一类奇次微分系统的极限环的存在唯一性

运用Ｇ Ｓａｎｓｏｎｅ定理和旋转向量场理论，研究奇次微分系统ｘ＝－ｙ（１－ａｘ）（１－ｂｘ）＋δｘ－ｌｘ＾２ｎ＋１，ｙ＝ｘ（１－ａｘ）（１－ｂｘ）的极限环的存在唯一性。证明了：当δｌ≤０时不存在极限环，当δｌ〉０，│δ│〈│ｌ│／ｍａｘ｛ａ＾２ｎ，ｂ＾２ｎ｝时存在唯一的极限环；当δｌ〉０，│δ│≥│ｌ│／ｍａｘ｝ａ＾２ｎ，ｂ＾２ｎ｝，时不存在极限环。     

吸附式制冷中回质过程的作用

引入回质循环，设计了一套使用活性炭－氨为工质对，用发动机余热驱动的吸附式汽车空调，建立了回质循环的计算模型，对样机的回质过程及其对吸附式制冷循环性能的影响进行了定性分析和定量计算，并与基本循环、回热循环进行了对比，同时引入了回质系数表征回质完善度，结果表明，回质过程大幅度提高了循环制冷量，但在某些工况下，也有可能降低系统的性能系数；金属及流体热容变化对回质过程的作用不明显；回质对性能的影响主要取于工质对的吸附特性，在不同的回质系数下，回质循环的性能变化遵循基本一致的规律。回质过程对于循环性能系数的影响没有对循环制冷量的影响大。     

Predicting Recessions with Factor Linear Dynamic Harmonic Regressions

We propose a new framework for building composite leading indicators for the Spanish economy using monthly targeted predictors and small‐scale dynamic factor models. Our leading indicator index, based on the low‐frequency components of four monthly economic variables, is able to predict the onset of the Spanish recessions as well as the gross domestic product (GDP) growth cycles and classical industrial production cycles, both historically and in real time. Also, our leading indicator provides substantial aid in forecasting annual and quarterly GDP growth rates. Using only real data available at the beginning of each forecast period, our indicator one‐step‐ahead forecasts shows substantial improvements over other alternatives. Copyright © 2013 John Wiley & Sons, Ltd.     

Halin图在环面上嵌入的性质

利用拓扑的方法,研究了Halin图在环面上的不同嵌入数目与其叶圈是否可收缩有关,并给出了Halin图在环面上的简单圈基性质,从而推广了Josef Leydold、Peter F.Stadler等人的相关结果.     

A class of periodic trend models for seasonal time series

Trend and seasonality are the most prominent features of economic time series that are observed at the subannual frequency. Modeling these components serves a variety of analytical purposes, including seasonal adjustment and forecasting. In this paper we introduce unobserved components models for which both the trend and seasonal components arise from systematically sampling a multivariate transition equation, according to which each season evolves as a random walk with a drift. By modeling the disturbance covariance matrix we can encompass traditional models for seasonal time series, like the basic structural model, and can formulate more elaborate ones, dealing with season specific features, such as seasonal heterogeneity and correlation, along with the different role of the nonstationary cycles defined at the fundamental and the harmonic frequencies in determining the shape of the seasonal pattern.     

冻融循环对大尺寸陶粒混凝土冲击压缩性能的影响

首次采用卧式Hopkinson束杆装置进行冲击压缩实验，研究了冻融循环试验过程中裂缝发展和动弹性模量变化的规律及冻融循环周次对陶粒混凝土大尺寸试样冲击压缩性能的影响.实验结果表明动态抗压强度随着冻融循环周次的增加而降低，随陶粒体积分数增加而降低，最大抗压强度随加载应变率的增加而增加.     

辽河盆地新生界火山喷发旋回和期次及其油气地质意义

基于300口钻遇火山岩层系的岩心及岩屑薄片、测井和地震等资料,依据火山地层学方法及地震火山地层学理论,通过火山地层界面识别,研究辽河盆地新生界火山喷发旋回和期次,对各个喷发旋回、期次火山地层进行平面成图,揭示火山活动时空规律;进一步结合火山地层分布与油气的关系,探究火山喷发旋回、期次的油气地质意义。结果表明:辽河盆地新生界火山岩系可划分为4旋回15期;底部旋回一和顶部旋回四为玄武岩,显示火山喷发以基性岩开始,又以基性岩结束;中部的旋回二和三均为玄武岩→粗面岩→玄武岩的岩性序列,构成本区火山地层的主体。火山岩受北东向主干断裂控制,最大厚度位于断裂带附近;早期(期次1至期次2)全区分布,末期(期次15)分布局限;中期(期次3至期次14)表现为喷发中心由北向南依次迁移特征。该结果提高了火山岩序列的纵向刻画精度,厘清了有利火山岩层系的空间分布,有助于寻找火山岩勘探新层系。以往辽河盆地火山岩勘探主要集中于沙三段中亚段粗面岩(期次5),本次研究发现与粗面岩相邻的期次4、期次6、期次7玄武岩亦展现出良好的油气勘探前景,为下一步勘探指明了方向。     

初始含水量及冻融循环对黄土微结构的影响

冻融循环作用是季节性冻土地区工程病害发生的主要致灾因子。在冻融循环作用下,土体结构性逐渐丧失、强度不断劣化,最终导致灾害的发生。以延安市延安新区黄土为研究对象,配置不同初始含水量试样,经历0、1、3、6、10、15次冻融循环,通过SIGMA500扫描电子显微镜观察试样微观结构的演化规律。试验结果表明:随着冻融循环次数的增加,试样内部裂纹、裂缝不断发育演化,水分迁移通道不断扩展;初始含水量高的试样裂纹裂缝发育演化越明显;冻融循环作用使得试样内部大颗粒分解为若干小颗粒、颗粒表面的棱角不断磨圆、表面起伏不断减小;当冻融循环10次以后,颗粒大小、颗粒形状、表面起伏趋于稳定,试样颗粒尺寸趋于统一,试样大孔隙减小,小空隙增多,总体孔隙率增大。试样颗粒间的胶结强度随着冻融循环次数的增加不断减小,破碎作用产生的小颗粒造成粒间的接触点增多,致使试样的内摩擦角增大。     

Paleosol evolution and environmental change in the Huang-Huai-Hai Plain, China

Paleosols in the Huang-Huai-Hai Plain occur mainly in the Huaibei, Xuhuai, Yischuhe and Jiaolai areas. They result from 3 sedimentation-soil formation cycles since the Late Pleistocene. Each cycle left calcareous concretions, a dark soil horizon, and a topsoil horizon and/or a stratified soil horizon all derived from loess. This paper examines the composition of the concretions, compares this with that of the enclosing soil horizons, and draws some environmental conclusions. Three types occur: embryonic calcareous concretions, mature calcareous concretions, and calcareous hardpans (petrocalcic horizons). The embryonic concretions formed during the mid-Holocene (6780±130 yr. B.P.), mature calcareous concretions during the late-Pleistocene (weighted average of 31 samples = 15670±370 yr. B.P.), and calcareous hardpans (petrocalcic horizons) from 16 to 40 ka B.P. The calcium carbonate content increases from 412 g/kg in the embryonic concretions, to 551 g/kg in the mature concretions, and to 691 g/kg in the hardpan, whereas contents of SiO_2, Al_2O_3 and TiO_2 decrease accordingly. Spore pollen analysis shows that the late-Pleistocene there was dry and cool, whereas the mid-Holocene was warm and humid and lakes were more extensive than today.