反馈控制器的降阶问题

根据线性离散随机系统的包含原理,研究了系统的状态反馈和输出反馈控制器的降阶问题．给出了控制器降阶两种类型：聚集和约束．通过一个9阶系统控制器的设计,讨论降阶控制器和全阶控制器的性能．     

Synthesis of high molecular weight polylactic acid from aqueous lactic acid co-catalyzed by tin（Ⅱ）chloride dihydrate and succinic anhydride

Polylactic acid was synthesized from commercial available cheap aqueous lactic acid （85%-90% w/w） using succinic anhydride and SnCl2·2H2O as catalyst in the absence of organic solvents. As a result, polylactic acid with a molecular weight of 60000 was prepared in 10 h. The new procedure is much simple, cheap and outstanding in that the start material is aqueous lactic acid; the catalytic system is environmentally benign.     

The secretion of lecithinase of Pseudomonas alcaligenes S2 was via type Ⅱ secretion pathway

Strain S2 is a lecithin （or phosphatidylcholine）- solubilizing bacterium, which was isolated from the rice rhizosphere in rural areas of Beijing, China. On the basis of a polyphasic study involving phenotypic tests, physiological and biochemical tests, 16S rDNA sequence analysis, G＋C content determination and DNA-DNA hybridizations analysis, strain S2 was identified as Pseudomonas alcaligenes. R alcaligenes S2 was mutagenized with Tn5 and four mutants showing decreased or increased solubilizing ability of lecithin were isolated based on the halo size around colonies on the solid plate supplemented with egg yolk. To characterize the genes of R alcaligenes S2 involved in solubilization of lecithin, the EcoR I fragments of the chromosomes from the four mutant strains carrying a single transposon were cloned, and the DNA sequences flanking the Tn5 were determined. The Tn5 insertion sites in the mutants M808, M1329 and M1400, showing decreased solubilizing ability of lecithin, were found to be located in the xcpS, xcpX and xcpW , respectively, whose products XcpS, XcpX and XcpW were the components of type Ⅱ secretion pathway. Complementation of xcpS, xcpX and xcpW could restore the corresponding mutants M808, M1329 and M1400 to solubilize lecithin. The data suggested that mutation in one of these xcp genes would lead to the absence of mature lecithinase secretion into the extracellular medium. The data also indicated that the secretion of lecithin-hydrolyzing enzyme of R alcaligenes was via type Ⅱ secretion pathway. In the mutant M20 showing increasing lecithin-hydrolyzing activity, the interrupted gene showed 86% identity with chpA of Pseudomonas aeruginosa PAO1, whose product plays an important role in controlling twitching motility of the bacterial ceils.     

Physical effect of cloud seeding revealed by NOAA satellite imagery

The pioneering work on cloud seeding began in 1946,when Vincent Schaefer noticed that a small piece of solidcarbon dioxide (dry ice) can generate a large number ofice crystals on its falling path in a laboratory-generated data, which make the numerica…     

ADP-flow velocity profile to interpret hydromorphological features of China''''s Yangtze Three-Gorges valley

Land and sea are linked closely by large rivers throughrunoff and sediment discharging and biochemical materialtransferring into the sea[1?3]. The processes carried out byenergy exchange have been in a sensitive response toglobal change[4]. To study the mechanism of sediment transport in the river basin as to reflecting hydromor- phological and climatological controls is thus becoming vital for earth scientists, at present and in the near future since any change in fluvial landform is of a gre…     

“Chi-Fang-Qi”: Is it the aureole of an ancient supernova?

An annotation for the statement about JingXing (Great Star) in the most famous Chinese ancient historical book Ski Ji Historical Records authored by Sima Qian reads as follows: “There was a red aureole (“Chi-Fang-Qi”) which connected with a deep-color aureole (“Qing-Fang-Qi”). Two yellaw stars were in the red aureole,one yellow star was in the deep-color aureole”. The author of the annotation was Meng Kang, an officer as well as a scholar of the Wei State in the Three Kingdoms period. The same records are to be found in two other Chinese histurical books compiled by the authors of later ages in Tang Dynasty——Jin History and Sui History. The scene illustrated by the record of “Chi-Fang-Qi” is very similar to the pictures of SN1987A taken by the Hubble Space Telescope. Let it be noted that although the ancient authors were often with serious wrong understandings of some astronomical phenomena such as supernovae, their depictions about natural phenomena they witnessed were mostly objective, and it was unlikely that they fictionally made the record of “Chi-Fang-Qi”. We infer that the ancient observers might have ever watched a very bright supernnva with an aureole structure in its remnant and then left such a record. Meng Kang perhaps was the first to give the record about“Chi-Fang-Qi”, and he might have lived in the period from about AD 180 to AD250, very near to AD 185. so, here the supernova the ancient people watched was most likely the one in the year of AD 185. This supposition is consistent with the distance parameter of the most possible remnant of SN185 derived by some modern measurements. If the correlation between the record of “Chi-Fang-Qi” and the supernova remnant can he further proven true, it would be an important verification of the modern theory about stellar evolution.     

Capacity of soil to protect organic carbon and biochemical characteristics of density fractions in Ziwulin Haplic Greyxems soil

Physical protection is one of the important ways to stabilize organic carbon in soils. In order to understand the role of soils as a carbon sink or source in global climatic change and carbon cycles and properly manage soils as a carbon sink, we ought to know how many organic carbon (OC) in a given soil could be protected. By a density fractionation approach and ultrasonic technique, each soils ample was divided into three fractions: free light fraction (free-LF), occluded fraction (occluded-LF) and heavy fraction (HF). The obtained fractions were analyzed for total OC content, carbohydrate content and recalcitrant OC content. The results showed: ( i ) In the whole soil profile, dominance of OC consistently decreased in the following order: HF, free-LF, occluded-LF. This suggested that OC in soils were mostly protected. From 0---10 to 60---80 cm horizons, the OC in free-LF decreased from 25.27% to 3.72%, while OC in HF they were increased from 72.57% to 95.39%. The OC in occluded-LF was between 2.16% and 0.89%. (ii) Organic carbon recalcitrance in free-LF was similar to that in HF, and was even higher than that in HF below the surface horizon. This suggested that free-LF was not always the most fresh and non-decomposed fraction. OM quality of HF was higher than that of free-LF in the surface 10 cm below, namely the protected OM had higher quality than free OM in these horizons.