排序方式： 共有18条查询结果，搜索用时 15 毫秒
11.
Y. Uchida S. Hirose S. Morita M. Torii T. Tanaka T. Yabiku T. Miyagoshi S. Uemura T. Yamaguchi 《Astrophysics and Space Science》1998,264(1-4):145-169
We discuss here some of the new aspects about solar flares and active regions found by the Solar X-ray Satellite Yohkoh, by
taking advantage of the wider dynamic range and higher cadence observations with higher spatial resolution compared with the
previous satellites. Those new aspects have lead us to new ways of understandings, with contradictions to the previous views
about flares and active regions that are widely conceived for a long time. We give some models that explain those newly revealed
observational results.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
Ccile L. Blanchet Nicolas Thouveny Laurence Vidal Guillaume Leduc Kazuyo Tachikawa Edouard Bard Luc Beaufort 《Quaternary Science Reviews》2007,26(25-28):3118-3133
The sediments deposited off south-western Baja California have recorded millennial-scale fluctuations in biogenic compounds and trace metals accumulation during the last glacial period [Ortiz, J.D., O’Connell, S.B., DelViscio, J., Dean, W.E., Carriquiry, J.D., Marchitto, T., Zheng, Y., van Geen, A., 2004. Enhanced marine productivity off western North America during warm climate intervals of the past 52 ky. Geology 32, 521–524; Dean, W.E., Zheng, Y., Ortiz, J.D., van Geen, A., 2006. Sediment Cd and Mo accumulation in the oxygen-minimum zone off western Baja California linked to global climate over the past 52 ka. Paleoceanography 21, PA4209]. Since the variations in trace metals concentration appear to result from dilution with nonbiogenic matter, the variability of the terrigenous sedimentation needs to be addressed. Therefore, we performed rock magnetic and geochemical analysis on a 38 m-long sediment core collected from the slope off Baja California. The temporal framework provided by 14C dating and identification of palaeoclimatic transitions allows assigning the sequence to the last glacial–interglacial cycle (last 120 ka). The comparison of magnetic and geochemical properties led to retain the hypothesis of a primary modulation of iron oxides quantity and quality by terrigenous input variations, with a secondary diagenetic amplification. Two magnetic mineral input regimes are distinguished: (i) magnetic susceptibility variations reveal changes in titano-magnetite concentration related to fluvial transport of the terrigenous fraction; (ii) coercivity changes allow detecting variations of hematite or goethite concentrations, minerals generally issued from aeolian deflation of weathered rock surfaces. These two regimes are paced by two distinct climatic forcing: the millennial-scale changes in titano-magnetite input are related to the northern hemisphere climatic variability whilst the record of wind-blown magnetic mineral input contains its major power in the precessional frequency band, with higher input during low insolation periods (and conversely). This record highlights the great sensibility of this region to high and low latitudes climatic regimes. 相似文献
13.
14.
15.
Analyses of gallium content were made by the fluorometric method on 57 samples of seaweeds which were composed of 30 species. As the result of it, the gallium content was found ranging from 0.02 to 0.64g g–1 and the average was 0.14g g–1 in the dried seaweeds.Generally, the gallium content in seaweeds had a close relationship to the aluminium and iron contents. The average weight ratio of Ga/Al was 3.8×10–4 and one of Ga/Fe was 4.0×10–4. The average Ga/Al weight ratio (3.8×10–4) was very similar to that reported for shallow-water deposits (2.1×10–4), but was definitely lower than that in sea water (1.5×10–2). 相似文献
16.
A magnetodynamic model to deal with the acceleration and collimation of jets as a part of the global process of gravitational
contraction of the magnetized gas to the central gravitator is discussed. We first review its application to the star forming
jet case with several observational supporting evidence. Then, a justification will be given for the extension of this to
the AGN jet case, despite of the difference in orders of magnitudes in the scales as well as in the physical parameters. The
results of actual application of this magnetodynamic mechanism to the AGN case will be presented together with the discussions
for the origin of the radio lobes and hotspots, and we show that this mechanism can explain the enhancement of accretion and
the formation of the jet + lobe system consistently with the genetic consideration of the system.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Kazuyo Tachikawa Olivier Cartapanis Laurence Vidal Luc Beaufort Tatiana Barlyaeva Edouard Bard 《Quaternary Science Reviews》2011,30(25-26):3716-3727
The low-latitude hydrological cycle is a key climate parameter on different timescales, as it contributes to various feedback processes. Modelling studies suggest that the interhemispheric insolation contrast is the major factor controlling the cycle, although the influence of glacial conditions and the phase relationships relative to insolation forcing remain undetermined. In this work, we studied precipitation variability over Papua New Guinea (PNG, 3°S) for the past 400 ka using terrigenous fractions transported by the Sepik River to the Western Pacific Warm Pool (WPWP). A multi-decadal to centennial resolution of the elemental content was obtained using X-ray fluorescence scanning of a marine sediment core using an age model based on 14C dates and benthic foraminiferal δ18O. Indicators of the coarse river particulate fraction (bulk and CaCO3-free basis Ti concentrations, the log intensity ratios of Ti/K and Ti/Ca) displayed a dominant 23 ka periodicity without a clear glacial–interglacial trend. Our precipitation records showed a tight relationship with local summer insolation (3°S, January) with time-dependent lag of 0 to 4 ka. They were generally in anti-phase for U–Th dated Chinese speleothem δ18O records. Based on an analogy to modern climate, we propose that precipitation over PNG was primarily determined by interhemispheric insolation contrast, and the contribution of austral fall/winter precipitation added second-order variability that formed the lags. For the last four climate cycles, the WPWP hydrological cycle was closely associated with the eastern Asian monsoon, and the influence of glacial conditions on the low-latitude hydrological cycle was estimated to be limited. 相似文献
18.
Akinobu Miyakoshi Makoto Taniguchi Yasukuni Okubo Takeshi Uemura 《Physics of the Earth and Planetary Interiors》2005,152(4):335-342
Subsurface temperature is affected by heat advection due to groundwater flow and surface temperature changes. To evaluate their effects, it was implemented the measurements of temperature-depth profile (T-D profile) and the continuous monitoring of soil temperature in the southern part of Kamchatka which has not affected by human activity. Additionally, stable isotopic compositions of surface water and groundwater were analyzed. T-D profile and stable isotopic compositions show groundwater flow system is differ from the shallow aquifer to the deep aquifer. In the shallow aquifer, T-D profile suggests the existence of upward groundwater flux. On the other hand, the annual variation of soil temperature is divided into the large variation period (VP) and the stable period (SP) by the magnitude of daily and seasonal variation. VP and SP correspond to the summer and the winter season, respectively, and it considers that the difference between VP and SP is caused by the effect of snow cover. Therefore, the T-D profile is affected by not only upward groundwater flux but also the surface warming particularly in the summer season (VP). 相似文献