Domino Hydroformylation-Wittig Reactions

Methallyl and homomethallyl alcohols can undergo stereoselective hydroformylation-Wittig and hydroformylation-Wittig-hydrogenation reactions in one-pot domino processes. This sequential transformation allows the formation of C−C bonds and the generation of a new stereogenic center, and gives preparatively interesting compounds [Eq. (a)]. The reaction products are obtained in satisfactory to good yields and in diastereoselectivities of 90:10 to >98:2. CDG=catalyst-directing group; R′=H; R″=OEt, Me.     

Ultra-thin PTCDA layers studied by optical spectroscopies

3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) was deposited using organic molecular beam deposition (OMBD) onto various substrates, i.e. mica(0001), Au(111) layers on mica, and Se-passivated GaAs(100). Layer thicknesses were from 2 to 30 nm. Reflectance and transmittance measurements were performed in order to identify PTCDA absorption features and find suitable laser wavelengths for subsequent Raman investigations. Despite the low thicknesses the Raman spectra reveal strong scattering by the molecular vibrational modes, in particular above 1200 cm^–1. Frequency shifts of various modes in the layers from their values in PTCDA source material may indicate the influence of the substrates. Similar shifts were also observed in infrared spectra of the same materials. Received: 5 August 1998 / Received: 25 October 1998 / Accepted: 26 October 1998     

On the change of low-temperature thermal conductivity of gap after bending

The thermal conduction of a sulphur-doped single crystal plastically deformed by bending at 963 K was measured between 2 and 50 K. The thermal resistivity W at temperatures > 14 K is practically independent on deformation. At lower temperatures W is found to be proportional to AT⁻³ before and to AT⁻³ + BT⁻² after deformation. A is due to boundary scattering, B due to dislocations.     

Chemie und Aufbau der Wolle

Wool is a fibrous biomaterial with an exceptional multicellular structure and complex chemical composition. This is shown for some selected topics.     

Magnetic Fluid and Nanoparticle Applications to Nanotechnology

Magnetic field based micro/nanoelectromechanical systems (MEMS/NEMS) devices are proposed that use 10 nm diameter magnetic particles, with and without a carrier fluid, for a new class of nanoduct flows, nanomotors, nanogenerators, nanopumps, nanoactuators, and other similar nanoscale devices. A few examples of macroscopic ferrohydrodynamic instabilities that result in patterns, lines, and structures are shown that can be scaled down to sub-micron dimensions.     

Turbulent Transport in Stellar Interiors

Differential rotation is probably the major cause of turbulence in stably stratified stellar interiors. The boundary of the superficial solar convection zone plays a critical role for both the large scale circulation and the differential rotation. The turbulence arises from the barotropic instability in a vertically stratified medium and is expected to be anisotropic. It tends to suppress one of its causes, namely differential rotation in latitude. It offers an explanation for the thinness of the solar tachocline, the boundary layer beneath the convection zone where solar seismology shows that rotation varies from differential above to apparently uniform below. The anisotropy of turbulence also strongly reduces the efficiency of vertical particle transport. We show that for an anisotropy A of horizontal to vertical velocities, the vertical diffusivity is a factor A ² less than the horizontal diffusivity. Transport by meridional circulation is also reduced, as well as the efficiency of a composition gradient in suppressing meridional circulation. These effects of anisotropy explain the very small upper limit that observations of the concentration of chemical elements impose to vertical transport in stars. However the recent results of helioseismology, that the solar core rotates at nearly the same rate as the whole radiative zone, cannot currently be explained by anisotropic turbulent transport. It suggests the need for an additional transport process such as a magnetic torquing or gravity waves. Furthermore, near the base of the convection zone, magnetic instabilities could provide an alternate mechanism to mix angular momentum preferentially in latitude compared with radial mixing. The quality of the helioseismology data is improving very rapidly. It holds the promise to determine, within the next few years, the velocity field within the Sun to great accuracy. This should allow us to distinguish between the various hydrodynamical and hydromagnetic models. Received 20 May 1997 and accepted 4 January 1998     

The application of homotopy analysis method to solve nonlinear differential equation governing Jeffery–Hamel flow

In this paper Jeffery–Hamel flow has been studied and its nonlinear ordinary differential equation has been solved through homotopy analysis method (HAM). The obtained solution in comparison with the numerical ones represents a remarkable accuracy. The results also indicate that HAM can provide us with a convenient way to control and adjust the convergence region.