Spatial variation in soil inorganic nitrogen across an arid urban ecosystem

We explored variations in inorganic soil nitrogen (N) concentrations across metropolitan Phoenix, Arizona, and the surrounding desert using a probability-based synoptic survey. Data were examined using spatial statistics on the entire region, as well as for the desert and urban sites separately. Concentrations of both NO₃-N and NH₄-N were markedly higher and more heterogeneous amongst urban compared to desert soils. Regional variation in soil NO₃-N concentration was best explained by latitude, land use history, population density, along with percent cover of impervious surfaces and lawn, whereas soil NH₄-N concentrations were related to only latitude and population density. Within the urban area, patterns in both soil NO₃-N and NH₄-N were best predicted by elevation, population density and type of irrigation in the surrounding neighborhood. Spatial autocorrelation of soil NO₃-N concentrations explained 49% of variation among desert sites but was absent between urban sites. We suggest that inorganic soil N concentrations are controlled by a number of ‘local’ or ‘neighborhood’ human-related drivers in the city, rather than factors related to an urban-rural gradient.     

Dementia Problem Behavior and the Production of Informal Caregiving Services

Informal caregivers of individuals with Alzheimer's disease spend a considerable amount of time providing care. In this paper, we use Grossman's health production and Becker's time allocation models to develop a model of informal care provision to elderly dementia patients. In our model, time inputs produce caregiving services, which provides utility to the caregiver, but reduces leisure. We assume that time is less productive of services on the margin as the disease progresses. In this framework, an increase in patients' disease severity does not necessarily increase informal caregiver time input. The cost of formal care establishes a reservation price for informal caregiving. When the costs of informal caregiving rise above this reservation level, the patient is institutionalized. We test empirically the effect of deterioration in the patients' condition, proxied by both disease severity and dementia problem behavior, on informal caregiving time. We find that dementia-related problem behaviors and functional limitations significantly increase inputs of informal caregiving time. Patients' problem behavior exerts a modifying effect on functional limitations, and patients' comorbidities have no effect on informal caregiving time.     

中日银行不良债权成因比较分析

银行不良债权是中日两国面临的共同问题。本文在分析中日不良债权现状的基础上,从微观经济学和制度经济学视角对两国不良债权的成因进行了比较分析,并结合我国国情,得出解决这一问题的关键是消除形成金融不良资产的制度性根源,最后提出了化解我国不良债权的几点针对性措施。     

印度与非洲（1947—2004）

虽然非洲是一个被忽视了的大陆,但在地理上与历史上与印度关系密切.如今,非洲在印度的对外战略中占有重要地位.本文论述了印度对非洲的外交政策与实践.     

从交流和传播的视角解读越文化

本组讨论以越文化研究为例,探索地域文化研究的方法与视角。朱文斌一文检讨了当前越文化研究范式的局限,提出了范式转换的问题;陈越、梁涌两文分别从空间与时间的存在与发展上对越文化作了动态描述。其中,陈文从文化模式的角度,把越文化概括为“剑—书”文化;梁文则从交流与传播的角度,揭示了越文化的形成与发展。     

Bootstrap Estimation of Benchmark Doses and Confidence Limits with Clustered Quantal Data

The benchmark dose (BMD) is an exposure level that would induce a small risk increase (BMR level) above the background. The BMD approach to deriving a reference dose for risk assessment of noncancer effects is advantageous in that the estimate of BMD is not restricted to experimental doses and utilizes most available dose-response information. To quantify statistical uncertainty of a BMD estimate, we often calculate and report its lower confidence limit (i.e., BMDL), and may even consider it as a more conservative alternative to BMD itself. Computation of BMDL may involve normal confidence limits to BMD in conjunction with the delta method. Therefore, factors, such as small sample size and nonlinearity in model parameters, can affect the performance of the delta method BMDL, and alternative methods are useful. In this article, we propose a bootstrap method to estimate BMDL utilizing a scheme that consists of a resampling of residuals after model fitting and a one-step formula for parameter estimation. We illustrate the method with clustered binary data from developmental toxicity experiments. Our analysis shows that with moderately elevated dose-response data, the distribution of BMD estimator tends to be left-skewed and bootstrap BMDL s are smaller than the delta method BMDL s on average, hence quantifying risk more conservatively. Statistically, the bootstrap BMDL quantifies the uncertainty of the true BMD more honestly than the delta method BMDL as its coverage probability is closer to the nominal level than that of delta method BMDL. We find that BMD and BMDL estimates are generally insensitive to model choices provided that the models fit the data comparably well near the region of BMD. Our analysis also suggests that, in the presence of a significant and moderately strong dose-response relationship, the developmental toxicity experiments under the standard protocol support dose-response assessment at 5% BMR for BMD and 95% confidence level for BMDL.     

学习策略的培养在外语多媒体教学中的必要性

课堂价值的核心在于培养学生主动学习、健康发展的意识和能力。一次为期两个学年的实证性教学实践证实:学习策略的培养在多媒体外语教学中是完全有必要性的,它不仅可以削减多媒体教学方式的负迁移,而且是实现课堂教学价值观的关键。     

民意调查在中国的发展和应用

民意调查在中国出现较早,但其发展还是始于党的十一届三中全会。1992年以后,中国的民意调查形成了调查主体、资金来源、调查内容多元化的发展态势,并且具有了新的发展特点。民意调查应用于社会的各个方面,主要表现在反映社会评价、辅助决策、社会监测、舆论沟通和学术促进等几个方面。     

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。