Search for color singlet technicolor particles in p&pmacr; collisions at radicals = 1.8 TeV

We search for color singlet technirho and technipion production in p&pmacr; collisions at sqrt[s] = 1.8 TeV recorded with the Collider Detector at Fermilab. These exotic technimesons are present in a model of walking technicolor. The signatures studied are lepton plus two jets plus E(T) and multijet final states. No excess of events is seen in either final state. We set an upper limit on the technirho production cross section and exclude a region in the technipion mass versus technirho mass plane.     

Diffractive dijets with a leading antiproton in &pmacr;p collisions at sqrt

We report results from a study of events with a leading antiproton of beam momentum fraction 0.9057 GeV. Using the dijet events, we evaluate the diffractive structure function of the antiproton and compare it with expectations based on results obtained in diffractive deep inelastic scattering experiments at the DESY ep collider HERA.     

An improved error bound for a finite element approximation of a model for phase separation of a multi-component alloy

Using the approach of Rulla (1996 SIAM J. Numer. Anal. 33, 68-87)for analysing the time discretization error and assuming moreregularity on the initial data, we improve on the error boundderived by Barrett and Blowey (1996 IMA J. Numer. Anal. 16,257-287) for a fully practical piecewise linear finite elementapproximation with a backward Euler time discretization of amodel for phase separation of a multi-component alloy.     

On the elucidation of the mechanism of Vinca alkaloid fluorination in superacidic medium

Detailed investigations on one of the key steps of the superacidic fluorination of Vinca alkaloids that is the origin of C20' activation are reported. While two different pathways can be envisioned for the emergence of the transient secondary carbocationic intermediate, isotopic labeling experiments unambiguously revealed the involvement of a 1,2-hydride shift mechanism.     

Atomic spectroscopy with surface wave plasmas

The use of microwave induced plasmas, particularly of surface wave plasmas, as detectors in atomic emission spectrometry for elemental analysis is reviewed. Surface wave plasmas have been produced at low HF power and used as gas chromatographic detectors. The analytical performances for the detection of non-metals with a Fourier transform spectrometer and a two-channel filter unit are reported. The excitation behavior of non-metals in helium-based mixed gas-plasmas has also be studied. In particular, the effect of power and of nitrogen concentration on the bromine emission has been systematically investigated. A nine-fold improvement of the detection limits for bromine can be obtained in a high power (900 W) helium-nitrogen (0.1–0.2%) plasma.     

A new microwave plasma at atmospheric pressure

Plasma at atmospheric pressure can be obtained by surface wave propagation with a surfatron. If the plasma is produced within a quartz tube, it is constricted to a diameter of approx. 1 or 2 mm but its length can attain some tens of centimeters with microwave power as low as 100 W. This plasma is quite uniform along the axis, with a typical electron density of 3 × 10¹⁴ electrons/cm³. Since the excitation and gas temperatures are lower than 4000 K, the plasma is far from local thermodynamic equilibrium. High stability and repeatability is achieved with an argon flow of 0.2–17 l/min. Applications are foreseen in the field of optical spectroscopy and plasma chemistry.     

Synthesis of pyridazine-based scaffolds as alpha-helix mimetics

The synthesis of several amphiphilic, nonpeptidic scaffolds that mimic the presentation of i, i + 3 or i + 4, and i + 7 residues of a peptide alpha-helix is described. The approach uses a pyridazine core, and the synthesis involves only a few steps and minimizes the number of C-C bond-forming reactions. The versatility of the synthesis makes it suitable for the preparation of small libraries of low molecular weight alpha-helix mimetics that could be targeted to certain protein/protein interactions.     

General approach for the synthesis of organic-inorganic hybrid nanoparticles mediated by supercritical CO2

We report in this paper novel chemistry that addresses the problem of surfactant solubility in supercritical CO2 for metal nanoparticle synthesis. This new approach for the preparation of organic-functionalized inorganic nanoparticles relies on the reduction of a metal precursor in a CO2-containing insoluble polymer. Reduction of the metal with H2 leads to small nanocrystals stabilized by the polymer with a relatively small polydispersity. The functionalized metal nanoparticles are recovered as a dry powder, free of any organic solvents, which can then be resuspended in an appropriate solvent. This approach limits the number of steps for the preparation of functional nanoparticles which are ready for use. To illustrate this, we report results of the preparation of palladium and silver nanoparticles of 3-5 nm size stabilized with hyperbranched polyamines, functionalized with perfluoroalkyl, perfluorooligoether, non-fluorinated alkyl, polysiloxane, or polyethylene glycol moieties.     

Ring expansions of a spirocyclohexadienone system

The unexpected rearrangement of spirocyclohexadienone 2 under acidic or basic conditions is reported.