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time lag effect of vegetation response to seasonal precipitation in the Mara River Basin

Ecological Processes 2023年第4期12卷 23-37页

作者： Shouming Feng Zhenke Zhang Shuhe Zhao Xinya Guo Wanyi Zhu Priyanko Das School of Geography and Oceanography Sciences Nanjing University Institute of African Studies Nanjing University Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and Application

Background Mara River Basin is an ecologically fragile area in East Africa, with a pattern of alternating wet and dry seasons shaped by periodic precipitation. Considering the regional biological traits and climatic change, the vegetation's response to seasonal variation is complicated and frequently characterized by time lags. This study analyzed the variation of the Normalized Difference Vegetation Index(NDVI) and investigated its time lag to precipitation at the monthly scale. NDVI characteristic peaks were proposed from the perspective of seasonal mechanisms and were quantified to assess the lag *** The results showed that the Anomaly Vegetation Index could identify low precipitation in 2006, 2009, and 2017. The NDVI showed an increasing trend in 75% of areas of the basin, while showed a decreased significance in 3.5% of areas, mainly in savannas. As to the time lag, the 1-month lag effect dominated most months, and the spatiotemporal disparities were noticeable. Another method considering the alternations of wet and dry seasons found that the time lag was approximately 30 days. Based on the time distribution of NDVI characteristic peaks, the average time lag was 35.5 days and increased with the range of *** The findings confirmed an increasing trend of NDVI in most regions from 2001 to 2020, while the trends were most obvious in the downstream related to human activities. The results could reflect the time lag of NDVI response to precipitation, and the 1-month lag effect dominated in most months with spatial heterogeneity. Four NDVI characteristic peaks were found to be efficient indicators to assess the seasonal characteristics and had a great potential to quantify vegetation variation.

关键词： Mara River Basin NDVI Seasonal precipitation Characteristic peak time lag

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time lag between reduction of sediment supply and coastal erosion

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International Journal of Sediment Research 2011年第1期26卷 27-35页

作者： HUANG Guangwei~1 University of Tokyo,Japan, Dr. University of Tokyo Japan

The disruption of sediment supply from river to coast by dam development has been a topic of global *** Japan,among the top 30 dams in terms of height,14 dams were constructed prior to 1970 and another 6 dams before ***,the coastline erosion did not surface up as a grievous problem until the *** to the River Bureau of Japan,the overall erosion rate along the coastline of Japan was 0.72×10~6 m~2/yr prior to 1980,but sharply increased to 1.6×10~6 m~2/yr since ***,there was a time lag between the disruption of sediment supply by dam and beach *** paper presents a case study on what may have delayed the response of beach to the effect of dam construction.

关键词： Erosion Sediment supply Dam Sand mining time lag

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Learning dynamic dependency network structure with time lag

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Science China(Information Sciences) 2018年第5期61卷 125-140页

作者： Sizhen DU Guojie SONG Haikun HONG Dong LIU Key Laboratory of Machine Perception Ministry of Education Peking University Institute of Electronics Chinese Academy of Sciences School of Computer and Information Engineering Henan Normal University

Characterizing and understanding the structure and the evolution of networks is an important problem for many different fields. While in the real-world networks, especially the spatial networks, the influence from one node to another tends to vary over both space and time due to the different space distances and propagation speeds between nodes. Thus the time lag plays an essential role in interpreting the temporal causal dependency among nodes and also brings a big challenge in network structure *** most of the previous researches aiming to learn the dynamic network structure only treat the time lag as a predefined constant, which may miss important information or include noisy information if the time lag is set too small or too large. In this paper, we propose a dynamic Bayesian model with adaptive lags(DBAL)which simultaneously integrates two usually separate tasks, i.e., learning the dynamic dependency network structure and estimating time lags, within one unified framework. Specifically, we propose a novel weight kernel approach for time series segmenting and sampling via leveraging samples from adjacent segments to avoid the sample scarcity. Besides, an effective Bayesian scheme cooperated with reversible jump Markov chain Monte Carlo(RJMCMC) and expectation propagation(EP) algorithm is proposed for parameter inference. Extensive empirical evaluations are conducted on both synthetic and two real-world datasets,and the results demonstrate that our proposed model is superior to the traditional methods in learning the network structure and the temporal dependency.

关键词： dependency network time lag dynamic network

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Predicting Wavelet-Transformed Stock Prices Using a Vanishing Gradient Resilient Optimized Gated Recurrent Unit with a time lag

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Journal of Data Analysis and Information Processing 2023年第1期11卷 49-68页

作者： Luyandza Sindi Mamba Antony Ngunyi Lawrence Nderu Department of Mathematics Institute for Basic Sciences Technology and Innovation The Pan African University Nairobi Kenya Department of Statistics and Actuarial Sciences Dedan Kimathi University of Technology Nyeri Kenya Department of Computing School of Computing and Information Technology Jomo Kenyatta University of Agriculture and Technology Nairobi Kenya

The development of accurate prediction models continues to be highly beneficial in myriad disciplines. Deep learning models have performed well in stock price prediction and give high accuracy. However, these models are largely affected by the vanishing gradient problem escalated by some activation functions. This study proposes the use of the Vanishing Gradient Resilient Optimized Gated Recurrent Unit (OGRU) model with a scaled mean Approximation Coefficient (AC) time lag which should counter slow convergence, vanishing gradient and large error metrics. This study employed the Rectified Linear Unit (ReLU), Hyperbolic Tangent (Tanh), Sigmoid and Exponential Linear Unit (ELU) activation functions. Real-life datasets including the daily Apple and 5-minute Netflix closing stock prices were used, and they were decomposed using the Stationary Wavelet Transform (SWT). The decomposed series formed a decomposed data model which was compared to an undecomposed data model with similar hyperparameters and different default lags. The Apple daily dataset performed well with a Default_1 lag, using an undecomposed data model and the ReLU, attaining 0.01312, 0.00854 and 3.67 minutes for RMSE, MAE and runtime. The Netflix data performed best with the MeanAC_42 lag, using decomposed data model and the ELU achieving 0.00620, 0.00487 and 3.01 minutes for the same metrics.

关键词： Optimized Gated Recurrent Unit Approximation Coefficient Stationary Wavelet Transform Activation Function time lag

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time-lag Effect on the Capture Capability of Pursuit-Control

Time-Lag Effect on the Capture Capability of Pursuit-Control

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第二十六届中国控制会议

作者： Wu Wenhai1,Qu Jianling2 1.Naval Aeronautical Engineering Academy Qingdao Branch,Qingdao 266041,P.R.China2.Naval Aeronautical Engineering Academy Qingdao Branch,Qingdao 266041,P.R.China

The time-lag problem is one of the most important problems in both the fields of mathematics and *** many research results have been presented,under the effect of control-lag,there are no any related report on such topics in the pursuit-evasion problem,to the best knowledge of *** may be for the reason that the dynamic equations of the pursuit-evasion system are too complex to solve ***,there are only some research reports on the study of its capture capability based on idea assumptions,without consideration of any time lag of pursuit control.A new study method on the capture capability is presented in this paper,under the effect of ***,the no-time-lag theoretical results of PPN are validated by simulation,which not only demonstrates the correctness of theorem but also indicates the validity of the system modeling and simulation *** based on the modeling system with different control lag times,some useful results on pursuit control time-lag are drawn from the simulation of two different aspects,effect on capture probability and pursuit *** lag effect on short-distance pursuit is greater than long-distance pursuit,if the ratio of the pursuer velocity to target velocity （VROPT） is constant: ① When the initial relative distance is more than 10 km,the capturability decreases less than 5% compared to that without time lag,even if with a time lag up to 3 seconds during the given pursuit-evasion states.② While the initial distance is less than 3km,if the lag time is up to 3s it decreases about 50%.③ The capture capability is almost unchanged if the control-lag is no more than 0.5 *** also show that the effect on the pursuit-evasion process is *** the constant time lag,VROPT has effect on the *** show that the capturability is improved as the increase of the ***,the pursuit lag time has negative effect on the capturability,especially during short-d

关键词： Simulation Pursuit Capture Set time lag Navigation-Interception Capture Capability

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Dynamic thermal performance of multilayer hollow clay walls filled with insulation materials:Toward energy saving in hot climates

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Energy and Built Environment 2024年第1期5卷 70-80页

作者： Yassine Chihab Mohammed Garoum Najma Laaroussi Mohammed V University in Rabat MaterialsEnergy and Acoustics TEAMRabatMorocco

This study examines the benefits of incorporating passive techniques into multilayer hollow clay brick walls to improve their dynamic thermal *** finite element approach was used to solve the incompressible Navier-Stokes and energy equations to analyze the dynamic thermal response of walls exposed to real thermal excitations of the Marrakesh *** results show that increasing the emissivity from 0.1 to 0.9 significantly increases the total heat load over 24 ***,filling 100% of the cavities with insulation materials delayed the temperature peak by about 2.3 h and lowered the decrement factor by roughly 43%,with a value smaller than *** addition,it is demonstrated that the total thermal load is reduced by approximately 28% for improved wall configurations(100% insulation filling cavities)compared to traditional wall configurations(100% air filling cavities),which aids in improving building energy efficiency.

关键词： time lag Decrement factor Coupled heat transfer Analytical solution Hollow clay brick Insulation filling cavities Energy savings in building

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Numerical analysis on phase change progress and thermal performance of different roofs integrated with phase change material(PCM)in Moroccan semi-arid and Mediterranean climates

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Building Simulation 2023年第1期16卷 69-85页

作者： Yanqiu Huang Shan Yang Moussa Aadmi Yi Wang Mustapha Karkri Zhenhao Zhang State Key Laboratory of Green Building in Western China Xi'an University of Architecture and TechnologyNo.13 Yanta RD.Xi'an 710055China School of Building Services Science and Engineering Xi'an University of Architecture and TechnologyNo.13 Yanta RD.Xi'an 710055China LMASI ElectromagnetismPhysics of Plasmas and ApplicationsPolydisciplinary Faculty of NadorMohammed First UniversityB.P 30062700SelouaneNadorMorocco CERTES Univ Paris Est Creteil61 Avenue du Général de GaulleF-94010 CreteilFrance

Phase change material(PCM)applied to roofs can weak external heat entering the room to reduce air-conditioning energy *** this study,three forms of macro-encapsulated PCM roofs with different PCMs(RT27,RT31,RT35HC,PT37)are *** effects of PCM thickness,the encapsulation forms,and different PCMs on the thermal performance of the roof are discussed in Moroccan semi-arid and Mediterranean *** results show that as the PCM thickness increases,the peak temperature attenuation of the roof inner surface *** two climates,the pure PCM layer among the three encapsulation forms(*** PCM layer,PCM in aluminum tubes,PCM in triangular aluminum)is the easiest to appear the phenomenon of insufficient heat storage and release,while the reduction of the peak inner surface temperature and time lag is the most *** the PCM in the aluminum tube,phase change time is the shortest and the latent heat utilization ratio is the highest,while thermal regulation performance is the least *** PCM in triangular aluminum can improve the latent heat utilization ratio significantly,and its thermal regulation performance is in the *** semi-arid climate,the time lag increases with phase change temperature *** time lag could reach up to 6 h with 37℃phase transition *** Mediterranean climate,the longest time lag with RT31 is 5 h,while the lowest peak inner surface temperature appears with *** obtained conclusions could provide guidance for the application of PCM roofs in these two climates.

关键词： numerical simulation PCM roof thermal performance inner surface temperature time lag

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Lost in transition： Forest transition and natural forest loss in tropical China

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Plant Diversity 2017年第3期39卷 149-153页

作者： Deli Zhai Jianchu Xu Zhicong Dai Dietrich Schmidt-Vogt Centre for Mountain Ecosystem Studies (CMES) Kunming Institute of Botuny (CAS) Lanhei Road 132 Kunming 650201 China World Agroforestry Centre (ICRAF) Central and East Asia Office Lanhei Road132 Kunming 650201 China Instituteof-Environment and Ecology School of the Environment and Safety Engineering fiangsu University No. 301 Xuefu Road Zhenjiang 212013 China Mountain Societies Research Institute University of Central Asia 138 Toktogul Street Bishkek 720001 Kyrgyzstan

The term forest transition refers to a change in forest cover over a given area from a period of net forest area loss to a period of net gain. Whether transitioning from deforestation to reforestation can lead to improved ecosystem services, depends on the quality and characteristics of the newly established forest cover. Using publicly available data, we examine forest transition in two regions of tropical China: Hainan Island and Xishuangbanna. We found that the overall increase of forest cover in both areas during the1980 s was due to an increase in plantation forests rather than to increases in the area covered by natural forest. We also found a time lag between the increase in overall forest cover and an increase in natural forest. On Hainan Island, natural forest continued to decline beyond the point in time when overall forest cover had started to increase, and only began to recover ten years after the turning point in 1978. In Xishuangbanna, where the transition point occurred ten years later, the decline of natural forest cover is still going on. These divergent trends underlying forest transition are concealed by the continued practice to apply the term "forest" broadly, without distinguishing between natural forests and planted *** to the use of undiscriminating terminology, the loss of natural forest may go unnoticed, increasing the risk of plantation forests displacing natural forests in the course of forest transition. Our findings are important for programs related to forest management and ecosystem services improvement, including reforestation and Payments for Ecosystem Services programs.

关键词： Deforestation Forest transition Rubber plantation time lag Tropical China

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Climate warming increases biodiversity of small rodents by favoring rare or less abundant species in a grassland ecosystem

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Integrative Zoology 2013年第2期8卷 162-174页

作者： Guangshun JIANG Jun LIU Lei XU Guirui YU Honglin HE Zhibin ZHANG College of Wildlife Resources Northeast Forestry UniversityHarbinChina Inner Mongolia Center for Endemic Diseases Control and Research HuhehotChina Information Management Group for the Synthesis Center of Chinese Ecosystem Research Network Institute of Geographic Sciences and Natural Resources ResearchChinese Academy of SciencesBeijingChina State Key Laboratory of Integrated Management of Pest Insects and Rodents in Agriculture Institute of ZoologyChinese Academy of SciencesBeijingChina

Our Earth is facing the challenge of accelerating climate change,which imposes a great threat to *** published studies suggest that climate warming may cause a dramatic decline in biodiversity,especially in colder and drier *** this study,we investigated the effects of temperature,precipitation and a normalized difference vegetation index on biodiversity indices of rodent communities in the current or previous year for both detrended and nondetrended data in semi-arid grassland of Inner Mongolia during *** results demonstrate that temperature showed predominantly positive effects on the biodiversity of small rodents;precipitation showed both positive and negative effects;a normalized difference vegetation index showed positive effects;and cross-correlation function values between rodent abundance and temperature were negatively correlated with rodent *** results suggest that recent climate warming increased the biodiversity of small rodents by providing more benefits to population growth of rare or less abundant species than that of more abundant species in Inner Mongolia grassland,which does not support the popular view that global warming would decrease biodiversity in colder and drier *** hypothesized that higher temperatures might benefit rare or less abundant species(with smaller populations and more folivorous diets)by reducing the probability of local extinction and/or by increasing herbaceous food resources.

关键词： climate change cross-correlation function rare species small mammal biodiversity time lag

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Fuzzy Prediction of Silicon Content for BF Hot Metal

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Journal of Iron and Steel Research(International) 2005年第6期12卷 1-4页

作者： LI Qi-hui LIU Xiang-guan Zhejiang University Hangzhou 310027 China

Some key operation variables influencing hot metal silicon content were selected, and time lag of each of them was obtained. A standardized fuzzy system model was developed to approach the random nonlinear dynamic system of the change of silicon content, forecast the change of silicon content and calculate silicon content. The prediction of hot metal silicon content is very successful with the data collected online from BF No. 1 at Laiwu Iron and Steel Group Co.

关键词： hot metal silicon content time lag fuzzy prediction

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