Experimental assessment of contact forces on a rigid base following footing uplift          下载免费PDF全文

Yuanzhi Chen  Tam Larkin  Nawawi Chouw 《地震工程与结构动力学》2017,46(11):1835-1854

A number of investigations in the recent decades have shown that footing uplift can reduce the seismic loading on a structure. Guidelines to design a structure with seismic uplift capability have been proposed. However, these studies mainly focus on the structural response and neglect the impact forces on the footing from re‐contact between the footing and the supporting medium. A small number of computational studies of the induced forces on the footing have been performed. This paper presents the results of free vibrations and shake table tests on a single degree‐of‐freedom model of a bridge pier with footing uplift on a rigid base. Two support conditions are considered, that is, footing fixed to the base and footing free to uplift on a rigid base. Load cells were placed at the interface of the footing and rigid base to measure the contact forces during structural vibration. The footing responses of both flexible and rigid structures due to free vibration are compared. The results show that the flexibility of the structure has significant effects on footing uplift duration and amplitude and reduces the contact force, in some cases very significantly. The flexible structure was also subjected to harmonic base excitations. It is found that varying the characteristics of the excitation changes the uplift amplitude but does not affect the contact force significantly. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Effects of Wastewater-borne Heavy Metals on Mangrove Plants and Soil Microbial Activities   总被引：11，自引：0，他引：11  

M. W. Yim  N. F. Y. Tam   《Marine pollution bulletin》1999,39(1-12):179-186

Effects of wastewater-borne heavy metals on growth of young plants (9-month-old Bruguiera gymnorrhiza) and soil microbial activities in mangrove microcosms were evaluated. During the 26-week loading period, each mangrove microcosm received 31.2 litres synthetic wastewater of three strengths: normal, medium (5 times of normal strength) and strong (10 times of normal strength). Normal strength wastewater had Cu, Zn, Cd, Cr and Ni concentrations of 3, 5, 0.2, 2 and 3 mg l⁻¹, respectively. Plant growth and total plant biomass in wastewater-treated microcosms were lower than that in the control, and the maximum reduction was found in microcosms receiving strong wastewater. Alkaline phosphatase activity and ATP contents of the mangrove soils receiving wastewater were also reduced. More than 95% reduction in these two parameters was found in soils loaded with strong wastewater. Microtox test demonstrated that soil elutriates obtained from microcosms receiving strong wastewater were of the greatest toxicity (EC₅₀ was 23%). These results show that high concentrations of heavy metals present in strong wastewater were toxic and posed negative effects to both mangrove plants and soil microbial activities. Microbial activities were generally more sensitive to the toxicity of heavy metals than plants.  相似文献   

Modification of the SWAT model to simulate regional groundwater flow using a multicell aquifer          下载免费PDF全文

Van Tam Nguyen  Jörg Dietrich 《水文研究》2018,32(7):939-953

The soil and water assessment tool (SWAT) has been widely used and thoroughly tested in many places in the world. The application of the SWAT model has pointed out that 2 of the major weaknesses of SWAT are related to the nonspatial reference of the hydrologic response unit concept and to the simplified groundwater concept, which contribute to its low performance in baseflow simulation and its inability to simulate regional groundwater flow. This study modified the groundwater module of SWAT to overcome the above limitations. The modified groundwater module has 2 aquifers. The local aquifer, which is the shallow aquifer in the original SWAT, represents a local groundwater flow system. The regional aquifer, which replaces the deep aquifer of the original SWAT, represents intermediate and regional groundwater flow systems. Groundwater recharge is partitioned into local and regional aquifer recharges. The regional aquifer is represented by a multicell aquifer (MCA) model. The regional aquifer is discretized into cells using the Thiessen polygon method, where centres of the cells are locations of groundwater observation wells. Groundwater flow between cells is modelled using Darcy's law. Return flow from cell to stream is conceptualized using a non‐linear storage–discharge relationship. The SWAT model with the modified aquifer module, the so‐called SWAT‐MCA, was tested in 2 basins (Wipperau and Neetze) with porous aquifers in a lowland area in Lower Saxony, Germany. Results from the Wipperau basin show that the SWAT‐MCA model is able (a) to simulate baseflow in a lowland area (where baseflow is a dominant source of streamflow) better than the original model and (b) to simulate regional groundwater flow, shown by the simulated groundwater levels in cells, quite well.  相似文献   

Provenance of Cretaceous synorogenic sediments from the NW Dinarides (Croatia)     

Borna Lu?ar-Oberiter  Tamás Mikes  István Dunkl  Ljubomir Babi?  Hilmar von Eynatten 《Swiss Journal of Geoscience》2012,105(3):377-399

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Using web demographics to model population change of Vietnamese-Americans in Texas between 2000 and 2009     

Tzee?Kiu?Edwin?ChowEmail author  Yan?Lin  Niem?Tu?Huynh  John?M.?Davis 《GeoJournal》2012,77(1):119-134

With respect to the great wealth of information available online, the Internet can be viewed as a gigantic database with diverse resources. One of the pressing issues is to investigate the effectiveness and usefulness of the available information over the Internet. This research modeled the population change of Vietnamese-Americans (VA) in Texas from 2000 to 2009 by obtaining web demographic data from the Internet. The project objective is to pilot study a novel approach to conducting online “census” by using Web 2.0 technologies and to investigate the effectiveness of web data for GIS-based demographic application. The solicited VA demographics were geocoded at both county and census tract levels and compared with the Census 2000 demographics in the Geographic Information Systems. Spatial and statistical analyses were used to explore the spatial distribution of VA and to model their population change between 2000 and 2009. The findings of this study include: (1) in general, there are significant differences in the spatial distribution of the VA population between the web demographics and Census 2000 at both county and census tract levels, (2) the Hoover Indices of VA population in Texas at 2000 and 2009 revealed a trend of deconcentration which conforms to the general rural-urban-suburban migration among major metropolitan areas in Texas. This study sheds new insights to using web demographic data for population predictions and applications to plan services for ethnic groups.  相似文献   

Origin and ascent history of unusually crystal-rich alkaline basaltic magmas from the western Pannonian Basin     

M. Éva Jankovics  Gábor Dobosi  Antal Embey-Isztin  Balázs Kiss  Tamás Sági  Szabolcs Harangi  Theodoros Ntaflos 《Bulletin of Volcanology》2013,75(9):1-23

The last eruptions of the monogenetic Bakony-Balaton Highland Volcanic Field (western Pannonian Basin, Hungary) produced unusually crystal- and xenolith-rich alkaline basalts which are unique among the alkaline basalts of the Carpathian–Pannonian Region. Similar alkaline basalts are only rarely known in other volcanic fields of the world. These special basaltic magmas fed the eruptions of two closely located volcanic centres: the Bondoró-hegy and the Füzes-tó scoria cone. Their uncommon enrichment in diverse crystals produced unique rock textures and modified original magma compositions (13.1–14.2 wt.% MgO, 459–657 ppm Cr, and 455–564 ppm Ni contents). Detailed mineral-scale textural and chemical analyses revealed that the Bondoró-hegy and Füzes-tó alkaline basaltic magmas have a complex ascent history, and that most of their minerals (～30 vol.% of the rocks) represent foreign crystals derived from different levels of the underlying lithosphere. The most abundant xenocrysts, olivine, orthopyroxene, clinopyroxene, and spinel, were incorporated from different regions and rock types of the subcontinental lithospheric mantle. Megacrysts of clinopyroxene and spinel could have originated from pegmatitic veins/sills which probably represent magmas crystallized near the crust–mantle boundary. Green clinopyroxene xenocrysts could have been derived from lower crustal mafic granulites. Minerals that crystallized in situ from the alkaline basaltic melts (olivine with Cr-spinel inclusions, clinopyroxene, plagioclase, and Fe–Ti oxides) are only represented by microphenocrysts and overgrowths on the foreign crystals. The vast amount of peridotitic (most common) and mafic granulitic materials indicates a highly effective interaction between the ascending magmas and wall rocks at lithospheric mantle and lower crustal levels. However, fragments from the middle and upper crust are absent from the studied basalts, suggesting a change in the style (and possibly rate) of magma ascent in the crust. These xenocryst- and xenolith-rich basalts yield divers tools for estimating magma ascent rate that is important for hazard forecasting in monogenetic volcanic fields. According to the estimated ascent rates, the Bondoró-hegy and Füzes-tó alkaline basaltic magmas could have reached the surface within hours to few days, similarly to the estimates for other eruptive centres in the Pannonian Basin which were fed by “normal” (crystal and xenoliths poor) alkaline basalts.  相似文献   

Effects of environmental stresses on the responses of mangrove plants to spent lubricating oil     

Ke L  Zhang C  Guo C  Lin GH  Tam NF 《Marine pollution bulletin》2011,63(5-12):385-395

The influence of different environmental stresses, including salinity (5-35‰), tidal cycle (6/6, 12/12 and 24/24 h of high/low tidal regimes) and nutrient addition (1-6 times background nitrogen and phosphorus content) on Bruguiera gymnorrhiza and Aegiceras corniculatum grown in sediment contaminated with spent lubricating oil (7.5 L m(-2)) were investigated. The oil-treated 1-year-old mangrove seedlings subject to low (5‰) and high (35‰) salinity had significantly more reduction in growth, more release of superoxide radical (O2·-) and higher activity of superoxide dismutase (SOD) than those subject to moderate salinity (15‰). Extended flooding (24/24 h of high/low tidal regime) enhanced O2·- release and malondialdehyde (MDA) content in both oil-treated species but had little negative effects on biomass production (P>0.05) except the stem of A. corniculatum (P=0.012). The addition of nutrients had no beneficial or even posed harmful effects on the growth and cellular responses of the oil-treated seedlings.  相似文献   

Multiple provenance of detrital zircons from the Permian–Triassic boundary in the Bükk Mts., Hungary     

Norbert Zajzon  Zsófia Szabó  Tamás Gábor Weiszburg  Teresa Elizabeth Jeffries 《International Journal of Earth Sciences》2011,100(1):125-138

Detailed zircon analyses were carried out on samples from the Bálvány North section, which contains the Permian–Triassic boundary. A fine-grained sandstone bed within the “boundary shale” contains a significant amount of zircon crystals. Pupin morphological, scanning electron microscopy [secondary electron, back-scattered electron, cathodoluminescence (CL)] and laser ablation inductively coupled mass spectrometry (LA-ICP-MS) investigations were done in selected single grains to combine morphological information with radiometric ages, and infer the provenance of zircons. Three populations are distinguished on the basis of Pupin morphology. Their centres of gravity are S17, S2 and P1. The LA-ICP-MS radiometric ages reveal three main age groups and a smaller one, apart from a few scattered old ages. The largest group, comprising ca. 50% of the measured grains, has an age of 470–440 Ma. The two other main groups, which together represent ca. 25% of the measured grains, are around 280 and 600 Ma. The 280 Ma group contains slightly more grains than the 600 Ma group. A small group has an age of 370–340 Ma. In addition, there are some older grains with ages of 850, 969, 1,050 and 2,150 Ma. Based on the zircon morphology no clear separation of the different age groups could be made. Both the 280 Ma and the 470–440 Ma age groups tend to show zircon crystals derived from three types of sources: crustal granites, calc-alkaline granitoids and alkali granites and/or their volcanic equivalents. Zircons in the 450 Ma group have a magmatic rim around their altered, relict core, as revealed by CL images. Post-magmatic processes also affected the rim. The age of the core is possibly reset during the formation of the magmatic rim. This suggestion is supported by the LA-ICP-MS data, because no difference was seen between the core and the rim. The different roundness of the zircons, the well-sorted crystals and the at least five different source rocks indicate previous concentration of the grains, before their transportation into the “boundary shale”. Austroalpine and Southern Alpine rocks could be the sources of the zircon crystals, which fit well into the paleogeographical model of the area, which suggests that the Bükk Mts. was located in the foreground of the Alpine units.  相似文献   

Chandra monitoring of the candidate anomalous X-ray pulsar AX J1845.0-0258     

Cindy R. Tam  Victoria M. Kaspi  Bryan M. Gaensler  Eric V. Gotthelf 《Astrophysics and Space Science》2007,308(1-4):519-523

The population of clearly identified anomalous X-ray pulsars has recently grown to seven, however, one candidate anomalous X-ray pulsar (AXP) still eludes re-confirmation. Here, we present a set of seven Chandra ACIS-S observations of the transient pulsar AX J1845.0-0258, obtained during 2003. Our observations reveal a faint X-ray point source within the ASCA error circle of AX J1845.0-0258’s discovery, which we designate CXOU J184454.6-025653 and tentatively identify as the quiescent AXP. Its spectrum is well described by an absorbed single-component blackbody (kT∼2.0 keV) or power law (Γ∼1.0) that is steady in flux on timescales of at least months, but fainter than AX J1845.0-0258 was during its 1993 period of X-ray enhancement by at least a factor of 13. Compared to the outburst spectrum of AX J1845.0-0258, CXOU J184454.6-025653 is considerably harder: if truly the counterpart, then its spectral behavior is contrary to that seen in the established transient AXP XTE J1810-197, which softened from kT∼0.67 keV to ∼0.18 keV in quiescence. This unexpected result prompts us to examine the possibility that we have observed an unrelated source, and we discuss the implications for AXPs, and magnetars in general.   相似文献   

海南海莲红树林土壤CH₄的产生及其某些影响因素   总被引：7，自引：0，他引：7  

卢昌义  叶勇  林鹏  黄玉山  谭凤仪 《海洋学报》1998,20(6):132-138

全球CH₄预算的估算表明,湿地是大气CH₄最大的生物排放源[1].旨在估算全球大气CH₄湿地源强的工作大多集中在内陆淡水环境,因为在此环境的CH₄通量较大[2].国外对海岸盐沼的CH₄排放也有一些报道,发现其通量变化范围较大,并进而研究了温度、土壤湿度、盐度以及土壤有机碳含量等因素对CH₄排放的影响[3].  相似文献