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排序方式: 共有1147条查询结果,搜索用时 15 毫秒
81.
George D. Panagiotou Manolis D. Tzirakis John Vakros Loukia Loukatzikou Michael Orfanopoulos Christos Kordulis Alexis Lycourghiotis 《Applied Catalysis A: General》2010,372(1):16-25
Simple or successive incipient wetness impregnation followed by heating at 180 °C is proved an efficient preparation method for dispersing effectively onto the silica surface various amounts of C60 in the range 1–4% (w/w). BET, XRD, DRS, TGA, microelectrophoresis and photoluminescence have been used to characterize the photocatalysts prepared. A high dispersion was obtained for the quite stable supported C60 phase, comprised mainly from relatively small or medium size C60 clusters/aggregates. The photocatalytic activity was assessed in the singlet oxygen oxidation of alkenes by examining the photo-oxygenation of 2-methyl-2-heptene as a probe reaction. The catalytic tests were carried out at 0–5 °C in CH3CN, under oxygen atmosphere and using a 300 W xenon lamp as the light source. The heterogeneous catalysts obtained were proved to be active in the photocatalytic oxidation of olefins via a 1O2 ene reaction. The catalysts exhibited significant conversion, turnover number and turnover frequency values, substantially higher than those achieved over the unsupported C60. The conversion increases with the amount of the supported C60 up to a value equal to 3% (w/w) and then it decreases whereas turnover number and turnover frequency decreases monotonically as the amount of the supported C60 increases. The easy separation of these solid catalysts from the reaction mixture, the high activity and stability as well as the retained activity in subsequent catalytic cycles, make these supported catalysts suitable for a small-scale synthesis of fine chemicals. 相似文献
82.
Horst Biermann Ulrich Martin Christos G. Aneziris Anja Kolbe Angelika Müller Wolfgang Schärfl Mathias Herrmann 《Advanced Engineering Materials》2009,11(12):1000-1006
Novel composites on basis of austenitic stainless TRIP‐steel as matrix with reinforcements of Mg‐PSZ are presented. Compact rods were produced by cold isostatic pressing and sintering, square honeycomb samples by the ceramic extrusion technique. The samples are characterized by optical and scanning electron microscopy before and after deformation, showing the microstructure and the deformation‐ induced martensite formation. The mechanical properties of samples with 5 vol% zirconia are superior compared to zirconia‐free samples and composites with higher zirconia contents in terms of bending and compression tests. The honeycomb samples exhibit extraordinary high specific energy absorption in compression. 相似文献
83.
We introduce a new representation for time series, the Multiresolution Vector Quantized (MVQ) approximation, along with a distance function. Similar to Discrete Wavelet Transform, MVQ keeps both local and global information about the data. However, instead of keeping low-level time series values, it maintains high-level feature information (key subsequences), facilitating the introduction of more meaningful similarity measures. The method is fast and scales linearly with the database size and dimensionality. Contrary to previous methods, the vast majority of which use the Euclidean distance, MVQ uses a multiresolution/hierarchical distance function. In our experiments, the proposed technique consistently outperforms the other major methods. 相似文献
84.
Christos K. Datsikas Kostas P. Peppas Fotis I. Lazarakis George S. Tombras 《AEUE-International Journal of Electronics and Communications》2010,64(11):1094-1099
In this paper we present analytical expressions for the lower bounds of the error performance of dual-hop amplify-and-forward transmissions over independent and not necessarily identical Generalized-K fading channels. Using a tight upper bound for the end-to-end SNR, a novel expression for the probability density function is derived. Based on the abovementioned formula, tight lower bounds for the average bit error probability for a variety of modulation schemes are derived. In order to validate the accuracy of the proposed mathematical analysis, various numerical and computer simulation results are presented. 相似文献
85.
86.
Christos Bouras Apostolos Gkamas Georgios Kioumourtzis 《International Journal of Communication Systems》2010,23(3):299-333
In this paper we propose a new single‐rate multicast congestion control scheme named Adaptive Smooth Multicast Protocol (ASMP), for multimedia transmission over best‐effort networks. The smoothness lays in the calculation and adaptation of the transmission rate, which is based on dynamic estimations of protocols' parameters and dynamic adjustment of the ‘smoothness factor’, as well. ASMP key attributes are: (a) TCP‐friendly behavior, (b) adaptive scalability to large sets of receivers, (c) high bandwidth utilization, and finally (d) smooth transmission rates, which are suitable for multimedia applications. We evaluate the performance of ASMP and investigate its behavior under various network conditions through extensive simulations conducted with the network simulator software (ns2). Simulation results show that ASMP can be regarded as a serious competitor of TFMCC and PGMCC. In many cases, ASMP outperforms TFMCC in terms of TCP‐friendliness and smooth transmission rates, while PGMCC presents lower scalability than ASMP. We have implemented ASMP on top of RTP/RTCP protocols in ns2 by adding all the RTP/RTCP protocol's attributes that are defined in RFC 3550 and related to quality of service metrics. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
88.
89.
Multiobjective Optimization: Improved FPTAS for Shortest Paths and Non-Linear Objectives with Applications 总被引:1,自引:0,他引:1
We provide an improved FPTAS for multiobjective shortest paths—a fundamental (NP-hard) problem in multiobjective optimization—along
with a new generic method for obtaining FPTAS to any multiobjective optimization problem with non-linear objectives. We show how these results can be used to obtain better approximate solutions to three related problems, multiobjective
constrained [optimal] path and non-additive shortest path, that have important applications in QoS routing and in traffic
optimization. We also show how to obtain a FPTAS to a natural generalization of the weighted multicommodity flow problem with
elastic demands and values that models several realistic scenarios in transportation and communication networks.
This work was partially supported by the Future and Emerging Technologies Unit of EC (IST priority—6th FP), under contracts
No. IST-2002-001907 (integrated project DELIS) and No. FP6-021235-2 (project ARRIVAL), and the Action PYTHAGORAS of the Operational
Programme for Educational & Vocational Training II, with matching funds from the European Social Fund and the Greek Ministry
of Education. 相似文献
90.
Christos G. Papadimitriou Anna Vafopoulou-Mastrojiannaki Sofia Vieira Silva Ana-Maria Gomes Francisco Xavier Malcata Efstathios Alichanidis 《Food chemistry》2007,105(2):647-656
Two sets of traditional Greek sheep milk yoghurt were produced: the first one (YC) using normal yoghurt culture (Lactobacillus delbrueckii subsp. bulgaricus ?10.13 and Streptococcus thermophilus ?10.7) and the second (PR) with the same normal culture mixed with Lactobacillus paracasei subsp. paracasei DC412. YC and PR had similar physicochemical properties and proteolysis patterns throughout storage. Both products showed similar peptide profiles by RP-HPLC but quantitative differences were observed in respect to storage time. Single-strain cultures of the microorganisms used showed similar peptide profiles for both lactobacilli, yet L. delbrueckii subsp. bulgaricus was the most proteolytic of all three microorganisms. The peptide content and the ACE-inhibitory activity of the water-soluble extracts of yoghurts, YC and PR, increased throughout storage. Major peptides were identified from yoghurt PR and from the separate cultures of L. delbrueckii subsp. bulgaricus and L. paracasei subsp. paracasei. Most of these peptides were derived from β-casein. A peptide, β-CN f114-121, with well-established ACE-inhibitory and opiate-like activity was identified in yoghurt PR. Further identified peptides were regarded as potential ACE-inhibitors according to their sequence. 相似文献