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排序方式: 共有552条查询结果,搜索用时 15 毫秒
1.
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
2.
The majority of patients with soft tissue or bone sarcomas of the upper extremity can be treated today with limb-saving procedures using combined modality therapies. For patients with a tumor in the shoulder area, sometimes an interscapulothoracic amputation is the only radical surgical treatment. However, in selected cases, in which the tumor does not involve the neurovascular bundle, a limb-sparing alternative might be the Tikhoff-Linberg resection. Normal function of the hand and forearm, with reasonable function of the elbow, can be maintained by this procedure. Four case histories are reported. 相似文献
3.
Undecalcified embedment of large bone specimens is often challenging. A method is presented here that is suitable for methacrylate embedment of sections of canine vertebrae while retaining the ability to localize tartrate-resistant acid phosphatase and alkaline phosphatase activity. Specimens also retained tetracycline labelling, and sectioned preparations were readily stained with routine bone procedures. A modification of the Bodian silver stain, used for examining the nerves and spinal cord in these specimens, provided a useful stain for canaliculi and cement lines in trabecular and cortical bone. This stain is advantageous when both bone and nerve tissue are of interest, as in spinal fusion studies. 相似文献
4.
Prochazka T. Fischer M. Gruber B. Manner R. Matz R. Walter S. 《Components and Packaging Technologies, IEEE Transactions on》2003,26(3):591-597
Design and technology of microwave conductor lines embedded in low-temperature cofired ceramic (LTCC) multilayer substrates are summarized with a focus on achieving the highest possible quality (Q) factor for a given line inductance. The work was initiated to test the integrability of base station voltage-controlled oscillators (VCOs) in ceramic multilayer substrates. This approach leads to a miniaturization of current versions by a factor of 2 to 4. However, base station specifications for phase noise and hence resonator Q are extremely demanding. Therefore, both the design and the processing technology were optimized. By choosing a twin-line design with two parallel lines vertically separated by a single LTCC layer, Q factors of 90 and 180 have been achieved for integrated 5.5 nH inductors at frequencies of 640 MHz and 1650 MHz, respectively. Application of this result to VCO modules in standard LTCC technology already yields low phase noise levels, e.g., -136 dBc/Hz at 100 kHz offset, which is suitable for base station applications. However, further noise reduction is expected from a dedicated high Q fabrication process that uses conventional via punching and filling steps to replace the ceramic material between the two lines by conductive silver paste. This raises the Q to 120 and 200, respectively, at the two frequencies and adds extra degrees of freedom to LTCC design for low-loss wireless solutions. 相似文献
5.
Three methods are presented for the determination of external surface of large lipid vesicles of different lamellarity with 2% absolute accuracy. These methods (referred to as EPR, NBD and TNBS assays) use different marker lipids which provide signals (electron paramagnetic resonance, fluorescence of N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) residues, and UV absorption increase of 2,4,6-trinitrobenzenesulfonic acid after reaction with aminolipids, respectively). The signals change upon addition of different membrane-impermeant reagents due to reaction with marker lipids at the external vesicle surface. They were applied to the same vesicle samples, including unilamellar and multilamellar vesicles, both at two different lipid compositions. External surface data matched for the three assays within 2%, but only after appropriate redesign or adaptation of so far published procedures. Main improvements related to slow influx of reagents (TNBS and NBD assays) or to redistribution of marker lipids (EPR assay), obscuring determination of outer vesicle surface from fast reaction between reagent and readily accessible marker lipids. Furthermore, suitable strategies were found to obtain accurate 100% values (reaction of all marker lipids present), required to relate external vesicle surface to total surface. This included corrections for light scattering (NBD assay) and for turbidity (TNBS assay). These three methods appear to close a gap in the methodology to determine external surface of vesicles for typical practical needs. In particular, the reliability range of the NBD assay could be extended to marker lipid densities as low as 1 marker lipid per 3000 lipids. 相似文献
6.
S. Chevolleau J. F. Mallet E. Ucciani J. Gamisans M. Gruber 《Journal of the American Oil Chemists' Society》1992,69(12):1269-1271
Hexane and methanol leaf extracts of sixteen Mediterranean plant species were obtained by percolation. Higher yields were
observed for methanol (16.4–47.8%) than for hexane extracts (1.3–13%). Antioxidant activity of these extracts was determined
by a rapid spectrophotometric method involving the combined oxidation of beta-carotene and linoleic acid. Leaf extracts were
thus characterized by an Antioxidant Activity Coefficient (AAC) ranging from 0 to 1000. Hexane extracts gave much higher AAC
values than the corresponding methanol extracts. In both cases, myrtle (Myrtus communis) showed the best antioxidant effectiveness. 相似文献
7.
PVC is the second largest polymer produced and used in the U.S. It is a self-extinguishing material with excellent chemical resistance and good dimensional stability. It's greatest asset, however, is it's versatility. By specifically formulating PVC with the numerous types of additives available, a balance of properties can be tailored for a wide range of applications. The most serious disadvantage of PVC is it's low heat resistance which limits the service temperature of finished articles to about 70°C. Now an additive is available that can be formulated with PVC to form miscible, transparent blends with increased service temperature. With proper formulating, the higher HDT can be achieved without sacrificing other properties. It is especially important in clear PVC applications where no increase in haze was noted with the addition of the acrylic imide copolymer. Indications are that substantial market opportunities exist for a high heat PVC. Major market segments include clear packaging with it's need for hot-fill containers, building products where the desire to use darker colors provides the driving force, and in custom injection molding applications where improved heat resistance would allow vinyl to compete more effectively with FR-styrenics. 相似文献
8.
As a result of advances in such properties as processability and thermal stability, vinyl may now compete with ABS and many engineering resins in a broad number of injection molding applications. However, do past experiences with PVC compounds prevent molders from quoting on new vinyl jobs? What do molders think of vinyl's physical properties and molding characteristics versus other resins? Independent research conducted in 1989 questioned a broad range of molders in the United States regarding their perception of vinyl versus other resins as an injection molding material. The results highlight the fact that molders are aware of the benefits of vinyl in finished part applications, but require training to overcome the perceptions of past molding experiences. This paper shares the results of this survey. 相似文献
9.
Sibylle Gruber Joy Kreeft Peyton Bertram C. Bruce 《Computer Supported Cooperative Work (CSCW)》1994,3(3-4):247-269
Research in computer-supported writing has traditionally compared electronic communication with oral, face-to-face communication to identify the benefits and weaknesses of each, as if they entailed dichotomous choices. In this article, we challenge that view and argue instead that any form of communication and its educational usefulness is shaped by the situation in which it is used, the backgrounds and goals of the participants, the institutional and technological setup, and the intended purpose of the medium. Three modes of communication in one graduate course are examined — oral discussion, synchronous written discussion on a local area network, and asynchronous written postings on an email list set up for the class. It was found that patterns of participation, topic introduction, and topic development differed across the three communication modes, but that the three were interwoven with each other and embedded within the larger classroom context and forms of knowledge creation in the class. Thus, rather than examining different communication media separately, researchers interested in understanding computer-supported collaborative writing need to look at how different media are used to create a meta-medium, which is established by the discourse community involved. 相似文献
10.
Oxidative Stress Imaging: Visualizing Oxidative Cellular Stress Induced by Nanoparticles in the Subcytotoxic Range Using Fluorescence Lifetime Imaging (Small 23/2018) 下载免费PDF全文