检索结果-南通市图书馆

Effect of Exposure to Trace Elements in the Soil on the Prevalence of Neural Tube Defects in a High-Risk Area of China

在线全文

学校读者我要写书评

暂无评论

Biomedical and Environmental Sciences 2011年第2期24卷 94-101页

作者： HUANG Jing WU JiLei LI TieJun SONG XinMing ZHANG BingZi ZHANG PingWen ZHENG XiaoYing School of Mathematical Sciences Peking University Beijing 100871 China Institute of Population Research Peking University Beijing 100871 China

Objective Our objective is to build a model that explains the association between the exposure to trace elements in the soil and the risk of neural tube defects. Methods We built a function with different parameters to describe the effects of trace elements on neural tube defects. The association between neural tube defects and trace element levels was transformed into an optimization problem using the maximum likelihood method. Results Tin, lead, nickel, iron, copper, and aluminum had typical layered effects （dosage effects） on the prevalence of neural tube defects. Arsenic, selenium, zinc, strontium, and vanadium had no effect, and molybdenum had one threshold value that affected the prevalence of birth defects. Conclusion As an exploratory research work, our model can be used to determine the direction of the effect of the trace element content of cultivated soil on the risk of neural tube defects, which shows the clues by the dosage effect of their toxicological characteristics. Based on our findings, future biogeochemical research should focus on the direct effects of trace elements on human health.

关键词： Trace element Neural tube defects Risk factors identification poisson model Maximum likelihood estimation

models and estimators linking individual-based and sample-based rarefaction, extrapolation and comparison of assemblages

在线全文

学校读者我要写书评

暂无评论

Journal of Plant Ecology 2012年第1期5卷 3-21页

作者： Robert K.Colwell Anne Chao Nicholas J.Gotelli Shang-Yi Lin Chang Xuan Mao Robin L.Chazdon John T.Longino Department of Ecology and Evolutionary Biology University of ConnecticutStorrsCT 06269USA Institute of Statistics National Tsing Hua UniversityHsin-Chu 30043Taiwan Department of Biology University of VermontBurlingtonVT 05405USA School of Statistics and Management Shanghai University of Finance and EconomicsShanghai 200433China Department of Biology University of UtahSalt Lake CityUT 84112USA

Aims In ecology and conservation biology,the number of species counted in a biodiversity study is a key metric but is usually a biased underestimate of total species richness because many rare species are not ***,comparing species richness among sites or samples is a statistical challenge because the observed number of species is sensitive to the number of individuals counted or the area *** individual-based data,we treat a single,empirical sample of species abundances from an investigator-defined species assemblage or community as a reference point for two estimation objectives under two sampling models:estimating the expected number of species(and its unconditional variance)in a random sample of(i)a smaller number of individuals(multinomial model)or a smaller area sampled(poisson model)and(ii)a larger number of individuals or a larger area *** sample-based incidence(presence–absence)data,under a Bernoulli product model,we treat a single set of species incidence frequencies as the reference point to estimate richness for smaller and larger numbers of sampling *** The first objective is a problem in interpolation that we address with classical rarefaction(multinomial model)and Coleman rarefaction(poisson model)for individual-based data and with sample-based rarefaction(Bernoulli product model)for incidence *** second is a problem in extrapolation that we address with sampling-theoretic predictors for the number of species in a larger sample(multinomial model),a larger area(poisson model)or a larger number of sampling units(Bernoulli product model),based on an estimate of asymptotic species *** published methods exist for many of these objectives,we bring them together here with some new estimators under a unified statistical and notational *** novel integration of mathematically distinct approaches allowed us to link interpolated(rarefaction)curves and extrapolated curves to plot a unified

关键词： Bernoulli product model Coleman curve multinomial model poisson model random placement species–area relation

A new maximum-likelihood phase estimation method for X-ray pulsar signals

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Journal of Zhejiang University-Science C(Computers and Electronics) 2014年第6期15卷 458-469页

作者： Hua ZHANG Lu-ping XU Yang-he SHEN Rong JIAO Jing-rong SUN School of Aerospace Science and Technology Xidian University

X-ray pulsar navigation(XPNAV) is an attractive method for autonomous navigation of deep space in the future. Currently, techniques for estimating the phase of X-ray pulsar radiation involve the maximization of the general non-convex object functions based on the average profile from the epoch folding method. This results in the suppression of useful information and highly complex computation. In this paper, a new maximum likelihood(ML) phase estimation method that directly utilizes the measured time of arrivals(TOAs) is presented. The X-ray pulsar radiation will be treated as a cyclo-stationary process and the TOAs of the photons in a period will be redefined as a new process, whose probability distribution function is the normalized standard profile of the pulsar. We demonstrate that the new process is equivalent to the generally used poisson model. Then, the phase estimation problem is recast as a cyclic shift parameter estimation under the ML estimation, and we also put forward a parallel ML estimation method to improve the ML solution. Numerical simulation results show that the estimator described here presents a higher precision and reduces the computational complexity compared with currently used estimators.

关键词： X-ray pulsar poisson model Phase estimation Maximum likelihood

A Computational Workflow to Identify Allele-specifc Expression and Epigenetic Modifcation in Maize

在线全文

学校读者我要写书评

暂无评论

Genomics, Proteomics & Bioinformatics 2013年第4期11卷 247-252页

作者： Xiaoxing Wei Xiangfeng Wang Department of Basic Medicine Medical College of Qinghai University School of Plant Sciences University of ArizonaTucson AZ 85715 USA

Allele-specific expression refers to the preferential expression of one of the two alleles in a diploid genome, which has been thought largely attributable to the associated cis-element variation and allele-specific epigenetic modification patterns. Allele-specific expression may contribute to the heterosis （or hybrid vigor） effect in hybrid plants that are produced from crosses of closely-related species, subspecies and/or inbred lines. In this study, using Illumina high-throughput sequencing of maize transcriptomics, chromatic H3K27me3 histone modification and DNA methylation data, we developed a new computational framework to identify allele-specifically expressed genes by simul- taneously tracking allele-specific gene expression patterns and the epigenetic modification landscape in the seedling tissues of hybrid maize. This approach relies on detecting nucleotide polymorphisms and any genomic structural variation between two parental genomes in order to distinguish pater- nally or maternally derived sequencing reads. This computational pipeline also incorporates a mod- ified Chi-square test to statistically identify allele-specific gene expression and epigenetic modification based on the poisson distribution.

关键词： Allele-specific expression Epigenetic modification poisson model Hybrid maize Illumina sequencing

The Geographical Rotation of Local Officials and Enterprise Cross-city Mergers and Acquisitions in China

在线全文

学校读者我要写书评

暂无评论

China & World Economy 2023年第4期31卷 66-89页

作者： Liangxiong Huang Peilun Li Xianbin Wang Caiting Yang School of Economics and Finance South China University of TechnologyChina School of Business Administration South China University of TechnologyChina College of Economics Jinan UniversityChina School of Management Lanzhou UniversityChina

The economic impact of the geographical rotation of local officials is important in China's official management *** study used a zero-inflated poisson regression model and found that the geographical rotation of local officials significantly increased cross-city mergers and acquisitions(M&As)of *** impact of local officials'geographical rotation on M&As was more pronounced under certain *** conditions included:(i)when officials were transferred from cities with a higher development level to cities with a lower development level;(ii)when the outflow cities were municipalities directly governed by the central government,provincial capitals,or separately listed cities;(iii)when the transfers of officials occurred within the same province;(iv)when the transfers took place before 2012;and(v)when the transfers happened in the years following significant central government conferences,which provided strong political incentives for M&As.

关键词： geographical rotation of local officials M&As poisson model

The stress release model and results from modelling features of some seismic regions in China

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Seismologica Sinica(English Edition) 1998年第1期11卷 56-66页

作者：庄建仓马丽

The stress release model is a stochastic point process model developed from the theory of elastic rebound. It can be used to analyse, simulate or predict the seismicity in a certain seismic region. This paper first gives a brief representation of the theory of the stress release model and the method of how to use it to analyse earthquake data, then this model is to fit the earthquake data in North China, Southwest China and Taiwan. The results show that the stress release model fits to the data better than the poisson model. The different features of stress accumulation and release in these regions imply that the seismic activity is essentially different among these regions.

关键词： stress release model poisson model conditional intensity AIC

A Direct Phase Estimation Method of X-ray Pulsar Signal Without Epoch Folding

在线全文

学校读者我要写书评

暂无评论

A Direct Phase Estimation Method of X-ray Pulsar Signal With...

第五届中国卫星导航学术年会

作者： Hua ZHANG Lu-ping XU Rong JIAO Yang-He SHEN Jing-Rong SUN School of Aerospace Science and Technology Xidian University

X-ray Pulsar Navigation（XPNAV） is an attractive method for the future deep space autonomous ***,techniques for the phase estimation of X-ray pulsar radiation involves maximization of generally non-convex object functions based on average profile from epoch folding method,which results in suppression of useful information and high *** this paper,a new maximum likelihood（ML） directly utilizing the measured Time of Arrivals（TOAs） is *** x-ray pulsar radiation will be traded as a cyclostationary process and the TOAs of the photons in a period will be redefined as a new process,whose probability distribution function is the normalized standard profile of the *** proved the new process is equivalent to the general used poisson ***,the phase estimation problem is recast as a cyclic shift parameter estimation process under ML estimation,and we also put forwards a parallel ML estimation method to improve the ML ***,numerical simulation results show how the herein described estimator present a higher precision and reduced computation complexity compared with the current estimators.

关键词： X‐ray pulsar poisson model phase estimation maximum likelihood

来源： cnki会议评论

在线全文

cnki会议

学校读者我要写书评

暂无评论

细分市场间产品线水平延伸的因素分析

低生育意愿的一个解释：养儿防老向商业保险养老转变

市场营销（理论版） 2010年第4期

作者：白让让

从构建市场结构、能力与产品线水平延伸关系的理论假设出发，运用泊松计数模型对180个混同样本数据进行了验证，主要结论包括：①市场集中度与企业产品线的水平长度显著负相关：竞争性品种的增加会导致容量有限市场中延伸激励的下降，... 详细信息

从构建市场结构、能力与产品线水平延伸关系的理论假设出发，运用泊松计数模型对180个混同样本数据进行了验证，主要结论包括：①市场集中度与企业产品线的水平长度显著负相关：竞争性品种的增加会导致容量有限市场中延伸激励的下降，而在高成长市场中则会引发跟随效应。②市场占有率越高，企业越有能力进入高端市场。③本土企业与合资企业的细分市场偏好存在显著的差异，产业内生命周期的延伸会影响延伸行为的变化。这些发现对本土企业优化产品线策略有参考价值。

关键词：产品线水平延伸轿车企业泊松模型 product line horizontal extension car manufacturers poisson model

来源：人大复印报刊资料评论

在线全文

人大复印报刊资料

学校读者我要写书评

暂无评论