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排序方式: 共有417条查询结果,搜索用时 31 毫秒
121.
F. Moallemi G. Batley V. Dupont T. J. Foster M. Pourkashanian A. Williams 《Catalysis Today》1999,47(1-4):235-244
This work reports experimental measurements and a modelling study carried out on palladium and platinum based catalytic monoliths used as methane combustors for heating purposes. It concentrates on the effects of operating conditions on combustion, heat transfer efficiency and pollutant formation. The development of a detailed homogeneous/heterogeneous chemical kinetics model for methane–air combustion over palladium using literature data was undertaken to model the behaviour of one of the experimental catalytic heaters. In addition, a published detailed chemical mechanism for methane combustion over platinum was used in the platinum catalyst model. The fuel–air equivalence ratios ranged from 0.3 to 0.6 and the space velocities used were between 24 000 and 72 000 h−1. Although the model assumed perfectly stirred reactor (PSR) conditions and was applied to localised regions of the monoliths where little radial gradients of temperature and concentrations were measured, it predicted the surface temperature, methane slippage, CO and NOx at the downstream face of the monolith with reasonable accuracy in some cases, but also highlighted the shortcomings of the PSR assumption in other cases. 相似文献
122.
M. C. Haag J. H. Z. Dos Santos F. C. Stedile M. A. De Araújo J. Dupont I. J. R. Baumvol 《应用聚合物科学杂志》1998,68(4):535-541
A series of ethylene–propylene-2-ethylidenebicyclo[2.2.1]hept-5-ene terpolymers have been prepared using the VOCl3/Al2Et3Cl3 catalyst under various initial Al/V ratios and diene concentrations. The V/C and Al/V ratios in EPDM films were determined by Rutherford backscattering spectrometry. The concentration of incorporated vanadium increases with the increase of the iodine number, i.e., with the number of double bonds in the polymer. However, the concentration of incorporated V in the terpolymers remains relatively low, which is attributed to the small percentage of V(III) active species due to the presence of the diene. On the other hand, the Al/V molar ratio in the terpolymers was seen to be roughly constant (between 6 and 8), independent of the iodine number and of the initial Al/V molar ratio in the reaction mixture. The polymerization yield was seen to increase with the augmentation of the initial Al/V ratio and of the diene concentration, until reaching a maximum of about 500 g polymer/g V. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 535–541, 1998 相似文献
123.
N. Mellouk C. Rame J.L. Touzé E. Briant L. Ma D. Guillaume D. Lomet A. Caraty T. Ntallaris P. Humblot J. Dupont 《Journal of dairy science》2017,100(10):8518-8533
This study aimed to investigate the association between plasma adipokine concentrations and metabolic and reproductive parameters in Holstein dairy cows fed diets with different energy levels during the peripartum period. The experiment started 1 mo before first calving and was maintained for 2 lactations. Dry matter intake and energy balance in animals fed a low-energy (LE) diet were significantly lower than that of animals fed a high-energy (HE) diet in the first lactation. Body weight, milk production, back fat thickness, and plasma concentrations of fatty acids, glucose, and insulin were not affected by diet, whereas plasma leptin and adiponectin concentrations were lower and plasma resistin concentrations higher in animals fed the LE diet. Unlike concentrations of adiponectin, plasma resistin concentrations were positively correlated with back fat thickness and plasma fatty acids concentrations and negatively correlated with dry matter intake and plasma leptin concentrations. No effect of diet was found on reproductive variables; that is, pregnancy rates at 35 or 90 d after artificial insemination (AI); numbers of small (3–5 mm), medium (>5 and ≤7 mm), and large (>7 mm) follicles; calving-to-AI and calving-to-calving intervals; and magnitude and duration of the LH surge. However, the commencement of luteal activity after first calving occurred sooner and the frequency of LH pulses was higher in the HE group than in the LE group. A significant positive correlation was found between the number of follicles (of any size) and the area under the curve of plasma resistin concentrations. The number of small follicles was also positively correlated with the nadir of plasma resistin concentrations. Taken together, these results suggest that dietary energy content in the range applied here can alter the resumption of ovarian activity and LH pulsatility without affecting fat mobilization. Plasma adipokine profiles (leptin, resistin, and adiponectin) were significantly altered by diet and negative energy balance but relationships with reproductive variables were limited to follicular growth characteristics and plasma resistin concentrations. 相似文献
124.
Stoffer BB; Dupont C; Frandsen TP; Lehmbeck J; Svensson B 《Protein engineering, design & selection : PEDS》1997,10(1):81-87
To mimic the structure of the 1.8-fold more active (k(cat)) Rhizopus oryzae
glucoamylase (GA), Aspergillus niger GA was subjected to site- directed
mutagenesis in the Trp170-Tyr175 segment of the third of the six
well-conserved alpha-->alpha connecting loops of the catalytic
(alpha/alpha)6-barrel. While the Trp170-->Phe, Gln172-->Asn and
Tyr175-- >Phe mutants showed an up to 1.7-fold increased k(cat) and
Gly174-->Cys GA and approximately 2-fold reduced k(cat) towards
maltotriose and longer substrates, Asn171-->Ser, Thr173-->Gly and
A.niger wild-type GA had very similar kcat and K(m) values for the
hydrolysis of isomaltose and the malto-oligosaccharides of DP 2-7. Crystal
structures of pseudotetrasaccharide inhibitor complexes of Aspergillus
awamori var. X100 GA, which is 94% identical to A.niger GA, indicate that
Tyr175 is located at binding subsite 4, while the preceding target residues
and the high-mannose type unit on Asn171 are at a larger distance from the
site of catalysis. The mutations had a modest effect on thermostability;
the temperature for 50% inactivation, Tm, was thus unchanged for Tyr175
-->Phe GA and reduced by 0.2-2.9 degrees C for the other mutants. The
deletion of the N-linked high-mannose unit-in Asn171 -->Ser and
Thr173-->Gly GAs-appeared to be of minor importance for enzyme activity
and thermostability, and did not increase the sensitivity to proteolysis.
相似文献
125.
Capucine Dupont Jean-Michel Commandré Guillaume Boissonnet Daniel Schweich 《Fuel》2008,87(7):1155-1164
Experiments are performed in an entrained flow reactor to better understand the kinetic processes involved in biomass pyrolysis under high temperatures (1073-1273 K) and fast heating condition (>500 K s−1). The influence of the particle size (0.4 and 1.1 mm), of the temperature (1073-1273 K), of the presence of steam in the gas atmosphere (0 and 20 vol%) and of the residence time (between 0.7 and 3.5 s for gas) on conversion and selectivity is studied. Under these conditions, the particle size is the most crucial parameter that influences decomposition. For 1.1 mm particles, pyrolysis requires more than 0.5 s and heat transfer processes are limiting. For 0.4 mm particles, pyrolysis seems to be finished before 0.5 s. More than 70 wt% of gas is produced. Forty percent of the initial carbon is found in CO; less than 5% is found in CO2. The hydrogen content is almost equally distributed among H2, H2O and light hydrocarbons (CH4, C2H2, C2H4). Under these conditions, the evolution of the produced gas mixture is not very significant during the first few seconds, even if there seems to be some reactions between H2, the C2 and tars. 相似文献
126.
A population suffering from a serious form of malnutrition was examined. The effectiveness of nutritional rehabilitation is demonstrated by the statistically significant changes observed in clinical and laboratory indicators. Several anthropometric measurements related to nutritional status are also compared with total body potassium (TBK) in patients with a positive nitrogen balance during the process of nutritional rehabilitation. It is concluded that weight (W), arm circumference (AC), middle arm muscle circumference (MAMC) and skinfold thickness (ST) measures are useful, and sufficiently accurate and precise to follow the evolution of nutritional status and body compartments. 相似文献
127.
A total of 78 mental health clients participating in therapy groups completed self-report measures corresponding to narcissistic personality defects derived from a self-psychology perspective and ratings of themselves on a checklist of interpersonal behavior. Also, pairs of group leaders were asked to rate clients on interpersonal behaviors. Results indicated a clear convergence of narcissistic needs and self-perceptions of interpersonal behaviors: Those with strong grandiose–exhibitionistic needs viewed themselves as having both dominant and friendly behavior, whereas those with strong idealizing needs viewed themselves as being submissive and moderately hostile. Therapist ratings of interpersonal behavior did not yield as many significant correlations with self-ratings of narcissistic needs: Those with grandiose–exhibitionistic needs were observed using dominant behavior and those with idealizing needs were observed using submissive behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
128.
129.
B Tavernier O Makhotine G Lebuffe J Dupont P Scherpereel 《Canadian Metallurgical Quarterly》1998,89(6):1313-1321
BACKGROUND: Monitoring left ventricular preload is critical to achieve adequate fluid resuscitation in patients with hypotension and sepsis. This prospective study tested the correlation of the pulmonary artery occlusion pressure, the left ventricular end-diastolic area index measured by transesophageal echocardiography, the arterial systolic pressure variation (the difference between maximal and minimal systolic blood pressure values during one mechanical breath), and its delta down (dDown) component (= apneic - minimum systolic blood pressure) with the response of cardiac output to volume expansion during sepsis. METHODS: Preload parameters were measured at baseline and during graded volume expansion (increments of 500 ml) in 15 patients with sepsis-induced hypotension who required mechanical ventilation. Each volume-loading step (VLS) was classified as a responder (increase in stroke volume index > or = 15%) or a nonresponder. Successive VLSs were performed until a nonresponder VLS was obtained. RESULTS: Thirty-five VLSs (21 responders) were performed. Fluid loading caused an overall significant increase in pulmonary artery occlusion pressure and end-diastolic area index, and a significant decrease in systolic pressure variation and delta down (P < 0.01). There was a significant difference between responder and nonresponder VLSs in end-diastolic area index, systolic pressure variation, and dDown, but not in pulmonary artery occlusion pressure. Receiver-operator curve analysis showed that dDown was a more accurate indicator of the response of stroke volume index to volume loading than end-diastolic area index and pulmonary artery occlusion pressure. A dDown component of more than 5 mmHg indicated that the stroke volume index would increase in response to a subsequent fluid challenge (positive and negative predictive values: 95% and 93%, respectively). CONCLUSION: The dDown component of the systolic pressure variation is a sensitive indicator of the response of cardiac output to volume infusion in patient with sepsis-induced hypotension who require mechanical ventilation. 相似文献
130.
A. Crespy C. Caze D. Coupe P. Dupont J. P. Cavrot 《Polymer Engineering and Science》1992,32(4):273-279
We have studied the impact strength, by Charpy and Izod tests, of blends of polyamide 6 with different rubbers, 10 wt% of each, or rubbers and glass fibers (8.5 wt% and 15 wt% respectively). The rubbers are from three different families: ( i ) a nonreactive cross-linked terpolymer, methyl methacrylate/butadiene/styrene (17/64.5/18.5); ( ii ) two block copolymers compatible with the matrix, poly(tetramethylene glycol)/polamide 12 (70/30 or 34/66); and ( iii ) two polymers containing reactive functionality, a terpolymer ethylene/ethyl acrylate/maleic anhydride (68/30.5/1.5) and a copolymer ethylene/acrylic acid (90/10). The classification of additives in regard to improved impact depends on the procedure used for the impact strength measurement, particularly on whether the samples are notched or unnotched. The results are discussed in relation to the dimensions and the adhesion of the rubber particles. The level of adhesion has been estimated from observations in scanning electron microscopy of cavities due to pullout nodules and of nonextracted rubber after treatment in boiling xylene. Strong variations in the morphologies are found, depending on the chemical nature of the rubber. The crystalline state of the polyamide in the blends has also been evaluated from differential scanning calorimetry. 相似文献