Comparison of anaerobic dechlorinating enrichment cultures maintained on tetrachloroethene,trichloroethene, cis-dichloroethene and vinyl chloride

An anaerobic mixed microbial culture was enriched from soil and groundwater taken from a site contaminated with trichloroethene (TCE). This enrichment culture was divided into four subcultures amended separately with either perchloroethene (PCE), TCE, cis-dichloroethene (cDCE) or vinyl chloride (VC). In each of the four subcultures, the chlorinated ethenes were rapidly, consistently, and completely converted to ethene at rates of 30-50 micromol/l of culture per day, or an average 160 micro-electron equivalents/l of culture per day. These cultures were capable of sustained and rapid dechlorination of VC, and could not dechlorinate 1,2-dichloroethane, differentiating them from Dehalococcoides ethenogenes, the only known isolate capable of complete dechlorination of PCE to ethene. Chloroform (CF) and 1,1,1-trichloroethane, frequent groundwater co-contaminants with TCE and PCE, inhibited chlorinated ethene dechlorination. Most strongly inhibited was the final conversion of VC to ethene, with complete inhibition occurring at an aqueous CF concentration of 2.5 microM. Differences in rates and community composition developed between the different subcultures, including the loss of the VC enrichment culture's ability to dechlorinate PCE. Denaturing gradient gel electrophoresis of amplified bacterial 16S rRNA gene fragments identified three different DNA sequences in the enrichment cultures, all phylogenetically related to D. ethenogenes. Based on the PCR-DGGE results and substrate utilization patterns, it is apparent that significant mechanistic differences exist between each step of dechlorination from TCE to ethene, especially for the last important dechlorination step from VC to ethene.     

On a class of pseudo‐logarithmic amplifiers suitable for use with digitally switched resistors

This paper describes three circuits that implement pseudo‐logarithmic functions, which are simple and easy to implement. The circuits can be realized using operational amplifiers or current feedback amplifiers. Tuning can be achieved using switched resistors, or active resistors, or tunable transconductors, but are best suited for use with digitally switched resistors. Frequency response and stability considerations for two of the circuits are thoroughly discussed and PSPICE results confirming the theoretical results are presented alongside measured results. Copyright © 2007 John Wiley & Sons, Ltd.     

Structure oriented library design in gas phase oxidation catalysis

Structure oriented screening techniques are discussed with regard to their usefulness and applicability in catalyst screening in research projects with different degrees of exploratory character. Structure oriented screening approaches were applied to build libraries for two target reactions in two case studies presented in this paper one challenging exploratory ammon-oxidation reaction for the conversion of C₆-feedstocks to adipodinitrile precursors with currently no relevant useful materials and no technical solution known. In this study the structure driven approach helped to identify lead structures for the conversion. The second case study focuses on the oxidation of acrolein and methacrolein to the corresponding unsaturated acids. Here technical catalyst candidate materials are known and are applied in the actual industrial applications. Therefore, the focus of the second case study is to find a superior material or alternative candidate materials with improved properties with this research strategy. For both case studies the effectiveness of the structure based approach is evaluated and put into perspective with state of the art library design and research strategies in high throughput experimentation and combinatorial catalysis.     

Efficient stabilization of bulk fish oil rich in long‐chain polyunsaturated fatty acids

The aim of the present study was to systematically investigate the possibilities of stabilizing a bulk oil rich in long‐chain polyunsaturated fatty acids under ambient conditions. Combinations of different antioxidants (α‐, γ‐ and/or δ‐tocopherol, rosmarinic acid and rosemary extract rich in carnosic acid) as well as lecithin and citric acid were systematically investigated. Efficient stabilization was achieved by choosing a combination of tocopherols rich in γ‐ or δ‐tocopherol and low in α‐tocopherol, by including tocopherol‐sparing synergists like ascorbyl palmitate and carnosic acid from rosemary extract and metal‐chelating agents. For carnosic acid, a concentration of 400 mg/kg oil provides sufficient protection; the concentration of the metal chelator should be adapted to the concentration of metal ions present in the oil. As an alternative ingredient with metal‐chelating and tocopherol‐sparing activity, lecithin may be included in the formulation, but its poor solubility in bulk oils limits its use.     

Quantitative measurement of gas hold-up distribution in a stirred chemical reactor using X-ray cone-beam computed tomography

Cone-beam type X-ray computed tomography (CBCT) is a potential method to measure three-dimensional phase distributions in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. Such data are highly valuable for the assessment and evaluation of chemical processes, for optimisation of the reactor and stirrer design, and for evaluation of computational fluid dynamics codes used to model the fluid flow and heat transfer in reactive systems. However, there are considerable difficulties for accurate quantitative measurements due to beam hardening and radiation scattering effects. In a theoretical and experimental work we have investigated the non-linear effects of both physical phenomena and developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate measurement of void fraction profiles with CBCT.     

Mesoporous ordered silica structures modified by metal organic reagents and their application in catalytic Michael additions

Periodic mesoporous silica was modified with metal organic reagents via direct surface substitution reactions, thus introducing functional groups into the channels of the structure. Using materials functionalised with basic aromatic molecules as catalysts, the efficient Michael addition of diethyl malonate to trans-β-nitrostyrene was achieved. The catalysts anchored to the silica surface show high activity in the catalytic process even at low concentrations and low temperatures. The catalysts also prove to be stable during many recycling procedures. In combination with the remarkably reduced cost for the synthesis of these solid bases, the new hybrid systems are promising candidates for a new generation of catalysts.     

An Eigen-Analysis of Compact Antenna Arrays and Its Application to Port Decoupling

Placing the radiators of antenna arrays closer than aggravates the problem of power mismatch. Based on efficiency considerations, a general analysis of this effect is presented, putting forward a simple tool to quantify, compare, and optimize the performance of antenna arrays. This analysis is not restricted with respect to the number of radiators or the degree of compactness. In order to improve power matching, a systematic approach for the design of lossless decoupling and matching networks based on 180 directional couplers is suggested for up to eight radiators. Implications of network losses, which have not yet received appropriate attention by researchers in the past, will be analyzed and discussed by means of a manufactured three-element prototype array.     

Humic acid assisted synthesis of silver nanoparticles and its application to herbicide detection

Silver nanoparticles have been synthesized by reduction of silver nitrate in the presence of humic acids (HA) which acted as capping agents. The HA protected nanoparticles were found to be sensitive to increasing concentrations of sulfurazon-ethyl herbicide in solution which induced a variation in color of the nanoparticles solution from yellow to purple. The effect of the humic acid concentration used in the nanoparticles synthesis was studied by varying the [Ag⁺:HA] ratio content from [1:1] to [1:100]. UV–Vis spectroscopy was used to monitor the extinction spectra of silver nanoparticles after the synthesis and in the herbicide sensing experiments. An average silver nanoparticles size of 5 nm was confirmed by transmission electron microscope (TEM). When exposed to increasing concentration of sulfurazon-ethyl (0, 100, 200, 300, 400, 500 ppm), the solution of nanoparticles was found to changes from yellow color to orange red and purple with increasing herbicide concentration.     

香辛料提取物及其在肉制品抑菌防腐中的应用进展

肉品腐败被认为是食品工业中最重要的经济和健康问题之一,而抑菌防腐剂的应用是阻止化学变质和微生物腐败的主要手段.由于消费者对化学防腐剂安全性的担忧,相对更为安全的天然或\"绿色\"的替代品越来越受到关注.研究表明,天然香辛料提取物具有显著的抑菌性和抗氧性,其作用机理是基于对微生物细胞壁的降解、细胞膜的破坏、膜蛋白的损伤,以及...