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排序方式: 共有452条查询结果,搜索用时 15 毫秒
71.
Rolando Herrero 《Telecommunication Systems》2017,66(4):579-588
Internet firewalls are typically configured to allow web friendly traffic transported by means of the Transmission Control Protocol (TCP) and, simultaneously as security measure, reject any other type of transport. This is a problem for real time communications that heavily rely on transport types like User Datagram Protocol or those associated to the Internet Security Protocol. A mechanism to overcome this limitation is through stream tunneling where media frames that would be typically rejected by firewalls are encapsulated on top of TCP transport. In this paper, a novel mathematical model that links application layer packet loss to bursty network packet loss in the context of fading channels characteristic of wireless communications is presented for both, datagram and stream encapsulation. This model is compared with experimental scenarios of tunneling applied to state of the art speech codecs such that quality scores are obtained and correlated against theoretical results. 相似文献
72.
In this work, a new chiral micellar electrokinetic chromatography with laser-induced fluorescence detection (chiral-MEKC-LIF) method is proposed to identify and quantify D- and L-amino acids in three lines of transgenic maize and their corresponding nontransgenic parental lines grown under identical conditions. The optimized procedure includes amino acids extraction, derivatization with FITC and chiral-MEKC-LIF separation in a background electrolyte composed of 100 mM sodium tetraborate, 80 mM SDS, and 20 mM beta-CD at pH 10.0. The D- and L-forms of Arg, Ser, Ala, Glu, and Asp, corresponding to the majority amino acids usually found in maize, are separated in less than 25 min with efficiencies up to 890,000 plates/m and high sensitivity (i.e., LODs as low as 160 nM were obtained for D-Arg for a signal-to-noise ratio of three), allowing the detection of 1% D-Arg in the presence of 99% of its opposite enantiomer. Using this method, different D-amino acids are detected in all investigated maize samples providing the reproducible quantification of the D-enantiomeric excess (% d-aa) for each amino acid calculated as % D-aa = 100D-aa/(D-aa + L-aa). Thus, significant differences were observed among the % d-aa values for the different conventional varieties (Aristis, Tietar, and PR33P66 maize) as could be expected from their natural variability. More interestingly, comparing each conventional maize with its corresponding transgenic line, very similar % D-aa values were obtained for one of the studied maize couples (Tietar vs Tietar-Bt) what could be presented as a new proof of their substantial equivalence. However, significant differences in the % d-aa values were observed for the other lines of maize studied. It is concluded that enantioselective procedures can open new perspectives in the study of transgenic organisms in order to corroborate (or not) the equivalence with their conventional counterparts. 相似文献
73.
Oxidation of BN/Nicalon Fiber Interfaces in Ceramic-Matrix Composites and Its Effect on Fiber Strength 总被引:1,自引:0,他引:1
José Pérez-Rigueiro José Antonio Celemín Javier LLorca Pilar Herrero 《Journal of the American Ceramic Society》1999,82(12):3494-3500
Microstructural changes at the interface were analyzed in two Nicalon-fiber ceramic-matrix composites with a dual BN/SiC coating on the fibers after thermal exposure at different temperatures (in the range 800°-1400°C) and in different environments (air and argon). The outer SiC coating acted as a barrier to oxygen, which penetrated into the composite via pipeline diffusion along the BN/fiber interfaces. Oxygen penetration led to the formation of an SiO2 layer by oxidation of the fiber surfaces. The in situ fiber strength at different temperatures, as determined from the radius of the mirror region on the fiber fracture surface, indicated that this SiO2 layer severely degraded the fiber strength. Oxidation was highly dependent on the nature of the BN/fiber interface. The presence of a thin carbon-rich interlayer, which burned out rapidly at high temperature, favored the entry of oxygen and accelerated oxidation of the fibers. 相似文献
74.
75.
Gemma Bellí Eloi Garí Martí Aldea Enrique Herrero 《Yeast (Chichester, England)》1998,14(12):1127-1138
A promoter-substitution cassette has been constructed that allows one-step substitution of chromosomal gene promoters for the tetracycline-regulatable tetO promoter in yeast cells, which uses kanMX4 as selective marker for geneticin resistance. Oligonucleotides for PCR amplification of the cassette are designed to allow homologous recombination through short flanking regions of homology with the upstream sequences of the chromosomal gene, upon transformation of target cells. By testing three essential genes of chromosome XV (YOL135c, YOL142w and YOL144w), the system causes tetracycline-dependent conditional growth of the cells, being modulatable by intermediate concentrations of the effector. Analysis of terminal phenotypes of the promoter-substituted cells in the presence of the antibiotic may facilitate functional analysis of essential orphan genes. © 1998 John Wiley & Sons, Ltd. 相似文献
76.
A. M. Chaparro M. T. Gutirrez J. Herrero J. Klaer M. J. Romero M. M. Al‐Jassim 《Progress in Photovoltaics: Research and Applications》2002,10(7):465-480
Thin‐film solar cells of CuInS2/Zn(Se,O)/ZnO configuration have been studied from the point of view of their dependence on the Zn(Se,O) chemical bath deposition (CBD) conditions. The kinetics of deposition of the Zn(Se,O) buffer is followed during cell processing with a quartz crystal microbalance (QCM). Two different CBD growth mechanisms yield buffer layers with different properties. Under a predominant electroless deposition reaction, the resulting buffer layer has mixed ZnSe–ZnO composition. The solar cells with this buffer type show higher fill factor (FF) and lower open‐circuit voltage (Voc). Under a chemical growth regime, the buffer layer has higher ZnSe proportion, giving rise to cells with higher VOC, but lower FF and stability. The parameters of this second type of cell also show major dependence on illumination effects (light‐soaking effects). Electron‐beam‐induced current (EBIC) and cathodoluminescence (CL) measurements are carried out to characterise the CuInS2/Zn(Se,O) junctions formed under the two buffer growth regimes. Cross‐sectional EBIC shows a wider space charge region (SCR) than expected for p‐CuInS2 in contact with Zn(Se,O), and the p–n junction is driven within the CuInS2 phase. These results reflect a chemical modification of CuInS2, most probably caused by the ammonia of the bath solution. CL shows more defective interfaces when Zn(Se,O) is deposited under the chemical mechanism (slower deposition rate, hence longer contact time of the CuInS2 with the bath solution) than under the electroless kinetics (faster deposition rate). Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
77.
Cu(In,Ga)Se2 thin films have been prepared by selenization of the evaporated metallic precursors on transparent and conductive ITO-coated
as well as uncoated glass substrates, by starting from slightly Cu-rich or Cu-poor overall metallic proportions. The objective
is to determine the influence of the Cu availability on the constituents distribution achieved after selenization, by means
of data obtained at several film depths by grazing incidence X-ray diffraction and X-ray photoelectron spectroscopy that have
been related to the overall optical and structural characteristics of the material. This study points out the possibility
of achieving homogeneous or graded absorber layers, showing for homogeneous samples an ITO/Cu(In,Ga)Se2 interface with ohmic electrical characteristics suitable to act as back contact for semitransparent photovoltaic devices. 相似文献
78.
R. Herrero Martín J. Pérez-García A. García F.J. García-Soto E. López-Galiana 《Solar Energy》2011,85(3):455-469
Solar liquid collectors are potential candidates for enhanced heat transfer, but there are just a few studies focused on this topic. However, enhancement techniques can be applied to thermal solar collectors to produce more compact and efficient designs. This work presents the study of heat transfer enhancement in a tube-on-sheet solar panel with wire-coil inserts, using TRNSYS as the simulating tool. The numerical simulation methodology predicts the thermohydraulic flow behaviour of enhanced and standard tube-on-sheet solar collectors, evaluating the local losses, friction coefficients and Nusselt numbers as functions of the operating parameters. The standard and the enhanced collectors have been simulated under the same ambient, radiant and operating conditions. The standardized efficiency curves according to the standard UNE-EN 12975-2 are provided. The enhanced collector increases the thermal efficiency values by 4.5%. A parametric study was performed to relate the fluid and flow characteristics with the heat transfer enhancement by wire-coil inserts. The simulations were performed for different working fluids (water and propylene glycol/water mixtures) in a mass flow rate range from 15 to 120 l/h m2. 相似文献
79.
80.
Hydroxytyrosol and its complex forms (secoiridoids) modulate aorta and heart proteome in healthy rats: Potential cardio‐protective effects 下载免费PDF全文