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61.
Griselda A. Eimer Liliana B. Pierella Gustavo A. Monti Oscar A. Anunziata 《Catalysis Letters》2002,78(1-4):65-75
A novel route in the synthesis of Al-MCM-41 and Al-MCM-48, using tetraethoxysilane (TEOS) and sodium aluminate (NaAlO2) as Si and Al source has been obtained. The effect of surfactant nature and the synthesis conditions such as surfactant/Si ratio and hydrothermal treatment time on the formed mesostructure regularity has been studied. Different methods of template removal have also been evaluated. The samples were characterized by X-ray diffraction, nitrogen physisorption, FT-IR, and solid-state MAS NMR spectroscopy. 相似文献
62.
63.
Mercier Gustavo A. Jr; Osman Roman; Weinstein Harel 《Protein engineering, design & selection : PEDS》1988,2(4):261-270
A proton transfer triggered by a ligand interacting with thereceptor had been suggested as the initial step in the activationof a receptor for the neurotransmitter serotonin (5-hydroxy-tryptamine;5-HT). To evaluate the role of the receptor macromolecule inmodulating the primary molecular event in ligand-mediated activation,the process of proton transfer was analysed in the environmentof a protein model for the 5-HT receptor. In the absence ofa detailed receptor structure, the enzyme actinidin was chosenas the model for the receptor based on criteria obtained fromstructure-activity considerations on the ligands. The firstsimulation of a mechanism for receptor activation was performedon this model using methods of theoretical chemistry to studythe effect of specific structural elements. The premise is thatthe role of the elements of secondary structure of soluble proteins(e.g. actinidin) in determining structure-function relationsin these macromolecules is maintained when these elements arepart of membrane-bound receptor proteins. Results from the calculationsof the effects of the six alpha helices of actinidin on theproton transfer process from the imidazolium side chain of His162 to the thiol side chain of Cys 25 in the protein show thatthe helices contribute in different ways to modulate the energyof proton transfer. The largest helix, Al, opposes the protontransfer through the effect of the helix dipole. The chargedresidues (primary structure) in helix A3 favor the proton transfer,and mask the effect of its helix dipole (secondary structure)which opposes the transfer. The direction of the proton transfersimulated for the activation mechanism is opposite to that assumedin the catalytic process of the thiol protease, and the entireprotein environment opposes the transfer. This supports thespecific role of the ligand in triggering the proton transferas a response to its binding. 相似文献
64.
This paper introduces a novel solution for the multi‐input multi‐output (MIMO) quantitative feedback theory control design problem with tracking error specifications. Looking for a minimum controller overdesign, the technique finds new controller quantitative feedback theory bounds based on necessary and sufficient conditions for the existence of suitable associated prefilter matrix elements. It improves previous approaches to the subject and includes (i) the possibility of a free selection of the nominal plant, (ii) a less conservative application of the Schwartz inequality to decisively reduce the potential controller overdesign, (iii) a methodology to design independently the elements of the prefilter matrix, and (iv) a scope of application to both sequential and nonsequential MIMO controller design methods. The benefits of the new control design technique are illustrated by means of two examples. The first one, a standard 2 × 2 MIMO problem, is provided for comparison purposes with previous approaches. The second example, included as a major control challenge, deals with a well‐known demanding distillation column benchmark problem. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
65.
Mejía-Centeno Isidro Martínez-Hernández Angel Fuentes Gustavo A. 《Topics in Catalysis》2007,42(1-4):381-385
The use of low-sulfur fuel is known to improve the performance of the three-way catalytic converter (TWC). However, in this
work we report how low-sulfur operation of commercial TWC also favors formation of N2O and NH3 as by products. We found that low-sulfur rich operation above 300 °C increases the production of NH3, inhibiting the formation of N2O characteristic of high-sulfur operation. During lean operation, the production of N2O near the stoichiometric point is not significantly affected by the sulfur level. The large production of N2O observed during light-off is not affected by SO2 when the operation is lean, but under rich conditions N2O is produced up to 575 °C. The increased production of NH3 and N2O in TWC as a result of the introduction of low-sulfur gasoline is an area that requires further analysis because of its implication
upon public health in large urban settings. 相似文献
66.
C. Busigin G. M. Martinez R. T. Woodhams R. Lahtinen 《Polymer Engineering and Science》1983,23(14):766-770
Water-ground Phlogopite mica (Kemira Siilinjarvi phlogopite) has been evaluated as a reinforcing filler in polypropylene. The major factors which influence the composite strength and modulus include the size, aspect ratio, and uniformity of the mica flakes. Aqueous delamination permits the production of very small flakes (less than 44 microns diameter) with aspect ratios near 50. Such small flakes impart greater tensile and modulus values to polypropylene than larger flakes and the former can also be reprocessed many times without any deterioration of properties. Surface treatment is necessary for adequate dispersion and coupling, particularly with the finely divided mica fillers. Other properties such as the heat-distortion temperature, fracture toughness, and gas permeability are also influenced by the mean size and aspect ratio of the mica filler. Guidelines are presented to indicate the preferred characteristics of mica fillers for optimum performance. 相似文献
67.
Belletier Clément Charkhabi Morteza Pires de Andrade Silva Gustavo Ametepe Kevin Lutz Mathieu Izaute Marie 《Cognition, Technology & Work》2021,23(1):103-116
Cognition, Technology & Work - Rapid technological innovations are constantly influencing the complexification and automatization of the work lines pushing human operators to use diverse... 相似文献
68.
B. Campillo C. Rodriguez J. Genesca J. Juarez-lslas . Flores L Martinez 《Journal of Materials Engineering and Performance》1997,6(4):449-453
Commercial magnesium anodes were evaluated using ASTM G 97-89 for a standard test along with a technique of electrochemical
impedance. Several heat treatments were performed, and the anodic efficiency was determined, showing an incremental increase
of 10 to 12 % of the efficiency demonstrated by the nontreated commercial anodes (as-cast condition). The increase in efficiency
was related to the microstructural characteristics. The appearance of second phase particles influenced the form of the corrosion
process. 相似文献
69.
AC and DC electrochemical experiments were performed as a function of humidity and contaminant concentration in an effort to identify the range of atmospheric environments where corrosion processes could be detected and possibly quantified. AC measurements exhibited two time constants at 25% relative humidity (RH), possibly indicating the ability to resolve both electrolyte resistance and interfacial impedance. Galvanic current measurements were sensitive to the presence of Cl2(g) at 30% RH and electrochemical transients were detected at both 30% and 50% RH levels, also indicating sensitivity to interfacial processes. Higher humidity levels allowed better quantification due to decreasing electrolyte and interfacial impedances. 相似文献
70.
Francisco J. Gutierrez Sergio F. Ochoa Gustavo Zurita Nelson Baloian 《Information Systems Frontiers》2016,18(1):7-21
Participation is the cornerstone of any community. Promoting, understanding and properly managing it allows not only keeping the community sustainable, but also providing personalized services to its members and managers. This article presents a case study in which student participation in a course community was motivated using two different extrinsic mechanisms, and mediated by a software platform. The results were compared with a baseline community of the same course, in which participation was not motivated by external means. The analysis of these results indicates that managing a partially virtual course community requires the introduction of monitoring services, community managers and extrinsic mechanisms to motivate participation. These findings allow community managers to improve their capability for promoting participation and keeping the community sustainable. The findings also raise several implications that should be considered in the design of software supporting this kind of community, when managing the participation of its members. 相似文献