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An online maximum power point capturing technique for highefficiency power generation of solar photovoltaic systems 预览
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作者 Lijun ZHANG Samson Shenglong YU +2 位作者 Tyrone FERNANDO Herbert Ho-Ching IU Kit Po WONG 《现代电力系统与清洁能源学报(英文)》 CSCD 2019年第2期357-368,共12页
This paper proposes a novel high-efficiency generation technique for photovoltaic(PV) system,named maximum power point capturing(MPPC) technique. This is an aperiodic perturbation MPPC technique compared to the conven... This paper proposes a novel high-efficiency generation technique for photovoltaic(PV) system,named maximum power point capturing(MPPC) technique. This is an aperiodic perturbation MPPC technique compared to the conventional periodic perturbation maximum power point tracking technique. Firstly, under a closed-loop circuit and an open-loop circuit,the complete I-V curves and P-V curves are defined. Secondly, the proposed MPPC technique is based on the complete I-V curves and a practical model of solar PV systems.The proposed method realizes that maximum power point(MPP) is captured online, and its control strategy is designed to set a steady operating area around MPP. The duty cycle keeps constant when the operating point is within the steady operating area, i.e., aperiodic perturbation, and when the operating point is outside the steady operating area, MPPC is triggered to capture a new MPP with an updated steady operating area. Simulation results demonstrate that no oscillations exist in steady-state;dynamic performances are improved;and only two perturbations are required to capture the new MPP. Using the proposed MPPC method,low voltage ride through and high voltage ride through can be prevented. 展开更多
关键词 PHOTOVOLTAIC systems MAXIMUM POWER POINT tracking(MPPT) MAXIMUM POWER POINT capturing(MPPC) Complete I–V CURVES
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High-order phase-field model with the local and second-order max-entropy approximants
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作者 Fatemeh AMIRI 《结构与土木工程前沿:英文版》 EI CSCD 2019年第2期406-416,共11页
We approximate the fracture surface energy functional based on phase-field method with smooth local maximum entropy (LME) and second-order maximum entropy (SME) approximants. The higher-order continuity of the meshfre... We approximate the fracture surface energy functional based on phase-field method with smooth local maximum entropy (LME) and second-order maximum entropy (SME) approximants. The higher-order continuity of the meshfree methods such as LME and SME approximants allows to directly solve the fourth-order phase-field equations without splitting the fourth?ordcr differential equation into two second-order differential equations. We will first show that the crack surface functional can be captured more accurately in the fourth-order model with smooth approximants such as LME, SME and B-spline. Furthermore, smaller length scale parameter is needed for the fourth-order model to approximate the energy functional. We also study SME approximants and drive the formulations. The proposed meshfree fourth-order phase-field formulation show more stable results tor SME compared to LME meshfree methods. 展开更多
关键词 SECOND-ORDER MAXIMUM ENTROPY LOCAL MAXIMUM ENTROPY second-and fourth-order PHASE-FIELD models B-spline
Local scour around two side-by-side cylindrical bridge piers under ice-covered conditions 预览
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作者 Mohammad reza Namaee Jueyi Sui 《国际泥沙研究:英文版》 SCIE 2019年第4期355-367,共13页
In the current study, 108 flume experiments with non-uniform, cohesionless sediments have been done to investigate the local scour process around four pairs of side-by-side bridge piers under both open channel and ice... In the current study, 108 flume experiments with non-uniform, cohesionless sediments have been done to investigate the local scour process around four pairs of side-by-side bridge piers under both open channel and ice-covered flow conditions. Similar to local scour around bridge piers under open channel conditions and a single bridge pier, it was observed in the experiments that the maximum scour depth always occurred at the upstream face of the pier under ice-covered conditions. Further, the smaller the pier size and the greater the spacing distance between the bridge piers, the weaker the horseshoe vortices around the bridge piers, and, thus, the shallower the scour holes around them. Finally, empirical equations were developed to estimate the maximum scour depth around two side-by-side bridge piers under both open channel and ice-covered flow conditions. 展开更多
关键词 Bridge PIER Local SCOUR Maximum SCOUR DEPTH NON-UNIFORM sediment ROUGHNESS of COVER SCOUR pattern
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Maximum Force of Inclined Pullout of A Torpedo Anchor in Cohesive Beds 预览
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作者 WANG Cheng CHEN Xiao-hui YU Guo-liang 《中国海洋工程:英文版》 SCIE EI CSCD 2019年第3期333-343,共11页
Torpedo anchors have been used in mooring systems for deep-water oil and gas projects owing to their prominent advantages, such as low cost and easy installation. The maximum force of torpedo anchors is crucial not on... Torpedo anchors have been used in mooring systems for deep-water oil and gas projects owing to their prominent advantages, such as low cost and easy installation. The maximum force of torpedo anchors is crucial not only to the safety and stability of vessels and other marine facilities, but also for an economical design. It is necessary to develop reliable formula for fast predicting their maximum inclined force of a torpedo anchor in cohesive beds. In this study, the maximum inclined force of a torpedo anchor vertically embedded in cohesive beds was extensively investigated. 316 sets of inclined pullout laboratory tests were carried out for 9 differently shaped torpedo anchors which were vertically embedded in different cohesive beds. The loading curves were automatically acquisitioned and their characteristics were analyzed. The load angle relative to the horizontal varied from 20° to 90°. A new formula for fast calculating the maximum inclined force of the torpedo anchor vertically embedded in cohesive beds was obtained based on force analysis and a nonlinear regression on the data from the present and other studies. Effect aspects on the tests are discussed and further studies are highlighted. 展开更多
关键词 TORPEDO ANCHOR MAXIMUM inclined FORCE COHESIVE bed load angle EMBEDMENT depth
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Powertrain control of a solar photovoltaic-battery powered hybrid electric vehicle
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作者 P.PADMAGIRISAN V.SANKARANARAYANAN 《能源前沿:英文版》 CSCD 2019年第2期296-306,共11页
This paper proposes a powertrain controller for a solar photovoltaic battery powered hybrid electric vehicle (HEV). The main objective of the proposed controller is to ensure better battery management, load regulation... This paper proposes a powertrain controller for a solar photovoltaic battery powered hybrid electric vehicle (HEV). The main objective of the proposed controller is to ensure better battery management, load regulation, and maximum power extraction whenever possible from the photovoltaic panels. The powertrain controller consists of two levels of controllers named lower level controllers and a high-level control algorithm. The lower level controllers are designed to perform individual tasks such as maximum power point tracking, battery charging, and load regulation. The perturb and observe based maximum power point tracking algorithm is used for extracting maximum power from solar photovoltaic panels while the battery charging controller is designed using a PI controller. A high-level control algorithm is then designed to switch between the lower level controllers based on different operating conditions such as high state of charge, low state of charge, maximum battery current, and heavy load by respecting the constraints formulated. The developed algorithm is evaluated using theoretical simula-tion and experimental studies. The simulation and experimental results are presented to validate the proposed technique. 展开更多
关键词 BATTERY management system hybrid electric vehicles (HEVs) MAXIMUM power point TRACKING (MPPT) solar PHOTOVOLTAIC
Constrained maximum weighted bipartite matching:a novel approach to radio broadcast scheduling
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作者 Shaojiang WANG Tianyong WU +2 位作者 Yuan YAO Dongbo BU Shaowei CAI 《中国科学:信息科学(英文版)》 SCIE EI CSCD 2019年第7期156-169,共14页
Given a set of radio broadcast programs, the radio broadcast scheduling problem is to allocate a set of devices to transmit the programs to achieve the optimal sound quality. In this article, we propose a complete alg... Given a set of radio broadcast programs, the radio broadcast scheduling problem is to allocate a set of devices to transmit the programs to achieve the optimal sound quality. In this article, we propose a complete algorithm to solve the problem, which is based on a branch-and-bound(BnB) algorithm. We formulate the problem with a new model, called constrained maximum weighted bipartite matching(CMBM),i.e., the maximum matching problem on a weighted bipartite graph with constraints. For the reduced matching problem, we propose a novel BnB algorithm by introducing three new strategies, including the highest quality first, the least conflict first and the more edge first. We also establish an upper bound estimating function for pruning the search space of the algorithm. The experimental results show that our new algorithm can quickly find the optimal solution for the radio broadcast scheduling problem at small scales, and has higher scalability for the problems at large scales than the existing complete algorithm. 展开更多
关键词 RADIO broadcast scheduling BRANCH-AND-BOUND ALGORITHM CONSTRAINED MAXIMUM WEIGHTED bipartite matching Kuhn-Munkres ALGORITHM strategy combinations
A maximum margin clustering algorithm based on indefinite kernels
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作者 Hui XUE Sen LI +1 位作者 Xiaohong CHEN Yunyun WANG 《中国计算机科学前沿:英文版》 SCIE EI CSCD 2019年第4期813-827,共15页
Indefinite kernels have attracted more and more attentions in machine learning due to its wider application scope than usual positive definite kernels. However, the research about indefinite kernel clustering is relat... Indefinite kernels have attracted more and more attentions in machine learning due to its wider application scope than usual positive definite kernels. However, the research about indefinite kernel clustering is relatively scarce. Furthermore, existing clustering methods are mainly designed based on positive definite kernels which are incapable in indefinite kernel scenarios. In this paper, we propose a novel indefinite kernel clustering algorithm termed as indefinite kernel maximum margin clustering (IKMMC) based on the state-of-the-art maximum margin clustering (MMC) model. IKMMC tries to find a proxy positive definite kernel to approximate the original indefinite one and thus embeds a new F-norm regularizer in the objective function to measure the diversity of the two kernels, which can be further optimized by an iterative approach. Concretely, at each iteration, given a set of initial class labels, IKMMC firstly transforms the clustering problem into a classification one solved by indefinite kernel support vector machine (IKSVM) with an extra class balance constraint and then the obtained prediction labels will be used as the new input class labels at next iteration until the error rate of prediction is smaller than a prespecified tolerance. Finally, IKMMC utilizes the prediction labels at the last iteration as the expected indices of clusters.Moreover, we further extend IKMMC from binary clustering problems to more complex multi-class scenarios. Experimental results have shown the superiority of our algorithms. 展开更多
关键词 INDEFINITE KERNEL MAXIMUM MARGIN CLUSTERING support vector machine KERNEL method
A Note on Strong Edge Coloring of Sparse Graphs
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作者 Wei DONG Rui LI Bao Gang XU 《数学学报:英文版》 SCIE CSCD 2019年第4期577-582,共6页
A strong edge coloring of a graph is a proper edge coloring where the edges at distance at most 2 receive distinct colors. The strong chromatic index χs^′(G) of a graph G is the minimum number of colors used in a st... A strong edge coloring of a graph is a proper edge coloring where the edges at distance at most 2 receive distinct colors. The strong chromatic index χs^′(G) of a graph G is the minimum number of colors used in a strong edge coloring of G. In an ordering Q of the vertices of G, the back degree of a vertex x of G in Q is the number of vertices adjacent to x, each of which has smaller index than x in Q. Let G be a graph of maximum degree Δ and maximum average degree at most 2 k. Yang and Zhu [J. Graph Theory, 83, 334–339(2016)] presented an algorithm that produces an ordering of the edges of G in which each edge has back degree at most 4 kΔ-2 k in the square of the line graph of G, implying that χs^′(G)≤ 4 kΔ-2 k + 1. In this note, we improve the algorithm of Yang and Zhu by introducing a new procedure dealing with local structures. Our algorithm generates an ordering of the edges of G in which each edge has back degree at most(4 k-1)Δ-2 k in the square of the line graph of G, implying that χs^′(G)≤(4 k-1)Δ-2 k + 1. 展开更多
关键词 STRONG edge COLORING maximum AVERAGE degree SPARSE GRAPH
Vegetation pattern of Northeast China during the special periods since the Last Glacial Maximum
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作者 Xiaoqiang LI Chao ZHAO Xinying ZHOU 《中国科学:地球科学英文版》 SCIE EI CAS CSCD 2019年第8期1224-1240,共17页
Since the Last Glacial Maximum(LGM), the global climate has experienced several stages, such as cold and warming events, which provide an ideal model for evaluating climate change in the future. Based on the pollen re... Since the Last Glacial Maximum(LGM), the global climate has experienced several stages, such as cold and warming events, which provide an ideal model for evaluating climate change in the future. Based on the pollen records in Northeast(NE) China, the vegetation pattern during special periods since the LGM was reconstructed in this work. During the LGM(approximately 18,000 cal yr BP), the steppes expanded rapidly in NE China, and a cold-dry meadow-steppe developed on the Songnen Plain. The Liaohe Plain and the Hulun Buir Plateau were occupied by a steppe-desert, with forest-steppe vegetation grown in the central and southern plains;there were cold-dry coniferous forests and mixed conifer-broadleaf forests in mountainous areas. In the early Holocene(10,000–9,000 cal yr BP), Changbai mountain(CBM) forests thrived in the eastern hilly area and the Sanjiang Plain, while the central region was dominated by steppes, and warm-temperate broadleaf forests developed northward. During the Holocene warm period(approximately 6,000 cal yr BP), CBM forests and cold-temperate coniferous forests developed in the north, while spruce-fir forests developed in the eastern Xiao Hinggan Mountains and the Sanjiang Plain. The distribution centre of deciduous broadleaf forests migrated to the south of the Changbai Mountains and the Liaodong Peninsula. The isolated woodlands increased on the Songnen Plain and the meadow-steppes expanded to the Liaohe Plain. Therefore, the increase in temperature leads to the increase of monsoon precipitation in NE China, which is beneficial to the development of warm-temperate forest vegetation. The increase of summer monsoons and precipitation caused by climate warming may be the main reason for the improved plant load. 展开更多
关键词 Last GLACIAL Maximum HOLOCENE WARM period Vegetation pattern NORTHEAST China
A multi-model analysis of glacier equilibrium line altitudes in western China during the last glacial maximum
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作者 Dabang JIANG Yeyi LIU Xianmei LANG 《中国科学:地球科学英文版》 SCIE EI CAS CSCD 2019年第8期1241-1255,共15页
Based on numerical experiments undertaken with nine climate models, the glacier equilibrium line altitudes(ELAs)in western China during the last glacial maximum(LGM) are investigated to deepen our understanding of the... Based on numerical experiments undertaken with nine climate models, the glacier equilibrium line altitudes(ELAs)in western China during the last glacial maximum(LGM) are investigated to deepen our understanding of the surface environment on the Tibetan Plateau. Relative to the preindustrial period, the summer surface air temperatures decrease by 4–8°C while the annual precipitation decreases by an average of 25% across the Tibetan Plateau during the LGM. Under the joint effects of reductions in summer temperature and annual precipitation, the LGM ELAs in western China are lowered by magnitudes that vary with regions. The ELAs in the southern margin and northwestern Tibetan Plateau decline by approximately 1100 m;the central hinterland, by 650–800 m;and the eastern part, by 550–800 m, with a downward trend from southwest to northeast. The reduction in ELAs is no more than 650 m in the Tian Shan Mountains within China and approximately 500–600 m in the Qilian Mountains and Altai Mountains. The high-resolution models to reproduce the low values of no more than 500 m in ELA reductions in the central Tibetan Plateau, which are consistent with the proxy records from glacier remains. The accumulation zones of the Tibetan Plateau glaciers are mainly located in the marginal mountains during the LGM and have areas 2–5 times larger than those of the modern glaciers but still do not reach the central part. 展开更多
关键词 Last GLACIAL maximum Western China EQUILIBRIUM line ALTITUDES GLACIER Simulation
Spatiotemporal evolution of C3/C4 vegetation and its controlling factors in southern China since the last glacial maximum
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作者 Linlin CUI Jianfang HU Xu WANG 《中国科学:地球科学英文版》 SCIE EI CAS CSCD 2019年第8期1256-1268,共13页
To date, few research have been reported on the evolution of C3/C4 vegetation in southern China, and the main mechanism influencing the evolution of C3/C4 vegetation is unclear. That makes it difficult for researchers... To date, few research have been reported on the evolution of C3/C4 vegetation in southern China, and the main mechanism influencing the evolution of C3/C4 vegetation is unclear. That makes it difficult for researchers to understand the competition mechanism of C3 and C4 plants under different climate environments and its relationship with the climate factors. It is also not conducive for researchers to assess the influence of future climate change on regional C3/C4 vegetation. Exactly, C3/C4 vegetation change in the regional-scale will have a significant impact on the global carbon cycle and agricultural production.Therefore, it is especially important to reconstruct the evolutionary history of C3/C4 vegetation in southern China and clarify the influencing mechanism of climate change. In this study, we systematically analyzed stable carbon isotope(δ13 C) of the longchain n-alkanes in sediment samples from eight lakes and four peat profiles in southern China, to reconstruct the spatiotemporal evolution of C3/C4 vegetation in these regions since the Last Glacial Maximum(LGM) and to investigate the climate factors that affect the C4 plant abundance change in the research area. The integrated long-chain n-alkane(C27–C33) stable carbon isotope results of samples from Zhanjiang Huguangyan Maar Lake, Xingyun Lake, Lugu Lake and Dingnan peat showed that, from the LGM to the Early Holocene, C4 plant relative abundance exhibited a gradually increasing trend from 21% to 34%. In the Middle Holocene, the C4 plant abundance significantly declined and reached a lowest value of 10%. In space, the C4 plant abundance generally exhibited a gradually declining trend from south to north in the LGM and the Early Holocene, while it showed an opposite trend in the Holocene Climate Optimum(6.0 cal ka BP). It reflected that the main influencing factor on C4 plants spatial distribution was changing from temperature to precipitation. This study indicated that temperature was the dominant factor affecting C4 plant distribution in southern 展开更多
关键词 Stable carbon isotope LONG-CHAIN N-ALKANES C3/C4vegetation Last GLACIAL Maximum HOLOCENE Climate Optimum period
Spatial patterns of vegetation and climate in the North China Plain during the Last Glacial Maximum and Holocene climatic optimum
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作者 Manyue LI Shengrui ZHANG +2 位作者 Qinghai XU Jule XIAO Ruilin WEN 《中国科学:地球科学英文版》 SCIE EI CAS CSCD 2019年第8期1279-1287,共9页
Reconstructing the spatial patterns of regional climate and vegetation during specific intervals in the past is important for assessing the possible responses of the ecological environment under future global warming ... Reconstructing the spatial patterns of regional climate and vegetation during specific intervals in the past is important for assessing the possible responses of the ecological environment under future global warming scenarios. In this study, we reconstructed the history of regional vegetation and climate based on six radiocarbon-dated pollen records from the North China Plain. Combining the results with existing pollen records, we reconstruct the paleoenvironment of the North China Plain during the Last Glacial Maximum(LGM) and the Holocene Climatic Optimum(HCO). The results show that changes in the regional vegetation since the LGM were primarily determined by climatic conditions, the geomorphic landscape and by human activity.During the LGM, the climate was cold and dry;mixed broadleaf-coniferous forest and deciduous-evergreen broadleaf forest developed in the southern mountains, and cold-resistant coniferous forest and mixed broadleaf-coniferous forest were present in the northern mountains. The forest cover was relatively low, with mesophytic and hygrophilous meadow occupying the southern part of the plain, and temperate grassland and desert steppe were distributed in the north;Chenopodiaceae-dominated halophytes grew on the exposed continental shelf of the Bohai Sea and Yellow Sea. During the HCO, the climate was warm and wet;deciduous broadleaf forest and deciduous-evergreen broadleaf forest, with subtropical species, developed in the southern mountains, and deciduous broadleaf forest with thermophilic species was present in northern mountains. Although the degree of forest cover was greater than during the LGM, the vegetation of the plain area was still dominated by herbs, while halophytes had migrated inland due to sea level rise. In addition, the expansion of human activities, especially the intensification of cultivation,had a significant influence on the natural vegetation. Our results provide data and a scientific basis for paleoclimate modelling and regional carbon cycle assessment in north China, w 展开更多
关键词 North China Plain Last GLACIAL Maximum HOLOCENE Climatic OPTIMUM POLLEN VEGETATION PALEOENVIRONMENT
Age factor affects reading acuity and reading speed in attaining text information
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作者 Ai-Hong Chen Nursyairah Mohd Khalid Noor Halilah Buari 《国际眼科杂志:英文版》 SCIE CAS 2019年第7期1170-1176,共7页
AIM: To investigate the effect of age on reading acuity and reading speed in attaining text information in healthy eyes.METHODS: Reading acuity, critical print size, reading speed and maximum reading speed were measur... AIM: To investigate the effect of age on reading acuity and reading speed in attaining text information in healthy eyes.METHODS: Reading acuity, critical print size, reading speed and maximum reading speed were measured in groups of 40 children (8 to 12 years old), 40 teenagers (13 to 19 years old), 40 young adults (20 to 39 years old), and 40 adults (40 years old and above) using the Buari-Chen Malay Reading Chart [contextual sentences (CS) set and random words (RW) set] in a cross-sectional study design.RESULTS: Reading acuity was significantly improved by 0.04 logMAR for both CS set and RW set from children to teenagers, then gradually worsened from young adults to adults (CS set: 0.06 logMAR;RW set: 0.08 logMAR). Critical print size for children showed a significant improvement in teenagers (CS set: 0.14 logMAR;RW set: 0.07 logMAR), then deteriorated from young adults to adults by 0.09 logMAR only for CS set. Reading speed significantly increased from children to teenagers,[CS set: 46.20 words per minute (wpm);RW set: 42.06 wpm], then stabilized from teenagers to young adults, and significantly reduced from young adults to adults (CS set: 28.58 wpm;RW set: 24.44 wpm). Increment and decrement in maximum reading speed measurement were revealed from children to teenagers (CS set: 39.38 wpm;RW set: 43.38 wpm) and from young adults to adults (CS set: 22.26 wpm;RW set: 26.31 wpm) respectively.CONCLUSION: The reference of age-related findings in term of acuity and speed of reading should be incorporated in clinical practice to enhance reading assessment among healthy eyes population. 展开更多
关键词 READING ACUITY critical PRINT size readingspeed MAXIMUM READING SPEED age effect
The exponentiated generalized power Lindley distribution: Properties and applications 预览
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作者 S.M.T.K. MirMostafaee Morad Alizadeh +1 位作者 Emrah Altun Saralees Nadarajah 《高校应用数学学报:英文版(B辑)》 SCIE CSCD 2019年第2期127-148,共22页
In this paper, we introduce a new extension of the power Lindley distribution, called the exponentiated generalized power Lindley distribution. Several mathematical properties of the new model such as the shapes of th... In this paper, we introduce a new extension of the power Lindley distribution, called the exponentiated generalized power Lindley distribution. Several mathematical properties of the new model such as the shapes of the density and hazard rate functions, the quantile function, moments, mean deviations, Bonferroni and Lorenz curves and order statistics are derived. Moreover, we discuss the parameter estimation of the new distribution using the maximum likelihood and diagonally weighted least squares methods. A simulation study is performed to evaluate the estimators. We use two real data sets to illustrate the applicability of the new model. Empirical findings show that the proposed model provides better fits than some other well-known extensions of Lindley distributions. 展开更多
关键词 Anderson-Darling test statistic Exponentiated GENERALIZED class of DISTRIBUTIONS Lambert function Maximum LIKELIHOOD method POWER Lindley DISTRIBUTION
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Hypothesis Testing with Paired Partly Interval Censored Data
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作者 Ding-jiao CAI Bo LU Xing-wei TONG 《应用数学学报:英文版》 SCIE CSCD 2019年第3期541-548,共8页
Partly interval censored data frequently occur in many areas including clinical trials,epidemiology research,and medical follow-up studies.When data come from observational studies,we need to carefully adjust for the ... Partly interval censored data frequently occur in many areas including clinical trials,epidemiology research,and medical follow-up studies.When data come from observational studies,we need to carefully adjust for the confounding bias in order to estimate the true treatment effect.Pair matching designs are popular for removing confounding bias without parametric assumptions.With time-to-event outcomes,there are some literature for hypothesis testing with paired right censored data,but not for interval censored data.O’Brien and Fleming extended the Prentice Wilcoxon test to right censored paired data by making use of the PrenticeWilcoxon scores.Akritas proposed the Akritas test and established its asymptotic properties.We extend Akritas test to partly interval censored data.We estimate the survival distribution function by nonparametric maximum likelihood estimation(NPMLE),and prove the asymptotic validity of the new test.To improve our test under small sample size or extreme distributions,we also propose a modified version using the rank of the score difference.Simulation results indicate that our proposed methods have very good performance. 展开更多
关键词 partly INTERVAL censored data NONPARAMETRIC MAXIMUM LIKELIHOOD estimation Wilcoxon SIGNED RANK test
The East Asian Monsoon since the Last Glacial Maximum:Evidence from geological records in northern China
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作者 Shiling YANG Xinxin DONG Jule XIAO 《中国科学:地球科学英文版》 SCIE EI CAS CSCD 2019年第8期1181-1192,共12页
The impact of global warming on the climate of northern China has been investigated intensively, and the behavior of the East Asian monsoon during previous intervals of climatic warming may provide insight into future... The impact of global warming on the climate of northern China has been investigated intensively, and the behavior of the East Asian monsoon during previous intervals of climatic warming may provide insight into future changes. In this study, we use paleovegetation records from loess and lake sediments in the marginal zone of the East Asian summer monsoon(EASM) to reconstruct the EASM during the interval of warming from the Last Glacial Maximum(LGM) to the Holocene. The results show that during the LGM, desert steppe or dry steppe dominated much of northern China;in addition, the southeastern margin of the deserts east of the Helan Mountains had a distribution similar to that of the present-day, or was located slightly further south, due to the cold and dry climate caused by a strengthened East Asian winter monsoon(EAWM) and weakened EASM. During the last deglaciation, with the strengthening of the EASM and concomitant weakening of the EAWM, northern China gradually became humid. However, this trend was interrupted by abrupt cooling during the Heinrich 1(H1) and Younger Dryas(YD) events. The EASM intensified substantially during the Holocene, and the monsoon rain belt migrated at least 300 km northwestwards, which led to the substantial shrinking of the desert area in the central and eastern part of northern China, and to the large expansion of plants favored by warm and humid conditions. Paleoclimatic records from the marginal zone of the EASM all show that the EASM reached its peak in the mid-Holocene, and past global climatic warming significantly strengthened the EASM, thereby greatly improving the ecological environment in northern China. Thus, northern China is expected to become wetter as global warming continues. Finally, high resolution Holocene vegetation records are sparse compared with the numerous records on the orbital timescale, and there is a need for more studies of Holocene climatic variability on the centennial-to-decadal scale. 展开更多
关键词 East Asian MONSOON Last GLACIAL Maximum HOLOCENE PALEOVEGETATION Global warming
Mask-based denoising scheme for ghost imaging
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作者 周阳 郭树旭 +1 位作者 钟菲 张天 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第8期148-155,共8页
Ghost imaging(GI)is thought of as a promising imaging method in many areas.However,the main drawback of GI is the huge measurement data and low signal-to-noise ratio.In this paper,we propose a novel mask-based denoisi... Ghost imaging(GI)is thought of as a promising imaging method in many areas.However,the main drawback of GI is the huge measurement data and low signal-to-noise ratio.In this paper,we propose a novel mask-based denoising scheme to improve the reconstruction quality of GI.We first design a mask through the maximum between-class variance(OTSU)method and construct the measurement matrix with speckle patterns.Then,the correlated noise in GI can be effectively suppressed by employing the mask.From the simulation and experimental results,we can conclude that our method has the ability to improve the imaging quality compared with traditional GI method. 展开更多
关键词 GHOST imaging MAXIMUM between-class variance MASK image quality
Assessment of widely used methods to derive depositional ages from detrital zircon populations 预览
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作者 Daniel S.Coutts William A. Matthews Stephen M. Hubbard 《地学前缘:英文版》 CAS CSCD 2019年第4期1421-1435,共15页
The calculation of a maximum depositional age(MDA)from a detrital zircon sample can provide insight into a variety of geological problems.However,the impact of sample size and calculation method on the accuracy of a r... The calculation of a maximum depositional age(MDA)from a detrital zircon sample can provide insight into a variety of geological problems.However,the impact of sample size and calculation method on the accuracy of a resulting MDA has not been evaluated.We use large populations of synthetic zircon dates(N≈25,000)to analyze the impact of varying sample size(n),measurement uncertainty,and the abundance of neardepositional-age zircons on the accuracy and uncertainty of 9 commonly used MDA calculation methods.Furthermore,a new method,the youngest statistical population is tested.For each method,500 samples of n synthetic dates were drawn from the parent population and MDAs were calculated.The mean and standard deviation of each method ove r the 500 trials at each n-value(50-1000,in increments of 50)were compa red to the known depositional age of the synthetic population and used to compare the methods quantitatively in two simulation scenarios.The first simulation scenario varied the proportion of near-depositional-age grains in the synthetic population.The second scenario varied the uncertainty of the dates used to calculate the MDAs.Increasing sample size initially decreased the mean residual error and standard deviation calculated by each method.At higher n-values(>~300 grains),calculated MDAs changed more slowly and the mean resid ual error increased or decreased depending on the method used.Increasing the p roportion of near-depositional-age grains and lowering measurement uncertainty decreased the number of measurements required for the calculated MDAs to stabilize and decreased the standard deviation in calculated MDAs of the 500 samples.Results of the two simulation scenarios show that the most successful way to increase the accuracy of a calculated M DA is by acquiring a large number of low-uncertainty measurements(300300)approach is used if the calculation of accurate MDAs are key to research goals.Other acquisition method s,such as high-to moderate-precision measurement methods(e.g.,1%-5%,2σ)acquiring lo 展开更多
关键词 DETRITAL ZIRCON Maximum DEPOSITIONAL age Geochronology Basin CHRONOLOGY LA-ICP-MS
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舰载导弹发射筒指向精度研究 预览
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作者 王勇 赵喜磊 李翔宇 《舰船科学技术》 北大核心 2019年第7期142-147,共6页
指向精度是衡量导弹发射筒发射精度的一项重要指标,为导弹提供了初始的出筒角度,是导弹是否能够准确命中目标的关键因素之一。本文通过剖析某舰载倾斜固定式导弹发射筒的总体结构,确定了影响导弹发射筒指向精度的因素,运用基于均方根值... 指向精度是衡量导弹发射筒发射精度的一项重要指标,为导弹提供了初始的出筒角度,是导弹是否能够准确命中目标的关键因素之一。本文通过剖析某舰载倾斜固定式导弹发射筒的总体结构,确定了影响导弹发射筒指向精度的因素,运用基于均方根值和最大值相结合的误差分析理论对导弹发射筒的指向精度进行统计计算,结合数据对比分析,提出1套可靠且系统的研究方法。该研究方法在一定程度上解决了影响导弹发射筒指向精度各个因素之间的相位角问题,较为客观地反映了指向精度的真实情况,对导弹发射筒总体设计具有一定的指导意义和应用价值。 展开更多
关键词 指向精度 导弹发射筒 均方根值 最大值 相位角
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Slavery Act:Modification of the Hungarian Labour Code--Legal Analysis 预览
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作者 Gábor Kertész 《管理研究:英文版》 2019年第4期338-345,共8页
In the middle of December 2018,Hungary has suddenly appeared in the headlines of international news.Although marketing teaches that“all PR is good PR”,as a lawyer,the author thinks it is worth examining the facts be... In the middle of December 2018,Hungary has suddenly appeared in the headlines of international news.Although marketing teaches that“all PR is good PR”,as a lawyer,the author thinks it is worth examining the facts behind the catchy headlines well before making our business decisions.The news is based on the amendment of the Labour Code,which is called the“Slavery Act”in the media.The demonstrations and atrocities reported by the international media have broken out as a result of the interpretation of the amendment by some part of the media,which was recently adopted by Parliament.The President of Hungary promulgated the act when this article was completed.What does the new amendment say?Could an employee become a“slave”of the employer,or rather it would help people’s prosperity by allow them to work more to earn more money?Considering the interests of the citizens/employees,can the choice between adoption or rejection of the law be the only possibility,does the new system also have a third possibility using the law’s and the economy’s own logic,or should only a small“fine-tuning”be implemented on the new system? 展开更多
关键词 labour law working TIME FRAME OVERWORK MAXIMUM working TIME
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