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排序方式: 共有140条查询结果,搜索用时 31 毫秒
31.
We present observations of thermal emission from fifteen transneptunian objects (TNOs) made using the Spitzer Space Telescope. Thirteen of the targets are members of the Classical population: six dynamically hot Classicals, five dynamically cold Classicals, and two dynamically cold inner Classical Kuiper belt objects (KBOs). We fit our observations using thermal models to determine the sizes and albedos of our targets finding that the cold Classical KBOs have distinctly higher visual albedos than the hot Classicals and other TNO dynamical classes. The cold Classicals are known to be distinct from other TNOs in terms of their color distribution, size distribution, and binarity fraction. The Classical objects in our sample all have red colors yet they show a diversity of albedos which suggests that there is not a simple relationship between albedo and color. As a consequence of high albedos, the mass estimate of the cold Classical Kuiper belt is reduced from approximately 0.01 M⊕ to approximately 0.001 M⊕. Our results also increase significantly the sample of small Classical KBOs with known albedos and sizes from 21 to 32 such objects. 相似文献
32.
Aerosol depolarization ratio and aerosol optical depth (AOD) were measured at Chungli (24.58° N, 121.1° E), Taiwan during the period from 2002–2004. The depolarization ratios of background aerosol have values mostly less than 0.06. The maximum AOD in the altitude range of 0.7 to 2km occurs in the summer (June–August) while between 2 and 5km, the spring (March–May) shows the maximum. The former is mainly related to strong convection and humidity; however the latter is due to anthropogenic aerosols transported from East China and Southeast Asia based on calculations of backward trajectories. This seasonal variation of AOD inferred from different transport mechanisms and aerosol compositions which are supported by the height distributions of aerosol extinction and origins. 相似文献
33.
Alternative water resources in granitic rock: a case study from Kinmen Island,Taiwan 总被引:1,自引:1,他引:0
Tai-Sheng Liou Yuan-Hsi Lee Li-Wei Chiang Wayne Lin Tai-Rong Guo Wen-Shan Chen Jeng-Ming Chien 《Environmental Earth Sciences》2010,59(5):1033-1046
Kinmen Island is a small, tectonically stable, granitic island that has been suffering from a scarcity of fresh water resources
due to excessive annual evapotranspiration over annual precipitation. Recent studies further indicate that shallow (0–70 m)
sedimentary aquifers, the major sources of groundwater supply, have already been over-exploited. Therefore, this preliminary
study is to investigate the existence of exploitable water resources that can balance the shortage of fresh water on this
island. Site characterization data are obtained from island-wide geophysical surveys as well as small-scale tests performed
in a study area formed by three deep (maximum depth to 560 m) vertical boreholes installed in mid-east Kinmen northeast to
Taiwu Mountain. Vertical fracture frequency data indicate that the rock body is fractured with a spatially correlated pattern,
from which three major fracture zones (depths 0–70, 330–360, and below 450 m) can be identified. Geologic investigations indicate
that the deepest fracture zone is caused by the large-scale, steeply dipping Taiwushan fault. This fault may have caused a
laterally extensive low-resistivity zone, a potential fractured aquifer, near Taiwu Mountain. The middle fracture zone is
induced by the Taiwushan fault and intersects the fault approximately 21 m southeast of the study area below a depth of 350 m.
Slug testing results yield fracture transmissivity varying from 4.8 × 10−7 to 2.2 × 10−4 m2/s. Cross-hole tests have confirmed that hydraulic connectivity of the deeper rock body is controlled by the Taiwushan fault
and the middle fracture zone. This connectivity may extend vertically to the sedimentary aquifers through high-angle joint
sets. Despite the presence of a flow barrier formed by doleritic dike at about 300 m depth, the existence of fresh as well
as meteoric water in the deeper rock body manifests that certain flow paths must exist through which the deeper fractured
aquifers can be connected to the upper rock body. Therefore, groundwater stored within the Taiwushan fault and the associated
low-resistivity zone can be considered as additional fresh water resources for future exploitation. 相似文献
34.
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36.
Experimental evaluation of piecewise exact solution for predicting seismic responses of spherical sliding type isolated structures 总被引:1,自引:0,他引:1
The use of base isolation for enhancing seismic resistibility has been proven as an efficient method in experimental and theoretical studies. It is usual to insert a flexible device in the horizontal direction to permit the most of relative deformation of a structure at this level. Because the rigidity of the superstructure is much higher than that of the base isolator underneath the structure, the behavior of the superstructure can be idealized as a rigid body during earthquakes. In general, hundreds of degrees of freedom and a step‐by‐step time history analysis are the basic requirements for calculating the seismic response of a base‐isolated structure under earthquakes. In order to develop a simple tool which can be easily adopted for calculating the seismic responses of the spherical sliding type isolated structures, a piecewise exact solution for predicting the seismic responses of base‐isolated structures has been derived in this study. The comparison between the experimental results conducted at the National Center for Research on Earthquake Engineering (NCREE) in Taiwan and the analytical results obtained from the piecewise exact solution show that the formulation derived in this study can predict the seismic responses of the base‐isolated structure with a very high accuracy. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
37.
Bing-Ru Wu Nai-Chi Hsiao Pei-Yang Lin Ting-Yu Hsu Chiou-Yun Chen Shieh-Kung Huang Hung-Wei Chiang 《Journal of Seismology》2017,21(1):165-180
An earthquake early warning (EEW) system with integration of regional and onsite approaches was installed at nine demonstration stations in several districts of Taiwan for taking advantages of both approaches. The system performance was evaluated by a 3-year experiment at schools, which experienced five major earthquakes during this period. The blind zone of warning was effectively reduced by the integrated EEW system. The predicted intensities from EEW demonstration stations showed acceptable accuracy compared to field observations. The operation experience from an earthquake event proved that students could calmly carry out correct action before the seismic wave arrived using some warning time provided by the EEW system. Through successful operation in practice, the integrated EEW system was verified as an effective tool for disaster prevention at schools. 相似文献
38.
JN Kathena A Kokkalis MW Pedersen JE Beyer UH Thygesen 《African Journal of Marine Science》2018,40(3):293-302
There is global interest in providing scientific advice on optimal harvesting of all commercially exploited fish stocks. Nevertheless, many commercially important stocks lack analytical assessments. Therefore, we evaluate a data-moderate stock assessment method: the stochastic surplus production model in continuous time (SPiCT). The method was applied to two Namibian stocks: (i) the data-rich Cape monkfish Lophius vomerinus, where results are compared to a new data-rich assessment using a state–space assessment model (SAM); and (ii) the data-moderate west coast sole Austroglossus microlepis, which is an important bycatch species in the Cape monkfish fishery, but currently unassessed. The information available to the data-moderate assessment is total commercial catch, commercial catch per unit effort (CPUE), and survey CPUE. SPiCT and SAM gave largely consistent estimates of relative fishing mortality (F/FMSY) and relative exploitable biomass (B/BMSY) for the Cape monkfish stock, although with some discrepancies. Differences in the biomass estimates between the two assessments suggest that further investigation is required to understand the cause, and that some caution is necessary when considering the biomass of the stock. SPiCT shows that the west coast sole may be overexploited, although the confidence bounds were too wide for a firm conclusion. Similarity in the estimates of F/FMSY for Cape monkfish in recent years, using SPiCT relative to SAM, likewise indicates the suitability of SPiCT for managing west coast sole. 相似文献
39.
MW Farthing AC Winkler K Anderson S Kerwath C Wilke WM Potts 《African Journal of Marine Science》2018,40(2):187-196
The hottentot seabream Pachymetopon blochii is a small-sized (maximum 2.67 kg) sparid endemic to southern Africa. It is an important target in South Africa's Western Cape traditional linefishery, particularly in the absence of more valuable pelagic species (such as Thyrsites atun and Seriola lalandi). In 2000, South Africa's linefishery was declared to be in a state of emergency, and commercial fishing effort was consequently reduced by 70%. A subsequent increase in stock biomass and intraspecific competition, coupled with environmental changes, were hypothesised to have thereafter altered the growth rate of hottentot, from 2000 to 2010. This study aimed to revise outdated age–growth models for the hottentot by using modern techniques (sectioned otoliths), and to compare age–growth relationships before and after the declared linefish state of emergency. The maximum age observed was 19 years, with no difference in the growth rate between sexes (p = 0.39–0.43) or time-periods (p = 0.96). Although the growth rate did not change, there is evidence that the age structure of the stock changed between time-periods as a result of changes in fishing pressure between 2000 and 2010. The enhanced recent growth model for hottentot, described as Lt = 418.063 (1 – e?0.104(t – [?4.709])) (pooled sexes; n = 206), indicates a considerably slower growth rate for this species than was proposed previously using whole otoliths and has major implications for effective stock management. 相似文献
40.
Digital mobile mapping, the method that integrates digital imaging with direct geo-referencing, has developed rapidly over
the past 15 years. The Kalman filter (KF) is considered an optimal estimation tool for real-time INS/GPS integrated kinematic
positioning and orientation determination. However, the accuracy requirements of general mobile mapping applications cannot
be easily achieved even when using the KF scheme. Therefore, this study proposes an intelligent scheme combining ANN and RTS
backward smoother to overcome the limitations of KF and to enhance the overall accuracy of attitude determination for tactical
grade and MEMS INS/GPS integrated systems.
相似文献
Yun-Wen Huang (Corresponding author)Email: |