Hints of a new relativity principle from p-brane quantum mechanics

This report is an extension of a previous one hep-th/9812189. Several quantum mechanical wave equations for p-branes are proposed. The most relevant p-brane quantum mechanical wave equations determine the quantum dynamics involving the creation/destruction of p-dimensional loops of topology S^p, moving in a D-dimensional spacetime background, in the quantum state Φ. To implement full covariance we are forced to enlarge the ordinary relativity principle to a new relativity principle, suggested earlier by the author based on the construction of C-space, and also by Pezzaglia's poly-dimensional relativity, where all dimensions and signatures of spacetime should be included on the same footing.     

Effects of layering and working pressure on magnetic and magnetotransport properties of as sputtered multilayered granular Co/Cu films

Heterogeneous films of CoCu having high giant magnetoresistance (MR) were prepared in the form of multilayered granular specimens by a two-target RF sputtering. MR performances of 11% at 293 K were obtained in as deposited granular films. The magnetic and magnetotransport properties could be changed to a large extent, by varying the thickness of the deposited Co (Cu) layer as well as the Ar pressure. The effect of Co concentration, in the range 5–30%, and the influence of thermal treatments were also analysed.     

Magnetic properties of RSr2RuCu2O8+δ (R=Eu and Gd)

The non superconducting RSr₂RuCu₂O_8+δ (R=Eu and Gd) compounds are magnetically ordered below T_N=168 and 185 K, respectively. Magnetic susceptibility (ac and dc) studies indicate that the magnetic ordering is due to the Ru sublattice. The Gd sublattice in GdSr₂RuCu₂O₈ is antiferromagnetically ordered at 2.8 K. Irreversibility phenomena and magnetic anomalies, observed at low magnetic fields, originate from antisymmetric exchange coupling of the Dzyaloshinsky–Moria type, and from spin reorientation of the Ru moments. The magnetic behavior of this system and that of the well-known itinerant ferromagnet SrRuO₃ are compared.     

ZnSe-based heterostructures for blue-green lasers

We review the current status of research activity on ZnSe-based heterostructures for bluegreen laser diodes (LDs), focusing on a few selected critical issues. Early investigations on defect microstructures allowed to strongly enhance the lifetime of LDs. However, the LD lifetime seems to saturate now, and we point out that the model proposed for explaining the degradation of LD does not predict such a saturation. Next, we detail the mechanisms responsible for carrier compensation in p-type ZnSe and we survey the properties of ZnMgSSe and ZnMgBeSe wide bandgap quaternary alloys which are used as cladding layers in LDs. We emphasize that the low p-type dopability of ZnSe and related materials has a dramatic impact on the performance of LDs in terms of emitted wavelength as well as device lifetime.     

Implementation and performance of the needle chain-algorithm for Brownian dynamics simulation

The first algorithm for Brownian dynamics (BD) simulation of needle chains (the NC-algorithm) was developed recently by Nyland et al. (J. Chem. Phys. 1996;105:1198). Here we report on an implementation of the NC-algorithm using N_n rigid segments composed of N_bn spherical beads, and its efficiency relative to the Ermak–McCammon BD algorithm (J. Chem. Phys. 1978;69:1352) used to simulate bead-spring polymer chains consisting of N_b beads arranged into N_n stiff segments each composed of N_bn beads. For segmented chains the NC-algorithm can use a dimensionless time-step that is about four orders of magnitude larger than that of the bead-spring BD algorithm. In addition, the computer time required to perform a single dimensionless time-step scales as N_b² and N_b³ for the NC-algorithm and the bead-spring algorithms, respectively. This demonstrates that, for polymer chains consisting of needles or rigid segments with aspect ratios larger than three, the NC-algorithm is vastly more efficient than the Ermak–McCammon BD algorithm.     

A short-step synthesis of trans-whisky lactone by an asymmetric Michael reaction

trans-Whisky lactone 6 was synthesized enantioselectively in only six steps from readily available 2-trimethylsilyloxyfurans and 3-crotonoyl-1,3-oxazolidin-2-one using an asymmetric Michael reaction as the key step.