Heat shock induces thermotolerance and inhibition of lysis in a lysogenic strain of Lactococcus lactis.

In this preliminary work, the heat shock response of lactic acid bacteria was investigated and characterized. Log-phase Lactococcus lactis cells pre-incubated at 40 degrees C before heat challenge at 52 degrees C for 30 min demonstrated increased thermotolerance as compared with cells pre-incubated at 30 degrees C. The response persisted for at least 60 min. Additionally, we demonstrated that: (i) the physiological expression of the heat shock response is temperature dependent; (ii) ethanol 4.0% (v/v) caused, to a lesser extent, a response similar to the heat shock; and (iii) hydrogen peroxide failed to induce a detectable response. Furthermore, we suggest that the induction of the heat shock response increases the resistance of a lysogenic strain of L. lactis, treated by mitomycin C (1.25 micrograms/ml), to lysis by the bacteriophage.     

Kinetics and mechanism of ferrous spinel oxidation studied by electrical conductivity and thermogravimetry

A mechanism of valence transfer between Fe²⁺ and Fe³⁺ ions in the octahedral, as well as the tetrahedral position of the spinel lattice is suggested to account for the electrical behaviour with the number of Fe²⁺-Fe³⁺ pairs in either position for oxidation reactions in finely-grained ferrous spinels. From the =f(t) curves which are identified with those obtained in thermogravimetry, it was established for inverse spinels such as Fe₃O₄ or for normal spinels such as FeCr₂O₄ that the kinetics is governed by a diffusion law under variable working conditions. For more complex spinels such as chromium-or titanium-substituted magnetites which exhibit both Fe²⁺ ions on octahedral and tetrahedral sites, the results are discussed only qualitatively although the profile of the =f(t) curves can also be related to the electronic exchange between the Fe²⁺ and Fe³⁺ ions from the two cation sites.     

Study of the oxidation kinetics of finely-divided magnetites. II - Influence of chromium substitution

The oxidation kinetics of magnetites substituted by chromium (Fe²⁺Fe³⁺_2?xCr³⁺_x)O^2?₄ (0 < x < 2) into γ(Fe³⁺_1?yCr³⁺_y)₂O^2?₃, (x = 3y), which is a metastable phase, was found out to be ruled by the law of diffusion, under variable working conditions, of vacancies generated at the surface. The chemical diffusion coefficient is a function of the substitution ratio, crystallite size and the number of vacancies in the spinel lattice. Contrary to magnetites substituted by aluminum, the activation energy varies irregularly with the substitution ratio.     

The LixMPn4 phases (M/Pn = Ti/P, V/As): new negative electrode materials for lithium ion rechargeable batteries

Li_xTiP₄ ternary phases (x=7 and 9) show very close electrochemical behaviors versus lithium compared to the previously reported Li₉VAs₄ and Li₇VP₄. Up to seven lithium ions reversibly react with Li₉TiP₄, leading to specific and volumetric capacities of 970 mAh/g and 1650 mAh/cm³, respectively, at average potentials close to 1 V. Galvanostatic and potentiodynamic experiments reveal that lithium extraction/insertion follow different mechanisms: a two-phase process is evidenced on charge whereas a more complex process is achieved on discharge. Besides, in situ X-ray diffraction (XRD) patterns show that both Li₉TiP₄ and Li₉VAs₄ undergo a reversible crystalline to amorphous structural phase transition upon cycling.     

The kinetics and mechanism of the low temperature reaction between tin and copper(I) chloride powders

The solid state reaction between tin and copper(I) chloride powders was studied by means of thermogravimetry under vacuum using non-isothermal and isothermal method of analysis. It is established that the kinetics in the temperature range 150 to 210 °C is governed by a diffusion-controlled process in terms of the Jander equation with an apparent activation energy of 110 KJ mol⁻¹. In the first stage, the rate determined step is the best described by an interfacial reaction. Two intermetallic compounds η-Cu₆Sn₅ and ε-Cu₃Sn predicted from the phase diagram have been identified in the reaction products and the presence of tin whiskers on the surface on the grains has been observed.     

Kinetic study of the reaction between copper(I) chloride and commercial silicon or silicides

The reaction of CuCl with silicon containing as impurities Al, Fe, Ca and Ti or with some silicides (Si₂Ca, Si₂Fe, Si₂Ti) has been investigated in the temperature range 250–310 °C. For the reaction between CuCl and commercial Si, it has been found that at 282 °C, the aluminium promotes the reaction between Cu₃Si and CuCl while its rate of consumption is greatly decreased by the presence of iron impurity. The combined action of these two impurities improves the quantity of the copper-silicon alloy formed. In the presence of silicides, the reaction with CuCl leads to copper formation with a high degree of dispersion.     

Study by thermogravimetry,electrical conductivity and IR spectrometry of the phase transition for manganese cation deficient spinels

Thermogravimetry, electrical conductivity and IR spectrometry were used to study the crystal structure change of the metastable manganese cation deficient spinels that occur during the oxidation of manganese ions above 500° C. The kinetic of the transformation is found to be governed by a nucleation growth mechanism with an activation energy varying with the amount of Mn³⁺ ions. The nature of the inversion products depends on the manganese substitution extent. We observe for a substitution extent x<0.72 a phase with a corundum structure which is a solid solution of -(MnFe)₂O₃ and for x>0.72 a mixture of two phases -(MnFe)₂O₃ + Mn₂O₃ of orthorhombic structure.