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排序方式: 共有154条查询结果,搜索用时 265 毫秒
1.
I.L. Lehr 《Corrosion Science》2007,49(5):2210-2225
This work is a study of the electropolymerisation of pyrrole onto iron electrodes in the presence of sodium bis(2-ethylhexyl) sulfosuccinate in a wide pH interval. The characterisation of the films was done using electrochemical techniques, SEM/EDX and IR spectroscopy. We show that it is possible to synthesise homogeneous, adherent and very compact films in the pH range between 7 and 12 under potentiodynamic, galvanostatic and potentiostatic conditions without substrate dissolution. The effects of various parameters on electrodeposition were investigated. The new procedure for the electrochemical synthesis of polypyrrole results in improved anticorrosion properties. The inhibition is proposed to be due to the sum of a repulsion of chloride ions because AOT remains entrapped in the polymer matrix and the presence of the iron oxide. Advantages of the use of surfactants in the electropolymerisation solution are discussed. 相似文献
2.
A time-limited lease is a set of rights that expires after a specified duration. We analyze ways to use leases to facilitate innovation in radio devices and wireless communication. In our vision, manufacturers include in their devices a simple, secure subsystem that contains a clock and disables specific transmit capabilities if no extension message is received by the end of the lease period. When devices provide this support, regulators may use certification leases rather than permanent grants to accelerate deployment of innovative radios. Spectrum rights holders may use leases to reduce risk in secondary spectrum market transactions. Firms collaborating in innovative wireless service business models can better retain control of their respective rights. We examine both the technical and policy issues associated with leases. 相似文献
3.
COGNITIVE RADIOS FOR DYNAMIC SPECTRUM ACCESS - The Path to Market Success for Dynamic Spectrum Access Technology 总被引:2,自引:0,他引:2
Rapid progress is being made in the technology for dynamic spectrum access (DSA) radio systems. However, the structure and dynamics of the wireless services market must also evolve for DSA to succeed. This article examines the interlinked technical and economic issues associated with markets for DSA-based wireless services. We use this analysis to make technical and policy recommendations supporting the commercial success of DSA technology 相似文献
4.
In this paper some trends of gerontology during the last 45 years in Germany are described. A survey of the development of gerontology in the former GDR is followed by an analysis of the "Zeitschrift für Alternsforschung" from 1980-1990. The main result is the predominance of publications on the care system since the middle of the 1980s. With regard to the development of gerontology in the western part of Germany, an analysis of publications in the "Zeitsschrift für Gerontologie" from 1968-1991 shows changes in the main topics during this period. Until the middle of the 1970s there was a predominance of publications in the field of: intelligence, learning, memory and perception. The emphasis of publications from 1977-1985 was on stress and coping. In the middle of the 1980s there was an increasing interest in the analysis of social network and competence in the elderly. The paper discusses these trends of gerontological research in the eastern and western parts of Germany. 相似文献
5.
Fang Liang Jorge Lehr Lisa Danielczak Richard Leask Anne-Marie Kietzig 《International journal of molecular sciences》2014,15(8):13681-13696
Nature shows many examples of surfaces with extraordinary wettability, which can often be associated with particular air-trapping surface patterns. Here, robust non-wetting surfaces have been created by femtosecond laser ablation of polytetrafluoroethylene (PTFE). The laser-created surface structure resembles a forest of entangled fibers, which support structural superhydrophobicity even when the surface chemistry is changed by gold coating. SEM analysis showed that the degree of entanglement of hairs and the depth of the forest pattern correlates positively with accumulated laser fluence and can thus be influenced by altering various laser process parameters. The resulting fibrous surfaces exhibit a tremendous decrease in wettability compared to smooth PTFE surfaces; droplets impacting the virgin or gold coated PTFE forest do not wet the surface but bounce off. Exploratory bioadhesion experiments showed that the surfaces are truly air-trapping and do not support cell adhesion. Therewith, the created surfaces successfully mimic biological surfaces such as insect wings with robust anti-wetting behavior and potential for antiadhesive applications. In addition, the fabrication can be carried out in one process step, and our results clearly show the insensitivity of the resulting non-wetting behavior to variations in the process parameters, both of which make it a strong candidate for industrial applications. 相似文献
6.
The influence of magnetic fields on dielectric surface flashover 总被引:3,自引:0,他引:3
Korzekwa R. Lehr F.M. Krompholz H.G. Kristiansen M. 《Electron Devices, IEEE Transactions on》1991,38(4):745-749
The influence of low-amplitude magnetic fields, in a variety of configurations, on pulsed dielectric surface flashover has been investigated. These variations include DC magnetic fields; pulsed magnetic fields simulating conditions for magnetic self-insulation; and different environments (vacuum, ambient, gas, plasma), geometries, dielectric materials, and orientations of the magnetic field. For field amplitudes of 0.3 T, typically a doubling of the flashover voltage is observed, if the E ×B drift is away from the surface. For flashover in vacuum, it is sufficient to place permanent magnets in the cathode vicinity to increase the flashover voltage. The observations are consistent with the saturated surface secondary avalanche model and electron-induced gas desorption. The pulse shape of light emission during the prebreakdown phase depends on the orientation and amplitude of the magnetic field and shows that the electron trajectories above the surface are altered by magnetic fields 相似文献
7.
Cationic poly(lactide-co-glycolide) nanoparticles as efficient in vivo gene transfection agents 总被引:3,自引:0,他引:3
Kumar MN Mohapatra SS Kong X Jena PK Bakowsky U Lehr CM 《Journal of nanoscience and nanotechnology》2004,4(8):990-994
Poly(lactide-co-glycolide) (PLGA), a biocompatible and biodegradable polyester co-polymer of PLA and PGA, has been recognized for its ability to deliver genes. However, gene delivery by PLGA nanoparticles is limited by their negative charge and their poor transport through mucosal barriers. In this study, PLGA nanoparticles were surface modified with cationic chitosan in an effort to improve their gene delivery capability. PLGA nanoparticles were synthesized by emulsion-diffusion-evaporation technique using PVA-chitosan (PLGA1) or PVA-chitosan-PEG (PLGA2) blend as stabilizers. This method is reproducible and produces nanoparticles with hydrodynamic diameter <200 nm. The nanoparticles were characterized by zetasizer, photon correlation spectroscopy and atomic force microscopy. A549 epithelial cells were transfected in vitro with PLGA particles complexed with a reporter plasmid encoding green fluorescent protein. PLGA particles transferred EGFP gene, but were less efficient than the lipofectamine control. The nanoparticles were also tested for their ability to transport across the nasal mucosa in vivo in mice. The results show that both PLGA1 and PLGA2 facilitate gene delivery and expression in vivo with increased efficiency and without causing inflammation, as measured by IL-6. Together, these results indicate that chitosan-modified PLGA nanoparticles have greater potential as gene carriers. 相似文献
8.
Real-time detection of nucleic acid interactions by total internal reflection fluorescence 总被引:2,自引:0,他引:2
This paper describes the development of an optical readout system for the real-time analysis of fluorescent-labeled DNA microarrays is described. The system is targeted toward research applications in genomics, agriculture, and life sciences, where the end-point detection of state-of-the-art readout systems does not provide sufficient information on the hybridization process. The hybridization progress of molecules from the liquid phase in a flow cell to immobilized oligonucleotides on a transducer surface can be observed. The excitation of fluorochromes is realized by a semiconductor laser, and the fluorescence emission is collected by a cooled CCD camera. Quantitative data can be extracted from the images for analysis of the microarray. For the signal transduction, the principle of total internal reflection is used. With a multiple internal reflection arrangement, the sensor chip was adapted to the standard microscope slide format and a homogeneous evanescent illumination of the active area of the sensor surface was achieved. An application measurement was carried out with this readout system. The hybridization of Cy5-labeled 30-mer single-stranded oligonucleotides to fully complementary immobilized strands was observed in real time. A kinetic analysis was demonstrated with the recorded data. Melting curves of a 140-mer PCR product from a hemochromatosis patient sample hybridized to immobilized wild-type mutant 15- and 17-mer oligonucleotides were recorded and single-point mutations could be detected. 相似文献
9.
Visualizing performance debugging 总被引:1,自引:0,他引:1
The authors examine a special software development environment called the Parallel Programming and Instrumentation Environment (PIE). PIE is designed to develop performance-efficient parallel and sequential computations. Following an explanation of PIE's general theory and features, PIE's visualization tools are used to isolate and repair the parallelism problem of an eight-process computation. Two more difficult examples using PIE are discussed. Some of the issues involved in correctly presenting visual information, such as the features users ask for and what can be done about a performance monitor's perturbation of computations, are addressed 相似文献
10.
Widrow B. Lehr M.A. 《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1990,78(9):1415-1442
Fundamental developments in feedforward artificial neural networks from the past thirty years are reviewed. The history, origination, operating characteristics, and basic theory of several supervised neural-network training algorithms (including the perceptron rule, the least-mean-square algorithm, three Madaline rules, and the backpropagation technique) are described. The concept underlying these iterative adaptation algorithms is the minimal disturbance principle, which suggests that during training it is advisable to inject new information into a network in a manner that disturbs stored information to the smallest extent possible. The two principal kinds of online rules that have developed for altering the weights of a network are examined for both single-threshold elements and multielement networks. They are error-correction rules, which alter the weights of a network to correct error in the output response to the present input pattern, and gradient rules, which alter the weights of a network during each pattern presentation by gradient descent with the objective of reducing mean-square error (averaged over all training patterns) 相似文献