A Spectral Estimator of Arma Parameters from Thresholded Data

We consider computationally-fast methods for estimating parameters in ARMA processes from binary time series data, obtained by thresholding the latent ARMA process. All methods involve matching estimated and expected autocorrelations of the binary series. In particular, we focus on the spectral representation of the likelihood of an ARMA process and derive a restricted form of this likelihood, which uses correlations at only the first few lags. We contrast these methods with an efficient but computationally-intensive Markov chain Monte Carlo (MCMC) method. In a simulation study we show that, for a range of ARMA processes, the spectral method is more efficient than variants of least squares and much faster than MCMC. We illustrate by fitting an ARMA(2,1) model to a binary time series of cow feeding data.     

描述数控铣床伺服进给系统跟踪性能的新概念——跟踪精度初探

本文针对数控铣床伺服进给系统跟踪性能目前还缺乏定量描述的问题,提出了描述和评价数控铣床伺服进给系统跟踪性能好坏的新概念———跟踪精度;并且对常用的全闭环系统跟踪精度的计算公式进行了推导。以此来定量描述其跟踪性能。     

变速箱多向挤压铸造补缩位置和补缩力的研究

针对目前复杂铸件成形存在的缩松缩孔问题,以某铝合金摩托车变速箱为研究对象,利用专业铸造软件Procast 进行数值模拟。研究了铸件充型和凝固过程的温度场,预测了缩松缩孔的位置。模拟结果表明,缩松缩孔位置出现在气 缸孔处,因此将挤压头设置在该处进行锻压补缩。根据经验公式初步确定补缩力大小,然后对变速箱进行多向挤压铸造 模拟,最终确定补缩力大小。最后,根据优化的工艺参数开展试验研究,获得高品质铸件。     

Medicalized mothering: experiences with breastfeeding in Canada and Norway

This paper explores infant feeding practices and experiences of mothers in Canada and Norway, two countries where breastfeeding rates are relatively high. Based on interviews with 33 Canadian mothers and 27 Norwegian mothers, we also examine how mothers feel, think and talk about their infant feeding decisions and experiences, and examine similarities and divergences across their stories. Our findings reveal that infant feeding is very much organized according to the logic of the broader medical discourse, a finding which lends support to arguments that contemporary parenthood is characterized by a process of increasing medicalization. Our findings also reveal the existence of a broader culture of pressure, competition, judgement and surveillance regarding breastfeeding, suggesting that the high breastfeeding rates in these two countries are not merely a result of favourable structural conditions, but also of strong cultural expectations towards breastfeeding. We discuss our findings in connection with the broader argument that medical discourses and health professionals are becoming the primary authorities and moral gatekeepers of contemporary parenthood.     

Why Reduced-Form Regression Models of Health Effects Versus Exposures Should Not Replace QRA: Livestock Production and Infant Mortality as an Example

Do pollution emissions from livestock operations increase infant mortality rate (IMR)? A recent regression analysis of changes in IMR against changes in aggregate “animal units” (a weighted sum of cattle, pig, and poultry numbers) over time, for counties throughout the United States, suggested the provocative conclusion that they do: “[A] doubling of production leads to a 7.4% increase in infant mortality.” Yet, we find that regressing IMR changes against changes in specific components of “animal units” (cattle, pigs, and broilers) at the state level reveals statistically significant negative associations between changes in livestock production (especially, cattle production) and changes in IMR. We conclude that statistical associations between livestock variables and IMR variables are very sensitive to modeling choices (e.g., selection of explanatory variables, and use of specific animal types vs. aggregate “animal units). Such associations, whether positive or negative, do not warrant causal interpretation. We suggest that standard methods of quantitative risk assessment (QRA), including emissions release (source) models, fate and transport modeling, exposure assessment, and dose-response modeling, really are important—and indeed, perhaps, essential—for drawing valid causal inferences about health effects of exposures to guide sound, well-informed public health risk management policy. Reduced-form regression models, which skip most or all of these steps, can only quantify statistical associations (which may be due to model specification, variable selection, residual confounding, or other noncausal factors). Sound risk management requires the extra work needed to identify and model valid causal relations.     

破解资源节约与扩大内需的矛盾

在粗放的增长模式下,资源节约与扩大内需构成了一对现实的矛盾,同时实现这两个目标的关键是如何看待内需。作为增长动力的需求是具有层次的,并不是任何消费需求都是合理的,因此,需求结构的优化应当成为扩大内需的基本思路。本文从发展模式角度破解我国资源节约与扩大内需的现实矛盾,并主张从健康的城市化、大幅提高人力资本积累与反哺自然三个方面来实现资源节约与内需扩大的融合。     

中国农业政策研究:一个财政视角

讨论经济发展中的三种农业问题及针对这些问题采取的不同的农业政策。通过对我国指标的考察,我国农业中存在的是相对贫困问题,应该采取从剥夺农业向反哺农业过渡的政策。我国财政视角下的农业政策与实证分析的结论不相一致,如何改变这种现状成为今后我国农业政策调整的方向。     

全舍式饲养杂交商品鸭的试验

试验就天府肉鸭(♂)与四川麻鸭(♀)的杂交商品鸭的饲养方式进行了初步探讨,结果表明:采用全舍式饲养杂交商品鸭比采用网上平养定时放水的饲养方式平均日增重提高14.3％,饲料转化率提高11.0％,每饲喂一只鸭子平均经济效益提高27.1％,经X~2检验,两种饲养方式其发病率无显著差异(P>0.05)。     

试论剑阁县畜牧业的发展

本文运用系统理论的原理分析了剑阁县畜牧业的基本状况、有利条件、限制因子、存在的问题、总体设想和相应对策。     

Sexual differences in natal dispersal and philopatry of the grey-sided vole

The natal dispersal distance of the grey-sided vole,Clethrionomys rufocanus (Sundevall), was measured in a large outdoor enclosure (2.1 ha) in Hokkaido, Japan. Voles in about half of the enclosure (1 ha) were fed. Distance from the natal site to the site of reproduction was significantly greater in males (64.9 m) than in females (35.3 m). In males, 24.8% settled within one home range length of their natal site and 49.6% settled further than two range lengths from their natal site. In femles, the respective percentages were reversed: 51.2% and 22.0%. The timing of large movements (≥50 m) was related to body mass in both sexes. The population density was always higher on the fed grid than on the control grid, which resulted in the frequency of large movements being greater on the fed grid that on the control grid. Thus, the percentage of voles performing a large movement was not different between the grids in both sexes.