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101.
Statistical modeling for the mitigation of GPS multipath delays from day-to-day range measurements 总被引:1,自引:0,他引:1
Based on a least-squares model for double-difference GPS pseudoranges and carrier-phases, measurement residuals expressed
in time series during an observation session are positively correlated between one sidereal day and the preceding days. As
a result of the satellite’s period, the phenomenon, which takes place at a user receiving site, is attributed to multipath
interference. Examples from a weekly measurement dataset of control baselines are shown, where the known end-point coordinates
also serve as a benchmark for assessing positioning accuracy. The system of error equations for mixed-model adjustment is
divided into two subsystems. One set of the error equations is related to the real range measurements, while the other involves
the pseudo-observation with an empirical sample variance. According to the existing correlation between day-to-day residual
estimates, a multipath-mitigating algorithm is proven to improve the accuracy of the GPS height determination by at least
40%. It is also found that the algorithm depends on a variance-component estimator that adaptively scales an error covariance
matrix for both the real range and empirical delay measurements. 相似文献
102.
Jens M. Turowski Niels Hovius Hsieh Meng‐Long Dimitri Lague Chen Men‐Chiang 《地球表面变化过程与地形》2008,33(3):353-363
Lateral erosion in bedrock rivers is an important control on the shape of channel cross‐sections, and the coupling of channels and hillslopes. Recent observations link lateral erosion to the variability of flow. We propose two mechanisms to explain this. One is based on changing shear stress distributions within the channel with varying flood level, the other on the competition between cover and tool effects in fluvial bedrock erosion. We assess these processes for the Liwu River, Taiwan, and conclude that cover and tool effects dominate the partitioning of lateral and vertical erosion in this case. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
103.
Parameter identification for on‐line model updating in hybrid simulations using a gradient‐based method 下载免费PDF全文
Ming‐Chieh Chuang Shang‐Hsien Hsieh Keh‐Chyuan Tsai Chao‐Hsien Li Kung‐Juin Wang An‐Chien Wu 《地震工程与结构动力学》2018,47(2):269-293
To improve the efficiency of model fitting, parameter identification techniques have been actively investigated. Recently, the applications of parameter identification migrated from off‐line model fitting to on‐line model updating. The objective of this study is to develop a gradient‐based method for model updating to advance hybrid simulation also called hybrid test. A novel modification of the proposed method, which can reduce the number of design variables to improve the identification efficiency, is illustrated in detail. To investigate the model updating, simulated hybrid tests were conducted with a 5‐story steel frame equipped with buckling‐restrained braces (BRBs) utilized in the shaking table tests conducted in E‐Defense in Japan in 2009. The calibrated analytical model that was verified with the test results can serve as the reference model. In the simulated hybrid tests, the physical BRB substructure is numerically simulated by utilizing a truss element with the 2‐surface model identical to the part of the reference model. Such numerical verification allows simulation of measurement errors for investigation on the performance of the proposed method. Moreover, the feasibility of sharing the identified parameter values, which were obtained from the physical substructure responses, with the relevant numerical models is also verified with the artificial component responses derived from the physical experiments. 相似文献
104.
Characterization of horseshoe vortex in a developing scour hole at a cylindrical bridge pier 总被引:1,自引:0,他引:1
Since local scour at bridge piers in rivers and estuaries is a major cause of bridge failure, estimation of the maximum local scour depth is of great importance to hydraulic and coastal engineers. Although numerous studies that focus on scour-depth prediction have been done and published, understanding of the flow and turbulence characteristics of the horseshoe vortex that drives the scour mechanism in a developing scour hole still is immature. This study aims to quantify the detailed turbulent flow field in a developing clear-water scour hole at a circular pier using Particle Image Velocimetry (PIV). The distributions of velocity fields, turbulence intensities, and Reynolds shear stresses of the horseshoe vortex that form in front of the pier at different scour stages (t=0, 0.5, 1, 12, 24, and 48 h) are presented in this paper. During scour development, the horseshoe vortex system was found to evolve from one initially small vortex to three vortices. The strength and size of the main vortex are found to increase with increasing scour depth. The regions of both the maximum turbulence intensity and Reynolds shear stress are found to form at a location upstream of the main vortex, where the large turbulent eddies have the highest possibility of occurrence. Results from this study not only provide new insight into the complex flow-sediment interaction at bridge piers, but also provide valuable experimental databases for advanced numerical simulations. 相似文献
105.
This study was undertaken to investigate patterns of pyrite accumulation found in aJuncus roemerianus tidal marsh of north Florida. We speculate that the pattern of pyrite accumulation was caused mainly by the distribution of roots. Sediment cores from living stands (LS), dead stands (DS), and recently killed stands (RKS) were collected and analyzed for dissolved organic carbon (DOC), sulfate, chloride, Cr(II)-reducible sulfide, and biomass of roots and rhizomes. Living roots were distributed mainly in the upper 16 cm and concentrated 4–10 cm below the sediment surface. Pyrite accumulations were significantly different among the three types of sediment cores in the upper 16 cm sediment and follow the descending order of DS (615 μmol cm?3)>RKS (547 μmol cm?3)>LS (368 μmol cm?3). Between 20 cm and 30 cm, pyrite contents approached values of 40 μmol cm?3 and 55 μmol cm?3 in all sediment cores. The degree of pyritization approaches 92–94% between 14 cm and 20 cm where pyrite accumulation was probably limited by available iron. Root distribution also affected the redistribution of iron through iron sulfide formation. Sulfate depletion in the upper 16 cm was higher in RKS (79.3 μmol cm?3) than DS (49.1 μmol cm?3). No significant sulfate depletion was found in LS. Sulfate reduction under DS was likely limited by the readily available substrates. Root distribution had a major influence on pyrite accumulation and sulfate reduction of the marsh, and its effects need to be addressed in studies of wetland sulfur dynamics. 相似文献
106.
Cheng-Chao Lee Louis Loung-Yie Tsai Chieh-Hou Yang Kuo-Liang Wen Zi-Bin Wang Zhi-Hsian Hsieh Hsing-Chang Liu 《Environmental Geology》2009,58(7):1397-1406
A slope on the west border of the foothill near 921 surface rupture (caused by the 1999 Chi-Chi earthquake) in central Taiwan
shows distinctive topographic expression that was prone to be considered as a fault scarp formed by a preexisting active fault.
The 2D and 3D resistivity images clearly delineate rock surfaces which show steep, deep, gentle, and subvertical displacement
beneath the slope, the toe of slope, the non-lateritic terrace, and 921 surface rupture, respectively, which can be attributed
to the significant contrast of resistivity between gravel and rock. The horizontal sand bed and clast-supported gravel were
deposited in a fluvial environment, whereas wedge-shaped gravel and colluvium were scarp-induced colluvial deposits in the
trench profile. The layers shown in the depth of excavation, except for rock, has no offset or disturbance by fault ever since
at least 2,480 ± 50 year B.P., based on carbon 14 dating of charcoal sample at the bottom of trench profile. According to
information from two boreholes close to the slope, an over 20-m-thick marker bed with transported shell fragments, was found
for correlation. This correlation further implies the slope was not formed by fault. On the other hand, two boreholes which
are far from the slope and located on the flat non-lateritic terrace frequently show fractured and sheared features. By comparison,
the locations around these two boreholes indicate a reverse fault or faults that occurred before the deposition of gravel.
Later on, the paleostream was developed along the foot of fault scarp that was subjected to erosion and led to subsequent
retrogression or retreat of the slope. Consequently, the incision of paleostream is believed to be responsible for the high
relief of rock surface around the slope. Furthermore, from resistivity and borehole data, the rock surface underlying terrace
is gentle where no faults occur after the deposition of gravel. The result of RIP crossing the 921 surface rupture displays
about 10 m difference in elevation of rock surface on both sides, which is greater than that of 3–4 m caused by Chi-Chi earthquake.
This indicates that the 921 surface rupture is a preexisting thrust fault that resulted from several thrusting events since
terrace gravel was deposited. So it is not necessary to establish an extra restricted zone for construction in study area,
except close to the 921 surface rupture. 相似文献
107.
A.J. Coates R.A. Frahm D.O. Kataria G. Collinson J.D. Winningham S. Barabash R. Lundin Y. Futaana A. Grigoriev H. Gunell J.-J. Thocaven W. Baumjohann H. Koskinen J.U. Kozyra Y. Ma A. Galli P. Bochsler E.C. Roelof N. Krupp M. Fraenz S. McKenna-Lawlor R. Cerulli-Irelli A. Milillo C.C. Curtis K.C. Hsieh A. Asamura 《Planetary and Space Science》2008,56(6):802-806
We report the detection of electrons due to photo-ionization of atomic oxygen and carbon dioxide in the Venus atmosphere by solar helium 30.4 nm photons. The detection was by the Analyzer of Space Plasma and Energetic Atoms (ASPERA-4) Electron Spectrometer (ELS) on the Venus Express (VEx) European Space Agency (ESA) mission. Characteristic peaks in energy for such photoelectrons have been predicted by Venus atmosphere/ionosphere models. The ELS energy resolution (ΔE/E∼7%) means that these are the first detailed measurements of such electrons. Considerations of ion production and transport in the atmosphere of Venus suggest that the observed photoelectron peaks are due primarily to ionization of atomic oxygen. 相似文献
108.
This paper aims to investigate the mechanical behaviour of a hybrid reinforced earth embankment built in limited width adjacent to a slope. This embankment system incorporates reinforced earth embankments with soil nails, installed in the existing ground. Soil nails work to provide additional resisting forces to stabilize the embankment which may be unstable due to insufficient reinforcement length. Nail forces developed in the hybrid reinforced earth embankment with various geometric conditions in the fill space are analyzed. The FE method is used to simulate the construction of the hybrid reinforced earth embankment. Influence of reinforcement length, reinforcement stiffness, and slope gradient on the nail forces developed following the construction is analyzed and discussed. Additionally, design concerns for the hybrid reinforced earth embankment system are also studied. Simple charts for estimating the maximum nail force mobilized at back of the hybrid reinforced earth embankment are established in this research and can be helpful in the design of the soil nails in the system. 相似文献
109.
Monsoon-driven succession of the larval fish assemblage in the East China Sea shelf waters off northern Taiwan 总被引:2,自引:0,他引:2
Hung-Yen Hsieh Wen-Tseng Lo Long-Jing Wu Dong-Chung Liu Wei-Cheng Su 《Journal of Oceanography》2011,67(2):159-172
The seasonal variation in the larval fish community related to the hydrography in the East China Sea (ECS) off northern Taiwan
was studied from February to November 2004. Hydrographic conditions in the southern ECS are strongly influenced by the different
water masses due to the seasonal monsoon system. A total of 173 taxa of larval fish belonging to 68 families and 105 genera
were identified during the study period. The highest abundance of larval fish was recorded in winter, a moderate abundance
was seen in late spring and summer, and the lowest abundance in autumn. Significantly higher abundances were usually found
in the mixing zone than in ECS and the Kuroshio Current, and the number of species of larval fish was greater during the warm
period than during the cold period. The larval fish fauna in the southern ECS is a mixture of endemic and exotic species;
the latter come from the coastal waters of mainland China when the northeasterly monsoon prevails, from the South China Sea
during the southwesterly monsoon, and from the Kuroshio waters year-round. The succession of water masses induced by the monsoon
systems and the high nutrient levels caused by frontal turbulence and topographic upwelling may determine the distributions
of larval fish in terms of abundance and composition. 相似文献
110.
A shock absorbing cushion has never been introduced into any traditional weir surface repair layer design.However,shocks induced by high discharge with heavy sediment can easily produce brittle fracture and peeling over a weir surface repair layer as it is impacted by floods accompanied by particles of different sizes.In this study,transcending traditional designs,the authors developed a composite unit designed with a shock absorbing cushion that has performed well during field tests,proving that the weir body can be effectively protected even if the composite units are directly laid on a severely uneven weir surface repair layer. 相似文献