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111.
We developed a simple, handheld, and user-friendly magnetic susceptibility meter specialized for the identification of meteorites. The measurement is based on an LC resonance circuit. When provided with a rough estimate of the sample mass, the instrument displays directly the mass-normalized magnetic susceptibility expressed in logχm (with χm in 10−9 m3 kg−1), a parameter that is widely used in the classification of meteorites. Moreover, the measurement of the impedance of the LC resonator provides a proxy of the electrical conductivity (C-index) that can be helpful to distinguish metal-bearing samples from magnetite-bearing samples. This C-index offers an additional diagnostic for the identification of meteorites. Our tests demonstrate that the precision and the accuracy of this instrument called “Meteorite meter” (MetMet) are sufficient to allow distinguishing most meteorites from most terrestrial rocks, for a minimum recommended sample mass of 5 g. The distinction of some meteorite groups is also possible, in particular the separation of the three ordinary chondrite groups. Meteorite hunters, collectors, and curators and non-specialists, including children, can use this instrument as a guidance in the identification and classification of meteorites. This kind of instrument has an immense advantage over the widely used testing of meteorites with magnets, as it does not affect the paleomagnetic records of meteorites that are highly valuable for scientists. 相似文献
112.
We analyzed the community structure of marine ammonia-oxidizing archaea (AOA) by sequencing the ammonia monooxygenase subunit
A (amoA) gene. Cells were grown in ammonium-enriched seawater at various temperatures. Most amoA clones retrieved prior to cultivation belonged to Water Column Cluster B (WCB); however, most clones retrieved after incubation
at high temperature belonged to Water Column Cluster A (WCA) or the Nitrosopumilus maritimus-like (NM) group. Some operational taxonomic units in the NM and WCA groups may be better adapted to higher temperature than
those in WCB. Hence, differing temperature adaptations among AOA groups may be related to community structures and depth distributions. 相似文献
113.
Assessment of shallow groundwater in Lake Nyos catchment (Cameroon,Central-Africa): implications for hydrogeochemical controls and uses 总被引:1,自引:0,他引:1
Brice T. Kamtchueng Wilson Y. Fantong Akira Ueda Edwige R. Tiodjio Katsuro Anazawa Mengnjo J. Wirmvem Joseph O. Mvondo Luc S. Nkamdjou Minoru Kusakabe Takeshi Ohba Gregory Tanyileke Joseph V. Hell 《Environmental Earth Sciences》2014,72(9):3663-3678
In 1986, carbon dioxide gas exploded from Lake Nyos and killed about 1,800 people. After that disaster, various administrative and research activities have been conducted to mitigate subsequent disasters. However, none of those endeavors have characterized the groundwater chemistry to identify hydrogeochemical processes that control the water chemistry, and the quality of the water for domestic and agricultural uses that support the lives of un-official resettlers around Lake Nyos. Conventional hydrochemical techniques coupled with statistical and graphical analysis were therefore employed to establish the baseline hydrochemical conditions, assess processes controlling solutes distribution in shallow groundwater in the Lake Nyos catchment and explore its usability. Groundwater samples were analyzed for their physical and chemical properties. The wide ranges of electrical conductivity and total dissolved solid values reveal the heterogeneous distribution of groundwater within the watershed. The relative abundance of major dissolved species was Ca > Mg > Na > K for cations and HCO3 >>> Cl > SO4 > NO3 for anions. Piper diagram classified almost all water samples into mixed CaMg–HCO3 water type. Major ion geochemistry reveals that, in addition to silicates weathering (water–rock interaction), ion exchange processes regulate the groundwater chemistry. Principal component analysis supports the occurrence of water rock interaction. Hierarchical cluster analysis showed that the chemistry of groundwater in the study area is controlled by three main factors, and suggests no hydraulic connectivity between deep lake water and groundwater in the catchment. The quality assessment of the groundwater showed that groundwater parameters are within the acceptable limit of the World Health Organization and Nigeria guidelines for drinking and domestic uses, and water found to be good for irrigation. 相似文献
114.
黄祥飞 《中国海洋湖沼学报》1997,15(2):181-185
Ofmorethan9OtaxaoftheRottherafoundinD0nghuLakeanditSnearbypondsinWuhan,Hubei,severalwerenewtaxaandl2fustamrdedfromChina(Sudzuki,l995).OIily7newtaxaaredescribedinthispaper.MareRIusroMErnODSSamP1eswercolleCtedbyustogetherwithmemersoftheD0nghuLakeExperi-mentalStation,ChineseAcadeTnyofSdenas,usingr0utinemethodsduringSept.14-l6,l994fromStationsI-IlIofD0nghuLake(i.e.,IfShuigu0Lake,IIfGuochengLake,IIIfTanglinhakeandthefouropch)srnallpondsofboththeInstituteofHydrobiologyandtheriverd… 相似文献
115.
Tomoki Watanabe Hiroaki Takahashi Masayoshi Ichiyanagi Muneo Okayama Masamitsu Takada Riyo Otsuka Kenji Hirata Shigehiko Morita Minoru Kasahara Hitoshi Mikada 《Tectonophysics》2006,426(1-2):107
Japan Marine Science and Technology Center installed a cabled geophysical observatory system off Kushiro, Hokkaido Island in July 1999. This observatory system comprises three ocean bottom seismographs (OBSs), two tsunami gauges, and a geophysical/geochemical monitoring system. 4 years and 2 months after the installation, a megathrust earthquake (the 2003 Tokachi-Oki earthquake, 26th September in Japan Standard Time (JST), MJMA 8.0) occurred along a plate boundary underneath a forearc basin where the system is located. The system recorded clear unsaturated seismograms just at 28.6 km from the epicenter. This paper demonstrates advantages brought by the cabled observatory to record the megathrust earthquake showing how earthquake detectability is improved dramatically combining permanent OBS and land-based observations around the region, and importance of the in situ monitoring on the seismogenic zone. In the present study, processing OBSs and land-based network together, and comparing magnitudes of common observed earthquakes with national authorized network, event detection level improved down to M 1.5, which is much lower than the previously designed as down to M 2. Comparing detection level before and after installing OBSs, we found dramatic improvement of the earthquake detection level in the interesting region. Real-time continuous observations of microearthquakes since 1999 have brought us tremendous findings. First, a seismic quiescence started about 10 days before the 2003 Tokachi-Oki earthquake. Second, aftershock distribution is not uniform over the focal area and can be divided into several sub-regions, which might indicate an existence of several asperities. We think that the geophysical observations helped to understand the initiation process of the rupture of the 2003 Tokachi-Oki earthquake and that observations including seismological, geodynamic, hydrogeological, and the other multidisciplinary observations would provide a clue to future understanding of seismogenic processes at subduction zones. 相似文献
116.
Shuichi Hasegawa Ranjan Kumar Dahal Minoru Yamanaka Netra Prakash Bhandary Ryuichi Yatabe Hideki Inagaki 《Environmental Geology》2009,57(6):1423-1434
Geologically and tectonically active Himalayan Range is characterized by highly elevated mountains and deep river valleys.
Because of steep mountain slopes, and dynamic geological conditions, large-scale landslides are very common in Lesser and
Higher Himalayan zones of Nepal Himalaya. Slopes along the major highways of central Nepal namely Prithvi Highway, Narayangadh-Mugling
Road and Tribhuvan Highway are considered in this study of large-scale landslides. Geologically, the highways in consideration
pass through crushed and jointed Kathmandu Nappe affected by numerous faults and folds. The relict large-scale landslides
have been contributing to debris flows and slides along the highways. Most of the slope failures are mainly bechanced in geological
formations consisting phyllite, schist and gneiss. Laboratory test on the soil samples collected from the failure zones and
field investigation suggested significant hydrothermal alteration in the area. The substantial hydrothermal alteration in
the Lesser Himalaya during advancement of the Main Central Thrust (MCT) and thereby clay mineralization in sliding zones of
large-scale landslide are the main causes of large-scale landslides in the highways of central Nepal. This research also suggests
that large-scale landslides are the major cause of slope failure during monsoon in the Lesser Himalaya of Nepal. Similarly,
hydrothermal alteration is also significant in failure zone of the large-scale landslides. For the sustainable road maintenance
in Nepal, it is of utmost importance to study the nature of sliding zones of large-scale landslides along the highways and
their role to cause debris flows and slides during monsoon period. 相似文献
117.
118.
Abstract— Yamato 000593, a nakhlite, was analyzed in terms of its magnetic record and magnetomineralogy. The natural remanent magnetization (NRM: 3.55–6.07 times 10?5 Am2/kg) was thermally demagnetized at ~320 °C, and it was unstable against alternating field demagnetization. Based on analyses of thermomagnetic curves, the temperature dependence of hysteresis parameters, and microscopic observations, the magnetic minerals mainly consist of magnetite (0.68 wt% of the sample, including ~5% Fe2TiO4) of less than 100 μm in size, associated with minor amounts of monoclinic pyrrhotite (<0.069 wt% of the sample) and goethite. Thermal demagnetization of NRM at ~330 °C is explained due to an offset of magnetization of antipodal NRM components of magnetite, whereas it is not due to a pyrrhotite Curie point. Large magnetite grains show exsolution texture with ilmenite laths, and are cut by silicate (including goethite) veins that formed along cracks. Numerous single‐domain (SD) and pseudo‐single‐domain (PSD) magnetite grains are scattered in the mesostasis and adjacent olivine grains. Moderate coercive forces of HC = 6.8 mT and HRC = 31.1 mT suggest that Yamato 000593 is fundamentally able to carry a stable NRM; however, NRM was found to be unstable. Accordingly, the meteorite was possibly crystallized at 1.3 Ga under an extremely weak or absent magnetic field, or was demagnetized by impact shock at 12 Ma (ejection age) on Mars. This finding differs from the results of previous paleomagnetic studies of SNC (shergottites, nakhlites, chassignites, and orthopyroxenite) Martian meteorites. The significant dipole magnetic field resulting from the molten metallic core was probably absent during the Amazonian Epoch (after 1.8 Ga) on Mars. 相似文献
119.
Aka Festus Tongwa Buh Gaston Wung Fantong Wilson Yatoh Issa Zouh Isabella Tem Djomou Serges Laurent Bopda Ghogomu Richard Tanwi Gibson Terry Marmol del Mary-Ann Sigha Luc Nkamdjou Ohba Takeshi Kusakabe Minoru Yoshida Yutaka Tanyileke Gregory Nnange Joseph Metuk Hell Joseph Victor 《Natural Hazards》2017,87(1):57-81
This paper presents a simulation of three components of near-field ground shaking recorded during the main shock at three stations of the September 16, 1978, Tabas (M w = 7.4), Iran, earthquake, close to the causative fault. A hybrid method composed of a discrete wavenumber method developed by Bouchon (Bouchon in Bull Seismol Soc Am 71:959–971, 1981; Cotton and Coutant in Geophys J Int 128:676–688, 1997) and a stochastic finite-fault modeling based on a dynamic corner frequency proposed by Motazedian and Atkinson (Bull Seismol Soc Am 95:995–1010, 2005), modified by Assatourians and Atkinson (Bull Seismol Soc Am 97:935–1949, 2007), is used for generating the seismograms at low (0.1–1.0 Hz) and high frequencies (1.0–20.0 Hz), respectively. The results are validated by comparing the simulated peak acceleration, peak velocity, peak displacement, Arias intensity, the integral of velocity squared, Fourier spectrum and acceleration response spectrum on a frequency-by-frequency basis, the shape of the normalized integrals of acceleration and velocity squared, and the cross-correlation with the observed time-series data. Each characteristic is compared on a scale from 0 to 10, with 10 being perfect agreement. Also, the results are validated by comparing the simulated ground motions with the modified Mercalli intensity observations reported by reconnaissance teams and showed reasonable agreement. The results of the present study imply that the damage distribution pattern of the 1978 Tabas earthquake can be explained by the source directivity effect. 相似文献
120.