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231.
David A Williams 《Astrophysics and Space Science》1995,224(1-2):591-595
232.
Study of the material composition of Fe-Mn crusts from submarine rises in the central part of the Sea of Japan, with modern
precision methods applied, has yielded a high (up to 854 g/t) concentration of gallium contained in sorbed form. The new data
obtained have allowed a new genetic type of gallium deposits—hydrothermal-sedimentary—to be distinguished. 相似文献
233.
To study the crystal chemistry of bernalite, Fe(OH)3, and the nature of the octahedral Fe3+ environment, Mössbauer spectra were recorded from 80 to 350 K, optical spectra were recorded at room temperature and a sample was studied using transmission electron microscopy. The Mössbauer spectrum of bernalite consists of a single six-line magnetic spectrum at 80 K. A broadened six-line magnetic spectrum with significantly less intensity is observed at higher temperatures, and is attributed to a small fraction of bernalite occurring as small particles. The variation of hyperfine magnetic field data for bulk bernalite with temperature is well described by the Weiss molecular field model with parameters of H
0 = 55.7±0.3 T and T
N = 427±5K. The centre shift data were fitted to the Debye model with parameters 0=0.482±0.005 mm/s (relative to -Fe) and M=492±30 K. The quadrupole shift is near zero at 300 K, and does not vary significantly with temperature. Absorption spectra in the visible and near infrared range show three crystal field bands of Fe3+ at 11 300, 16000 and 23 200 cm-1, giving a crystal field splitting of 14 570 cm-1 and Racah parameters of B=629 cm-1 and C=3381 cm-1. Infrared reflection spectra show two distinct OH-stretching frequencies, which could correspond to two structurally different types of OH groups. A band was also observed at 2250 cm-1, suggesting the presence of molecular CO2 in the large cation site. Analytical transmission electron microscopy indicates that Si occurs within the bernalite structure as well as along domain boundaries. Electron diffraction and imaging show that bernalite is polysynthetically twinned along {100} planes with twin domains ranging from 3 to 20 nm in thickness. Results are discussed with respect to the nature of the octahedral Fe3+ site, and compared with values for other iron oxides and hydroxides. 相似文献
234.
The first small active regions of the last two new cycles seem to be formed, in its very first, preparatory stage, close to the equator with uncertain magnetic orientation, and as secondary products at the periphery of equatorial `magnetic bubbles' of the new magnetic flux still belonging to the old cycle. At the real beginning of the new cycle, at the periphery of its higher-latitude `magnetic bubbles', the opposite applies to the secondary regions of the ending cycle. It seems that two modes of magnetic flux supply the visible layers of the photosphere during the cycle transition phase: the emergence of the magnetic flux from the depth of the convective zone, and the mutual interaction of the earlier emerging fluxes, or the action of the `local dynamo', giving rise to the new local magnetic field concentrations. 相似文献
235.
Scott B. Smithson Roy A. Johnson Yun K. Wong 《Earth and Planetary Science Letters》1981,53(3):323-332
Mean crustal velocity is a critical parameter for genesis of continental crystalline crust because it is a function of mean crustal composition and therefore may be used to resolve continental crustal growth in space and time. Although the best values of mean crustal velocity are determined from wide-angle reflection measurements, most studied here necessarily come from vertical averages in crustal refraction determinations. The mode of 158 values of mean crustal velocity is 6.3 km/s, a velocity which corresponds to a mean crustal composition of granodiorite to felsic quartz diorite; Archean crust may be slightly more mafic. Mean crustal velocities range from 5.8 to 7.0 km/s. The lowest values invariably are found in thermally disturbed rift zones and the highest values correspond to velocities in gabbro. Velocities in island arcs may be as low as 6.0 km/s but are typically 6.5–6.9 km/s which corresponds to andesitic composition; estimates of island arc composition are andesitic. If values of mean crustal velocity are not biased, this observation suggests that continental crust did not grow simply by addition of island arc material. Possibilities are that crust formed from fusion of island arcs and was later changed to more felsic composition by addition of material from the mantle or that the late Archean episode of major crustal growth did not involve processes similar to younger island arcs. Some crustal blocks might be changed in composition and thickness by such processes as underplating, interthrusting, necking and sub-crustal erosion. Specially designed experiments are suggested to determine this parameter so critical for understanding genesis of continental crust. 相似文献
236.
The distribution of sites where globular clusters have crossed the Galactic disk during the last 100 million years has been analyzed using the most recent kinematic data for 133 globular clusters (GCs). ThreeGCs (NGC 6341, NGC 7078, and ω Cen) whose distances between the positions where they crossed the Galactic disk and trajectories of the Gould Belt are less than 20% of their heliocentric distances at the crossing time (82, 98, and 96 million years ago, respectively) have been identified. For each of the clusters, this was their next to last, rather than their last, crossing of the Galactic disk. The passage of any one of these three GCs through the disk could potentially have initiated the formation of the Gould Belt. 相似文献
237.
Jay Lee William A. Kretzschmar Jr 《International journal of geographical information science》2013,27(6):541-560
Abstract During the 1980s techniques for analysis of geographical patterns have been refined to the point that they may be applied to data from many fields. Quantitative spatial analysis and existing functions available in geographical information systems (GIS) enable computerized implementations of these spatial analysis methods. This paper describes the application of quantitative spatial analysis and GIS functions to analysis of language data, using the extensive files of the Linguistic Atlas of the Middle and South Atlantic States (LAMSAS). A brief review of recent development of using quantitative and statistical methods for analysing linguistic data is also included. 相似文献
238.
Summary Much literature has reported on the concept of increased surface temperature variability during cool periods, although analyses
on temperature records have rendered inconsistent results. In addition, temperature variability during transition periods
has been rarely investigated. This study examines temperature variability during wintertime cooling (1947–1977) and warming
(1978–1992) periods for the conterminous United States to determine both whether temperature variability is different during
warming or cooling periods, and whether the change in variability is supported by midtropospheric circulation conditions.
Our results indicate that regions with high temperature variability are mostly found below the troughs in the midtropospheric
pressure fields. The direction of change in temperature variability corresponding to cooling or warming conditions, however,
varied spatially. For the southeastern and northeastern United States, winter temperatures were more variable during the cooling
period than during the warming period, while the northern and central Great Plains had greater temperature variability during
the warming period than the cooling period. Similar spatial patterns are also found for the changes in the variability of
geopotential height fields. Such spatial patterns in the temperature and height variability during warming and cooling periods
may be related to the dominant midtropospheric circulation patterns, such as the different phases of the Pacific-North American
teleconnection pattern, and the El Ni?o/Southern Oscillation events. It is concluded that the response of interannual temperature
variability to climatic changes is determined by the variation in circulation patterns, and therefore, not spatially uniform.
Received September 26, 1996 Revised April 2, 1998 相似文献
239.
A. Collier Cameron 《Astrophysics and Space Science》1998,261(1-4):71-80
I review recent progress in the field of stellar surface imaging, with particular reference to advanced methods for mapping
surface-brightness inhomogeneities and the surface vector magnetic field on magnetically active late-type stars. New signal
enhancement techniques, utilising profile information from hundreds or thousands of photospheric lines simultaneously, allow
images to be derived for stars several magnitudes fainter than was previously possible. For brighter stars, the same techniques
make it possible to map features as small as two or three degrees in extent on the stellar surface. This opens up whole new
areas of research, such as the ability to use starspot tracking to study surface differential rotation patterns on single
and binary stars, and to follow the secular evolution of the magnetic field itself.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
240.
In well velocity surveys made to calibrate Sonic (CV) Logs the calibration survey uses frequencies around 50 Hz whereas the Sonic Logging tool uses frequencies around 20 kHz. There thus exists the possibility of making a direct measure of velocity dispersion. In any one survey the disturbing factors, both instrumental and operational, will often mask any dispersive effect that might exist. Consequently this paper reports on a statistical analysis of the velocity differences resulting from calibration surveys and Sonic logs. Only Borehole Compensated Sonic Logs were used. Four areas were investigated: the North Sea, Abu Dhabi, Libya and Alaska. After rejecting logs and calibration records which were obviously in error there remained 424000 feet (about 130 km) of usable log distributed throughout 66 wells. The four areas were analysed separately and in no case was the estimated dispersion significantly different from zero. However, the mean values did correlate with lithology from (? 0.17 ± 0.18)% for the essentially carbonate section in Abu Dhabi to (+ 0.45 ± 0.25)% for the sand-shale section in Alaska, a positive sign meaning that the higher frequencies travelled faster. Except for Alaska the calibration surveys were made with a wall-clamp geophone, and for these areas amplitude measurements were made. After suitable corrections estimates of the absorption parameter Q were obtained. These varied from 20 to 200 with mean values of 63 for Libya, 70 for Abu Dhabi and 88 for the North Sea (excluding the Tertiary). If, as is usually assumed, the absorption mechanism is linear and is described by a Q which is independent of frequency, then these values would necessarily imply dispersion of several percent. As instanced above no such dispersion was observed. It is possible that the expected dispersion was compensated for by invasion of the mud filtrate into the borehole walls, but it is more likely that the absorption mechanism was substantially non-linear. 相似文献