Manganese precipitation in NaCl induced by room temperature X-irradiation

In the present paper, Electron Paramagnetic Resonance, Ionic Thermocurrents and photoluminescence (emission and excitation) measurements have been performed in crystals of manganese- doped NaCl which were exposured to room temperature X-irradiation. The results obtained indicate that the diffusion of the Mn²⁺ - cation vacancy dipoles, originally present in the quenched samples, is considerably enhanced by ionizing radiation leading to the formation of a second phase precipitate which appears to be related with the Suzuki phase of the manganese ions in the host NaCl, as revealed from the EPR and optical data.     

Pentafluorobutane; an example of long-range five bond H?F coupling

The complete analysis of the spectrum of 2,2,4,4,4-pentafluoro-n-butane is reported. From the sum of the vicinal proton-fluorine coupling constants an estimate of the conformational energy has been obtained and successively the long-range coupling of the individual conformers has been calculated.     

Arithmétique fonctorielle des topologies de Grothendieck

Riassunto Il punto di partenza di questo lavoro è l'interpretazione delle topologie di Grothendieck nel linguaggio dei sistemi relazionali (cfr. [5]); ciò permette uno studio aritmetico di tali topologie. Attraverso nuove tecniche, qui introdotte, si ottengono risultati non privi di interesse, tra i quali una caratterizzazione degli spazi topologici noetheriani, ed ulteriori strutture topologiche di tipo locale (siti tangenti), per le quali vengono dimostrate numerose proprietà. Vengono, infine, date alcune applicazioni alla teoria degli schemi, utilizzando il funtore inviluppo affine.

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Summary The starting point of this paper is the interpretation of Grothendieck's topologies in the language of relational systems (cfr. [5]); this permits an arithmetical study of these topologies. By applying new techniques introduced here, we have achieved interesting results. These include a new characterization of Noetherian topological spaces, and further topological structures of local type (tangent sites) for which we have shown numerous properties. Finally, we have used the affine-envelope functor to illustrate some applications to the theory of schemes.

     

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.     

Fission-fragment energy correlation measurements for 252Cf(sf) and structures in far-out asymmetric fission

Fragment-mass and kinetic-energy distribution measurements for ²⁵²Cf(sf) have been extended to the far-out asymmetric low-yield fission region of M_H = 190 compared with the existing data that go up to M_H ≈ 168. The mass yield Y(m) shows a shoulder for M_H ≈ 163 and an important enhancement for M_H ? 176. The 〈E_K〉(m), σ_EK(m) and, to a lesser extent, Y(m) distributions show strong and correlated amplitude fluctuations for M_H ? 170. These data indicate strong and rapid changes in deformation of the nascent fragments and the coexistence of more than one deformed-shell stabilized scission configuration for the same mass splits. These structures and those present in the relatively high-yield regions are discussed in terms of the static macro-microscopic potential-energy calculations.     

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.     

Exactly solvable spin-12 quantum chains with multispin interactions

A generalized spin-$\text{1}\text{2}$ quantum chain with m (n) spin interactions for the z (x) component of the spins is shown to be self-dual. Through duality, the m arbitrary, n = 2 version of the model is transformed into m independent Ising chains in a transverse field, allowing us to get the exact values of the critical exponents for any m (v = s = z = 1; β = m/8; n_x = m/4) and the spectrum. The anisotropic XY chain is a particular case with = 2.