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FlexPolh adaptive event polling for network-intensive applications

Frontiers of Computer Science 2016年第3期10卷 532-542页

作者： Xingbo WU xiang long Lei WANG School of Computer Science and Engineering Beihang University Beijing 100191 China

In today＇s data centers supporting Internet-scale computing and input/output （I/0） services, increasingly more network-intensive applications are deployed on the network as a service. To this end, it is critical for the applications to quickly retrieve requests from the network and send their responses to the network. To facilitate this network func- tion, operating system usually provides an event notification mechanism so that the applications （or the library） know if the network is ready to supply data for them to read or to receive data for them to write. As a widely used and repre- sentative notification mechanism, epoll in Linux provides a scalable and high-performance implementation by allowing applications to specifically indicate which connections and what events on them need to be watched. As epoll has been used in some major systems, includ- ing key-value （KV） systems, such as Redis and Memcached, and web server systems such as NGINX, we have identified a substantial performance issue in its use. For the sake of efficiency, applications usually use epoll＇s system calls to inform the kernel exactly of what events they are interested in and always keep the information up-to-date. However, in a system with demanding network traffic, such a rigid main- tenance of the information is not necessary and the excess number of system calls for this purpose can substantially de- grade the system＇s performance. In this paper, we use Redis as an example to explore the issue. We propose a strategy of informing the kernel of the interest events in a manner adaptive to the current network load, so that the epoll system calls can be reduced and the events can be efficiently deliv- ered. We have implemented an event-polling library, named as FlexPoll, purely in user-level without modifying any ker- nel code. Our evaluation on Redis shows that the query through- put can be improved by up to 46.9% on micro-benchmarks, and even up to 67.8% on workloads emulating real-world a

关键词： operating systems performance evaluation andmodeling storage systems and networks workload characterization

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Dynamic Power Saving via Least-Square Self-Tuning Regulator in the Virtualized Computing Systems

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Journal of Systems Science & Complexity 2015年第1期28卷 60-79页

作者： WEN Chengjian long xiang MU Yifen School of Computer Science and Engineering Beihang University Key Laboratory of Systems and Control Institute of Systems ScienceAcademy of Mathematics and Systems ScienceChinese Academy of Sciences

In recent years,power saving problem has become more and more important in many fields and attracted a lot of research *** this paper,the authors consider the power saving problem in the virtualized computing *** there are multiple objectives in the system as well as many factors influencing the objectives,the problem is complex and *** authors will formulate the problem as an optimization problem of power consumption with a prior requirement on performance,which is taken as the response time in the *** solve the problem,the authors design the adaptive controller based on least-square self-tuning regulator to dynamically regulate the computing resource so as to track a given reasonable reference performance and then minimize the power consumption using the tracking result supplied by the controller at each *** is implemented based on the data collected from real machines and the time delay of turning on/off the machine is included in the *** results show that this method based on adaptive control theory can save power consumption greatly with satisfying the performance requirement at the same time,thus it is suitable and effective to solve the problem.

关键词： Adaptive control green computing least square self-tuning regulator (LS-STR) performance constraint power saving.

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A fast decoupled ISAR high-resolution imaging method using structural sparse information under low SNR

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Journal of Systems Engineering and Electronics 2019年第3期30卷 492-503页

作者： xiang long LI Shaodong YANG Jun CHEN Wenfeng xiang Hu Department of Air Defense Early Warning Equipment Air Force Early Warning Academy Wuhan 430019 China Unit 93253 of the PLA Dalian 116000 China

Inverse synthetic aperture radar (ISAR) image can be represented and reconstructed by sparse recovery (SR) approaches. However, the existing SR algorithms, which are used for ISAR imaging, have suffered from high computational cost and poor imaging quality under a low signal to noise ratio (SNR) condition. This paper proposes a fast decoupled ISAR imaging method by exploiting the inherent structural sparse information of the targets. Firstly, the ISAR imaging problem is decoupled into two sub-problems. One is range direction imaging and the other is azimuth direction focusing. Secondly, an efficient two-stage SR method is proposed to obtain higher resolution range profiles by using jointly sparse information. Finally, the residual linear Bregman iteration via fast Fourier transforms (RLBI-FFT) is proposed to perform the azimuth focusing on low SNR efficiently. Theoretical analysis and simulation results show that the proposed method has better performence to efficiently implement higher-resolution ISAR imaging under the low SNR condition.

关键词： sparse recovery inverse synthetic aperture radar (ISAR) imaging high-resolution signal to noise ratio (SNR) structural sparse information

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Fairness-oriented physical layer network coding in cooperative multiple access channels due to MRC and SIC

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The Journal of China Universities of Posts and Telecommunications 2012年第6期19卷 45-51页

作者： CHENG Yu-lun YANG long-xiang Jiangsu Key Laboratory of Wireless Communications Nanjing University of Posts and Telecommunications Key Laboratory of Broadband Wireless Communication and Sensor Network Technology Nanjing University of Posts and Telecommunications

This paper investigates the impacts of network coding （NC） on user fairness from the network perspective in multiple access channels. Firstly, simultaneous outage is exploited as the metric to evaluate user fairness. To optimize it, a fairness-oriented physical layer NC scheme is proposed, in which users＇ signals are superimposed in specific calculated proportion at relay and then decoded by maximal ratio combination （MRC） and serial interference cancellation （SIC） at destination. Furthermore, the influence of power allocation coefficient error on simultaneous outage is also analyzed to reveal its correlation with user fairness. Simulation results indicate that the proposed scheme can supply approximately equal performance promotion for each cooperation-participated user and outperform those without fairness consideration in terms of the employed metric.

关键词： cooperative system user fairness simultaneous outage MRC SIC

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Low complexity power allocation for hybrid amplify-and-forward opportunistic relay ordering cooperation

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The Journal of China Universities of Posts and Telecommunications 2013年第3期20卷 26-31页

作者： CHENG Yu-lun YANG long-xiang Jiangsu Key Laboratory of Wireless Communications Key Laboratory on Wideband Wireless Communications and Sensor Network Technology of Ministry of Education Nanjing University of Posts and Telecommunications

In this paper, to enhance the robustness against link imbalance, a hybrid cooperative protocol is proposed for amplify-and-forward （AF） opportunistic cooperation, where opportunistic relaying and multi-hop cooperation with relay ordering （RO） are dynamically selected to maximize the end to end signal-noise ratio （SNR）, and the power allocation coefficient is optimized under total power constraint accordingly. Furthermore, a suboptimum allocation scheme with low complexity is proposed by employing the upper bound of harmonic mean. Simulation results show that the proposed scheme outperforms conventional AF opportunistic cooperation in variety of line type topology. Moreover, the efficiency of the proposed suboptimum allocation is also validated in large SNR region.

关键词： opportunistic cooperation multi-hop RO AF power allocation

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Boundedness for multilinear fractional integral operators on Herz type spaces

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Applied Mathematics(A Journal of Chinese Universities) 2008年第4期23卷 437-446页

作者： SHI Yan-long TAO xiang-xing Dept. of Math. Faculty of Science Ningbo Univ. Ningbo 315211 China

In this paper the boundedness for the multilinear fractional integral operator Iα^（m） on the product of Herz spaces and Herz-Morrey spaces are founded, which improves the Hardy- Littlewood-Sobolev inequality for classical fractional integral Iα. The method given in the note is useful for more general multilinear integral operators.

关键词： multilinear fractional integral Herz space homogeneous Herz-Morrey space product space

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Rational Design of Colloidal Core/Shell Quantum Dots for Optoelectronic Applications

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Journal of Electronic Science and Technology 2020年第2期18卷 105-118页

作者： xiang-long Huang Xin Tong Zhiming MWang Institute of Fundamental and Frontier Sciences University of Electronic Science and Technology of China

Colloidal core/shell quantum dots(QDs) are promising for solar technologies because of their excellent optoelectronic properties including tunable light absorption/emission spectra, high photoluminescence quantum yield(PLQY), suppressed Auger recombination, efficient charge separation/transfer, and outstanding photo-/thermal-/chemical stability. In this review, engineered core/shell QDs with various types of band structures and corresponding device performance in luminescent solar concentrators(LSCs), light-emitting diodes(LEDs), solar-driven photoelectrochemical(PEC) devices, and QDs-sensitized solar cells(QDSCs) are summarized. In particular, the applications of interfacial layer engineering and eco-friendly, heavy metal-free core/shell QDs in optoelectronic devices are highlighted. Finally, strategies towards the developments and practical perspectives of core/shell QDs are briefly mentioned to offer guidelines for achieving prospective high-efficiency and long-term stable QD devices.

关键词： stability. quantum mentioned

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Hydrogeochemical and Isotopic Evidence for Flow Paths of Karst Waters Collected in the Heshang Cave,Central China

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Journal of Earth Science 2015年第1期26卷 149-156页

作者： xiang long Ziyong Sun Aiguo Zhou Deliang Liu School of Environmental Studies China University of Geosciences

Understanding of hydrological processes in caves is important to help us interpret paleoclimate records from speleothems. In this study, we integrated hydrogeological and hydrogeochemical properties to characterize the hydraulic behavior of karst waters in the Heshang Cave, Central China. Using geological and topographical analyses, we identified regional watershed boundaries and hydrogeological connections that were controlled by anticlinal geometry and faults. Water samples were collected from the Heshang Cave and potential recharge sites. Geochemical data of c（Sr^2＋）/c（Ca^2＋） and c（Mg^2＋）/c（Ca^2＋） ratios suggest that the drainage system in Heshang Cave consists of two flow paths. For vadose waters, including drip water and rimstone pool water, c（Sr^2＋）/c（Ca^2＋） ratio ranges from 0.000 6 to 0.001 1, and c（Mg^2＋）/c（Ca^2＋） ratio ranges from 0.97 to 1.1, indicating that recharge was mainly from rainfall infiltration through the overlying Cambrian dolomite stratum. In contrast, slope current and underground river waters have higher c（Sr^2＋）/c（Ca^2＋） ratios （values from 0.002 2 to 0.002 8）, and lower c（Mg2＋）/c（Ca^2＋） ratios （values from 0.50 to 0.64）. These waters show homogeneous isotopic composition （δ^18O： -7.15‰- -6.95‰; δD： -52.73‰- -51.31‰）, implying recharge of allogeneic water from the Xiaocr River via karst conduits that pass through Ordovician limestone and Cambrian dolomite stratum.

关键词： karst water hydrogeochemistry stable isotope flow path Heshang Cave.

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CO2 emission of urban passenger transportation in China from 2000 to 2014

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Advances in Climate Change Research 2019年第1期10卷 59-67页

作者： YUAN Rui-Qiang TAO Xin YANG xiang-long School of Environment and Resources Shanci UniversitTaiyuan030006China

This study reviewed the urban passenger transportation(UPT)development of seven typical cities in China from 2000 to 2014,estimated the UPT CO2emission,analyzed the structure,and discussed the main factors of UPT CO,*** showed that increases of GDP,population,and UPT scale of the cities have speeded *** most significant development of UPT is that the growth of private vehicles is greatly faster than that of public *** total and per-capita UPT CO2 emissions both *** share of private vehicles emission to total UPT CO2emission has increased,with the share in range of 65%-88%in 2014,exponentially leading to the increases of total and per-capita UPT CO2 *** UPT CO2 emission structure with more share of public transportation would slow down the UPT CO2emission increase,private vehicle CO2 emission is recognized as the dominated driving *** of driving factors,such as GDP,population,private vehicle CO2 emissions,to UPT CO2 emission are different among the *** vehicle CO2 *** the dominated factor for UPT CO2emission in Beijing and *** private vehicle CO2emission,GDP also plays an important role in UPT CO2emissions of Chengdu,Shanghai,Guangzhou,and *** of private vehicle CO2 emission and GDP to UPT CO2 emission are almost same in Xi'an.

关键词： Urban passenger transport CO2 emissions Low-carbon transport China

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MIMO Underwater Acoustic Communication in Shallow Water with Ice Cover

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China Ocean Engineering 2019年第2期33卷 237-244页

作者： HAN Xiao YIN Jing-wei LIU Bing GUO long-xiang Acoustic Science and Technology Laboratory Harbin Engineering University Key Laboratory of Marine Information Acquisition and Security (Harbin Engineering University) Ministry of Industry and Information Technology College of Underwater Acoustic Engineering Harbin Engineering University

Although multiple-input multiple-output(MIMO) underwater acoustic(UWA) communication has been intensively investigated in the past years, existing works mainly focus on open-water environment. There is no work reporting MIMO acoustic communication in under-ice environment. This paper presents results from a recent MIMO acoustic communication experiment which was conducted in Bohai Gulf during winter. In this experiment, high frequency MIMO signals centered at 10 kHz were transmitted from a two-element source array to a four-element vertical receiving array at 1 km range. According to the received signal of different array elements, MIMO acoustic communication in under-ice environment suffers less effect from co-channel interference compared with that in open-water environment. In this paper, time reversal followed by a single channel decision feedback equalizer is used to process the experimental data. It is demonstrated that this simple receiver is capable of realizing robust performance using fewer hydrophones(i.e. 2) without the explicit use of complex co-channel interference cancelation algorithms, such as parallel interference cancelation or serial interference cancelation.

关键词： underwater acoustic communication MIMO shallow water ice cover

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