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51.
Wdowiak TJ Lee W Cronin J Beegle LW Robinson MS 《Planetary and Space Science》1995,43(10-11):1175-1182
Processes resulting in the formation of hydrocarbons of carbonaceous chondrites and the identity of the interstellar molecular precursors involved are an objective of investigations into the origin of the solar system and perhaps even life on earth. We have combined the resources and experience of an astronomer and physicists doing laboratory simulations with those of a chemical expert in the analysis of meteoritic hydrocarbons, in a project that investigated the conversion of polycyclic aromatic hydrocarbons (PAHs) formed in stellar atmospheres into alkanes found in meteorites. Plasma hydrogenation has been found in the University of Alabama at Birmingham Astrophysics Laboratory to produce from the precursor PAH naphthalene, a new material having an IR absorption spectrum (Lee, W. and Wdowiak, T.J., Astrophys. J. 417, L49-L51, 1993) remarkably similar to that obtained at Arizona State University of the benzene-methanol extract of the Murchison meteorite (Cronin, J.R. and Pizzarello, S., Geochim. Cosmochim. Acta 54, 2859-2868, 1990). There are astrophysical and meteoritic arguments for PAH species from extra-solar sources being incorporated into the solar nebula, where plasma hydrogenation is highly plausible. Conversion of PAHs into alkanes could also have occurred in the interstellar medium. The synthesis of laboratory analogs of meteoritic hydrocarbons through plasma hydrogenation of PAH species is underway, as is chemical analysis of those analogs. The objective is to clarify this heretofore uninvestigated process and to understand its role during the origin of the solar system as a mechanism of production of hydrocarbon species now found in meteorites. Results have been obtained in the form of time-of-flight spectroscopy and chemical analysis of the lab analog prepared from naphthalene. 相似文献
52.
Lee W. Casperson 《Astrophysics and Space Science》1977,48(2):389-399
A modification of the rotating-star model has been developed to interpret the periodic energy bursts from pulsars. This new configuration involves -directed oscilltion modes in the stellar atmosphere or magnetosphere, and most aspects of the typical pulse characteristics are well accounted for. Gain is provided by resonant interactions with particles trapped in the stellar magnetic field. The most significant feature is the fact that highly directional beaming of the output energy results as a natural consequence of coherence between the radiation fields emerging from various locations about the pulsar; and a localized radiation origin is not required. 相似文献
53.
A centrifugal mill is a high-power intensity media mill that can be used for ultra-fine grinding, employing centrifugal forces generated by gyration of the axis of the mill tube in a circle. The mill charge motion is quite different depending on the ratio of the gyration diameter to the mill diameter (G / D ratio), varying from a motion similar to that of a conventional tumbling media mill to that of a vibration mill. In this study, a centrifugal mill was constructed with an arrangement where the gyration diameter could be readily adjusted. The batch grinding characteristics of three different minerals (limestone, talc and illite) in water with dispersing agent were investigated at various G / D ratios. It was found that the optimum G / D ratio in terms of the specific energy consumption to give a desired fineness of product was different for the three minerals. This was due to their different reactions to the breakage mechanisms provided by the mill charge motion at varying G / D ratios. The size distributions became progressively narrower at increased grinding times, and particles finer than about 0.1 μm were not detected even for prolonged grinding times. Measurement of specific surface areas indicated that this was not due to an artifact of the size measurements by laser diffractometry. This implies that there is a limitation in which particles finer than 0.1 μm are not produced under the conditions tested in this type of mill, but further investigation is needed for experimental verification of this limit of comminution. 相似文献
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55.
A. F. Kholtygin G. A. Galazutdinov T. E. Burlakova G. G. Valyavin S. N. Fabrika B. -C. Lee 《Astronomy Reports》2006,50(3):220-231
We present the results of a search for and analysis of line-profile variations in the spectrum of the star ι Her. The observations were acquired with the 1.8 m telescope of the Bohyunsan Optical Astronomy Observatory (Republic of Korea) in May–June 2004. We obtained 69 spectra of the star with signal-to-noise ratios ≈300 and a time resolution of 5–7 min. Profile variability was revealed for six lines of HI, HeI, and SiIII, in the central parts of the lines. The variability amplitude is ≈(1–2)% in units of the intensity of the adjacent continuum. Evidence was found for cyclic variations of the lines, with periods from ≈7h to ≈2.9d. We conclude that ι Her belongs to the group of slowly pulsating stars. 相似文献
56.
A short reply to discussion by Chanson. 相似文献
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58.
Summary ?This study deals with the climatological aspect of seasonal rainfall distribution in the East Asian monsoon region, which
includes China, Korea and Japan. Rainfall patterns in these three countries have been investigated, but little attention has
been paid to the linkages between them. This paper has contributed to the understanding of the inter-linkage of various sub-regions.
Three datasets are used. One consists of several hundred gauges from China and South Korea. The second is based on the Climate
Prediction Center (CPC) Merged Analysis of Precipitation (CMAP). The two sources of precipitation information are found to
be consistent. The third dataset is the NCEP/NCAR reanalysis 850-hPa winds.
The CMAP precipitation shows that the seasonal transition over East Asia from the boreal winter to the boreal summer monsoon
component occurs abruptly in mid-May. From late March to early May, the spring rainy season usually appears over South China
and the East China Sea, but it is not so pronounced in Japan. The summer monsoon rainy season over East Asia commonly begins
from mid-May to late May along longitudes of eastern China, the Korean Peninsula, and Japan. A strong quasi-20-day sub-seasonal
oscillation in the precipitation appears to be dominant during this rainy season. The end date of the summer monsoon rainy
season in eastern China and Japan occurs in late July, while the end date in the Korean Peninsula is around early August.
The autumn rainy season in the Korean Peninsula has a major range from mid-August to mid-September. In southern China, the
autumn rainy season prevails from late August to mid-October but a short autumn rainy season from late August to early September
is noted in the lower part of the Yangtze River. In Japan, the autumn rainy season is relatively longer from mid-September
to late October.
The sub-seasonal rainfall oscillation in Korea, eastern China and Japan are explained by, and comparable to, the 850-hPa circulation.
The strong westerly frontal zone can control the location of the Meiyu, the Changma, and the Baiu in East Asia. The reason that the seasonal sea surface temperature change in the northwestern Pacific plays a critical role
in the northward advance of the onset of the summer monsoon rainfall over East Asia is also discussed.
Received October 5, 2001; revised April 23, 2002; accepted May 11, 2002 相似文献
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