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排序方式: 共有168条查询结果,搜索用时 15 毫秒
1.
Altschuh Daniele; Tessier Daniel C.; Vernet Thierry 《Protein engineering, design & selection : PEDS》1994,7(6):769-776
The two main catalytic residues Cys25 and Hisl59 of the monomericcysteine protease papain are located on different walls of acleft formed by two domains. This topology suggests a possiblerelationship between relative domain organization and catalyticmechanism. The effect on enzymatic parameters of structuralmodifications at various locations of the twodomain interfaceof papain was examined by individual or double replacementsby Ala of pairs of interacting residues. Most modificationshad no effect on enzyme activity. However, the enzyme's substrateturnover (kcat) decreased following simultaneous alterationof the two most conserved residues, forming an apolar contactlocated 15 Å away from the active site. The pH activityprofile of the double mutant was unchanged, indicating a conservedionization state of the active site thiolate-imidazolium ionpair. This state is strongly dependent on the distance separatingthe two residues, thus suggesting that the active site geometryhas not been significantly altered. Efficient enzymatic activityin papain requires more than a correct active site geometryand is influenced by domain packing properties in a region remotefrom the active site. 相似文献
2.
Jose Hoyos Flavio Prieto Guillem Alenyà Carme Torras 《Journal of Intelligent and Robotic Systems》2016,82(1):81-99
Programming by demonstration techniques facilitate the programming of robots. Some of them allow the generalization of tasks through parameters, although they require new training when trajectories different from the ones used to estimate the model need to be added. One of the ways to re-train a robot is by incremental learning, which supplies additional information of the task and does not require teaching the whole task again. The present study proposes three techniques to add trajectories to a previously estimated task-parameterized Gaussian mixture model. The first technique estimates a new model by accumulating the new trajectory and the set of trajectories generated using the previous model. The second technique permits adding to the parameters of the existent model those obtained for the new trajectories. The third one updates the model parameters by running a modified version of the Expectation-Maximization algorithm, with the information of the new trajectories. The techniques were evaluated in a simulated task and a real one, and they showed better performance than that of the existent model. 相似文献
3.
J-C. Hénaux G. Vernet R. Adde 《Journal of Infrared, Millimeter and Terahertz Waves》1983,4(4):665-680
The system temperature of a receiver using a Josephson junction as a self oscillator mixer has been measured in the range 0.6 to 2 THz. The experimental value TS=53000K (DSB) at 900 GHz is in good agreement with the calculated value. A TS~12 000 K is predicted with a 30 K i.f. amplifier Possible applications are related to fast frequency tunable receivers (over one octave) with limited spectral resolution. 相似文献
4.
Here, we report a straightforward synthesis process to produce colloidal Eu3+-activated nanophosphors (NPs) for use as bioimaging probes. In this procedure, poly(ethylene glycol) serves as a high-boiling
point solvent allowing for nanoscale particle formation as well as a convenient medium for solvent exchange and subsequent
surface modification. The La(OH)3:Eu3+ NPs produced by this process were ~3.5 nm in diameter as determined by transmission electron microscopy. The NP surface was
coated with aminopropyltriethoxysilane to provide chemical functionality for attachment of biological ligands, improve chemical
stability and prevent surface quenching of luminescent centers. Photoluminescence spectroscopy of the NPs displayed emission
peaks at 597 and 615 nm (λex = 280 nm). The red emission, due to 5D0 → 7F1 and 5D0 → 7F2 transitions, was linear with concentration as observed by imaging with a conventional bioimaging system. To demonstrate the
feasibility of these NPs to serve as optical probes in biological applications, an in vitro experiment was performed with
HeLa cells. NP emission was observed in the cells by fluorescence microscopy. In addition, the NPs displayed no cytotoxicity
over the course of a 48-h MTT cell viability assay. These results suggest that La(OH)3:Eu3+ NPs possess the potential to serve as a luminescent bioimaging probe. 相似文献
5.
Guillem Godoy Hugo Hernández 《Applicable Algebra in Engineering, Communication and Computing》2009,20(2):187-205
Reachability, joinability and confluence properties are known to be undecidable for flat term rewrite systems (TRS). We give
shorter and conceptually simpler proofs of these results. We also prove undecidability of weak normalization and unique normalization
properties for flat TRS.
The first author was supported by Spanish Ministry of Education and Science by the FORMALISM project (TIN2007-66523) and by
the LOGICTOOLS-2 project (TIN2007-68093-C02-01). The second author was supported by Spanish Ministry of Education and Science
by the FORMALISM project (TIN2007-66523). 相似文献
6.
Fibre/matrix interphase has a dramatic influence on the composite performances. For the best understanding of interfacial phenomena, sizing has been characterized “in situ” by dynamic mechanical analysis, and sizing extract part, by different techniques. To know sizing impact on interphase nature and properties in the composite, four types of samples have been realized: three composites, which have been elaborated according to the technique of vacuum molding and differed by sizing state, and neat resin samples. The dynamic mechanical analysis (DMA) has allowed us to study both these composites and their interphases. Moreover, micro-thermal analysis has been a good technique for interphase investigation in our composites. 相似文献
7.
Frank A. Hoeberichts Jorge Perez‐Valle Consuelo Montesinos Jos M. Mulet María D. Planes Guillem Hueso Lynne Yenush Sukesh C. Sharma Ramn Serrano 《Yeast (Chichester, England)》2010,27(9):713-725
Glucose, in the absence of additional nutrients, induces programmed cell death in yeast. This phenomenon is independent of yeast metacaspase (Mca1/Yca1) and of calcineurin, requires ROS production and it is concomitant with loss of cellular K+ and vacuolar collapse. K+ is a key nutrient protecting the cells and this effect depends on the Trk1 uptake system and is associated with reduced ROS production. Mutants with decreased activity of plasma membrane H+‐ATPase are more tolerant to glucose‐induced cell death and exhibit less ROS production. A triple mutant ena1‐4 tok1 nha1, devoid of K+ efflux systems, is more tolerant to both glucose‐ and H2O2‐induced cell death. We hypothesize that ROS production, activated by glucose and H+‐ATPase and inhibited by K+ uptake, triggers leakage of K+, a process favoured by K+ efflux systems. Loss of cytosolic K+ probably causes osmotic lysis of vacuoles. The nature of the ROS‐producing system sensitive to K+ and H+ transport is unknown. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
8.
D Gulino E Delachanal E Concord Y Genoux B Morand MO Valiron E Sulpice R Scaife M Alemany T Vernet 《Canadian Metallurgical Quarterly》1998,273(45):29786-29793
Although cadherins appear to be necessary for proper cell-cell contacts, the physiological role of VE-cadherin (vascular endothelium cadherin) in adult tissue has not been clearly determined. To shed some light on this question, we have disturbed the adhesive function of VE-cadherin in human endothelial cell culture using a polyclonal anti-VE-cadherin antibody. This antibody disrupts confluent endothelial cell monolayers in vitro and transiently generates numerous gaps at cell-cell junctions. The formation of these gaps correlates with a reversible increase in the monolayer permeability. We present evidence that destruction of the homotypic interactions between the extracellular domains of VE-cadherin induces a rapid resynthesis of VE-cadherin, leading to restoration of endothelial cell-cell contacts. The expression of new molecules of VE-cadherin correlates with a modest but significant increase in VE-cadherin mRNA synthesis. Altogether, these results establish a critical role for VE-cadherin in the maintenance and restoration of endothelium integrity. 相似文献
9.
Arcidiacono C Diolaiti E Tordi M Ragazzoni R Farinato J Vernet E Marchetti E 《Applied optics》2004,43(22):4288-4302
The Layer-Oriented Simulation Tool (LOST) is a numerical simulation code developed for analysis of the performance of multiconjugate adaptive optics modules following a layer-oriented approach. The LOST code computes the atmospheric layers in terms of phase screens and then propagates the phase delays introduced in the natural guide stars' wave fronts by using geometrical optics approximations. These wave fronts are combined in an optical or numerical way, including the effects of wave-front sensors on measurements in terms of phase noise. The LOST code is described, and two applications to layer-oriented modules are briefly presented. We have focus on the Multiconjugate adaptive optics demonstrator to be mounted upon the Very Large Telescope and on the Near-IR-Visible Adaptive Interferometer for Astronomy (NIRVANA) interferometric system to be installed on the combined focus of the Large Binocular Telescope. 相似文献
10.
Performance Analysis of Multiuser Detectors for Uplink Quasi-synchronous MC-CDMA Systems 总被引:1,自引:1,他引:1
Felip Riera-Palou Guillem Femenias Jaume Ramis 《Wireless Personal Communications》2007,43(4):1511-1521
This paper analyses and compares the average bit error rate (BER) of different multiuser detectors (MUD) in the uplink of
a multicarrier code- division multiple access (MC-CDMA) system. In particular, maximum likelihood, zero-forcing, minimum mean-square
error and interference cancellation-based multiuser detectors have been analysed for the special case of uncorrelated subcarriers.
The derived BER expressions are based upon previous results on diversity combining and also on recent findings on multiple
input multiple output (MIMO) architectures. The subcarrier correlation is considered in the context of physical parameters
currently under discussion for future wireless systems to give an indication up to what extent the assumption of uncorrelated
subcarrier fading is plausible. 相似文献