Capacitance-voltage profiling and thermal evolution of the conduction band-offset of unstrained Ga0.47In0.53As/InP single quantum well

We report the results of capacitance-voltage (C-V) and Deep Level Transient Spectroscopy (DLTS) measurements performed upon a Ga_0.47In_0.53As/InP quantum well structure. At room temperature, a conduction-band offset ΔE_c=(200±10)meV and charge densities σ_I=±(3±1)*10¹¹ times the electronic charge per cm² have been measured from C-V experiments. At lower temperature (T≤150K) we have observed an important decrease of the band-offset, considerably larger than a pure thermal effect. We have shown that the explanation lies in the presence of a high concentration of deep traps located at the well-barrier interfaces. Two species A and B have been detected through DLTS experiments with activation energies E_tA=90 meV and E_tB=195 meV, respectively. The filling of these trap levels at low temperature lowers the band offset from 200 to 120 meV, owing to band repulsion effects.     

Nanoscale damage during fracture in silica glass

We report here atomic force microscopy experiments designed to uncover the nature of failure mechanisms occuring within the process zone at the tip of a crack propagating into a silica glass specimen under stress corrosion. The crack propagates through the growth and coalescence of nanoscale damage spots. This cavitation process is shown to be the key mechanism responsible for damage spreading within the process zone. The possible origin of the nucleation of cavities, as well as the implications on the selection of both the cavity size at coalescence and the process zone extension are finally discussed.     

Relationship between migration potential and structural parameters in crosslinked polyethylenes

Interactions between water and crosslinked polyethylenes (XPE) pipes are subject to regulatory control. In line with this, the objective of our work has been to identify some methods enabling to predict the behaviour of XPE vis à vis its contents. In our study, series of PEHD were crosslinked by β-irradiation at various crosslinking densities. With regard to the structural parameters measured for XPE, we were led to select the evaluation of crystallinity by DSC, the evaluation of crosslink density through its gel fraction and through dynamic mechanical analysis in the rubbery state. These properties are supposed to have a significant effect on the migration potential. With regard to the measurement of the migration potential, an organic solvent was used to accelerate the migration process and the quantity of migrating species was evaluated using gas chromatography. Our results show that irradiation increase the degree of crosslinking, which has the effect of reducing the potential of migration. It comes out of these conclusions that the measurement of structural characteristics of XPE may be a relevant way to predict their potential migration.     

Impairment of muscle energy metabolism in patients with sleep apnoea syndrome

Impairment of muscle energy metabolism has been demonstrated in normal subjects with chronic hypoxaemia (altitude chronic respiratory failure). The purpose of this study was to verify the hypothesis that a comparable condition could develop in patients with sleep apnoea syndrome (SAS), considering that they are exposed to prolonged and repeated hypoxaemia periods. Muscle metabolism was assessed in 11 patients with SAS performing a maximal effort on cycloergometer. In comparison with normal subjects, SAS patients reached lower maximal loads [144 +/- 7 vs. 182 +/- 10 W (P < 0.005)] and lower peak oxygen uptakes [26.4 +/- 1.2 vs 33.2 +/- 1.4 ml kg-1 min-1 (P < 0.005)]. Abnormal metabolic features were found: maximal blood lactate concentration was significantly lower than in normal subjects [0.034 +/- 0.004 vs. 0.044 +/- 0.002 mmol l-1 W-1 (P < 0.05)]; and lactate elimination rate, calculated during a 30-min recovery period, was reduced [0.127 +/- 0.017 vs, 0.175 +/- 0.014 mmol l-1 min-1 (P < 0.025)]. The extent of these anomalies correlated with the severity of SAS. The patients also showed higher maximal diastolic blood pressures than normal subjects [104 +/- 5 vs. 92 +/- 4 mmHg (P < 0.05)]. These results can be interpreted as indications of an impairment of muscle energy metabolism in patients with SAS. Decrease in maximum blood lactate concentration suggests an impairment of glycolytic metabolism, while decrease in the rate of lactate elimination indicates a defect in oxidative metabolism. Since no respiratory pathology apart from SAS was found in this group of patients, it seems legitimate to link the genesis of these impairments to repeated bouts of nocturnal hypoxaemia.     

Activated carbon porosity tailoring by cyclic sorption/decomposition of molecular oxygen

Activated-carbon pore size tailoring is usually achieved by pore size reduction, pore size widening or more rarely by direct activation. Successive widening cycles composed of an initial molecular oxygen sorption step, followed by a carbonization step under nitrogen, have been applied to three different materials in order to study their gradual pore size modifications. For years, the whole microporosity obtained after several cycles is known to present better pore size distribution than those inherited from conventional activations. Moreover, as shown in the present paper, the gradual obtained microporosities cover a wide and valuable range of porous textures highly dependent on the initial material origin and initial activation. Gradual mean pore size evolutions of 1 or 2 Å per cycle were observed linked to a simultaneous increase in microporous specific volume in the case of pitch-based and coconut activated carbons, respectively. Comparatively, the microporous specific volume of a commercial coconut carbon molecular sieve was increased by 26% without modification of its mean pore size and therefore of its sieving effect. Those results have been used to test a simple textural model of activated carbon porosity proposed in the recent literature.     

Aroma characterization of various apricot varieties using headspace–solid phase microextraction combined with gas chromatography–mass spectrometry and gas chromatography–olfactometry

The characterization of the aromatic profile of several apricot cultivars with molecular tracers in order to obtain objective data concerning the aromatic quality of this fruit was undertaken using headspace–solid phase microextraction (HS–SPME). Six apricot cultivars were selected according to their organoleptic characteristics: Iranien, Orangered, Goldrich, Hargrand, Rouge du Roussillon and A4025. The aromatic intensity of these varieties measured by HS–SPME–Olfactometry were defined and classified according to the presence and the intensity of grassy, fruity and apricot like notes. In the six varieties, 23 common volatile compounds were identified by HS–SPME–GC–MS. Finally, 10 compounds, ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, linalool, β-ionone, menthone and (E)-hexen-2-al were recognized by HS–SPME–GC–O as responsible of the aromatic notes involved in apricot aroma and considered as molecular tracers of apricot aromatic quality which could be utilized to discriminate apricot varieties.     

Performance of MUF honeymoon adhesive for glulam

Glulam beams were prepared using pine boards glued together with a melamine-urea–formaldehyde (MUF) adhesive by means of an experimental fast-setting process called “honeymoon”. In this process, MUF is spread on the face of the first part, then an acid is spread on the face of the second part and the two are assembled. Mechanical properties of the beams remain very good even after severe water exposure in a delamination test. Moreover, the short pressing time of this honeymoon process (the adhesive is perfectly hardened after 3 h) makes it perfectly suitable for industrial applications.     

Temperature effect in the maximum propagation rate of a liquid metal filled crack: The T91 martensitic steel/Lead–Bismuth Eutectic system

The liquid metal embrittlement sensitivity of a modified 9Cr1Mo martensitic steel in contact with Lead–Bismuth Eutectic was studied as a function of the temperature in a wide range of deformation rate. A fracture mechanics approach (crack tip opening displacement and J-Δa) combined to a fractographic study was applied to study the maximum brittle crack propagation rate. Comparison of these data with the temperature evolution expected from the stress assisted dissolution model discards this model as the embrittlement mechanism. Thermally activated ductility recovery mechanisms fail to account for the experimental results. However, the data is compatible with a physi-sorption rate limiting process. The adsorption energy extracted from the temperature evolution of the maximum crack propagation rate compares favourably with existing Ab-Initio calculations. This strongly suggests that the LME mechanism is linked with the direct effect of surface adsorption.     

Magnetic properties of GdBa2Cu3O7crystals in high magnetic field

The magnetic properties of single crystals of GdBa₂Cu ₃O₇ were investigated in a magnetic field of up to 20 T applied parallel to the c axis in the 1.7-300 K temperature range. In the superconducting state, the field and temperature dependences of the critical current densities were deduced from the hysteresis of the half-cycle using Bean's critical state model. The Gd³⁺ paramagnetic moment was then studied. Above about 20 K, the M(H) isotherms were found to be given, at different temperatures, by the Brillouin function of the free Gd³⁺ ion. Below 20 K, the average magnetization does not obey the Brillouin law. The normal-state susceptibility was described by the free-ion Curie-Weiss law