Damping characteristics of friction damped braced frame and its effectiveness in the mega-sub controlled structure system   总被引：11，自引：1，他引：10  

连业达  张询安 《地震工程与工程振动(英文版)》2007,6(2):171-181

Based on energy dissipation and structural control principle, a new structural configuration, called the mega- sub controlled structure (MSCS) with friction damped braces (FDBs), is first presented. Meanwhile, to calculate the damping coefficient in the slipping state a new analytical method is proposed. The damping characteristics of one-storey friction damped braced frame (FDBF) are investigated, and the influence of the structural parameters on the energy dissipation and the practical engineering design are discussed. The nonlinear dynamic equations and the analytical model of the MSCS with FDBs are established. Three building structures with different structural configurations, which were designed with reference to the conventional mega-sub structures such as used in Tokyo City Hall, are comparatively investigated. The results illustrate that the structure presented in the paper has excellent dynamic properties and satisfactory control effectiveness.  相似文献   

Light requirements of seagrassesHalodule wrightii andSyringodium filiforme derived from the relationship between diffuse light attenuation and maximum depth distribution     

W. Judson Kenworthy  Mark S. Fonseca 《Estuaries and Coasts》1996,19(3):740-750

The correspondence between maximum depth of growth (Z_max) for two seagrases,Halodule wrightii andSyringodium filiforme, and the attenuation of diffuse photosynthetically active radiation (K_dPAR) were evaluated over a 3.5-yr period in the southern Indian River Lagoon, Florida. The lower limit of seagrass depth distribution was controlled by light availability. Both species grew to the same maximum depth, indicating they have similar minimum light requirements. Based on average annual values of K_dPAR, estimates of seagrass minimum light requirements ranged from 24% to 37% of the light just beneath the water surface (I_o), much hgiehr than a photic zone for many phytoplankton and macroalgae (1–5% incident light). In less transparent waters of Hobe Sound, where turbidity (NTU) and color (Pt-Co) had their highest concentrations, minimum light requirements for growth were greatest. These results suggest that more sophisticated optical models are needed to identify specific water quality constituents affecting the light environment of seagrasses. Water quality criteria and standards needed to protect seagrasses from decreasing water transparency must be based on parameters that can be routinely measured and reasonably managed.  相似文献   

Precipitate flotation of copper as the sulfide,using recyclable amphoteric surfactants     

Carl P. Beitelshees  C.Judson King  Hugo H. Sephton 《International Journal of Mineral Processing》1981,8(2):97-110

An experimental study was made to identify surfactants which are effective for removal of copper from dilute aqueous solution (100–500 ppm) by precipitate flotation as the sulfide, and which at the same time can be recovered from the CuS product for recycle. Batch flotation experiments confirmed that a cationic surfactant was necessary for flotation of CuS from such dilute suspensions; however, no satisfactory way could be found for recovering cationic surfactants from the CuS. This led to consideration of amphoteric surfactants, which are cationic at low pH and anionic at high pH. It was found that a change to negative, rather than simply neutral, charge was required for efficient surfactant recovery. It was further found, through the assistance of experiments in which the CuS suspension was agitated with solvents, that certain functional groups which interact chemically with the CuS surface should also be absent from the surfactant molecule. Following this logic, Amphoterge K-2 (Lonza Chemical Co.) was identified as a suitable surfactant, provided CuS was precipitated with S^2? in excess. Tests established that 95% of adsorbed Amphoterge K-2 could be recovered by raising the pH to 11 and boiling the suspension for one hour, followed by decanting. Surfactant thus recovered was effective in a second flotation test. Foamate solids settled rapidly; such behavior would help reduce the consumption of chemicals for the pH change.Column flotation studies were made using Amphoterge K-2 for removal of Cu²⁺ present at 100 ppm and pH = 2. High removals of CuS could be obtained at concentrations of surfactant above about 25 ppm, for which conditions a substantial fraction of the surfactant remains in solution rather than being adsorbed onto the CuS. The recovery of CuS would be improved by introducing the surfactant in a separate feed, below the feed of CuS suspension. Adding some surfactant in the CuS feed, as well as in a lower feed, gave an even better recovery of CuS (99.8%) at sufficiently high surfactant loadings.  相似文献   

Paleomagnetic stratigraphy of Pliocene Centerville Beach section,northern California     

J. Robert Dodd  Judson Mead  Robert J. Stanton 《Earth and Planetary Science Letters》1977,34(3):381-386

Samples from the upper two-thirds of the approximately 1900 m thick Neogene section exposed south of Centerville Beach on the northern California coast have predominantly reversed detrital remanent magnetism. Fossil evidence suggests a lower Pliocene through lower Pleistocene age for the section. The combined paleomagnetic and fossil data indicate that a large part of the section was deposited during the Matayama reversed epoch (2.4-0.7 million years ago). Samples from correlative sections exposed a few kilometers inland from the Centerville Beach section have a predominantly normal polarity and appear to have been remagnetized. The Centerville Beach section is important because it may serve as a standard with which to compare both other on-land Pliocene sections from western North America and nearby Deep Sea Drilling Project cores.  相似文献   

Contrasting geochemical signatures on land from the Middle and Late Permian extinction events     

Nathan D. Sheldon  Ramananda Chakrabarti  Gregory J. Retallack  Roger M. H. Smith 《Sedimentology》2014,61(6):1812-1829

The end of the Palaeozoic is marked by two mass‐extinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative δ¹³C anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new high‐resolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, ?W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant syn‐extinction and post‐extinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coal‐beds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates.  相似文献   

POLAR spacecraft observations of helium ion angular anisotropy in the Earth’s radiation belts     

W. N. Spjeldvik  T. A. Fritz  J. Chen  R. B. Sheldon 《Annales Geophysicae》1999,17(6):723-733

New observations of energetic helium ion fluxes in the Earth’s radiation belts have been obtained with the CAMMICE/HIT instrument on the ISTP/GGS POLAR spacecraft during the extended geomagnetically low activity period April through October 1996. POLAR executes a high inclination trajectory that crosses over both polar cap regions and passes over the geomagnetic equator in the heart of the radiation belts. The latter attribute makes possible direct observations of nearly the full equatorial helium ion pitch angle distributions in the heart of the Earth’s radiation belt region. Additionally, the spacecraft often re-encounters the same geomagnetic flux tube at a substantially off-equatorial location within a few tens of minutes prior to or after the equatorial crossing. This makes both the equatorial pitch angle distribution and an expanded view of the local off-equatorial pitch angle distribution observable. The orbit of POLAR also permitted observations to be made in conjugate magnetic local time sectors over the course of the same day, and this afforded direct comparison of observations on diametrically opposite locations in the Earth’s radiation belt region at closely spaced times. Results from four helium ion data channels covering ion kinetic energies from 520 to 8200 KeV show that the distributions display trapped particle characteristics with angular flux peaks for equatorially mirroring particles as one might reasonably expect. However, the helium ion pitch angle distributions generally flattened out for equatorial pitch angles below about 45°. Significant and systematic helium ion anisotropy difference at conjugate magnetic local time were also observed, and we report quiet time azimuthal variations of the anisotropy index.  相似文献   

Analytical and Numerical Modeling of Solute Intrusion,Recovery, and Rebound in Fractured Bedrock     

Ranjeet M. Nagare  Young-Jin Park  Trevor Butterfield  Chad Belenky  Sheldon Scyrup 《Ground water》2020,58(1):56-69

Contaminated groundwater in fractured bedrock can expose ecosystems to undesired levels of risk for extended periods due to prolonged back-diffusion from rock matrix to permeable fractures. Therefore, it is key to characterize the diffusive mass loading (intrusion) of contaminants into the rock matrix for successful management of contaminated bedrock sites. Even the most detailed site characterization techniques often fail to delineate contamination in rock matrix. This study presents a set of analytical solutions to estimate diffusive mass intrusion into matrix blocks, it is recovered by pumping and concentration rebound when pumping ceases. The analytical models were validated by comparing the results with (1) numerical model results using the same model parameters and (2) observed chloride mass recovery, rebound concentration, and concentration in pumped groundwater at a highly fractured bedrock site in Alberta, Canada. It is also demonstrated that the analytical solutions can be used to estimate the total mass stored in the fractured bedrock prior to any remediation thereby providing insights into site contamination history. The predictive results of the analytical models clearly show that successful remediation by pumping depends largely on diffusive intrusion period. The results of initial mass from the analytical model was used to successfully calibrate a three-dimensional discrete fracture network numerical model further highlighting the utility of the simple analytical solutions in supplementing the more detailed site numerical modeling. Overall, the study shows the utility of simple analytical methods to support long-term management of a contaminated fractured bedrock site including site investigations and complex numerical modeling.  相似文献   

Development and Testing of a Field Screening Method Based on Bubbling Extraction and Photoionization Detection for Measurement of Benzene and Total VOCs     

Catalina Espino Devine  Peter Bennett  Karen Synowiec  Sheldon Nelson  Rachel Mohler  Murray Einarson 《Ground Water Monitoring & Remediation》2014,34(3):95-104

A field screening method was developed for rapid measurement of benzene and gasoline range total petroleum hydrocarbons (TPHg) concentrations in groundwater. The method is based on collecting photoionization detector (PID) measurements from vapor samples. The vapor samples are collected by bubbling air through groundwater samples (air sparging) with a constant volume, temperature and sparging rate. The level of accuracy, sensitivity, precision, and statistical significance of the estimated concentrations, derived from the screening method, are comparable to conventional laboratory analytical results at concentrations equal to or greater than 150 µg/L for benzene and greater than 50 µg/L for TPHg. The method's concentration estimations can assist in making real‐time decisions regarding location of dissolved plumes and light nonaqueous phase liquid (LNAPL) source zones at many fuel release sites. The screening method was tested in the laboratory and in the field with 208 and 107 samples, respectively. The study concludes that the screening method can be used as a tool to aid in completing a site conceptual model as well as analyzing groundwater from monitoring wells.  相似文献   

Identifying subsoil sediment sources with carbon and nitrogen stable isotope ratios   总被引：2，自引：0，他引：2       下载免费PDF全文

J. Patrick Laceby  Jon Olley  Timothy J. Pietsch  Fran Sheldon  Stuart E. Bunn 《水文研究》2015,29(8):1956-1971

Increased sediment loads from accelerated catchment erosion significantly degrade waterways worldwide. In the South East Queensland region of Australia, sediment loads are degrading Moreton Bay, a Ramsar listed wetland of international significance. In this region, like most parts of coastal Australia, sediment is predominantly derived from gully and channel bank erosion processes. A novel approach is presented that uses carbon and nitrogen stable isotope ratios and elemental composition to discriminate between these often indistinguishable subsoil sediment sources. The conservativeness of these sediment properties is first tested by examining the effect of particle size separation (testing for consistency during transport) and the effect of sampling at different times (testing for temporal source consistency). The discrimination potential of these sediment properties is then assessed with the conservative properties, based on the particle size and temporal analyses, modelled to determine sediment provenance in three catchments. Nitrogen sediment properties were found to have significant particle size enrichment and high temporal variance indicative of non‐conservative behaviour. Conversely, carbon stable isotopes had very limited particle size and temporal variability highlighting their suitability for sediment tracing. Channel erosion was modelled to be a significant source of sediment (μ 51%, σ 9%) contrasting desktop modelling research that estimated gully erosion is the predominant sediment source. To limit the supply of sediment to Moreton Bay, channel bank and gully erosion must both be targeted by sediment management programs. By distinguishing between subsoil sediment sources, this approach has the potential to enhance the management of sediment loads degrading waterways worldwide. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

The potential for convection and implications for geothermal energy in the Perth Basin, Western Australia     

Heather A. Sheldon  Brendan Florio  Michael G. Trefry  Lynn B. Reid  Ludovic P. Ricard  K. Ameed R. Ghori 《Hydrogeology Journal》2012,20(7):1251-1268

Convection of groundwater in aquifers can create areas of anomalously high temperature at shallow depths which could be exploited for geothermal energy. Temperature measurements in the Perth Basin (Western Australia) reveal thermal patterns that are consistent with convection in the Yarragadee Aquifer. This observation is supported by Rayleigh number calculations, which show that convection is possible within the range of aquifer thickness, geothermal gradient, salinity gradient and permeability encountered in the Yarragadee Aquifer, assuming that the aquifer can be treated as a homogeneous anisotropic layer. Numerical simulations of convection in a simplified model of the Yarragadee Aquifer show that: (1) the spacing of convective upwellings can be predicted from aquifer thickness and permeability anisotropy; (2) convective upwellings may be circular or elongate in plan view; (3) convective upwellings create significant temperature enhancements relative to the conductive profile; (4) convective flow rates are similar to regional groundwater flow rates; and (5) convection homogenises salinity within the aquifer. Further work is required to constrain the average horizontal and vertical permeability of the Yarragadee Aquifer, to assess the validity of treating the aquifer as a homogeneous anisotropic layer, and to determine the impact of realistic aquifer geometry and advection on convection.  相似文献