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排序方式: 共有732条查询结果,搜索用时 31 毫秒
121.
Edilson M. Pinto A. Sofia Ramos M. Teresa Vieira Christopher M.A. Brett 《Corrosion Science》2010,52(12):3891-3895
Thin nanocrystalline, compact films, based on the copper–nitrogen system, up to 2.5 μm thickness and 3.5% nitrogen, were deposited by magnetron sputtering at different partial pressure ratios of N2 and Ar, without formation of CuxN compounds, the nitrogen concentration influencing grain size (down to 30 nm) and film homogeneity. Electrochemical corrosion properties were investigated using polarization curves and electrochemical impedance spectroscopy in 0.5 M NaCl aqueous solution, and compared with pure bulk copper; morphology was examined by scanning electron microscopy. Significant variations in corrosion currents between samples were attributed to grain size and structural defects on the grain boundaries. 相似文献
122.
The processing technique is decisive for the characteristics of a coating. This is because the heat supply, which depends on the technique and on the parameters, has an influence on the dilution and the solidification rate. In alloys with low metallurgical complexity, the effect of processing with deposition techniques that give a higher cooling rate may be translated into refining of the microstructure. A more refined microstructure is expected to result in higher mechanical strength of the coating. However, in the deposition of alloys that are more complex metallurgically this does not always occur, because the high cooling rate may suppress formation/precipitation of phases responsible for strength. The influence of processing on the microstructure and hardness of coatings of alloy Colmonoy-6® was assessed in this study. The alloy was processed by plasma transferred arc and high-power diode laser on plates of AISI 304 with two levels of dilution. In both cases, good-quality, defect-free coatings were obtained. Increase in Fe content (dilution) and different cooling rates result from processing with different parameters and techniques. This leads to significant changes in microstructure and hardness of the coatings, associated with the distribution, morphology and chemical composition of the carbides and particularly of the borides. 相似文献
123.
Sónia Simões Filomena Viana A. Sofia Ramos M. Teresa Vieira Manuel F. Vieira 《Journal of Materials Science》2013,48(21):7718-7727
This study investigated the interfacial structure of solid state diffusion bonding of TiNi to Ti6Al4V using reactive Ni/Ti multilayer thin films. The TiNi and Ti6Al4V surfaces were modified by sputtering, by deposition of alternated Ni and Ti nanolayers, to increase the diffusivity at the interface. Bonding experiments were performed at 750, 800 and 900 °C at a pressure of 10 MPa with a dwell time of 60 min. The reaction zone was characterized by high-resolution scanning and transmission electron microscopy. Joints free from porosity and cracks were produced with Ni/Ti reactive multilayer thin films. Several phases formed at the interface, ensuring the bonding of these alloys. The reaction zone was constituted by columnar grains of Ti2Ni and AlNi2Ti, close to the Ti6Al4V base material, and by alternate layers of Ti2Ni and TiNi equiaxed grains. The grain size decreased from Ti6Al4V to TiNi base materials. Nanometric grains were observed in the layers closest to the TiNi base material. 相似文献
124.
Pettersson S Pérez-Nueno VI Ros-Blanco L Puig de La Bellacasa R Rabal MO Batllori X Clotet B Clotet-Codina I Armand-Ugón M Esté J Borrell JI Teixidó J 《ChemMedChem》2008,3(10):1549-1557
HIV cell fusion and entry have been validated as targets for therapeutic intervention against infection. Bicyclams were the first low-molecular-weight compounds to show specific interaction with CXCR4. The most potent bicyclam was AMD3100, in which the two cyclam moieties are tethered by a 1,4-phenylenebis(methylene) bridge. It was withdrawn from clinical trials owing to its lack of oral bioavailability and cardiotoxicity. We have designed a combinatorial library of non-cyclam polynitrogenated compounds by preserving the main features of AMD3100. At least two nitrogen atoms on each side of the p-phenylene moiety, one in the benzylic position and the other(s) in the heterocyclic system were maintained, and the distances between them were similar to the nitrogen atom distances in cyclam. A selection of diverse compounds from this library were prepared, and their in vitro activity was tested in cell cultures against HIV strains. This led to the identification of novel potent CXCR4 coreceptor inhibitors without cytotoxicity at the tested concentrations. 相似文献
125.
Simon A. Cotton Victoria M.A. Fisher Paul R. Raithby Stefanie Schiffers Simon J. Teat 《Inorganic chemistry communications》2008,11(7):822-824
Reaction of hydrated scandium nitrate with 1,10-phenanthroline (phen) in methanol leads to formation of the unusual dimeric complex [(phen)(NO3)2Sc(μ-OMe)2Sc(NO3)2(phen)], in which the scandium centres are eight co-ordinate. The complex features two bridging methoxy ligands, as well as bidentate nitrates and chelating 1,10-phenanthroline ligands. 相似文献
126.
Gallo S Oberhuber M Sigel RK Kräutler B 《Chembiochem : a European journal of chemical biology》2008,9(9):1408-1414
Riboswitches are regulatory elements in the 5'-untranslated region (5'-UTR) of bacterial mRNAs that bind certain metabolites with high specificity and affinity. The 202 nucleotide (nt)-long btuB riboswitch RNA of E. coli interacts specifically with coenzyme B12 and its derivatives thereby leading to changes in the RNA structure and hence to an altered expression of the downstream btuB gene. We report the investigations of the rearrangement of the three-dimensional structure of the btuB riboswitch upon binding to four different B12 derivatives: coenzyme B12, vitamin B12, adenosyl factor A and adenosyl-cobinamide. In-line probing experiments have shown that the corrin ring plays the crucial role in switching the three-dimensional riboswitch structure. Instead, the apical ligands influence only the binding affinity of the B12 derivative to the btuB riboswitch. 相似文献
127.
The formation of an integral asymmetric membrane composed of a cylinder‐forming polystyrene‐block‐poly(2‐vinylpyridine) on a nonwoven by using solvent casting followed by solvent/nonsolvent exchange (phase inversion) is reported for the first time. The influence of parameters such as solvent composition, evaporation time of the solution‐cast block copolymer film before phase inversion, and immersion bath temperature is demonstrated. The optimized membranes are characterized in terms of stimuli‐responsive water flux properties. The morphologies of the membranes as well as of the bulk of the block copolymer are imaged by scanning force microscopy, scanning electron microscopy, and transmission electron microscopy.
128.
Dr. Sofia Gama Dr. Filipa Mendes Dr. Teresa Esteves Dr. Fernanda Marques Dr. António Matos Dr. José Rino Dr. Joana Coimbra Dr. Mauro Ravera Dr. Elisabetta Gabano Dr. Isabel Santos Dr. António Paulo 《Chembiochem : a European journal of chemical biology》2012,13(16):2352-2362
New [PtCl(pz*NN)]n+ complexes anchored by pyrazolyl‐diamine (pz*NN) ligands incorporating anthracenyl or acridine orange DNA‐binding groups have been synthesized so as to obtain compounds that would display synergistic effects between platination and intercalation of DNA. Study of their interaction with supercoiled DNA indicated that the anthracenyl‐containing complex L2Pt displays a covalent type of binding, whereas the acridine orange counterpart L3Pt shows a combination of intercalative and covalent binding modes with a strong contribution from the former. L2Pt showed a very strong cytotoxic effect on ovarian carcinoma cell lines A2780 and A2780cisR, which are, respectively, sensitive to and resistant to cisplatin. In these cell lines, L2Pt is nine to 27 times more cytotoxic than cisplatin. In the sensitive cell line, L3Pt showed a cytotoxic activity similar to that of cisplatin, but like L2Pt was able significantly to overcome cisplatin cross‐resistance. Cell‐uptake studies showed that L2Pt accumulates preferentially in the cytoplasm, whereas L3Pt reaches the cell nucleus more easily, as clearly visualized by time‐lapse confocal imaging of live A2870 cells. Altogether, these findings seem to indicate that interaction with biological targets other than DNA might be involved in the mechanism of action of L2Pt because this compound, despite having a weaker ability to target the cell nucleus than L3Pt , as well as an inferior DNA affinity, is nevertheless more cytotoxic. Furthermore, ultrastructural studies of A2870 cells exposed to L2Pt and L3Pt revealed that these complexes induce different alterations in cell morphology, thus indicating the involvement of different modes of action in cell death. 相似文献
129.
How should architects hammer out their own personal design approach in relation to a wider cultural identity? Chilean architects Mauricio Pezo and Sofia von Ellrichshausen of Pezo von Ellrichshausen outline how their first years of practice have been dedicated to developing their own specific working methods. Drawing on the physical experience of space, their own evocative thoughts and sensations, they transform the simple natural structures of their local surrounding into idealised forms. 相似文献
130.
Rigas G Tzallas AT Tsipouras MG Bougia P Tripoliti EE Baga D Fotiadis DI Tsouli SG Konitsiotis S 《IEEE transactions on information technology in biomedicine》2012,16(3):478-487
Tremor is the most common motor disorder of Parkinson's disease (PD) and consequently its detection plays a crucial role in the management and treatment of PD patients. The current diagnosis procedure is based on subject-dependent clinical assessment, which has a difficulty in capturing subtle tremor features. In this paper, an automated method for both resting and action/postural tremor assessment is proposed using a set of accelerometers mounted on different patient's body segments. The estimation of tremor type (resting/action postural) and severity is based on features extracted from the acquired signals and hidden Markov models. The method is evaluated using data collected from 23 subjects (18 PD patients and 5 control subjects). The obtained results verified that the proposed method successfully: 1) quantifies tremor severity with 87 % accuracy, 2) discriminates resting from postural tremor, and 3) discriminates tremor from other Parkinsonian motor symptoms during daily activities. 相似文献