Theoretical interpretation of the existence at 35°C of an absolute maximum of the hydration rate of calcium sulfate hemihydrate

Isothermal calorimetric measurements of β-CaSO₄ · 0.5 H₂O hydration by liquid water between 5 and 50°C show that the hydration rate passes through a maximum at about 35°C. This phenomenon is explained theoretically by consideration of the crystallization and dissolution constant rates and the solubility diagram.It results from the fact that the usual increase of rate constants with temperature is associated with a variation, in opposite directions of the positive difference of solubility between the two salts. This phenomenon is certainly general and may be found in the study of other pairs of salts.     

Transmission d'images et d'hologrammes par une nappe de fibres optiques au moyen d'un codage chromatique

A new method of addition of 2-D complex optical signals is proposed. The addition is performed by suitably matched spatial filtering. For that purpose the effect of compacting of periodic objects images is employed.     

The problem of the 27Al neutron spin-dependent scattering length

Early measurements of the neutron spin-dependent scattering length of ²⁷Al by neutron precession have given two values, consistent within the limits of accuracy, whose mean value is b₊?b_? = + 0.52 ± 0.02 fm. The positive sign was recently put in doubt from known values of neutron resonance parameters. New experiments were undertaken on a sample of ²⁷Al, a compound sample of ²⁷Al and ⁴⁵Sc, together with a redetermination of the sign of the ²⁷Al gyromagnetic ratio. These experiments confirmed in sign and magnitude the b₊?b_? value previously found. We have so far no explanation of the discrepancy.     

A note on the ‘loser wins’ game

A simple explanation if provided for the ‘loser wins paradox’ and properties of the corresponding game are explored.     

Simple plant location under uniform delivered pricing

Given a geographical system of demand functions, the simple-plant location problem under uniform delivered pricing consists in determining the delivered price taken as uniform for all customers, the number, the locations, the sizes and the market areas of the plants which supply these customers, in order to maximize the profit of the firm. A model is proposed, which allows, moreover, to integrate some aspects of the commercial policy of the firm, i.e., its decision to satisfy all markets with positive demands or profitable markets only, or to allow a maximum unit loss or require a minimum unit gain on each served market. An efficient algorithm is presented and illustrated by an example. Computational results with a code using recursively Erlenkotter's DUALOC program as a subroutine are summarized.     

Preferential Solvation of the Sodium Cation in Binary Mixtures of Tetrahydrofuran with Unidentate Nitrogen Ligands

²³Na-chemical shifts for the NaClO₄ solute depend markedly upon the composition of binary solvent mixtures of THF with amines (pyridine, piperidine, pyrrolidine, aniline, propylamine, and isopropylamine). These changes, analyzed in a novel application of the Hill formalism, show equality of the intrinsic equilibrium constant K for the successive steps, upon displacement of THF from sodium coordination by one of these amines. The results, which are entirely consistent with tetracoordination of the sodium cation by these solvents, also indicate proportionality of the K values to the amine chemical shifts.     

Effets de cryptands et activation de bases—II: Genese d'enolates et essais d'activation de LiH,NaH et KH dans l'ether,le THF et le benzene

The generation of the lithium, sodium and potassium enolates of cyclohexanone using LiH, NaH and KH has been investigated. The utilization of macrocyclic ligands (which selectively complex the metal cation) activated the alkaline hydride reagent. However, the most dramatic effect was the activation of the enolate, enabling proton abstraction from the solvent.     

The lowest triplet state of the biexciton may be bound

Using Haken's hamiltonian and a simple variational wavefunction, the (1_σg, 1_σu)³Σ_u state of the biexciton in a polar crystal is found to be stable with respect to dissociation into two ground-state excitons, for ceratain range of (realistec) material parameters, unlike the corresponding state in the H₂ molecule.