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211.
CO2‐assisted polymer processing is proposed as an alternative route for intractable and high molecular weight polymers based on the plasticization effects of CO2 and its direct effect on the melting behavior of semicrystalline polymers. A modified processing system was used to process a variety of polymers in the presence of high‐pressure CO2. The system includes an extruder that was modified to allow for high pressures created by the injection of CO2. The new design includes a modified feed section that allows a given mass of polymer to interact with CO2 before and during the extrusion process. The inherent shear mixing and the presence of CO2 allow for a specific control over the extrudate morphology. Results suggest that this alternative design provides a new and easy route to melt process high melt viscosity polymers of commercial importance, such as polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer (FEP), and syndiotactic polystyrene (s‐PS). The increased processability of these systems in CO2 is related to the plasticization effect of CO2 that was quantified through a depression in the glass‐transition temperature according to the Chow model. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1501–1511, 2004 相似文献
212.
The group of conjugated fatty acids known as conjugated linoleic acid (CLA) isomers have been extensively studied with regard to their bioactive potential in treating some of the most prominent human health malignancies. However, CLA isomers are not the only group of potentially bioactive conjugated fatty acids currently undergoing study. In this regard, isomers of conjugated α‐linolenic acid, conjugated nonadecadienoic acid and conjugated eicosapentaenoic acid, to name but a few, have undergone experimental assessment. These studies have indicated many of these conjugated fatty acid isomers commonly possess anti‐carcinogenic, anti‐adipogenic, anti‐inflammatory and immune modulating properties, a number of which will be discussed in this review. The mechanisms through which these bioactivities are mediated have not yet been fully elucidated. However, existing evidence indicates that these fatty acids may play a role in modulating the expression of several oncogenes, cell cycle regulators, and genes associated with energy metabolism. Despite such bioactive potential, interest in these conjugated fatty acids has remained low relative to the CLA isomers. This may be partly attributed to the relatively recent emergence of these fatty acids as bioactives, but also due to a lack of awareness regarding sources from which they can be produced. In this review, we will also highlight the common sources of these conjugated fatty acids, including plants, algae, microbes and chemosynthesis. 相似文献
213.
214.
A thermostable variant of fructose bisphosphate aldolase constructed by directed evolution also shows increased stability in organic solvents 总被引:4,自引:0,他引:4
Thermostable variants of the Class II fructose bisphosphate aldolase have been isolated following four rounds of directed evolution using DNA shuffling of the fda genes from Escherichia coli and Edwardsiella ictaluri. Variants from all four generations of evolution have been purified and characterized. The variants show increased thermostability with no loss of catalytic function at room temperature. The temperature at which 50% of the initial enzyme activity is lost after incubation for 10 min (T50) of the most stable variant, 4-43D6, is increased by 11-12 degrees C over the wild-type enzymes and the half-life of activity at 53 degrees C is increased approximately 190-fold. In addition, variant 4-43D6 shows increased stability to treatment with organic solvents. DNA sequencing of the evolved variants has identified the mutations which have been introduced and which lead to increased thermostability, and the role of the mutations introduced is discussed. 相似文献
215.
Dongguang Wei James G. GoodwinJr. Rachid Oukaci Alan H. Singleton 《Applied Catalysis A: General》2001,210(1-2):137-150
There exists much current interest in the use of supported Co catalysts and slurry bubble column reactors (SBCR) for the conversion of natural gas to higher hydrocarbons via the Fischer–Tropsch (F–T) synthesis. Catalyst attrition resistance is extremely important in the operation of slurry-phase reactor systems because of potential problems with plugging of system filters and/or contamination of the liquid products. This paper addresses the effects of different supports, promoters, and preparation methods on the attrition resistance of Co F–T catalysts for SBCR use. Loading of Co onto the supports improved the attrition resistances of both alumina and silica significantly. It has essentially no effect on titania. The resulting catalysts had attrition resistances in the order The addition of small amounts of metal (Ru, Cu) and oxide (La, Zr, K, Cr) promoters had mainly small effects on the attrition resistance of the supported Co catalysts. However, it would appear that the addition of Zr to Co/alumina had a negative impact on its attrition resistance. The different preparation methods used in this study (aqueous impregnation, non-aqueous impregnation, and kneading) did not appear to have a significant effect on catalyst attrition resistance. 相似文献
The calcined supports had attrition resistances (inversely related to % fines <11 μm generated during attrition testing) as follows:
−Al2O3>TiO2(rutile)SiO2
Co/Al2O3>Co/SiO2>Co/TiO2(rutile)>Co/TiO2(anatase)
216.
Jon R Saunders Heather Allison Chloe E James Alan J McCarthy Richard Sharp 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2001,76(7):662-666
Bacteriophages as accessory genetic elements play a crucial role in the dissemination of genes and the promotion of genetic diversity within bacterial populations. Such horizontal transfer of DNA is critical in the emergence of new pathogenic organisms, through the dissemination of genes encoding virulence factors such as toxins, adhesins and agressins. Phages can transfer genes that are not necessary for bacteriophage persistence and are generally recognised by their ability to convert their host bacteria to new phenotypes. This phenomenon is known as phage conversion. If such converting genes encode for virulence factors, the consequences of phage infection may include increased virulence of the host bacteria, and the conversion of a non‐pathogenic strain to a potentially dangerous pathogen. A number of virulence factors in bacteria causing diseases in plants, animals and humans are encoded by converting phages, the vast majority of which are temperate as opposed to lytic in nature. © 2001 Society of Chemical Industry 相似文献
217.
Enhanced gravimetric CO2 capacity and viscosity for ionic liquids with cyanopyrrolide anion 下载免费PDF全文
Paul Brown Burcu E. Gurkan T. Alan Hatton 《American Institute of Chemical Engineers》2015,61(7):2280-2285
Ionic Liquids (ILs) are considered as alternative solvents for the separation of CO2 from flue gas due mainly to their CO2 affinity and thermal stability. The cation architecture in a matrix of ammonium and mostly phosphonium‐based ILs with 2‐cyanopyrrolide as the anion to evaluate its impact on gravimetric CO2 absorption capacity, viscosity, and thermal stability and the three fundamental properties vital for application realization are systematically investigated. Among the investigated ILs, [P2,2,2,8][2‐CNpyr] demonstrated the lowest viscosity, 95 cP at 40°C, and highest CO2 uptake, 114 mg CO2 per g IL at 40°C. Combined effects of asymmetry and the optimized chain lengths also resulted in improved thermal stability for [P2,2,2,8][2‐CNpyr], with a mass loss rate of 1.35 × 10?6 g h?1 (0.0067 mass % h?1) at 80°C. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2280–2285, 2015 相似文献
218.
The color discrimination capacity of color vision normal observers can be assessed using color aptitude tests (CATs), although data on the test/retest reliability and inter‐test agreement of such tests using appropriate statistical measures is limited. In this study, 32 color vision normal observers twice performed each of five CATs, being the Farnsworth‐Munsell 100 hue test, HVC Color Vision Skills Test, inter‐Society Color Council Color Aptitude Test, the Nagel Anomaloscope (Nagel), and a custom designed two‐color discrimination test. Two methods of determining the Nagel matching range were used based on the initially accepted matching range or on repeated measures. The test/retest performance of each test was determined using the method outlined by Bland and Altman[Lancet 1986;1:307–310] and the inter‐test agreement was analyzed using the same method, after converting test scores into z score units. No test was found to have a significant systematic alteration in test performance between test and retest. Test/retest performance was generally poor, indicating that tests can only reliably classify observers into very broad performance bands. All tests failed to show inter‐test agreement, and our data indicate a primary reason for this: as test/retest performance is generally poor, inter‐test agreement must also be poor as no test can agree more with another test than it agrees with itself. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 224–231, 2015 相似文献
219.
Aspects of physical aging,mechanical rejuvenation,and thermal annealing in a new copolyester 下载免费PDF全文
Long‐term effects of physical aging and mechanical rejuvenation are monitored through dynamic mechanical properties of an amorphous glassy polymer. These phenomena are investigated through dynamic mechanical testing that evaluates in situ the evolution of the storage modulus with time during annealing and physical aging. Comparisons are made on samples with different thermal histories and mechanical treatment (rejuvenation). The polymer characterized in this contribution is a new commercially available copolyester under the tradename of Tritan?. The results are discussed in context to different aging rates obtained from the various thermal and mechanical treatments; both measurements of aging rates are compared. POLYM. ENG. SCI., 55:1941–1950, 2015. © 2014 Society of Plastics Engineers 相似文献
220.
Surface grafting of poly(pentafluorostyrene) on the iron and iron oxide particles via reversible addition fragmentation chain transfer (RAFT) polymerization 下载免费PDF全文
A surface grafting technique is reported for synthesis of poly(pentafluorostyrene) via reversible addition fragmentation chain transfer onto iron (iron oxide) particles. 4‐Methoxydithiobenzoate is used for the RAFT chain transfer agent. The molecular weight, surface morphology, thickness, thermal properties, and monomer conversion of the grafted polymer are reported. The grafted poly(pentafluorostyrene)–iron particles show a higher thermal transition temperature compared to the nongrafted polymer because it is speculated that the covalent bond between the polymer backbone and the surface of the iron particles restricts the molecular mobility. The monomer conversion increases in proportion to the amount of chain transfer agent (CTA) concentration at early polymerization time. The grafted poly(pentafluorostyrene) shows a “hairy” like polymer architecture with fibril thickness in the range of 80 to 100 nm. A thin coating is expected to maintain the magnetic saturation properties of iron particles. To the best of our knowledge, this is the first time that poly(pentafluorostyrene) has been grafted onto the iron particles utilizing RAFT and 4‐methoxydithiobenzoate as a CTA. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44898. 相似文献