Study by electrical conductivity and infrared spectrometry of the thermal stability of defective iron spinels with aluminium and chromium

Precipitation in defective chromium- or aluminium-substituted magnetites, \(\gamma - \left( {Fe_{\left( {8/3} \right) - \left( {8/9} \right)x}^{3 + } M_{\left( {8/9} \right)x}^{3 + } \square _{1/3} } \right)O_4^{2 - } \left( {M^{3 + } = Al^{3 + } ,Cr^{3 + } ;0< x< 2} \right)\) , and defective iron aluminium chromium spinels, \(\gamma - \left( {Fe_{8/9}^{3 + } Al_{\left( {8/9} \right)\left( {2 - x} \right)}^{3 + } Cr_{\left( {8/9} \right)x}^{3 + } \square _{1/3} } \right)O_4^{2 - } \) has been investigated by electrical conductivity and infrared spectrometry in the temperature range 600 to 1200° C. For highly γ-AI-substituted magnetites and γ-iron aluminium chromium spinels the transformation of the spinel lattice into an α-rhombohedral lattice has been found to be preceded by the formation of an intermediate phase at about 900° C with a high alumina content, approximately identical to disordered γ-Al₂O₃. It is only at higher temperatures (> 1100° C) that the formation of an α-rhombohedral phase is observed. In the case of γ-Cr-substituted magnetites, temperatures of only about 700° C are required for the transformation γ → α.     

Superficial veins of the lower limbs

This study, limited to the superficial veins of 123 limbs (108 normal and 15 suffering from frank varicose disease) and only vessels with a caliber of at least 2 mm, reveals a certain degree of constancy of anatomical pattern. The initial network is defined embryologically and subsequent haemodynamic phenomena model the final veins. In particular, the topography of the main perforating veins is relatively fixed. Due to their double antihypertensive valve and aspirating pump function while walking, these vessels drain into saphenous veins. They are beneficial when they return reflux into the deep vessels. Conversely, perforator incompetence contaminates the superficial network in the case of deep reflux. The perforating vessels also have a relatively fixed position in relation to other structures: the main saphenous collateral veins, their duplicated branches, their communicating veins and the main valves. This results in large junctions typically associating a saphenous valve, one or several collateral veins, one or several communicating veins, and one or several perforating veins. Typical examples are the garter junction for the long saphenous vein, and the junction of the tip of the calf for the short saphenous vein. Other haemodynamic levels are situated at various sites, particularly in the leg, reflecting the existence, in some cases, of symmetrical "mirror", medial and lateral perforating veins. Morphological analysis of 15 limbs with obvious varicose veins of the trunk of the long saphenous vein defined the routes of transmission of reflux to the leg. Finally, the authors present several technical considerations which they hope will be useful for Doppler operators and surgeons.     

Electrical conductivity study of oxidation process in manganese-substituted magnetites

During oxidation in air of finely-grained manganese-substituted magnetites (Mn _0.8x ²⁺ Fe _1–0.8x ³⁺ )_A– (Fe _1+0.6x ³⁺ Fe _1–0.8x ²⁺ Mn _0.2x ³⁺ )_BO ₄ ^2– (A=tetrahedral, B=octahedral) the temperature dependence of the electrical conductivity over a temperature range of 100 to 700° C was investigated. Below 500° C the evolution of electrical conductivity might be closely associated with the position and nature of cations in the spinel lattice. The profile of the =f(t) curves show that the mechanism of electrical conduction in the temperature range 150 to 300° C can be explained in terms of the oxidation of Fe²⁺ to Fe³⁺ ions at octahedral sites. For the temperature range 300 to 400° C the conductivity involves the hopping of electrons from tetrahedral-site Mn²⁺ ions to tetrahedral-site Mn³⁺ ions. Above 500° C the oxidation of Mn²⁺ ions leads to an increase in conductivity with the generation of new phases of -Fe₂O₃, Mn₂O₃ and -(MnFe)₂O₃.     

Manufacturing process and thermal characterization of a fast temperature switching microdevice for real-time biological experiments

Rapid switching and measurement of the temperature in a small volume of liquid are of paramount importance for the real-time observation of biomolecular events such as protein folding–unfolding or enzymatic reactions. We present a microthermodevice for high-speed biological measurements that combines a heater for fast temperature shifting (millisecond range) and a Thin Film Thermocouple (TFTC) for accurate temperature measurement during microscopic observation. Device manufacturing as well as its thermal characterization are shown. The device is successfully employed to measure the fluorescent quenching of double-stranded DNA coupled with fluorescent intercalator on millisecond time scale, thus demonstrating its capacity for innovative biological experiments.     

Etude par conductivite electrique et par spectrometrie d'absorption infra-rouge de la precipitation d'hematite a partir de ferrites lacunaires

The hematite precipitation from zinc or cobalt-substituted defective spinels of type $\text{(M}{}_{\mathrm{x}}{}^{\mathrm{2+}}\text{Fe}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>(8?2x)</mtext><mtext>3</mtext>}}\text{■}{}_{\mathrm{<mtext>(1?x)</mtext><mtext>3</mtext>}}\text{)O}{}_4{}^{\mathrm{2?}}$ has been investigated using electrical conductivity and infrared spectrometry. The experimental data show that the temperature and kinetic of hematite precipitation depend of substitution extent x and might be closely associated with the cation vacancy in the spinel lattice. Stabilization of spinel solid solution by the cation is more pronounced for zinc than for cobalt and the effect of the cation is interpreted in terms of cation distribution in the spinel lattice.     

Initial mechanisms involved in substituted magnetite oxidation

The oxidation kinetics of slightly-substituted and pure magnetites, at low conversion ratio is controlled, both by diffusion and surface reaction. However, for highly-subtituted magnetites, diffusion is the sole regulating process. The results are related to the semiconducting properties of the compounds.     

Study of the oxidation kinetics of finely-divided magnetites III — Influence of chromium and aluminum surstitution

The oxidation kinetics of aluminum and chromium-substituted magnetites (Fe²⁺Cr³⁺_xAl³⁺_2?x)O^2?₄ (0< x < 2) into the γ defect phase of type $\text{γ(}\text{Fe}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Al}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext><mtext>?</mtext><mtext>y</mtext>}}\text{Cr}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>y</mtext>}}\text{)}{}_2\text{O}{}^{\mathrm{2?}}{}_3$ is found to be governed by the diffusion under variable working conditions for samples prepared at 700°C and whose size is less than 400 Å. When particle size is caused to increase by annealing the kinetic curves are sigmoidal but only for specimens with high chromium substitution. For compounds rich in chromium observations of morphology show facetting during oxidation but no fracturing was observed.     

Initial manifestations and late diagnosis in chronic atrophic polychondritis: apropos of a series of 15 patients

An auricular or nasal chondritis or a saddle nose deformity are the initial manifestation in half of cases of relapsing polychondritis; the other initial manifestations are various and less evocative; polyarthritis, laryngo-tracheal symptoms, episcleritis which delay the diagnosis. From 15 cases of relapsing polychondritis, the diagnosis time from the first symptom are studied; this one is long, about 3 years and 6 months (from 3 months to 17 years) in 13/15 of the cases even if the first manifestation is typical (external chondritis). In two cases only, the diagnosis was established after the first attack. This late of diagnosis had socioeconomical impact and exposed to severe complications like tracheal chondritis.     

Pure epicarditis after surgical repair of atrial septal defect: a rare form of constrictive pericarditis. Apropos of a case

The authors report a case of constrictive pericarditis occurring two years after surgical repair of an atrial septal defect in a 37 year-old-man. The diagnosis was made by right heart catheterisation and magnetic resonance imaging. The special feature of this clinical case was the exclusive localisation of the fibrosis on the visceral pericardium or epicarditis. The outcome was favourable after resection of the visceral pericardium respecting the parietal pericardium. Magnetic resonance imaging and right heart catheterisation performed 6 months after surgery were normal. Constrictive pericarditis is a classical complication of cardiac surgery but relatively rare after repair of an atrial septal defect. Isolated involvement of the visceral pericardium is rare and allows surgical correction by exclusive epicardectomy respecting the parietal pericardium.