Comparing the accuracy of density forecasts from competing models

A rapidly growing literature emphasizes the importance of evaluating the forecast accuracy of empirical models on the basis of density (as opposed to point) forecasting performance. We propose a test statistic for the null hypothesis that two competing models have equal density forecast accuracy. Monte Carlo simulations suggest that the test, which has a known limiting distribution, displays satisfactory size and power properties. The use of the test is illustrated with an application to exchange rate forecasting. Copyright © 2004 John Wiley & Sons, Ltd.     

鄂温克语变迁探析——以查巴奇鄂温克民族村为个案

在经济、文化等各领域全方位全球化的语境下,少数民族语言正经历着前所未有的变迁,这种趋势对人口较少民族语言的冲击尤为明显。通过田野访谈和问卷调查的方法,对查巴奇鄂温克民族村鄂温克语的变迁情况进行了个案调查,试图分析当地鄂温克语变迁的主要原因,并提出相应的对策。     

The structural intolerance of the PrP α-fold for polar substitution of the helix-3 methionines

The conversion of the cellular prion protein (PrP^C) into its disease-associated form (PrP^Sc) involves a major conformational change and the accumulation of sulfoxidized methionines. Computational and synthetic approaches have shown that this change in the polarity of M206 and M213 impacts the C-terminal domain native α-fold allowing the flexibility required for the structural conversion. To test the effect in the full-length molecule with site-specificity, we have generated M-to-S mutations. Molecular dynamics simulations show that the replacement indeed perturbs the native state. When this mutation is placed at the conserved methionines of HaPrP(23–231), only substitutions at the Helix-3 impair the α-fold, stabilizing a non-native state with perturbed secondary structure, loss of native tertiary contacts, increased surface hydrophobicity, reduced thermal stability and an enhanced tendency to aggregate into protofibrillar polymers. Our work supports that M206 and M213 function as α-fold gatekeepers and suggests that their redox state regulate misfolding routes.     

手机英文短信的语体特征与修辞艺术

随着通讯技术的发展，手机短信日益成为人们交际的一种新型文体。与手机中文短信一样，手机英文短信呈现出独特的语体特征：短小精练、通俗形象，幽默风趣、轻松诙谐，委婉含蓄、抒情浪漫，等等。多种修辞法的运用是促成这些语体特征的主要原因。     

单板条层积材力学模型的验证与分析

在利用弹性力学能量原理建立的单板条层积材力学模型基础上,应用层合板理论计算单板条层积材的宏观弹性常数。通过在单板条上黏贴应变片的方法测定杨木单板条的各项弹性常数,并得出了单板条弹性常数与单板条对应密度的关系方程。在此基础上,通过压制不同铺装角度和不同组坯结构的单板条层积材来对计算结果进行验证,验证结果表明,以能量原理为基础,采用层合板理论来预测单板条层积材的力学模型精度较高。     

An endocannabinoid mechanism for stress-induced analgesia

Acute stress suppresses pain by activating brain pathways that engage opioid or non-opioid mechanisms. Here we show that an opioid-independent form of this phenomenon, termed stress-induced analgesia, is mediated by the release of endogenous marijuana-like (cannabinoid) compounds in the brain. Blockade of cannabinoid CB(1) receptors in the periaqueductal grey matter of the midbrain prevents non-opioid stress-induced analgesia. In this region, stress elicits the rapid formation of two endogenous cannabinoids, the lipids 2-arachidonoylglycerol (2-AG) and anandamide. A newly developed inhibitor of the 2-AG-deactivating enzyme, monoacylglycerol lipase, selectively increases 2-AG concentrations and, when injected into the periaqueductal grey matter, enhances stress-induced analgesia in a CB1-dependent manner. Inhibitors of the anandamide-deactivating enzyme fatty-acid amide hydrolase, which selectively elevate anandamide concentrations, exert similar effects. Our results indicate that the coordinated release of 2-AG and anandamide in the periaqueductal grey matter might mediate opioid-independent stress-induced analgesia. These studies also identify monoacylglycerol lipase as a previously unrecognized therapeutic target.     

透过学习策略看公外学生对英语的自主学习

通过对公外学生的英语学习策略即认知策略、元认知策略和社会情感策略的调查,发现公外学生的英语自主学习能力较弱,从改进课堂教学方式、提高元认知及自主学习意识、鼓励学生了解自身认知风格、协助学生确立学习目标和树立终身学习英语的意识几方面提出相应的改进建议。