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1.
In this work we propose an MILP multiperiod formulation for the optimal design and planning of the Argentinean biodiesel supply chain, considering land competition and alternative raw materials. The country is divided into twenty three regions, each one including existing crops, oil and biodiesel plants and potential ones. The model includes intermediate and final products, i.e., seed, flour, pellets and expellers, oil, pure and blending biodiesel and glycerol. Crop fields, storage and production plants, as well as distribution centers for internal and external markets are also represented. We consider the possibility of sowing energetic crops, such as Jatropha curcas, in marginal areas. The time horizon is of seven years, divided into 84 periods. The mathematical model has been implemented in GAMS providing a powerful decision-making tool that can be applied to other regions or countries by adjusting specific data. 相似文献
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新型工艺胶乳法氯化天然橡胶(CNR)产品在干燥过程中会有HCl脱出,其脱出量对CNR的制备、性能等有一定的影响。采用电导法可连续测定CNR在干燥历程中脱HCl量及速率,这是研究CNR在低温下热降解行为的有效方法。用改进工艺的"胶乳法"制备出湿的CNR,并在一定温度下通入氮气进行干燥,在此历程中会发生脱氯化氢反应,其反应过程可分为诱导期、恒速期和低速期。文中使用Friedman法分析该过程在恒速期、低速期的反应动力学参数,其脱氯化氢反应分别为0级反应、1级反应,活化能分别为26.65,36.79 kJ/mol。在80℃以下对产品进行加热(或干燥),虽有少量HCl脱出,但并不会对产品质量造成影响。所以干燥温度应以低于80℃为宜。 相似文献
3.
The crystallisation kinetics of high molecular weight fractions of polyethylene oxide have been measured dilatometrically and also with a polarising light microscope. In general, marked deviations from the Avrami equation with exponent of 3.0 are observed which cannot alone be accounted for either in terms of rejection of low molecular weight molecules or secondary crystallisation by which crystal perfection occurs. Anomalies in nucleation, and the presence of induction periods, are present, which can account for the apparent low values of the Avrami exponent, i.e. 2.0. 相似文献
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MOISTURE MOVEMENT IN SOFTWOOD TIMBER AT ELEVATED TEMPERATURES 总被引:2,自引:0,他引:2
The anatomy of a common plantation-grown softwood in New Zealand, Pinna radiata, is reviewed and the differences between the drying behaviour of softwoods and hardwoods are discussed. These differences have significant effects on the paths for moisture movement, and this review of the timber physiology has been used as the basis for a model of the moisture movement at elevated temperatures which distinguishes between the drying behaviour of sapwood and heartwood. It is postulated for the drying of heartwood that liquid flow does not occur within a board due to the aspirated state of the pits, so an evaporative plane at the boiling point of water sweeps through the timber until the centre of the board is reached. In the case of the much wetter sapwood where the pits are not initially aspirated, we assume that liquid flow initially maintains an evaporative plane just below the surface until the moisture is no longer funicular. Thereafter, drying proceeds in a similar way to heartwood. Independent experimental measurements of the temperature profiles at the centre and surface of heartwood and sapwood bkards (100 × 50 mm) have been compared with model predictions, and the close agreement gives some confidence in the model. The model predicts that the drying process for this timber can be divided into three periods, marked by transitions in the gradients of the drying rates when plotted against the average moisture contents. This behaviour has been observed experimentally for Pinus radiata, giving us further confidence that our drying model includes the important physical processes for moisture movement in this timber. 相似文献
6.
壳聚糖氧化降解性能的研究 总被引:3,自引:0,他引:3
对壳聚糖在2%乙酸溶液中的氧化降解行为进行了探讨,着重考察了温度、时间和用量比R(H2O2与糖单元的物质量比)对相对分子质量的影响。同时对氧化降解的动力学规律作了初步研究,结果表明,氧化降解分为两个阶段,在后阶段的降解行为符合无规降解规律。 相似文献
7.
《Drying Technology》2013,31(6):1303-1318
Abstract: Solidified porous slab is formed through convective drying of glass particle layer wetted with aqueous dilute agar gel. Measured critical mean moisture content increases with increasing initial moisture or agar content. The agar gel moves in viscous flow caused by capillary pressure during drying. A new drying model based on the receding evaporation plane model is proposed. Drying period is divided into surface and internal evaporation periods. Wet slab consists of dried and wet zones during the internal evaporation period, while the wet slab consists of wet zone only during the surface evaporation period. In the new model, the evaporation rate from the wet zone in the internal drying period is estimated with the linear driving force (LDF) approximation in the field of adsorption engineering. Critical moisture content, that is, mean moisture content between the surface and internal periods, is estimated with a mass balance on the surface. Simulated results by the new drying model with reasonable fitting parameters agree very well with measured drying data. 相似文献
8.
Hironobu Imakoma Kazuya Kubo Hiroshi Yoshiba Masamichi Yoshida 《Drying Technology》2005,23(6):1303-1318
Solidified porous slab is formed through convective drying of glass particle layer wetted with aqueous dilute agar gel. Measured critical mean moisture content increases with increasing initial moisture or agar content. The agar gel moves in viscous flow caused by capillary pressure during drying. A new drying model based on the receding evaporation plane model is proposed. Drying period is divided into surface and internal evaporation periods. Wet slab consists of dried and wet zones during the internal evaporation period, while the wet slab consists of wet zone only during the surface evaporation period. In the new model, the evaporation rate from the wet zone in the internal drying period is estimated with the linear driving force (LDF) approximation in the field of adsorption engineering. Critical moisture content, that is, mean moisture content between the surface and internal periods, is estimated with a mass balance on the surface. Simulated results by the new drying model with reasonable fitting parameters agree very well with measured drying data. 相似文献
9.
Microwave vacuum drying experiments were performed on a laboratory scale dryer with a two-level porosity material: a packed bed of porous alumina beads. The incident microwave power and the vacuum pressure level were fixed, the main varying parameters being the beads diameter and porosity, and the mean pore diameter. The drying kinetics and the evolution of the product temperature are presented. The drying kinetics can be divided into two main periods. The first one corresponds to the drying from the bed voids according to evaporation mechanism that we describe with a stagnant film law. The second one corresponds to the drying from the particle pores and we divide it into two parts: we suggest that the former is dominated by capillarity driven moisture transport, and the latter is limited by the desorption kinetics of the few water layers left. 相似文献
10.
《Drying Technology》2013,31(8):1527-1548
Abstract Microwave vacuum drying experiments were performed on a laboratory scale dryer with a two-level porosity material: a packed bed of porous alumina beads. The incident microwave power and the vacuum pressure level were fixed, the main varying parameters being the beads diameter and porosity, and the mean pore diameter. The drying kinetics and the evolution of the product temperature are presented. The drying kinetics can be divided into two main periods. The first one corresponds to the drying from the bed voids according to evaporation mechanism that we describe with a stagnant film law. The second one corresponds to the drying from the particle pores and we divide it into two parts: we suggest that the former is dominated by capillarity driven moisture transport, and the latter is limited by the desorption kinetics of the few water layers left. 相似文献
11.
Suspension cultures of finely divided soybean cells established from callus were incubated with sodium [1(14)C] acetate for periods up to 86 hr. Lipids and fatty acids were analyzed for radioactivity in samples harvested at logarithmic time periods. Incorporation of acetate into cell lipid was directly proportional to the logarithm of time up to 32 hr, after an initial lag of 4-6 hr. Most of the lipid radioactivity was found in the phospholipid fraction, and all common soybean fatty acids became labeled within 6 hr. The order of labeling and distribution of radioactivity with time were essentially the same as in tissues from intact growing plants. These results support the concept of sequential desaturation of oleic acid in the cells. It was concluded that valid studies of the biosynthesis of common lipids in the soybean can be carried out for extended periods of time by use of undifferentiated cells in suspension cultures. 相似文献
12.
The distribution of phospholipids as well as their fatty acid compositions of rat mammary tissues were examined during pregnant,
lactating, and post-weaning periods. There was no apparent change in phospholipids and their acyl groups during the early
and late pregnant periods. However, tissue phospholipid composition was different during pregnant, early, and late lactating
periods. After parturition, there was a marked increase in the proportion of diacyl-glycerophosphorylcholine in the phospholipids
of mammary tissue, but this proportion decreased gradually during lactation. The decrease in diacyl-glycerophosphorylcholine
during lactation was marked by a corresponding increase in diacyl-glycerophosphorylethanolamine. Although the shorter chain
fatty acids of triglycerides were increased during lactation, only a small proportion of these fatty acids was found in the
phosphoglycerides. Marked changes in acyl group composition of individual phospholipids are found during these different physiological
stages. In general, there was a rapid decrease in 20∶4 and an increase in 18∶2 in the major phosphoglycerides during parturition.
The proportion of 20∶4 in the phosphoglycerides remained low throughout the entire lactating period, while that of 18∶2 continued
to increase 2–3 fold. Most of the changes in acyl group of the phosphoglycerides during lactation returned to normal ca. 10
days after weaning. A possible relationship of the variation of phospholipid and acyl group compositions in mammary tissue
to changes in hormonal pattern during different physiological stages is discussed. 相似文献
13.
Bertrand W. Mathäus 《Journal of the American Oil Chemists' Society》1996,73(8):1039-1043
The oxidative stability of five different oils was determined by Rancimat analysis with conductivity and chemiluminescence
measurements for evaluation of the induction periods. Samples of oil, taken at intervals from the Rancimat apparatus, were
used for chemiluminescence measurements. The chemiluminescence results were plotted vs. time, and the resulting curves were
evaluated with a graphical tangential procedure in the same way as the curves of the Rancimat method (conductivity measurement).
Induction periods of the oils assessed by Rancimat and chemiluminescence methods showed a significant linear correlation (r=0.9865). The temperature dependence of the induction periods evaluated by chemiluminescence and by conductivity was investigated
with walnut oil. A marked temperature dependence was observed for both. 相似文献
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Effects of caffeine on lipoprotein lipase gene expression during the adipocyte differentiation process 总被引:1,自引:0,他引:1
Cyril Couturier Brigitte Janyier Delphine Girlich Gilbert Béréziat Marise Andréani-Mangeney 《Lipids》1998,33(5):455-460
In this study, the effects of caffeine on lipoprotein lipase (LPL) gene expression were investigated in the 3T3-F442A preadipocyte
cell line during the adipocyte differentiation process by determining LPL enzymatic activity and its messenger RNA (mRNA)
level. The results demonstrate that caffeine acts on the gene expression of LPL, an early marker of adipocyte differentiation.
It has a biphasic action: it increases gene expression in terms of mRNA when it is added to preadipocytes during the early
stage of differentiation, but this is accompanied by a reduction of enzymatic activity. On the other hand, when caffeine is
added for long periods during differentiation and/or when it is added to mature adipocytes, it induces marked inhibition of
mRNA levels, correlated with a marked reduction of secreted enzymatic activity. The inhibitory effect of caffeine on LPL mRNA
level can be reproduced by theophylline, a phosphodiesterase inhibitor, and by dibutyryl cyclic AMP, a non-metabolizable analog
of cyclic AMP. However, the effect of caffeine and theophylline lasts longer than that of cyclic AMP, suggesting that a mechanism
other than inhibition of cyclic AMP hydrolysis may be involved in the action of caffeine. 相似文献
18.
James E. Childs Djamshid Shirazian James B. Gloer Everett L. Schiller 《Journal of chemical ecology》1986,12(8):1729-1738
Chemical orientation of adult maleSchistosoma mansoni was studied during cultivation in vitro. Directional preference was assessed in culture vessels marked with compass coordinates by the application of circular statistics for determining clustering and orientation to a predicted direction. Organic solvent extracts of fresh female schistosomes and supernatant fluids from 72-hr cultures of female parasites were tested for potential chemotactic activity. Analysis showed significant (P < 0.05) directional preference and clustering of male worms towards test compounds at all time periods (24, 48, and 72 hr) with one mixture of female extracts and at one of three time periods with a second female extract. Male worms did not respond to ecdysone, cholesterol, or solvent controls by orienting in predicted direction, although clustering was observed on two of 12 occasions. These results indicate the presence of a chemoattractant compound(s) in female extracts. 相似文献
19.
阐述了目前被许多研究者所运用的模型匹配方法求解动力学参数的不足之处,并从动力学补偿效应的角度来说明一组实验数据可以与多个模型匹配的情况。然后应用 Friedman 法求出了黄桷树叶在4个不同升温速率条件下,黄桷树叶热解的活化能与转化率之间的关系,判断出整个反应过程不遵循单一的动力学反应机制。根据活化能在各个阶段受转化率的影响将黄桷树叶的热解过程划分为两个阶段,然后分别求出了两个阶段的活化能,以它们作为参考活化能,运用 Freeman-Carroll 法求出了反应级数和指前因子。 相似文献
20.
《Journal of Adhesion Science and Technology》2013,27(10):1129-1137
Polyethylene and polystyrene film surfaces have been plasma-oxidized and subsequently characterized by X-ray core level and valence band spectroscopies. The extent of polyethylene surface oxidation was found to be dependent on the power of the oxygen glow discharge employed and the length of time that the treated sample was left exposed to air prior to analysis. In marked contrast to these observations, plasma-oxidized polystyrene surfaces were much less dependent on the oxygen glow discharge power and were also found to retain their oxygenated character over much longer periods of ageing. These differences in oxidative behaviour are explained in terms of the molecular structures of the respective polymers. 相似文献