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991.
Amélie Desmarais Jean-Louis Sébédio Khaled Belkacemi Joseph Arul Paul Angers 《Journal of the American Oil Chemists' Society》2020,97(6):615-624
Cyclic fatty acid monomers (CFAM) are formed at low levels in edible oils during thermal processing operations such as frying or refining, and inevitably become part of the diet. These proatherogenic agents may increase the levels of oxidative stress markers, and induce hepatomegaly and steatosis. However, the kinetics involved in their formation is not well known. The objective of the present study was to evaluate the effects of cis and trans isomers on cyclization reactions involved in the thermal transformation of alpha-linolenic acid (ALA). Geometrical isomers of ALA were obtained from all-cis ALA by nitric acid treatment. Mono-trans isomers were concentrated using silver nitrate-silica gel chromatography. All-cis ALA, isomerized ALA, and a fraction at 85% mono-trans isomers were heat treated at 275 °C in hexadecane for periods up to 24 hours, and the formation of geometrical isomers and CFAM was monitored by GC. The results show that mono-trans isomers at carbon 9 and carbon 15 form CFAM at an accelerated rate, compared to the corresponding cis isomers, resulting in the formation of higher levels of CFAM over shorter time periods. The validation of the kinetic model was performed by solving simultaneously and nonlinearly fitting the system of coupled differential equations with experimental data. Good agreement was found between the experimental data and the predicted values. This work suggests that the use of polyunsaturated vegetable oils over extended periods for thermal processing of food may result in the formation of CFAM, in particular, if mono-trans isomers are present in the oil. 相似文献
992.
Hakan F. Oztop Khaled Al-Salem Yasin Varol Ioan Pop 《International Journal of Heat and Mass Transfer》2011,54(11-12):2253-2261
This paper examines the steady natural convection in a partially opened enclosure filled with porous media using the Brinkman–Forchheimer model. Whilst the part of the left vertical wall of the cavity is heated, the other walls are adiabatic or thermally insulated Based upon numerical predictions, the effects of pertinent parameters such as Grashof number, Darcy number, porosity, length of the heated wall and the location center of the opened cavity are examined. It is found that as the Grashof number increases, due to strengthening buoyancy driven flows, the local Nusselt number from partially heated vertical wall, at a given position on this wall increases. This, in turn, increases the temperature of the heated wall. The results of this study can be used in the design of an effective cooling system for electronic components to help ensure effective and safe operational conditions. 相似文献
993.
994.
鲁卜哈利盆地B区块近地表快速建模研究与应用 总被引:1,自引:1,他引:0
沙特阿拉伯鲁卜哈利盆地B区块地表多为沙丘、戈壁,近地表地质条件复杂,横向速度变化大,静校正问题严重。B区块勘探程度低,微测井数量少,原有的近地表模型不能很好地解决资料处理中的静校正问题,给最终的处理结果带来影响。针对这一问题,在充分考虑油气勘探对数据处理的精度要求和时效性基础上,探讨了B区块近地表建模的难点,提出了一种快速近地表模型建立方法。首先将B区块划分为沙丘、戈壁和沙丘一戈壁过渡带等不同类型的近地表区域;然后根据划分结果分别采用不同的建模方法,对沙丘底面进行准确定义,对微测井空白区带的速度误差进行校正,将沙丘压实曲线应用到模型的建立中,最终获得了能准确描述B区块近地表介质特征的模型,解决了原模型在近地表速度变化区(带)、微测井空白区(带)描述中存在的问题。利用新建立的近地表模型对二维、三维地震资料进行了处理,得到了品质较好的叠加剖面。 相似文献
995.
Poly(3‐hydroxybutyrate), PHB, is a widely distributed carbon storage polymer among prokaryotes including Rhizobium. Capacities of Rhizobium etli R13 to produce the bioplastic during growth on media with different carbon sources appeared to be specific carbon‐source. In fed batch fermentation, R. etli R13 resulted in cell dry weight 6.2 g/L and PHB 51.4%. Gas chromatography‐mass spectrometry and gel permeation chromatography analysis revealed that PHB produced from R. etli R13 was solely composed of 3‐hydroxybutyric acid and the molecular mass of the purified PHB was 3.4 × 105 Da with polydispersity 1.47. Dielectric relaxation of PHB has been studied in the temperature and frequency ranges 300–440 K and 10 kHz–4 MHz, respectively. A clear dielectric α and ρ‐relaxation processes are observed in these studied ranges of temperature and frequency. The first process is due to the dipole relaxation in the crystalline phase of PHB. The second one is due to the space‐charge formation or Maxwell‐Wagner‐polarization. The α‐relaxation process has been investigated by semiempirical Havriliak‐Negami relaxation function. The activation energy (Ea) and the relaxation time (τ0) are calculated using the Arrhenius equation. The dielectric relaxation strength (Δε) is strongly temperature dependent. The calculated values of Ea for ac conductivity, ln(σ), of PHB provide information about the presence of electronic conduction. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
996.
Md. Rezaur Rahman Sinin Hamdan Abu Saleh Ahmed Md. Saiful Islam Z.A. Talib W.F. Wan Abdullah M.S. Che Mat 《乙烯基与添加剂工艺杂志》2011,17(3):177-183
Mercerized wood species were impregnated with N,N‐dimethylacetamide. Their Fourier transform infrared spectra then showed enhanced absorption at 1419 cm?1 (? C? /CH3), and the 1267‐cm?1 (? N? /CH3) stretching band confirmed the occurrence of a modification reaction. Thermogravimetric investigation of the resultant wood polymer composites (WPCs) indicated a better thermal stability in comparison with that of the raw wood. The dynamic Young's modulus of the WPCs was significantly increased compared with that of raw wood. After modification, analysis by scanning electron microscopy showed porous cells of raw wood filled with the polymer, which led to the better stability of WPCs. Analysis by XRD indicated that the crystallinity of WPCs increased because of an increase in the stiffness and the thermal stability of the composites. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers 相似文献
997.
This paper presents a novel design scheme for traveling wave thermo‐acoustic Stirling engines (TASEs) based on a target frequency using genetic algorithm (GA). First, the effects of engine design parameters on the system performance are studied via root locus method. Accordingly, it is found that the resonator length, the inertance diameter, and the hot gas temperature are the most effective parameters in the engine design procedure. Next, the relation between the closed‐loop poles positions of the thermo‐acoustic system and the effective design variables are described parametrically. Consequently, in order to estimate the optimum values of the effective design parameters as well as the unknown positions of the nondominant poles, an appropriate fitness function based on the desired engine frequency is proposed. Subsequently, a GA is used to achieve the optimal values of design parameters so as to minimize the considered cost function. Finally, the validity of the proposed design technique is verified by comparing the obtained results with the available data of an experimental case study. 相似文献
998.
Al‑Alotaibi Amal L. Altamimi N. Howsawi E. Elsayed Khaled A. Massoudi Imen Ramadan A. E. 《Journal of Inorganic and Organometallic Polymers and Materials》2021,31(9):3904-3904
Journal of Inorganic and Organometallic Polymers and Materials - A correction to this paper has been published: https://doi.org/10.1007/s10904-021-02038-6 相似文献
999.
Danish Joshua A. Enyedy Noel Saleh Asmalina Humburg Megan 《International Journal of Computer-Supported Collaborative Learning》2020,15(1):49-87
International Journal of Computer-Supported Collaborative Learning - This paper proposes the Learning in Embodied Activity Framework (LEAF) which aims to synthesize across individual and... 相似文献
1000.
Optical Networking: Past, Present, and Future 总被引:1,自引:0,他引:1
Berthold J. Saleh A.A.M. Blair L. Simmons J.M. 《Lightwave Technology, Journal of》2008,26(9):1104-1118
Over the past 25 years, networks have evolved from being relatively static with fairly homogeneous traffic to being more configurable and carrying a heterogeneous array of services. As the applications are ultimately the driver of network evolution, the paper begins with a brief history of circuit, packet, and wave services, along with the development of the corresponding transport layers. The discussion then moves to the evolution of network-node architecture, with an emphasis on the optical-electrical-optical and optical-bypass paradigms. Scalability and cost-effectiveness in meeting network demands are two key factors in the discussion. The evolution of networking equipment, along with the development of the optical control plane, has facilitated a configurable optical layer. The enabling technologies, along with their ramifications, are discussed. Finally, the paper speculates on how capacity might evolve in the future, to handle the undoubtedly new services that are on the horizon. 相似文献