Coupled Stokes and Antistokes radiation in Raman scattering

An analysis of the coupled Stokes and Antistokes radiation in Raman scattering, including laser depletion, is found to predict a finite gain at perfect momentum matching. This is in contradiction to the results of Bloembergen and Shen who treated the laser as a constant and hence predicted zero gain at perfect momentum matching.     

Flywheel batteries come around again

Today's flywheel batteries, embody technological advances, and they are serious contenders for a variety of important energy-storage applications. They are, for example, competitive with chemical batteries in applications like transportation or improving power quality, which involve many charge-discharge cycles and little in the way of long-term storage. Progress in power electronics, particularly in high-power insulated-gate bipolar transistors (IGBTs) and field-effect transistors (FETs), underlies higher-power flywheel operation. While the stored energy is determined by the speed, mass, and geometry of the wheel, the limits on input and output power are in general set by the power electronics. With these higher power devices, fewer individual components are needed, so the power electronics package can be comparable in size to the flywheel plus motor-generator combination. This paper describes the main features of flywheel energy storage systems and space, hybrid electric vehicle, and combat vehicle applications     

Crystal and molecular structure of voacangine: An alkaloid fromStemmadenia Donnell-Smithii

C₂₂H₂₈N₂O₃,M _r=368.5, orthorhombic, D ₂ ⁴ -P2₁2₁2₁. Unit cell dimensions at 293 K area=8.753(3),b=9.252(2),c=24.422(7) Å,V=1978(1) ų,D _c=1.24 g cm^–3, andZ=4. The structure has been determined from single-crystal data collected with a four-circle diffractometer and refined from 1562 reflections down toR=0.050 andwR=0.055. The structural features determined from chemical and spectroscopic studies are confirmed and extended. The stereochemistry at C(4) and C(18) is 4S and 18S. The indole ring is not planar and the seven-membered nitrogen-containing ring adopts a distorted-chair conformation. The indole and seven-membered rings lie on the same plane with a dihedral angle of 0.7 (1)°, while the C(5)-N(6)-C(19)-C(2) atoms of the central axis of the iso-quinuclidine tricyclic structure is perpendicular to seven-membered ring [dihedral angle is 92.7 (1)°]. The packing in the crystal is entirely due to van der Waals forces.     

Quantum dynamics of bouncing atoms in a stable gravitational cavity

Two-level atoms bouncing in a stable gravitational cavity are considered, where the atomic mirror at the bottom of the bounces is an evanescent wave caused by an internally reflected intense Gaussian-mode laser beam. We consider the broadening mechanisms of the atoms from their initially tightly spaced position distribution, using a phenomenological semi-classical model, which includes spontaneous emission. A fully quantum model, which neglects spontaneous emission, is derived, and the broadening of the atomic wave function in the quantum model is compared with the broadening of the atomic distribution in an analogous classical simulation where spontaneous emission is similarly neglected. We find that the broadening is correctly described by the classical simulations in the horizontal directions, while it significantly underestimates the broadening in the vertical direction.Dedicated to H. Walther on the occasion of his 60th birthday     

Optical multistability and self oscillations in three level systems

The steady state behaviour of two cavity modes of the electromagnetic field interacting with a three level atomic medium is studied. This system may display optical tri- and quadra-stability. The results of Kitano et al. appear as a limit of our solutions in the dispersive and unsaturated regime. With the inclusion of saturation in the dispersive limit the asymmetric steady state may become unstable and give rise to self oscillations, period doubling and a new form of “optical turbulence”.     

Further studies on hydroxyperezone derivatives

Hydroxyperezone monoangelate (2c) was transformed into the mixture of α-(8) and β-perezols (9). Separation of these compounds permitted stereochemical assignments by NMR and ORD. The position of the angeloyl moiety in 2c was independently tested by its conversion to O-methylhydroxyperezone (1d) identified with a sample synthesised from perezone (1a). Several reactions distinguished the natural hydroxyperezone (2a) from the synthetic hydroxyperezone hydrate (3).