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排序方式: 共有359条查询结果,搜索用时 15 毫秒
81.
Nikhil Murthy Stephen Berkebile Amarendra K. Rai Eric Hille Jeffrey Ewin 《摩擦学汇刊》2013,56(6):1117-1130
AbstractWe show how various concentrations ranging from 0 to 5.0?wt% of the ionic liquid (IL) trihexyltetradecylphosphonium bis(2-ethylhexyl)phosphate added to a fully formulated aviation DOD-PRF-85734 gearbox lubricant affects the properties of the lubricant, including scuffing resistance under starved lubrication conditions, coefficient of friction (COF), wear rate, and lubricant chemical stability. Specimen surfaces were then characterized using scanning electron microscopy, energy-dispersive spectroscopy, and auger electron spectroscopy. Scuffing and wear properties were found to generally improve with IL concentration, which we hypothesize is due to the presence of a phosphorous-rich film observed on specimens exposed to IL. 相似文献
82.
Dynamic Extracellular Imaging of Biochemical Cell Activity Using InGaN/GaN Nanowire Arrays as Nanophotonic Probes 下载免费PDF全文
Sara Hölzel Mikhail V. Zyuzin Jens Wallys Ervice Pouokam Jan Müßener Pascal Hille Martin Diener Wolfgang J. Parak Martin Eickhoff 《Advanced functional materials》2018,28(39)
The application of InGaN/GaN nanowire heterostructure arrays as photonic probes for dynamic imaging of biochemical and cellular processes in an incident light fluorescence microscope is demonstrated. The photoluminescence intensity of InGaN/GaN nanowires sensitively depends on the pH value of the surrounding solution, making them suitable probes for the optical detection of biochemical processes accompanied by local pH variations. Grown on a conductive substrate, the nanowire arrays can be operated in a well‐defined electrochemical working point with high sensitivity and stability. The achievable pH and bias resolution as well as signal‐to‐noise ratio are assessed as a function of the working point and for different integration times. A bias resolution of 1 mV and a pH resolution of 0.03 are achieved at a time resolution below 25 ms. The application for dynamic imaging of the activity of isolated intestinal crypts from Wistar rats is demonstrated. Here, the pH change in the vicinity of the crypt is quantified and attributed to the activity of the sodium‐proton exchanger (NHE). Imaging of the effect of amiloride and NH4Cl on its activity is demonstrated with a spatial resolution of <0.63 µm and reveals that NH4Cl‐induced NHE activation preferentially occurs in the upper part of the crypt. 相似文献
83.
The Mononuclear Molybdenum Enzymes 总被引:2,自引:0,他引:2
Hille R 《Chemical reviews》1996,96(7):2757-2816
84.
J Sun MA Kahlow TM Kaysser JP Osborne JJ Hill RJ Rohlfs R Hille RB Gennis TM Loehr 《Canadian Metallurgical Quarterly》1996,35(7):2403-2412
Cytochrome bd oxidase is a bacterial terminal oxidase that contains three cofactors: a low-spin heme (b558), a high-spin heme (b595), and a chlorin d. The center of dioxygen reduction has been proposed to be a binuclear b595/d site, whereas b558 is mainly involved in transferring electrons from ubiquinol to the oxidase. Information on the nature of the axial ligands of the three heme centers has come from site-directed mutagenesis and spectroscopy, which have implicated a His/Met coordination for b558 (Spinner, F., Cheesman, M. R., Thomson, A. J., Kaysser, T., Gennis, R. B., Peng, Q., & Peterson, J. (1995) Biochem. J. 308, 641-644; Kaysser, T. M., Ghaim, J. B., Georgiou, C., & Gennis, R. B. (1995) Biochemistry 34, 13491-13501), but the ligands to b595 and d are not known with certainty. In this work, the three heme chromophores of the fully reduced cytochrome bd oxidase are studied individually by selective enhancement of their resonance Raman (rR) spectra at particular excitation wavelengths. The rR spectrum obtained with 413.1-nm excitation is dominated by the bands of the 5cHS b595(2+) cofactor. Excitation close to 560 nm yields a rR spectrum dominated by the 6cLS b558(2+) heme. Wavelengths between these values enhance contributions from both b595(2+) and b558(2+) chromophores. The rR bands of the ferrous chlorin become the major features with red laser excitation (595-650 nm). The rR data indicate that d2+ is a 5cHS system whose axial ligand is either a weakly coordinating protein donor or a water molecule. In the low-frequency region of the 441.6-nm spectrum, we assign a rR band at 225 cm-1 to the (b595)Fe(II)-N(His) stretching vibration, based on its 1.2-cm(-1) upshift in the 54Fe-labeled enzyme. This observation provides the first physical evidence that the proximal ligand of b595 is a histidine. Site-directed mutagenesis had suggested that His 19 is associated with either b595 or d (Fang, H., Lin, R. -J., & Gennis, R. B. (1989) J. Biol. Chem. 264, 8026-8032). On the basis of the present study, we propose that the proximal ligand of b595 is His 19. We have also studied the reaction of cyanide with the fully reduced cytochrome bd oxidase. In approximately 700-fold excess cyanide (approximately 35 mM), the 629-nm UV/vis band of d2+ is blue-shifted to 625 nm and diminished in intensity. However, the rR spectra at each of three different gamma(0) (413.1, 514.5, and 647.1 nm) are identical with or without cyanide, thus indicating that both b595 and d remain as 5cHS species in the presence of CN-. This observation leads to the proposal that a native ligand of ferrous chlorin d is replaced by CN- to form the 5cHS d2+ cyano adduct. These findings corroborate our companion study of the "as-isolated" enzyme in which we proposed a 5cHS d3+ cyano adduct (Sun, J., Osborne, J. P., Kahlow, M. A., Kaysser, T. M., Hill, J. J., Gennis, R. B., & Loehr, T. M. (1995) Biochemistry 34, 12144-12151). To further characterize the unusual and unexpected nature of these proposed high-spin cyanide adducts, we have obtained EPR spectral evidence that binding of cyanide to fully oxidized cytochrome bd oxidase perturbs a spin-state equilibrium in the chlorin d3+ to yield entirely the high-spin form of the cofactor. 相似文献
85.
Minds and Machines - Modern computing is generally taken to consist primarily of symbol manipulation. But symbols are abstract, and computers are physical. How can a physical device manipulate... 相似文献
86.
Laura M. F. Bertens Jetty Kleijn Sander C. Hille Monika Heiner Maciej Koutny Fons J. Verbeek 《Natural computing》2016,15(4):665-675
Both Petri nets and differential equations are important modeling tools for biological processes. In this paper we demonstrate how these two modeling techniques can be combined to describe biological gradient formation. Parameters derived from partial differential equation describing the process of gradient formation are incorporated in an abstract Petri net model. The quantitative aspects of the resulting model are validated through a case study of gradient formation in the fruit fly. 相似文献
87.
Ratcliff R Hasegawa YT Hasegawa RP Childers R Smith PL Segraves MA 《Neural computation》2011,23(7):1790-1820
Simultaneous recordings were collected from between two and four buildup neurons from the left and right superior colliculi in rhesus monkeys in a simple two-choice brightness discrimination task. The monkeys were required to move their eyes to one of two response targets to indicate their decision. Neurons were identified whose receptive fields were centered on the response targets. The functional role of inhibition was examined by conditionalizing firing rate on a high versus low rate in target neurons 90 ms to 30 ms before the saccade and examining the firing rate in both contralateral and ipsilateral neurons. Two models with racing diffusion processes were fit to the behavioral data, and the same analysis was performed on simulated paths in the diffusion processes that have been found to represent firing rate. The results produce converging evidence for the lack of a functional role for inhibition between neural populations corresponding to the two decisions. 相似文献
88.
89.
D. Dietrich ÖVE G. Russ C. Tamarit G. Koller W. Ponweiser M. Vincze 《e & i Elektrotechnik und Informationstechnik》2001,118(11):545-555
The OSI model and the system of profiles defined for various branches are the most important models for describing the communication of technical units in the area of home automation. But they are not enough for describing complex expiry scenarios in houses and buildings as a whole. The following paper presents such a model, which is presently being realized in the Smart Kitchen project. In doing so we will be able to cover, amongst other things, aspects like reliability, availability, maintainability, interoperability and profitability. Several institutes are involved in this project. 相似文献
90.