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排序方式: 共有279条查询结果,搜索用时 15 毫秒
51.
52.
Multi-aquifer pumping tests, using a multi-screen pumping well and multi-level piezometers, were carried out for groundwater flow control in a large-scale excavation site in Tokyo, Japan. The site was underlain by multi-layered confined aquifers. In the tests, pumping was carried out using a multi-aquifer pumping well in which a screen depth was chosen arbitrarily. Changes in groundwater pressure heads in each aquifer were measured at each screen position of the multi-aquifer pumping well. Hydraulic conductivity (K) and specific storage (S s) of not only aquifers, but also for low permeability layers between the aquifers, were estimated using the Cooper-Jacob method, and calibrated by a finite element method (FEM) groundwater model. Four different cutoff wall lengths were assumed for final excavation depth, and correlations among wall length, pumping discharge and drawdown at the back of the cutoff wall were obtained from simulations using the K and S s parameters in the FEM model. Then, the most suitable wall length was selected based on the simulated correlations considering environmental condition, construction period and cost of the cutoff wall. 相似文献
53.
Maintaining real-time precise point positioning during outages of orbit and clock corrections 总被引:1,自引:1,他引:0
The precise point positioning (PPP) is a popular positioning technique that is dependent on the use of precise orbits and clock corrections. One serious problem for real-time PPP applications such as natural hazard early warning systems and hydrographic surveying is when a sudden communication break takes place resulting in a discontinuity in receiving these orbit and clock corrections for a period that may extend from a few minutes to hours. A method is presented to maintain real-time PPP with 3D accuracy less than a decimeter when such a break takes place. We focus on the open-access International GNSS Service (IGS) real-time service (RTS) products and propose predicting the precise orbit and clock corrections as time series. For a short corrections outage of a few minutes, we predict the IGS-RTS orbits using a high-order polynomial, and for longer outages up to 3 h, the most recent IGS ultra-rapid orbits are used. The IGS-RTS clock corrections are predicted using a second-order polynomial and sinusoidal terms. The model parameters are estimated sequentially using a sliding time window such that they are available when needed. The prediction model of the clock correction is built based on the analysis of their properties, including their temporal behavior and stability. Evaluation of the proposed method in static and kinematic testing shows that positioning precision of less than 10 cm can be maintained for up to 2 h after the break. When PPP re-initialization is needed during the break, the solution convergence time increases; however, positioning precision remains less than a decimeter after convergence. 相似文献
54.
Akihiko Ito 《Climatic change》2017,142(1-2):53-66
Geoengineering such as solar radiation management (SRM) can be an emergent option to avoid devastating climatic warming, but its ramifications are barely understood. The perturbation of the Earth’s energy balance, atmospheric dynamics, and hydrological cycling may exert unexpected influences on natural and human systems. In this study, I evaluate the impacts of SRM deployment on terrestrial ecosystem functions using a process-based ecosystem model (the Vegetation Integrative Simulator for Trace gases, VISIT) driven by the climate projections by multiple climate models. In the SRM-oriented climate projections, massive injection of sulphate aerosols into the stratosphere lead to increased scattering of solar radiation and delayed anthropogenic climate warming. The VISIT simulations show that canopy light absorption and gross primary production are enhanced in subtropics in spite of the slight decrease of total incident solar radiation. The retarded temperature rise during the deployment period leads to lower respiration, and consequently, an additional net terrestrial ecosystem carbon uptake by about 20%. After the SRM termination, however, along with the temperature rise, this carbon is released rapidly to the atmosphere. As a result of altered precipitation and radiation budget, simulated runoff discharge is suppressed mainly in the tropics. These SRM-induced influences on terrestrial ecosystems occurr heterogeneously over the land surface and differed among the ecosystem functions. These responses of terrestrial functions should be taken into account when discussing the costs and benefits of geoengineering. 相似文献
55.
Unpolarized infrared (IR) reflectance spectra for MgSiO3 ilmenite taken from a single-crystal and from a densly packed polycrystalline sample possessed all eight peaks mandated by symmetry between 337 and 850 cm?1. Polarizations were inferred from intensity differences between the two samples. IR peak positions differ by up to 250 cm?1 from recent calculations, but on average are within 11%. Heat capacity C p calculated from these data by using a Kieffer-type model are within the experimental uncertainty of calorimetric measurements from 170 to 700 K. Outside this range, calculated C p is probably accurate within a few percent, based on recent results for garnets. Calculated entropy is only slightly less accurate, giving S 0 (298.15 K) as 54.1 ±0.5 J/ mol-K, which is 10% lower than recent estimates based on phase equilibria. The slope of the phase boundary between ilmenite and perovskite is used to predict S 0 (298.15 K) of perovskite as 58.7 ±1.4 J/mol-K, which is 10% lower than previous values. 相似文献
56.
Abundances and biomasses of planktonic ciliates and copepod nauplii, major components of the microzooplankton community, were investigated in the subarctic North Pacific and the Bering Sea in summer of 1997. Their regional variation was illustrated by demarcating the entire area into five regions. Ciliates always predominated both in abundance (>94%) and biomass (>78%) over nauplii. Regional means of ciliates in the water column were higher in the Alaskan Gyre (120 × 106 cells/m2) and the Western Subarctic Gyre (110 × 106 cells/m2) in terms of abundance, and rich in the Bering Sea Gyre (360 mgC/m2) and the Western Subarctic Gyre (340 mgC/m2) in terms of biomass. By contrast, standing crops of ciliates were poor in the Oyashio Region (67 × 106 cells/m2; 170 mgC/m2) and the Transition Region (64 × 106 cells/m2; 160 mgC/m2). The values of biomass reported here are generally in agreement with the values reported previously from the Bering Sea Gyre and the Alaskan Gyre but are considerably higher than the previous value found in the Western Subarctic Gyre. No significant correlations could be found between chlorophyll a crop and standing crops of ciliates and copepod nauplii over the entire subarctic North Pacific and the Bering Sea during this summer. 相似文献
57.
Yoshihiro Iijima Tsuneo Kawaragi Takehiko Ito Kanat Akshalov Atsushi Tsunekawa Masato Shinoda 《水文研究》2008,22(16):2974-2981
In drylands, water deficit is the primary factor limiting plant growth. In the present study, surface energy balance and plant growth (above‐ground and below‐ground biomass) were measured continuously during the 2002 growing season in semiarid grassland in the northern part of Kazakhstan, Central Asia. Although there was above normal total rainfall during the 2002 growing season (May–November; 244 mm over 183 days), there was a dry period during July and August. Evaporative water was effectively supplied by precipitation and surface soil moisture during the wet season (May and June), during which time above‐ground biomass increased. During the early stages of the dry period, mature plants were likely to tap deeper sources of soil moisture, representing stored snowmelt water. As the soil moisture content decreased during the summer dry period due to the high levels of evapotranspiration and lack of precipitation, the evaporative fraction and above‐ground biomass rapidly decreased, whereas the below‐ground biomass increased. These results suggest that in summer, soil moisture acts to store water, and that soil moisture is essential for plant growth as a direct source of water during the dry period in natural grasslands in the Kazakhstan steppe. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
58.
Hirotaka Ito Motoki Kino Nozomu Kawakatu Naoki Isobe Shoichi Yamada 《Astrophysics and Space Science》2007,311(1-3):335-339
We investigate the total kinetic powers (L
j) and ages (t
age) of powerful jets of four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C 219) by the detail comparison of the dynamical
model of expanding cocoons with observed ones. It is found that these sources have quite large kinetic powers with the ratio
of L
j to the Eddington luminosity (L
Edd) resides in 0.02<L
j/L
Edd<10. Reflecting the large kinetic powers, we also find that the total energy stored in the cocoon (E
c) exceed the energy derived from the minimum energy condition (E
min ): 2<E
c/E
min <160. This implies that a large amount of kinetic power is carried by invisible components such as thermal leptons (electron
and positron) and/or protons. 相似文献
59.
Masato Naruse Tetsuya Ito Yutaro Sekimoto Hiroyuki Toba Naohisa Satou Masahiro Sugimoto Wenlei Shan Yoshizou Iizuka Toshiaki Kamba Mamoru Kamikura Yasutaka Serizawa 《Experimental Astronomy》2009,24(1-3):89-107
We have developed a near-field vector beam measurement system covering the range of frequencies from 385 to 500 GHz. The measurement set-up is capable of measurements with dynamic range exceeding 50 dB and amplitude and phase stability respectively of 0.1 dB/h and 1 degree/5 min at room temperature. Beam patterns of the ALMA band 8 corrugated horns and receiver optics block were measured at room temperature and lately compared with physical optics calculations obtained in the far-field. Both co-polar and cross-polar beam patterns of a qualification model of the ALMA band 8 cartridge cooled in a cartridge-test-cryostat have also been measured in the near-field as a detector of a submillimeter vector network analyzer. The measurements presented in this work refer to the lowest, middle and upper frequencies of band 8. The comparisons between software model and experimental measurements at these frequencies show good agreement down to ?30 dB for the main polarization component. The cross-polarization level of the beam propagating through the receiver optics block was also characterized. We found that a cross-polarization level better than ?28 dB can be achieved at all measured frequencies. The measured beam pattern of this receiver corresponds to efficiency of greater than 92% at the sub reflector (diameter of 750 mm) of the ALMA 12 m optics. 相似文献
60.
Shin Ozawa Eiji Ohtani Masaaki Miyahara Akio Suzuki Makoto Kimura Yoshinori Ito 《Meteoritics & planetary science》2009,44(11):1771-1786
Abstract— The high‐pressure polymorphs of olivine, pyroxene, and plagioclase in or adjacent to shock melt veins (SMVs) in two L6 chondrites (Sahara 98222 and Yamato 74445) were investigated to clarify the related transformation mechanisms and to estimate the pressure‐temperature conditions of the shock events. Wadsleyite and jadeite were identified in Sahara 98222. Wadsleyite, ringwoodite, majorite, akimotoite, jadeite, and lingunite (NaAlSi3O8‐hollandite) were identified in Yamato 74445. Wadsleyite nucleated along the grain boundaries and fractures of original olivine. The nucleation and growth of ringwoodite occurred along the grain boundaries of original olivine, and as intracrystalline ringwoodite lamellae within original olivine. The nucleation and growth of majorite took place along the grain boundaries or fractures in original enstatite. Jadeite‐containing assemblages have complicated textures containing “particle‐like,” “stringer‐like,” and “polycrystalline‐like” phases. Coexistence of lingunite and jadeite‐containing assemblages shows a vein‐like texture. We discuss these transformation mechanisms based on our textural observations and chemical composition analyses. The shock pressure and temperature conditions in the SMVs of these meteorites were also estimated based on the mineral assemblages in the SMVs and in comparison with static high‐pressure experimental results as follows: 13–16 GPa, >1900 °C for Sahara 98222 and 17–24 GPa, >2100 °C for Yamato 74445. 相似文献