摘要：
Heavy metal contamination in environment and food has attracted intensive attention from the public since it poses serious threats to ecological system and human health. Traditional detection methods for heavy metals such as atomic absorption spectrometry have a fairly low detection limit, but the methods have many limitations and disadvantages. Therefore, it is of significance to develop a rapid technology for real-time and online detection of heavy metals. The electrochemical aptasensor-based technology is promising in the detection of heavy metals with advantages of high sensitivity, specificity, and accuracy. Although its development is rapid, more researches should be carried out before this technology can be used for on-site detection. In this review, the origin, basic principles and development of electrochemical aptasensors are introduced. The applications of nanomaterials and electrochemical aptasensors for the detection of heavy metals (mainly mercury, lead, cadmium, and arsenic) are summarized. The research and application tendency of electrochemical aptasensors for detection of heavy metals are prospected.
摘要：
The European Journal of Migration and Law is a quarterly journal onmigration law and policy with specific emphasis on the European Union, theCouncil of Europe and migration activities within the Organisation forSecurity and Cooperation in Europe. This journal differs from othermigration journals by focusing on both the law and policy within the fieldof migration, as opposed to examining immigration and migration policiesfrom a wholly sociological perspective. This Journal is the initiative ofthe Centre for Migration Law of the University of Nijmegen, in co-operationwith the Brussels-based Migration Policy Group.The European Journal of Migration and Law provides an invaluable source ofinformation and a platform for discussion for government and publicofficials, academics, lawyers and NGOs interested in migration issues in theEuropean context. Devoted exclusively to migration law and policy, theoriginal research and analysis the Journal presents will emphasize thedevelopment of migration policies across Europe. Each issue will have across-disciplinary approach to migration and social issues such as access ofmigrants to social security and assistance benefits, including socio-legaland meta-juridical perspectives.This journal will be of inestimable value to people working on policy issuesand academics as well as lobbyists, NGOs and policy makers. The informationand articles will also be of interest to lawyers specialising in migrationlaw who wish to keep abreast of developments at the European level.Coverage in the Journals@Ovid database begins with the Volume 2, Issue 1, 2000 issue.
期刊：
CONCURRENCY AND COMPUTATION-PRACTICE & EXPERIENCE,2020年35(18):e6276- ISSN：1532-0626
通讯作者：
Yu, Lina;Li, Wenfa
作者机构：
[Yu, Lina; Li, WF; Ning, Xin; Li, Wenfa] Chinese Acad Sci, Inst Semicond, Beijing, Peoples R China.;[Ning, Xin; Xu, Shaohui; Zhang, Liping] Cognit Comp Technol Joint Lab, Wave Grp, Beijing, Peoples R China.;[Ning, Xin; Xu, Shaohui] Shenzhen Wave Kingdom Co Ltd, Shenzhen, Peoples R China.;[Wang, Xinran] Beijing Univ Posts & Telecommun, Beijing, Peoples R China.;[Cai, Weiwei] Cent South Univ Forestry & Technol, Sch Logist & Transportat, Changsha, Peoples R China.
通讯机构：
[Yu, LA; Li, WF] C;[Li, Wenfa] B;Chinese Acad Sci, Inst Semicond, Beijing, Peoples R China.;Beijing Union Univ, Coll Robot, Beijing, Peoples R China.
关键词：
co‐training algorithm;label confidence;machine learning;semi‐supervised learning;unlabeled data
摘要：
Co-training algorithm is one of the main methods of semi-supervised learning in machine learning, which explores the effective information in unlabeled data by multi-learner collaboration. Based on the development of co-training algorithm, the research work in recent years was further summarized in this article. In particular, three main steps of relevant co-training algorithms are introduced: view acquisition, learners' differentiation, and label confidence estimation. Finally, we summarized the problems existing in the current co-training methods, gave some suggestions for improvement, and looked forward to the future development direction of the co-training algorithm.
摘要：
Aiming at the problems of low efficiency and poor accuracy of traditional CAPTCHA recognition methods, we have proposed a more efficient way based on deep convolutional neural network (CNN). The Dense Convolutional Network (DenseNet) has shown excellent classification performance which adopts cross-layer connection. Not only it effectively alleviates the vanishing-gradient problem, but also dramatically reduce the number of parameters. However, it also has caused great memory consumption. So we improve and construct a new DenseNet for CAPTCHA recognition (DFCR). Firstly, we reduce the number of convolutional blocks and build corresponding classifiers for different types of CAPTCHA images. Secondly, we input the CAPTCHA images of TFrecords format into the DFCR for model training. Finally, we test the Chinese or English CAPTCHAs experimentally with different numbers of characters. Experiments show that the new network not only keeps the primary performance advantages of the DenseNets but also effectively reduces the memory consumption. Furthermore, the recognition accuracy of CAPTCHA with the background noise and character adhesion is above 99.9%.
摘要：
Mobile edge computing (MEC) is a promising technique to enhance computation capacity at the edge of mobile networks. The joint problem of partial offloading decision, offloading scheduling, and resource allocation for MEC systems is a challenging issue. In this paper, we investigate the joint problem of partial offloading scheduling and resource allocation for MEC systems with multiple independent tasks. A partial offloading scheduling and power allocation (POSP) problem in single-user MEC systems is formulated. The goal is to minimize the weighted sum of the execution delay and energy consumption while guaranteeing the transmission power constraint of the tasks. The execution delay of tasks running at both MEC and mobile device is considered. The energy consumption of both the task computing and task data transmission is considered as well. The formulated problem is a nonconvex mixed-integer optimization problem. In order to solve the formulated problem, we propose a two-level alternation method framework based on Lagrangian dual decomposition. The task offloading decision and offloading scheduling problem, given the allocated transmission power, is solved in the upper level using flow shop scheduling theory or greedy strategy, and the suboptimal power allocation with the partial offloading decision is obtained in the lower level using convex optimization techniques. We propose iterative algorithms for the joint problem of POSP. Numerical results demonstrate that the proposed algorithms achieve near-optimal delay performance with a large energy consumption reduction.
摘要：
Energy harvesting (EH) from ambient energy sources can potentially reduce the dependence on the supply of grid or battery energy, providing many benefits to green communications. In this paper, we investigate the device-to-device (D2D) user equipments (DUEs) multiplexing cellular user equipments (CUEs) downlink spectrum resources problem for EH-based D2D communication heterogeneous networks (EH-DHNs). Our goal is to maximize the average energy efficiency of all D2D links, in the case of guaranteeing the quality of service of CUEs and the EH constraints of the D2D links. The resource allocation problems contain the EH time slot allocation of DUEs, power and spectrum resource block (RB) allocation. In order to tackle these issues, we formulate an average energy efficiency problem in EH-DHNs, taking into consideration EH time slot allocation, power and spectrum RB allocation for the D2D links, which is a nonconvex problem. Furthermore, we transform the original problem into a tractable convex optimization problem. We propose joint the EH time slot allocation, power and spectrum RB allocation iterative algorithm based on the Dinkelbach and Lagrangian constrained optimization. Numerical results demonstrate that the proposed iterative algorithm achieves higher energy efficiency for different network parameters settings.
作者机构：
[Huang, Lihong; Wang, Jiafu; Wang, JF; Huang, LH; Huang, Chuangxia] Changsha Univ Sci & Technol, Sch Math & Stat, Changsha 410114, Hunan, Peoples R China.;[Wang, Jiafu] Cent South Univ Forestry & Technol, Inst Math & Phys, Changsha 410004, Hunan, Peoples R China.
通讯机构：
[Wang, JF; Huang, LH] C;Changsha Univ Sci & Technol, Sch Math & Stat, Changsha 410114, Hunan, Peoples R China.
关键词：
Planar piecewise linear system;Limit cycle;Lienard-like canonical form;Stability;Discontinuity
摘要：
The aim of this paper is to deal with the problem of limit cycles for a general planar piecewise linear differential system of saddle-focus type. By using the Lienard-like canonical form with five parameters and dividing the total parameter space into several regions, the number of limit cycles is discussed in detail. In particular, we give parameter regions where there are at least two limit cycles. Moreover, we investigate the existence and stability of exactly two nested limit cycles in some parameter regions. (c) 2019 Elsevier Ltd. All rights reserved.
期刊：
International Journal of Molecular Sciences,2019年20(3) ISSN：1422-0067
通讯作者：
Huang, Li-Jun
作者机构：
[Li, Ning; Huang, Li-Jun; Yuan, Deyi] Cent South Univ Forestry & Technol, Minist Educ, State Key Lab Cultivat & Protect Nonwood Forest T, Changsha 410004, Hunan, Peoples R China.;[Han, Xiao; Feng, Dan] Fuzhou Univ, Coll Biol Sci & Engn, Fuzhou 350116, Fujian, Peoples R China.;[Han, Xiao; Feng, Dan] Chinese Acad Agr Sci, Biotechnol Res Inst, Beijing 100081, Peoples R China.
通讯机构：
[Huang, Li-Jun] C;Cent South Univ Forestry & Technol, Minist Educ, State Key Lab Cultivat & Protect Nonwood Forest T, Changsha 410004, Hunan, Peoples R China.
关键词：
hormones;plant defense;signaling pathway
摘要：
During their lifetime, plants encounter numerous biotic and abiotic stresses with diverse modes of attack. Phytohormones, including salicylic acid (SA), ethylene (ET), jasmonate (JA), abscisic acid (ABA), auxin (AUX), brassinosteroid (BR), gibberellic acid (GA), cytokinin (CK) and the recently identified strigolactones (SLs), orchestrate effective defense responses by activating defense gene expression. Genetic analysis of the model plant Arabidopsis thaliana has advanced our understanding of the function of these hormones. The SA- and ET/JA-mediated signaling pathways were thought to be the backbone of plant immune responses against biotic invaders, whereas ABA, auxin, BR, GA, CK and SL were considered to be involved in the plant immune response through modulating the SA-ET/JA signaling pathways. In general, the SA-mediated defense response plays a central role in local and systemic-acquired resistance (SAR) against biotrophic pathogens, such as Pseudomonas syringae, which colonize between the host cells by producing nutrient-absorbing structures while keeping the host alive. The ET/JA-mediated response contributes to the defense against necrotrophic pathogens, such as Botrytis cinerea, which invade and kill hosts to extract their nutrients. Increasing evidence indicates that the SA- and ET/JA-mediated defense response pathways are mutually antagonistic.
期刊：
Journal of Mathematical Analysis and Applications,2019年469(1):405-427 ISSN：0022-247X
通讯作者：
Wang, Jiafu
作者机构：
[Huang, Lihong; Wang, Jiafu] Changsha Univ Sci & Technol, Sch Math & Stat, Changsha 410114, Hunan, Peoples R China.;[Chen, Xiaoyan] Cent South Univ Forestry & Technol, Inst Math & Phys, Changsha 410004, Hunan, Peoples R China.
通讯机构：
[Wang, Jiafu] C;Changsha Univ Sci & Technol, Sch Math & Stat, Changsha 410114, Hunan, Peoples R China.
关键词：
Limit cycle;Poincare-Bendixon theorem;Stability;Piecewise linear differential systems
摘要：
The objective of this paper is to study the number and stability of limit cycles for planar piecewise linear (PWL) systems of node-saddle type with two linear regions. Firstly, we give a thorough analysis of limit cycles for Lienard PWL systems of this type, proving one is the maximum number of limit cycles and obtaining necessary and sufficient conditions for the existence and stability of a unique limit cycle. These conditions can be easily verified directly according to the parameters in the systems, and play an important role in giving birth to two limit cycles for general PWL systems. In this step, the tool of a Bendixon-like theorem is successfully employed to derive the existence of a limit cycle. Secondly, making use of the results gained in the first step, we obtain parameter regions where the general PWL systems have at least one, at least two and no limit cycles respectively. In addition for the general PWL systems, some sufficient conditions are presented for the existence and stability of a unique one and exactly two limit cycles respectively. Finally, some numerical examples are given to illustrate the results and especially to show the existence and stability of two nested limit cycles. (C) 2018 Elsevier Inc. All rights reserved.
摘要：
The red coloration of pear (Pyrus pyrifolia) results from anthocyanin accumulation in the fruit peel. Light is required for anthocyanin biosynthesis in pear. A pear homolog of Arabidopsis thaliana BBX22, PpBBX16, was differentially expressed after fruits were removed from bags and may be involved in anthocyanin biosynthesis. Here, the expression and function of PpBBX16 were analysed. PpBBX16's expression was highly induced by white-light irradiation, as was anthocyanin accumulation. PpBBX16's ectopic expression in Arabidopsis increased anthocyanin biosynthesis in the hypocotyls and tops of flower stalks. PpBBX16 was localized in the nucleus and showed trans-activity in yeast cells. Although PpBBX16 could not directly bind to the promoter of PpMYB10 or PpCHS in yeast one-hybrid assays, the complex of PpBBX16/PpHY5 strongly trans-activated anthocyanin pathway genes in tobacco. PpBBX16's overexpression in pear calli enhanced the red coloration during light treatments. Additionally, PpBBX16's transient overexpression in pear peel increased anthocyanin accumulation, while virus-induced gene silencing of PpBBX16 decreased anthocyanin accumulation. The expression patterns of pear BBX family members were analysed, and six additional BBX genes, which were differentially expressed during light-induced anthocyanin biosynthesis, were identified. Thus, PpBBX16 is a positive regulator of light-induced anthocyanin accumulation, but it could not directly induce the expression of the anthocyanin biosynthesis-related genes by itself but needed PpHY5 to gain full function. Our work uncovered regulatory modes for PpBBX16 and suggested the potential functions of other pear BBX genes in the regulation of anthocyanin accumulation, thereby providing target genes for further studies on anthocyanin biosynthesis.
摘要：
Iron-based magnetic materials are deemed to be promising catalysts for various catalytic reactions and can be recovered conveniently by an external magnetic field. MnFe2O4 nanoparticle and MnFe2O4/biochar composite with different bio-char contents were prepared to activate hydrogen peroxide for the degradation of tetracycline (TC). The catalysts were characterized by SEM, BET, XRD, FTIR, VSM and XPS. The results indicated that MnFe2O4 had a spherical shape and was successfully loaded onto the surface of bio-char. The introduction of bio-char effectively suppressed the aggregation of MnFe2O4 and drastically increased the specific surface area. Both MnFe2O4 and MnFe2O4/bio-char composite can be separated easily by an external magnetic field. Using 1:2 composite as heterogeneous photo-Fenton catalyst obtained a degradation of 95% through visible light irradiation of 40 mg L-1 solution at natural pH (pH = 5.5) in the presence of 100 mmol L-1 H2O2 for 2 h. Free radical quenching experiment and the ESR results confirm that hydroxyl radicals play the main role for TC degradation. XPS measurements show that both Fe and Mn ions simultaneously participate in the activation of H2O2. The bio-char not only restrains the aggregation of MnFe2O4 leading to the improved removal efficiency of TC, but also has side effects by consuming hydroxyl radicals. By cyclic degradation experiments, the performance of MnFe2O4/bio-char composite is stable and almost unchanged, and the leaching metal ions of both Fe and Mn are neglectful (both below 0.2 mg L-1). Besides, steady performance of MnFe2O4/bio-char catalyst to remove TC from tap water and river water has been certified. Published by Elsevier Ltd.
