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Status of dark matter detection

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Frontiers of physics 2013年第6期8卷 794-827页

作者： xiao-Jun bi Peng-Fei Yin Qiang Yuan Key Laboratory of Particle Astrophysics Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China

The detection of dark matter has made great progresses in recent years. We give a brief review on the status and progress in dark matter detection, including the progresses in direct detection, collider detection at LHC and focus on the indirect detection. The results from PAMELA, ATIC, Fermi-LAT and relevant studies on these results are introduced. Then we give the progress on indirect detection of gamma rays from Fermi-LAT and ground based Cerenkov telescopes. Finally the detection of neutrinos and constraints on the nature of dark matter are reviewed briefly.

关键词： dark matter annihilation cosmic rays gamma rays

Heuristic Virtual Machine Allocation for Multi-Tier Ambient Assisted Living Applications in a Cloud Data Center

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China Communications 2016年第5期13卷 56-65页

作者： Jing bi Haitao Yuan Ming Tie xiao Song School of Software Engineering Beijing University of TechnologyBeijing 100124China Beijing Engineering Research Center for IoT Software and Systems Beijing 100124China School of Software Engineering Beijing Jiaotong UniversityBeijing 100044China Science and Technology on Space Physics Laboratory Beijing 100076China Beijing Institute of Near space Vehicle's Systems Engineering Beijing 100076China School of Automation Science and Electrical Engineering Beihang UniversityBeijing 100191China

Cloud computing provides the essential infrastructure for multi-tier Ambient Assisted Living(AAL) applications that facilitate people's lives. Resource provisioning is a critically important problem for AAL applications in cloud data centers(CDCs). This paper focuses on modeling and analysis of multi-tier AAL applications, and aims to optimize resource provisioning while meeting requests' response time constraint. This paper models a multi-tier AAL application as a hybrid multi-tier queueing model consisting of an M/M/c queueing model and multiple M/M/1 queueing models. Then, virtual machine(VM) allocation is formulated as a constrained optimization problem in a CDC, and is further solved with the proposed heuristic VM allocation algorithm(HVMA). The results demonstrate that the proposed model and algorithm can effectively achieve dynamic resource provisioning while meeting the performance constraint.

关键词： ambient assisted living cloud computing resource provisioning virtual machine heuristic optimization

Adjoining Batch Markov Arrival Processes of a Markov Chain

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Acta Mathematicae Applicatae Sinica 2018年第1期34卷 1-10页

作者： xiao-yun MO Xu-yan xiang xiang-qun YANG College of Mathematics and Statistics Hunan University of Finance and Economics Changsha 410205 China College of Mathematics and Computational Science Hunan University of Arts and Science Changde 415000 China Key Laboratory of High performance Computing and Stochastic Information Processing Ministry of Education of China College of Mathematics and Computer Science Hunan Normal University Changsha 410081 China Hunan Province Cooperative Innovation Center for the Construction and Development of Dongting Lake Ecological Economic Zone Changde 415000 China

A batch Markov arrival process（BMAP） X^＊=（N, J） is a 2-dimensional Markov process with two components, one is the counting process N and the other one is the phase process J. It is proved that the phase process is a time-homogeneous Markov chain with a finite state-space, or for short, Markov chain. In this paper,a new and inverse problem is proposed firstly： given a Markov chain J, can we deploy a process N such that the 2-dimensional process X^＊=（N, J） is a BMAP？ The process X^＊=（N, J） is said to be an adjoining BMAP for the Markov chain J. For a given Markov chain the adjoining processes exist and they are not unique. Two kinds of adjoining BMAPs have been constructed. One is the BMAPs with fixed constant batches, the other one is the BMAPs with independent and identically distributed（i.i.d） random batches. The method we used in this paper is not the usual matrix-analytic method of studying BMAP, it is a path-analytic method. We constructed directly sample paths of adjoining BMAPs. The expressions of characteristic（D_k, k = 0, 1, 2· · ·）and transition probabilities of the adjoining BMAP are obtained by the density matrix Q of the given Markov chain J. Moreover, we obtained two frontal Theorems. We present these expressions in the first time.

关键词： Markov chain batch Markov arrival process (BMAP) adjoining BMAP fixed constant batch independent identically distributed (i.i.d) random batch

Disinfection byproduct precursor removal by enhanced coagulation and their distribution in chemical fractions

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Journal of Environmental Sciences 2013年第11期25卷 2207-2213页

作者： Yanmei Zhao Feng xiao Dongsheng Wang Mingquan Yan Zhe bi Research Center for Eco-Environmental Sciences Chinese Academy of Sciences Department of Environmental Engineering Peking University

Raw water from the Songhua River was treated by four types of coagulants, ferric chloride （FeC13）, aluminum sulfate （A12（504）3）, polyaluminum chloride （PACl） and composite polyaluminum （HPAC）, in order to remove dissolved organic matter （DOM）. Considering the disinfection byproduct （DBP） precursor treatability, DOM was divided into five chemical fractions based on resin adsorption. Trihalomethane formation potential （THMFP） and haloacetic acid formation potential （HAAFP） were measured for each fraction. The results showed that hydrophobic acids （HoA）, hydrophilic matter （HIM） and hydrophobic neutral （HoN） were the dominant fractions. Although both HoN and HoA were the main THM precursors, the contribution for THMFP changed after coagulation. Additionally, HoA and HiM were the main HAA precursors, while the contribution of HoN to HAAFP significantly increased after coagulation. HoM was more easily removed than HiM, no matter which coagulant was used, especially under enhanced coagulation conditions. DOC removal was highest for enhanced coagulation using FeCl3 while DBPFP was lowest using PAC1. This could indicate that not all DOC fractions contained the precursors of DBPs. Reduction of THMFP and HAAFP by PAC1 under enhanced coagulation could reach 51% and 59% respectively.

关键词： trihalomethanes haloacetic acids dissolved organic matter chemical fractionation enhanced coagulation

Three-dimensional porous bimetallic metal–organic framework/gelatin aerogels: A readily recyclable peroxymonosulfate activator for efficient and continuous organic dye removal

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Chinese Journal of Chemical Engineering 2024年第7期71卷 193-202页

作者： Wenlong xiang Xian Zhang Rou xiao Yanhui Zhang College of Chemistry Chemical Engineering and EnvironmentFujian Province Key Laboratory of Morden Analytical Science and Separation TechnologyMinnan Normal UniversityZhangzhou 363000China Fujian Provincial University Key Laboratory of Pollution Monitoring and Control Minnan Normal UniversityZhangzhou 363000China

As promising catalysts for the degradation of organic pollutants,metal–organic frameworks(MOFs)often face limitations due to the particle agglomeration and challenging recovery in liquid-catalysis application,stemming from their powdery *** macroscopic structures from pulverous MOF is thus of great importance for broadening their practical *** this study,three-dimensional porous MOF aerogel catalysts were successfully fabricated for degrading organic dyes by activating peroxymonosulfate(PMS).MOF/gelatin aerogel(MOF/GA)catalysts were prepared by directly integrating bimetallic FeCo-BDC with gelatin solutions,followed by freeze-drying and low-temperature *** FeCo-BDC-0.15/GA/PMS system exhibited remarkable performance in degrading various organic dyes,eliminating 99.2%of rhodamine B within a mere 5 *** to the GA/PMS system,there was over a 300-fold increase in the reaction rate ***,high removal efficiency was maintained across varying conditions,including different solution pH,co-existing inorganic anions,and natural water *** trapping experiments and electron paramagnetic resonance analysis revealed that the degradation involved radical(SO_(4)^(-)·)and non-radical routes(^(1)O_(2)),of which ^(1)O_(2) was ***,even after a continuous 400-min reaction in a fixed-bed reactor at a liquid hourly space velocity of 27 h^(-1),the FeCo-BDC/GA composite sustained a degradation efficiency exceeding 98.7%.This work presents highly active MOF-gelatin aerogels for dye degradation and expands the potential for their large-scale,continuous treatment application in organic dye wastewater management.

关键词： Catalyst Environment Wastewater Metal–organic framework Gelatin aerogel Peroxymonosulfate

Experimental Study of Molecular Fluctuation in the Living Cells

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Chinese Physics Letters 1996年第1期13卷 77-80页

作者： TANG xiao-wei LIU Jin-bo WU bi-chu Institute of High Energy Physics Academia Sinica.Beijing 100039 Department of Physics Beijing Polytechnic UniversityBeijing 100022

The velocity non-uniformity of the particle movement in the living cells is *** the concept of molecular fluctuation in the living cells,the phenomenon of the velocity non-uniformity is explained.A quantitative relati... 详细信息

关键词： movement Molecular uniformity

The Nonlinear Lopsided HSS-Like Modulus-Based Matrix Splitting Iteration Method for Linear Complementarity Problems with Positive-Definite Matrices

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Communications on Applied Mathematics and Computation 2021年第1期3卷 109-122页

作者： Lu Jia xiang Wang xiao-Yong xiao Department of Mathematics Nanchang UniversityNanchang 330031China Numerical Simulation and High-Performance Computing Laboratory Nanchang UniversityNanchang 330031China

In this paper,by means of constructing the linear complementarity problems into the corresponding absolute value equation,we raise an iteration method,called as the nonlinear lopsided HSS-like modulus-based matrix splitting iteration method,for solving the linear complementarity problems whose coefficient matrix in R^(n×n)is large sparse and positive *** the convergence analysis,it is appreciable to see that the proposed method will converge to its accurate solution under appropriate *** examples demonstrate that the presented method precede to other methods in practical implementation.

关键词： Linear complementarity problem Modulus-based matrix splitting Lopsided HSS

Distortion-aware beamforming design for multi-beam satellite communications with nonlinear power amplifiers

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Science China(Information Sciences) 2024年第6期67卷 359-369页

作者： xiang xiao Li YOU Kezhi WANG Xiqi GAO National Mobile Communications Research Laboratory Southeast University Purple Mountain Laboratories Department of Computer Science Brunel University London

Hardware components can cause different impairments, including power amplifier(PA) nonlinearities, which inevitably impact the system performance of satellite communications(SATCOM). In this work, we consider a multi-beam SATCOM downlink system and investigate the distortion-aware beamforming scheme with the characteristics of PA non-linearities. Notably, we aim to maximize the resource efficiency(RE), defined as the weighted sum of energy efficiency(EE) with spectral efficiency(SE), to obtain a flexible EE-SE tradeoff while accounting for the characteristics of PA distortion and the total power *** that the optimization objective is a sum of ratios and the high non-convexity involved in constraints,we propose an efficient approach that exploits the quadratic transformation, the Lagrange multiplier method,and the gradient ascent approach to handle this issue. Simulation results demonstrate the effectiveness of the distortion-aware beamforming approach in achieving the EE-SE tradeoff and exhibit a substantial RE performance gain over the conventional approach with ideal linear PAs assumed at the satellite transmitters.

关键词： multi-beam satellite communications nonlinear power amplifier energy and spectral efficiency tradeoff resource efficiency robust beamforming

Study on analytical noise propagation in convolutional neural network methods used in computed tomography imaging

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Nuclear Science and Techniques 2022年第6期33卷 114-127页

作者： xiao-Yue Guo Li Zhang Yu-xiang Xing Department of Engineering Physics Tsinghua UniversityBeijing 100084China Key Laboratory of Particle and Radiation Imaging Tsinghua UniversityBeijing 100084China

Neural network methods have recently emerged as a hot topic in computed tomography(CT) imaging owing to their powerful fitting ability;however, their potential applications still need to be carefully studied because their results are often difficult to interpret and are ambiguous in generalizability. Thus, quality assessments of the results obtained from a neural network are necessary to evaluate the neural network. Assessing the image quality of neural networks using traditional objective measurements is not appropriate because neural networks are nonstationary and nonlinear. In contrast, subjective assessments are trustworthy, although they are time-and energy-consuming for radiologists. Model observers that mimic subjective assessment require the mean and covariance of images, which are calculated from numerous image samples;however, this has not yet been applied to the evaluation of neural networks. In this study, we propose an analytical method for noise propagation from a single projection to efficiently evaluate convolutional neural networks(CNNs) in the CT imaging field. We propagate noise through nonlinear layers in a CNN using the Taylor expansion. Nesting of the linear and nonlinear layer noise propagation constitutes the covariance estimation of the CNN. A commonly used U-net structure is adopted for validation. The results reveal that the covariance estimation obtained from the proposed analytical method agrees well with that obtained from the image samples for different phantoms, noise levels, and activation functions, demonstrating that propagating noise from only a single projection is feasible for CNN methods in CT reconstruction. In addition, we use covariance estimation to provide three measurements for the qualitative and quantitative performance evaluation of U-net. The results indicate that the network cannot be applied to projections with high noise levels and possesses limitations in terms of efficiency for processing low-noise projections. U

关键词： Noise propagation Convolutional neural network Image quality assessment