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排序方式: 共有198条查询结果,搜索用时 15 毫秒
1.
RJ Linnola RP Happonen OH Andersson E Vedel AU Yli-Urpo U Krause L Laatikainen 《Canadian Metallurgical Quarterly》1996,63(4):471-478
The current problem with keratoprosthesis is the ingrowth of corneal or conjunctival epithelium into the anterior chamber. This may lead to infections and extrusion of the prosthesis as well as to the development of retroprosthetic membrane and secondary glaucoma. Glass-ceramic coated and uncoated titanium has been tested as material for the keratoprosthesis to prevent epithelial ingrowth. Twenty-two Supra-Descemet's membrane keratoprostheses were inserted in the eyes of 22 rabbits for 1, 2, 4, 8, or 12 months. The prosthesis had an optic part made of polymethylmetacrylate (PMMA). The support for the optic part and the flange of the prosthesis were made of titanium. Eleven of the prostheses were coated with glass-ceramic. The histological sections of the enucleated eyes were prepared through the central part of the cornea and the prosthesis using a cutting-grinding method. The histological analysis was made on both halves of the implants separately giving two analysis areas in each eye. All 11 titanium prostheses were retained for the time period planned. Two glass-ceramic coated prostheses were lost at 2 and 4 weeks, respectively. This was caused by difficulties at surgery due to a thick coating. These eyes were excluded from the histological analysis. No significant ingrowth of epithelium was seen in 15/18 (83%) and in 16/22 (73%) of the analysed areas of the glass-ceramic coated and titanium prostheses, respectively. Titanium appears to be a suitable material for the keratoprosthesis. The ingrowth of the epithelium may be hindered further by coating the titanium with bioactive glass-ceramic. 相似文献
2.
A Bedekar RM Zink DH Sherman TV Line JF Van Pilsum 《Canadian Metallurgical Quarterly》1998,119(4):677-690
The amino acid sequences of the amidinotransferases and the nucleotide sequences of their genes or cDNA from four Streptomyces species (seven genes) and from the kidneys of rat, pig, human and human pancreas were compared. The overall amino acid and nucleotide sequences of the prokaryotes and eukaryotes were very similar and further, three regions were identified that were highly identical. Evidence is presented that there is virtually zero chance that the overall and high identity regions of the amino acid sequence similarities and the overall nucleotide sequence similarities between Streptomyces and mammals represent random match. Both rat and lamprey amidinotransferases were able to use inosamine phosphate, the amidine group acceptor of Streptomyces. We have concluded that the structure and function of the amidinotransferases and their genes has been highly conserved through evolution from prokaryotes to eukaryotes. The evolution has occurred with: (1) a high degree of retention of nucleotide and amino acid sequences; (2) a high degree of retention of the primitive Streptomyces guanine + cytosine (G + C) third codon position composition in certain high identity regions of the eukaryote cDNA; (3) a decrease in the specificities for the amidine group acceptors; and (4) most of the mutations silent in the regions suggested to code for active sites in the enzymes. 相似文献
3.
Grigoriev O.N. Panasyuk A.D. Brodnikovskyy M.P. Podchernyaeva I.O. Melakh L.M. Yurechko D.V. Vedel D.V. Kozak I.V. 《Powder Metallurgy and Metal Ceramics》2022,60(9-10):626-634
Powder Metallurgy and Metal Ceramics - Hot pressing was used to produce compact ceramic samples with the following composition (wt.%): 60 ZrB2 + 20 SiC + 20 (Al2O3 + 32 t-ZrO2). The tetragonal... 相似文献
4.
Despite the potential benefits of virtual teams, current literature suggests that virtual teamwork is rife with complex challenges. We frame some of these challenges as paradoxes inherent in the concept of virtual teamwork. Based on interviews with 42 leaders and members of virtual teams, we identify five paradoxes: (1) virtual teams require physical presence; (2) flexibility of virtual teamwork is aided by structure; (3) interdependent work in virtual teams is accomplished by members' independent contributions; (4) task-oriented virtual teamwork succeeds through social interactions; and (5) mistrust is instrumental to establishing trust among virtual team members. In addition, we identify strategies that respondents used to cope with, or 'survive' the paradoxes of virtual teamwork. 相似文献
5.
Maria João Cardoso Anca Ioana Nicolau Daniela Borda Line Nielsen Rui Leandro Maia Trond Møretrø Vânia Ferreira Susanne Knøchel Solveig Langsrud Paula Teixeira 《Comprehensive Reviews in Food Science and Food Safety》2021,20(3):2716-2741
Nontyphoidal salmonellae are among the most prevalent foodborne pathogens causing gastrointestinal infections worldwide. A high number of cases and outbreaks of salmonellosis are associated with the consumption of eggs and egg products, and several of these occur at the household level. The aim of the current study is to critically evaluate the current status of knowledge on Salmonella in eggs from a consumer's perspective, analyzing the hazard occurrence and the good practices that should be applied to reduce salmonellosis risk. Following a HACCP (Hazard Analysis and Critical Control Point) based approach, some steps along the food journey were identified as Critical Consumer Handling (CCH)—steps in which consumers, through their behavior or choice, can significantly reduce the level of Salmonella in eggs and egg products. From shopping/collecting to consumption, each of these steps is discussed in this review to provide an evidence-based overview of risk factors of human salmonellosis related to egg consumption. The main message to consumers is to choose Salmonella-free eggs (those that some official entity or producer guarantees that does not contain Salmonella), when available, especially for dishes that are not fully heat treated. Second, as guaranteed Salmonella-free eggs are only available in a few countries, refrigerated storage from the point of collection and proper cooking will significantly reduce the risk of salmonellosis. This will require a revision of the actual recommendations/regulations, as not all ensure that eggs are maintained at temperatures that prevent growth of Salmonella from collection until the time of purchasing. 相似文献
6.
7.
The new concept, anion substitution, is explored for possible improvement of hydrogen storage properties in the system LiBH4-LiI. The structural chemistry and the substitution mechanism are analyzed using Rietveld refinement of in situ synchrotron radiation powder X-ray diffraction (SR-PXD) data, attenuated total reflectance infrared spectroscopy (ATR-IR), differential scanning calorimetry (DSC) and Sieverts measurements. Anion substitution is observed as formation of two solid solutions of Li(BH4)1−xIx, which merge into one upon heating. The solid solutions have hexagonal structures (space group P63mc) similar to the structures of h-LiBH4 and β-LiI. The solid solutions have iodide contents in the range ∼0-62 mol% and are stable from below room temperature to the melting point at 330 °C. Thus the stability of the solid solutions is higher as compared to that of the orthorhombic and hexagonal polymorphs of LiBH4 and α- and β-LiI. Furthermore, the rehydrogenation properties of the iodide substituted solid solution Li(BH4)1−xIx, measured by the Sieverts method, are improved as compared to those of LiBH4. After four cycles of hydrogen release and uptake the Li(BH4)1−xIx solid solution maintains 68% of the calculated hydrogen storage capacity in contrast to LiBH4, which maintains only 25% of the storage capacity after two cycles under identical conditions. 相似文献
8.
Line Riis Christensen Ole Hassager Anne Ladegaard Skov 《American Institute of Chemical Engineers》2020,66(8):e16275
Multiple breakdown phenomena may take place when operating dielectric elastomers. Thermal breakdown, which occurs due to Joule heating, becomes of special importance when using multilayered stacks of dielectric elastomers, due to the large volume-to-surface-area-ratio. In this article, a 2D axisymmetric finite-element model of a multilayered stack of dielectric elastomers is set up in COMSOL Multiphysics®. Both the electro-thermal and electro-mechanical couplings are considered, allowing for determination of the onset of thermal breakdown. Simulation results show that an entrapped particle in the dielectric elastomer drastically reduces the possible number of layers in the stack. Furthermore, the possible number of layers is greatly affected by the ambient temperature and the applied voltage. The performance of three hyperelastic material models for modeling the elastomer deformation are compared, and it is established that the Gent model yields the most restrictive prediction of breakdown point, while the Ogden model yields the least restrictive estimation. 相似文献
9.
The purpose of these studies was to develop a conductimetric method for the rapid detection of Campylobacter jejuni. Numerous basal medium components were analyzed to develop a growth-enhancing broth medium for detection of freeze-injured Campylobacter cells using a conductimetric system. The final medium was composed of a modified Campy-Line agar from which the agar and triphenyltetrazolium chloride were removed and the amino acid, L-arginine was added. Pure isolates of C. jejuni. (frozen and thawed to produce stressed cells) were utilized to test the detection methodology. Monitoring of significant changes in the capacitance signal was found suitable for detection of Campylobacter proliferation. Using stressed pure cultures, Campylobacter growth was repeatedly detected at very low inoculum levels (about one cell per well). There was a direct linear relationship between detection times (DTs) and the initial inoculum level. For example, using a single strain, the mean DT (n = 20) at the 10 CFU/ml inoculum level was 28.6 h, with 100% of the inoculated wells detecting. The mean DTs at the 100, 1,000, and 10,000 CFU/ml inoculum levels were 24.9, 21.4, and 17.0 h, respectively. This study demonstrates that conductimetric methods can be utilized for the rapid detection of C. jejuni. 相似文献
10.