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Search Results: 1 - 10 of 32609 matches for " Hui Zeng "
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Oscillation of Solutions to Systems of Partial Differential Equations with Nonlinear Diffusion Coefficient
ZENG Yun-hui
Journal of Chongqing Normal University , 2010,
Abstract: In this paper, we studied the oscillation of solutions to systems of delay hyperbolic Partial differential equations with nonlinear diffusion coefficient. The oscillatory problem of solution to the systems of hyperbolic partial differential equations with nonlinear diffusion coefficient is reduced to which differential inequality has noteventual positive solution by using the Green's formula and boundary value conditions. Thereby, sufficient condition * for each solution to be oscillation is obtained under Robin boundary value condition * by using Riccati transformation and the method of diferential inequality.(* Indicates a formula, please see the full text)
Impacts of urban landscape structure on urban sprawl: A case researches in Nanchang


生态学报 , 2004,
Abstract: Urban sprawl led by continuous expansion of urban built-up areas is one of the essential features of landscape change in regions experiencing rapid urbanization. Expansion of urban built-up areas is constrained by both the external factors ((e.g.,) topography, land use, and enforced protection measures) and the development needs within cities (e.g. growth of the socio-economic activities and population). Meanwhile, the existing urban structures, such as size and shape of the urbanized patches, and their d...
Human impacts on landscape structure in Wolong Natural Reserve


生态学报 , 2001,
Abstract: Influences of human activities on landscape structure and human-induced ecological degradation in protected areas have been given considerable attention in landscape ecological studies. We use methods of quantitative analysis to precisely assess human impacts on landscape structure in Wolong Natural Reserve, China. Based on the landscape map compiled with satellite remotely sensed data (TM data) from 1997, four aspects of analysis were carried out using the buffer zone method: 1) A t test is utilized to und...
Landscape structure study of Longhua Area in Shenzhen City during the fast urbanization processStructure and heterogeneity analysis of forest land


生态学报 , 2000,
Abstract: Remotely sensed mapping data and methods of landscape structure analysis were used to study the structure and dynamics of forest patches during the fast urbanization process of Longhua Area,Shenzhen City.The key points of the study are the changes of the ordinary structure features and spatial distribution of the forest from 1988 to 1996.Results indicated that during the study period,the fast urbanization process have made strong cutting and transforming impacts on forest,the total area losing approached 49%,landscape structure characteristics such as fragmentation and neighborhood indices changed significantly.The changing process of forest patches can be divided into two stages.In the first stage from 1988 to 1992,some big forest patches were cut to small ones,and made the patch amount increase to the peak value in 1992.The second stage was from 1992 to 1996,since a lot of small forest patches were used for the expanding of town area,the former continuously distributed forests have been divided into several isolated patches.Three types of distribution pattern were identified in this study.In 1988,forest spatial distribution in the study area showed macroscopic heterogeneity with low lacunarity value;but because of patch fragmentation,it looked like a little bit random distribution in 1992;and in 1996,the distribution became macroscopic heterogeneity again with higher lacunarity value than 1988.Advantages of information entropy and lacunarity index methods can be good supplement for each other,so using both of them simultaneously can make us acquire more detailed information of landscape heterogeneity.
Dynamic analysis of urban landscape using a modified conversion matrix method:A case study in Nanchang City


生态学报 , 2003,
Abstract: In this paper, we used TM satellite images of Nanchang City from five different periods between 1988 and 2000 to conduct a dynamic urban landscape analysis. Using a modified conversion matrix method, we calculated the conversion probability matrix for all the landscape types. We rely primarily on three parameters conversion in rate, conversion out rate, and specific conversion process contribution rate to analyze the landscape changes and the driving mechanism behind these changes. It was found that dramatic changes in landscape structure occurred in Nanchang City during the study period. Because of the rapid urban sprawl, there was an increase in urban land use and concomitant decline in forest land, farmland, and water bodies. Dominant process analysis shows considerable conversion from agricultural land and natural landscapes to urban ones, with complicated inter conversion among the other landscape types. In particular, we also noticed the dominant conversion to farmland as an important process to landscape dynamics. Analysis on the combination of conversion out and conversion in rates indicates that farmland has kept high conversion in rate as well as high conversion out rate. Water body conversion is affected by both urban development and agriculture management, and is strongly constrained by hydrological changes. Because of the unique topography of the study area, forest land is the most stable among all the landscape types. Grassland and shrub have always had high turnover rates. Conversion of bare land is exceptional, as it is strongly constrained by hydrological changes as well as large scale urban development activities. The main dynamic changes in the study area were primarily conversion from farmland to built up areas and from other landscape types to farmland. Urban development is the driving force behind the dramatic change of the landscape structures in the whole study area. Needs for the stability of agricultural management is the direct reason for the dominant conversion processes from other landscape elements to farmland. Natural environment conditions like topography and hydrological changes are secondary constraint forces upon the conversion of forest and water body, but have primary effects upon some specific dominance conversion process, e.g. from farmland to water body. The modified conversion matrix analysis is an effective method for studying landscape dynamics. But it should be complemented by some supplementary analysis methods that can reflect the importance of basic landscape types and their conversion processes. Only in this way, can the various conversion processes in the dynamic landscape change be effectively characterized, and in turn facilitate the subsequent analysis on the driving mechanisms of landscape dynamics.
Effects of Forest Age on Soil Autotrophic and Heterotrophic Respiration Differ between Evergreen and Deciduous Forests
Wei Wang, Wenjing Zeng, Weile Chen, Yuanhe Yang, Hui Zeng
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0080937
Abstract: We examined the effects of forest stand age on soil respiration (SR) including the heterotrophic respiration (HR) and autotrophic respiration (AR) of two forest types. We measured soil respiration and partitioned the HR and AR components across three age classes ~15, ~25, and ~35-year-old Pinus sylvestris var. mongolica (Mongolia pine) and Larix principis-rupprechtii (larch) in a forest-steppe ecotone, northern China (June 2006 to October 2009). We analyzed the relationship between seasonal dynamics of SR, HR, AR and soil temperature (ST), soil water content (SWC) and normalized difference vegetation index (NDVI, a plant greenness and net primary productivity indicator). Our results showed that ST and SWC were driving factors for the seasonal dynamics of SR rather than plant greenness, irrespective of stand age and forest type. For ~15-year-old stands, the seasonal dynamics of both AR and HR were dependent on ST. Higher Q10 of HR compared with AR occurred in larch. However, in Mongolia pine a similar Q10 occurred between HR and AR. With stand age, Q10 of both HR and AR increased in larch. For Mongolia pine, Q10 of HR increased with stand age, but AR showed no significant relationship with ST. As stand age increased, HR was correlated with SWC in Mongolia pine, but for larch AR correlated with SWC. The dependence of AR on NDVI occurred in ~35-year-old Mongolia pine. Our study demonstrated the importance of separating autotrophic and heterotrophic respiration components of SR when stimulating the response of soil carbon efflux to environmental changes. When estimating the response of autotrophic and heterotrophic respiration to environmental changes, the effect of forest type on age-related trends is required.
Soil Respiration and Organic Carbon Dynamics with Grassland Conversions to Woodlands in Temperate China
Wei Wang, Wenjing Zeng, Weile Chen, Hui Zeng, Jingyun Fang
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0071986
Abstract: Soils are the largest terrestrial carbon store and soil respiration is the second-largest flux in ecosystem carbon cycling. Across China's temperate region, climatic changes and human activities have frequently caused the transformation of grasslands to woodlands. However, the effect of this transition on soil respiration and soil organic carbon (SOC) dynamics remains uncertain in this area. In this study, we measured in situ soil respiration and SOC storage over a two-year period (Jan. 2007–Dec. 2008) from five characteristic vegetation types in a forest-steppe ecotone of temperate China, including grassland (GR), shrubland (SH), as well as in evergreen coniferous (EC), deciduous coniferous (DC) and deciduous broadleaved forest (DB), to evaluate the changes of soil respiration and SOC storage with grassland conversions to diverse types of woodlands. Annual soil respiration increased by 3%, 6%, 14%, and 22% after the conversion from GR to EC, SH, DC, and DB, respectively. The variation in soil respiration among different vegetation types could be well explained by SOC and soil total nitrogen content. Despite higher soil respiration in woodlands, SOC storage and residence time increased in the upper 20 cm of soil. Our results suggest that the differences in soil environmental conditions, especially soil substrate availability, influenced the level of annual soil respiration produced by different vegetation types. Moreover, shifts from grassland to woody plant dominance resulted in increased SOC storage. Given the widespread increase in woody plant abundance caused by climate change and large-scale afforestation programs, the soils are expected to accumulate and store increased amounts of organic carbon in temperate areas of China.
Nitrogen Deposition Enhances Carbon Sequestration by Plantations in Northern China
Zhihong Du, Wei Wang, Wenjing Zeng, Hui Zeng
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0087975
Abstract: Nitrogen (N) deposition and its ecological effects on forest ecosystems have received global attention. Plantations play an important role in mitigating climate change through assimilating atmospheric CO2. However, the mechanisms by which increasing N additions affect net ecosystem production (NEP) of plantations remain poorly understood. A field experiment was initialized in May 2009, which incorporated additions of four rates of N (control (no N addition), low-N (5 g N m?2 yr?1), medium-N (10 g N m?2 yr?1), and high-N (15 g N m?2 yr?1)) at the Saihanba Forestry Center, Hebei Province, northern China, a locality that contains the largest area of plantations in China. Net primary production (NPP), soil respiration, and its autotrophic and heterotrophic components were measured. Plant tissue carbon (C) and N concentrations (including foliage, litter, and fine roots), microbial biomass, microbial community composition, extracellular enzyme activities, and soil pH were also measured. N addition significantly increased NPP, which was associated with increased litter N concentrations. Autotrophic respiration (AR) increased but heterotrophic respiration (HR) decreased in the high N compared with the medium N plots, although the HR in high and medium N plots did not significantly differ from that in the control. The increased AR may derive from mycorrhizal respiration and rhizospheric microbial respiration, not live root respiration, because fine root biomass and N concentrations showed no significant differences. Although the HR was significantly suppressed in the high-N plots, soil microbial biomass, composition, or activity of extracellular enzymes were not significantly changed. Reduced pH with fertilization also could not explain the pattern of HR. The reduction of HR may be related to altered microbial C use efficiency. NEP was significantly enhanced by N addition, from 149 to 426.6 g C m?2 yr?1. Short-term N addition may significantly enhance the role of plantations as an important C sink.
Oscillation Theorems for Second-Order Damped Nonlinear Differential Equations
Hui-Zeng Qin,Yongsheng Ren
International Journal of Differential Equations , 2009, DOI: 10.1155/2009/714357
Abstract: We present new oscillation criteria for the differential equation of the form [()()]
Analysis of condenser shell side pressure drop based on the mechanical energy loss
Hui Zeng,JiAn Meng,ZhiXin Li
Chinese Science Bulletin , 2012, DOI: 10.1007/s11434-012-5558-4
Abstract: The condenser performance is strongly affected by the tube arrangement. The steam pressure drop in the tube bundle influences the condenser back pressure, which is an important indicator of the condenser performance used to compare different condenser tube arrangements. The condenser shell side pressure drop is studied here using the mechanical energy loss of the steam flow in the condensers. The mechanical energy loss is due to the flow resistance of the tube bundle and the steam condensation. Three typical tube arrangements are analyzed numerically. The results show that a higher condenser shell side pressure drop for different tube arrangements always corresponds to a larger mechanical energy loss. The mechanical energy loss is mainly in the periphery of the tube bundle, indicating that the flow pattern and the mechanical energy losses are markedly determined by the tube bundle profile. The condenser shell side pressure drop can be reduced by reducing the total mechanical energy loss when the steam enters the tube bundle more uniformly. Thus, a well designed tube arrangement will reduce the mechanical energy loss, and also the shell side pressure drop.
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