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排序方式: 共有958条查询结果,搜索用时 15 毫秒
1.
作为一个全新的概念,下一代网络(NGN)常常被人们用来描绘未来电信网的概貌。但是,不同的运营商、制造商或业务提供商对NGN有着不同的理解而且差别甚大,故希望在NGN的定义上能够统一,并能最终实现标准化。这就是国际电信联盟标准委员会(ITU-T)决定启动NGN项目的原因。该项工作由其下属的第13研究组(SG-13)负责。该项目的研究目标将与原有 相似文献
2.
R Legouis M Cohen-Salmon I del Castillo J Levilliers L Capy JP Mornow C Petit 《Canadian Metallurgical Quarterly》1993,17(2):516-518
The human KAL gene, responsible for the X-linked Kallmann syndrome, was isolated previously. Southern blot analysis using human cDNA probes detected cross-hybridization with DNA from several organisms, including chicken and quail. The entire coding sequences of chicken and quail KAL cDNAs were determined. A comparison of these cDNAs with the human KAL cDNA reveals an overall identity of 73 and 72%, respectively. This results in 76 and 75% identity at the protein level. The highest conservation was found in the WAP four-disulfide core motif and in two of the four fibronectin type III repeats reported in the human protein. These results further support the hypothesis that the KAL protein is an extracellular matrix component with anti-protease and adhesion functions. 相似文献
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In order to enhance the performance of self-consolidating concrete, it is important to have a better understanding of the rheological behavior of the material. The initial rheological parameters and their variations with time are closely affected by material temperature, type and dosage of high range water-reducing admixture (HRWRA), and elapsed time. This paper presents the results of an investigation aimed at evaluating the coupled influence of time and temperature on the variations of yield value with time of mortars made with two types of HRWRA: polynaphtalene sulfonate and polycarboxylate polymer. Four mortars extracted from self-consolidating concrete mixtures proportioned with various binder types and with water-to-binder ratios of 0.42 and 0.53 were prepared at 10 to 30 °C.Test results show that the yield value varies linearly with the coupled effect of time and temperature during the dormant period for mixtures made with polynaphtalene sulfonate-based HRWRA. However, such changes are found to depend on the mixture temperature for mixtures made with polycarboxylate-based HRWRA, which can influence the dispersion efficiency of the polycarboxylate polymer. The threshold temperature of mixtures made with PCP-HRWRA is shown to vary with mixture composition. Below a given threshold temperature, the mortar exhibits a considerable degree of retention or even reduction in yield value over 30% of the dormant period. A sharp increase in yield value is observed beyond 30% of the dormant period. Above this threshold temperature, the yield value is shown to increase linearly with time. 相似文献
5.
The degradation of perchloroethylene (PCE) by UV/TiO2 photocatalysis in gas phase was studied. The degradation efficiency has been compared in different continuous flow reactors: a photocatalytic tangential reactor (PTR) where the air flows tangentially over the catalytic medium and two photocatalytic filtering reactors (PFR) where the air flows through the porous catalytic medium. The degradation rate shows a linear dependence with the concentration of pollutants (up to 350 mg PCE/N m3) for the PTR, but the degradation was negligible for the PFR. The degradation rate was enhanced by accelerating the chlorine radicals’ formation (by adding HCl in catalytic quantity in the air flow or by PCE over-heating). In these conditions, the oxidation rate constant of PCE in the PFR was about five times higher than that in the PTR, although the mass of catalyst involved in the PFR was about 10 times lower and the contact time was about a 1000 times shorter than that of the PTR. Thus, the catalyst is globally more efficiently used in the PFR, as the mass transfer is not limiting. As a result, a degradation mechanism of PCE, involving the generation of free chlorine radicals, as the first limiting step, has been confirmed. 相似文献
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J de Seze JC Hache P Vermersch CF Arndt CA Maurage F Pasquier JL Laplanche MM Ruchoux D Leys A Destée H Petit 《Canadian Metallurgical Quarterly》1998,51(4):962-967
OBJECTIVE: The predictive value of electrophysiologic visual testing in Creutzfeldt-Jakob disease (CJD) was investigated, and the retinal pathologic findings in three cases are reported. BACKGROUND: The fatal prognosis of CJD, its transmissibility, and the lack of treatment make early diagnosis essential in averting human-to-human transmission. Electroretinogram and visual evoked potentials have been studied in few cases of CJD. METHODS: A visual electrophysiologic examination was performed in 41 consecutive patients referred with suspected CJD. The disease had been diagnosed in 24 patients (CJD group; 15 were confirmed neuropathologically and 9 by clinicolaboratory methods in accordance with diagnostic criteria). The remaining 17 patients were diagnosed with other neurologic disorders, and served as a control group. RESULTS: Flash electroretinogram revealed a significant decrease in the amplitude of the B1 wave (<60 microV) and the B/A ratio (<2) in the CJD group compared with those in the control group. Flash visual evoked potentials revealed no significant difference in latency, but amplitude was increased (>10 microV) in the CJD group, especially in patients with myoclonus. CONCLUSIONS: The visual electrophysiologic abnormalities provide an interesting noninvasive diagnostic tool in idiopathic CJD. The B1-wave decrease is closely correlated with the outer plexiform layer abnormalities observed on neuropathologic examination. 相似文献
8.
Phillip H. Henna Dejan D. Andjelkovic Petit P. Kundu Richard C. Larock 《应用聚合物科学杂志》2007,104(2):979-985
New polymeric thermosets were prepared through the bulk free‐radical copolymerization of 100% conjugated linseed oil, acrylonitrile, and divinylbenzene. Under the appropriate reaction conditions and with the appropriate curing sequence, 61–96 wt % of the oil was incorporated into the crosslinked thermosets. The resulting yellow, transparent thermosets varied from being soft and flexible to being hard and brittle. Dynamic mechanical analysis and thermogravimetric analysis showed that these thermosets had good mechanical properties and thermal stability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 979–985, 2007 相似文献
9.
NOx sorption and reduction capacities of 12-tungstophosphoric acid hexahydrate (H3PW12O40·6H2O, HPW) were measured under representative alternating conditions of lean and rich exhaust-type gas mixture. Under lean conditions, the sorption of NOx is large and is equivalent to 37 mg of NOx/gHPW. Although a part of these NOx remains unreduced, HPW is able to reduce some of the NOx to produce N2 by a reaction between the sorbed NO2 and hydrocarbon (HC), but this process is slow. The addition of 1% Pt affects strongly the chemical behaviour occurring during the course of a rich operation. The NO desorption observed at the beginning of the rich phase is strongly accelerated. The direct correlation between NO2 consumption and CO2 production shows that the principal pathway is the reaction CO+NO2→CO2+NO. In a mixture of reducing gas (CO, HC, H2), the competition is strongly in favour of CO though in its absence the reaction observed was the hydrogenation of propene to propane. 相似文献
10.
Maud Cansell Noredine Moussaoui Alain Pierre Petit Alain Denizot Nicole Combe 《European Journal of Lipid Science and Technology》2006,108(6):459-467
Two n‐3 polyunsaturated fatty acid (PUFA)‐rich diets differing in their chemical and physical forms were given to rats during 2 wk. Liposomes [phospholipids (PL) organized in bilayer structures] made from a natural marine lipid extract or a mixture of fats containing fish oil [similar fatty acids esterified in triacylglycerols (TAG)] were used. The influence of n‐3 PUFA dietary sources on plasma parameters, i.e. TAG, cholesterol and PL concentrations, was investigated. A similar hypotriglyceridemic effect of n‐3 PUFA from liposomes or fish oil was observed. In contrast, feeding rats with liposomes led to different PL and cholesterol patterns. In the plasma of rats fed liposomes, total cholesterol amounts were positively correlated with PL levels. Liposome and fish oil feedings caused a marked increase in the amounts of n‐3 PUFA, which occurred mainly at the expense of n‐6 PUFA. However, the enrichment in n‐3 PUFA in the different plasma lipid classes differed substantially when ingested in the form of fish oil or liposomes. These results were interpreted in terms of different lipid bioavailability and metabolic fate during the digestive steps and in the liver, with the dietary source. 相似文献