Abnormal optical behaviour of InAsSb quantum dots grown on GaAs substrate by molecular beam epitaxy

InAs(Sb) quantum dots (QDs) samples were grown on GaAs (001) substrate by Molecular Beam Epitaxy (MBE). The structural characterization by Atomic Force Microscopy (AFM) of samples shows that InAsSb islands size increases strongly with antimony incorporation in InAs/GaAs QDs and decreases with reducing the growth temperature from 520 °C to 490 °C. Abnormal optical behaviour was observed in room temperature (RT) photoluminescence (PL) spectra of samples grown at high temperature (520 °C). Temperature dependent PL study was investigated and reveals an anomalous evolution of emission peak energy (EPE) of InAsSb islands, well-known as “S-inverted curve” and attributed to the release of confined carriers from the InAsSb QDs ground states to the InAsSb wetting layer (WL) states. With only decreasing the growth temperature, the S-inverted shape was suppressed indicating a fulfilled 3D-confinement of carriers in the InAsSb/GaAs QD sample.     

Chain dynamic of calcified tissue

Thermally stimulated current spectroscopy has been applied to the investigation of molecular mobility in human calcified tissue. A comparative study of extracts and residues at various stages of demineralization is presented. Results show that:

The Potential Use of Phosphatic Limestone Wastes in the Passive Treatment of AMD: A Laboratory Study

In Morocco, there are many sedimentary phosphate mines that produce large quantities of phosphatic limestone wastes (PLW) that contain calcite (46 wt%) and dolomite (16 wt%). These mines are located near contaminated sites, such as the abandoned Kettara pyrrhotite mine. The surface drainage water at the Kettara mine site has a pH of 2.9–4.2 and elevated concentrations of SO₄ (from 47 to 5,000 mg/L) and Fe (from 1 to 1,200 mg/L). The efficiency of PLW was assessed in the laboratory as an alternative alkaline material for passive acidic mine drainage (AMD) treatment. A series of experiments were carried out using a synthetic AMD (pH 3) containing Fe (500 mg/L), SO₄ (3.4 g/L), Ca (220 mg/L), Al (160 mg/L), Mn (20 mg/L), Zn (15 mg/L), Cu (23 mg/L), and trace amounts of Co, Cr, and Ni. Experiments were done in both anoxic and oxic conditions, in batch and column tests, with hydraulic retention times of 24 and 15 h, respectively. The PLW efficiently increased the alkalinity and pH, inducing precipitation of most metals. The neutralizing capacity of PLW prepared at different particle sizes (0.8 mm–0.5 cm, 0.5–1, 1–2, and 2–3 cm) was found to be similar in batch tests. The initial AMD value increased from 3 to 5–6.5 during the batch tests and 6.5–8 in the columns. In batch tests under anoxic and oxic conditions, there was a significant decrease in concentrations of Fe (500–120 mg/L), Al (160–1.7 mg/L), and Cu (23–0.002 mg/L). In the column tests, Al and Cu decreased (177–2.5 and 26–0.002 mg/L, respectively), while Fe decreased less significantly (618–300 mg/L). The availability and low cost of the PLW make its use in passive AMD treatment potentially feasible.     

硝酸浓度对橄榄石基活性炭特性的影响(英文)

In this work we investigated the effect of nitric acid concentration on the pore structure, surface chemistry and liquid phase adsorption of olive stone based activated carbon prepared by mixing process using phosphoric acid and steam as activating agents. Chemicals and textural characterization show that the increase of HNO3 concentration increases considerably the total acidic groups but decreases specific surface area and pore volume. The study of adsorption in aqueous solutions of two organics, phenol and methylene blue, on raw and oxidized activated carbon indicates that the treatment of mixed activated carbon with different concentrations of nitric acid improves the adsorbent capacity for methylene blue at HNO3 concentrations less or equal to 2 mol·L 1, while it has a negative effect on phenol adsorption.     

Efficient Enantioselective Syntheses of Sertraline, 2‐Epicatalponol and Catalponol from Tetralin‐1,4‐dione

Tetralin‐1,4‐dione, the stable tautomer of dihydroxynaphthalene, was reduced with catecholborane in the presence of 3,3‐diphenyl‐1‐butyltetrahydro‐3H‐pyrrolo[1,2‐c][1,3,2]oxazaborole as catalyst to give enantiomerically highly enriched 4‐hydroxy‐1‐tetralone (99% ee) in an efficient one‐pot procedure. The R‐enantiomer provided a rapid access to sertraline while the S‐enantiomer was converted into 2‐epicatalponol and catalponol. A more selective enantioselective route to the antithermitic catalponol made use of the planar chiral tricarbonylchromium complex of hydroxytetralone. Its precursor chromium(tricarbonyl)[η⁶‐(1‐4,4a,8a)‐tetralin‐5,8‐dione] was obtained via direct complexation of 1,4‐dihydroxynaphthalene using chromium(tricarbonyl)‐ tris(ammonia) and boron trifluoride etherate as source of the chromium(tricarbonyl) fragment. Enolate prenylation was best carried out in the presence of a tetraamine ligand. Complete inversion of the stereogenic center bearing the prenyl group of the initially obtained tetralone complex was achieved via enolate formation followed by protonation.     

Thermodynamic Modeling of the Use of Alkane Mixtures as Working Fluids in Absorption Cycles

The main objective is to show the effect of the choice of the most adequate combination of activity‐fugacity coefficient models on the vapor‐liquid phase equilibrium (VLE) data quality and on the calculation of the enthalpies of the different vapor and liquid streams in a refrigeration absorption machine. Six alkane binary mixtures, i.e. propane or n‐butane as refrigerants and n‐heptane, n‐octane, or n‐decane as absorbents, were considered as working fluids for their proven positive characteristics. Two activity coefficient models, UNIFAC and NRTL, and two equations of state, virial and Peng‐Robinson (PR), were tested. The obtained results showed that the UNIFAC‐PR combination reproduced the VLE data reasonably well; hence, it should be recommended for this type of refrigeration systems operating with alkanes.     

Analysis of fouling mechanisms in anaerobic membrane bioreactors

In this paper, we investigate the fouling mechanisms responsible for MF and UF membrane flux decline in Anaerobic Membrane Bioreactors (AnMBR). We have used the fouling mechanism models proposed by Hermia (1982), namely pore constriction, cake formation, complete blocking and intermediate blocking. Based on an optimization approach and using experimental data extracted from the literature, we propose a systematic procedure for identifying the most likely fouling mechanism in play. Short-term as well as long-term experiments are considered and discussed. It was found that short-term experiments are usually characterized by two fouling phases during which the same fouling mechanism or two different mechanisms affect the process. In contrast, in long-term experiments involving cleaning cycles, membrane fouling appears to be better ascribed to one phase only.The impact of abiotic parameters on membrane fouling mechanisms is reviewed and discussed in the light of these results. Finally, it is shown that the mechanism most responsible for membrane fouling in an AnMBR is cake formation. This main result will be useful for the future development of simple integrated models for optimization and control.     

Recycling poly(ethylene terephtalate) wastes: Properties of poly(ethylene terephtalate)/polycarbonate blends and the effect of a transesterification catalyst

The article addresses the issue of recycling of poly(ethylene terephtalate) (PET) by melt blending with polycarbonate (PC). PET/PC blends containing various amounts of the immiscible polymers were prepared in a twin‐screw extruder. Selected compositions were also prepared in the presence of an Sn‐based catalyst to assess the influence of transesterification during melt mixing. The degree of miscibility in the blends was studied using differential scanning calorimetry, scanning electron microscopy, and mechanical testing. PET/PC blends exhibit enhanced tensile properties in comparison to neat components for compositions of PET higher than 50% and these properties are improved by the addition of a transesterification catalyst. The PET/PC blend containing 20 wt% of PC, prepared with stannous octoate, shows the smallest size of the dispersed phase because of transesterification reactions that generate copolymer molecules at the interface between the immiscible polymers. The melting temperature of PET is decreased with the increase of the PC content in blends extruded in the presence of the catalyst. Also, the temperatures of the cold crystallization of PET are higher than those of similar blends without added catalyst. Both features give rise to better molding properties because of a shortening of the cooling time in the range of 50–90 wt% of PET. POLYM. ENG. SCI. 46:1378–1386, 2006. © 2006 Society of Plastics Engineers     

Heterostructure formation in nanowhiskers via diffusion mechanism

The formation of axial heterostructures in filamentary nanocrystals (nanowhiskers) is considered within the framework of a two-component diffusion growth model. An expression for the thickness of a heteroboundary is obtained, which is consistent with the available experimental data. Under the usual growth conditions, the thickness of the zone of diffusion smearing of the heteroboundary is on the order of one atomic monolayer, which ensures the high quality of heteroboundaries in nanowhiskers.