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Search Results: 1 - 10 of 97537 matches for " WEN Yan-xu "
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WEN Yan-xu,SHI Jian-yong,

岩石力学与工程学报 , 2005,
Abstract: From common consolidation tests,a new oedometer which can measure the pore pressure from the bottom of specimen is employed. A phenomenon is found that the pore pressure in the specimen inclines to delay. Compared curves of the pore pressure and the displacement,it can be concluded that around the appearance of the of peak value pore pressure,the displacement curve finds its first turn. When the pore pressure reaches its total dissipation,the displacement curve finds its second turn. Because the pore pressure has strong relationship with the displacement,research work is carried out to reveal the cause of the delay. With further experiments under various conditions,it can be found that the side friction and the degree of saturation have strong influences on the delay of pore pressure in the specimen. So the delay rance of pore pressure should be considered in determining the consolidation coefficient,and at last,the measuring relative methods are discussed.
Utilization zoning of cultivated land based on net primary productivity in Guanzhong-Tianshui Economic Region
基于净初级生产力的关中--天水经济区耕地 利用分区研究

YANG Hai-Juan,WEN Xiao-Jin,LIU Yan-Xu,

中国生态农业学报 , 2013,
Abstract: As a populous nation, improve grain production capacity along with rational use and protection of cultivated land resources has posed a considerable challenge in domestic agriculture and land related research in China. Higher NPP for cultivated lands has suggested the existence of more organic biomass. This has been critical for the final production of food crops in the country. It was therefore likely for research on NPP to provide the basis for resolving food security issues. Functional zoning has been the commonly used method to guarantee sustainable use of land. Presently, however, heavily fragmented research merely described real supply of cultivated lands. A deeper understand on the potential reserves of cultivated lands was needed in this regard. Based on remote sensing observation, it is possible to have statistics of the output of a large number of cultivated lands within a short time. Compared with the yearbook data, remote sensing observation has advantages including timeliness and spatial precision. Remote sensing observations have therefore been strongly supplemental to statistical data. NPP estimated by remote sensing was used as crop biomass in cultivated lands instead of the traditional calculations based statistics data. Cultivated land in the Guanzhong-Tianshui Economic Region (GTER) was zoned by using neural network algorithm model and remote sensing data in 2001-2009 substituting for statistic crop yield data. Then the wavelet neural network was used to predict the NPP in the zoned regions. Three results were eventually attained. 1) From 2002 to 2009, total estimated NPP per year in GTER was 1.6×107 t. It showed large variation patterns between estimated NPP data and statistics grain data for cultivated lands in GTER. This suggested statistical and remote sensing data were not substitutable for one another. As clustering function was unknown, zoning via estimated NPP data reflected a more universal adaptability than via statistical data. 2) The final zonal type relatively corresponsed with common cognitions in the study area. It was important to emphasize counties in central GTER and Weihe River Valley (WRV) in the agriculture development of GTER. It was also important for government to set up precision agriculture and agricultural integration in these zones. 3) The prediction calculation by the wavelet neural network showed higher per unit area NPP as the principal trend in 2010 to 2015. Because of the reflected fluctuation patterns varied considerably for different data, it was important to note the differences in data sources and find the driving factors for the reflection of different pressures in cultivated lands. The discussions on data errors suggested that remote sensing data and statistical data should be compared in the study. As rapidly enhancing total crops biomass increase was difficult in the short term, the most effective way of remitting pressure on croplands was to improve use ratio of crop bio-energy.
Improving performances of ITO/GaP contact on AlGaInP light-emitting diodes

Li Chun-Wei,Zhu Yan-Xu,Shen Guang-Di,Zhang Yong-Hui,Qin Yuan,Gao Wei,Jiang Wen-Jing,Zhou De-Shu,

中国物理 B , 2010,
Distribution Behaviors of Phenanthrene to Humic Fractions in Natural Soil

LIN Xiu-mei,PAN Bo,LIU Wen-xin,YUAN Hui-shi,ZHANG Xian-ming,ZHANG Yan-xu,XIAO Yang,DAI Han-cheng,TAO Shu,

环境科学 , 2006,
Abstract: After adsorption of phenanthrene by the natural soil under different concentrations initially added,the soil sample was extracted for humic acid fraction(including humic acid and fulvic acid),and the sorption amount of phenanthrene in humin fraction was calculated to investigate the adsorption/distribution kinetics in two soil organic fractions and the corresponding influence of original phenanthrene concentration.The experimental data were fitted using Freundlich equation.The results show that,distribution of phenanthrene in the soil exhibited a multi-stage property,i.e.,from a first fast sorption to a breakthrough at about(48 h,) then followed by a slow sorption procedure.In the fast sorption stage(before 48 h),there was an up-to-down fluctuation of phenanthrene sorption ratio(sorption amount/added amount) in humic acid fraction,possibly due to surface sorption by minerals and competitive sorption by humin fraction.In the slow sorption stage,variations in sorption ratio in humic acid fraction was very small,and the influence of original concentration of phenanthrene was slight;while for humin fraction,the sorption ratio of phenanthrene at lower initial concentration was significantly higher than at higher one,in addition,the sorption ratio showed a gradually increasing trend,indicated humin fraction as the main domain in charge of the slow sorption.The fitting results of model parameters demonstrated that,sorption nonlinearity of phenanthrene in the natural soil increased in the following order: humic acid fraction
Contrast in vegetation net primary productivity estimation models and ecological effect value evaluation in Northwest China
西北地区植被净初级生产力估算模型对比与 其生态价值评价

REN Zhi-Yuan,LIU Yan-Xu,

中国生态农业学报 , 2013,
Abstract: Net primary productivity (NPP) is the total dry organic matter produced by green plants in unit time and area. It is one of the key parameters used in carbon and oxygen cycle research. Not much NPP research has covered the whole of Northwest China and model estimates of NPP have also varied considerably. Photosynthesis is the main mode vegetation generates dry mater and is the core link between natural carbon and oxygen cycles. The synthesis of NPP is accompanied by energy fixing, carbon sinking and oxygen production; which are three indispensable ecological processes for human survival and development. By estimation of NPP based on photosynthetic equation, ecological effects via the synthesis of NPP can be effectively and quantitatively evaluated. This study compared different NPP evaluation models and analyzed (at both temporal and spatial scales) different characteristics of NPP for the period from 2000 to 2009 in Norwest China. The study showed that the Comprehensive model and the Beijing model most closely with the CASA model estimates. Calculated mean NPP for croplands, grasslands and evergreen needle leaf forests were 4.15 t·hm-2, 4.87 t·hm-2 and 7.35 t·hm-2, respectively. Human activity had enhanced vegetation in dry areas not to completely depend on rain. This implied that some differences existed in the estimation of the NPP by statistical models. Estimation results of NPP values by different methods through evaluating dry matter production, carbon fixing and oxygen release functions showed that NPP values increased with time. Also NPP values for grass increased at the fastest rate in the study area, which was 7.91×1011 Yuan in 2009. NPP value recalculated based on county unit showed three spatial-temporal patterns: in the high value area, it first decreased then increased; in low value area, it first increased then decreased; NPP value gradually diversely distributed. The spatial agglomeration tendency of change in NPP showed that the lowest value units rose rapidly, the highest value units rose gradually and the medium units dropped gradually. The asymmetry and deviation from the mean intensified and the agglomeration of high values also strengthened. The rise in NPP was more apparent than the decline, which lead to smaller NPP values difference from the east to the west and higher NPP values difference from the south to the north. The spatial decentralization development of counties favored a better ecological environment, although with local deterioration. For the weak ecological environment in Northwest China, it was necessary to partition NPP into ecological services value estimation and ecological safety evaluation at regional scale. The combination of direct agricultural income and potential ecological assets was more effective for sustainable regional development planning and control.

ZHANG Yan-Xu,LIU Jing,

红外与毫米波学报 , 2004,
Abstract: Several important factors, including Gaussian blurring,finite imaging region, and discrete computation, were considered to study the stability of moment invariants in practical application. The effect and rules of each factor to the moment invariants were investigated. The stability of moment invariant on the discrete data case was analyzed. The experiments show that it is possible to recognize the blurred and rotated images accurately by the suggested invariants. All these researches will provide important theoretical and experimental foundations for practical imaging recognition systems.
Realization of High Optical Density Rb Magneto-optical Trap

HAN Yan-Xu,LIU Yong-Hong,ZHANG Chun-Hong,LI Shu-Jing,WANG Hai,

中国物理快报 , 2009,

YANG Rui-Li,WANG Ying-Chun,CHANG Yan-Xu,

植物生态学报 , 2008,
Abstract: 研究荒漠旱生小灌木长叶红沙(Reaumuria trigyna)劈裂生长过程的形态发生及其内源激素含量的变化。结果表明:1)劈裂发生部位形成层活动不均匀,次生木质部的导管口径缩小,数量减少,木纤维含量增多,由此向内形成缢缩,之后缢缩部位前端的细胞不断解体,使得缢缩不断加深,相邻的两个缢缩部位通常要延伸到劈裂发生部位的中心位置连接在一起,整个维管束裂成多个单独的维管束,并相互分离。劈裂发生部位木质部中有异常的类似形成层的结构,木质部被几层扁平的细胞环分割成数轮,推测其与劈裂生长的发生密切相关。2)内源激素在长叶红沙不同部位含量不同,尤其在刚刚开始劈裂的过渡植株的劈裂发生部位IAA和ZR的积累量比根部大,可能共同调节这个部位细胞的生长和分裂,促进劈裂生长的发生。
Suppression Subtractive Hybridization Analysis of Genes Regulated by Application of Exogenous Abscisic Acid in Pepper Plant (Capsicum annuum L.) Leaves under Chilling Stress
Wei-Li Guo, Ru-Gang Chen, Zhen-Hui Gong, Yan-Xu Yin, Da-Wei Li
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0066667
Abstract: Low temperature is one of the major factors limiting pepper (Capsicum annuum L.) production during winter and early spring in non-tropical regions. Application of exogenous abscisic acid (ABA) effectively alleviates the symptoms of chilling injury, such as wilting and formation of necrotic lesions on pepper leaves; however, the underlying molecular mechanism is not understood. The aim of this study was to identify genes that are differentially up- or downregulated in ABA-pretreated hot pepper seedlings incubated at 6°C for 48 h, using a suppression subtractive hybridization (SSH) method. A total of 235 high-quality ESTs were isolated, clustered and assembled into a collection of 73 unigenes including 18 contigs and 55 singletons. A total of 37 unigenes (50.68%) showed similarities to genes with known functions in the non-redundant database; the other 36 unigenes (49.32%) showed low similarities or unknown functions. Gene ontology analysis revealed that the 37 unigenes could be classified into nine functional categories. The expression profiles of 18 selected genes were analyzed using quantitative RT-PCR; the expression levels of 10 of these genes were at least two-fold higher in the ABA-pretreated seedlings under chilling stress than water-pretreated (control) plants under chilling stress. In contrast, the other eight genes were downregulated in ABA-pretreated seedlings under chilling stress, with expression levels that were one-third or less of the levels observed in control seedlings under chilling stress. These results suggest that ABA can positively and negatively regulate genes in pepper plants under chilling stress.
Flip-Chip GaN-Based Light-Emitting Diodes with Mesh-Contact Electrodes
ZHU Yan-Xu,XU Chen,HAN Jun,SHEN Guang-Di,

中国物理快报 , 2007,
Abstract: GaN-based light-emitting diodes (LEDs) with mesh-contact electrodes have been developed. The p-type ohmic contact layer is composed of oxidized Ni/Au mesh and NiO overlay (20A). An Ag (3000A) omni-directional reflector covers the p-type contact. The n-type contact is a Ti/AI planar film with a 10-μm-width Ti/AI stripe. The Ti/AI stripe surrounds the centre of LED mesa. With a 20-mA current injection, the light output power of GaN-based LEDs with mesh-contact electrodes is 23% higher than that of the conventional LEDs.
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