共查询到20条相似文献，搜索用时 671 毫秒
1.
Instantaneous deformation from continuous GPS: contributions from quasi-periodic loads 总被引：3，自引：0，他引：3
Richard A. Bennett 《Geophysical Journal International》2008,174(3):1052-1064
Continuous GPS (CGPS) coordinate time-series are known to experience repeating deformation signals with seasonal and other periods. It is unlikely that these signals represent perfect sinusoids with temporally constant amplitude. We develop an analysis method that accommodates temporal variations in the amplitudes of sinusoidal signals. We apply the method to simulated coordinate time-series to numerically explore the potential consequences of neglecting decadal variation in amplitude of annual motions on the residual-error spectra of CGPS measurements, as well as potential bias in estimates for secular site velocity. We find that secular velocity bias can be appreciable for shorter time-series, and that residual-error time-series of longer duration may contain significant power in a broad band centred on semi-annual frequency if temporal variation in the amplitude of annual motions is not accounted for in the model used to reduce the observations to residuals. It may be difficult to differentiate the bandpass filtered signature of mismodelled loading signals from power-law noise, using residual-error spectra for shorter time-series. We provide an example application to a ∼9-yr coordinate time-series for a CGPS station located in southern California at Carbon Creek Control Structure (CCCS), which is known to experience large amplitude seasonal motions associated with the Santa Ana aquifer system. 相似文献
2.
3.
4.
5.
6.
7.
《New Zealand geographer》1958,14(2):188-189
Book reviewed in this article:
HYDROTOWN: THE SOCIAL HISTORY OF AN INDUSTRIAL BOOM SETTLEMENT. By W. J. Campbell 相似文献
HYDROTOWN: THE SOCIAL HISTORY OF AN INDUSTRIAL BOOM SETTLEMENT. By W. J. Campbell 相似文献
8.
9.
10.
《The Journal of geography》2012,111(1)
Abstract In geographic education, a scientific approach is typically acclaimed as the most appropriate approach to teach, model, and use in the schools. This approach, however, is more honored in the professional literature and meetings than in teaching. Admittedly, many practical problems provide opportunities and challenges for teachers to use the scientific approach. The recent trend toward “standards” in the profession, moreover, may also prove more a hindrance than a help in achieving scientific literacy. 相似文献
11.
12.
Saigon from the diaspora 总被引：1，自引：1，他引：0
Ashley Carruthers 《Singapore journal of tropical geography》2008,29(1):68-86
In the wake of reform in Vietnam and the end of the cold war, overseas Vietnamese are returning to their former homeland in increasing numbers. For most of the first generation in the diaspora, memories of wartime Saigon are now being augmented by a touristic experience of contemporary Saigon/Ho Chi Minh City. This essay asks how the co-presence of these differently spatialized and temporalized ways of knowing the city affects the production and consumption of images of Saigon in overseas Vietnamese communities in the West. Based on media ethnography carried out in Vietnamese households in Sydney, the paper argues that changes in the way Saigon is represented in overseas Vietnamese popular culture reflect a shift in the larger politics of diasporic identity. While narratives of exile and refugeehood remain potent forms of affective (if not instrumental) politics in overseas Vietnamese contexts, transnational forms of consciousness and identification are beginning to enter into diasporic public culture, albeit in a highly contested way. 相似文献
13.
We report on calculations of the on-shore run-up of waves that might be generated by the impact of subkilometre asteroids into the deep ocean. The calculations were done with the COULWAVE code, which models the propagation and shore-interaction of non-linear moderate- to long-wavelength waves ( kh < π) using the extended Boussinesq approximation. We carried out run-up calculations for several different situations: (1) laboratory-scale monochromatic wave trains onto simple slopes; (2) 10–100 m monochromatic wave trains onto simple slopes; (3) 10–100 m monochromatic wave trains onto a compound slope representing a typical bathymetric profile of the Pacific coast of North America; (4) time-variable scaled trains generated by the collapse of an impact cavity in deep water onto simple slopes and (5) full-amplitude trains onto the Pacific coast profile. For the last case, we also investigated the effects of bottom friction on the run-up. For all cases, we compare our results with the so-called 'Irribaren scaling': The relative run-up R / H 0 =ξ= s ( H 0 / L 0 )−1/2 , where the run-up is R , H 0 is the deep-water waveheight, L 0 is the deep-water wavelength, s is the slope and ξ is a dimensionless quantity known as the Irribaren number. Our results suggest that Irribaren scaling breaks down for shallow slopes s ≤ 0.01 when ξ < 0.1 − 0.2 , below which R / H 0 is approximately constant. This regime corresponds to steep waves and very shallow slopes, which are the most relevant for impact tsunami, but also the most difficult to access experimentally. 相似文献
14.
15.
16.
17.
Seismic Energy from Explosions 总被引：1，自引：0，他引：1
P. N. S. O'Brien 《Geophysical Journal International》1960,3(1):29-44
18.
Although recent studies have quantified effects upon river channel morphology downstream of reservoirs, urban areas and channelization schemes, consideration has not been given to effects upon channels downstream of road bridges. Engineering literature focuses upon hydrologic considerations involving estimation of peak flow at the bridge site, and upon hydraulic aspects including backwater effects and scour around the bridge and piers. A reconnaissance survey at 19 bridges in the New Forest shows that channel shape changes below many bridges with width-depth ratios increasing substantially to double their value; that apparent channel capacities may increase below the bridge to twice their above-bridge value, due to incision and scour; and that such effects can be evident for distances downstream of the bridge of the order of 10 times channel width. Reference to large-scale topographic maps for one site, and to maps and large-scale aerial photographs for 15 sites in south central England, shows how these sources can be used to provide measurements of channel width above and below bridges and this indicates that the average downstream width is 1.99 times the upstream width. Such channel adjustments should be considered when measuring morphological and ecological characteristics of river channels and when explaining reaches of rapid channel adjustment. 相似文献
19.
20.
Summary. Electrical and magnetic fields due to arbitrarily oriented lightning over an imperfectly conducting ground have been obtained. The theory has been applied to K -changes, return strokes and horizontal lightning. The results are in good agreement with the experimental observations previously reported by many workers. 相似文献