Model analysis method (MAM) on the effect of the second-order ionospheric delay on GPS positioning solution

In this paper,we develop an approach to study the effect of second-order ionospheric delay on GPS positioning based on the ionosphere-free combination (abbreviated to Lc) of GPS dual-frequency carrier phase observables,in which the first-order ionospheric delay has been eliminated.GPS data from IGS WUHN tracking station during April 9 23,2003 is used to perform the above approach,and results show that the second-order ionospheric delay in GPS so-called ionosphere-free observables will result in the regular ...     

Genome research profile of two <Emphasis Type="Italic">Cordyceps sinensis</Emphasis> cDNA libraries

Cordyceps sinensis (CS) is well known as an ancient Chinese herb. It is used to expand bronchial smooth muscles, inhibit tumor growth and decrease blood pressure. Cordyceps sinensis is composed of two parts. One is the dead larvae body; the other is the stroma like withered grass. Up to now, few genome database articles about Cordyceps sinensis have been reported. In this study, two cDNA libraries were constructed using the worm part and grass part respectively for the first time. 12192 and 15456 clones fro...     

Quantitative analysis of lake area variations and the influence factors from 1971 to 2004 in the Nam Co basin of the Tibetan Plateau

By using remote sensing and GIS technologies, spatial analysis and statistic analysis, we calculated the water area and volume variations of the Nam Co Lake from 1971-2004, and discussed their influence factors from the viewpoints of climatic change and water balance. Data source in this study includes bathymetric data of the lake, aerial surveyed topographic maps of 1970, remote sensing images of 1991 and 2004 in the lake catchment, meteorological data from 17 stations within 1971-2004 in the adjacent area...     

Pre-<Emphasis Type="Italic">Archaeopteryx</Emphasis> coelurosaurian dinosaurs and their implications for understanding avian origins

The last two decades have witnessed great advances in reconstructing the transition from non-avian theropods to avians, but views in opposition to the theropod hypothesis still exist. Here we highlight one issue that is often considered to raise problems for the theropod hypothesis of avian origins, i.e. the “temporal paradox” in the stratigraphic distribution of theropod fossils — the idea that the earliest known avian is from the Late Jurassic but most other coelurosaurian groups are poorly known in the Jurassic, implying that avians arose before their supposed ancestors. However, a number of Jurassic non-avian coelurosaurian theropods have recently been discovered, thus documenting the presence of most of the major coelurosaurian groups in the Jurassic alongside, or prior to, avians. These discoveries have greatly improved the congruence between stratigraphy and phylogeny for derived theropods and, effectively, they reject the “temporal paradox” concept. Most importantly, these discoveries provide significant new information that supports the relatively basal positions of the Tyrannosauroidea and Alvarezsauroidea among the Coelurosauria. Indeed, they imply a new phylogenetic hypothesis for the interrelationships of Paraves, in which Archaeopteryx, the Dromaeosauridae, and the Troodontidae form a monophyletic group while the Scansoriopterygidae, other basal birds, and probably also the Oviraptorosauria, form another clade. Mapping some of the salient features onto a temporally-calibrated theropod phylogeny indicates that characteristics related to flight and arboreality evolved at the base of the Paraves, earlier than the Late Jurassic.     

Records of the East Asian winter monsoon from the mud area on the inner shelf of the East China Sea since the mid-Holocene

AMS¹⁴C dating and analysis of grain size, major elements and clay minerals were applied to Core MZ01 from the mud area on the inner shelf of the East China Sea. Based on the environmentally sensitive grain size, clay mineral and major element assemblages, the history of the East Asia winter monsoon since the mid-Holocene could be reconstructed. These three proxies, mean grain size (>9.71 μm), chemical index of alteration (CIA) and ratio of smectite to kaolinite in particular, show similar fluctuation patterns. Furthermore, 10 extreme values corresponding to the contemporary cooling events could be recognized since the mid-Holocene; these extreme values are likely to have been caused by the strengthening of the East Asia winter monsoon. The cooling events correlated well with the results of the δ¹⁸O curves of the Dunde ice core and GISP2, which therefore revealed a regional response to global climate change. Four stages of the East Asia winter monsoon were identified, i.e. 8300–6300 a BP, strong and unstable; 6300–3800 a BP, strong but stable; 3800–1400 a BP, weak and unstable; after 1400 a BP, weak but stable.     

Recent area and ice volume change of Kangwure Glacier in the middle of Himalayas

This paper calculated and evaluated the area and ice volume changes of Kangwure Glacier in Mt. Xixiabangma, middle of Himalayas in the past 3 decades, based on the field survey of glacier boundary position by differential GPS and glacier depth by Ground Penetrating Radar (GPR), together with the topographic map and remote sense data. The studied data showed that the Kangwure Glacier has experienced significant mass deficit since the 1970s, with 34.2% of area loss, 48.2% of ice volume loss and 7.5 m of average thickness decrease. This result revealed that the ice volume loss of Himalayan glaciers was more serious than expected. Analysis of meteorological data from two weather stations in the region of Mt. Xixiabangma, shows that the air temperature of this region has risen from the middle of the 20th century to the beginning of the 21st century. Significant retreat of Himalayas glacier driven by climatic warming will have a remarkable impact on hydrology and ecosystem.     

Encumbering the intramolecular π donation by using a bridge: A strategy for designing metal-free compounds to hydrogen activation

On the basis of the FLP (frustrated Lewis pair) principle, a new strategy has been proposed to construct the “frustration” in designing metal-free hydrogen activation compounds, by using FMO (frontier molecular orbital) analyses and quantum mechanics calculations. Unlike the known FLPs which use bulky substituents to prevent them from forming stable Lewis acid/base complexes, the new approach encumbers the intramolecular π donation from the electron donor to the acceptor (e.g. in BH₂NH₂) by using a CH₂ bridge (giving BH₂CH₂NH₂). The strategy is simple and effective. Its effectiveness is demonstrated by the small hydrogen activation energy (12.0 kcal/mol) of the model molecule (BH₂CH₂NH₂), which is significantly less than the 42.7 kcal/mol of BH₂NH₂ and also less than the 18.5 kcal/mol of BH₂PH₂ whose derivative, R₂PB(C₆F₅)₂, has been experimentally shown to be able to activate hydrogen. We also exemplified how to use the strategy to design experimentally more realizable molecules. The example shows promises as a hydrogen activation agent. The strategy can be used to design metal-free catalysts for direct hydrogenation.     

First imaging observation of the gravity waves in the mesopause region in China

The first imaging observation experiment of the atmospheric gravity waves in the mesopause region with the all-sky OH Meinel band airglow CCD imager is made during 02:00 to 06:00 on January 5,2009,at Hancun (39.4°N,116.6°E),Langfang,Hebei in China.Quasi-monochromatic gravity waves (QMGWs) are found clearly in the observation data.Case studies show that their horizontal wavelengths,horizontal phase velocities,azimuth angles of horizontal propagation directions and periods of three QMGW examples are about 12....     

Change of NO<Subscript>2</Subscript> column density over Beijing from satellite measurement during the Beijing 2008 Olympic Games

The effect of the air quality ensuring measures for the Beijing 2008 Olympic Games in reducing air pollution during the game period is assessed using the tropospheric NO₂ column density retrieved from Ozone Monitoring Instrument onboard AURA satellite. The basic method of the assessment is the comparison of the NO₂ column densities during the game period with that during the corresponding period of 2005−2007 for the Beijing area, and the comparison among Beijing and neighbouring cities Tianjin and Tangshan, which are of similar situation in air pollution of NO₂ in recent years. The images of tropospheric NO₂ column densities over Northern China during the Beijing 2008 Olympic Games show the remarkable effect of the air quality ensuring measures in reducing NO₂ pollution: the tropospheric NO₂ column density in Beijing is much lower than that in Tianjin and Tangshan, while there were very similar values in the three large cities during the same period of the last three years. About 40% reduction in tropospheric NO₂ column density over the Beijing area is obtained from the assessment during July to August, 2008, a key period of air quality ensuring measures for the Beijing 2008 Olympic Games.     

Establishment of a high-throughput screening system for universal anti-HIV targets

The process of identifying novel human immunodeficiency virus 1 (HIV-1) inhibitors presents a challenge for industrial and scientific research.Virus-cell-based screening approaches offer some advantages in the quest for novel inhibitors because they include multiple targets in a single screen and in some cases reveal targets not captured in biochemical assays.In this study,a high-throughput screening (HTS) system for HIV-1 inhibitors was developed,which allows the simultaneous screening of all the HIV-1 tar...