Characterstics of seasonal variations of leaf n-alkanes and n-alkenes in modern higher plants in Qingjiang, Hubei Province, China

On the basis of GC and GC-MS analyses, the seasonal variation of leaf lipids is observed in five plant species in Qingjiang in Hubei Province. The CPI values （carbon preference index） of n-alkanes decrease gradually from May to November, though the carbon number distributions and the predominant carbon number in an individual species keep unchanged. The declined CPI values might be caused by the leaf fading, which is further supported by a comparison of the defoliated leaves with the fresh leaves. This observation infers the CPI values of n-alkanes in Quaternary sediments can be used as a tool to index the humification, and thus the climatic and the environmental conditions. The plants analyzed here show a remarkable difference in n-alkanes abundance, suggesting their differential contribution to the n-alkanes identified in sediments. The abundance and the compound species of the n-alkenes detected in the plant leaves change greatly with the seasons due to the influence of temperature, with the least compounds being identified in August.     

一种用于机床角度头故障诊断的双重降噪方法

角度头是数控机床必不可少的加工附件,由于长期处于恶劣的加工工况下,极易受到损坏。采集角度头的振动信号时,环境中大量的随机噪声会湮没故障特征信息,从而造成角度头故障特征提取困难。针对此问题,提出了一种基于总体平均经验模态分解（ensemble empirical mode decomposition,EEMD）及自相关的双重降噪方法。该方法采用自相关滤波方法对振动信号进行降噪预处理,再对降噪后的信号进行EEMD分解,随后采用遗传算法对EEMD输入参数优化,依据相关峭度系数准则筛选分解得到的固有模态函数（intrinsic mode function,IMF）分量进行信号重构。最后,对重构信号进行时频分析,提取角度头故障特征。对仿真和实测信号分析的结果表明,本文方法能够有效抑制噪声干扰,可准确提取到角度头的故障特征信息,为机床角度头的故障诊断提供依据。     

A comparative study of n -alkane biomarker and pollen records: an example from southern China

We report the results of a comparative study of n-alkane biomarkers and pollens in lacustrine and peat deposits at Dingnan, Jiangxi Province in southern China, and discuss the likely causes for the discrepancy in the interpretations of the n-alkane biomarker and pollen records in terms of climate and vegetation change. The results show that past changes in climate and vegetation revealed by the n-alkane record are not always consistent with the pollen assemblage record in the whole section. Biomarkers do not permit direct identification of the plant family and/or genus and mainly record compositions of local plant remains, while pollens mainly reflect the regional vegetation change. Biomarkers and pollen records complement each other, providing a better picture of local and regional environments. Furthermore, biomarkers are more sensitive than pollen to climatic and vegetational change. Several climatic events are clearly identified by the n-alkane biomarker proxies, such as C₃₁/(C₂₇+C₂₉+C ₃₁) ratio and can be correlated to the North Atlantic Heinrich event, B/A, YD and two dry-cool events during the early Holocene such as the periods of 9850 to 9585 cal a B.P. and 8590 to 7920 cal a B.P. These events are consistent with those found in the surrounding regions, suggesting that the regional climate was coupled with global-scale abrupt climatic events. Our results suggest that biomarker and pollen data can record the more detailed climate and vegetation information, thus improving the resolution and precision of vegetation and climate reconstruction. Supported by National Natural Science Foundation of China (Grant No. 40602004) and National Basic Research Program of China (Grant No. 2004CB720200)     

Geomicrobial functional groups: A window on the interaction between life and environments

Microbes are well-known for their great diversity and abundance in modern natural environments.They also are believed to pro-vide critical links among higher organisms and their associated environments.However,the low diversity of morphological fea-tures and structures of ancient microbes preserved in sediments and rocks make them difficult to identify and classify.This diffi-culty greatly hinders the investigation of geomicrobes throughout Earth history.Thus,most previous paleontological studies have focused on faunal and floral fossils.Here,geomicrobial functional groups(GFGs),or a collection of microbes featured in specific ecological,physiological or biogeochemical functions,are suggested to provide a way to overcome the difficulties of ancient mi-crobe investigations.GFGs are known for their great diversity in ecological,physiological and biogeochemical functions.In addi-tion,GFGs may be preserved as the biogeochemical,mineralogical and sedimentological records in sediments and rocks.We reviewed the functions,origins and identification diagnostics of some important GFGs involved in the elemental cycles of carbon,sulfur,nitrogen and iron.GFGs were further discussed with respect to their significant impacts on paleoclimate,sulfur chemistry of ancient seawater,nutritional status of geological environments,and the deposition of Precambrian banded iron formations.     

Holocene vegetation cover in Qin’an area of western Chinese Loess Plateau revealed by n-alkane

Previous studies have found that wetlands prevailed in western Chinese Loess Plateau and pine pollen could reach up to 80% in Qin＇an area of the plateau during middle Holocene. It was then deduced that forest vegetation covered Qin＇an area in a warm and wet climate during middle Holocene. The proxies of molecule biomarkers from two Holocene sections, a swamp-alluvial loess section and a typical Ioess-paleosol section are used to reconstruct regional vegetation history. It is found that the heavy-molecular-weight （HMW） homologues of the n-alkanes in all samples exhibit a pronounced odd-over-even predominance, maximizing at C31 and the abundance of the nC27-alkanes is the lowest in nC27, nC29, nC31, i.e. C27〈C29〈C31, a typical grass n-alkanes model. The results are the same as those of model surface soil samples under grass cover but different from both forest cover and modern pine leaves, which yield preferentially nC29-alkanes peak. It could be inferred that the area was dominated by grass cover but not forest cover during whole Holocene epoch. The study shows that combining both molecule biomarkers and pollen analysis can avoid the disadvantage of pollen analysis in reconstruction of regional vegetation cover.     

基于果蝇算法的转子不平衡参数辨识研究

为识别转子的不平衡参数,建立了转子-轴承有限元模型,在逆问题的识别理论基础上通过理论故障力与等效估计的不平衡力构建目标函数,运用果蝇优化算法进行目标函数优化,从而识别出不平衡参数,并将果蝇算法识别的结果与模拟退火算法、遗传算法的结果进行对比。仿真和实验结果均表明,相比其他两种算法,果蝇算法有更高的识别精度和效率。     

大数据时代的天文学研究

天文学已经进入数据密集型时代或者说大数据时代.面对海量天文数据在存储、计算、网络、软件、算法乃至工作模式等方面的需求和挑战,天文学家连同计算机和信息技术领域的专家正努力使基于科学数据的知识发现过程变得更加容易.虚拟天文台旨在实现科学数据的互操作,打造一个全球性的数据网格.天文信息学则从分支学科的高度来考虑天文学的长远发展.数据挖掘和知识发现在数据密集型时代大有可为,自身也必将获得长足发展.本文简要论述天文学研究在数据密集型时代所面临的挑战,介绍虚拟天文台理念和最新进展,探讨天文信息学发展的必要性和所包含的研究内容,阐明数据挖掘和知识发现的必要性和发展方向.     

羰基合成丁醛反应过程的模拟

对丁醛生产流程中的羰基合成反应过程进行了模型化和动态模拟技术的研究。根据体系的物料平衡和能量平衡的分析,在可靠的热力学和反应动力学基础上,建立了丙烯氢甲酰化全混釜反应系统的数学模型。并根据合理的求解计算方法求解模型体系,最后完成本反应器的动态模拟过程。计算的结果和对比分析表明,本次动态模拟能很好地体现生产变化规律。     

Preliminary Mo isotope data of Phanerozoic clastic sediments from the northern margin of the Yangtze block and its implication for paleoenvironmental conditions

Mo isotopes along with Nd isotopes and other geochemical characteristics of the Phanerozoic clastic sediments from the northern margin of the Yangtze block were analyzed by MC-ICP-MS and some other techniques, spanning the period from Cambrian to Jurassic. The δ 98Mo values and εNd(t ) in these sedimets were observed to exhibit a large range of variation (?0.65‰―+1.87‰, ?1.46―?10.90, respec-tively). Specifically, the sample from Late Permian Maokou Formation has relatively positive values in both δ 98Mo and...