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101.
Sekiguchi T. Watanabe J. Fukushima H. Yamamoto T. Yamamoto N. 《Earth, Moon, and Planets》1997,78(1-3):143-148
In order to monitor the various phenomena of comets, we continuously made the near-nucleus imaging observations of comets
at National Astronomical Observatory, Mitaka. Here we report on the results of the observations of two spectacular comets.
One is the analysis of photometry of C2 emission images in the coma of comet Hyakutake (C/1996 B2). By comparing the production rates of C2 radicals with C2H2 molecules, we conclude that the most C2 radicals were originated from C2H2, while some of them might be produced from other parents. The second item is the analysis of the morphology of C2 emission images in the coma of comet Hale-Bopp(C/1995 O1). By applying a ring masking technique, we detected asymmetrical
distribution of the C2 molecules. The results of these two comets might suggest that a portion of C2 radicals were formed by the disintegration of the small organic dust grains, like the so-called CHON particles.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
102.
103.
Yukiyoshi Iwata Tomoyoshi Hirota Masaki Hayashi Shinji Suzuki Shuichi Hasegawa 《水文研究》2010,24(13):1755-1765
Despite the potential impact of winter soil water movements in cold regions, relatively few field studies have investigated cold‐season hydrological processes that occur before spring‐onset of snowmelt infiltration. The contribution of soil water fluxes in winter to the annual water balance was evaluated over 5 years of field observations at an agricultural field in Tokachi, Hokkaido, Japan. In two of the winters, soil frost reached a maximum depth of 0·2 m (‘frozen’ winters), whereas soil frost was mostly absent during the remaining three winters (‘unfrozen’ winters). Significant infiltration of winter snowmelt water, to a depth exceeding 1·0 m, occurred during both frozen and unfrozen winters. Such infiltration ranged between 126 and 255 mm, representing 28–51% of total annual soil water fluxes. During frozen winters, a substantial quantity of water (ca 40 mm) was drawn from deeper layers into the 0–0·2 m topsoil layer when this froze. Under such conditions, the progression and regression of the freezing front, regulated by the thickness of snow cover, controlled the quantity of soil water flux below the frozen layer. During unfrozen winters, 13–62 mm of water infiltrated to a depth of 0·2 m, before the spring snowmelt. These results indicate the importance of correctly evaluating winter soil water movement in cold regions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
104.
Blanco AC Watanabe A Nadaoka K Motooka S Herrera EC Yamamoto T 《Marine pollution bulletin》2011,62(4):770-785
Radon (222Rn) measurements were conducted in Shiraho Reef (Okinawa, Japan) to investigate nearshore submarine groundwater discharge (SGDnearshore) dynamics. Estimated average groundwater flux was 2-3 cm/h (maximum 7-8 cm/h). End-member radon concentration and gas transfer coefficient were identified as major factors influencing flux estimation accuracy. For the 7-km long reef, SGDnearshore was 0.39-0.58 m3/s, less than 30% of Todoroki River’s baseflow discharge. SGDnearshore was spatially and temporally variable, reflecting the strong influence of subsurface geology, tidal pumping, groundwater recharge, and hydraulic gradient. SGDnearshore elevated nearshore nitrate concentrations (0.8-2.2 mg/l) to half of Todoroki River’s baseflow -N (2-4 mg/L). This increased nearshore Chl-a from 0.5-2 μg/l compared to the typically low Chl-a (<0.1-0.4 μg/l) in the moat. Diatoms and cyanobacteria concentrations exhibited an increasing trend. However, the percentage contributions of diatoms and cyanobacteria significantly decreased and increased, respectively. SGD may significantly induce the proliferation of cyanobacteria in nearshore reef areas. 相似文献
105.
Tsunamis are high-impact disasters that can cause death and destruction locally within a few minutes of their occurrence and
across oceans hours, even up to a day, afterward. Efforts to establish tsunami warning systems to protect life and property
began in the Pacific after the 1946 Aleutian Islands tsunami caused casualties in Hawaii. Seismic and sea level data were
used by a central control center to evaluate tsunamigenic potential and then issue alerts and warnings. The ensuing events
of 1952, 1957, and 1960 tested the new system, which continued to expand and evolve from a United States system to an international
system in 1965. The Tsunami Warning System in the Pacific (ITSU) steadily improved through the decades as more stations became
available in real and near-real time through better communications technology and greater bandwidth. New analysis techniques,
coupled with more data of higher quality, resulted in better detection, greater solution accuracy, and more reliable warnings,
but limitations still exist in constraining the source and in accurately predicting propagation of the wave from source to
shore. Tsunami event data collected over the last two decades through international tsunami science surveys have led to more
realistic models for source generation and inundation, and within the warning centers, real-time tsunami wave forecasting
will become a reality in the near future. The tsunami warning system is an international cooperative effort amongst countries
supported by global and national monitoring networks and dedicated tsunami warning centers; the research community has contributed
to the system by advancing and improving its analysis tools. Lessons learned from the earliest tsunamis provided the backbone
for the present system, but despite 45 years of experience, the 2004 Indian Ocean tsunami reminded us that tsunamis strike
and kill everywhere, not just in the Pacific. Today, a global intergovernmental tsunami warning system is coordinated under
the United Nations. This paper reviews historical tsunamis, their warning activities, and their sea level records to highlight
lessons learned with the focus on how these insights have helped to drive further development of tsunami warning systems and
their tsunami warning centers. While the international systems do well for teletsunamis, faster detection, more accurate evaluations,
and widespread timely alerts are still the goals, and challenges still remain to achieving early warning against the more
frequent and destructive local tsunamis. 相似文献
106.
Abstract— In order to study abundances of alkali metals in chondrules, 25 petrographically characterized chondrules, including 18 barred olivine (BO) chondrules from the Allende (CV3) meteorite, were analyzed for alkalis (K and Rb) and alkaline earths (Sr, Ba, Ca and Mg) by mass spectrometric isotope dilution. Most BO chondrules with higher alkalis (>CI level) have nearly CI-chondritic Rb/K ratios, while those with lower alkalis clearly show higher Rb/K ratios than the CI-chondritic. In general, BO chondrules with higher Rb/K exhibit more depletion of alkalis relative to Ca. The mean olivine Fa for individual chondrules positively correlates with bulk alkali concentrations in BO type but not in porphyritic type chondrules. These observations suggest that some BO chondrules formed from more reducing assemblages of precursor minerals, which experienced more intensive vaporization losses of alkalis, accompanied by Rb/K fractionation, during the chondrule-formation melting. 相似文献
107.
108.
Satoshi Yamamoto 《Journal of Oceanography》1979,35(2):91-99
Anisotropic detrital mineral grains were segregated microscopically from the suspended matter in surface waters of the Yellow Sea and East China Sea. Microscopic grain-size measurements of the anisotropic minerals were carried out for more than 80 slide specimens which are distributed homogeneously in the Yellow Sea and East China Sea. The distribution maps of mean grain size and sorting coefficients indicate that the mean size becomes coarser as one goes offshore, and the sorting coefficients are larger in the southern portion and smaller in the northern portion of this region. The clay-sized minerals in the suspended sediments carried out by the deltaic rivers of the continent were deposited in the nearshore area while coarser silt-sized minerals were suspended in offshore waters. The larger sorting coefficients (standard deviations) in the southern portion may imply that the silt-sized grains of offshore waters contain coarser sand-sized grains. The sand-sized grains may be supplied from offshore Taiwan and the Bashi Channel and transported by the main flow of the Kuroshio current. 相似文献
109.
Tetsuo Yamamoto 《Earth, Moon, and Planets》1981,24(2):175-188
Density distribution in cometary comae resulting from photodissociation, ionization and ion-molecule reaction of H2O is investigated in an analytic manner. It is assumed that particles expand isotropically around the nucleus, and that each species has its own constant radial velocity. Formulae for the density distribution of photochemical products are presented throught the coma, and approximate formulae are given for the distribution of ion-molecule reaction products in the inner coma. Characterictics of the density profile are discussed on the basis of these analytic formulae. 相似文献
110.
Tetsuo Yamamoto 《Earth, Moon, and Planets》1981,24(4):453-463
The formation of cometary CN, C2 and C3 radicals is investigated in a photochemical reaction scheme. From an analysis of the observed brightness profiles of these radicals, it is shown that CN is formed as a primary product in the photolysis of its parent molecules, whereas C2 and C3 are formed via two-step photodissociation of their parents. We suggest that major parent of C2 is different species from those of CN and C3 on the basis of the difference of the variation with heliocentric distance of the sublimation rate of the parents of these radicals. Parent molecules and reaction schemes for the formation of these radicals are discussed. 相似文献