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971.
Orthogonal frequency division multiplexing (OFDM) has been widely considered as a key technique for next generation mobile communication systems. Meanwhile, relaying technologies can improve users’ quality of service, increase network capacity and enlarge cellular coverage at a low cost. In this paper, we focus on subcarrier allocation and utilization in multi-hop OFDM access (OFDMA) wireless networks, and propose two efficient subcarrier allocation schemes aiming to increase network throughput and subcarrier utilization. The first scheme selects suitable links for data transmission from base stations to terminals at the beginning. Then, interference-free links are included into the same group for network resource reuse. For the purpose of global optimization, we propose a Tabu-based searching algorithm as the second subcarrier allocation scheme. Simulation results demonstrate that our proposed algorithms outperform other schemes in both network throughput and subcarrier utilization. 相似文献
972.
Yongqiang Gao Haibing Guan Zhengwei Qi Tao Song Fei Huan Liang Liu 《Computers & Electrical Engineering》2014
As cloud computing has become a popular computing paradigm, many companies have begun to build increasing numbers of energy hungry data centers for hosting cloud computing applications. Thus, energy consumption is increasingly becoming a critical issue in cloud data centers. In this paper, we propose a dynamic resource management scheme which takes advantage of both dynamic voltage/frequency scaling and server consolidation to achieve energy efficiency and desired service level agreements in cloud data centers. The novelty of the proposed scheme is to integrate timing analysis, queuing theory, integer programming, and control theory techniques. Our experimental results indicate that, compared to a statically provisioned data center that runs at the maximum processor speed without utilizing the sleep state, the proposed resource management scheme can achieve up to 50.3% energy savings while satisfying response-time-based service level agreements with rapidly changing dynamic workloads. 相似文献
973.
本文采用Lichrosorb Si-60色谱柱,以正二十二烷为内标,高效液相色谱分析除草净粉剂有效成分扑草净,乙草胺,苄嘧黄隆含量的方法,扑草净,乙草胺,苄嘧黄隆变异系数分别为0.47,0.39,0.45,线性相关系数分别为0.9981,0.9992,0.9997。 相似文献
974.
The molecular orientation and deformation mechanisms of a quenched isotactic polypropylene (iPP) film deformed at temperatures between 303 K and the melting point are studied. At draw temperature TE less than 400 K where the degree of crystallinity does not change markedly, a linear relationship between molecular orientations of the crystalline and the amorphous phases is revealed and the slope is estimated about 1.82. The interpenetrating network (IPN) model, that takes into account the plastic response of the crystalline (C) network formed by a small portion of crystallites adhered through intercrystalline links and the pseudo-affine deformation of the crystallite enhanced amorphous matrix (CEAM) network, is able to account for inhomogeneous deformation behavior on the mesoscale accompanied with the localized necking in this TE range. Meanwhile, the initial Young's modulus and the true yield stress exerted by the deformation of the rigid C network exhibit the Arrhenius type of dependence on TE. The apparent shear modulus of the CEAM network as a function of TE is discussed in relation to variations in numbers and average molecular weights of the crystalline and the amorphous sequences being manifested by small consecutive endothermic and exothermic peaks in the DSC curve. The IPN model becomes invalid for deformations above TE=400 K where morphological changes are induced due to melting of crystallites as proved from the DSC measurement. 相似文献
975.
Self-Organizing Networks (SONs) are attractive for applications where flexibility, resilience, and a large network service area are required. In order to meet the requirements of those applications, the principal issue is to guarantee efficient routing in SONs. Hence, the design and selection of appropriate routing metrics is important. A mass of metrics have been proposed in the past several decades. Among all the metrics, Expected Transmission Count (ETX) has drawn the most attention. Since the proposal of ETX, many ETX-based or extended metrics have been proposed. ETX and its descendants compose the ETX family. This paper is an attempt to analyze, compare and summarize traffic-based routing metrics in the ETX family. Details of each routing metric are presented and analyzed. Some of our viewpoints on the principal for designing metrics in SONs are presented. 相似文献
976.
利用高速纺丝法与纺丝拉伸一步法两种不同的方法制备聚萘二甲酸乙二酯 ( PEN)纤维 ,以DSC、X射线衍射、声速、力学测试等手段分析其结构、热学及力学性能并进行比较。结果表明 :以上两种纺丝法所制备 PEN纤维的晶型、晶粒尺寸不同 ;在所采用的高速纺丝速度范围内 ,分别以 6,7,8km/m in的速度纺制的试样结构性能基本相同 ;而纺丝拉伸一步法中不同的拉伸倍数对纤维的取向度影响较大 ,进而使杨氏模量、断裂强度和断裂伸长率变化较大 相似文献
977.
Woon-Jae Lee Sang-Done Kim Byung-Ho Song 《Korean Journal of Chemical Engineering》2002,19(6):1091-1096
To produce low calorific value gas, Australian coal has been gasified with air and steam in a fluidized bed reactor (0.1 m-I.Dx1.6
m-high) at atmospheric pressure. The effects of fluidizing gas velocity (2–5 Uf/Umf), reaction temperature (750–900 °C), air/coal ratio (1.6-3.2), and steam/coal ratio (0.63–1.26) on gas composition, gas yield,
gas calorific value of the product gas and carbon conversion have been determined. The calorific value and yield of the product
gas, cold gas efficiency, and carbon conversion increase with increasing fluidization gas velocity and reaction temperature.
With increasing air/coal ratio, carbon conversion, cold gas efficiency and yield of the product gas increase, but the calorific
value of the product gas decreases. When steam/coal ratio is increased, cold gas efficiency, yield and calorific value of
the product gas increase, but carbon conversion is little changed. Unburned carbon fraction of cyclone fine decreases with
increasing fluidization gas velocity, reaction temperature and air/coal ratio, but is nearly constant with increasing steam/coal
ratio. Overall carbon conversion decreases with increasing fluidization velocity and air/ coal ratio, but increases with increasing
reaction temperature. The particle entrainment rate increases with increasing fluidization velocity, but decreases with increasing
reaction temperature.
This paper is dedicated to Professor Dong Sup Doh on the occasion of his retirement from Korea University. 相似文献
978.
Xueyan Hou Cunjin Xue Wanjiao Song Lijuan Qin Xing Fan 《International journal of remote sensing》2014,35(11-12):4138-4155
The northwestern Pacific Ocean is a complex region with significant biological spatial variations on a seasonal timescale. To investigate the joint variation patterns on both seasonal and interannual timescales, a season-reliant empirical orthogonal function (S-EOF) analysis was applied to seasonal mean chlorophyll-a concentration (chl-a) anomalies in the northwestern Pacific Ocean during the period 1998–2010. The first two dominant modes accounted for nearly 31% of the total interannual variance, with the second S-EOF mode (S-EOF2) lagging behind the first S-EOF mode (S-EOF1) by one year. S-EOF1 featured a strong variation pattern to the north of 30° N, with maximum chl-a in winter and minimum chl-a in summer. However, S-EOF2 indicated an opposite seasonally evolving pattern compared with S-EOF1, with chl-a increasing along the Kuroshio and extension current from boreal winter to autumn. Both these modes revealed significant relationships with climate-related indices. The two modes corresponded to the central Pacific (CP) La Niña developing episodes and the turnaround from eastern Pacific (EP) La Niña to CP El Niño, respectively. Both modes were associated with the cold phase of the Pacific Decadal Oscillation, which played an important role in prolonging the impact of the El Niño/Southern Oscillation on chl-a seasonal evolution from 1998 to 2010. In addition, we discuss the possible factors dominating chl-a seasonal variation, in terms of the subregions of the northwestern Pacific Ocean. In the subtropical northwestern Pacific Ocean (15° N – 30° N), the chl-a growth was primarily nutrient-limited, whereas in the mid-latitude northwestern Pacific Ocean (35° N – 50° N), the chl-a growth was mainly light-limited. 相似文献
979.
980.
Yan Song Wenming Qiao Seong‐Ho Yoon Isao Mochida Quangui Guo Lang Liu 《应用聚合物科学杂志》2007,106(4):2151-2157
Adsorption of low concentration formaldehyde on pitch‐based, rayon‐based, and PAN‐based activated carbon fibers (ACFs) and an unactivated PAN‐based carbon fiber (PAN‐CF) was investigated by a dynamic method. The pore structure and surface chemistry of these samples were characterized by liquid nitrogen adsorption, elemental analysis, and X‐ray photoelectron spectroscopy. Results revealed that the pore structure, especially surface chemical composition, greatly influence the formaldehyde adsorption. PAN‐based ACFs showed the highest formaldehyde adsorption capacity because there are more abundant nitrogen‐containing groups, especially pyrrolic, pyridonic, pyridinic, and quaternary on the surface. The breakthrough time and formaldehyde adsorption capacity of one kind of PAN‐ACF were 361 min and 0.478 mmol/g, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 相似文献