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11.
Rocío Fayó Marcela A. Espinosa Camilo A. Vélez-Agudelo Jerónimo Pan Federico I. Isla 《Journal of Paleolimnology》2018,60(3):427-443
Diatom assemblages recovered from a Colorado River delta core in northern Patagonia, Argentina were analyzed in order to assess past environmental conditions. A total of 35 samples were selected from a 172-cm core extracted 37 km from the mouth (39°36′19.6″S; 62°29′26.1″W). One-hundred and thirty-eight taxa were recognized and grouped according to life forms. Two diatom zones were identified by cluster analysis. At the base of the sequence, the Diatom Zone I (DZI; 4132 ± 35 ??2919?±?27 14C yr BP), consisted of clays, and was characterized by assemblages dominated by aerophilous and benthic taxa and chrysophyte stomatocysts, which led to inferences of a sedimentary environment corresponding to a pond experiencing dry periods. The upper section (DZII) was dominated by fine sands and silts encompassing the last ~?150 yr with abundant planktonic and tychoplanktonic diatoms. Benthic diatoms were abruptly replaced by planktonic forms in this zone indicating a shift to deeper waters. These results characterize the meandering dynamics of a deltaic system. During the Mid-Holocene, more arid periods would have favored the deactivation of meanders and the formation of riverine and oxbow wetlands. In Late-Holocene and historical times, more humid conditions and the hydrological system across the floodplain reactivated the paleochannel. Today, the dominant diatom species are brackish/freshwater fragilaroids. A non-multidimensional scaling analysis showed a lack of analogy between fossil and modern samples. The change in diatom floras in recent historical times was attributed to anthropogenic disturbances, a consequence of the regulation of the river flow. This regulation is evidenced by less discharge, morphological modifications in the floodplain and increased salinity in the last decade. 相似文献
12.
Miloš Miler Bojan Ambrožič Breda Mirtič Mateja Gosar Sašo Šturm Matej Dolenec Miha Jeršek 《Meteoritics & planetary science》2014,49(10):1875-1887
The Jezersko meteorite is a newly confirmed stony meteorite found in 1992 in the Karavanke mountains, Slovenia. The meteorite is moderately weathered (W2), indicating short terrestrial residence time. Chondrules in partially recrystallized matrix are clearly discernible but often fragmented and have mean diameter of 0.73 mm. The meteorite consists of homogeneous olivine (Fa19.4) and low‐Ca pyroxenes (Fs16.7Wo1.2), of which 34% are monoclinic, and minor plagioclase (Ab83An11Or6) and Ca‐pyroxene (Fs6Wo45.8). Troilite, kamacite, zoned taenite, tetrataenite, chromite, and metallic copper comprise about 16.5 vol% of the meteorite. Phosphates are represented by merrillite and minor chlorapatite. Undulatory extinction in some olivine grains and other shock indicators suggests weak shock metamorphism between stages S2 and S3. The bulk chemical composition generally corresponds to the mean H chondrite composition. Low siderophile element contents indicate the oxidized character of the Jezersko parent body. The temperatures recorded by two‐pyroxene, olivine‐chromite, and olivine‐orthopyroxene geothermometers are 854 °C, 737–787 °C, and 750 °C, respectively. Mg concentration profiles across orthopyroxenes and clinopyroxenes indicate relatively fast cooling at temperatures above 700 °C. A low cooling rate of 10 °C Myr?1 was obtained from metallographic data. Considering physical, chemical, and mineralogical properties, meteorite Jezersko was classified as an H4 S2(3) ordinary chondrite. 相似文献
13.
Natural Hazards - This study presents MERLIN, an innovative flood hazard forecasting system for predicting discharges and water levels at flood prone areas of coastal catchments. Discharge... 相似文献
14.
Pao‐Chun Lin Keh‐Chyuan Tsai Kung‐Juin Wang Yi‐Jer Yu Chih‐Yu Wei An‐Chien Wu Ching‐Yi Tsai Chih‐Han Lin Jia‐Chian Chen Andreas H. Schellenberg Stephen A. Mahin Charles W. Roeder 《地震工程与结构动力学》2012,41(5):1001-1020
A series of hybrid and cyclic loading tests were conducted on a three‐story single‐bay full‐scale buckling‐restrained braced frame (BRBF) at the Taiwan National Center for Research on Earthquake Engineering in 2010. Six buckling‐restrained braces (BRBs) including two thin BRBs and four end‐slotted BRBs, all using welded end connection details, were installed in the frame specimen. The BRBF was designed to sustain a design basis earthquake in Los Angeles. In the first hybrid test, the maximum inter‐story drift reached nearly 0.030 rad in the second story and one of the thin BRBs in the first story locally bulged and fractured subsequently before the test ended. After replacing the BRBs in the first story with a new pair, a second hybrid test with the same but reversed direction ground motion was applied. The maximum inter‐story drifts reached more than 0.030 rad and some cracks were found on the gusset welds in the second story. The frame responses were satisfactorily predicted by both OpenSees and PISA3D analytical models. The cyclic loading test with triangular lateral force distribution was conducted right after the second hybrid test. The maximum inter‐story drift reached 0.032, 0.031, and 0.008 rad for the first to the third story, respectively. This paper then presents the findings on the local bulging failure of the steel casing by using cyclic test results of two thin BRB specimens. It is found that the steel casing bulging resistance can be computed from an equivalent beam model constructed from the steel core plate width and restraining concrete thickness. This paper concludes with the recommendations on the seismic design of thin BRB steel casings against local bulging failure. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
15.
Although the design and applications of linear tuned mass damper (TMD) systems are well developed, nonlinear TMD systems are still in the developing stage. Energy dissipation via friction mechanisms is an effective means for mitigating the vibration of seismic structures. A friction‐type TMD, i.e. a nonlinear TMD, has the advantages of energy dissipation via a friction mechanism without requiring additional damping devices. However, a passive‐friction TMD (PF‐TMD) has such disadvantages as a fixed and pre‐determined slip load and may lose its tuning and energy dissipation abilities when it is in the stick state. A novel semi‐active‐friction TMD (SAF‐TMD) is used to overcome these disadvantages. The proposed SAF‐TMD has the following features. (1) The frictional force of the SAF‐TMD can be regulated in accordance with system responses. (2) The frictional force can be amplified via a braking mechanism. (3) A large TMD stroke can be utilized to enhance control performance. A non‐sticking friction control law, which can keep the SAF‐TMD activated throughout an earthquake with an arbitrary intensity, was applied. The performance of the PF‐TMD and SAF‐TMD systems in protecting seismic structures was investigated numerically. The results demonstrate that the SAF‐TMD performs better than the PF‐TMD and can prevent a residual stroke that may occur in a PF‐TMD system. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
16.
This study consists of two parts. In this two‐part research, four two‐story narrow steel plate shear walls (SPSWs) were cyclically tested at the Taiwan National Center for Research on Earthquake Engineering in 2007. This paper, Part 1, proposes a capacity design method for the first‐story boundary column of the SPSW to ensure that the plastic hinges form at the column bottom ends when the SPSW develops the plastic mechanism. The design method was developed based on the superposition method considering the frame sway action and the panel force effects of the SPSW. Restrained steel plate shear wall (R‐SPSW) studied herein adopts pairs of the horizontal restrainers sandwiching over both sides of the infill panels and connected to the boundary columns. Analytical studies on four SPSW example designs using nonlinear finite element (FE) models and the simplified strip models confirm that the restrainers could also effectively reduce the column force demands and allow the infill panel to stretch more uniformly. In addition, the FE analytical studies verify the effectiveness of the proposed column capacity design method and the seismic design recommendations for the restrainer. This paper introduces the designs of the four narrow SPSW specimens, presenting the selections of the boundary beams and columns, the designs of the beam‐to‐column connections and the construction details of the restrainers. The experimental results, key observations and the design implications are reported in the companion paper. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
17.
Enrique Peña González Joaquín Suárez López Jordi Delgado Martín Alfredo Jácome Burgos Jerónimo Puertas Agudo 《Environmental Geology》2006,50(6):823-834
The cutting operations of dimension stone at quarries produce a large amount of fines that, in turn, cause a negative environmental impact over local surface waters. This article presents a detailed analysis of the mobilized contamination associated with runoff waters in a large granite quarry (～200 ha) which is located in Porriño (Galicia, NW Spain), the most important production centre of dimension stone in Spain. There, an intensive monitoring survey was developed in order to characterize the hydrology of the system as well as the release and transport of pollutants. This was accomplished by means of different control sections for the flow and by the collection of 52 random water samples. Automatic samplers were also used to collect 192 water samples associated with runoff generated by significant rain events. For each of the samples collected, a wide battery of analytic determinations was performed, including solid loads, turbidity, organic pollution, nutrient and selected metals. Upon careful examination it has been possible to obtain different parameters related to the contamination control, like the “event mean concentration” (EMC), maximum concentrations and specific sediment loads. Moreover, a comprehensive statistical study including parameter correlation and cumulative probability analyses helped to understand the pollutant mobilization behaviour within the quarry system. It can be concluded that mobilized contamination shows the anomalous presence of some metals, whose concentrations are in excess when compared to the natural rock. This excess metal amount must be attributed to an anthropogenic source associated to mining and cutting operations. 相似文献