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排序方式: 共有1261条查询结果,搜索用时 31 毫秒
961.
Multimedia streaming over wireless networks - often called mobile multimedia streaming lets users access music, movie, and news services at any time, regardless of location. Given that multimedia streaming is a key goal of third-generation and future wireless networks, vendors will soon deploy streaming clients in advanced mobile terminals. Current mobile terminals, however, fail to adequately support mobile multimedia communication because wireless networks have high packet-loss rates. To eliminate packet loss during handover, we use a packet path diversity scheme and an end-to-end bicasting mechanism that enables soft IP handover. To offset wireless errors, we use a forward error correction (FEC) scheme and embed it in the bicasting mechanism. Our bicasting method encodes the data stream and then splits it, providing more effective diversity than general bicasting, which sends the same data down both paths.' To support our method, we propose the mobile multimedia streaming protocol (MMSP), a new transport-layer protocol that supports multihoming and bicasting in combination with FEC. 相似文献
962.
The insolubility of giant polycyclic aromatic hydrocarbons (PAHs) prevents their characterization by conventional analytical methods, which require a solubilization of the analyte. Laser desorption mass spectrometry may be used to analyze insoluble samples but is limited to relatively low molecular weights (approximately 2000), in the case of PAHs. To overcome this limitation, we applied MALDI-TOF mass spectrometry. Since MALDI sample preparation also requires solubility of analyte and matrix molecules, the sample preparation needed modification. The giant PAHs (>2000 Da) were investigated after using a new sample preparation, consisting of mechanically mixing analyte and matrix without any solubilization procedures. This solvent-free process allows insoluble compounds to be characterized. Furthermore, new organic molecules can be used as a matrix. Indeed, 7,7,8,8-tetracyanoquinodimethane, a new matrix with promising properties, has proven to be particularly suitable for the measurement of PAHs. Thanks to the successful characterization with MALDI-TOF mass spectrometry, the chemical design of giant PAHs, which was hindered until now for a lack of analytical methods, can now continue to develop. 相似文献
963.
Single-phase potassium tantalate (KT) thin films with excellent film flatness and crystallinity have been synthesized on a tantalum substrate in 2.0 M KOH solution at 150°C by a hydrothermal-electrochemical method under a galvanostatic condition. A pyrochlore structure of the thin KT films was identified by XRD pattern analysis. The films show good adherence to the substrate and the film thickness could be as much as 2 m. The electrical properties of the films were characterized through the determination of capacitance by electrochemical impedance spectroscopy at room temperature. Dielectric constants yielded from capacitance measurements have been calculated to have values higher than 300. The dependence of cell voltage on reaction time reflects the mechanism of film formation. The preparation conditions and morphology of the films were consistent with the proposed film formation mechanism. 相似文献
964.
Topology optimization of fluid problems using genetic algorithm assisted by the Kriging model
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M. Yoshimura K. Shimoyama T. Misaka S. Obayashi 《International journal for numerical methods in engineering》2017,109(4):514-532
A non‐gradient‐based approach for topology optimization using a genetic algorithm is proposed in this paper. The genetic algorithm used in this paper is assisted by the Kriging surrogate model to reduce computational cost required for function evaluation. To validate the non‐gradient‐based topology optimization method in flow problems, this research focuses on two single‐objective optimization problems, where the objective functions are to minimize pressure loss and to maximize heat transfer of flow channels, and one multi‐objective optimization problem, which combines earlier two single‐objective optimization problems. The shape of flow channels is represented by the level set function. The pressure loss and the heat transfer performance of the channels are evaluated by the Building‐Cube Method code, which is a Cartesian‐mesh CFD solver. The proposed method resulted in an agreement with previous study in the single‐objective problems in its topology and achieved global exploration of non‐dominated solutions in the multi‐objective problems. © 2016 The Authors International Journal for Numerical Methods in Engineering Published by John Wiley & Sons Ltd 相似文献
965.
Quantitative determination of interlaminar fracture toughness that governs onset and growth of delamination is essential for engineering of composite materials and structures. This study proposes a new approach to evaluate both the initial fracture toughness and the crack growth resistance property of pure mode II delamination by tensile tests of specimens having two initial cracks, which were conceived from double-lap joints. The proposed test method achieves stable growth of mode II delamination using a fundamental testing system. This study presents the specimen configuration, the theory to evaluate the energy release rate, and experiment results. The mode II initial fracture toughness measured by the present approach agreed well with the results of conventional end-notched flexure tests. Furthermore, the crack growth resistance curves were evaluated by unloading-reloading tests of the proposed doubly end-notched tension specimens. 相似文献
966.
Hydrothermal processing of materials: past,present and future 总被引:1,自引:0,他引:1
The hydrothermal technique provides an excellent possibility for processing of advanced materials whether it is bulk single
crystals, or fine particles, or nanoparticles. The advantages of hydrothermal technology have been discussed in comparison
with the conventional methods of materials processing. The current trends in hydrothermal materials processing has been described
in relation to the concept of soft solution processing, as a single-step low energy consuming fabrication technique. Also
some recent developments in multi-energy processing of materials such as microwave-hydrothermal, mechanochemical-hydrothermal,
electrochemical-hydrothermal, sonar-hydrothermal, etc. have been discussed. An overview of the past, present and future perspective
of hydrothermal technology as a tool to fabricate advanced materials has been given with appropriate examples. 相似文献
967.
Fukae K Takahashi T Yoshimura T Fujimura N 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2008,55(5):1056-1060
Hexagonal RMnO(3) is known as one of the candidates for multiferroic materials. We have focused on YbMnO(3), which has ferroelectricity along the c axis below 1000 K and antiferromagnetic ordering below 80 K. We have reported that magnetic, field-induced ferromagnetism in YbMnO(3) epitaxial thin films. In this study, we investigate the substitutional effect of the nonmagnetic element, Al, for Mn ions with triangular spin ordering on the ferroelectric and magnetic properties of YbMnO(3). 相似文献
968.
Line edge roughness (LER) of patterned features in chemically amplified (CA) resists is formed in the acid generation stage and expected to be moderated by the acid diffusion and development process. It is essential to obtain information on the limit of LER in order to realize next-generation lithographies such as electron beam or extreme ultraviolet. Here, we report for the first time a process simulator based on physical and chemical reaction mechanisms. The LER of a positive-tone CA resist after development is investigated by Monte Carlo simulation and Mack's dissolution model. We found that the LER (high frequency) of less than 1.2?nm is achievable, although the process conditions and material design for achieving such a small LER are strict. 相似文献
969.
Yoshimura HN Cesar PF Soki FN Gonzaga CC 《Journal of materials science. Materials in medicine》2008,19(5):1945-1951
The stress intensity factor threshold (KI0) is related to the stress level at which cracks start to grow stably, causing the weakening of porcelain prostheses during
their use. The values of KI0 of seven dental porcelains (with and without reinforcing leucite crystal, KAlSi2O6) stored in air (22 °C, 60% relative humidity) and artificial saliva (37 °C) were determined by measuring the crack growth
velocity of radial cracks generated at the corner of Vickers indentations. The results of KI0 were correlated with the leucite content, fracture toughness (KIc), and chemical composition of the porcelains. It was observed that KI0 increased with the increase of leucite content (only for the leucite-based porcelains) and with the increase of KIc. The increase in Al2O3 content or the decrease in the alkali oxide (K2O and Na2O) content of the material’s glassy matrix tended to increase the KI0 values. Storage media (air and saliva) did not significantly affect the KI0 of porcelains tested, indicating that the control parameter of KI0 value was not the water content of the storage media. 相似文献
970.
To elucidate the transepithelial transport characteristics of lipophilic compounds, the cellular uptake of tocopherol and
tocotrienol isomers were investigated in Caco2 cell monolayer models. These vitamin E isomers formed mixed micelles consisting
of bile salts, lysophospholipids, free fatty acid, and 2-monoacylglycerols, then the micelles were supplied to Caco2 cells.
The initial accumulation of tocotrienol isomers in Caco2 cells was larger than those of corresponding tocopherol isomers.
There was little difference among the cellular accumulations of four tocopherol isomers. These findings suggested that the
difference between the molecular structures of the C16 hydrocarbon chain tail in tocopherol and tocotrienol was strongly responsible
for the rapid epithelial transport into the Caco2 cells membranes rather than the difference in the molecular structures of
their chromanol head groups. Furthermore, the secretion of α-tocopherol and γ-tocotrienol from Caco2 cells was investigated
using Caco2 cells plated on a transwell. The time courses of their secretions from Caco2 cells showed that the initial secretion
rate of γ-tocotrienol was also larger than that of α-tocopherol. To investigate the intestinal uptake of α-tocopherol and
γ-tocotrienol in vivo, the mice were fed single doses of α-tocopherol or γ-tocotrienol with triolein. The γ-tocotrienol responded
faster in plasma than α-tocopherol, although the maximal level of γ-tocotrienol was lower than that of α-tocopherol. This
suggested that the intestinal uptake properties of administered α-tocopherol and γ-tocotrienol would characterize their plasma
level transitions in mice. 相似文献