排序方式： 共有18条查询结果，搜索用时 609 毫秒
1.
Yan Gong Xin Wang Zheng Zheng Xue-Lei Chen National Astronomical Observatories Chinese Academy of Sciences Beijing China Graduate University of Chinese Academy of Sciences Beijing China Institute for Advanced Study Einstein Drive Princeton NJ USA Center of High Energy Physics Peking University Beijing China Kavli Institute for Theoretical Physics China CAS Beijing 《中国天文和天体物理学报》2010,10(2)
The primordial non-Gaussianity (PNG) in the matter density perturbation is a very powerful probe of the physics of the very early Universe. The local PNG can induce a distinct scale-dependent bias on the large scale structure distribution of galaxies and quasars, which could be used for constraining it. We study the detection limits of PNG from the surveys of the LAMOST telescope. The cases of the main galaxy survey, the luminous red galaxy (LRG) survey, and the quasar survey of dif- ferent magnitude limits... 相似文献
2.
Aaron P. Potito Craig A. Woodward Michelle McKeown David W. Beilman 《Journal of Paleolimnology》2014,52(4):385-404
Ireland provides a unique setting for the study of past climates, as its climate is dominated by westerly airflow from the North Atlantic and readily responsive to changes in North Atlantic circulation patterns. Although there has been substantial research on Ireland’s past environments, quantitative palaeolimnological research, especially chironomid-based research, has been lacking. In order to further develop chironomid-based palaeolimnological investigations, a calibration set was constructed to determine the dominant environmental controls on modern chironomids in western Ireland. Chironomid subfossils were collected from surface sediments of 50 lakes. The lakes were characterised with 36 environmental variables, including physical attributes, lake water characteristics, lake sediment characteristics and land cover within each catchment. In this exploratory study, no specific environmental variable was targeted and lakes were chosen to span gradients of latitude, elevation, depth and trophic status. Redundancy analysis showed that six environmental variables—mean July air temperature, lake depth, dissolved organic carbon, and percentage catchment land cover of agriculture, peat bog and scrubland—captured a large and statistically significant portion of the variance in the chironomid data. July temperature and agricultural land cover were the most dominant environmental variables, with July temperature proving the most suitable for inference model development. A classical weighted-averaging model was developed to estimate July air temperature, with a coefficient of determination (r jack 2 ) of 0.60 and root mean square error of prediction (RMSEP) of 0.57 °C. Results suggest that summer temperature is the dominant influence on chironomid distribution across a wide variety of lake types, and the relatively small RMSEP should allow for more accurate reconstructions of Ireland’s relatively subdued Holocene temperature fluctuations. 相似文献
3.
Juveniles of the Cape white seabream Diplodus capensis were observed cleaning adult conspecifics in a large tidepool off Sodwana Bay, South Africa. Although nine other tropical fish species were present and interacted with a nearby pair of Labroides cleaner wrasses, only adults of D. capensis posed for and were cleaned by the D. capensis juveniles. Such cleaning interactions have not been reported previously for this species or among marine fishes off South Africa, and thus add to the growing list of facultative cleaners globally. 相似文献
4.
David A. McKeown 《Physics and Chemistry of Minerals》2008,35(5):259-270
Polarized Raman spectra were collected for single crystal buergerite (NaFe3Al6(BO3)3Si6O18(O0.92(OH)0.08)3F) from room temperature to near 1,375°C. Vibrational assignments to features in the room temperature spectra were determined
by lattice dynamics calculations, where internal BO3 motions dominate modes near 1,300 cm−1, internal SiO4 displacements dominate modes between 900 and 1,200 cm−1, while less localized displacements within the isolated Si6O18 ring mix with motions within Na, Fe, Al, F, and BO3 environments for fundamental modes below 780 cm−1. At elevated temperatures, most buergerite Raman features broaden and shift to lower frequencies up to 900°C. Above this
temperature, the lattice mode peaks evolve into broad bands, while OH stretch modes near 3,550 cm−1 disappear. According to Raman spectroscopy, X-ray diffraction, differential thermal analysis, and scanning electron microscopy,
buergerite undergoes a complex transition that starts near 700°C and extends over a 310°C interval, where initially, Al and
Fe probably become disordered within the Y- and Z-sites, and most F and all OH are later liberated. A reversible crystal-to-amorphous
transition is seen by Raman for buergerite fragments heated as high as 930°C. Buergerite becomes permanently altered when
heated to temperatures greater than 930°C; after cooling to room temperature, these altered fragments are comprised of mullite
and Fe-oxide crystals suspended in an amorphous borosilicate matrix. 相似文献
5.
B. A. McKeown 《Marine environmental research》1981,5(4):295-300
The toxicity of crude oil and the dispersant BP1100X was tested in sea water and in each case was much less than the toxicity to fish in fresh water. Uptake of oil from water, with or without dispersant, was similar after a short exposure to 200 ppm. The oil was cleared from the fish in three weeks. A long-term exposure to oil or oil plus dispersant at a concentration of 5 ppm showed a slow accumulation but significantly above exposure levels. Thus, salmon exposed to oil in sea water can take up the hydrocarbons but appear to cleanse themselves rapidly. 相似文献
6.
McKeown M. Keenan F.P. Ramsbottom C.A. Bell K.L. Ryans R.S.I. Reid R.H.G. 《Solar physics》1999,186(1-2):231-242
Recent calculations of electron and proton impact excitation rates in Nevii are used to calculate theoretical emission line ratios involving both n=0 (2–2) and n=1 (2–3) transitions in the 97–895 Å wavelength range. A comparison of these with existing solar observations, obtained by instruments on rocket flights and on the Skylab mission, reveals generally good agreement between theory and observation. This provides experimental support for the accuracy of the atomic data adopted in the line ratio calculations, and implies that the latter may be applied with confidence to the analysis of solar and stellar spectra from current and future satellite missions. 相似文献
7.
One of the great environmental problems of our age is the safe disposal of radioactive waste for geological time periods. Britain is currently investigating a potential site for underground burial of waste, near the Sellafield nuclear plant. Future leakage of radionuclides depends greatly on subsurface water flows; these must be understood from the past, to predict hydrogeology 104 –105 years into the future. We have taken information from the present-day, published by the government company Nirex, and used a finite-element steady-state fluid flow computer code to examine water flows in the subsurface. We find that flow directions at the planned Repository are persistently upwards, and that geologically significant flow rates could occur. How rates are particularly sensitive to uncertainties of rock permeability (conductivity) measurements made from site investigation boreholes. The hydrogeology at this site needs longer term investigation before a confident and credible prediction can be made. 相似文献
8.
AJE Healey NJ McKeown WM Potts CL de Beer W Sauer PW Shaw 《African Journal of Marine Science》2017,39(3):307-313
Accurate species identification and biogeographic characterisation are fundamental for appropriate management of expanding cephalopod fisheries. This study addresses this topic within the common cuttlefish Sepia officinalis species complex (S. officinalis, S. hierredda and S. vermiculata), with an emphasis on occurrence in African waters. Tissue samples from the currently presumed distributions of S. vermiculata and S. hierredda (from South Africa and Ghana/Angola, respectively) were sequenced for the cytochrome c oxidase subunit I (COI) and the cytochrome b (cytb) genes of the mitochondrial genome and then compared to existing S. officinalis sequences. Three highly divergent and reciprocally monophyletic clades, corresponding to S. officinalis, S. hierredda and S. vermiculata, were resolved, representing the first molecular confirmation of the distinct species status of S. hierredda and S. vermiculata. The sequences also revealed that, contrary to expectations based on presently published information, all samples from southern Angola were S. vermiculata. These results indicate that the range of S. vermiculata extends beyond the currently described northern limit and that S. hierredda and S. vermiculata may be indiscriminately harvested in Angolan waters. Finer-scale patterns within S. vermiculata phylogeography also indicate that the Benguela Current System and/or other environmental factors serve to isolate northern and southern stocks. 相似文献
9.
A nondestructive method of measuring in situ the oil-water interface in a sunken oil barge is described. The method makes use of the different acoustic absorption properties of water and BunkerC oil to detect the oil-water interface and can be implemented using a standard 200-kHz echo sounder. An electrically driven bottom-crawling remotely controlled vehicle used to carry out field tests on a sunken oil barge is described, and samples of the sounder records obtained are presented. Results indicate the method is feasible for tanks of simple geometry that have distinct layers of liquids with sufficiently different acoustic absorption properties. 相似文献
10.
David A. McKeown 《Physics and Chemistry of Minerals》1989,16(7):678-683
Al X-ray absorption K-edge spectra were calculated for atom clusters which simulate Al surrounded by oxygens in tetrahedral and octahedral environments in five minerals, and are compared with experimental Al K-edge spectra from the same minerals. The experimental data show simple edges, for Al tetrahedra, that are shifted to lower energy by 2 eV compared with more complicated edges for Al octahedra. The calculated edge itself is due to a strong 1s to 3p resonance in the μ0 for Al. The shifting of the calculated edges is due to different molecular potentials used and different types of atomic scattering. The calculated edge features for tetrahedral Al are all similar, and are due primarily to single scattering from the tetrahedral oxygens. Calculated edge features for octahedral Al are more complicated and are dominated by multiple scattering. The calculated edge features resemble the experimental data, but are much larger in amplitude than their experimental counterparts. 相似文献