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排序方式: 共有10000条查询结果,搜索用时 590 毫秒
921.
CP Kubicek R Messner F Gruber M Mandels EM Kubicek-Pranz 《Canadian Metallurgical Quarterly》1993,268(26):19364-19368
We prepared [U-14C]cellobiose by cultivating Acetobacter pasteurianus in the presence of [U-14C]glucose and hydrolyzing the [U-14C]cellulose formed with beta-glucosidase-free cellulase from Trichoderma reesei. This 14C-labeled cellobiose was used to investigate the presence of an uptake system for cellobiose in T. reesei. Evidence was obtained for the presence of a high affinity (Km for cellobiose 0.3 microM) but low activity (2.5 milliunits/mg fungal dry weight) cellobiose permease. The permease is formed constitutively, but higher levels are formed after addition of sophorose (glucosyl-beta-1,2-diglucoside), a reputed cellulase inducer. The permease appears to be specific for beta-diglucosides, as the uptake of [U-14C]cellobiose is inhibited by sophorose, gentiobiose (glucosyl-beta-1,3-glucoside), and cellobiose. Under these conditions, cellooligodextrines (n, 4-7; final concentration, 1 mM) are not inhibitors. Glucose, but no other monosaccharides, inhibits the permease. The hypersecretory mutant T. reesei RUT C-30 exhibits elevated permease activities, whereas in T. reesei QM 9979, a mutant strain defective in the induction of cellulases by cellulose or sophorose, strongly reduced permease activities were demonstrated. The results stress a hitherto not recognized point of control in the induction of cellulases by T. reesei at the level of uptake of cellulose oligosaccharides. 相似文献
922.
The morphologic changes and signal intensity of the spinal cord on preoperative magnetic resonance images were correlated with postoperative outcomes in 74 patients undergoing decompressive cervical surgery for compressive myelopathy. The transverse area of the spinal cord on T1-weighted images at the level of maximum compression was closely correlated with the severity of myelopathy, duration of disease, and recovery rate as determined by the Japanese Orthopaedic Association score. In patients with ossification of the posterior longitudinal ligament or cervical spondylotic myelopathy, the increased intramedullary T2-weighted magnetic resonance imaging signal at the site of maximal cord compression and duration of disease significantly influenced the rate of recovery. A multiple regression equation was then developed with these three variables to predict surgical outcomes. 相似文献
923.
Spontaneous nasal tumors are rare in mice, and only one adenocarcinoma and two more primary neoplasms of the nose have been observed in our files of long-term feeding studies, which are composed of 3,419 male and 3,521 female CD-1 (Crl:CD-1 (ICR)BR) mice. This adenocarcinoma was a 1-cm-diameter mass observed grossly in the right nasal cavity of a 454-day-old, male CD-1 mouse from a treated group in a bioassay study conducted with 340 males and 340 females. The neoplastic epithelial cells affected the normal nasal architecture on the right side of the nose. Roughly, tumor neoplastic cells of the outer, lateral portion occurred as cuboidal to low columnar cells with basilarily located nuclei and eosinophilic cytoplasm. These cells were arranged in cylindrical profiles and frequently entrapped acini of the glands of the maxillary sinus. Neoplastic epithelial cells of the inner, medial portion appeared as serous acinar or ductular structures circumscribed by multiple lagers of myoepithelial-like cells. Staining failed to demonstrate mucous secretion. The site of origin of this neoplasm appeared to be the serous glands of the maxillary sinus. The adenocarcinoma was believed to be spontaneous. 相似文献
924.
Low concentrations of some neutral dipeptides, such as L-Ala-L-Ala, rapidly disrupt rat liver lysosomes. The phenomenon has been attributed to an osmotic imbalance generated by the production of amino acids in the lysosome by lysosomal dipeptidase activity. This hypothesis is challenged by testing several pairs of dipeptides available in both D- and L-forms and a range of dipeptides whose susceptibility to lysosomal dipeptidase activity is known. A good correlation was found between the lytic ability of dipeptides and their capacity to cross the lysosome membrane and be hydrolysed by lysosomal dipeptidase. The osmotic-imbalance hypothesis is critically evaluated in the light of the results and of recent information concerning the carrier-mediated transport of amino acids and dipeptides across the lysosome membrane. It is concluded that intralysosomal generation of amino acids remains the most plausible explanation of the lytic activity of dipeptides, and that the dipeptide porter(s) in the lysosome membrane must have higher Km than the amino acid porters. 相似文献
925.
Kollipara R.T. Arodzero A. Bashindzhagyan G. Brau J.E. Frey R. Gao D. Mason D. Sinev N. Strom D. Yang X. 《IEEE transactions on nuclear science》1995,42(2):92-101
The SSC GEM silicon Central Tracker design incorporated 18-cm long single-sided AC-coupled silicon microstrip ladders. Compared to the 12-cm long ladders considered in the preliminary stages of the tracker design, the 18-cm long ladders have the advantage of reduced cost, channel count and overall power consumption, and led to a simplified tracker assembly. However, such long ships also present the challenge of maintaining satisfactory performance. The increased capacitance and series resistance contribute to lower signal-to-noise ratios, longer time walk, higher power consumption per channel and increased probability of crosstalk to neighboring channels. In this paper, an accurate method to calculate the geometric capacitance of the AC-coupled microstrips is presented and the calculated results are compared with measurements, SPICE simulations are performed to predict the noise, the extent of interstrip capacitive coupling and the dispersion of the detector signal due to the finite series resistance of the metal strips and the long length of the detector. The influence of the preamplifier current and the shaping time on the signal and noise levels is also presented. The study concludes that the 18-cm long ladders can successfully satisfy the performance goals of the GEM silicon Central Tracker 相似文献
926.
R Spanagel SM H?lter K Allingham R Landgraf W Zieglg?nsberger 《Canadian Metallurgical Quarterly》1996,305(1-3):39-44
Acamprosate (calcium-acetyl homotaurinate) is a new compound in the treatment of alcoholism. Its efficacy has been proven in several clinical trials and registration is now pending in most European countries. The basic mechanisms by which acamprosate elicits its anti-craving action, thereby leading to reduced relapse rates, is not known at the moment. In the present study we describe a rat model of long-term alcohol-drinking which mimics relapse behavior in human alcoholics. The effect of acamprosate was studied in this model. Wistar rats had a free choice between water and alcohol solutions of different concentrations (5, 10, 20% v/v). After two months of continuous alcohol access, rats were deprived of alcohol for three days. Following this deprivation phase, all alcohol solutions were presented again. This procedure was repeated monthly for the following six months. The rats consumed 3.5 +/- 0.3 g/kg alcohol a day. After alcohol deprivation, alcohol intake rose to 5.2 +/- 0.3 g/kg per day resulting in blood alcohol levels of 30 +/- 6 mg/dl. Interestingly, the addition of quinine to the alcohol solutions or the additional presentation of a 5% sucrose solution did not affect the alcohol-deprivation effect after eight months of this intermittent alcohol exposure. However, when acamprosate (50-200 mg/kg i.p.) was administered twice daily, alcohol-drinking following an alcohol-deprivation phase was decreased dose dependently. Given at the highest dose alcohol intake even dropped significantly below baseline drinking. Together, these results show that acamprosate effectively diminishes the alcohol-deprivation effect. Furthermore, the described model seems to be a suitable animal model to screen compounds for their anti-relapse properties and subsequently for their anti-craving action. 相似文献
927.
928.
The constant modulus (CM) array is a blind adaptive beamformer capable of recovering a narrowband signal among several cochannel sources without using a pilot or training signal. It is a conventional weight-and-sum adaptive beamformer whose weights are updated by the constant modulus algorithm. An adaptive signal canceller follows the beamformer to remove the captured signal from the array input and to provide an estimate of its direction vector. Based on a Wiener model, we investigate the steady-state properties of the CM array and the signal canceller. For mutually uncorrelated sources and noise, it is shown that the signal canceller exactly removes the source captured by the array. Thus, identical stages of the CM array and signal canceller may be used in a multistage system to recover several cochannel sources. Computer simulations are presented to verify the analytical results and to illustrate the transient behavior of the system 相似文献
929.
Exchange and oxidation of C16O were investigated at 450°C on 18O-predosed Rh and Pt catalysts supported on A12O3, CeO2 and CeO2-Al2O3. In all cases, a rapid exchange of C16O with the surface can be observed. CO oxidation leads to C16O2, C16O18O and C18O2. Significant formation of C16O2 is due to the relatively high 16O coverage in reaction resulting from the C16O exchange and from an exchange between O surface species and 16O internal atoms. Hydrogen is also formed via a water-gas shift reaction (CO + surface OH) in higher proportion on CeO2-containing catalysts than on A12O3. Chlorine inhibits all the reactions (exchange, oxidation and WGS) and particularly the internal exchange. 相似文献
930.
V. N. Antsiferov V. G. Gilev A. G. Lanin R. M. Yakushev 《Refractories and Industrial Ceramics》1996,37(11):382-386
Results obtained in a study of factors that affect shaping and sintering of highly porous materials are presented. A technology providing highly porous silicon nitride materials that is based on shaping preliminarily fabricated pieces of thermoplastic slip makes it possible to use initial silicon powders of different dispersities. Highly porous materials can also be produced on the basis of sialons and exhibit a diminished thermal conductivity and a heat resistance at the level of similar silicon nitride materials.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 8 – 13, November, 1996. 相似文献