A simple,automatic and adaptive bivariate density estimator based on conditional densities

The standard approach to non-parametric bivariate density estimation is to use a kernel density estimator. Practical performance of this estimator is hindered by the fact that the estimator is not adaptive (in the sense that the level of smoothing is not sensitive to local properties of the density). In this paper a simple, automatic and adaptive bivariate density estimator is proposed based on the estimation of marginal and conditional densities. Asymptotic properties of the estimator are examined, and guidance to practical application of the method is given. Application to two examples illustrates the usefulness of the estimator as an exploratory tool, particularly in situations where the local behaviour of the density varies widely. The proposed estimator is also appropriate for use as a pilot estimate for an adaptive kernel estimate, since it is relatively inexpensive to calculate.     

Improved Monte Carlo inference for models with additive error

Some statistical models defined in terms of a generating stochastic mechanism have intractable distribution theory, which renders parameter estimation difficult. However, a Monte Carlo estimate of the log-likelihood surface for such a model can be obtained via computation of nonparametric density estimates from simulated realizations of the model. Unfortunately, the bias inherent in density estimation can cause bias in the resulting log-likelihood estimate that alters the location of its maximizer. In this paper a methodology for radically reducing this bias is developed for models with an additive error component. An illustrative example involving a stochastic model of molecular fragmentation and measurement is given.     

我国区域经济差距的空间演变趋势及其成因

文章采用空间马尔科夫链方法分析了我国区域差距和经济发展的空间效应及演变趋势,发现地理背景对经济类型转移具有显著影响,区域经济类型不会发生明显的跃迁,经济增长存在空间相关性和路径依赖性。然后,利用Kernel密度分布法提供了同时考察经济增长及区域差距的新分析框架,从经济增长分布演进的视角,分析了我国区域经济差距的原因。研究结果显示,中国经济差距扩散的动力来源于效率改进而非要素投入。     

几种药物对降低尿素分解液中氨浓度的试验

在相同的外界条件下,在相同浓度的等量脲酶尿素液中加入脲酶抑制剂、吸附剂,在不同时间进行pH值和NH_3—N值的测定,研究各药物对降低氨浓度的强弱。结果表明:各试验组氨浓度极显著低于对照组(P<0.01);在添加剂量相同的情况下,脲酶抑制剂和药用炭的作用较强(P<0.05),二者之间差异不显著(P>0.05);浮石、滑石粉、BIO—ADE作用较弱且三者之间差异不显著(P>0.05),三者中以选择滑石粉较好(价格较便宜)。     

有限温度格点U(1)及定模U(1)-Higgs模型Symanzik作用量的解析研究

本文用变分累积展开方法(VCE)解析研究了Symanzik作用量形式的有限温度格点U(1)及定模U(1)-Higgs规范模型,并计算了序参量Polyakov线〈L〉及临界指数β。结果表明,采用Symanzik作用量的变分累积展开比Wilson作用量收敛快。     

甜菜施肥和种植密度综合效应初探

应用多元二次肥料效应数学模型,根据种肥、追肥、密度和甜菜产量结果,得出粉沙壤土肥料密度综合效应方程y＝1954．524＋10．334x1＋31．890x2＋130．027x3＋68．925x1x2＋7．775x1x3＋26．700x2x3＋124．435＋41．082－124．811。用此方程估测甜菜产量和实际产量极为接近。     

玉米种植密度与双棒率及空杆率的调查分析

玉米双棒率与空杆率是影响产量的两个因素,经调查研究表明：双棒率与种植密度有关,密度小,双棒率高,经测验差异显著;空杆率与密度无关,差异不显著。