MARSIS radar sounder evidence of buried basins in the northern lowlands of Mars

A hemispheric dichotomy on Mars is marked by the sharp contrast between the sparsely cratered northern lowland plains and the heavily cratered southern highlands. Mechanisms proposed to remove ancient crust or form younger lowland crust include one or more giant impacts, subcrustal transport by mantle convection, the generation of thinner crust by plate tectonics, and mantle overturn following solidification of an early magma ocean. The age of the northern lowland crust is a significant constraint on these models. The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument on the European Space Agency's Mars Express spacecraft is providing new constraints on the martian subsurface. Here we show evidence of buried impact basins ranging in diameter from about 130 km to 470 km found over approximately 14 per cent of the northern lowlands. The number of detected buried basins >200 km in diameter indicates that the lowland crust is ancient, dating back to the Early Noachian epoch. This crater density is a lower limit because of the likelihood that not all buried basins in the area surveyed by MARSIS have been detected. An Early Noachian age for the lowland crust has been previously suggested on the basis of a large number of quasi-circular topographic depressions interpreted to be evidence of buried basins. Only a few of these depressions in the area surveyed by MARSIS, however, correlate with the detected subsurface echoes. On the basis of the MARSIS data, we conclude that the northern lowland crust is at least as old as the oldest exposed highland crust. This suggests that the crustal dichotomy formed early in the geologic evolution of Mars.     

连载二洋兰

4.卡特兰属的古塔塔C.guttata（同种异名C.leopoldii）卡特兰属中蛔古塔塔C.guttata（同种异名C.leopoldii）是卡特兰属中双叶小花系种类,原生于巴西东海岸低地至海拔400米左右的地区。古塔塔guttata的语意是[泪斑],是因花瓣上有似泪花斑点,而被除数定为种名。南半球的巴西是在1-2月开花,北半球是在7月左右开花。花数可有6-15朵,花虽不很大,植株可高达1.5米,是卡特兰中植株最高的种类。花期长,有芳香味,花的色彩也很多。     

New evidence on the robust identification of news shocks: Role of revisions in utilization‐adjusted TFP series and term structure data

Data revisions and selections of appropriate forwarding‐looking variables have a major impact on true identification of news shocks and quality of research findings derived from structural vector autoregression (SVAR) estimation. This paper revisits news shocks to identify the role of different vintages of total factor productivity (TFP) series and term structure of interest rates as major prognosticators of future economic growth. There is a growing strand of literature regarding the use of utilization‐adjusted TFP series, provided by Fernald (Federal Reserve Bank of San Francisco, Working Paper Series, 2014) for identification of news shocks. We reestimate Barsky and Sims' (Journal of Monetary Economics, 2011, 58, 273–289) empirical analysis by employing 2007 and 2015 vintages of TFP data. We find substantial quantitative as well as qualitative differences among impulse response functions when using 2007 and 2015 vintages of TFP data. Output and hours initially decline, followed by quick reversal of both variables. In sharp contrast to results achieved by the 2007 vintage of TFP data, results achieved by the 2015 vintage of TFP data depict that output and hours will increase in response to positive TFP shock. By including term structure data in our VAR specification, total surprise technology shock and news shock account for 97% and 92% of the forecast error variance in total TFP and total output respectively. We find that revisions in TFP series over time ultimately impact the conclusion regarding news shocks on business cycles. Our results support the notion that term structure data help in better identification of news shock as compared to other forward‐looking variables.     

存在镜面反射时的双目立体匹配

传统的立体匹配方法建立在Lambertian的漫反射模型之上,漫反射模型的立体匹配在一个图像的大多部分是有效的,但是在处理图像中包含镜面反射的部分时结果会产生严重的匹配错误。笔者利用漫反射和镜面反射在灰度和最大色度上的不同,分离出镜面反射的像素,然后采用一种针对镜面反射的匹配测度,在图像中漫反射部分和镜面反射部分都能匹配得到正确的视差。结果证明了方法的有效性。     

连载一洋兰

在中国兰花的栽培有悠久的历史，中国在《易经》中已有“同心之言，其臭如兰”的说法。孔子在过隐谷时，见幽兰独茂，叹曰：“夫兰当为王者香，今乃与众草为伍；譬贤者不逢时？鄙夫为伦也。”以兰花的幽香来比喻人之高雅。     

连载一洋兰

在中国，兰花的栽培有悠久的历史，中国在《易经》中已有“同心之言，其臭如兰”的说法。孔子在过隐谷时，见幽兰独茂，叹曰：“夫兰当为王者香，今乃与众草为伍；譬贤者不逢时？鄙夫为伦也。”以兰花的幽香来比喻人之高雅。     

悬空轨枕对轨道结构动力响应的影响

首先建立了带有悬空轨枕的铁路轨道数学模型,在此基础上推导了车—轨系统运动方程,其中考虑了轮轨非线性接触力引起的非线性问题,然后利用逐步积分法解方程重点分析了悬空轨枕对轨道各个组成部分动力响应的影响,结果表明如果在悬空部分存在轨道不平顺,会引起很大的轨枕加速度和轮轨接触力     

Deep Geothermal:The‘Moon Landing’ Mission in the Unconventional Energy and Minerals Space

Deep geothermal from the hot crystalline basement has remained an unsolved frontier for the geothermal industry for the past 30 years. This poses the challenge for developing a new un-conventional geom...