Direct measurement of the W boson width in p&pmacr; collisions at radicals = 1.8 TeV

This Letter describes a direct measurement of the W boson total decay width, gamma(W), using the Collider Detector at Fermilab. The measurement uses an integrated luminosity of 90 pb(-1), collected during the 1994-1995 run of the Fermilab Tevatron p&pmacr; collider. The width is determined by normalizing predicted signal and background distributions to 49 844 W-->enu candidates and 21 806 W-->&mgr;nu candidates in the transverse-mass region M(T)<200 GeV and then fitting the predicted shape to the 438 electron events and 196 muon events in the high- M(T) region, 100相似文献   

Effect of pyrogallol-poly(ethylene glycol) on stabilization,structure, and interparticle potential of concentrated nickel nanoparticle suspensions

Nickel nanoparticles with an average diameter of 90 nm have been dispersed in de-ionized water with addition of pyrogallol-poly(ethylene glycol) polymers, hereafter termed Gallol-PEG, of different molecular weights as a surfactant. Measurement of zeta potential, infrared spectrum, and adsorption isotherm confirms the preferential anchoring from polar end of the surfactant molecules on the particle surface, forming a Langmuir-typed adsorption layer (adlayer) to provide an electrosteric stabilization. Concentrated nanoparticle suspensions with a solids loading up to 40 vol.% and an apparent viscosity lower than 10 Pa s at a shear rate of 100 s⁻¹ have been obtained, indicating that the Gallol-PEG adsorption is effective in facilitating the suspension flow under stress. The suspensions are yet fractal in structure with an experimentally determined fractal dimension of 2.1, revealing that a reaction-limited cluster–cluster aggregation is operative. This weakly coagulated fractal structure stems primarily from the shallow interparticle attraction operative over a moderate interparticle separation (~5–10 nm), and is prone to the adlayer thickness and the molecular conformation of the surfactant.     

NMR study of solid C60(γ-cyclodextrin)2

A solid complex of C₆₀ with γ-cyclodextrin (γ-CyD) was examined with NMR spectroscopic methods in order to understand the dynamics of C₆₀, and the interaction between C₆₀ and γ-CyD. A ¹³C solid-state cross-polarization magic angle spinning (CP/MAS) NMR spectra shows C₆₀ resonance at 142.6 ppm. This provides the evidence of interaction between ¹³C spins in C₆₀ and ¹H spins in the γ-CyD host. Ambient temperature experiments on the ¹³C CP/MAS NMR, with varying contact time, shows that the water associated with γ-CyDs plays an important role in the nuclear relaxation processes. The dynamics of C₆₀ in γ-CyD was investigated using temperature and field-dependent ¹³C spin-lattice relaxation time measurements. The influence of water on the dynamics of C₆₀ was less significant below 250 K.     

Kinetics of the reaction of 4,4′‐biphenol with bromoethane and 1‐bromobutane by phase‐transfer catalysis

The reaction of 4,4′‐biphenol and two species of bromoalkanes (e.g., bromoethane and 1‐bromobutane) to synthesize two symmetric products (4,4′‐diethanoxy biphenyl and 4,4′‐dibutanoxy biphenyl) and one asymmetric product (4‐ethanoxy, 4′‐butanoxy biphenyl) was successfully carried out under two‐phase phase‐transfer catalysis conditions. A rational mechanism and kinetic model were built up by considering the reactions both in aqueous phase and in organic phase. The first active catalyst (QO(Ph)₂OQ) was also synthesized under two‐phase reaction and was identified by instruments. The experimental data were explained satisfactorily by the pseudo‐steady‐state hypothesis. Two sets of rate constants of organic reactions, i.e. primary (k₁ and k₂) and secondary (k₁₁, k₁₂, k₂₁, and k₂₂) rate constants participate in the kinetic model. The two primary rate constants were obtained individually via experimental data for synthesizing the symmetric products. The ratios of the other four secondary rate constants were obtained from the reaction of synthesizing asymmetric products and determined from the initial yield rates of symmetric products. The effects of the ratio of bromoethane and 1‐bromobutane, temperature, organic solvents, amount of catalyst, and amount of sodium hydroxide on the reaction rate and the selectivity of products were investigated in detail. The results were explained satisfactorily by the interaction between the reactants and the environmental species. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 139–153, 2003     

Synthèses dans la série des-indéno-fluorénes,VII. Le trioxo-5,12,13-dihydro-12,13-5H-bis-indéno[2.1-a; 2′.1′-g] fluoréne

Starting from 9-oxo-fluorene-1-carbaldehyde, the title compound, XII, a trioxoderivative of a new biangular diindenofluorene system, has been synthesized in 5 steps (overall yield 37,5%). The corresponding hydrocarbon could not be obtained by reduction of XII. Attempts to synthesize the isomer XX of the trioxoderivative XII are described.     

Determination of thiobarbituric acid adduct of malondialdehyde using on-line microdialysis coupled with high-performance liquid chromatography.

An on-line analytical system for the continuous monitoring of malondialdehyde (MDA) was developed. This method involves the use of microdialysis perfusion, on-line derivatization and on-line HPLC analysis. This method gave a linear response for MDA concentrations and HPLC peak areas in the range from 0.051 microM to 2.43 microM. The intra-day (RSD = 1.6-10.5%) and inter-day (RSD = 1.1-9.3%) precisions were acceptable. The average in vitro probe recovery of MDA standard was 18.4 +/- 1.0%. The detection limit was 0.03 microM, corresponding to 0.6 pmol for an injection volume of 20 microl. This method was used for in vitro peroxidation investigations, which provided evidence for elevated MDA levels following the incubation of metal ions to a linoleic acid solution.     

Preconcentration on hydrous magnesium oxide for neutron activation analysis

It was found that trace amount of various ions could be effectively adsorbed onto hydrous magnesium oxide from aqueous solution. Attempts were made to investigate the feasibility of using hydrous magnesium oxide as preconcentration agent for neutron activation analysis (NAA). The procedure was successfully applied for the measurements of trace amounts of elements in the surface water of a number of large rivers which play very important roles in the lives of local people. Some of them are polluted rather badly. In order to improve the living standards it is rather important to establish reliable analytical methods so that more effective surveillance may be enforced on pollution control problems. NAA is generally accepted as one of the most suitable methods for simultaneous and multielemental determination of trace amounts of elements. In this work polluted surface waters were investigated by NAA using Tsing Hua Open-pool Reactor (THOR).     

A simple regioselective synthesis of pyrimido[1,2-a]benzimidazoles

2-Aminobenzimidazoles were reacted with enaminones in acetic acid to give pyrimido[1,2-a]benzimidazoles. With a substituted enaminone only one regioisomer was obtained. Structural assignments based on nmr and uv spectroscopy are presented. Possible pathways leading to the products are discussed.     

SCF-Xα-SW calculation on the molecule N2 using theoretical αta

The first calculation of a molecule, N₂, by the SCF -Xα-SW method using the theoretically derived parameter α_ta is reported.