Diffusive transport across unconfined hollow fiber membranes

The mass transfer characteristics of gas permeable, hollow fiber membranes in a liquid jet mixed reactor are studied. A membrane module, operated in the sealed-end mode, was pressurized with oxygen at the base of the fibers and centered within a submerged jet discharge. Unlike conventional membrane module designs, this configuration did not have the hollow fibers enclosed within a tubular shell. The membranes were unconfined and free to move within the generated flow field. This design is especially well suited for use in waters containing high solid concentrations. The membranes have a greater degree of freedom for movement and are therefore less likely to become fouled due to solids being lodged within the fiber bundle. Mass transfer rates were measured over a practical range of physical and process parameters. A mass transfer correlation for the unconfined configuration is presented and the transfer performance of this configuration is compared with conventional membrane contactor designs.     

Influence of mass ratio and calcination temperature on physical and photoelectrochemical properties of ZnFe-layered double oxide/cobalt oxide heterojunction semiconductor for dye degradation applications

A visible light-active photoelectrocatalyst, ZnFe-layered double oxide (LDO)/cobalt(II,III) oxide (Co₃O₄) composites were obtained by calcining the Co loaded ZnFe-layered double hydroxide (LDH) prepared by a hydrothermal and microwave hydrothermal method. The morphological studies revealed that the ZnFe-LDO/Co₃O₄ composites exhibited a flower-like structure comprising Co₃O₄ nanowires and ZnFe-LDO nanosheets. Further, when the mass ratio of Co(NO₃)₂·6H₂O/LDH was 1:1.8 and the calcination temperature was 550 °C, the ZnFe-LDO/Co₃O₄ composite exhibited 93.3% degradation efficiency for methylene blue (MB) at the applied voltage of 1.0 V under visible light after 3 h. Furthermore, the Mott-Schottky model experiments showed that the formation of a p-n heterojunction between ZnFe-LDO and Co₃O₄ could effectively inhibit the recombination of electrons and holes in the photoelectrocatalytic process. Meanwhile, free radical scavenging experiments showed that the active radicals of ⋅OH played an important role in the degradation of MB. Therefore, the photoelectrocatalytic effect of ZnFe-LDO/Co₃O₄ provides a simple and effective strategy for the removal of organic pollutants.     

Asymmetric peroxidation of prochiral allylic and benzylic compounds with tert-butyl hydroperoxide and chiral bisoxazoline–copper complexes

The first enantioselective peroxidation of prochiral allylic and benzylic C–H compounds by the use of chiral bisoxazoline–copper(I) complexes, generated in situ from the ligands 3 and 4a–d, and t-BuOOH as oxidant is reported. Cyclohexene 1, cyclopentene 5, α-angelica lactone 7, allylbenzene 9 and 2-phenylbutane 11 were converted into the optically active allylic and benzylic tert-butyl peroxides 2, 6, 8, 10a and 12 in good yields and ee values of 4–20%. Oxidations of 1-substituted 1-cyclohexenes 13a–c led to mixtures of regioisomeric peroxides 16a–c, 17a–c and 18a–c with different regio- and enantioselectivities, depending on the 1-substituent and the ligand used. The highest ee values (up to 84%) were observed for (S)-3-tert-butylperoxy-1-methyl-1-cyclohexene 17a.     

Chemo-enzymatic synthesis of the active enantiomer of the anorressant 2-benzylmorpholine

Baker's yeast reduction of (Z)-α-bromocinnamaldehyde 1 in the presence of absorbing resins allows the easy preparation of the corresponding saturated bromo-alcohol 2 in high yields and enantiomeric excess. The absolute configuration is assigned through conversion into the (R)-phenyl oxirane 3 and 1-phenyl-2-propanol 4 of (S) absolute configuration. The (R)-epoxide is transformed into 6, the pharmacologically active enantiomer of the appetite suppressant 2-benzylmorpholine, to which the (R) configuration is assigned.     

Enantioselective oxidation of vic-diols to optically active α-hydroxy ketones by a fructose-derived dioxirane

Optically active α-hydroxy ketones 3 have been prepared in moderate to good enantioselectivities through asymmetrization of meso-, and kinetic resolution of, racemic vic-diols 2 by enantioselective oxidation with the in situ generated dioxirane from the fructose-derived ketone 1; the opposite sense in the enantioselectivity of the two processes is explained in terms of the hydrogen-bonded transition-state structures for the concerted C–H oxygen insertion.     

电感耦合等离子体原子发射光谱(ICP-AES)法测定TB9钛合金中微量Si

采用电感耦合等离子体原子发射光谱(ICP-AES)法对TB9钛合金中微量Si的测定进行了研究。总结了基体对较灵敏Si的8条分析线的光谱干扰,发现从Si 185.067nm到Si 288.158nm均有不同基体元素的干扰,对微量Si的测定影响很大。经研究对比,选用背景相对低且信噪比高的Si 288.158nm线,以试剂加定量V为空白来校正基体V的光谱叠加干扰,标准加入法测定。方法检出限0.04μg/mL,标准加入校准曲线的线性相关系数0.999 9。样品加标回收率为100%~105%,相对标准偏差(n=8)小于2.0%。方法简便可靠,可获得满意的分析结果。     

Quality assessment in in vivo NMR spectroscopy: I. Introduction,objectives, and activities

By enabling noninvasive measurements of tissue biochemistry, nuclear magnetic resonance spectroscopy (MRS) provides a unique means of characterizing tissues. Differences in equipment, techniques, and methodology between different laboratories cause major difficulties when comparing results, whether from measurements of tissue metabolism, or from the effects of different therapies. This is of concern in critically evaluating work from different laboratories and centres, causing potential difficulties in reproducing results, limiting the establishment of MRS as a standard method of diagnosis and of characterising disease and response to therapy in the laboratory and clinic. It also poses particular problems in establishing the multicentre clinical trials of MRS that are now required to provide adequate statistical power in confirming the encouraging preliminary clinical observations. These difficulties arise principally from imperfect localization of signal from selected regions of interest in the body, and from the subsequent analyses of the MRS spectra. Improvement is possible by establishing agreed procedures for test measurements and for data analysis, and by using appropriate test objects and test substances to establish the quality of measurements. A concerted research project on characterisation of biological tissues by NMR, principally concerned with MR imaging (MRI), was activated in 1984 by the European Economic Community as part of its third Medical and Health Research Programme, under the auspices of the Biomedical Engineering Concerted Actions' Committee (COMAC-BME). In 1988, this project was prolonged for 5 years, when the programme was expanded to encompass MRS. A series of five accompanying papers describes (a) the test protocols and objects agreed for assessing the quality of volume selective MRS measurements; (b) the experimental trials performed for a multicentre evaluation of these procedures on experimental and clinical systems; and (c) the results of a joint quantitative data analysis study on in vivo NMR time-domain test signals.     

Synthetic,kinetic and analytical studies on titanium (IV) arsenosilicate ion exchanger: Separation of lead from its synthetic alloys

Titanium (IV) arsenosilicate has been synthesized as a new cation exchanger and has been characterized on the basis of its chemical composition, ion-exchange behaviour, pH titrations, TGA, IR and X-ray studies. On the basis of the distribution studies, the exchanger was found to be highly selective for lead and, hence, has been used for the separation of this metal ion from some synthetic lead alloys. A kinetic study has also been conducted for the exchange of some heavy pollutants.     

Surface segregation of phosphorus in titanium stabilized and cold-worked austenitic stainless steel

Auger Electron Spectroscopy (AES) is applied to examine the surface segregation activity of phosphorus in AISI 321 titanium stabilized and cold-worked austenitic stainless steel which was annealed at temperatures ranging from 400° to 1000°C. An increase in deformation is found for the temperature interval 400–600°C which corresponded to a pronounced surface segregation of phosphorus. This was not observed in the undeformed state of the material.A gradual reversal of segregation pattern is observed when the specimens are reheated successively to higher temperatures. Such information can be useful for the better understanding of the gradual deterioration of austenitic stainless steel exposed to service temperatures.     

Study of hopeite coatings: II. Study of polycationic hopeites: structure and dehydration process

The structures and the dehydration processes of phosphates, formed on galvanized steel sheets treated in polycationic solutions containing Zn²⁺, Ni²⁺ and Mn²⁺ as dihydrogenophosphates, are studied using differential and gravimetric thermal analysis (DTA, TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The compounds constituting the phosphated layers, and the crystals precipitated in a stove at 70° C from the same solutions, are structurally substituted-hopeites, (Zn, Mn, Ni)₂(PO₄)₂·4H₂O. Their thermal behaviour is strongly influenced by the presence of Ni²⁺ and Mn²⁺ ions. The dihydrate (Zn₃(PO₄)₂·2H₂O), whose structure conformation has been determined at first, is identified as the main component in the dehydration products of these compounds. The knowledge of the dihydrate conformation allows the understanding of the specificity of the dehydration processes of substituted hopeites whose transformation temperatures and dehydration modes depend on the nature of the substituting cations.