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51.
Eduardo J. Lamas 《Electrochimica acta》2006,51(26):5904-5911
Classical molecular dynamics simulations are performed to obtain insights into structural and dynamical behavior of water and O2 transport through a model polymer membrane, and at the interface of such hydrated polymer with graphite-supported nanocatalyst platinum particles. Water clustering is observed near the membrane hydrophilic sites constituted by sulfonic groups, which due to their affinity with platinum, are located near the metallic surface. It is found that the diffusion of water through the model hydrated polymer membrane depends strongly on the level of membrane hydration due to contribution from various mechanisms whose relative weights change with the degree of hydration. Possible scenarios for O2 diffusion are also analyzed. 相似文献
52.
Yukiko Hirano Ilde Guedes Marcus Grimsditch Chun-Keung Loong Nobuyoshi Wakabayashi Lynn A. Boatner 《Journal of the American Ceramic Society》2002,85(4):1001-1003
The room-temperature elastic constants of ErVO4 were considerably smaller than those of isostructural silicate and phosphate analogs. The generally "less-rigid" crystalline lattice and weaker metal-oxygen bond-strength in the RVO4 (R = rare earth elements) phases indicates that these materials are of interest for potential applications as an interphase component in toughened oxide ceramic composites. 相似文献
53.
Molecular dynamics (MD) simulations of-Al2O3, using a pairwise additive interaction potential of Pauling's type with four different radii for aluminum atoms, were analysed in order to determine the influence of the radius on the modification of coordination numbers of A1 relative to the ideal structure, at two different temperatures of 300 and 1500 K. It is found that the best choice is the radius of penta-coordinated aluminum, reproducing structural and vibrational properties of the compound in excellent agreement with experimentally observed properties. 相似文献
54.
Jose Saldana Julián Fernández-Navajas José Ruiz-Mas Eduardo Viruete-Navarro Luis Casadesus 《Multimedia Tools and Applications》2014,71(3):1823-1856
First Person Shooters are a genre of online games in which users demand a high interactivity, because the actions and the movements are very fast. They usually generate high rates of small packets which have to be delivered to the server within a deadline. When the traffic of a number of players shares the same link, these flows can be aggregated in order to save bandwidth. Certain multiplexing techniques are able to merge a number of packets, in a similar way to voice trunking, creating a bundle which is transmitted using a tunnel. In addition, the headers of the original packets can be compressed by means of standard algorithms. The characteristics of the buffers of the routers which deliver these bundled packets may have a strong influence on the network impairments (mainly delay, jitter and packet loss) which determine the quality of the game. A subjective quality estimator has been used in order to study the mutual influence of the buffer and multiplexing techniques. Taking into account that there exist buffers which size is measured in terms of bytes, and others measured in packets, both kinds of buffers have been tested, using different sizes. Traces from real game parties have been merged in order to obtain the traffic of 20 simultaneous players sharing the same Internet access. The delay and jitter produced by the buffer of the access router have been obtained using simulations. In general, the quality is expected to be reduced as the background traffic grows, but the results show an anomalous region in which the quality rises with the background traffic amount. Small buffers present better subjective quality results than bigger ones. When the total traffic amount gets above the available bandwidth, the buffers measured in bytes add to the packets a fixed delay, which grows with buffer size. They present a jitter peak when the offered traffic is roughly the link capacity. On the other hand, buffers which size is measured in packets add a smaller delay, but they increase packet loss for gaming traffic. The obtained results illustrate the need of knowing the characteristics of the buffer in order to make the correct decision about traffic multiplexing. As a conclusion, it would be interesting for game developers to identify the behaviour of the router buffer so as to adapt the traffic to it. 相似文献
55.
Maria T. M. Bizarria André L. F. de M. Giraldi Cesar M. de Carvalho Jose I. Velasco Marcos A. d'Ávila Lucia H. I. Mei 《应用聚合物科学杂志》2007,104(3):1839-1844
Recycled PET/organoclay nanocomposites were prepared by melt intercalation process with several amounts (1, 3, and 5 wt %) of clay modified with quaternary ammonium salt (DELLITE 67G) dispersed in a recycled poly(ethylene terephthalate) (rPET) matrix. The resultant mechanical properties (modulus and yield strength) of the nanocomposites were found to be different from those of rPET. Wide angle X‐ray scattering (WAXS) and Transmission Electron Microscopy (TEM) measurements have shown that although complete exfoliation was not achieved, delaminated clay platelets could be observed. Thermal analysis did not show significant changes in the thermal properties from those of recycled PET. Mechanical testing showed that nanocomposite properties were superior to the recycled PET in terms of strength and elasticity modulus. This improvement was attributed to nanoscale effects and strong interaction between the rPET matrix and the clay interface, as revealed by WAXS and TEM. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1839–1844, 2007 相似文献
56.
Delba N.C. Melo Eduardo C. Vasco De Toledo Marcela M. Santos Salah D.M. Hasan Maria Regina Wolf Maciel Rubens Maciel Filho 《Computers & Chemical Engineering》2005,29(11-12):2485
In order to develop and test the integration procedure, in this paper a real time process integration involving the optimization and control of the process is presented, in this case, with the two-layer approach. The used optimization algorithms were Levenberg–Marquardt and SQP that solve a non-linear least square problem subject to bounds on the variables. The two-layer approach is a hierarchical control structure where an optimization layer calculates the set points and manipulated variables to the advanced controller, which is based on the dynamic matrix control with constraints (QDMC). The non-isothermal dynamic model of the three-phase slurry catalytic reactor with appropriate solution procedure was utilized in this work (Vasco de Toledo, E. C., Santana, P. L., Maciel, M. R. W., & Maciel Filho, R. (2001). Dynamic modeling of a three-phase catalytic slurry reactor. Chemical Engineering Science, 56, 6055–6061). The model consists on mass and heat balance equations for the catalyst particles as well as for the bulk phases of gas and liquid. The model was used to describe the dynamic behavior of hydrogenation reaction of o-cresol to obtain 2-methil-cyclohexanol, in the presence of a catalyst Ni/SiO2. 相似文献
57.
This article introduces a new method for model falsification using set‐valued observers, which can be applied to a class of discrete linear time‐invariant dynamic systems with time‐varying model uncertainties. In comparison with previous results, the main advantages of this approach are as follows: The computation of the convex hull of the set‐valued estimates of the state can be avoided under certain circumstances; to guarantee convergence of the set‐valued estimates of the state, the required number of previous steps is at most as large as the number of states of the nominal plant; and it provides a straightforward nonconservative method to falsify uncertain models of dynamic systems, including open‐loop unstable plants. The results obtained are illustrated in simulation, emphasizing the advantages and shortcomings of the suggested method. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
58.
George Teodoro Eduardo Valle Nathan Mariano Ricardo Torres Wagner Meira Jr Joel H. Saltz 《The VLDB Journal The International Journal on Very Large Data Bases》2014,23(3):427-448
Similarity search in high-dimensional spaces is a pivotal operation for several database applications, including online content-based multimedia services. With the increasing popularity of multimedia applications, these services are facing new challenges regarding (1) the very large and growing volumes of data to be indexed/searched and (2) the necessity of reducing the response times as observed by end-users. In addition, the nature of the interactions between users and online services creates fluctuating query request rates throughout execution, which requires a similarity search engine to adapt to better use the computation platform and minimize response times. In this work, we address these challenges with Hypercurves, a flexible framework for answering approximate k-nearest neighbor (kNN) queries for very large multimedia databases. Hypercurves executes in hybrid CPU–GPU environments and is able to attain massive query-processing rates through the cooperative use of these devices. Hypercurves also changes its CPU–GPU task partitioning dynamically according to the observed load, aiming for optimal response times. In our empirical evaluation, dynamic task partitioning reduced query response times by approximately 50 % compared to the best static task partition. Due to a probabilistic proof of equivalence to the sequential kNN algorithm, the CPU–GPU execution of Hypercurves in distributed (multi-node) environments can be aggressively optimized, attaining superlinear scalability while still guaranteeing, with high probability, results at least as good as those from the sequential algorithm. 相似文献
59.
Paula Relgio Marie-Thrse Charreyre Jos Paulo S. Farinha Jos M.G. Martinho Christian Pichot 《Polymer》2004,45(26):8639-8649
N,N-dimethylacrylamide (DMA) and N-acryloxysuccinimide (NAS) were copolymerized by the reversible addition–fragmentation chain transfer (RAFT) polymerization technique, to obtain random and block copolymer precursors onto which different side-groups may be statistically grafted via the reactive NAS units. These reactive copolymers have interesting applications in various fields such as coatings and paints, water purification and biology. Random poly(DMA-co-NAS) copolymer chains were synthesized with a 75/25 molar ratio, high conversion, an excellent molecular weight (MW) control from 5000 to 130 000 g mol−1, and low polydispersity index (Mw/Mn<1.1). Poly(DMA-b-NAS) block copolymers were synthesized by a two step method, in which a poly(DMA) homopolymer was prepared first and then used as macro-chain transfer agent to polymerize NAS. For example, a poly(DMA-b-NAS) sample was obtained with an average molecular weight of 44 300/7400 g mol−1 corresponding to 447 DMA and 44 NAS units. Such block copolymers had not yet been synthesized by any controlled polymerization technique. They can be used to prepare polymers with exactly the same backbone and an increasing number of different side groups (e.g. hydrophobic, ionic or fluorescent). 相似文献
60.
Very long chain (VLC) PUFA of the n−6 and n−3 series are known to occur in mammalian testis. The aim of this work was to characterize
further two testicular lipid classes with VLCPUFA, cholesterol esters (CE) and total triglycerides (TG) in rat and mouse testis.
The VLCPUFA predominating in these lipids were a series of n−6 pentaenes and tetraenes with 24 to 32 carbons, including small
amounts of odd-chain PUFA, 28∶5n−6 and 24∶5n−6 prevailing in CE and TG, respectively. Most of the VLCPUFA of TG were concentrated
in a small fraction of TG, made up by 1-O-alkyl-2,3-DAG. This TG subclass was absent altogether from the TG of sexually immature testis. The TG and the CE with VLCPUFA
only occurred in testis of adult fertile animals. The proportion of VLCPUFA in total TG and CE was higher in rodents than
in other mammals. In the n−6 PUFA-rich adult mouse testis, the amounts of testicular triacylglycerols decreased significantly
after consumption of fish oil for 2 wk. Whereas 18∶2n−6 was significantly reduced, the amounts of 22∶5n−6 and longer n−6 PUFA
were less affected in all mamor testicular lipids including PC and PE, where they were unchanged. The 1-O-alkyl-2,3-DAG and their n−6 VLCPUFA were virtually unaffected by the diet. The VLCPUFA-containing molecular species of CE
and TG may represent a form of storage of cholesterol and polyenoic FA required to sustain spermatogenesis. Via chain-shortening, VLCPUFA stored in the neutral lipids may serve as precursors of the major C22 PUFA typical of cell membrane glycerophospholipids, protecting testicular cells against shifts in FA composition induced
by dietary changes. 相似文献