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排序方式: 共有193条查询结果,搜索用时 15 毫秒
1.
The distribution of total uptime during a given time interval for a repairable system is obtained. The total uptime is the total amount of time the system is up (in operation) during the interval. It is assumed that: (1) the system starts to operate at the beginning of the interval and alternately takes only the two states, up and down (under repair); (2) repair restores the system to “like-new”. A simple approximation to the distribution function of total uptime for a shorter interval is presented 相似文献
2.
Crystal phase transition between the low- and high-temperature phases has been investigated for ethylene (E)-tetrafluoroethylene (TFE) alternating copolymer (ETFE) containing the third monomeric species by the temperature dependent measurements of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) and differential scanning calorimetry. Nonafluoro-1-hexene (NFH) and hexafluoropropylene (HFP) were chosen as the third monomers, where they are different in the side-branch length, -(CF2)3CF3 and -CF3, respectively. In the case of E/TFE/NFH copolymer (ET-C4F9), the crystal phase transition temperature of the original ETFE two-components copolymer was not very much affected by the existence of NFH in the range of NFH content from 0.7 to 3 mol%. Contrarily, the crystal phase transition temperature of E/TFE/HFP copolymer (ET-CF3) was found to decrease drastically with increasing HFP content. The melting temperature and the higher-order structure were also affected sensitively depending on the HFP content. This difference in phase transition behavior between ET-C4F9 and ET-CF3 copolymers is reasonably interpreted as follows: the short side groups (-CF3) of HFP monomeric unit are included in the crystal lattice of E/TFE chains and the unit cell is expanded gradually with an increment of the HFP content, resulting in the decrease in phase transition point because of easier thermal motion of the chains. On the other hand, the long side groups [-(CF2)3CF3] of NFH monomeric units are excluded out of the crystal lattice and located on the lamellar surfaces or in the amorphous region and do not affect very much the phase transition temperature even when the NFH content is increased. In association with such a change in crystal structure, the long period of stacked lamellar structure was found to decrease remarkably in the case of NFH, whereas it does not change very much for HFP, consistent with the interpretation of the above-mentioned WAXD data. 相似文献
3.
Cationic chitosan (CT) and anionic dextran sulfate (Dex) were layer-by-layer (LbL) assembled from aqueous solutions containing
1 M NaCl on a quartz crystal microbalance (QCM) substrate, and the original films ((CT-Dex)3-CT)) were end-capped with LbL assembly from CT solutions containing 1 M NaCl and Dex solutions without NaCl. The enzymatic
degradation of films by chitosanase was quantitatively analyzed by QCM in terms of numbers of end-capping steps. The degradation
of films end-capped with (Dex-CT)3 was considerably prolonged when compared to those end-capped with other end-capping steps. A mechanism for the prolonged
degradation was proposed by quantitative QCM data and zeta potential results. 相似文献
4.
We have been developed novel catalysts for gasification of biomass with much higher energy efficiency than conventional methods (non-catalyst, dolomite, commercial steam reforming Ni catalyst). From the result of the gasification of cellulose over novel Rh/CeO2/SiO2 catalysts, it is found that the gasification process consists of the reforming of tar and the combustion of solid carbon. We also tested novel Rh/CeO2/SiO2 in the gasification with air, pyrogasification, and steam reforming of cedar wood. As a result, Rh/CeO2/SiO2 gave higher yield of syngas than the conventional steam reforming Ni catalyst. Furthermore, we compared the performance between single and dual bed reactors. Single bed reactor was effective in the gasification of cedar, however, it was not suitable for the gasification of rice straw since a rapid deactivation was observed. Gasification of rice straw, jute stick, baggase using the fluidized dual-bed reactor and Rh/CeO2/SiO2 was also investigated. Especially, the catalyst stability in the gasification of rice straw clearly was enhanced by using the fluidized dual bed reactor. 相似文献
5.
Keiichi Tomishige Tomohisa Miyazawa Takeo Kimura Kimio Kunimori Naoto Koizumi Muneyoshi Yamada 《Applied catalysis. B, Environmental》2005,60(3-4):299-307
In the partial oxidation of tar derived from the pyrolysis of cedar wood, the effect of H2S addition was investigated over non-catalyst, steam reforming Ni catalyst, and Rh/CeO2/SiO2 using a fluidized bed reactor. In the non-catalytic gasification, the product distribution was not influenced by the presence of H2S. Steam reforming Ni catalyst was effective for the tar removal without H2S addition, however, the addition of H2S deactivated drastically. In contrast, Rh/CeO2/SiO2 exhibited higher and more stable activity than the Ni catalyst even under the presence of high concentration of H2S (280 ppm). On the Ni catalyst, the adsorption of sulfur was observed by XPS and Ni species was oxidized during the partial oxidation of tar. In the case of Rh/CeO2/SiO2, the adsorption of sulfur was below the detection limit of XPS. This can be related to the self-cleaning of catalyst surface during the circulation in the fluidized bed reactor for the partial oxidation of tar derived from cedar pyrolysis. 相似文献
6.
Keiichi Tomishige Shogo Kanazawa Motoki Sato Kenji Ikushima Kimio Kunimori 《Catalysis Letters》2002,84(1-2):69-74
Pt(0.3)/Ni(10)/Al2O3, prepared by a sequential impregnation method, exhibited a more excellent performance in methane reforming with CO2 and O2 in terms of the catalytic activity and the temperature profile of the catalyst bed than Pt(0.3) + Ni(10)/Al2O3 prepared by a coimpregnation method, Ni(10)/Al2O3, Pt(0.3)/Al2O3, and Pt(10)/Al2O3. It is thought that this is because the surface Pt atoms on Ni catalyst can contribute to the enhancement of the catalyst reducibility. 相似文献
7.
A case of bilateral hypernephroma treated by right heminephrectomy in situ and "benchwork" excision of two tumors from the left kidney followed by autotransplantation is presented. Follow-up examination has demonstrated good renal function with no evidence of tumor recurrence or metastasis. This case illustrates the feasibility of benchwork operation and its application to renal tumors, particularly when these tumors are bilateral and preservation of renal tissue is imperative. Long-term follow-up of patients managed by this technique is mandatory. 相似文献
8.
Dietary eritadenine-induced alteration of molecular species composition of phospholipids in rats 总被引:1,自引:0,他引:1
The effect of dietary eritadenine, a hypocholesterolemic compound found in the mushroomLentinus edodes, on the fatty acid and molecular species profiles of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in the plasma
and liver microsomes was investigated in relation to the hypocholesterolemic action of the compound in rats. Animals were
fed the control or eritadenine-supplemented (50 mg/kg diet) diet for 14 d. Eritadenine supplementation significantly decreased
the plasma concentrations of cholesterol and phospholipids, but not triglycerides. The PC/PE ratio of liver microsomes, but
not plasma, was also markedly decreased by eritadenine. Eritadenine supplementation was found to increase the proportion of
18:2n-6 and, inversely, to decrease the proportion of 20:4n-6 and 22:5n-6 in plasma PC and liver microsomal PC and PE, indicating
that eritadenine depressed the metabolism of linoleic acid. The effect of eritadenine on the profile of n-3 fatty acids was
dissimilar in PC and PE. These changes in fatty acid composition were selectively reflected in the molecular species composition
of both PC and PE; the extent of increase in 16:0–18:2 molecular species or decrease in 18:0–20:4 molecular species was apparently
greater than that of other molecular species containing 18:2 or 20:4 in the sn-2 position. These results suggest that, in
addition to the decrease in liver microsomal PC/PE ratio, the alteration of plasma PC molecular species composition might
also participate in the hypocholesterolemic action of eritadenine. 相似文献
9.
Sudo J Iwase H Higashiyama K Kakuno K Miyasaka F Meguro T Takayama K 《Drug development and industrial pharmacy》2002,28(1):59-65
To increase delivery of L-dopa in its transdermal absorption, a new lipophilic derivative of L-dopa, L-dopa-butylester, was synthesized. An in-vitro study employing two-chamber diffusion cells, in which the excised rat abdominal skin was mounted, revealed that, in the presence of L-menthol and ethanol, L-dopa-butylester penetrated in its original form more effectively than L-dopa. L-Dopa-butylester sheets were made by immersing wiper sheets in methanol containing the compound, and then evaporating the methanol. An extraction study of the compound from the sheets revealed that its stability was maintained for at least 12 weeks. In an in-vivo cutaneous absorption study, an L-dopa-butylester sheet was attached to the shaved rat abdominal skin. A hydrogel containing L-menthol and ethanol was spread on vinyl tape, and this sheet was placed over it. In plasma, the L-dopa level rose linearly between 30 and 180 min after the cutaneous application; L-dopa-butylester was not detected. The L-dopa level was higher than that in which L-dopa was applied. These findings indicated that the lipophilic nature of L-dopa-butylester further increased its penetration through the skin, and that L-dopa-butylester that was taken up into the general circulation system was rapidly converted to L-dopa by hydrolysis in the body. 相似文献
10.
Continuously variable transmission (CVT) provides an automobile with the ability to change the gear ratio continuously, which can then improve not only ride quality such as acceleration performance but also fuel‐efficiency. However, to take advantage of the ability, a control system that can precisely control the gear ratio is required. This paper proposes such a control system for a belt‐driven CVT system. For controller design, first the CVT system is modeled by analytical and experimental approaches. The resultant static and dynamic characteristics provide a nonlinear first‐order model with an uncertain time constant and time delay. The nonlinear steady‐state gain is adjusted to one by a gain‐scheduled pre‐compensator. Thereby the plant model becomes a linear first‐order lag system with a dead time. The next step is controller design using the plant model. To guarantee stability and control performance against the parameter variation and time delay, the μ‐synthesis, a robust control method, is employed for feedback control. In addition, a feedforward controller is incorporated into the feedback control system to obtain better output response. The feedforward controller is given by a combination of the inverse system of the plant and a reference model that gives desired output response. As a result, the control system becomes a two‐degree‐of‐freedom control system. To evaluate the performance of the control system and its effectiveness on the fuel‐efficiency, computer simulation and driving tests were conducted. The simulation and experiment results prove that the proposed control system can make the gear ratio track a reference output quickly and precisely in the presence of the uncertainties. The results also show that the control system improves fuel‐efficiency by changing the gear ratio so that the engine torque and its revolution speed can satisfy optimum‐efficiency operating condition. 相似文献