Energy dependence of the S1 -decay of propynal and propynal-d1 and the influence of collisions

The collision-free lifetime and the quenching rate of S₁(¹A″) vibrational levels of propynal and propynal-d₁ have been measured in the pressure range O.1-1OmTorr at room temperature. The collision-free decay of propynal is dominated by internal conversion that of propynal-d₁ by fluorescence. In both molecules the internal conversion rate is dependent on specific vibrational modes, in particular of the most efficient promoting mode v₁₀[CH(ald) wagging mode]. The intersystem crossing process of propynal, inefficient at the vibrationless S_1, level, remains unimportant at least up to an excess energy ≈ 3000 cm^-1. The quenching of the fluorescence is due to a very efficient collision-induced intersystem crossing (130 <σ_ISC^cl ? 600 A²). The strongly varying rates of this process, apparently dependent on the vibronic level, have been measured with propynal (propynal-d₁), argon, and butane as collision partners.     

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Applying tabu search to the job-shop scheduling problem

In this paper, we apply the tabu-search technique to the job-shop scheduling problem, a notoriously difficult problem in combinatorial optimization. We show that our implementation of this method dominates both a previous approach with tabu search and the other heuristics based on iterative improvements.Partially supported by research contracts MPI 40% and 60% of the Italian Ministry of University and Scientific Research.     

Synthesis and Ruthenium-Catalyzed Enantioselective Hydrogenation of 3-O-Substituted 1,3-Dihydroxypropan-2-ones. Part 2

A number of 3-O-substituted 1,3-dihydroxypropan-2-ones have been synthesized in view of their potential use as prochiral precursors of optically active glycerols. Indeed, the oxo-ethers have been reduced to the corresponding 3-O-substituted glycerols via chiral Ru complexes derived from (S)-binap, ( =(?)-(S)-2,2′-bis(diphenylphosphino)-1,1′-binaphthalene) with enantiomeric excesses up to 93%. The steric course of the catalytic reduction appears to be essentially dependent on the steric encumbrance of the substituents; indeed, a dramatic increase of the enantiomeric excess is observed when the bulky trityl group is substituted by the less encumbering benzyl or octadecyl groups.     

On simple radical difference families

For q a prime power and k odd (even), we define a (q,k,1) difference family to be radical if each base block is a coset of the kth roots of unity in the multiplicative group of GF(q) (the union of a coset of the (k ? 1)th roots of unity in the multiplicative group of GF(q) with zero). Such a family will be denoted by RDF. The main result on this subject is a theorem dated 1972 by R.M. Wilson; it is a sufficient condition for the existence of a (q,k, 1)-RDF for any k. We improve this result by replacing Wilson's condition with another sufficient but weaker condition, which is proved to be necessary at least for k ? 7. As a consequence, we get new difference families and hence new Steiner 2-designs. © 1995 John Wiley & Sons, Inc.     

Chiral symmetry on the lattice with Wilson fermions

The chiral properties of the continuum limit of lattice QCD with Wilson fermions are studied. We show that a partially conserved axial current can be defined, satisfying the usual current algebra requirements.A proper definition of the chiral symmetry order parameter, $\text{〈0|}\text{ψ}\text{ψ|0〉}$, is given, and the chiral properties of composite operators are investigated. The implications of our analysis to the lattice determination of non-leptonic weak amplitudes are also discussed.     

Flow-injection amperometric determination of chlorine at a gold electrode

The applied potential is +0.2 V vs. SCE, flow rate is 1 ml min^?1 and sample volume is 30 μ1. The background electrolyte is 0.05 M phosphate, pH 7.4. Electrode pretreatment is +1.3 V vs. SCE for 40 s, followed by a pre-injection delay of 20 s. Peak current over a receding baseline is used. Linear range extends down to 0.4 μM for chloramine and 0.2 μM for hypochlorite. Sensitivities are 70 and 95 nA μM^? respectively. Time per determination is less than 1.5 min. Monochlorinated glycine is active whereas chlorinated cyanuratesshow no response. Chlorine and monochloramine in river water were determined.     

Contribution of soft zone-center transverse optical phonons to the shift and width of sharp line electronic transitions in ferroelectrics

The contribution of soft zone-center transverse optical phonons to the shift and width of sharp line electronic transitions in ferroelectrics is assessed. It is pointed out that the soft modes may be important for transitions involving ions at sites lacking inversion symmetry, where a direct coupling to the displacement field is allowed, but are probably not important for ions at centro-symmetric sites where the coupling to the long-wavelength modes is through the strain field.