Magnesium halide-catalyzed anti-aldol reactions of chiral N-acylthiazolidinethiones

[reaction: see text] Diastereoselective direct aldol reactions of chiral N-acylthiazolidinethiones occur in high yield with preference for the illustrated anti diastereomer. This reaction is catalyzed by 10% MgBr2.OEt2 in the presence of triethylamine and chlorotrimethylsilane. Yields range from 56 to 93% with diastereoselectivity up to 19:1 for a variety of N-acylthiazolidinethiones and unsaturated aldehydes.     

Edge-localized-mode--induced transport of impurity density, energy, and momentum

High temporal and spatial resolution measurements of impurity dynamics associated with an edge-localized mode (ELM) indicate that the ELM perturbation consists of two distinct parts: a rapid (< 300 micros) expulsion of impurity density at the time of the instability followed by a slower time scale (< 1 ms) decrease in the ion temperature. While the density perturbation remains nearly constant over a wide range of plasma collisionality, the temperature perturbation decreases as the collisionality increases. Analysis of the radial electric field E(r) evolution indicates that the E(r) well normally present in H-mode plasmas is modified strongly by the ELM and that the size of the temperature perturbation is correlated with the associated change in the E x B shear.     

Upper limits on a stochastic background of gravitational waves

The Laser Interferometer Gravitational-Wave Observatory has performed a third science run with much improved sensitivities of all three interferometers. We present an analysis of approximately 200 hours of data acquired during this run, used to search for a stochastic background of gravitational radiation. We place upper bounds on the energy density stored as gravitational radiation for three different spectral power laws. For the flat spectrum, our limit of omega0 < 8.4 x 10(-4) in the 69-156 Hz band is approximately 10(5) times lower than the previous result in this frequency range.     

Direct measurements of Ab and Ac using vertex and kaon charge tags at the SLAC detector

Exploiting the manipulation of the SLAC Linear Collider electron-beam polarization, we present precise direct measurements of the parity-violation parameters A(c) and A(b) in the Z-boson-c-quark and Z-boson-b-quark coupling. Quark-antiquark discrimination is accomplished via a unique algorithm that takes advantage of the precise SLAC Large Detector charge coupled device vertex detector, employing the net charge of displaced vertices as well as the charge of kaons that emanate from those vertices. From the 1996-1998 sample of 400 000 Z decays, produced with an average beam polarization of 73.4%, we find A(c)=0.673+/-0.029(stat)+/-0.023(syst) and A(b)=0.919+/-0.018(stat)+/-0.017(syst).     

Synthesis and characterization of processable polyborate precursors

Polyborates have been formed by disproportionation and polycondensation of trimethoxyboroxine and also of trimethoxyboroxine and boric acid. The crtiical role of stoichiometry in the formation of polyborates without requiring incorporation of a metal counter ion is revealed. The emphasis is on integration of this chemistry with fabrication processes. Incorporation of an appropriate linear organic polymer is shown to yield the required rheological and thermal characteristics in this regard. These polyborates are inferred to be suitable as precursors for boron nitride in geometrical forms that can be processed as supported structures. However, they are also determined to be unsuitable as precursors for boron nitride fibers, oriented or isotropic, primarily due to their low glass transition temperature.     

Thrust ine + e −-annihilation

The thrust distribution ine ⁺ e ^–-annihilation is analysed in perturbative QCD. Proper account is taken of multiple emission of gluons. Scaling holds for this quantity in the sense that its energy dependence comes only through the change in the QCD effective coupling. It thus provides an ideal means to determine the value of the QCD mass scale experimentally. From the data atW=91 GeV by the ALEPH collaboration at LEP, we obtain .     

The development of an alpha/beta separation liquid scintillation cocktail for aqueous samples

Scintillation cocktail components were studied with regard to their impact on pulse decay discimination (PDD) and hence the separation of alpha from beta activity, using a Packard 2250 CA /. Di-isopropyl naphthalene (DIN) was found to be the most suitable solvent, both from safety considerations and also the fact that it acts in a very similar manner to naphthalene in stretching the pulses produced at the photomultiplier tube anode and hence enhancing the separation. Increasing the surfactant concentration and the use of dimethylanthracene (DMA) as secondary fluor degraded the cocktail's performance. PMT anode pulse shapes were found to be a useful indicator of PDD efficiency but could not give a quantitative guide.