the Weber number. The linear stability of the deformed shapes described above to small surface disturbances is studied. The stability analysis shows the effect of the surrounding gas flow on the natural frequencies of oscillation (vibration) of the liquid drop. The liquid drop is found to be stable in the region of low Weber numbers studied with a decrease in oscillation frequency proportional to the Weber number. This is in agreement with existing experimental data. Extrapolation of the results here lead to a Weber number of W=5.33 for breakup, again in agreement with experimental correlations.     

Organische S?uren und S?ureanhydride

Ohne Zusammenfassung     

potential theory and analytic properties of self-similar fractal and multifractal distributions

By the use of recursion relations and analytic techniques we deduce general analytic results pertaining to the electrostatic potential, moments, and Fourier transform of exactly self-similar fractal and multifractal charge distributions. Three specific examples are given: the binomial distribution on the middle-third Cantor set, which is a multifractal distribution, the uniform distribution on the Menger sponge, which illustrates the added complication of higher dimensionality, and the uniform distribution on the von Koch snowflake, which illustrates the effect of rotations in the defining transformations.     

Active sites of adsorption on cleaved and sputtered indium phosphide surfaces

From the initial uptake of atomic hydrogen at room temperature the active sites on cleaved and sputtered InP(110)-surfaces were determined using high resolution electron energy loss spectroscopy (HREELS), low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS, XAES). It is found that the In-H stretching mode intensity is dominant for the cleavage surface, which is known to be P-rich due to surface relaxation. For the Ar⁺-ion bombarded surface (In-rich) the P–H stretching mode is very strong if compared to the corresponding In-H mode. From these observations it may be deduced that both, the chemical bonding situation and the geometric configuration, are reflected in our HREELS-results. For the cleavage surface the initial adsorption for atomic hydrogen is interpreted in the framework of existing models for the (1×1) relaxation in terms of its chemical bonding configuration. The sputtered surface is assumed to be amorphous consisting of In-clusters and predominantly broken P-bonds, which are passivated after hydrogen exposure. For high hydrogen exposures, a strong decrease of the phosphor hydride lines may be interpreted as phosphine desorption.