34,226 research outputs found

    Futher studies on the relationship between IRSL and BLSL at relatively temperatures for potassium-feldspar from sediments

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    In optical dating of potassium-feldspar, the luminescence signals can be stimulated by both infrared (IR) light and blue light (BL). To develop reliable dating methods using different stimulation light sources for feldspars, it is important to understand the sources of the traps associated with the infrared stimulated luminescence (IRSL) and blue light stimulated luminescence (BLSL) and their relationship. In this study, we explored the luminescence characteristics of IRSL and BLSL at different stimulation temperatures (from 60 °C to 200 °C) and their relationship based on five sets of experiments, i.e. post-IR BLSL, post-BL IRSL experiments, pulse annealing test, dose–response test and laboratory fading rate test. Our results suggest that the luminescence characteristics of IRSL and BLSL and their relationship are dependent on stimulation temperature. For IR stimulation at a relatively high temperature of 200 °C, at least two components of IRSL signals are involved in the process. One component of IRSL signals can be easily bleached by BL stimulation at 60 °C, while the other is relatively hard to be bleached by BL stimulation at 60 °C. The two components have different luminescence properties, such as thermal stability, dose–response and laboratory fading rate.postprin

    Late Quaternary faulting on the Manas and Hutubi reverse faults in the northern foreland basin of Tian Shan, China

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    The Tian Shan Range lies in the actively deforming part of the India–Asia collision zone. In the northern foreland basin of Tian Shan, the strata were intensively deformed by Cenozoic folding and faulting. Slip rate studies along these faults are important for understanding the dynamics of crustal deformation and evaluating the seismic hazards in the region. Two reverse faults (the Manas and Hutubi faults) in the northern foreland basin were investigated. Due to past faulting events along these faults, the terrace treads along the Manas River were ruptured, forming fault scarps several meters in height. Loess deposits were trapped and preserved at the surface ruptures along these scarps. The thickness of the trapped loess is dependent on the size of the ruptures. The minimum and maximum ages of these scarps are constrained by dating the loess preserved at the surface ruptures and the terrace treads, respectively, using the quartz optically stimulated luminescence (OSL) dating technique. Our dating results suggest that the loess trapped at the ruptures was deposited from the early to mid-Holocene at the Hutubi Fault, and from the mid- to late-Holocene at the Manas Fault. The vertical displacements of the faults were evaluated by measuring the topographic profiles across the investigated fault scarps using the differential global position system (DGPS). Our results suggest that, during the late Quaternary in the studied region, the vertical slip rates of the Manas Fault were between ∼0.74mm/yr and ∼1.6mm/yr , while the Hutubi Fault had a much lower vertical slip rate between ∼0.34mm/yr and ∼0.40mm/yr . The tectonic implications of our results are discussed.postprin

    Reply to comment by Huntley on "isochron dating of sediments using luminescence of K-feldspar grains"

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    Low temperature thermochronology using thermoluminescence signals from quartz

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    Isothermal thermoluminescence (ITL) and thermoluminescence (TL) signals from quartz were studied. A single aliquot regenerative dose protocol has been applied for ITL De determination (SAR-ITL). In the SAR-ITL protocol, the preheat condition was a cutheat to 10 °C higher than measurement temperature. The test dose was approximate to the expected De, and a 450 °C heat was given at end of each cycle to minimize signal build-up. Based on signals strength and dose recovery test, temperatures of 235 and 255 °C were selected for the ITL De measurement. A multiple aliquots regenerative protocol has been applied for TL De determination (MAR-TL). The preheat procedure was a cutheat of 235 °C and a second glow TL of 175 Gy was used for normalization. The sensitivity change of first heating to 450 °C was negligible, supported by comparison between additive and regenerative dose growth curves. Based on the natural TL signal and preheat condition studies, De values at temperatures of 250–330 °C were used for thermochronological study. These two protocols were applied to rock samples collected at different elevations from Nujiang River (also called Salween River) valley slope. The SAR-ITL gave De results consistent with the MAR-TL at temperatures of 40–50 °C higher. The results clearly demonstrate the differences in the thermal histories between the analyzed samples. The SAR-ITL and MAR-TL protocols were both found to be suitable for application in thermochronology.postprin

    Human settlement of the last glaciation on the Tibetan plateau

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    An archaeological site with 19 handprints and footprints of Homo sapiens and the remnant of a fireplace have been found on hot spring travertine at an elevation of 4200 m on the Tibetan plateau. The prints were pressed on soft travertine by humans. The age of the prints and fireplace is estimated to be around 20,000 years using the optically stimulated luminescence method. The result suggests that humans came to the plateau much earlier than was previously thought. This evidence of human settlement implies that the Tibetans occupy high plateau much earlier than the Andeans and the ice sheet did not cover the entire Tibetan plateau during the Last Glacial Maximum.published_or_final_versio

    Editorial

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    Experimental study of moderately reinforced concrete beams strengthened with bolted-side steel plates

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    Shear transfer in bolted side-plated reinforced concrete beams

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    Reinforced concrete (RC) beams strengthened with bolted steel plates on their vertical faces are known as bolted side-plated (BSP) beams. The behaviour and performance of BSP beams are controlled by the arrangement of the steel plates and the interfacial slips caused by the shear deformation of anchor bolts due to shear force transfer. In this study, a nonlinear finite element model validated by available experimental results has been used to investigate the shear stress transfer in BSP beams. The effects of loading arrangements and the stiffnesses of RC beams, steel plates and bolt connections were investigated in detail by a parametric study. The results of this study shed light on the basic understanding of the internal shear transfer mechanism between steel plates and RC beams. A new design approach is also provided to help structural engineers in the determination of the shear transfer profile and the critical bolt shear force in the design of BSP beams.postprin
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