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31.
Reaction‐induced vitrification takes place in the network‐forming epoxy–amine system diglycidyl ether of bisphenol A (DGEBA) + methylenedianiline (MDA) when the glass‐transition temperature (Tg) rises above the cure temperature (Tcure). This chemorheological transition results in diffusion‐controlled reaction and can be followed simultaneously with the reaction rate in modulated‐temperature DSC (MTDSC). To predict the effect of Tcure and the NH/epoxy molar mixing ratio (r) on the reaction rate in chemically controlled conditions, a mechanistic approach was used based on the nonreversing heat flow and heat capacity MTDSC signals, in which the reaction steps of primary (E1OH = 44 kJ mol?1) and secondary amine (E2OH = 48 kJ mol?1) with the epoxy–hydroxyl complex predominating. The diffusion factor DF as defined by the Rabinowitch approach expresses whether the chemical reaction rate or the diffusion rate determines the overall reaction rate. A model based on the free volume theory together with an Arrhenius temperature dependency was used to calculate the diffusion rate constant in DF as a function of conversion (x) and Tcure. The relation between x, r, and Tg, needed in this model, can be predicted with the Couchman equation. An experimental approximation for DF is the mobility factor DF* obtained from the heat capacity signal at a modulation frequency of 1/60 Hz, normalized for the effect of the reaction heat capacity in the liquid state and the change in Cp in the glassy region with x and Tcure. In this way, an optimized set of diffusion parameters was obtained that, together with the optimized kinetic parameters set, can predict the reaction rate for different cure schedules and for stoichiometric and off‐stoichiometric mixtures. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2814–2833, 2004 相似文献
32.
Recent progress in road and lane detection: a survey 总被引:2,自引:0,他引:2
The problem of road or lane perception is a crucial enabler for advanced driver assistance systems. As such, it has been an active field of research for the past two decades with considerable progress made in the past few years. The problem was confronted under various scenarios, with different task definitions, leading to usage of diverse sensing modalities and approaches. In this paper we survey the approaches and the algorithmic techniques devised for the various modalities over the last 5 years. We present a generic break down of the problem into its functional building blocks and elaborate the wide range of proposed methods within this scheme. For each functional block, we describe the possible implementations suggested and analyze their underlying assumptions. While impressive advancements were demonstrated at limited scenarios, inspection into the needs of next generation systems reveals significant gaps. We identify these gaps and suggest research directions that may bridge them. 相似文献
33.
Stan De Spiegelaere Guy Van Gyes Hans De Witte Wendy Niesen Geert Van Hootegem 《Creativity & Innovation Management》2014,23(3):318-330
European policy is focusing on innovation as a way out of the economic crisis. At the same time, job insecurity is rising as Europe is still in crisis. In this paper, we examine whether job insecurity affects the innovative work behaviour of employees by focusing on the relation between job insecurity, job autonomy, work engagement and innovative work behaviour (IWB). Using employee level survey data, we use structural equation modelling to disentangle the relations between these variables. The partially mediated model shows the best fit with the data. This model shows that job insecurity and autonomy are both directly and indirectly, through work engagement, related with IWB. For autonomy these relations are positive, while they are negative (and smaller) for job insecurity. Moreover, a negative covariance is observed between job insecurity and autonomy. 相似文献
34.
V. Issoupov Ph. Demont C. Lacabanne O. V. Startsev V. Viel M. Dinguirard 《应用聚合物科学杂志》2002,85(2):342-350
Thermally Stimulated Creep (TSCr) mechanical spectroscopy has been used to analyze molecular movements in KMU‐4lcarbon/epoxy composite material around the glass transition temperature. This technique is powerful to characterize the microstructure and micromechanical properties of the epoxy matrix and their evolution upon thermal aging. Three cooperative submodes have been distinguished by resolving the fine structure of the material complex α‐retardation mode. The elementary processes constituting this mode possess activation enthalpies and preexponential factors that strongly depend on the thermal history of the sample. The activation parameters of the composite are subject to perceptible evolution due to postcuring degradation. The α‐mode associated complex spectrum shifts towards higher temperatures by 27°C as a consequence of a series of quenching in the temperature range 260 to 0°C; the material shows a rise in the fragility and a deterioration in the crack‐growth resistance qualities. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 342–350, 2002 相似文献
35.
36.
A good performance of the solid‐liquid unit operation is required for the economical exploitation of the Bayer process. A computational fluid dynamics (CFD) model simulating the operation of the last washing stage mud thickener of a large Canadian alumina plant is presented. The parametric study of the impact of changes in four parameters shows that the diameter of flocculated red mud particles, the feed flow rate and the radius of the feed well are critical parameters for the operation of the thickener. 相似文献
37.
M. P. Murari R. Murari S. Parthasarathy C. A. Guy V. V. Kumar B. Malewicz Wolfgang J. Baumann 《Lipids》1990,25(10):606-612
Described is a reaction sequence for the total synthesis of lyso platelet activating factor (lysoPAF; 1-O-alkyl-sn-glycero-3-phosphocholine) and its enantiomer. The procedure is versatile and yields optically pure isomers of defined chain
length. The synthesis is equally suited for the preparation of lysoPAF analogues and its enantiomers with unsaturation in
the long aliphatic chain. First,rac-1(3)-O-alkylglycerol is prepared by alkylation ofrac-isopropylideneglycerol with alkyl methanesulfonate followed by acid-catalyzed removal of the ketal group. The primary hydroxy
group of alkylglycerol is then protected by tritylation, the secondary hydroxy group is acylated, and the protective trityl
group is removed under mild acidic conditions with boric acid on silicic acid, essentially without acyl migration. Condensation
of the diradylglycerol with bromoethyl dichlorophosphate in diethyl ether, hydrolysis of the resulting chloride, and nucleophilic
displacement of the bromine with trimethylamine givesrac-1-O-alkyl-2-acylglycero-3-phosphocholine in good overall yield. The racemic alkylacylglycerophosphocholine is finally treated
with snake venom phospholipase A2 (Ophiophagus hannah) which affords 1-O-alkyl-sn-glycero-3-phosphocholine (lysoPAF) of natural configuration in optically pure form. The “unnatural” 3-O-alkyl-2-O-acyl-sn-glycerol-1-phosphocholine enantiomer, which is not susceptible to phospholipase A2 cleavage, gives 3-O-alkyl-sn-glycero-1-phosphocholine upon deacylation with methanolic sodium hydroxide. Homogeneity and structure of the intermediates
and final products were ascertained by carbon-13 nuclear magnetic resonance spectroscopy on monomeric solutions. 相似文献
38.
Nocturnal intragastric feeding has been shown to be an effective means to improve clinical and biochemical features in glycogen
storage disease type I (GSD-I). In this study, we investigated the fatty acid patterns in a whole plasma and in circulating
lipoproteins in patients on this therapy. The results demonstrated massive concentration of total fatty acids coupled with
higher levels of triglycerides, free cholesterol, cholesterol ester and phospholipids. This hyperlipidemia involved all fatty
acids without distinction of carbon or bond numbers. However, the increase was more pronounced for saturated than polyunsaturated
fatty acids, as was demonstrated by the ratios of both oleic acid to linoleic acid (1.91±0.40 vs 0.80±0.09 in controls) and
of ω3+ω6 to ω9 fatty acid families (0.92±0.11 vs 1.66±0.08 in controls). The fatty acid patterns in very low (VLDL), low (LDL)
and high (HDL) density lipoprotein showed substantial differences in composition, reflecting an association between an abnormal
lipoprotein pattern and essential fatty acid deficiency. Furthermore, GSD-I patients exhibited a significant increase in VLDL
(17±2 vs 47±7 mg/dl) and LDL cholesterol (124±7 vs 206±24 mg/dl), coupled with a decrease in HDL cholesterol (49±4 vs 28±3
mg/dl). These data documenting high LDL cholesterol and low HDL cholesterol associated with an increased concentration and
proportion of saturated fatty acids suggest that GSD-I patients on nocturnal intragastric feeding are at high risk for atherosclerosis
and its complications. 相似文献
39.
Aurélien Plyer Guy Le Besnerais Frédéric Champagnat 《Journal of Real-Time Image Processing》2016,11(4):713-730
This paper deals with dense optical flow estimation from the perspective of the trade-off between quality of the estimated flow and computational cost which is required by real-world applications. We propose a fast and robust local method, denoted by eFOLKI, and describe its implementation on GPU. It leads to very high performance even on large image formats such as 4 K (3,840 × 2,160) resolution. In order to assess the interest of eFOLKI, we first present a comparative study with currently available GPU codes, including local and global methods, on a large set of data with ground truth. eFOLKI appears significantly faster while providing quite accurate and highly robust estimated flows. We then show, on four real-time video processing applications based on optical flow, that eFOLKI reaches the requirements both in terms of estimated flows quality and of processing rate. 相似文献
40.
Guy Jobbins Jack Kalpakian Abdelouahid Chriyaa Ahmed Legrouri El Houssine El Mzouri 《国际水资源开发杂志》2015,31(3):393-406
This article draws on three case studies of drip irrigation adoption in Morocco to consider the water–energy–food nexus concept from a bottom-up perspective. Findings indicate that small farmers' adoption of drip irrigation is conditional, that water and energy efficiency does not necessarily reduce overall consumption, and that adoption of drip irrigation (and policies supporting it) can create winners and losers. The article concludes that, although the water–energy–food WEF nexus concept may offer useful insights, its use in policy formulation should be tempered with caution. Technical options that appear beneficial at the conceptual level can have unintended consequences in practice, and policies focused on issues of scarcity and efficiency may exacerbate other dimensions of poverty and inequality. 相似文献