Ξ Resonances in Ξ− Be interactions II. Properties of Ξ(1820) and Ξ(1960) in the\Lambda \bar K^0 and\Sigma ^0 \bar K^0 channels

In an experiment at the CERN-SPS charged hyperon beam, we have investigated the inclusive \(\Lambda \bar K^0 \) and \(\Sigma ^0 \bar K^0 \) final states formed in Ξ^? Be interactions. In the \(\Lambda \bar K^0 \) channel, we observe a signal at 1826 MeV/c² which can be identified with the known Ξ(1820) resonance. We determine its mass and width to be:M=1826±4 MeV/c², Г=12±14 MeV/c². A moment analysis is consistent with a spin of 3/2 and indicates a negative parity for this spin assignment. Also in the \(\Lambda \bar K^0 \) channel, we observe a 3.6σ signal with the following parameters:M=1963±5 MeV/c², Г=25±15 MeV/c². This state, which we call Ξ(1960), is not observed in the \(\Sigma ^0 \bar K^0 \) channel, leading to an upper limit on the ratio of partial widths \(\Sigma \bar K/\Lambda \bar K\) of 2.3 (90% confidence level). A moment analysis of the \(\Lambda \bar K^0 \) final state indicates a spin of 5/2 or greater in the natural spin-parity series 5/2⁺, 7/2^?, etc.     

Millimeter and submillimeter detection using Ga1?xAlxAs/GaAs heterostructures

We have shown that a Ga_1–xAl_xAs/GaAs heterostructure can be used as a sensitive tunable detector of mm-wave/sub-mm-wave radiation. The mechanism for detection requires the application of a magnetic field varying from approximately 0.2T at 94GHz (3.2mm wavelength) to 6.2T at 2500GHz (119m wavelength). The responsivity and N.E.P. at 3.2mm have been roughly estimated at 200V/W and 5×10^–11W/Hz respectively. The speed of such a detector could be several orders of magnitude greater than comparable InSb detectors.     

Use of the64Ni(36S,34,35Si)66,65Zn reactions to measure the masses of34Si and35Si

The ground-state masses of³⁵Si and³⁴Si have been measured using the reactions⁶⁴Ni(³⁶S,^35,34Si)^65,66Zn at a³⁶S beam energy of 198 MeV.^34,35Si¹⁴⁺ ions were analysed and identified in a QMG/2 magnetic spectrometer and gas-filled focal-plane detector. The experimental mass excess of³⁵Si was determined to be ?14.58± _0.12 ^0.07 MeV while that of³⁴Si was measured as ?19.961±0.034 MeV. A comparison is made with the results of mass model predictions.     

The esterolytic activity of poly(N-alkylimidazoles). The effect of ester chain length in the substrate and alkyl chain length in the catalyst on the esterolytic activity of poly(N-alkylimidazoles).

In an effort to exploit the enhancement in catalytic activity which might be derived through hydrophobic interactions between polymeric catalyst and substrate, 1-methyl-5-vinylimidazole (1-Me-5-VIm), 1-methyl-4-vinylimidazole (1-Me-4-VIm), 1-butyl-5-vinylimidazole (1-Bu-5-VIm), and 1-butyl-4-vinylimidazole (1-Bu-4-VIm) have been synthesized and polymerized. In 28.5% ethanol-water, poly(1-alkyl-5-vinylimidazoles)proved to be efficient catalysts for the hydrolysis of various 3-nitro-4-acyloxybenzoic acids (Sn-, where n denotes the acyl chain length). Order of magnitude rate enhancements, as compared to the model compound, 1,5-dimethylimidazole (1,5-DMIm) were observed in the poly(1-alkyl-5-vinylimidazole)-catalyzed solvolysis of S12- and S18-. Poly(1-Me-5-VIm) catalyzes the hydrolysis of S18-88 times faster than does 1,5-DMIm. The poly(1-Me-5-VIm)-catalyzed hydrolysis of S18- in ethanol-water was analyzed in terms of a simple Michaelis-Menten type mechanism. Vmax and Km were determined to be 40.2 X 10(-7) M min-1 and 2.20 X 10(-5) M, respectively.     

Characterization of the Phosphoryl-Nitrogen Linkages in Histone H4

In earlier work we nave described and partially characterized two histone kinases from regenerating rat liver and other tissues which catalyze the transfer of the γ-phosphoryl group from ATP to histones. The histone phosphates thus formed were observed to be acid-labile and base-stable. In the present study we report on the specificity of one of these enzymes, namely, the kinase which is optimally active at pH 9. This enzyme appears to be relatively specific for the two histidine residues of histone H4. These histidines occur at positions 18 and 75, and both are phosphorylated. However, when regenerating rat liver was the source of enzyme, the product was 1-phosphohistidine, whereas the enzyme from Walker-256 carcinosarcoma catalyzed the formation of 3-phosphohistidine.     

Reactions of Molecules with Two Equivalent Functional Groups. 5. Anomalous Reactivity of 1,10-Cyclooctadecanedione. Crystal and Molecular Structures of cis,cis-1,10-Diphenyl-1,10-cyclooctadiene and the Stereoisomers of 1,10-Diphenyl-1,10-cyclooctadecanediol(1)

The reaction of the title diketone (3) with phenyl Grignard produces (with rate constant k(1)) the conjugate base (6-M) of 10-hydroxy-10-phenylcyclooctadecanone (6), which is subsequently converted (with rate constant k(2)) to the conjugate base of the title diol, as a mixture of the cis (7, 55%) and trans (8, 45%) isomers. The ratio k(2)/k(1), 2.2 +/- 0.4, indicates that the carbonyl group in 6-M is 4.4 times as reactive as each carbonyl in 3. Competition experiments further demonstrate that the relative rates (per carbonyl) for addition of phenylmagnesium bromide to 3, 10-methylenecyclooctadecanone (11), and cyclopentadecanone (12) are 1.0:0.60:1.92. Possible reasons for this order of reactivity are discussed. Diols 7 and 8 undergo facile double dehydration to form the title diene 13, which is predicted by molecular mechanics calculations to be the most stable of the four possible symmetrical diene isomers. The structures of 7, 8, and 13 were secured by single-crystal X-ray studies.