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排序方式: 共有217条查询结果,搜索用时 15 毫秒
81.
A brief historical review of solar and interplanetary magnetic field modeling and analysis is presented. The modeling was initiated with the routine observation of longitudinal magnetograms and the application of current free potential magnetic fields for its interpretation. Almost simultaneously, the development of detailed H observation motivated the constant-, force-free magnetic field analysis. Subsequent development of transverse magnetograms leads not only to further refinements of the analysis and modeling but also to many physically meaningful interpretations of the observations. In this review, historical development is traced with the emphasis placed on the yet unanswered questions. 相似文献
82.
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84.
Endo T Yong-Un M Baker CS Funahashi N Lavery S Dalebout ML Lukoschek V Haraguchi K 《Marine pollution bulletin》2007,54(6):669-677
Levels of total mercury (T-Hg) were surveyed in red meat (n=73) and liver (n=3) from toothed whales, dolphins and porpoises (odontocetes) sold for human consumption in the coastal cities of South Korea. High concentrations of T-Hg were found in the liver products of finless porpoises (18.7 and 156 microg/wet g) and common dolphins (13.2 microg/wet g). The T-Hg concentrations in red meat products were highest in the false killer whale (9.66+/-12.3 microg/wet g, n=9), bottlenose dolphin (10.6+/-12.6 microg/wet g, n=3) and killer whale (13.3 microg/wet g, n=1), and lowest in Cuvier's beaked whale and the harbour porpoise (0.4-0.5 microg/wet g). Thus, most of the products that originated from odontocetes exceeded the safety limit of 0.5 microg/wet g for T-Hg set by the South Korean health authorities for the fishery industry. Pregnant women and other vulnerable sectors of the population living in South Korea should therefore limit their consumption of odontocete products. 相似文献
85.
Koichi Mimura Michioki Okamoto Kenichiro Sugitani Shigemasa Hashimoto 《Meteoritics & planetary science》2007,42(3):347-355
Abstract— We performed shock‐recovery experiments on insoluble organic matter (IOM) purified from the Murchison meteorite, and determined the abundances and isotope ratios of hydrogen and carbon in the shocked IOM sample. We also performed shock experiments on type III kerogen and compared the results of these experiments with the experimental results regarding IOM. The shock selectively released D and 13C from the IOM, while it preferably released H and 12C from the kerogen. The release of these elements from IOM cannot be explained in terms of the isotope effect, whereas their release from kerogen can be explained by this effect. The selective release of heavier isotopes from IOM would be due to its structure, in which D and 13C‐enriched parts are present as an inhomogeneity and are weakly attached to the main network. Shock gave rise to a high release of D even at a lower degree of dehydrogenation compared with the stepwise heating of IOM. This effective release of D is probably an inherent result of shock, in which a dynamic high‐pressure and high‐temperature condition prevails. Thus, shock would effectively control the hydrogen isotope behavior of extraterrestrial organic matter during the evolution of the solar nebula. 相似文献
86.
The effect of background plasma on particle acceleration via Poynting fluxes is studied in 3D PIC simulation of electron-positron
and electron-ion plasmas. When a strongly magnetized ejecta at the center expands to low-temperature electron-positron ambient
plasma background and a low-density clump, electromagnetic wave front accelerates particles in the background and clump, and
captures them in the Ponderomotive potential well. We do not observe any instability, and the momentum distributions of background
and clump form a power law of slope close to −1.5 with a sharp peak in the middle. When an ejecta expands to the ion-electron
interstellar medium (ISM), the acceleration via Poynting flux is severely damped due to the charge separation. 相似文献
87.
Tomonori Kume Odair J Manfroi Masakazu Suzuki Katsunori Tanaka Koichiro Kuraji Michiko Nakagawa Hikaru Komatsu Tomo'omi Kumagai 《水文研究》2008,22(18):3689-3696
South‐east Asian Bornean tropical rainforests have large and complex canopy structures. To clarify how forest structure affects wet‐canopy evaporation, it is necessary to consider wet‐canopy evaporation processes within the forest canopy, such as vertical profiles of canopy drying time. In a previous study a method was proposed that utilizes sap flow measurements to estimate canopy drying time after rainfall (CDTobs) during daytime. In this present study, the method was applied to estimations of the vertical variations in CDTobs in 11 individual trees of various heights, ranging from 2·7 m to 53 m. The study derived vertical profiles and showed that the lengths of CDTobs in lower canopy trees were 2–4 h longer than those in the upper canopy trees. The new method for CDTobs profiles presented in this study, which is available for validation of multi‐layer biosphere‐atmospheric models, is a useful illustration for clarifying wet‐canopy evaporation processes in tropical rainforests. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
88.
M. Nakagawa K. Wada T. Thordarson C. P. Wood J. A. Gamble 《Bulletin of Volcanology》1999,61(1-2):15-31
Ruapehu volcano erupted intermittently between September and November 1995, and June and July 1996, producing juvenile andesitic
scoria and bombs. The volcanic activity was characterized by small, sequential phreatomagmatic and strombolian eruptions.
The petrography and geochemistry of dated samples from 1995 (initial magmatic eruption of 18 September 1995, and two larger
events on 23 September and 11 October), and from 1996 (initial and larger eruptions on 17–18 June) suggest that episodes of
magma mixing occurred in separate magma pockets within the upper part of the magma plumbing system, producing juvenile andesitic
magma by mixing between relatively high (1000–1200 °C)- and low (∼1000 °C)- temperature (T) end members. Oscillatory zoning
in pyroxene phenocrysts suggests that repeated mixing events occurred prior to and during the 1995 and 1996 eruptions. Although
the 1995 and 1996 andesitic magmas are products of similar mixing processes, they display chronological variations in phenocryst
clinopyroxene, matrix glass, and whole-rock compositions. A comparison of the chemistry of magnesian clinopyroxene in the
four tephras indicates that, from 18 September through June 1996, the tephras were derived from at least two discrete high-temperature
(high-T) batches of magma. Crystals of magnesian clinopyroxene in the 23 September and 11 October tephras appear to be derived
from different high-T magma batches. Whole-rock and matrix-glass compositions of all tephras are consistent with their derivation
from distinct mixed melts. We propose that, prior to 1995 there was a shallow low-temperature (low-T) magma storage system
comprising crystal-rich mush and remnant magma from preceding eruptive episodes. Crystal clots and gabbroic inclusions in
the tephras attest to the existence of relict crystal mush. At least two discrete high-T magmas were then repeatedly injected
into the mush zone, forming discrete and mixed magma pockets within the shallow system. The intermittent 1995 and 1996 eruptions
sequentially tapped these magma pockets.
Received: 1 April 1998 / Accepted: 22 December 1998 相似文献
89.
A large area (5×1010km2) of a coronal hole disappeared in concert with a transient brightening of a nearby high-latitude coronal arcade in the northern hemisphere on 15 May 1992. This coronal-hole disappearance took place in a time scale of half a day. It is suggested that the large-scale and quick change in coronal-hole geometry induced the eruption of originally closed coronal magnetic structure of the high-latitude arcade. An associated solar wind disturbance with the plasma speed of >700 km/sec was observed by IPS, and geomagnetic sudden commencement was reported on 18 May 1992. 相似文献
90.
Shiki Machida Kentaro Nakamura Tetsu Kogiso Ryo Shimomura Koichi Horinouchi Kyoko Okino Yasuhiro Kato 《Island Arc》2021,30(1):e12395
A broad area densely covered by ferromanganese nodules was recently discovered around Minamitorishima (Marcus) Island, representing a high-potential metal resource, particularly for Co, Ni, Mo, and W. We studied 16 nodule samples from nodule fields around Minamitorishima Island. To define the fine-scale chemostratigraphy of the nodules, polished cross-sections of the samples were analyzed by microfocus X-ray fluorescence. Our results show that a general pattern of compositional variation was common throughout the growth history of the nodules in all the regions we studied. Chemical mapping clarified changes in the chemical signature and proportion of five lithological components throughout the growth history: Mn represented columnar δ-MnO2; Fe represented layered amorphous FeOOH*xH2O; Ti represented TiO2*2H2O intergrown with an amorphous FeOOH phase; P, Ca and Y represented particles of biogenic calcium phosphate; and Si, Al, K, Cu, and Ni represented pelagic sediment infills. We proposed a method for a creating a multi-dimensional compositional map of the fine-scale chemostratigraphy observed in the ferromanganese oxide layers on the basis of merging the mapped Mn, Fe, Ti, P, Si and Cu intensities. Multi-dimensional compositional mapping of the sampled nodules from the western North Pacific revealed two fundamental findings: (1) previously recognized first-order Fe–Mn layers, L0, L1, and L2, were further divided into two, three, and four sublayers, respectively, and (2) a delayed supply of material to be nuclei of nodule or a growth hiatus of Fe–Mn layer(s), leading to missing sublayers in the layers L0 and L2, regulated the nodule size. In contrast, layer L1, which does not have any missing sublayers, was commonly observed in the samples for this study and has been reported in studies of other regions in the western Pacific. We propose, therefore, that the layer L1 is a key facies for examining chemostratigraphic correlations with other areas of seafloor. 相似文献