Os(VIII)-catalysed oxidation of sulfides by sodium salt of N-chlorobenzenesulfonamide

Catalytic activity of Os(VIII) in the oxidation of some twenty organic sulfides with sodium salt of N-chlorobenzenesulfonamide (CAB) has been investigated in alkaline (pH8.7) t-butanol–water (1:1 v/v) medium. Significant retarding influence of [OH⁻] on the reactivity is exhibited. The catalysed reaction is strongly accelerated in the presence of Hg(II). Imperfections are observed in the linear Hammett relationship in the case of –NO₂ substituents.     

Reaction of 2, 3, 4-pentantrione-3-arylhydrazones with N,N-dimethylhydrazine: Formation of substituted 1H-pyrazoles via demethylation

A novel one-step synthesis of 4-arylazo-1H-1, 3, 5-trimethylpyrazoles is accomplished by reaction of N, N-dimethylhydrazine with 2, 3, 4-pentantrione-3-arylhydrazones via an unusual demethylation.     

Simulating the introduction of a sapphire crystal into an epithermal neutron beamline

The epithermal beamline at the Portuguese Research Reactor is being optimized for Prompt Gamma Neutron Activation Analysis (PGNAA). One of the major changes is to thermalise the beam by the introduction of a sapphire crystal into the beamline. Placing the sapphire at the exit of the beamline would greatly reduce the alterations and work necessary to the port and make the crystal easily removable. However, the scattered neutrons from the sapphire would increase both the neutron-induced detector damage and the background radiation. MCNPX was used to simulate the crystal in the beam port and at the exit of the port.     

Fortschritte in der analytischen Chemie seltener Metalle

Ohne Zusammenfassung     

Eine volumetrische Methode zur Bestimmung des Magnesiums

Ohne Zusammenfassung     

Flow activation free energy in cholesteric lyotropic liquid crystals

The flow activation free energy ( ΔG *) is the minimum energy necessary to induce a flow in a system that is at rest. It can be calculated from the system viscosity using the Andrade--Eyring theory. In the present work the flow activation free energy of cholesteric lyotropic liquid crystals was studied as a function of D-(+)-mannose concentration added to a nematic mesophase. The results obtained showed that all the systems can be characterized as Newtonian, but a smooth time-dependent effect can be observed mainly in systems with a lower chiral inductor concentration. It has also been observed that an increase of cholestericity leads to a decrease of ΔH * values until a limit is reached at 1 mol % of inductor. From a positive ΔS * variation it was possible to verify the existence of a locally less organized transient state during the process of micellar diffusion. When the cholesterization process was considered, the increase of the inductor concentration leads to a decrease of ΔS * and consequently to a system, as a whole, more orderly, possibly as a result of the restriction of movement caused by the presence of chiral interactions.     

On optimal zero-preserving corrections for inconsistent linear systems

This paper addresses the problem of finding an optimal correction of an inconsistent linear system, where only the nonzero coefficients of the constraint matrix are allowed to be perturbed for reconstructing a consistent system. Using the Frobenius norm as a measure of the distance to feasibility, a nonconvex minimization problem is formulated, whose objective function is a sum of fractional functions. A branch-and-bound algorithm for solving this nonconvex program is proposed, based on suitably overestimating the denominator function for computing lower bounds. Computational experience is presented to demonstrate the efficacy of this approach.