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Search Results: 1 - 10 of 55222 matches for " Lei Xu "
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Fertility Preferences of the Post-1980s Generation in Urban China  [PDF]
Lei Xu
Chinese Studies (ChnStd) , 2013, DOI: 10.4236/chnstd.2013.24025
Abstract: Born under the one-child policy and growing up in an environment of tremendous socioeconomic change, the post-1980s generation of China tends to have interesting fertility preferences. This study explores the fertility desire, gender preference, and potential utilization of fetal ultrasound among the post-1980s individuals in urban China, based on a survey conducted in Beijing and Puyang, China. The ideal number of children among the post-1980s was substantially lower than the replacement level. 26% of the respondents considered China’s family planning policies as the most important determinant of their fertility desire, whereas 57% of the respondents indicated economic factors as the major determinant. With respect to gender preference, nearly half of the respondents who desired one child indicated no preference, and 79% of those who desired two children preferred 1 boy and 1 girl. In terms of potential utilization of ultrasound, the large majority of the respondents indicated an intention to use ultrasound to check the wellness of the fetus. Nearly half of them wanted to know the gender of the fetus via ultrasound examination, which is illegal in China. The findings imply that urban China has been experiencing a transition from a top-down governmental promoted fertility decline to a bottom-up individual voluntary choice of low fertility. In the context of below replacement fertility and population ageing, step-by-step relaxations of the family planning policies may lead to a small, gradual, and beneficial fertility increase.
Liquid drop splashing on smooth, rough and textured surfaces
Lei Xu
Physics , 2007, DOI: 10.1103/PhysRevE.75.056316
Abstract: Splashing occurs when a liquid drop hits a dry solid surface at high velocity. This paper reports experimental studies of how the splash depends on the roughness and the texture of the surfaces as well as the viscosity of the liquid. For smooth surfaces, there is a "corona" splash caused by the presence of air surrounding the drop. There are several regimes that occur as the velocity and liquid viscosity are varied. There is also a "prompt" splash that depends on the roughness and texture of the surfaces. A measurement of the size distribution of the ejected droplets is sensitive to the surface roughness. For a textured surface in which pillars are arranged in a square lattice, experiment shows that the splashing has a four-fold symmetry. The splash occurs predominantly along the diagonal directions. In this geometry, two factors affect splashing the most: the pillar height and spacing between pillars.
Instability development of a viscous liquid drop impacting a smooth substrate
Lei Xu
Physics , 2010, DOI: 10.1103/PhysRevE.82.025303
Abstract: We study the instability development during a viscous liquid drop impacting a smooth substrate, using high speed photography. The onset time of the instability highly depends on the surrounding air pressure and the liquid viscosity: it decreases with air pressure with the power of minus two, and increases linearly with the liquid viscosity. From the real-time dynamics measurements, we construct a model which compares the destabilizing stress from air with the stabilizing stress from liquid viscosity. Under this model, our experimental results indicate that at the instability onset time, the two stresses balance each other. This model also illustrates the different mechanisms for the inviscid and viscous regimes previously observed: the inviscid regime is stabilized by the surface tension and the viscous regime is stabilized by the liquid viscosity.
Intertemporal Pricing and Allotment of Sea-cargo Capacity under Reference Effect  [PDF]
Xiangzhi Bu, Lei Xu, Li Su
Journal of Service Science and Management (JSSM) , 2008, DOI: 10.4236/jssm.2008.13022
Abstract: Reference effect influences the shippers’ purchase behavior to some extent, and it makes shippers’ behavior more mys-terious. Furthermore, it leads to complex to coordinate procurement and pricing of forwarder and carrier. Firstly, we introduce the reference effect into the sea-cargo service supply chain composed with carriers and forwarders, and build the game-theoretical model to decide the optimal contract price and order quantity. Considering the situation where the market demand is affected by current price and reference price, we adopt dynamic programming and classical varia-tion method to analyze the dynamic equilibrium of the game under reference effect with symmetric information or not, respectively. Finally, this paper analyzes the reference effect to price, procurement and profit of carrier with digital analysis.
The Models of Investing Schools  [PDF]
June Liu, Lei Chai, Zina Xu
Journal of Applied Mathematics and Physics (JAMP) , 2016, DOI: 10.4236/jamp.2016.46113
Abstract: In this paper, we build the Linear Programming (LP) model, factor analysis model and return on investment model to measure the investment amount and which year to invest of each selected schools. We firstly analyze the indicators from attached files, and select effective indexes to choose schools donated. Then we select 17 indexes out after preprocessing all the indices. Secondly, we extract 1064 schools by MATLAB which is the Potential Candidate Schools from the table of attached files; we extract 10 common factors of these schools by factor analysis. After calculation, we rank the universities and select the top 100. We calculate the Return on Investment (ROI) based on these 17 indexes. Thirdly, we figure out the investment amount by conducting LP model through MATLAB. According to the property of schools, we calculate the annual limit investment and the mount of investment of each school. Fourthly, we determine which year to invest by ROI model which is operated by LINGO. In order to achieve optimal investment strategy and not duplication of investment, for five years, starting July 2016, we assume that the time duration that the organization’s money should be provided is one year, and the school return to the Good grant Foundation only one year. Then we can get the investment amount per school, the return on that investment, and which years to invest. Fifthly, by changing parameter, the sensitivity analysis is conducted for our models. The result indicates that our models are feasible and robust. Finally, we evaluate our models, and point out the strengths and weakness. Through previous analysis, we can find that our models can be applied to many fields, which have a relatively high generalization.
Forecast of China Population under Different Fertility Policy  [PDF]
Jun’e Liu, Lei Chai, Zina Xu
Open Journal of Social Sciences (JSS) , 2016, DOI: 10.4236/jss.2016.47031
Abstract: In this paper, we use queue elements prediction and forecasting software PADIS-INT, set three different fertility programs, and predict China’s total population and the trends of population structural change in 2015-2050, based on the fifth and sixth national census data. The results show that since implementation of the two-child family planning policy, the aging trend of the population structure will be significantly improved, and after 2030 our population structure will be gradually younger. In view of the problem of population sex ratio imbalance, we verified it, and the results showed that by 2020 there will be a bachelor phenomenon, but the number did not report as much. Finally, we gave a brief summary and recommendations for our studies.
Effects of Wheat-Faba Bean Intercropping on Soil Microbial Community Structure in the Rhizosphere  [PDF]
Yongbo Xu, Baokun Lei, Yanfeng Tang
Agricultural Sciences (AS) , 2018, DOI: 10.4236/as.2018.911096
Abstract: Phospholipid fatty acids (PLFA) analysis and real-time quantitative PCR were used to investigate the effect of wheat-faba bean intercropping on soil microbial community in the rhizosphere and ammonia monooxygenase (amoA) gene abundances of ammonia-oxidizing archaea (AOA) and bacteria (AOB) at harvest stage via field trials in the red soil. We found that the bacteria and fungi of faba bean and actinomycetes of wheat in the rhizosphere showed significant (p < 0.05) difference between intercrops and monocrops at harvest. In total, 37 PLFA were detected at harvest stage in the rhizosphere, including 31 bacterial PLFA, 3 fungal PLFA, and 3 actinomycete PLFA. Compared with the rhizosphere of monocropped faba bean, a lower AOB abundance was found in the intercropping at harvest stage, whereas no significant difference in the AOB abundance was found in the rhizosphere of monocropped and intercropped wheat. There was no significant difference in the AOA abundance between monocrops and intercrops rhizosphere, but a higher AOA abundance in the intercropping systems was found. After intercropping, the abundance of AOB in rhizosphere was significantly higher than that of AOA. Our findings suggest that wheat-faba bean intercropping may change the micro-environment and microbial community structure in the rhizosphere.
The Research on Stability of DC/DC in Parallel System  [PDF]
Ye Xu, Pengfei Hou, Jinquan Wang, Lei Xu, Chaohong Shi
Energy and Power Engineering (EPE) , 2013, DOI: 10.4236/epe.2013.54B154

In this paper, a main structure of DC distributed power system is introduced; the stability of the output voltage in parallel system is put forward. This paper analyses the output impedance of master-slave current sharing mode and average current sharing, analyses the stability of parallel system through simulation, there is Right-half plane (RHP) polar in the Bode plot of input impedance. At last this paper distinguishes whether this system is stability and verifies the validity of the simulation.

The Roles of Several Residues of Escherichia coli DNA Photolyase in the Highly Efficient Photo-Repair of Cyclobutane Pyrimidine Dimers
Lei Xu,Guoping Zhu
Journal of Nucleic Acids , 2010, DOI: 10.4061/2010/794782
Abstract: Escherichia coli DNA photolyase is an enzyme that repairs the major kind of UV-induced lesions, cyclobutane pyrimidine dimer (CPD) in DNA utilizing 350–450?nm light as energy source. The enzyme has very high photo-repair efficiency (the quantum yield of the reaction is ~0.85), which is significantly greater than many model compounds that mimic photolyase. This suggests that some residues of the protein play important roles in the photo-repair of CPD. In this paper, we have focused on several residues discussed their roles in catalysis by reviewing the existing literature and some hypotheses. 1. Introduction The sun gives warmth and light to the living beings on the earth. However, the ultra-violet (UV) radiation in the sunlight stimulates lesions forming in DNA. The UV-induced lesions in DNA block the replication and transcription events in the living cells, cause growth delay, mutagenesis, or lethal effects to organisms [1]. In order to survive under the sunlight, the organisms have evolved several repair mechanisms to resist the harmfulness of UV. Direct reversal by DNA photolyases is one of the mechanisms. There are two types of DNA photolyases, CPD photolyases and (6-4) photolyases, which, respectively, reverse the two major UV-induced lesions in DNA, cyclobutane pyrimidine dimers (CPD), and (6-4) photoproducts, utilizing blue or near-UV light (350–450?nm) as energy source [1–4]. CPD photolyases can be further categorized into two subclasses, class I (microbial) and class II (animal and plant), based on their amino acid sequence similarity [3, 5, 6]. Flavin adenine dinucleotide (FAD) is catalytic cofactor of all photolyases [3]. And a second cofactor, usually a derivative of folate, deazaflavin or flavin, acts as a photoantenna to increase the repair efficiency of the enzymes under limiting light conditions [3, 7–9]. The repair reactions are proposed through a photon-induced electron transfer mechanism which is supported by many model compounds studies. However, the quantum yields ( = 0.7–0.98) in the repair of pyrimidine dimers by DNA photolyase is significantly higher [3, 10–13] than those model compounds ( = 0.016–0.4) [14–16]. These results indicate that some amino acid residues of photolyases play important roles in the repair reactions. Escherichia coli DNA photolyase is a representative of them. By reviewing the existing literature and some hypotheses, we discussed the roles of some residues of E. coli photolyase in the highly efficient catalysis. This paper would provide the further insights into the catalytic mechanism of the enzyme. 2.
GPS-Free Localization Algorithm for Wireless Sensor Networks
Lei Wang,Qingzheng Xu
Sensors , 2010, DOI: 10.3390/s100605899
Abstract: Localization is one of the most fundamental problems in wireless sensor networks, since the locations of the sensor nodes are critical to both network operations and most application level tasks. A GPS-free localization scheme for wireless sensor networks is presented in this paper. First, we develop a standardized clustering-based approach for the local coordinate system formation wherein a multiplication factor is introduced to regulate the number of master and slave nodes and the degree of connectivity among master nodes. Second, using homogeneous coordinates, we derive a transformation matrix between two Cartesian coordinate systems to efficiently merge them into a global coordinate system and effectively overcome the flip ambiguity problem. The algorithm operates asynchronously without a centralized controller; and does not require that the location of the sensors be known a priori. A set of parameter-setting guidelines for the proposed algorithm is derived based on a probability model and the energy requirements are also investigated. A simulation analysis on a specific numerical example is conducted to validate the mathematical analytical results. We also compare the performance of the proposed algorithm under a variety multiplication factor, node density and node communication radius scenario. Experiments show that our algorithm outperforms existing mechanisms in terms of accuracy and convergence time.
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