Critical response of structures to multicomponent earthquake excitation     

Oscar A. Lopez  Anil K. Chopra  Julio J. Hernandez 《地震工程与结构动力学》2000,29(12):1759-1778

This paper aims to develop an improved understanding of the critical response of structures to multicomponent seismic motion characterized by three uncorrelated components that are defined along its principal axes: two horizontal and the vertical component. An explicit formula, convenient for code applications, has been derived to calculate the critical value of structural response to the two principal horizontal components acting along any incident angle with respect to the structural axes, and the vertical component of ground motion. The critical response is defined as the largest value of response for all possible incident angles. The ratio r_cr/r_srss between the critical value of response and the SRSS response—corresponding to the principal components of ground acceleration applied along the structure axes—is shown to depend on three dimensionless parameters: the spectrum intensity ratio γ between the two principal components of horizontal ground motion characterized by design spectra A(T_n) and γA(T_n); the correlation coefficient α of responses r_x and r_y due to design spectrum A(T_n) applied in the x‐ and y‐directions, respectively; and β = r_y/r_x. It is demonstrated that the ratio r_cr/r_srss is bounded by 1 and . Thus the largest value of the ratio is , 1.26, 1.13 and 1.08 for γ = 0, 0.5, 0.75 and 0.85, respectively. This implies that the critical response never exceeds times the result of the SRSS analysis, and this ratio is about 1.13 for typical values of γ, say 0.75. The correlation coefficient α depends on the structural properties but is always bounded between −1 and 1. For a fixed value of γ, the ratio r_cr/r_srss is largest if β = 1 and α = ±1. The parametric variations presented for one‐storey buildings indicate that this condition can be satisfied by axial forces in columns of symmetric‐plan buildings or can be approximated by lateral displacements in resisting elements of unsymmetrical‐plan buildings. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Estimating sand concentrations using ADCP-based acoustic inversion in a large fluvial system characterized by bi-modal suspended-sediment distributions     

Ricardo N. Szupiany  Cecilia Lopez Weibel  Massimo Guerrero  Francisco Latosinski  Molly Wood  Lucas Dominguez Ruben  Kevin Oberg 《地球表面变化过程与地形》2019,44(6):1295-1308

Quantifying sediment flux within rivers is a challenge for many disciplines due, mainly, to difficulties inherent to traditional sediment sampling methods. These methods are operationally complex, high cost, and high risk. Additionally, the resulting data provide a low spatial and temporal resolution estimate of the total sediment flux, which has impeded advances in the understanding of the hydro-geomorphic characteristics of rivers. Acoustic technologies have been recognized as a leading tool for increasing the resolution of sediment data by relating their echo intensity level measurements to suspended sediment. Further effort is required to robustly test and develop these techniques across a wide range of conditions found in natural river systems. This article aims to evaluate the application of acoustic inversion techniques using commercially available, down-looking acoustic Doppler current profilers (ADCPs) in quantifying suspended sediment in a large sand bed river with varying bi-modal particle size distributions, wash load and suspended-sand ratios, and water stages. To achieve this objective, suspended sediment was physically sampled along the Paraná River, Argentina, under various hydro-sedimentological regimes. Two ADCPs emitting different sound frequencies were used to simultaneously profile echo intensity level within the water column. Using the sonar equation, calibrations were determined between suspended-sand concentrations and acoustic backscatter to solve the inverse problem. The study also analyzed the roles played by each term of the sonar equation, such as ADCP frequency, power supply, instrument constants, and particle size distributions typically found in sand bed rivers, on sediment attenuation and backscatter. Calibrations were successfully developed between corrected backscatter and suspended-sand concentrations for all sites and ADCP frequencies, resulting in mean suspended-sand concentration estimates within about 40% of the mean sampled concentrations. Noise values, calculated using the sonar equation and sediment sample characteristics, were fairly constant across evaluations, suggesting that they could be applied to other sand bed rivers. © 2018 John Wiley & Sons, Ltd.  相似文献   

Video-monitoring of wood discharge: first inter-basin comparison and recommendations to install video cameras     

Hossein Ghaffarian  Hervé Piégay  Diego Lopez  Nicolas Rivière  Bruce MacVicar  Aurelie Antonio  Emmanuel Mignot 《地球表面变化过程与地形》2020,45(10):2219-2234

Wood in rivers plays a major role both ecologically and morphologically. In recent decades, due to human activities in the river channels and along the riparian zone, wood obstruction and jamming has exacerbated flooding hazards and infrastructure damage. Therefore, it is necessary to quantify the wood flux and discharge in rivers to improve wood hazard management. Among the various methods for monitoring the wood flux in a river, the streamside videography technique is effective given its high temporal and spatial resolution. Previous work monitored the wood discharge (m³/s) using this technique in the Ain River (France) during three floods (MacVicar and Piégay, 2012), and the same method is implemented on the Isère River (France) to obtain the statistics of wood discharge for two floods. Comparison between the two sites supports the generalization of both the monitoring technique and the link between wood discharge and flood characteristics. We first show that the maximum wood discharge is observed at bankfull discharge, and we confirm the three stage model proposed by MacVicar and Piégay (2012). Additionally, transverse distributions of the number of wood pieces and corresponding wood length appear to be similar for different flood magnitudes on each site. As a technical contribution, the use of the same technique on two sites allows for recommendations on key decisions related to the location and implementation of the equipment. Both statistical and technical contributions can be used by decision makers to implement this monitoring technique, acquire the wood transport parameters, and evaluate the potential wood hazards at local scale or along a river. © 2020 John Wiley & Sons, Ltd.  相似文献   

New proper motions for some AGK3 stars     

Carlos E. Lopez 《Astrophysics and Space Science》1991,177(1-2):73-77

In a program conducted to isolate AGK3 stars with large proper motions, it has been found that more than one hundred stars seem to be affected by large errors in their published proper motions. For some of those objects south of +25 degrees, new proper motions are being obtained using, as first-epoch positions, the published material of the Astrographic Catalogue. Second-epoch positions are derived from new plates taken with the Yale Southern Observatory double astrograph.  相似文献   

Progressive Build Up Of Co 2 In The AtmosphereOf Venus Through Multiple Volcanic Resurfacing Events     

Lopez  Ivan  Oyarzun  Roberto  Marquez  Alvaro  Doblas-Reyes  Francisco  Laurrieta  Alejandro 《Earth, Moon, and Planets》1998,81(3):187-192

In absence of other mechanisms, the main input of CO₂into the Venusian atmosphere is via volcanic out gassing. Since Venus can be regarded as a planet-wide large igneous province, we can expect large quantities of CO₂ being transferred into its atmosphere via volcanic out gassing. We have quantified the maximum possible amount of CO₂ that can be out gassed via a single massive episode of resurfacing of the planet. This figure (5.6 × 10¹⁹ kg of CO₂) is about 8 times smaller than the total CO₂ present in the Venusian atmosphere (4.55 × 10²⁰ kg CO₂). The lack of planet-wide, efficient mechanisms for the recycling of CO₂ on Venus indicates that CO₂ has progressively accumulated in the atmosphere. Based on these considerations we suggest that the “equivalent” to eight global resurfacing episodes would be required to account for the present values of CO_{2 atmosphere}. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Molecular clouds around outflow sources     

L. Verdes-Montenegro  J. M. Torrelles  L. F. Rodriguez  G. Anglada  R. Lopez  R. Estallella  J. Canto  P. T. P. Ho 《Astrophysics and Space Science》1990,171(1-2):161-162

The (J, K)=(1,1) ammonia transition emission has been observed toward six regions with signs of active star formation (AFGL 5142, HH 33/40, AFGL 5157, AFGL 6366S, HHL 73, and S140N), using the 37 m antenna of the Haystack Observatory. We detected and mapped the ammonia emission in all of these sources with the exception of HH 33/40. The (J, K)-(2,2), ammonia transition was also observed at the peak position of each source in order to obtain the rotational temperature of the ammonia clumps.Paper presented at the 11th European regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

The garnets of the eastern area of the Sierra de Guadarrama,Sistema Central,Spain     

J. Lopez Ruiz  L.A. Garcia Cacho 《Chemical Geology》1974,13(4):269-283

Electron-probe microanalysis of a series of garnets in metapelitic rocks of the chloritoid staurolite, kyanite and sillimanite metamorphic zones, eastern area of the Sierra de Guadarrama, Sistema Central, Spain, manifest the well-known cryptozonation commonly observed in these minerals, with MgO and FeO increasing and MnO and CaO decreasing from the center to the outer rim of the crystals.The differences in composition of the garnets, from one metamorphic zone to another, is mainly a result of small differences in composition of the host-rock, since: (1) the amounts of MnO in the garnet are controlled by the amounts of SiO₂, Al₂O₃ and FeO present in the host-rock; and (2) the percentages of MnO and MgO of the parent-rock influence in some way the concentration of CaO in the garnet, and those of MnO, Al₂O₃ and CaO influence the concentration of FeO. Nevertheless, the amount of FeO in the garnet is finally controlled, due to the diadochy, by the concentration of MnO + CaO in this mineral.  相似文献   

Arsenic in geothermal sources at the north-central Andean region of Ecuador: concentrations and mechanisms of mobility     

Luis Cumbal  Paulina Vallejo  Brigida Rodriguez  Dina Lopez 《Environmental Earth Sciences》2010,61(2):299-310

The arsenic content of geothermal hot springs and their sediments in the north-central Andean region of Ecuador has been investigated. The area of study is located between parallels 1°11′N and 1°30′S and includes five provinces. The area is rich in geothermal surface manifestations that are mainly used for medicinal baths in recreational complexes. Unfortunately, water residuals without treatment are released from the recreational facilities to surrounding water bodies. The results indicate that total arsenic in geothermal waters in this region has a range of 2–969 μg As/L, and sediments contain arsenic ranging from 1.6 to 717.6 mg/kg. Chemical analyses of sediment samples show the presence of sulfur, iron, aluminum and calcium. A high concentration of natural organic matter was also found in some samples (20–29.5%); thus sorption and coprecipitation can be the main mechanisms of As immobilization on mineral phases and natural organic matter.  相似文献   

Waste feed from coastal fish farms: A trophic subsidy with compositional side-effects for wild gadoids     

Damian Fernandez-Jover  Laura Martinez-Rubio  Pablo Sanchez-Jerez  Just T. Bayle-Sempere  Jose Angel Lopez Jimenez  Francisco Javier Martínez Lopez  Pl-Arne Bjrn  Ingebrigt Uglem  Tim Dempster 《Estuarine, Coastal and Shelf Science》2011,91(4):666

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Inner radii of dust shells and stellar diameters obtained by an infrared stellar interferometer at 11 micron wavelength     

W. C. Danchi  M. Bester  L. J. Greenhill  C. G. Degiacomi  N. Geis  D. Hale  B. Lopez  C. H. Townes 《Astrophysics and Space Science》1995,224(1-2):447-448

Visibility data and analyses are discussed for 16 late-type stars observed with the Infrared Spatial Interferometer (ISI) of the University of California, Berkeley.  相似文献